Dihydroxyoligosilanes as novel ligands in coordination chemistry - First synthesis of 2,5-dioxa-3,4-disilatitanacyclopentanes

Article abstract of DOI:10.1016/S0022-328X(02)01776-X

The reaction of two equivalents of (Me₃Si)₂RSi-K x 3THF (1 R = SiMe₃, 2 R = Ph) with Cl₂MeSi-SiMeCl₂, followed by hydrolysis in the presence of NH₄(NH₂COO) leads to the formation

Full text of DOI:10.1016/S0022-328X(02)01776-X

Journal of Organometallic Chemistry 662 (2002) 1Á8
/
www.elsevier.com/locate/jorganchem
Dihydroxyoligosilanes as novel ligands in coordination chemistry*
/
first synthesis of 2,5-dioxa-3,4-disilatitanacyclopentanes
Douglas Hoffmann, Helmut Reinke, Clemens Krempner *
Fachbereich Chemie der Universitat Rostock, Einsteinstr. 3a, D-18055 Rostock, Germany
¨
Received 12 April 2002; received in revised form 18 June 2002; accepted 5 July 2002
Abstract
The reaction of two equivalents of (Me3Si)2RSiÃ
hydrolysis in the presence of NH4(NH2COO) leads to the formation of the dihydroxyoligosilanes MeR(HO)SiÃ
Si(SiMe3)3, 6 RꢁSi(SiMe3)2Ph] as diastereomeric mixtures. Addition of two equivalents of n-BuLi to the diastereomerically pure
ligands (meso)-4/6 and (rac)-4/6, respectively, and subsequent treatment with Cp2TiCl2 yields the (Z) and (E) arranged five-
membered rings (MeRSiÃO)2TiCp2 [7 RꢁSi(SiMe3)3, 8 RꢁSi(SiMe3)2Ph], respectively. The crystal structures of the ligand (rac)-6
/
Kꢀ
/
3THF (1 Rꢁ
/
SiMe3, 2 Rꢁ
/
Ph) with Cl2MeSiÃ
/
SiMeCl2, followed by
/
Si(OH)RMe [4 Rꢁ
/
/
/
/
/
as well as of the titanacycles (E)-8 and (Z)-7 are reported.
# 2002 Published by Elsevier Science B.V.
Keywords: Silicon; Titanium; Titanacycles; Dihydroxydisilanes; Hexasilanes
1. Introduction
generation of a wide variety of metallasiloxanes with
different coordination geometries [6].
The chemistry of transition metal siloxide complexes
Our interest in this area lies mainly in the develop-
ment of well defined new transition metal complexes
using novel bidentate ligands on the basis of oligosilanes
which possess two silanol functionalities. Of special
interest are compounds in which the hydroxy groups are
fixed at different silicon atoms along the oligosilane
chain. Due to their high condensation tendency only
some of those derivatives, namely a,v-dihydroxyoligo-
silanes, have been prepared and for a few of those
compounds the X-ray crystal structures were reported
[7]. The coordination chemistry of these compounds that
might be of interest as ligands for the construction of
chelate complexes with different ring sizes is relatively
unknown [8]. In context with studies concerning the
electronic influence of the silicon backbone on the
structure and reactivity of polyhydroxyoligosilanes, we
report herein the synthesis of dihydroxyoligosilanes of
containing SiÃ
/
OÃ/M linkages has continued to attract
considerable attention in the field of material science [1]
and catalysis [2], particularly over the last 20 years. The
synthesis, reactivity, and bonding of such complexes in a
wide variety of supporting ligand environments con-
tinues to be explored. In this regard numerous silane-
diols, disilanols and silanetriols have been described in
the literature [3], which could be used as building blocks
for the preparation of novel titanium containing hetero-
cubanes and titanasiloxanes [3b,4]. For example, Feher
et al. reported the synthesis of incompletely condensed
polyhedral oligosilasesquioxanes (POSS) bearing three
free SiÃ
/
OH groups [5]. This class of polydentate ligands
has been extensively exploited as a source for the
the type MeR(HO)SiÃ
/
Si(OH)RMe [RꢁSi(SiMe3)3,
/
Si(SiMe3)2Ph]. With the aim of exploring the complex
chemistry of these disiloxide ligands, some novel dioxa-
disilatitanacyclopentanes have been synthesized and
structurally characterized.
* Corresponding author. Tel.: ꢂ
/
49-381-498-6406; fax: ꢂ49-381-
/
498-6382
E-mail address: clemens.krempner@chemie.uni-rostock.de (C.
Krempner).
0022-328X/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 7 7 6 - X

2
D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á8
/
2. Results and discussion
the mixture, (rac)-4 and (meso)-4 could be obtained in
an overall yield of 39 and 41%. By analogy with the
preparation and separation of 4, the phenyl substituted
1,2-dihydroxyhexasilanes (rac)-6 and (meso)-6 (2:1 mix-
ture) were isolated in an overall yield of 53 and 27%.
