The present study focuses on the Mn(salen)-catalyzed epoxidation of the ethylene by peracetic acid. We also acknowledge the use of computational resources of the Cherry L. Emerson Center of Emory University, supported in part by National Science Foundation Grant CHE-0079627 and an IBM Shared University Research Award. Please note: If you switch to a different device, you may be asked to login again with only your ACS ID. 1953, 7, 378. The details of the mechanism are described in our previous article.24 An interesting feature of this reaction system is the co-existence of two liquid phases, an aqueous phase, where the perhydrolysis takes place, and the organic phase where the epoxidation occurs. The epoxidation may proceed in a concerted and/or radical-mediated stepwise manner. be used in these epoxidations (see below). Consequently, it is reasonable to suppose that larger olefins show better enantioselectivity due to multiple interactions with the critical chirality regions of the catalyst. The epoxidation of an alkene with peracid to give an oxirane. Reaction mechanisms for the liquid-phase epoxidation of alkenes are reviewed critically: the classical Prilezhaev reaction, catalytic epoxidation with participation of hydrogen peroxide and of organic hydroperoxides, reactions for the production of alkene oxides in the oxidation of unsaturated hydrocarbons, reaction of a combined oxidation of alkenes with aldehydes. The final product is the epoxide weakly coordinated to the salen complex. Although there are frontier orbital interactions in both directions, the peracid is generally viewed as the electrophile and the alkene as the nucleophile. However, because these epoxidation pathways are bimolecular with barriers >17 kcal/mol, they are unlikely to compete with Prilezhaev epoxidation. 1061-1074). Electron donating substituents on the alkene promote the reaction. The proposed reaction mechanism for epoxidation in the absence and presence of axial ligands is schematically drawn in Fig. not otherwise permitted to reproduce, republish, redistribute, or sell any Supporting Information The ground state of the MnV–trans-oxo species has been predicted to be singlet, triplet, or quintet. You have to login with your ACS ID befor you can login with your Mendeley account. Because the ethylene in all the transition states samples only one phenyl ring at a time, the only explanation to the increase in the energy difference is the folding of the catalyst along the NO edges due to the axial ligand. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Epoxidation by oxo Complexes. For example, the relative rates of epoxidation increases upon methyl substitution of the alkene (the methyl groups increase the electron density of the double bond by hyperconjugation): ethylene (1, no methyl groups), propene (24, one methyl group), cis-2-butene (500, two methyl groups), 2-methyl-2-butene (6500, three methyl groups), 2,3-dimethyl-2-butene (>6500, four methyl groups). The cisNO-oxo species is very different from the cisON and trans-L-oxo species. In the case of MnV–cis-oxo species, both quintet and triplet spin states form radical intermediates, with one unpaired electron on the C2 atom coupled to three unpaired electrons on the Mn atom in ferromagnetic and antiferromagnetic fashion, respectively. Jacobsen-Katsuki Epoxidation Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Understanding the mechanism of the epoxidation and the origin of asymmetric induction can lead to the development of new efficient catalysts and therefore is actively pursued (5–19). This interaction accounts for the observed overall nucleophilic character and electrophilic character of the alkene and peracid, respectively. For the trans-MnV-oxo species, Jacobsen and Cavallo (11) and Houk et al. We verify this assumption by studying both spin states rigorously, although quintet cis oxo species should not contribute to enantioselectivity (42). Epoxidation by acylperoxo complexes in the absence of axial ligand. ↵ DOI: 10.1021/cr00020a002. Throughout this work we used a double-ζ LANL2DZ (BS1) (43) basis set with associated Hay–Wadt nonrelativistic effective core potential on Mn (44, 45) for geometry optimizations using the unrestricted B3LYP method.‡ Unless otherwise stated, for the optimized structures we performed and used in discussion single-point energy calculations with triple-ζ quality basis set BS2, comprised of Stuttgart–Dresden basis set (8s7p6d1f)/[6s5p3d1f], with associated effective core potential on Mn (46), and 6-311+G(d) basis set (47) on the other atoms. Asymmetric induction by the trans-MnV-oxo species, besides the chiral C8, C8′ atoms, is believed to result from (i) catalyst twist due to the puckered Mn(NC8C8′N′) ring (28) and (ii) asymmetric fold along the NO edges of the catalyst due to the axial-ligand strain (23). Find more information about Crossref citation counts. The olefin can approach the reactive MnO fragment of both cis and trans-l-isomers of the plain oxo species along multiple distinct directions: native approaches. Vibrational frequency calculations at the B3LYP/BS1 level have been performed only for the transition states to confirm their nature.
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