Metal organic frameworks IRMOF 8, ZIP 9, MOF 199 and IRMOF 3 as catalysts for the friedel crafts acylation, knoevenagel, aza michael and paal knorr reactions

ABSTRACT Highly porous metal-organic framework such as IRMOF-8, ZIF-9, MOF-199 and IRMOF-3 were synthesized by a solvothermal method, and used as an efficient heterogeneous catalyst for

VIETNAM NATIONAL UNIVERSITY – HO CHI MINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

NGUYEN THI LE LIEN

METAL-ORGANIC FRAMEWORKS IR8, ZIF-9,

MOF-199 AND IRMOF-3 AS CATALYSTS FOR THE FRIEDEL– CRAFTS ACYLATION, KNOEVENAGEL, AZA-MICHAEL

AND PAAL-KNORR REACTIONS

PhD THESIS

HO CHI MINH CITY 2013

VIETNAM NATIONAL UNIVERSITY – HO CHI MINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

NGUYEN THI LE LIEN

METAL-ORGANIC FRAMEWORKS IR8, ZIF-9,

MOF-199 AND IRMOF-3 AS CATALYSTS FOR THE FRIEDEL– CRAFTS ACYLATION, KNOEVENAGEL, AZA-MICHAEL

AND PAAL-KNORR REACTIONS

Major: Organic chemical Technology

Major code: 62527505

Supervisor : Assoc.Prof.Dr Phan Thanh Sơn Nam

Independent examiner 1: Assoc.Prof.Dr Vu Anh Tuan

Independent examiner 2: Assoc.Prof.Dr Pham Thanh Huyen

Examiner 1: Assoc.Prof.Dr Tran Đai Lam

Examiner 2: Dr Nguyen Quoc Chinh

Examiner 3: Assoc.Prof.Dr Pham Thanh Quan

DECLARATION OF ORIGINALITY

I hereby declare that this is my own research study The research results and conclusions in this dissertation are true, and are not copied from any other resources The literature references have been quoted with clear citation as requested

Dissertation Author

THESIS SUMMARY

The thesis consists of four chapters, including the literature reviews in chapter one, which provide brief introduction of metal organic framework materials, their properties, and their application Besides, in chapter one, we will collect and summary information from international researcher’s publication on the field of MOF application in organic synthesis reaction as heterogeneous catalyst, which are directly related to our study

The main part of this thesis is written in Chapter 2 and Chapter 3 In Chapter 2, the materials, equipment and methodology which are used in our study are presented Our experiment consisted of two parts: (1) Synthesize and characterization of MOFs, and (2) Study the ability of these materials to catalyze organic reactions Chapter 3 will present the experimental results and discussions Chapter 4 is to summarize our significant results with conclusion

Four different MOF materials such as IRMOF-8, ZIF-9, MOF-199, IRMOF-3 are synthesized by solvothermal methods in the existent laboratory conditions The yielded materials were analyzed and characterized by modern analytical methods to confirm their structure and properties The analysis techniques included X-ray powder diffraction, SEM micrography and TEM micrography to confirm the crystalline and porous structure of the synthesized catalyst materials Metal concentration in the solid MOFs was determined by AAS techniques, and their functional groups were characterized by FT-IR spectrometer The surface areas of MOFs were determined by Nitrogen physisorption measurements, given the high surface area materials of the four MOFs synthesized in this study

The four MOFs: IRMOF-8, ZIF-9, MOF-199, IRMOF-3 were applied as catalysts in the four organic reactions: Friedel- Craft acylation of toluene with benzoyl chloride, Knoevenagel reaction between benzaldehyde and malononitrile, aza-Michael reaction of benzylamine with ethyl acrylate and the Paal-Knorr reaction of benzyl amine with 2,5-hexanedione, respectively Different reaction conditions were

investigated included the effect of catalyst concentration, reagent ratio, solvents, and the effect of substituents of the reagents on the efficiency of the MOF based catalysts The results show that catalytic properties of the MOFs were good as compared to other solid catalysts The most important experiment was to investigate the leaching of active site of the solid catalysts into the reaction solution Experimental results show that there was no any leaching or homogenous catalytic occurred in the four examined reaction Lastly, the feasibility for the catalyst recyclability was tested and results show that the four catalysts were able to be reused up to five times without any significant degradation

Based on the results obtained in this study, it can be concluded that MOF materials can be applied as catalysts in various reactions with advantages such as high efficiency, environment-friendly, and recyclability

