Kinetic Isotope Effects in the Study of Organometallic Reaction Mechanisms

Gallego, Manuel Requena; Sierra, Miguel Á.

doi:10.1021/cr100436k

Cited by 676 publications

(474 citation statements)

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“…The KIE of 1.42 was therefore assigned to the dehydrogenation cycle, and the value is considered too high for a normal secondary KIE. 18 A Hammett study provides precious knowledge about the mechanism, but unfortunately due to the high reaction temperature and the low boiling point of the generated aryl compounds, a regular Hammett plot was not obtainable. Instead, three aryl alcohols affording high boiling products and with very different electronic properties were compared in competitive rate experiments.…”

Section: Resultsmentioning

confidence: 99%

Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

et al. 2015

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ABSTRACT:The mechanism for the iridium-BINAP catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of molecular hydrogen and carbon monoxide was studied experimentally and computationally. The reaction takes place by tandem catalysis through two catalytic cycles involving dehydrogenation of the alcohol and decarbonylation of the resulting aldehyde. The square planar complex IrCl(CO)(rac-BINAP) was isolated from the reaction between [Ir(cod)Cl] 2 , rac-BINAP and benzyl alcohol. The complex was catalytically active and applied in the study of the individual steps in the catalytic cycles. One carbon monoxide ligand was shown to remain coordinated to iridium throughout the reaction and release of carbon monoxide was suggested to occur from a dicarbonyl complex. IrH 2 Cl(CO)(rac-BINAP) was also synthesized and detected in the dehydrogenation of benzyl alcohol. In the same experiment, IrHCl 2 (CO)(rac-BINAP) was detected from the release of HCl in the dehydrogenation and subsequent reaction with IrCl(CO)(rac-BINAP). This indicated a substitution of chloride with the alcohol to form a square planar iridium alkoxo complex that could undergo a β-hydride elimination. A KIE of 1.0 was determined for the decarbonylation and 1.42 for the overall reaction. Electron rich benzyl alcohols were converted faster than electron poor alcohols, but no electronic effect was found when comparing aldehydes of different electronic character. The lack of electronic and kinetic isotope effects implies a rate determining phosphine dissociation for the decarbonylation of aldehydes.

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Section: Resultsmentioning

confidence: 99%

Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

et al. 2015

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“…Determination of the 13 C and 2 H kinetic isotope effect (KIE) is a powerful and widely applied tool for gaining insights into the mechanism of organic and organometallic reactions [1]. In particular, KIEs can give useful information regarding which bonds are being rehybridized, broken or formed during the rate determining step of the reaction [2,3].…”

Section: Introductionmentioning

confidence: 99%

“…Singleton and co-workers have demonstrated that the KIE values of multiple H (or C) can be determined simultaneously using a competition experiment at natural abundance of the heavy isotope ( Fig. 1) [5,6] 1 . During the course of the reaction, positions in the starting material subject to a KIE will exhibit a change in the amount of heavy isotope.…”

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Determination of 2H KIEs from Competition Experiments: Increased Accuracy via Isotopic Enrichment

2017

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“…69,[71][72][73][74][75][76]77 It seemed unlikely that the nucleophilic (electron-rich) metal center, (i.e., Ru 0 ) and electrophilic metal centers (i.e., Pt II and Ir . 69,71,74,76,84 These intermediates are typically highly reactive species. When the thermodynamically preferred product is the alkyl hydride, the cleavage of the C−H bond and conversion to the more stable product is rapid.…”

Section: C−h Activation By Organometallic Routesmentioning

confidence: 99%

The Development of PtII Complexes as Catalyst Precursors for Transition Metal Mediated Olefin Hydroarylation

McKeown

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Olefin hydroarylation is an important C−C bond forming reaction for the synthesis of alkyl arenes. The transformation is traditionally catalyzed using acid-based methodologies, which suffer several deficiencies inherent to the reaction mechanism.Selective transition metal catalysts for olefin hydroarylation are potentially viable alternatives. However, such a process has been difficult to realize as catalysts for olefin hydroarylation via a non-acidic pathway must be able to mediate two fundamentally The bipyridyl scaffold presents an excellent opportunity to develop catalyst structure/activity relationships for future catalyst design. Electronic effects on catalyst activity and selectivity have been isolated with negligible influence on the catalyst steric profile by incorporating various functionality in the 4,4′-positions of bipyridine.Moreover, the consequence of steric perturbations have been evaluated through modulating the dipyridyl chelate ring size and incorporating steric hinderance in the 6,6′-positions of the pyridyl rings.In addition, compatibility with functionalized substrates with bipyridyl based catalyst precursors and ligand sets outside the dipyridyl motif have been investigated for efficacy. III AcknowledgementsI finally stand at the end of a long road that has taken almost six years to traverse. In all honesty, I did not think it would be a journey that I would get to see through to the end.There are so many people who have assisted me along the way and deserve more thanks than can adequately be expressed in a brief acknowledgement.

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Kinetic Isotope Effects in the Study of Organometallic Reaction Mechanisms

Cited by 676 publications

References 554 publications

Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

Determination of 2H KIEs from Competition Experiments: Increased Accuracy via Isotopic Enrichment

The Development of PtII Complexes as Catalyst Precursors for Transition Metal Mediated Olefin Hydroarylation

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