Neutral and cationic methylaluminium complexes of 2-anilinotropone ligands: Synthesis, characterization, and reactivity toward ethylene

Article abstract of DOI:10.1002/ejic.200300116

Some new aluminium complexes bearing bidentate monoanionic 2-anilinotroponate ligands have been synthesized and characterized. Reaction of 2-(2,6-diisopropylanilino)tropone or 2-(perfluoroanilino)tropone with AlMe ₃ (1 equiv.) gave, by methane

Full text of DOI:10.1002/ejic.200300116

FULL PAPER
Neutral and Cationic Methylaluminium Complexes of 2-Anilinotropone
Ligands: Synthesis, Characterization, and Reactivity toward Ethylene
Daniela Pappalardo,*[b] Mina Mazzeo,[a] Pasquale Montefusco,[a] Consiglia Tedesco,[a] and
Claudio Pellecchia[a]
Keywords: Aluminium / N,O ligands / Alkenes / Cations / Polymerizations
Some new aluminium complexes bearing bidentate
monoanionic 2-anilinotroponate ligands have been synthe-
sized and characterized. Reaction of 2-(2,6-diisopropylanilin-
determined by single-crystal X-ray diffraction, showing a
five-coordinate aluminium atom with a distorted trigonal-bi-
pyramidal geometry. Compounds 1 and 3 underwent methyl
o)tropone or 2-(perfluoroanilino)tropone with AlMe3 (1 abstraction reactions with B(C6F5)3; the resulting cationic
equiv.) gave, by methane elimination, compounds [2-(2,6-di- species was trapped in the presence of THF in dichlorome-
isopropylanilino)tropone]AlMe2 (1) and [2-(perfluoroanilino)- thane solution. The reactivity of the synthesized compounds
tropone]AlMe2 (2), respectively, as yellow solids. Reaction of
1 with 1 equiv. of the ligand furnished, by protodealumin-
ation of a second Al−CH3 bond, the [2-(2,6-diisopropylanilin-
in ethylene polymerisation has also been explored.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
o)tropone]2AlMe derivative 3. The structure of 3 has been Germany, 2004)
Introduction
[B(C6F5)4]}, some activity for ethylene polymerisation ca-
talysis. In this regard, we reported recently the synthesis of
alkylaluminium compounds bearing phenoxy-imine or N,N
imino-amide ligands that undergo decomposition reactions
after alkyl abstraction with B(C6F5)3; the cationic species
were instead obtained in the presence of THF. Toluene
solutions of the aluminium salicylaldiminate compounds, if
activated with B(C6F5)3, polymerise ethylene to solid poly-
ethylene with low activity.[16] Furthermore, the simple
bis(dichloroaluminium)ethane[17] and alkylaluminium com-
pounds themselves,[18] activated with ionising agents, can
catalyse the polymerisation of ethylene, also with low ac-
tivity.
Organometallic aluminium complexes are widely em-
ployed in organic synthesis and in catalysis.[1] In particular,
organoaluminium compounds are currently used in polym-
erisation chemistry, e.g. in cationic,[2,3] anionic,[4Ϫ6] and
ring-opening polymerisation.[7] In addition, alkylaluminium
complexes have long been known to catalyse olefin oligo-
merizations,[8] and are the preferred cocatalysts in various
important industrial processes catalysed by transition met-
als, such as the ZieglerϪNatta olefin polymerisation,[9] the
Wilke alkene dimerization[10] and the Ziegler nickel ef-
fect.[11]
The disclosure by Coles and Jordan in 1997 that certain
cationic methylaluminium amidinate compounds promote
ethylene polymerisation, although with low activity,[12] has
encouraged a growing interest in exploring the reactivity of
various aluminium compounds. Dialkylaluminium com-
pounds bearing monoanionic chelating ligands, such as the
N,N bidentate aminotroponiminate,[13] the tridentate N,N,N
pyridylaminoamide[14] or the tridentate O,N,N and O,N,O
pendant arm Schiff-base ligands[15] showed, after activation
with the ionising agents traditionally used in homogeneous
ZieglerϪNatta catalysis {i.e. B(C6F5)3 or [(C6H5)3C]-
Although cationic alkyl complexes have been isolated and
characterized, it is still unclear if they are directly respon-
sible for the catalytic activity. Monitoring the reaction of
alkylaluminium aminotroponiminate cationic complex with
[D4]ethylene, Jordan excluded that intact cationic species
are the active ethylene polymerisation catalysts, while their
main reaction is a β-H transfer to generate the correspond-
ing cationic aluminium hydride.[13b] In fact, according to
recent theoretical studies on ethylene polymerisation at alu-
minium centres, mononuclear aluminium species are un-
likely to produce polymers, because chain transfer is too
easy relative to propagation.[19] Therefore, more complex
structures for the active species have to be considered. Com-
putational studies showed that dinuclear species could be
involved and, recently,[19c] an aluminium bis(iminophos-
phorano)methanediide complex, based on a spirocyclic car-
bon centre subtended by two AlMe2 units, was shown to
polymerise ethylene with higher activity.[20]
[a]
`
Dipartimento di Chimica, Universita di Salerno,
84081 Baronissi, Salerno, Italy
Fax: (internat.) ϩ 39-089-965296
E-mail: pappalardo@unisannio.it
[b]
Permanent address: Dipartimento di Scienze Geologiche e
`
Ambientali, Universita del Sannio,
Via Port’Arsa 11, 82100 Benevento, Italy
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DOI: 10.1002/ejic.200300116
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Neutral and Cationic Methylaluminium Complexes of 2-Anilinotropone Ligands
FULL PAPER
We report here the synthesis and characterization of above and below the plane. Thus, the molecule belongs to
some new aluminium complexes carrying bidentate the Cs symmetry group.
monoanionic anilinotropone ligands[21] (Scheme 1), along
with their reactivity with ion-generating activators, and
some preliminary data on their reactivity in ethylene polym-
erisation.
