One- and Two-Electron Reduced 1,2-Diketone Ligands in [ZnII(L•)2(Et2O)], [CoII(L•)2(Et2O)], and Na2(Et2O)4[CoII(LRed)2]

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-center dot)(2)(Et2O)] (1) and [Co-II(L-center dot)(2)(Et2O)] (2), which were characterized by X-ray crystallography, magnetochemistry, IR, electron paramagnetic resonance, and UV-vis spectroscopy. When 4 equiv of sodium were added, complex Na-2(Et2O)(4)[Co-II(L-Red)(2)[ (4) was isolated, which included some crystals of a minor (<2%) product Na(Et2O)(2)[Co-III(L-Red)(2)] (3). (L-center dot)(-) represents the T-radical monoanion of the 1,2-diketone, and (L-Red)(2-) is its enediolate(2-) analogue. The electronic structures of 1, 2, and 4 have been elucidated by spectroscopy, and results are corroborated by broken-symmetry density functional theory calculations using the B3LYP functional. 1 possesses an S = 0 ground state with an excited triplet state that is 130 cm(-1) higher in energy; 2 and 4 have an S = 1/2 ground state. These complexes corroborate the notion that acyclic 1,2-diketones are redox noninnocent ligands.