Synthesis and structural characterization of chiral amine alcohol complexes of aluminum

Article abstract of DOI:10.1021/om9509913

The syntheses and full characterization of chiral amine alcohol complexes of aluminum are reported. These complexes are of two general formulae, those resulting from the reaction of 1 equiv of an aluminum reagent with an amine alcohol, [AA-AlR₂

Full text of DOI:10.1021/om9509913

2308
Organometallics 1996, 15, 2308-2313
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of Ch ir a l
Am in e Alcoh ol Com p lexes of Alu m in u m
David A. Atwood,*,† Francois P. Gabbai,‡ J ianliang Lu,† Michael P. Remington,†
Drew Rutherford,† and Mukund P. Sibi*,†
Center for Main Group Chemistry, Department of Chemistry, North Dakota State University,
Fargo, North Dakota 58105, and Institute of Inorganic and Analytical Chemistry,
The Technical University of Munich, Garching, Germany
Received December 29, 1995X
The syntheses and full characterization of chiral amine alcohol complexes of aluminum
are reported. These complexes are of two general formulae, those resulting from the reaction
of 1 equiv of an aluminum reagent with an amine alcohol, [AA-AlR2]2 (where AA )
phenylglycinol (PGly), R ) Me (1), Et (2), SiMe3 (3); phenylalaninol (PAla), R ) Me (4), Et
(5), SiMe3 (6); and diphenylalaninol (DPAla), R ) Me (7), Et (8), SiMe3 (9), and the series
resulting from the reaction of 2 equiv of AlMe3 with an amine alcohol, AA(AlMe2)-AlMe3
(where AA ) PGly (10), PAla (11), and DPAla (12)). These compounds significantly increase
the number of chiral group 13 complexes that have been reported in the literature.
Additionally, the crystal structures of 5, 6, and 11 have been obtained.
In tr od u ction
of structure is crucial since there will be a direct
correlation between structure and the behavior of these
complexes in both catalytic and biological environments.
Organoaluminum reagents are widely employed in
such reactions as the reduction of aldehydes and ke-
tones1 and have been used in molecular recognition2 and
as living polymerization catalysts.3 In many of these
reactions chiral aluminum complexes would be particu-
larly useful, being able to support stereospecific trans-
formations. However, fully characterized chiral alumi-
num complexes are very rare and few have been
structurally characterized. Some recent structurally
characterized examples include aluminum complexes
with optically active alcohols,4 mixed oxygen-nitrogen
systems,5 and a diazaaluminolidine.6 Considering the
biological origin of many of the ligands in these systems,
these types of compounds may also be used in studies
concerning the toxic effects of aluminum compounds,7,8
as models for heavier group 13 imaging agents,9 and as
catalysts for biological reactions.10 An understanding
For these reasons we have begun a fundamental
study of the synthesis and characterization of such
group 13 complexes, focusing on those incorporating
aluminum. In the present manuscript are reported
aluminum complexes derived from three chiral amine
alcohols, (Figure 1a-c). On the basis of the stoichiom-
etry of the aluminum reagent, the resulting complexes
are either dimeric (Figure 1d) or monomeric (Figure 1e).
They have been characterized by physical and spectro-
scopic techniques and, in three instances, by X-ray
crystallography. Compounds 3, 6, and 9 incorporate the
relatively underutilized SiMe3 group on aluminum and
may be viewed as potential precursors to biologically
active Al-O-Si compounds.
Resu lts a n d Discu ssion
† North Dakota State University.
The amine alcohols (Figure 1a-c) are soluble in
solvents such as H2O and alcohols, solvents that are
generally reactive toward group 13 reagents. Thus,
compounds 1-9 are prepared by the addition of the
group 13 reagent to a slurry of the amine alcohol (AA)
in toluene (eq 1). The exothermic reaction quickly
‡ The Technical University of Munich.
X Abstract published in Advance ACS Abstracts, April 15, 1996.
(1) Yamamoto, H. In Organometallics in Synthesis; Schlosser, M.,
Ed.; J ohn Wiley & Sons Ltd.: Chichester, England, 1994; p 510.
(2) (a) Maruoka, K.; Nagahara, S.; Yamamoto, H. Tetrahedron Lett.
1990, 31, 5475. (b) Maruoka, K.; Nagahara, S.; Yamamoto, H. J . Am.
Chem. Soc. 1990, 112, 6115.
(3) (a) Le Borgne, A.; Vincens, V.; J ouglard, M.; Spassky, N.
Makromol. Chem. Macromol. Symp. 1993, 73, 37. (b) Sugimoto, H.;
Kawamura, C.; Kuroki, M; Aida, T.; Inoue, S. Macromolecules 1994,
27, 2013. (c) Atwood, D. A.; J egier, J . A.; Rutherford, D. J . Am. Chem.
Soc. 1995, 117, 6779. (c) Atwood, D. A.; J egier, J . A.; Rutherford, D.
Inorg. Chem. 1996, 35, 63.
(4) (a) Sierra, M. L.; Kumar, R.; J . de Mel, V. S.; Oliver, J . P.
Organometallics 1992, 11, 206. (b) Kumar, R.; Sierra, M. L.; Oliver, J .
P. Organometallics 1994, 13, 4285.
(5) (a) Sierra, M. L.; J . de Mel, V. S.; Oliver, J . P. Organometallics
1989, 8, 2486. (b) van Vliet, M. R. P.; van Koten, G.; Rotteveel, M. A.;
Schrap, M.; Vrieze, K.; Kojic-Prodic, B.; Spek, A. L.; Duisenberg, A. J .
M. Organometallics 1986, 5, 1389.
(8) For studies involving biologically active group 13 compounds
see: (a) Liu, S.; Rettig, S. J .; Orvig, C. Inorg. Chem. 1992, 31, 5400.
(b) Hoveyda, H. R.; Karunaratne, V.; Rettig, S. J .; Orvig, C. Inorg.
Chem. 1992, 31, 5408. (c) Liu, S.; Wong, E.; Karunaratne, V.; Rettig,
S. J .; Orvig, C. Inorg. Chem. 1993, 32, 1756.
(6) Corey, E. J .; Sarshar, S. J . Am. Chem. Soc. 1992, 114, 7938.
