Design and synthesis of new nanosized C 3-symmetrical tricarboxylic acids: Key elongated ligands for the preparation of highly porous MOFs

Article abstract of DOI:10.1055/s-0035-1560207

The synthesis of two new C ₃-symmetrical nanosized tricarboxylic acids bearing triphenylmethane cores and three imines linkages is presented. The new elongated tripods were designed to stabilise highly porous metal-organic frameworks (MOFs) and

Full text of DOI:10.1055/s-0035-1560207

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Georg Thieme Verlag Stuttgart · New York
2015, 26, 2659–2662
2659
letter
Synlett
M. S. Markoulides et al.
Letter
Design and Synthesis of new Nanosized C -Symmetrical Tricarbox-
3
ylic Acids: Key Elongated Ligands for the Preparation of Highly
Porous MOFs
Marios S. Markoulides*
Constantinos G. Efthymiou
Anastasios J. Tasiopoulos
Nikos Chronakis*
Department of Chemistry, University of Cyprus, University Str. 1,
Building No. 13, Aglantzia, 2109 Nicosia, Cyprus
markoulides.marios@ucy.ac.cy
nchronak@ucy.ac.cy
Received: 03.07.2015
Accepted: 08.08.2015
Published online: 02.09.2015
DOI: 10.1055/s-0035-1560207; Art ID: st-2015-d0497-l
Abstract The synthesis of two new C -symmetrical nanosized tricar-
3
boxylic acids bearing triphenylmethane cores and three imines linkages
is presented. The new elongated tripods were designed to stabilise
highly porous metal-organic frameworks (MOFs) and were synthesized
by a threefold Schiff base condensation reaction between the reduced
leuco form of pararosaniline hydrochloride salt and an appropriate alde-
hyde.
Key words Schiff bases, condensation reaction, tricarboxylic acid li-
gands, metal-organic frameworks (MOFs)
Nikos Chronakis was born in Heraklion, Crete, in 1971. He received his
BSc from the University of Crete in 1994 and his PhD in 2000 under the
supervision of Prof. Michael Orfanopoulos. Following postdoctoral stud-
ies at the ETH Zürich in Switzerland (2002–2003) with Prof. François
Metal-organic frameworks (MOFs) are a unique class of
materials endowed with a plethora of structural topologies
and extraordinary physical properties. The high porosity
Diederich and at the University of Erlangen-Nürnberg in Germany
(2003–2005) with Prof. Andreas Hirsch, he joined the Chemistry De-
partment of the University of Cyprus in 2005 as a Lecturer in Organic
Chemistry. Since 2009 he is Assistant Professor, and his research is fo-
cused on the regio- and diastereoselective synthesis of C60 multiad-
ducts for the construction of functional supramolecular assemblies.
1
and enormous internal surface areas, together with the
high degree of variability for both the organic and inorganic
components of their structures, set MOFs as potential can-
didates in applications including gas storage and separa-
2a–f
2g
2h
2i
tion,
catalysis, drug delivery, and sensing.
The predominant strategy that has been developed for
the synthesis of highly porous MOFs involves the use of
elongated polytopic organic ligands. This approach deals
with the enlargement of the organic linkers between the
inorganic secondary building units (SBUs) of a given topol-
such type of ligands consist of phenyl rings which are either
directly connected or linked through various rigid (e.g.,
alkynes)3 or less rigid (e.g., amides) groups.
d,e
3f
A major drawback of utilizing elongated polytopic li-
gands arises from the limited robustness of the resulting
three-dimensional frameworks, as they tend to collapse
upon removal of their guest molecules. The design of ex-
tended organic molecules with rigid linkages can stabilize
quite robust MOFs. As such, the insertion of imine linkages
within the arms of the bulky elongated organic ligands
could restrict the flexibility of these molecules and en-
hance the rigidity of the corresponding MOFs. Very recent-
ly, semi-rigid iminocarboxylic ligands have been used in the
chemistry of MOFs, providing significant stability and in-
3
a,b
ogy and is known as reticular synthesis.
