Dialkylaluminum complexes with chelating anilido-imine ligands: Synthesis, structures, and luminescent properties

Article abstract of DOI:10.1021/om049143a

Syntheses of three new chelating anilido-imine conjugated ligands, ortho-C₆H₄NHAr′)-(CH=NAr″) [Ar′ = Ar″ = 2,6-Me₂C₆H₃ (2b); Ar′ = p-MeC₆H₄, Ar″ = 2,6-ⁱPr₂C

Full text of DOI:10.1021/om049143a

1614
Organometallics 2005, 24, 1614-1619
Dialkylaluminum Complexes with Chelating
Anilido-Imine Ligands: Synthesis, Structures, and
Luminescent Properties
Xiaoming Liu,† Wei Gao,† Ying Mu,*,† Guanghua Li,‡ Ling Ye,† Hong Xia,†
Yi Ren,† and Shouhua Feng‡
Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, School
of Chemistry, Jilin University, 10 Qianwei Road, Changchun 130012, People’s Republic of
China, and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, School of
Chemistry, Jilin University, 10 Qianwei Road, Changchun 130012, People’s Republic of China
Received November 7, 2004
Syntheses of three new chelating anilido-imine conjugated ligands, ortho-C6H4(NHAr′)-
(CHdNAr′′) [Ar′ ) Ar′′ ) 2,6-Me2C6H3 (2b); Ar′ ) p-MeC6H4, Ar′′ ) 2,6-iPr2C6H3 (2c); Ar′ )
Ar′′ ) p-MeC6H4 (2d)], as well as their four-coordinate dialkyl aluminum complexes, ortho-
C6H4(NAr′)(CHdNAr′′)AlMe2 [Ar′ ) Ar′′ ) 2,6-iPr2C6H3 (3a); Ar′ ) Ar′′ ) 2,6-Me2C6H3 (3b);
Ar′ ) p-MeC6H4, Ar′′ ) 2,6-iPr2C6H3 (3c); Ar′ ) Ar′′ ) p-MeC6H4 (3d)], are described.
Complexes 3a-d were synthesized from the reaction of AlMe3 with the corresponding ligand
1
at room temperature by alkane elimination. All complexes were characterized by H and
13C NMR spectroscopy, and the molecular structures of complexes 3a, 3c, and 3d were
determined by X-ray crystallography. Luminescent properties of the ligands 2a-d and the
complexes 3a-d in solution were studied, and it was found that emission maxima of 3a-d
are in the range 519-582 nm, depending on the substituents on the aryl rings of their ligands.
Complexes 3a-d exhibit intense photoluminescence in the solid state, and the maximum
emission wavelengths at room temperature are in the range 532-552 nm.
Introduction
olinyl)aluminum (Alq3) and a large number of its
derivatives with modified 8-hydroxyquinoline ligands
have been investigated;2,6,7 aluminum complexes with
nitrogen-containing ligands have also been reported.8
It has been demonstrated that the emission color of
aluminum complexes can be modulated in a wide range
by modifying their ligands or coordination environments
around the aluminum atom.9
Luminescent coordination compounds have been one
of the most active research areas because of their
potential application in light emitting diodes (LEDs).1
Luminescent main group and transition metal com-
plexes, such as Al(III),2 Zn(II),3 Pt(II),4 and Ir(III)5
complexes, have been designed and synthesized in
recent years. Particularly, chelated aluminum com-
plexes have attracted much attention due to their good
luminescent properties. For example, tri(8-hydroxyquin-
A critical issue to be considered in designing, synthe-
sizing, and fabricating luminescent materials is the
control of their emission wavelengths.2,4a,5b,10 Emission
* To whom correspondence should be addressed. E-mail:
ymu@mail.jlu.edu.cn. Fax: (+86)431-5193421.
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H.; Yonemoto, Y.; Kawami, S.; Imai, K. Appl. Phys. Lett. 1994, 65, 807.
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G.; Tao, Y.; D’Iorio, M.; Wang, S. Chem. Mater. 2000, 12, 79. (f) Jang,
H.; Do, L.-M.; Kim, Y.; Kim, J. G.; Zyung, T.; Do, Y. Synth. Met. 2001,
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† Key Laboratory for Supramolecular Structure and Materials of
Ministry of Education.
‡ State Key Laboratory of Inorganic Synthesis and Preparative
Chemistry.
(1) (a) Wang, S. N. Coord. Chem. Rev. 2001, 215, 79. (b) Chen, C.
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10.1021/om049143a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/23/2005

Dialkylaluminum Complexes
Organometallics, Vol. 24, No. 7, 2005 1615
Scheme 1. Synthetic Procedure of Ligands 2a-d
and Synthetic Procedure of Complexes 3a-d
properties of coordination compounds are in general
controlled by a number of factors, including electronic
properties of ligands and metal ions, coordination bond
lengths and angles that affect the energy mixing, and
splitting of electronic states involved in the emission.
