The functionalization of methane and other hydrocarbons mediated by organometallic nitrosyl complexes of tungsten

The novel family of Cp*W(NO)(H)(η³-allyl) complexes has been synthesized and characterized. Upon thermolysis these compounds generate 16e Cp*W(NO)(η²-alkene) intermediate complexes that have been trapped as their corresponding 18e PMe₃ adducts. In neat alkane solutions, these Cp*W(NO)(η²-alkene) compounds effect three successive C-H activations of the alkane to produce a new Cp*W(NO)(H)(η³-allyl) complex in which the allyl ligand is derived from the alkane solvent. In the presence of CO, the Cp*W(NO)(H)(η³-allyl) complexes effect the regiospecific generation of saturated unsymmetrical ketones from hydrocarbons and CO gas via C-H activation and the formation of two new C-C bonds. For instance, the complex Cp*W(NO)(H)(η³-CH₂CHCMe₂) effects the conversion of benzene and mesitylene into the ketones 4-methyl-1-phenylpentan-1-one and 1-(3,5-dimethylphenyl)-5-methylhexan-2-one, respectively. The organometallic product of these reactions is Cp*W(NO)(CO)₂ which can be converted into the Cp*W(NO)(H)(η³-allyl) reactant in three steps, thereby completing a complete cycle with respect to tungsten. The conversion of methane into the β,γ-unsaturated ketone, 5-methylhex-4-en-2-one, is initiated by the complex Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂). In a cyclohexane solution, the complex effects the C-H activation of methane to produce Cp*W(NO)(CH₃)(η³-CH₂CHCMe₂) which has been fully characterized. Under CO pressure, the methyl ligand is converted into an acyl ligand in Cp*W(NO)(C(=O)CH₃)(η³-CH₂CHCMe₂), and then the acyl and allyl ligands couple to give Cp*W(NO)(CO)(η²-CH₂=CHCMe₂C(=O)CH₃) which contains an η²-bound ketone ligand. Finally, the ketone is released at 170 °C under CO pressure and Cp*W(NO)(CO)₂ is obtained which again can be converted back into the starting organometallic compound. Each of these organometallic complexes has been isolated and fully characterized, thereby allowing the stepwise transformation of methane through C-H activation and C-C bond-forming reactions to be definitively established. In a similar fashion, the complex Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) converts methane and ethane to the corresponding η²-bound ketone complexes, Cp*W(NO)(CO)(η²-PhCH=CHCH₂C(=O)CH₃) and Cp*W(NO)(CO)(η²-PhCH=CHCH₂C(=O)Et). The Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) complex also effects the terminal C-H activation of other alkanes and heteroatom-containing hydrocarbons. The carbonylation of ligands derived from a long-chain alkane and ether has been performed. In addition, the activation of methane, ethane, and propane has been optimized for the compound Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCHMe). Finally, the bound ketone ligands of complexes Cp*W(NO)(CO)(η²-PhCH=CHCH₂C(=O)(alkyl)) have been photolytically released as the cis and trans β,γ-unsaturated ketone products.Science, Faculty ofChemistry, Department ofGraduat

Insights into the Intermolecular C–H Activations of Hydrocarbons Initiated by Cp*W(NO)(η³‑allyl)(CH₂CMe₃) Complexes

Thermolyses of 18e Cp*W­(NO)­(η³-allyl)­(CH₂CMe₃) compounds (Cp* = η⁵-C₅Me₅) result in the intramolecular elimination of CMe₄ and the formation of 16e η²-diene and/or η²-allene intermediate complexes that effect a variety of intermolecular C–H activations of hydrocarbons. The outcomes of the reactions of the Cp*W­(NO)­(η³-allyl)­(CH₂CMe₃) compounds with both C­(sp³)–H and C­(sp²)–H bonds of hydrocarbons are dependent on the natures of the allyl ligands in ways that are not immediately obvious. In an effort to better understand the different selectivities of the various C–H activation processes, we have examined several of these transformations by DFT calculations. The results of these computational investigations have provided several interesting and useful insights into the mechanistic pathways involved. Specifically, they have established that geminal dialkyl substituents on the allyl ligands markedly stabilize the η²-allene intermediate complexes, whereas the absence of such substituents favors the formation of the η²-diene complexes. In the case of the analogous molybdenum systems, the η²-diene intermediate complexes undergo rapid isomerization to the η⁴-diene complexes and do not effect intermolecular C–H activations. In some instances involving the tungsten complexes, the initially formed η¹-hydrocarbyl product (which may or may not be isolable) isomerizes by intramolecular exchange of the newly formed hydrocarbyl ligand with a hydrogen atom on the allyl ligand or undergoes additional C–H activations and is converted to a new hydrido allyl compound. DFT methods indicate that a plausible mechanism for the latter transformation involves a β-hydrogen abstraction from the lateral alkyl chain by the allyl ligand. The rate-determining step of this process is thus the formation of a 16e η²-olefin complex with the olefin originating from the alkyl chain, and this process should be favored by relatively electron-rich Cp*W­(NO)­(η³-allyl)­(<i>n</i>-alkyl) complexes, as is experimentally observed. In all cases of benzene C­(sp²)–H activations by the tungsten systems, the η²-allene intermediate complexes exhibit better reactivity than the η²-diene intermediates. However, theoretical considerations indicate that the stereochemical properties of the first-formed Cp*W­(NO)­(η³-allyl)­(Ph) products determine their differing thermal stabilities. If the aryl–allyl coupling product, Cp*W­(NO)­(η²-allyl-Ph), contains an activatable C–H bond close to the tungsten center, then the thermodynamically favored intramolecular exchange of the phenyl ligand with a hydrogen atom on the allyl ligand occurs. Otherwise, it does not, and the Cp*W­(NO)­(η³-allyl)­(Ph) complexes persist

