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Dissecting Anion Effects in Gold(I)-Catalyzed Intermolecular Cycloadditions
Anna Homs1, Carla Obradors1, David Lebœuf1
1Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16 43007 Tarragona, Spain, ;
Advanced Synthesis & Catalysis
|July 21, 2015
Summary
The bulky BAr4F- anion in gold(I) complexes significantly enhances intermolecular gold-catalyzed reactions by improving yields by 10-30%. This is achieved by preventing unproductive digold(I) complex formation during alkyne activation.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Synthetic Organic Chemistry
Background:
- Gold(I) complexes are effective catalysts for various organic transformations.
- The nature of the counteranion can significantly influence catalyst activity and selectivity.
- Optimizing gold(I) catalysts for intermolecular reactions remains an active area of research.
Purpose of the Study:
- To investigate the effect of different anions on the performance of gold(I) catalysts in intermolecular reactions.
- To elucidate the mechanism of gold(I)-catalyzed [2+2] cycloaddition reactions, focusing on the role of the anion.
- To identify the optimal gold(I) complex for improved catalytic efficiency.
Main Methods:
- Synthesis and characterization of a series of gold(I) complexes with varying anions, including [t-BuXPhosAu(MeCN)]X.
- Evaluation of catalytic activity in intermolecular gold(I)-catalyzed reactions.
- Kinetic studies of the [2+2] cycloaddition of alkynes with alkenes.
- Computational analysis to understand anion effects on reaction intermediates.
Main Results:
- The gold(I) complex featuring the bulky and soft BAr4F- [3,5-bis(trifluoromethyl)phenylborate] anion demonstrated superior performance, improving yields by 10-30% compared to previous protocols.
- Kinetic studies indicated that ligand exchange to form the (η2-phenylacetylene)gold(I) complex is the rate-determining step in the [2+2] cycloaddition.
- The BAr4F- anion was found to destabilize the conjugate acid formed, significantly reducing the formation of unproductive σ,π-(alkyne)digold(I) complexes.
Conclusions:
- The choice of anion in gold(I) complexes is crucial for optimizing catalytic performance in intermolecular reactions.
- The bulky BAr4F- anion enhances catalytic efficiency by promoting productive reaction pathways and suppressing side reactions.
- Understanding anion effects provides a pathway for designing more effective gold(I) catalysts for organic synthesis.
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