Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes

Article abstract of DOI:10.1039/b820092k

The dinuclear dialkoxo-bridged complexes [(TiCl)₂(μ-O ₂L)(μ-{(η⁵-C₅Me₄SiMeO) ₂(μ-O)})] (O₂L = 1,2-O₂C₂H ₄1a, 1,2-O₂C₆H

Full text of DOI:10.1039/b820092k

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www.rsc.org/dalton | Dalton Transactions
Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes†
Lorena Postigo, Javier Sa´nchez-Nieves, Pascual Royo* and Marta E. G. Mosquera‡
Received 10th November 2008, Accepted 18th February 2009
First published as an Advance Article on the web 18th March 2009
DOI: 10.1039/b820092k
5
The dinuclear dialkoxo-bridged complexes [(TiCl)2(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})] (O2L =
1,2-O2C2H4 1a, 1,2-O2C6H4 1b, 1,2-(OCH2)2C6H4 1c, O2SiPh2 1d) were obtained by reaction of
5
[(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (A) with the corresponding dilithium salt (1a) or diol (1b, 1c,
5
1d). Alkylation of 1a and 1b with ClRMg afforded [(TiR)2(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})]
(O2L = 1,2-O2C2H4, R = Me 2a, Bz 3a; O2L = 1,2-O2C6H4, R = Me 2b, Bz 3b). Addition of four equiv.
5
of LiOiPr to A afforded [{Ti(OiPr)2}2(m-{(h -C5Me4SiMeO)2(m-O)})] (4). Reaction of 1a with
5
Al(C6F5)3 produced the elimination of the dialkoxo ligand to give [{TiCl(C6F5)}2(m-{(h -C5Me4-
SiMeO)2(m-O)})] (5), whereas the same reaction of 1b with Al(C6F5)3 produced the oxo-alane adduct
5
[(TiCl)2(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O·Al{C6F5}3)})] (O2L = 1,2-O2C6H4 6) which was further
5
transformed to give a mixture of 5 and [(TiCl){Ti(C6F5)}(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})]
(O2L = 1,2-O2C6H4 7). One benzyl group of complexes 3 was abstracted with E(C6F5)3 (E = B, Al) to
5
give the monoionic compounds [Ti(TiBz)(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})][BzE(C6F5)3] (O2L =
1,2-O2C2H4, E = B 8B, Al 8Al; O2L = 1,2-O2C6H4, E = B 9B), although 8Al was unstable in CD2Cl2
5
evolving to a mixture of compounds where [(TiBz)2(m-Cl)(m-{(h -C5Me4SiMeO)2(m-O)})][BzAl(C6F5)3]
(10) was identified, and compound 9B was also unstable at ambient temperature. Polymerization of
e-caprolactone was only achieved with the tetraalkoxo compound 4. All of these complexes were
characterized by NMR spectroscopy and 1a, 1b and 7 by X-ray diffraction studies.
Introduction
The design of ligands to generate bimetallic systems has been
developed with the aim of finding reactivity patterns different
from those observed for similar monometallic complexes.1 In this
regard, olefin polymerization and copolymerization processes with
group 4 dinuclear complexes have provided modified final products
with respect to those obtained using mononuclear derivatives.2–14
Alkoxo, aryloxo and related ligands stabilize high oxidation
metal complexes and chelating diol derivatives are adequate
ligands for generating bimetallic systems. Furthermore, modi-
fications of the oxygen substituents may also affect the M–O
interaction.1,15 However, the alkoxo group is not only an ancillary
ligand, but also plays an important role in the activation of cyclic
esters such as caprolactone and lactide.16–23
Fig. 1 Compound A.
presented two stereogenic Si atoms although formation of the
Si–O–Si bridge required the reaction to be regioselective and only
one diastereoisomer of C2 symmetry was obtained.
Whereas these types of dinuclear complexes have two poten-
tially active metal centres for olefin polymerization, reactions
5
of the titanium complexes [(TiBz2)2(m-{h -C5Me4SiMe2O}2)] and
Our interest in studying functionalized cyclopentadienyl com-
pounds with SiClMe2 moieties,24–32 moved our research group to
synthesize bimetallic cyclopentadienyl disiloxane derivatives with
Si–O–Si bridges for Nb,25,31,33 Mo30 and W30 and with Si–O–M
bridges for group 4 metals26,32,34 and Nb25,33 by hydrolysis of the
Si–Cl bonds or CO2 insertion into Si–N bonds. Conversely, hydrol-
ysis of the functionalized cyclopentadienyl titanium compound
5
[(TiBz2)2(m-{(h -C5Me4SiMeO)2(m-O)})] with Lewis acids formed
benzyl bridges between the Ti atoms, which react further in
halogenated solvents providing halogen bridges.36,37 The ease of
formation of bridges caused complex A to be inactive in ethylene
5
polymerization, although the methyl derivative [(TiMe2)2(m-{(h -
C5Me4SiMeO)2(m-O)})] was active in MMA polymerization.36
Abstraction of two alkyl groups was only possible in the reaction
5
[Ti{h -C5Me4(SiMeCl2)}Cl3]35 with a SiCl2Me moiety gave the
5
of complex [(TiBz2)2(m-{(h -C5Me4SiMeO)2(m-O)})] with excess
5
dititanium derivative [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (A,
B(C6F5)3 for several days, although the transformation was not
complete.
Fig. 1) with both Si–O–Si and Si–O–Ti bridges.36 Complex A
In view of these results and with the aim of generating dicationic
dititanium compounds, we report in this paper the synthesis of
dialkoxo-bridged dinuclear titanium compounds from complex
A. Alkylation reactions of the new complexes, their reactivity
toward Lewis acids and finally their activity for polymerization
of e-caprolactone are also presented.
Departamento de Qu´ımica Inorga´nica, Universidad de Alcala´, Campus
Universitario, E-28871, Alcala´ de Henares, Madrid, Spain. E-mail: pascual.
royo@uah.es; Fax: +34 91 885 4683
† CCDC reference numbers 708809–708811. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b820092k
‡ X-Ray diffraction studies.
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diastereoisomer were observed in the NMR spectra. Hence, the
C2 symmetry complexes 1a–d presented an ABCD spin system
for the equivalent C5Me4Si substituents, one resonance for the
equivalent Si–Me groups and the resonances corresponding for
the symmetric bridge. In the particular case of the ethylene bridge
of 1a and the methylene groups of the dialkoxo bridge of 1c, the 1H
NMR spectra showed two doublets for the diastereotopic protons
of both CH2 groups.
Results and discussion
Synthesis of dialkoxo-bridged compounds
5
The dinuclear disiloxane complex [(TiCl2)2(m-{(h -C5Me4-
SiMeO)2(m-O)})] (A) reacted with the lithium salt Li2(OCH2)2 and
the free diol compounds (HO)2L [(HO)2L = 1,2-(HO)2C6H4, 1,2-
(HOCH2)2C6H4, (HO)2SiPh2], in the presence of NEt3, in toluene
5
to give the dialkoxo-bridged compounds [(TiCl)2(m-O2L)(m-{(h -
Complexes 1a and 1b reacted with two equiv. of ClRMg (R =
C5Me4SiMeO)2(m-O)})] (O2L = OCH2CH2O 1a, 1,2-O2C6H4 1b,
1,2-(OCH2)2C6H4 1c, O2SiPh2 1d) (Scheme 1). The resulting yields
of these reactions and the stability of these compounds were
dependent on the bridge length. Thus, the four-atom bridged
compounds 1a and 1b were obtained in good yield and were stable
atroomtemperature, whereasthesix-atomandthree-atombridged
derivatives 1c and 1d were respectively obtained in low and rather
poor yield, and were also more air sensitive.
5
Me, Bz) to afford the alkyl derivatives [(TiR)2(m-O2L)(m-{(h -
C5Me4SiMeO)2(m-O)})] (O2L = 1,2-O2C2H4, R = Me 2a, Bz 3a;
O2L = 1,2-O2C6H4, R = Me 2b, Bz 3b) (Scheme 1). Addition
of excess Grignard reagent afforded the tetraalkyl derivatives
5
[(TiR2)2(m-{(h -C5Me4SiMeO)2(m-O)})]. The NMR spectra of
complexes 2 and 3 showed similar patterns to those observed for
compounds 1a and 1b, with new resonances for the equivalent
Ti–Me and Ti–Bz groups, respectively, consistent with C2-sym-
1
metric compounds. Furthermore, the H NMR spectrum of the
benzyl complexes showed two doublets for the diastereotopic CH2
protons of the benzyl ligands.
5
The tetraalkoxo derivative [{Ti(OiPr)2}2(m-{(h -C5Me4-
SiMeO)2(m-O)})] (4) was obtained in good yield upon addition
of four equiv. of LiOiPr to compound A. Compound 4 was also
1
air sensitive but thermally stable; its H and 13C NMR spectra
corresponded to a C2 symmetry complex with resonance patterns
similar to those discussed for complexes 1–3. Furthermore, in the
1H and 13C NMR spectra two sets of resonances were observed
for the two diastereotopic OiPr groups of each Ti atom.
Reactions with the Lewis acids E(C6F5)3 (E = B, Al)
Neither of the chloro derivatives 1a and 1b reacted with
B(C6F5)3. However, the ethyleneglycolate derivative 1a reacted
with Al(C6F5)3 with substitution of the dialkoxo ligand by
5
two pentafluorophenyl groups to give [{TiCl(C6F5)}2(m-{(h -
C5Me4SiMeO)2(m-O)})] (5) as the unique titanium product
(Scheme 2). Transfer of one C6F5 group from the Al atom to
each Ti atom with exchange of the dialkoxo ligand is consistent
with the higher oxophilicity of the Al atom, although we could not
identify the aluminium species formed in this reaction. Compound
5 retained the C2 symmetry of the starting product 1a, as evidenced
by its NMR spectra, with the two C6F5 groups located opposite
to the Si–O–Si bridge, in the position previously occupied by
the alkoxo bridge, consistent with the concerted mechanism of
1
this metathesis reaction. Hence, the H and 13C NMR spectra
also presented an ABCD spin system for the equivalent C5Me4Si
substituents, one resonance for the equivalent Si–Me groups, and
Scheme 1 (i) Li2(OCH2)2 or (HO)2L/NEt3 ((HO)2L = 1,2-(HO)2C6H4,
1,2-(HOCH2)2C6H4, (HO)2SiPh2), toluene; (ii) ClRMg (R = Me, Bz),
Et2O; (iii) LiOiPr, toluene.
These new dialkoxo-bridged compounds present two new
stereogenic Ti atoms in addition to the two stereogenic Si atoms.
However, formation of the dialkoxo bridge, which was located
opposite to the Si–O–Si bridge, was regioselective due to the
presence of the disiloxane moiety; therefore signals for only one
Scheme 2
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three resonances for the three types of F nuclei were observed in
the 19F NMR spectrum for the C6F5 groups.
note that formation of 7 should be independent of the formation
of adduct 6, de-coordination of Al(C6F5)3 from the oxygen atom
of 6 is required to obtain 7. Compound 7 is an asymmetric
molecule and thus, its 1H and 13C NMR spectra showed resonances
for two C5Me4Si ABCD spin systems, two resonances for both
SiMe groups and four multiplets for the four protons of the
catecholate bridge in the 1H NMR spectrum. Furthermore, three
resonances for the Ti(C6F5) moiety were observed in the 19F NMR
spectrum.
Conversely, the reaction of Al(C6F5)3 with the catecholate-
bridged complex 1b gave the oxo-alane adduct [(TiCl)2(m-O2L)(m-
5
{(h -C5Me4SiMeO)2(m-O·Al{C6F5}3)})] (O2L = 1,2-O2C6H4 6)
(Scheme 3), which was identified by NMR spectroscopy. For-
mation of the oxo-alane adduct 6 at ambient temperature can
be attributed to the lower accessibility of the oxygen atom in
the phenylenedialkoxo-bridged complex 1b with respect to the
ethyleneglycolate complex 1a, due to the higher steric requirement
of the phenylene moiety and also to its p acceptor capability. The
1H and 13C NMR spectra of 6 showed resonances very close to
those of 1b, although the most remarkable feature that confirmed
the formation of an oxo-alane adduct was the 19F NMR spectrum
which showed the three expected resonances characteristic of these
type of complex.
The methyl derivatives 2, when treated with any of the Lewis
acids E(C6F5)3 (E = B, Al), decomposed even at low temperatures.
In contrast, the benzyl compounds 3 reacted with one equiv. of
B(C6F5)3 to give the asymmetric monoionic complexes [Ti(TiBz)-
5
(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})][BzB(C6F5)3] (O2L = 1,2-
O2C2H4 8B, O2L = 1,2-O2C6H4 9B) (Scheme 4). However,
9B was unstable at ambient temperature. The same reac-
tion employing Al(C6F5)3 as Lewis acid afforded the anal-
5
ogous compound [Ti(TiBz)(m-O2L)(m-{(h -C5Me4SiMeO)2(m-
O)})][BzAl(C6F5)3] (O2L = 1,2-O2C2H4 8Al) for 3a, while only
decomposition was observed for the catecholate derivative 3b.
The cation of 8Al was also unstable at room temperature
and was further transformed into a mixture of compounds
5
in which the chloro-bridged compound [(TiBz)2(m-Cl)(m-{(h -
C5Me4SiMeO)2(m-O)})][BzAl(C6F5)3] (10) was identified.36 The
same reaction employing [Ph3C][B(C6F5)4] resulted in decomposi-
tion of the starting materials.
These Ti complexes are asymmetric cations presenting eight
resonances for two ABCD C5Me4Si spin systems and two reso-
1
nances for both SiMe groups in their H and 13C NMR spectra.
Four multiplets for the four protons of the dialkoxo bridge and two
doublets for both protons of the Ti-CH2 groups were also observed
1
in the H NMR spectra. The 19F NMR spectra of the borate
anions of derivatives 8B and 9B showed an important difference
regarding the type of anion–cation interactions.38 For 8B, with the
ethylenedialkoxo bridge, the Dd(Fp–Fm) of 2.8 indicated unpaired
ions, whereas for 9B, with the phenylenedialkoxo bridge, the
Dd(Fp–Fm) of 5.4 was indicative of an ion-pair interaction. This
difference is consistent with the donor ability of each dialkoxo
bridge, which is related to the p acceptor contribution of the
phenylene ring.
Addition of excess E(C6F5)3 (E = B, Al) did not result in
abstraction of the second benzyl group in these monocationic
derivatives, where no reaction was observed even after heating.
In addition, the abstraction did not occur in the presence of
donor ligands such as THF or pyridine or by addition of one
equiv. of [Ph3C][B(C6F5)4]. It would seem that generation of a
cationic titanium atom hinders the abstraction of the remaining
benzyl ligand bounded to the other metal centre, although both
titanium atoms are separated by bridges and also are bound to
electronegative and p donor oxygen atoms, which should help to
stabilize the metal’s electron deficiency.
Scheme 3 (i) Al(C6F5)3, 5 min; (ii) 3 days.
Compound 6 was unstable and further transformation oc-
curred at ambient temperature to give a mixture of 5 and
5
[(TiCl){Ti(C6F5)}(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})] (O2L =
1,2-O2C6H4 7) in a 2 : 3 molar ratio after three days (Scheme 3).
The resulting aluminium by-product could not be identified.
This process required de-coordination of the Al(C6F5)3 moiety
from the oxygen atom in compound 6, recovering the initial
reaction products as a consequence of the weak O–Al interaction.
Formation of compound 7 as the major reaction product can also
be justified by the different steric and electronic characteristic of
the phenylenedialkoxo bridge, with regard to the ethylenedialkoxo
bridge, which would make the approach of Al(C6F5)3 to the
bridging oxygen atoms difficult, rather favouring exchange of the
chloro ligand with the C6F5 group. However, it is important to
X-Ray diffraction studies
The molecular structures of 1a, 1b and 7 are illustrated in Fig. 2
and 3. Selected bond lengths and angles for these structures are
listed in Table 1. The molecular structures of these three complexes
consist of a dinuclear molecule formed by two Ti atoms connected
5
by two bridging [m-(h -C5R4SiMe2O)] fragments, each of these Ti
3758 | Dalton Trans., 2009, 3756–3765
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Scheme 4 (i) B(C6F5)3, CD2Cl2; (ii) Al(C6F5)3, CD2Cl2; (iii) CD2Cl2.
5
Fig. 2 ORTEP diagrams of [(TiCl)2(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})] (O2L = 1,2-O2C2H4 1a, 1,2-O2C6H4 1b). Hydrogen atoms have been omitted
and thermal ellipsoids are shown at the 30% level.
geometry of compound A. Furthermore, both Ti atoms are also
bridged by a chelating ethyleneglycolate (1a) or catecholate (1b, 7)
ligands, located opposite to the Si–O–Si bridge. The environment
about each Ti atom corresponds to the typical pseudo-tetrahedral
geometry found in such compounds and the coordination sphere
of each Ti atom is completed by one Cl ligand (1a, 1b) or one Cl
and one C6F5 group (7).
5
The bond distances and angles within the [Ti2(m-{h -
C5Me4SiMeO}2)] moiety are very similar to 1a, 1b, 7 and A and
are also close to those found for related Si–O–Ti bridged dinuclear
5
compounds [(TiCl2)2(m-{h -C5R4SiMe2O}2)] (R = H32 B, Me39
5
C) and [(TiMe2)2(m-CH2)(m-{h -C5Me4SiMe2O}2)]40 (D), with the
exception of the Ti(1)–O–Si(1) angle which is clearly smaller for
1a, 1b, 7, A, due to the bridging Si–O–Si system. The tightening of
5
this angle is also observed in the methylidene-bridged derivative
Fig. 3 ORTEP diagrams of [(TiCl){Ti(C6F5)}(m-O2L)(m-{(h -C5Me4-
D. The presence of the dialkoxo bridge in complexes 1a, 1b and
7 causes both Ti atoms to be closer compared with A, B and C,
although it was smaller than that observed for compound D with
a shorter one-atom methylidene bridge.
SiMeO)2(m-O)})] (7). Hydrogen atoms have been omitted and thermal
ellipsoids are shown at the 30% level.
5
atoms is bound to one h -C5R4Si ring and to one oxygen atom
A striking structural feature for all of these complexes is the
disposition of the cyclopentadienyl rings. While for complexes
k-O of the different bridges. One additional oxygen atom also
links both bridges through a Si–O–Si system, retaining the initial
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◦
5
5
˚
Table 1 Selected bond distances (A) and angles ( ) of compounds 1a·0.5C6H14, 1b, 7, [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (A), [(TiCl2)2(m-{h -
C5R4SiMe2O}2)] (R = H B,32 Me C39) and [(TiMe2)2(m-CH2)(m-{h -C5Me4SiMe2O}2)]40 (D)
5
Complex
1a·0.5C6H14
1b
7
A
B
C
D
Ti(1)–O(1)
Si(1)–O(1)
Si(1)–O(3)
1.857(3)
1.640(3)
1.655(3)
2.061
4.467
2.864
148.98(18)
146.65(17)
1.005
119.06(16)
109.02(16)
1.778(3)
1.794(3)
158.0(3)
162.1(3)
110.5(3)
50.60
1.837(2)
1.644(2)
1.660(2)
2.056
4.479
2.891
149.03(12)
143.59(12)
0.828
121.12(11)
108.04(11)
1.810(2)
1.843(3)
1.645(3)
1.658(3)
2.049
4.434
2.889
147.47(17)
147.56(16)
0.931
120.83(16)
100.96(19)
1.813(3)
1.815(3)
169.6(3)
165.8(3)
119.7(3)
44.70
1.803(1)
1.643(1)
1.640(1)
2.038
5.193
2.845
1.767(2)
1.653(1)
1.771(4)
1.650(4)
1.827(1)
1.640(1)
Ti ◊ ◊ ◊ Cp
2.026
5.255
4.700
2.031
5.099
4.829
2.058
3.371
4.535
Ti ◊ ◊ ◊ Ti
Si ◊ ◊ ◊ Si
Ti(1)–O(1)–Si(1)
Ti(2)–O(2)–Si(2)
PCp ◊ ◊ ◊ Oa
147.96(9)
160.2(1)
159.8(2)
150.09(7)
0.463
120.2(1)
108.63
0.631
1.047
1.625
Si(1)–O(3)–Si(2)
C–Si(1)–O(1)
Ti(2)–O(4)
106.40
108.29
107.21
Ti(1)–O(5)
1.818(2)
Ti(1)–O(5)–C
Ti(2)–O(4)–C
O(5)–C(1)–C(2)
PCp–PCpa
166.61(19)
163.73(19)
119.8(12)
43.11
29.06
0.000
0.000
28.78
a PCp stands for the plane containing the cyclopentadienyl ring and PCp–PCp corresponds to the angle formed by planes containing both cyclopentadienyl
ligands.
B and C the planes containing the cyclopentadienyl ligands are
parallel, for A and D, with one additional bridge between the
Si and Ti atoms respectively, they form an angle of about 30◦.
Furthermore, the presence of the dialkoxo bridge between the
Ti atoms in complexes 1a, 1b and 7 forces this angle to open,
also noting an increasing value from 1b and 7, with the planar
phenylenedialkoxo bridge, with respect to the ethylenedialkoxo-
bridged compound 1a.
with compound E were also are very similar to those reported for
[TiCp(OiPr)3].42
These polymers showed a striking difference among themselves
with respect to their molecular weight, which for the dinuclear
compound 4 was close to twice the molecular weight of PCL
obtained with the mononuclear derivative E. Probably, in the
dinuclear compound 4 the proximity of both titanium atoms
allows polymerization at only one of them, with the other titanium
atom blocked by the growing chain. Similar behaviour was
described for a titanium–aluminium dinuclear compound.43
Activation of e-CL with complexes 4 and E proceeded in both
cases by cleavage of the acyl–oxygen bond, confirmed by 1H NMR
spectroscopy with the resonances at about d 5.0 and d 1.3 ascribed
to an ester isopropoxy group.16–23
The molecular structures of all of these complexes (1a, 1b, 7,
5
A–D) resembles that of the dinuclear derivative [(TiCl2)2(m-{(h -
C5H4B{NHMe2}O)2(m-O)})].41 In this last case, the smaller size
of the boron atom favours the approximation of both Ti atoms
˚
to a value (4.647 A) similar to those observed in the alkoxo-
bridged compounds 1a, 1b and 7, although the angle between
the cyclopentadienyl rings of 27.60◦ is comparable with that of A,
without dialkoxo bridges.
Conclusions
Polymerization of e-caprolactone (e-CL)
The dinuclear compound with Ti–O–Si and Si–O–Si bridges
5
The dinuclear dialkoxo-bridged 1a and 1b and tetraalkoxo 4 and
the mononuclear trialkoxo [TiCp*(OiPr)3] (E) complexes were
tested as catalysts for the polymerization of e-CL (Table 2).
Whereas no activity was observed for the chloro derivatives 1a and
1b, the alkoxo complexes 4 and E displayed parallel behaviour in
[(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] reacts with dilithium
salts or diols to give the new dinuclear complexes with bridging
5
dialkoxo ligands [(TiCl)2(m-O2L)(m-{(h -C5Me4SiMeO)2(m-O)})]
(O2L = OCH2CH2O 1a, 1,2-O2C6H4 1b, 1,2-(OCH2)2C6H4 1c,
O2SiPh2 1d). These complexes are stable and are also obtained
in good yield for the four-membered bridged derivatives 1a and
1b.
◦
the polymerization conditions, the yield obtained at 100 C was
lower (ca. 13%) than that at 140 ◦C (ca. 75%). The results observed
5
Table 2 e-CL polymerization with complexes [{Ti(OiPr)2}2(m-{(h -C5Me4SiMeO)2(m-O)})] (4) and [TiCp*(OiPr)3] (E)a
Run
Complex
T/◦C
PCL/g
Yield (%)
Mwb/104
Mw/Mnb
1
2
3
4
E
4
E
4
100
100
140
140
0.14
0.12
0.76
0.75
14
12
76
75
—
—
1.63
2.95
—
—
1.11
1.24
a Polymerization conditions: dinuclear complexes [4] = 0.04 mmol and mononuclear complex [E] = 0.08 mmol, toluene (5 mL), 1 g e-caprolactone,
[e-caprolactone]/[nTi] = 110 (n = number of titanium atoms per molecule). b Determined by GPC in THF vs. polystyrene standard.
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The reactivity of the chloro derivatives 1a and 1b toward
Al(C6F5)3 depends on the type of bridging dialkoxo ligand,
the ethyleneglycolate bridge is totally transferred to aluminium
whereas substitution of one chloro ligand is preferred for the
catecholate-bridged compound 1b. This difference is attributed
to the lesser accessibility of the p electrons of the oxygen atoms
in this last type of bridging group, due to higher arene ring
acidity, which should hinder the interaction with the Lewis
acid.
(s, 6 H, C5Me4), 2.25 (s, 6 H, C5Me4), 2.30 (s, 6 H, C5Me4), 3.54
(dd, 2 H, 2J = 8 Hz, 3J = 2 Hz, O2C2H4), 4.63 (dd, 2 H, 2J = 8 Hz,
3J = 2 Hz, O2C2H4); 13C-NMR (C6D6): -0.6 (SiMe), 10.7, 13.4,
14.0 and 14.1 (C5Me4), 75.8 (O2C2H4), 122.3, 129.3, 134.2, 134.9
and 136.3 (C5Me4). Anal. Calcd for C22H34O5Si2Ti2Cl2 (600.57):
C, 43.94; H, 5.66%. Found: C, 44.75; H, 5.36%.
[(TiCl)2(l-1,2-O2C6H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (1b).
5
A solution of [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (1.00 g,
1.63 mmol) in toluene (50 mL) was treated with two equivalents
of NEt3 (0.33 g, 3.26 mmol) and one equivalent of catechol
(1,2-(OH)2C6H4, 0.18 g, 1.63 mmol). The mixture was stirred
overnight at ambient temperature. Hexane (30 mL) was then
added and the solution was filtered. The red residue was
extracted again into a mixture of solvents toluene–hexane (30
mL/20 mL). The volatiles were pumped off yielding 1b as a red
solid (0.90 g, 85%). Data for 1b: 1H-NMR (C6D6): 0.35 (s, 6
H, SiMe), 1.72 (s, 6 H, C5Me4), 2.01 (s, 6 H, C5Me4), 2.20 (s, 6
H, C5Me4), 2.25 (s, 6 H, C5Me4), 6.67 (m, 2 H, O2C6H4), 6.93
(m, 2 H, O2C6H4); 13C-NMR (C6D6): -0.8 (SiMe), 11.0, 12.9,
13.4 and 14.2 (C5Me4), 120.2, 122.9 and 155.6 (Ci) (O2C6H4),
123.4, 132.4, 134.5, 136.7 and 138.5 (C5Me4). Anal. Calcd for
C26H34O5Si2Ti2Cl2 (648.62): C, 48.10; H, 5.24%. Found: C, 49.06;
H, 5.28%.
Reactions of the corresponding benzyl derivatives [(TiBz)2(m-
5
O2L)(m-{(h -C5Me4SiMeO)2(m-O)})] (O2L = OCH2CH2O 3a, 1,2-
O2C6H4 3b) with the Lewis acids E(C6F5)3 (E = B, Al) showed
behaviour that was also dependent on the dialkoxo bridge. In
both cases, abstraction of one benzyl group occurred, although
19F NMR spectroscopic measurements indicated the absence of
ion-pairing for the ethyleneglycolate derivative whereas an ion-
pairing interaction was observed for the catecholate compound.
