Syntheses of cationic four-coordinated aluminum complexes: Counter-ion induced aggregation through the N-HI hydrogen bonds

Article abstract of DOI:10.1016/S0022-328X(99)00641-5

Synthesis of cationic aluminum complexes from the reactions of Lewis bases with Me₂AlI is reported. The reactions of two molar equivalents of (S)-(-)-1-phenylethylamine, (R)-(-)-pantolactone (PL-H), or (S)-(-)-ethyl lactate (EL-H) with Me₂

Full text of DOI:10.1016/S0022-328X(99)00641-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 598 (2000) 13–19
Syntheses of cationic four-coordinated aluminum complexes:
counter-ion induced aggregation through the NꢀH···I hydrogen
bonds
Bao-Tsan Ko, Ying-Chieh Chao, Chu-Chieh Lin *
Department of Chemistry, National Chung-Hsing Uni6ersity, Taichung 402, Taiwan, ROC
Received 2 September 1999; received in revised form 5 October 1999; accepted 16 October 1999
Abstract
Synthesis of cationic aluminum complexes from the reactions of Lewis bases with Me2AlI is reported. The reactions of two
molar equivalents of (S)-(−)-1-phenylethylamine, (R)-(−)-pantolactone (PLꢀH), or (S)-(−)-ethyl lactate (ELꢀH) with Me2AlI
(1), generated in situ from the reaction of Me3Al with one molar equivalent of I2 in toluene at room temperature, afford white
crystalline solids [Me2Al((S)-NH2(Ph)C(H)CH3)2]+I− (2), [(PL)2Al]+I− (3) or [(EL)2Al]+I− (4), respectively. However, Me3Al
reacts with one molar equivalent of PLꢀH producing [(Me2Al(m-PL))2 (5). The reaction of Me2AlI with 2,2%-ethylidene-bis-(4,6-di-
tert-butylphenol) (EDBPꢀH2) yields [Al(EDBP)I(Et2O)] (6) which further reacts with one molar equivalent or two molar
equivalents of OPPh3 giving a neutral complex [Al(EDBP)(OPPh3)I] (7) or a cationic complex [Al(EDBP)(OPPh3)2]+I− (8).
However, the cationic aluminum derivative [Al(EDBP)(HMPA)2]+I− (9) is prepared from the reaction of 6 with excess of HMPA.
Crystal structures of 2, 5, and 8 determined by X-ray diffraction method are also presented. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Aluminum; Cation; Aggregation; Hydrogen bond
directed toward the preparation and use of aluminum
derivatives as Lewis acid for the catalysis of Diels–
Alder reactions and ring-opening polymerization [5].
Our interest in cationic aluminum chemistry has led us
to investigate a feasible way for the preparation of a
variety of cationic aluminum complexes. Me2AlI is
chosen as a starting material because of the weak AlꢀI
bond, therefore, it is easy to break the AlꢀI bond using
Lewis bases. In this paper, we report the preparation
and characterization of several four-coordinated
cationic aluminum complexes. The first examples that
cationic aluminum complexes are stabilized by lactate or
lactonate ligand and the formation of supramolecular
structure via NꢀH···I hydrogen bonds will be presented.
1. Introduction
Cationic aluminum complexes are of great interest
because of their potential use as living polymerization
catalysts [1] as well as their role in the Lewis acid
promoted Diels–Alder reactions [2]. Although many
cationic aluminum complexes have been reported; how-
ever, four-coordinated aluminum cations are relatively
rare but are still remain attractive as these complexes are
not completely coordinated saturate and are electron
deficient [3]. Recently Atwood and Jegier have demon-
strated that the formation of aluminum cations is af-
fected by the nature of halogen in Me2AlX [4]. In which
he describes that Me2AlBr reacts with excess tert-butyl
amines resulting in a cationic aluminum complex
[(tBuNH2)2AlMe2]+Br− formation, whereas, Me2AlCl
reacts with tert-butyl amines leading only to a neutral
adduct [(tBuNH2)Al(Cl)Me2]. Recently, we have been
2. Experimental
2.1. General
All manipulations were carried out under a dry nitro-
gen atmosphere. Solvents were dried by refluxing at
* Corresponding author. Fax: +886-4-286-2547.
E-mail address: cchlin@mail.nchu.edu.tw (C.-C. Lin)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00641-5

14
B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
least 24 h over sodium–benzophenone (toluene, hex-
ane, diethyl ether, tetrahydrofuran) or phosphorus pen-
taoxide (CH2Cl2) and freshly distilled prior to use.
