Dichiral [4.4.3.01,5]tridecane copper(II) cluster derived from a tripodal ligand having unsymmetrical podands and the linker: Synthesis, structure, surface grafting and catalytic aspects

Article abstract of DOI:10.1002/aoc.6075

Pseudo-atranes have a significant role in catalysis; however, obtaining chiral pseudo-atranes for covalent functionalization of heterogeneous catalytic surfaces is very challenging. Herein, synthesis of a chiral tripodal amine [N{CH (CH₂Ph)CH

Full text of DOI:10.1002/aoc.6075

Received: 23 July 2020
DOI: 10.1002/aoc.6075
Revised: 28 September 2020
Accepted: 5 October 2020
F U L L P A P E R
Dichiral [4.4.3.01,5]tridecane copper(II) cluster derived from
a tripodal ligand having unsymmetrical podands and the
linker: Synthesis, structure, surface grafting and catalytic
aspects
Hemant Singh1
Varinder Kaur1
| Navneet Taya1
| Jyoti Agarwal1
| Raghubir Singh2
|
1Department of Chemistry, Panjab
University, Chandigarh, India
2DAV College, Chandigarh, India
Pseudo-atranes have a significant role in catalysis; however, obtaining chiral
pseudo-atranes for covalent functionalization of heterogeneous catalytic sur-
faces is very challenging. Herein, synthesis of a chiral tripodal amine [N{CH
(CH2Ph)CH2OH}{CH2(4 Br C6H3OH)}{CH2(2 CHO 4 Me C6H2OH)}] (1)
and a dichiral [4.4.3.01,5]tridecane copper(II) cluster, that is, (Cu[N{CH
(CH2Ph)CH2OH}{CH2(4 Br C6H3O)}{CH2(2 CHO 4 Me C6H2O)}])2 (2) is
described. The compounds are characterized by elemental analyses, Fourier
transform infrared (FT-IR) spectroscopy, mass spectrometry and single-crystal
X-ray crystallography (for 2). The compound 2 is the first example of chiral
pseudo-copper(II)atrane in which three unsymmetrical arms (two phenolic
and a chiral ethanolic arm) are fused via Cu N transannular bond. The free
CHO group present in one of the tricyclic arms of the 2 is tested as a linker
to load it on 3-aminopropyltriethoxysilane-functionalized magnetic nanosilica
for catalytic applications. The loading of 2 on magnetic nanosilica through
CHO was confirmed by FT-IR spectroscopy, and the 2-loaded magnetic
nanosilica (Fe3O4@SiO2/2) was characterized by powder X-ray diffraction,
vibrating sample magnetometry, scanning electron microscopy, energy-
dispersive X-ray spectroscopy and elemental mapping. The Fe3O4@SiO2/2 was
found highly efficient, retrievable, eco-friendly and green catalyst for obtaining
β-amino alcohols in excellent yields in an aqueous medium. Overall, present
work is the first report on synthetic, structural and catalytic aspects of dichiral
cluster of copper(II)atrane possessing unsymmetrical tricyclic arms.
Correspondence
Raghubir Singh, DAV College, Sector
10, Chandigarh 160011, India.
Email: raghubirsingh@davchd.ac.in
Varinder Kaur, Department of Chemistry,
Panjab University, Chandigarh 160014,
India.
Email: var_ka04@pu.ac.in
Funding information
Science and Engineering Research Board,
Grant/Award Number:
EMR/2016/006530; DST-FIST, Grant/
Award Number: SR/FST/college-
335/2016; UGC-JRF, Grant/Award
Number: 2061510021
K E Y W O R D S
bisphenolate, pseudo-atrane, functionalized magnetic silica, unsymmetrical tripod, epoxide ring-
opening
Appl Organomet Chem. 2020;e6075.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6075

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SINGH ET AL.
1 | INTRODUCTION
azomethinic bond was confirmed by Fourier transform
infrared (FT-IR) spectroscopy and Fe3O4@SiO2/2 was
characterized by powder X-ray diffraction (PXRD),
vibrating sample magnetometry (VSM), scanning elec-
tron microscopy (SEM), energy-dispersive X-ray spectros-
copy (EDS) and elemental mapping.
The [4.4.3.01,5]tridecane metal cages are continuously
achieving interest due to their fascinating structural attri-
butes and relevance in catalysis.[1–6] These are named as
‘pseudo-atranes’ due to their structural analogy with
metallatranes. The pseudo-atranes with [4.4.3.01,5
tridecane cage differ from the atranes (having [3.3.3.01,5
]
]
In the past, some excellent reports are available on
the usage of copper functionalized magnetic nanosilica
for catalyzing organic reactions like asymmetric Henry
reaction (by bis(oxazoline)copper(II) complex grafted
undecane metal cages) in terms of the number or compo-
sition of the tricyclic ring atoms.[7–11] The bulky and less
flexible skeletons of [4.4.3.01,5]tridecane cages encapsu-
late the metal from one side making the other side avail-
able for catalytic reactions. For example, tripodal ligands
with bisphenolate arms serve as best ancillary ligating
frameworks in catalytic applications due to their struc-
tural rigidity. The most recent contribution of
bisphenolate armed [4.4.3.01,5]tridecane metallatranes as
reaction mediators includes copolymerization reactions
of CO2 and cyclohexene oxide, polymerization of methac-
rylate, hydrophosphination of alkenes, alkynes and
heterocumulenes, ring-opening polymerization of L-lactic
acid, o-carboxy anhydrides and L-lactide, epoxidation,
sulfoxidation and catechol oxidation and cycloaddition of
epoxides.[12–24] The metal centres of metallatrane cata-
lysts are widely distributed among various elements, that
is, s-block (K), p-block (Al), d-block (Ti, Zr, Zn, Cr, V,
Mo, W) and f-block elements (Y, Yb, Nd, La, Sm).
Although bisphenolate atranes of Fe(III), Co(III), Cu(II),
Si(IV) and Sn(IV) are known; however, their use in catal-
ysis is rarely reported.[1,25,26] The inexpensiveness, conve-
nient synthetic protocols and broad spectrum of
copper(II) complexes in catalysis[27–29] inspired us to syn-
thesize the copper(II)atrane complex and extend its appli-
cation in the catalysis.
magnetic
mesoporous
silica[30]),
synthesis
of
3,4-dihydropyrimidin-2(1H)-ones (by magnetic meso-
porous SBA-15[31]), Beckmann rearrangement in
poly(ethylene glycol) (by copper(II) complex supported
magnetic nanoparticles[32]), synthesis of pyrano[2,3-b]
pyridine-3-carboxamide (by Schiff-base copper(II) com-
plex grafted magnetic material[33]), Suzuki reaction
(by copper/ppm palladium nanoparticles[34]), aerobic oxi-
dation of alcohols (by copper complex-grafted magnetic
graphene oxide[35]), click reaction (magnetic copper-
pectin composite[36]) and oxidation reactions at room
temperature
(chitosan-dithiocarbamate
magnetic
nanocomposite).[37] Besides, grafting of chiral copper
complexes on nonmagnetic mesostructured silica sur-
faces is also reported which includes bis(oxazoline)cop-
per(II) complex for kinetic resolution of hydrobenzoin,
enantioselective cyclopropanation Cu(II)salen complex
grafted for Henry reaction and amino indanol-based
copper(II) complex for the asymmetric hetero-Diels-Alder
reaction.[38–41] This is the first report where a dichiral
[4.4.3.01.5]tridecane cage of copper is directly loaded to
the magnetic nanosilica and the fabricated material was
tested for catalyzing the synthesis of β-amino alcohols
(precursors of many biological active compound, syn-
thetic products and unsaturated amino acids[42–44]) in
aqueous conditions. Although the chiral copper com-
plexes yield optically active compounds in bulk amounts
even when present in traces and catalyse, a wide range of
Therefore, a novel amine ligand N{CH (CH2Ph)
CH2OH}{CH2(4 Br C6H3OH)}
{CH2(2 CHO 4 Me C6H2OH)} (1) having an ethanolic
and two distinct phenolate podands was synthesized. The
ligand was designed to introduce chirality in the flexible
ethanolic arm so that a chiral centre could be generated
for its application in asymmetric catalysis. Besides, one of
the phenolate arms of 1 was introduced with CHO
group so that the ligating skeleton or its complex could
be grafted on the solid surface to obtain the heteroge-
neous catalyst. The tripodal amine 1 was used as a ligand
to obtain symmetric dinuclear cluster of copper(II)
pseudo-atrane 2 which has two chiral centres in each tri-
cyclic unit. The copper(II) pseudo-atrane was successfully
loaded on magnetic silica nanoparticles by Schiff base
(SB) condensation reaction of free CHO group (of the
enantioselective
reactions
(Diels-Alder
reaction,
enantioselective aziridination and cyclopropanetrione,
hydrosilylation of ketones and asymmetric Friedel-Crafts
alkylation)[45–49] unfortunately, Fe3O4@SiO2/2 did not
yield enantioselective products in ring-opening of epox-
ides. However, it offered exceptional advantages and is
better over some copper(II)-based catalysts reported in
the past for the synthesis of β-amino alcohols. For
instance,
it
is
better
in
terms
of
high
yields, heterogeneous catalytic surface (over homogenous
catalysts copper-indole derivative,[50] copper(II) tetra
-fluoroborate,[51] copper(II) acetoacetate complex[52] and
in situ generated copper-allenylidiene intermediate[53]),
reusability and retrievability (over polymer-supported
copper sulphate[54] and copper coordination polymer
tricyclic
nanoparticles to obtain Fe3O4@SiO2/2. The loading of
on Fe3O4@SiO2 surface by the formation of
cage) and
amino-functionalized
silica
2

