Organometallic Iron Indium Derivatives Prepared by the Reaction of Carbonyliron Compounds with the Alkylindium(I) Derivative In4[C(SiMe3)3]4

Article abstract of DOI:10.1021/ic9704804

The monomeric fragment In-C(SiMe₃)₃ with a monovalent indium atom is isolobal with carbon monoxide. It is probably formed as a reactive intermediate on heating solutions of the tetrahedral cluster compound In₄[C(SiMe₃)₃]₄ (1) in hexane and reacts with Fe₃(CO)₁₂ and Fe₂(CO)₉ to yield by the substitution of bridging CO ligands three novel iron indium compounds, Fe₃(CO)₁₀(μ-InR)2 (2), Fe₂(CO)₈(μ-InR) (3), and Fe₂(CO)₆(μ-CO)(μ-InR)₂ (4), which all were characterized by crystal structure determinations (2: C₃₀H₅₄Fe₃In₂O₁₀Si ₆, monoclinic, P2₁, a = 1436.1(2) pm, b = 1992.9(3) pm, c = 1764.8(3) pm, β= 107.02(2)°. 3: C₁₈H₂₇Fe₂InO₈Si₃, monoclinic, C2/c, a = 1527.8(3) pm, b = 960.3(2) pm, c = 3755.4(8) pm, β= 90.17(3)°. 4: C₂₇H₅₄Fe₂In₂O₇Si ₆, triclinic, P1?, a = 959.3(1) pm, b = 1506.7(2) pm, c = 1561.4(1) pm, α = 86.11(1)°, β= 88.76(1)°, γ = 73.57(1)°). While both products 2 and 4 are isostructural with the pure carbonyls with two or three bridging groups, respectively, compound 3 has only one bridging InR group besides eight terminal carbonyl ligands. The Fe-In bond lengths are quite similar (255.9-260.5 pm), but the Fe-Fe distances differ significantly with 286.7(1) pm for the bridged Fe-Fe bond in 2, 289.3(1) pm in 3, and 275.87(5) pm in 4. They all are much elongated compared to the starting carbonyl complexes.

Full text of DOI:10.1021/ic9704804

5478
Inorg. Chem. 1997, 36, 5478-5482
Organometallic Iron Indium Derivatives Prepared by the Reaction of Carbonyliron
†
Compounds with the Alkylindium(I) Derivative In4[C(SiMe3)3]4
Werner Uhl,* Sven Uwe Keimling, Michael Pohlmann, Siegfried Pohl, and Wolfgang Saak
Fachbereich Chemie, Universita¨t Oldenburg, Postfach 2503, D-26111 Oldenburg, Germany
Wolfgang Hiller and Markus Neumayer
Anorganisch-chemisches Institut, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
D-85747 Garching, Germany
ReceiVed April 25, 1997X
The monomeric fragment In-C(SiMe3)3 with a monovalent indium atom is isolobal with carbon monoxide. It
is probably formed as a reactive intermediate on heating solutions of the tetrahedral cluster compound
In4[C(SiMe3)3]4 (1) in hexane and reacts with Fe3(CO)12 and Fe2(CO)9 to yield by the substitution of bridging CO
ligands three novel iron indium compounds, Fe3(CO)10(µ-InR)2 (2), Fe2(CO)8(µ-InR) (3), and Fe2(CO)6(µ-CO)-
(µ-InR)2 (4), which all were characterized by crystal structure determinations (2: C30H54Fe3In2O10Si6, monoclinic,
P21/n, a ) 1436.1(2) pm, b ) 1992.9(3) pm, c ) 1764.8(3) pm, â ) 107.02(2)°. 3: C18H27Fe2InO8Si3, monoclinic,
C2/c, a ) 1527.8(3) pm, b ) 960.3(2) pm, c ) 3755.4(8) pm, â ) 90.17(3)°. 4: C27H54Fe2In2O7Si6, triclinic,
P1h, a ) 959.3(1) pm, b ) 1506.7(2) pm, c ) 1561.4(1) pm, R ) 86.11(1)°, â ) 88.76(1)°, γ ) 73.57(1)°).
