Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

Article abstract of DOI:10.1016/j.jorganchem.2011.09.020

The present contribution describes the synthesis and structural characterization of structurally diverse organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al complexes are all derived from the reaction of AlMe

Full text of DOI:10.1016/j.jorganchem.2011.09.020

Journal of Organometallic Chemistry 696 (2012) 4248e4256
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural diversity and versatility for organoaluminum complexes supported
by mono- and di-anionic aminophenolate bidentate ligands
Aline Maisse-François b, Laurine Azor a, Anne-Laure Schmitt a, Ariane Coquel a, Lydia Brelot c,
,
a,
*
Richard Welter a, Stéphane Bellemin-Laponnaz b , Samuel Dagorne
*
a Laboratoire DECOMET, Institut de Chimie (CNRS UMR 7177), Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg, France
b Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), (CNRS UMR 7504), Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg, France
c Service de Radiocristallographie, Institut de Chimie (CNRS UMR 7177), Université de Strasbourg 1, rue Blaise Pascal, 67070 Strasbourg, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The present contribution describes the synthesis and structural characterization of structurally diverse
organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al
complexes are all derived from the reaction of AlMe3 with aminophenols 2-CH2NH(R)-C6H3OH (1a,
R ¼ mesityl (Mes); 1b, R ¼ 2,6-di-isopropylphenyl (Diip)) and 2-CH2NH(R)-4,6-tBu2-C6H2OH (1c,
R ¼ Mes; 1d, R ¼ Diip). The low temperature reaction of AlMe3 with 1aeb readily affords the corre-
Received 26 July 2011
Received in revised form
3 September 2011
Accepted 26 September 2011
sponding Al dimeric species [
membered ring aluminacycles with two
crystallographic studies. Heating a toluene solution of 2a (80 ꢀC, 3 h) affords the quantitative and direct
formation of the dinuclear aluminium complex Al[
2-N; 2-O-{2-CH2N(Mes)-C6H4O}](AlMe2) (4a)
while species 2b, under the aforementioned conditions, affords the formation of the Al dimeric species
2-N,O-{2-CH2N(Dipp)-C6H4O}AlMe]2 (3b), as deduced from X-ray crystallography for both 3b and 4a. In
contrast, the reaction of bulky aminophenol pro-ligands 1ced with AlMe3 afford the corresponding
monomeric Al aminophenolate chelate complexes
2-N,O-{2-CH2NH(R)-4,6-tBu2-C6H2O}AlMe2 (5ced;
m- ,h
h1 1-N,O-{2-CH2NH(R)-C6H4O}]2Al2Me4 (2aeb), consisting of twelve-
Keywords:
Organoaluminium
NO ligands
Aminophenol
Structural characterization
m- ,h
h1 1-N,O-aminophenolate units, as determined by X-ray
h
m,h
[
h
h
R ¼ Mes, Diip; Scheme 3) as confirmed by X-ray crystallographic analysis in the case of 5d. Subsequent
heating of species 5ced yields, via a methane elimination route, the corresponding Al-THF amido species
h
2-N,O-{2-CH2N(R)-4,6-tBu2-C6H2O}Al(Me)(THF) (6ced; R ¼ Mes, Diip). Compounds 6ce6d, which are of
the type {X2}Al(R)(L) (L labile), may well be useful as novel well-defined Lewis acid species of potential
use for various chemical transformations. Overall, the sterics of the aminophenol backbone and, to
a lesser extent, the reaction conditions that are used for a given ligand/AlMe3 set essentially govern the
rather diverse “structural” outcome in these reactions, with a preference toward the formation of
mononuclear Al species (i.e. species 5ced and 6ced) as the steric demand of the chelating N,O-ligand
increases.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
group 13 metal species is greatly influenced by their molecular
structure which, to some extent, may be dictated by appropriate
Well-defined organoaluminum compounds supported by
various N- and/or O-based multidentate chelating ligands, such as,
for instance, salen- and salan-derived ligands have found
numerous applications in homogeneous catalysis ranging from
their use in the mediation of various Lewis acid-assisted organic
reactions to that in polymerization catalysis of polar monomers
(cyclic esters, epoxides) [1e3]. In general, the reactivity of such
ligand design. In this regard, the well-known propensity of group
13 metal complexes towards aggregates formation (through diverse
binding/bridging modes) often complicates their coordination
chemistry and the obtainment of the envisioned species. Yet,
despite the frequent requirement for thorough characterization,
knowledge of the coordination trends (of a given class of ligand)
towards Al appears to be crucial so that to gain insight on their
potential reactivity and usefulness as catalysts.
Over the past few years, we have been interested into the
coordination chemistry of LXꢁ-type bidentate aminophenolate (A,
chart 1) towards organoaluminum compounds and showed that
the derived species may yield structurally diverse mono- and
* Corresponding authors.
E-mail addresses: bellemin@unistra.fr (S. Bellemin-Laponnaz), dagorne@unistra.
fr (S. Dagorne).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.020

A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
4249
2.2. Organoaluminum complexes supported by sterically open
aminophenolates (2aeb, 3b, 4aeb): synthesis and structural
R'
R'
variety
O
N
R
A
O
N
R
B
As an entry point to organoaluminum complexes supported by
X2-type aminophenolate, the aminophenol derivatives 1aeb were
reacted with AlMe3 under controlled and low temperature reaction
conditions to disfavor the formation of a mixture of compounds.
Thus, slow addition of AlMe3 to one equiv. of pro-ligands 2-
CH2NH(R)-C6H4OH (1aeb) in toluene (ꢁ40 ꢀC, 1 h) readily yields,
R
Chart 1. N,O bidentate aminophenolate ligands.
via a methane elimination route, the corresponding Al dimers [m-
h1
,
h
1-N,O-{2-CH2NH(R)-C6H4O}]2Al2Me4 (2aeb; R ¼ Mes, Diip;
dinuclear aluminium species whose reactivity may greatly depend
on the steric and electronic properties of the bidentate ligand [4].
These were thus far found to be effective in the mediation of several
transformations ranging from the polymerization of polar mono-
mers such cyclic esters and epoxides to the hydroalumination of
aldehydes and ketones [2i,4bef].
Scheme 1), as deduced from NMR data and X-ray crystallographic
analysis. An identical outcome was observed when pro-ligands
1aeb were slowly added (ꢁ40 ꢀC, 1 h) to a precooled AlMe3 solu-
tion. Compounds 2aeb were both isolated in high yields (91% and
82%, respectively) as air-sensitive colorless solids found to be
sparingly soluble in common organic solvents with the exception of
THF. In the case of compound 2a, its dimeric nature in the solid
state was unambiguously established by X-ray crystallographic
analysis.
Over the past ten years, dianionic X2--type aminophenolate of
(B, Chart 1) have been found to be suitable N,O-type chelating
bidentate ligands for coordination to oxophilic and high-oxidation-
state metals such group 4 metals and lanthanides frequently
yielding complexes of interest as olefin polymerization catalysts
[5]. In contrast, their coordination chemistry towards group 13
metals, in particular that of aluminium, remains essentially unex-
plored [6].
