Unsymmetrical Saturated Ketones Resulting from Activations of Hydrocarbon C(sp3)–H and C(sp2)–H Bonds Effected by CpW(NO)(H)(η3‑allyl) Complexes

C–H activations of a C­(sp2)–H bond in benzene or a C­(sp3)–H bond in mesitylene at 80 °C under CO pressure in undried solvents without rigorous exclusion of air and moisture can be effected with the 18e complexes Cp*W­(NO)­(H)­(η3-CH2CHCMe2) (1), Cp*W­(NO)­(H)­(η3-CH2CHCHMe) (2), and Cp*W­(NO)­(H)­(η3-CH2CHCHPh) (3) (Cp* = η5-C5Me5). These activations are regiospecific and afford in the case of complex 1 good yields of the unsymmetrical saturated ketones 4-methyl-1-phenylpentan-1-one (5) and 1-(3,5-dimethylphenyl)-5-methylhexan-2-one (8), respectively, in which the alkyl groups result from hydrogenation of the allyl ligand in the organometallic reactant. Complex 2 reacts similarly, but complex 3 only produces the ketone from its reaction with CO in benzene. Theoretical calculations indicate that the key mechanistic feature of these conversions is the formation of a 16e η2-alkene complex which is generated by the regiospecific migration of the hydride ligand onto the tertiary carbon of the allyl ligand. The 16e Cp*W­(NO)­(η2-CH2CHCHMe2) and Cp*W­(NO)­(η2-MeCHCHPh) intermediate complexes formed in this manner by complexes 1 and 3, respectively, have been trapped as the corresponding 18e CO adducts Cp*W­(NO) (CO)­(η2-CH2CHCHMe2) (10) and Cp*W­(NO) (CO)­(η2-MeCHCHPh) (11). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two isomers of 11 have been established by single-crystal X-ray crystallographic analyses. This new and facile method of synthesizing saturated unsymmetrical ketones via C–C bond formation not only is atom economical but also is part of a complete synthetic cycle, since Cp*W­(NO)­(CO)2 (4) is the final organometallic product formed in all cases, and it can be readily reconverted to the hydrido allyl reactants 1–3 in three steps via Cp*W­(NO)­Cl2.