Synthesis and characterization of silicon-based group 14 dendrimers Si{(CH2)2Sn[(CH2)4MPh 3]3}4 (M = Ge, Sn)

Article abstract of DOI:10.1021/om060853l

The catalytic hydrogermylation of Si(CH=CH₂)₄ with Ph₃GeH yielded Si(CH₂CH₂GePh₃) ₄ (1). In contrast, Sn(CH=CH₂)₄ and Sn(CH ₂CH=CH₂)

Full text of DOI:10.1021/om060853l

Organometallics 2007, 26, 397-402
397
Synthesis and Characterization of Silicon-Based Group 14
Dendrimers Si{(CH2)2Sn[(CH2)4MPh3]3}4 (M ) Ge, Sn)
Herbert Schumann* and Yilmaz Aksu
Institut fu¨r Chemie der Technischen UniVersita¨t Berlin, Strasse des 17. Juni 135,
D-10623 Berlin, Germany
ReceiVed September 18, 2006
The catalytic hydrogermylation of Si(CHdCH2)4 with Ph3GeH yielded Si(CH2CH2GePh3)4 (1). In
contrast, Sn(CHdCH2)4 and Sn(CH2CHdCH2)4 reacted with Ph3GeH under the same conditions,
forming Ph3Ge(CH2)2GePh3 (2) and Ph3Ge(CH2)3GePh3 (3), respectively, whereas the reaction of
Sn(CH2CH2CHdCH2)4 and Ph3GeH afforded the expected tin-based metallodendrimer Sn[(CH2)4-
GePh3]4 (4). The reactions of Si[(CH2)2SnBr3]4 with the Grignard reagents RMgBr (R ) CHdCH2,
CH2CHdCH2, (CH2)2CHdCH2)) produced Si[(CH2)2Sn(CHdCH2)3]4 (5), Si[(CH2)2Sn(CH2CHdCH2)3]4
(6), and Si[(CH2)2Sn(CH2CH2CHdCH2)3]4 (7). While hydrogermylation of 5 and 6 with Ph3GeH resulted
in the formation of 2 and 3, respectively, compound 7 reacted with Ph3GeH, providing the expected
second-generation Si/Ge/Sn heterometallodendrimer Si{(CH2)2Sn[(CH2)4GePh3]3}4 (8). Correspondingly,
hydrostannylation of 7 with Ph3SnH yielded Si{(CH2)2Sn[(CH2)4SnPh3]3}4 (9). All compounds were
characterized by multinuclear NMR studies (1H, 13C, 119Sn), mass spectrometry (MALDI-TOF, EI), and
elemental analyses.
dendrimers have been described in the literature,7 only few
reports concerning the synthesis of main group metal based
dendrimers are known so far.8
Introduction
In the past decade, dendrimers attracted enormous attention
due to their unique chemical properties arising from their special
and well-defined architecture1 and their potential application
in catalysis,2 medicine,3 material sciences,4 or host guest
chemistry.5 Metallodendrimers6 represent a new class of den-
drimers in which metal ions or metal complexes either are
connected to outer functional groups of the pure organic
dendrimer, thus forming the surface of the basic framework,
or, in favorable cases, are part of the interior of the dendrimer.
Within a short time, metallodendrimers took over an important
role in the development of quite new materials useful in electro-,
photo-, and magnetochemistry. In contrast to the preparation
of pure organic dendrimerssthe majority of which were
obtained by the basic divergent or convergent routesthe
synthesis of metallodendrimers, especially of those containing
covalently bonded metal-carbon moieties, suffers from limita-
tions in suitable reagents and synthetic methods. Although
several methods for the preparation of transition metal containing
A further challenge was the synthesis of heterometallic den-
drimers, which were suggested to improve specific chemical
and physical properties of the homometallic dendrimers.9 How-
ever, preparative methods for the synthesis of metallodendrimers
containing different metals, in particular main group metals, are
hardly developed.10 The only examples reported up to now are
silicon-based dendrimers with alternating direct bonded silicon
and germanium atoms11 as well as peripherally substituted
carbosilane dendrimers containing lithium and organotin frag-
ments.12
(7) (a) Achar, S.; Puddephatt, J. Organometallics 1995, 14, 1681. (b)
Stebani, U.; Lattermann, G.; Wittenberg, M.; Wendorff, J. H. Angew. Chem.
1996, 108, 1941; Angew. Chem., Int. Ed. Engl. 1996, 35, 1858. (c) Balzani,
V.; Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi, M. Acc. Chem.
Res. 1998, 31, 26. (d) Reetz, M. T.; Giebel, D. Angew. Chem. 2000, 112,
2614; Angew. Chem., Int. Ed. 2000, 39, 2498. (e) Lang, H.; Lu¨hmann, B.
AdV. Mater. 2001, 13, 1523.
(8) (a) Beer, P. D.; Kocian, O.; Mortimer, R. J.; Ridgway, C. J. Chem.
Soc., Chem. Commun. 1991, 1460. (b) Nagasaki, T.; Kimura, O.; Ukon,
M.; Arimori, S.; Hamachi, I.; Shinkai, S. J. Chem. Soc., Perkin Trans. 1
1994, 75. (c) Bochkarev, M. N.; Katkova, M. Usp. Khim. 1995, 64, 1106.