Again, this difference is attributed to the diverse donor ability of
the bridging dialkoxo ligands.
Polymerization of e-CL with the tetraalkoxo dinuclear com-
5
pound [{Ti(OiPr)2}2(m-{(h -C5Me4SiMeO)2(m-O)})] (4) and with
the mononuclear derivative [TiCp*(OiPr)3] (E) gave polycaprolac-
tone in good yield at high temperature, while the chloro derivatives
were inactive. The e-CL was activated by the nucleophilic attack
of an isopropoxo ligand on the acyl carbon atom, as was shown
by 1H NMR of the PCL.
[(TiCl)2{l-1,2-(OCH2)2C6H4 }(l-{(g5 -C5Me4SiMeO)2(l-O)})]
5
(1c).
A
solution of [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})]
(0.70 g, 1.14 mmol) in toluene (50 mL) was treated with two
equivalents of NEt3 (0.23 g, 2.28 mmol) and one equivalent of
1,2-benzenedimethanol (0.15 g, 1.14 mmol). The mixture was
stirred overnight at ambient temperature. Hexane (30 mL) was
added and the solution was filtered. The yellow residue was
extracted again into a mixture of solvents toluene–hexane (30 mL/
20 mL). The volatiles were pumped off yielding a yellow solid
(0.20 g). The isolated solid consisted mainly of 1c, but it contained
some irremovable decomposition products, which prevented us
from obtaining a correct elemental analysis, though satisfactory
spectroscopy data were obtained. Data for 1c: 1H-NMR (CDCl3):
0.33 (s, 6 H, SiMe), 1.96 (s, 6 H, C5Me4), 2.06 (s, 6 H, C5Me4),
Experimental section
General considerations
All manipulations were carried out under an argon atmosphere
and solvents were purified from appropriate drying agents.
NMR spectra were recorded at 400.13 (1H), 376.70 (19F) and
100.60 (13C) MHz on a Bruker AV400. Chemical shifts (d)
are given in ppm. 1H and 13C resonances were measured rel-
ative to solvent peaks considering TMS = 0 ppm, meanwhile
19F resonance were measured relative to external CFCl3. As-
signment of resonances was made from HMQC and HMBC
NMR experiments. Elemental analyses were performed on a
Perkin-Elmer 240C. (HO)2L ((HO)2L = HOCH2CH2OH, 1,2-
(HO)2C6H4, 1,2-(HOCH2)2C6H4, (HO)2SiPh2) and LiOiPr were
purchased from Aldrich, degassed and stored under argon with
molecular sieves (HOCH2CH2OH) or sublimed ((HO)2L = 1,2-
(HO)2C6H4, 1,2-(HOCH2)2C6H4, (HO)2SiPh2). Li2(OCH2)2 was
prepared by addition of 2 equiv. of LiBu to HOCH2CH2OH
2
2.22 (s, 6 H, C5Me4), 2.26 (s, 6 H, C5Me4), 5.50 (d, 2 H, J =
12 Hz, (OCH2)2C6H4), 5.33 (d, 2 H, 2J = 12 Hz, (OCH2)2C6H4),
7.32 (bs, 4 H, (OCH2)2C6H4); 13C-NMR (CDCl3): -1.0 (SiMe),
11.2, 13.3, 13.7 and 13.9 (C5Me4), 64.2 ((OCH2)2C6H4), 123.4,
132.4, 134.5 and 136.1 (C5Me4), 129.0, 131.3 and 139.3 (Ci)
((OCH2)2C6H4).
[(TiCl)2(l-O2SiPh2)(l-{(g5-C5Me4SiMeO)2(l-O)})] (1d).
A
in hexane. Compounds [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})],36
5
5
solution of [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (0.20 g,
0.32 mmol) in dichloromethane (20 mL) was treated with two
equivalents of NEt3 (0.06 g, 0.64 mmol) and one equivalent of
(HO)2SiPh2 (0.08 g, 0.32 mmol). The mixture was stirred for
three days at ambient temperature. The volatiles were then pumped
off and the remaining solid was extracted into a mixture of solvents
toluene–hexane (20 mL/10 mL). The volatiles were pumped off
yielding a yellow solid (0.10 g). The isolated solid consisted
mainly of 1d, but it contained some irremovable decomposition
products, which prevent us from obtaining correct elemental
analysis, though satisfactory spectroscopy data were obtained.
Data for 1d: 1H-NMR (CDCl3): 0.43 (s, 6 H, SiMe), 1.81 (s, 6 H,
C5Me4), 1.95 (s, 6 H, C5Me4), 2.32 (s, 6 H, C5Me4), 2.36 (s, 6 H,
B(C6F5)3,44 0.5(toluene)·Al(C6F5)3 and [Ph3C][B(C6F5)4]46 were
45
prepared by literature methods and [TiCp*(OiPr)3]47 was prepared
from [TiCp*Cl3]48 and Li(OiPr) in toluene.
[(TiCl)2(l-1,2-O2C2H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (1a).
5
A suspension of [(TiCl2)2(m-{(h -C5Me4SiMeO)2(m-O)})] (0.60 g,
0.98 mmol) and Li2(OCH2)2 (0.11 g, 1.47 mmol) was stirred in
toluene (30 mL) for 5 h at ambient temperature. Afterwards,
hexane (10 mL) was added and the solution was filtered. The
yellow residue was extracted again into a mixture of solvents
toluene–hexane (20 mL/10 mL). The volatiles were removed
under vacuum, leaving a yellow solid (0.35 g, 60%). Data for 1a:
1H-NMR (C6D6): 0.39 (s, 6 H, SiMe), 1.72 (s, 6 H, C5Me4), 2.17
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C5Me4), 7.30 (m, 6 H, C6H5), 7.63 (m, 4 H, C6H5); 13C-NMR
(CDCl3): -0.8 (SiMe), 11.4, 13.3, 14.3 and 15.7 (C5Me4), 122.2,
135.2, 137.1, 138.3 and 138.6 (C5Me4), 127.7, 129.84, 134.3 and
133.1 (Ci) (C6H5).
2J = 10 Hz, PhCH2-Ti), 2.26 (d, 2 H, 2J = 10 Hz, PhCH2-Ti), 6.79
(bs, 4 H, O2C6H4), 7.01–7.22 (m, 10 H, C6H5); 13C-NMR (C6D6):
-0.5 (SiMe), 10.6, 11.5, 11.9 and 14.0 (C5Me4), 77.5 (PhCH2Ti),
120.0, 121.3, 122.5, 127.0, 129.2, 149.9 (Ci, PhCH2Ti) and 154.8
(Ci, O2C6H4) (C6H5, O2C6H4), 120.0, 126.1, 128.8, 130.8 and
131.8 (C5Me4). Anal. Calcd for C40H48O5Si2Ti2 (759.72): C, 63.18;
H, 6.31%. Found: C, 62.69; H, 5.83%.