To widen the potential scope of applications of aminophenolate-
supported aluminium compounds, we have become interested into
studying the coordination chemistry of X22ꢁ - type dianionic N,O-
aminophenolate (type B, Chart 1) towards simple organo-
aluminum species of the type AlR3. Apart from its fundamental
interest, derived from the likely structural diversity of the envi-
sioned aminophenolate Al compounds, we aimed at the synthesis
of organoaluminium species of type (X2)Al(R)(L), where X22- is an
The molecular structure of 2a is depicted in Fig. 1, and selected
bond distances and angles are summarized in Fig. 1. The Al methyl
compound 2a may be described as a centrosymmetric dimer in
which the two Al centers are connected to one another through two
bridging LXꢁ-type aminophenolate
m- ,h
h1 1-N,O-2-CH2NH(Mes)-
C6H4Oꢁ, resulting in the formation of a twelve-membered ring Al
dimer. Both Al centers adopt a slightly distorted geometry due
a small NeAleO bond angle (92.4(1)ꢀ vs. 109.49ꢀ for an ideal
tetrahedron), resulting, in turn, in an opening of the C(1)eAleC(2)
bond angle (120.4(2)ꢀ). The AleO phenolate (1.777(2) Å) and AleN
amine (2.018(3) Å) bond distances lie within the expected range
aminophenolate of type
B and L labile. Organoaluminum
compounds of the type (X2)Al(R)(L), which may be seen as well-
defined Lewis acids, are widely used as such for the mediation of
various chemical transformations [1].
Here we report a full account on the synthesis and structural
characterization of aluminium complexes supported by LX- and X2-
type aminophenolate ligand of type B. As will be seen, various
structural types/coordination modes may be observed for these Al
complexes depending on the chelating ligand sterics and/or the
reaction conditions.
2. Results discussion
2.1. Aminophenol pro-ligands 1aed
The aminophenol derivatives 1aed (Schemes 1 and 3) were
synthesized following a classical amine condensation procedure (in
the presence of Na2SO4 and a catalytic amount of formic acid) with
a subsequent imine reduction (NaBH4 for 1aeb and LiAlH4 for
1ced) [7].
Me
Me
Al
OH
Ar
toluene
C
O
N
H
+ AlMe3
H
N
NH
Ar
O
Al
Ar
Fig. 1. ORTEP view of complex 2a. The ellipsoids enclose 50% of the electronic density.
The H atoms, except H1, as well as the solvent molecules (C6H6) are omitted for clarity.
Symmetry codes for equivalent position’: ꢁx, ꢁy, ꢁz. Selected bond lengths (Å) and
bond angles (ꢀ): AleC(1), 1.950(4); AleC(2), 1.956(4); AleO, 1.777(2); AleN, 2.018(3);
NeAleO, 92.4(1); C(1)eAleC(2), 120.36(16); C(2)eAleN, 108.03(13); C(1)eAleO,
112.84(14); OeAleC(2), 110.39(14).
Me
Me
2a, 2b
Ar = Mes; 1a
Ar = Dipp; 1b
Scheme 1. Synthesis of organoaluminum complexes 2a and 2b.

4250
A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
and are comparable to those observed in related N,O-supported
aluminium species reported so far [4,8]. From a general structural
point of view, dimer 2a, which features two N,O-bidentate adopting
a
m- ,
h1 h1 bridging mode, may be related to dimeric eight-
membered ring amidate and amidinate Al complexes of the type
Me2Al{
m,
h1 h1 e(N(R)C(R0)O)}2AlMe2 and Me2Al{ h1 h1-(N(R)C(R0)
,
m- ,
N(R))}2AlMe2, respectively [9,10]. The latter two classes of
compounds were also found to readily form upon reaction of AlMe3
with relatively unhindered amides or amidines.
The NMR data for complexes 2aeb under the studied conditions
(thf-d8, room temperature) closely relate to one another and are all
consistent with effective Cs-symmetric structures for both
complexes which, in the case of 2a, agree with its solid state
structure being retained in solution. In particular, the NMR spec-
trum for complex 2a features two characteristic doublet resonances
(d
3.22 and 4.34, 4H) corresponding to the PhCHH’ moieties along
with a typical resonance for the NH moiety ( 4.74, 2H).
d
While the organoaluminum dimers 2aeb are stable for weeks
under inert atmosphere in thf solution, they both readily react upon
heating, yet in a somewhat different manner. Thus, heating
a toluene solution of 2a (80 ꢀC, 3 h) affords the quantitative and
direct formation of the dinuclear aluminium complex Al[
2-O-{2-CH2N(Mes)-C6H4O}](AlMe2) (4a, Scheme 2); in contrast,
species 2b yields under the aforementioned conditions the
formation of [
2-N,O-{2-CH2N(Dipp)-C6H4O}AlMe]2 (3b, Scheme 2)
h
2-N;
m,h
h
Fig. 2. ORTEP view of complex 3b. The ellipsoids enclose 50% of the electronic density.
The H atoms are omitted for clarity. Symmetry codes for equivalent position ’: ꢁx, ꢁy,
1ꢁz. Selected bond lengths (Å) and bond angles (ꢀ): AleC(20), 1.931(2); AleN, 1.786(1);
AleO, 1.856(1); Al0eO, 1.863(1); NeAleO, 98.21(7); C(20)eAleO, 121.86(4); C(20)e
AleN, 122.77(5); AleOeAl0, 99.97(6); O0eAleO, 80.03(6).
as the major product. Both Al species 4a and 3b were isolated as
colorless solids and, unlike compounds 2aeb, solubilize well in
common aromatic solvents. The molecular structures of both
complexes were determined by X-ray crystallography analysis and
are depicted in Figs. 2 and 3; their overall structural features are
briefly discussed below (for 3b and 4a, see captions of Figs. 2 and 3
for selected bond distances and angles).
complexes with, for instance, an AleO bond distance of 1.875(2) Å
(average) for the dimer [(iBu)2Al(
m
-OPh)]2 [11]. Both Al centers
As illustrated in Fig. 2, compound 3b [h
2-N,O-{2-CH2N(Dipp)-
feature distorted tetrahedral geometries as result of the
a
C6H4O}AlMe]2 crystallizes as a centrosymmetric dimer and its
molecular structure may be formally described as two three-
geometrical constraints imposed by the O-bridging phenolates and
the h2-(NO)Al chelate [NeAleO ¼ 98.21(7)ꢀ compensated for by an
opening of the C(20)eAleO and C(20)eAleN bond angles,121.86(4)
and 122.77(5)ꢀ, respectively]. It is finally noteworthy that the
terminal amido AleN bond distance (AleN ¼ 1.786(1) Å) is among
the shortest reported to date (typical range 1.78e1.86 Å), which,
given the fact that the nature of the AleN bond is very likely to be
essentially electrostatic based on various reports on that matter,
coordinate
linked to one another via the two
h
2-N,O-{2-CH2N(Dipp)-C6H4O}AlMe moieties being
m,h
2-O phenolates; this results in
the formation of a centrally located and nearly planar Al2O2 core
with the two Al-bonded methyl groups being disposed in a trans
fashion relative to the Al2O2 core. Both bridging oxygens are
symmetrically bonded to each Al center as reflected from the nearly
identical AleO and Al’eO bond distances (1.856(1) and 1.863(1) Å).
