Competing Reaction Mechanisms for the Carbonylation of Neutral Palladium(II) Complexes Containing Bidentate Ligands:  A Theoretical Study

Frankcombe, Katrina E.; Cavell, Kingsley J.; Yates, Brian F.; Knott, Robert

doi:10.1021/om970063z

Cited by 31 publications

(17 citation statements)

References 30 publications

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“…At the CCSD(T) level, 2-TS isomztn is 6.1 kcal/mol lower than 2b-TS (Table ). Other isomerization mechanisms might offer even lower barriers, but a more elaborate investigation that would consider, for example, solvent-assisted or dissociative pathways, which do have precedence, , is beyond the scope of the present study.…”

Section: Resultsmentioning

confidence: 98%

Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role oftransInfluence in Determining Agostic Bond Strengths

et al. 2012

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Theoretical methods (B3LYP, M06, and CCSD(T)) have been used to study the kinetics and thermodynamics of ethyl migratory insertion in a series of square-planar [(X ∧ Y)Ni(ethyl)(ethylene)] complexes (X ∧ Y = anionic bidentate ligand). The results are discussed qualitatively using general trans-influence arguments. When X ≠ Y, the reactions of the two possible isomers have been compared. The results reveal that when one of the coordinating groups exerts a strong trans influence (STI) and the other a weak trans influence (WTI), as in a STI ∧ WTI chelating ligand such as a phosphinoenolate (P ∧ O), one of the two isomers has an activation energy for ethylene insertion (i.e., ethyl migration) that is much less than that calculated for symmetrical bidentate ligands of either the WTI ∧ WTI or STI ∧ STI types. Specifically, a low activation energy is found when an ethyl group, coordinated trans to the STI group, migrates to the ethylene coordinated trans to the WTI group. The converse pathway in the STI ∧ WTI system, wherein ethyl migrates from a position trans to a WTI group, encounters a very high barrier. However, the kinetic barrier to isomerization (prior to migration) is sufficiently low to allow repeated insertions to proceed via the low-barrier pathway, in which an alkyl group in effect migrates from the position trans to the STI group to the position trans to the WTI group. The overall barrier (isomerization plus insertion) for an [(STI ∧ WTI)Ni(ethyl)(ethylene)] complex is less than that calculated for insertion in a WTI ∧ WTI analogue. Ethylene dissociation from [(X ∧ Y)Ni(ethyl)-(ethylene)] leads to an intermediate exhibiting a Ni−ethyl β-agostic bond. Unexpectedly, the data reveal that increased trans influence exerted by the ligand trans to the ethyl α-carbon results in a strengthening of the β-agostic interactions. The [(STI ∧ STI)Ni(ethyl)] species, therefore, have a surprisingly low energy agostic resting state. As a result, ethylene binding to [(STI ∧ STI)Ni(ethyl)] is predicted to be endoergic; this contributes to an overall barrier to catalytic ethylene insertion which is greater than that calculated for (STI ∧ WTI)Ni-based species. These results may explain, at least in part, the favorable role of STI ∧ WTI chelating ligands in nickel-catalyzed olefin oligomerization. They likely also have bearing on factors influencing the activity of late-transition-metal catalysts for olefin oligomerization and polymerization more generally.

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Section: Resultsmentioning

confidence: 98%

Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role oftransInfluence in Determining Agostic Bond Strengths

et al. 2012

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“…Thus, we assumed that the reaction proceeds through the neutral acyl carbonyl palladium complex 4 a , and that acyl and carbonyl ligands are in cis arrangement to allow the second carbonylation of the aryl substrate. In any case, cis ‐to‐ trans isomerisation in four‐coordinate Pd II complexes is known to be an easy process 16c. 17…”

Section: Resultsmentioning

confidence: 99%

Pd‐Catalysed Mono‐ and Dicarbonylation of Aryl Iodides: Insights into the Mechanism and the Selectivity

