Convergent synthesis and characterization of organotin dendrimers Sn{(CH2)nSn[(CH2)4SnPh 3]3}4 (n = 3, 4)

Article abstract of DOI:10.1021/om0602005

The reaction of the ω-haloalkyltin trihalides Br(CH₂) ₃SnBr₃ and Br(CH₂)₄SnBr₃ with 3 equiv of but-3-enylmagnesium bromide yielded Br(CH₂) ₃Sn(CH₂CH₂

Full text of DOI:10.1021/om0602005

3
428
Organometallics 2006, 25, 3428-3434
Convergent Synthesis and Characterization of Organotin
Dendrimers Sn{(CH ) Sn[(CH ) SnPh ] } (n ) 3, 4)
2
n
2 4
3 3 4
Herbert Schumann,* Yilmaz Aksu, and Birgit C. Wassermann
Institut f u¨ r Chemie der Technischen UniVersit a¨ t Berlin, Strasse des 17. Juni 135,
D-10623 Berlin, Germany
ReceiVed March 2, 2006
The reaction of the ω-haloalkyltin trihalides Br(CH
but-3-enylmagnesium bromide yielded Br(CH Sn(CH
CHdCH (4). Both dendritic branches can be converted into their corresponding Grignard reagents,
whose consequent treatment with 0.25 M amounts of SnCl resulted in the formation of the den-
drimers Sn[(CH Sn(CH CH CHdCH (5) and Sn[(CH Sn(CH CH CHdCH (6), respectively.
The subsequent hydrostannation of 5 and 6 delivered Sn{(CH Sn[(CH SnPh (7) and
Sn{(CH Sn[(CH SnPh (8) as dendrimers of the second generation. All compounds were
2
)
3
SnBr
3
and Br(CH
2
)
4
SnBr
3
with 3 equiv of
2
)
3
2
CH CHdCH
2
)
2 3
(3) and Br(CH
2
)
4
Sn(CH CH
2
2
-
2 3
)
4
2
)
3
2
2
2
)
3
]
4
2
)
4
2
2
2 3 4
) ]
2
)
3
2
)
4
3 3 4
] }
2
)
4
2
)
4
3 3 4
] }
1
13
119
characterized by elemental analysis, H, C, and Sn NMR spectroscopy, and MALDI-TOF mass
spectrometry.
Introduction
An increasing expectance for materials with new properties
based on the synthesis of dendritic arms (dendrons) and the
subsequent condensation of them with a multifunctional core
unit. Due to the multiple reactive sites of the dendrons, it is
11
focused interest on polymer research, from the traditional linear
polymers to the more promising hyperbranched and dendritic
polymers.1 Such fascinating macromolecules found rapidly
essential to develop a strategy that leads to no damage of those
intermediate compounds during their gradual synthesis and the
-6
12-15
final linkage with the nuclei.
7
widespread applications in many fields of modern chemistry.
In contrast to pure organic dendrimers, the number of
metallodendrimers, especially those consisting of covalently
Although most of the first dendrimers were prepared by the
divergent route, the concept of convergent synthesis occupied
in a short time an important place in the development of new
bonded metal-carbon moieties, is very limited, mainly due to
16-18
the lack of suitable reagents and synthetic methods.
Only
8
dendritic macromolecules. The attractiveness of this method
a very few main group metal based dendrimers have been
is based on the ability to prepare pure dendrimers free of any
19,20
described so far.
Recently we have been successful in the
imperfectly built architectures.9 The convergent approach is
,10
21
synthesis of organotin dendrimers analogous to the well-known
organosilicon and organogermanium dendrimers. On the
basis of the results of our previous work
2
2
23
*
To whom correspondence should be addressed. E-mail:
Schumann@chem.tu-berlin.de.
1) Issbener, J.; Moors, R.; V o¨ gtle, F. Angew. Chem. 1994, 106, 2507;
Angew. Chem., Int. Ed. Engl. 1994, 33, 2413.
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Tetrahedron 1998, 54, 8543.
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24,25
in this area, we
(
(11) Matthews, O. A.; Shipway, A. N.; Stoddart, J. F. Prog. Polym. 1998,
23, 1.
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1330.
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(18) Astruc, D. C. R. Acad. Sci. Paris 1996, 322, 757.
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Soc., Chem. Commun. 1991, 1460. (b) Nagasaki, T.; Kimura, O.; Ukon,
M.; Arimori, S.; Himachi, I.; Shinkai, S. J. Chem. Soc. Perkin Trans. 1
1994, 75.
(
(
1
(
Appl. Chem. 1978, 50, 871. (c) Lehn, J. M. Science 1985, 227, 849. (d)
Lehn, J. M. Angew. Chem. 1988, 100, 91; Angew. Chem., Int. Ed. Engl.
1
988, 27, 89.
5) (a) Hyatt, J. A. J. Org. Chem. 1978, 43, 1808. (b) V o¨ gtle, F.; Weber,
E. Angew. Chem. 1974, 86, 896; Angew. Chem., Int. Ed. Engl. 1974, 13,
14.
6) . Murakami, Y.; Nakano, K.; Akiyoshi, K. F. J. Chem. Soc., Perkin
Trans. 1 1981, 2800.
7) For recent reviews see: (a) Tomalia, D. A.; Naylor, A. M.; Goddard,
W. A., III. Angew. Chem. 1990, 102, 119; Angew. Chem., Int. Ed. Engl.
990, 29, 138. (b) Mekelburger, H. B.; Jaworek, W.; V o¨ gtle, F. Angew.
(
8
(
(20) Suzuki, H.; Kurata, H.; Matano, Y. J. Chem. Soc., Chem. Commun.
1997, 2295.
(21) Schumann, H.; Aksu, Y.; Wassermann, B. C. J. Organomet. Chem.
2006, 691, 1703.
