Synthesis of amino- and amido-aluminium derivatives and investigation of their dynamics in solution

Article abstract of DOI:10.1039/b211720g

The salts Li[Al(C₄H₈N)₄]·nC ₄H₈NH (n = 1, 2; C₄H₈NH = pyrrolidine) have been prepared and characterised in solution by ¹H-, ¹³C-, ⁷Li- and ²

Full text of DOI:10.1039/b211720g

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Synthesis of amino- and amido-aluminium derivatives and
investigation of their dynamics in solution
Vincenzo Passarelli,* Giovanni Carta, Gilberto Rossetto and Pierino Zanella
ICIS–CNR, Area della Ricerca di Padova, Corso Stati Uniti 4, I–35127 Padova, Italy.
E-mail: passarel@server1.dcci.unipi.it
Received 27th November 2002, Accepted 12th February 2003
First published as an Advance Article on the web 21st February 2003
The salts Li[Al(C4H8N)4]ؒnC4H8NH (n = 1, 2; C4H8NH = pyrrolidine) have been prepared and characterised in
solution by 1H-, 13C-, 7Li- and 27Al-NMR spectroscopy. Their reaction with AlCl3 (Cl/Li molar ratio = 3) affords the
binary amido derivative [Al(C4H8N)3]2, which, on turn, is reactive towards AlX3, yielding [AlX2(C4H8N)]2 (X = Cl,
CH3). The binuclear derivatives [AlY2(C4H8N)]2 (Y = Cl, CH3, C4H8N) react with [NH2Et2]Cl affording the amine
complexes AlY2Cl(C4H8NH)n (Y = CH3, n = 1; Y = Cl, n = 1, 2). Alternatively, the monochloro species Al(CH3)2Cl-
(C4H8NH) results from the reaction of Al(CH3)3(C4H8NH) and AlCl3(C4H8NH) (CH3/Cl molar ratio = 2). The
dichloro-methyl derivative Al(CH3)Cl2(C4H8NH) is obtained by reacting Al(CH3)3(C4H8NH) and AlCl3(C4H8NH)
(Cl/CH3 molar ratio = 2). The Lewis adducts AlCl3(amine)n (amine = pyrrolidine, n = 1, 2; amine = N,N,NЈ-trimethyl-
propanediamine, n = 1) have been isolated when AlCl3 was contacted with the stoichiometric amount of the amine.
At variance with N,N,NЈ-trimethylpropanediamine, N,N,NЈ-trimethylethylenediamine and N,N,NЈ,NЈ-tetramethyl-
ethylenediamine react with AlCl3 yielding the salt derivatives [AlCl2(amine)2][AlCl4].
The dynamic processes of the coordinated amine ligands of AlCl3(amine)n (amine = pyrrolidine, n = 1, 2; amine =
N,N,NЈ-trimethylpropanediamine, n = 1) and [AlCl2(amine)2][AlCl4] (amine = N,N,NЈ,NЈ-tetramethylethyl-
enediamine) have been investigated in solution by NMR spectroscopy.
ligands such as methyl and chloride; (b) elucidating their
Introduction
molecular structures and dynamics in solution by multinuclear
Amido-aluminium derivatives such as [Al(NR2)3]2, [HAl(NR2)]2
1D and 2D NMR spectroscopy.
(R = Me, Et),1 [AlMe2(NH2)]2 2 and [AlMe2(NPr2)]2 3 have been
successfully used as single-source precursors in the deposition
of AlN via CVD.
In this connection, aiming at depositing thin layers of AlN
Results and discussion
via CVD, we have been interested in the synthesis of novel
amido- and amino-aluminium derivatives, potentially usable as
single source precursors.
Amido- and amino-methyl derivatives
Our synthetic investigation started with the preparation of the
lithium salt Li[Al(C4H8N)4], potential precursor for binary
amido derivatives (vide supra). Smith and coworkers7 have
already reported the synthesis of this compound, obtained in
the form Li[Al(C4H8N)4]ؒ2C4H8NH from a THF solution, in
mixture with the THF solvento species Li[Al(C4H8N)4]ؒ2THF,
the compound being isolated as a pure material after crystal-
lisation from toluene. Noteworthy, the molecular structure
of Li[Al(C4H8N)4]ؒ2C4H8NH has been determined7 showing
the presence of the bimetallic core [Li(NC4H8)2Al], being the
coordination sphere of Al completed by two pyrrolidinide
groups, and that of lithium by two pyrrolidine ligands.
A survey of the literature has shown4 that two basic pro-
cedures are applicable to the synthesis of aluminium amides
(Scheme 1): (a) the reaction of the alkali metal amide (lithium
Interestingly, in the course of this work, the compounds
Li[Al(C4H8N)4]ؒnC4H8NH (n = 1, 2) have been obtained as pure
materials when pyrrolidine was reacted with LiAlH4 (according
to the appropriate C4H8NH/Li molar ratio) in Et2O, rather than
THF [eqn. (1)].
Scheme 1
or sodium derivative) with the [Al–Cl] functionality; (b) the
reaction of the [Al–H] or [Al–alkyl] functionalities with a
secondary amine. Moreover, it has been reported5 that the
binary aluminium compound [Al(NMe2)3]2 has been prepared
by reacting the secondary amine NHMe2 with LiAlH4, and then
the resulting lithium aluminium amide with AlCl3 (Scheme 1, c).
As far as amino-aluminium derivatives are concerned, it
is reported6 that amine adducts of aluminium halides or of
organoaluminium compounds result from the direct interaction
of the amine with the appropriate reagent, i.e. AlX3 (X = Cl, Br,
I, alkyl). Noteworthy, if the amine is secondary or primary, the
elimination of alkane is eventually observed from compounds
of general formula AlR3(amine).
(1)
At room temperature, as far as the chemical shifts are con-
cerned, the 1H-NMR spectra of the two compounds Li[Al-
(C4H8N)4]ؒnC4H8NH (n = 1, 2) are similar (Table 1).
