OXYGEN ATOM TRANSFER IN THE REACTION BETWEEN HEXAKIS(DIMETHYL-TERT-BUTYLSILOXY)DITUNGSTEN AND NITRIC-OXIDE - A REMARKABLE DIFFERENCE IN THE REACTIVITY OF THE TUNGSTEN TUNGSTEN TRIPLE BOND AS A FUNCTION OF THE ATTENDANT LIGANDS - BUTO VERSUS BUTME2SIO

The siloxy complex W2(OSiMeBut)6 (I) and NO react in hydrocarbon solvents in the presence of pyridine (py) to give the oxo tungsten compounds W(O)(OSiMe2But)4(py) (II), W2(O)4(OSiMe2BUt)4(py)2 (M) and W(NO)(OSiMe2But)3(py)2 (IV). The relative amounts of the oxo compounds II and III to the nitrosyl complex IV depends upon the reaction temperature with low temperatures (-72-degrees-C) favoring the nitrosyl derivative IV. An intermediate in the reaction is formulated as W2(mu-O)(OSiMe2But)6(py)2 and is formed along with N2O after the coupling of two nitrosyl ligands. The N2O liberated in the reaction is then also active in oxygen atom transfer to yield II and III along with N2. Compounds II, III and IV are inert with respect to further reactions with NO and N2O under the conditions leading to their formation. An alternative synthesis of IV involves the reaction between W(NO)(OBUt)3(py) and ButMe2SiOH (3 equiv.) in the presence of pyridine. Compounds II, III and IV have been characterized by single crystal X-ray crystallography, H-1 and C-13 NMR spectroscopy, IR spectroscopy and elemental analysis. Reactions employing (NO)-N-15-O-18 have been monitored by N-15 NMR spectroscopy and the products analyzed by mass spectrometry and IR spectroscopy. Compound II contains a distorted octahedral geometry about tungsten with trans oxo and pyridine ligands: W=O = 1.68(1), W-O(siloxide) = 1.90(1) (av.), W-N = 2.44(1) angstrom. Compound III involves an edge-shared bioctahedron with terminal and bridging oxo ligands: W-O(oxo) = 1.72(1), W-mu-oxo = 1.95(1) (av.), W-O(siloxide) = 1.89(1) (av.) and W-N = 2.42(1) angstrom. Compound IV is pseudo-octahedral with trans nitrosyl and pyridine ligands: W-N(nitrosyl) = 1.74(1), W-N(pyridine-trans) = 2.34(1), W-N(pyridine-cis) = 2.29(1), W-0 = 1.59(1) (av.) angstrom. A derivative of the intermediate W2(mu-O)(OSiMe2But)6(py)2 was characterized by X-ray crystallography as W2(mu-O)(mu-OBut)(OSiMe2But)5(py)2 (V). Compound V contains bridging oxo and t-butoxide ligands that span a formal tungsten-tungsten double bond, W-W = 2.488(1) angstrom. In contrast to the above Mo2(OSiMe2But)6 (VI) (made by the addition of ButMe2SiOH (6 equiv.) to Mo2(OBut)6) and NO (>2 equiv.) react in hydrocarbon solutions to give [Mo(NO)(OSiMe2But)3]2 (VII), an analogue of the previously structurally characterized compound [Mo(NO)(OBut)3]2 that contains a centrosymmetric (ON)(O2M(mu-O)2MO2(NO) skeleton with a linear M-N-O moiety and no M---M bond. Crystallographic data for the compounds: II: space group P1BAR, a = 17.414(5), b =22.679(7), c = 11.519(3) angstrom, alpha = 99.77(2), beta = 102.15(2), gamma = 108.13(1)-degrees, V = 4089.00 angstrom3 , Z = 4; III: space group P1BAR, a = 10.708(3), b = 12.469(4), c = 10.185(3) angstrom, alpha = 107.44(1), beta = 111.56(1), gamma = 90.53(2)-degrees, V = 1195.75 angstrom3, Z = 1; IV: space group P2(1)/c, a = 14.049(3), b = 10.832(2), c = 24.807(5) angstrom, beta = 102.00(1)-degrees, V = 3692.74 angstrom3, Z = 4; V: space group P1BAR, a = 14.881(3), b = 17.245(3), c = 12.830 angstrom, alpha = 91.20(1), beta = 102.23(1), gamma = 76.34(1)-degrees, V = 3125.26 angstrom3, Z = 2.