The three palladacycle complexes of the type [RC(O)CHPPh₂(CH₂)₂PPh₂CHC(O)R]PdCl₂, where R=2-naphtyl, 2,4-dichlorophenyl and 3-nitrophenyl, contain a seven-membered C,C-chelate ring. Palladium complexes were synthesized and investigated by physicochemical techniques. We used a palladium(II) complex (R=3-nitrophenyl) as a highly efficient catalyst for the Suzuki coupling reaction of various aryl halides.

The reaction of 1,2-bis(diphenylphosphino)ethane (dppe) with various ketones in acetone produces the new phosphonium salts [RC(O)CH₂PPh₂(CH₂)₂PPh₂CH₂C(O)R]X₂ (R=2-naphtyl, X=Br (1); R=2,4-dichlorophenyl, X=Cl (2); R=3-nitrophenyl, X=Br (3)). Further treatment with a base gives the symmetrical phosphorus ylides, RC(O)CHPPh₂(CH₂)₂PPh₂CHC(O)R (R=2-naphtyl (4), 2,4-dichlorophenyl (5), 3-nitrophenyl (6)). These ligands react with Pd(II) chloride to form C,C-chelated complexes with the composition [RC(O)CHPPh₂(CH₂)₂PPh₂CHC(O)R]PdCl₂, where R=2-naphtyl (7), 2,4-dichlorophenyl (8), 3-nitrophenyl (9). These compounds have been characterized by elemental analysis and spectroscopic methods and consist of seven-membered rings formed by the coordination of the ligands through the two ylidic carbon atoms to the metal center. The structure of compound 5 has been characterized crystallographically. The palladium complex 9 is employed in the Suzuki cross-coupling reaction between phenylboronic acid and several aryl halides. It was found to be a competent catalyst for a variety of substrates to afford the coupled products in high yields using DMF as a solvent. The biaryl products were obtained under aerobic conditions in short reaction times with a lower loading of the catalyst (0.001mol%).