M2+ and Ln3+-catalyzed synthesis of a [1,2,4]triazine core via intramolecular C-H/N-H functionalization and C-N bond formation (M = Mn, Zn, Cd; Ln = Dy, Tb)

Article abstract of DOI:10.1039/c4nj01027b

A novel approach for the direct synthesis of a 1,2,4-triazine core starting from eight azo conjugated aromatic compounds, 5-azo-(1,2,4-triazolyl) salicylic acid, 5-azo-(3-methyl-1,2,4-triazolyl) salicylic acid, 5-azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid, 5-azo-(1,2-pyrazolyl) salicylic acid, 4-azo-(1,2,4-triazolyl) phenol, 4-azo-(3-carboxyl-1,2,4-triazolyl) phenol, 4-azo-(1,2-pyrazolyl) phenol, and 5-azo-(1,2,4-triazolyl) acetylsalicylic acid, via transition or lanthanide metal catalyzed intramolecular C-H/N-H functionalization and C-N bond formation has been developed under one-step hydrothermal synthetic conditions.

Full text of DOI:10.1039/c4nj01027b

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M2+ and Ln3+-catalyzed synthesis of a [1,2,4]triazine
core via intramolecular C–H/N–H functionalization
and C–N bond formation (M = Mn, Zn, Cd;
Ln = Dy, Tb)†
Cite this:DOI: 10.1039/c4nj01027b
Wen-Bin Chen, Zhi-Xin Li, Xin-Wei Yu, Meng Yang, Yan-Xuan Qiu and Wen Dong*
A novel approach for the direct synthesis of a 1,2,4-triazine core starting from eight azo conjugated
aromatic compounds, 5-azo-(1,2,4-triazolyl) salicylic acid, 5-azo-(3-methyl-1,2,4-triazolyl) salicylic acid,
5-azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid, 5-azo-(1,2-pyrazolyl) salicylic acid, 4-azo-(1,2,4-triazolyl)
phenol, 4-azo-(3-carboxyl-1,2,4-triazolyl) phenol, 4-azo-(1,2-pyrazolyl) phenol, and 5-azo-(1,2,4-triazolyl)
acetylsalicylic acid, via transition or lanthanide metal catalyzed intramolecular C–H/N–H functionalization
and C–N bond formation has been developed under one-step hydrothermal synthetic conditions.
Received (in Montpellier, France)
23rd June 2014,
Accepted 25th November 2014
DOI: 10.1039/c4nj01027b
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bonds to synthesize the six-membered nitrogen containing hetero-
cyclic ring of a 1,2,4-triazine core via transition metal or lanthanide
Introduction
Substituted 1,2,4-triazine derivatives have attracted intense interest metal-catalyzed cross-dehydrogenative coupling reaction, to the best
due to their great importance as biological agents in medicinal and of our knowledge, has not been reported although many synthetic
agricultural fields.1 In pursuit of various new medicinal agents con- methods for substituted 1,2,4-triazine derivatives have been well-
taining a 1,2,4-triazine core, additional nitrogen-containing hetero- documented.1–3 Therefore, it is considered as a great challenge to
cyclic scaffolds such as pyrrole, imidazole and triazole, have been synthesize a 1,2,4-triazine core via the transition or lanthanide metal-
usually incorporated into the 1,2,4-triazine core via various synthetic catalyzed inter- and intramolecular C–H and N–H functionalization
methods.1–3 Sadchikova and Partridge reported the synthesis of a reactions and C–N bond formation. Herein, we describe a new
substituted 1,2,4-triazine derivative of [1,2,4]triazolo[5,1-c][1,2,4]- approach to the direct construction of the 1,2,4-triazine core
benzotriazine-8-ol (TBT) and pyrazolo[5,1-c][1,2,4]benzotriazine-8- starting from eight azo conjugated aromatic compounds via
ol (PBT) via the progress of intramolecular dealcoholization and transition or lanthanide metal catalyzed cross-dehydrogenative
dehydration reactions of azo based heterocyclic compounds, coupling reactions under hydrothermal conditions. Six 1,2,4-
respectively.3 Recently, the transition metal-catalyzed inter- and triazine derivatives,hydrated[1,2,4]triazolo[5,1-c][1,2,4]benzotriazine-