The latter has
been proven successful for the synthesis of MOFs with high
internal surface areas and/or large pore volumes. For exam-
3
c
3d
3e
3e
ple, MOF-210, NU-100, NU-109E, and NU-110E pos-
sess Brunauer–Emmett–Teller (BET) surface areas greater
2
than 6000 m /g. These highly porous MOFs require the uti-
lization of at least one C -symmetrical tripodal tritopic or
3
hexatopic carboxylic organic ligand. The tripodal arms of
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M. S. Markoulides et al.
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troducing flexibility into the structures of the newly syn-
thesized MOFs. This allows structural alterations during the
adsorption processes (e.g., pore expansion and breathing
effects), without the deterioration of the crystalline frame-
In this respect, the synthesis of ligands 4a and 4b start-
ed with the reduction of pararosaniline hydrochloride salt
1 to the leuco form 5 (Scheme 2). Following the procedure
6
reported by Houjou et al., 1 was reduced to 5 using NaBH
4
3g,h
works.
in ethanol as a solvent and was obtained in 52% yield after
column chromatographic purification on silica gel using ac-
In continuation of our previous work on the synthesis
and gas sorption studies of a highly porous double-inter-
penetrated MOF (3) with a high internal surface area
7
1
etone–Et N (9:0.08) as an eluent. The H NMR spectrum of
3
5 displayed the characteristic singlet absorption at δ = 4.97
2
4
(
<2600 m /g), we wish to report herein a facile synthetic
ppm which corresponds to the methyne hydrogen which
13
access to a new series of elongated C -symmetrical nano-
was correlated with the signal at δ = 53.80 ppm in the
C
3
sized tricarboxylic acid ligands (4a and 4b, Scheme 1). In
NMR spectrum (see Supporting Information).7
addition to the imine linkages – that were shown to provide
sufficient rigidity to the structure of MOFs and the possi-
bility of elongation targeting a higher internal surface area
In the next step, 4,4′,4′′-triaminotriphenylmethane (5)
was subjected in a typical Schiff base condensation with 4-
formylbenzoic acid (6) in ethanol, followed by stirring at
room temperature for a prolonged time (Scheme 2). Despite
the low solubility of 4a, purification by column chromato-
graphy on silica gel was achieved using CHCl –MeOH–Et N
4
–
ligands 4a and 4b were designed to support a more stable
triphenylmethane core compared with ligand 2 (Scheme 1).
In our previous report, tricarboxylic acid ligand 2 was syn-
thesized starting form pararosaniline hydrochloride salt (1)
in two steps by the conversion of 1 into pararosaniline car-
binol base, followed by a Schiff base condensation with 4-
3
3
8
(9:1:0.15) as an eluent. The structure of 4a was unambigu-
1
13
ously assigned by H NMR, C NMR, UV spectroscopies and
by mass spectrometry (see Supporting Information). Char-
acteristically, the absorption spectrum of 4a (λ = 344 nm) is
4
formylbenzoic acid (Scheme 1). However, the triphenyl-
methanol core in 2 loses its hydroxyl group readily, and this
results in a virtually planar methylium system, which is re-
sponsible for the vivid colours of synthetic dyes such as
shifted by 46 nm compared to 5 (λ = 298 nm) due to the ex-
1
tension of conjugation. In addition, the H NMR (DMSO-d )
6
spectrum of 4a displayed a singlet absorption at δ = 8.74
5
crystal violet and malachite green.
Scheme 1 Novel nanosized C -symmetrical tricarboxylic acid ligands 4a and 4b
3
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M. S. Markoulides et al.
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NH2
temperature for ten days, yielded – after successive wash-
ings with EtOH, CHCl , MeCN, THF, and Et O – the targeted
3
2
Cl
H
elongated ligand 4b in 63%, as an off-white solid (Scheme
NaBH4
EtOH, r.t., 3 h
NH2
10
3).
