Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

Rosalyn L. Falconer; Gary S. Nichol; Michael J. Cowley

doi:10.1021/acs.inorgchem.9b01061

Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

Falconer, Rosalyn L.; Nichol, Gary S.; Cowley, Michael J. 2019-08-14 00:00:00 This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes. Article pubs.acs.org/IC Cite This: Inorg. Chem. 2019, 58, 11439−11448 Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes Rosalyn L. Falconer, Gary S. Nichol, and Michael J. Cowley* School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K. * Supporting Information ABSTRACT: Aluminum hydrides, once a simple class of stoichiometric reductants, are now emerging as powerful catalysts for organic transformations such as the hydroboration or hydrogenation of unsaturated bonds. The coordination chemistry of aluminum hydrides supported by P donors is relatively underexplored. Here, we report aluminum dihydride and dimethyl complexes supported by amidophosphine ligands and study their coordination behavior in solution and in the solid state. All complexes exist as κ -N,P complexes in the solid state. However, we ﬁnd that for amidophosphine ligands bearing bulky aminophosphine donors, aluminum dihydride and dimethyl complexes undergo a “ligand-slip” rearrangement in solution to generate κ -N,N complexes. Thus, importantly for catalytic activity, we ﬁnd that the coordination behavior of the P donor can be modulated by controlling its steric bulk. We show that the reported aluminum hydrides catalyze the hydroboration of alkynes by HBPin and that the variable coordination mode exhibited by the amidophosphine ligand modulates the catalytic activity. INTRODUCTION Aluminum hydrides such as LiAlH , sodium bis(2-methox- yethoxy)aluminum hydride (RedAl), and AlH are ubiquitous in synthetic chemistry for their use as reducing agents. Recently, the scope of the reactivity of these simple aluminum hydrides has been expanded into catalytic hydroboration of alkenes and alkynes, a development of signiﬁcant environ- mental and economic importance because of the high abundance and relatively low toxicity of aluminum compared 2,3 to platinum group metals. Numerous other uncomplicated Figure 1. Literature examples of aluminum dihydride and dimethyl aluminum hydride compounds are also capable of hydro- complexes stabilized by N-based ligands (I−III) or mixed donor 9−11,15,20,21 i boration or even hydrogenation of unsaturated polar bonds ligands (IV−VI). (I and IV have Ar = 2,6-C H Pr , and VI 6 3 2 4,5 i i such as aldehydes, ketones, or imines. Aluminum hydride has R = R′ = Ph, Pr or R = Ph and R′ = Pr). compounds with more complex ligands have also been investigated. For example, N-heterocyclic imine-coordinated array of ligand classes is essential for the expansion of aluminum hydrides catalyze carbonyl hydroboration while the aluminum hydride chemistry and catalysis. β-diketiminate-stabilized aluminum dihydride I (Figure 1) also Aluminum dihydrides or related species with P-based ligands catalyzes the hydroboration of alkynes. The dihydride I is also are much rarer. A few examples of dimethylaluminum a precursor to β-diketiminate-stabilized aluminum(I) species complexes with mixed-donor ligands are known, in which (at least within the coordination sphere of a transition metal). bidentate ligands having one N donor also contain a “soft” 14−18 Reported aluminum dihydride complexes overwhelmingly donor, such as S or P (IV and V; Figure 1). The likely 9−13 use N-donor ligands (e.g., I−III; Figure 1). Typically, more labile Al−Pinteraction oﬀers the possibility of hemilability, which can be useful in the stabilization of these ligands are also multidentate (to stabilize the intrinsically catalytic transition or resting states. Indeed, Fryzuk et al. electron-poor Al center) and sterically hindered, in order to used NMR spectroscopy to demonstrate the ﬂuxional prevent dimerization or oligimerization by bridging inter- actions. In coordination chemistry, ligands greatly inﬂuence the chemistry at the metal center. Thus, the investigation and Received: April 15, 2019 development of aluminum hydride chemistry using a diverse Published: August 14, 2019 © 2019 American Chemical Society 11439 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article coordination of P-donor atoms in V,resulting in an Scheme 1. Lithiation of Ligand 1 To Form 2 Followed by equilibrium between four- and ﬁve-coordinate Al centers. Reaction with Dimethylaluminum Chloride To Form In comparison to mixed-donor methyl complexes, mixed- Dimethylaluminum Complexes 3a−3c donor aluminum dihydride complexes are scarce, with only a single example. Most P-coordinated aluminum hydrides are limited to simple adducts between phosphines and alane, with the exception of VI (Figure 1), reported by Liang et al. in 2009, which was synthesized via the reduction of the 21,22 corresponding aluminum dichloride using LiAlH . Hemil- ability of the P donors was not found in this example, likely because of the rigidity of the ligand backbone. Herein, we describe novel aluminum dimethyl and dihydride species stabilized by mixed N,P-donor ligands that display ﬂexible coordination modes based on a “ligand-slip” phenom- pentane, followed by ﬁltration and evaporation of the solvent enon. aﬀorded 3a−3c as yellow air-sensitive solids. Complexes 3a and 3c could be isolated as analytically pure solids by RESULTS AND DISCUSSION ■ crystallization, while 3b was clearly identiﬁed but resisted Theamidophosphineligands 1a−1c (Figure 2)have puriﬁcation attempts. All three complexes 3a−3c were previously been used to prepare nickel and palladium extremely sensitive to air and moisture. The solid-state structures of 3a and 3c were determined by X-ray crystallography (Figure 3). Both compounds have a tetrahedral Al center with coordinated N and P donors, forming a planar ring. The ring is heavily skewed with (as might be expected) a substantially shorter interaction between Al and the N donor than with the phosphine [e.g., 3a, Al1−N1 1.8985(14) Å vs Al1−P1 2.4800(6) Å]. Both the Al−N and Al−P distances are comparable to those previously reported, for example the N,P-coordinated dimethylaluminum complex Figure 2. Mixed-donor ligands 1a−1c. IV [Al−N 1.894(6) Å; Al−P 2.477(3) Å]. The Al−N bond distances of 3a and 3c are indistinguish- complexes, as well as to support reactive silicon(II) able, but the Al−P bond length is slightly longer in the latter at 24−27 compounds. The steric bulk around both the N and P 2.5304(8) Å, indicating that P is less strongly bound to the Al centers of 1a−1c has not only enabled the isolation of reactive center. The aminophosphine donor of 3c is more electron- species such as silicon(II) hydrides but also modulates donating than the dialkylphosphine donor of 3a, which would II IV reversible Si /Si oxidative additions/reductive eliminations. be expected to give rise to the opposite trend. The origin of At the P donor in particular, both steric bulk and electron- the diﬀerence is likely due to steric eﬀects: the greater steric donating ability are readily tunable. We were interested in bulk in 3c prevents the close approach of the phosphine to the whether this class of ligands could be employed to support Al Al center. Indeed, this can be observed in the C1−Al1−C2 centers and whether they could be used to modulate their angle, which is smaller in the case of 3c [106.4(2)°] than 3a structure and reactivity. [109.00(9)°] despite the similar bite angles of the two [3a, Synthesis and Solid-State Structures of Aluminum 86.67(4)°; 3c, 85.59(8)°]. Dimethyl Complexes. Dimethylaluminum complexes are a Solution Behavior of 3a−3c. Despite their similar solid- broad class of compounds that have been reported as catalysts state structures, solution-phase NMR spectroscopy revealed 28−30 or cocatalysts in alkene polymerization. Complexes of diﬀerences in the coordination behavior among the dimethy- dimethylaluminum stabilized by many N- or mixed-donor laluminum complexes 3a−3c. No signals were observed for any ligands have been reported, rendering this class of compounds of the compounds by Al NMR spectroscopy. ideal for benchmarking the coordination abilities of ligands NMR spectroscopy of dimethylaluminum complexes 3a and 1a−1c. We decided to ﬁrst investigate the coordination of 3b was consistent with the solid-state structure determined for 31 1 ligand 1 to dimethylaluminum moieties. 3a. P{ H} NMR spectroscopy revealed a single resonance for IV The coordination of 1b and 1c to Si centers has been each (3a, 1.6 ppm; 3b, 64.0 ppm) shifted upﬁeld compared to reported and was achieved by deprotonation before treatment the respective free ligand resonances [Δ∂(3a)= −54.4 ppm; 31 1 with the appropriate silicon halide. Accordingly, ligands 1a− Δ∂(3b)= −83.3 ppm]. The P{ H} NMR resonances for 3a 1c were deprotonated with nBuLi at −78 °Cto aﬀord yellow and 3b were also signiﬁcantly broadened in comparison to the solutions of 2a−2c (Scheme 1). A characteristic resonance is free ligands 1a and 1b, presumably as a result of coordination 31 1 5 observed in the P{ H} NMR spectra of these solutions in the of the P to the quadrupolar (I = / ) Al nucleus [3a, full width form of a 1:1:1:1 quartet upﬁeld compared to the free ligand. at half-maximum (Δν ) = 21.1 Hz; 1a, Δν = 2.7 Hz]. 1/2 1/2 The 1:1:1:1 multiplicity indicates coordination to Li (e.g., 2a, In the HNMR spectraof 3a and 3b,resonances 31 1 7 P{ H} NMR δ 10.9, J = 54 Hz). Similarly, in the Li NMR corresponding to the aluminum methyl groups appear as PLi doublets arising from coupling to P (3a, δ −0.33 and −0.19, spectra, doublets are observed because of coupling with P (e.g., 2 1 J = 2.5 Hz). The H NMR spectrum also shows that each 2a, Li NMR δ 1.3, J = 54 Hz). HP LiP The dimethylaluminum complexes 3a−3c were obtained by CH group in the 2,6-diisopropylphenyl (Dipp) substituent is reaction of the in situ generated lithiated ligand 2 with 1 equiv inequivalent, indicating restricted rotation likely because of of dimethylaluminum chloride. Extraction of the products in steric constraints. 11440 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Figure 3. Molecular structures of 3a (left) and 3c (right) with thermal ellipsoids drawn at the 50% probability level. H and disordered ligand atoms are omitted for clarity. Selected bond distances (Å) and angles (deg) for 3a:N1−Al1 1.895(14), P1−Al1 2.4800(6), Al1−C1 1.9652(19), Al1−C2 1.970(2); N1−Al1−P1 86.67(4), N1−Al1−C1 116.12(8), N1−Al1−C2 115.25(8), P1−Al1−C1 114.53(7), P1−Al1−C2 114.00(7), C1−Al1−C2 109.00(9). Selected bond distances (Å) and angles (deg) for 3c:N1−Al1 1.917(3), P1−Al1 2.5304(9), Al1−C1 1.967(4), Al1−C2 1.964(4); N1− Al1−P1 85.59(8), N1−Al1−C1 116.14(19), N1−Al1−C2 116.19(19), P1−Al1−C1 115.98(13), P1−Al1−C2 115.99(14), C1−Al1−C2 106.4(2). Crystalline 3c was also characterized by solution-phase spectroscopic experiments veriﬁed that in both isomers the 31 1 NMR spectroscopy. Surprisingly, the P{ H} NMR spectrum ligand backbone was intact and undisturbed. The possibility of contained two resonances, at 99.9 and 49.7 ppm, in a ratio of a dimeric κ -N isomer of 3c (with, e.g., bridging methyl 1 1 3:2 (the same ratio was observed by H NMR spectroscopy). ligands) was excluded based on analysis of the H DOSY NMR spectrum, which indicated that both of the observed isomers The resonance at 49.7 ppm is broadened (Δν = 47.5 Hz) 1/2 and downﬁeld (Δ∂ = −40.9 ppm) from that of 1c and so is diﬀused at the same rate in solution. Similarly, high-resolution consistent with coordination of P to the Al center as in 3a and mass spectrometry (HRMS) also identiﬁed the product as 3c, 3b. Conversely, the resonance at 99.9 ppm is sharp (Δν = with no evidence of a dimeric species observed. 1/2 5.3 Hz) and close in chemical shift to that of the free ligand 1c Synthesis of Aluminum Dihydride Complexes. Follow- ing the preparation of the dimethylaluminum complexes 3a− (Δ∂ = +9.3 ppm), which indicates that P in this environment is 3c, we turned our attention to the preparation of aluminum not coordinated to the Al center. On the basis of the P NMR spectroscopic data and by dihydride complexes. Ligands 1a−1c do not react with analogy with the behavior more fully studied in the hydride Me EtN·AlH , in contrast to the observed reactivity of amidine 2 3 analogue 5c (see below), we propose that 3c exists in two ligands, which evolve H and form aminidinatoaluminum dihydrides. Treatment with LiAlH also had no eﬀect. Thus, forms in solution, in which the ligand exhibits a variable 2 2 we used the lithiated ligands 2a−2c as precursors instead. coordination mode, having either κ -N,P or κ -N,N coordina- Treatment of 2b with a single equivalent of Me EtN·AlH tion (Scheme 2). In the solid state, κ -coordination is 2 3 exclusively observed. In solution, however, the two isomers resulted in a yellow solution, the P NMR spectrum of which are present as a result of the ﬂexible coordination mode of the revealed a quartet (δ 110.8, J = 34 Hz), which collapsed to a PH 31 1 singlet in the P{ H} NMR spectrum. This evidence, as well ligand. 