Factors Influencing the Outcomes of Intermolecular C–H Activations of Hydrocarbons Initiated by CpW(NO)(CH₂CMe₃)(η³-allyl) Complexes (Cp = η⁵-C₅Me₅ (Cp*), η⁵-C₅Me₄H (Cp′))

Abstract

Gentle thermolyses of CpW(NO)(CH2CMe3)(η3-allyl) complexes (Cp = η5-C5Me5 (Cp*), η5-C5Me4H (Cp′)) in neat hydrocarbon solutions result in the loss of neopentane from the metal’s coordination spheres and the transient formation of the 16-electron (16e) intermediate species CpW(NO)(η2-allene) and/or CpW(NO)(η2-diene). These transient intermediates can react with hydrocarbon substrates, RH (R = alkyl, aryl), to form three different types of organometallic products. The first products are the desired CpW(NO)(η3-allyl)(η1-R) complexes that result from the selective single activation of a C–H bond of RH. The second class of products involves CpW(NO)(H)[η3-(R)-allyl] complexes that are isomers of the CpW(NO)(η3-allyl)(η1-R) compounds resulting from an intramolecular R/allyl H exchange. Finally, the third type of products contains CpW(NO)(H)[η3-hydrocarbyl] species that result from three successive C–H activations of hydrocarbon substrates such as R′CH2CH2CH3 and loss of the original allyl ligand. Just which organometallic products ultimately result from the reactions of the CpW(NO)(CH2CMe3)(η3-allyl) complexes with hydrocarbons depends on several factors, including the natures of the cyclopentadienyl and allyl ligands, the hydrocarbon substrates themselves, the electron density at the metal centers, and the experimental conditions employed. This article documents these dependences and identifies the optimum CpW(NO)(CH2CMe3)(η3-allyl) compounds and experimental conditions for effecting the selective single C–H bond activations of hydrocarbon substrates such as benzene as a representative arene and methylcyclohexane as a representative alkane. During the course of these investigations all new organometallic complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of several of them have been established by single-crystal X-ray crystallographic analyses.