A case study of Pd?Pd intramolecular interaction in a benzothiazole based palladacycle; catalytic activity toward amide synthesisviaan isocyanide insertion pathway

Article abstract of DOI:10.1039/d0nj06301k

An acetate bridge benzothiazolepalladacycle containing a rare metallophilic intramolecular Pd?Pd interaction was synthesized and thoroughly characterized. The synthesized benzothiazolepalladacycle directly anchored on SBA-15 to form an efficient heterogen

Full text of DOI:10.1039/d0nj06301k

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A case study of Pdꢀ ꢀ ꢀPd intramolecular interaction
in a benzothiazole based palladacycle; catalytic
activity toward amide synthesis via an isocyanide
insertion pathway†
Cite this: New J. Chem., 2021,
45, 3290
Masood Loni,a Yaser Balmohammadi,a Reza Dadgar Yeganeh,a Kaveh Imani,a
a
Behrouz Notashb and Ayoob Bazgir
*
Received 29th December 2020,
Accepted 19th January 2021
An acetate bridge benzothiazolepalladacycle containing a rare metallophilic intramolecular Pdꢀ ꢀ ꢀPd
interaction was synthesized and thoroughly characterized. The synthesized benzothiazolepalladacycle
directly anchored on SBA-15 to form an efficient heterogeneous catalyst for amide synthesis via the
migratory isocyanide insertion pathway.
DOI: 10.1039/d0nj06301k
rsc.li/njc
and R-NC has been reported for amide synthesis via the migratory
1. Introduction
isocyanide insertion reaction (MIIr) in the absence of amine.8 The
The amide functional group has an important role in the first study has been described by Jiang and co-workers using PdCl2
synthesis of pharmacological compounds and materials.1 The and PPh3 as an ancillary ligand.7 In 2014, the second study was
direct condensation of carboxylic acids and amines is the reported by Yavari and co-workers using Cu2O in the presence of
traditional route for amides synthesis which needs external phenanthroline-based ligands.9 The last study for isocyanide
acids or bases, wholly anhydrous conditions and high tempera- insertion into the Pd–C bond has been reported by Lei and
ture. Indeed, it is not applicable for some of the sensitive co-workers.10 They used phenylboronic acids instead of aryl
substrates such as amino acids and natural products.2 Due to halides for amide synthesis via the MIIr strategy in the presence
the disadvantages and limitations, an alternative amide synthesis of a bimetallic Pd/Cu catalyst.
involves nucleophilic acyl substitutions through the pre- or in situ
Cyclometalated Pd(II) complexes that contain a Pd–C bond
activation of the carboxylic acid partner (typically activation of the are intramolecularly stabilized by at least one donor atom
carboxylic group either as acyl chlorides or reactive anhydrides known as palladacycles.11 They have emerged as a popular
and esters or, alternatively, the use of coupling reagents).3 How- category of organometallic pre-catalyst for C–C and C–heteroatom
ever, most of the methods suffer from limitations such as the use coupling reactions.12 A 2-Aryl benzothiazole ligand is a pro-
of toxic and expensive reagents, by-product generation and low mising candidate for much broader application in palladacycle
atom economy. Additionally, due to unsuitable sterics and elec- chemistry.13 Easy accessibility, thermal stability, participation
tronics, limitations in scope are still observed.3 Thus, the modern in five-membered palladacycles14 and easily changing different
approaches of synthesizing amides focus on organoborons as a substituents have motivated us to use this ligand in the
catalyst4 or mediator5 or transition metal-catalyzed reactions.6,7 amidation reaction via MIIr. Herein, for the first time, the
Carbonylation of aryl halides with gaseous CO in the presence of migratory isocyanide insertion amidation was reported by a
amines is one of the TMC reactions for amide synthesis. Never- heterogeneous catalyst. The benzothiazolepalladacycle system
theless, the use of CO and complicated ligands are the limitations was used as a common electron rich ligand.
of the reaction.6 The isocyanides (R-NC) and CO are isoelectronic
and show similar reactivity.6 Recently, by the replacement of CO
with R-NC, the transition metal-catalyzed reaction of aryl halides
2. Results and discussion
a Department of Chemistry, Shahid Beheshti University, Tehran 1983963113, Iran.
