title: Anion Effects in Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions of Cu(II) Chlorodiketonate Complexes.
abstract: Aliphatic oxidative carbon-carbon bond cleavage reactions involving Cu(II) catalysts and O2 as the terminal oxidant are of significant current interest. However, little is currently known regarding how the nature of the Cu(II) catalyst, including the anions present, influence the reaction with O2. In previous work, we found that exposure of the Cu(II) chlorodiketonate complex [(6-Ph2TPA)Cu(PhC(O)CClC(O)Ph)]ClO4 (1) to O2 results in oxidative aliphatic carbon-carbon bond cleavage within the diketonate unit, leading to the formation of benzoic acid, benzoic anhydride, benzil, and 1,3-diphenylpropanedione as organic products. Kinetic studies of this reaction revealed a slow induction phase followed by a rapid decay of the absorption features of 1. Notably, the induction phase is not present when the reaction is performed in the presence of a catalytic amount of chloride anion. In the studies presented herein, a combination of spectroscopic (UV-vis, EPR) and density functional theory (DFT) methods have been used to examine the chloride and benzoate ion binding properties of 1 under anaerobic conditions. These studies provide evidence that each anion coordinates in an axial position of the Cu(II) center. DFT studies reveal that the presence of the anion in the Cu(II) coordination sphere decreases the barrier for O2 activation and the formation of a Cu(II)-peroxo species. Notably, the chloride anion more effectively lowers the barrier associated with O-O bond cleavage. Thus, the nature of the anion plays an important role in determining the rate of reaction of the diketonate complex with O2. The same type of anion effects were observed in the O2 reactivity of the simple Cu(II)-bipyridine complex [(bpy)Cu(PhC(O)C(Cl)C(O)Ph)ClO4] (3).
authors.affiliation: Department of Chemistry & Biochemistry, Utah State University , Logan, Utah 84322-0300, United States.
authors.forename: Sushma L
authors.initials: SL
authors.lastname: Saraf
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Science , Krakow 30-239, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Miłaczewska
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Science , Krakow 30-239, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Borowski
authors.affiliation: Department of Chemistry and Biochemistry, Miami University , Oxford, Ohio 45056, United States.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: James
authors.affiliation: Department of Chemistry and Biochemistry, Miami University , Oxford, Ohio 45056, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Tierney
authors.affiliation: Department of Chemistry & Biochemistry, Utah State University , Logan, Utah 84322-0300, United States.
authors.forename: Marina
authors.initials: M
authors.lastname: Popova
authors.affiliation: Department of Chemistry, University of Utah , Salt Lake City, Utah 84112-0850, United States.
authors.forename: Atta M
authors.initials: AM
authors.lastname: Arif
authors.affiliation: Department of Chemistry & Biochemistry, Utah State University , Logan, Utah 84322-0300, United States.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Berreau