A bromine adduct of 2,3,6,7,14,15-hexamethyl-9,10-distibatriptycene. The first stibonium-stiborate zwitterion

Article abstract of DOI:10.1246/cl.2005.966

2,3,6,7,14,15-Hexamethyl-9,10-distibatriptycene (3) reacted with bromine to give an adduct 4 with the composition of 3·2Br₂. X-ray structure analysis and ¹H NMR studies revealed that the bromine adduct 4 forms an intramolecular salt composed of a tetracoordinate bromostibonium ion moiety, R₃SbBr⁺, and a hexacoordinate tribromostiborate ion moiety, R₃SbBr₃^-, both in the crystalline state and in solution. Copyright

Full text of DOI:10.1246/cl.2005.966

9
66
Chemistry Letters Vol.34, No.7 (2005)
A Bromine Adduct of 2,3,6,7,14,15-Hexamethyl-9,10-distibatriptycene.
The First Stibonium–Stiborate Zwitterion
ꢀ
Yosuke Uchiyama and Gaku Yamamoto
Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555
(Received April 20, 2005; CL-050544)
2,3,6,7,14,15-Hexamethyl-9,10-distibatriptycene (3) react-
ed with bromine to give an adduct 4 with the composition of
.
2Br2. X-ray structure analysis and H NMR studies revealed
that the bromine adduct 4 forms an intramolecular salt composed
1
3
þ
of a tetracoordinate bromostibonium ion moiety, R3SbBr , and a
ꢁ
hexacoordinate tribromostiborate ion moiety, R3SbBr3 , both in
the crystalline state and in solution.
Triptycene analogs with Group-15 elements (N, P, As, Sb,
and Bi) at the two bridgehead positions have been reported in
the literature, but their chemistry are hardly known because of
1
the synthetic difficulty and the insolubility of reaction products.
9,10-Distibatriptycene (1) was first synthesized in 1985 by the
reaction of o-phenylenemercury with Sb powder, but its reactiv-
ity has not been explored.
2
Y
Me
Figure 1. ORTEP drawing of 3. Hydrogen atoms and C6F6 are
ꢂ
ꢀ
Y
Me
omitted for clarity. Selected bond lengths (A) and angles ( ):
Sb1–C1, 2.151(2); Sb1–C2, 2.149(2); Sb1–C3, 2.156(3); C1–
Sb1–C2, 95.4(1); C1–Sb1–C3, 93.6(1); C2–Sb1–C3, 94.1(1);
C4–C1–Sb1, 121.7(2); C5–C2–Sb1, 122.3(2); C6–C3–Sb1,
122.0(2); Sb2–C4, 2.154(3); Sb2–C5, 2.150(2); Sb2–C6,
2.151(2); C4–Sb2–C5, 93.7(1); C4–Sb2–C6, 94.0(1); C5–Sb2–
C6, 94.6(1); C1–C4–Sb2, 122.5(2); C2–C5–Sb2, 122.2(2); C3–
C6–Sb2, 122.7(2); Sb1ꢃꢃꢃSb2, 3.692.
X
Br
+
X
X
X
Br
Sb
Sb
Sb Br
–
Y
Me
Me
Sb
Y
Me
Me
Y
X
Br
X
Y
•
1
: X = Y = H
3 2Br2 (4)
The synthetic procedures are shown in Scheme 1. The reac-
4
2
3
: X = Y = F
ꢂ
tion of 4,5-dibromo-o-xylene (5) with n-BuLi at ꢁ110 C and
: X = H, Y = Me
then with SbCl3 gave tris(2-bromo-4,5-dimethylphenyl)stibine
5
Chart 1.
(6). Compound 6 was treated with t-BuLi and then with SbBr3
6
to afford the 9,10-distibatriptycene 3 in 20% yield.
The X-ray molecular structure of 3 crystallized from C6F6 is
The only reported reaction is the chlorination of perfluoro-
3
9
,10-distibatriptycene (2). The authors claimed to have ob-
7
shown in Figure 1. The molecule has a nearly D3h geometry.
.
tained an adduct 2 2Cl2, but poorly elucidated the structure be-
cause of facile hydrolysis of the adduct. We have been interested
in reactions, especially those with halogens, of 1 and its deriva-
tives, and found that 2,3,6,7,14,15-hexamethyl-9,10-distibatri-
ptycene (3) is a suitable target compound. We report here the
synthesis of 3, the bromination of 3 to give an adduct 3 2Br2
(4), X-ray crystallography of 3 and 4, and dynamic behavior
of 4 in solution.
ꢀ
The Sb–C bond lengths and C–Sb–C angles are 2.152 A and
ꢂ
9
4.2 , respectively, in average.
Treatment of 3 with bromine gave an adduct 4 with the
.
composition of 3 2Br2. The adduct 4 showed good solubility
in common organic solvents and high stability toward air and
.
8
moisture.
