First synthesis and properties of dendritic Bin-bismuthanes

Article abstract of DOI:10.1039/a706338e

Directed tris-ortholithiation of tris[2-(diethylaminosulfonyl)phenyl]bismuthane 1 with tert-butyllithium followed by treatment with 3 equiv. of bis[2-(diethylaminosulfonyl)-phenyl]bismuth iodide 2a gives a symmetrically branched Bi₄-bismuthane 5a, which, on a similar treatment, is converted in a one-pot synthesis into a highly branched Bi₁₀-bismuthane 6a.

Full text of DOI:10.1039/a706338e

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First synthesis and properties of dendritic Bin-bismuthanes
Hitomi Suzuki,* Haruto Kurata and Yoshihiro Matano
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan
Directed tris-ortholithiation of tris[2-(diethylaminosul-
fonyl)phenyl]bismuthane 1 with tert-butyllithium followed
by treatment with 3 equiv. of bis[2-(diethylaminosulfonyl)-
phenyl]bismuth iodide 2a gives a symmetrically branched
Bi4-bismuthane 5a, which, on a similar treatment, is
converted in a one-pot synthesis into a highly branched Bi10-
bismuthane 6a.
278 °C. An isomeric linear Bi4-bismuthane was not formed
under the conditions employed. When bis(4-methylphenyl)bis-
muth chloride4 2b was used in place of iodide 2a, tolyl-
substituted analogues 3b, 4b and 5b were obtained in 2, 6 and
11% isolated yields, respectively (entry 5). Three of four
bismuth atoms in Bi4-bismuthane 5b readily underwent oxida-
tive chlorination with an excess of sulfuryl chloride in CH2Cl2
at room temp. to give a hexachloride 7b in 55% yield, in which
the central bismuth atom is intact, while the outer three bismuth
atoms are oxidized to BiV (Scheme 1). The reduction of
hexachloride 7b with saturated aqueous Na2S2O3 smoothly
regenerated the original Bi4-bismuthane 5b in 92% yield. All
Bin-bismuthanes 3a,b, 4a,b and 5a,b and hexachloride 7b
obtained were characterized by NMR and MALDI-TOF mass
spectroscopies as well as by elemental analyses.
Owing to excellent contrast density of bismuth toward X-rays of
short wavelength, the synthesis of water-soluble non-ionic
organobismuth compounds represents an interesting area of
research in pursuit of iodine-free positive X-ray contrast agents.
High bismuth content (m/m %) is a prerequisite for such a
purpose and the incorporation of multiple bismuth atoms into a
molecule is a straightforward approach to this. However, the
literature to date contains no report of the synthesis of
organobismuth compounds bearing more than two bismuth
atoms in the molecule. Several tetraorganyldibismuthanes
(R2BiBiR2) are known,1 but they are quite sensitive to air and
light and difficult to handle. During the course of our effort to
synthesize polybismuth compounds, we came across a simple
one-pot method for introducing three diarylbismuthyl units
directly into the three aromatic rings of a triarylbismuthane and
this methodology has now enabled us to gain easy access to
highly branched aromatic polybismuth compounds. Herein we
report the first synthesis of dendrimer-type aromatic poly-
bismuth compounds bearing up to ten bismuth atoms in a single
molecule,2 utilizing the directed ortholithiation of triarylbismu-
thanes bearing a sulfonamide function at the ortho position of
each aromatic ring.
Bi4-bismuthane 5a bears acidic protons at the positions ortho
to the sulfonamide group in the six outer aromatic rings. This
structural advantage enabled us to extend the present method-