While both products 2 and 4 are isostructural with the pure carbonyls with two or three bridging groups, respectively,
compound 3 has only one bridging InR group besides eight terminal carbonyl ligands. The Fe-In bond lengths
are quite similar (255.9-260.5 pm), but the Fe-Fe distances differ significantly with 286.7(1) pm for the bridged
Fe-Fe bond in 2, 289.3(1) pm in 3, and 275.87(5) pm in 4. They all are much elongated compared to the
starting carbonyl complexes.
Introduction
with octacarbonyldicobalt, in which, depending on the stoichio-
metric ratio of the components, one or both bridging CO ligands
are replaced by InR.5 These reactions differ significantly from
the formerly described reactions of In(I) halides with dinuclear
carbonyl complexes, in which an insertion into the metal-metal
bond is observed instead of a substitution of CO ligands.7
Transition metal carbonyl analogues of the Al(I) derivative
AlCp* with an η5-pentamethylcyclopentadienyl group were
recently published by Schno¨ckel et al.8 and Fischer et al.;9 a
dinickel derivative with two bridging AlCp* moieties similar
to CpNi(µ-CO)2NiCp was synthesized by the reaction of
dicyclopentadienylnickel with Al4Cp*4,8 while a terminal AlCp*
ligand was observed in Fe(CO)4(AlCp*), which is isostructural
with pentacarbonyliron.9 Theoretical investigations confirm a
σ-donor/π-acceptor bonding model in the iron complex with
the back-donation of electron density from iron to aluminum.9
We wish to report here the reactions of 1 with the iron carbonyl
complexes Fe3(CO)12 and Fe2(CO)9, with two or three bridging
CO ligands, which we hoped to replace gradually by systemati-
cally changing the reaction conditions.
The tetraalkyltetraindium(I) derivative In4[C(SiMe3)3]4 (1)
was recently synthesized in a high yield by our group1 and the
group of Cowley2 by the reaction of InBr or InCl with LiC-
(SiMe3)3‚2THF. 1 possesses a nearly undistorted tetrahedron
of four In atoms in the solid state and remains a tetramer in
dilute benzene solutions, while in conventional mass spectra
the monomer is observed as the highest mass.1 The monomeric
fragment In-C(SiMe3)3 can be trapped by refluxing solutions
of 1 in n-hexane in the presence of 1,4-dihetero butadienes like
benzil derivatives.3 It exhibits two empty p orbitals perpen-
dicular to the In-C bond axis and one lone electron pair and is
therefore isolobal4 with carbon monoxide. InR would thus
belong to the intensively studied group of CO-analogous
compounds like isonitriles or phosphorus trifluoride, which have
been successfully applied as σ-donor/π-acceptor ligands in
transition metal complexes. Indeed, we succeeded in substitut-
ing CO ligands of binuclear transition metal carbonyl complexes
5
by the reaction of 1 with Co2(CO)8 or Mn2(CO)10,6 but the
InR groups occupy exclusively bridging positions between both
metal centers in all products. Two derivatives were isolated
Experimental Section
† Dedicated to Prof. Dr. M. Weidenbruch on the occasion of his 60th
birthday.
All procedures were carried out under an atmosphere of purified
argon in dried solvents (n-hexane and cyclopentane over LiAlH4;
toluene over Na/benzophenone). 1 was prepared according to the
literature,1 and the carbonyl complexes Fe2(CO)9 and Fe3(CO)12 were
purchased from ABCR GmbH (Karlsruhe, Germany); while Fe3(CO)12
X Abstract published in AdVance ACS Abstracts, November 1, 1997.
(1) Uhl, W.; Graupner, R.; Layh, M.; Schu¨tz, U. J. Organomet. Chem.
1995, 493, C1.
(2) Schluter, R. D.; Cowley, A. H.; Atwood, D. A.; Jones, R. A.; Atwood,
J. L. J. Coord. Chem. 1993, 30, 25.
(3) Uhl, W.; Keimling, S. U.; Pohl, S.; Saak, W.; Wartchow, R. Chem.
