Indium(I) trifluoromethanesulfonate and other soluble salts for univalent indium chemistry

Article abstract of DOI:10.1039/b312983g

Herein we report the synthesis, structure and preliminary reactivity studies of a series of unusually soluble indium(I) salts that are improved alternatives to indium(I) halide reagents.

Full text of DOI:10.1039/b312983g

Indium( ) trifluoromethanesulfonate and other soluble salts for univalent
I
indium chemistry
Charles L. B. Macdonald,* Andrea M. Corrente, Christopher G. Andrews, Alexis Taylor and Bobby
D. Ellis
Department of Chemistry and Biochemistry, The University of Windsor, Windsor, Ontario N9B 3P4,
Canada. E-mail: cmacd@uwindsor.ca; Fax: (519) 973-7098; Tel: (519) 253-3000 ext. 3991
Received (in West Lafayette, IN, USA) 16th October 2003, Accepted 6th November 2003
First published as an Advance Article on the web 10th December 2003
Herein we report the synthesis, structure and preliminary
reactivity studies of a series of unusually soluble indium( ) salts
that are improved alternatives to indium( ) halide reagents.
A packing diagram of 1, depicted in Fig. 2, shows that the
structure consists of columns of In cations that are aligned along the
crystallographic a axis, and thus possess an In–In distance of
I
I
4
.9834(4) Å. These In cation columns are separated from each other
The chemistry of group 13 elements in the +1 oxidation state has
been an area of extensive investigation over the last decade.1 Such
compounds are of interest both for the fundamental insights they
provide and because of their utility as reagents or as precursors for
by columns of triflate anions. Perhaps the most surprising aspect of
the crystal structure is the lack of solvent of crystallisation. It is
,2
well-known that In(II) halides of the form In
disproportionate in aromatic solvents to give [In][InX
2
X
4
typically
4
] salts, which
3
,4
6
the formation of clusters and materials. While Tl(
I) salts are
crystallise with arenes that are h -coordinated to the univalent In
ion. It is likely that the numerous contacts between the In ions and
the O and F atoms obviate the need for arene solvation in 1.
A more economical synthesis of 1 is provided by the reaction of
a suspension of InCl in toluene and HOTf in toluene, followed by
the removal of volatiles and washing with pentane. This procedure
also provides 1 in greater than 80% yield with physical and
spectroscopic features that are indistinguishable from those of the
material produced using the protonolysis method described
above.
commonplace and are useful metathesis reagents, many of the
lighter homologues are either unknown or have properties that
preclude their use in synthesis. For example, there are no stable
monomeric boron(
nium( ) and gallium(
in the gas-phase and stabilised with donor solvents. The only
commonly-used gallium( ) halide is the ill-defined material known
as “GaI” obtained from the sonocation of Ga metal and one half
I) halides and the well-characterised alumi-
I
I
) halides are metastable species that are made
5
I
6
equivalent of I
2
. While indium( ) halides do exist, the salts are
I
virtually insoluble in most organic solvents. Some +2 oxidation
state group 13 halides disproportionate to +1 and +3 species in
aromatic solvents, however these revert to the +2 species in the
The most important property of [In][OTf] is its incredible
solubility in organic solvents. For example, 1 is readily soluble
(more than 100 mg mL ) in toluene and THF and is somewhat less
soluble in diethyl ether and dichloromethane. It appears that 1 is
only virtually insoluble in alkanes such as pentane or hexanes. This
remarkable solubility of 1 makes it a uniquely useful reagent for
2
1
7
presence of electron donors. Herein we report the synthesis of
[
In][SO
3
CF
3
] 1 which is a stable In(
I) salt that is soluble in many
organic solvents and may be used as an alternative to In(
I
) halides.
In addition, we detail some of our initial results regarding the
coordination chemistry of this unique source of univalent indium.
Protonolysis of cyclopentadienide substituents has proven useful
for the synthesis of main group cations from groups 13 and 14
8
,9
cyclopentadienyl compounds. In this context, the reaction of
1
0
Cp*In (Cp* = C
5
Me
5
)
with trifluoromethane sulfonic acid
(
HO SCF , HOTf) in toluene solution results in the elimination of
3
3
Cp*H and the formation of the colourless salt [In][OTf] upon
concentration, as shown in Scheme 1. The hygroscopic, air-
sensitive salt is isolated in more than 83% yield after washing with
pentane (this yield is relatively low only because of mechanical
losses) and melts without decomposition at 162–165 °C under an
Fig. 1 Thermal ellipsoid (30%) plot of the asymmetric unit of [In][OTf] 1.
Selected metrical parameters, distances in angstroms and angles in degrees:
In(1)–O(11), 2.579(6); In(2)–O(22), 2.589(6); S(1)–O(11), 1.462(6); S(1)–
O(12), 1.434(6); S(1)–O(13), 1.428(6); O(11)–S(1)–O(12), 113.2(4);
O(11)–S(1)–O(13), 113.4(4); O(12)–S(1)–O(13), 116.8(4).
1
9
2 6 6
N atmosphere. The F NMR spectrum in C D consists of a single
1
3
resonance at 279.5 ppm and the C NMR spectrum exhibits a
1
quartet at 119.9 ppm ( JC–F 318 Hz). Analytical data are consistent
with the proposed composition.†
Needle-shaped crystals of [In][OTf] that are suitable for X-ray
diffraction are readily obtained through the concentration of
toluene solutions of the salt.‡ The asymmetric unit of 1, shown in
Fig. 1, consists of two independent ion pairs each having one
particularly short In–O contact of 2.579(6) Å or 2.589(6) Å.
Overall, the coordination environment about each In ion is
complex, including: four close (less than 3 Å) contacts to oxygen
atoms on different triflate anions arranged in a roughly see-saw
geometry, and a total of 12 contacts to O and F atoms within a 4 Å
radius. The metrical parameters of the triflate anions are consistent
3
with a partially localized SO fragment, in that there are two shorter
S–O distances (1.428(6) and 1.434(6) Å [1.436(6) and 1.437(7) Å])
and a longer distance to the O atom that is closest to an In atom
(1.462(6) Å [1.450(6) Å]).
Fig. 2 Depiction of the crystal structure of 1 showing the columnar nature
Scheme 1 (X = OTf or BF
4
).
of the [In] and [OTf] ion packing.
2
50
C h e m . C o m m u n . , 2 0 0 4 , 2 5 0 – 2 5 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 4