ABSTRACT

Highly porous metal-organic framework such as IRMOF-8, ZIF-9, MOF-199 and

IRMOF-3 were synthesized by a solvothermal method, and used as an efficient

heterogeneous catalyst for the Friedel-Crafts acylation reaction, Knoevenagel reaction,

Aza Micheal reaction and Pal Knorr reaction The solid catalyst was characterized by

X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission

electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform

infrared spectroscopy (FT-IR), atomic absorption spectrophotometry (AAS), and

nitrogen physisorption measurements High conversions were achieved in the presence

of a catalytic amount of the MOFs without the need for an inert atmosphere The solid

catalyst could be facilely separated from the reaction mixture by simple centrifugation,

and could be reused without a significant degradation in catalytic activity No

contribution from homogeneous catalysis of active acid species leaching into the

reaction solution was detected

ACKNOWLEDGMENT

First and foremost I offer my sincerest gratitude to my supervisor, Prof Phan Thanh Son Nam, who has supported me throughout my thesis with his patience, motivation, enthusiasm and immense knowledge His guidance helped me in all the time of research and writing of this thesis

Besides my advisor, I would like to thank Dr Le Thi Hong Nhan for her encouragement, insightful comments

My sincere thanks also go to my fellow labmates and students in Organic Chemistry division and Manar lab for the stimulating discussions, which helps me a lot

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 31

2.1 Materials and instrumentation 31

2.2 MOF synthesis 32

2.2.1 IRMOF-8 32

2.2.2 ZIF-9 32

2.2.3 MOF-199 33

2.2.4 IRMOF-3 33

2.3 Catalytic studies 33

2.3.1 The Friedel-Crafts acylation reaction 33

2.3.2 The Knoevenagel reaction 34

2.3.3 Aza-Michael Reaction 35

2.3.4 The Paal-Knorr reaction 35

CHAPTER 3 RESULTS AND DISCUSSIONS 37

3.1 Catalyst characterization 37

3.1.1 IRMOF-8 37

3.3.2 ZIF-9 41

3.3.3 MOF-199 45

3.3.4 IRMOF-3 49

3.2 Catalytic studies 53

3.2.1 The Friedel-Crafts acylation reaction 53

3.2.2 The Knoevenagel reaction 62

3.2.3 The aza-Michael reaction 73

3.2.4 The Paal-Knorr reaction 86

CHAPTER 4 CONCLUSIONS 98

LIST OF PUBLICATIONS 101

REFERENCES 102

LIST OF TABLES

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

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-(4-pyridyl)amide] 20

Figure 3.1 XRD of the IRMOF-8 39

Figure 3.2 SEM micrograph of the IRMOF-8 39

Figure 3.3TEM micrograph of the IRMOF-8 40

Figure 3.4 TGA analysis of IRMOF-8 40

Figure 3.5 FT-IR spectra of the IRMOF-8 (a), and 2,6-napthalenedicarboxylic acid (b) 41

Figure 3.6 XRD of the ZIF-9 43

Figure 3.7 SEM micrograph of the ZIF-9 43

Figure 3.8 TEM micrograph of the ZIF-9 44

Figure 3.9 TGA analysis of ZIF-9 44

Figure 3.10 FT-IR spectra of the ZIF-9 (a) and benzimidazole (b) 45

Figure 3.11 XRD of the MOF-199 46

Figure 3.12 SEM micrograph of the MOF-199 47

Figure 3.13 TEM micrograph of the MOF-199 47

Figure 3.15 FT-IR spectra of the MOF-199 (a) and the 1,3,5-benzenetricarboxylic acid (b) 48

Figure 3.14 TGA analysis of MOF-199 48

Figure 3.16 XRD of the IRMOF-3 50

Figure 3.17 SEM micrograph of the IRMOF-3 51

Figure 3.18 TEM micrograph of the IRMOF-3 51

Figure 3.19 TGA analysis of IRMOF-3 52

Figure 3.20 FT-IR spectra of the IRMOF-3 (a) and the 2-amino-1,4-benzenedicarboxylic acid (b) 52

Figure 3.21 Effect of temperature on reaction conversion 54

Figure 3.22 Effect of benzoyl chloride: toluene molar ratio on reaction conversion 54

Figure 3.23 Effect of catalyst concentration on reaction conversion 58

Figure 3.24 Leaching test indicated no contribution from homogeneous catalysis of active acid species leaching into reaction solution 58

Figure 3.25 Catalyst recycling studies 60

Figure 3.26 Effect of substituents on reaction conversion 60

Figure 3.27 Effect of benzaldehyde : malononitrile molar ratio on reaction conversion 66