Ber. 1997, 130, 1269.
(4) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
(5) Uhl, W.; Keimling, S. U.; Hiller, W.; Neumayer, M. Chem. Ber. 1996,
129, 397.
(7) (a) Clarkson, L. M.; Norman, N. C.; Farrugia, L. J. J. Organomet.
Chem. 1990, 390, C10. (b) Hsieh, A. T. T.; Mays, M. J. Inorg. Nucl.
Chem. Lett. 1971, 7, 223 and references therein.
(8) Dohmeier, C.; Krautscheid, H.; Schno¨ckel, H. Angew. Chem., Int. Ed.
Engl. 1994, 33, 2482.
(6) Uhl, W.; Keimling, S. U.; Hiller, W.; Neumayer, M. Chem. Ber. 1995,
128, 1137.
(9) Weiss, J.; Stetzkamp, D.; Nuber, B.; Fischer, R. A.; Boehme, C.;
Frenking, G. Angew. Chem., Int. Ed. Engl. 1997, 36, 70.
S0020-1669(97)00480-1 CCC: $14.00 © 1997 American Chemical Society

Organometallic Iron Indium Derivatives
Inorganic Chemistry, Vol. 36, No. 24, 1997 5479
Table 1. Crystallographic Data for 2-4
was used without further purification, Fe2(CO)9 was washed with
hydrochloric acid, water, ethanol, and diethyl ether and dried in vacuum.
Fe3(CO)10(µ-InR)2 (2). A suspension of In4[C(SiMe3)3]4 (1) (210
mg, 0.152 mmol) and Fe3(CO)12 (155 mg, 0.308 mmol) in n-hexane is
refluxed for 4 h. The color changes to deep red. The mixture is filtered
to remove traces of a gray powder of elemental indium or iron, and
the filtrate is evaporated in vacuo. Recrystallization of the residue from
cyclopentane (20 °C/-30 °C) yields the product 2 as deep red crystals.
Yield: 270 mg (78% based on 1). Mp (argon, closed capillary): 150
°C. FD MS: m/z 1137.4, 1139.5, 1140.4, 1141.5 (all M+) correspond-
ing with a calculated isotope pattern. 1H NMR (C6D6, 300 MHz): δ
0.36 (s, SiMe3). 13C NMR (C6D6, 75.5 MHz): δ 212.2 (s, CO), 6.3 (s,
SiMe3); InC not detected. IR (paraffin, CsBr plates, cm-1): 2066 s,
2010 s, 1985 m, 1973 vs, 1931 m ν(CO); 1462 vs, 1377 vs paraffin;
1304 w, 1262 m, 1254 m δ(CH3); 1169 vw, 1154 vw; 855 vs, 841 sh,
777 w, 721 m F(CH3(Si)); 677 w, 652 w νas(SiC); 610 m, 600 m, 581
w, 565 w ν(FeC); 476 w, 469 w ν(InC); 442 vw, 390 vw, 360 vw
δ(SiC). UV/vis (n-pentane, nm, (log ꢀ)): 210 (br, 5.0), 275 (sh, 4.6),
326 (sh, 4.3), 400 (sh, 3.8). Anal. Calcd for C30H54Fe3In2O10Si6: Fe,
14.69; In, 20.14. Found: Fe, 14.72; In, 20.13.
Fe2(CO)8(µ-InR) (3) and Fe2(CO)6(µ-CO)(µ-InR)2 (4). In4-
[C(SiMe3)3]4 (1) (410 mg, 0.296 mmol) is treated with a 5-fold molar
excess of Fe2(CO)9 (538 mg, 1.48 mmol) in 30 mL of boiling n-hexane
for 70 min. The solution is concentrated and cooled to precipitate the
dark green byproduct Fe3(CO)12. Further concentration and cooling
to -30 °C give dark red crystals of compound 4 with two bridging
InR groups, which can be further purified by recrystallization from
toluene. The dark red compound 3 with only one bridging InR group
crystallizes in several fractions from the hexane mother liquor after
further concentration and cooling to -30 °C. Yields: 200 mg of 3
(25% based on 1) and 208 mg of 4 (35% based on 1).
