Palladium Nanoparticles Supported on Fibrous Silica (KCC-1-PEI/Pd): A Sustainable Nanocatalyst for Decarbonylation Reactions

Article abstract of DOI:10.1002/cplu.201600245

A practical and convenient decarbonylation of a variety of aromatic, heteroaromatic, and alkenyl aldehydes by using palladium nanoparticles supported on novel, fibrous nanosilica, named KCC-1-PEI/Pd, has been developed. Complete conversion of aldehyde functionalities into deformylated products was achieved in all cases and in nearly all cycles tested by reusing the catalyst systems. This method eliminates further purification of products after their isolation. Syntheses of at least three different deformylated products have been shown in sequence with the same catalyst system, which neither requires use of any additives, such as oxidants and bases, nor CO scavengers.

Full text of DOI:10.1002/cplu.201600245

Accepted Article
Title: Fibrous-Silica Supported Palladium-Nanoparticles (KCC-1- PEI/Pd): A Su-
stainable Nanocatalyst for Decarbonylation Reactions
Authors: Pintu K. Kundu; Mahak Dhiman; Atanu Modak; Arindam Chowdhury; Vivek
Polshettiwar; Debabrata Maiti
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soon as possible and may be different to this Accepted Article as a result of editing.
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To be cited as: ChemPlusChem 10.1002/cplu.201600245
Link to VoR: http://dx.doi.org/10.1002/cplu.201600245
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ChemPlusChem
10.1002/cplu.201600245
COMMUNICATION
Fibrous-Silica Supported Palladium-Nanoparticles (KCC-1-
PEI/Pd): A Sustainable Nanocatalyst for Decarbonylation
Reactions
[a]
[b]
[a]
[a]
[b]
Pintu K. Kundu, Mahak Dhiman, Atanu Modak,
Arindam Chowdhury,* Vivek Polshettiwar,*
[a]
Debabrata Maiti *
Abstract: A practical and convenient decarbonylation of a variety of
aromatic, heteroaromatic and alkenyl aldehydes using palladium
molecules, such as 5-hydroxymethylfurfural and furfural have
been achieved via Pd-nanoparticles which were impregnated on
mesoporous silica support-SBA-15 to provide furfuryl alcohol
and furan respectively. Though the procedure looked excellent
for converting bio-mass derived molecules but suffers from
(Pd) nanoparticles supported on novel, fibrous nanosilica, named
KCC-1-PEI/Pd have been developed. Complete conversion of
aldehyde functionalities to deformylated products were achieved in
all the cases and nearly in all the cycles tested by reusing the
catalyst systems. This method eliminates further purification of
products after their isolation. Syntheses of at-least three different
deformylated products have been shown in sequence with the same
catalyst system which neither require use of any additives such as
oxidants and/ bases nor CO-scavengers.
limitations such as substrate scopes and recyclability. We have
[36, 37]
recently observed
that support morphology has dramatic
effects on its catalytic activity: multifold enhancement of
nitridated base-catalyzed Knoevenagel condensations and
trans-esterification reactions were seen when replacing the solid
support from conventional silica like SBA-15 with fibrous
nanosilica, KCC-1.
In view of catalysis on solid support, metal nanoparticles with a
support of choice provides a large field for the discovery of new,
highly active nanocatalysts for important and challenging
reactions, which also offer the additional advantage of
Owing to its immense importance in chemistry, including
[38, 39]
synthesis of natural products,
there is a need to develop an
[
1-3]
environmentally benign decarbonylation method. The protocol is
expected to show the substrate scopes like transition-metal
catalyzed homogeneous reactions along with acceptable
catalyst-recyclability and efficiency like heterogeneous reactions
and preferentially easy product separation without extra steps of
purification. Herein, we report a practical and convenient way of
decarbonylation reaction using palladium nanoparticles
supported on fibrous silica, KCC-1.
recyclability.
These systems have several advantages over
conventional catalysts, such as superior activity and improved
stability. With the innovation of high-surface-area silica with a
[
4]
unique fibrous morphology (KCC-1) where the surface area of
KCC-1 is attributable to fibres and not to pores, paved the way
to enhanced accessibility of catalytic active sites. Towards
sustainable nanocatalysis, this unique property of silica-
[
5-9]
supported nanocatalysts
has been successfully used to
demonstrate various catalytic reactions, such as hydro-
[
7]
metathesis of olefins using a KCC-1/TaH catalyst system,
[
8]
Suzuki coupling reactions using KCC-1/Pd and hydrogenolysis
[
9]
of propane and ethane using KCC-1/Ru nanocatalyst etc.
[10]
Functional groups removal from organic molecules,
especially decarbonylation of aldehydes has drawn considerable
attention over the decades since such processes enable
provisional use of the beneficial features of the –CHO
[
11]
functionality such as regio-selectivity in Diels–Alder reaction,
[
12]
domino oxa-Michael-aldol reaction, biosynthesis of alka(e)nes
[
13, 14]
from fatty aldehydes[
etc. Metal-complexes of transition
15]
[16]
[17-22] [23-28]
metals such as Ru,
Ir,
Rh,
and Pd
have been
successfully used for deformylation reactions but they usually
require high temperature. Various supported-noble-metal
catalyzed reactions were also employed for the same
[
29-31]
purpose.
protocol where commercially available Pd(OAc)
and shown wide substrate scopes with 8-16 mol% catalyst
Recently, we have observed a cost-effective
2
has been used
[
32-34]
loading under mild conditions.
On the other hand, there is
only a single report of selective deformylation reaction using
[35]
metal nanoparticles. Here decarbonylation of biomass-derived
Figure 1. TEM images (a, b, c), particle size distribution (d), and EDS
mapping (e, f, g, h) of KCC-1-PEI/Pd
[
[
a]
b]
Dr. Pintu K. Kundu, Mr. Atanu Modak, Prof. Arindam Chowdhury,
Prof. Debabrata Maiti
Department of Chemistry
Indian Institute of Technology Bombay, Powai, Mumbai 400076,
India.
E-mail: dmaiti@chem.iitb.ac.in
Mr. Mahak Dhiman, Prof. Vivek Polshettiwar
Department of Chemical Sciences
Tata Institute of Fundamental Research (TIFR), Mumbai
Email: vivekpol@tifr.res.in
Supporting information for this article is given via a link at the end of
the document
Prompted by the efficiency of high-surface-area fibrous silica
(
KCC-1), we planned to modify the fibres with Pd nanoparticles
to use the final materials towards deformylation reactions. The
modification of KCC-1 with Pd-nanoparticles has been achieved
as follows: KCC-1 was first functionalized with 3-
glycidoxypropyltrimethoxysilane (GTMS) which acted as a linker
between the silanols of silica surface and amine functionalities of
polyethylenimine (PEI). Epoxy group of GTMS underwent ring
2
N
opening during S
reaction to produce highly branched network
of polymeric amines on KCC-1 fibers, further termed as KCC-1-

