A Highly Efficient and Broadly Applicable Cationic Gold Catalyst

Malhotra, Deepika; Mashuta, Mark S.; Hammond, Gerald B.; Xu, Bo

doi:10.1002/ange.201310239

Cited by 29 publications

(8 citation statements)

References 44 publications

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“…With this in mind, we designed ligand A1 (Table 2) that features two electron-rich and sterically demanding o-biphenyl groups and one electron-rich cyclohexyl group. 22 We prepared A1 in one step from readily available starting materials. The crystallographic structure of A1−AuCl proved that the two o-biphenyl motifs surrounded the gold center.…”

Section: Ligand Designmentioning

confidence: 77%

Improving Homogeneous Cationic Gold Catalysis through a Mechanism-Based Approach

Hammond

2019

Acc. Chem. Res.

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Conspectus Homogeneous gold catalysis is regarded as a landmark addition to the field of organic synthesis. It is the most effective way to activate alkynes for the addition of a diverse host of nucleophiles. However, the literature reveals that a relatively high catalyst loading is needed in many gold-catalyzed applications (1–10 mol %), which is impractical in large-scale synthesis or multistep synthesis because of the high price and recyclization difficulty of the gold. A more thorough understanding of the factors that operate on homogeneous gold catalysis can provide better guidelines for the future design of more efficient gold-catalyzed reactions. In this Account, we will summarize our group’s extensive investigation of factors impacting cationic gold catalysis, namely, the effects of ligands, counterions, additives, and catalyst decay and deactivation, using a mechanism-based approach with the aim of improving the efficiency of homogeneous gold catalysis. Through NMR-assisted kinetic studies, we investigated the above factors. Our systematic ligand effect investigation provided a clearer understanding of how ligands influence each of the three stages in the gold catalytic cycle. On the basis of this study, we synthesized a novel phosphine ligand and achieved parts per million-level gold catalysis by manipulating the electron density of the substituents and the steric strain around phosphorus. Our investigation of counterion effects led to the design of a gold affinity index and hydrogen-bonding basicity index for counterions, which can forecast the reactivity of counterions in cationic gold catalysis. We studied the adverse silver effects in cationic gold catalyst activation and proposed a more efficient practical guide. Our additive effect investigation revealed that additives that are good hydrogen-bond acceptors increase the efficiency of gold-catalyzed reactions in those occurrences where protodeauration is the rate-determining step. The first detailed experimental analysis of gold catalyst decay and the influence of each component in the reaction system (substrate, counterion, solvent) on the decay process was also conducted. We found that high-gold-affinity impurities (halides, bases) in solvents, starting materials, filtration, or drying agents decrease the reactivity of a gold catalyst but that a suitable acid activator can reactivate the gold catalyst and enable the reaction to proceed smoothly at competitively low gold catalyst loadings. The effects of acid additives were also systematically investigated using typical reactions. We are convinced that better mechanistic understandings will offer clearer guidelines for the search for more efficient gold-catalyzed reactions.

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Section: Ligand Designmentioning

confidence: 77%

Improving Homogeneous Cationic Gold Catalysis through a Mechanism-Based Approach

Hammond

2019

Acc. Chem. Res.

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“…On the other hand, since NHC is considered a stronger electron donor, the metal fragment [L-Au] + should be less acidic and should not deplete the charge on the unsaturated substrate bond as much. 21 However, this picture has been recently questioned. The ligand ability to donate electron density to gold has been quantified by some of us in a series of [L-Au-(CO)] +/0 complexes.…”

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confidence: 99%

Unraveling the Anion/Ligand Interplay in the Reaction Mechanism of Gold(I)-Catalyzed Alkoxylation of Alkynes

et al. 2017

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In this work DFT calculations have been performed to investigate the anion/ligand interplay in the reaction mechanism of alkoxylation of alkynes promoted by gold(I) catalysts of general formula [L-Au-X] (L = NHC, P(tBu)3and X = OTs-, OTf-, BF4-, TFA-) on the basis of available experimental data. The observed catalytic efficiency trend in this series of compounds strictly depends on the specific anion/ligand combination used, thus suggesting that it cannot be estimated by evaluating the properties of L and X separately. Similarly to [NHC-Au-X], for the [P(tBu)3-Au-X] catalyst series, we demonstrate that the anion effect in the reaction mechanism can be predicted on the basis of its coordinating/proton acceptor properties. A comparison between the P(tBu)3/OTs-and NHC/OTs-settings shows that the anion/ligand interplay has a crucial role in the nucleophilic attack step of the reaction mechanism. A charge-displacement (CD) analysis reveals that the activation of the unsaturated hydrocarbon multiple bond (alkyne) by the [L-Au]+fragment depends both on the ligand-withdrawing ability at the outer region of the CC bond and on the counterion affinity for the cationic fragment, both affecting in the opposite way the electrophilic character of the alkyne at the transition state

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“…One approach to induce added stability to the cationic gold complexes and to allow the lowering of catalyst load has been the electronic modification in novel catalyst ligands. Thus, gold complexes bearing a ligand L7 , presenting two electron‐donating biphenyl groups, have been reported to catalyze the cycloisomerization of allenone 2‐diPh‐Me into furan 133 a (Scheme 26a) [94] . A low 0.01 mol% load of catalyst was found to be effective to achieve the synthesis of 133 a with quantitative yield, among many other related transformations (Scheme 26a) [94] .…”

Section: Synthetic Utilitymentioning

confidence: 99%

Highlighting the Rich Chemistry of the Allenone Moiety

Almendros

Alonso

2023

Adv Synth Catal

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Conjugated and non-conjugated allenones appear as recurring motifs in organic synthesis, natural products and mechanistic investigations showing unique properties and applications. The ability of allenones to build cycles has provided a direct access to strained systems, medium-sized rings, arenes, heterocycles and complex polycycles. In addition, allenones have served as models in mechanistic investigations and catalysis. The critic compilation herein presented will provide an exhaustive overview of the synthetic possibilities allenones may offer, which certainly will inspire our community in their search of more efficient synthetic methodologies, preparation of biological and pharmaceutical targets, and improve our knowledge in theoretical organic chemistry. Great part of this review will discuss synthetic aspects, catalysis innovation and mechanistic insights of the chemical transformations implying the allenone motif. In addition, many examples on total synthesis and pharmacologically active compounds will be described. We hope that this overview will be attractive to the organic chemistry, synthetic chemistry, catalysis, theoretical chemistry, natural products and medicinal chemistry communities. 3.5. Synthesis of Spirocycles and Bridged Structures 3.6. Open-Chain Structures from Allenones 3.7. Allenones in Total Synthesis 4.

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A Highly Efficient and Broadly Applicable Cationic Gold Catalyst

Cited by 29 publications

References 44 publications

Improving Homogeneous Cationic Gold Catalysis through a Mechanism-Based Approach

Improving Homogeneous Cationic Gold Catalysis through a Mechanism-Based Approach

Unraveling the Anion/Ligand Interplay in the Reaction Mechanism of Gold(I)-Catalyzed Alkoxylation of Alkynes

Highlighting the Rich Chemistry of the Allenone Moiety

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