Characterization of 3. Mp (argon, closed capillary): 123 °C. FD
MS: m/z 682.1 and 683.1 (both M+) corresponding with a calculated
isotope pattern. 1H NMR (C6D6, 300 MHz): δ 0.249 (s, SiMe3). 13C
NMR (C6D6, 75.5 MHz): δ 210.7 (s, CO), 5.6 (s, SiMe3); InC not
detected. IR (paraffin, CsBr plates, cm-1): 2076 vs, 2052 sh, 2023
vs, 2010 vs, 1987 vs, 1941 sh ν(CO); 1452 vs, 1377 vs paraffin; 1294
m, 1254 vs δ(CH3); 1169 w, 1155 w, 1080 vw, 1042 vw, 1009 w; 856
vs, 777 s, 721 s F(CH3(Si)); 675 m, 650 w νas(SiC); 617 vs, 604 vs
ν(FeC); 548 s, 523 m, 503 m ν(InC); 430 w, 392 w δ(SiC). UV/vis
(n-pentane, nm (log ꢀ)): 245 (4.4), 320 (sh, 4.0), 355 (sh, 3.7), 420
(sh, 3.5). Anal. Calcd for C18H27Fe2InO8Si3: Fe, 16.37; In, 16.83.
Found: Fe, 16.12; In, 16.95.
Characterization of 4. Dec pt (argon, closed capillary): 238 °C.
FD MS: m/z 998.4, 1000.0, 1001.2, 1002.1 (all M+) corresponding
with a calculated isotope pattern. 1H NMR (C6D6, 300 MHz): δ 0.269
(s, SiMe3). 13C NMR (C6D6, 75.5 MHz): δ 215.7 (s, CO), 49.9 (InC),
5.9 (s, SiMe3). IR (paraffin, CsBr plates, cm-1): 2023 s, 1985 s, 1956
s, 1942 s ν(CO) (terminal); 1786 s ν(CO) (bridge); 1461 vs 1377 vs
paraffin; 1298 m, 1262 sh, 1252 vs δ(CH3); 1169 w, 1042 w; 856 vs,
841 vs, 775 s, 721 s F(CH3(Si)); 677 s, 648 s νas(SiC); 617 s, 594 vs,
579 vs ν(FeC); 488 s, 473 m ν(InC); 424 w, 401 m δ(SiC). UV/vis
(n-pentane, nm (log ꢀ)): 240 (4.5), 440 (3.4). Anal. Calcd for C27-
H54Fe2In2O7Si6: Fe, 11.16; In, 22.95. Found: Fe, 11.40; In, 22.72.
