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(P_A)–24.2, δ(P_B)–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 CC 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 (Δν_½= 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.