Cyanide-bridged heterobimetallic complexes of the group 6 metal carbonyls and copper(I). X-ray structures of (CO)(5)MCNCu(PPh(3))(3) (M=Cr, W) derivatives

The cyanide-bridged compounds (CO)(5)MCNCu(PPh(3))(3) where M = W in 1, and M = Cr in 2 have been prepared by the reaction of NaM(CO)(5)CN with Cu(CH3CN)(4)BF4 and PPh(3), and their solid-state structures have been determined crystallographically. In 1, the CN bond length was 1.15(2) Angstrom, and the bridge was slightly bent with angles of W-C(6)-N(1) = 175.9(14)degrees and Cu-N(1)-C(6) = 176(2)degrees. Crystal data for 1: monoclinic, space group P2(1)/n, a = 20.376(4) Angstrom, b = 12.436(3) Angstrom, c = 22.423(5) Angstrom, beta = 97.28(3)degrees, Z = 4, R = 7.90%. The chromium analog, complex 2, was isomorphous with 1. In addition, the isocyanide-bridged complex (CO)(5)WNCCu(PPh(3))(3) (3) was prepared by the reaction of CuCN with PPh(3) and W(CO)(5)(THF) at -78 degrees C. The structure of this compound was determined by infrared and C-13 NMR measurements. The isocyanide-bridged 3 was found to undergo thermal rearrangement to yield the cyanide-bridged 1. In the C-13 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 C-13 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 (CN)-C-13 peak of 1 is found at 149.0 ppm, shows W-183 satellites (J(WC) = 96 Hz), and has a line width of 12 Hz. In the C-13 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 C-13 NMR measurements on 3 revealed no ion pair exchange as high as 40 degrees C. The C-13 NMR spectrum of (CuCN)-C-13(PPh(3))(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.