One of the convenient ways to tune the emission color
of a series of complexes is to modify the ligands.11 It
has been reported that â-diketiminato (nacnac) alumi-
num complexes with different substituted aryl groups
in the nacnac ligand can be easily synthesized.12 How-
ever, there are few reports on the luminescent proper-
ties of similar aluminum complexes. We have synthe-
sized a number of new aluminum complexes with
similar chelating anilido-imine conjugated ligands and
found that they are efficient fluorescent materials and
their emission color can be modulated in the range 519-
582 nm by ligand modification. We report here the
syntheses, characterizations, and fluorescent properties
of three new ligands, ortho-C6H4(NHAr′)(CHdNAr′′)
[Ar′ ) Ar′′ ) 2,6-Me2C6H3 (2b); Ar′ ) p-MeC6H4, Ar′′ )
2,6-iPr2C6H3 (2c); Ar′ ) Ar′′ ) p-MeC6H4 (2d)], and their
four-coordinate alkyl aluminum complexes, ortho-C6H4-
(NAr′)(CHdNAr′′)AlMe2 [Ar′ ) Ar′′ ) 2,6-iPr2C6H3 (3a);
Ar′ ) Ar′′ ) 2,6-Me2C6H3 (3b); Ar′ ) p-MeC6H4, Ar′′ )
2,6-iPr2C6H3 (3c); Ar′ ) Ar′′ ) p-MeC6H4 (3d)].
Results and Discussion
1a-c by corresponding LiN(H)Ar (Scheme 1). The
reactions of 1a-c with 1 equiv of LiN(H)Ar were carried
out in THF, and the crude products were purified from
methanol. These compounds (1a-c, 2a-d) are very
soluble in most organic solvents. Compounds 2b-d were
Ligand Synthesis. Pre-ligand compounds ortho-
C6H4F(CHdNAr) [Ar ) 2,6-iPr2C6H3 (1a); Ar ) 2,6-
Me2C6H3 (1b); Ar ) p-MeC6H4 (1c)] were prepared
according to a literature procedure13 in high yields by
condensation reaction of ortho-fluorobenzaldehyde with
1 equiv of relevant amine in hexane (Scheme 1).
Compound 1a is a known compound, while 1b and 1c
are new compounds. 1b was obtained as a greenish oil,
but 1c was isolated as a white solid. Compounds 1a-c
1
characterized by H and 13C NMR spectroscopy along
with elemental analyses. The 1H NMR spectra of these
compounds exhibit resonances in the region δ 8.32-8.68
for the CH imine protons, with the corresponding 13C
NMR resonances occurring in the range δ 162.3-166.3.
The NH resonances appear at characteristically low
field (δ 10.5-11.2). The infrared absorption bands of the
1
were characterized by H NMR spectroscopy and ele-
mental analyses. The 1H NMR spectra of these pre-
ligands exhibit resonances in the region δ 8.57-8.81 for
the CH imine protons. The ligand ortho-C6H4(NHAr′)-
(CHdNAr′′) [Ar′ ) Ar′′ ) 2,6-iPr2C6H3 (2a)] is a known
compound that was synthesized by the literature
method.13 The new ligands 2b-d were synthesized by
the same procedure in good yields (>70% isolated yields)
via a nucleophilic aromatic displacement of fluoride in
imine CdN stretch occur in the region 1615-1634 cm-1
.
Complex Synthesis. Treatment of 2a-d with 1
equiv of trimethylaluminum in hexane at room temper-
ature caused the evolution of methane and afforded the
corresponding dimethyl aluminum complexes 3a-d in
good yields (>80%) as yellow or orange crystalline solids
(Scheme 1). The reaction can also be carried out in
toluene, but the products were obtained in lower yields.
Complexes 3a-d were all characterized by elemental
analyses and 1H and 13C NMR spectroscopy, and
satisfactory analytic results were obtained on all com-
pounds. In the 1H NMR spectra of these complexes, the
resonances for the CH imine protons (δ 7.32-7.85) shift
about 1 ppm toward high field compared to the corre-
sponding signals of free ligands, while the resonances
(δ 167.9-171.9) for the CH imine carbons in 13C NMR
spectra shift to low field in comparison with the corre-
sponding ones of free ligands. The disappearance of the
N-H signal of the ligands and the appearance of
resonances for AlMe2 protons in high-field region (δ
-0.24 to -0.52) in the 1H NMR spectra of 3a-d
demonstrate the formation of the aluminum complexes.
1H and 13C NMR spectra reveal that these complexes
all have Cs-symmetric structures in solution. For com-
pounds 3a and 3c, coordination of the anilido-imine
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W. E.; Parvez, M. Organometallics 2003, 22, 1577.

1616 Organometallics, Vol. 24, No. 7, 2005
Liu et al.
