Reactions of bis(ethylene)(tricyclohexyl- and triphenyl-phosphine)platinum with quinones. Crystal structure of ethylene(2–3-η-2,3,5,6-tetramethylbenzo-1,4-quinone)(tricyclohexylphosphine)platinum

Abstract

A series of complexes [Pt(η²-quinone)(C₂H₄){P(cyclo-C₆H₁₁)₃}] has been prepared by treating [Pt(C₂H₄)₂{P(cyclo-C₆H₁₁)₃}] with benzo-1,4-quinones. Carbon-13 n.m.r. studies on the compounds containing the ligands 2,3-dimethyl-, 2,5-dimethyl-, 2,5-diphenyl-benzo-1,4-quinone, and naphtho-1,4-quinone revealed that although the C₂H₄ group is undergoing rapid rotation, the η²-bonded quinone is rigid on the n.m.r. time scale. In contrast, in the derivatives from 2,6-dimethyl-, 2,6-di-t-butyl-, 2,6-dimethoxy-, and 2,3,5,6-tetramethyl-benzo-1,4-quinone, the quinone ligands are also undergoing dynamic behaviour. The η² ground-state structure was established by an X-ray diffraction study on the compound [Pt(η₂-C₆Me₄O₂)(C₂H₄){P(cyclo-C₆H₁₁)₃}]. Crystals are triclinic, space group P, Z= 2, in a unit cell with lattice parameters a= 9.818(3), b= 10.489(3), c= 14.486(3)Å, α= 97.27(2), β= 97.93(2), and γ= 91.33(3)°. The structure has been refined to R 0.027 (R′ 0.033) for 6 467 independent reflections collected at 200 K for 2.9 ⩽ 2θ⩽ 55°(Mo-K_αX-radiation). The results establish that the 2,3,5,6-tetramethylbenzo-1,4-quinone ligand is attached to the platinum by two carbon atoms of one C(Me)C(Me) group, and the metal is in a trigonal planar environment with the midpoint of this group, the phosphorus atom, and the midpoint of the C–C bond of the ethylene ligand, with all these co-ordinated atoms lying within 0.1 Å of the co-ordination plane.