intramolecular C–H and N–H functionalization or activation and 8-ol (TBT) of molecular formula C32H26N20O7 (1); three complexes
C–N bond formation for the direct synthesis of five-membered of [M(TBT)2(H2O)4]Á2H2O (M = Mn (2), Zn (3), and Cd (4)); hydrated
nitrogen containing heterocyclic ring derivatives (e.g., carbazole) 5-methyl-[1,2,4]triazolo[5,1-c][1,2,4]benzotriazine-8-ol (MTBT)
have shown increasing popularity.4,5 The C–H bond functionaliza- of molecular formula C18H16N10O3 (5) and another organic
tion has shown widespread applications and industrial potential.4,6 compound of pyrazolo[5,1-c][1,2,4]benzotriazine-8-ol (PBT) (6), were
Two possible mechanisms of Heck-type and Wacker-type cyclization/ synthesized. In particular, the reaction conditions described herein
(-hydride elimination) for construction of heterocyclic rings have significantly improved the efficiency and practicality of 1,2,4-triazine
been proposed when Pd metal serves as a catalyst.4b,7 On the other core formation via a transition or lanthanide metal catalyzed cross-
hand, activation of C–H bonds induced by a lanthanide metal dehydrogenative coupling reaction under a one-step hydrothermal
has also been developed and proven to be particularly effective.8 synthetic method. Most of the target products with high yields are
However, the synthetic method via direct conversion of C–H to C–N crystals and are easy-to-handle, and this synthetic protocol is thus
simple and easily controlled.
School of Chemistry and Chemical Engineering, Guangzhou Key Laboratory for
Environmentally Functional Materials and Technology, Guangzhou University,
Guangzhou, 510006, China. E-mail: dw320@aliyun.com
† Electronic supplementary information (ESI) available: 1H NMR spectra, X-ray data
Experimental
and crystal structures of 1–5, photoluminescent spectra of 2–6, and fluorescent
All the commercial reagents and solvents were used without further
purification unless otherwise stated.
images of 2–6. CCDC 940757–940760 and 979363 for 5. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c4nj01027b
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Quantum calculations
4-Azo-(1,2,4-triazolyl) phenol
All the quantum-chemical calculations were done using the Yellow solid; 86% (3.251 g, 0.0172 mol) yield, based on 1.68 g of
Gaussian 09 suite. The calculations were performed using 0.02 mol 3-amino-1,2,4-triazole. Anal. calcd of C8H7N5O (%): C,
the time dependent density functional theory (TD-DFT) at the 50.79; H, 3.73; N, 37.02. Found (%): C, 50.70; H, 3.75; N, 36.99.
B3LYP/6-31G* level based on the crystal structures of the solid FT-IR (KBr, cmÀ1): 3348s, 3131s, 1671m, 1610m, 1590s, 1486s,
samples obtained in this work.
1486s, 1342m, 1266s, 1150s, 977m, 882m, 842s, 761m, 637m,
Eight azo conjugated aromatic compounds, 5-azo-(1,2,4- 520m; 1H NMR (400 MHz, DMSO) d 14.51 (s, 1H), 10.47 (s, 1H),
triazolyl) salicylic acid, 5-azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid, 8.69 (s, 1H), 7.84 (d, J = 7.7 Hz, 2H), 6.97 (d, J = 7.9 Hz, 2H);
4-azo-(1,2,4-triazolyl) phenol, 4-azo-(3-carboxyl-1,2,4-triazolyl) MS (ESI) m/z [M À H]À C8H6N5OÀ requires 188.0, found 187.9;
phenol, 5-azo-(1,2,4-triazolyl) acetylsalicylic acid, 5-azo-(3- [M + H]+ C8H8N5O+ requires 190.0, found 189.9.
methyl-1,2,4-triazolyl) salicylic acid, 4-azo-(1,2-pyrazolyl) phenol
4-Azo-(3-carboxyl-1,2,4-triazolyl) phenol
and 5-azo-(1,2-pyrazolyl) salicylic acid, were synthesized accord-
ing to the literature procedures.9,10
Yellow solid; 81% (3.775 g, 0.0162 mol) yield, (based on 2.56 g
of 0.02 mol 3-carboxyl-5-amino-1,2,4-triazole). Anal. calcd of
C9H11N5O5 (%): C, 40.11; H, 4.09; N, 26.00. Found (%): C, 40.08;
H, 4.10; N, 25.96. FT-IR (KBr, cmÀ1): 3335s, 1644s, 1549m,
1436s, 1337m, 1267m, 1145s, 1025m, 843m, 764w, 649w, 528m.
