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

Abstract

Cp*W(NO)(CH 2 CMe 3 )(η 3 -CH 2 CHCMe 2 ) (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)(CH 3 )(η 3 -CH 2 CHCMe 2 ) (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−CH 3 linkage of 2 and formation of the yellow acyl complex Cp*W(NO)(C(O)CH 3 )(η 3 -CH 2 CHCMe 2 ) (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 η 2 -unsaturated-ketone complexes Cp*W(NO)(CO)(η 2 -Me 2 CCHCH 2 C(O)CH 3 ) (6a) and Cp*W(NO)(CO)(η 2 -H 2 CCHCMe 2 C(O)CH 3 ) (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-5methylhex-3-en-2-one (9c) in a 92:5:3 ratio. Similarly, maintaining an Et 2 O 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)Cl 2 , which in turn is cleanly obtained by treatment of 8 with PCl 5 . 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. ■ RESULTS AND DISCUSSIONModified Synthesis of Complex 1. Compound 1 is best synthesized via a modification of the published procedure, 4

Allyl Complexes of Tungsten from the Rearrangement of Transient Cyclopropyl Precursors

“…Inspired by the remarkable achievements of the Legzdins group in the area of CH bond activation with group 6 organometallics of the type [Cp′M(NO)RR′] (Cp′ = a substituted cyclopentadienyl ligand; M = Mo, W; R, R′ = hydrocarbyl ligands),, many of them occurring through the β‐H abstraction/1,3‐CH bond activation sequence, we initiated a study aimed at extending our work to this organometallic platform. In a preliminary account, we reported that while the cyclopropyl complex [Cp*W(NO)( c ‐C 3 H 5 )(CH 2 SiMe 3 )] (Cp* = η 5 ‐C 5 Me 5 ) could be cleanly generated at low temperature, it was thermally unstable with respect to cyclopropyl ring opening such that the β‐H abstraction could not be studied, the isomeric η 3 ‐allyl complex [Cp*W(NO)(η 3 ‐C 3 H 5 )(CH 2 SiMe 3 )] being formed instead.…”

Room temperature olefination of methane with titanium–carbon multiple bonds

“…We were inspired by a few well-defined organometallic complexes that can undergo methyl migration by forming C–C bonds, especially under mild conditions. 4 – 9 Notably, in two examples the methyl moiety was derived from methane as in Cp* 2 Sc(CH 3 ) 8 and Cp*W(NO)(CH 3 )(η 3 -CH 2 CHCMe 2 ). 9 In the case of Sc, Tilley and Sadow reported the catalytic hydromethylation of propene with methane by Cp* 2 Sc(CH 3 ) at room temperature.…”

“…4 – 9 Notably, in two examples the methyl moiety was derived from methane as in Cp* 2 Sc(CH 3 ) 8 and Cp*W(NO)(CH 3 )(η 3 -CH 2 CHCMe 2 ). 9 In the case of Sc, Tilley and Sadow reported the catalytic hydromethylation of propene with methane by Cp* 2 Sc(CH 3 ) at room temperature. 8 This process requires σ-bond metathesis, migratory insertion of an olefin such as propene, and finally σ-bond metathesis again to form a homologation product according to the reaction CH 4 + H 2 C CHCH 3 → H 3 CCH(CH 3 ) 2 .…”

“…More recently, Legzdins and co-workers found that addition of CO under high pressure to Cp*W(NO)(CH 3 )(η 3 -CH 2 CHCMe 2 ), a species derived from methane activation, could result in insertion into the methyl ligand ultimately leading to extrusion of a mixture of β,γ-unsaturated ketones. 9 …”

Terminal Mo Carbide and Carbyne Reactivity: H2 Cleavage, B–C Bond Activation, and C–C Coupling

“…Improved understanding can lead to rationally tuned catalysts, greater selectivity toward desired products, and, importantly, reduced cost . Toward this end, discrete organometallic model systems have been investigated as a means of parsing the elementary steps of C–O bond cleavage, C–C coupling, and hydrogenation. − Of these, complexes with multiply bonded ligands including terminal carbides, alkylidynes, and alkylidenes remain of interest, as these have been invoked as intermediates of hydrogenation and oligomerization to catenated products. , While the C–C coupling of alkylidyne and alkylidene complexes has been extensively studied, ,− the reactivity of carbides remains much more poorly understood, likely owing to the rarity of these structures, particularly the more reactive terminal examples. − Still, terminal carbides have strong potential for the development of new catalytic methodologies owing to their steric accessibility and reactivity.…”