DFT and experimental characterization of 1-heteroatom-substituted alkylmagnesium chlorides

In addition to exhibiting nucleophilic reactivity, some alkylmagnesium chlorides that possess a heteroatom substituent at the 1-position can exhibit carbene-like reactivity. Herein, DFT calculations and experiments were performed to study the reactivity of several 1-heteroatom-substituted alkylmagnesium chlorides. The carbene character of 1-heteroatom-substituted 2-methylpropylmagneisum chlorides was evaluated using the geometric parameters in their DFT-optimized structures and the activation energies for the 1,2-hydrogen shift estimated by DFT calculations. 1-Heteroatom-substituted alkylmagnesium chlorides were generated from 1-heteroatom-substituted alkyl p-tolyl sulfoxides and isopropylmagnesium chloride via a sulfoxide/magnesium exchange reaction, and the reactivity of these species was evaluated based on the product ratio. The results revealed that 1-amino- and 1-thioalkylmagnesium chlorides were carbanions because the reaction yielded protonated products. In contrast, 1-haloalkylmagnesium chlorides were magnesium carbenoids because the reaction yielded alkene and cyclopropane without haloalkanes. Lastly, 1-pivaloxyalkylmagnesium chloride was a hybrid between carbanions and magnesium carbenoids. The order of carbene character estimated based on the theoretical results was consistent with the experimental results.