PCP Pincer Palladium Complexes and Their Catalytic Properties: Synthesis via the Electrophilic Ligand Introduction Route

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A variety of PCP pincer palladium complexes having phosphinito groups [2,6-(R 2 PO) 2 C 6 H 3 PdI (R = alkyl, aryl and Et 2 N)] 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.