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

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

Effects of the η⁵‑C₅H₄^<i>i</i>Pr Ligand on the Properties Exhibited by Its Tungsten Nitrosyl Complexes

Reaction of Na­[η⁵-C₅H₄^<i>i</i>Pr] with W­(CO)₆ in refluxing THF for 4 days generates a solution of Na­[(η⁵-C₅H₄^<i>i</i>Pr)­W­(CO)₃] that when treated with <i>N</i>-methyl-<i>N</i>-nitroso-<i>p</i>-toluenesulfonamide at ambient temperatures affords (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(CO)₂ (<b>1</b>) that is isolable in good yield as an analytically pure orange oil. Treatment of <b>1</b> with an equimolar amount of I₂ in Et₂O at ambient temperatures affords (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­I₂ (<b>2</b>) as a dark brown solid in excellent yield. Sequential treatment at low temperatures of <b>2</b> with 0.5 equiv of Mg­(CH₂CMe₃)₂ and Mg­(CH₂CHCMe₂)₂ in Et₂O produces the alkyl allyl complex, (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(CH₂CMe₃)­(η³-CH₂CHCMe₂) (<b>3</b>), as a thermally sensitive yellow liquid. Complex <b>3</b> may also be synthesized, albeit in low yield, in one vessel at low temperatures by reacting <b>1</b> first with 1 equiv of PCl₅ and then with the binary magnesium reagents specified above. Interestingly, similar treatment of <b>1</b> in Et₂O with PCl₅ and only 0.5 equiv of Mg­(CH₂CHCMe₂)₂ results in the formation of the unusual complex (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(PCl₂CMe₂CHCH₂)­Cl₂ (<b>4</b>), which probably is formed via a metathesis reaction of the binary magnesium reagent with (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(PCl₃)­Cl₂. The C–D activation of C₆D₆ by complex <b>3</b> has been investigated and compared to that exhibited by its η⁵-C₅Me₅, η⁵-C₅Me₄H, and η⁵-C₅Me₄^<i>n</i>Pr analogues. Kinetic analyses of the various activations have established that the presence of the η⁵-C₅H₄^<i>i</i>Pr ligand significantly increases the rate of the reaction, an outcome that can be attributed to a combination of steric and electronic factors. In addition, mechanistic studies have established that in solution <b>3</b> loses neopentane under ambient conditions to generate exclusively the 16e η²-diene intermediate complex (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(η²-CH₂CMeCHCH₂), which then effects the subsequent C–D activations. This behavior contrasts with that exhibited by the η⁵-C₅Me₅ analogue of <b>3</b> which forms both η²-diene and η²-allene intermediates upon thermolysis. Sixteen-electron (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(η²-CH₂CMeCHCH₂) has been isolated as its 18e PMe₃ adduct. All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two of them have been established by single-crystal X-ray crystallographic analyses

Effects of the η⁵‑C₅H₄^<i>i</i>Pr Ligand on the Properties Exhibited by Its Tungsten Nitrosyl Complexes

