Hydration of alkynes catalyzed by [Au(X)(L)(ppy)]X in the green solvent γ-valerolactone under acid-free conditions: the importance of the pre-equilibrium step

Segato, Jacopo; Zotto, Alessandro Del; Belpassi, Leonardo; Belanzoni, Paola; Zuccaccia, Daniele

doi:10.1039/d0cy01343a

Cited by 11 publications

(31 citation statements)

References 100 publications

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“…The first step of the reaction mechanism is represented by the pre-equilibrium, where the substrate (alkyne) replaces the anion in the initial complex, binds to the gold center, and is activated for the nucleophilic attack. However, in the alkyne hydration reaction, where H 2 O is the nucleophile, the anion substitution by the water molecule, i.e., formation of the water adduct from the corresponding initial complex, has been shown to be both thermodynamically and kinetically favored with respect to the formation of alkyne complex, in agreement with the experimental evidence (see also Introduction and Scheme 1 for details) [ 40 ]. Therefore, starting from the experimentally isolated and characterized 3 , we will explore the pre-equilibrium step consisting of H 2 O substitution by the alkyne and rationalize the reason why 2 is not experimentally observed.…”

Section: Resultssupporting

confidence: 71%

“…The catalytic activity of [(ppy)Au(IPr)Cl]Cl ( 1 ) in the 3-hexyne hydration reaction has shown a not completely satisfactory efficiency of this complex [ 40 ].…”

Section: Resultsmentioning

confidence: 99%

“…The pre-equilibrium is a key step in the Au(III)-catalyzed alkyne hydration reaction [ 40 ]. Despite its importance, the Au(III) complexes affinity towards different species involved in the catalytic cycle (water, counterions and alkynes) is far to be understood.…”

Section: Discussionmentioning

confidence: 99%

“…The mechanism of the hydration of 3-hexyne catalyzed by [(ppy)Au(IPr)Cl]Cl ( 1 ) [ppy = 2-phenylpyridine, IPr = 1,3- bis (2,6-di-isopropylphenyl)-imidazol-2-ylidene] in γ-valerolactone (GVL) as the solvent has been investigated by some of us both experimentally (NMR) and computationally (DFT), demonstrating that the pre-equilibrium step is effectively the RDS. As a matter of fact, water or counterion substitution by 3-hexyne in the first co-ordination sphere of Au(III) is crucial for the whole process [ 40 ]. The hydration of alkynes is an important reaction in organic chemistry, and it turns to be one of the most environmentally friendly methods to form the C=O bond [ 41 , 42 ].…”

Section: Introductionmentioning

confidence: 99%

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Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

et al. 2021

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The coordination ability of the [(ppy)Au(IPr)]2+ fragment [ppy = 2-phenylpyridine, IPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl−, BF4−, OTf−, H2O, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF4− and OTf− have very similar coordination ability towards [(ppy)Au(IPr)]2+ and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)]2+ fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)]2+ (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf− and BF4−, in agreement with experiment. Effect of the ancillary ligand substitution demonstrates that the coordination ability of Au(III) is quantitatively strongly affected by the nature of the ligands (even more than the net charge of the complex) and that all the investigated gold fragments coordinate to alkynes more strongly than H2O. Remarkably, a stabilization of the water-coordinating species with respect to the alkyne-coordinating one can only be achieved within a microsolvation model, which reconciles theory with experiment. All the results reported here suggest that both the Au(III) fragment coordination ability and its proper computational modelling in the experimental conditions are fundamental issues for the design of efficient catalysts.

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Section: Resultssupporting

confidence: 71%

“…The catalytic activity of [(ppy)Au(IPr)Cl]Cl ( 1 ) in the 3-hexyne hydration reaction has shown a not completely satisfactory efficiency of this complex [ 40 ].…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

et al. 2021

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“…Therefore, the main arguments stem from the relative intermediate energies, which in turn dictate the distribution of the pre-equilibria. 39 The gas-phase energies showed a high-energy intermediate between cyclic structures iii and iv . However, the transition from ii to iv was in a reasonable range.…”

Section: Resultsmentioning

confidence: 97%

Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach

et al. 2022

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In a recent report on the synthetic approach to the novel substance class of 1-alkylidene/arylidene-1,2,4-triazolinium salts, a reaction mechanism suggesting a regioselective outcome was proposed. This hypothesis was tested via a combined NMR and density functional theory (DFT) approach. To this end, three experiments with 13 C-labeled carbonyl reactants were monitored in situ by solution-state NMR. In one experiment, an intermediate as described in the former mechanistic proposal was observed. However, incorporation of 13 C isotope labels into multiple sites of the heterocycle could not be reconciled with the “regioselective mechanism”. It was found that an unproductive reaction pathway can lead to 13 C scrambling, along with metathetical carbonyl exchange. According to DFT calculations, the concurring reaction pathways are connected via a thermodynamically controlled cyclic 1,3-oxazetidine intermediate. The obtained insights were applied in a synthetic study including aliphatic ketones and para-substituted benzaldehydes. The mechanistic peculiarities set the potential synthetic scope of the novel reaction type.

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Shape Selectivity in the Gold‐Catalyzed Hydration of Alkynes Using a Cavity‐Shaped Phosphine

2023

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A cavity-shaped gold(I) complex derived from a bulky tri-(orthobiaryl)-phosphine ligand shows preferred selectivity towards terminal functionalities in the gold(I)-catalysed hydration of alkynes under mild heating due to a well-defined pocket as catalytic active site. The confinement-induced size-exclusion selectivity investigated for eight alkynes contrasts with other gold(I) complexes bearing bulky phosphine ligands that show reduced selectivity or even similar behaviour towards both internal and terminal alkynes. We also interrogate the potential of gold(III) derivatives for the same catalytic process.

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Hydration of alkynes catalyzed by [Au(X)(L)(ppy)]X in the green solvent γ-valerolactone under acid-free conditions: the importance of the pre-equilibrium step

Cited by 11 publications

References 100 publications

Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach

Shape Selectivity in the Gold‐Catalyzed Hydration of Alkynes Using a Cavity‐Shaped Phosphine

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