Reactions of amides with organoaluminium: A useful synthetic route to aluminium diketiminates

Article abstract of DOI:10.1039/b009070k

The reaction of N-tert-butylbenzamide (^tBuNHCOPh) with 1.1 molar equivalents of Me₃Al in refluxing hexane afforded a five-coordinated dimeric compound [Me₂Al{η²-^tBuNC(Ph) (μ-O)}]₂ 1, whereas 2.2 molar equivalents yielded a monomeric compound [Me₂Al{η²-^tBuNCPh(μ-O)} AlMe₃] 2. Reaction of PhCONHAr with 1 molar equivalent of Me₃Al in toluene at 25°C, gave four-coordinated dimeric eight-membered ring compounds [Me₂-Al{μ-η²-(p-XC₆H₄) NC(Ph)O}]₂ (X = OMe 3 or 4). Benzanilide (PhNHCOPh) with 1.2 molar equivalents of Me₃Al in refluxing toluene resulted in aluminium amidate 4 and a trace amount of an aluminium diketiminate, [Me₂Al-{η²-PhNC(Ph)C(H)C(Ph)NPh}] 5. Furthermore, PhCONHC₆H₄X-p reacts with 2 molar equivalents of R₃Al in refluxing toluene affording aluminium diketiminate compounds, [R₂Al{η²-(p-XC₆H₄)NC(Ph) C(R′)C(Ph)-N(p-XC₆H₄)}] (R = Et, R′ = Me, X = H 6; R = Et, R′ = Me, X = Cl 7; R = Me, R′ = H, X = Cl 8; R = Me, R′ = H, X = Me 9; R = Et, R′ = Me, X = Me 10). Thus, this process offers a readily available synthetic route to the preparation of aluminium diketiminates which is otherwise difficult with aromatic substituents.

Full text of DOI:10.1039/b009070k

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Reactions of amides with organoaluminium: a useful synthetic
route to aluminium diketiminates†
Yi-Lun Huang, Bor-Hunn Huang, Bao-Tsan Ko and Chu-Chieh Lin*
Department of Chemistry, National Chung-Hsing University, Taichung 402, Taiwan,
Republic of China
Received 13th November 2000, Accepted 14th February 2001
First published as an Advance Article on the web 27th March 2001
The reaction of N-tert-butylbenzamide (tBuNHCOPh) with 1.1 molar equivalents of Me3Al in refluxing hexane
afforded a five-coordinated dimeric compound [Me2Al{η2-tBuNC(Ph)(µ-O)}]2 1, whereas 2.2 molar equivalents
yielded a monomeric compound [Me2Al{η2-tBuNCPh(µ-O)}AlMe3] 2. Reaction of PhCONHAr with 1 molar
equivalent of Me3Al in toluene at 25 ЊC, gave four-coordinated dimeric eight-membered ring compounds [Me2-
Al{µ-η2-(p-XC6H4)NC(Ph)O}]2 (X = OMe 3 or 4). Benzanilide (PhNHCOPh) with 1.2 molar equivalents of Me3Al
in refluxing toluene resulted in aluminium amidate 4 and a trace amount of an aluminium diketiminate, [Me2Al-
{η2-PhNC(Ph)C(H)C(Ph)NPh}] 5. Furthermore, PhCONHC6H4X-p reacts with 2 molar equivalents of R3Al in
refluxing toluene affording aluminium diketiminate compounds, [R2Al{η2-(p-XC6H4)NC(Ph)C(RЈ)C(Ph)-
N(p-XC6H4)}] (R = Et, RЈ = Me, X = H 6; R = Et, RЈ = Me, X = Cl 7; R = Me, RЈ = H, X = Cl 8; R = Me, RЈ = H,
X = Me 9; R = Et, RЈ = Me, X = Me 10). Thus, this process offers a readily available synthetic route to the preparation
of aluminium diketiminates which is otherwise difficult with aromatic substituents.
because they serve as precursors for cationic aluminium
Introduction
complexes.8 Cationic aluminium diketiminates have demon-
The reactions between aldehydes, ketones, carboxylic acids or
amidines and trialkylaluminium compounds which yield
strated enhanced activities in olefin polymerization.9 Several
methods are available for the preparation of diketimines,10 but
products of alkyl addition and further enolization have been
their synthesis is still of interest due to their utility in the
extensively studied.1 However, reports on the reactions of
preparation of versatile compounds, such as N-heterocycles,
amides with trialkylaluminium compounds are scant, despite
β-aminoalcohols, and diketones.11 In this paper we discuss the
amidato groups being common ligands in transition metal
role of the Lewis basicity of amides affecting the coordination
mode of the amidato ligand on aluminium and report a useful
synthetic route to aluminium diketiminates via reactions of
amides with trialkylaluminium compounds and, in turn, to
coordination chemistry.2 For an amidato group coordinated to
aluminium there are several coordination modes possible as
shown in Chart 1. The first organoaluminium amidates,
[Me2Al(RNC(O)RЈ)]2, have independently been reported by
diketimines.
Wade3 and Lappert and co-workers4 as dinuclear complexes
that possess an eight-membered ring with the mode VI based
on spectroscopic studies. The coordination mode for [Me2Al-
(PhNC(O)Ph)]2 has been confirmed by Kakudo and co-
workers5 using X-ray crystallography. However, [Me2Al(PhN-
C(O)Ph)(ONMe3)] is a monomer in which the amidato and
ONMe3 groups are both coordinated to the aluminium atom
through oxygen atoms.6 More recently, Barron and co-workers7
reported the monomeric feature of [(BHT)2Al(MeNCOPh)]
(BHT-H = 2,6-di-tert-butyl-4-methylphenol) according to 27Al
NMR and other spectroscopic studies.
