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Download fileTerpyridine–Ru Complexes Noncovalently Supported on Cobalt Magnetic Nanoparticles for Nitroarene Transfer Hydrogenation
journal contribution
posted on 2020-11-20, 17:38 authored by Houria Asri, Olivier Dautel, Armelle OualiThis work reports the preparation
and characterization of active
and recyclable supported catalysts involving molecular Ru–terpyridine
complexes and their ability to promote the transfer hydrogenation
of nitroarenes in 2-propanol. The system proposed is based on the
design of original pyrene-tagged terpyridine ligands, either monomeric
“1tpy” (one pyrene
tag for one terpyridine) or multivalent “5tpy” (one pyrene tag for five terpyridines),
able to interact with the graphene surface of commercially available
cobalt magnetic nanoparticles (MNPs) through π-stacking interactions.
The existence of noncovalent interactions between the pyrene-tagged
terpyridines and the MNP surface at 20 °C was assessed by fluorescence
spectroscopy for the first time in 2-propanol, an organic medium.
Interestingly, 1tpy and 5tpy were shown to be released upon
temperature increase (80 °C) while the association was restored
upon temperature decrease (20 °C). The reversibility of this
phenomenon enabled to reach high activities in nitroarene transfer
hydrogenation for the corresponding Ru complexes (catalytic species
are free in refluxing 2-propanol) and high recyclabilities (noncovalent
interactions are restored upon cooling). It is noteworthy that the
multivalent ligand 5tpy displaying,
as expected, the higher terpyridine loading (0.15 mmol of tpy/g of
MNPs vs 0.03 mmol for 1tpy) also
gave rise to the Ru catalyst with the best recyclability (8 consecutive
cycles with no loss of activity against 5 cycles for the catalyst
based on the monomeric ligand 1tpy). In both cases, the ruthenium leaching was found to be low and
the expected aniline met the requirements of the pharmaceutical industry
(<10 ppm Ru) from the third run.