Non-Covalent Immobilization of Chiral (Salen) Complexes on HF-treated Mesoporous MFI-type Zeolite for Asymmetric Catalysis

A wide variety of [Co(salen)] catalysts with different structures designed to enhance salen–salen cooperative interactions have been reported as catalysts for the hydrolytic kinetic resolution (HKR) of epoxides. However, the myriad catalysts have been evaluated under inconsistent experimental conditions, at different catalyst loadings, at different temperatures, with various epoxides and in several different laboratories, making rigorous comparisons between the catalysts impossible. To this end, 12 representative catalysts from our studies, as well as catalysts originally described by others, are reported in the HKR of epichlorohydrin under rigorously identical conditions. The comparison of the reactivity and selectivity of the different catalysts indicates that the soluble, oligomeric [Co(salen)] catalysts with cyclic frameworks impart the highest activity and enantioselectivity (>99 % ee, krel>99) in this representative reaction, requiring very short reaction times (<30 min), including the most active catalyst reported to date for the target reaction. In general, it is found that soluble polymer or oligomer‐supported catalysts are more active than insoluble supported catalysts under the conditions used. Among the insoluble catalysts, a polymer resin supported [Co(salen)] catalyst with excellent enantioselectivity (>99 % ee, krel>99) and medium reaction time (222 min), is the most active and selective of the class. The lessons demonstrated herein regarding design of active and selective catalysts offer useful insights into refining design strategies for other related cooperative catalytic reactions, suggesting emphases on catalyst flexibility and solubility under reaction conditions.

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Asymmetric Hydrolytic Kinetic Resolution with Recyclable Macrocyclic Co^III–Salen Complexes: A Practical Strategy in the Preparation of (R)‐Mexiletine and (S)‐Propranolol

Sadhukhan

Khan

Roy

et al. 2012

Chemistry A European J

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A chiral cobalt(III) complex (1e) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R-(-)-1,2-diaminocyclohexane with trigol bis-aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47% with respect to the epoxides, 53% with respect to the diols) and high enantioselectivity (ee>99% for the epoxides, up to 96% for the diols) were achieved in 2.5-16 h. The Co(III) macrocyclic salen complex (1e) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)-mexiletine and (S)-propranolol.

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Non-Covalent Immobilization of Chiral (Salen) Complexes on HF-treated Mesoporous MFI-type Zeolite for Asymmetric Catalysis

Cited by 9 publications

References 20 publications

Enantioselective Cobalt‐Catalysed Transformations

Enantioselective Cobalt‐Catalysed Transformations

Kinetic Evaluation of Cooperative [Co(salen)] Catalysts in the Hydrolytic Kinetic Resolution of rac‐Epichlorohydrin

Asymmetric Hydrolytic Kinetic Resolution with Recyclable Macrocyclic Co^III–Salen Complexes: A Practical Strategy in the Preparation of (R)‐Mexiletine and (S)‐Propranolol

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Non-Covalent Immobilization of Chiral (Salen) Complexes on HF-treated Mesoporous MFI-type Zeolite for Asymmetric Catalysis

Cited by 9 publications

References 20 publications

Enantioselective Cobalt‐Catalysed Transformations

Enantioselective Cobalt‐Catalysed Transformations

Kinetic Evaluation of Cooperative [Co(salen)] Catalysts in the Hydrolytic Kinetic Resolution of rac‐Epichlorohydrin

Asymmetric Hydrolytic Kinetic Resolution with Recyclable Macrocyclic CoIII–Salen Complexes: A Practical Strategy in the Preparation of (R)‐Mexiletine and (S)‐Propranolol

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Product

Resources

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Asymmetric Hydrolytic Kinetic Resolution with Recyclable Macrocyclic Co^III–Salen Complexes: A Practical Strategy in the Preparation of (R)‐Mexiletine and (S)‐Propranolol