These values are comparable to related bridging phenolate Al
Me
Me
(Ar = Mes)
Al
Ar
Ar
Ar
Me
Me
N
N
O
O
O
N
H
toluene
C (3h)
- 2 CH4
H
N
Al
Al
O
Ar
Al
Me
Me
2a, 2b
4a, 4b
(Ar = Dipp)
toluene
C (18h)
toluene
C (3h)
Ar
N
- 2 CH4
Al
Me
O
Fig. 3. ORTEP view of complex 4a. The ellipsoids enclose 50% of the electronic density.
The H atoms are omitted for clarity with the exception of H16A and H32A which are
O
Me
Al
implicated in CH-p interactions (dashed lines). Selected bond lengths (Å) and bond
N
angles (ꢀ): Al(1)eN(1), 1.776(3); Al(1)eN(2), 1.774(3); Al(1)eO(1), 1.843(3); Al(1)eO(2),
1.845(3); Al(2)eO(1), 1.856(3); Al(2)eO(2), 1.864(3); Al(2)eC(1), 1.940(5); Al(2)eC(2),
1.936(5); H(16a)eAr, 3.557(5); H(32a)eAr, 3.539(5); N(1)eAl(1)eN(2), 118.57(14);
O(1)eAl(1)eO(2), 80.12(12); O(1)eAl(2)eO(2), 79.29(11); C(1)eAl(2)eC(2), 125.2(2);
O(1)eAl(2)eO(2)eAl(1), 0.90(12).
Ar
3b (Ar = Dipp)
Scheme 2. Synthesis of aminophenolate dinuclear aluminum species 3b, 4a and 4b.

A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
4251
most probably reflects a highly polar AleN bond in 3b [12]. In
solution, the 1H and 13C NMR data for 3b are all consistent with the
presence of center of inversion, and thus with an effective Ci-
symmetric structure, under the studied conditions (room temper-
ature, C6D6). In addition, species 3b appears to be rather robust at
room temperature in solution with no sign of dissociation in
a coordinative solvent such as THF. In contrast, 3b readily reacts in
hot THF (60 ꢀC), yet to yield an untractable mixture of products.
Structurally different from dimer 3b, compound 4a, whose
molecular structure is depicted in Fig. 3, is a dinuclear Al species
Altogether, the latter observations and experimental data for the 2b
system clearly show the initial formation of 3b as a kinetic product,
susceptible to be converted to the thermodynamically more stable
dinuclear species 4b. In the case of the more sterically open
mesityl-substituted amido analogue 2a, despite the use of various
reaction conditions, the formation of a putative kinetic product
“[h
2-N,O-{2-CH2N(Dipp)-C6H4O}AlMe]2” analogous to 3b, was not
observed: this strongly suggests that such a species, if it forms, is
merely an intermediate that readily reacts (to yield 4a) under the
conditions required for its formation.
featuring two
both of which being in a quite different coordination environment.
Thus, while Al(1) is
2-chelated by two X2-type N,O-amino-
phenolate to adopt a distorted tetrahedral environment, Al(2) is
connected to Al(1) via two -O oxygen phenolates (O(1) and O(2))
m,h
2-aminophenolate units bridging two Al centers,
2.3. Organoaluminum complexes supported by sterically bulky
aminophenolates (5ced, 6ced)
h
m
The reaction of bulky aminophenol pro-ligands 1ced, which
both contain tert-butyl ortho-substituted phenol groups, with
AlMe3 was studied as the derived aminophenolate Al complexes,
for steric reasons, may be less prone to the formation of aggregates
and thus favour the obtainment of mononuclear Al species struc-
turally different from those reported herein thus far. The use of
with the rest of its coordination sphere being completed by two
methyl groups. Overall, species 4a nearly exhibits a C2-symmetric
structure (with a C2 axis defined by the two Al atoms Al(1) and
Al(2)) and, with the exception of rather short terminal amido AleN
bond distances (1.775(6) Å average), its structural features (as
deduced from bonding and geometrical parameters, Fig. 3) are
rather normal. As for the solution structure of 4a, the room
temperature NMR data agree with a C2-symmetric species under
the studied conditions: it thus appears likely that 4a retains its
solid-state molecular structure in solution.
t
chelating ligands containing Bu-ortho-substituted phenol entities
has been previously shown to promote the formation of well-
defined mononuclear Al species. Representative examples in this
area include the synthesis of various alumatranes, in which the Al
metal center is effectively h
4-chelated by an amino-trisphenolate
The difference of reactivity (upon heating) between the twelve-
membered ring Al dimer 2a and its analogue 2b, which only differ
by the size of the N-R amido substituent (Mes vs. Diip, respectively),
prompted us to also investigate the relative reactivity of the derived
products (4a and 3b, respectively) so that to gain a better under-
standing of these Al aminophenolate systems. Thus, while dinu-
clear Al compound 4a is stable for days in refluxing toluene with no
sign of decomposition (as deduced from an NMR monitoring), the
Al dimer 3b was found to quantitatively afford in toluene (80 ꢀC,
tri-anionic tetradentate ligand [13].
The aminophenol derivative 2-CH2NH(R)-4,6-tBu2-C6H2OH
(1ced; R ¼ Mes or Diip) readily reacted with one equiv. AlMe3 via
a methane elimination route (toluene, ꢁ40 ꢀC to 0 ꢀC, 1 h) to afford
the corresponding monomeric Al aminophenolate chelate
complexes
h
2-N,O-{2-CH2NH(R)-4,6-tBu2-C6H2O}AlMe2 (5ced;
R ¼ Mes, Diip; Scheme 3), as deduced from NMR data and X-ray
crystallographic analysis. Compounds 5ced were isolated as
colorless solids in high yield and are highly soluble species in
common hydrocarbon solvents. In the case of 5d, its molecular
structure was determined by X-ray crystallographic studies
unambiguously establishing 5d as a monomeric species. As depic-
ted in Fig. 5, compound 5d crystallizes as a four-coordinate Al
18 h) the dinuclear Al species Al[h m,h
2-N; 2-O-{2-CH2N(Diip)-
C6H4O}](AlMe2) (4b, Scheme 2), isostructural to species 4a as
determined by X-ray crystallographic studies (see Fig. 4 for the
molecular structure and selected bonding parameters). In addition,
as may be expected, a prolonged heating of dimer 2b (toluene,
80 ꢀC, 24 h) afforded the quantitative and direct formation of 4b.
dimethyl species effectively
h
2-N,O-chelated by the LXꢁ-type 2-
CH2NH(Diip)-4,6-tBu2-C6H2Oꢁ anionic aminophenolate ligand.
The Al center in 5d adopts a slightly distorted tetrahedral structure
with a (NO)Al bite angle (O(1)eAl(1)eN(1) ¼ 95.43(7)ꢀ) along with
larger along with larger C(28)eAl(1)eC(29) etc.
