Substituted 1,3,5-triazine hexacarboxylates as potential linkers for MOFs

Article abstract of DOI:10.3390/molecules24193480

Hexacarboxylates are promising linkers for MOFs such as NU-109 or NU-110, which possess large values for surfaces and pore volumina. Starting from 2,4,6-tris(bromoaryl)-1,3,5-triazines, palladium-catalyzed cross coupling reactions (Suzuki-Miyaura, Sonogas

Full text of DOI:10.3390/molecules24193480

molecules
Article
Substituted 1,3,5-Triazine Hexacarboxylates as
Potential Linkers for MOFs
Arne Klinkebiel, Ole Beyer and Ulrich Lüning *
Otto-Diels-Institut für Organische Chemie der Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany;
aklinkebiel@oc.uni-kiel.de (A.K.); obeyer@oc.uni-kiel.de (O.B.)
* Correspondence: luening@oc.uni-kiel.de; Tel.: +49-431-880-2450
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Received: 4 September 2019; Accepted: 24 September 2019; Published: 25 September 2019
ꢀꢁꢂꢃꢄꢅꢆ
Abstract: Hexacarboxylates are promising linkers for MOFs such as NU-109 or NU-110, which possess
large values for surfaces and pore volumina. Starting from 2,4,6-tris(bromoaryl)-1,3,5-triazines,
palladium-catalyzed cross coupling reactions (Suzuki-Miyaura, Sonogashira-Hagihara) form
elongated hexacarboxylate linkers. Eight new 2,4,6-tris(biphenyl) and 2,4,6-tris(phenylethynylphenyl)
1,3,5-triazines have been prepared in quantities ranging from 40 mg to 1.1 g. In five cases, one of the
arms of the linker carries an additional functionality (NO2 or OMe).
Keywords: ligands; metal organic framework; Sonogashira reaction; Suzuki reaction; triazine
1. Introduction
Porous metal-organic frameworks (MOFs) [1–4] are interesting materials for many applications,
for instance gas absorption and storage. Large surfaces and pore volumes have been sought after,
and excellent results were obtained when hexadendate linkers were employed in the syntheses of
MOFs [5–11]. Remarkable values for surfaces and pore volumina have been measured for NU-109 and
NU-110 (>7000 m2/g, 4 cm3/g) [10]. In these MOFs, hexadentate linkers based on 1,3,5-trisubstituted
benzenes have been used, which carry isophthalic acids at the end of each substituent.
The properties of MOFs can be altered by the introduction of additional substituents. There are
two general approaches: substituted linkers can be used, or the additional functionality is introduced
post-synthetically. However, post-synthetic modifications are rarely quantitative and are frequently
accompanied by decomposition especially when the material possesses a high porosity. Therefore,
the use of already functionalized linkers will lead to more homogeneous MOFs.
In this work, we describe the syntheses of mono-functionalized hexadentate ligands. In contrast
to the linkers used in NU-109 and NU-110, we have chosen a 1,3,5-triazine as the central aromatic ring
because triaryltriazines are more planar than triarylbenzenes [12
,13]. A variety of related tridentate and
monofunctionalized triazine linkers and have been synthesized (see Figure 1) [14]. Some of them
1
2
have already been used in the syntheses of MOFs, yielding PCN-6 analogues that contain additional
functionalities such as NO2 and NH2 [13–16].
Molecules 2019, 24, 3480; doi:10.3390/molecules24193480
www.mdpi.com/journal/molecules

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Figure 1. Tridentate mono-substituted triazine based linkers 1 and 2 [13,14]. The elongated tricarboxylic
acids 2 were synthesized from the respective tribromides 3a–c using Suzuki-Miyaura couplings.
2. Results and Discussion
For the extension of 3a–c, Suzuki-Miyaura couplings and other transition metal–catalyzed
cross-couplings can be utilized, for instance the Sonogashira-Hagihara reaction. To finally obtain
a hexacarboxylate, the coupling partners must contain two carboxylic acid functions. Hence,
isophthalic acid derivatives have to be used, many of which are commercially available or have
been described in the literature. For the syntheses of the hexadentate linkers
6 and 11, 5-boron- and
5-iodo-substituted isophthalic derivatives 4 and 5, respectively, were needed (Figure 2).
Figure 2. Necessary isophthalates
hexadentate linkers 6 and 8.
4 and 5 for the palladium catalyzed cross-coupling reactions to form
Boronate 4 is commercially available but was synthesized in this work from dimethyl isophthalate
via its 5-bromoderivative by palladium(0)-catalyzed boronation with bis(pinacolato)diboron [17].
Anhydrous conditions are necessary to avoid coupling of the brominated starting compound with the
product to give an undesired biphenyl derivative carrying four ester groups.
Diethyl iodoisophthalate
5 was synthesized from 5-aminophthalic acid. After esterification,
the iodo function was introduced by a Sandmeyer analogous iodination following a procedure from
the literature [18].
2.1. 2,4,6-Tris(biphenyl)-1,3,5-triazine Hexacarboxylates
The Suzuki-Miyaura reaction is a well-established method to connect aromatic rings. Consequently,
unsubstituted and nitro- and methoxy-substituted 2,4,6-tribromo-1,3,5-triazines 3a
with boronate (Figure 3). The respective hexamethyl hexacarboxylates could be isolated in an 81 to
88% yield. The last step in the synthesis of the functionalized hexadentate linkers , hydrolyses of the
esters , was performed with lithium hydroxide in a mixture of water and THF in an 89 to >99% yield.
–c were coupled
4
6
7
6
However, it should be noted that the esters can also be used in MOF syntheses, as long as hydrolytic
conditions are used. In these cases, the esters are hydrolysed yielding the corresponding carboxylates
as the actual linkers.

