New isopropylmaltol - Ti synthesis and its use as a catalyst for olefin polymerization

Article abstract of DOI:10.5935/0103-5053.20140192

This report describes a new synthesis of isopropylmaltol from furfural. This organic compound was used as ligand to obtain a new complex, the dichlorobis-(3-hydroxy-2-isopropyl-4-pyrone) titanium(IV). 1H nuclear magnetic ressonance, elemental analysis and UV-Vis analysis confirm the complex formation. This complex was investigated in ethylene polymerization using methylaluminoxane (MAO) as cocatalyst. The catalytic activity was low, however, there were obtained very high molecular weight polyethylenes, which are interesting for various special applications.

Full text of DOI:10.5935/0103-5053.20140192

http://dx.doi.org/10.5935/0103-5053.20140192
J. Braz. Chem. Soc., Vol. 25, No. 12, 2258-2265, 2014.
Printed in Brazil - ©2014 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
New Isopropylmaltol - Ti Synthesis and its Use as a Catalyst for Olefin
Polymerization
Grasiela Gheno,a Nara R. S. Basso,b Marco A. Ceschi,a Jessie S. Costa,a
Paolo R. Livottoa and Griselda B. Galland*,a
aInstituto de Química, Universidade Federal do Rio Grande do Sul,
Avenida Bento Gonçalves No. 9500, 91501-970 Porto Alegre-RS, Brazil
bFaculdade de Química, Pontifícia Universidade Católica do Rio Grande do Sul,
Avenida Ipiranga No. 6681, 90619-900 Porto Alegre-RS, Brazil
Este artigo mostra a síntese e caracterização do ligante isopropilmaltol obtido a partir do
furfural e também um novo complexo diclorobis-(3-hidroxi-2-isopropil-4-pirona)titânio(IV) com
estrutura cis. Dados de ressonância magnética nuclear de 1H, análise elementar e UV-Vis confirmam
a formação do complexo. Este complexo foi estudado em reações de polimerização de etileno
utilizando metilaluminoxano (MAO) como co-catalisador. A atividade catalítica deste complexo
é baixa, entretanto foram obtidos polietilenos com alto peso molecular que são interessantes para
diferentes aplicações.
This report describes a new synthesis of isopropylmaltol from furfural. This organic compound
was used as ligand to obtain a new complex, the dichlorobis-(3-hydroxy-2-isopropyl-4-pyrone)
titanium(IV). 1H nuclear magnetic ressonance, elemental analysis and UV-Vis analysis confirm
the complex formation. This complex was investigated in ethylene polymerization using
methylaluminoxane (MAO) as cocatalyst. The catalytic activity was low, however, there were
obtained very high molecular weight polyethylenes, which are interesting for various special
applications.
Keywords: synthesis, complex, isopropylpyrone, polymerization, polyethylene
Introduction
prevent many diseases. Divalent ions such as Zn2+, Ru2+,
[VO]2+, [MoO2]2+ and trivalent cations (Fe3+, Al3+, Ga3+)
may be used in the synthesis of thermodynamically stable
complexes with hydroxypyrone ligands.1 Some studies
with the 2-methyl-3-hydroxypyrone complex (maltolato)
are reported in the literature for biomedical purposes such
as maltol-oxovanadium(III),2 maltol-ruthenium,3 maltol-
molybdenum(IV),4 among others.
In parallel to the studies focused on medicine, the
coordination chemistry of organometallic complexes
containing hydroxypyrone ligands with transition metals
have also been investigated. These ligands can also form
ML2X2 complexes, where X = halogen and M = metal, with
group IV transition metals, such as Ti and Zr.5 In 2001,
Sobota et al.6 synthesized a new non-metalloceneTi-complex
based on bidentate maltol ligand, dichlorobis-(3-hydroxy-
2-methyl-4-pyrone)titanium(IV). This complex was tested
in homogeneous olefin polymerization. The complex was
obtained in octahedral coordination where the Ti metal is
Hydroxypyrones are versatile compounds that have
been used in food, pharmaceutical, biological and medical
applications. These compounds are six-membered
heterocyclics with a hydroxyl group bonded in the ortho
position, in relation to ketone group, providing two donor
oxygens (Figure 1). Several studies have shown that
these compounds can form stable complexes with various
metal ions to be used in the body as a way to combat and
Figure 1. Structure of maltolato compounds.
