Theoretical investigations of the reactivities of lattice-framework carbene analogues of the group 14 elements.

The potential energy surfaces for the chemical reactions of lattice-framework group 14 heavy carbene species have been studied using density functional theory (B3LYP/LANL2DZ) and the Gibbs free energy method. Five lattice-framework group 14 heavy carbene species, L-F-X: , where X = C, Si, Ge, Sn, and Pb, have been chosen as model reactants in this study. Also, four kinds of chemical reactions, O-H bond insertion, C-H bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these species. Basically, our present theoretical work predicts that the larger the ∠C(1)XC(2) bond angle of the lattice-framework group 14 heavy carbene species, the smaller the singlet-triplet splitting, the lower the activation barrier, and, therefore, the greater the rates of its chemical reactions with various other species. Moreover, the theoretical investigations suggest that the relative lattice-framework reactivity decreases in the order: C > Si > Ge > Sn ≫ Pb. That is, the heavier the group 14 atom (X), the more stable is its lattice-framework carbene towards chemical reactions. As a result, we predict that the L-F-Pb should be stable, and can be synthesized and isolated at room temperature. Furthermore, the singlet-triplet energy splitting of the lattice-framework group 14 carbene species, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made.