Mono- and Dinuclear Heteroleptic Cobalt Complexes with α-Diimine and Polyarene Ligands

Reactions of the dimeric cobalt complex [(L^-Co)₂] (1, L=[(2,6-iPr₂C₆H₃)NC(Me)]₂) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η⁴-anthracene)] (2), [LCo(μ-η⁴:η⁴-naphthalene)CoL] (3), and [LCo(μ-η⁴:η⁴-phenanthrene)CoL] (4). The pyrene complexes [{Na₂(Et₂O)₂}{LCo(μ-η³:η³-pyrene)CoL}] (5) and [{Na₂(Et₂O)₃}{LCo(η³-pyrene)}] (6) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α-diimine and polyarene ligands. Through a combination of X-ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2-4 have a high-spin Co^I center coupled with a radical α-diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic. Mono- and dinuclear heteroleptic cobalt complexes that contain the non-innocent α-diimine and polyarene ligands have been synthesized, and their crystal and electronic structures have been characterized by experimental and theoretical methods, which include X-ray crystallography, EPR spectroscopy, magnetism measurements, and DFT computations (see scheme).