2.1. Synthesis and characterization of the catalyst
E-mail: a_bazgir@sbu.ac.ir
b Department of Inorganic Chemistry and Catalysis, Shahid Beheshti University,
The preparation process of the benzothiazolepalladacycle (BTP) is
illustrated in Scheme 1. First, the 4-hydroxyphenyl-benzothiazole
(3) was synthesized by the reaction of 2-aminothiophenol (1) and
4-hydroxybenzaldehyde (2).15 The BTP was constructed by the
Evin, Tehran, Iran
† Electronic supplementary information (ESI) available. CCDC 1968870. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0nj06301k
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Scheme 1 Synthesis of benzothiazolepalladacycle (BTP).
reaction of (3) and Pd(OAc)2 in HOAc under an inert atmosphere
under reflux conditions.14
The BTP was characterized by various techniques. The IR
spectrum of BTP exhibits one broad absorption band for a
carbonyl group of acetate at 1693 cmꢁ1, and two absorption
bands for the CQN and C–S groups of a benzothiazole ring at
703 and 1604 cmꢁ1, respectively (ESI†). The 1H-NMR spectrum
of BTP shows a broad signal for the hydroxy group at
10.22 ppm. Moreover, the aromatic hydrogen atoms of BTP
give rise to characteristic signals in the aromatic region. The
best evidence for the formation of BTP is the appearance of a
Fig. 1 (a) The asymmetric units of BTP and the thermal ellipsoids at the
40% probability level (all of hydrogen atoms and MeOH as crystallization
solvent are omitted for clarity); (b) electrostatic potential of the Pd1ꢀ ꢀ ꢀPd2
axis analyzed by the Hirshfeld diagram. High electron density is depicted as
red and low electron density as blue.
singlet up-field signal at 5.92 ppm related to the aromatic Information File (CIF). The geometrical parameters of the
hydrogen near to Pd14 and a signal at 2.19 ppm for the acetate optimized structure and experimental X-ray structure revealed
bridge16 (ESI†). The 13C-NMR of BTP shows two signals for the a successful optimization (ESI†). The NBO analysis was per-
acetate bridge at 25.6 and 176 ppm plus characteristic signals formed to evaluate the Pdꢀ ꢀ ꢀPd interaction. This analysis
of the aromatic region of the ligand. Moreover, the crystal reveals that BD (bonding), CR (Atomic Core State), LP (Lone
structure determination (Fig. 1a) confirms the exact creation Pair) and LP* (Lone Pair star) orbitals of a Pd1 atom act as a
of the BTP complex containing dimeric Pd(II) centers coordi- donor, while LP*, RY* (Rydberg State), and BD* (Anti Bonding)
nated to nitrogen of thiazole rings, carbons of the phenyl ring, orbitals of a Pd2 atom act as an acceptor. From the other side,
and acetate bridges which grow in the P21 space group in an LP, LP*, and BD* orbitals of the Pd2 atom act as a donor, while
orthorhombic system. The geometrical parameters indicate LP*, RY*, and BD* orbitals of the Pd1 atom act as an acceptor.
lightly folded square-planar geometry around the palladium The existence of metallophilic interaction between two palla-
in which the angles (N1–Pd1–C9) and (N1–Pd1–O1) are 82.701 dium atoms with the donor–acceptor nature was graphically
and 98.941, respectively. Moreover, the benzothiazole ligands shown by molecular orbitals. The HOMO and LUMO orbitals
are transoid in the BTP dimeric backbone. The most desirable and the gap between them have been calculated (Fig. 2). As a
feature of BTP is a rare intramolecular palladium-palladium result of high electron density between the Pd1ꢀ ꢀ ꢀPd2 axis in the
interaction. The small Pd1ꢀ ꢀ ꢀPd2 distance (2.862 Å) is 12.2% HOMO of BTP, the Pd atoms and the ligands have more
less than the sum of the van der Waals radius of two palladium contributions in the HOMO and LUMO, respectively (Scheme 2).
atoms (3.26 Å) and longer than the sum of covalent radii (2.62
The QTAIM is a potent and applicable tool to analyse
Å). The Hirshfeld diagram analysis around the Pd1ꢀ ꢀ ꢀPd2 axis chemical bonds and interactions in various aspects.17 As can
demonstrates a high electrostatic potential, which indicates be seen in the molecular graph of the BTP (Fig. 3) and contour
that Pd1 and Pd2 are involved in an interaction (Fig. 1b).
