Synthesis and characterization of {[tris(trimethylsilyl)silyl]methyl} silanes of the formula type Me4- nSi[CH2Si(SiMe 3)3]n (n = 1-3) and derivatives

Article abstract of DOI:10.1021/om100721t

In context with systematic studies on multifunctional tetraorganylsilanes of the formula type R_4-nSi(CH₂X)_n (R = organyl, X = functional group, n = 2-4), a series of new (silylmethyl)silanes of the formula types Me_4-n

Full text of DOI:10.1021/om100721t

4548 Organometallics 2010, 29, 4548–4554
DOI: 10.1021/om100721t
Synthesis and Characterization of
{[Tris(trimethylsilyl)silyl]methyl}silanes of the Formula Type
Me4-nSi[CH2Si(SiMe3)3]n (n=1-3) and Derivatives
ꢀ
Andre Berkefeld, Dennis Troegel, Christian Burschka, and Reinhold Tacke*
€
€
Universitat Wurzburg, Institut fur Anorganische Chemie, Am Hubland, D-97074 Wurzburg, Germany
€
€
Received July 23, 2010
In context with systematic studies on multifunctional tetraorganylsilanes of the formula type
R4-nSi(CH2X)n (R=organyl, X=functional group, n =2-4), a series of new (silylmethyl)silanes
of the formula types Me4-nSi[CH2Si(SiMe3)3]n [n = 1 (5), n = 2 (6), n = 3 (7)] and
Me3-n(TMOP)Si[CH2Si(SiMe3)3]n [TMOP=2,4,6-trimethoxyphenyl, n =1 (9), n=2 (10)] was
synthesized by treatment of the corresponding (chloromethyl)silanes with [tris(trimethylsilyl)silyl]potassium-
18-crown-6 (12). Reaction of tetrakis(chloromethyl)silane (4) with 12, however, yielded the un-
expected disilacyclobutane derivative 1,1-bis(trimethylsilyl)-3,3-bis{[tris(trimethylsilyl)silyl]methyl}-1,3-
disilacyclobutane (11). Compounds 5-7 and 9-11 were characterized by elemental analyses (C, H) and
NMR spectroscopic studies in solution (1H, 13C, 29Si). In addition, compounds 6, 7, and 9-11 were
structurally characterized by single-crystal X-ray diffraction (7 was studied as the solvate 7 0.46Et2O).
3
Introduction
in situ from bromochloromethane and n-butyllithium
in tetrahydrofuran.2-5 In continuation of our systematic
studies on multifunctional tetraorganylsilanes of the type
Multifunctional tetraorganylsilanes of the formula type
R4-nSi(CH2X)n (R=organyl group, X=functional group,
n=2-4) are versatile building blocks in organosilicon chem-
istry and are also useful for diverse practical applications. For
example, (i) (nitratomethyl)silanes [R4-nSi(CH2ONO2)n]
have been demonstrated to be highly potent explosives,1 (ii)
(mercaptomethyl)silanes [R4-nSi(CH2SH)n] have been used
as multidentate ligands in iron complexes,2 and (iii) tris-
(mercaptomethyl)silanes [RSi(CH2SH)3] have been applied
as tripodal adsorbate molecules for the fabrication of self-
assembled monolayers on Au(111).3 The corresponding
multifunctional (chloromethyl)silanes [R4-nSi(CH2Cl)n]
are the most versatile starting materials in this chemistry
and can be prepared by treatment of the respective chlorosi-
lanes [R4-nSiCln] with (chloromethyl)lithium, generated
1-3,5,6
R4-nSi(CH2X)n
and inspired by studies of Marschner
et al.,7 we have been interested in the reactivity of (chloromethyl)-
silanes of the type R4-nSi(CH2Cl)n against silyl anions and have
attempted to synthesize {[tris(trimethylsilyl)silyl]methyl}-
silanes of the type Me4-nSi[CH2Si(SiMe3)3]n (n=1-4), com-
pounds 5-8,7 starting from the corresponding (chloromethyl)-
silanes 1-4. Owing to their reactive Si-Si bonds, the target
compounds 5-8 are expected to be versatile starting materials
for the synthesis of a variety of further multifunctional tetra-
organylsilanes. In addition, we attempted to synthesize the
related silanes 9 and 10, which are derivatives of 1 and 2,
respectively, that contain a silicon-bound 2,4,6-trimethoxy-
phenyl (TMOP) group instead of a methyl substituent. As the
TMOP moiety is a protection group for silicon,5a,6b,8 the
{[tris(trimethylsilyl)silyl]methyl}silanes 9 and 10 should allow
for additional functionalization at the central silicon atom.
Wereport hereon the syntheses of compounds5-7 and 9-11.
The synthesis of 8 failed; instead the 1,3-disilacyclobutane
*To whom correspondence should be addressed. Phone: þ49-931-31-
85250. Fax: þ49-931-31-84609. E-mail: r.tacke@uni-wuerzburg.de.
€
(1) (a) Klapotke, T. M.; Krumm, B.; Ilg, R.; Troegel, D.; Tacke, R.
€
J. Am. Chem. Soc. 2007, 129, 6908–6915. (b) Evangelisti, C.; Klapotke,
T. M.; Krumm, B.; Nieder, A.; Berger, R. J. F.; Hayes, S. A.; Mitzel, N. W.;
Troegel, D.; Tacke, R. Inorg. Chem. 2010, 49, 4865–4880.
(2) (a) Apfel, U.-P.; Troegel, D.; Halpin, Y.; Tschierlei, S.; Uhlemann,
(6) (a) Ilg, R.; Troegel, D.; Burschka, C.; Tacke, R. Organometallics
2006, 25, 548–551. (b) Troegel, D.; Walter, T.; Burschka, C.; Tacke, R.
Organometallics 2009, 28, 2756–2761. (c) Troegel, D.; Moller, F.; Burschka,
C.; Tacke, R. Organometallics 2009, 28, 5765–5770.
(7) Synthesis of Me3SiCH2Si(SiMe3)3: (a) Marschner, C.; Wallner,
A. Unpublished results. (b) Wallner, A., Dissertation, TU Graz,
Austria, 2006.
