Solvent-free synthesis of some triazole-based bis(N-heterocyclic carbene) ligands

Article abstract of DOI:10.3184/174751911X13220695999324

Two series of bistriazolium dibromides with different alkyl bridged length (n = 2-4) were synthesised through a simple solvent-free method. Six of these compounds were prepared from the reaction of 1-R-1H-1,2,4-triazole with dibromoalkane in moderate to excellent yield (45-98%). However, the other six compounds were prepared from the reaction of alkyl bridged bistriazole with bromoalkane in 55-99% yield. All compounds are new and were fully characterised by IR, NMR and elemental analyses.

Full text of DOI:10.3184/174751911X13220695999324

6
86 RESEARCH PAPER
DECEMBER, 686–688
JOURNAL OF CHEMICAL RESEARCH 2011
Solvent–free synthesis of some triazole-based bis(N-heterocyclic carbene)
ligands
a
a
a
a
a,c
b
Jianfeng Zhao , Long Yang , Lingqiao Zhang , Jin Guo , Yanhui Shi *, Guangsheng Pang
a
and Changsheng Cao
a
School of Chemistry and Chemical Engineering and Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials,
Xuzhou Normal University, Xuzhou, Jiangsu 221116, P. R. China
bState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, Jilin 130012,
P. R. China
cState Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, Jiangsu 210093, P. R. China
Two series of bistriazolium dibromides with different alkyl bridged length (n = 2–4) were synthesised through a
simple solvent-free method. Six of these compounds were prepared from the reaction of 1-R-1H-1,2,4-triazole with
dibromoalkane in moderate to excellent yield (45–98%). However, the other six compounds were prepared from
the reaction of alkyl bridged bistriazole with bromoalkane in 55–99% yield. All compounds are new and were fully
characterised by IR, NMR and elemental analyses.
Keywords: solvent free method, N-heterocyclic carbene ligand, bistriazolium dibromides
N-heterocyclic carbenes (NHCs) have proven to be versatile
Starting from 1H-1,2,4-triazoles, the two series of bistriazole
salts were prepared in two ways (Scheme 1). In the first way,
compounds 1–6 were synthesised by the reaction of 2 equiv.
of N-alkyl triazoles which were generated from 1H-1,2,4-
triazole, with dibromoalkanes. As both N-alkyl triazoles and
dibromoalkanes are liquid at room temperature, completion of
the reactions was easily monitored by the formation of solid
compounds in the reaction mixture. The other way was that
bridged bistriazoles generated from 1H-1,2,4-triazole reacted
with 2 equiv. of bromoalkanes to produce compounds 7–12.
As bridged bistriazoles are melted at elevated temperatures,
the reactions actually took place homogenously as well. In
order to optimise the reaction conditions, the effects of reaction
temperature were tested on compound 1 (Table 1, entries 1–6).
The results showed that the better yield was obtained with
higher temperature when the reaction was heated from 80 to
120 °C for 6 hours. For example, no product can be produced
at 80 °C compared to 63% of yield at 120 °C. However, the
yield was reduced at 130 °C probably due to a byproduct
generated at high temperature. Then, the reaction was tested at
120 °C for an optimised reaction time (Table 1, entries 8–10).
The results showed that the reaction could be completed within
1
–5
ligands in organometallic chemistry and catalysis. Despite
the large library of NHC ligands available, there are a relatively
scarce number of such ligands containing triazole-based
6–11
rings.
Triazolylidenes are an interesting class of NHCs
because the presence of the three nitrogen atoms in the azole
rings provides asymmetry and reduces the electron donation of
the ligands. Furthermore, the asymmetric distribution of the
nitrogens in the azole rings allows two different structures only
by exchanging the position of the linkers between the azole
rings and the terminal groups. We have been interested in the
chemistry of bis-carbene ligands due to their higher stability to
heat and air, and their improved catalytic performances.
Previously, we have reported the synthesis of bis-NHC ligands
1
2
based on imidazole, and also developed a preparation of a
1
3,14
series of imidazolium salts under solvent-free procedure.
Asanextensiontopreviouswork, wenowreportthepreparation
of two series of triazole-based bis-NHC ligands under solvent-
free conditions using 1H-1,2,4-triazole as a building block.
Compared with conventional methods, this protocol features
short reaction times, good yields, an eco-friendly process and
easy control and handling.
Scheme 1 Synthesis of alkyl-bridged bis-triazolium dibromides.
