In3I2[C(SiMe3)3]3 : Synthesis of a diiodotrialkyltriindane(5) containing two in-in single bonds

Article abstract of DOI:10.1021/om0102302

Treatment of the tetrahedral indium(I) cluster compound In₄[C(SiMe₃)₃]₄ (1) with a mixture of All₃ and I₂ afforded the yellow diiodotriindium compound In₃I₂[C(SiMe₃)₃]₃ (2) in 73% yield. 1 contains a chain of three indium atoms connected by In-In single bonds. A trigonal bipyramidal structure resulted in the solid state by two iodide bridges between the terminal indium atoms.

Full text of DOI:10.1021/om0102302

Organometallics 2001, 20, 3355-3357
3355
In I [C(SiMe ) ] : Syn th esis of a
3
2
3 3 3
Diiod otr ia lk yltr iin d a n e(5) Con ta in in g Tw o In -In Sin gle
Bon d s
Werner Uhl,* Sandra Melle, Gertraud Geiseler, and Klaus Harms
Fachbereich Chemie der Philipps Universit a¨ t Marburg, Hans-Meerwein-Strasse,
D-35032 Marburg, Germany
Received March 23, 2001
Summary: Treatment of the tetrahedral indium(I) clus-
ter compound In4[C(SiMe3)3]4 (1) with a mixture of AlI3
and I2 afforded the yellow diiodotriindium compound
In3I2[C(SiMe3)3]3 (2) in 73% yield. 1 contains a chain of
three indium atoms connected by In-In single bonds. A
trigonal bipyramidal structure resulted in the solid state
by two iodide bridges between the terminal indium
atoms.
Ch a r t 1
In tr od u ction
The synthesis of organoelement cluster compounds of
the heavier elements of the third main group has been
1
,2
of considerable interest in the past decade. Besides
their fascinating structures and bonding, these com-
pounds are of particular importance owing to their
2
singular chemical properties. Our efforts have been
focused on the investigation of the reactivity of the
tetrahedral cluster compounds E4[C(SiMe3)3]4 (E ) Ga,
In (1)), which are readily prepared by the reduction of
the corresponding alkyltrichlorogallate with Rieke mag-
gens with these group 13 tetrahedrans gave hetero-
cubane type structures, and a remarkable product
3
2
nesium or by the reaction of indium(I) bromide with
LiC(SiMe3)3‚2THF.4 The monomeric fragments of these
clusters (E-R) are isolobal with carbon monoxide, and
we synthesized many derivatives analogous to transition
metal carbonyl complexes. The compounds M[EC-
,5
containing mixed-valent indium atoms was isolated with
9
the sulfur compound In S[C(SiMe ) ] . White phospho-
4
3 3 4
rus reacted with the tetragallium derivative to yield a
Ga P cage compound by the insertion of three Ga-R
3
4
SiMe3)3]4 (E ) Ga, In; M ) Ni, Pt),6,7 which contain
10
(
monomers into three P-P bonds. Halogen derivatives
of the clusters to date have not been prepared, and we
were interested in synthesizing such compounds that
retain the gallium or indium atoms in a low oxidation
state. Such halogen derivatives may be useful in further
development of group 13 cluster chemistry and may
open a route to the synthesis of novel compounds with
subvalent gallium and indium atoms by salt elimina-
tion.
nickel and platinum atoms tetrahedrally coordinated by
four E-R ligands, are of particular interest. Consider-
able π-back-bonding of electron density from filled
transition metal orbitals to the vacant p-orbitals of the
unsaturated gallium or indium atoms was verified by
7
,8
quantum-chemical calculations. Reactions of chalco-
(1) (a) Uhl, W. Angew. Chem. 1993, 105, 1449; Angew. Chem., Int.
Ed. Engl. 1993, 32, 1386. (b) Dohmeier, C.; Loos, D.; Schn o¨ ckel, H.
