Controlled synthesis of novel aryloxide polynuclear aluminum species. Study of their catalytic properties in polymerization processes

Article abstract of DOI:10.1021/om800086a

The reaction of AlMe₃ with 3,5-(CF₃) ₂C₆H₃OH at room temperature renders the dinuclear [AlMe₂(OR)]₂ (1) (OR = 3,5-(CF₃) ₂C₆H₃O), trinu

Full text of DOI:10.1021/om800086a

2300
Organometallics 2008, 27, 2300–2305
Controlled Synthesis of Novel Aryloxide Polynuclear Aluminum
Species. Study of Their Catalytic Properties in Polymerization
Processes†
Gema Martínez, Sergio Pedrosa, Vanessa Tabernero, Marta E. G. Mosquera,* and
Tomás Cuenca*
Departamento de Química Inorgánica. Facultad de Farmacia, UniVersidad de Alcalá.
28871 Alcalá de Henares, Madrid, Spain
ReceiVed January 31, 2008
The reaction of AlMe3 with 3,5-(CF3)2C6H3OH at room temperature renders the dinuclear [AlMe2(OR)]2
(1) (OR ) 3,5-(CF3)2C6H3O), trinuclear {[AlMe2(OR)]2[AlMe(OR)2]} (2), or tetranuclear {[AlMe2(OR)]2-
[AlMe(OR)2]2} (3) derivative depending on the reaction conditions (solvent and stoichiometry of the
reagents). All compounds have been characterized by elemental analysis and NMR spectroscopy, and
their crystal structures determined by X-ray diffraction methods. Catalytic studies reveal that these
compounds show high activity in ring-opening polymerization of cyclohexene oxide (CHO). The activity
in the catalytic process varies significantly with solvent and temperature conditions.
by a rich structural chemistry; thus aluminum derivatives of a
vast nuclearity range have been described.21–28
Introduction
Aluminum organometallic and coordination compounds gen-
erate great interest due to their key role in many catalytic
reactions.1–5 Since the discovery of MAO,6,7 different alkyla-
luminoxanes have held a vital role as cocatalysts in Ziegler–
Natta polymerization processes.8–14 In addition, aluminum
alkoxide derivatives have proven to be very efficient catalysts
in many polymerization reactions, such as ring-opening
polymerization.15–20 The appeal of aluminum is complemented
In this note we report the synthesis and structural character-
ization of new aluminum aryloxide complexes. A large number
of aluminum aryloxide compounds have been described,29
containing in most cases nonfunctionalized aryl groups. Our
work is focused on the study of new aryloxide derivatives with
functionalized aryl moieties since we are interested in analyzing
the influence of functionality on the compounds’ properties. In
this context, we have studied the reaction between the fluorinated
phenol 3,5-(CF3)2C6H3OH and AlMe3. The outcome of the
reaction depends strongly on the reaction conditions; varying
the solvent, reaction time, and Al:phenol ratio allows the
synthesis of di-, tri-, and tetrametallic derivatives. The behavior
of these aluminum species in polymerization processes is also
described.
† In memory of Juan Antonio Delgado, deceased on July 14, 2007.
* Corresponding authors. Tel: 34918854779. Fax: 34 918854683. E-mail:
tomas.cuenca@uah.es; martaeg.mosquera@uah.es.
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Results and Discussion
Reactions of AlMe3 with 3,5-(CF3)2C6H3OH. Trimethyl
aluminum reacts with 3,5-(CF3)2C6H3OH at room temperature,
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2008 American Chemical Society
Publication on Web 04/16/2008

Aryloxide Polynuclear Aluminum Species
Organometallics, Vol. 27, No. 10, 2008 2301
Scheme 1
the pentacoordinated aluminum atom in 2 and 3 (δ -0.21 for
2, δ -0.19 for 3) appear shifted low field with respect to the
methyl protons linked to the tetracoordinated aluminum center
(δ -0.53 for 2, δ -0.52 for 3), indicating a more acidic
character for the pentacoordinated aluminum atom. The same
spectroscopic features for the methyl groups bonded to the
aluminum centers are observed in the 13C{1H} NMR spectra
data.