SINGH ET AL.
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nanocrystals[55]) and efficacy in the aqueous medium
(copper doped spinal nano ferrites[56]). Moreover, incor-
poration of the catalytic site on the surface of magnetic
silica nanoparticles offers a clean, efficient and trouble-
free separation with maximum recovery of the catalyst
from the reaction mixture by using a magnet which is
supported by previous literature.[34–37]
phenolic OH arms (ethanolic proton remained intact)
which coordinated with the copper ion to form a din-
uclear cluster of dichiral [4.4.3.01,5]tridecane copper(II)
cage, (Cu[N{CH (CH2Ph)CH2OH}{CH2(4 Br C6H3O)}
{CH2(2 CHO 4 Me C6H2O)}])2 (2).
2.2 | Spectroscopic aspects
2 | RESULTS AND DISCUSSION
2.1 | Synthetic aspects
The FT-IR spectrum of SB showed a strong band at 1633
and 3366 cm−1 due to CH N and OH stretching,
respectively. In rSB, OH vibrational band was observed
as broadband in the region 2700–3000 cm−1 along with
NH stretching as a sharp single band at 3316 cm−1
suggesting the reduction of SB. The tripodal ligand
1 showed a vibrational band at 1651 cm−1 due to C O
vibration confirming the introduction of the phenolic
arm with CHO group (see Figures S1–S3).
Synthesis of novel chiral tripodal ligand [N{CH (CH2Ph)
CH2OH}{CH2(4 Br C6H3OH)}{CH2(2 CHO 4 Me
C6H2OH)} (1) was a three-step reaction. In the first
step, equimolar amounts of L-phenylalaniol and 5-
bromosalicylaldehyde were reacted to undergo a conden-
sation reaction, which resulted in the formation of a
chiral Schiff base (SB) with ONO donor system. In the
second step, SB was reduced to generate secondary
amine at the azomethinic position using NaBH4 which
afforded a dipodal-reduced Schiff base product (rSB)
having a chiral ethanolic arm and a bisphenolate arm. It
was further reacted with 3-(chloromethyl)-2-hydroxy-
5-methylbenzaldehyde to introduce the third arm via a
condensation reaction to obtain tertiary amine
1 (Scheme 1). The tripodal amine 1 consisted of a
tetradentate NO3 ligating framework with three distinct
arms: a chiral ethanolic arm, the Br substituted pheno-
lic arm and the CHO and CH3 substituted phenolic
The 1H NMR spectrum of SB showed a singlet at
8.27 ppm for azomethinic proton (H7) along with double
doublets at 2.82 and 3.00 ppm for diastereotopic protons
0
H10a and H10a . The phenolic OH and ethanolic OH
resonances were observed as broad signals at 13.73 and
4.98 ppm, respectively. The signals for chiral proton H8
and diastereotopic H9b were merged to give a multiplet in
1
the range 3.47–3.55 ppm. In contrast, H NMR spectrum
of rSB consisted of four doublets of doublets (dd) centred
0
at 3.30 ppm (for H9b), 3.41 ppm (H9b ), 3.82 ppm (for H7c)
0
and 3.87 ppm (H7c ), respectively. The phenolic OH,
ethanolic OH and secondary amine NH resonances
1
were observed as a broad signal at 5.83 ppm. The H
arm. The reaction of
1
with Cu (OAc)2.2H2O
NMR of tripodal ligand 1 exhibited a singlet at 9.83 ppm
(in equimolar amount) in the presence of a base (sodium
methoxide) afforded a green coloured complex. In the
course of the reaction, sodium methoxide produced a
tetradentate dianionic ligand by the deprotonation of
for aldehydic proton (H24) and doublets of doublets each
0
for diasterotopic protons H10a and H10a , H9a and H9b, H7c
0
0
and H7c and H17d and H17d showing AB spin system of
diastereotopic protons. The signals of phenolic OH and
SCHEME 1 A scheme for the synthesis of
Schiff base (SB), reduced Schiff base (rSB),
tripodal ligand 1 and [4.4.3.01.5]tridecane cluster
2 [where a = 3-(chloromethyl)-2-hydroxy-
5-methylbenzaldehyde, b = Cu(OAc)2.2H2O] (the
atoms are numbered to assign the NMR signals)

