CYCLOMETALATED COMPLEXES OF PALLADIUM(II) AND PLATINUM(II) - CIS-CONFIGURED HOMOLEPTIC AND HETEROLEPTIC COMPOUNDS WITH AROMATIC C-N LIGANDS

The palladium(II) and platinum(II) bis-homoleptic complexes M(C^N)(2), where C^N is benzo[h]quinoline (H-bhq), 2-phenylpyridine (H-phpy), 2- (2'-benzothienyl)pyridine (H-bthpy), 2-(2'-thienyl)quinoline (H-thq), and 2-(2'- thienyl)pyridine (H-thpy), were prepared by metal exchange of the lithiated ligands C^N with M(Et(2)S)(2)Cl-2. The palladium(II) bis-heteroleptic complexes, Pd(C^N)(C'^N'), were synthesized from Pd(C ^N)(2) bis-homoleptic complexes, which were converted by HCl into the dichloro-bridged compounds [Pd(C^N)Cl](2). By addition of Et(2)S, the Pd(C^N)(Et(2)S)Cl complexes were formed, which were allowed to react w ith LI(C'^N'), yielding M(C^N)-(C'^N') compounds. An alternative way f or obtaining the bis-heteroleptic molecules is by ligand exchange, acc ording to the equilibrium M(C^N)(2) + M(C'^N')(2) = 2M(C^N)(C'^N'). Th e crystal structures of Pt(bhq)(2) (1) and Pt(thq)(2) (3) present an i mportant distortion of the square planar (SP-4) geometry toward a two- bladed helix. Bis-homoleptic and some bis-heteroleptic complexes of pa lladium(II) have also been synthesized. In both cases, the steric inte ractions between the two ligands cause again a helical distortion rath er than yielding trans compounds. For cis-bis(benzo[h]quinoline)platin um(II) (1), in the crystal (monoclinic, space group P2(1)/n, a = 13.72 8(3) Angstrom, b = 6.9537(15) Angstrom, c = 19.701(5) Angstrom, beta = 106.17(2)degrees, Z = 4, rho(calcd) = 2.028 g . cm(-3); diffractomete r measurements, block-matrix least-squares refinement, R = 0.043, R(w) = 0.047) the average Pt-N and Pt-C distances are 2.151(6) and 1.988(7 ) Angstrom, respectively. One benzo[h]quinoline ligand is significantl y less planar than the other. For cis-bis[2-(2'-thienyl)quinoline]plat inum(II) (3), in the crystal (trigonal, space group P3(2)21, a = b = 9 .373(1) Angstrom, c = 20.152(3) Angstrom, Z = 3, rho(calcd) = 2.022 g . cm(-3); diffractometer measurements, full-matrix least-squares refin ement, R = 0.010, R(w) = 0.010) the molecule has C-2 symmetry and is c hiral. The Pt-N and Pt-C bond lengths are 2.156(2) and 1.984(3) Angstr om, respectively. The quinoline moitey is not planar but bent about th e fused bond by 6.8 degrees. The thiophene moiety is inclined to the b est plane through the quinoline moiety by 24.4 degrees.