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

Cp*W­(NO)­(CH₂CMe₃)­(η³-CH₂CHCMe₂) (<b>1</b>) initiates a stepwise conversion of methane into unsymmetrical unsaturated ketones. The first step involves the activation of methane by <b>1</b> in cyclohexane to form Cp*W­(NO)­(CH₃)­(η³-CH₂CHCMe₂) (<b>2</b>) 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 <b>2</b> 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 <b>2</b> and formation of the yellow acyl complex Cp*W­(NO)­(C­(O)­CH₃)­(η³-CH₂CHCMe₂) (<b>5</b>). Additional carbonylation of <b>2</b> 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) (<b>6a</b>) and Cp*W­(NO)­(CO)­(η²-H₂CCHCMe₂C­(O)­CH₃) (<b>6b</b>) in a 60:40 ratio. Finally, exposure of <b>2</b> to CO under more forcing conditions (1000 psig at 170 °C for 3 days) produces Cp*W­(NO)­(CO)₂ (<b>8</b>) and the isomeric β,γ-unsaturated ketones 5-methylhex-4-en-2-one (<b>9a</b>), 3,3-dimethylpent-4-en-2-one (<b>9b</b>), and <i>trans</i>-5-methylhex-3-en-2-one (<b>9c</b>) in a 92:5:3 ratio. Similarly, maintaining an Et₂O solution of <b>1</b> at 1000 psig of CO and 170 °C for 3 days results in the complete conversion of <b>1</b> into <b>8</b> and liberates 2,2,7-trimethyloct-6-en-4-one (<b>10</b>). The final organometallic complex, <b>8</b>, can be reconverted into the initial reactant <b>1</b> via Cp*W­(NO)­Cl₂, which in turn is cleanly obtained by treatment of <b>8</b> 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