Square Planar (SP-4) and Octahedral (OC-6) Complexes of Platinum(II) and -(IV) with Predetermined Chirality at the Metal Center

Abstract

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 Δ-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 P2₁2₁2₁, with a = 12.973(1) Å, b = 13.619(2) Å, c = 17.665(2) Å, α = β = γ = 90°, 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 P6₁, with a = 11.5465(4) Å, b = 11.5465(4) Å, c = 35.356(3) Å, α = β = 90°, γ = 120°, and Z = 6. Final R = 0.0424 and R_w = 0.0845 for 2660 observed reflections. Neither molecule possesses a crystallographic C₂ symmetry.