(CAAC)CuCl: A Competent Precatalyst for Carbonyl and Ester Hydrosilylation
Sudip Baguli1, Soumajit Nath1, Abhishek Kundu2
1Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, West Bengal, India.
Inorganic Chemistry
|September 25, 2024
Summary
Cyclic(alkyl)(amino)carbenes (CAACs) are introduced as effective ligands for copper-catalyzed hydrosilylation of carbonyls and esters. These ligands enhance catalyst stability and activity, enabling challenging ester transformations.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Synthetic Chemistry
Background:
- Copper-catalyzed hydrosilylation relies on ligated copper hydride species, where ligand properties critically influence catalyst performance.
- N-heterocyclic carbenes (NHCs) are established ligands for copper catalysts in hydrosilylation, but other strong σ-donors like cyclic(alkyl)(amino)carbenes (CAACs) have not been explored.
- CAACs offer stronger σ-donation and unique steric properties compared to NHCs, suggesting potential advantages in copper catalysis.
Purpose of the Study:
- To investigate the efficacy of cyclic(alkyl)(amino)carbenes (CAACs) as ligands in copper-catalyzed hydrosilylation reactions.
- To explore the application of CAAC-ligated copper catalysts in both carbonyl and ester hydrosilylation.
- To synthesize and characterize new CAAC-copper complexes and elucidate the catalytic mechanism.
Main Methods:
- Synthesis and characterization of novel (CAAC)CuCl complexes.
- Evaluation of precatalyst activity in copper-catalyzed carbonyl and ester hydrosilylation.
- In situ generation and trapping of a proposed (CAAC)CuH intermediate.
- Computational studies to investigate the reaction mechanism, including the rate-limiting step.
Main Results:
- The [(Me2CAAC)CuCl] complex demonstrated potent catalytic activity in carbonyl hydrosilylation.
- This CAAC-based copper precatalyst also successfully catalyzed the more challenging ester hydrosilylation, a rare capability for copper.
- Three new (CAAC)CuCl complexes with varying aryl substituents on the CAAC ligand showed comparable activity, indicating steric openness is advantageous.
- Computational analysis identified carbonyl insertion into a (CAAC)Cu-H species as the rate-limiting step.
- An in situ generated (CAAC)CuH intermediate was successfully trapped as its BH3 adduct, confirming its involvement.
Conclusions:
- CAACs represent a highly effective ligand platform for copper-catalyzed hydrosilylation, outperforming traditional NHCs in certain aspects.
- CAAC-ligated copper catalysts are versatile, enabling both carbonyl and ester hydrosilylation with high efficiency.
- The findings open new avenues for developing advanced copper catalysts with tunable CAAC ligands for challenging transformations.
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