Figure 3.28 Effect of catalyst concentration on reaction conversion 66

Figure 3.29 Leaching test indicated no contribution from homogeneous catalysis of active species leaching into reaction solution 67

Figure 3.30 Effect of solvent on reaction conversion 67

Figure 3.32 Catalyst recycling studies 69

Figure 3.31 Catalytic recycling study 69

Figure 3.33 Effect of different substituents on reaction conversion 72

Figure 3.34 FT-IR spectra of the reused (a) and fresh (b) ZIF-9 72

Figure 3.35 NH3-TPD spectra of the MOF-199 measured between 100 oC and 400 oC 75

Figure 3.36 Effect of benzylamine: ethyl acrylate molar ratio on reaction conversion 75 Figure 3.37 Effect of catalyst concentration on reaction conversion 76

Figure 3.38 Effect of different catalysts on reaction conversion 79

Figure 3.39 Effect of solvent on reaction conversion 80

Figure 3.40 FT-IR spectra of the fresh (a) and reused (b) MOF-199 83

Figure 3.41 X-ray powder diffractogram of the fresh (a) and reused (b) MOF-199 83

Figure 3.42 Leaching test indicated no contribution from homogeneous catalysis of active species leaching into reaction solution 85

Figure 3.43 Catalyst recycling studies of the aza-Michael reaction 85

Figure 3.44 Effect of different amines on reaction conversion 86

Figure 3.45 Effect of benzylamine:2,5-hexanedione molar ratio on reaction conver-sion 87

Figure 3.46 Effect of catalyst concentration on reaction conversion 88

Figure 3.47 Leaching test indicated no contribution from homogeneous catalysis of active species leaching into reaction solution 89

Figure 3.48 Effect of different catalysts on reaction conversion 91

Figure 3.49 Effect of different solvents on reaction conversion 92

Figure 3.50 Effect of different amines on reaction conversion 93

Figure 3.51 Effect of different diketones on reaction conversion 95

Figure 3.52 Catalyst recycling studies of the Paal Knorr reaction 95

Figure 3.53 FT-IR spectra of the fresh (a) and reused (b) IRMOF-3 97

Figure 3.54 X-ray powder diffractogram of the fresh (a) and reused (b) IRMOF-3 97

IRMOF isorecticular metal organic framework

MCM Mobil Composition of Matter

MIL Mate´riauxs de l’Institut Lavoisier

MOF Metal organic framework

salenMn (R,R)-(-)-1,2-cyclohexanediamino-N,N

-bis(3-tertbutyl-5-(4-pyridyl)salicyli-dene)MnCl SBUs Secondary Building Units

SEM scanning electron microscopy

t-BuOOH tert-butylhydroperoxide

TEM transmission electron microscopy

TGA thermogravimetric analysis

XRD X-ray powder diffraction

ZIF zeolitic immidazole framework

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 co-workers 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]

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

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

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

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)

Table 1.1: The surface area of some materials

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

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

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]

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

Catalyzed reactions Active

[RhCl(CO)(1,4-dicb)][M(4,4’-[RuCl2(1,4-dicb)3] [In2(OH)3(bdc)1.5] [Pd(2-pymo)2] IRMOF-3-SI-Au (SI-salicylideneimine)

[Cd(4,4’-bpy)2](NO3)2 [Cu3(btc)2] (MOF-199) MIL-101(Cr)

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

Mn(III) (tpcpp) (PIZA-3) [Pd(2-pymo)2]

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

[Co(bpb)] (MFU-3) [Cu2(1,4-chdc)2] [Cu(5-mipt)]

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

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

[43] [44], [45]

[46] [47] [48] [49]

[50] [51] [52] [53]

[54] [48] [55]

[56]

[57] [58]

[59] [53]

[60] [61]

Hydrogenation Reactions

Navarro et al described the preparation of a Pd containing MOF using hydroxypyrimidine 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

2-Pd The presence of a regular pore system in the Pd-MOF can introduce selectivity effects for hydrogenations, as only smaller olefins that can diffuse through the pores will be hydrogenated, while bulkier molecules will not [48]

shape-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 comparison 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

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

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 methylisophthalate 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,

5-100% 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]

Knoevenagel 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

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]

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

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]

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 MOF [Al2(BDC)3] (BDC=1,4-benzenedicarboxylate) [76]