The 13C-NMR spectra show the characteristic resonances
of the amido groups [C4H8N]Ϫ (Li[Al(C4H8N)4]ؒC4H8NH:
δ 50.1, CH2CH2N; 27.5, CH2CH2N; Li[Al(C4H8N)4]ؒ2C4H8-
NH: δ 50.6, CH2CH2N; 27.5, CH2CH2N) and those of the
coordinated pyrrolidine (Li[Al(C4H8N)4]ؒC4H8NH:
δ 47.0,
In this perspective, our study aimed at: (a) synthesising novel
amido- and amino-aluminium derivatives, containing ancillary
CH2CH2N; 25.5, CH2CH2N; Li[Al(C4H8N)4]ؒ2C4H8NH:
7
δ 47.2, CH2CH2N; 25.7, CH2CH2N). The 27Al- and Li-NMR
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 1H chemical shifts (ppm) of Li[Al(C4H8N)4]ؒnC4H8NH (n = 1,
AlH3(L)2 (L = THF, NMe3); moreover, the solid state molecular
structure of [Al(C4H8N)3]2 has been determined,7 showing the
presence of the bimetallic core [Al(C4H8N)2Al] and of four
terminal amido groups (two per Al). In agreement with the
2)
n = 1
n = 2
1
solid state structure, the H-NMR spectrum of the compound
[C4H8N]Ϫ
C4H8NH
3.20 (CH2CH2N)
1.74 (CH2CH2N)
2.27 (CH2CH2N)
3.22 (CH2CH2N)
1.72 (CH2CH2N)
2.44 (CH2CH2N)
1.90 (NH )
(recorded in the course of this study as well as reported in the
literature7) shows the characteristic resonances of the terminal
and bridging pyrrolidinide ligands, respectively, at 3.21 (CH2-
CH2N) and 1.71 ppm (CH2CH2N), and 2.98 (CH2CH2N)
and 1.49 ppm (CH2CH2N). Furthermore, four resonances are
observed in the 13C-NMR spectrum of the compound (terminal
pyrrolidinides: δ 50.0, CH2CH2N; 27.2, CH2CH2N; bridging
pyrrolidinides: δ 49.7, CH2CH2N; 25.4, CH2CH2N).
The reaction of [Al(C4H8N)3]2 with stoichiometric amounts
of AlX3 (X = CH3, Cl) yields the amido derivative [AlX2-
(C4H8N)]2 (Scheme 3). The 1H- and 13C-NMR spectra of [AlX2-
(C4H8N)]2 show the characteristic resonances of the bridging
pyrrolidinide ligand (1H, X = CH3: δ 2.62, CH2CH2N; 1.33,
CH2CH2N; X = Cl: δ 2.81, CH2CH2N; 1.24, CH2CH2N; 13C,
X = CH3: δ 49.7, CH2CH2N; 25.1, CH2CH2N; X = Cl: δ 50.6,
CH2CH2N; 24.5, CH2CH2N). In addition the signals of the
methyl groups at Ϫ0.57 and Ϫ11.9 ppm have been observed
in the 1H- and 13C-NMR spectra of [Al(CH3)2(C4H8N)]2,
respectively. The resonances of the 27Al centres in [AlCl2(C4-
H8N)]2 and [Al(CH3)2(C4H8N)]2 are observed at 117.2 and 165.6
ppm, respectively.
1.20 (CH2CH2NϩNH )
1.31 (CH2CH2N)
spectra show similar chemical shifts for the two derivatives
(7Li, about 13.5 ppm; 27Al, about 105 ppm).
Interestingly, the 1H- and 7Li-NMR spectra of Li[Al-
(C4H8N)4]ؒ2C4H8NH are little affected by the temperature.
On the other hand, at 183 K the 7Li-NMR spectrum of
Li[Al(C4H8N)4]ؒC4H8NH shows two lines (13.4, 13.1 ppm).
1
Moreover, at the same temperature, the H-NMR show three
lines at 3.58, 3.40 and 3.05 ppm (integral ratio 1 : 2 : 1) and 1.95,
1.88 and 1.67 ppm (integral ratio 1 : 2 : 1) for the methylene
protons of the amido group (CH2CH2N and CH2CH2N,
respectively). Moreover, the resonance of the CH2CH2N and
CH2CH2N protons of C4H8NH are observed at 2.30 and 1.17
ppm, respectively, as broad lines.
On this basis and keeping in mind the molecular structure of
Li[Al(C4H8N)4]ؒ2C4H8NH, we propose that (a) an equilibrium
exists involving two isomers (Scheme 2), namely (C4H8NH)-
Li(C4H8N)2Al(C4H8N)2 (Scheme 2, A) and (C4H8NH)Li-
(C4H8N)Al(C4H8N)3 (Scheme 2, B); (b) this equilibrium slows
down at 183 K; (c) a fast exchange occurs among the amido
groups of the isomer B, thus making equivalent their methylene
protons, even at 183 K.† The proposed assignment of the
7Li and 1H resonances is reported in Scheme 2.
Scheme 2
As expected, Li[Al(C4H8N)4]ؒnC4H8NH (n = 1, 2) proved to
be good precursors for the synthesis of [Al(C4H8N)3]2. As a
matter of fact, Li[Al(C4H8N)4]ؒnC4H8NH (n = 1, 2) reacts with
AlCl3 (Li/Cl molar ratio = 1) affording the above mentioned
binary compound [eqn. (2)].
Scheme 3
(2)
It is noteworthy that the methyl derivative [Al(CH3)2(C4H8-
N)]2 is already known,6b being obtained by reacting [Al(CH3)3]2
and pyrrolidine and then by decomposing the resulting adduct
Al(CH3)3(C4H8NH) (Scheme 3). Moreover, interestingly, in the
course of this work, the interaction of [Al(CH3)3]2 with pyrroli-
dine was re-examined showing that Al(CH3)3(C4H8NH) is not
the only product,6b the adduct Al(CH3)3(C4H8NH)2 being iso-
lated when the [Al(CH3)3]2 is reacted with C4H8NH according
to the Al/C4H8NH molar ratio 1/2 (Scheme 3), as well as by
reacting Al(CH3)3(C4H8NH) with C4H8NH (Scheme 3).
It is noteworthy that the synthesis of [Al(C4H8N)3]2 has already
been described in the literature7 starting from pyrrolidine and
† As far as the different lability of the Li–N (pyrrolidinide) bond in A
and B (i.e. four equivalent pyrrolidinides in compound B, and two pairs
of nonequivalent pyrrolidinide ligands in A) we propose that the lith-
ium reduced coordination number in B with respect to A is responsible
for the faster shift of lithium from one nitrogen to the other one and, as
a consequence, of the observed equivalency of the pyrrolidinide groups
in the compound B.
The 1H- and 13C-NMR spectra of the 1 : 2 adduct Al-
(CH3)3(C4H8NH)2 show the resonances of the coordinated
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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pyrrolidine (1H: δ 2.44, CH2CH2N; 1.79, NH; 1.20, CH2CH2N;
13C: δ 46.9, CH2CH2N; 25.5, CH2CH2N) and of the methyl
groups (1H, Ϫ0.49 ppm; 13C, Ϫ9.1 ppm).