H2N
HO
+
O
52%
The structure of 4b was confirmed by 1H NMR, 13C NMR,
H2N
O
H
UV spectroscopies and by mass spectrometry (see Support-
1
6
ing Information). All spectroscopic data were in full agree-
NH2
NH2
5
10
ment with the C -symmetrical structure of 4b.
3
H
N
EtOH, r.t.
In conclusion, to facilitate investigations on the synthe-
sis of highly porous MOFs with unique physical properties,
an efficient synthetic strategy has been developed for the
7
d
89%
N
N
O
O
preparation of new nanosized C -symmetrical tricarboxylic
3
HO
OH
acid ligands. The key synthetic intermediate 5, which is the
reduced leuco form of pararosaniline hydrochloride salt (1),
was subjected to a threefold Schiff base condensation reac-
tion with aldehydes 6 and 8. Despite the low solubility of
the synthesized ligands 4a and 4b, they were isolated in
high purity in two steps (46% overall yield) and three steps
HO
O
4a
(
25% overall yield), respectively. The synthesis and charac-
Scheme 2 Synthesis of tricarboxylic acid ligand 4a, bearing a triph-
enylmethane core and three imine linkages
terization of new MOFs based on these elongated tricarbox-
ylic ligands is in progress, and the results of these studies
will be reported in the near future.
ppm corresponding to the imine hydrogens and the expect-
ed absorptions of the methyne, phenyl, and carboxylic acid
hydrogens. Finally, the 13C NMR spectrum of 4a displayed
Acknowledgment
eleven signals, clearly indicating a C -symmetrical struc-
ture.
3
We gratefully acknowledge the University of Manchester for high res-
olution mass measurements.
8
NaOH,
MeO
O
O
H
MeOH–H2O (3:1)
HO
O
O
H
Supporting Information
5
5–60 °C, 14 d
77%
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1560207.
7
8
S
u
p
p
ortioIgnfmr oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
H
N
5
, EtOH, r.t.
1
0 d
N
N
63%
References and Notes
O
OH
(1) (a) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.;
O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319.
HO
O
(
b) Férey, G. Chem. Soc. Rev. 2008, 37, 191. (c) Horike, S.;
Shimomura, S.; Kitagawa, S. Nat. Chem. 2009, 1, 695.
d) Bradshaw, D.; Claridge, J. B.; Cussen, E. J.; Prior, T. J.;
(
Rosseinsky, M. J. Acc. Chem. Res. 2005, 38, 273.
(2) (a) Morris, R. E.; Wheatley, P. S. Angew. Chem. Int. Ed. 2008, 47,
4
966. (b) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim,
J.; O’Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127. (c) Hayashi,
H.; Côté, A. P.; Furukawa, H.; O’Keeffe, M.; Yaghi, O. M. Nat.
Mater. 2007, 6, 501. (d) Zheng, S.; Wu, T.; Zhang, J.; Chow, M.;
Nieto, R. A.; Feng, P.; Bu, X. Angew. Chem. Int. Ed. 2010, 49, 5362.
O
OH
4b
Scheme 3 Synthesis of the extended tricarboxylic acid ligand 4b
(
e) Hasegawa, S.; Horike, S.; Matsuda, R.; Furukawa, S.;
Mochizuki, K.; Kinoshita, Y.; Kitagawa, S. J. Am. Chem. Soc. 2007,
29, 2607. (f) Neofotistou, E.; Malliakas, C. D.; Trikalitis, P. N.
Elongation of the arms in the designed ligand 4b was
succeeded by using 4′-formyl-(1,1′-biphenyl)-4-carboxylic
acid (8) which was obtained in good yield (77%) after basic
hydrolysis of the corresponding methyl ester 7 (Scheme 3).9
A threefold Schiff base condensation reaction between the
carboxylic acid 8 and the triamine 5, in ethanol at room
1
Chem. Eur. J. 2009, 15, 4523. (g) Ma, L.; Falkowski, J. M.; Abney,
C.; Lin, W. Nat. Chem. 2010, 2, 838. (h) Horcajada, P.; Serre, C.;
Maurin, G.; Ramsahye, N. A.; Balas, F.; Vallet-Regi, M.; Sebban,
M.; Taulelle, F.; Férey, G. J. Am. Chem. Soc. 2008, 130, 6774.