(d) Huc, V.; Boussaguet, P.; Mazerolles, P. J. Organomet. Chem. 1996,
521, 253. (e) Suzuki, H.; Kurata, H.; Matano, Y. Chem. Commun. 1997,
2295. (f) Majoral, A. M.; Caminade, A. Chem. ReV. 1999, 99, 845. (g)
Semchikov, Yu. D.; Bochkarev, M. N. Vysokomol. Soedin., Ser. A Ser. B
2002, 44, 2293. (h) Pestova, I. I.; Khanov, E. N.; Kulikova, T. I.; Kurskii,
Yu. A.; Khorshev, S. Ya.; Bustina, T. G.; Zaitsev, S. D.; Semchikov, Yu.
D.; Bochkarev, M. N. Vysokomol. Soedin., Ser. A Ser. B 2004, 46, 1438.
(9) Angurell, I.; Rossell, O.; Seco, M.; Ruiz, E. Organometallics 2005,
24, 6365.
(10) (a) Benito, M.; Rossell, O.; Seco, M.; Segale´s, G. Organometallics
1999, 18, 5191. (b) Alonso, E.; Astruc, D. J. Am. Chem. Soc. 2000, 122,
3222. (c) Casado, C. M.; Gonza´lez, B.; Cuadrado, I.; Alonso, B.; Mora´n,
M.; Losada, J. Angew. Chem., Int. Ed. 2000, 39, 2235. (d) Angurell, I.;
Muller, G.; Rocamora, M.; Rossell, O.; Seco, M. Dalton Trans. 2003, 1194.
(e) Angurell, I.; Muller, G.; Rocamora, M.; Rossell, O.; Seco, M. Dalton
Trans. 2004, 2450.
* To whom correspondence should be addressed. E-mail: schumann@
chem.tu-berlin.de.
(1) (a) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic
Molecules: Concepts, Syntheses, PerspectiVes; VCH: Weinheim, Germany,
1996. (b) Dendrimers II: Architecture, Nanostructure and Supramolecular
Chemistry; Vo¨gtle, F., Ed.; Topics in Current Chemistry 210; Springer-
Verlag: Berlin, Germany, 2000.
(2) (a) Astruc, D.; Chardac, F. Chem. ReV. 2001, 101, 2991. (b) Oosterom,
G. E.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Angew.
Chem. 2001, 113, 1878; Angew. Chem., Int. Ed. 2001, 40, 1828.
(3) Krause, W.; Hackmann-Schlichter, N.; Maier, F. K.; Mu¨ller, R.
Dendrimers in Diagnostics. In Dendrimers II: Architecture, Nanostructure
and Supramolecular Chemistry; Vo¨gtle, F., Ed.; Topics in Current Chemistry
210; Springer-Verlag: Berlin, Germany, 2000; pp 261-308.
(4) (a) Venturi, M.; Serroni, S.; Juris, A.; Campagna, S.; Balzani, V.
Top. Curr. Chem. 1998, 197, 193. (b) Hecht, S.; Fre´chet, J. M. J. Angew.
Chem. 2001, 113, 76; Angew. Chem., Int. Ed. 2001, 40, 74.
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10.1021/om060853l CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/10/2006

398 Organometallics, Vol. 26, No. 2, 2007
Schumann and Aksu
Recently, we succeeded in the sythesis of the tin analogues13
of the organosilicon7e,14 and organogermanium8c,d,g,h dendrimers
already known. In the meantime, we developed a method to
synthesize the first all-tin dendrimer by the divergent15 as well
as by the convergent16 route and consequently prepared a series
of novel tin-based dendrimers.17 In this paper we describe a
simple method for the synthesis of hybrid metallodendrimers
of group 14 elements, resulting in the isolation of the first
Si/Ge/Sn heterotrimetallic dendrimer.
Si(CH2CH2GePh3)4 (1).
A
stirred solution containing
Si(CHdCH2)4 (0.39 g, 2.89 mmol) and 5 drops of a solution of
H2PtCl6 (0.1 M) in isopropanol was treated with Ph3GeH (4.40 g,
14.43 mmol) at 45 °C. After stirring the reaction mixture for 24 h
at this temperature it was cooled to room temperature. The addition
of pentane (25 mL) caused the precipitation of a white solid, which
was separated, redissolved in toluene (5 mL), and again precipitated
by adding pentane (25 mL). The precipitate was separated, washed
several times with a mixture of pentane/diethyl ether (1:1), and
then carefully dried in vacuum, giving 1 as white solid (3.65 g,
1
93%). Mp: 111 °C. H NMR (400.13 MHz, CDCl3): δ 0.68-
Experimental Section
0.80 (m, 8H, SiCH2), 1.22-1.34 (m, 8H, GeCH2), 7.28-7.40 (m,
36H, Ph-Hpara/meta), 7.40-7.45 (m, 24H, Ph-Hortho). 13C{1H} NMR
(100.61 MHz, CDCl3): δ 4.30 (SiCH2), 6.70 (GeCH2), 128.18
(Ph-Cmeta), 128.85 (Ph-Cpara), 134.98 (Ph-Cortho), 137.01
(Ph-Cipso). MS MALDI-TOF (IAA, THF): 1379.80 (calcd 1379.30)
[M + Na]+, 1419.8 [M + Na + K]+ (calcd 1418.30). Anal. Calcd
for C80H76Ge4Si (1355.93): C, 70.87; H, 5.65. Found: C, 70.73;
H, 5.57.
