New aryloxy and benzyloxy derivatives of titanium as catalysts for bulk ring-opening polymerization of ε-caprolactone and δ-valerolactone

Article abstract of DOI:10.1002/ejic.200900280

A variety of aryloxy compounds and benzyloxy derivatives of Ti^IV were synthesized from. Ti(iP:rO)₄ using the alcoholysis route, These compounds were characterized using various analytical methods and single-crystal X-ray diffraction,

Full text of DOI:10.1002/ejic.200900280

FULL PAPER
DOI: 10.1002/ejic.200900280
New Aryloxy and Benzyloxy Derivatives of Titanium as Catalysts for Bulk
Ring-Opening Polymerization of ε-Caprolactone and δ-Valerolactone
Ravikumar R. Gowda,[a] Debashis Chakraborty,*[a] and Venkatachalam Ramkumar[a]
Keywords: Titanium(IV) / ε-Caprolactone / δ-Valerolactone / Polymerization / Titanium / Lactones
A variety of aryloxy compounds and benzyloxy derivatives
of TiIV were synthesized from Ti(iPrO)4 using the alcoholysis
route. These compounds were characterized using various
analytical methods and single-crystal X-ray diffraction. Mul-
tinuclear NMR studies prove high degree of fluxional be-
havior of these compounds in solution. They adopt a dimeric
structure in the solid state as seen from X-ray diffraction
studies on a few of them. These compounds are powerful cat-
alysts for the ring-opening polymerization of ε-caprolactone
(CL) and δ-valerolactone (VL) resulting in high polymers
with good number average molecular weights (Mn). Signifi-
cant control can be achieved by performing such polymeriza-
tions in the presence of benzyl alcohol (BnOH). This is re-
flected by higher Mn and much narrower molecular weight
distributions (MWDs) of the resulting polymers. Kinetic stud-
ies reveal that the rates of such polymerizations are much
higher in the presence of BnOH. 1H NMR and MALDI-TOF
studies of low molecular weight oligomers suggest that these
polymerizations proceed by the activated monomer mecha-
nism in the presence of BnOH.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
with one or more alkoxide-based initiating groups. The es-
tablishment of such a principle has been documented re-
cently by demonstrating the applications of alkoxides with
a ligating backbone containing chiral phenoxyimine,[28] tris-
(phenoxy)amine,[29] bis(β-ketoamidate),[30] bis(iminophen-
oxy),[31–32] N-heterocyclic carbene,[33] bis(phenoxy)-
amine,[34–36] pyrrolylamine,[37] tris(alkoxy),[38–39] tris(alkoxy)-
amine,[40–42] bis(amido),[43] chalcogen-bridged bis(aryl-
oxy)[44] and methylene-bridged bis(phenoxy)[45] derivatives.
In addition, there are reports employing titanium n-butox-
ide, zirconium n-propoxide[46] and titanium phenoxide[47] as
initiators. A Ti-alkoxide-based metal organic framework
was recently reported to possess activity for such pro-
cesses.[48] The use of metallocene ester enolates for the poly-
merization of lactide has been reported recently.[49] Only a
few compounds derived from these ligands have been em-
ployed towards the polymerization of CL.[30,35–37,41,43–46,48]
The polymerizations described from such initiators have ex-
clusively relied upon the coordination-insertion mecha-
nism.[1] Systematic correlation between the structural com-
positions of such ligands with polymer properties along
with any practical advantage on polymer microstructure is
not available.
Introduction
In the recent years, the increasing need to search alterna-
tive polymeric materials to those based on nonrenewable
petroleum resources, along with the desire to produce envi-
ronmentally benign biodegradable plastics has provided
active impetus towards the polymerization of cyclic es-
ters.[1–5] The applications of aliphatic polyesters have been
popularly widespread in biomedical and pharmaceutical in-
dustries including drug delivery, production of implants
and scaffolds for tissue engineering.[6] Their uses have been
implicated in the film and fiber applications industry.[7] The
potential for such utility stems as a result of their perme-
ability, biocompatibility and biodegradability.[8–10]
One of the convenient strategies in synthesizing these
polymers is the ring-opening polymerization of the corre-
sponding cyclic lactone monomers or lactide.[6,11–12] The
coordination-insertion ring-opening mode of polymeriza-
tion is the most popular because of its capability in produc-
ing high polymers with narrow MWDs.[1,11,13–24] Group 4,
the most versatile in homogeneous olefin polymerization
catalysis[25–27], has been exploited in the ring-opening poly-
merization of cyclic esters.
The popular methodology of catalyst construction is to
use a rigid ligating environment around the metal center
Another approach to the polymerization of cyclic esters
is the activated monomer mechanism[50–54] whose practical
utility has not been substantially investigated as compared
to the coordination-insertion mechanism. None of the initi-
ators derived from the above ligand backbone have been
investigated in this regard. A reason that may be attributed
to this observation is the use of protic initiators along with
these organometallic alkoxides as catalysts which may not
[a] Department of Chemistry, Indian Institute of Technology Ma-
dras,
Chennai-600 036, Tamil Nadu, India
Fax: +91-44-2257-4202
E-mail: dchakraborty@iitm.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900280.
Eur. J. Inorg. Chem. 2009, 2981–2993
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. R. Gowda, D. Chakraborty, V. Ramkumar
FULL PAPER
be tolerated by them. Hence, there are possibilities of loss
of catalyst identity during the polymerization process.
Our recent results indicate that iron and ruthenium chlo-
ride catalysts in the presence of protic initiators like
alcohols produce comparable or better results for CL and
VL polymerization, using the activated monomer mecha-
nism,[55] as compared to the ones reported for alkoxide initi-
ators containing bulky ligands wherein the polymerization
proceeds by the coordination-insertion mechanism.[20]
Using such a methodology, much shorter polymerization
time, far higher Mn and low MWDs were observed. This
proved our initial contentions that elaborate ligands may
not be an absolute necessary requirement in the develop-
ment of such a technology.[55] The chain-end groups for the
poly(caprolactone) and poly(valerolactone) obtained using
either of the mechanisms are identical.[50–54] This has
prompted us to investigate extensively the role of aryloxy
and benzyloxy compounds of titanium in the polymeriza-
tion of CL and VL using the coordination-insertion mecha- Scheme 1. Synthesis of titanium aryloxy compounds.
nism. The possibility to explore such compounds as cata-
lysts in the presence of protic initiators was additionally an
important milestone. This methodology is anticipated to il-
lustrate possible advantages in terms of polymerization
For the synthesis of 15–18, a 1:4 stoichiometry reaction
time, Mn and MWDs of the resulting polymers and may be between the reactants (Scheme 1) yielded the required prod-
thought to proceed via the activated monomer mechanism. uct along with unreacted phenol. These were prepared by
It must be mentioned that VL polymerization using group 4 reacting Ti(iPrO)4 with 2 equivalents of phenol in toluene
metals have not been reported.
at 80 °C.
The benzyloxy derivatives namely [Ti(OCH2–4-
MeC6H4)4]2 (19) and [Ti(OCH2–4-OMeC6H4)4(iPrOH)]2
(20) were prepared by reacting Ti(iPrO)4 with the appropri-
ate substituted benzyl alcohol derivative, using a procedure
identical to those of the aryloxy compounds. The yields of
these viscous yellow oils were high.
Results and Discussion
Synthesis and Characterization of Compounds 1–20
The alcoholysis route[56–57] has been employed for the
The aforementioned compounds 1–20 have been charac-
synthesis of a variety of titanium aryloxy compounds 1–18 terized thoroughly by 1H and 13C NMR spectroscopy, elec-
starting from Ti(iPrO)4 and several phenols, bearing dif- trospray ionization mass spectrometry (ESI-MS) and their
ferent substituents on the phenyl ring (Scheme 1). Com- purity has been assured by correct elemental analysis val-
pounds 1–14 were prepared by heating Ti(iPrO)4 with the ues.
