Constrained geometry titanium complexes: Exceptionally robust systems for living polymerization of methacrylates at high temperature and model studies toward chain transfer polymerization with thiols

Article abstract of DOI:10.1021/om060838g

The 1:1 combination of Ti{CGC}Me₂ (1; CGC = Me ₂Si(Me₄C₅)(tBuN)) with B(C₆F ₅)₃ was found to feature a so far unrevealed thermal robustness in methacrylate polymerization that enables it to operate in a broad temperature range (0-100°C) with a living behavior. Highly effective (576 kg PMMA·mol Ti^-1·h^-1) and productive (monomer-to-Ti ratio up to 5000) homopolymerization of methyl methacrylate (MMA) and effective diblock and triblock copolymerization of MMA with butyl methacrylate (BMA) were thus achieved at 80°C. The robust constrained geometry titanium system has been used to investigate thiols as possible chain transfer agents in MMA polymerization. Neutral alkylthiolato and thiophenolato complexes [Ti{CGC}(X)(Y)] (2, X = Me, Y = tBuS; 3, X = Me, Y = o-MeOC₆H₄S; 4, X = Y = iPrS; 5, X = Y = PhCH₂S) have been synthesized by protonolysis of 1 with thiols and shown to polymerize MMA once activated by a Lewis acid such as B(C₆F₅) ₃. Combinations 1/B(C₆F₅)₃/tBuSH polymerized quantitatively MMA in toluene to yield PMMAs with narrow polydispersity (M_w/M_n ?1 .10), but no effective chain transfer was evidenced, whatever the conditions used. The stoichiometric reaction of tBuSH and o-MeOC₆H₄SH with the cationic enolate complex [Ti{CGC}(O(OiPr)C=CMe₂)-(THF)]⁺[MeB(C ₆F₅)₃]^- (8) revealed that thiols do cleave the Ti-O(enolate) bond of 8 to give the alkylthiolato and thiophenolato titanium cationic species; however, this pathway proceeds remarkably slowly in comparison with that with a similar Zr-O(enolate) bond.

Full text of DOI:10.1021/om060838g

Organometallics 2007, 26, 187-195
187
“Constrained Geometry” Titanium Complexes: Exceptionally
Robust Systems for Living Polymerization of Methacrylates at High
Temperature and Model Studies toward Chain Transfer
Polymerization with Thiols
Bing Lian,† Christophe M. Thomas,† Christophe Navarro,‡ and Jean-Franc¸ois Carpentier*,†
Catalyse et Organome´talliques, UMR 6226, UniVersity of Rennes 1, 35042 Rennes Cedex, France, and
Arkema, Lacq Research Center, PO Box 34, 64170 Lacq, France
ReceiVed September 13, 2006
The 1:1 combination of Ti{CGC}Me2 (1; CGC ) Me2Si(Me4C5)(tBuN)) with B(C6F5)3 was found to
feature a so far unrevealed thermal robustness in methacrylate polymerization that enables it to operate
in a broad temperature range (0-100 °C) with a living behavior. Highly effective (576 kg PMMA‚mol
Ti-1‚h-1) and productive (monomer-to-Ti ratio up to 5000) homopolymerization of methyl methacrylate
(MMA) and effective diblock and triblock copolymerization of MMA with butyl methacrylate (BMA)
were thus achieved at 80 °C. The robust “constrained geometry” titanium system has been used to
investigate thiols as possible chain transfer agents in MMA polymerization. Neutral alkylthiolato and
thiophenolato complexes [Ti{CGC}(X)(Y)] (2, X ) Me, Y ) tBuS; 3, X ) Me, Y ) o-MeOC6H4S; 4,
X ) Y ) iPrS; 5, X ) Y ) PhCH2S) have been synthesized by protonolysis of 1 with thiols and shown
to polymerize MMA once activated by a Lewis acid such as B(C6F5)3. Combinations 1/B(C6F5)3/tBuSH
polymerized quantitatively MMA in toluene to yield PMMAs with narrow polydispersity (Mw/Mn =
1.10), but no effective chain transfer was evidenced, whatever the conditions used. The stoichiometric
reaction of tBuSH and o-MeOC6H4SH with the cationic enolate complex [Ti{CGC}(O(OiPr)CdCMe2)-
(THF)]+[MeB(C6F5)3]- (8) revealed that thiols do cleave the Ti-O(enolate) bond of 8 to give the
alkylthiolato and thiophenolato titanium cationic species; however, this pathway proceeds remarkably
slowly in comparison with that with a similar Zr-O(enolate) bond.
complex Cp2ZrMe[O(OMe)CdCMe2] as initiator and cationic
complex [Cp2Zr(THF)Me]+[BPh4]- as catalyst.1b,c The isolation
of the neutral zirconocene enolate in its pure form established
unambiguously, via detailed kinetic studies, a group-transfer-type
bimetallic propagating mechanism. Recently, Chen and co-work-
ers have reported the isolation of the cationic ansa-zirconocene
ester enolate complex [rac-(EBI)Zr(THF){O(OiPr)CdCMe2}]+-
[MeB(C6F5)3]- (EBI ) ethylenebis(indenyl)) and the generation
of the cationic “constrained geometry” Ti ester enolate complex
[(CGC)Ti(THF){O(OiPr)CdCMe2}]+[MeB(C6F5)3]- (CGC )
Me2Si(Me4C5)(tBuN)), which were both shown to be highly
active for the polymerization of MMA.2h,i The rate-limiting step
in those monocomponent systems4 involves either the intramo-
lecular Michael addition2i or regeneration of the monomer-
coordinated enolate active species via ring-opening of the
resting eight-membered cyclic enolate.2j A major point of
interest in these group 4 metal systems is the high degree of
control, i.e., the livingness and stereochemistry of polymeriza-
tion, they exhibit under suitable conditions. Particularly interest-
Introduction
Methacrylate polymerization mediated by group 4 metal
systems has attracted much attention in recent years.1-3 Living
polymerization of methyl methacrylate (MMA) with two-
component Zr systems was first reported by Collins and co-
workers in 1992 using [Cp2Zr(THF)Me]+[BPh4]- and Cp2-
ZrMe2,1a and further by combination of the neutral enolate
* Corresponding author. Fax:
jean-francois.carpentier@univ-rennes1.fr.
† Universite´ de Rennes 1.
(+33)(0)223-236-939. E-mail:
‡ Arkema.
(1) (a) Collins, S.; Ward, D. G. J. Am. Chem. Soc. 1992, 114, 5460-
5462. (b) Collins, S.; Ward, D. G.; Suddaby, K. H. Macromolecules 1994,
27, 7222-7224. (c) Li, Y.; Ward, D. G.; Reddy, S. S.; Collins, S.
Macromolecules 1997, 30, 1875-1883. (d) Nguyen, H.; Jarvis, A. P.;
Lesley, M. J. G.; Kelly, W. M.; Reddy, S. S.; Taylor, N. J.; Collins, S.
Macromolecules 2000, 33, 1508-1510. (e) Stojcevic, G.; Kim, H.; Taylor,
N. J.; Marder, T. B.; Collins, S. Angew. Chem. Int. Ed. 2004, 43, 5523-
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(2) (a) Chen, E. Y.-X.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J. J.
Am. Chem. Soc. 1998, 120, 6287-6305. (b) Bolig, A. D.; Chen, E. Y.-X.
J. Am. Chem. Soc. 2001, 123, 7943-7944. (c) Jin, J.; Chen, E. Y.-X.
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Am. Chem. Soc. 2002, 124, 5612-5613. (f) Chen, E. Y.-X.; Cooney, M. J.
J. Am. Chem. Soc. 2003, 125, 7150-7151. (g) Mariott, W. R.; Chen, E.
Y.-X. J. Am. Chem. Soc. 2003, 125, 15726-15727. (h) Bolig, A. D.; Chen,
E. Y.-X. J. Am. Chem. Soc. 2004, 126, 4897-4906. (i) Rodriguez-Delgado,
A.; Mariott, W. R.; A.; Chen, E. Y.-X. Macromolecules 2004, 37, 3092-
3100. (j) Rodriguez-Delgado, A.; Chen, E. Y.-X. Macromolecules 2005,
38, 2587-2594. (k) Mariott, W. R.; Rodriguez-Delgado, A.; Chen, E. Y.-
X. Macromolecules 2006, 39, 1318-1327. (l) Rodriguez-Delgado, A.;
Mariott, W. R.; Chen, E. Y.-X. J. Organomet. Chem. 2006, 691, 3490-
3497.
