Solid-state phosphorus-31 NMR spectroscopy of a multiple-spin system: an investigation of a rhodium-triphosphine complex

31P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere

The NMR chemical shift has been the most versatile marker of chemical structures, by reflecting global and local electronic structures, and is very sensitive to any change within the chemical species. In this work, Ru(II) complexes with the same five ligands and a variable sixth ligand L (none, H₂O, H₂S, CH₃SH, H₂, N₂, N₂O, NO⁺, C═CHPh, and CO) are studied by using as the NMR reporter the phosphorus P_A of a coordinated bidentate P_A-N ligand (P_A-N = o-diphenylphosphino-N,N'-dimethylaniline). The chemical shift of P_A in RuCl₂(P_A-N)(PR₃)(L) (R = phenyl, p-tolyl, or p-FC₆H₄) was shown to increase as the Ru-P_A bond distance decreases, an observation that was not rationalized. This work, using density functional theory (DFT) calculations, reproduces reasonably well the observed ³¹P chemical shifts for these complexes and the correlation between the shifts and the Ru-P_A bond distance as L varies. An interpretation of this correlation is proposed by using a natural chemical shift (NCS) analysis based on the natural bonding orbital (NBO) method. This analysis of the principal components of the chemical shift tensors shows how the σ-donating properties of L have a particularly high influence on the phosphine chemical shifts.