1 2 as further characterization by multinuclear NMR spectroscopy The H NMR spectrum of 3c is consistent with both the κ - and mass spectrometry, conﬁrmed formation of the aluminate N,P and κ -N,N isomers existing in solution, with two sets of complex 4b (Scheme 3). resonances present in a ratio of 57:43 (consistent with the 3:2 ratio observed by P NMR). Multinuclear 2D NMR The addition of a second equivalent of Me EtN·AlH to 2 3 31 1 solutions of 4b was monitored by P{ H} NMR spectroscopy, 2 2 a which revealed complete consumption of 4b and the formation Scheme 2. Proposed Structures of κ -N,P- and κ -N,N-3c Scheme 3. Proposed Mechanism for the Reaction of 2 with Me EtN·AlH (NR = NMe or NMe Et) To Form the 2 3 3 3 2 Aluminum Dihydride 5 via the Charged Intermediate 4 a 2 In the solid state, only κ -N,P-3c is observed, while in solution, both 2 2 the κ -N,P- and κ -N,N isomers are observed. 11441 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Figure 4. Molecular structures of 5b (left) and 5c (right). The aluminum hydride atoms were located using a diﬀerence map and allowed to reﬁne freely. H and disordered ligand atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) for 5b:N1−Al1 1.8972(15), P1−Al1 2.4442(7); N1−Al1−P1 87.47(5). Selected bond lengths (Å) and angles (deg) for 5c:N1−Al1 1.892(2), P1−Al1 2.4790(10); N1−Al1−P1 86.60(6). of a new species represented by a broad singlet (61.3 ppm, indicating continued restricted rotation. Compound 5c has more complex solution behavior that will be discussed below. Δν = 55.7 Hz), indicating P coordination to Al. Analysis of 1/2 the Al NMR spectrum revealed the formation of LiAlH .On IR spectroscopy of the solid-state samples of 5a−5c revealed the expected symmetric and antisymmetric Al−H stretches the basis of this evidence, the reaction pathway shown in −1 −1 (5a, 1810 and 1786 cm ; 5b, 1831 and 1816 cm ; 5c, 1825 Scheme 3 is proposed: the reaction of 2b with Me EtN·AlH 2 3 −1 and 1801 cm ) for a four-coordinate aluminum dihydride proceeds by forming 4b by displacement of the amine from 33,34 center. Me EtN·AlH . The second 1 equivalent of Me EtN·AlH 2 3 2 3 Solid-State Structures of 5b and 5c. The structures of abstracts a hydride from 4b, generating 5b and LiAlH and 5b and 5c were veriﬁed by X-ray diﬀraction (Figure 4). eliminating the amine. Broadly, the structures are analogous to those of 3a and 3c. When 2a was treated with 1 equiv of Me EtN·AlH , the 2 3 The amidophosphine ligand in each compound is κ -N,P- resulting pale-yellow solution was revealed to contain a mixture 31 1 coordinated, which together with the hydride ligands (located of compounds by P{ H} NMR spectroscopy. In addition to using a diﬀerence map and allowed to reﬁne freely) results in a residual lithiated ligand 2a, equal quantities of the aluminate tetrahedral environment at the Al center. The two structures intermediate 4a (8.0 ppm) and the neutral aluminum have statistically identical N−Al bond distances [5b, dihydride 5a (−10.1 ppm) were observed. LiAlH was also 1.8972(15) Å; 5c, 1.892(2) Å], which are essentially identical observed by Al NMR spectroscopy. The 2:1:1 ratio of the with those observed for the dimethyl analogues 3a and 3c.A three species reveals that the lithiated ligand 2a and the more substantial diﬀerence is observed in the P−Al bond intermediate aluminate 4a react at comparable rates with distances, which for the dihydride 5c is shorter than that in the Me EtN·AlH to generate a statistical mixture. This contrasts 2 3 corresponding dimethyl complex 3c [Al1−P1: 5c, 2.4791(10) to the situation for 4b, where hydride abstraction by Me EtN· Å; 3c, 2.5304(8) Å]. Contraction of this bond can be explained AlH is much slower than its coordination to the lithiated by the smaller size of the hydride substituents. Similarly, a ligand 2b. Upon the addition of a second equivalent of comparison between the two dihydrides 5b and 5c reveals a Me EtN·AlH to 4a, the reaction mixture turned colorless and 2 3 shorter Al1−P1 distance for 5b as a result of reduced bulk at 31 1 the P{ H} NMR spectrum showed complete conversion to the P center in comparison to 5c [5b, 2.4442(7) Å; 5c, 5a (7.5 ppm). 2.4791(10) Å]. The larger bite angles for the dihydrides 5b Preparatively, the dihydride complexes 5a−5c were obtained and 5c [5b, 87.47(5)°; 5c, 86.60(6)°] compared to those of in multigram quantities from treatment of the lithiated ligands the dimethyl compounds are also due to the smaller hydride 2a−2c with 2 equiv of Me N·AlH or Me EtN·AlH . All three 3 3 2 3 substituents compared to the methyl groups. compounds could be isolated as colorless solids in excellent Solution-Phase NMR Characterization of 5c. Like its yields of 80−90%. Dihydrides 5b and 5c could be further dimethyl analogue 3c, the dihydride 5c exhibits variable puriﬁed by crystallization from hexane. coordination modes in solution. Upon dissolution of crystalline 31 1 In the H NMR spectra of 5a and 5b,Al−H resonances are 5c, the P{ H} NMR spectrum revealed the presence of two visible as very broad singlets at 4.6 ppm (5a, Δν = 71.6 Hz; broad singlets at 96.9 ppm (Δν = 137.9 Hz) and 47.8 ppm 1/2 1/2 5b, Δν = 125.3 Hz) because of the inﬂuence of the (Δν = 96.6 Hz) in a ratio of 1:2. By H NMR, two sets of 1/2 1/2 quadrupolar Al atom. Despite the lower steric inﬂuence of the resonances were also observed for all proton environments, hydride ligands compared to the methyl ligands of 3a and 3b, including the dihydride ligands (signals at κ -N,N-5c, 4.3 ppm, the methyl groups of the Dipp substituent remain inequivalent, κ -N,P-5c, 4.6 ppm; the ratio of the two species as measured by 11442 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article H NMR in a ratio of 35:65, consistent with that observed in the P NMR spectrum). The two solution-phase isomers of 5c were determined to be 2 2 κ -N,P-5c, as observed in the solid state, and a κ -N,N isomer in which the phosphine ligand has “slipped” and coordinates through one of the P-bound N atoms (Scheme 4). Evidence for the κ -N,N coordination mode is as follows: 2 2 2 2 1 Scheme 4. Proposed Structures of κ -N,P- and κ -N,N-5c Figure 5. Computed energies of κ -N,P-, κ -N,N-, and κ -N-5c [M062X/6,31G+(d,p)/Lanl2DZ]. more stable; DFT does not replicate the experimentally observed order of stability, although it does correctly place the two species very close in energy). Calculated Al−H stretching 2 2 frequencies for κ -N,P- and κ -N,N-5c (1863, 1845, and 1860, −1 1813 cm , respectively) are suﬃciently close in order to explain the single peak observed in the experimental solution- −1 phase spectrum (1829 cm ). 2 2 The ligand-slip rearrangement of 5c from κ -N,P to κ -N,N a 2 In the solid state, only κ -N,P-5c is observed, while in solution, both is likely driven by a preference for the “hard” N-donor 2 2 the κ -N,P and κ -N,N isomers are observed. functionality of the diaminophosphine donor over the “softer” P center. The increased proportion of the κ -N,N isomer for the dimethyl complex 3c compared to the dihydride 5c (1) The two isomers are both monomeric species, as suggests that the ring expansion that occurs as a consequence revealed by H DOSY NMR measurements, which indicate 2 2 of isomerization from κ -N,P to κ -N,N may also be favorable similar diﬀusion coeﬃcients. Thus, we were able to rule out the as a route to relieve steric strain. The more restrained, sterically presence of a dimeric species with bridging hydrides crowded, and less basic (due to the silyl substituent) tert- (consistent with solution- and solid-phase IR spectroscopy, butylamino groups of 3b and 5b cannot favorably participate in which did not reveal evidence of bridging hydride ligands). 31 1 the same isomerization as 3c and 5c. (2) In the P{ H} NMR spectrum, the resonance at 96.9 2 2 Interconversion between κ -N,P- and κ -N,N-3c or -5c in ppm is assigned to the κ -N,N isomer because of its similarity solution was not observable, and we were thus unable to to that observed for the free ligand 1c (90.6 ppm), which determine the activation barriers for this process. Although indicates that the P center is not coordinated to Al. The resonances for the coordinated and free phosphine centers in resonance at 47.8 ppm is assigned to the κ -N,P isomer both isomers of 5c are broad, using NMR spectroscopy, we observed in the solid state (conﬁrmed by solid-state NMR could ﬁnd no evidence for exchange between the two sites, measurements; see below). even at elevated temperatures. The variable coordination mode (3) The aluminum hydride stretching frequencies recorded −1 of the ligand in both 3c and 5c appears to provide them with for 5c in solution (1823 cm ) and in the solid state (1825 and −1 higher reactivity and renders them the most sensitive 1801 cm ) are consistent with a four-coordinate aluminum derivatives in these series. Indeed, 3c was found to be dihydride species in both phases, ruling out a κ -N isomer in extremely challenging to handle because of its high sensitivity which the phosphine is uncoordinated. to air and moisture. (4) Using density functional theory (DFT), we performed Solid-State NMR Spectroscopy. To further conﬁrm our geometry optimization and frequency calculations on κ -N,P 31 2 2 assignment of P resonances for the κ -N,P and κ -N,N isomers of 5a−5c at the M062X/Def2SVPP and M062X/ isomers of 3c and 5c, we undertook solid-state NMR 6,31G+(d,p)/Lanl2DZ levels (Table S1). Following the lead of spectroscopy because from crystallographic studies κ -N,P- Crimmin et al., we found that calculations using the split basis 31 1 coordination is exclusively observed. The P{ H} MAS NMR set were essential to replicating experimentally observed Al−H spectra of 3c and 5c are consistent with X-ray crystallography, stretching frequencies. The calculations accurately repro- revealing only a single-P environment for each compound duced the experimentally observed geometries and IR (Figure 6). In both cases, the solid-state chemical shift is stretching frequencies for 5a−5c, enabling us to use this almost identical with the solution-phase signal assigned to the computational methodology to assign the identity of the κ -N,P isomers (e.g., 3c, solid phase, 47.8 ppm, solution, 49.7 solution-phase isomer of 5c. ppm; 5c, solid phase, 47.5 ppm, solution, 47.8 ppm). (5) A relaxed potential energy surface (PES) scan of 5c in 31 1 Furthermore, the line shapes observed in the P{ H} NMR which the Al−P distance was increased systematically starting spectra indicate quadrupolar coupling between Al and P, from the κ -N,P geometry revealed two potential minima explaining the observed variation from the expected (Figure S1), which were reoptimized at the M062X/6,31G 1:1:1:1:1:1 sextet. No other resonances were observed in the +(d,p)/Lanl2DZ level (Figure 5 and Table S2). A κ -N isomer 31 1 2 −1 2 P{ H} MAS NMR spectra, ruling out the presence of the κ - was found to be 22.6 kcal mol higher in energy than the κ - N,P isomer (the calculated Al−H stretching frequencies for N,N isomer in the solid state. this three-coordinate aluminum dihydride of 1934 and 1922 For 3a, 3b, 5a, and 5b, which all display exclusive κ -N,P −1 31 1 cm were also inconsistent with the experimental values). coordination in solution, the observed P{ H} MAS NMR However, the κ -N,N isomer located in the PES scan was spectra each contain a single resonance extremely close in 2 −1 found to be very close in energy to κ -N,P-5c (−0.8 kcal mol chemical shift to that observed in solution (e.g., 5a, solution 11443 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article EXPERIMENTAL SECTION General Procedures. All manipulations were carried out under an argon atmosphere using standard Schlenk or glovebox techniques. Reactions were carried out in glass Schlenk tubes, which were dried for 16 h at 110 °C before use. Solvents were obtained from an inert solvent puriﬁcation system and stored over 4 Å molecular sieves. C D 6 6 and tetrahydrofuran (THF)-d were dried over potassium, then vacuum-distilled, and stored over 4 Å molecular sieves. 23 24 Ligands 1b and 1c, their precursors [imine and chlorophos- t 23 t 35 phines PCl(N Bu) SiMe and PCl(N BuCH ) ], and [H Al· 2 2 2 2 3 NMe ] were synthesized according to literature procedures. SiMe (NH Bu) was synthesized according to a modiﬁed literature 2 2 procedure (see the SI). tert-Butylamine was dried over calcium hydride and vacuum-distilled prior to use. LiAlH was puriﬁed by extraction with diethyl ether and ﬁltration to aﬀord a white solid, which was stored under an inert atmosphere. Trimethylammonium 31 1 Figure 6. P{ H} (9.4 T, 14 kHz, MAS) NMR spectra for 3c (top) chloride was dried under vacuum at 50 °C for 3 h prior to use. All and 5c (bottom). other reagents were purchased from commercial suppliers and used without further puriﬁcation. General Synthesis of 2. To a solution of 1 in THF cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes, 1 equiv). The phase, 8.0 ppm, solid phase, 8.9 ppm). Although we were cold bath was removed, and the resultant yellow solution was stirred 31 1 unable to observe any resonances for any of the compounds at room temperature for 1 h. Monitoring by P{ H} NMR spectroscopy revealed the presence of the lithiated ligand 2, which reported here by solution-phase Al NMR spectroscopy, solid- 27 1 was characterized in situ. state experiments were more successful. Details of the Al{ H} 31 1 2a. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 10.9 (1:1:1:1 4 8 CPMG NMR spectra for 3a−3c and 5a−5c are provided in quartet, J = 54 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.3 P−Li 4 8 the Supporting Information. (d, J = 54 Hz). Li−P 31 1 2b. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 96.4 (1:1:1:1 4 8 CONCLUSIONS quartet, J = 63 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.1 P−Li 4 8 (d, J = 63 Hz). Li−P In summary, we have synthesized aluminum dimethyl and 31 1 2c. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 68.6 (1:1:1:1 4 8 dihydride complexes with a series of amidophosphine ligands 7 quartet, J = 54 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.5 P−Li 4 8 of varying steric bulk. The bulky bidentate ligands 1a−1c (d, J = 54 Hz). Li−P enable the isolation of reactive aluminum dihydrides, the General Synthesis of 3. To a solution of 1 in THF cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes, 1 equiv). The synthesis of which was observed to proceed through ﬁve- cold bath was removed, and the resultant yellow solution was stirred coordinate aluminate intermediates (4a−4c). Evidence from at room temperature for 1 h. The reaction mixture was cooled to −78 X-ray crystallography and solid-state NMR spectroscopy °C, and Me AlCl (1.0 M in hexanes) was added dropwise. The cold indicates that, for all dimethyl and dihydride complexes, both bath was removed, and the resultant solution was stirred at room N- and P-donor atoms are bound to the Al centers in the solid temperature for 1 h. The solvent was removed in vacuo, and the state. In solution, however, altering the steric bulk of the ligand product was extracted in hexane and dried to aﬀord 3a−3c. enables control over the coordination mode at the Al center: 3a. 1a (0.40 g, 0.97 mmol), THF (20 mL), nBuLi (0.39 mL, 0.97 for the bulkiest ligand employed, 1c, both the dimethyl and mmol, 1.0 equiv), and Me AlCl (0.97 mL, 0.97 mmol, 1.0 equiv) dihydride complexes 3c and 5c exist as a mixture of κ -N,P and yielded 3a (0.34 g, 75%) as a pale-yellow solid. Colorless crystals suitable for X-ray crystallography were grown from a saturated diethyl κ -N,N isomers. 1 3 ether solution at 4 °C. H(C D , 500 MHz, 300 K): δ −0.33 (d, J 6 6 HP The variable coordination mode of the ligand is encouraging = 2.5 Hz, 3H, AlCH ), −0.19 (d, J = 2.5 Hz, 3H, AlCH ), 1.10 (m, 3 HP 3 as a potential route to controlling the stoichiometric or 1 3 3 1H, / CH ), 1.19 (d, J = 8.6 Hz, 9H, CH ), 1.22 (d, J = 2 2Norb HP 3tBu HP catalytic reactivity of the aluminum dihydride centers. For 8.6 Hz, 9H, CH ), 1.24 (d, J = 6.8 Hz, 3H, CH ), 1.26 (d, 3tBu HH 3iPr example, preliminary results indicate that 5a−5c are active 3 3 J = 6.8 Hz, 3H, CH ), 1.37 (d, J = 6.8 Hz, 6H, CH ), 1.43 HH 3iPr HH 3iPr catalysts for the hydroboration of alkyl- and arylalkynes with (m, 2H, CH ), 1.55 (m, 1H, / CH ), 1.61 (m, 2CbridgeheadCP 2 2CbridgeheadCN 1 1 HBPin (see the SI). The accessibility of the κ -N,N 1H, / CH ), 1.66 (m, 1H, / CH ), 2.50 (br s, 1H, 2 2Norb 2 2CbridgeheadCN coordination mode for 5c has a clear eﬀect on the reactivity. PCCH ), 2.95 (br s, 1H, NCCH ), 3.44 (sept, J = 6.8 bridgehead bridgehead HH While all three dihydrides catalyze the hydroboration of Hz, 1H, CH ), 3.61 (sept, J = 6.8 Hz, 1H, CH ), 7.17−7.19 (m, iPr HH iPr 3H, H ). C NMR (C D , 126 MHz, 300 K): δ −5.7 (br s, phenylacetylene with HBPin, 5a and 5b are signiﬁcantly more aromatic 6 6 AlCH ), −4.3 (br s, AlCH ), 25.2 (s, CH ), 25.4 (s, CH ), 25.7 3 3 3iPr 3iPr eﬃcient, with conversions of 79 and 83% after 2 h at 110 °C (s, CH ), 25.8 (s, CH ), 25.9 (d, J = 2 Hz, CH ), 3iPr 3iPr CP 2CbridgeheadCP compared to 53% for 5c. We are now further exploring the 27.6 (s, CH ), 27.7 (s, CH ), 30.0 (s, CH ), 30.1 (d, J iPr iPr 2CbridgeheadCN CP coordination chemistry, reactivity, and catalytic applications of = 5 Hz, CH ), 30.5 (d, J = 5 Hz, CH ), 34.4 (d, J = 30 Hz, 3tBu CP 3tBu CP the dihydrides 5a−5c (Scheme 5). CtBu), 34.8 (d, J = 31 Hz, CtBu), 43.8 (d, J = 9 Hz, PCCH), 44.1 CP CP (d, J = 2 Hz, NCCH), 48.3 (d, J = 3 Hz, CH ), 80.2 (d, J = CP CP 2Norb CP Scheme 5. Catalytic Hydroboration of Phenylacetylene and 42 Hz, PCCH), 124.2 (s, C ), 124.3 (s, C ), 126.1 (s, C ), meta meta para 141.7 (d, J = 3 Hz, NC ), 147.1 (s, CCH ), 147.4 (s, CCH ), 2-Cyclooctyne Using 5a−5c CP Ar iPr iPr 31 1 185.1 (d, J = 21 Hz, NCCH). P{ H} NMR (C D , 162 MHz, 300 CP 6 6 K): δ 1.6 (s, Δν = 21.1 Hz). HRMS (APPI): m/z 469.341919 1/2 ([C H AlNP] ; theoretical m/z 469.341252). Elem anal. Found: C, 29 49 74.13; H, 10.38; N, 2.85. Calcd for C H AlNP: C, 74.16; H, 10.52; 29 49 N, 2.98. 11444 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article 1 1 1 3b. 1b (0.3 g, 0.60 mmol), THF (20 mL), nBuLi (0.24 mL, 0.60 (m, 1H, / NCH ), 2.66 (m, 1H, / NCH ), 2.82 (m, 1H, / NCH ), 2 2 2 2 2 2 mmol, 1.0 equiv), and Me AlCl (0.60 mL, 0.60 mmol, 1.0 equiv) 2.89 (m, 1H, NCH ), 3.05 (br s, 1H, CH ), 3.52 (sept, J 2 2 bridgeheadCN HH yielded 3b (0.17 g, 56%) as a yellow solid. Some impurities (less than = 6.8 Hz, 1H, CH ), 3.74 (sept, J = 6.8 Hz, 1H, CH ), 7.15− iPr HH iPr 10%) were observed by NMR spectroscopy because of reaction with 7.20 (m, 3H, H ). C NMR (C D , 126 MHz, 300 K): δ −4.2 aromatic 6 6 (s, AlMe), −3.5 (s, AlMe), 25.2 (s, CH ), 25.4 (s, CH ), 25.68 (s, water but could not be separated because crystallization of 3b was not 3iPr 3iPr CH ), 25.84 (s, CH ), 27.4 (s, CH ), 27.6 (s, CH ), possible. 3iPr 2CbridgeheadCP iPr iPr 1 3 29.2 (s, CH ), 29.4 (d, J = 2.2 Hz, CH ), 29.7 (d, J H NMR (C D , 500 MHz, 300 K): δ −0.26 (d, J = 3.9 Hz, 3H, 3tBu CP 2CbridgeheadCN CP 6 6 HP = 7.6 Hz, CH ), 42.0 (d, J = 4.2 Hz, CH ), 43.6 (s, AlCH ), −0.12 (d, J = 3.9 Hz, 3H, AlCH ), 0.27 (s, 3H, SiCH ), 3tBu CP bridgeheadCN 3 HP 3 3 2 1 NCH ), 44.2 (d, J = 9.9 Hz, CH ), 44.3 (s, NCH ), 46.6 0.32 (s, 3H, SiCH ), 1.12 (d, J = 8.1 Hz, 1H, / CH ), 1.25 (s, 2 CP bridgeheadCP 2 3 HH 2 2Norb (d, J = 5.3 Hz, CH ), 52.5 (d, J = 11.7 Hz, C Bu), 52.8 (d, J 9H, CH ), 1.26 (s, 9H, CH ), 1.25 (d, J = 6.8 Hz, 3H, CP 2Norb CP CP 3tBu 3tBu HH 3 3 = 8.8 Hz, C Bu), 95.5 (d, J = 33.5 Hz, PCCH), 124.29 (s, C ), CH ), 1.26 (d, J = 6.8 Hz, 3H, CH ), 1.32 (d, J = 6.8 Hz, CP meta 3iPr HH 3iPr HH 124.32 (C ), 126.2 (s, C ), 142.0 (d, J = 3.9 Hz, NC ), 146.7 3H, CH ), 1.41 (d, J = 6.8 Hz, 3H, CH ), 1.42 (m, 2H, meta para CP Ar 3iPr HH 3iPr 2 1 (s, CCH ), 148.0 (s, CCH ), 185.3 (d, J = 34.1 Hz, NCCH). CH ), 1.60 (d, J = 8.1 Hz, 1H, / CH ), 1.69 (m, 3iPr 3iPr CP 2CbridgebeadCP HH 2 2Norb 31 1 P{ H} NMR (C D , 162 MHz, 300 K): δ 49.7 (s, Δν = 47.5 Hz). 2H, CH ), 2.53 (br s, 1H, CH ), 3.13 (br s, 1H, 6 6 1/2 2CbridgeheadCN bridgeheadCP 3 3 HRMS (EI): m/z 525.37703 ([C H AlN P] ; theoretical m/z CH ), 3.51 (sept, J = 6.8 Hz, CH ), 3.70 (sept, J = 31 53 3 bridgeheadCN HH iPr HH 525.37871). Elem anal. Found: C, 70.71; H, 10.18; N, 8.03. Calcd for 6.8 Hz, CH ), 7.11−7.21 (m, 3H, H ). C NMR (C D , 126 iPr aromatic 6 6 C H AlN P: C, 70.82; H, 10.16; N, 7.99. MHz, 300 K): δ −6.3 (br d, J = 24.8 Hz, AlCH ), −5.4 (br d, J = 31 53 3 CP 3 CP Synthesis of 4b. To a solution of 1b (0.10 g, 0.2 mmol) in THF 19.9 Hz, AlCH ), 4.6 (d, J = 1.4 Hz, SiCH ), 6.7 (d, J = 3.7 Hz, 3 CP 3 CP (20 mL) at −78 °C was added dropwise nBuLi (2.5 M in hexanes, SiCH ), 25.3 (s, CH ), 25.4 (s, CH ), 25.6 (s, CH ), 26.0 (s, 3 3iPr 3iPr 3iPr 0.08 mL, 0.2 mmol, 1 equiv). The cold bath was removed, and the CH ), 26.3 (s, CH ), 27.6 (s, CH ), 27.8 (s, CH ), 3iPr 2CbridgeheadCP iPr iPr resultant yellow solution was stirred at room temperature for 1 h. The 29.4 (s, CH ), 32.3 (d, J = 5.4 Hz, CH ), 32.7 (d, J 2CbridgeheadCN CP 3tBu CP reaction mixture was cooled to −78 °C, and H Al·NMe Et (0.5 M in = 4.9 Hz, CH ), 40.6 (d, J = 3.5, CHCN), 44.3 (d, J = 43.9, 3 2 3tBu CP CP toluene, 0.4 mL, 1 equiv) was added dropwise. The cold bath was CHCP), 46.6 (d, J = 4.7 Hz, CH ), 50.8 (d, J = 3.9 Hz, C Bu), CP 2Norb CP removed, the resultant yellow solution was stirred at room 50.9 (d, J = 2.8 Hz, C Bu), 99.1 (d, J = 29.2 Hz, PCCH), 124.3 (s, CP CP temperature for 20 min, and the solvent was removed in vacuo to C ), 124.3 (s, C ), 126.3 (s, C ), 141.2 (d, J = 3.1 Hz, NC ), meta meta para CP Ar aﬀord the product as a yellow oil. No further puriﬁcation was 146.6 (s, CCH ), 147.0 (s, CCH ), 186.8 (d, J = 33.9 Hz, iPr iPr CP 31 1 attempted. NCCH). P{ H} (C D , 162 MHz, 300 K): δ 64.0 (s, Δν = 35.8 6 6 1/2 H NMR (C D O, 500 MHz, 300 K): δ 0.29 (s, 3H, SiCH ), 0.33 Hz). HRMS (APPI): m/z 555.371654 ([C H AlN PSi] ; theoreti- 4 8 3 31 55 3 1 3 (s, 3H, SiCH ), 0.84 (m, 1H, / CH ), 1.07 (d, J = 6.8 Hz, 3H, cal m/z 555.371277). 3 2 2Norb HH 3 3 CH ), 1.08 (d, J = 6.8 Hz, 3H, CH ), 1.12 (d, J = 6.8 Hz, 3c. 1c (0.43 g, 0.92 mmol), THF (20 mL), nBuLi (0.37 mL, 0.92 3iPr HH 3iPr HH 3H, CH ), 1.14 (d, J = 6.8 Hz, 3H, CH ), 1.18 (m, 2H, mmol, 1.0 equiv), and Me AlCl (0.92 mL, 0.60 mmol, 1.0 equiv) were 3iPr HH 3iPr CH ), 1.19 (s, 9H, CH ), 1.21 (s, 9H, CH ), 1.25 (m, 2CbridgeheadCP 3tBu 3tBu mixed. To gain analytically pure material, 3c was further puriﬁed by 1 1 1H, / CH ), 1.54 (m, 1H, / CH ), 1.62 (m, 1H, 2 2Norb 2 2CbridgeheadCN recrystallization from hexanes at −20 °C to yield colorless crystals / CH ), 2.19 (br s, 1H, CH ), 3.35 (br s, 1H, 2 2CbridgheadCN bridgeheadCP (0.23 g, 48%). Two isomers were identiﬁed in the NMR spectra with 3 3 2 2 CH ), 3.54 (sept, J = 6.8 Hz, 1H, CH ), 3.63 (sept, J bridgeheadCN HH iPr HH an approximate ratio of 4:3 of κ -N,N-3c to κ -N,P-3c at 300 K = 6.8 Hz, 1H, CH ), 6.83−6.90 (m, 3H, H ). Note: It was not iPr aromatic (determined from the H NMR spectrum). Because of the high air 1 31 possible to locate the Al−H resonances even with the use of H{ P} sensitivity of this species, some impurities were observed in solution 31 1 NMR experiments, likely because of extremely high line width. C NMR spectra ( P{ H} NMR spectrum, 10% unidentiﬁed impurity at NMR (C D O, 126 MHz, 300 K): δ 6.5 (s, SiCH ), 8.3 (d, J = 5.7 4 8 3 CP 75.1 ppm). 2 1 Hz, SiCH ), 24.3 (d, J = 10.2 Hz, CH ), 26.0 (d, J = 15.2 Hz, 3 CP 3iPr CP κ -N,N-3c. H NMR (C D , 500 MHz, 300 K): δ −0.67 (s, 3H, 6 6 CH ), 27.2 (s, CH ), 28.11 (s, CH ), 28.13 (s, CH ), 3iPr 2CbridgeheadCP iPr iPr AlMe), −0.13 (s, 3H, AlMe), 0.89 (m, 1H, / CH ), 1.18 (m, 1H, 2 2Norb 1 3 30.1 (s, CH ), 32.9 (d, J = 5.4 Hz, CH ), 33.4 (d, J 2CbridgeheadCN CP 3tBu CP / CH ), 1.21 (s, 18H, CH ), 1.24 (d, J = 6.8 Hz, 6H, 2 2Norb 3tBu HH = 4.8 Hz, CH ), 42.1 (d, J = 1.5 Hz, CH ), 46.5 (s, 3tBu CP bridgeheadCN CH ), 1.27 (d, J = 6.8 Hz, 3H, CH ), 1.45 (m, 2H, 3iPr HH 3iPr CH ), 47.2 (d, J = 5.5 Hz, CH ), 51.4 (d, J = 11.5 2Norb CP bridgeheadCP CP CH ), 1.47 (d, J = 6.8 Hz, 3H, CH ), 1.63 (m, 1H, 2CbridgeheadCP HH 3iPr t t Hz, C Bu), 51.6 (d, J = 14.6 Hz, C Bu), 111.2 (d, J = 43.1 Hz, 1 1 CP CP / CH ), 1.72 (m, 1H, / CH ), 2.49 (br s, 1H, 2 2CbridgeheadCN 2 2CbridgeheadCN PCCH), 123.1 (d, J = 10.0 Hz, C ), 124.2 (s, C ), 146.7 (s, 1 1 CP meta para CH ), 2.82 (m, 1H, / NCH ), 2.83 (m, 1H, / NCH ), bridgeheadCP 2 2 2 2 CCH ), 148.0 (s, CCH ), 150.7 (s, NC ), 174.2 (d, J = 33.2 Hz, 1 3 iPr iPr Ar CP 2.97 (m, CH ), 3.15 (m, 1H, / NCH ), 3.73 (sept, J = 31 2 bridgeheadCN 2 2 HH NCCH). P NMR (C D O, 162 MHz, 300 K): δ 110.8 (q, J =34 3 4 8 PH 6.8 Hz, 1H, CH ), 3.85 (sept, J = 6.8 Hz, 1H, CH ), 3.88 (m, 7 iPr HH iPr Hz). Li NMR (C D O, 194.4 MHz, 300 K): δ −0.43 (s). HRMS 1 13 4 8 1H, / NCH ), 7.15−7.20 (m, 3H, H ). C NMR (C D , 126 + 2 2 aromatic 6 6 (EI): m/z 528.34912 ([C H N AlPSi] ;theoretical m/z 29 52 3 MHz, 300 K): δ −5.5 (s, AlMe), −4.7 (s, AlMe), 24.3 (s, CH ), 3iPr 528.34891). 24.8 (s, CH ), 25.75 (s, CH ), 25.97 (s, CH ), 26.1 3iPr 3iPr 2CHbridgeheadCP General Synthesis of 5. To a solution of ligand 1a−1c in THF (s, CH ), 27.0 (s, CH ), 28.2 (s, CH ), 29.3 (s, CH ), 3iPr iPr iPr 2CbridgeheadCN cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes). The 29.7 (d, J = 9.5 Hz, CH ), 29.73 (d, J = 7.7 Hz, CH ), 29.8 CP 3tBu CP 3tBu cold bath was removed, and the resultant yellow solution was stirred (d, J = 5.6 Hz, CH ), 43.84 (s, CH ), 43.88 (d, J = 12.6 Hz, CP 3tBu 2Norb CP at room temperature for 1 h. The reaction mixture was cooled to −78 NCH ), 45.3 (s, CH ), 45.7 (d, J =42.0Hz, 2 bridgeheadCP CP °C, and a solution of H Al·NMe in THF was added dropwise. The 3 3 CH ), 48.8 (d, J = 2.8 Hz, NCH ), 53.2 (d, J = 6.0 bridgeheadCN CP 2 CP cold bath was removed, and the resultant colorless solution was t t Hz, C Bu), 63.7 (d, J = 11.7 Hz, C Bu), 103.5 (d, J = 37.7 Hz, CP CP stirred at room temperature for 1 h. The solvent was removed in PCCH), 123.9 (s, C ), 124.5 (s, C ), 125.2 (s, C ), 144.1 (s, meta meta para vacuo, and the product was extracted in hexane and dried to aﬀord a NC ), 146.5 (s, CCH ), 147.0 (s, CCH ), 165.0 (d, J = 5.0 Hz, Ar iPr iPr CP white solid. H Al·NMe Et (0.5 M in toluene) can be used in place of 3 2 31 1 NCCH). P{ H} NMR (C D , 162 MHz, 300 K): δ 99.9 (s, Δν = 6 6 1/2 H Al·NMe . In this work, H Al·NMe Et was used for initial test 3 3 3 2 5.3 Hz). reactions to synthesize up to 0.2 g of 5 using a procedure identical 2 1 3 κ -N,P-3c. H NMR (C D , 500 MHz, 300 K): δ −0.27 (d, J = 6 6 HP with that described above. 