General Comments. All manipulations involving air-sensitive
compounds were carried out in dry, oxygen-free solvents and under
an inert atmosphere of nitrogen using standard Schlenk techniques.
Melting points were measured in sealed capillaries with a Bu¨chi
510 melting point determination apparatus and are uncorrected.
Elemental analyses were performed on a Perkin-Elmer Series II
CHNS/O analyzer 2400. The NMR spectra were recorded on Bruker
ARX 200 (1H, 200.13 MHz; 13C, 50.32 MHz) and ARX 400 (1H,
400.13 MHz; 13C, 100.64 MHz; 119Sn, 149.21 MHz) spectrometers
at ambient temperature. Chemical shifts are reported in ppm and
Attempted
Hydrogermylation
of
Sn(CHdCH2)4.
Sn(CHdCH2)4 (0.45 g, 1.98 mmol) was dropped slowly to a stirred
mixture of Ph3GeH (3.02 g, 9.92 mmol) and AIBN (0.08 g, 5 mol
%, 0.50 mmol). Stirring of the reaction mixture at 45 °C for 24 h
and subsequent workup as in the case of 1 afforded Ph3Ge(CH2)2-
GePh3 (2) as white powder (0.52 g, 0.82 mmol). 1H NMR (400.13
MHz, CDCl3): δ 1.72 (s, 4H, GeCH2), 7.32-7.42 (m, 18H,
Ph-Hpara/meta), 7.44-7.49 (m, 12H, Ph-Hortho). 13C{1H} NMR
(100.61 MHz, CDCl3): δ 8.32 (GeCH2), 36.80 (Ph-Cipso), 128.23
(Ph-Cmeta), 128.94 (Ph-Cpara), 135.06 (Ph-Cortho). EI MS (185
°C, m/z (%)): 636.2 (4) [M]+, 608.1 (13.5) [M - C2H4]+, 305.2
(100) [HGe(C6H5)3]+, 227.1 (8.8) [HGe(C6H5)2]+, 151.1 (7.8) [HGe-
(C6H5). Anal. Calcd for C38H34Ge2 (635.87): C, 71.78; H, 5.39.
Found: C, 71.39; H, 5.43.
1
referenced to the H and 13C residues of the deuterated solvents
(1H and 13C) and to (CH3)4Sn (119Sn), respectively. IR spectra were
obtained by using 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 the 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 reflectron mode on
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 spectrometer was externally calibrated with
a mixture of three peptides. trans-Indolacrylicacid (IAA, used as
purchased) served as MALDI matrix in concentrations of 0.2 and
10 mM in THF/CH3CN (3:1), respectively. Sample solutions were
prepared with an approximate concentration of 1 mM in THF or
CH2Cl2. Solutions containing 2 mM CH3COONa, KCl, or AgI were
used as ionization agents. Sonication was applied to speed up
mixing. One microliter 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.
CH2dCHBr, CH2dCHCH2Br, CH2dCHCH2CH2Br, Ph3GeH,
Si(CHdCH2)4, Sn(CHdCH2)4, and Sn(CH2CHdCH2)4 were
used as purchased. Ph3SnH,18 Sn(CH2CH2CHdCH2)4,19 and
Attempted Hydrogermylation of Sn(CH2CHdCH2)4. The
reaction of Sn(CH2CHdCH2)4 (0.38 g, 1.34 mmol), Ph3GeH (2.05
g, 6.70 mmol), and AIBN (0.06 g, 5 mol %, 0.34 mmol) under the
conditions described above afforded Ph3Ge(CH2)3GePh3 (3)20 as a
white powder (0.32 g, 0.5 mmol). EI MS (185 °C, m/z (%)): 650.1
(0.3) [M]+, 606.9 (0.3) [M - C3H6]+, 573.1 (0.4) [M - C6H5]+,
531 (0.3) [M - C3H6 - C6H5]+, 454 (0.3) [M - C3H6 - 2C6H5]+,
377 (1.5) [M - C3H6 - 3C6H5]+, 305.1 (100) [HGe(C6H5)3]+, 227.1
(10) [HGe(C6H5)2]+, 151.1 (2) [HGe(C6H5)]. Anal. Calcd for
C39H36Ge2 (649.92): C, 72.07; H, 5.58. Found: C, 78.63; H, 8.72.
Sn[(CH2)4GePh3]4 (4). To a stirred mixture of Ph3GeH (3.36 g,
11.01 mmol) and AIBN (0.10 g, 5 mol %, 0.61 mmol) kept at 45
°C was added freshly distilled Sn(CH2CH2CHdCH2)4 (0.75 g, 2.21
mmol). Stirring of the reaction mixture for 24 h and workup in
analogy with 1 afforded 4 as white solid (3.15 g, 91%). Mp: 121
°C. 1H NMR (400.13 MHz, CDCl3): δ 0.51-0.70 (m, 8H, SnCH2),
1.31-1.54 (m, 24H, SnCH2CH2CH2CH2Ge), 7.31-7.38 (m, 36H,
Ph-Hmeta/para), 7.45-7.52 (m, 24H, Ph-Hortho). 13C{1H} NMR
13a
Si(CH2CH2SnBr3)4 were prepared according to published pro-
cedures.
(13) (a) Schumann, H.; Wassermann, B. C.; Frackowiak, M.; Omotowa,
B.; Schutte, S.; Velder, J.; Mu¨hle, S. H.; Krause, W. J. Organomet. Chem.