2.1. Synthesis of the ligands MeR(HO)SiÃ
/Si(OH)RMe
As mentioned above, simple 1,2-dihydroxydisilanes
are proven to be unstable due to their high condensation
tendency. Therefore, the aim was to synthesize 1,2-
The hexasilanes 3Á6 are air-stable colourless solids
/
and the proposed structures are in full agreement with
the straightforward NMR spectra as well as the IR and
1
dihydroxydisilanes, in which each of this two SiÃ
/
OH
the MS data. In the H-NMR spectra as well as in the
13C-NMR spectra of 4 only one signal was found for the
SiMe3 groups, and also the 29Si-NMR spectra show only
one signal for the SiMe3 silicon atoms. In comparison to
this NMR spectra of 6 exhibit two signals for the
diastereotopic SiMe3 groups, respectively.
In addition, the molecular structure of (rac)-6 has
been derived from X-ray diffraction data. Single crystals
suitable for an X-ray structure analysis were grown from
nitromethane at room temperature. The central silicon
atoms show a slightly distorted tetrahedral configura-
units are surrounded by sterically demanding substitu-
ents, preventing condensation reactions. Our strategy
for preparing this class of compounds involved the
selective 1,2-linkage of two equivalents of bulky silylpo-
tassium derivatives with Cl2MeSiÃ
hydrolyses of the two retained SiÃ
In fact, the hexasilanes 3Á6 were synthesized accord-
ing to the procedure outlined in Scheme 1. (Me3Si)3SiÃ
Kꢀ3THF was reacted with Cl2MeSiÃSiMeCl2 in
pentane at ꢃ78 8C to yield the dichlorohexasilane 3
/SiMeCl2, followed by
/Cl units.
/
/
/
/
/
exclusively. Finally, without isolation 3 was hydrolyzed
in an aqueous solution of NH4(NH2COO) to give the
1,2-dihydroxyhexasilane 4 consistent with a 1:1 mixture
of (rac)-4 and (meso)-4 as determined by 1H-NMR
analysis. After column chromatographic separation of
tion with SiÃ
112.75(9)8. The SiÃ
within the range of 2.355Á
/
SiÃ
/
Si bond angles being 110.24(9) and
/Si bond lengths lie unremarkably
˚
/
2.360 A. The SiÃ
/
O bond
˚
˚
O1) and 1.682(4) A
lengths amount to 1.673(5) A (Si3Ã
/
(Si4ÃO2) which are longer than the corresponding SiÃ
/
/O
˚
distance of approximately 1.66 A in 1.2-dihydroxyte-
tramethyldisilane [7b]. The results of the X-ray analysis
give a good idea on the steric congestion in the
molecules and reveal that the two hydroxy groups are
fully enclosed by the two (Me3Si)2PhSi substituents. The
conformation of (rac)-6 is predominantly determined by
the steric repulsion of the two bulky (Me3Si)2PhSi
substituents, while the two hydroxy groups are playing
a minor role (Fig. 1). The arrangement gives a roughly
eclipsed conformation of the silicon backbone at the two
Scheme 1. Synthesis of the dihydroxyhexasilanes 3Á6.
/
˚
Fig. 1. Molecular structure of (rac)-6 in the crystal (ORTEP, 30% probability level, H-atoms omitted for clarity). Selected bond lengths [A] and angles
[8]: Si3Ã
Si2ÃC4 1.891(6), Si2Ã
109.0(2), O1ÃSi3ÃSi4Ã
/
O1 1.673(5), Si4Ã
Si3Ã
O2 99.2(3), Si2Ã
/
O2 1.682(4), Si3Ã
Si4 110.24(9), Si5Ã
Si3ÃSi4Ã
/
Si4 2.365(2), Si2Ã
Si4ÃSi3 112.75(9), O1Ã
O2 20.8(2), C10ÃSi3Ã
/
Si3 2.358(2), Si4Ã
Si3ÃSi4 110.83(18), O2Ã
Si4ÃC11 25.8(4), O1Ã
/
Si5 2.359(2), Si3Ã
Si4Ã
Si3Ã
/
C10 1.845(6), Si4Ã
Si3 110.2(2), C10Ã
Si4ÃSi5 22.3(3), Si2Ã
/
C11 1.828(6), Si5Ã
Si3ÃSi4 110.4(3), C11Ã
Si3ÃSi4ÃSi5 142.24(9).
/
C12 1.885(6),
/
/
/
/
/
/
/
/
/
/
/
/
Si4ÃSi3
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á
/8
3
central silicon atoms; the dihedral angles were found to
be 142.24(9)8 (Si2ÃSi3ÃSi4ÃSi5) and 99.2(3)8 (O1ÃSi3Ã
Si4ÃO2). Thus, it is not unexpected that (rac)-6 realizes
neither intermolecular hydrogen bonds in the solid state
as observed for the 1.2-dihydroxytetra-methyldisilane
reported by Kelling et al. [7b].
yhexasilanes (meso)-4 (dꢁ
/
18.4), (rac)-4 (dꢁ
/
20.1),
/
/
/
/
/
(meso)-6 (dꢁ15.3) and (rac)-6 (dꢁ
/
/16.9).
The solid state structures of (Z)-7 and (E)-8 were
investigated by single crystal X-ray diffraction. Single
crystals suitable for an X-ray structure analysis were
grown from pentane at 0 8C. A perspective view of the
molecular structures of (Z)-7 and (E)-8 is shown in Figs.
2 and 3.
/
In complex (E)-8, the tetrahedrally surrounded tita-
nium atom is bonded in a chelate fashion to both
siloxide groups of the ligand, giving a nearly planar five-
membered ring. The roughly eclipsed conformation of
the substituents at the two ring silicon atoms is
comparable to that found in the dihydroxyhexasilane
(rac)-6. The geometry around the titanium atom is
2.2. Synthesis and characterization of the
dioxadisilatitanacyclopentanes 7 and 8
The dioxadisilatitanacyclopentanes 7 and 8 were
synthesized according to the procedure outlined in
Scheme 2. Deprotonation of the diastereomerically
pure 3.4-dihydroxyhexasilanes 4/6 by equimolar
amounts of n-BuLi in heptane solutions selectively
afforded white powders of the corresponding dilithium
salts. Reactions of toluene solutions of the dilithium
described best as distorted tetrahedral, with a CpÃ
Cp (centroid) angle of 129.58 and a O1ÃTi1ÃO2 chelate
O1 [1.886(2) A] and Ti1ÃO2
[1.881(2) A] bond lengths are considerably longer than
those found in other related SiÃOÃTi complexes. Of
course, as a consequence of the five-membered ring
/
TiÃ
/
/
/
˚
angle of 91.05(9)8. The Ti1Ã
/
/
˚
salts with titanocenedichloride in toluene at ꢃ78 8C
/
/
/
proceed selectively, providing the corresponding com-
plexes 7/8 in excellent yields (Scheme 2). 7/8 are soluble
in common organic solvents (heptane, pentane, THF
formation the Si3Ã
/
O1Ã
/
Ti1 [127.83(12)8] and Si1Ã
/
O2Ã
/
Ti1 [128.40(12)8] bond angles are remarkably smaller
than values observed for linear complexes containing
and ether) and form redÁorange crystals which are
/
stable on air but decompose slowly in solution.
SiÃ
silicon atoms is also strongly distorted tetrahedral with
small SiÃSià bond angles being 94.25(9)8 and
95.06(9)8 and remarkably widened central SiÃSiÃSi
angles being 121.99(5)8 and 125.82(5)8. The Si1ÃO2
O1 [1.644(2) A] bond lengths of
/
OÃ/Ti units. The geometry around the two ring-
The proposed structures of the titanacycles 7/8 were
confirmed by NMR and MS data and were in full
agreement with the results of an X-ray crystal structure
analysis. The NMR (1H, 13C, 19Si) spectra of 7/8 are
rather straightforward and show roughly the same
features as observed for the corresponding ligands 4
/
/
O
/
/
/
˚
˚
[1.637(2) A] and Si3Ã
/
(E)-8 are somewhat shorter than those found in the
dihydroxyhexasilane (rac)-6. Due to the space demand
1
and 6. The H-NMR spectra of (E)-7/(E)-8 show one
singlet and of (Z)-7/(Z)-8 show two singlets for the
protons of the cyclopentadienyl groups. For the com-
plexes, the 29Si-NMR spectra display three resonances
for 7 and four resonances for 8, due to the two
diastereotopic SiMe3 groups. The 29Si-NMR spectro-
scopy proves to be a very useful tool for the character-
ization of the complexes, as the differences in chemical
shift are large enough to distinguish between bonded
and unbonded ligands. For example, the signals for the
cyclic silicon atoms are significantly shifted to lower
of the (Me3Si)2PhSi substituents and the ring strain in
˚
Si3 bond [2.3908(14)A] is
elongated.
As the most interesting result the structural analysis
of (Z)-7 revealed that the two (Me3Si)3Si substituents
adopt a Z position. Nevertheless, the structural feature
of the titanacycle in (Z)-7 is quite similar to that in (E)-
the titanacycle the central Si1Ã
/
8. Only the Si1Ã
/
O1Ã
/
Ti1 [129.18(13)8] and Si2Ã
/
O2Ã
/
Ti1
[130.78(13)8] angles of (Z)-7 are somewhat larger than
those found in (E)-8. Interestingly, the spatial demand
of the two extended hemispherical (Me3Si)3Si groups
field [(Z)-7 dꢁ
/
52.6, (E)-7 dꢁ
/
52.4, (Z)-8 dꢁ48.9, (E)-
/
8 dꢁ/49.5] in comparison to that of the 1.2-dihydrox-
leads to a significant elongation of the SiÃ
/
Si bonds [Si2Ã
Si3 2.3898(16) A] and an extreme
SiÃSi angles to values of 136.84(6)8
and 136.29(6)8. Moreover, the Si1ÃSi2 distance
[2.4404(15) A] is remarkably longer than the value
/
˚
˚
Si4 2.3933(16) A; Si1Ã
/
widening of the SiÃ
/
/
/
˚
˚
Si3, 2.3908(14) A], presumably
observed for (E)-8 [Si1Ã
/
due to the high steric congestion of the (Me3Si)3Si
substituents, which adopt a (Z)-position.
In summary, it should be stated that in both
complexes relatively long TiÃ
tances as well as small TiÃOÃSi bond angles allow only
weak oxygen ppÁdp donation of both siloxide groups to
the titanium centre. Interestingly, the values of the OÃ
/
O and short SiÃ
/
O dis-
/
/
/
Scheme 2. Synthesis of the titanacycles 7/8.
/

4
D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á8
/
˚
Fig. 2. Molecular structure of (E)-8 in the crystal (ORTEP, 30% probability level, H-atoms omitted for clarity). Selected bond lengths [A] and angles
[8]: Ti1ÃO1 1.886(2), Ti1ÃO2 1.893(2), Si1ÃO2 1.637(2), Si3ÃO1 1.644(2), Si1ÃSi3 2.3908(14), Si1ÃSi4 2.3773(14), Si3ÃSi5 2.3794(14), O1ÃTi1ÃO2
91.05(9), O2ÃSi1ÃSi3 94.25(9), O1ÃSi3ÃSi1 95.06(9), Si3ÃO1ÃTi1 127.83(12), Si1ÃO2ÃTi1 128.40(12), Si5ÃSi3ÃSi1 125.82(5), Si4ÃSi1Ã
121.99(5), O2ÃSi1ÃSi3ÃO1 16.13(11), Si1ÃSi3ÃO1ÃTi1 15.43(15), O2ÃTi1ÃO1ÃSi3 8.06(16), Si3ÃSi1ÃO2ÃTi1 16.81(15), O1ÃTi1ÃO2Ã
10.08(17).
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
Si3
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/Si1
SÃ
SÃ
an envelope conformation: NÃ
NÃSiꢁ119.0(4)8, 118.0(4)8 and NÃ
/
TiÃ
/
Sꢁ
/
93.9(2)8, TiÃ
99.0(2)8, 100.9(2)8, whereas the diaza one has
TiÃNꢁ100.2(3)8, TiÃ
SiÃSiꢁ99.5(3)8,
/
SÃ
/
Siꢁ113.2(2)8, 109.7(2)8 and
/
/
SiÃSiꢁ
/
/
/
/
/
/
/
/
/
/
/
98.2(3)8. However, these are the only other structurally
characterized compounds with comparable ring struc-
tures [11].
2.3. Conclusions
We have prepared diastereomerically pure hexasilanes
4 and 6 containing two vicinal hydroxy groups which are
surrounded by sterically demanding substituents. These
chelate ligands react cleanly with Cp2TiCl2 to give the
(Z) and (E) configurated dioxadisilatitanacyclopentanes
7 and 8 in high yields. The X-ray structural analysis of
the complexes (Z)-7 and (E)-8 revealed nearly planar
but strained geometries of the five-membered ring
structures. Despite the extensive shielding of the two
Fig. 3. Molecular structure of (Z)-7 in the crystal (ORTEP, 30%
probability level, H-atoms omitted for clarity). Selected bond lengths
˚
[A] and angles [8]: Ti1Ã
/
O1 1.886(2), Ti1Ã
O2 1.644(3), Si1ÃSi2 2.4404(15), Si2Ã
2.3898(16), O2ÃTi1ÃO1 90.66(10), O1ÃSi1Ã
Si1 93.76(9), Si1ÃO1ÃTi1 129.18(13), Si2ÃO2Ã
Si1ÃSi2 136.84(6), Si4ÃSi2ÃSi1 136.29(6), O1ÃSi1Ã
Si2ÃSi1ÃO1ÃTi1 11.95(17), O2ÃTi1ÃO1ÃSi1 12.49(18), O1Ã
O2ÃSi2 6.52(19), Si1ÃSi2ÃO2ÃTi1 1.40(18).
/
O2 1.881(2), Si1Ã
Si4 2.3933(16), Si1Ã
Si2 94.40(9), O2ÃSi2Ã
Ti1 130.78(13), Si3Ã
Si2ÃO2 5.20(13),
Ti1Ã
/
O1 1.652(2),
SiÃ
/
OH functions, the ligands 4 and 6 are proven to be
Si2Ã
/
/
/
/
Si3
reactive, and their complex behaviour towards early
transition metals is the subject of current studies.
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
3. Experimental
TiÃ
/
O, TiÃ
/
OÃ
/
Si and OÃ
/
SiÃ/Si bond angles are similar to
3.1. General procedures and materials
those found in the five-membered and isoelectronic
dithia [9] and diaza [10] titanium complexes. The dithia
cycle adopts a half-chair conformation with bond angles
All reactions involving organometallic reagents were
carried out under an atmosphere of Ar using standard

D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á
/8
5
Schlenk techniques. 1,2-Dimethyl-1,1,2,2-tetrachlorodi-
silane [12], tris(trimethylsilyl)silylpotassiumꢀ3THF (1)
and phenylbis(trimethylsilyl)silyl-potassiumꢀ3THF (2)
3.3. Hydrolysis of the dichlorohexasilanes 3 and 5
/
/
3.3.1. General procedure
were prepared as previously described [13]. NMR:
Bruker AC 250, Bruker ARX 300, Bruker ARX 400
Without isolation, the crude products 3 and 5,
prepared as described above, were dissolved in 200 ml
of ether and added to 40 ml (1 M) of an aqueous
solution of NH4(NH2COO) and 100 ml of water. The
mixture was vigorously stirred at r.t. After 3 days the
organic phases were separated, dried with MgSO4, and
evaporated. Drying in the vacuum (10ꢃ2 mbar, 70 8C)
yielded white powders consistent with a 1:1 diastereo-
meric mixture of 3 and a 2:1 diastereomeric mixture of 5,
1
(250, 62.9, 79.5 and 235.3 MHz, for H, 13C and 29Si
1
respectively). For H-, 13C- and 29Si-NMR, benzene-d6
as solvent, Me4Si as internal standard. IR: Nicolet 205
FT-IR. MS: Intectra AMD 402, chemical ionization
with isobutane as the reactant gas.
3.2. Synthesis of the dichlorohexasilanes 3 and 5
1
respectively, as determined by H-NMR analysis. The
mixtures were purified and separated as described
below.
4: The residue was separated by column chromato-
3.2.1. General procedure
To
tris(trimethylsilyl)silylpotassiumꢀ
yl-bis(trimethylsilyl)silylpotassiumꢀ
ml of pentane, respectively, were added 20 mmol of
1,2-dimethyl-1,1,2,2-tetrachlorodisilane at ꢃ78 8C. Stir-
a
solution
of
3THF (1) and phen-
3THF (2) in 200
40
mmol
/
graphy on silica gel (heptaneÁ
/
EtOAcꢁ100/1) to give
/
/
over all 5.05 g of (meso)-4 (41%) and 4.75 g of (rac)-4
(39%).
/
ring was continued for 1 h and the mixture was allowed
to warm up to room temperature (r.t.) within 2 h. After
filtration of the reaction mixture, the solvent was
removed under reduced pressure. Drying in the vacuum
(10ꢃ2 mbar, 70 8C) yielded white powders, respectively,
consistent with a 1.3:1 diastereomeric mixture of 3 and a
3.3.2. (meso)-3,4-Dihydroxy-1,1,1,3,4,6,6,6-octamethyl-
2,2,5,5-tetrakis(trimethylsilyl)hexasilane (4)
M.p. 213Á
1H-NMR: dꢁ
0.35 (s, SiMe3, 54H). 13C-NMR: dꢁ
(SiMe3). 29Si-NMR: dꢁ
128.9 (Si
MeOH), ꢃ9.9 (SiMe3). MS: (CI) m/z (%)ꢁ
[Mꢂ], 597 (70) [MꢂꢃOH], 541 (50) [Mꢂꢃ
SiMe3], 351
(100) [Mꢂꢃ
OSi(SiMe)3]; exact mass calc. for
/
214 8C. IR (nujol) n˜
0.70 (s, OH, 2H), 0.83 (s, SiMeOH, 6H),
7.2 (SiMeOH), 3.5
SiMe3), 18.3 (Si-
614 (35)
/
ꢁ
/
3670.7 cmꢃ1 (OH).
/
/
/
ꢃ
/
/
/
1
10:1 diastereomeric mixture of 5, as determined by H-
NMR analysis.
/
/
/
/
/
C20H62Si10O2 614.2443; found 614.2467. Anal. Calc.
for C20H62O2Si10, (615.57): C, 39.02; H, 10.15. Found:
C, 38.47; H, 9.89%.
3.2.2. 3,4-Dichloro-1,1,1,3,4,6,6,6-octamethyl-2,2,5,5-
tetrakis(trimethylsilyl)hexasilane (3)
Raw 3 was suspended in cold acetonitrile and filtered
off, yield 11.2 g (86%). m.p. 245Á
1.06, 0.85 (2s, SiMeCl, 6H), 0.39, 0.38 (2s, SiMe3, 54H).
13C-NMR: dꢁ6.9, 6.6 (SiMeCl), 3.4, 3.3 (SiMe3). 29Si-
NMR: dꢁ 119.6, ꢃ120.1 (SiSiMe3), 22.3, 19.9 (Si-
MeCl), ꢃ9.3, ꢃ9.4 (SiMe3). MS: (CI) m/z (%)ꢁ652
(12) [Mꢂ], 637 (55) [MꢂꢃMe], 615 (95) [Mꢂꢃ
Cl], 290
/
250 8C. 1H-NMR: dꢁ
/
3.3.3. (rac)-3,4-Dihydroxy-1,1,1,3,4,6,6,6-octamethyl-
2,2,5,5-tetrakis(trimethylsilyl)hexasilane (4)
/
M.p. 217Á
1H-NMR: dꢁ
0.36 (s, SiMe3, 54H). 13C-NMR: dꢁ
(SiMe3). 29Si-NMR: dꢁ
129.1 (Si
MeOH), ꢃ9.9 (SiMe3). MS: (CI) m/z (%)ꢁ
[Mꢂ], 597 (33) [MꢂꢃOH], 541 (99) [Mꢂꢃ
SiMe3], 351
(100) [Mꢂꢃ
OSi(SiMe)3]; exact mass calc. for
/
218 8C. IR (nujol) n˜
1.02 (s, OH, 2H), 0.67(s, SiMeOH, 6H),
5.8 (SiMeOH), 3.3
SiMe3), 20.1 (Si-
614 (40)
/
ꢁ
/
3668.2 cmꢃ1 (OH).
/
ꢃ
/
/
/
/
/
/
/
/
/
/
/
/
ꢃ
/
/
/
(100) [SiMeSi(SiMe3)3]; exact mass calc. for
35
C19H57Si Cl2 635.1530; found 635.1540. Anal. Calc.
/
/
10
/
/
for C20H60Si10Cl2, (652.46): C, 36.82; H, 9.27. Found: C,
34.79; H, 8.98%.
/
C20H62Si10O2 614.2443; found 614.2391. Anal. Calc.
for C20H62O2Si10, (615.57): C, 39.02; H, 10.15. Found:
C, 38.00; H, 9.88%.
3.2.3. 3,4-Dichloro-2,5-diphenyl-1,1,1,3,4,6,6,6-
octamethyl-2,5-bis(trimethylsilyl)hexasilane (5)
6: The residue was separated by column chromato-
Raw 5 was suspended in cold acetonitrile and filtered
1
graphy on silica gel (heptaneÁ
over all 3.32 g of (meso)-6 (27%) and 6.63 g of (rac)-6
(53%).
/
EtOAcꢁ50/1) to give
/
off, yield 10.55 g (80%). m.p. 124 8C. H-NMR: dꢁ
/
7.80Á
SiMeCl, 6H), 0.43, 0.31, 0.38, 0.34 (4s, SiMe3, 2ꢀ
13C-NMR: dꢁ
137.4, 133.2, 128.7, 128.3 (C-aromat.),
3.7 (SiMeCl), 1.8, 1.5 (SiMe3). 29Si-NMR: dꢁ
68.8
(SiPh), 16.3 (SiMeCl), ꢃ10.9, ꢃ12.9 (SiMe3). MS: (CI)
m/z (%)ꢁ Me], 623 (100)
660 (12) [Mꢂ], 645 (30) [Mꢂꢃ
[Mꢂꢃ
SiMe3]. Anal. Calc. for C26H52Cl2Si8, (660.29):
C, 47.30; H, 7.94. Found: C, 47.05; H, 7.79%.
/
7.63, 7.19Á/7.10 (2m, phenyl, 10H), 1.05, 0.63 (2s,
/18H).
/
3.3.4. (meso)-3,4-Dihydroxy-2,5-diphenyl-
1,1,1,3,4,6,6,6-octamethyl-2,5-
/
ꢃ
/
/
/
bis(trimethylsilyl)hexasilane (6)
/
/
M.p. 76 8C. IR (nujol) n˜
(OH). 1H-NMR: dꢁ
0.63 (s, OH, 2 H), 7.74Á
7.21Á7.07 (2m, phenyl, 10H), 0.50 (s, SiMeOH, 6H),
/
ꢁ
/
3666.1 and 3596.2 cmꢃ1
7.70,
/
/
/
/

6
D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á8
/
1
0.35, 0.30 (2s, SiMe3, 2ꢀ
135.6, 128.4, 128.3 (C-aromat.), 4.6 (SiMeOH), 1.7, 1.4
(SiMe3). 29Si-NMR: dꢁ
73.8 (SiPh), 15.3 (SiMeOH),
13.7, ꢃ12.0 (SiMe3). MS: (CI) m/z (%)ꢁ622 (3)
[Mꢂ], 604 (9) [MꢂꢃH2O], 451 (100) [Mꢂꢃ
Me-
/
18H). 13C-NMR: dꢁ
/
137.1,
M.p. 240 8C (dec.). H-NMR: dꢁ
1.12 (s, SiMeOTi, 6H), 0.44 (s, SiMe3, 54H). 13C-NMR:
dꢁ
116.6 (C5H5), 10.7 (SiMeOTi), 3.8 (SiMe3). 29Si-
NMR: dꢁ 125.2 (SiSiMe3), 52.4 (SiMeOTi), ꢃ9.9
(SiMe3). MS: (70 eV) m/z (%)ꢁ
790 (11) [Mꢂ], 725 (8)
[MꢂꢃCp], 178 (100) [Cp2Tiꢂ]. Anal. Calc. for
/
6.07 (s, C5H5, 10H),
/
ꢃ
/
/
ꢃ
/
/
/
/
ꢃ
/
/
/
/
/
/
/
2C6H6]. Anal. Calc. for C26H54O2Si8, (623.40): C,
50.09; H, 8.73. Found: C, 49.74; H, 8.88%.
/
C35H82O2Si10Ti, (863.777): C, 48.67; H, 9.57. Found:
C, 48.23; H, 9.27%.
3.3.5. (rac)-3,4-Dihydroxy-2,5-diphenyl-1,1,1,3,4,6,6,6-
octamethyl-2,5-bis(trimethylsilyl)hexasilane (6)
3.4.4. (Z)-1,1-Dicyclopentadienyl-3,4-dimethyl-3,4-
bis[phenyl-bis(trimethylsilyl)silyl]-2,5-dioxa-3,4-
disilatitanacyclopentane (8)
The residue was dried in vacuum (10ꢃ2 mbar,
100 8C), leaving (Z)-8 as an orange foam, yield 0.67 g
(84%). Due to its extreme solubility of in common
organic solvents, purification by means of recrystalliza-
tion proved to be impossible. M.p. 65 8C (dec.). 1H-
M.p. 90Á
NMR: dꢁ0.83 (s, OH, 2H), 7.74Á
phenyl, 10H), 0.56 (s, SiMeOH, 6H), 0.34, 0.33 (2s,
SiMe3, 2ꢀ 137.0, 135.6, 128.6,
18H). 13C-NMR: dꢁ
128.4 (C-aromat.), 4.1 (SiMeOH), 1.6, 1.4 (SiMe3). 29Si-
NMR: dꢁ 73.7 (SiPh), 16.9 (SiMeOH), ꢃ13.7, ꢃ11.9
(SiMe3). MS: (CI) m/z (%)ꢁ
622 (11) [Mꢂ], 604 (23)
[MꢂꢃH2O], 451 (100) [Mꢂꢃ
Meꢃ2C6H6]. Anal. Calc.
/
91 8C. IR (nujol) n˜
/
ꢁ
/
3604.1 cmꢃ1 (OH). 1H-
7.71, 7.20Á7.05 (2m,
/
/
/
/
/
/
ꢃ
/
/
/
/
/
/
/
NMR: dꢁ
6.01, 5.91 (2s, C5H5, 2ꢀ
0.38, 0.31 (2s, SiMe3, 2ꢀ
136.0, 128.4, 128.1 (C-aromat.), 117.4, 116.5 (C5H5), 7.2
(SiMeOTi), 2.1, 1.8 (SiMe3). 29Si-NMR: dꢁ
68.7
(SiPh), 48.9 (SiMeOTi), ꢃ14.8, ꢃ11.3 (SiMe3). MS:
Cp], 178
/
7.83Á
/
7.80, 7.16Á
5H), 0.94 (s, SiMeOTi, 6H),
18H). 13C-NMR: dꢁ
137.6,
/
7.01 (2m, phenyl, 10H),
for C26H54O2Si8, (623.40): C, 50.09; H, 8.73. Found: C,
49.91; H, 8.79%.
/
/
/
3.4. Synthesis of the dioxadisilatitanacyclopentanes 7 and
8
/
ꢃ
/
/
/
(CI) m/z (%)ꢁ
/
798 (21) [Mꢂ], 733 (33) [Mꢂꢃ
/
3.4.1. General procedure
To a solution of 1 mmol of 4 or 6 in 10 ml of toluene,
(100) [(Cp2Tiꢂ]. Anal. Calc. for C36H62O2Si8Ti,
(799.452): C, 54.09; H, 7.82. Found: C, 53.87; H, 7.69%.
3.2 ml (2 mmol) of 1.6 M n-BuLi were added at ꢃ78 8C.
/
After the mixture was stirred for 1 h, a solution of 0.25 g
(1 mmol) of titanocendichloride in 10 ml of toluene was
3.4.5. (E)-1,1-Dicyclopentadienyl-3,4-dimethyl-3,4-
bis[phenyl-bis(trimethylsilyl)silyl]-2,5-dioxa-3,4-
disilatitanacyclopentane (8)
added at ꢃ78 8C. After stirring for 1 h the mixture was
/
allowed to warm up, stirred overnight and then filtered
to remove LiCl. The solvent was evaporated under
reduced pressure, yielding the dioxadisilatitanacyclopen-
tanes 7 and 8, which were purified as described below.
Crystallization from pentane at ꢃ
8 as red crystals, yield 0.63 g (79%). M.p. 135 8C (dec.).
1H-NMR: dꢁ
7.89Á7.85, 7.30Á7.10 (2m, phenyl, 10H),
5.78 (s, C5H5, 10H), 0.84 (s, SiMeOTi, 6H), 0.44, 0.39
(2s, SiMe3, 2ꢀ 137.6, 136.5, 128.2,
18H). 13C-NMR: dꢁ
128.2 (C-aromat.), 116.9 (C5H5), 7.9 (SiMeOTi), 2.1
(SiMe3). 29Si-NMR: dꢁ
71.0 (SiPh), 49.5 (SiMeOTi),
14.1, ꢃ12.0 (SiMe3). MS: (CI) m/z (%)ꢁ798 (60)
[Mꢂ], 733 (50) [MꢂꢃCp], 178 (100) [(Cp2Tiꢂ]. Anal.
/
40 8C afforded (E)-
/
/
/
/
/
3.4.2. (Z)-1,1-Dicyclopentadienyl-3,4-dimethyl-3,4-
bis[tris(trimethylsilyl)silyl]-2,5-dioxa-3,4-disila-
titanacyclopentane (7)
/
ꢃ
/
ꢃ
/
/
/
Crystallization from pentane at ꢃ
/
40 8C afforded (Z)-
/
7 as orange needles, yield 0.56 g (71%). M.p. 183Á
/
Calc. for C36H62O2Si8Ti, (799.452): C, 54.09; H, 7.82.
