Cyclopropanation of olefins with diazoalkanes, catalyzed by Co-II(porphyrin) complexes : A synthetic and mechanistic investigation and the molecular structure of Co-III(TPP)(CH2CO2Et) (TPP = dianion of meso-tetraphenylporphyrin)

Cobalt(II) porphyrin complexes catalyze reactions between ethyl diazoacetate (EDA) and styrenes to give the corresponding cyclopropanes with trans selectivity. The reactions of other diazoalkanes and other olefins have also been carried out, and the mechanism of the reaction has been investigated. Kinetic data and stoichiometric reactions support the formation of a diazoalkane cobalt-porphyrin complex that reacts with the olefins to generate the cyclopropane. Diethyl maleate and fumarate are not formed in the presence of an excess of olefin. On treatment of EDA with Co-II(TPP) (TPP = dianion of meso-tetraphenylporphyrin) in the absence of the olefin, an alkyl cobalt(III) complex Co-III(TPP)(CH2CO2Et) was isolated, and its structure has been solved by X-ray diffraction.