(
1
Chem. 1992, 104, 1609; Angew. Chem., Int. Ed. Engl. 1992, 31, 1571. (c)
Tomalia, D. A.; Durst, H. D. Top. Curr. Chem. 1993, 165, 193. (d)
Newkome, G. R.; Moorefield, C. N. Macromol. Symp. 1994, 77, 63. (e)
Newkome, G. R.; Moorefield, C. N.; V o¨ gtle, F. In Dendritic Molecules:
Concepts, Syntheses, PerspectiVes; VCH: Weinheim, 1996.
(22) (a) van der Made, A. W.; van Leeuwen, P. W. N. N. J. Chem. Soc.,
Chem. Commun. 1992, 1400. (b) van der Made, A. W.; van Leeuwen, P.
W. N. N.; de Wilde, J. C. AdV. Mater. 1993, 466. (c) Seyferth, D.; Son, D.
Y.; Rheingold, A. L.; Ostrander, R. L. Organometallics 1994, 13, 2682.
(d) Majoral, J. P.; Caminade, A. M. Chem. ReV. 1999, 99, 845.
(23) Huc, V. P.; Boussaget, P.; Mazerolles, P. J. Organomet. Chem. 1996,
521.
(24) Schumann, H.; Wassermann, B. C.; Frackowiak, M.; Omotowa, B.;
Schutte, S.; Velder, J.; M u¨ hle, S. H.; Krause, W. J. Organomet. Chem.
2000, 609, 189.
(
8) (a) Hawker, C. J.; Fr e´ chet, J. M. J. J. Am. Chem. Soc. 1990, 112,
7
1
638. (b) Hawker, C. J.; Fr e´ chet, J. M. J. J. Chem. Soc., Chem. Commun.
990, 1010.
(
9) Xu, Z.; Kahr, M.; Walker, K. L.; Wilkins, C. L.; Moore, J. S. J. Am.
Chem. Soc. 1994, 116, 4537.
10) Wooley, K. L.; Hawker, C. J.; Fr e´ chet, J. M. J. J. Am. Chem Soc.
991, 113, 4252.
(
(25) Schumann, H.; Wassermann, B. C.; Schutte, S.; Velder, J.; Aksu,
Y.; Krause, W.; Rad u¨ chel, B. Organometallics 2003, 22, 2034.
1
1
0.1021/om0602005 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/01/2006

ConVergent Synthesis of Organotin Dendrimers
Organometallics, Vol. 25, No. 14, 2006 3429
a
b
c
d
Br (2).28 In analogy with the syn-
(25.4 g, 91 mmol), 1,4-
(1.2 g, 5.7 mmol)
focused our intention on developing a method to prepare
organotin dendrimers by the convergent way. In this paper, we
report the preparation of dendritic organotin dendrons and their
utilization for the convergent synthesis of organotin dendrimers.
Br
thesis of 1, a mixture of anhydrous SnBr
dibromobutane (98.3 g, 455 mmol), and SbEt
was stirred for 5 h at 150-160 °C. After complete conversion of
SnBr , the remaining 1,4-dibromobutane was removed under
3 2 2 2 2
SnC H C H C H C H
2
3
2
-
2
vacuum (10 mbar) and the crude product was distilled, leaving 2
as a light brown oil (32.3 g, 72%). Bp: 112-113 °C/0.3 mbar
Experimental Section
General Comments. All manipulations involving air-sensitive
compounds were carried out in dry, oxygen-free solvents under an
inert atmosphere of nitrogen using standard Schlenk techniques.
Melting points were measured in sealed capillaries with a B u¨ chi
28
1
(
3
123-124°C/0.1 mmHg ). H NMR (200.13 MHz, CDCl ): δ 2.47
2
1
117/119
a
b,c
(
3
m, | J( H
Sn)| ) 73.07/76.29 Hz, 2H, H ), 2.03 (m, 4H, H ),
d
13
1
.46 (m, 2H, H ). C{ H} NMR (50.32 MHz, CDCl
3
): δ 33.11
a
1
13 117/119
b
2
13 117/119
(
)
C , | J( C
Sn)| ) 558.31/584.19 Hz), 24.13 (C , | J( C
Sn)|
5
10 melting point determination apparatus and are uncorrected.
c
3
13 117/119
49.59/51.50 Hz), 33.79 (C , | J( C
Sn)| ) 120.44/125.89
Elemental analyses were performed on a Perkin-Elmer Series II
CHNS/O 2400 analyzer. The NMR spectra were recorded on Bruker
d
4
13 119
119
1
Hz), 31.99 (C , | J( C Sn)| ) 8.17 Hz. Sn{ H} NMR (149.21
MHz, CDCl
3
): δ -151.93. MS (100 °C, m/z (%)): 438 (19) [M
1
13
1
ARX 200 ( H, 200.13 MHz; C, 50.32 MHz) and ARX 400 ( H,
4
+
+
+
-
(
C
H
4 8
] , 415 (9) [M - Br] , 360 (58) [M - Br - C
4 8
H
] , 335
00 MHz; 13C, 100.64 MHz; Sn, 149.21 MHz) spectrometers at
119
+
+
+
+
5) [M - 2Br] , 281 (5) [SnBr
2
] , 200 (5) [SnBr] , 120 (6) [Sn] ,
ambient temperature. Chemical shifts are reported in ppm and
+
8
1
0 (6) [Br] . Anal. Calcd for C
4
H
8
Br
4
Sn (494.41): C, 9.72; H,
1
13
referenced to the H and C residues of the deuterated solvents.
.63. Found: C, 9.59; H, 1.48.
