Titanium ester enolate complex supported by a tetradentate bis(phenolato) ligand: Synthesis, structure, and activity in methacrylate polymerization

Article abstract of DOI:10.1021/om700785c

Reaction of the titanium dichloro complex containing a [OSSO]-type bis(phenolate) ligand (edtbp)TiCl₂ (1) (edtbpH₂ = (HOC₆H₂-^tBu₂-4,6) ₂(SCH₂CH₂S)) with 2 equiv of AlMe₃ produces the methylchloro complex (edtbp)TiMeCl (2) in 77% yield, alternatively prepared from comproportionation of 1 and the dimethyl complex (edtbp)TiMe ₂ (3). The titanium ester enolate complex (edtbp)TiMe{O( ¹PrO)C=CMe₂] (4) was synthesized by reaction of 2 with lithium isopropylisobutyrate, LiO(¹PrO)C=CMe₂, in a 1:1 molar ratio. This complex reacted with alcohols ROH (R = ⁱPr, Ph, Ph₃C) to give alkoxy complexes (edtbp)TiMe(OR) (6-8) and with acetone under C-C coupling to afford an aldolate complex (edtbp)TiMe(OCMe ₂CMe₂CO₂ⁱPr) (9). Methyl abstraction from the neutral complexes 4, 7, and 9 using with B(C₆Fs) ₃ gave the corresponding cationic species [(edtbp)Ti(OR)(THF).,] [MeB(C₆F₅₈)₃]. All complexes have been characterized by multinuclear NMR spectroscopy and elemental analysis. Single-crystal X-ray diffraction studies were performed for complexes 2, 4, and 9. Cationic titanium enolate species initiate the polymerization of methyl methacrylate (MMA) at room temperature, producing syndiotactic-enriched poly(methyl methacrylates) (PMMAs). In the presence of the neutral enolate complex, MMA polymerization proceeds in a living fashion. The neutral titanium enolate complex 4 was found to be moderately active in n-butyl acrylate (n-BA) polymerization.

Full text of DOI:10.1021/om700785c

Organometallics 2007, 26, 6653–6660
6653
Titanium Ester Enolate Complex Supported by a Tetradentate
Bis(phenolato) Ligand: Synthesis, Structure, and Activity in
Methacrylate Polymerization
Bing Lian, Thomas P. Spaniol, and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed August 6, 2007
Reaction of the titanium dichloro complex containing a [OSSO]-type bis(phenolate) ligand (edtbp)TiCl2
(1) (edtbpH2 ) (HOC6H2-tBu2-4,6)2(SCH2CH2S)) with 2 equiv of AlMe3 produces the methylchloro
complex (edtbp)TiMeCl (2) in 77% yield, alternatively prepared from comproportionation of 1 and the
dimethyl complex (edtbp)TiMe2 (3). The titanium ester enolate complex (edtbp)TiMe{O(iPrO)C)CMe2}
(4) was synthesized by reaction of 2 with lithium isopropylisobutyrate, LiO(iPrO)C)CMe2, in a 1:1
i
molar ratio. This complex reacted with alcohols ROH (R ) Pr, Ph, Ph3C) to give alkoxy complexes
(edtbp)TiMe(OR) (6-8) and with acetone under C-C coupling to afford an aldolate complex
i
(edtbp)TiMe(OCMe2CMe2CO2 Pr) (9). Methyl abstraction from the neutral complexes 4, 7, and 9 using
with B(C6F5)3 gave the corresponding cationic species [(edtbp)Ti(OR)(THF)n][MeB(C6F5)3]. All complexes
have been characterized by multinuclear NMR spectroscopy and elemental analysis. Single-crystal X-ray
diffraction studies were performed for complexes 2, 4, and 9. Cationic titanium enolate species initiate
the polymerization of methyl methacrylate (MMA) at room temperature, producing syndiotactic-enriched
poly(methyl methacrylates) (PMMAs). In the presence of the neutral enolate complex, MMA polymer-
ization proceeds in a living fashion. The neutral titanium enolate complex 4 was found to be moderately
active in n-butyl acrylate (n-BA) polymerization.
involving the neutral complex Cp2ZrMe{O(tBuO)C)CMe2} as
initiator and a cationic complex [Cp2ZrMe(THF)][BPh4] as
catalyst.1b,c To find a suitable model for the propagating
species, various neutral and cationic group 4 metallocene ester
enolate complexes have been prepared and examined for their
suitability in the living polymerization of methacrylate
and acrylate monomers, e.g. Cp2ZrMe{O(tBuO)C)CMe2},3c
[Cp2Zr{O(tBuO)C)CMe2}(THF)]+[MeB(C6F5)3]-,3h [(rac-
EBI)Zr{O(iPrO)C)CMe2}(THF)]+[MeB(C6F5)3]- (EBI ) ethyl-
ene-bis(indenyl)),2h and [(η5-C5Me4SiMe2NtBu)Ti{O(iPrO)C)CMe2}-
(THF)]+[MeB(C6F5)3]-.2i,3j These systems allow to control the
livingness and stereochemistry of the polymerization. However,
group 4 metal enolate complexes based on nonmetallocene
frameworks have not been well developed so far.31,4 We have
recently introduced configurationally rigid titanium complexes
Introduction
Group 4 metallocene-mediated polymerization of alkyl meth-
acrylate and acrylate monomers has attracted considerable
attention in the recent past.1–3 Although methyl methacrylate
(MMA) polymerization by discrete group 4 metal comp-
lexes such as Cp2MCl{O(MeO)C)CMe2} (M ) Ti, Zr),
(iPrO)3Ti{O(MeO)C)CMe2} and (Et2N)3Ti{O(MeO)C)CMe2}
was disclosed in the early patent literature,3l living polymeri-
zation of methyl methacrylate with a zirconocene-based two-
component system was first reported by Collins et al. in 1992
* Corresponding author. Fax: +49 241 8092644. E-mail: jun.okuda@
ac.rwth-aachen.de.
(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–
5526.
(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) Stuhldreier, T.; Keul, H.; Höcker, H.; Englert, U.
Organometallics 2000, 19, 5231–5234. (d) Frauenrath, H.; Keul, H.; Höcker,
H. Macromolecules 2001, 34, 14–19. (e) Batis, C.; Karanikolopoulos, G.;
Pitsikalis, M.; Hadjichristidis, N. Macromolecules 2003, 36, 9763–9774.
(f) Jensen, T. R.; Yoon, S. C.; Dash, A. K.; Luo, L.; Marks, T. J. J. Am.
Chem. Soc. 2003, 125, 14482–14494. (g) Strauch, J. W.; Fauré, J.-L.;
Bredeau, S.; Wang, C.; Kehr, G.; Fröhlich, R.; Luftmann, H.; Erker, G.
J. Am. Chem. Soc. 2004, 126, 2089–2104. (h) Lian, B.; Toupet, L.;
Carpentier, J.-F. Chem. Eur. J. 2004, 10, 4301–4307. (i) Lian, B.; Lehmann,
C. W.; Navarro, C.; Carpentier, J.-F. Organometallics 2005, 24, 2466–
2472. (j) Lian, B.; Thomas, C. M.; Navarro, C.; Carpentier, J.-F. Organo-
metallics 2007, 26, 187–195. (k) Lian, B.; Thomas, C. M.; Navarro, C.;
Carpentier, J.-F. Macromolecules 2007, 40, 2293–2294. (l) Farnham, W. B.;
Hertler, W. R. U.S. Pat. 4,728,706, 1988.
(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.
Organometallics 2002, 21, 13–15. (d) Jin, J.; Wilson, D. R.; Chen, E.
Y.-X. Chem. Commun. 2002, 708–709. (e) Bolig, A. D.; Chen, E. Y.-X.
J. 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.; 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. (m) Ning, Y.; Zhu, H.; Chen, E. Y.-X. J. Organomet. Chem. 2007,
692, 4535–4544. (n) Miyake, G. M.; Mariott, W. R.; Chen, E. Y.-X. J. Am.
Chem. Soc. 2007, 129, 6724–6725.
(4) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428–447. (b) Gibson, V. C.; Spitzmesser, S. K. Chem.
ReV. 2003, 103, 283–315. (c) For acrylate polymerization catalyzed by a
dinuclear zinc complex, see: Garner, L. E.; Zhu, H.; Hlavinka, M. L.;
Hagadorn, J. R.; Chen, E. Y.-X. J. Am. Chem. Soc. 2006, 128, 14822–
14823.