Correspondent. E-mail: yhshi_2000@126.com
*

JOURNAL OF CHEMICAL RESEARCH 2011 687
Table 1 Reaction conditions of alkyl-bridged bis-triazolium
1,1′-Di-n-butyl-4,4′-(1,3-propanediyl)bistriazolium dibromide (2):
dibromides
M.p. 158.2–159 °C. IR (KBr): 3105, 3025, 2956, 2875, 1577, 1462,
1
1
391, 1282, 1158, 1074, 694, 619. H NMR (400 MHz, DMSO-d ):
6
Entry
Product
Temp.
/°C
Time
/h
Isolated
yield /%
δ = 10.49 (s, 2H, NCHN), 9.43 (s, 2H, NCHN), 4.41 (m, 8H, NCH2),
.56 (m, 2H, CH CH CH ), 1.86 (m, 4H, NCH CH ), 1.32 (m, 4H,
2
2
2
2
2
2
13
1
2
3
4
5
6
7
8
9
1
1
80
90
6
6
6
6
6
6
1
2
3
4
4
4
4
4
4
4
4
4
4
4
4
None
17
68
58
63
44
42
58
75
71
98
86
43
86
99
50
72
80
55
70
75
CH CH ), 0.91 (t, J = 7.2 Hz, 6H, CH ). C NMR (100 MHz, DMSO-
2
3
3
d ): δ = 144.5, 142.6, 51.3, 44.2, 29.8, 28.5, 18.7, 13.2. Anal. Calcd
6
−
1
1
100
110
120
130
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
for C H Br N (452.23 g mol ): C, 39.84; H, 6.24; N, 18.58. Found:
15 28 2 6
1
C, 39.57; H, 6.36; N, 18.44%.
1,1′-Di-n-butyl-4,4′-(1,4-butanediyl)bistriazolium dibromide (3):
1
1
M.p. 157.5–159.7 °C. IR (KBr): 3113, 3028, 2956, 2873, 1576, 1454,
1
1
1
386, 1156, 1073, 637, 619. H NMR (400 MHz, DMSO-d ):
6
1
δ = 10.51 (s, 2H, NCHN), 9.43 (s, 2H, NCHN), 4.38 (m, 8H, NCH2),
.85 (m, 4H, NCH CH ), 1.93–1.82 (m, 4H, CH CH ), 1.31 (m, 4H,
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8
9
0
1
1
13
CH CH ), 0.91 (t, J = 7.2 HZ, 6H, CH ). C NMR (100 MHz, DMSO-
2
3
3
2
d ): δ = 144.5, 142.4, 51.3, 46.6, 29.9, 25.3, 18.6, 13.2. Anal. Calcd
6
3
−
1
for C H Br N (466.26 g mol ): C, 41.22; H, 6.49; N, 18.02. Found:
16
30
2
6
4
C, 41.54; H, 6.27; N, 18.25%.
,1′-Di-benzyl-4,4′-(1,2-ethanediyl)bistriazolium dibromide (4):
M.p. 257–258 °C. IR (KBr): 3098, 3032, 2963, 2920, 2341, 1570,
5
1
6
7
1
1
456, 1431, 1154, 1066, 726. 641. H NMR (400 MHz, DMSO-d ):
8
6
9
δ = 10.40 (s, 2H, NCHN), 9.31 (s, 2H, NCHN), 7.49–7.39 (m, 10H,
13
10
11
12
ArH), 5.70 (s, 4H, Ar-CH ), 4.90 (s, 4H, CH ). C NMR (100 MHz,
2 2
DMSO-d ): δ = 145.0, 143.1, 132.9, 129.0, 128.9 128.8, 54.8, 46.6.
6
−1
Anal. Calcd for C H Br N (506.24 g mol ): C, 47.45; H, 4.38; N,
20
22
2
6
1
6.60. Found: C, 47.31; H, 4.53; N, 16.77%.
,1′-Di-benzyl-4,4′-(1,3-propanediyl)bistriazolium dibromide (5):
M.p. 220–221 °C. IR (KBr): 3098, 3020, 2963, 2933, 2341, 1571,
1
1
1
455, 1431, 1148, 1047, 716. 644. H NMR (400 MHz, DMSO-d ):
6
4
h. The reaction time was largely shortened to a few hours
δ = 10.52 (s, 2H, NCHN), 9.41 (s, 2H, NCHN), 7.51–7.40 (m, 10H,
ArH), 5.68 (s, 4H, Ar-CH ), 4.43 (t, J = 7.2 Hz, 4H, CH ), 2.55 (m, 2H,
because of an enhancement in kinetics due to the high concen-
tration of the reactants in the solvent-free conditions. Therefore,
1
2
2
13
CH2). C NMR (100 MHz, DMSO-d ): δ = 144.9, 142.8, 133.0,
6
20 °C and 4 hours were chosen for the rest of the reactions.
