Resolving the Two-Electron Process for the Couple [(C5Me5)M(N∧N)Cl]+/[(C5Me5)M(N∧N)] (M = Rh, Ir) into Two One-Electron Steps Using the 2,2‘-Azobis(pyridine) N∧N Ligand, Fast Scan Cyclovoltammetry, and Spectroelectrochemistry: Detection of Radicals instead of MIIIntermediates

The complex cations [(C 5 Me 5 )M(abpy)Cl] + (M = Rh, Ir; abpy = 2,2‘-azobis(pyridine)) are reduced to the coordinatively unsaturated compounds [(C 5 Me 5 )M(abpy)] via the EPR and UV/vis spectroelectrochemically detectable radical intermediates [(C 5 Me 5 )M III (abpy - I )Cl] • . Fast-scan cyclic voltammetry allowed us to establish the electrochemical potentials. This stepwise mechanism differs from the two-electron processes observed for the analogous systems [(C 5 Me 5 )M(N ∧ N)Cl] + /[(C 5 Me 5 )M(N ∧ N)] with N ∧ N = 2,2‘-bipyridines, bidiazines, 1,4-diaza-1,3-butadienes. In contrast to cobalt systems such as [(C 5 Me 5 )Co(bpy)Cl] + the one-electron reduction does not involve the metal. The role of the abpy ligand as an intermediate one-electron storage component for a metal-centered two-electron process is discussed. Further reduction of [(C 5 Me 5 )M(abpy)] to [(C 5 Me 5 )M II (abpy - II )] - at very negative potentials illustrates the extremely strong π back-donation from the 14-valence-electron fragments (C 5 Me 5 )M (M = Rh, Ir).