Facile catalytic coupling of aryl bromides with terminal alkynes by phospha-palladacycles

An efficient synthesis of tolane derivatives from substituted aryl bromides and phenylacetylene catalyzed by air- and moisture-stable phospha-palladacycles is described. This procedure works without addition of cupric salts. Reaction rates and yields are sensitive to the nature of solvent and base. Mechanistic features are discussed for a catalytic cycle with Pd(II) and Pd(IV) intermediates. Constitutional stability of the palladacyclic catalyst under reaction conditions is likely; precipitation of palladium black is not observed.