1
28.9, 128.8, 128.7, 54.7, 44.4, 28.4. Anal. Calcd for C H Br N
21 24 2 6
1
−
The detailed reaction conditions and isolated yields of the
products are shown in Table 1. The yield of products is higher
with a bridged chain of three and four carbons between the
triazoles.
In conclusion, we have demonstrated a solvent-free method
to prepare various bistriazolium bromides. The advantages
of this procedure are shorter reaction times, environmental
friendliness, mild reaction conditions, and good yields.
(520.26 g mol ): C, 48.48; H, 4.65; N, 16.15. Found: C, 48.67; H,
4.46; N, 15.91%.
1,1′-Di-benzyl-4,4′-(1,4-butanediyl)bistriazolium dibromide (6):
M.p. 192.6–193.6 °C. IR (KBr): 3098, 3023, 2953, 2933, 2341, 1574,
1
1
455, 1432, 1147, 725, 641. H NMR (400 MHz, DMSO-d ):
6
δ = 10.42 (s, 2H, NCHN), 9.33 (s, 2H, NCHN), 7.48–7.42 (m, 10H,
ArH), 5.66 (s, 4H, Ar-CH ), 4.34 (m, 4H, CH ), 1.92 (m, 4H,
2
2
13
CH2). C NMR (100 MHz, DMSO-d ): δ = 144.9, 142.7, 133.1,
6
1
28.9, 128.8, 128.7, 54.6, 46.7, 25.3. Anal. Calcd for C H Br N
22 26 2 6
1
−
(
534.29 g mol ): C, 49.46; H, 4.90; N, 15.73. Found: C, 49.67; H,
4.69; N, 15.51%.
,4′-Di-n-butyl-1,1′-(1,2-ethanediyl)bistriazolium dibromide (7):
M.p. 218–219 °C. IR (KBr): 2929, 1818, 1584, 1524, 1423, 1574,
Experimental
4
General procedures: All reagents were commercially available and
were used without further purification. H NMR spectra were recorded
on a Bruker DPX 400 MHz spectrometer at room temperature and
referenced to the residual H signals of the solvent. Coupling con-
1
1
1
167, 1072, 722, 624. H NMR (400 MHz, DMSO-d ): δ = 10.41
6
1
(s, 2H, NCHN), 9.39 (s, 2H, NCHN), 5.00 (s, 4H, NCH ), 4.30
2
(
t, J = 7.2 Hz, 4H, NCH ), 1.80 (m, J = 7.2 Hz, 4H, CH ), 1.29 (m, 4H,
2 2
13
stants J are given in Hz. IR spectra were recorded on KBr pellets on a
FTIR-Tensor 27 spectrometer. Melting points were detected by micro-
scope melting point apparatus. Elemental analyses were performed on
a EuroVektor Euro EA-300 elemental analyser. All compounds are
unknown compounds, so they are fully characterised by IR, NMR
spectroscopy and elemental analyses.
Typical procedure: Method 1: N-alkyl triazoles (2 mmol) and
dibromoalkane (1 mmol) were heated to 120 °C for 4 h in a 10 mLAce
pressure tube. The complete change of the colourless solution to a
white solid is the sign of the completion of the reaction. After comple-
tion, the reaction mixture was cooled to room temperature and was
washed with acetone to give a pure product, which was dried under
vacuum. Method 2: N, N′-bridged bistriazoles (1 mmol) and bromoalk-
ane (2 mmol) were heated to 120 °C for 4 h in a 10 mL Ace pressure
tube. The complete change of the colourless solution to a white solid
is the sign of the completion of the reaction. After completion, the
reaction mixture was cooled to room temperature and was washed
with acetone to give a pure product, which was dried under vacuum.
CH ), 0.90 (t, J = 7.2 Hz, 6H, CH ). C NMR (100 MHz, DMSO-d ):
2
3
6
δ = 144.8, 143.6, 49.7, 47.2, 30.6, 18.6, 13.2. Anal. Calcd for
−1
C H Br N (438.20 g mol ): C, 38.37; H, 5.98; N, 19.18. Found: C,
14 26
2
6
38.62; H, 5.86; N, 19.29%.
