REACTIVITY OF BIS(ALKYNE) CARBORANE COMPLEXES OF MOLYBDENUM AND TUNGSTEN TOWARD TERT-BUTYL ISOCYANIDE

Treatment of the complex [Mo(CO)(eta2-MeC2Me)2(eta5-7,8-Me2-7,8-C2B9H9)] (5a) in CH2Cl2 with ca. 4 mol equiv of CNBu(t) affords the compounds [Mo(CO)(CNBu(t))3(eta5-7,8-Me2-7,8-C2B9H9)] (6) and [Mo(CNBu(t))4(eta5-7,8-Me2-7,8-C2B9H9)] (7a). However, reactions between [M(CO)(eta2-MeC2Me)2(eta5-7,8-C2B9H11)] (5b, M = Mo; 5c, M = W) and an excess of CNBu(t) in CH2Cl2 give [M(CNBU(t))4(eta5-7,8-C2B9H11)] (7b, M = Mo; 7c, M = W) and [M{= C[N(H)Bu(t)]C(Me) = C-(Me)[C(O)N(H)Bu(t)]}(CNBU(t))2(ns-7,8-C2B9H11)] (8a, M = Mo; 8b, M = W). The structure of 8b has been established by an X-ray diffraction study. Crystals are triclinic, space group P1BAR (No. 2) with a = 10.913(2) angstrom, b = 11.992(2) angstrom, c = 14.852(2) angstrom, alpha = 73.12(l)-degrees, beta = 82.48(l)-degrees, gamma = 74.138(16)-degrees, and Z = 2. The tungsten atom is ligated by the nido-C2B9H11 cage in the normal pentahapto manner, by two isocyanide molecules (W-CNBu(t) average 2.02 angstrom), and by a vinylcarbene moiety [W = C = 2.018(7) angstrom, W-C = 2.308(8) and 2.335(8) angstrom]. The latter group is formed at the metal center by coupling of one but-2-yne ligand with two isocyanide molecules, followed by reaction with H2O. Methylation of the complex [Mo(CNBU(t))4(eta5-7,8-C2B9H11)] (7b) with CF3SO3Me yields initially the species [MoMe(CNBU(t))4(eta5-7,8-C2B9H11)] [SO3CF3] (9), which rearranges to [Mo(CNBU(t))3{eta2-C(Me) = NBu(t)}(eta5-7,8-C2B9H11)][SO3CF3] (10). The structure of 10 has been determined by X-ray diffraction. Crystals are monoclinic, space group C2/c (No. 15) with a = 41.569(4) angstrom, b = 9.465(2) angstrom, c = 20.381(2) angstrom, beta = 105.616(7)-degrees, and Z = 8. The molybdenum atom is coordinated by a nido-C2B9H11 cage, three isocyanide molecules (Mo-CNBu(t) average 2.11 angstrom), and an eta2-C(Me) = NBu(t) moiety [Mo-C = 2.10(1) angstrom, mo-N = 2.14(1) angstrom]. In addition to the X-ray crystal structure determinations, the IR and NMR data for the new complexes are reported and discussed in relation to their structures.