2000, 609, 189. (b) Krause, W.; Schumann, H. (Schering AG, Germany)
German Patent DE 197 26 340, 1999; Chem. Abstr. 1998, 128, 180522. (c)
Schumann, H.; Wassermann, B. C.; Schutte, S.; Velder, J.; Aksu, Y.; Krause,
W.; Radu¨chel, B. Organometallics 2003, 22, 2034.
(14) (a) van der Made, A. W.; van Leeuwen, P. W. N. M. J. Chem.
Soc., Chem. Commun. 1992, 1400. (b) van der Made, A. W.; van Leeuwen,
P. W. N. M.; de Wilde, J. C.; Brandes, R. A. C. AdV. Mater. 1993, 5, 466.
(c) Seyferth, D.; Son, D. Y.; Rheingold, A. L.; Ostrander, R. L. Organo-
metallics 1994, 13, 2682. (d) Majoral, J.-P.; Caminade, A.-M. Chem. ReV.
1999, 99, 845.
(15) Schumann, H.; Aksu, Y.; Wassermann, B. C. J. Organomet. Chem.
2006, 691, 1703.
(16) Schumann, H.; Aksu, Y.; Wassermann, B. C. Organometallics 2006,
25 (14), 3428.
(17) Schumann, H.; Aksu, Y.; Schutte, S.; Wassermann, B. C.; Mu¨hle,
S. H. J. Organomet. Chem. 2006, 691, 1417.
(18) Van der Kerk, G. J. M.; Noltes, J. G.; Luijten, J. G. A. J. Appl.
Chem. 1957, 7, 366.
(100.61 MHz, CDCl3): δ 8.43 (SnCH2, | J(13C117/119Sn)| ) 296.25/
1
310.23 Hz), 13.66 (SnCH2CH2CH2CH2, | J(13C119Sn)| ) not
4
detected), 29.77 (SnCH2CH2CH2, | J(13C117/119Sn)| ) 54.84 Hz),
3
2
30.86 (SnCH2CH2, | J(13C119Sn)| ) 19. 36 Hz), 128.13 (Ph-Cmeta),
128.79 (Ph-Cpara), 134.94 (Ph-Cortho), 137.36 (Ph-Cipso). 119Sn-
{1H} NMR (149.21 MHz, CDCl3): δ -11.80. MS MALDI-TOF
(IAA, THF): 1582.73 [M + Na]+ (calcd 1581.82), 1406.89 [M -
2C6H5]+. Anal. Calcd for C88H92Ge4Sn (1558.75): C, 67.81; H,
5.95. Found: C, 67.68; H, 5.83.
Si[(CH2)2Sn(CHdCH2)3]4 (5). To a solution of Si[(CH2)2SnBr3]4
(4.1 g, 2.61 mmol) in THF (50 mL) was added a solution of
CH2dCHMgBr in THF (47.9 mL, 0.85 M, 40.72 mmol) at 0 °C in
the course of 1 h. The brown reaction mixture was stirred at 75 °C
for 4 h and then at room temperature for 12 h. The resulting mixture
was carefully hydrolyzed at 0 °C and filtered off from precipitated
(19) Petersen, D. J.; Robbins, M. D.; Hansen, J. R. J. Organomet. Chem.
1974, 73, 237.
(20) Gilman, H.; Gerow, C. W. J. Am. Chem. Soc. 1957, 79, 342.

Silicon-Based Group 14 Dendrimers
Organometallics, Vol. 26, No. 2, 2007 399
magnesium salt (D4-frit). The residue was extracted three times
with diethyl ether (20 mL). The combined organic phases were
washed once with a saturated aqueous solution of NH4Cl (50 mL)
and three times with a saturated aqueous solution of NaCl (50 mL
each). Drying of the organic phase over Na2SO4 and subsequent
evaporation of the solvents in vacuum (10-2 mbar) gave 5 as
light yellow oil (2.21 g, 90%). IR (KBr, film): ν(CdC) 1639 cm-1
(s). 1H NMR (200.13 MHz, CDCl3): δ 0.75-1.86 (m, 16H,
CH2CH2Sn), 5.70-5.86 (m, 24H, Sn(CHdCH2)3), 6.20-6.58 (m,
12H, Sn(CHdCH2)3). 13C{1H} NMR (50.32 MHz, CDCl3): δ 2.45
Ph-Hortho). 13C{1H} NMR (100.61 MHz, CDCl3): δ 0.47 (SiCH2),
1
6.44 (SiCH2CH2), 8.29 (SnCH2CH2CH2CH2, | J(13C117/119Sn)| )
4
288.88/302.17 Hz), 13.65 (SnCH2CH2CH2CH2, | J(13C119Sn)| ) not
3
detected), 29.85 (SnCH2CH2CH2CH2, | J(13C119Sn)| ) 54.84 Hz),
2
30.94 (SnCH2CH2CH2CH2, | J(13C119Sn)| ) 18.82 Hz), 128.12
(Ph-Cmeta), 128.78 (Ph-Cpara), 134.90 (Ph-Cortho), 137.29 (Ph-
Cipso). 119Sn{1H} NMR (149.21 MHz, CDCl3): δ -7.35. MS
MALDI-TOF (IAA, THF): 4958.20 [M + Na]+ (calcd 4958.47),
4783.9 [M - 2C6H5]+. Anal. Calcd for C272H292Ge12SiSn4
(4935.24): C, 66.20; H, 5.96. Found: C, 65.88; H, 5.71.
