PCP pincer palladium complexes and their catalytic properties: Synthesis via the electrophilic ligand introduction route

A variety of PCP pincer palladium complexes having phosphinito groups [2,6-(R2PO)(2)C6H3PdI (R = alkyl, aryl and Et2N)] were synthesized via the electrophilic ligand introduction route with high efficiency. Thus, trans-(2,6-dihydroxyphenyl)iodobis(triphenylphosphine)palladium was prepared by the reaction of 2-iodoresorcinol with tetrakis(triphenylphosphine) palladium, and the palladium complex was converted to the PCP pincer palladium complexes by treatment with chlorophosphines in the presence of triethylamine in 82-95% yield. X-ray molecular structure analyses of the pincer complexes revealed that the molecules adopted distorted square-planar geometries. The Suzuki coupling reaction of 4-bromoacetophenone with phenylboronic acid took place in the presence of 0.1-0.01 mol % of the pincer complexes to give 4-acetylbiphenyl with turnover numbers of 328-5790.