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 |
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Hauptverfasser: | , , , , , , , , , , , |
Format: | Artikel |
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. |
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ISSN: | 1144-0546 1369-9261 |
DOI: | 10.1039/c9nj02278c |