Table 1. Selected Bond Lengths (Å) and Angles
(deg) for 3a, 3c, and 3d
Complex 3a
Al(1)-N(1)
Al(1)-N(2)
Al(1)-C(33)
Al(1)-C(32)
N(1)-C(1)
N(2)-C(7)
1.889(1) N(1)-Al(1)-C(33)
1.963(1) C(33)-Al(1)-N(2)
1.960(2) N(1)-Al(1)-C(32)
111.59(7)
114.97(7)
115.66(7)
1.968(2) C(33)-Al(1)-C(32) 113.83(8)
1.370(2) N(2)-Al(1)-C(32)
1.298(2) C(7)-N(2)-Al(1)
105.32(7)
121.07(10)
121.99(9)
N(1)-Al(1)-N(2) 93.79(5) C(20)-N(2)-Al(1)
Complex 3c
Al(1)-N(1)
1.890(3)
1.955(3)
1.956(5)
1.956(5)
1.357(4)
1.309(4)
93.9(1)
N(2)-Al(1)-C(28)
N(1)-Al(1)-C(27)
N(2)-Al(1)-C(27)
C(28)-Al(1)-C(27)
C(1)-N(1)-Al(1)
C(20)-N(1)-Al(1)
C(7)-N(2)-Al(1)
C(8)-N(2)-Al(1)
110.7(2)
110.0(2)
112.1(2)
115.3(2)
127.7(2)
111.8(2)
122.7(2)
122.3(2)
Al(1)-N(2)
Al(1)-C (28)
Al(1)-C (27)
N(1)-C(1)
N(2)-C(7)
N(1)-Al(1)-N(2)
N(1)-Al(1)-C(28)
Figure 1. Structure of complex 3a (thermal ellipsoids are
drawn at the 30% probability level).
113.0(2)
Complex 3d
Al(1)-N(1)
1.874(2)
1.932(2)
1.942(2)
1.943(3)
1.360(3)
1.305(3)
110.9(1)
94.49(8)
C(22)-Al(1)-N(2)
N(1)-Al(1)-C(23)
C(22)-Al(1)-C(23)
N(2)-Al(1)-C(23)
C(1)-N(1)-Al(1)
C(15)-N(1)-Al(1)
C(7)-N(2)-Al(1)
C(8)-N(2)-Al(1)
111.5(9)
113.8(1)
116.7(1)
107.3(1)
129.0(1)
114.7(1)
123.4(2)
120.7(1)
Al(1)-C(22)
Al(1)-N(2)
Al(1)-C(23)
N(1)-C(1)
N(2)-C(7)
N(1)-Al(1)-C(22)
N(1)-Al(1)-N(2)
tate ligand via the imine and amido nitrogen atoms. In
these three complexes, the six-membered chelating ring
is nearly planar, with the aluminum atom lying 0.556,
0.289, and 0.059 Å out of the plane, respectively. The
dihedral angles between the six-membered chelating
ring and aromatic ring attached to the amido nitrogen
atom are 69.2°, 85.9°, and 85.1°, and the dihedral angles
between the six-membered chelating ring and aromatic
ring attached to the imine nitrogen atom are 88.1°,
88.1°, and 61.7°, respectively. The imino CdN bonds in
these complexes retain their double-bond character,
being 1.298(2), 1.309(4), and 1.305(3) Å for 3a, 3c, and
3d, respectively. The Al-N (amido) distances (1.889(1)
Å for 3a, 1.890(3) Å for 3c, and 1.874(2) Å for 3d) are
much shorter than the Al-N (imine) distances (1.963(1)
Å for 3a, 1.955(3) Å for 3c, and 1.942(2) Å for 3d)
because the anionic amido nitrogen can also π-donate
to the aluminum, whereas the neutral imine nitrogen
does not have an available lone pair for π-donation. The
Al-N (imine) distances are shorter than the value
(1.972(3) Å) previously reported for {3,5-tBu2-2-(O)C6H2-
Figure 2. Structure of complex 3c (thermal ellipsoids are
drawn at the 30% probability level).
Figure 3. Structure of complex 3d (thermal ellipsoids are
drawn at the 30% probability level).
ligands to the aluminum center causes rotation about
the N-aryl bond to become slow on the NMR time scale
and renders the individual methyl groups of an isopro-
pyl unit inequivalent in the 1H NMR spectrum. All
complexes have good solubility in most organic solvents,
including saturated hydrocarbons such as n-pentane or
n-hexane. They are air and moisture sensitive in both
the solid state and solution, while they have pretty good
thermal stability in solution and can be heated in boiling
toluene for several hours without obvious decomposition.
Crystal Structures. Crystals of 3a, 3c, and 3d
suitable for X-ray crystal structure determination are
grown from n-hexane at room temperature or 0 °C. The
ORTEP drawings of the molecular structures of 3a, 3c,
and 3d are shown in Figure 1, Figure 2 and Figure 3,
respectively. Selected bond lengths and angles for 3a,
3c, and 3d are given in Table 1. X-ray analysis reveals
that 3a, 3c, and 3d adopt a distorted tetrahedral
geometry with the metal center chelated by the biden-
i
CHdNC6H3 Pr2-2,6}AlMe2,14 but larger than those val-
ues (1.922(2) and 1.935(2) Å) in Dipp2nacnacAlMe2.15
The N-Al-N angles (93.8° for 3a, 93.9° for 3c, and 94.5°
for 3d) in these complexes are similar to that (94.72°)
of a diketiminatolaluminum complex {CH[CMeN(p-
MeC6H4)]2AlMe2},15 while they are larger than those in
the four-membered chelating ring (69°) of {tBuC(NCy)2}-
16
AlMe2 and the five-membered chelating ring (84°) of
{(iPr)2ATI}AlR2.17
UV-Vis and Fluorescent Properties. Table 3
summarizes the UV-vis and fluorescent properties of
(14) Cameron, P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Solan,
G. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans.