(i) Chen, B.; Wang, L.; Zapata, F.; Qian, G.; Lobkovsky, E. B. J. Am.
Chem. Soc. 2008, 130, 6718.
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Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2659–2662

2
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M. S. Markoulides et al.
Letter
(
3) (a) Furukawa, H.; Cordova, K. E.; O’Keefe, M.; Yaghi, O. M. Science
129.69 (CH arom.), 128.62 (CH arom.), 121.26 (CH arom.), 54.42
+
2
2
013, 341, 1230444. (b) Senkovska, I.; Kaskel, S. Chem. Commun.
014, 50, 7089. (c) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.;
(CH). HRMS (TOF MS AP+): m/z [M + H] calcd for C43
H
N O :
32
3
6
–1
686.2291; found: 686.2323. UV/vis (DMSO): λ
(ε/dm3 mol
max
–1
Choi, S. B.; Choi, E.; Yazaydin, A. Ö.; Snurr, R. Q.; O’Keeffe, M.;
Kim, J.; Yaghi, O. M. Science 2010, 329, 424. (d) Farha, O. K.;
Yazaydin, A. Ö.; Eryazici, I.; Malliakas, C. D.; Hauser, B. G.;
Kanatzidis, M. G.; Nguyen, S. T.; Snurr, R. Q.; Hupp, J. T. Nat.
Chem. 2010, 2, 944. (e) Farha, O. K.; Eryazici, I.; Jeong, N. C.;
Hauser, B. G.; Wilmer, C. E.; Sarjeant, A. A.; Snurr, R. Q.; Nguyen,
S. T.; Yazaydin, A. Ö.; Hupp, J. T. J. Am. Chem. Soc. 2012, 134,
cm ): 260 nm (79873), 344 nm (25047).
(9) Synthesis of 4′-Formyl-(1,1′-biphenyl)-4-carboxylic Acid (8)
NaOH (497 mg, 12.4 mmol) was added into a stirred solution of
methyl 4-(4-formylphenyl)benzoate (7, 2.13 g, 8.9 mmol) in
MeOH–H O (3:1, 500 mL) in a 1000 mL single-neck round-bot-
2
tomed flask, and the resulting mixture was stirred at an ele-
vated temperature of 55–60 °C for two weeks. During this time
the consumption of the starting material was monitored by
means of TLC (hexane–EtOAc = 4:1). Upon completion, MeOH
was evaporated under reduced pressure, and 1 M NaOH (25 mL)
was added. The aqueous solution was washed with EtOAc
(3 × 150 mL) and finally made acidic with 3 M HCl. The precipi-
tate was then filtered under suction on a sintered funnel to give
an off-white solid which was washed successively with water,
CHCl , MeCN, and finally with Et O. Residual solvent traces
15016. (f) Zheng, B.; Bai, J.; Duan, J.; Wojtas, L.; Zaworotko, M. J.
J. Am. Chem. Soc. 2011, 133, 748. (g) Manos, M. J.; Kyprianidou,
E.; Papaefstathiou, G. S.; Tasiopoulos, A. J. Inorg. Chem. 2012, 51,
6308. (h) Efthymiou, C. G.; Kyprianidou, E. J.; Milios, C. J.;
Manos, M. J.; Tasiopoulos, A. J. J. Mater. Chem. A 2013, 1, 5061.
4) Manos, M. J.; Markoulides, M. S.; Malliakas, C. D.;
Papaefstathiou, G. S.; Chronakis, N.; Kanatzidis, M. G.; Trikalitis,
P. N.; Tasiopoulos, A. J. Inorg. Chem. 2011, 50, 11297.
5) Duxbury, D. F. Chem. Rev. 1993, 93, 381.
