Activation of E-H and E-E (E = S, O) Bonds by Heterobimetallic Zr/Co Complexes: Evidence for Both One- and Two-Electron Processes.

The reactivity of the reduced ZrIIICo0 heterobimetallic complex [(thf)Zr(MesNP iPr2)3CoN2] ( 1a) towards O-H, S-H, S-S, and O-O bonds has been investigated. Complex 1a reacts readily with PhOH, EtOH, and H2O to generate the one-electron-oxidized complexes [(RO)Zr(MesNP iPr2)3CoN2] [R = Et ( 2), Ph ( 3), H ( 4)]. In contrast, PhSH and PhS-SPh react by means of overall two-electron processes to form [(η2-MesNP iPr2)Zr(μ-SPh)(MesNP iPr2)2Co(SPh)] ( 5a). Addition of stoichiometric diethyl peroxide to 1a generates 2, but further equivalents lead to the two-electron oxidized product [(EtO)Zr(MesNP iPr2)3Co(OEt)] ( 6). More sterically hindered peroxides such as dicumyl peroxide or di- tert-butyl peroxide do not react with 1a under ambient conditions, but upon photolysis, di- tert-butyl peroxide reacts with 1a to form [( tBuO)Zr(MesNP iPr2)3CoN2] ( 7). These results imply that an inner-sphere electron-transfer process is occurring at the Zr site of 1a upon treatment with these chalcogen-based substrates, and a dissociative electron-transfer mechanism is proposed. [ABSTRACT FROM AUTHOR]