Hydrogenation of carbon dioxide to methanol using a homogeneous ruthenium-Triphos catalyst: from mechanistic investigations to multiphase catalysis.
Hydrogenation of carbon dioxide to methanol using a homogeneous ruthenium-Triphos catalyst: from mechanistic investigations to multiphase catalysis.
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DOI：
10.1039/c4sc02087a
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发表时间：
2015-01-01
期刊：
影响因子：
8.4
通讯作者：
Leitner W
中科院分区：
文献类型：
--
作者：
Wesselbaum S;Moha V;Meuresch M;Brosinski S;Thenert KM;Kothe J;Stein TV;Englert U;Hölscher M;Klankermayer J;Leitner W
首次证明了在不存在醇添加剂的情况下使用可回收的分子有机金属催化剂将二氧化碳加氢为甲醇。 CO2 加氢为甲醇可以使用单分子有机金属催化剂来实现。虽然均相催化剂以前被认为只能通过甲酸酯作为稳定的中间体进行氢化，但目前的机理研究表明，多步转化可以直接发生在 Ru-Triphos（Triphos = 1,1,1-三（二苯基膦甲基）乙烷）中心。阳离子甲酸络合物 [(Triphos)Ru(η2-O2CH)(S)]+（S = 溶剂）被确定为关键中间体，从而合成了类似的乙酸盐络合物作为催化转化的稳健且稳定的前体。使用 DFT 计算进行的详细机理研究表明，一系列连续的氢化物转移和质子分解步骤可以解释 CO2 在单个 Ru-Triphos 片段的配位范围内通过甲酸盐/甲酸转化为羟基甲醇盐/甲醛，最后转化为甲醇盐/甲醇。系统参数优化的所有实验结果与该机理图完全一致。基于这些发现，开发了一种由 H2O 和 2-MTHF 组成的双相系统，其中活性阳离子 Ru 络合物驻留在有机相中进行回收，并用水相萃取甲醇。
The hydrogenation of CO2 to methanol using a recyclable molecular organometallic catalyst in the absence of an alcohol additive is demonstrated for the first time. The hydrogenation of CO2 to methanol can be achieved using a single molecular organometallic catalyst. Whereas homogeneous catalysts were previously believed to allow the hydrogenation only via formate esters as stable intermediates, the present mechanistic study demonstrates that the multistep transformation can occur directly on the Ru–Triphos (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane) centre. The cationic formate complex [(Triphos)Ru(η2-O2CH)(S)]+ (S = solvent) was identified as the key intermediate, leading to the synthesis of the analogous acetate complex as a robust and stable precursor for the catalytic transformation. A detailed mechanistic study using DFT calculations shows that a sequential series of hydride transfer and protonolysis steps can account for the transformation of CO2via formate/formic acid to hydroxymethanolate/formaldehyde and finally methanolate/methanol within the coordination sphere of a single Ru–Triphos-fragment. All experimental results of the systematic parameter optimisation are fully consistent with this mechanistic picture. Based on these findings, a biphasic system consisting of H2O and 2-MTHF was developed, in which the active cationic Ru-complex resides in the organic phase for recycling and methanol is extracted with the aqueous phase.
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