The palladium(II) and platinum(II) bis-homoleptic complexes M(C&arcraise;N)(2), where C&arcraise;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&arcraise;N with M(Et(2)S)(2)Cl(2). The palladium(II) bis-heteroleptic complexes, Pd(C&arcraise;N)(C'&arcraise;N'), were synthesized from Pd(C&arcraise;N)(2) bis-homoleptic complexes, which were converted by HCl into the dichloro-bridged compounds [Pd(C&arcraise;N)Cl](2). By addition of Et(2)S, the Pd(C&arcraise;N)(Et(2)S)Cl complexes were formed, which were allowed to react with Li(C'&arcraise;N'), yielding M(C&arcraise;N)(C'&arcraise;N') compounds. An alternative way for obtaining the bis-heteroleptic molecules is by ligand exchange, according to the equilibrium M(C&arcraise;N)(2) + M(C'&arcraise;N')(2) = 2M(C&arcraise;N)(C'&arcraise;N'). The crystal structures of Pt(bhq)(2) (1) and Pt(thq)(2) (3) present an important distortion of the square planar (SP-4) geometry toward a two-bladed helix. Bis-homoleptic and some bis-heteroleptic complexes of palladium(II) have also been synthesized. In both cases, the steric interactions between the two ligands cause again a helical distortion rather than yielding trans compounds. For cis-bis(benzo[h]quinoline)platinum(II) (1), in the crystal (monoclinic, space group P2(1)/n, a = 13.728(3) Å, b = 6.9537(15) Å, c = 19.701(5) Å, beta = 106.17(2) degrees, Z = 4, rho(calcd) = 2.028 g.cm(-)(3); diffractometer 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) Å, respectively. One benzo[h]quinoline ligand is significantly less planar than the other. For cis-bis[2-(2'-thienyl)quinoline]platinum(II) (3), in the crystal (trigonal, space group P3(2)21, a = b = 9.373(1) Å, c = 20.152(3) Å, Z = 3, rho(calcd) = 2.022 g.cm(-)(3); diffractometer measurements, full-matrix least-squares refinement, R = 0.010, R(w) = 0.010) the molecule has C(2) symmetry and is chiral. The Pt-N and Pt-C bond lengths are 2.156(2) and 1.984(3) Å, respectively. The quinoline moitey is not planar but bent about the fused bond by 6.8 degrees. The thiophene moiety is inclined to the best plane through the quinoline moiety by 24.4 degrees.

cis-Bis-homoleptic platinum(II) complexes, with predetermined helical chirality at the metal center, can be obtained by using strongly sterically interacting ligands. With this aim, two new ligands, (8R,10R)-2-(2'-thienyl)-4,5-pinenopyridine, th4,5ppy (2), and (8R,10R)-2-(2'-thienyl)-5,6-pinenopyridine, th5,6ppy (4), were synthesized and coordinated to platinum. The structures of the resulting complexes, Pt(th4,5ppy)(2) (5) and Pt(th5,6ppy)(2) (6), were determined by X-ray diffraction, and it was found that they both crystallize with a Delta-cis configuration. Thermal oxidative additions (TOA) of alkyl halides were performed with both complexes leading, in the case of 5, to a mixture of isomers and, in the case of 6, to isomerically pure products. The predetermination of chirality at the metal center is therefore preserved in the octahedral (OC-6) platinum(IV) complexes. Crystals of Pt(th4,5ppy)(2) (5) are orthorhombic, of space group P2(1)2(1)2(1), with a = 12.973(1) Å, b = 13.619(2) Å, c = 17.665(2) Å, alpha = beta = gamma = 90 degrees, and Z = 4. Final R = 0.0268 and R(w) = 0.0424 for 3101 observed reflections. Crystals of Pt(th5,6ppy)(2) (6) are hexagonal, of space group P6(1), with a = 11.5465(4) Å, b = 11.5465(4) Å, c = 35.356(3) Å, alpha = beta = 90 degrees, gamma = 120 degrees, and Z = 6. Final R = 0.0424 and R(w) = 0.0845 for 2660 observed reflections. Neither molecule possesses a crystallographic C(2) symmetry.