Dalton Transactions

doi: 10.1039/b919216fpmid: N/A

doi: 10.1039/b919223apmid: N/A

Raubenheimer, Helgard G.; Cronje, Stephanie; Strasser, Christoph E.

doi: 10.1039/b906840fpmid: 19789765

With the simplest of anionic Fischer-type carbene complexes acting as ligands, Cp2Zr(Cl){OCMe}M(CO)5 compounds (M = Cr or W) promote α-olefin oligomerization and polymerization in the presence of MAO. Attaching an N-heterocyclic ring to the carbene carbon atom in similar precursors, allows a variety of hard metal ions and fragments to be captured by external bidentate coordination. The outcome of the attachment of a phosphorus or sulfur functionality to an α-carbon of an O-anionic carbene is formation of a bidentate ligand and then internal four-membered carbene–heteroatom chelate formation. α-Deprotonated carbene complexes are also precursors for remote, one-N, six-membered carbene complexes of various metals whereas α-C-, α-N- or α-O-deprotonated as well as β-deprotonated Fischer-type carbene complexes display unique synthon properties towards Ph3PAu+ and partake in unusual ensuing coordination of liberated group 6 metal carbonyl moieties to form dinuclear products.

José Calhorda, Maria; Jorge Costa, Paulo

doi: 10.1039/b910207hpmid: 19789766

Organometallic complexes of transition metals in high oxidation states, namely Re(v) and Mo(vi), have been shown experimentally to catalyze a variety of reduction reactions, such as hydrosilylation of ketones, alkyne hydrogenation, sulfoxide reduction (deoxygenation), etc, often under mild conditions and with high yields and selectivity. These recently found reactions apparently contrast with the traditional oxidation of alkenes in the presence of an oxygen source. We describe a series of DFT calculations, showing that most X–H bonds are activated by [MoO2Cl2], forming a hydride complex, which is the catalytic active species in catalysis. This occurs by a [2 + 2] addition of the X–H bond to the MoO bond of the Mo(vi) complex. While hydrosilylation is particularly effective, hydrogenation is deactivated in many systems by the reduction of the catalyst, rather than the substrate, to a stable Mo(iv) complex, and P–H activation in HP(O)(OR)2 molecules takes place through a different route. The activation of O–H from HOOR differs significantly, since the high electronegativity of oxygen results in an “inverse” addition with formation of OH and a complex of OOR.

Haddadpour, Sima; Niedermeyer, Heiko; Clérac, Rodolphe; Dehnen, Stefanie

doi: 10.1039/b914674cpmid: 19789767

[{Mn(tmeda)}3{GeSe3(OMe)}2] (1), synthesized by the reaction of [K4(H2O)3][Ge2Se6] with MnCl2·4H2O in MeOH–tmeda (tmeda = N,N,N′,N′-tetramethyl-1,2-diaminoethane), exhibits an isosceles triangular arrangement of Mn2+ ions that are antiferromagnetically coupled with an S = 3/2 ground state.

Constable, Edwin C.; Zhang, Guoqi; Housecroft, Catherine E.; Neuburger, Markus; Schaffner, Silvia

doi: 10.1039/b916996mpmid: 19789768

A pair of enantiomerically pure ligands have been prepared from the condensation of (S)-(−)-1,1′-binaphthalene-2,2′-diamine or (R)-(+)-1,1′-binaphthalene-2,2′-diamine with two equivalents of 2,2′-bipyridine-6-carbaldehyde. The reaction of these new hexadentate ligands with iron(II) salts results in diastereomerically pure complexes in which the stereochemistry at the metal is fully defined by the chiral ligand scaffold. The simplicity of synthesis of the ligand suggests that conjugates of this type could play an important role in inorganic stereoselective synthesis.

Bevers, Loes E.; Hagen, Wilfred R.

doi: 10.1039/b914697kpmid: 19789769

Reversible binding of the tetrahedral oxoanions MoO42− and WO42− to two carboxylato ligands of the soluble scavenger protein WtpA from the hyperthermophilic archaeon Pyrococcus furiosus enforces a quasi-octahedral MO6 coordination in which the +VI oxidation state is destabilized.