(
3
2
(
(
were removed under high vacuum to afford product 8 as an off-
white solid (1.54 g, 77%). IR (ATR): νmax = 3072 (br), 3043 (br),
2951 (m), 2372 (w), 1713 (m), 1682 (m), 1603 (s), 1558 (w),
1425 (w), 1404 (w), 1296 (m), 1247 (m), 1219 (m), 1172 (w),
6) Houjou, H.; Koga, T.; Akiizumi, M.; Yoshikawa, I.; Araki, K. Bull.
Chem. Soc. Jpn. 2009, 82, 730.
(7) 4,4′,4′′-Triaminotriphenylmethane (5) was prepared according
6
–1 1
to
a
literature procedure. Purification was performed by
1113 (w), 1007 (m), 827 (s) cm . H NMR (500 MHz, DMSO-d ):
6
column chromatography on silica gel (acetone–Et N = 9:0.08) to
afford product 5 as a greyish-pink solid (52%); mp 210 °C
δ = 13.10 (1 H, br s, CO H), 10.08 (1 H, s, CHO), 8.07–8.02 (4 H,
3
2
6
m, 4 × CH arom.), 7.98 (2 H, d, J = 8.0 Hz, 2 × CH arom.), 7.90 (2
13
(
(
(
(
dec.). R = 0.65 (acetone–Et N = 9:0.08). IR (ATR): ν
= 3468
H, d, J = 8.0 Hz, 2 × CH arom.). C NMR (125 MHz, DMSO-d ): δ
f
3
max
6
br w), 3427 (br w), 3377 (br w), 3348 (br w), 3211 (br w), 3011
w), 2357 (w), 2318 (w), 1622 (m), 1510 (s), 1435 (w), 1273
m), 1176 (m), 1122 (w), 1084 (w), 1016 (w), 827 (m), 779 (m).
= 192.72 (CHO), 166.90 (CO H), 144.55 (C arom.), 142.78 (C
2
arom.), 135.54 (C arom.), 130.53 (C arom.), 130.11 (CH arom.),
129.96 (CH arom.), 127.67 (CH arom.), 127.28 (CH arom.).
–1
1
+
cm . H NMR (500 MHz, DMSO-d ): δ = 6.70 (6 H, d, J = 8.1 Hz,
HRMS (TOF MS AP+): m/z [M + H] calcd for C H11O : 227.0708;
6
14
3
3
–1
–1
CH arom.), 6.44 (6 H, d, J = 8.1 Hz, CH arom.), 4.97 (1 H, s), 4.83
found: 227.0713. UV/vis (DMSO): λmax (ε/dm mol cm ): 252
13
(
6 H, s, 3 × NH2). C NMR (125 MHz, DMSO-d ): δ = 146.17 (C
nm (13111), 295 nm (21370).
6
arom.), 132.78 (C arom.), 129.14 (CH arom.), 113.51 (CH arom.),
(10) Synthesis
of
4′,4′′′,4′′′′′-{[Methanetriyltris(benzene-4,1-
+
53.80 (CH). HRMS (TOF MS AP+): m/z [M + H] calcd for
diyl)tris(azanylylidene)]tris(methanylylidene)}tris(1,1′-bi-
phenyl)-4′-carboxylic Acid (4b)
C19H20N : 290.1657; found: 290.1652. UV/vis (DMSO): λ
3
max
3
–1
–1
(
ε/dm mol cm ): 259 nm (34792), 298 nm (8418).
