Metal-Metal Bonding in Low-Coordinate Dicobalt Complexes Supported by Phosphinoamide Ligands

Homobimetallic dicobalt complexes featuring metal centers in different coordination environments have been synthesized, and their multielectron redox chemistry has been investigated. Treatment of CoX2 with MesNkP(i)Pr(2) leads to self-assembly of [(THF)Co(MesNP(i)Pr(2))(2)(mu-X)CoX] [X = Cl (1), I (2)], with one Co center bound to two amide donors and the other bound to two phosphine donors. Upon two-electron reduction, a ligand rearrangement occurs to generate the symmetric species (PMe3)Co(MesNP(i)Pr(2))(2)Co(PMe3) (3), where each Co has an identical mixed P/N donor set. One-electron oxidation of 3 to generate a mixed valence species promotes a ligand reararrangement back to an asymmetric configuration in [(THF)Co(MesNP(i)Pr(2))(2)Co(PMe3)][PF6] (4). Complexes 1-4 have been structurally characterized, and their metal-metal interactions are discussed in the context of computational results.