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(AltBu2)C(H)–Ph]2 (1) by dual hydroalumination. The aluminum atoms of 1 are attached to the carbon atoms in α-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–CC–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(tert-butyl)aluminum hydride resulted in cleavage and isolation of the monoalkenyl compound tBu2Al–C[C(H)–Ph]–SiPh2–CC–Ph (5). The molecular structure of 5 showed a close interaction between the α-carbon atom of the triple bond and the coordinatively unsaturated aluminum atom.