Synthesis and structure of four-coordinate dimethyl aluminium complexes incorporating new N,O-chelating arylamido ligands

Article abstract of DOI:10.1016/S0022-328X(03)00790-3

A new type of arylamido ligands with an intramolecular coordinating ortho -ether-substituent (i.e. a O,N^- chelating ligand) is introduced. The achiral and chiral 4-coordinate dimethyl aluminium complexes [2-ROC₆H₄NR′] AlMe

Full text of DOI:10.1016/S0022-328X(03)00790-3

Journal of Organometallic Chemistry 682 (2003) 240ꢂ247
/
www.elsevier.com/locate/jorganchem
Synthesis and structure of four-coordinate dimethyl aluminium
complexes incorporating new N,O-chelating arylamido ligands
Pierre Haquette a, Samuel Dagorne a,*, Richard Welter b, Ge´rard Jaouen a
a Laboratoire de Chimie Organome´tallique, UMR CNRS 7576, Ecole Nationale Supe´rieure de Chimie de Paris, 11, rue Pierre et Marie Curie, F-75231
Paris cedex 05, France
b Laboratoire DECMET, Institut Le Bel, Universite´ Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
Received 23 June 2003; received in revised form 22 July 2003; accepted 28 July 2003
Abstract
A new type of arylamido ligands with an intramolecular coordinating ortho-ether-substituent (i.e. a O,Nꢀ chelating ligand) is
introduced. The achiral and chiral 4-coordinate dimethyl aluminium complexes [2-ROC6H4NR?]AlMe2 (4a: Rꢁ
(ꢀ)-menthyl, R?ꢁCy, 4c: Rꢁ(ꢀ)-menthyl, R?ꢁCPh3) have been prepared by reaction of the appropriate amido Li salt with
ClAlMe2. Complex 4a could also be obtained, via methane elimination, by reaction of AlMe3 with the corresponding ligand. The
presence of two rotamers in solution at room temperature for 4b and for 4c is most likely due to a restricted rotation of the (ꢀ)-
/
R?ꢁ
/
Cy; 4b: Rꢁ
/
/
/
/
/
/
/
menthyl group at this temperature due to severe steric interactions with the rest of the complex.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Synthesis; Dimethyl aluminium; N,O-Chelating arylamido ligands
1. Introduction
A, Chart 1) constitutes the only reports on that matter
[4].
Mononuclear aluminum(III) complexes (Lꢂ
(Rꢁalkyl group) incorporating one monoanionic li-
gand of the Lꢂ
Xꢀ type with a chelated four coordinate
/
X)AlR2
We are interested in the synthesis of mononuclear 4-
coordinate dialkyl aluminium complexes incorporating
/
Nꢀ chelating ligand i.e. a N-anion with a
/
one OÃ
/
metal center have been widely investigated over the past
20 years due to their practical and fundamental im-
portance [1]. For example, stable aluminium compounds
containing nitrogen substituents are useful in the pre-
paration of AlN-containing materials [2]. More recently,
pendant ethereal oxygen. The presence of an ethereal
oxygen, which can be considered as a weak Lewis base
center as compared to a neutral amine nitrogen or an
alkoxide oxygen [1d], should, in turn, yield a more
electrophilic, and thus more reactive, Al center. This
feature is of interest for any potential application in
Lewis acid catalysis of the derived Al complexes.
Arylamido ligands with an intramolecular coordinat-
ing ortho-ether-substituent (B, Chart 1) appeared sui-
table for this purpose because they may form a stable 5-
membered ring Al metallocycle upon coordination to an
Al(III) center. The ortho-ether-substituent in B is
expected to provide steric shielding of the metal center
as well as the electron donation to the metal center, and
thus to favor the formation of mononuclear Al com-
plexes. In addition, as presented in this work, the
synthesis of chiral versions of such ligands is relatively
easy, which opens the way to new chiral aluminium
complexes.
dialkyl complexes (Lꢂ
/
X)AlR2 (Lꢂ
/
X
ꢀ ꢁ
/
NÃ
/
Oꢀ, NÃ
/
Nꢀ; Rꢁ
/alkyl group) were found to be effective
precursors to highly reactive cationic aluminum alkyls,
which are of interest as epoxide and ethylene polymer-
ization catalysts [3].
In contrast to the NÃ
ligands, monoanionic amido-ether bidentate ligands
(OÃ
Nꢀ) appear to be rarely used for coordination to
a Group 13 metal center. In fact, thus far, the generation
of [Me2Si(OtBu)(NtBu)]MR2 (Mꢁ
Al, Ga; RꢁMe, Cl;
/
Oꢀ and NÃ
/
Nꢀ bidentate
/
/
/
* Corresponding author. Tel.:
43260061.
E-mail address: dagorne@ext.jussieu.fr (S. Dagorne).
ꢃ
/
33-1-44276699; fax:
ꢃ/33-1-
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00790-3

P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ
/247
241
The reaction of the Li salt [2-CyOC6H4NCy][Li],
generated by reaction of 2-CyOC6H4NHCy with one
n
equivalent of BuLi, with one equivalent of ClAlMe2 in
toluene for 18 h at room temperature yields the
formation of the chelate dimethyl complex [2-Cy-
OC6H4NCy]AlMe2 (4a, Scheme 2) isolated in good
yield.