Scheme 2. Reaction conditions: (i): AlMe3, toluene, 0 °C
The compound was further characterized by both FT-IR
spectroscopy and EI mass spectrometry. The slight differ-
ence in the FT-IR spectrum between the stretching fre-
quency of the carbonyl group in 1 (1598 cmϪ1) and in the
Scheme 1
ligand (1601 cmϪ1) could be explained by considering that
in 1 the carbonyl group is reasonably coordinated to the
metal atom while in the free ligand the CϭO group is in-
volved in hydrogen bonding with the NH group. The molec-
ular ion peak in the EI mass spectrum is at m/z ϭ 336.
The reaction of 2-(perfluoroanilino)tropone with AlMe3
Results and Discussion
(1 equiv.) in toluene, at 0 °C, proceeds similarly (Scheme 3),
Synthesis of [2-(Anilino)tropone]AlMe2 Derivatives
affording [2-(perfluoroanilino)tropone]AlMe2 (2) as a yel-
low solid, which has been characterized by 1H and 13C
NMR analysis and EI mass spectrometry. The NMR spec-
troscopic data are compatible with a mirror symmetry pass-
ing through the seven-membered tropone ring and perpen-
dicular to the perfluorophenyl group, as hypothesized for 1.
Recently, Brookhart has described neutral anilinotro-
pone-based nickel() compounds[22] that can polymerise
ethylene in the absence of an activator, with an activity
higher than the analogous neutral nickel salicylaldiminate
compounds reported by Grubbs.[23] We therefore synthe-
sized the [2-(anilino)tropone]dimethylaluminium derivatives
1 and 2 to test their reactivity with olefins.
Treatment of 2-(2,6-diisopropylanilino)tropone[21] with
AlMe3 (1 equiv.) in toluene at 0 °C for 2 h produces [2-(2,6-
diisopropylanilino)tropone]AlMe2 (1) as a yellow solid. The
reaction proceeds by protodealumination of the AlϪCH3
bond, with concomitant elimination of methane
1
(Scheme 2), as evidenced by H and 13C NMR analysis. In
the 1H NMR spectrum ([D6]benzene, room temperature)
the NH singlet (δ ϭ 8.86 ppm) of the ligand disappears,
while a new singlet appears at high field [δ ϭ Ϫ0.21 ppm
(6 H)] accounting for the AlMe2 protons. Similarly, in the
13C NMR spectrum ([D6]benzene, room temperature) a new
signal at δ ϭ Ϫ8.3 ppm is observed, which is attributable
to AlMe2 carbon atoms. The signal of the carbonyl carbon
atom shifts from δ ϭ 177.3 ppm in the free ligand to δ ϭ
173.7 ppm in the aluminium compound 1, indicating a
change in electronic density after coordination to Al. The
1H NMR spectrum has one signal for the AlMe2 protons,
one multiplet for CHMe2 [δ ϭ 3.09 ppm (2 H)] and two
doublets for the methyl groups of CHMe2 [δ ϭ 1.21 ppm
(6 H) and 0.89 ppm (6 H)]. The 13C NMR spectrum con-
firms this picture: one signal for CHMe2 (δ ϭ 28.7 ppm),
two signals for the methyl carbon atoms of CHMe2 (δ ϭ
25.9 and 24.5 ppm), one signal for the AlMe2 groups. This
pattern is compatible with a mirror symmetry passing
through the tropone seven-membered ring, and perpendicu-
lar to the 2,6-disubstituted phenyl group; the AlMe2 groups
Scheme 3. Reaction conditions: (i): AlMe3, toluene, 0 °C
Synthesis of [2-(2,6-Diisopropylanilino)tropone]2AlMe (3)
The title compound was initially obtained as a secondary
product in a preparation of 1, upon accidentally using an
excess of ligand, and was identified by NMR spectroscopy
in [D6]benzene solution. Compound 1 can be converted
quantitatively into 3 by simply adding 1 equiv. of the ligand
in toluene solution at room temperature (Scheme 4).
Scheme 4. Reaction conditions: (i): 2-(2,6-diisopropylanilino)tro-
are equivalent, therefore they should lie symmetrically pone, toluene, room temperature
Eur. J. Inorg. Chem. 2004, 1292Ϫ1298
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FULL PAPER
1
Compound 3 has been fully characterised by H and 13C
NMR spectroscopy, elemental analyses, EI MS, FT-IR
spectroscopy, and single-crystal X-ray diffraction. Diagnos-
1
tic signals in the H NMR spectrum ([D6]benzene, room
temperature; Figure 1) are a singlet at δ ϭ Ϫ0.06 ppm
(3 H), attributable to the AlMe protons, four doublets at
δ ϭ 0.99, 1.03, 1.06, 1.48 ppm (6 H each) that are attribu-
table to the CHMe2 protons, and two multiplets for CHMe2
at δ ϭ 3.07 (2 H) and 3.37 ppm (2 H). The 13C NMR spec-
trum exhibits resonances for the corresponding carbon
atoms: one signal at δ ϭ Ϫ6.7 ppm, attributable to AlMe,
four signals for the methyl carbon atoms at δ ϭ 23.9, 25.4,
25.5 and 26.5 ppm, and two signals at δ ϭ 28.8 and
29.8 ppm for the CHMe2 carbon atoms. This picture is con-
sistent with a C2 symmetry of the molecule in solution.
