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

Abstract

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 )₃CuCl]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 )₃CuX]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 ³¹P CP-MAS n.m.r. spectra of the complexes at B = 7.05 T show well resolved asymmetric quartets with a ∆v₃/∆v₁ of 1.4 for the PcuX₂ complexes and 1.1-1.2 for the PcuX₂N 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 v( CuX ), this assignment being supported by a normal coordinate analysis on the Cu₂X₂ core.