The molecular structure of 4a was determined by X-
ray crystallography analysis and is illustrated in Fig. 1.
Compound 4a crystallizes on a C2 axis: i.e. the Al atom
(4e position of the C2/c group) and the middle of the
Chart 1.
Here we report our early findings on the synthesis and
structure of new mononuclear dialkyl aluminium com-
plexes incorporating achiral and chiral arylamido li-
gands with an intramolecular coordinating ortho-ether-
substituent.
C(1)Ã/C(1a) contact are on the C2 axis. In these
conditions, the atomic arrangement observed by X-ray
diffraction must be considered as an average of two
chemically true molecules, rotated by 1808 around the
C2 axe in the crystal.
1
The H- and 13C-NMR spectra of 4a in C6D6 both
2. Results and discussion
contain one resonance for the AlMe2, one OÃ
/
CH
resonance and one NÃCH resonance, which is consis-
/
2.1. Synthesis of 2-ROC6H4NHR? ligands 3aꢂc
/
tent with an effective Cs symmetry of 4a in solution and
with the chelate solid state structure being retained in
solution. In addition, no reaction was observed between
4a and THF (one equivalent) after overnight at 75 8C in
C6D6, which indicates the excellent stability in solution
of the chelate complex in the presence of such a Lewis
base.
The reaction of AlMe3 with one equivalent of 2-
CyOC6H4NHCy (3a) at room temperature for 1 h leads
to the quantitative formation of the adduct 3a-AlMe3
(Scheme 3).
The new achiral and chiral 2-alkoxy-N-alkylaniline
ligands 2-ROC6H4NHR? 3a (RꢁR?ꢁcyclohexyl), 3b
(Rꢁ(ꢀ)-menthyl, R?ꢁcyclohexyl) and 3c (Rꢁ(ꢀ)-
menthyl, R?ꢁCPh3) were prepared by adapting litera-
/
/
/
/
/
/
/
/
ture methods [5]: 1-fluoro-2-nitrobenzene was reacted
with the appropriate alcoholate potassium salt in THF
at room temperature to give the corresponding 1-
alkoxy-2-nitrobenzene (1aꢂ
reduction of the nitro group with hydrazine on Pd led to
the respective 2-alkoxyanilines (2aꢂb, Scheme 1).
/
b, Scheme 1), which after
/
The adduct 3a-AlMe3 was not isolated and was only
Subsequent N-alkylation with ClCPh3 or with cyclo-
hexanone in a reducing medium afforded the 2-alkoxy-
1
1
characterized by H-NMR spectroscopy. It is H-NMR
spectrum exhibits a characteristic NH doublet (dꢁ5.29,
3JHÃH
10 Hz), which is significantly downfield shifted
as compared to that of the free ligand (br, dꢁ4.30). The
/
N-alkylaniline ligands (3aꢂc, Scheme 1) as white
/
ꢁ
/
powders in moderate overall yields.
/
rest of the proton ligand resonances are nearly un-
changed by the coordination to AlMe3. Thus, the NMR
data are consistent with the coordination of AlMe3 to 3a
through the nitrogen atom. The adduct 3a-AlMe3 slowly
decomposes at room temperature in pentane to yield 4a
over the course of several days with elimination of
methane. This decomposition is quantitative after heat-
ing 3a-AlMe3 in C6D6 at 75 8C for 18 h (Scheme 3).
2.2. Synthesis and structure of [ROC6H4NR?]AlMe2
(4aꢂc)
/
The synthesis of 4a was carried out using the two
general methods employed for the obtention of such
complexes: i.e. the salt metathesis and the methane
elimination routes.
Scheme 1.

242
P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ247
/
Scheme 2.
temperature with an equimolar amount of ClAlMe2 to
afford 4b and 4c, respectively (Scheme 2). Compounds
4bꢂc are isolated as colorless solids and are both air-
/
and moisture-sensitive, decomposing over a period of
seconds in the solid state after exposure to air. Heating a
C6D6 solution of 4b at 70 8C for 5 h (or of 4c for 8 h)
yielded the quantitative decomposition of the corre-
sponding Al complex to unidentified species, showing
that 4bꢂ
decreased stability of 4bꢂ
the increased steric hindrance around the metal center
when changing from a OÃCy group to a O-menthyl
group. As a consequence, the poor stability of 4bꢂ
/c are less stable than 4a in solution. The
/c vs. 4a may be attributed to
/
/
c
precluded their obtention via the methane elimination
method. As monitored by an NMR scale reaction, the
formation of 4b (or 4c) did occur when an equimolar
amount of AlMe3 and 3b (or 3c) was heated in C6D6 at
70 8C; however, their formation was concomitant with
their decomposition at this temperature [6].
Molecular weight measurements for 4bꢂ
suggest that both species are essentially monomeric in
solution (4b: Mtheo 385.29, Mfound 386.21; 4c:
Mtheo 545.32, Mfound 545.72). Although the pre-
sence of a small amount of 4bꢂc in a dimeric form
cannot be entirely ruled out by these measurements, we
assumed that compounds 4bꢂc are exclusively mono-
/
c in benzene
ꢁ
ꢁ
/
ꢁ
/
ꢁ
/
/
/
Fig. 1. Molecular structure of 4a as determined by X-ray crystal-
lography.
