Electron-Transfer Processes in Indium(II) Iodide-o-Quinone Systems

Article abstract of DOI:10.1021/ic9508132

Indium(II) iodide reacts with various substituted o-quinones in nonaqueous solution by successive one-electrontransfer reactions to give (SQ)InI₂ products (SQ = semiquinonate radical anion). Electron spin resonance spectroscopy demonstrates the presence of both mono- and diradical species in the reaction mixture. Addition of 4-picoline to a mixture of In₂L₄ and TBQ (=3,5-di-tert-butyl-o-quinone) in toluene causes the precipitation of the indium(III)-semiquinonate complex (TBSQ)InI₂(pic)₂ whose structure has been established by X-ray crystallography: space group P1?, with a = 13.013(3) ?, b = 13.317(3) ?, c = 10.828(5) ?, α = 97.71(3)°, β= 107.98(3)°, y = 103.92(3)°, V = 1684.8(1.2) ?₃, Z = 2. Refinement converged at R = 0.051 and R_w = 0.064 for 5918 reflections at 23 °C. The InO₂N₂I₂ kernel is pseudooctahedral, and the structure confirms the presence of the semiquinonate ligand. A reaction scheme which incorporates these results is proposed.

Full text of DOI:10.1021/ic9508132

1560
Inorg. Chem. 1996, 35, 1560-1563
Electron-Transfer Processes in Indium(II) Iodide-o-Quinone Systems
Martyn A. Brown, Bruce R. McGarvey, Andrzej Ozarowski, and Dennis G. Tuck*
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4
X
ReceiVed June 29, 1995
Indium(II) iodide reacts with various substituted o-quinones in nonaqueous solution by successive one-electron-
transfer reactions to give (SQ)InI2 products (SQ ) semiquinonate radical anion). Electron spin resonance
spectroscopy demonstrates the presence of both mono- and diradical species in the reaction mixture. Addition of
4
-picoline to a mixture of In2I4 and TBQ ()3,5-di-tert-butyl-o-quinone) in toluene causes the precipitation of the
indium(III)-semiquinonate complex (TBSQ)InI2(pic)2 whose structure has been established by X-ray crystal-
lography: space group P 1h , with a ) 13.013(3) Å, b ) 13.317(3) Å, c ) 10.828(5) Å, R ) 97.71(3)°, â )
3
1
07.98(3)°, γ ) 103.92(3)°, V ) 1684.8(1.2) Å , Z ) 2. Refinement converged at R ) 0.051 and Rw ) 0.064
for 5918 reflections at 23 °C. The InO2N2I2 kernel is pseudooctahedral, and the structure confirms the presence
of the semiquinonate ligand. A reaction scheme which incorporates these results is proposed.
Introduction
(Aldrich). Indium(II) iodide was prepared by reducing InI
3
(prepared
3
in xylene from In + / I ) with indium metal in situ, using previously
2 2
The study of electron-transfer processes in the redox reactions
of main group elements and compounds has been the subject
of a number of publications from this laboratory.1 The most
important general conclusion is that many processes which were
earlier believed to involve the concerted transfer of a pair of
electrons in fact proceed via successive single-electron transfers.
Of particular relevance to the present work are the reactions of
reported methods.8
Infrared spectra were recorded on a Nicolet 4DX instrument, and
H and C nuclear magnetic resonance spectra (NMR) on a Bruker
1
13
AC-300L spectrometer. Electron spin resonance spectra (ESR) were
obtained on a Bruker ESP-300E instrument, using methods described
earlier.5 Elemental analysis was by Canadian Microanalytical Services
Ltd.