Deuterated solvents were dried over molecular sieves.
AlMe3 (2.0 M in toluene), (S)-(−)-1-phenylethylamine,
(R)-(−)-pantolactone, (S)-(−)-ethyl lactate, 2,2%-
ethylidene-bis-(4,6-di-tert-butylphenol), iodine, tri-
phenylphosphine oxide, hexamethylphosphinoamide
were purchased and used without further purification.
Melting points were determined with a Buchi 535 digi-
2.4. Preparation of [Al((S)-OC(H)(CH3)-
COOEt)2]+I− (4)
To an ice cold solution (0°C) of iodine (0.52 g, 2.0
mmol) in CH2Cl2 (20 ml), AlMe3 (1.0 ml, 2.0 mmol)
was added slowly and stirred for 30 min. (S)-(−)-ethyl
lactate (0.46 ml, 4.0 mmol) was added and the resulting
mixture was stirred for 3 h. The volatile materials were
removed in vacuo and the residue was extracted with 20
ml of CH2Cl2. Colorless crystalline solids were obtained
24 h after the addition of hexane (40 ml). Yield: 0.48 g
(62%). Anal. Calc. for C10H18O6AlI: C, 30.95; H, 4.67.
1
tal melting point apparatus. H- and 13C-NMR spectra
were recorded on a Varian VXR-300 (300 MHz) or a
Mercury-400 (400 MHz) spectrometer with chemical
shifts given in ppm from the internal TMS. Micro-
analyses were performed using a Heraeus CHN-O-
RAPID instrument. Infrared spectra were obtained
from a Brucker Equinox 55 spectrometer.
1
Found: C, 30.83; H, 5.19%. H-NMR (CDCl3, ppm): l
4.26 (q, 2H, CH, J=6.8 Hz), 4.25 (q, 4H, OCH2CH3,
J=7.0 Hz); 1.42 (d, 6H, CH3, J=6.8 Hz); 1.31 (t, 6H,
OCH2CH3, J=7.0 Hz). IR (KBr, wCO): 1646 cm−1
.
M.p. 160°C (dec.).
2.2. Preparation of [Me2Al((S)ꢀNH2PhCH-
(CH3))2]+I− (2)
2.5. Preparation of [Me2Al(v-(R)-pantolactonato)]2 (5)
To an ice cold solution (0°C) of (R)-pantolactone
(0.26 g, 2.0 mmol) in ether (30 ml), an AlMe3 (1.2 ml,
2.0 M in toluene, 2.4 mmol) solution was added slowly.
The mixture was stirred for 2.5 h and then was dried in
vacuo to give a white powder. The residue was ex-
tracted with 30 ml of ether and then concentrated to ca.
20 ml. Colorless crystals were obtained, after cooling to
−20°C overnight. Yield: 0.29 g (79%). Anal. Calc. for
C16H30Al2O6: C, 51.61; H, 8.12. Found: C, 51.23; H,
To an ice cold solution (0°C) of iodine (0.52 g, 2.0
mmol) in toluene (20 ml), an AlMe3 (1.0 ml, 2.0 M in
toluene, 2.0 mmol) solution was added slowly. The
solution changes color from purple to colorless in 20
min, followed by the addition of (S)-(−)-1-phenylethyl-
amine (0.52 ml, 4.0 mmol). The resulting mixture was
stirred for 2 h, during which a white precipitate formed
and then was dried in vacuo. The residue was extracted
with 30 ml of CH2Cl2 and recrystallized from 3:1
hexane–CH2Cl2. Colorless crystals were obtained after
24 h. Yield: 0.81 g (95%). Anal. Calc. for C18H28AlIN2:
C, 50.71; H, 6.62; N, 6.57. Found: C, 50.53; H, 6.65; N,
1
7.89%. H-NMR (CDCl3, ppm): l 4.94 (s, 1H, OCH);
4.15 (s, 2H, OCH2); 1.32, 1.09 (s, 6H, C(CH3)2), −0.82
(s, 6H, AlCH3). 13C-NMR (CDCl3, ppm): l 182.86
(CꢁO), 79.47 (OCH), 77.44 (OCH2), 42.43 (C(CH3)2),
22.46, 18.46 (C(CH3)2), −8.96 (AlCH3). IR (KBr, wCO):
1
6.65%. H-NMR (CDCl3, ppm): l 7.41–7.30 (m, 10H,
Ph); 5.14 (br, 4H, NH2); 4.15 (q, 2H, CH(CH3), J=6.8
Hz); 1.60 (d, 6H, CH(CH3), J=6.8 Hz); −1.05
(AlCH3). 13C-NMR (CDCl3, ppm): l 139.94, 129.05,
128.68, 126.82 (Ph); 52.72 (CH(CH3)); 24.34
(CH(CH3)); −10.43 (AlCH3).