/
meric and thus, adopt a chelate structure similar to that
of 4a in the solid state. Numerous attempts to obtain X-
ray quality single crystals of either 4b or 4c remained
unsuccessful.
The synthesis of chiral dialkyl aluminium complexes
[2-(ꢀ
R?ꢁCPh3) was carried out using the salt metathesis
method. The pregenerated Li salts [2-(ꢀ)-menthy-
lOC6H4NR?][Li] were reacted in toluene at room
/
)-menthylOC6H4NR?]AlMe2 (4b, R?ꢁCy; 4c,
/
/
The 1H- and 13C-NMR spectra of 4bꢂ
temperature contain two similar sets of resonances in a
/
c at room
/
Scheme 3.

P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ
/247
243
proposal appears unlikely to us because the high
1
temperature H-NMR spectra for 4c in the presence of
one equivalent of THF in C6D6 are essentially un-
changed as compared to those of 4c alone, suggesting
that a putative de-coordination of the ethereal oxygen is
slow on the NMR time scale under these conditions even
in the presence of such a Lewis base. A de-/re-
coordination exchange process may be markedly accel-
erated by Lewis bases due to facile cleavage of the AlÃ
/
Chart 2.
O(menthyl) bond by attack of Lewis bases on the Al
center [9]. The de-coordination of the ethereal oxygen is
thus unlikely to be involved in the interconversion
process.
10/1 ratio for 4b and in a 4/1 ratio for 4c, which are
assigned to two different rotamers (C and D, Chart 2).
1
For example, the H-NMR spectrum of 4c contains
two sets of two singlets in the AlMe region (d ꢀ
0.57 for the major one; d ꢀ0.81, ꢀ0.37 for the minor
CH resonances also in a 4/1 ratio. Each
rotamer exhibits two AlMe resonances by H- and 13C-
NMR showing that the two methyl groups attached to
the Al center are inequivalent, as expected by the
/
0.60,
2.3. Conclusions
ꢀ
/
/
/
one) and two OÃ
/
A new type of achiral and chiral OÃ
/
Nꢀ bidentate
1
arylamido-based ligands has been described. The de-
rived Li salts readily react with ClAlMe2 via salt
metathesis to afford the corresponding dimethyl alumi-
nium complexes. The presence of two rotamers in
solution at room temperature for the chiral dimethyl
Al complexes is due to steric interactions of the chiral
group with the rest of the complex and suggests that the
coordination sphere of the Al center in these complexes
is severely crowded.
presence of the chiral (ꢀ
coordination environment of the Al center. The coordi-
nation of the ethereal oxygen to the Al center in 4bꢂc is
also evident by NMR spectroscopy. In particular, for 4c,
/)-menthyl group in the
/
1
the H-NMR OÃ
/
CH resonances (d (average) 4.55) are
significantly downfield shifted as compared to that of
the free ligand 3c (d 4.00) [7], as expected by the chelate
structure of 4c.
Further studies will focus on the conversion of the
obtained complexes to alkyl aluminium cations and on
reactivity studies of these cations.
The presence of two rotamers in 4bꢂ
temperature can be ascribed to a restricted rotation
around the OÃCH(menthyl) bond due to severe steric
/
c at room
/
interactions of the menthyl group with the Ph group
and/or with the methyl groups attached to the Al center.
Similar hindered rotations were also observed for the
3. Experimental
All experiments were carried out under N2 using
standard Schlenk techniques or in a Mbraun Unilab
glovebox. Toluene, pentane and THF were distilled
from Na/benzophenone and stored over activated mo-
˚
lecular sieves (4 A) in a glovebox prior to use. C6D6 was
degassed under a N2 flow and stored over activated
related dimeric dialkyl Al complexes {R2Al(m-mentho-
i
Me, Bu) and for other organoaluminium
late)}2 (Rꢁ
/
complexes containing bulky alkoxide ligands [8]. To
probe this issue further, high temperature NMR experi-
ments were performed and are discussed in the case of 4c
(Fig. 2). As shown in Fig. 2, raising the temperature
from 298 to 338 K, causes, in particular, the broadening
and then the coalescence of all four AlMe resonances.
˚
molecular sieves (4 A) in a glovebox prior to use. C6D6
was purchased from Eurisotope (CEA, Paris, France).
All other chemicals were purchased from Aldrich and
were used as received. All NMR spectra were recorded
Similarly, the two OÃ
338 K. Finally, at 348 K, the presence of only one well-
resolved OÃCH resonance and two AlMe singlets show
/
CH resonances coaslesce around
in CDCl3 or in C6D6. The NMR data for 1aꢂ
and 3aꢂc were obtained on a Bruker AC 200 MHz. The
NMR data for 4aꢂc were obtained on a Bruker AC 400
/
c, 2aꢂc
/
/
/
that the interconversion of the two rotamers is fast at
/
this temperature on the NMR timescale.
Two possible mechanisms for the rotamers intercon-
version were considered: first, as the temperature is
MHz spectrometer, in Teflon-valved J-young tubes at
ambient temperature, unless otherwise indicated. 1H and
13C chemical shifts are reported vs. SiMe4 and were
determined by reference to the residual 1H and 13C
solvent peaks. Molecular weights measurements for 4b
and 4c were made in benzene with the use of an
instrument similar to that described by Clark [10].