A series of 1H-NMR spectra of the methyl derivatives
Al(CH3)3(C4H8NH)n (n = 1, 2) was recorded at different tem-
peratures (193–293 K): on lowering the temperature, both for
Al(CH3)3(C4H8NH) and Al(CH3)3(C4H8NH)2, the methylene
resonances shift up-field, while the methyl signals down-field.
On the other hand, a different behaviour is observed for
the two compounds as far as the NH resonance is concerned
(Fig. 1, A): the aminic proton resonance of Al(CH3)3(C4H8NH)
is shifted up-field on lowering the temperature, while the same
proton is shifted down-field (more drastically) in Al(CH3)3-
(C4H8NH)2 (Fig. 1, A). Reasonably these different trends
are related to the different geometries of the two compounds
and to the consequently different field experienced by the
aminic proton.
Scheme 4
coordinated pyrrolidine, making free a coordination site at the
aluminium centre for the coordination of the chloride.
1
The H-NMR spectra of the two compounds Al(CH3)2Cl-
(C4H8NH) and Al(CH3)Cl2(C4H8NH) are similar showing the
characteristic resonances of the coordinated pyrrolidine and
methyl groups [Al(CH3)2Cl(C4H8NH): δ 2.34, CH2CH2N; 2.15,
NH; 0.96, CH2CH2N; Ϫ0.41, CH3; Al(CH3)Cl2(C4H8NH):
δ 3.03, NH; 2.56, CH2CH2N; 1.15, CH2CH2N; Ϫ0.21, CH3].
It is noteworthy that the number of chlorines bonded to the
aluminium centre strongly affects the chemical shift of both the
methyl and methylene protons. As a matter of fact, the methyl-
ene protons in Al(CH3)2Cl(C4H8NH) show up-field shifted
resonances with respect to Al(CH3)Cl2(C4H8NH), in fair
agreement with the major electronegativity of the chlorine.
1
Moreover, a progressive down-field shift for the H-resonance
of the methyl group in Al(CH3)3–nCln(C4H8NH) is observed on
increasing the number of chlorine bonded to the aluminium
centre: n = 0, Ϫ0.51 ppm;‡ n = 1, Ϫ0.41 ppm; n = 2, Ϫ0.21 ppm.
The 13C-NMR spectra of the two compounds are similar
and show the resonances characteristic of the coordinated
pyrrolidine [Al(CH3)2Cl(C4H8NH): 46.5, 24.5 ppm; Al(CH3)-
Cl2(C4H8NH): 46.8, 24.4 ppm].
Interaction of AlCl3 with amines
The reaction of AlCl3 with pyrrolidine (C4H8NH) affords AlCl3-
(C4H8NH) or AlCl3(C4H8NH)2 depending on the molar ratio
Al/C4H8NH (Scheme 5). Alternative routes to AlCl3(C4H8NH)2
are the reaction of the binary amido derivative [Al(C4H8N)3]2
with stoichiometric amounts of [NH2Et2]Cl (Scheme 5) and,
obviously, the reaction of AlCl3(C4H8NH) with 1 mol of
C4H8NH. On the other hand, AlCl3(C4H8NH) is alternatively
obtained from the reaction of [AlCl2(C4H8N)]2 and the
stoichiometric amount of [NH2Et2]Cl (Scheme 5).
Fig. 1 (a) Variation of the chemical shift [∆δ = δH(T) Ϫ δH(293)] of the
aminic proton in Al(CH3)3(C4H8NH)n (n = 1, 2). (b) Signal of NH in the
1H-NMR spectrum (toluene-d8) of Al(CH3)3(C4H8NH) at different
temperatures.
The 13C-NMR spectra of the adducts AlCl3(C4H8NH)n (n = 1,
2) are similar and show the resonances characteristic of the
coordinated pyrrolidine (n = 1, 24.3, 47.5 ppm; n = 2, 24.9,
Moreover, it is noteworthy that the resonance of the aminic
proton of Al(CH3)3(C4H8NH) at 223 K appears as a quintet
(Fig. 1, B): reasonably, at this temperature, the exchange pro-
cesses, involving the aminic proton, slow down thus allowing
the vicinal coupling to the methylene protons to be observed,
despite the quadrupolar effects of the 14N nucleus. At variance
with Al(CH3)3(C4H8NH), the resonance of the aminic proton in
Al(CH3)3(C4H8NH)2 is observed as a broad line even at 188 K.
The reaction of Al(CH3)3(C4H8NH) with AlCl3(C4H8NH)
(vide infra for details about this compound) affords the methyl-
chloro derivatives Al(CH3)2Cl(C4H8NH) or Al(CH3)Cl2(C4H8-
NH) depending on the starting Al(CH3)3(C4H8NH)/AlCl3-
(C4H8NH) molar ratio (Scheme 4).
1
47.7 ppm). On the other hand, the H-NMR spectra of the
compounds are strongly affected by the temperature [as an
example, the 1H-NMR spectra of AlCl3(C4H8NH)2 recorded at
different temperatures are reported in Fig. 2]. The spectra
recorded at 363 K are “regular”, both AlCl3(C4H8NH) and
AlCl3(C4H8NH)2 showing three resonances (Table 2), assigned
to the methylene protons and to the NH functionality.
On lowering the temperature the lines at 2.58 and 1.11 ppm
of AlCl3(C4H8NH), and at 2.88 and 1.24 ppm of AlCl3-
(C4H8NH)2 splits into two resonances (Fig. 2, Table 2) thus
Alternatively, Al(CH3)2Cl(C4H8NH) results from the reaction
of [Al(CH3)2(C4H8N)]2 with [NH2Et2]Cl (Scheme 4): reason-
ably, the protonation of the bridging amido groups [C4H8N]
yields the fragmentation of the dinuclear core and affords the
‡ The compound Al(CH3)3(C4H8NH) has been prepared by following
1
the procedure reported in the literature6b and the H-NMR spectrum
has been recorded on a solution of the compound in C6D6, at 293 K.
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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Table 2 Selection of 1H-NMR data (toluene-d8) of AlCl3(C4H8NH)n (n = 1, 2)
AlCl3(C4H8NH)
AlCl3(C4H8NH)2
δH
δH
Structure
Position
223 K
363 K
T coalescence /K
223 K
363 K
T coalescence /K
H1, H1Ј
H2, H2Ј
H3
2.34, 2.08
0.88, 0.68
5.24
2.58
1.11
2.80
313
318
–
3.00, 2.82
1.22, 0.86
2.68
2.88
1.24
3.51
313
310
–
H8NH) and AlCl3(C4H8NH)2. The geminal coupling between
the inequivalent methylene protons (both CH2CH2N and
CH2CH2N) yields the crosspeaks between the resonances at
2.08 and 2.34 ppm, and 0.88 and 0.68 ppm for the 1 : 1 adduct,
and between the resonances at 1.22 and 0.86 ppm, and 3.00 and
2.82 ppm for the 1 : 2 adduct. Moreover the crosspeaks between
the resonances at both 2.34 and 2.08 ppm and those at 0.88 and
0.68 ppm for AlCl3(C4H8NH) and between the resonances
at both 3.00 and 2.82 ppm and those at 1.22 and 0.86 ppm
for the AlCl3(C4H8NH)2 are indicative of the vicinal coupling
between the methylene protons CH2CH2N and CH2CH2N.