1.2.2 MOFs with Reactive Functional Groups

There are MOFs with functional groups in the organic ligands that are able to catalyze a given reaction, i.e., the active sites are located at the organic molecule and not at the metal ion The number of MOFs belonging to this category with demonstrated catalytic activity is very limited This is because the reactive groups need to be free and accessible to interact with the catalytic substrates and not be coordinated to the metal ions of the MOF Therefore, the difficulty in preparing MOFs containing organic reactive groups lies in the natural tendency of metals to interact with all the available functional groups of the ligand

POST-1 was obtained by reaction between Zn2+ ions and the chiral molecule derived from tartaric acid (Fig 1.1) containing a carboxylic acid and a pyridine group The uncoordinated pyridyl groups conferred catalytic activity for transesterification reactions of 2,4-dinitrophenylacetate with 1-phenyl-2-propanol [79]

Figure 1.2 The ligand of POST-1

Metal organic framework structures with uncoordinated amino groups, for example, IRMOF- 3 and MIL- 53, were stable base catalysts for the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate or ethyl acetoacetate

IRMOF-3 showed the same activity as the known active catalysts The selectivity for the condensation products was 100 % Consequently, the aromatic

amino group of the MOF was more active than that of the homogeneous catalyst aniline [32] The increased basicity of IRMOF-3 over other amminic catalysts has

been explained via the formation of protonated conjugate derivatives, involving hydrogen-bonds and originating quasi-planar 6-term rings Several plausibile reaction

steps have been moreover taken into account and a mechanism for the Knoevenagel condensation, including catalyst deactivation, has been proposed for aniline molecules and embedded aniline moieties [80] As a catalyst, IRMOF-3 is stable under the reaction conditions and, therefore, can be reused The activity of the metal organic framework structure is comparable to the activity of the best known solid base catalysts

Hwang reported that Cr(III) in inorganic nodes of the framework was coordinated to one of the two nitrogen atoms of a diamine molecule (ethylenediamine and diethylenetriamine) to obtain modified MIL-101 with grafted amino groups (ED-MIL-101 and APS-M1L-101) Free terminal amines show appreciable activity as Brönsted base catalysts in the Knoevenagel condensation with a selectivity of 99.3% for the condensation product Since the reaction takes place inside the pores, the formation of bulky condensation products is hindered Therefore, high selectivity was directly related to the structural features of the MOF itself Palladium containing APS-MIL-101 and ED-MIL-101 show an increased activity in the catalysis of the Heck cross-coupling reaction (393°С) [81]

Knoevenagel condensation reaction is the prototypical example of a reaction catalyzed by MOFs with basic centers, which usually consist of amino or amide groups belonging to the organic ligand

The first example of a Knoevenagel condensation reaction catalyzed by a MOF was reported by Hasegawa et al.[82] The authors prepared a material with composition [Cd(4-btapa)2(NO3)2 ·6H2O· 2dmf (4-btapa = 1,3,5-benzene

tricarboxylic acid tris[N-(4-pyridyl)amide]) The ligand used contains three amide

groups that are responsible for the catalytic activity, and three pyridyl groups that coordinate to Cd2+ ions The basic catalytic properties of this MOF were demonstrated for the reaction between benzaldehyde and malononitrile

Figure 1.3 The schematic view of 1,3,5-benzene tricarboxylic acid

Amino

Amino Proline

POST-1

[Cu2(pzdc)2(4,4’-bpy)]

[Cd(4-btapa)2(NO3)2]

[Zn4(O)(ata)3] (IRMOF-3) MIL-53(NH2)

MIL-101(Cr)-ED MIL-101(Cr)-proline

[79]

[83] [82] [84]

[85] [86]

1.2.3 Grafted species as an active site

None of the components of the MOF is directly involved in catalysis The porous system of the material provides the physical space where the catalysis occurs (nanometric reaction cavity) or serves as a cage where the catalytic centers are encapsulated (host matrices) In the later case, the MOF materials play a role as catalyst support The use of MOF as a support for an active metal is a way that is well known as typical heterogeneous catalysts There were a few ways to introduce ions of

catalytically active transition metals into the framework of the synthesized MOFs: incipient wetness impregnation, (introducing a metal into a porous coordination polymer by metal organic chemical vapor deposition), coprecipitation and postsynthetic modification

Opelt used coprecipitation method to prepare palladium supported on MOF-5 catalysts It was shown that the specific activity of Pd supported on MOF-5 was twice

as high as that of a commercial Pd/C catalyst with almost the same Pd content in the hydrogenation of ethyl cinnamate [87]

