synthesis and characterisation of catalytically active
TRANSCRIPT
Synthesis and characterisation of catalytically active metal-organic frameworks based on porphyrins
Úlfar Þór Björnsson Árdal
Faculty of Physical Science University of Iceland
2017
Synthesis and characterisation of catalytically active metal-organic frameworks based on porphyrins
Úlfar Þór Björnsson Árdal
15 ECTS thesis submitted in partial fulfillment of a Baccalaureus Scientiarum degree in chemistry
Advisor Dr. Krishna Kumar Damodaran
Faculty of Physical Science School of Engineering and Natural Sciences
University of Iceland Reykjavík, May 2017
Synthesis and characterisation of catalytically active metal-organic frameworks based on porphyrins. Synthesis of catalytically active porphyrin MOFs. 15 ECTS thesis submitted in partial fulfilment of a Baccalaureus Scientiarum degree in chemistry. Copyright © 2017 Úlfar Þór Björnsson Árdal All rights reserved Faculty of Physical Science School of Engineering and Natural Sciences University of Iceland VR II, Hjarðarhagi 2-6 107 Reykjavík Telephone: +354 525 4700 Bibliographic information: Úlfar Þór Björnsson Árdal, 2017, Synthesis and characterisation of catalytically active metal-organic frameworks based on porphyrins, B.Sc. Thesis, Faculty of Physical Science, University of Iceland, 45 pp. Printing: Háskólaprent Reykjavík, May 2017
Útdráttur Málm-lífrænar grindur (MOFs) reynast vera áhugaverð gerð efna með ótal áður óþekkta eiginleika eins og gas geymslu og aðskilnað, sértækt aðsog og aðskilnað á lífrænum efnum, jónaskipti og hvatavirkni. Aðaláhersla þessarar rannsóknar er að tengja fjölvirk lífræn efni sem, ef best væri á kosið, innihalda tvö mismunandi tengisvæði (aðal og auka) sem byggingareiningar fyrir hvatavirk MOFs. Tengiefnið sem skoðað verður í þessari rannsókn er porfýrin með karboxýl sýru hóp og hefur því tvö mismunandi tengisvæði, porfýrin kjarnann og karboxýl sýru hópinn. Í þessari rannsókn verður farið þriggja skrefa ferli til þess að mynda 4,4',4'',4'''-(porfýrin-5,10,15,20-tetrayl) tetrabenzoic sýru, sem að verður svo hvarfað við málm komplexa eins og Zn(II) og Cu(II) til þess að mynda MOF. Lokaskrefið er svo að breyta þessum MOFs í hvatavirk efni með því að innlima mólýbdenum með eftir-efnasmíðar málmun. Röntgen bylgjubeygju greining á porfýrin ester kristalnum sem að myndaðist leiddi í ljós að porfýrin kjarninn var tengdur við sink atóm. Þessar niðurstöður benda til þess að málmtengla aðferð gæti verið notuð til þess að fá MOF, með því að tengja fyrst mólýbdenum við porfýrin kjarnann (málmtengill) í framhaldi af því er efnahvarf framkvæmt þar sem karboxýl sýran tengist við annan málm, til að mynda hvatavirkt MOF. Sama hvor leiðin verður fyrir valinu þá hefur góður grunnur verið unninn fyrir áframhaldandi rannsókn.
Abstract Metal-organic frameworks (MOFs) are proving to be an exciting class of materials with unprecedented properties and high potential applications such as gas storage and separation, selective adsorption and separation of organic molecules, ion exchange and catalysis. The main aim of this work is to incorporate multifunctional organic ligands, which ideally contain two types of coordinating sites (primary and secondary), as building blocks for constructing catalytically active MOFs. The ligand chosen for this study was porphyrin with carboxylic group which has two types of coordinating sites; porphyrin core and carboxylic moiety. In this thesis, a three-step synthesis will be conducted to yield 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid, which will react with metal complexes such as Zn(II) or Cu(II) to form the MOF. The final target is to convert these MOFs into active catalyst by incorporating molybdenum via post-synthetic metalation. X-ray diffraction analysis of the crystals of the synthesized porphyrin ester revealed that the porphyrin core was coordinated to zinc atom. This result indicates that a metalloligand approach could also be used to get the MOF, by first incorporating the molybdenum to the porphyrin core (metalloligand) followed by the reaction of carboxylic groups with other metals to form the catalytically active MOF. Which either way is chosen, a solid ground work has been done for the continued research.