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Figure 3. Syntheses of hexadentate mono-substituted triazine based linkers 6 and 7: a) in dioxane/water
(10:1): Pd(dppf)Cl2, KOAc (6a, 88%), Pd(PPh3)4, K3PO4 (6b, 83%; 6c, 81%). b) LiOH, H2O (7a, quant.;
7b, quant.; 7c, 89%).
2.2. 2,4,6-Tris(phenylethynylphenyl)-1,3,5-triazine Hexacarboxylates
The reason to use a triazine core for linkers with three arms rather than a benzene ring - i.e. using
for instance TATB (1,3,5,-triazine-2,4,6-tribenzoate) instead of BTB (1,3,5-benzenetribenzoate), see above
and ref. [12
,13] - is the more pronounced planarity of the aromatic rings in the triaryltriazine system.
However, in the hexadentate linkers
6
and , biphenyl substructures have been generated by the
7
cross-coupling reaction. The repulsion of the ortho hydrogen atoms in the biphenyls will lead to twists
in the “arms.” This problem will even be larger if each arm contained more aryl rings—for instance,
if it was a p-terphenyl. We have therefore chosen an alternative structure by exchanging the central
aromatic ring of a potential p-terphenyl by an alkyne. NU-109 also contains aryl-alkyne-aryl subunits
instead of aryl-aryl ones as present in NU-110 [10]. In terms of coupling chemistry in the syntheses of
the linkers, Sonogashira-Hagihara couplings have to be performed instead of Suzuki-Miyaura reactions
(Figure 4).
Starting from the tribromides 3a
trimethylsilyl-protected ethyne gave 2,4,6-tris(trimethylsilylethynylphenyl)-1,3,5-triazines
94% yield. The TMS protecting groups in were easily cleaved off by treatment with potassium
–
c, a first triple Sonogashira-Hagihara coupling with
8
9
in 72 to
9
carbonate in methanol [19]. The unsubstituted and the methoxy-substituted linkers 10a and 10c could
be isolated in a >99% yield, while the nitro compound 10b could not be purified sufficiently. Therefore,
the final step, a triple Sonogashira reaction of the triynes with diethyl 5-iodoisophthalate
out with 10a and , and the hexaethyl hexacarboxylates 11a and 11c were obtained in yields of 79 and
81%. These yields correspond to >92% yield for each single coupling step.
While the hexaesters 6a could be hydrolyzed to yield the corresponding hexaacids 7a
analytically pure form (see above), we were not able to isolate the hexaacids derived from 11a or
5, was carried
c
–
c
–
c
c
in
in
a sufficiently pure form. Nevertheless, esters can be employed in MOF syntheses as well because most
solvothermal reactions conditions hydrolyze esters anyway.

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Figure 4. Syntheses of hexadentate mono-substituted alkyne containing triazine based linkers 11: a)
Pd(PPh3)4, CuI, NEt3 (9a: 75%; 9b: 72%; 9c: 94%); b) K2CO3, MeOH (10a 10c: quant.); c) Pd(PPh3)2Cl2,
,
CuI, NEt3 (11a: 79%; 11c: 81%).
3. Experimental Section
General Remarks:
ABCR, Karlsruhe, Germany), bis(triphenylphosphine)palladium(II) dichloride (98%, ABCR),
tetrakis(triphenylphosphine)palladium(0) (99%, ABCR), and trimethylsilylethyne ( , 98%, ABCR)
1,10-Bis(diphenylphosphine)ferrocene-palladium(II) chloride (99.9%,
8
were purchased and used without further purification. Dry solvents were obtained using suitable
desiccants. Other solvents were distilled before use. Melting points were measured with a Gallenkamp
MPD350.BM2.5 instrument. NMR spectra were recorded with a Bruker DRX 500 or Avance 600
instrument at 300 K (Billerica, MA, USA). Assignments are supported by COSY, HSQC, and HMBC.
Even when obtained by DEPT, the type of 13C signal is always listed as singlet, doublet, etc. All chemical
1
shifts are referenced to tetramethylsilane or the residual proton or carbon signals of the solvent. H
and 13C-NMR spectra of compounds
6, 7, 9, 10, and 11 can be found in the Supplementary Materials.
HRMS-EI mass spectra were recorded with JEOL AccuTOF GCV 4G (Tokyo, Japan). MALDI-TOF
mass spectra were recorded with a Bruker-Daltronics Biflex III (Billerica, MA, USA) with Cl-CCA
(4-chloro-α-cyanocinnamic acid) as matrix. IR spectra were recorded with a Perkin-Elmer Spectrum
100 spectrometer (Waltham, MA, USA) equipped with a Golden Gate Diamond ATR unit A-531-G.
Elemental analyses were carried out with a Euro EA 3000 Elemental Analyzer from Euro Vector (Pavia,
Italy). Traces of solvent originated from the purification step. The analytical sample of 11a was
obtained from an NMR solution.

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3.1. 2,4,6-Tris[30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-1,3,5-triazine (6a)
Under nitrogen, a solution of 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (3a, 803 mg, 1.47 mmol) [20],
dimethyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-isophthalate 1.69 g, 5.28 mmol),
potassium acetate (1.30 g, 13.2 mmol), and 1,10-bis(diphenylphosphine)ferrocene-palladium(II) chloride
(120 mg, 164 mol) in a 10:1 mixture (90 mL) of 1,4-dioxane and water was heated to reflux for 48 h.
(4,
µ
After evaporation of the dioxane, deionized water (100 mL) was added, and the aq. layer was extracted
with chloroform (3 × 100 mL). The combined organic extract was washed with brine (100 mL), dried with
magnesium sulfate, and filtered. Activated charcoal was added, and the mixture was heated and filtered
while hot. After reduction of the volume, the crude product was recrystallized from chloroform/petrol
ether, yielding 1.14 g (1.29 mmol, 88%) of a colorless solid. M. p.: >300 ◦C. 1H NMR (600 MHz, CDCl3):
δ =
8.88 (mc(d), 6 H, J = 8.1 Hz, Ar-H-3,5), 8.69 (s, 3 H, Ar-H-40), 8.56 (s, 6 H, Ar-H-20,60), 7.87 (mc(d), 6 H, J = 8.1
Hz, Ar-H-2,6), 4.01 (s, 18 H, CO2CH3) ppm. 13C NMR (150 MHz, CDCl3):
δ = 171.2 (s, tri-C-2,4,6), 166.1 (s,
CO2Me), 142.9 (s, Ar-C-1), 141.1 (s, Ar-C-10), 136.0 (s, Ar-C-4), 132.4 (d, Ar-C-20,60), 131.3 (s, Ar-C-30,50), 129.9
(d, Ar-C-40), 129.7 (d, Ar-C-3,5), 127.4 (d, Ar-C-2,6), 52.6 (q, CO2CH3) ppm. MS (MALDI, Cl-CCA): m/z =
+
e
886 [M + H] . IR (ATR):
ν
= 3005 (aryl-H), 2993 (C-H-val.), 1690 (C=O), 1609, 1581, 1509 (arom. C=C, arom.
C=N), 1435 (CH-def.), 1349 (C-N-val.), 813 (1,4-disubst. aryl, 1,3,5-trisubst. aryl) cm−1. Elemental analysis
(C51H39N3O12) (885.87): calcd. C 69.15 H 4.44 N 4.74; (C51H39N3O12
4.39 N 4.68; found C 68.26 H 4.28 N 4.81.
·0.1 CHCl3) (897.81): calcd. C 68.36 H