Angew. Chem. 1996, 108, 141; Angew. Chem., Int. Ed. Engl. 1996, 35,
1
2
1
29. (c) Linti, G.; Schn o¨ ckel, H. Coord. Chem. Rev. 2000, 206-207,
85. (d) Wiberg, N.; Blank, T.; N o¨ th, H.; Ponikwar, W. Angew. Chem.
999, 111, 887; Angew. Chem., Int. Ed. 1999, 38, 839. (e) Eichler, B.
Resu lts a n d Discu ssion
E.; Hardman, N. J .; Power, P. P. Angew. Chem. 2000, 112, 391; Angew.
Chem., Int. Ed. 2000, 39, 383. (f) Linti, G.; Rodig, A. Chem. Commun.
2
To obtain an iodine derivative of the indium cluster,
we treated 1 with equivalent quantities of elemental
iodine. But in no case did we succeed in isolating any
pure product. Instead mixtures of unknown products
together with the starting compound 1 were formed. 1,2-
Diiodoethane, a mild halogenation reagent, gave an
inseparable mixture of 1 together with an unknown
000, 127.
(
2) Uhl, W. Rev. Inorg. Chem. 1998, 18, 239.
(3) (a) Uhl, W.; J antschak, A. J . Organomet. Chem. 1998, 555, 263.
(b) Uhl, W.; Hiller, W.; Layh, M.; Schwarz, W. Angew. Chem. 1992,
1
04, 1378; Angew. Chem., Int. Ed. Engl. 1992, 31, 1364.
4) Uhl, W.; Graupner, R.; Layh, M.; Sch u¨ tz, U. J . Organomet. Chem.
995, 493, C1.
5) Schluter, R. D.; Cowley, A. H.; Atwood, D. A.; J ones, R. A.;
Atwood, J . L. J . Coord. Chem. 1993, 30, 25.
6) (a) Uhl, W.; Pohlmann, M.; Wartchow, R. Angew. Chem. 1998,
10, 1007; Angew. Chem., Int. Ed. 1998, 37, 961. (b) Uhl, W.; Melle, S.
Z. Anorg. Allg. Chem. 2000, 626, 2043.
7) Uhl, W.; Benter, M.; Melle, S.; Saak, W.; Frenking, G.; Uddin,
(
1
(
(
(8) (a) Uddin, J .; Boehme, C.; Frenking, G. Organometallics 2000,
19, 571. (b) Uddin, J .; Frenking, G. J . Am. Chem. Soc. 2001, 123, 1683.
(9) Uhl, W.; Graupner, R.; Hiller, W.; Neumayer, M. Angew. Chem.
1997, 109, 62; Angew. Chem., Int. Ed. Engl. 1997, 36, 62.
(10) Uhl, W.; Benter, M. Chem. Commun. 1999, 771.
1
(
J . Organometallics 1999, 18, 3778.
1
0.1021/om0102302 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/16/2001

3
356 Organometallics, Vol. 20, No. 15, 2001
Notes
product upon reaction in a stoichiometric 1 to 1 ratio in
toluene at 60 °C. An excess of 1,2-diiodoethane resulted
in the formation of a mixture of unknown products, none
of which could be purified by recrystallization. We
believe that the reaction with pure iodine failed because
the strongly oxidizing halogen molecule may not only
attack the In4 cluster in a nonspecific way but also
cleave In-C bonds. Therefore, we hoped to observe a
more specific reaction when we employed an AlI3/I2
mixture as the iodine source. The aluminum component
polarizes the iodine molecules, possibly by forming an
intermediate complex [I3AlIδ-‚‚‚I ], and the iodine
atom that bears a partial positive charge may react
preferably at the electron-rich cluster center of the
molecule. Indeed, we observed a clean reaction with
almost quantitative formation of only one product which
showed two resonances of trimethylsilyl groups in the
δ+ 11
1
H NMR spectrum in an intensity ratio of 2 to 1. The
product (2) was crystallized from toluene to give yellow
crystals in 73% yield. Compound 2 is thermally quite
stable in the solid state and decomposes only at 200 °C
with the formation of elemental indium. It is only
marginally stable in solution; indium powder precipi-
tates when it is stored in benzene or cyclohexane at
room temperature after about 1 h, forming several new
products, none of which could be isolated in pure form.
