Enhanced cooperativity through design: pendant Co(III)--salen polymer brush catalysts for the hydrolytic kinetic resolution of epichlorohydrin (salen=N,N'-bis(salicylidene)ethylenediamine dianion).
The Co(III)--salen-catalyzed (salen=N,N'-bis(salicylidene)ethylenediamine dianion) hydrolytic kinetic resolution (HKR) of racemic epoxides has emerged as a highly attractive and efficient method of synthesizing chiral C(3) building blocks for intermediates in larger, more complex molecules. HKR reaction rates have displayed a second order dependency on the concentration of active sites, and thus researchers have proposed a bimetallic transition state for the HKR mechanism. Here we report the utilization of pendant Co(III)--salen catalysts on silica supported polymer brushes as a catalyst for the HKR of epichlorohydrin. The novel polymer brush architecture provided a unique framework for promoting site-site interactions as required in the proposed bimetallic transition state of the HKR mechanism. Furthermore, the polymer brushes mimic the environment of soluble polymer-based catalysts, whereas the silica support permitted facile recovery and reuse of the catalyst. The polymer brush catalyst displayed increased activities over the soluble Jacobsen Co--salen catalyst and was observed to retain its high enantioselectivities (>99 %) after each of five reactions despite decreasing activities. Analysis indicated decomposition of the salen ligand as an underlying cause of catalyst deactivation.
Gill
Christopher S
CS
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, USA.
Venkatasubbaiah
Krishnan
K
Phan
Nam T S
NT
Weck
Marcus
M
Jones
Christopher W
CW
D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004811:Epichlorohydrin / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D046529:Microscopy, Electron, Transmission; D011108:Polymers / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
D005029:Ethylenediamines; D011108:Polymers; D004811:Epichlorohydrin; D003035:Cobalt; C011452:disalicylaldehyde ethylenediamine