1757 cm−1
.
2.6. Preparation of [Al(EDBP)I(Et2O)] (6)
To an ice cold solution (0°C) of iodine (1.04 g, 4.0
mmol) in toluene (30 ml), an AlMe3 (2.0 ml, 2.0 M in
toluene, 4.0 mmol) solution was added slowly. After 20
min the mixture became colorless, 2,2%-ethylidene-
bis(4,6-di-tert-butylphenol) (1.76 g, 4.0 mmol) in ether
(20 ml) was added. The resulting mixture was stirred
for 2 h and then dried in vacuo. The residue was
extracted with 35 ml of ether and the extraction was
then concentrated to ca. 20 ml and cooled to −20°C to
furnish colorless crystals. Yield: 2.10 g (79%). Anal.
Calc. for C34H54AlIO3: C, 61.44; H, 8.19. Found: C,
2.3. Preparation of [((R)-pantolactonato)2Al]+I− (3)
To an ice cold solution (0°C) of iodine (0.52 g, 2.0
mmol) in CH2Cl2 (20 ml), AlMe3 (1.0 ml, 2.0 mmol)
was added slowly. After the mixture was stirred for 30
min, (R)-(−)-pantolactone (0.52 g, 4.0 mmol) was
added and the resulting mixture was stirred for 3 h. The
volatile materials were removed in vacuo and the
residue was extracted with 20 ml of CH2Cl2. Colorless
crystalline solids were obtained 24 h after the addition
of hexane (40 ml). Yield: 0.65 g (79%). Anal. Calc. for
C12H18O6AlI: C, 34.97; H, 4.40. Found: C, 35.41; H,
1
60.76; H, 7.44%. H-NMR (CDCl3, ppm): l 7.38 (d,
2H, Ph, J=2.4 Hz), 7.14 (d, 2H, Ph, J=2.4 Hz); 4.51
(br, 4H, OCH2CH3); 4.40 (q, 1H, CH(CH3), J=7.2
Hz); 1.68 (d, 3H, CH(CH3), J=7.2 Hz); 1.53 (br, 6H,
OCH2CH3); 1.42 (s, 18H, C(CH3)3); 1.30 (s, 18H,
C(CH3)3). 13C-NMR (CDCl3, ppm): l 150.7, 140.9,
137.6, 133.4, 121.6, 120.9 (Ph); 70.1 (OCH2CH3); 35.3,
1
4.51%. H-NMR (CDCl3, ppm): l 4.11 (s, 2H), 4.04 (d,
2H, CH2, J=8.8 Hz), 3.95 (d, 2H, CH2, J=8.8 Hz),
1.25 (s, 6H, CH3), 1.09 (s, 6H, CH3). IR (KBr, wCO):
1736 cm−1. M.p. 179°C (dec.).

B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
15
1
34.5, 31.8, 30.5 (tBu); 30.9 (CH(CH3)); 22.4 (CH(CH3));
13.9 (OCH2CH3).
8.89. Found: C, 53.45; H, 8.32; N, 8.74%. H-NMR
(CDCl3, ppm): l 7.33 (d, 2H, Ph, J=2.4 Hz), 7.05 (d,
2H, Ph, J=2.4 Hz); 4.33 (q, 1H, CH(CH3), J=7.2
Hz); 2.80 (d, 18H, OP[N(CH3)2]3, JHꢀP=10 Hz), 2.79
(d, 18H, OP[N(CH3)2]3, JHꢀP=10 Hz), 1.63 (d, 3H,
CH(CH3), J=7.2 Hz); 1.37 (s, 18H, C(CH3)3); 1.28 (s,
18H, C(CH3)3). 13C-NMR (CDCl3, ppm): l 150.8,
140.1, 135.9, 133.2, 121.0, 120.8 (Ph); 36.96, 36.91 (d,
P[N(CH3)2]3, JCꢀP=18.4 Hz); 35.1, 34.3, 31.7, 29.9
(tBu); 31.1 (CH(CH3)); 22.8 (CH(CH3)).
