THE SYNTHESIS AND CHARACTERIZATION OF W(SEMES)4.THF (MES = MESITYL) -A POSSIBLE HOMOLEPTIC MONONUCLEAR TUNGSTEN SELENOLATE - ITS REACTION WITH CN'BU TO YIELD ('BUNC)(MESSE)(2)W(MU-SE)(2)W(SEMES)2(CN'BU)

The reaction of NaSeMes (Mes = mesityl, 2,4.6-(CH3)3C6H2) with WCl4(PP h2Me)2 in THF leads to the formation of W(SeMes)4-THF (1), a possible mononuclear tetrakis(selenolato) complex of tungsten. The identity of the red crystal-line material has been confirmed by elemental analysis and NMR spectroscopic methods (H-1, C-13, and Se-77 NMR). The reactio n of W(SeMeS)4.THF with tert-butyl isocyanide results in the formation of ((t)BuNC)(MesSe)2W(mu-Se)2W(SeMes)2(CN(t)Bu) (2). Compound 2 cryst allized in the monoclinic space group C2/c (no. 15) with a = 23.933(2) angstrom, b = 16.776(2) angstrom, c = 15.595(2) angstrom, beta = 122. 98(2)-degrees, and four formula units per unit cell. Refinement by ful l-matrix least squares gave final residuals of R = 0.038 and R(w) = 0. 028. The two metal centres in 2 are in a trigonal bipyramidal (tbp) co ordination environment. The two tbps are connected via a common edge ( axial-equatorial). The W-W bond length of 2.732(1) angstrom and the di amagnetism of 2 indicate the presence of a metal-metal bonding interac tion.