3.1 Hz, 3H, AlMe), −0.14 (d, J = 3.1 Hz, 3H, AlMe), 1.06 (dm, HP 5a. 1a (1.63 g, 0.0039 mol), THF (50 mL), nBuLi (1.6 mL, 0.0039 2 1 3 J = 8.1 Hz, 1H, / CH ), 1.25 (d, J = 6.8 Hz, 3H, CH ), HH 2 2Norb HH 3iPr mol, 1.0 equiv), and H Al·NMe (0.84 g, 0.0037 mol, 2.4 equiv) in 3 3 1.26 (d, J = 6.8 Hz, 3H, CH ), 1.30 (s, 9H, CH ), 1.32 (s, 9H, THF (20 mL) yielded 5a (1.57 g, 91%). HH 3iPr 3tBu 1 2 CH ), 1.33 (m, 1H, / CH ), 1.38 (m, 1H, H NMR (C D , 500 MHz, 300 K): δ 1.11 (dm, J = 8.1 Hz, 1H, 3tBu 2 2CbridgeheadCP 6 6 HH 1 3 1 3 3 / CH ), 1.40 (d, J = 6.8 Hz, 3H, CH ), 1.42 (d, / CH ), 1.19 (d, J = 14.2 Hz, 9H, CH ), 1.22 (d, J = 2 2CbridgeheadCP HH 3iPr 2 2Norb HP 3tBu HP 3 2 1 3 J = 6.8 Hz, 3H, CH ), 1.56 (m, J = 8.1 Hz, 1H, / CH ), 14.2 Hz, 9H, CH ), 1.28 (d, J = 6.8 Hz, 3H, CH ), 1.29 (d, HH 3iPr HH 2 2Norb 3tBu HH 3iPr 1.63 (m, 2H, CH ), 2.48 (br s, 1H, CH ), 2.59 J = 6.8 Hz, 3H, CH ), 1.31 (m, 2H, CH ), 1.42 (d, 2CbridgeheadCN bridgeheadCP HH 3iPr 2CbridgeheadCP 11445 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article 3 3 J = 6.8 Hz, 3H, CH ), 1.44 (d, J = 6.8 Hz, 3H, CH ), 1.51 CH ), 44.2 (s, CH ), 45.1 (s, CH ), 45.7 (s, HH 3iPr HH 3iPr 2CbridgeaheadCN 2Norb bridgeheadCN 1 2 NCH ), 45.8 (d, J = 39.1 Hz, CH ), 48.8 (d, J = 3.3 Hz, (m, 1H, / CH ), 1.62 (dm, J =8.1 Hz,1H, 2 2CbridgeheadCN HH 2 CP bridgeheadCP CP t t 1 1 NCH ), 53.5 (d, J = 5.0 Hz, C Bu), 53.8 (d, J = 3.9 Hz, C Bu), / CH ), 1.67 (m, 1H, / CH ), 2.53 (br s, 1H, 2 CP CP 2 2Norb 2 2CbirdgeheadCN 104.8 (d, J = 36.9 Hz, PCCH), 123.9 (s, C ), 124.6 (s, C ), CP meta meta PCCH ), 2.94 (br s, 1H, NCCH ), 3.42 (sept, J = 6.8 bridgehead bridgehead HH 125.2 (s, C ), 143.22 (s, NC ), 145.8 (CCH ), 146.53 (s, para Ar iPr Hz, CH ), 3.63 (sept, J = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, iPr HH iPr 31 1 CCH ), 167.4 (d, J = 2.7 Hz, NCCH). P{ H} NMR (C D , 162 iPr CP 6 6 AlH ), 7.16−7.22 (m, 3H, H ). C NMR (C D , 126 MHz, 300 2 aromatic 6 6 MHz, 300 K): δ 96.9 (s, Δν = 137.9 Hz). 1/2 K): δ 24.0 (s, CH ), 24.7 (s, CH ), 25.2 (d, J = 1.8 Hz, 3iPr 3iPr CP 2 1 2 κ -N,P-5c. H NMR (C D , 500 MHz, 300 K): δ 1.07 (dm, J = 6 6 HH CH ), 25.8 (s, CH ), 25.9 (s, CH ), 28.0 (s, CH ), 2CbridgeheadCP 3iPr 3iPr iPr 1 3 8.4 Hz, 1H, / CH ), 1.29 (d, J = 6.8 Hz, 3H, CH ), 1.30 (d, 2 2Norb HH 3iPr 28.1 (s, CH ), 29.6 (d, J =4.5 Hz,CH ), 30.1 (s, iPr CP 3tBu J = 6.8 Hz, 3H, CH ), 1.32 (s, 9H, CH ), 1.35 (s, 9H, HH 3iPr 3tBu CH ), 30.1 (d, J = 4.0 Hz, CH ), 34.1 (d, J = 2CbridgeheadCN CP 3tBu CP t t CH ), 1.39 (m, 2H, CH ), 1.42 (d, J = 6.8 Hz, 3H, 18.2 Hz, C Bu), 34.3 (d, J = 18.9 Hz, C Bu), 43.6 (d, J = 9.1 Hz, 3tBu 2CbridgeheadCP HH CP CP CH ), 1.45 (d, J = 6.8 Hz, 3H, CH ), 1.56 (m, 1H, 3iPr HH 3iPr CH ), 44.1 (d, J = 2.1 Hz, CH ), 48.6 (d, J = bridgeheadCP CP bridgeheadCN CP / CH ), 1.63 (m, 2H, CH ), 2.52 (m, 1H, 3.9 Hz, CH ), 81.0 (d, J = 44.5 Hz, PCCH), 124.1 (s, C ), 2 2Norb 2CbridgeheadCN 2Norb CP meta 1 1 CH ), 2.60 (m, 1H, / NCH ), 2.72 (m, 1H, / NCH ), 124.2 (s, C ), 126.3 (s, C ), 141.4 (d, J = 3.0 Hz, NC ), 146.8 bridgeheadCP 2 2 2 2 meta para CP Ar 2.79 (m, 1H, / NCH ), 2.88 (m, 1H, NCH ), 3.02 (m, 1H, (s, CCH ), 147.1 (s, CCH ), 185.1 (d, J = 20.1 Hz, NCCH). 2 2 2 iPr iPr CP 3 3 31 1 CH ), 3.54 (sept, J = 6.8 Hz, 1H, CH ), 3.76 (sept, J P{ H} NMR (C D , 162 MHz, 300 K): δ 8.0 (s, Δν = 34.7 Hz). bridgeheadCN HH iPr HH 6 6 1/2 = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, AlH ), 7.18−7.21 (m, 3H, iPr 2 HRMS (EI): m/z 441.30855 ([C H AlNP] ; theoretical m/z 27 45 H ). C NMR (C D , 126 MHz, 300 K): δ 24.0 (s, CH ), aromatic 6 6 3iPr 441.30996). Elem anal. Found: C, 73.11; H, 10.39; N, 3.13. Calcd −1 24.7 (s, CH ), 25.3 (s, CH ), 25.8 (s, CH ), 25.86 (s, 3iPr 2CbridgeheadCP 3iPr for C H AlNP: C, 73.43; H, 10.27; N, 3.17. IR (solid, cm ): 1810, 27 45 −1 CH ), 27.9 (s, CH ), 28.1 (s, CH ), 29.0 (d, J = 4.6 Hz, 3iPr iPr iPr CP 1786. IR (solution, cm ): 1811. CH ), 29.3 (s, CH ), 29.9 (d, J = 4.6 Hz, CH ), 3tBu 2CbridgeheadCN CP 3tBu 5b. 1b (3.00 g, 0.0060 mol), THF (80 mL), nBuLi (2.4 mL, 0.0060 42.7 (d, J = 4.4 Hz, CH ), 43.6 (d, J = 9.9 Hz, CP bridgeheadCN CP mol, 1.0 equiv), and H Al·NMe (1.28 g, 0.014 mol, 2.4 equiv) in 3 3 CH ), 43.9 (s, NCH ), 44.2 (s, NCH ), 46.6 (d, J = 4.9 bridgeheadCP 2 2 CP THF (15 mL) yielded 5b (2.95 g, 93%). Colorless crystals suitable for Hz, CH ), 53.4 (d, J = 9.8 Hz, C Bu), 53.6 (d, J = 5.4 Hz, 2Norb CP CP X-ray crystallography were grown from a saturated hexane solution at C Bu), 97.0 (d, J = 35.3 Hz, PCCH), 124.1 (s, C ), 124.3 (s, CP meta −20 °C. 1 C ), 126.4 (s, C ), 141.0 (d, J = 4.0 Hz, NC ), 146.51 (s, meta para CP Ar H NMR (C D , 500 MHz, 300 K): δ 0.24 (s, 3H, SiCH ), 0.29 (s, 6 6 3 2 1 4 CCH ), 146.8 (s, CCH ), 185.4 (d, J = 34.0 Hz, NCCH). iPr iPr CP 3H, SiCH ), 1.13 (d, J = 8.1 Hz, 1H, / CH ), 1.28 (d, J = 3 HH 2 2Norb HP 31 1 4 P{ H} NMR (C D , 162 MHz, 300 K): δ 47.8 (s, Δν = 96.6 Hz). 6 6 1/2 0.8 Hz, 9H, CH ), 1.29 (d, J = 0.8 Hz, 9H, CH ), 1.30 (d, 3tBu HP 3tBu 3 3 HRMS (EI): m/z 497.35079 ([C H AlN P] ; theoretical m/z 29 49 3 J = 6.8 Hz, 3H, CH ), 1.31 (d, J = 6.8 Hz, 3H, CH ), 1.38 HH 3iPr HH 3iPr 3 497.34741). Elem anal. Found: C, 69.80; H, 9.80; N, 8.33. Calcd for (m, 2H, CH ), 1.44 (d, J = 6.8 Hz, 3H, CH ), 1.45 2CbridgeheadCP HH 3iPr −1 3 2 1 C H AlN PSi: C, 69.99; H, 9.92; N, 8.44. IR (solid, cm ): 1825, 29 51 3 (d, J = 6.8 Hz, 3H, CH ), 1.62 (d, J = 8.1 Hz, / CH ), HH 3iPr HH 2 2Norb −1 1801. IR (solution, cm ): 1823. 1.67 (m, 2H, CH ), 2.57 (br s, 1H, CH ), 3.12 2CbridgeheadCN bridgeheadCP (br s, 1H, CH ), 3.53 (sept, J = 6.8 Hz, 1H, CH ), 3.74 bridgeheadCN HH iPr ASSOCIATED CONTENT (sept, J = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, Al−H), 7.17−7.23 (m, HH iPr 3H, H ). C NMR (C D , 126 MHz, 300 K): δ 4.4 (d, J = 1.6 aromatic 6 6 CP * Supporting Information Hz, SiCH ), 6.3 (d, J = 3.2 Hz, SiCH ), 24.1 (s, CH ), 24.6 (s, 3 CP 3 3iPr The Supporting Information is available free of charge on the CH ), 25.6 (d, J = 1.0 Hz, CH ), 25.8 (s, CH ), 25.9 3iPr CP 2CbridgeheadCP 3iPr ACS Publications website at DOI: 10.1021/acs.inorg- (s, CH ), 28.0 (s, CH ), 28.3 (s, CH ), 29.3 (s, CH ), 3iPr iPr iPr 2CHbridgheadCN chem.9b01061. 32.3 (d, J = 5.4 Hz, CH ), 32.7 (d, J = 5.2 Hz, CH ), 40.7 (d, CP 3tBu CP 3tBu J = 3.9 Hz, CH ), 43.9 (d, J = 9.7 Hz, CH ), 46.8 CP bridgheadCN CP bridgheadCP Experimental procedures, full characterization of com- (d, J = 4.9 Hz, CH ), 51.4 (d, J = 2.5 Hz, C Bu), 51.5 (d, J = CP 2Norb CP CP pounds, crystallographic details, solid-state NMR details, 3.6 Hz, C Bu), 99.7 (d, J = 32.6 Hz, PCCH), 124.1 (s, C ), 124.2 CP meta and solution-phase NMR spectra (PDF) (s, C ), 126.5 (s, C ), 140.8 (d, J = 3.5 Hz, NC ), 146.4 (s, meta para CP Ar C CH ), 146.5 (s, C CH ), 187.6 (d, J = 33.9 Hz, NCCH). Ar iPr Ar iPr CP Crystallographic data (ZIP) 31 1 P{ H} NMR (C D , 162 MHz, 300 K): δ 61.3 (s, Δν = 65.4 Hz). 6 6 1/2 HRMS (EI): m/z 527.33886 ([C H AlN PSi] ; theoretical m/z Accession Codes 29 51 3 527.33998). Elem anal. Found: C, 65.95; H, 9.66; N, 7.83. Calcd for CCDC 1905997 and 1906037−1906039 contain the supple- −1 C H AlN PSi: C, 66.00; H, 9.74; N, 7.96. IR (solid, cm ): 1831, 29 51 3 mentary crystallographic data for this paper. These data can be −1 1816. IR (solution, cm ): 1820. obtained free of charge via www.ccdc.cam.ac.uk/data_request/ 5c. 1c (2.00 g, 0.0043 mol), THF (100 mL), nBuLi (1.7 mL, cif,orbyemailing data_request@ccdc.cam.ac.uk,orby 0.0043 mol, 1.0 equiv), and H Al·NMe (0.91 g, 0.010 mol, 2.4 equiv) 3 3 contacting The Cambridge Crystallographic Data Centre, 12 in THF (15 mL) were mixed. The ﬁnal product was further puriﬁed Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. by recrystallization from hexanes at −20 °C to yield 5c as colorless crystals (1.68 g, 79%). Two isomers were identiﬁable in the solution- 2 2 phase NMR spectra in a ratio of 4:7 for κ -N,N-5c to κ -N,P-5c at 300 AUTHOR INFORMATION K (determined from the H NMR spectrum). 2 1 Corresponding Author κ -N,N-5c. H NMR (C D , 500 MHz, 300 K): δ 0.91 (m, 1H, 6 6 1 4 3 *E-mail: michael.cowley@ed.ac.uk (M.J.C.). / CH ), 1.18 (d, J = 1.3 Hz, 9H, CH ), 1.23 (d, J = 6.8 2 2Norb HP 3tBu HH 1 3 Hz, 3H, CH ), 1.25 (m, 1H, / CH ), 1.31 (d, J = 6.8 Hz, 3iPr 2 2Norb HH ORCID 6H, CH ), 1.32 (s, 9H, CH ), 1.43 (m, 2H, CH ), 1.60 3iPr 3tBu 2CbridgeheadCP Michael J. Cowley: 0000-0003-0664-2891 3 1 (d, J = 6.8 Hz, 3H, CH ), 1.65 (m, 1H, / CH ), 1.71 HH 3iPr 2 2CbridgeheadCN Author Contributions (m, 1H, / CH ), 2.56 (m, 1H, CH ), 2.70 (m, 2 2CbridgeheadCN bridgeheadCP 1 1 1H, / NCH ), 2.78 (m, 1H, / NCH ), 2.97 (m, 1H, CH ), R.L.F. conceived and performed experiments and cowrote the 2 2 2 2 bridgeheadCN 1 1 3 3.33 (m, 1H, / NCH ), 3.56 (m, 1H, / NCH ), 3.85 (sept, J = 2 2 2 2 HH manuscript, G.S.N. contributed to crystallographic studies, and 6.8 Hz, 1H, CH ), 3.98 (sept, J = 6.8 Hz, 1H, CH ), 4.3 (br s, iPr HH iPr M.J.C. designed and coordinated the study and cowrote the 2H, AlH ) 7.18−7.21 (m, 3H, H ). C NMR (C D , 126 MHz, 2 aromatic 6 6 manuscript. 300 K): δ 25.4 (s, CH ), 25.6 (s, CH ), 25.7 (s, CH ), 2CbridgeheadCP 3iPr 3iPr Notes 25.92 (s, CH ), 27.5 (s, CH ), 28.9 (s, CH ), 29.0 (d, J = 4.6 3iPr iPr iPr CP Hz, CH ), 29.6 (d, J = 10.7 Hz, CH ), 29.8 (d, J = 1.8 Hz, The authors declare no competing ﬁnancial interest. 3tBu CP 3tBu CP 11446 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article (18) Liang, L.-C. Metal complexes of chelating diarylamido ACKNOWLEDGMENTS phosphine ligands. Coord. Chem. Rev. 2006, 250 (9), 1152−1177. Mass spectrometry was performed at the Scottish Instrumen- (19) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. The Transition tation and Resource Centre for Advanced Mass Spectrometry Metal Coordination Chemistry of Hemilabile Ligands. In Progress in at the University of Edinburgh by Faye Cruikshank (APPI) Inorganic Chemistry; Karlin, K. D., Ed.; John Wiley & Sons, Inc., 1999; and Alan Taylor (EI). This project received funding from the Vol. 48, pp 233−350. (20) Fryzuk, M. D.; Giesbrecht, G. R.; Olovsson, G.; Rettig, S. J. European Research Council under the European Union’s Synthesis and Characterization of Four- and Five-Coordinate Horizon 2020 research and innovation program (Grant ERC- Organoaluminum Complexes Incorporating the Amido Diphosphine 2016-STG-716315). Ligand System N(SiMe CH PPr ) . Organometallics 1996, 15 (22), 2 2 2 2 4832−4841. REFERENCES (21) Lee, P.-Y.; Liang, L.-C. Synthesis and Structural Character- ization of Five-Coordinate Aluminum Complexes Containing Diary- (1) Cox, L. R. Science of Synthesis; Thieme Chemistry, 2008; Vol. 36, lamido Diphosphine Ligands. Inorg. Chem. 2009, 48 (12), 5480− p 55. (2) Bismuto, A.; Thomas, S. P.; Cowley, M. J. Aluminum Hydride (22) Jones, C.; Koutsantonis, G. A.; Raston, C. L. Lewis base Catalyzed Hydroboration of Alkynes. Angew. Chem., Int. Ed. 2016, 55 adducts of alane and gallane. Polyhedron 1993, 12 (15), 1829−1848. 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Park, K.; Zachariah, M. R. Surface Passivation of Bare Aluminum 11447 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Nanoparticles Using Perfluoroalkyl Carboxylic Acids. Chem. Mater. 2005, 17 (11), 2987−2996. 11448 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Inorganic Chemistry Pubmed Central http://www.deepdyve.com/lp/pubmed-central/flexible-coordination-of-n-p-donor-ligands-in-aluminum-dimethyl-and-8sUaircqfP

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Publisher: Pubmed Central
Copyright: Copyright © 2019 American Chemical Society
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DOI: 10.1021/acs.inorgchem.9b01061
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Abstract