(3) (a) Deng, H.; Shiono, T.; Soga, K. Macromolecules 1995, 28, 3067-
3073. (b) Cameron, P. A.; Gibson, V. C.; Graham, A. J. Macromolecules
2000, 33, 4329-4335. (c) Frauenrath, H.; Keul, H.; Ho¨cker, H. Macro-
molecules 2001, 34, 14-19. (d) Batis, C.; Karanikolopoulos, G.; Pitsikalis,
M.; Hadjichristidis, N. Macromolecules 2003, 36, 9763-9774. (e) Jensen,
T. R.; Yoon, S. C.; Dash, A. K.; Luo, L.; Marks, T. J. J. Am. Chem. Soc.
2003, 125, 14482-14494. (f) Strauch, J. W.; Faure´, J.-L.; Bredeau, S.;
Wang, C.; Kehr, G.; Fro¨hlich, R.; Luftmann, H.; Erker, G. J. Am. Chem.
Soc. 2004, 126, 2089-2104. (g) Lian, B.; Toupet, L.; Carpentier, J.-F. Chem.
Eur. J. 2004, 10, 4301-4307. (h) Stuhldreier, T.; Keul, H.; Ho¨cker, H.;
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(4) For a DFT study see: Tomasi, S.; Weiss, H.; Ziegler, T. Organo-
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10.1021/om060838g CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/30/2006

188 Organometallics, Vol. 26, No. 1, 2007
Lian et al.
Scheme 1
ing are the technologically significant olefin polymerization
“constrained geometry” Ti{CGC} systems5 that are used in
forming methyl methacrylate (MMA) polymers (PMMAs) with
a highly syndiotactic-enriched microstructure ([rr] ) 82%, Pr
) 0.90) at ambient temperature.2i
The use of a stoichiometric amount of metal complex per
macromolecular chain remains, however, a major limitation of
initiating polymerization systems. To transform initiators into
true catalysts, the search for effective chain transfer agents
(CTAs) is of high industrial relevance. In this process, three
essential objectives must be achieved: (i) CTAs must cleave
the growing PMMA chain, (ii) the resulting new cationic species
must reinitiate polymerization of MMA, and (iii) an adequate
kinetic regime must be reached. Organic acids such as enolizable
ketones (or esters) and alkylthiols have been recently investi-
gated for such purposes with neutral lanthanidocenes6 and by
both Chen’s group2k and our group7 with cationic zirconocenes.
Herein, we report some related studies using “constrained
geometry” titanium systems. The first aim of this work was to
investigate MMA polymerization mediated by Ti{CGC}Me2/
activator binary systems, especially the influence of temperature.
It has been eventually evidenced that Ti{CGC} systems feature
high efficiency and productivity, and a thus far unrevealed
thermal robustness that enables them to operate in a broad
temperature range (0-100 °C) while keeping a living behavior.
The second and central aim of this work was to investigate the
use of thiols as potential CTAs for MMA polymerization
mediated by the robust Ti{CGC} systems. Results from po-
lymerization experiments and stoichiometric studies with model
alkylthiolato-, thiophenolato-, and enolato-Ti complexes are
described.
quantitatively at 80 °C to yield also the corresponding mono-
thiophenolato complex 3. Interestingly, NMR monitoring of this
reaction at 20 °C showed that a mixture formed within 2.5 h
that consisted of 3 (42% NMR yield) and the alcoholysis product
of the Ti-N(CGC) bond,8 i.e., [Ti{Me2Si(Me4C5)(tBuNH)}(o-
MeOC6H4S)Me2] (3′, 22% NMR yield); complex 3′ was
completely converted to 3 within 12 h upon raising the
temperature to 80 °C, re-forming the Ti{C5R4SiMe2NtBu}
chelate ring via methane elimination.8 Single crystals of 3
suitable for X-ray diffraction were grown from pentane (Table
1, Figure 1). As anticipated, the o-methoxy group coordinates
to the Ti center, which is thus five-coordinated in the solid state
showing a pseudo-pentahedral environment. The configuration
of the {CGC}Ti moiety is similar to that reported previously
for similar species,5 indicative of a constrained geometry around
the Ti center. The unit cell of 3 contains two different
stereoisomers that originate from opposite chelation of the
[o-MeOC6H4S]- group onto Ti.9 The two stereoisomers feature
slight differences in the bond angles, e.g., S(5)-Ti(1)-(41),
72.20(9)° vs S(4)-Ti(1)-O(51), 74.11(18)°; on the other hand,
the Ti-O(thiophenolato) bonds are significantly different (Ti-
(1)-O(41), 2.430(3) vs Ti(1)-O(51), 2.262(7) Å), while the
Ti-S bonds are similar (Ti(1)-S(4), 2.4664(11) vs Ti(1)-S(5),
2.461(2) Å). In comparison with a Ti-ethylthiolato complex (Ti-
S(1), 2.398(3) Å; Ti-S(1)-C(1), 108.2(3)°),10 the latter Ti-S
bonds are somewhat longer with narrower Ti-S-C bond angles
(Ti(1)-S(4)-C(61A), 99.88(9)°; Ti(1)-S(5)-C(62A), 103.08-
(11)°), reflecting the presence of a thiophenolato group and
likely also the additional OMe group coordinated to the Ti
center.
Results and Discussion
Synthesis of Neutral Alkylthiolato- and Thiophenolato-
Titanium Precursors [Ti{Me2Si(Me4C5)(tBuN)}(X)(Y)] (X,
Y ) Me, RS). A series of neutral “constrained geometry”
alkylthiolato- and thiophenolato-titanium complexes [Ti{CGC}-
(X)(Y)] (2, X ) Me, Y ) tBuS; 3, X ) Me, Y ) o-MeOC6H4S;
4, X ) Y ) iPrS; 5, X ) Y ) PhCH2S) were synthesized by
protonolysis of the dimethyltitanium precursor 1 with the desired
alkylthiol or thiophenol (Scheme 1). The reaction of 1 with
2 equiv of tBuSH proceeded quantitatively at 80 °C to yield
the mono-tert-butylthiolato complex 2. Despite the presence of
excess thiol, the bis-tert-butylthiolato complex was not detected,
even after prolonged reaction times at this temperature. Com-
bination of 1 with 1 equiv of o-MeOC6H4SH proceeded
On the other hand, upon using 2 equiv of the less bulky thiols
iPrSH or PhCH2SH, the corresponding bis-alkylthiolato com-
plexes 4 and 5 were obtained in 100% NMR yield. When the
same reactions were performed with 1 equiv of these thiols,
(5) For the initial design of this ligand system see: (a) Shapiro, P. J.;
Bunel, E.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9, 867-
869. (b) Piers, W. E.; Shapiro, P. J.; Bunel, E.; Bercaw, J. E. Synlett 1990,
2, 74-84. (c) Shapiro, P. J.; Cotter, W. D.; Schaefer, W. P.; Labinger, J.
A.; Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623-4640. For selected
examples see: (d) Stevens, J. C.; Timmers, F. J.; Rosen, G.; Knight, G.
W.; Lai, S. Y. (Dow Chemical Co.) Eur. Pat. App., EP 0416815 A2, 1991.
(e) Canich, J. A. (Exxon Chemical Co.) Eur. Pat. App., EP 0420436 A1,
1991. (f) Stevens, J. C. In Studies in Surface Science and Catalysis; Soga,
K., Terano, M., Eds.; Elsevier: Amsterdam, 1994; Vol. 89, pp 277-284.
(g) Chen, Y.-X.; Marks, T. J. Organometallics 1997, 16, 3649-3657. (h)
Soga, K.; Uozomi, T.; Nakamura, S.; Toneri, T.; Teranishi, T.; Sano, T.;
Arai, T. Macromol. Chem. Phys. 1996, 197, 4237-4251. (i) McKnight, A.
L.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587-2598. (j) Li, L.; Metz,
M. V.; Li, H.; Chen, M.-C.; Marks, T. J.; Liable-Sands, L.; Rheingold, A.
L. J. Am. Chem. Soc. 2002, 124, 12725-12741.
(8) (a) Key 1H NMR data for 3′: 1H NMR (C6D6): δ 3.41 (s, 3H, OCH3),
2.28 (s, 6H, CH3C5), 1.84 (s, 6H, CH3C5), 1.15 (s, 9H, NC(CH3)3), 1.03 (s,
6H, Ti(CH3)2), 0.57 (s, 6H, Si(CH3)2), resonances for Ph overlapped with
those of 3 and unreacted o-MeOC6H4SH. (b) For a similar observation
during the alcoholysis of {SiMe2(C5R4)(NtBu)}Ti complexes, see: Car-
pentier, J.-F.; Maryin, V. P.; Luci, J.; Jordan, R. F. J. Am. Chem. Soc. 2001,
123, 898-909. (c) For other reactions in which the {SiMe2(C5R4)(NtBu)}M
chelate ring in constrained geometry complexes is cleaved see: Carpenetti,
D. W.; Kloppenburg, L.; Kupec, J. T.; Petersen, J. L. Organometallics 1996,
15, 1572-1581. (d) Kloppenburg, L.; Petersen, J. L. Organometallics 1996,
15, 7-9.
(9) Stereoisomers 3A and 3B are not distinguished by NMR spectroscopy
at room temperature in C6D6 solution.
(10) Calhorda, M. J.; Carrondo, M. A. A. F. C. T.; Dias, A. R.; Fraza˜o,
C. F.; Hursthouse, M. B.; Simo˜es, J. A. M.; Teixeira. C. Inorg. Chem. 1988,
27, 2513-2518.
(6) (a) Nodono, M.; Tokimitsu, T.; Tone, S.; Makino, T.; Yanagase, A.
Macromol. Chem. Phys. 2000, 201, 2282-2288. (b) Yanagase, A.; Tone,
S.; Tokimitsu, T.; Nodono, M. (Mitsubishi Rayon) Eur. Pat. Appl.
0919569A1, 1999.
(7) Lian, B.; Lehmann, C. W.; Navarro, C.; Carpentier, J.-F. Organo-
metallics 2005, 24, 2466-2472.

“Constrained Geometry” Titanium Complexes
Organometallics, Vol. 26, No. 1, 2007 189
Table 1. Crystal Data and Structure Refinement for 3
newly prepared neutral alkylthiolato and thiophenolato com-
plexes 2-5 were investigated for MMA polymerization after
activation with 1 equiv of a molecular Lewis acid to generate
in situ the corresponding cationic species (Scheme 3). For
comparison purposes, the performances of the polymerization
systems based on the dimethyl precursor 1 were first investigated.2i
High-Temperature Living Polymerization of Methacry-
lates with Ti{CGC}Me2/Activator Systems. Representative
MMA polymerization results obtained from the simple dim-
ethyltitanium precursor 1 in toluene solution are summarized
in Table 2. As previously reported,2i combinations of 1 with
usual molecular activators led to quantitative conversion of
MMA at room temperature (entries 2-4). The PMMAs obtained
under these conditions had a relatively narrow molecular weight
distribution (Mw/Mn ) 1.17-1.28) and a syndiotactic-enriched
microstructure, the best results being observed with B(C6F5)3
(entry 2). Decreasing the temperature to 0 °C proved deleterious
in terms of control and initiation efficiency (entry 1). On the
other hand, surprisingly good performances were obtained at
higher temperatures (entries 5-17). The active cationic [Ti-
{CGC}(enolato-PMMA)(L)n]+ species, generated in situ from
1, B(C6F5)3 and MMA, remains stable at least up to 100 °C,
yielding quantitatively PMMAs with an excellent match between
experimental and calculated number average molecular weights
considering a monometallic initiating system, along quite narrow
polydispersities. The latter seem even to narrow as the temper-
ature increases, suggesting a better control of the polymerization
at high temperature. This is a rather counterintuitive observation
for most chemists, who are used to lowering temperature to
minimize side reactions, e.g., back biting, and achieve better
control of the polymerization. In fact, “living-controlled”
polymerizations of methacrylates with early transition metal
systems are carried out at most at room temperature.12 As
expected, however, the syndiotacticity decreased to some extent
from 80% rr at 20 °C to ca. 67% rr at 80 °C.
A series of experiments were carried out at 80 °C to
investigate the influence of the MMA-to-Ti ratio (entries 7,
9-13). Full conversions were observed for monomer-to-initiator
ratios up to 5000, yielding within short reaction times PMMAs
with high molecular weight that fit well with the calculated Mn
values and still with a very narrow polydispersity (Figure 3). It
is noteworthy that similar performances were obtained when
the polymerization was performed in bulk (entry 11). A kinetic
monitoring established also that average number molecular
weights increase linearly with MMA conversion (entries 13-
17, Figure 4). In a separate experiment, MMA polymerization
was performed for 10 min at 80 °C with [MMA]/[Ti] ) 4000,
giving a TOF value of 576 kg PMMA‚mol Ti-1‚h-1. All these
results demonstrate the high productivity and degree of living-
ness of the 1/B(C6F5)3 system at 80 °C.
empirical formula
fw
temperature/K
C23H37NOSSiTi
451.59 g‚mol-1
100 (2)
wavelength/Å
0.71073
cryst syst
orthorhombic
space group
Pcab
a/Å
14.7578(7)
b/Å
15.1980(7)
c/Å
20.8733(10)
R/deg
90
90
90
4681.7(4)
â/deg
γ/deg
volume/Å3
Z
8
density (calcd)/Mg‚m-3
absorp coeff/mm-1
F(000)
1.281
0.520
1936
0.4 × 0.35 × 0.1
2.37 to 27.52
-19 e h e 19,
-19 e k e 19,
-27 e l e 19
45 743
5378 [Rint ) 0.0408]
99.9%
semiempirical from equivalents
full-matrix least-squares on F2
5378/0/281
cryst size/mm3
θ range for data collection/deg
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ ) 26.40°
absorp corr
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.066
R1 ) 0.0402, wR2 ) 0.0991
R1 ) 0.0502, wR2 ) 0.1037
0.367 and -0.330
largest diff peak and hole/e Å-3
mixtures of mono- and bis-alkylthiolato species were obtained,
from which the complexes could not be efficiently separated.
Generation of Cationic Species [Ti{Me2Si(Me4C5)(tBuN)}-
(SR)(L)n]+. Model reactions were attempted to characterize the
cationic species [Ti{CGC)}(SR)(L)n]+ (L ) solvent, n ) 0,1),
putatively generated upon activation with an appropriate
abstractor and which may act further as initiators toward
methacrylate polymerization (vide infra). The reactions of
neutral [Ti{CGC}(X)(Y)] complexes 2, 4, and 5 with B(C6F5)3
or [HNMe2Ph][B(C6F5)4] in THF-d8 or toluene-d8 solution at
low temperature led invariably to complicated mixtures of
products, as assessed by multinuclear NMR spectroscopy. We
assume that this reflects the poor stability of the corresponding
[Ti{CGC}(SR)(L)n]+ cationic species derived from aliphatic
monodentate alkylthiolato ligands (tBuS, iPrS, and PhCH2S,
respectively). A more stable cationic species (6) was generated
in ca. 95% NMR purity from the o-methoxythiophenolato
complex 3 by methyl abstraction with 1 equiv of B(C6F5)3 in
THF-d8 solution (Scheme 2). Alternatively, cationic complex
6-d8 was also prepared by the methane elimination reaction
between [Ti{CGC}(Me)(THF-d8)]+ (7-d8) and 1 equiv of
1
o-MeOC6H4SH in THF-d8. The low-temperature (213 K) H
The livingness of the 1/B(C6F5)3 system in toluene at high
temperature (80 °C) was further illustrated by sequential diblock
PMMA-b-PBMA (BMA ) n-butyl methacrylate) and triblock
PMMA-b-PBMA-b-PMMA copolymerizations. Experiments
were performed with [MMA]/[BMA]/[Ti] ) 200:200:1 and
[MMA]/[BMA]/[MMA]/[Ti] ) 200:200:200:1, respectively.
NMR spectrum of 6-d8 in THF-d8 shows resonances for an
asymmetric structure on the NMR time scale, including four
singlets for the C5Me4 methyl groups (Figure 2). Upon warming,
those resonances coalesce and collapse to two singlets at room
temperature. This fluxional behavior is consistent with either
an exchange process between the coordinated THF molecule
and [o-MeOC6H4S]- group and/or exchange of the thiophenolato
and methoxy ligands within the latter chelated moiety, as
observed in the solid state for 3 (vide supra). Complex 6 is
stable in THF solution at low temperature but decomposes at
room temperature within 3 days to form a new species, which
could not be so far identified.11
(11) Key NMR data for the decomposition species from 6: 1H NMR
(THF-d8): δ 7.20 (m, Ph), 7.11 (m, Ph), 6.87 m, Ph), 3.80 (s, OCH3), 2.29
(s, CH3C5), 2.27 (s, CH3C5), 2.06 (s, CH3C5), 2.05 (s, CH3C5), 1.28 (s,
NC(CH3)3), 0.74 (s, Si(CH3)2), 0.75 (s, Si(CH3)2).
(12) Systems based on combinations of dialkyl zirconocenes with borane
or borate co-activators have been used for bulk MMA polymerization at
high temperature (155-190 °C), but offered PMMAs with relatively broad
molecular weight distributions (PDI ) 1.6 for Cp2ZrMe2 at 155 °C and 2.4
for (EBI)ZrMe2 at 105 °C); see: Rhodes, L. F.; Goodall, B. L.; Collins, S.
US Pat. 5668234, 1997.
Methacrylate Polymerization with [Ti{Me2Si(Me4C5)-
(tBuN)}(X)(Y)] (X, Y ) Me, SR)/Activator Systems. The

190 Organometallics, Vol. 26, No. 1, 2007
Lian et al.
Figure 1. The two independent molecules found in the solid-state structure of 3. Selected bond lengths (Å) and angles (deg) (molecule
3B): Ti(1)-N(1), 1.9506(17); Ti(1)-C(30), 2.157(2); Ti(1)-O(51), 2.262(7); Ti(1)-S(4), 2.4664(11); Ti(1)-C(31), 2.2884(19); Ti(1)-
C(32), 2.368 (2); Ti(1)-C(33), 2.497(2); Ti(1)-C(34), 2.4908(19); Ti(1)-C(35), 2.3710(19); C(61A)-S(4), 1.865(3); N(1)-Ti(1)-C(30),
94.85(9); N(1)-Ti(1)-O(51), 93.47(16); C(30)-Ti(1)-O(51), 131.4(2); O(51)-Ti(1)-S(4), 74.11(18); C(30)-Ti(1)-S(4), 68.85(10); Ti-
(1)-S(4)-C(61A), 99.88(9); N(1)-Ti(1)-C5Me4(centroid C(31)-C(35), 107.63. Selected bond lengths (Å) and angles (deg) (molecule
3A): Ti(1)-S(5), 2.461(2); Ti(1)-O(41), 2.430(3); O(41)-Ti(1)-S(5), 72.20(9), Ti(1)-S(5)-C(62A), 103.08(11).
Scheme 2
Scheme 3
1
Figure 2. Selected region of the variable-temperature H NMR
spectra (300 MHz, THF-d8) of [Ti{CGC}(o-OMeC6H4S)(THF-d8)]-
[MeB(C6F5)3] (6-d8). Descriptors * and “s” refer to (CH3)4C5 and
residual solvent resonances, respectively. The vertical expansion
is different for each temperature.
on 2 in toluene ([rr] ) 75-81%) is comparable to that of the
corresponding systems based on 1, with triad distributions charac-
teristic of chain-end control mechanism.13 The reaction protocol
proved very important with these alkylthiolato-Ti systems. Addi-
tion of a stabilizing base (THF or MMA; protocols B and C) to
the highly sensitive, in situ generated ionic species was found
to improve significantly polymerization control. Under such
conditions, precursor 2 led to PMMAs with very narrow
molecular weight distributions (Mw/Mn ) 1.05-1.10) and
The results obtained are summarized in Table 3. In both cases,
the final polymers recovered had narrow polydispersity, and
Mn values in close agreement with the calculated values were
obtained. Also, the 1H NMR spectra of the copolymers showed
composition of PMMA-to-PBMA as 1.16:1 and 2.10:1, respec-
tively, which is very close to the starting monomer ratios. The
GPC traces of intermediary and final polymers clearly evidence
the living nature of the polymerizations (Figure 5).
experimental Mn values in good agreement with the calculated
values (entries 24, 25). These data indicate that the correspond-
ing tert-butylthiolato ionic complex [Ti{CGC}(StBu)]+[anion]-,
despite its apparent thermal sensitivity (in the absence of MMA;
vide supra), is an effective initiator.
On the other hand, whatever the activation protocol used,
PMMAs with molecular weight much higher than that expected
and bimodal distributions were obtained from the thiophenolato
complex 3 in toluene (e.g., entry 26). We assume that the low
efficiency of this system likely reflects the poor ability of the
weakly basic thiophenolato group to undergo nucleophilic
addition onto coordinated MMA and/or the instability of the in
situ generated cationic species in a nonpolar solvent, as observed
Polymerization of Methacrylates with Ti{CGC}(SR)(Y)/
Activator Systems. Representative polymerization results ob-
tained with the new alkylthiolato and thiophenolato precursors
are summarized in Table 4. Very high to quantitative MMA
conversions were reached with the tert-butylthiolato precursor
2 provided the polymerization is carried out in toluene. In fact,
both the yield and syndiotacticity of PMMA dramatically
decreased when the polymerization is carried out in THF
solution (entry 20), evidencing the detrimental influence of such
a coordinating solvent. The syndiospecificity of systems based
(13) Triad distribution at 23 °C: 81% rr, 4% mm, 15% mr.

“Constrained Geometry” Titanium Complexes
Organometallics, Vol. 26, No. 1, 2007 191
Table 2. Living Polymerization of MMA Mediated by Ti{CGC}Me2 (1)/B(C6F5)3 Systemsa
d
entry
temp (°C)
[MMA]/[Ti]
timeb (min)
yield (%)
Mn,calc (g‚mol-1
)
Mn,expd (g‚mol-1
)
Mw/Mn
[rr]e (%)
1
2
0
20
20
20
40
60
80
100
80
80
80
80
80
80
80
80
80
200
200
200
200
200
200
200
200
400
1000
1000
2000
5000
2000
2000
2000
2000
1440
1440
1440
1440
1440
1440
30
1440
30
60
1080
120
1080
3
6
10
95
>99
96
93
95
96
96
>99
98
98
96
95
98
15
45
65
96
19 000
20 000
19 200
18 600
19 000
19 200
19 200
20 000
39 200
98 000
96 000
190 000
480 000
30 000
90 000
130 000
192 000
28 600
24 700
24 000
31 400
22 100
17 600
20 000
21 200
37 200
95 600
92 600
180 100
531 100
35 400
82 600
113 800
175 700
1.54
1.17
1.23
1.28
1.09
1.07
1.06
1.06
1.05
1.05
1.13
1.08
1.24
1.05
1.05
1.06
1.06
73
80
78
74
75
71
69
60
67
67
64
67
66
nd
nd
nd
67
3f
4g
5
6
7
8
9
10
11h
12
13
14
15
16
17
20
a Polymerization conditions unless otherwise stated: [MMA] ) 5.0 M in toluene; 1 and B(C6F5)3 ) 0.05 mmol; addition order of reagents: [Ti +
b
activator], then MMA within 20 s. Reaction time was not necessarily optimized; reactions carried out at 20 °C with [MMA]/[Ti] ) 200 were usually
c
completed within 6-8 h, while those carried out at 80 °C with [MMA]/[Ti] ) 2000 required 10-15 min to go to completion. Calculated Mn values from
d
e
f
conv × [MMA]/[Ti] × 100 g‚mol-1. Determined by GPC in THF vs PMMA standards. Determined by 1H NMR. [CPh3][B(C6F5)4] was used as activator.
g[HNMe2Ph][B(C6F5)4] was used as activator. Bulk polymerization (i.e., <0.1 mL of toluene).
h
Figure 4. Dependence of Mn on monomer conversion in the
polymerization of MMA promoted by 1/B(C6F5)3 in toluene at
80 °C. [: Mn values determined by GPC vs PMMA standards;
dashed line: calculated Mn values in a monometallic system.
Figure 3. Dependence of Mn on monomer-to-titanium ratio in the
polymerization of MMA promoted by 1/B(C6F5)3 in toluene at
80 °C (conversion >95%). [: Mn values determined by GPC vs
PMMA standards; dashed line: calculated Mn values in a mono-
metallic system.
been investigated in terms of chemical compatibility and chain
transfer activity toward Ti{CGC}Me2 (1)/B(C6F5)3 systems.
Representative MMA polymerization experiments are sum-
marized in Table 5. The active Ti species proved intolerant of
an ester-functionalized alkylthiol (HSCH2CO2CH3) since the
addition of only 5 equiv (vs Ti) of it completely inhibited MMA
polymerization (entry 44). Significantly decreased PMMA yields
were observed in the presence of thiophenols (2-naphthylthiol,
p-ClC6H4SH, and o-MeOC6H4SH) (entries 45-47). The addition
of up to 5 equiv of other alkylthiols (tBuSH, iPrSH, PhCH2SH,
and CF3CH2SH) did not preclude the polymerization (entries
31-43), but an important decrease in the PMMA yield was
observed when larger amounts (50 equiv) of tBuSH were used
(entry 39). Intermediary results in terms of polymerization
activity were observed in the presence of nC4H9SH (entry 41).
With all active combinations, the observed Mn values were
always much higher than the calculated values, considering one
polymer chain per added thiol; the molecular weight distribu-
tions remained in most cases quite narrow. Modification of the
reaction conditions (temperature, solvent) using tBuSH as the
thiol had a small influence on the polymerization results,
although a slight, but noticeable, decrease of Mn values was
by NMR (vide supra). High polymerization yields were obtained
with the bis(alkylthiolato)titanium complexes 4 and 5, but also
with somewhat larger molecular weight distributions and lower
initiation efficiency (entries 27-30).
The above results confirm that [Ti{CGC}(enolate)(L)n]+
species are very effective methacrylate polymerization initiators.
Their high activity and productivity, and so far unrevealed
thermal robustness that enables them to operate in a broad
temperature range (0-100 °C) with a living behavior, make
them a good candidate for possible transfer agents. Also,
combinations of a neutral [Ti{CGC}(SR)(Y)] precursor with a
molecular activator can efficiently polymerize MMA, indicating
that some in situ generated [Ti{CGC}(SR)(L)n]+ cationic species
are good initiators. Further to our initial studies on the search
for chain transfer agents with zirconocene systems,7 we therefore
investigated MMA polymerization with Ti{CGC}Me2/activator
systems in the presence of thiols.
Investigations of MMA Chain Transfer Polymerization
Using Ti{CGC}Me2/B(C6F5)3/Thiols Systems. A series of
alkylthiols and thiophenols varying in bulkiness and acidity have

192 Organometallics, Vol. 26, No. 1, 2007
Lian et al.
Table 3. Sequential Diblock and Triblock Copolymerization of MMA and BMA Mediated by the Ti{CGC}Me2 (1)/B(C6F5)3
System at 80 °Ca
b
entry
polymer type
time (h)
yield (%)
M
n,cal (g‚mol-1
)
Mn,expb (g‚mol-1
)
Mw/Mn
[rr]c (%)
18
19
PMMA-b-PBMA
PMMA-b-PBMA-b-PMMA
1 + 1
1 + 1 + 1
>99
97
48 400
66 400
49 500
60 400
1.06
1.20
65
64
b
c
a 1 ) 0.05 mmol; Ti/B(C6F5)3 ) 1; 200 equiv of monomer at each feed; toluene ) 6 mL. Determined by GPC in THF vs PMMA standards. Determined
1
by H NMR.
complex [ZrCp2(OC(OiPr)dCMe2)(THF)]+[MeB(C6F5)3]- (10).3h
In fact, the complete consumption of 8 and tBuSH, and
concomitant generation of 9 and release of 1 equiv of isopropyl
isobutyrate, requires 3 days, while it takes place within only
1 h with 10 under the same conditions.7 The reaction of 8 with
1 equiv of the more acidic thiophenol o-MeOC6H4SH in THF-
1
d8 was also investigated (Scheme 4). A H NMR monitoring
showed that 8 is consumed within 2 days to form 6 with
concomitant release of 1 equiv of isopropyl isobutyrate. This
reaction proceeds much faster in the weakly coordinating solvent
CD2Cl2, but still requires 6 h. Reasons for this remarkably slow
cleavage pathway are still unclear.14
Conclusions
We have shown that Ti{CGC}Me2/activator combinations are
highly effective and productive systems for living polymeriza-
tion of methacrylates in an unexpected and exceptionally broad
temperature range, from 20 °C up to 100 °C. To the best of our
Figure 5. GPC traces (THF, 23 °C, flow rate 1 mL/min) of
knowledge, this is the highest temperature reported for “living-
controlled” polymerization of MMA mediated by an early
transition metal system.12
(bottom) PMMA-b-PBMA diblock copolymer and (top) PMMA-
b-PBMA-b-PMMA triblock copolymer. Descriptors a, b, and c refer
to PMMA, PMMA-b-PBMA, and PMMA-b-PBMA-b-PMMA,
respectively.
In combination with a Lewis acid, “constrained geometry”
alkylthiolato and thiophenolato titanium complexes (2-5)
proved able to initiate the polymerization of MMA. The
stoichiometric reactivity of thiols toward a model Ti-enolate
species (8) revealed also that thiols do cleave the Ti-O(enolate)
bond to yield the corresponding alkylthiolato and thiophenolato
Ti cationic species. However, cleavage of the Ti-O(enolate)
bond by thiols proceeds very slowly, which is likely the main
reason to account for the poor efficiency of chain transfer
polymerization with Ti{CGC}Me2/abstractor/RSH systems.
observed with increasing temperature in the range 0-80 °C
using the 1/B(C6F5)3/tBuSH system. This indicates that no
effective chain transfer polymerization occurred under the above
conditions.
Two possibilities can be envisioned to account for the
inefficiency of thiols (e.g., tBuSH) to act as chain transfer
agents: (a) thiols are inactive, i.e., they do not cleave growing
PMMA chains from the Ti-enolate intermediate species during
the time period necessary for complete conversion of MMA.
(b) Thiols are extremely active, i.e., they are consumed by active
Ti-enolate species in the early stage of the reaction. In the latter
hypothesis, one should expect the formation of oligomers end-
capped with alkylthiolato (tBuS) groups, which was observed
neither by 1H NMR analysis nor by MALDI-TOF mass
spectrometry.
To support the validity of the first hypothesis, the stoichio-
metric reactivity of alkylthiols and thiophenols toward cationic
Ti-enolate species was next investigated. The model species
[Ti{CGC}(OC(OiPr)dCMe2)(THF)]+[MeB(C6F5)3]- (8), which
mimics the propagating intermediate in the Ti-mediated polymer-
ization of MMA,2i was selected for this purpose. Complex 8
reacts with 1 equiv of tBuSH in THF-d8 at room temperature
via protonolysis of the Ti-O(enolate) bond to yield the
corresponding [Ti{CGC}(StBu)(THF)]+ cationic species (9)
with concomitant release of 1 equiv of isopropyl isobutyrate
(Scheme 4). Although 9 is not stable at room temperature and
slowly decomposes into an unidentified species (consistent with
the aforementioned unsuccessful attempts to isolate such species
from Ti{CGC}(StBu)Me (2)), this is the pathway expected to
take place while using tBuSH as a transfer agent in the
polymerization of MMA. However, cleavage of the Ti-
O(enolate) bond in 8 by tBuSH proceeds remarkably slowly in
comparison with that of the Zr-O(enolate) bond in the parent
Experimental Section
General Procedures. All experiments were carried out under
purified argon using standard Schlenk techniques or a glovebox
(<1 ppm O2, 5 ppm H2O). Hydrocarbon solvents, diethyl ether,
and tetrahydrofuran were distilled from Na/benzophenone; toluene
and pentane were distilled from Na/K alloy under nitrogen and
degassed by freeze-thaw-vacuum prior to use. Chlorinated
solvents were distilled from calcium hydride. Deuterated solvents
were purchased from Eurisotop and purified before use. Methyl
methacrylate (MMA, Acros) and n-butyl methacrylate (BMA,
Acros) were distilled twice under argon over CaH2. tBuSH, iPrSH,
nC4H9SH, CF3CH2SH, PhCH2SH, and HSCH2CO2CH3 (all Aldrich)
and thiophenols p-ClC6H4SH, 2-naphthylthiol, and o-MeOC6H4-
SH (all Acros) were distilled before use. MeLi (1.6 M solution in
diethyl ether, Acros), Ti{Me2Si(Me4C5)(tBuN)}Cl2 (Boulder Sci-
entific Co.), [Ph3C][B(C6F5)4] (Boulder Scientific Co.), and [HNMe2-
(14) A possible cleavage process of the Ti-O(enolate) bond in [Ti-
{CGC}(enolate)]+ species by thiols includes initial THF dissociation, then
thiol coordination, and finally generation of the [Ti{CGC}(SR)(L)n]+ species
(Scheme 5). Preliminary decoordination of THF from Ti is supported by
enhanced cleavage kinetics in a weakly coordinating solvent such as CD2-
Cl2, as compared to THF (vide supra). Similar observations have been made
and conclusions drawn for cationic Zr systems; see ref 3g and: Piers, W.
E.; Koch, L.; Ridge, D. S.; MacGillivray, L. R.; Zaworotko, M. Organo-
metallics 1992, 11, 3148-3152.