The X-ray molecular structure of 4 recrystallized from
9
CHCl3–mesitylene (1:5) is shown in Figure 2. One of the anti-
mony atoms, Sb1, bonds to three Br atoms, constituting a hexa-
coordinate tribromostiborate ion structure. The average C–Sb1–
Me
Me
Br
Br
Me
Me
Br
i, ii
iii, iv
v
3
4
ꢂ
ꢂ
Sb
C and trans-C–Sb1–Br angles are 94.9 and 173.4 respectively,
indicating that Sb1 has a slightly distorted octahedral geometry.
It is noted that the pyramidality around Sb1 atom is almost the
same as that observed in 3. The other antimony atom, Sb2, bonds
to one Br atom, resulting in a tetracoordinate bromostibonium
ion structure with a slightly distorted tetrahedral geometry.
3
(20%)
(64%)
5
6 (63%)
Reagents and conditions: i) n-BuLi (1.0 equiv.), THF−Et O
2
(
1:1), −110 °C, ii) SbCl (0.33 equiv.), iii) t-BuLi (6.0 equiv.),
3
THF, −78 °C, iv) SbBr (1.0 equiv.), v) Br (2.2 equiv.),
3
2
CH Cl , 0 °C.
2
2
ꢂ
The average C–Sb2–C and C–Sb2–Br angles are 103.7 and
ꢂ
Scheme 1.
111.2 , respectively. The Sb2 moiety forms a flatter pyramid
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.7 (2005)
967
Compound 4 is the first example of a tetracoordinate bro-
mostibonium ion observed in the crystalline state, and also of
a stibonium–stiborate zwitterion. Studies on reactions of 3 with
other halogens are in progress.
This study was supported by a Grant-in-Aid for Encourage-
ment of Young Scientists (B) to Y. U. (No. 16750041) from the
Ministry of Education, Culture, Sports, Science and Technology
of Japan.
References and Notes
1
2
3
4
A. G. Massey, Adv. Inorg. Chem., 33, 1 (1989); A. Ishii and
J. Nakayama, Rev. Heteroat. Chem., 11, 1 (1994).
N. A. A. Al-Jabar, D. Bowen, and A. G. Massey, J. Organo-
met. Chem., 295, 29 (1985).
N. A. A. Al-Jabar and A. G. Massey, J. Organomet. Chem.,
276, 331 (1984).
Figure 2. ORTEP drawing of 4. Hydrogen atoms and CHCl3
ꢀ
are omitted for clarity. Selected bond lengths (A) and angles
ꢂ
P. R. Ashton, U. Girreser, D. Giuffrida, F. H. Kohnke, J. P.
Mathias, F. M. Raymo, A. M. Z. Slawin, J. F. Stoddart,
and D. J. Williams, J. Am. Chem. Soc., 115, 5422 (1993).
Tris(2-bromo-4,5-dimethylphenyl)stibine (6): white solids
(
): Sb1–C1, 2.190(3); Sb1–C2, 2.213(3); Sb1–C3, 2.200(3);
Sb1–Br1, 2.6691(4); Sb1–Br2, 2.6339(4); Sb1–Br3, 2.6359(4);
C1–Sb1–Br1, 173.6(1); C2–Sb1–Br2, 172.0(1); C3–Sb1–Br3,
174.6(1); C1–Sb1–C2, 92.9(1); C1–Sb1–C3, 95.6(1); C2–Sb1–
5
ꢂ
C3, 96.3(1); C4–C1–Sb1, 121.5(2); C5–C2–Sb1, 123.1(2); C6–
C3–Sb1, 121.5(2); Sb2–Br4, 2.4066(4); Sb2–C4, 2.096(3);
Sb2–C5, 2.086(3); Sb2–C6, 2.080(3); C4–Sb2–C5, 100.5(1);
C4–Sb2–C6, 105.0(1); C5–Sb2–C6, 105.7(1); C4–Sb2–Br4,
(from AcOEt), mp 251–252 C (dec). Anal. Found: C,
42.74; H, 3.80%. Calcd for C24H24Br3Sb: C, 42.77; H,
1
3
(
.59%, H NMR (300 MHz, CDCl3) ꢀ 2.05 (9H, s), 2.23
9H, s), 6.77 (3H, s), 7.36 (3H, s). C NMR (75 MHz,
13
1
08.4(1); C5–Sb2–Br4, 116.8(1); C6–Sb2–Br4, 108.4(1); C1–
C4–Sb2, 114.8(2); C2–C5–Sb2, 113.2(2); C3–C6–Sb2,
13.4(2); Sb1ꢃꢃꢃSb2, 3.426.
CDCl3) ꢀ 19.4, 19.5, 129.4, 132.8, 136.5, 138.2, 139.8,
þ
1
2,3,6,7,14,15-Hexamethyl-9,10-distibatriptycene (3); white
39.9. MS (70 eV) m=z 670 (M , 100%).
1
6
7
8
ꢂ
solids (from benzene), mp 285–290 C (dec). Anal. Found:
C, 52.00; H, 4.46%. Calcd for C24H24Sb2: C, 51.85; H,
ꢀ
than in 3 to result in the smaller SbꢃꢃꢃSb distance in 4 (3.43 A)
ꢀ
than in 3 (3.69 A).
