Journal
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
Volume 316, Issue 1-2, Pages 8-15Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.molcata.2009.10.025
Keywords
Cobalt-salen; Homogeneous catalysis; Asymmetric synthesis; Hydrolytic kinetic resolution (HKR)
Categories
Funding
- U.S. Department of Energy [DE-FG02-03ER15459, DE-FG02-03ER15460]
- U.S. Department of Energy (DOE) [DE-FG02-03ER15459] Funding Source: U.S. Department of Energy (DOE)
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The recyclability of Co(III)-salen catalysts, where salen is defined by (R,R)-N,N'-bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediamine, for the hydrolytic kinetic resolution (HKR) of racemic epichlorohydrin is a strong function of the counterion of the Co(III)-salen catalyst. The nature of the counterion determines whether the HKR reaction follows primarily a bimetallic or monometallic reaction path, which significantly affects catalyst recyclability. For example, Co(III)-salen initially containing the nucleophilic Cl- counterion catalyzes the HKR of epichlorohydrin according to a bimetallic reaction path but loses activity upon recycle, as Cl- is replaced with OH- during the reaction. In contrast, a Co(III)-salen catalyst containing non-nucleophilic SbF6- counterion catalyzes the reaction according to a monometallic reaction path and is quite stable during multiple recycles, albeit at a low rate with less selectivity. A mixed catalyst system with Co(III)-salen initially containing Cl- to which Co(III)-salen with SbF6- is later added demonstrates high activity and high stability to recycling. Additional experiments with Co(III)-salen initially containing the acetate counterion reveal a progressive decline in activity with multiple recycles even after regeneration with acetic acid between runs, suggesting a destructive role of the regeneration process. (C) 2009 Elsevier B.V. All rights reserved.
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