Abstract
The O(2)-dependent carbon-carbon (C-C) bond cleavage reactions of the mononuclear Cu(II) chlorodiketonate complexes [(6-Ph(2)TPA)Cu(PhC(O)CClC(O)Ph)]ClO(4) (1-ClO (4) ) and [(bpy)Cu(PhC(O)CClC(O)Ph)(ClO(4))] (3-ClO (4) ) have been further examined in terms of their anion and water dependence. The bpy-ligated Cu(II) chlorodiketonate complex 3-ClO (4) is inherently more reactive with O(2) than the 6-Ph(2)TPA-ligated analog 1-ClO (4) . Added chloride is needed to facilitate O(2) reactivity for 1-ClO (4) but not for 3-ClO (4) at 25(1) °C. Evaluation of k (obs) for the reaction of 1-ClO (4) with O(2) under pseudo first-order conditions as a function of the amount of added chloride ion produced saturation type behavior. The bpy-ligated 3-ClO (4) exhibits different behavior, with rate enhancement resulting from both the addition of chloride ion and water. Computational studies indicate that the presence of water lowers the barrier for O(2) activation for 3-ClO (4) by ~12 kcal/mol whereas changing the anion from perchlorate to chloride has a smaller effect (lowering of the barrier by ~3 kcal/mol). Notably, the effect of water for 3-ClO (4) is of similar magnitude to the barrier-lowering chloride effect found in the O(2) activation pathway for 1-ClO (4) . Thus, both systems involve lower energy O(2) activation pathways available, albeit resulting from different ligand effects. Probing the effect of added benzoate anion, it was found that the chloro substituent in the diketonate moiety of 1-ClO (4) and 3-ClO (4) will undergo displacement upon treatment of each complex with tetrabutyl ammonium benzoate to give Cu(II) benzoyloxydiketonate complexes (4 and 5). Complexes 4 and 5 exhibit slow O(2)-dependent C-C cleavage in the presence of added chloride ion. These results are discussed in the context of the chemistry identified for various divalent metal chlorodiketonate complexes, which have relevance to catalytic systems and metalloenzymes that mediate O(2)-dependent C-C cleavage within diketonate substrates.