Asymmetric epoxidation of olefins using novel chiral dinuclear Mn(III)‐Salen complexes with inherent phase‐transfer capability in ionic liquids

Abstract

Two new chiral dinuclear Mn(III)-Salen complexes with inherent phase-transfer capability have been synthesized, which serve as catalysts in the asymmetric epoxidation of nonfunctionalized alkenes. Experimental results show these complexes are effective catalysts for the asymmetric epoxidation of some cyclic alkenes and the catalysts have certain inherent phase-transfer capability during the epoxidation because of their weak water solubility. In general, good enantioselectivity and acceptable yields were achieved when NaClO was used as oxidant under three different reaction systems. Among these alkenes, the catalyst 6a gave the highest ee (94%) for 6-chloro-2,2-dimethylchromene in the presence of ionic liquid 2. Additionally, the recovery and recycling of one dimeric Mn(III)-Salen complex were tested to investigate atom efficiency of the catalyst in different reaction systems on the alkenes epoxidations. The catalyst 6a could be recovered and recycled for six times without losing activity and selectivity.

Retracted Article: Olefin epoxidation with chiral salen Mn(iii) immobilized on ZnPS-PVPA upon alkyldiamine

“…To address this issue, heterogeneous chiral catalysts are developed by anchoring chiral Mn(III) salen complexes on polymer supports, inorganic solid supports of varied porosity, polysiloxane membranes, and in ionic liquids. [11][12][13][14][15][16][17][18][19][20] Over the last few decades, we have focused on the immobilization of Jacobsen's catalysts, such as the supported chiral salen Mn(III) catalysts on zirconium oligostyrenylphosphonatephosphate (ZSPP), zirconium poly(styrene-phenylvinylphosphonate)-phosphate (ZPS-PVPA) and zinc poly(styrenephenylvinylphosphonate)-phosphate (ZnPS-PVPA) as well as calcium poly(styrene-phenylvinylphosphonate)-phosphate (CaPS-PVPA). It is noteworthy that the heterogeneous chiral salen Mn(III) catalysts show higher enantioselectivities than the homogeneous catalysts and superior reusabilities under the same conditions.…”

Ionic Liquids in Asymmetric Synthesis: An Overall View from Reaction Media to Supported Ionic Liquid Catalysis

“…In 2011, Ta ng and co-workers employed two new chiral dinuclear Mn III -salen complexes in the asymmetric epoxidation of alkenes, specifically cyclic alkenes, by using NaOCla st he oxidant and pyridine N-oxide as ac o-catalyst. [71] Because of the high cost of these ligands, recycling is av ery important issue to be resolved. The authors note that ionic liquid solvents increase the activity of the catalyst by stabilizing the catalysto r ionic intermediates.…”

Organic carbonates as solvents in macrocyclic Mn(III) salen catalyzed asymmetric epoxidation of non-functionalized olefins

“…To make Mn(III) salen catalyst recyclable, strategies like its immobilization on organic polymers [5], inorganic supports [6][7][8], encapsulation in zeolite cavities [9], physical entrapment in siloxane membranes [10], tuneable solubility and multiphase methods have been reported. In the past, the ecologically sensible media have been used, notable among these are water [11][12][13], fluorinated hydrocarbons [14], supercritical CO 2 [15][16][17][18], and ionic liquids [19,20]. To our best knowledge there are no reports on the use of organic carbonates as solvent in asymmetric epoxidation reaction.…”