This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes. Article pubs.acs.org/IC Cite This: Inorg. Chem. 2019, 58, 11439−11448 Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes Rosalyn L. Falconer, Gary S. Nichol, and Michael J. Cowley* School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K. * Supporting Information ABSTRACT: Aluminum hydrides, once a simple class of stoichiometric reductants, are now emerging as powerful catalysts for organic transformations such as the hydroboration or hydrogenation of unsaturated bonds. The coordination chemistry of aluminum hydrides supported by P donors is relatively underexplored. Here, we report aluminum dihydride and dimethyl complexes supported by amidophosphine ligands and study their coordination behavior in solution and in the solid state. All complexes exist as κ -N,P complexes in the solid state. However, we ﬁnd that for amidophosphine ligands bearing bulky aminophosphine donors, aluminum dihydride and dimethyl complexes undergo a “ligand-slip” rearrangement in solution to generate κ -N,N complexes. Thus, importantly for catalytic activity, we ﬁnd that the coordination behavior of the P donor can be modulated by controlling its steric bulk. We show that the reported aluminum hydrides catalyze the hydroboration of alkynes by HBPin and that the variable coordination mode exhibited by the amidophosphine ligand modulates the catalytic activity. INTRODUCTION Aluminum hydrides such as LiAlH , sodium bis(2-methox- yethoxy)aluminum hydride (RedAl), and AlH are ubiquitous in synthetic chemistry for their use as reducing agents. Recently, the scope of the reactivity of these simple aluminum hydrides has been expanded into catalytic hydroboration of alkenes and alkynes, a development of signiﬁcant environ- mental and economic importance because of the high abundance and relatively low toxicity of aluminum compared 2,3 to platinum group metals. Numerous other uncomplicated Figure 1. Literature examples of aluminum dihydride and dimethyl aluminum hydride compounds are also capable of hydro- complexes stabilized by N-based ligands (I−III) or mixed donor 9−11,15,20,21 i boration or even hydrogenation of unsaturated polar bonds ligands (IV−VI). (I and IV have Ar = 2,6-C H Pr , and VI 6 3 2 4,5 i i such as aldehydes, ketones, or imines. Aluminum hydride has R = R′ = Ph, Pr or R = Ph and R′ = Pr). compounds with more complex ligands have also been investigated. For example, N-heterocyclic imine-coordinated array of ligand classes is essential for the expansion of aluminum hydrides catalyze carbonyl hydroboration while the aluminum hydride chemistry and catalysis. β-diketiminate-stabilized aluminum dihydride I (Figure 1) also Aluminum dihydrides or related species with P-based ligands catalyzes the hydroboration of alkynes. The dihydride I is also are much rarer. A few examples of dimethylaluminum a precursor to β-diketiminate-stabilized aluminum(I) species complexes with mixed-donor ligands are known, in which (at least within the coordination sphere of a transition metal). bidentate ligands having one N donor also contain a “soft” 14−18 Reported aluminum dihydride complexes overwhelmingly donor, such as S or P (IV and V; Figure 1). The likely 9−13 use N-donor ligands (e.g., I−III; Figure 1). Typically, more labile Al−Pinteraction oﬀers the possibility of hemilability, which can be useful in the stabilization of these ligands are also multidentate (to stabilize the intrinsically catalytic transition or resting states. Indeed, Fryzuk et al. electron-poor Al center) and sterically hindered, in order to used NMR spectroscopy to demonstrate the ﬂuxional prevent dimerization or oligimerization by bridging inter- actions. In coordination chemistry, ligands greatly inﬂuence the chemistry at the metal center. Thus, the investigation and Received: April 15, 2019 development of aluminum hydride chemistry using a diverse Published: August 14, 2019 © 2019 American Chemical Society 11439 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article coordination of P-donor atoms in V,resulting in an Scheme 1. Lithiation of Ligand 1 To Form 2 Followed by equilibrium between four- and ﬁve-coordinate Al centers. Reaction with Dimethylaluminum Chloride To Form In comparison to mixed-donor methyl complexes, mixed- Dimethylaluminum Complexes 3a−3c donor aluminum dihydride complexes are scarce, with only a single example. Most P-coordinated aluminum hydrides are limited to simple adducts between phosphines and alane, with the exception of VI (Figure 1), reported by Liang et al. in 2009, which was synthesized via the reduction of the 21,22 corresponding aluminum dichloride using LiAlH . Hemil- ability of the P donors was not found in this example, likely because of the rigidity of the ligand backbone. Herein, we describe novel aluminum dimethyl and dihydride species stabilized by mixed N,P-donor ligands that display ﬂexible coordination modes based on a “ligand-slip” phenom- pentane, followed by ﬁltration and evaporation of the solvent enon. aﬀorded 3a−3c as yellow air-sensitive solids. Complexes 3a and 3c could be isolated as analytically pure solids by RESULTS AND DISCUSSION ■ crystallization, while 3b was clearly identiﬁed but resisted Theamidophosphineligands 1a−1c (Figure 2)have puriﬁcation attempts. All three complexes 3a−3c were previously been used to prepare nickel and palladium extremely sensitive to air and moisture. The solid-state structures of 3a and 3c were determined by X-ray crystallography (Figure 3). Both compounds have a tetrahedral Al center with coordinated N and P donors, forming a planar ring. The ring is heavily skewed with (as might be expected) a substantially shorter interaction between Al and the N donor than with the phosphine [e.g., 3a, Al1−N1 1.8985(14) Å vs Al1−P1 2.4800(6) Å]. Both the Al−N and Al−P distances are comparable to those previously reported, for example the N,P-coordinated dimethylaluminum complex Figure 2. Mixed-donor ligands 1a−1c. IV [Al−N 1.894(6) Å; Al−P 2.477(3) Å]. The Al−N bond distances of 3a and 3c are indistinguish- complexes, as well as to support reactive silicon(II) able, but the Al−P bond length is slightly longer in the latter at 24−27 compounds. The steric bulk around both the N and P 2.5304(8) Å, indicating that P is less strongly bound to the Al centers of 1a−1c has not only enabled the isolation of reactive center. The aminophosphine donor of 3c is more electron- species such as silicon(II) hydrides but also modulates donating than the dialkylphosphine donor of 3a, which would II IV reversible Si /Si oxidative additions/reductive eliminations. be expected to give rise to the opposite trend. The origin of At the P donor in particular, both steric bulk and electron- the diﬀerence is likely due to steric eﬀects: the greater steric donating ability are readily tunable. We were interested in bulk in 3c prevents the close approach of the phosphine to the whether this class of ligands could be employed to support Al Al center. Indeed, this can be observed in the C1−Al1−C2 centers and whether they could be used to modulate their angle, which is smaller in the case of 3c [106.4(2)°] than 3a structure and reactivity. [109.00(9)°] despite the similar bite angles of the two [3a, Synthesis and Solid-State Structures of Aluminum 86.67(4)°; 3c, 85.59(8)°]. Dimethyl Complexes. Dimethylaluminum complexes are a Solution Behavior of 3a−3c. Despite their similar solid- broad class of compounds that have been reported as catalysts state structures, solution-phase NMR spectroscopy revealed 28−30 or cocatalysts in alkene polymerization. Complexes of diﬀerences in the coordination behavior among the dimethy- dimethylaluminum stabilized by many N- or mixed-donor laluminum complexes 3a−3c. No signals were observed for any ligands have been reported, rendering this class of compounds of the compounds by Al NMR spectroscopy. ideal for benchmarking the coordination abilities of ligands NMR spectroscopy of dimethylaluminum complexes 3a and 1a−1c. We decided to ﬁrst investigate the coordination of 3b was consistent with the solid-state structure determined for 31 1 ligand 1 to dimethylaluminum moieties. 3a. P{ H} NMR spectroscopy revealed a single resonance for IV The coordination of 1b and 1c to Si centers has been each (3a, 1.6 ppm; 3b, 64.0 ppm) shifted upﬁeld compared to reported and was achieved by deprotonation before treatment the respective free ligand resonances [Δ∂(3a)= −54.4 ppm; 31 1 with the appropriate silicon halide. Accordingly, ligands 1a− Δ∂(3b)= −83.3 ppm]. The P{ H} NMR resonances for 3a 1c were deprotonated with nBuLi at −78 °Cto aﬀord yellow and 3b were also signiﬁcantly broadened in comparison to the solutions of 2a−2c (Scheme 1). A characteristic resonance is free ligands 1a and 1b, presumably as a result of coordination 31 1 5 observed in the P{ H} NMR spectra of these solutions in the of the P to the quadrupolar (I = / ) Al nucleus [3a, full width form of a 1:1:1:1 quartet upﬁeld compared to the free ligand. at half-maximum (Δν ) = 21.1 Hz; 1a, Δν = 2.7 Hz]. 1/2 1/2 The 1:1:1:1 multiplicity indicates coordination to Li (e.g., 2a, In the HNMR spectraof 3a and 3b,resonances 31 1 7 P{ H} NMR δ 10.9, J = 54 Hz). Similarly, in the Li NMR corresponding to the aluminum methyl groups appear as PLi doublets arising from coupling to P (3a, δ −0.33 and −0.19, spectra, doublets are observed because of coupling with P (e.g., 2 1 J = 2.5 Hz). The H NMR spectrum also shows that each 2a, Li NMR δ 1.3, J = 54 Hz). HP LiP The dimethylaluminum complexes 3a−3c were obtained by CH group in the 2,6-diisopropylphenyl (Dipp) substituent is reaction of the in situ generated lithiated ligand 2 with 1 equiv inequivalent, indicating restricted rotation likely because of of dimethylaluminum chloride. Extraction of the products in steric constraints. 11440 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Figure 3. Molecular structures of 3a (left) and 3c (right) with thermal ellipsoids drawn at the 50% probability level. H and disordered ligand atoms are omitted for clarity. Selected bond distances (Å) and angles (deg) for 3a:N1−Al1 1.895(14), P1−Al1 2.4800(6), Al1−C1 1.9652(19), Al1−C2 1.970(2); N1−Al1−P1 86.67(4), N1−Al1−C1 116.12(8), N1−Al1−C2 115.25(8), P1−Al1−C1 114.53(7), P1−Al1−C2 114.00(7), C1−Al1−C2 109.00(9). Selected bond distances (Å) and angles (deg) for 3c:N1−Al1 1.917(3), P1−Al1 2.5304(9), Al1−C1 1.967(4), Al1−C2 1.964(4); N1− Al1−P1 85.59(8), N1−Al1−C1 116.14(19), N1−Al1−C2 116.19(19), P1−Al1−C1 115.98(13), P1−Al1−C2 115.99(14), C1−Al1−C2 106.4(2). Crystalline 3c was also characterized by solution-phase spectroscopic experiments veriﬁed that in both isomers the 31 1 NMR spectroscopy. Surprisingly, the P{ H} NMR spectrum ligand backbone was intact and undisturbed. The possibility of contained two resonances, at 99.9 and 49.7 ppm, in a ratio of a dimeric κ -N isomer of 3c (with, e.g., bridging methyl 1 1 3:2 (the same ratio was observed by H NMR spectroscopy). ligands) was excluded based on analysis of the H DOSY NMR spectrum, which indicated that both of the observed isomers The resonance at 49.7 ppm is broadened (Δν = 47.5 Hz) 1/2 and downﬁeld (Δ∂ = −40.9 ppm) from that of 1c and so is diﬀused at the same rate in solution. Similarly, high-resolution consistent with coordination of P to the Al center as in 3a and mass spectrometry (HRMS) also identiﬁed the product as 3c, 3b. Conversely, the resonance at 99.9 ppm is sharp (Δν = with no evidence of a dimeric species observed. 1/2 5.3 Hz) and close in chemical shift to that of the free ligand 1c Synthesis of Aluminum Dihydride Complexes. Follow- ing the preparation of the dimethylaluminum complexes 3a− (Δ∂ = +9.3 ppm), which indicates that P in this environment is 3c, we turned our attention to the preparation of aluminum not coordinated to the Al center. On the basis of the P NMR spectroscopic data and by dihydride complexes. Ligands 1a−1c do not react with analogy with the behavior more fully studied in the hydride Me EtN·AlH , in contrast to the observed reactivity of amidine 2 3 analogue 5c (see below), we propose that 3c exists in two ligands, which evolve H and form aminidinatoaluminum dihydrides. Treatment with LiAlH also had no eﬀect. Thus, forms in solution, in which the ligand exhibits a variable 2 2 we used the lithiated ligands 2a−2c as precursors instead. coordination mode, having either κ -N,P or κ -N,N coordina- Treatment of 2b with a single equivalent of Me EtN·AlH tion (Scheme 2). In the solid state, κ -coordination is 2 3 exclusively observed. In solution, however, the two isomers resulted in a yellow solution, the P NMR spectrum of which are present as a result of the ﬂexible coordination mode of the revealed a quartet (δ 110.8, J = 34 Hz), which collapsed to a PH 31 1 singlet in the P{ H} NMR spectrum. This evidence, as well ligand. 1 2 as further characterization by multinuclear NMR spectroscopy The H NMR spectrum of 3c is consistent with both the κ - and mass spectrometry, conﬁrmed formation of the aluminate N,P and κ -N,N isomers existing in solution, with two sets of complex 4b (Scheme 3). resonances present in a ratio of 57:43 (consistent with the 3:2 ratio observed by P NMR). Multinuclear 2D NMR The addition of a second equivalent of Me EtN·AlH to 2 3 31 1 solutions of 4b was monitored by P{ H} NMR spectroscopy, 2 2 a which revealed complete consumption of 4b and the formation Scheme 2. Proposed Structures of κ -N,P- and κ -N,N-3c Scheme 3. Proposed Mechanism for the Reaction of 2 with Me EtN·AlH (NR = NMe or NMe Et) To Form the 2 3 3 3 2 Aluminum Dihydride 5 via the Charged Intermediate 4 a 2 In the solid state, only κ -N,P-3c is observed, while in solution, both 2 2 the κ -N,P- and κ -N,N isomers are observed. 