Full Papers
doi.org/10.1002/cctc.202100635
ChemCatChem
Convenient and Reusable Manganese-Based Nanocatalyst
for Amination of Alcohols
Murugan Subaramanian,[a] Palmurukan M. Ramar,[a] Ganesan Sivakumar,[a]
Ravishankar G. Kadam,[b] Martin Petr,[b] Radek Zboril,[b] Manoj B. Gawande,[b] and
Ekambaram Balaraman*[a]
The development of new sustainable nanocatalytic systems for
green chemical synthesis is a growing area in chemical science.
Herein, a reusable heterogeneous N-doped graphene-based
manganese nanocatalyst (Mn@NrGO) for selective N-alkylation
of amines with alcohols is described. Mechanistic studies
illustrate that the catalytic reaction follows a domino dehydro-
genation-condensation-hydrogenation sequence of alcohols
and amines with the formation of water as the sole by-product.
The scope of the reaction is extended to the synthesis of
pharmaceutically important N-alkylated amine intermediates.
The heterogeneous nature of the catalyst made it easy to
separate for long-term performance, and the recycling study
revealed that the catalyst was robust and retained its activity
after several recycling experiments.
Introduction
metals[6] as well as base-metal catalysts have been well
developed for the BH reactions.[7a]
N-alkylated amines are widely employed for the synthesis of
various biologically active molecules, agrochemicals, surfac-
tants, and pharmaceutical drugs.[1] Conventionally, the N-
alkylation of amines has been achieved by utilizing the
corresponding activated derivatives[2] or by reductive amination
of carbonyl compounds.[3] However, most of these methods
require harsh or potentially hazardous reaction conditions and
generate stoichiometric waste. The borrowing hydrogenation
(BH) deploying simple and abundantly available alcohols as
alkylating agents for the CÀ C or CÀ N bond-forming reactions
has recently received considerable attention.[4] The formation of
water as the only byproduct makes this process environ-
mentally benign and alternative to conventional methods.[2,5]
The BH approach fundamentally comprises several mechanisti-
cally distinguished pathways such as dehydrogenation, con-
densation, and hydrogenation in a single process. It finally
yields CÀ N or CÀ C bonded compounds with an excellent step-
and atom-economy. Thus, the use of widespread alcohol as the
alkylating agent for the BH method ensures the sustainability of
the synthesis of N-alkyl amines. Indeed, several efficient
homogeneous catalytic reactions based on precious noble
However, the requirement of an extensive ligand synthesis,
sensitivity, handling under practical conditions, and poor
recovery of the catalysts are potential disadvantages. Providing
earth-abundant base metal catalysts as an alternative to
precious noble metal catalysts represents a key challenge in
contemporary science.[7] Similarly, alternative benign ap-
proaches to employing stoichiometric reagents in industrially
important reactions are vital. In this direction, the prime
research objective of the chemical and pharmaceutical indus-
tries is to convert homogeneous catalytic reactions into
heterogeneous versions through the immobilization of catalyti-
cally active sites on stable supports.[8] Heterogeneous catalysts
have numerous advantages over homogeneous ones, including
high recyclability and easy recovery from the reaction mixture.
Various heterogeneous cobalt,[9] nickel,[10] and iron- based
catalysts[11] have made a substantial contribution to the field of
dehydrogenation and related reactions. Notably, the employ-
ment of the manganese-based catalytic system, the third most
abundant metal in the earth’s crust, found manifold applica-
tions in synthetic transformation.[12] In recent years, remarkable
progress in homogeneous Mn-catalyzed acceptorless dehydro-
genation (AD) and BH reactions has been made by several
research groups including Milstein, Beller, Kirchner, Sortais,
Kempe, and others (Scheme 1).[7,13] However, a reusable hetero-
geneous manganese-based catalyst system for the BH strategy
remains elusive. Particularly, the N-alkylation of amines under
the BH strategy using heterogeneous catalyzed conditions is
very limited and rarely reported.[10,14]
[a] M. Subaramanian, P. M. Ramar, G. Sivakumar, Prof. E. Balaraman
Department of Chemistry
Indian Institute of Science Education and Research (IISER) Tirupati
517507, Tirupati (India)
E-mail: eb.raman@iisertirupati.ac.in
[b] Dr. R. G. Kadam, Dr. M. Petr, Prof. R. Zboril, Prof. M. B. Gawande
Regional Centre of Advanced Technologies and Materials
Palacky University
Of late, a variety of noble-metal nanoparticles decorated on
an electron-rich carbon, which delivers active sites for the
catalyst, have been widely investigated. Sustainable develop-
ment of the heteroatom-doped carbon-based supports is
fascinating due to their semiconductive nature, in which
electronic density can be tuned by the amount of heteroatom
doping. Due to the presence of lone pairs, the heteroatom
78371, Olomouc (Czech Republic)
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This publication is part of a Special Collection on “Supported Nanoparticles
and Single-Atoms for Catalysis: Energy and Environmental Applications”.
Please check the ChemCatChem homepage for more articles in the col-
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ChemCatChem 2021, 13, 1–9
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