1H NMR (400 MHz, DMSO) d 7.82 (d, J = 8.8 Hz, 2H), 6.98
(d, J = 8.8 Hz, 2H), MS (ESI) m/z [M À H]À C9H11N5O5À requires
232.0, found 231.9.
5-Azo-(1,2,4-triazolyl) salicylic acid
Yellow solid; 88% (4.101 g, 0.0176 mol) yield, based on 1.68 g of
0.02 mol 3-amino-1,2,4-triazole. Anal. calcd of C9H11N5O5 (%):
C, 40.11; H, 4.08; N, 26.0. Found (%): C, 40.03; H, 4.32; N,
25.81. FT-IR (KBr, cmÀ1): 3485s, 1628s, 1577m, 1434m, 1386m,
1297m, 1178m, 1076w, 877m, 839m, 555w. The 1H NMR
spectrum and crystallographic data were reported in our pre-
vious literature.10
4-Azo-(1,2-pyrazolyl) phenol
Brown solid; 78% (2.933 g, 0.0156 mol) yield, based on 1.66 g of
0.02 mol 3-aminopyrazole. Anal. calcd of C9H8N4O (%): C, 57.44;
H, 4.28; N, 29.77. Found (%): C, 57.46; H, 4.23; N, 29.85. FT-IR
5-Azo-(3-methyl-1,2,4-triazolyl) salicylic acid
Yellow solid; 80% (3.952 g, 0.016 mol) yield, based on 1.96 g of (KBr, cmÀ1): 3256s, 1591s, 1478s, 1376s, 1246s, 1148s, 1093m,
0.02 mol 3-methyl-5-amino-1,2,4-triazole. Anal. calcd of C10H9N5O3 1059m, 1004m, 844s, 778s, 609m, 532m. 1H NMR (400 MHz,
(%): C, 48.58; H, 3.67; N, 28.33. Found (%): C, 48.43; H, 3.69; N, DMSO) d = 13.32 (s, 1H), 10.27 (s, 1H), 7.83 (s, 1H), 7.76
28.31. FT-IR (KBr, cmÀ1): 3537s, 3329m, 2800s, 1666s, 1588s, (d, J = 8.1 Hz, 2H), 6.94 (d, J = 8.2 Hz, 2H), 6.48 (s, 1H), MS
1487s, 1366s, 1290s, 1226s, 1187s, 1061s, 942m, 890m, 836s, (ESI) m/z [M À H]À C9H7N4OÀ requires 187.0, found 187.0;
770s, 693m, 659m, 560s, 513m. MS (ESI) m/z [M À H]À [M + H]+ C9H9N4O+ requires 189.0, found 188.9.
À
C10H8N5O3 requires 246.20, found 246.25.
5-Azo-(1,2,4-triazolyl) acetylsalicylic acid
Pale yellow solid; 67% (3.685 g, 0.0134 mol) yield, based on 1.68 g
of 0.02 mol 3-amino-1,2,4-triazole. Anal. calcd of C11H9N5O4 (%):
C, 48.00; H, 3.30; N, 25.45. Found (%): C, 47.96; H, 3.31; N, 25.42.
FT-IR (KBr, cmÀ1): 3116s, 2913s, 1673s, 1587s, 1485s, 1446m,
1344m, 1266m, 1227s, 1188s, 981m, 801m, 757m, 675m, 561m.
5-Azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid
Yellow solid; 83% (4.598 g, 0.0166 mol) yield, (based on 2.56 g
of 0.02 mol 3-carboxyl-5-amino-1,2,4-triazole). Anal. calcd of
C
10H7N5O5 (%): C, 43.33; H, 2.55; N, 25.27. Found (%): C, 43.39;
H, 2.50; N, 25.31. FT-IR (KBr, cmÀ1): 3113s, 2908s, 2808m,
1672s, 1587s, 1542m, 1485s, 1443s, 1345s, 1303m, 1262s, 1228s,
1200s, 980m, 840m, 801m, 758m, 675m, 560m. MS (ESI) m/z
2À
MS (ESI) m/z [M À 2H]2À C11H7N5O4 requires 137.60, found
137.22.