I would like to dedicate this thesis to my father, Björn Ragnarsson.
vii
Table of Contents List of Figures .......................................................................................................... viii
List of Tables ............................................................................................................. ix
List of Schemes ............................................................................................................x
List of Abbreviations ................................................................................................ xi
Acknowledgement ................................................................................................... xiii
1 Introduction ............................................................................................................1
2 Aims and objectives ................................................................................................72.1 Aims ................................................................................................................72.2 Strategy ...........................................................................................................8
3 Experimental Section .............................................................................................93.1 Materials and Method .....................................................................................93.2 Synthesis .........................................................................................................9
3.2.1 Isopropyl 4-formylbenzoate ..................................................................93.2.2 Ethyl 4-formylbenzoate .......................................................................103.2.3 Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate 103.2.4 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid ................113.2.5 MOF experiment with Cu(NO3)2 ........................................................123.2.6 MOF experiment with Zn(NO3)2 .........................................................13
4 Results and discussions ........................................................................................154.1 Synthesis .......................................................................................................15
4.1.1 Isopropyl 4-formylbenzoate ................................................................154.1.2 Ethyl 4-formylbenzoate .......................................................................154.1.3 Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate 164.1.4 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid ................164.1.5 MOF experiment with Cu(NO3)2 ........................................................164.1.6 MOF experiment with Zn(NO3)2 .........................................................16
5 Conclusion .............................................................................................................19
Supplementary Information ....................................................................................21
Reference ...................................................................................................................29
viii
List of Figures Figure 1. The terminology of MOF compared to coordination polymer. .....................1
Figure 2. Structure of metalloligands and using metalloligands to build a MOF .........3
Figure 3. Crystal structure of Ir-PMOF-1(Zr), Ir (dark red), N (blue), C (gray) and the yellow blocks are the metal nodes .............................................................4
Figure 4. PCN-222-Pd(II), red and yellow for the nodes and grey for carbon .............5
Figure 5. Tetra carboxyl phenyl porphyrin with its two coordination sites for metals, primary (red) and secondary (blue) ............................................................7
Figure 6. UA_01-Zn-9, Zn (blue-gray), N (blue), C (grey), S (yellow), O (red) and H (white). .....................................................................................................17
Figure 7. 1H-NMR spectra of ISO4FB in CDCl3 ........................................................21
Figure 8. 13C-NMR of ISO4FB in CDCl3 ...................................................................22
Figure 9. IR spectrum of ISO4FB in a KBr pellet ......................................................22
Figure 10. 1H-NMR of E4FB in CDCl3 ......................................................................23
Figure 11. 13C-NMR of E4FB in CDCl3 .....................................................................23
Figure 12. IR spectrum of E4FB in a NaCl crystal window .......................................24
Figure 13. 1H-NMR of UA_01-03 in CDCl3 ..............................................................24
Figure 14. IR spectrum of UA_01-03 in a KBr pellet ................................................25
Figure 15. 1H-NMR spectrum of TPPCOOMe in CDCl3 ...........................................25
Figure 16. 13C-NMR of TPPCOOMe in CDCl3 .........................................................26
Figure 17. IR spectrum of TPPCOOMe in a KBr pellet .............................................26
Figure 18. 1H-NMR of H2TCPP in DMSO .................................................................27
Figure 19. IR spectrum of H2TCPP in a KBr pellet ....................................................27
ix
List of Tables Table 1. Cu(NO3)2 MOF experiment ..........................................................................12
Table 2. Zn(NO3)2 MOF experiment ..........................................................................13
Table 3. Crystal data for UA_01-Zn-9 ........................................................................14
x
List of Schemes Scheme 1. Three step synthesis for H2TCPP ................................................................8
Scheme 2. Synthesis of isopropyl 4-formylbenzoate ....................................................9
Scheme 3. Synthesis of ethyl 4-formylbenzoate .........................................................10
Scheme 4. Synthesis of tetraethyl 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate ............................................................................................10
Scheme 5. Synthesis of 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid .11
xi
List of Abbreviations rt - Room temperature P.E. - Petroleum ether EtOAc - Ethyl acetate THF - Tetrahydrofuran DMF - N,N-dimethylformamide DMSO - Dimethyl sulfoxide DMA - N,N-dimethylacetamide Et2O - Diethyl ether EtOH - Ethanol TLC - Thin layer chromatography MS - Mass spectrum IR - Infrared NMR - Nuclear Magnetic Resonance ∂ - Chemical shift s - Singlet d - Doublet t - Triplet q - Quartet hept - Septet MOF - Metal-organic framework IRMOF - Isoreticular metal-organic framework PSM - Post-synthetic modification PSMet - Post-synthetic metalation ML - Metalloligand ISO4FB - Isopropyl 4-formylbenzoate E4FB - Ethyl 4-formylbenzoate TPPCOOMe - Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate H2TCPP - 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid
xiii
Acknowledgement I would like to thank Dr. Krishna Kumar Damodaran for providing me the opportunity to
work alongside him and gain experience in the laboratory. I would also like to thank Dr.