Scheme 2
Structural studies using single-crystal X-ray diffraction
methods were performed and clearly confirmed the nuclearity
of the species 1-3. Figure 1 shows ORTEP views of the
structures along with the atom-labeling schemes. Selected bond
distances and bond angles with their standard deviations are
listed in Table 1. In the dinuclear structure of compound 1, the
Al centers exhibit a typically tetrahedral coordination, being
bonded to two methyl groups and two aryloxide bridging
ligands. Al-O distances (1.8778(18) and 1.8829(19) Å) are
within the usual range found for similar alkoxide aluminum
derivatives.32,33 The aryl rings are in a plane nearly perpen-
dicular to the Al2O2 plane, a different disposition from that
observed for the derivative AlMe2(OC6F5), where the aryl rings
and the Al2O2 core adopt a nearly coplanar arrangement.34
Compound 2 shows a linear trinuclear structure formed by
two Al2O2 rings sharing an Al atom. Two different environments
are observed for the aluminum centers. The terminal dispositions
exhibit tetrahedral geometry, whereas the central aluminum atom
shows square-based pyramidal coordination geometry. The
Al-C distances (average 1.953 Å) are similar for all the Al
centers and are within the expected range.3,35–37 Two different
values are observed for the four Al-O distances around the
pentacoordinated aluminum atom, two of which are longer
(1.973 and 1.961 Å vs 1.867 and 1.863 Å). The phenyl rings
are in parallel planes and could be affecting the angle between
the Al2O2 planes, 119.49°. It is noteworthy that although several
compounds with an AlO2AlO2Al linear core are known, in the
majority the bridging groups are aliphatic or aromatic dialkoxide
ligands,3,33,35 no examples containing monoaryloxide bridging
ligands have been described to date, and 2 is the first complex
of this type to be fully characterized.
giving different products depending on the reaction conditions
(Scheme1),asfrequentlyobservedinthealuminumchemistry.30,31
Thus, when the reaction was carried out in hexane with Al:
phenol ratio 1:1, the dinuclear derivative [AlMe2(OR)]2 (1) (OR
) 3,5-(CF3)2C6H3O) was formed after stirring the reaction
mixture for 30 min. The same reaction using an Al:phenol ratio
of 1:1.15 for longer reaction times affords the trinuclear
derivative {[AlMe2(OR)]2[AlMe(OR)2]} (2). The transformation
of compound 1 into 2, with the elimination of AlMe3 in the
absence of free alcohol, has been observed, indicating that a
possible route to 2 could involve an initial intermolecular
phenoxide-methyl exchange between two molecules of 1,
generating intermediate diaryloxide species “AlMe(OR)2”. The
reaction between this species and the remaining molecules of 1
would give 2 (Scheme 2). However, the proposed intermediate
“AlMe(OR)2” species have not been unequivocally identified.
When a mixture of 1 and 2 is formed, fractional recrystallization
from hexane solution affords a convenient separation method,
as the trinuclear complex is less soluble than the dinuclear
derivative. When toluene is used as reaction media and the ratio
Al to phenol is 1:1.35, the formation of a precipitate containing
a mixture of 2 and the tetranuclear derivative {[AlMe2-
(OR)]2[AlMe(OR)2]2} (3) is observed after stirring the solution
for 4 h. The tetranuclear compound is insoluble in hexane and
barely soluble in toluene, so the mixture was separated by
fractional recrystallization from a toluene solution.
Compounds 1–3 are air sensitive and should be stored under
argon or dinitrogen. They were characterized by elemental
analysis and multinuclear NMR spectroscopy. The analytical
composition exactly fits the proposed formulation. The molec-
ular structures of these compounds were determined by X-ray
diffraction methods. In the 19F{1H} NMR spectra, only one
signal was observed around δ 63, indicating all fluorine atoms
are equivalent (δ 62.9 for 1, δ 63.2 for 2, δ 63.4 for 3). The 1H
NMR spectra show the expected high-field shifted resonances
for the protons of the methyl groups bonded to the aluminum.