[(TiMe)2(l-1,2-O2C2H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (2a).
A solution of 1a (0.56 g, 0.93 mmol) in diethyl ether (40 mL)
at -78 ◦C was treated with two equivalents of a solution of LiMe
(1,5 M, 1.24 mL, 1.86 mmol). The reaction mixture was warmed
to room temperature and stirred overnight. 10 mL of hexane was
then added and the solution was filtered. The yellow residue was
extracted again into a mixture of solvents diethyl ether–hexane
(20 mL/10 mL). The volatiles were pumped off to give a mixture
[{Ti(OiPr)2}2(l-{(g5-C5Me4SiMeO)2(l-O)})]
(4). Toluene
5
(25 mL) was added to a mixture of [(TiCl2)2(m-{(h -C5Me4-
SiMeO)2(m-O)})] (0.33 g, 0.53 mmol) and LiOiPr (0.18 g,
2.65 mmol) at -78 ◦C. The cooling bath was removed and the
reaction mixture was allowed to warm to ambient temperature
and further stirred overnight. 10 mL of hexane was then added
and the solution was filtered. The volatiles were pumped off to
5
of compounds 2a and [(TiMe2)2(m-{(h -C5Me4SiMeO)2(m-O)})]
(0.36 g) in 3 : 1 molar ratio. Data for 2a: 1H-NMR (C6D6): 0.45 (s,
6 H, SiMe), 0.82 (s, 6 H, Me-Ti), 1.67 (s, 6 H, C5Me4), 1.98 (s, 6
H, C5Me4), 2.20 (s, 6 H, C5Me4), 2.47 (s, 6 H, C5Me4), 3.70 (dd, 2
H, 2J = 8 Hz, 3J = 2 Hz, O2C2H4), 4.67 (dd, 2 H, 2J = 8 Hz, 3J =
2 Hz, O2C2H4); 13C-NMR (C6D6): 0.1 (SiMe), 10.7, 11.9, 13.7 and
13.9 (C5Me4), 44.7 (Me-Ti), 74.3 (O2C2H4), 116.6, 126.0, 127.4,
128.8 and 130.8 (C5Me4).
1
yield 4 as a yellow solid (0.29 g, 80%). Data for 4: H-NMR
(CDCl3): 0.26 (s, 6 H, SiMe), 1.12 (m, 24 H, Me2CH), 2.03 (s,
6 H, C5Me4), 2.05 (s, 6 H, C5Me4), 2.21 (s, 6 H, C5Me4), 2.22 (s,
6 H, C5Me4), 4.68 (m, 4 H, Me2CH); 13C-NMR (CDCl3): -0.7
(SiMe), 11.9, 12.0, 13.7 and 14.0 (C5Me4), 25.7 (Me2CH), 26.1,
26.4, 26.5 and 26.7 (Me2CH), 118.8, 127.6, 127.7, 129.4 and 129.7
(C5Me4). Anal. Calcd for C32H58O7Si2Ti2 (705.72): C, 54.41; H,
8.21%. Found: C, 53.86; H, 7.95%.
[(TiMe)2(l-1,2-O2C6H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (2b).
The same procedure described aboved for 2a was applied by using
1b (0.30 g, 0.46 mmol) and LiMe (1.5 M, 0.60 mL, 0.92 mmol)
to give 2b as a yellow solid (0.22 g, 80%). Data for 2b: 1H-NMR
(C6D6): 0.43 (s, 6 H, SiMe), 1.03 (s, 6 H, Me-Ti), 1.64 (s, 6 H,
C5Me4), 2.02 (s, 6 H, C5Me4), 2.16 (s, 12 H, C5Me4), 6.74 (m,
2 H, O2C6H4), 6.82 (m, 2 H, O2C6H4); 13C-NMR (C6D6): -0.1
(SiMe), 10.7, 11.9, 12.6 and 14.0 (C5Me4), 48.7 (Me-Ti), 117.3,
129.1, 129.5, 130.2 and 131.0 (C5Me4), 120.2, 121.5 and 155.3 (Ci)
(O2C6H4). Anal. Calcd for C28H40O5Si2Ti2 (607.72): C, 55.28; H,
6.58%. Found: C, 54.67; H, 5.84%.
[{TiCl(C6F5)}2(l-{(g5-C5Me4SiMeO)2(l-O)})]
(5). Com-
pounds 1a (0.040 g, 0.06 mmol) and (0.5toluene)·Al(C6F5)3
(0.038 g, 0.06 mmol) were stirred in toluene (2 mL) for 12 h.
The solution was filtered and the volatiles were removed under
vacuum leaving an oil that was washed with hexane (2 ¥ 2 mL)
1
to give 5 as a yellow solid (0.031 g, 60%). Data for 5: H-NMR
(C6D6) 0.33 (s, 6 H, SiMe), 1.98 (s, 6 H, C5Me4), 2.04 (s, 6 H,
C5Me4), 2.15 (s, 6 H, C5Me4), 2.39 (s, 6 H, C5Me4); 13C-NMR
(C6D6): -2.0 (SiMe), 12.8, 13.3, 15.1 and 15.9 (C5Me4), 119.3,
138.7, 139.1, 141.3 and 144.7 (C5Me4), 139.2, 145.4 and 150.1
(m, C6F5); 19F-NMR (C6D6): -120.1 (o-C6F5), -153.4 (p-C6F5),
-162.3 (m-C6F5). Anal. Calcd for C32H30O3Si2Ti2Cl2F10 (874.50):
C, 43.91; H, 3.43%. Found: C, 43.99; H, 4.11%.
[(TiBz)2(l-1,2-O2C2H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (3a).
BzMgCl (2 M, 1.66 mL, 3.32 mmol) was injected to a solution of
1a (1.00 g, 1.66 mmol) in diethyl ether (50 mL) at -78 ◦C. The
reaction mixture was warmed to room temperature and stirred
overnight. 10 mL of hexane were added and the solution was
filtered. The red residue was extracted again into a mixture of
solvents diethyl ether–hexane (30 mL/20 mL). The volatiles were
pumped off and the remaining solid was washed with 10 mL of
hexane to isolate 1c as a red solid (0.71 g, 60%). Data for 3a:
1H-NMR (C6D6): 0.45 (s, 6 H, SiMe), 1.62 (s, 6 H, C5Me4), 1.79
Reaction of 1b with Al(C6F5)3. Formation of [(TiCl)2(l-1,
2-O2C6H4 ){l-({g5 -C5Me4SiMeO}2 {l-O·Al(C6F5)3 })}] (6) and
[(TiCl){Ti(C6F5 )}(l-1, 2-O2C6H4 )(l-{(g5 -C5Me4SiMeO)2
5
(l-O)})] (7).
