Cyanide-Bridged Heterobimetallic Complexes of the Group 6 Metal Carbonyls and Copper(I). X-ray Structures of (CO)5MCNCu(PPh3)3 (M = Cr, W) Derivatives

The cyanide-bridged compounds (CO)5MCNCu(PPh3)3 where M = W in 1, and M = Cr in 2 have been prepared by the reaction of NaM(CO)5CN with Cu(CH3CN)4BF4 and PPh3, and their solid-state structures have been determined crystallographically. In 1, the CN bond length was 1.15(2) Å, and the bridge was slightly bent with angles of W−C(6)−N(1) = 175.9(14)° and Cu−N(1)−C(6) = 176(2)°. Crystal data for 1: monoclinic, space group P21/n, a = 20.376(4) Å, b = 12.436(3) Å, c = 22.423(5) Å, β = 97.28(3)°, Z = 4, R = 7.90%. The chromium analog, complex 2, was isomorphous with 1. In addition, the isocyanide-bridged complex (CO)5WNCCu(PPh3)3 (3) was prepared by the reaction of CuCN with PPh3 and W(CO)5(THF) at −78 °C. The structure of this compound was determined by infrared and 13C NMR measurements. The isocyanide-bridged 3 was found to undergo thermal rearrangement to yield the cyanide-bridged 1. In the 13C NMR spectrum of 1 at room temperature, the CN peak is very broad (fwhh = 47 Hz) and can be found at 147.8 ppm. Dynamic 13C NMR measurements on 1 revealed that this complex undergoes an equilibrium reaction in THF-d 8 solution. Two possibilities are presented which are consistent with the observations. One is a contact ion pair/solvent-separated ion pair exchange reaction which involves breakage of the Cu−N bond and insertion of a solvent molecule. The second is dissociation/recoordination of a triphenylphosphine ligand from Cu(I). Differentiation between the two is impossible on the basis of the available data. In the slow-exchange limit, the 13CN peak of 1 is found at 149.0 ppm, shows 183W satellites (J WC = 96 Hz), and has a line width of 12 Hz. In the 13C NMR spectrum of 3 at room temperature, the CN peak is sharp (fwhh = 0.75 Hz) and can be found at 160.7 ppm. Dynamic 13C NMR measurements on 3 revealed no ion pair exchange as high as 40 °C. The 13C NMR spectrum of Cu13CN(PPh3)3 was also recorded at room temperature, and the CN peak can be found at 152.3 ppm with a line width of 15 Hz.