Structural and solid-state 31P nuclear magnetic resonance studies on 1 : 1 : 1 mixed nitrogen and phosphine base complexes with copper(I) halides

Abstract

1 : 1 : 1 Adducts of copper(I) halides with phosphine and amine donor ligands, [{CuX[PPh₂(C₆H₄Me-o)](cpy)}₂] and [{CuX(PPh₃)(pip)}₂](cpy = 4-cyanopyridine, pip = piperidine; X = Cl, Br or I) have been synthesized as crystalline dihalide-bridged binuclear complexes and characterized by single-crystal structure determinations and solid-state ³¹P cross-polarization magic angle spinning (CPMAS) NMR spectroscopy. The [{CuX[PPh₂(C₆H₄Me-o)](cpy)}₂] complexes are isomorphous with their PPh₃ analogues, crystallizing as centrosymmetric dimers in space group P2₁/n with a≈ 15.5, b≈ 8.0, c≈ 18.7 Å, β≈ 104°(Z= 2 dimers). Introduction of the o-tolyl group into the phosphine ligand increases all of the Cu–p, Cu–N and Cu–X bond distances by 1–2% with the increase in Cu–X accommodated primarily by an increase in the Cu ⋯ Cu distances by 2–6%. For [{CuX(PPh₃)(pip)}₂] the chloride and bromide complexes are isomorphous, crystallizing in space group Pbca with a≈ 16.5, b≈ 18.0, c≈ 14.6 Å(Z= 4 dimers). The monomer/asymmetric units are disposed close to a centre of symmetry but the two Cu–X distances at each copper site differ by over 0.3 Å and the resultant ‘dimers’ are better described as associated monomers with three- rather than four-co-ordinate copper. The iodide complex crystallizes in space group P, with a= 17.442(9), b= 16.532(6), c= 13.801(3)Å, α= 92.78(2), β= 112.08(3), γ= 112.65(3)°(Z= 3 dimers). The unit cell contains independent centro- and non-centro-symmetric dimers with significant differences in the geometric parameters of the two. Differences in the Cu–X distances are much smaller than for the X = Cl and Br complexes. The piperidine ligand co-ordinates through the nitrogen lone pair with the Cu–N bond approximately perpendicular to the Cu₂X₂ plane and is disposed away from the Cu₂X₂ plane and towards the phosphine ligand for all dimers except the centrosymmetric iodide dimer. The Cu ⋯ Cu distances are 7–11% longer than those of the corresponding pyridine base complexes, but are shorter than those in complexes with acetonitrile as the base. The solid-state ³¹P CP MAS NMR spectra of the complexes at B= 9.4 T show well resolved asymmetric quartets arising from a combination of scalar and dipolar coupling between the quadrupolar spin 3/2; copper and the spin ½ phosphorus nuclei. The structural and spectroscopic data are discussed in relation to steric and electronic properties of the donor ligands and the influence of these on the size and shape of the Cu₂X₂ core.