“Constrained Geometry” Titanium Complexes
Organometallics, Vol. 26, No. 1, 2007 193
Table 4. Polymerization of MMA Mediated by 2-5/Activator Systemsa
d
entry
comp
activator
B(C6F5)3
protocolb
yield (%)
Mn,calc (g‚mol-1
)
Mn,expd (g‚mol-1
)
Mw/Mn
[rr]e (%)
20f
21
22
23
24
25
26
27
28
29
30
2
2
2
2
2
2
3
4
5
5
5
A
A
A
A
B
C
B
B
B
B
B
35
96
96
95
95
96
>99
92
7000
19 200
19 200
19 000
19 000
19 200
20 000
18 400
18 600
12 000
19 400
22 400
31 300
28 600
28 800
18 500
22 000
198 000g
73 500
64 300
105 200
33 800
1.05
1.10
1.09
1.10
1.07
1.09
1.18g
1.13
1.20
1.24
1.23
73
81
77
75
75
78
74
73
72
75
73
B(C6F5)3
[HNMe2Ph][B(C6F5)4]
[Ph3C][B(C6F5)4]
B(C6F5)3
B(C6F5)3
B(C6F5)3
[HNMe2Ph][B(C6F5)4]
[HNMe2Ph][B(C6F5)4]
B(C6F5)3
93
60
97
[Ph3C][B(C6F5)4]
a Polymerization conditions unless otherwise stated: [MMA] ) 5.0 M in toluene; Ti ) 0.05 mmol; [Ti]/[activator]/[MMA] ) 1:1:200, T ) 20 °C;
b
reaction time ) 24 h (unoptimized). Protocol A: precursor, then activator, then MMA; protocol B: precursor in THF, then activator, then dried, then
c
MMA; protocol C: Precursor in 0.1 g of MMA, then activator, then rest of MMA. Calculated Mn values from conv × [MMA]/[Ti] × 100 g‚mol-1
.
dDetermined by GPC in THF vs PMMA standards. Determined by H NMR spectroscopy. THF solvent. A second distribution that accounts for ca. 5%
e
1
f
g
of the sample was observed with Mn ) 27 600 and Mw/Mn ) 1.06.
Table 5. Polymerization of MMA Using Ti{CGC}Me2 (1) Precursor in the Presence of Thiols as Potential Chain Transfer
Agent (CTA)a
b
entry
thiol
tBuSH
CTA (equiv)
temp (°C)
yield (%)
Mn,calcc (g/mol)
Mn,expb (g/mol)
Mw/Mn
31
32d
33
34
35e
36
37
38
39f
40
1
5
5
5
5
5
5
5
50
5
20
20
0
20
20
40
60
80
20
20
92
7
18 400
1400
3800
3680
3680
3800
3680
3720
80
24 500
n.d.
1.41
n.d.
tBuSH
tBuSH
tBuSH
tBuSH
tBuSH
tBuSH
tBuSH
tBuSH
iPrSH
95
92
96
95
96
93
20
85
28 600
23 900
23 500
21 800
18 800
19 200
5800
(40%) 52 900
(60%) 16 000
19 300
22 300
31 600
1.54
1.15
1.21
1.08
1.06
1.06
1.20
1.19
1.06
1.17
1.28
1.18
3400
41
42
43
44
45
46
47
nC4H9SH
PhCH2SH
CF3CH2SH
HSCH2CO2CH3
2-naphthylthiol
p-ClC6H4SH
o-MeOC6H4SH
5
5
5
5
5
5
5
20
20
20
20
20
20
20
38
92
95
<1
5
1520
3680
3800
200
600
680
12 000
11 700
(60%) 91 200
(40%) 15 100
1.14
1.19
1.03
1.19
15
17
a Polymerization conditions unless otherwise stated: toluene ) 2 mL; 1 ) 0.05 mmol; activator ) B(C6F5)3 (1 equiv vs 1); [MMA]/[Ti] ) 200; reaction
b
time ) 24 h (unoptimized); addition order of reagents: [Ti + activator], then [CTA + MMA] within 20 s. Determined by GPC in THF vs PS standards.
d
e
f
cCalculated Mn values considering one polymer chain per CTA. CH2Cl2 as solvent. [CPh3][B(C6F5)4] as activator. [HNMe2Ph][B(C6F5)4] as activator.
Scheme 4
Scheme 5
Ph][B(C6F5)4] (Boulder Scientific Co.) were used as received.
B(C6F5)3 (Boulder Scientific Co.) was sublimed twice before use.
Complexes 15d and 82i were synthesized as previously reported.
NMR spectra were recorded on Bruker AC-200, AC-300, and
AM-500 spectrometers in Teflon-valved NMR tubes at 23 °C unless
otherwise stated. 1H and 13C NMR chemical shifts were determined
using residual solvent resonances and are reported vs SiMe4.
Assignment of signals was made from H-13C HMQC and H-
13C HMBC 2D NMR experiments. Coupling constants are given
in hertz. Cationic Ti complexes containing MeB(C6F5)3- are totally
dissociated in THF-d8 or CD2Cl2 solution, and the NMR resonances
for this anion are almost identical (see below). Elemental analyses
(C, H, N, S) were performed by the Microanalytical Laboratory at
the Institute of Chemistry of Rennes and are the average of two
independent determinations. Molecular weights of PMMA (or block
copolymers) were determined by gel permeation chromatography
(GPC) at room temperature on a Waters apparatus equipped with
1
1
five PL gel columns (Polymer Laboratories Ltd), a Waters WISP
717 autosampler, and a Shimadzu RID 6A differential refractometer.
THF was used as eluent at a flow rate of 1.0 mL‚min-1. PS or
PMMA standards were used for molecular weight calibration. The
microstructure of polymers was determined by 1H NMR in CDCl3.
NMR Data for the Free Anion MeB(C6F5)3
.
- 15 1H NMR (THF-
d8): δ 0.50 (br s, 3H, BCH3). H NMR (CD2Cl2): δ 0.54 (br s,
1

194 Organometallics, Vol. 26, No. 1, 2007
Lian et al.
3H, BCH3). 13C{1H} NMR (THF-d8): δ 148.5 (dm, JC-F ) 252,
o-C6F5), 137.4 (dm, JC-F ) 247, p-C6F5), 136.2 (dm, JC-F ) 229,
m-C6F5), 129.7 (Cipso), 9.7 (br, BCH3). 13C{1H} NMR (CD2Cl2):
δ 148.3 (dm, JC-F ) 238, o-C6F5), 137.4 (dm, JC-F ) 257, p-C6F5),
(CH3)2), 0.52 (s, 6H, Si(CH3)2). 13C{1H} NMR (C6D6): δ 135.6
(C5CH3), 133.0 (C5CH3), 102.3 (C5SiMe2), 61.2 (NC(CH3)3), 41.9
(CH(CH3)2), 33.8 (NC(CH3)3), 28.3 (CH(CH3)2), 16.4 (C5CH3), 12.1
(C5CH3), 5.9 (SiCH3). Anal. Calcd for C21H41NS2SiTi (447.64):
C, 56.35; H, 9.23; N, 3.13; S, 14.33. Found: C, 57.1; H, 9.7; N,
3.3; S, 14.1.
136.4 (dm, JC-F ) 245, m-C6F5), 128.9 (Cipso), 9.9 (br, BCH3). 11
B
NMR (THF-d8): δ -14.8 (s, BCH3). 11B NMR (CD2Cl2): δ -14.9
(s, BCH3). 19F NMR (THF-d8): δ -134.5 (d, 3JC-F ) 21, 6F, o-F),
-168.5 (t, 3JF-F ) 21, 3F, p-F), -170.6 (m, 3JF-F ) 18, 6F, m-F).
19F NMR (CD2Cl2): δ -133.6 (d, 3JF-F ) 18, 6F, o-F), -165.6 (t,
Ti{Me2Si(Me4C5)(tBuN)}(SCH2Ph)2 (5). This product was
prepared as described above for 2 starting from 1 (18.2 mg,
0.056 mmol) and PhCH2SH (13.8 mg, 0.11 mmol) to give 5 as a
3
3JF-F ) 22, 3F, p-F), -168.2 (t, JF-F ) 22, 6F, m-F).
1
red, oily solid (19.5 mg, 64%). H NMR (C6D6): δ 7.43 (m, 4H,
Ti{Me2Si(Me4C5)(tBuN)}(StBu)Me (2). Ti{Me2Si(Me4C5)-
(tBuN)}Me2 (1, 17.6 mg, 0.054 mmol) and tBuSH (9.7 mg, 0.11
mmol) were charged in a Teflon-valved NMR tube, and C6D6 (ca.
