A novel cyclic titanasiloxane derived from [Ph2Si(OH)]2O: Synthesis and crystal structure of [Cp*Ti(Cl)(OSiPh2OSiPh2OSiPh2O)]

Article abstract of DOI:10.1016/S0022-328X(00)00946-3

Reaction of Cp*Ti(OAr)C1₂ (Ar=2,6-Me₂C₆H₃) with dilithium salt of [Ph₂Si(OH)]₂O in a 1:1 molar ratio in toluene at room temperature yields titanatrisiloxane ring compound [Cp*Ti(Cl)(OSiPh₂OSiPh₂OSiPh₂O)] (1). Siloxane chain-expansion effect has been observed in the product formation, which is presumed to be a consequence of the ring strain in the titanadisiloxane system. Compound 1 has been characterized by microanalysis, IR, and NMR spectroscopic techniques. The molecular structure of 1 determined by X-ray diffraction reveals that the central eight-membered TiSi₃O₄ siloxane-ring exists in an unusual butterfly-like conformation.

Full text of DOI:10.1016/S0022-328X(00)00946-3

Journal of Organometallic Chemistry 625 (2001) 195–199
www.elsevier.nl/locate/jorganchem
A novel cyclic titanasiloxane derived from [Ph2Si(OH)]2O:
synthesis and crystal structure of
[Cp*Ti(Cl)(OSiPh2OSiPh2OSiPh2O)]
Ramaswamy Murugavel *, Vivekanand S. Shete, Kanhayalal Baheti, Paul Davis
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076, India
Received 20 October 2000; received in revised form 2 December 2000; accepted 2 December 2000
Dedicated to Professor B. Viswanathan on the occasion of his 60th birthday
Abstract
Reaction of Cp*Ti(OAr)C12 (Ar=2,6-Me2C6H3) with dilithium salt of [Ph2Si(OH)]2O in a 1:1 molar ratio in toluene at room
temperature yields titanatrisiloxane ring compound [Cp*Ti(Cl)(OSiPh2OSiPh2OSiPh2O)] (1). Siloxane chain-expansion effect has
been observed in the product formation, which is presumed to be a consequence of the ring strain in the titanadisiloxane system.
Compound 1 has been characterized by microanalysis, IR, and NMR spectroscopic techniques. The molecular structure of 1
determined by X-ray diffraction reveals that the central eight-membered TiSi3O4 siloxane-ring exists in an unusual butterfly-like
conformation. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Titanasiloxanes; Cyclopentadienyl complexes; Silanols; Siloxides
1. Introduction
larities of modified silica surfaces to molecular metal-
lasiloxanes [6].
Organosilicon compounds containing SiꢀOꢀM link-
age have been around for the last hundred years [1–3].
However, only recently, metallasiloxanes derived from
discrete molecular silanols such as silanediols
R2Si(OH)2, silanetriols RSi(OH)3, and incompletely
condensed silasesquioxanes (c-C6H11)7Si7O9(OH)3 have
been reported [4–6]. Their chemistry has evoked a lot
of interest among chemists, material scientists and
physicists in view of their potential applications. The
presence of metal in the siloxane framework often
results in high thermal stability, catalytic and conduct-
ing properties. Moreover, silicon polymers containing
metal centers in the backbone have metallasiloxanes as
their precursors. A variety of organic transformations,
which are catalyzed by transition metal complexes an-
chored on silica surfaces, make the metallasiloxane
chemistry more relevant because of the structural simi-
In view of the proven properties of titanasilicates as
catalysts in several organic transformations, there has
been an upsurge in the synthesis of molecular and
organic-soluble titanasiloxanes with a variety of struc-
tures [7,8]. A few examples of recently reported ring-
like and cage-like molecular titanasiloxanes are shown
in Charts 1 and 2, respectively. As these examples
indicate, it is possible to vary the titanium to silicon
ratio by a proper choice of the starting materials. Thus,
titanasiloxanes with a Ti:Si ratio of 1:1, 1:3, 1:4, 1:6,
1:7, and 1:8 have been so far realized [8–18]. Among
these titanasiloxanes, compound E (Chart 2) [16] has
been in focus in view of its diverse utility as (a) a
homogeneous catalyst [19]; (b) a heterogeneous catalyst
after anchoring inside MCM-41 [20]; and (c) a molecu-
lar precursor for mixed oxide materials [21].
Continuing our interest in the chemistry of ti-
tanasiloxanes [22], we wish to report in this paper on
the synthesis and characterization of a novel ti-
tanasiloxane with a ring structure having a metal to
silicon ratio of 1:3.
* Corresponding author.
E-mail address: rmv@ether.chem.iitb.ernet.in (R. Murugavel).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00946-3

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R. Muruga6el et al. / Journal of Organometallic Chemistry 625 (2001) 195–199
2. Results and discussion
(OH)]2O was carried out at the room temperature (r.t.)
(Scheme 1). The work-up of the reaction mixture to
remove LiCl followed by slow crystallization of the
resulting brownish–yellow solid from light petroleum
ether solution resulted in the deposition of golden-yel-
low crystals of 1 along with a dark-brown amorphous
material which could not be fully characterized. Ti-
tanosiloxane 1 did not contain the aryloxide group, and
it has probably formed via an aryloxide–siloxide ex-
change reaction. The examination of the dark-brown
Apart from the above described interest in the chem-
istry of titanasilicates, the last few years have also
witnessed a sudden upsurge in the chemistry of tita-
nium aryloxides due to their use as Diels–Alder and
cross-coupling/oligomerization catalysts [23]. There
have been also reports on the use of [Cp*Ti(OAr)C12]
[24,25] for the preparation of cationic alkyl derivatives
of titanium which have been found to be useful homo-
geneous catalysts [23b]. In order to study the reactivity
of these aryloxide compounds, we have now investi-
gated the reactions of [Cp*Ti(OAr)C12] with
[Ph2Si(OH)]2O.
1
byproduct by H-NMR showed the presence of aryloxy
groups, indicating a possible redistribution reaction
during the formation of 1.
The titanasiloxane 1 has been fully characterized with
the aid of elemental analysis, and IR and NMR spec-
troscopic studies. The compound shows good thermal
stability and melts only at 206°C. It can also be handled
in air for extended periods, suggesting its good hy-
drolytic stability. The microanalysis of the product
suggested a possible ring-expansion reaction to result in
a trisiloxane unit compared to the disiloxane unit in the
starting material.
2.1. Synthesis and characterization of
[Cp*Ti(Cl){O(SiPh2O)2SiPh2O}} (1)
A 1:1 molar ratio reaction of [Cp*Ti(OAr)C12]
(Ar=2,6-Me2C6H3) with dilithium salt of [Ph2Si-
The IR spectrum of the compound contains bands
due to the w(TiꢀO) at ca. 910 cm−1 and w(SiꢀOꢀSi) at
ca. 1156 cm−1. There is also strong absorption around
980 cm−1 which we attribute to the TiꢀOꢀSi stretching
vibration based on the earlier assignment made by
Roesky and coworkers through 18O labeling studies
[10]. However, it should be mentioned that this vibra-
tion has been attributed to the TiꢁO group by some
authors [26] and SiꢀO [27] or SiꢀOd−ꢀTid+ [28] by
1
others. The H-NMR spectrum of 1 shows a singlet for
the protons of the methyl groups of C5Me5 ring (l 1.94)
and a very complex multiplet pattern for the protons of
the phenyl rings present on the three different silicon
atoms.
Chart 1. Cyclic titanosiloxanes derived from Ph2SiO2 unit.
2.2. Crystal structure of
[Cp*Ti(Cl){(O(SiPh2O)2SiPh2O}] (1)
In order to clearly establish the structure of 1 in the
solid-state, its molecular structure was determined by a
single crystal X-ray diffraction study. A perspective
view of the molecule in the asymmetric part of the unit
cell is depicted in Fig. 1. The Ti atom in the compound
has a distorted tetrahedral geometry. Further, the struc-
ture of 1 reveals that the eight-membered siloxane ring
exists in a butterfly-like conformation, in contrast to the
commonly observed crown structure in several metal-
lasiloxanes [4]. This conformation of the Si3TiO4 ring is
quite evident when the ring is viewed along the Ti···Si
axis as shown in Fig. 2. Titanasilixoanes with an eight-
membered ring structure serve as useful model for the
S4R secondary building units of titanasilicates and
zeolites [29]. Compound 1 is one of the rare examples
of such a system, especially with titanium to silicon
Chart 2. Cage-like titanosiloxanes.
Scheme 1. Synthesis of 1.

R. Muruga6el et al. / Journal of Organometallic Chemistry 625 (2001) 195–199
197
Selected bond distances and angles in molecule 1 are
listed in Table 1. A structural comparison of 1 with
related titanasiloxanes Ti(O(SiPh2O)3 SiPh2O)2 (A) [18]
and cis-[Ti{O(SiPh2O)2SiPh2O}(py)2] (D) [14] is pre-
sented in Table 2. The formation of all the products
listed in Table 2 has involved a chain-expansion reac-
tion in order to relieve the ring strain in the titanadis-
iloxane system. The bond parameters for all the three
compounds are almost similar. The Si atom adopt
nearly ideal tetrahedral geometry; the average OꢀSiꢀO
angle around it being 109.62°.
3. Conclusion
Thus, it has been shown here that the reaction be-
tween the aryloxy derivative of Cp*TiCl3 and a disilox-
anesilanediol can be used to synthesize an
eight-membered ring titanatrisiloxane which struc-
turally resembles the S4R secondary building unit of
zeolites [29]. The presence of a reactive TiꢀCl bond in
complex 1 offers additional opportunities for further
derivatization reactions (e.g. substitution of Cl by an
alkyl, ꢀOH or ꢀNR2 groups).
Fig. 1. A perspective view of titanasiloxane 1.
4. Experimental
Fig. 2. A plot depicting the conformation of the central eight-mem-
bered ring in 1.
All the experimental manipulations were carried out
in a dry pre-purified nitrogen atmosphere using Schlenk
techniques excluding moisture and air. Solvents were
purified by conventional procedures and were freshly
distilled prior to use. Unless otherwise stated, reagents
were obtained from commercial sources and used as
received. [Cp*Ti(OAr)C12] (Ar=2,6-Me2C6H3) was
prepared according to a reported method [25].
Table 1
,
Selected bond lengths (A) and angles (°) for 1
Ti(1)ꢀO(1)
Ti(l)ꢀCl(1)
Si(1)ꢀO(1)
Si(2)ꢀO(3)
Si(3)ꢀO(3)
1.804(2)
2.271(1)
1.629(2)
1.630(2)
1.631(2)
Ti(1)ꢀO(4)
Si(1)ꢀO(2)
Si(2)ꢀO(2)
Si(3)ꢀO(4)
1.825(2)
1.625(2)
1.614(2)
1.627(2)
IR spectra was recorded in Nujol mulls between CsI
pellets over the range 4000–400 cm−1 on a Nicolet
Impact-400 FTIR spectrophotometer. The 1H-NMR
spectra were recorded on a Varian VXR 300S spec-
trometer. Chemical shifts (l ppm) were measured rela-
tive to residual 1H-resonances for chloroform-d1 used as
O(1)ꢀTi(1)ꢀO(4)
O(4)ꢀTi(1)ꢀCl(1)
O(4)ꢀTi(1)ꢀC(61)
O(1)ꢀTi(1)ꢀC(65)
Cl(1)ꢀTi(1)ꢀC(65)
O(4)ꢀTi(1)ꢀC(62)
O(1)ꢀTi(1)ꢀC(64)
CI(1)ꢀTi(1)ꢀC(64)
O(4)ꢀTi(1)ꢀC(63)
O(2)ꢀSi(1)ꢀO(1)
O(1)ꢀSi(1)ꢀC(11)
O(1)ꢀSi(1)ꢀC(1)
Si(1)ꢀO(1)ꢀTi(1)
Si(2)ꢀO(3)ꢀSi(3)
103.9(1)
103.3(1)
93.1(1)
139.5(1)
112.1(1)
126.4(1)
135.4(1)
85.7(1)
146.1(1)
109.5(1)
107.9(1)
108.3(1)
152.7(1)
144.9(1)
O(1)ꢀTi(1)ꢀCl(1)
O(1)ꢀTi(1)ꢀC(61)
Cl(1)ꢀTi(1)ꢀC(61)
O(4)ꢀTi(1)ꢀC(65)
O(1)ꢀTi(1)ꢀC(62)
Cl(1)ꢀTi(1)ꢀC(62)
O(4)ꢀTi(1)ꢀC(64)
O(1)ꢀTi(1)ꢀC(63)
Cl(1)ꢀTi(1)ꢀC(63)
O(2)ꢀSi(1)ꢀC(11)
O(2)ꢀSi(1)ꢀC(1)
C(11)ꢀSi(1)ꢀC(1)
Si(2)ꢀO(2)ꢀSi(1)
Si(3)ꢀO(4)ꢀTi(1)
102.3(1)
105.2(1)
143.4(1)
88.7(1)
84.8(1)
126.7(1)
116.9(1)
100.9(1)
93.5(1)
108.8(1)
107.6(1)
114.8(1)
156.8(2)
163.0(1)
Table 2
Comparison of structural parameters of 1 with related ring ti-
tanosiloxanes derived from disilanediols
Parameter
1
A
D
Av. TiꢀO(endo) 1.815
1.782
1.623
1.855
1.618
,
(A)
Av. SiꢀO(endo) 1.626
ratio of 1:3. Incidentally, only one other titanatrisilox-
ane, [Ti(acac)2{O(SiPh2O)2SiPh2O}], with this Ti:Si sto-
ichiometry has been reported earlier [30]. However, in
this molecule, the titanium atom is in an octahedral
coordination environment, compared to the pseudo-te-
trahedral environment around Ti in 1.
,
(A)
SiꢀOꢀSi (°)
SiꢀOꢀTi (°)
Av. OꢀSiꢀO (°) 109.62
Av. OꢀTiꢀO (°) 103.92
144.85, 156.8
157.865
143.8–172.5
156.4–173.3
109.2
146.4, 156.0
154.85
111.53
109.467
99.05

198
R. Muruga6el et al. / Journal of Organometallic Chemistry 625 (2001) 195–199
solvent. C, H and N analyses were carried out on a
Carlo Eraba 1106 microanalyser. The X-ray intensity
data for 1 were obtained on a Nonius MACH-3 X-ray
diffractometer at r.t.
Acknowledgements
This work was financially supported by the Depart-
ment of Atomic Energy in the form of a DAE Young
Scientist Research Award (to R.M.). Thanks are also
due to the DST funded X-ray Facility at IIT-Bombay
for the diffraction data of 1 and the RSIC, IIT-Bombay
for the spectral measurements. P.D. thanks the DAE
for a research fellowship.
4.1. Synthesis of [CP*Ti(Cl){O(SiPh2O)2SiPh2O}] (1)
A solution of Cp*Ti(OAr)C12 (Ar=2,6-Me2C6H3)
[25] (0.648 g, 1.72 mmol) in toluene (50 ml) was added
to a solution of dilithium salt of [Ph2Si(OH)]2O [31]
(0.737 g, 1.7 mmol) in THF and the mixture was stirred
overnight at 25°C. It was then refluxed for 5 h and the
solvent was removed in vacuo. The residue was redis-
solved in petroleum ether (b.p. 60–80°C) and the solu-
tion was filtered off. The solution is concentrated by
removing half of the solvent in vacuo and left for
crystallization. Golden yellow crystals were obtained at
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5. Supplementary material
Crystallographic data for the structural analysis have
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