2-15N-5-chloro-1,3-diphenyltetrazolium tetrafluoroborate and
N,NЈ-Bis(1,3-diphenyltetrazolium-5-yl)biphenyl-4,4Ј-diamide
15N2-hydrazine sulfate.
(6). A mixture of 5-chloro-1,3-diphenyltetrazolium tetrafluoro-
borate (0.35 g, 1.0 mmol) and benzidine (0.18 g, 1.0 mmol) in
acetonitrile (3.0 ml) was stirred at room temperature for 24 h.
Water was added and the resulting precipitate was filtered and
washed with water. The product was suspended in DCM (30
ml) and aqueous NaOH (1 M, 10 ml) was added. The mixture
was vigorously stirred and the red DCM layer was separated,
dried over anhydrous sodium sulfate, and evaporated. A dark-
red solid (0.25 g, 79%) was obtained, which was recrystallised
from DCM (ca. 15 ml) to give the pure product (0.18 g, 55%);
mp > 300 ЊC (Found: C, 72.5; H, 4.6; N, 22.2. Calc. for
C38H28N10ؒ0.5H2O: C, 72.0; H, 4.6; N, 22.1%); νmax/cmϪ1 1620,
1580, 1488, 1370, 1334, 1286, 1254, 1210, 1174, 1110, 1070, 962,
826, 756, 680; λmax (CHCl3)/nm 296 (log ε 4.46) and 376 (sh,
3.18); δH (200 MHz; CDCl3) 7.42 (2H, t, J 8), 7.48–7.70 (18H,
m), 8.22 (4H, m) and 8.40 (4H, br d, J 8); δC (100 MHz, CDCl3)
120.2, 121.3, 122.9 (C-o and C-Ar); 126.7 (C-Ar), 127.9 (C-p),
129.1 (C-m), 129.6 (C-m), 131.2 (C-p); 134.0, 135.3, 136.4 (C-i
and Cq-Ar); 147.4 (Ar-C-N) and 154.3 (Cϩ); m/z (FD) 624
(Mϩ).
Dication (12؉). Crystals of 1 (0.30 g, 0.63 mmol) were added
in portions to concentrated nitric acid (10 ml), and the mixture
was stirred for 10 min. NaBF4 (11 g) in water (20 ml) was added
and the resulting orange crystals were filtered, washed with
water, and dried to give 12ϩ (0.36 g, 87%); mp 193–196 ЊC
(Found: C, 48.3; H, 3.2; N, 21.85. Calc. for C26H20B2F8N10:
C, 48.3; H, 3.1; N, 21.7%); νmax/cmϪ1 1492, 1460, 1374, 1308,
1290, 1246, 1180, 1060, 1000, 926, 786, 770, 710, 696 and 684;
λmax (MeCN)/nm 293 (log ε 4.49), 352 (sh, 4.15) and 446 (3.88);
δH (90 MHz; CF3CO2D) 7.76–8.14 (12H, m, Ph), 8.14–8.36 (4H,
m, Ph) and 8.36–8.70 (4H, m, Ph); δC (50 MHz, CF3CO2D)
123.5 (C-o), 127.6 (C-o), 132.9 (C-m), 133.0 (C-m), 133.3 (C-i),
136.6 (C-p), 137.4 (C-p), 137.1 (C-i) and 161.8 (Cϩ).
Oxidation of radical cation 1 ϩ to dication 12ϩ. Radical cation
ϩ
1
ؒBF4Ϫ (26 mg, 0.047 mmol) was added to concentrated nitric
acid (0.50 ml). The mixture was ultrasonicated for 5 min and
worked up as above to give 12ϩ (29 mg, 95%).