2.7. Preparation of [(Ph3PꢁO)Al(EDBP)I] (7)
A solution of triphenylphosphine oxide (0.56 g, 2.0
mmol) in toluene (20 ml) was added to a rapidly
stirring solution of [Al(EDBP)I(Et2O)] (1.33 g, 2.0
mmol) in toluene (30 ml). The reaction mixture was
stirred at room temperature (r.t.) for 2 h, during which
a white precipitate formed. The volatiles were removed
under vacuum and the residue was dissolved in hot
toluene (50 ml). The hot toluene solution was allowed
to cool to −20°C, affording colorless crystalline
product after 24 h. Yield: 1.56 g (90%). Anal. Calc. for
C48H59AlIO3P: C, 66.36; H, 6.84. Found: C, 66.92; H,
2.10. X-ray crystallographic studies
Suitable crystals of 2, 5, and 8 were sealed in thin-
walled glass capillaries under a nitrogen atmosphere
and mounted on a Siemens P4 diffractometer. The
crystallographic data were collected using a ꢀ–2q scan
mode with Mo–Ka radiation. Cell constants were ob-
tained by least-squares analysis on positions of at least
25 randomly selected reflections in the 2q range of
4–28°. The space group determination was based on a
check of the Laue symmetry and systematic absences,
and was confirmed using the structure solution. The
structure was solved by direct methods using a Siemens
SHELXTL PLUS package [6]. All non-H atoms and hy-
drogen atoms attached on nitrogen were located from
successive Fourier maps. Other H-atoms were refined
using a riding model [7]. Anisotropic thermal parame-
ters were used for all non-H atoms, and fixed isotropic
parameters were used for H atoms. Crystallographic
data of 2, 5 and 8 are listed in Table 1.
1
6.73%. H-NMR (CDCl3, ppm): l 7.79–7.39 (m, 15H,
Ph); 7.38, 7.30, 7.10, 7.02 (d, 4H, Ph, J=2.4 Hz); 4.88,
4.64 (q, 1H, CH(CH3), J=7.2 Hz); 1.68, 1.46 (d, 3H,
CH(CH3), J=7.2 Hz); 1.42, 1.29 (s, 18H, C(CH3)3);
1.19 (s, 18H, C(CH3)3).
2.8. Preparation of [Al(EDBP)(OꢁPPh3)2]+I− (8)
To a rapidly stirring solution of [Al(EDBP)I(Et2O)]
(1.33 g, 2.0 mmol) in toluene (30 ml), triphenylphos-
phine oxide (1.12 g, 4.0 mmol) in toluene (20 ml) was
added. The reaction mixture was stirred at r.t. for 2 h,
during which a white precipitate formed. The volatile
materials were removed under vacuum and the residue
was extracted with 40 ml of THF and was then concen-
trated to ca. 30 ml and cooled to −20°C to furnish
colorless crystals. Yield: 2.04 g (89%). Anal. Calc. for
C66H74AlIO4P2: C, 69.10; H, 6.50. Found: C, 68.95; H,
3. Results and discussion
1
6.08%. H-NMR (CDCl3, ppm): l 7.79–7.39 (m, 30H,
Ph); 7.21 (d, 2H, Ph, J=2.0 Hz), 7.06 (d, 2H, Ph,
J=2.0 Hz); 4.09 (q, 1H, CH(CH3), J=6.8 Hz); 1.27 (s,
18H, C(CH3)3); 1.18 (s, 18H, C(CH3)3); 0.93 (d, 3H,
CH(CH3), J=6.8 Hz). 13C-NMR (CDCl3, ppm): l
150.5, 140.4, 136.1, 133.1, 120.9, 120.8 (Ph); 135.0,
132.2 (d), 132.1 (d), 129.8 (d), 129.5 (d), 124.4 (d), 123.8
(d) (PPh); 35.0, 34.2, 29.9, 29.7 (tBu); 31.6 (CH(CH3));
21.6 (CH(CH3)).
3.1. Synthesis and spectroscopic studies of 1–5
The reactions of two molar equivalents of (S)-(−)-1-
phenylethylamine, (R)-(−)-pantolactone (PLꢀH), or
(S)-(−)-ethyl lactate (ELꢀH) with Me2AlI (1), gener-
ated in situ from the reaction of Me3Al with one molar
equivalent of I2 in toluene at 0°C, afford cationic alu-
minum complexes [Me2Al((S)-NH2(Ph)C(H)CH3)2]+I−
(2), [(PL)2Al]+I− (3) or [(EL)2Al]+I− (4), respectively
(shown in Scheme 1). However, the reaction of one
molar equivalent of (R)-(−)-pantolactone with Me3Al
yields a neutral pentacoordinated aluminum complex
[(m-PL)AlMe2]2 (5). Compound 5 is readily dissolved in
toluene. However, compounds 2, 3 and 4 are sparing
soluble in warm toluene but readily dissolve in cold
dichloromethane indicating an ionic feature of these
compounds. Despite attempts in vain to obtain the
solid state structure of 3 and 4, the ionic feature of
3 and 4 can be established by IR spectroscopic studies.
