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Hydride, alkyl, and alkenyl complexes of tungsten

University of British Columbia

Hydrogenation of Cp*W(NO)(CH₂SiMe₃)₂ affords the 16-electron alkyl hydride complex, Cp*W(NO)(CH₂SiMe₃)H, as a reactive intermediate. The tungsten-hydride bond of this complex inserts unsaturated reagents such as nitriles, ketones and aldehydes, imines, and acetylenes to form stable products containing azomethine, alkoxide, amide and alkenyl ligands respectively. Hydrogenation of Cp*W(NO)(CH₂SiMe₃)₂ in the presence of dienes results in the formation of Cp*W(NO)(ŋ⁴-trans-diene) species. Hydrogenation in the presence of PPh₃ affords Cp*W(NO)(H)(ŋ²-PPh₂(C₆H₄)). Cp*W(NO)(R)Cl complexes are produced by the reaction of dialkyl- or diarylmagnesium reagents with Cp*W(NO)(Cl)₂. Reaction of Cp*W(NO)(CH₂SiMe₃)CI with (p-tolyl)₂Mg Xdioxane results in the formation of the mixed alkyl aryl complex, Cp*W(NO)(CH₂SiMe₃)(p-tolyl). Cp*W(NO)(CH₂SiMe₃)(NHtBu) is formed by the reaction of excess t-butylamine with the same alkyl chloride compound. The Lewis-base adducts Cp*W(NO)(CH₂SiMe₃)(L)Cl[L=Pme₃, pyridine] are formed upon exposure of Cp*W(NO)(CH₂SiMe₃)CI to PMe₃ or pyridine. Reaction of the PMe₃ adduct with LDA affords the tucked-in Cp* complex, (ŋ⁵, ŋ¹- C₅Me₄CH₂)W(NO)(CH₂CMe₃)(PMe₃). The tungsten-alkyl bond in Cp*W(NO)(CH₂Me₃)CI inserts CO and isonitriles to form ŋ²-acyl and ŋ²-iminoacy1 compounds. Halide abstraction from the alkyl chloride using AgBF₄ in acetonitrile affords the organometallic cation [Cp*W(NO)(CH₂SiMe₃)(NCMe)₂]⁺BF₄⁻ The bimetallic species Cp*W(NO)(CH₂CM₃)]μ-N[Cp*W(0)(CH₂Me₃] is formed upon reduction of the alkyl chloride with zinc, but if the same reaction is performed in the presence of PhSSPh, Cp*W(NO)(CH₂Me₃)Sph isolated. A number ofmixed alkyl and aryl complexes Cp*W(NO)(R)R¹ [R≠R¹,R,R¹=CH₂CMe₃,CH₂SiMe₃, Ch₂Me₂Ph, Ph o-tolyl, Me] have been prepared from Cp*W(NO)(R)Cl species and dialkyl- or diarylmagnesium reagents. These mixed-ligand compounds insert CO into one of their tungsten-carbon a-bonds. By determining which ligands insert preferentially, the relative migratory aptitudes of the ligands can be ranked: CH₂Me₃ > CH₂SiMe₃ > o-tolyl > Ph > Me. Thermolysis of Cp*W(NO)(CH₂CMe₃)Ph in benzene orp-xylene in the presence of PMe₃ causes the formation of Cp*W(NO)(Ph)₂PMe₃ and Cp*W(NO)(Ph)(2, 5-Me₂C₆H₄)PMe3 respectively, via a proposed benzyne intermediate. The proposed mechanism of formation of Cp*W(NO)(H)(ŋ²-PPh₂(C₆H₄)) via hydrogenation of Cp*W(NO)(CH₂SiMe₃)₂ in the presence of PPh₃ involves the formation of the intermediate Cp*W(NO)(CH₂SiMe₃)(H)PPh₃. This species undergoes RH elimination and then metallation of the phosphine ligand to afford the observed product. Addition of PPh₃ to a solution of the metallated complex induces the formation of Cp*W(NO)(PPh₃)₂. Thermolysis of Cp*W(NO)(H)( ŋ²-PPh₂(C₆H₄)) in acetone or acetonitrile affords Cp*W(NO)(PPh₃)(ŋ²-L) species [L = Me₂CO, NCMe]. A kinetic investigation of the acetone addition reaction indicates that the reaction is second order overall, first order in each reactant. Thermolysis of Cp*W(NO)(H)( ŋ²-PPh₂(C₆H₄)) in benzene results in solvent activation to form Cp*W(NO)(PPh₃)(Ph)H. A kinetic isotope effect of 1.9 ± 0.5 has been measured for this activation process. Reaction of Cp*W(NO)(CH₂SiMe₃)C1 with (PhC=CH₂)₂MgXdioxane produces the alkyl alkenyl species, Cp*W(NO)(CH₂SiMe₃)(CPh=CH2) in good yield. Upon thermolysis, this complex loses TMS and activates C-H bonds. Cp*W(NO)(CPhCH₂)Ph is formed when the thermolysis is performed in benzene. Hexanes, pentane, and Et₂0 are also activated to form the compounds Cp*W(NO)(ŋ⁴-CH₂CHRCH₂CHPh) [R = butyl, propyl, OEt respectivelyj. These species contain a metallacyclic ligand that also exhibits an ŋ³-ben.zy1 interaction between the ligand and the metal center. An unsaturated ŋ²-alkyne complex is proposed as an intermediate in these thermal reactions. Thermolysis of Cp*W(NO)(CH₂SIMe₃)(CPh=CH₂) in the presence of PMe3 results in the formation of the metallacyclopropane compound, Cp*W(NO)(CH₂SiMe₃)(ŋ²-C {PMe₃ }PhCH₂).

Thesis/Dissertation

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2009-04-14

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http://hdl.handle.net/2429/7061

Chemistry

University of British Columbia

UBCV

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