Structural and 31P CP MAS NMR spectroscopic studies of the P2CuN2 copper(I) complexes [Cu(PPh3)2(MeCN)2]X for X = PF6, BF4 and ClO4

Abstract

The mixed ligand P₂CuN₂ copper(I) complexes [Cu(PPh₃)₂(MeCN)₂]X have been studied by one- and two-dimensional ³¹P CP MAS NMR spectroscopy for X = PF₆, BF₄ or ClO₄ and single crystal X-ray diffraction for X = PF₆ and ClO₄, completing availability of precise structural data for this isomorphous series. The compounds crystallise as discrete cations and anions in space group P2₁/n with a ≈ 15, b ≈ 27, c ≈ 9 Å, β = 95°, Z = 4. The anion is located ca. 6 Å from the copper atom and adjacent to a cleft formed between the acetonitrile ligands and phosphine ligand 2 while the crystallographically independent PPh₃ ligands adopt staggered three-bladed propeller-type conformations of opposite chirality. The geometric symmetry of the P₂CuN₂ co-ordination sphere is low with Cu–P(1) 2.276(4)–2.287(2), Cu–P(2) 2.258(4)–2.269(1) Å, Cu–N 2.023(9)–2.053(3) Å, P–Cu–P 126.82(4)–127.73(5), N–Cu–N 99.5(4)–100.3(1), P(1)–Cu–N 100.87(8)–102.34(9) and P(2)–Cu–N 110.4(1)–111.9(3)°. One- and two-dimensional solid state ³¹P CP MAS NMR spectra of the compounds at 9.40 T show chemical shift differences of 6 ppm between the signals arising from the two P sites which form part of an ABX spin system with ¹J[³¹P(1)–⁶³Cu] 1.13–1.14 kHz, ¹J[³¹P(2)–⁶³Cu] 1.30 kHz and ²J(³¹P–³¹P) 75 Hz. The copper quadrupolar induced distortion of the line spacings is different for the two sites and is postulated to be a consequence of variation in the angle between the Cu–P vectors and the z axis of the electric field gradient tensor. The magnitude of the distortion is relatively small and consistent with small copper quadrupolar coupling constants for the compounds and a balanced electronic charge distribution about the copper(I) site in spite of the low geometric symmetry of the P₂CuN₂ co-ordination sphere.