Sigríður Jónsdóttir for the carrying out NMR and MS measurements. Thanks to the rest of
Krishna’s group; Mr. Dipankar Ghosh, Mr. Daníel Arnar Tómasson and Mr. Alfreð
Aðalsteinsson. Special thanks to my family and friends.
1
1 Introduction The foundation of inorganic chemistry are coordination compounds, but to know what a
coordination compound is we must to look in the “Red Book”. Where it says:
A coordination compound is any compound that contains a coordination entity. A
coordination entity is an ion or neutral molecule that is composed of a central atom, usually
that of a metal, to which is attached a surrounding array of atoms or groups of atoms, each
of which is called ligands. [1]
With that in mind we can talk about coordination polymers as it is just a coordination
compound with a coordination entity that extends in one, two or three dimensions. But to
define compounds further, we need a new terminology. We can define coordination
polymers as coordination networks extending in one dimension, but with a link between two
or more polymers through loops or spiro-links. Coordination polymers with repeating
coordination entities in two or three dimensions are also categorized as a coordination
network.
Metal-organic frameworks is the terminology used for coordination networks that have
organic linkers, which are connected by a metal cluster and containing potentials voids that
can be used for various different things[2]. MOFs and their various applications are the
Figure 1. The terminology of MOF compared to coordination polymer.
2
reason for the fast-growing field of MOF research as they can be used for gas adsorption,
carbon capturing, energy storage, drug delivery, light harvesting and catalysis[3]. The
extended structures in the MOF with cavities of uniform size make them ideal for selective
gas adsorption. One of the advantages of MOFs is that you can change the length of the
organic linker or even add a functional group to the linker without changing the topology,
which is called isoreticular MOF or IRMOF[4]. By changing the organic linker, the IRMOF
has changed its pore size and can therefore block bigger molecules from entering the IRMOF
because they are bigger than the pore. Furthermore, adding a functional group to the ligands
in IRMOF results in the variation of adsorption properties for example it has the tendency to
adsorb carbon dioxide rather than nitrogen. Specifically, the presence of single–site active
species in an identical environment within the crystalline matrix, porous architecture and
their tuneable structure makes them excellent heterogeneous catalyst[5].
Homogeneous transition metal catalysts despite having high chemo-, diastereo-, and
enantioselectivities in large scale production of organic compounds, often suffer from
disadvantages, such as recovering metal from the reaction products, expensive metal losses,
and limited solubility. An alternative approach is the use of heterogeneous catalysts, w.
which are more stable; (less degradation) compared to their homogeneous counterparts,
reusable and the final products are readily separated from the catalyst. Extensive efforts have
been directed toward the development of efficient and recyclable heterogeneous catalysts[6]
to overcome these problems. An alternative approach is the introduction of these catalytic
centres as part of the framework for example incorporation of the catalytic site in metal–
organic frameworks (MOFs). However, MOFs have not been able to surpass the advantages
of their homogenous counterparts since the catalytic active sites are not retained in the
MOFs. This is due to the limitations of MOFs synthetic procedure which requires high
temperature and pressure, resulting in the decomposition of catalytically active metal centres
in the MOFs with few exceptions. The catalytic properties of MOFs can be enhanced by
post-synthetic modification (PSM)[7].
MOFs are highly stable but can be modified by using as a reagent in a reaction without
breaking or changing its topology, which is called PSM. PSM can be used in various ways;
to deprotect a functional group, introduce a functional group, it can even be used to introduce
a new metal into the MOF by post-synthetic metalation (PSMet). By using PSMet it is
possible to introduce a metal with a vacant site into the MOF, which will function as a
3
catalytic centre. The advantage of having MOF as a heterogeneous catalyst is that it can be
recycled after the reaction via filtration and be used again, unlike most of the catalysts used
today which are homogeneous single usage catalysts.
The main goal of catalysts is to have a high conversion rate. This applies to MOF
Pd/MIL101[8],which is chromium terephthalate (MIL, Material Institut Lavoisier) was
reported to convert over 99,9% of phenol to cyclohexanone with a selectivity of more than
99,9%. MOF Pd/MIL101 were reusable and still showed excellent catalytic activity, which
can be considered as a good catalyst. But as there are many chemical reactions that need help
from catalysts it is also important that we can make a good catalyst for those reactions. MOF
catalysts have been made for many of those for example Friedel-Crafts addition, CO2
addition, Knoevenagel condensation, transesterification and many more.