4 of 14
SINGH ET AL.
ethanolic OH were not observed (see Figures S4–S6).
The 13C NMR spectra of SB, rSB and 1 showed character-
istic signals at 160.3 (for C N), 47.0 (for C N) and 192.5
(for CHO), respectively (see Figures S7–S9). Further,
electrospray-ionization mass spectra (ESI-MS) of SB, rSB
and 1 exhibited molecular ion peaks at m/z 335.19,
336.23 and 484.01, respectively (see Figures S10–S12).
The copper atrane cage 2 consisted of vibrational bands
at 1659 and 433 cm−1 due to >C O and Cu N stretching,
respectively. The Cu O stretching vibrations generally lie
between 345 and 305 cm−1, therefore, were not observed in
the FT-IR spectrum recorded in 4000–400 cm−1.[57] The
ESI-MS spectrum was consisted of a peak at m/z 1091.88
due to dinuclear cluster (Cu[N{CH (CH2Ph)CH2OH}
{CH2(4 Br C6H3O)}{CH2(2 CHO 4 Me C6H2O)}])2
(see Figures S13–S15).
optical rotation value, that is, [α]D = 234.76. Therefore,
complex 2 could be configured as S or R at the nitrogen
atom. It was clear from the asymmetric unit (Figure 1b)
that N and N10 acquired R and S configurations, respec-
tively. So, the presence of two individual mononuclear
entities with the opposite configuration in an asymmetric
unit indicated the crystallization of 2 as a racemic mix-
ture to tripodal nitrogen configuration (see Figure S16).
Based on the crystal structure, overall configuration of
chiral centres at N and C (i.e., N1, N10, C18 and C180)
could be assigned as R, S, S and S (Figure 1b). The impor-
tant structural parameters (i.e., bond angles and bond
length), data collection parameters and structure refine-
ment parameters for 2 are given in Tables 1 and 2.
The pentacoordinate Cu(II) exhibited distorted square
pyramidal geometry with O1, O10, O3 and N1 at basal
positions and O2 from the ethanolic arm at the apical
position. The bond lengths of Cu O bonds that lie in the
basal plane are found to be Cu1 O1, 1.983(6) Å;
Cu1 O10, 1.958(6) Å; Cu1 O3, 1.951(6) Å and Cu1 N1,
2.045(7) Å transannular. The bond length of apical bond,
that is, Cu1 O2, 2.326(6) Å was found longest among all
the basal bond lengths. The sum of all the basal angles is
found to be 359.1ꢀ (∠O11 Cu1 O1 (75.2(3)ꢀ),
∠O11 Cu1 O3 (94.5(3)ꢀ), ∠O1 Cu1 N1 (92.6(3)ꢀ),
∠N1 Cu1 O3 (96.8(3)ꢀ) and that for the angle formed
with the apical O2 atom is 377.3ꢀ (∠O2 Cu1 O11 (103.7
(2)ꢀ), ∠O2 Cu1 O1 (97.1(2)ꢀ), ∠O2 Cu1 N1 (80.4(3)ꢀ),
∠O2 Cu1 O3 (96.1(3)ꢀ)). The efficient criterion for the
‘GOODNESS’ of the square pyramidal geometry is find-
ing the difference of basal and apical angles from the
ideal square pyramidal geometry, that is, ΔΣ(ϑ)ꢀ
2.3 | Structural aspects
All the efforts to crystallize SB, rSB and 1 for single-
crystal X-ray diffraction analysis were failed however
2 was crystallized from its ethanolic solution by slow
evaporation. It was crystallized in an orthorhombic crys-
tal system with P21212 chiral space group. The structure
of 2 consisted of a twofold symmetric dinuclear cluster
formed by two [4.4.3.01.5]tridecane cages. Each tricyclic
cage Cu[N{CH (CH2Ph)CH2OH}{CH2(4 Br C6H3O)}
{CH2(2 CHO 4 Me C6H2O)}] was constructed by two
phenolate arms and an ethanolate arm which were fused
to form a Cu N transannular bond. The two [4.4.3.01.5
]
tridecane cages were joined together via μ O bridges
formed by bromophenolate arms. This resulted in the for-
mation of a rectangular core Cu2 (μ OPh)2 where two
tricyclic cages were joined together (Figure 1a). Because
all the three arms attached to nitrogen in the tripodal sys-
tem were distinct, hence, 2 also acquired chirality with
respect to nitrogen. The chirality of 2 was supported by
ꢀ
ꢀ
(basal) = 360- Σ(ϑ)b , where Σ(ϑ)b is the sum of basal
angles, and ΔΣ(ϑ)ꢀ (apical) = 360- Σ(ϑ)a , where Σ(ϑ)a is
the sum of apical angles. The goodness value of 2 around
the copper for basal and apical atoms is 0.9ꢀ (360ꢀ–
359.1ꢀ) and 17.3ꢀ (360ꢀ–377.3ꢀ), respectively (359.1ꢀ and
377.3ꢀ are the sums of basal and apical angles of
ꢀ
ꢀ
FIGURE 1 (a) ORTEP presentation of
2 with partial numbering scheme (thermal
ellipsoids are drawn at 50% probability for
nonhydrogen atoms and radius of hydrogen
atoms were eliminated for clarity); (b) labelling
of chiral centres to show stereospecific
configuration

