Different Patterns of Pd-Promoted C-H Bond Activation in (Z)-4-Hetarylidene-5(4H)-oxazolones and Consequences in Photophysical Properties

Martínez, Miguel ; Dalmau, David ; Crespo, Olga (Universidad de Zaragoza) ; García-Orduña, Pilar ; Lahoz, Fernando ; Martín, Antonio ; Urriolabeitia, Esteban P.

Resumen: This work aims to amplify the fluorescence of (Z)-4-hetarylidene-5(4H)-oxazolones 1 by suppression of the hula-twist non-radiative deactivation pathway by C^N-orthopalladation of the 4-hetarylidene ring. Different (Z)-4-hetarylidene-2-phenyl-5(4H)-oxazolones, 1a–1c, prepared by the Erlenmeyer–Plöchl method, have been studied. The orthopalladation of (Z)-2-phenyl-4-(5-thiazolylmethylene)-5(4H)-oxazolone (1a) takes place by C-H bond activation of the H4 of the heterocycle and C^N-chelation, giving the dinuclear trifluoroacetate derivative 2a. By further metathesis of bridging ligands in 2a, complexes containing the orthometalated oxazolone and a variety of ligands 3a–5a, were prepared. The study of the photophysical properties of 1a–5a shows that the bonding of the Pd metal to the 4-hetaryliden-5(4H)-oxazolone does not promote, in these cases, an increase in fluorescence. Interestingly, the orthopalladation of (Z)-2-phenyl-4-(4-thiazolylmethylene)-5(4H)-oxazolone (1b) gives orthopalladated 2b, where the incorporation of the Pd to the oxazolone takes place by C-H bond activation of the ortho-H2 of the 2-phenyl group, ring opening of the oxazolone heterocycle and simultaneous N,N-bonding of the N atoms of the thiazole ring and the generated benzamide fragment. This N^N^C-tridentate dianionic bonding mode is obtained for the first time in oxazolones. Despite a similar lock of the hula-twist deactivation, 2b does not show fluorescence.

Idioma: Inglés

DOI: 10.3390/inorganics12100271

Año: 2024

Publicado en: Inorganics 12, 10 (2024), 271 [16 pp.]
ISSN: 2304-6740

Financiación: info:eu-repo/grantAgreement/ES/DGA/E07-23R
Financiación: info:eu-repo/grantAgreement/ES/DGA/E17-23R
Financiación: info:eu-repo/grantAgreement/ES/MICINN AEI/PID2022-136861NB-I00
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2019-106394GB-I00
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2021-122869NB-I00

Tipo y forma: Article (Published version)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)