ology further, making access possible to a highly branched
dendrimer-type Bi10-bismuthane 6a. Thus, treatment of Bi4-
bismuthane 5a with 6.6 equiv. of tert-butyllithium in THF at
0 °C for 1 h followed by the addition of 6 equiv. of iodide 2a at
278 °C afforded a crude Bi10-bismuthane 6a in ca. 20% yield,
accompanied by small amounts of Bi8- and Bi9-congeners. The
Bi10-dendrimer 6a, isolated by gel permeation chromatography
and further purified by column chromatography on silica gel, is
a white powder which begins to decompose above 180 °C
without melting. It is readily soluble in dichloromethane and
chloroform, but insoluble in methanol and ethanol. Its MALDI-
TOF mass spectrum showed a (M + Na)+ peak at m/z 6558.1
(calc; 6561.9). In its 13C NMR spectrum, three distinct sets of
13C absorptions were observed for non-equivalent ethyl groups
at d 41.8, 40.3 and 40.0 for methylene carbons and at d 14.1,
13.0 and 12.7 for methyl carbons, respectively. Simple NMR
peak patterns observed suggest a high molecular symmetry in
accord with the dendritic structure of bismuthane 6a. In the
sense of atomic mass of a key element involved, the dendrimer
6a represents the heaviest example of dendrimers so far
reported. Attempts to elucidate the molecular geometry of
compound 5a by X-ray analysis have so far met with failure
owing to the rapid efflorescence of the specimen crystals in
air.
Since the sulfonamide group is a good directing group in the
ortholithiation of arenes,3 tris[2-(diethylaminosulfonyl)-
phenyl]bismuthane4 1 was chosen as the starting material for
water-soluble neutral polybismuth compounds. This bismu-
thane was synthesized by the ortholithiation of N,N-diethyl-
benzenesulfonamide with butyllithium followed by treatment
with 1/3 BiCl3 in THF at 278 °C. Compound 1 contains acidic
protons ortho to the sulfonyl group on the three aromatic rings,
so it can be further lithiated in the presence of an excess of an
alkyllithium. When compound 1 was lithiated with 1.1 equiv. of
tert-butyllithium in THF at 278 °C for 1 h and then treated
with
1
equiv. of bis[2-(diethylaminosulfonyl)phenyl]-
bismuth iodide5 2a, Bi2-bismuthane 3a and Bi3-bismuthane 4a
were obtained in 37 and 18% yields, respectively, together with
25% of recovered starting material 1, where Bin-bismuthane
represents a bismuthane bearing n bismuth atoms in one
molecule (Table 1, entry 1). When 3.3 equiv. of tert-
butyllithium was used under appropriate conditions, a symmet-
rically branched Bi4-bismuthane 5a was obtained as the main
product. The yields of these bismuthanes varied considerably
depending on the temperatures employed; compound 5a was
obtained in moderate and good isolated yield when the reaction
mixture was warmed to 220 and 0 °C before iodide 2a was
added (entries 3 and 4, respectively), whereas Bi4-bismuthane
5a was not formed at all when bismuthane 1 was reacted with
tert-butyllithium followed by iodide 2a at 278 °C (entry 2).
These results suggest that the tris-ortholithiation of compound 1
was the crucial step for the formation of a dendrimer-type Bi4-
bismuthane 5a and that it did not proceed to completion at
Table 1 Reaction of lithiated bismuthane 1 with halides 2
Conditions for step i
ButLi
Yield (%)a
Entry
Halide
(equiv.)
T/°C
1
3
4
5
1
2
3
4
5
2a
2a
2a
2a
2b
1.1
3.3
3.3
3.3
3.3
278
25 37
18
31
11
8
0
0
13
49
11
278
9
4
6
2
7
9
2
2
278 to 220
278 to 0
278 to 0
6
a Based on total bismuth (1 + 2) employed.
Chem. Commun., 1997
2295

