A contribution to the chemistry of 2,2,6,6-tetramethylpiperidino aluminium compounds

Abstract

tmpAlBr2 (tmp = 2,2,6,6-tetramethylpiperidino) was prepared from AlBr3 and tmp2AlBr at 90°C in the absence of a solvent, but could not be crystallised from toluene or hexane because it reacted with the solvents to form tmpH·AlBr3 in high yield. tmpH·AlMeCl2, obtained from the components, decomposes at elevated temperatures but no tmpAlCl2 could be isolated. Attempts to generate the cation [tmp-Al-tmp]+ from tmp2AlBr or tmp2AlCl by halide abstraction with B(C6F 5)3, Ph3C(SnCl5) or SbCl5 or from tmp2AlR (R = Me, Ph) and B(C6F5) 3 have failed. An unexpected reaction occurred on treatment of tmp-B=P(tBu)AlBr3 with BH3 in THF which led to the formation of [AlBr2(thf)4][AlBr4]. The attempted synthesis of tBu2Al(tmp) from tBu2AlBr and Li(tmp) gave a product which, on exposure to CO2 at dry ice temperature, yielded the salt [(tBuAl)2(O2C(tmp)) 3][tBu3 Al-Br-AltBu3] in low yield. All isolated products were characterized by NMR spectroscopy and by X-ray determination of their molecular structures. © 2005 Verlag der Zeitschrift für Naturforschung.