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Catalysis Science & Technology
Page 8 of 10
ARTICLE
Journal Name
Conclusions
DOI: 10.1039/D0CY00707B
A functionalized imidazolium salt precursor of a flexible
lutidine-derived polydentate ligand having NHC and -OMe as
side donor functions has been prepared from commercially
available 2,6-bis(bromomethyl)pyridine in two steps.
Deprotonation of the imidazolium salt by [Ir(µ-OMe)(cod)]2
affords the diene complex [IrBr(cod)(C-tBuImCH2PyCH2OMe)]
which on its turn reacts with carbon monoxide rendering the
the carbonyl compound [IrBr(CO)2(C-tBuImCH2PyCH2OMe)]
The polydentate ligand in these iridium(I)-NHC compounds
exhibits a 1C coordination mode with an uncoordinated
pyridine fragment.
York, 2005.
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Compound [IrBr(CO)2(C-tBuImCH2PyCH2OMe)] is an efficient
pre-catalyst for the selective N-monomethylation of
nitroarenes using methanol as both the reducing agent and
the C1 source. A range of functionalized nitroarenes having
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both
electron-donating
and
electron-withdrawing
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substituents, including heterocyclic or sterically hindered
derivatives, have been efficiently converted to the
corresponding N-methyl amines in good to excellent yields at
low catalyst loadings using sub-stoichiometric amounts of
Cs2CO3 as base. Mechanistic investigations based on
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deuterium-labelling experiments support
a
borrowing-
hydrogen mechanism in which methanol acts as hydrogen
source and methylating agent. The study of influence of the
temperature on the selectivity of the N-methylation of
nitrobenzene at a short reaction time and the observed
activity and selectivity for the N-methylation of azobenzene
suggest that the reduction of nitrobenzene by hydrogen
transfer under optimized reaction conditions proceeds
through the direct route.
The modular synthetic approach to the lutidine-based
NHC/OMe ligand opens the way for finely tuning the catalyst in
order to achieve improved performances. Further mechanistic
studies in order ascertain the role of the pyridine and methoxy
donor functions in the catalyst are currently underway in our
laboratory.
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Conflicts of interest
The authors declare no conflict of interest.
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Acknowledgements
Financial support from the Ministerio de Ciencia e Innovación
(MICINN/FEDER) under the Project CTQ2016-75884-P and the
Regional Government of Aragón/FEDER 2014-2020 “Building
Europe from Aragón” (group E42_17R) is gratefully
acknowledged. M. G.-L. thanks MINECO for a predoctoral
fellowship (BES-2014-069624).
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B. Paul, S. Shee, K. Chakrabarti and S. Kundu, ChemSusChem,
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Notes and references
1
(a) S. A. Lawrence, Amines: Synthesis Properties and
Applications, Cambridge University Press, Cambridge, UK,
8 | J. Name., 2012, 00, 1-3
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