Effect of the nitrogen substituent on the reactions of alane towards imino- and aminophenols: Generation of a dinuclear aluminoxane

Article abstract of DOI:10.1002/ejic.201200255

AlH₃·NEtMe₂ reacts with salicylaldimines 3,5-tBu₂-2-(OH)C₆H₂CH=NR [R = C ₆F₅ (1a), 2,6-Me₂C₆H₃ (1b); 0.5 equiv.] to give the bisphenoxido-amido-imino compounds [Al{3,5-tBu₂-2-(O)C₆H₂CH=NR}{3,5-tBu ₂-2-(O)C₆H₂CH₂-NR}] [R = C ₆F₅ (4a), 2,6-Me₂C₆H₃ (4b)]. When the substituent on the nitrogen is 2,6-Me₂C ₆H₃, it is possible to isolate the bis(phenoxido-imino) hydride [AlH{3,5-tBu₂-2-(O)C₆H₂CH=N-2,6-Me ₂C₆H₃}₂] (3) if the reaction is performed at low temperature. Compound 4a is converted in wet toluene at room temperature readily and quantitatively into the aluminoxane [(Al{3,5-tBu ₂-2-(O)C₆H₂CH=NC₆F ₅}{3,5-tBu₂-2-(O)C₆H₂CH ₂-NHC₆F₅})₂O] (5). The mononuclear bis(phenoxido-amino) hydrides [AlH{3,5-tBu₂-2-(O)C₆H ₂CH₂-NHR}₂] [R = 2,6-Me₂C ₆H₃ (6b), tBu (6c)] are obtained by treatment of AlH ₃·NEtMe₂ with aminophenols 3,5-tBu ₂-2-(OH)C₆H₂CH₂-NHR [R = 2,6-Me ₂C₆H₃ (2b), tBu (2c); 0.5 equiv.] in toluene at -78 °C. Compound 6b evolves into [Al{3,5-tBu₂-2-(O)C ₆H₂CH₂-NH-2,6-Me₂C₆H ₃}{3,5-tBu₂-2-(O)C₆H₂CH ₂-N-2,6-Me₂C₆H₃}] (7), which can also be generated by the direct reaction of 2b with AlH₃· NEtMe₂ (0.5 equiv.) at room temperature. The molecular structures of 4b and 5 have been determined by X-ray diffraction analysis. Reaction of different phenol amines and phenol imines with alane leads to new phenoxido-amino, phenoxido-amido and phenoxido-imino derivatives. The result of these reactions depends heavily on the nitrogen substituent. When this group is an electron attractor, such as C₆F₅, the isolation of the dinuclear aluminoxane [(Al{3,5-tBu₂-2-(O)C₆H ₂CH=NC₆F₅}{3,5-tBu₂-2-(O)C ₆H₂CH₂-NHC₆F₅}) ₂O] is achieved. Copyright

Full text of DOI:10.1002/ejic.201200255

Job/Unit: I20255
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FULL PAPER
DOI: 10.1002/ejic.201200255
Effect of the Nitrogen Substituent on the Reactions of Alane towards Imino-
and Aminophenols: Generation of a Dinuclear Aluminoxane
Gema Martínez,[a] Tomás Cuenca,*[a] and Marta E. G. Mosquera*[a]
Keywords: Aluminum / Hydrides / Dinuclear complexes / Substituent effects / Phenols
AlH3·NEtMe2 reacts with salicylaldimines 3,5-tBu2–2-(OH)-
C6H2CH=NR [R = C6F5 (1a), 2,6-Me2C6H3 (1b); 0.5 equiv.] to
give the bisphenoxido-amido-imino compounds [Al{3,5-
tBu2–2-(O)C6H2CH=NR}{3,5-tBu2–2-(O)C6H2CH2–NR}] [R =
C6F5 (4a), 2,6-Me2C6H3 (4b)]. When the substituent on the
nitrogen is 2,6-Me2C6H3, it is possible to isolate the bis-
(phenoxido-imino) hydride [AlH{3,5-tBu2–2-(O)C6H2CH=N–
2,6-Me2C6H3}2] (3) if the reaction is performed at low tem-
perature. Compound 4a is converted in wet toluene at room
temperature readily and quantitatively into the aluminoxane
NHC6F5})2O] (5). The mononuclear bis(phenoxido-amino)
hydrides [AlH{3,5-tBu2–2-(O)C6H2CH2–NHR}2] [R 2,6-
=
Me2C6H3 (6b), tBu (6c)] are obtained by treatment of
AlH3·NEtMe2 with aminophenols 3,5-tBu2–2-(OH)C6H2CH2–
NHR [R = 2,6-Me2C6H3 (2b), tBu (2c); 0.5 equiv.] in toluene
at –78 °C. Compound 6b evolves into [Al{3,5-tBu2–2-
(O)C6H2CH2–NH–2,6-Me2C6H3}{3,5-tBu2–2-(O)C6H2CH2–
N–2,6-Me2C6H3}] (7), which can also be generated by the di-
rect reaction of 2b with AlH3·NEtMe2 (0.5 equiv.) at room
temperature. The molecular structures of 4b and 5 have been
[(Al{3,5-tBu2–2-(O)C6H2CH=NC6F5}{3,5-tBu2–2-(O)C6H2CH2– determined by X-ray diffraction analysis.
