Dalton Transactions

doi: 10.1039/b616270npmid: N/A

doi: 10.1039/b616271cpmid: N/A

Knijnenburg, Quinten; Gambarotta, Sandro; Budzelaar, Peter H. M.

doi: 10.1039/b612251epmid: 17117213

The diiminepyridine ligand, made famous by Brookhart and Gibson a decade ago through its use in the first iron-containing olefin polymerization catalyst, also displays an amazing variety of ligand-centred reactions, including electron transfer, alkylation, dimerization and deprotonation. The present Perspective summarizes these reactions and also speculates on the links between ligand- and metal-centred reactivity.

Clark, Thomas E.; Makha, Mohamed; Raston, Colin L.; Sobolev, Alexandre N.

doi: 10.1039/b611399kpmid: 17117214

-Bu-calix[5]arene forms crystalline inclusion complexes with - and -carboranes in toluene or dichloromethane–hexane, but not with the -isomer, the extended structures being based on 1 : 1 host–guest supermolecules, with the -Bu-substituents creating a snug fit for - and -carborane; -carborane forms a highly hexane soluble complex, induced by grinding, which crystallizes as fibres. Solution phase studies showed the presence of a 1 : 1 host–guest stoichiometry with all three isomeric carboranes as determined from Job plots. The association constants for the - and -carborane complexes are 6.4 ± 0.3 M and 3.8 ± 0.1 M respectively, whereas the -isomer is only weakly associated. Competition experiments involving all three isomers show rapid exchange on the NMR time scale, and no selectivity in solution is evident. Selective association involving the - and -isomers in the solid state is therefore remarkable, and it is a manifestation of crystal packing forces which embodies the differences in dipole moments of the carboranes.

Huang, Yi-Luen; Chang, Chin-Pei; Hong, Fung-E

doi: 10.1039/b611359apmid: 17117215

In the process of isolation under aerobic conditions phenylethynyl-di-(-butyl)-phosphine bridged dicobalt complex [(µ-PPhCHPPh)Co(CO)(µ,η-PhCCP(-Bu))] underwent a partial oxidation. The identity of the oxidized product, [(µ-PPhCHPPh)Co(CO)(µ,η-PhCC–O–P(O)(-Bu))] , was established by spectroscopic means as well as the single-crystal X-ray diffraction method. This is the first crystallographic evidence that unambiguously supports the formation of an organometallic version of a phosphinate ester. The mechanism for the formation of from was proposed, and its validity was examined by DFT means. For the purpose of comparison, a similar mechanism illustrating the transformation of PhCCP(-Bu) into PhCC–O–P(O)(-Bu), the organic counterpart of , was examined by the same method. It was found that the metal fragment is indeed capable of assisting the oxidation process by lowering the activation energy, although the effect is small. The impact of the presence of an electron-withdrawing substituent such as a fluorine atom in the alkynylphosphine was also investigated. Results demonstrated that the conversion of fluorine-substituted phosphines to the corresponding phosphinate esters can be achieved more readily. In addition, the energy barrier for the reaction of a phosphine with dioxygen yielding the phosphine oxide was calculated to be much lower than that on the way to the phosphinate ester.

Fey, Natalie; Howell, James A. S.; Lovatt, Jonathan D.; Yates, Paul C.; Cunningham, Desmond; McArdle, Patrick; Gottlieb, Hugo E.; Coles, Simon J.

doi: 10.1039/b610123bpmid: 17117216

A molecular mechanics force field has been developed which accurately reproduces experimental solid state structures and conformer interconversion barriers for a series of sterically congested diaryl and triaryl phosphines and some of their chalcogenide and Cr(CO) derivatives.

Cavigliasso, Germán; Kaltsoyannis, Nikolas

doi: 10.1039/b613446gpmid: 17117217

Density functional and multiconfigurational () calculations have been performed on [MX] (X = Cl, Br, I) complexes of 4d (Mo, Tc, Ru), 5d (W, Re, Os), and 5f (U, Np, Pu) metals in order to investigate general trends, similarities and differences in the electronic structure and metal–metal bonding between f-block and d-block elements. Multiple metal–metal bonds consisting of a combination of σ and π interactions have been found in all species investigated, with δ-like interactions also occurring in the complexes of Tc, Re, Np, Ru, Os, and Pu. The molecular orbital analysis indicates that these metal–metal interactions possess predominantly d (σ), d and d (π), or d and d (δ) character in the d-block species, and f (σ), f and f (π), or f and f (δ) character in the actinide systems. In the latter, all three (σ, π, δ) types of interaction exhibit bonding character, irrespective of whether the molecular symmetry is or . By contrast, although the nature and properties of the σ and π bonds are largely similar for the and forms of the d-block complexes, the two most relevant metal–metal δ-like orbitals occur as a bonding and antibonding combination in symmetry but as a nonbonding level in symmetry. Multiconfigurational calculations have been performed on a subset of the actinide complexes, and show that a single electronic configuration plays a dominant role and corresponds to the lowest-energy configuration obtained using density functional theory.

