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Metal organic framworks IRMOF 8, ZIF 9, MOF 199 and IRMOF 3 as catalysts for friedel crafts acylation, knoevenagel, azamichel and pall knorr reactions

TABLE OF CONTENTS

LIST OF TABLES ...................................................................................................... viii
LIST OF FIGURES ........................................................................................................ix
LIST OF ABBREVIATION......................................................................................... xii
INTRODUCTION ...........................................................................................................1
CHAPTER 1

LITERATURE REVIEWS...................................................................4

1.1 Metal organic framework.............................................................................4
1.1.1 Introduction ............................................................................................ 4
1.1.2 MOF properties ......................................................................................5
1.1.3 MOF synthesis .......................................................................................6
1.1.4 MOF application ....................................................................................7
1.2

The application of MOFs in catalysis ......................................................8

1.2. 1 MOFs with Metal Active Sites ............................................................. 9
1.2.2 MOFs with Reactive Functional Groups .............................................18

1.2.3 Grafted species as an active site .......................................................... 20
CHAPTER 2

EXPERIMENTAL .............................................................................30

2.1 Materials and instrumentation ....................................................................30
2.2 MOF synthesis ............................................................................................ 31
2.2.1 IRMOF-8 ............................................................................................. 31
2.2.2 ZIF-9 ....................................................................................................31
2.2.3 MOF-199 ............................................................................................. 32
2.2.4 IRMOF-3 ............................................................................................. 32
2.3 Catalytic studies .......................................................................................... 32
vi


2.3.1 The Friedel-Crafts acylation reaction ..................................................32
2.3.2 The Knoevenagel reaction ...................................................................33
2.3.3 Aza-Michael Reaction .........................................................................34
2.3.4 The Paal-Knorr reaction.......................................................................34
CHAPTER 3

RESULTS AND DISCUSSIONS ......................................................36

3.1 Catalyst characterization ............................................................................36
3.1.1 IRMOF-8 ............................................................................................. 36
3.3.2 ZIF-9 ....................................................................................................40
3.3.3 MOF-199 ............................................................................................. 44
3.3.4 IRMOF-3 ............................................................................................ 48
3.2 Catalytic studies .......................................................................................... 52
3.2.1 The Friedel-Crafts acylation reaction .................................................52
3.2.2 The Knoevenagel reaction ...................................................................61
3.2.3 The aza-Michael reaction.....................................................................72
3.2.4 The Paal-Knorr reaction.......................................................................85
CHAPTER 4

CONCLUSIONS ................................................................................97

LIST OF PUBLICATIONS ..............................................................................99
REFERENCES ............................................................................................................100


vii


LIST OF TABLES

Table 1.1: The surface area of some materials ................................................................ 6
Table 1.2 Reported catalytic properties of MOF compounds with active metal sites ....9
Table 1.3. Reported catalytic properties of MOF compounds with reactive functional
groups ............................................................................................................................ 20

viii


LIST OF FIGURES
Figure 1.1. Examples of inorganic and organic SBUs [22].............................................5
Figure 1.2 The ligand of POST-1 ..................................................................................18
Figure 1.3. The schematic view of 1,3,5-benzene tricarboxylic acid tris[N-(4pyridyl)amide] ...............................................................................................................20
Figure 3.1 XRD of the IRMOF-8 ..................................................................................38
Figure 3.2 SEM micrograph of the IRMOF-8 ............................................................... 38
Figure 3.3TEM micrograph of the IRMOF-8 ............................................................... 39
Figure 3.4. TGA analysis of IRMOF-8 .........................................................................39
Figure 3.5 FT-IR spectra of the IRMOF-8 (a), and 2,6-napthalenedicarboxylic acid (b).
.......................................................................................................................................40
Figure 3.6 XRD of the ZIF-9 ......................................................................................... 42
Figure 3.7 SEM micrograph of the ZIF-9 ....................................................................42
Figure 3.8 TEM micrograph of the ZIF-9 .....................................................................43
Figure 3.9 TGA analysis of ZIF-9 .................................................................................43
Figure 3.10 FT-IR spectra of the ZIF-9 (a) and benzimidazole (b). ............................. 44
Figure 3.11 XRD of the MOF-199 ................................................................................45
Figure 3.12 SEM micrograph of the MOF-199 ............................................................ 46
Figure 3.13 TEM micrograph of the MOF-199 ............................................................ 46
Figure 3.15 FT-IR spectra of the MOF-199 (a) and the 1,3,5-benzenetricarboxylic acid
(b)...................................................................................................................................47
Figure 3.14 TGA analysis of MOF-199 ........................................................................47
Figure 3.16 XRD of the IRMOF-3 ................................................................................49
Figure 3.17 SEM micrograph of the IRMOF-3 ............................................................. 50
Figure 3.18 TEM micrograph of the IRMOF-3 ............................................................ 50
Figure 3.19 TGA analysis of IRMOF-3. .......................................................................51
Figure