oxido-imido (hemisalen) and phenoxido-amino bidentate
Introduction
systems are very attractive ligands due to their steric and
electronic properties and their amenability to modifica-
tion.[2j,2k,10–17] Many studies have been performed with
salen-type ligands to generate aluminium deriva-
tives.[2h,18–22] However, fewer compounds have been re-
ported when using the related hemisalen species.[2j,12,23–26]
In particular, studies on reactions with alanes are
scarce,[14,15,27] although these kind of species have proven
to be suitable starting materials for the generation of
aluminoxanes.[9,28,29]
In our studies, we are interested in the reaction of
phenol-imino and phenol-amino proligands with various
aluminium compounds. In a previous work, we synthesized
N,O bidentate aluminium hydride complexes and rational-
ized the steric and electronic factors that favour the forma-
tion of mono- or dinuclear structures.[27] In those com-
pounds, the final nuclearity that was formed was highly in-
fluenced by the nature of the nitrogen substituent. The
marked effect of this substituent in the catalytic activity of
related aluminium derivatives has also been reported and it
is particularly strong when fluorinated.[23,30] The present
work focuses on the study of the reactions between phenol-
imino and phenol-amino N,O-donor proligands and the al-
ane AlH3·NEtMe2 when using a 2:1 (ligand/Al) stoichiome-
try. In these processes, a clear influence of the nitrogen sub-
stitution is manifested and, depending on this group, it was
possible to isolate phenoxido-amido, phenoxido-amino, or
phenoxido-imino derivatives. The presence of Al–H and
Al–N bonds in the resultant products renders them poten-
tial reactive sources to undergo selective hydrolysis and con-
sequently furnish new aluminoxanes.
Aluminium organometallic derivatives that contain Al–
O bonds are very attractive species due to their remarkable
properties in catalytic reactions.[1] As such, aluminium alk-
oxides are very active in catalytic polymerizations.[2] Also,
the role of methylaluminoxane (MAO) as cocatalyst in
Ziegler–Natta olefin polymerization processes is particu-
larly remarkable.[3]
Although MAO has been used for decades in the indus-
try, its structure is still not very well defined and gaining a
better knowledge remains as a challenging prospect. Studies
oriented toward the controlled hydrolysis of aluminium alk-
yls with water or reactive oxygen-containing species has led
to the isolation and structural characterization of interest-
ing aluminoxanes.[4] However, these species easily undergo
association to give oligomeric structures.[4j,4k,5,6] Therefore
organically modified aluminoxanes that show a low associa-
tion degree are not common,[3c,4l,7] even though they are
highly desirable species on account of their potential appli-
cation in catalysis.
A strategy to hinder the aggregation of the hydrolysis
products and generate low nuclearity aluminoxane deriva-
tives consists of the coordination of bulky ligands to the
aluminium.[8,9] The use of phenols with ortho substituents,
which potentially could give intramolecular coordination,
provides an alternative to steric bulk. In this context, phen-
[a] Departamento de Química Inorgánica, Facultad de Farmacia,
Universidad de Alcalá,
28871 Alcalá de Henares, Madrid, Spain
Fax: +34-918854683
E-mail: martaeg.mosquera@uah.es
tomas.cuenca@uah.es
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G. Martínez, T. Cuenca, M. E. G. Mosquera
FULL PAPER
sphere and is highly soluble in common organic solvents.
Very few molecular aluminoxane species have been re-
Results and Discussion
The proligands 3,5-tBu2–2-(OH)C6H2CH=NR [R = C6F5 ported. In particular, some dinuclear aluminoxanes have
(1a), 2,6-Me2C6H3 (1b)] and 3,5-tBu2–2-(OH)- been described [37 in the CSD version 5.32 updates (August
C6H2CH2–NHR [R = 2,6-Me2C6H3 (2b), tBu (2c)] were 2011) search]; however, in most cases, the aluminium coor-
prepared in good yields (80–95%) as yellow to orange crys- dination sphere is stabilized by nitrogen- or carbon-donor
talline solids in a similar way to analogous procedures pre- ligands and is more scarce than those that bear N,O-donor
viously reported.[11,31–34]
Compounds
(0.5 equiv.) in toluene at room temperature to yield the bis- hemisalen moieties.
ligands. Although five species have been described with
1
were treated with AlH3·NEtMe2 salen ligands[1c,20,35] none have been reported that bear
phenoxido amido-imino species [Al{3,5-tBu2–2-(O)-
The behaviour observed with the different imino groups
C6H2CH=NR}{3,5-tBu2–2-(O)C6H2CH2–NR}] [R = C6F5 might reflect the electron-withdrawing character of the sub-
(4a), 2,6-Me2C6H3 (4b)] with high yields (77 and 91%, stituents. Hence, fluoro substituents on the ring (C6F5)
respectively). When the reaction was performed with 1b in compared with the aliphatic substitution (2,6-Me2C6H3)
toluene at –78 °C, the bis(phenoxido-imino) hydride may induce lower electronic density on the imino carbon,
[AlH{3,5-tBu2–2-(O)C6H2CH=N–2,6-Me2C6H3}2] (3) was thereby turning the hydride migration from the aluminium
obtained. This compound is not stable in solution at room centre to the CH=N group more favourable. Consequently,
temperature and undergoes further evolution to give 4b the formation of compound 4a from the corresponding pre-
through hydrogen transfer from the aluminium centre to cursor Al–H would take place very quickly, and even at low
the carbon backbone of one imino ligand (Scheme 1). This temperature it is not possible to observe the intermediate
result suggests that the reaction that produces 4 occurs with analogous to 3.
evolution of hydrogen from an alcoholysis process, followed
The presence of the rather strong electron-withdrawing
by a hydroalumination reaction. The reaction with 3,5- C6F5 group would also be responsible for the different be-
tBu2–2-(OH)C6H2CH=NtBu was also investigated; how- haviour between 4a and 4b in the presence of water. The
ever, only an intractable solid was obtained.
