Generation of bis(dithiolene)dioxo molybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media
Generation of bis(dithiolene)dioxo molybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media
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通过在水介质中质子耦合电子转移从双(二硫醇)单氧钼(IV)络合物生成双(二硫醇)二氧代钼(VI)络合物
DOI：
10.1039/c0dt00763c
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发表时间：
2011
影响因子：
4
通讯作者：
S. Itoh
中科院分区：
文献类型：
--
作者：
H. Sugimoto;H. Tano;H. Miyake;S. Itoh
研究了二硫代戊烯单氧钼（IV）（MoIVOLX）配合物的电子转移氧化反应，作为亚砷酸盐氧化酶钼酶氧化半反应的模型。这些反应涉及质子耦合电子转移。MoIVORx的电化学氧化在碱性溶液中产生相应的双（二硫杂环戊烯）二氧代钼（VI）络合物，其中在相同条件下，由较小的供电子二硫杂环戊烯配体（1，2-二甲氧羰基-1，2-二硫醇盐，Ldmed）支撑的MoIVOLdmed向MoVIO 2Ldmed的转化比具有较大的供电子二硫杂环戊烯配体（1，2-苯二硫醇盐，Lbdt）的MoIVOLbdt更快。电化学氧化的滴定实验表明，该反应涉及两个电子的氧化和两个当量的OH−消耗每MoIVORx。在MoIVORx转化为MoVIO 2Lx的过程中，五配位的双（二硫戊烯）单氧代钼（V）配合物（MoVORx）是MoIVORx的单电子氧化物种，建议与OH−反应。MoVORx与CH 3CN或C2 H5 CN中的OH−以2：2的比例反应，得到1当量的MoIVORx和1当量的MoVIO 2Lx，这通过UV-vis和IR光谱证实。 低温停流分析允许研究MoVORx与OH−的反应机理。MoVOLDmed与OH−反应的动力学研究表明，MoVOLDmed与OH−反应生成六配位氧代-羟基-钼（V）物种MoVO（OH），然后，所得物种通过另一个OH−进行连续的去质子化，并通过剩余的MoVOLDmed进行氧化，以1：1的比例产生最终产物MoIVOLDmed和MoVIO 2Ldmed络合物。 在这种情况下，MoVO 2物种作为中间体参与反应。另一方面，在MoVOLbdt与OH−的反应中，OH−与MoV中心配位生成六配位MoVO（OH）Lbdt物种成为速率限制步骤，并且没有建议其他中间体。在此基础上，讨论了二硫纶配体对双二硫纶钼配合物反应活性的影响。
Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum(IV) (MoIVOLx) 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 MoIVOLx yields the corresponding bis(dithiolene)dioxomolybdenum(VI) complexes in basic solution, where the conversion of MoIVOLdmed supported by a smaller electron donating dithiolene ligand (1,2-dicarbomethoxyethylene-1,2-dithiolate, Ldmed) to MoVIO2Ldmed is faster than that of MoIVOLbdt with a larger electron donating dithiolene ligand (1,2-benzenedithiolate, Lbdt) 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 MoIVOLx. In the conversion process of MoIVOLx to MoVIO2Lx, the five-coordinate bis(dithiolene)monooxomolybdenum(V) complex (MoVOLx) being a one-electron oxidized species of MoIVOLx is suggested to react with OH−. MoVOLx reacts with OH− in CH3CN or C2H5CN in a 2 : 2 ratio to give one equivalent MoIVOLx and one equivalent MoVIO2Lx, 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 MoVOLx with OH−. The kinetic study for the reaction of MoVOLdmed with OH− suggests that MoVOLdmed reacts with OH− to give a six-coordinate oxo-hydroxo-molybdenum(V) species, MoVO(OH), and, then, the resulting species undergoes successive deprotonation by another OH− and oxidation by a remaining MoVOLdmed to yield the final products MoIVOLdmed and MoVIO2Ldmed complexes in a 1 : 1 ratio. In this case, the MoVO2 species are involved as an intermediate in the reaction. On the other hand, in the reaction of MoVOLbdt with OH−, coordination of OH− to the MoV centre to give a six-coordinate MoVO(OH)Lbdt 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.