New approach to dichloroindium amides

Article abstract of DOI:10.1039/a904655k

Two different routes are presented for the synthesis of dichloroindium amides. On the one hand we prepared (THF)₃Li(μ-Cl)Cl₂InN(SiMe₃)(Dipp) (1) (Dipp = 2,6-diisopropylphenyl) by the reaction of indium trichloride with the

Full text of DOI:10.1039/a904655k

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New approach to dichloroindium amides
Jörg Prust, Peter Müller, Carsten Rennekamp, Herbert W. Roesky* and Isabel Usón
Institut für Anorganische Chemie der Georg August Universität Göttingen, Tammannstrasse 4,
D-37077, Göttingen, Germany
Received 22nd March 1999, Accepted 11th June 1999
Two different routes are presented for the synthesis of
dichloroindium amides. On the one hand we prepared
(THF)3Li(ì-Cl)Cl2InN(SiMe3)(Dipp) (1) (Dipp ؍ 2,6-
diisopropylphenyl) by the reaction of indium trichloride
with the lithiated aniline, on the other hand Cl2InNEt2 (2)
by trimethylsilyl chloride elimination. Compound 1 was
characterized by X-ray structural analysis.
Organoindium compounds were introduced by Rochow et al.
in 1934.1 In recent years interest in the synthesis of organo-
indium amides, phosphides, selenides and arsenides has
increased owing to their application in the fields of CVD
(Chemical Vapour Deposition) and MOCVD (Metal Organic
Chemical Vapour Deposition) for the production of thin
layers.2–4 In this respect dimethylindium dimethylamide should
be mentioned as a precursor for the synthesis of ceramics.5,6
Therefore new routes to indium compounds for use as
single source precursors and their corresponding starting
materials is an important target of current indium research.
The syntheses of alkylindium dichlorides and dialkylindium
amides have been thoroughly investigated.7 Two pathways for
the syntheses of these compounds were found to work in
high yields: on the one hand the commutation reaction of
trialkylindium compounds with InCl3 for the preparation of
alkylindium dichlorides, and on the other hand the reaction
of trialkylindium derivatives with amines, with alkane elimin-
ation, for the synthesis of In–N compounds.8,9 The alternative
route to these compounds via the reaction of InCl3 with lithi-
ated alkyls or amides has been of no practical use until now.
These reactions mostly lead to lower product yields due to
metallic indium formation which is favoured in the presence
of the lithiated amide or alkyl species.10 In contrast to these
observations the reaction of a lithiated tris(trimethylsilyl)-
methane with InCl3 yields an alkylindium dichloride–lithium
chloride adduct in 87% yield, which has been characterized
by X-ray structural analysis.11
Fig. 1 X-Ray structure of 1 with atomic numbering scheme. Hydrogen
atoms have been omitted for clarity. Selected bond distances [Å] and
angles [Њ]: In(1)–N(1) 2.054(2), In(1)–Cl(1) 2.4152(8), In(1)–Cl(2)
2.3760(5), In(1)–Cl(3) 2.3614(8), Li(1)–Cl(1) 2.392(4); Cl(1)–In(1)–
Cl(2) 104.56(3), Cl(1)–In(1)–Cl(3) 106.30(4), Cl(2)–In(1)–Cl(3)
105.31(3), Cl(1)–In(1)–N(1) 110.41(6), Cl(2)–In(1)–N(1) 115.12(6),
Cl(3)–In(1)–N(1) 114.32(5), Li(1)–Cl(1)–In(1) 116.3(1).
TMS
Cl
TMS
Li
0 °C, THF
N
+
Cl
Cl
InCl3
N
(THF)3Li
In
1
Scheme 1
The single crystal X-ray structural analysis shows 1 to
crystallize in the monoclinic space group P21/n with one mole-
cule in the asymmetric unit. The core of the structure consists
of an indium centre which is tetrahedrally coordinated by three
chlorine atoms and one N-trimethylsilyl-2,6-diisopropylaniline
ligand. One of the chlorine atoms bridges the indium to a
lithium cation whose tetrahedral coordination sphere is com-
pleted by three THF molecules (Fig. 1). As expected the bridg-
ing In(1)–Cl(1) bond length of 2.4152 Å is longer than the
terminal ones (2.3760 and 2.3614 Å). The bond lengths and
angles are comparable to those in [Li(THF)3(µ-Cl)InCl2-
{C(SiMe3)3}].†11
To the best of our knowledge a successful synthesis of
dichloroindium amides, or rather their derivatives, has not been
reported yet.
For the preparation of a dichloroindium amide we chose
lithiated N-trimethylsilyl-2,6-diisopropylaniline for the reaction
with InCl3, owing to its high sterical demand. In our previous
work we established N-trimethylsilyl-2,6-diisopropylanilide as a
bulky ligand for the production of stable silanetriol and silane-
triamide systems.12 After the successful syntheses of gallium and
aluminium amide systems using this ligand we are now inter-
ested in the corresponding indium compounds.
A solution of 2.49 g (10 mmol) lithiated N-trimethylsilyl-2,6-
diisopropylaniline in THF (20 ml) was added to a solution of
2.21 g (10 mmol) InCl3 in THF (50 ml) at 0 ЊC and stirred for an
additional 1 h. The solution was allowed to reach room tem-
perature, refluxed for 1 h and stirred at room temperature for
another 6 h. THF was removed in vacuo and the remaining solid
was dissolved in toluene. After filtration from the residue the
solvent was removed in vacuo and 1 was isolated as a colourless
solid in 83% yield (5.75 g). No reduction of In() was observed
during the reaction (shown in Scheme 1). A sample of 1 was
dissolved in n-hexane and kept for one week at room temper-
ature. Single crystals suitable for X-ray crystallography were
obtained from this solution.
The 1H NMR data are consistent with 1. The singlet (δ 0.28)
is assigned to the protons of the SiMe3 group. The expected
doublets (δ 1.13 and 1.19) and septets (δ 2.86 and 3.65) for the
isopropyl groups are found, whereas the aromatic protons give
a multiplet (δ 6.98 to 7.06). Signals for the THF groups are
observed in the expected range (δ 1.20 and 3.67). The consist-
ency of the solid state structure also in solution of 1 can be
7
proved by integration of the proton signals. In the Li NMR
spectrum of 1 a singlet is found (δ Ϫ0.21) assignable to Li
coordinated to THF and the 29Si NMR data result in a singlet (δ
4.07) for the SiMe3 group. The mass spectrum shows fragments
of 1 assigned to DippNH2 (177; 30%), DippH (162; 100%),
InCl (150; 48%) and In (115; 41%). The composition of 1 was
confirmed by elemental analysis. We obtained dichloroindium
J. Chem. Soc., Dalton Trans., 1999, 2265–2266
2265