fluoro substitution (C6F5) might reduce the basicity of the
Compound 4b was isolated in a pure form by washing nitrogen atom relative to the alkyl substitution (2,6-
the solid with hexanes and further recrystallization from Me2C6H3), thus weakening the Al–N interaction and facili-
toluene. However, under similar conditions, 4a evolved at tating the insertion of a molecule of water to give the alumi-
room temperature quantitatively into the aluminoxane noxane 5. The effect of undergoing an easier hydrolysis pro-
[(Al{3,5-tBu2–2-(O)C6H2CH=NC6F5}{3,5-tBu2–2-(O)
cess has also been observed in Al compounds with diketini-
C6H2CH2–NHC6F5})2O] (5) through a hydrolysis reaction minate ligands that bear C6F5 substituents.[36]
that involved the Al–N amido bond cleavage to give an
The spectroscopic data and the elemental analysis concur
amine group and a new Al–O bond. Compound 5 is stable with the proposed structures. For 3, the 1H NMR spectrum
over a long period of time when stored under an inert atmo- (C6D6) shows two equal intensity singlets at δ = 2.70 and
Scheme 1.
2
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Reactions of Alane towards Imino- and Aminophenols
1.88 ppm on account of the methyl group and two singlets tance being within the range for a multiple bond,
at δ = 1.40 and 1.22 ppm for the tBu groups, thereby re- 1.306(6) Å. The other metallacycle is the outcome of the
flecting a C2 symmetry. A resonance at δ = 7.53 ppm for coordination of a phenoxido-amido moiety and shows a
the imine CH hydrogen, with the corresponding 13C NMR puckered geometry with
a longer C1–N1 distance,
spectroscopic signal at δ = 171.7 ppm, together with a 1.495(7) Å. The deviation from the ideal tetrahedral geome-
broad signal at δ = 4.24 ppm that indicates the presence of try around the aluminium centre is imposed by the geomet-
a hydride, concurs with the formation of the bis(phenoxido- ric restrictions of the planar phenoxido-imino ring.
imino) hydride. A further confirmation of the presence of a
Table 2. Selected bond lengths [Å] and angles [°] for 5·5C6H6.
hydride hydrogen comes from the IR spectrum that displays
Angles[a]
a strong Al–H stretching absorption at 1760.5 cm–1.[37]
As proposed in Scheme 1, the aluminium centre in 4a
and 4b is bonded to two different phenoxido-imino and
phenoxido-amido chelate ligands in a four-coordinate ge-
ometry. Spectroscopic data show the lack of symmetry in
these chiral derivatives. The 1H NMR spectra (C6D6) of
4a and 4b highlight the diastereotopic nature of the benzyl
methylene protons and show a set of doublets in the δ =
4.20–4.50 ppm region. The imine protons give singlets at δ
= 7.27 ppm for 4b and δ = 7.40 ppm for 4a, with the 13C
NMR spectroscopic signals occurring at δ = 177.6 and
179.2 ppm, respectively. Four resonances for the tBu groups
are observed between δ = 1.63 and 1.14 ppm. For 4b the
methyl groups appear at δ = 1.21 and 2.64 ppm with high-
field-shifted signals on account of the anisotropic effect
from the phenol portion of the ligand.
Bond lengths
Al1–O1
Al1–O3
Al1–O2
Al1–N1
O2–C1
O3–C22
N1–C15
N1–C16
N2–C37
N2–C36
1.6972(8)
1.7329(19)
1.7667(19)
1.949(2)
1.334(3)
1.365(3)
1.318(3)
1.448(4)
1.399(4)
1.477(4)
O1–Al1–O3
O1–Al1–O2
O3–Al1–O2
O1–Al1–N1
O3–Al1–N1
O2–Al1–N1
Al1–O1–Al1#1
C1–O2–Al1
C22–O3–Al1
C15–N1–C16
C15–N1–Al1
C16–N1–Al1
C37–N2–C36
O2–C1–C14
O2–C1–C2
115.13(8)
116.12(8)
109.91(10)
109.61(8)
108.37(10)
95.77(9)
180.00(5)
131.59(17)
142.73(18)
116.5(2)
121.63(19)
121.77(17)
122.5(3)
120.6(2)
120.8(2)
[a] Symmetry transformations used to generate equivalent atoms:
#1 –x + 1, –y, –z + 1.
For compound 5, the 1H NMR spectrum (C6D6) exhibits
a resonance at δ = 7.37 ppm due to the imino protons, with
the corresponding 13C NMR spectroscopic signal at δ =
178.4 ppm. The diastereotopic benzylic methylene protons
are observed as multiplets at δ = 4.61 and 4.16 ppm. A
characteristic NH signal appears as a broad multiplet at δ
= 4.44 ppm. Four high-field-shifted singlets are observed
due to the environmentally different tBu groups.
The structure in the solid state for 4b and 5 was con-
firmed by a study of single-crystal X-ray diffraction. Crys-
tals of 4b suitable for analysis were grown from a hexane
solution. The selected bond lengths and angles are listed in
Tables 1 and 2, and crystallographic data are summarized
in Table 3. The quality of the data was poor; however, the
geometry around the aluminium atom is unambiguous. As
shown in Figure 1, the metal shows that a distorted tetrahe-
dral environment is the common mode of two metallacycles.
One of them is planar and results from the coordination of
a phenoxido-imino ligand, as revealed by the C2–N2 dis-
Figure 1. ORTEP plot of compound 4b showing thermal ellipsoid
plots (30% probability). The methyl groups of the tBu moieties
have been omitted for clarity.
Crystals of 5 suitable for X-ray analysis were grown from
C6H6. Selected bond lengths and angles are listed in Table 2
and in Figure 2 an ORTEP plot of 5 is depicted. As shown,
this compound is a centrosymmetric molecule that consists
of two Al[3,5-tBu2–2-(O)C6H2CH=NC6F5][3,5-tBu2–2-(O)-
C6H2CH2–NHC6F5] moieties linked by an oxo group. The
linear geometry around the μ-O atom with a Al1–O1–
Al1#1 bond angle of 180.00(5)° is imposed since O1 occu-
pies a crystallographic inversion centre. The Al1–O1 dis-
tance [1.6972(8) Å] is comparable to those found for oxo-
bridged aluminium.[9,33,38,39] Although the metal environ-
ments are chiral, the molecule 5 is not on account of the
presence of the inversion centre. The aluminium atoms
present a very distorted tetrahedral geometry with the re-
maining three positions occupied by the chelate phenoxido-
Table 1. Selected bond lengths [Å] and angles [°] for compound 4b.
Bond lengths
Angles
Al1–O2
Al1–O1
Al1–N1
Al1–N2
N1–C1
N2–C2
O1–C10
O2–C20
C1–C11
C2–C21
1.752(4)
1.749(4)
1.813(5)
1.945(4)
1.495(7)
1.306(7)
1.379(6)
1.333(6)
1.527(8)
1.453(8)
O2–Al1–O1
O2–Al1–N1
O2–Al1–N2
O1–Al1–N2
N1–Al1–N2
C1–N1–Al1
C2–N2–Al1
C10–O1–Al1
C20–O2–Al1
N1–C1–C11
N2–C2–C21
115.9(2)
120.0(2)
103.5(2)
95.02(19)
105.9(2)
116.1(2)
108.4(3)
123.1(4)
125.0(3)
132.5(3)
114.6(5)
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imino ligand and the oxygen atom from the newly generated
phenoxido-amino ligand. The Al1–O2 and Al1–O3 bond
lengths [1.7666(18) and 1.7329(19) Å] are longer than the
one between the metal and the oxo-ligand, and within the
range for aluminium derivatives that bear salicylaldiminate
ligands. The Al1–N1 distance, 1.947(2) Å, is also in the
range observed for these systems.
Scheme 2.
Al–H signals appear as an enhancement base line at δ =
4.43 and 4.35 ppm. In the IR spectra, νAl–H bands at
1844.7 cm–1 for 6b and 1841.1 cm–1 for 6c are observed as
well.[37] The spectroscopic data for compound 7 evidence
the lack of symmetry in this chiral compound. A set of
doublets at δ = 4.62 and 3.70 ppm confirms the AB spin
system for the benzylic methylene group protons in the
phenoxido-amido ligand. The methylene protons of the
phenoxido-amino ligand exhibit coupling constants with
the NH group, which appear as two multiplets at δ = 4.12
Figure 2. ORTEP plot of compound 5 showing thermal ellipsoid
plots (30% probability).
1
Compound 5 crystallizes with five C6H6 that have a great
impact on the packing, as the molecules associate in the
crystal by π stacking and C–H···F interactions amongst the
compound and the solvent molecules.
and 3.03 ppm in the H NMR spectrum. The NH proton
appears as a broad mutiplet at δ = 5.22 ppm. The presence
of four singlets between δ = 1.62 and 3.30 ppm corroborates
the inequivalent nature of the methyl groups.
In a procedure similar to that for 3, the proligands 3,5-
tBu2–2-(OH)C6H2CH2–NHR [R = 2,6-Me2C6H3 (2b), tBu
(2c)] were treated with AlH3·NEtMe2 (0.5 equiv.) in toluene
at –78 °C to give the mononuclear bis(phenoxido-amino)
hydrides [AlH{3,5-tBu2–2-(O)C6H2CH2–NHR}2] [R = 2,6-
Me2C6H3 (6b), tBu (6c)] in good yield, which are thermally
stable in the solid state under inert atmosphere but air-sen-
sitive. Again, a different behaviour in solution at room tem-
perature is observed depending on the substituent on the
nitrogen. Whereas in 6c a hydridic hydrogen atom remains
bonded to the aluminium centre, 6b undergoes aminolysis
with loss of hydrogen to give the new chiral derivative
[Al{3,5-tBu2–2-(O)C6H2CH2–NH–2,6-Me2C6H3}{3,5-
tBu2–2-(O)C6H2CH2–N–2,6-Me2C6H3}] (7). Compound 7
can also be obtained alternatively by the direct reaction of
2b with AlH3·NEtMe2 (0.5 equiv.) at room temperature
In view of this experimental result, we suggest that both
the conformation and basicity of the amine groups influ-
ence the formation of 7. A favourable disposition in 6b, in
which the amine hydrogen adopts the same orientation as
the axial hydride bonded to aluminium, could facilitate the
loss of hydrogen, thereby affording compound 7. Aromatic
substitution (2,6-Me2C6H3) on the nitrogen induces a lower
basicity to the amine with respect to the aliphatic substitu-
tion (tBu), thus rendering the hydrogen atom more pro-
tonic. In consequence, the evolution of hydrogen to afford
the corresponding chiral tetracoordinate compound should
be easier for compound 6b than for 6c.