In the supporting catalytic functions, ions of catalytically active transition metals are introduced into the framework of the synthesized MOFs These ions play the main role in catalytic activities Some drawbacks can be seen For instance, after the introduction of metal ions, the specific areas will decrease thermal stability of the metal organic framework support

Ru nanoparticles were immobilized on metal organic framework nano rods by supercritical CO2-methanol solution This kind of catalyst performed highly efficient catalyst for the hydrogenation of cyclohexene and benzene [88]

Y Huang did experiments on impregnation MIL-53(Al)-NH2 in solution of

H2PdCl4 (containing ca.1.0 wt % of Pd at pH ~ 4) to form catalyst This catalyst was used for Suzuki–Miyaura coupling reactions of aryl halides and phenylboronic acid at good yields [89]

Scheme 1.4 Suzuki–Miyaura coupling reactions of aryl halides and phenylboronic acid

Cirujano also did that method to synthesis Pd@MIL-101 It demonstrated good catalytic characteristic in conversion 86% of citronellal to menthol in one-pot [90]

In Viet Nam, conventional inorganic materials such as silicas and zeolites have been intensively investigated by many research groups over the last thirty years Their works focus on the field of adsorption and catalysis, and many publications on popular silica-based materials such as SBA-15 and MCM-41 have appeared However, to the

best of our knowledge, research on MOFs in Viet Nam is still in its early stage, and definitely it will attract further research in the near future The MOFs research group

in the Ho Chi Minh City University of Technology (VNU-HCM) is the first group starting the study on MOFs in Viet Nam in 2008 After that, others research groups from The MANAR Center (VNU-HCM), The University of Sciences (VNU-HCM), The key Laboratory for Nanotechnology (VNU-HCM), The Institute of Chemical Technology at Ho Chi Minh City (VAST), The Institute of Applied Materials Science

at Ho Chi Minh City (VAST), The Institute of Chemistry at Ha Noi (VAST), The Institute of Materials Science at Ha Noi (VAST), and The Ha Noi University of Science and Technology (MOET) have also started to explore the field of MOFs However, to the best of our knowledge, up to the January of 2014, other research groups working on MOFs in Viet Nam have not published any paper on refereed ISI journals

1.3 Aim and objectives of the study

In recent years, the synthetic organic process has been under increasing pressure and scrutiny to develop cleaner and “greener” technologies One important aspect of research toward more sustainable processes for chemical synthesis is the scientific evaluation of potential replacements for traditional catalysts

MOF materials appear with many advantaged features, such as highly porous, highly internal surface areas In addition, high metal site density could be expected in MOFs materials, which should enhance catalytic activity over metal particles and may also generate different selectivity Experiments have demonstrated that MOFs were solid catalysts, which mean MOFs allow easier post-reaction separation and recyclability than homogeneous catalysts However, up to now, there have still been relatively few reports of actual catalytic activity, and detailed investigations have been particularly lacking The application of MOFs in catalysis, therefore, still opens for further investigation

This work, thus, aims to examine the feasibility to use MOFs as efficient heterogeneous catalysts in organic synthesis, according to greener environment The study was scoped in four typical organic synthesis reactions consisted of Friedel -Craft

acylation, Knoevenagel reaction, aza-Michael reaction and Paal-Knorr reaction, which will be discussed below

Friedel–Crafts acylation provides fundamental and useful method for the

synthesis of aromatic ketones, which are important intermediates for preparing fine chemicals in the field of pharmaceuticals, naproxen, ibuprofen and dyes, agrochemicals, and fragrances Typically, the Friedel–Crafts acylation reaction is performed using acyl chloride in the presence of a little of more than one equivalent of Lewis acids, such as anhydrous AlCl3, TiCl4, and FeCl3 This method is limited by high amounts, toxicity and corrosion of the catalysts, which are non-recoverable materials after aqueous work-up, generation of a large amount of waste, and difficult purification of the desired products [91] To overcome these problems, over the last few years, several solid acid catalysts have been developed for the reaction, such as metal triflate loaded SBA-15 [92], mesoporous superacid catalyst , zeolite [93-95], hybrid zeolitic-mesostructured materials [96], modified clay [97, 98], nafion/silica composite materials [99], mesoporous sulphated zirconia [100], and mesoporous sieve AlKIT-5 [101] Although interesting results have been achieved for the Friedel-Crafts acylation reaction, they have not led to any very important industrial application