C(28)eAl(1)eC(29) and N(1)eAl(1)eC(29) bond angles
(117.0(1)ꢀ and 116.90(9)ꢀ, respectively). The six-membered-ring Al
metallacycle is significantly puckered with the Al-NH(Diip) moiety
well above the nearly planar C(15)eC(6)eO(1)eAl(1) backbone, as
shown by the O(1)eC(1)eC(15)eN(1) and C(15)eC(6)eAl(1)eO(1)
torsion angles (54.73 and 50.57ꢀ, respectively), thus resulting in an
overall C1 symmetry for compound 5d in the solid state. The AleO
and AleN bond distances (1.768(2) and 2.049(2) Å, respectively) are
in the normal range found for aluminium phenolates (1.640(5)-
1.773(2) Å) [14] and for AleN dative bonds (1.957(3)-2.238(4) Å)
[15], respectively. As for the behaviour of compound 5d in the
t-Bu
t-Bu
OH
toluene
-40 C
t-Bu
O
t-Bu
Me
Me
+ AlMe3
Fig. 4. ORTEP view of complex 4b. The ellipsoids enclose 50% of the electronic density.
The H atoms are omitted for clarity, with the exception of H27C and H37C which are
Al
N
H
NH
Ar
implicated inCH-p interactions (dashed lines). Selected bond lengths (Å) and bond
Ar
angles (ꢀ): Al(2)eN(1), 1.7816(19); Al(2)eN(2), 1.7759(19); Al(2)eO(1), 1.8402(14);
Al(2)eO(2), 1.8463(15); Al(1)eO(1), 1.8591(15); Al(1)eO(2), 1.8678(15); Al(1)eC(1),
1.932(3); Al(2)eC(2), 1.937(3); H(27C)eAr, 3.724(3); H(36C)eAr, 3.822(4); N(1)eAl(2)e
N(2), 125.47(8); O(1)eAl(2)eO(2), 80.60(6); O(1)eAl(1)eO(2), 79.55(6); O(1)eAl(1)e
C(1), 110.42(10); C(1)eAl(1)eC(2), 126.61(2).
Ar = Mes 1c
Ar = Dipp 1d
5c, 5d
Scheme 3. Preparation of mononuclear organoaluminum 5c and 5d.

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A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
Fig. 5. ORTEP view of complex 5d. The ellipsoids enclose 50% of the electronic density.
The H atoms are omitted for clarity except for H(1N). Selected bond lengths (Å) and
bond angles (ꢀ): C(28)eAl(1), 1.970(3); C(29)eAl(1), 1.945(2); N(1)eAl(1), 2.049(2);
O(1)eAl(1), 1.7679(16); O(1)eAl(1)eC(29), 112.99(11); C(29)eAl(1)eC(28), 117.01(11);
O(1)eAl(1)eN(1), 95.43(7); C(29)eAl(1)eN(1), 116.90(9); N(1)eAl(1)eC(28), 99.30(10).
Fig. 6. ORTEP view of complex 6d. The ellipsoids enclose 50% of the electronic density.
The H atoms are omitted for clarity. Selected bond lengths (Å) and bond angles (ꢀ):
AleO(1), 1.740(2); AleN, 1.795(3); AleO(2), 1.896(3); AleC(18), 1.948(4); O(1)eAleN,
101.79(12); O(2)eAleC(28), 104.06(14); NeAleO(2), 110.18(13).
solution, all NMR data agree with the effective chelation of the LXꢁ-
type {2-CH2NH(Diip)-4,6-tBu2-C6H2O}ꢁ anion onto Al along with
an overall C1 symmetry. For instance, the 1H NMR spectrum
contains two Al-Me singlet resonances (
sets of signals for the PhCHH’ groups ( 3.31 and 4.75) and a doublet
5.18, JHH ¼ 11Hz) assigned to the NH entity. The
d
ꢁ0.49 and ꢁ0.18), two
d
solvents. As depicted in Fig. 6, the X-ray-determined molecular
3
resonance (
d
structure of 6d features a monomeric Al species in which the Al
observation of such a doublet (due to a strong 2JHH vicinal coupling
of the NH moiety to one of the PhCH2 hydrogens) versus, for
instance, a triplet-type resonance has to be related to quite
different H-C-N-H dihedral angles for the two PhCH2 hydrogens in
5d: the latter, based on classical Karplus curve correlations, may
greatly impact the values of coupling constants [16]. In the present
case, from a solution structure point of view, this suggests that the
six-membered-ring Al aminophenolate metallacycle in 5d is rather
rigid in solution under the studied conditions (room temperature,
C6D6) with, presumably, slow conformation changes on the NMR
time scale. As a comparison, under similar conditions, related Al
center is effectively chelated in a
h
2- fashion by the dianionic
chelating aminophenolate
h
2-N,O-2-CH2N(Diip)-4,6-tBu2-C6H2O2ꢁ
,
resulting in the formation of a severely distorted six-membered Al
metallacycle. The structural and bonding parameters for 6d (see
Fig. 6) overall relate to those for 5d discussed above. As expected
when going from an Al amino to an Al-amido bond, the Al-N bond
distance in 6d (1.795(3) Å) is significantly shorter than that in 5d
(2.049(2) Å). The NMR data for species 6ced in solution (C6D6,
room temperature) are consistent an overall C1-symmetric struc-
ture, the effective coordination of THF to the Al center and, in the
case of 6d, with its solid state structure being retained in solution
under the studied conditions. Thus, for instance, the 1H NMR
spectrum for 6c exhibits three Me-mesityl singlet resonances while
that for 6d displays four distinct doublets for the Me-iPr groups. In
contrast, species 6c and 6d both feature an effective Cs-symmetric
structure in the presence of excess THF suggesting fast coordina-
tion/decoordination process (presumably via an associative mech-
anism) of THF on the NMR time scale under the studied conditions
(C6D6, room temperature). The latter observations also establish
compounds 6ce6d as species of the type {X2}Al(R)(L) (L labile), thus
susceptible to act as well-defined Lewis acids and/or to be interest
for the activation/polymerization of polar monomers.
aminophenolate complexes such as
h
2-N,O-{2-CH2NR2-6-tBu-
C6H3O}AlMe2 (R ¼ alkyl) were found to undergo a fast conforma-
tion change of the six-membered metallacycle [2i]. In the case of
complex 5d, the severe steric crowding along with bonding
requirements within the Al metallacycle rationalizes such
a robustness. Based on NMR data, the mesityl analogue 5c is
structurally similar to 5d.
Though compounds 5ced were found to afford an untractable
mixture of product upon heating in toluene (80 ꢀC), well-defined Al
species may be obtained under the latter conditions but in the
presence of a few equiv. of a Lewis base such as THF. Thus,
compounds 5ced can be cleanly converted (80 ꢀC, toluene, 3 equiv.
of THF), via a methane elimination route, to the corresponding X2-
3. Summary e conclusion
aminophenolate Al methyl complexes
h
2-N,O-{2-CH2N(R)-
4,6-tBu2-C6H2O}Al(Me)(THF) (6ced; R ¼ Mes, Diip; Scheme 4).
Compounds 6ced were isolated in reasonable yields as analytically
pure colourless solids found to be highly soluble in hydrocarbon
The present work shows that the reaction of variously
substituted N,O-X2-type aminophenol pro-ligands 1aed with
AlMe3 may open the way to structurally diverse and well-defined
di- and mononuclear organoaluminum species bearing either
a monoanionic LXꢁ-type or a dianionic X22ꢁ-type aminophenolate
chelating ligand. The observed structural variety is clearly related to
the bonding versatility of the aminophenolate moiety as reflected
by the diverse bonding modes that may be adopted upon coordi-
t-Bu
t-Bu
O
toluene
t-Bu
O
t-Bu
Me
Me
THF (3 equiv.)
