Aluminium and gallium compounds of salicylic and anthranilic acids: Examples of weak intra-molecular hydrogen bonding

Article abstract of DOI:10.1039/b008858g

Reaction of M(^tBu)₃ with anthranilic, salicylic and ortho-toluic acids yields [(^tBu)₂M(μ-O₂CC₆ H₄-2-NH₂)]₂, M = Al (1), Ga (2), [(^tBu)₂Ga(μ-O₂CC₆ H₄-2-OH)]₂ (3), and [(^tBu)₂Ga(μ-O₂CC₆ H₄-2-Me)]₂ (4), respectively. Reaction of anthranilic acid with two equivalents of Al(^tBu)₃ allows for the isolation of (^tBu)₂Al(μ-O₂CC₆ H₄-2-NH₂)Al(^tBu)₃ (5). Compounds 1-5 have been characterized by NMR and IR spectroscopy, mass spectrometry, and X-ray crystallography. The presence of intra-molecular hydrogen bonding, in compounds 1-3, is probed by the orientation of the aromatic rings. Compound 5 is proposed to be a Lewis acid stabilized complex of the intermediate in the synthesis of compound 1.

Full text of DOI:10.1039/b008858g

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Aluminium and gallium compounds of salicylic and anthranilic
acids: examples of weak intra-molecular hydrogen bonding
Catherine S. Branch,a Janusz Lewinski,*b Iwona Justyniak,b Simon G. Bott,c Janusz Lipkowskid
and Andrew R. Barron*a
a Department of Chemistry, Rice University, Houston, Texas 77005, USA.
E-mail: arb@rice.edu
b Department of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664
Warsaw, Poland. E-mail: lewin@ch.pw.edu.pl
c Department of Chemistry, University of Houston, Houston, Texas 77204, USA
d Institute of Physical Chemistry of the Polish Academy of Sciences, Kasparzaka 44/52,
01-224 Warsaw, Poland
Received 1st November 2000, Accepted 8th February 2001
First published as an Advance Article on the web 30th March 2001
Reaction of M(tBu)3 with anthranilic, salicylic and ortho-toluic acids yields [(tBu)2M(µ-O2CC6H4-2-NH2)]2, M = Al
(1), Ga (2), [(tBu)2Ga(µ-O2CC6H4-2-OH)]2 (3), and [(tBu)2Ga(µ-O2CC6H4-2-Me)]2 (4), respectively. Reaction of
anthranilic acid with two equivalents of Al(tBu)3 allows for the isolation of (tBu)2Al(µ-O2CC6H4-2-NH2)Al(tBu)3
(5). Compounds 1–5 have been characterized by NMR and IR spectroscopy, mass spectrometry, and X-ray
crystallography. The presence of intra-molecular hydrogen bonding, in compounds 1–3, is probed by the orientation
of the aromatic rings. Compound 5 is proposed to be a Lewis acid stabilized complex of the intermediate in the
synthesis of compound 1.
V, due to the reaction of the hydroxide with additional
Introduction
aluminium alkyl.5,6 We now report the synthesis and charac-
We have recently become interested in the presence of strong
terization of the sterically more demanding tert-butyl
aluminium and gallium derivatives.
intra-molecular hydrogen bonding of alcohol-amines (I) and
diamines (II) upon coordination to a Group 13 Lewis acid.1
The increase in the hydrogen bond strength in comparison to
the “free” compounds is due to a dramatic increase in the
acidity of the alcohol or amine proton. We have used this
“enhanced” hydrogen bonding strength to create compounds
possessing desirable crystallographic architectures.2
Based on these results we are interested in determining if
hydrogen bonding strength may be increased through activation
Results and discussion
The reaction of M(tBu)3 (M = Al, Ga) with one molar equiva-
of the Lewis base termini of the hydrogen bond (i.e.,
lent of the ortho-substituted carboxylic acids, HO2CC6H4-2-X,
X–H ؒ ؒ ؒ XЈ), rather than the Brønsted acidic termini (i.e.,
yields the dimeric carboxylates, [(tBu)2M(µ-O2CC6H4-2-X)]2, in
X–H ؒ ؒ ؒ XЈ). In this regard, salicylic acid (III) and anthranilic
moderate to high yield, where X = NH2, M = Al (1), Ga (2) and
acid (IV), both of which have intra-molecular hydrogen bonds
in the solid state,3,4 should offer a suitable system of study.
