Linked Life Data

11466066

Source:http://linkedlifedata.com/resource/pubmed/id/11466066

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
16
pubmed:dateCreated
2001-7-23
pubmed:abstractText
The (salen)Mn(III)-catalyzed epoxidation reaction mechanism has been investigated using density functional theory (DFT). There is considerable interest in and controversy over the mechanism of this reaction. The results of experimental studies have offered some support for three different reaction mechanisms: concerted, stepwise radical, and metallooxetane mediated. In this paper, a theoretical examination of the reaction suggests a novel mechanism that describes the reaction as a multichannel process combining both concerted and stepwise radical pathways. The competing channels have different spin states: the singlet, the triplet, and the quintet. The singlet reaction pathway corresponds to a concerted mechanism and leads exclusively to a cis epoxide product. In contrast, the triplet and quintet reactions follow a stepwise mechanism and lead to a product mixture of cis and trans epoxides. We show that the experimentally observed dependence of isomer product ratios on electronic effects connected with the substitution of the catalyst ligands is due to changing the relative position and, hence, the relative activities of the channels with different cis-trans yields. Because the results and conclusions of the present work dramatically differ from the results and conclusion of the recent DFT theoretical investigation (Linde, C.; Akermark, B; Norrby, P.-O.; Svensson, M. J. Am. Chem. Soc. 1999, 121, 5083.), we studied possible sources for the deep contradictions between the two works. The choice of the DFT functional and a model has been shown to be crucial for accurate results. Using high level ab initio calculations (coupled cluster-CCSD(T)), we show that the computational procedure employed in this study generates significantly more reliable numerical results. It is also shown that the smaller cationic model without a chlorine ligand that was used by Linde et al. is too oversimplified with respect to our larger neutral model. For this reason, using the cationic model led to a qualitatively wrong quintet reaction profile that played a key role in theoretical postulates in the earlier work.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0020-1669
pubmed:author
pubmed:issnType
Print
pubmed:day
30
pubmed:volume
40
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
4040-8
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2001
pubmed:articleTitle
(Salen)Mn(III)-catalyzed epoxidation reaction as a multichannel process with different spin states. Electronic tuning of asymmetric catalysis: a theoretical study.
pubmed:affiliation
Advanced Biomedical Computing Center, National Cancer Institute at Frederick, SAIC Frederick, P.O. Box B, Frederick, MD 21702-1201, USA.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S.