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3.2. 2-[30,50-Bis(methoxycarbonyl)-2-nitrobiphenyl-4-yl]-4,6-bis[30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-1,3,
5-triazine (6b)
Under nitrogen, a mixture of 2-(4-bromo-3-nitrophenyl)-4,6-bis(4-bromophenyl)-1,3,5-triazine
(3b, 100 mg, 170
µmol) [13], dimethyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-isophthalate
(4
, 245 mg, 765 mol), tetrakis(triphenylphosphine)-palladium(0) (30 mg, 26 µ
µ
mol), and potassium
phosphate (234 mg, 1.10 mmol) in a mixture of 1,4-dioxane (10 mL) and deionized water (1 mL) was
heated to reflux for 48 h. After evaporation of the dioxane in vacuo, the residue was dissolved in
water (25 mL) and extracted with chloroform (3
×
25 mL). The combined organic layer was washed
with brine (25 mL), dried with magnesium sulfate, and filtered. Activated charcoal was added to the
filtrate, and the mixture was heated and filtered through celite while hot. The solvent was evaporated
in vacuo and the residue was recrystallized from a hot mixture of toluene and n-heptane yielding
131 mg (141 µ δ = 9.33
mol, 83%) of a colorless solid, m. p.: >300 ◦C. 1H NMR (500 MHz, CDCl3):
(s, 1 H, Ar-H-3), 9.02 (d, 1 H, J = 7.0 Hz, Ar-H-5), 8.86 (d, 4 H, J = 8.0 Hz, Ar0-H-3,5), 8.75 (s, 1 H,
Ar-H-40), 8.69 (s, 2 H, Ar-H-20,60), 8.53 (s, 4 H, Ar0-H-20,60), 8.23 (s, 2 H, Ar0-H-40), 7.87 (d, 4 H, J = 8.0
Hz, Ar0-H-2,6), 7.65 (d, 1 H, J = 7.0 Hz, Ar-H-6), 4.01 (s, 12 H, Ar0-CO2CH3), 3.98 (s, 6 H, Ar-CO2CH3)
ppm. 13C NMR (125 MHz, CDCl3):
δ = 171.6 (s, tri-C-4,6), 169.3 (s, tri-C-2), 166.0 (s, Ar-CO2Me), 166.0
(s, Ar0-CO2Me), 149.1 (s, Ar-C-2), 143.3 (s, Ar0-C-1), 140.8 (s, Ar0-C-10), 138.0 (s, Ar-C-1), 137.2 (Ar-C-10),
135.2 (s, Ar0-C-4), 133.1 (d, Ar0-C-40), 132.5 (d, Ar-C-5), 132.4 (d, Ar0-C-20,60), 132.4 (d, Ar-C-6), 131.4
(s, Ar0-C-30,50), 131.3 (s, Ar-C-30,50), 130.6 (d, Ar-C-40), 130.0 (s, Ar-C-4), 129.9 (d, Ar-C-20,60), 129.7
(d, Ar0-C-3,5), 127.5 (d, Ar0-C-2,6), 124.8 (d, Ar-C-3), 52.6 (q, Ar-CO2CH3), 52.6 (q, Ar0-CO2CH3) ppm.
+
e
MS (MALDI, Cl-CCA): m/z = 931 [M + H] . IR (ATR):
ν
= 3005 (aryl-H), 2992, 2952 (C-H-val.), 1719
(C=O), 1607, 1575, 1506 (arom. C=C, arom. C=N), 1515 (NO2), 1431 (CH-def.), 1341 (C-N-val.), 817
(1,4-disubst. aryl, 1,3,4-trisubst. aryl) cm−1. Elemental analysis (C51H38N4O14) (930.87): calcd. C 65.80
H 4.11 N 6.02; found C 65.50 H 4.12 N 5.91.

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3.3.
2-[2-Methoxy-30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-4,6-bis[30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-1,3,
5-triazine (6c)
Under nitrogen, 2-(4-bromo-3-methoxyphenyl)-4,6-bis(4-bromophenyl)-1,3,5-triazine (3c, 100 mg,
175
788
µ
mol) [13], dimethyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-isophthalate (
4, 252 mg,
µmol) and potassium phosphate (234 mg, 1.10 mmol) were mixed with a mixture of 1,4-dioxane
(10 mL), and deionized water (1 mL). Tetrakis(triphenylphosphine)-palladium(0) (30 mg, 26 µmol)
was added, and the mixture was stirred for 48 h at 100 ◦C. After evaporation of the dioxane in vacuo,
chloroform (25 mL) was added to the residue, and the resulting mixture was washed with deionized
water (3
×
25 mL). The organic layer was dried with magnesium sulfate, filtered, and heated with little
activated charcoal. After filtration through celite while hot, the solvent was evaporated in vacuo until
the residue turned turbide. Recrystallization from a boiling mixture of chloroform and petrol ether (b.
p. 40–60 ◦C) yielded 130 mg (142
CDCl3):
µ
mol, 81 %) of a colorless solid, m. p.: >300 ◦C. 1H NMR (500 MHz,
= 8.88 (d, 4 H, J = 8.5 Hz, Ar0-H-3,5), 8.70 (t, 2 H, J = 1.5 Hz, Ar0-H-40), 8.67 (t, 1 H, J = 1.6 Hz,
δ
Ar-H-40), 8.55 (d, 4 H, J = 1.5 Hz, Ar0-H-20,60), 8.49 (dd, 1 H, J = 7.9 Hz, J = 1.4 Hz, Ar-H-5), 8.47 (d, 2 H,
J = 1.6 Hz, Ar-H-20,60), 8.42 (d, 1 H, J = 1.4 Hz, Ar-H-3), 7.88 (d, 4 H, J = 8.5 Hz, Ar0-H-2,6), 7.56 (d, 1 H,
J = 7.9 Hz, Ar-H-6), 4.07 (s, 3 H, Ar-OCH3), 4.01 (s, 12 H, Ar0-CO2CH3), 3.99 (s, 6 H, Ar-CO2CH3) ppm.
13C NMR (125 MHz, CDCl3):
δ = 171.2 (s, tri-C-4,6), 171.1 (s, tri-C-2), 166.3 (s, Ar-CO2Me), 166.1 (s,
Ar0-CO2Me), 156.7 (s, Ar-C-2), 143.0 (s, Ar0-C-1), 141.0 (s, Ar0-C-10), 138.7 (s, Ar-C-10), 137.4 (s, Ar-C-4),
135.9 (s, Ar0-C-4), 134.9 (d, Ar-C-20,60), 132.7 (s, Ar-C-1), 132.3 (d, Ar0-C-20,60), 131.4 (s, Ar-C-30,50).
131.0 (d, Ar-C-6), 130.5 (s, Ar0-C-30,50), 129.9 (d, Ar0-C-40), 129.7 (d, Ar0-C-3,5), 129.6 (d, Ar-C-40), 127.4
(d, Ar0-C-2,6), 121.9 (d, Ar-C-5), 111.2 (d, Ar-C-3), 55.9 (q, Ar-OCH3), 52.5 (q, Ar0-CO2CH3), 52.4 (q,
+
~
e
Ar-CO2CH3) ppm. MS (MALDI, Cl-CCA): m/z = 916 [M + H] . IR (ATR):
ν
= 3005 (aryl-H), 2954
(C-H-val.), 1728 (C=O), 1606, 1578, 1517 (arom. C=C, arom. C=N), 1429 (CH-def.), 1371 (OCH3), 1342
(C-N-val.), 809 (1,4-disubst. aryl, 1,3,4-trisubst. aryl) cm−1. Elemental analysis (C52H41N3O13) (915.89):
calcd. C 68.19 H 4.51 N 4.59; (C52H41N3O13
66.34 H 4.74 N 4.86.
·
0.2 CHCl3) (939.71): calcd. C 66.71 H 4.42 N 4.47; found C