X = OH, Ga (3). Attempts to prepare the aluminium analog of
compound 3 were unsuccessful, resulting in a complex mixture
of products.
Compounds 1–3 have been characterized by IR and NMR
spectroscopy (see Experimental section) and the spectra are
consistent with the solid state structures as determined by X-ray
crystallography. The molecular structures of compounds 2 and
3 are shown in Figs. 1 and 2, respectively; compound 1 is
isostructural to compound 2. Selected bond lengths and angles
for compounds 1–3 are given in Table 1.
The structures of compounds 1–3 consist of centro-
symmetric dimers of two (tBu)2M units bridged by two
carboxylate groups. This is consistent with previous reports of
We have previously reported that the reaction of salicylic acid
with AlR3 (R = Me, Et) yields the tetra-aluminium compound,
DOI: 10.1039/b008858g
J. Chem. Soc., Dalton Trans., 2001, 1253–1258
This journal is © The Royal Society of Chemistry 2001
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Table
1
Selected bond lengths (Å) and angles (Њ) in [(tBu)2-
M(µ-O2CC6H4-2-X)]2
M
X
Al
NH2
(1)
Ga
NH2
(2)
Ga
OH
(3)
Ga
Me
(4)
M(1)–O(1)
M(1)–O(2Ј)
M(1)–C(11)
M(1)–C(21)
O(1)–C(1)
O(2)–C(1)
1.801(2)
1.817(2)
1.991(3)
1.977(3)
1.261(3)
1.268(3)
1.946(3)
1.941(3)
1.988(5)
1.972(5)
1.262(5)
1.255(5)
1.963(3)
1.938(3)
1.975(4)
1.968(4)
1.253(5)
1.244(4)
1.966(2)
1.954(2)
1.987(3)
1.988(3)
1.262(3)
1.256(3)
O(1)–M(1)–O(2Ј)
O(1)–M(1)–C(11)
O(1)–M(1)–C(21)
O(2Ј)–M(1)–C(11)
O(2Ј)–M(1)–C(21)
C(11)–M(1)–C(21)
109.4(1)
105.6(1)
107.2(1)
104.0(1)
106.0(1)
124.0(1)
107.5(2)
102.1(2)
106.8(2)
101.8(2)
106.8(2)
130.3(2)
105.2(1)
102.3(2)
105.0(2)
102.6(2)
107.5(2)
131.7(2)
102.6(1)
102.6(1)
109.0(1)
103.0(1)
107.4(1)
129.3(1)
Fig. 1 Molecular structure of [(tBu)2Ga(µ-O2CC6H4-2-NH2)]2 (2).
Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
bound to carbon are omitted for clarity. Hydrogen bonding interactions
are denoted by a dashed line.
Fig.
3
Molecular structure of [(tBu)2Ga(µ-O2CC6H4-2-Me)]2 (4).
Thermal ellipsoids are shown at the 30% level, and hydrogen atoms are
omitted for clarity.
Fig. 2 Molecular structure of [(tBu)2Ga(µ-O2CC6H4-2-OH)]2 (3).
Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
bound to carbon are omitted for clarity. Hydrogen bonding interactions
are denoted by a dashed line.
near-planar geometry of the arene and carboxylate groups (e.g.,
the maximum deviation from planarity in salicylic acid is 0.028
Å3). Similarly, the phenyl substituents on the anthranilate and
salicylate ligands in compounds 1–3 are near coplanar with the
carboxylate moiety; O(1)–C(1)–C(2)–C(3) = 2.8Њ (1), 9.2Њ (2)
and 2.9Њ (3). We have previously reported the molecular struc-
tures of [(tBu)2M(µ-O2CPh)]2 in which the equivalent torsion
angles are 5.9Њ and 0.12Њ for M = Al8 and Ga,9 respectively.
