Selective cyclometalation of disubstituted acetylenes and ethylene with diethylmagnesium and ethylmagnesium halides in the presence of zirconium complexes

Catalytic cyclometalation of disubstituted acetylenes and ethylene with ethylmagnesium halides EtMgHlg (Hlg = Cl, Br) and diethylmagnesium Et2Mg in the presence of Cp2ZrCl2 gave tetrasubstituted magnesacyclopenta-2,4-dienes and disubstituted magnesacyclopent-2-enes. A probable scheme of formation of cyclic unsaturated organomagnesium compounds was proposed, according to which the reactive intermediates in the cyclometalation process are zirconacyclopentadienes and zirconacyclopentenes generated from Cp2ZrCl2, EtMgHlg, Et2Mg, acetylenes, and ethylene.