A systematic decrease in the carbonyl stretching
frequency (wCO) from the free (R)-pantolactone (1760
2.9. Preparation of [Al(EDBP)(HMPA)2]+I− (9)
Hexamethylphosphoramide (1.40 ml, 8.0 mmol) was
added to a rapidly stirring solution of [Al(EDBP)I-
(Et2O)] (1.33 g, 2.0 mmol) in toluene (30 ml). The
reaction mixture was stirred overnight at r.t., during
which a white precipitate formed. The volatile materials
were removed under vacuum to give a white powder.
The residue was dissolved in hot toluene (40 ml). The
hot toluene solution was allowed to cool to 5°C, afford-
ing colorless crystals after 48 h. Yield: 1.51 g (80%).
Anal. Calc. for C42H76AlIN6O4P2: C, 53.39; H, 8.11; N,

16
B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
cm−1) to the neutral compound [Me2Al(m-PL)]2 (5)
(1757 cm−1) and to cationic compound 3 (1736 cm−1
is observed. Similarly, wCO decreases from the free ethyl
lactate (1738 cm−1) to neutral compound [Me2Al(m-
(S)-(−)OC(H)(Me)C(O)OEt)]2 (A) (1687 cm−1) [8]
and to cationic compound 4 (1646 cm−1). This dra-
matic decrease in wCO (21–41 cm−1) from the neutral
compound (A or 5) to the cationic compound (3 or 4)
is consistent with our expectation. There is more elec-
tron density donating from the carbonyl to aluminum
center in cationic aluminum complex than that in neu-
tral complex resulting in the weaken of CꢁO bond.
)
Table 1
Crystallographic data of compounds 2, 5, and 8
2
5
8·2THF
Formula
C18H30AlIN2O
444.3
C16H30Al2O6
372.4
Colorless parallelepiped
C74H90AlIO6P2
1291.3
Colorless parallelepiped
P21/n
13.823(2)
18.068(2)
29.100(3)
100.22(2)
7152.5(15)
4
Formula weight
Crystal system
Space group
Colorless needle
P212121
6.888(1)
17.782(4)
19.090(2)
–
2338.2(9)
4
1.262
P212121
13.269(2)
17.244(2)
18.763(2)
–
4293.2(9)
8
1.152
,
A (A)
,
B (A)
,
C (A)
i (°)
3
,
V (A )
Z
Dcalc (Mg m−3
)
1.199
,
u (Mo–Ka) (A)
0.7107
1.414
3.5–48.0
2q–q
0.7107
0.159
4.0–45
2q–q
0.7107
0.553
3.5–45
2q–q
Absorption coefficient (mm−1
2q Range (°)
)
Scan type
Reflections collected
Observed reflections
4205
2421 (F\4|(F))
210
4.63
4.36
6240
4791 (F\4|(F))
433
3.98
4.30
9688
6240 (F\4|(F))
766
5.74
6.36
No. of refined parameters
a
R
for significant reflections (%)
b
Rw for significant reflections (%)
Goodness-of-fit c
1.13
1.18
1.83
a R=ꢀS(ꢀFo−Fcꢀ)/ꢀSꢀFoꢀꢀ.
b Rw=ꢀSꢁw(ꢀFo−Fcꢀ)/ꢀSꢁwꢀFoꢀꢀ; w=1/[|2(F)+0.0006]F2 for 2; w=1/[|2(F)+0.001]F2 for 5 and 8.
c Goodness-of-fit=[Sw(ꢀFo−Fcꢀ)2/(Nrflns−Nparams)]1/2
.
Scheme 1.

B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
17
Table 2
,
Selected bond distances (A) and bond angles (°) of 2
Bond lengths
AlꢀN(1)
AlꢀC(1)
1.977(6)
1.958(10)
AlꢀN(2)
AlꢀC(2)
1.971(7)
1.960(9)
Bond angles
N(1)ꢀAlꢀN(2)
N(2)ꢀAlꢀC(1)
N(2)ꢀAlꢀC(2)
98.4(3)
105.9(3)
110.2(4)
N(1)ꢀAlꢀC(1)
N(1)ꢀAlꢀC(2)
C(1)ꢀAlꢀC(2)
108.8(3)
108.3(4)
122.6(4)
Scheme 2.
aluminum atom. However, two sets of resonances are
observed for compound 7 with a relative ratio of 3:1 in-
dicating the presence of two geometric isomers for com-
pound 7 as shown in Scheme 2. It is believed that the
formation of 8 from 7 involves initial generation of the
3-coordinate Al derivative [(EDBP)Al(OPPh3)]+ (B),
which is rapidly trapped by OPPh3.