2
1
(CH2CH2Sn, | J(13C119Sn) ) 34.61 Hz), 6.35 (CH2Sn, | J(13C117/119Sn)|
Si{(CH2)2Sn[(CH2)4SnPh3]3}4 (9). In analogy with the synthesis
of 4, Ph3SnH (4.95 g, 14.10 mmol), AIBN (0.12 g, 5 mol %, 0.73
mmol), and 7 (1.20 g, 0.94 mmol) were reacted to yield 9 as a
viscous, yellowish oil (3.24 g, 63%). 1H NMR (400.13 MHz,
CDCl3): δ 0.53-0.60 (m, 16H, SiCH2CH2), 0.60-0.73 (m, 24H,
SnCH2CH2CH2CH2), 1.33-1.60 (m, 72H, SnCH2CH2CH2CH2),
7.22-7.42 (m, 108H, Ph-Hmeta/para), 7.43-7.58 (m, 72H,
Ph-Hortho). 13C{1H} NMR (100.61 MHz, CDCl3): δ 0.75 (SiCH2),
2
) 385.01/403.00 Hz), 135.52 (Sn(CHdCH2)3, | J(13C119Sn)| ) not
1
detected), 136.45, (Sn(CHdCH2)3, | J(13C117/119Sn)| ) 438.42/
458.85 Hz). 119Sn{1H} NMR (149.21 MHz, CDCl3): δ -122.75.
EI MS (114 °C; m/z (%)): 940.7 (0.7) [M]+, 482.9 (23) [M -
2C2H4Sn(CHdCH2)3]+, 456 (6) [M - 2C2H4Sn(CHdCH2)3
-
CHdCH2]+, 428.8 (3) [M - 2CHdCH2 - 2C2H4Sn(CHdCH2)3]+,
401.8 (4) [M - 2C2H4Sn(CHdCH2)3 - 3CHdCH2]+, 347.9 (4)
[M - 2C2H4Sn(CHdCH2)3 - 5CHdCH2]+, 201 (100) [C2H4Sn-
(CHdCH2)3]+. Anal. Calcd for C32H52SiSn4 (939.61): C, 40.91;
H, 5.58. Found: C, 40.68; H, 5.51.
1
6.55 (SiCH2CH2), 8.16 (SnCH2CH2CH2CH2SnPh3, | J(13C117/119Sn)|
1
)286.92/301.91Hz),10.60(SnCH2CH2CH2CH2SnPh3,| J(13C117/119Sn)|
)
376.02/393.73 Hz), 31.47 (SnCH2CH2CH2CH2SnPh3,
2
3
| J(13C119Sn)|
)
22.07 Hz, | J(13C119Sn)|
) 57.77 Hz),
Si[(CH2)2Sn(CH2CHdCH2)3]4 (6). To a solution of Si[(CH2)2-
SnBr3]4 (3.8 g, 2.42 mmol) in THF (50 mL) was added a solution
of CH2dCHCH2MgBr in THF (57.2 mL, 0.66 M, 37.75 mmol) at
0 °C. Workup similar to that used for the synthesis of 5 yielded 6
as a yellowish, viscous oil (2.12 g, 79%). IR (KBr, film): ν
31.88 (SnCH2CH2CH2CH2SnPh3, | J(13C119Sn)| ) 18.80 Hz,
2
3
3
| J(13C119Sn)| ) 64.03 Hz), 128.41 (Ph-Cmeta, | J(13C119Sn)| )
47.14 Hz), 128.75 (Ph-Cpara, | J(13C119Sn)| ) 11.99 Hz), 139.03
4
(Ph-Cipso
,
| J(13C117/119Sn)|
) 458.86/480.11 Hz), 136.97
1
(Ph-Cortho, | J(13C119Sn)| ) 34.88 Hz), 119Sn{1H} NMR (149.21
MHz, CDCl3): δ -7.24 (Snint), -99.31 (Snperiph). MS MALDI-
TOF (IAA, THF): 5510.9 [M + Na]+ (calcd 5511.7), 5621.2 [M
+ Na + Ag]+ (calcd 5619.5). Anal. Calcd for C272H292SiSn16
(5488.44l): C, 59.53; H, 5.36. Found: C, 59.10; H, 5.14.
2
1
(CdC) 1622 cm-1(s). H NMR (200.13 MHz, CDCl3): δ 0.64-
0.97 (m, 16H, CH2CH2Sn), 1.84-1.96 (d, 24H, Sn(CH2CHdCH2)3,
2
| J(13H119Sn)| ) 61.04 Hz), 4.60-4.93 (m, 24H, Sn(CH2CHd
CH2)3), 5.80-6.10 (m, 12H, Sn(CH2CHdCH2)3). 13C{1H} NMR
1
(50.32 MHz, CDCl3): δ 1.67 (CH2CH2Sn, | J(13C117/119Sn)| )
2
305.45/319.35 Hz), 6.69 (CH2CH2Sn, | J(13C119Sn)| ) 34.88 Hz),
1
15.97 (Sn(CH2CHdCH2)3, | J(13C117/119Sn)| ) 239.51/250.41 Hz),
Results and Discussion
3
110.54 (Sn(CH2CHdCH2)3, | J(13C119Sn)| ) not detected), 137.01
The goal of our investigations was to synthesize metalloden-
drimers of the second generation containing different group 14
elements. For that purpose, we started with the synthesis of first-
generation silicon-centered dendrimers having terminal trior-
ganogermanium or triorganotin groups, which in turn could be
further functionalized.