A
solution of [(TiCl)2(m-1,2-O2C6H4)(m-{(h -
C5Me4SiMeO)2(m-O)})] (1b) (0.020 g, 0.03 mmol) in C6D6
2
in NMR tube was treated with one equivalent of
a
(s, 6 H, C5Me4), 1.84 (s, 6 H, C5Me4), 1.97 (d, 2 H, J = 10 Hz,
2
0.5(toluene)·Al(C6F5)3 (0.017 g, 0.03 mmol). The reaction was im-
mediately monitored by NMR spectroscopy, showing a complete
transformation into 6 after 5 min. The solution of 6 evolved to a
mixture of 7 and 5 in ca. 2 : 1 after two days at ambient temperature.
PhCH2-Ti), 2.10 (d, 2 H, J = 10 Hz, PhCH2-Ti), 2.18 (s, 6 H,
C5Me4), 3.51 (dd, 2 H, 2J = 8 Hz, 3J = 2 Hz, O2C2H4), 4.05 (dd, 2
H, 2J = 8 Hz, 3J = 2 Hz, O2C2H4), 6.82–7.23 (m, 10 H, PhCH2Ti);
13C-NMR (C6D6): -0.2 (SiMe), 10.5, 11.4, 13.2 and 14.1 (C5Me4),
73.8 (PhCH2–Ti), 74.0 (O2C2H4), 121.8, 127.5, 128.9, 152.0 (Ci)
(PhCH2Ti) 117.3, 126.1, 127.2, 130.1 and 130.9 (C5Me4). Anal.
Calcd for C36H48O5Si2Ti2 (711.67): C, 60.70; H, 6.74%. Found: C,
60.94; H, 6.62%.
1
Data for 6: H-NMR (C6D6): 0.31 (s, 6 H, SiMe), 1.64 (s, 6 H,
C5Me4), 1.84 (s, 6 H, C5Me4), 2.03 (s, 6 H, C5Me4), 2.19 (s, 6 H,
C5Me4), 6.65 (m, 2 H, O2C6H4), 6.78 (m, 2 H, O2C6H4); 13C-NMR
(C6D6): -1.7 (SiMe), 10.9, 12.6, 13.1 and 14.1 (C5Me4), 119.9,
123.9 and 154.9 (Ci) (O2C6H4), 122.3, 132.4, 135.2, 137.8, 141.1
(C5Me4), 137.2, 141.3 and 150.9 (m, C6F5); 19F-NMR (C6D6):
-121.1 (o-C6F5), -151.2 (p-C6F5), -160.7 (m-C6F5). Data for 7:
1H-NMR (C6D6): 0.40 (s, 3 H, SiMe), 0.48 (s, 3 H, SiMe), 1.40 (s,
3 H, C5Me4), 1.69 (s, 3 H, C5Me4), 1.71 (s, 3 H, C5Me4), 1.93 (s, 3
H, C5Me4), 2.03 (s, 3 H, C5Me4), 2.19 (s, 3 H, C5Me4), 2.25 (s, 3
H, C5Me4), 2.26 (s, 3 H, C5Me4), 6.95–7.23 (m, 4 H, O2C6H4);
[(TiBz)2(l-1,2-O2C6H4)(l-{(g5-C5Me4SiMeO)2(l-O)})] (3b).
The same procedure described above for 3a was applied by using
1b (0.40 g, 0.61 mmol) and MgClBz (2 M, 0.62 mL, 1.22 mmol)
to give 3b as an orange solid (0.28 g, 60%). Data for 3b: 1H-NMR
(C6D6): 0.42 (s, 6 H, SiMe), 1.49 (s, 6 H, C5Me4), 1.59 (s, 6 H,
C5Me4), 1.88 (s, 6 H, C5Me4), 2.17 (s, 6 H, C5Me4), 2.20 (d, 2 H,
3762 | Dalton Trans., 2009, 3756–3765
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©

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Table 3 Crystal data and structure refinement details for 1a·0.5C6H14, 1b and 7
1a·0.5C6H14
1b
7
Formula
FW
C25H41Cl2O5Si2Ti2
644.46
C26H34Cl2O5Si2Ti2
649.41
C32H34ClF5O5Si2Ti2
781.02
Color/habit
Cryst. dimensions/mm
Cryst. syst.
Space group
Yellow/block
0.48 ¥ 0.43 ¥ 0.36
Monoclinic
P21/c
17.207(5)
11.438(3)
17.691(3)
116.591(10)
3113.5(14)
4
200
1.375
0.793
1348
3.56–27.51
67211
7118/0.0667
5599
0.0646/0.1616
0.0799/0.1711
0.058(3)
Red/prism
0.49 ¥ 0.35 ¥ 0.31
Monoclinic
P21/c
14.112(3)
10.4098(7)
21.228(3)
104.083(14)
3024.7(8)
4
200
1.426
0.817
1344
3.15–27.50
21976
6948/0.0674
4787
0.0441/0.1067
0.0808/0.1184
Orange/prism
0.45 ¥ 0.20 ¥ 0.10
Monoclinic
P21/c
11.597(4)
17.888(3)
16.826(5)
95.61(2)
3473.8(15)
4
200
1.493
0.671
1600
3.53–27.50
70795
7957/0.1090
4936
0.0583/0.1427
0.1132/0.1613
0.0080(9)
1.046
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z
T/K
rc/g cm-3
m/mm-1
F(000)
q range/◦
no. of rflns collected
no. of indep. rflns/Rint
no. of obsd rflns (I > 2s(I))
R1, wR2 (I > 2s(I))a
R1, wR2 (all data)a
Extinction coefficient
GOF (on F2)a
1.089
+0.664/-0.617
1.039
0.549/-0.437
-3
˚
Largest diff. peak/hole/e A
+0.495/-0.539
19F-NMR (C6D6): -114.7 (o-C6F5), -154.3 (p-C6F5), -162.1
(m-C6F5).
C5Me4), 2.36 (s, 3 H, C5Me4), PhCH2-Al was not observed, 2.47 (d,
1 H, 2J = 12 Hz, PhCH2-Ti), 2.89 (s, 3 H, C5Me4), 3.36 (d, 1 H, 2J =
12 Hz, PhCH2-Ti), 3.79 (m, 1 H, O2C2H4), 3.91 (m, 1 H, O2C2H4),
4.62 (m, 2 H, O2C2H4), 6.81–7.42 (m, 10 H, C6H5); 13C-NMR
(CD2Cl2): -2.0 (SiMe), -1.9 (SiMe), 11.5, 12.3, 12.6, 12.9, 13.8,
15.9, 16.4 and 16.6 (C5Me4), PhCH2–Al was not observed, 67.2
and 75.2 (O2C2H4), 99.4 (PhCH2–Ti), 120.6 (Ci), 121.7 (Ci), 126.8,
126.9 (Ci), 127.4, 127.5 (Ci), 127.8 (Ci), 129.8, 129.8 (Ci), 130.2,
130.2 (Ci) and 133.3 (PhCH2–Al, C5Me4, PhCH2–Ti); 19F-NMR
(CD2Cl2): -120.1 (o-C6F5), -155.8 (p-C6F5), -161.7 (m-C6F5).