(7) For
a discussion of the possible role of aluminum in brain
disorders see: (a) Candy, J . M.; Edwardson, J . A.; Klinowski, A. E.;
Oakley, A. E.; Perry, E. K.; Perry, R. H. In Senile Dementia of the
Alzheimer Type; Traber, J ., Gispen, W. H., Eds.; Springer-Verlag:
Heidelberg, 1985; pp 183-97. (b) Candy, J . M.; Klinowski, J .; Perry,
R. H.; Perry, E. K.; Fairbairn, A.; Oakley, A. E.; Carpenter, T. A. Lancet
1986, 354. (c) Edwardson, J . A.; Klinowski, J .; Oakley, A. E.; Perry, R.
H.; Candy, J . M. In Ciba Foundations Symposium 121. Silicon
Biochemistry; J ohn Wiley: Chichester, U.K., 1986; pp 160-179.
(9) (a) Borgia, B.; Hugi, A. D.; Raymond, K. N. Inorg. Chem. 1989,
28, 3538. (b) Zhang, Z.; Lyster, D. M.; Webb, G. A.; Orvig, C. Nucl.
Med. Biol. 1992, 19, 327. (c) Bollinger, J . E.; Roundhill, D. M. Inorg.
Chem. 1993, 32, 2821. (d) Liu, S.; Wong, E.; Rettig, S. J .; Orvig, C.
Inorg. Chem. 1993, 32, 4268. (e) Bollinger, J . E.; Mague, J . T.;
Roundhill, D. M. Inorg. Chem. 1994, 7, 1241.
(10) (a) Szpoganicz, B.; Martell, A. E. Inorg. Chem. 1985, 24, 2414.
(b) Taylor, P. A.; Martell, A. E. Inorg. Chim. Acta 1988, 152, 181.
S0276-7333(95)00991-5 CCC: $12.00 © 1996 American Chemical Society

Chiral Amine Alcohol Complexes of Aluminum
Organometallics, Vol. 15, No. 9, 1996 2309
bond which would possess more s character and show
a more acidic, downfield shift, as the steric bulk on Al
grows. This is partially borne out by the increasing
average Al-N bond distances for 5 and 6 of 2.18(1) and
2.26(1) Å, respectively. Moreover, this explanation is
supported by work on the Me3Al-PR3 systems where
the increasing bulk of the alkyl group leads to more
downfield 1H and 13C NMR resonances of the Me3Al
fragment.11
The addition of 2 equiv of AlMe3 to the amine alcohol
leads to monomeric 2:1 complexes (eq 2) in reasonable
yields. However, attempts to conduct this reaction with
AlEt3 and AliBu3 lead to complex mixtures of products
as evidenced by the 1H NMR data. However, in the case
of Al(SiMe3)3, the mixture could be separated to produce
high yields of 3, 6, 9, and unreacted Al(SiMe3)3. From
these results it is clear that a steric effect inhibits the
formation of the 2:1 complexes in cases where the alkyl
is more sterically encumbered than methyl. This sce-
nario is also supported by the crystal structure data for
11 (vide infra). These compounds are highly air sensi-
tive, with reactivity approaching that of free AlMe3. For
instance, after isolation these compounds will show
signs of decomposition even while being handled under
dry nitrogen. This reactivity also led to problems
getting accurate elemental analyses; in all cases, after
repeated runs, the values were found to be low. A low
value is what would be expected if some of the Al-Me
groups were being converted into Al-OH groups.
F igu r e 1. Chiral amine alcohols (a-c) and the structural
formulae for the group 13 compounds reported in this study
(d and e).
produces a pale yellow solution and is allowed to stir
for several hours. Following this, the solution is con-
centrated under vacuum and cooled to -30 °C to yield
the compounds as pale yellow or white solids in moder-
ate to high yield.
1
A listing of selected H NMR data and the νNH IR shift
1
for compounds 1-12 is shown in Table 1. The H NMR
data for these compounds demonstrated complex pat-
terns of coupling due to the chirality of the ligands.
Primarily, this involves the coupling of diastereotopic
protons on the same carbon atom. For example, the
spectrum of 4 (Figure 2) demonstrates that the proton
on the chiral carbon (c) is coupled to four separate
protons (Ha,b,d,e) producing a complex multiplet. Hy-
drogens a, b are coupled to one another as well as c,
producing two doublet of doublets. The same situation
is observed for d and e. The unassigned singlets at δ
2.1 and 0.28 are due to toluene and silicon grease,
respectively.
1
The H NMR spectra for 10-12 are similar to that
seen for 1-9 with one exception. There are now three
types of Al-Me groups, which is manifested as three
singlets in the NMR spectrum. On the basis of the
integrations, there is one resonance for the AlMe3 group
and one resonance each for the remaining two Al-Me
groups. Compared to the 1:1 complexes this implies
that the adduct formation between the second AlMe3
group and ligand oxygen prevents dissociation of the
amine portion of the ligand. In the subsequent absence
of dynamic behavior the inequivalence of the Al-Me
resonances is observed.
Crystals suitable for X-ray diffraction for 5, 6, and
11 were grown from a toluene solution cooled to -30
°C for at least 24 h. In keeping with the chirality of
the starting materials, each of these compounds adopt
noncentrosymmetric space groups (P21, P1, and P212121,
respectively). A summary of crystallographic data is
shown in Table 2. Molecular structures and atom
numbering schemes for 5, 6, and 11 are shown in
Figures 3-5, respectively. Atomic coordinates are given
in the Supporting Information. Selected bond distances
and angles are given in Table 3.
A significant feature of this spectrum and, indeed, the
spectra for the other 1:1 complexes is the fact that only
one sharp Al-R resonance is detected at 25 °C. In
similar systems reported by Oliver (R2Al complexes with
optically active alcohols)4 the room-temperature NMR
data indicated that rapid dissociation of the amine
portion of the ligand produced a singlet for the AlR
protons. Upon cooling, however, this resonance split,
indicating a slowing of the dynamic behavior and
consequent inequivalence of the AlR groups. On the
basis of the ligand chirality, a similar situation is
expected for 1-9.