1
3
low-oxidation state In chemistry and In cluster chemistry in that it
eliminates the need for the use of heterogeneous mixtures of
reagents.
investigating analogous Cp* protonolysis reactions using Cp*Al
and Cp*Ga14 to determine if this relatively gentle synthetic method
can be applied to the synthesis of lighter, and typically less stable,
univalent group 13 reagents.
Products obtained from investigations of the acceptor chemistry
of univalent group 13 compounds often result from the dis-
In conclusion, we have prepared a new series of In(
of which are remarkably soluble in organic solvents and may be
used as alternatives to In( ) halides. The donor, acceptor and
I
) salts, some
1
1
proportionation of the group 13 metal. As an initial study of the
acceptor chemistry of the In( ) salt, 1 was mixed with triisopropyl-
I
I
3
1
phosphite in toluene solution. Although the P NMR spectra of the
reaction mixtures indicate the presence of a coordination complex
metathesis chemistry of these and related salts is currently under
investigation.
31
in solution (d P: broad singlet at 6.6), we have only been able to
isolate crystals of 1 and free donor upon concentration of the
solution. The absence of observable disproportionation products in
this reaction suggests that the triflate salt may be more resistant to
redox reactions than are the analogous halide salts, however
experiments with other donors are currently underway to prove this
hypothesis.
We would like to thank the Natural Sciences and Engineering
Research Council (Canada), the Canada Foundation for Innovation,
the Ontario Innovation Trust and the Ontario Research and
Development Challenge Fund (University of Windsor Centre for
Catalysis and Materials Research) for equipment and funding.
Notes and references
[
In][OTf] was mixed with an equimolar amount of InOTf
ascertain whether such a reaction would yield the comproportiona-
tion In(II) product (TfO) In–In(OTf) 2a or the mixed valence salt
In][In(OTf) ] 2b. The white powder obtained upon concentration
3
to
†
Selected characterisation data for 1, 2 and 3.
: Colourless crystals, yield 83%, mp 162–165 °C. F NMR d: 279.5(s).
19
1
2
2
13
C NMR d: 119.9(q, JC–F, 318 Hz). IR (Nujol mull on KBr plates, cm ):
1
21
[
4
1299s, 1198s, 1025s, 800m, 750w, 638s, 583w, 526m, 510m. Elemental
Analysis (CF InO S, 263.88), Calcd: C 4.55; O 18.19; F 21.60; S 12.15.
of the reaction mixture decomposes at 325 °C and has an infrared
3
3
spectrum that is not consistent with the superposition of the spectra
Found: C 4.55; O 17.75; F 22.24; S 12.14%.
1
9
2: Colourless microcrystalline powder, yield 53%, dp 325 °C. 19F NMR
3 6 6
of 1 and In(OTf) . Furthermore, the F NMR spectrum in C D
13
1
1
3
d: 278.2(s). C NMR d: 120.6(q, JC–F, 317 Hz). IR (Nujol mull on KBr
consists of a single resonance at 278.2 ppm and the C NMR
21
1
plates, cm ): 1318s, 1204s, 1164m, 1138m, 1029s, 992w, 663m, 519w.
Elemental Analysis (C 12In , 825.92), Calcd: C 5.82; O 22.25; F
7.60; S 15.53. Found: C 5.73; O 23.50; F 28.20; S 16.10%.
spectrum displays a quartet at 120.6 ppm ( JC–F 317 Hz). Analytical
4
F
2 12 4
O S
data are consistent with the proposed composition.† While we have
not yet been able to obtain crystalline material suitable for
crystallographic examination to date, the reaction of 2 with two
equivalents of triisopropylphosphite results in the regeneration of
crystalline 1 in high yield and the concomitant formation of
2
3
: Cream-coloured microcrystalline solid, yield 83%, mp 135–137 °C.
11
19
B NMR d: 21.36 (sharp s). F NMR d: 2153.2(s). IR (Nujol mull on
KBr plates, cm21): 1278w, 1019s(br), 795w, 761w, 514w. Elemental