Clearly, the presence of coplanarity within the anthranilate and
salicylate ligands is not in itself an indication of the presence of
intra-molecular hydrogen bonding and could be an artifact of
intra-molecular steric interactions.
In an effort to ascertain the magnitude of such steric effects
the molecular structure was determined for the ortho-toluic acid
derivative, [(tBu)2Ga(µ-O2CC6H4-2-Me)]2 (4), see Experimental
section and Table 1. As may be seen from Fig. 3, the aromatic
ring is twisted away from co-planarity with the carboxylate
group, i.e., O(1)–C(1)–C(2)–C(3) = 42.6Њ. Thus, if steric factors
were dominating in compounds 1–3, a similar twist would be
expected due to the comparable steric bulk of CH3, NH2 and
OH groups. The planarity of the anthranilate and salicylate
ligands is therefore a further indication that the orientations of
the ligands are due to intra-molecular hydrogen bonding.
The IR spectra for compounds 1 and 2, both in toluene solu-
tion and solid state, show the presence of two bands associated
with the amine’s νN–H stretch (e.g., Fig. 4a) consistent with
retention of N–H ؒ ؒ ؒ O bonding on IR time scale. However,
variable temperature solution 1H NMR show single broad
resonances [δ 5.02 (1) and 5.11 (2)], down to Ϫ115 ЊC, indicat-
alkylaluminium and alkylgallium carboxylates.7–10 The M–O
bond lengths to the carboxylate ligands in these dimeric systems
(Table 1) are within the range expected for aluminium
[1.767(7)–1.837(6) Å]8 and gallium [1.956(7)–1.967(8) Å] carb-
oxylates.8,9,10,11 The carboxylate’s O–C bond lengths in each
compound are similar [∆(O–C) ≈ 0.01 Å], indicative of a
symmetrically bound acid group that is unaffected by the
carboxylate organic substituents. The bond lengths and angles
within the carboxylate unit are typical of such moieties. The
ligand bite distances [M(1) ؒ ؒ ؒ M(1a) = 4.20 Å (1), 4.26 Å (2),
4.39 Å (3)] are comparable to the ranges previously observed for
alkylaluminium (3.26–4.18 Å)12,13 and alkylgallium (4.35–4.68
Å)10 carboxylates.
As may be seen from Figs. 1 and 2, the NH2 in 2 and OH in
3 are oriented such that a hydrogen bonding interaction is
possible with one of the carboxylate oxygens, O(1). The
N(3) ؒ ؒ ؒ O(1) distance in compounds 1 and 2 (2.73 and 2.72 Å,
respectively) are longer than observed in the free ligand
[2.688(4) and 2.682(7) Å4], but shorter than reported for N–
H ؒ ؒ ؒ O=C interactions (ca. 2.85 Å).14 The O(3) ؒ ؒ ؒ O(1)
distance in compound 3 (2.627 Å) is the same as in the free
ligand (2.620 Å).3 Thus, based upon these distances it appears
that although the intra-molecular H-bond remains intact, they
are not enhanced by the presence of the Group 13 metal as
compared to the free ligand.
It has been previously shown that the intra-molecular
hydrogen bonding in anthranilic and salicylic acids results in a
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Table 2 Selected bond lengths (Å) and angles (Њ) for (tBu)2Al-
(µ-O2CC6H4-2-NH2)Al(tBu)3 (5)
Al(1)–O(1)
Al(1)–C(11)
Al(2)–O(2)
Al(2)–C(41)
O(1)–C(1)
1.822(2)
1.960(4)
1.896(2)
2.005(4)
1.270(3)
Al(1)–N(1)
Al(1)–C(21)
Al(2)–C(31)
Al(2)–C(51)
O(2)–C(1)
2.003(3)
1.958(3)
2.021(3)
2.001(3)
1.250(3)
O(1)–Al(1)–N(1)
O(1)–Al(1)–C(21)
N(1)–Al(1)–C(21)
O(2)–Al(2)–C(31)
O(2)–Al(2)–C(51)
C(31)–Al(2)–C(51)
89.1(1)
108.9(1)
107.8(1)
98.3(1)
104.6(1)
114.9(2)
O(1)–Al(1)–C(11)
N(1)–Al(1)–C(11)
C(11)–Al(1)–C(21)
O(2)–Al(2)–C(41)
C(31)–Al(2)–C(41)
C(41)–Al(2)–C(51)
113.1(1)
108.6(1)
123.7(2)
106.0(1)
115.0(2)
115.4(2)
Fig. 4 IR spectra of [(tBu)2Ga(µ-O2CC6H4-2-NH2)]2 in toluene solu-
tion (a) and the solid state (b) showing the presence of discreet hydrogen
bonded and the non-hydrogen bonded N–H groups.