An interesting trend can be seen in the chemical shifts
attributed to the NH groups. They progressively be-
come more deshielded as the size of the R group grows.
For example, in 1-3 the values are δ 1.38, 1.59, and
1.95 ppm, respectively. This may be interpreted in
terms of a lengthening of the Al-N bond due to the
increasing steric bulk. This bond change would lead to
slight change in hybridization on the Al atom (the
lengthened bond would possess more p character) and,
consequently, on N as well. This would lead to an N-H
The 1:1 complexes (5 and 6) form oxygen-bridged
dimers wherein the aluminum atom is five-coordinate
and in a distorted trigonal bipyramidal geometry. Thus,
for 5 the axial atoms (O(1) and N(2)) form an O-Al-N
angle of 152.4(7)°. The atoms C(1), O(2), and C(3), form
equatorial angles that fall in the range 125.2(10)°-
(11) Barron, A. R. J . Chem. Soc., Dalton Trans. 1988, 3047.
(12) Coordination Chemistry of Aluminum; Robinson, G. H., Ed.;
VCH Publishers, Inc.: New York, 1993; pp 38 and 81.
(13) (a) Rosch, L. Angew. Chem., Int. Ed. Engl. 1977, 16, 480. (b)
Rosch, L.; Altman, G. J . Organomet. Chem. 1980, 195, 47.

2310 Organometallics, Vol. 15, No. 9, 1996
Atwood et al.
Ta ble 1. Selected Sp ectr oscop ic Da ta for Com p ou n d s 1-12
δ (ppm)
compd
NH
NCH
OCH
PhCH
νNH (cm-1
)
[PGly(AlMe2)]2 (1)
1.38 (d)
3.59 (m)
3.32 (m)
3.85 (dd)
3.34 (m)
3.91 (dd)
3.53 (m)
3.95 (dd)
3.13 (dd)
3.57 (dd)
3.15 (dd)
3.65 (dd)
3.12 (m)
3.73 (dd)
3.37 (m)
3.72 (m)
3.24 (m)
3.73 (dd)
3.26 (m)
3349
[PGly(AlEt2)]2 (2)
1.59 (d)
1.95 (d)
1.05 (d)
1.35 (d)
1.69 (d)
1.46 (d)
1.55 (d)
2.03 (d)
3.69 (m)
3.87 (m)
2.70 (m)
2.78 (m)
2.97 (m)
3.51 (m)
3.55 (m)
3.80 (m)
3249
3524
3349
3349
3348
3343
3354
3283
[PGly(Al(SiMe3)2)]2 (3)
[PAla(AlMe2)]2 (4)
1.94 (dd)
2.18 (dd)
1.95 (dd)
2.20 (dd)
1.96 (dd)
2.15 (dd)
3.36 (m)
[PAla(AlEt2)]2 (5)
[PAla(Al(SiMe3)2)]2 (6)
[DPAla(AlMe2)]2 (7)
[DPAla(AlEt2)]2 (8)
[DPAla(Al(SiMe3)2)]2 (9)
3.24 (m)
3.26 (m)
3.80 (m)
PGly(AlMe2)-AlMe3 (10)
PAla(AlMe2)-AlMe3 (11)
1.31 (m)
1.17 (dd)
1.34 (dd)
1.33 (m)
3.92 (m)
2.58 (m)
3.32 (m)
3.28 (dd)
3.60 (dd)
3.36 (dd)
3.50 (dd)
3302
3304
DPAla(AlMe2)-AlMe3 (12)
3.14 (m)
3.34 (d)
3273
Ta ble 2. Cr ysta l Da ta for [P Ala (AlEt2)]2 (5),
[P Ala (AlSiMe3)2)]2 (6), a n d P Ala (AlMe2)-AlMe3 (11)
compound
5
6
11
formula
fw
C26H44Al2N2O2 C30H60Al2N2O2Si4 C14H27Al2NO
470.6
647.1
279.3
cryst system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
monoclinic
P21
6.717(4)
17.153(2)
12.687(3)
triclinic
P1
orthorhombic
P212121
8.266(1)
10.519(1)
20.910(2)
9.009(1)
9.624(1)
12.873(1)
71.21(1)
77.31(1)
84.45(1)
1030.4(2)
1
103.55(3)
1424.7(9)
2
1.97
1809.3(3)
4
1.025
F igu r e 2. Representative 1H NMR spectrum of [PAla-
(AlMe2)]2 (4).
Z
Dcalc (g/cm3)
1.043
cryst size (mm) (0.4)3
0.4 × 0.3 × 0.2
0.5 × 0.4 × 0.3
temp (K)
298
298
298
116.9(11)°. Similarly, for 6, the axial atoms (O(2) and
N(1)) form an angle of 153.3(4)° with the atoms O(1),
Si(1), and Si(2) forming equatorial angles in the range
124.2(2)°-115.6(2)°. The presence of distorted trigonal
bipyramidal geometries in these systems is in keeping
with the general trend seen for other five-coordinate
aluminum complexes incorporating open-chain ligands.12
The structures of 5 and 6 are of the same morphology
as other ligand systems possessing both NH and OH
functionalities. For example, the reaction of alkylalu-
minum reagents, such as AlMe3, with l-ephedrine leads
to a dimeric complex having this general structure
(Figure 1d).5a The Al atom in this complex also adopts
a trigonal bipyramidal geometry with a long Al-N axial
bond (2.193 (8) Å). This bond in 5 is roughly of the same
value (Al(1)-N(2) ) 2.190(14) Å) while that for 6 is
somewhat longer (2.241(8) Å). The central Al2O2 four-
membered rings in 5 and 6 are planar with the ligands
adopting a trans orientation.