[Ti(TiBz)(l-1,2-O2C2H4)(l-{(g5-C5Me4SiMeO)2(l-O)})][BzB-
(C6F5)3] (8B). A solution of 3a (0.100 g, 0.14 mmol) and B(C6F5)3
(0.071 g, 0.14 mmol) in CH2Cl2 (2 mL) were stirred for 5 min.
The volatiles were removed under vacuum leaving an oil that was
washed with hexane (2 ¥ 2 mL) to give 8B as an orange solid
1
(0.146 g, 85%). Data for 8B: H-NMR (CD2Cl2): 0.47 (s, 3 H,
SiMe), 0.54 (s, 3 H, SiMe), 1.77 (s, 3 H, C5Me4), 1.84 (s, 3 H,
C5Me4), 2.05 (s, 3 H, C5Me4), 2.09 (s, 3 H, C5Me4), 2.26 (s, 3 H,
C5Me4), 2.27 (s, 3 H, C5Me4), 2.34 (s, 6 H, C5Me4), 2.71 (d, 1
[Ti(TiBz)(l-1,2-O2C6H4)(l-{(g5-C5Me4SiMeO)2(l-O)})][BzB-
(C6F5)3] (9B). 0.5 mL of CD2Cl2 previously cooled at -78 ◦C
were added to a mixture of 3b (0.030 g, 0.03 mmol) and B(C6F5)3
(0.025 g, 0.03 mmol) in a NMR tube cooled at -78 ◦C. The NMR
spectra, run at -20 ◦C, showed formation of 9B as the only product.
2
H, J = 12 Hz, PhCH2-Ti), 2.77 (bs, 2 H, PhCH2-B), 3.15 (d, 1
2
H, J = 12 Hz, PhCH2-Ti), 3.40 (m, 1 H, O2C2H4), 3.70 (m, 2
H, O2C2H4), 4.25 (m, 1 H, O2C2H4), 6.70–7.26 (m, 10 H, C6H5);
13C-NMR (CD2Cl2): -1.5 (SiMe), -0.8 (SiMe), 12.1, 12.4, 13.2,
13.5, 15.1, 15.9, 16.3 and 17.0 (C5Me4), 31.9 (PhCH2–B), 68.8 and
77.4 (O2C2H4), 95.0 (PhCH2–Ti), 121.9 (Ci), 122.7, 126.2 (Ci),
126.4 (Ci), 126.5, 126.8, 127.0, 128.7 (Ci), 128.9, 129.3, 129.9,
131.7 (Ci), 135.8 (Ci), 137.4 (Ci), 138.3 (Ci), 141.3 (Ci), 141.40
(Ci), 149.24 (Ci), 151.03 (Ci) (PhCH2–B, C5Me4, PhCH2–Ti); 19F-
NMR (CD2Cl2): -127.9 (o-C6F5), -161.5 (p-C6F5), -164.4 (m-
C6F5). Anal. Calcd for C54H48O5Si2Ti2BF15 (1223.20): C, 52.96; H,
3.92%. Found: C, 53.50; H, 4.21%.
1
Data for 9B: H-NMR (CD2Cl2): 0.26 (s, 3 H, SiMe), 0.37 (s, 3
H, SiMe), 1.42 (s, 3 H, C5Me4), 1.47 (s, 3 H, C5Me4), 1.91 (s, 3 H,
C5Me4), 1.93 (s, 3 H, C5Me4), 2.12 (s, 3 H, C5Me4), 2.17 (bs, 1 H,
PhCH2-Ti), 2.24 (s, 3 H, C5Me4), 2.29 (s, 3 H, C5Me4), 2.41 (bs,
2 H, PhCH2-Ti), 2.46 (s, 3 H, C5Me4), 2.71 (bs, 1 H, PhCH2-
B), 6.70–7.20 (m, 10 H, C6H5, O2C6H4); 13C-NMR (CD2Cl2):
-2.1 (SiMe), -2.0 (SiMe), 11.2, 12.4, 13.1, 13.8, 14.7, 15.2, 15.8
and 16.6 (C5Me4), 38.4 (PhCH2–B), 80.2 (PhCH2–Ti), 120.1–
140.3 (C6H5, C6F5, O2C6H4, C5Me4); 19F-NMR (CD2Cl2): -133.1
(o-C6F5), -158.4 (p-C6F5), -163.8 (m-C6F5).
[Ti(TiBz)(l-1,2-O2C2H4 )(l-{(g5 -C5Me4SiMeO)2 (l-O)})]-
[BzAl(C6F5)3] (8Al). Compounds 3a (0.020 g, 0.02 mmol) and
0.5(toluene)·Al(C6F5)3 (0.032 g, 0.04 mmol) were loaded into a
NMR tube and 0.5 mL of CD2Cl2 was added. The tube was
then shaken vigorously and the reaction was monitored by NMR
spectroscopy at 25 ◦C, formation of 8Al occurred immediately.
Polymerization of e-caprolactone with dinuclear complex 4.
e-Caprolactone (1 g) was added via syringe to a stirred solution
of complex 4 (0.04 mmol) in toluene (5 mL), in a glove box. The
polymerization mixture was stirred at the desired temperature.
After the measured time interval, the flask was quenched by
adding 5 mL of MeOH–HCl diluted. The quenched mixture was
precipitated into 150 mL of methanol, stirred overnight, filtered,
1
Data for 8Al: H-NMR (CD2Cl2): 0.62 (s, 3 H, SiMe), 0.69 (s, 3
H, SiMe), 1.36 (s, 3 H, C5Me4), 1.71 (s, 3 H, C5Me4), 2.00 (s, 3 H,
C5Me4), 2.06 (s, 3 H, C5Me4), 2.24 (s, 3 H, C5Me4), 2.32 (s, 3 H,
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and washed with methanol. The polymer collected was dissolved
in acetone, precipitated in methanol at 0 ◦C, filtered, and dried
in a vacuum oven at 80 ◦C. A 1H NMR (CDCl3) spectrum
of the polymer was obtained for an end group analysis. Gel
permeation chromatography (GPC) analyses of polymer samples
were carried out in THF as solvent at 25 ◦C (Varian HPLC) in
Alcala´ University.
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X-Ray structure determination of 1a·0.5C6H14, 1b and 7
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49
˚
monochromated Mo-Ka radiation (l = 0.71073 A). Multiscan
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ꢀ
˜
2
squares refinements were carried out by minimizing w(Fo
-
Fc )2 with the SHELXL-97 weighting scheme and stopped at
shift/err < 0.001. The final residual electron density maps
showed no remarkable features. Also in 1a a molecule of hexane
crystallized with every two molecules of the compound. This
solvent molecule was found in the difference Fourier map but
was very disordered and it was not possible to get a chemical
sensible model for it, so Squeeze procedure52 was used to remove
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2
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Acknowledgements
We gratefully acknowledge Ministerio de Educacio´n y Ciencia
(project MAT2007–60997) and DGUI-Comunidad de Madrid
(programme S-0505/PPQ-0328 COMAL-CM) (Spain) for finan-
cial support. L. P. acknowledges DGUI-CM for Fellowship.
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