3.20

FT-IR

spectra

of

the

IRMOF-3

(a)

and

the

2-amino-1,4-

benzenedicarboxylic acid (b) ......................................................................................... 51
ix


Figure 3.21 Effect of temperature on reaction conversion ............................................53
Figure 3.22 Effect of benzoyl chloride: toluene molar ratio on reaction conversion....53
Figure 3.23 Effect of catalyst concentration on reaction conversion ............................ 57
Figure 3.24 Leaching test indicated no contribution from homogeneous catalysis of
active acid species leaching into reaction solution ........................................................ 57
Figure 3.25 Catalyst recycling studies...........................................................................59
Figure 3.26 Effect of substituents on reaction conversion ............................................59
Figure 3.27 Effect of benzaldehyde : malononitrile molar ratio on reaction conversion
.......................................................................................................................................65
Figure 3.28 Effect of catalyst concentration on reaction conversion ............................ 65
Figure 3.29 Leaching test indicated no contribution from homogeneous catalysis of
active species leaching into reaction solution ............................................................... 66
Figure 3.30 Effect of solvent on reaction conversion ...................................................66
Figure 3.32 Catalyst recycling studies...........................................................................68
Figure 3.31. Catalytic recycling study...........................................................................68
Figure 3.33 Effect of different substituents on reaction conversion ............................. 71
Figure 3.34 FT-IR spectra of the reused (a) and fresh (b) ZIF-9 ..................................71
Figure 3.35 . NH3-TPD spectra of the MOF-199 measured between 100 oC and 400 oC
.......................................................................................................................................74
Figure 3.36 Effect of benzylamine: ethyl acrylate molar ratio on reaction conversion 74
Figure 3.37 Effect of catalyst concentration on reaction conversion ............................ 75
Figure 3.38 Effect of different catalysts on reaction conversion ..................................78
Figure 3.39. Effect of solvent on reaction conversion ..................................................79
Figure 3.40. FT-IR spectra of the fresh (a) and reused (b) MOF-199........................... 82
Figure 3.41. X-ray powder diffractogram of the fresh (a) and reused (b) MOF-199....82
Figure 3.42. Leaching test indicated no contribution from homogeneous catalysis of
active species leaching into reaction solution ............................................................... 84
Figure 3.43 Catalyst recycling studies of the aza-Michael reaction.............................. 84
Figure 3.44. Effect of different amines on reaction conversion ....................................85
Figure 3.45 Effect of benzylamine:2,5-hexanedione molar ratio on reaction conversion................................................................................................................................. 86
x


Figure 3.46. Effect of catalyst concentration on reaction conversion. .......................... 87
Figure 3.47. Leaching test indicated no contribution from homogeneous catalysis of
active species leaching into reaction solution. .............................................................. 88
Figure 3.48. Effect of different catalysts on reaction conversion. ................................ 90
Figure 3.49 Effect of different solvents on reaction conversion. ..................................91
Figure 3.50 Effect of different amines on reaction conversion. ....................................92
Figure 3.51 Effect of different diketones on reaction conversion. ................................ 94
Figure 3.52 Catalyst recycling studies of the Paal Knorr reaction ................................ 94
Figure 3.53 FT-IR spectra of the fresh (a) and reused (b) IRMOF-3............................ 96
Figure 3.54 X-ray powder diffractogram of the fresh (a) and reused (b) IRMOF-3.....96

xi


LIST OF ABBREVIATION
1,4-dicb

1,4-diisocyanobenzene

2,3-pydca

pyridine-2,3-dicarboxylate

2,4-pydca

pyridine-2,4-dicarboxylate

2-pymo

2-hydroxypyrimidinolate

4,5-idc

4,5-imidazoledicarboxylate

5-mipt

5-methylisophthalate

AAS

atomic absorption spectrophotometry

BDC

benzenedicarboxylate

BTC

benzenetricarboxylate

DCM

dichloromethane

DLS

dynamic laser light scattering

DMF

dimethylformamide

FT-IR

Fourier transform infrared spectroscopy

H3BTC

1,3,5-benzenetricarboxylic acid

HKUST

Hong Kong University of Science and Technology

im

imidazolate

IRMOF

isorecticular metal organic framework

MCM

Mobil Compostion of Matter

MIL

Mate´riauxs de l’Institut Lavoisier

MOF

Metal organic framwwork

NDC

2,6-napthalenedicarboxylate

NDCH

2,6-naphthalenedicarboxylic acid

oba

4,4-oxybis(benzoate)

phen

1,10-phenanthroline

PIZA

Porphyrinic Illinois Zeolite Analogue

pz

pyrazine

pzdc

pyrazine-2,3-dicarboxylate
xii


salenMn

(R,R)-(-)-1,2-cyclohexanediamino-N,N-bis(3-tertbutyl-5-(4pyridyl)salicyli-dene)MnCl

