| Abstract
| - Diphosphine ligands possessing a barbiturate-binding receptor have been synthesized with the goal of preparing new palladium(0) complexes for the Heck reaction. Some of the diphosphines prepared were found to efficiently form macrocyclic bisphosphine palladium(0) complexes even though a 26-membered cycle is produced.
- A series of diphosphine ligands possessing a barbiturate-binding receptor have beensynthesized with the goal of preparing new palladium(0) complexes for the Heck reaction,which position the alkene with respect to the metal center and thereby control theregioselectivity of the insertion step. Some of the diphosphines prepared were found toefficiently form macrocyclic bisphosphine palladium(0) complexes even though a 26-memberedcycle is produced. A significant solvent effect for the oxidative addition of the Pd0 complexeswith phenyl iodide was noted in the case of one of the diphosphine ligands. This descrepancymay well be accounted for by the ability of the ligand when complexed to Pd0 to possessdifferent conformational preferences in the solvents tested, which influences the bite angleto the metal center. The receptors possessing an isophthaloyl connector bind barbital withaffinities corresponding to those of the previously reported open receptors. However, uponcomplexation with Pd(dba)2, none of the bidentate ligands revealed a capacity to bind barbital,reflecting again the conformational changes that occur upon coordination to Pd0. The newpalladium(0) complexes were tested for their ability to promote the Heck reaction betweenaryl halides and n-butyl acrylate. Whereas all the ligand:Pd0 complexes were found to catalyzethis reaction with reactivities similar to triphenylphosphine, in one case a higher reactivitywas noted.
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