€
U.; Gorls, H.; Schmitt, M.; Popp, J.; Dunne, P.; Venkatesan, M.; Coey,
€
M.; Rudolph, M.; Vos, J. G.; Tacke, R.; Weigand, W., Inorg. Chem. DOI:
10.1021/ic101399k. (b) Troegel, D. Dissertation, University of W€urzburg,
W€urzburg, Germany, 2009.
(3) Weidner, T.; Ballav, N.; Siemeling, U.; Troegel, D.; Walter, T.;
Tacke, R.; Castner, D. G.; Zharnikov, M. J. Phys. Chem. C 2009, 113,
19609–19617.
(8) (a) Daiss, J. O.; Penka, M.; Burschka, C.; Tacke, R. Organome-
€
(4) (a) Kobayashi, T.; Pannell, K. H. Organometallics 1990, 9, 2201–
2203. (b) Kobayashi, T.; Pannell, K. H. Organometallics 1991, 10, 1960–
1964.
tallics 2004, 23, 4987–4994. (b) Popp, F.; Natscher, J. B.; Daiss, J. O.;
Burschka, C.; Tacke, R. Organometallics 2007, 26, 6014–6028. (c) Tacke,
R.; Popp, F.; M€uller, B.; Theis, B.; Burschka, C.; Hamacher, A.; Kassack,
M. U.; Schepmann, D.; W€unsch, B.; Jurva, U.; Wellner, E. ChemMedChem
2008, 3, 152–164. (d) Tacke, R.; Nguyen, B.; Burschka, C.; Lippert, W. P.;
Hamacher, A.; Urban, C.; Kassack, M. U. Organometallics 2010, 29, 1652–
1660.
(5) (a) Daiss, J. O.; Barth, K. A.; Burschka, C.; Hey, P.; Ilg, R.;
Klemm, K.; Richter, I.; Wagner, S. A.; Tacke, R. Organometallics 2004,
€
23, 5193–5197. (b) Troegel, D.; Lippert, W. P.; Moller, F.; Burschka, C.;
Tacke, R. J. Organomet. Chem. 2010, 695, 1700–1707.
r
pubs.acs.org/Organometallics
Published on Web 10/04/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 20, 2010 4549
derivative 11 was obtained. Compounds 5-7 and 9-11 were
characterized by elemental analyses, NMR studies in solution
(1H, 13C, 29Si), and crystal structure analyses (except for 5).
A potential mechanism for the formation of the 1,3-
disilacyclobutane 11 is depicted in Scheme 2. Successive
substitution of three of the four chlorine atoms of 4 leads to
the intermediate 14, which upon reaction with 12 affords
the intermediate 15 and tetrakis(trimethylsilyl)silane (13),
the formation of which could be established by GC/EI-MS
studies of the reaction mixture. In the last step, the inter-
mediate 15 undergoes an intramolecular cyclization (elimi-
nation of potassium chloride) to furnish the 1,3-disilacyclo-
butane 11.
The {[tris(trimethylsilyl)silyl]methyl}silanes 9 and 10 were
synthesized according to Scheme 3, starting from chloro-
(chloromethyl)dimethylsilane and trichloro(methyl)silane,
respectively. Thus, treatment of Me2Si(CH2Cl)Cl and
MeSiCl3 with 1 molar equiv of (2,4,6-trimethoxyphenyl)lithium
afforded the corresponding (2,4,6-trimethoxyphenyl)silanes 16
(63% yield) and 17 (62% yield). Reaction of 17 with (chlo-
romethyl)lithium, generated in situ from bromochlorometh-
ane and n-butyllithium in tetrahydrofuran, furnished the bis-
(chloromethyl)silane 18 (59% yield). Treatment of 16 and 18
with 12 finally afforded compounds 9 (76% yield) and 10 (77%
yield), respectively.
Compounds 6, 7, and 9-11 were isolated as colorless crys-
talline solids, whereas 5 was obtained as a colorless liquid.
The identities of all these compounds were established by
elemental analyses (C, H) and NMR spectroscopic studies
in solution (1H, 13C, 29Si). In addition, compounds 6, 7, and
9-11 were characterized by crystal structure analyses.
Crystal Structure Analyses. Compounds 6, 7, and 9-11
were structurally characterized by single-crystal X-ray diffrac-
tion. Compound 7 was studied as the solvate 7 0.46Et2O. The
3
crystal data and the experimental parameters used for these
studies are given in Table 1. The molecular structures of 7, 10,
and 11 are depicted in Figures 1-3; selected bond lengths
and angles are given in the respective figure legends (for
further details concerning the crystal structure analyses, see
the Supporting Information).
Most of the bond lengths and angles of 6, 7, and 9-11
(Figures 1-3, Supporting Information) are in the expected
ranges and therefore do not need any further comments,
except for following structural features. The Si-C-Si angles
of the SiCH2Si(SiMe3)3 moieties of the compounds studied
[119.67(5)-127.27(8)°] deviate significantly from the ideal
tetrahedral angle, probably due to the steric demand of the
two bulky substituents bound to the methylene group. Addi-
tionally, the Si4-Si1-C10 angle of 10 [117.41(9)°] is also
significantly widened [probably due to steric repulsion be-
tween the trimethylsilyl group (Si4) and the 2,4,6-trimeth-
oxyphenyl moiety], leading to a decrease of the Si3-Si1-C10
angle [101.42(9)°]. Similar structural features were also ob-
served for the related (2,4,6-trimethoxyphenyl)silane 9. The
Si-C-Si and C-Si-C angles of the 1,3-disilacyclobutane
skeleton of 11 are in the range 88.46(4)-91.59(5)°; as a con-
sequence, the angles C1-Si1-C4, C2-Si1-C3, C3-Si4-
Si12, and C4-Si4-Si11 are significantly widened [116.23(5)-
120.99(4)°].