Results and discussion
Syntheses and spectroscopic studies
The reaction of N-tert-butylbenzamide (tBuNHCOPh) with 1.1
molar equivalents of Me3Al in refluxing hexane afforded a
five-coordinated, dimeric compound [Me2Al{η2-tBuNC(Ph)-
(µ-O)}]2 1 which further reacted with another equivalent of
Me3Al to give a monomeric product [Me2Al{η2-tBuNC(Ph)-
(µ-O)}AlMe3] 2 as shown in Scheme 1. Compound 2 can also be
prepared directly in high yield by the reaction of PhCONHBut
with 2.2 molar equivalents of Me3Al in refluxing hexane. The
yield of 1 as determined by NMR spectroscopy was above 80%,
however, due to the similar solubility of 1 and 2, the isolated
yield was only 50% and the microanalysis of 1 was incorrect. In
contrast, the reaction of PhCONHAr with 1 molar equivalent
of Me3Al at room temperature afforded four-coordinate,
Aluminium diketiminates, which are usually prepared by
reactions of diketimines with R3Al, are currently interesting
† Electronic supplementary information (ESI) available: 1H NMR
spectra of reactions of compound 4 with Me3Al, schemes showing reac-
tions of amides with R3Al. See http://www.rsc.org/suppdata/dt/b0/
b009070k/
Chart 1 Several possible coordination modes of amidate ligands on aluminium.
DOI: 10.1039/b009070k
J. Chem. Soc., Dalton Trans., 2001, 1359–1365
This journal is © The Royal Society of Chemistry 2001
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dimeric eight-membered ring aluminium compounds [Me2-
Al{µ-η2-ArNC(Ph)O}]2 (Ar = 4-MeO-C6H4 3 or Ph 43–5) as
shown in Scheme 2. All of these compounds have been charac-
terized by spectroscopic studies as well as elemental analyses.
The structures have been verified by X-ray diffraction studies of
compounds 1, 2 and 3. It seems that the coordination modes of
aluminium amidates are dependent on the amides.
diketiminates and their aluminium amidate precursors, the
isolated yields were low. Hydrolysis of the aluminium
diketiminate 8, followed by extraction with diethyl ether, gave
the corresponding diketimine in 93% yield. This procedure
offers a useful synthetic route to aluminium diketiminate
derivatives containing aromatic substituents that are important
precursors for the preparation of β-diketimines12 and of
cationic aluminium complexes that have potential applications
as catalysts for the polymerization of ethylene.
It is interesting that the reaction of benzanilide (PhNHC-
(Ph)O) with 1.2 molar equivalents of Me3Al in refluxing tolu-
ene resulted in formation of a four-coordinate, dimeric com-
pound [Me2Al{µ-η2-PhNC(Ph)O}]2 4 and a trace amount of an
aluminium diketiminate, [Me2Al{η2-PhNC(Ph)C(H)C(Ph)-
NPh}] 5. However, in the presence of 2.4 molar equivalents of
Me3Al, benzanilide in refluxing toluene yields 80% 5. Com-
pound 5 can also be prepared from the reaction of 4 with 2.2
molar equivalents of Me3Al in refluxing toluene. The formation
of aluminium diketiminate 5 prompted us to further investigate
similar types of reactions in order to determine (1) the reactiv-
ity of R3Al in general, (2) the source of the methine carbon
atom and (3) the possible mechanism for formation of the alu-
minium diketiminate 5. For this purpose, several reactions have
been examined. Reactions of PhCONHC6H4X-p with 2 molar
equivalents of R3Al in refluxing toluene afforded aluminium
diketiminate compounds, [R2Al{η2-(p-XC6H4)NC(Ph)C(RЈ)-
C(Ph)N(p-XC6H4)}] (R = Et, RЈ = Me, X = H 6; R = Et,
RЈ = Me, X = Cl 7; R = Me, RЈ = H, X = Cl 8; R = Me, RЈ = H,
X = Me 9; R = Et, RЈ = Me, X = Me 10) (Scheme 3). The yields
as determined by NMR spectroscopy were above 85% for com-
pounds 5–10 and the isolated yields of 5–7 were also good. In
the case of 8–10 due to similar solubilities of the aluminium
We found that in the absence of Me3Al not even a trace of
compound 5 was detected on refluxing 4 in toluene for 24 h.
However, in the presence of 2.2 molar equivalents of Me3Al, 5
could be obtained easily in 85% yield when 4 was heated in
refluxing toluene for 16 h. This suggests the possibility that the
methine carbon of the diketiminate fragment is derived from
the methyl group of the Me3Al present. In addition, in the reac-
tion of 4 with 3 molar equivalents of Et3Al in refluxing toluene
a mixture of 5 and 6 with a ratio of 1 : 11 was obtained as
1
determined by H NMR spectroscopic studies. Based on these
observations, we propose that the formation of aluminium
diketiminate, 5, is initiated by the dealkylation of the alu-
minium amido complex leading to aluminium amidate complex
A as illustrated in Scheme 4. A then dimerizes rapidly to 4
which is stable in the absence of Me3Al. In the presence of
an excess of Me3Al coordination of 4 with Me3Al occurs
forming the intermediate B. Methylation of the amide and
further enolization of the imine gives C and D as inter-
mediates. Proton abstraction and intramolecular rearrange-
ment, result in the final product 5. The formation of B from 4
can be further verified by 1H NMR studies of the reaction of 4
with Me3Al.