2001, 1472.
(15) Qian, B.; Ward, M. L.; Smith, M. R., III. Organometallics 1998,
17, 3070.
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Organometallics 1997, 16, 5183.
(17) Dias, H. V.; Jin, R. W.; Ratcliff, R. E. Inorg. Chem. 1995, 34,
6100.

Dialkylaluminum Complexes
Organometallics, Vol. 24, No. 7, 2005 1617
Table 2. Crystal Data and Structural Refinements Details for 3a, 3c, and 3d
3a
3c
3d
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
C
33H45AlN2
C28H35AlN2
426.56
C23H25AlN2
356.43
monoclinic
P2(1)/c
11.960(2)
8.9673(18)
19.415(4)
90
96.72(3)
90
2068.0(7)
4
496.69
monoclinic
P2(1)/c
17.671(4)
10.496(2)
17.695(4)
90
108.54(3)
90
3111.5(11)
4
triclinic
P1h
9.826(3)
10.000(3)
14.755(5)
106.875(4)
103.857(4)
100.180(5)
1298.9(7)
2
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
Dcalcd (g cm-3
F(000)
)
1.060
1080
1.091
460
1.145
760
θ range for data collection
limiting indices
3.04° to 27.48°
-22 e h e 22
-13 e k e 13
-22 e l e 22
7092/0/325
1.051
2.20° to 25.00°
-5 e h e 11
-8 e k e11
-17 e l e 14
3822/0/280
1.019
1.71° to 27.36°
0 e h e 15
0 e k e 11
-25 e l e 24
4517/0/247
0.860
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1a ) 0.0477
wR2b ) 0.1399
R1a ) 0.0654
wR2b ) 0.1510
0.238, -0.222
R1a ) 0.0610
wR2b ) 0.1597
R1a ) 0.1027
wR2b ) 0.1886
0.238, -0.323
R1a ) 0.0523
wR2b ) 0.1172
R1a ) 0.1186
wR2b ) 0.1328
0.184, -0.172
R indices (all data)
largest diff peak/hole (e‚Å-3
)
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]]1/2
.
Table 3. Optical Properties of Compounds 2a-d
and 3a-d in n-Hexane
compound
abs λ (nm)
ꢀ (M-1 cm-1
)
Em λ (nm)
2a
2b
2c
2d
3a
3b
3c
3d
370
373
382
395
454
455
463
475
9011
13 214
10 745
13 300
8056
419
423
430
450
519
519
547
582
8287
8156
8085
compounds 2a-d and 3a-d determined in hexane. By
examining the data in Table 3, it can be seen that the
UV-vis absorption and fluorescent emission peaks for
these compounds are red shifted with the decrease in
the size of the substituents at the ortho-positions of the
two rotatable aryl rings, which might be because larger
ortho-substituents on the aryl rings would lower the
chance for the rotatable aryl rings to have coplanar
conformations with the chelating ring, thus reducing the
conjugated extent of the compounds.
The free ligands 2a-d all display weak blue fluores-
cence with emission maxima of 419, 423, 430, and 450
nm, respectively. In comparison, complexes 3a-d pro-
duce bright fluorescence from green to orange-red in
solution with emission maxima of 519, 519, 547, and
582 nm, respectively, as seen in Figure 4. It is remark-
able that the emission maxima of complexes 3a-d span
63 nm between 519 and 582 nm just because of the
differences in the number and size of the ortho-substit-
uents on the rotatable aryl rings of their ligands that
might affect the conjugated extent of these complexes
as mentioned above. These results provide a new way
to modulate the emission color of organic, organome-
tallic, or coordination compounds with rotatable aryl
groups. It can be clearly seen that the absorption and
emission frequencies of the complexes 3a-d change
with the same trend as those of the free ligands 2a-d
do. However, complexes 3a and 3b in solid state emit
bright fluorescence with emission maxima of 532 and
Figure 4. Emission spectra of complexes 3a-d in n-
hexane.
533 nm (Figure 5), which are red shifted in comparison
with their emission maxima in solution, while the
emission maxima of complexes 3c and 3d (545 and 552
nm, respectively) in solid state are blue shifted com-
pared to their corresponding emission maxima in solu-
tion. The red shift of the emission wavelength from
solution to solid state is likely caused by π-π stacking
of aromatic rings in the molecules in solid state, while
the blue shift of the emission wavelength for 3c and 3d
from solution to solid state probably results from the
reduced conjugated extent of the two complexes since
the free rotation of the aryl rings in these complexes is
blocked in the solid state. According to published
literatures, the emissions of these complexes could be
attributed to a π*-π transition of their ligands.18 The
role of the aluminum atom in the luminescence of 3a-d
might be 2-fold. First, the formation of covalent bonds
(18) (a) Ballardini, R.; Varani, G.; Indelli, M. T.; Scandola, F. Inorg.