*e-mail: griselda.barrera@ufrgs.br

Vol. 25, No. 12, 2014
Gheno et al.
2259
surrounded by four oxygen atoms from two ligand molecules
and two chlorines in the cis position. This complex was
active in ethylene polymerization reactions, suggesting that
maltolato ligands could represent a good alternative to the
cyclopentadienyl ring of metallocene catalysts.6
2 mol L−1 in ethyl ether), furfural (Aldrich, 99%), meta-
chloroperoxybenzoicacid- m-CPBA (Acros-Organics,
70-75%), methyl iodide (Aldrich, 99%), silver oxide
(Aldrich), hydrogen peroxide (Nuclear, 30%) and
1,4-dioxane (GrupoQuímica). Ethyl ether was dried by
initial refluxing over potassium hydroxide and posterior
refluxing over metallic sodium and benzophenone as
indicator. Dichloromethane was dried by refluxing over
phosphorus pentoxide. Acetone was dried by refluxing over
magnesium permanganate (KMnO4) and magnesium sulfate
(MgSO4). Purification by column chromatography was
carried out on silica gel 60 (70-230 mesh). Analytical thin
layer chromatography (TLC) was conducted on aluminum
plates with 0.2 mm of silica gel 60F-254 (Macherey e Nagel).
Subsequently, our research group synthesized the
analogous zirconium complex, dichlorobis-(3-hydroxy-2-
methyl-4-pyrone)zirconium(IV), and also dichlorobis-(2-
hydroxy-1,4-naphthoquinone)zirconium(IV). The catalytic
activity of these complexes was compared in homogeneous
and heterogeneous ethylene polymerization. The complex
from the methylpyrone ligand was more active than the
one with naphthoquinone ligand, in both homogeneous
and heterogeneous conditions, when supported on SiO2 and
SiO2/methylaluminoxane (MAO) modified silica.7 Later, we
studied the catalytic activity of the dichlorobis-(3-hydroxy-2-
methyl-4-pyrone)titanium(IV) complex in different supports,
such as SiO2, SiO2/MAO, MCM-41, Al2O3, ZrO2 and MgO.
Results of ethylene polymerization reactions showed that
most of these heterogeneous systems were more active than
the homogeneous complex, and the complexes supported
in SiO2 948, MCM-41 and alumina showed the highest
catalytic activities.8 Basso noted that the catalytic activity
of titanium and zirconium complexes from methylpyrone
ligand depends on the metal and the Al/M ratio. In this
study, the Zr complex was more active than the analogous Ti
complex in the ethylene polymerization usingAl/M = 2500,
while the Ti complex was more active at lowerAl/M ratios.9
Other analogous bidentate zirconium complex derived from
3-hydroxy-2-ethyl-4-pyrone (ethylmaltol) has been proposed
for the ethylene polymerization. The polyethylene obtained
showed, depending on the synthesis conditions, high
molecular weight polyethylene. These studies have shown
that the exchange of the methyl substituent by an ethyl in
the pyrone ligand exerts a great influence on the catalytic
activity, regardless of the metal used, resulting in higher
catalytic activities.10
For synthesis of the complex
All experiments were performed under argon atmosphere
using the schlenk technique. Titanium tetrachloride (Merck)
was used without purification. Dichloromethane was dried
by refluxing over phosphorus pentoxide. Ethyl ether,
hexane and toluene (Nuclear) were dried by refluxing over
metallic sodium, under nitrogen, and using benzophenone
as indicator. MAO (Witco, 10% m/mAl in toluene solution)
was employed as received.
Synthesis of the isopropylmaltol ligand
1-(2-furyl)-2-methyl-1-propanol (1)
Isopropylmagnesium chloride (35 mL, 71.0 mmol) was
added to a solution of furfural (5.5 g, 57.0 mmol) in dried
Et2O (60 mL) at −78 °C under an argon atmosphere. The
reaction was stirred at the same temperature for 45 min.
