Intermolecular C–H Activations of Hydrocarbons Initiated by Cp*M(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) Complexes (M = Mo, W)

Thermolysis of Cp*W(NO)(CH 2 CMe 3 )(η 3 -CH 2 CHCHPh) ( 1 ) at 55 °C leads to the loss of neopentane and the formation of the 16e η 2 -allene intermediate complex Cp*W(NO)(η 2 -CH 2 ═C═CHPh) ( A ), which has been isolated as its 18e PMe 3 adduct ( 2 ). Further support for the existence of the allene intermediate A is provided by the thermolysis of 1 in cyclohexene, which affords Cp*W(NO)(H)(η 3 -CH 2 C(3-cyclohexenyl)CHPh) ( 3 ) as the principal organometallic product. In the presence of n -heptane, n -octane, or n -pentane, A effects C–H activations of the hydrocarbons exclusively at their terminal carbons and forms 18e Cp*W(NO)( n -alkyl)(η 3 -CH 2 CHCHPh) complexes ( 4 – 6 ). Similarly, treatments of 1 with mesitylene, methylcyclohexane, and ethylcyclohexane all lead to the corresponding primary sp 3 C–H activation products ( 7 – 9 ). Complex mixtures of organometallic products result when 1 is thermolyzed in p -xylene and toluene, reflecting the occurrence of both aryl and benzylic C–H activations. Interestingly, the aryl C–H activations do not afford the expected Cp*W(NO)(aryl)(η 3 -CH 2 CHCHPh) products but rather their Cp*W(NO)(H)[η 3 -CH(aryl)CHCHPh] isomers resulting from aryl–H exchange. The thermal chemistry of the molybdenum analogue of 1, namely Cp*Mo(NO)(CH 2 CMe 3 )(η 3 -CH 2 CHCHPh) ( 14 ), has also been investigated, and it turns out to be much more limited in scope. When 14 is heated at 35 °C in neat mesitylene for 22 h, it results in conversion to the mesitylene-activated product Cp*Mo(NO)(CH 2 C 6 H 3 -3,5-Me 2 )(η 3 -CH 2 CHCHPh) ( 15 ) in low yield, but thermolyses of 14 in other hydrocarbons do not produce tractable organometallic materials. The results of DFT calculations on the model reaction of CpW(NO)(η 2 -CH 2 ═C═CHMe) with propane confirm that the rate-determining step is the cleavage of a propane C–H bond and that the lower energy anti conformers favor terminal activation by 11.5 kJ/mol. 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 X-ray crystallographic analyses.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.