2À
[M À 2H]2À C10H5N5O5 requires 137.56, found 137.18. 1H NMR
General procedure for the synthesis of the [1,2,4]triazine core
(400 MHz, DMSO) d 8.33 (d, J = 2.5 Hz, 1H), 8.07 (dd, J = 8.9, 2.6 Hz,
1H), 7.14 (d, J = 8.9 Hz, 1H).
A mixture of the reaction substrate (0.1 mmol), catalysts
(0.05 mmol), and deionized water (15 mL) was heated in a
25 mL Teflon-lined autoclave at 160 1C for 72 h, followed by
slow cooling (5 1C hÀ1) to room temperature. The compounds
5-Azo-(1,2-pyrazolyl) salicylic acid
Brown yellow solid; 80% (3.008 g, 0.016 mol) yield, based on 1–6 were obtained.
1.66 g of 0.02 mol 3-aminopyrazole. Anal. calcd of C10H8N4O3
[1,2,4]Triazolo[5,1-c][1,2,4]benzotriazine-8-ol (1). Yellow crystal,
(%): C, 51.73; H, 3.47; N, 24.13. Found (%): C, 51.70; H, 3.49; N, 83% (0.0666 g, 0.083 mmol) yield (based on 0.4 mmol 5-azo-(1,2,4-
24.10. FT-IR (KBr, cmÀ1): 3305s, 1667m, 1588s, 1484s, 1343s, triazolyl) salicylic acid). Anal. calcd for 1 of C32H26N20O7 (%): C,
1259s, 1175s, 1098m, 1074m, 824m, 795m, 766m, 677m, 555m, 47.84; H, 3.24; N, 34.88. Found (%): C, 47.83; H, 3.28; N, 34.86.
517m; 1H NMR (400 MHz, DMSO) d 13.30 (s, 1H), 10.25 (s, 1H), FT-IR (KBr, cmÀ1): 3428s, 3039s, 1619s, 1540m, 1511s, 1473w,
7.83 (s, 1H), 7.75 (d, J = 8.4 Hz, 2H), 6.93 (d, J = 8.4 Hz, 2H), 6.48 1403m, 1344s, 1309s, 1279m, 1233s, 1213s, 1152s, 857m, 668w,
(s, 1H), MS (ESI) m/z [M À H]À C10H7N4O3 requires 231.0, 502w. H NMR (400 MHz, DMSO) d 12.15 (s, 1H), 8.90 (s, 1H),
À
1
found 230.9; [M + H]+ C10H9N4O3+ requires 233.0, found 232.9. 8.64 (d, J = 9.1 Hz, 1H), 7.67 (s, 1H), 7.44 (d, J = 9.1 Hz, 1H),
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MS (ESI) m/z found [M À H]À 185.7, C8H4N5OÀ requires 186.0.