Results and Discussion
Synthesis. The {[tris(trimethylsilyl)silyl]methyl}silanes 5-7
were synthesized according to Scheme 1, starting from the
corresponding (chloromethyl)silanes 1-3. Thus, treatment of
1-3 with [tris(trimethylsilyl)silyl]potassium-18-crown-6 (12),
generated from tetrakis(trimethylsilyl)silane9 [Si(SiMe3)4 (13)]
with potassium tert-butoxide in toluene in the presence of
1 molar equiv of 18-crown-6,10,11 yielded the compounds 5-7
(yield: 5, 82%; 6, 72%; 7, 86%). Treatment of tetrakis(chloro-
methyl)silane (4) with 12, however, did not afford the expected
tetrakis{[tris(trimethylsilyl)silyl]methyl}silane (8); instead the
1,3-disilacyclobutane derivative 11 was obtained (Scheme 1,
38% yield).
(9) Gilman, H.; Smith, C. L. J. Organomet. Chem. 1967, 8, 245–253.
(10) Synthesis and reactivity of K[Si(SiMe3)3]: (a) Marschner, C. Eur.
J. Inorg. Chem. 1998, 221–226. (b) Kayser, C.; Fischer, R.; Baumgartner, J.;
Marschner, C. Organometallics 2002, 21, 1023–1030. (c) Marschner, C.
Organometallics 2006, 25, 2110–2125. (d) Niemeyer, M. Inorg. Chem.
2006, 45, 9085–9095.
(11) Synthesis and reactivity of KSi(SiMe3)2(SiMe2)nSi(SiMe3)2K
(n=1-3): (a) Fischer, R.; Frank, D.; Gaderbauer, W.; Kayser, C.;
Mechtler, C.; Baumgartner, J.; Marschner, C. Organometallics 2003, 22,
3723–3731. (b) Zirngast, M.; Baumgartner, J.; Marschner, C. Organome-
tallics 2008, 27, 6427–6478.
Conclusions
Multifunctional tetraorganylsilanes are versatile building
blocks for synthetic organosilicon chemistry and are also
useful for diverse practical applications. In this study, we have
evaluated the potential of multifunctional (chloromethyl)-
silanes of the formula types Me4-nSi(CH2Cl)n [n=1-4 (1-4)]

4550 Organometallics, Vol. 29, No. 20, 2010
Berkefeld et al.
Scheme 1
and Me3-n(TMOP)Si(CH2Cl)n [TMOP=2,4,6-trimethoxyphe-
nyl; n =1 (16), 2 (18)] as starting materials for the prepara-
tion of a series of novel {[tris(trimethyl)silyl]methyl}silanes.
We have succeeded in synthesizing compounds of the for-
mula types Me4-nSi[CH2Si(SiMe3)3]n [n = 1-3 (5-7)] and
Me3-n(TMOP)Si[CH2Si(SiMe3)3]n [n = 1 (9), 2 (10)] by
treatment of the corresponding (chloromethyl)silanes with
allow transformations at both the peripheral silicon atoms and
the silicon atom in the 1,3-disilacyclobutane ring system (in this
context, see for example ref 10b). Future studies have to
evaluate the synthetic potential of compounds 5-7 and 9-11.
Experimental Section
(Me3Si)3SiK 18-crown-6. Unexpectedly, the analogous treat-
3
General Procedures. All syntheses were carried out under dry
nitrogen. The organic solvents used were dried and purified
according to standard procedures and stored under dry nitro-
ment of Si(CH2Cl)4 (4) with (Me3Si)3SiK 18-crown-6 resulted
3
in the formation of the 1,3-disilacyclobutane 11, which con-
tains two silicon-bound Me3Si groups and (Me3Si)3SiCH2
moieties. Compound 5-7, 9, and 10 with their reactive Si-Si
bonds are expected to be versatile starting materials for the
synthesis of a variety of further multifunctional tetraorganyl-
silanes, and compounds 9 and 10 with their silicon-bound
2,4,6-trimethoxyphenyl moiety (a protection group for silicon)
should allow for additional functionalization at the central
silicon atoms. Reactions at the Si-Si bonds of 11 should also
€
gen. A Buchi GKR-51 apparatus was used for the bulb-to-bulb
distillations. The 1H, 13C, and 29Si NMR spectra were recorded
at 23 °C on a Bruker DRX-300 (1H, 300.1 MHz; 13C, 75.5 MHz;
29Si, 59.6 MHz), a Bruker Avance 400 (1H, 400.1 MHz; 13C,
100.6 MHz; 29Si, 79.5 MHz), or a Bruker Avance 500 NMR
spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz; 29Si, 99.4 MHz).
CDCl3, CD2Cl2, or C6D6 were used as the solvent. Chemical
shifts (ppm) were determined relative to internal CHCl3 (1H, δ
7.24; CDCl3), internal CDCl3 (13C, δ 77.0; CDCl3), internal

Article
Organometallics, Vol. 29, No. 20, 2010 4551
Scheme 2
Scheme 3
CHDCl2 (1H, δ 5.32; CD2Cl2), internal CD2Cl2 (13C, δ 53.8;
CD2Cl2), internal C6HD5 (1H, δ 7.28; C6D6), internal C6D6
(13C, δ 128.0; C6D6), or external TMS (29Si, δ 0; CDCl3, CD2Cl2,
C6D6). Analysis and assignment of the 1H NMR data were
supported by 1H,1H COSY, 13C,1H HMQC, and 13C,1H HMBC
experiments. Assignment of the 13C NMR data was support-
ed by DEPT 135, 13C,1H HMQC, and 13C,1H HMBC experi-
ments. Reverse-phase medium-pressure liquid chromatography
(RP-MPLC) was performed as follows: pressure, 16 bar; col-
umn, 50 ꢀ 2.5 cm; RP-18 silica gel, YMC ODS-A, 15 μm; detec-
tor, Knauer Variable Wavelength Monitor. Melting points were
€
determined with a Buchi Melting Point B-540 apparatus using
samples in open glass capillaries.
(Chloromethyl)trimethylsilane (1). This compound was com-
mercially available (Aldrich).
Bis(chloromethyl)dimethylsilane (2). This compound was com-
mercially available (Aldrich).
Preparation of Tris(chloromethyl)methylsilane (3). This com-
pound was synthesized according to ref 2.