ing facile rotation about the C(3)–N(3) bond. Thus, we can
estimate that the lifetime of the intra-molecular N–H ؒ ؒ ؒ O
bonds in compounds 1 and 2 is between 10Ϫ5 and 10Ϫ12 s. In
addition, it is worth noting that in the solid state IR spectrum
of compound 2 solid state splitting of the νN–H resonances is
observed (see Fig. 4b) with a νL of 8 cmϪ1
.
The position of the O–H band in the IR spectra of com-
pound 3 (solid and solution) shows intra-molecular hydrogen
bonding to be present in both solid state (3298 cmϪ1) and
solution (3298 cmϪ1). The 1H NMR chemical shift of the O–H
peak is found to be temperature dependent, suggesting fluxion-
ality on the NMR time scale. However, no asymptote was
reached down to Ϫ115 ЊC.
Fig. 5 Molecular structure of (tBu)2Al(µ-O2CC6H4-2-NH2)Al(tBu)3
(5). Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
are omitted for clarity.
In conclusion, we have found that the intra-molecular
hydrogen bonds in the anthranilate and salicylate ligands
remain present in the Group 13 compounds. However, com-
plexation of a Group 13 metal to the donor (i.e., O–H ؒ ؒ ؒ X–
M; where X = N, O) does not appear to enhance the strength
of the hydrogen bond as it does when complexed to the
acceptor (i.e., M–O–H ؒ ؒ ؒ X). We note, however, that the
presence of hydrogen bonding in the anthranilate complex
[Me2In(O2CC6H4-2-NH2)]∞,15 leads to
a decrease in the
indium coordination number as compared to the acetate
complex.16
Reaction of Al(tBu)3 with anthranilic acid in a 2 : 1 ratio
yields the dialuminium compound, (tBu)2Al(µ-O2CC6H4-2-
NH2)Al(tBu)3 (5), see Experimental. The molecular structure of
compound 5 has been determined by X-ray crystallography
(Fig. 5); selected bond lengths and angles are given in Table 2.
The Al(2)–O(2) [1.896(2) Å] is slightly longer than Al(1)–O(1)
[1.822(2) Å] consistent with the difference in bonding to a
neutral Al(tBu)3 versus a cationic Al(tBu)2 moiety. The Al(1)–
N(1) distance [2.003(3) Å] is within the range expected for
amine complexes of aluminium (1.94–2.10 Å).17
Based upon the isolation of compound 5, and its conversion
to compound 1 during physical grinding (see Experimental
section), we propose that the formation of compounds 1 and
2 (and possibly 3) occurs via a chelate species, (tBu)2M(O2CC6-
H4-2-X) (VI).
The related chelate complexes VII18 and VIII19 have been
reported in which the VI-like structure is stabilized by an
extended hydrogen bond network rather than Lewis acid–base
interaction, as we observe in compound 5.
We have previously demonstrated that, although the chelate
binding (IX) of a carboxylate to aluminium (or gallium) is
highly disfavored (ca. 130 kJ molϪ1) as compared to bridging
(X), it is favored (ca. 75 kJ molϪ1) over the monodentate modes
[i.e., eclipsed and staggered (XI)].
In the present case, the Lewis base substituents (OH or NH2)
in the ortho position on the phenyl ring provide an alternative
stabilization to the monomeric derivatives. The stability of VI
will be dependent on the strength of the M–X interaction.