1
appropriate phenol in 1:4 stoichiometric ratio in toluene at
The H NMR of these compounds reveals the expected
80 °C with the exception of 5, 9, 12, 13 and 14 where stir- signals in the correct ratio of integration. Compounds 7,
ring the reaction mixture at room temperature in toluene 12, 13 and 14 have residual lattice toluene which could not
followed by evaporation of solvent afforded the expected be removed by drying them under high vacuum (10–6 Torr)
product. These products were purified by crystallization for several hours. These compounds (1–18) have a tendency
and obtained in high yields as orange-yellow to orange-red for degradation when heated under such conditions. For the
solids with high melting points (140–188 °C). Some of these aryloxy compounds, which are iPrOH adducts (2, 5–7, 10–
compounds (1, 3, 8, 9, 11, and 13) have been reported in 14), the signals appear broad, suggesting a high degree of
the literature. Compound 1 and 8 are reported to be synthe- fluxional behavior of such molecules (see Supporting Infor-
sized by reacting Ti(OBu)4 with the corresponding phe- mation). The CH signal of coordinated iPrOH is deshielded
nol.[58] The reported procedure for 3,[59] 9[60] and 13[61] is to a greater extent in 2, 13 and 14 (δ = 4.69–4.83 ppm) as
the direct reaction of titanium halide with the appropriate compared to the other derivatives (δ = 4.22–4.40 ppm) as a
phenol. Compound 11, was synthesized using the reported consequence of higher Lewis acidity of the titanium centers
procedure.[62] These compounds were characterized by mea- because of electron-withdrawing ligands. Such deshielding
suring ebullioscopic constants in benzene, measurement of is also observed for the Me protons of coordinated iPrOH
melting point and elemental analyses. Our contribution has in 13 and 14 respectively. The OH proton of coordinated
been in the synthesis of these compounds by the route iPrOH remain NMR silent. For the others, broadening of
shown in Scheme 1 and characterizing them completely by signals is seen at lower temperatures (see Supporting Infor-
NMR, mass spectrometry and single-crystal X-ray diffrac- mation). Such observations of fluxionality and oligomer
tion studies on a few of them.
formation have been well documented in the literature per-
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Ti-Catalyzed Polymerization of ε-Caprolactone and δ-Valerolactone
taining to metal alkoxides.[63–64] For 15–18, the extent of
1
broadening of signals in H NMR is moderate (see Sup-
porting Information). The signals corresponding to the
iPrO moiety are deshielded (δ = 4.77–4.92 ppm for CH and
1.24–1.36 for Me) significantly because of bond formation
with titanium. The benzyloxy derivative 20 shows a higher
degree of broadening of the signals in the 1H NMR as com-
pared to 19 as a result of iPrOH coordination. The presence
of coordinatively unsaturated titanium atoms provides a rel-
atively easy associative route for either internal ligand
scrambling or external ligand exchange.
1
Variable-temperature H NMR studies were conducted
using 2 and 18. For 2, the spectrum becomes complicated
as the temperature is lowered from 25 °C to –55 °C. New
peaks appear in the aromatic region, whose intensities be-
come prominent as the temperature is lowered gradually.
The broad CH peak of coordinated iPrOH at δ = 4.69 ppm
broadens gradually and eventually separates into two peaks
Figure 1. Variable-temperature 1H NMR spectrum of 18 in CDCl3.
at –55 °C (see Supporting Information). Such observations contributed by the other carbon atoms of the phenyl ring.
suggest fluxionality and are indicative of complicated solu- The CH peak of iPrO group in 15–18 (δ = 78.39–
tion dynamics.[63,65] We have done similar studies using 18 88.97 ppm) is deshielded considerably as compared to that
(Figure 1). Upon lowering the temperature gradually the seen for cases that have coordinated iPrOH (2, 5–7, 10–14)
peaks at δ = 7.97 ppm (phenyl), 4.92 ppm (CH of iPrO) and (δ = 70.94–76.94 ppm). Similar conclusions are seen for the
1.36 (Me of iPrO) broaden and new peaks are eventually benzyloxy derivatives 19 and 20 respectively.
seen. In addition to the signal for the CH moiety constitut-
The 47/49Ti NMR spectra for a few compounds (6, 10, 12
ing the iPrO group at δ = 4.92 ppm, there are two others and 17) with different electronic environments on the tita-
at δ = 5.22 ppm and 5.95 ppm respectively. This may be nium centers were studied. The results are concordant in
rationalized by considering the equilibrium depicted in correlation with the expectation that the position of the sig-
Scheme 2 where contributing structures have the iPrO moi- nal with be gradually deshielded with electronic with-
ety in different environments.
drawing substituents on the phenyl ring.[66] The signals are
13C NMR of these compounds at 25 °C shows broad sig- broad (see Supporting Information), suggesting the flux-
nals with extremely poor intensities and resolution. How- ional behavior of such molecules.
ever, the spectral characteristics at –55 °C were reasonable,
ESI-MS studies reveal the presence of {M2 – (OAr) +
in accord to the conclusions drawn from H NMR studies Na}+ [M = Ti(OAr)4 (1, 3–4, 8–9), Ti(OAr)4(iPrOH) (2, 5–
(see Supporting Information). In all the aryloxy com- 7, 10–14), Ti(OAr)2(iPrO)2 (15–18), Ti(OCH2Ar)4 (19–20)]
pounds 1–18, the ipso carbon of the phenyl ring is peak as the sodium adduct in prominent intensity (see Sup-
deshielded with respect to the corresponding phenol and porting Information). These observations indicate that such
there is no appreciable change in the position of the signals molecules exist predominantly as dimers.
1
Scheme 2. Solution dynamics of 18.
Eur. J. Inorg. Chem. 2009, 2981–2993
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R. R. Gowda, D. Chakraborty, V. Ramkumar
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Single-Crystal X-ray Diffraction Studies
are almost indistinguishable suggesting nearly equal coval-
ent and dative contributions, leading to a stable dimeric
core. The coordinated iPrOH can be easily identified by the
bond length Ti(1)–O(5), being much longer than the other
Ti–O distances. The distorted octahedral environment
around the titanium centers is apparent from the bond
angles. There is hydrogen bonding [2.376(3) Å in 2,
2.062(2) Å in 5, 2.135(3) Å in 6 and 1.985(3) Å in 11] be-
tween the OH group of iPrOH coordinated to a titanium
and to one of the terminal OAr ligands of the neighboring
titanium. All the structure parameters match well with the
literature precedents.[62,66]
Examination of the structural differences between these
compounds through space-filling models suggests steric
congestion as a common feature. This is particularly en-
hanced in cases with a halogen substituent at the 2-position
of the phenyl ring. This may be understood by considering
the space-filling model of 2 (Figure 4). The titanium centers
are embedded within the aryloxy periphery and coordina-
tion of iPrOH may not be as facile, although the enhance-
ment of Lewis acidity of the Ti centers is expected. With
larger electron-withdrawing substituents (Cl and Br in 3
and 4) at the 2-position, the coordination of iPrOH may
not be favored in spite of an increase in the Lewis acidity
of the titanium center. Hence, iPrOH adducts are not seen.
Such steric considerations do not play an important role
with substituents at 3- and 4-positions of the phenyl ring.
Hence compounds with electron-withdrawing substituents
at these positions (5–7 and 10–12) appear as iPrOH ad-
ducts. In the case of 13 and 14, the Lewis acidity of Ti is
enhanced to a very large extent, forcing iPrOH coordina-
tion even under nonfavorable steric constraints.