Preparation of Trimethyl{[tris(trimethylsilyl)silyl]methyl}silane
(5). Potassium tert-butoxide (189 mg, 1.68 mmol) and 18-crown-6
(453 mg, 1.71 mmol) were added one after another to a stirred
solution of 13 (500 mg, 1.56 mmol) in toluene (15 mL), and the
resulting mixture was stirred at 20 °C for 2 h. Subsequently,
compound 1 (191 mg, 1.56 mmol) was added dropwise to the
stirred mixture at 20 °C within 10 min, and stirring was continued
for a further 4 h. The solvent was removed under reduced pres-
sure, diethyl ether (15 mL) and water (15 mL) were added to the
residue, the organic phase was separated, and the aqueous phase
was extracted with diethyl ether (3 ꢀ 10 mL). The combined
organic extracts were dried over anhydrous sodium sulfate, the
solvent was removed under reduced pressure, and the low-boiling
components were removed by bulb-to-bulb distillation (80 °C/1
mbar). The resulting crude product was purified by column chro-
matography on RP-18 silica gel [5-20 μm, 10 g (LiCHroprep,
Merck); eluent, methanol/water (95:5 (v/v))] and subsequent RP-
MPLC on RP-18 silica gel [eluent, methanol/water (95:5 (v/v); flow
rate, 12 mL min-1]. The solvent of the eluate was removed under
reduced pressure and the residue dried in vacuo (0.01 mbar, 20 °C,
2 h) to give 5 in 82% yield as a colorless liquid (428 mg, 1.28 mmol).
Preparation of Tetrakis(chloromethyl)silane (4). This com-
pound was synthesized according to ref 5a.

4552 Organometallics, Vol. 29, No. 20, 2010
Berkefeld et al.
Table 1. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 6, 7 0.46Et2O, 9, 10, and 11
3
10
6
7 0.46Et2O
3
9
11
empirical formula
formula mass, g mol-1
collection T, K
λ(Mo KR), A
cryst syst
C22H64Si9
581.54
193(2)
0.71073
monoclinic
P21/c (14)
16.138(2)
13.614(2)
18.046(2)
90
93.836(15)
90
3955.9(10)
4
0.976
C31H90Si13 0.46C4H10
3
O
C21H46O3Si5
487.03
173(2)
0.71073
triclinic
P1 (2)
9.8311(13)
11.0157(13)
15.9346(19)
79.739(14)
84.820(15)
63.886(13)
1524.6(3)
2
C30H72O3Si9
733.69
193(2)
0.71073
monoclinic
Pm (6)
10.017(2)
26.789(4)
10.0531(17)
90
118.64(2)
90
2367.8(7)
2
1.029
0.277
804
C28H80Si12
754.00
100(2)
0.71073
monoclinic
P21/n (14)
19.2212(15)
26.902(2)
19.2710(14)
90
95.416(4)
90
9920.2(13)
8
1.010
862.13
193(2)
˚
0.71073
orthorhombic
Pca21 (29)
24.156(4)
14.3086(17)
34.201(5)
90
90
90
11821(3)
8
0.972
space group (no.)
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
D(calcd), g cm-3
μ, mm-1
F(000)
1.061
0.252
532
0.312
1288
0.304
3832
0.330
3328
cryst dimens, mm
θ range, deg
index ranges
0.5 ꢀ 0.5 ꢀ 0.5
5.42-58.26
-22 e h e 22,
-18 e k e 18,
-24 e l e 24
58 711
10 362
0.0497
10 362
0
300
1.035
0.0596/0.2742
0.0356
0.0987
þ0.372/-0.292
0.5 ꢀ 0.5 ꢀ 0.5
4.42-56.06
-31 e h e 31,
-18 e k e 18,
-44 e l e 45
150 836
28 371
0.0642
28 371
1
873
0.4 ꢀ 0.4 ꢀ 0.1
5.02-58.24
-13 e h e 13,
-14 e k e 15,
-21 e l e 21
17 727
7820
0.0328
7820
2
276
1.069
0.0681/0.1048
0.0387
0.1161
þ0.459/-0.337
0.5 ꢀ 0.4 ꢀ 0.3
4.56-53.84
-12 e h e 12,
-33 e k e 33,
-12 e l e 12
24 080
10 099
0.0549
10 099
0
440
1.060
0.0797/0.8833
0.0464
0.1314
þ0.595/-0.329
0.30 ꢀ 0.22 ꢀ 0.132
2.60-66.48
-29 e h e 29,
-40 e k e 41,
-28 e l e 29
223 384
37 929
0.0591
37 929
0
769
1.061
0.0329/2.7925
0.0334
0.0946
þ0.540/-0.368
no. of collected reflns
no. of indep reflns
Rint
no. of reflns used
no. of restraints
no. of params
Sa
1.036
weight params a/bb
R1c [I > 2σ(I)]
wR2d (all data)
max./min. resid
0.0724/0.6252
0.0438
0.1126
þ0.532/-0.298
-3
˚
electron dens, e A
P
aS = { [w(Fo2 - Fc2)2]/(n - p)}0.5; n = no. of reflections; p = no. of parameters. b w-1 = σ2(Fo2) þ (aP)2 þ bP, with P = [max(Fo2,0) þ 2Fc2]/3.
P
P
P
P
cR1 = ||Fo| - |Fc||/ |Fo|. d wR2 = { [w(Fo2 - Fc2)2]/ [w(Fo2)2]}0.5
.
1H NMR (400.1 MHz, CD2Cl2): δ -0.18 (s, 2 H, SiCH2Si), 0.05
(s, 9 H, CSiCH3), 0.17 (s, 27 H, SiSiCH3). 13C NMR (100.6 MHz,
CD2Cl2): δ -8.3 (SiCH2Si), 1.3 (SiSiCH3), 1.6 (CSiCH3). 29Si
NMR (79.5 MHz, CD2Cl2): δ -85.1 (CH2SiSi), -12.7 (SiSiCH3),
2.0 (CSiC). Anal. Calcd for C13H38Si5: C, 46.63; H, 11.44. Found:
C, 45.19;12 H, 11.43.
low-boiling components and was then crystallized from diethyl
ether (1 mL; slow cooling to -20 °C and crystallization over a
period of 5 days). The product was isolated by removal of the
mother liquor via a syringe and dried in vacuo (0.01 mbar, 20 °C,
2 h) to give 7 in 86% yield as a colorless crystalline solid (370 mg,
1
447 μmol); mp 180-181 °C. H NMR (500.1 MHz, CDCl3): δ
Preparation of Dimethylbis{[tris(trimethylsilyl)silyl]methyl}silane
(6). This compound was synthesized analogously to 5 by using
13 (500 mg, 1.56 mmol), potassium tert-butoxide (189 mg, 1.68
mmol), 18-crown-6 (453 mg, 1.71 mmol), 2 (122 mg, 777 μmol),
and toluene (15 mL). The crude product was purified by bulb-to-
bulb distillation (120 °C/8 mbar) to remove the low-boiling com-
ponents and was then crystallized from n-hexane (1 mL; slow
cooling to -20 °C and crystallization over a period of 2 days).