Chem. 1986, 25, 3858. (b) Yang, W.; Schmider, H.; Wu, Q.; Zhang, Y.;
Wang, S. Inorg. Chem. 2000, 39, 2397.

1618 Organometallics, Vol. 24, No. 7, 2005
Liu et al.
sis was performed on a Perkin-Elmer 2400 analyzer. UV-vis
absorption spectra were recorded on an UV-3100 spectropho-
tometer. Fluorescence measurements were carried out on a
RF-5301PC.
ortho-C6H4F(CHdNC6H3Me2-2,6) (1b). A mixture of ortho-
fluorobenzaldehyde (5.0 mL, 47.1 mmol), 2,6-dimethylaniline
(5.8 mL, 47.1 mmol), and MgSO4 (1.0 g) in n-hexane (30 mL)
was stirred for 2 h. The mixture was filtered and evaporated
to dryness in vacuo to give the product as a yellowish oil (6.4
g, 60%). Anal. Calcd for C15H14NF (227.28): C 79.27, H 6.21,
1
N 6.16. Found: C 79.16, H 6.30, N 6.24. H NMR (CDCl3): δ
2.19 (s, 6H, CH3), 6.97-7.32 (m, 5H, Ph-H), 7.51 (t, 1H, Ph-
H), 8.30 (t, 1H, Ph-H), 8.58 (s, 1H, CHdNAr) ppm. 13C{1H}
NMR (CDCl3): δ 18.5 (Me), 116.2 (d, 2JCF ) 21 Hz, Ph), 124.1
(d, 3JCF ) 4 Hz), 124.2 (Ph), 124.8 (Ph), 127.3 (Ph), 127.9 (Ph),
3
128.3 (Ph), 133.3 (d, JCF ) 9 Hz, Ph), 151.5 (quaternary
3
1
aromatic), 156.5 (d, JCF ) 5 Hz, CHdNAr), 163.1 (d, JCF
256 Hz, CF) ppm.
)
ortho-C6H4F(CHdNC6H4Me-p) (1c). A mixture of ortho-
fluorobenzaldehyde (5.0 mL, 47.1 mmol), p-toluidine (5.0 g,
47.1 mmol), and MgSO4 (1.0 g) in n-hexane (30 mL) was stirred
for 2 h. The mixture was filtered, and the filtrate was
concentrated to about 10 mL and kept at -20 °C overnight.
Pure product was obtained as yellow crystals (8.2 g, 82%).
Anal. Calcd for C14H12NF (213.25): C 78.85, H 5.67, N 6.57.
Figure 5. Emission spectra of complexes 3a-d in the solid
state.
between the Al and N atoms via the donation of lone
pairs of the N atom to the Al atom changes the emission
energy, perhaps owing to the lowering of the energy gap
between π* and π. Second, after coordination with the
Al atom, the rigidity of the ligands becomes stronger in
comparison with free ligands, which can reduce the loss
of energy via vibrational motions and increase the
emission efficiency, a phenomenon well known to coor-
dination complexes containing luminescence ligand.19
1
Found: C 78.80, H 5.70, N 6.54. H NMR (CDCl3): δ 2.39 (s,
3H, CH3), 7.50 (t, 1H, Ph-H), 8.21 (t, 1H, Ph-H), 7.10-7.31
(m, 6H, Ph-H), 8.81 (s, 1H, CHdNAr) ppm. 13C{1H} NMR
2
(CDCl3): δ 21.2 (Me), 116.1 (d, JCF ) 21 Hz, Ph), 121.2 (Ph),
2
3
124.3 (d, JCF ) 9 Hz, quaternary aromatic), 124.7 (d, JCF
)
3
5 Hz, Ph), 128.1 (Ph), 130.0 (Ph), 133.0 (d, JCF ) 9 Hz, Ph),
3
136.5, 149.6 (2 quaternary aromatic), 152.8 (d, JCF ) 5 Hz,
1
CHdNAr), 163.0 (d, JCF ) 256 Hz, CF) ppm.
Summary
ortho-C6H4{NH(C6H3Me2-2,6)}(CHdNC6H3Me2-2,6) (2b).