Reaction of Na­[η⁵-C₅H₄^<i>i</i>Pr] with W­(CO)₆ in refluxing THF for 4 days generates a solution of Na­[(η⁵-C₅H₄^<i>i</i>Pr)­W­(CO)₃] that when treated with <i>N</i>-methyl-<i>N</i>-nitroso-<i>p</i>-toluenesulfonamide at ambient temperatures affords (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(CO)₂ (<b>1</b>) that is isolable in good yield as an analytically pure orange oil. Treatment of <b>1</b> with an equimolar amount of I₂ in Et₂O at ambient temperatures affords (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­I₂ (<b>2</b>) as a dark brown solid in excellent yield. Sequential treatment at low temperatures of <b>2</b> with 0.5 equiv of Mg­(CH₂CMe₃)₂ and Mg­(CH₂CHCMe₂)₂ in Et₂O produces the alkyl allyl complex, (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(CH₂CMe₃)­(η³-CH₂CHCMe₂) (<b>3</b>), as a thermally sensitive yellow liquid. Complex <b>3</b> may also be synthesized, albeit in low yield, in one vessel at low temperatures by reacting <b>1</b> first with 1 equiv of PCl₅ and then with the binary magnesium reagents specified above. Interestingly, similar treatment of <b>1</b> in Et₂O with PCl₅ and only 0.5 equiv of Mg­(CH₂CHCMe₂)₂ results in the formation of the unusual complex (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(PCl₂CMe₂CHCH₂)­Cl₂ (<b>4</b>), which probably is formed via a metathesis reaction of the binary magnesium reagent with (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(PCl₃)­Cl₂. The C–D activation of C₆D₆ by complex <b>3</b> has been investigated and compared to that exhibited by its η⁵-C₅Me₅, η⁵-C₅Me₄H, and η⁵-C₅Me₄^<i>n</i>Pr analogues. Kinetic analyses of the various activations have established that the presence of the η⁵-C₅H₄^<i>i</i>Pr ligand significantly increases the rate of the reaction, an outcome that can be attributed to a combination of steric and electronic factors. In addition, mechanistic studies have established that in solution <b>3</b> loses neopentane under ambient conditions to generate exclusively the 16e η²-diene intermediate complex (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(η²-CH₂CMeCHCH₂), which then effects the subsequent C–D activations. This behavior contrasts with that exhibited by the η⁵-C₅Me₅ analogue of <b>3</b> which forms both η²-diene and η²-allene intermediates upon thermolysis. Sixteen-electron (η⁵-C₅H₄^<i>i</i>Pr)­W­(NO)­(η²-CH₂CMeCHCH₂) has been isolated as its 18e PMe₃ adduct. All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two of them have been established by single-crystal X-ray crystallographic analyses

Selective Functionalization of a Variety of Hydrocarbon C(sp³)–H Bonds Initiated by Cp*W(NO)(CH₂CMe₃)(η³‑CH₂CHCHPh)

Cp*W­(NO)­(CH₂CMe₃)­(η³-CH₂CHCHPh) (<b>1</b>) effects C­(sp³)–H activations of methane, ethane, propane, and <i>n</i>-butane exclusively at their terminal carbons and forms the corresponding Cp*W­(NO)­(alkyl)­(η³-CH₂CHCHPh) complexes. It also activates (<i>n</i>-Bu)₂O, 1-chloropropane, and Me₄Si in a similar manner. Exposure of the Cp*W­(NO)­(alkyl)­(η³-CH₂CHCHPh) complexes to carbon monoxide results in initial 1,1-CO insertion into the newly formed tungsten–alkyl bonds and formation of the corresponding η¹-acyl complexes, some of which can be isolated. Additional functionalization of the C–H activation products occurs upon exposure to CO under more forcing conditions. Such treatment produces η²-bound unsaturated-ketone complexes resulting from CO insertion into the W–alkyl σ bonds followed by cross-coupling of the η¹-acyl and the η³-allyl ligands and coordination of CO at the resulting vacant coordination site at tungsten. The unsaturated ketones can be released from the metal’s coordination spheres either by photolysis of the complexes in MeCN or by further exposure of them to CO. All new compounds have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of six of them have been established by single-crystal X-ray crystallographic analyses

Unsymmetrical Saturated Ketones Resulting from Activations of Hydrocarbon C(sp³)–H and C(sp²)–H Bonds Effected by Cp*W(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) (<b>1</b>), Cp*W­(NO)­(H)­(η³-CH₂CHCHMe) (<b>2</b>), and Cp*W­(NO)­(H)­(η³-CH₂CHCHPh) (<b>3</b>) (Cp* = η⁵-C₅Me₅). These activations are regiospecific and afford in the case of complex <b>1</b> good yields of the unsymmetrical saturated ketones 4-methyl-1-phenylpentan-1-one (<b>5</b>) and 1-(3,5-dimethylphenyl)-5-methylhexan-2-one (<b>8</b>), respectively, in which the alkyl groups result from hydrogenation of the allyl ligand in the organometallic reactant. Complex <b>2</b> reacts similarly, but complex <b>3</b> 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 <b>1</b> and <b>3</b>, respectively, have been trapped as the corresponding 18e CO adducts Cp*W­(NO) (CO)­(η²-CH₂CHCHMe₂) (<b>10</b>) and Cp*W­(NO) (CO)­(η²-MeCHCHPh) (<b>11</b>). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two isomers of <b>11</b> 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 (<b>4</b>) is the final organometallic product formed in all cases, and it can be readily reconverted to the hydrido allyl reactants <b>1</b>–<b>3</b> in three steps via Cp*W­(NO)­Cl₂