SBUs

Secondary Building Units

SEM

scanning electron microscopy

t-BuOOH

tert-butylhydroperoxide

TEM

transmission electron microscopy

TGA

thermogravimetric analysis

T-H

tetralin

THF

tetrahedrohydrofuran

TOF

turnover frequency

T-OOH

R-tetralinhydroperoxide

tpcpp

tetra(p-carboxyphenyl)porphyrin

XRD

X-ray powder diffraction

ZIF

zeolitic immidazole framework

xiii


INTRODUCTION
During the past decade, thousands works on several aspects of MOFs have been
published on refereed ISI journals of Science, Nature, American Chemical Society,
Royal Society of Chemistry, ScienceDrect, WileyInterscience ect. MOFs are extended
porous structures composed of transition metal ions or clusters that are linked by
organic bridges. Compared to conventionally used microporous and mesoporous
inorganic materials, these metal-organic structures have the potential for more flexible
rational design, through control of the architecture and functionalization of the pores
[1].
Conventional storage of large amounts of hydrogen in its molecular form is
difficult and expensive because it requires employing either extremely high pressures
as a gas or very low temperatures as a liquid [2]. The desire to store hydrogen with
sufficient efficiency to allow its use in stationary and mobile fueling applications is
spurring a worldwide effort in new materials development [3, 4]. The Department of
Energy, has set performance targets for on-board automobile storage systems to have
densities of 60 mg H2/g (gravimetric) and 45 g H2/L (volumetric) [5]. Yaghi and coworkers previously investigated the synthesis of different MOFs based on
Zn4O(COO)6 , Zn3[(O)3(COO)3] , Cu2(COO)4 and carboxylate organic linkers. These
MOFs were used as adsorbents for hydrogen storage. Among these MOFs, MOF-177,
constructed from Zn4O(COO)6 and 1,3,5-benzenetribenzoic acid as organic linker,
could afford surface areas of 5640 m2/g. Moreover, surface areas of 4590 m2/g were
achieved for MOF-20, a MOF with thieno[3,2-b]thiophene-2,5-dicarboxylic acid as
organic linker [5]. Hydrogen storage capacity of these MOFs were investigated,
showing that MOF-177 and MOF-20 exhibited highest capacity of up to 7.5% and
6.7% (wt/wt), respectively [6]. Furthermore, they found that binding of hydrogen at
the inorganic cluster sites was affected by the nature of the organic linkers. The sites
on the organic link had lower binding energies, but a much greater capacity for
increases in hydrogen loading, which demonstrated their importance for hydrogen
uptake by these materials [7, 8].

1


Reducing anthropogenic carbon dioxide emission as well as lowering the
amount of greenhouse gases in the atmosphere is apparently one of the most crucial
environmental issues that should be seriously taken into consideration [9, 10]. Yaghi
and co-workers previously pointed out that removal of carbon dioxide from flue gas,
synthesis gas and other industrial gases by chilling and pressurizing the exhaust or by
passing the fumes through a fluidized bed of aqueous base solution was significantly
expensive and inefficient. Using MOFs for carbon dioxide capture and storage has
been one of the best options [11-13]. Yaghi and co-workers employed MOF-199 as
adsorbent for carbon dioxide storage. Silica- and carbon-based physisorptive materials
such as zeolites and activated carbons were referenced as benchmark materials.
Remarkably, they found that, at 35 bar, a container filled with MOF-177 could capture
9 times the amount of carbon dioxide in a container without adsorbent, and about 2
times the amount when filled with benchmark materials [14].
Metal open framework materials (MOFs), include zeolitic imidazolate
frameworks (ZIFs) exhibit unique and outstanding properties, and therefore can be
regarded as a “new” class of catalytic materials. The structural nanoporosity of
MOF materials places them at the frontier between zeolites and surface metal organic
catalysts. The possible organization and functionalization of active sites on the
nanoscale provides organic basis to develop materials specifically adapted to catalytic
challenges like complex chemo-, region-, or stereo-selectivity [15, 16]. Employing
MOFs as catalysts is a young research area, as compared with the field of gas capture
and storage. Indeed, MOFs have emerged as a hot topic in heterogeneous catalysis.
Similarly to zeolites, the large surface area and open porosity of MOFs allows the
access of substrates to the active sites present inside the crystal structure.
One of the advantages of MOFs compared to zeolites is the large diversity of
transition metals and organic linkers that can be used for the synthesis of MOFs [17].
There should be a certain interest in the chemical industry in exploiting MOFs as
heterogeneous catalysts. The main reason for this interest is that currently industry is
using transition metal carboxylates in some processes mostly as Lewis acids and
oxidation catalysts [18]. Considering the simplicity of the synthesis of MOFs and their
affordability, it will be important to know if MOFs can outperform in large-scale

2


reactions, advantageously replacing the homogeneous processes [19]. There is no
doubt that, as in the case of zeolites, gradual introduction of MOFs as industrial
catalysts will give relevance to this area and will trigger further research in this area
[20]. The number of publications on MOFs as catalysts was significantly lower than
the case of MOFs as adsorbents for gas capture and storage.

