The Methylene-bridged Dialuminium Compound R2Al-CH2-AlR2 [R=CH(SiMe3)2] as an Effective Chelating Lewis Acid – Adducts with Halides, Perchlorate and Isopropylamide

The new methylene-bridged dialuminium compound Aryl Al-CH -AlAryl 1b was synthesised from Cl Al-CH -AlCl and four equivalents of LiAryl [Aryl=C (2,4,6-i-Pr) ]. A 1 : 2 stoichiometric ratio of the starting compounds afforded the dimeric aluminium halide (Aryl AlCl) (2) by dismutation. The coordination behaviour of the related, but more easily available dialuminium compound R Al-CH -AlR [R=CH(SiMe ] 1a was explored. It yields the Lewis acid base adducts [M][R Al-CH -AlR (μ-X)] [3a, M=Li(TMEN) , X=Cl; 3b, M=Li(TMEN) , X=Br; 3c, M=K(18-crown-6), X=ClO ; 3d, M=Li(TMEN) , X=NH(i-Pr)] with X residing in a bridging position between the two Al atoms as evident from NMR spectroscopy and X-ray crystallography (3b, 3c, 3d). Compound 3c is a unique example of a stable, in organic solvents soluble adduct that features a ClO anion coordinated by an alkylaluminium compound via two of its oxygen atoms.