11441 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Figure 4. Molecular structures of 5b (left) and 5c (right). The aluminum hydride atoms were located using a diﬀerence map and allowed to reﬁne freely. H and disordered ligand atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) for 5b:N1−Al1 1.8972(15), P1−Al1 2.4442(7); N1−Al1−P1 87.47(5). Selected bond lengths (Å) and angles (deg) for 5c:N1−Al1 1.892(2), P1−Al1 2.4790(10); N1−Al1−P1 86.60(6). of a new species represented by a broad singlet (61.3 ppm, indicating continued restricted rotation. Compound 5c has more complex solution behavior that will be discussed below. Δν = 55.7 Hz), indicating P coordination to Al. Analysis of 1/2 the Al NMR spectrum revealed the formation of LiAlH .On IR spectroscopy of the solid-state samples of 5a−5c revealed the expected symmetric and antisymmetric Al−H stretches the basis of this evidence, the reaction pathway shown in −1 −1 (5a, 1810 and 1786 cm ; 5b, 1831 and 1816 cm ; 5c, 1825 Scheme 3 is proposed: the reaction of 2b with Me EtN·AlH 2 3 −1 and 1801 cm ) for a four-coordinate aluminum dihydride proceeds by forming 4b by displacement of the amine from 33,34 center. Me EtN·AlH . The second 1 equivalent of Me EtN·AlH 2 3 2 3 Solid-State Structures of 5b and 5c. The structures of abstracts a hydride from 4b, generating 5b and LiAlH and 5b and 5c were veriﬁed by X-ray diﬀraction (Figure 4). eliminating the amine. Broadly, the structures are analogous to those of 3a and 3c. When 2a was treated with 1 equiv of Me EtN·AlH , the 2 3 The amidophosphine ligand in each compound is κ -N,P- resulting pale-yellow solution was revealed to contain a mixture 31 1 coordinated, which together with the hydride ligands (located of compounds by P{ H} NMR spectroscopy. In addition to using a diﬀerence map and allowed to reﬁne freely) results in a residual lithiated ligand 2a, equal quantities of the aluminate tetrahedral environment at the Al center. The two structures intermediate 4a (8.0 ppm) and the neutral aluminum have statistically identical N−Al bond distances [5b, dihydride 5a (−10.1 ppm) were observed. LiAlH was also 1.8972(15) Å; 5c, 1.892(2) Å], which are essentially identical observed by Al NMR spectroscopy. The 2:1:1 ratio of the with those observed for the dimethyl analogues 3a and 3c.A three species reveals that the lithiated ligand 2a and the more substantial diﬀerence is observed in the P−Al bond intermediate aluminate 4a react at comparable rates with distances, which for the dihydride 5c is shorter than that in the Me EtN·AlH to generate a statistical mixture. This contrasts 2 3 corresponding dimethyl complex 3c [Al1−P1: 5c, 2.4791(10) to the situation for 4b, where hydride abstraction by Me EtN· Å; 3c, 2.5304(8) Å]. Contraction of this bond can be explained AlH is much slower than its coordination to the lithiated by the smaller size of the hydride substituents. Similarly, a ligand 2b. Upon the addition of a second equivalent of comparison between the two dihydrides 5b and 5c reveals a Me EtN·AlH to 4a, the reaction mixture turned colorless and 2 3 shorter Al1−P1 distance for 5b as a result of reduced bulk at 31 1 the P{ H} NMR spectrum showed complete conversion to the P center in comparison to 5c [5b, 2.4442(7) Å; 5c, 5a (7.5 ppm). 2.4791(10) Å]. The larger bite angles for the dihydrides 5b Preparatively, the dihydride complexes 5a−5c were obtained and 5c [5b, 87.47(5)°; 5c, 86.60(6)°] compared to those of in multigram quantities from treatment of the lithiated ligands the dimethyl compounds are also due to the smaller hydride 2a−2c with 2 equiv of Me N·AlH or Me EtN·AlH . All three 3 3 2 3 substituents compared to the methyl groups. compounds could be isolated as colorless solids in excellent Solution-Phase NMR Characterization of 5c. Like its yields of 80−90%. Dihydrides 5b and 5c could be further dimethyl analogue 3c, the dihydride 5c exhibits variable puriﬁed by crystallization from hexane. coordination modes in solution. Upon dissolution of crystalline 31 1 In the H NMR spectra of 5a and 5b,Al−H resonances are 5c, the P{ H} NMR spectrum revealed the presence of two visible as very broad singlets at 4.6 ppm (5a, Δν = 71.6 Hz; broad singlets at 96.9 ppm (Δν = 137.9 Hz) and 47.8 ppm 1/2 1/2 5b, Δν = 125.3 Hz) because of the inﬂuence of the (Δν = 96.6 Hz) in a ratio of 1:2. By H NMR, two sets of 1/2 1/2 quadrupolar Al atom. Despite the lower steric inﬂuence of the resonances were also observed for all proton environments, hydride ligands compared to the methyl ligands of 3a and 3b, including the dihydride ligands (signals at κ -N,N-5c, 4.3 ppm, the methyl groups of the Dipp substituent remain inequivalent, κ -N,P-5c, 4.6 ppm; the ratio of the two species as measured by 11442 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article H NMR in a ratio of 35:65, consistent with that observed in the P NMR spectrum). The two solution-phase isomers of 5c were determined to be 2 2 κ -N,P-5c, as observed in the solid state, and a κ -N,N isomer in which the phosphine ligand has “slipped” and coordinates through one of the P-bound N atoms (Scheme 4). Evidence for the κ -N,N coordination mode is as follows: 2 2 2 2 1 Scheme 4. Proposed Structures of κ -N,P- and κ -N,N-5c Figure 5. Computed energies of κ -N,P-, κ -N,N-, and κ -N-5c [M062X/6,31G+(d,p)/Lanl2DZ]. more stable; DFT does not replicate the experimentally observed order of stability, although it does correctly place the two species very close in energy). Calculated Al−H stretching 2 2 frequencies for κ -N,P- and κ -N,N-5c (1863, 1845, and 1860, −1 1813 cm , respectively) are suﬃciently close in order to explain the single peak observed in the experimental solution- −1 phase spectrum (1829 cm ). 2 2 The ligand-slip rearrangement of 5c from κ -N,P to κ -N,N a 2 In the solid state, only κ -N,P-5c is observed, while in solution, both is likely driven by a preference for the “hard” N-donor 2 2 the κ -N,P and κ -N,N isomers are observed. functionality of the diaminophosphine donor over the “softer” P center. The increased proportion of the κ -N,N isomer for the dimethyl complex 3c compared to the dihydride 5c (1) The two isomers are both monomeric species, as suggests that the ring expansion that occurs as a consequence revealed by H DOSY NMR measurements, which indicate 2 2 of isomerization from κ -N,P to κ -N,N may also be favorable similar diﬀusion coeﬃcients. Thus, we were able to rule out the as a route to relieve steric strain. The more restrained, sterically presence of a dimeric species with bridging hydrides crowded, and less basic (due to the silyl substituent) tert- (consistent with solution- and solid-phase IR spectroscopy, butylamino groups of 3b and 5b cannot favorably participate in which did not reveal evidence of bridging hydride ligands). 31 1 the same isomerization as 3c and 5c. (2) In the P{ H} NMR spectrum, the resonance at 96.9 2 2 Interconversion between κ -N,P- and κ -N,N-3c or -5c in ppm is assigned to the κ -N,N isomer because of its similarity solution was not observable, and we were thus unable to to that observed for the free ligand 1c (90.6 ppm), which determine the activation barriers for this process. Although indicates that the P center is not coordinated to Al. The resonances for the coordinated and free phosphine centers in resonance at 47.8 ppm is assigned to the κ -N,P isomer both isomers of 5c are broad, using NMR spectroscopy, we observed in the solid state (conﬁrmed by solid-state NMR could ﬁnd no evidence for exchange between the two sites, measurements; see below). even at elevated temperatures. The variable coordination mode (3) The aluminum hydride stretching frequencies recorded −1 of the ligand in both 3c and 5c appears to provide them with for 5c in solution (1823 cm ) and in the solid state (1825 and −1 higher reactivity and renders them the most sensitive 1801 cm ) are consistent with a four-coordinate aluminum derivatives in these series. Indeed, 3c was found to be dihydride species in both phases, ruling out a κ -N isomer in extremely challenging to handle because of its high sensitivity which the phosphine is uncoordinated. to air and moisture. (4) Using density functional theory (DFT), we performed Solid-State NMR Spectroscopy. To further conﬁrm our geometry optimization and frequency calculations on κ -N,P 31 2 2 assignment of P resonances for the κ -N,P and κ -N,N isomers of 5a−5c at the M062X/Def2SVPP and M062X/ isomers of 3c and 5c, we undertook solid-state NMR 6,31G+(d,p)/Lanl2DZ levels (Table S1). Following the lead of spectroscopy because from crystallographic studies κ -N,P- Crimmin et al., we found that calculations using the split basis 31 1 coordination is exclusively observed. The P{ H} MAS NMR set were essential to replicating experimentally observed Al−H spectra of 3c and 5c are consistent with X-ray crystallography, stretching frequencies. The calculations accurately repro- revealing only a single-P environment for each compound duced the experimentally observed geometries and IR (Figure 6). In both cases, the solid-state chemical shift is stretching frequencies for 5a−5c, enabling us to use this almost identical with the solution-phase signal assigned to the computational methodology to assign the identity of the κ -N,P isomers (e.g., 3c, solid phase, 47.8 ppm, solution, 49.7 solution-phase isomer of 5c. ppm; 5c, solid phase, 47.5 ppm, solution, 47.8 ppm). (5) A relaxed potential energy surface (PES) scan of 5c in 31 1 Furthermore, the line shapes observed in the P{ H} NMR which the Al−P distance was increased systematically starting spectra indicate quadrupolar coupling between Al and P, from the κ -N,P geometry revealed two potential minima explaining the observed variation from the expected (Figure S1), which were reoptimized at the M062X/6,31G 1:1:1:1:1:1 sextet. No other resonances were observed in the +(d,p)/Lanl2DZ level (Figure 5 and Table S2). A κ -N isomer 31 1 2 −1 2 P{ H} MAS NMR spectra, ruling out the presence of the κ - was found to be 22.6 kcal mol higher in energy than the κ - N,P isomer (the calculated Al−H stretching frequencies for N,N isomer in the solid state. this three-coordinate aluminum dihydride of 1934 and 1922 For 3a, 3b, 5a, and 5b, which all display exclusive κ -N,P −1 31 1 cm were also inconsistent with the experimental values). coordination in solution, the observed P{ H} MAS NMR However, the κ -N,N isomer located in the PES scan was spectra each contain a single resonance extremely close in 2 −1 found to be very close in energy to κ -N,P-5c (−0.8 kcal mol chemical shift to that observed in solution (e.g., 5a, solution 11443 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article EXPERIMENTAL SECTION General Procedures. All manipulations were carried out under an argon atmosphere using standard Schlenk or glovebox techniques. Reactions were carried out in glass Schlenk tubes, which were dried for 16 h at 110 °C before use. Solvents were obtained from an inert solvent puriﬁcation system and stored over 4 Å molecular sieves. C D 6 6 and tetrahydrofuran (THF)-d were dried over potassium, then vacuum-distilled, and stored over 4 Å molecular sieves. 23 24 Ligands 1b and 1c, their precursors [imine and chlorophos- t 23 t 35 phines PCl(N Bu) SiMe and PCl(N BuCH ) ], and [H Al· 2 2 2 2 3 NMe ] were synthesized according to literature procedures. SiMe (NH Bu) was synthesized according to a modiﬁed literature 2 2 procedure (see the SI). tert-Butylamine was dried over calcium hydride and vacuum-distilled prior to use. LiAlH was puriﬁed by extraction with diethyl ether and ﬁltration to aﬀord a white solid, which was stored under an inert atmosphere. Trimethylammonium 31 1 Figure 6. P{ H} (9.4 T, 14 kHz, MAS) NMR spectra for 3c (top) chloride was dried under vacuum at 50 °C for 3 h prior to use. All and 5c (bottom). other reagents were purchased from commercial suppliers and used without further puriﬁcation. General Synthesis of 2. To a solution of 1 in THF cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes, 1 equiv). The phase, 8.0 ppm, solid phase, 8.9 ppm). Although we were cold bath was removed, and the resultant yellow solution was stirred 31 1 unable to observe any resonances for any of the compounds at room temperature for 1 h. Monitoring by P{ H} NMR spectroscopy revealed the presence of the lithiated ligand 2, which reported here by solution-phase Al NMR spectroscopy, solid- 27 1 was characterized in situ. state experiments were more successful. Details of the Al{ H} 31 1 2a. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 10.9 (1:1:1:1 4 8 CPMG NMR spectra for 3a−3c and 5a−5c are provided in quartet, J = 54 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.3 P−Li 4 8 the Supporting Information. (d, J = 54 Hz). Li−P 31 1 2b. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 96.4 (1:1:1:1 4 8 CONCLUSIONS quartet, J = 63 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.1 P−Li 4 8 (d, J = 63 Hz). Li−P In summary, we have synthesized aluminum dimethyl and 31 1 2c. P{ H} NMR (C H O, 202.5 MHz, 300 K): δ 68.6 (1:1:1:1 4 8 dihydride complexes with a series of amidophosphine ligands 7 quartet, J = 54 Hz). Li NMR (C H O, 194.4 MHz, 300 K): δ 1.5 P−Li 4 8 of varying steric bulk. The bulky bidentate ligands 1a−1c (d, J = 54 Hz). Li−P enable the isolation of reactive aluminum dihydrides, the General Synthesis of 3. To a solution of 1 in THF cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes, 1 equiv). The synthesis of which was observed to proceed through ﬁve- cold bath was removed, and the resultant yellow solution was stirred coordinate aluminate intermediates (4a−4c). Evidence from at room temperature for 1 h. The reaction mixture was cooled to −78 X-ray crystallography and solid-state NMR spectroscopy °C, and Me AlCl (1.0 M in hexanes) was added dropwise. The cold indicates that, for all dimethyl and dihydride complexes, both bath was removed, and the resultant solution was stirred at room N- and P-donor atoms are bound to the Al centers in the solid temperature for 1 h. The solvent was removed in vacuo, and the state. In solution, however, altering the steric bulk of the ligand product was extracted in hexane and dried to aﬀord 3a−3c. enables control over the coordination mode at the Al center: 3a. 1a (0.40 g, 0.97 mmol), THF (20 mL), nBuLi (0.39 mL, 0.97 for the bulkiest ligand employed, 1c, both the dimethyl and mmol, 1.0 equiv), and Me AlCl (0.97 mL, 0.97 mmol, 1.0 equiv) dihydride complexes 3c and 5c exist as a mixture of κ -N,P and yielded 3a (0.34 g, 75%) as a pale-yellow solid. Colorless crystals suitable for X-ray crystallography were grown from a saturated diethyl κ -N,N isomers. 