ChemPlusChem
10.1002/cplu.201600245
COMMUNICATION
PEI. After that, metalation was carried out between sodium
tetrachloropalladate (II) and KCC-1-PEI which on reduction by
observed complete consumption of starting aldehyde after 20 h
(SI: 3A) to produce a single product i.e. naphthalene (1a,
Scheme 1). The decarbonylated product thus formed was
separated simply by decantation/filtration after centrifuge. The
filtrate along with washings was evaporated to get the pure
product directly with excellent yield (96%). The remaining solid
was activated by heating under reduced pressure and reused
as-it-is for the next cycles. It was seen that the catalyst system is
as effective as the initial reaction cycle even after using the
same for 8 times without losing its efficiency of conversion, yield
and purity of the product (Table 1, left). In a similar manner,
decarbonylation of 9-anthracenecarboxaldehyde with KCC-1-
PEI/Pd proceeded smoothly to provide solid anthracene, 1b with
more than 95% yield (done up to six cycles) and excellent purity
of solid anthracene just after isolation and without further
purification (Table 1, right).
4
NaBH yielded highly monodispersed palladium nanoparticles
(
PdNPs). TEM analysis of synthesized catalyst showed large
number of Pd nanoparticles supported on KCC-1 with very
narrow particle size distribution ranging from 1.8 to 3.5 nm
(
Figure 1). EDS elemental mapping indicated that the fibers of
KCC-1 were fully loaded with well-dispersed PdNPs, re-
establishing the advantage of using KCC-1 with unique fibrous
morphology. Palladium loading in the KCC-1-PEI/Pd catalyst
was found to be 9.7% (weight %) by carrying out EDS at 10
.
[40]
different well-separated positions
Nitrogen-sorption measurements were carried out to assess
the textural properties and surface area of synthesized catalyst.
On investigation KCC-1, KCC-1-PEI and KCC-1-PEI/Pd showed
type-IV isotherm with H1 type hysteresis (Figure 2a). BET
2
surface area of the synthesized KCC-1 was 530 m /g, which on
Table 1. Recyclability of catalyst systems for decarbonylation.
2
PEI functionalization was reduced to 271 m /g. This decrease in
surface area was accompanied by decrease in pore volume
3
from 0.69 to 0.42 cm /g. Thermogravimetric analysis was carried
out in air to estimate the loading of PEI on KCC-1. After the
initial weight loss due to water, pure KCC-1 showed no further
weight loss indicating the high thermal stability. The 19 and
18% weight loss observed in case of KCC-1-PEI and KCC-1-
PEI/Pd respectively and was attributed to the loss of covalently
bonded PEI (Figure 2c). Covalent attachment between KCC-1
2
9
and PEI was also validated by Si CP-MAS NMR analysis.
Signals at −90.3, −97.8, and −106.8 ppm, are characteristics of
2
3
4
Q , Q and Q sites, and signals at −54.6 and −63.1 ppm are
2
3
due to the T and T sites of silica respectively, which indicates
the formation of silica-carbon bond via covalent attachment of
PEI with KCC-1 (Figure 2d).
a
b
isolated yield with conversion in parenthesis; conversion determined by gas
c
1
chromatography; conversion determined by H NMR technique.
Encouraged by the successful deformylation of non-functional
fused-ring aryl aldehydes, benzaldehyde-derivatives having
different functionalities have been reacted under the optimized
reaction conditions (Table 2). p/m-Nitro benzaldehyde under the
above Pd nanoparticles-catalyzed reaction provided complete
deformylation with excellent yield of nitrobenzene (2a and 2b,
96%, 94%, respectively) and also the yield of the reactions were
unaffected with a number of recycled catalyst systems. Nearly
similar conversion and yield of decarbonylated product (2c,
99%) was found with p-methoxy benzaldehyde, thus promised to
have huge functional group tolerance including electron
withdrawing and donating groups attached to aromatic
aldehydes. Both, acid and base sensitive (towards hydrolysis)
cyano-functionality was found to be unaltered in our protocol and
provided excellent yield of m/p-benzonitrile (2d and 2e, 99-95%)
in all cycles studied. Benzaldehydes containing other functional
groups such as 4-chloro-, 4-carboxy-, 3,4-dimethoxy-, and
densely functionalized 3,4,5-trimethoxy-benzaldehyde as well as
methyl 4-formylbenzoate proceeds well with excellent yield (2f-j)
Figure 2.
(a) Nitrogen adsorption-desorption isotherm, (b) pore size
and recyclability.
On the other hand, bis-formylated
distribution, (c) thermogravimetric profile of KCC-1, KCC-1-PEI and KCC-1-
PEI/Pd, and (d) 29Si CP-MAS NMR spectrum of KCC-1-PEI.
benzaldehyde, such as terephthaladehyde with a little higher
catalyst loading of KCC-1-PEI/Pd (7.5 mol% Pd) undergoes di-
deformylation to yield benzene (2k) with 100% conversion.
However, ortho-substituted
methoxy-1-naphthaldehyde
napthaldehyde particularly, 2-
proceeded well with the
deformylation reaction to yield 2-methoxynaphthalene in
excellent yield (1c, 95%) but the conversion as well as product
Scheme 1. KCC-1-PEI/Pd catalyzed decarbonylation of 2-naphthaldehyde.
nd
rd
yield diminished with recycling (product yield at 2 and 3 cycle:
3% and 83% respectively).
We started our investigations using 2-naphthaldehyde as
substrate and reacted with KCC-1-PEI/Pd (5 mol% Pd) in a
9
a
º
Table 2. Decarbonylation of a variety of aromatic aldehydes
cyclohexane suspension at 130 C (Scheme 1). Notably the
reaction can be carried out in air along with molecular sieves
and thereby the methodology is found to be user-friendly. We