Thermal Chemistry of Cp*W(NO)(H)(η³‑allyl) Complexes

The thermal properties of Cp*W­(NO)­(H)­(η³-CH₂CHCMe₂) (<b>1</b>), Cp*W­(NO)­(H)­(η³-CH₂CHCHPh) (<b>2</b>), and Cp*W­(NO)­(H)­(η³-CH₂CHCHMe) (<b>3</b>) (Cp* = η⁵-C₅Me₅) have been investigated. Thermolyses of <b>1</b>–<b>3</b> in <i>n</i>-pentane lead to the loss of the original allyl ligand and the formation of the same mixture of isomeric products, namely, Cp*W­(NO)­(H)­(η³-CH₂CHCHEt) (<b>4a</b>) and Cp*W­(NO)­(H)­(η³-MeCHCHCHMe) (<b>4b</b>) and their coordination isomers. Similarly, <b>1</b> reacts with cyclohexane and <i>n</i>-heptane to form Cp*W­(NO)­(H)­(η³-C₆H₉) and isomers of Cp*W­(NO)­(H)­(η³-C₇H₁₃), respectively. It is likely that complexes <b>1</b>–<b>3</b> first effect the selective, single-terminal C–H activation of the linear alkanes, but the first-formed products are thermally unstable and undergo two additional successive C–H activations to form the final allyl complexes. Consistent with this view is the fact that a bis­(alkyl) intermediate complex can be trapped with <i>N</i>-methylmorpholine. Thus, the thermolysis of <b>1</b> in <i>N</i>-methylmorpholine affords a single organometallic complex, Cp*W­(NO)­(η²-CH₂NC₄H₈O)­(η¹-CH₂CH₂CHMe₂) (<b>7</b>). Complexes <b>2</b> and <b>3</b> react with <i>N</i>-methylmorpholine in an identical manner. Finally, <b>1</b> effects the multiple C–H activations of 1-chloropropane and 1-chlorobutane and forms the corresponding Cp*W­(NO)­(Cl)­(η³-allyl) complexes. All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses

Synthesis, Characterization, and Some Properties of Cp*W(NO)(H)(η³‑allyl) Complexes

Sequential treatment at low temperatures of Cp*W­(NO)­Cl₂ in THF with 1 equiv of a binary magnesium allyl reagent, followed by an excess of LiBH₄, affords three new Cp*W­(NO)­(H)­(η³-allyl) complexes, namely, Cp*W­(NO)­(H)­(η³-CH₂CHCMe₂) (<b>1</b>), Cp*W­(NO)­(H)­(η³-CH₂CHCHPh) (<b>2</b>), and Cp*W­(NO)­(H)­(η³-CH₂CHCHMe) (<b>3</b>). Complexes <b>1</b>–<b>3</b> are isolable as air-stable, analytically pure yellow solids in good to moderate yields by chromatography or fractional crystallization. In solutions, complex <b>1</b> exists as two coordination isomers in an 83:17 ratio differing with respect to the <i>endo</i>/<i>exo</i> orientation of the allyl ligand. In contrast, complexes <b>2</b> and <b>3</b> each exist as four coordination isomers, all differing by the orientation of their allyl ligands which can have either an <i>endo</i> or an <i>exo</i> orientation with the phenyl or methyl groups being either proximal or distal to the nitrosyl ligand. A DFT computational analysis using the major isomer of Cp*W­(NO)­(H)­(η³-CH₂CHCHMe) (<b>3a</b>) as the model complex has revealed that its lowest-energy thermal-decomposition pathway involves the intramolecular isomerization of <b>3a</b> to the 16e η²-alkene complex, Cp*W­(NO)­(η²-CH₂CHCH₂Me). Such η²-alkene complexes are isolable as their 18e PMe₃ adducts when compounds <b>1</b>–<b>3</b> are thermolyzed in neat PMe₃, the other organometallic products formed during these thermolyses being Cp*W­(NO)­(PMe₃)₂ (<b>5</b>) and, occasionally, Cp*W­(NO)­(H)­(η¹-allyl)­(PMe₃). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses