Donor-acceptor substituted cyclohexasilanes: Materials with potential nonlinear optical properties

Article abstract of DOI:10.1007/s007060170108

The dipolar cyclohexasilanes 1-ferrocenyl-4-((2,2-dicyanoethenyl)-phenyl)-decamethyl-cyclohexasilane (1) and 1-ferrocenyl-3-((2,2-dicyanoethenyl)-phenyl)-decamethylcyclohexasilane (2) were synthesized by conventional methods and fully characterized. Elect

Full text of DOI:10.1007/s007060170108

Monatshefte fuÈr Chemie 132, 453±464 (2001)
Donor-Acceptor Substituted Cyclohexasilanes:
Materials with Potential Nonlinear Optical
Properties
Ã
Christa Grogger, Hermann Rautz, and Harald StuÈger
È
Institut fuÈr Anorganische Chemie, Technische Universitat Graz, A-8010 Graz, Osterreich
È
Summary. The dipolar cyclohexasilanes 1-ferrocenyl-4-((2,2-dicyanoethenyl)-phenyl)-decamethyl-
cyclohexasilane (1) and 1-ferrocenyl-3-((2,2-dicyanoethenyl)-phenyl)-decamethylcyclohexasilane
(2) were synthesized by conventional methods and fully characterized. Electronic absorption
spectroscopic studies suggest increased ꢀ-ꢁ interactions in the cyclohexasilane derivatives when
compared to their open-chained analogues. Small but noticeable electron transmission effects via the
cyclohexasilanyl group can be derived from cyclic voltammetric data. Signi®cantly increased values
of the quadratic hyperpolarizabilities ꢂ in solution for 1 and 2 are shown by preliminary results of
measurements using the EFISH technique.
Keywords. Polysilanes; UV spectroscopy; Cyclic voltammetry; Nonlinear optics.
Introduction
Interactions in materials showing nonlinear optical (NLO) properties change the
nature of the incident light such that new ®eld components are produced. These
materials are of technological importance in areas that utilize optical devices, with
potential applications in optical signal processing, switching, and frequency genera-
tion [1]. Whereas inorganic solids such as LiNbO3 and KH2PO4 have traditionally
been the NLO materials of choice, recent results suggest that molecule-based
organic or organometallic materials possess superior NLO characteristics [2]. Key
advantages of all organic NLO materials include the high intrinsic nonlinearities of
individual organic molecules, the ability to use molecular engineering to tailor
properties for speci®c applications, low DC dielectric constants, low temperature
processing, and sometimes very fast response times. Organometallic structures ad-
ditionally permit NLO responses to be tuned in ways not possible for purely organic
molecules simply by variation in metal, oxidation state, ligand environment, and
geometry. The search for novel organic and organometallic molecules displaying
optimal nonlinear optical properties is therefore currently an intense area of research
in both academia and industry.
Ã
Corresponding author

454
C. Grogger et al.
Quite recently, organic materials with second-order nonlinear optical properties
have been the subject of intense investigation, leading to the development of certain
structure/NLO property relationships. Thus, large second-order molecular hyper-
polarizabilities ꢀꢂ† are always associated with chromophores comprised of electron
donors and acceptors linked by a conjugated ꢁ-system. The majority of systems
which have been explored for second order nonlinear optics fall into the classes of
donor-acceptor substituted benzenes, biphenyls, stilbenes, thiophenes, and related
structures. The nonlinearity of such molecules can be enhanced by either increasing
the conjugation length, thereby increasing electron delocalization, or increasing the
strength of donor or acceptor groups to improve electron asymmetry within the
molecule. Several reports have appeared in the recent literature quoting appreciable
second-order nonlinear optical susceptibilities for organometallic chromophores
containing ferrocene as a donor. Two molecules, trans-1-ferrocenyl-2-(N-methyl-
pyridinium-4-yl)-ethylene iodide [3] and cis-1-ferrocenyl-2-(4-nitrophenyl)-ethyl-
ene [4] have been reported to possess rather large powder nonlinearities (220 and
62Âurea, respectively) and have sparked subsequent research activity in this area.
Nowadays, ferrocene-based systems are prominent in the class of organometallic
NLO compounds [2b, c], what is mainly due to attractive features like stability
towards air, elevated temperatures, or light and synthetic versatility.
An undesirable feature associated with nearly all organic and organometallic
NLO materials is their often strong absorption in the visible light region, thus
dramatically limiting the applicability of the corresponding materials e.g. for
frequency doubling of the fundamental wavelength of a 820 nm laser requiring
transparency at the ®rst and second harmonic wavelengths near 800 and 400 nm.
Consequently, the search for new compounds with increased transparency combined
with high nonlinear ef®ciency remains a crucial challenge for various applications.
Recently, several reports have appeared in the literature [5] concerning the synthesis
and characterization of dipolar silicon compounds of the type shown below with an
extended transparency range combined with interesting nonlinear optical activities.
Connecting the donor and acceptor groups by polysilane backbones is con-
sidered to be attractive because of the following features: i) increased polarizability
of silicon chains as compared to the carbon analogues, ii) ꢀ-ꢁ-interactions (ꢀ(Si)-
ꢁ(C)), and iii) electron delocalization over the Si±Si bonds via ꢀ-conjugation [6].