García, M. Esther; Melón, Sonia; Ramos, Alberto; Ruiz, Miguel A.

doi: 10.1039/b909493hpmid: 19789770

Tetrahydrofuran solutions of the 30-electron anions [Mo2Cp2(μ-PA2)(μ-CO)2]− (A = Cy, Et, Ph, OEt) are conveniently prepared through a two-step approach. In the first step, [Mo2Cp2(CO)6] is treated with the chlorophosphines ClPR2 (R = Cy, Et, Ph) or the chlorophosphite ClP(OEt)2, in refluxing toluene or diglyme respectively, to give the corresponding 32-electron chloro-complexes [Mo2Cp2(μ-Cl)(μ-PA2)(CO)2] as major products. In the second step, these air-sensitive intermediates are treated in tetrahydrofuran solution at room temperature with one of several reducing agents such as Li[BHEt3], Li(Hg), Na(Hg) or K[BHsBu3] to give red solutions of the corresponding alkali-metal salts of the anions, which display significant ion pairing involving one or both oxygen atoms of the bridging carbonyl ligands, depending on the cation. All these triply bonded species are quite air-sensitive and could not be isolated as pure solids, but they can be easily protonated using a weak acid such as [NH4]PF6 to give with good yield the corresponding unsaturated hydrides [Mo2Cp2(μ-H)(μ-PA2)(CO)2], which are species of low to moderate sensitiveness to air, and also formally containing an intermetallic triple bond. The reactivity of the dicyclohexylphosphide-bridged anion (mainly as its Li+ salt) towards different hydrocarbon halides RX was studied in detail. These reactions were found to be rather complex, critically depending on the reagent used, and generally resulting in the formation of several products, of which four types were identified: (a) the known agostic products [Mo2Cp2(μ-PCy2)(μ-R)(CO)2] (R = Me, CH2Ph), (b) the new alkoxycarbyne products [Mo2Cp2(μ-COR)(μ-PCy2)(μ-CO)] [R = Me, Et, C(O)Ph, iPr, Cy], which could be conveniently isolated as pure solids, (c) the iodoxycarbyne complex [Mo2Cp2(μ-COI)(μ-PCy2)(μ-CO)], a very unstable species formed in the reaction with EtI, and (d) the halide complexes [Mo2Cp2(μ-PCy2)(μ-X)(CO)2] [X = Cl, Br, I], which were more conveniently prepared by the direct reaction of the anion with the pertinent halogen (X = Br, I). The analysis of the above results suggests that at least three primary reaction pathways are in operation: (a) nucleophilic attack of the anion through its dimetal centre, (b) nucleophilic attack of the anion through the oxygen atoms of its bridging carbonyls and (c) electron-transfer with the reagent, this being the main path to the halo-complexes [Mo2Cp2(μ-PCy2)(μ-X)(CO)2].

Fey, Natalie; Haddow, Mairi F.; Harvey, Jeremy N.; McMullin, Claire L.; Orpen, A. Guy

doi: 10.1039/b909229cpmid: 19789771

We describe the development of a ligand knowledge base designed to capture the properties of C-donor ligands coordinating to transition metal centres, LKB-C. This knowledge base has been developed to describe both singlet (Arduengo and Fischer) and triplet (Schrock) carbenes, as well as related neutral monodentate C-donor ligands. The descriptors evaluated and used have been derived from a range of coordination environments to maximise their transferability and hence utility for the investigation of such ligands. These descriptors have been analysed with different statistical approaches, both individually to determine their chemical context, and collectively by principal component analysis thereby allowing the derivation of maps of ligand space for different ligand sets. The utility of such maps for investigating ligand similarity and identification of target areas for future ligand designs has been discussed. In addition, linear regression models have been fitted for the prediction of a calculated response variable, highlighting further potential applications of such a knowledge base.

Du, Yi; Rees, Nicholas; O'Hare, Dermot

doi: 10.1039/b909853dpmid: 19789772

A study of the mechanism of phosphate adsorption by magnesium iron hydroxycarbonate, [Mg2.25Fe0.75(OH)6](CO3)0.37·0.65H2O over a range of pH has been carried out. The efficiency of the phosphate removal from aqueous solution has been investigated between pH 3–9 and the resulting solid phases have been studied by elemental analysis, XRD, FT-IR, Raman, HRTEM, EDX and solid-state MAS 31P NMR. The analytical and spectroscopic data suggest that phosphate removal from solution occurs not by anion intercalation of the relevant phosphorous oxyanion (H2PO4− or HPO42−) into the LDH but by the precipitation of either an insoluble iron hydrogen phosphate hydrate and/or a magnesium phosphate hydrate.