Figure 2. Molecular structure of 3; thermal ellipsoids are drawn at
20% probability; H atoms omitted for clarity
˚
Table 1. Selected bond lengths [A] and angles [°]; symmetry-equiva-
lent atoms indicated with the letter ‘‘e’’
Al(1)ϪO(1)
Al(1)ϪN(1)
Al(1)ϪC(20)
O(1)ϪC(1)
N(1)ϪC(7)
N(1)ϪC(8)
C(1)ϪC(2)
C(1)ϪC(7)
C(2)ϪC(3)
C(3)ϪC(4)
C(4)ϪC(5)
C(5)ϪC(6)
C(6)ϪC(7)
1.865(3)
1.956(4)
1.981(6)
1.292(5)
1.335(5)
1.429(6)
1.405(6)
1.432(6)
1.415(7)
1.367(8)
1.377(8)
1.370(6)
1.435(6)
N(1)ϪAl(1)ϪO(1)
N(1)ϪAl(1)ϪO(1e)
O(1)ϪAl(1)ϪO(1e)
N(1)ϪAl(1)ϪN(1e)
N(1)ϪAl(1)ϪC(20)
O(1)ϪAl(1)ϪC(20)
80.85(16)
91.43(16)
164.0(2)
122.3(2)
118.84(12)
97.99(11)
1
Figure 1. H NMR spectrum of 3 (C6D6, room temperature)
The compound was further characterized by EI mass
spectrometry, which shows the molecular ion peak at m/z ϭ
603 [M]ϩ and a peak at m/z ϭ 587 [M Ϫ CH3]ϩ. In the FT-
IR spectrum, the stretching frequency of the carbonyl
group appears at 1597 cmϪ1
.
Complex 3 crystallized as regular yellow prisms from
toluene at Ϫ20 °C. The molecular structure of 3 (Figure 2)
and the corresponding selected interatomic distances and
angles (Table 1) are reported here. The X-ray structure de-
termination shows that the space group is C2/c, with a crys-
tallographic twofold axis parallel to the b axis and passing
through the Al atom and methyl group C atom. Therefore
the C2 molecular axis, observed in solution, is preserved in
the crystal. The unit cell contains four molecules of 3 and
eight molecules of toluene disordered over a mirror plane;
this feature affects the overall quality of the structural data.
The compound contains a five-coordinate Al atom with
a highly distorted, approximate trigonal-bipyramidal geo-
metry (tbp).[24] The O atoms occupy the apical positions,
while the N atoms and the methyl group carbon atom lie in
the equatorial plane; the C2 molecular axis bisects the angle
between the two N atoms.
˚
˚
A] is longer than in the free ligand (1.252 A), while C7ϪN1
˚
[1.335(5) A] is statistically almost the same as in the free
˚
ligand (1.355 A). Some contribution from resonance form
B in Scheme 5 cannot be excluded.
Scheme 5
The seven-membered tropone ring is almost planar with
˚
rmsd 0.024 A; carbon atoms C1 and C7 deviate most from
The aniline six-membered ring is almost perfectly planar
˚
the seven-atoms least-squares plane by 0.039(4) and (rmsd 0.005 A), with the N1, C14, and C17 atoms practi-
˚
Ϫ0.034(4) A, respectively. A comparison between the cally lying in the same plane. The aniline ring forms a di-
carbonϪheteroatom bond lengths in compound 3 and in hedral angle of 58.6(1)° with the plane defined by the tro-
the free ligand[22] evidenced that the C1ϪO1 bond [1.292(5) pone seven-membered ring.
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Eur. J. Inorg. Chem. 2004, 1292Ϫ1298

Neutral and Cationic Methylaluminium Complexes of 2-Anilinotropone Ligands
FULL PAPER
Five-coordinate aluminium complexes play an important atoms, instead, appear as a multiplet centred at δ ϭ
role as initiators for the controlled polymerisation of polar 2.25 ppm (4 H). After addition of a further equivalent of
monomers. Complexes bearing tetradentate macrocyclic or THF, the THF methylenic hydrogen atoms in α-positions
chelating ligands (such as porphyrins,[25] salen-type li- with respect to the oxygen atom coalesce in a multiplet cen-
gands[26]), or bulky monoanionic bidentate ligands,[27] cata- tered at δ ϭ 4.20 ppm, and the numbers and multiplicity of
lyse the living ring-opening polymerisation of propene ox- the signals are the same as in the neutral starting com-
ide. The generation of highly electrophilic cationic species pound, i.e. one signal for the CHMe2 and two doublets for
and their catalytic application has also been explored.[7b,28] the methyl groups of the CHMe2. Such behaviour can,
probably, be explained by assuming, in the presence of ex-
Generation of Cationic Species and Their Reactivity
Toward Ethylene
cess THF, there is a rapid exchange process between free
and bound THF.
