Degree of vinylidene character of α-heteroatom-substituted vinylmagnesium chlorides: a DFT study to discern the role of the halogen atom in magnesium alkylidene carbenoid chemistry

DFT calculations were performed on a series of α-heteroatom-substituted vinylmagnesium chlorides, CH2CXMgCl·2(OMe2) (X=NMe2, OMe, F, SMe, Cl, SeMe, and Br), at the B3LYP/6-311++G(d,p) level to elucidate the degree of vinylidene character of such species. α-Halo-substituted vinylmagnesium chlorides were found to have considerable vinylidene character. A donor-acceptor interaction between the C-Mg bonding orbital and the C-X antibonding orbital was responsible for the vinylidene character of α-heteroatom-substituted vinylmagnesium chlorides. A sulfoxide/magnesium exchange reaction of 1-halovinyl phenyl sulfoxides with i-PrMgCl was more exothermic than the exchange reaction of phenyl vinyl sulfoxide with i-PrMgCl by 12.8-13.9 kcal/mol.