3


CHAPTER 1

LITERATURE REVIEWS

1.1 Metal organic framework
1.1.1 Introduction
Metal organic frameworks (MOFs) are crystalline coordination polymers built
from organic linkers (bridging ligands) and inorganic nodes which are called
secondary building units (SBU). Secondary building units (SBUs) are molecular
complexes and cluster entities in which ligand coordination modes and metal
coordination environments can be utilized in the transformation of these fragments
into extended porous networks using polytypic linkers. Consideration of the geometric
and chemical attributes of the SBUs and linkers leads to prediction of the framework
topology, and in turn to the design and synthesis of a new class of porous materials
with robust structures and high porosity [21].
The modular nature (a combination of inorganic and organic components) of
these new porous materials is perfectly suited for chemical manipulations aimed at fine
tuning of the structures and functions of metal organic frameworks in accordance with
their specific application.

4


Organic SBUs

Inorganic SBUs

Figure 1.1. Examples of inorganic and organic SBUs [22].
1.1.2 MOF properties
One of the most remarkable features of MOFs is their extremely high porosity.
Depending on the sizes of ligands and inorganic building units, as well as the
framework connectivity, open channels and pores with sizes ranging from a few
angstroms to several nanometers are present in metal organic frameworks.
One of the outstanding properties of porous materials in the comparison with
other material is their high surface areas. Such materials are of critical importance to
many applications involving catalysis, separation and gas storage. The claim for the
highest surface area of a disordered structure is for carbon, at 2,030 m2.g-1 .Until
recently, the largest surface area of an ordered structure was that of zeolite, recorded at
904 m2g-1. However, with the introduction of metal-organic framework materials, this
has been exceeded, with values up to 6,000 m2 g -1 (Table 1.1)

5


Table 1.1: The surface area of some materials
Surface area
Materials

(BET)(m2/g)

Ref.

Active carbon

2400

[23]

Zeolite beta

200-500

[24]

MOF-5

2449

[25]

MOF-177

3275

[26]

MOF-210

6240

[10]

Thermal stability is also a noticeable property of MOFs. MOFs are stable with
the temperature that ranges from about 300 oC to 400 oC [27]. As a result, MOFs has
been applied in many fields with a wide range of temperature. The most common
method for examining the stability of a MOF in the absence of its original guests is a
powder X-ray diffraction (XRD) analysis of the bulk material after heating and/or
evacuation, referenced to the calculated pattern of the host structure. This is then
correlated with Thermal Gravimatric Analysis (TGA), in which framework stability is
indicated by negligible weight loss between the temperatures of guest desorption and
framework decomposition.
With all of these advantages, MOFs is highly promising material for gas
separation, gas storage and catalysis.
1.1.3 MOF synthesis
MOFs are synthesized by mixing organic ligands and metal salts under
solvothermal reaction conditions at relatively low temperatures (typically, below
300°C). The properties of organic ligands (bond angles, the ligand chain length,
volume, chiral properties, etc.) play a key role in the formation of a particular type of
metal_organic framework. Topology of the structure of MOFs is determined by the
coordination number of the metal ion. The reagents are mixed in high boiling polar
solvents, such as water, N,N_dialkyl formamides, dimethyl sulfoxide, and acetonitrile.

6


The most important parameters of solvothermal synthesis are temperature,
concentrations of the metal salt and organic ligand, solubility of the reactants in the
solvent, and pH of the solution. In addition, the direct mixing method has been
developed, which is adapted, at present, for the synthesis of MOF_5 and a number of
homologous metal_organic frameworks (IRMOFs) [28]. A number of synthetic
methods developed for the production of MOFs also include premixing of immiscible
solvents. One of the most promising techniques is the microwave_assisted
solvothermal synthesis, which makes it possible to carry out the process over a wide
temperature range, to reduce the time of crystallization, and to control the morphology
and particle_size distribution [29].
1.1.4 MOF application
MOFs with significant properties such as high surface areas, highly porous,
tunable framework, large pore size have been applied in many fields. Gas storage in
micro porous MOFs were studied from the past few decades. Hydrogen saturation
uptake in several kinds of MOFs was investigated by Yaghi group indicating the
potential application of MOFs in the area . Other studies also demonstrated the MOF’s
ability in methane storage [21]. The inert gases mixtures was separated from each
other by continuous adsorption on electrochemically produced Cu-BTC-MOF
[30].Coordination unsaturated metal sites (MOF-74 and MOF-199] and amino
functionality (IRMOF-3) proved effective adsorption contaminants including SO2,
NH3, Cl2, C6H6 and CH2Cl2 [31].
Over the past 10 years, the use of MOFs as solid catalysts was particularly
interesting because the pore size and functionality of the framework could be adjusted
over a range for a variety of catalytic reactions. The catalytic properties of MOF
related not only to the presence of framework or extra framework metal cations or
reduced metals, but also to the presence of functional groups on the inner surface of
the MOFs voids and channels [32]
A number of application areas of MOFs in catalysis proposed on the basis of the
elaborated synthetic principles are successfully developing at present; they include the
heterogenization of the conventional homogeneous catalysts [14]; stabilization in
metal organic framework of catalytically active nanosized particles, which are unstable
7