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3.4. 2,4,6-Tris[30,50-dicarboxybiphenyl-4-yl]-1,3,5-triazine (7a)
A mixture of 2,4,6-tris[30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-1,3,5-triazine (6a, 1.04 g,
1.17 mmol) and lithium hydroxide monohyd◦rate (1.38 g, 32.8 mmol) in tetrahydrofuran (130 mL) and
deionized water (15 mL) was heated to 60 C for 48 h. After evaporation of the solvent in vacuo,
a small amount of deionized water was added, and the mixture was acidified with hydrochloric acid
(6 M). The precipitate was filtered off, washed with deionized water and chloroform, and dried in
vacuo, yielding 939 mg (1.17 mmol, > 99%) of a yellow solid, m. p.: >300 ◦C. 1H NMR (600 MHz,
DMSO-d6):
δ
= 8.76 (d, 6 H, J = 8.3 Hz, Ar-H-3,5), 8.47 (t, 3 H, J = 1.4 Hz, Ar-H-40), 8.41 (d, 6 H, J = 1.4
Hz, Ar-H-20,60), 7.94 (d, 6 H, J = 8.3 Hz, Ar-H-2,6) ppm. 13C NMR (150 MHz, DMSO-d6):
δ = 170.6 (s,
tri-C-2,4,6), 166.4 (s, CO2H), 142.5 (s, Ar-C-1), 140.0 (s, Ar-C-10), 135.0 (s, Ar-C-4), 132.2 (s, Ar-C-30,50),
131.4 (d, Ar-C-20,60), 129.5 (d, Ar-C-40), 128.8 (d, Ar-C-3,5), 127.4 (d, Ar-C-2,6) ppm. MS (MALDI,
+
e
Cl-CCA): m/z = 802 [M + H] . IR (ATR):
ν
= 3018 (br., OH), 1690 (C=O), 1603, 1578, 1508, 1412 (arom.
C=C, arom. C=N), 1367 (C-N-val.), 815 (1,3,5-trisubst. aryl) cm−1. Elemental analysis (C45H27N3O12)
(801.71): calcd. C 67.42 H 3.39 N 4.87; (C45H27N3O12
3.55 N 4.94; found C 63.87 H 3.67 N 4.87.
·
1.4 H2O 0.2 CHCl3) (850.80): calcd. C 63.81 H
·
3.5. 2-[30,50-Dicarboxy-2-nitrobiphenyl-4-yl]-4,6-bis[30,50-dicarboxybiphenyl-4-yl]-1,3,5-triazine (7b)
Asuspensionof2-[30,50-bis(methoxycarbonyl)-2-nitrobiphenyl-4-yl]-4,6-bis[30,50-bis(methoxycarbonyl)
-biphenyl-4-yl]-1,3,5-triazine (6b, 44 mg, 47 µmol) and lithium hydroxide monohydrate (101 mg, 2.41 mmol)

