Molecular Catalysis
Diaza crown-type macromocycle (kryptofix 22) functionalised carbon
nanotube for efficient Ni2+ loading; A unique catalyst for cross-coupling
reactions
a
a,
b,
Michael Aalinejad , Nader Noroozi Pesyan *, Esmail Doustkhah *
a
Department of Organic Chemistry, Faculty of Chemistry, Urmia University, 57159, Urmia, Iran
International Center for Materials Nanoarchitechtonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Raising the capability of supporting and suppressing the leaching possibility to a very insignificant level has still
remained challenging for some class of transition metals, i.e. Ni . Here we present the covalent functionali-
2
+
Carbon nanotube
CeC coupling
eCN coupling
eCO coupling
Kryptofix 22
sation of macrocyclic ligand, 4,13-diaza-18-crown-6 (kryptofix 22), on the surface of carbon nanotube (CNT),
2+
leading to a unique adsorptive capability for supporting Ni . This material was incorporated as a promising
catalyst in coupling reactions including CeC, CN, and COee cross-coupling reactions. We demonstrate that the
kryptofix 22 functionalisation on the surface of CNT has a key role in the enhancement of the adsorption cap-
ability Ni2+ and subsequent catalytic activity. We further prove that this ligand causes a significant boost in the
4
,13-diaza-18-crown-6
2
+
recyclability of the reactions due to the extremely trivial Ni
reactions.
leaching from the CNT’s surface during the
1
. Introduction
even gaseous compounds [26–28]. Therefore, we used kryptofix 22 to
functionalise the surface of CNT to reinforce the surface loading cap-
ability. Kryptofix 22 is a highly potential macrocyclic compound for
incorporating in variety of applications due to its strong complexation
capability [29–31]. This macrocyclic compound can compose an orga-
nometallic complex with a broad number of metal ions by wrapping
and surrounding the metal with several nitrogen and oxygen atoms
[31]. Therefore, kryptofix 22 is expectable to have a high capacity in
loading metal ions and therefore, it is a promising candidate to be
functionalised on a heterogeneous surface to act as a ligand. The use of
Ni species as catalyst can be of great importance since Ni is a great
alternative to precious metals for coupling reactions from viewpoint of
cost-efficiency.
Nanoarchitecture of carbon-based materials toward a unique and
smart heterogeneous catalyst has acquired a significant attention in
recent years toward green chemical processes [1–4]. Heterogeneous
catalysts, among them, with transition metal basis as the frontiers of
green catalysis for chemical processes have granted many break-
throughs in the field [5–8], however, several transition metal ions like
2
+
Ni
are suffering from the high efficiency being efficiently loaded on
the surface with insignificant leaching [9–14]. Therefore, researches to
develop the textural ability of a heterogenous surface for a stronger
bonding to the metal ions are still ongoing. Among the candidates, pure
carbon-based materials can have only some weak bonding or interac-
tions with most metal ions and therefore, lead to an inefficient catalyst
due to low loading capacity and high leaching possibility [15–17].
However, bearing in mind that some of carbon materials (e.g. CNT)
have a high surface area, stability and potential in surface modification
In this work, we designed a catalyst by modifying the CNT surface
with kryptofix 22 to enhance the Ni2+ loading capacity [32], and
subsequent rise in the catalytic activity in the recyclability. This catalyst
3
was incorporated in the cross coupling of Ph SnCl with three different
[
18,19], it can easily convert to an exceptional material through
species including aromatic amine (CeN coupling), aromatic halides
(CeC coupling), and phenols (CeO coupling). We present a catalyst
high stability, surface area and recyclability for coupling reactions.
modifying the surface [16,20–25]. Therefore, we aimed to design a
catalyst based on CNT with subsequent modification toward a Ni2+
supported catalyst.
On the basis of previous reports, crown ether macrocyclic com-
pounds have an excellent capacity toward adsorption of metal ions,
⁎
Received 20 April 2020; Received in revised form 8 June 2020; Accepted 6 July 2020
2468-8231/ © 2020 Elsevier B.V. All rights reserved.