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
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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) , 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) , b = 12.436(3) , c = 22.423(5) , = 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 -78C. 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-d8 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 (Jwc = 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 40C. 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.