A solution of nBuLi (30.32 mL, 48.5 mmol) in hexanes was
added to a solution of 2,6-dimethylaniline (6.0 mL, 48.5 mmol)
in THF (30 mL) at -78 °C. The mixture was allowed to warm
to room temperature and stirred overnight. The resulting
solution of LiNHAr (Ar ) C6H3Me2-2,6) was transferred into
a solution of ortho-C6H4F(CHdNC6H3Me2-2,6) (11.0 g, 48.5
mmol) in THF (40 mL) at 25 °C. After stirring for 2 h, the
reaction was quenched with H2O (25 mL) and extracted with
n-hexane, and the organic phase was evaporated to dryness
in vacuo to give the crude product as a yellow solid. Pure
product (11.5 g, 72%) was obtained as yellowish-green crystals
by recrystallization from ethanol at -20 °C. Anal. Calcd for
C23H24N2 (328.45): C 84.11, H 7.37, N 8.52. Found: C 84.18,
H 7.25, N 8.57. 1 H NMR (CDCl3): δ 2.22 (s, 6H, CH3), 2.26 (s,
6H, CH3), 6.32 (d, 1H, Ph-H), 6.76 (t, 1H, Ph-H), 7.01 (t, 1H,
Ph-H), 7.12-7.24 (m, 6H, Ph-H), 7.37 (d, 1H, Ph-H), 8.42 (s,
1H, CHdNAr), 10.60 (s, 1H, NH) ppm. 13C{1H} NMR
(CDCl3): δ 18.6 (CH3), 18.8 (CH3), 112.0, 115.6, 117.0, 124.1,
126.6, 127.9, 128.4, 128.6, 132.5, 134.8, 137.0, 137.7, 148.7,
151.0, 166.2 (CHdNAr) ppm.
Our research results indicate that the new chelating
bidentate anilido-imine conjugated ligands are well
suited for synthesizing the four-coordinate alkyl alumi-
num complexes by alkane elimination reaction of AlMe3
with corresponding ligands at room temperature. 1H and
13C NMR spectra reveal that these aluminum complexes
have Cs-symmetric structures in solution, and X-ray
diffraction analysis indicates that the six-membered
chelating ring in these complexes is nearly planar, with
the aluminum lying slightly out of the plane. These new
complexes produce bright fluorescence in both solution
and the solid state, and the emission color in solution
can be tuned by the ortho substituents on the rotatable
aryl rings of the ligands.
Experimental Section
All reactions were performed using standard Schlenk tech-
niques in an atmosphere of high-purity nitrogen or glovebox
techniques. Toluene, hexane, THF, and diethyl ether were
dried by refluxing over sodium and benzophenone and distilled
under nitrogen prior to use. C6D6 was dried over activated 4
Å molecular sieves and vacuum-transferred to a sodium-
mirrored air-free flask. CDCl3 was dried over CaH2 for 48 h
and vacuum-transferred to an air-free flask. AlMe3 and nBuLi
were purchased from Aldrich and used as received. The ortho-
i
ortho-C6H4{NH(C6H4Me-p)}(CHdNC6H3 Pr2-2,6) (2c). A
solution of nBuLi (29.2 mL, 46.7 mmol) in hexanes was added
to a solution of p-toluidine (5.0 g, 46.7 mmol) in THF (30 mL)
at -78 °C. The reaction mixture was allowed to warm to room
temperature and stirred overnight. The resulting solution of
LiNHAr (Ar ) C6H4Me-p) was transferred into a solution of
i
ortho-C6H4F(CHdNC6H3 Pr2-2,6) (13.2 g, 46.7 mmol) in THF
(40 mL) at 25 °C. After stirring for 2 h, the reaction was
quenched with H2O (20 mL) and extracted with n-hexane, and
the organic phase was evaporated to dryness in vacuo to give
the crude product as a yellow solid. Pure product (11.9 g, 69%)
was obtained as yellow crystals by recrystallization from
ethanol at -20 °C. Anal. Calcd for C26H30N2 (370.53): C 84.28,
H 8.16, N 7.56. Found: C 84.19, H 8.21, N 7.60. 1H NMR
(CDCl3): δ 1.19 (d, 6H, CH(CH3)2), 1.21 (d, 6H, CH(CH3)2), 2.36
(s, 3H, CH3), 3.07 (sept, 2H, CH(CH3)2), 6.81 (t, 1H, Ph-H),
7.14-7.38 (m, 10H, Ph-H), 8.32 (s, 1H, CHdNAr), 11.16 (s,
i
C6H4F(CHdNC6H3 Pr2-2,6) and ortho-C6H4(NHAr′)(CHdNAr′)
(Ar′ ) Ar′′ ) 2,6-iPr2C6H3) were synthesized according to
literature procedures.13 NMR spectra were measured using a
Varian Mercury-300 NMR spectrometer. The elemental analy-
(19) (a) Fluorescence and Phosphorescence; Rendell, D., Eds.;
Wiley: New York, 1987. (b) Photochemistry and Photophysics of
Coordination Compounds; Yersin, H., Vogler, A., Eds.; Springer-
Verlag: Berlin, 1987. (c) Concepts of Inorganic Photochemistry; Ad-
amson, A. W., Fleischauer, P. D., Eds.; Wiley: New York, 1975.

Dialkylaluminum Complexes
Organometallics, Vol. 24, No. 7, 2005 1619
1H, NH) ppm. 13C{1H} NMR (CDCl3): δ 21.1 (CH3), 23.8 (CH-
(CH3)2), 28.3 (CH(CH3)2), 112.7, 116.8, 117.8, 123.0, 123.3,
124.7, 130.1, 132.3, 133.3, 135.2, 138.4, 147.2, 148.8, 165.7
(CHdNAr) ppm.