J. Chem. Soc., Dalton Trans., 2001, 1253–1258
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Based upon known Lewis acid–base bond strength for
aluminium alkyls, the interaction is expected to be ca. 80 kJ
molϪ1 for X = OH and ca. 125 kJ molϪ1 for X = NH2. The
greater stability of the anthranilate complex (VI where
X = NH2) presumably is such to allow VI to be “trapped” by the
presence of an excess of Al(tBu)3 and thus forming compound
5. In contrast, the similarity in stabilization for salicilate
between the chelate carboxylate (IX) and chelation via the
hydroxide (VI where X = OH), as well as the greater acidity of
the hydroxide, may explain the observation that a complex
mixture of products is obtained with the reaction of salicylic
acid with either an equimolar equivalent or excess of Al(tBu)3.
1.27 [36H, s, C(CH3)3]. 13C NMR: δ 179.7 (O2C), 151.3 (1-C),
135.3 (2-C), 133.3 (6-CH), 117.4 (4-CH), 116.8 (5-CH), 113.2
(3-CH), 30.3 (CH3), 25.0 [C(CH3)3].
[(tBu)2Ga(ꢀ-O2CC6H4-2-OH)]2 (3)
To a toluene (40 mL) solution of salicylic acid (1.12 g, 4.04
mmol) at Ϫ78 ЊC was added Ga(tBu)3 (1.95 g, 4.04 mmol). The
clear reaction mixture was allowed to warm to room temper-
ature and then to stir for three hours. The solution was filtered
and placed in a freezer, yielding colorless crystals. Yield: 50%.
Mp: 150 ЊC (decomp.). Anal. (%, calc.): C, 55.6 (56.1); H, 6.96
(7.22). MS (EI): m/z 320 (Mϩ, 10), 263 (Mϩ Ϫ tBu, 38), 206
(Mϩ Ϫ 2 tBu, 10), 189 [Ga(O2CC6H4), 72], 69 (Ga, 28), 57 (tBu,
100). IR (cmϪ1): 3324 (w), 3180 (w), 3078 (w), 1613 (s), 1567
(w), 1526 (w), 1398 (s), 1250 (s), 1165 (w), 1147 (m), 1034 (w),
896 (w), 866 (w), 850 (w), 825 (w), 758 (m), 712 (w), 681 (w), 543
Experimental
Mass spectra were obtained on a Finnigan MAT 95 mass
spectrometer operating with an electron beam energy of 70 eV
for EI mass spectra. IR spectra (4000–400 cmϪ1) were obtained
using an Nicolet 760 FT-IR infrared spectrometer. IR samples
were prepared as either Nujol mulls between KBr plates or
toluene solution (0.1 mM). Due to the partial conversion of
compound 5 to compound 1 upon mechanical grinding
required for KBr sample preparation, the IR spectrum of
compound 5 was determined by a computer subtraction of a
reference spectrum of compound 1. NMR spectra were
obtained on Bruker AM-250 and Avance 400 spectrometers
using d8-toluene solutions. Chemical shifts are reported relative
to internal solvent resonances. The synthesis of Al(tBu)3 and
Ga(tBu)3 were performed according to literature methods.20,21
Salicylic and anthranilic acids were obtained from Aldrich and
used without further purification.
1
(s). H NMR: δ 10.26 (2H, s, OH), 8.04 [2H, d, J(H–H) = 6.6
Hz, 6-CH], 7.03 [2H, t, J(H–H) = 8.4 Hz, 4-CH], 6.90 [2H, d,
J(H–H) = 8.2 Hz, 3-CH], 6.60 [2H, t, J(H–H) = 6.5 Hz, 5-CH],
1.19 [36H, s, C(CH3)3]. 13C NMR: δ 178.2 (O2C), 168.3 (1-C),
138.0 (2-C), 133.5 (6-CH), 123.1 (4-CH), 118.1 (3-CH), 112.9
(5-CH), 24.8 [C(CH3)3], 21.0 [C(CH3)3].