Crystal Structure Determinations. Dark red single crystals of
compound 2 were obtained by recrystallization from toluene; dark red
single crystals of 3 and 4 were obtained from n-hexane. The X-ray
data collections were performed on the four-circle diffractometers AED
2 (2) and CAD 4 (3 and 4) with graphite-monochromated Mo KR
radiation. The crystals (2, 0.4 × 0.5 × 1.0 mm; 3, 0.5 × 0.4 × 0.3
mm; 4, 0.5 × 0.4 × 0.4 mm) were mounted under an atmosphere of
argon in glass capillaries, which were then sealed off. The intensity
data were collected at room temperature (2), 199 K (3), and 193 K (4)
in the 2θ ranges of 3-50° for 2 and 6-52° for 3 and 4, spanning the
respective octants 0 e h e 17, 0 e k e 23, -20 e l e 20; -18 e h
e 18, -11 e k e 7, -46 e l e 46; and -11 e h e 11, 0 e k e 18,
-19 e l e 19. A total of 8860 reflections was collected for compound
2 (9660 for 3 and 8400 for 4), from which 8500 independent reflections
were used for structure solution and refinement (5313 for 3 and 8393
for 4). All structures were solved by direct methods using the program
system SHELXTL PLUS11 and refined with the SHELXL-9311 program
via full-matrix least-squares calculations based on F2. All non-hydrogen
2
3
4
empirical
formula
fw
C30H54Fe3In2O10- C18H27Fe2InO8- C27H54Fe2In2O7-
Si6
Si3
682.19
Si6
1000.58
1140.46
space group P21/n; No. 1410
C2/c; No. 1510 P1h; No. 210
a (pm)
b (pm)
c (pm)
R (deg)
â (deg)
γ (deg)
1436.1(2)
1992.9(3)
1764.8(3)
90.00
1527.8(3)
960.3(2)
3755.4(8)
90.00
90.17(3)
90.00
959.3(1)
1506.7(2)
1561.4(1)
86.11(1)
88.76(1)
73.57(1)
2159.7(4)
2
107.02(2)
90.00
V (10-30 m3) 4830(1)
5510(2)
8
Z
4
temp (K)
λ (Å)
293
199
0.710 73
1.645
2.036
0.0465
0.1451
193
0.710 73
1.539
1.914
0.0231
0.0644
0.710 73
1.568
2.012
0.0386
0.1259
F
calc (g cm-3
)
µ (mm-1
R1a
)
wR2b
a R1 ) ∑||Fo| - |Fc||/∑|Fo| (F > 4 σ(F)). b wR2 ) [∑w(Fo2 - Fc2)2/
2
∑w(Fo )2]1/2 (all data).
atoms were refined with anisotropic displacement parameters; hydrogen
atoms were calculated on ideal positions and allowed to ride on the
bonded atom with U ) 1.2Ueq(C). The crystallographic data and details
of the final R values are provided in Table 1. Conventional R factors
(R1) are based on F using reflections with F > 4σ(F) (6515 reflections
for 2, 4321 for 3, and 7761 for 4); weighted R factors (wR2) are based
on F2. The number of refined parameters was 478 (2), 299 (3), and
416 (4). Further details of the crystal structure determinations are
available from the Fachinformationszentrum Karlsruhe, D-76344
Eggenstein-Leopoldshafen, Germany, on quoting the depository num-
bers CSD-406859 (2), -406858 (3), and -406857 (4).
Results and Discussion
Syntheses. The triiron compound Fe3(CO)12 reacts in boiling
n-hexane with In4[C(SiMe3)3]4 (1) in the stoichiometric ratio
of 2:1 (eq 1) to yield only one product (2), which is isolated
In4[C(SiMe3)3]4 + 2Fe3(CO)12 f
1
2Fe3(CO)10[µ-InC(SiMe3)3]2 + 4CO (1)
2
after recrystallization from cyclopentane in a yield of 78% as
dark red crystals. The IR spectrum of 2 shows absorptions of
the CO stretching vibrations only between 1931 and 2066 cm-1
,
which is consistent with an exclusively terminal coordination
of CO, and both bridging CO ligands of the starting carbonyl
complex are replaced by InR groups, as clearly shown by
elemental analysis and mass spectroscopy. The SiMe3 groups
exhibit sharp singlets in the 1H and 13C NMR spectra, and only
one resonance of the carbonyl carbon atoms is observed, similar
to the case of Fe3(CO)12,12 with a chemical shift of 212.2 ppm.
The resonance of the R-carbon atom of the tris(trimethylsilyl)-
methyl group bonded to indium could, however, not be detected.
The UV/vis spectrum shows a very broad absorption at 210
nm with several shoulders up to 400 nm. Reactions with an
excess of the iron carbonyl did not yield another derivative with,
for instance, one bridging CO and one bridging InR ligand,
similar to the reactions of Co2(CO)85 discussed above; instead,
(10) Hahn, T., Ed. International Tables for Crystallography, Space Group
Symmetry; Kluwer Academic Publishers: Dordrecht, The Netherlands,
1989; Vol. A.
(11) SHELXTL PLUS REL. 4.1; Siemens Analytical X-Ray Instruments
Inc.: Madison, WI, 1990. Sheldrick, G. M. SHELXL-93, Program
for the Refinement of Structures; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1993.