Chemical shifts for 1 Sn are given relative to (CH
19
3 4
) Sn. IR spectra
g
f
e
d
a
b
c
(
C H
2
dC HC H
2
C H
2
)
3
SnC H
2
C H
2
C H
2
Br (3). A solution of
were obtained on a Nicolet Magna System 750 spectrometer. Mass
spectra (EI, 70 eV) were recorded on a Varian MAT 311 A/AMD
instrument. Only characteristic fragments containing isotopes of
the highest abundance are listed. Relative intensities are given in
parentheses.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-
TOF) mass spectrometry was performed in the reflection mode of
an Applied Biosystems Voyager-Elite mass spectrometer equipped
with a nitrogen laser emitting at 337 nm. Acceleration voltage was
set to 20 and 25 kV, respectively, with positive or negative
ionization. The mass spectrometers were externally calibrated with
a mix of three synthesized peptides. trans-Indoleacrylic acid (IAA)
was used as a MALDI matrix at concentrations of 0.2 M and 10
1
(11.6 g, 24 mmol) in THF (50 mL) was placed in a 250 mL
three-necked flask equipped with a reflux condenser and an addition
funnel. Then 77 mL (96 mmol) of a 1.25 M (but-3-enyl)magnesium
bromide solution in THF was added slowly at 0 °C. After stirring
for 4 h at room temperature, the reaction was cooled again to 0 °C
and hydrolyzed cautiously with water. The organic fraction was
extracted with diethyl ether, washed several times with saturated
NH
4 2 4
Cl solution, and dried over Na SO . After the removal of all
volatiles, 3 was obtained as a light yellow oil (9.35 g, 96%). Bp:
1
5
3
5-56 °C/0.1 mbar. H NMR (200.13 MHz, CDCl ): δ 0.90 (m,
2
1
117/119
c
a
b
|
J( H
Sn)| ) 48.14/50.29 Hz, 2H, H ,), 2.07 (m, 2H, H ), 3.41
2
1
117/119
d
(
m, 2H, H ), 1.03 (m, | J( H
Sn)| ) 47.07/49.00 Hz, 6H, H ,),
e
f
g
13
1
2
.34 (m, 6H, H ), 5.91 (m, 3H, H ), 5.02 (m, 6H, H ). C{ H}
mM in THF/CH
prepared with an approximate concentration of 1mM in THF or
CH Cl . Solutions containing 2 mM CH COONa, KCl, or AgI were
3
CN (3:1), respectively. Sample solutions were
a
1
13 117/119
NMR (50.32 MHz, CDCl
3
): δ 7.89 (C , | J( C
Sn)| ) 282.83/
b
2
13 119
c
2
95.91 Hz), 30.55 (C , | J( C Sn)| ) 14.17 Hz), 37.06 (C ,
2
2
3
3
13 117/119
d
1
13 117/119
|
J( C
Sn)| ) 75.20/78.20 Hz), 8.36 (C , | J( C
Sn)| )
used as ionization agents. Sonification was applied to speed up
mixing. One µL of the sample was mixed with 1 µL of the matrix
solution, and 1 µL of the resulting mixture was deposited on a
stainless steel flat plate and allowed to dry at room temperature.
trans-Indoleacrylic acid, R-cyano-4-hydroxycinnamic acid,
e
2
13 119
3
05.18/319.35 Hz), 30.62 (C , | J( C Sn)| ) 18.53 Hz), 141.43
f
3
13 117/119
g
119
1
(
C , | J( C
Sn)| ) 46.89/49.05 Hz), 113.13 (C ). Sn{ H}
3
NMR (149.21 MHz, CDCl
): δ -5.77. MS (100 °C, m/z (%)):
+
+
4
C
C
05 (0.3) [M] , 351 (28) [M - C
4
H
7
] , 309 (100) [M - C
4
H
H
7
-
-
+
+
3
H
H
6
] , 255 (5) [M - 2C
] , 120 (6) [Sn] , 80 (1) [Br] . Anal. Calcd for C15
4
H
7
- C
3
H
6
] , 199 (15) [M - 3C
4
7
BrCH
Sb
to use. Ph
procedures.
2
CH
, and AlEt
SnH26 and SbEt
2
CHdCH
2
, Br(CH
2
)
3
Br, Br(CH
2
)
4
Br, SnBr
was distilled prior
were prepared according to published
2 3
, Ph SnCl,
+
+
+
3
6
H27BrSn
2
O
3
3
were used as purchased. SnCl
4
(
405.97): C, 44.38; H, 6.70. Found: C, 44.14; H, 6.58.
27
3
3
h
g
f
e
a
b
c
d
(
C H
2
dC HC H
2
C H
2
)
3
SnC H
2
C H
2
C H
2
C H
2
Br (4). In anal-
a
b
c
Br (1).28 Anhydrous SnBr
ogy with the synthesis of 3, a solution of 2 (13.5 g, 27 mmol) in
THF (50 mL) was treated at 0 °C with 73 mL (90 mmol) of a 1.25
M (but-3-enyl)magnesium bromide solution in THF. Appropriate
Br
mmol), 1,3-dibromopropane (89.2 g, 442 mmol), and SbEt
.7 mmol) were placed in a 100 mL three-necked flask equipped
3
SnC H
2
C H
2
C H
2
2
(24.6 g, 88
3
(1.2 g,
5
workup gave 4 as a light yellow oil (11.11 g, 98%). Bp: 66-67
with a reflux condenser and an addition funnel. The suspension
was warmed slowly to 155 °C within 45 min and stirred for 5 h at
1
°
|
C/0.1 mbar. H NMR (200.13 MHz, CDCl