[(tBu)2Ga(ꢀ-O2CC6H4-2-Me)]2 (4)
To a hexane (30 mL) slurry of o-toluic acid (0.565 g, 4.15 mmol)
at Ϫ78 ЊC was added Ga(tBu)3 (1.0 g, 4.15 mmol). The clear
reaction mixture was allowed to warm to room temperature
and then to stir for three hours. The solution was filtered and
placed in a freezer, yielding colorless crystals. Yield: 75%. Mp:
160 ЊC. Anal. (%, calc.): C, 60.2 (60.2); H, 7.69 (7.90). MS
t
(EI,%): m/z 205 (Mϩ Ϫ 2 Bu ϩ H, 30), 91 (C6H4Me, 10), 69
[(tBu)2Al(ꢀ-O2CC6H4-2-NH2)]2 (1)
(Ga, 40), 57 (tBu, 100). IR (cmϪ1): 3336 (w), 3168 (w), 3075 (w),
2730 (w), 2350 (w), 1605 (w), 1585 (m), 1561 (m), 1457 (s), 1413
(m), 1373 (m), 1299 (w), 1166 (w), 1102 (w), 1018 (w), 939 (w),
To a toluene (40 mL) slurry of anthranilic acid (0.693 g, 5.05
mmol) at Ϫ78 ЊC was added Al(tBu)3 (1.0 g, 5.05 mmol). The
yellow reaction mixture was allowed to warm to room temper-
ature and then to stir for three hours. The solution was filtered
and placed in a freezer, yielding yellow crystals. Yield: 70%.
Mp: 170 ЊC (decomp.). Anal. (%, calc.): C, 64.9 (64.9); H, 8.58
(8.72); N, 4.29 (5.05). MS (EI,%): m/z 497 (2Mϩ Ϫ tBu, 35), 439
(2Mϩ Ϫ 2 tBu Ϫ H, 52), 277 (Mϩ, 10), 220 (Mϩ Ϫ tBu, 35), 120
(O2CC6H4, 30). IR (cmϪ1): 3513 (w), 3411 (w), 1629 (m), 1577
(m), 1545 (m), 1419 (w), 1301 (w), 1163 (w), 1010 (w), 973 (w),
1
855 (w), 821 (w), 747 (w), 668 (w). H NMR: δ 8.27 [2H, dd,
J(H–H) = 7.6 Hz, J(H–H) = 1.5 Hz, 6-CH], 7.03 [2H, ddd,
J(H–H) = 7.4 Hz, J(H–H) = 7.4 Hz, J(H–H) = 1.6 Hz, 4-CH],
6.98 [2H, ddd, J(H–H) = 7.6 Hz, J(H–H) = 7.4 Hz, J(H–H) =
1.7 Hz, 5-CH], 6.91 [2H, dd, J(H–H) = 7.4 Hz, J(H–H) = 0.9
Hz, 3-CH], 2.67 (6H, s, CH3), 1.26 [36H, s, C(CH3)3]. 13C
NMR: δ 179.7 (O2C), 140.6 (2-C), 132.9 (4-CH), 132.4 (1-C),
132.1 (6-CH), 128.0 (3-CH), 126.2 (5-CH), 30.2 [C(CH3)3],
24.9[C(CH3)3], 23.2 (CH3).
1
722 (w), 543 (s). H NMR: δ 8.19 [2H, dd, J(H–H) = 9.1 Hz,
J(H–H) = 1.7 Hz, 6-CH], 6.92 [2H, ddd, J(H–H) = 8.4 Hz,
J(H–H) = 7.2 Hz, J(H–H) = 1.5 Hz, 4-CH], 6.44 [2H, ddd,
J(H–H) = 8.2 Hz, J(H–H) = 7.0 Hz, J(H–H) = 1.1 Hz, 5-CH],
6.03 [2H, dd, J(H–H) = 8.6 Hz, J(H–H) = 0.9 Hz, 3-CH], 5.02
(2H, s, NH2), 1.20 [36H, s, C(CH3)3]. 13C NMR: δ 175.4 (O2C),
152.5 (1-C), 133.6 (2-C), 121.5 (6-CH), 117.8 (4-CH), 117.2
(5-CH), 109.8 (3-CH), 30.3 [C(CH3)3].