2θ range (deg)
scan type
scan speed
(deg/min)
3.5-45
2θ-θ
8-60
3.5-45
2θ-θ
3.5-45
2θ-θ
8-60
8-60
scan range (deg) 0.40
0.30
3263
3255
2331
(F > 4.0σ(F))
358
0.0423
0.0426
0.78
0.31
1907
1738
915
(F > 4.0σ(F))
163
0.0571
0.0585
1.46
reflcns collcd
indp reflcns
obsd reflcns
2697
2062
851
(F > 6.0σ(F))
288
0.0556
0.0591
1.58
no. of params
R
Rw
GOF
lar diff peak
0.22
0.29
0.26
(e/Å3)
9 this group apparently behaves in a manner analogous
to traditional alkyl groups (such as Me and Et) and has
the steric requirements similar to a tert-butyl group. The
Al-Si bond distances in 6 average 2.48(1) Å. This
compares closely to [(SiMe3)2AlNH2]2 where the average
distance is 2.48(1) Å.14a As stated previously, the
primary importance of an Al-S linkage in these mol-
ecules lies in their use as precursors to aluminosilicates
bound by the amine alcohols.
There are relatively few compounds reported which
possess the AlSiMe3 moiety.14 In compounds 3, 6, and
When 2 equiv of R3Al are added to the amine alcohols
(eq 2), the dimerization seen for the 1:1 complexes is
(14) (a) J anik, J . F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1987,
26, 4341. (b) J anik, J . F.; Duesler, E. N.; Paine, R. T. Inorg. Chem.
1987, 26, 4341. (c) J anik, J . F.; Duesler, E. N.; McNamara, W. F.;
Westerhausen, M.; Paine, R. T. Organometallics 1989, 8, 506.
(15) Nicolas, E.; Russell, K. C.; Hruby, V. J . J . Org. Chem. 1993,
58, 766.
(16) Gage, J . R.; Evans, D. A. Org. Synth. 1989, 68, 77.
(17) Sibi, M. P.; Deshpande, P. K.; La Loggia, A. J .; Christensen, J .
W. Tetrahedron Lett. 1995, 36, 8961.

Chiral Amine Alcohol Complexes of Aluminum
Organometallics, Vol. 15, No. 9, 1996 2311
Con clu sion
The present work represents an expansion of the
number of chiral aluminum complexes that have been
reported in the literature along with structural char-
acterization of three representative examples. Further
work will be focused on applying the information gained
on compounds 1-9 to applications in catalysis and the
activity of aluminum in the biosphere.
Exp er im en ta l Section
Figu r e 3. Molecular structure and atom-numbering scheme
for [PAla(AlEt2)]2 (5).
Gen er a l Con sid er a tion s. All manipulations were con-
ducted using Schlenk techniques in conjunction to an inert
atmosphere glovebox. All solvents were rigorously dried prior
to use. The ligands (S)-phenylglycinol (PGly),15 (S)-phenyla-
laninol (PAla),16 and (R)-diphenylalaninol (DPAla)17 were
synthesized as previously described. NMR data were obtained
on J EOL-GSX-400 and -270 instruments at 270.17 (1H) and
62.5 (13C) MHz. Chemical shifts are reported relative to SiMe4
and are in ppm. Elemental analyses were obtained on a
Perkin-Elmer 2400 Analyzer. Infrared data were recorded as
KBr pellets on a Matheson Instruments 2020 Galaxy Series
spectrometer and are reported in cm-1
.
Syn th esis of [P Gly(AlMe2)]2 (1). To a rapidly stirring
solution of (S)-phenylglycinol (0.510 g, 3.72 mmol) in 20 mL
of toluene was added trimethylaluminum (0.270 g, 3.75 mmol)
neat at 25 °C. The exothermic reaction was allowed to stir
for 48 h at 25 °C. The toluene was removed in vacuo, and the
remaining white solid was washed with diethyl ether and then
filtered. The residual ether was removed in vacuo yielding
the title compound as a white solid (yield 0.54g, 75%): Mp
153-157 °C; 1H NMR (270 MHz, C6D6) δ -0.41 (s, 6H, AlCH3),
1.38 (d, 2H, NH2), 3.32 (app t, 1H, OCH2), 3.54-3.66 (m, 1H,
NCH), 3.85 (dd, 1H, OCH2), 6.38 (d, 2H, PhH), 6.91-7.11 (m,
3H, PhH); IR (KBr) 3349 s, 2965 s. 2918 s, 1262 vs, 1092 vs,
1024 vs, 802 vs, 696 vs. Anal. Calcd: C, 62.16; H, 8.35.
Found: C, 62.01; H, 8.28.
F igu r e 4. Molecular structure and atom numbering
scheme for [PAla(AlSiMe3)2)]2 (6).
Syn th esis of [P Gly(AlEt2)]2 (2). To a rapidly stirring
solution of (S)-phenylglycinol (0.500 g, 3.64 mmol), in 20 mL
of toluene, was added triethylaluminum (1.0 M in hexane,
0.692 g/mL, 2.519 g, 3.64 mmol) in 15 mL of toluene at 25 °C.
The exothermic reaction was allowed to stir at 25 °C for 4 h.
The resulting solution was filtered and the solvent removed
in vacuo. The white solid was washed with hexane and the
hexane removed via cannula, the residual hexane removed in
vacuo leaving the title compound as a white solid (0.580 g,
72%): Mp 125-127 °C;
Figu r e 5. Molecular structure and atom-numbering scheme
for PAla(AlMe2)-AlMe3 (11).
1H NMR (270 MHz, C6D6) δ -0.17 (q, 4H, AlCH2CH3), 1.45
(t, 6H, AlCH2CH3), 1.59 (d, 2H, NH2), 3.34 (app t, 1H, OCH2),
3.59-3.79 (m, 1H, NCH), 3.91 (dd, 1H, OCH2), 6.47 (d, 2H,
PhH), 6.95-7.10 (m, 3H, PhH); 13C NMR (62.5 MHz, C6D6) δ
1.37 (AlCH2CH3), 11.50 (AlCH2CH3), 57.08 (OCH2), 127.75
(Ph), 127.87 (Ph), 128.10 (Ph), 128.23 (Ph), 128.82 (Ph); IR
(KBr) 3249 s, 3285 s, 2953 vs, 2855 vs, 1588 s, 1262 vs, 1088
vs, 1022 vs, 802 vs. Anal. Calcd: C, 65.14; H, 9.11. Found:
C, 64.82; H, 8.96.
prevented, and monomeric 2:1 complexes (Scheme 1e)
are obtained. For the AlMe3 reaction, an X-ray crystal-
lographic study confirmed that the second AlR3 group
forms an adduct with the oxygen of the ligand (Figure
5). The methyl groups adopt a staggered conformation
to reduce the steric repulsions. The closest approach
of two of the methyl groups in this conformation is 3.85
Å, with the hydrogens at 2.56 Å. With groups other
than methyl these interactions would be even more
pronounced and prevent the 2:1 complex from forming.