10.1021/om700785c CCC: $37.00
2007 American Chemical Society
Publication on Web 11/20/2007

6654 Organometallics, Vol. 26, No. 26, 2007
Lian et al.
Scheme 1
Scheme 2
Scheme 3
1.85 ppm (td)). The 1H-13C HMQC spectrum shows these 1H
NMR resonances to be correlated with two 13C NMR resonances
at δ 40.84 (1H: δ 2.54 and 2.21 ppm) and 36.57 ppm (1H: δ
2.34 and 1.85 ppm), respectively.
In order to investigate its activity as precursor for the
methacrylate (MMA) polymerization, the synthesis of a titanium
enolate complex (edtbp)TiMe{O(iPrO)C)CMe2} (4) was
attempted.2i Treating 2 with 1 equiv of lithium isopropylisobu-
tyrate, LiO(iPrO)C)CMe2, in toluene gave 4 as red crystals in
containing a linked bis(phenolato) [OSSO]-type ligand that
polymerize styrene isospecifically when activated to give the
corresponding alkyl cation.5 To explore the suitability of this
nonmetallocene titanium system for the controlled and stereo-
selective polymerization of alkyl methacrylate and acrylate
monomers, we have prepared both neutral and cationic titanium
enolate complexes based on this [OSSO]-type ligand and
investigated their reactivity.
1
65% yield (Scheme 2). In the H NMR spectrum of 4, two
singlets were observed at δ 2.13 and 1.82 ppm for the two
)C(CH3)2 methyl groups as well as two sets of doublets at δ
i
1.22 and 1.18 ppm for the PrO methyl groups. These diaste-
reotopic groups indicate the presence of a configurationally
stable, chiral [OSSO] ligand sphere at titanium. Upon addition
of the electrophilic borane B(C6F5)3 in toluene-d8, CD2Cl2, or
C6D5Br, thermally labile titanium enolate cation formed. In the
presence of a Lewis base such as THF, the cationic species
[(edtbp)Ti{O(iPrO)C)CMe2}(THF)2]+[MeB(C6F5)3]- (5(THF)2)
could be cleanly generated and was found to be stable at room
temperature at least for one day. This product, which may act
as model for the key intermediate in the (edtbp)Ti-mediated
polymerization of methyl methacrylate (vide infra), was char-
acterized by 1H, 13C, 11B, and 19F NMR spectroscopy (Scheme
Results and Discussion
Synthesis of the Titanium Complexes. The reaction of
titanium dichloro complex containing a [OSSO]-type bis(phe-
nolate) ligand (edtbp)TiCl2 (1) (edtbpH2 ) (HOC6H2-tBu2-
4,6)2(SCH2CH2S)) with 2 equiv of AlMe3 in toluene at room
temperature affords the methyl chloro complex (edtbp)TiMeCl
(2), which could be isolated as orange crystals in 77% yield.
The Tebbe-type µ-methylene complex A was not observed even
in the crude product (Scheme 1).6 Alternatively, complex 2 could
be synthesized by combining the dichloro complex 1 with the
dimethyl complex 3 in C6D6. This reaction required higher
temperatures (60 °C) to go to completion as shown by 1H NMR
spectroscopy. Complex 2 was characterized by elemental
1
3). Notably, the H NMR spectrum of the analogous cationic
species 5 in CD2Cl2, generated in the presence of protio THF
instead of THF-d8, indicates the coordination of two THF
1
molecules (1H: δ 3.76 and 1.85 ppm versus H: δ 3.40 and
1.62 ppm for free THF in CD2Cl2).
Reaction of the Enolate Complex (edtbp)TiMe{O(iPrO)C)
1
analysis and NMR spectroscopy. The H NMR spectrum of 2
i
CMe2} (4) with Alcohols ROH (R ) Pr, Ph, Ph3C). During
in C6D6 at room temperature exhibits an ABCD-spin system
MMA polymerization acidic compounds may act as chain-
transfer agent.3i Thus, the reaction of the enolate complex with
various alcohols was examined. In an NMR experiment, 1 equiv
of 2-propanol was added to the methyl enolate titanium complex
4 in C6D6 at room temperature. Within a few minutes, the red
color of the solution faded. 1H NMR spectroscopy showed the
formation of the titanium methyl isopropoxy complex (edtbp)-
TiMe(OiPr) (6), which resulted from the selective protonolysis
of the Ti-O (enolate) bond with release of isopropyl isobutyrate
(Scheme 4). The more acidic phenol reacted in an analogous
manner to give the methyl phenolato complex (edtbp)TiMe-
(OPh) (7) with concomitant formation of one equiv of isopropyl
isobutyrate. Whereas this reaction occurred faster than the
formation of the methyl isopropoxy complex 6, enolate complex
for the SCH2CH2S bridge (δ 2.54 (dt), 2.34 (dt), 2.21 (td), and
(5) (a) Capacchione, C.; Proto, A.; Ebeling, H.; Mülhaupt, R.; Möller,
K.; Spaniol, T. P.; Okuda, J. J. Am. Chem. Soc. 2003, 125, 4964–4965. (b)
Capacchione, C.; Manivannan, R.; Barone, M.; Beckerle, K.; Centore, R.;
Oliva, L.; Proto, A.; Tuzi, A.; Spaniol, T. P.; Okuda, J. Organometallics
2005, 24, 2971–2982. (c) Beckerle, K.; Manivannan, R.; Spaniol, T. P.;
Okuda, J. Organometallics 2006, 25, 3019–3026. (d) Beckerle, K.;
Manivannan, R.; Lian, B.; Meppelder, G.-J. M.; Raabe, G.; Spaniol, T. P.;
Ebeling, H.; Pelascini, F.; Mülhaupt, R.; Okuda, J. Angew. Chem., Int. Ed.
2007, 46, 4790–4793. (e) Lian, B.; Beckerle, K.; Spaniol, T. P.; Okuda, J.
Angew. Chem., Int. Ed. 2007, 46,in press, http://dx.doi.org/10.1002/
anie.200703218.
(6) (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J. Am. Chem. Soc.
1978, 100, 3611–3613. (b) Brown-Wensley, K. A.; Buchwald, S. L.;
Cannizzo, L.; Clawson, L.; Ho, S.; Meinhardt, D.; Stille, J. R.; Straus, D.;
Grubbs, R. H. Pure Appl. Chem. 1983, 55, 1733–1744.

Synthesis and ActiVity of Titanium Enolate Complexes
Organometallics, Vol. 26, No. 26, 2007 6655
Scheme 4
Scheme 5
Scheme 6
abstracting the methyl group of 7 and 9 with 1 equiv of B(C6F5)3
in the presence of a Lewis base such as THF (Scheme 6). The
cationic species 10(THF-d8)n and 11(THF-d8)n were fully charac-
terized by 1H, 13C, 11B, and 19F NMR spectroscopy and found to
be stable at room temperature at least for one day. The experimental
data do not suggest a rigid coordination of the carbonyl group to
the titanium center in 11(THF-d8)n. Attempts to grow crystals of
this product were unsuccessful. In separate experiments, the cationic
alkoxide complexes 10 and 11 were found not to initiate MMA
polymerization.3i
X-ray Crystal Structures of 2, 4, and 9. Complexes 2, 4,
and 9 have been characterized by single-crystal X-ray diffraction
studies. The molecular structures of 2, 4, and 9 in the solid
state as well as the selected bond lengths and bond angles are
shown in Figures 1–3. Details of the crystal structure determi-
nation are given in Table 1. All of these compounds are
monomeric in the solid state.
The octahedrally coordinated titanium center in complex 2
is coordinated by two trans-oxygen atoms, two sulfur donor
atoms, and the cis-arranged methyl and chloro ligands (Figure
1). The (edtbp)Ti moiety adopts a C2-symmetric helical
framework. The bond angles of S1-Ti-S2 (75.17(2)°) in 2 are
close to the value in the dimethyl complex 3 (74.04(2)°); the
Ti-S bond distance (2.6986(8) Å and 2.6756(8) Å) in 2 is
slightly shorter than in 3 (2.8056(7) Å and 2.8417(7) Å).5e The
Ti-C bond distance (2.129(2) Å) is comparable to the values
in 3 (2.077(2) Å and 2.084(2) Å).
