Structure, Bonding, and Hyperconjugation of Germaallene: A Theoretical Study

Abstract

A theoretical study on germaallene molecules, including monogermaallenes, digermaallenes, and trigermaallene, was performed based on B3LYP and ab initio methods. The following results were observed: (a) symmetric 1,3-digermaallene has a linear allenic-type structure and 1,2-digermaallene is bent at the central germanium atom with a GeGeC bond angle of 142.2°. (b) Only 2-germaallene, 1,2-digermaallene, and trigermaallene have cyclic isomers. The germacyclopropylidene and digermacyclopropylidene are the global minima on their bending potential energy surfaces, and the high-energy cyclic isomer of trigermaallene is unstable. (c) The deviation of the germaallenic skeleton from linearity is strengthened with increasing Ge═Ge bonds. NPA and WBI analyses reveal that there are double bonds between the terminal and central Ge or C atom for monogermaallenes and digermaallenes, the central Ge atom of trigermaallene does not adopt the orbital hybridization, and a partial bond exists between two terminal Ge atoms for the interaction of their p orbitals. The π−σ hyperconjugation strengths of germaallenes were estimated on the basis of the total NBO second-order perturbation energy. The hyperconjugation strengths of monogermaallenes and digermaallenes follow in the order 1-germaallene > 1,3-digermaallene > 2-germaallene > 1,2-digermaallene.