Though previous work in this area has shown that a va-
riety of Lewis bases such as amines, crown ethers,
TMEDA, THF, acac, etc. [9] has led to the formation of
aluminum cations; to our knowledge, there has been no
example available on aluminum cation stabilized with
lactone or lactate as coordinating ligand. Thus, com-
pounds 3 and 4 stand as the first example of aluminum
cations stabilized by lactate or lactonate ligand.
3.3. Molecular structure of 2, 5 and 8
3.2. Synthesis and spectroscopic studies of 6–9
The ionic feature of 2 is further verified by the X-ray
crystal structure determination and the ORTEP of
[Me2Al((S)ꢀNH2(Ph)C(H)CH3)2]+ as shown in Fig. 1.
[Al(EDBP)I(Et2O)] (6) was synthesized in 79% yield
from the reaction of 2,2%-ethylidene-bis(4,6-di-tert-
butylphenol) (EDBPꢀH2) with Me2AlI in diethyl ether,
followed by the recrystallization from diethyl ether.
Treatment of 6 with one molar equivalent of Ph3PꢁO,
yielded a neutral complex [Al(EDBP)I(OPPh3)] (7). The
cationic aluminum derivative [Al(EDBP)(OPPh3)2]+I−
(8) is prepared either from the reaction of 7 with one
molar equivalent of Ph3PꢁO or from the reaction of 6
with two molar equivalents of Ph3PꢁO. In addition, the
reaction of 6 with excess of HMPA in toluene yields
cationic complex [Al(EDBP)(HMPA)2]+I− (9). The 1H-
NMR data of 6, 8 and 9 reveal only one set of reso-
nances for tert-butyl groups of phenyl ring in EDBP2−
ligand. Similarly, one set of two resonances for the two
hydrogens on both aryl moieties was observed. These
observations suggest that these two aryl moieties are
chemically equivalent and that requires a s-plane of
symmetry pass through the C-7 methine carbon and the
,
Selected bond distances (A) and bond angles (°) of 2 are
listed in Table 2. The aluminum center is tetrahedrally
coordinated by two amine molecules and two methyl
groups in which the bond distances of AlꢀN bond are
found to be similar with AlꢀN(1) 1.977(7) and AlꢀN(2)
,
1.971(7) A, respectively. It is worth noting the polymeric
feature of compound 2 in solid state in which
[Me2Al((S)ꢀNH2(Ph)C(H)CH3)2]+ cations are con-
nected through the NꢀH···I hydrogen bonds with iodide
counterions to form a polymeric aggregate as shown in
Fig. 2. Iodide anion is bonded to four hydrogen atoms
from three independent amine molecules with the
,
(N)HꢀI distances ranging from 2.773 to 3.242 A and the
correspondent IꢀN distances ranging from 3.542 to
,
3.790 A as shown in Table 3. The NꢀH···I hydrogen
bond distances and angles lie in the range generally ex-
pected for NꢀH···I hydrogen bonding [10]. Strong hy-
drogen bonds in the formation of supramolecular
Fig. 1. The ORTEP of [Me2Al((S)ꢀNH2PhCH(CH3))2]+ with the atom labeling scheme.

18
B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
Table 4
structures have played important role among the or-
ganic and inorganic compounds and have been widely
investigated [11].
