Synthesis of an Aluminatacyclopropene Derivative with an AlC₂ Heterocycle and an Exocyclic AlR₂ Substituent:  Evidence for a Nonclassical Bonding Situation

Abstract

An aluminatacyclopropene derivative ( 2 ) was synthesized by the reaction of tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 with lithium phenylethynide, of which the anionic carbon atom was inserted into the Al−Al single bond. By the interaction of the second ethynide carbon atom with one of the aluminum atoms a three-membered heterocycle resulted containing an Al atom and a C C double bond. As shown by a crystal structure determination, hyperconjugation makes an important contribution to the bonding in the anionic heterocyclic part of the molecule. The exocyclic Al−C bond to the unsaturated Al atom is very short (188.6 pm), while one of the endocyclic Al−C bonds is lengthened to 205.2 pm. Quantum chemical calculations verified a 3c2e AlCAl bond and a bonding situation, that is similar to that observed before in some boron compounds.