The proposed dynamic processes involving the coordinated
pyrrolidine of both AlCl3(C4H8NH) and AlCl3(C4H8NH)2 are
reported in Scheme 6.
Scheme 5
Scheme 6
Finally the 27Al-NMR spectra of AlCl3(C4H8NH) and AlCl3-
(C4H8NH)2 show resonances at 113.0 and 62.9 ppm, respec-
tively, thus confirming the proposed coordination number 4 for
AlCl3(C4H8NH), and 5 for AlCl3(C4H8NH)2.§
The reaction of AlCl3 with N,N,NЈ-trimethylpropane-
diamine (C6H16N2, TMPDA) affords the Lewis adduct
AlCl3(C6H16N2) [eqn. (3)] as a sticky colourless material.
The 1H-NMR spectrum of AlCl3(C6H16N2) is strongly
affected by the temperature (Fig. 3). As a matter of fact, the
1H-NMR spectrum at 363 K shows two singlets of the methyl
groups at 2.39 and 2.00 ppm, for the NH(CH3) and N(CH3)2
functionalities, respectively.
Fig. 2 1H-NMR spectra of AlCl3(C4H8NH)2 at different temperatures
(the resonance at about 2.1 ppm is due to the residual protons of
toluene-d8).
indicating that a dynamic process is slowing down and that, as a
consequence, each proton in the methylene groups experiments
a different chemical environment.
§ It is reported that the chemical shift of 27Al is sensitive to the co-
ordination number,8,9 i.e. on increasing the coordination number
of the aluminium centre, the 27Al-NMR resonance shifts up-field.
Interestingly, in the laboratories where this work has been carried
out, the Lewis adducts AlCl3(NHiPr2) and AlCl3(NHMeBu)2 have been
synthesised and crystallographically characterised in the solid state:10
AlCl3(NHiPr2) contains the metal centre tetrahedrally coordinated by
three chlorines and the nitrogen of the amine; on the other hand, the
aluminium centre in AlCl3(NHMeBu)2 is pentacoordinated (trigonal
bypiramid coordination polyhedron) to three chlorines (equatorial)
and two nitrogen atoms (apical). The 27Al-NMR spectra of these
compounds have been recorded at room temperature and resonances
at 105.8 and 64.0 ppm have been observed for AlCl3(NHPr2) and
AlCl3(NHMeBu)2, respectively.
As a matter of fact, the coordination of the pyrrolidine to
the metal centre makes chemically different the two faces of
the pyrrolidine, i.e. the geminal methylene protons experiment
different chemical environments depending on whether they
“look” at the metal centre or not. On the basis of the NMR
data, the two faces of the coordinated pyrrolidine are not
interconverting at 223 K, the resonances of geminal protons
coalescing above 310 K (Table 2).
This picture is fairly confirmed by the proton COSY spectra
recorded at 223 K on toluene-d8 solutions of both AlCl3(C4-
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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Table 3 Selection of 1H-NMR data (toluene-d8) of AlCl3(N,N,NЈ-trimethylpropanediamine)a
δH
Structure
Position
363 K
213 K
NH
4.78 [br]
2.00 [s]
2.38 [s]
2.92 [t]
2.16 [t]
1.28 [qn]
5.75 [br]
1.92 [s]
N(CH3)2
NH(CH3)
H3, H3Ј
H1, H1Ј
H2, H2Ј
2.41 [s], 2.43 [s]
3.70 (H3) [t], 2.35 (H3Ј) [d]
2.52 (H1) [t], 1.77 (H1Ј) [d]
1.23 (H2) [qr], 0.59 (H2Ј) [d]
a br: broad; s, singlet; d, doublet; t, triplet; qr, quartet; qn, quintet.
Interestingly, the singlet of the methyl group in the NH-
(CH3)2 functionality splits into two lines (2.41 and 2.43 ppm,
at 213 K) reasonably due to the two possible orientations of the
methyl with respect to the molecular plane, i.e. in the plane or
perpendicular to it (Scheme 7).
Due to the geminal coupling between the methylene protons,
the proton COSY spectrum, recorded at 213 K, shows cross-
peaks between the resonances at 1.23 and 0.59 ppm, 2.52 and
1.77 ppm, and 3.70 and 2.35 ppm. Moreover the crosspeaks
between the resonances at 1.23 and 2.52 ppm, and 1.23 and
3.70 ppm indicate the 1H–1H vicinal axial–axial coupling.
Five lines are observed in the 13C{1H}-NMR spectrum
(ppm 59.4, CH2; 51.8, CH2; 45.1, CH3; 34.2, CH3; 21.3, CH2),
and the 27Al-NMR spectrum show a resonance at 73.9 ppm,
thus confirming the proposed coordination number 5.§
At variance with TMPDA, AlCl3 reacts with N,N,NЈ-tri-
methylethylenediamine (TRMEDA) or N,N,NЈ,NЈ-tetra-
methylethylenediamine (TMEDA) affording the salts [AlCl2-
(amine)2][AlCl4] [eqn. (4)].
Fig. 3 1H-NMR spectra of AlCl3(N,N,NЈ-trimethylpropanediamine)
at different temperatures (the resonance at about 2.1 ppm is due to the
residual protons of toluene-d8).
(4)
(3)
The 27Al-NMR spectra of the compounds show the signal of
the [AlCl4]Ϫ anion (about 100 ppm), moreover a resonance
is observed at 27.4 ([AlCl2(TRMEDA)2][AlCl4]) and 63.2 ppm
([AlCl2(TMEDA)2][AlCl4]), due to the cation [AlCl2(amine)2]ϩ,
thus suggesting that the aluminium centre has different co-
ordination numbers in the two cations, reasonably five in [AlCl2-
(TMEDA)2]ϩ, and six in [AlCl2(TRMEDA)2]ϩ.§
As far as [AlCl2(TRMEDA)2][AlCl4] is concerned, a cluster
of signal is observed in the 1H-NMR spectrum (cf. Experi-
mental), and, on the other hand, the 13C{1H}-NMR spectrum
shows ten lines (cf. Experimental). If an octahedral arrange-
ment of the donor atoms around the metal centre is assumed,
five structures for the cation [AlCl2(TRMEDA)2]ϩ are postula-
table (Scheme 8).
