Catalysis in dipolar aprotic solvents. Proton-relay mechanism resembling the mechanism of action of serine enzyme

Haake, Paul; Wallerberg, Gun; Boger, Joshua

doi:10.1021/ja00748a063

Cited by 19 publications

(4 citation statements)

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“…Although a proton relay has not been previously proposed for CO 2 reduction in the Py/p-GaP system, proton shuttling mechanisms have been proposed for a number of other processes. − While enthalpic barriers to reaction generally determine the kinetics of reactions, especially at low to moderate temperatures, entropic considerations should not be neglected. For example, because CO 2 reduction in the Py/p-GaP system occurs in aqueous solvent, pathways that involve specific solvent configurations may be entropically disfavored.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

2012

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We employ quantum chemical calculations to investigate the mechanism of homogeneous CO(2) reduction by pyridine (Py) in the Py/p-GaP system. We find that CO(2) reduction by Py commences with PyCOOH(0) formation where: (a) protonated Py (PyH(+)) is reduced to PyH(0), (b) PyH(0) then reduces CO(2) by one electron transfer (ET) via nucleophilic attack by its N lone pair on the C of CO(2), and finally (c) proton transfer (PT) from PyH(0) to CO(2) produces PyCOOH(0). The predicted enthalpic barrier for this proton-coupled ET (PCET) reaction is 45.7 kcal/mol for direct PT from PyH(0) to CO(2). However, when PT is mediated by one to three water molecules acting as a proton relay, the barrier decreases to 29.5, 20.4, and 18.5 kcal/mol, respectively. The water proton relay reduces strain in the transition state (TS) and facilitates more complete ET. For PT mediated by a three water molecule proton relay, adding water molecules to explicitly solvate the core reaction system reduces the barrier to 13.6-16.5 kcal/mol, depending on the number and configuration of the solvating waters. This agrees with the experimentally determined barrier of 16.5 ± 2.4 kcal/mol. We calculate a pK(a) for PyH(0) of 31 indicating that PT preceding ET is highly unfavorable. Moreover, we demonstrate that ET precedes PT in PyCOOH(0) formation, confirming PyH(0)'s pK(a) as irrelevant for predicting PT from PyH(0) to CO(2). Furthermore, we calculate adiabatic electron affinities in aqueous solvent for CO(2), Py, and Py·CO(2) of 47.4, 37.9, and 66.3 kcal/mol respectively, indicating that the anionic complex PyCOO(-) stabilizes the anionic radicals CO(2)(-) and Py(-) to facilitate low barrier ET. As the reduction of CO(2) proceeds through ET and then PT, the pyridine ring becomes aromatic, and thus Py catalyzes CO(2) reduction by stabilizing the PCET TS and the PyCOOH(0) product through aromatic resonance stabilization. Our results suggest that Py catalyzes the homogeneous reductions of formic acid and formaldehyde en route to formation of CH(3)OH through a series of one-electron reductions analogous to the PCET reduction of CO(2) examined here, where the electrode only acts to reduce PyH(+) to PyH(0).

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Section: Resultsmentioning

confidence: 99%

Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

2012

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“…In the polymeric systems the cooperative action of anions and cations corresponding to different, but spatially proximal, imidazolium units would increase the catalytic efficiency in comparison with the monomeric counterpart. This cooperative assistance can be considered similar to the proton relay systems observed in enzymatic catalysis . The additional ionic liquid like units present in the main polymeric chain can also be involved in the activation process, forming hydrogen bonds with the aldehyde or with water molecules.…”

Section: Resultsmentioning

confidence: 70%

“…This cooperative assistance can be considered similar to the proton relay systems observed in enzymatic catalysis. 67 The additional ionic liquid like units present in the main polymeric chain can also be involved in the activation process, forming hydrogen bonds with the aldehyde or with water molecules. This would be similar to the dual "electrophilic/nucleophilic" activation mechanism described for some Lewis basic ILs.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