[M(TBT)2(H2O)4]Á2H2O (M = Mn (2), Zn (3), Cd (4)). 2: Yellow
crystal, 83% (0.0414 g, 0.083 mmol) yield (based on 0.2 mmol
Table 1 Optimization of reaction conditions
5-azo-(1,2,4-triazolyl) salicylic acid). Anal. calcd for
2 of
C
16H16N10O6Mn (%): C, 38.45; H, 3.20; N, 28.04. Found (%):
C, 38.47; H, 3.19; N, 28.06. FT-IR (KBr, cmÀ1): 3164s, 1609s,
1539m, 1483m, 1417m, 1365s, 1282w, 1241m, 1221m, 1180m,
1150m, 1109w, 1025m, 858m, 750m, 639w, 514m; 3: Yellow
crystal, 82% (0.0418 g, 0.082 mmol) yield (based on 0.2 mmol
Yield (%) (i–v)
Entry Time (h) Temp. (1C)
5-azo-(1,2,4-triazolyl) salicylic acid). Anal. calcd for
3 of
C
16H16N10O6Zn (%): C, 37.66; H, 3.14; N, 27.46. Found (%): C,
1
2
3
4
5
72
48
24
72
72
160
160
160
140
120
82(i) 81(ii) 79(iii) 73(iv) 71(v)
76(i) 75(ii) 74(iii) 68(iv) 66(v)
68(i) 67(ii) 64(iii) 58(iv) 59(v)
78(i) 78(ii) 77(iii) 69(iv) 68(v)
75(i) 74(ii) 73(iii) 66(iv) 65(v)
37.67; H, 3.13; N, 27.47. FT-IR (KBr, cmÀ1): 3173s, 1610s, 1539s,
1484s, 1419s, 1364s, 1286m, 1240s, 1218s, 1180m, 1148m,
1109w, 1026m, 855m, 750m, 639w, 514m; 4: Yellow crystal,
81% (0.0451 g, 0.081 mmol) yield (based on 0.2 mmol 5-azo-
(1,2,4-triazolyl) salicylic acid). Anal. calcd for 4 of C16H16N10O6Cd
(%): C, 34.51; H, 2.90; N, 25.16. Found (%): C, 34.58; H,
2.83; N, 25.27. FT-IR (KBr, cmÀ1): 3154s, 1610s, 1540s, 1485s,
1420s, 1366s, 1284m, 1242s, 1219s, 1180m, 1148m, 1108w,
i–v: catalysts (i = MnCl2, ii = ZnCl2, iii = CdCl2, iv = Dy(OAc)3, and v =
Tb(OAc)3). The calculated yields are based on TBT from the crystals and
power products.
1026m, 857m, 749m, 639w, 513m. 5-methyl-[1,2,4]triazolo[5,1- based on the directly obtained product of TBT. Controlled
c][1,2,4]benzotriazine-8-ol (5). Yellow crystal, 72% (0.0303 g, experiments confirmed that no cyclization reactions were
0.072 mmol) yield (based on 0.2 mmol 5-azo-(3-methyl-1,2,4- observed in the absence of metal salts as catalysts or using
triazolyl) salicylic acid). Anal. calcd for 5 of C18H16N10O3 (%): C, CuCl2 as the catalyst. Using salts of i–v as catalysts, the effect of
51.38; H, 3.81; N, 33.30. Found (%): C, 51.40; H, 3.80; N, 33.31. temperature and reaction time were studied, and the reaction
FT-IR (KBr, cmÀ1): 3177s, 3067s, 1615s, 1471s, 1369s, 1328m, conditions of 160 1C and 72 h afforded the best results. When
1257s, 1197s, 1153s, 1116m, 1064m, 846s, 775m, 670m, 613m, reaction temperatures were controlled in the range from 120 to
542m. MS (ESI) m/z [M À H]À C9H6N5OÀ requires 200.2, 140 1C, the powder products with lower yields were obtained.
1
found 199.9. H NMR (300 MHz, DMSO) d 10.41 (s, 1H), 7.77 From the results described above we conclude that the optimal
(d, J = 8.6 Hz, 1H), 6.93 (d, J = 8.6 Hz, 2H), 2.41 (s, 3H). reaction conditions call for the use of MCl2 or Ln(OAc)3 in water
pyrazolo[5,1-c][1,2,4]benzotriazine-8-ol (6). Brown solid; 70% at 160 1C for 72 h under one-step hydrothermal conditions.
(0.0263 g, 0.14 mmol) yield (based on 0.2 mmol 5-azo-(1,2-
Under the optimal reaction conditions, the scope of the
pyrazolyl) salicylic acid). Anal. calcd for 6 of C9H6N4O (%): C, substrates and the generality of the protocol were also studied
58.06; H, 3.25; N, 30.09. Found (%): C, 58.04; H, 3.26; N, 30.05. (Table 2). When 5-azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid,
FT-IR (KBr, cmÀ1): 3254s, 1591s, 1477s, 1375m, 1245s, 1147s, 4-azo-(1,2,4-triazolyl) phenol, 4-azo-(3-carboxyl-1,2,4-triazolyl)
1092m, 1059m, 1003m, 844m, 775m, 610m, 531m. 1H NMR phenol and 5-azo-(1,2,4-triazolyl) acetylsalicylic acid served as
(400 MHz, DMSO) d 13.45 (s, 1H), 8.29 (s, 1H), 8.05 (d, J = 8.8 Hz, reaction substrates, the same products of TBT were obtained in
1H), 7.86 (s, 1H), 7.16 (d, J = 8.9 Hz, 1H), 6.56 (s, 1H), MS (ESI) good yields. When 5-azo-(3-methyl-1,2,4-triazolyl) salicylic acid
m/z [M À H]À C9H5N4OÀ requires 185.0, found 184.9.