The product was isolated by removal of the mother liquor via
a syringe and dried in vacuo (0.01 mbar, 20 °C, 2 h) to give 6 in
72% yield as a colorless crystalline solid (325 mg, 559 μmol); mp
-0.08 (s, 6 H, SiCH2Si), 0.15 (s, 3 H, CSiCH3), 0.17 (s, 81 H,
SiSiCH3). 13C NMR (125.8 MHz, CDCl3): δ -5.5 (SiCH2Si), 1.3
(SiSiCH3), 2.3 (CSiCH3). 29Si NMR (99.4 MHz, CDCl3): δ -84.9
(CH2SiSi), -12.7 (SiSiCH3), 7.3 (CSiC). Anal. Calcd for
C
31H90Si13: C, 44.96; H, 10.95. Found: C, 43.84;12 H, 10.60.
Preparation of Dimethyl(2,4,6-trimethoxyphenyl){[tris(trimethyl-
silyl)]methyl}silane (9). This compound was synthesized analo-
gously to 5 by using 13 (500 mg, 1.56 mmol), potassium tert-but-
oxide (189 mg, 1.68 mmol), 18-crown-6 (453 mg, 1.71 mmol), 16
(428 mg, 1.56 mmol), and toluene (15 mL). The crude product
was purified by bulb-to-bulb distillation (100 °C/3 mbar) to
remove the low-boiling components and was then crystallized
from n-pentane (1 mL; slow cooling to -20 °C and crystallization
over a period of 2 days). The product was isolated by removal of
the mother liquor via a syringe and dried in vacuo (0.01 mbar,
20 °C, 2 h) to give 9 in 76% yield as a colorless crystalline solid
1
125-127 °C. H NMR (500.1 MHz, CDCl3): δ 0.05 (s, 4 H,
SiCH2Si), 0.09 (s, 6 H, CSiCH3), 0.13 (s, 54 H, SiSiCH3). 13C
NMR (125.8 MHz, CDCl3): δ -6.5 (SiCH2Si), 1.3 (SiSiCH3), 2.6
(CSiCH3). 29Si NMR (99.4 MHz, CDCl3): δ -84.7 (CH2SiSi),
-12.4 (SiSiCH3), 4.4 (CSiC). Anal. Calcd for C22H64Si9: C,
45.44; H, 11.09. Found: C, 43.81;12 H, 10.91.
1
(577 mg, 1.18 mmol); mp 66-67 °C. H NMR (300.1 MHz,
Preparation of Methyltris{[tris(trimethylsilyl)silyl]methyl}-
silane (7). This compound was synthesized analogously to 5 by
using 13 (500 mg, 1.56 mmol), potassium tert-butoxide (189 mg,
1.68 mmol), 18-crown-6 (453 mg, 1.71 mmol), 3 (100 mg,
522 μmol), and toluene (15 mL). The crude product was purified
by bulb-to-bulb distillation (120 °C/8 mbar) to remove the
CD2Cl2): δ 0.11 (s, 27 H, SiSiCH3), 0.20 (s, 2 H, SiCH2Si), 0.30 (s,
6 H, CSiCH3), 3.71 (s, 6 H, o-OCH3, C6H2(OCH3)3), 3.79 (s, 3 H,
p-OCH3, C6H2(OCH3)3), 6.05 (s, 2 H, H-3/H-5, C6H2(OCH3)3).
13C NMR (75.5 MHz, CD2Cl2): δ -8.0 (SiCH2Si), 1.3 (SiSiCH3),
3.2 (CSiCH3) 55.2 (o-OCH3, C6H2(OCH3)3), 55.5 (p-OCH3,
C6H2(OCH3)3), 90.6(C-3/C-5, C6H2(OCH3)3), 106.4 (C-1, C6H2-
(OCH3)3), 163.5 (C-4, C6H2(OCH3)3), 166.6 (C-2/C-6, C6H2-
(OCH3)3). 29Si NMR (59.6 MHz, CD2Cl2): δ -85.3 (CH2SiSi),
-12.5 (SiSiCH3), -4.6 (CSiC). Anal. Calcd for C21H46O3Si5: C,
51.79; H, 9.52. Found: C, 51.40; H, 9.32.
(12) The product isolated was NMR-spectroscopically pure. The devia-
tion of the experimental carbon content from the calculated value might be
explained by partial SiC formation in the course of the elemental analysis.

Article
Organometallics, Vol. 29, No. 20, 2010 4553
Figure 3. Molecular structure of one of the two crystallogra-
phically independent molecules of 11 in the crystal (probability
level of displacement ellipsoids 50%). The hydrogen atoms
Figure 1. Molecular structure of one of the two crystallogra-
phically independent molecules of 7 in the crystal of 7 0.46Et2O
(probability level of displacement ellipsoids 50%). The hydrogen
3
˚
˚
atoms are omitted for clarity. Selected bond distances (A) and
are omitted for clarity. Selected bond distances (A) and angles
(deg): Si1-C1 1.8713(10), Si1-C2 1.8700(10), Si1-C3 1.8991-
(11), Si1-C4 1.8968(10), Si2-Si5 2.3571(4), Si2-Si6 2.3560(4),
Si2-Si7 2.3497(4), Si2-C1 1.9167(10), Si4-Si11 2.3540(4),
Si4-Si12 2.3524(4), Si4-C3 1.9125(11), Si4-C4 1.9151(11),
Si5-C5 1.8785(13), Si5-C6 1.8812(13), Si5-C7 1.8811(13), Si11-
C23 1.8791(12), Si11-C24 1.8745(11), Si11-C25 1.8796(12); Si1-
C1-Si2 120.67(5), Si1-C2-Si3 119.67(5), Si1-C3-Si4 88.47(4),
Si1-C4-Si4 88.46(4), Si2-Si5-C5 114.79(5), Si2-Si5-C6
108.35(4), Si2-Si5-C7 110.15(4), Si4-Si11-C23 111.36(4),
Si4-Si11-C24 114.64(4), Si4-Si11-C25 105.83(4), Si5-Si2-
C1 111.58(4), Si6-Si2-C1 103.33(3), Si7-Si2-C1 118.88(3),
Si11-Si4-Si12 109.542(17), Si11-Si4-C3 107.28(4), Si11-Si4-
C4 120.99(4), Si12-Si4-C3 116.31(4), Si12-Si4-C4 111.21(3),
C1-Si1-C2 108.69(5), C1-Si1-C3 112.46(5), C1-Si1-C4
117.67(5), C2-Si1-C3 116.23(5), C2-Si1-C4 109.67(5), C3-
Si1-C4 91.59(5), C3-Si4-C4 90.62(5).