map of the electron density’s Laplacian (ESI†), the bond critical
To scrutinize and clarify the existence and the nature of point (BCP) between two palladium atoms discloses an inter-
Pdꢀ ꢀ ꢀPd (d8–d8) interaction, density functional theory (DFT) action between two palladium atoms. To elucidate this inter-
calculations, quantum theory of atoms in molecules (QTAIM) action, some applications of the QTAIM were used. Based on
analysis, the natural bond orbital (NBO) method, and non- Bader’s criteria,18 the electron density of BCP (rBCP) for a
covalent interaction reduced density gradient (NCI-RDG) analysis closed-shell interaction is less than 0.10 a.u. Consequently,
were performed. Noticeably, the selected data regarding Pdꢀ ꢀ ꢀPd the Pdꢀ ꢀ ꢀPd interaction in BTP with rBCP = 0.0171 a.u. is a
interaction were cut out directly from the crystallographic closed-shell interaction. Likewise, based on the positive value
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Fig. 2 The HOMO and LUMO orbitals of the system.
Scheme 2 Synthesis of BTP@SBA.
2
of electron density laplacian (r rBCP), this interaction cate-
gorises as a closed-shell one. According to kraka’s criteria,19 the
positive value of local energy density at BCP (H(BCP)) proves the
closed-shell nature for an interaction observable for (H(BCP)) of
Pdꢀ ꢀ ꢀPd interaction. Similarly, by Espinosa’s criteria,20 the
PdꢀꢀꢀPd interaction displays a closed-shell interaction with
(|V(BCP)|/G(BCP)) o 1 and for BTP = 0.965. All results of theore-
tical studies corroborated a closed shell or a non-covalent inter-
action. Moreover, mapping the real-space was obtained by the
(NCI-RDG). This method is based on the electron density and its
gradient (sign(l2)r).21,22 The Pdꢀ ꢀ ꢀPd interaction was evaluated
by NCI-RDG and the results of s(r) versus sign(l2)r and s(r)-
isosurface have been shown in Fig. 3B and C. According to the
plots, the negative value of sign(l2)r and the green colour
Fig. 3 (a) The molecular graph for BTP determined by the B3LYP/
LANL2DZ computational level. The green dots stand for the bond critical
points (BCPs), the red dots stand for the ring critical points (RCPs), and the
blue ones stand for cage critical points (CCPs). Red, white, blue, gray and
yellow atoms represent O, H, N, C and S elements, respectively. (b) The
plots of RDG, s(r), versus sign(l2)r, and finally (c) coloured s(r)-isosurface
in B3LYP/LANL2DZ computational methods.
isosurface between two palladium atoms demonstrate a van Wiberg bond indices and NAO are 0.0912 and 0.1814, respec-
der Waals nature of this interaction. Based on the experimental tively (ESI†).
and theoretical findings the Pdꢀ ꢀ ꢀPd interaction in the BTP case
After BTP characterization, the BTP was directly anchored to
study is an intramolecular d8–d8 metallophilic interaction. In SBA-15 to form a heterogeneous catalyst (Scheme 3). For the
addition, the bond order of the PdꢀꢀꢀPd interaction was calcu- synthesis of the heterogeneous catalyst, the SBA-15 was reacted
lated by two NBO criteria; Wiberg bond indices and NAO (natural
atomic orbital) bond order. The calculated bond orders based
with thionyl chloride to afford the corresponding chlorinated
SBA-15 (SBA-Cl).23 Finally, the benzothiazolepalladacycle bonded
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Fig. 4 The EDX elemental analysis of BTP@SBA.
Fig. 5 The TGA of BTP@SBA up to 900 1C.
groups from the catalyst. This demonstrates that the catalyst
Scheme 3 Synthesis of amides.
has suitable thermal stability until B300 1C. The palla-
dium content of the catalyst was calculated (0.49 mmol gꢁ1
by FAAs.
)
to SBA-15 (BTP@SBA) was formed by the addition of the dried
solution of BTP to dispersed SBA-Cl.