For catalytic applications, cationic aluminium species are
more attractive than neutral ones, because of their increased
Lewis acidity. The stability of group-13 alkyl cations de-
pends strongly on the ancillary ligand and the kind of coun-
ter anion. Bochmann has described the preparation of the
bis(cyclopentadienyl)aluminium cation from the corre-
sponding methyl compound after reaction with B(C6F5)3;[3]
however, simple alkylaluminium compounds, if treated
with the activators commonly used in homogeneous
olefin polymerisation catalysis {i.e. B(C6F5)3 or
Scheme 6. Reaction conditions: (i): B(C6F5)3, THF in CD2Cl2
[(C6H5)3C][B(C6F5)4]}, undergo degradation reaction with
Attempts to generate clean cationic species from the
cleavage of a BϪC6F5 bond.[29] The cationic alkylalu-
monomethylaluminium compound 3 with B(C6F5)3 in the
minium species was trapped in the presence of bases[7a] or
absence of coordinating agents were unsuccessful, leading
using coordinating solvents, such as diethyl ether and
always to a mixture of unidentified species. Addition of eth-
THF.[30]
ylene to a freshly prepared solution of 3 and B(C6F5)3 did
We have generated cationic complexes from the synthe-
not result in monomer consumption or production of solid
sized aluminium compounds by NMR tube reactions with
polymer, unlike the behaviour of 1 in the analogous experi-
B(C6F5)3. When 1 and B(C6F5)3 are mixed in C6D6 at room
ment (see above). Since compounds 1 and 3 were prepared
temperature, a brown oil precipitates, thus preventing NMR
using the same reagents, but in different stoichiometric ra-
solution analysis. The reaction was consequently studied in
tios, the implication of some metal impurity in the polymer-
CD2Cl2 solution. After in situ treatment of 1 with of
ization activity of the aluminium species 1 can be ruled
1
B(C6F5)3 (1 equiv.), the H NMR spectrum shows a reson-
out.[19] In fact, while the reaction of 1 with B(C6F5)3 (1
ance at δ ϭ ϩ0.45 ppm, which is attributable to the free
equiv.) generates a cationic methylaluminium compound,
anion [MeB(C6F5)3]Ϫ,[31] therefore indicating that the main
abstraction of the methyl group from 3 generates a cationic
reaction is methyl abstraction by B(C6F5)3. The initially
species that lacks any AlϪC bond suitable for chain growth
formed cationic species is degraded rapidly, generating a
by ethylene insertion.
mixture of unidentified organometallic species. Ethylene
The cationic species {[2-(2,6-diisopropilanylino)tropone]2-
was added to a freshly prepared solution of 1 and B(C6F5)3
Al(THF)}ϩ[MeB(C6F5)3]Ϫ (3a) was cleanly generated by
in CD2Cl2; monitoring the reaction at room temperature
the reaction of 3 with of B(C6F5)3 (1 equiv.) in the presence
showed that ethylene was consumed and that a solid poly-
of THF (1 equiv.) in CD2Cl2 (Scheme 7). The product was
mer was formed.
1
characterized by H and 13C NMR spectroscopy at room
Attempts to isolate and better characterize the cationic
species in the absence of bases were unsuccessful. Trapping
temperature.
of the cationic species was instead achieved in the presence
of THF. When B(C6F5)3 (1 equiv.) was added to a CD2Cl2
solution of 1 containing THF (1 equiv.), the THF-coordi-
nated methyl cation of {[2-(2,6-diisopropylanilino)-
tropone]AlMe(THF)}ϩ[MeB(C6F5)3]Ϫ (1a) was formed
(Scheme 6). Characteristic 1H NMR resonances are the sig-
nals at δ ϭ Ϫ0.27 ppm for AlMeϩ (3 H) and at δ ϭ
1
0.45 ppm for BMe (3 H). The pattern of signals in the H
NMR spectrum is consistent with the C1 symmetry group
Scheme 7. Reaction conditions: (i): B(C6F5)3, THF in CD2Cl2
(i.e. two signals for the CHMe2 groups and four doublets
for the methyl groups of CHMe2). Accordingly, the THF
1
In the H NMR spectrum, the singlet of AlMe of the
methylenic hydrogen atoms in α-positions with respect to neutral starting compound 3 disappears, while a new signal
the oxygen atom are diastereotopic, and appear as two mul- appears at δ ϭ 0.45 ppm, which is attributable to the ‘‘free’’
tiplets at δ ϭ 4.40 (2 H) and 4.26 ppm (2 H); the β-hydrogen anion [MeB(C6F5)3]Ϫ, indicating that alkyl abstraction has
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D. Pappalardo, M. Mazzeo, P. Montefusco, C. Tedesco, C. Pellecchia
FULL PAPER
occurred. The numbers of signals (i.e. four doublets for the
CHMe2 protons, and two multiplets for CHMe2 in the H
Experimental Section
1
NMR spectrum; four signals for the methyl carbon atoms
and two signals for the isopropylic CHMe2 carbon atom in
the 13C NMR spectrum) indicate that the cation preserves
the C2 symmetry observed in solution in the neutral com-
pound. Integration shows that the cation is supported by
one molecule of coordinated THF. Interestingly, the THF
methylenic hydrogen atoms in α-positions with respect to
the oxygen atom, being diastereotopic, appear as two mul-
tiplets at δ ϭ 4.38 (2 H) and 3.93 ppm (2 H); the β-hydrogen
atoms, instead, appear as a multiplet centred at δ ϭ
2.13 ppm (4 H) (Figure 3). This suggests that the THF mol-
ecule substitutes the methyl group of the corresponding
neutral compound, and therefore is situated on the C2 sym-
metry axis.
General: Sensitive materials were manipulated under dry nitrogen
using Schlenk or glove-box techniques. Toluene, heptane, and THF
were heated under reflux in the presence of sodium and benzo-
phenone and distilled under nitrogen prior to use. AlMe3 was pur-
chased from Aldrich and used as received. The 2-(2,6-diisopro-
pylanilino)tropone and (perfluoroanilino)tropone ligands,[21] and
[30]
B(C6F5)3
were synthesized according to literature procedures.
NMR spectra were recorded with a Bruker Avance 400 MHz spec-
trometer; chemical shifts were referenced to the residual protio im-
purity of the deuterated solvent. EI MS data were obtained with a
Finnigan Thermoquest GCQ Plus 2000 spectrometer, using a direct
exposure probe. Infrared spectra were recorded with a FT-IR
Bruker Vector 22.