Me
Al
Al
THF
nation to Al, which include: (i) an LXꢁ-type
mode for 2aeb, (ii) a X22ꢁ-type 2-N,O bridging mode for
ꢁO,
compounds 3b and 4aeb, (iii) an LXꢁ-type 2-N,O chelating mode
for compounds 5ced and (iv) a X22ꢁ-type 2-N,O chelating mode for
derivatives 6ced. Overall, the sterics of the aminophenol backbone
m-h h
1-N, 1-O bridging
N
H
N
Ar
- CH4
Ar
m
h
h
5c, 5d
6c, 6d
h
Scheme 4. Synthesis of the Al-THF adducts 6c and 6d.

A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
4253
and, to a lesser extent, the reaction conditions that are used for
given ligand/AlMe3 set essentially govern the “structural”
outcome in these reactions, with a preference toward the formation
of mononuclear Al species (i.e. species 5ced and 6ced) as the steric
demand of the chelating N,O-ligand increases.
122.2, 53.5 (CH2), 35.1, 34.2, 31.7 (tBu), 29.7 (tBu), 20.7, 18.4; MS
(ESI): m/z: 354.276 (M þ H)þ.
a
4.2.4. 2-[(2,6-Disopropylphenylamino)methyl]-4,6-di-tert-
butylphenol (1d)
42% yield. 1H NMR (CDCl3, 298 K):
d 10.1 (broad s, 1H, OH or NH),
4. Experimental section
7.33 (m, 1H, CHarom.), 7.19 (s, 3H, CH2-6-disopro.), 6.92 (s, 1H, CHarom),
4.14 (s, 2H, CH2), 3.33 (m, 3J ¼ 6.8 Hz, 2H, eCHMe2), 1.48 (s, 9H, tBu),
1.32e1.16 (m, 21H, tBu, CHMe2); 13C {1H} NMR (CDCl3, 298 K):
4.1. General procedures
d
154.5, 150.4, 141.0, 136.5, 131.8, 129.9, 124.9, 123.6, 123.4, 122.2,
All experiments were carried out under N2 using standard
Schlenk techniques or in a Mbraun Unilab glovebox, with the
exception of those involving the synthesis of the aminophenol pro-
ligands 1aed. Toluene, pentane, diethyl ether and tetrahydrofuran
were collected after going through drying columns (SPS apparatus,
MBraun) and stored over activated molecular sieves (4 Å) for 24 h in
a glovebox prior to use. CD2Cl2, C6D6 and thf-d8 were distilled from
CaH2, degassed under a N2 flow and stored over activated molecular
sieves (4 Å) in a glovebox prior to use. AlMe3 was purchased from
Strem and used as received. All deuterated solvents were obtained
from Eurisotop (CEA, Saclay, France). All other chemicals were
purchased from Aldrich and were used as received. NMR spectra
were recorded on Bruker AC 300 or 400 MHz NMR spectrometers at
ambient temperature and in Teflon-valved J-Young NMR tubes for
all aluminum complexes. 1H and 13C chemical shifts are reported vs.
53.5 (CH2), 35.1, 34.2, 31.7 (tBu), 29.7 (tBu), 20.7, 18.4; MS (ESI): m/z:
354.276 (M þ H)þ.
4.2.5. [m- ,h
h1 1-N,O-{2-CH2NH(Mes)-C6H4O}]2Al2Me4 (2a)
To a precooled toluene solution (ꢁ40 ꢀC, 2 mL) of the amino-
phenol derivative 1a (89.0 mg, 0.373 mmol), a toluene solution
(1 mL) of AlMe3 (26.9 mg, 0.373 mmol), also precooled at ꢁ40 ꢀC, was
added dropwise via a pipette. Upon addition of AlMe3, the initial
colorless solution immediately became cloudy to eventually
a colorless suspension. After the addition, the mixture was allowed
to warm to room temperature and stirred for 1 h, after which it was
filtered through a glass frit under reduced pressure. The collected
solid was washed twicewith pentane and dried invacuo to afford the
Al compound 2a (110 mg, 91% yield) as an analytically pure colorless
solid. The outcome and yield of the latter reaction are identical when
a precooled toluene solution of ligand 2a is slowlyadded a precooled
toluene solution of AlMe3. Anal. Calcd for C36H48Al2N2O2: C, 72.70;
H, 8.13; N, 4.71. Found: C, 72.93; H, 8.34; N, 4.85. 1H NMR (300 MHz,
SiMe4 and were determined by reference to the residual 1H and 13
C
solvent peaks. Elemental analysis for all compounds were per-
formed at the Services de Microanalyse of the Université Pierre et
Marie Curie (Paris, France) and the Université de Strasbourg
(Strasbourg, France).
thf-d8):
d
ꢁ0.67 (s, 6H, AlMe2), ꢁ0.54 (s, 6H, AlMe2),1.71 (s, 6H, Mes),
3
1.98 (s, 6H, Mes), 2.17 (s, 6H, Mes), 3.22 (d, JHH ¼ 11.1 Hz, 2H,
PhCHHʹ), 4.34 (t, JHH ¼ 11.5 Hz, 2H, PhCHHʹ), 4.74 (d, 3JHH ¼ 11.5 Hz,
2H, NH), 6.59 (s, 2H, Mes), 6.65 (s, 2H, Mes), 6.77 (t, 3JHH ¼ 6.5 Hz, 2H,
4.2. Synthesis of aminophenol ligands 1aed
Ph), 6.82 (d, JHH ¼ 6.2 Hz, 2H, Ph), 6.95e7.23 (m, 4H, Ph). 13C{1H}
3
The aminophenol precursors 1aed were prepared by conden-
sation of the amine with the 2-hydroxybenzaldehyde derivative in
methanol and in the presence of Na2SO4 and a catalytic amount of
formic acid. The crude product was then reduced using NaBH4 in
methanol (for 1aeb) or LiAlH4 in diethyl ether (for 1ced) to yield
the desired product after purification by flash chromatography
(SiO2, CH2Cl2).
NMR (100 MHz, thf-d8):
d
ꢁ10.5 (AlMe), ꢁ9.7 (AlMe), 17.6 (br, Mes),
21.3 (Mes), 22.2 (Mes), 55.2 (PhCH2), 123.1 (Ph), 125.2 (Ph), 126.0
(Ph), 127.4 (Ph), 129.3 (Ph), 136.2 (Ph), 136.8 (Ph), 137.1 (Ph), 137.5
(Ph), 139.2 (Ph), 139.9(Ph), 157.2 (Ph).
4.2.6. [m- ,h
h1 1-N,O-{2-CH2NH(Dipp)-C6H4O}]2Al2Me4 (2b)
The dinuclear organoaluminum complex 2b was synthesized and
isolated using an identical procedure to that for the synthesis of
complex 2a, using an equimolar amount of the aminophenol deriv-
ative 1b (700.0 mg, 2.42 mmol) and of AlMe3 (174.5 mg, 2.42 mmol).