Donor-Acceptor Substituted Cyclohexasilanes
455
Silicon, however, was found to be only a weak charge transmitter when donor and
acceptor phenyl-Si-phenyl moieties are connected in compounds of type I. The
nonlinear optical behaviour as shown by measurements of the quadratic hyper-
polarizablities ꢂ using the EFISH technique easily can be accounted for by a
vectorial additive model where the charge transfer interactions contributing to the
overall nonlinearity are con®ned within the donor and the acceptor subunits. Quite
similar results have been independently obtained by Pannell et al. [7] and in our
laboratories [8] for linear polysilanes containing ferrocene as a donor and various
organic acceptor groups.
In the present work the in¯uence of the structure of the polysilane bridge on
charge transfer properties in related donor-acceptor substituted organosilicon
compounds is studied. In cyclic polysilanes, delocalization of ꢀ(Si-Si) electrons
over the ring silicon atoms gives these molecules a variety of properties resembling
those of aromatic hydrocarbons [9]. Cyclopolysilanes, therefore, might be much
more effective charge transmitters in dipolar structures like I compared to the open
chained analogues. Thus, we report the synthesis and UV/Vis absorption spectro-
scopic as well as electrochemical studies of the novel cyclohexasilane derivatives 1
and 2 bearing ferrocene as a donor and the (2,2-dicyanoethenyl)-phenyl group as an
acceptor.
Results and Discussion
Synthesis
The method used to prepare compounds 1 and 2 in this work mainly follows
reaction sequences originally developed by Pannell [7] and Mignani [5b] for the
synthesis of similar donor-acceptor substituted oligosilanes. The description of the
synthesis of 1 is shown in Scheme 1. Compound 2 has been prepared analogously
starting from 1,3-dichlorodecamethylcyclohexasilane. In both cases, the E,E-isomer
has been isolated selectively by crystallization from hexane and used for further
studies.
Closely related reaction sequences were used to prepare the reference com-
pounds ((2,2-dicyanoethenyl)-phenyl)-undecamethylcyclohexasilane (3) and ferro-

456
C. Grogger et al.
Scheme 1. Synthesis of compound 1
cenylundecamethylcyclohexasilane (4) from chloroundecamethylcyclohexasilane
and 1,4-dibromobenzene or ferrocenyllithium, respectively (Eqs. (1) and (2)).
CH2ꢀCN†
Piperidine
1† LiPhBr 2† BuLi
2
Me11Si6Cl
! Me11Si6PhCHO
! Me11Si6PhCHˆCꢀCN† ꢀ1†
2
3† DMF
3
ferrocenyllithium
Me11Si6Cl
! Me11Si6ꢀꢀC5H4†FeꢀC5H5††
ꢀ2†
4
All products were characterized by standard spectroscopic techniques (29Si, 13C,
1
and H NMR, EI-MS) and elemental analysis. The results are in accordance with
the proposed structures in all cases.

Donor-Acceptor Substituted Cyclohexasilanes
457
Table 1. Electronic absorption and cyclic voltammetric data for compounds 1±4
1
ꢃmax=nma
"=mol Á cm
Ef=Vb;c
Epa=Vb
Epc=Vb
1 a
1
2
230 sh
279
20000
10100
17500
21000
12600
17300
12300
23000
220d
0.04
0.97
1.68
368
230 sh
281
0.04
0.02
0.97
1.10
1.67
1.69
367
3
4
289
366
456d
328d
260 sh
225 sh
160d
0.93
8500
20300
a
Data measured for cyclohexane solutions of c ˆ 2 Á 10 5 M; b conditions: sample concentration
10 3 M, electrolyte Bu4NBF4 (0.1 M), CH2Cl2 solution, scan rate 50 mV, potentials quoted vs.
ferrocene/ferrocenium; c Ef ˆ ꢀEpa ‡ Epc†=2, ÁEp ˆ 180 mV; d sample concentration 4 Á 10 4 M
Electrochemical studies
To gain more insight into the electronic properties of compounds 1 and 2, we
studied their redox behavior by cyclic voltammetry. The pertinent data are presented
in Table 1 together with data obtained for the reference compounds 3 and 4 which
represent reasonable model systems to estimate the properties of the donor and the
acceptor group in the absence of interaction. The representative cyclic voltam-
mogram of compound 1 is shown in Fig. 1.
The irreversible wave at high cathodic potential can be attributed to reduction
processes of the dicyanovinyl group. The electron donating ferrocene moiety
affects the reduction potentials; thus, 1 and 2 exhibit 10 and 20 mV anodic shifts,
respectively, in the reduction potential relative to 4.
Fig. 1. Cyclic voltammogram for 1

458
C. Grogger et al.
The ®rst anodic wave observed in 1, 2, and 4 displays electrochemical
reversibility with a peak potential Epa positioned close to that of the unsubstituted
ferrocene. It is therefore reasonable to assign it to the ferrocene moiety. Due to the
electron withdrawing dicyanovinyl group, 1 and 2 exhibit 20 mV anodic shifts
relative to 4. The ÁEp values ꢀEpꢀanodic† Epꢀcathodic†† of the standard ferrocene and
the compounds used in this study fall in the same range. Thus, the ferrocene
oxidation may be termed as reversible or quasi-reversible one electron transfer. In
contrast, the second oxidation step in 1, 2, and 4 (and the ®rst one in 3) displays
complete electrochemical irreversibility. Comparing the shape and maximum with
unsubstituted Si6Me12 ꢀEpa ˆ 1:06 V† it seems clear that this irreversible oxidation
occurs in the cyclohexasilanyl part of the molecule. Including reference com-
pounds 3 and 4, the differences in the oxidation potentials re¯ect the electron
withdrawing or donating properties of the substituents. Thus, the cyclohexasilanyl
group shows signi®cant higher oxidation potentials in 1 and 2 than in 3, but lower
ones than in 4.
Although a measuring accuracy below 10 mV seems not defendable with regard
to the rather high peak separation of 180 mV for the ferrocene/ferrocenium couple,
the data underline that there is a noticeable transmission effect via the cyclo-
hexasilanyl group. However, it is rather small compared to that of a vinyl bridge.
Cyclic voltammetric studies of 2-(4-(2-ferrocenylvinyl)-benzylidene)-malononitrile
showed an anodic shift of 70 mV for the ferrocene group [10], which is about twice
as much compared to 1 and 2.
UV/Vis spectra
Solution electronic absorption spectroscopic studies of compounds designed to
possess second order NLO properties are important to determine the transparency
region and to study the solvatochromic behavior of the sample. Pronounced
solvatochromism is generally considered as indicative of intramolecular charge
transfer upon electronic excitation, what is a prerequisite for high molecular
hyperpolarizabilities ꢂ. The electronic absorption spectra of compounds 1 and 2
were recorded in solvents of different polarity; the corresponding data are
presented in Tables 1 and 2. The UV absorption spectra of 1 and 2 are
displayed in Fig. 2. Figure 3 shows the spectra of the reference chromophores 3
and 4.
The spectrum of compound 4 exhibits two weak absorption maxima near 460
and 330 nm (compare Fig. 2) typical for silylated ferrocenes, which are nearly
unaffected by the structure of the silyl substituent attached [11]. These bands
apparently are superimposed by much stronger bands appearing around 280 and
370 nm in the spectra of 1, 2, and 3.
As shown in Fig. 2, the spectra of 1 and 2 resemble the calculated sum
spectrum of the separate chromophores as represented by compounds 3 and 4. The
absorption spectra of 1 and 2, therefore, seem to ful®ll the classical expectation for
nonconjugatively connected chromophores.
Furthermore, the solvatochromic shifts are small ꢀ< 5 nm† when the solvent is
changed from apolar to polar (compare Table 2). In agreement with the electro-
chemical studies, the above features indicate rather limited intramolecular charge