Moreover, a broad line is observed for the aminic proton at
4.76 ppm. The resonances of the methylene groups are
observed at 2.92 [CH2NH(CH3)], 2.16 [CH2N(CH3)2] and 1.28
ppm (CH2CH2CH2). In addition, due to the 1H–1H vicinal
coupling, the resonances at 2.92 and 2.16 ppm are triplets
(3JHH = 5.9 Hz) and that at 1.28 is a quintet (3JHH = 5.9 Hz).
On lowering the temperature up to the room temperature,
the 1H-NMR spectrum changes, the amininc proton resonance
shifting up-field and the methylene resonances appearing as
three unresolved broad lines at 2.99, 2.12 and 1.12 ppm
(Fig. 3).
Noteworthily at 213 K, each methylene resonance splits into
two signals (Table 3), thus indicating that the inversion of the
six-membered ring [AlN2C3] (Scheme 7) is slowing down and, as
a consequence, each methylene proton experiments a different
chemical environment, in dependence of the orientation with
respect to the ring (axial or equatorial) (Table 3). Moreover,
the observed structure of each signal suggests that spin–spin
coupling occurs between geminal and vicinal (axial–axial)
protons, the estimated coupling constants being about 12 Hz.
Scheme 7
Scheme 8
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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Table 4 Selection of 1H-NMR data (THF-d8, 183 K) with the pro-
posed structure of the cation [AlCl2(N,N,NЈ,NЈ-tetramethylethylene-
diamine)2]ϩ and the assignment
of the mono-dentate coordinated amine. On the other hand,
two N,N,NЈ-trimethylethylenediamines coordinate bidentatedly
to the aluminium centre in [AlCl2(amine)2]ϩ, thanks to the
reduced steric hindrance of H with respect to CH3. Similarly,
as far as N,N,NЈ-trimethylpropanediamine is concerned, the
presence of three methylene units connecting the two amine
ends enlarges the bite angle of the bidentate ligand with respect
to N,N,NЈ-trimethylethylenediamine, thus preventing the co-
ordination of a further amine molecule and, as a consequence,
the splitting of the [AlCl3] moiety.
Structure
Position
δH
CH2N(CH3)2
N(CH3)2
CH2N(CH3)2Al
AlN(CH3)2
2.90
2.71
2.66
2.40
Conclusions
The ligand exchange reactions between [Al(C4H8N)3]2 and AlX3
(X = Cl, CH3) or Al(CH3)3(C4H8NH) and AlCl3(C4H8NH) are a
valuable tool for the synthesis of novel aluminium derivatives
(Scheme 10).
The structure D should account for the 13C-NMR spectrum,
indicating ten inequivalent carbon atoms, but it cannot be
excluded that a mixture of two or more isomers is present.
Therefore, no decisive conclusions has been drawn about the
solution structure of the cation [AlCl2(TRMEDA)2]ϩ. On the
other hand, many attempts have been carried out to grow
single crystals suitable for a diffractometric measurement, but
unfortunately they were unsuccessful.
The 1H-NMR spectrum of the cation [AlCl2(TMEDA)2]ϩ
is strongly affected by the temperature. As a matter of fact,
at 293 K, two lines have been observed at 2.64 (CH2) and 2.39
(CH3) ppm (Fig. 4). On the other hand, at 183 K (Fig. 4),
four lines have been observed whose assignment is reported
in Table 4, together with the proposed structure of the cation
[AlCl2(TMEDA)2]ϩ.
Scheme 10
On the other hand, the protonation reaction of amido deriv-
atives is an alternative route affording chloro- or methyl-chloro-
derivatives (Scheme 10).
The course of the reaction of AlCl3 with aliphatic amines
strongly depends on the nature of the amine. The monodentate
amine pyrrolidine affords the 1 : 1 or the 1 : 2 adducts
AlCl3(C4H8NH)n (n = 1, 2). In a similar way, the Lewis adduct
AlCl3(amine) is obtained when the bidentate amine N,N,NЈ-
trimethylpropanediamine is reacted with AlCl3. On the other
hand, the reaction of N,N,NЈ-trimethylethylenediamine or
N,N,NЈ,NЈ-tetramethylethyenediamine with AlCl3 proceeds
through the splitting of AlCl3 yielding the salt [AlCl2(amine)2]-
[AlCl4].
Fig. 4 1H-NMR spectra (THF-d8) of [AlCl2(N,N,NЈ,NЈ-tetramethyl-
ethylenediamine)2]ϩ
in
[AlCl2(N,N,NЈ,NЈ-tetramethylethylenedi-
As far as the adducts AlCl3(amine)n (amine = pyrrolidine, n =
1, 2; amine = N,N,NЈ-trimethylpropanediamine, n = 1) and the
salt [AlCl2(amine)2][AlCl4] (amine = N,N,NЈ,NЈ-tetramethyl-
ethylenediamine) are concerned, variable temperature NMR
investigations indicate the presence of dynamic processes
involving the coordinated amine ligands, i.e. (a) the inversion
of the six-membered ring [AlN2C3] of AlCl3(TMPDA); (b) the
exchange between the mono- and bidentate amines in [AlCl2-
(amine)2]ϩ (amine = N,N,NЈ,NЈ- tetramethylethylenediamine);
(c) the inversion of the coordinated pyrrolidine in AlCl3(C4-
H8NH)n (n = 1, 2).
amine)2][AlCl4] at different temperatures.
It is noteworthy that the variation of the 1H-NMR spectra as
a function of the temperature (Fig. 4) indicates the exchange
between the mono- and bi-dentate amines (Scheme 9).
Experimental
Scheme 9
All operations were carried out in a glove-box, under an
atmosphere of dinitrogen. Elemental analyses (C, H, N) were
performed using a Fisons Instruments analyser (Mod. EA
1108); the chlorine content of the samples was determined by
potentiometric titration using a standard solution of silver
Reason suggests that the different reactivities of N,N,NЈ-tri-
methylpropanediamine, N,N,NЈ-trimethylethylenediamine and
N,N,NЈ,NЈ-tetramethylethylenediamine towards AlCl3 are
due to the different steric hindrances. As a matter of fact, the
presence of two methyl groups on each nitrogen in N,N,NЈ,NЈ-
tetramethylethylenediamine (TMEDA) prevents the chelation
nitrate (Aldrich). NMR spectra were recorded with
a
BRUKER AMX 300 spectrometer (300 MHz for 1H). 1H- and
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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13C-NMR spectra are referred to TMS; 27Al-NMR spectra are
referred to [Al(H2O)6]3ϩ in H2O. 7Li-NMR spectra are referred
to a 0.1 M solution of LiCl in D2O. Multiplicity is indicated as
s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet).