(12) Cotton, F. A.; Hunter, D. L. Inorg. Chim. Acta 1974, 11, L9.

5480 Inorganic Chemistry, Vol. 36, No. 24, 1997
Uhl et al.
compound 2 was exclusively formed, and the excess Fe3(CO)12
could quantitatively be recovered as the less soluble component
after the concentration and cooling of the reaction mixture in
n-hexane.
The reaction of Fe2(CO)9 with 1 is much more complicated.
An excess of the iron carbonyl with a molar ratio of at least
5:1 is required to completely consume 1 in boiling n-hexane
over a period of about 1 h. Two main products (3 and 4, eq 2)
In4[C(SiMe3)3]4 + Fe2(CO)9 -CO8
1
Fe2(CO)8[µ-InC(SiMe3)3] +
3
Figure 1. Molecular structure and numbering scheme of 2. The thermal
ellipsoids are drawn at the 40% probability level; hydrogen and methyl
carbon atoms are omitted for clarity.
Fe2(CO)6(µ-CO)[µ-InC(SiMe3)3]2 (2)
4
Table 2. Important Bond Lengths (pm) and Angles (deg) for 2
are formed, which can be separated by recrystallization from
n-hexane. Some byproducts of the reaction could be isolated
or identified: (i) dark green Fe3(CO)12 as the most sparingly
soluble component of the reaction mixture, which results from
a partial decomposition of Fe2(CO)9; (ii) a small amount of HC-
(SiMe3)3, formed by a decomposition of 1; and (iii) a further
iron indium derivative, which we could, however, isolate only
as an impure 1:1 mixture with 4. The NMR spectroscopically
determined yield of the unknown derivative in the crude product
in relation to 3 and 4 increases with an increasing excess of
Fe(1)-Fe(2)
Fe(1)-Fe(3)
Fe(2)-Fe(3)
In(1)-C(A)
In(2)-C(B)
286.7(1)
272.3(1)
270.3(1)
220.1(5)
219.4(5)
In(1)-Fe(1)
In(1)-Fe(2)
In(2)-Fe(1)
In(2)-Fe(2)
260.49(8)
260.47(8)
258.91(8)
259.00(9)
n ) 1
n ) 2
n ) 3
Fe(1)-C(n)
Fe(2)-C(n)
Fe(3)-C(n)
177.3(6)
177.2(6)
176.4(6)
n ) 4
177.1(6)
n ) 5
178.4(6)
n ) 6
176.1(5)
1
Fe2(CO)9. The H and 13C NMR shifts of the SiMe3 groups
n ) 7
182.5(8)
n ) 8
180.4(8)
n ) 9
179.9(7)
n ) 10
178.9(7)
(δ(1H) ) 0.36 ppm; δ(13C) ) 6.3 ppm) coincide with the
resonances of two compounds: the Fe3In2 derivative 2, which
could have been formed by the reaction of the byproduct
Fe3(CO)12 with 1, and (CO)3Fe(µ-InR)3Fe(CO)3, which formally
is the product of the replacement of all bridging CO ligands of
Fe2(CO)9 and was recently obtained in our group by the reaction
of 1 with Fe(CO)3COT (COT ) cyclooctatetraene).13 Both
compounds differ in the resonances of the carbonyl groups
(212.2 compared to 217.6 ppm), but despite changing the
recording conditions, we were not able to obtain a clearly
resolved 13C NMR spectrum of the mixture in that region; a
small resonance at 212 ppm possibly indicates compound 2.
The Fe2In3 compound is only sparingly soluble in hexane;13 thus
we believe that, owing to the high solubility of the unknown
component of the reaction mixture in hexane and to the higher
yield with increasing excess of the iron carbonyl, probably
compound 2 has formed as a byproduct.