SINGH ET AL.
5 of 14
TABLE 1 Parameters of X-ray diffraction data collection and structure refinement of 2
Parameters name
Parameter value
C54H66Br2Cu2N2O13
1237.98
Parameters name
F(000)
Crystal size/mm3
Parameter value
2544
Empirical formula
Formula weight
0.24 × 0.11 × 0.06
Mo Kα (λ = 0.71073)
4.94 to 50.1
Temperature/K
99.99(10)
orthorhombic
P21212
Radiation
Crystal system
2Θ range for data collection/ꢀ
Index ranges
Space group
−25 ≤ h ≤ 30, −20 ≤ k ≤ 20, −8 ≤ l ≤ 14
a/Å
25.3120(15)
17.4464(8)
12.3943(7)
90
Reflections collected
Independent reflections
Data/restraints/parameters
Absorption correction
Tmin/Tmax
23183
b/Å
9693 [Rint = 0.0517, Rsigma = 0.0811]
9693/84/611
c/Å
α/ꢀ
Multiscan
β/ꢀ
90
0.893/1.000
γ/ꢀ
90
Goodness-of-fit on F2
Final R indexes [I > =2σ (I)]
Final R indexes (all data)
Largest diff. peak/hole/e Å−3
Flack parameter
1.041
Volume/Å3
5473.4(5)
4
R1 = 0.0599, wR2 = 0.1412
R1 = 0.0774, wR2 = 0.1551
1.55/−1.12
Z
ρ
calcg/cm3
μ/mm−1
1.502
2.301
−0.005(7)
TABLE 2 Some important bonding parameters of 2
Bond lengths of 2 (Å) at 100 K
Bond angels of 2 (ꢀ) at 100 K
Br1 C4
Cu1 Cu11
Cu1 O1
Cu1 O11
Cu1 O2
Cu1 O3
Cu1 N1
O1 C1
1.893(4)
3.025(2)
1.983(6)
1.958(6)
2.326(6)
1.951(6)
2.045(7)
1.358(7)
1.353(8)
1.442(11)
1.221(12)
1.519(12)
1.502(11)
1.504(11)
Br10-C40
1.882(4)
3.019(2)
1.967(6)
1.941(6)
1.897(7)
2.359(6)
2.045(8)
1.342(7)
1.359(8)
1.426(12)
1.230(15)
1.497(12)
1.509(11)
1.510(11)
O11 Cu1 Cu11
O1 Cu1 Cu11
O11 Cu1 O1
O11 Cu1 O3
O1 Cu1 O3
O1 Cu1 N1
O11 Cu1 N1
O2 Cu1 Cu11
O2 Cu1 O11
O2 Cu1 O1
O2 Cu1 O3
O2 Cu1 N1
O3 Cu1 Cu11
N1 Cu1 Cu11
N1 Cu1 O3
40.18(18)
39.56(17)
75.2(3)
O101 Cu10 Cu101
O10 Cu10 Cu101
O10 Cu10 O101
O10 Cu10 O30
O101 Cu10 O30
O101 Cu10 N10
O10 Cu10 N10
O20 Cu10 Cu101
O20 Cu10 O101
O20 Cu10 O10
O20 Cu10 O30
O20 Cu10 N10
O30 Cu10 Cu101
N10 Cu10 Cu101
N10 Cu10 O30
39.09(18)
39.73(18)
76.3(3)
Cu10 Cu101
Cu10 O101
Cu10 O10
Cu10 O20
Cu10 O30
Cu10 N10
O10 C10
94.5(3)
92.1(2)
164.9(3)
92.6(3)
100.7(2)
170.1(3)
93.9(3)
167.5(3)
117.36(16)
103.7(2)
97.1(2)
126.9(2)
93.2(3)
O3 C8
O20 C80
O2 C17
O4 C15
N1 C7
O30 C170
O40 C150
N10 C70
165.3(3)
100.0(3)
96.2(3)
96.1(3)
80.4(3)
N1 C14
N1 C18
N10 C140
N10 C180
126.50(19)
127.4(2)
96.8(3)
108.84(15)
131.1(2)
81.0(3)
compound 2, whereas 360ꢀ is that of the ideal geometry).
The tau (τ) is another parameter (can be calculated as
τ = (β − α)/60, where α and β are greatest basal angels
and β > α) is found to be 0.043 for this compound using
the angles ∠O11 Cu1 N1, 167.5(3)ꢀ and ∠O1 Cu1 O3,
164.9(3)ꢀ, indicating its distorted square pyramidal geom-
etry.[58] The deviation from the ideal square pyramidal
(τ = 0) indicates distortion in the geometry.
2.4 | Surface functionalization aspects
The cluster of copper(II) pseudo-atrane was grafted
directly on the surface of amino-functionalized magnetic
nanosilica to fabricate Fe3O4@SiO2/2 (Scheme 2).
For this, magnetic silica nanoparticles (synthesized via
sol-gel method[59,60]
3-aminopropylsilatrane
)
were functionalized with
(via to
silanization[59,60]
)

6 of 14
SINGH ET AL.
SCHEME 2 Fabrication of
magnetic nanosilica Fe3O4@SiO2/2
(where 3-APS is 3-aminopropylsilatrane)
introduce NH2 functionalities and the resulting mate-
rial Fe3O4@SiO2/NH2 was reacted with 2. The NH2
groups present on the surface of Fe3O4@SiO2/NH2 were
reacted with free CHO group on the ligating skeleton of
2 via Schiff base condensation yielding Fe3O4@SiO2/2.
This led to the covalent binding of 2 with the magnetic
silica surface through azomethinic ( N CH ) bond. To
confirm the formation of azomethinic bond, FT-IR spec-
tra of Fe3O4@SiO2/NH2 and Fe3O4@SiO2/2 were com-
pared. Both the materials showed some common
vibrational bands at 590 cm−1 (for Fe O stretching),
804 cm−1 (for Si O Si symmetric), 959 cm−1 (for Si O
symmetric stretching), 1090 cm−1 (for Si O Si asymmet-
ric stretching) and some weak bands in the region
2800–3000 cm−1 (for >CH2 stretching and bending vibra-
tions). However, FT-IR of Fe3O4@SiO2/2 exhibited a
vibrational band at 1633 cm−1 due to azomethinic bond
and very weak bands in the range 1450–1670 cm−1 due to
aromatic skeleton vibrations, which evidenced the immo-
bilization of 2 on the surface of magnetic nanosilica via
SB condensation (Figure 2a). The reaction of the carbonyl
group with the 3-aminopropylsilyl group is very well
known in literature.[61–63]
The PXRD patterns of Fe3O4@SiO2/NH2 and
Fe3O4@SiO2/2 were found similar to patterns reported
in the Joint Committee on Powder Diffraction Standards
[JCPDS, ref. 19-629] with Bragg's diffraction peaks at
30.0ꢀ, 35.4ꢀ, 43.0ꢀ, 53.4ꢀ, 56.9ꢀ and 62.51ꢀ with reference
FIGURE 2 Comparison of characterization data of Fe3O4@SiO2/NH2 (B) and Fe3O4@SiO2/2 (A); (a) Fourier transform infrared
(FT-IR) spectra (b) powder X-ray diffraction (PXRD) curves (c) thermogravimetric analysis (TGA) plots

