1,4-Dialkyl-1,4-diazabutadienes: Their reactions with aluminum and indium halides

Article abstract of DOI:10.1039/c3nj01226c

Reactions of 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1), 1,4-bis[(R) 1′-chlorobutan-2′-yl]-1,4-diazabutadiene (2), 1,4-bis[(S,S) 1′-chloro-1′-phenyl-propan-2′-yl]-1,4-diazabutadiene (3), and 1,4-di-tert-butyl-1,4-diazabutadiene (4) with aluminum and

Full text of DOI:10.1039/c3nj01226c

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1,4-Dialkyl-1,4-diazabutadienes: their reactions
with aluminum and indium halides†
Cite this:DOI: 10.1039/c3nj01226c
Hector Rojas-Saenz, Galdina V. Suarez-Moreno, Iris Ramos-Garcıa,
´
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Angelica M. Duarte-Hernandez, Edgar Mijangos, Adrian Pena-Hueso,
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Rosalinda Contreras and Angelina Flores-Parra*
Reactions of 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1), 1,4-bis[(R) 10-chlorobutan-20-yl]-1,4-diazabutadiene
(2), 1,4-bis[(S,S) 10-chloro-10-phenyl-propan-20-yl]-1,4-diazabutadiene (3), and 1,4-di-tert-butyl-1,4-
diazabutadiene (4) with aluminum and indium halides were performed. Reaction of 1,4-diazabutadienes
1–4 with two equivalents of aluminum halides in toluene afforded ionic aluminum coordination com-
pounds (5–10) which in THF solution are transformed into 1,3-dialkyl-2-methaneiminealkyl imidazolium
heterocycles (11–14) by condensation of two 1,4-diazabutadienes and elimination of amine
hydrochloride. Equimolar reactions of 1–4 with InCl3 in dry acetonitrile at ꢀ78 1C afforded the neutral
and diamagnetic InCl3 coordination compounds (15–18), which are stable in the solid state under dry
conditions, but in THF solution are slowly transformed into the corresponding 1,3-dialkyl-imidazolium
heterocycles 19–22. The X-ray diffraction analyses of compounds 2, 3, 10, 11, 14 and 17 are described.
Quantum mechanical calculations were performed in order to find the minimum energy conformers of
1,4-diazabutadienes, 1,3-dialkyl-2-methaneiminealkyl imidazolium and 1,3-dialkyl-imidazolium deriva-
tives as well as the aluminum and indium coordination compounds.
Received (in Porto Alegre, Brazil)
6th October 2013,
Accepted 4th November 2013
DOI: 10.1039/c3nj01226c
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Introduction
Enantiomerically pure ligands are relevant for the preparation
of coordination compounds which may be used as reagents or
catalyzing agents in enantioselective reactions.1–4 In our
research program concerning enantiomerically pure metal
coordination compounds,5–9 we are interested in the synthesis
of optically active aluminum and indium derivatives and there-
fore we have investigated the reactions of aluminum and
indium halides with 1,4-dialkyl-1,4-diazabutadienes. These
Scheme 1 Neutral, anion and dianionic oxidation states of 1,4-
diazabutadienes.
ligands have two sp2 nitrogen atoms as metal coordination radical anion or the dianion have been widely explored. Reactions
sites and their N-substituents may have stereogenic centers. of group 13 elements in the low oxidation state give paramagnetic
1,4-Diazabutadienes can be found in three different oxidation products.12–17 The synthesis of coordination compounds could
states: neutral, a p radical monoanion or a reduced dianion, be complicated by competition between addition and coupling
Scheme 1.10,11 Coordination compounds formed with the processes.18 The coordination chemistry of neutral diazabutadienes
is less known, reactions give diamagnetic ionic coordination
derivatives,19 as was described for the reaction of di-tert-butyl-
Department of Chemistry, Cinvestav, AP 14-740, CP 07000, Mexico DF.
diazabutadiene with GaCl3.20
E-mail: aflores@cinvestav.mx
† Electronic supplementary information (ESI) available: X-ray diffraction analysis
Herein, we described the reactions of aluminum and indium
of (R)-1-chloro-butan-2-amine hydrochloride (S1). Macromolecular helix arrange-
halides with 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1),
ment in the crystal of compound 2 (S2). Theoretical conformational analysis of
1,4-dialkyl-1,4-diazabutadienes 1–4 (S3). Anagostic interactions Hꢁ ꢁ ꢁAl found in 1,4-bis[(R) 10-chlorobutan-20-yl]-1,4-diazabutadiene (2), 1,4-bis[(S,S)
10-chloro-10-phenylpropan-20-yl]-1,4-diazabutadiene (3) and
1,4-di-tert-butyl-1,4-diazabutadiene (4). Ligands 1–3 have tertiary
N-substituents whereas those of 4 are quaternary, Scheme 2.
the X-ray diffraction analysis of compound 10 (S4). Cell packing representation of
compound 14 with [I3]ꢀ as the anion. (S5) Optimized conformers of compounds:
5, 17, 18, 20–22 (S6). Representation of the electrostatic potentials of the indium
compounds 16–18 and of the ligand 3 coordinated to one and two InCl3
Compounds 1–3 have phenyl groups and/or chlorine atoms
which could give rise to intra- and intermolecular weak
molecules (S7). CCDC 960655–960662. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c3nj01226c
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Scheme 2 1,4-Dialkyl-1,4-diazabutadiene compounds 1–4.
interactions promoting crystallization or supramolecular arrange- in turn reacted with aqueous glyoxal and Na2CO3. It was
ments of their derivatives. The chloro substituents could be used to crystallized from CHCl3 and the X-ray diffraction structure was
add other coordinating functional groups, such as phosphines.21 It obtained. Compound 3 was synthesized by the condensation reac-
is known that diazabutadiene 4 is able to stabilize metallic tion of (1S,2S)-1-chloro-1-phenyl-propan-2-amine hydrochloride24
derivatives because of the steric hindrance that inhibits subsequent with aqueous glyoxal and Na2CO3, Scheme 3. 1,4-dialkyl-1,4-
reactions once the coordination compound is formed.22,23
diazabutadiene 1 is a liquid, whereas 2–4 are crystalline solids.
Compounds 2 and 3 are new. Their X-ray diffraction analyses
were performed. They have in common a planar arrangement
for the CH–NQCH–CHQN–CH chain in trans conformation
and imines in E configuration. Selected bond lengths and
angles are in Tables 1 and 2. The C3 substituents are perpendicular
to the diazabutadiene plane with the chlorine atoms pointing to the
same side.
Results and discussion
Synthesis and structures of 1,4-diazabutadienes 1–4
Diazabutadienes 1 and 4 were prepared by reactions of aqueous
glyoxal with two equivalents of the primary amines: (S)-methyl-
benzylamine and tert-butylamine. Compound 2 was prepared in
two steps. First, (R)-2-amino-butan-1-ol was chlorinated with SOCl2
in THF to give the (R)-1-chloro-butan-2-amine hydrochloride, which
In compound 2, six CHꢁ ꢁ ꢁN and two CHꢁ ꢁ ꢁCl hydrogen
bonds, together with two contacts of chlorine atoms with the
Scheme 3 Synthesis of diazabutadienes 1–4.
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nitrogen p electrons (3.17 Å; SvdWr Cl–N = 3.42 Å25–27) stabilize
the conformation. In the crystal, the molecules of 2 are
arranged in a helix, with a path of four molecules.
Table 1 Selected bond lengths and angles for 1,4-diazabutadiene 2(S)
In compound 3, the phenyl groups are parallel to the
diazabutadiene plane. The chlorine atoms have short distances
to the nitrogen atoms (3.08 and 3.09 Å). The Ci–C5–C3 and
Ci–C7–C4 angles are wide (115.0 and 114.21) indicating repulsion
between methyl and phenyl groups. One of the chlorine atoms
has a C–Hꢁ ꢁ ꢁCl hydrogen bond and a Clꢁ ꢁ ꢁp-interaction with
another molecule, Fig. 1.
It was found in the solid state and in solution that the more
stable conformation of 1,4-diazabutadienes is the s-trans E,E.
The bidentate coordination of these ligands needs rotation of
C2–C20 in order to get the s-cis E,E conformation. The energy
barrier for this isomerization in compounds 1–4 was calculated
Bond lengths
Bond angles
N1–C1
N2–C2
C1–C2
N1–C3
N2–C4
C3–C5
C4–C8
Cl2–C8
Cl1–C5
1.259(3)
1.264(4)
1.471(4)
1.457(3)
1.451(4)
1.511(5)
1.495(5)
1.790(4)
1.787(4)
N1–C1–C2
N2–C2–C1
C1–N1–C3
C2–N2–C4
C4–C8–Cl2
C3–C5–Cl1
N2–C4–C8
N2–C4–C9
120.3(3)
119.4(3)
118.4(2)
117.6(2)
111.4(2)
112.0(3)
108.8(3)
107.5(3)
using a quantum mechanical approach,28 DG* = 37.0 kJ molꢀ1
.
