Hydroalumination of bis(alkynyl)germanes and -silanes: Generation of a chelating Lewis-acid and observation of a dismutation reaction

Treatment of diphenyl-di(phenylethynyl) germane with two equivalents of di(tert-butyl) aluminum hydride afforded the corresponding dialkenyl derivative, Ph2Ge[C(AltBu(2))=C(H)-Ph](2) (1) by dual hydroalumination. The aluminum atoms of 1 are attached to the carbon atoms in a-position to germanium. They are coordinatively unsaturated and are able to act as chelating Lewis-acids and to coordinate donors such as chloride or bromide anions in a chelating manner (2, 3). The analogous reaction of the corresponding silicon-centered dialkyne with two equivalents of dimethylaluminum hydride gave a mixture of unknown compounds. Interestingly, equimolar quantities of the hydride and the dialkyne resulted in dismutation and the formation of the unprecedented compound MeAl[C(=CH-Ph)-SiPh2-C C-Ph](2) (4). Compound 4 has two alkenyl groups bonded to the central aluminum atom and a terminal alkynyl group attached to each silicon atom. An attempt to reduce the remaining triple bonds by reaction with di(tertbutyl) aluminum hydride resulted in cleavage and isolation of the monoalkenyl compound tBu(2)Al-C[=C(H)-Ph]-SiPh2-C C-Ph (5). The molecular structure of 5 showed a close interaction between the a-carbon atom of the triple bond and the coordinatively unsaturated aluminum atom. (C) 2011 Elsevier B.V. All rights reserved.