期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 20, 期 14, 页码 3966-3973出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201303885
关键词
carbocations; catalysis; electrocyclization; reaction mechanisms; supramolecular chemistry
资金
- NSF [CHE-0233882, CHE-0840505]
- Office of Science, Office of Basic Energy Sciences
- Division of Chemical Sciences, Geosciences, and Biosciences of the U.S. Department of Energy at LBNL [DE-AC02-05CH11231]
The self-assembled supramolecular host [Ga4L6](12-) (1; L=N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) catalyzes the Nazarov cyclization of 1,3-pentadienols with extremely high levels of efficiency. The catalyzed reaction proceeds at a rate over a million times faster than that of the background reaction, an increase comparable to those observed in some enzymatic systems. A detailed study was conducted to elucidate the reaction mechanism of both the catalyzed and uncatalyzed Nazarov cyclization of pentadienols. Kinetic analysis and O-18-exchange experiments implicate a mechanism, in which encapsulation, protonation, and water loss from substrate are reversible, followed by irreversible electrocyclization. Although electrocyclization is rate determining in the uncatalyzed reaction, the barrier for water loss and for electrocyclization are nearly equal in the assembly-catalyzed reaction. Analysis of the energetics of the catalyzed and uncatalyzed reaction revealed that transition-state stabilization contributes significantly to the dramatically enhanced rate of the catalyzed reaction.
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