The energy difference between the more stable trans isomers
and the cis isomers was also calculated. The values were: 1
(27.1 kJ molꢀ1), 2 (24.4 kJ molꢀ1), 3 (25.6 kJ molꢀ1) and 4
(30.4 kJ molꢀ1). The energy difference is related to the steric
effects of the tertiary or quaternary substituents.
Reactions of diazabutadienes 1–4 with aluminum halides in
toluene
Table 2 Selected bond lengths and angles for 1,4-diazabutadiene 3(S,S)
Reactions of 1,4-diazabutadienes 1–4 with two equivalents of
aluminum halides at ꢀ78 1C in toluene and in a N2 atmosphere
gave the corresponding ionic aluminum coordination com-
pounds 5–10, Scheme 4. Aluminum compounds were mainly
characterized by 27Al NMR, Table 3. Each spectrum presented
two resonances: broad signals for the cations and sharp reso-
nances for the anions. Compounds 5–7 are brown solids which
precipitate from the reaction mixture. In THF solution, they
are transformed into imidazole derivatives as will be later
discussed. N-tert-Butyl derivatives 8–10 are more stable than
5–7, they were isolated as yellow solids. The X-ray diffraction
analysis of compound 10 was conducted.
Bond lengths
Bond angles
N1–C1
N2–C2
C1–C2
N1–C3
N2–C4
C3–C5
C4–C7
Cl2–C7
Cl1–C5
1.270(4)
1.266(4)
1.466(4)
1.456(4)
1.460(4)
1.538(3)
1.514(5)
1.815(3)
1.824(3)
N1–C1–C2
N2–C2–C1
C1–N1–C3
C2–N2–C4
C4–C7–Cl2
C3–C5–Cl1
Ci–C7–C4
Ci–C5–C3
120.5(3)
119.3(3)
118.6(3)
118.2(3)
108.7(2)
110.2(2)
114.2(2)
115.0(2)
1H and 13C NMR spectra of compounds 5 and 8–10 were
obtained. Comparison with data of the starting diazabutadienes
shows that the C2–H protons in the coordination compounds are
shifted to higher frequencies: 5 (Dd 0.26 ppm); 8 (Dd 1.26 ppm),
Fig. 1 Intermolecular contacts in the enantiomerically pure compound 3 (S,S).
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Scheme 4 Ionic aluminum coordination compounds 5–10.
Table 3 27Al NMR data [d, ppm] and (D1/2, Hz) of compounds 5–10
5
6
7
8
9
10
[AlXY]+
+34 (1250)
+107.1 (94)
+62 (3036)
+100.1 (40)
+68 (3754)
+100.2 (80)
+97 (3550)
+102.0 (154)
+89 (2050)
+20.0 (137)
+130 (2000)
+102.0 (22)
[AlX3Y]ꢀ
9 (Dd 1.49 ppm), 10 (Dd 1.20 ppm), whereas the C2 signals
appear at lower frequencies with respect to those of the
diazabutadienes, the explanation could be based on the change
of the ligand conformation from trans to cis.
The ionic coordination compound 10 crystallized from
CHCl3 and the X-ray diffraction analysis was performed,
selected bond lengths and angles are in Table 4. The aluminum
atom is bound to the nitrogen atoms, to a chlorine atom and to
a methyl group, the [AlCl3Me]ꢀ anion neutralizes the cation.
The tert-butyl protons have a short distance to the aluminum
atom giving rise to anagostic interactions (2.78 and 2.99 Å,
SvdWr = 3.3 Å29). The exocyclic N–C bonds of the tert-butyl
groups present alternate conformations with respect to the ring
Fig. 2 Intermolecular interactions in the crystal of compound 10. The
aluminum compounds form chains by Clꢁ ꢁ ꢁCQC p contacts (Clꢁ ꢁ ꢁC
distances are in the range of 3.17–3.27 Å; SvdWr 3.55 Å28).
plane. Each ring has two intermolecular Clꢁ ꢁ ꢁp interactions,
Fig. 2.25–27
Table 4 Selected bond lengths and angles for the coordination com-
pound 10
Due to the fact that we were unable to get crystals for
compounds 6 and 7 we decided to calculate their structures
in order to get some information about the possible weak
interactions of the substituent chlorine atoms. The minimum
energy conformers for the aluminum cations in compounds 6
and 7 were calculated,28 Fig. 3. The optimized conformer of
compound 6 shows that a short contact of a chlorine atom with
the aluminum (2.93 Å) atom and an Hꢁ ꢁ ꢁCl intramolecular
hydrogen bond stabilize the structure. A short C–Hꢁ ꢁ ꢁAl distance
(2.85 Å) was also found. In the calculated structure of compound
7, the chlorine atoms are oriented towards the CQN bonds with
short distances (3.08 and 3.12 Å; SvdWr = 3.55 Å). The methyl
protons have short distances to the aluminum atom (3.08 Å).
Bond lengths
Bond angles
Reactions of 1,4-diazabutadienes 1–4 with aluminum
halides in THF
Al1–N1
Al1–N2
N1–C1
N2–C2
C1–C2
Al1–C5
Cl1–Al1
N1–C3
N2–C4
1.956(5)
1.971(5)
1.284(7)
1.279(8)
1.459(9)
1.971(5)
2.077(3)
1.508(7)
1.507(8)
N1–Al1–N2
C5–Al1–Cl1
C1–N1–Al1
C2–N2–Al1
N1–C1–C2
N2–C2–C1
C1–N1–C3
C2–N2–C4
84.6(2)
121.7(2)
110.1(4)
110.2(4)
117.9(5)
117.1(6)
121.3(5)
121.7(5)
Equimolar reactions of diazabutadienes 1–4 with AlX3 (X = Cl, I)
in dry THF at ꢀ78 1C for 2 h were performed. Examination of
the reaction mixtures by 27Al NMR in THF showed the presence
of aluminates [AlCl4]ꢀ (d27Al +101.3, D1/2 215 Hz) or [AlI4]ꢀ
(d 27Al ꢀ20.2, D1/2 137 Hz). Reactions performed with AlI3 in the
presence of CH2Cl2 afforded the corresponding [AlCl4]ꢀ anions.
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Fig. 3 Calculated minimum energy structures for cations 6 and 7.
Scheme 5 Transformation of compounds 5–8 into 11–14.
Solvent extraction of the reaction products and water washing angle is 131). The benzylic carbon atoms of the intracyclic
gave the heterocycles stabilized by chloride anions. Compounds nitrogen atoms are also in the imidazolium plane. The phenyl
11, 13 and 14 are brown solids, whereas 12 is a viscous liquid. groups are pointing to the opposite sides of the ring plane. The
Compounds were characterized by IR, mass spectrometry and conformation of one of the endocyclic N-substituents is fixed by
elemental analyses. The 1H and 13C NMR spectra indicate a hydrogen bond between the benzylic proton and the exocyclic
the formation of 1,3-dialkyl-2-methaneiminealkyl imidazolium imine (2.47 Å). The other endocyclic N-substituent presents
heterocycles 11–14, Scheme 5. To our knowledge the aluminum some disorder due to its free rotation. One of the chlorine
compounds’ transformation into the imidazolium heterocycles atoms of the [AlCl4]ꢀ anion has a Clꢁ ꢁ ꢁC p-interaction (3.41 Å)
has not been described before. The new compounds show with the imidazolium C2 (not shown).25–27
an imine group attached to C2, as a result of the condensation
The reaction of 4 with AlCl3 afforded crystals of 14 with
of one diazabutadiene with half of another diazabutadiene. [AlCl4]ꢀ as the anion whereas the AlI3 reaction product treated
1,3-Dialkyl-2-methaneiminealkyl imidazoliums (11–14) are with water and extracted with CH2Cl2 afforded crystals of 14
analogues of a,b-unsaturated acyl imidazolium cations, inter- with [I3]ꢀ as the anion. The two crystals were subjected to the
mediates in polymer syntheses.30 They are also structurally X-ray diffraction analyses; selected bond lengths and angles are
related to imidazolium 2-carboxylates used as pre-catalysts for in Table 6.
polyurethane formation.31
The cation has the same conformation in both crystals. The
A possible reaction path for the synthesis of 1,3-dialkyl-2- plane of the exocyclic imine is perpendicular to the imidazolium
methaneiminealkyl imidazolium compounds under anhydrous ring, Fig. 4A. This conformation is different from that of 11, and
conditions and in HCl was proposed earlier.32 A similar path is attributed to the steric effect. Two tert-butyl methyl groups
can be depicted for the AlCl3 reaction. It is assumed that the have two C–Hꢁ ꢁ ꢁC p-interactions (2.32 and 2.34 Å) with the
aluminum coordination compounds 5–10 could suffer
a
exocyclic imine. The imidazolium ring is aromatic (bond lengths
nucleophilic attack from a diazabutadiene to one of the carbon vary from 1.34 to 1.37 Å). In the crystal of 14 [AlCl4]ꢀ, one
atoms of the metallacycle with elimination of AlCl2NHR, chlorine atom has a p contact25–27 with the imidazolium C2,
Scheme 6.