Although PSM is a good technique, conversion of active sites are not complete and another
approach to solve this problem will be metalloligand approach. Metalloligands (MLs) are
metal complexes that contain two or more Lewis–base sites that are able to bridge with other
metal ions[9], which ideally contain two types of coordinating sites; primary and secondary
(Figure 2). Primary groups react with the metal centre to form MLs whereas the secondary
one will be utilized for forming the MOFs by coordinating to different metal. MLs are very
useful as one of their advantages is that the researcher has control of the placement metal
into the organic linker. Another advantage is that the presence of the metal center in ML
make it more rigid compared to the organic linker. The metal introduces structural rigidity
to the network and therefore the MOF becomes robust and the pores even better defined. By
using a ML it is also possible to have two or more metals in the MOF, a primary metal in
the ML and secondary metal in the cluster that connects the organic linkers to form the
MOF[9]. In this project, porphyrin moiety have been selected as organic linker for MOF
metal
+ M1
M2M2
M1
M2M1
M2 M1 M2 M1
M1
M2
M1
M1
M2
ligand metalloligand
M1 =Catalyticmetal{Rh2+,Cu2+,Zn2+ etc.}M2 =Metal{Ag+,Al3+,Co3+,Fe3+ etc.}
PrimarygroupSpacer
Secondarygroup
LigandDesign
M1
Figure 2. Structure of metalloligands and using metalloligands to build a MOF
4
synthesis because it could act as either modified using PSMet or use as MLs and can exhibit
a very large surface area or more than 2000 m2g-1.
Porphyrins are organic chromophores that absorb visible light and are therefore good
candidates for artificial photosynthetic systems and because of the four nitrogens in the
porphyrin core it becomes an excellent platform to research PSMet by introducing a new
metal to coordinate with the nitrogen atoms. It has been demonstrated that Fe3+ and Cu2+
could be introduced in the porphyrin when the MOF was already formed but interestingly
the pre-metalized porphyrin with Fe3+ could not be used form the MOF[10].
Metalloporphyrin MOFs are great catalysts as the vacant site on the metal in the porphyrin
can act as a catalytic centre. An iridium(III)-porphyrin MOF was described as an excellent
catalyst for O-H insertion [11]. The MOF Ir-PMOF-1(Zr) had a conversion rate of 94% in
heterogeneous condition after ten minutes to convert ethyl diazoacetate with isopropanol to
ethyl 2-isopropoxyacetate. The molar ratio of Ir-PMOF-1(Zr)/ethyl diazoacetate/isopropanol
respectively 0.01/1/5 at room temperature in dichloromethane. Even after reducing the molar
ratio of Ir-PMOF-1(Zr) to 0.1% the conversion was 77% but it took a lot longer, or 2.5 hours.
The vacant coordination site on the Ir in the porphyrin is believed to be the reason for the
high conversion rate and the large and uniform pores are considered to make each active Ir-
site accessible for catalytic purposes. When isopropanol was changed to methanol and
ethanol the conversion rates were 80% and 87% respectively. Due to that the catalyst is
Figure 3. Crystal structure of Ir-PMOF-1(Zr), Ir (dark red), N (blue), C (gray) and
the yellow blocks are the metal nodes
5
heterogeneous and can be recycled. The catalyst was used nine times in which the conversion
rate had a range of 88-94%. But when it was used for the tenth time the conversion rate was
reduced to 64%[11].
Another paper reported a MOF with H2TCPP organic linker with palladium(II) encapsulated
in the porphyrin[12]. The MOF, PCN-222-Pd(II), has a strong affinity to bind Cu(II) to the
porphyrin rather than the Pd(II). This is due to the strong binding affinity between the
porphyrin and the copper. This means that the MOF can detect Cu(II) with high sensitivity
and selectivity over other transition metals. This is important because high concentration of
Cu(II) can cause health issues but with this new technique a new method has been observed
to detect metal ions in liquids. This discovery without a doubt will contribute to new
discoveries of MOFs that can detect metal ions in solutions[12].
MOFs based on molybdenum is a field of current interest. The transition metal molybdenum
is the key for many catalytic reactions such as nitrogenase reactions where dinitrogen (N2)
is reduced to ammonia (NH3). This reaction is done in microorganisms that contain that
nitrogenase catalyst in their enzyme, as an example. These enzymes contain an iron
molybdenum cofactor to reduce the dinitrogen[13]. But the molybdenum does not always
need a cofactor to catalyze a reaction and molybdenum can also be incorporated into a MOF
so that the catalyst can be recycled. Noh and coworkers reported a MOF containing Mo(IV)
in the node that was exceptionally stable in their own words[14]. The MOF, Mo-SIM serves
as a great catalyst for epoxidation of cyclohexene with a yield of 93% and a selectivity of
99%. Despite the well-known problem of loss of Mo in the catalyst causing deactivation,
Figure 4. PCN-222-Pd(II), red and yellow for the nodes and grey for carbon
6
Mo-SIM showed no loss of Mo(IV) before and after the catalysis. If Mo-SIM was compared
to a zirconium supported analogue (Mo-ZrO2) the yield of the Mo-ZrO2 was higher or 97%
but the selectivity was the same or 99%. But then they tried to recycle the catalyst it had lost
80 weight % of the active species. This loss of activity goes to show that the recyclable Mo-
SIM is preferable as the yield difference is not much but it can be used repeatedly[14].