1H NMR studies of the reaction between Me3Al and compound 4
The reaction of compound 4 with 3 molar equivalents of
Scheme 1
Scheme 2
Scheme 3
Scheme 4
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Table 1 Selected bond lengths (Å) and angles (Њ) for compound 1
Al–O
Al–C(12)
Al–N
O–C(1)
N–C(1)
1.9096(17)
1.955(3)
2.157(2)
1.338(3)
1.276(3)
Al–C(13)
Al–O(0a)
Al–C(1)
O–Al(a)
N–C(8)
1.947(3)
2.0019(18)
2.484(2)
2.0019(18)
1.475(3)
O–Al–C(13)
C(13)–Al–C(12)
C(13)–Al–O(0a)
O–Al–N
C(12)–Al–N
O–Al–C(1)
C(12)–Al–C(1)
N–Al–C(1)
C(1)–O–Al(a)
C(1)–N–C(8)
C(8)–N–Al
119.13(11)
123.51(13)
99.62(11)
63.14(7)
101.03(11)
32.23(8)
112.27(11)
30.91(7)
154.52(15)
128.8(2)
O–Al–C(12)
O–Al–O(0a)
C(12)–Al–O(0a)
C(13)–Al–N
O(0a)–Al–N
C(13)–Al–C(1)
O(0a)–Al–C(1)
C(1)–O–Al
117.26(12)
72.75(7)
99.50(11)
100.79(11)
135.89(7)
113.04(10)
104.98(7)
98.22(14)
107.25(7)
88.83(14)
109.81(19)
116.8(2)
Al–O–Al(a)
C(1)–N–Al
N–C(1)–O
142.29(16)
133.4(2)
N–C(1)–C(2)
O–C(1)–C(2)
Table 2 Selected bond lengths (Å) and angles (Њ) for compound 2
Fig. 1 Molecular structure of compound 1, 20% ellipsoids and all
hydrogens omitted for clarity as in all cases shown.
Al(1)–C(1)
Al(1)–C(2)
Al(2)–O
1.915(4)
1.931(3)
1.9366(16)
1.950(3)
1.354(3)
1.498(3)
Al(1)–O
Al(1)–N
Al(2)–C(4)
Al(2)–C(3)
N–C(6)
1.9172(16)
1.949(2)
1.950(3)
1.973(3)
1.279(3)
1.476(3)
Al(2)–C(5)
O–C(6)
N–C(13)
C(6)–C(7)
C(1)–Al(1)–O
O–Al(1)–C(2)
O–Al(1)–N
114.10(16)
112.11(13)
67.63(7)
C(1)–Al(1)–C(2)
C(1)–Al(1)–N
C(2)–Al(1)–N
C(2)–Al(1)–C(6)
O–Al(2)–C(5)
O–Al(2)–C(3)
C(5)–Al(2)–C(3)
C(6)–O–Al(2)
C(6)–N–C(13)
C(13)–N–Al(1)
N–C(6)–C(7)
122.98(19)
114.84(15)
112.39(13)
116.94(14)
107.78(11)
97.14(12)
113.13(18)
136.31(14)
128.6(2)
C(1)–Al(1)–C(6)
O–Al(2)–C(4)
C(4)–Al(2)–C(5)
C(4)–Al(2)–C(3)
C(6)–O–Al(1)
Al(1)–O–Al(2)
C(6)–N–Al(1)
N–C(6)–O
120.09(16)
104.76(13)
115.49(18)
116.05(19)
90.95(12)
131.42(9)
91.83(14)
109.58(19)
117.90(18)
139.39(16)
132.5(2)
O–C(6)–C(7)
AlOAl(a)O(0a) being only 0.8Њ. The bond lengths of C(1)–N
1.276(3) and C(1)–O 1.338(3) Å indicate a localized structure
with a C᎐N double bond and a C–O single bond. The Al–O
᎐
distances within the four-membered Al2O2 chelate ring are
asymmetric with bond lengths Al–O 1.910(2) and Al–O(0a)
2.002(2) Å and they are similar to normal Al–O distances in
other five-coordinate aluminium alkoxides.14 The Al–O bond in
the Al2O2 core is detached by the addition of an excess of
Me3Al to give monomeric complex 2. The geometry around
oxygen in 2 is distorted from trigonal planar with bond angles
of Al(1)–O–C(6) 90.95(12), Al(2)–O–C(6) 136.31(14), and
Al(1)–O–Al(2) 131.42(9)Њ. The bond lengths C(6)–N 1.279(3)
and C(6)–O 1.354(3) Å in 2 are found to be similar to those in 1
Fig. 2 Molecular structure of compound 2.
Me3Al in toluene-d8 was monitored by 1H NMR spectroscopy.
Only one peak was observed in the Al–Me region at ambient
temperature indicating that an equilibrium exists between the
adduct B, 4 and Me3Al.13 When the mixture was heated to
100 ЊC for 5 h a resonance at δ 3.34 corresponding to the form-
ation of an intermediate after the alkylation of 4 started to
appear. This peak increased slowly as the reaction proceeded. A
new peak at δ 5.40 corresponding to compound 5 appeared
after 32 h and kept increasing in intensity as heating is con-
tinued. These NMR studies are consistent with our proposal
that the formation of aluminium diketiminate 5 is initiated by
dealkylation of aluminium amido complex 4.
indicating a localized structure with a C᎐N double bond and a
᎐
C–O single bond character.
The molecular structure of compound 3 is depicted in Fig. 3
and selected bond lengths and angles are listed in Table 3.
Complex 3 crystallizes in a dimeric form and is composed of a
centrosymmetrical eight-membered ring (mode VI). The bridg-
ing NCO group coordinates to two aluminium atoms through
both nitrogen and oxygen atoms. The aluminium atom has a
distorted tetrahedral coordination consisting of two methyl
carbons, nitrogen and oxygen atoms. The bond lengths C(1)–N
1.307(2) and C(1)–O(1) 1.300(2) Å indicate a delocalized struc-
ture within the OCN group. N, C(1), O(1), C(2), and C(8) are
coplanar with deviations of only 0.012 Å. The bond distances
Al–O(1) 1.818(1), Al–N(0a) 1.965(1), Al–C(15) 1.950(2), and
Al–C(16) 1.959(2) Å in 3 are all similar to those of its analog
[Me2Al(µ-η2-PhNCOPh)]2.4 Based on the crystal structures
of 1, 2, 3 and [Me2Al(µ-η2-PhNCOPh)]2, it seems that the
coordination mode of the amidato ligand on aluminium is
Molecular structures of compounds 1, 2, 3, 7 and 8
The molecular structures of compounds 1 and 2 are depicted in
Figs. 1 and 2 and selected bond distances and bond angles are
listed in Tables 1 and 2, respectively. Complex 1 is dimeric
adopting mode IV in which the N-tert-butylbenzamidato group
acts as a chelating ligand bridging two aluminium atoms
through the oxygen atom. An interesting feature is that it con-
tains a 4,4,4-fused ring where Al, N, C(1), and O atoms are
coplanar with the angle between plane AlNC(1)O and plane
J. Chem. Soc., Dalton Trans., 2001, 1359–1365
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Table 3 Selected bond lengths (Å) and angles (Њ) for compound 3
Table 5 Selected bond lengths (Å) and angles (Њ) for compound 8
Al–O(1)
1.8177(10)
1.9587(17)
1.2997(15)
1.9650(11)
Al–C(15)
Al–N(0a)
N–C(1)
1.9503(17)
1.9650(11)
1.3073(18)
Al–N(2)
1.9170(15)
1.951(2)
1.7418(18)
1.335(2)
1.343(2)
1.402(2)
1.392(2)
Al–N(1)
Al–C(29)
Cl(2)–C(25)
N(1)–C(4)
N(2)–C(22)
C(1)–C(10)
1.9266(15)
1.961(2)
1.740(2)
1.440(2)
1.436(2)
1.493(2)
Al–C(16)
O(1)–C(1)
N–Al(0a)
Al–C(28)
Cl(1)–C(7)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
O(1)–Al–C(15)
C(15)–Al–C(16)
C(15)–Al–N(0a)
C(1)–O(1)–Al
C(1)–N–C(8)
C(8)–N–Al(a)
O(1)–C(1)–C(2)
108.67(6)
116.45(9)
111.98(7)
127.83(8)
122.44(11)
118.97(8)
116.25(11)
O(1)–Al–C(16)
O(1)–Al–N(0a)
C(16)–Al–N(0a)
C(11)–O(2)–C(14)
C(1)–N–Al(a)
O(1)–C(1)–N
109.23(7)
102.72(5)
106.90(6)
118.45(15)
118.25(9)
117.14(11)
126.56(11)
N(2)–Al–N(1)
N(1)–Al–C(28)
N(1)–Al–C(29)
C(1)–N(1)–C(4)
C(4)–N(1)–Al
C(3)–N(2)–Al
N(1)–C(1)–C(2)
C(2)–C(1)–C(10)
N(2)–C(3)–C(2)
94.94(6)
109.64(8)
111.51(8)
119.73(14)
116.72(10)
122.48(12)
122.25(15)
115.85(15)
122.73(15)
N(2)–Al–C(28)
N(2)–Al–C(29)
C(28)–Al–C(29)
C(1)–N(1)–Al
C(3)–N(2)–C(22)
C(22)–N(2)–Al
N(1)–C(1)–C(10)
C(3)–C(2)–C(1)
N(2)–C(3)–C(16)
111.72(9)
108.63(8)
118.01(9)
123.54(12)
119.80(14)
117.70(11)
121.82(15)
128.26(16)
120.70(15)
N–C(1)–C(2)
Table 4 Selected bond lengths (Å) and angles (Њ) for compound 7
Al–N(1)
1.918(4)
1.890(7)
1.344(5)
1.335(5)
1.403(5)
1.396(5)
Al–N(2)
Al–C(31)
N(1)–C(4)
N(2)–C(23)
C(1)–C(10)
C(2)–C(16)
1.928(4)
1.969(8)
1.446(5)
1.438(5)
1.498(5)
1.523(5)
Al–C(29)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
C(29)–Al–N(1)
N(1)–Al–N(2)
N(1)–Al–C(31)
C(1)–N(1)–C(4)
C(4)–N(1)–Al
113.6(3)
91.57(15)
112.0(3)
119.6(3)
117.6(3)
122.5(3)
123.3(4)
119.1(3)
118.0(3)
123.8(4)
118.0(3)
C(29)–Al–N(2)
C(29)–Al–C(31)
N(2)–Al–C(31)
C(1)–N(1)–Al
C(3)–N(2)–C(23)
C(23)–N(2)–Al
N(1)–C(1)–C(10)
C(3)–C(2)–C(1)
C(1)–C(2)–C(16)
N(2)–C(3)–C(17)
C(9)–C(4)–C(5)
112.0(3)
112.8(4)
113.2(3)
122.3(3)
120.0(3)
116.9(3)
117.5(3)
124.1(3)
117.9(4)
118.2(4)
118.8(4)
C(3)–N(2)–Al
N(1)–C(1)–C(2)
C(2)–C(1)–C(10)
C(3)–C(2)–C(16)
N(2)–C(3)–C(2)
C(2)–C(3)–C(17)
Fig. 4 Molecular structures of (a) [Et2Al{η2-(p-ClC6H4)NC(Ph)-
C(Me)C(Ph)N(p-ClC6H4)}] 7 and (b) [Me2Al{η2-(p-ClC6H4)NC(Ph)-
C(H)C(Ph)N(p-ClC6H4)}] 8.
