A remarkably stable indium trihydride complex: Synthesis and characterisation of [InH3{P(C6H11)3}]

Article abstract of DOI:10.1039/a809279f

The reaction of [InH₃(NMe₃)] with P(C₆H₁₁)₃ affords the first example of a phosphine-indium trihydride complex, [InH₃{P(C₆H₁₁)₃}], which exhibits remarkable thermal stability; the X-ray crystal structure of the complex is described.

Full text of DOI:10.1039/a809279f

A remarkably stable indium trihydride complex: synthesis and
characterisation of [InH3{P(C6H11)3}]
David E. Hibbs, Cameron Jones* and Neil A. Smithies
Department of Chemistry, University of Wales, Cardiff, PO Box 912, Park Place, Cardiff, UK CF1 3TB.
E-mail: jonesca6@cardiff.ac.uk
Received (in Cambridge, UK) 27th November 1998, Accepted 15th December 1998
The reaction of [InH3(NMe3)] with P(C6H11)3 affords the
first example of a phosphine–indium trihydride complex,
[InH3{P(C6H11)3}], which exhibits remarkable thermal sta-
bility; the X-ray crystal structure of the complex is de-
scribed.
The solution NMR data† for 3 support its proposed structure.
Its 1H NMR spectrum exhibits the expected resonances for the
phosphine ligand in addition to a broad hydride resonance that
integrates for three hydrogens at d 5.61 (cf. d 5.58 in 14,5) which
is significantly downfield with respect to the related resonances
in 4 (d 4.326) and 5 (d 4.257). The 31P NMR spectrum of 3
displays a singlet at d 7.43 which can be compared to d 11.1 for
the free ligand.7 A strong, broad In–H stretching absorbance
was observed at 1661 cm21 (cf. 1640 cm21 for 15) in its IR
spectrum (Nujol mull). This is at a lower frequency than the
corresponding M–H stretches in 4 (1800 cm21)6 and 5 (1750
cm21)7 and reflects the relative weakness of the M–H bonds in
3. No molecular ion was seen in the mass spectrum of 3 but a
fragment corresponding to the free phosphine ligand was
observed.
The utility of Lewis base adducts of AlH3 and GaH3 as chemical
vapour deposition precursors to thin films of the group 13
metal1 or semiconducting materials2 has led to their chemistry
being extensively studied over the last decade.3 Until very
recently no corresponding InH3 complexes were known,
presumably because of thermal instability that arises from the
weakness of the In–H bond. We have reversed this situation
with the syntheses of [InH3{CNPRiC2Me2NPri}] 1 and [In-
H3(NMe3)] 2,4,5 the former being stabilised by coordination to
a highly nucleophilic ‘Arduengo’ carbene. Despite this, 1 is not
stable in the solid state above 25 °C (decomp. > 220 °C in
solution) and 2 is only stable in dilute solutions below 230 °C.
It seems likely that if InH3 complexes are to find similar
applications to their aluminium and gallium counterparts, then
examples will need to be found that are stable at room
temperature. Herein we report the synthesis and structural
characterisation of such a compound, [InH3(PCy3)] 3 (Cy =
cyclohexyl), which represents the first example of a phosphine
adduct of InH3, and the first InH3 complex to have had its
hydride ligands located by X-ray crystallography.
An X-ray crystal structure analysis‡ of 3 (Fig. 1) was carried
out and it was found to be isomorphous to its aluminium and
gallium counterparts, 5 and 4, respectively. The quality of the
X-ray data allowed the three hydride ligands to be located from
difference maps and their positional and isotropic thermal
parameters to be refined. The complex is monomeric and shows
no evidence of intermolecular interactions through bridging
hydrides. As in 4, the metal centre has a slightly flattened
tetrahedral geometry [P–In–H 101.4° (av.), H–In–H 116.2°
(av.)] with an average In–H distance of 1.68 Å. This distance
compares well with the only other structurally characterised
terminal In–H bond in a neutral complex, viz. 1.69(3) Å in
[InH{2-Me2NCH2(C6H4)}]2.8 Not surprisingly both these dis-
tances are shorter than bridging In–H distances, e.g. 1.87 Å (av.)
Treatment of an ethereal solution of [InH3(NMe3)]5 with 1
equiv. of PCy3 at 240 °C led to the high yield formation (71%)
of 3 after recrystallisation from toluene (Scheme 1). Inter-
estingly, 3 could not be formed from the direct reaction of PCy3
with LiInH4 (LiH elimination) which is in contrast to the high
yield preparation of [GaH3(PCy3)] 4 from the reaction of
LiGaH4 and PCy3 in diethyl ether.6 In addition, there was no
evidence for the formation of 3 from the reaction of a 1:1
mixture of PCy3 and anhydrous HCl with LiInH4 in diethyl
ether at 240 °C {cf. the formation of [AlH3(PCy3)] 5 by a
similar route7}.
Compound 3 is remarkably thermally stable and decomposes
in the solid state only at temperatures in excess of 50 °C
to indium metal, hydrogen gas and PCy3 (cf. 4, decomp.
> 130 °C;6 5, decomp. > 160 °C7). At room temperature (25 °C)
crystalline samples of 3 showed only minimal decomposition
over a period of 7 days under an argon atmosphere, as
1
determined from the H NMR of the sample after that period.
Surprisingly, 3 also displays considerable stability to oxygen
and moisture in the solid state as it shows no decomposition in
air over 24 h at room temperature. In benzene solutions samples
of 3 are less stable but still take ca. 1 h to decompose at 25 °C.
As has been suggested for 4 and 5, the unusual stability of 3 can
probably be attributed to the steric properties of the phosphine
ligand.
Fig. 1 Molecular structure of [InH3{P(C6H11)3}] 3. Selected bond lengths
(Å) and angles (°): In(1)–P(1) 2.6474(6), In(1)–H(01) 1.81(2), In(1)–H(02)
1.62(3), In(1)–H(03) 1.62(3), P(1)–C(13) 1.8433(17), P(1)–C(7)
1.8448(17), P(1)–C(1) 1.8632(17); P(1)–In(1)–H(01) 103.4(7), P(1)–In(1)–
H(02) 97.3(11), P(1)–In(1)–H(03) 103.6(11), H(01)–In(1)–H(02)
121.3(13), H(01)–In(1)–H(03) 111.0(13), H(02)–In(1)–H(03) 116.4(16).
Scheme 1 Reagents and conditions: i, PCy3, 2NMe3, Et2O, 240 °C, 2 h.
Chem. Commun., 1999, 185–186
185

in [Li(tmeda)2][Me3In–H–InMe3].9 The In–P distance in 3
[2.6474(6) Å] is in the normal region for such interactions
though is slightly longer than In–P distances in four co-ordinate
tertiary phosphine adducts of indium halides, e.g. 2.569 Å in
[InI3(PPri3)]10 and 2.603 Å in [InI3(PPh3)].11
The remarkable thermal stablity of 3 has prompted us to
begin an investigation of its chemistry and the preparation of a
range of related phosphine– and arsine–indium hydride com-
plexes. The results of these investigations will form the basis of
a later publication.
and 0.559 for all data. CCDC 182/121. See http://www.rsc.org/suppdata/cc/
1999/185 for crystallographic files in .cif format.
1 M. G. Simmonds and W. L. Gladfelter, in The Chemistry of Metal CVD,
ed. T. Kodas and M. Hampden-Smith, VCH, Weinheim, 1994 and
references therein.
2 J. N. Kidder, H. K. Yun, J. W. Rogers and T. P. Pearsall, Chem. Mater.,
1998, 10, 777.
3 C. Jones, G. A. Koutsantonis and C. L. Raston, Polyhedron, 1993, 12,
1829; M. G. Gardiner and C. L. Raston, Coord. Chem. Rev., 1997, 166,
1; Chemistry of Aluminium, Gallium, Indium and Thallium, ed. A. J.
Downs, Blackie, Glasgow, 1993 and references therein.
4 D. E. Hibbs, M. B. Hursthouse, C. Jones and N. A. Smithies, Chem.
Commun., 1998, 869.
We gratefully acknowledge financial support from the
EPSRC (studentship for N. A. S.).
5 M. D. Francis, D. E. Hibbs, M. B. Hursthouse, C. Jones and N. A.
Smithies, J. Chem. Soc., Dalton Trans., 1998, 3249.
6 J. L. Atwood, K. D. Robinson, F. R. Bennett, F. M. Elms, G. A.
Koutsantonis, C. L. Raston and D. J. Young, Inorg. Chem., 1992, 31,
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8 C. Ku¨mmel, A. Meller and M. Noltemeyer, Z. Naturforsch., Teil B,
1996, 51, 209.
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Notes and references
1
† Spectroscopic data for 3: H NMR (400 MHz, C6D6, SiMe4, 298 K) d
0.92–1.75 (m, 33H, C6H11), 5.61 (br s, 3H, In–H); 13C NMR (100.6 MHz,
C6D6, 298 K) d 26.6 (s, CH2), 27.7 (d, CH2, 2JPC 10.2 Hz), 30.5 (s, CH2),
31.8 (d, CH, 1JPC 13.0 Hz); 31P NMR (36.3 MHz, C6D6, 85% H3PO4, 298
K) d 7.43, IR n 1661 cm21 (s, br, In–H str.); MS EI m/z (%): 280 (PCy3
,
+
63), 197 (PCy2+, 100), 114 (PCy+, 78).
¯
‡ Crystal data for 3: C18H36InP M = 398.26 triclinic, space group P1, a =
8.1147(10), b = 10.897(2), c = 11.4273(10) Å, a = 74.940(9), b =
88.665(10), g = 81.840(10)°, V = 965.8(2) Å3, Z = 2, Dc = 1.369 g cm23
,
F(000) = 416, m = 12.98 cm21, crystal 0.20 3 0.20 3 0.20 mm, radiation
Mo-Ka (l = 0.71073 Å), 150(2) K.
11 M. A. Brown, D. G. Tuck and E. J. Wells, Can. J. Chem., 1996, 74,
1535.
12 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
13 G. M. Sheldrick, SHELXL-93 Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Germany, 1993.
All crystallographic measurements were made using an Enraf-Nonius
CAD4 diffractometer. The structure was solved by heavy atom methods
(SHELXS86)12 and refined on F2 by full matrix least squares (SHELX93)13
using all unique data. All non-hydrogen atoms are anisotropic with H-atoms
[except those attached to In(1)] included in calculated positions (riding
model). Neutral-atom complex scattering factors were employed.13 Empiri-
cal absorption corrections were carried out by the DIFABS method.14 Final
R (on F) and wR (on F2) were 0.0199 and 0.0513 for I > 2s(I), and 0.229
14 N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39,
158.
Communication 8/09279F
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Chem. Commun., 1999, 185–186