Syn th esis of [P GlyAlTMS2]2 (3). (S)-Phenylglycinol (0.465
g, 3.39 mmol) was suspended in 25 mL of toluene, and
Al(SiMe3)3‚THF (1.08 g, 3.39 mmol) was added at room tem-
perature. The reaction was stirred at room temperature for
8 h, during which time the amino alcohol gradually dissolved.
The reaction was concentrated to 1/2 volume and stored at -30
°C, and colorless crystals grew after 2 days (0.543 g, 52%). A
second batch of crystals was isolated from the filtrate after 1
week at -30 °C (combined yield, 0.797 g, 76%): Mp 184-186
Both Al atoms in 11 adopt Td geometries. For Al(2)
this geometry is nearly ideal. For Al(1) the geometry
is somewhat distorted due to the chelation of the ligand
with the maximum deviation occurring in the C-Al-C
angle (119.8(6)°). The five-membered ring formed by
the ligand chelation is planar. The five-membered ring
made up of the chelating ligand and Al(1) takes a
nonplanar conformation where the O(1) atoms is pro-
jected 0.59 Å above the plane defined by Al(1), N(1),
C(1), and C(2). By comparison, 11 is of the same overall
morphology as Me2Al(tBu)NdCHC(Me)2OAlMe3.5b
1
°C; H NMR (270 MHz, C6D6) δ 0.31 (s, 18H, SiCH3), 1.95 (d,
J ) 8 Hz, 2H, NH2), 3.53 (t, J ) 10 Hz, 1H, OCH2), 3.84-3.90
(m, 1H, NCH), 3.95 (dd, J ) 5, 10 Hz, 1H, OCH2), 6.82-7.01,
m, 5H, Ph-H); 13C NMR (100 MHz, C6D6) δ 3.0 (SiCH3), 58.1
(OCH2), 64.4 (NCH), 126.5 (Ph), 128.7, 129.5, 139.9; IR (neat)
3524, 3346, 3298, 2942, 2886, 1578, 1456, 1231, 1071, 1013,

2312 Organometallics, Vol. 15, No. 9, 1996
Atwood et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles (d eg) for Com p ou n d s 5, 6, a n d 11
[PAla(AlEt2)]2 (5) [PAla(Al(SiMe3)2]2 (6) PAla(AlMe2)-AlMe3 (11)
Al(2)-O(1)
1.850(13)
1.947(13)
2.181(13)
1.973(26)
1.967(23)
1.960(13)
1.852(15)
2.190(14)
1.954(25)
1.967(28)
1.393(20)
1.410(22)
1.462(26)
1.489(28)
Al(1)-Si(1)
2.485(5)
2.474(4)
1.850(8)
1.935(6)
2.241(8)
2.493(6)
2.466(5)
1.922(7)
1.843(9)
2.274(8)
1.405(12)
1.427(14)
1.496(15)
1.469(14)
Al(1)-O(1)
Al(1)-N(1)
Al(1)-C(10)
Al(1)-C(11)
Al(2)-O(1)
Al(2)-C(12)
Al(2)-C(13)
Al(2)-C(14)
O(1)-C(1)
1.807(8)
2.005(9)
Al(2)-O(2)
Al(2)-N(1)
Al(2)-C(5)
Al(2)-C(7)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-N(2)
Al(1)-C(1)
Al(1)-C(3)
O(1)-C(9)
O(2)-C(18)
N(1)-C(10)
N(2)-C(19)
Al(1)-Si(2)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-N(1)
Al(2)-Si(3)
Al(2)-Si(4)
Al(2)-O(1)
Al(2)-O(2)
Al(2)-N(2)
O(1)-C(1)
O(2)-C(16)
N(1)-C(2)
N(2)-C(17)
1.930(10)
1.934(12)
1.895(8)
1.950(12)
1.963(11)
1.963(12)
1.409(12)
1.488(14)
N(1)-C(2)
O(1)-Al(1)-O(2)
O(1)-Al(1)-N(2)
O(2)-Al(1)-N(2)
O(1)-Al(1)-C(1)
O(2)-Al(1)-C(1)
N(2)-Al(1)-C(1)
O(1)-Al(1)-C(3)
O(2)-Al(1)-C(3)
N(2)-Al(1)-C(3)
C(1)-Al(1)-C(3)
O(1)-Al(2)-O(2)
O(1)-Al(2)-N(1)
O(2)-Al(2)-N(1)
O(1)-Al(2)-C(5)
O(2)-Al(2)-C(5)
N(1)-Al(2)-C(5)
O(1)-Al(2)-C(7)
O(2)-Al(2)-C(7)
N(1)-Al(2)-C(7)
C(5)-Al(2)-C(7)
Al(2)-O(1)-Al(1)
Al(2)-O(1)-C(9)
Al(1)-O(1)-C(9)
Al(2)-O(2)-Al(1)
Al(2)-O(2)-C(18)
Al(1)-O(2)-C(18)
Al(2)-N(1)-C(10)
Al(1)-N(2)-C(19)
Al(1)-C(1)-C(2)
Al(1)-C(3)-C(4)
75.2(6)
152.4(7)
77.6(6)
97.3(8)
117.8(8)
98.9(7)
100.4(8)
125.2(10)
92.0(8)
116.9(11)
75.5(5)
Si(1)-Al(1)-Si(2)
Si(1)-Al(1)-O(1)
Si(2)-Al(1)-O(1)
Si(1)-Al(1)-O(2)
Si(2)-Al(1)-O(2)
O(1)-Al(1)-O(2)
Si(1)-Al(1)-N(1)
Si(2)-Al(1)-N(1)
O(1)-Al(1)-N(1)
O(2)-Al(1)-N(1)
Si(3)-Al(2)-Si(4)
Si(3)-Al(2)-O(1)
Si(4)-Al(2)-O(1)
Si(3)-Al(2)-O(2)
Si(4)-Al(2)-O(2)
O(1)-Al(2)-O(2)
Si(3)-Al(2)-N(2)
Si(4)-Al(2)-N(2)
O(1)-Al(2)-N(2)
O(2)-Al(2)-N(2)
