Clarifying the structures of imidines: using crystallographic characterization to identify tautomers and localized systems of π-bonding.

Autor: Aristov MM; Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, WI 53703, USA., Geng H; Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, WI 53703, USA., Harris JW; Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, WI 53703, USA., Berry JF; Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, WI 53703, USA.
Jazyk: angličtina
Zdroj: Acta crystallographica. Section C, Structural chemistry [Acta Crystallogr C Struct Chem] 2023 Apr 01; Vol. 79 (Pt 4), pp. 133-141. Date of Electronic Publication: 2023 Mar 15.
DOI: 10.1107/S2053229623002036
Abstrakt: Nitrogen heterocycles are a class of organic compounds with extremely versatile functionality. Imidines, HN[C(NH)R] 2 , are a rare class of heterocycles related to imides, HN[C(O)R] 2 , in which the O atoms of the carbonyl groups are replaced by N-H groups. The useful synthesis of the imidine compounds succinimidine and glutarimidine, as well as their partially hydrolyzed imino-imide congeners, was first described in the mid-1950s, though structural characterization is presented for the first time in this article. In the solid state, these structures are different from the proposed imidine form: succinimidine crystallizes as an imino-amine, 2-imino-3,4-dihydro-2H-pyrrol-5-amine, C 4 H 7 N 2 (1), glutarimidine as 6-imino-3,4,5,6-tetrahydropyridin-2-amine methanol monosolvate, C 5 H 9 N 3 ·CH 3 OH (2), and the corresponding hydrolyzed imino-imide compounds as amino-amides 5-amino-3,4-dihydro-2H-pyrrol-2-one, C 4 H 6 N 2 O (3), and 6-amino-4,5-dihydropyridin-2(3H)-one, C 5 H 8 N 2 O (4). Imidine 1 was also determined as the hydrochloride salt solvate 5-amino-3,4-dihydro-2H-pyrrol-2-iminium chloride-2-imino-3,4-dihydro-2H-pyrrol-5-amine-water (1/1/1), C 4 H 8 N 3 + ·Cl - ·C 4 H 7 N 3 ·H 2 O (1·HCl). As such, 1 and 2 show alternating short and long C-N bonds across the molecule, revealing distinct imino (C=NH) and amine (C-NH 2 ) groups throughout the C-N backbone. These structures provide definitive evidence for the predominant imino-amine tautomer in the solid state, which serves to enrich the previously proposed imidine-focused structures that have appeared in organic chemistry textbooks since the discovery of this class of compounds in 1883.
(open access.)
Databáze: MEDLINE
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