(tBu)2Al(ꢀ-O2CC6H4-2-NH2)Al(tBu)3 (5)
To a toluene (40 mL) solution of anthranilic acid (0.277 g, 2.0
mmol) at Ϫ78 ЊC was added Al(tBu)3 (0.8 g, 4.0 mmol). The
orange reaction mixture was allowed to warm to room tempera-
ture and then to stir for three hours. The solution was filtered
and placed in a freezer, yielding yellow crystals. Mechanical
grinding of a sample resulted in its slow conversion to
[(tBu)2Ga(ꢀ-O2CC6H4-2-NH2)]2 (2)
compound 1 and Al(tBu)3 as confirmed by H NMR spectro-
1
scopy. Yield: 65%. Mp: 80 ЊC. MS (EI): m/z 475 (Mϩ, 35), 418
To a toluene (40 mL) solution of anthranilic acid (1.93 g, 7.03
mmol) at Ϫ78 ЊC was added Ga(tBu)3 (3.40 g, 7.03 mmol). The
bright yellow reaction mixture was allowed to warm to room
temperature and then to stir for three hours. The solution was
filtered and placed in a freezer, yielding yellow crystals. Yield:
60%. Mp: 243 ЊC (decomp.). Anal. (%, calc.): C, 55.8 (56.3); H,
7.53 (7.56); N, 3.67 (4.38). MS (EI): m/z 319 (Mϩ, 10), 262
(Mϩ Ϫ tBu, 50), 205 (Mϩ Ϫ 2 tBu, 12), 120 (O2CC6H4, 100), 92
(C6H4NH2, 15), 69 (Ga, 25), 57 (tBu, 85). IR (cmϪ1): 3509 (m),
3492 (m), 3398 (m), 3383 (m), 1623 (s), 1580 (s), 1536 (s), 1305
t
(Mϩ Ϫ tBu, 55), 361 (Mϩ Ϫ 2 Bu, 100), 277 [Mϩ Ϫ Al(tBu)3,
10]. IR (cmϪ1): 3513 (w), 3416 (w), 2724 (w), 2366 (w), 2325 (w),
1629 (m), 1577 (m), 1552 (m), 1470 (s), 1413 (m), 1378 (s), 1306
(m), 1255 (m), 1163 (w), 825 (w), 753 (w), 676 (w). H NMR:
1
δ 8.33 (1H, m, 3-CH), 6.64 (2H, m, 6-CH and 4-CH), 5.61 (1H,
m, 5-CH), 1.60 [27H, s, C(CH3)3], 0.84 [18H, s, C(CH3)3]. 13C
NMR: δ 170.2 (O2C), 135.8 (1-C), 134.9 (2-C), 134.6 (4-CH),
133.9 (6-CH), 126.2 (3-CH), 124.4 (5-CH), 34.0 [C(CH3)3], 30.8
[C(CH3)3] 29.8 [C(CH3)3], 24.9 [C(CH3)3].
1
(s), 1255 (s), 1163 (m), 1020 (w), 985 (w), 825 (w), 499 (s). H
Crystallographic studies
NMR:
δ 8.25 [2H, dd, J(H–H) = 8.1 Hz, J(H–H) = 1.5
Hz, 6-CH], 6.99 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) = 6.9
Hz, J(H–H) = 1.6 Hz, 4-CH], 6.54 [2H, ddd, J(H–H) = 8.1 Hz,
J(H–H) = 7.1 Hz, J(H–H) = 1.0 Hz, 5-CH], 6.15 [2H, dd,
J(H–H) = 8.3 Hz, J(H–H) = 0.7 Hz, 3-CH], 5.11 (4H, s, NH2),
Crystals of all compounds were sealed in glass capillaries
under argon.