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unique 6753 (Rint = 0.0512). Final R indices: R1 = Σ|Fo Ϫ Fc|/Σ|Fo| =
amide as the LiCl adduct, which is in good agreement with the
product proposed in Scheme 1.
4
0.0262, wR2 = [Σw(Fo2 Ϫ Fc2)2/ΣwFo ]1/2 = 0.0627 on data with I > 2σ(I)
and R1 = 0.0316, wR2 = 0.0681 on all data, goodness of fit S =
[Σw(Fo2 Ϫ Fc2)2/Σ(n Ϫ p)]1/2 = 1.161. The crystal was mounted on a
glass fibre in a rapidly cooled perfluoropolyether.13 Diffraction data
were collected on a Stoe-Siemens-Huber four-circle diffractometer
coupled to a Siemens CCD area detector at 133(2) K, with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å), performing φ- and
ω-scans. The structure was solved by direct methods using SHELXS-
9714 and refined against F2 on all data by full-matrix least squares with
SHELXL-97.15 All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were included in the model at geometrically calcu-
lated positions and refined using a riding model. The disordered SiMe3
group in 1 was modelled with the help of similarity restraints for 1–2
and 1–3 distances and displacement parameters as well as rigid bond
restraints for anisotropic displacement parameters. The occupancies for
the disordered parts were refined and eventually set at the convergence
value.
For the synthesis of dichloroindium diethylamide an altern-
ative approach proved to be applicable. To avoid reduction
by any lithiated amine a trimethylsilyl chloride elimination
reaction of the trimethylsilyl derivative of diethylamine with
InCl3 (Scheme 2) was carried out instead.
toluene
8 h reflux
Cl
Cl
Et
Et
Et
Et
+
N
TMS
N In
InCl3
–TMSCl
2
Scheme 2
A solution of 1.44 g (10 mmol) (SiMe3)NEt2 in toluene (20
ml) was added to a suspension of 2.21 g (10 mmol) InCl3 in
toluene (50 ml) at 0 ЊC. The suspension was allowed to reach
room temperature and refluxed for 8 h. Toluene was removed
in vacuo and the remaining solid was treated with n-hexane.
After filtration the solvent was removed in vacuo and 2 was
isolated as a colourless solid in 78% yield (2.01 g).
CCDC reference number 186/1505. See http://www.rsc.org/suppdata/
dt/1999/2265/ for crystallographic files in .cif format.
‡ The infrared spectrum of 2 was recorded in CsI and shows the stretch-
ing of terminal In–Cl (279 and 259 cmϪ1) and bending of In–µ-N (447
cmϪ1). Owing to the air and moisture sensitivity of 2 cryoscopic meas-
urements for the molecular weight determination were not successful.
The 1H NMR data show the expected signals for 2. The trip-
let (δ 1.28) and the quartet (δ 3.11) are assigned to the protons
of the ethyl group. The mass spectrum (EI) shows fragments of
the monomer assigned to M (258 m/z; 53%) and InCl (150;
100%). The composition of 2 was confirmed by elemental
analysis. The spectroscopic characterization established that the
dimer of dichloroindium diethylamide was the product. This
interpretation is supported by previous investigations of com-
parable alkylindium amides, as well as by infrared spectra,
which reveal the nitrogen bridged dimeric system of 2.‡
With these two routes for the synthesis of compounds 1 and 2
we have opened up the field of dichloroindium amides. Further
investigations in our laboratory will focus on exchange reac-
tions of the halides in these systems to obtain new single source
precursors for the CVD process.
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Acknowledgements
This work was supported by the Deutsche Forschungsgemein-
schaft. C. R. is grateful to the Fonds der Chemischen Industrie
for a fellowship.
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Notes and references
† Crystal structure analysis of 1: C27H50Cl3InLiNO3Si, Mr = 692.88,
monoclinic, P21/n, unit cell dimensions: a = 9.472(2) Å, b = 24.866(5) Å,
c = 14.625(3) Å, β = 91.58(3)Њ, V = 3444(1) Å3, Z = 4, ρcalc. = 1.336 Mg
m
Ϫ3, µ = 0.980 mmϪ1; total number of reflections measured 60120,
Communication 9/04655K
2266
J. Chem. Soc., Dalton Trans., 1999, 2265–2266