Al(1)-O(1)-Al(2)
Al(1)-O(1)-C(1)
Al(2)-O(1)-C(1)
Al(1)-O(2)-Al(2)
Al(1)-O(2)-C(16)
Al(2)-O(2)-C(16)
Al(1)-N(1)-C(2)
Al(2)-N(2)-C(17)
124.2(2)
119.2(2)
115.6(2)
102.5(3)
100.6(2)
75.1(3)
90.3(3)
90.9(2)
78.2(3)
153.3(4)
120.6(2)
103.6(3)
103.4(2)
123.2(3)
114.4(3)
75.6(3)
87.4(3)
92.1(3)
152.3(4)
77.1(3)
O(1)-Al(1)-N(1)
O(1)-Al(1)-C(10)
N(1)-Al(1)-C(10)
O(1)-Al(1)-C(11)
N(1)-Al(1)-C(11)
C(10)-Al(1)-C(11)
O(1)-Al(2)-C(12)
O(1)-Al(2)-C(13)
C(12)-Al(2)-C(13)
O(1)-Al(2)-C(14)
C(12)-Al(2)-C(14)
C(13)-Al(2)-C(14)
Al(1)-O(1)-Al(2)
Al(1)-O(1)-C(1)
Al(2)-O(1)-C(1)
Al(1)-N(1)-C(2)
85.6(3)
113.0(4)
111.2(5)
114.6(5)
107.1(5)
119.8(6)
103.2(5)
103.6(4)
113.3(5)
103.6(4)
114.4(5)
116.4(5)
126.4(3)
115.5(7)
117.8(7)
105.9(6)
78.1(6)
153.5(6)
118.5(10)
101.5(8)
93.4(7)
121.2(8)
96.2(7)
95.0(7)
120.2(10)
104.4(6)
122.8(13)
132.6(13)
104.9(6)
128.5(13)
124.0(13)
105.3(10)
111.2(12)
120.5(16)
123.6(23)
104.6(3)
121.8(6)
132.0(7)
104.4(4)
131.1(7)
124.2(6)
108.4(5)
103.9(5)
824, 663, 590, 542, 472 cm-1. Anal. Calcd for C28H56N2O2Al2-
Si4: C, 54.34; H, 9.14; N, 4.52. Found: C, 54.10; H, 8.23; N,
4.32.
analysis were grown by redissolving the white solid in toluene
and cooling to -30 °C (0.597 g, 77%): Mp 100-103 °C (dec);
1H NMR (270 MHz, C6D6) δ 0.90 (q, 4H, AlCH2CH3), 1.29 (t,
6H, AlCH2CH3), 1.35 (d, 2H, NH2), 1.95 (dd, 1H, PhCH2), 2.20
(dd, 1H, PhCH2), 2.71-2.85 (m, 1H, NCH2), 3.15 (dd, 1H,
OCH2), 3.65 (dd, 1H, OCH2), 6.75 (d, 2H, PhH), 6.98-7.15 (m,
3H, PhH); IR (KBr) 3349 s, 3291 s, 2924 s, 2859 vs, 2787 vs,
1586 s, 1495 s, 1453 s, 1082 vs, 1028 vs, 650 vs. Anal. Calcd:
C, 66.36; H, 9.42. Found: C, 66.14; H, 9.25.
Syn th esis of [P AlaAlTMS2]2 (6). (S)-Phenylalaninol (0.119
g, 0.79 mmol) was suspended in 10 mL of toluene and
Al(SiMe3)3-THF (0.250 g, 0.79 mmol) was added at room
temperature. The reaction was stirred at room temperature
Syn th esis of [P Ala (AlMe2)]2 (4). Trimethylaluminum
(0.240 g, 3.31 mmol), in 10 mL of toluene, was added to a
rapidly stirring solution of (S)-phenylalaninol (0.500 g, 3.31
mmol) in 35 mL of toulene at 25 °C. The exothermic reaction
was stirred at 25 °C for 3 h. The toluene was removed in vacuo
leaving the title compound as a white solid (0.597 g, 87%): Mp
137-139 °C; 1H NMR (270 MHz, C6D6) δ -0.52 (s, 6H, AlCH3),
1.05 (d, J ) 7 Hz, 2H, NH2), 1.94 (dd, J ) 9, 14 Hz, 1H, CH2-
Ph), 2.18 (dd, J ) 6, 14 Hz, 1H CH2Ph), 2.67-2.73, (m, 1H,
NCH), 3.13 (dd, J ) 8, 10 Hz, 1H, CH2O), 3.57 (dd, J ) 5, 10
Hz, 1H, CH2O), 6.75 (d, J ) 7 Hz, 2H, PhH), 6.98-7.15 (m,
3H, PhH); 13C NMR (62.5 MHz, C6D6) δ -7.92 (AlCH3), 39.5
(PhCH2), 53.7 (NCH), 62.7 (OCH2), 126.9 (Ph), 128.9 (Ph),
129.1 (Ph), 129.3 (Ph), 137.8 (Ph); IR (KBr) 3349 s, 3279 s,
for 12 h during which time the amino alcohol gradually
1
dissolved. The reaction was concentrated to
/ volume and
2
stored at -30 °C, and colorless crystals suitable for X-ray
analysis grew after 1 day (0.211 g, 83%): Mp 145-146 °C; 1H
NMR (270 MHz, C6D6) δ 0.24 (s, 18H, SiCH3), 1.69 (d, J ) 8
Hz, 2H, NH2), 1.96 (dd, J ) 14, 7 Hz, 1H, PhCH2), 2.15 (dd, J
) 14, 6 Hz, 1H, PhCH2), 2.97 (m, 1H, NCH2), 3.12 (dd, J ) 10
Hz, 1H, OCH2), 3.73 (dd, J ) 10, 4 Hz, 1H, OCH2), 6.73-7.10
(m, 5H, Ph-H); 13C NMR (100 MHz, C6D6) δ 2.9 (SiCH3), 39.5
(PhCH2), 54.7 (NCH), 63.3 (OCH2), 127.4 (Ph), 129.0, 129.1,
136.3; IR (neat) 3348, 3277, 2935, 3891, 1582, 1454, 1231,
1051, 847, 822, 671, 546 cm-1. Anal. Calcd for C30H60N2O2-
Al2Si4: C, 55.73; H, 9.29. Found: C, 55.20; H, 9.18.
