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Title: Insights into the photochemistry of 5-aminotetrazole derivatives with applications in coordination chemistry. Effect of the saccharyl moiety on the photostability
Authors: Ismael, Amin 
Abe, Manabu
Lourenço, Rui Fausto Martins Ribeiro da Silva 
Cristiano, Maria L. S. 
Keywords: 5-aminotetrazoles; ICPOC-24; Light-induced selectivity; Photocleavage mechanisms; Reactive intermediates; Substituent effects; Tetrazole-saccharinates
Issue Date: 2020
Publisher: De Gruyter
Project: info:eu-repo/grantAgreement/FCT/04326/2013/PT 
info:eu-repo/grantAgreement/POCI-01-0145- FEDER-016617 
info:eu-repo/grantAgreement/FCT/SFRH/BD/ 90435/2012 
Serial title, monograph or event: Pure and Applied Chemistry
Volume: 92
Issue: 1
Abstract: The properties and applications of 2-methyl-(2H)-tetrazole-5-amino-saccharinate (2MTS) in catalysis and chelant-based chemotherapy stimulated investigations on its photostability. The photochemistry of monomeric 2MTS in solid argon (15 K) was compared with those of 2-methyl-(2H)-tetrazole-5-amine (2MT) and 1-methyl-(2H)-tetrazole-5-amine (1MT). Compounds were subjected to in situ narrowband UV-irradiation at different wavelengths. Reactions were followed by infrared spectroscopy, supported by B3LYP/6-311++G(d,p) calculations. Photochemical pathways for 2MT and 2MTS proved similar but photodegradation of 2MTS was 20× slower, unraveling the photostabilizing effect of the saccharyl moiety that extends into the nitrilimine formed from 2MTS and its antiaromatic 1H-diazirene isomer, which proved photostable at 290 nm, unlike the 1H-diazirene formed from 2MT. Analysis of the photochemistries of 2MTS/2MT (250 nm) and 1MT (222 nm), including energy trends calculated for the isomeric C2H5N3 species postulated/observed from photolysis and EPR results, enabled a deeper insight into the photodegradation mechanisms of 1,5-substituted and 2,5-substituted tetrazoles. We postulate a pivotal singlet state imidoylnitrene species, sN1, as common intermediate, which undergoes a Wolff-type isomerization to a stable carbodiimide. Photo-extrusion of N2 from 1,5-substituted tetrazoles generates sN1 directly but from 2,5-substituted tetrazoles it originates a nitrilimine, then a diazirene, which finally leads to sN1. Selective formation of cyanamide from 1MT requires photoisomerization between sN1 and sN2, accessible at 222 nm. EPR studies enabled the detection of methyl nitrene, arising from photolysis of 1H-diazirene intermediate.
ISSN: 1365-3075
DOI: 10.1515/pac-2019-0402
Rights: embargoedAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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