2
(Sn(CH2CHdCH2)3, | J(13C119Sn)|
)
45.78 Hz). 119Sn{1H}
NMR (149.21 MHz, CDCl3): δ -34.23. MS MALDI-TOF
(2-(4-hydroxiphenylazo)benzoic acid (HABA), THF): 1131 [M +
Na]+ (calcd 1131). Anal. Calcd for C44H76SiSn4 (1107.93): C,
47.70; H, 6.91. Found: C, 47.39; H, 6.73.
Si[(CH2)2Sn(CH2CH2CHdCH2)3]4 (7). To a solution of
Si[(CH2)2SnBr3]4 (4.0 g, 2.55 mmol) in THF (50 mL) was added
a solution of CH2dCHCH2CH2MgBr in THF (113.7 mL, 0.35 M,
39.78 mmol) at 0 °C. Workup similar to that used for the synthe-
sis of 5 afforded 7 as a yellowish, viscous oil (2.71 g, 83%). IR
(KBr, film): ν(CdC) 1639 cm-1(s). 1H NMR (200.13 MHz,
CDCl3): δ 0.67-0.77 (m, 16H, SiCH2CH2Sn), 0.95 (t, 24H
Synthesis of Si/Ge Dendrimers. In analogy with the
synthesis of tetrakis[2-(triphenylstannyl)ethyl]silane,17 we ob-
tained the corresponding germanium derivative Si(CH2CH2-
GePh3)4 (1) by hydrogermylation of tetravinylsilane with
triphenylgermane. In the presence of H2PtCl6 triphenylgermane
adds cleanly to the olefinic ligands of the educt following the
anti-Markownikow rule, thus affording 1 in almost quantitative
yields. The course of the reaction can easily be controlled by
IR spectroscopy. The signal of the vinyl double bond of the
educt decreases continuously and disappears completely after
24 h. To facilitate the mixing of the reactants by stirring despite
the absence of a solvent, the reaction was carried out at 45 °C,
that means above the melting point of Ph3GeH. This hydro-
germylation reaction runs slower than the analogous hydrostan-
nylation of tetravinylsilane17 (Scheme 1).
2
Sn(CH2CH2CHdCH2)3, | J(13H117/119Sn)| ) 45.78/47.93 Hz), 2.20-
2.37 (m, 24H, Sn(CH2CH2CHdCH2)3), 4.86-5.08 (m, 24H, Sn-
(CH2CH2CHdCH2)3), 5.75-5.99 (m, 12H, Sn(CH2CH2CHd
CH2)3). 13C{1H} NMR (50.32 MHz, CDCl3): δ 1.33 (CH2CH2Sn,
1
| J(13C117/119Sn)|
) 305.45/319.62 Hz), 6.64 (CH2CH2Sn,
2
| J(13C119Sn)| ) 31. 61 Hz), 8.15 (Sn(CH2CH2CHdCH2)3,
1
| J(13C117/119Sn)| ) 289.65/303.00 Hz), 30.90 (Sn(CH2CH2CHd
CH2)3, | J(13C119Sn)| ) 17.71 Hz), 112.97 (Sn(CH2CH2CHdCH2)3,
2
4
| J(13C119Sn)| ) not detected), 141.93 (Sn(CH2CH2CHdCH2)3,
3
| J(13C119Sn)| ) 48.77 Hz). 119Sn{1H} NMR (149.21 MHz,
Compound 1 could be isolated in high purity after workup
with pentane as an air- and moisture-stable white solid that melts
at 166 °C without decomposition. It is soluble in tetrahydrofuran,
toluene, and halogenated hydrocarbons but insoluble in alkanes
and diethyl ether. The 1H NMR spectrum shows two multiplet
signals for the ethylene groups at 0.68 to 0.80 (SiCH2) and 1.22
CDCl3): δ -3.07. MS MALDI-TOF (IAA, THF): 1384.61 [M +
Ag]+ (calcd 1384.19), 1430.43 [M + 2Na + Ag]+ (calcd 1430.19).
Anal. Calcd for C56H100SiSn4 (1276.26): C, 52.70; H, 7.90.
Found: C, 52.47; H, 7.69.
