Thermal Chemistry of a
Tungsten Trimethylsilylallyl
Complex in Benzene and Fluorobenzenes
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Abstract
The thermolysis of Cp*W(NO)(Npt)(η<sup>3</sup>-CH<sub>2</sub>CHCHSiMe<sub>3</sub>) (<b>1</b>; Cp* = η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>; Npt = CH<sub>2</sub>CMe<sub>3</sub>) in benzene
at 55 °C generates three isomeric products having the composition
Cp*W(NO)(H)(η<sup>3</sup>-Me<sub>3</sub>SiCHCHCHPh) (<b>2</b>). These are isomers of the expected Cp*W(NO)(Ph)(η<sup>3</sup>-Me<sub>3</sub>SiCHCHCH<sub>2</sub>) compound and result from an
intramolecular Ph/allyl H exchange. Thermolysis of <b>2</b> in
the presence of pyridine produces the η<sup>2</sup>-olefin pyridine
adduct Cp*W(NO)(η<sup>2</sup>-Me<sub>3</sub>SiCH<sub>2</sub>CHCHPh)(C<sub>5</sub>H<sub>5</sub>N) (<b>3</b>). However,
when the same reaction is carried out in deuterobenzene with 10 equiv
of pyridine, NMR spectroscopic data suggest that the meso hydrogen
of the allyl ligand is exchanged for a deuterium atom before pyridine
trapping occurs. The activation of fluorobenzenes (i.e., pentafluorobenzene, <i>p</i>-difluorobenzene, and <i>o</i>-difluorobenzene)
by Cp*W(NO)(Npt)(η<sup>3</sup>-CH<sub>2</sub>CHCHSiMe<sub>3</sub>) has also been studied, and for these substrates, C–H bond
activation occurs exclusively. Selectivity for the activation of these
C–H bonds appears to be determined by sterics. Intramolecular
migration of the newly formed fluoroaryl ligands onto the allyl ligands
does not occur when there is a fluorine atom in the position ortho
to the newly formed W–C bond. This behavior is probably a manifestation
of the fact that metal–<i>o</i>-fluoroaryl bonds
tend to be stronger than metal–aryl linkages. All new complexes
have been characterized by conventional spectroscopic and analytical
methods, and the solid-state molecular structures of most of them
have been established by single-crystal X-ray crystallographic analyses