angles (deg): Si1-C1 1.878(3), Si1-C21.884(2), Si1-C3 1.879(2),
Si1-C4 1.881(2), Si2-Si3 2.3562(10), Si2-Si4 2.3611(9), Si2-Si5
2.3616(9), Si2-C2 1.926(2), Si3-C5 1.881(3), Si3-C6 1.876(4),
Si3-C7 1.883(4); Si1-C2-Si2 125.89(12), Si1-C3-Si6 125.54-
(13), Si1-C4-Si10 125.60(13), Si2-Si3-C5 111.62(13), Si2-
Si3-C6 108.27(14), Si2-Si3-C7 113.58(13), Si3-Si2-Si4 111.00-
(4), Si3-Si2-Si5 109.23(4), Si3-Si2-C2 115.93(8), Si4-Si2-Si5
105.28(4), Si4-Si2-C2 111.18(8), Si5-Si2-C2 103.40(7), C1-
Si1-C2 109.96(12), C1-Si1-C3 108.42(13), C1-Si1-C4 109.54-
(13), C2-Si1-C3 110.03(11), C2-Si1-C4 109.09(10), C3-Si1-
C4 109.79(11), C5-Si3-C6 107.4(2), C5-Si3-C7 108.0(2), C6-
Si3-C7 107.7(2).
18 (219 mg, 708 μmol), and toluene (10 mL). Deviating from the
synthesis of 5, the reaction mixture was additionally stirred at
55 °C for 1 h. The crude product was purified by bulb-to-bulb
distillation (120 °C/0.1 mbar) to remove the low-boiling compo-
nents and was then crystallized from n-pentane (1 mL; slow
cooling to -20 °C and crystallization over a period of 2 days).
The product was isolated by removal of the mother liquor via a
syringe and dried in vacuo (0.01 mbar, 20 °C, 2 h) to give 10 in
77% yield as a colorless crystalline solid (400 mg, 545 μmol); mp
162-164 °C. 1H NMR (500.1 MHz, CDCl3): δ -0.06 (δA) and
2
0.49 (δB) (SiCHAHBSi, 4 H, JAB = 13.6 Hz), 0.07 (s, 54 H,
SiSiCH3), 0.46 (s, 3 H, CSiCH3), 3.64 (s, 3 H, o-OCH3, C6H2-
(OCH3)3), 3.74 (s, 3 H, o-OCH3, C6H2(OCH3)3), 3.78 (s, 3 H,
p-OCH3, C6H2(OCH3)3), 5.99 (s, 1 H, H-3 or H-5, C6H2-
(OCH3)3), 6.03 (s, 1 H, H-3 or H-5, C6H2(OCH3)3). 13C NMR
(125.8 MHz, CDCl3): δ -5.7 (SiCH2Si), 1.4 (SiSiCH3), 4.9
(CSiCH3), 54.5 (o-OCH3, C6H2(OCH3)3), 55.2 (o-OCH3, C6H2-
(OCH3)3), 55.6 (p-OCH3, C6H2(OCH3)3), 90.46 (C-3 or C-5,
C6H2(OCH3)3), 90.51 (C-3 or C-5, C6H2(OCH3)3), 106.0 (C-1,
C6H2(OCH3)3), 163.6 (C-4, C6H2(OCH3)3), 166.5 (C-2 or C-6,
C6H2(OCH3)3), 167.0 (C-2 or C-6, C6H2(OCH3)3). 29Si NMR
(99.4 MHz, CDCl3): δ -85.1 (CH2SiSi), -12.5 (SiSiCH3), -2.0
(CSiC). Anal. Calcd for C30H72O3Si9: C, 49.11; H, 9.89. Found:
C, 47.27;12 H, 9.75.
Preparation of 1,1-Bis(trimethylsilyl)-3,3-bis{[tris(trimethylsilyl)-
silyl]methyl}-1,3-disilacyclobutane (11). This compound was syn-
thesized analogously to 5 by using 13 (1.00 g, 3.12 mmol), potas-
sium tert-butoxide (378 mg, 3.37 mmol), 18-crown-6 (906 mg, 3.43
mmol), 4 (176 mg, 779 μmol), and toluene (15 mL). Deviating
from the synthesis of 5, the reaction mixture was additionally
stirred at 55 °C for 6 h. The crude product was purified by bulb-
to-bulb distillation (160 °C/8 mbar) to remove the low-boiling
Figure 2. Molecular structure of one of the two crystallogra-
phically independent molecules of 10 in the crystal (probability
level of displacement ellipsoids 50%). The hydrogen atoms are
˚
omitted for clarity. Selected bond distances (A) and angles (deg):
Si1-Si2 2.3749(13), Si1-Si3 2.3534(12), Si1-Si4 2.3577(13),
Si1-C10 1.923(3), Si2-C1 1.867(5), Si2-C2 1.878(5), Si2-
C3 1.899(4), Si5-C10 1.875(3), Si5-C11 1.876(5), Si5-C12
1.920(4); Si1-Si2-C1 115.08(15), Si1-Si2-C2 110.41(17),
Si1-Si2-C3 109.04(15), Si1-C10-Si5 126.13(16), Si2-Si1-
Si3 107.56(5), Si2-Si1-Si4 111.00(5), Si2-Si1-C10 109.96(10),
Si3-Si1-Si4 108.68(5), Si3-Si1-C10 101.42(9), Si4-Si1-C10
117.41(9), C1-Si2-C2 106.5(2), C1-Si2-C3 107.9(2), C2-
Si2-C3 107.6(2), C10-Si5-C11 108.96(13), C10-Si5-C12
109.80(12), C10-Si5-C10A 104.71(18), C11-Si5-C12 114.2(2),
C11-Si5-C10A 108.96(13), C12-Si5-C10A 109.80(12).