8) Synthesis of 4,4′,4′′-{[Methanetriyltris(benzene-4,1-diyl)-
tris(azanylylidene)]tris(methanylylidene)}tribenzoic Acid
4a)
A solution of 4′-formyl-(1,1′-biphenyl)-4-carboxylic acid (8, 203
mg, 0.89 mmol) in absolute EtOH (15 mL) was added into a
stirred solution of 4,4′,4′′-triaminotriphenylmethane (5, 78.6
mg, 0.27 mmol) in absolute EtOH (35 mL), in a dry 100 mL
single-neck round-bottomed flask. The resulting mixture was
stirred for 10 d at r.t., under an atmosphere of dry nitrogen. The
reaction mixture was then filtered under suction on a sintered
funnel to give an off-white solid which was washed successively
with EtOH, CHCl , MeCN, THF, and finally with Et O. Residual
solvent traces were removed under high vacuum to afford
product 4b as an off-white solid (157 mg, 63%). IR (ATR): νmax
2989 (br w), 2871 (br w), 2656 (br w), 2543 (br w), 2362 (br),
1697 (s), 1610 (m), 1571 (w), 1510 (m), 1413 (m), 1364 (w),
1298 (s), 1199 (m), 1168 (w), 1117 (w), 1015 (w), 962 (w), 857
(
(
A solution of 4-formylbenzoic acid (6, 189 mg, 1.25 mmol) in
absolute EtOH (15 mL) was added into a stirred solution of
4,4′,4′′-triaminotriphenylmethane (5, 110 mg, 0.38 mmol) in
absolute EtOH (40 mL), in a predried 100 mL single-neck round-
bottomed flask equipped with a magnetic stirrer. The resulting
mixture was stirred for seven days at r.t., under an atmosphere
of dry nitrogen. The reaction mixture was then filtered under
suction on a sintered funnel to give a greyish pink solid which
was washed with absolute EtOH (60 mL). Purification of the
solid was performed by column chromatography on silica gel
3
2
=
–1 1
(
CHCl –MeOH–Et N = 9:1:0.15) to afford product 4a as a grey
(w), 838 (w), 786 (m) cm . H NMR (500 MHz, DMSO-d ): δ =
3
3
6
solid (232 mg, 89%); mp 237 °C (dec.). R = 0.38 (CHCl –MeOH–
13.06 (3 H, br s, 3 × CO H), 8.72 (3 H, s, N=CH), 8.04 (13 H, br s,
f
3
2
Et N = 9:1:0.15). IR (ATR): ν
= 2991 (br w), 2879 (br w), 2667
13 × CH arom.), 7.90 (13 H, br s, 13 × CH arom.), 7.31 (5 H, br s,
3
max
(br w), 2540 (br w), 2358 (br), 2328 (br), 1691 (s), 1624 (m),
5 × CH arom.), 7.25 (5 H, br s, 5 × CH arom.), 5.76 (1 H, s, CH). 13
C
1570 (w), 1500 (m), 1421 (m), 1286 (s), 1196 (m), 1172 (w),
NMR (125 MHz, DMSO-d ): δ = 167.04 (CO H), 159.83, 159.56,
6
2
1
cm
3
112 (w), 1014 (m), 958 (w), 889 (w), 856 (w), 839 (w), 771 (s)
149.53, 143.24, 141.88, 141.58, 135.82, 129.99, 129.82, 129.29,
127.33, 126.92, 121.19, 66.98 (CH). HRMS (MALDI TOF, positive
mode, reflectron, HCCA matrix on Prespotted AnchorChip PAC II
–1
1
. H NMR (500 MHz, DMSO-d ): δ = 13.08 (3 H, br s,
6
× CO H), 8.74 (3 H, s, N=CH), 8.06 (12 H, app. q, J = 7.9 Hz, CH
2
+
arom.), 7.31 (6 H, d, J = 8.2 Hz, CH arom.), 7.23 (6 H, d, J = 8.2 Hz,
CH arom.), 5.76 (1 H, s, CH). C NMR (125 MHz, DMSO-d ): δ =
384/96): m/z [M + H] calcd for C61H44N O : 914.3225; found:
3
6
13
3
–1
–1
914.3221. UV/vis (DMSO): λmax (ε/dm mol cm ): 258 nm
6
1
66.84 (CO H), 159.61 (N=CH), 149.20 (C arom.), 142.13 (C
(57011), 303 nm (77785), 351 nm (37277).
2
arom.), 139.65 (C arom.), 132.87 (C arom.), 129.84 (CH arom.),
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2659–2662