C(A)-In(1)-Fe(1)
C(A)-In(1)-Fe(2)
Fe(1)-In(1)-Fe(2)
In(1)-Fe(1)-C(1)
In(1)-Fe(1)-C(2)
In(1)-Fe(1)-C(3)
In(2)-Fe(1)-C(1)
In(2)-Fe(1)-C(2)
In(2)-Fe(1)-C(3)
In(1)-Fe(1)-In(2)
In(1)-Fe(1)-Fe(3)
In(1)-Fe(1)-Fe(2)
In(2)-Fe(1)-Fe(2)
Fe(3)-Fe(1)-C(1)
Fe(3)-Fe(1)-C(2)
Fe(3)-Fe(1)-C(3)
Fe(2)-Fe(1)-C(1)
Fe(2)-Fe(1)-C(2)
Fe(2)-Fe(1)-C(3)
In(2)-Fe(1)-Fe(3)
Fe(2)-Fe(1)-Fe(3)
Fe(1)-Fe(3)-C(7)
Fe(1)-Fe(3)-C(8)
Fe(1)-Fe(3)-C(9)
Fe(1)-Fe(3)-C(10)
Fe(1)-Fe(3)-Fe(2)
145.3(1)
147.7(1)
66.78(2) Fe(1)-In(2)-Fe(2)
85.5(2)
177.6(2)
87.3(2)
176.8(2)
83.9(2)
88.9(2)
94.44(2) In(1)-Fe(2)-Fe(1)
94.09(3) In(2)-Fe(2)-Fe(1)
56.61(2) Fe(1)-Fe(2)-Fe(3)
56.41(2) In(1)-Fe(2)-In(2)
86.2(2)
84.1(2)
178.5(2)
121.3(2)
120.9(2)
122.9(2)
C(B)-In(2)-Fe(1)
C(B)-In(2)-Fe(2)
147.9(1)
144.6(1)
67.22(2)
174.4(2)
86.2(2)
89.7(2)
82.4(2)
178.8(2)
86.6(2)
56.62(2)
56.37(2)
58.45(3)
94.43(3)
81.0(2)
In(1)-Fe(2)-C(4)
In(1)-Fe(2)-C(5)
In(1)-Fe(2)-C(6)
In(2)-Fe(2)-C(4)
In(2)-Fe(2)-C(5)
In(2)-Fe(2)-C(6)
Fe(3)-Fe(2)-C(4)
Fe(3)-Fe(2)-C(5)
Fe(3)-Fe(2)-C(6)
In(1)-Fe(2)-Fe(3)
In(2)-Fe(2)-Fe(3)
Fe(1)-Fe(2)-C(4)
90.0(2)
175.2(2)
94.57(3)
90.95(3)
117.9(2)
124.8(2)
122.9(2)
91.8(2)
Elemental analysis and mass spectroscopy show that in the
slightly less soluble product (4) two CO groups are replaced
by two InR ligands, while in the second isolated product (3)
only one CO group is substituted. Both 3 and 4 exhibit sharp
90.53(3) Fe(1)-Fe(2)-C(5)
57.77(3) Fe(1)-Fe(2)-C(6)
91.1(2)
81.0(2)
160.9(2)
98.7(3)
Fe(2)-Fe(3)-C(7)
Fe(2)-Fe(3)-C(8)
Fe(2)-Fe(3)-C(9)
81.9(2)
97.6(2)
1
singlets of the SiMe3 substituents in the H and 13C NMR
Fe(2)-Fe(3)-C(10) 162.4(3)
spectra. The carbonyl carbon atoms resonate at 210.7 (3) and
215.7 ppm (4). The R-carbon atom of the C(SiMe3)3 group
could only be detected for compound 4 at 49.9 ppm; it is shifted
to lower field compared to that range usually observed with
alkylindium(III) derivatives (δ < 30 ppm).14 The tetraindium
compound 1 with a tetrahedral In4 molecular center shows a
stronger shift to 72 ppm, which is caused by the delocalized
molecular orbitals of the cluster as shown by up to now
unpublished theoretical calculations. Similar unusual shifts as
for 4 occur with the cobalt and manganese derivatives bridged
by InR groups (495 and 526 ppm, respectively); they possibly
63.78(3)
indicate some electronic π interactions between the iron and
the electronically unsaturated indium atoms. Only stretching
vibrations of terminal CO groups between 1941 and 2076 cm-1
can be determined for product 3, while the derivative 4 shows
an absorption at 1786 cm-1, characteristic of a bridging CO
ligand; the vibrations of the terminal groups lie between 1942
and 2023 cm-1
.