The solid-state structure of the enolate complex 4 also
features a six-coordinated titanium center with a C2-sym-
metric helical (edtbp)Ti fragment (Figure 2). The O1-Ti-O2
(152.80(14)°) bond angle is slightly decreased in comparison
with that of analogous (edtbp)Ti complexes, in the range of
156.7(2)-157.82(10)°,5 indicating the generation of a rather
open titanium coordination sphere. The Ti-O3 (1.798(3) Å)
bond distance and Ti-O3-C32 (163.9(3)°) bond angle (close
to linear) are similar to an analogous titanium enolate
complex containing a linked amido-cyclopentadienyl ligand
(Ti-O, 1.826(2) Å and Ti-O-C, 159.6(2)°)2i or a titanium
amide enolate complex {(3,5-Me2-C6H3)tBuN}3TiOC-
(CH2)NPhMe (Ti-O, 1.847(3) Å and Ti-O-C, 159.0(2)°).8a
These observations indicate a pπ-dπ interaction between the
4 reacted more slowly with the bulky trityl alcohol Ph3COH.
Monitoring the reaction by 1H NMR spectroscopy showed that
the conversion of 4 to (edtbp)TiMe(OCPh3) (8) was complete
within 2 h at a higher temperature 60 °C. At the same time, the
resonances for the ester isopropyl isobutyrate were observed.
Although the rate of alcoholysis appears to correlate with the
i
pKA values of the alcohol (pKA in DMSO for PrOH: 29.3,
PhOH: 18.0, Ph3COH: 25.5), steric influence may have influence
as well.7a
Reaction of the Enolate Complex (edtbp)TiMe{O(iPrO)C)
CMe2} (4) with Acetone. The reaction of complex 4 with 1 equiv
of enolizable acetone in C6D6 at room temperature quantitatively
i
gave the aldolate-type product (edtbp)TiMe(OCMe2CMe2CO2 Pr)
(9) within a few minutes (Scheme 5). Complex 9 was isolated as
yellow crystals and fully characterized by 1D/2D NMR spectros-
copy, elemental analysis, and single crystal X-ray analysis.
Characteristic 1H NMR resonances include four singlets at δ 1.78,
1.76, 1.67, and 1.63 ppm for the diastereotopic methyl groups of
the TiOC(CH3)2C(CH3)2 group. The observed reactivity behavior
confirms that enolizable acetone acts as an electrophile toward the
titanium enolate complex 4 rather than as a Brönsted acid to cleave
the Ti-O(enolate) bond.1a,7b It is notable that thermodynamically
unfavorable formation of a vicinal quaternary carbon centers under
equilibrium condition is observed. Reaction of the prochiral
substrate acetophenone resulted in a 1:1 mixture of diastereomeric
products, suggesting that the helical [OSSO] ligand framework does
not exert any significant stereochemical bias during the aldol-type
C-C coupling reaction.
Alkoxy Cations. The cationic complexes [(edtbp)Ti(OR)-
(THF)n]+[MeB(C6F5)3]- (R ) Ph, 10(THF-d8)n; R ) CMe2CMe2
i
CO2 Pr, 11(THF-d8)n) were cleanly generated in CD2Cl2 by
(7) (a) Miller, J. B.; Schwartz, J.; Carroll, K. M. Organometallics 1993,
12, 4204–4206. (b) Ghosh, A. K.; Shevlin, M. In Modern Aldol Reactions;
Mahrwald, R., Ed.; Wiley-VCH: Weinheim, 2004; Vol. 1, pp 63–125.

6656 Organometallics, Vol. 26, No. 26, 2007
Lian et al.
Figure 1. Molecular structure of complex (edtbp)TiMeCl (2)
(hydrogen atoms were omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ti-C31, 2.129(2); Ti-Cl, 2.2893(8); Ti-O1,
1.8726(17); Ti-O2, 1.8651(17); Ti-S1, 2.6986(8); Ti-S2, 2.6756(8);
O1-C1, 1.345(3); C2-S1, 1.777(2); Cl-Ti-C31, 105.32(7);
O1-Ti-C31, 95.85(8); O2-Ti-C31, 93.85(8); O1-Ti-O2,
160.47(7); S1-Ti-S2, 75.17(2); S1-Ti-O1, 74.62(5).
Figure 3. Molecular structure of the aldolate complex (edtbp)-
TiMe(OCMe2CMe2CO2 Pr) (9) (hydrogen atoms were omitted for
i
clarity, for the atoms of the ester alkoxy group only one the refined
split positions are shown). Selected bond lengths (Å) and angles (deg):
Ti-O1, 1.8815(16); Ti-O2, 1.8898(15), Ti-O3, 1.7622(16); Ti-S1,
2.7156(8); Ti-S2, 2.7227(8); Ti-C31, 2.099(2); Ti-O3-C(32a),
147.4(3); O3-Ti-C31,102.43(9); O1-Ti-C31,96.38(9); O2-Ti-C31,
95.45(8); O1-Ti-O2, 154.44(7); S1-Ti-S2 77.05(2).
and C37 of 1.334(7) Å as well as the sum of angles around
C37 agree with a C32-C37 double bond.
The single crystal of complex (edtbp)TiMe(OCMe2CMe2CO2iPr)
(9) was obtained from hexane at -30 °C and measured at 243 K
on a CCD diffractometer due to a solid-phase transformation at
110 K, resulting in the transformation from transparent yellow
crystals to a powder. The geometry around the six-coordinated
titanium center is similar to that of 2 and 4 with a C2-symmetric
(edtbp)Ti moiety (Figure 3). A slightly shortened Ti-C31 bond
(2.099(2) Å in 9 vs 2.129(2) Å in 2) was found. The alkoxy group
i
of the ester fragment (Ti(OCMe2CMe2CO2 Pr) is disordered and
was refined with split positions. The oxygen atom of the carbonyl
group is not coordinated to the titanium center, although seven-
coordination can be achieved at the titanium center within the
[OSSO]-type ligand sphere, as observed in the titanium methyl
cation [(edtbp)TiMe(dmpe)][MeB(C6F5)3].5e The small Ti-O3-
C32a bond angle (147.4(3)°) indicates a less pronounced pπ-dπ
Ti-O interaction as compared to that in 4. Probably the steric
crowding around the titanium center precludes the coordination
of the carbonyl oxygen, a structural feature that is rather common.8a
Figure 2. Molecular structure of the complex (edtbp)TiMe-
{O(iPrO)C)CMe2} (4) (hydrogen atoms were omitted for clarity-the
disordered tert-butyl group and oxygen atom O4 are shown with one
split position). Selected bond lengths (Å) and angles (deg): Ti-C31,
2.095(5); Ti-O1, 1.879(3); Ti-O2, 1.892(3), Ti-O3, 1.798(3);
Ti-S1, 2.6389(15); Ti-S2, 2.7327(14); C32-C37, 1.334(7); C37-C38,
1.493(7); C37-C39, 1.489(7); Ti-O3-C32, 163.9(3); O3-Ti-C31,
99.72(18); O1-Ti-C31, 100.50(17); O2-Ti-C31, 95.84(17); O1-
Ti-O2, 152.80(14); S1-Ti-S2, 79.28(4); C32-C37-C39, 122.1(5);
C(32)-C37-C38, 122.8(5); C38-C37-C39, 115.2(5).
MMA and nBA Polymerization by Titanium Enolate
Complexes. Methyl methacrylate (MMA) and n-butyl acrylate
(nBA) polymerization with the titanium enolate complexes 4
and 5 was investigated. Representative results are summarized
in Table 2. The polymerization of MMA was carried out using
various addition sequences (entries 1–7). When complex 4 was
(8) (a) Agapie, T.; Diaconescu, P. L.; Mindiola, D. J.; Cummins, C. C.
Organometallics 2002, 21, 1329–1340. (b) For other examples for titanium
enolate complexes, see: Curtis, M. D.; Thanedar, S.; Butler, W. M.
Organometallics 1984, 3, 1855–1859. (c) Veya, P.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. Organometallics 1993, 12, 4892–4898. (d) Hortmann,
K.; Diebold, J.; Brintzinger, H.-H. J. Organomet. Chem. 1993, 445, 107–
109.
electron-deficient titanium center and the partly sp-hybridized
oxygen atom.3c,8,9 The oxygen atom O4 was found to be
disordered in the solid state and refined with split positions.
In each case, the sum of angles around C32 is close to 360°
(O4a, 359.2° vs O4b, 357.2°). The bond length between C32
(9) For the pπ-dπ interaction in a zirconium complex, see: Collins, S.;
Koene, B. E.; Ramachandran, R.; Taylor, N. J. Organometallics 1991, 10,
2092–2094.

