Reaction of indium metal with R3PI2 (R = Ph, Pri, Prn); structural characterisation of the novel 'subvalent' indium(II) complex In2I4(PPrn 3)2 which contains an In-In bond, the four- and five- coordinate indium(III) complex InI3(PPh3)2 ·InI3

Article abstract of DOI:10.1039/a608230k

Reaction of R₃PI₂ (R = Ph, Prⁿ, Prⁱ) with indium metal powder produces a variety of novel indium metal complexes: where R = Ph, the four- and five-coordinate metal(III) complex InI₃(PPh₃)₂·InI₃(PPh ₃) results; where R = Prⁿ, the 'subvalent' indium(II) complex In₂I₄(PPrⁿ₃)₂ is formed, the first example of an indium tertiary phosphine complex containing an indium-indium bond; whereas for R = Prⁱ, the monomeric tetrahedral indium(III) complex InI₃(PPrⁱ₃) results; these complexes illustrate the subtle effect of the organic substituents on the phosphorus atom for the reaction of R₃PI₂ with indium metal powder and the novel indium complexes which are available.

Full text of DOI:10.1039/a608230k

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Reaction of indium metal with R3PI2 (R = Ph, Pri, Prn); structural
characterisation of the novel ‘subvalent’ indium(ii) complex In2I4(PPrn )
3 2
which contains an In–In bond, the four- and five-coordinate indium(iii)
complex InI3(PPh3)2·InI3(PPh3), and the tetrahedral indium(iii) complex
InI3(PPri3)
Stephen M. Godfrey, Katharine J. Kelly, Peter Kramkowski, Charles A. McAuliffe and Robin G. Pritchard
Department of Chemistry, University of Manchester Institute of Science and Technology, Manchester, UK M60 1QD
Reaction of R3PI2 (R = Ph, Prn, Pri) with indium metal
powder produces a variety of novel indium metal complexes:
where R = Ph, the four- and five-coordinate metal(III)
complex InI3(PPh3)2·InI3(PPh3) results; where R = Prn, the
the insolubility of InX and of InX3, and so the approach taken
by us represents a significant advance.
Ph3Pl2 reacts with indium metal powder in a 3:2 stoi-
chiometric ratio, eqn. (1).
‘subvalent’ indium(II) complex In2I4(PPrn ) is formed, the
3 2
ca. 7d, Et OÆ
2
first example of an indium tertiary phosphine complex
containing an indium–indium bond; whereas for R = Pri,
the monomeric tetrahedral indium(III) complex InI3(PPri3)
results; these complexes illustrate the subtle effect of the
organic substituents on the phosphorus atom for the reaction
of R3PI2 with indium metal powder and the novel indium
complexes which are available.
InI3(PPh3)2◊InI3(PPh3)
3Ph3PI2 + 2In
N2, room temp.
(1)
1
Recrystallisation of the pale yellow powder from diethyl
ether produced yellow crystals, one of which was selected for
analysis by single-crystal X-ray diffraction. The structure of the
indium(iii) complex was revealed to be InI3(PPh3)2·InI3(PPh3),
1. Surprisingly, the structure contains both tetrahedral and
trigonal-bipyramidal indium(iii) centres within the unit cell. No
complex of indium(iii) of this stoichiometry has previously
been identified.
Virtually nothing was known about the coordination chemistry
of indium with tertiary phosphines until the pioneering work of
Carty and Tuck,1–4 who produced tetrahedral InX3(PR3),
trigonal-bipyramidal InX3(PR3)2, and the molecular octahedral
species InX3(PR3)3, although for this last stoichiometry it was
found that one mole of tertiary phosphine was easily removed
by the application of a vacuum. No complex of stoichiometry
InX3(PR3) containing a tertiary phosphine ligand has been
crystallographically characterised, but the analogous complexes
InI3(PHR2) (R = Ph, But) containing secondary phosphines
have recently been structurally characterised.5 The trigonal-
bipyramidal molecules InX3(PR3)2 have received a little more
attention: the first structurally characterised complex of this
stoichiometry, InCl3(PPh3)2, was reported in 1969,6 and has the
expected trigonal-bipyramidal geometry exhibiting very long
axial indium–phosphorus bonds, 2.71(1) Å. The
trimethylphosphine derivative InCl3(PMe3)2 has been structur-
ally characterised7 as have InBr3(PPhMe2)2 and InI3-
(PPh2Me)2;8 all these complexes exhibit regular trigonal-
bipyramidal geometry.
We are engaged in a study of the oxidising power of a variety
of R3EX2 compounds (E = P, As, Sb; X2 = Br2, I2, IBr) with
unactivated metal powders in diethyl ether solution. The strong
oxidising power of some of these reagents, e.g. Me3EI2 (E = P,
As), is illustrated by their ability to oxidise crude nickel,
cobalt9–14 and even gold15 metal powders directly to the
tripositive oxidation state in a simple one-step reaction.
We have now turned out attention to the reaction of these
agents with indium metal powder, principally for three reasons:
firstly, little is known concerning the coordination chemistry of
indium halides with tertiary phosphine donor ligands; secondly,
as we have already seen, novel complexes unobtainable from
established synthetic techniques are available from our syn-
thetic route, so there is the possibility of synthesising previously
unavailable indium halide tertiary phosphine complexes; if such
compounds are available they may have applications in the
microelectronics industry as precursors for MOCVD. Finally,
indium chemistry has been hampered by the difficulty of
synthetic entries, i.e. the relatively low activity of the metal and
Prn PI2 reacts with indium metal powder according to
3
eqn. (2).
ca. 2d, Et OÆ
2
2Prn3PI2 + 2In
[InI2 (PPrn3)]2
(2)
N2, room temp.
2
Recrystallisation of the white powder from diethyl ether
solution at 60 °C and subsequent cooling to room temp. pro-
duced a large quantity of colourless crystals, from which one
was selected for analysis by single-crystal X-ray diffraction,†
revealing the dinuclear indium(ii) complex [InI2(PPrn )]2, 2‡
3
Fig. 1. This is an unusual result, since we had anticipated a
monomeric tetrahedral or a trigonal-bipyramidal indium(iii)
complex, in agreement with all previous studies of the
conventional reaction of indium(iii) halides with tertiary
phosphines; 2 therefore represents a new, previously uncon-
sidered, indium(ii) halide complex containing tertiary phos-
phine ligands, and the first example of such a complex
containing an indium–indium bond; d(In–In) in 2 is 2.745(3) Å.
Our new synthesis may offer a route to ‘subvalent’ group 13
metal complexes. Although there are no examples of tertiary
phosphine complexes containing an indium–indium bond, the
organometallic species In2[CH(SiMe3)2]4 has been charac-
terised by Uhl et al.16 and In2IBr3(C6H16N2)2 by Tuck and
coworkers.17 The In–In bond distances for these complexes are
2.828(5) and 2.775(2) Å, respectively; both complexes were
prepared from the conventional reaction of an indium(ii) halide
with the appropriate ligand(s).
Pri3Pl2 reacts with indium metal powder according to
eqn. (3).
ca. 7d, Et O Æ
2
3Pri PI + 2In
2InI3(PPri )
(3)
3
2
3
N2, room temp.
3
Recrystallisation of the white powder from diethyl ether
produced colourless crystals. One of these was selected for
Chem. Commun., 1997
1001