ChemPlusChem
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COMMUNICATION
heterocylic carbaldehyde such as N-methyl indole-3-
carboxaldehyde, 4-pyridinecarboxaldehyde and O-heterocylic
carbaldehyde namely furan-2-carbaldehyde were completely
consumed to yield 1–methylindole pyridine and furan,
respectively with excellent yield (3a: 94%, 3b: 99%, 3c: 100%)
and catalyst recyclability. Notably, unlike furan-carboxaldehyde,
N-heteroaromatic-aldehyde under similar reaction conditions
with Pd(OAc)[ , one of the best known methodologies for
2
32]
deformylation,
the other hand, 3-thiophenecarboxaldehyde, with KCC-1-PEI/Pd,
7.5 mol% Pd) transformed completely to thiophene (3d, 93%)
without any side product (16 mol% Pd loading of Pd(OAc)
provided less yield of the desired product. On
(
2
3
2
provided at most 66% yield of the product ). However, both the
conversion of 3-thiophenecarboxaldehyde as well as yield of the
product reduces significantly while recycling.
We have also explored the scope of the decarbonylation
reaction with alkenylaldehydes using our protocol (Table 3).
Unlike previously reported procedures of deformylation, trans-
cinamaldehyde and α-methyl-trans-cinnamaldehyde produced
with 85-100% conversion to product in high yield of styrene (4a,
87%) and β-methylstyrene (4b, 90%), respectively. Aliphatic
aldehydes were moderately active under similar reaction
conditions; 2-phenyl-acetaldehyde and n-octaldehyde provided
moderate to high yield of deformylated product (4c: 80%, 4d:
68%) and recyclability.
a
b
cy. refers to cycle number; yield with conversion in parenthesis; isolated
c
d
yield; GC yield (due to high volatility of the product) 7.5mol% Pd loading.
a
Table 3. Decarbonylation of heteroaromatic, alkane and alkenylaldehydes
Scheme 2. Decarbonylation in a sequence by recycling the catalyst systems
(100% conversions in all cases, isolated yield of products given)
To check further the efficiency of the present protocol,
several aldehydes were reacted in a series upon recycling the
catalytic systems (Scheme 2). After isolating pure naphthalene
st
(
1a, 96%) from the
1
cycle (deformylation of 2–
naphthaldehyde) just by filtrating the supernatant from
centrifuged reaction tube (also the washings), the recovered
nd
catalyst systems were used directly after its activation in 2
cycle.
Subsequently,
deformylation
of
9-
anthracenecarboxaldehyde proceeded well with complete
consumption of the starting material to yield anthracene (1b,
9
8%) as the sole product. In a similar fashion, the recovered
nd
catalyst-systems from
2
cycle were used to treat 4-
formylbenzoic acid which showed benzoic acid (2g, 94%) as the
only product.
a
b
cy. refers to cycle number; yield with conversion in parenthesis; for entryd
c
3
a,3b 5 mol% Pd and for entry 3c-4d 7.5 mol% Pd was used isolated yield;
GC yield (due to high volatility of the product)
Next, we looked into more challenging substrate like
heteroaromatic and aliphatic aldehydes and it was found that for
most of the hetero aromatic (except 3a and 3b, Table 3) and
aliphatic aldehyde more catalyst loading required (7.5 mol% Pd)
for desired conversion of the substrates (Table 3). Both, N-
Scheme 3. Proposed catalytic cycle for decarbonylation of aldehyde.