3
,5-di-tert-butyl-o-benzoquinone (TBQ) with indium metal,
Reactions with Indium(II) Iodide. (i) In
2 4
I + 2TBQ. A solution
2
where the product is the indium(I) semiquinone, In(TBSQ),
of In (0.74 g, 1 mmol) in toluene (10 mL) was added to TBQ (0.44
2 4
I
g, 2 mmol) in the same solvent (10 mL). The resultant brown solution
was stirred for 3 h, the solvent partially removed, and excess 4-picoline
added, at which point the solution became green. The air-sensitive
crystals which deposited when this solution was cooled overnight were
collected, washed with toluene, and dried in vacuo. Yield: 0.78 g,
and of this and other o-quinones with indium(I) halides to give
XIn(CAT) species (where CAT2- is the corresponding substi-
tuted catecholate) via o-semiquinone complexes.3
,4
More
recently, we showed that bis(semiquinone) derivatives of
indium(III) halides exist in nonaqueous solution and that
intramolecular electron-transfer reactions are important in the
chemistry of such compounds.5
An investigation of the analogous reactions between o-
quinones and indium(II) iodide, the best characterized of the
indium(II) halides, provides an obvious and interesting extension
of these studies. The indium(II) halides are dimeric species
5
3%. Anal. Calcd for (TBSQ)InI(pic)
2
7 8 42 2 2
‚C H , C33H N O InI: C, 53.5;
H, 5.72. Found: C, 53.7; H, 5.70. Spectral data confirmed the
formulation of this compound. IR (KBr): 3020-2954 (C-H), 1621
-
1
1
(4-pic), 1487, 1439 (C-O), 1420 cm (C-O). H NMR: 8.41 (4H,
pic), 7.23-7.15 (6H, pic + TBC), 2.30 (6H, CH
t-Bu), 1.21 ppm (9H, t-Bu). 13C NMR: 149.0 (br), 124.5 (TBC), 31.9
t-Bu), 29.8 (t-Bu), 20.5 ppm (CH , pic).
(ii) In I + 4TBQ. The procedure was identical to that described
3
of pic), 1.31 (9H,
(
3
+
-
for X ) Br and I, either of the ionic form In [InX4] or of the
2 4
above except that 4 equiv of TBQ was used. Partial removal of solvent,
followed by cooling, gave an air-sensitive red powder, which was
metal-metal-bonded form X2InInX2; the latter structure is seen
in the anions In2X62- and the adducts In2X4L2, and organo
washed with toluene and dried in vacuo. This solid is (TBSQ)InI
2
.
6
derivatives In2R4 of this type are also known. Indium(II) iodide
Anal. Calcd for C14 InI : C, 28.5; H, 3.42. Found: C, 28.6; H,
H
20
O
2
2
I
III
has been shown to be In [In I4] in the solid state, and the reasons
3
.70. IR (KBr): 3040-2980 (C-H), 1489 (C-O), 1443 (C-O), 1446
II II
for this being more stable than I2In In I2 have been discussed
-1
cm (C-O). Addition of 4-picoline to the dissolved solid in toluene
resulted in the deposition of air-sensitive pale green needlelike crys-
tals of the bis(picoline) adduct, (TBSQ)InI (pic) . Anal. Calcd for
elsewhere.7 The present paper describes the reaction of In2I4
with various substituted o-quinones in toluene in terms of the
solution behavior of indium(II) and of the electron-transfer
reactions involved.
2
2
C
26
H
34
O
2
2
N InI
2
: C, 40.3; H, 4.42. Found: C, 40.4; H, 4.50. IR
(KBr): 3090-3010 (C-H), 1635 (pic), 1486 (C-O), 1394 (C-H),
-
1
1
420 cm (C-H). A crystallographic study of this compound is
Experimental Section
reported below.
General Data. All solvents were dried and degassed by standard
procedures. o-Quinones were the commercially available materials
In two later experiments, excess triphenylphosphine was added to
the reaction mixture, at either the beginning or the end. In each case,
9
the product was a precipitate of InI
3
‚PPh . Mp: 195-197 °C (lit.
3
X
Abstract published in AdVance ACS Abstracts, February 1, 1996.
1
2
3
95 °C). Anal. Calcd for C18H15InI P: C, 24.9; H, 2.50. Found: C,
(
(
1) Tuck, D. G. Coord. Chem. ReV. 1992, 112, 215.
2) Annan, T. A.; McConville, D. H.; McGarvey, B. R.; Ozarowski, A.;
Tuck, D. G. Inorg. Chem. 1989, 28, 1664.
8.5; H, 2.00.
2 4
(iii) In I + 2 Phenanthrene-9,10-quinone (PQ). The procedure
(
(
3) Annan, T. A.; Tuck, D. G. Can. J. Chem. 1988, 66, 2935.
4) Annan, T. A.; Chadha, R. K.; Doan, P.; McConville, D. G.; McGarvey,
B. R.; Ozarowski, A.; Tuck, D. G. Inorg. Chem. 1990, 29, 3936.
5) Annan, T. A.; Brown, M. A.; El-Hadad, A.; McGarvey, B. R.;
Ozarowski, A.; Tuck, D. G. Inorg. Chim. Acta 1994, 225, 207.
6) Tuck, D. G. Chem. Soc. ReV. 1993, 269 and references therein.
7) Tuck, D. G. Polyhedron 1990, 9, 377.
was identical to that for TBQ except that the reaction time was 12 h.
Partial removal of solvent and subsequent cooling led to the deposition
of a purple powder, shown by analysis to be the semiquinone derivative
(
(
(
(8) Freeland, B. H.; Tuck, D. G. Inorg. Chem. 1976, 15, 475.
(9) Carty, A. J.; Tuck, D. G. J. Chem. Soc. A 1996, 1081.
0
020-1669/96/1335-1560$12.00/0 © 1996 American Chemical Society

Indium(II) Iodide-o-Quinone Systems
Inorganic Chemistry, Vol. 35, No. 6, 1996 1561
Table 2. Interatomic Distances (Å) and Angles (deg) for
Table 1. Summary of X-ray Crystallograhic Data for
(TBSQ)InI
2
(pic)
2
2 2
In(TSQ)InI (pic)
empirical formula
fw
a
b
c
R
â
γ
V
C
26
H
34
O
2
N
2
InI
2
Z
2
I(1)-In(1)
I(2)-In(1)
In(1)-O(1)
In(1)-O(2)
In(1)-N(1)
In(1)-N(2)
2.773(1) O(1)-C(6)
2.772(1) O(2)-C(1)
2.206(7) N(1)-C(13)
2.192(8) N(1)-C(17)
1.31(1)
1.29(1)
1.31(2)
1.33(2)
1.32(1)
1.33(2)
775.20
space group P 1h (No. 2)
T
13.013(3) Å
13.317(3) Å
10.828(5) Å
97.71(3) Å
107.98(3) Å
103.92(3) Å
1684.8(1.2) Å
23 °C
0.710 69 Å
1.52 g cm
25.49
5.1
λ
-
3
F
calcd
2.31(1)
N(2)-C(7)
-
1
µ, cm
R, %
2.325(9) N(2)-C(11)
a
b
O(1)-In(1)-N(1)
O(1)-In(1)-N(2)
O(2)-In(1)-N(1)
O(2)-In(1)-N(2)
N(1)-In(1)-N(2)
In(1)-O(1)-C(6)
In(1)-O(2)-C(1)
In(1)-N(1)-C(13) 123(1)
In(1)-N(1)-C(17) 121.0(8)
O(2)-C(1)-C(6)
C(2)-C(1)-C(6)
C(7)-N(2)-C(11)
85.0(3)
83.7(3)
85.2(3)
85.8(3)
167.1(3)
113.4(7)
114.0(7)
I(1)-In(1)-I(2)
I(1)-In(1)-O(1)
I(1)-In(1)-O(2)
I(1)-In(1)-N(1)
I(1)-In(1)-N(2)
I(2)-In(1)-O(1)
I(2)-In(1)-O(2)
I(2)-In(1)-N(1)
I(2)-In(1)-N(2)
102.55(4)
92.9(2)
167.8(2)
92.7(3)
94.1(2)
164.5(2)
89.7(2)
95.7(3)
93.6(2)
R
w
, %
6.4
a
b
2
2]1/2
.
o
o
R ) ∑||F | - |F
c
||/∑|F
o
|.
