Simple palladacyclic and platinacyclic catalysts for the 1,4-conjugate addition of arylboronic acids and arylsiloxanes to enones

A range of palladacyclic, platinacyclic, and pincer-based catalysts have been tested for activity in 1,4-conjugate addition reactions. pi-Acidic palladacycles show excellent activity at room temperature in the reaction of enones with arylboronic acids and reasonable activity when the arylboronic acids are replaced by arylsiloxanes. The X-ray structures of three new palladium kappa(3)-PCP-pincer complexes are presented; surprisingly, these complexes show no activity, despite the fact that notionally related phosphine and carbene adducts of palladacycles do.