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Resolving the Two-Electron Process for the Couple (C5Me5)M(NN̂)Cl+/(C5Me5)M(NN̂) (M = Rh, Ir) into Two One-Electron Steps Using the 2,2'-Azobis(pyridine) NN̂ Ligand, Fast Scan Cyclovoltammetry, and Spectroelectrochemistry: Detection of Radicals instead of MII Intermediates

, , , and . Organometallics, 22 (11): 2240--2244 (2003)
DOI: 10.1021/om020860j

Abstract

(C5Me5)M(abpy)Cl+ M = Rh, Ir; abpy = 2,2'-azobis(pyridine) are reduced to the coordinatively unsatd. compds. (C5Me5)M(abpy) via the EPR and UV/visible spectroelectrochem. detectable radical intermediates (C5Me5)MIII(abpy-I)Cl.bul.. Fast-scan cyclic voltammetry allowed the authors to establish the electrochem. potentials. This stepwise mechanism differs from the two-electron processes obsd. for the analogous systems (C5Me5)M(NN̂)Cl+/(C5Me5)M(NN̂) with NN̂ = 2,2'-bipyridines, bidiazines, 1,4-diaza-1,3-butadienes. In contrast to Co systems such as (C5Me5)Co(bpy)Cl+ the 1-electron redn. does not involve the metal. The role of the abpy ligand as an intermediate 1-electron storage component for a metal-centered two-electron process is discussed. Further redn. of (C5Me5)M(abpy) to (C5Me5)MII(abpy-II)- at very neg. potentials illustrates the extremely strong p back-donation from the 14-valence-electron fragments (C5Me5)M (M = Rh, Ir). on SciFinder(R)

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