As these researchers show MOFs are very diverse and they are an expanding research field.
So perhaps mixed metal MOFs will be the breakthrough to adsorb and catalyze reaction to
reduce the carbon dioxide in the world. Maybe they will clean insanitary water so that it is
safe for human consumption. In this project, MOFs based on mixed metal such as
copper/zinc and molybdenum will be designed and synthesized.
7
2 Aims and objectives 2.1 Aims The aim and objective of this thesis is to make a MOF, which contains two different metals
and multi-functional organic linker that is a porphyrin species. The organic linker in this case
will be a tetra carboxy phenyl porphyrin, which has two sites for metal coordination namely
porphyrin core (red) and carboxylic (blue) groups (Figure 5). The two metal centres have
completely different purposes. The primary metal will be positioned at the centre of the
porphyrin and is only coordinated in four sites and therefore has a vacant metal site, which
will act as a catalyst. The primary metal and the organic linker make up the ML in the MOF.
The secondary metal will react with the carboxylate groups and connect ML together to form
a three-dimensional structure.
The aims are therefore to synthesize tetra carboxy phenyl porphyrin and characterize it with
various analytical techniques. The porphyrin will then be reacted with the secondary metal
and will from the MOF. If the MOF is obtained, then PSM will be used to introduce the
primary metal into the porphyrin. But if complexes are obtained then metalloligand approach
will be used to make the final MOFs. X-ray structural analysis will determine if the primary
metal has kept its catalytically active site.
HN
N
NH
N
OHO OH
O
HOOHO
O
Figure 5. Tetra carboxyl phenyl porphyrin with its two coordination sites for metals, primary (red) and
secondary (blue)
8
2.2 Strategy The organic linker will be 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid
(H2TCPP) which will be synthesized from 4-formylbenzoic acid. Through a 3-step synthesis.
The primary metal will be molybdenum and the secondary metal will either be zinc or
copper.
O
OO NH
N
NH
N
OO O
O
OOO
O
NH
N
NH
N
OHO OH
O
OHOHO
O
O
OHO
O
OO
Scheme 1. Three step synthesis for H2TCPP
9
3 Experimental Section 3.1 Materials and Method All starting materials and reagents were purchased from Sigma Aldrich and no further
purification used. 1H- and 13C-NMR spectrums were recorded on Bruker Advance 400
spectrometer. IR spectrums were recorded on a Thermo Nicolet FT-IR iS 10 spectrometer,
on a KBr pallet for crystalline materials or as a neat liquid oil with a NaCl crystal window.
Mass spectrums were acquired on a Bruker micrOTOF-Q mass spectrometer. Bruker
D8Venture (Photon100 CMOS detector) diffractometer was used to collect crystal data.
3.2 Synthesis
3.2.1 Isopropyl 4-formylbenzoate
Scheme 2. Synthesis of isopropyl 4-formylbenzoate
To a solution of 4-formylbenzoic acid (2.0 g, 13.4 mmol) in DMF (52 mL) was added finely
grounded potassium carbonate (3.6 g, 26 mmol) and 2-iodopropane (3.4 mL, 34 mmol). The
reaction was stirred at rt until completion and was monitored by TLC (P.E./EtOAc:6/1). The
solution was then diluted with water and extracted with Et2O three times. The organic layers
were then combined and washed with brine, dried over Na2SO4, filtered and the solvents
evaporated under reduced pressure in rotavapor. Purification by flash column
chromatography was achieved on SiO2 (P.E./EtOAc:6/1) to afford a yellow oil (0.28 g,
11%). 1H NMR (400 MHz, Chloroform-d) δ 10.10 (s, 1H), 8.19 (d, J = 8.3 Hz, 2H), 7.94 (d,
J = 8.5 Hz, 1H), 5.28 (hept, J = 6.3 Hz, 1H), 1.39 (d, J = 6.3 Hz, 6H). 13C NMR (101 MHz,
Chloroform-d) δ 191.69, 165.05, 139.03, 135.92, 130.12, 129.44, 69.24, 21.91. MS:
Calculated for C11H12O3: 192.08, Found: 192.13.