°C with stirring. The mixture was stirred at 0 °C for 30 min
and at room temperature for additional 2 h, then was
concentrated to about 10 mL and kept at -20 °C overnight to
let the product crystallize. The product was obtained as orange
crystals (0.21 g, 91%). Anal. Calcd for C28H35N2Al (426.56): C
78.84, H 8.27, N 6.57. Found: C 78.73, H 8.11, N 6.69. 1H NMR
(C6D6, 293 K): δ -0.38 (s, 6H, Al(CH3)), 0.92 (d, 6H, CH(CH3)2),
1.27 (d, 6H, CH(CH3)2), 2.10 (s, 3H, Ph-CH3), 3.34 (sept, 2H,
CH(CH3)2), 6.28 (t, 1H, Ph-H), 6.67 (d, 1H, Ph-H), 6.78 (d, 1H,
Ph-H), 6.87 (t, 1H, Ph-H), 6.99-7.20 (m, 7H, Ph-H), 7.84 (s,
1H, HCdN) ppm. 13C{1H} NMR (C6D6, 293 K): δ -8.0 (Al-
(CH3)2), 20.9 (CH3), 22.7 (CH(CH3)2), 26.0 (CH(CH3)2), 28.5
(CH(CH3)2), 114.7, 115.5, 117.7, 124.4, 130.9, 134.8, 136.8,
136.9, 143.1, 143.2, 143.7, 157.9, 171.5 (CHdNAr) ppm.
ortho-C6H4{NH(C6H4Me-p)}(CHdNC6H4Me-p) (2d). A
solution of nBuLi (29.2 mL, 46.7 mmol) in hexanes was added
to a solution of p-toluidine (5.0 g, 46.7 mmol) in THF (30 mL)
at -78 °C. The reaction mixture was allowed to warm to room
temperature and stirred overnight. The resulting solution of
LiNHAr (Ar ) C6H4Me-p) was transferred into a solution of
ortho-C6H4F(CHdNC6H4Me-p) (9.9 g, 46.7 mmol) in THF (40
mL) at 25 °C. After stirring for 2 h, the reaction was quenched
with H2O (20 mL) and extracted with n-hexane, and the
organic phase was evaporated to dryness in vacuo to give the
crude product. Pure product was obtained by recrystallization
from ethanol at -20 °C as orange crystals (9.8 g, 70%). Anal.
Calcd for C21H20N2 (300.40): C 83.96, H 6.71, N 9.33. Found:
C 83.86, H 6.78, N 9.36. 1H NMR (CDCl3): δ 2.43 (s, 3H, CH3),
2.45 (s, 3H, CH3), 6.85 (t, 1H, Ph-H), 7.21-7.37 (m, 10H, Ph-
H), 7.47 (d, 1H, Ph-H), 8.67 (s, 1H, CHdNAr), 11.24 (s, 1H,
NH) ppm. 13C{1H} NMR (CDCl3): δ 21.1 (CH3), 21.2 (CH3),
112.9, 116.9, 118.4, 121.1, 123.0, 130.0, 130.1, 132.0, 133.2,
135.1, 135.9, 138.6, 147.0, 148.9, 162.3 (CHdNAr) ppm.
ortho-C6H4N(C6H3iPr2-2,6)(CHdNC6H3iPr2-2,6)Al-
ortho-C6H4N(C6H4Me-p)(CHdNC6H4Me-p)Al(CH3)2 (3d).
A solution of ortho-C6H4{NH(C6H4Me-p)}(CHdNC6H4Me-p)
(0.20 g, 0.67 mmol) in 10 mL of n-hexane was slowly added to
a solution of AlMe3 (0.67 mmol) in 15 mL of n-hexane at 0 °C
with stirring. The mixture was stirred at 0 °C for 30 min and
at room temperature for additional 2 h, then was concentrated
to about 10 mL and kept at -20 °C overnight to let the product
crystallize. The product was obtained as orange crystals (0.20
g, 85%). Anal. Calcd for C23H25N2Al (356.44): C 77.50, H 7.07,
1
N 7.86. Found: C 77.62, H 7.16, N 7.74. H NMR (C6D6, 293
i
(CH3)2 (3a). A solution of ortho-C6H4{NH(C6H3 Pr2-2,6)}(CHd
K): δ -0.25 (s, 6H, Al(CH3)2), 2.02 (s, 3H, Ph-CH3), 2.11 (s,
3H, Ph-CH3), 6.31 (t, 1H, Ph-H), 6.65 (d, 1H, Ph-H), 6.68 (d,
1H, Ph-H), 6.83-7.20 (m, 9H, Ph-H), 7.65 (s, 1H, CHdN) ppm.
13C{1H} NMR (C6D6, 293 K): δ -7.7 (Al(CH3)2), 20.8 (CH3),
20.9 (CH3), 114.5, 116.3, 117.4, 122.7, 130.3, 130.9, 134.9,
136.6, 137.1, 137.4, 143.8, 145.6, 157.7, 168.0 (CHdNAr) ppm.
X-ray Structure Determinations of 3a, 3c, and 3d.
