Functionalization of Methane Initiated by Cp*W(NO)(CH2CMe3)(η3‑CH2CHCMe2)

Cp*W­(NO)­(CH2CMe3)­(η3-CH2CHCMe2) (1) initiates a stepwise conversion of methane into unsymmetrical unsaturated ketones. The first step involves the activation of methane by 1 in cyclohexane to form Cp*W­(NO)­(CH3)­(η3-CH2CHCMe2) (2) in good yield as a mixture of two isomers that differ with respect to the exo/endo orientation of their allyl ligands. Subsequent exposure of a cyclohexane solution of 2 to 500 psig of CO pressure and 75 °C for 3 h results in the 1,1-insertion of CO into the W–CH3 linkage of 2 and formation of the yellow acyl complex Cp*W­(NO)­(C­(O)­CH3)­(η3-CH2CHCMe2) (5). Additional carbonylation of 2 can be effected by maintaining the cyclohexane solution at 750 psig of CO pressure and 75 °C for 3 days, a process that results in the formation of the isomeric η2-unsaturated-ketone complexes Cp*W­(NO)­(CO)­(η2-Me2CCHCH2C­(O)­CH3) (6a) and Cp*W­(NO)­(CO)­(η2-H2CCHCMe2C­(O)­CH3) (6b) in a 60:40 ratio. Finally, exposure of 2 to CO under more forcing conditions (1000 psig at 170 °C for 3 days) produces Cp*W­(NO)­(CO)2 (8) and the isomeric β,γ-unsaturated ketones 5-methylhex-4-en-2-one (9a), 3,3-dimethylpent-4-en-2-one (9b), and trans-5-methylhex-3-en-2-one (9c) in a 92:5:3 ratio. Similarly, maintaining an Et2O solution of 1 at 1000 psig of CO and 170 °C for 3 days results in the complete conversion of 1 into 8 and liberates 2,2,7-trimethyloct-6-en-4-one (10). The final organometallic complex, 8, can be reconverted into the initial reactant 1 via Cp*W­(NO)­Cl2, which in turn is cleanly obtained by treatment of 8 with PCl5. All new compounds have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of five of them have been established by single-crystal X-ray crystallographic analyses.