Reversible Carbon–Carbon Bond Formation Induced by Oxidation and Reduction at a Redox-Active Cobalt Complex

The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, (iPrPIEA)­CoN2 (iPrPIEA = 2-(2,6-iPr2–C6H3NCMe)-6-(2,6-iPr2–C6H3NCCH2)­C5H3N), was determined and is best described as a low-spin cobalt­(II) complex antiferromagnetically coupled to an imine radical anion. Addition of potential radical sources such as NO, PhSSPh, or Ph3Cl resulted in C–C coupling at the enamide positions to form bimetallic cobalt compounds. Treatment with the smaller halocarbon, PhCH2Cl, again induced C–C coupling to form a bimetallic bis­(imino)­pyridine cobalt chloride product but also yielded a monomeric cobalt chloride product where the benzyl group added to the enamide carbon. Similar cooperative metal–ligand addition was observed upon treatment of (iPrPIEA)­CoN2 with CH2CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-(iPrPDI)­CoCl (Coupled-(iPrPDI)­CoCl = [2-(2,6-iPr2–C6H3NCMe)-C5H3N-6-(2,6-iPr2–C6H3NCCH2−)­CoCl]2) with NaBEt3H led to quantitative formation of (iPrPIEA)­CoN2, demonstrating the reversibility of the C–C bond forming reactions. The electronic structures of each of the bimetallic cobalt products were also elucidated by a combination of experimental and computational methods.