SYNTHESIS AND CHARACTERIZATION OF DINUCLEAR HYDRIDE COMPLEXES OF PLATINUM(II) WITH CHIRAL DIPHOSPHINES - CRYSTAL AND MOLECULAR-STRUCTURE OF [PT2((R)-BUTAPHOS)2(H)3][BF4].(CH3)2CO, BUTAPHOS=1-(DIPHENYLPHOSPHINOXY)-2[N-ETHYL-N-(DIPHENYLPHOSPHINO)AMINO]BUTANE

The dinuclear complexes [Pt2{(S)-prolophos}2(H)3][BF4], 1, and [Pt2{(R)-butaphos}2(H)3][BF4], 2, [prolophos = N-(diphenylphosphino)-2-[(diphenylphosphinoxy)methyl]pyrrolidine; butaphos = 1-(diphenylphosphinoxy)-2-[N-ethyl-N-(diphenylphosphino)amino]butane}, were prepared and characterized by H-1, C-13, P-31, and Pt-195 NMR solution spectra. At room temperature complex 2 exists as two isomers, 2a and 2b, with similar NMR parameters: one of them, 2a, was isolated in the solid state. Variable-temperature NMR spectra show that at low temperature both 1 and 2 (2a and 2b) give rise to two isomers. In all the species the hydride ligands display a fluxional behaviour which persists down to -80-degrees-C. The structure of 2a as the acetone solvate was solved by X-ray diffraction: C63H75BF4N2O3P4Pt2, orthorhombic, space group P2(1)2(1)2, with cell dimensions a = 18.308(3) angstrom, b = 18.301(3) angstrom, c = 18.691(7) angstrom, Z = 4, and V = 6263(3) angstrom3. The structure was refined to a conventional R factor 0.033 (R(w) = 0.037) for 3959 observed reflections with I> 3sigma(I). Two hydrides, one terminal and one bridging, were located, whereas the terminal position of the third one was inferred from symmetry considerations. The Pt-Pt separation is 2.736(1) angstrom and the dihedral angle between the two P-Pt-P coordination planes is 86.0(1)-degrees. If the Pt-Pt vector is ignored, the coordination around each platinum atom can be considered as distorted square-planar. The seven-membered ring, formed by chelation of the diphosphine, displays a twisted-boat conformation. Compound 2a is the first complex of butaphos characterized in the solid state.