Enhanced activity of enantioselective (salen)Mn(III) epoxidation catalysts through supramolecular complexation

Abstract

Abstract(Salen)Mn(III) catalysts show increased turnover numbers in the catalytic asymmetric epoxidation of conjugated olefins upon addition of bulky Lewis acids (LA) such as zinc tetraphenylporphyrin (ZnTPP). Up to 3-fold increase in total catalytic activity and at least a 20-fold increase in catalyst stability was observed with a (salen)Mn catalyst bearing pendant 5,5 -bis-pyridyl groups. This latter enhancement is primarily attributed to formation of a coordination triad, which provides steric protection for the catalyst from bimolecular decomposition. Supramolecular complex formation enhanced the catalyst's stability without compromising its enantioselectivity.

Material Applications for Salen Frameworks

“…[20] Interestingly, the supramolecular complex showed a threefold increase in catalyst activity in the ARO of styrene and dimethylchromene, and also a significant increase in catalyst lifetime resulting from the steric protection of the Mn III metal center. [20] Interestingly, the supramolecular complex showed a threefold increase in catalyst activity in the ARO of styrene and dimethylchromene, and also a significant increase in catalyst lifetime resulting from the steric protection of the Mn III metal center.…”

Selective Molecular Recognition, C−H Bond Activation, and Catalysis in Nanoscale Reaction Vessels

“…[22][23][24][25][26][27][28][29] Since this Account is not intended to be a comprehensive review, but rather an illustration of a rapidly developing topic, only a few examples of such studies are discussed below.…”

“…22,24 Hupp and co-workers have also utilized porphyrins as molecular panels around a reactive metal center. 25,26 When coordinative directed assembly is used with octahedral rhenium metal centers at the corners, in combination with zinc porphyrin walls, a supramolecular square with a large internal cavity is formed, where a catalytically active manganese porphyrin moiety binds to the zinc walls. Since the porphyrin walls prevent the bimolecular decomposition that is typical for the unbound catalyst, encapsulation results in improved catalyst stability and a 10-to 100-fold increase in the turnover numbers for epoxidation reactions of various alkenes.…”

Investigation of a new oxidative catalytic system involving Jacobsen's catalyst in the absence of organic solvents

“…However, one of the major drawbacks of the use of homogeneous metal complexes as catalysts is their irreversible deactivation via formation of m-oxo and m-peroxo dimers [49,50]. Product and catalyst separation also remains troublesome with these homogeneous systems [6].…”