NHO催化二氧化碳与环氧化物反应生成环碳酸酯的机理研究

Mechanism for NHO-Catalyzed Synthesis of Cyclocarbonates from CO_2 and Exopides: A DFT Study

采用B3LYP的方法,6-311G(d,p)的基组,考虑PCM模型的溶剂化效应(DCM)以及DFT-D3模型的色散校正,对氮杂卡宾烯(NHO)催化二氧化碳和环氧化物生成环碳酸酯的反应机理进行了详细研究和讨论。该反应包括2个反应机理(M-1和M-2)。机理M-1由3个反应步骤组成,二氧化碳的加成反应是无势垒的,其中最后一步的势垒(168.74 k J/mol)最高,是整个反应的决速步。机理M-2包括4个反应步骤,第3步具有最高势垒136.98 k J/mol,是整个路径的最高鞍点。机理M-1和M-2在动力学上是相互竞争的,而由于机理M-2的决速步势垒比机理M-1的低,所以机理M-2是较优机理。

The mechanisms for N-heterocyclic Olefin-catalyzed formation of cyclic carbonate from CO2 and epoxide were studied by means of comprehensive density functional theory calculations at the the B3LYP/6-311G（d,p） level. For inclusion of salvation effect, single point energy calculations were performed using the integral equation formalism polarizable continuum model （IEF-PCM） with radius and the static relationship taken from SMD model. In addition, the empirical dispersion correction recommended by Grimme was added to the B3LYP energies. The formation of cyclic carbonate from CO2 and epoxide con- tains two mechanisms （M-1 and M-2）. M-1 is composed of three steps,the step of CO2 addition in M-1 is barrierless, and the final step with the highest barrier （168.74 kJ/mol） is the rate determining step of the reaction. M-2 includes four reaction steps, the third step with a barrier of 136.98 kJ/mol ,is the highest saddle point of the reaction path. M-1 and M-2 may play as kinetically competing mechanisms, M-2 is the predominant one with the lower barrier for the rate controlling step.