Hydroalumination of dialkynylgermanes-synthesis of alkenyl-alkynylgermanes with intramolecular aluminium-carbon interactions

Reactions of dialkylaluminium hydrides, R(2)AlH [R = CH(2)CMe(3), CMe(3), CH(SiMe(3))(2)], with di(phenylethynyl)germanes, R(2)Ge(C C-C(6)H(5))(2) [R = CH(3) (1), C(6)H(5) (2)], afforded mixed alkenyl-alkynylgermanes, R(2)Ge(C C-C(6)H(5))[C(AlR(2))= C(H)-C(6)H(5)] (3 to 7), by hydroalumination of one of the C C triple bonds. In all cases the cis-arrangement of the Al and H atoms across the resulting C = C double bond was observed. Crystal structure determinations revealed relatively strong intramolecular bonding interactions between the coordinatively-unsaturated aluminium atoms and the alpha-carbon atoms of the intact triple bonds bearing a partial negative charge. This interaction is only prevented by application of the very bulky bis(trimethylsilyl)methyl substituent.