,
Selected bond distances (A) and bond angles (°) of 5
Bond lengths
Suitable crystals for structure determination of 5 are
obtained from ether solution at −18°C and its ORTEP
Al(1)ꢀO(1)
Al(1)ꢀC(1)
Al(1)ꢀO(4)
Al(2)ꢀO(4)
Al(2)ꢀC(21)
1.865(2)
1.953(4)
1.934(2)
1.873(2)
1.947(4)
Al(1)ꢀO(2)
Al(1)ꢀC(2)
O(1)ꢀAl(2)
Al(2)ꢀO(5)
Al(2)ꢀC(22)
2.315(3)
1.956(4)
1.933(2)
2.355(3)
1.957(4)
,
is shown in Fig. 3. Selected bond distances (A) and
bond angles (°) of 5 are listed in Table 4. The structure
of 5 shows a dimeric feature which contains 5.5.4.5.5-
fused rings with an Al2O2 core and a lactonate group
bonded to Al through the CꢁO. The coordination
Bond angles
O(1)ꢀAl(1)ꢀO(2)
O(2)ꢀAl(1)ꢀC(1)
O(2)ꢀAl(1)ꢀC(2)
O(2)ꢀAl(1)ꢀAl(2) 116.7(1)
C(2)ꢀAl(1)ꢀAl(2) 107.9(1)
O(2)ꢀAl(1)ꢀO(4)
C(2)ꢀAl(1)ꢀO(4)
Al(1)ꢀAl(2)ꢀO(5) 115.7(1)
O(4)ꢀAl(2)ꢀO(5) 77.1(1)
O(1)ꢀAl(2)ꢀC(21) 107.3(1)
O(5)ꢀAl(2)ꢀC(21) 87.6(2)
O(1)ꢀAl(2)ꢀC(22) 100.8(1)
O(5)ꢀAl(2)ꢀC(22) 89.0(1)
78.3(1)
87.9(2)
88.3(1)
O(1)ꢀAl(1)ꢀC(1)
O(1)ꢀAl(1)ꢀC(2)
C(1)ꢀAl(1)ꢀC(2)
C(1)ꢀAl(1)ꢀAl(2)
O(1)ꢀAl(1)ꢀO(4)
C(1)ꢀAl(1)ꢀO(4)
O(1)ꢀAl(2)ꢀO(4)
O(1)ꢀAl(2)ꢀO(5)
Al(1)ꢀAl(2)ꢀC(21)
O(4)ꢀAl(2)ꢀC(21)
Al(1)ꢀAl(2)ꢀC(22)
O(4)ꢀAl(2)ꢀC(22)
C(21)ꢀAl(2)ꢀC(22)
116.9(2)
118.1(2)
122.7(2)
124.5(2)
76.8(1)
154.9(1)
100.7(1)
106.0(2)
76.7(1)
153.6(1)
125.4(1)
117.2(2)
108.2(1)
118.6(2)
121.6(2)
polyhedron of the central five-coordinated aluminum
atom is somewhat distorted from perfect trigonal
bipyramidal geometry with two carbons, and one of
two bridging oxygen atoms siting on equatorial posi-
tions. The aluminum atom, two ligating carbon atoms,
and one of two bridging oxygen atoms are almost
coplanar. The two equatorial AlꢀC bonds average 1.953
,
A that are similar to normal AlꢀC bonds in five-coordi-
nated complexes. However, the average AlꢀO distance
Fig. 2. Structure of 2 in the solid state demonstrates polymeric feature
through NꢀH···I interactions.
,
for the dative CꢁO“Al bond in 5 is 2.335(4) A which
,
is 0.36 A longer than its lactate congener [Me2Al(m-(S)-
Table 3
,
,
Selected hydrogen bond lengths (A) and angles (°) in 2·H2O
(−)OC(H)(Me)C(O)OEt)]2 [8] and is about 0.62 A
longer than the longest dative bond from an oxygen to
a four-coordinated aluminum for an ester group [12].
The longer AlꢀO distance in 5 than that in [Me2Al(m-
(S)-(−)OC(H)(Me)C(O)OEt)]2 is resulting from the
ring strain of pantolactone group.
NꢀH···I
H···I
N···I
NꢀHꢀI Symmetry
N(1)ꢀH(1a)···I
N(1)ꢀH(1b)···I
N(2)ꢀH(2a)···I
N(2)ꢀH(2b)···I
3.242 3.790 156.1
2.981 3.691 165.1
2.859 3.586 159.1
2.773 3.542 158.0
x−1, y, z
x, y, z
−1/2+x, 1/2−y, 2−z
x, y, z
The cationic formulation was confirmed by the X-ray
determination of 8 and the molecular structure of the
,
cation is shown in Fig. 4. Selected bond distances (A)
and bond angles (°) of 8 are listed in Table 5. The
cation consists of a central four-coordinate aluminum
atom in a distorted tetrahedral geometry where alu-
minum is bonded to two oxygens of aryloxides and two
oxygens of phosphine oxides with AlꢀO(1)=1.693 (4),
AlꢀO(2)=1.721 (4), AlꢀO(3)=1.750 (4), AlꢀO(4)=
,
1.743 (4) A. The short average AlꢀO bond length of
,
1.747 A (phosphine oxide), which is only slightly longer
,
than that of AlꢀO 1.707 A (aryl oxide), and the linear-
ity AlꢀOꢀP angles of 157.9(3) and 171.1(3)°, respec-
tively, indicate the existence of a strong interaction
between Al and OPPh3. It is interesting to note that the
,
AlꢀO(4) distance of 1.743(4) A is similar to the AlꢀO(3)
Fig. 3. Molecular structure and atom numbering scheme for [(m-
PL)AlMe2]2 (5).