Conclusion
This work provides insight into the reactivity of phenol-
(Scheme 2). Also, we performed the reaction with 3,5-tBu2– imine and phenol-amine organic molecules towards
2-(OH)C6H2CH2–NHC6F5 without achieving clear results. AlH3·NEtMe2 when using a 2:1 stoichiometry. The final
The NMR spectra (C6D6) for compounds 6 confirm the isolated structures are highly dependent on the nitrogen
coordination of the phenoxido-amino ligands {3,5-tBu2–2- substituent. As such, reactions of phenol-imine compounds
(O)C6H2CH2–NHR} to the aluminium centre to give a with AlH3·NEtMe2 proceed through formal loss of hydro-
symmetrical structure. The NH protons are shown as a gen, consistent with alcoholysis and hydroalumination, to
broad signal at δ = 5.39 and 2.76 ppm. The characteristic render the tetracoordinate chiral complexes 4 that contain
4
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Reactions of Alane towards Imino- and Aminophenols
[C(CH3)3], 34.1 [C(CH3)3], 35.1 [C(CH3)3], 35.2 [C(CH3)3], 54.0
(CH2–N), 118.8, 121.7, 118.5, 122.9, 123.0, 124.2, 125.4, 128.6,
128.8, 129.2, 130.0, 130.1, 132.2, 132.7, 133.9, 136.9, 137.5, 139.6,
140.6, 141.0, 141.4, 142.3, 155.0, 164.0 (all Ar-C), 179.2 (CH=N)
ppm. 19F NMR: δ = –148.0 (2 F), –152.5 (1 F), –155.7 (2 F), –160.0
(2 F), –165.8 (2 F), –173 (1 F) ppm. C42H43AlF10N2O2 (824.78):
calcd. C 61.2, H 5.2, N 3.4; found C 60.9, H 4.9, N 3.2.
chelating phenoxido-imino and phenoxido-amido ligands.
When the substituent on the nitrogen atom is a mesytil
group, the pentacoordinate bis(phenoxido-imino) hydride 3
is obtained if the reaction is performed at –78 °C. Only if
the substituent was a perfluorinated arene was it possible
to isolate the dinuclear aluminoxane 5 by a hydrolysis reac-
tion of 4a. Analogous reactions with phenol-amines at
room temperature gave the bis(phenoxido-amino) hydrides
6. Again, the substituent on the nitrogen determines the
fate of the compounds and derivative 6b evolves into the
chiral phenoxido-amino phenoxido-amido compound 7 by
means of formal loss of hydrogen.
[Al{3,5-tBu2–2-(O)C6H2CH=N–2,6-Me2C6H3}{3,5-tBu2–2-(O)-
C6H2CH2–N–2,6-Me2C6H3}] (4b): A solution of 1b (0.50 g,
1.48 mmol) in toluene (10 mL) was added dropwise to a solution
of AlH3·NEtMe2 (0.5 m, 1.50 mL, 0.74 mmol) in toluene (20 mL)
at room temperature. The mixture was stirred for 12 h. Then the
volatiles were removed under reduced pressure and the product was
dissolved in hexane (10 mL). The extract was filtered and the fil-
trate was cooled to –30 °C to give yellow crystals of 4b; yield 77%
Experimental Section
1
(0.40 g, 0.57 mmol). H NMR (C6D6): δ = 1.19 [s, 9 H, C(CH3)3],
General Considerations: All manipulations were conducted using
Schlenk techniques in conjunction with an inert atmosphere
glovebox. All solvents were rigorously dried prior to use. NMR
spectra were recorded at 400.13 (1H), 376.00 (19F) and 100.60 MHz
(13C) with a Bruker AV400. Chemical shifts (δ) are given in ppm
using C6D6 as solvent. 1H and 13C resonances were measured rela-
tive to solvent peaks considering TMS δ = 0 ppm, whereas 19F
was measured relative to external CFCl3. Elemental analyses were
obtained with a Perkin–Elmer Series II 2400 CHNS/O analyzer.
Infrared data were recorded as KBr pellets at room temperature
with a Perkin–Elmer Spectrum-2000 FT-IR spectrometer and are
reported in cm–1. All reagents, 3,5-di-tert-butyl-2-hydroxybenzalde-
hyde, tert-butylamine, 2,6-dimethylaniline, pentafluoroaniline and
the alane aluminium complex solution AlH3·NEtMe2 were com-
mercially obtained and used without further purification.
1.21 (s, 3 H, Ar–CH3), 1.31 [s, 9 H, C(CH3)3], 1.58 [s, 9 H,
C(CH3)3], 1.63 [s, 9 H, C(CH3)3], 1.73 (br. s, 3 H, Ar–CH3), 2.31 (s,
3 H, Ar–CH3), 2.64 (br. s, 3 H, Ar–CH3), 4.20 (d, JH,H = 15.0 Hz, 1
4
H, CH2–N), 4.28 (d, JH,H = 15.0 Hz, 1 H, CH2–N), 6.67 (d, JH,H
4
= 2.0 Hz, 1 H, OAr–H), 6.73 (m, 2 H, NAr–H), 6.84 (d, JH,H
=
2.0 Hz, 1 H, OAr–H), 6.89 (m, 2 H, NAr–H), 7.01 (m, 2 H, NAr–
4
H), 7.27 (s, 1 H, CH=N), 7.47 (d, JH,H = 2.0 Hz, 1 H, OAr–H),
7.76 (d, 4JH,H = 2.0 Hz, 1 H, OAr–H) ppm. 13C NMR (C6D6): δ =
17.6 (NAr–CH3), 18.1 (NAr–CH3), 19.2 (NAr–CH3), 20.1 (NAr–
CH3), 29.6 [C(CH3)3], 30.5 [C(CH3)3], 31.0 [C(CH3)3], 31.8
[C(CH3)3], 34.0 [C(CH3)3], 34.1 [C(CH3)3], 35.3 [C(CH3)3], 35.4
[C(CH3)3], 58.0 (CH2–N), 118.8, 121.7, 122.9, 123.0, 128.6, 128.8,
129.2, 130.0, 132.2, 132.7, 133.9, 137.5, 139.6, 140.6, 141.4, 145.3,
150.7, 155.6, 162.7 (all Ar–C), 177.6 (CH=N) ppm. C46H61AlN2O2
(700.98): calcd. C 78.9, H 8.7, N 3.9; found C 78.5, H 9.1, N 4.0.
