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Characterization of Co-C Bonding in Dichlorovinyl Cobaloxime Complexes

Follett, A. D.; McNabb, K. A.; Peterson, A. A.; Scanlon, J. D.; Cramer, C. J.; McNeill, K.
Inorg. Chem. 2007, 46, 1645.

This study combines theory and experiment in an examination of Co-C bonding and reductive Co-C cleavage in cobalt dichlorovinyl complexes. It is motivated by the role of dichlorovinyl complexes as intermediates in the dechlorination of trichloroethylene by cobalamin and cobalamin model complexes. A series of seven cis-1,2-dichlorovinyl(L)cobaloxime complexes were prepared (L = m- and p-substituted pyridines; cobaloxime = bis-(dimethylglyoximato)cobalt). The complexes were characterized using 1H NMR, 13C NMR, cyclic voltammetry, and X-ray crystallography. Examination of the metrical parameters of the Co-C=C unit across the series shows very little change in the C=C bond length and a slight increase in the Co-C bond length with increasing electron-donating ability of the pyridine ligand. These structural changes along with electronic structure calculations indicate that Co-C π-bonding is not important in these complexes. The stronger Co-C bonds of vinylcobaloximes compared to alkylcobaloximes are best explained by the higher s-character at C. Changes in the reduction potential across the series indicate that the pyridine-bound form is the primary electrochemically active species. Theoretical examination of the Co-C cleavage following reduction supports the direct formation of cis-1,2-dichlorovinyl anion and not cis-1,2-dichlorovinyl radical.

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