Synthesis and ActiVity of Titanium Enolate Complexes
Organometallics, Vol. 26, No. 26, 2007 6657
Table 1. Crystal Data and Structure Refinement for 2, 4, and 9
2
4
9
formula
Mr
C31H47ClO2S2Ti
599.16
C38H60O4S2Ti
692.88
C41H66O5S2Ti
750.96
T/K
130(2)
130(2)
243(2)
crystal size/mm
crystal system
space group
a/Å
b/Å
c/Å
0.3 × 0.2 × 0.12
monoclinic
P21/c
15.968(3)
12.0901(19)
17.509(3)
0.27 × 0.25 × 0.05
monoclinic
P21/c
10.0930(11)
15.7694(16)
25.037(2)
0.40 × 0.18 × 0.17
triclinic
P-1
10.8126(10)
13.3683(12)
16.3273(15)
105.4805(15)
94.0812(16)
94.0877(16)
2258.6(4)
2
R/deg
ꢀ/deg
104.801(4)
100.761(3)
γ/deg
U/Å3
3268.0(10)
4
1.218
0.496
3914.8(7)
4
1.176
0.361
Z
Dc/g cm-3
1.104
0.319
812
µ/mm-1
F(000)
1280
1496
θ range/deg
data collected (hkl)
no. of reflns collected
no. of independent reflns
Rint
2.07 – 28.42
(21, –16 to 13, –23 to 20
26485
8160
0.0552
1.53 – 25.08
-12 to 11, ( 18, -28 to 29
31518
6925
0.1023
2.31 – 28.38
(14, ( 17, ( 21
31347
11211
0.0536
final R1, wR2[I > 2σ(I)]
R1, wR2 (all data)
goodness of fit on F2
∆Fmax, min/e Å-3
0.0512, 0.1260
0.0757, 0.1382
1.054
0.0651, 0.1335
0.1227, 0.1689
0.958
0.0521, 0.1091
0.1117, 0.1229
0.800
1.114, -0.585
0.528, -0.477
0.465, -0.243
Table 2. Polymerization of MMA and nBA Using the Precursors 4/E(C6F5)3 (E ) B, Al) and 5 Systema
b
b
entry
cat.
activator
monomer
T (°C)
yield (%)
Mn,exp
Mw/Mn
mmc
mrc
rrc
1
4
4
4
5
5
4
4
5
4
4
4
B(C6F5)3
B(C6F5)3
B(C6F5)3 · THF
MMA
MMA
MMA
MMA
MMA
MMA
MMA
nBA
20
20
20
20
60
20
20
20
20
20
60
<1
5
8
52
2
65
72
<1
<1
28
15
n.d.
n.d.
n.d.
15
9
12
n.d.
2
n.d.
28
38
33
n.d.
27
n.d.
57
53
55
n.d.
71
2d
3
10 800
12 700
16 000
n.d.
20 600
19 300
n.d.
n.d.
112 400
58 100
1.19
1.22
2.63
n.d.
1.09
1.10
n.d.
n.d.
2.12
1.96
4
5
6d
7d
8
Al(C6F5)3
2 Al(C6F5)3
3
27
70
n.d.
n.d.
19
14
n.d.
n.d.
29
n.d.
n.d.
52
9
10
11
B(C6F5)3 · THF
nBA
nBA
nBA
30
56
a Polymerization conditions: solvent ) 2 mL of toluene; cat. ) 0.02 mmol; monomer/cat./activator ) 200:1:1; polymerization time ) 24 h; protocol:
cat.+ activator, then MMA. b Determined by GPC in THF vs polystyrene standards. c Determined by 1H NMR (PMMA) or 13C NMR (PnBA)
spectroscopy in CDCl3; mm, mr, and rr refer to isotactic, atactic, and syndiotactic triads. d Protocol: cat. + MMA, then activator E(C6F5)3.
combined in situ with the activator B(C6F5)3 and MMA was
added, no polymerization was observed (entry 1). By changing
the addition sequence (entry 2) and when B(C6F5)3 · THF was
used as activator (entry 3), the yield for PMMA (5–8%) only
slightly improved. However, the cationic species 5 did polymer-
ize MMA at room temperature resulting in a moderate yield of
52% PMMA (entry 4). The PMMA obtained has a molecular
weight (Mn ) 16 000) that is larger than the calculated one (Mn
) 10 400) considering one metal center per polymer chain. The
polydispersity was high, although monomodal distribution was
detected. Raising the polymerization temperature to 60 °C did
not improve the MMA conversion (entry 5). The obtained
PMMAs have a syndiotactic microstructure (55–57% rr).
Obviously, the higher intensity of rr relative to mm is
consistent with chain-end control (either monometallic or
bimetallic)1b,c,2i,3j rather than enantiomorphic site control,2h
under which the last inserted MMA monomer is responsible
for the stereoselectivity over the microstructure of the resultant
polymer. In a separate experiment, the dimethyl complex 3
activated with B(C6F5)3 or B(C6F5)3 · THF was shown to be
inactive in the MMA polymerization. These observations suggest
that the cationic titanium enolate species are active in the
polymerization of MMA. However, the propagating species that
contains a bis(phenolato) [OSSO]-framework are somewhat
labile and follow deactivation pathways (back-biting). Upon
activation with 1 or 2 equiv of Al(C6F5)3 (entries 6 and 7), which
may involve a bimetallic chain propagation fashion,2m complex
4 was found to give PMMAs with narrow polydispersities
(1.09–1.10), albeit with moderate yield (65–72%). Notably, a
mixture of the neutral complex 4 and the cationic complex 5 in
1:1 ratio, MMA polymerization was complete in less than 5
min with a living characteristic (MMA/4/5 ) 200:1:1, Mn )
22 200, Mw/Mn ) 1.08, rr ) 67%).
Complex 4 was also assessed for the polymerization of nBA
containing an active R-H (entries 8–11). In contrast to MMA
polymerization, the cationic titanium enolate species were totally
inactive (entries 8 and 9). Notably, only the neutral precursor 4
showed a low activity toward nBA polymerization, giving high
molecular weight P(nBA) with a rather low initiation efficiency
(ca. 6% both at 20 °C and at 60 °C) (entries 10 and 11). The
13C NMR spectra of P(nBA) also show a syndiotactically
enriched microstructure (rr, 52–56%).
Conclusion
In conclusion, the readily synthesized titanium enolate
complex 4 exhibits a rather high basicity/nucleophilicity in the
presence of enolizable acetone resulting in a remarkable aldol-

6658 Organometallics, Vol. 26, No. 26, 2007
Lian et al.
SCH2), 1.78 (s, 9H, C(CH3)3), 1.75 (s, 9H, C(CH3)3), 1.21 (s, 9H,
C(CH3)3), 1.19 (s, 9H, C(CH3)3). 13C{1H} NMR (C6D6): δ 167.09
(Ph-C1), 166.81 (Ph-C1′), 144.39 (Ph-C6), 144.14 (Ph-C6′), 137.96
(Ph-C4), 137.06 (Ph-C4′), 127.08 (Ph-C5), 126.67 (Ph-C5′), 126.59
(Ph-C3), 126.45 (Ph-C3′), 120.24 (Ph-C2), 119.39 (Ph-C2′), 74.75
(TiCH3), 40.84 (SCH2), 36.57 (SCH2), 35.86 (C(CH3)3), 35.74
(C(CH3)3), 34.55 (C(CH3)3), 34.50 (C(CH3)3), 31.46 (C(CH3)3),
31.22 (C(CH3)3), 29.75 (C(CH3)3), 29.68 (C(CH3)3). Anal. Calcd
for C31H47ClO2S2Ti (599.15): C, 62.14; H, 7.91. Found: C, 62.28;
H, 7.73.
type C-C coupling reaction. At the same time, a pronounced
Lewis acidic property of the titanium center accounts for the
facile protonolysis reaction with alcohols and phenols. Thus, 4
reacts with alcohols and phenol to selectively cleave the
Ti-O(enolate) bond affording the alkoxy/phenoxy methyl
complexes 6–8. Although enolizable, acetone functions as an
electrophile to form the structurally characterized aldolate
complex 9. Upon acitvation with a Lewis acid E(C6F5)3 (E )
B, Al), the titanium enolate complex is converted into the enolate
cation that is active in MMA polymerization, producing
syndiotactic-enriched PMMAs. In the light of the well controlled
MMA and nBA polymerizations mediated by the titanium
enolate precursors supported by the linked amido-cyclopenta-
dienyl ligand,2i,3j,k the present results point at the suitability of
group 4 nonmetallocene complexes for methacrylate and acrylate
polymerization. However, the low stereoselectivity during MMA
polymerization will require an improved design of the [OSSO]-
type ligand, despite its certain resemblance to the EBI ligand
in zirconocene catalysts.2h
Formation of 2 from (edtbp)TiCl2 (1) and (edtbp)TiMe2 (3).
