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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/4105
Title: Synthesis of anionic hypervalent cyclic selenenate esters: Relevance to the hypervalent intermediates in nucleophilic substitution reactions at the selenium (II) center
Authors: Selvakumar K.
Singh H.B.
Goel N.
Singh U.P.
Butcher R.J.
Published in: Chemistry - A European Journal
Abstract: The synthesis of a diaryl diselenide that contains 2,6-dicarboxylic acid groups, 2,2'-diselanediylbis(5-tertbutylisophthalic acid) (10), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5-tertbutyl- 3-oxo-3H-benzo[c] [1,2]oxaselenole- 7-carboxylic acid (11). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4'-bipyridine, to form pyridinium 5-tert-butyl-3- oxo-3H-benzo[c] [1,2]oxaselenole-7-carboxylate (14), adeninium 5-tert-butyl-3-oxo-3H-benzo[c] [1,2]oxaselenole-7-carboxylate (15), and 4,4'-bipyridiniumbis( 5-tert-butyl-3-oxo-3H-benzo[c]-[1,2]oxaselenole-7- carboxylate) (16), respectively. However, 2,2'-diselanediyldibenzoic acid (22) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 14-16 revealed that the Se⋯O (COO-) secondary distances (2.170, 2.075, and 2.176 Ã…) were significantly shorter than the corresponding Se⋯O distances (2.465, 2.472, and 2.435 Ã…) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). 1H, 13C, and 77Se NMR spectroscopy of compounds 11 and 14-16 reveal that the aryl protons of compound 11 and the organic cations of compounds 14-16 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate (14b, pyridinium selenuranide) for compound 14 was detected at low temperatures using 77Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate-exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT-B3LYP/6- 311+g(d) calculations and their structural features compared with the X-ray structure of anionic selenenate esters 14-16. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.
Citation: Chemistry - A European Journal (2012), 18(5): 1444-1457
URI: https://doi.org/10.1002/chem.201003725
http://repository.iitr.ac.in/handle/123456789/4105
Issue Date: 2012
Keywords: Cyclization
Hypervalent compounds
Nucleophilic substitution
Selenenate esters
Selenium
ISSN: 9476539
Author Scopus IDs: 24173504100
35612432200
7102536856
57203181883
7201947292
Author Affiliations: Selvakumar, K., Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
Singh, H.B., Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
Goel, N., Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247677, India
Singh, U.P., Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247677, India
Butcher, R.J., Department of Chemistry, Howard University, Washington, DC 20059, United States
Corresponding Author: Singh, H.B.; Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India; email: chhbsia@chem.iitb.ac.in
Appears in Collections:Journal Publications [CY]

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