Fig. 4B. The X-ray diffraction structure of 1,3-di-tert-butyl-2-
Compound 11 crystallized from CHCl3. Selected bond [N-tert-butylmethanimine]-imidazolium having Clꢀ as the anion
lengths and angles are in Table 5. The exocyclic imine is almost is known. The compound was synthesized by reaction of the
coplanar with the imidazolium ring (the N–C–C–N dihedral diazabutadiene with dry HCl in anhydrous toluene.32
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Scheme 6 1,3-Dialkyl-2-methaneiminealkyl imidazolium heterocycles could be formed by the nucleophilic attack of diazabutadienes to the aluminum
coordination compounds.
Table 5 Selected bond lengths and angles for the imidazolium cation 11
Table 6 Selected bond lengths and angles for the imidazolium cation 14
14[AlCl4]
14[I3]
Bond lengths
Bond angles
Bond lengths
Bond angles
Bond lengths Bond angles
C3–N1
C3–N2
C1–N1
C2–N2
C2–C1
C3–C4
C4–N3
C5–N1
C6–N2
C7–N3
1.345(5)
1.344(5)
1.373(5)
1.368(5)
1.338(6)
1.465(5)
1.243(5)
1.503(5)
1.483(5)
1.467(5)
N1–C3–N2
C3–N1–C1
C3–N2–C2
C2–C1–N1
C1–C2–N2
N3–C4–C3
C3–N1–C5
C3–N2–C6
C4–N3–C7
N1–C3–C4
N2–C3–C4
107.6(3)
108.4(3)
108.5(3)
107.5(3)
107.9(3)
120.8(3)
127.2(3)
126.5(3)
117.6(3)
124.4(3)
128.0(3)
N1–C3 1.339(6) N2–C3–N1 107.9(4) C3–N1 1.28(3) N1–C3–N2 112(2)
N2–C3 1.333(6) C3–N1–C1 108.7(4) C3–N2 1.34(2) C3–N1–C1 107(2)
N1–C1 1.391(6) C3–N2–C2 107.8(4) C1–N1 1.39(3) C3–N2–C2 104(2)
N2–C2 1.372(6) C2–C1–N1 106.1(5) C2–N2 1.41(3) C2–C1–N1 108(2)
C2–C1 1.315(7) C1–C2–N2 109.5(5) C2–C1 1.29(3) C1–C2–N2 109(2)
C3–C4 1.482(7) N3–C4–C3 119.1(5) C3–C4 1.49(3) N3–C4–C3 121(2)
N3–C4 1.240(6) C3–N1–C5 128.9(4) C4–N3 1.26(3) C3–N1–C5 130(2)
N1–C5 1.518(6) C3–N2–C6 127.2(4) C5–N1 1.52(3) C3–N2–C6 131(2)
N2–C6 1.522(6) C4–N3–C7 123.9(7) C6–N2 1.47(3) C4–N3–C7 123(2)
N3–C7 1.50(2)
C7–N3 1.48(3)
Optimization of the minimum energy conformations of
In order to know the contribution of the exocyclic imine to
1,3-dialkyl-2-methaneiminealkyl imidazolium compounds 11–14 the stabilization of the molecule, we have calculated the energy
was performed.28 The calculated structures of cations 11 and 14 of two conformers for the hypothetical molecule 1,3-di(methyl)-
are similar to their X-ray diffraction structures; therefore 2-[N-methylmethanimine]-imidazolium, where the steric effect
we have concluded that calculated cations 12 and 13 (Fig. 5) has been minimized. We have found that the coplanar con-
could be used to analyze their conformations and possible formation of the exocyclic imine is more stable than the
weak interactions. In both structures the exocyclic imines are perpendicular conformation by 13.6 kJ molꢀ1, Fig. 6.
coplanar with the imidazolium ring due to the electronic
Reactions of 1,4-diazabutadienes 1–4 with InCl3 in acetonitrile
delocalization and formation of a CHꢁ ꢁ ꢁN hydrogen bond
[C–Hꢁ ꢁ ꢁN distances: 2.27 Å (12) and 2.17 Å (13)]. The N-tertiary Reactions of compounds 1–4 with one or two equivalents of
carbon reduces the steric effect and allows formation of a InCl3 in dry acetonitrile and a N2 atmosphere at ꢀ78 1C gave the
stabilizing hydrogen bond. In cations 12 and 13 some chlorine indium coordination compounds 15–18, Scheme 7. Neutral
atoms are oriented towards the p electrons of the ring nitrogen and diamagnetic indium coordination compounds derived
atoms (12 3.15 Å; 13 3.05 Å).
from 1,4-diazabutadienes are not described in the literature.
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Fig. 4 X-Ray diffraction structure of imidazolium 14. (A) The cation has four hydrogen bonds to the exocyclic CQN bond (2.37–2.95 Å). (B) One chlorine
atom of the anion has a Clꢁ ꢁ ꢁC2 p-interaction.
Fig. 5 Optimized minimum energy conformers for imidazolium heterocycles 12 and 13.
Fig. 6 Calculated minimum energy conformers for 1,3-dimethyl-2-[N-methylmethanimine]-imidazolium.
(1633 cmꢀ1) become broad and are shifted towards lower
frequencies (1605 cmꢀ1). In the NMR spectra, the C2–H protons
signals are shifted to the higher frequencies with respect to the
starting diazabutadienes, whereas the chemical shifts of C2 are
shielded (between 2–4 ppm) probably due to the diazabutadiene
conformational change. A similar behavior was found for the
aluminum compounds 5, 8–10.
We have followed the reactions of compound 3 with one and
two equivalents of InCl3 in THF by 1H and 13C NMR at low
temperature. The spectra of the reaction of 3 with one equivalent
of InCl3 in TDF at ꢀ65 1C show at least five compounds out of
Scheme 7 Synthesis of indium compounds 15–18.
which one was predominant [1H: 8.9 (H1), 5.9 (H4), 4.4 (H3), 1.3
(H5) ppm; 13C: 158.7 (C1), 138.7 (Ci), 75.9 (C4) and 19.0 (C5) ppm].
Compounds are stable in the solid state under dry conditions. All signals were very broad, indicating isomers in equilibrium.
In the IR spectra the CQN bands of the starting diazabutadienes When the solution was heated at +20 1C, only one set of broad
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Scheme 8 Proposed equilibrium between isomers in the InCl3 coordination compound.
138.6 (Ci), 71.9 (C4), 66.0 (C3) and 18.5 (C5) ppm] was attributed
to the complex of the 1,4-diazabutadiene with two molecules of
InCl3 (B65%), Scheme 9. Calculation of the optimized structure
is shown in Fig. 7. The Inꢁ ꢁ ꢁCl distances (3.61 Å, SvdWr = 4.0 Å29)
indicate that the C–Cl chlorine atoms have stabilizing contacts
with the indium atom. A similar fluxional behavior was found for
a platinum derivative of ligand 4.33
From the reaction of diazabutadiene 3 with InCl3, a solid
was obtained which was dissolved in THF and crystals of
compound 17 suitable for X-ray diffraction analyses were
obtained. Selected bond lengths and angles are in Table 7.