Elemental analysis were all performed by the micro-
analysis laboratory of the Universite´ Pierre et Marie
raised, fast rotation around the OÃ/CH(menthyl) causes
a rapid interconversion without modification of the
chelate structure of 4c; second, it was also considered
that the exchange could proceed via initial de-coordina-
tion of the etherealꢂ
tion around the OÃ
coordination of the oxygen to the Al center. The second
/menthyl oxygen followed by rota-
/CH(menthyl) bond and then re-
Curie (Paris, France), except those for 4aꢂc performed
/

244
P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ247
/
Fig. 2. Variable temperature of [2-(ꢀ)-menthylOC6H4NCPh3]AlMe2 (4c) in C6D6. The resonances are expanded off-scale for clarity.
/
by Mikroanalytisches Labor Pascher, Remagenꢂ
dorf, Germany. Silica gel Merck Gerudan SI (40ꢂ
nm) was used for column chromatography.
/
Ban-
Chromatography on silica gel (elution with Pentane/
EtOAc 98/2) yielded 8.72 g (31.4 mmol, 66%) of 1b as a
white solid.
/63
Anal. Calc. for C16H23NO3: C, 69.29; H, 8.36; N,
5.05. Found: C, 69.13; H, 8.56; N, 5.03%. 1H-NMR
3.1. Synthesis of 1-cyclohexyloxy-2-nitrobenzene (1a)
(CDCl3): d 0.73ꢂ
1H, Jꢁ10.5 and 4.1 Hz, CH Ã
(d, 1H, Jꢁ8.2 Hz, Ar), 7.47 (t, 1H, Ar), 7.75 (d, 1H,
Jꢁ
8.1 Hz, Ar). 13C-NMR (CDCl3): d 16.3, 20.6, 21.9,
/
2.30 (m, 18H, menthyl), 4.20 (t. of d,
To a suspension of KH (2.12 g, 52.9 mmol) in 70 ml of
THF was added dropwise at room temperature (r.t.)
under argon cyclohexanol (5.59 ml, 52.9 mmol). The
mixture was stirred for 16 h at r.t. and then cooled to
/
/O), 6.95 (t, 1H, Ar), 7.09
/
/
23.4, 25.7, 31.3, 34.1, 39.6, 47.5 (menthyl), 79.2 (CHÃ
/
ꢀ78 8C. 1-Fluoro-2-nitrobenzene (5.58 ml, 52.9 mmol)
/
O), 115.0, 119.5, 125.4, 133.5, 140.8, 151.4 (Ar).
was then slowly added and the solution was allowed to
warm to r.t. and stirred for 2 h. Fifty milliliters of
CH2Cl2 were then added and the organic phase was
washed with a saturated NH4Cl solution. The aqueous
phase was extracted with CH2Cl2 and the combined
organic layers were dried over MgSO4 and evaporated.
Chromatography on silica gel (elution with Pentane/
EtOAc 98/2) yielded 9.1 g (41.1 mmol, 78%) of 1a as a
white solid.
3.3. Synthesis of 2-cyclohexyloxyaniline (2a)
To a mixture of compound 1a (4.5 g, 20.4 mmol) Pd
(10 wt.%)/C (0.8 g) in EtOH (100 ml) was added very
slowly 6.06 ml (125 mmol) of NH2Ã
/
NH2×/H2O. After the
addition was completed, the mixture was heated to
reflux for 1 h. The suspension was then filtered through
a pad of celite, and the solvent was evaporated.
Chromatography on silica gel (elution with Pentane/
EtOAc 95/5) yielded 3.23 g (16.9 mmol, 83%) of
compound 2a as a crystalline white solid.
Anal. Calc. for C12H15NO3: C, 65.14; H, 6.83; N,
6.33. Found: C, 65.68; H, 6.88; N, 6.11%. 1H-NMR
(CDCl3): d 1.25ꢂ
6.96 (t, 1H, qꢁ7.5Hz, Ar), 7.08 (d, 1H, Jꢁ
7.47 (t, 1H, Jꢁ7.5 Hz, Ar), 7.75 (d, 1H, Jꢁ
/
1.95 (m, 10H, XC), 4.44 (m, 1H, XCH),
/
/
7.5 Hz, Ar),
7.5 Hz, Ar).
/
/
Anal. Calc. for C12H17NO: C, 75.35; H, 8.96; N, 7.32.
Found: C, 75.36; H, 8.87; N, 7.23%. 1H-NMR (CDCl3):
3.2. Synthesis of 1-(ꢀ)-menthyloxy-2-nitrobenzene (1b)
/
d 1.33ꢂ
(m, 1H, OÃ
(CDCl3): d 23.8, 25.7, 32.1 (Cy), 76.0 (OÃ
115.4, 118.3, 121.1, 137.4, 145.2 (Ar).
/
2.05 (m, 10H, Cy), 3.81 (s large, 2H, NH2), 4.25
CH), 6.66ꢂ
6.86 (m, 4H, Ar). 13C{1H}-NMR
CH), 114.0,
/
/
Following the same procedure as for 1a from 7.44 g
(47.6 mmol) of (ꢀ)-menthol, 1.91 g (47.6 mmol) of KH
and 5.0 ml (48 mmol) of 1-fluoro-2-nitrobenzene.
/
/

P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ
/247
245
3.4. Synthesis of 2-menthyloxyaniline (2b)
Hz, CH Ã
/
O), 4.22 (br s, 1H, NH), 6.57ꢂ
/
6.88 (m, 4H,
Ar). 13C{1H}-NMR (CDCl3): d 16.8, 20.7, 22.0, 23.8,
24.9, 25.9, 26.2, 31.3, 33.3, 33.4, 34.5, 40.5, 48.1
Following the same procedure as for 2a, from 1.86 g
(6.71 mmol) of compound 1b, 0.29 g of Pd (10 wt.%)/C
(menthyl), 51.3 (NÃ
115.6, 121.0, 138.6, 144.9 (Ar).
/
CH), 78.2 (CHÃ/O), 110.6, 112.5,
and 2 ml (41.2 mmol) of NH2Ã
/
NH2×/H2O. Chromato-
graphy on silica gel (elution with Pentane/EtOAc 95/5)
yielded 1.39 g (5.63 mmol, 84%) of compound 2b as a
crystalline white solid.
3.7. Synthesis of 2-(ꢀ)-menthyloxo-N-
triphenylmethylaniline (3c)
/
Anal. Calc. for C16H25NO: C, 77.68; H, 10.19; N,
1
5.66. Found: C, 77.57; H, 10.14; N, 5.57%. H-NMR
(CDCl3): d 0.81ꢂ
2H, NH2), 4.08 (t. of d, 1H, Jꢁ
O), 6.67ꢂ
6.86 (m, 4H, Ar). 13C{1H}-NMR (CDCl3): d
16.6, 20.8, 22.0, 23.6, 26.0, 31.3, 34.5, 40.4, 48.1
(menthyl), 77.8 (CHÃO), 113.0, 115.2, 118.3, 120.7,
137.3, 145.5 (Ar).
/
2.33 (m, 18H, menthyl), 3.80 (s large,
To a solution of 0.5 g (2.02 mmol) of compound 2b in
/
10.4 and 4.1 Hz, CH Ã
/
6 ml of THF at ꢀ
/
78 8C was added dropwise 0.9 ml (2.25
mmol) of BuLi (2.5 M in hexanes). The solution was
stirred at ꢀ78 8C for 0.5 h and a solution of 0.845 g
/
n
/
/
(3.03 mmol) of Ph3CCl in 3 ml of THF was added. The
red suspension was allowed to warm to r.t. and was
stirred at this temperature for 1 h. The solvent was
evaporated. Chromatography of the residue on silica gel
(elution with Pentane/EtOAc 98/2) yielded 0.32 g (0.65
mmol, 32%) of a slightly yellow oil which readily
3.5. Synthesis of 2-cyclohexyloxy-N-cyclohexylaniline
(3a)
To a suspension of Zn powder (2.23g) in 16.8 ml of
AcOH was added 1.30 g (6.81 mmol) of compound 2a
and 0.85 ml (8.20 mmol) of cyclohexanone. The mixture
crystallized from MeOH at ꢀ20 8C.
/
Anal. Calc. for C35H39NO: C, 85.84; H, 8.03; N,
1
2.86%. Found: C, 85.76; H, 8.14; N, 2.58%. H-NMR
was heated to 65ꢂ70 8C under argon for 40 h. The
/
mixture was cooled to r.t. and 40 ml of MeOH were
added. The suspension was filtered and the obtained
white solid was washed with MeOH. To the combined
organic layers were added 50 ml of dichloromethane and
30 ml of water. A NH4OH solution was added until
(CDCl3): d 0.84ꢂ
1H, Jꢁ10.4 and 4.1 Hz, CH Ã
6.08 (d, 1H, Jꢁ7.9 Hz, Ar), 6.44 (t, 1H, Jꢁ
6.55 (t, 1H, Jꢁ7.7 Hz, Ar), 6.81 (d, 1H, Jꢁ
7.21ꢂ
16.9, 20.6, 22.1, 23.8, 26.4, 31.4, 34.4, 40.9, 48.3
(menthyl), 70.8 (Ph3C), 78.9 (CHÃO), 111.7, 115.2,
/
2.35 (m, 18H, menthyl), 4.10 (t. of d,
/
/O), 5.94 (br s, 1H, NH),
/
/7.7 Hz, Ar),
/
/7.9 Hz, Ar),
/
7.46 (m, 15H, CPh3). 13C{1H}-NMR (CDCl3): d
pHꢀ10. The organic layer was separated and the
/
aqueous layer was extracted with dichloromethane.
The combined organic layers were dried on Na2SO4
and the solvent was evaporated. Chromatography on
silica gel (elution with Pentane/EtOAc 96/4) yielded 0.78
g (2.86 mmol, 42%) of compound 3a as a white solid.
Anal. Calc. for C18H27NO: C, 79.07; H, 9.95; N, 5.12.
Found: C, 79.43; H, 10.16; N, 5.03%. 1H-NMR
/
116.2, 119.7, 126.5, 127.7, 129.0, 129.4, 137.0, 145.7
(Ar).