Preparation of Methyl(2,4,6-trimethoxyphenyl)bis{[tris(trimethyl-
silyl)silyl]methyl}silane (10). This compound was synthesized ana-
logously to 5 by using 13 (500 mg, 1.56 mmol), potassium tert-
butoxide (189 mg, 1.68 mmol), 18-crown-6 (453 mg, 1.71 mmol),

4554 Organometallics, Vol. 29, No. 20, 2010
Berkefeld et al.
components and was then crystallized from n-hexane (1 mL; slow
cooling to -20 °C and crystallization over a period of 8 days).
The product was isolated by removal of the mother liquor via
a syringe and dried in vacuo (0.01 mbar, 20 °C, 2 h) to give 11 in
38% yield as a colorless crystalline solid (222 mg, 294 μmol); mp
167-168 °C. 1H NMR (500.1 MHz, CD2Cl2): δ 0.19 (s, 18 H, Si-
(Si(CH3)3)2), 0.21 (s, 54 H, Si(Si(CH3)3)3), 0.22 (s, 4 H, SiCH2Si-
(Si(CH3)3)3), 0.32 (s, 4 H, SiCH2Si(Si(CH3)3)2). 13C NMR (125.8
MHz, CD2Cl2): δ -4.1 (SiCH2Si(Si(CH3)3)3), -0.1 (Si(Si-
(CH3)3)2), 0.2 (SiCH2Si(Si(CH3)3)2), 2.2 (Si(Si(CH3)3)3). 29Si
NMR (99.4 MHz, CD2Cl2): δ -85.0 (Si(Si(CH3)3)3), -46.5 (Si-
(Si(CH3)3)2), -15.5 (Si(Si(CH3)3)2), -12.7 (Si(Si(CH3)3)3), 18.7
(SiC4). Anal. Calcd for C28H80Si12: C, 44.61; H, 10.69. Found: C,
43.28;12 H, 10.71.
Preparation of Bis(chloromethyl)methyl(2,4,6-trimethoxyphe-
nyl)silane (18). A 2.5 M solution of n-butyllithium in hexanes
(3.84 mL, 9.60 mmol of n-BuLi) was added dropwise at -70 °C
((3 °C, temperature measurement within the flask) within 4 h
to a stirred mixture of 17 (1.35 g, 4.80 mmol), bromochloro-
methane (1.86 g, 14.4 mmol), and THF (100 mL) (the n-butyl-
lithium solution was added via a special horizontally elongated
side neck of the three-necked flask, which itself was immersed in
the cooling bath to ensure precooling of the n-butyllithium
solution before making contact with the reaction mixture). After
the addition was complete, the mixture was stirred at -70 °C for
2 h and was then allowed to warm to 20 °C within 17 h. The
solvent was removed under reduced pressure, and diethyl ether
(50 mL) and half-saturated aqueous sodium hydrogen carbo-
nate solution (50 mL) were added sequentially to the residue.
The organic phase was separated, and the aqueous phase was
extracted with diethyl ether (3 ꢀ 25 mL) and discarded. The
combined organic extracts were dried over anhydrous sodium
sulfate, the solvent was removed under reduced pressure, and
the residue was purified by column chromatography on silica gel
[40-63 μm, 150 g (Merck); eluent, n-hexane/ethyl acetate/triethy-
lamine (12:7:1 (v/v/v))]. The resulting product was dissolved in a
boiling mixture of n-hexane (9.7 mL) and triethylamine (0.3 mL),
and the resulting solution was cooled to 20 °C within 30 min and
then kept undisturbed at this temperature for 3 days. The resulting
precipitate was isolated by filtration and dried in vacuo (0.001
mbar, 20 °C, 2 h) to give 18 in 59% yield as a colorless crystalline
solid (872 mg, 2.82 mmol); mp 42-43 °C. 1H NMR (300.1 MHz,
C6D6): δ 0.74 (s, 3 H, SiCH3), 3.22 (s, 6 H, o-OCH3, C6H2-
(OCH3)3), 3.42 (s, 3 H, p-OCH3, C6H2(OCH3)3), 3.46 (δA) and
3.56 (δB) (SiCHAHBCl, 2 H, 2JAB=13.4 Hz), 6.02 (s, 2 H, H-3/H-
5, C6H2(OCH3)3). 13C NMR (125.8 MHz, C6D6): δ -4.6 (SiCH3),
29.6 (SiCH2Cl), 54.7 (o-OCH3, C6H2(OCH3)3), 54.8 (p-OCH3,
C6H2(OCH3)3), 99.3 (C-3/C-5, C6H2(OCH3)3), 162.3 (C-1, C6H2-
(OCH3)3), 164.8 (C-4, C6H2(OCH3)3), 167.0 (C-2/C-6, C6H2-
(OCH3)3). 29Si NMR (59.6 MHz, C6D6): δ 14.9. Anal. Calcd for
C12H18Cl2O3Si: C, 46.60; H, 5.87. Found: C, 46.38; H, 5.82.
Crystal Structure Analyses. Suitable single crystals of 6,
Tetrakis(trimethylsilyl)silane (13). This compound was com-
mercially available (ABCR).
Preparation of (Chloromethyl)dimethyl(2,4,6-trimethoxyphe-
nyl)silane (16). A 2.5 M solution of n-butyllithium in hexanes
(98.0 mL, 245 mmol of n-BuLi) was added dropwise at 20 °C
within 30 min to a stirred suspension of 1,3,5-trimethoxyben-
zene (40.0 g, 238 mmol) in a mixture of N,N,N0,N0-tetrameth-
ylethylenediamine (TMEDA) (28.2 g, 243 mmol) and n-hexane
(250 mL), and stirring was continued for a further 5 h at 20 °C.