otherwise [14]; encapsulation of catalysts in the molecular framework [15]; the
combination of catalysis with chemical separation [33], postsynthesis introduction of
catalytic metal sites [17–19]; and catalysis with molecular sieve selectivity [6, 14, 17,
20].
1.2 The application of MOFs in catalysis
A characteristic of MOF materials is porosity which yields internal surface areas
that are relatively large, facilitating their catalytic reactivity. MOF catalytic selectivity
are enhanced by their pore and channel sizes. These relevant features of MOFs are
similar to zeolites - the most important class of industrial heterogeneous catalysts.
However, the capabilities of zeolites are limited in pore size (1 nm) and geometry [34].
Meanwhile, MOFs contain bulky organic components and can be formed from an
infinite set of building blocks, which make it possible to finely tune their porous
properties. While many MOFs show good thermal stability – a few even showing
stability to 5000C, none approach the stability of zeolites. Instead, their catalytic
application is suitable for high-value-added reactions in production of fine chemicals,
delicate molecules, individual enantiomers, etc, that can be accomplished under mild
conditions [35].
The catalytic properties of a metal organic framework relate not only to the
presence of frame work or extra framework metal cations or reduced metals, but also
to the presence of functional groups on the inner surface of the MOF voids and
channels [36]. Moreover, the ability to incorporate functional groups into porous
MOFs also makes them be unique candidates for heterogeneous catalysts [37].
The main issue in the designing of MOFs based catalysts lies in how the
coordinately saturated metals containing nodes of the framework can perform a
catalytic effect. If the coordination sphere of the metal ions is completely blocked by
organic bridges, the ions have no free positions available for interaction or activation
with reactants. In the process of designing MOFs for catalytic purposes, researchers
have always considered the problems. As several MOFs possess metal sites with
potential coordinative unsaturations, their application in heterogeneous catalysis is
undoubtedly an area that will attract further research in the near future [38-41].

8


Several published data show that there are some basic approaches to design
heterogeneous catalysts based on MOFs such as supports for an active metal, bringing
ligands as an active site, inorganic node as an active site, introduction of guest
molecules containing an active site and the post synthetic modification of the
framework.
The utilization of MOFs as solid catalysts is particularly interesting. Although a
large number of different MOFs are known, only a few of them have been tested in
catalytic reactions so far. It is still an enormous challenge to find out whether the metal
centers, the ligands or functionalized ligands, or even metal–ligand interactions or
differences in particle size, can cause unusual catalytic properties.
In all MOF compounds, three different parts can be clearly differentiated: (i) the
metallic component, (ii) the organic ligand, and (iii) the pore system.
Potential catalytic activity of MOFs can be envisaged from a direct inspection of
their structure, like those containing, e.g., redox active centers in a given coordination
environment, organic groups with basic properties (such as amides or amines), or
metal sites with potential coordinative unsaturations, which could behave as active
centers for certain Lewis catalyzed processes. MOFs can be of interest since they
allow high density of catalytic sites, in particular when these active sites are transition
metals. In this regard, it is interesting to note the need of theoretical work rationalizing
the catalytic activity of MOFs and predicting appropriate active sites and crystal
structures.
1.2. 1 MOFs

with Metal Active Sites

The catalytic activity observed for these materials is directly related to their
metallic components, either as isolated metal centers or as clusters [42] connected
through the organic linkers. This group of MOFs includes materials with only one type
of metal center (M), which simultaneously acts as a structural building component and
a catalytic active site. Many reports on the application of MOFs in catalysis have been
published and listed in Table 1.2.

Table 1.2 Reported catalytic properties of MOF compounds with active metal sites

9


Catalyzed reactions

Active

MOF

Ref

metal
Hydrogenation
1-hexene hydrogenation

Rh+

[RhCl(CO)(1,4-dicb)][M(4,4’-

[43]

M=Pd0,

dicbp)x]

[44],

Pt0
Hydrogenation

[45]

of

nitroaromatics

Ru2+

[RuCl2(1,4-dicb)3]

[46]

Hydrogenation of olefins

In3+

[In2(OH)3(bdc)1.5]

[47]

[Pd(2-pymo)2]

[48]

IRMOF-3-SI-Au

[49]

Hydrogenation

of

1,3- Pd2+

butadiene

Au3+

(SI-salicylideneimine)
Cyanosilylation
Cyanosilylation of imines

Cd2+

[Cd(4,4’-bpy)2](NO3)2

[50]

Aldehyde cyanosilylation

Cu2+

[Cu3(btc)2] (MOF-199)

[51]

Cr3+

MIL-101(Cr)

[52]

Mn2+

Mn3[(Mn4Cl)3(btt)8(CH3OH)10]2

[53]

Hydoxylation

Mn3+

Mn(III) (tpcpp) (PIZA-3)

[54]

Oxidation of alcohols

Pd2+

[Pd(2-pymo)2]

