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

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)CoI–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.