0.5 mL) was vacuum transferred. The tube was sealed and kept at
80 °C, and 1H NMR spectroscopy was recorded periodically. Over
12 h, complex 2 formed quantitatively together with release of CH4
(1H NMR (C6D6): δ 0.16). Volatiles were removed under vacuum,
the residue was washed with a minimal amount of cold pentane,
and complex 2 was obtained as a red, oily solid (14 mg, 64%).
NMR data for 2: 1H NMR (C6D6): δ 2.21 (s, 3H, CH3C5), 2.07
(s, 3H, CH3C5), 2.05 (s, 3H, CH3C5), 1.92 (s, 3H, CH3C5), 1.67 (s,
9H, SC(CH3)3), 1.53 (s, 9H, NC(CH3)3), 0.83 (s, 3H, TiCH3), 0.50
Ph), 7.13 (m, 6H, Ph), 4.74 (s, 2H, CH2Ph), 4.73 (s, 2H, CH2Ph),
2.12 (s, 6H, CH3C5), 2.09 (s, 6H, CH3C5), 1.59 (s, 9H, NC(CH3)3),
0.53 (s, 6H, Si(CH3)2). 13C{1H} NMR (C6D6): δ 143.3 (Ph), 135.7
(C5CH3), 133.6 (C5CH3), 129.1 (Ph), 128.8 (Ph), 126.3 (Ph), 103.4
(C5SiMe2), 62.2 (NC(CH3)3), 42.4 (CH2Ph), 34.3 (NC(CH3)3), 16.1
(C5CH3), 12.6 (C5CH3), 5.9 (SiCH3). Anal. Calcd for C29H41NS2-
SiTi (543.73): C, 64.06; H, 7.60; N, 2.58; S, 11.79. Found: C,
64.8; H, 7.9; N, 2.7; S, 11.4.
Generation of [Ti{Me2Si(Me4C5)(tBuN)}(o-MeOC6H4S)(THF-
d8)][MeB(C6F5)3] (6-d8) from [Ti{Me2Si(Me4C5)(tBuN)}Me-
(THF-d8)][MeB(C6F5)3] (7-d8). A solution of 1 (18.0 mg, 0.055
mmol) in THF-d8 (ca. 0.5 mL) was prepared in a Teflon-valved
NMR tube, and B(C6F5)3 (28.1 mg, 0.055 mmol) was added at room
temperature. The tube was sealed and agitated for 10 min, and 1H
NMR spectroscopy was recorded, showing quantitative conversion
1
(s, 3H, SiCH3), 0.39 (s, 3H, SiCH3). H NMR (THF-d8): δ 2.27
(s, 3H, CH3C5), 2.22 (s, 3H, CH3C5), 1.99 (s, 3H, CH3C5), 1.96 (s,
3H, CH3C5), 1.57 (s, 9H, SC(CH3)3), 1.40 (s, 9H, NC(CH3)3), 0.54
(s, 3H, SiCH3), 0.53 (s, 3H, SiCH3), 0.42 (s, 3H, TiCH3). 13C{1H}
NMR (C6D6): δ 135.0 (C5CH3), 132.5 (C5CH3), 131.7 (C5CH3),
131.1 (C5CH3), 100.8 (C5SiMe2), 59.5 (SC(CH3)3), 57.5 (q, J )
97, TiCH3), 50.0 (NC(CH3)3), 36.4 (NC(CH3)3), 34.7 (SC(CH3)3),
15.4 (C5CH3), 15.1 (C5CH3), 13.9 (C5CH3), 12.0 (C5CH3), 6.4
(SiCH3), 5.7 (SiCH3). Anal. Calcd for C20H39NSSiTi (401.55): C,
59.82; H, 9.79; N, 3.49; S, 7.99. Found: C, 59.1; H, 10.2; N, 3.8;
S, 7.6.
1
of 1 to 7-d8. H NMR of 7-d8 (THF-d8): δ 2.42 (s, 3H, CH3C5),
2.15 (s, 3H, CH3C5), 2.09 (s, 3H, CH3C5), 2.01 (s, 3H, CH3C5),
1.48 (s, 9H, NC(CH3)3), 1.02 (s, 3H, TiCH3), 0.72 (s, 3H, Si(CH3)2),
-
0.68 (s, 3H, Si(CH3)2). The NMR data of free anion MeB(C6F5)3
were the same as those described above. To the above solution of
7-d8, o-MeOC6H4SH (7.7 mg, 0.055 mmol) was added via mi-
1
crosyringe. The tube was sealed and H NMR spectroscopy was
recorded. The conversion of 7-d8 to 6-d8 was >95% after 2 h. NMR
data for 6-d8: 1H NMR (THF-d8, 23 °C): δ 7.26 (t, 3J ) 8.0, 1H,
Ph), 7.17 (d, 3J ) 8.0, 1H, Ph), 7.09 (d, 3J ) 8.0, 1H, Ph), 6.96 (t,
3J ) 8.0, 1H, Ph), 3.89 (s, 3H, OCH3), 2.31 (s, 6H, CH3C5), 2.18
(s, 6H, CH3C5), 1.27 (s, 9H, NC(CH3)3), 0.77 (s, 6H, Si(CH3)2).
1H NMR (THF-d8, -60 °C): δ 7.34-6.81 (m, 5H, Ph), 3.84 (s,
3H, OCH3), 2.45 (s, 3H, CH3C5), 2.31 (s, 3H, CH3C5), 2.13 (s,
3H, CH3C5), 1.85 (s, 3H, CH3C5), 1.49 (s, 9H, NC(CH3)3), 0.86 (s,
3H, Si(CH3)2), 0.78 (s, 3H, Si(CH3)2). 13C{1H} NMR (THF-d8): δ
155.8 (Ph), 141.1 (C5CH3), 139.8 (C5CH3), 132.4 (Ph), 129.3 (Ph),
122.3 (Ph), 112.1 (Ph), 110.2 (C5Si(CH3)2), 66.7 (NC(CH3)3), 56.9
(OCH3), 31.9 (NC(CH3)3), 16.3 (C5CH3), 11.5 (C5CH3), 3.9
Ti{Me2Si(Me4C5)(tBuN)}(o-OMeC6H4S)(Me) (3). This product
was prepared as described above for 2 starting from 1 (113.0 mg,
0.34 mmol) and o-MeOC6H4SH (53.2 mg, 0.38 mmol) to give 3
as a red, oily solid (110 mg, 71%). Single crystals suitable for X-ray
diffraction were obtained from a concentrated solution in pentane
at -30 °C. 1H NMR (C6D6): δ 7.58 (d, 3J ) 8.0, 1H, Ph), 6.97 (t,
3J ) 8.0, 1H, Ph), 6.79 (t, 3J ) 8.0, 1H, Ph), 6.51 (t, 3J ) 8.0, 1H,
Ph), 3.38 (s, 3H, OCH3), 2.15 (s, 3H, CH3C5), 2.04 (s, 3H, CH3C5),
1.99 (s, 3H, CH3C5), 1.96 (s, 3H, CH3C5), 1.42 (s, 9H, NC(CH3)3),
0.83 (s, 3H, TiCH3), 0.53 (s, 3H, Si(CH3)2), 0.44 (s, 3H, Si(CH3)2).
1H NMR (THF-d8): δ 7.17 (d, 3J ) 8.0, 1H, Ph), 7.01 (t, 3J ) 8.0,
1H, Ph), 6.85 (t, 3J ) 8.0, 1H, Ph), 6.74 (t, 3J ) 8.0, 1H, Ph), 3.83
(s, 3H, OCH3), 2.19 (s, 3H, CH3C5), 2.06 (s, 3H, CH3C5), 2.03 (s,
3H, CH3C5), 1.88 (s, 3H, CH3C5), 1.35 (s, 9H, NC(CH3)3), 0.55 (s,
3H, TiCH3), 0.49 (s, 3H, Si(CH3)2), 0.46 (s, 3H, Si(CH3)2). 13C-
{1H} NMR (C6D6): δ 157.9 (Ph), 135.4 (C5CH3), 134.9 (Ph), 132.0
(Ph), 131.8 (C5CH3), 128.2 (Ph), 120.9 (Ph), 111.3 (Ph), 101.2 (C5-
Si(CH3)2), 59.9 (NC(CH3)3), 55.9(OCH3), 53.6 (TiCH3), 33.6 (NC-
(CH3)3), 15.6 (C5CH3), 12.0 (C5CH3), 5.9 (SiCH3). Anal. Calcd for
C23H37NOSSiTi (451.56): C, 61.18; H, 8.26; N, 3.10; S, 7.10.