3
): δ 0.86 (m,
2
1
117/119
Sn)| ) 48.63/50.86 Hz, 2H, H ), 1.64 (m, 2H, H ), 2.86
c d 2 1 117/119
a
b
J( H
this temperature. After complete conversion of SnBr
1
2
, the remaining
,3-dibromopropane was removed under vacuum (10-2 mbar) and
(m, 2H, H ), 3.43 (m, 2H, H ), 0.94 (m, | J( H
Sn)| ) 46.58/
e
f
g
4
8.73 Hz, 6H, H ), 2.27 (m, 6H, H ), 5.85 (m, 3H, H ), 4.98 (m,
the crude product was distilled, leaving 1 as a light orange oil (35.5
h
13
1
a
28
1
3
6H, H ). C{ H} NMR (50.32 MHz, CDCl ): δ 8.11 (C ,
g, 84%). Bp: 94-95 °C/0.2 mbar (111-112 °C/0.1 mmHg ). H
1
13 117/119
b
2
13 119
2
1
117/119
| J( C
17.74 Hz), 37.01 (C , | J( C
(C ), 8.25 (C , | J( C
Sn)| ) 298.40/312.38 Hz), 25.29 (C , | J( C Sn)| )
NMR (200.13 MHz, CDCl
7
NMR (50.32 MHz, CDCl
5
3
): δ 2.54 (m, | J( H
Sn)| ) 73.07/
c 13 1
c 3 13 117/119
a
b
Sn)| ) 55.51/58.07 Hz), 33.28
6.51 Hz, 2H, H ), 2.28 (m, 2H, H ), 3.54 (m, 2H, H ). C{ H}
d
e
1
13 117/119
f
a
1
13 117/119
Sn)| ) 301.09/315.07 Hz), 30.73 (C ,
3
): δ 32.39 (C , | J( C
Sn)| )
2
13 119
g
3
13 119
b
2
13 119
| J( C Sn)| ) 18.28 Hz), 141.78 (C , | J( C Sn)| ) 48.93 Hz),
h 119 1
3
77.65/604.36 Hz), 33.93 (C , | J( C Sn)| ) 45.78 Hz), 27.80
c 3 13 117/119 119 1
113.08 (C ). Sn{ H} NMR (149.21 MHz, CDCl ): δ -6.75. MS
(
C , | J( C
Sn)| ) 137.60/143.60 Hz). Sn{ H} NMR (149.21
): δ -152.33. MS (100 °C; m/z (%)): 438 (0.05) [M
+
+
(
100 °C, m/z (%)): 419 (0.6) [M] , 365 (86) [M - C
4 7
H
] , 309
MHz, CDCl
-
(
3
+
+
+
+
+
(100) [M - 2C H ] , 285 (72) [M - Br - C H ] , 255 (7) [M -
C
H
3 6
] , 401 (9) [M - Br] , 359 (19) [M - Br - C
3
H
6
+
] , 280
4
7
4
7
+
+
+
+
+
3C H ] , 175 (57) [M - Br - 3C H ] , 120 (4) [Sn] , 81 (0.6)
3) [SnBr
2
] , 199 (11) [M - 3Br - C
3
H
6
] , 120 (2) [Sn] , 80 (1)
4
7
4
7
+
+
[Br] . Anal. Calcd for C H BrSn (420.00): C, 45.76; H, 6.96.
[
Br] . Anal. Calcd for C Br Sn (480.39): C, 7.50; H, 1.26.
3
H
6
4
16 29
Found: C, 45.57; H, 6.68.
Found: C, 7.39; H, 1.19.
z
c
b
a
p
d
e
f
g
2 2 2 2 2 2 3 4
Sn [C H C H C H Sn (C H C H C HdC H ) ] (5). The Grig-
(26) Van der Kerk, G. J. M.; Noltes, J. G.; Luijten, J. G. A. J. Appl.
nard reagent 3a was prepared from 3 (15.2 g, 37.4 mmol) and
magnesium turnings (1.8 g, 73.9 mmol) in THF (75 mL) in the
presence of 1,2-dibromoethane (1.0 g, 5.3 mmol). After treatment
of the vigorously stirred solution with ultrasound for 0.5 h and
Chem. 1957, 7, 366.
(
27) Stamm, W.; Breindl, A. Angew. Chem. 1994, 96, 99.
(28) Bulten, E. J.; Gruter, H. F. M.; Martens, H. F. J. Organomet. Chem.
1
976, 117, 329.

3
430 Organometallics, Vol. 25, No. 14, 2006
Schumann et al.
ortho
2
13 119
p
subsequently boiling for 5 h, the reaction mixture was cooled to
room temperature and was stirred further overnight. The unreacted
Mg was separated, and the filtrate was cooled to 0 °C. Then freshly
458.85/ 480.11 Hz), 136.94 (Ph-C , | J( C Sn )| ) 34.88 Hz),
meta
3
13 119
p
para
128.39 (Ph-C , | J( C Sn )| ) 47.14 Hz), 128.73 (Ph-C
,
4
13 119
p
119
p 1
| J( C Sn )| ) 13.08 Hz).
Sn { H} NMR (149.21 MHz,
z
m
p
distilled SnCl
4
(1.66 g, 6.37 mmol) was dropped in cautiously,
CDCl
3
): δ -13.30 (Sn ), -14.93 (Sn ), -98.98 (Sn ). MS-
+
and the reaction mixture was warmed to room temperature and
stirred for 5 h. The solution was then hydrolyzed with water at
MALDI-TOF (matrix IAA): m/z 5659.40 [M + Na] (calcd
5658.40). Anal. Calcd for C276
H300Sn17 (5635.15): C, 58.83; H,
0
°C, and the residue was extracted with diethyl ether. The result-
5.37. Found: C, 58.41; H, 5.03.
z
d
c
b
a
m
e
f
g
h
p
ing organic phase was washed, dried with Na SO , filtered, and
2
4
Sn {C H
(8). 8 was prepared by a procedure analogous with that described
for 7 with Ph SnH (10.2 g, 29.1 mmol), AIBN (0.24 g, 1.5 mmol,
2 2 2 2 2 2 2 2 6 5 3 3 4
C H C H C H Sn [C H C H C H C H Sn (C H ) ] }
-
2
concentrated under vacuum (10 mbar). The crude product
was purified by column chromatography over silica gel (eluent
hexane). 5 was obtained as a viscous light yellow oil (6.43 g, 71%).