[AlH{3,5-tBu2–2-(O)C6H2CH=N–2,6-Me2C6H3}2] (3): A solution
of 1b (0.50 g, 1.48 mmol) in toluene (10 mL) was added dropwise to
a solution of AlH3·NEtMe2 (0.5 m, 1.50 mL, 0.74 mmol) in toluene
(20 mL) at –78 °C. The pale yellow solution was stirred for 30 min
to allow gas evolution and then brought quickly to room tempera-
ture. The solvent was removed in vacuo, and compound 3 was iso-
lated as a yellow solid; yield 86% (0.44 g, 0.62 mmol). 1H NMR
(C6D6): δ = 1.22 [s, 18 H, C(CH3)3], 1.40 [s, 18 H, C(CH3)3], 1.88
(s, 6 H, Ar–CH3), 2.70 (s, 6 H, Ar–CH3), 4.24 (br. s, 1 H, AlH),
6.81 (d, 4JH,H = 2.5 Hz, 2 H, OAr–H), 6.94 (m, 2 H, NAr–H), 7.01
[(Al{3,5-tBu2–2-(O)C6H2CH=NC6F5}{3,5-tBu2–2-(O)C6H2CH2–
NHC6F5})2O] (5): Compound 5 was obtained in quantitative yield
as bright yellow crystals from a solution of 4a in wet toluene at
room temperature. Crystals suitable for X-ray diffraction were
1
grown from a C6H6 solution. H NMR (C6D6): δ = 1.18 [s, 18 H,
C(CH3)3], 1.26 [s, 18 H, C(CH3)3], 1.38 [s, 18 H, C(CH3)3], 1.49 [s,
18 H, C(CH3)3], 4.16 (m, 2 H, CH2–N), 4.44 (m, 2 H, NH), 4.61
4
(m, 2 H, CH2–N), 6.76 (d, JH,H = 2.0 Hz, 2 H, OAr–H), 7.01 (d,
4
4JH,H = 2.0 Hz, 2 H, OAr–H), 7.35 (d, JH,H = 2.0 Hz, 2 H, OAr–
4
4
H), 7.37 (s, 2 H, CH=N), 7.74 (d, JH,H = 2.0 Hz, 2 H, OAr–H)
(m, 4 H, NAr–H), 7.52 (d, JH,H = 2.5 Hz, 2 H, OAr–H), 7.53 (s,
ppm. 13C NMR (C6D6): δ = 29.30 [C(CH3)3], 29.5 [C(CH3)3], 30.9
[C(CH3)3], 31.6 [C(CH3)3], 33.8 [C(CH3)3], 33.9 [C(CH3)3], 34.9
[C(CH3)3], 35.3 [C(CH3)3], 51.7 (CH2–N), 118.9–164.7 (all Ar–C),
178.4 (CH=N) ppm. 19F NMR: δ = –146.2 (4 F), –155.0 (4 F),
–155.8 (4 F), –159.9 (4 F), –165.8 (4 F) ppm. C84H88Al2F20N4O5
(1666.6): calcd. C 60.5, H 5.3, N 3.3; found C 60.4, H 5.2, N 3.1.
2 H, CH=N) ppm. 13C NMR (C6D6): δ = 19.2 (NAr–CH3), 20.8
(NAr–CH3), 29.6 [C(CH3)3], 31.7 [C(CH3)3], 33.8 [C(CH3)3], 35.3
[C(CH3)3], 121.7, 125.9, 128.3, 128.4, 129.0, 129.9, 131.4, 132.7,
138.5, 140.1, 149.4, 160.8, (all Ar–C), 171.7 (CH=N) ppm. IR (KBr
pellet): ν
= 1760.5 (st) cm–1. C46H61AlN2O2 (700.98): calcd. C
˜
Al–H
78.9, H 8.7, N 3.9; found C 78.2, H 9.2, N 4.1.
