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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron-Transfer Oxidation of Coenzyme B_(12) Model Compounds and Facile Cleavage of the Cobalt(IV)-Carbon Bond via Charge-Transfer Complexes with Bases.A Negative Temperature Dependence of the Rates
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Electron-Transfer Oxidation of Coenzyme B_(12) Model Compounds and Facile Cleavage of the Cobalt(IV)-Carbon Bond via Charge-Transfer Complexes with Bases.A Negative Temperature Dependence of the Rates

机译：辅酶B_（12）模型化合物的电子转移氧化和通过碱的电荷转移配合物容易地裂解钴（IV）-碳键。速率的负温度依赖性

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The electron-transfer oxidation and subsequent cobalt-carbon bond cleavage of vitamin B_(12) model complexes were investigated using cobaloximes,(DH)_2Co~(III)(R)(L),where DH~- = the anion of dimethylglyoxime,R = Me,Et,Ph,PhCH_2,and PhCH(CH_3),and L = a substituted pyridine,as coenzyme B_(12) model complexes and [Fe(bpy)3](PF_6)_3 or [Ru(bpy)_3](PF_6)_3 (bpy = 2,2'-bipyridine) as a one-electron oxidant.The rapid one-electron oxidation of (DH)_2Co~(III)(Me)(py) (py = pyridine) with the oxidant gives the corresponding Co(IV) complexes,[(DH)_2Co~(IV)(Me)(py)]~+,which were well identified by the ESR spectra.The reorganization energy (A) for the electron-transfer oxidation of (DH)_2Co(Me)(py) was determined from the ESR line broadening of [(DH)_2Co-(Me)(py)]~+ caused by the electron exchange with (DH)_2Co(Me)(py).The gamma value is applied to evaluate the rate constants of photoinduced electron transfer from (DH)_2Co(Me)(py) to photosensitizers in light of the Marcus theory of electron transfer.The Co(IV)-C bond cleavage of [(DH)_2Co(Me)(py)]~+ is accelerated significantly by the reaction with a base.The overall activation energy for the second-order rate constants of Co(IV)-C bond cleavage of [(DH)_2Co~(IV)(Me)(py)]~+ in the presence of a base is decreased by charge-transfer complex formation with a base,which leads to a negative activation energy for the Co(IV)-C cleavage when either 2-methoxypyridine or 2,6-dimethoxypyridine is used as the base.
机译：使用钴肟（DH）_2Co〜（III）（R）（L）研究了维生素B_（12）模型配合物的电子转移氧化和随后的钴碳键裂解，其中DH〜-=二甲基乙二肟的阴离子， R = Me，Et，Ph，PhCH_2和PhCH（CH_3），L =取代的吡啶，作为辅酶B_（12）模型配合物和[Fe（bpy）3]（PF_6）_3或[Ru（bpy）_3 ]（PF_6）_3（bpy = 2,2'-bipyridine）作为单电子氧化剂。（DH）_2Co〜（III）（Me）（py）（py =吡啶）的快速单电子氧化氧化剂产生相应的Co（IV）配合物[（DH）_2Co〜（IV）（Me）（py）]〜+，通过ESR光谱可以很好地识别。电子转移氧化的重组能（A）由（DH）_2Co（Me）（py）的电子交换引起的[（DH）_2Co-（Me）（py）]〜+的ESR线加宽确定（DH）_2Co（Me）（py）的摩尔数根据马库斯电子转移理论，将伽玛值用于评估从（DH）_2Co（Me）（py）到光敏剂的光诱导电子转移的速率常数与碱反应显着促进了[[DH] _2Co（Me）（py）]〜+的Co（IV）-C键裂解.Co（）的二级速率常数的总活化能[（DH）_2Co〜（IV）（Me）（py）]〜+在碱的存在下通过与碱的电荷转移络合物的形成而降低了IV）-C键的裂解，这导致了负活化能当使用2-甲氧基吡啶或2,6-二甲氧基吡啶作为碱基时，Co（IV）-C的裂解。

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