IR (KBr/film): ν(CdC) 1639 cm (s). H NMR (200.13 MHz,
CDCl
3
5 mol %), and 6 (2.3 g, 1.56 mmol). The product was obtained as
a viscous white oil (6.37 g, 72%). H NMR (200.13 MHz,
-
1
1
1
a,c
b
e
f,g,h
): δ 0.83-0.97 (m, 16H, H ), 1.56-1.89 (m, 8 H, H ), 0.94
3
CDCl ): δ 0.85-1.15 (m, 24H, H ), 1.58-1.97 (m, 72H, H ),
3
2
1
117/119
d
a,d
b,c
(
8
m, | J( H
Sn)| ) 46.42/48.14 Hz, 8H, H ), 2.19-2.36 (m,
1.15-1.31 (m, 16H, H ), 1.97-2.22 (m, 16H, H ), 7.85-7.98
e
f
g
13
1
ortho
meta/para 13
1
H, H ), 5.75-5.98 (m, 4H, H ), 4.86-5.08 (m, 8H, H ). C{ H}
(m, 72H, Ph-H ), 7.56-7.75 (m, 108H, Ph-H
). C{ H}
a
1
13 117/119
p
a,d,e
1
13 117/119
NMR (50.32 MHz, CDCl
3
): δ 12.15 (C , | J( C
Sn )|
NMR (50.32 MHz, CDCl
3
): δ 8.40 (C , | J( C
Sn)|
b
2
13 117/119
z,p
b,c
f
3
13 119
p
)
309.81/325.61 Hz), 18.94 (C , | J( C
Sn )|
)
) 294.82/308.17 Hz), 32.14 (C ), 31.79 (C , | J( C Sn )| )
c
1
13 117/119
z
63.49 Hz, |
) 55.04 Hz, |
376.29/393.73 Hz), 139.01 (Ph-Cipso
2
J(13
C
119 Sn
C
m
)| ) 19.07 Hz), 31.37 (C
)| ) 22.34 Hz), 10.70 (C
g
, |
3
J(13
C
119 Sn
117/119Sn
119Sn
m
)|
5
3.77/56.24 Hz), 8.48 (C , | J( C
Sn )| ) 294.82/308.38 Hz),
d
1
13 117/119
z
2
J(13
119Sn
p
h
, |
1
J(13
C
p
)|
8
.33 (C , | J( C
Sn )|
)
296.46/310.08 Hz), 30.86
e
2
13 119
z
f
3
13 119
z
)
,
|
1
J(13
C
p
)|
)
(
4
C , | J( C Sn )| ) 17.71 Hz), 141.95 (C , | J( C Sn )| )
ortho
2
13 119
p
g
119
1
458.58/479.83 Hz), 136.95 (Ph-C , | J( C Sn )| ) 35.15 Hz),
8.50/50.68 Hz), 113.90 (C ).
Sn{ H} NMR (149.21 MHz,
meta
3
13 119
p
para
z
p
128.40 (Ph-C , | J( C Sn )| ) 47.96 Hz), 128.73 (Ph-C
,
CDCl
3
):
δ
-10.84 (Sn ), -7.60 (Sn ). MS-MALDI-TOF
4
13 119
p
119
p 1
+
| J( C Sn )| ) 13.08 Hz).
Sn { H} NMR (149.21 MHz,
(matrix IAA): m/z 1425.68 [M] (calcd 1424.40). Anal. Calcd for
z
m
p
CDCl
3
): δ -11.89 (Sn ), -11.42 (Sn ), -98.88 (Sn ). MS-
60 5
C H108Sn (1422.97): C, 50.64; H, 7.65. Found: C, 50.47; H, 7.51.
+
z
d
c
b
a
p
e
f
g
h
MALDI-TOF (matrix IAA): m/z 5714.60 [M + Na] (calcd
2 2 2 2 2 2 2 3 4
Sn [C H C H C H C H Sn (C H C H C HdC H ) ] (6). The
+
5
+
714.5), 5783.71 [M + 4Na] (calcd 5783.50), 5823.70 [M + Na
Grignard reagent 4a was prepared by a procedure analogous to
that described for 3a from magnesium turnings (1.8 g, 73.9 mmol),
+
Ag] (calcd 5823.50). Anal. Calcd for C280
C, 59.09; H, 5.45. Found: C, 58.73; H, 5.23.
H
308Sn17 (5691.26):
1
,2-dibromoethane (1 g, 5.3 mmol), and 4 in THF (75 mL). To
this solution was added dropwise freshly distilled SnCl (1.58 g,
.07 mmol) at 0 °C. The reaction mixture was stirred for 5 h
at room temperature and then hydrolyzed slowly with water at
°C. Appropriate workup with water and purification by column
4
Results and Discussion
6
The simplest method of a convergent preparation of organotin
dendrimers consists of condensation of the well-established
haloalkyltin compounds R3Sn(CH2)nX with tin tetrachloride,
but our first attempt to synthesize a dendrimer using this
procedure resulted in no isolable products. However, ω-ha-
loalkyltin trihalides, first reported by Bulten, are suitable
reagents for the synthesis of a variety of ω-haloalkyltin
compounds. They are excellent reactive key intermediates for
the convergent preparation of organotin dendrimers. Such
0
chromatography in an inert atmosphere over dried silica gel
and hexane as eluent gave 6 as a viscous light yellow oil (6.55 g,
7
2
9
3%). IR (KBr/film): ν(CdC) 1639 cm- (s). H NMR (200.13
1
1
3
0
a,d
MHz, CDCl ): δ 0.70-0.90 (m, 16H, H ), 1.32-1.74 (m, 16H,
3
2
8
b,c
2
1
117/119
f
p
e
H ), 0.94 (m, | J( H
Sn )| ) 46.42/48.34 Hz, 24H, H ),
g
2
.19-2.36 (m, 24H, H ), 5.75-6.00 (m, 12H, H ), 4.85-5.10
h
13
1
(
m, 24H, H ).