[2-(2,6-Diisopropylanilino)tropone]AlMe2 (1): A toluene solution of
0.21  AlMe3 (4 mL, 0.85 mmol) was slowly added to a solution
of 2-(2,6-diisopropylanilino)tropone (240 mg, 0.85 mmol) in tolu-
ene (15 mL) at 0 °C with stirring. The solution was then stirred for
2 h. Subsequently, the volatiles were removed under reduced press-
1
ure to give the product as an orange solid (yield 229 mg, 80%). H
NMR (400 MHz, C6D6): δ ϭ 7.17 (d, 2 H, CH), 7.07 (d, 1 H, CH),
6.55 (m, 1 H, CH), 6.44 (d, 1 H, CH), 6.34 (m, 1 H, CH), 6.11 (t,
1 H, CH), 3.09 [m, 2 H, CH(CH3)2], 1.21 [d, 6 H, CH(CH3)2],
1
0.89 [d, 6 H, CH(CH3)2], Ϫ0.21 [s, 6 H, Al(CH3)2] ppm. H NMR
(400 MHz, CD2Cl2): δ ϭ 7.38Ϫ7.28 (m, 3 H, CH), 7.28 (t, 2 H,
CH), 6.87 (t, 2 H, CH), 6.57 (d, 1 H, CH), 2.93 [m, 2 H,
CH(CH3)2], 1.20 [d, 6 H, CH(CH3)2], 0.99 [d, 6 H, CH(CH3)2],
Ϫ0.74 [s, 6 H, Al(CH3)2] ppm. 13C NMR (100 MHz, C6D6): δ ϭ
173.7 (CϭO), 167.4 (CϪN), 144.4, 139.9 (CH), 138.4 (CH), 126
(CH), 125.7 (CH), 123.6 (CH), 122.3 (CH), 28.7 [CH(CH3)2], 25.9
[CH(CH3)2], 24.5 [CH(CH3)2], Ϫ8.3 [Al(CH3)2] ppm. EI MS
(35 eV): m/z ϭ 336 [M]ϩ, 324 [M Ϫ CH3]ϩ. FT-IR: ν˜ ϭ 1598 (Cϭ
O) cmϪ1. C21H28AlNO (337.44): calcd. C 74.75, H 8.36, N 4.15;
found C 74.54, H 8.56, N 4.29.
1
Figure 3. H NMR spectrum of 3a (CD2Cl2, room temperature)
[2-(Perfluoroanilino)tropone]AlMe2 (2): A solution of 2-(perfluoro-
anilino)tropone (300 mg, 1.04 mmol) in dry toluene (10 mL) was
added dropwise to a toluene solution of 0.26  AlMe3 (10 mL,
1.14 mmol) at 0 °C. The solution was then stirred for 2 h and left to
reach room temperature. The resulting solution was subsequently
concentrated and cooled to Ϫ20 °C; compound then 2 precipitated
as an orange powder; yield 150 mg (42%). 1H NMR (400 MHz,
C6D6): δ ϭ 6.99 (d, 1 H, CH), 6.52 (t, 2 H, CH), 6.18 (t, 2 H, CH),
Ϫ0.17 [s, 6 H, Al(CH3)2]. 13C NMR (100 MHz, C6D6): δ ϭ 175.1
(C-1), 165.8 (C-2), 139.7 (CH), 139.1 (CH), 126.2 (CH), 124.3
(CH), 118.9 (CH), Ϫ9.3 [Al(CH3)2] ppm. EI MS(35 eV): m/z ϭ 346
[M]ϩ, 328 [M Ϫ CH3]ϩ.
Conclusions
Two new 4-coordinate aluminium complexes, namely
[2-(2,6-diisopropylanilino)tropone]AlMe2 (1) and [2-(per-
fluoroanilino)tropone]AlMe2 (2), have been synthesized. A
five-coordinate bis[2-(2,6-diisopropylanilino)tropone]AlMe
derivative (3) has also been synthesized and characterized
by single-crystal X-ray diffraction studies, which indicate a
distorted trigonal-bipyramidal geometry around Al. Com-
pounds 1 and 3 undergo methyl abstraction reactions with
B(C6F5)3; the resulting cationic species are stable in the
presence of THF in dichloromethane solution. The reactiv-
[2-(2,6-Diisopropylanilino)tropone]2AlMe (3): [2-(2,6-Diisopropilan-
ilino)tropone]AlMe2 (82 mg, 0.24 mmol) was dissolved in dry tolu-
ity of the synthesized compounds in ethylene polymeris- ene (10 mL). A solution of 2-(2,6-diisopropylanilino)tropone
(68 mg, 0.24 mmol) in toluene (5 mL) was then added and the re-
sulting solution stirred at room temperature for 2 h. The volatiles
were then removed under reduced pressure to give the product as
ation has also been explored. Interestingly, after reaction
with B(C6F5)3, compound 1 polymerizes ethylene to give a
solid polymer, whereas compound 3 does not. This finding
indicates that polymerization does not occur at a different
metal contaminant.[19]
As Lewis acids, neutral, but especially cationic alu-
minium compounds, should be useful as catalysts to poly-
merize substrates containing a Lewis-basic atom. Experi-
ments are in progress to ascertain if these compounds could
be involved in the polymerization of polar monomers.
