Mechanistic aspects of the rhodium-catalyzed hydrogenation of CO2 to formic acid - A theoretical and kinetic study
Mechanistic aspects of the rhodium-catalyzed hydrogenation of CO2 to formic acid - A theoretical and kinetic study
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DOI：
10.1021/ja961579x
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发表时间：
1997-05-14
影响因子：
15
通讯作者：
Leitner, W
中科院分区：
文献类型：
--
作者：
Hutschka, F;Dedieu, A;Leitner, W
以配合物[（dppp）Rh（hfacac）]（A）（dppp = Ph_2P（CH_2）（3）PPh_2，hfacac =六氟乙酰丙酮）为催化剂前体，在DMSO/NEt_3体系中，通过初始速率测量和以顺式-[（H_3P）（2）Rh]为催化活性中心模型碎片的从头计算，研究了铑催化CO_2加氢制甲酸的反应机理.动力学数据是一致的机制，涉及速率限制产品的形成释放甲酸从中间体，形成通过两个可逆反应的实际催化活性物质首先与CO2，然后与H-2。计算首次提供了一个完整的催化循环的CO2加氢的理论分析。它们详细地介绍了可能的中间体的结构及其在各个步骤中的转化。结果表明，σ-键复分解作为一个替代的低能量途径，以经典的氧化加成/还原消除序列的甲酸中间体与二氢的反应。
The mechanism of the rhodium-catalyzed hydrogenation of CO2 to formic acid was investigated by initial rate measurements using the complex [(dppp)Rh(hfacac)] (A) (dppp = Ph2P(CH2)(3)PPh2, hfacac = hexafluoroacetyl-acetonate) as a catalyst precursor in DMSO/NEt3 and by ab initio calculations using cis-[(H3P)(2)Rh] as a model fragment for the catalytically active site. The kinetic data are consistent with a mechanism that involves rate limiting product formation by liberation of formic acid from an intermediate that is formed via two reversible reactions of the actual catalytically active species first with CO2 and then with H-2. The calculations provide for the first time a theoretical analysis of the full catalytic cycle of CO2 hydrogenation. They give detailed insight into the structure of possible intermediates and their transformations during the individual steps. The results suggest sigma-bond metathesis as an alternative low energy pathway to a classical oxidative addition/reductive elimination sequence for the reaction of the formate intermediate with dihydrogen.