O
O
OO
OH
OI
DMF
K2CO3
+
10
3.2.2 Ethyl 4-formylbenzoate
Scheme 3. Synthesis of ethyl 4-formylbenzoate
To a solution of 4-formylbenzoic acid (10.0 g, 67 mmol) in DMF (270 mL) was added finely
ground potassium carbonate (18.0 g, 130.0 mmol) and iodoethane (13 mL, 170 mmol). The
reaction was stirred at rt overnight. The solution was then diluted with water and extracted
with Et2O three times. The organic layers were then combined and washed with brine, dried
over Na2SO4, filtered and the solvents removed under reduced pressure in rotavapor.
Purification by flash column chromatography was achieved on SiO2 (P.E./EtOAc:6/1) to
afford a yellow/white oil (11.3 g, 94%). 1H NMR (400 MHz, Chloroform-d) δ 10.03 (s, 1H),
8.13 (td, 2H), 7.88 (td, 1H), 4.35 (q, J = 7.1 Hz, 2H), 1.35 (t, J = 7.1 Hz, 4H). 13C NMR (101
MHz, Chloroform-d) δ 190.64, 164.55, 138.07, 134.46, 129.13, 128.46, 60.59, 13.25. MS:
Calculated for C10H10O3: 178.06, Found: 178.13.
3.2.3 Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate
Scheme 4. Synthesis of tetraethyl 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate
To a solution of propionic acid (120 mL) ethyl 4-formylbenzoate (5.3 g, 29.8 mmol) and
pyrrole (2.4 mL, 33.9 mmol) were added and stirred. The solution was refluxed at 140 °C
overnight. After cooling to rt the filtrate was collected via suction filtration. The filtrate was
then thoroughly washed with EtOH, EtOAc and THF. After that it was dried in a desiccator
for two days. Purple crystals were obtained (1.78 g, 24%). 1H NMR (400 MHz, Chloroform-
O
O
OO
OH
O IDMF
K2CO3
+
HN
N
NH
N
O
O O
O
O
OO
O
O
O
O
NH Propionic acid+
11
d) δ 8.84 (s, 8H), 8.47 (td, 8H), 8.31 (td, 8H), 4.59 (q, J = 7.1 Hz, 8H), 1.57 (t, J = 7.2 Hz,
12H), -2.78 (s, 2H). 13C NMR (101 MHz, Chloroform-d) δ 166.78, 146.56, 134.51, 130.17,
127.98, 119.47, 61.39, 14.54. MS: Calculated for C56H46N4O8: 902.33, Found: (M+H)
903.33.
3.2.4 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid
Scheme 5. Synthesis of 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid
Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate (1.7 g, 1.9 mmol) was
dissolved in MeOH (40 mL), THF (40 mL) and KOH (7 g, 124.8 mmol) in H2O (40 mL).
The reaction mixture was refluxed at 75 °C overnight. After cooling to rt the solvents were
evaporated under reduced pressure in rotavapor. Additional water was added, followed by
acidification by 1 M HCl until solution was 6 on a pH scale. The precipitate was collected
via suction filtration. The filtrate was then washed with water and dried in fume hood for 3
days. Purple solid was obtained (1.2 g, 84%). 1H NMR (400 MHz, DMSO-d6) δ 8.92 (s, 8H),
8.44 (d, J = 8.2 Hz, 7H), 8.39 (d, J = 8.3 Hz, 7H), -2.86 (s, 2H). MS: Calculated for
C48H30N4O8: 790.21, Found: (M+H) 791.20
HN
N
NH
N
OH
O OH
O
HO
OHO
O
HN
N
NH
N
O
O O
O
O
OO
O
1) KOH, THF/MeOH/H2O
2) 1M HCl
12
3.2.5 MOF experiment with Cu(NO3)2
4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid, Cu(NO3)2 and benzoic acid were
ultrasonically dissolved in a 7 mL vial with the solvent. The vial was then closed and heated
at 125 °C for 48 hours.
Table 1. Cu(NO3)2 MOF experiment
Name PorphA (mg)
Cu(NO3)2 (mg)
Solvent (mL)
Benzoic acid (g)
Initial observation
Final observation
Cu-1 50.1 30.2 DMF (4) 2.7 Dark red No crystals
Cu-2 50.7 29.8 DMF (3) 2.7 Dark red No crystals
Cu-3 50.2 45.7 DMF (3) 2.7 Dark red No crystals
Cu-4 50.1 29.6 DMA (4) 2.7 Dark red No crystals
Cu-5 49.4 29.9 DMA (3) 2.7 Dark red No crystals
Cu-6 49.8 45.8 DMA (3) 2.7 Dark red No crystals
Cu-7 50.4 30.0 DMSO (4) 2.7 Dark red No crystals
Cu-8 49.6 29.8 DMSO (3) 2.7 Dark red No crystals
Cu-9 49.6 45.8 DMSO (3) 2.7 Dark red No crystals
13
3.2.6 MOF experiment with Zn(NO3)2
4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid, Zn(NO3)2 and benzoic acid were
ultrasonically dissolved in a 7 mL vial with the solvent. The vial was then closed and heated
at 127 °C for 48 hours.
