Theoretical investigations of the reactivities of cationic six-membered carbene analogues of group 14 elements

The potential energy surfaces for the chemical reactions of cationic six-membered group 14 heavy carbene species have been studied using density functional theory (B3LYP/LANL2DZ) and CCSD (CCSD/LANL2DZ//B3LYP/LANL2DZ) methods. Five six-membered group 14 cationic heavy carbene species, HC(CMeNPh)2E:](+), where E = C, Si, Ge, Sn, and Pb, have been chosen as model reactants in this work. Also, four kinds of chemical reaction, C-H bond insertion, multiple bond cycloaddition, dimerization, and O-H bond insertion, have been used to study the chemical reactivities of these group 14 cationic carbene species. Basically, our present theoretical work predicts that the larger the angle NEN bond angle and the smaller the singlet-triplet splitting of the carbene, the lower its activation barriers will be and, in turn, the more rapid are its chemical reactions with other species. Moreover, the theoretical investigations suggest that the relative carbenic reactivity decreases in the order C > Si > Ge > Sn > Pb. That is, the heavier the group 14 atom (E), the more stable is its cationic carbene toward chemical reaction. As a result, we predict that the cationic six-membered group 14 carbene species (E = C, Si, Ge, Sn, and Pb) should be stable, readily synthesized, and isolated at room temperature. Our computational results are in good agreement with the available experimental observations. Furthermore, the singlet-triplet energy splitting of the carbene, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict its reactivities. The results obtained allow a number of predictions to be made.