3.8. Synthesis of (2-CyOC6H4NHCy)-AlMe3 (3a-
AlMe3)
(CDCl3): d 1.21ꢂ
CH), 4.28 (m, 2H, OÃ
Ar), 6.83ꢂ
6.94 (m, 2H, Ar). 13C{1H}-NMR (CDCl3): d
23.8, 24.9, 25.7, 26.0, 32.0, 33.4 (Cy), 51.3 (NÃCH), 76.2
(OÃCH), 110.7, 113.3, 115.60, 121.3, 138.7, 144.6 (Ar).
/
2.15 (m, 20H, Cy), 3.33 (m, 1H, NÃ
/
/
CH and NH), 6.60ꢂ6.72 (m, 2H,
/
/
In a glove box, compound 3a (310 mg, 1.13 mmol)
was added to a 15 ml vial sample and dissolved in 2 ml
of pentane. The vial was then stored in the freezer at
/
/
ꢀ35 8C for 30 min. After this time, it was taken out of
/
3.6. Synthesis of 2-(ꢀ
(3b)
/
)-menthyloxy-N-cyclohexylaniline
the freezer and AlMe3 (81.2 mg, 1.13 mmol) was quickly
added. The colorless reaction mixture was allowed to
warm to r.t. and stirred for 1 h at r.t., which resulted in
the precipitation of a white crystalline solid. The vial
The same procedure than that for 3a was followed
using 1 g (4.05 mmol) of 2b, 1.33 g of Zn powder and 0.5
ml (4.82 mmol) of cyclohexanone in 10 ml of AcOH.
Chromatography on silica gel (elution with Pentane/
EtOAc 96/4) yielded 0.51 g (1.55 mmol, 38%) of
compound 3b as a white solid.
was then stored at ꢀ35 8C overnight which provoked
/
further precipitation. Filtration through a glass frit and
drying under vacuum afforded the AlMe3 adduct (3a-
AlMe3, 325 mg) along with minor impurities, according
1
1
to the H-NMR spectrum. H-NMR (C6D6): d ꢀ
(s, 9H, AlÃCH3), 0.85ꢂ2.48 (m, 20H, Cy), 3.23 (m, 1H,
NÃCH), 3.94 (m, 1H, OÃCH), 5.29 (d, 1H, JHÃH 10
Hz, NH), 6.48ꢂ7.12 (m, 4H, Ar).
/
0.40
Anal. Calc. for C22H35NO: C, 80.19; H, 10.71; N,
1
4.25%. Found: C, 80.08; H, 10.88; N, 4.15%. H-NMR
/
/
/
/
ꢁ
/
(CDCl3): d 0.82ꢂ
/
2.31 (m, 28H, Cy and menthyl), 3.28 (s
10.5 and 4.1
/
large, 1H, CH ÃN), 4.05 (t. of d, 1H, Jꢁ
/
/

246
P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ247
/
3.9. Synthesis of [2-CyOC6H4NCy]AlMe2 (4a)
3.10. Synthesis of [2-(ꢀ
/
)-menthylOC6H4NCy]AlMe2
(4b) and [2-(ꢀ)-menthylOC6H4NCPh3]AlMe2 (4c)
/
3.9.1. First method (via salt metathesis)
The aluminium dimethyl compounds 4b and 4c were
synthesized following the salt metathesis route used for
4a. The Li salts menthylOC6H4-2-NCyLi (255 mg, 0.774
mmol) and menthylOC6H4-2-NCPh3Li (570.0 mg, 1.164
mmol) were synthesized and used as starting material
for the obtention of 4b and 4c, respectively. In both
In a dry box, the ligand CyOC6H4-2-NHCy (3a, 840.0
mg, 3.070 mmol) was charged in a 50 ml round-bottom
flask and dissolved in 10 ml of pentane. The resulting
solution was cooled to ꢀ
40 8C and nBuLi (3.070 mmol,
/
1.92 ml of a 1.6 M hexanes solution) was added
dropwise via a pipette. Upon addition of nBuLi, the
formation of a white precipitate and gas formation
(nBuH) are also immediately observed. After the addi-
tion, the reaction mixture was allowed to warm to r.t.
and then stirred for 3 h. The mixture was filtered
through glass frit and dried under vacuum to yield the
extremely air-sensitive colorless solid Li salt CyOC6H4-
2-N(Cy)(Li) (670 mg, 80% yield), which was used
without further purification.
1
cases, the H-NMR spectrum of crude product in C6D6
clearly showed the presence of two rotamers in slow
exchange on the NMR timescale in 1/10 and 1/4 ratios
for 4b and 4c, respectively. Compound 4b was isolated
in a pure form as a colorless solid from recrystallization
of the crude product from pentane at ꢀ35 8C (55%
/
yield). Pure 4c (colorless solid) was obtained by a
pentane wash of the crude product followed by filtration
through frit and drying under vacuum.
