Metal-Free Acetylene Coupling by the (C6 F5 )2 B-X 1,2-Halogenoboration Reaction.

(C6 F5 )2 B-halides were conveniently prepared by treatment of (C6 F5 )2 BH with tritylchloride or -bromide, respectively. With cyclopropylacetylene, (C6 F5 )2 BBr underwent sequential cis-1,2-halogenoboration followed by 1,2-carboboration to give the 4-bromo-2,4-dicyclopropylbutadienyl-B(C6 F5 )2 product. It reacted further with additional cyclopropylacetylene to give the linear triene and tetraene products in a metal-free alkyne oligomerization reaction. The pyridine adduct of the initial diene product was characterized by X-ray diffraction. (C6 F5 )2 BCl reacted analogously. Similar (C6 F5 )2 BX induced oligomerization reactions were carried out with two conjugated enynes.