Clarkson, Guy J.; Gibson, Vernon C.; Goh, Peter K. Y.; Hammond, Max L.; Knight, Paul D.; Scott, Peter; Smit, Theo M.; White, Andrew J. P.; Williams, David J.

doi: 10.1039/b610555fpmid: 17117218

The structural properties of three new classes of titanium and zirconium complex bearing tetradentate salicylaldiminato proligands are elucidated using X-ray diffraction and NMR spectroscopy. On activation with MAO co-catalyst, their behaviour in ethene polymerization depends strongly on the nature of the structure and the substitution pattern. One titanium complex based on a 2-aminobenzylamine (C-chain) backbone has a arrangement of the co-ligand sites and, unsurprisingly, does not polymerize ethene. The 1,8-diaminonaphthalene (C-chain) backbone gives a rather ring-strained complex, but was also unproductive. A range of complexes of zirconium with the 2,2′-diaminobibenzyl (C-chain) backbone give low to moderate productivities of multimodal poly(ethene), while in contrast the structurally analogous titanium compounds provide highly active, single site catalysts. Thermal degradation of these catalysts is slowed significantly by a substitution pattern on the phenolate unit which sterically protects the imine donor unit; a phenomenon which has been previously observed in much lower activity catalysts based on 2,2′-diaminobiphenyl (C-chain) but which does not improve the stability of the very highly active unbridged systems.

Moxham, Gemma L.; Douglas, Thomas M.; Brayshaw, Simon K.; Kociok-Köhn, Gabriele; Lowe, John P.; Weller, Andrew S.

doi: 10.1039/b612049kpmid: 17117219

Iridium hydridophosphine complexes of general formula [Ir(PR)H(anion)](PR= PPh, PMePh; anion =[1--CBHCl], [1--CBHI], [BAr]) have been prepared by hydrogenation of cyclooctadiene precursor complexes. Solid-state structures of selected examples of these complexes reveal intimate contacts between the carborane anion and cation, with the anion binding through two lower-hemisphere halogen ligands. In CDCl solution the very weakly coordinating anions [1--CBHCl] and [BAr] are suggested to favour the formation of solvent complexes such as [Ir(PR)H(solvent)][anion], while the [1--CBHI] anion forms a tightly bound complex with the cationic iridium fragment. Calculated Δ‡ values for anion reorganisation in -toluene reflect this difference in interaction between the anions and cation. With the bulky anion [1--CBMeI] different complexes are formed: Ir(PPh)H(1--HCBMeI) and [(PPh)Ir(H)H][1--HCBMeI] which have been characterised spectroscopically. Diffusion measurements in CDCl are also consistent with larger, solvent coordinated, complexes for the more weakly coordinating anions and a tighter interaction between anion and cation for [1--CBHI]. All the complexes show some ion-paring in solution. Comparison with data previously reported for the [1--CBHBr] anion shows that this anion—as expected—fits between [1--CBHCl] and [1--CBHI] in terms of coordinating ability. Although not coordinating, the large [1--CBHCl] and [BAr] anions do provide some stabilisation towards the metal centre, as decomposition to the hydride bridged dimer [Ir(PPh)H] is retarded. This is in contrast to the [PF] salt where decomposition is immediate. As expected, complexes with the smaller phosphine PMePh form tighter interactions with the carborane anions. These observations on the interaction between anion and cation in solution are reflected in benchmark hydrogenation studies that show a significant attenuation in rate of hydrogenation of cyclohexane on using the [1--CBHI] anion or complexes with the PMePh phosphine. We also comment on the reusability of the catalysts and their tolerance to water and oxygen impurities. Overall the catalyst with the [1--CBHBr] anion shows the best combination of rate of hydrogenation, reusability and tolerance to impurities.

Meier, Roland; Molinier, Michel; Anson, Chris; Powell, Anne K.; Kallies, Bernd; van Eldik, Rudi

doi: 10.1039/b605056epmid: 17117220

The results of a detailed solid state and solution structural study of the Fe bis-mida complex [Fe(mida)] (mida = -methyl-iminodiacetate) are reported. The structure of the sodium salt Na[Fe(mida)][NaClO]·3HO () was determined by single-crystal X-ray analysis. The complex anion in contains a six-coordinate Fe centre bound to two tridentate mida ligands arranged in the meridional configuration, and the FeNO chromophore shows a high degree of distortion from regular octahedral symmetry. Raman- and UV/VIS/NIR spectroscopic measurements showed that no gross changes take place in the Fe coordination sphere upon redissolution in water. Quantum chemical calculations of all three possible configurations of the [Fe(mida)] complex ion in the gas phase support the finding that the isomer is more stable than the u- () and s- () isomers. Redox potential measurements of the Fe(mida) couple in dependence of pH led to the following values for the equilibrium contants: log = 11.98 ± 0.05, log = 20.49 ± 0.01, p = 7.81; log = 6.17 ± 0.01, log = 11.39 ± 0.01.