Katarzyna Grubel - Mechanistic Studies of the O2-Dependent Aliphatic Carbon−Carbon Bond Cleavage Reaction of a Nickel Enolate Complex

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      Publication Details (including relevant citation   information):

      Lisa M. Berreau, Tomasz Borowski, Katarzyna Grubel, Caleb J.   Allpress, Jeffrey P. Wikstrom, Meaghan E. Germain, Elena V.   Rybak-Akimova, and David L. Tierney Inorg. Chem.  2011,   50, 1047–1057;   DOI: 10.1021/ic1017888



      Abstract Image 

        The mononuclear nickel(II) enolate complex     [(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph]ClO4    (I) was the first reactive model complex for     the enzyme/substrate (ES) adduct in nickel(II)-containing     acireductone dioxygenases (ARDs) to be reported. In this     contribution, the mechanism of its O2-dependent     aliphatic carbon−carbon bond cleavage reactivity was further     investigated. Stopped-flow kinetic studies revealed that the     reaction of I with O2 is     second-order overall and is 80     times slower at 25 °C than the reaction involving the enolate     salt [Me4N][PhC(O)C(OH)C(O)Ph]. Computational     studies of the reaction of the anion     [PhC(O)C(OH)C(O)Ph] with O2 support a     hydroperoxide mechanism wherein the first step is a redox     process that results in the formation of     1,3-diphenylpropanetrione and HOO. Independent     experiments indicate that the reaction between     1,3-diphenylpropanetrione and HOO results in     oxidative aliphatic carbon−carbon bond cleavage and the     formation of benzoic acid, benzoate, and CO:CO2    (12:1).     Experiments in the presence of a nickel(II) complex gave a     similar product distribution, albeit benzil [PhC(O)C(O)Ph] is     also formed, and the CO:CO2 ratio is 1.5:1.     The results for the nickel(II)-containing reaction match those     found for the reaction of I with O2    and provide support for a trione/HOO pathway for     aliphatic carbon−carbon bond cleavage. Overall,     I is a reasonable structural model for the ES     adduct formed in the active site of NiIIARD.     However, the presence of phenyl appendages at both C(1) and     C(3) in the [PhC(O)C(OH)C(O)Ph] anion results in a     reaction pathway for O2-dependent aliphatic     carbon−carbon bond cleavage (via a trione intermediate) that     differs from that accessible to C(1)−H acireductone species.     This study, as the first detailed investigation of the     O2 reactivity of a nickel(II) enolate complex of     relevance to NiIIARD, provides insight toward     understanding the chemical factors involved in the     O2 reactivity of metal acireductone species.  

      Address (URL): http://pubs.acs.org/doi/abs/10.1021/ic1017888