Among the several compounds synthesized in this study,
suitable crystals for X-ray diffraction studies could be ob-
tained from 2, 5, 6 and 11 respectively. Although the syn-
thesis of 11 is reported, we considered it worthwhile under-
taking crystallographic studies since it has substitution on
the phenyl ring at the 4-position and crystals suitable for
X-ray diffraction could be grown easily. Single crystals were
grown in a glove box at –23 °C from dilute toluene solu-
tions of the respective compounds over a period of two
weeks. The molecular structures of 2 and 6 are depicted in
Figures 2 and 3, respectively (for 5 and 11, see Supporting
Information).
Figure 2. Molecular structure of 2; thermal ellipsoids were drawn
at 30% probability level.
Figure 4. Space filling model of 2 (Ti in black).
Polymerization Activity and Characteristics
Recent results from our group indicate that metal initia-
tors with elaborate ligands constituting the backbone are
not an essential requirement towards the polymerization of
lactones. Utilizing the activated monomer mechanism it is
possible to produce high polymers with good MWDs by
Figure 3. Molecular structure of 6; thermal ellipsoids were drawn
at 30% probability level.
The molecules discussed exhibit centrosymmetric dimeric performing such polymerizations in the presence of al-
structure in the solid state possessing edge shared distorted coholic initiators.[55] Our impetus in this direction obtained
octahedral titanium centers coordinated to a molecule of a boost from the recent description of employing Ti(OPh)4
iPrOH. The two titanium centers are separated by ca. 3.3 Å. as the initiator for the polymerization of CL.[47] The poly-
The terminal Ti–O bonds of the phenoxy moieties are merizations were reported to proceed via the coordination-
shorter than those contributing towards the formation of insertion mechanism. The conclusions were confirmed
the bridged bonds. The four Ti–O bonds forming the core using rheological methods. The studies described did not
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Ti-Catalyzed Polymerization of ε-Caprolactone and δ-Valerolactone
provide correlation between polymerization characteristics Table 2. Results of CL polymerization using various aryloxy com-
pounds and benzyloxy derivatives in the presence of benzyl alcohol
in 200:1:5 ratio at 80 °C.
and ligand environment as they were confined to Ti(OPh)4
alone. We surmised that a variation of electronic environ-
ments of the phenyl ring constituting the OAr moiety must
have a consequence in such polymerizations.
Entry Catalyst Time[a] /s
% Yield[b] 103 Mn
/
PDI
[c]
g/mol
(Mw/Mn)
Our studies were confined to using these compounds
alone in the form of initiators for the polymerization of CL
and VL and using them in the form of catalysts in the pres-
ence of BnOH as initiator. To the best of our belief, such
polymerizations in the presence of an alcoholic initiator like
BnOH has not been reported so far using titanium deriva-
tives.[30,35–37,41,43–46,48] We also considered it appropriate to
compare the results using different aryloxy compounds 1–
18 to those using the benzyloxy derivatives 19 and 20,
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
28
3
39
82
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
10.61
13.65
14.77
136.45
9.92
1.40
1.42
1.41
1.45
1.47
1.48
1.49
1.41
1.43
1.47
1.44
1.43
1.48
1.46
1.48
1.46
1.44
1.45
1.49
1.42
125
133
223
37
133
127
224
197
254
301
36
49
65
67
224
298
16.48
30.49
80.33
78.69
136.75
72.62
114.38
11.30
20.39
39.61
67.59
75.21
95.74
7.97
9
10
11
9
10
11
12
13
14
15
16
17
18
19
20
respectively. These polymerizations were performed under 12
bulk conditions at 80 °C using 1–20. In addition, there is
13
14
no report of bulk polymerization of lactones using organo-
15
metallic titanium derivatives. Polymerization under ambient
16
temperatures yielded low molecular weight oligomers. The
results are summarized in Tables 1, 2, 3, and 4 respectively.
17
18
19
20
22.11
Table 1. Results of CL polymerization using various aryloxy com-
pounds and benzyloxy derivatives in 200:1 ratio at 80 °C.
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards with Mark–Houwink corrections for Mn.
[c]
Entry Initiator Time[a] /s
% Yield[b] 103 Mn
/
PDI
g/mol
(Mw/Mn)
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
40
5
50
98
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
6.37
7.10
13.57
92.23
4.02
2.32
2.02
2.12
2.53
2.62
2.60
2.59
2.22
2.46
2.26
2.35
2.16
2.54
2.51
2.19
2.69
2.79
2.55
2.04
2.72
Table 3. Results of VL polymerization using various aryloxy com-
pounds and benzyloxy derivatives in 200:1 ratio at 80 °C.
153
240
305
55
210
270
300
307
345
360
45
60
79
88
348
355
Entry Initiator Time[a] /s
% Yield[b]
103 Mn
/
PDI
[c]
7.44
g/mol
(Mw/Mn)
26.33
79.39
68.97
64.73
54.30
95.76
6.36
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
420
510
600
720
98
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
23.13
24.20
60.10
70.37
19.17
11.45
19.29
32.86
138.12
18.88
24.67
22.58
10.41
10.43
14.18
71.37
79.65
113.96
4.65
2.34
2.80
2.40
2.49
2.20
2.25
2.17
2.03
2.79
2.16
2.10
2.73
2.65
2.88
2.18
2.76
2.42
2.74
2.01
2.19
9
9
10
11
12
13
14
15
16
17
18
19
20
10
11
12
13
14
15
16
17
18
19
20
720
790
310
800
820
1000
1200
960
1080
624
800
878
957
628
750
9.39
30.19
50.42
53.36
70.30
5.11
9
9
10
11
12
13
14
15
16
17
18
19
20
10
11
12
13
14
15
16
17
18
19
20
20.57
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards with Mark–Houwink corrections for Mn.
Analysis of the results depicted in Table 1, Table 2,
Table 3, and Table 4 reveal that for compounds containing
strongly electron-withdrawing ligands 2, 5–6, 13–15, com-
9.07
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
paratively faster transesterification reactions occur leading yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards.
to the formation of poly(lactones) with low to modest Mn.
The benzyloxy derivatives 19 and 20 are inferior to the ary-
loxy compounds 1–18. In the presence of BnOH, reasonable was found to proceed to completion much faster as re-
degree of control in the polymerization process was re- flected by the polymerization time. In the presence of
flected in terms of lower MWDs (Entry 1–20 of Table 1 vs. BnOH, the observed Mn of the polymers were found to be
Entries 1–20 of Table 2 and Entry 1–20 of Table 3 vs. En- much higher in magnitude. Hence it may be concluded that
tries 1–20 of Table 4) and enhanced molecular weights (Mn) the rates of initiation and propagation are much more rapid
of the resulting polymers. In such cases the polymerization than that of chain transfer. As a consequence, a better con-
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R. R. Gowda, D. Chakraborty, V. Ramkumar
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Table 4. Results of VL polymerization using various aryloxy com- by BnOH since the latter is in excess and being a primary
pounds and benzyloxy derivatives in the presence of benzyl alcohol
in 200:1:5 ratio at 80 °C.
alcohol. This is concluded by analyzing the methylene peak
in the H NMR spectrum. The closed structure of 9 pre-
1
Entry Catalyst Time[a] /s % Yield[b] 103 Mn
/
PDI
[c]
vents the coordination of BnOH. In summary, the catalyst
identity remains unaltered in the presence of BnOH during
polymerization reactions (see Supporting Information).
The dependence of Mn upon varying the feed ratio of
CL to BnOH as initiator was examined using 6, 14, 17 and
20. The Mn increased almost linearly with increasing feed
ratio of CL to BnOH. Similar inferences were drawn using
VL (see Supporting Information).
g/mol
(Mw/Mn)
1
2
3
4
5
6
7
8
1
325
445
466
600
77
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
35.74
27.87
70.38
73.10
22.10
15.19
24.28
34.71
272.86
29.12
36.82
36.06
18.70
19.47
25.65
74.53
111.57
255.68
12.51
18.71
1.46
1.45
1.48
1.49
1.41
1.47
1.41
1.42
1.49
1.43
1.46
1.42
1.42
1.47
1.43
1.34
1.48
1.45
1.44
1.40
2
3
4
5
6
668
698
228
725
742
885
950
725
805
828
910
510
705
506
664
7
8
9
9
10
11
12
13
14
15
16
17
18
19
20
10
11
12
13
14
15
16
17
18
19
20
Kinetics of Polymerization
The kinetic studies for the polymerization of CL and VL
using 6, 14, 17 and 20 in the absence and presence of BnOH
were studied. The kinetic studies for the polymerization of
CL in ratio [CL]o/[Ti]o = 1000 and [CL]o/[Ti]o/[BnOH]o =
1000:1:5 were performed at 80 °C (see Supporting Infor-
mation). The results are depicted in Figure 5 and Figure 6
respectively. The plots suggest that there is a first-order de-
pendence of the rate of polymerization on monomer con-
centration. There is no induction period.
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards.
trol over Mn is observed. For polymerizations where there
is slow initiation or rapid transesterification, the observed
Mn is lower in magnitude than those expected.[67–69]
Some of our results (Entries 4, 10 and 12 of Table 2 and
Entries 9, 17 and 18 of Table 4) deserve special mention
because of exceptionally high magnitudes of Mn of the re-
spective polymers. We have obtained the highest mole-
cular weight poly(caprolactone) in comparison to the re-
sults known for organometallic initiators of tita-
nium.[30,35–37,41,43–46,48]
The variations of Mn with [CL]o/[Ti]o ratio using 6, 14,
17 and 20 for CL polymerizations were studied. The plots
are linear indicating that there is a continual rise in Mn with
an increase in [CL]o/[Ti]o ratio. Similar conclusions were
drawn for VL polymerizations (see Supporting Infor-
mation).
Figure 5. Semilogarithmic plots of CL conversion in time initiated
by 6, 14, 17 and 20: [CL]o/[Ti]o = 1000 at 80 °C.
The ln[CL]o/[CL]t vs. time plots (Figures 5 and 6) exhibit
It may be intriguing to understand what happens to the linear variation. From the slope of the plots, the values of
identity of 1–20 in the presence of BnOH added during po- the apparent rate constant (kapp) for CL polymerizations
lymerization. To answer this, we have independently per- initiated by 6, 14, 17 and 20 were found to be
formed reactions by heating 9, 13 and 20 in the presence of 11.00ϫ10–2 min–1, 18.04ϫ10–2 min–1, 26.62ϫ10–2 min–1
5 equiv. BnOH at 80 °C in toluene for 4 hours. At the end, and 16.29ϫ10–2 min–1 in the absence of BnOH and
all volatiles were removed in vacuo and the residue was sub- 15.07ϫ10–2 min–1, 23.40ϫ10–2 min–1, 31.65ϫ10–2 min–1
1
jected to H NMR studies. To our surprise in the case of 9 and 20.82ϫ10–2 min–1 in the presence of BnOH. For VL,
and 13, peaks corresponding to BnOH alone were ob- the conclusions are similar and the apparent rate constant
served. This implies very clearly that the iPrOH coordina- (kapp) for polymerizations initiated by 6, 14, 17 and 20 were
tion in 13 is loose and upon the addition of BnOH, it has found to be 9.13ϫ10–2 min–1, 5.17ϫ10–2 min–1,
a spontaneous tendency to escape the coordination sphere 12.23ϫ10–2 min–1 and 6.01ϫ10–2 min–1 in the absence of
whereas BnOH being comparatively bulky finds it difficult BnOH
and
12.42ϫ10–2 min–1,
14.15ϫ10–2 min–1,
to coordinate. These conclusions are in agreement to our 19.14ϫ10–2 min–1 and 11.36ϫ10–2 min–1 in the presence of
expectations using space-filling model. Compound 20, be- BnOH (see Supporting Information). These results indicate
ing a more open structure allows the replacement of iPrOH that the rates are faster in the presence of BnOH. To the
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2981–2993

Ti-Catalyzed Polymerization of ε-Caprolactone and δ-Valerolactone
heptane. In all the cases, the residue after removal of hep-
tane were analyzed thoroughly using MALDI-TOF and 1H
NMR spectroscopy.
Using 2, the major product of the composition iPrO-
[CO(CH2)5O]nH is formed as understood through the
1
analysis of MALDI-TOF and H NMR spectra, depicted
in Figures 7 and 8 respectively. This is an implication that
coordinated iPrOH has an active role as an initiator and
the polymerization proceeds through the activated mono-
mer mechanism.[50–55]
Figure 6. Semilogarithmic plots of CL conversion in time initiated
by 6, 14, 17 and 20: [CL]o/[Ti]o/[BnOH]o = 1000:1:5 at 80 °C.
best of our knowledge, there is no report stating kapp mag-
nitudes using titanium derivatives for CL polymerization.
Kinetic studies using a protic initiator like BnOH have not
been attempted previously. Polymerization studies on VL
using titanium compounds are not reported.
Insight into Polymerization Mechanism
A convenient tool to gain insight into the polymerization
mechanism using 1–20 is a thorough understanding of the
polymer composition upon using these compounds as initi-
ators or catalyst through MALDI-TOF and 1H NMR spec-
troscopy. We selected 2 and 9 as prototype representatives
1
Figure 8. H NMR spectrum of the crude product obtained from
a reaction between CL and 2 in 20:1 ratio.
In case of 9, the major product is 4-tBuC6H4O[CO-
for compounds with iPrOH coordination and without. Low (CH2)5O]nH as seen from MALDI-TOF and 1H NMR
molecular weight oligomers of poly(caprolactone) were syn- spectra (see Supporting Information). Here, the polymeriza-
thesized by stirring CL with 2 or 9 in 20:1 molar ratio under tion proceeds by the conventional coordination-insertion
neat conditions at 80 °C. The product was extracted with mechanism.[1]
Figure 7. MALDI-TOF of the crude product obtained from a reaction between CL and 2 in 20:1 ratio.
Eur. J. Inorg. Chem. 2009, 2981–2993
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2987

R. R. Gowda, D. Chakraborty, V. Ramkumar
FULL PAPER
Figure 9. MALDI-TOF of the crude product obtained from a reaction between CL and 2 along with BnOH in 20:1:5 ratio.
1
To understand the effect of BnOH, CL along with 2 or using MALDI-TOF and H NMR spectroscopy. In both
9 and BnOH in the ratio 20:1:5 were reacted neat at 80 °C. cases an activated monomer mechanism[50–55] prevails and
On a similar basis the reaction mixtures were analyzed results in the formation of the product PhCH2O[CO-
(CH2)5O]nH. For 2, BnOH dominates over iPrOH as the
initiator since it is used in excess and being a primary
alcohol. The role of iPrOH as a competing initiator is not
seen from the results using MALDI-TOF and 1H NMR
spectroscopy. The results for 2 are shown in Figures 9 and
10, respectively (see Supporting Information for results
using 9).
Comparison of Polymerization Results
In order to compare our results with those known for
CL polymerization using titanium, we present here results
for polymerizations conducted in the presence of toluene
(Tables 5 and 6, respectively).
In the presence of toluene these polymerizations are
more controlled and result in good MWDs. Our results are
superior or at least comparable to literature re-
ports.[30,35–37,41,43–46,48] Such observations are also seen for
1
the bulk polymerizations conducted in the absence of sol-
vents.
Figure 10. H NMR spectrum of the crude product obtained from
a reaction between CL and 2 along with BnOH in 20:1:5 ratio.
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Eur. J. Inorg. Chem. 2009, 2981–2993

Ti-Catalyzed Polymerization of ε-Caprolactone and δ-Valerolactone
corded relative to TiCl4 as an external standard. ESI-MS spectra
of the samples were obtained from Waters Q-Tof micro mass spec-
Table 5. Results of CL polymerization using 6, 9, 14, 17 and 20 in
200:1 ratio at 80 °C in toluene.
trometer. MALDI-TOF measurements were performed on
a
[c]
Entry
Initiator Time[a] /s % Yield[b] 103 Mn
/
PDI
(Mw/Mn)
Bruker Daltonics instrument in dihydroxy benzoic acid matrix. Ele-
mental analyses were done with a Perkin–Elmer Series 11 analyzer.
All phenols and benzyl alcohol derivatives used in this study along
with Ti(iPrO)4 were purchased from Aldrich and used without sub-
sequent purification. CL and VL were purchased from Aldrich,
dried with CaH2 overnight and distilled fresh prior to use. Com-
pound 11 was prepared using the literature procedure.[62]
g/mol
1
2
3
4
5
6
560
480
740
280
820
100
100
100
100
100
5.15
50.86
9.12
45.36
11.57
1.30
1.31
1.35
1.37
1.34
9
14
17
20
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards with Mark–Houwink corrections for Mn.
[Ti(O-2-MeC6H4)4]2 (1): Under an argon atmosphere, to a stirred
solution of 2-MeC6H4OH (0.25 g, 2.32 mmol) in 5 mL of toluene
at 27 °C, was added Ti(iPrO)4 (0.16 g, 0.58 mmol). An orange solu-
tion resulted immediately. The reaction mixture was heated to
80 °C for a period of 3h. The contents were cooled to ambient
temperature. The solvent was removed under reduced pressure to
yield an orange-yellow solid which was purified by recrystallization
from toluene at –20 °C. The crystallized solid was recovered by
filtration and dried in vacuo; yield 0.49 g, 91%; m.p. 162 °C. 1H
NMR (400 MHz, CDCl3): δ = 7.0–6.8 (16 H, ortho, meta, para),
2.11 (s, 12 H, ArMe) ppm. 13C NMR (100 MHz, CDCl3, –55 °C):
δ = 164.88 (Ar-O), 130.81 (Ar-C), 127.48 (Ar-C), 126.78 (Ar-CH3),
122.74 (Ar-C), 115.23 (Ar-C), 16.85 (Ar-CH3) ppm. ESI-MS: m/z
= 868 {(Ti(O-2-MeC6H4)4)2 – (O-2-MeC6H4) + Na}+. C28H28O4Ti
(476.39): calcd. C 70.59, H 5.92; found C 70.78, H 5.69.
Table 6. Results of CL polymerization using 6, 9, 14, 17 and 20 in
the presence of BnOH in 200:1:5 ratio at 80 °C in toluene.
[c]
Entry Initiator Time[a] /s % Yield[b] 103 Mn
/
PDI
(Mw/Mn)
g/mol
1
2
3
4
5
6
350
325
620
200
670
100
100
100
100
100
7.30
1.15
1.26
1.29
1.20
1.20
9
61.85
24.97
56.12
12.10
14
17
20
[a] Time of polymerization measured by quenching the polymeriza-
tion reaction when all monomer was found consumed. [b] Isolated
yield. [c] Measured by GPC at 27 [°C] in THF relative to polysty-
rene standards with Mark–Houwink corrections for Mn.
[Ti(O-2-FC6H4)4(iPrOH)]2 (2): 2-FC6H4OH (0.25 g, 2.24 mmol)
and Ti(iPrO)4 (0.16 g, 0.56 mmol) were reacted and an identical
procedure used for the synthesis of 1 was employed; yield 0.55 g,
89%; m.p. 168 °C. 1H NMR (400 MHz, CDCl3): δ = 6.9–6.7 (16
H, ortho, meta, para), 4.69 (br., 1 H, CHMe2), 1.18 (br., 6 H,
CHMe2) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 153.10
(Ar-F), 151.87 (Ar-O), 124.90 (Ar-C), 123.82 (Ar-C), 122.90 (Ar-
C), 115.87 (Ar-C), 71.46 (CHMe2), 24.1 (CHMe2) ppm. ESI-MS:
m/z = 1016 {(Ti(O-2-FC6H4)4(iPrOH))2 – (O-2-FC6H4) + Na}+.
C27H24F4O5Ti (552.34): calcd. C 58.71, H 4.38; found C 59.01, H
4.52.
Conclusions
In summary, we have used the alcoholysis route for syn-
thesizing several new aryloxy compounds and benzyloxy
derivatives of titanium. These compounds have high degree
of fluxionality and possess an inherent tendency for oligo-
merization in solution. They are potent activators for the
polymerization of CL and VL and some of them produce
products with exceptionally high molecular weights. The
tendency of such polymerizations can be enhanced con-
siderably by using BnOH as an initiator, resulting in telech-
elic polymers. These results are based upon a simplified ap-
proach to the polymerization of cyclic esters using mild
Lewis acids as catalysts and alcoholic initiators, using the
activated monomer mechanism. The methodology em-
ployed and the concepts reported may be considered crucial
for bulk scale procedures. The achievement of obtaining
good molecular weights without having to resort to elabo-
rate ligands is a noted feature for our system.
[Ti(O-2-ClC6H4)4]2 (3): 2-ClC6H4OH (0.25 g, 1.92 mmol) and
Ti(iPrO)4 (0.14 g, 0.48 mmol) were reacted and an identical pro-
cedure used for the synthesis of 1 was employed; yield 0.46 g, 87%;
m.p. 163 °C. 1H NMR (400 MHz, CDCl3): δ = 7.1–6.7 (16 H, ortho,
meta, para) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 161.50
(Ar-O), 129.43 (Ar-C), 128.80 (Ar-C), 123.83 (Ar-Cl), 123.12
(Ar-C), 121.14 (Ar-C) ppm. ESI-MS: m/z = 1012 {(Ti(O-2-
ClC6H4)4)2 – (O-2-ClC6H4) + Na}+. C24H16Cl4O4Ti (558.06):
calcd. C 51.65, H 2.89; found C 51.94, H 3.24.
[Ti(O-2-BrC6H4)4]2 (4): 2-BrC6H4OH (0.25 g, 1.44 mmol) and Ti-
(iPrO)4 (0.10 g, 0.36 mmol) were reacted and an identical procedure
used for the synthesis of 1 was employed; yield 0.44 g, 85%; m.p.
158 °C. 1H NMR (400 MHz, CDCl3): δ = 7.2–6.6 (16 H, ortho,
meta, para) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 162.76
(Ar-O), 132.74 (Ar-C), 128.64 (Ar-C), 122.15 (Ar-C), 116.53 (Ar-
Experimental Section
C), 113.83 (Ar-Br) ppm. ESI-MS: m/z
= 1323 {(Ti(O-2-
BrC6H4)4)2 – (O-2-BrC6H4) + Na}+. C24H16Br4O4Ti (735.86):
General Procedure: All reactions were performed under dry argon
atmosphere using standard Schlenk techniques or in a glove box
with rigorous exclusion of moisture and air. Toluene was dried by
heating under reflux over sodium and benzophenone and distilled
fresh prior to use. CDCl3 used for NMR spectral measurements
was dried with calcium hydride, distilled and stored in a glove box.
1H, 13C and 47/49Ti NMR spectra were recorded with a Bruker Av-
ance 400 instrument. Chemical shifts for 1H and 13C NMR spectra
were referenced to residual solvent resonances and are reported as
parts per million relative to SiMe4. 47/49Ti NMR spectra were re-
calcd. C 39.17, H 2.19; found C 39.38, H 1.87.
[Ti(O-3-FC6H4)4(iPrOH)]2 (5): Under an argon atmosphere, to a
stirred solution of 3-FC6H4OH (0.25 g, 2.24 mmol) in 5 mL of tol-
uene at 27 °C, was added Ti(iPrO)4 (0.16 g, 0.56 mmol). An orange
solution resulted immediately. The reaction mixture was stirred at
this temperature for a period of 12h. The solvent was removed
under reduced pressure to yield an orange yellow solid which was
purified by recrystallization from toluene at –20 °C. The crys-
tallized solid was recovered by filtration and dried in vacuo; yield
Eur. J. Inorg. Chem. 2009, 2981–2993
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2989

R. R. Gowda, D. Chakraborty, V. Ramkumar
FULL PAPER
0.56 g, 90%; m.p. 173 °C. H NMR (400 MHz, CDCl3): δ = 7.1–
(iPrOH))2 – (O-4-CF3C6H4) + Na}+. C31H24F12O5Ti (752.37):
1
6.3 (16 H, ortho, meta, para), 4.24 (br., 1 H, CHMe2), 1.16 (br., 6 calcd. C 49.49, H 3.22; found C 50.01, H 2.89.
H, CHMe2) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 164.74
[Ti(O-4-IC6H4)4(iPrOH)]2 (12): 4-IC6H4OH (0.25 g, 1.12 mmol)
(Ar-F), 162.29 (Ar-O), 130.29 (Ar-C), 114.87 (Ar-C), 109.20 (Ar-
C), 106.60 (Ar-C), 72.13 (CHMe2), 25.14 (CHMe2) ppm. ESI-MS:
m/z = 1016 {(Ti(O-3-FC6H4)4(iPrOH))2 – (O-3-FC6H4) + Na}+.
C27H24F4O5Ti (552.34): calcd. C 58.71, H 4.38; found C 59.12, H
4.56.
and Ti(iPrO)4 (0.08 g, 0.28 mmol) were reacted and an identical
procedure used for the synthesis of 5 was employed; yield 0.49 g,
89%; m.p. 185 °C. 1H NMR (400 MHz, CDCl3): δ = 7.4–6.4 (16
H, ortho, meta) 7.26–7.18 (m, C7H8), 4.22 (br., 1 H, CHMe2), 2.38
(s, C7H8), 1.12 (br., 6 H, CHMe2) ppm. 13C NMR (100 MHz,
CDCl3, –55 °C): δ = 164.60 (Ar-O), 137.80 (C7H8), 137.76 (Ar-C),
129.18 (C7H8), 128.37 (C7H8), 125.44 (C7H8), 121.17 (Ar-C), 85.50
(Ar-I), 70.40 (CHMe2), 24.76 (CHMe2), 21.92 (C7H8) ppm. 47/49Ti
NMR (22.54 MHz, CDCl3): δ = –175.72 ppm. ESI-MS: m/z = 1772
{(Ti(O-4-IC6H4)4(iPrOH))2 – (O-4-IC6H4) + Na}+. C27H24I4O5Ti
(983.96): calcd. C 32.96, H 2.46; found C 33.42, H 2.87.
[Ti(O-3-CF3C6H4)4(iPrOH)]2
(6):
3-CF3C6H4OH
(0.25 g,
1.56 mmol) and Ti(iPrO)4 (0.11 g, 0.39 mmol) were reacted and an
identical procedure used for the synthesis of 1 was employed; yield
1
0.51 g, 89%; m.p. 186 °C. H NMR (400 MHz, CDCl3): δ = 7.2–
6.6 (16 H, ortho, meta, para), 4.29 (br., 1 H, CHMe2), 1.14 (br., 6
H, CHMe2) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 164.57
(Ar-O), 132.25 (Ar-CF3), 130.14 (Ar-C), 123.73 (CF3), 122.36 (Ar-
C), 121.81 (Ar-C), 115.67 (Ar-C), 71.32 (CHMe2), 24.85 (CHMe2)
ppm. 47/49Ti NMR (22.54 MHz, CDCl3): δ = –28.07 ppm. ESI-MS:
m/z = 1366 {(Ti(O-3-CF3C6H4)4(iPrOH))2 – (O-3-CF3C6H4) +
Na}+. C31H24F12O5Ti (752.37): calcd. C 49.49, H 3.22; found C
49.65, H 2.96.
[Ti(OC6F5)4(iPrOH)]2 (13): C6F5OH (0.25 g, 1.36 mmol) and Ti(i-
PrO)4 (0.1 g, 0.34 mmol) were reacted and an identical procedure
used for the synthesis of 5 was employed; yield 0.50 g, 89%; m.p.
188 °C. 1H NMR (400 MHz, CDCl3): δ = 7.25–7.18 (m, C7H8),
4.72 (br., 1 H, CHMe2), 2.36 (s, C7H8), 1.34 (br., 6 H, CHMe2)
ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 141.29 (Ar-F),
139.41 (Ar-F), 137.00 (Ar-F), 136.99 (C7H8), 129.31 (C7H8), 129.29
(Ar-O), 128.48 (C7H8), 125.55 (C7H8), 76.94 (CHMe2), 24.31
(CHMe2), 21.20 (C7H8) ppm. ESI-MS: m/z = 1520 {[Ti(O-C6F5)4-
(iPrOH)]2 – (O-C6F5) + Na}+. C27H8F20O5Ti (840.18): calcd. C
38.60, H 0.96; found C 39.19, H 1.17.
[Ti(O-3-NO2C6H4)4(iPrOH)]2
(7): 3-NO2C6H4OH
(0.25 g,
1.80 mmol) and Ti(iPrO)4 (0.13 g, 0.45 mmol) were reacted. The
reaction mixture was stirred at 80 °C for 12h and a procedure iden-
tical to that used for the synthesis of 1 was followed; yield 0.53 g,
90%; m.p. 184 °C. 1H NMR (400 MHz, CDCl3): δ = 7.8–7.1 (16
H, ortho, meta, para), 7.25–7.18 (m, C7H8), 4.40 (br., 1 H, CHMe2),
2.35 (m, C7H8), 1.19 (br., 6 H, CHMe2) ppm. 13C NMR (100 MHz,
CDCl3, –55 °C): δ = 156.17 (Ar-O), 148.39 (Ar-NO2), 137.90
(C7H8), 130.45 (Ar-C), 129.07 (C7H8), 128.27 (C7H8), 125.26
(C7H8), 122.38 (Ar-C), 117.75 (Ar-C), 110.31 (Ar-C), 76.83
(CHMe2), 24.87 (CHMe2), 23.20 (C7H8) ppm. ESI-MS: m/z = 1205
[Ti(OC6Cl5)4(iPrOH)]2 (14): C6Cl5OH (0.25 g, 0.92 mmol) and Ti-
(iPrO)4 (0.07 g, 0.23 mmol) were reacted and an identical procedure
used for the synthesis of 5 was employed; yield 0.47 g, 87%; m.p.
178 °C. 1H NMR (400 MHz, CDCl3): δ = 7.25–7.18 (m, C7H8),
4.83 (br., 1 H, CHMe2), 2.38 (s, C7H8), 1.33 (br., 6 H, CHMe2)
ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 147.76 (Ar-O),
138.42 (Ar-Cl), 138.09 (C7H8), 131.19 (Ar-Cl), 129.08 (C7H8),
128.28 (C7H8), 125.28 (C7H8), 122.79 (Ar-Cl), 119.39 (Ar-Cl), 76.84
(CHMe2), 24.80 (CHMe2) 21.72 (C7H8) ppm. ESI-MS: 2094
{(Ti(O-3-NO2C6H4)4(iPrOH))2
–
(O-3-NO2C6H4)
+
Na}+.
C27H24N4O13Ti (660.37): calcd. C 49.11, H 3.66, N 8.48; found C
49.53, H 3.39, N 8.99.
[Ti(O-4-MeC6H4)4]2 (8): 4-MeC6H4OH (0.25 g, 2.32 mmol) and Ti-
(iPrO)4 (0.16 g, 0.58 mmol) were reacted and an identical procedure
used for the synthesis of 1 was employed; yield 0.48 g, 89%; m.p.
150 °C. 1H NMR (400 MHz, CDCl3): δ = 7.02 (d, 8 H, meta), 6.71
(d, 8 H, ortho), 2.27 (s, 12 H, ArMe) ppm. 13C NMR (100 MHz,
CDCl3, –55 °C): δ = 173.62 (Ar-O), 153.81 (Ar-C), 130.40 (Ar-
CH3), 115.41 (Ar-C), 20.8 (Ar-Me) ppm. ESI-MS: m/z = 868
{[Ti(O-C6Cl5)4(iPrOH)]2–(O-C6Cl5)
+
Na}+. C27H8Cl20O5Ti
(1169.28): calcd. C 27.73, H 0.69; found C 28.17, H 0.89.
[Ti(2,4,6-F3C6H2)2(iPrO)2]2 (15): 2,4,6-F3C6H2OH (0.20 g,
1.36 mmol) and Ti(iPrO)4 (0.19 g, 0.68 mmol) were reacted. The
reaction mixture was stirred at 80 °C for 12h and a procedure iden-
tical to that used for the synthesis of 1 was followed; yield 0.54 g,
86%; m.p. 140 °C. 1H NMR (400 MHz, CDCl3): δ = 6.48 (4 H,
meta), 4.81 (br., 2 H, CHMe2), 1.24 (br., 12 H, CHMe2) ppm. 13C
NMR (100 MHz, CDCl3, –55 °C): δ = 154.86 (Ar-F), 152.05 (Ar-
F), 138.62 (Ar-O), 99.47 (Ar-C), 82.88 (CHMe2), 24.88 (CHMe2)
ppm. ESI-MS: m/z = 795 {(Ti(2,4,6-F3C6H2)2(iPrO)2)2 – (O-2,4,6-
F3C6H2) + Na}+. C18H18F6O4Ti (460.19): calcd. C 46.98, H 3.94;
found C 47.32, H 4.36.
{(Ti(O-4-MeC6H4)4)2
– (O-4-MeC6H4) +
Na}+. C28H28O4Ti
(476.39): calcd. C 70.59, H 5.92; found C 70.80, H 5.62.
[Ti(O-4-tBuC6H4)4]2 (9): 4-tBuC6H4OH (0.25 g, 1.68 mmol) and
Ti(iPrO)4 (0.12 g, 0.42 mmol) were reacted and an identical pro-
cedure used for the synthesis of 5 was employed; yield 0.47 g, 88%;
m.p. 175 °C. 1H NMR (400 MHz, CDCl3): δ = 6.94 (d, 8 H, meta),
6.26 (d, 8 H, ortho), 1.15 (36 H, CMe3) ppm. 13C NMR (100 MHz,
CDCl3, –55 °C): δ = 163.93 (Ar-O), 143.77 (Ar-t-Bu), 125.56 (Ar-
C), 118.18 (Ar-C), 34.35 (CMe3), 31.69 (CMe3) ppm. ESI-MS: m/z
[Ti(2,4,6-Cl3C6H2)2(iPrO)2]2 (16): 2,4,6-Cl3C6H2OH (0.50 g,
2.52 mmol) and Ti(iPrO)4 (0.36 g,1.26 mmol) were reacted. The re-
action mixture was stirred at 80 °C for 12h and a procedure iden-
tical to that used for the synthesis of 1 was followed; yield 1.20 g,
86%; m.p. 155 °C. 1H NMR (400 MHz, CDCl3): δ = 7.24 (4 H,
meta), 4.77 (br., 2 H, CHMe2), 1.28 (br., 12 H, CHMe2) ppm. 13C
NMR (100 MHz, CDCl3, –55 °C): δ = 157.27 (Ar-O), 128.01 (Ar-
C), 124.35 (Ar-Cl), 121.18 (Ar-Cl), 78.39 (CHMe2), 24.71 (CHMe2)
ppm. ESI-MS: m/z = 944 {(Ti(2,4,6-Cl3C6H2)2(iPrO)2)2 – (O-2,4,6-
Cl3C6H2) + Na}+. C18H18Cl6O4Ti (558.92): calcd. C 38.68, H 3.25;
found C 39.01, H 3.30.
=
1163 {(Ti(O-4-tBuC6H4)4)2
–
(O-4-tBuC6H4)
+
Na}+.
C40H52O4Ti (644.71): calcd. C 74.52, H 8.13; found C 74.76, H
7.89.
[Ti(O-4-CF3C6H4)4(iPrOH)]2
(10): 4-CF3C6H4OH (0.25 g,
1.56 mmol) and Ti(iPrO)4 (0.11 g, 0.39 mmol) were reacted and an
identical procedure used for the synthesis of 1 was employed; yield
1
0.50 g, 88%; m.p. 180 °C. H NMR (400 MHz, CDCl3): δ = 7.4–
6.7 (16 H, ortho, meta), 4.27 (br., 1 H, CHMe2), 1.11 (br., 6 H,
CHMe2) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ = 166.90
(Ar-O), 126.50 (Ar-C), 122.38 (CF3), 120.20 (Ar-C), 115.30 (Ar-C), [Ti(O–2,4,6-Br3C6H2)2(iPrO)2]2 (17): 2,4,6-Br3C6H2OH (0.25 g,
70.94 (CHMe2), 24.82 (CHMe2) ppm. 47/49Ti NMR (22.54 MHz,
CDCl3): δ = –19.14 ppm. ESI-MS: m/z = 1366 {(Ti(O-4-CF3C6H4)4-
0.76 mmol) and Ti(iPrO)4 (0.10 g, 0.38 mmol) were reacted. The
reaction mixture was stirred at 80 °C for 12h and a procedure iden-
2990
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2981–2993

Ti-Catalyzed Polymerization of ε-Caprolactone and δ-Valerolactone
tical to that used for the synthesis of 1 was followed; yield 0.53 g,
84%; m.p. 160 °C. 1H NMR (400 MHz, CDCl3): δ = 7.57 (4 H,
(br., 6 H, CHMe2) ppm. 13C NMR (100 MHz, CDCl3, –55 °C): δ
= 157.80 (Ar-OCH3), 133.84 (OCH2Ar), 128.13 (Ar-C), 112.97 (Ar-
meta), 4.82 (br., 2 H, CHMe2), 1.32 (br., 12 H, CHMe2) ppm. 13C C), 76.35 (CHMe2), 74 ppm. 59 (OCH2Ar), 55.22 (Ar-OCH3),
NMR (100 MHz, CDCl3, –55 °C): δ = 158.29 (Ar-O), 133.70 (Ar-
C), 114.43 (Ar-Br), 113.38 (Ar-Br), 89.03 (CHMe2), 25.47
26.42 (CHMe2) ppm. ESI-MS: m/z
OMeC6H4)4(iPrOH))2 (O-CH2-4-OMeC6H4)
C35H44O9Ti (656.59): calcd. C 64.02, H 6.75; found C 64.29, H
=
1199 {(Ti(O-CH2-4-
–
+
Na}+.
(CHMe2) ppm. 47/49Ti NMR (22.54 MHz, CDCl3):
δ
=
–25.41 ppm. ESI-MS: m/z = 1343 {(Ti(2,4,6-Br3C6H2)2(iPrO)2)2 – 6.71.
(O-2,4,6-Br3C6H2) + Na}+. C18H18Br6O4Ti (825.62): calcd. C
26.19, H 2.20; found C 26.28, H 2.32.
X-ray Structure Determination of Compounds 2, 5, 6 and 11: Single
crystals suitable for structural studies were obtained by crystalli-
zation from toluene at –23 °C. X-ray data collection was performed
with Bruker AXS (Kappa Apex 2) CCD diffractometer equipped
with graphite-monochromated Mo (Kα) (λ = 0.7107 Å) radiation
source. The data were collected with 100% completeness for θ up
to 25°. ω and φ scans was employed to collect the data. The frame
width for ω was set to 0.5° for data collection. The frames were
integrated and data were reduced for Lorentz and polarization cor-
rections using SAINT-NT. The multi-scan absorption correction
was applied to the data set. All structures were solved using SIR-
92 and refined using SHELXL-97.[70] The crystal data are summa-
rized in Table 7. The non-hydrogen atoms were refined with aniso-
tropic displacement parameter. All the hydrogen atoms could be
located in the difference Fourier map. The hydrogen atoms bonded
to carbon atoms were fixed at chemically meaningful positions and
were allowed to ride with the parent atom during refinement. In 2,
the carbon atoms C(15), C(16) and C(17) in the phenyl ring are
distorted over two orientations in the ratio of 0.3985(3): 0.6015(2).
The fluorine atoms F(3) and F(4) are disordered over two orienta-
tions in the ratio of 0.8223(2): 0.1777(2) and 0.7103(3): 0.2897(3)
respectively.
[Ti(O–2,4,6-I3C6H2)2(iPrO)2]2 (18): 2,4,6-I3C6H2OH (0.50 g,
1.06 mmol) and Ti(iPrO)4 (0.15 g, 0.53 mmol) were reacted. The
reaction mixture was stirred at 80 °C for 12h and a procedure iden-
tical to that used for the synthesis of 1 was followed; yield 1.0 g,
83%; m.p. 162 °C. 1H NMR (400 MHz, CDCl3): δ = 7.97 (4 H,
meta), 4.92 (br., 2 H, CHMe2), 1.36 (br., 12 H, CHMe2) ppm. 13C
NMR (100 MHz, CDCl3, –55 °C): δ = 162.91 (Ar-O), 146.32 (Ar-
C), 88.97 (CHMe2), 83.93 (Ar-I), 83.40 (Ar-I), 25.71 (CHMe2)
ppm. ESI-MS: m/z = 1767 {(Ti(2,4,6-I3C6H2)2(iPrO)2)2 – (O-2,4,6-
I3C6H2) + Na}+. C18H18I6O4Ti (1107.63): calcd. C 19.52, H 1.64;
found C 19.93, H 1.31.
[Ti(O-CH2–4-MeC6H4)4]2 (19): 4-MeC6H4CH2OH (0.25 g,
2.00 mmol) and Ti(iPrO)4 (0.14 g, 0.50 mmol) were reacted and an
identical procedure used for the synthesis of 1 was employed. A
yellow oil was obtained; yield 0.47 g, 89%. 1H NMR (400 MHz,
CDCl3): δ = 7.1–7.0 (16 H, ortho, meta), 4.57 (s, 8 H, OCH2Ar),
2.17 (s, 12 H, ArCH3) ppm. 13C NMR (100 MHz, CDCl3, –55 °C):
δ = 138.32 (OCH2Ar), 137.71 (Ar-CH3), 129.40 (Ar-C), 127.49 (Ar-
C), 64.96 (OCH2Ar), 22.13 (Ar-CH3) ppm. ESI-MS: m/z = 967
{(Ti(O-CH2-4-MeC6H4)4)2
–
(O-CH2-4-MeC6H4)
+
Na}+.
C32H36O4Ti (532.49): calcd. C 72.18, H 6.81; found C 72.39, H
6.69.
General Procedure for the Polymerization of CL and VL: For CL
polymerization, 23.6 µmol of the aryloxy compound and benzyloxy
[Ti(O-CH2-4-OMeC6H4)4(iPrOH)]2 (20): 4-MeOC6H4CH2OH derivative alone or along with requisite amount of benzyl alcohol
(0.25 g, 1.80 mmol) and Ti(iPrO)4 (0.13 g, 0.45 mmol) were reacted
and an identical procedure used for the synthesis of 1 was em-
were taken in a flask under an argon atmosphere. The contents
were stirred at 80 °C and 0.50 mL of CL (0.54 g, 4.71 mmols) was
ployed. A pale yellow oil was obtained; yield 0.53 g, 90%. 1H NMR added neat. The mixture was rapidly stirred at the given tempera-
(400 MHz, CDCl3): δ = 7.1–6.7 (16 H, ortho, meta), 5.14 (br., 8 H,
OCH2Ar), 4.42 (br., 1 H, CHMe2), 3.75 (br., 12 H, ArOCH3), 1.12
ture. A rise in viscosity was observed and finally the stirring ceased.
For VL polymerization, 26.9 µmol was used for 0.50 mL (0.54 g,
Table 7. Crystal data for the structures 2, 5, 6 and 11.[a]
Compound
2
5
6
11
Empirical formula
Formula weight
Crystal system
Space group
Temp. [K]
Wavelength [Å]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C54H48F8O10Ti2
1104.72
monoclinic
P21/n
C27H24F4O5Ti
552.36
triclinic
P1
173
C31H24F12O5Ti
752.37
triclinic
P1
173
C27H24F4O5Ti
552.36
monoclinic
P21/c
173
173
0.71073
10.6437(5)
17.6519(10)
13.9814(8)
90
103.592(2)
90
2553.3(2)
2
1.432
0.71073
0.71073
0.71073
19.1921(5)
15.2752(3)
17.7851(4)
90
98.995(10)
90
5149.8(2)
8
1.425
11.1460(3)
13.5661(4)
18.7052(5)
101.2210(10)
96.7120(10)
110.5170(10)
2545.04(12)
4
1.442
34037
11677
1.028
11.2724(7)
12.0050(7)
13.1236(8)
102.526(3)
103.107(3)
105.029(3)
1598.01(17)
2
1.562
21633
6639
1.023
γ [°]
V [Å3]
Z
Dcalc [Mg/m3]
Reflections collected
Independent reflections
GOF
18679
5856
1.030
65450
12563
1.225
Final R indices [IϾ2σ(I)]
R1 = 0.0462
wR2 = 0.1150
R1 = 0.0719
wR2 = 0.1310
R1 = 0.0474
wR2 = 0.1379
R1 = 0.0623
wR2 = 0.1513
R1 = 0.0633
wR2 = 0.1613
R1 = 0.0984
wR2 = 0.1848
R1 = 0.0475
wR2 = 0.1485
R1 = 0.0763
wR2 = 0.1780
R indices [all data]
[a] R1 = ∑|Fo| – |Fc|/∑|Fo|, wR2 = [∑ (Fo – Fc ) /∑w(Fo2)2]1/2
.
2
2 2
Eur. J. Inorg. Chem. 2009, 2981–2993
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www.eurjic.org
2991

R. R. Gowda, D. Chakraborty, V. Ramkumar
FULL PAPER
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Supporting Information (see also the footnote on the first page of
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CCDC-724718 (for 2), -724721 (for 5), -724720 (for 6) and -724719
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Acknowledgments
This work was supported by Department of Science and Technol-
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under the FIST program, sponsored by the Department of Science
and Technology, New Delhi is gratefully acknowledged. The au-
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Received: March 25, 2009
Published Online: June 3, 2009
Eur. J. Inorg. Chem. 2009, 2981–2993
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2993