title: Reversible carbon-carbon bond formation induced by oxidation and reduction at a redox-active cobalt complex.
abstract: The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, ((iPr)PIEA)CoN2 ((iPr)PIEA = 2-(2,6-(i)Pr2-C6H3N═CMe)-6-(2,6-(i)Pr2-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 ((iPr)PIEA)CoN2 with CH2═CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-((iPr)PDI)CoCl (Coupled-((iPr)PDI)CoCl = [2-(2,6-(i)Pr2-C6H3N═CMe)-C5H3N-6-(2,6-(i)Pr2-C6H3N═CCH2-)CoCl]2) with NaBEt3H led to quantitative formation of ((iPr)PIEA)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.
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Crisita Carmen Hojilla
authors.initials: CC
authors.lastname: Atienza
authors.forename: Carsten
authors.initials: C
authors.lastname: Milsmann
authors.forename: Scott P
authors.initials: SP
authors.lastname: Semproni
authors.forename: Zoë R
authors.initials: ZR
authors.lastname: Turner
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Chirik
mesh_terms: D002244:Carbon / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004583:Electrons; D007097:Imines / Q000737:chemistry; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D056831:Coordination Complexes; D007097:Imines; D011725:Pyridines; D003035:Cobalt; D002244:Carbon; C018021:cobaltous chloride; D009584:Nitrogen