The small-angle (0 o y o 101) XRD pattern of SBA-15 and
BTP@SBA indicates the two-dimensional hexagonal ordered
The BTP@SBA catalyst was characterized by thermogravi- symmetry with a typical pattern of the (100) plane of mesopores
metric analysis (TGA), Fourier transform infrared spectroscopy (2y = 1.471) (Fig. 6a). This proves that modification of SBA-15
(FT-IR), flame atomic absorption (FAAs), energy-dispersive X- with BTP does not affect the crystallinity of SBA-15.24 The SEM
ray spectroscopy (EDX), transmission electron microscopy images reveal that the BTP@SBA particles have a nearly regular
(TEM), scanning electron microscopy (SEM), small angle X-ray hexagonal shape25 with the particle size in the range of 400 nm
scattering (S-XRD) and nitrogen sorption analysis. The FT-IR (ꢂ50nm)26 (Fig. 6b). N2(g) adsorption–desorption of the catalyst
spectrum of the catalyst exposed a broad characteristic between shows typical IV type curves in which the surface area and pore
1000 and 1200 cmꢁ1 for Si–O–Si stretching bonds of the SBA volume of the catalyst are 329.31 m2 gꢁ1 and 0.5629 cm3 gꢁ1
,
structure. Additionally, a peak at 1667 cmꢁ1 is related to the respectively (ESI†). The surface area and pore volume of
carbonyl group of acetate bridges of BTP (ESI†). The surface BTP@SBA are smaller than the fresh SBA-15 (726 m2 gꢁ1 and
composition was determined by EDX. The elements of Si, Pd, O, 0.9842 cm3 gꢁ1). This indicates the BTP anchored mostly inside
C, N, and S in the EDX spectrum are related to the BTP the channel of SBA-15. Furthermore, the value of Barrett-Joyder-
modified on SBA-15 (Fig. 4).
Halenda (BjH) (ESI†) shows an average pore diameter of
TGA was further used to study the heating resistance of the 3.58 nm in excellent agreement with the TEM result (ESI†).
catalyst (Fig. 5). A TGA plot of the catalyst shows a weight loss at Likewise, the BJH distribution curve depicts a narrow pore size
B100 1C, which was assigned to adsorbed water. The 6.95% distribution (less than 10 nm).
weight loss at above B300 1C (and continuing up to B530 1C)
The TEM image of BTP@SBA displays highly ordered meso-
is related to the decomposition of covalently bonded organic porous channels with a complete 2D (P6mm) hexagonal
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2.2. Catalytic activity of BTP@SBA
After preparation and characterization of BTP@SBA, its catalyst
performance and selectivity were appraised in MIIr of aryl
halides and isocyanides. First, the various solvents, tempera-
tures, bases, amount of catalyst, and reaction times were tested
to obtain the best reaction conditions (Table 1). An initial
assessment of the catalytic activity of BTP@SBA (0.5 mol% with
respect to Pd content) for an amidation reaction via MIIr was
tested for the reaction of Ph-I (4a) and tert-butyl isocyanide (5b)
as a model reaction. The reaction at 100 1C in DMSO and in the
presence of K2CO3 gave 67% isolated yield of the corresponding
amides (6a) (Table 1, entry 1). Then, some inorganic and
organic bases such as K2CO3, Cs2CO3, Et3N, NaOH and CsF
were tested in the model reaction in DMSO at 100 1C (Table 1,
entries 1–5). The results show that the Cs2CO3 was the super-
lative base (entry 2). Afterward, the effect of Pd content was
investigated using Cs2CO3 as an ideal base. When the amount
of Pd increased from 0.5 to 1 and 1.5 mol%, the isolated yield of
the corresponding amide was not affected impressively (entries
2, 6 and 7). 0.3 mol% of the catalyst resulted in the amidation
in lower yield (entry 8). When the reaction was carried out
without catalyst, the isolated yield of the corresponding amide
was trace (entry 9). Therefore, 0.5 mol% of Pd content was
sufficient to push the reaction forward. To monitor the effect of
temperature, the reaction was carried out at room temperature,
60, 80, and 120 1C to result in the product in trace, 31, 54 and
68% isolated yield, respectively (entries 10–13). Finally, DMSO,
CHCl3, DMF, toluene, H2O and DMSO/H2O (1 : 1) were checked
as different solvents in the MIIr reaction (entries 14–18). As
shown, the reaction worked most efficiently in DMSO/H2O
(1 : 1) (entry 18). The optimum conditions were obtained with
Fig. 6 (a) The low angle P-XRD of BTP@SBA; (b) the SEM image of
BTP@SBA.