The Li salt CyOC6H4-2-N(Cy)(Li) (250.0 mg, 0.895
mmol) was charged in a 15 ml vial and dissolved in 5 ml
of toluene to yield a pale yellow solution. The solution
was cooled to ꢀ35 8C in a freezer for 30 min, after
/
3.10.1. Data for 4b
Anal. Calc. for C24H40AlNO: C, 74.76; H, 10.46.
which it was taken out. ClAlMe2 (0.895 mmol, 0.90 ml
of 1 M of hexanes solution) was then rapidly added to
the reaction mixture via a syringe. The resulting solution
was allowed to warm to r.t. and stirred overnight
causing the initial solution to turn into a colorless light
suspension due to LiCl precipitation. The mixture was
then filtered through frit and the volatiles removed
under vacuum to give a colorless solid. Recrystallization
of the crude product from a 1/1 toluene/ether mixture
afforded analytically pure [CyOC6H4-2-NCy]AlMe2 4a
as an air-sensitive colorless crystalline solid (180 mg,
61% yield).
1
Found: C, 74.40; H, 10.70%. H-NMR (C6D6) (minor
rotamer): d ꢀ
CH3), 4.62 (br, 1H, OÃ
d ꢀ0.23 (s, 3H, AlÃCH3), ꢀ
0.56ꢂ2.30 (m, 28H, Cy and menthyl), 3.27 (m, 1H, NÃ
CH), 4.56 (m, 1H, OÃ
6.70 (d, 1H, Jꢁ7 Hz, Ar), 6.75 (d, 1H, Jꢁ
7.07 (t, 1H, Jꢁ
5.3 (AlÃCH3), ꢀ
25.2, 26.2, 26.3, 26.5, 32.0, 33.7, 34.6, 34.7, 39.6, 46.3
CH), 110.8,
/
0.27 (s, 3H, AlÃ
CH). 1H-NMR (major rotamer):
0.18 (s, 3H, AlÃCH3),
/
CH3), ꢀ
/
0.17 (s, 3H, AlÃ
/
/
/
/
/
/
/
/
/
CH), 6.45 (t, 1H, Jꢁ/7 Hz, Ar),
/
/
7 Hz, Ar),
/
7 Hz, Ar). 13C{1H}-NMR (C6D6): d
ꢀ
/
/
/
3.6 (AlÃ
/
CH3), 15.6, 20.7, 21.7, 23.2,
Anal. Calc. for C20H32AlNO: C, 72.91; H, 9.79.
Found: C, 72.35; H, 9.56%. 1H-NMR (C6D6): d ꢀ
(Cy and menthyl), 54.0 (NÃ
/
CH), 85.2 (OÃ
/
/
111.0, 111.1, 125.9, 144.6, 144.7 (Ar).
0.23 (s, 6H, AlÃ
(m, 1H, NÃCH), 4.19 (m, 1H, OÃ
Ar), 6.66 (d, 1H, Jꢁ7 Hz, Ar), 7.05 (t, 1H, Jꢁ
Ar). 13C{1H}-NMR (C6D6): d ꢀ
4.40 (AlÃCH3), 24.9,
CH), 81.9 (OÃCH),
/
CH3), 0.68ꢂ
/
2.30 (m, 20H, Cy), 3.25
CH), 6.43 (m, 2H,
7 Hz,
/
/
/
/
3.10.2. Data for 4c
Anal. Calc. for C37H44AlNO: C, 81.43; H, 8.13.
/
/
26.2, 26.5, 31.3, 34.5 (Cy), 53.9 (NÃ
110.1, 110.6, 110.7, 125.5, 143.4, 144.2 (Ar).
/
/
1
Found: C, 80.90; H, 7.90%. H-NMR (C6D6) (major
rotamer): d ꢀ
AlÃCH3), 0.54ꢂ
OÃCH), 6.24ꢂ
7.65 (m, 22H, Ar). 1H-NMR (C6D6)
(minor rotamer): d ꢀ0.81 (s, 0.6H, AlÃCH3), ꢀ0.37
(s, 0.6H, AlÃCH3), 0.54ꢂ2.34 (m, 18H, menthyl), 4.63
(m, 1H, OÃCH), 6.24ꢂ
7.65 (m, 22H, Ar). 13C{1H}-
NMR (C6D6) (major rotamer): d ꢀ6.7 (AlÃC), ꢀ5.2
(AlÃC), 15.7, 20.9, 21.8, 23.3, 25.2, 32.3, 33.7, 33.7, 39.5,
46.2 (menthyl), 73.7 (NÃCPh3), 88.0 (OÃCH), 111.8,
113.4, 120.5, 123.9, 143.4, 145.3 (Ar). 13C{1H}-NMR
(C6D6) (minor rotamer): d ꢀ8.8 (AlÃC), ꢀ7.3 (AlÃC),
16.6, 20.9, 21.9, 24.5, 25.5, 32.5, 33.9, 38.4, 47.7
(menthyl), 73.5 (NÃCPh3), 89.2 (OÃCH), 113.0, 116.1,
120.3, 124.5, 142.3, 144.9 (Ar).
/
0.60 (s, 2.4H, AlÃ
/
CH3), ꢀ
/
0.57 (s, 2.4H,
/
/
2.34 (m, 18H, menthyl), 4.48 (m, 1H,
3.9.2. Second method (via methane elimination)
/
/
In a glove box, a J-Young NMR tube was charged
with CyOC6H4-2-NHCy (3a, 31.0 mg, 0.11 mmol) and
0.75 ml of C6D6 was added. AlMe3 (8.2 mg, 0.11 mmol)
was then added to the ligand solution via a microsyr-
inge. The NMR tube was vigorously shaken and an 1H-
NMR spectrum was immediately recorded showing the
quantitative formation of the AlMe3 adduct 3a-AlMe3.
