Pauson-Khand reactions catalyzed by entrapped rhodium complexes
Kuang Hyun Park, Seung Uk Song and Young Keun Chung*
*School of Chemistry for Molecular Catalysis, Seoul National University,
Seoul 151-747, South Korea, Email: ykchung
plaza.snu.ac.kr
K. H. Park, S. U. Song, Y. K. Chung, Tetrahedron Lett., 2003, 44, 2827-2830.
DOI: 10.1016/S0040-4039(03)00434-9
Abstract
An entrapped Rh catalyst derived by a sol-gel process has been used in a Pauson-Khand reaction under mild conditions. The catalyst can be reused at least 10 times without losing activity. This catalytic system is not effective for intermolecular reactions.
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Details
The document discusses the use of an entrapped rhodium complex as a catalyst in the Pauson–Khand reaction, a method for synthesizing cyclopentenones. Traditionally, cobalt has been used for this reaction, but it requires harsh conditions. Rhodium, although expensive, allows for milder conditions. The study focuses on creating a reusable rhodium catalyst through a sol–gel process, which immobilizes the rhodium complex in a silica matrix. This entrapped catalyst demonstrated high activity and could be reused at least 10 times without losing effectiveness, maintaining yields around 90% under optimal conditions (100°C and 5 atm CO). The catalyst showed negligible rhodium leaching, making it efficient for recycling. Various substrates were tested, showing high yields for substituted enynes but lower effectiveness for intermolecular reactions. An attempt at an asymmetric Pauson–Khand reaction using (R)-BINAP as a chiral ligand resulted in poor enantiomeric excess (up to 13%). The study concludes that the entrapped rhodium complex is a viable catalyst for the Pauson–Khand reaction under mild conditions, with excellent reusability, though improvements are needed for asymmetric applications.
Key Words
Pauson-Khand Reaction, Pauson-Khand Cyclopentenone Annulation, Cyclopentenones, Enones
ID: J72-Y2003-060
