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Intermolecular hydroacylation: high activity rhodium catalysts containing small-bite-angle diphosphine ligands
Adrian B Chaplin1, Joel F Hooper, Andrew S Weller
1Department of Chemistry, Inorganic Chemistry Laboratories, University of Oxford, South Parks Road, Oxford OX1 3QR, UK.
Highly efficient rhodium catalysts enable intermolecular hydroacylation of unactivated alkenes and alkynes using aldehydes. These catalysts operate at low loadings, achieving high turnover frequencies for valuable organic synthesis.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Organic Synthesis
Background:
- Rhodium complexes with methylene-bridged diphosphine ligands are effective precatalysts.
- These catalysts facilitate the intermolecular hydroacylation of unactivated alkenes and alkynes.
- The reaction utilizes β-S-substituted aldehydes as acylating agents.
Purpose of the Study:
- To develop practical and highly efficient rhodium precatalysts for intermolecular hydroacylation.
- To characterize intermediate and product complexes involved in the catalytic cycle.
- To elucidate the catalytic mechanism, including key steps and potential side reactions.
Main Methods:
- Synthesis and characterization of novel rhodium-diphosphine complexes.
- Stoichiometric reactions to isolate and study intermediate acyl hydride and decarbonylation products.
- X-ray crystallography for structural determination of key complexes.
- Kinetic Isotope Effect (KIE) and deuterium labeling studies to probe reaction mechanisms.
Main Results:
- Bench-stable rhodium complexes with methylene-bridged diphosphine ligands were prepared.
- These complexes efficiently catalyze the intermolecular hydroacylation of diverse alkenes and alkynes with aldehydes.
- Intermediate acyl hydride and decarbonylation products were characterized, providing mechanistic insights.
- Optimized conditions allowed for very low catalyst loadings (0.1 mol %) and high turnover frequencies (>300 h⁻¹).
Conclusions:
- Judicious selection of solvent and concentration allows tuning between decarbonylation and productive hydroacylation.
- A proposed mechanism involves reversible oxidative addition and alkene insertion steps.
- The catalytic system demonstrates high efficiency and broad applicability in organic synthesis.
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