[Al{3,5-tBu2–2-(O)C6H2CH=NC6F5}{3,5-tBu2–2-(O)C6H2CH2–
NC6F5}] (4a): A solution of 1a (0.20 g, 0.50 mmol) in toluene
(10 mL) was added dropwise to a solution of AlH3·NEtMe2 (0.5 m,
0.50 mL, 0.25 mmol) in toluene (20 mL) at –78 °C. The yellow solu-
tion was stirred for 30 min to allow gas evolution and then brought
quickly to room temperature. The solvent was removed in vacuo,
thus leaving a yellow microcrystalline that corresponded to com-
[AlH{3,5-tBu2–2-(O)C6H2CH2–NH–2,6-Me2C6H3}2] (6b): A solu-
tion of 2b (0.30 g, 0.88 mmol) in toluene (10 mL) was added drop-
wise to a solution of AlH3·NEtMe2 (0.5 m, 0.88 mL, 0.44 mmol)
in toluene (20 mL) at –78 °C. The reaction was warmed to room
temperature and then stirred for 12 h. Volatiles were removed under
reduced pressure and the product was extracted into hexane
(10 mL). Compound 6b was isolated as white microcrystalline so-
1
pound 4a; yield 91% (0.18 g, 0.22 mmol). 1H NMR (C6D6): δ = lid; yield 84% (0.26 g, 0.38 mmol). H NMR (C6D6): δ = 1.27 [s,
1.14 [s, 9 H, C(CH3)3], 1.19 [s, 9 H, C(CH3)3], 1.34 [s, 9 H,
C(CH3)3], 1.62 [s, 9 H, C(CH3)3], 4.35 (d, JH,H = 14.8 Hz, 1 H,
18 H, C(CH3)3], 1.61 [s, 18 H, C(CH3)3], 2.20 (br. s, 12 H, Ar–
CH3), 4.42 (m, 4 H, CH2–N), 4.43 (br. s, 1 H, AlH), 5.39 (m, 2 H,
4
4
CH2–N), 4.47 (d, JH,H = 14.8 Hz, 1 H, CH2–N), 6.79 (d, JH,H
=
NH), 6.69 (d, JH,H = 2.4 Hz, 2 H, OAr–H), 6.76 (m, 4 H, NAr–
4
4
2.0 Hz, 1 H, OAr–H), 7.27 (d, JH,H = 2.0 Hz, 1 H, OAr–H), 7.40
H), 6.81 (m, 2 H, NAr–H), 7.55 (d, 2 H, JH,H = 2.4 Hz, OAr–H)
(s, 1 H, CH=N), 7.48 (d, JH,H = 2.0 Hz, 1 H, OAr–H), 7.73 (d,
ppm. 13C NMR (C6D6): δ = 19.54 (NAr–CH3), 30.1 [C(CH3)3],
31.5 [C(CH3)3], 33.9 [C(CH3)3], 35.0 [C(CH3)3], 55.2 (CH2–N),
4
4JH,H = 2.0 Hz, 1 H, OAr–H) ppm. 13C NMR (C6D6): δ = 28.7
[C(CH3)3], 29.8 [C(CH3)3], 30.6 [C(CH3)3], 31.7 [C(CH3)3], 33.9 123.6, 123.9, 125.4, 129.0, 130.0, 133.6, 136.6, 139.6, 142.2, 157.4
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5

Job/Unit: I20255
/KAP1
Date: 25-06-12 10:15:09
Pages: 8
G. Martínez, T. Cuenca, M. E. G. Mosquera
FULL PAPER
(all Ar–C) ppm. IR (KBr pellet): ν
C46H65AlN2O2 (705.0): calcd. C 78.4, H 9.2, N 3.9; found C 78.2,
H 8.9, N 3.6.
= 1844.7 (st) cm–1.
atoms bonded to the disorder C42 atom that were not placed. As
well in 5 the hydrogen atoms on N2, C15, C15D and C14D were
found in the Fourier map and refined. Full-matrix least-squares
refinements were carried out by minimizing Σw(F2o – Fc2)2 with the
SHELXL-97 weighting scheme and stopped at shift/err Ͻ 0.001.
The final residual electron-density maps showed no remarkable fea-
tures. CCDC-870482 (for 4b) and -870483 (for 5·5C6H6) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
˜
Al–H
[AlH{3,5-tBu2–2-(O)C6H2CH2–NHtBu}2] (6c): The reaction be-
tween 2c (0.30 g, 1.03 mmol) and AlH3·NEtMe2 (0.5 m, 1.03 mL,
0.51 mmol) was carried out in the same way as described for the
synthesis of 6b. The product was extracted into hexane (10 mL).
Filtration followed by cooling at –30 °C afforded 6c as a white so-
1
lid; yield 81% (0.25 g, 0.41 mmol). H NMR (C6D6): δ = 1.15 [s,
18 H, C(CH3)3], 1.42 [s, 18 H, C(CH3)3], 1.61 [s, 18 H, C(CH3)3],
2.76 (m, 2 H, NH), 3.57 (m, 2 H, CH2–N), 4.35 (m, 2 H, CH2–N),
Table 3. Crystallographic data for 4b and 5·5C6H6.
4
4.35 (br. s, 1 H, AlH), 6.95 (d, JH,H = 2.0 Hz, 1 H, OAr–H), 7.51
4
4b
5·5C6H6
(d, JH,H = 2.0 Hz, 1 H, OAr–H) ppm. 13C NMR (C6D6): δ = 28.3
[C(CH3)3], 29.8 [C(CH3)3], 34.1 [C(CH3)3], 34.0 [C(CH3)3], 34.1
[C(CH3)3], 34.6 [C(CH3)3], 46.8 (CH2–N), 122.8, 123.9, 124.2,
Formula
C46H61AlN2O2
700.95
C114H118Al2F20N4O5
2058.08
Mr
Colour/habit
Crystal dimensions [mm]
Crystal system
Space group
a [Å]
white/prism
white/prism
136.4, 138.8, 157.2 (all Ar–C) ppm. IR (KBr pellet): νAl–H = 1841.1
˜
0.40ϫ0.33ϫ0.30 0.39ϫ0.35ϫ0.29
monoclinic
P21/n
14.528(3)
17.127(4)
16.875(4)
90
90.291(16)
90
(st) cm–1. C38H65AlN2O2 (608.5): calcd. C 75.0, H 10.6, N 4.6;
found C 75.5, H 10.3, N 4.0.