Interestingly, the resonances for the methyl protons bonded to
Compound 3 shows an unusual structure with a linear
AlO2AlO2AlO2Al core formed by three quasi-planar Al2O2 rings
linked by two Al atoms (Al(3) and Al(2)). The aluminum atoms
shared by two rings display a pentacoordinated environment,
similar to Al(2) in 2. In this core, Al-C and Al-O bonds follow
a pattern similar to that in 2. The aryl rings located on each
side of the core are placed in near-parallel planes and could
have some influence on the disposition of the Al2O2 rings. In
Figure 2, side views of the molecular structures of 2 and 3 are
displayed, showing that in 3 the Al4 core presents a distorted
ladder structure, exhibiting different values for the dihedral
angles between the Al2O2 planes (122.72° and 109.93°). The
orientation of the Al2O2 rings forces the disposition of the methyl
groups bonded to Al(3) and Al(2) to be located in opposite
directions. It is interesting to point out the scarcity of examples
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2302 Organometallics, Vol. 27, No. 10, 2008
Martínez et al.
Figure 1. Molecular structures of 1-3, showing thermal ellipsoid plots (30% probability). In 3 fluorine atoms have been omitted for
clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compounds 1–3a
Compound 1
Al(1)-O(1)#1
Al(1)-O(1)
Al(1)-C(2)
1.8778(18)
1.8829(19)
1.945(3)
Al(1)-C(1)
O(1)-C(3)
1.948(3)
1.392(3)
O(1)#1-Al(1)-O(1)
Al(1)#1-O(1)-Al(1)
78.68(8)
101.32(8)
Compound 2
Al(1)-O(2)
Al(1)-O(1)
Al(1)-C(1)
Al(1)-C(2)
Al(2)-O(4)
Al(2)-O(1)
Al(2)-O(3)
Al(2)-C(3)
1.855(2)
1.881(2)
1.950(4)
1.958(4)
1.863(2)
1.867(2)
1.961(2)
1.955(3)
Al(2)-O(2)
Al(3)-O(3)
Al(3)-O(4)
Al(3)-C(4)
Al(3)-C(5)
O(1)-C(10)
O(3)-C(30)
O(2)-C(20)
O(4)-C(41)
1.973(2)
1.875(2)
1.881(2)
1.950(4)
1.952(4)
1.406(3)
1.379(3)
1.388(3)
1.402(3)
O(2)-Al(1)-O(1)
Al(1)-O(1)-Al(2)
Al(1)-Al(2)-Al(3)
O(3)-Al(3)-O(4)
O(4)-Al(2)-O(1)
O(4)-Al(2)-O(3)
O(4)-Al(2)-C(3)
O(1)-Al(2)-C(3)
O(3)-Al(2)-C(3)
78.48(8)
104.33(9)
127.07(4)
77.56(9)
120.77(10)
75.88(8)
117.43(13)
121.80(13)
103.18(12)
C(3)-Al(2)-O(2)
102.82(12)
91.38(9)
75.91(8)
153.98(9)
91.05(9)
101.38(9)
101.23(9)
104.89(9)
O(4)-Al(2)-O(2)
O(1)-Al(2)-O(2)
O(3)-Al(2)-O(2)
O(1)-Al(2)-O(3)
Al(3)-O(3)-Al(2)
Al(1)-O(2)-Al(2)
Al(2)-O(4)-Al(3)
Compound 3
Al(1)-O(1)
Al(1)-O(2)
Al(1)-C(2)
Al(1)-C(1)
Al(2)-O(2)
Al(2)-O(3)
Al(2)-O(4)
Al(2)-O(1)
Al(2)-C(3)
Al(3)-O(3)
Al(3)-O(4)
1.854(5)
1.884(4)
1.919(8)
1.945(7)
1.883(5)
1.896(4)
1.917(4)
1.976(4)
1.953(7)
1.861(4)
1.947(4)
Al(3)-C(4)
Al(3)-O(5)
Al(3)-O(6)
Al(4)-O(5)
Al(4)-O(6)
C(11)-O(1)
C(61)-O(6)
C(51)-O(5)
C(41)-O(4)
C(31)-O(3)
