Isomeric Effects in Diphosphine Carbonyl Ruthenium(II) Complexes Influence the Catalytic Transfer Hydrogenation of NADH

The study investigates the influence of the CO group orientation on the reactivity of two geometric isomers [Ru(bipy)]_m (meridional) and [Ru(bipy)]_f (facial). In aprotic solvents, the strong trans effect exerted by the CO ligand in [Ru(bipy)]_m labilizes the P–Ru bond and leads to the formation of a ruthenium species [Ru(bipy)]_p where the phosphine is monodentate, and the acetate reaches a η² coordination. The equilibrium can be reversed upon the addition of a protic solvent. Furthermore, ¹H and ³¹P NMR, as well as UV–visible absorption spectroscopy, were employed to investigate the isomeric effects on the compounds’ hydrolysis and catalytic oxidation of NADH. A thorough density functional theory (DFT) analysis was conducted, using water as implicit solvent, aiming at rationalizing experimental findings and disentangling the mechanistic aspects of the reaction, leading to the formation of Ru(II) hydride species.