Lewis-base adducts of Group 11 metal(I) compounds. Part 28. Solid-state phosphorus-31 cross-polarization magic-angle spinning nuclear magnetic resonance and structural studies on the mononuclear 3: 1 adducts of triphenylphosphine with copper(I) halides

Abstract

Solid-state cross-polarization magic-angle spinning ³¹P n.m.r. data and single-crystal X-ray diffraction structure determinations are reported for solvated and unsolvated 3 : 1 adducts of triphenylphosphine with copper(I) halides, [Cu(PPh₃)₃X]. The structures of the unsolvated bromide and iodide complexes are isomorphous with the previously studied chloride analogue, crystallizing in the trigonal space group P3 with three independent molecules each disposed about a crystallographic three-fold symmetry axis. Two of the molecules are related by a pseudo-inversion centre. The PPh₃ ligands adopt a skewed conformation about Cu–P with respect to Cu–X [X–Cu–P–C(l11) angles 30.6–34.1 °]. The Cu–P distances are not halide dependent [Br, 2.351(4), 2.340(4), and 2.369(4)Å; I, 2.362(3), 2.346(5), and 2.357(5)Å] and all P–Cu–P angles are close to the tetrahedral value. Solid-state ³¹P n.m.r. spectra of each halide reveal two symmetric quartets in an intensity ratio of 2: 1; average chemical shifts overall are –10, –13, and –17 p.p.m. for X = Cl, Br, and I respectively. The splittings within each quartet are also halide independent ranging between 900 and 940 Hz. The high intensity quartet is assigned to the two enantiomerically related molecules. The acetone solvated structures crystallize in the triclinic space group P with the bromide and iodide isomorphous. Solvation changes the conformation of the PPh₃ ligands about Cu–P from skewed to staggered, with X–Cu–P–C(l11) 45.5–56.3°. The potential increase in back strain because of this conformational change is relieved by an increase of 5° in the P–Cu–P angles. The Cu–P and P–Cu–P bond lengths and angles again do not change significantly with halogen within the series. The solid-state ³¹P n.m.r. spectra each reveal a single quartet shifted downfield by 6–10 p.p.m.; the quartets are slightly more asymmetric than in the trigonal phase with splitting values lying in the range 890–980 Hz.