Copper(I) and gold(I) complexes with cis-bis(diphenylphosphino)ethylene. Crystal structures and 31P cross-polarization magic angle spinning nuclear magnetic resonance studies.

Abstract

The synthesis, structural and solid-state 31P cross-polarization magic angle spinning (CP MAS) NMR characterization of cis-bis(diphenylphosphino)ethylene (dppey) and the copper(I) and gold(I) complexes [M(dppey)2]PF6 has been carried out. The complexes, which have been shown to exhibit cytotoxic and antitumour activity, belong to the relatively rare class of copper(I) and gold(I) complexes with tetrahedral CuP4 and AuP4 co-ordination spheres. Crystals of dppey 1 are monoclinic with space group P21/c and a= 12.861(8), b= 13.097(2), c= 14.228(8)Å, β= 116.15(3)°; R was 0.047 for 3117 ‘observed’ reflections. The solid-state CP MAS 31P NMR spectrum consists of an AB multiplet with δ(PA)–24.2, δ(PB)–27.2 and J(P–P)= 126 Hz. Crystals of [Cu(dppey)2]PF62 are orthorhombic with space group P212121 and a= 14.479(5), b= 16.703(4), c= 20.891(4)Å; R was 0.046 for 3138 ‘observed’ reflections. The CuP4 co-ordination sphere is regular within the constraints of chelation with Cu–P in the range 2.276(2)–2.289(2)Å. The copper atom lies on a pseudo two-fold axis of symmetry bisecting the C[double bond, length half m-dash]C bonds. Charge-transfer interactions between phenyl rings on each ligand contribute to the stabilization of the structure of the cation. The solid-state 31P NMR spectrum consists of four broad bands (Δν½= 300 Hz) centred at δ 8 with J(Cu–P)≈ 820 Hz. Distortion of the quartet spacings by quadrupolar interaction with the copper nuclei is minimal. Crystals of [Au(dppey)2]PF63 are isomorphous with 2 with a= 14.644(4), b= 16.703(1), c= 20.699(5)Å; R was 0.025 for 3947 ‘observed’ reflections. The Au–P distances lie in the narrow range 2.377(2)–2.388(2)Å. Solid-state CP MAS 31P NMR of this complex and the analogous nitrate and chloride complexes at magnetic field strengths of 2.11, 7.05 and 9.40 T reveal splitting of the phosphorus signal into a quartet ascribed to Au–P spin–spin coupling effects with J(Au–P) estimated to be 200 Hz. As for the copper complex, distortion of the quartet spacings is minimal and indicative of a small 197Au quadrupolar coupling constant. Solution and solid-state 31P NMR chemical shift parameters are similar, supporting the hypothesis that the tetrahedral bis(chelated) cations are also stable in solution. Spin–spin coupling to the quadrupolar (197Au or 63/65Cu) nuclei was not resolved in the solution spectra, however, due to rapid quadrupolar relaxation.