SINGH ET AL.
7 of 14
to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) crystal
planes of cubic spinel Fe3O4, respectively (Figure 2b).
The identical peaks in the X-ray diffraction patterns after
modification of magnetic nanosilica indicated that the
crystalline nature of the particles persisted even after the
incorporation of silica and copper complex. The observed
PXRD patterns are also supported by the literature
reports.[64] The average crystal size of nanosilica was
obtained by the Debye Scherrer formula (Dhkl = Kλ/b
cosθ), where D is the size of the axis parallel to the (hkl)
plane, K is a constant with a typical value of 0.89 for
spherical particles, λ is the wavelength of radiation, b is
full width at half maxima in radians and θ is the position
of the diffraction maximum of the peak with the highest
intensity from the PXRD pattern. The crystallite size was
found to be 14.7 and 14.4 nm for NH2-Fe3O4@SiO2 and
Fe3O4@SiO2/2, respectively. The values showed a slight
reduction in crystallite size of Fe3O4@SiO2/2 as com-
pared with Fe3O4@SiO2/NH2 because the decrease in
the average crystallinity of Fe3O4@SiO2/2 due to coating
of 2 resulted in the peak broadening. This proves the
inverse relationship between crystallite size and full
width at half maxima (b). Thermogravimetric
(TG) curves of Fe3O4@SiO2/NH2 showed a decrease in
mass up to 550ꢀC because of the loss of physically
adsorbed molecules like moisture, ethanol and alkyl
chain; however, mass loss in Fe3O4@SiO2/2 was continu-
ous up to 1000ꢀC indicating the loss of covalently bound
FIGURE 3 (a) Scanning electron microscopy (SEM) images of Fe3O4@SiO2/NH2 (A and B) and Fe3O4@SiO2/2(C and D); (b) energy-
dispersive X-ray spectroscopy (EDS) of Fe3O4@SiO2/2, (see Figure S17 EDS of Fe3O4@SiO2/NH2); (c) elemental mapping of
Fe3O4@SiO2/2 (A) area under observation, (B) elemental distribution of C, N, O, Fe, Si, Cu and Br, (C) distribution of carbon,
(D) distribution of nitrogen, (E) distribution of oxygen, (F) distribution of iron, (G) distribution of silicon, (H) distribution of copper,
(I) distribution of bromine (see Figure S18 for elemental mapping of Fe3O4@SiO2/NH2); (d) vibrating sample magnetometry (VSM) plot of
Fe3O4@SiO2/NH2 and Fe3O4@SiO2/2 and magnified view of the plot near the coercive field

8 of 14
SINGH ET AL.
alkyls and aryls. In the end, amounts left as oxides were
85.40 and 53.16% for Fe3O4@SiO2/NH2 and
Fe3O4@SiO2/2, respectively (Figure 2c).
to study the effect of grafted organic moieties on the
magnetization behaviour of fabricated materials. The
hysteresis curves revealed a reduction in saturation mag-
netization when Fe3O4@SiO2/NH2 (39.50 emu g−1) was
The SEM images of Fe3O4@SiO2/NH2 and
Fe3O4@SiO2/2 displayed a roughly spherical morphology
(Figure 3a). The surface roughening of Fe3O4@SiO2/2
was apparent due to the deposition of silica shell around
the magnetic core. Interestingly, no separate aggregates
of silica were observed in the SEM images of the
Fe3O4@SiO2/2 which suggested that precipitation of
silica was carried out only on the surface of the
magnetic core.
The EDS of Fe3O4@SiO2/NH2 (see Figure S17)
exhibited peaks of iron, oxygen, silicon, nitrogen and car-
bon verifying the coating of aminopropylsilicate on mag-
netic nanocores. In contrast, EDS of Fe3O4@SiO2/2
consisted of additional peaks for copper and bromine
confirming the grafting of 2 on the surface. The elemen-
tal mapping images of Fe3O4@SiO2/2 clearly showed a
uniform distribution of iron, oxygen, carbon, nitrogen,
copper and bromine confirming the uniformity in the
coating on the surface (Figure 3b). Further, elemental
mapping images of Fe3O4@SiO2/2 were compared with
images of Fe3O4@SiO2/NH2. The elemental mapping
images of Fe3O4@SiO2/NH2 clearly showed a uniform
distribution of carbon, nitrogen, oxygen, silicon and iron
(see Figure S18). Similarly, a uniform distribution of iron,
oxygen, carbon, nitrogen, copper and bromine was
observed in case of Fe3O4@SiO2/2, thus confirming the
incorporation of copper complex 2 on the surface of
nanosilica (Figure 3c). The VSM studies were performed
derivatized to Fe3O4@SiO2/2 (23.40 emu g−1
)
(Figure 3d). This phenomenon confirmed the dilution of
magnetic centres due to loading of 2 on the surface of
magnetic nanosilica. However, sufficient magnetization
was observed for the separation of Fe3O4@SiO2/2 from
reaction media by applying a magnetic field. Moreover,
Fe3O4@SiO2/2 was found superparamagnetic because
both magnetization, as well as demagnetization curves,
passed through the origin showing negligible coercivity
and remanence.
2.5 | Catalytic aspects
The catalytic activity of Fe3O4@SiO2/2 was investigated
for ring-opening reactions of epoxides (3) with
substituted anilines (4). The effect of various important
parameters such as catalyst loading, reaction time, tem-
perature and solvent was optimized to achieve an opti-
mum reaction condition. Initially, catalytic activity was
investigated for the ring-opening reaction of cyclohexene
oxide (3a) with aniline (4a). The reaction was performed
in acetonitrile at different temperatures and with varying
amounts of the catalyst which exhibited very low conver-
sion of the reactants to product 5a (ca. 22%–27% yields)
even after a prolonged time of stirring (Table 3,
entries 1–4).
TABLE 3 Optimization of the
reaction conditions
S. no.
1.
Catalyst loading (mg)
Solvent
ACN
Temp (ꢀC)
Time (h)
Yielda (%)
20
20
30
100
100
100
20
20
10
5
50
70
48
24
27
27
22
27
22
84
98
82
94
84
2.
ACN
3.
ACN
rt
168
48
4.
ACN
70
5.
Toluene
Water
Water
Water
Water
Water
110
100
80
24
6.
22
7.
22
8.
100
80
24
9.
22
10.
80
22
aIsolated yield.

SINGH ET AL.
9 of 14
Then, the same reaction was performed in toluene
catalyst to afford the product 5a in 98% and 82% yields,
respectively (Table 3, entries 7 and 8). On the further
decrease in catalyst loading to 10 and 5 mg at 80ꢀC, a
slight decrease in product yields to 94% and 84%, respec-
tively, was observed (Table 3, entries 9 and 10).
Further, we investigated the substrate scope for the
reaction. For that purpose, the reaction of cyclic and
acyclic epoxides (3a–c) with various substituted aniline
with 100 mg catalyst loading at reflux temperature,
which yielded 22% of product 5a (see Table 3, entry 5).
Fortunately, when the reaction was performed in water
using 100 mg catalyst loading at reflux temperature, 84%
yield was obtained in 22 h (ca. 84%) (see Table 3, entry
6). Then, catalyst loading was reduced and next two reac-
tions were carried out at 80ꢀC and 100ꢀC using 20 mg of
TABLE 4 Substrate scope for the
ring-opening reaction catalysed by
Fe3O4@SiO2/2.
Aniline
Product (s)
Structure
S.
Time
(h)
Yield
(%)
no.
Epoxide
R
No.
4a
No.
5a
TON
1.
H
22
94
503
2.
3.
4.
4
OMe
4b
4c
4d
5b
5c
5d
21
24
32
90
91
86
481
487
460
4
Cl
2
Cl
5.
H
4a
6a
18
92
492
6.
H
4a
7a
28
52
278

