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Keywords:

  • Rhodium;
  • Iridium;
  • Mixed-valent compounds;
  • Imines;
  • Electron transfer;
  • Redox noninnocent ligands

Abstract

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.