R
w
) [∑w(|F
o
| - |F
c
|) /∑wF
(
PSQ)InI
2
. Anal. Calcd for C14
H
8
O
2
2
InI : C, 29.2; H, 1.40. Found:
C, 29.3; H, 1.50. IR (KBr): 3060-3020 (C-H), 1476 (C-O), 1441
-
1
(
C-O), 1425 cm (C-O).
(
iv) In + 2 Tetrabromo-o-benzoquinone. Again the procedure
2 4
I
119(1)
120(1)
117(1)
N(1)-C(17)-C(16) 123(1)
N(1)-C(13)-C(14) 124(1)
was identical to (i) except that the reaction time was longer at 15 h.
Removal of solvent left a dark brown solid, which was washed with
N(2)-C(7)-C(8)
122(1)
cold benzene and dried in vacuo. Anal. Calcd for C
6 4 2 2
Br O InI : C,
C(13)-N(1)-C(17) 116(1)
In(1)-N(2)-C(7) 120.5(8)
In(1)-N(2)-C(11) 122.1(8)
N(2)-C(11)-C(10) 122(1)
O(1)-In(1)-O(2)
O(1)-In(1)-N(1)
9
.10; H, 0.0. Found: C, 9.20; H, 0.05. IR (KBr): 3045-2965 (C-
75.0(3)
85.0(3)
-
1
H), 1496 (C-O), 1456 (C-O), 1425 cm (C-O).
v) In + 2 1,2-Naphthoquinone (NQ). A reaction time of 24 h
(
2 4
I
phenyl ring
mean C-C
mean C-C-C
1.41(2)
1.20(1)
1.56(2)
1.57(2)
1.40(2)
1.39(2)
gave a black solid, which was collected by filtration, washed with
toluene, and dried in vacuo. This material was identified as (NSQ)-
InI . Anal. Calcd for C10H O InI : C, 22.8; H, 1.15. Found: C, 22.9;
2 6 2 2
tert-butyl group at C(4)
tert-butyl group at C(2)
picoline ligands
mean C(23)-C(24,25,26)
mean C(19)-C(20,21,22)
N(1): mean C-C
H, 1.20. IR (KBr): 3060-3005 (C-H), 1487 (C-O), 1458 (C-O),
-
1
1
416 cm (C-O).
N(2): mean C-C
2 2
Crystallographic Analysis. A crystal of (TBSQ)InI (pic) , 1,
mounted in a glass capillary, was sited in a four-circle Rigaku AFC6
4
and is closely related to that of the bromo compound (TBSQ)-
InBr2(pic)2; in particular, the bond distances and angles
in the InO2C2 ring of the indium-semiquinonate system are
identical within experimental error in the two compounds, as
are the indium-picoline parameters. The average C-O dis-
tance of 1.30(1) Å in the semiquinonate ligand is almost
exactly that reported in many other analogous main group
complexes of this type. The other feature of interest is the
indium-iodine bond distance of 2.774(1) Å. We have recently
reviewed the published data for indium(III)-iodine bond
distances, with specific reference to the effect of coordination
number; the range for six-coordinate species is 2.83 ( 0.04
Å, and the present results are clearly in keeping with these
limits.
In addition to these structural details, the crystallographic
results are important in that they demonstrate the role of
o-semiquinone radicals in these reactions and, so, support the
reaction mechanism discussed below.
diffractometer using graphite-monochromatized Mo KR radiation (λ
)
0.710 69 Å). The unit cell constants and an orientation matrix for
data collection were obtained from 24 centered reflections (15° < 2θ
35°). Crystal parameters and details of the data collection methods
<
are summarized in Table 1. The intensities of three standard reflections
were recorded every 150 reflections and showed no statistically
significant changes over the duration of the data collection. The
intensity data were collected using the ω-2θ scan technique, in four
shells (2θ < 30, 40, 45, and 50°). In view of the large absorption
coefficient, an absorption correction was applied to the data, which
were processed using the TEXSAN software package on an SG1
computer. Refinement was carried out by using full-matrix least-
18
2
squares techniques on F, minimizing the function ∑w(|F
o
| - |F
c
|) ,
2
where w ) 1/σ (F
o
) and F
o
and F
c
are the observed and calculated
structure factors. Fixed H atom contributions were included, with C-H
distances of 0.95 Å and thermal parameters 1.2 times the isotropic
thermal parameters of the bonded carbon atoms. Hydrogen atoms were
not refined, but all values were updated as the refinement proceeded.
Convergence was achieved at final values of R ) 0.051 and R
w
)
0
.064 for 5918 unique observed reflections. The programs and
ESR Studies. The most complete series of spectroscopic
results apply to the reaction of In I with 2 equiv of TBQ in
correction procedures used are listed in refs 10-17. Significant bond
distances and bond angles are given in Table 2, and the structure is
shown in Figure 1. Tables of thermal parameters, positional parameters,
and hydrogen atom coordinates are available as Supporting Information.
2
4
toluene. The ESR spectrum of the resultant solution, shown in
Figure 2A, clearly contains two components. The more sharply
defined of these has the characteristics g ) 2.0034, AIn ) 5.06
G, and AH ) 3.40 G, which identify the parent species as an
Results
•
4
indium(III)-TBSQ complex. Addition of excess picoline to
this solution leads to the removal of the broad feature, giving
the spectrum in Figure 2B, for which we found g ) 2.003 91
at 300 K. This very well resolved spectrum (Figure 3) shows
a splitting of 0.36 G due to the nine hydrogens of one of the
tert-butyl groups, in addition to the splittings due to indium
and one of the ring hydrogens of 4.86 and 3.42 G, respectively.
The indium hyperfine constant changes with temperature from
Crystallographic Study. The structure of 1 is clearly that
of a six-coordinate indium(III) species, with an InO2N2I2 kernel,
(
10) Walker, N.; Stuart, D. DIFABS. Acta Crystallogr., Sect. A 1983, 39,
158.
(
(
11) Gilmore, D. J. MITHRIL. J. Appl. Crystallogr. 1984, 17, 42.
12) Beurskens, P. T. DIRDIF. Technical Report I; Crystallography
Laboratory: Toernooiveld, 6526 ED Nijmegen, The Netherlands, 1984.
13) Johnson, C. K. ORTEP II. Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
14) Cromer, D. T.; Waber, T. J. International Tables for X-ray Crystal-
lography; Kynoch: Birmingham, U.K., 1974; Vol. IV.
(
(
5
.61 G to 240 K to 4.00 G at 360 K; g changes over the same
temperature range from 2.003 85 to 2.003 94, while the hyper-
fine constants for the ring hydrogens and the tert-butyl
hydrogens remain essentially unchanged. Even at this very good
resolution, we could not see any splitting due to the second
(
(
15) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
16) Motherwell, S.; Clegg, W. PLUTO. University of Cambridge, U.K.,
1978.
(
17) TESAN. Texray Structure Analysis Package; Molecular Structure
Corp: Houston, TX, 1985.
(18) Brown, M. A.; Tuck, D. G. Inorg. Chim. Acta, in press.

1
562 Inorganic Chemistry, Vol. 35, No. 6, 1996
Brown et al.
Figure 4. ESR spectrum of a frozen solution (77 K) containing In
2 4
I
+
TBQ, showing presence of a diradical species.
solution, and this is supported by the frozen-solution spectra
see below). The reaction scheme discussed later accommodates
(
both these possibilities, which cannot be differentiated on the
present evidence.
The spectrum of the frozen solution shows, in addition to
the central features, a half-field resonance indicating the presence
of a biradical species. The presence of unresolved extensive
hyperfine splitting due to the indium nucleus makes a detailed
analysis of the fine structure rather difficult, but we were able
to estimate a value of D ∼ 250 G from the central region of
the spectrum (Figure 4) as well as from the position of the half-
field signal. Comparison with earlier results for M(TBSQ)2
complexes and their analysis identify the arrangement of the
ligands as cis. The half-field resonance is absent from a frozen
solution prepared from In2I4 + 2TBQ + excess picoline. The
remaining central portion of this spectrum is well resolved and
shows the presence of an anisotropic hyperfine coupling to
indium.
