Maxwell J L, Brown K C, Bartley D W, Kodadek T
Science. 1992 Jun 12;256(5063):1544-7. doi: 10.1126/science.256.5063.1544.
The rhodium porphyrin-catalyzed cyclopropanation of alkenes by ethyl diazoacetate (EDA) is representative of a number of metal-mediated cyclopropanation reactions used widely in organic synthesis. The active intermediate in these reactions is thought to be a metal carbene complex, but evidence for the involvement of metal-olefin pi complexes has also been presented. Low-temperature infrared and nuclear magnetic resonance spectroscopies have been used to characterize a rhodium porphyrin-diazoalkyl adduct that results from the stoichiometric condensation of the catalyst and EDA. Optical spectroscopy suggests that this complex is the dominant steady-state species in the catalytic reaction. This compound decomposes thermally to provide cyclopropanes in the presence of styrene, suggesting that the carbene is indeed the active intermediate. Metal-alkene pi complexes have also been detected spectroscopically. Kinetic studies suggest that they mediate the rate of carbene formation from the diazoalkyl complex but are not attacked directly by EDA.
铑卟啉催化重氮乙酸乙酯（EDA）对烯烃进行环丙烷化反应，是有机合成中广泛使用的多种金属介导环丙烷化反应的代表。这些反应中的活性中间体被认为是金属卡宾配合物，但也有证据表明金属-烯烃π配合物也参与其中。低温红外光谱和核磁共振光谱已被用于表征由催化剂与EDA化学计量缩合产生的铑卟啉-重氮烷基加合物。光谱学表明，该配合物是催化反应中的主要稳态物种。该化合物在苯乙烯存在下热分解生成环丙烷，这表明卡宾确实是活性中间体。金属-烯烃π配合物也已通过光谱检测到。动力学研究表明，它们介导从重氮烷基配合物形成卡宾的速率，但不会直接被EDA进攻。
