New palladium() complexes with 3-(2-pyridyl)-5-alkyl-1,2,4-triazole ligands as recyclable C-C coupling catalysts

A series of palladium( ii ) complexes with 3-(2-pyridyl)-5 R -1,2,4-triazoles Pd(L R ) 2 (R = ethyl ( 4a ), n -propyl ( 4b ), i-propyl ( 4c ) and t -butyl ( 4d )) have been synthesised and characterised by NMR, IR, UV-vis spectroscopy, ESI and MALDI-TOF mass spectrometry. Single-crystal X-ray diffra...

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Veröffentlicht in:New journal of chemistry 2019-07, Vol.43 (27), p.1973-1984
Hauptverfasser: Zakharchenko, Borys V, Khomenko, Dmytro M, Doroshchuk, Roman O, Raspertova, Ilona V, Starova, Viktoriia S, Trachevsky, Volodymyr V, Shova, Sergiu, Severynovska, Olga V, Martins, Luísa M. D. R. S, Pombeiro, Armando J. L, Arion, Vladimir B, Lampeka, Rostyslav D
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Sprache:eng
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Zusammenfassung:A series of palladium( ii ) complexes with 3-(2-pyridyl)-5 R -1,2,4-triazoles Pd(L R ) 2 (R = ethyl ( 4a ), n -propyl ( 4b ), i-propyl ( 4c ) and t -butyl ( 4d )) have been synthesised and characterised by NMR, IR, UV-vis spectroscopy, ESI and MALDI-TOF mass spectrometry. Single-crystal X-ray diffraction study of 4a-d revealed a square-planar coordination geometry, in which the N^N chelating monoanionic ligands adopt a trans -configuration around Pd( ii ) and show notable intraligand C-H N hydrogen bonding within the complex. The solid state emission and excitation spectra of 4a-d showed vibronic structure of the spectra at room temperature. The TG/DTA curves of 4a-c revealed that the complexes are stable up to ca. 250 °C, whereas 4d starts to decompose at 230 °C. Compounds 4a-d efficiently catalyse the nitroaldol (Henry) reaction of benzaldehyde with nitroethane in water, methanol and ethanol with appreciable diastereoselectivity in favour of the syn -isomer ( syn  :  anti up to 81 : 19). In addition, 4a-d catalyse the microwave-assisted Suzuki-Miyaura cross-coupling reaction of bromoanisole with phenyl boronic acid, in the presence of a base. Moreover, these heterogeneous catalysts can be recovered and reused without losing activity for several consecutive cycles. Compounds 4a-d revealed good catalytic activity and prospects for use as mesomorphic materials.
ISSN:1144-0546
1369-9261
DOI:10.1039/c9nj02278c