The resulting suspension was then added via a dropping funnel
at 0 °C within 30 min to a vigorously stirred solution of chloro-
(chloromethyl)dimethylsilane (32.3 g, 226 mmol) in diethyl
ether (200 mL), followed by stirring for 17 h. Water (300 mL)
was added to the reaction mixture, the organic phase was sepa-
rated, and the aqueous phase was extracted with diethyl ether
(3 ꢀ 200 mL) and discarded. The combined organic extracts
were dried over anhydrous sodium sulfate, the solvent was
removed under reduced pressure, and the residue was purified
by bulb-to-bulb distillation (190 °C/1 mbar) to give 16 in 63%
yield as a colorless crystalline solid (46.3 g, 168 mmol); mp 32-33
°C. 1H NMR (300.1 MHz, CD2Cl2):δ0.35 (s, 6 H, SiCH3), 3.15 (s,
2 H, SiCH2Cl), 3.74 (s, 6 H, o-OCH3, C6H2(OCH3)3), 3.81 (s, 3 H,
p-OCH3, C6H2(OCH3)3), 6.08 (s, 2 H, H-3/H-5, C6H2(OCH3)3).
13C NMR (75.5 MHz, CD2Cl2): δ -2.2 (SiCH3), 33.8 (SiCH2Cl),
55.5 (o-OCH3, C6H2(OCH3)3), 55.6 (p-OCH3, C6H2(OCH3)3),
90.6 (C-3/C-5, C6H2(OCH3)3), 102.5 (C-1, C6H2(OCH3)3), 164.2
(C-4, C6H2(OCH3)3), 166.7 (C-2/C-6, C6H2(OCH3)3). 29Si NMR
(59.6 MHz, CD2Cl2): δ -5.6. Anal. Calcd for C12H19ClO3Si: C,
52.45; H, 6.97. Found: C, 52.66; H, 6.97.
7 0.46Et2O, 9, 10, and 11 were obtained by crystallization from
3
n-hexane (6, 11), diethyl ether (7 0.46Et2O), or n-pentane (9, 10) at
-20 °C. The crystals were mounted in inert oil (perfluoropolyalkyl
ether, ABCR) on a glass fiber and then transferred to the cold
3
nitrogen gas stream of the diffractometer (6, 7 0.46Et2O, 9, and 10:
3
Preparation of Dichloro(methyl)(2,4,6-trimethoxyphenyl)silane
(17). A 2.5 M solution of n-butyllithium in hexanes (10.3 mL, 25.8
mmol of n-BuLi) was added dropwise at 20 °C within 10 min to
a stirred suspension of 1,3,5-trimethoxybenzene (4.20 g, 25.0
mmol) in a mixture of TMEDA (2.96 g, 25.5 mmol) and n-hexane
(30 mL). The resulting suspension was stirred at 20 °C for 17 h
and was then added at 0 °C within 30 min to a stirred solution of
trichloro(methyl)silane (3.55 g, 23.7 mmol) in n-hexane (30 mL).
The mixture was stirred at 0 °C for 2 h and then at 20 °C for a
further 17 h. Diethyl ether (20 mL) was added, and the resulting
mixture was stirred for 1 h at 20 °C. The precipitate was separated
by filtration and washed with diethyl ether (3 ꢀ 10 mL), and the
filtrate and the wash solutions were combined. The solvent was
removed under reduced pressure, the residue was dissolved in
boiling n-hexane (20 mL), and the resulting hot solution was
filtered. The filtrate was cooled to 20 °C within 30 min and then
kept undisturbed at this temperature for 2 h, and the resulting
precipitate was isolated by filtration to give 17 in 62% yield as a
Stoe IPDS, graphite-monochromated Mo KR radiation (λ =
0.71073 A); 11: Bruker Nonius KAPPA APEX II CCD system
˚
˚
with Montel mirror, Mo KR radiation (λ = 0.71073 A)). The
structures were solved by direct methods (SHELXS-97).13 Except
for the solvent in the structure of 7, all non-hydrogen atoms were
refined anisotropically (SHELXL-97).13 A riding model was em-
ployed in the refinement of the hydrogen atoms.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with The
Cambridge Crystallographic Data Centre as supplementary pub-
lication nos. CCDC-790857 (6), CCDC-790858 (7 0.46Et2O),
3
CCDC-790859 (9), CCDC-790860 (10), and CCDC-790861 (11).
Copies of the data can be obtained free of charge on application to
the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax,
(þ44)1223/336033; e-mail, deposit@ccdc.cam.ac.uk).
Acknowledgment. We thank Professor C. Marschner,
Technical University of Graz, Austria, for his advice in
1
colorless crystalline solid (4.10 g, 14.6 mmol). H NMR (300.1
context with the preparation of (Me3Si)3SiK 18-crown-6
and Me3SiCH2Si(SiMe3)3.
3
MHz, C6D6): δ 1.27 (s, 3 H, SiCH3), 3.30 (s, 6 H, o-OCH3,
C6H2(OCH3)3), 3.37 (s, 3 H, p-OCH3, C6H2(OCH3)3), 5.97 (s, 2
H, H-3/H-5, C6H2(OCH3)3). 13C NMR (125.8 MHz, C6D6):
δ 11.3 (SiCH3), 55.3 (o-OCH3, C6H2(OCH3)3) 55.5 (p-OCH3,
C6H2(OCH3)3), 91.3 (C-3/C-5, C6H2(OCH3)3), 93.9 (C-1, C6H2-
(OCH3)3), 166.3 (C-4, C6H2(OCH3)3), 167.2 (C-2/C-6, C6H2-
(OCH3)3). 29Si NMR (59.6 MHz, C6D6): δ 14.9. Anal. Calcd
for C10H14Cl2O3Si: C, 42.71; H, 5.02. Found: C, 42.72; H, 5.02.
Supporting Information Available: Crystallographic data for
6, 7 0.46Et2O, 9, 10, and 11. This material is available free of
charge via the Internet at http://pubs.acs.org.
3
(13) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.