1
an orange solid in almost quantitative yield. H NMR (400 MHz,
C6D6): δ ϭ 7.34 (d, 4 H, CH), 7.26 (m, 2 H, CH), 6.68 (d, 2 H,
CH), 6.49 (m, 4 H, CH), 6.47 (t, 2 H, CH), 6.04 (t, 2 H, CH),
3.37 [m, 2 H, CH(CH3)2], 3.07 (m, 2 H, CH(CH3)2], 1.48 [d, 6 H,
CH(CH3)], 1.06 [d, 6 H, CH(CH3)], 1.03 [d, 6 H, CH(CH3)], 099 [d,
1
6 H, CH(CH3)], Ϫ0.06 (s, 3 H, AlCH3) ppm. H NMR (400 MHz,
CD2Cl2): δ ϭ 7.32Ϫ7.03 (m, 10 H, CH), 6.70 (m, 4 H, CH), 6.46
(d, 2 H, CH), 3.05 [m, 2 H, CH(CH3)2], 2.77 [m, 2 H, CH(CH3)2],
1296
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Eur. J. Inorg. Chem. 2004, 1292Ϫ1298

Neutral and Cationic Methylaluminium Complexes of 2-Anilinotropone Ligands
1.27 [d, 6 H, CH(CH3)], 1.16 [d, 6 H, CH(CH3)], 1.05 [d, 6 H, atoms of the methyl groups were assumed to be disordered over
FULL PAPER
CH(CH3)], 0.78 [d, 6 H, CH(CH3)], Ϫ0.83 (s, 3 H, AlCH3) ppm.
two sites rotated 60° to each other. Anisotropic displacement par-
ameters were used for all non-hydrogen atoms except those belong-
13C NMR (100 MHz, C6D6): δ ϭ 175.2 (CϭO); 166.6 (CϪN);
144.4, 143.8, 142.3, 138.4, 137.5, 127.0, 125.5, 124.4, 124.1, 122.5, ing to the solvent molecule. Hydrogen atoms were positioned geo-
121.1; 29.8 and 28.8 [CH(CH3)2]; 26.5, 25.5, 25.4, and 23.9
metrically and refined using a riding model. Finally, a total of 226
parameters were refined considering 4174 intensity data. Maximum
[CH(CH3)2]; Ϫ6.7 (AlCH3) ppm. EI MS(35 eV): m/z ϭ 603 [M]ϩ,
587 [M Ϫ CH3]ϩ. FT-IR: ν˜ ϭ 1597 (CϭO) cmϪ1. C39H47N2O2Al and minimum residual densities were 0.35 and Ϫ0.34 e·AϪ3, respec-
˚
(602.79): calcd. C 77.71, H 7.86, N 4.65; found C 77.23, H 8.16,
N 4.34.
tively. Final disagreement indices were R1 ϭ 0.0829 for 1336 reflec-
tions with Fo Ͼ 4σ(Fo), R1 ϭ 0.255 and wR2 ϭ 0.146 for all 4174
data. ORTEP drawings performed by means of the program
Generation of {[2-(2,6-Diisopropylanilino)tropone]AlMe(THF)}؉-
[MeB(C6F5)3]؊ (1a): Compound 1 (17 mg, 50 µmol) was dissolved
in CD2Cl2 (0.5 mL). THF (4 µL, 50 µmol) and B(C6F5)3 (26 mg,
50 µmol) were then added sequentially, and the so-obtained solu-
ORTEP32.[35]
Crystallographic
data
for
3:
Formula:
C39H47AlN2O2·2C7H8, M ϭ 787.03, system: monoclinic, space
˚
group C2/c, Z ϭ 4; a ϭ 18.321(6), b ϭ 10.145(3), c ϭ 25.506(7) A;
3
β ϭ 91.40(3)°, V ϭ 4739(2) A , Dx ϭ 1.103 g·cmϪ3, µcalcd. ϭ 0.08
˚
1
tion was analysed by NMR spectroscopy at room temperature. H
mmϪ1. Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data Centre
as supplementary publications no. CCDC-204539. Copies of the
data may be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 EZ, UK [Fax: (internat.) ϩ 44-1223-
336-033; E-mail: deposit@ccdc.cam.ac.uk].
NMR (400 MHz, CD2Cl2): δ ϭ 7.76 (m, 2 H, CH), 7.66 (m, 1 H,
CH), 7.46Ϫ7.35 (m, 4 H, CH), 6.99 (d, 1 H, CH), 4.40 (m, 2 H,
OCH2), 4.26 (m, 2 H, O-CH2), 2.66 (m, 1 H, CH(CH3)2], 2.57 (m,
1 H, CH(CH3)2], 2.25 (s, 4 H, CH2), 1.21 (d, 6 H, CHCH3), 1.01
(d, 3 H, CHCH3), 0.92 (d, 3 H, CHCH3), 0.45 (s, 3 H, BCH3),
Ϫ0.27 (s, 3 H, AlCH3) ppm. 13C NMR (100 MHz, CD2Cl2): δ ϭ
169.4 (CϭO), 168.0, 144.4, 143.8, 142.3, 141.3, 134.5, 133.2, 129.5,
128.0, 126.6, 125.8, 125.3, 76.2 (OCH2), 29.2 (2 peaks overlapped,
CH), 25.9 (CH2CH2O), 25.0, 24.8, 23.9 (CHCH3), 10.0 (BCH3)
ppm. Successively, one further eqivalent of THF was added to the
solution, and the sample analysed by NMR spectroscopy at room
temperature. 1H NMR (400 MHz, CD2Cl2): δ ϭ 7.65 (m, 2 H, CH),
7.55 (m, 1 H, CH), 7.46Ϫ7.27 (m, 4 H, CH), 6.90 (d, 1 H, CH),
4.20 (s, 8 H, OCH2), 2.60 [m, 2 H, CH(CH3)2], 2.11 (s, 8 H, CH2),
1.20 (d, 6 H, CHCH3), 1.00 (d, 6 H, CHCH3), 0.46 (s, 3 H, BCH3),
Ϫ0.48 (s, 3 H, AlCH3) ppm. 13C NMR (100 MHz, CD2Cl2): δ ϭ
169.4 (CϭO), 167.9, 144.0, 143.2, 142.2, 133.0, 129.4, 127.8, 126.2,
125.3, 125.2; 76.0 (OCH2), 29.2 (CH), 25.7 (CH2CH2O), 25.4, 23.7
(CHCH3), 10.2 (BCH3), Ϫ14.0 (AlCH3) ppm.
