title: Hydrogen atom abstraction from hydrocarbons by a copper(III)-hydroxide complex.
abstract: With the aim of understanding the basis for the high rate of hydrogen atom abstraction (HAT) from dihydroanthracene (DHA) by the complex LCuOH (1; L = N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide), the bond dissociation enthalpy of the reaction product LCu(H2O) (2) was determined through measurement of its pK(a) and E(1/2) in THF solution. In so doing, an equilibrium between 2 and LCu(THF) was characterized by UV-vis and EPR spectroscopy and cyclic voltammetry (CV). A high pK(a) of 18.8 ± 1.8 and a low E(1/2) of -0.074 V vs Fc/Fc(+) in THF combined to yield an O-H BDE for 2 of 90 ± 3 kcal mol(-1) that is large relative to values for most transition metal oxo/hydroxo complexes. By taking advantage of the increased stability of 1 observed in 1,2-difluorobenzene (DFB) solvent, the kinetics of the reactions of 1 with a range of substrates with varying BDE values for their C-H bonds were measured. The oxidizing power of 1 was revealed through the accelerated decay of 1 in the presence of the substrates, including THF (BDE = 92 kcal mol(-1)) and cyclohexane (BDE = 99 kcal mol(-1)). CV experiments in THF solvent showed that 1 reacted with THF via rate-determining attack at the THF C-H(D) bonds with a kinetic isotope effect of 10.2. Analysis of the kinetic and thermodynamic data provides new insights into the basis for the high reactivity of 1 and the possible involvement of species like 1 in oxidation catalysis.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Debanjan
authors.initials: D
authors.lastname: Dhar
authors.forename: William B
authors.initials: WB
authors.lastname: Tolman
mesh_terms: D003300:Copper / Q000737:chemistry*; D006838:Hydrocarbons / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D006838:Hydrocarbons; D006878:Hydroxides; D009942:Organometallic Compounds; D003300:Copper; D006859:Hydrogen