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. π-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 κ3-“PCP”-pincer complexes are presented; surprisingly, these complexes show no activity, despite the fact that notionally related phosphine and carbene adducts of palladacycles do.