1-SILA-3-ALUMINA-4-ALUMINATACYCLOPENTANE WITH AN A1-A1 BOND AND A C2A1SI HETEROCYCLE

Tetrakis[bis(trimethylsilyl)methyl]dialuminium (1) with an aluminium-a luminium bond reacts in the presence of tetramethylethylenediamine (TM EDA) with the sterically highly shielded bases bis(trimethylsilyl)meth yllithium or bis(dimethylphosphanyl)methyllithium to yield under depro tonation of a methyl group a carbanionic species, which is stabilized by an interaction with one of the coordinatively unsaturated Al atoms. The five-membered heterocycle 5 is formed containing two Al, one Si a nd two C atoms. The Al-Al bond remains uncleaved. Interestingly, 5 cry stallizes in different crystals with and without crystal ether, which were both characterized by crystal-structure determinations. The Al-Al bond length in 5 [264.1(2) and 266.5(3) pm, respectively] is only sli ghtly changed in comparison to the neutral starting compound 1 (266.0 pm). Under similar conditions the sterically less demanding ethyllithi um leads to a beta-elimination and addition of the thereby formed LiH to one of the two Al atoms to give the recently published hydridodialu minate(5) Li(TMEDA)(2)(+) [R(2)Al-AlHR2](-) (2).