Single crystals of 3a, 3c, and 3d suitable for X-ray structural
analysis were obtained from n-hexane. Diffraction data were
collected at 293 K on a Bruker SMART-CCD diffractometer
using graphite-monochromated Mo KR radiation (λ ) 0.71073
Å) for 3c and on a Rigaku R-AXIS RAPID IP diffractometer
equipped with graphite-monochromated Mo KR radiation (λ
) 0.71073 Å) for 3a and 3d. Details of the crystal data, data
collections, and structure refinements are summarized in
Table 2. The structures were solved by direct methods20 and
refined by full-matrix least-squares on F2. All non-hydrogen
atoms were refined anisotropically, and the hydrogen atoms
were included in idealized position. All calculations were
performed using the SHELXTL21 crystallographic software
packages.
i
NC6H3 Pr2-2,6) (0.20 g, 0.46 mmol) in 10 mL of n-hexane was
slowly added to a solution of AlMe3 (0.46 mmol) in 15 mL of
n-hexane at 0 °C with stirring. The mixture was stirred at 0
°C for 30 min and at room temperature for additional 2 h, then
was concentrated to about 10 mL and kept at -20 °C overnight
to let the product crystallize. The product was obtained as
orange-green crystals (0.20 g, 88%). Anal. Calcd for C33H45N2-
Al (496.70): C 79.80, H 9.13, N 5.64. Found: C 79.71, H 9.08,
N 5.78. 1H NMR (C6D6, 293 K): δ -0.52 (s, 6H, Al(CH3)2), 1.02,
1.11 (d, 2 × 6H, CH(CH3)2), 1.31, 1.37 (d, 2 × 6H, CH(CH3)2),
3.41, 3.53 (sept, 2 × 2H, CH(CH3)2), 6.25 (t, 1H, Ph-H), 6.33
(d, 1H, Ph-H), 6.78 (m, 2H, Ph-H), 7.09-7.24 (m, 6H, Ph-H),
7.86 (s, 1H, HCdN) ppm. 13C{1H} NMR (C6D6, 293 K): δ -9.0
(Al(CH3)2), 22.7, 24.7, 25.6, 25.8 (4 × CH(CH3)2), 28.4, 28.5 (2
× CH(CH3)2), 115.1, 115.7, 119.4, 124.4, 124.8, 126.9, 128.1,
135.9, 136.9, 140.8, 142.9, 143.3, 146.6, 158.2, 171.5 (CHdNAr)
ppm.
ortho-C6H4N(C6H3Me2-2,6)(CHdNC6H3Me2-2,6)Al-
(CH3)2 (3b). A solution of ortho-C6H4{NH(C6H3Me2-2,6)}(CHd
NC6H3Me2-2,6) (0.20 g, 0.61 mmol) in 10 mL of n-hexane was
slowly added to a solution of AlMe3 (0.61 mmol) in 15 mL of
n-hexane at 0 °C with stirring. The mixture was stirred at 0
°C for 30 min and at room temperature for additional 2 h, then
was concentrated to about 10 mL and kept at -20 °C overnight
to let the product crystallize. The product was obtained as
orange-green crystals (0.21 g, 90%). Anal. Calcd for C25H29N2-
Al (384.49): C 78.09, H 7.60, N 7.29. Found: C 78.21, H 7.51,
N 7.37. 1H NMR (C6D6, 293 K): δ -0.50 (s, 6H, Al(CH3)2), 2.15
(s, 6H, Ph-CH3), 2.29 (s, 6H, Ph-CH3), 6.31 (t, 1H, Ph-H), 6.73
(d, 1H, Ph-H), 6.80-7.16 (m, 8H, Ph-H), 7.32 (s, 1H, HCdN)
ppm. 13C{1H} NMR (C6D6, 293 K): δ -7.6 (Al(CH3)2), 18.6
(CH3), 18.7 (CH3), 114.6, 115.7, 116.5, 126.0, 127.2, 129.1,
129.4, 132.3, 136.1, 137.1, 137.4, 142.9, 145.6, 156.7, 171.9
(CHdNAr) ppm.
Acknowledgment. This work was supported by
the National Natural Science Foundation of China
(No. 20374023 and 29734143) and Ministry of Science
and Technology of China (No. 2002CB6134003).
Supporting Information Available: 1H and 13C NMR
spectra for 1b, 1c, 2b-d, and 3a-d. X-ray crystallographic
files (CIF) for 3a, 3c, and 3d. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM049143A
i
ortho-C6H4N(C6H4Me-p)(CHdNC6H3 Pr2-2,6)Al(CH3)2
(20) SHELXTL; PC Siemens Analytical X-ray Instruments: Madi-
son, WI, 1993.
(21) Sheldrick, G. M. SHELXTL Structure Determination Programs,
Version 5.0; PC Siemens Analytical Systems: Madison, WI, 1994.
i
(3c). A solution of ortho-C6H4{NH(C6H4Me-p)}(CHdNC6H3 Pr2-
2,6) (0.20 g, 0.54 mmol) in 10 mL of n-hexane was slowly added
to a solution of AlMe3 (0.54 mmol) in 15 mL of hexanes at 0