AuNP–Polymeric Ionic Liquid Composite Multicatalytic Nanoreactors for One-Pot Cascade Reactions

et al. 2016

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Registro de acceso restringido Este recurso no está disponible en acceso abierto por política de la editorial. No obstante, se puede acceder al texto completo desde la Universitat Jaume I o si el usuario cuenta con suscripción. Registre d'accés restringit Aquest recurs no està disponible en accés obert per política de l'editorial. No obstant això, es pot accedir al text complet des de la Universitat Jaume I o si l'usuari compta amb subscripció. Restricted access item This item isn't open access because of publisher's policy. The full--text version is only available from Jaume I University or if the user has a running suscription to the publisher's contents.

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“…This cooperative assistance can be considered similar to the proton relay systems observed in enzymatic catalysis. 35 On the other hand, the organized polymeric structure can also implement the activation process of both the nucleophile and the electrophile when the prolinate anion is present. Most likely, adjacent prolinate groups can participate in the catalytic process, one of them activating the nucleophile via enamine formation, and the adjacent one activating the electrophile via hydrogen bond formation.…”

Section: Catalysis In Water As the Solventmentioning

confidence: 99%

An enzymatic biomimetic system: enhancement of catalytic efficiency with new polymeric chiral ionic liquids synthesised by controlled radical polymerisation

et al. 2014

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The controlled radical polymerization of monomeric units containing chiral ionic liquids (CILs) allows the synthesis of intrinsically chiral polymers through a bottom-up design. These polymeric chiral ionic liquids (PCILs) show a well-defined three dimensional structure organized as the result of a complex noncovalent network of hydrogen-bonding contacts driven by the C2 hydrogen atoms of the imidazolium aromatic rings and the OH moieties present in the side functionalities of the main polymeric chain. The exchange of the chloride counter ion by the L-prolinate anion leads to new types of polymeric catalysts, which behave as efficient artificial aldolase biomimetic systems, being highly active and selective for the aldol reaction in water. These new polymeric catalysts are significantly more active than the corresponding monomeric counterpart when the reaction is performed either in water or in the presence of water. The increase in catalytic efficiency can be related to their 3D structure, displaying helical chirality in the polymeric chain as a function of their preparation methodology. Under suitable experimental conditions, these polymers are able to catalyse the consecutive aldol-dehydration process, behaving as synthetic mimics of the aldolase-dehydrogenase enzymatic system. Moderate enantioselectivities can be achieved under suitable conditions.

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Catalysis in dipolar aprotic solvents. Proton-relay mechanism resembling the mechanism of action of serine enzyme

Abstract: 21) Such an analysis for a crystal of ( -)s46-Co(acac)s which we have grown would require determination of the coordinates for two independent molecules (44 atoms) since the crystal has space group P2i, a = 11.31, b = 12.47, c = 12.50 , ß = 101.04°, Z = 4.

Cited by 19 publications

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Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

AuNP–Polymeric Ionic Liquid Composite Multicatalytic Nanoreactors for One-Pot Cascade Reactions

An enzymatic biomimetic system: enhancement of catalytic efficiency with new polymeric chiral ionic liquids synthesised by controlled radical polymerisation

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Catalysis in dipolar aprotic solvents. Proton-relay mechanism resembling the mechanism of action of serine enzyme

Abstract: 21) Such an analysis for a crystal of ( -)s46-Co(acac)s which we have grown would require determination of the coordinates for two independent molecules (44 atoms) since the crystal has space group P2i, a = 11.31, b = 12.47, c = 12.50 , ß = 101.04°, Z = 4.

Cited by 19 publications

References 0 publications

Mechanism of Homogeneous Reduction of CO2 by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

Mechanism of Homogeneous Reduction of CO2 by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

AuNP–Polymeric Ionic Liquid Composite Multicatalytic Nanoreactors for One-Pot Cascade Reactions

An enzymatic biomimetic system: enhancement of catalytic efficiency with new polymeric chiral ionic liquids synthesised by controlled radical polymerisation

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Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization

Mechanism of Homogeneous Reduction of CO₂ by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization