Structure and reactivity of organoaluminum derivatives of amino acids

Article abstract of DOI:10.1021/om030484i

The reaction of AlR₃ with 1 molar equiv of anthranilic acid yields the dimeric carboxylates [R₂Al(O₂CC₆ H₄-2-NH₂)]₂ [R = Me (3a) or Et (3b)] in high yields. The addition of 2 molar equiv of AlR₃ to anthranilic acid results in the formation of the tetranuclear complexes [R₂Al]₄ [μ-O₂CC₆H₄-2-μ-NH]₂ [R = Me (4a) or Et (4b)], where both protic functionalities are involved in the alkane elimination. The addition of γ-picoline to a solution of 4b in toluene results in a disruption of the tetranuclear cluster and affords Et₂Al(η-O₂CC₆H₄-2-NH) AlEt₂ (py-4-Me) (5). The reaction of 2 molar equiv of AlMe₃ with glycine yields the alkylaluminum carboxylate Me₂Al(O₂CCH₂NH₂)AlMe₃ (6), in which only the carboxylic group is deprotonated. When more equivalents of AlMe₃ are employed, the alkylation of the carboxylate group of glycine occurs and the aluminum alkoxide Me₂Al[OC(CH₃)₂CH₂NH₂] AlMe₃ (7) was isolated as one of the products of the complex postreaction mixture. The resulting compounds have been characterized by NMR and IR spectroscopy, and the molecular structure of compounds 4b and 7 has been confirmed by X-ray crystallography. On the basis of the reported studies, the general pathway for an interaction of amino acids with aluminum alkyls is proposed and some new insight into the reaction mechanism of the carboxylate group alkylation is provided.

Full text of DOI:10.1021/om030484i

Organometallics 2003, 22, 4151-4157
4151
Str u ctu r e a n d Rea ctivity of Or ga n oa lu m in u m
Der iva tives of Am in o Acid s
J anusz Lewin´ski,*,† Iwona J ustyniak,†,‡ J anusz Zachara,† and Ewa Tratkiewicz†
Department of Chemistry, Warsaw University of Technology, Noakowskiego 3,
00-664 Warsaw, Poland, and Institute of Physical Chemistry, Polish Academy of Sciences,
Kasprzaka 44, 01-224 Warsaw, Poland
Received J une 11, 2003
The reaction of AlR3 with 1 molar equiv of anthranilic acid yields the dimeric carboxylates
[R2Al(O2CC6H4-2-NH2)]2 [(R ) Me (3a ) or Et (3b)] in high yields. The addition of 2 molar
equiv of AlR3 to anthranilic acid results in the formation of the tetranuclear complexes [R2-
Al]4[µ-O2CC6H4-2-µ-NH]2 [(R ) Me (4a ) or Et (4b)], where both protic functionalities are
involved in the alkane elimination. The addition of γ-picoline to a solution of 4b in toluene
results in a disruption of the tetranuclear cluster and affords Et2Al(η-O2CC6H4-2-NH)AlEt2-
(py-4-Me) (5). The reaction of 2 molar equiv of AlMe3 with glycine yields the alkylaluminum
carboxylate Me2Al(O2CCH2NH2)AlMe3 (6), in which only the carboxylic group is deprotonated.
When more equivalents of AlMe3 are employed, the alkylation of the carboxylate group of
glycine occurs and the aluminum alkoxide Me2Al[OC(CH3)2CH2NH2]AlMe3 (7) was isolated
as one of the products of the complex postreaction mixture. The resulting compounds have
been characterized by NMR and IR spectroscopy, and the molecular structure of compounds
4b and 7 has been confirmed by X-ray crystallography. On the basis of the reported studies,
the general pathway for an interaction of amino acids with aluminum alkyls is proposed
and some new insight into the reaction mechanism of the carboxylate group alkylation is
provided.
In tr od u ction
exploring the coordination chemistry of aluminum car-
boxylates. In particular, we have demonstrated that the
anti direction is the most likely location of the aluminum
center relative to the carboxylate group and proved that
a bidentate carboxylate group is isomorphic with an
alkoxide ligand.4-6 On the other hand, we have dem-
onstrated that organometallic complexes derived from
anthranilic acid and related carboxylic acids provide the
means to study intra- and intermolecular forces result-
ing from donor-acceptor and hydrogen-bonding interac-
tions. For instance, the reaction of anthranilic acid with
1 and 2 equiv of Al(tBu)3 afforded the dimeric carboxy-
late [(tBu2)Al(O2CC6H4-2-NH2)]2 (1), consisting of the
weak intramolecular hydrogen bonding and the dialu-
minumcarboxylate chelate complex (tBu2)Al(O2CC6H4-
2-NH2)Al(tBu)3 (2), respectively.7 In both cases only the
CO2H proton was involved in the alkane elimination
and the carboxylate moiety acts as a monoanionic LH
ligand, and for compound 1 the NH2 group does not
participate in the coordination to the metal center but
is involved in an intramolecular hydrogen bond.7
The study of the reaction of carboxylic acids with
aluminum compounds is applicable to material science,1
bioinorganic chemistry,2 and organic synthesis.3 With
a view to investigate what effect both the metal alkyl
and the organic residue have on the formation of group
13 carboxylates, we have carried out reactions of MR3
t
(M ) Al, Ga, and In; R ) Me, Et, or Bu) with a variety
of bifunctional carboxylic acids, LH2 type reagents.4-8
The organoaluminum derivatives of salicylic acid (2-
hydroxybenzoic acid) or phthalic acid, the tetranuclear
[R2Al]4[L]2 type complexes, are interesting models for
* Corresponding author. E-mail: lewin@ch.pw.edu.pl.
† Warsaw University of Technology.
‡ Polish Academy of Sciences.
(1) Yamane, H.; Kimura, Y. Polymeric Materials Encyclopedia;
Salamone, J . C., Ed.; CRS Press: Boca Raton, FL, 1996; Vol. 1, p 202,
and references therein. Landry, C. C.; Pappe, N.; Mason, M. R.; Apblett,
A. W.; Tyler, A. N.; McInnes, A. N.; Barron, A. R. J . Mater. Chem.
1995, 5, 331. Kareiva, A.; Harlan, C. J .; McQueen, D. B.; Cook, R. L.;
Barron, A. R. Chem. Mater. 1996, 8, 2331. Defriend, K. A.; Barron, A.
R. J . Mater. Sci. 2003, 38, 927.
(2) See for example: Powell, A. K.; Heath, S. L. Coord. Chem. Rev.
1996, 149, 59, and references therein. Kiss, T.; So´va´go´, I.; To´th, I.;
Lakatos, A.; Bertani, R.; Tapparo, A.; Bombi, G.; Martin, R. B. J . Chem.
Soc., Dalton Trans. 1997, 1967.
We report here on the related reactions of lower
aluminum alkyls with anthranilic acid and glycine. The
obtained results provide some new insight into the
reaction mechanisms of amino acids with aluminum
alkyls and the reaction stages of the carboxylate group
(3) Gibson, V. C.; Redshaw, C.; White, A. J . P.; Williams, D. J . Chem.
Commun. 2001, 79.
(4) Lewin´ski, J .; Zachara, J .; J ustyniak, I. Organometallics 1997,
16, 3859.
(5) Lewin´ski, J .; Zachara, J .; J ustyniak, I. Inorg. Chem. 1998, 37,
2575.
(6) Lewin´ski, J .; J ustyniak, I.; Lipkowski, J .; Zachara, J . Inorg.
Chem. Commun. 2000, 3, 700.
(7) Branch, C. S.; Lewin´ski, J .; J ustyniak, I.; Bott, S. G.; Lipkowski,
J .; Barron, A. R. J . Chem. Soc., Dalton Trans. 2001, 1253.
(8) For selected examples on the reactions of aluminum alkyls with
monodentate carboxylic acids, see: Bethley, C. E.; Aitken, C. L.;
Harlan, C. J .; Koide, Y.; Bott, S. G.; Barron, A. R. Organometallics
1997, 16, 329. Pietrzykowski, A.; Pasynkiewicz, S.; Popławska, J . Main
Group Metal. Chem. 1996, 18, 651.
10.1021/om030484i CCC: $25.00 © 2003 American Chemical Society
Publication on Web 08/27/2003

4152 Organometallics, Vol. 22, No. 20, 2003
Lewin´ski et al.
C-alkylation proposed by Mole.9 Our data are also of
particular interest with respect to the recent report of
Gibson and co-workers where the reaction of AlMe3 with
anthranilic acid, followed by treatment with acetonitrile,
has been recognized as a potentially valuable tool for
preparing N-heterocycles.3 An additional interesting
aspect of the latter reaction is the presence of alumox-
ane moieties in the organometallic product backbone,
which indicates that aluminum carboxylates can serve
as interesting starting materials for various aluminox-
anes.10
F igu r e 1. ORTEP view of [Et2Al]4[(µ-O2C)C6H4-2-µ-NH]2
(4b) with atom-numbering scheme. Thermal ellipsoids are
shown at the 30% probability level. Methyl groups of the
ethyl substituents are omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 4b a n d 7
4ba
7
Al(1)-O(2)
Al(1)-N(1′)
Al(1)-C(11)
Al(1)-C(13)
Al(2)-O(1)
Al(2)-N(1)
Al(2)-C(15)
Al(2)-C(17)
O(1)-C(7)
O(2)-C(7)
N(1)-C(6)
1.835(3)
1.990(4)
1.950(2)
1.962(3)
1.843(3)
1.953(4)
1.950(2)
1.950(2)
1.265(4)
1.272(4)
1.444(4)
Al(1)-O(1)
Al(2)-O(1)
Al(2)-N(1)
Al(1)-C(7)
Al(1)-C(8)
Al(1)-C(9)
Al(2)-C(5)
Al(2)-C(6)
O(1)-C(1)
N(1)-C(2)
C(1)-C(2)
1.8890(14)
1.8332(15)
1.998(2)
1.976(3)
1.986(2)
1.970(2)
1.945(3)
1.950(3)
1.463(2)
1.474(4)
1.523(4)
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r e of Alk yla lu m in u m De-
r iva tives of An th r a n ilic Acid . The reaction of AlR3
(R ) Me or Et) with 1 molar equiv of anthranilic acid
yields the dimeric carboxylates [R2Al(O2CC6H4-2-NH2)]2
(3) in high yields. Both compounds, the methyl (3a ) and
ethyl (3b) derivatives, are unstable at ambient temper-
ature in a solution that follows from the 1H NMR study.
The low-temperature NMR and IR spectra are consis-
tent with that observed for the tert-butyl derivative 1,7
which indicates that all three compounds have similar
structures. Unfortunately, difficulties in isolating 3a or
3b preclude its structural characterization by X-ray
crystallography.
O(2)-Al(1)-N(1′) 101.14(13) O(1)-Al(2)-N(1) 86.83(8)
O(1)-Al(2)-N(1) 90.36(14) Al(1)-O(1)-Al(2) 118.90(7)
Al(2)-N(1)-Al(1′) 116.76(17) C(5)-Al(2)-C(6) 120.69(14)
C(7)-O(1)-Al(2)
C(7)-O(2)-Al(1)
C(6)-N(1)-Al(2)
126.2(2)
132.1(3)
110.4(2)
C(1)-O(1)-Al(1) 126.46(12)
C(1)-O(1)-Al(2) 114.15(12)
C(2)-N(1)-Al(2) 105.86(15)
C(6)-N(1)-Al(1′) 114.6(3)
C(2)-C(1)-O(1)
105.15(19)
The addition of 2 molar equiv of AlR3 (R ) Me or Et)
to anthranilic acid results in the formation of the
tetranuclear complexes [R2Al]4[µ-O2CC6H4-2-µ-NH]2 (4).
Thus, in this case both protic functionalities (i.e., CO2H
and NH2 groups) are involved in the alkane elimination,
unlike the analogous reaction with Al(tBu)3.7 Compound
4 is the only product formed even when excess AlR3 is
employed, which indicates that the carboxylate group
of the aromatic acid derivative is resistant to C-
alkylation (vide infra). The methyl derivative 4a is
insoluble in common noncoordinating solvents and was
characterized only by IR spectroscopy. It is solubilized
upon addition of γ-picoline (py-4-Me), followed by heat-
ing in dichloromethane. Filtration and cooling to room
temperature afforded 4a as bright yellow crystals.
Undoubtedly, the solubilization is accompanied by a
complex formation of 4a with added py-4-Me (vide
infra). The ethyl compound 4b is isolated as a yellow
aromatic hydrocarbon-soluble, oxygen- and moisture-
sensitive crystalline solid. No decomposition of 4a and
O(1)-C(7)-O(2)
O(1)-C(7)-C(1)
O(2)-C(7)-C(1)
120.3(4)
121.4(3)
118.4(3)
a
Data for one of two similar molecules in the unit cell. Atoms
labeled with a prime belong to the centrosymmetric counterpart
of the dimeric units, symmetry code (-x, -y, -z).
4b was observed after refluxing in toluene for several
hours. The molecular structure of 4b has been deter-
mined by a single-crystal X-ray diffraction study, and
the solution structure has been confirmed by NMR and
IR spectroscopy and cryometric molecular weight mea-
surements.
The molecular structure of 4b and atom-numbering
scheme are shown in Figure 1, and selected bond
lengths and angles are given in Table 1. The unit cell
contains two unique molecules which reside on inversion
centers and are essentially identical. The central core
in 4b consists of two dianionic anthranilate moieties
joined by two bridging diethylaluminum species. Ad-
ditionally, the diethylaluminum units form intramo-
lecular bridges between the carboxylate and amide
functionalities. The carboxylate group is rotated about
the C-C bond relative to the aromatic ring by 17.3(2)°,
and the O(1)-Al(2)-N(1) bite angle is 90.4(1)°. The
carboxylate groups display a bidentate coordination
(9) Meisters, A.; Mole, T. Aust. J . Chem. 1974, 27, 1665.
(10) Very recently, the formation of alumoxane moieties in the
organometallic backbone has also been observed in the reaction of
hydroxy carboxylic acids with AlMe3. Skrok, T.; Pietrzykowski, A.;
Radzymin´ski, T. XIVth FECHEM Conference on Organometallic
Chemistry, Gdan´sk, 2001; Book of Abstracts, p 33.

Organoaluminum Derivatives of Amino Acids
Organometallics, Vol. 22, No. 20, 2003 4153
mode in a syn-anti conformation with two aluminum
atoms. These metal centers are slightly deviated above
and below the plane of the carboxylate group [0.145(5)
Å, Al(1), and 0.260(5) Å, Al(2)]. The N(1)-Al(2) bond
length [1.953(4) Å] is shorter than that observed for
N(1)-Al(1′) [1.990(4) Å]. As seen from Figure 1, the Al-
(1′)-N(1) bond lies in the plane almost perpendicular
to the aromatic ring, as indicated by the Al(1′)-N(1)-
C(6)-C(5) torsion angle of 89.0(4)°. The Al(2)-O(1) bond
situated in the anti direction with respect to the
carboxylate group [1.843(3) Å] is slightly longer than
that in the syn direction [1.835(3) Å], which is opposite
the expected strength order in regard to the preferred
coordination mode of aluminum relative to a carboxylate
group.5 Finally, the structure of 4b is of the same
morphology as the related aluminum derivative of
salicylic acid, [Et2Al]4[(µ-O2C)C6H4-2-µ-O]2.4
The tetranuclear structure of compound 4b is retained
in solution. The 1H NMR spectrum consists of two
overlapping pairs of quartets for the methylene Al-CH2-
CH3 protons and four well-separated triplets for the
methyl Al-CH2CH3 protons. These four pairs of ethyl
resonances correspond to the equivalent in pairs of ethyl
groups of the diethylaluminum units in the dimeric
compound. The 13C NMR data are also consistent with
the tetranuclear structural motif. The 27Al NMR spec-
trum of 4b shows one broad resonance at 140.5 ppm,
whose chemical shift is similar to that observed for other
four-coordinate dialkylaluminum complexes with O,N-
bidentate ligands.11 It is worth noting that the intensity
of the resonance signal is relatively low and there is a
problem with the detection of resonance signals result-
ing from the quadruple moment of aluminum and
nitrogen.12
isolating 5 preclude its structural characterization by
X-ray crystallography.
Rea ction s of Glycin e w ith AlMe3. The reaction of
2 molar equiv of AlMe3 with glycine yields the alkyl-
aluminum carboxylate Me2Al(O2CCH2NH2)AlMe3 (6), in
which only the carboxylic group is deprotonated. Com-
pound 6 is stable below 0 °C in solution and has been
characterized by low-temperature 1H and 13C NMR and
1
IR spectroscopy. The H NMR spectrum of 6 shows one
resonance pattern with a broad single resonance of the
Al-Me protons in the temperature range 0 to -70 °C.
On the basis of the reported structure of the tert-butyl
derivative 2,7 it is reasonable to assume an analogous
structure for adduct 6. The occurrence of one broad
signal due to the Al-Me groups indicates the operation
of a dynamic process. However, we cannot exclude other
type species in solution.
Addition of γ-picoline to a solution of 4b in toluene
results in a disruption of the tetranuclear cluster to
afford Et2Al(η-O2CC6H4-2-NH)AlEt2(py-4-Me) (5). The
1
resulting compound has been characterized by H and
13C NMR and IR spectroscopy and cryometric molecular
weight measurements. The molecular weight measure-
ments have revealed that 5 occurs as a monomeric
species in solution. The 1H NMR spectrum of compound
5 contains two types of Al-Et groups and one Me group
of py-4-Me. On the basis of the integrations, only one
py-4-Me is coordinated to one of the Et2Al moieties. On
the basis of these data and the structure characteriza-
tion of the related gallium derivative of salicylic acid,
Me2Ga(η2-O2CC6H4-2-O)GaMe2(py-4-Me),13 the struc-
ture of adduct 5 may be best described as a monomeric
complex in which one AlEt2 moiety is chelated by the
carboxylate oxygen and amide nitrogen and the second
AlEt2 moiety is terminally bonded to the carboxylate
group. To the terminal AlEt2 unit is additionally coor-
dinated one py-4-Me molecule. Adduct 5 is relatively
unstable in solution and slowly disproportionates to
unidentified products. Unfortunately, difficulties in
Several attempts to obtain crystals of compound 6
suitable for X-ray analysis were unsuccessful. Surpris-
ingly, this effort yielded a small amount of the alumi-
num alkoxide Me2Al[OC(CH3)2CH2NH2]AlMe3 (7). The
isolation of compound 7 as a side product, in ca. 5%
yield, from the reaction mixture indicated the alkylation
of the carboxylate group during the course of the
reaction. Therefore we have also studied the reaction
of glycine with greater than 2 equiv of AlMe3. The
addition of excess AlMe3 to glycine results in the
formation of a complex mixture of products as deter-
1
mined by H and 13C NMR spectroscopy. In this case,
undoubtedly the alkylation reaction is favored, which
was confirmed by the observation of a resonance in the
13C NMR for a quaternary carbon and the loss of the
carboxylate resonance. In fact, it is also likely that
additional AlMe3 promotes the subsequent alkane elimi-
nation in compound 4, which afforded the glycinate
analogue of the tetranuclear compound 4, i.e., the
intermediate compound [Me2Al]4[µ-O2CCH2-µ-NH]2 (8),
as well as the deprotonation of the amine in compound
7, resulting in the formation of the trinuclear compound
[AlMe2]2[{OC(CH3)2CH2NH}2AlMe] (9). We have been
unable to isolate compounds 8 and 9 from the postre-
action mixtures, but formulation of 8 is consistent with
the reaction of anthranilic acid with AlMe3, and formu-
(11) Lewin´ski, J . Heteronuclear NMR Applications (B, Al. Ga, In,
Tl), In Encyclopedia of Spectroscopy and Spectrometry; Lindon J . C.,
Tranter G. E., Holmes J . L., Eds.; Academic Press: London, 1999; Vol.
1, pp 691-703.
(12) We have observed the same effect for dialkylaluminum chelate
complexes derived from N-phenylsalicylideneimine: Lewin´ski, J .;
Zachara, J .; Starowieyski, K. B.; Ochal, Z.; J ustyniak, I.; Kopec´, T.;
Stolarzewicz, P.; Dranka, M. Organometallics 2003, 18, 3773.
(13) J ustyniak, I.; Lewin´ski, J .; Zachara, J . XIIIth FECHEM Confer-
ence on Organometallic Chemistry; Lisboa, 1999; Book of Abstracts, p
210.

4154 Organometallics, Vol. 22, No. 20, 2003
Lewin´ski et al.
lation of 9 is consistent with our previous studies that
have demonstrated the ready formation of analogous
trinuclear compounds in the reaction of 2 equiv of AlMe3
with 2-(hydroxymethyl)aniline, i.e., [AlMe2]2[(OCH2C6H4-
2-NH)2AlMe].14
The observed complexity of the postreaction mixture
may also result from the fact that the carboxylate
C-alkylation appears to proceed with concomitant alu-
F igu r e 2. ORTEP view of Me2Al[OC(CH3)2CH2NH2]AlMe3
(7) with atom-numbering scheme. Thermal ellipsoids are
shown at the 30% probability level. Hydrogen atoms
(excluding amine hydrogens) are omitted for clarity.
1
moxane (MAO) formation (vide infra). Notably, the H
NMR spectrum of the reaction mixture (i.e., glycine with
3 equiv of AlMe3) shows, in addition to other Al-Me
signals, a well-separated broad resonance at -0.30 ppm,
which is often interpreted as indicative of methylalu-
moxane.15 On the other hand, the recent studies show
that (MeAlO)n units are often involved in the organo-
metallic product backbone3,10,16 and can even catalyze
some transformations.15a Therefore, it is reasonable to
assume that the reaction of glycine with more than 2
equiv of AlMe3 affords some organometallic species
involving alumoxane and alkoxyaluminum moieties. It
is worth noting that the analysis of the outcome of the
reaction of glycine with 3 equiv of AlMe3 confirms
complete conversion of glycine toward 1-amino-2-meth-
yl-2-propanol after hydrolysis of the postreaction mix-
ture (eq 1).
dral geometry due to the small bite angle of the chelate
ligand [O(1)-Al(2)-N(1) 86.83(8)°]. The five-membered
chelate ring Al(2)-O(1)-C(1)-C(2)-N(1) is puckered,
as demonstrated by the twisting on the C(1)-C(2) bond
in order to minimize the ring strain.
Mech a n istic Con sid er a tion s. On the basis of our
studies we propose the following general pathway for
an interaction of amino acids with aluminum alkyls and
provide some new insight into the reaction mechanism
of the carboxylate group alkylation (Scheme 1). Initially,
depending on the reactant molar ratio, the reaction of
amino acids with AlR3 leads to compound I or II, which
consist of only a deprotonated carboxylic group. The
relative stability of the type I and II compounds is
determined by the nature of both the amino acid and
aluminum-bonded alkyl substituents. For the lower
alkyls the adduct II can readily be transformed into
tetrametallic compound III upon deprotonation of the
amine functionality (path 1), or the C-monoalkylation
of the carboxylate group with the formation of species
IV can take place (path 2), depending on the nature of
the amine carboxylate ligand. Clearly, the further
reaction course is controlled by the Bro¨nsted acidity of
the amine termini and the carboxylate group propensity
toward C-alkylation. Thus, the more acidic anthranilate
NH2 group undergoes alkane elimination according to
path 1, whereas the less acidic glycinate NH2 remains
intact in similar reaction conditions and the C-alkyl-
ation is favored. According to Scheme 1, the formation
of the alkoxide compound VI, an analogue of the isolated
Me2Al[OC(CH3)2CH2NH2]AlMe3 (7), is initiated by the
attack of the Al-Me group at the carboxylate electro-
philic carbon atom of II to produce intermediate IV. In
the presence of an excess of Me3Al the subsequent
C-nucleophile addition, for example proceeding through-
out intermediate V, leads to dimetallic adduct VI with
concomitant formation of an alumoxane moiety, MAO.18,19
Thus, according to our mechanistic consideration, alu-
The molecular structure of the alkoxide adduct 7 has
been determined by a single-crystal X-ray diffraction
study, and the solution structure has been confirmed
by 1H and 13C NMR spectroscopy (see Experimental
Section). The molecular structure of compound 7 (Figure
2) is analogous to the previously reported dinuclear
adducts derived from aluminum alkyls and amine
alcohols.17 The alkoxide ligand with amine termini
chelates the Me2Al(2) moiety, while the Me3Al(1) unit
binds to the alkoxide oxygen atom. The Al(2)-O(1) and
Al(2)-N(1) bond distances are 1.8332(15) and 1.998(2)
Å, respectively, and are comparable with the distances
observed in analogous complexes.17 The aluminum
coordination sphere is distorted from an ideal tetrahe-
(14) Lewin´ski, J .; Zachara, J .; Kopec´, T. Inorg. Chem. Commun.
1998, 1, 182.
(15) See for example: (a) Obrey, S. J .; Bott, S. G.; Barron, A. R.
Organometallics 2001, 20, 5162. (b) Resconi, L.; Bossi, S.; Abis, L.
Macromolecules 1990, 23, 4489.
(16) Sobota, P.; Utko, J .; Ejfler, J .; J erzykiewicz, L. B. Organome-
tallics 2000, 19, 4929.
(18) It should be noted that MAO is known to be mixture of species,
ordinarily obtained by adding water to AlMe3, in which the Al:Me ratio
is variable; however, for the present study a general formula of [MAO]n
will be employed for convenience.
(19) For structural aspects of alumoxanes see for example: Pasyn-
kiewicz, S. Polyhedron 1990, 9, 429. Mason, M. R.; Smith, J . M.; Bott,
S. G.; Barron, A. R. J . Am. Chem. Soc. 1993, 115, 4971.
(17) 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. Atwood, D. A.; Gabbai, F. P.; Lu, J .;
Remington, M. P.; Rutherford, D.; Sibi, M. P.; Organometallics 1996,
15, 2308. McMahon, C. N.; Bott, S. G.; Barron, A. R. J . Chem. Soc.,
Dalton Trans. 1998, 3301.

Organoaluminum Derivatives of Amino Acids
Organometallics, Vol. 22, No. 20, 2003 4155
Sch em e 1
were purified and dried by standard techniques. The NMR
spectra, in C6D6 unless otherwise stated, were recorded on a
Varian 300VXL spectrometer, and the IR spectra (4000-400
cm-1) were recorded as CH2Cl2 solution or Nujol mulls on a
Specord-75IR spectrophotometer. Molecular weight measure-
ments were carried out cryoscopically in benzene. Com-
mercially available reagents were used as purchased.
Sch em e 2. Rea ction Sta ges for th e C-Alk yla tion of
th e Ca r boxyla te Gr ou p by AlMe3 P r op osed by
Mole9
[Me2Al(O2CC6H4-2-NH2)]2 (3a ). To a suspension of anthra-
nilic acid (0.96 g, 7 mmol) in CH2Cl2 (15 mL) was added
dropwise AlMe3 (0.50 g, 7 mmol) at -78 °C. The reaction
mixture was allowed to warm to 10 °C and then cooled to -30
°C for 1 day to yield yellow crystals (1.18 g, 87%). Anal. Calcd
for C18H24Al2N2O4: C 55.96, H 6.26, N 7.25. Found: C 55.78,
H 6.34, N 7.18. IR (Nujol, cm-1): 3510 (w), 3399 (w), 1616 (m),
1576 (m), 1533 (m), 1461 (s), 1413 (m), 1378 (w), 1301 (w),
moxanes (or MAO) can be easily formed in the reaction
of carboxylic acids with aluminum alkyls even at ambi-
ent temperature. It is worth noting that the literature
precedent for the C-alkylation of the carboxylate group
by AlMe3 includes the conversion of aluminum carboxy-
lates to corresponding ketones, which is followed by
further methylation to a hemialkoxide (Scheme 2).9
Furthermore, on the basis of our studies it becomes
clear that the reaction of Me3Al with anthranilic acid
followed by treatment with acetonitrile, recently de-
scribed by Gibson et al.,3 involves formation of the
tetrametallic complex 4a , its adduct with a Lewis base,
VII, and a subsequent N-heterocycle VIII formation
(Scheme 3). In this reaction acetonitrile addition to the
methyl compound 4a is essential for the generation of
the soluble monomeric analogue of compound 5a , i.e.,
Me2Al(η2-O2CC6H4-2-NH)AlMe2(CH3CN). Further, ac-
cording to the authors’ suggestion the final reaction
product arises via insertion of acetonitrile into Al-N
bonds, and in the latter reaction MAO is involved in
the organometallic product backbone.
1
1254 (m), 1164 (m), 751 (w), 524 (w). H NMR (d8-toluene, 0
°C): δ -0.25 (s, 6H, Al-CH3), 4.92 (s, 2H, NH2), 5.95 (d, 1H,
CH), 6.37 (t, 1H, CH), 6.91 (t, 1H, CH), 7.95 (d, 1H, CH). 27Al
NMR: δ 149 (w1/2 ) 2190 Hz).
[Et2Al(O2CC6H4-2-NH2)]2 (3b). This compound was pre-
pared in an analogous manner to compound 3a using AlEt3
(0.80 g, 7 mmol) and anthranilic acid (0.96 g, 7 mmol). Yield:
1.40 g, 90%. Anal. Calcd for C22H32Al2N2O4: C 59.72, H 7.29,
N 6.33. Found: C 59.61, H 7.37, N 6.31. IR (Nujol, cm-1): 3503
(w), 3389 (w), 1620 (m), 1576 (m), 1539 (m), 1458 (s), 1439
(m), 1377 (w), 1304 (w), 1258 (m), 1161 (m), 986 (w), 753 (w),
709 (w), 530 (w). 1H NMR (d8-toluene, 0 °C): δ 0.39 [q, 4H,
Al(CH2CH3)], 1.37 [t, 6H, Al(CH2CH3)], 4.97 (s, 2H, NH2), 5.98
(d, 1H, CH), 6.39 (t, 1H, CH), 6.91 (t, 1H, CH), 8.05 (d, 1H,
CH). 27Al NMR: δ 151 (w1/2 ) 2550 Hz).
[Me2Al]4[(µ-O2C)C6H4-2-µ-NH]2 (4a ). To a suspension of
anthranilic acid (0.96 g, 7 mmol) in CH2Cl2 (15 mL) was added
dropwise AlMe3 (1.00 g, 14 mmol) at -78 °C. The reaction
mixture was allowed to warm to room temperature. After
stirring for an additional 1 h at ambient temperature, the
resulting mixture was filtered. Yield: 1.55 g, 89%. Anal. Calcd
for C22H34Al4N2O4: C 53.01, H 6.88, N 5.62. Found: C 52.79,
H 6.97, N 5.64. IR (Nujol, cm-1): 3233 (w), 1614 (s), 1601 (m),
Exp er im en ta l Section
All operations were carried out under a nitrogen atmosphere
using standard Schlenk and high-vacuum techniques. Solvents

4156 Organometallics, Vol. 22, No. 20, 2003
Lewin´ski et al.
Sch em e 3
Ta ble 2. Su m m a r y of Cr ysta l Da ta a n d Str u ctu r e
Deter m in a tion for 4b a n d 7
1559 (m), 1461 (s), 1426 (m), 1377 (w), 1334 (w), 1307 (w), 1259
(w), 1200 (m), 1164 (w), 1101 (w), 942 (w), 825 (w), 804 (w),
575 (w).
molecular formula
fw
temperature, K
cryst size, mm
wavelength (λ, Å)
cryst syst
space group
a, Å
b, Å
C
30H50Al4N2O4
C9H25Al2NO
217.26
293(2)
[Et2Al]4[(µ-O2C)C6H4-2-µ-NH]2 (4b). To a suspension of
anthranilic acid (0.96 g, 7 mmol) in CH2Cl2 (15 mL) was added
dropwise AlEt3 (1.6 g, 14 mmol) at -78 °C. The reaction
mixture was allowed to warm to room temperature. After
stirring for an additional 1 h, the solution was concentrated
and then cooled to -15 °C for 1 day to yield yellow crystals
(1.94 g, 91%). Anal. Calcd for C30H50Al4N2O4: C 59.01, H 8.25,
N 4.59. Found: C 58.88, H 8.31, N 4.58. IR (CH2Cl2, cm-1):
3376 (w), 1619 (s), 1568 (s), 1524 (s), 1464 (s), 1416 (m), 1352
(m), 1304 (w), 1232 (w), 1212 (w), 1160 (m), 1068 (w), 1044
610.65
293(2)
0.40 × 0.22 × 0.14 0.42 × 0.30 × 0.24
Mo KR (0.71073)
triclinic
P1h (No. 2)
10.6073(12)
10.6835(11)
17.244(2)
97.884(9)
95.339(9)
107.868(8)
1823.2(4)
2
Mo KR (0.71073)
monoclinic
P21/n (No. 14)
6.9415(6)
13.7945(12)
15.0859(13)
90
91.281(7)
90
1444.2(2)
4
c, Å
R, deg
â, deg
1
(m), 988 (m), 952 (w), 812 (m), 532 (w), 492 (w). H NMR (25
γ, deg
V, Å3
°C): δ -0.18 [m, 8H, Al(CH2CH3)], 0.44 [q, 8H, Al(CH2CH3)],
0.88 [t, 6H, Al(CH2CH3)], 1.12 [t, 6H, Al(CH2CH3)], 1.25 [t, 6H,
Al(CH2CH3)], 1.44 [t, 6H, Al(CH2CH3)], 2.91 (s, 2H, NH); 6.04
(d, 2H, CH), 6.62 (t, 2H, CH), 6.86 (t, 2H, CH), 7.98 (d, 2H,
CH). 13C NMR: δ -2.43, -1.16, -0.68, -0.35, 7.96, 8.09, 8.72,
9.09, 121.04, 124.10, 125.05, 133.412, 136.17, 147.98, 176.22.
27Al NMR δ 140.5 (broad). Cryoscopic molecular weight,
benzene solution, formula weight calcd for C30H50Al4N2O4:
610.65, found 610.
Et2Al(η-O2CC6H4-2-NH)AlEt2(p y-4-Me) (5). To a solution
of 4b (0.98 g, 1.6 mmol) in toluene (5 cm3) was added γ-picoline
(0.30 g, 3.2 mmol) at room temperature. After stirring for 5
min, solvent and excess γ-picoline were removed in vacuo to
leave quantitatively a yellow solid, which was then washed
with hexane. Anal. Calcd for C21H32Al2N2O2: C 63.30, H 8.09,
N 7.03. Found: C 63.24, H 8.18, N 7.08. IR (CH2Cl2, cm-1):
3376 (w), 1616 (s), 1568 (s), 1524 (s), 1464 (s), 1416 (m), 1352
(m), 1304 (w), 1232 (w), 1212 (m), 1188 (w), 1160 (m), 1068
(w), 1044 (m), 988 (m), 952 (w), 920 (w), 852 (w), 812 (m), 648
(s), 492 (w). 1H NMR (25 °C): δ 0.27 [q, 4H, Al(CH2CH3)], 0.43
[q, 4H, Al(CH2CH3)], 1.35 [t, 6H, Al(CH2CH3)], 1.39 [t, 6H, Al-
(CH2CH3)], 2.32 (s, 3H, CH3), 3.97 (s, 1H, NH), 6.19 (d, H, CH),
6.32 (t, H, CH), 6.35 (d, 2H, CHpy-4-Me), 6.94 (t, H, CH), 8.01
(d, 2H, CHpy-4-Me), 8.03 (d, 1H, CH). 13C NMR: δ -1.39, -0.77,
8.58, 9.65, 21.4, 107.42, 112.71, 121.15, 126.33, 132.72, 135.75,
146.71, 153.54, 160.78, 175.80. 27Al NMR δ ) 141 (broad).
Cryoscopic molecular weight, benzene solution, formula weight
calcd for C21H32Al2N2O2: 398.45, found 401.
Me2Al(O2CCH2NH2)AlMe3 (6). To a suspension of glycine
(0.60 g, 8 mmol) in toluene (15 mL) was added dropwise AlMe3
(1.15 g, 16 mmol) at -78 °C. The reaction mixture was allowed
to warm to 0 °C and then to stir for 3 h. Addition of hexane at
-20 °C followed by filtration afforded a white solid precipitate.
Yield: 1.35 g, 83%. Anal. Calcd for C7H19Al2NO2: C 41.38, H
9.42, N 6.89. Found: C 41.12, H 9.48, N 6.94. IR (CH2Cl2,
cm-1): 3944 (w), 3300 (w), 1632 (s), 1548 (s), 1442 (s), 1352
(w), 1262 (s), 896 (m), 604 (w), 596 (w), 564 (w), 488 (w). 1H
NMR (d8-toluene, 0 °C): δ -0.51 (s, 15H, Al-CH3), 3.64 (s,
2H, CH2), 3.02 (br, 2H, NH2). 13C NMR (d8-toluene, 0 °C): δ
-8.67 (broad), 53.42, 186.5. 27Al NMR (d8-toluene, 0 °C): δ
148 (broad).
Z
density calc, g‚cm-3
linear abs coeff, mm-1
F(000)
1.112
0.160
656
0.999
0.174
480
θ range, deg
no. of reflns collected
no. of ind reflns
2.0-25.0
3.2-29.0
6785
28 401
6410 (Rint ) 0.019) 3698 (Rint ) 0.066)
no. of data/restr/params 6410/172/486
3698/0/150
1.103
0.0548, 0.1339
goodness-of-fit on F2
final R1, wR2 values
[I > 2σ(I)]a
0.952
0.0565, 0.1076
wR2 (all data)a
0.1608
0.1555
+0.25/-0.25
residual extreme, e‚Å-3 +0.20/-0.18
R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo - Fc2)2/∑w(Fo4)]1/2
.
a
2
the reaction mixture of glycine with 2 equiv of AlMe3 was
allowed to warm to room temperature and then recrystallized
in CH2Cl2 (-20 °C), yielding colorless crystals (in ca. 15%
yield). Anal. Calcd for C9H25Al2NO: C 49.75, H 11.60, N 6.45.