The reaction mixture was warmed to 0 °C and stirred for
an additional 2 h. The consumption of starting material
was observed by TLC. Next, the reaction mixture was
cooled again to −78 °C and was quenched with saturated
NH4Cl solution. The organic layer was separated and the
aqueous layer was extracted with Et2O (3 × 100 mL).
The combined organic layers were dried over anhydrous
Na2SO4, filtered and evaporated under reduced pressure to
afford 1 (43.9 mmol, 6.1 g, 77%) as a yellow oil. 1H NMR
(300 MHz, CDCl3/TMS), d (ppm): 7.35 (dd, J 1.8, 0.9 Hz,
=CH), 6.32 (dd, J 3.3, 1.8 Hz, =CH), 6.21 (d, J 3.3 Hz,
=CH), 4.80-4.60 (m, CHOH), 2.23 (br, OH), 2.02-2.16
(m, CH), 1.00 (d, J 6.7 Hz, CH3), 0.84 (d, J 6.7 Hz, CH3);
13C NMR (75 MHz, CDCl3/TMS), d (ppm): 156.4, 141.8,
110.2, 106.6, 73.6, 33.4, 18.8, 18.4.
As part of our studies directed towards organometallics
complex synthesis, this paper reports a new synthesis of
a maltolato compound, isopropylmaltol, its complexation
with TiCl4 and the use as catalyst in the ethylene
polymerization.
Experimental
Reagents and materials
For the synthesis of the isopropylmaltol ligand
All solvents (Nuclear, Aldrich, FMaia, Ecibra) and
chemicals were reagent grade and used without further
purification: isopropylmagnesium chloride (Aldrich,
6-hydroxy-2-isopropyl-3-pyrone (2)
To a solution of 1 (700.9 mg, 5.0 mmol) in dried CH2Cl2
(24 mL) at 0 °C was slowly added m-CPBA (1.72 g,

2260
New Isopropylmaltol - Ti Synthesis and its Use as a Catalyst for Olefin Polymerization
J. Braz. Chem. Soc.
10.0 mmol). The resulting mixture was stirred for 1 h at
this same temperature. After this time, the mixture was
cooled to −75 °C and filtered on Büchner funnels. The
solvent was removed under reduced pressure, and the crude
product purified by column chromatography on silica gel
(eluting with hexane:ethyl acetate:acetic acid, 90:9:1) to
afford 2 (468 mg, 3.0 mmol, 60%) as a yellow oil and as a
7:3 mixture of diastereomers. 1H NMR (300 MHz, CDCl3/
TMS), d (ppm): 6.97-6.88 (m, =CH), 6.17-6.08 (m, =CH),
5.70-5.62 (m, =CH), 4.42 (d, J 2.4 Hz, majority isomer,
CHCO), 3.92 (dd, J 2.5, 1.0 Hz, minority isomer, CHCO),
4.00 (br, OH), 2.50-2.38 (m, CH(CH3)2), 1.03 and 0.88
(2d, J 5.1 Hz, majority isomer, 2CH3), 1.05 and 0.94 (2d,
J 5.1 Hz, minority isomer, 2CH3); 13C NMR (75 MHz,
CDCl3/TMS), d (ppm): majority isomer: 197.7, 145.4,
127.8, 87.5, 78.4, 28.7, 19.0, 16.3; minority isomer: 197.1,
149.1, 129.3, 91.2, 83.1, 28.9, 19.1, 16.5.
3-hydroxy-2-isopropyl-4-pyrone (5)
1,4-dioxane (1.8 mL) and H2O (0.9 mL) were added
to the previous crude product. To the resulting solution
concentrated H2SO4 (0.35 mL) was added. The reaction
mixture was stirred under reflux for 5 h. Next, H2O (5 mL)
was added, and the reaction mixture was extracted with
CH2Cl2 (4 × 5 mL). The combined organic layers were
dried over anhydrous Na2SO4, filtered and evaporated
under reduced pressure. The crude product was purified
by column chromatography on silica gel (eluting with
hexane:ethyl acetate, 80:20) to afford 5 (170 mg, 1.1 mmol,
55% over two steps) as a yellow oil. 1H NMR (300 MHz,
CDCl3/TMS), d (ppm): 7.77 (d, J 5.5 Hz, =CH), 6.45 (d,
J 5.5 Hz, =CH), 3.38 (septet, J 6.9 Hz, CH(CH3)2), 1.26
13
(d, J 6.9 Hz, 2 CH3); C NMR (75 MHz, CDCl3/TMS),
d (ppm): 173.6, 157.1, 154.4, 141.7, 113.1, 27.5, 19.3.
Synthesis of the dichlorobis-(3-hydroxy-2-isopropyl-4-
pyrone)titanium(IV) complex
2-isopropyl-6-methoxy-3-pyrone (3)
A mixture of compound 2 (312.4 mg, 2.0 mmol),
methyl iodide (1 mL, 16.0 mmol) and Ag2O (231.7 mg,
1.0 mmol) was stirred at room temperature for 18 h with
the exclusion of light. The crude mixture was purified
by column chromatography on silica gel (eluting with
hexane:ethyl acetate, 97:3) to afford 3 (255 mg, 1.5 mmol,
75%) as a yellow oil. 1H NMR (300 MHz, CDCl3/TMS),
d (ppm): 6.86 and 6.84 (2dd, J 10.2, 1.5 Hz and J 10.2,
3.6 Hz, =CH), 6.12 and 6.07 (2dd, J 10.2, 1.6 Hz and
J 10.2, 0.6 Hz, =CH), 5.24 (dd, J 3.0, 1.5 Hz, CHOCH3),
5.13 (d, J 3.6 Hz, CHOCH3), 4.25 (d, J 2.7 Hz, CH),
3.86 (dd, J 3.7, 1.3 Hz, CH), 3.57 and 3.50 (2s, 2OCH3),
2.42 (m, CH(CH3)2), 1.08 and 1.05 (2d, J 5.7 Hz, 2CH3),
0.95 and 0.89 (2d, J 6.7 Hz, 2CH3); 13C NMR (75 MHz,
CDCl3/TMS), d (ppm): 196.7, 196.3, 147.1, 143.3, 129.6,
128.2, 97.2, 94.1, 83.0, 78.0, 56.3, 56.1, 29.2, 28.3, 19.2,
19.1, 16.7, 16.0.
To a solution of isopropylmaltol ligand (130 mg,
0.84 mmol) in dichloromethane, in argon atmosphere was
dropwise added titanium tetrachloride, TiCl4, (0.05 mL,
0.45 mmol) using a syringe. The mixture was stirred at
room temperature for 1.5 h. Then, the solid was washed
twice with diethyl ether, dissolved in dichloromethane and
recrystallized in hexane. The complex was dried under
vacuum. The dichlorobis(3-hydroxy-2-isopropyl-4-pyrone)
titanium(IV), isopropylmaltol-Ti, complex yield 85% a
brown solid. Elemental analysis: % theoretical calculated
for C16H18O6TiCl2 (M = 424.77 g mol−1): C 45.20%,
H 4.24%, found: C 43.92%, H 4.07%; 1H NMR (300 MHz,
CDCl3), d (ppm): 8.07 (d, J 5.1 Hz, 1H, H6, isomerA), 7.35
(d, J 6.2 Hz, 1H, H6, isomer B), 6.64 (d, J 5.1 Hz, 1H, H5,
isomerA), 6.06 (d, J 6.2 Hz, 1H, H5, isomer B), 3.48 (m(7),
J 6.9 Hz, 1H, H7, isomer A), 2.78 (m(7), J 6.8 Hz, 1H, H7,
isomer B), 1.31 (d, J 6.9 Hz, 6H, H8,9, isomer A), 1.10 (d,
J 6.8 Hz, 6H, H8,9, isomer B).
2-isopropyl-6-methoxy-3-pyrone (4)
To a solution of compound 3 (340.4 mg, 2.0 mmol) in
ethyl ether (4 mL) at 0 °C was added 5% aqueous Na2CO3
(1 mL) and 15% H2O2 (0.9 mL). The resulting mixture was
stirred at 0 °C for 2.5 h. Next, 30% H2O2 (0.45 mL) was
additionally added and the reaction remained at the same
temperature. After 2 h, 30% H2O2 (0.45 mL) was further
added and the reaction mixture was stirred at 0 °C for an
additional 2 h. Then saturated NaCl (4 mL) was added
and the aqueous layer was extracted with Et2O (4 × 5 mL).
The combined organic layers were dried over anhydrous
Na2SO4, filtered and evaporated under reduced pressure.
The resulting oil was directly used for the next step without
further purification.
Polymerization reactions
Ethylene polymerizations were performed in a PARR
4843 reactor with 100 mL capacity. Into the reactor was
added 30 mL of toluene, methylaluminoxane as co-catalyst
(co-catalyst/catalyst ratio: 1500 and 2500) and 1 µmol of
catalyst. The polymerization reactions were performed at
2.8, 4 and 6 bar of ethylene at 40 °C during 30 min. The
polymerization temperature of 40 °C was chosen because
previous works9 showed that similar Ti complexes have the
highest catalytic activities at this temperature. Acidified
ethanol with chloride acid was used to quench the process,

Vol. 25, No. 12, 2014
Gheno et al.
2261
and reaction products were separated by filtration, washed
with ethanol and acetone, and finally dried.
(HT6, HT5, HT4, HT3). The mobile phase used was
trichlorobenzene (TCB) with 0.1% of butyl hydroxytoluene
(BHT) at 150 °C at a flow rate of 1 mL min−1.
Ligand and complex characterization
Results and Discussion
1
The H NMR spectra of the organic compounds of
ligand synthesis and the complex were recorded on a
Varian Inova 300 Spectrometer, using CDCl3 as solvent.
The UV-Vis absorption spectra of the isopropylmaltol
ligand and the complex were recorded on aVarian Cary 100
spectrophotometer with quartz cells of 1 cm path length
at room temperature. The analyses were performed using
toluene as solvent. Elemental analysis (C, H) of the complex
was performed in a 240 PERKIN-ELMER.
The synthesis of isopropylmaltol was previously
reported by Thompson et al., that obtained 15% yield
starting from furanaldehyde.18 For this synthesis, molecular
bromine was used in the conversion of 1-(2-furyl)-2-
methyl-1-propanol in isopropylmaltol, this reaction is
also known as Achmatowicz rearrangement which may
alternatively employ different oxidants and reaction
conditions.19 Several attempts made in our laboratory to
obtain the isopropylmaltol using the procedure described
by Thompson failed. Thus, we have developed a synthetic
method for obtaining isopropylmaltol as shown in Scheme 1.
The transformation of 1-(2-furyl)-2-methyl-1-propanol to
pyranone was performed in presence of m-CPBA. Column
chromatography provided the compound in 60% yield.
Subsequent allylic alcohols were O-methylated with MeI
and Ag2O followed by epoxidation with 30% H2O2. The
resulting oil was directly used for the next step without
further purification.
Next, isopropylmaltol was conveniently obtained by
heating the intermediate in the presence of sulfuric acid
and dioxane, as outlined by Torii protocol, to afford the
product with 55% of yield over two steps.20 Figure 2 shows
1H NMR andAPT 13C NMR of the isopropylmaltol ligand.
The complex isopropylmaltol-Ti was synthesized
from the isopropylmaltol ligand and TiCl4 (Figure 3).
The complexation reaction in dichloromethane at room
temperature is extremely rapid. When adding the metal salt
to the ligand, an orange color typical of titanium complex,
is observed immediately. The complex formation can be
proved comparing the NMR spectra of the ligand and the
complex (Figures 2 and 4).
Theoretical calculations
The geometries and energies of all possible isomeric
species of the complex and their conformers, were obtained
by full unconstrained optimizations performed at density
functional theory (DFT) level using the B3LYP hybrid
functional obtained by the three parameter fit of the
exchange-correlation potential suggested by Becke,11 and
the gradient corrected correlation functional of Lee, Yang
and Parr.12 The polarized Dunning-Huzinaga DZ basis
setwas used for the hydrogen, carbon, oxygen and chlorine
atoms.13,14 For the titanium atom, the inner shell electrons
were represented by the LosAlamos effective core potential
(LANL2) of Hay and Wadt,15,16 and the valence electrons
were explicitly included using the associated DZ basis
set. All calculations were performed with the Gaussian
03 program using standard procedures and parameters.17
Polymer characterization
The melting points (Tm) and crystallinities (Xc) of the
polymers were determined using a differential scanning
calorimeter (DSC) Q20 TA Instruments with heating of
20-160 °C and heating rate of 10 °C min−1 with 50 mL min−1
of N2 flow rate. The heating cycle was performed twice,
but only the results of the last scan were considered. The
molar masses and molar mass distributions were measured
by gel permeation chromatography (GPC) PL 220 Polymer
with RI and VI detector equipped with Water columns
The hydroxyl group resonance signal at 7.00 ppm in the
1H NMR spectrum of the isopropylmaltol ligand disappears
in the complex spectrum, indicating deprotonation of the
ligand and insertion of the titanium metal. Furthermore,
it was visualized the formation of two isomers of the
isopropylmaltol-Ti complex, A and B, which, through the
integrals of the respective protons, it was observed that A
Scheme 1. Steps of the synthesis of isopropylmaltol ligand.

2262
New Isopropylmaltol - Ti Synthesis and its Use as a Catalyst for Olefin Polymerization
J. Braz. Chem. Soc.
Figure 2. NMR spectra of isopropylmaltol ligand: (a) 1H NMR and (b) APT 13C NMR.
Figure 3. Synthesis of the isopropylmaltol-Ti complex from
isopropylmaltol.
isomer is found in greatest proportion (90%) in relation to
B isomer (10%). The coordination of the oxygen atoms
ligand with the metal also deshielded proton H5 and H6
from the major isomer (A) showing a donation of electron
density to the metal.
Figure 4. 1H NMR spectra of the isopropylmaltol-Ti complex.
The formation of isomers in the complex was studied by
theoretical calculations using the DFT. Table 1 shows the
relative energies and percentage population of each possible
isomer. The calculations indicate the existence of five
possible different stable geometric isomers resulting from
different arrangements of chlorine atoms in the titanium
complex. Two isomers can have trans configuration and
three cis configuration. Each isomer can also have four
conformers and, in the higher symmetry isomers, equivalent
conformers can also occur. Table 1 shows the molecular
and relative energies of the lowest energy configuration
of the system, as well as a percentage population estimate
for each isomeric species discriminated in its possible
conformations considering 298 K temperature. Figure 6

Vol. 25, No. 12, 2014
Gheno et al.
2263
Table 1. Molecular energies and energies relating to more stable
configuration of isopropylmaltol-Ti complex
proportion is cis3 with 96.72% of the total population,
followed by cis2 with 3.28% percentage share. The other
isomers have insignificant percentage and should not be
observed in the NMR spectrum. In fact, Figure 5 shows
the presence of only two isomers, A and B, in different
proportions. Probably, the major isomer, A, is the cis3
structure and the lower abundance, B, is the cis2. The
production of compounds with chlorides in the cis position
is desirable because only the cis structures are active in
the olefin polymerization.9 Therefore, the two isomers
obtained in this complex synthesis can be considered active
in ethylene polymerization reactions.
The isopropylmaltol-Ti complex was also characterized
by UV-Vis spectroscopy. The ligand absorption due
maltolate group appears as narrow peak at λmax = 378 nm.
The spectra of the titanium complex presents an absorption
at λmax = 355 nm, as a broad band attributable to metal-to-
ligand charge transfer transitions between titanium and
isopropylmaltol ligand suggesting the coordination of the
maltolate ligand.4
Relative energy /
Isomer
Energy / hartree
Population / %a
(kcal mol–1)
8.735
9.424
9.238
9.923
6.084
6.843
7.682
5.940
6.528
7.135
1.977
2.656
2.675
3.354
0.000
0.656
1.215
Trans1aa
Trans1ab
Trans1ba
Trans1bb
Trans2aa
Trans2ab
Trans2bb
Cis1aa
−1160.2388974
−1160.2377985
−1160.2380957
−1160.2370044
−1160.2431210
−1160.2419126
−1160.2405752
−1160.2433504
−1160.2424144
−1160.2414471
−1160.2496661
−1160.2485844
−1160.2485542
−1160.2474714
−1160.2528171
−1160.2517721
−1160.2508806
−
−
−
−
−
−
−
−
Cis1ab
−
Cis1bb
−
Cis2aa
1.89
0.61
0.59
0.19
54.05
35.72
6.95
Cis2ab
Cis2ba
Cis2bb
Cis3aa
Cis3ab
Cis3bb
aat room temperature, 298 K.
shows calculated structure cis2 and cis3 isomer in its
lowest energy conformation that it is responsible for
the largest fraction population percentage. From all the
isomeric structures calculated, only two isomers with cis
configuration, cis2 and cis3, have energies related to lower
energy configuration lower than 4 kcal mol−1 and population
percentage over 0.01%. The isomer which is in greater
Figure 5. 1H NMR expanded spectra of the isopropylmaltol-Ti complex.
Figure 6. Structure of the Cis2 and Cis3 possible isomer isopropylmaltol-Ti complex.

2264
New Isopropylmaltol - Ti Synthesis and its Use as a Catalyst for Olefin Polymerization
J. Braz. Chem. Soc.
Table 2. Catalytic activity and properties of the homogeneous ethylene polymerization catalyzed by isopropylmaltol-Ti complex at different conditions
Ethylene pressure
/ bar
Activity/
(kgPE mol−1 h−1 bar−1)
Mwc × 103 /
(g mol−1)
entry
Al/M
Tm / °C
Tc / °C
χc / %
Mw/Mn
1
2
3
4
1500
1500
2500
2500
2.8
6
20
25
45
32
134
135
138
136
118
118
116
117
45
32
43
45
nd
nd
5.3
3.8
5.1
870
690
870
4
6
Reaction conditions: solvent: toluene; time: 30 min; cocatalyst: methylaluminoxane; [catalyst]: 10−6 mol; temperature: 40 °C; nd: not determined;
χc: crystallinity.
Ethylene polymerization
Acknowledgements
The results of the ethylene polymerization reactions
with the synthesized isopropylmaltol-Ti complex are
shown in Table 2. It can be observed that, despite the
low catalytic activity presented by the complex, it was
possible to polymerize ethylene in the presence of MAO
as cocatalyst, at ratios ofAl/Ti 1500 and 2500. Comparing
these results with those presented by Basso,9 with the
analogue complex dichlorobis(3-hydroxy-2-methyl-
pyrone)titanium(IV) under the same reaction conditions
(Al/Ti = 2500, T = 40 °C) is observed that both complexes
have very similar catalytic activities.
The polymers obtained were high density polyethylene
as it can be seen by the melting and crystallization
temperatures and the degree of crystallization. The
materials have all very high molecular weight with
distribution between 3.8-5.3. This high polydispersity could
be attributed to the presence of more than one isomer active
in the ethylene polymerization. However, a more detailed
work must be done in the future in order to understand better
the catalytic system. Those results show the potentiality of
these products that can be interesting for production of high
density polyethylene (HDPE) with good processability.
We thank CAPES, FAPERGS-PRONEX and CNPq for
financial support.
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Conclusions
A new methodology was described for isopropylmaltol
synthesis. The Ti-complex was synthesized using metal salt,
TiCl4, and it was obtained as two isomers with the chlorine
atoms in cis position, what it was proven by NMR and
DFT theory. The isopropylmaltol-Ti complex was used as
catalyst on ethylene polymerization. Different experimental
conditions were tested such as ethylene pressures and
cocatalyst (methylalumonixane)/catalyst ratios but the
catalytic activities were low, however, similar to analogous
complexes described in the literature. Moreover, it was
obtained high density polyethylenes with very high
molecular weights, which could be interesting for several
uses (ex. fibers, etc.).
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Submitted on: June 9, 2014
Published online: August 15, 2014