Paper
Catalysis Science & Technology
in aniline's 4-position led to lower 28% yield even with
higher temperature and base loading (3ea). Interestingly, no
significant hydrogenation of the nitro group was observed
here. Halide-substituted anilines including 4-iodoaniline
(3fa) were selectively methylated without significant
dehalogenation side-reactions. Additionally, electron-rich
4-methoxyaniline gave the corresponding product with a high
yield or 85% (3ha). Furthermore, 2-aminopyridine allowed for
methylation, albeit with lower reactivity, while the
corresponding 2-amino pyrimidine was not methylated at all
(3ja). On the other hand, 1-amino naphthalene did not cause
many problems, so that the corresponding product was
obtained in 65% yield (3ka). Interestingly, 4-amidoaniline
gave very good 92% of the corresponding product without
methylation of the amido-group (3la). Unfortunately testing
primary aliphatic amines as substrates under analogous
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conditions
methylation.
revealed
only
negligible
reactivity
for
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Conclusions
To sum up, in this work cyclometalated ruthenium
complexes have been established as novel catalysts for the
methylation of anilines using methanol via a hydrogen
autotransfer procedure. The optimal system 9 bearing a
phenyl imidazoline as bidentate ligand likely works in a
homogenous manner with β-hydride elimination of
methanol to form
a
Ru–H species being the rate
determining step. Compared to other known catalysts for
this transformation, 9 allows to work under very mild
reaction conditions without the necessity of strong/
expensive bases.
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
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We thank the state of Mecklenburg-Vorpommern, the
Bundesministerium für Bildung und Forschung (BMBF), and
the European Research Council (ERC Advanced grant
NoNaCat) for financial support. We also thank the analytical
department of LIKAT for technical support.
29 M. Huang, Y. Li, Y. Li, J. Liu, S. Shu, Y. Liu and Z. Ke, Chem.
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2516 | Catal. Sci. Technol., 2021, 11, 2512–2517
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