Mechanisms for the Reaction of Water, Butadiene, and Palladium Complex with 1,2-Dimetallacyclohexene (R2M=MR2, M = C, Si, Ge, Sn, Pb). A Theoretical Study

The potential energy surfaces for the chemical reactions of six-membered cyclic dimetallaalkenes containing the M=M doubly bonded species Rea-M=M, where M = C, Si, Ge, Sn, and Pb, were studied, using the density functional theory (B3LYP/LANL2DZ) method. Three kinds of chemical reaction, water addition, [2+4] Diels-Alder cycloaddition, and palladium complexation, were also used to study the chemical reactivity of these group 14 Rea-M=M molecules. In principle, our present theoretical work suggests that the smaller the singlet-triplet splitting of the Rea-M=M, the lower are its activation barriers and, in turn, the more rapid are its chemical reactions with other molecules. These theoretical investigations indicate that the relative chemical reactivity increases in the order Rea-M=M-C < Rea-M=M-Si < Rea-M=M-Ge < Rea-M=M-Sn < Rea-M=M-Pb. That is, the smaller the atomic weight of the group 14 atom (M), the more stable is its Rea-M=M to chemical reaction. As a result, we predict that the group 14 Rea-M=M (M = C and Si) compounds should be stable and readily synthesized and isolated at room temperature. Our computational results are in good agreement with the available experimental observations. The present explanation for the reactivity of six-membered cyclic Rea-M=M compounds promises a deeper understanding and may have a future application in main group chemistry.