It was found that the indium atom is hexacoordinated with an
Scheme 9 Proposed structure for
compound.
a dinuclear InCl3 coordination
signals was observed [1H: 8.0 (H2), 5.0 (H4), 3.7 (H3), 1.0 (H5) ppm; octahedral geometry. It is chelated by the diazabutadiene and
13C: 161.7 (C2), 139.1 (Ci), 71.9 (C4), 65.0 (C3) and 19.0 (C5) ppm], coordinated to three chlorine atoms and to one THF molecule.
which reveals that isomers are in fast equilibrium and that their The THF is located perpendicular to the metallacycle plane. The
signals were averaged, Scheme 8. It is assumed that the indium is C–Cl atoms are in opposite faces of the ring with short distances to
coordinated by nitrogen and chlorine atoms because, all carbon the nitrogen atoms (3.06 and 3.15 Å). The coordinated oxygen atom
and hydrogen atoms showed broad signals, Scheme 9.
has a planar geometry attributed to sp2 hybridization. The chlorine
The reaction of 3 with two equivalents of InCl3 in TDF at atoms situated in the metallacycle plane have hydrogen bonds with
ꢀ65 1C showed seven sets of broad signals attributed to isomers the methyl and benzylic groups Cl4ꢁꢁꢁH–C19 (2.643 Å), Cl5ꢁꢁꢁH–C6
of coordination compounds. When the solution reached +20 1C, (2.641 Å). Intermolecular interactions are depicted in Fig. 8.
only two sets of broad signals were observed, indicating the
To our knowledge there is only another X-ray diffraction analysis
existence of fast equilibrium between the isomeric species. One reported for an indium compound where the metal atom is
of the signal sets corresponds to that observed in the spectrum coordinated to a 1,4-diazabutadiene.15 It is a paramagnetic
of the equimolar reaction (B35%). Whereas, the second set compound of formula LInCl2ꢁTHF (L = 1,4-diisopropylphenyl-
[1H: 7.8 (H2), 5.6 (H4), 4.4 (C3) and 1.3 (5) ppm; 13C: 159.1 (C2), 1,4-diazabutadiene), in the reported compound the indium is
Fig. 7 Calculated minimum energy structure for diazabutadiene 3 coordinated to two InCl3.
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Table 7 Selected bond lengths and angles for compound 17
Bond lengths
Bond angles
In–N1
In–N2
N1–C1
N2–C2
C1–C2
N1–C3
N2–C4
Cl1–C5
Cl2–C7
In–Cl3
In–Cl4
In–Cl5
In–O1
2.313(7)
2.380(6)
1.242(9)
1.26(1)
N1–In–N2
Cl4–In–Cl5
Cl3–In–O1
N1–In–Cl4
N2–In–Cl5
C1–N1–In1
C2–N2–In1
C1–N1–C3
C2–N2–C4
C3–C5–Cl1
C4–C7–Cl2
72.2(2)
95.06(8)
172.4(2)
98.3(2)
Fig. 9 Calculated structure of the coordination compound 16.
1.50(1)
93.6(2)
indium coordination compounds was observed, and then
the signals for the 1,3-dialkyl-imidazolium tetrachloroindates
19–22 slowly emerged, Scheme 10. The transformations
attained after one week were 21% for 19; 98% for 20, 25% for
21 and 25% for 22. It was observed that these reactions slowed
down in the dark; therefore they could be photo-induced.34
The transformation of the ionic indium coordination compound
into the imidazoliums 19–21 is interesting because the only evident
source for the carbon introduced into the imidazole ring was the
ligand itself. Therefore it is assumed that the C–H imidazolium
compounds may come from the 1,3-dialkyl-2-methaneiminealkyl
imidazolium derivatives (11–14), which in the presence of InCl3 are
transformed into the relatively stable carbene-InCl3.35–37 The latter
by reaction with labile protons affords the C–H derivatives,
Scheme 11.
1.453(9)
1.492(9)
1.817(9)
1.825(9)
2.438(2)
2.434(2)
2.427(2)
2.287(6)
114.8(6)
112.1(5)
116.3(7)
117.9(7)
106.9(6)
108.7(7)
In order to check the latter statement, we have isolated the
chloride of the 1,3-dialkyl-2-methaneiminealkyl imidazolium
12, dissolved it in CH2Cl2 and added one equivalent of InCl3,
1
afterwards the reaction was followed by H and 13C NMR. Two
weeks later compound 12 was transformed into compound
20 (60%). An inverse reaction is known for the alkylation
of an imidazole carbene by an a,b-unsaturated enol ester.38
The observation of these transformations is relevant because
1,3-dialkyl-imidazolium compounds are precursors of imidazole
carbenes; important ligands for metal derivatives39 also used as
reagents40 and as ionic liquids.41 Optically active carbenes are
catalyzing agents for enantiosynthesis.42,43
Fig. 8 The indium coordination compound 17 forms chains by coopera-
tive C–Hꢁ ꢁ ꢁCl hydrogen bonds (Cl3ꢁ ꢁ ꢁH–C3 2.762 Å, Cl4ꢁ ꢁ ꢁH–C3 2.865 Å)
and Cl5ꢁ ꢁ ꢁp-interactions [Cl5ꢁ ꢁ ꢁC3 (3.35 Å); Cl5ꢁ ꢁ ꢁC4 (3.24 Å)].
The structure of compounds 19–22 was determined by NMR.
The aromatic character of the ring is denoted by the 1H and 13
C
pentacoordinated, the THF is in the anti position to one nitrogen
atom and the ligand is a radical monoanion.
NMR chemical shifts. C1–H protons for 19–22 appear in the
range of 8.3–10.63 ppm which indicates its positive character,
whereas C2–H is observed at 7.14–8.08 ppm. 13C NMR C1
signals are found at 130.2–138.4 ppm and C2 appears between
at 120.7 and 122.4 ppm. The 1,3-dialkyl-imidazoliums 19–22
were observed in the (+)TOF mass spectra and the [InCl4]ꢀ
anion in the (ꢀ)TOF spectra.
The optimized conformation for compound 17 is similar to
its X-ray diffraction analysis structure; therefore calculations
could provide a good approach for determining the structure of
coordinated indium compounds that could not be crystallized.
The calculated minimum energy conformer29 for compound 16
coordinated to THF is shown in Fig. 9. The chlorine atoms in
the structure are oriented towards the imine p electrons.
Calculations of the minimum energy structures of 1,3-
dialkylimidazolium heterocycles show that there is no steric
effect between the ring and the N-substituents, which freely
Reactions of diazabutadienes 1–4 with InCl3 in THF
The reactions of ligands 1–4 with InCl3 in THF at room rotate.28 The rotational barrier for the t-butyl group rotamers in
temperature were followed by NMR. The formation of the compound 22 was calculated to be 2.57 kJ molꢀ1
.
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Scheme 10 Synthesis of compounds 19–22.
Scheme 11 Plausible transformation of 1,3-dialkyl-2-methaneiminealkyl imidazolium into the 1,3-dialkyl-imidazolium, promoted by InCl3 through an
intermediate carbene which is protonated.
Conclusions
compounds 15–18 could be explained, if it is assumed that 1,3-
dialkyl-2-methaneiminealkyl imidazoliums are previously formed
and cleaved by the InCl3 to give the corresponding carbenes
stabilized by the InCl3. Consequent reactions of the carbenes with
labile protons afford the C–H imidazolium heterocycles (19–22).
It was found that in the X-ray diffraction analyses and in
calculations of compounds derived from ligands 2 and 3 that
the chlorine atoms have stabilizing contacts with the p system
of the imines.
In the reactions of AlCl3 and InCl3 with 1,4-dialkyl-1,4-
diazabutadienes (1–4) the nature of the metal halides, the
nitrogen substituents and the solvent determine the reaction
products. The two metal coordination compounds transformations
into imidazolium derivatives are of interest in the heterocyclic
chemistry.
Two new 1,4-dialkyl-1,4-diazabutadienes bearing two optically active
N-substituents: 1-chlorobutan-2-yl (2) and 1-chloro-1-phenyl-propan-
2-yl (3) and their X-ray diffraction analyses are reported. The solid
state conformation showed that the diazabutadiene system adopts
the more stable anti conformation with imines in E configuration.
The reactions of diazabutadienes 1–4 with aluminum halides in
toluene afforded unstable ionic coordination compounds. The X-ray
diffraction of one of them was obtained. The aluminum coordi-
nation compounds in THF solution are slowly and completely
transformed into 1,3-dialkyl-2-methaneiminealkyl imidazolium
heterocycles (11–14). This transformation has not been described
before. The X-ray diffraction analysis of compounds 11 and 14
indicated that the conformation of the exocyclic imine was deter-
mined by the steric effect of the nitrogen substituents. Calculations
showed that the most stable conformations were those found in the
solid state.
Reactions of InCl3 with diazabutadienes 1–4 in acetonitrile
afforded the corresponding neutral and diamagnetic indium
coordination compounds 15–18. To our knowledge these are the
first examples of diamagnetic and neutral indium coordination
compounds derived from 1,4-diazabutadiene ligands. They are
stable in the solid state and could be isolated. The X-ray
diffraction analyses of the THF adduct of the indium coordina-
tion compound 17 was obtained.
