Intermolecular C–H Activations of Hydrocarbons Initiated by a Tungsten Trimethylsilylallyl Complex

Abstract

Thermolysis of Cp*W(NO)(Npt)(η3-CH2CHCHSiMe3) [Cp* = η5-C5Me5; Npt = CH2CMe3] at 55 °C leads to the loss of neopentane and the formation of the 16-electron η2-allene intermediate Cp*W(NO)(η2-CH2═C═CHSiMe3), which activates hydrocarbons at their methyl groups. In the case of linear alkanes, only terminal C–H activation occurs. This selectivity persists in the presence of an ether functionality, but not with other oxygen-containing substrates such as aldehydes and alcohols. With these latter substrates, the organometallic complex is oxidized to Cp*W(O)2(Npt). The existence of the allene intermediate has been confirmed by its reaction with PMe3 to form the 18-electron adduct and by its diagnostic reaction with cyclohexene. Carbonylation of Cp*W(NO)(Npt)(η3-CH2CHCHSiMe3) with CO (550 psig) at room temperature results in the clean formation of the corresponding Cp*W(NO)(η1-C(═O)Npt)(η3-CH2CHCHSiMe3) complex, which exists as a mixture of two interconverting isomers differing in their modes of attachment of the ...