CARBORANE FORMATION IN ALKYNE-BORANE GAS-PHASE SYSTEMS .3. FLASH REACTIONS OF SMALL BORANES

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 dimethyl acetylene 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. © 1969, American Chemical Society. All rights reserved.