Facile hydroboration with the dimethylsulfide adducts of mono- and bis-(pentafluorophenyl)borane

The dimethylsulfide adduct of bis(pentafluorophenyl)borane HB(C6F5)2·SMe2 reacts on mixing with alkenes such as 1-hexene and styrene, with selectivities closely following those of the Me2S-free reagent. The mono(pentafluorophenyl)borane H2B(C6F5)·SMe2 also undergoes rapid hydroboration reactions to give the dialkylboranes R2B(C6F5). Treatment of the boranes with trimethylsilylacetylene results in rapid hydroboration to give the trans-vinylborane. The reaction of H2B(C6F5)·SMe2 with 1,5-cyclooctadiene at room temperature yields a kinetic mixture of the 1,4- and 1,5-dihydroboration products which quantitatively isomerizes on heating to the 1,5-isomer, pentafluorophenyl-9-borobicyclo[3.3.1]nonane. This bicyclic borane crystallizes as the SMe2 adduct, which has been characterized by X-ray crystallography.