Aluminium chloride (AlCl3, Fluka) was sublimed at 363 K,
5 × 10Ϫ3 atm and stored under dinitrogen. Lithium aluminium
hydride (LiAlH4, Aldrich) was used dissolved in Et2O (a known
quantity of the commercial product was contacted with Et2O
for 3 h; the undissolved solid was filtered off, dried in vacuo and
weighed, thus allowing the calculation of the title of the
ethereal solution). Al(CH3)3(C4H8NH) was prepared according
to the procedure reported in the literature.6b Pyrrolidine (C4-
H8NH, Aldrich) was refluxed over BaO for 12 h, then distilled
and stored under dinitrogen. N,N,NЈ-trimethylethylenediamine
(C5H14N2, Aldrich), N,N,NЈ-trimethylpropanediamine (C6-
H16N2, Aldrich) and N,N,NЈ,NЈ-tetramethylethylenediamine
(C6H16N2, Aldrich) were stored over molecular sieves (4A)
under an atmosphere of dinitrogen. Aluminium trimethyl ([Al-
(CH3)3]2, Fluka, purum and 11.2% w/w solution in toluene)
and diethylamine hydrochloride ([NH2Et2]Cl, Fluka) were used
as received.
Synthesis of [AlX2(C4H8N)]2 (X ؍ Cl, CH3)
X ؍ Cl. A suspension of AlCl3 (520 mg, 3.90 mmol) in
toluene (15 ml) was treated with [Al(C4H8N)3]2 (462 mg,
1.95 mmol of aluminium). AlCl3 promptly dissolved and after
3 h stirring the solution was evaporated yielding a colourless
residue which was washed with pentane, dried in vacuo and
identified as [AlCl2(C4H8N)]2 (765 mg, 78% yield). Found: C,
28.5; H, 4.8; Cl, 42.0; N, 8.0. C4H8AlCl2N requires C, 28.6;
H, 4.8; Cl, 42.2; N, 8.3%. δH (C6D6, 293 K): 2.81 (br, 4H,
CH2CH2N), 1.24 (m, 4H, CH2CH2N). δC (C6D6, 293 K): 50.6
1
1
(CH2CH2N, t, JCH = 141.8 Hz), 24.5 (CH2CH2N, JCH
=
133.2 Hz). δAl (C6D6, 293 K): 117.2.
X ؍ CH3. A 11.2% w/w toluene solution of [Al(CH3)3]2
(2.86 g of solution, 4.44 mmol of aluminium) was added to a
solution of [Al(C4H8N)3]2 (528 mg, 2.22 mmol of aluminium)
in toluene (20 ml). After 3 h stirring, the solution was evaporated
yielding a colourless residue which was dried in vacuo and
identified as [Al(CH3)2(C4H8N)]2 (650 mg, 77% yield). Found:
C, 56.5; H, 10.8; N, 11.4. C6H14AlN requires C, 56.7; H, 11.1;
N, 11.0%. δH (C6D6, 293 K): 2.62 (4H, m, CH2CH2N), 1.33
(4H, m, CH2CH2N), Ϫ0.57 (6H, s, CH3). δC (C6D6, 293 K): 49.7
Synthesis of LiAl(C4H8N)4ؒnC4H8NH (n ؍ 1, 2)
1
1
(CH2CH2N, t, JCH = 138.7 Hz), 25.1 (CH2CH2N, t, JCH
=
Only the procedure for n = 1 is reported in detail, the synthesis
of LiAl(C4H8N)4ؒ2C4H8NH being similar except for the C4H8-
NH/LiAlH4 molar ratio (5, n = 1; 6, n = 2).
132.1 Hz), Ϫ11.9 (CH3). δAl (C6D6, 293 K): 165.6.
Synthesis of Al(CH3)3(C4H8NH)2
A solution of pyrrolidine, C4H8NH, (4.92 g, 69.2 mmol) in
50 ml of Et2O was added dropwise (about 1 h) to a solution of
LiAlH4 (520 mg, 13.7 mmol) in 130 ml of Et2O. Gas evolution
was observed during the addition and in the following 2 h. After
6 h stirring, the solvent was removed in vacuo until a suspension
of a colourless solid resulted (about 10 ml of residual solvent).
The suspension was filtered, the solid dried in vacuo and finally
identified as LiAl(C4H8N)4ؒC4H8NH (4.75 g, 90% yield).
Found: C, 62.1; H, 10.5; N, 18.2. C20H41AlLiN5 requires C,
62.3; H, 10.7; N, 18.2%. δH (toluene-d8, 293 K): 3.20 (br, 16H,
CH2CH2N), 2.27 (br, 4H, CH2CH2NH), 1.74 (br, 16H, CH2-
CH2N), 1.20 (br, 5H, CH2CH2NHϩNH ). δC (C6D6, 298K):
50.1 (CH2CH2N), 47.0 (CH2CH2NH), 27.5 (CH2CH2N), 25.5
(CH2CH2NH). δLi (toluene-d8, 293 K): 13.5. δAl (C6D6, 293 K):
105.2.
The aluminium derivative Al(CH3)3(C4H8NH) (350 mg, 2.44
mmol) was contacted with C4H8NH (175 mg, 2.46 mmol). The
liquid material obtained was stirred for 2 h and finally identified
as Al(CH3)3(C4H8NH)2. Found: C, 61.3; H, 12.8; N, 13.0.
C11H27AlN2 requires C, 61.6; H, 12.7; N, 13.1%. δH (C6D6, 293
K): 2.44 (m, 8H, CH2CH2N), 1.79 (br, 2H, NH ), 1.20 (m, 8H,
CH2CH2N), Ϫ0.49 (s, 9H, CH3). δC (toluene-d8, 293 K): 46.9
(CH2CH2N), 25.5 (CH2CH2N), Ϫ9.1 (CH3).
Synthesis of Al(CH3)2Cl(C4H8NH)
Reaction of [Al(CH3)2(C4H8N)]2 with [NH2Et2]Cl. A sus-
pension of [NH2Et2]Cl (700 mg, 6.39 mmol) in THF (30 ml)
was treated with [Al(CH3)2(C4H8N)]2 (820 mg, 6.45 mmol of
aluminium): a colourless solution promptly resulted. After 2 h
stirring, the solvent was removed in vacuo yielding a colourless
solid which was identified as Al(CH3)2Cl(C4H8NH) (1.00 g,
95% yield). Found: C, 43.8; H, 9.1; Cl, 21.5; N, 8.8. C6H15Al-
ClN requires C, 44.0; H, 9.2; Cl, 21.7; N, 8.6%. δH (C6D6,
293 K): 2.34 (m, 4H, CH2CH2N); 2.15 (br, 1H, NH ); 0.96 (m,
4H, CH2CH2N); Ϫ0.41 (s, 6H, CH3). δC (C6D6, 293 K): 46.5
LiAl(C4H8N)4ؒ2C4H8NH (80% yield). Found: C, 63.0; H,
11.2; N, 18.7. C24H50AlLiN6 requires C, 63.1; H, 11.0; N, 18.4%.