Analysis (BF In, 201.62), Calcd: F 37.69. Found: F 37.36%.
4
i
31
(
PrO)
3
P–InOTf
3
(d P: 8.4) upon concentration. This result,
‡ Suitable single crystals of 1 were covered with mineral oil and mounted
in the 174 K N stream of a Bruker Apex CCD diffractometer equipped with
2
a Mo Ka radiation (l = 0.71073 Å) source. The structure was solved by
direct methods and refined using full matrix, least squares on F . Crystal
outlined in Scheme 2, suggests that 2 exists in the mixed valence
form rather than as an In(II) species, which would be expected to
provide a simple donor–acceptor adduct.
Another important aspect of the work presented herein is the
generality of the Cp* protonolysis reaction; many strong, non-
oxidizing protic acids are suited to this synthetic method. For
2
3
data for 1: CF InO
3
S, triclinic, P1, a = 4.8934(4), b = 7.2298(6), c =
1
5
6.950(2) Å, a = 91.011(2)° b = 93.835(2)°, g = 107.711(2)°,V =
3
23
21
85.56(9) Å , Z = 4, Dcalcd = 2.993 g cm , m (Mo Ka) = 4.389 mm
.
A total of 5,324 reflections was collected in the range 2.40 < 2q < 55.02.
Of these, 2,619 were considered observed (I > 2.0s(I)); wR2 = 0.1213, R
example, the reaction of an ethereal solution of [H][BF
Cp*In in toluene produces the new salt [In][BF ] 3 in high yield
, 83% isolated
product). The tetrafluoroborate salt melts without decomposition at
35–137 °C and exhibits analytical and spectroscopic data
4
] with
4
=
0.0479. CCDC 222071. See http://www.rsc.org/suppdata/cc/b3/
1
(
6 6
quantitative formation of Cp*H by H NMR in C D
b312983g/ for crystallographic data in .cif or other electronic format.
1
2
G. Linti and H. Schnockel, Coord. Chem. Rev., 2000, 206, 285.
H. Schnockel and A. Schnepf, Adv. Organomet. Chem., 2001, 47,
235.
1
1
1
consistent with the proposed formulation.† In particular the B and
19
F NMR spectra and the IR spectrum suggest the presence of an
3 A. Schnepf and H. Schnockel, Angew. Chem., Int. Ed., 2002, 41,
intact tetrafluoroborate anion in both solution and the solid state.
While we have not yet been able to obtain crystals suitable for
analysis by single-crystal X-ray diffraction, preliminary powder X-
ray diffraction experiments show that 3 produces an XRD spectrum
3533.
4
5
R. A. Fischer and J. Weiss, Angew. Chem. Int. Ed., 1999, 38, 2831.
C. Dohmeier, D. Loos and H. Schnockel, Angew. Chem. Int. Ed. Engl.,
996, 35, 129.
M. L. H. Green, P. Mountford, G. J. Smout and S. R. Speel, Polyhedron,
990, 9, 2763.
1
6
1
2
4
similar to that of [Tl][BF ]. Although 3 dissolves in polar
1
solvents, its solubility is generally less than that of 1 in the solvents
we have investigated.
7
8
H. Schmidbaur, Angew. Chem., Int. Ed. Engl., 1985, 24, 893.
P. Jutzi and N. Burford, Chem. Rev., 1999, 99, 969.
In addition to allowing variation in the nature of the anion, the
protonolysis approach may also be applicable to the synthesis of the
lighter group 13 analogues. In this context, we are presently
9 A. H. Cowley, C. L. B. Macdonald, J. S. Silverman, J. D. Gorden and A.
Voigt, Chem. Commun., 2001, 175.
10 O. T. Beachley, Jr., M. R. Churchill, J. C. Fettinger, J. C. Pazik and L.
Victoriano, J. Am. Chem. Soc., 1986, 108, 4666.
1
1 R. J. Baker, H. Bettentrup and C. Jones, Eur. J. Inorg. Chem., 2003,
446.
2
1
1
2 H. Moller and H. D. Lutz, Z. Kristallogr., 1992, 201, 285.
3 C. Dohmeier, C. Robl, M. Tacke and H. Schnockel, Angew. Chem., Int.
Ed. Engl., 1991, 30, 564.
Scheme 2
14 D. Loos and H. Schnoeckel, J. Organomet. Chem., 1993, 463, 37.
C h e m . C o m m u n . , 2 0 0 4 , 2 5 0 – 2 5 1
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251