Experimental section
General remarks
Reagents were purchased from Sigma-Aldrich Chemical, Fluka
Chemika and Strem Chemical, and were not purified. Vacuum
line techniques were employed for all manipulations of air and
moisture sensitive compounds. THF, toluene, CH2Cl2 and
acetonitrile were dried prior to use44 Dry CDCl3, DMSO-d6,
THF-d8, were purchased from Aldrich and used without further
purification. (1S,2S)-1-Chloro-1-phenyl-2-aminepropane hydro-
chloride was prepared as reported,24 as well as compounds
145,46 and 4.47
The reactions of InCl3 in THF also gave the neutral diamagnetic
InCl3 coordination compounds 15–18, however in the THF solution
they are slowly transformed into the 1,3-dialkyl imidazolium
heterocycles 19–21. This transformation has not been reported
before in the literature. The origin of 1,3-dialkylimidazolium
Melting points were obtained using a Mel-Temp II apparatus
and are uncorrected. Mass spectra were obtained by LC/MSD
TOF on an Agilent Technologies instrument with ESI as an
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ionization source. Elemental analyses were performed on Flash Synthesis of the compounds
(EA) 1112 series equipment. IR spectra were recorded on a KBr disc
(R)-(ꢀ)-1-Chloro-butan-2-amine hydrochloride. To a solution
of (R)(ꢀ)-2-aminobutanol (10 g, 112 mmol) in THF (50 mL) at
0 1C, SOCl2 (16.4 mL, 224 mmol) was added. The solution was
stirred for 12 h at 70 1C and the resulting mixture filtered and
washed with acetone. The (R)(ꢀ)-2-chlorobutylamine hydro-
chloride is a colorless solid (13.8 g, 86%), it crystallized from
CHCl3. Mp. 180 1C. [a]D ꢀ91 (EtOH, 25 1C). NMR (D2O, 25 1C;
d ppm), 1H: 3.57 (qd, 3J 3.46, 3.21 Hz, 1H, H4, 3.87 (dd, 3J 3.46,
5.96 Hz, 2H, H3), 1.77 (qd, 3J 7.42 Hz, 2H, H5), 0.99 (t, J 7.42 Hz,
3H, H6); 13C: 53.7 (C3), 44.4 (C4), 23.3 (C5), 9.0 (C6). Anal. calcd
for [C4H11Cl2N]: C, 33.52; H, 7.68; N, 9.77%; found: C, 32.84; H,
7.79; N, 9.43%.
1,4-Bis[(R)-10-chlorobutan-20-yl]-1,4-diazabutadiene (2). To a
solution of (R)-(ꢀ)-1-chloro-butan-2-amine hydrochloride (5 g,
35 mmol) in EtOH/CH2Cl2 [2 : 1] (100 mL), Na2CO3 (3.71 g,
35 mmol) and then aq. glyoxal 40% (2 mL, 17.5 mmol) were
slowly added and stirred for 15 h at rt. The reaction mixture was
extracted with CH2Cl2, and dried with Na2SO4, filtered and the
solvent evaporated. Compound 2 is a yellow solid (5.8 g, 70%).
Mp 56–58 1C. [a]D = + 292.45 (EtOH, 25 1C). NMR (CDCl3, 25 1C;
d ppm), 1H: 7.89 (s, 2H, H2), 3.23 (m, 2H, H3), 3.67 (dd,
3J 4.35 Hz, 2H, H4a), 3.57 (dd, 3J 7.70 Hz, 2H, H4b), 1.60
(qdd, 3J 4.07 Hz, 2H, H5a), 1.77 (qdd, 3J 4.22 Hz, 2H, H5b),
0.83 (t, 3J 7.44 Hz, 6H, H6). 13C:162.5 (C2), 73.6 (C3), 47.5 (C4),
using a FT Spectrum GX Perkin Elmer spectrometer. NMR spectra
were obtained on a Jeol GSX-270, Jeol Eclipse 400 MHz and Bruker
Avance 300 MHz. 1H, 13C, 27Al [X 26.077, Al(NO3)3]. Numbering of
atoms for identification of the NMR signals is shown in Scheme 2.
Calculations were performed in order to obtain the molecular
geometries using the Gaussian 0328 using DFT and the hybrid
method B3LYPP/6-31+G(d,p). For indium compounds, the base
used was 3-21G. Geometries were checked to be the minimal by
the frequency analysis.
Crystallographic data were measured using a Nonius Kappa
CCD instrument with a CCD area detector using graphite-
monochromated MoKa radiation. Intensities were measured
using j+o scans. Crystal data are in Tables 8 and 9. Structures
were solved using direct methods with SHELX-97,48 Sir 2002
and Sir 2004.49
The refinement for all structures (based on F2 of all data)
was performed by full matrix least-squares techniques using
Crystals 12.84.50 All non-hydrogen atoms were refined anisotropi-
cally. Crystallographic data have been deposited at the Cambridge
Crystallographic Data Centre with numbers: 2 (960655), 3(S,S)
(960656), 3(meso) (960657), 10(960658), 11 (960659), 14(AlCl4)ꢀ
(960660), 14(I3)ꢀ (960661), 17 (960662), (R)-(ꢀ)-1-chloro-butan-2-
amine hydrochloride (960663).
Table 8 Crystallographic data for compounds 2, 3, 10 and 11
Compd
2
3(S,S)
10
11
Empirical formula
Formula weight
Crystal size [mm]
Crystal shape
Crystal color
Crystal system
Space group
a [Å]
C10H18Cl2N2
237.16
C20H22Cl2N2
361.30
C11H23AlClN2CH3AlCl3
394.11
C28H30N3AlCl4
577.33
0.4 ꢂ 0.2 ꢂ 0.2
0.23 ꢂ 0.05 ꢂ 0.05
0.4 ꢂ 0.15 ꢂ 0.05
0.5 ꢂ 0.4 ꢂ 0.35
Prism
Needle
Prism
Prism
Colorless
Orthorhombic
P212121
13.2941 (5)
4.6884 (2)
21.0334 (10)
90.000
Colorless
Monoclinic
P21
5.6218 (2)
26.6363 (11)
6.8310 (2)
90.000
Colorless
Orthorhombic
Pbca
11.6141 (3)
17.4168 (5)
21.0756 (8)
90.000
Colorless
Monoclinic
P21
6.988 (10)
23.822 (2)
9.334 (5)
90.000
b [Å]
c [Å]
a [1]
b [1]
90.000
90.000
1310.97
4
1.202
0.46
504
113.898 (2)
90.000
935.20 (6)
2
1.279
0.35
90.000
90.000
4263.2 (2)
8
1.228
0.63
1648
101.68
90.000
1521 (9)
2
1.26
0.44
600
g [1]
V [Å3]
Z
Dx (calcd) (mg mꢀ3
)
m [mmꢀ1
F(000)
]
380
Temperature [K]
y range for data collection
Index ranges
293
173
1–27.5
ꢀ7 r h r 7
ꢀ20 r k r 34
ꢀ8 r l r 8
6597
2908
2618
0.035
293
293
4.2–27.5
ꢀ17 r h r 17
ꢀ6 r k r 5
ꢀ27 r l r 27
5462
2940
1788
2.9–27.5
ꢀ14 r h r 14
ꢀ22 r k r 22
ꢀ27 r l r 27
8869
4677
1948
0.8–27.5
ꢀ8 r h r 8
ꢀ29 r k r 30
ꢀ12 r l r 12
13 617
6327
4427
Reflections measured
Independent reflections
Reflections observed [I > 2s(I)]
R(int)
0.056
0.105
0.032
Number of parameters
Weighting scheme R/wR
GOOF
177
0.0497/0.1768
1.02
0.051
0.131
305
0.0282/0.4729
1.06
0.039
0.089
189
0.1191/3.1453
1.02
0.088
0.278
294
0.065/0.6828
1.03
0.062
0.163
R [F > 2s(F2)]
wR (F2)
Largest residual peak [e Åꢀ3
]
0.21, ꢀ0.16
0.24, ꢀ0.27
0.52, ꢀ0.39
0.42, ꢀ0.28
w = 1/[s2(Fo2) + (aP)2 + bP] where P = (Fo + 2Fc2)/3.
