Reactivities of Adamantyl-Substituted Metallenes with a C=E (E = C, Si, Ge, Sn, and Pb) Double Bond. A Theoretical Study

The potential energy surfaces for the chemical reactions of adamantyl-substituted compounds containing the C=E double bond, Rea-C=E, where E = C, Si, Ge, Sn, and Pb, were studied using density functional theory (B3LYP/LANL2DZ). Three kinds of chemical reactions-methanol addition, [2 + 4] Diels-Alder cycloaddition with 1-methoxybutadiene, and [2 + 2] cycloaddition with a ketone were used to study the chemical reactivity of these Rea-C=E molecules. Our theoretical findings reveal that the smaller the singlet triplet splitting of the Rea-C=E, the lower its activation barriers and, in turn, the more rapid its chemical reactions with other chemical molecules. Theoretical studies suggest that the relative chemical reactivity increases in the order C=C << C=Si < C=Ge < C=Sn < C=Pb. That is, the smaller the atomic weight of the group 14 atom (E), the smaller the atomic radius of E and the more stable its adamantyl-substituted Rea-C=E to chemical reaction. It is predicted that the adamantyl-substituted Rea-C=E (E = C and Si) compound should be stable and readily synthesized and isolated at room temperature. Our computational results are in accordance with the available experimental observations. Moreover, our theoretical findings demonstrate that both electronic and steric factors play a key role in determining the chemical reactivity of the group 14 adarnantyl-substituted Rea-C=E molecules, both kinetically and thermodynamically. The present understanding of the reactivity of adamantyl-substituted doubly bonded C=E molecules provides a useful building block for a future, deeper understanding of this field of organometallic chemistry.