Aerobic Oxidation Reactivity of Well-Defined Cobalt(II) and Cobalt(III) Aminophenol Complexes

This paper describes the synthesis and reactivity studies of three cobalt complexes bearing aminophenol-derived ligands without nitrogen substitution: CoII(tBu2APH)2(tBu2AP)2(1), CoIII2(tBu2APH)2(tBu2AP)2(mu-tBu2BAP)2(2), and CoIII(tBu2AP)3(3), wheretBu2APH = 2-amino-4,6-di-tert-butylphenol,tBu2AP = 2-amino-4,6-di-tert-butylphenolate, and mu-tBu2BAP = bridging 2-amido-4,6-di-tert-butylphenolate. Stoichiometric reactivity studiesof these well-defined complexes demonstrate the catalyticcompetency of both cobalt(II) and cobalt(III) complexes in theaerobic oxidative cyclization oftBu2APH withtert-butylisonitrile.Reactions with O2reveal the aerobic oxidation of the cobalt(II)complex1to generate the cobalt(III) species2and3.UV-visible time-course studies and electron paramagnetic resonancespectroscopy indicate that this oxidation proceeds through a ligand-based radical intermediate. These studies represent thefirstexample of well-defined cobalt aminophenol complexes that participate in catalytic aerobic oxidation reactions and highlight a key role for a ligand radical in the oxidation sequence

Automated summary

This paper describes the synthesis and reactivity studies of three cobalt complexes with aminophenol-derived ligands without nitrogen substitution. The catalytic competency of these complexes in the aerobic oxidative cyclization reaction is demonstrated, and the oxidation process from cobalt(II) to cobalt(III) is shown to proceed through a ligand-based radical intermediate.