10 of 14
SINGH ET AL.
(4a–d) derivatives were performed at 80ꢀC with 10 mg cat-
alyst loading in water as a solvent. All reactions worked
well, and excellent yields of the corresponding products
were obtained. For example, in the reaction of 3a with
4-methoxyaniline 4b, the excellent yield for product 5b
(90%) was obtained in 21 h (Table 4, entry 2). The reactions
of chloro substituted anilines 4c and 4d took 24 and 32 h
for completion to afford the products 5c and 5d in 91% and
86% yields, respectively (Table 4, entries 3 and 4). The
lower yield and more reaction time for the 2-chloroaniline
(4d) may be attributed to the steric hindrance caused by
ortho substitution. When the reaction of cyclopentene
oxide (3b) was performed with aniline (4a), product 6a
was achieved in 92% yield (Table 4, entry 5). The reaction
of styrene oxide (3c) with aniline (4a) provided only 52%
yield of the product 7a in 28 h (Table 4, entry 6) (see Fig-
ures S19–S24 for 1H NMR data).
The recyclability of the catalyst in aqueous medium
was investigated for the reaction between cyclohexane
(3a) and aniline (4a). The reaction was performed
under optimized conditions as mentioned above. After
the completion of the reaction, ethyl acetate was added,
and the organic layer was extracted. This process was
repeated for four times until the complete separation of
organic compounds from the catalyst present in the
aqueous layer was achieved. The organic layers were
combined, dried over anhydrous sodium sulphate and
evaporated to obtain a crude product, which was puri-
fied by using column chromatography. The catalyst was
recovered from aqueous layer magnetically. Then, it
was dried overnight at high temperature (above 100ꢀC)
in the oven and was used for subsequent cycles. The
results obtained from the reusability of catalyst showed
that Fe3O4@SiO2/2 can be reused as an efficient cata-
lyst for multiple runs but with slight loss of its catalytic
activity (see Figure S25). The consistency in properties
of the material was also supported by FT-IR and PXRD
data of the material obtained after catalysis (see
Figures S26 and S27).
reaction time. Besides, usage of Fe3O4@SiO2/2 was
found beneficial over complex 2 because leaching of the
catalyst was minimal due to covalent binding of the cop-
per complex on the magnetic nanosilica. It was evidenced
by the EDS data of recovered catalyst Fe3O4@SiO2/2
(after catalytic reaction) which showed the presence of
1.10% (wt/wt) of copper in the material. Thus,
Fe3O4@SiO2/2 can be used as an eco-friendly and green
catalyst for the synthesis of β-amino alcohols.
Although the stereoselective ring-opening of epox-
ides was not observed in the present case, however, it
offered various advantages like excellent yields under
mild reaction conditions, applicability in aqueous sys-
tems, easy isolation by using a magnet and reusability
up to four cycles. Moreover, it is the first report where
a copper(II)atrane complex is loaded on the solid sur-
face and utilized for the catalytic purpose. The plausible
cause for nonstereoselective results may be attributed
either to the formation of the copper complex as a race-
mic mixture for chiral centre present at tripodal nitro-
gen atom or comparatively less loading of the complex
on the magnetic nanosilica.
2.6 | Conclusion
A dinuclear cluster of dichiral copper(II)atrane can be
derived from a tripodal ligand via step by step construc-
tion from L-phenylalaniol and 5-bromosalicylaldehyde.
It consists of two [4.4.3.01.5]tridecane cages joined
together through bridges formed by bromophenolate
arms. Out of the remaining two arms of the tricyclic
cage, ethanolic arm consists of a chiral centre and phe-
nolate arm carries a free aldehydic ( CHO) functional-
ity. This functionality can be used for the covalent
grafting of copper(II) pseudo-atrane cluster on magnetic
nanosilica Fe3O4@SiO2/2. The 2 functionalized nano-
silica can be utilized for catalyzing ring-opening of
epoxides with aromatic amines which offers advantages
of excellent yields even under mild reaction conditions
and in the aqueous medium.
The catalytic efficiency of the Fe3O4@SiO2/2 was
very high in water and provided the ring-opening prod-
ucts in excellent yields with very low catalyst loading.
The quantitative loading of copper in the catalytic surface
was obtained from EDS data of Fe3O4@SiO2/2 which
showed 1.19% (wt/wt) loading. It was used to calculate
the turnover number (TON) using a formula reported in
the literature.[65] The tested catalytic system showed high
catalytic efficiency with moderate to good TON (Table 4).
When the reaction was performed in the presence of
unsupported complex 2, only 5%–10% conversion of reac-
tants was observed even after 48 h stirring at 80ꢀC. How-
ever, loading of the complex 2 on the magnetic nanosilica
improved the conversion percentage and reduced the
3 | EXPERIMENTAL
3.1 | Materials and methods
Syntheses of all the compounds were performed under
a dry nitrogen atmosphere using Schlenk technique.
Solvents toluene (Avra), tetrahydrofuran (THF) (Finar),
ethanol (Merck) and methanol (Avra) were purchased
commercially, dried and purified by standard proce-
dures before use and stored under nitrogen atmosphere.