Table 2. Zn(NO3)2 MOF experiment
Name PorphA (mg)
Cu(NO3)2 (mg)
Solvent (mL)
Benzoic acid (mg)
Initial observation
Final observation
Zn-1 50.6 38.6 DMF (3) 1000 Dark red No crystals
Zn-2 50.1 28.7 DMF (2) 675 Dark red Plates
Zn-3 49.7 57.2 DMF (2) 675 Dark red No crystals
Zn-4 50.5 37.9 DMA (3) 1000 Dark red No crystals
Zn-5 50.3 38.7 DMA (2) 675 Dark red Plates
Zn-6 49.8 57.4 DMA (2) 675 Dark red No crystals
Zn-7 50.6 38.6 DMSO (3) 1000 Dark red No crystals
Zn-8 50.2 38.8 DMSO (2) 675 Dark red Needles
Zn-9 50.2 57.9 DMSO (2) 675 Dark red Needles
X-ray Data collection details: X-ray quality single crystals were obtained by transferring
the mother liquor to a beaker and finding a good crystal at the bottom of the vial. The crystals
transferred from the vial with a brush and immersed in cryogenic oil and then mounted. The
X-ray single crystal data was collected using MoKα radiation (λ =0.71073Å) on a Bruker
D8Venture (Photon100 CMOS detector) diffractometer equipped with a Cryostream
(Oxford Cryosystems) open-flow nitrogen cryostats at the temperature 150.0(2)K. The unit
cell determination, data collection, data reduction, structure solution/refinement and
empirical absorption correction (SADABS) were carried out using Apex-III (Bruker AXS:
Madison, WI, 2015). The structure was solved by direct method and refined by full-matrix
least squares on F2 for all data using SHELXTL[15] and Olex2[16] software. All non-
disordered non-hydrogen atoms were refined anisotropically and the hydrogen atoms were
placed in the calculated positions and refined in riding model.
14
Table 3. Crystal data for UA_01-Zn-9
Empirical formula C60H56N4O10S2Zn
Colour Purple
Formula weight (g/mol) 1122.57
Crystal size (mm) 0.2 x 0.08 x 0.05
Crystal system Monoclinic
Space group P21/c
a (Å) 22.916(2)
b (Å) 10.7278(9)
c (Å) 23.925(2)
b (0) 115.895(2)
Volume (Å3) 5291.1(8)
Z 4
Dcalc. (g/cm3) 1.409
F(000) 2344
µ MoKa (mm-1) 0.609
Temperature (K) 150.0(2)
Reflections collected/unique/observed [I>2σ(I)] 111184/13297/6716
Data/restraints/parameters 13297/0/711
Goodness of fit on F2 1.041
Final R indices [I>2σ(I)] R1 = 0.0915
wR2 = 0.1542
R indices (all data) R1 = 0.2174
wR2 = 0.1893
15
4 Results and discussions As with all experiments sometimes the outcome is something unexpected and these are as
important as the outcomes that the researcher was looking for. If nobody batted an eye to
these unexpected outcomes the world would be very different from that world we live in
today. In 1895, a scientist named Wilhelm Röntgen was conducting an experiment that lead
to the accidental discovery of X-rays and without them the research of MOFs would be a lot
harder[17].
4.1 Synthesis
4.1.1 Isopropyl 4-formylbenzoate
The synthesis is an easy one but the yield was not great so instead of protecting the acid with
2-iodopropane it was decided to use iodoethane as a reactant as it should have a greater yield.
4.1.2 Ethyl 4-formylbenzoate
After changing iodoethane the yield improved to 83%. After initial mixing of the reactant
the reaction solution is white but as the reaction is stirred it slowly turns yellow. The product
was sometimes yellow and sometimes white, 1H-NMR showed no difference between the
two. The oil solidified when kept in fridge. At one time while working up the reaction MeOH
was accidentally added instead of water and the obtained product, called UA_01-03, became
a mixture of two substances. MS sample was prepared and the mass spectrum showed two
peaks. One with the mass of M: 178.13 which is the same mass as ethyl 4-formyl benzoate
but the other peak with the mass of M: 164.08. The 1H-NMR of the product indicated that
the products were both ethyl and methyl 4-formylbenzoate and the peaks from the mass
spectra correspond to that indicating the possibility of transesterification. The experiment
was first done in a 1 gram scale and it was believed that the yield would be less if the scale
of the experiment was increased but that turned out to be wrong as the best yield in a gram
scale was 64% but prior to that discovery the experiment had already been done many times
and taken up a lot of time that could have been used for better purposes.