Donor-Acceptor Substituted Cyclohexasilanes
459
Fig. 2. Electronic absorption spectra of 1 and 2 ꢀc ˆ 2 Á 10 5 M† in cyclohexane solution and
calculated sum spectrum of 3 and 4
transfer from the donor to the acceptor group via the polysilanyl bridge upon
electronic excitation in 1 and 2.
Most striking is the close similarity of the absorption spectra of 1, 2, and 3,
regardless of the presence of ferrocene and of the relative position of the donor and
the acceptor moiety at the cyclohexasilane ring in 1 and 2. The 280 nm band
Ã
appearing in the spectra of 1, 2, and 3 can be assigned to the perturbed ꢀ-ꢀ
transition within the cyclohexasilanyl ring simply by comparison with literature
values [12]. According to literature data available for linear polysilanes containing
the dicyanovinyl acceptor along with various donor groups [5a,b,f], the 370 nm
Ã
band can be assigned to the ꢁ-ꢁ transition of the acceptor-containing phenyl ring.
In 1, 2, and 3, however, the band appears considerably red shifted (20±30 nm) due
to enhanced ꢀ-ꢁ interaction of the cyclohexasilane ꢀ-(Si-Si)- and the phenyl ꢁ-
system. Compared to open chained organosilicon fragments, therefore, the cyclo-
hexasilane ring should be markedly more effective as an electron releasing group
[13]. In preliminary studies quite exceptional values of the ®rst hyperpolarizability
ꢂ have been measured for compounds 1 and 2 (up to 3 times that of the open
chained analogues) using the EFISH technique [14]. This improved optical
nonlinearity very likely may be attributed to the increased donor capacity of the
cyclohexasilane ring mentioned above, hence facilitating intramolecular charge

460
C. Grogger et al.
Fig. 3. Electronic absorption spectra of 3 and 4 in cyclohexane solution
Table 2. Solvatochromic data for compounds 1±4
C6H12
CH3CN
CH2Cl2
1a
2a
3a
4b
279
368
281
367
289
366
328
456
281
364
280
363
292
364
325
455
278
363
279
364
296
378
325
458
a
b
Data measured for solutions of c ˆ 2 Á 10 5 M; sample concentration 10 3 M
transfer from the Si6 fragment to the dicyanovinyl acceptor via the aromatic ring
[5a]. The question to what extent the presence of the ferrocene group is crucial for
the magnitude of ꢂ in 1 and 2 at all is currently the matter of ongoing investi-
gations.