The cell determination and intensity data for compound 1
were performed using a NONIUS KappaCCD system. The
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J. Chem. Soc., Dalton Trans., 2001, 1253–1258

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Table 3 Summary of X-ray diffraction data
[(tBu)2Al(µ-O2CC6H4- [(tBu)2Ga(µ-O2CC6H4- [(tBu)2Ga(µ-O2CC6H4- [(tBu)2Ga(µ-O2CC6H4- (tBu)2Al(µ-O2CC6H4-2-
Compound
2-NH2)]2 (1)
2-NH2)]2 (2)
2-OH)]2 (3)
2-Me)]2 (4)
NH2)Al(tBu)3 (5)
Empirical formula
Formula weight
C30H48Al2N2O4
554.68
C30H48Ga2N2O4
640.17
C30H46Ga2O6
642.14
C32H50Ga2O4
638.19
C34H59Al2NO2
567.81
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
Triclinic
P1
Monoclinic
P21/n
¯
a/Å
b/Å
c/Å
α/Њ
9.411(2)
16.601(3)
10.923(2)
8.927(2)
12.645(3)
14.662(3)
8.984(2)
17.028(3)
11.064(2)
8.601(2)
10.433(2)
11.225(2)
101.40(3)
110.76(3)
108.61(3)
835.9(3)
1
9.008(2)
19.590(4)
21.077(4)
β/Њ
106.58(3)
101.17(3)
103.35(3)
93.33(3)
γ/Њ
V/Å3
1635.6(5)
2
1.22
1623.7(6)
2
1.693
1646.8(6)
2
1.67
3713.0(1)
4
1.10
Z
µ/cmϪ1
1.64
T/K
293
298
7171
2321
298
7307
2372
298
3821
2392
298
16880
5321
3006 (|Fo| > 6.0σ|Fo|)
0.10, 0
No. collected
No. independent
No. observed
Weighting scheme
(SHELXTL)
R
7257
3717
3717
1833 (|Fo| > 4.0σ|Fo|)
0.1017, 0.0834
1806 (|Fo| > 6.0σ|Fo|)
0.067, 0
2194 (|Fo| > 6.0σ|Fo|)
0.0625, 0
0.0816
0.2280
0.78
0.0496
0.136
1.80
0.0397
0.1032
0.50
0.0348
0.0918
0.87
0.0591
0.1496
0.24
Rw
Largest difference
peak/e ÅϪ3
structure was solved by direct methods22 and refined by full-
matrix least squares on F2.22 Hydrogen atoms were added at the
final steps of refinement as ‘riding’ on the respective carbon
atoms. The amine hydrogens were ignored. A relatively high
residual electron density maximum (ca. 2 e ÅϪ3) was found at
the position which suggested some orientational disorder of the
aromatic ring around the C(9)–C(10) bond. Introducing two
‘half nitrogen’ atoms at the two possible positions, i.e. at
C(15) and C(11), led to site occupation factors 0.654 and
0.346(6) respectively. This model was used in the final cycles
of refinement; the hydrogens at the nitrogen atom in the two
positions being ignored.
Data for compounds 2–5 were collected on a Bruker CCD
SMART system, equipped with graphite monochromated
Mo-Kα radiation (λ = 0.71073 Å) and corrected for Lorentz
and polarization effects. The structures were solved using the
direct methods program XS22 and difference Fourier maps and
refined by using full-matrix least squares method.22 Disorder
and/or high thermal motion were noted, usually associated with
the tert-butyl groups. Of particular note were the observations
of two positions each for the methyl carbons [C(16)–C(18)] of a
tert-butyl group in compound 3 (in a 1 : 1 ratio). A peak of
unassigned electron density was noted close to the aromatic
ring but no rational disodered model could be developed. The
toluene of solvation in compound 5 was disordered in a 1 : 1
ratio. The best model that could be developed was one in which
both possible sites shared one carbon atom and are related by a
small rotation about that atom to present a “V” shaped appear-
ance. The carbon atoms adjacent to the common carbon could
not be resolved into two peaks. All other carbons were so
resolved and refined. All non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms involved in
hydrogen bonding were found, but not refined. Remaining
hydrogen atoms were placed in calculated positions [Uiso = 0.08;
d(C–H) = 0.96 Å] for refinement. Refinement of positional
and anisotropic thermal parameters led to convergence (see
Table 3).
System Diffractometer was funded by the Robert A. Welch
Foundation and the Bruker Avance 400 NMR spectrometer
was provided by Halliburton Energy Services, Inc.
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Acknowledgements
Financial support for this work is provided by the Robert A.
Welch Foundation and the Polish State Committee for
Scientific Research (504/M/1020/0607). The Bruker CCD Smart
J. Chem. Soc., Dalton Trans., 2001, 1253–1258
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J. Chem. Soc., Dalton Trans., 2001, 1253–1258