Figure 1. Molecular structure of (TBSQ)InI
probability ellipsoids), with hydrogen atoms omitted.
2
(ORTEP diagram, 30%
1
9
The reactions of In2I4 with 2 equiv of phenanthrene-9,10-
quinone, tetrabromo-o-quinone, and 1,2-naphthoquinone all
follow the same course, in that strongly colored solids with the
composition (SQ)InI2 are obtained, either immediately or
subsequently on removal of solvent. These compounds show
ESR activity in the solid state. The spectra of the reaction
mixtures confirm the presence of indium(I) and indium(III)
semiquinone species, and/or of indium(III) biradical complexes,
indicating a reaction pathway similar to that set out in Scheme
2 4
Figure 2. ESR spectra of (A, top) the In I + TBQ reaction mixture
and (B, bottom) the same solution after adding picoline, both at room
temperature.
1
. The major differences are that the products (SQ)InI2 are
much less soluble than in the case of the TBQ system and that
these final products do not require the ligation of a base to form
stable insoluble products. We were not able to obtain suitable
crystals of any of these compounds for X-ray analysis.
Discussion
Reaction Scheme. The ESR results, and the crystallographic
structure of 1, show beyond question that semiquinonate anion
radicals are essential intermediates in the reaction between In2I4
+
-
4
and TBQ. As noted above, In2I4 has the structure In [InI ] in
Figure 3. High-field region of the ESR spectrum of a solution
containing In I + TBQ + picoline, recorded at 300 K.
2 4
the solid state, and this apparently persists in solutions in
aromatic solvents due to solvation of the In cation;6
+
a
crystalline disolvate has been characterised in the system In2-
ring hydrogen, and there was no evidence of spin density on
the picoline nitrogen.
2
0
Br4-1,3,5-Me3C6H3. We therefore assume that the reaction
+
involves the solvated In cation, presumably present as part of
The broader component in the spectrum of Figure 2A can be
interpreted in either of two ways. If it is assumed that the
observed features are the visible portion of a broad multiplet
centered on g ) 2.000, one can extract a hyperfine coupling
+
-
an ion-pair [In(S) ] [InI ], and the o-quinone. Furthermore,
n
4
-
given that there are no known cases of InI4 acting as an
•
-
(19) Ozarowski, A.; McGarvey, B. R.; Peppe, C.; Tuck, D. G. J. Am. Chem.
Soc. 1991, 113, 3288.
constant of 10 G, typical of AIn for species in which TBSQ is
4
bonded to indium(I). The alternative explanation is that this
(20) Ebenh o¨ ch, J.; M u¨ ller, G.; Reide, J.; Schmidbaur, H. Angew. Chem.,
is a broad signal due to an indium(III) biradical complex in the
Int. Ed. Engl. 1984, 23, 386.

Indium(II) Iodide-o-Quinone Systems
Inorganic Chemistry, Vol. 35, No. 6, 1996 1563
Scheme 1
Scheme 1 therefore represents a good overall model in the case
of the reaction between In2I4 and 2 equiv of TBQ. On the
preparative scale, the air-sensitive compound In(TBSQ)I2 was
obtained from the solution as the bis(picoline) adduct, suggesting
that the left-hand pathway of Scheme 1 is the dominant process
in these circumstances.
The result of adding excess triphenylphosphine to a mixture
of In2I4 + 4Q is the precipitation of the 1:1 adduct InI3‚PPh3.
The ESR spectrum of the residual solution shows the presence
of a biradical species, and this can be understood in terms of
Scheme 1, since by following the left-hand side sequence, one
can write
2
(SQ)InI + excess Ph P f InI ‚PPh + (SQ) InI (2)
2 3 3 3 2
The most significant difference between the triphenylphosphine
reaction and that with 4-picoline is probably the precipitation
of the 1:1 adduct in the former system.
