THE ANION [R(2)AL-ALR(2)BR](-) (R=CH(SIME (3),)(2)) WITH AN ALUMINUM-ALUMINUM AND A TERMINAL ALUMINUM-BROMINE BOND

Tetrakis[bis(trimethylsilyl)methyl]dialane (1) with an Al-Al bond reac ts with LiBr in n-pentane in the presence of chelating N,N,N',N'-tetra methylethylenediamine (TMEDA) to yield the monobromo adduct [Li(TMEDA) (2)](+)[R(2)Al-AlR(2)Br](-) 4. Compound 4 is unstable in ethereal solu tion and decomposes with quantitative formation of LiBr and the starti ng compound 1. Crystal structure determination of 4.C5H10 shows a term inal Al-Br bond in an anion with a four-coordinated aluminium atom nei ghbouring a three-coordinated, coordinatively unsaturated aluminium at om. While the Al-Al bond length is not significantly different (264.3 pm) as compared to the data for 1, the Al-Br bond is rather long (247. 6 pm) indicating a weak coordinative bonding.