One- and Two-Electron Reduced 1,2-Diketone Ligands in [Zn^II(L^•)₂(Et₂O)], [Co^II(L^•)₂(Et₂O)], and Na₂(Et₂O)₄[Co^II(L^Red)₂]

Abstract

The reaction of 1,2-diketone bis(2,6-diisopropylphenyl)glyoxal (L^Ox) with ZnCl₂ or CoCl₂ (ratio 2:1) in dry diethyl ether with 2 equiv of sodium (per transition-metal ion) afforded the neutral complexes [Zn^II(L^•)₂(Et₂O)] (<b>1</b>) and [Co^II(L^•)₂(Et₂O)] (<b>2</b>), which were characterized by X-ray crystallography, magnetochemistry, IR, electron paramagnetic resonance, and UV−vis spectroscopy. When 4 equiv of sodium were added, complex Na₂(Et₂O)₄[Co^II(L^Red)₂] (<b>4</b>) was isolated, which included some crystals of a minor (<2%) product Na(Et₂O)₂[Co^III(L^Red)₂] (<b>3</b>). (L^•)⁻ represents the π-radical monoanion of the 1,2-diketone, and (L^Red)²⁻ is its enediolate(2−) analogue. The electronic structures of <b>1</b>, <b>2</b>, and <b>4</b> have been elucidated by spectroscopy, and results are corroborated by broken-symmetry density functional theory calculations using the B3LYP functional. <b>1</b> possesses an <i>S</i> = 0 ground state with an excited triplet state that is 130 cm⁻¹ higher in energy; <b>2</b> and <b>4</b> have an <i>S</i> = ¹/₂ ground state. These complexes corroborate the notion that acyclic 1,2-diketones are redox noninnocent ligands.