运用NMR和DFT研究Michael加成反应的动力学行为及反应机理：(CO)5W=C(OEt)C2Ph作为底物

利用核磁共振方法研究了取代吡唑对炔基Fischer卡宾化合物的Michael加成的动力学行为，该反应为典型的二级反应。当吡唑的3，5-位由较大基团取代时，反应速率常数变小，而活化焓和活化熵明显增大。利用密度泛函理论研究了炔基钨卡宾为底物的Michael加成反应机理，发现吡唑上取代基团的增大可以导致第三步反应的活化能大于第一步，从而使反应的决速步骤由原来的第一步转变为第三步。

Mechanistic Studies on Michael Type Addition by NMR Technique and DFT Methods:(CO)5W=C(OEt)C2Ph as the Substrate

Kinetics of Michael type addition using alkynyl carbene complex as substituent was studied by ¹H NMR technique. To either substituted pyrazols or tungsten Fischer carbene, the reaction is of first order. And when the substituted groups at 3,5-positions become larger, the reaction rates slow down, with the obvious increase in activation enthalpies and entropies. Through density functional calculations, the mechanism of Michael type addition was investigated with alkynyl carbene complex as the substrate and 3,5-diphenyl-pyrazole (or 3,5-ditertbutyl-pyrazole) as the nucleophile. It was found that the large substituted groups will increase greatly the activation barrier of step 3, making it larger than that of step 1. Accordingly, the rate-determining step should be step 3, which is different from the Michael reactions with pyrazoles containing smaller substituted groups or without substituted groups.