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A zwitterion produced by a strong intramolecular N→B interaction in 1‐hydroxy‐2‐(pyridin‐2‐ylcarbonyl)benzo[ d ][1,2,3]diazaborinine
Author(s) -
Sarina Evan A.,
Olmstead Marilyn M.,
Kanichar Divya,
Groziak Michael P.
Publication year - 2015
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229615021841
Subject(s) - intramolecular force , chemistry , zwitterion , lewis acids and bases , boron , chemical shift , stereochemistry , crystal structure , crystallography , chelation , nuclear magnetic resonance spectroscopy , medicinal chemistry , molecule , catalysis , inorganic chemistry , organic chemistry
2‐Acylated 2,3,1‐benzodiazaborines can display unusual structures and reactivities. The crystal structure analysis of the boron heterocycle obtained by condensing 2‐formylphenylboronic acid and picolinohydrazide reveals it to be an N→B‐chelated zwitterionic tetracycle (systematic name: 1‐hydroxy‐11‐oxo‐9,10,17λ 5 ‐triaza‐1λ 4 ‐boratetracyclo[8.7.0.0 2,7 .0 12,17 ]heptadeca‐3,5,7,12,14,16‐hexaen‐17‐ylium‐1‐uide), C 13 H 10 BN 3 O 2 , produced by the intramolecular addition of the Lewis basic picolinoyl N atom of 1‐hydroxy‐2‐(pyridin‐2‐ylcarbonyl)benzo[ d ][1,2,3]diazaborinine to the boron heterocycle B atom acting as a Lewis acid. Neither of the other two pyridinylcarbonyl isomers ( viz . nicotinoyl and isonicotinoyl) are able to adopt such a structure for geometric reasons. A favored yet reversible chelation equilibrium provides an explanation for the slow D 2 O exchange observed for the OH resonance in the 1 H NMR spectrum, as well as for its unusual upfield chemical shift. Deuterium exchange may take place solely in the minor open (unchelated) species present in solution.