δH (toluene-d8, 293 K): 3.22 (br, 16H, CH2CH2N), 2.44 (br, 8H,
CH2CH2NH), 1.90 (br, 2H, NH ), 1.72 (br, 16H, CH2CH2N),
1.31 (br, 8H, CH2CH2NH). δC (C6D6, 293 K): 50.6 (CH2CH2N,
t, 1JCH = 131.1 Hz), 47.2 (CH2CH2NH, t, 1JCH = 124.8 Hz), 27.5
1
1
(CH2CH2N, t, JCH = 129.0 Hz), 25.7 (CH2CH2NH, t, JCH
=
1
1
(CH2CH2N, t, JCH = 142.3 Hz); 24.5 (CH2CH2N, t, JCH
=
131.8 Hz). δLi (toluene-d8, 293 K): 13.4. δAl (C6D6, 293 K):
104.9.
1
133.4 Hz); Ϫ9.2 (CH3, q, JCH = 61.0 Hz). δAl (C6D6, 293 K):
158.6.
Synthesis of [Al(C4H8N)3]2
Reaction of AlCl3(C4H8NH) with Al(CH3)3(C4H8NH). A
solution of Al(CH3)3(C4H8NH) (282 mg, 1.97 mmol) in toluene
(20 ml) was treated with AlCl3(C4H8NH) (200 mg, 0.98 mmol).
After 3 h stirring at 333 K, the solution was evaporated and
the residue identified (spectroscopically and analytically) as
Al(CH3)2Cl(C4H8NH) (463 mg, 96% yield).
Only the procedure starting from LiAl(C4H8N)4ؒC4H8NH is
described in detail, that one from LiAl(C4H8N)4ؒ2C4H8NH
being similar.
A solution of AlCl3 (375, 2.81 mmol) in Et2O/THF (5/10 ml)
was added to a solution of LiAl(C4H8N)4ؒC4H8NH (3.25 g, 8.43
mmol) in THF (50 ml). The mixture was stirred for 6 h, then
the solvent was removed in vacuo and the solid suspended
in toluene (30 ml). The suspension was stirred for 1 h, then the
solid was filtered off and dried (colourless, 340 mg). The
solution was evaporated yielding a colourless residue which was
dried in vacuo and identified as [Al(C4H8N)3]2 (2.50 mg, 94%
yield). Found: C, 61.0; H, 10.0; N, 17.4. C12H24AlN3 requires
C, 60.7; H, 10.2; N, 17.7%. δH (C6D6, 293 K): 3.21 (m, 2H, CH2-
CH2N); 2.98 (m, 1H, CH2CH2N); 1.71 (m, 2H, CH2CH2N);
1.49 (m, 1H, CH2CH2N). δC (C6D6, 293 K): 50.0 (CH2CH2N);
49.7 (CH2CH2N); 27.2 (CH2CH2N); 25.4 (CH2CH2N).
δAl (C6D6, 293 K): 105.9.
Synthesis of Al(CH3)Cl2(C4H8NH)
A solution of Al(CH3)3(C4H8NH) (200 mg, 1.40 mmol) in
toluene (20 ml) was treated with AlCl3(C4H8NH) (572 mg, 2.80
mmol). After 3 h stirring at 333 K, the solution was evaporated
and the residue identified as Al(CH3)Cl2(C4H8NH) (710 mg,
92% yield). Found: C, 32.5; H, 6.2; Cl, 38.8; N, 7.6. C5H12Al-
Cl2N requires C, 32.6; H, 6.6; Cl, 38.5; N, 7.6%. δH (C6D6,
293 K): 3.03 (br, 1H, NH ), 2.56 (br, 4H, CH2CH2N), 1.15 (br,
4H, CH2CH2N), Ϫ0.21 (s, 3H, CH3). δC (C6D6, 293 K): 46.8
(CH2CH2N), 24.4 (CH2CH2N).
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
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Synthesis of AlCl3(C4H8NH)n (n ؍ 1, 2)
toluene (20 ml). After 12 h stirring, a colourless suspension
resulted; the solid was filtered off, washed with pentane, dried
in vacuo and finally identified as [AlCl2(C6H16N2)2][AlCl4]
(1.38 g, 77% yield). Found: C, 28.5; H, 6.5; Cl, 42.7; N, 11.3.
C6H16AlCl3N2 requires C, 28.9; H, 6.5; Cl, 42.6; N, 11.2%.
δH (THF-d8, 293 K): 2.60 (br, 1H, CH2), 2.37 (br, 3H, CH3).
δC (THF-d8, 293 K): 57.4 (CH2), 46.4 (CH3). δAl (THF-d8,
293 K): 100.0, 63.2.
Reaction of AlCl3 with C4H8NH. Only the procedure for n = 1
is reported in detail, the other being similar except for the
AlCl3/C4H8NH molar ratio (1, n = 1; 0.5, n = 2). A suspension
of AlCl3 (1.32 g, 9.90 mmol) in toluene (30 ml) was treated with
C4H8NH (700 mg, 9.84 mmol): the solid promptly dissolved.
After 12 h stirring, the solution was evaporated until a suspen-
sion resulted (about 10 ml of residual solvent). The solid was
filtered off, dried in vacuo and identified as AlCl3(C4H8NH)
(1.70 g, 84% yield). Found: C, 23.2; H, 4.5; Cl, 52.2; N, 6.9.
C4H9AlCl3N requires C, 23.5; H, 4.4; Cl, 52.0; N, 6.8%.
δH (toluene-d8, 293 K): 5.49 (br, 1H), 2.45 (br, 1H), 2.25 (br,
1H), 1.06 (br, 1H), 0.82 (br, 1H) (see Results and discussion for
the assignment). δC (toluene-d8, 293 K): 47.5 (CH2CH2N),
24.3 (CH2CH2N). δAl (toluene-d8, 293 K): 113.0.