Si{(CH2)2Sn[(CH2)4GePh3]3}4 (8). In analogy with the synthesis
of 4, Ph3GeH (4.66 g, 15.28 mmol), AIBN (0.13 g, 5 mol %,
0.79 mmol), and 7 (1.30 g, 1.02 mmol) were reacted to afford 8 as
a viscous, white oil (3.60 g, 72%). 1H NMR (400.13 MHz,
CDCl3): δ 0.53-0.60 (m, 16H, SiCH2CH2), 0.60-0.73 (m, 24H,
SnCH2CH2CH2CH2), 1.33-1.60 (m, 72H, SnCH2CH2CH2CH2),
7.22-7.42 (m, 108H, Ph-Hmeta/para), 7.43-7.58 (m, 72H,
Scheme 1

400 Organometallics, Vol. 26, No. 2, 2007
Schumann and Aksu
azoisobutyronitrile (AIBN) to give the redistribution products
Ph3GeCH2CH2GePh3 (2) and Ph3GeCH2CH2CH2GePh3 (3)20
instead of the expected hydrogermylation products tetrakis[2-
(triphenylgermyl)ethyl]stannane and tetrakis[2-(triphenylger-
myl)propyl]stannane (Scheme 2). Variation of the reaction
temperature, use of other solvents, changing the stoichiometry,
or using other catalysts did not result in the formation of even
traces of the desired dendrimers.21 The hydrostannylation of
tetravinyl- and tetraallylstannane with Ph3SnH runs in a similar
way.15
In contrast to the results described above and again in analogy
with our earlier investigations on corresponding hydrostanny-
lation reactions,16 tetra(but-3-enyl)stannane reacts with tri-
phenylgermane in the presence of 5 mol % of AIBN, yielding
tetrakis[4-(triphenylgermyl)butyl]stannane (4) (Scheme 2). The
pure white solid obtained in almost quatitative yields is soluble
in all commonly used organic solvents except alkanes and
diethyl ether. It is stable in air and water and melts at 121 °C.
Figure 1. MALDI-TOF mass spectrum of tetrakis[4-(triphenylger-
myl)butyl]stannane (4).
Scheme 2
1
The H NMR spectrum of 4 shows two multiplets for the
butyl chain at 0.51-0.70 (SnCH2) and 1.31-1.54 ppm
(CH2CH2CH2CH2GePh3).
The magnitudes of the J(13C117/119Sn) coupling constants
observed for the methylene group resonances in the 13C{1H}
NMR spectrum of 4 allow the assignment of the signals
1
3
2
according to the generally established series | J| > | J| > | J|
> | J|, but in this connection it is worth noting that the 119Sn
4
coupling signals of the CH2 group, at a distance of four bonds
from the tin atom and bonded to the germanium atom, could
to 1.34 ppm (GeCH2), and the 13C{1H} NMR spectrum also
reflects the constitution of the compound, revealing two sharp
resonances at 4.30 and 6.70 ppm for the silicon- and germanium-
bonded ethylene groups, respectively. In the MALDI-TOF mass
spectrum appear signals at m/z 1379.8 (calcd 1379.3) and 1419.8
(calcd 1418.3), corresponding to the molecular ions [M + Na]+
and [M + Na + K]+. No significant fragmentation was
observed. The attempts to grow dendrimers of the second
generation via functionalization of the outer triphenylgermanium
groups of 1 failed. Bromination of 1 did not afford isolable
uniform products.
not be detected: δ (ppm) 8.43 (SnCH2, | J(13C117/119Sn)| )
1
296.25/310.23 Hz), 29.77 (SnCH2CH2CH2, | J(13C117/119Sn)| )
3
54.84 Hz), 30.86 (SnCH2CH2, | J(13C119Sn)| ) 19. 36 Hz), and
2
13.66 (SnCH2CH2CH2CH2Ge, | J(13C119Sn)| ) not detected).
4
The 119Sn{1H} NMR spectrum shows only one signal at
-11.80 ppm, improving the uniformity of the dendrons and their
proposed empirical formula.
The MALDI-TOF mass spectrum confirms the constitution
of the molecule according to a signal at m/z ) 1582.73 for [M
+ Na]+. The absence of signals for molecules being only
partially hydrogermylated proves the structural uniformity of
the compound. The signal at m/z ) 1406.89 corresponds to a
Synthesis of Sn/Ge Dendrimers. Tetravinyl- and tetraallyl-
stannane react with Ph3GeH in the presence of 5 mol % of
Figure 2. 119Sn{1H} NMR spectra of compounds 5, 6, and 7 in CDCl3.

Silicon-Based Group 14 Dendrimers
Organometallics, Vol. 26, No. 2, 2007 401
Figure 3. 13C{1H} NMR spectrum of tetrakis{2-[tris{4-(triphenylgermyl)butyl}stannyl]ethyl}silane (8) in CDCl3.
Scheme 3
Scheme 4
fragment formed by the loss of two phenyl groups by Ge-C
bond cleavage (Figure 1).
Until now, we did not succeed in preparing dendrimers of
the second generation via substitution of the 12 germanium
bonded phenyl groups by, for example, bromine.
Synthesis of Si/Sn/Ge Dendrimers. To grow dendrimers of
the second generation containing three different group 14
elements, we used the divergent route and started with tetrakis-
[2-(tribromostannyl)ethyl]silane,13a which was converted to
tetrakis[2-(trivinylstannyl)ethyl]silane (5), tetrakis[2-(triallyl-
stannyl)ethyl]silane (6), and tetrakis[2-(tributenylstannyl)ethyl]-
silane (7) by reaction with the appropriate Grignard reagents in
THF (Scheme 3).
5, 6, and 7 were isolated in yields of 80 to 90% as light
yellow, fairly air- and water-stable oils. Their 1H NMR spectra
show the characteristic resonances of the protons of the
respective vinyl group as two multiplets in the regions between
5.70 and 6.58 (5), 4.60 and 6.10 (6), and 4.86 and 5.99 Hz (7).
The 13C{1H} NMR spectra display distinguishable signals for
all carbon atoms. Except for the signals of the appropriate
terminal methylene group, all other signals show 119Sn coupling
satellites. Position and intensity of the signals as well as the
magnitude of the tin coupling constants allow a clear assignment.