Compound2b(673mg, 82% yield)wasisolatedasananalyticallypure
solid. Anal. Calcd for C42H60Al2N2O2: C, 74.30; H, 8.91; N, 4.13. Found:
4.2.1. 2-[(Mesitylamino)methyl]phenol (1a)
70% yield. 1H NMR (CDCl3):
d
7.24 (dd, 3J ¼ 7.8 Hz, 1H, CHmeta),
7.06 (d, 3J ¼ 7.5 Hz,1H, CHortho), 6.95 (d, 3J ¼ 8.0 Hz,1H, CHmeta), 6.91
(s, 2H, CHmesityl), 6.83 (dd, 3J ¼ 7.5 Hz, 1H, CHpara); 4.15 (s, 2H, CH2),
2.38 (s, 6H, CH3 ortho), 2.28 (s, 3H, CH3 para); 13C {1H} NMR (CDCl3):
C, 74.78; H, 8.66; N, 4.21. 1H NMR (300 MHz, thf-d8):
d
ꢁ0.78 (s, 6H,
d
157.9, 140.8, 134.4, 131.7, 129.9, 129.2, 128.4, 122.6, 119.5, 116.8,
AlMe2), ꢁ0.62(s, 6H,AlMe2),0.91(d, 3JHH ¼ 7.0Hz,6H,Me-iPr),1.12(d,
3JHH ¼ 7.0 Hz, 6H, Me-iPr), 1.29 (d, 3JHH ¼ 7.0 Hz, 6H, Me-iPr), 1.37 (d,
3JHH ¼ 7.0 Hz, 6H, Me-iPr), 2.45 (sept., 3JHH ¼ 6.9 Hz, 2H, CH-iPr), 2.88
(sept., 3JHH ¼ 6.9 Hz, 2H, CH-iPr), 3.31 (d, 3JHH ¼ 11.0 Hz, 2H, PhCHH’),
4.12 (t, JHH ¼ 11.1 Hz, 2H, PhCHH’), 4.85(d, 3JHH ¼ 11.2Hz, 2H, NH), 6.85
(t, 3JHH ¼ 6.5 Hz, 2H, Ph), 6.92 (d, 3JHH ¼ 6.2 Hz, 2H, Ph), 7.01e7.45 (m,
52.8 (CH2), 20.7 (CH3 ortho), 18.3 (CH3 para); MS (ESI) m/z: 242.156
(M þ H)þ.
4.2.2. 2-[(2,6-Diisopropylphenylamino)methyl]phenol (1b)
71% yield. 1H NMR (CDCl3):
d
7.25 (dd, 3J ¼ 7.8 Hz, 1H, CHmeta),
7.19 (s, 3H, CH2-6-disopro.), 7.07 (d, 3J ¼ 7.4 Hz, 1H, CHortho), 6.97 (d,
3J ¼ 8.2 Hz, 1H, CHmeta), 6.86 (dd, 3J ¼ 8.5 Hz, 1H, CHpara); 4.16 (s, 2H,
CH2), 3.29 (m, 3J ¼ 6.8 Hz, 2H, -CHMe2), 1.30 (d, 3J ¼ 6.8 Hz, 12H,
10H, Ph). 13C{1H} NMR (100 MHz, thf-d8):
d
ꢁ10.1 (br, AlMe), ꢁ7.2
(AlMe), 21.4 (Me-iPr), 22.2 (Me-iPr), 23.7 (Me-iPr), 23.8 (Me-iPr), 29.1
(CH-iPr), 29.5 (CH-iPr), 53.3 (PhCH2),123.5 (Ph),125.5 (Ph),126.5(Ph),
126.9 (Ph), 128.4 (Ph), 129.7(Ph), 135.6 (Ph), 137.1 (Ph), 137.7 (Ph),
138.9 (Ph), 139.4(Ph), 154.7 (Ph).
-CHMe2); 13C {1H} NMR (CDCl3):
d 157.8, 143.0, 140.3, 129.3, 128.5,
125.9, 124.0, 122.5, 119.5, 116.8, 55.9 (CH2), 28.2 (CHMe2), 24.3
(CHMe2); MS (ESI) m/z: 284.203 (M þ H)þ.
4.2.7. [h
2-N,O-{2eCH2N(Dipp)eC6H4O}AlMe]2 (3b)
4.2.3. 2-[(Mesitylamino)methyl]-4,6-di-tert-butylphenol (1c)
The dimeric organoaluminum complex 2b (300.0 mg,
0.442 mmol) and 5 mL of toluene were charged in a Schlenk flask
equipped with a Teflon-inside-cover screw cap. The glassware was
tightly sealed, immersed in a preheated oil at 80 ꢀC and was vigor-
ously stirred at this temperature for 3 h. After time, the initial
colorless suspension had completely yielded a pale yellow solution
53% yield. 1H NMR (CDCl3, 298 K):
d 10.4 (broad s, 1H, OH or NH),
7.22 (s, 1H, CHarom.), 6.93 (s, 1H, CHarom.), 6.91 (s, 2H, CHmes), 4.12 (s,
2H, CH2), 3.4 (broad s, 1H, XH), 2.39 (s, 6H, CH3 ortho), 2.28 (s, 3H,
t
t
CH3 para), 1.48 (s, 9H, Bu), 1.32 (s, 9H, Bu); 13C {1H} NMR (CDCl3,
298 K):
d 154.5, 150.4, 141.0, 136.5, 131.8, 129.9, 124.9, 123.6, 123.4,

4254
A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
that was evaporated under reduced pressure to afford a colorless
solid residue. As deduced from NMR data, the latter solid consisted of
a mixture of 3b and 4b in a 3/1 ratio. Subsequent recrystallization of
this residue from a 5/1 Et2O/toluene (3 mL) solution at ꢁ40 ꢀC
afforded complex 3b as an analytically pure colorless crystals in 43%
yield (121 mg). Anal. Calcd for C40H52Al2N2O2: C, 74.28; H, 8.10; N,
the aminophenol ligand 1c (490 mg, 1.39 mmol), also precooled
at ꢁ40 ꢀC, was added dropwise via a pipette. Upon addition of the
aminophenol, the initial colorless solution turned progressively
pale yellow. After the addition, the mixture was allowed to warm
to room temperature and stirred for 1 h, after which it was
evaporated to dryness in vacuo to yield crude 5c as a pale yellow
solid residue, as deduced from NMR data. Recrystallization of the
latter solid from cold pentane (ꢁ40 ꢀC) afforded compound 5c as
analytically pure colorless crystals (313 mg, 55% yield). Anal. Calcd
for C26H40AlNO: C, 76.24; H, 9.84; N, 3.42. Found: C, 76.56; H, 9.88;
4.33. Found: C, 74.52; H, 8.45; N, 4.52. 1H NMR (300 MHz, C6D6):
3
d
ꢁ0.23 (s, 6H, AlMe), 0.91 (d, JHH ¼ 7.0 Hz, 6H, Me-iPr), 1.21 (d,
3JHH ¼ 6.8 Hz, 6H, Me-iPr),1.34 (d, 3JHH ¼ 6.5 Hz, 6H, Me-iPr), 1.39 (d,
3JHH ¼ 7.0 Hz, 6H, Me-iPr), 2.86 (d, 2JHH ¼ 13.9 Hz, 2H, PhCHH’), 2.71
(sept., JHH ¼ 6.9 Hz, 2H, CH-iPr), 3.26 (sept., JHH ¼ 6.9 Hz, 2H,
CH-iPr), 4.23 (d, 2JHH ¼ 14.0 Hz, 2H, PhCHH’), 6.68 (t, 3JHH ¼ 6.5 Hz, 2H,
Ph), 6.96 (d, 3JHH ¼ 6.2 Hz, 2H, Ph), 7.23e7.72 (m, 10H, Ph). 13C{1H}
N, 3.56. 1H NMR (300 MHz, C6D6):
d
ꢁ0.57 (s, 3H, AlMe), ꢁ0.28 (s,
3
3
t
t
3H, AlMe), 1.38 (s, 9H, Bu), 1.65 (s, 3H, Mes), 1.75 (s, 9H, Bu), 1.96
(s, 3H, Mes), 2.23 (s, 3H, Mes), 2.98 (d, 2JHH ¼ 11.2 Hz, 1H, PhCHH0),
4.52 (t, JHH ¼ 11.5 Hz, 1H, PhCHH’), 4.70 (d, 2JHH ¼ 11.5 Hz, 1H, NH),
6.41 (s, 1H, Ph-Mes), 6.55 (s, 1H, Ph-Mes), 6.88 (s, 1H, Ph-O), 7.73
NMR (100 MHz, C6D6):
d
ꢁ5.2 (br, AlMe), 17.8 (Me-iPr),19.2 (Me-iPr),
21.7 (Me-iPr), 22.8 (Me-iPr), 27.1 (CH-iPr), 28.5 (CH-iPr), 52.7 (PhCH2),
123.5 (Ph), 124.3 (Ph), 126.5 (Ph), 126.9 (Ph), 128.4 (Ph), 129.7(Ph),
134.2 (Ph), 137.1 (Ph), 137.7 (Ph), 138.9 (Ph), 139.4(Ph), 154.7 (Ph).