C{ H} NMR (50.32 MHz, CDCl
3
):
δ
a
1
13 117/119
z
9
.12 (C , | J( C
Sn )|
) 306.54/321.52 Hz), 31.85
b
3
13 117/119
z
2
13 119
p
ω-haloalkyltin trihalides are readily accessible by the reaction
(
C , | J( C
Hz), 31.98 (C , | J( C
19.35 Hz), 8.75 (C , | J( C
.33 (C , | J( C Sn )|
Sn )| ) 52.32/54.50 Hz, | J( C Sn )| ) 20.16
c
3 13 117/119 p 2 13 119 z
of the corresponding haloalkyls with stannous halides.28
Sn ) ) 53.95/56.13 Hz, | J( C Sn )|
d
1
13 117/119
p
)
8
(
4
Sn )| ) 295.91/309.81 Hz),
Thus, the treatment of stannous bromide with an excess of
1,3-dibromopropane and 1,4-dibromobutane in the presence
of triethylantimony at 150-160 °C resulted in the formation
of the appropriate (3-bromopropyl)tribromostannane (1) and
(4-bromobutyl)tribromostannane (2), respectively (Scheme 1).
e
1
13 117/119
p
)
296.18/309.81 Hz), 30.86
f
2
13 119
p
g
3
13 119
p
C , | J( C Sn )| ) 17.71 Hz), 141.90 (C , | J( C Sn )| )
h
119
1
8.23/50.41 Hz), 112.94 (C ).
Sn{ H} NMR (149.21 MHz,
z
p
CDCl
3
):
δ
-11.32 (Sn ), -6.98 (Sn ). MS-MALDI-TOF
+
(matrix IAA): m/z 1479.20 [M] (calcd 1480.40). Anal. Calcd for
64 5
C H116Sn (1479.08): C, 51.97; H, 7.91. Found: C, 50.72; H, 7.75.
Scheme 1
z
c
b
a
m
d
e
f
g
p
Sn {C H
2
C H
2
C H
2 2 2 2 2 6 5 3 3 4
Sn [C H C H C H C H Sn (C H ) ] } (7).
A mixture of Ph
3
SnH (11.1 g, 31.6 mmol) and AIBN (0.26 g, 1.6
mmol, 5 mol %) was stirred at room temperature for 0.5 h. To this
mixture was dropped slowly 5 (2.5 g, 1.76 mmol), and the solution
was stirred until after 48 h the signals corresponding to ethylenic
protons in the IR and NMR spectra of the solution disappeared.
After addition of pentane (25 mL) to the reaction mixture, a pasty-
white precipitate was formed. Repeated purification by washing
of the crude product with a mixture of pentane/diethyl ether (1:1)
several times yielded pure 7 as a viscous white oil (7.66 g, 77%).
The air- and moisture-sensitive compounds 1 and 2 are
soluble in chlorinated hydrocarbons and tetrahydrofuran, but
insoluble in diethyl ether, alkanes, and aromatic solvents.
1
Although H NMR and some physical data have already been
28
13
reported for both compounds, no spectroscopic details ( C
1
a,c,d
H NMR (200.13 MHz, CDCl
3
): δ 0.75-1.35 (m, 40H, H ),
119
1
and Sn{ H} NMR, mass spectral data) were given. Com-
g
b,e,f
1
.86-2.17 (m, 24H, H ), 1.53-1.86 (m, 56H, H ), 7.85-7.89
13
1
pounds 1 and 2 show the C-SnBr3 resonances in the C{ H}
ortho
meta/para 13
1
(
m, 72H, Ph-H ), 7.48-7.65 (m, 108H, Ph-H
). C{ H}
a
NMR spectra, recorded in CDCl3, at 32.39 (C ) and 33.11 ppm
a,c,d
1
13 117/119
NMR (50.32 MHz, CDCl
3
): δ 8.47 (C , | J( C
Sn)| )
a
119
1
(
C ), respectively. The
Sn{ H} NMR chemical shifts of
b
e
3
13 119
p
2
92.37/307.90 Hz), 24.89 (C ), 31.84 (C , | J( C Sn )| ) 63.76
2 13 119 m f 3 13 119 m
Hz, | J( C Sn )| ) 18.53 Hz), 31.38 (C , | J( C Sn )| )
(
(
29) Gielen, M.; Topart, J. Bull. Soc. Chim. Belg. 1971, 80, 655.
30) Aksu, Y. Ph.D. Thesis, Technische Universit a¨ t Berlin, Berlin,
2
13 119
p
g
1
13 117/119
p
5
4.77 Hz, | J( C Sn )| ) 21.53 Hz), 10.66 (C , | J( C
Sn )|
ipso
1
13 119
)
375.75/395.37 Hz), 138.98 (Ph-C
,
| J( C Sn)|
)
Germany, 2005.

ConVergent Synthesis of Organotin Dendrimers
152.33 and -151.93 ppm, as well as the corresponding
Organometallics, Vol. 25, No. 14, 2006 3431
-
Sn carbon signals appear at 7.89 (3) and 8.11 ppm (4),
respectively, significantly upfield of the parent complexes and
in the expected region observable for comparable substituted
1
13 117/119
coupling constants of | J( C
Sn)| ) 577.65/604.36 Hz and
5
58.31/584.19 Hz, respectively, are very representative for
31
31
organotin trihalides and indicate the tin atom in both com-
organotin compounds. The corresponding coupling constants
13
1
1
13 a117/119
pounds to be tetracoordinated. However, the C{ H} NMR
chemical shifts of 1, measured in THF-d8, differ slightly from
the respective values obtained in CDCl3. In contrast, the drastic
| J( C
Sn)| ) 282.83/295.91 Hz (3) and 298.40/312.38
Hz (4), which feature a decrease by an average of about 284
Hz in comparison with 1 and 2, evidence the diminished Lewis
acidity at the metal center with loss of the electron-rich bromine
atoms and fall into the range of those reported for tetracoordi-
1
13 117/119
enlarged coupling constant of | J( C
Sn)| ) 719.89/753.13
Hz and the strong upfield shifted 1 Sn{ H} resonance at
19
1
32,33
34
-306.88 ppm suggest a higher coordination at the tin atom.
nated organotin analogues. The butenyl groups deshield the
119
The Lewis acidity of the metal center, due certainly to the
presence of the electronegative bromine atoms, seems to be
sufficient for a coordination with donor ligands, like tetrahy-
drofuran.
Sn resonances by 146 to -5.77 ppm (3) and by 145 to -6.75
ppm (4) as compared with those found for 1 and 2, corroborating
1
19
the deshielding of the Sn resonances as halogen atoms are
3
4
replaced with alkene or alkyl groups.