Fernández-Alvarez

Fuente

Godard

et al. 2014

Chemistry A European J

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The mechanism of the experimentally reported phosphine-free palladium-catalysed carbonylation of aryl iodides with amines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base was investigated at the DFT level. Paths were identified for both di- and monocarbonylation, and the calculated selectivity for three different substrates was in agreement with experiment. In dicarbonylation yielding α-ketoamides, formation of the second carbon-carbon bond occurs through reductive elimination in the Pd acyl amide intermediate after DBU-assisted nucleophilic attack of an amine at a terminal CO ligand. This path yields the major product with iodobenzene and the almost exclusive product with p-methoxyiodobenzene. Two different possible pathways yield the monocarbonylated amide product. In one of them, which affords the minor product for iodobenzene, base-assisted nucleophilic attack of the amine takes place on a Pd-bound acyl ligand. For substrates with electron-withdrawing substituents, such as p-cyanoiodobenzene, aryl migration to the CO ligand is disfavoured, and this allows base-assisted amine attack at a terminal CO ligand early in the catalytic cycle. From the resulting Pd amide aryl complex, the subsequent reductive elimination occurs easily, and monocarbonylation becomes favoured.

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“…[107,108] To the best of our knowledge, in no case has such an adduct been isolated in the solid state. Moreover, calculations show that the structure of these intermediates may not be trivial, [109][110][111][112][113] making the structural characterization of one of them especially interesting.…”

Section: Dimerization and Deprotonation Of Benzoic And Diphenylphosph...mentioning

confidence: 99%

Mechanistic Study of the Palladium–Phenanthroline Catalyzed Carbonylation of Nitroarenes and Amines: Palladium–Carbonyl Intermediates and Bifunctional Effects

Ragaini

Gasperini

Cenini

et al. 2009

Chemistry A European J

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Palladium-phenanthroline complexes catalyze both the nitroarene carbonylation reaction and the amine oxidative carbonylation reaction to give, depending on the conditions, carbamates and ureas. There is evidence that the key step in both processes is the amine carbonylation. Here, we show that when the reaction is run in methanol key intermediate compounds have the general formula [Pd(RPhen)(COOMe)(2)] (1) (RPhen = 1,10-phenanthroline or one of its substituted derivatives). The kinetics of the reaction of 1 with toluidine in the presence of a carboxylic or phosphorus acid is first-order with respect to complex, acid, and toluidine. A CO atmosphere is also required for the reaction to proceed. Acid dimerization was shown not to be influential under the concentration conditions examined, but reaction between the acid and toluidine is not negligible and a correction has to be applied. Diphenylphosphinic acid is more effective than any carboxylic acid in promoting this reaction, as also observed under catalytic conditions. A series of equilibria and an irreversible acid-assisted proton transfer explain the observed data. Formation of an adduct between complexes of the kind 1 and CO was spectroscopically observed when RPhen = 2,9-Me(2)Phen. Several analogous complexes were also spectroscopically characterized and the X-ray structure of [Pd(2,9-Me(2)Phen)Cl(2)(CO)] was solved. This shows an asymmetric coordination of the nitrogen ligand. Kinetic measurements were also conducted under catalytic conditions. An Eyring plot shows that the effect of the acidic promoter is to decrease the DeltaS(double dagger) value, whereas no positive effect is observed on DeltaH(double dagger). A temperature-dependent correction for the reaction between the acid and aniline and phenanthroline present under the reaction conditions has to be applied. Comparison of the results obtained under stoichiometric and catalytic conditions strongly supports the view that 1 is involved even in the latter and that the acid is acting as a bifunctional promoter.

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Competing Reaction Mechanisms for the Carbonylation of Neutral Palladium(II) Complexes Containing Bidentate Ligands: A Theoretical Study

Cited by 31 publications

References 30 publications

Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role oftransInfluence in Determining Agostic Bond Strengths

Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role oftransInfluence in Determining Agostic Bond Strengths

Pd‐Catalysed Mono‐ and Dicarbonylation of Aryl Iodides: Insights into the Mechanism and the Selectivity

Mechanistic Study of the Palladium–Phenanthroline Catalyzed Carbonylation of Nitroarenes and Amines: Palladium–Carbonyl Intermediates and Bifunctional Effects

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