Acknowledgments
The authors are grateful to Professor A. Immirzi for valuable dis-
cussions, to Dr. A. Moresco (ICIS, CNR, Padova, Italy) for the
elemental analyses and to Mr. R. Miranda for EI MS measure-
ments. This work was supported by the Italian Ministry of Univer-
sity and Research (Progetto Giovani Ricercatori 2001 and PRIN
2002).
[1]
J. J. Eish, ‘‘Aluminum’’ in: Comprehensive Organometallic
Chemistry II (Eds.: E. W. Abel, F. G. A. Stone, G. Wilkinson),
Elsevier, Oxford, UK, 1995, chapter 10, pp. 431Ϫ502.
Cationic Polymerization: Mechanism, Synthesis and Appli-
[2]
Generation of {[2-(2,6-Diisopropylanilino)tropone]2Al(THF)}؉-
[MeB(C6F5)3]؊ (3a): Compound 3 (15 mg, 25 µmol) was dissolved
in CD2Cl2 (0.5 mL). Dry THF (2 µL, 25 µmol) and B(C6F5)3
(13 mg, 25 µmol) were then added sequentially, and the resulting
solution was analysed by NMR spectroscopy at room temperature.
1H NMR (300 MHz, CD2Cl2): δ ϭ 7.60Ϫ7.10 (m, 14 H) and 6.85
(d, 2 H) (phenyl and tropone H), 4.38 (m, 2 H, OCHaHb), 3.93 (m,
2 H, OCHaHb), 2.67 [m, 2 H, CH(CH3)2], 2.59 [m, 2 H, CH(CH3)2],
2.13 (m, 4 H, CH2), 1.32 [d, 6 H, CH(CH3)], 1.08 [d, 6 H,
CH(CH3)], 0.93 [d, 6 H, CH(CH3)], 0.72 [d, 6 H, CH(CH3)], 0.45
(s, 3 H, BCH3) ppm. 13C NMR (75 MHz, CD2Cl2): δ ϭ 169.9 (Cϭ
O), 167.4, 143.8, 143.2 (quaternary carbon atoms), 140.8 (CH),
140.2 (CH), 138.5 (quaternary carbon atom), 130.3 (CH), 128.3
(CH), 125.4 (CH), 123.9 (CH), 75.7 (OCH2CH2), 29.7 [CH(CH3)2],
29.2 [CH(CH3)2], 25.9 (OCH2CH2), 24.9 [CH(CH3)], 23.7
[CH(CH3)] ppm.
cations (Ed.: K. Matyjaszewski), Marcel Dekker, New York,
1996.
M. Bochmann, D. M. Dawson, Angew. Chem. Int. Ed. Engl.
[3]
1996, 35, 2226Ϫ2228.
[4]
[4a] M. Kukoki, T. Aida, S. Inoue, J. Am. Chem. Soc. 1987, 109,
[4b]
4737Ϫ4738.
M. Kukoki, T. Watanabe, T. Aida, S. Inoue, J.
Am. Chem. Soc. 1991, 113, 5903Ϫ5904.
[5] [5a]
˘
M. Dimonie, D. Mardare, S. Coca, V. Dragutan, I. Ghivi-
[5b]
˘
riga, Macromol. Rapid Commun. 1992, 13, 37Ϫ44.
D. Mar-
dare, K. Matyjaszewski, Macromol. Rapid Commun. 1994, 15,
37Ϫ44.
[6]
`
F. Cosledan, P. B. Hitchcock, M. F. Lappert, Chem. Commun.
1999, 13, 705Ϫ706.
[7] [7a]
J. A. Jeger, D. A. Atwood, Inorg. Chem. 1997, 37,
2034Ϫ2039. [7b] M. A. Munoz-Hernandez, M. L. McKee, T. S.
Keizer, B. C. Yearwood, D. A. Atwood, J. Chem. Soc., Dalton
[7c]
Trans. 2002, 410Ϫ414.
S. Inoue, J. Polym. Sci., Part A.:
Polym. Chem. 1998, 21, 3114 and refs therein. [7d] Z. Zhong, P.
J. Dijkstra, J. Feijen, Angew. Chem. Int. Ed. 2002, 41,
4510Ϫ4513.
X-ray Crystallography: A prismatic yellow crystal of 3 (0.56 ϫ 0.48
ϫ 0.40 mm) was selected and mounted in a Lindemann capillary
under an inert gas. Diffraction data were then measured at room
temperature with a Rigaku AFC7S diffractometer using graphite-
[8]
K. Ziegler, H.-G. Gellert, K. Zosel, E. Holzkamp, J. Schneider,
M. Söll, W.-R. Kroll, Justus, Liebigs Ann. Chem. 1960, 629,
121Ϫ166.
J. Boor, Jr., ZieglerϪNatta Catalysts and Polymerizations, Aca-
demic Press, New York, 1979.
U. Birkenstock, H. Bönneman, B. Bogdanovic, D. Walter, G.
Wilke, in: Advances in Chemistry Series, American Chemical
Society, Washington, DC, 1968, vol. 70, p. 250.
K. Fischer, K. Jonas, P. Misbach, R. Stabba, G. Wilke, Angew.
Chem. 1973, 85, 1002; Angew. Chem. Int. Ed. Engl. 1973, 12,
943.