served as the reaction substrate, a novel organic cyclization
product of 5-methyl-[1,2,4]triazolo[5,1-c][1,2,4]benzotriazine-8-ol
(MTBT) of molecular formula C18H16N10O3 (5) was obtained
with 67–72% yield. When 4-azo-(1,2-pyrazolyl) phenol and
5-azo-(1,2-pyrazolyl) salicylic acid served as reaction substrates,
Results and discussion
The cyclization of azo conjugated aromatic compounds was the power product of PBT was obtained. The products 1–5
optimized using 5-azo-(1,2,4-triazolyl) salicylic acid as a model are confirmed by X-ray crystallographic analysis (Fig. 1 and Fig.
substrate (Table 1). The substrate readily underwent conversion S1, ESI†).
to give TBT crystals when lanthanide metal salts, Ln(OAc)3,
The atomic labeling diagrams of 1 and 2 are shown in Fig. 1a
were employed as homogeneous catalysts under hydrothermal and b, respectively. Each unit cell of 1 contains four funda-
synthetic conditions. However, when transition metal salts, mental TBT molecules and three lattice water molecules. The
MCl2, were employed as homogeneous catalysts under the bond length of N1–C4 and N6–C12 of the triazine ring is
same hydrothermal synthetic conditions, the same precursor 1.371(2) and 1.3731(19) Å, respectively. The bond length of
gave TBT complexes crystals of [M(TBT)2(H2O)4]Á2H2O. But the C6–O1 and C14–O2 is 1.350(7) and 1.330(7) Å, respectively,
same crystal products of TBT were readily obtained when the indicating the formation of an enol. The TBT is coplanar with a
complex crystals of [M(TBT)2(H2O)4]Á2H2O were dissolved in dihedral angle of 2.261 between the triazole and phenyl rings.
2 mol dmÀ3 HCl solution and underwent recrystallization. A face-to-face alignment between the aromatic rings with the
Screening of the transition and lanthanide metal salts of i–v separated interplanar center-to-center distance of 3.41 to 3.45 Å
revealed that lanthanide metal salts afforded superior results exhibits a p–p stacking interaction (Fig. S2a, ESI†). Two kinds of
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Table 2 Cyclization of seven other azo conjugated aromatic compounds
Entry Substrates
Products
Yields (%) (i–v)
83(i), 82(ii), 81(iii),
80(iv), 79(v)
1
69(i), 68(ii), 66(iii),
66(iv), 65(v)
2
3
67(i), 65(ii), 62(iii),
68(iv), 69(v)
56(i), 55(ii), 51(iii),
50(iv), 51(v)
4
5
Fig. 1 (a)–(c) ORTEP drawing of 1, 2 and 5 respectively.
72(i), 71(ii), 70(iii),
68(iv), 67(v)
carbazole.4 The proposed catalytic cyclization using 5-azo-(1,2,4-
triazolyl) salicylic acid as a model reaction substrate is shown in
Scheme S1, ESI.† The reaction pathway may undergo decarbox-
ylation and an azolated amide-directed Wacker-type cyclization
via transition or lanthanide metal homogeneous catalytic reac-
tions under hydrothermal conditions of 120–160 1C.
Fig. 2a and b show a room-temperature photoluminescent
emission peak at around 500 nm for two aqueous solutions of 1
with a concentration of 10À4 mol dmÀ3 under 290 nm excitation.
