Pd complexes based on phosphine-linked cyclophosphazenes: synthesis, characterization and application in Suzuki coupling reactions

Palladium complexes were obtained by reaction of phosphine-linked cyclophosphazenes, (P3N3)(O-C6H4-PR2)6, where R = phenyl, i-propyl or cyclohexyl, with using a Pd/ligand molar ratio of 3/1. The (P3N3)(O-C6H4-PR2)6Pd3(dba)x complexes were characterized by elemental analyses, mass spectrometry, 31P NMR and FT-IR where a characteristic νC=C band of dba coordinated to palladium was always observed. All complexes were tested in Suzuki coupling reactions between phenylboronic acid and aryl halides. Turnover numbers as high as ca. 17,500 for the coupling of 2-bromotoluene with chlorophenylboronic acid could be obtained for R = cyclohexyl. The complex based on -PPh2 was also immobilized in silica matrixes by the sol-gel method. Preliminary experiments showed that the immobilized catalyst could be used in at least three consecutive Suzuki reactions with the same catalytic activity.