Owing to this instability, the NMR spectroscopic char-
acterization of 2 remained incomplete. The inner carbon
atoms attached to indium, which, owing to the quad-
rupole moment of the indium atoms, usually give very
broad signals, could not be detected unambiguously in
the 13C NMR spectrum of 2.
F igu r e 1. Molecular structure of 2. The thermal ellipsoids
are drawn at the 40% probability level. Methyl groups are
omitted for clarity. Important bond lengths (Å) and angles
(deg): In(1)-In(2) 2.8099(4), In(2)-In(3) 2.8186(4), In(1)-
I(1) 2.9880(4), In(1)-I(2) 3.0218(4), In(3)-I(1) 3.0189(4),
In(3)-I(2) 3.0034(4), In(1)-C(1) 2.218(4), In(2)-C(2)
2
.225(4), In(3)-C(3) 2.220(4), In(1)-In(2)-In(3) 82.44(1),
In(1)-I(1)-In(3) 76.26(1), In(1)-I(2)-In(3) 75.98(1).
trigallium compound of similar structure with a chain
of three gallium atoms has been reported. However, it,
surprisingly, has a strongly asymmetric, poorly under-
12
stood structure with one very long Ga-Ga distance.
A chain of three gallium atoms in a noncage structure
was observed for a trigallium pentaiodide in which all
gallium atoms are coordinatively saturated by the
Elemental indium precipitated in the course of that
1
reaction, and H-C(SiMe3)3 was detected by an H NMR
13
coordination of triethylphosphane ligands. The In-
spectrum of the crude product. Owing to the integration
of the spectrum, a 2 to 1 molar ratio resulted between
the product 2 and the alkane derivative. That alkane
is known as a decomposition product of the cluster and
may be formed via a radical intermediate after cleavage
of an In-C bond and the reaction of the radical with
the solvent, for instance. Interestingly, AlI3 alone gave
the same product (2) upon treatment with 1; however,
owing to unknown impurities, we did not succeed in
isolating the pure compound.
In bond lengths (2.814 Å on average) of 2 are shorter
than the In-In distances of the cluster compound 1
4
(
3.002 Å), which has a multicenter bonding situation.
They are in the normal range of In-In single bonds
observed for tetraalkyldiindium derivatives, R2In-
14,15
InR2.
Shorter ones were observed in the remarkable
triangular triindium compound In(InR2)3 (R ) 2,4,6-
15
iPr3C6H2). The In-I separations deviate only slightly
from the average value of 3.008 Å. They are similar to
those in other symmetrically bridged dimetallic spe-
The molecular structure of 2 (Figure 1) comprises a
short, nonlinear chain of three indium atoms which are
connected by In-In single bonds. Each indium atom is
bonded to one C(SiMe3)3 substituent, and the terminal
indium atoms also are attached to iodine atoms. The
iodine atoms bridge the terminal indium atoms, and a
trigonal bipyramidal cage structure results that has
both iodine atoms and one indium atom (In(2)) in the
equatorial plane and the remaining indium atoms
16
cies. Despite the different coordination geometries and
oxidation states (+1 at In2, +2 at In1 and In3) of the
indium atoms, the In-C bond lengths are almost
indistinguishable (2.221 Å on average). A similarly long
In-C distance was observed in the starting indium(I)
(12) Li, X.-W.; Wei, P.; Beck, B. C.; Xie, Y.; Schaefer, H. F., III; Su,
J .; Robinson, G. H. Chem. Commun. 2000, 453.
(13) Schnepf, A.; Doriat, C.; M o¨ llhausen, E.; Schn o¨ ckel, H. Chem.
Commun. 1997, 2111.
(
In(1) and In(3)) in the apical positions. Thus, In1 and
(14) (a) Uhl, W.; Layh, M.; Hiller, W. J . Organomet. Chem. 1989,
68, 139. (b) Wochele, R.; Schwarz, W.; Klinkhammer, K. W.; Locke,
K.; Weidlein, J . Z. Anorg. Allg. Chem. 2000, 626, 1963. (c) Wiberg, N.;
Amelunxen, K.; N o¨ th, H.; Schmidt, M.; Schwenk, H. Angew. Chem.