2909 vs, 1591 s, 1497 s, 1454 s, 1179 vs, 1045 vs, 700 vs cm-1
;
MS (DIP/MS) m/e 399 (D+ - Me), 384 (D+ - 2Me), 367, (D+
-
3Me - 2H), 323 (D+ - PhCH2), 207 (M+), 192 (M+ - Me), 175
(M+ - 2Me - 2H), 91 (PhCH2+), 57 (AlCH2+). Anal. Calcd:
C, 63.77; H, 8.70. Found: C, 63.66; H, 8.62.
Syn th esis of [P Ala (AlEt2)]2 (5). To a rapidly stirring
solution of (S)-phenylalaninol (0.500 g, 3.31 mmol) in 35 mL
of toluene was syringed triethylaluminum (1.0 M in hexane,
3.31 mL) at 25 °C. The exothermic reaction was allowed to
stir at 25 °C for 3 h. The toluene was removed in vacuo leaving
the title compound as a white solid. Crystals suitable for X-ray
Syn th esis of [DP Ala (AlMe2)]2 (7). To a rapidly stirring
solution of (R)-diphenylalaninol (0.400 g, 1.76 mmol) in 20 mL

Chiral Amine Alcohol Complexes of Aluminum
Organometallics, Vol. 15, No. 9, 1996 2313
of toluene was added trimethylaluminum (0.13 g, 1.80 mmol)
neat at 25 °C. The exothermic reaction was allowed to stir
for 12 h at 25 °C. The toluene was removed in vacuo, and the
remaining solid was washed with hexane and then filtered.
The residual hexane was removed in vacuo leaving the title
compound as a white solid (0.36 g, 71%): Mp 174-178 °C (dec);
1H NMR (270 MHz, C6D6) δ -0.42 (s, 6H, AlCH3), 1.46 (d, 2H,
NH2), 3.34-3.40 (m, 2H, Ph2CH and OCH2), 3.48-3.55 (m, 1H,
NCH), 3.70-3.74 (m, 1H, OCH2), 7.08-7.28 (m, 10H, PhH);
IR (KBr) 3343 vs, 3283 s, 3025 s, 2828 s, 1588 vs, 1493 vs,
1453 vs, 1181 vs, 1086 vs, 1011 vs, 750 s. Anal. Calcd: C,
72.06; H, 7.83. Found: C, 71.89; H, 7.71.
Syn th esis of [DP Ala (AlEt2)]2 (8). To a rapidly stirring
solution of (R)-diphenylalaninol (1.137 g, 5.0 mmol) in 25 mL
of toluene was added triethylaluminum (1.0 M in hexane, 0.692
g/mL, 3.460 g, 5.0 mmol) in 15 mL of toluene at 25 °C. The
exothermic reaction was allowed to stir at 25 °C for 15 h. The
toluene was removed in vacuo leaving the title compound as
a white crystalline solid (1.23 g, 79%): mp 157-161 °C (dec);
1H (270 MHz, C6D6) δ 0.07 (q, 4H, AlCH2CH3), 1.32 (t, 6H,
AlCH2CH3), 1.55 (d, 2H, NH2), 3.21-3.27 (m, 2H, PhCH and
OCH2), 3.51-3.59 (m, 1H, NCH), 3.73 (dd, 1H, OCH2), 6.89-
7.04 (m, 10H, PhH); IR (KBr) 3354 s, 3084 s, 3028 s, 2930 vs,
2851 vs, 1587 s, 1493 s, 1452 s, 1262 s, 1084 vs, 1010 vs, 802
s, 704 vs, 637 vs. Anal. Calcd: C, 73.28; H, 8.42. Found: C,
73.31; H, 8.45.
and then allowed to stir at this temperature for 4 h. The
toluene was removed in vacuo to yield the title compound as
an off-white crystalline solid (0.662 g, 76%): Mp 104-107 °C
(dec); 1H NMR (270 MHz, C6D6) δ -0.59 (s, 3H, AlCH3), -0.45
(s, 3H, AlCH3), -0.33 (s, 9H, AlCH3), 1.17 (dd, J ) 8, 13 Hz,
1H, NH), 1.34 (dd, J ) 4, 13 Hz, 1H, NH), 1.93 (dd, J ) 10, 14
Hz, 1H), 2.15 (dd, J ) 5, 14 Hz, 1H), 2.55-2.60 (m, 1H, NCH),
3.28 (dd, J ) 7, 11 Hz, 1H, OCH2), 3.60 (dd, J ) 4, 11 Hz, 1H,
OCH2), 6.70 (d, J ) 7 Hz, 2H, Ph-H), 7.05-7.19 (m, 3H, Ph-
H); 13C NMR (100 MHz, C6D6) δ -9.5 (AlCH3), -8.6 (AlCH3),
-7.4 (AlCH3), 37.3 (PhCH2), 54.2 (NCH), 65.1 (OCH2), 127.4
(Ph), 128.9, 129.5, 135.2; IR (neat) 3304, 3252, 2922, 1587,
1454, 1196, 1043, 723 cm-1
. Anal. Calcd for C14H27NOAl2:
C, 60.22; H, 9.68. Found: C, 57.30; H, 8.49.
