C-H bond activation of hydrocarbons by a tungsten allene complex

Gentle thermolysis of the 18e alkyl-allyl complex, Cp*W(NO)(CH₂CMe₃)(η³-1,1-Me₂C₃H₃) (1.1), generates a reactive 16e allene intermediate, Cp*W(NO)(η²-H₂C=C=CMe₂) (A), by a first-order process with concomitant evolution of neopentane via hydrogen abstraction from the dimethylallyl ligand. Intermediate A has been structurally characterized as its PMe₃ adduct, and is capable of effecting both single and multiple intermolecular C-H bond activations of hydrocarbon solvents to form alkyl-allyl and allyl-hydrido complexes. The products of reactions of A with methyl-substituted arenes (i.e. sp² C-H vs sp³ C-H) indicate an inherent preference for the activation of stronger arene C-H bonds, however steric effects are also relevant as indicated by the exclusive formation of benzylic C-H activation products in mesitylene. Thermolyses of 1.1 in alkane solvents generate products resulting from three successive C-H bond-activation reactions. Preliminary studies suggest that allyl-hydrido complexes are formed along with an organic product; for example, in cyclohexane, 1,1- dimethylpropylcyclohexane results from coupling of a solvent molecule and a fragment derived from the precursor dimethylallyl ligand. The allyl-hydrido complexes have potential synthetic utility, since studies conducted on structurally and electronically related CpMo complexes show that they may be capable of ultimately producing homoallylic alcohols.Science, Faculty ofChemistry, Department ofGraduat