In the glovebox, a Teflon-valved NMR tube was charged with
complexes (edtbp)TiCl2 (10.7 mg, 0.017 mmol) and (edtbp)TiMe2
(10.0 mg, 0.017 mmol), and C6D6 (ca. 0.5 mL) was vacuum
transferred. The tube was sealed and kept at 60 °C. Periodic NMR
spectroscopic monitoring revealed quantitative formation of (edt-
bp)TiMeCl (2) within 2 days. The NMR data were the same as
those described above.
Synthesis of (edtbp)TiMe(O(iPrO)C)CMe2) (4). To a solution
of 2 (0.5 g, 0.83 mmol) in toluene (30 mL) was slowly added 25
mL of a toluene solution of LiO(iPrO)C)CMe2 (0.114 g, 0.83
mmol) at -50 °C. The reaction mixture was warmed to room
temperature and further stirred overnight. After evaporation of
volatile under vacuum, the residue was recrystallized with pentane
to give (edtbp)TiMe{O(iPrO)C)CMe2} (4) as red crystals (0.38
g, 65%). A crystal of 4 suitable for X-ray diffraction analysis was
Experimental Section
General Procedures. All experiments were carried out under
purified argon using standard Schlenk techniques or a glovebox
(<1 ppm O2, 1 ppm H2O). Toluene, pentane, diethyl ether,
dichloromethane, and THF were purified from the MBraun SPS-
800 system prior to use. Deuterated solvents were purchased from
Aldrich and purified before use. All other chemicals were com-
mercially available and used after appropriate purification. Com-
plexes (edtbp)TiCl2 (1),5a (edtbp)TiMe2 (3),5e LiO(iPrO)C)CMe2,2h
and Al(C6F5)3 · 0.5C7H810 were synthesized according to literature
methods. NMR spectra were recorded on Bruker DRX 400 (1H,
400 MHz; 13C, 101 MHz) and Varian 200 spectrometers in Teflon-
1
4
selected. H NMR (C6D6): δ 7.55 (d, JHH ) 2.4 Hz, 1 H, Ph-5-
H), 7.50 (d, 4JHH ) 2.4 Hz, 1 H, Ph-5′-H), 7.26 (d, 4JHH ) 2.4 Hz,
4
1 H, Ph-3-H), 7.09 (d, JHH ) 2.4 Hz, 1 H, Ph-3′-H), 4.85 (sept,
3JHH ) 6.1 Hz, 1H, OCH(CH3)2), 2.63 (dt, JHH ) 13.5 Hz, JHH
2
3
2
3
) 3.2 Hz, 1H, SCH2), 2.43 (dt, JHH ) 13.5 Hz, JHH ) 3.2 Hz,
1H, SCH2), 2.30 (td, 2JHH ) 13.5, 3JHH ) 3.2, 1H, SCH2), 2.13 (s,
2
3
3H, )C(CH3)2), 2.02 (td, JHH ) 13.5 Hz, JHH ) 3.2 Hz, 1H,
SCH2), 1.82 (s, 3H, )C(CH3)2), 1.79 (s, 3H, TiCH3), 1.69 (s, 18H,
C(CH3)3), 1.23 (s, 9H, C(CH3)3), 1.22 (d, JHH ) 6.1 Hz, 3H,
OCH(CH3)2), 1.19 (s, 9H, C(CH3)3), 1.18 (d, JHH ) 6.1 Hz, 3H,
1
valved NMR tubes at 25 °C otherwise stated. H and 13C NMR
3
chemical shifts were determined using residual solvent resonances
and are reported vs SiMe4. Assignment of signals was made from
1H-13C HMQC and 1H-13C HMBC 2D NMR experiments.
Coupling constants are given in hertz. Elemental analyses were
performed by the Microanalytical Laboratory of this department.
Molecular weights of polymers were determined by gel permeation
chromatography (GPC) at room temperature in THF and calibrated
with respect to polystyrene standards. The microstructure of polymer
3
OCH(CH3)2). 13C{1H} NMR (C6D6): δ 167.42 (Ph-C1), 166.72 (Ph-
C1′), 159.70 (C ) C(CH3)2), 143.10 (Ph-C6), 142.47 (Ph-C6′),
137.24 (Ph-C4), 137.22 (Ph-C4′), 127.26 (Ph-C5), 126.97 (Ph-C5′),
126.41 (Ph-C3), 126.26 (Ph-C3′), 119.88 (Ph-C2), 117.62 (Ph-C2′),
90.83 ()C(CH3)2), 69.44 (OCH(CH3)2), 56.26 (TiCH3), 40.27
(SCH2), 36.27 (SCH2), 35.71 (C(CH3)3), 35.60 (C(CH3)3), 34.44
(C(CH3)3), 34.37 (C(CH3)3), 31.54 (C(CH3)3), 31.53 (C(CH3)3),
29.69 (C(CH3)3), 29.67 (C(CH3)3), 22.00 (OCH(CH3)2), 21.97
(OCH(CH3)2), 18.04 ()C(CH3)2), 17.12 ()C(CH3)2). Anal. Calcd
for C38H60O4S2Ti (692.88): C, 65.87; H, 8.73. Found: C, 66.39; H,
9.07.
Generation of the Ion Pair [(edtbp)Ti{O(iPrO)C)CMe2}(THF-
d8)2]+[MeB(C6F5)3]- (5(THF-d8)2). In the glovebox, a Teflon-valved
NMR tube was charged with complex (edtbp)TiMe{O(iPrO)C)CMe2}
(4) (10 mg, 0.014 mmol) and B(C6F5)3 (7.4 mg, 0.014 mmol), and
CD2Cl2 was vacuum transferred in the presence of one drop of THF-
d8 (THF free cationic species was found not stable in CD2Cl2 at room
temperature). The tube was sealed, and NMR spectroscopy was
recorded, which revealed quantitative formation of cationic species
[(edtbp)Ti{O(iPrO)C)CMe2}(THF-d8)2]+[MeB(C6F5)3]- (5(THF-
1
was determined by H NMR and 13C NMR in CDCl3.
Synthesis of (edtbp)TiMeCl (2). To a solution of (edtbp)TiCl2
(0.5 g, 0.81 mmol) in toluene (20 mL) was slowly added AlMe3
(0.81 mL, 2 M in hexane, 1.62 mmol) at –30 °C. The reaction
mixture was warmed to room temperature and further stirred
overnight. After evaporation of volatile under vacuum, the residue
was recrystallized with pentane to give the orange crystals as
(edtbp)TiMeCl (2) (0.37 g, 77%). A crystal of 2 suitable for X-ray
diffraction analysis was selected. 1H NMR (CDCl3): δ 7.39 (d, 4JHH
4
) 2.4 Hz, 1 H, Ph-5-H), 7.36 (d, JHH ) 2.4 Hz, 1 H, Ph-5′-H),
7.17 (d, 4JHH ) 2.4 Hz, 1 H, Ph-3-H), 7.11 (d, 4JHH ) 2.4 Hz, 1 H,
2
3
Ph-3′-H), 3.23 (dt, JHH ) 13.2, JHH ) 3.2 Hz, 1H, SCH2), 3.03
2
3
2
(dt, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H, SCH2), 2.52 (td, JHH
)
3
2
13.2 Hz, JHH ) 3.2 Hz, 1H, SCH2), 2.13 (td, JHH ) 13.2 Hz,
3JHH ) 3.2 Hz, 1H, SCH2), 1.78 (s, 3H, TiCH3), 1.61 (s, 9H,
C(CH3)3), 1.58 (s, 9H, C(CH3)3), 1.28 (s, 9H, C(CH3)3), 1.25 (s,
9H, C(CH3)3); 1H NMR (C6D6): δ 7.56 (d, 4J ) 2.4, 1 H, Ph-5-H),
1
4
d8)2). H NMR (CD2Cl2): δ 7.48 (d, JHH ) 2.2 Hz, 2 H, Ph-5-H),
7.28 (br s, 2 H, Ph-3-H), 4.25 (sept, 3JHH ) 6.1 Hz, 1H, OCH(CH3)2),
2
2
3.32 (d, JHH ) 11.2 Hz, 2H, SCH2), 2.73 (d, JHH ) 11.2 Hz, 2H,
SCH2), 1.80 (s, 6H, )C(CH3)2), 1.43 (s, 18H, C(CH3)3), 1.27 (s, 18H,
4
4
7.52 (d, J ) 2.4, 1 H, Ph-5′-H), 7.13 (d, J ) 2.4, 1 H, Ph-3-H),
C(CH3)3), 1.01 (d, 3JHH ) 6.1 Hz, 3H, OCH(CH3)2), 0.85 (d, 3JHH
)
7.01 (d, 4J ) 2.4, 1 H, Ph-3′-H), 2.54 (dt, 2JHH ) 13.2 Hz, 3JHH
)
6.1 Hz, 3H, OCH(CH3)2); 13C{1H} NMR (CD2Cl2): δ 167.43 (C )
C(CH3)2), 164.50 (Ph-C1), 148.49 (Ph-C6), 145.64 (Ph-C4), 136.52
(Ph-C5), 128.16 (Ph-C3), 127.07 (Ph-C2), 102.40 ()C(CH3)2), 72.47
(OCH(CH3)2), 38.69 (SCH2), 35.13 (C(CH3)3), 34.52 (C(CH3)3), 31.34
(C(CH3)3), 29.56 (C(CH3)3), 21.48 (OCH(CH3)2), 21.32 (OCH(CH3)2),
17.68 ()C(CH3)2). NMR data for the free anion [MeB(C6F5)3]-: 1H
3.2 Hz, 1H, SCH2), 2.34 (dt, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H,
SCH2), 2.21 (td, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 2.20
2
3
(s, 3H, TiCH3), 1.85 (td, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H,
(10) Feng, S.; Roof, G. R.; Chen, E. Y.-X. Organometallics 2002, 21,
832–839.