(s, Ph-O). 13C{1H} NMR (100 MHz, C6D6):
d
ꢁ8.9 (br, AlMe), 17.2
(Mes), 20.7 (Mes), 22.2 (Mes), 29.9 (tBu), 31.5 (tBu), 34.0 (tBu), 35.3
(tBu), 53.9 (PhCH2), 123.1 (Ph), 123.4 (Ph), 124.9 (Ph), 129.5 (Ph),
130.2 (Ph), 130.7 (Ph), 132.0 (Ph), 133.1 (Ph), 135.5 (Ph), 136.3 (Ph),
139.2 (Ph), 157.0 (Ph).
4.2.8. Al[h ,h
2-N; m2 2-O-{2eCH2N(Mes)eC6H4O}](AlMe2) (4a)
Dinuclear organoaluminum complex 2a (400 mg, 0.672 mmol)
and 10 mL of toluene were charged in a Schlenk flask equipped with
a Teflon-inside-cover screw cap. The reaction flask was tightly
sealed, immersed in a preheated oil at 80 ꢀC and kept at this
temperature under vigorous stirring for 3 h. Over this period of
time, the initial colorless suspension turned to a colorless solution,
which was subsequently evaporated under reduced pressure to
yield crude 4a as an off-white solid as deduced from NMR data.
4.2.11.
h
2-N,O-{2-CH2NH(Diip)-4,6-tBu2-C6H2O}AlMe2 (5d)
The N,O-supported mononuclear Al complex 5d was synthe-
sized following an identical procedure to that used for 5c using
equimolar amounts of aminophenol 1d (541.0 mg) and AlMe3 (100.
0 mg, 1.39 mmol). The desired Al complex was isolated in a pure
form as a colorless crystalline powder from a concentrated
pentane solution stored at ꢁ40 ꢀC (320 mg, 51% yield). Anal. Calcd
for C29H46AlNO: C, 77.12; H, 10.27; N, 3.10. Found: C, 77.56; H,
Subsequent recrystallization from
a
cooled Et2O solution
(5 mL, ꢁ40 ꢀC) afforded complex 4a as analytically pure colorless
needle-like crystals in 74% yield (280 mg). Anal. Calcd for
C34H40Al2N2O2: C, 72.58; H, 7.17; N, 4.98. Found: C, 73.01; H, 7.38; N,
10.42; N, 2.89. 1H NMR (300 MHz, C6D6):
d
ꢁ0.49 (s, 3H,
AlMe), ꢁ0.18 (s, 3H, AlMe), 0.79 (d, 3JHH ¼ 7.0 Hz, 3H, Me-iPr), 0.83
5.12. 1H NMR (300 MHz, C6D6):
d
ꢁ0.33 (s, 6H, AlMe2), 1.29 (s, 6H,
(d, JHH ¼ 6.8 Hz, 3H, Me-iPr), 0.91 (d, JHH ¼ 6.5 Hz, 3H, Me-iPr),
3
3
Mes), 2.14 (s, 6H, Mes), 2.54 (s, 6H, Mes), 3.35 (d, 2JHH ¼ 15.2 Hz, 2H,
1.19 (d, 3JHH ¼ 7.0 Hz, 3H, Me-iPr), 1.35 (s, 9H, tBu), 1.74 (s, 9H, tBu),
2
3
2
PhCHH’), 4.85 (d, JHH ¼ 15.1 Hz, 2H, PhCHH’), 6.46e7.15 (m, 12H,
2.73 (sept., JHH ¼ 6.9 Hz, 1H, CH-iPr), 3.31 (d, JHH ¼ 11.2 Hz, 1H,
Ph). 13C{1H} NMR (100 MHz, C6D6):
d
ꢁ6.8 (AlMe), 18.2 (Mes), 20.7
PhCHH’), 3.42 (sept., JHH
¼
6.9 Hz, 1H, CH-iPr), 4.75 (t,
3
(Mes), 23.2 (Mes), 51.4 (PhCH2), 123.1 (Ph), 125.7 (Ph), 126.4 (Ph),
127.9 (Ph), 128.8 (Ph), 135.8 (Ph), 136.7 (Ph), 137.5 (Ph), 137.9 (Ph),
139.6 (Ph), 140.1 (Ph), 156.4 (Ph).
JHH ¼ 11.4 Hz, 1H, PhCHH’), 5.18 (d, 2JHH ¼ 11.5 Hz, 1H, NH), 6.80 (s,
1H, Ph-O), 6.80e7.15 (m, 3H, Ph), 6.88 (s, 1H, Ph-O), 7.87 (s, Ph-O).
13C{1H} NMR (100 MHz, C6D6):
d
ꢁ6.7 (br, AlMe), 17.1 (Me-iPr), 18.3
(Me-iPr), 22.3 (Me-iPr), 24.3 (Me-iPr), 29.5 (CH-iPr), 29.7 (CH-iPr),
54.5 (PhCH2), 123.4 (Ph), 124.9 (Ph), 126.8 (Ph), 128.9 (Ph), 129.1
(Ph), 129.9 (Ph), 136.4 (Ph), 137.1 (Ph), 137.6 (Ph), 138.3 (Ph), 139.4
(Ph), 156.6 (Ph).