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◦
in a mixture of tetrahydrofuran (10 mL) and deionized water (1.5 mL) was stirred at 60 C for 24 h.
After evaporation of the tetrahydrofuran in vacuo, some deionized water was added to the residue.
Acidification with hydrochloric acid (6 M) produced a precipitate which was filtered off and washed
thoroughly with deionized water and chloroform yielding 39 mg (46 µmol, >99%) of a yellow solid, m. p.:
>300 ◦C. 1H NMR (500 MHz, DMSO-d6):
δ = 9.21 (d, 1 H, J = 1.6 Hz, Ar-H-3), 9.01 (dd, 1 H, J = 8.0 Hz, J =
1.6 Hz, Ar-H-5), 8.81 (d, 4 H, J = 8.4 Hz, Ar0-H-3,5), 8.53 (t, 1 H, J = 1.5 Hz, Ar-H-40), 8.48 (t, 2 H, J = 1.5
Hz, Ar0-H-40), 8.43 (d, 4 H, J = 1.5 Hz, Ar0-H-20,60), 8.15 (d, 2 H, J = 1.5 Hz, Ar-H-20,60), 7.98 (d, 4 H, J =
8.4 Hz, Ar0-H-2,6), 7.88 (d, 1 H, J = 8.0 Hz, Ar-H-6) ppm. 13C NMR (125 MHz, DMSO-d6):
δ = 171.4 (s,
tri-C-4,6), 169.4 (s, tri-C-2), 166.8 (s, Ar0-CO2H), 166.5 (s, Ar-CO2H), 149.3 (s, Ar-C-2), 143.3 (s, Ar0-C-1),
140.9 (s, Ar-C-4), 140.4 (s, Ar0-C-4), 137.7 (s, Ar-C-1), 137.1 (s, Ar-C-4), 136.8 (s, Ar-C-10), 135.1 (s, Ar0-C-10),
133.4 (d, Ar-C-6), 133.0 (d, Ar-C-5), 132.9 (d, Ar-C-20,60), 132.6 (s, Ar-C-30,50), 132.4 (s, Ar0-C-30,50), 131.9 (d,
Ar0-C-20,60), 130.2 (d, Ar-C-40), 130.1 (d, Ar0-C-3,5), 129.99 (s, Ar-C-10), 129.95 (Ar0-C-40), 127.9 (d, Ar0-C-2,6),
+
e
124.5 (d, Ar-C-3) ppm. MS (MALDI, Cl-CCA): m/z = 847 [M + H] . IR (ATR):
ν
= 3080 (OH), 2921, 2854
(CO2H), 1696 (C=O), 1608, 1576, 1515, 1456 (arom. C=C, arom. C=N), 1360 (C-N-val.), 1243 (NO2), 813
(1,4-disubst. aryl, 1,3,5-trisubst. aryl) cm−1. Elemental analysis (C45H26N4O14) (846.71): calcd. C 63.83 H
3.10 N 6.62; (C45H26N4O14
3.04 N 5.43.
·
0.95 CHCl3 0.05 H2O) (960.95): calcd. C 57.43 H 2.84 N 5.83; found C 57.80 H
·
3.6. 2,4-Bis[30,50-dicarboxybiphenyl-4-yl]-6-[30,50-dicarboxy-2-methoxybiphenyl-4-yl]-1,3,5-triazine (7c)
A
suspension
of
2-[2-methoxy-30,50-bis(methoxycarbonyl)-biphenyl-4-yl]-4,6-bis[30,50-bis
mol) and lithium hydroxide monohydrate
(methoxycarbonyl)-biphenyl-4-yl]-1,3,5-triazine (6c, 50 mg, 54
µ
(101 mg, 2.41 mmol) in a mixture of tetrahydrofuran (10 mL) and deionized water (1.5 mL) was heated to
60 ◦C for 24 h. After evaporation of tetrahydrofuran in vacuo, the aqueous residue was diluted slightly
with deionized water and acidified with hydrochloric acid (6 M). The precipitate was washed with
deionized water and chloroform, yielding 40 mg (48
NMR (600 MHz, DMSO-d6):
µ
mol, 89%) of a yellow solid, m. p.: >300 ◦C. 1H
δ
= 13.39 (br. s, 6 H, CO2H), 8.84 (d, 4 H, J = 8.2 Hz, Ar0-H-3,5), 8.51–8.50 (m,
2 H, Ar0-H-40), 8.48–8.47 (m, 5 H, Ar0-H-20,60, Ar-H-40), 8.44 (mc(d), 1 H, J = 7.8 Hz, Ar-H-5), 8.41 (s, 1 H,
Ar-H-3), 8.34 (mc(d), 2 H, J = 1.1 Hz, Ar-H-20,60), 8.01 (d, 4 H, J = 8.2 Hz, Ar0-H-2,6), 7.66 (d, 1 H, J = 7.8 Hz,
Ar-H-6), 4.04 (s, 3 H, OCH3) ppm. 13C NMR (150 MHz, DMSO-d6):
δ = 170.7(s, tri-C-4,6), 170.4 (s, tri-C-2),
166.5 (s, Ar-CO2H), 166.4 (s, Ar0-CO2H), 156.4 (s, Ar-C-2), 142.6 (s, Ar0-C-1), 140.0 (s, Ar0-C-10), 137.9 (s,
Ar-C-10), 136.7 (s, Ar-C-4), 135.1 (s, Ar0-C-4), 134.0 (d, Ar-C-20,60), 132.3 (s, Ar-C-1), 132.2 (s, Ar0-C-30,50),
131.5 (d, Ar-C-5), 131.3 (s, Ar-C-30,50), 131.0 (d, Ar-C-6), 129.6 (d, Ar0-C-3,5), 129.3 (d, Ar0-C-20,60), 129.0
(d, Ar0-C-40), 127.5 (d, Ar0-C-2,6), 121.6 (d, Ar-C-40), 111.2 (d, Ar-C-3), 55.8 (q, OCH3) ppm. MS (MALDI,
+
e
Cl-CCA): m/z = 832 [M + H] . IR (ATR):
ν
= 3100 (br., OH), 1692 (C=O), 1603, 1578, 1509, 1405 (arom.
C=C, arom. C=N), 1360 (C-N-val.), 1221 (aryl-OCH3), 810 (1,3,5-trisubst. aryl) cm−1. Elemental analysis

Molecules 2019, 24, 3480
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(C46H29N3O13) (831.17): calcd. C 67.42 H 3.39 N 4.87; (C46H29N3O13
C 59.47 H 3.28 N 4.44; found C 59.58 H 3.40 N 4.48.
·
0.45 H2O 0.9 CHCl3) (947.28): calcd.
·
3.7. 2,4,6-Tris{4-[(trimethylsilyl)ethynyl]-phenyl}-1,3,5-triazine (9a)
Under nitrogen, trimethylsilylethyne (8, 972 µL, 6.88 mmol) was added to a mixture of
2,4,6-tris(4-bromophenyl)-1,3,5-triazine (3a, 1.00 g, 1.83 mmol) [20] in tetrahydrofuran (200 mL)
and triethylamine (120 mL). After the addition of tetrakis(triphenylphosphine)-palladium(0) (240
mg, 208 µmol), copper(I) iodide (40 mg, 208 µmol), and triethylamine (120 mL), the mixture was
stirred for 48 h at 40 ◦C (TLC control, silica gel, cyclohexane, Rf = 0.23). Solvents were distilled off in
vacuo, and the residue was mixed with deionized water (100 mL) and extracted with ethyl acetate
(
3 × 100 mL). The combined organic layer was washed with brine (100 mL), dried with magnesium
sulfate, and filtered. The solvent was distilled off in vacuo, and the residue was dissolved in toluene
and filtered through neutral aluminium oxide. After evaporation of the solvent in vacuo, the residue
was recrystallized from boiling n-heptane yielding 826 mg (1.38 mmol, 75%) of a colorless solid, m.
1
p.: 274 ◦C (ref. [19]: no m.p. given). H NMR (600 MHz, CDCl3):
δ = 8.67 (mc(d), 6 H, J = 8.4 Hz,
Ar-H-3,5), 7.64 (mc(d), 6 H, J = 8.4 Hz, Ar-H-2,6), 0.30 (s, 27 H, Si(CH3)3) ppm. 13C NMR (150 MHz,
CDCl3): = 171.0 (s, tri-C-2,4,6), 135.7 (s, Ar-C-1), 132.2 (d, Ar-C-2,6), 128.7 (d, Ar-C-3,5), 127.4 (s,
Ar-C-4), 104.7 (s, Ar-C C), 97.5 (s, Ar-C C), 0.0 (s, Si(CH3)3) ppm. HRMS (EI): m/z = calcd. 597.2451;
found 597.2441 ( 1.78 ppm). Elemental analysis (C36H39N3Si3) (597.97): calcd. C 72.31 H 6.57 N 7.03;
δ
≡
≡
∆
found C 72.17 H 6.52 N 6.93.
3.8. 2-{3-Nitro-4-[(trimethylsilyl)ethynyl]-phenyl}-4,6-bis{4-[(trimethylsilyl)ethynyl]-phenyl}-1,3,5-triazine (9b)

