Hydrolytic kinetic resolution of racemic glycidyl esters on a polymer supported chiral salen cobalt(iii) complex

Agnieszka BUKOWSKA*, Wiktor BUKOWSKI, Sabina KLECZYŃSKA, Katarzyna MATKIEWICZ – Faculty of Chemistry, Rzeszów University of Technology, Rzeszów, Poland
Please cite as: CHEMIK 2016, 70, 7, 375–382

The hydrolytic kinetic resolution (HKR) of racemic epoxides occurring in the presence of chiral salen cobalt(III) complex I (Scheme 1) has been discovered accidentally by Jacobsen and coworkers during the studies of the catalytic activity of this complex in the reaction of epoxides with benzoic acid [1]. The presence of a diol with an enantiomeric excess above 98% was observed besides the expected products (a chiral epoxide and an ethylene glycol monoester) after complete reaction. It was formed as a side product in the reaction of hydration of one of the epoxide isomers occurring under influence of the water molecules introduced as an impurity to the reaction mixture. This finding turned the attention of Jacobsen’s group to water as the best attractive reactant for the kinetic resolution of racemic epoxides. Simultaneous producing two valuable products (a chiral epoxide and a diol) contributed to the rapid spread of the HKR technology on an industrial scale [2].

The kinetic studies performed in the presence complex II (Scheme 1) led Jacobsen to a conclusion that cooperative acting of two catalytic moieties of the complex plays a key role in epoxide hydration. One of them is responsible for epoxide activation and the second delivers OH anions [3]. The privileged bimolecular path of the reaction of epoxide hydration has inspired Jacobsen and other researchers to undertake the attempts to improve the activity and stability of salen catalysts by developing the systems which will facilitate the mutual contact between two catalytic moieties. Dimeric [4, 5] and oligomeric [6, 7] catalytic systems, and those with (salen)Co(III) complexes immobilized on organic [8, 9] and inorganic [10] supports were developed as a result. The new catalysts were characterized by much higher activity than that observed for complex II.

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