C(21)-O(2)
1.950(7)
1.972(4)
1.862(4)
1.853(5)
1.892(5)
1.412(7)
1.404(7)
1.429(7)
1.400(6)
1.395(6)
1.405(7)
O(1)-Al(1)-O(2)
O(2)-Al(2)-O(3)
O(2)-Al(2)-O(4)
O(3)-Al(2)-O(4)
O(2)-Al(2)-O(1)
O(3)-Al(2)-O(1)
O(4)-Al(2)-O(1)
O(2)-Al(2)-C(3)
O(3)-Al(2)-C(3)
O(4)-Al(2)-C(3)
O(1)-Al(2)-C(3)
O(3)-Al(3)-O(6)
O(3)-Al(3)-O(4)
O(6)-Al(3)-O(4)
77.85(18)
118.3(2)
92.13(19)
75.17(17)
74.94(18)
92.13(18)
155.1(2)
125.7(3)
115.9(3)
103.2(2)
101.6(2)
120.2(2)
75.24(17)
91.30(19)
O(3)-Al(3)-C(4)
C(4)-Al(3)-O(5)
O(6)-Al(3)-C(4)
O(4)-Al(3)-C(4)
O(3)-Al(3)-O(5)
O(6)-Al(3)-O(5)
O(4)-Al(3)-O(5)
Al(1)-O(1)-Al(2)
Al(1)-O(2)-Al(2)
Al(3)-O(3)-Al(2)
Al(3)-O(4)-Al(2)
Al(4)-O(5)-Al(3)
Al(3)-O(6)-Al(4)
116.1(3)
98.4(2)
123.6(3)
103.7(2)
95.33(18)
76.10(18)
158.0(2)
102.27(19)
104.7(2)
106.60(19)
102.45(18)
101.03(19)
103.7(2)
a Symmetry transformations used to generate equivalent atoms: 1: #1 -x + 1, -y, -z.
of tetranuclear metal alkoxide derivatives with this geometry;
the few compounds reported occur mainly in group 13.38,39
Cyclohexene Oxide Polymerization. In pursuit of our aim
to study the catalytic properties of the aluminum derivatives
prepared, we investigated their behavior as cocatalysts in
ethylene polymerization processes using ZrCp2Cl2 as a precata-
lyst. However, no activity was observed, and when the reaction
The tests for the ROP were performed with a subtrate:catalyst
molar ratio of 2000:1, during 30 min. The experiments were
carried out at 25 and 0 °C, using methylene chloride or toluene
as solvents. The catalyst was, first, dissolved at the appropriate
temperature, and then CHO was slowly added to the vigorously
stirred resultant solution. Yield values and polymer data are
collected in Table 2.
1
of ZrCp2Cl2 with 2 was monitored by H NMR spectroscopy,
The activity of the aluminum catalysts as initiators in the
polymerization of cyclohexene oxide varies significantly with
solvent and temperature conditions. The higher activity is
exhibited at 25 °C in methylene chloride (Table 2, entries 3, 7,
and 10). Under these conditions the three aluminum compounds
show similar activities, generating comparable quantities of
polymer. The polymerization yields are found to be practically
quantitative (ca. 96% yield for 1, 97% yield for 2 and 3), with
high molecular weights (102 866 g/mol for 1, 43 043 g/mol for
an alkoxide transfer reaction to the Zr center was observed with
the formation of ZrCp2(OR)2. Since the ability of aluminum
derivatives as catalysts in ring-opening polymerization processes
is well-known,15–20 we tried to study the activity of 1–3 in
cyclohexene oxide (CHO) polymerization reactions.
(38) Nöth, H.; Schlegel, A.; Knizek, J.; Schwenk, H. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2640–2643.
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Can. Chim. 2005, 83, 922–928.

Aryloxide Polynuclear Aluminum Species
Organometallics, Vol. 27, No. 10, 2008 2303
Figure 2. Side view of molecular structures of 2 and 3, showing thermal ellipsoid plots (30% probability). CF3 groups have been omitted
for clarity.
Table 2. Cyclohexene Oxide Polymerization Resultsa
n × 105
T
yield
Mw/
Mn
b
b
entry catalyst
mol
(°C) solvent (%)
Mn
Mw
1
2
3
4
5
6
7
8
9
10
1
1
1
1
2
2
2
2
3
3
3.6
3.6
3.6
3.6
1.9
1.9
1.9
1.9
1.3
1.3
25 toluene 75 53 851 97 461 1.8
toluene 70 40 552 70 533 1.7
25 CH2Cl2 96 68 837 102 866 1.5
CH2Cl2 90 51 068 80 532 1.6
25 toluene 85 36 048 65 569 1.8
toluene 72 18 748 31 103 1.6
0
0
0
25 CH2Cl2 97
2575 43 043 1.7
0
CH2Cl2 89 27 788 44171 1.6
25 toluene 95 45 045 76 707 1.7
25 CH2Cl2 97 55 711 105 765 1.8
a Experimental conditions: time 30 min, catalyst 21 mg, proportion
catalyst/CHO 1/2000. b Determined by gel permeation chromatography
relative to polystyrene standards.
Figure 3. Comparative yields for the aluminum catalysts 1, 2, and
3 upon activation with benzenesulfonyl chloride.
the exact nature of the intermediate species involved in these
catalytic reactions.
2, and 105 765 g/mol for 3). The narrow polydispersity indexes
(1.5 with 1, 1.7 with 2, and 1.8 with 3) and the long polymer
chains suggest single-site behavior. Lower values of activity
are reached in toluene (Table 2, entries 1, 5, and 9), and the
yields vary significantly, from 75% for the dinuclear derivative
1 to 95% for the tetranuclear compound (2 shows an intermedi-
ate value of 85%). Interestingly, the highest yield is observed
for 3, in agreement with the relatively higher Lewis acidity of
the pentacoordinated aluminum atoms, as shown in the NMR
spectroscopic studies. Nevertheless, although the catalytic
activity is strongly influenced by the experimental conditions,
the molecular weights and the polydispersity indexes are
comparable in all cases.
In order to understand the role of the solvent in the reaction
process, we have performed a series of CHO polymerization
tests in toluene using benzenesulfonyl chloride as activator.
Treatment of the initial solution of the catalysts in toluene with
benzenesulfonyl chloride (catalyst:activator molar ratio 1:1)
affords active polymerization catalytic species that give higher
yields than in the absence of the chloride source. In the presence
of the chloride-containing activator, the polymerization yield
values increase from 75% to 88% for 1, from 85% to 97% for
2, and from 95% to 98% for 3 (Figure 3). Thus, the activities
of the toluene/benzenesulfonyl system are similar to the values
obtained for the same catalysts in methylene chloride (Table 2,
entries 3, 7, and 10). Consequently, the presence of a chloride-
containing activator in the reaction mixture increases the activity
of these aluminum derivatives, as previously reported for other
aluminum systems in ethylene polymerization.4 An interaction
between the aluminum catalyst and the chloride source or,
alternatively, the direct activation of the monomer by the
chloride reagent could be proposed as potential factors to explain
the observed effect. More work is in progress to understand
The stereochemistry of the isolated poly(1,2-cyclohexene
1
oxide) was investigated by H NMR and 13C NMR spectro-
scopic studies.40–42 The 1H NMR spectra of the polymers
obtained in CDCl3 with the three aluminum catalysts are
1
identical. In the H NMR spectra, the methine hydrogens in
R-positions of the ether bridges appear around δ 3.5, while the
protons of the methylene groups of the cyclohexyl fragment
are located between δ 1.2 and 1.9. The signal of the methine
protons appears in the form of three peaks (δ 3.52, 3.39, and
3.36), which can be attributed to syndiotactic (rr), heterotactic
(mr and rm), and isotactic (mm) triads, respectively. Three main
signals were found in the 13C NMR spectra for the methine
carbons at δ 80.0, 78.7, and 75.6, confirming the presence of
several regions of different tacticity in the polymers. The
remaining methylene groups of the cyclohexene moieties
belonging to the polymer backbone were found in two set of
resonances ranging from δ 30.0 to 37.1 and δ 24.8 to 20.8.
Polydispersity values and stereochemistry of the isolated
polymers are comparable to the reported data for polymers
obtained using similar aluminum compounds as catalysts.20
In conclusion, we report here the synthesis and the structural
characterization of new aryloxide aluminum compounds. The
nature of the final product formed in the synthetic reactions
strongly depends on the reaction conditions (solvent and
stoichiometry of the alcohol reagent); hence it is possible to
tune the nuclearity of the derivatives obtained. The aluminum
compounds prepared showed no activity as cocatalysts in
(40) Bacskai, R. J. Polym. Sci., Part A 1963, 1, 2777–2780.
(41) Malhotra, S. L.; Blanchard, L. P. J. Macromol. Sci. Chem. A 1978,
A12, 1379–1391.
(42) Hasebe, Y.; Tsuruta, T. Makromol. Chem. 1987, 188, 1403–1414.

2304 Organometallics, Vol. 27, No. 10, 2008
Martínez et al.
Table 3. Crystallographic Data for 1, 2, and 3
C20H18Al2F12O2 C37H27Al3F24O4
572.30
formula
C54H36Al4F36O6
1572.75
fw
1072.53
color/habit
cryst dimens, mm3
cryst syst
space group
a, Å
white/prism
0.43 × 0.41 × 0.37
monoclinic
P21/n
9.9720(16)
7.6787(10)
17.488(3)
92.638(15)
1337.7(3)
2
white/prism
0.48 × 0.46 × 0.45
monoclinic
P21/a
16.9230(15)
17.111(3)
17.928(3)
116.438(12)
4648.5(13)
4
white/prism
0.55 × 0.48 × 0.37
monoclinic
P21/c
17.285(4)
12.598(3)
30.701(6)
90.248(13)
6686(3)
b, Å
c, Å
ꢀ, deg
V, Å3
Z
4
T, K
200
1.421
0.207
576
200
1.533
0.215
2144
200
1.563
0.216
3136
F
calcd, g cm-3
µ, mm-1
F(000)
θ range, deg
3.35-27.50
3.55–27.54
101 993
10 662/0.0692
6534
10 662/264/776
0.0593/0.1520
0.1085/0.1867
0.0054(6)
1.025
3.08-25.01
no. of rflns collected
no. of indep rflns/Rint
no. of obsd rflns (I > 2σ(I))
no. of data/restraints/params
R1/wR2 (I > 2σ(I))a
R1/wR2 (all data)a
extinction coeff
27 149
60 568
3035/0.0532
1983
3035/136/191
0.0555/0.1405
0.0960/0.1593
0.014(3)
11 709/0.0840
7725
11 709/0/974
0.0746/0.1736
0.1250/0.2140
0.0055(5)
1.029
GOF (on F2)a
1.052
+0.364/-0.343
largest diff peak/hole, e Å-3
0.538/-0.490
0.597/-0.347
a R1 ) ∑(Fo| - |Fc)/∑|Fo|; wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2; GOF ) {∑[w(Fo - Fc ) ]/(n - p)}1/2
.
2
2 2
2
2 2
{[AlMe2(OR)]2[AlMe(OR)2]}, 2. In a procedure similar to that
described for compound 1, AlMe3 (1.8 mL, 3.6 mmol) reacted with
3,5-(CF3)2C6H3OH (0.6 mL, 4.13 mmol) for 4 h. The solvent was
reduced under vacuum to ca. 7 mL, and the solid produced was
redissolved by heating the mixture. The colorless solution was stored
at room temperature overnight, and some crystals of compound 2
Ziegler–Natta ethylene polymerization processes. Catalytic tests
showed that these aluminum compounds are highly active in
the ring-opening polymerization of cyclohexene oxide (CHO).
Two different solvents were used, giving dissimilar results; thus,
in toluene there is a clear increase in catalyst activity with the
compound’s nuclearity, but in dichloromethane the outcome is
very similar for the three compounds. Overall, the process is
more active in the halogenated solvent. Investigations to clarify
the role of the solvent are continuing; we are also studying the
extension of these studies to other functionalized monomers.
1
were formed (800 mg, 72% yield). H NMR (C6D6): δ 7.33 (m,
4H, p-Ph), 7.10 (m, 8H, o-Ph), -0.21 (s, 3H, CH3-AlO4), -0.53
(s, 12H, (CH3)2-AlO2). 13C NMR (C6D6): δ 151.9 (Cipso-Ph), 134.0
(q, JC-F ) 34 Hz, CF3), 123.7 (Cpara-Ph), 120.5 (Corto-Ph), 118.7
(Cmeta-Ph), -10.8 (CH3-AlO4), -12.1 ((CH3)2-AlO2). 19F{1H} NMR
(C6D6): δ 63.2 (s, CF3). Anal. Calcd (%) for C37H27Al3F24O4
(1072.53): C 41.43, H 2.53. Found: C 41.35, H 2.76.
Experimental Section
{[AlMe2(OR)]2[AlMe(OR)2]2}, 3. A solution of AlMe3, 2 M in
toluene (2.07 mL, 4.14 mmol), was diluted in 10 mL of toluene. 3,5-
(CF3)2C6H3OH (0.85 mL, 5.58 mmol) was dissolved in 10 mL of
toluene, and the solution was added slowly to the AlMe3 solution.
Initially the reaction mixture heated up and some gas evolved. The
solution was stirred for 4 h, the solid produced was redissolved by
heating the mixture, the resulting colorless solution was stored at room
temperature overnight, and some crystals of compound 3 were formed
(211 mg, 15% yield). 1H NMR (CD2Cl2): δ 7.37 (m, 6H, p-Ph), 7.16
(m, 12H, o-Ph), -0.19 (s, 6H, CH3-AlO4), -0.52 (s, 12H, (CH3)2-
AlO2). 19F{1H} NMR (C6D6): δ 63.4 (s, CF3). The low solubility of
3 prevented us from obtaining 13C NMR data. Anal. Calcd (%) for
C54H36Al4F36O6 (1572.75): C 41.24, H 2.31. Found: C 41.15, H 2.02.
General Procedure for the Polymerization Experiments. Typi-
cally, the catalyst was dissolved in dry solvent under argon at the
appropriate temperature. CHO was then slowly added to the vigorously
stirred catalyst solution. In all cases (dinuclear, trinuclear, and
tetranuclear compounds) the reaction mixture rapidly became syrupy
and the reaction was stirred for 30 min. In order to isolate the final
poly(cyclohexene oxide) product of the reaction and separate it from
the catalyst, the reaction mixture was further diluted with the solvent
used for the polymerization reaction and added dropwise to a
vigorously stirred methanol/HCl mixture. The polymer was vigorously
stirred for 2 h, then filtered and dried under vacuum at 75 °C overnight.
General Procedures. All manipulations were carried out under
an argon atmosphere using standard Schlenk and glovebox tech-
niques. Solvents were purified from appropriate drying agents. NMR
spectra were recorded at 400.13 (1H), 376.70 (19F), and 100.60
(13C) MHz on a Bruker AV400. Chemical shifts (δ) are given in
1
ppm using C6D6 as solvent, unless otherwise stated. H and 13C
resonances were measured relative to solvent peaks considering
TMS ) 0 ppm, while 19F resonance were measured relative to
external CFCl3. Elemental analyses were performed on a Perkin-
Elmer 240C. Cycloxene oxide was purchased from Fluka, distilled
over CaH2, and stored under an inert atmosphere prior to its use.
All other reagents were commercially obtained and used without
further purification.
[AlMe2(OR)]2, 1. A solution of AlMe3 2 M in toluene (2.07
mL, 4.14 mmol), was diluted in 10 mL of hexane. 3,5-(CF3)2-
C6H3OH (0.6 mL, 4.14 mmol) was dissolved in 10 mL of hexane
and added slowly to the AlMe3 solution. Initially the reaction
mixture heated up and some gas evolved. After stirring for 30 min
the solvent was reduced under vacuum to ca. 5 mL. The resulting
colorless solution was stored at -20 °C overnight, and some crystals
were formed and identified as compound 1 (590 mg, 47% yield).
1H NMR (C6D6): δ 7.40 (m, 2H, p-Ph), 7.32 (m, 4H, o-Ph), -0.54
(s, 12H, (CH3)2-AlO2). 13C NMR (C6D6): δ 151.8 (Cipso-Ph), 134.2
(q, JC-F ) 34 Hz, CF3), 124.0 (Cpara-Ph), 118.6 (Corto-Ph), 118.2
(Cmeta-Ph), -10.8 (CH3).19F{1H} NMR (C6D6): δ 62.9 (s, CF3).
Anal. Calcd (%) for C20H18Al2F12O2 (572.30): C 41.97, H 3.17.
Found: C 42.06, H 2.94.
Single-Crystal X-ray Structure Determination of Com-
pounds 1, 2, and 3. Details of the X-ray experiment, data reduction,
and final structure refinement calculations are summarized in Table

Aryloxide Polynuclear Aluminum Species
Organometallics, Vol. 27, No. 10, 2008 2305
3. Suitable single crystals of 1, 2, and 3 for the X-ray diffraction
study were selected. The crystals covered with perfluorinated ether
oil were mounted on a Bruker-Nonius Kappa CCD single-crystal
diffractometer equipped with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Data collection was performed at 200(2)
K. Multiscan43 absorption correction procedures were applied to
the data. The structures were solved, using the WINGX package,44
by direct methods (SHELXS-97) and refined using full-matrix least-
squares against F2 (SHELXL-97).45 Hydrogen atoms were geo-
metrically placed and left riding on their parent atoms. All non-
hydrogen atoms were anisotropically refined apart from C5 on
compound 3, which was disordered. In compound 3, C5 and C6
showed disorder that was treated. In the three compounds, fluorine
atoms on the CF3 groups were disordered around the local C3 axis,
and the disorder was partially modeled. Some restraints were applied
(DELU). Compound 3 was refined as a racemic twin using the
TWIN and BASF instructions; the final value of the BASF
parameter was 0.36458. Full-matrix least-squares refinements were
2
carried out by minimizing ∑w(Fo - Fc2)2 with the SHELXL-97
weighting scheme and stopped at shift/err < 0.001. The final
residual electron density maps showed no remarkable features.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publica-
tion nos. CCDC-676066 [1], CCDC-676067 [2], and CCDC-676068
[3]. Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
(+44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgment. Financial support for this research by
DGICYT (Project MAT2007-60997) and CAM (Project
S-0505-PPQ/0328-02) is gratefully acknowledged.
Supporting Information Available: Crystallographic data in
CIF format for complexes 1, 2, and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
(43) Blessing, R. H. SORTAV, Acta Crystallogr. 1995, A51, 33–38.
(44) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–938.
(45) Sheldrick, G. M. SHELXL-97; Universität Göttingen: Göttingen
(Germany), 1998.
OM800086A