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Nitrosyl hydrides and cations of Group VI transition metals

University of British Columbia

The novel bimetallic hydrides [(n⁵-C₅H₅)W(N0)IH]₂ and [(n⁵-C₅H₅)W(N0)H₂]₂ can be prepared sequentially by the metathesis of [(n⁵-C₅H₅)W(N0)IH₂]₂ with Na[H₂Al(0CH₂CH₂0CH₃)₂]. Analyses of the ¹H NMR spectra of C[(n⁵-C₅H₅)W(N0)IH]₂ and [(n⁵-C₅H₅)W(N0)IH₂]₂ show the former contains hydride ligands bound to tungsten in a terminal fashion, while the latter possesses two terminal and two bridging hydrides. Addition of a Lewis base to [(n⁵-C₅H₅)W(N0)IH]₂ results in the formation of hydride species (n⁵-C₅H₅)W(N0)IHL (L = P(0Ph)₃, P(0Me)₃, PPh₃); in like manner, the dimer [(n⁵-C₅H₅)W(N0)IH₂]₂ is cleaved by triphenylphosphite to form the monomer cis or trans [(n⁵-C₅H₅)W(N0)IH₂[P(0Ph)₃]. A comparison is made of the reactivity of the tungsten-hydrogen link in the nitrosyl hydrides (n⁵-C₅H₅)- W(N0)IH[P(0Ph)₃], (n⁵-C₅H₅)W(N0)₂H, and (n⁵-C₅H₅)W(N0)IH₂[P(0Ph)₃]. The Mo(N0)₂²⁺ unit is obtained as the tetrakis-solvate via chloride abstraction from Mo(N0)₂Cl₂ by AgBF₄ or nitrosylation of Mo(C0)₆ by NOPF₆ in coordinating solvents such as nitromethane, acetonitrile, or tetrahydro-furan. The unsolvated complex [Mo(N0)₂(PF₆)₂][aub=n] is produced if the latter reaction is performed in dichloromethane; however, it readily converts to [Mo(N0)₂S₄](PF₆)₂ upon exposure to coordinating solvents (S). Hard Lewis bases (L = CH₃CN , 0PPh₃ or L₂ = 2 ,2-bipyridine replace the solvent molecules in [Mo(N0)₂S₄]X₂ (X = BF₄⁻, PF₆⁻) forming complexes [Mo(N0)₂L₄]²⁺ or [Mo(N0)₂L₂S₂]²⁺ depending upon the solvent employed. Reagents capable of being oxidized appear to reduce the dinitrosyl dication without permanent coordination to the molybdenum centre. Reduction of [Mo(NO)₂S₄](PF₆)₂ or [Mo(N0)₂(PF₆)₂][sub=b] is effected by sodium amalgam (one equivalent); addition of a ligand L₂ (L₂ = 2,2-bipyridyl, 3,4,7,8-tetramethyl-1,1O-phenanthroline) to the reaction mixture permits the isolation of [M(NO)₂L₂]₂(PF₆)₂. Addition of excess ligand results in the formation of non-nitrosyl containing species [Mp(L₂)₃]PF₆ (L = 0PPh₃ or L₂ = 3,4,7,8-tetramethyl-1 ,10-phenanthro- line). Decomposition of the nitrosyl species results from attempts to reduce [Mo(NO)₂S₄]²⁺ by two electrons. New complexes are identified by the aid of IR and ¹H, ¹⁹F, or ³¹P NMR spectroscopy and conductance measurements. Attempts to prepare thionitrosyl analogues of [Mo(N0)₂L₄]²⁺ have met with limited success; the only wel1-characterized thionitrosyls isolated in this study are the known (n⁵-C₅H₅)Cr(C0)₂NS and the new [(n⁵-C₅H₅)Mo-(N0)(NS)PPh₃]BF₄. Also discussed is the interaction of NOPF₆ with solvents. NOPF₆ has been found to react slowly with acetonitrile, a common solvent for nitro-sonium salts.

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2010-05-02

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http://hdl.handle.net/2429/24339

Chemistry

University of British Columbia

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