CYCLOMETALATED COMPLEXES OF PALLADIUM(II) AND PLATINUM(II) WITH N-BENZYL-ALPHA-BENZOYLBENZYLIDENEAMINE AND N-(PHENYLETHYL)-ALPHA-BENZOYLBENZYLIDENEAMINE - DELOCALIZATION IN THE CYCLOMETALATED RING AS A DRIVING-FORCE FOR THE ORTHOMETALATION

The cyclometalation of N-benzyl- and N-(phenylethyl)-alpha-benzoylbenz ylideneamines with Pd(II) and Pt(II) salts has been studied. The struc tures of the Pt derivatives are very similar to those of the correspon ding Pd complexes. The endo five-membered metallocycle, involving the less activated aromatic rings, is formed in all cases, regardless of t he solvent used. The structures of the complexes are based on their IR and H-1 and C-13 NMR data. They were confirmed by X-ray studies of [P t(C6H4(C6H5C=O)C=N-CH2C6H5)(mu-OAc)]2 and [Pd(C6H4(C6H5C=O)C=N-CH(Me)C 6H5)(O=SMe2)Cl]. The first crystallizes in the centrosymmetric group P 1 with unit cell parameters a = 11.371 (2) angstrom, b = 12.074(2) ang strom c = 11.149(3) angstrom, alpha = 79.35(2)degrees, beta = 89.50(3) degrees, gamma = 77.94(2)degrees, V = 2270(1) angstrom3, rho(calcd) = 1.750 g cm-3, and R = 0.042. The crystal structure of the second compl ex obtained by crystallization of [Pd(C6H4(CrH5C=O)C=N-CH(Me)C6H5)(mu- Cl)]2 from DMSO is the first reported DMSO O-bonded cyclometalated com plex. The complex crystallizes in the orthorhombic system, with Z = 8, in the spatial group Pbcn with unit cell parameters a = 17.975(3) ang strom, b = 16.215(3) angstrom, c = 15.973(3) angstrom, V = 4656(3) ang strom3, rho(calcd) = 1.519 g cm-3, and R = 0.038. From these and other previously studied X-ray crystallographic data and by taking into acc ount the chemical shift of the carbon atoms remaining to the cyclometa lated rings, a strong delocalization into the metalated ring can be pr oposed, which suggests that it could be one of the main driving forces to the preferred formation of endo metallocycles.