Highly efficient and regioselective production of trisubstituted alkenes through heck couplings catalyzed by a palladium phosphinito PCP pincer complex

The PCP ligand precursor 1,3-bis(diisopropylphosphinito)benzene is convenie ntly prepared from the reaction of chlorodiisoprogylphosphine and resorcino l in the presence of 4-dimethylaminopyridine. Refluxing the bis(phosphinito )benzene with Pd(COD)Cl-2 in toluene for 5 h yields the palladium complex P dCl{C6H3-2,6-(OPPr2i)(2)} (1). The molecular structure of the complex was d etermined through a single-crystal X-ray diffraction study. The complex is a highly efficient catalyst for the olefinic coupling of aryl bromo and iod o compounds under aerobic conditions. Disubstituted alkenes were obtained i n good yields from the catalytic coupling of styrene and aryl iodides, wher eas styrene reactions with aryl bromides yield exclusively trisubstituted a lkenes. Trisubstituted alkenes were also obtained from the reactions of 1,1 disubstituted alkenes (alpha-methylstyrene, n-butylacrylate) and bromobenz ene. Conditions have been found which result in the regioselective product ion of one isomer of the trisubstituted alkene products in greater than or equal to 90% yield. (C) 2000 Elsevier Science S.A. All rights reserved.