Selvakumar, Karuthapandi;
Singh, Harkesh B.;
Goel, Nidhi;
Singh, Udai P.;
Butcher, Ray J.
Synthesis of Anionic Hypervalent Cyclic Selenenate Esters: Relevance to the Hypervalent Intermediates in Nucleophilic Substitution Reactions at the Selenium(II) Center
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Medientyp:
E-Artikel
Titel:
Synthesis of Anionic Hypervalent Cyclic Selenenate Esters: Relevance to the Hypervalent Intermediates in Nucleophilic Substitution Reactions at the Selenium(II) Center
Beteiligte:
Selvakumar, Karuthapandi;
Singh, Harkesh B.;
Goel, Nidhi;
Singh, Udai P.;
Butcher, Ray J.
Erschienen:
Wiley, 2012
Erschienen in:
Chemistry – A European Journal, 18 (2012) 5, Seite 1444-1457
Sprache:
Englisch
DOI:
10.1002/chem.201003725
ISSN:
0947-6539;
1521-3765
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The synthesis of a diaryl diselenide that contains 2,6‐dicarboxylic acid groups, 2,2′‐diselanediylbis(5‐<jats:italic>tert</jats:italic>‐butylisophthalic acid) (<jats:bold>10</jats:bold>), is described. Diselenide<jats:bold>10</jats:bold>undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5‐<jats:italic>tert</jats:italic>‐butyl‐3‐oxo‐3<jats:italic>H</jats:italic>‐benzo[<jats:italic>c</jats:italic>][1,2]oxaselenole‐7‐carboxylic acid (<jats:bold>11</jats:bold>). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4′‐bipyridine, to form pyridinium 5‐<jats:italic>tert</jats:italic>‐butyl‐3‐oxo‐3<jats:italic>H</jats:italic>‐benzo[<jats:italic>c</jats:italic>][1,2]oxaselenole‐7‐carboxylate (<jats:bold>14</jats:bold>), adeninium 5‐<jats:italic>tert</jats:italic>‐butyl‐3‐oxo‐3<jats:italic>H</jats:italic>‐benzo[<jats:italic>c</jats:italic>][1,2]oxaselenole‐7‐carboxylate (<jats:bold>15</jats:bold>), and 4,4′‐bipyridiniumbis(5‐<jats:italic>tert</jats:italic>‐butyl‐3‐oxo‐3<jats:italic>H</jats:italic>‐benzo[<jats:italic>c</jats:italic>][1,2]oxaselenole‐7‐carboxylate) (<jats:bold>16</jats:bold>), respectively. However, 2,2′‐diselanediyldibenzoic acid (<jats:bold>22</jats:bold>) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters<jats:bold>14</jats:bold>–<jats:bold>16</jats:bold>revealed that the Se⋅⋅⋅O (COO<jats:sup>−</jats:sup>) secondary distances (2.170, 2.075, and 2.176 Å) were significantly shorter than the corresponding Se⋅⋅⋅O distances (2.465, 2.472, and 2.435 Å) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt).<jats:sup>1</jats:sup>H,<jats:sup>13</jats:sup>C, and<jats:sup>77</jats:sup>Se NMR spectroscopy of compounds <jats:bold>11</jats:bold>and<jats:bold>14</jats:bold>–<jats:bold>16</jats:bold>reveal that the aryl protons of compound<jats:bold>11</jats:bold>and the organic cations of compounds<jats:bold>14</jats:bold>–<jats:bold>16</jats:bold>exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate (<jats:bold>14 b</jats:bold>, pyridinium selenuranide) for compound<jats:bold>14</jats:bold>was detected at low temperatures using<jats:sup>77</jats:sup>Se 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<jats:bold>14</jats:bold>–<jats:bold>16</jats:bold>.</jats:p>