Reaction of carbon monoxide with (.eta.5-pentamethylcyclopentadienyl)tetramethyltantalum. Intramolecular reductive coupling of carbon monoxide via an ".eta.2-acetone" intermediate

Wood, C. D.; Schrock, Richard R.

doi:10.1021/ja00512a055

Cited by 63 publications

(44 citation statements)

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“…The formation of acetone was confirmed by both GC—MS (20% yield)3 and isolation of the 2,4-dinitrophenylhydrazone derivative (43% yield). The release of a ketone and formation of a dicarbonyl adduct suggest analogies with previous work on dialkyl metallocenes of the group 4 triad4 and on η 2 -acetone complexes in group 5 systems 5,6…”

supporting

confidence: 78%

An Unusally Diverse Array of Products Formed upon Carbonylation of a Dialkylniobium Complex

et al. 2008

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The clean, efficient utilization of carbon monoxide as a C 1 source continues to represent a significant chemical challenge. Many homogeneous late metal-mediated industrial processes have been developed which center on the utility of well-studied transition metal acyl intermediates. 1 Stoichiometric reactions of carbon monoxide with simple alkyl and dialkylmetal complexes usually lead cleanly to carbonylation products. This is true irrespective of the precise conditions employed, although some substrates may require more forcing conditions (e.g., high temperature or pressure) than others. Through this stoichiometric chemistry, many of the classic primary steps in homogeneous late metal-mediated catalytic organometallic reactions, such as migratory CO insertion, have been identified. Herein we describe the carbonylation reaction of the dimethylniobium complex (BDI)Me 2 Nb(N t Bu) (1, BDI = β-diketiminate), 2 in which the relative amounts of an unusually wide range of products change dramatically in response to very modest changes in reaction conditions. Four different stable products, in which CO insertion takes place coupled with metal reduction, enediolate formation and C-H activation, are formed in these transformations. By careful adjustment of reaction conditions, the majority of these materials have been isolated and fully characterized.On adding 3.0 equiv of CO to a solution of 1 in THF at -72 °C, stirring rapidly for 5 min, then warming directly to room temperature, a brown solution was obtained from which a green product was isolated by crystallization. The products were identified as acetone and the Nb (III) dicarbonyl adduct (BDI)(CO) 2 Nb(N t Bu)(2, 42% isolated yield, Scheme 1), which can be considered to result from transfer of both methyl groups to one CO, followed by the displacement of acetone by two molecules of CO (ν CO (2) = 1988, 1893 cm −1 ). The formation of acetone was confirmed by both GC-MS (20% yield) 3 and isolation of the 2,4-dinitrophenylhydrazone derivative (43% yield). The release of a ketone and formation of a dicarbonyl adduct suggest analogies with previous work on dialkyl metallocenes of the group 4 triad 4 and on η 2 -acetone complexes in group 5 systems. 5,6The outcome of the reaction of 1 with CO may be altered dramatically by using pentane as the solvent in place of THF and by allowing the reaction mixture to remain at -72 °C for 2 h prior to warming to room temperature. In so doing, a second product may be isolated by crystallization, whose analytical data are consistent with its formulation as the enediolate species (BDI iPr )(Me 2 C 2 O 2 )Nb(N t Bu) (3, 54% yield, Scheme 1), presumably formed via the intramolecular coupling of two Nb-acyl fragments, 7-10 though other mechanisms cannot be ruled out. NMR spectral analysis of the crude reaction mixture indicates that the product distribution has inverted from 4:1 mixtures of 2:3 obtained when THF is used as the solvent to 1:4 mixtures of 2:3 obtained when pentane is used and longer reaction times are employed.Correspondenc...