The left blue lines show the excitation spectra with the monitored
incident beam at 500 nm. The inset shows the green fluorescent
images observed using a fluorescence microscope under blue light
excitation. The aqueous solutions of 2–6 display similar photo-
luminescence properties as 1 (Fig. S5, ESI†). The photoluminescent
spectra of the solid phase of 1 are depicted in Fig. 2b. Under
460 nm blue light excitation, the solid phase of 1 exhibits two
maximum emissive peaks at around 560 and 670 nm and the
observed green-yellow and red images taken using a fluorescence
microscope under blue and green light excitation have confirmed
the multi-colour fluorescence properties. The compounds 2–6 show
similar photoluminescence properties as 1 (Fig. S6, ESI†).
63(i), 62(ii), 60(iii),
61(iv), 60(v)
6
7
70(i), 69(ii), 68(iii),
65(iv), 63(v)
O–HÁ Á ÁO and O–HÁ Á ÁN hydrogen-bonds with the OÁ Á ÁO and
OÁ Á ÁN distances of 2.620 to 2.913 Å and the p–p stacking
interaction are responsible for the stabilization of the supra-
molecular structure (Fig. S2a, ESI†). In 2, each Mn2+ ion
coordinates to two nitrogen atoms of two triazole moieties
and four water molecules to form an octahedral geometry.
The bond length of N1–C4 of the triazine ring is 1.3721(18). A
p–p stacking interaction with a separated interplanar center-to-
center distance of 3.371 to 3.382 Å and two kinds of O–HÁ Á ÁO
and O–HÁ Á ÁN hydrogen-bonds with the OÁ Á ÁO and OÁ Á ÁN dis-
tances of 2.672 to 2.901 Å are observed. (Fig. S2b, ESI†)
Complexes 3 and 4 are isostructural with 2 and their atomic
labeling and molecular packing diagrams, see Fig. S1 and S3,
ESI.† The atomic labeling diagram of 5 is shown in Fig. 1c.
Each unit cell of 5 contains two fundamental MTBT molecules
and a lattice water molecule. The bond length of C5–N3 and
C14–N8 is 1.363(3) and 1.369(3), respectively. A p–p stacking
interaction between the aromatic rings with a separated inter-
planar center-to-center distance of 3.41 to 3.45 Å is also
observed in 5 (Fig. S4, ESI†).
Fig. 2 (a) Photoluminescent spectra of aqueous solution of 1. The inset
shows the fluorescent image under blue light excitation. (b) The photo-
luminescent spectra of the crystal phase of 1. The inset shows the
fluorescent image of the solid phase under blue and green light excitation.
The above reaction mechanism for synthesis of the 1,2,4-
triazine core can be demonstrated by b-hydride elimination that
is similar to Pd catalyzed Wacker-type cyclization to generate the
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Program Foundation of the second batch of innovation teams
of Guangzhou Bureau of Education (13C04).
Notes and references
´
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˘
J. Muslehiddinoglu, W. P. Gallagher, N. J. Simon and J. Burt,
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of 1 displaying two maximum absorption peaks at around 221
and 316 nm, which are attributed to the HOMO À 2-LUMO + 2
and HOMO-LUMO + 1 electronic transitions of the enol
isomer, respectively (Fig. S7a and b, ESI†). The calculated blue
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of 1 are attributed to the HOMO-LUMO electronic transitions
of two different keto isomers that come from the excited-state
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an intramolecular O–H proton transfer occurs in two different
N atoms of the triazole ring (Fig. 3a and b).
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Conclusions
In summary, we have developed a novel protocol for the
synthesis of the 1,2,4-triazine core via C–H/N–H functionaliza-
tion followed by intramolecular amination employing MCl2 or
Ln(OAc)3 as catalysts under one-step hydrothermal synthetic
conditions. This method offers a straightforward access to a
wide range of 1,2,4-triazine derivatives, important structural
motifs as biological agents in natural and designed compounds.
It is also noteworthy for the developed reaction, a feature that
should permit further transformation of the 1,2,4-triazine pro-
duct and provide an entry to structurally diverse heterocycles. In
view of the growing understanding of transition or lanthanide-
metal-mediated C–H/N–H activation processes, the reaction
described herein showcased a reactivity profile that is different
from those previously reported. Further studies to understand
the precise mechanism and to expand the range of substrates
as well as to expand their application will be carried out in
our laboratory.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 21271052), Science and Technology
Program Foundation of Guangzhou (No. 2013J4100016) and
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