吡啶甲酸铑阳离子催化甲醇羰基化反应机理的理论计算

摘要

采用有效核近似从头算方法,在HF/LANL2DZ水平下用Berny优化法,对吡啶甲酸铑阳离子催化剂催化甲醇羰基化反应中各基元反应的中间体、过渡态和产物的几何结构进行了优化,过渡态结构通过振动分析进行了确认;计算了各反应的活化位垒.CH_3OH与CO在吡啶甲酸铑阳离子催化剂的作用下反应分4步进行:(1)CH3I氧化加成反应;(2)羰基重排反应:(3)羰基配位反应;(4)CH_3COI还原消除反应.对于各基元反应,CH3I氧化加成反应位垒最高(167.78kJ/mol),是整个反应过程的决速步骤;羰基重排反应和CH_3COI还原消除反应的活化位垒分别为110.67和62.94 kJ/mol,羰基配位反应的位垒为零.与[Rh(CO)_2I_2]-催化剂相比,吡啶甲酸铑阳离子催化剂具有相同的催化机理,但后者催化剂上各步反应的位垒较低.%The reaction mechanism of methanol carbonylation catalyzed by pyridine carbonylic acid rhodium cation ([MRh(CO)_2]~+, where M rn=pyridine carbonylic acid ligand) catalyst was studied by the ab initio method with the effective core potential approximation in the HF/LANL2DZ level. The results indicated that the whole reaction process was composed of four steps: (I) CH_3I oxidative addition; (2) car-bonyl rearrangement reaction; (3) carbonyl coordination; (4) reductive elimination of CH_3COI. With the consideration of zero-point energy correction, the activation barriers of the four steps were 167.78, 110.67, O, and 62.94 kJ/mol, respectively. The CH_3I oxidative addition was a rnrate-controlling step, which corresponded to the highest activation barrier. The reaction mechanism of methanol carbonylation catalyzed by [MRh(CO)_2]~+ was similar to that by [Rh(CO)_2I_2]~-. The reaction activation harriers over [MRh(CO)_2]~+ were lower than those over [Rh(CO)_2I_2]~- in all four steps.