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Under nitrogen, tetrakis(triphenylphosphine)-palladium(0) (88 mg, 77
copper(I) iodide (15 mg, 77
4,6-bis(4-bromophenyl)-1,3,5-triazine (3b, 500 mg, 850
µ
mol) and
µ
mol) were added to a mixture of 2-(4-bromo-3-nitrophenyl)-
µ
mol) [13] in tetrahydrofuran (100 mL) and
triethylamine (60 mL). After the addition of trimethylsilylethyne (8, 726 µL, 5.10 mmol), the mixture was
stirred for 48 h at 55 ◦C (TLC control, silica gel, cyclohexane/ethyl acetate, 10:1, Rf = 0.76). The solvent
was evaporated in vacuo, and chloroform (150 mL) was added to the residue. The organic layer was
washed with deionized water (3
charcoal was added, and the mixture was heated and filtered through celite and silica gel. The solvent
×
100 mL), dried with magnesium sulfate, and filtered. Activated
was evaporated in vacuo, and the crude product was recrystallized from boiling n-heptane yielding
391 mg (608
1 H, J = 1.4 Hz, Ar-H-2), 8.88 (dd, 1 H, J = 8.1 Hz, J = 1.4 Hz, Ar-H-6), 8.67 (d, 4 H, J = 8.4 Hz, Ar0-H-2,6),
7.82 (d, 1 H, J = 8.1 Hz, Ar-H-5), 7.65 (d, 4 H, J = 8.4 Hz, Ar0-H-3,5), 0.32 (s, 9 H, Ar-C
C-Si(CH3)3),
= 171.4 (s, tri-C-4,6), 169.2 (s,
µ δ = 9.31 (d,
mol, 72%) of a colorless solid, m. p.: 273–275 ◦C. 1H NMR (500 MHz, CDCl3):
≡
0.30 (s, 18 H, Ar0-C C-Si(CH3)3) ppm. 13C NMR (125 MHz, CDCl3):
δ
≡
tri-C-2), 150.7 (s, Ar-C-3), 136.9 (s, Ar-C-1), 135.4 (d, Ar-C-5), 135.2 (s, Ar0-C-1), 132.3 (d, Ar0-C-3,5),
132.2 (d, Ar-C-6), 128.8 (d, Ar-C-2,6), 127.9 (s, Ar0-C-4), 124.7 (d, Ar-C-2), 121.7 (s, Ar-C-4), 107.2 (s,
Ar-C
Ar-C
≡
C), 104.5 (s, Ar-C
≡
C), 99.2 (s, Ar0-C
≡
C), 98.0 (s, Ar0-C
≡
C), 0.3 (q, Ar0-C
≡
C-Si(CH3)3), 0.0 (q,
C), 1603, 1570,
e
≡
C-Si(CH3)3) ppm. IR (ATR):
ν
= 3005 (aryl-H), 2957, 2901 (C-H-val.), 2155 (C
≡
1504, 1407 (arom. C=C, arom. C=N), 1537 (NO2), 1355 (C-N-val.), 838 (1,4-disubst. aryl, 1,3,4-trisubst.
aryl) cm−1. HRMS (EI): m/z = calcd. 642.2302; found 642.2295 (
∆ 1.11 ppm). Elemental analysis
(C36H38N4O2Si3) (642.97): calcd. C 67.25 H 5.96 N 8.71; found C 67.32 H 6.25 N 8.46.
3.9. 2-{3-Methoxy-4-[(trimethylsilyl)ethynyl]-phenyl}-4,6-bis{4-[(trimethylsilyl)ethynyl]-phenyl}-1,3,
5-triazine (9c)
Under nitrogen, tetrakis(triphenylphosphine)-palladium(0) (45 mg, 39
copper(I) iodide (8 mg, 0.04 mmol) were added to mixture of 2-(4-bromo-3-
methoxyphenyl)-4,6-bis(4-bromophenyl)-1,3,5-triazine (3c, 250 mg, 434 mol) [13] in tetrahydrofuran
(50 mL) and triethylamine (30 mL). Trimethylsilylethyne ( , 370 L, 2.60 mmol) was added and the
mixture was stirred for 48 h at 55 ◦C. After removal of the volatiles in vacuo, the residue was dissolved
in chloroform (50 mL) and washed with deionized water (3 50 mL). The organic layer was dried
µmol) and
a
µ
8
µ
×
with magnesium sulfate, filtered, and heated with activated charcoal. After filtration through celite,
the solvent was removed in vacuo. The residue was recrystallized from boiling n-heptane yielding 255
mg (406 µ δ = 8.67 (mc(d), 4 H,
mol, 94%) of a colorless solid, m. p. 212 ◦C. 1H NMR (500 MHz, CDCl3):
J = 8.7 Hz, Ar0-H-2,6), 8.31 (dd, 1 H, J = 8.0 Hz, J = 1.4 Hz, Ar-H-6), 8.24 (d, 1 H, J = 1.4 Hz, Ar-H-2),
7.65 (mc(d), 4 H, J = 8.7 Hz, Ar0-H-3,5), 7.61 (d, 1 H, J = 8.0 Hz, Ar-H-5), 4.08 (s, 3 H, OCH3), 0.31 (s, 9
H, Ar-C
≡
C-Si(CH3)3), 0.29 (s, 18 H, Ar0-C C-Si(CH3)3) ppm. 13C NMR (125 MHz, CDCl3):
δ = 171.0
≡
(s, tri-C-4,6), 171.0 (s, tri-C-2), 160.6 (s, Ar-C-3), 137.4 (s, Ar-C-1), 135.7 (s, Ar0-C-1), 134.3 (d, Ar-C-2),
132.3 (d, Ar0-C-3,5), 128.7 (d, Ar0-C-2,6), 127.5 (s, Ar0-C-4), 121.2 (d, Ar-C-6), 116.8 (s, Ar-C-4), 110.5 (d,