1996, 108, 110; Angew. Chem., Int. Ed. Engl. 1996, 35, 65. (d) von
H a¨ nisch, C.; Fenske, D.; Kattannek, M.; Ahlrichs, R. Angew. Chem.
3
In3 are coordinatively saturated with coordination
number 4, while In2 is attached only to three atoms
(In1, In3, C2) in an almost ideal planar coordination
geometry (sum of the angles ) 359.7°). A diphosphorus-
1
999, 111, 2900; Angew. Chem., Int. Ed. 1999, 38, 2736. (e) Schluter,
R. D.; Cowley, A. H.; Atwood, D. A.; J ones, R. A.; Bond, M. R.; Carrano,
C. J . J . Am. Chem. Soc. 1993, 115, 2070.
(15) Brothers, P. J .; H u¨ bler, K.; H u¨ bler, U.; Noll, B. C.; Olmstead,
M. M.; Power, P. P. Angew. Chem. 1996, 108, 2528; Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2355.
(16) (a) Haupt, H.-J .; Wolfes, W.; Preut, H. Inorg. Chem. 1976, 15,
2920. (b) Haupt, H.-J .; Preut, H.; Wolfes, W. Z. Anorg. Allg. Chem.
1979, 448, 93. (c) Leman, J . T.; Ziller, J . W.; Barron, A. R. Organo-
metallics 1991, 10, 1766.
(
11) (a) The polarization of halogen molecules by Lewis acids as
discussed here is well accepted for the chlorination or bromination of
aromatic compounds, while the mechanism of the corresponding
reactions with less reactive iodine seems to be more complicated:
March, J . Advanced Organic Chemistry, 3rd ed.; Wiley: New York,
1
985; p 476. (b) The occurrence of I+ as a reactive intermediate has
been discussed in the literature, for instance: Baird, W. C., J r.;
Surridge, J . H. J . Org. Chem. 1970, 35, 3436.

Notes
Organometallics, Vol. 20, No. 15, 2001 3357
4
compound 1 (2.25 Å) and in an adduct of the tetraalkyl-
diindium(II) compound R2In-InR2 (R ) CH(SiMe3)2),
in which one indium atom was tetracoordinated by the
(SiMe
3
of the terminal In atoms); InC not detected owing to
the instability with time of 2 in solution. IR (CsBr plates,
-1
paraffin, cm ): 1300 w, 1252 s δCH
vw, 1008 vw; 858 vs, 840 vs, 774 w, 722 m FCH
48 w νasSiC; 615 vw ν SiC; 590 w νInC; 375 vw, 318 vw δSiC.
3
; 1175 vw, 1156 vw, 1078
1
7
3
(Si); 675 w,
addition of an ethynyl ligand (In-C 2.26 Å). The
intramolecular contact distances between indium and
iodine atoms (In1‚‚‚In3 3.709 Å, In2‚‚‚I1, I2 3.859 Å on
average, I1‚‚‚I2 4.178 Å) are similar to the sum of the
van der Waals radii (3.80, ∼3.90, and ∼4.00 Å) and
confirm a localized bonding situation. Owing to the
steric interaction between the bulky alkyl substituents,
the apical In-C bonds are tilted toward the iodine
bridges.
6
s
UV/vis (n-hexane): λmax (nm) (log ꢀ) 225 (3.4), 304 (2.9).
