NDLI: Generation of bis(dithiolene)dioxomolybdenum( VI) complexes from bis(dithiolene)monooxomolybdenum( IV) complexes by proton -coupled electron transfer in aqueous media

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Miyake, Hiroyuki Itoh, Shinobu Tano, Hiroyuki Sugimoto, Hideki
Description	Author Affiliation: Sugimoto H ( Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan. sugimoto@mls.eng.osaka-u.ac.jp)
Abstract	Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum( IV) ( Mo $^{IV}OL$ $^{x}$ ) complexes is studied as a model of oxidative-half reaction of arsenite oxidase molybdenum enzymes. The reactions are revealed to involve proton -coupled electron transfer . Electrochemical oxidation of Mo $^{IV}OL$ $^{x}$ yields the corresponding bis(dithiolene)dioxomolybdenum( VI) complexes in basic solution, where the conversion of $Mo^{IV}OL^{dmed}$ supported by a smaller electron donating dithiolene ligand ( 1,2-dicarbomethoxyethylene-1,2-dithiolate , $L^{dmed})$ to $Mo^{VI}O_{2}L^{dmed}$ is faster than that of $Mo^{IV}OL^{bdt}$ with a larger electron donating dithiolene ligand ( 1,2-benzenedithiolate , $L^{bdt})$ under the same conditions. Titration experiments for the electrochemical oxidation reveal that the reaction involves two-electron oxidation and two equivalents of OH $^{−}$ consumption per Mo $^{IV}OL$ $^{x}$ . In the conversion process of Mo $^{IV}OL$ $^{x}$ to Mo $^{VI}O$ $_{2}L$ $^{x}$ , the five-coordinate bis(dithiolene)monooxomolybdenum( V) complex ( Mo $^{V}OL$ $^{x}$ ) being a one-electron oxidized species of Mo $^{IV}OL$ $^{x}$ is suggested to react with OH $^{−}.$ Mo $^{V}OL$ $^{x}$ reacts with OH $^{−}$ in CH $_{3}CN$ or C $_{2}H$ $_{5}CN$ in a 2:2 ratio to give one equivalent Mo $^{IV}OL$ $^{x}$ and one equivalent Mo $^{VI}O$ $_{2}L$ $^{x}$ , which is confirmed by the UV–vis and IR spectroscopies . The low temperature stopped-flow analysis allows investigations of the mechanism for the reaction of Mo $^{V}OL$ $^{x}$ with OH $^{−}.$ The kinetic study for the reaction of $Mo^{V}OL^{dmed}$ with OH $^{−}$ suggests that $Mo^{V}OL^{dmed}$ reacts with OH $^{−}$ to give a six-coordinate oxo - hydroxo - molybdenum( V) species, Mo $^{V}O(OH)$ , and, then, the resulting species undergoes successive deprotonation by another OH $^{−}$ and oxidation by a remaining $Mo^{V}OL^{dmed}$ to yield the final products $Mo^{IV}OL^{dmed}$ and $Mo^{VI}O_{2}L^{dmed}$ complexes in a 1:1 ratio. In this case, the Mo $^{V}O$ $_{2}$ species are involved as an intermediate in the reaction. On the other hand, in the reaction of $Mo^{V}OL^{bdt}$ with OH $^{−},$ coordination of OH $^{−}$ to the Mo $^{V}$ centre to give a six-coordinate Mo $^{V}O(OH)L$ $^{bdt}$ species becomes the rate limiting step and other intermediates are not suggested. On the basis of these results, the ligand effects of the dithiolene ligands on the reactivity of the bis(dithiolene)molybdenum complexes are discussed.
ISSN	14779226
Issue Number	10
Volume Number	40
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2011-03-14
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Coordination Complexes Chemistry Molybdenum Protons Electrochemical Techniques Electron Transport Hydrogen-Ion Concentration Kinetics Oxidation-Reduction Oxidoreductases Metabolism Spectrophotometry, Ultraviolet Water Journal Article Research Support, Non-U.S. Gov't
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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