Synthesis and ActiVity of Titanium Enolate Complexes
Organometallics, Vol. 26, No. 26, 2007 6659
NMR (CD2Cl2): δ 0.45 (br s, 3H, BCH3). 13C{1H} NMR (CD2Cl2):
δ 148.61 (dm, 1JCF ) 231 Hz, o-C6F5), 137.90 (dm, 1JCF ) 231 Hz,
p-C6F5), 136.63 (dm, 1JCF ) 250 Hz, m-C6F5), 130.52 (Cipso), 10.07
(br, BCH3). 11B NMR (CD2Cl2): δ -14.9 (s, BCH3). 19F NMR
(CD2Cl2): δ –133.1 (d, 3JFF ) 19 Hz, 6F, o-F), -165.3 (t, 3JFF ) 19
Hz, 3F, p-F), -167.9 (m, 3JFF ) 19 Hz, 6F, m-F).
and the residue was recrystallized with pentane to give 7 as yellow
crystals (31 mg, 80%). 1H NMR (C6D6): δ 7.54 (d, 4JHH ) 2.4 Hz,
4
1 H, Ph-5-H), 7.52 (d, JHH ) 2.4 Hz, 1 H, Ph-5′-H), 7.29 (dd,
3JHH ) 7.2 Hz, 4JHH ) 2.1 Hz, 2H, OPh-o-H), 7.26 (d, 4JHH ) 2.4
Hz, 1 H, Ph-3-H), 7.10 (d, 4JHH ) 2.4 Hz, 1 H, Ph-3′-H), 7.06 (dt,
3JHH ) 7.2 Hz, 4JHH ) 2.1 Hz, 2H, OPh-m-H), 7.06 (tt, 3JHH ) 7.2
4
2
3
Generation of Cationic Species [(edtbp)Ti{O(iPrO)C)
CMe2}(THF)2]+[MeB(C6F5)3]- (5(THF)2). The same procedure
was followed as mentioned above, using protio THF instead of
Hz, JHH ) 2.1 Hz, 1H, OPh-p-H), 2.64 (dt, JHH ) 13.2, JHH
)
3.2 Hz, 1H, SCH2), 2.45 (dt, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H,
SCH2), 2.35 (td, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 2.02
2
3
1
4
(td, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H, SCH2), 1.85 (s, 3H,
TiCH3), 1.68 (s, 9H, C(CH3)3), 1.62 (s, 9H, C(CH3)3), 1.22 (s, 9H,
C(CH3)3), 1.20 (s, 9H, C(CH3)3); 13C{1H} NMR (C6D6): δ 167.38
(Ph-C1), 166.84 (Ph-C1′), 166.38 (OPh-ipso-C), 143.32 (Ph-C6),
142.81 (Ph-C6′), 137.47 (Ph-C4), 137.40 (Ph-C4′), 128.90 (OPh-
m-C), 128.53 (Ph-C5), 128.40 (Ph-C5′), 126.54 (Ph-C3), 126.49
(Ph-C3′), 121.90 (Ph-C2), 121.42 (OPh-p-C), 119.45 (Ph-C2′),
119.03 (OPh-o-C), 56.60 (TiCH3), 39.93 (SCH2), 36.15 (SCH2),
35.64 (C(CH3)3), 35.61 (C(CH3)3), 34.50 (C(CH3)3), 34.39
(C(CH3)3), 31.64 (C(CH3)3), 31.62 (C(CH3)3), 29.73 (C(CH3)3),
29.70 (C(CH3)3). Anal. Calcd for C37H52O3S2Ti (656.8): C, 67.66;
H, 7.98. Found: C, 67.74; H, 7.68.
THF-d8. H NMR (CD2Cl2): δ 7.50 (d, JHH ) 2.2 Hz, 2 H, Ph-
4
4
5-H), 7.34 (d, JHH ) 2.2 Hz, 1 H, Ph-3-H), 7.22 (d, JHH ) 2.2
3
Hz, 1 H, Ph-3′-H), 4.26 (sept, JHH ) 6.1 Hz, 1H, OCH(CH3)2),
2
3.76 (m, 8H, O(CH2CH2)2), 3.31 (d, JHH ) 11.2 Hz, 2H, SCH2),
2
2.74 (d, JHH ) 11.2 Hz, 2H, SCH2), 1.85 (m, 8H, O(CH2CH2)2),
1.81 (s, 6H, )C(CH3)2), 1.46 (s, 9H, C(CH3)3), 1.42 (s, 9H,
C(CH3)3), 1.29 (s, 9H, C(CH3)3), 1.28 (s, 9H, C(CH3)3), 1.02 (d,
3
3JHH ) 6.1 Hz, 3H, OCH(CH3)2), 0.87 (d, JHH ) 6.1 Hz, 3H,
OCH(CH3)2); 13C{1H} NMR (CD2Cl2): δ 167.57 (C ) C(CH3)2),
166.38 (Ph-C1), 165.32 (Ph-C1′), 149.17 (Ph-C6), 146.85 (Ph-C6′),
137.47 (Ph-C4), 136.96 (Ph-C4′), 128.91 (Ph-C5), 128.35 (Ph-C5′),
127.92 (Ph-C3), 127.57 (Ph-C3′), 119.59 (Ph-C2), 117.95 (Ph-C2′),
102.59 ()C(CH3)2), 72.11 (OCH(CH3)2), 68.62 (O(CH2CH2)2),
41.38 (SCH2), 38.63 (SCH2), 35.78 (C(CH3)3), 35.63 (C(CH3)3),
35.25 (C(CH3)3), 35.05 (C(CH3)3), 31.37 (C(CH3)3), 31.20
(C(CH3)3), 29.66 (C(CH3)3), 29.52 (C(CH3)3), 25.41 (O(CH2CH2)2),
21.01 (OCH(CH3)2), 20.86 (OCH(CH3)2), 17.25 ()C(CH3)2). NMR
data for the free anion [MeB(C6F5)3]- were the same as those
described above.
Synthesis of (edtbp)TiMe(OCPh3) (8). To a solution of 4 (30
mg, 0.043 mmol) in C6D6 (ca. 0.5 mL) in a Teflon-valved NMR
tube was added at room temperature trityl alcohol (11.3 mg, 0.043
mmol). The tube was kept at 60 °C and NMR spectra were recorded.
The conversion of 4 to 8 was virtually quantitative after 2 h. The
solvent was removed under vacuum, and the residue was recrystal-
1
lized with pentane to give 8 as brown crystals (28 mg, 78%). H
3
4
Synthesis of (edtbp)TiMe(OiPr) (6). To a solution of
(edtbp)TiMe{O(iPrO)C)CMe2} (4) (30 mg, 0.043 mmol) in C6D6
(ca. 0.5 mL) in a Teflon-valved NMR tube was added at room
temperature isopropanol (2.6 mg, 0.043 mmol) via a microsyringe.