The 119Sn{1H} NMR spectra of 5, 6, and 7 (Figure 2) display
only one resonance signal, thus confirming the uniform structure
of the appropriate dendritic molecules.
Whereas the EI mass spectrum of 5 exhibits the molecular
ion peak at m/z 940.07, the EI mass spectra of 6 and 7 show an
extensive fragmentation of the molecules according to the
fragility of the allyl- and butenyltin units. However, the MALDI-
TOF mass spectra of 6 and 7 reveal the corresponding ion peaks
at m/z 1131 [M + Na]+ (calcd 1131) and m/z 1384.61 [M +
Ag]+ (calcd 1384.19), respectively.
The hydrogermylation as well as the hydrostannylation of 5
and 6 with Ph3GeH and Ph3SnH, respectively, did not result in
the formation of the expected dendrimers Si{(CH2)2Sn[(CH2)n-
GePh3]3}4 and Si{(CH2)2Sn[(CH2)nSnPh3]3}4 (n ) 2, 3), but
afforded Ph3Ge(CH2)nGePh3 (n ) 2 (2), 3 (3)20) and Ph3Sn-
(CH2)nSnPh3 (n ) 2,22 323), respectively. In contrast, 7 reacts
with Ph3GeH and Ph3SnH in the desired way, forming tetrakis-
(21) Aksu, Y. Ph.D. Thesis, Technische Universita¨t Berlin, Berlin,
Germany, 2005.

402 Organometallics, Vol. 26, No. 2, 2007
Schumann and Aksu
to the chemical shift value of the corresponding tin atom in 4
(-11.8 ppm). The 119Sn chemical shift of the peripheral tin atom
in 9 (-99.31 ppm) is in accordance to that in Sn{(CH2)4Sn-
[(CH2)4SnPh3]3}4 (-98.88 ppm).16
The perfect monodisperse nature of both compounds was
confirmed by their MALDI-TOF mass spectra, displaying
signals for the molecular ions augmented by sodium at m/z
4958.20 for 8 and 5510.9 for 9. In the case of 8, there are also
fragmentation peaks corresponding to the successive loss of two
phenyl groups from the germanium atom. Significant peaks
attributable to impurities or defect structures were not detected
(Figure 4).
Conclusion
Novel first-generation silicon- and tin-centered dendrimers
carrying peripheral triphenylgermanium and trivinyl-, triallyl-,
and tributenyltin groups have been prepared by hydrogermy-
lation of Si(CHdCH2)4 and Sn(CH2CH2CHdCH2)4 and by
metathetical reactions of Si(CH2CH2SnBr3)4 with the Grignard
reagents RMgBr (R ) CHdCH2, CH2CHdCH2, CH2CH2CHd
CH2). 1H, 13C, and 119Sn NMR spectroscopic as well as MALDI-
TOF mass spectrometric investigations evidenced that all
synthetic steps proceed efficiently without steric hindrance and
competitive reactions. It could be demonstrated that only the
first-generation dendrimer with peripheral tributenyltin groups
could be hydrometalated to give Si{(CH2)2Sn[(CH2)4GePh3]3}4
and Si{(CH2)2Sn[(CH2)4SnPh3]3}4 as the first metallodendrimers
of the second generation containing different group 14 elements.
Figure 4. MALDI-TOF mass spectrum of Si{(CH2)2Sn[(CH2)4-
GePh3]3}4 (8).
{2-[tris{4-(triphenylgermyl)butyl}stannyl]ethyl}silane (8) and
tetrakis{2-[tris{4-(triphenylstannyl)butyl}stannyl]ethyl}silane (9),
respectively, which were isolated as air-stable viscous oils
(Scheme 4). In spite of all efforts, we were not successful in
crystallizing these products, until now.
The absence of the resonances belonging to the vinyl part of
the starting material and the appearance of five multiplets for
the protons of the SiCH2CH2, SnCH2, SnCH2(CH2)3, PhHmeta+para
,
and Phortho groups with an intensity ratio 4:6:18:27:18 in the
1H NMR spectra of 8 and 9 reflect the complete hydrometala-
tion of 7. Further proofs for the clear formation of 8 and 9
are their 13C{1H} NMR spectra, which are almost identical
with those for the organotin dendrimers of the second-genera-
tion Sn{(CH2)3Sn[(CH2)4SnPh3]3}4 and Sn{(CH2)4Sn[(CH2)4-
SnPh3]3}4.16 The spectrum of 8 is depicted in Figure 3.
Acknowledgment. Financial support by the Bundesminis-
terium fu¨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
“Synthetische, mechanistische und reaktionstechnische Aspekte
von Metallkatalysatoren” at the TU Berlin. We are grateful to
Dr. Sevil Aksu, Akdeniz U¨ niversitesi, Antalya/Turkey, and Prof.
Dr. Ingeborg Schumann for helpful discussions.
The 119Sn{1H} NMR spectra of 8 and 9 show the resonances
for the internal tin atom at -7.35 (8) and -7.24 ppm (9),
respectively. They are slightly shifted to higher fields compared
(22) Kaufmann, T.; Kriegesmann, R.; Altpeter, B.; Steinseifer, F. Chem.
Ber. 1982, 115, 1810.
(23) Ducharme, Y.; Latour, S.; Wuest, J. D. Organometallics 1984, 3,
208.
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