1
Found: C 49.55, H 11.69, N 6.38. H NMR (25 °C): δ -0.56
(s, 6H, Al-CH3), -0.20 (s, 9H, Al-CH3), 1.44 (s, 6H, CH3).
2.68 (br, 2H, CH2), 3.07 (br, 2H, NH2). 13C NMR: δ -10.66,
-8.91, 26.76, 46.34, 73.92.
Alk yla tion of Glycin e w ith AlMe3. To a suspension of
glycine (0.60 g, 8 mmol) in toluene (15 mL) was added dropwise
AlMe3 (1.73 g, 24 mmol) at -78 °C. The reaction mixture was
allowed to warm to room temperature and then to stir for 3 h.
The solution was later treated with KF and water to form a
white precipitate. Vigorous stirring of the resulting suspension
was continued at ambient temperature, and after 0.5 h the
organic products formed were extracted with ethyl ether.
Etherate was later removed, dried with anhydrous MgSO4, and
analyzed by HPLC and 1H NMR.
X-r a y Str u ctu r e Deter m in a tion . Single crystals of 4b and
7, suitable for X-ray diffraction studies, were placed in thin
walled capillary tubes (Lindemann glass 0.5 mm) in an inert
atmosphere. The selected crystallographic data, the param-
eters of data collections, and refinement procedures are
presented in Table 2. Data for compound 4b were collected on
a four-circle P3 (Siemens AG) diffractometer. The crystal class
and the orientation matrix were obtained from the least-
squares refinement of 26 well-centered reflections randomly
selected in the 2θ range 12.9-28.3°. The intensities were
Me2Al[OC(CH3)2CH2NH2]AlMe3 (7). This compound was
prepared in a manner similar to that for compound 6; however,

Organoaluminum Derivatives of Amino Acids
Organometallics, Vol. 22, No. 20, 2003 4157
collected in the ω-2θ mode. A meaningful crystal decay of 26%
was noticed. After correction for the Lorentz-polarization
effect and crystal decomposition, the equivalent reflections
were averaged. The structure was solved by direct methods
using the SHELXS-86 program.20a The distribution of the
peaks showed that compound 4b crystallizes with two crys-
tallographically independent half-molecules in the asymmetric
unit, resulting in Z of 2. Full-matrix least-squares refinement
method against F2 values was carried out by using the
SHELXL-97 program.20b All non-hydrogen atoms were refined
with anisotropic displacement parameters. The H atoms except
N-H atoms (refined isotropically) were refined with fixed
geometry, riding on carbon atoms, with a fixed isotropic
displacement parameter equal to 1.2 or 1.5 (methyl group)
times the value of the equivalent isotropic displacement
parameter of the parent carbon. Difference Fourier maps
indicated disorder of ethyl groups in both independent mol-
ecules. Final results with R ) 0.0565 were obtained with a
restraint model in which atoms of the ethyl groups were
disordered over two sets of positions with adjusted occupancy
factors (the final SOF values being in the range 0.65(4)-0.81-
(2) for major conformers) and restraining chemically equivalent
Al-C and C-C distances to be equal. Refinement of positional
and thermal parameters led to convergence. The final weight-
ing scheme for 4b was w-1 ) σ2(Fo2) + (0.0586P)2, where P )
a CCD detector. Intensities of 28 968 reflections were corrected
for Lorentz and polarization effects, and an empirical absorp-
tion correction was applied. The structure was solved by direct
methods and refined by using the full-matrix least-squares
method on F2.20 All of the non-hydrogen atoms were refined
with anisotropic thermal parameters. The amine hydrogens
were located from the difference Fourier map and isotropically
refined. The hydrogen atoms of the methyl groups, bonded to
the aluminum atom Al(2), were refined as a disordered group
with two positions rotated by 60° about the Al-C vector. The
remaining H atoms were introduced at geometrically idealized
coordinates. Final weighting scheme: w-1 ) σ2(Fo ) + (0.0768P)2,
2
2
where P ) (Fo + 2Fc2)/3. The largest positive and negative
peaks on the difference Fourier map have no significant
chemical meaning, and the maximum shift/error ratios in the
final cycle of refinement were less than 0.001.
Ack n ow led gm en t. We thank Prof. Andrew R. Bar-
ron (Rice University) for very helpful discussions.
Financial support for this work is provided by the State
Committee for Scientific Research (Grant No. 3 T09A
066 19).
Su p p or tin g In for m a tion Ava ila ble: Full details of the
X-ray structural analysis of 4b and 7 including complete tables
of crystal data, atomic coordinates, bond lengths and angles,
and positional and anisotropic thermal parameters. This
material is available free of charge via the Internet at
http://pubs.acs.org.
2
(Fo + 2Fc2)/3.
Diffraction measurements of compound 7 were made on a
KM4 goniometer (Kuma/Oxford Instruments) equipped with
(20) (a) Sheldrick, G. M. SHELXS-86. Acta Crystallogr., Sect. A
1990, 46, 467. (b) Sheldrick, G. M. SHELXL-97, Program for the
Refinement of Crystal Structures; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
OM030484I