triclinic
¯
P1
14.711(4)
14.767(3)
16.424(2)
64.273(15)
67.655(13)
62.596(17)
2780.0(9)
1
[Al{3,5-tBu2–2-(O)C6H2CH2–NH–2,6-Me2C6H3}{3,5-tBu2–2-(O)-
b [Å]
c [Å]
C6H2CH2–N–2,6-Me2C6H3}] (7):
A solution of 2b (0.30 g,
α [°]
0.88 mmol) in toluene (10 mL) was added dropwise to a solution
of AlH3·NEtMe2 (0.5 m, 0.88 mL, 0.44 mmol) in toluene (20 mL)
at room temperature. The yellow solution was stirred for 4 h. Vola-
tiles were removed under reduced pressure and the product was
extracted into hexane (10 mL). Filtration followed by cooling at
–30 °C afforded 7 as a white microcrystalline solid; yield 87%
β [°]
γ [°]
V [Å3]
4198.8(16)
4
Z
T [K]
200
200
ρcalcd. [gcm–3]
1.109
1.229
μ [mm–1]
0.086
0.112
1
(0.27 g, 0.38 mmol). H NMR (C6D6): δ = 1.30 [s, 9 H, C(CH3)3],
F(000)
1520
1076
θ range [°]
3.01–25.00
27603
3.09–25.00
18727
1.39 [s, 9 H, C(CH3)3], 1.41 [s, 9 H, C(CH3)3], 1.62 (s, 3 H, Ar–
CH3), 1.66 (s, 3 H, Ar–CH3), 1.75 [s, 9 H, C(CH3)3], 2.09 (s, 3 H,
Ar–CH3), 3.03 (s, 3 H, Ar–CH3), 3.03 (m, 1 H, CH2–NH), 3.70 (d,
JH,H = 14.4 Hz, 1 H, CH2–N), 4.12 (m, 1 H, CH2–NH), 4.62 (d,
JH,H = 14.4 Hz, 1 H, CH2–N), 5.22 (m, 1 H, NH), 6.50 (m, 2 H,
Reflections collected
Independent reflections Rint
Data/restraints/parameters
R1/wR2 [IϾ2σ(I)][a]
R1/wR2 (all data)[a]
Extinction coefficient
GoF (on F2)[b]
Largest diff. peak/hole [eÅ–3]
7383/0.1316
7383/0/474
0.1552/0.2220
0.2069/0.2414
0.0029(5)
1.224
9756/0.0360
9756/0/671
0.0681/0.1753
0.1013/0.1966
4
NAr–H), 6.69 (m, 2 H, NAr–H), 6.76 (d, JH,H = 2.4 Hz, 1 H,
1.090
+0.549/–0.514
4
OAr–H), 6.80 (d, JH,H = 2.4 Hz, 1 H, OAr–H), 7.00 (m, 2 H,
0.359/–0.469
4
4
NAr–H), 7.37 (d, JH,H = 2.4 Hz, 1 H, OAr–H), 7.61 (d, JH,H
=
[a] R1 = Σ(||Fo| – |Fc||)/Σ|Fo|; wR2 = {Σ[w(F2o – Fc2)2]/Σ[w(F2o)2]}1/2
.
2.4 Hz, 1 H, OAr–H) ppm. 13C NMR (C6D6): δ = 17.4 (NAr–CH3),
17.5 (NAr–CH3), 18.8 (NAr–CH3), 18.9 (NAr–CH3), 29.9
[C(CH3)3], 30.2 [C(CH3)3], 31.7 [C(CH3)3], 31.8 [C(CH3)3], 34.0
[C(CH3)3], 34.1 [C(CH3)3], 34.9 [C(CH3)3], 35.3 [C(CH3)3], 55.5
(CH2–NH), 57.9 (CH2–N), 121.7, 121.9, 123.1, 123.2, 123.6, 123.7,
125.0, 125.4, 128.5, 128.6, 129.6, 129.8, 131.3, 132.6, 136.6, 137.1,
137.2, 137.9, 139.7, 139.9, 141.1, 150.5, 155.0, 157.1 (all Ar–C)
ppm. C46H63AlN2O2 (702.5): calcd. C 78.6, H 9.0, N 3.9; found C
78.9, H 8.8, N 3.5.
[b] GOF = {Σ[w(F2o – F2c)2]/(n – p)}1/2
.
Acknowledgments
Financial support by the Spanish Ministerio de Economía y Com-
petitividad (project number CTQ2011-23497) is gratefully acknowl-
edged. G. M. acknowledges the Comunidad Autónoma de Madrid
for a research contract.
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Eur. J. Inorg. Chem. 0000, 0–0

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Received: March 13, 2012
Published Online: ᭿
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7

Job/Unit: I20255
/KAP1
Date: 25-06-12 10:15:09
Pages: 8
G. Martínez, T. Cuenca, M. E. G. Mosquera
FULL PAPER
Aluminoxane Chemistry
Reaction of different phenol amines and
phenol imines with alane leads to new
phenoxido-amino, phenoxido-amido and
phenoxido-imino derivatives. The result of
these reactions depends heavily on the ni-
trogen substituent. When this group is an
electron attractor, such as C6F5, the iso-
lation of the dinuclear aluminoxane
[(Al{3,5-tBu2–2-(O)C6H2CH=NC6F5}{3,5-
G. Martínez, T. Cuenca,*
M. E. G. Mosquera* ......................... 1–9
Effect of the Nitrogen Substituent on the
Reactions of Alane towards Imino- and
Aminophenols: Generation of a Dinuclear
Aluminoxane
Keywords: Aluminum / Hydrides / Di-
nuclear complexes / Substituent effects /
Phenols
tBu2–2-(O)C6H2CH2–NHC6F5})2O]
is
achieved.
8
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