2
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Table 9 Crystallographic data for compounds 14 and 17
Compd
14[AlCl4]
14[I3]
17
Chlorohydrate
Empirical formula
Formula weight
Crystal size [mm]
Crystal shape
Crystal color
Crystal system
Space group
a [Å]
C16H31N3AlCl4
433.21
C16H30N3I3
645.13
0.25 ꢂ 0.13 ꢂ 0.03
Fragment
Red
Monoclinic
P21/c
13.533 (2)
11.4237 (13)
18.787 (2)
90.000
C24H30Cl5InN2OC4H8O
726.67
C4H11ClNCl
144.04
0.38 ꢂ 0.3 ꢂ 0.15
0.25 ꢂ 0.05 ꢂ 0.05
0.45 ꢂ 0.2 ꢂ 0.15
Prism
Needle
Prism
Colorless
Orthorhombic
Pbca
10.9102 (3)
20.2966 (5)
21.7692 (7)
90.000
Colorless
Orthorhombic
P212121
6.9619 (2)
13.4095 (5)
35.1631 (9)
90.000
Colorless
Tetragonal
I4
14.5159 (3)
14.5159 (3)
7.1671 (2)
90.000
b [Å]
c [Å]
a [1]
b [1]
90.000
90.000
4820.6 (2)
8
1.194
0.53
1824
125.466 (8)
90.000
2365.5 (5)
4
1.811
3.97
90.000
90.000
3282.67 (18)
4
1.47
1.15
1480
90.000
90.000
1510.19 (8)
8
1.267
0.76
608.0
g [1]
V [Å3]
Z
Dx (calcd) (mg mꢀ3
)
m [mmꢀ1
F(000)
]
1224
Temperature [K]
y range for data collection
Index ranges
293
293
173
293
3.3–27.5
ꢀ13 r h r 13
ꢀ25 r k r 26
ꢀ28 r l r 28
10 069
5386
2246
0.8–27.5
ꢀ16 r h r 15
ꢀ13 r k r 14
ꢀ18 r l r 23
4431
3093
1598
1.0–27.5
ꢀ9 r h r 5
ꢀ17 r k r 10
ꢀ45 r l r 28
14 201
7082
3687
0.8–27.5
ꢀ18 r h r 18
ꢀ18 r k r 17
ꢀ9 r l r 9
11 708
1686
1490
Reflections measured
Independent reflections
Reflections observed [I > 2s(I)]
R(int)
0.154
0.065
0.088
0.041
Number of parameters
Weighting scheme R/wR
GOOF
279
0.0983/3.5245
1.02
0.088
0.251
0.38, ꢀ0.34
2
209
428
0.0476
0.99
0.071
0.144
0.90, ꢀ0.60
108
0.030/0.1586
1.09
0.026
0.059
0.1434/27.4624
1.15
0.109
0.366
1.04, ꢀ1.60
R [F > 2s(F2)]
wR (F2)
Largest residual peak [e Åꢀ3
]
0.12, ꢀ0.16
w = 1/[s2(Fo2) + (aP)2 + bP] where P = (Fo + 2Fc2)/3.
26.5 (C5), 10.5 (C6). IR (KBr, nmax cmꢀ1): 1625 (CQN), 729 compound 13 was obtained as a brown solid. Mp. 144–145 1C. IR
1
(C–Cl). Anal. calcd for [C10H18Cl2N2]: C, 50.64; H, 7.65; N, (KBr, nmax cmꢀ1) 1647. NMR (THF-d8, 25 1C d ppm) H: 8.43 (br s,
11.81%; found: C, 50.58; H, 8.08; N, 11.62%.
1H, H2), 7.40–7.50 (br, 10H, Ph), 6.06 (q, 3J 6.6 Hz, 2H, H3), 1.55 (d, 3J
1,4-Bis[(S,S)-10-chloro-10-phenylpropan-20-yl]-1,4-
6.6 Hz, 6H, H4). 13C: 159.6 (C2), 130–127 (Ph), 62.0 (C3), 21.8 (C4).
diazabutadiene (3). Compound 3 (1S,2S) was prepared from 27Al: +107.1 (D1/2 94 Hz), +34 (D1/2 1250 Hz). Anal. calcd for
(1R,2S)-1-chloro-1-phenylpropan-2-amine hydrochloride (5 g, [C18H20N2Al2Cl6]: C, 40.71; H, 3.80; N, 5.28%; found: C, 40.29; H,
24 mmol), Na2CO3 (2.54 g, 24 mmol), EtOH–CH2Cl2 [2 : 1] 4.34; N, 4.99%.
(100 mL), and 40% aq. glyoxal (1.4 mL, 12 mmol). The reaction
2,2-Dichloro-1,3-bis[(R)-10-chlorobutan-20-yl]-1,3-diaza-2-alumina-
mixture was extracted with CH2Cl2, and dried with Na2SO4, cyclopenta-3,5-diene tetrachloro aluminate (6). Compound 2 (0.27 g.
filtered and the solvent evaporated. Compound 2 (1R,2R) is a 1.1 mmol) in toluene (10 mL) was added to AlCl3 (0.30 g, 2.3 mmol)
yellow solid, it crystallized from EtOH–CH2Cl2 (8.3 g, 96%). Mp in toluene (10 mL). A brown oil was separated from the reaction
120–122 1C. [a]D ꢀ138 (CH2Cl2, 25 1C). NMR (CDCl3, 25 1C d ppm), mixture and isolated using a canula. Brown solid, mp 119–121 1C.
3
1H: 8.06 (s, 2H, H2), 3.78 (dq, J 7.68 and 6.59 Hz, 2H, H3), 4.92 IR (KBr, nmax cmꢀ1) 1636. 27Al NMR (THF-d8, 25 1C d ppm): +100.1
(d, 3J 7.68 Hz, 2H, H4), 1.05 (d, 3J 6.59 Hz, 6H, H5), 7.36 (m, 10H, (D1/2 92 Hz), +62 (D1/2 3036 Hz). Anal. calcd for [C10H18Cl2N2Al2Cl6]:
H–Ph). 13C: 162.3 (C2), 72.3 (C3), 67.3 (C4), 20.2 (C5), 138.9 (Ci), C, 23.84; H, 3.60; N, 5.56%; found: C, 23.31; H, 3.68; N, 5.07%.
128.7 (Co), 128.7 (Cm), 127.9 (Cp). IR (KBr, nmax cmꢀ1): 1632 (CQN),
2,2-Dichloro-1,3-bis[(S,S)-10-chloro-10-phenylpropan-20-yl]-1,3-
736 (C–Cl). Anal. calcd for [C20H22Cl2N2]: C, 66.49; H, 6.14; N, diaza-2-alumina-cyclopenta-3,5-diene tetrachloroaluminate (7).
7.75%; found: C, 66.11; H, 6.18; N, 7.68%. Compound 3 (0.39 g, 1.1 mmol) in toluene (10 mL) was added
2,2-Dichloro-1,3-bis[(S) 1-methylbenzyl]-1,3-diaza-2-aluminacyclo- to AlCl3 (0.29 g. 2.2 mmol) in toluene (10 mL). A viscous brown
penta-3,5-diene tetrachloro aluminate (5). A general procedure was solid was obtained. IR (KBr, nmax cmꢀ1) 1634. 27Al NMR (THF-d8,
used for synthesizing aluminum compounds 5–10. To a solution of 25 1C; d ppm): +100.2 (D1/2 80 Hz), +68 (D1/2 3754 Hz).
compound 1 (0.27 g, 1.0 mmol) in toluene (10 mL) and in a N2
2,2-Dichloro-1,3-di-tert-butyl-1,3-diaza-2-aluminacyclopenta-
atmosphere previously cooled at ꢀ78 1C, AlCl3 (0.27 g, 2.0 mmol) 3,5-diene tetrachloro aluminate (8). Compound 4 (0.5 g,
dissolved in toluene (10 mL) at ꢀ78 1C was added. The resulting 3.0 mmol) in toluene (20 mL) was added to AlCl3 (0.8 g,
mixture was stirred for 2 h. Then, the solution was evaporated and 6.0 mmol) in toluene (20 mL). Compound 13 is obtained as a
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yellow solid (0.81 g, 90%). Mp 43 1C. NMR (CDCl3, 25 1C; NMR (CDCl3, 25 1C; d ppm), 1H: 7.71 (s, 2H, H2), 5.27 (br s, 2H,
d ppm), 1H: 9.04 (s, 2H, H2), 1.71 (s, 18H, H4). 13C: 163.3 H3), 3.86 (br s, 4H, H4), 1.99 (br s, 4H, H5), 0.84 (br s, 6H, H6),
(C2), 65.9 (C3), 29.7 (C4). 27Al: +102.3 (D1/2 150 Hz, Alꢀ), +94.6 [substituent in C1: 8.53 (s, 1H, H20), 4.27 (br s, 1H, H30), 3.76
(D1/2 3550 Hz, Al+). (+)TOF, m/z (amu): calcd for [C10H20N2AlCl2]: (br s, 2H, H40), 1.94 (br s, 2H, H50), 0.78 (br s, 3H, H60)]. 13C
265.0818; found; 265.0816. (ꢀ)TOF, m/z (amu): calcd for 138.7 (C1), 121.2 (C2), 62.0 (C3), 46.2 (C4), 25.4 (C5), 10.0 (C6),
[AlCl4]ꢀ 126.9045; found: 126.9055. IR (KBr, nmax cmꢀ1): [substituent in C1: 145.4 (C20), 74.0 (C30), 47.1 (C40), 26.3 (C50),
1644 (CQN), 1482 (C–N), 1381 (C–C). Anal. calcd for 10.2 (C60)]. (+)TOF, m/z (amu): calcd for [C16H27N3Cl3]+ 366.1265;
[C10H20N2Al2Cl6]: C, 27.61; H, 4.63; N, 6.44%; found: C, 27.11; found: 366.1275.