N,NЈ-Bis(1,3-diphenyltetrazolium-5-yl)-m-phenylenediamide
(7). A mixture of 5-chloro-1,3-diphenyltetrazolium tetrafluoro-
borate (0.41 g, 1.2 mmol) and m-phenylenediamine (0.13 g, 1.2
mmol) in acetonitrile (3.0 ml) was stirred at room temperature
for 24 h. Water was added and the resulting precipitate was
filtered, washed with water, and dried to give crystals of the
conjugate acid (0.22 g, 51%); mp 112–120 ЊC. The acid (0.13 g,
0.18 mmol) was dissolved in acetonitrile (2.0 ml) and aqueous
NaOH (1 M, 6.0 ml) was added. A reddish-purple precipitate
was formed immediately, which was filtered, washed with water,
and dried to give N,NЈ-bis(1,3-diphenyltetrazolium-5-yl)-m-
phenylenediamide (89 mg, 92%); recrystallisation from ethanol
gave a pure sample (28 mg, 27%); mp 83 ЊC (Found: C, 66.3; H,
4.25; N, 24.1. Calc. for C32H24N10ؒ1.5H2O: C, 66.8; H, 4.7; N,
24.3%); νmax/cmϪ1 1620, 1556, 1484, 1466, 1364, 1322, 1278,
1238, 1202, 1148, 1104, 1064, 952, 904, 872, 816, 750 and 678;
λmax (CHCl3)/nm 272 (log ε 4.50) and 448 (sh, 3.20); δH (200
MHz; [2H6]DMSO) 6.93 (2H, d, J 8), 7.10 (1H, t, J 8), 7.46–7.68
(13H, m), 8.15 (4H, br d, J 8, Ph) and 8.37 (4H, br d, J 8, Ph);
δC (100 MHz; CDCl3) 116.0 (C-Ar), 117.6 (C-Ar), 120.3 (C-o),
121.3 (C-o), 127.7 (C-p), 128.6 (C-Ar), 129.1 (C-m), 129.5
(C-m), 131.1 (C-p), 135.7 (C-i), 136.5 (C-i), 149.3 (Ar-C-N) and
154.3 (Cϩ); m/z 548 (Mϩ, 100%), 353 (34), 328 (34), 245 (8), 169
(48), 105 (PhN2, 8) and 77 (Ph, 61).
ϩ
Reduction of radical cation 1 to azine 1. A mixture of
radical cation 1 ϩ (39 mg, 0.070 mmol) and zinc powder (14 mg,
0.21 mmol) in acetonitrile (10 ml) was stirred for 10 min under
argon. The solvent was removed under reduced pressure and
the residue was dissolved in DCM. The mixture was shaken
with aqueous NaHCO3 (5%). The organic layer was separated,
dried (Na2SO4), and evaporated. The residue was column-
chromatographed on silica gel (DCM–acetone = 4:1) to give 1
(25 mg, 76%).
Reduction of dication 12ϩ to azine 1. A mixture of dication 12ϩ
(42 mg, 0.065 mmol) and zinc powder (71 mg, 1.1 mmol) in
acetonitrile (20 ml) was stirred for 20 h. The solvent was
removed under reduced pressure and the residue was dissolved
in DCM. The solution was shaken with aqueous NaHCO3
(5%). The organic layer was separated, dried (Na2SO4), and
evaporated. The residue was column-chromatographed on
alumina (DCM–acetone = 4:1) to give 1 (20 mg, 65%).