Fig. 3 Molecular structure of compound 3.
N(1) 1.344(5), C(3)–N(2) 1.335(5), C(1)–C(2) 1.403(5), and
C(2)–C(3) 1.396(5) Å present further evidence for a delocalized
structure within the diketiminato ligand which has also been
observed in other aluminium diketiminates.16 Compound 8 dif-
fers from 7 by replacing the methyl groups on aluminium with
ethyl as well as a proton at the 2 position instead of methyl on
the diketiminate group. The geometry around Al in 8 is nearly
identical to that for 7 with bond distances Al–N(1) 1.927(2),
Al–N(2) 1.917(2), Al–C(28) 1.951(2), and Al–C(29) 1.961(2) Å,
respectively.
highly dependent on the basicity of the amide and the steric
hindrance of the substituent on nitrogen. The more acidic
and less steric hindered amides such as benzanilide tend to
form eight-membered ring complexes. In contrast less acidic
and more sterically hindered amides, such as N-tert-
butylbenzamide, prefer to have four-membered rings.15 Fur-
ther studies of the Lewis acidity and steric effect of amides
on the coordination modes of amidato ligands on aluminium
are in progress.
The molecular structures of compounds 7 and 8 are shown in
Fig. 4 and bond lengths and angles are listed in Tables 4 and 5,
respectively. The geometry around aluminium in 7 is distorted
from tetrahedral with the bond distance Al–N(1) at 1.918(4),
Al–N(2) at 1.928(4), Al–C(29) at 1.890(7), and Al–C(31) at
1.969(8) Å. The AlNCCCN backbone of the aluminium
diketiminate is essentially planar. Similar bond lengths of C(1)–
In conclusion, we have developed a useful synthetic route
to the preparation of aluminium diketiminate derivatives
by reactions of amides with trialkylaluminium. Aluminium
diketiminates are useful precursors for many applications. They
can easily be converted into diketimines and their derivatives
that also represent useful precursors for further synthetic
purposes.
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was then concentrated to ca. 25 ml and allowed to cool to room
Experimental
General
temperature giving [Me2Al{µ-η2-PhNC(Ph)O}]2 4 (71%). The
residue was redissolved in toluene (10 ml) followed by cooling
to Ϫ20 ЊC yielding yellow crystals of [Me2Al{η2-PhNC(Ph)-
C(H)C(Ph)NPh}] 5 (5%). Compound 4 (Calc. for C15H16AlNO:
C, 71.13; H, 6.37; N, 5.53%. Found: C, 70.90; H, 5.93; N,
5.89%): 1H NMR (CDCl3) δ 7.35–6.97 (m, 10H, Ph) and Ϫ0.89
(s, 3H, CH3). 13C NMR (CDCl ) δ 174.58 (C᎐N), 142.66,
All experiments were carried out under a dry nitrogen atmos-
phere. Solvents were dried by refluxing for at least 24 hours
over sodium–benzophenone (toluene, hexane), or phosphorus
pentaoxide (CH2Cl2) and freshly distilled prior to use. Deuteri-
ated solvents were dried over molecular sieves. Me3Al (2.0 M
in toluene) and Et3Al (1.9 M in toluene) were purchased and
used without further treatment. Benzanilide was recrystallized
prior to use. N-tert-Butylbenzamide, PhCONHC6H4OMe-p,
PhCONHC6H4Cl-p, and PhCONHC6H4Me-p were prepared
according to the literature method.17 Melting points were
determined with a Buchi 535 digital melting point apparatus.
1H and 13C NMR spectra were recorded on a VXR-200 (200
MHz) or a VXR-300 (300 MHz) spectrometer with chemical
shifts given in ppm from internal TMS. The temperatures for
the VT NMR studies were calibrated with the methanol peaks.
Microanalyses were performed using a Heraeus CHN-O-
RAPID instrument. Infrared spectra were obtained from a
Bruker Equinox 55 spectrometer.
᎐
3
133.96, 130.62, 129.35, 128.77, 127.72, 126.53, 125.94 (Ph) and
Ϫ10.8(CH3); IR (KBr, cmϪ1, 1500–1700 cmϪ1) 1656(s), 1591(s)
and 1533 (s). mp 103–105 ЊC.