H, 4.43; N, 6.25%.
1,3-Bis[(S,S)-10-chloro-10-phenylpropan-20-yl]-2-[N-(S,S)-100-chloro-
2,2-Diiodo-1,3-di-tert-butyl-1,3-diaza-2-aluminacyclopenta-3,5- 100-phenylpropan-200-yl-methanimine]-imidazolium chloride (13).
diene tetraiodo aluminate (9). Compound 4 (0.5 g, 3.0 mmol) in Compound 3 (0.5 g, 1.39 mmol) in THF (50 mL) was added to
toluene (20 mL) was added to AlI3 (2.43 g, 6.0 mmol) in toluene AlI3 (0.56 g, 1.39 mmol) in THF (20 mL). Compound 13 is obtained
(20 mL). Compound 9 is obtained as a brown solid (2.52 g, 85%). as a dark solid (0.56 g, 88%). Mp 92 1C. [a]D +58.82 (CH2Cl2, 25 1C).
Mp 43 1C. NMR (CDCl3, 25 1C; d ppm), 1H: 9.27 (s, 2H, H2), 1.83 NMR (CDCl3, 25 1C; d ppm), 1H: 8.99 (s, 2H, H2), 7.47–7.27 (m, 15H,
(s, 18H, H4). 13C: 160.0 (C2), 65.2 (C3), 30.6 (C4). 27Al: +89.4 (D1/2 Ph), 5.99 (t, J 5.9 Hz, 2H, H3), 5.91 (d, J 7.8 Hz, 2H, H4), 1.55 (d, J 5.9
2050 Hz, Al+), ꢀ20.2 (D1/2 137.3 Hz, Alꢀ). IR (KBr, nmax cmꢀ1): Hz, 6H, H5), [substituent in C1: 9.11 (s, 1H, H20), 4.87 (t, J 5.9 Hz,
1644 (CQN): Anal. calcd for [C10H20N2Al2I6]: C, 12.21; H, 2.05; N, 1H, H30), 4.08 (d, J 8.5 Hz, 1H, H40), 0.96 (d, J 5.9 Hz, 3H, H50). 13C:
2.85%; found: C, 11.88%, H, 2.42; N, 2.96%.
138.5 (C1), 121.9 (C2), 136.5 (2Ci), 129.1 (4Co), 129.0 (2Cp), 127.9
2,2-Dichloro-1,3-di-tert-butyl-1,3-diaza-2-aluminacyclopenta- (4Cm), 65.5 (C3), 61.2 (C4), 18.9 (C5), [substituent in C1: 145.3 (C20),
0
0
0
0
0
3,5-diene trichloromethyl aluminate (10). Compound 4 (0.5 g, 138.1 (Ci ), 129.6 (2Co ), 129.0 (Cp ), 128.1 (2Cm ), 72.6 (C3 ), 67.3
3.0 mmol) in toluene (50 mL) was added to a 1 M solution of (C40), 20.3 (C50)]. IR (KBr, nmax cmꢀ1): 1737 [CQN], 1677 [CQN],
AlMeCl2 in hexane (6 mL, 6.0 mmol). Compound 15 is obtained 1554 [C–N]. (+)TOF, m/z (amu): calcd for [C31H33N3Cl3]+, 552.1734;
as a crystalline solid. Suitable crystals for X-ray diffraction found, 552.1742. Anal. calcd for (C31H33N3Cl4ꢁ3H2O): C, 57.86; H,
analysis were obtained CHCl3 (1.03 g, 80%). Dec 50 1C. NMR 6.11; N, 6.53%; found: C, 58.54; H, 6.12; N, 6.65%.
1
(CDCl3, 25 1C; d ppm), H: 8.98 (s, 2H, H2), 1.62 (s, 18H, H4),
N-tert-Butyl-1-[1,3-di-tert-butyl-methanimine]-imidazol-1-ium-2-
+
ꢀ0.53 (s, 3H, AlMe2 ), ꢀ0.17 (s, 3H, AlMe4ꢀ); 13C: 162.8 (C2), yl triiodide (14). Compound 4 (0.5 g, 3 mmol) in THF (50 mL) was
+
64.2 (C3), 29.6 (C4), ꢀ8.9 (AlMe2 ), ꢀ8.3 (AlMe4ꢀ). 27Al: +130.1 added to AlI3 (1.22 g, 3 mmol) in THF (20 mL). A viscous dark
(D1/2 2016 Hz, Al+), +102.1 (D1/2 22.3 Hz, Alꢀ). IR (KBr, liquid was obtained (0.7 g, 73%).
nmax cmꢀ1) 1650 (CQN).
Crystallization from methanol affords compound 14 with I3
1,3-Bis[(S)-methylbenzyl]-2-[N-(S)-methylbenzyl]-methanimine- as the anion. Mp 146–148 1C. (+)TOF, calcd for [C16H30N3]+, m/z
imidazolium tetrachloro aluminate (11). General procedure for (amu): 264.2434; found: 264.2435. (ꢀ)TOF, calcd. for [I]ꢀ, m/z
imidazoles 11–14. To a solution of diazabutadiene 1 (1.0 g, (amu): 126.9045; found: 126.9048. NMR (CDCl3, 25 1C; d ppm),
3.78 mmol) in THF (50 mL) and in a N2 atmosphere, AlCl3 1H: 7.43 (s, 2H, H2), 1.59 (s, 18H, H4), [substituent in C1: 8.37
(0.54 g, 3.78 mmol) in THF (20 mL) previously cooled at ꢀ78 1C (s, 1H, H20), 1.31 (s, 9H, H40)] 13C: 119.5 (C2), 140.2 (C1), 63.1
was slowly added. The reaction mixture was stirred for 2 h at rt; (C3), 30.2 (C4), [substituent in C1: 145.4 (C20), 61.4 (C30), 27.8
the solvent was evaporated in vacuum. The product was dissolved (C40)]. IR (KBr, nmax cmꢀ1): 1641 [CQN], 1596 [C–N]. Anal. calcd
in CH2Cl2 and washed with water (5 mL). The organic solution for [C16H30N3I3ꢁ1/2I]: C, 27.12; H, 4.27; N, 5.93%; found: C,
was dried with Na2SO4, filtered and evaporated (1.0 g, 98%). 27.42; H, 4.34; N, 6.33%. Crystals were subjected to X-ray
Crystals of 11, suitable for X-ray diffraction were obtained from diffraction analyses.
CHCl3. Mp 126–128 1C. NMR (CDCl3, 25 1C; d ppm), 1H: 7.53
Crystallization from CHCl3 gave compound 14 having AlCl4 as
3
(s, 2H, H2), 7.34–6.78 (m, 15H, Ph), 6.17 (q, J 6.3 Hz, 2H, H3), the anion. (+)TOF, m/z (amu): calcd for [C16H30N3]: 264.2435; found:
3
1.85 (d, J 6.3 Hz, 6H, H4), [substituent in C1: 8.43 (s, 1H, H20), 264.2437. (ꢀ)TOF, m/z (amu): calcd for [AlCl4]ꢀ 126.9045; found:
4.60 (q, 3J 6.3 Hz, 1H, H30)]. 13C: 141.9 (Ci), 137.1 (C1), 129.5 (4Co), 126.9055. Crystals were subjected to X-ray diffraction analyses.
129.1 (2Cp), 126.5 (4Cm), 121.3 (C2), 59.2 (C3), 21.4 (C4)),
2,2,2-Trichloro-1,3-di[(S) methylbenzyl]-1,3-diaza-2-indacyclo-
0
0
0
[substituent in C1: 143.8 (C2 ), 138.2 (2Ci ), 128.9 (2Co ), 127.8 penta-3,5-diene (15). A general procedure was used for com-
(Cp ), 126.9 (2Cm ), 70.8 (C3 ), 23.5 (C5 )]. 27Al: 101.3 (D1/2 215 Hz). pounds 15–18. Compound 15 was prepared at ꢀ75 1C in a N2
IR (KBr, nmax cmꢀ1): 1638 [CQN]. (+)TOF, m/z (amu): calcd for atmosphere by addition of a solution of InCl3 (0.17 g, 0.76 mmol)
[C28H30N3]+: 408.2434; found: 408.2436. (ꢀ)TOF, m/z (amu): calcd. in dry acetonitrile (10 mL) to a solution of 2 (0.1 g, 0.38 mmol) in
for [AlCl4]ꢀ 126.9045; found: 126.9055. Anal. calcd for dry acetonitrile (10 mL). The solvent was evaporated in vacuum.