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confidence: 78%

An Unusally Diverse Array of Products Formed upon Carbonylation of a Dialkylniobium Complex

et al. 2008

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“…Additionally, the two methylene proton resonances appear at distinct chemical shifts: a doublet at 3.02 ppm ( 3 J = 3.3 Hz) and a singlet at 3.94 ppm, both integrating to one proton. Cross-peaks between these proton signals and the methylene carbon resonance were observed in a 1 H− 13 C HSQC NMR spectrum of 7 (Figure S33).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…In the realm of Ta carbonylation chemistry, Schrock and co-workers first reported this reactivity pattern in 1979: Ta(η 5 -Cp*)Me 4 reacted with one equivalent of CO to form the η 2 -acetone complex Ta(η 5 -Cp*)(OCMe 2 )Me 2 . 13 This complex reacted with a further equivalent of CO to produce a mixture of oxo-bridged oligomeric Ta(V) species containing one enolate ligand per Ta center. Neither the η 2acetone complex nor the oligomeric products were crystallographically characterized.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…6,7 If more than one alkyl group is present on the transition metal center, successive methyl transfers can be observed, yielding products containing more than one new C−C bond. 8,9 Using this strategy, a wide array of C 2 −C n products can be accessed under mild conditions, including ketones, 9 enediols, 10−12 enols, 13,14 alcohols, 10 and ketenes, 15 depending on the number and nature of alkyl groups, the metal center, and reaction conditions that are employed.…”

Section: ■ Introductionmentioning

confidence: 99%

“…We focused on Ta, as a few prior studies of Ta alkyl systems have demonstrated the ability of more than two methyl groups to react with CO, yielding oligomeric enolate-containing products. 13,14 These reports invariably use a Cp* (Cp* = pentamethylcyclopentadienyl) ligand to support the Ta metal center. In the present study, we forego Cp* in favor of a bidentate N-heterocyclic carbene (NHC) ligand.…”

Section: ■ Introductionmentioning

confidence: 99%

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A Diverse Array of C–C Bonds Formed at a Tantalum Metal Center

et al. 2021

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We demonstrate the formation of a diverse array of organic and organometallic products containing newly formed C−C bonds via successive methyl transfers from di-, tri-, and tetramethyl Ta(V) precursors to unsaturated small molecule substrates under mild conditions. The reactions of Ta(V) methyl complexes 1−X [H 2 B( Mes Im) 2 ]TaMe 3 X (X = Me, Cl; Im = imidazole, Mes = 2,4,6trimethylphenyl) with CO led to oxo enolate Ta(V) products, in which the enolate ligands were constructed from Ta-Me groups and two equivalents of CO. Similarly, the reaction of 1-Me with CNXyl yielded an imido enamine Ta(V) product. Surprisingly, 1-Cl reacted with CNXyl (1 equiv) at the borate backbone of the [H 2 B( Mes Im) 2 ] ligand with concomitant methyl transfer from the metal center to form a new, dianionic scorpionate ligand that supported a Ta(V) dimethyl chloro complex (6). Treatment of 1-Cl with further CNXyl led to an azaallyl scorpionate complex, and an imido isocyanide scorpionate complex, along with propene and xylyl ketenimine. Complex 6 reacted with CO to yield a pinacol scorpionate complex 10a new reaction pathway in early transition metal chemistry. Mechanistic studies revealed that this proceeded via migratory insertion of CO into a Ta-Me group, followed by methyl transfer to form an η 2 -acetone intermediate. Elimination of acetone furnished a CO-stabilized Ta(III) intermediate capable of rebinding and subsequently coupling two equivalents of CO-derived acetone to form the pinacol ligand in 10.

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Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium- and -tantalum Complexes − X-ray Structure of [TaCp*Cl2(CH2CMe2Ph){η2-C(CH2CMe2Ph)=N(2,6-Me2C6H3)}] and Unexpected Decomposition of Alkyldichloro(η2-iminoacyl) Complexes of Tantalum

Castro

Galakhov

Gómez

et al. 2000

Eur. J. Inorg. Chem.

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Reaction of carbon monoxide with (.eta.5-pentamethylcyclopentadienyl)tetramethyltantalum. Intramolecular reductive coupling of carbon monoxide via an ".eta.2-acetone" intermediate

Cited by 63 publications

References 1 publication

An Unusally Diverse Array of Products Formed upon Carbonylation of a Dialkylniobium Complex

An Unusally Diverse Array of Products Formed upon Carbonylation of a Dialkylniobium Complex

A Diverse Array of C–C Bonds Formed at a Tantalum Metal Center

Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium- and -tantalum Complexes − X-ray Structure of [TaCp*Cl2(CH2CMe2Ph){η2-C(CH2CMe2Ph)=N(2,6-Me2C6H3)}] and Unexpected Decomposition of Alkyldichloro(η2-iminoacyl) Complexes of Tantalum

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