SINGH ET AL.
11 of 14
The chemicals such as 5-bromo-2-hydroxybenzaldehyde
3.3 | Synthetic procedures
3.3.1 | Synthesis of SB
(Aldrich),
2-hydroxy-5-methylbenzaldehyde
(TCI),
copper(II)acetate dihydrate (Merck), ferric sulphate
(Merck), ferrous sulphate heptahydrate (Merck),
3-aminopropyltriethoxysilane
(Aldrich),
sodium
In a double-neck round bottom flask fitted with Dean
Stark trap, solution of 5-bromosalicylaldehyde
methoxide (Aldrich), sodium borohydride (Avra),
sodium bicarbonate (Avra) and tetraethoxysilane
(Aldrich) were used as such without any purification.
The compounds L-phenylalaniol,[66] 3-(chloromethyl)-
2-hydroxy-5-methylbenzaldehyde[67] and 3-aminopropy
-lsilatrane[62,68] were synthesized using procedures
reported in literature. The magnetic nano-cores
(Fe3O4), magnetic nanosilica (Fe3O4@SiO2) and
a
(13.22 mmol, 2.66 g dissolved in 50 ml toluene) was
added to L-phenylalaniol (13.22 mmol, 2.00 g dissolved in
50 ml toluene). The reaction mixture was heated to reflux
for 5 h, and water produced during the reaction was
removed azeotropically. The contents were cooled to
room temperature, and toluene was removed under vac-
uum. The yellowish oily product was washed several
times with fractions of hexane which yielded a yellow
powder. Yield: 96% (12.66 mmol, 4.23 g), M.p.:
100–102ꢀC; [α]D = −195.7; elemental analysis: Anal. Cal-
culated for C16H16BrNO2: C, 57.50; H, 4.83; N, 4.19;
found: C, 57.76; H, 4.38; N, 4.09; % error: C, 0.26; H,
0.45; N, 0.01; FT-IR (cm−1): 703 (C Br), 1089, 1127
(C O), 1367 (>CH2, bending), 1476, 1571, 1601
( C C , Aromatic), 1633 ( C N), 2864, 2917, 3027
aminopropyl
functionalized
magnetic
nanosilica
(Fe3O4@SiO2/NH2) were synthesized according to pre-
viously reported methods in literature[51,52] (for detail
procedure see Sections S2.1–S2.3).
3.2 | Physical measurements
1
The FT-IR spectra were recorded on Thermo Fischer
Scientific NICOLET IS50-FT-IR for compounds and
Perkin Elmer RX-I FT-IR spectrophotometer for silica
nanoparticle materials. The NMR (H1-NMR and C13-
NMR) were recorded in CDCl3 or DMSO-d6 at room
temperature by using Bruker Avance II FT NMR
(AL 400 MHz) spectrometer. All chemical shifts (δ)
were given in ppm relative to tetramethylsilane (TMS).
The VG Analytical (70-S) spectrometer equipped with
ESI source with capillary voltage 2500 V was used for
ESI-MS measurements. Elemental analyses C, H and N
were obtained by using a FLASH-2000 organic elemen-
tal analyser. The TG analyses of materials were done
using an SDTQ-600 (TA instruments New Castle, DE).
The magnetic studies of the materials were done using
a VSM instrument Micro Sense EZ7. The PXRD data
were obtained from PANalytical's X'Pert PRO diffrac-
tometer using Cu Kα radiation of wavelength 1.541 Å
in 2θ range from 20ꢀ to 80ꢀ curves. The morphology
was investigated by EDS and elemental mapping of
materials was performed on Tescan Mira 3 field emis-
sion scanning electron microscopy (FESEM) instrument.
All specific rotations ([α]D) were measured using
Rudolph's AUTOPOL I Automatic polarimeter with sin-
gle wavelength 589 nm (sodium lamp). The single-
crystal X-ray diffraction data were collected on XtaLAB
Mini (ROW) diffractometer using Mo Kα radiation
(λ = 0.71073 Å). The crystal was kept at 99.99(10) K
during data collection. Using Olex2, the structure was
solved with the ShelXT structure solution program
using intrinsic phasing and refined with the ShelXL
using least squares minimization.[69–71]
(>CH2), 3366 (O H); H NMR (DMSO-d6, 400 MHz): δ
(ppm) 2.82 (dd, 1H10a
,
2,3J = 13.5, 8.1 Hz), 3.00 (dd,
0
1H10a
,
2,3J = 13.5, 4.0 Hz), 3.47–3.55 (m, 2H8,9b), 3.66 (dd,
2J = 9.6 Hz) 4.98 (b, 1H, OH), 6.85 (d, 1H2,
0
1H9b
,
3J = 8.8 Hz), 7.14–7.27 (m, 5H12–16), 7.43 (dd, 1H3,
3,4J = 8.8, 2.8 Hz), 7.57 (d, 1H5, 4J = 2.8 Hz), 8.28 (s, 1H7),
13.73 (b, 1H, Ph OH); 13C NMR (DMSO-d6, 100 MHz): δ
(ppm) 38.2 (C10), 64.1 (C8), 72.0 (C9), 108.8 (C4), 119.0
(C2), 120.2 (C14), 126.1 (C6), 128.2 (C12,16), 129.3 (C13,15),
133.4 (C5), 134.6 (C3), 138.4 (C11), 160.3 (C7), 164.2 (C1);
ESI-MS: m/z (relative abundance (%), fragment assigned):
334.04 [100, M + H]+, 336.04 [99, M + 2 + H]+.
3.3.2 | Synthesis of rSB
Sodium borohydride (14.95 mmol, 0.57 g) was added to
100 ml methanolic solution of SB (2.99 mmol, 1.00 g)
under nitrogen atmosphere. The clear solution was
stirred for 2 h at 50ꢀC. The solvent was evaporated under
vacuum and the residue was dissolved in chloroform
(100 ml). The solution was shaken with distilled water
(2 × 75 ml) to remove excessive sodium borohydride. The
organic layer was separated, dried over anhydrous
sodium sulphate and filtered. The solvent was removed
under reduced pressure to afford rSB as a white solid.
Step 2 yield: 94% (2.81 mmol, 0.95 g), Overall yield: 90%
(2.68 mmol, 0.90 g); M.p.: 124–126ꢀC; [α]D = −18.60; ele-
mental analysis: Anal. Calculated for C16H16BrNO2: C,
57.16; H, 5.40; N, 4.17; found: C, 57.56; H, 5.07; N, 4.24;
% error: C, 0.40; H, 0.33; N, 0.07; FT-IR (cm−1):
706 (C Br), 1106, 1129 (C O), 1343 (>CH2, Bending),