Donor-Acceptor Substituted Cyclohexasilanes
461
Conclusions
In conclusion, it has been shown by UV/Vis and electrochemical studies that the
ferrocenyl donor and the (2,2-dicyanoethenyl)-phenyl acceptor group interact only
weakly when linked through a cyclohexasilanyl bridge. UV/Vis absorption
spectroscopy, however, provides evidence that ꢀ(Si-Si)-ꢁ(phenyl) interactions
and, consequently, the electron releasing character of the polysilanyl fragment are
enhanced in the cyclohexasilane derivatives investigated as compared to their open-
chained analogues. Improved optical nonlinearities observed for compounds 1 and 2
in preliminary studies may be due to more facile charge transfer processes within
the cyclohexasilanyl-phenyl acceptor moiety. Further studies to substantiate this
assumption are currently in progress in our laboratories.
Experimental
All experiments were performed under a nitrogen atmosphere using standard Schlenk techniques. All
solvents were dried with sodium-potassium alloy and distilled under nitrogen prior to use. Malono-
nitrile, tri¯ic acid, and 1,4-dibromobenzene were used as purchased without further puri®cation.
Ê
N,N-Dimethylformamide was allowed to stand over 4 A molecular sieve and distilled from CaH2
prior to use. Ferrocenyllithium [15] and the starting silicon compounds 1-chloroundecamethyl-
cyclohexasilane [16], 1,3-dichlorodecamethylcyclohexasilane, and 1,4-dichlorodecamethylcyclo-
hexasilane [17, 18] were synthesized as previously reported. Cyclic voltammetric studies were
performed at room temperature with a Wenking LB 95 M potentiostat and a Wenking POS 73 scan
generator using a 0.1 M solution of Bu4NBF4 in CH2Cl2, a platinum disk (500 mm) microelectrode,
a Pt counter electrode, and a Ag/AgCl reference electrode. The sample concentration was 10 3 M
and the scan rate 50 mV. Potentials are quoted relative to the ferrocene/ferrocinium redox
couple [19].
1,4-Bis-(4-bromophenyl)-decamethylcyclohexasilane
To a solution of 35.0 g (89.8 mmol) of 1,4-dichlorodecamethylcyclohexasilane in 100 cm3 diethyl
ether, a 70ꢁC cold solution of 4-bromophenyllithium (prepared from 65.1 g, 276.1 mmol of 1,4-
dibromobenzene, and 276.1 mmol of n-butyllithium in 2000 cm3 of diethyl ether) was added
dropwise [20]. The mixture was stirred for 2 h at room temperature and subsequently re¯uxed for 1 h.
After aqueous workup with 50 cm3 of saturated NH4Cl solution, the combined organic layers were
dried over Na2SO4, and the solvent was stripped off in vacuum. Recrystallization of the crude
product from 200 cm3 of 1-propanol affords pure white crystals of 1,4-bis-(4-bromophenyl)-
decamethylcyclohexasilane in 65% yield.
1-Chloro-4-(4-bromophenyl)-decamethylcyclohexasilane
5.9 cm3 (67.6 mmol) of tri¯ic acid were added to a solution of 40.6 g (64.4 mmol) of 1,4-bis-(4-
bromophenyl)-decamethylcyclohexasilane in 1000 cm3 of toluene at 20ꢁC over a period of 7 h. The
mixture was stirred at room temperature overnight, and 300 cm3 of toluene were removed in vacuum
and replaced by diethyl ether. 6.1 g (144.2 mmol) of anhydrous LiCl were added at 0ꢁC, and the
mixture was stirred for another 12 h at room temperature. After removal of the solvent in vacuum,
200 cm3 of petroleum ether were added, and the solution was ®ltered. Petroleum ether was stripped
off from the ®ltrate, and the resulting solid residue was sublimed at 120ꢁC and 10 2 mbar to give the
title compound in 75% yield.