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SO2NEt2
Ar Cl
Ar Bi
Cl
Bi
3
Ar
Bi
R
R
1
R
R
Bi
Cl Ar
Bi
Ar
Bi
R
Ar
i
Cl
R
+
3
Li
R
R
Cl Bi Cl
Ar Ar
Ar
Bi
7b
Bi
Ar
m
3-m
Ar
Ar
Bi
R
R
4
Bi
Bi
Ar
ii
Ar
Ar
Bi
Ar
R
R
iii
R
+
Bi
Bi
iv
Ar
Ar
Ar
Ar
Bi
R
R
R
Bi
R
Bi
Ar
Ar
R = SO2NEt2
a; Ar = 2-(Et2NSO2)C6H4, X = I
b; Ar = 4-MeC6H4, X = Cl
Ar
Bi
R
R
Ar
Bi
R
R
v, vi
Bi
R
Bi
R
Bi
Ar
Ar
Ar
Bi
Bi
Ar
Ar
Ar
5
6a
Scheme 1 Reagents and conditions: i, ButLi, THF, 278 to ca. 0 °C, 1 h; ii, Ar2BiX 2, 278 °C to room temp.; iii, SO2Cl2 (3.5 equiv.), CH2Cl2, room temp.,
3 h, 55%; iv, Na2S2O3 (aq), CH2Cl2, room temp., 1 h, 92%; v, ButLi (6.6 equiv.), THF, 278 to 0 °C, 1 h; vi, Ar2BiI 2a (6 equiv.), 278 °C to room
temp.
mixture was allowed gradually to warm to room temp. and quenched with
brine. The aqueous phase was extracted twice with ethyl acetate, and the
combined extracts were dried over MgSO4, and evaporated under reduced
Footnotes and References
* E-mail: suzuki@kuchem.kyoto-u.ac.jp
† Selected data for 5a: mp 162–164 °C (Found: C, 39.63; H, 4.61; N, 4.50.
pressure to leave a white solid, which was chromatographed on silica gel
C90H123Bi4N9O18S9 requires C, 39.40; H, 4.52; N, 4.59%); dH (200 MHz,
using hexane–ethyl acetate as the eluent to give bismuthane 1, Bi2-
CDCl3) 7.97 (6 H, d, J 7.6 Hz), 7.89 (3 H, d, J 7.3 Hz), 7.80 (3 H, d, J 7.3
Hz), 7.67 (6 H, d, J 7.6 Hz), 7.45 (6 H, t, J 7.6 Hz), 7.30 (6 H, t, J 7.6 Hz),
7.16 (3 H, t, J 7.3 Hz), 3.27 (36 H, q, J 6.6 Hz), 1.13 (54 H, t, J 6.6 Hz);
MALDI-TOF, m/z 2766.2 ([M + Na]+ requires 2766.5). For 5b: mp
bismuthane 3a and Bi3-bismuthane 4a in this elution order in 25, 37 and
18% isolated yields, respectively.
110–112 °C (Found: C, 43.03; H, 4.00; N, 2.03. C72H81Bi4N3O6S3 requires
1 A. J. Ashe III, Adv. Organomet. Chem., 1990, 30, 77. Also see: H. Suzuki
C, 42.88; H, 4.05; N, 2.08%); dH (CDCl3) 8.11 (3 H, dd, J 7.3, 1.2 Hz), 7.85
and Y. Matano, in Chemistry of Arsenic, Antimony and Bismuth, ed. N. C.
(3 H, dd, J 7.3, 1.2 Hz), 7.58 (12 H, d, J 7.8 Hz), 7.3–7.1 (15 H, m), 3.22 (12
Norman, Blackie Academic, Glasgow, 1997.
2 For a survey of dendrimers, see: J. M. J. Fre´chet, C. J. Hawker, I. Gitsov
and J. W. Leon, J. Macromol. Sci., Pure Appl. Chem., 1996, A33, 1399;
J. Issberner, R. Moors and F. Vo¨gtle, Angew. Chem., Int. Ed. Engl., 1994,
H, q, J 7.0 Hz), 2.30 (18 H, s), 1.01 (18 H, t, J 7.0 Hz); MALDI-TOF, m/z
2039.6 ([M + Na]+ requires 2039.6). For 7b: mp 156–157 °C (Found: C,
38.55; H, 3.62; N, 1.90. C72H81Bi4Cl6N3O6S3 requires C, 38.79; H, 3.66; N,
1.88%); dH (CDCl3) 8.5–8.3 (12 H, m), 7.87 (3 H, d, J 7.0 Hz), 7.79 (3 H,
33, 2413 and references therein.
d, J 7.0 Hz), 7.63 (3 H, t, J 7.0 Hz), 7.5–7.3 (12 H, m), 3.34 (12 H, q, J 7.2
3 A. I. Meyers and K. Lutomski, J. Org. Chem., 1979, 44, 4464;
H. Watanabe, R. A. Schwarz, C. R. Hauser, J. Lewis and D. W. Slocum,
Can. J. Chem., 1969, 47, 1543. For reviews of directed orthometalation,
Hz), 2.42, 2.37 (18 H, two s), 1.02 (18 H, t, J 7.2 Hz); MALDI-TOF, m/z
2252.2 ([M + Na]+ requires 2252.3). For 6a: (Found: C, 38.72; H, 4.40; N,
4.62. C210H285Bi10N21O42S21 requires C, 38.57; H, 4.39; N, 4.50%); dH
(CDCl3) 8.0–7.8 (21 H, m), 7.8–7.7 (9 H, m), 7.7–7.6 (12 H, m), 7.5–7.2 (24
H, m), 7.2–7.1 (9 H, m), 3.26 (84 H, br q), 1.12 (126 H, br t); dC (200 MHz
CDCl3) 178.6, 175.5, 174.3, 147.1, 144.4, 140.8, 139.9, 138.3, 135.2, 129.3,
127.8, 41.8, 40.3, 40.0, 14.1, 13.0, 12.7.
‡ General procedure: To a solution of bismuthane 1 (0.42 g, 0.5 mmol) in
THF (7 ml) was added tert-butyllithium (n-pentane solution; 1.9 m 3 0.29
ml, 0.55 mmol) at 278 °C. After stirring for 1 h at this temperature, a THF
solution (5 ml) of iodide 2a (0.38 g, 0.5 mmol) was added. The reaction
see: V. Snieckus, Chem. Rev., 1990, 90, 879; P. Beak and V. Snieckus,
Acc. Chem. Res., 1982, 15, 306.
4 H. Suzuki, T. Murafuji and N. Azuma, J. Chem. Soc., Perkin Trans. 1,
1993, 1169.
5 H. Suzuki and T. Murafuji, J. Chem. Soc., Chem. Commun., 1992,
1143.
Received in Cambridge, UK, 1st September 1997; 7/06338E
2296
Chem. Commun., 1997