| Abstract
| - Activation of hydrocarbons, RH, by trans-Cp*W(NO)(CH2EMe3)(H)(PMe3) (E = C, Si) complexes under ambient conditions produces cis-Cp*W(NO)(R)(H)(PMe3) compounds, the particular case of benzene activation being illustrated. Kinetic, mechanistic, and theoretical investigations of these benzene C−H activation processes are consistent with initial trans to cis isomerization of the reactants followed by intramolecular reductive elimination of EMe4 to form the 16-electron Cp*W(NO)(PMe3) intermediate, which subsequently oxidatively adds the incoming benzene.
- trans-Cp*W(NO)(CH2EMe3)(H)(PMe3) (E = C, Si) complexes can be prepared by thehydrogenation at 1 atm of the appropriate Cp*W(NO)(CH2EMe3)2 precursor in the presenceof a slight excess of PMe3. (Our designation of a particular geometrical isomer as cis ortrans in this family of complexes indicates the relative positions of the hydrocarbyl and thehydrido ligands in the base of a four-legged piano-stool molecular structure.) The use of D2in place of H2 during these syntheses affords the corresponding trans-Cp*W(NO)(CH2EMe3)(D)(PMe3) (E = C, Si) complexes. The cis-Cp*W(NO)(CH2EMe3)(H)(PMe3) isomers areobtainable by C−H bond-activation reactions of the trans precursors. Thus, activation ofSiMe4 by trans-Cp*W(NO)(CH2CMe3)(H)(PMe3) under ambient conditions produces cis-Cp*W(NO)(CH2SiMe3)(H)(PMe3). Similarly, activations of C6H6 and C6D6 at 20−27 °C by the trans-Cp*W(NO)(CH2EMe3)(H)(PMe3) complexes produce cis-Cp*W(NO)(C6H5)(H)(PMe3) and cis-Cp*W(NO)(C6D5)(D)(PMe3), respectively, and the solid-state molecular structure of the lattercomplex has been established by a single-crystal X-ray crystallographic analysis. Kinetic,mechanistic, and theoretical investigations of these benzene C−H activation processes areconsistent with initial trans to cis isomerization of the reactants followed by intramolecularreductive elimination of EMe4 to form the 16-electron Cp*W(NO)(PMe3) intermediate.Subsequent oxidative addition of the incoming benzene substrate to this coordinativelyunsaturated intermediate produces the final cis hydrido phenyl complex. These single C−Hactivation processes are the requisite first steps in the development of these organometalliccomplexes as catalysts for the selective functionalization of hydrocarbons. All new complexeshave been characterized by conventional spectroscopic methods.
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