Carborane formation in alkyne-borane gas-phase systems. III. Flash reactions of small boranes

Article abstract of DOI:10.1021/ic50071a013

Thermally induced flash reactions of tetraborane(10) and pentaborane(11) with acetylene, methylacetylene, and dimethylacetylene have been studied, and the volatile products, consisting almost exclusively of parent or alkyl closed-cage carboranes and hydrocarbons, have been individually isolated and characterized. Both the total carborane yield and the relative yields of B₃ and B₄ carboranes are largest in reactions of dimethylacetylene and least in those of acetylene. Derivatives of 1,2-C₂B₃H₅ are formed in significant amounts from alkylacetylenes but not from acetylene. The results are compared with previous work on borane-alkyne systems, particularly the electric-discharge and flash reactions of diborane with acetylene, and implications in regard to reaction pathways are discussed. The pentaborane(11)-dimethylacetylene system is exceptional; flash reactions are not observed in 1:1 mixtures, but a 2:1 alkyne:borane ratio results in flash reaction below room temperature in which largely noncarborane products are obtained.