1 3 ether solution at 4 °C. H(C D , 500 MHz, 300 K): δ −0.33 (d, J 6 6 HP The variable coordination mode of the ligand is encouraging = 2.5 Hz, 3H, AlCH ), −0.19 (d, J = 2.5 Hz, 3H, AlCH ), 1.10 (m, 3 HP 3 as a potential route to controlling the stoichiometric or 1 3 3 1H, / CH ), 1.19 (d, J = 8.6 Hz, 9H, CH ), 1.22 (d, J = 2 2Norb HP 3tBu HP catalytic reactivity of the aluminum dihydride centers. For 8.6 Hz, 9H, CH ), 1.24 (d, J = 6.8 Hz, 3H, CH ), 1.26 (d, 3tBu HH 3iPr example, preliminary results indicate that 5a−5c are active 3 3 J = 6.8 Hz, 3H, CH ), 1.37 (d, J = 6.8 Hz, 6H, CH ), 1.43 HH 3iPr HH 3iPr catalysts for the hydroboration of alkyl- and arylalkynes with (m, 2H, CH ), 1.55 (m, 1H, / CH ), 1.61 (m, 2CbridgeheadCP 2 2CbridgeheadCN 1 1 HBPin (see the SI). The accessibility of the κ -N,N 1H, / CH ), 1.66 (m, 1H, / CH ), 2.50 (br s, 1H, 2 2Norb 2 2CbridgeheadCN coordination mode for 5c has a clear eﬀect on the reactivity. PCCH ), 2.95 (br s, 1H, NCCH ), 3.44 (sept, J = 6.8 bridgehead bridgehead HH While all three dihydrides catalyze the hydroboration of Hz, 1H, CH ), 3.61 (sept, J = 6.8 Hz, 1H, CH ), 7.17−7.19 (m, iPr HH iPr 3H, H ). C NMR (C D , 126 MHz, 300 K): δ −5.7 (br s, phenylacetylene with HBPin, 5a and 5b are signiﬁcantly more aromatic 6 6 AlCH ), −4.3 (br s, AlCH ), 25.2 (s, CH ), 25.4 (s, CH ), 25.7 3 3 3iPr 3iPr eﬃcient, with conversions of 79 and 83% after 2 h at 110 °C (s, CH ), 25.8 (s, CH ), 25.9 (d, J = 2 Hz, CH ), 3iPr 3iPr CP 2CbridgeheadCP compared to 53% for 5c. We are now further exploring the 27.6 (s, CH ), 27.7 (s, CH ), 30.0 (s, CH ), 30.1 (d, J iPr iPr 2CbridgeheadCN CP coordination chemistry, reactivity, and catalytic applications of = 5 Hz, CH ), 30.5 (d, J = 5 Hz, CH ), 34.4 (d, J = 30 Hz, 3tBu CP 3tBu CP the dihydrides 5a−5c (Scheme 5). CtBu), 34.8 (d, J = 31 Hz, CtBu), 43.8 (d, J = 9 Hz, PCCH), 44.1 CP CP (d, J = 2 Hz, NCCH), 48.3 (d, J = 3 Hz, CH ), 80.2 (d, J = CP CP 2Norb CP Scheme 5. Catalytic Hydroboration of Phenylacetylene and 42 Hz, PCCH), 124.2 (s, C ), 124.3 (s, C ), 126.1 (s, C ), meta meta para 141.7 (d, J = 3 Hz, NC ), 147.1 (s, CCH ), 147.4 (s, CCH ), 2-Cyclooctyne Using 5a−5c CP Ar iPr iPr 31 1 185.1 (d, J = 21 Hz, NCCH). P{ H} NMR (C D , 162 MHz, 300 CP 6 6 K): δ 1.6 (s, Δν = 21.1 Hz). HRMS (APPI): m/z 469.341919 1/2 ([C H AlNP] ; theoretical m/z 469.341252). Elem anal. Found: C, 29 49 74.13; H, 10.38; N, 2.85. Calcd for C H AlNP: C, 74.16; H, 10.52; 29 49 N, 2.98. 11444 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article 1 1 1 3b. 1b (0.3 g, 0.60 mmol), THF (20 mL), nBuLi (0.24 mL, 0.60 (m, 1H, / NCH ), 2.66 (m, 1H, / NCH ), 2.82 (m, 1H, / NCH ), 2 2 2 2 2 2 mmol, 1.0 equiv), and Me AlCl (0.60 mL, 0.60 mmol, 1.0 equiv) 2.89 (m, 1H, NCH ), 3.05 (br s, 1H, CH ), 3.52 (sept, J 2 2 bridgeheadCN HH yielded 3b (0.17 g, 56%) as a yellow solid. Some impurities (less than = 6.8 Hz, 1H, CH ), 3.74 (sept, J = 6.8 Hz, 1H, CH ), 7.15− iPr HH iPr 10%) were observed by NMR spectroscopy because of reaction with 7.20 (m, 3H, H ). C NMR (C D , 126 MHz, 300 K): δ −4.2 aromatic 6 6 (s, AlMe), −3.5 (s, AlMe), 25.2 (s, CH ), 25.4 (s, CH ), 25.68 (s, water but could not be separated because crystallization of 3b was not 3iPr 3iPr CH ), 25.84 (s, CH ), 27.4 (s, CH ), 27.6 (s, CH ), possible. 3iPr 2CbridgeheadCP iPr iPr 1 3 29.2 (s, CH ), 29.4 (d, J = 2.2 Hz, CH ), 29.7 (d, J H NMR (C D , 500 MHz, 300 K): δ −0.26 (d, J = 3.9 Hz, 3H, 3tBu CP 2CbridgeheadCN CP 6 6 HP = 7.6 Hz, CH ), 42.0 (d, J = 4.2 Hz, CH ), 43.6 (s, AlCH ), −0.12 (d, J = 3.9 Hz, 3H, AlCH ), 0.27 (s, 3H, SiCH ), 3tBu CP bridgeheadCN 3 HP 3 3 2 1 NCH ), 44.2 (d, J = 9.9 Hz, CH ), 44.3 (s, NCH ), 46.6 0.32 (s, 3H, SiCH ), 1.12 (d, J = 8.1 Hz, 1H, / CH ), 1.25 (s, 2 CP bridgeheadCP 2 3 HH 2 2Norb (d, J = 5.3 Hz, CH ), 52.5 (d, J = 11.7 Hz, C Bu), 52.8 (d, J 9H, CH ), 1.26 (s, 9H, CH ), 1.25 (d, J = 6.8 Hz, 3H, CP 2Norb CP CP 3tBu 3tBu HH 3 3 = 8.8 Hz, C Bu), 95.5 (d, J = 33.5 Hz, PCCH), 124.29 (s, C ), CH ), 1.26 (d, J = 6.8 Hz, 3H, CH ), 1.32 (d, J = 6.8 Hz, CP meta 3iPr HH 3iPr HH 124.32 (C ), 126.2 (s, C ), 142.0 (d, J = 3.9 Hz, NC ), 146.7 3H, CH ), 1.41 (d, J = 6.8 Hz, 3H, CH ), 1.42 (m, 2H, meta para CP Ar 3iPr HH 3iPr 2 1 (s, CCH ), 148.0 (s, CCH ), 185.3 (d, J = 34.1 Hz, NCCH). CH ), 1.60 (d, J = 8.1 Hz, 1H, / CH ), 1.69 (m, 3iPr 3iPr CP 2CbridgebeadCP HH 2 2Norb 31 1 P{ H} NMR (C D , 162 MHz, 300 K): δ 49.7 (s, Δν = 47.5 Hz). 2H, CH ), 2.53 (br s, 1H, CH ), 3.13 (br s, 1H, 6 6 1/2 2CbridgeheadCN bridgeheadCP 3 3 HRMS (EI): m/z 525.37703 ([C H AlN P] ; theoretical m/z CH ), 3.51 (sept, J = 6.8 Hz, CH ), 3.70 (sept, J = 31 53 3 bridgeheadCN HH iPr HH 525.37871). Elem anal. Found: C, 70.71; H, 10.18; N, 8.03. Calcd for 6.8 Hz, CH ), 7.11−7.21 (m, 3H, H ). C NMR (C D , 126 iPr aromatic 6 6 C H AlN P: C, 70.82; H, 10.16; N, 7.99. MHz, 300 K): δ −6.3 (br d, J = 24.8 Hz, AlCH ), −5.4 (br d, J = 31 53 3 CP 3 CP Synthesis of 4b. To a solution of 1b (0.10 g, 0.2 mmol) in THF 19.9 Hz, AlCH ), 4.6 (d, J = 1.4 Hz, SiCH ), 6.7 (d, J = 3.7 Hz, 3 CP 3 CP (20 mL) at −78 °C was added dropwise nBuLi (2.5 M in hexanes, SiCH ), 25.3 (s, CH ), 25.4 (s, CH ), 25.6 (s, CH ), 26.0 (s, 3 3iPr 3iPr 3iPr 0.08 mL, 0.2 mmol, 1 equiv). The cold bath was removed, and the CH ), 26.3 (s, CH ), 27.6 (s, CH ), 27.8 (s, CH ), 3iPr 2CbridgeheadCP iPr iPr resultant yellow solution was stirred at room temperature for 1 h. The 29.4 (s, CH ), 32.3 (d, J = 5.4 Hz, CH ), 32.7 (d, J 2CbridgeheadCN CP 3tBu CP reaction mixture was cooled to −78 °C, and H Al·NMe Et (0.5 M in = 4.9 Hz, CH ), 40.6 (d, J = 3.5, CHCN), 44.3 (d, J = 43.9, 3 2 3tBu CP CP toluene, 0.4 mL, 1 equiv) was added dropwise. The cold bath was CHCP), 46.6 (d, J = 4.7 Hz, CH ), 50.8 (d, J = 3.9 Hz, C Bu), CP 2Norb CP removed, the resultant yellow solution was stirred at room 50.9 (d, J = 2.8 Hz, C Bu), 99.1 (d, J = 29.2 Hz, PCCH), 124.3 (s, CP CP temperature for 20 min, and the solvent was removed in vacuo to C ), 124.3 (s, C ), 126.3 (s, C ), 141.2 (d, J = 3.1 Hz, NC ), meta meta para CP Ar aﬀord the product as a yellow oil. No further puriﬁcation was 146.6 (s, CCH ), 147.0 (s, CCH ), 186.8 (d, J = 33.9 Hz, iPr iPr CP 31 1 attempted. NCCH). P{ H} (C D , 162 MHz, 300 K): δ 64.0 (s, Δν = 35.8 6 6 1/2 H NMR (C D O, 500 MHz, 300 K): δ 0.29 (s, 3H, SiCH ), 0.33 Hz). HRMS (APPI): m/z 555.371654 ([C H AlN PSi] ; theoreti- 4 8 3 31 55 3 1 3 (s, 3H, SiCH ), 0.84 (m, 1H, / CH ), 1.07 (d, J = 6.8 Hz, 3H, cal m/z 555.371277). 3 2 2Norb HH 3 3 CH ), 1.08 (d, J = 6.8 Hz, 3H, CH ), 1.12 (d, J = 6.8 Hz, 3c. 1c (0.43 g, 0.92 mmol), THF (20 mL), nBuLi (0.37 mL, 0.92 3iPr HH 3iPr HH 3H, CH ), 1.14 (d, J = 6.8 Hz, 3H, CH ), 1.18 (m, 2H, mmol, 1.0 equiv), and Me AlCl (0.92 mL, 0.60 mmol, 1.0 equiv) were 3iPr HH 3iPr CH ), 1.19 (s, 9H, CH ), 1.21 (s, 9H, CH ), 1.25 (m, 2CbridgeheadCP 3tBu 3tBu mixed. To gain analytically pure material, 3c was further puriﬁed by 1 1 1H, / CH ), 1.54 (m, 1H, / CH ), 1.62 (m, 1H, 2 2Norb 2 2CbridgeheadCN recrystallization from hexanes at −20 °C to yield colorless crystals / CH ), 2.19 (br s, 1H, CH ), 3.35 (br s, 1H, 2 2CbridgheadCN bridgeheadCP (0.23 g, 48%). Two isomers were identiﬁed in the NMR spectra with 3 3 2 2 CH ), 3.54 (sept, J = 6.8 Hz, 1H, CH ), 3.63 (sept, J bridgeheadCN HH iPr HH an approximate ratio of 4:3 of κ -N,N-3c to κ -N,P-3c at 300 K = 6.8 Hz, 1H, CH ), 6.83−6.90 (m, 3H, H ). Note: It was not iPr aromatic (determined from the H NMR spectrum). Because of the high air 1 31 possible to locate the Al−H resonances even with the use of H{ P} sensitivity of this species, some impurities were observed in solution 31 1 NMR experiments, likely because of extremely high line width. C NMR spectra ( P{ H} NMR spectrum, 10% unidentiﬁed impurity at NMR (C D O, 126 MHz, 300 K): δ 6.5 (s, SiCH ), 8.3 (d, J = 5.7 4 8 3 CP 75.1 ppm). 2 1 Hz, SiCH ), 24.3 (d, J = 10.2 Hz, CH ), 26.0 (d, J = 15.2 Hz, 3 CP 3iPr CP κ -N,N-3c. H NMR (C D , 500 MHz, 300 K): δ −0.67 (s, 3H, 6 6 CH ), 27.2 (s, CH ), 28.11 (s, CH ), 28.13 (s, CH ), 3iPr 2CbridgeheadCP iPr iPr AlMe), −0.13 (s, 3H, AlMe), 0.89 (m, 1H, / CH ), 1.18 (m, 1H, 2 2Norb 1 3 30.1 (s, CH ), 32.9 (d, J = 5.4 Hz, CH ), 33.4 (d, J 2CbridgeheadCN CP 3tBu CP / CH ), 1.21 (s, 18H, CH ), 1.24 (d, J = 6.8 Hz, 6H, 2 2Norb 3tBu HH = 4.8 Hz, CH ), 42.1 (d, J = 1.5 Hz, CH ), 46.5 (s, 3tBu CP bridgeheadCN CH ), 1.27 (d, J = 6.8 Hz, 3H, CH ), 1.45 (m, 2H, 3iPr HH 3iPr CH ), 47.2 (d, J = 5.5 Hz, CH ), 51.4 (d, J = 11.5 2Norb CP bridgeheadCP CP CH ), 1.47 (d, J = 6.8 Hz, 3H, CH ), 1.63 (m, 1H, 2CbridgeheadCP HH 3iPr t t Hz, C Bu), 51.6 (d, J = 14.6 Hz, C Bu), 111.2 (d, J = 43.1 Hz, 1 1 CP CP / CH ), 1.72 (m, 1H, / CH ), 2.49 (br s, 1H, 2 2CbridgeheadCN 2 2CbridgeheadCN PCCH), 123.1 (d, J = 10.0 Hz, C ), 124.2 (s, C ), 146.7 (s, 1 1 CP meta para CH ), 2.82 (m, 1H, / NCH ), 2.83 (m, 1H, / NCH ), bridgeheadCP 2 2 2 2 CCH ), 148.0 (s, CCH ), 150.7 (s, NC ), 174.2 (d, J = 33.2 Hz, 1 3 iPr iPr Ar CP 2.97 (m, CH ), 3.15 (m, 1H, / NCH ), 3.73 (sept, J = 31 2 bridgeheadCN 2 2 HH NCCH). P NMR (C D O, 162 MHz, 300 K): δ 110.8 (q, J =34 3 4 8 PH 6.8 Hz, 1H, CH ), 3.85 (sept, J = 6.8 Hz, 1H, CH ), 3.88 (m, 7 iPr HH iPr Hz). Li NMR (C D O, 194.4 MHz, 300 K): δ −0.43 (s). HRMS 1 13 4 8 1H, / NCH ), 7.15−7.20 (m, 3H, H ). C NMR (C D , 126 + 2 2 aromatic 6 6 (EI): m/z 528.34912 ([C H N AlPSi] ;theoretical m/z 29 52 3 MHz, 300 K): δ −5.5 (s, AlMe), −4.7 (s, AlMe), 24.3 (s, CH ), 3iPr 528.34891). 24.8 (s, CH ), 25.75 (s, CH ), 25.97 (s, CH ), 26.1 3iPr 3iPr 2CHbridgeheadCP General Synthesis of 5. To a solution of ligand 1a−1c in THF (s, CH ), 27.0 (s, CH ), 28.2 (s, CH ), 29.3 (s, CH ), 3iPr iPr iPr 2CbridgeheadCN cooled to −78 °C was added dropwise nBuLi (2.5 M in hexanes). The 29.7 (d, J = 9.5 Hz, CH ), 29.73 (d, J = 7.7 Hz, CH ), 29.8 CP 3tBu CP 3tBu cold bath was removed, and the resultant yellow solution was stirred (d, J = 5.6 Hz, CH ), 43.84 (s, CH ), 43.88 (d, J = 12.6 Hz, CP 3tBu 2Norb CP at room temperature for 1 h. The reaction mixture was cooled to −78 NCH ), 45.3 (s, CH ), 45.7 (d, J =42.0Hz, 2 bridgeheadCP CP °C, and a solution of H Al·NMe in THF was added dropwise. The 3 3 CH ), 48.8 (d, J = 2.8 Hz, NCH ), 53.2 (d, J = 6.0 bridgeheadCN CP 2 CP cold bath was removed, and the resultant colorless solution was t t Hz, C Bu), 63.7 (d, J = 11.7 Hz, C Bu), 103.5 (d, J = 37.7 Hz, CP CP stirred at room temperature for 1 h. The solvent was removed in PCCH), 123.9 (s, C ), 124.5 (s, C ), 125.2 (s, C ), 144.1 (s, meta meta para vacuo, and the product was extracted in hexane and dried to aﬀord a NC ), 146.5 (s, CCH ), 147.0 (s, CCH ), 165.0 (d, J = 5.0 Hz, Ar iPr iPr CP white solid. H Al·NMe Et (0.5 M in toluene) can be used in place of 3 2 31 1 NCCH). P{ H} NMR (C D , 162 MHz, 300 K): δ 99.9 (s, Δν = 6 6 1/2 H Al·NMe . In this work, H Al·NMe Et was used for initial test 3 3 3 2 5.3 Hz). reactions to synthesize up to 0.2 g of 5 using a procedure identical 2 1 3 κ -N,P-3c. H NMR (C D , 500 MHz, 300 K): δ −0.27 (d, J = 6 6 HP with that described above. 3.1 Hz, 3H, AlMe), −0.14 (d, J = 3.1 Hz, 3H, AlMe), 1.06 (dm, HP 5a. 1a (1.63 g, 0.0039 mol), THF (50 mL), nBuLi (1.6 mL, 0.0039 2 1 3 J = 8.1 Hz, 1H, / CH ), 1.25 (d, J = 6.8 Hz, 3H, CH ), HH 2 2Norb HH 3iPr mol, 1.0 equiv), and H Al·NMe (0.84 g, 0.0037 mol, 2.4 equiv) in 3 3 1.26 (d, J = 6.8 Hz, 3H, CH ), 1.30 (s, 9H, CH ), 1.32 (s, 9H, THF (20 mL) yielded 5a (1.57 g, 91%). HH 3iPr 3tBu 1 2 CH ), 1.33 (m, 1H, / CH ), 1.38 (m, 1H, H NMR (C D , 500 MHz, 300 K): δ 1.11 (dm, J = 8.1 Hz, 1H, 3tBu 2 2CbridgeheadCP 6 6 HH 1 3 1 3 3 / CH ), 1.40 (d, J = 6.8 Hz, 3H, CH ), 1.42 (d, / CH ), 1.19 (d, J = 14.2 Hz, 9H, CH ), 1.22 (d, J = 2 2CbridgeheadCP HH 3iPr 2 2Norb HP 3tBu HP 3 2 1 3 J = 6.8 Hz, 3H, CH ), 1.56 (m, J = 8.1 Hz, 1H, / CH ), 14.2 Hz, 9H, CH ), 1.28 (d, J = 6.8 Hz, 3H, CH ), 1.29 (d, HH 3iPr HH 2 2Norb 3tBu HH 3iPr 1.63 (m, 2H, CH ), 2.48 (br s, 1H, CH ), 2.59 J = 6.8 Hz, 3H, CH ), 1.31 (m, 2H, CH ), 1.42 (d, 2CbridgeheadCN bridgeheadCP HH 3iPr 2CbridgeheadCP 11445 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article 3 3 J = 6.8 Hz, 3H, CH ), 1.44 (d, J = 6.8 Hz, 3H, CH ), 1.51 CH ), 44.2 (s, CH ), 45.1 (s, CH ), 45.7 (s, HH 3iPr HH 3iPr 2CbridgeaheadCN 2Norb bridgeheadCN 1 2 NCH ), 45.8 (d, J = 39.1 Hz, CH ), 48.8 (d, J = 3.3 Hz, (m, 1H, / CH ), 1.62 (dm, J =8.1 Hz,1H, 2 2CbridgeheadCN HH 2 CP bridgeheadCP CP t t 1 1 NCH ), 53.5 (d, J = 5.0 Hz, C Bu), 53.8 (d, J = 3.9 Hz, C Bu), / CH ), 1.67 (m, 1H, / CH ), 2.53 (br s, 1H, 2 CP CP 2 2Norb 2 2CbirdgeheadCN 104.8 (d, J = 36.9 Hz, PCCH), 123.9 (s, C ), 124.6 (s, C ), CP meta meta PCCH ), 2.94 (br s, 1H, NCCH ), 3.42 (sept, J = 6.8 bridgehead bridgehead HH 125.2 (s, C ), 143.22 (s, NC ), 145.8 (CCH ), 146.53 (s, para Ar iPr Hz, CH ), 3.63 (sept, J = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, iPr HH iPr 31 1 CCH ), 167.4 (d, J = 2.7 Hz, NCCH). P{ H} NMR (C D , 162 iPr CP 6 6 AlH ), 7.16−7.22 (m, 3H, H ). C NMR (C D , 126 MHz, 300 2 aromatic 6 6 MHz, 300 K): δ 96.9 (s, Δν = 137.9 Hz). 