12 of 14
SINGH ET AL.
1493, 1601( C C , aromatic), 2858, 2916, 3031, 3058
(C14), 127.7 (C21), 128.2 (C12,16,20), 129.0 (C13,15), 130.6
(C22), 132.8 (C5), 137.3 (C11), 140.0 (C23), 155.4 (C1),
158.1 (C19), 192.5 (C24); ESI-MS m/z (relative abun-
dance (%), fragment assigned): 484.01 [100, M + H]+,
486.02 [88, M + 2 + H], 336.35 [39, rSB + H]+, 300.35
[45, M CH2Ph(OH)(Br)]+.
(>CH2), 3316 (>N H), 3300–2700 (broad, O H
1
stretching, intramolecular hydrogen bonded); H NMR
0
(DMSO-d6, 400 MHz): δ (ppm) 2.67–2.76 (m, 3H8,10a,10a ),
0
3.30 (dd, 1H9b, 2,3J = 10.9, 5.0 Hz), 3.41 (dd, 1H9b
,
2,3J = 10.9, 4.0 Hz), 3.82 (d, 1H7c, J = 14.5 Hz), 3.87 (d,
2
0
1H7c , J = 14.5 Hz), 5.83 (b, 3H, OH, Ph OH, NH), 6.67
(d, 1H2), 7.19–7.30 (m, 7H3,5,12–16); 13C NMR (DMSO-d6,
100 MHz): δ (ppm) 37.0 (C10), 47.0 (C7), 59.9 (C8), 61.6
(C9), 109.5 (C4), 117.3 (C3), 125.8 (C2), 127.9 (C6), 128.1
(C12,16), 129.2 (C13,15), 130.1 (C14), 130.8 (C5), 139.4 (C11),
156.4 (C1); ESI-MS: m/z (relative abundance (%),
fragment assigned): 336.06 [100, M + H]+, 338.05
[99, M + 2 + H]+.
2
3.3.4 | (Cu[N{CH (CH2Ph)CH2OH}
{CH2(4 Br C6H3O)}
{CH2(2 CHO 4 Me C6H2O)}])2 (2)
The tripodal ligand 2 (1.03 mmol, 0.50 g) and sodium
methoxide (3.09 mmol, 0.17 g) were dissolved in metha-
nol (50 ml). The solution was stirred for 10 min at room
temperature. Then, copper acetate dihydrate (1.00 mmol,
0.21 g) was added to the solution. The mixture was
refluxed for 2 h, and the solvent was evaporated under
vacuum. It resulted in a dark green residue which was
dissolved in dichloromethane (30 ml) and washed with
distilled water (2 × 30 ml). The organic layer was then
separated, dried over anhydrous sodium sulphate and fil-
tered, and the solvent was removed under reduced pres-
sure to afford a dark green solid. The compound was
recrystallized from ethanol by slow evaporation of sol-
vent which resulted in crystals suitable for X-ray diffrac-
tion. Yield: 36% (0.20 g, 0.17 mmol, Step yield), Overall
yield: 30% (0.17 g, 0.14 mol); M.p.: 236ꢀC; [α]D = 234.76;
3.3.3 | Tripodal ligand N{CH (CH2Ph)
CH2OH}{CH2(4 Br C6H3OH)}
{CH2(2 CHO 4 Me C6H2OH)} (1)
3-(chloromethyl)-2-hydroxy-5-methylbenzaldehyde
(5.94 mmol, 1.10 g) and sodium bicarbonate
(11.90 mmol, 1.00 g) were dissolved in THF (60 ml) in
a
two-necked flask fitted with a condenser and
dropping funnel. Then, a solution of rSB (5.94 mmol,
2.00 g in 40 ml THF) was added to the mixture drop-
wise. The contents were heated to 50ꢀC and stirred
under nitrogen for 48 h. The progress of reaction was
monitored with TLC. Then, the suspension (containing
solid NaCl as by-product) was filtered and washed with
THF. The solvent was removed under reduced pressure
to afford a pale yellow solid. Step 3 yield: 94% (2.72 g,
5.64 mmol), Overall yield: 85% (2.45 g, 5.05 mmol); M.
p.: 79ꢀC–81ꢀC; [α]D = 5.35; elemental analysis: Anal.
Calculated for C16H16BrNO2: C, 61.99; H, 5.41; N, 2.89;
found: C, 62.23; H, 5.58; N, 2.66; % error: C, 0.24; H,
0.17; N, 0.23; FT-IR (cm−1): 698 (C Br), 1030, 1112
(C O), 1375 (>CH2, bending), 1477, 1603 ( C C ,
Aromatic), 1651 (>C O), 2846, 2918, 3027 (>CH2)
3500–2700 (broad, O H stretching, intramolecular
hydrogen bonded); 1H NMR (CDCl3, 400 MHz): δ
elemental
analysis:
Anal.
Calculated
for
C50H48Br2Cu2N2O8: C, 55.00; H, 4.43; N, 2.57; found: C,
54.39; H, 4.75; N, 2.30; % error: C, 0.61; H, 0.32; N, 0.27;
FT-IR (cm−1): 706 (C Br), 1568, 1614 ( C C , aro-
matic), 1659 (>C O), 2864, 2974 (>CH2); ESI-MS m/z
(relative abundance [%], fragment assigned): 1091.88 [7,
M + H]+, 1093.89 [4, M + 2 + H]+, 484.00 [100, 2 + H]+,
336.22 [22, M CH2Ph(OH)(CHO)(CH3)]+, 300.35 [41,
M CH2Ph(OH)(Br)]+.
3.3.5 | Grafting of 2 on magnetic silica
nanoparticles (Fe3O4@SiO2/2) and catalysis
(ppm) 2.20 (s, 3H25), 2.54 (dd, 1H10a
,
2,3J = 13.2,
0
9.3 Hz), 3.07 (dd, 1H10a
,
2,3J = 13.2, 4.5 Hz), 3.10–3.16
A mixture of Fe3O4@SiO2/NH2 (1.00 g) and 2 (2.00 mmol,
2.38 g) in 100 ml ethanol was stirred at room temperature
for 24 h. The resulting composite was removed magneti-
cally, washed thoroughly with ethanol and dried. It
was characterized by FT-IR, PXRD, SEM, EDS, VSM
and TGA analysis, and the data were compared with
Fe3O4@SiO2/NH2 to confirm the formation of
Fe3O4@SiO2/2. The fabricated material was used for
catalyzing the synthesis of β-amino alcohols via ring-
opening reactions (see Sections S2.4 and S2.5 for syn-
thetic procedures and characterization details).
(m, 1H8), 3.52 (d, 1H7c, 2J = 13.0), 3.62 (dd, 1H9b,
2
2,3J = 12.2, 4.0 Hz), 3.66 (d, 1H17d, J = 14.1), 3.81 (dd,
0
0
1H9b
,
2,3J
=
12.1, 8.6 Hz), 4.04 (d, 1H17d
,
0
2J = 14.1 Hz), 4.16 (d, 1H7c
,
2J = 13.0 Hz), 6.57 (d,
1H2 3J = 8.5 Hz), 7.02 (d, 1H5, J = 2.4 Hz), 7.08 (s,
4
,
1H23), 7.10 (s, 1H21), 7.16 (dd, 1H3, 3,4J = 8.5, 2.4 Hz)
7.20–7.28 (m, 5H12–16), 9.82 (s, 1H24); 13C NMR
(DMSO-d6, 100 MHz): δ (ppm) 19.9 (C25), 31.8 (C10),
48.3 (C7), 49.8 (C17), 59.5 (C9), 62.5 (C8), 109.9 (C4),
117.2 (C3), 121.5 (C2), 125.6 (C18), 125.9 (C6), 126.7

SINGH ET AL.
13 of 14
ASSOCIATED CONTENT
Jyoti Agarwal https://orcid.org/0000-0001-5516-7906
Supporting information—Procedure for the preparation
of magnetite nanoparticles (Fe3O4), silica encapsulated
Raghubir Singh https://orcid.org/0000-0003-1156-9174
Varinder Kaur https://orcid.org/0000-0002-4585-0426
magnetic
nanocores
(Fe3O4@SiO2),
amino-
functionalized silica magnetic nanocores (Fe3O4@SiO2/
NH2), ORTEP presentation of the asymmetric unit of 2,
thermogravimetric analysis of catalyst, energy dispersive
X-ray spectrum of (Fe3O4@SiO2/NH2) elemental map-
ping data, catalytic recyclability data; FT-IR spectrum of
the catalyst after the fourth cycle; PXRD data of catalyst
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Experimental data and results are available in article sup-
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ORCID
Hemant Singh https://orcid.org/0000-0001-5056-6131
Navneet Taya https://orcid.org/0000-0002-0717-3145
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