Computation provides chemical insight into the diverse hydride NMR chemical shifts of [Ru(NHC)(L)H] species (NHC = N-heterocyclic carbene; L = vacant, H, N, CO, MeCN, O, P, SO, H, F and Cl) and their [Ru(RPCHCHPR)(L)H] congeners.

Relativistic density functional theory calculations, both with and without the effects of spin-orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)(L)H] species (NHC = N-heterocyclic carbene; L = vacant, H, N, CO, MeCN, O, P, SO, H, F and Cl), as well as selected phosphine analogues [Ru(RPCHCHPR)(L)H] (R = Pr, Cy; L = vacant, O). Inclusion of spin-orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl, F) being reinforced by the contribution from spin-orbit coupling.

Computational studies on the mechanism of the gold(I)-catalysed rearrangement of cyclopropenes.

Density functional theory calculations have been employed to investigate the mechanism of gold(I)-catalysed rearrangements of cyclopropenes. Product formation is controlled by the initial ring-opening step which results in the formation of a gold-stabilised carbocation/gold carbene intermediate. With 3-phenylcyclopropene-3-methylcarboxylate, the preferred intermediate allows cyclisation via nucleophilic attack of the carbonyl group and hence butenolide formation.

Smooth C(alkyl)-H bond activation in rhodium complexes comprising abnormal carbene ligands.

Rhodation of trimethylene-bridged diimidazolium salts induces the intramolecular activation of an alkane-type C-H bond and yields mono- and dimetallic complexes containing a formally monoanionic C,C,C-tridentate dicarbene ligand bound to each rhodium centre. Mechanistic investigation of the C(alkyl)-H bond activation revealed a significant rate enhancement when the carbene ligands are bound to the rhodium centre via C4 (instantaneous activation) as compared to C2-bound carbene homologues (activation incomplete after 2 days). The slow C-H activation in normal C2-bound carbene complexes allowed intermediates to be isolated and suggests a critical role of acetate in mediating the bond activation process.

Experimental and computational investigation of C-N bond activation in ruthenium N-heterocyclic carbene complexes.

A combination of experimental studies and density functional theory calculations is used to study C-N bond activation in a series of ruthenium N-alkyl-substituted heterocyclic carbene (NHC) complexes. These show that prior C-H activation of the NHC ligand renders the system susceptible to irreversible C-N activation. In the presence of a source of HCl, C-H activated Ru(I(i)Pr(2)Me(2))'(PPh(3))(2)(CO)H (1, I(i)Pr(2)Me(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) reacts to give Ru(I(i)PrHMe(2))(PPh(3))(2)(CO)HCl (2, I(i)PrHMe(2) = 1-isopropyl-4,5-dimethylimidazol-2-ylidene) and propene.

The influence of N-heterocyclic carbenes (NHC) on the reactivity of [Ru(NHC)(4)H](+) with H(2), N(2), CO and O(2).

The five-coordinate ruthenium N-heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr(2)Me(2))(4)H][BAr(F) (4)] (1; IiPr(2)Me(2)=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; Ar(F)=3,5-(CF(3))(2)C(6)H(3)), [Ru(IEt(2)Me(2))(4)H][BAr(F) (4)] (2; IEt(2)Me(2)=1,3-diethyl-4,5-dimethylimidazol-2-ylidene) and [Ru(IMe(4))(4)H][BAr(F) (4)] (3; IMe(4)=1,3,4,5-tetramethylimidazol-2-ylidene) have been synthesised following reaction of [Ru(PPh(3))(3)HCl] with 4-8 equivalents of the free carbenes at ambient temperature. Complexes 1-3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about delta -41.

Formation of [Ru(NHC)4(eta(2)-O2)H]+: an unusual, high frequency hydride chemical shift and facile, reversible coordination of O2.

Reaction of the purple tetrakiscarbene ruthenium cation [Ru(I(i)Pr(2)Me(2))(4)H](+) (1, I(i)Pr(2)Me(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with oxygen affords the pink eta(2)-O(2) hydride species [Ru(I(i)Pr(2)Me(2))(4)(eta(2)-O(2))H](+) (2). 2 displays (i) a very facile, reversible O(2) coordination and (ii) an unexpectedly positive hydride chemical shift, and both these features can be predicted and explained by density functional theory (DFT) calculations.

Activation of an alkyl C-H bond geminal to an agostic interaction: an unusual mode of base-induced C-H activation.

Deuterium labeling studies indicate that base-induced intramolecular C-H activation in the agostic complex 2-D proceeds with exclusive removal of a proton from the methyl arm of an (i)Pr substituent on the N-heterocyclic carbene (NHC) ligand. Computational studies show that this alkyl C-H bond activation reaction involves deprotonation of one of the C-H bonds that is geminal to the agostic interaction, rather than the agostic C-H bond itself. The reaction is readily accessible at room temperature, and a computed activation barrier of DeltaE (double dagger)(calcd) = +11.

Neptunium(vi) chain and neptunium(vi/v) mixed valence cluster complexes.

The synthesis of [Np(VI)O(2)Cl(2)(thf)](n) offers the potential for more detailed exploration of neptunyl(vi) chemistry, while the synthesis of the mixed valence cluster complex [{Np(VI)O(2)Cl(2)}{Np(V)O(2)Cl(thf)(3)}(2)] allows molecular neptunyl(v) 'cation-cation' interactions to be probed.

A structural and theoretical investigation of equatorial cis and trans uranyl phosphinimine and uranyl phosphine oxide complexes UO2Cl2(Cy3PNH)2 and UO2Cl2(Cy3PO)2.

Phosphinimine ligands (Cy3PNH) readily react with UO2Cl2(THF)3 (THF=tetrahydrofuran) to give UO2Cl2(Cy3PNH)2, which contains strong U-N interactions and exists as cis and trans isomers in the solid and solution state. Solution NMR experiments and computational analysis both support the trans form as the major isomer in solution, although the cis isomer becomes more stabilized with an increase in the dielectric constant of the solvent. Mayer bond orders, energy decomposition analysis, and examination of the molecular orbitals and total electron densities support a more covalent bonding interaction in the U-NHPCy3 bond compared with the analogous bond of the related U-OPCy3 compounds.

Density functional theory investigation of the geometric and electronic structures of [UO2(H2O)m(OH)n](2 - n) (n + m = 5).

Gradient corrected density functional theory has been used to calculate the geometric and electronic structures of the family of molecules [UO2(H2O)m(OH)n](2 - n) (n + m = 5). Comparisons are made with previous experimental and theoretical structural and spectroscopic data. r(U-O(yl)) is found to lengthen as water molecules are replaced by hydroxides in the equatorial plane, and the nu(sym) and nu(asym) uranyl vibrational wavenumbers decrease correspondingly.