Electron and Oxygen Atom Transfer Chemistry of Co(II) in a Proton Responsive, Redox Active Ligand Environment.

The bis-pyrazolato pyridine complex LCo(PEt3 )2 serves as a masked form of three-coordinate CoII and shows diverse reactivity in its reaction with several potential outer sphere oxidants and oxygen atom transfer reagents. N-Methylmorpholine N-oxide (NMO) oxidizes coordinated PEt3 from LCo(PEt3 )2 , but the final cobalt product is still divalent cobalt, in LCo(NMO)2 . The thermodynamics of a variety of oxygen atom transfer reagents, including NMO, are calculated by density functional theory, to rank their oxidizing power. Oxidation of LCo(PEt3 )2 with AgOTf in the presence of LiCl as a trapping nucleophile forms the unusual aggregate [LCo(PEt3 )2 Cl(LiOTf)2 ]2 held together by Li+ binding to very nucleophilic chloride on Co(III) and triflate binding to those Li+ . In contrast, Cp2 Fe+ effects oxidation to trivalent cobalt, to form (HL)Co(PEt3 )2 Cl+ ; proton and the chloride originate from solvent in a rare example of CH2 Cl2 dehydrochlorination. An unexpected noncomplementary redox reaction is reported involving attack by 2e reductant PEt3 nucleophile on carbon of the 1e oxidant radical Cp2 Fe+ , forming a P-C bond and H+ ; this reaction competes in the reaction of LCo(PEt3 )2 with Cp2 Fe+ .