The tube was then immersed in an oil bath pre-heated at
75 8C and the reaction was monitored by 1H-NMR,
which showed the complete conversion of 3a-AlMe3 to
4a along with methane formation, after overnight at
75 8C.
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

P. Haquette et al. / Journal of Organometallic Chemistry 682 (2003) 240ꢂ
/247
247
3.11. Crystal data for 4a
Acknowledgements
Crystals of 4a suitable for X-ray diffraction were
obtained at r.t. by slow evaporation of a concentrated
toluene solution of 4a.
The authors thank the C. N. R. S. (Centre National
de la Recherche Scientifique) for financial support, Dr
Phil Dyer (University of Leicester, UK) for molecular
Compound 4a: C20H32AlNO, Mꢁ
colorless crystal; crystal size : 0.13ꢄ0.10ꢄ
monoclinic; space groupe C2/c; aꢁ12.271(5), bꢁ
90.171(5)8; Zꢁ4;
0.113 mmꢀ1; a total
30.028, 2767 independent
reflections with 2155 having I ꢀ2s(I); 175 parameters;
final results: R(F)ꢁ0.045; Rw(F)ꢁ0.013, Goodness-of-
fitꢁ1.11, maximum residual electronic densityꢁ0.384
e Aꢀ3. A selected crystal was mounted on a Nonius
Kappa-CCD area detector diffractometer (MoꢂKa, lꢁ
/
329.45 g molꢀ1
0.08 mm3;
;
weight measurements of 4bꢂc and M.-N. Rager
/
/
/
(ENSCP, Paris, France) for NMR assistance.
/
/
˚
12.313(5), cꢁ
Dcalc
1.16 g cmꢀ3; m (Moꢂ
of 6297 reflections; 2.34Bu B
/
12.480(5) A; bꢁ
/
/
ꢁ
/
/
Ka)ꢁ
/
/
/
References
/
/
/
[1] For representative examples, see: (a) H. Schumann, S. Dechert, S.
/
/
Schutte, J.-Y. Hyeon, M. Hummert, B.C. Wassermann, W.
˚
Kaminsky, A. Eisenhardt, K. Kohler, J. Eichborn, Organome-
¨
/
/
tallics 22 (2003) 1391;
˚
0.71073 A). The complete conditions of data collection
(Denzo software) and structure refinements are given
below. The cell parameters were determined from
reflections taken from one set of 10 frames (1.08 steps
in phi angle), each at 20 s exposure. The structure was
solved using direct methods (SIR97) and refined against
F2 using the SHELXL97 software. The absorption was
not corrected. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were generated ac-
cording to stereo-chemistry and refined using a riding
model in SHELXL97. All hydrogen atoms were placed
from fourier differences and refined isotropically. It is
important to stress that this molecule crystallizes on a C2
axe (i.e. the Al atom (4e position of the C2/c group) and
(b) C. Niamh McMahon, J.A. Francis, S.G. Bott, A.R. Barron, J.
Chem. Soc., Dalton Trans. (1999) 67;
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(1997) 4597;
(e) B. Qian, D.L. Ward, M.R. Smith, Organometallics 17 (1998)
3070;
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(b) M.P. Coles, R.F. Jordan, J. Am. Chem. Soc. 119 (1997) 8125;
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[5] (a) T.F. Woiwode, C. Rose, T.J. Wandless, J. Org. Chem. 63
(1998) 9594;
the middle of the C(1)Ã
/
C(1a) contact are on the C2 axe.
In these conditions, the atomic arrangement observed by
X-ray diffraction must be considered as an average of
two chemically true molecules, rotate by 1808 around
the C2 axe in the crystal. The structural resolution test in
the triclinic system gives not realistic solutions.
(b) P.R. Ashton, B. Horner, O. Kocian, S. Menzer, A.J.P. White,
¨
J. Fraser Stoddart, D.J. Williams, Synthesis (1996) 930;
(c) I.V. Micovic, M.D. Ivanovic, D.M. Piatak, V.Dj. Bojic,
Synthesis (1991) 1043.
[6] The formation of 4b and 4c via methane elimination at room
temperature is extremely slow.
4. Supplementary material
[7] The 1H-NMR spectrum of 2-(ꢀ
was also recorded in C6D6.
/)-menthylOC6H4NHCPh3 (3c)
Crystallographic data (excluding structure factors)
have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC no. 212662 for compound
4a. Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: ꢃ44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
[8] (a) M.L. Sierra, R. Kumar, V.S.J. de Mel, J.P. Oliver, Organo-
metallics 11 (1992) 206;
(b) R. Kumar, M.L. Sierra, V.S.J. de Mel, J.P. Oliver, Organo-
metallics 9 (1990) 484.
[9] D. Cho, J.E. Park, B.-J. Bae, K. Lee, B. Kim, J.T. Park, J.
Organomet. Chem. 592 (1999) 162.
[10] E.P. Clark, Ind. Eng. Chem. Anal. Ed. 13 (1941) 820.
/