Syn t h esis of DP Ala (AlMe2)-AlMe3 (12). To a rapidly
stirring solution of (R)-diphenylalaninol (0.500 g, 2.20 mmol)
in 10 mL of toluene was added trimethylaluminum (0.350 g,
4.86 mmol) in 20 mL of toluene at -10 °C. The exothermic
reaction was allowed to warm to 25 °C and then stirred at 25
1
°C for 1 h. The solution was concentrated to /5 volume and
stored at -30 °C, which produced a white precipitate. After
filtration, the title compound was collected as a colorless solid
1
(0.693 g, 89%): Mp 211-214 °C; H NMR (270 MHz, C6D6) δ
-0.52 (s, 3H, AlCH3), -0.42 (s, 3H, AlCH3), -0.31 (s, 9H,
AlCH3), 1.23-1.43 (m, 2H, NH), 3.08-3.20 (m, 1H, NCH), 3.34
(d, J ) 15 Hz, 1H, Ph2CH), 3.36 (dd, J ) 7, 9 Hz, 1H, OCH2),
3.50 (dd, J ) 4, 11 Hz, 1H, OCH2), 6.77-7.14 (m, 10H, Ph-H);
13C NMR (100 MHz, C6D6) δ -9.3 (AlCH3), -8.5 (AlCH3), -7.7
(AlCH3), 53.4 (Ph2CH), 56.0 (NCH), 63.6 (OCH2), 127.0 (Ph),
129.3, 129.8, 139.6; IR (neat) 3273, 3233, 3150, 2920, 1584,
Syn th esis of [DP Ala AlTMS2]2 (9). (R)-Diphenylalaninol
(0.570 g, 2.51 mmol) was suspended in 25 mL of toluene, and
Al(SiMe3)3‚THF (0.825 g, 2.59 mmol) was added at room
temperature. The reaction was stirred at room temperature
for 8 h during which time the amino alcohol gradually
1495, 1400, 1150, 1047, 702 cm-1
NOAl2: C, 67.61; H, 8.73. Found: C, 65.13; H, 7.88.
. Anal. Calcd for C20H31-
1
dissolved. The reaction was concentrated to
/ volume and
2
stored at -30 °C, and a white powder precipitated (0.663 g,
66%). A second batch of colorless crystals grew from the
filtrate after 2 weeks at -30 °C (combined yield, 0.946 g,
X-r a y Exp er im en ta l Deta ils. Details of the crystal data
and a summary of data collection parameters for 5, 6, and 11
are given in Table 1. Data were collected on a Siemens P4
diffractometer using graphite-monochromated Mo ΚR (0.710 73
Å) radiation. The check reflections, measured every 100
reflections, indicated a less than 5% decrease in intensity over
the course of data collection, and hence, no correction was
1
94%): Mp 193-194 °C; H NMR (270 MHz, C6D6) δ 0.24 (s,
18H, SiCH3), 2.03 (d, J ) 8 Hz, 2H, NH2), 3.26 (m, 2H, Ph2CH
and OCH2), 3.80 (m, 2H, NCH and OCH2), 6.91-7.12 (m, 10H,
Ph-H); 13C NMR (100 MHz, C6D6) δ 3.0 (SiCH3), 58.9 (Ph2CH),
59.0 (NCH), 63.5 (OCH2), 127.6 (Ph), 127.8, 129.2, 129.6, 140.4,
140.8; IR (neat) 3283, 3352, 3030, 2934, 2881, 1588, 1452,
applied. All calculations were performed on
a personal
computer using the Siemens software package, SHELXTL-
Plus. The structures were solved by direct methods and
successive interpretation of difference Fourier maps, followed
by least-squares refinement. All non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were included
in the refinement in calculated positions using fixed isotropic
parameters. The data obtained for 5 and 11 were somewhat
weak. This serves to explain the relatively large deviations
observed for the positional parameters.
1229, 1078, 993, 820, 702, 669 cm-1
42H68N2O2Al2Si4: C, 63.12; H, 8.59. Found: C, 63.46; H, 8.53.
Syn th esis of P Gly(AlMe2)-AlMe3 (10). To a rapidly
.
Anal. Calcd for
C
stirring solution of (S)-phenylglycinol (0.225 g, 1.64 mmol) in
10 mL of toluene at -10 °C was added trimethylaluminum
(0.245 g, 3.40 mmol) in 10 mL of toluene at -10 °C. The
exothermic reaction was allowed to warm to 25 °C and then
1
stirred at 25 °C for 7 h. The solution was concentrated to /2
volume and stored at -30 °C, which produced a white
precipitate. After filtration, the title compound was collected
as a colorless solid (0.342 g, 79%): Mp 134-138 °C (dec); H
Ack n ow led gm en t. Gratitude is expressed to the
National Science Foundation (Grant RII-861075), the
donors of the Petroleum Research Fund, administered
by the American Chemical Society (Grant 30057-G3),
and the National Science Foundation CAREER pro-
gram. M.P.S. thanks the National Institutes of Health
and FMC Lithium for research support. The technical
assistance of Tate Roth is appreciated.
1
NMR (270 MHz, C6D6) δ -0.44 (s, 3H, AlCH3), -0.42 (s, 3H,
AlCH3), -0.22 (s, 9H, AlCH3), 1.20-1.43 (m, 2H, NH), 3.22-
3.42 (m, 2H, OCH2), 3.85-3.99 (m, 1H, NCH), 6.18 (d, 2H, Ph-
H), 6.88-7.08 (m, 3H, Ph-H); 13C NMR (100 MHz, C6D6) δ -9.1
(AlCH3), -7.6 (AlCH3), 56.8 (OCH2), 66.0 (NCH), 126.3 (Ph),
129.1, 129.3, 134.8; IR (neat) 3302, 3246, 2926, 2890, 1578,
1198, 1148, 1030, 719, 673 cm-1
NOAl2: C, 60.22; H, 9.68. Found: C, 57.30; H, 8.49.
. Anal. Calcd for C13H25-
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths and angles, positional and thermal parameters, and
anisotropic thermal parameters and unit cell views (26 pages).
Ordering information is given on any current masthead page.
Syn th esis of P Ala (AlMe2)-AlMe3 (11). To a rapidly
stirring solution of (S)-phenylalaninol (0.471 g, 3.11 mmol) in
15 mL of toluene was added trimethylaluminum (0.471 g, 6.53
mmol) in 15 mL of toluene at -78 °C via cannula. The
exothermic reaction was allowed to warm to 25 °C with stirring
OM9509913