[Me2Al{ꢁ2-PhNC(Ph)C(H)C(Ph)NPh}] 5. To
a rapidly
stirred solution of compound 4 (2.02 g, 4.0 mmol) in toluene
(10 ml) was added Me3Al (4.2 ml, 8.4 mmol). The reaction
mixture was then refluxed for 16 h and the volatile materials
were removed under vacuum. The residue was extracted by hot
hexane (75 ml) and the filtrate allowed to concentrate to
ca. 25 ml. Greenish yellow crystals were obtained overnight at
room temperature. Yield: 1.46 g (85%). Calc. for C29H27AlN2:
C, 80.91; H, 6.32; N, 6.51%. Found: C, 80.73; H, 6.21; N, 6.91%.
1H NMR (CDCl3): δ 7.26–6.91 (m, 10H, Ph), 5.28 (s, 1H, CH),
4.63 and Ϫ0.81 (s, 3H, CH3). 13C NMR (CDCl3): δ 168.8
Preparations
(C᎐N), 142.01, 139.37, 128.87, 128.35, 128.28 (Ph), 101.63
᎐
[Me2Al(ꢀ-ꢁ2-ButNCOPh)]2 1. To a rapidly stirred solution of
N-tert-butylbenzamide (0.71 g, 4.0 mmol) in hexane (10 ml) was
added Me3Al (2.2 ml, 4.4 mmol). The reaction mixture was
heated to reflux for 24 h and the volatile materials were removed
under vacuum giving white solids. The residue was taken up
in toluene (30 ml) and the insoluble material removed by
filtration. The filtrate was allowed to concentrate to ca. 15 ml
and colorless crystals were obtained at Ϫ20 ЊC after 12 h. Yield:
0.47 g (50%). 1H NMR (CDCl3): δ 7.45–7.38 (m, 5H, Ph), 1.10
(s, 9H, But), Ϫ0.86 (s, 6H, AlCH3). 13C NMR (CDCl3): δ 167.10
(C᎐C) and Ϫ8.87 (CH ). IR (KBr, cmϪ1, 1500–1700 cmϪ1):
᎐
3
1655(s) and 1591(s). mp 126–128 ЊC.
General procedures for compounds 6–10. To a rapidly stirred
solution of benzanilide (0.79 g, 4.0 mmol) in toluene (10 ml)
was added Et3Al (4.2 ml, 8.0 mmol). The reaction mixture
was refluxed for 16 h and the volatile materials were removed
under vacuum. The residue was extracted with hot hexane
(25 ml) and the extract allowed to concentrate to ca. 10 ml.
Greenish yellow crystals were obtained at room temperature
overnight.
Compound 6. Yield: 1.72 g (67%). Calc. for C32H33AlN2: C,
81.83; H, 7.10; N, 6.25%. Found: C, 81.33; H, 7.04; N, 5.93%.
1H NMR (CDCl3): δ 7.36–6.91 (m, 10H, Ph), 1.34 (s, 1H, CH),
0.81 (t, 3H, CH3) and Ϫ0.20 (q, 2H, CH2). 13C NMR (CDCl3):
(C᎐N), 133.80, 129.82, 128.06, 127.26 (Ph), 52.89 (C-N), 31.11
᎐
(C(CH3)3) and Ϫ10.8 (AlCH3). mp 113–115 ЊC.
[Me2Al{ButNCOPh)}AlMe3] 2. Following the same
procedures as above but with 2.2 molar equivalents of
Me3Al, colorless crystals of 2 were obtained. Yield: 1.0 g
(82%). Calc. for C16H29Al2NO: C, 62.93; H, 9.57; N, 4.59%.
Found: C, 62.50; H, 9.36; N, 4.86%. 1H NMR (CDCl3): δ 7.62–
7.36 (m, 5H, Ph), 1.19 (s, 9H, But), Ϫ0.45 (s, 6H, AlMe2)
and Ϫ0.86 (s, 9H, AlMe3). 13C NMR (CDCl3): δ 172.68
δ 171.03 (C᎐N), 146.42, 138.66, 129.40, 128.03, 127.79, 126.49,
᎐
124.18 (Ph), 100.99 (CCH3), 20.60 (CCH3), 9.33 (CH2CH3) and
0.77 (CH2CH3). IR (KBr, cmϪ1, 1500–1700 cmϪ1): 1655 (s),
1595 (s) and 1536 (s). mp 128.5–130.5 ЊC.
Compound 7. Yield: 1.72 g (86%). Calc. for C32H31AlCl2N2: C,
70.98; H, 5.77; N, 5.17%. Found: C, 70.51; H, 5.60; N, 5.62%.
1H NMR (CDCl3): δ 7.26–6.78(m, 18H, Ph), 1.32 (s, 1H, CH),
0.80 (t, 3H, CH3) and Ϫ0.22 (q, 2H, CH2). 13C NMR (CDCl3):
(C᎐N), 131.46, 129.57, 128.38, 127.42 (Ph), 54.43 (C–N),
᎐
30.69 (C(CH3)3), Ϫ8.06 (AlMe 3) and Ϫ10.27 (AlMe2). mp
86–90 ЊC.
δ 171.33 (C᎐N), 144.95, 138.19, 130.17, 129.78, 129.26, 128.25,
128.10, 127.57 (Ph), 20.60 (CCH3), 9.31 (CH2CH3) and 0.61
(CH2CH3). mp: 160–162 ЊC.