With their very reactive SnBr3 units, 1 and 2 are suitable
starting materials for the synthesis of a variety of novel types
of functionally substituted organotin compounds by reaction with
Grignard or organolithium reagents. On the other hand, the
C-Br bond of the alkyl chain is inert enough toward such
reagents, so it is needless to protect it. It remains intact during
the reaction and could serve in turn for further activation and
functionalization of those compounds. In a previous paper, we
reported the synthesis of the first all-tin dendrimer and
investigated its synthetic potential for the preparation of new
derivatives.21 During our research we realized, that vinylic and
allylic derivatives of tin are very sensitive toward electrophilic
reagents. Redistribution reactions caused the formation of
unexpected products. Therefore, we chose the γ-butenyl chain
as building blocks for dendrons, which seem to be chemically
more stable.
In contrast to 1 and 2, the dendrons 3 and 4 are sufficiently
thermostable, allowing characterization by mass spectrometry.
The appropriate molecular ion peaks were observed at m/z 405
and 419, respectively.
The following transformation of 3 and 4 to their correspond-
ing Grignard reagents 3a and 4a by usual treatment with excess
magnesium turnings afforded only poor yields. The process
seems to be very slow and inefficacious, probably because of
the insufficient polarity of the C-Br bond, which prevents a
satisfactory conversion to the Grignard reagent. However, after
activation with 1,2-dibromoethane, treating with ultrasound for
0.5 h, and subsequent refluxing in tetrahydrofuran for 5 h, the
reaction of 3 and 4 with a surplus of magnesium produced
rapidly the desired Grignard reagents 3a and 4a in good yields
(Scheme 3). Dropwise addition of tin tetrachloride to 4 molar
equiv of solutions of 3a and 4a in tetrahydrofuran at 0 °C,
followed by stirring at ambient temperature for 5 h, resulted
rapidly in the formation of the corresponding dendrimers
tetrakis[4-(tribut-3-enylstannyl)propyl]stannane (5) and tetrakis-
[3-(tribut-3-enylstannyl)butyl]stannane (6), respectively (Scheme
3). The crude products, slightly contaminated with unreacted 3
and 4, could be purified by column chromatography in an inert
atmosphere with dried silica gel and hexane as eluent to give 5
and 6 as yellowish oils, which are moderately air sensitive and
soluble in polar solvents such as tetrahydrofuran and diethyl
ether, as well as in alkanes and aromatic solvents.
Compounds 1 and 2 react with 3 molar equiv of (but-3-enyl)-
magnesium bromide in tetrahydrofuran after 0 °C and at
completion of the reaction at room temperature for 4 h to give
(3-bromopropyl)tribut-3-enylstannane (3) and (4-bromobutyl)-
tribut-3-enylstannane (4), respectively, as light yellow liquids
in excellent yield (Scheme 2). In contrast to their parent
compounds, 3 and 4 are fairly air and moisture stable. They
are soluble in all common organic solvents.
Scheme 2
Scheme 3
1
The H NMR spectra of 3 and 4 show distinguishable and
good separated signals for all groups of protons. The relative
intensities of the butenyl substituents are stronger than those of
the butyl or propyl chain, allowing a simple location of the
a
signals. The resonances attributed to the -C H2Sn fragments
appear at 0.90 and 0.86 ppm, respectively, upfield of the
corresponding signals observed for the parent compounds 1 and
Due to the symmetry of the molecules, 5 and 6 show in their
NMR spectra only one signal for each of the different carbon
atoms in the four inner and 12 outer branches of the dendrimers,
2
, confirming the complete substitution of all bromine atoms
13
1
by the butenyl groups. The C{ H} NMR spectra reflect the
1
H NMR results. However, it must be noted that the intensity
13
confirming a complete conversion. The C NMR chemical shift
difference between the signals of the butenyl and the butyl or
c
d
values of C (3) and C (4) especially reflect the successful
condensation of the dendrons with the tin nuclei. The linkage
of the dendritic branches to the metal center results in a shielding
of these carbon atoms: The upfield shift of their resonances at
13
1
propyl substituent is more distinguishable in the C{ H} NMR
1
3
2
4
spectra. According to | J| > | J| > | J| > | J|, the assignment
a
of the signals can be established without difficulties. The -C H2-
3
7.06 and 33.28 ppm as compared to 5 (8.48 ppm) and 6 (8.75
(
(
(
31) Mitchell, T. N. J. Organomet. Chem. 1973, 59, 189.
32) Al-Allaf, T. A. K. J. Organomet. Chem. 1986, 306, 337.
33) (a) Holecek, J.; Nadvornik, M.; Handlir, K. J. Organomet. Chem.
(34) (a) Mitchell, T. N.; Walter, G. J. Organomet. Chem. 1976, 121,
1
983, 241, 177. (b) Holecek, J.; Nadvornik, M.; Handlir, K. J. Organomet.
177. (b) Mitchell, T. N.; Amamria, A.; Fabisch, B. J. Organomet. Chem.
1983, 259, 157.
Chem. 1984, 275, 43.

3
432 Organometallics, Vol. 25, No. 14, 2006
Schumann et al.
Figure 1. 13C NMR spectrum of Sn[(CH
) Sn(CH CH CHdCH ) ] (6) in CDCl .
2 4 2 2 2 3 4 3
2 3 2 2 2 3 4
Figure 2. MALDI-TOF mass spectrum of Sn[(CH ) Sn(CH CH CHdCH ) ] (5).
ppm) establishes the formation of the new compounds (Figure
[tris(4-triphenylstannylbutyl)stannyl]propyl}stannane (7) and
tetrakis{4-[tris(4-triphenylstannylbutyl)stannyl]butyl}stannane
(8), respectively (Scheme 4). Compounds 7 and 8 were isolated
from the reaction medium as very viscous white oils in moderate
yields, by repeatedly washing with a mixture of pentane/diethyl
ether (1:1). The air- and moisture-stable dendrimers are soluble
in tetrahydrofuran, chlorinated alkanes, and aromatic solvents
such as toluene, but almost insoluble in diethyl ether and
alkanes.
