Stretched Central Double Bonds in Dialumene and Disilene by Amino Substituents: A Case of Lone Pair Repulsion.

Abstract

There have been remarkable advances in the syntheses and applications of groups 13 and 14 homonuclear ethene analogues. However, successes are largely limited to aryl- and/or silyl-substituted species. Analogues bearing two or more heteroatoms are still scarce. In this work, we employed the block-localized wavefunction (BLW) method at the density functional theory (DFT) level to study dialumene and disilene bearing two amino substituents whose optimal geometries exhibit significantly stretched central M=M (M = Al or Si) double bonds compared with aryl- and/or silyl-substituted species. Computational analyses showed that the repulsion between the lone electron pairs of amino substituents and M=M π bond plays a critical role in the elongation of the M=M bonds. Evidently, replacing the substituent groups -NH2 with -BH2 can enhance the planarity and shorten the central double bonds due to the absence of lone pair electrons in BH2.