title: Computation provides chemical insight into the diverse hydride NMR chemical shifts of [Ru(NHC)4(L)H]0/+species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H-, F-and Cl-) and their [Ru(R2PCH2CH2PR2)2(L)H]+congeners.
abstract: 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)4(L)H]0/+species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H-, F-and Cl-), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+(R =iPr, Cy; L = vacant, O2). 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 dπorbitals and the unoccupied σ*Ru-Horbital. In [Ru(NHC)4(η2-O2)H]+a δ-interaction with the O2ligand results in a low-lying LUMO of dπcharacter. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dπorbital under the Lzangular 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(iPr2PCH2CH2PiPr2)2(η2-O2)H]+(δ = -6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+(ca. -32 ppm, R =iPr, 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)4H]+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 BArF4-salts of [Ru(IMe4)4(L)H]+(IMe4= 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF= 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported.
authors.affiliation: Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. S.A.Macgregor@hw.ac.uk.
authors.forename: L Jonas L
authors.initials: LJ
authors.lastname: Häller
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. M.K.Whittlesey@bath.ac.uk.
authors.forename: Elena
authors.initials: E
authors.lastname: Mas-Marzá
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. M.K.Whittlesey@bath.ac.uk.
authors.forename: Mateusz K
authors.initials: MK
authors.lastname: Cybulski
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Rajashekharayya A
authors.initials: RA
authors.lastname: Sanguramath
authors.affiliation: Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. S.A.Macgregor@hw.ac.uk.
authors.forename: Stuart A
authors.identifier: http://orcid.org/0000-0003-3454-6776
authors.initials: SA
authors.lastname: Macgregor
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. M.K.Whittlesey@bath.ac.uk.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Mahon
authors.affiliation: Institut Charles Gerhardt, CNRS 5253, Université de Montpellier, Bâtiment 15, CC 1501, Place Eugène Bataillon, 34 095 Montpellier Cedex 5, France. Christophe.Raynaud1@umontpellier.fr.
authors.forename: Christophe
authors.identifier: http://orcid.org/0000-0003-0979-2051
authors.initials: C
authors.lastname: Raynaud
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Russell
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. M.K.Whittlesey@bath.ac.uk.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Whittlesey