1
4
(
1
.35%. H NMR (300 MHz, CDCl3) ꢀ 2.18 (18H, s), 7.81
ꢀ
The Sb2–Br bond (2.407 A) is considerably smaller than
ꢀ
the Sb1–Br bonds (2.65 A in average), reflecting the onium
1
3
6H, s). C NMR (75 MHz, CDCl3) ꢀ 19.4, 136.8, 137.6,
þ
46.0. MS (70 eV) m=z 554 (M , 13%), 226 (100%).
.
character in the tetracoordinate moiety: The Sb1–Br bond length
is comparable with that of dibromotriphenylstiborane (2.63–
Crystal data of 3: C24H24Sb2 0.5C6F6, fw 648.96, mono-
clinic, C2=c, a ¼ 26:4096ð10Þ Aꢀ , b ¼ 10:1131ð1Þ Aꢀ , c ¼
10
ꢀ
.64 A), where the bromine atoms are in the apical positions
2
of a pentacoordinate trigonalbipyramid structure.
ꢂ
3
ꢀ
ꢀ
2
8, D
0:5028ð9Þ A, ꢁ ¼ 116:9319ð5Þ , V ¼ 4882:1ð3Þ A , Z ¼
ꢁ3
ꢂ
1
ꢂ
¼ 1:766 gꢃcm , Temp ¼ ꢁ160 C, R1 ¼ 0:0273
calcd
H NMR spectra of 4 in CD2Cl2 at 27 C showed two sin-
for all data, wR2 ¼ 0:0660 for all 5283 unique reflections
glets at ꢀ 2.34 and 7.87 in a 3:1 ratio assigned to the methyl
and aromatic protons, respectively. Upon lowering the tempera-
ture, each singlet broadened and split into two equally intense
(
The bromine adduct 4: yellow solids (washing with hexane),
295 parameters), GOF ¼ 1:081. CCDC No. 269390.
ꢂ
ꢂ
mp 203–204 C (dec). Anal. Found: C, 33.20; H, 3.02%.
1
singlets. At ꢁ93 C, the methyl signals appeared at ꢀ 2.20 and
Calcd for C24H24Br4Sb2: C, 32.92; H, 2.76%. H NMR
2.29, and the aromatic signals at ꢀ 7.20 and 8.35. This lineshape
ꢂ
(
1
300 MHz, CD2Cl2, 27 C) ꢀ 2.34 (18H, s), 7.87 (6H, s);
C NMR (75 MHz, CD2Cl2, 27 C) ꢀ 20.0, 134.5,
change could be most reasonably explained in terms of the inter-
change between the two topomeric structures as shown in
Scheme 2. The topomerization rate depended on the concentra-
tion of 4,11 indicating the intermolecularity of the bromide ion
shifts, though the detailed mechanism awaits further study.
3
ꢂ
1
((C H (CH ) ) , 100%).
Crystal data of 4: C24H24Br4Sb2 CHCl3, fw 994.94, mono-
38.1, 142.3. MS (70 eV) m=z 795 (M ꢁ Br, 80%), 312
6
2
3 2 3
.
9
1
ꢀ
ꢀ
clinic, P21=n, a ¼ 11:0798ð4Þ A, b ¼ 18:9219ð7Þ A, c ¼
ꢂ
3
ꢀ
ꢀ
1
4
4:3459ð8Þ A, ꢁ ¼ 100:1844ð8Þ , V ¼ 2960:2ð2Þ A , Z ¼
Me
Me
ꢁ3
ꢂ
, Dcalcd ¼ 2:232 gꢃcm , Temp ¼ ꢁ160 C, R1 ¼ 0:0271
Me
Me
for all data, wR2 ¼ 0:0755 for all 5973 unique reflections
(
313 parameters), GOF ¼ 1:063. CCDC No. 269391.
0 M. J. Begley and D. B. Sowerby, Acta Crystallogr., C49,
1044 (1993); M. Weber, Acta Crystallogr., C54, 570 (1998).
11 The rate constants obtained by lineshape analysis
Br
+
Br
Br
–
Br
Sb Br
Sb
+
–
Me
Me
Me
Me
Sb
Sb
12
ꢂ
ꢁ1
z
Me
Me
Me
Me
(DNMR3 ) in CD2Cl2 at ꢁ83 C are 52, 83, and 113 s
Br
Br
for 2.63, 5.72, 10.8 M solutions, respectively. The ꢁG
ꢁ1
Br
values are 9.47, 9.29, and 9.17 kcal mol , respectively.
12 D. A. Kleier and G. Binsch, QCPE Program No. 165.
Scheme 2.
Published on the web (Advance View) June 4, 2005; DOI 10.1246/cl.2005.966