Compound 8. Yield: 0.48 g (22%). Calc. for C29H25AlCl2N2: C,
69.75; H, 5.05; N, 5.61%. Found: C, 69.19; H, 5.18; N,
5.99%. 1H NMR (CDCl3): δ 7.30–6.81(m, 18H, Ph), 5.30
(s, 1H, CH) and Ϫ0.83 (s, 6H, CH3). 13C NMR (CDCl3):
᎐
[Me2Al(ꢀ-ꢁ2-(4-MeO-C6H4)NCOPh)]2 3. To a rapidly stirred
solution of PhCONHC6H4OMe-p (0.91 g, 4.0 mmol) in hexane
(30 ml) was added Me3Al (2.1 ml, 4.2 mmol). The reaction
mixture was stirred at 25 ЊC for 16 h and the volatile materials
were removed under vacuum to give a white solid. The residue
was extracted by toluene (30 ml) and allowed to concentrate to
ca. 15 ml. Colorless crystals were obtained at room temperature
after 12 h. Yield: 1.10 g (50%). Calc. for C16H18AlNO2: C, 66.41;
δ 169.25 (C᎐N), 144.68, 138.91, 130.17, 128.90, 128.85, 128.64,
᎐
128.00, 127.44 (Ph), 102.23 (CH) and Ϫ9.18 (CH3). mp 157–
159 ЊC.
1
H, 6.69; N, 5.16%. Found: C, 65.93; H, 6.23; N, 5.68%. H
NMR (CDCl3): δ 7.37–6.51 (m, 8H, Ph), 3.75 (s, 3H, OCH3)
Compound 9. Yield: 0.21 g (23%). Calc. for C31H31AlN2:
C, 81.19; H, 6.81; N, 6.11%. Found: C, 81.80; H, 7.13; N, 5.50%.
1H NMR (CDCl3): δ 7.27–6.77 (m, 18H, Ph), 5.21 (s, 1H, CH),
2.20 (s, 6H, CH3) and Ϫ0.82 (s, 6H, CH3). 13C NMR (CDCl3):
δ 168.77 (C=N), 143.50, 139.70, 133.9, 129.04, 128.97, 128.30,
127.71, 126.08 (Ph), 101.46 (CH), 20.86 (CH) and Ϫ9.10
(AlCH3).
and Ϫ0.91 (s, 3H, CH3). 13C NMR (CDCl ): δ 174.81 (C᎐N),
᎐
3
157.58, 135.60, 134.18, 130.62, 129.45, 127.85, 114.05 (Ph),
55.08 (OCH3) and Ϫ10.41 (CH3). IR (KBr, cmϪ1, 1500–
1700 cmϪ1): 1656(s), 1591(s) and 1533 (s). mp 129–131 ЊC
(decomp.).
Thermal reaction of benzanilide with Me3Al. To a rapidly
stirred solution of benzanilide (0.79 g, 4.0 mmol) in toluene (30
ml) was added Me3Al (2.4 ml, 4.8 mmol). The reaction mixture
was refluxed for 24 h during which it changed from colorless to
yellow. The volatile materials were removed under vacuum and
the residue was extracted with hot hexane (75 ml). The extract
Compound 10. Yield: 0.25 g (25%). Calc. for C34H37AlN2:
C, 81.57; H, 7.45; N, 5.60%. Found: C, 81.80; H, 7.13; N, 5.50%.
1H NMR (CDCl3), δ 7.19–6.73 (m, 10H, Ph), 2.15 (s 6H, CH3),
1.30 (s, 1H, CH3), 0.81 (t, 3H, CH3) and Ϫ0.23 (q, 2H, CH2).
13C NMR (CDCl ): δ 170.84 (C᎐N), 143.80, 138.91, 133.46,
᎐
3
129.38, 128.63, 127.78, 127.60, 126.18 (Ph), 100.60 (CCH3),
J. Chem. Soc., Dalton Trans., 2001, 1359–1365
1363

View Article Online
Table 6 Crystallographic data for compounds 1, 2, 3, 7 and 8
1
2
3
7
8
Chemical formula
M
C13H20AlNO
233.3
C16H29Al2NO
305.4
C16H18AlNO2
283.3
C32H31AlCl2N2
541.5
C29H25AlCl2N2
499.4
Space group
Crystal system
a/Å
b/Å
C2/c
Pbca
P21/n
P21/n
P21/c
Monoclinic
22.798(3)
11.009(2)
12.582(2)
112.38(2)
2920.1(7)
8
Orthorhombic
14.576(1)
13.431(1)
21.021(2)
—
4115.4(5)
8
Monoclinic
10.102(1)
9.746(1)
16.249(1)
104.01(2)
1552.2(2)
4
Monoclinic
9.8996(7)
25.165(2)
12.537(1)
94.80(1)
3112.3(11)
4
Monoclinic
7.3864(5)
20.746(1)
17.518(1)
98.09(1)
2657.7(3)
4
c/Å
β/Њ
V/Å3
Z
T/K
293
0.121
2875
293
0.137
4050
293
0.131
3034
293
0.259
6131
293
0.297
5226
µ(Mo-Kα)/mmϪ1
No. observed reflections
[F > 4σ(F)]
No. parameters
R1
wR2
145
0.0582
0.1904
262
0.0546
0.1920
181
0.0366
0.1281
334
0.0771
0.2182
307
0.0420
0.1407
20.84 (CHCH3), 20.60 (CH3), 9.37 (CH2CH3) and 0.84
(CH2CH3).
