title: Multielectron Transfer at Cobalt: Influence of the Phenylazopyridine Ligand.
abstract: The dicationic complex [CpCo(azpy)(CH3CN)](ClO4)21 (azpy = phenylazopyridine) exhibits a reversible two-electron reduction at a very mild potential (-0.16 V versus Fc0/+) in acetonitrile. This behavior is not observed with the analogous bipyridine and pyrazolylpyridine complexes (3 and 4), which display an electrochemical signature typical of CoIIIsystems: two sequential one-electron reductions to CoIIat -0.4 V and CoIat -1.0 to -1.3 V versus Fc0/+. The doubly reduced, neutral complex [CpCo(azpy)] 2 is isolated as an air-stable, diamagnetic solid via chemical reduction with cobaltocene. Crystallographic and spectroscopic characterization together with experimentally calibrated density functional theory calculations illuminate the key structural and electronic changes that occur upon reduction of 1 to 2. The electrochemical potential inversion observed with 1 is attributed to effective overlap between the metal d and the low-energy azo π* orbitals in the intermediary redox state and additional stabilization of 2 from structural reorganization, leading to a two-electron reduction. This result serves as a key milestone in the quest for two-electron transformations with mononuclear first-row transition metal complexes at mild potentials.
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Waldie
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Srinivasan
authors.identifier: 0000-0003-3204-8095
authors.initials: S
authors.lastname: Ramakrishnan
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Sung-Kwan
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Jana K
authors.initials: JK
authors.lastname: Maclaren
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Christopher E D
authors.initials: CE
authors.lastname: Chidsey
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: Robert M
authors.identifier: 0000-0001-9862-9509
authors.initials: RM
authors.lastname: Waymouth