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analysis by single-crystal X-ray diffraction.† The structure of
3,§ Fig. 2, was revealed to be the tetrahedral monomeric
InI3(PPri3). Although the existence of complexes of this
stoichiometry has previously been postulated by Carty and
Tuck,4 this complex nevertheless represents the first indium(iii)
complex of this stoichiometry containing a tertiary phosphine
ligand to be crystallographically characterised. The indium–
iodine distances are 2.689(3), 2.701(3) and 2.705(3) Å and the
indium–phosphorus distance is 2.569(7) Å.
with indium metal powder produces the monomeric tetrahedral
3 2
indium(iii) complex InI3(PPri3). The compound In2I4(PPrn )
represents the first example of a dimeric complex containing
tertiary phosphine donor ligands, and since a complex of this
type has never previously been observed, its synthesis may be
attributed to our synthetic method and it may not be available
from conventional techniques.
In conclusion, these new results clearly indicate that subtle
changes in the nature of our oxidising agents result in the
production of different complexes of indium in different
oxidation states, viz. reaction of Ph3PI2 with indium metal
powder produces the indium(iii) complex InI3(PPh3)2·In-
I3(PPh3), containing the indium(iii) centres in trigonal-bipy-
Footnotes
* E-mail: e.jenkins@umist.ac.uk
† Crystal data: In2I4(PPrn3)2: monoclinic P21/n (no. 14), a = 9.166(4),
b = 97.41(4)°, U = 1699(2) Å3, Z = 2, Dc = 2.067 g cm23, m = 50.32
cm21, F(000) = 980. The structure analysis is based on 3319 reflections
(Mo-Ka, qmax = 50.0) 1189 observations [I > 3.00(I)], 118 parameters.
Absorption correction (min/max transmission 0.77–1.10). The structure was
solved by direct methods and refined by full-matrix least squares. Final
residuals R = 0.043, Rw = 0.051.
ramidal and tetrahedral geometry, and the reaction of Prn PI2
3
with indium metal powder produces the unique indium(ii)
3 2
tertiary phosphine complex, In2I4(PPrn ) , which contains an
InI3(PPri3): monoclinic Cc (no. 9), a = 11.836(2), b = 10.796(5),
c = 14.410(2) Å, U = 1820(1) Å3, Z = 4, Dc = 2.393 g cm23, m = 63.81
cm21, F(000) = 1191. The structure analysis is based on 1789 reflections
(Mo-Ka, qmax = 50.1°) 1209 observed [I > 3.00 s(I)], 125 parameters. The
structure was solved by direct methods and refined by full-matrix least
squares. Final residuals R = 0.052, Rw = 0.060.
indium–indium bond. On the other hand, the reaction of Pri3PI2
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/414.
‡ In2I4(PPrn3)2 colourless crystals, correct elemental analysis (C, H, I), mp
56–57 °C. 31P{H} NMR, d 8.74 (s); 1H NMR, d 1.0 (t), 1.1 (t), 1.7 (m), 2.3
(m), intensities approximately 1:3:3:2. Low-frequency Raman spectrum
(50–550 cm21): 136 cm21 (vs, sp), In–I; 186 cm21 (br), In–P; no band could
be readily assigned to n(In–In).
C(6)
C(5)
§ InI3(PPri3) colourless crystals, correct analysis (C, H, I), mp 110–111 °C.
31P{H} NMR, d 39.7 (s) 1H NMR, d 1.5 (spt), 2.8 (s), intensities ca. 9:1.
Low-frequency Raman spectrum (50–550 cm21): 56 cm21 (vs, br); 137
cm21 (vs, sp), In–I; 156 cm21 (s, sp), In–P.
C(3)
C(4)
C(2)
C(1)
I(2)
I(1)
C(7)
C(8)
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I(3)
Fig. 2 Perspective view of the molecular structure of InI3(PPri3): selected
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Received in Basel, Switzerland, 5th December 1996; Com.
6/08230K
1002
Chem. Commun., 1997