Snapshots of a reversible metal-ligand two-electron transfer step involving compounds related by multiple types of isomerism

An unusual and very fast equilibrium between two isomers, [(cod)Rh-I{(bpa - 2H)0}IrI(cod)][rlhar2][(cod)RhI{(bpa - 2H)2-}IrI(cod)], which simultaneously display multiple types of isomerism: ligand-metal redox (electromerism), linkage, bond-stretch and ring-slippage isomerism, has been studied by NMR spectroscopy and DFT calculations. Both isomers have been isolated by making rational use of their thermodynamic parameters (ΔH° = +1.93 kcal mol-1; ΔS° = +7.8 cal mol-1 K-1), and have been characterized by X-ray diffraction methods. The equilibrium that involves a two-electron exchange between a redox noninnocent ligand, which transforms from a deprotonated amido form into an imine, and a metal that is reduced, could elucidate a thus far obscure step in the oxidative dehydrogenation of amines to imines.