˚
monochromated Mo-Kα radiation (λ ϭ 0.71069 A). Data reduction
[9]
was performed with the crystallographic package TEXSAN.[32] The
ψ-scan method was used to correct data for absorption. Structures
were solved by direct methods using the program SIR92[33] and
refined by means of full-matrix least squares based on F2 including
all diffraction data using the program SHELXL-97.[34] The electron
density map revealed a disordered toluene molecule. A rigid body
refinement was performed for the solvent molecule, considering
two distinct toluene molecules with half occupancy. The hydrogen
[10]
[11]
[12] [12a]
M. P. Coles, R. F. Jordan, J. Am. Chem. Soc. 1997, 119,
Eur. J. Inorg. Chem. 2004, 1292Ϫ1298
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1297

D. Pappalardo, M. Mazzeo, P. Montefusco, C. Tedesco, C. Pellecchia
FULL PAPER
[12b]
8125Ϫ8126.
S. Dagorne, I. A. Guzei, M. P. Coles, R. F.
geometry and a value of 1 to a perfect trigonal-bipyramidal
Jordan, J. Am. Chem. Soc. 2000, 122, 274Ϫ289.
geometry. In this case τ ϭ 0.70.
[13] [13a] E. Ihara, V. G. Young, Jr., R. F. Jordan, J. Am. Chem. Soc.
[25] [25a] A. Le Borgne, N. Spassky, C. Lin Jun, A. Momtaz, Makro-
[13b]
[25b]
1998, 120, 8277Ϫ8278.
A. V. Korolev, E. Ihara, I. A. Gu-
mol. Chem. 1988, 189, 637Ϫ650.-.
H. Sugimoto, C. Kawa-
zei, V. G. Young, Jr., R. F. Jordan, J. Am. Chem. Soc. 2001,
mura, M. Kuroki, T. Aida, S. Inoue, Macromolecules 1994,
123, 8291Ϫ8309.
27, 2013Ϫ2018.
[14]
[15]
[26]
[27]
M. Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P.
White, D. J. Williams, Chem. Commun. 1998, 2523Ϫ2524.
P. A. Cameron, V. C. Gibson, C. Redshaw, J. A. Segal, M. D.
Bruce, A. J. P. White, D. J. Williams, Chem. Commun. 1999,
1883Ϫ1884.
D. Pappalardo, C. Tedesco, C. Pellecchia, Eur. J. Inorg. Chem.
2002, 621Ϫ628.
T. Aida, S. Inoue, Macromolecules 1981, 14, 1166Ϫ1169.
B. Antelmann, M. H. Chisholm, S. S. Iyer, J. C. Huffman, D.
Navarro-Llobet, M. Pagel, Macromolecules 2001, 34,
3159Ϫ3175.
[28]
D. A. Atwood, J. A. Jegier, D. Rutherford, J. Am. Chem. Soc.
1995, 117, 6779Ϫ6780.
[16]
[17]
[18]
[29] [29a]
The reaction between AlR3 and B(C6F5)3 has been de-
H. Martin, H. Bretinger, Makromol. Chem. 1992, 193,
1283Ϫ1288.
scribed in a patent application as a convenient approach to the
synthesis of Al(C6F5)3: P. Biagini, G. Lugli, L. Abis, P. And-
reussi (Enichem Elastomeri S. r. l.), Eur. Patent Appl. EP 0
694 548 A1 1996, p. 1Ϫ9. [29b]M. Bochmann, M. J. Sarfield,
Organometallics 1998, 17, 5908Ϫ5912.
G. Klosin, R. G. Roof, E. Y.-X. Chen, K. A Abboud, Or-
ganometallics 2000, 19, 4684Ϫ4686.
X. Yang, C. L. Stern, T. J. Marks, J. Am. Chem. Soc. 1994,
116, 10015Ϫ10031.
TEXSAN, Crystal Structure Analysis Package, Molecular
Structure Corporation, 1985؊1992.
A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.
C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994,
27, 435.
G. M. Sheldrick, SHELXL-97, A Program For Refining Crystal
Structures, University of Göttingen, Germany, 1997.
L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.
Received February 27, 2003
J. S. Kim, L. M Wojieinski II, S. Liu, J. C. Sworen, A. Sen, J.
Am. Chem. Soc. 2000, 122, 5668Ϫ5669.
[19] [19a] G. Talarico, P. H. M. Budzelaar, Organometallics 2000, 19,
[19b]
[30]
[31]
[32]
[33]
5691Ϫ5695.
G. Talarico, V. Busico, P. H. M. Budzelaar,
[19c]
Organometallics 2001, 20, 4721Ϫ4726.
G. Talarico, P. H.
M. Budzelaar, Organometallics 2002, 21, 34Ϫ38.
R. G. Cavell, K. Aparna, R. P. Kamalesh Babu, Q. Wang, J.
Mol. Cat. A: Chem. 2002, 189, 137Ϫ143.
[20]
[21]
F. A. Hicks, M. Brookhart, Org. Lett. 2000, 2, 219Ϫ221.
[22] [22a]
F. A. Hicks, M. Brookhart, Organometallics 2001, 20,
[22b]
3217Ϫ3219.
F. A. Hicks, J. C. Jenkins, M. Brookhart, Or-
ganometallics 2003, 22, 3533Ϫ3545.
[23]
[24]
[34]
[35]
T. R. Younkin, E. F. Connor, J. I. Henderson, S. K. Friedrich,
R. H. Grubbs, D. A. Bansleben, Science 2000, 287, 460Ϫ462.
The tbp geometry has been assessed, according to ref.[7b], using
the geometric parameter
τ ϭ (β Ϫ α)/60, where β ϭ
O1ϪAl1ϪO1 angle and α ϭ N1ϪAl1ϪN1 angle. A value of
zero applies to a compound with a perfect square-pyramidal
Early View Article
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1298
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Eur. J. Inorg. Chem. 2004, 1292Ϫ1298