Rhodium- and ruthenium-catalyzed dehydrogenative borylation of vinylarenes with pinacolborane: stereoselective synthesis of vinylboronates

The treatment of pinacolborane (4,4,5,5-tetramethyl-1,3,2-dioxaborolane) with vinylarenes in the presence of a catalytic amount of phosphine-free di-mu-chlorobis(1,5-cyclooctadiene)dirhodium(I) [RhCl(cod)](2), through dehydrogenative borylation, provides the corresponding regio- and stereodefined (E)-2-arylethenylboronates in high yields. Also, a ruthenium complex prepared in situ from (1,5-cyclooctadiene)(1,3,5-cyclooetatriene)ruthenium(O) [Ru(cod)(cot)] and P(4CF(3)C(6)H(4))(3) showed considerable catalytic activity for dehydrogenative borylation.