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首页> 外文期刊>Journal of the American Chemical Society >Role of protonation and of axial ligands in the reductive dechlorination of alkyl chlorides by vitamin B-12 complexes. Reductive cleavage of chloroacetonitrile by Co(I) cobalamins and cobinamides
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Role of protonation and of axial ligands in the reductive dechlorination of alkyl chlorides by vitamin B-12 complexes. Reductive cleavage of chloroacetonitrile by Co(I) cobalamins and cobinamides

机译：质子化和轴向配体在维生素B-12络合物对烷基氯还原脱氯中的作用。 Co（I）钴胺素和cobinamides对氯乙腈的还原裂解

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摘要

Cobalt(I) cobalamin and cobinamide are efficient catalysts of the hydrogenolysis of aliphatic chloro compounds. Taking chloroacetonitrile as example, the first requirement for high catalytic efficiency is fulfilled by the high reactivity of the Co(I) complex toward the substrate, leading to the alkylcobalt(III) complex. This is further reduced into the alkylcobalt(II) complex. However, the fact that these two reactions are fast is not enough to ensure an efficient catalysis: in DMF catalysis is very poor, while it is high in water. The experiments carried out in DMF with addition of an acid show that a crucial step in the catalytic process is the proton transfer decomposition of the alkylcobalt(II) complex, leading to the product, and closing the catalytic loop by regeneration of the cobalt(I) complex. Another important feature of these catalytic reactions is the role played by axial ligands present in the solution, particularly those that are produced by the catalytic reaction itself, namely, chloride ions and the counteranion of the added acid. The stronger these ligands, the more negative the potential required for the reduction of the alkylcobalt(III) complex. This amounts to a self-moderation effect: the more efficient catalysis, the slower its second step, i.e., the conversion of the alkylcobalt(III) complex into the alkylcobalt(II).
机译：钴（I）钴胺素和钴胺是脂肪族氯化合物氢解的有效催化剂。以氯乙腈为例，高催化效率的第一个要求是通过Co（I）配合物对底物的高反应性来满足的，从而生成烷基钴（III）配合物。将其进一步还原为烷基钴（II）配合物。但是，这两个反应很快的事实不足以确保有效的催化作用：在DMF中，催化作用很差，而在水中却很高。在DMF中添加酸进行的实验表明，催化过程中的关键步骤是烷基钴（II）配合物的质子转移分解，从而生成产物，并通过再生钴（I）封闭催化环。 ）复杂。这些催化反应的另一个重要特征是溶液中存在的轴向配体，特别是由催化反应本身产生的轴向配体，即氯离子和所加酸的抗衡阴离子，所起的作用。这些配体越强，还原烷基钴（III）络合物所需的电势就越负。这相当于自我调节作用：催化越有效，其第二步就越慢，即烷基钴（III）络合物向烷基钴（II）的转化。

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