Terminal Alkyne Coupling Reactions through a Ring: Mechanistic Insights and Regiochemical Switching

Angewandte Chemie International Edition, Год журнала: 2018, Номер 57(37), С. 12003 - 12006

Опубликована: Июль 13, 2018

The mechanism and selectivity of terminal alkyne coupling reactions promoted by rhodium(I) complexes NHC-based CNC pincer ligands have been investigated. Synthetic kinetic experiments support E- gem-enyne formation through a common reaction sequence involving hydrometallation rate-determining C-C bond reductive elimination. latter is significantly affected the ligand topology: Employment macrocyclic variant enforced exclusive head-to-head coupling, contrasting high for head-to-tail observed corresponding acyclic ligand.

Язык: Английский

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Catalytic Consequences of Oxidant, Alkene, and Pore Structures on Alkene Epoxidations within Titanium Silicates

ACS Catalysis, Год журнала: 2020, Номер 10(17), С. 10169 - 10184

Опубликована: Авг. 12, 2020

Ti atoms incorporated into the framework of zeolite *BEA (Ti-BEA) or grafted onto SBA-15 (Ti-SBA-15) catalyze alkene epoxidation with hydrogen peroxide (H2O2), t-butyl (TBHP), cumene hydroperoxide (CHP). The rates epoxidation, however, differ by orders magnitude depending on combination an oxidant, alkene, and a support used. Within Ti-BEA, 1-octene H2O2 are 30 170 times greater than reactions TBHP CHP, respectively. In contrast, in Ti-SBA-15 7- 40-fold higher Moreover, comparisons 1-alkene (C6–C10) epoxidations within Ti-BEA show that turnover depend differently length reactants oxidant identity, which is due to complex interactions among activated solvent-filled pore Ti-silicate. Thermochemical analyses apparent activation free energies Born–Haber cycle reveal three distinct contributions affect catalysis, include charge transfer between Ti-OOR C═C functions transition state; adsorption silicate pores; structural rearrangement reactive intermediates solvent accommodate alkene. First, give highest these oxidants because Ti-OOH more electrophilic Ti-OOtBu Ti-OOcumyl species as consequence electron donation from alkyl groups increase intrinsic barriers for O-atom transfer. Second, differences largely reflect changes stability alkenes adsorbed pores each silicate. Third, sensitivities identity caused inner-sphere surrounding environment. We present thermodynamic model quantitatively describes how states steric bulk reacting conferred topology pore. mesopores allow access conformations lower energy relative analogous explains why mesoporous solids less sensitive microporous silicates.

Язык: Английский

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Recent advances in pincer–nickel catalyzed reactions

Dalton Transactions, Год журнала: 2021, Номер 50(10), С. 3394 - 3428

Опубликована: Янв. 1, 2021

The utility of pincer−nickel complexes in catalyzing reactions such as cross−coupling, oxidation, (de)hydrogenation, hydrofunctionalization, C−H activation and CO₂ functionalization has been reviewed from a synthetic mechanistic point view.

Язык: Английский

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Carbene‐Catalyzed Enantioselective Hydrophosphination of α‐Bromoenals to Prepare Phosphine‐Containing Chiral Molecules

Angewandte Chemie International Edition, Год журнала: 2021, Номер 60(51), С. 26616 - 26621

Опубликована: Окт. 2, 2021

Disclosed herein is the first carbene-organocatalyzed asymmetric addition of phosphine nucleophiles to in situ generated α,β-unsaturated acyl azolium intermediates. Our reaction enantioselectively constructs carbon-phosphine bonds and prepares chiral phosphines with high optical purities. The products are suitable for transforming ligands or catalysts applications catalysis. diarylalkyl trialkyl from our catalytic reactions, air-sensitive reactive nature, can be trapped (and stored) their sulfur-oxidized form operational simplicities.

Язык: Английский

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Exterior decorating: Lewis acid secondary coordination spheres for cooperative reactivity

Trends in Chemistry, Год журнала: 2022, Номер 4(4), С. 331 - 346

Опубликована: Фев. 21, 2022

Язык: Английский

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