The three other o-quinones studied, namely phenanthrene-
9
,10-quinone, tetrabromo-o-benzoquinone, and 1,2-naphtho-
quinone, all give the appropriate (SQ)InI2 species as the reaction
products when reacted with In2I4 in a 1:2 ratio, and in each
case these insoluble products precipitated from the reaction
mixture without the addition of base. It is possible that the
insolubility and the stability in the absence of further coordinat-
ing agents point to the existence of these species as halide
bridged dimers
electron pair acceptor, the primary reaction must be nucleophilic
attack by the o-quinone at the In site.
+
The reaction scheme shown (Scheme 1) assumes that this
•
• +
first step yields an indium(III) semiquinonate cation [ In(SQ )] ,
which may then lead to two separate reaction sequences. One
of these involves dimerization by In-In bond formation, and
disproportionation of this dimer can yield both indium(III) and
indium(I)-semiquinone species. These processes, which have
4
been discussed in detail in an earlier paper, explain the ESR
spectrum in Figure 2 on the basis that semiquinone derivatives
of these two oxidation states are identified. In the competing
•
II
•
pathway, [ In (SQ )] may react with a second quinone to give
while higher order species might also involve bridging semi-
quinonate ligands.
III
•
+
[
In (SQ )2] , which explains the presence of diradical species,
with cis ligands in the solution. The most probable stereo-
An interesting general point is that although the reaction
scheme is based on the oxidation of the solvated In cation by
-
+
chemistry for this species, and its associated InI anion, is
4
o-quinones, there are significant differences from the comparable
reactions of two of these o-quinones with indium(I) halides.4
This may reflect the different reaction conditions used in the
two series of experiments; in the present case, the reactions were
homogeneous, while with the indium(I) halides, homogeneity
was only achieved by adding an excess of N,N,N′,N′-tetra-
methylethylenediamine to the toluene, since in the absence of
this base suspensions of InX formed the oxidation matrix.
Conclusion. The reaction of In2I4 with four different
substituted o-benzoquinones proceeds via attack of the quinone
in which the stereochemistry at the positive site is similar to
+
21
that in the [InI2(dmso)4] cation.
Iodide bridging is an
important feature of the structure of In2I6 both in the solid state
22
+
and in solution. Rearrangement of this species would give
on the solvated In cation which is present in solutions of In2I4
•
(
SQ )InI2.
in toluene. Subsequent reactions, which can be understood in
the light of previous work on indium(I)-o-quinone reactions,
give either (SQ)InI2 or (SQ)InI2(pic)2 as product, depending on
the particular o-quinone and on the reaction conditions. ESR
results support the proposed reaction mechanism.
The effect of excess picoline on each of these competing
processes will be to produce the complex In(SQ)InI2(pic)2. In
the case of the reaction proceeding via the left-hand pathway,
this is a straightforward addition and rearrangement reaction.
In the equilibrium mixture it seems likely that the indium(III)
Acknowledgment. This work was supported in part by
Operating Grants to B.R.M. and D.G.T. from the Natural
Sciences and Engineering Research Council of Canada.
-
species is associated with at least one and possibly two InI4
anions. Addition of excess picoline will convert this to (SQ)-
InI2(pic)2, thereby causing eq 1 to move to the right, with the
Supporting Information Available: Tables D.1-D.4, listing
additional X-ray crystallographic data, final fractional coordinates and
isotropic thermal parameters of non-hydrogen atoms, anisotropic thermal
parameters for non-hydrogen atoms, and final fractional coordinates
and isotropic thermal parameters for hydrogen atoms (7 pages).
Ordering information is given on any current masthead page. Structure
factor tables may be obtained directly from the authors.
•
II II
•
2+
III
•
2-
I
•
[
(SQ )In In (SQ )] h [In (SQ )] + In (SQ ) (1)
eventual conversion of all three species to the picoline adduct.
(
(
21) Einstein, F. W. B.; Tuck, D. G. Chem. Commun. 1970, 1182.
22) Taylor, M. J.; Brothers, P. J. In The Chemistry of Aluminium, Gallium,
Indium and Thallium; Downs, A. J., Ed.; Blackie: London, 1993; pp
132-3.
IC9508132