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Ar-C-5), 104.6 (s, Ar-C
≡
C), 101.8 (s, Ar-C
≡
C), 100.9 (s, Ar0-C
≡
C), 97.6 (s, Ar0-C
≡
C), 56.2 (q, OCH3), 0.00
(s, Ar-C
2903 (OCH3), 2060 (C
≡
C-Si(CH3)3), 0.01 (q, Ar0-C
≡
C-Si(CH3)3) ppm. IR (ATR):
ν
= 3005 (aryl-H), 2972 (C-H-val.),
e
≡
C), 1606. 1570, 1511, 1407 (arom. C=C, arom. C=N), 1357 (C-N-val.), 813
(1,4-disubst. aryl, 1,3,4-trisubst. aryl) cm−1. HRMS (EI): m/z = calcd. 672.2557; found 672.2543 (
∆
2.38
0.3
ppm). Elemental analysis (C37H41N3OSi3) (628.00): calcd. C 70.76 H 6.58 N 6.69; (C37H41N3OSi3
C7H16·0.4 H2O) (664.93): calcd. C 70.63 H 7.06 N 6.32; found C 70.97 H 6.78 N 5.99.
·
3.10. 2,4,6-Tris(4-ethynylphenyl)-1,3,5-triazine (10a)
A mixture of 2,4,6-tris{4-[(trimethylsilyl)ethynyl]-phenyl}-1,3,5-triazine (9a, 500 mg, 835 µmol)
and potassium carbonate (1.04 g, 7.50 mmol) in methanol (25 mL) was stirred for 24 h at room temp.
(TLC control, silica gel, cyclohexane, Rf = 0.15). After evaporation of the methanol, the residue was
dissolved in deionized water (25 mL) and extracted with chloroform (3
layer was washed with brine (25 mL) and dried with magnesium sulfate. After filtration and removal
of the solvent in vacuo, the crude product was recrystallized from a boiling mixture of toluene and
×
25 mL). The combined organic
n-heptane, yielding 315 mg (827
given). H NMR (500 MHz, CDCl3):
µ
mol, >99%) of a yellowish solid, m. p. >300 ◦C (ref. [19]: no m.p.
1
δ
= 8.63 (mc(d), 6 H, J = 8.9 Hz, Ar-H-3,5), 7.61 (mc(d), 6 H, J = 8.9
Hz, Ar-H-2,6), 3.24 (s, 3 H, C
(s, Ar-C-1), 132.2 (d, Ar-C-2,6), 128.6 (d, Ar-C-3,5), 126.3 (s, Ar-C-4), 83.10 (s, C
≡
CH) ppm. 13C NMR (125 MHz, CDCl3):
δ
= 170.9 (s, tri-C-2,4,6), 135.9
≡
CH), 80.0 (d, C CH)
≡
e
ppm. IR (ATR):
ν
= 3236 (C
≡
C-H), 3002 (aryl-H), 2160 (C C), 1606, 1574, 1505, 1408 (arom. C=C, arom.
≡
C=N), 1357 (C-N-val.), 813 (1,4-disubst. aryl) cm−1. HRMS (EI): m/z = calcd. 381.1266; found 381.1251
(
∆
3.85 ppm). Elemental analysis (C27H15N3) (381.43): calcd. C 85.02 H 3.96 N 11.02; found C 85.24 H
3.94 N 10.64.
3.11. 2,4-Bis(4-ethynylphenyl)-6-(3-methoxy-4-ethynylphenyl)-1,3,5-triazine (10c)
A mixture of 2-{3-methoxy-4-[(trimethylsilyl)ethynyl]-phenyl}-4,6-bis{4-[(trimethylsilyl)ethynyl]-
phenyl}-1,3,5-triazine (9c, 150 mg, 239
(7.5 mL) was stirred for 24 h at room temp. After evaporation of the solvent in vacuo, the residue was
dissolved in chloroform (25 mL) and washed with water (3 25 mL). The organic layer was dried
µmol) and potassium carbonate (297 mg, 2.15 mmol) in methanol
×

Molecules 2019, 24, 3480
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with magnesium sulfate, filtered, and the solvent was evaporated in vacuo. The crude product was
recrystallized from a boiling mixture of toluene and n-heptane, yielding 98 mg (239 mol, >99%) of
10c, m. p. >300 ◦C. 1H NMR (600 MHz, CDCl3): = 8.71 (d, 4 H, J = 8.3 Hz, Ar0-H-2,6), 8.35 (dd, 1 H,
J = 7.8 Hz, J = 1.2 Hz, Ar-H-6), 8.29 (br. s, 1 H, Ar-H-2), 7.70 (d, 4 H, J = 8.3 Hz, Ar0-H-3,5), 7.66 (d, 1 H,
J = 7.8 Hz, Ar-H-5), 4.12 (s, 3 H, OCH3), 3.50 (s, 1 H, Ar-C
CH), 3.28 (s, 1 H, Ar0-C CH) ppm. 13C NMR
(150 MHz, CDCl3):
= 171.1 (s, tri-C-2), 171.1 (tri-C-4,6), 160.5 (s, Ar-C-3), 136.1 (s, Ar0-C-1), 134.3 (d,
Ar-C-5), 132.4 (d, Ar0-C-3,5), 131.9 (s, Ar-C-1), 128.8 (d, Ar0-C-2,6), 126.4 (s, Ar0-C-4), 121.2 (d, Ar-C-6),
µ
δ
≡
≡
δ
115.5 (s, Ar-C-4), 83.7 (d, Ar-C
(q, OCH3) ppm. HRMS (EI): m/z = calcd. 411.1371; found 411.1367 (
3246 (C C-H), 3008 (aryl-H), 2970 (OCH3), 2926 (C-H-val.), 2160 (C
≡
CH), 83.2 (s, Ar0-C
≡
CH), 79.7 (s, Ar-C
≡
CH), 79.7 (d, Ar0-C
1.13 ppm). IR (ATR):
≡
CH), 56.0
e
∆
ν
= 3280,
≡
≡
C), 1606, 1574, 1504, 1408 (arom.
C=C, arom. C=N), 1437 (C-H-def.), 1353 (C-N-val.), 812 (1,4-disubst. aryl, 1,3,4-trisubst. aryl) cm−1
3.12. 2,4,6-Tris{4-[3,5-bis(ethoxycarbonyl)phenylethynyl]-phenyl}-1,3,5-triazine (11a)
.
Under nitrogen, 2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine (10a, 50.0 mg, 131
5-iodoisophthalate ( , 171 mg, 491 mol) were dissolved in a mixture of tetrahydrofuran (6 mL) and
triethylamine (4 mL). Bis(triphenylphosphine)-palladium(II) dichloride (10 mg, 14 mol) and copper(I)
iodide (3.0 mg, 14
mol) were added, and the mixture was stirred for 48 h at 50 ◦C. After evaporation
of the solvents in vacuo, chloroform (25 mL) was added to the residue. The organic layer was washed
with deionized water (3 25 mL) and brine (25 mL). After drying with magnesium sulfate and filtration,
µmol) and diethyl
5
µ
µ
µ
×
the solvent was removed in vacuo. The crude product was recrystallized from a boiling mixture of
toluene and n-heptane, yielding 108 mg (104 umol, 79%) of a yellowish solid, m. p. >300 ◦C. 1H NMR
(500 MHz, CDCl3):
J = 1.6 Hz, Ar0-H-2,6), 7.74 (d, 6 H, J = 8.4 Hz, Ar-H-3,5), 4.44 (q, 12 H, J = 7.1 Hz, CO2CH2CH3), 1.45 (t,
18 H, J = 7.1 Hz, CO2CH2CH3) ppm. 13C NMR (125 MHz, CDCl3):
= 171.0 (s, tri-C-2,4,6), 165.1 (s,
δ
= 8.75 (d, 6 H, J = 8.4 Hz, Ar-H-2,6), 8.64 (t, 3 H, J = 1.6 Hz, Ar0-H-4), 8.39 (d, 6 H,
δ
CO2Et), 136.5 (d, Ar0-C-2,6), 136.0 (s, Ar-C-1), 132.0 (d, Ar-C-3,5), 131.4 (s, Ar0-C-3,5), 130.3 (d, Ar0-C-4),
129.0 (d, Ar-C-2,6), 126.9 (s, Ar-C-4), 123.9 (s, Ar0-C-1), 90.9 (s, Ar-C
(t, CO2CH2CH3), 14.3 (q, CO2CH2CH3) ppm. MS (MALDI, Cl-CCA): m/z = 1042 [M + H] . IR (ATR):
= 3005 (aryl-H), 2985 (C-H-val.), 1690 (C=O), 1607, 1509 (arom. C=C, arom. C=N), 1429 (CH-def.),
1356 (C-N-val.), 825 (1,4-disubst. aryl, 1,3,5-trisubst. aryl) cm−1. Elemental analysis (C63H51N3O12)
≡
C-Ar0), 90.3 (s, Ar-C
≡
C-Ar0), 61.6
+
e
ν
(1042.04): calcd. C 72.61 H 4.93 N 4.03; (C63H51N3O12
3.90; found C 70.20 H 4.68 N 4.28.
·0.3 CDCl3) (1077.85): calcd. C 70.53 H 4.80 N

