HALOCARBONYLTUNGSTEN(II) COMPLEXES CONTAINING TRIPODAL TRIS(PYRAZOLYL)BORATE LIGANDS

The halo tricarbonyl complexes LWX(CO)(3) (X = I, Br, Cl) are formed w hen NEt4[LW(CO)(3)] is reacted with I-2, N-bromosuccinimide, and N-chl orosuccinimide (or PhICl2), respectively, while reaction of NEt4[(LW)- W-Pr(CO)(3)] and I-2 yields (LWI)-W-Pr(CO)(3) [L = hydrotris(3,5-dimet hylpyrazol-1-yl)borate, L-Pr = hydrotris(3-isopropylpyrazol-1-yl)borat e]. Reaction of Net(4)[LW(CO)(3)] with Br-2 yields mixtures of LWBr(CO )(3) and (LWBr)-W-Br(CO)(3) [L-Br = hydrotris(4-bromo-3,5-dimethylpyra zol-1-yl)borate] as a result of competitive bromination of both tungst en and ligand L. The complexes generally exhibit three nu(CO) bands, o ne at ca. 2025 cm(-1) and two between 1930 and 1900 cm(-1), and NMR sp ectra consistent with fluxional carbonyl-capped octahedral (C-s) struc tures. Crystals of (LWI)-W-Pr(CO)(3) . MeOH are orthorhombic, space gr oup Pbca, with a = 11.779(2) Angstrom, b = 15.975(4) Angstrom, c = 29. 476(3) Angstrom, and V = 5547(2) Angstrom(3) for Z = 8. The seven-coor dinate complex exhibits a 3:3:1 carbonyl-capped octahedral structure. In hot acetonitrile or tetrahydrofuran, the tricarbonyl complexes are converted into brown, paramagnetic (mu(eff) ca. 1.15 mu(B)) dicarbonyl species, LWX(CO)(2) and (LWBr)-W-Br(CO)(2), which exhibit two nu(CO) bands (ca. 1930 and 1840 cm(-1)) and isotropically shifted NMR spectra consistent with a mononuclear structure with C-s symmetry. Further de carbonylation of (LWBr)-W-Br(CO)(2) in refluxing acetonitrile results in the formation of (LWBr)-W-Br(MeCN-kappa(2)-N,C-(CO), which crystall izes in monoclinic space group C2/c, with a = 22.245(4) Angstrom, b = 19.077(4) Angstrom, c = 15.639(3) Angstrom, beta = 128.61(2)degrees, a nd V = 5286(2) Angstrom(3) for Z = 8. The seven-coordinate complex fea tures a ''side-on'' bonded, four-electron-donor acetonitrile ligand an d a completely 4-brominated L-Br ligand.