A series of two-coordinate copper tert-butoxide complexes bearing five-, six-, and seven-membered ring N-heterocyclic carbenes, prepared by protonolysis of (NHC)CuMes with t BuOH, have been used as catalytic precursors in the semihydrogenation of alkynes with silanes/ t BuOH and the hydroboration of alkynes with HBPin. Both processes proceed with high regioselectivity and show enhancements with six-and seven-membered ring carbenes.

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. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru d orbitals and the unoccupied σ* orbital. In [Ru(NHC)(η-O)H] a δ-interaction with the O ligand results in a low-lying LUMO of d character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) d orbital under the L angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(PrPCHCHPPr)(η-O)H] (δ = -6.2 ppm) and [Ru(RPCHCHPR)H] (ca. -32 ppm, R = Pr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of -41 ppm, similar to the [Ru(NHC)H] analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BAr salts of [Ru(IMe)(L)H] (IMe = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P, SO; Ar = 3,5-(CF)CH) and [Ru(IMe)(Cl)H] are also reported.

The efficient and highly selective room temperature hydrodefluorination (HDF) of fluoroarenes by the trans-[Ru(IMe ) H ] catalyst, 3, is reported. Mechanistic studies show 3 acts directly in catalysis without any ligand dissociation and DFT calculations indicate a concerted nucleophilic attack mechanism. The calculations fully account for the observed selectivities which corroborate earlier predictions regarding the selectivity of HDF.

The room temperature reaction of C6F6 or C6F5H with [Ru(IEt2Me2)2(PPh3)2H2] (; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) generated a mixture of the trans-hydride fluoride complex [Ru(IEt2Me2)2(PPh3)2HF] () and the bis-carbene pentafluorophenyl species [Ru(IEt2Me2)2(PPh3)(C6F5)H] (). The formation of resulted from C-H activation of C6F5H (formed from C6F6via stoichiometric hydrodefluorination), a process which could be reversed by working under 4 atm H2. Upon heating with C6F5H, the bis-phosphine derivative [Ru(IEt2Me2)(PPh3)2(C6F5)H] () was isolated. A more efficient route to involved treatment of with 0.33 eq. of TREAT-HF (Et3N·3HF); excess reagent gave instead the [H2F3](-) salt () of the known cation [Ru(IEt2Me2)2(PPh3)2H](+). Under catalytic conditions, proved to be an active precursor for hydrodefluorination, converting C6F6 to a mixture of tri, di and monofluorobenzenes (TON = 37) at 363 K with 10 mol% and Et3SiH as the reductant.

The all-trans isomer of Ru(IMe 4 ) 2 (PPh 3 ) 2 H 2 (ttt-4; IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene) reacts with C 6 F 6 at 70 °C to afford the hydride fluoride complex Ru(IMe 4 ) 2 (PPh 3 ) 2 HF (ttt-6). At room temperature, ttt-6 reacts with Et 3 SiH to give a mixture of products, one of which is assigned as the silyl trihydride complex Ru(IMe 4 ) 2 (PPh 3 )-(SiEt 3 )H 3 (8) by comparison to the isolated and structurally characterized analogue Ru(IMe 4 ) 2 (PPh 3 )(SiPh 3 )H 3 (9). As ttt-4 was re-formed cleanly upon heating ttt-6 with Et 3 SiH, it was tested in the catalytic hydrodefluorination (HDF) of C 6 F 6 (10 mol %, 90 °C), along with 9, Ru(IMe 4 ) 2 (P-P)HF (P-P = Ph 2 P(CH 2 ) 2 PPh 2 (dppe, cct-13), Ph 2 P(CH 2 ) 3 PPh 2 (dppp, cct-14), Ph 2 PCH 2 PPh 2 (dppm, cct-15)), Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 HF (cct-7; IEt 2 Me 2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)), and Ru(IEt 2 Me 2 ) 2 (dppe) 2 HF (cct-16) for comparison. Both cct-13 and cct-14 brought about near-quantitative conversion to C 6 FH 5 in 24 h, in comparison to ca. 50% conversion with ttt-4 in 144 h.