462
C. Grogger et al.
1-Ferrocenyl-4-(4-bromophenyl)-decamethylcyclohexasilane
A solution of ferrocenyllithium (prepared from 21 g (113 mmol) of ferrocene and 75 mmol of tert-
butyllithium in 150 cm3 of THF; ferrocenyllithium was crystallized by cooling the solution to 20ꢁC
overnight, ®ltering and washing with cold THF in order to remove excess ferrocene and tert-
butyllithium) was added slowly to a stirred solution of 24.9 g (48.7 mmol) of 1-chloro-4-(4-bromo-
phenyl)-decamethylcyclohexasilane in 50 cm3 of THF at room temperature. The mixture was
re¯uxed overnight. Subsequently, the solvent was stripped off, and residual ferrocene was removed
by sublimation at 50ꢁC and 10 2 mbar. After aqueous workup of the resulting orange residue
dissolved in diethyl ether with saturated NH4Cl solution, the combined organic layers were dried
over Na2SO4 and concentrated. Chromatography on a silica gel column developed by a mixture of
heptane/toluene (95:5) affords the desired compound in 27% yield.
1-Ferrocenyl-4-(4-formylphenyl)-decamethylcyclohexasilane
To a solution of 8.62 g (13.1 mmol) of 1-ferrocenyl-4-(4-bromophenyl)-decamethylcyclohexasilane
in 80 cm3 of THF at 78ꢁC, a pentane solution of 26.1 mmol of tert-butyllithium was added slowly.
The mixture was stirred for another 5 min and 10.4 cm3 of dry DMF were added. After stirring the
mixture overnight at room temperature, aqueous workup with saturated NH4Cl solution and
recrystallization of the crude product from pentane afforded 1-ferrocenyl-4-(4-formylphenyl)-
decamethylcyclohexasilane in 55% yield.
1-Ferrocenyl-4-((2,2-dicyanoethenyl)-phenyl)-decamethylcyclohexasilane (1; E,E-isomer)
To a solution of 4.3 g (7.1 mmol) of 1-ferrocenyl-4-(4-formylphenyl)-decamethylcyclohexasilane
dissolved in a mixture of 15 cm3 of THF and 80 cm3 of deoxygenated EtOH, 0.52 g (7.8 mmol) of
solid malononitrile and a drop of piperidine were added. An immediate colour change from orange to
dark red was observed. The mixture was stirred for 45 min (DC monitoring recommended), and the
solvents were removed in vacuum. After column chromatography (silica gel) with toluene as the
mobile phase and subsequent recrystallization from hexane, exclusively the E,E-isomer of the title
compound was obtained in 50% yield.
M.p.: 152±153ꢁC; C30H44FeN2Si6 (657.06); found: C 54.94, H 6.81, N 4.29; calcd.: C 54.84, H
6.75, N 4.21; 29Si NMR (Toluol/D2O, ext. TMS, 59.62 MHz): ꢄ ˆ 39:94, 40.68, 41.00,
1
41.64 ppm; H NMR (C6D6, ext. TMS, 300.13 MHz): ꢄ ˆ 7:354 (s, 2H, phenyl), 7.151 (s, 2H,
phenyl), 6.558 (s, 1H, HC=), 4.21 (t, 2H, ferrocene), 4.11 (s, 5H, ferrocene), 4.01 (t, 2H, ferrocene),
0.517 (s, 3H, Si(CH3)), 0.401 (s, 3H, Si(CH3)), 0.328 (s, 6H, Si(CH3)), 0.273 (s, 6H, Si(CH3)), 0.261
(s, 6H, Si(CH3)), 0.116 (s, 6H, Si(CH3)) ppm; 13C NMR (C6D6, ext. TMS, 75.47 MHz): ꢄ ˆ 159:09
(=C(CN)2), 149.15, 135.73, 131.16, 129.85 (phenyl), 114.60, 113.62 (=C(CN)2), 82.80 (HC=),
73.99, 71.35, 69.00 (ferrocene), 3.57, 3.79, 4.62, 5.24, 6.20, 6.42 (Si(CH3)) ppm; MS
‡
(70 eV): m=z (%) ˆ 656 (2.6, M ).
1-Ferrocenyl-3-((2,2-dicyanoethenyl)-phenyl)-decamethylcyclohexasilane (2; E,E-isomer)
The procedure followed was that used for 1 with 35.0 g (89.8 mmol) of 1,3-dichlorodecamethylcy-
clohexasilane, 65.1 g (276.1 mmol) of 1,4-dibromobenzene, and 276.1 mmol of n-butyllithium. The
E,E-isomer was isolated by fractional crystallization from hexane in yields comparable to 1.
M.p.: 152ꢁC; C30H44FeN2Si6 (657.06); found: C 55.20, H 6.82, N 4.28; calcd.: C 54.84, H 6.75,
N 4.21; 29Si NMR (Toluol/D2O, ext. TMS, 59.62 MHz): ꢄ ˆ 38:93, 40.99, 41.08, 41.19,
41.81 ppm; 1H NMR (C6D6, ext. TMS, 300.13 MHz): ꢄ ˆ 7:30, 7.28, 7.25, 7.23 (4H, phenyl), 6.51
(s, 1H, HC=), 4.30±4.26 (m, 2H, ferrocene), 4.09 (s, 5H, ferrocene), 4.05±3.94 (m, 2H, ferrocene),
0.53 (s, 3H, Si(CH3)), 0.45 (s, 3H, Si(CH3)), 0.35 (s, 3H, Si(CH3)), 0.34 (s, 3H, Si(CH3)), 0.27 (s,