AlCl3(C4H8NH)2 (78% yield). Found: C, 34.8; H, 6.6; Cl,
38.7; N, 10.1. C8H18AlCl3N2 requires C, 34.9; H, 6.6; Cl, 38.6;
N, 10.2%. δH (toluene-d8, 293 K): 2.90 (br, 1H), 2.83 (br, 1H),
2.49 (br, 1H), 1.29 (br, 1H), 0.97 (br, 1H) (see Results and
discussion for the assignment). δC (toluene-d8, 293 K): 47.7
(CH2CH2N), 24.9 (CH2CH2N). δAl (toluene-d8, 293 K): 62.9.
N,N,NЈ-Trimethylpropanediamine (C6H16N2). A solution of
C6H16N2 (620 mg, 5.33 mmol) in toluene (10 ml) was added
dropwise to a suspension of AlCl3 (700 mg, 5.25 mmol) in
toluene (20 ml). After 3 h stirring, the colourless solution was
evaporated and the residue washed with pentane, dried in vacuo
and finally identified as AlCl3(C6H16N2) (1.16 g, 85% yield).
Found: C, 29.1; H, 6.7; Cl, 42.3; N, 11.2. C6H16AlCl3N2 requires
C, 28.9; H, 6.5; Cl, 42.6; N, 11.2%. δH (C6D6, 293 K): 5.77 (br,
1H, NH ), 1.97 (br, 2H, CH2NHCH3), 2.41 (s, 3H, NHCH3),
2.08 (br, 2H, CH2N(CH3)2), 1.90 (s, 6H, N(CH3)2), 1.04 (br,
2H, CH2CH2CH2). δC (C6D6, 293 K): 59.4 (CH2N(CH3)2, t,
1
1JCH = 137.2 Hz), 51.8 (CH2NHCH3, t, JCH = 145.0 Hz),
1
45.1 (CH2N(CH3)2, q, JCH = 133.9 Hz), 34.2 (CH2NHCH3,
1
1
q, JCH = 143.6 Hz), 21.3 (CH2CH2CH2, t, JCH = 124.8 Hz).
δAl (C6D6, 293 K): 73.9.
Reaction of [AlCl2(C4H8N)]2 with [NH2Et2]Cl. A suspension
of [NH2Et2]Cl (900 mg, 8.21 mmol) in THF (20 ml) was treated
with [AlCl2(C4H8N)]2 (1.38 g, 8.21 mmol of aluminium). The
resulting solution was stirred for 4.5 h and then the solvent was
removed in vacuo. The solid was washed with pentane, dried
in vacuo and identified (analytically and spectroscopically) as
AlCl3(C4H8NH) (1.50 g, 89% yield).
Acknowledgements
VP is indebted to Dr. Sergio Tamburini (ICIS-CNR, Padova)
for support in acquiring and discussing 2D-NMR spectra.
Insightful comments and helpful discussions with Prof. Fausto
Calderazzo and Prof. Guido Pampaloni (Università di Pisa) are
kindly acknowledged.
Reaction of [Al(C4H8N)3]2 with [NH2Et2]Cl. A suspension of
[NH2Et2]Cl (1.30 g, 11.9 mmol) in THF (20 ml) was treated
with [Al(C4H8N)3]2 (920 mg, 3.88 mmol of aluminium). The
resulting solution was stirred for 6 h, and then the solvent was
removed. The solid was washed with pentane, dried in vacuo
and identified (analytically and spectroscopically) as AlCl3-
(C4H8NH)2 (900 mg, 84% yield).
References
1 Y. Takahashi, K. Yamashita, S. Motojima and K. Singiyama, Surf.
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therein.
Reaction of AlCl3 with bidentate amines
N,N,NЈ-Trimethylethylenediamine (C5H14N2). A solution of
C5H14N2 (1.19 g, 11.6 mmol) in toluene (10 ml) was added
dropwise to a suspension of AlCl3 (1.50 g, 11.2 mmol) in
toluene (20 ml). After 12 h stirring a colourless suspension
resulted; the solid was filtered off, washed with pentane, dried in
vacuo and finally identified as [AlCl2(C5H14N2)2][AlCl4] (1.88 g,
71% yield). Found: C, 25.4; H, 6.1; Cl, 45.5; N, 11.7. C5H14Al-
Cl3N2 requires C, 25.5; H, 6.0; Cl, 45.2; N, 11.9%. δH (THF-d8,
293 K): 4.9–4.4, 3.6–3.2, 3.2–2.0 (see Results and discussion).
δC (THF-d8, 293 K): 55.0 (CH2, t, 1JCH = 137.3 Hz), 54.5 (CH2,
t, 1JCH = 136.0 Hz), 45.9 (CH3, q, 1JCH = 141.6 Hz), 45.6 (CH3, q,
5 J. K. Ruff, J. Am. Chem. Soc., 1961, 83, 2835.
6 (a) M. J. Taylor, Aluminum and Gallium, in Comprehensive
Coordination Chemistry, ed. G. Wilkinson, R. D. Gillard and
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therein; (b) C. J. Thomas, L. K. Krannich and C. L. Watkins,
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Trans., 1996, 3297; (d ) D. C. Bradley, G. Coumbarides, I. S.
Harding, G. E. Hawkes, I. A. Maia and M. Motevalli, J. Chem.
Soc., Dalton Trans., 1999, 3553; (e) E. S. Bento, D. C. Bradley,
G. E. Hawkes, I. A. Maia and K. D. Sales, Magn. Reson. Chem.,
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1
1JCH = 146.7 Hz), 45.0 (CH3, q, JCH = 143.0 Hz), 44.1 (CH3,
q, 1JCH = 151.0 Hz), 43.1 (CH2, t, 1JCH = 142.1 Hz), 42.6 (CH2,
t, 1JCH = 135.8 Hz), 33.9 (CH3, q, 1JCH = 137.3 Hz), 33.8 (CH3, q,
1JCH = 137.3 Hz). δAl (THF-d8, 293 K): 99.8, 27.4.
7 M. M. Andrianarison, M. C. Ellerby, I. B. Gorrel, P. B. Hitchcock,
J. D. Smith and D. R. Stanley, J. Chem Soc., Dalton Trans., 1996,
211.
8 R. Benn, A. Rufinska, H. Lehmkuhl, E. Janssen and C. Krüger,
Angew. Chem., Int. Ed. Engl., 1983, 22, 779.
9 NMR and the periodic table, ed. R. K. Harris and B. E. Mann,
Academic Press, London, 1978.
10 M. Belogourova, F. Benetollo and P. Zanella, unpublished results.
N,N,NЈ,NЈ-Tetramethylethylenediamine (C6H16N2). A solu-
tion of C6H16N2 (850 mg, 7.31 mmol) in toluene (10 ml) was
added dropwise to a suspension of AlCl3 (970 g, 7.27 mmol) in
D a l t o n T r a n s . , 2 0 0 3 , 1 2 8 4 – 1 2 9 1
1291