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Synthesis and Reactivity of [Tp‘(CO)(PhC⋮CMe)WNPh]+ (Tp‘ = Hydridotris(3,5-dimethylpyrazolyl)borate)

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journal contribution
posted on 10.06.1997, 00:00 by Laura W. Francisco, Peter S. White, Joseph L. Templeton
The tungsten(IV) nitrene complex [Tp‘(CO)(PhC⋮CMe)WNPh]+ (cation of 1; Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) has been prepared by oxidation of the amido complex Tp‘(CO)(PhC⋮CMe)W(NHPh) (2) with elemental iodine in the presence of triethylamine. Oxidation in the absence of base also forms the aniline complex [Tp‘(CO)(PhC⋮CMe)W(NH2Ph)]+ (3), which has been independently synthesized. Reaction of 1 with 1 equiv of KBH4 adds hydride to the nitrene ligand to give the amido complex 2. Reaction of 1 with Li[HBEt3] forms the formyl adduct Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)H) (4) as an intermediate, which ultimately yields the hydride complex Tp‘(NPh)(PhC⋮CMe)W(H) (5) with loss of CO. The hydride complex is also formed from reaction of 1 with 10 equiv of KBH4. Addition of acid to the hydride complex 5 protonates the nitrene nitrogen to form [Tp‘(H)(PhC⋮CMe)W(NHPh)][BAr‘4] (6). Both 5 and 6 exhibit surprisingly low-field hydride resonances in the 1H NMR (13.5 and 20.6 ppm, respectively). Addition of methylmagnesium bromide to the nitrene complex leads to the methyl acyl intermediate Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)Me) (7), which readily adds a proton and cyclizes to [Tp‘(NHPh)W(C(Ph)C(Me)C(O)Me][BAr‘4] (8). Reaction of 1 with phenyllithium forms the phenyl acyl complex Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)Ph) (9). X-ray crystal structures have been determined for 1 and 8. The ring in complex 8 exhibits a structure similar to a folded envelope, with the flap containing the Cα, W, and O atoms. The ring is bonded in an η4 fashion to the metal center.