4,4′-Di-n-butyl-1,1′-(1,3-propanediyl)bistriazolium dibromide (8):
M.p. 188–190 °C. IR (KBr): 2961, 1818, 1577, 1523, 1455, 1159,
1
1074, 753, 625. H NMR (400 MHz, DMSO-d
): δ = 10.43(s, 2H,
), 2.52 (m, 2H,
), 0.90 (t, J = 7.2 Hz, 6H,
): δ = 144.6, 142.8, 48.3, 47.2,
6
6
NCHN), 9.37 (s, 2H, NCHN), 4.52 (m, 8H, NCH
2
CH
), 1.84 (m, 4H, CH
). C NMR (100 MHz, DMSO-d
30.6, 27.0, 18.7, 13.2. Anal. Calcd for C15H28Br N (452.23 g mol ):
), 1.33 (m, 4H, CH
2
2
2
13
CH
3
−
1
2 6
C, 39.84; H, 6.24; N, 18.58. Found: C, 39.61; H, 6.15; N, 18.73%.
4,4′-Di-n-butyl-1,1′-(1,4-butanediyl)bistriazolium dibromide (9):
M.p. 241.5–242.3 °C. IR (KBr): 2961, 1802, 1579, 1523, 1444, 1174,
1
1079, 673, 630. H NMR (400 MHz, DMSO-d
): δ = 10.30 (s, 2H,
), 4.27 (m, 4H,
N), 1.30 (m, 4H,
). C NMR (100 MHz, DMSO-
): δ = 144.6, 142.5, 50.7, 47.2, 30.6, 24.7, 18.7, 13.2. Anal. Calcd
6
NCHN), 9.30 (s, 2H, NCHN), 4.44 (m, 4H, NCH
NCH ), 1.93 (m, 4H, CH CH ), 1.83 (m, 4H, CH CH
CH CH ), 0.92 (t, J = 7.2 HZ, 6H, CH
2
2
2
2
2
2
13
1
,1′-Di-n-butyl-4,4′-(1,2-ethanediyl)bistriazolium dibromide (1):
2
3
3
M.p. 265.6–266.1 °C. IR (KBr): 3105, 3041, 2958, 2874, 1575, 1460,
d
6
1
−1
1
394, 1238, 1160, 1074, 651, 627. H NMR (400 MHz, DMSO-d ):
for C16H30Br N (466.26 g mol ): C, 41.22; H, 6.49; N, 18.02. Found:
2 6
6
δ = 10.43 (s, 2H, NCHN), 9.36 (s, 2H, NCHN), 4.93 (s, 4H, NCH N),
C, 41.50; H, 6.31; N, 18.19%.
2
4
.39 (t, J = 7.2 Hz, 4H, NCH ), 1.84 (m, 4H, NCH CH ), 1.30 (m, 4H,
4,4′-Di-benzyl-1,1′-(1,2-ethanediyl)bistriazolium dibromide (10):
2
2
2
13
CH CH ), 0.89 (t, J = 7.2 Hz, 6H, CH ). C NMR (100 MHz, DMSO-
M.p. 229.2–230 °C. IR (KBr): 3095, 3039, 1953, 1816, 1578, 1496,
2
3
3
1
d ): δ = 144.5, 142.8, 51.4, 46.4, 29.7, 18.6, 13.2. Anal. Calcd
1416, 1315, 1211, 1143, 729, 695, 608. H NMR (400 MHz, DMSO-
6
−1
for C H Br N (438.20 g mol ): C, 38.37; H, 5.98; N, 19.18. Found:
C, 38.55; H, 5.83; N, 19.31%.
d ): δ = 10.34 (s, 2H, NCHN), 9.39 (s, 2H, NCHN), 7.50–7.43
6
13
14
26
2
6
(m, 10H, ArH), 5.60 (s, 4H, Ar-CH ), 4.98 (s, 4H, CH ). C NMR
2 2

6
88 JOURNAL OF CHEMICAL RESEARCH 2011
(
4
100 MHz, DMSO-d ): δ = 144.8, 143.7, 133.4, 129.0, 128.6, 50.4,
of China (NSFC) (21071121, 21172188 and 21104064) for
financial support of this work.
6
−
1
9.8. Anal. Calcd for C H Br N (506.24 g mol ): C, 47.45; H, 4.38;
20 22 2 6
N, 16.60. Found: C, 47.67; H, 4.26; N, 16.33%.