(C28H38N3AlCl4)5(CHCl3)3: C, 52.28; H, 5.92; N, 6.40%; found: C, A brown solid was obtained (0.6 g, 91%). Mp 84–86 1C. NMR
0
0
0
0
52.33; H, 5.65; N, 6.54%.
(CD3CN, 25 1C; d ppm), 1H: 8.21 (s, 2H, H2), 7.40–7.50 (m, 10H,
1,3-Bis[(R)-10-chlorobutan-20-yl]-2-[N-(R)-100-chlorobutan-200-yl- Ph), 5.75 (q, J 7.0 Hz, 2H, H3), 1.74 (d, J 7.0 Hz, 6H, H4). 13C:
methanimine]-imidazolium chloride (12). Compound 3 (0.5 g, 156.6 (C2), 138.4 (Ci), 129.1 (Co), 128.9 (Cp), 128.5 (Cm), 63.0 (C3),
2.12 mmol) in THF (50 mL) was added to AlI3 (0.86 g, 2.12 mmol) 20.6 (C4). IR (KBr, n cmꢀ1): 1660, 1628 (CQN, Ph).
3
3
in THF (20 mL), at ꢀ78 1C. Compound 12 is obtained as a
2,2,2-Trichloro-1,3-bis[(R) 10-chlorobutan-20-yl]-1,3-diaza-2-
viscous dark liquid (0.4 g, 75%). [a]251 = ꢀ172.41 (CH2Cl2, 251). indacyclopenta-3,5-diene (16). InCl3 (0.1 g, 0.42 mmol) in
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acetonitrile (0.5 mL) was added to compound 2 (0.5 g, found 249.0924. (ꢀ)TOF, m/z (amu): calcd for [InCl4]ꢀ 254.7798;
0.21 mmol) in acetonitrile (0.5 mL). A colorless solid (0.1 g, found 254.7802. Anal. calcd for [C11H19N2Cl6In]: C, 26.07; H,
97%) was obtained. Mp 131–132 1C. NMR (CD3CN, 25 1C; 3.78; N, 5.53%; found: C, 25.88; H, 4.07; N, 5.86%.
d ppm), 1H: 8.31 (s, 2H, H2), 4.49 (m, 2H, H3), 4.20 (dd,
1,3-Bis[(S,S)-10-chloro-10-phenylpropan-20-yl]-imidazolium tetra-
2J 12.0, 6.3 Hz, 2H, H4A), 4.09 (dd, J 12.0, 2.9 Hz, 2H, H4B), chloroindate (21). Compound 2 (0.5 g, 1.4 mmol) in THF (20 mL)
2.06 (m, 2H, H5A), 1.93 (m, 2H, H5B), 0.92 (t, 6.0 Hz, 3H, H6). was added to InCl3 (0.31 g, 1.4 mmol) in THF (20 mL), in a N2
13C: 156.2 (C2), 69.2 (C3), 45.9 (C4), 23.7 (C5), 9.8 (C6). IR (KBr, atmosphere. The mixture was stirred for 12 h and the solvent was
n cmꢀ1): 1677, 1617 (CQN). Anal. calcd for [C10H18N2Cl5Inꢁ evaporated. The resulting solids were dissolved in CH2Cl2 and
1/2CH3CN]: C, 29.15; H, 4.48; N, 5.67%; found: C, 29.43; H, washed with water. In the organic solvent, compound 21 was
2
4.56; N, 5.41%.
obtained as a brown solid (0.1 g, 25%). Mp 104–106. NMR (CDCl3,
1
2,2,2-Trichloro-1,3-bis[(S,S) 10-chloro-10-phenylpropan-20-yl]- 25 1C; d ppm), H: 8.92 (s, 1H, H1), 8.08 (s, 2H, H2), 7.7–7.1 (m,
1,3-diaza-2-indacyclopenta-3,5-diene (17). InCl3 (0.3 g, 10H, Ph), 4.91 (m, 1H, H3), 4.03 (br s, 1H, H4), 1.07 (br s, 3H, H5).
1.4 mmol) in acetonitrile (10 mL), compound 3 (0.5 g, 1.4 mmol) 13C: 121.2 (C2), 138.4 (C1), 137.9 (Ci), 130.2 (Co), 129.8 (Cp), 128.5
in acetonitrile (10 mL). Crystalline solid (0.73 g, 91%). Mp (Cm), 64.3 (C4), 53.5 (C3), 15.8 (C5). IR (KBr, nmax cmꢀ1): 1669, 1633
122–124 1C. NMR (CD3CN, 25 1C, d ppm), 1H: 8.33 (s, 2H, and 1453. (+)TOF, m/z (amu): calcd for [C21H23N2Cl2]+ 373.1232,
H2), 7.40–7.37 (m, 10, Ph), 5.08 (d, 2H, H3), 4.12 (m, 2H, H4), found 373.1231. (ꢀ)TOF, m/z (amu): calcd for [InCl4]ꢀ 254.7798;
1.27 (d, 6H, H5). 13C: 158.2 (C2), 139.5 (Ci), 128.5 (Co, Cp), 128.2 found 254.7794. Anal. calcd for [C21H23N2Cl3ꢁH2O]: C, 58.96; H,
(Cm), 72.0 (C3), 66.6 (C4), 19.4 (C5). IR (KBr, n cmꢀ1): 1633, 1607 5.89; N, 6.55%; found: C, 58.73; H, 5.82; N, 6.60%.
(CQN, Ph). Anal. calcd for [C20H22Cl5N2Inꢁ1/2(C4H8O)]: C,
1,3-Bis[tert-butyl]-imidazolium tetrachloroindate (22). Com-
42.17%, H, 4.18; N, 4.47%; found: C, 41.97; H, 4.65; N, 4.50%. pound 4 (0.5 g, 3 mmol) in THF (20 mL) was added to InCl3
2,2,2-Trichloro-1,3-di-tert-butyl-1,3-diaza-2-indacyclopenta-3,5- (0.67 g, 3 mmol) in THF (20 mL), in a N2 atmosphere. The
diene (18). InCl3 (1.04 g, 6.0 mmol) in acetonitrile (10 mL) was mixture was stirred for 12 h and the solvent was evaporated.
added to compound 4 (0.5 g, 3.0 mmol) in acetonitrile (10 mL). From the NMR spectra the reaction yield was estimated to
1
A pink solid (1.1 g, 96%) was obtained. Mp 113–115 1C. NMR be 25%. NMR (CDCl3, 25 1C; d ppm) H: 7.37 (s, 2H, H2), 8.27
(CD3CN, 25 1C, d ppm), 1H: 8.35 (s, 2H, H2), 1.57 (s, 18H, H4). 13C: (s, 1H, H1), 1.30 ppm (s, 18H, H3); 13C: 120.7 (C2), 130.2
155.4 (C2), 66.4 (C3), 29.4 (C4). IR (KBr, n cmꢀ1): 1675, 1612 (C1), 60.4(C3), 29.6 ppm (C4)]. Mass spectrometry {(+)TOF,
(CQN). Anal. calcd for [C10H20N2Cl3In]: C, 30.85; H, 5.14; N, m/z (amu): calcd for [C11H21N2]+ 181.1704; found 181.1705.
7.20%; found: C, 30.73; H, 5.66; N, 5.63%.
(ꢀ)TOF, m/z (amu): calcd for [InCl4]ꢀ 254.7798; found
1,3-Di[(S)-methylbenzyl]-imidazolium tetrachloroindate (19). 254.7754}.
A general procedure was used for compounds 19–22. To a
solution of InCl3 (0.42 g, 1.9 mmol) in THF (20 mL) and in a
N2 atmosphere, compound 1 (0.5 g, 1.9 mmol) in THF (20 mL)
Acknowledgements
was added. The reaction mixture was stirred for 12 h and the
solvent evaporated. From the NMR spectra the reaction yield was H.R-S. and A.M.D-H. thank Conacyt for PhD scholarships. We
estimated to be 21%. The solid was dissolved in CH2Cl2 (30 mL) are grateful to Cinvestav for the facilities of the supercomputer
and washed three times with water (10 mL). Compound 19 (20%) HPC-cluster Xiuhcoatl. We thank Professor Angeles Paz-Sandoval
was obtained mixed with methylbenzyl ammonium as a brown for helpful discussions.
viscous liquid. NMR (CDCl3, 25 1C; d ppm), 1H: 9.11 (s, 1H, H1),
7.6–7.2 (m, 10H, Ph), 7.14 (s, 2H, H2), 4.55 (q, 3J 6.8 Hz, 2H, H3),
1.56 (d, 3J 6.8 Hz, 6H, H4). 13C: 122.4 (C2), 135.0 (C1), 137.2 (Ci),
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