Found: C, 53.85; H, 7.68%.
1
185 8C (dec.). H-NMR: dꢁ
5H), 0.95 (s, SiMeOTi, 6H), 0.45 (s, SiMe3, 54H), 0.88
(t, CH/3 CH/3 3H), 1.19Á1.31 (m, CH3Ã
(CH2)3Ã
CH/2)3Ã 117.0, 116.2 (C5H5),
CH3, 3H).13C-NMR: dꢁ
11.2 (SiMeOTi), 4.0 (SiMe3), 14.3 (CH/3 CH/3),
(CH2)3Ã
22.7 (CH3Ã CH/2)3Ã 120.5 (Si
CH3). 29Si-NMR: dꢁ
SiMe3), 52.6 (SiMeOTi), ꢃ10.2 (SiMe3). MS: (70 eV)
Cp], 178 (100)
/
6.14, 5.99 (2s, C5H5, 2ꢀ
/
Ã
/
/
,
/
/
3.5. Crystal structure determination of (rac)-6, (E)-8
and (Z)-7
(/
/
/
/
Ã
/
/
/(/
/
/
ꢃ
/
/
/
The crystal structure determinations of (E)-8 and (Z)-
7 were performed on a STOE-IPDS diffractometer with
/
m/z (%)ꢁ
/
790 (4) [Mꢂ], 725 (7) [Mꢂꢃ
/
graphite monochromated MoÁKa radiation at 293 K.
/
[Cp2Tiꢂ]. Anal. Calc. for C30H70O2Si10Ti, (791.629): C,
45.52; H, 8.91. Found: C, 45.39; H, 8.58%.
Crystals of (rac)-6 were investigated by using a Bruker
P4 diffractometer after taking rotational photographs at
293 K. The structures were solved by direct methods
3.4.3. (E)-1,1-Dicyclopentadienyl-3,4-dimethyl-3,4-
bis[tris(trimethylsilyl)silyl]-2,5-dioxa-3,4-
(
SHELXS-86) [14] and refined by full-matrix least-squares
(
techniques against F2
Analytical X-ray Instruments) was used for structure
SHELXL-93) [15]. XP (Siemens
disilatitanacyclopentaneꢀ
Crystallization from pentane at ꢃ
7 as orange microcrystalline material, yield 0.74 g (86%).
/
pentane (7)
/
78 8C afforded (E)-
representations (for full crystallographic data see Table
1).

D. Hoffmann et al. / Journal of Organometallic Chemistry 662 (2002) 1Á
/8
7
Table 1
Summary of crystal and structure solution data of (rac)-6, (Z)-7 and (E)-8
Compound
(rac)-6
(Z)-7
(E)-8
Empirical formula
Formula weight
Crystal system
C
623.41
26H54O2Si8
C35H82O2Si10Ti
863.78
Triclinic
C36H62O2Si8Ti
799.48
Monoclinic
P21/n
Monoclinic
P21/c
¯
P1
Space group
Unit cell dimensions
˚
a (A)
8.842(2)
38.166(10)
12.306(3)
90
9.840(2)
14.740(3)
18.710(4)
84.12(3)
85.10(3)
72.15(3)
18.152(4)
9.5950(19)
27.152(5)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
b (8)
106.690(10)
90
99.43(3)
90
99
3
˚
V (A )
3977.9(17)
4
1.041
2565.3(9)
2
1.025
4665.1(16)
4
1.138
Z
Dcalc (Mg mꢃ3
)
Absorption coefficient (mmꢃ1
F(000)
)
0.289
1352
0.422
856
0.417
1712
Crystal size (mm3)
0.57ꢀ0.44ꢀ0.30
0.4ꢀ0.3ꢀ0.2
0.4ꢀ0.3ꢀ0.2
Theta range for data collection (8) 2.03Á
/
22.00
1.89Á/24.18
1.52Á21.06
/
Index ranges
ꢃ95h 51, ꢃ405k 51,
ꢃ125l 512
6224
ꢃ105h 510, ꢃ165k 516,
ꢃ215l 521
16137
ꢃ185h 518, ꢃ95k 59,
05l 527
9043
Reflections collected
Independent reflections
4867
0.0692
7553
0.0532
4943
0.0314
[Rint
]
Completeness to U
228/99.9%
4867/0/327
24.188/91.9%
7553/0/388
0.709
21.068/97.8%
4943/0/424
0.868
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I ꢀ2s(I)]
R indices (all data)
1.001
R1ꢁ0.0646, wR2ꢁ0.1507
R1ꢁ0.1176, wR2ꢁ0.1805
R1ꢁ0.0400, wR2ꢁ0.0641
R1ꢁ0.1063, wR2ꢁ0.0728
0.290 and ꢃ0.183
R1ꢁ0.0342, wR2ꢁ0.0693
R1ꢁ0.0575, wR2ꢁ0.0744
0.262 and ꢃ0.205
Largest difference peak and hole (e 0.276 and ꢃ0.206
ꢃ3
˚
A
)
4. Supplementary material
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Acknowledgements
We thank Prof. Dr. H. Oehme for his generous
support and R. Kempe for carrying out the X-ray
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