Cr ysta l Str u ctu r e Deter m in a tion of 2‚Tolu en e. Single
crystals of 2‚toluene were obtained on cooling of a saturated
solution in toluene to -20 °C; the crystals include one molecule
of toluene in each formula unit of 2. The crystallographic data
1
8
were collected with a STOE IPDS diffractometer. C37
H
89
I
2
In
3
-
Si
9
: monoclinic, P2
2, temperature 193(2) K, Dcalcd ) 1.534 g/cm , a ) 9.1269(5)
1
, no. 4,19 Flack parameter -0.008(13), Z
3
)
Å, b ) 24.8574(10) Å, c ) 13.5416(8) Å, â ) 102.491(5)°, V )
-
30
3
-1
2
999.5(3) × 10
m , µ ) 2.375 mm , numerical absorption
Exp er im en ta l Section
correction, crystal dimensions 0.27 × 0.24 × 0.045 mm,
radiation Mo KR, graphite monochromator, 2θ range 3.2° e
All procedures were carried out under purified argon.
2
θ e 51.7°, index ranges -11 e h e 11, -30 e k e 30, -16 e
n-Hexane was dried over LiAlH
benzophenone. In [C(SiMe (1) was obtained according to
and I were freshly sublimed prior
4
, and toluene over Na/
l e 15; number of unique reflections 11 505; number of
4
3 3 4
) ]
4
parameters 501. The structure was solved by direct methods
and refined with the program SHELXL-97 by a full-matrix
a literature procedure. AlI
to use.
3
2
2
0
2
least-squares method based on F . R1 (10 721 reflections I >
Syn th esis of Com p ou n d 2. A solution of 0.113 g (0.445
mmol) of I in 60 mL of n-hexane was added dropwise to a
suspension of 0.182 g (0.445 mmol) of AlI in 25 mL of n-hexane
at room temperature. The mixture was stirred for 40 min, and
a solution of 0.617 g (0.445 mmol) of In [C(SiMe (1) in 50
2
σ(I)) ) 0.0238; wR2 (all data) ) 0.0701; max./min. residual
2
30 3
electron density ) 1.57/-0.37 × 10 e/m . The C(SiMe
3 3
) group
3
of the inner indium atom In2 is slightly disordered; the silicon
atoms were refined on split positions with occupation factors
of 0.88 and 0.12.
4
3 3 4
) ]
mL of n-hexane then was added. After 5 min at room
temperature the mixture was heated at 80 °C in a prewarmed
oil bath for 10 min. A solid with gray metallic and colorless
particles precipitated. After filtration the yellow solution was
evaporated at reduced pressure, and the oily residue was
crystallized from toluene (20/-70 °C) to yield yellow crystals
Ack n ow led gm en t. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for generous financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, isotropic and anisotropic displacement param-
eters, and all bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
Further details of the crystal structure determination are
available from the Cambridge Crystallographic Data Center
on quoting the depository number CCDC-160148.
2
of 2. Yield: 0.420 g (73% based on I ). 2 was obtained free of
toluene after thorough evacuation of the solid product; it is
only moderately stable in solution. Decomposition (toluene free
product, argon, sealed capillary): 200 °C. Anal. Calcd for
In (1293.0): C, 27.9; H, 6.3. Found: C, 28.2; H,
.3. H NMR (C , 200 MHz): δ 0.50 (54 H, s, SiMe of
terminal In atoms), 0.31 (27 H, s, SiMe of bridging In atom).
12, 200 MHz): δ 0.37 (54 H, s, SiMe of terminal
In atoms), 0.31 (27 H, s, SiMe
of bridging In atom). 13C NMR
, 100.6 MHz): δ 6.5 (SiMe of the bridging In atom), 6.1
C
6
30
H
81Si
9
3
I
2
1
6
D
6
3
3
1
H NMR (C
6
D
3
OM0102302
3
(
19) Hahn, T., Ed. International Tables for Crystallography, Space-
Group Symmetry, Vol. A; Kluwer Academic Publishers: Dordrecht,
989.
(20) SHELXTL-Plus, REL. 4.1; Siemens Analytical X-RAY Instru-
(C
6
D
6
3
1
(
(
17) Uhl, W.; Spies, T. Z. Anorg. Allg. Chem. 2000, 626, 1059.
18) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry,
ments Inc.: Madison, WI, 1990. Sheldrick, G. M. SHELXL-93, Program
4
th ed.; Harper Collins: New York, 1993.
for the Refinement of Structures; Universit a¨ t G o¨ ttingen, 1993.