16
4.1.3 Tetraethyl 4,4’,4’’,4’’’-(porphyrin-5,10,15,20-tetrayl) tetrabenzoate
The reaction solution was yellow after initial mixing but as the reaction reached reflux heat
the solution became very dark. When washing it was observed that the product was partly
soluble in THF and therefore it was not used to clean.
4.1.4 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzoic acid
Acidification should be monitored by pH litmus paper as the reaction mixture is not see
through so it is not possible to see when no more precipitate forms. The solution along with
its precipitate turns green if it is acidified it too much. The filtration is very slow, even with
a medium pour Büchner funnel it took more than a day and because of its dark colour the
researcher did not want to centrifuge it. Since the filtrate is washed with water it needs a
long time to dry because of the hydrogen bond from the acid to the water.
4.1.5 MOF experiment with Cu(NO3)2
All the vials contained a dark red solution and upon inspection in a microscope no crystals
were formed. Due to the solution not being see through it was transferred to a beaker and the
solution inspected thoroughly from there.
4.1.6 MOF experiment with Zn(NO3)2
All the vials were dark red to begin with but after 48 hours the solution had turned green.
The vials were not see through due to the dark solution. The solution was transferred to a
beaker and upon inspection vials Zn-8 and Zn-9 had crystals and vials Zn-2 and Zn-5 had
thin plates. A single crystal from Zn-8 was isolated, mounted and data was collected using
single crystal X-ray diffractometer. The structure of the crystal was solved. Single crystal X-
ray analysis revealed that UA_01-Zn-9 is the TPPCOOMe with a tetra-covalently bonded
zinc to the nitrogen atoms, distance 2.051 to 2.071 Å. The zinc is coordinated to a sulphur
molecule that is part of the solvent (DMSO) and the distance is 2.111 Å. The geometry for
the zinc is a distorted square pyramidal as the zinc is slightly out of plane from the nitrogen
17
atoms. There is another DMSO molecule in the crystal structure but it is not covalently
bonded to anything and it is distorted. The porphyrin is little twisted so it is no longer planar.
Figure 6. UA_01-Zn-9, Zn (blue-gray), N (blue), C (grey), S (yellow), O (red) and H (white).
19
5 Conclusion The aim of this thesis was to synthesise MOFs based on porphyrin metalloligands (MLs)
with two different metals. The porphyrin (H2TCPP) will be reacted with Cu or Zn nodes to
bind the organic linker in H2TCPP to form a three-dimensional structure. PSMet could then
be used to introduce molybdenum into the primary coordination site of the H2TCPP. In this
project, multi-functional organic linker H2TCPP was successfully synthesised and was
characterised by mass spectroscopy and 1H-NMR, which was used to form the MOF.
Various experiments were performed to synthesise MOFs but the condition to form the MOF
was not optimised due to time limitations. This has prompted us to explore the ML way to
form MOF and been successful in synthesising metal complex of TPPCOOMe. The X-ray
structure revealed that the Zn metal centre was covalently coordinated to the primary
coordination site of TPPCOOMe. This clearly indicates that if we need molybdenum in the
primary coordination, TPPCOOMe with molybdenum should be prepared. After that the
hydrolysis of ester and reacting the acid with either Cu or Zn will result in desired MOF with
two different metals. The author has therefore proven that both ways are viable options. Also
because of the discovery that esterification of 4-formylbenzoic acid can be made in bulk
without decreasing the yield the next researcher can save valuable time in the synthesis of
TPPCOOMe or H2TCPP depending on whether the PSMet or ML way is chosen.
21
Supplementary Information
Figure 7. 1H-NMR spectra of ISO4FB in CDCl3
22
Figure 8. 13C-NMR of ISO4FB in CDCl3
Figure 9. IR spectrum of ISO4FB in a KBr pellet
23
Figure 10. 1H-NMR of E4FB in CDCl3
Figure 11. 13C-NMR of E4FB in CDCl3
24
Figure 12. IR spectrum of E4FB in a NaCl crystal window
Figure 13. 1H-NMR of UA_01-03 in CDCl3
25
Figure 14. IR spectrum of UA_01-03 in a KBr pellet
Figure 15. 1H-NMR spectrum of TPPCOOMe in CDCl3
26
Figure 16. 13C-NMR of TPPCOOMe in CDCl3
Figure 17. IR spectrum of TPPCOOMe in a KBr pellet
27
Figure 18. 1H-NMR of H2TCPP in DMSO
Figure 19. IR spectrum of H2TCPP in a KBr pellet
29
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