arrangement of mesoporous. This shows the absence of Pd
nanoparticles on the surface of silica or inside the channels
(Fig. 7). Notably, the channels were largely preserved during
modification of BTP on SBA-15 and even under reflux of SOCl2
during catalyst preparation.27
Table 1 Screening the reaction conditions
Entry Catalyst (mol%) Base
Solvent
T (1C) Yielda (%)
1
2
3
4
5
6
7
8
0.5
0.5
0.5
0.5
0.5
1
1.5
0.3
—
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
K2CO3 DMSO
Cs2CO3 DMSO
100
100
100
100
100
100
100
100
100
80
60
120
r.t
reflux Trace
100
100
65
68
Trace
43
66
69
69
48
Trace
54
Et3N
NaOH DMSO
CsF DMSO
DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 DMSO
Cs2CO3 CHCl3
Cs2CO3 DMF
Cs2CO3 Toluene
Cs2CO3 H2O
9
10
11
12
13
14
15
16
17
18
31
68
Trace
63
49
reflux 18
73
Cs2CO3 DMSO/H2O (1 : 1) 100
Iodobenzene (1 mmol), t-BuNC (1.2 mmol), base (1 mmol) for 24 h.
Isolated yields.
a
Fig. 7 The TEM of BTP@SBA along the pore axis of BTP@SBA.
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Cs2CO3 as a base and DMSO/H2O as a solvent using 0.5 mol%
of BTP@SBA at 100 1C for 24 h.
To explore the scope of the reaction, diverse Ar–X 4 and
isocyanides 5 were screened in the reaction (Scheme 3). All aryl
iodides gave reasonable isolated yields without significant
by-products. Notably, superior activity for the amidation reac-
tion was obtained with cyclohexylisocyanide (6b). The reaction
with Ar–Br produced the desired amides in moderate yields.
The Ar–Cl with electron donating and electron withdrawing
groups were tested and the yields of products were trace
(Scheme 3). The (Het)Ar–Cl afforded the desired amides in
good yields (6m, 6n). To the best of our knowledge, there are
no examples of employing any heterogeneous catalysts and
palladacycle complexes for amide synthesis by MIIr.
The reusability and stability are hallmarks of heterogeneous
catalysts. To specify BTP@SBA is operating in a heterogeneous
or homogeneous pathway, a hot filtration test was performed
for MIIr of Ph-I and t-Bu-NC.28 In this way, the reaction was
stopped after the midpoint of reaction (12 h). Subsequently, the
hot filtrate was rapidly transferred to another vessel containing
Cs2CO3 and DMSO/H2O at 100 1C. By heating the catalyst-free
flask for 12 h, no significant progress was observed. Moreover,
using FAAs, the same reaction solution at the midpoint of
reaction completion indicated that no significant quantities
of palladium were lost to the reaction liquors during the
process.29 The recyclability of the catalyst was also studied in
the MIIr reaction of Ph-I and t-Bu-NC. After the accomplish-
ment of each run of the reaction, the catalyst was extracted by
centrifugation, followed by washing with an excess amount of
MeOH and acetone. The catalyst could be reused at least five
times successfully without significant loss in activity (yields:
73%, 73%, 71%, 69%, and 68%). Furthermore, the small angle
XRD analysis of the recycled BTP@SBA demonstrated the
homogeneity of the pores (ESI†). Moreover, the low angle sharp
peak was retained after five runs (Fig. 8a). The SEM image of
reused BTP@SBA proved the approximately hexagonal struc-
ture (Fig. 8b). Besides, the TEM analysis after five catalytic
cycles showed no conclusive evidence of colloidal Pd species
(Pd0-L)30 (Fig. 8c). The mercury poisoning test for MIIr does not
Fig. 8 (a) The powder XRD pattern; (b) the SEM image; and (c) the TEM of
reused BTP@SBA after 5 catalytic cycles.
show a remarkable discrepancy in isolated yield for 3a synth- BTP@SBA was performed using an electron microscopy Philips
esis. The results support that the BTP@SBA catalyzes the MIIr XL-30 ESEM. Transmission Electron Microscopy characteriza-
reaction by a quasi-heterogeneous nature that takes place tion of BTP@SBA was performed using a Philips CM-30 trans-
mainly via Pd+2/Pd+4 catalytic cycles. The proposed mechanism mission microscope with an accelerating voltage of 150 kV. The
can be found with more details in the ESI.†
concentration of Pd was estimated using a Shimadzu AA-680
flame atomic absorption spectrophotometer. The sorption analysis
was recorded by micromeritics Auto-chem II 2920. Furthermore,
TGA was accomplished by PerkinElmer TGA/DSC. Lastly, the CHNS
content was estimated by a PerkinElmer 2400 series.
