Structural and Spectroscopic Studies on the Dimeric Complexes of Tris(2-methylphenyl)phosphine with Copper(I) Halides

1:1 adducts of the copper(I) halides, CuX (X = Cl, Br, I), with the sterically hindered ligand tris(2-methylphenyl)phospine [P(o-tol)(3)] have been synthesized as crystalline dihalo-bridged centrosymmetric binuclear species; six compounds have been characterized by solid-state CP-MAS n.m.r. and far-infrared spectroscopy and by room-temperature single-crystal X-ray structure determination. For X = Cl, the dimeric complex, [P(o-tol)(3)CuCl](2), with three-coordinate copper atoms has been obtained from acetonitrile solution. Similar dimeric complexes for X = Br and I were obtained from toluene solution, the iodide adduct incorporating cocrystallized toluene. The X = Br and I complexes crystallized from acetonitrile solution yield mixed-ligand four-coordinate copper(I) dimers, [(MeCN)P( o-tol)(3)CuX]2, the iodide as a 2MeCN solvate. An additional crystalline phase incorporating crystallographically independent molecules of both the three-coordinate dimer and the four-coordinate mixed-ligand dimer has also been characterized for X = Br. Solid-state P-31 CP-MAS n.m.r. spectra of the complexes at B = 7.05 T show well resolved asymmetric quartets with a Delta nu(3)/Delta nu(1) of 1.4 for the PCuX(2) complexes and 1.1-1.2 for the PCuX(2)N complexes; these results reflect the geometric and bonding changes in the copper coordination sphere. Far-infrared spectra of the complexes show two strong halogen-sensitive bands, with a wavenumber separation of 30-40 cm(-1), which have been assigned to copper-halogen stretching modes nu(CuX), this assignment being supported by a normal coordinate analysis on the Cu(2)X(2) core.