[48]

[Cu(2-pymo)2],

[55]

Oxidation

Oxidation of tetralin with Cu2+,
air

Co2+

Oxidation of tetralin with Cr3+
t

[Co(bzim)2] (ZIF-9)
MIL-101(Cr)

[56]

BuOOH

Cyclohexene oxidation

Co2+

[Co(bpb)] (MFU-3)

[57]

Oxidation of alcohol

Cu2+

[Cu2(1,4-chdc)2]

[58]

CO oxidation to CO2

Cu2+

[Cu(5-mipt)]

Ni2+

[Na20(Ni8(4,5-IDC)12]

[59]

Mn2+

Mn3[(Mn4Cl)3(btt)8(CH3OH)10]2

[53]

Mukaiyama-aldol

10


condensation
Friedel-Crafts benzylation
Alkylation of aromatics

Fe3+

MIL-100(Fe)

[60]

IRMOF’s

[61]

Zn2+-OH

Hydrogenation Reactions
Navarro et al. described the preparation of a Pd containing MOF using 2hydroxypyrimidine as organic ligand, [Pd(2-pymo)2]·3H2O [16]. This material was
utilized for Pd- catalyzed reactions such as alcohol oxidation, Suzuki C-C coupling,
and olefins hydrogenation [48]. When 1-octene was contacted with the Pd-MOF under
mild conditions (2 bar H2 and 308 K), a complete conversion of the substrate was
observed after ca. 40 min. Analysis of the products showed a 59% yield of octane,
with the rest of the products being 2-octene. The 2-octene formed was ultimately
hydrogenated to octane after 2h reaction time. Furthermore, the Pd-MOF behaves as a
heterogeneous catalyst and can be reused without structure degradation or leaching of
Pd. The presence of a regular pore system in the Pd-MOF can introduce shapeselectivity effects for hydrogenations, as only smaller olefins that can diffuse through
the pores will be hydrogenated, while bulkier molecules will not [48].
Hydrogenation of 1,3-butadiene was performed using the Au(III)-MOF as
catalyst (fixed-bed reactor, atmospheric pressure, and 403 K) by Zhang et al [49]. The
Au(III)-MOF was prepared via a covalent postsynthesis modification through the two
step process [49]. This catalyst was prepared from the zinc aminoterephthalate
IRMOF-3, by reacting the available –NH2 group with an aldehyde to form the
corresponding imine, followed by complexation of a metal precursor NaAuCl4 to form
the Au(III) Schiff base complex. Samples of Au/TiO2 pretreated either in Argon at
403K or in H2 at 523K were also applied under the same conditions for catalytic
comparation. When the Au(III)-MOF was used as catalyst, almost total conversion of
1,3-butadiene was obtained, while much lower conversions (ca. 9%) were achieved
with both Au/TiO2 catalysts. Analysis of the reaction with Au(III)-MOF at a lower
level of conversion and shorter time on stream showed no evidence of any induction

11


period. Considering that both Au/TiO2 catalysts contain exclusively metallic gold, as
well as the lack of any induction period for the reaction catalyzed by Au(III)-MOF, the
results demonstrated that the oxidation state of gold is of paramount importance for the
hydrogenation of 1,3-butadiene. The Au(III)-MOF showed a very high selectivity (up
to 97%) for butenes, while production of butane was kept at a low value (3%) even at
total conversion of 1,3-butadiene. The Au(III)-MOF catalyst also showed a high
stability with time on stream (for at least 17 h under continuous operation).
Oxidation of Organic Substrates
There are some reported examples on the use of MOFs as catalysts for the
oxidation of organic substrates, using either O2 (or air) or hydroperoxides as oxidants.
The results obtained using MOFs as catalysts for oxidations of alcohols to aldehydes,
paraffins or naphthenes to alcohols or carbonyl compounds, olefins to epoxides,
sulfides to sulfoxides, and thiols to disulfides have been presented by various authors
(Table 1.2).
PIZA-3, contained Mn(III) tetra(p-carboxyphenyl)porphyrin coordinated to bent
trinuclear Mn(III) clusters was prepared by Suslick and co-workers [54]. This material
was tested as an oxidation catalyst for the hydroxylation of linear and cyclic alkanes,
using either iodosylbenzene or peracetic acid as oxidants. According to the authors, the
catalytic results obtained with PIZA-3 were comparable with those using other
manganese porphyrins in homogeneous systems or immobilized inside inorganic
supports as heterogeneous catalysts. Traces of metalloporphyrin or degradation
products were not observed in supernatant liquid after the catalytic reaction. When
peracetic acid was used as the oxidant, the solid MOF recovered after filtration was
reused without loss of activity. PIZA-3 was also found to be active for the oxidation of
1-hexanol to hexanal with 17% yield. PIZA-3was found also to be active for the
epoxidation of cyclokenes such as cyclooctene, cyclohexene, cyclopentene, with yield
to products of 74% for cyclooctene [54].
The catalytic activity of [Cu(2-pymo)2] and [Co(bzim)2] in the liquid-phase
oxidation of tetralin using air as the oxidant were studied [18]. The [Cu(2-pymo)2]
was found to be active and reusable. The initial product of tetralin (T-H) oxidation
12