4.2.9. Al[h ,h
2-N; m2 2-O-{2eCH2N(Diip)eC6H4O}](AlMe2) (4b)
Dinuclear organoaluminum complex 3b (300.0 mg, 0.442 mmol)
and 10 mL of toluene were charged in a Schlenk flask equipped with
a Teflon-inside-cover screwcap. Thereaction flask was tightlysealed,
immersed in a preheated oil at 80 ꢀC and kept at this temperature
under vigorous stirring for 18 h. Over this period of time, the initial
colorless suspension turned to a colorless solution, which was
subsequentlyevaporatedunderreducedpressuretoyieldcrude 4bas
an off-white solid as deduced from NMR data. Subsequent recrys-
tallization from a cooled Et2O solution (3 mL, ꢁ40 ꢀC) afforded
complex 4b as an analytically pure colorless solid in 61% yield
(174 mg). Anal. Calcd for C40H52Al2N2O2: C, 74.28; H, 8.10; N, 4.33.
4.2.12.
h
2-N,O-{2-CH2N(Mes)-4,6-tBu2-C6H2O}Al(Me)(THF) (6c)
h
2-N,O aluminium- coordinated amiphenolate complex 5c
The
(250. 0 mg, 0.610 mmol) was dissolved in toluene and three
equivalent of THF (150.0 L, 1.830 mmol) were added. The resulting
m
colorless solution was then charged in a Schlenk flask and heated at
80 ꢀC for 18 h affording a pale yellow solution that was allowed to
cool to room temperature. Subsequent evaporation under reduced
pressure resulted into the formation of an off-white solid residue
formulated as crude 6c on the basis of NMR data. Pure complex 6c
(162 mg, 57% yield) was obtained as a colorless powder by
recrystallization of the crude product from an Et2O solution cooled
at ꢁ40 ꢀC. Anal. Calcd for C29H44AlNO2: C, 74.80; H, 9.52; N, 3.01.
Found : C, 74.56; H, 8.21; N, 4.52.1H NMR (300 MHz, C6D6):
d
ꢁ0.35 (s,
6H, AlMe2), 0.17 (d, 3JHH ¼ 7.0 Hz, 6H, Me-iPr), 0.91 (d, 3JHH ¼ 6.8 Hz,
6H, Me-iPr), 1.06 (d, 3JHH ¼ 6.5 Hz, 6H, Me-iPr), 1.37 (d, 3JHH ¼ 7.0 Hz,
3
6H, Me-iPr), 2.98 (sept., JHH ¼ 6.9 Hz, 2H, CH-iPr), 3.36 (d,
2JHH ¼ 14.3Hz,2H,PhCHH’), 3.74(sept., 3JHH ¼ 6.9Hz,2H,CH-iPr), 4.97
Found: C, 75.02; H, 9.76; N, 3.16. 1H NMR (300 MHz, C6D6):
d
ꢁ0.45
(d, 2JHH ¼ 13.8 Hz, 2H, PhCHHʹ), 6.78e7.50 (m,14H, Ph). 13C{1H} NMR
(s, 3H, AlMe), 1.40 (s, 9H, Bu), 1.55 (s, 3H, Mes), 1.61 (m, 4H, THF),
1.77 (s, 9H, tBu), 2.01 (s, 3H, Mes), 2.13 (s, 3H, Mes), 3.22 (d,
2JHH ¼ 14.1 Hz,1H, PhCHH’), 3.65 (m, 4H, THF), 4.78 (t, JHH ¼ 13.9 Hz,
1H, PhCHH’), 6.50 (s, 1H, Ph-Mes), 6.59 (s, 1H, Ph-Mes), 6.79 (s, 1H,
t
(100 MHz, C6D6):
d
ꢁ4.7 (br, AlMe), 16.3 (Me-iPr), 18.6 (Me-iPr), 22.7
(Me-iPr), 22.9 (Me-iPr), 28.5 (CH-iPr), 29.4 (CH-iPr), 55.1 (PhCH2),
123.8 (Ph), 124.7 (Ph), 126.7 (Ph), 127.9 (Ph), 128.8 (Ph), 129.7 (Ph),
135.4 (Ph), 137.8 (Ph), 138.7 (Ph), 139.1 (Ph), 140.4 (Ph), 155.7 (Ph).
Ph-O), 7.72 (s, Ph-O). 13C{1H} NMR (100 MHz, C6D6):
d
ꢁ6.3 (br,
AlMe),16.8 (Mes), 20.5 (Mes), 21.9 (Mes), 25.5 (THF), 28.4 (tBu), 32.5
(tBu), 34.1 (tBu), 36.7 (tBu), 55.3 (PhCH2), 66.3 (THF), 122.5 (Ph),
124.4 (Ph), 125.5 (Ph), 129.7 (Ph), 130.6 (Ph), 131.4 (Ph), 132.7 (Ph),
133.5 (Ph), 135.9 (Ph), 136.9 (Ph), 140.7 (Ph), 156.2 (Ph).
4.2.10.
h
2-N,O-{2-CH2NH(Mes)-4,6-tBu2-C6H2O}AlMe2 (5c)
To a precooled toluene solution (5 mL) of AlMe3 (100.0 mg,
1.39 mmol) under vigorous stirring, a toluene solution (5 mL) of

A. Maisse-François et al. / Journal of Organometallic Chemistry 696 (2012) 4248e4256
4255
4.2.13.
h
2-N,O-{2-CH2N(Diip)-4,6-tBu2-C6H2O}Al(Me)(THF) (6d)
Appendix A. Supplementary material
Compound 6d was synthesized following an identical proce-
dure to that for 6c but using complex 5d (250.0 mg, 0.553 mmol)
and THF (3 equiv., 135.0 mL) as reagents. Pure complex 6d (118 mg,
CCDC 833219e833224; contains the supplementary crystallo-
graphic data for compounds 2a, 3b, 4a-b, 5d and 6d, respectively.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
42% yield) was isolated as colorless needle-shape crystals by
recrystallization of the crude product from a 1/1 Et2O/pentane
solution cooled at ꢁ40 ꢀC. Anal. Calcd for C32H50AlNO2: C, 75.70; H,
9.93; N, 2.76. Found: C, 75.96; H, 9.99; N, 3.01. 1H NMR (300 MHz,
3
CD2Cl2):
d
ꢁ0.83 (s, 3H, AlMe), 0.86 (d, JHH ¼ 7.0 Hz, 3H, Me-iPr),
Appendix. Supplementary information
1.05 (d, JHH ¼ 6.8 Hz, 3H, Me-iPr), 1.24 (d, JHH ¼ 6.5 Hz, 3H,
3
3
Me-iPr), 1.26 (s, 9H, tBu), 1.32 (d, 3JHH ¼ 7.0 Hz, 3H, Me-iPr), 1.51 (s,
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.09.020.
t
3
9H, Bu), 2.19 (m, 4H, THF), 3.36 (sept., JHH ¼ 6.9 Hz, 1H, CH-iPr),
3.50 (d, 2JHH ¼ 11.2 Hz, 1H, PhCHH’), 3.71 (sept., 3JHH ¼ 6.9 Hz, 2H,
CH-iPr), 4.38 (m, 4H, THF), 4.77 (t, JHH ¼ 11.4 Hz, 1H, PhCHH’), 6.74
(s, 1H, Ph-O), 7.06e7.12 (m, 3H, Ph), 7.16 (s, 1H, Ph-O). 13C{1H} NMR
References
(100 MHz, C6D6):
d
ꢁ9.4 (br, AlMe), 19.1 (Me-iPr), 20.3 (Me-iPr),
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Selected bond lengths and angles are gathered in figure captions.
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