1
13 117/119
1
2
). The corresponding coupling constants | J( C
Sn)| )
94.82/308.38 Hz (5) and 295.91/309.81 Hz (6) evidence
tetracoordination of the tin atoms.
The 119Sn NMR spectra of 5 and 6 reveal two signals each
z
p
z
at -10.84 (Sn ), -7.60 ppm (Sn ) for 5 and -11.32 (Sn ), -6.98
p
ppm (Sn ) for 6 with different intensities. The number of signals
indicates the absence of any byproducts and confirms the
equivalence of the branches of the dendrimers, which is in
1
13
1
agreement with the H and C{ H} NMR results.
Scheme 4
Due to their high molecular weights, 5 and 6 could not be
investigated with the classical ionization methods. As discussed
21,25
in previous papers,
MALDI-TOF mass spectrometry is more
suitable for the analysis of such macromolecules. Both den-
drimers were characterized with their corresponding molecular
ion peaks, which were detected at m/z 1425.68 (5) and 1479.20
(6), respectively (Figure 2). These values were obtained with
the appropriate isotopic resolution and are in very close
agreement with the simulated ones (see Experimental Section).
The absence of lower mass peaks or those assignable to
dendrimers with missing dendrons as well as other impurities
further proves the proposed structure of the compounds.
Reaction of 5 and 6 each with 12 molar equiv of triphenyltin
hydride in the presence of 5 mol % of AIBN at room
temperature gave the second-generation dendrimers tetrakis{3-
The most characteristic feature of the H and 13C NMR
spectra is the lack of the low-field signals of the olefin groups,
confirming that the hydrostannation of all butenyl groups had
taken place completely. With the achievement of the second-
generation dendrimers, some NMR signals, especially those of
1

ConVergent Synthesis of Organotin Dendrimers
Organometallics, Vol. 25, No. 14, 2006 3433
Figure 3. 119Sn NMR spectra (149.21 MHz) of 2 in THF-d
8 3
; 4, 6, and 8 in CDCl .
Figure 4. MALDI-TOF mass spectrum of tetrakis{4-[tris(4-triphenylstannylbutyl)stannyl]butyl}stannane (8).
the inner atoms, become magnetically indistinguishable and
appear therefore at the same chemical shifts, due to the high
symmetrical structures of the new dendritic molecules. This
manifests itself in the occurrence of only one resonance for the
upfield shifted signals belong to the phenyl-substituted peripheral
metal atoms at -98.98 ppm (Sn ) and -98.88 ppm (Sn ),
respectively.
p
p
The positive ion MALDI-TOF mass spectra of compounds
7 and 8 also indicate the completeness of the synthetic route
with isotopic multiplets centered at m/z 5659.40 and m/z
5714.60, respectively, corresponding to the sodium ion adducts
(Figure 4). The well-resolved isotopic cluster patterns of high
intensity bear a close resemblance to the simulated isotopic
distribution. Signals attributable to incompletely hydrostannated
byproducts, dendrimers with missing dendrons, or end groups
were not observed.
Attempts to grow dendrimers 7 and 8 via functionalization
of the outer 12 tin atoms have failed until now. Substitution of
one, two, or all three phenyl ligands at all tin atoms e.g., by
bromine, did not result in isolable compounds.
z
m
three carbon atoms bound to the internal tin atoms Sn and Sn ,
1
13 117/119
at 8.47 ppm, | J( C
Sn)| ) 292.37/307.90 Hz (7) and 8.40
1
13 117/119
ppm, | J( C
Sn)| ) 294.82/308.17 Hz (8). The carbon
atoms bound to the phenyl-substituted peripheral tin atoms were
shifted downfield at 10.66 (7) and 10.70 ppm (8), as reflected
1
13 117/119
p
by their coupling constants | J( C
Sn )| ) 375.75/395.37
and 376.29/393.73 Hz, respectively, with values clearly larger
than those estimated for the carbon atoms mentioned above.
The 1 Sn NMR spectra of compounds 7 and 8 (Figure 3
19
119
shows a comparison of the Sn NMR spectra of 2, 4, 6, and
) exhibit exactly three resonances each for the three tin atoms
8
present in the molecules, indicating the equivalence of the
1
dendrons, thus corroborating the results found in the H and
1
3
C NMR spectra. The downfield shifted signals belong to the
internal tin atoms and are assigned by their different intensities
Conclusion
z
m
at -13.30 ppm (Sn ) and -14.93 ppm (Sn ) for 7 as well as at
-
Novel organotin dendrimers of the first generation carrying
peripheral butenyl groups have been prepared by a convergent
z
m
11.89 ppm (Sn ) and -11.42 ppm (Sn ) for 8, whereas the

3434 Organometallics, Vol. 25, No. 14, 2006
Schumann et al.
method and used as starting materials for the construction of
Acknowledgment. Financial support by the Bundesminis-
terium f u¨ r Bildung und Forschung (grant no. 03 D 0057 3) and
by Schering AG is gratefully acknowledged. This work was
also supported by the Fonds der Chemischen Industrie and the
Deutsche Forschungsgemeinschaft via the Graduiertenkolleg
1
13
119
the second-generation dendrimers 7 and 8. H, C, and Sn
NMR spectroscopic as well as MALDI-TOF mass spectrometric
investigations evidenced that all synthetic steps proceeded
efficiently without steric hindrance and competitive reactions.
ω-Haloalkyltin trihalides are easily accessible synthons for the
preparation of suitable dendrons, providing a convenient entry
into dendritic macromolecules. The ability to synthesize a variety
of dendritic branches in two steps starting from the correspond-
ing dihaloalkanes and stannous bromide represents an efficient
route for the production of functionally substituted organotin
dendrimers.
“Synthetische, mechanistische und reaktionstechnische Aspekte
von Metallkatalysatoren” at the TU Berlin. We are grateful to
Dr. Sevil Aksu, Akdeniz U¨ niversitesi, Antalya/Turkey, for
helpful discussions.
OM0602005