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A Density Functional Study of Oxygen Atom Transfer Reactions between Biological Oxygen Atom Donors and Molybdenum(IV) Bis(dithiolene) Complexes

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journal contribution
posted on 2002-11-16, 00:00 authored by Anders Thapper, Robert J. Deeth, Ebbe Nordlander
Density functional calculations have been used to investigate oxygen atom transfer reactions from the biological oxygen atom donors trimethylamine N-oxide (Me3NO) and dimethyl sulfoxide (DMSO) to the molybdenum(IV) complexes [MoO(mnt)2]2- and [Mo(OCH3)(mnt)2]- (mnt = maleonitrile-1,2-dithiolate), which may serve as models for mononuclear molybdenum enzymes of the DMSO reductase family. The reaction between [MoO(mnt)2]2- and trimethylamine N-oxide was found to have an activation energy of 72 kJ/mol and proceed via a transition state (TS) with distorted octahedral geometry, where the Me3NO is bound through the oxygen to the molybdenum atom and the N−O bond is considerably weakened. The computational modeling of the reactions between dimethyl sulfoxide (DMSO) and [MoO(mnt)2]2- or [Mo(OCH3)(mnt)2]- indicated that the former is energetically unfavorable while the latter was found to be favorable. The addition of a methyl group to [MoO(mnt)2]2- to form the corresponding des-oxo complex not only lowers the relative energy of the products but also lowers the activation energy. In addition, the reaction with [Mo(OCH3)(mnt)2]- proceeds via a TS with trigonal prismatic geometry instead of the distorted octahedral TS geometry modeled for the reaction between [MoO(mnt)2]2- and Me3NO.

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