1/2 K): δ 24.0 (s, CH ), 24.7 (s, CH ), 25.2 (d, J = 1.8 Hz, 3iPr 3iPr CP 2 1 2 κ -N,P-5c. H NMR (C D , 500 MHz, 300 K): δ 1.07 (dm, J = 6 6 HH CH ), 25.8 (s, CH ), 25.9 (s, CH ), 28.0 (s, CH ), 2CbridgeheadCP 3iPr 3iPr iPr 1 3 8.4 Hz, 1H, / CH ), 1.29 (d, J = 6.8 Hz, 3H, CH ), 1.30 (d, 2 2Norb HH 3iPr 28.1 (s, CH ), 29.6 (d, J =4.5 Hz,CH ), 30.1 (s, iPr CP 3tBu J = 6.8 Hz, 3H, CH ), 1.32 (s, 9H, CH ), 1.35 (s, 9H, HH 3iPr 3tBu CH ), 30.1 (d, J = 4.0 Hz, CH ), 34.1 (d, J = 2CbridgeheadCN CP 3tBu CP t t CH ), 1.39 (m, 2H, CH ), 1.42 (d, J = 6.8 Hz, 3H, 18.2 Hz, C Bu), 34.3 (d, J = 18.9 Hz, C Bu), 43.6 (d, J = 9.1 Hz, 3tBu 2CbridgeheadCP HH CP CP CH ), 1.45 (d, J = 6.8 Hz, 3H, CH ), 1.56 (m, 1H, 3iPr HH 3iPr CH ), 44.1 (d, J = 2.1 Hz, CH ), 48.6 (d, J = bridgeheadCP CP bridgeheadCN CP / CH ), 1.63 (m, 2H, CH ), 2.52 (m, 1H, 3.9 Hz, CH ), 81.0 (d, J = 44.5 Hz, PCCH), 124.1 (s, C ), 2 2Norb 2CbridgeheadCN 2Norb CP meta 1 1 CH ), 2.60 (m, 1H, / NCH ), 2.72 (m, 1H, / NCH ), 124.2 (s, C ), 126.3 (s, C ), 141.4 (d, J = 3.0 Hz, NC ), 146.8 bridgeheadCP 2 2 2 2 meta para CP Ar 2.79 (m, 1H, / NCH ), 2.88 (m, 1H, NCH ), 3.02 (m, 1H, (s, CCH ), 147.1 (s, CCH ), 185.1 (d, J = 20.1 Hz, NCCH). 2 2 2 iPr iPr CP 3 3 31 1 CH ), 3.54 (sept, J = 6.8 Hz, 1H, CH ), 3.76 (sept, J P{ H} NMR (C D , 162 MHz, 300 K): δ 8.0 (s, Δν = 34.7 Hz). bridgeheadCN HH iPr HH 6 6 1/2 = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, AlH ), 7.18−7.21 (m, 3H, iPr 2 HRMS (EI): m/z 441.30855 ([C H AlNP] ; theoretical m/z 27 45 H ). C NMR (C D , 126 MHz, 300 K): δ 24.0 (s, CH ), aromatic 6 6 3iPr 441.30996). Elem anal. Found: C, 73.11; H, 10.39; N, 3.13. Calcd −1 24.7 (s, CH ), 25.3 (s, CH ), 25.8 (s, CH ), 25.86 (s, 3iPr 2CbridgeheadCP 3iPr for C H AlNP: C, 73.43; H, 10.27; N, 3.17. IR (solid, cm ): 1810, 27 45 −1 CH ), 27.9 (s, CH ), 28.1 (s, CH ), 29.0 (d, J = 4.6 Hz, 3iPr iPr iPr CP 1786. IR (solution, cm ): 1811. CH ), 29.3 (s, CH ), 29.9 (d, J = 4.6 Hz, CH ), 3tBu 2CbridgeheadCN CP 3tBu 5b. 1b (3.00 g, 0.0060 mol), THF (80 mL), nBuLi (2.4 mL, 0.0060 42.7 (d, J = 4.4 Hz, CH ), 43.6 (d, J = 9.9 Hz, CP bridgeheadCN CP mol, 1.0 equiv), and H Al·NMe (1.28 g, 0.014 mol, 2.4 equiv) in 3 3 CH ), 43.9 (s, NCH ), 44.2 (s, NCH ), 46.6 (d, J = 4.9 bridgeheadCP 2 2 CP THF (15 mL) yielded 5b (2.95 g, 93%). Colorless crystals suitable for Hz, CH ), 53.4 (d, J = 9.8 Hz, C Bu), 53.6 (d, J = 5.4 Hz, 2Norb CP CP X-ray crystallography were grown from a saturated hexane solution at C Bu), 97.0 (d, J = 35.3 Hz, PCCH), 124.1 (s, C ), 124.3 (s, CP meta −20 °C. 1 C ), 126.4 (s, C ), 141.0 (d, J = 4.0 Hz, NC ), 146.51 (s, meta para CP Ar H NMR (C D , 500 MHz, 300 K): δ 0.24 (s, 3H, SiCH ), 0.29 (s, 6 6 3 2 1 4 CCH ), 146.8 (s, CCH ), 185.4 (d, J = 34.0 Hz, NCCH). iPr iPr CP 3H, SiCH ), 1.13 (d, J = 8.1 Hz, 1H, / CH ), 1.28 (d, J = 3 HH 2 2Norb HP 31 1 4 P{ H} NMR (C D , 162 MHz, 300 K): δ 47.8 (s, Δν = 96.6 Hz). 6 6 1/2 0.8 Hz, 9H, CH ), 1.29 (d, J = 0.8 Hz, 9H, CH ), 1.30 (d, 3tBu HP 3tBu 3 3 HRMS (EI): m/z 497.35079 ([C H AlN P] ; theoretical m/z 29 49 3 J = 6.8 Hz, 3H, CH ), 1.31 (d, J = 6.8 Hz, 3H, CH ), 1.38 HH 3iPr HH 3iPr 3 497.34741). Elem anal. Found: C, 69.80; H, 9.80; N, 8.33. Calcd for (m, 2H, CH ), 1.44 (d, J = 6.8 Hz, 3H, CH ), 1.45 2CbridgeheadCP HH 3iPr −1 3 2 1 C H AlN PSi: C, 69.99; H, 9.92; N, 8.44. IR (solid, cm ): 1825, 29 51 3 (d, J = 6.8 Hz, 3H, CH ), 1.62 (d, J = 8.1 Hz, / CH ), HH 3iPr HH 2 2Norb −1 1801. IR (solution, cm ): 1823. 1.67 (m, 2H, CH ), 2.57 (br s, 1H, CH ), 3.12 2CbridgeheadCN bridgeheadCP (br s, 1H, CH ), 3.53 (sept, J = 6.8 Hz, 1H, CH ), 3.74 bridgeheadCN HH iPr ASSOCIATED CONTENT (sept, J = 6.8 Hz, 1H, CH ), 4.6 (br s, 2H, Al−H), 7.17−7.23 (m, HH iPr 3H, H ). C NMR (C D , 126 MHz, 300 K): δ 4.4 (d, J = 1.6 aromatic 6 6 CP * Supporting Information Hz, SiCH ), 6.3 (d, J = 3.2 Hz, SiCH ), 24.1 (s, CH ), 24.6 (s, 3 CP 3 3iPr The Supporting Information is available free of charge on the CH ), 25.6 (d, J = 1.0 Hz, CH ), 25.8 (s, CH ), 25.9 3iPr CP 2CbridgeheadCP 3iPr ACS Publications website at DOI: 10.1021/acs.inorg- (s, CH ), 28.0 (s, CH ), 28.3 (s, CH ), 29.3 (s, CH ), 3iPr iPr iPr 2CHbridgheadCN chem.9b01061. 32.3 (d, J = 5.4 Hz, CH ), 32.7 (d, J = 5.2 Hz, CH ), 40.7 (d, CP 3tBu CP 3tBu J = 3.9 Hz, CH ), 43.9 (d, J = 9.7 Hz, CH ), 46.8 CP bridgheadCN CP bridgheadCP Experimental procedures, full characterization of com- (d, J = 4.9 Hz, CH ), 51.4 (d, J = 2.5 Hz, C Bu), 51.5 (d, J = CP 2Norb CP CP pounds, crystallographic details, solid-state NMR details, 3.6 Hz, C Bu), 99.7 (d, J = 32.6 Hz, PCCH), 124.1 (s, C ), 124.2 CP meta and solution-phase NMR spectra (PDF) (s, C ), 126.5 (s, C ), 140.8 (d, J = 3.5 Hz, NC ), 146.4 (s, meta para CP Ar C CH ), 146.5 (s, C CH ), 187.6 (d, J = 33.9 Hz, NCCH). Ar iPr Ar iPr CP Crystallographic data (ZIP) 31 1 P{ H} NMR (C D , 162 MHz, 300 K): δ 61.3 (s, Δν = 65.4 Hz). 6 6 1/2 HRMS (EI): m/z 527.33886 ([C H AlN PSi] ; theoretical m/z Accession Codes 29 51 3 527.33998). Elem anal. Found: C, 65.95; H, 9.66; N, 7.83. Calcd for CCDC 1905997 and 1906037−1906039 contain the supple- −1 C H AlN PSi: C, 66.00; H, 9.74; N, 7.96. IR (solid, cm ): 1831, 29 51 3 mentary crystallographic data for this paper. These data can be −1 1816. IR (solution, cm ): 1820. obtained free of charge via www.ccdc.cam.ac.uk/data_request/ 5c. 1c (2.00 g, 0.0043 mol), THF (100 mL), nBuLi (1.7 mL, cif,orbyemailing data_request@ccdc.cam.ac.uk,orby 0.0043 mol, 1.0 equiv), and H Al·NMe (0.91 g, 0.010 mol, 2.4 equiv) 3 3 contacting The Cambridge Crystallographic Data Centre, 12 in THF (15 mL) were mixed. The ﬁnal product was further puriﬁed Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. by recrystallization from hexanes at −20 °C to yield 5c as colorless crystals (1.68 g, 79%). Two isomers were identiﬁable in the solution- 2 2 phase NMR spectra in a ratio of 4:7 for κ -N,N-5c to κ -N,P-5c at 300 AUTHOR INFORMATION K (determined from the H NMR spectrum). 2 1 Corresponding Author κ -N,N-5c. H NMR (C D , 500 MHz, 300 K): δ 0.91 (m, 1H, 6 6 1 4 3 *E-mail: michael.cowley@ed.ac.uk (M.J.C.). / CH ), 1.18 (d, J = 1.3 Hz, 9H, CH ), 1.23 (d, J = 6.8 2 2Norb HP 3tBu HH 1 3 Hz, 3H, CH ), 1.25 (m, 1H, / CH ), 1.31 (d, J = 6.8 Hz, 3iPr 2 2Norb HH ORCID 6H, CH ), 1.32 (s, 9H, CH ), 1.43 (m, 2H, CH ), 1.60 3iPr 3tBu 2CbridgeheadCP Michael J. Cowley: 0000-0003-0664-2891 3 1 (d, J = 6.8 Hz, 3H, CH ), 1.65 (m, 1H, / CH ), 1.71 HH 3iPr 2 2CbridgeheadCN Author Contributions (m, 1H, / CH ), 2.56 (m, 1H, CH ), 2.70 (m, 2 2CbridgeheadCN bridgeheadCP 1 1 1H, / NCH ), 2.78 (m, 1H, / NCH ), 2.97 (m, 1H, CH ), R.L.F. conceived and performed experiments and cowrote the 2 2 2 2 bridgeheadCN 1 1 3 3.33 (m, 1H, / NCH ), 3.56 (m, 1H, / NCH ), 3.85 (sept, J = 2 2 2 2 HH manuscript, G.S.N. contributed to crystallographic studies, and 6.8 Hz, 1H, CH ), 3.98 (sept, J = 6.8 Hz, 1H, CH ), 4.3 (br s, iPr HH iPr M.J.C. designed and coordinated the study and cowrote the 2H, AlH ) 7.18−7.21 (m, 3H, H ). C NMR (C D , 126 MHz, 2 aromatic 6 6 manuscript. 300 K): δ 25.4 (s, CH ), 25.6 (s, CH ), 25.7 (s, CH ), 2CbridgeheadCP 3iPr 3iPr Notes 25.92 (s, CH ), 27.5 (s, CH ), 28.9 (s, CH ), 29.0 (d, J = 4.6 3iPr iPr iPr CP Hz, CH ), 29.6 (d, J = 10.7 Hz, CH ), 29.8 (d, J = 1.8 Hz, The authors declare no competing ﬁnancial interest. 3tBu CP 3tBu CP 11446 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article (18) Liang, L.-C. Metal complexes of chelating diarylamido ACKNOWLEDGMENTS phosphine ligands. Coord. Chem. Rev. 2006, 250 (9), 1152−1177. Mass spectrometry was performed at the Scottish Instrumen- (19) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. The Transition tation and Resource Centre for Advanced Mass Spectrometry Metal Coordination Chemistry of Hemilabile Ligands. In Progress in at the University of Edinburgh by Faye Cruikshank (APPI) Inorganic Chemistry; Karlin, K. D., Ed.; John Wiley & Sons, Inc., 1999; and Alan Taylor (EI). This project received funding from the Vol. 48, pp 233−350. (20) Fryzuk, M. D.; Giesbrecht, G. R.; Olovsson, G.; Rettig, S. J. European Research Council under the European Union’s Synthesis and Characterization of Four- and Five-Coordinate Horizon 2020 research and innovation program (Grant ERC- Organoaluminum Complexes Incorporating the Amido Diphosphine 2016-STG-716315). Ligand System N(SiMe CH PPr ) . Organometallics 1996, 15 (22), 2 2 2 2 4832−4841. REFERENCES (21) Lee, P.-Y.; Liang, L.-C. Synthesis and Structural Character- ization of Five-Coordinate Aluminum Complexes Containing Diary- (1) Cox, L. R. Science of Synthesis; Thieme Chemistry, 2008; Vol. 36, lamido Diphosphine Ligands. Inorg. Chem. 2009, 48 (12), 5480− p 55. (2) Bismuto, A.; Thomas, S. P.; Cowley, M. J. Aluminum Hydride (22) Jones, C.; Koutsantonis, G. A.; Raston, C. L. Lewis base Catalyzed Hydroboration of Alkynes. Angew. Chem., Int. Ed. 2016, 55 adducts of alane and gallane. Polyhedron 1993, 12 (15), 1829−1848. 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Synthesis and Structure of a Monomeric (15) Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Aluminum Aluminum(I) Compound [{HC(CMeNAr) }Al] (Ar = Complexes Incorporating Bidentate Amido Phosphine Ligands. 2,6− Pr C H ): A Stable Aluminum Analogue of a Carbene. Angew. 2 6 3 Chem., Int. Ed. 2000, 39 (23), 4274−4276. Inorg. Chem. 2004, 43 (6), 2166−2174. (35) Krysiak, J.; Lyon, C.; Baceiredo, A.; Gornitzka, H.; Mikolajczyk, (16) DeMott, J. C.; Guo, C.; Foxman, B. M.; Yandulov, D. V.; M.; Bertrand, G. Stable Optically Pure Phosphino(silyl)carbenes: Ozerov, O. V. Five-coordinate aluminum complexes of a PNP ligand. Mendeleev Commun. 2007, 17 (2), 63−65. Reagents for Highly Enantioselective Cyclopropanation Reactions. (17) Lee, W.-Y.; Liang, L.-C. Organoaluminium complexes Chem. - Eur. J. 2004, 10 (8), 1982−1986. incorporating an amido phosphine chelate with a pendant amine (36) Jouet, R. J.; Warren, A. D.; Rosenberg, D. M.; Bellitto, V. J.; arm. Dalton Trans. 2005, No. 11, 1952−1956. Park, K.; Zachariah, M. R. Surface Passivation of Bare Aluminum 11447 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448 Inorganic Chemistry Article Nanoparticles Using Perfluoroalkyl Carboxylic Acids. Chem. Mater. 2005, 17 (11), 2987−2996. 11448 DOI: 10.1021/acs.inorgchem.9b01061 Inorg. Chem. 2019, 58, 11439−11448

Journal

Inorganic Chemistry – Pubmed Central

Published: Aug 14, 2019

References

Aluminum Hydride Catalyzed Hydroboration of Alkynes
Aluminum-Catalyzed Hydroboration of Alkenes
LiAlH4: From Stoichiometric Reduction to Imine Hydrogenation Catalysis
Lithium diamidodihydridoaluminates: bimetallic cooperativity in catalytic hydroboration and metallation applications
Aluminum Hydrides Stabilized by N-Heterocyclic Imines as Catalysts for Hydroborations with Pinacolborane
An Aluminum Dihydride Working as a Catalyst in Hydroboration and Dehydrocoupling
Room temperature catalytic carbon–hydrogen bond alumination of unactivated arenes: mechanism and selectivity
An Unusual Hydride-Bridged Aluminum Complex with a Square-Planar Tetraaluminum Core Stabilized by 2,5-Bis((Dimethylamino)methyl)pyrrole Ligands
Oxidative Addition of σ Bonds to an Al(I) Center
New developments in the chemistry of organoaluminum and organogallium hydrides
Hydrido and chloro gallium and aluminium complexes with the tridentate bis(2-dimethylaminoethyl)amide ligand
Cationic aluminium hydrides: [H2AlL]+[AlH4]−, L = N,N,N′,N″,N″-pentamethyldiethylenetriamine and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane
Aluminum Complexes Incorporating Bulky Nitrogen and Sulfur Donor Ligands
Aluminum Complexes Incorporating Bidentate Amido Phosphine Ligands
Five-coordinate aluminum complexes of a PNP ligand
Organoaluminium complexes incorporating an amido phosphine chelate with a pendant amine arm
Metal complexes of chelating diarylamido phosphine ligands
The Transition Metal Coordination Chemistry of Hemilabile Ligands
Synthesis and Characterization of Four- and Five-Coordinate Organoaluminum Complexes Incorporating the Amido Diphosphine Ligand System N(SiMe2CH2PPri2)2
Synthesis and Structural Characterization of Five-Coordinate Aluminum Complexes Containing Diarylamido Diphosphine Ligands
Lewis base adducts of alane and gallane
Method of Hydrosilylation Implementing an Organic Catalyst Derived from Germylene
Synthesis of New Phosphine Imine Ligands and Their Effects on the Thermal Stability of Late-Transition-Metal Olefin Polymerization Catalysts
Stable Phosphonium Sila-ylide with Reactivity as a Sila-Wittig Reagent
Synthesis and Structure of a Base-Stabilized C-Phosphino-Si-Amino Silyne
Synthesis of a Phosphine-Stabilized Silicon(II) Hydride and Its Addition to Olefins: A Catalyst-Free Hydrosilylation Reaction
Cationic Aluminum Alkyl Complexes Incorporating Amidinate Ligands. Transition-Metal-Free Ethylene Polymerization Catalysts
Commercially Available Metal Alkyls and Their Use in Polyolefin Catalysts
Insertion and β-Hydrogen Transfer at Aluminium
P–N bond formation as a route to highly electron rich phosphine ligands
Synthesis and Characterization of Thermally Robust Amidinato Group 13 Hydride Complexes
Preparation and properties of a series of structurally diverse aluminium hydrides supported by β-diketiminate and bis(amide) ligands
Synthesis and Structure of a Monomeric Aluminum(I) Compound [{HC(CMeNAr)2}Al] (Ar = 2,6–iPr2C6H3): A Stable Aluminum Analogue of a Carbene
Stable Optically Pure Phosphino(silyl)carbenes: Reagents for Highly Enantioselective Cyclopropanation Reactions
Surface Passivation of Bare Aluminum Nanoparticles Using Perfluoroalkyl Carboxylic Acids

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Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

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Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes

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