formed was tetralin hydroperoxide, T-OOH, and then conversed to T=O and -tetralol
(T-OH). After ca. 30h, conversion of T-H reached a plateau. The T=O/T-OH ratio,
which presents selectivity of the reaction, is 3.4 for the two successive cycles. Tetralin
oxidation using the Co2+ containing MOF as catalyst revealed lower conversion of
ca.23% but higher selectivity to T=O with a T=O/T-OH ratio of 11.3 after three runs. ,
Leaching of Cu2+ from the Cu-MOF was tested by hot filtration test, analysis of copper
in the catalyst and in the filtrate before and after reaction, and comparison with
homogeneous catalysts. The results showed that leaching was not occurring, and that
the catalytic process was heterogeneous.

Scheme 1.1. The oxidation process of tetralin
Kim et al. have reported on the catalytic activity of the chromium terephthalate
MIL-101 for the liquid-phase oxidation of tetralin, using either tBuOOH or acylperoxy
radicals generated in situ by reaction between trimethylacetaldehyde and O2 as
oxidants [56]. The authors have presented a thorough catalytic study in which the
effect of temperature, amount of catalyst, and nature of the solvent and oxidant are
contemplated. The catalytic reaction over MIL-101 was found to be heterogeneous, as
indicated by the hot filtration experiments and by the maintenance of the catalytic
activity and selectivity for at least 5 runs. Also the crystallinity of the catalyst
recovered after 5 uses was virtually identical to that of the fresh sample.
Oxidation of benzylic positions of aromatic hydrocarbons using hydrogen
peroxide as oxidizing reagent and Fe(BTC) MOF as catalyst has also been reported by
Dhakshinamoorthy et al. [20].
Zou et al described the preparation of a new copper MOF using 5methylisophthalate ligands, [Cu(5-mipt)(H2O)](H2O)2. The authors demonstrated that
the copper MOF was active for air oxidation of CO to CO2. The catalytic activity was
considerably higher than for the previously reported nickel containing MOF. Indeed,

13


100% conversion of CO was reached over the Cu-MOF at 473 K, while a conversion
of only 3% was obtained over Ni-MOF at the same temperature. The activity of the
Cu-MOF was found to be similar or higher than that reported for CuO and CuO/Al2O3,
with an activation energy (70.1 kJ mol-1) close to that of CuO (69.9 kJ mol-1).
Furthermore, the activity of the Cu MOF was stable with time at temperatures of 378
K or higher, and the material retained the framework integrity after the catalytic use, as
determined by XRD [62] .
Cho

et

al.

reported

the

use

of

bimetallic

mixed

ligand

MOF,

[Zn2(bphdc)2(salenMnCl)] (bphdc= 4,4’-biphenyldicarboxylate) for the asymmetric
epoxidation of 2,2-dimethyl-2-chromene using 2-(tert-butylsulfonyl)iodosylbenzene as
the oxidant. The catalytic activity of the MOF was compared with homogeneous free
(salenMn) complex, which initially showed a high activity but less steady after a few
hour. The MOF showed a steady catalytic activity with no signs of deactivation in 3.4h
and achieved a total conversion nearly four times that of the homogeneous (salenMn)
complex [63].
Carbonyl Cyanosilylation
The Lewis acid-catalyzed cyanosilylation reaction of carbonyl compounds with
trimethylsilyl cyanide yields the corresponding cyanohydrin trimethylsilyl ethers,
which can be further hydrolyzed to the cyanohydrins. Schlichte and co-workers have
reported on the catalytic activity for cyanosilylation of aldehydes of the well-known
copper trimesate Cu3(btc)2 named (HKUST-1) [51].

Knoevenagle condensation reaction
The Knoevenagel reaction of aldehydes with compounds containing activated
methylene groups has been widely employed in the synthesis of several fine chemicals
[64] as well as heterocyclic compounds of biological significance [65]. Over the last
few years, a wide range of solid catalysts have been investigated for this reaction such
as amino-functionalized mesoporous silica [66], diamine-functionalized mesopolymers
[67], amine-functionalized mesoporous zirconia [68], and superparamagnetic

14


mesoporous Mg–Fe bi-metal oxides [69]. Recently, Zhou et al. synthesized two
isostructural mesoporous metal-organic frameworks (MOFs) with cavities up to 2.73
nm, designated as PCN-100 and PCN-101 (PCN represents porous coordination
network). It was reported that both PCNs-100 and -101 exhibited size-selective
catalytic activity toward the Knoevenagel condensation reaction, thus offering
advantages over conventional solid catalysts in the Knoevenagel condensation reaction
[70].