Acknowledgements
Financial support from the National Science Council of the
Republic of China is gratefully acknowledged.
Hydrolysis of aluminium diketiminate
Compound 8 (0.20 g, 0.4 mmol) was suspended in water (30 ml)
and stirred at room temperature for 16 h. The mixture was then
extracted with diethyl ether (10 ml) twice. The extract was then
dried under vacuum to give a colorless solid. Yield: 0.16 g
(93%). Calc. for C27H20Cl2N2: C, 73.14; H, 4.55; N, 6.32%.
Reference
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1
Found: C, 73.09; H, 4.82; N, 6.90%. H NMR (CDCl3): δ 7.29
(m, 12H, Ph), 7.06 (d, J = 7.8, Ph), 6.65 (d, J = 8.8 Hz, Ph) and
5.39 (s, 1H, CH). 13C NMR (CDCl ): δ 161.37 (C᎐N), 143.94,
᎐
3
137.59, 128.76, 128.57, 128.35, 128.25, 127.92, 123.47 (Ph) and
102.48 (CH).
Thermal reaction of compound 4 with Et3Al
To a rapidly stirred solution of compound 4 (1.52 g, 3.0 mmol)
in toluene (10 ml) was added Et3Al (4.3 ml, 8.0 mmol). The
reaction mixture was then refluxed for 16 h and the volatile
materials were removed under vacuum. The residue was
extracted by hot hexane (50 ml) and the extract allowed to con-
centrate to ca. 25 ml. Greenish yellow crystals were obtained
1
overnight at room temperature. H NMR spectroscopic study
of the residue showed that it is a mixture of 5 and 6 with a
molar ratio 1 : 11.
X-Ray crystallographic studies
Suitable crystals of compound 1, 2, 3, 7 and 8 were sealed in
thin-walled glass capillaries under a nitrogen atmosphere and
mounted on a Bruker AXS SMART 1000 diffractometer.
Absorption corrections were made based on symmetry equiv-
alent reflections using the SADABS program.18 The space
group determination was based on a check of the Laue sym-
metry and systematic absences, and was confirmed using the
structure solution. The structures were solved by direct
methods using a SHELXTL package.19 All non-H atoms were
located from successive Fourier maps and hydrogen atoms
refined using a riding model. Anisotropic thermal parameters
were used for all non-H atoms, and fixed isotropic parameters
were used for H atoms. Crystallographic data are listed in Table
6. In compound 2 the tert-butyl group on the nitrogen atom is
disordered. There are two positions for each carbon atom
attached to the carbon attached to the nitrogen atom. The final
value for the site occupancy of the two tert-butyl groups is
60/40.
8 F. Cosledan, P. B. Hitchcock and M. F. Lappert, Chem. Commun.,
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and R. Ahlrichs, Angew. Chem., Int. Ed. Engl., 1993, 32, 1655.
10 A. Meister and T. Mole, Chem. Commun., 1969, 133; H. Hoberg and
J. Barluenga, Synthesis, 1970, 142; G. Wittig, S. Fisher and M.
Tanaka, Liebigs Ann. Chem., 1973, 1075.
11 J. Barluenga, H. Cuervo, B. Olano, S. Fustero and V. Gotor,
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12 L. Capuano and K. Gartner, J. Heterocycl. Chem., 1981, 18, 1341.
1
13 H NMR studies of the mixture of compound 4 with 3 molar
equivalents of Me3Al show one resonance at δ Ϫ0.34 at 20 ЊC
indicating fast exchange between three different Al–Me functions.
However, the resonance starts to broaden at 0 ЊC and there are two
peaks at δ Ϫ0.25 and Ϫ0.35 with a ratio of 4 : 9 in the Al–Me region
at Ϫ20 ЊC. The upfield resonance further splits into two peaks with
a ratio of 1 : 2 at Ϫ60 ЊC.
CCDCreferencenumbers139979,139980and152733–152735.
See http://www.rsc.org/suppdata/dt/b0/b009070k/ for crystal-
lographic data in CIF or other electronic format.
1364
J. Chem. Soc., Dalton Trans., 2001, 1359–1365

View Article Online
14 J. P. Oliver, R. Kumar and M. Taghiof, Coordination Chemistry of
Aluminum, ed. G. H. Robison, VCH Publisher, Inc., Weinheim, 1993,
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Y. L. Sun and C. C. Lin, J. Organomet. Chem., 1999, 587, 151; B. T.
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15 B. H. Huang, T. L. Yu, Y. L. Huang, B. T. Ko and C. C. Lin,
unpublished work.
16 B. Qian, D. L. Ward and M. R. Smith, III, Organometallics, 1998,
17, 3070; J. Feldman, S. J. Mclain, A. Parthasarathy, W. J. Marshall,
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17 F. G. Riddell and M. Rogerson, J. Chem. Soc., Perkin Trans. 2, 1996,
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18 G. M. Sheldrick, SADABS, Siemens Area Detector Absorption
Correction Software, University of Göttingen, 1998.
19 G. M. Sheldrick, SHELXTL-Plus, NT Crystallographic System,
Release 5.1, Bruker Analytical X-ray Systems, Madison, WI, 1998.
J. Chem. Soc., Dalton Trans., 2001, 1359–1365
1365