Donor-Acceptor Substituted Cyclohexasilanes
463
3H, Si(CH3)), 0.22 (s, 3H, Si(CH3)), 0.21 (s, 3H, Si(CH3)), 0.19 (s, 6H, Si(CH3)), 0.16 (s, 3H,
Si(CH3)) ppm; 13C NMR (C6D6, ext. TMS, 75.47 MHz): ꢄ ˆ 159:13 (=C(CN)2), 148.94, 135.93,
131.08, 129.81 (phenyl), 114.62, 113.61 (=C(CN)2), 82.66 (HC=), 74.61, 73.93, 71.64, 71.38, 70.58,
69.06, 69.00 (ferrocene), 3.43, 3.64, 3.32, 4.79, 4.85, 4.87, 5.76, 5.80, 6.78
‡
(Si(CH3)) ppm; MS (70 eV): m=z (%) ˆ 656 (100, M ).
(4-Bromophenyl)-undecamethylcyclohexasilane
The procedure followed was that used for 1,4-bis-(4-bromophenyl)-decamethylcyclohexasilane with
4.0 g (10.8 mmol) of chloroundecamethylcyclohexasilane, 3.7 g (16.2 mmol) of 1,4-dibromobenzene,
and 16.2 mmol of n-butyllithium. Yield: 5 g (90% based on chloroundecamethylcyclohexasilane).
(4-Formylphenyl)-undecamethylcyclohexasilane
The procedure followed was that used for 1-ferrocenyl-4-(4-formylphenyl)-decamethylcyclohexa-
silane with 4.3 g (8.8 mmol) of (4-bromophenyl)-undecamethylcyclohexasilane in 50 cm3 of THF,
17.6 mmol of tert-butyllithium, and 7 cm3 of DMF. Yield: 3.5 g (91%).
(2,2-Dicyanoethenyl)-phenylundecamethylcyclohexasilane (3)
The procedure followed was that used for 1-ferrocenyl-3-((2,2-dicyanoethenyl)-phenyl)-decamethyl-
cyclohexasilane with 3.1 g (7.1 mmol) of (4-formylphenyl)-undecamethylcyclohexasilane in 15 cm3
of THF and 80 cm3 of deoxygenated ethanol and 0.5 g (7.7 mmol) of solid molononitrile.
Yield: 2.8 g (81%); m.p.: 77±78ꢁC; C21H38N2Si6 (487.29); found: C 51.85, H 8.09; calcd.: C
51.78, H 7.86; 29Si NMR (Toluol/D2O, ext. TMS, 59.62 MHz): ꢄ ˆ 39:50, 41.08, 41.47,
1
41.98 ppm; H NMR (C6D6, ext. TMS, 300.13 MHz): ꢄ ˆ 7:0±7.4 (m, 4H, phenyl), 6.65 (s, 1H,
HC=), 0.39 (s, 3H, Si(CH3)), 0.22 (s), 0.213 (s), 0.210 (s), 0.20 (s, 24H, Si(CH3)), 0.11 (s, 3H,
Si(CH3)) ppm; 13C NMR (C6D6, ext. TMS, 75.47 MHz): ꢄ ˆ 159:74 (=C(CN)2), 148.70, 135.21,
130.53, 129.29 (phenyl), 114.07, 113.05 (=C(CN)2), 82.03 (HC=), 4.68, 5.43, 6.53, 6.61,
‡
7.21 (Si(CH3)); MS (70 eV): m=z (%) ˆ 486 (4.5, M ).
Ferrocenylundecamethylcyclohexasilane (4)
The procedure followed was that used for 1-ferrocenyl-4-(4-bromophenyl)-decamethylcyclohexa-
silane with 5.0 g (13.5 mmol) of chloroundecamethylcyclohexasilane, 5.8 g (31.4 mmol) of ferrocene,
and 9 mmol of tert-butyllithium in 10 cm3 of THF.
Yield: 5.6 g (80% based on chloroundecamethylcyclohexasilane); m.p.: 118±119ꢁC; C21H42FeSi6
(518.93); found: C 48.48, H 8.31; C 48.60, H 8.15; 29Si NMR (Toluol/D2O, ext. TMS, 59.62 MHz):
ꢄ ˆ 41:75, 41.78, 41.83, 42.20 ppm; 1H NMR (C6D6, ext. TMS, 300.13 MHz): ꢄ ˆ 4:18 (2H,
ferrocene), 4.09 (s, 5H, ferrocene), 4.00 (2H, ferrocene), 0.43 (s, 3H, Si(CH3)); 0.26 (s, 3H,
Si(CH3)); 0.24 (s, 3H, Si(CH3)); 0.22 (s, 3H, Si(CH3)); 0.21 (s, 3H, Si(CH3)); 0.15 (s, 6H, Si(CH3)2)
ppm; 13C NMR (C6D6, ext. TMS, 75.47 MHz): ꢄ ˆ 73:56, 70.63, 68.40 (ferrocene), 4.44, 5.54,
‡
5.63, 6.38, (Si(CH3)) ppm; MS (70 eV): m=z (%) ˆ 518 (49, M ).
Acknowledgements
È
We thank the Fonds zur Forderung der wissenschaftlichen Forschung (Wien, Austria) for ®nancial
support within the Spezialforschungsbereich Elektroaktive Stoffe and the Wacker Chemie GmbH
(Burghausen, Germany) for the donation of silane precursors.

464
C. Grogger et al.: Donor-Acceptor Substituted Cyclohexasilanes
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Received May 30, 2000. Accepted December 20, 2000