The color of the solution quickly changed from red to yellow and
NMR spectra were recorded (NMR data for the ester isopropyl
isobutyrate formed. 1H NMR (C6D6): δ 5.01 (sept, 3JHH ) 6.0 Hz,
1H, OCH(CH3)2), 2.34 (sept, 3JHH ) 7.0 Hz, 1H, (O)C)CH(CH3)2),
1.06 (d, 3JHH ) 6.0 Hz, 6H, OCH(CH3)2), 1.03 (d, 3JHH ) 7.0 Hz,
6H, (O)C)CH(CH3)2). 13C{1H} NMR (C6D6): δ 175.40 (COOiPr),
66.47 (OCH(CH3)2), 33.83 ((CH3)2CHCO), 21.30 (OCH(CH3)2),
18.59 ((CH3)2CHCO). The conversion of 4 to 6 was virtually
quantitative after 10 min. The solvent was removed under vacuum,
and the residue was recrystallized with pentane to give 6 as a yellow
solid (20 mg, 74%). 1H NMR (C6D6): δ 7.54 (d, 4JHH ) 2.4 Hz, 1
NMR (C6D6): δ 7.73 (dd, JHH ) 7.2 Hz, JHH ) 2.2 Hz, 6H,
4
4
OCPh3-o-H),7.54 (d, JHH ) 2.4 Hz, 1 H, Ph-5-H), 7.45 (d, JHH
4
) 2.4 Hz, 1 H, Ph-5′-H), 7.30 (d, JHH ) 2.4 Hz, 1 H, Ph-3-H),
7.12 (dt, 3JHH ) 7.2 Hz, 4JHH ) 2.2 Hz, 6H, OCPh3-m-H), 7.04 (tt,
3JHH ) 7.2 Hz, JHH ) 2.2 Hz, 3H, OCPh3-p-H), 6.92 (d, JHH
)
4
4
2
3
2.4 Hz, 1 H, Ph-3′-H), 2.58 (dt, JHH ) 13.2, JHH ) 3.2 Hz, 1H,
SCH2), 2.38 (dt, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 2.17
2
3
2
(td, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H, SCH2), 2.03 (td, JHH
)
13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 1.66 (s, 3H, TiCH3), 1.62 (s,
9H, C(CH3)3), 1.58 (s, 9H, C(CH3)3), 1.23 (s, 9H, C(CH3)3), 1.21
(s, 9H, C(CH3)3). 13C{1H} NMR (C6D6): δ 167.42 (Ph-C1), 166.78
(Ph-C1′), 148.01 (OCPh3-ipso-C), 142.64 (Ph-C6), 141.79 (Ph-C6′),
137.16 (Ph-C4), 137.06 (Ph-C4′), 128.78 (OCPh3-o-C), 128.53 (Ph-
C5), 128.42 (Ph-C5′), 127.41 (OCPh3-m-C), 126.87 (Ph-C3), 126.69
(OCPh3-p-C), 126.43 (Ph-C3′), 120.00 (Ph-C2), 117.61 (Ph-C2′),
97.50(OCPh3), 54.15 (TiCH3), 39.91 (SCH2), 36.20 (SCH2), 35.78
(C(CH3)3), 35.58 (C(CH3)3), 34.49 (C(CH3)3), 34.43 (C(CH3)3),
31.69 (C(CH3)3), 31.65 (C(CH3)3), 29.84 (C(CH3)3), 29.76
(C(CH3)3). Anal. Calcd for C50H62O3S2Ti (823.02): C, 72.97; H,
7.59. Found: C, 73.20; H, 7.39.
4
4
H, Ph-5-H), 7.53 (d, JHH ) 2.4 Hz, 1 H, Ph-5′-H), 7.30 (d, JHH
4
) 2.4 Hz, 1 H, Ph-3-H), 7.19 (d, JHH ) 2.4 Hz, 1 H, Ph-3′-H),
4.90 (sept, 3JHH ) 6.1 Hz, 1H, OCH(CH3)2), 2.69 (dt, 2JHH ) 13.2,
3JHH ) 3.2 Hz, 1H, SCH2), 2.54 (dt, JHH ) 13.2 Hz, JHH ) 3.2
2
3
2
3
Hz, 1H, SCH2), 2.33 (td, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H,
SCH2), 2.07 (td, 2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 1.73
(s, 9H, C(CH3)3), 1.71 (s, 9H, C(CH3)3), 1.59 (s, 3H, TiCH3), 1.34
i
Synthesis of (edtbp)TiMe(OCMe2CMe2CO2 Pr) (9). To a
solution of (edtbp)TiMe{O(iPrO)C)CMe2} (4) (30 mg, 0.043
mmol) in C6D6 (ca. 0.5 mL) in a Teflon-valved NMR tube was
added acetone (2.5 mg, 0.043 mmol) via a microsyringe at room
temperature. The color of the solution quickly changed from red
to a yellow and NMR spectra were recorded. The conversion of 4
to 9 was virtually quantitative after 10 min. The solvent was
removed under vacuum, and the residue was recrystallized from
pentane to afford 9 as yellow crystals (27 mg, 83%). A crystal of
9 suitable for X-ray diffraction analysis was selected. 1H NMR
3
3
(d, JHH ) 6.1 Hz, 3H, OCH(CH3)2), 1.31 (d, JHH ) 6.1 Hz, 3H,
OCH(CH3)2), 1.25 (s, 9H, C(CH3)3), 1.22 (s, 9H, C(CH3)3). 13C{1H}
NMR (C6D6): δ 167.79 (Ph-C1), 166.79 (Ph-C1′), 142.38 (Ph-C6),
141.59 (Ph-C6′), 137.37 (Ph-C4), 137.02 (Ph-C4′), 128.53 (Ph-
C5), 128.42 (Ph-C5′), 126.35 (Ph-C3), 126.26 (Ph-C3′), 119.62 (Ph-
C2), 117.08 (Ph-C2′), 80.14 (TiOCH(CH3)2), 49.00 (TiCH3), 38.94
(SCH2), 36.15 (SCH2), 35.81 (C(CH3)3), 35.75 (C(CH3)3), 34.52
(C(CH3)3), 34.44 (C(CH3)3), 31.74 (C(CH3)3), 31.62 (C(CH3)3),
30.00 (C(CH3)3), 29.61 (C(CH3)3), 25.67 (TiOCH(CH3)2). Anal.
Calcd for C34H54O3S2Ti (622.79): C, 65.57; H, 8.74. Found: C,
64.96; H, 8.77.
Synthesis of (edtbp)TiMe(OPh) (7). To a solution of 4 (40 mg,
0.058 mmol) in C6D6 (ca. 0.5 mL) in a Teflon-valved NMR tube
was added at room temperature phenol (5.4 mg, 0.058 mmol).
Immediately, the red solution changed to a yellow solution, and
NMR spectra were recorded. The conversion of 4 to 7 was virtually
quantitative after 10 min The solvent was removed under vacuum,
4
4
(C6D6): δ 7.54 (d, JHH ) 2.4 Hz, 1 H, Ph-5-H), 7.52 (d, JHH
)
2.4 Hz, 1 H, Ph-5′-H), 7.30 (d, 4JHH ) 2.4 Hz, 1 H, Ph-3-H), 7.17
(d, JHH ) 2.4 Hz, 1 H, Ph-3′-H), 4.93 (sept, JHH ) 6.1 Hz, 1H,
OCH(CH3)2), 2.66 (dt, JHH ) 13.2, JHH ) 3.2 Hz, 1H, SCH2),
4
3
2
3
2
3
2.53 (dt, JHH ) 13.2 Hz, JHH ) 3.2 Hz, 1H, SCH2), 2.25 (td,
2JHH ) 13.2 Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 2.07 (td, 2JHH ) 13.2
Hz, 3JHH ) 3.2 Hz, 1H, SCH2), 1.78 (s, 3H, TiOC(CH3)2), 1.76 (s,
3H, TiOC(CH3)2), 1.71 (s, 9H, C(CH3)3), 1.70 (s, 9H, C(CH3)3),
1.67 (s, 3H, C(CH3)2COOiPr), 1.63 (s, 3H, C(CH3)2COOiPr), 1.56

6660 Organometallics, Vol. 26, No. 26, 2007
Lian et al.