,
distance of 1.750(4) A indicating that no steric hin-

B.-T. Ko et al. / Journal of Organometallic Chemistry 598 (2000) 13–19
19
135271 for compound 2, 135272 for compound 5, and
135273 for compound 8.
Acknowledgements
Financial support by the National Science Council
(NSC88-2113-M-005-018) is gratefully acknowledged.
References
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molecules 27 (1994) 2013.
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(1993) 2986. (b) H. Yamamoto, in: M. Schlosser (Ed.),
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(Chapter 7).
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C.-C. Lin, J. Organomet. Chem. 587 (1999) 153.
.
Fig. 4. Molecular structure and atom numbering scheme for
[(EDBP)Al(OPPh3)2]+
.
Table 5
,
Selected bond distances (A) and bond angles (°) of 8
Bond lengths
AlꢀO(1)
AlꢀO(3)
P(1)ꢀO(3)
1.693(4)
1.750(4)
1.527(4)
AlꢀO(2)
AlꢀO(4)
P(2)ꢀO(4)
1.721(4)
1.743(4)
1.518(4)
[6] G.M. Sheldrick, SHELXTL PLUS User’s Manual, Revision 4.1,
Nicolet XRD Corporation, Madison, WI, 1991.
[7] Hydrogen atoms ride on carbons or oxygens in their idealized
Bond angles
O(1)ꢀAlꢀO(2)
O(2)ꢀAlꢀO(3)
O(2)ꢀAlꢀO(4)
O(3)ꢀP(1)ꢀC(31)
AlꢀO(4)ꢀP(2)
117.8(2)
109.7(2)
109.4(2)
109.4(3)
171.1(3)
O(1)ꢀAlꢀO(3)
O(1)ꢀAlꢀO(4)
O(3)ꢀAlꢀO(4)
AlꢀO(3)ꢀP(1)
107.2(2)
108.9(2)
102.7(2)
157.9(3)
,
position and are held fixed with the CꢀH distances of 0.96 A and
the OꢀH distances of 0.85 A.
,
[8] B.-T. Ko, F.-C. Wang, Y.-L. Sun, C.-H. Lin, C.-C. Lin, C.-Y.
Kuo, Polyhedron 17 (1998) 4257.
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(1985) 1796. (b) N.C. Means, C.M. Means, S.G. Bott, J.L.
Atwood, Inorg. Chem. 26 (1987) 1466. (c) S.G. Bott, A. Alva-
nipour, S.D. Morely, D.A. Atwood, C.M. Means, A.W. Cole-
man, J.L. Atwood, Angew. Chem. Int. Ed. Engl. 26 (1987) 485.
(d) J.A. Jegier, D.A. Atwood, Inorg. Chem. 36 (1997) 2034 and
Refs. therein.
drance difference for the phosphine oxide ligand trans/
cis to the C(7) hydrogen.
In conclusion, cationic aluminum complexes were
synthesized easily from the reactions of Lewis bases
with Me2AlI. The first characterized examples of alu-
minum cations stabilized by lactate or lactonate ligands
are reported. The formation of supramolecular struc-
ture via strong NꢀH···I hydrogen bonds has been ob-
served for compound 2.
[10] (a) The van der Waals radii used are as follows: H, 1.00; N, 1.55;
,
I, 2.15 A. (b) R. Taylor, O. Kennard, J. Am. Chem. Soc. 104
(1982) 5063.
[11] (a) T. Steiner, W. Saenger, J. Am. Chem. Soc. 115 (1993) 4540.
(b) G.C. Pimentel, A.L. McClellan, The Hydrogen Bond, W.H.
Freeman, San Francisco, CA, 1960.
[12] (a) J.P. Oliver, R. Kumar, M. Taghiof, in: G.H. Robinson (Ed.),
Coordination Chemistry of Aluminum, 1995 (Chapter 5).
(b) A.P. Shreve, R. Mulhaupt, W. Fultz, J. Calabrese, W.
Robbins, S.D. Ittel, Organometallics 7 (1988) 409. (c) M.B.
Power, S.G. Bott, J.L. Atwood, A.R. Barron, Organometallics 9
(1990) 3086.
4. Supplementary material
The crystal data have been deposited with the Cam-
bridge Crystallographic Data Centre with CCDC Nos.