Found: C, 61.50; H, 8.34; N, 2.94; S, 6.94.
-
(SiCH3). The NMR data of the free anion MeB(C6F5)3 were the
same as those described above.
Generation of [[Me2Si(Me4C5)(tBuN)]Ti(o-MeOC6H4S)(THF-
d8)][MeB(C6F5)3] (6-d8) from [{Me2Si(Me4C5)(tBuN)}TiMe(o-
MeOC6H4S) (3). A solution of 3 (10.0 mg, 0.023 mmol) in THF-
d8 (ca. 0.5 mL) was charged in a Teflon-valved NMR tube, and
B(C6F5)3 (11.6 mg, 0.023 mmol) was added at room temperature.
1
The tube was sealed, and H NMR spectroscopy was recorded
periodically. The conversion of 3 was almost quantitative within
30 min with ca. 95% selectivity for 6-d8. The NMR data were the
same as those reported above.
Ti{Me2Si(Me4C5)(tBuN)}(SiPr)2 (4). This product was prepared
as described above for 2 starting from 1 (17.6 mg, 0.054 mmol)
and iPrSH (8.4 mg, 0.11 mmol) to give 4 as a red oil (19 mg,
Reaction of [Ti{Me2Si(Me4C5)(tBuN)}(OC(OiPr)dCMe2)-
(THF-d8)][MeB(C6F5)3] (8-d8) with tBuSH in THF-d8. To a
solution of Ti{Me2Si(Me4C5)(tBuN)}(Me)(OC(OiPr)dCMe2)
(3.6 mg, 0.0082 mmol) in THF-d8 (ca. 0.5 mL) in a Teflon-valved
NMR tube was added at room temperature B(C6F5)3 (4.2 mg, 0.0082
mmol). The solution was left for 10 min at 20 °C to ensure the
complete formation of 8-d8, then tBuSH (0.73 mg, 0.0082 mmol)
was added via a microsyringe. 1H NMR spectra were periodically
recorded and revealed that the reaction was finished within 3 days,
with release of 1 equiv of isopropyl isobutyrate and a mixture of 9
and an unidentified decomposition product. NMR data for isopropyl
isobutyrate: 1H NMR (THF-d8): δ 4.96 (sept, 3J ) 6.0, 1H,
1
3
79%). H NMR (C6D6): δ 4.10 (sept, J ) 6.6, 2H, CH(CH3)2),
2.19 (s, 6H, CH3C5), 2.15 (s, 6H, CH3C5), 1.60 (s, 9H, NC(CH3)3),
3
3
1.46 (d, J ) 6.6, 6H, CH(CH3)2), 1.44 (d, J ) 6.6, 6H, CH-
(15) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994,
116, 10015-10031. (b) Horton, A. D.; de With, J.; Linden, J. v. d.; Weg,
H. v. d. Organometallics 1996, 15, 2672-2674. (c) Bochmann, M.; Green,
M. L. H.; Powell, A. K.; Sassmannshausen, J.; Triller, M. U.; Wocadlo, S.
J. Chem. Soc., Dalton Trans. 1999, 43-49. (d) Carpentier, J.-F.; Wu, Z.;
Lee, C. W.; Stro¨mberg, S.; Christopher, J. N.; Jordan, R. F. J. Am. Chem.
Soc. 2000, 122, 7750-7767. (e) Klosin, J.; Roof, G. R.; Chen. E. Y.-X.;
Abboud, K. A. Organometallics 2000, 19, 4684-4686.

“Constrained Geometry” Titanium Complexes
Organometallics, Vol. 26, No. 1, 2007 195
3
3
OCH(CH3)2), 2.43 (sept, J ) 7.0, 1H, (CH3)2CHCO), 1.18 (d, J
at calculated positions and forced to ride on the attached carbon
atom. The hydrogen atom contributions were calculated but not
refined. All non-hydrogen atoms were refined with anisotropic
displacement parameters. The locations of the largest peaks in the
final difference Fourier map calculation as well as the magnitude
of the residual electron densities were of no chemical significance.
Crystal data and details of data collection and structure refinement
are given in Table 1. Crystallographic data for 3 are also available
in cif format (see Supporting Information).
Typical Procedure for MMA Polymerization and MMA-
BMA Block Copolymerization. To a 10 mL flask equipped with
a magnetic stirrer, containing the Ti-{CGC} catalyst (0.05 mmol)
in toluene (or THF) solvent, was introduced the activator (B(C6F5)3,
[HNMe2Ph][B(C6F5)4], or [Ph3C][B(C6F5)4]) in toluene (or THF)
solvent and kept at the desired polymerization temperature. Then,
the proper amount of monomer was rapidly added (within 20 s) by
syringe. The polymerization was carried out for a time period, and,
in case of block copolymerization, a second or third injection (BMA
or MMA) was loaded. The reaction was then quenched by addition
of acidified methanol (3% HCl, 200 mL). The precipitated polymer
was filtered and dried overnight under vacuum at 60 °C.
3
) 6.0, 6H, OCH(CH3)2), 1.11 (d, J ) 7.0, 6H, (CH3)2CHCO).
13C{1H} NMR (THF-d8): δ 176.7 (COOiPr), 67.2 (OCH(CH3)2),
34.1 (CH3)2CHCO), 21.7 (OCH(CH3)2), 19.0 ((CH3)2CHCO).
Reaction of [Ti{Me2Si(Me4C5)(tBuN)}(OC(OiPr)dCMe2)-
(THF-d8)][MeB(C6F5)3] (8-d8) with o-MeOC6H4SH in THF-d8.
This reaction was conducted as described above starting from Ti-
{Me2Si(Me4C5)(tBuN)}(Me)(OC(OiPr)dCMe2) (3.8 mg, 0.0086
mmol), B(C6F5)3 (4.4 mg, 0.0086 mmol), and o-MeOC6H4SH
(1.2 mg, 0.0086 mmol). 1H NMR spectra were periodically recorded
and revealed that the reaction was finished within 2 days, with
release of 1 equiv of isopropyl isobutyrate and a mixture of 6 and
an unidentified decomposition product.
Reaction of [Ti{Me2Si(Me4C5)(tBuN)}(OC(OiPr)dCMe2)-
(THF)][MeB(C6F5)3] (8) with o-MeOC6H4SH in CD2Cl2. This
reaction was conducted as described above starting from Ti{Me2-
Si(Me4C5)(tBuN)}(Me)(OC(OiPr)dCMe2) (11.5 mg, 0.026 mmol),
B(C6F5)3‚THF (15.2 mg, 0.026 mmol), and o-MeOC6H4SH (3.65 mg,
0.026 mmol). 1H NMR spectra were periodically recorded and
revealed that the reaction was finished within 6 h, with release of
1 equiv of isopropyl isobutyrate and a mixture of 6 and an
unidentified decomposition product. NMR data for isopropyl
isobutyrate: 1H NMR (CD2Cl2): δ 4.97 (sept, 3J ) 6.3, 1H,
Acknowledgment. We thank Total and Arkema Co. (grant
to B.L.) and the Centre National de la Recherche Scientifique
for financial support of this work. We gratefully thank Dr. M.
Glotin and Dr. G. Meunier (Arkema Co.) for valuable discus-
sions.
3
3
OCH(CH3)2), 2.53 (sept, J ) 7.0, 1H, (CH3)2CHCO), 1.26 (d, J
3
) 6.3, 6H, OCH(CH3)2), 1.16 (d, J ) 7.0, 6H, (CH3)2CHCO).
Solid-State Structure Determination of Complex 3. A suitable
single crystal of 3 was mounted onto a glass fiber using the “oil-
drop” method. Diffraction data were collected at 100 K using a
NONIUS Kappa CCD diffractometer with graphite-monochroma-
tized Mo KR radiation (λ ) 0.71073 Å). A combination of ω- and
æ-scans was carried out to obtain at least a unique data set. Crystal
structures were solved by means of the Patterson method; remaining
atoms were located from difference Fourier synthesis, followed by
full-matrix least-squares refinement based on F2 (programs SHELXS-
97 and SHELXL-97).16 Many hydrogen atoms could be found from
the Fourier difference. Carbon-bound hydrogen atoms were placed
Supporting Information Available: Crystallographic data for
3 in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM060838G
(16) (a) Sheldrick, G. M. SHELXS-97, Program for the Determination
of Crystal Structures; University of Goettingen: Germany, 1997. (b)
Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Goettingen: Germany, 1997.