(s, 3H, TiCH3), 1.24 (s, 9H, C(CH3)3), 1.20 (s, 9H, C(CH3)3), 0.97
118.26 (Ph-C2), 99.12 (TiOC(CH3)2), 68.08 (COOC(CH3)2), 50.90
(C(CH3)2COOiPr), 39.49 (SCH2) 35.23 (C(CH3)3), 34.41 (C(CH3)3),
30.85 (C(CH3)3), 28.98 (C(CH3)3), 26.46 (TiOC(CH3)2), 21.35
(C(CH3)2COOiPr), 21.21 (COOC(CH3)2). NMR data for the free
anion [MeB(C6F5)3]- were the same as those described above.
Typical Procedure for MMA and nBA Polymerization. To a
20 mL flask equipped with a magnetic stirrer, containing the enolate
complex (0.02 mmol) in 2 mL of toluene solvent, was introduced
the proper amount of monomer. The polymerization was initiated
by injection of the activator B(C6F5)3 or Al(C6F5)3 · 0.5C7H8 in 0.5
mL of toluene as solvent. The polymerization was carried out for
a time period, then the reaction was quenched by addition of
acidified methanol (3% HCl, 200 mL). The precipitated polymer
was filtered and dried overnight under vacuum at 60 °C.
3
(d, JHH ) 6.1 Hz, 6H, OCH(CH3)2). 13C{1H} NMR (C6D6): δ
175.01 (COOC(CH3)2), 167.66 (Ph-C1), 166.66 (Ph-C1′), 142.53
(Ph-C6), 141.74 (Ph-C6′), 137.23 (Ph-C4), 136.91 (Ph-C4′), 128.53
(Ph-C5), 128.41 (Ph-C5′), 126.90 (Ph-C3), 126.26 (Ph-C3′), 119.59
(Ph-C2), 116.85 (Ph-C2′), 89.63 (TiOC(CH3)2), 66.92 (COOC-
(CH3)2), 51.40 (C(CH3)2COOiPr), 50.42 (TiCH3), 39.15 (SCH2),
36.17 (SCH2), 35.74 (C(CH3)3), 35.60 (C(CH3)3), 34.40 (C(CH3)3),
34.34 (C(CH3)3), 31.64 (C(CH3)3), 31.61 (C(CH3)3), 30.02
(C(CH3)3), 29.60 (C(CH3)3), 27.48 (TiOC(CH3)2), 21.53
(C(CH3)2COOiPr), 21.00 (COOC(CH3)2). Anal. Calcd for
C41H66O5S2Ti (750.96): C, 65.57; H, 8.86. Found: C, 65.35; H, 8.63.
Generation of the Ion Pair [(edtbp)Ti(OPh)(THF-d8)n]+
[MeB(C6F5)3]- (10(THF-d8)n). In the glovebox, a Teflon-valved
NMR tube was charged with complex (edtbp)TiMe(OPh) (7) (15
mg, 0.023 mmol) and B(C6F5)3 (11.7 mg, 0.023 mmol), and CD2Cl2
was vacuum transferred in the presence of one drop of THF-d8
(THF free cationic species was found not stable in CD2Cl2 at room
temperature). The tube was sealed and NMR spectroscopy was
recorded, indicating quantitative formation of the ion pair [(edt-
Crystal Structure Determination of Complexes 2, 4, and 9.
X-ray diffraction measurements were performed on a Bruker AXS
diffractometer with Mo KR radiation using ω-scans. Crystal
parameters and results of the structure refinements are given in
Table 1 and are also available as CIF files (see the Supporting
Information). Absorption corrections were carried out with the
multiscan method using SADABS.11 All structures were solved by
direct methods (SHELXS-86)12a and refined (SHELXS-97)12b
against all F2 data. The crystals of 4 and 9 contain disordered groups
and split positions were introduced. All nonhydrogen atoms except
for those in the disordered groups were refined with anisotropic
displacement parameters. Hydrogen atoms were included into
calculated positions. For the graphical representation, the program
ORTEP was used as implemented in the program system WinGX.13
CCDC reference numbers 661686 (2), 661687 (4), and 661688 (9);
these data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
1
bp)Ti(OPh)(THF-d8)n]+[MeB(C6F5)3]- (10 · (THF-d8)n). H NMR
(CD2Cl2): δ 7.51 (d, 4JHH ) 2.2 Hz, 2 H, Ph-5-H), 7.28 (d, 4JHH
)
2.2 Hz, 2 H, Ph-3-H), 7.26 (dt, 3JHH ) 7.2 Hz, 4JHH ) 2.1 Hz, 2H,
OPh-m-H), 7.09 (tt, 3JHH ) 7.2 Hz, 4JHH ) 2.1 Hz, 1H, OPh-p-H),
3
4
6.98 (dd, JHH ) 7.2 Hz, JHH ) 2.1 Hz, 2H, OPh-o-H), 3.39 (d,
2JHH ) 11.2 Hz, 2H, SCH2), 2.84 (d, 2JHH ) 11.2 Hz, 2H, SCH2),
1.47 (s, 18H, C(CH3)3), 1.29 (s, 18H, C(CH3)3). 13C{1H} NMR
(CD2Cl2): δ 167.42 (OPh-ipso-C), 165.71 (Ph-C1), 148.13 (Ph-
C6), 137.28 (Ph-C4), 129.40 (OPh-m-C), 128.65 (Ph-C5), 127.75
(Ph-C3), 125.28 (OPh-p-C), 119.33 (Ph-C2), 118.78 (OPh-o-C),
40.28 (SCH2), 35.37 (C(CH3)3), 34.35 (C(CH3)3), 30.84 (C(CH3)3),
29.07 (C(CH3)3). NMR data for the free anion [MeB(C6F5)3]- were
the same as those described above.
i
Generation of the Ion Pair [(edtbp)Ti(OCMe2CMe2CO2 Pr)
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie for
financial support. We are also grateful to Prof. U. Englert
and Mr. Y.-T. Wang for collecting the X-ray data and to
Dr. K. Beckerle for the GPC measurements.
(THF-d8)n]+[MeB(C6F5)3]- (11(THF-d8)n). In the glovebox, a
Teflon-valved NMR tube was charged with complex (edtbp)-
i
Ti(OCMe2CMe2CO2 Pr)Me (9) (10 mg, 0.013 mmol) and B(C6F5)3
(6.8 mg, 0.013 mmol) and CD2Cl2 was vacuum transferred in the
presence of one drop of THF-d8 (THF free cationic species was
found not stable in CD2Cl2 at room temperature). The tube was
sealed and NMR spectroscopy was recorded, indicating quantita-
tive formation of the ion pair [(edtbp)Ti(OCMe2CMe2-
Supporting Information Available: Crystallographic data for
2, 4, and 9 (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
i
CO2 Pr)(THF-d8)n]+[MeB(C6F5)3]- (11(THF-d8)n). 1H NMR
(CD2Cl2): δ 7.46 (d, 4JHH ) 2.2 Hz, 2 H, Ph-5-H), 7.26 (d, 4JHH
)
OM700785C
2.2 Hz, 2 H, Ph-3-H), 4.90 (sept, 3JHH ) 6.1 Hz, 1H, OCH(CH3)2),
3.31 (d, 2JHH ) 11.2 Hz, 2H, SCH2), 2.65 (d, 2JHH ) 11.2 Hz, 2H,
SCH2), 1.53 (s, 3H, TiOC(CH3)2), 1.44 (s, 18H, C(CH3)3), 1.38 (s,
3H, TiOC(CH3)2), 1.27 (s, 18H, C(CH3)3), 1.26 (s, 3H, C(CH3)2
(11) Siemens. ASTRO, SAINT and SADABS. Data Collection and
Processing Software for the SMART System; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1996.
(12) (a) Sheldrick, G. M. SHELXS-86, A Program for Crystal Structure
Solution; University of Göttingen: Göttingen, Germany, 1986. (b) Sheldrick,
G. M. SHELXL-97, A Program for Crystal Structure Refinement; University
of Göttingen: Göttingen, Germany, 1997.
3
COOiPr), 1.21 (s, 3H, C(CH3)2COOiPr), 1.20 (d, JHH ) 6.1 Hz,
3
3H, OCH(CH3)2), 1.18 (d, JHH ) 6.1 Hz, 3H, OCH(CH3)2).
13C{1H} NMR (C6D6): δ 174.15 (COOC(CH3)2), 166.85 (Ph-C1),
147.26 (Ph-C6), 137.11 (Ph-C4), 128.39 (Ph-C5), 127.61 (Ph-C3),
(13) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.