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10.1002/cplu.201600245
COMMUNICATION
[
23,34]
Based on literature report,
a
catalytic cycle of
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[
[
[
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heterogeneous catalytic protocol for decarbonylation reaction of
a variety of aldehydes with complete conversion to products and
thus ease of product purification (without chromatography) by
[
[
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alkenylaldehydes was also achieved. In addition, nanocatalysts
showed excellent stability (recyclability) and even after eight
cycles, used-catalyst was active like a fresh one. Owing to huge
functional group tolerance on aromatic ring systems and
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the efficiency of the catalytic systems in other organic
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10.1002/cplu.201600245
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
[
a]
[b]
A
practical
and
convenient
Pintu K. Kundu, Mahak Dhiman,
[
a]
decarbonylation of a variety of aromatic,
heteroaromatic and alkenyl aldehydes
using palladium (Pd) nanoparticles
supported on novel, fibrous nanosilica,
named KCC-1-PEI/Pd have been
Atanu
Chowdhury,*
Modak,
Arindam
[
a]
*[b]
Vivek Polshettiwar,
*
[a]
Debabrata Maiti
Page No. – Page No.
developed.
Complete conversion of
Fibrous-Silica Supported Palladium-
aldehyde functionalities to deformylated
products were achieved in all the cases
and nearly in all the cycles tested by
reusing the catalyst systems. This
method eliminates further purification of
products after their isolation. Syntheses
of at-least three different deformylated
products have been shown in sequence
with the same catalyst system which
neither require use of any additives such
as oxidants and/ bases nor CO-
scavengers.
Nanoparticles
Sustainable
Decarbonylation Reactions
(KCC-1-PEI/Pd):
Nanocatalyst
A
for