Monoanionic bis(carbene) pincer complexes featuring cobalt(I–III) oxidation states

Abstract

The synthesis and characterization of a series of cobalt complexes featuring a pincer bis(carbene) ligand of the meta-phenylene-bridged bis-N-heterocyclic carbene (^ArCCC, Ar = 2,6-diispropylphenyl or mesityl) are reported. Cleavage of the aryl C–H bond of the ligand was achieved in a one-pot metalation procedure using Co(N(SiMe₃)₂)₂(py)₂, an equivalent of exogenous base, and trityl chloride to form the (^DIPPCCC)CoCl₂py complex. This species could be reduced to the Co(II) and Co(I)–N₂ molecules with the appropriate equivalents of reductant. Subsequent generation of (^MesCCC)Co^I–III derivatives with the mesityl ligand proceeded in good yields. A suite of characterization techniques and the interconversion between all three oxidation states of the cobalt complexes is described.