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3.13. 2-{4-[3,5-Bis(ethoxycarbonyl)phenylethynyl]-3-methoxy-phenyl}-4,6-bis{4-[3,5-bis(ethoxycarbonyl)
phenylethynyl]-phenyl}-1,3,5-triazine (11c)
Under nitrogen, 2,4-bis(4-ethynylphenyl)-6-(3-methoxy-4-ethynylphenyl)-1,3,5-triazine (10c, 50.0 mg,
122
tetrahydrofuran(6mL)andtriethylamine(4mL).Aftertheadditionofbis(triphenylphosphine)-palladium(II)
dichloride (10 mg, 14 mol) and copper(I) iodide (3.0 mg, 14
mol), the mixture was stirred at 50 ◦C for
48 h. After evaporation of the volatiles, chloroform (25 mL) was added, and the mixture was extracted
with deionized water (3 25 mL) and brine (25 mL). The organic layer was dried with magnesium sulfate,
filtered, and the solvent was evaporated in vacuo. The crude product was recrystallized from a boiling
mixture of toluene n-heptane, yielding 106 mg (98.8
mol, 81%) of a yellowish solid, m. p. >300 ◦C.
1H NMR (500 MHz, CDCl3):
µmol) and diethyl 5-iodoisophthalate (5, 159 mg, 456 µmol) were dissolved in a mixture of
µ
µ
×
µ
δ
= 8.79 (d, 4 H, J = 8.2 Hz, Ar0-H-2,6), 8.66 (s, 2 H, Ar0-H-40), 8.65 (s, 1 H,
Ar-H-40), 8.44 (d, 2 H, J = 1.2 Hz, Ar-H-20,60), 8.43–8.41 (m, 5 H, Ar0-H-20,60, Ar-H-6), 8.35 (s, 1 H, Ar-H-2),
7.77 (d, 4 H, J = 8.2 Hz, Ar0-H-3,5), 7.72 (d, 1 H, J = 7.9 Hz, Ar-H-5), 4.48–4.42 (m, 12 H, OCH2CH3), 4.18 (s,
3 H, OCH3), 1.48–1-39 (m, 18 H, OCH2CH3) ppm. 13C NMR (125 MHz, CDCl3):
δ = 171.1 (s, tri-C-2), 171.0
(s, tri-C-4,6), 165.2 (s, Ar0-COEt), 165.1 (s, Ar-COEt), 161.0 (s, Ar-C-3), 136.5 (d, Ar-C-20,60), 136.5 (s, Ar-C-1),
136.0 (s, Ar0-C-1), 135.3 (d, Ar0-C-20,60), 133.9 (d, Ar-C-5), 132.1 (d, Ar0-C-3,5), 131.4 (s, Ar0-C-30,50), 131.3 (s,
Ar-C-30,50), 130.3 (d, Ar0-C-40), 130.0 (d, Ar-C-4), 129.0 (d, Ar0-C-2,6), 127.0 (s, Ar0-C-4), 121.4 (d, Ar-C-6),
116.20(s, Ar-C-4), 110.9 (d, Ar-C-2), 94.0 (s, Ar-C
≡
C), 90.7 (s, Ar0-C
≡
C), 90.1 (s, Ar0-C
≡
C), 87.8 (Ar-C C), 61.7
≡
e
(t, Ar -CO-CH2CH3), 61.6 (t, Ar-CO-CH2CH3), 56.1 (q, OCH3), 14.4 (q, OCH2CH3) ppm. IR (ATR):
ν
= 3075
(aryl-H), 2985, 2941 (C-H-val.), 1721 (C=O), 1599, 1569 (arom. C=C, arom. C=N), 1444 (CH-def.), 1366
(C-N-val.), 810 (1,4-disubst. aryl, 1,3,5-trisubst. aryl) cm−1. MS (MALDI, Cl-CCA): m/z = 1073 [M + H]+.
4. Conclusions
Extended, mono-substituted triazine-based hexacarboxylates have been synthesized starting
from mono-nitro and mono-methoxy substituted 2,4,6-tris(4-bromophenyl)-1,3,5-triazines 3b and
Five new extended hexaesters were obtained by either Suzuki-Miyaura coupling ( ) or two subsequent
Sonogashira-Hagihara couplings (11) in good yields and large quantities (up to >1 g). Hydrolyses of the
hexaesters to give hexacarboxylic acids were successful. Five of the new linkers carry an additional
functional group in one of the arms (NO2 or OMe). The extended linkers , or 11 must now be
c.
6
6
7
6, 7
employed in MOF syntheses, in the hope that the stiff structure of the linkers allows the formation of
isoreticular structures, as already observed for tridentate triazine–based linkers [14]. The influence

Molecules 2019, 24, 3480
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of the additional substituent, nitro or methoxy, on MOF formation and on MOF properties has to be
studied. Further modification of the substituents should also be possible. In the tridentate analogues,
for instance 2, reduction of the nitro group to give an amino group and cleavage of the methoxy group
to give a hydroxy function were successful [13].
Supplementary Materials: 1H and 13C-NMR spectra of compounds 6, 7, 9, 10, and 11 are available online.
Author Contributions: Conceptualization, U.L.; Data curation, A.K. and O.B.; Formal analysis, A.K. and O.B.;
Funding acquisition, U.L.; Investigation, A.K. and O.B.; Methodology, A.K. and O.B.; Project administration, U.L.;
Resources, U.L.; Supervision, U.L.; Writing—original draft, U.L., A.K. and O.B.; Writing—review & editing, U.L.
Funding: This work was supported by the Deutsche Forschungsgemeinschaft (Lu 378/24) as part of the priority
program SPP 1362 (porous metal-organic frameworks).
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds are not available.
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2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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