,4′-Di-benzyl-1,1′-(1,3-propanediyl)bistriazolium dibromide (11):
M.p. 207.8.2–208.9 °C. IR (KBr): 3041, 1579, 1496, 1434, 1291,
4
Received 18 October 2011; accepted 8 November 2011
Paper 1100939 doi: 10.3184/174751911X13220695999324
Published online: 27 December 2011
1
1
211, 729, 695, 608. H NMR (400 MHz, DMSO-d ): δ = 10.44
6
(
(
s, 2H, NCHN), 9.44 (s, 2H, NCHN), 7.57–7.42 (m, 10H, ArH), 5.60
s, 4H, Ar-CH ), 4.53 (t, J = 6.8 Hz, 4H, CH ), 2.51 (m, 4H, CH ).
13
C
2
2
2
NMR (100 MHz, DMSO-d ): δ = 144.6, 142.9, 133.5, 128.9 128.8,
6
References
−1
5
0.4, 48.5, 27.0. Anal. Calcd for C H Br N (520.26 g mol ): C,
21 24 2 6
1
S. Díez-González, N. Marion and S.P. Nolan, Chem. Rev., 2009, 109,
612.
4
8.48; H, 4.65; N, 16.15. Found: C, 48.75; H, 4.78; N, 15.96%.
,4′-Di-benzyl-1,1′-(1,4-butanediyl)bistriazolium dibromide (12):
M.p. 242–243 °C. IR (KBr): 2984, 1820, 1584, 1498, 1421, 1373,
3
4
2
3
4
5
6
O. Kuhl, Chem. Soc. Rev., 2007, 36, 592.
S. Würtz and F. Glorius, Acc. Chem. Res., 2008, 41, 1523.
S.P. Nolan, Acc. Chem. Res., 2011, 44, 1.
T.M. Trnka and R.H. Grubbs, Acc. Chem. Res., 2001, 34, 18.
S.K.U. Riederer, B. Bechlars, W.A. Herrmann and F.E. Kuehn, Eur. J.
Inorg. Chem., 2011, 2, 249.
1
1
152, 730, 701, 618. H NMR (400 MHz, DMSO-d ): δ = 10.33
6
(
(
s, 2H, NCHN), 9.38 (s, 2H, NCHN), 7.50–7.44 (m, 10H, Ar-H), 5.55
s, 4H, Ar-CH ), 4.43 (m, 4H, CH ), 1.91 (m, 4H, CH ). C NMR
2 2 2
13
(
5
100 MHz, DMSO-d ): δ = 144.6, 142.6, 133.4, 129.0, 128.7, 50.8,
6
1
−
7
8
9
V. Hornillos, J. Guerra, A. de Cozar, P. Prieto, S. Merino, M.A. Maestro,
E. Diez-Barra, J. Tejeda, Dalton Trans., 2011, 40, 4095.
S.K.U. Riederer, B. Bechlars, W.A. Herrmann and F.E. Kuehn, Dalton
Trans., 2011, 40, 41.
0.4, 24.7. Anal. Calcd for C H Br N (534.29 g mol ): C, 49.46; H,
22 26 2 6
4
.90; N, 15.73. Found: C, 49.72; H, 4.76; N, 15.56%.
S.C. Holm, A.F. Siegle, C. Loos, F. Rominger, B.F. Straub, Synthesis, 2010,
We gratefully acknowledge Qing Lan Project of Jiangsu
Education Committee (08QLT001 and 08QLD006), Graduate
Foundation of Jiangsu Education Committee (CXLX11-0910),
State Key Laboratory of Inorganic Synthesis and Preparative
Chemistry at Jilin University (2009-06), Scientific Research
Foundation (SRF) for the Returned Overseas Chinese Scholars
1
3, 2278.
1
1
0
1
A. Zanardi, J.A. Mata, E. Peris, Eur. J. Inorg. Chem. 2011, 3, 416.
M.P. Dukes, T.K. Hollis, Joint 66th Southwest and 62nd Southeast Regional
Meeting of the American Chemical Society, New Orleans, LA, United
States, December 1–4 (2010).
1
1
2
3
L. Zhang, L. Yang, P. He, P. Guan, Y. Shi, G. Pang and C. Cao, J. Chem.
Res., 2011, 35, 471.
C. Cao, Y. Zhuang, J. Zhao, Y. Peng, X. Li, Z. Shi, G. Pang, Y. Shi, Inorg.
(
ROCS), State Education Ministry (SEM), the Priority Aca-
demic Program Development of Jiangsu Higher Education
Instititions (PAPD) and National Natural Science Foundation
Chim. Acta., 2010, 363, 3914.
14 C. Cao, Y. Zhuang, J. Zhao, G. Pang, Y. Shi, J. Chem. Res., 2011, 35, 320.

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