Reduction of dication 12ϩ to radical cation 1 ϩ. A suspension
of dication 12ϩ (50 mg, 0.077 mmol) in ethanol (50 ml) was
stirred at room temperature for 24 h. The reaction mixture
turned from orange to greenish brown, and the crystals of 12ϩ
gradually went into solution. The solvent was evaporated and
the residue was chromatographed on silica gel (DCM–acetone)
N,NЈ-Bis(1,3-diphenyltetrazolium-5-yl)biphenyl-3,3Ј-diamide
(8). A mixture of 5-chloro-1,3-diphenyltetrazolium tetrafluoro-
borate (0.37 g, 1.1 mmol) and 3,3Ј-diaminobiphenyl11 (0.20 g,
1.1 mmol) in acetonitrile (5.0 ml) was stirred at room temper-
ature for 20 h. Aqueous NaOH (1 M, 30 ml) was added and the
product was extracted with DCM and dried (Na2SO4). Then,
the solvent was evaporated, giving a crude product (0.42 g),
which was recrystallised from a chloroform–ethanol mixture to
give the pure product (0.13 g, 38%) as a brick-red powder; mp
227 ЊC (dec.) (Found: C, 73.0; H, 4.5; N, 22.15. Calc. for
C38H28N10: C, 73.1; H, 4.5; N, 22.4%); νmax/cmϪ1 1622, 1564,
1490, 1468, 1368, 1330, 1288, 1206, 1160, 1112, 1070, 966, 758
and 680; λmax (MeCN)/nm 262 (log ε 3.70), 302 (3.72) and 442
(2.74); δH (400 MHz; CDCl3) 7.22 (2H, d, J 7.6), 7.32 (4H, m),
7.44 (12H, m), 7.78 (2H, t, J 1.8), 8.07 (4H, m) and 8.32 (4H, d,
J 7.9); δC (100 MHz; CDCl3) 119.9 (C-Ar), 120.0 (C-o), 121.1
(C-Ar), 121.2 (C-o), 122.1 (C-Ar), 127.8 (C-Ar or C-p), 128.6
(C-Ar or C-p), 129.1 (C-m), 129.5 (C-m), 131.1 (C-Ar or C-p),
135.4 (C-i), 136.3 (C-i), 142.4 (Cq-Ar), 149.1 (Ar-C-N) and
154.6 (Cϩ); m/z 624 (Mϩ, 0.3%), 404 (40) and 77 (Phϩ, 100).
ϩ
to give 1 ؒBF4Ϫ (21 mg, 49%).
N,NЈ-Bis(1,3-diphenyltetrazolium-5-yl)-p-phenylenediamide
(5). A mixture of 5-chloro-1,3-diphenyltetrazolium tetrafluoro-
borate (2.0 g, 5.8 mmol) and p-phenylenediamine (0.65 g, 6.0
mmol) in acetonitrile (17 ml) was stirred at room temperature
for 24 h. Water was added and the resulting precipitate was
filtered, washed with water, and dried to give crystals of the
conjugate acid (1.5 g, 70%); mp 260–262 ЊC. The acid (2.1 g, 2.9
mmol) was dissolved in acetonitrile (29 ml) and aqueous NaOH
(1 M, 87 ml) was added. A reddish-purple precipitate was
formed immediately, which was filtered, washed with water,
and dried to give N,NЈ-bis(1,3-diphenyltetrazolium-5-yl)-p-
phenylenediamide (1.6 g, 100%); mp 284–286 ЊC (Found: C,
69.2; H, 4.4; N, 25.3. Calc. for C32H24N10ؒ0.5H2O: C, 68.9; H,
4.5; N, 25.1%); νmax/cmϪ1 1614, 1590, 1484, 1464, 1368, 1322,
1288, 1252, 1196, 1170, 1148, 1112, 1090, 1064, 962, 750, 698
and 678; λmax (CHCl3)/nm 296 (log ε 4.96), 370 (sh, 4.04) and
443 (sh, 3.64); δH (200 MHz; CDCl3) 7.26 (4H, s, ArH), 7.39
(2H, t, J 8, Ph), 7.48–7.64 (10H, m, Ph), 8.21 (4H, m, Ph) and
8.43 (4H, br d, J 8, Ph); m/z 548 (Mϩ, 100%), 105 (PhN2, 15)
and 77 (Ph, 18).
Chemical reduction of 5 with zinc powder. A mixture of 5
(0.22 g, 0.39 mmol) and zinc powder (0.21 g, 3.2 mmol) was
994
J. Chem. Soc., Perkin Trans. 2, 1999, 985–995