The unusual results of the present authors' research work obtained for the last 3 years in the field of synthesis and transformation of organomagnesium compounds with metal complex catalysts are considered in this review. Special attention has been paid to catalytic cyclometallation of linear and cyclic olefins with n-R(2)Mg, synthesis of alkenyl organomagnesium compounds from alpha-olefins and R(2)Mg, and catalytic transformation of cyclopentanes in the presence of Cp(2)ZrCl(2). The reaction mechanism implying the formation of zircona-cyclopentane complexes as intermediate species are discussed.