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)(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.

Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

“… 63,64 The hydride is located trans to the coordinated oxygen on the basis of the observed chemical shift. 65 …”

“…63,64 The hydride is located trans to the coordinated oxygen on the basis of the observed chemical shift. 65 While reversible cyclometallation of 4-i Pr is not observed on the NMR timescale, it does occur on the laboratory timescale as probed by a variety of experiments, Schemes 3 and 4: (i) Addition of NBD quantitatively reforms 2-i Pr on time of mixing. (ii) Repeated charging of an o-xylene solution of 4-i Pr over two weeks with D 2 results in a significant, but slow, reduction in intensity of the hydride signal and the concomitant appearance of signals in the hydride and alkyl regions of the 2 H NMR spectrum.…”

Self-complementary nickel halides enable multifaceted comparisons of intermolecular halogen bonds: fluoride ligands vs. other halides

“…57 Large chemical shift anisotropies have recently been measured and calculated for metal hydrides. 58 , 59 …”

From Phosphidic to Phosphonium? Umpolung of the P4‐Bonding Situation in [CpFe(CO)(L)(η1‐P4)]+ Cations (L=CO or PPh3)

“…Analysis of cations 1 and 2 in CD 2 Cl 2 solution by multinuclear NMR spectroscopy readily identifies the coordination of an intact, but at room temperature highly fluxional P 4 cluster to the iron centers. This contrasts with previously reported η 1 ‐P 4 complexes of Fe, Ru and Os,– but has been observed in coinage metal complexes of P 4 . Thus, at 298 K the 1 H NMR spectrum of cation 1 shows a quintet resonance at δ H =5.52 for the protons residing on the Cp ring and in the 13 C{ 1 H} NMR spectrum a quintet is also observed for the carbonyl ligands at δ C =204.5.…”