Mechanistic Rationalization of Unusual Sigmoidal Kinetic Profiles in the Machetti–De Sarlo Cycloaddition Reaction

Mower, Matthew P.; Blackmond, Donna G.

doi:10.1021/ja512753v

Cited by 32 publications

(31 citation statements)

References 42 publications

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“…The acceleration arising by conducting the same experiment in sequential order supports the generation of an in situ generated active catalyst from 2al and A (Fig. 7b depicts accelerated kinetic trace with respect to standard conditions) 83 . The observation of a concave shaped profile indicates continual amplification (active catalyst increasing at an increasing rate) of the in situ catalyst, as the catalytic cycle proceeds upon 1c addition 86 .…”

Section: D-and L-glucal Substrates D-and L-galactal Substratessupporting

confidence: 53%

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

Xu¹,

Rao²,

Weigen³

et al. 2020

Nat Commun

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The development of noncovalent halogen bonding (XB) catalysis is rapidly gaining traction, as isolated reports documented better performance than the well-established hydrogen bonding thiourea catalysis. However, convincing cases allowing XB activation to be competitive in challenging bond formations are lacking. Herein, we report a robust XB catalyzed 2-deoxyglycosylation, featuring a biomimetic reaction network indicative of dynamic XB activation. Benchmarking studies uncovered an improved substrate tolerance compared to thiourea-catalyzed protocols. Kinetic investigations reveal an autoinductive sigmoidal kinetic profile, supporting an in situ amplification of a XB dependent active catalytic species. Kinetic isotopic effect measurements further support quantum tunneling in the rate determining step. Furthermore, we demonstrate XB catalysis tunability via a halogen swapping strategy, facilitating 2-deoxyribosylations of D-ribals. This protocol showcases the clear emergence of XB catalysis as a versatile activation mode in noncovalent organocatalysis, and as an important addition to the catalytic toolbox of chemical glycosylations.

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Section: D-and L-glucal Substrates D-and L-galactal Substratessupporting

confidence: 53%

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

Xu¹,

Rao²,

Weigen³

et al. 2020

Nat Commun

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“…It was postulated initially that the sigmoidal curve observed in the current system could be indicative of a quasi-heterogeneous process and autocatalysis. 18 Established tests 5 were therefore used to probe the catalytic behavior in our system ( Figure 2 a). Excess Hg (200 equiv) was added to the reaction mixture at 90 min (a well-known and widely applied heterogeneous catalyst poison), which had no effect on substrate turnover.…”

Section: Resultsmentioning

confidence: 99%

Mild and Regioselective Pd(OAc)₂-Catalyzed C–H Arylation of Tryptophans by [ArN₂]X, Promoted by Tosic Acid

et al. 2017

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A regioselective Pd-mediated C–H bond arylation methodology for tryptophans, utilizing stable aryldiazonium salts, affords C2-arylated tryptophan derivatives, in several cases quantitatively. The reactions proceed in air, without base, and at room temperature in EtOAc. The synthetic methodology has been evaluated and compared against other tryptophan derivative arylation methods using the CHEM21 green chemistry toolkit. The behavior of the Pd catalyst species has been probed in preliminary mechanistic studies, which indicate that the reaction is operating homogeneously, although Pd nanoparticles are formed during substrate turnover. The effects of these higher order Pd species on catalysis, under the reaction conditions examined, appear to be minimal: e.g., acting as a Pd reservoir in the latter stages of substrate turnover or as a moribund form (derived from catalyst deactivation). We have determined that TsOH shortens the induction period observed when [ArN2]BF4 salts are employed with Pd(OAc)2. Pd(OTs)2(MeCN)2 was found to be a superior precatalyst (confirmed by kinetic studies) in comparison to Pd(OAc)2.

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“…Four observationsthe symmetry of growth and decay, the sigmoidal shape of the kinetic profile, the first-and second-order [1 + ] terms in the rate law, and the saturation behavior of [OH − ]are most consistent with a chain reaction propagated by a small amount of non-steady-state catalytic intermediate. 40 In this type of chain reaction mechanism, the reactant is both a pre-catalyst and a participant in a catalytic cycle. The precatalyst activation step gives rise to the first-order term, and the reaction of the precatalyst with a catalytic intermediate gives the second-order term.…”

Section: ■ Kinetics and Proposed Mechanismmentioning

confidence: 99%

Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation

et al. 2015

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Artificial photosynthesis (AP) promises to replace society's dependence on fossil energy resources via conversion of sunlight into sustainable, carbon-neutral fuels. However, large-scale AP implementation remains impeded by a dearth of cheap, efficient catalysts for the oxygen evolution reaction (OER). Cobalt oxide materials can catalyze the OER and are potentially scalable due to the abundance of cobalt in the Earth's crust; unfortunately, the activity of these materials is insufficient for practical AP implementation. Attempts to improve cobalt oxide's activity have been stymied by limited mechanistic understanding that stems from the inherent difficulty of characterizing structure and reactivity at surfaces of heterogeneous materials. While previous studies on cobalt oxide revealed the intermediacy of the unusual Co(IV) oxidation state, much remains unknown, including whether bridging or terminal oxo ligands form O2 and what the relevant oxidation states are. We have addressed these issues by employing a homogeneous model for cobalt oxide, the [Co(III)4] cubane (Co4O4(OAc)4py4, py = pyridine, OAc = acetate), that can be oxidized to the [Co(IV)Co(III)3] state. Upon addition of 1 equiv of sodium hydroxide, the [Co(III)4] cubane is regenerated with stoichiometric formation of O2. Oxygen isotopic labeling experiments demonstrate that the cubane core remains intact during this stoichiometric OER, implying that terminal oxo ligands are responsible for forming O2. The OER is also examined with stopped-flow UV-visible spectroscopy, and its kinetic behavior is modeled, to surprisingly reveal that O2 formation requires disproportionation of the [Co(IV)Co(III)3] state to generate an even higher oxidation state, formally [Co(V)Co(III)3] or [Co(IV)2Co(III)2]. The mechanistic understanding provided by these results should accelerate the development of OER catalysts leading to increasingly efficient AP systems.

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Mechanistic Rationalization of Unusual Sigmoidal Kinetic Profiles in the Machetti–De Sarlo Cycloaddition Reaction

Cited by 32 publications

References 42 publications

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

Mild and Regioselective Pd(OAc)₂-Catalyzed C–H Arylation of Tryptophans by [ArN₂]X, Promoted by Tosic Acid

Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation

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Mechanistic Rationalization of Unusual Sigmoidal Kinetic Profiles in the Machetti–De Sarlo Cycloaddition Reaction

Cited by 32 publications

References 42 publications

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

Mild and Regioselective Pd(OAc)2-Catalyzed C–H Arylation of Tryptophans by [ArN2]X, Promoted by Tosic Acid

Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation

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Mild and Regioselective Pd(OAc)₂-Catalyzed C–H Arylation of Tryptophans by [ArN₂]X, Promoted by Tosic Acid