In many MOFs, the metal ions are saturated by coordinating organic ligands, and the real nature of active sites is poorly understood [62].IRMOF-8, constructed by 2,6- naphthalenedicarboxylate (ndc) linker joining Zn4O, was synthesized by Yaghi and coworkers [102-106] The material sample having Zn-OH defects and acid Lewis active site was used for alkylation of aromatic compounds with high efficiency , and therefore will be firstly tested for Friedel Craft acylation reaction of toluence with benzoyl chloride in our study It is proposed that benzoyl chloride is chemisorbed on the Lewis acid site of IRMOF-8 to yield the acylium ion species firstly, which attacks the  electrons of the aromatic C=C subsequently This destroys the aromaticity giving the cationic intermediates Then, the removal of the proton from the sp3 C bearing the acyl- group reforms the C=C and the aromatic system, generates HCl and regenerates the active catalyst

The Knoevenagel condensation is an organic reaction named after Emil

Knoevenagel It is a modification of the Aldol condensation A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated The liquid-phase Knoevenagel condensation of aldehydes with compounds containing activated methylene groups is one of the most useful and widely employed methods for carbon-carbon bonds formation with numerous applications in the synthesis of fine chemicals as well as heterocyclic compounds of biological significance [107], in the preparation of important intermediates in the pharmaceutical industry and is often used

as a test reaction for probing the activity of various solid base catalysts [108-110]

This reaction is conventionally catalyzed by alkali metal hydroxides or by organic bases like primary, secondary and tertiary amines under homogeneous conditions with the attendant difficulties in catalyst recovery and recycling [111] Over the last few years, a wide range of solid catalysts have been investigated for this reaction such as amino-functionalized mesoporous silica [112], diamine-functionalized mesopolymers[113], amine-functionalized mesoporous zirconia [114], superparamagnetic mesoporous Mg–Fe bi-metal oxides [115], mesoporous titanosilicate, basic MCM-41 silica [116-118], acid-base bifunctional mesoporous MCM-[41] silica , nanocrytalline ceria–zirconia [119], zeolites exchanged with alkylammonium cations, amine-functionalized superparamagnetic nanoparticles [120], chitosan hydrogel [121], acrylic resin immobilized lipase [122], organic-inorganic hybrid silica materials containing imidazolium and dihydroimidazolium salts [123], IRMOF-3 , and ZIF-8 [124]

The reaction may proceed according to two different mechanisms that depend essentially on the nature of the catalytic material used as solid base For strong bases, direct deprotonation of the methylene group on the catalyst surface and reaction of the deprotonated intermediate with the slightly acidic benzaldehyde takes place, leading to the product When weaker bases, such as amino groups are involved in the catalytic process, formation of an imine intermediate occurs with the benzaldehyde As consequence of the higher basicity of the formed benzaldimine compared to the free

amine, the deprotonation of the methylene group takes places followed by reaction, regenerating the active site The active methylene group can also react directly with the amino groups to form amides, inhibiting then the interaction amine–benzaldehyde and causing the deactivation of the catalyst Evidence for the formation of imine functionalities over modified silicas in the liquid phase using infrared spectroscopy has been recently reported [84]

The first example of a Knoevenagel condensation reaction catalyzed by a MOF was reported by Hasegawa et al [82] The author prepared MOF with composition [Cd(4-bpata)2(NO3)2] The ligand used contains three amide groups that are responsible for the catalytic activity of the condensation reaction between benzadehyde and malononitrile

Zeolite imidazolate frameworks (ZIFs), being classified as a new subclass of MOFs, have emerged as a novel type of highly porous materials, combining advantages from both zeolites and conventional MOFs [125], [126] ZIF-9 structure consists of cobalt atoms connected through nitrogen atoms by 2- phenyl imidazolate (PhIM) linkers to form neutral frameworks and to provide nanosized pores [127, 128] The ZIF-9 was synthesized using cobalt nitrate hexahydrate and 2- phenyl imidazole

by a solvothermal method, according to a literature procedure [129] ZIF-9 with basic groups similar to aniline will then be tested for the Knoevenagel condensation between benzaldehyde and malononitrile in this study

The aza-Michael reaction of amines and -unsaturated carbonyl compounds has attracted significant attention as one of the most effective methods to prepare -amino carbonyl compounds and their derivatives These structures serve as essential intermediates in the synthesis of a variety of biologically important natural products,

antibiotics, peptide analogues, chiral auxiliaries, and other nitrogen-containing

compounds [130]

In organic chemistry, Michael addition reactions was one of the oldest, but they have attracted much attention as the most important carbon-carbon and carbon-heteroatom bond forming reactions [131] Some bioactive alkaloids, antibiotics and