3. Experimental
3.1. Materials
The X-ray diffraction measurements were performed with a
All chemicals were purchased from Merck or Aldrich and were STOE IPDS-II diffractometer with graphite-monochromated
used without additional distillation. FT-IR spectra were taken MoKa radiation. Cell constants and an orientation matrix for
using a Bomem FT-IR MB spectrometer. The NMR spectra were data collection were obtained by least-squares refinement of
recorded on a BRUKER DRX-300 AVANCE spectrometer. Pow- diffraction data from 6743 and 3408 unique reflections for
der X-ray Diffraction data were collected on a STOE STADI P BTP. Data were collected at a temperature of 298(2) K to a
with a scintillation detector, secondary monochromator and maximum 2q value of 51.988 and in a series of w scans in 18
Cu-Ka1 radiation (l = 1.5406 Å). EDS characterization of oscillations and integrated using the Stoe X-AREA software
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package. The data were corrected for Lorentz and Polarizing product was purified by Column chromatography (EtOAc/n-
effects. The structures were solved by direct methods and refined Hexane (3/7)).
on F2 by a full-matrix least-squares procedure. All hydrogen
atoms were added at ideal positions and constrained to ride
on their parent atoms, with Uiso(H) = 1.2Ueq. All refinements were
4. Conclusions
performed by using the X-STEP32 crystallographic software
In this work, a benzothiazolepalladacycle containing metallo-
package. Complete crystallographic data for BTP have been
philic Pdꢀ ꢀ ꢀPd intramolecular interactions was synthesized and
deposited with the Cambridge Crystallographic Data Centre as
characterized by using experimental and computational meth-
supplementary publication no. CCDC 1968870.†
ods. Furthermore, the heterogenized system of the organome-
tallic complex was found to be an easy-synthesis and efficient
catalyst for amidation reaction via the migratory isocyanide
insertion pathway. The availability of the catalyst, recyclability
and use of small amounts of palladium precursor in a vital
reaction model in the isocyanide insertion area are important
features of this study.
3.2. Synthesis of 4-hydroxy 2-phenyl benzothiazole (3)
The 2-aminothiophenol (1 mmol) and 4-hydroxybenzaldehyde
(1 mmol) were stirred in MeOH at room temperature to afford
yellow imine sediment. Subsequently, NH2SO3H (10 mol%) was
added to the reaction mixture. After 4 h, light yellow sediment
was achieved and recrystallized in MeOH/H2O to afford a pure
product.
Conflicts of interest
3.3. Synthesis of 4-hydroxy 2-phenyl benzothiazole
palladacycle (BTP)
There are no conflicts to declare.
The dimeric acetate palladacycle (BTP) was obtained by the
reaction of (3) (1 mmol) and Pd(OAc)2 (1 mmol) in HOAc under
reflux conditions and an inert atmosphere for 2 h. Afterward,
an excess amount of N-hexane was added to the reaction
mixture and the sediment gained by simple filtration as a greyish-
green colour.
Acknowledgements
We gratefully acknowledge the financial support from the
Shahid Beheshti University and the Iran National Science
Foundation (INSF) for proposal No. 96001796.
3.4. Synthesis of chlorinated SBA-15
Fresh SBA-15 was kept overnight under 120 1C to evaporate
adsorbed water. The SBA-Cl was obtained by chlorination of
dried SBA-15 nanoparticles. SBA-15 (3 g) was refluxed in 60 mL
SOCl2 in a round bottomed flask fortified with a drying tube,
condenser and inert atmosphere for 24 h. The excess amount of
thionyl chloride was distilled off and the resulting solid product
was flame-dried as a light-greyish colour and stored in a sealed
vessel under N2(g).
Notes and references
´
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3.5. Synthesis of BTP directly bonded to SBA-15 (BTP@SBA)
The BTP (0.5 mmol, 0.39 g) was dissolved in 40 mL dried DMF.
The soluble of BTP was added dropwise to the round bottom
flask containing dried chlorinated SBA-15 under N2(g). The
reaction was accompanied by emission of gaseous HCl. The
reaction was stirred for 24 h at room temperature. Then, 60 ml
of MeOH was added to the reaction. Afterward, the BTP@SBA
was separated by centrifugation and washed several times with
MeOH and H2O in order to neutralize the pH.
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3.6. General procedure for the migratory isocyanide insertion
reaction
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