Friedel-Crafts reaction
Fe(III)-MIL100 was used as catalyst for the Friedel-Crafts reaction of benzene
with benzyl chloride to render diphenylmethane at 343 K [60]. The catalytic activity.
of Fe(III)-MIL100 was compared with that exhibited by Cr(III)-MIL100 and two acid
zeolites, namely, HBEA and HY. It was observed that Cr(III)-MIL100 was notably
inactive. With Fe(III)-MIL100, about 100% benzyl chloride conversion affording
diphenylmethane with complete selectivity was obtained rapidly after an induction
period of 5 min. Catalysis by zeolites occurs also with complete selectivity toward
diphenylmethane, but the reaction is considerably slower as compared to Fe(III)MIL100.
Suzuki C-C coupling
Pd-MOF can act as a heterogeneous catalyst for the Suzuki C-C coupling of
phenylboronic acid and 4-bromoanisole as the substrates [48]. The Pd-MOF catalyst
(2.5 mol % Pd) could afford 85% conversion of 4-bromoanisole after 5 h (at 423 K in
o-xylene), with >99% selectivity to the cross coupling product, 4-methoxybiphenyl.
The crystalline structure of the solid was preserved under these experimental
conditions, and the solid was reused without a significant loss of activity. According to
the inductively coupled plasma (ICP) analysis, no loss of Pd was detected after the
reaction.

15


Alkylation
Ravon et al. have successfully used zinc dicarboxylates IRMOF-1 and IRMOF-8
as heterogeneous catalysts for the alkylation of aromatics [61]. Alkylation of either
toluene or biphenyl with tert-butyl chloride was performed at 443 K in the presence of
IRMOFs. For both substrates, the reaction was complete after 2 h, thus showing a
catalytic activity similar to that of AlCl3 or an acidic zeolite H-beta. Both IRMOFs
gave selectivities to the corresponding para-substituted product, while both AlCl3 and
the acidic zeolite beta gave mixtures of ortho- and para substituted molecules and
dialkylated products.
Domino coupling and cyclization reaction
Zhang et al also applied Au(III)-MOF to the three component domino coupling
and cyclization of ethylaniline, aldehyde, and amine, yielding the corresponding indole
[49]. The performance of the Au(III)-MOF was compared with other representative
examples of soluble gold salt (AuCl3), soluble gold(III) salen complex, and gold
supported on metal oxide capable of stabilizing cationic species (Au/ZrO2). The
results demonstrated the superiority of the Au(III)-MOF over the rest of the catalysts.
Soluble gold salts and the gold salen complex were found to suffer from irreversible
deactivation, and therefore, the initial reaction rate (TOF) and maximum conversion
attained were lower compared to those for the Au(III)-MOF [71].
Other reactions
Free metal centers in [Cu3(pdtc)L2(H2O)3].2DMF.10H2O made it had catalytic
characteristic and was tested for catalysis in Henry reaction of aromatic aldehydes with
nitroalkane at moderate to high yields [72].

Scheme 1.2 Henry reaction of aromatic aldehydes with nitroalkane [49]

16


The activated [Cu3(BTC)2] framework formed upon the detachment of water
molecules from MOF-199 (HKUST-1) exhibited hard Lewis acid characteristic and
was found to be the first MOF catalyst deployed for the Friedlander reaction between
2-aminobenzophenones and acetyl acetone under mild conditions, leading to the
corresponding quinolines with excellent yield. It also catalyzed for the synthesis of
pyrimidine chalcones with efficient yields after 11th cycle of reuse [73].
In the role of a Lewis acid, Fe (BTC) performed a great catalytic activity in
Claisen–Schmidt condensation. The reaction conversion was over 98% [74].

Scheme 1.3 Claisen–Schmidt condensation of benzaldehyde with acetophenone using
MOFs as heterogeneous catalyst [74]
Amarajothi demonstrated that Fe(III) active sites and Al(III) sites in MOF had
catalytic characteristic, especially for oxidation and reduction reaction. Fe(BTC)
showed its ability of oxidation by converting benzyl amines into benzyl imines [75].
Besides that, BTC had enhanced the Claisen–Schmidt condensation in good yield . In
the other hand, MOF-199 catalyzed for acetalization of aldehydes [76]. Al (III) had
demonstrated the ability of reduction C=C bond with yield of 98% [77].
Luz showed that [Cu(2-pymo)2] ,[Cu(im)2] , [Cu(BDC)] , and [Cu3(BTC)2] with
Cu2+ sites in their structure were effective catalysts in synthesis of propargylamines,
indoles and Imidazopyridines [78]. Imidazopyridine was archived nearly 100% in
with Cu(BDC) as catalyst.
Room temperature acetalization of aldehydes with methanol has been carried
out using metal organic frameworks (MOFs) as solid heterogeneous catalysts. Of the
MOFs

tested,

a

copper-containing

MOF

[Cu3(BTC)2]

(BTC=1,3,5-

benzenetricarboxylate) showed better catalytic activity than an iron-containing MOF
[Fe(BTC)]

and

an

aluminum

containing

benzenedicarboxylate) [76].

17

MOF

[Al2(BDC)3]

(BDC=1,4-


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