A Series of Dimeric Cobalt Complexes Bridged by N-Heterocyclic Phosphido Ligands.

A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multielectron redox processes that are both metal- and ligand-centered. Reduction of (PPP)CoCl () with excess magnesium affords the CoCo N-heterocyclic phosphido (NHP)-bridged symmetric dimer [(μ-PPP)Co] (). Two-electron oxidation of with FcPF generates an asymmetrically bridged dication [(μ-PPP)Co][PF] () in which the oxidation has occurred in a delocalized fashion throughout the CoP core. In contrast, [(μ-PPP)Co] (), which can be generated either by one-electron oxidation of with FcPF or comportionation of and , features an asymmetric geometry and localized mixed valence. Treatment of with the milder reductants CoCp and KBEtH does not lead to formation of , , or but instead generates dimeric species [(PPP)CoCl] () and [(PPP)CoH] (). Unlike -, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex and are connected solely by NHP ligands that bridge the two (PPP)Co fragments.