Crystal Structures. The molecular structure of compound
2 is shown in Figure 1. The compound is isostructural with
the starting carbonyl Fe3(CO)12 and consists of a three-
membered ring of iron atoms with one of the Fe-Fe bonds
symmetrically bridged by two In-C(SiMe3)3 groups. The Fe-
In bond lengths (259.7 pm on average, Table 2) to the axial Fe
atoms Fe(1) and Fe(2) are in that range normally observed.13,15
The lengths of the bonds Fe(1)-Fe(3) and Fe(2)-Fe(3) (271.3
(13) Uhl, W.; Pohlmann, M. Organometallics 1997, 16, 2478.
(14) (a) Uhl, W.; Layh, M.; Hiller, W. J. Organomet. Chem. 1989, 368,
139. (b) Carty, A. J.; Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.;
Singh, A.; Taylor, N. J. Inorg. Chem. 1980, 19, 3637. (c) Neumu¨ller,
B.; Gahlmann, F.; Scha¨fer, M. S.; Magull, S. J. Organomet. Chem.
1992, 440, 263.

Organometallic Iron Indium Derivatives
Inorganic Chemistry, Vol. 36, No. 24, 1997 5481
Table 3. Important Bond Lengths (pm) and Angles (deg) for 3
In(1)-C(1)
Fe(1)-Fe(2)
218.0(6)
289.3(1)
In(1)-Fe(1)
In(1)-Fe(2)
257.4(1)
255.9(1)
n ) 2
n ) 2
n ) 4
n ) 5
Fe(1)-C(n)
Fe(2)-C(n)
179.5(8)
181.5(7)
177.5(8)
179.6(7)
n ) 6
179.5(7)
n ) 7
176.8(7)
n ) 8
179.7(8)
n ) 9
181.8(7)
n ) 2
90.2(2)
80.0(2)
n ) 3
n ) 4
177.1(3)
124.1(3)
n ) 5
94.4(2)
80.5(2)
Fe(2)-Fe(1)-C(n)
In(1)-Fe(1)-C(n)
81.8(2)
137.2(2)
n ) 6
84.5(2)
84.9(2)
n ) 7
100.1(2)
156.0(2)
n ) 8
87.1(2)
89.0(2)
n ) 9
156.8(2)
100.9(2)
Figure 2. Molecular structure and numbering scheme of 3. The thermal
ellipsoids are drawn at the 40% probability level; hydrogen atoms are
omitted for clarity.
In(1)-Fe(2)-C(n)
Fe(1)-Fe(2)-C(n)
In(1)-Fe(1)-Fe(2) 55.45(3) Fe(1)-In(1)-Fe(2)
In(1)-Fe(2)-Fe(1) 55.93(3) Fe(1)-In(1)-C(1)
Fe(2)-In(1)-C(1)
68.62(3)
142.6(2)
148.7(2)
Table 4. Important Bond Lengths (pm) and Angles (deg) for 4
Fe(1)-Fe(2)
Fe(1)-In(1)
Fe(1)-In(2)
Fe(2)-In(1)
Fe(2)-In(2)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
275.87(5)
259.13(5)
256.36(5)
257.49(6)
259.51(5)
199.2(3)
178.9(3)
179.0(3)
Fe(1)-C(9)
Fe(2)-C(3)
Fe(2)-C(4)
Fe(2)-C(5)
Fe(2)-C(6)
In(1)-C(1)
In(2)-C(2)
180.0(3)
179.4(3)
178.6(3)
179.6(3)
197.9(3)
217.7(3)
217.7(3)
Figure 3. Molecular structure and numbering scheme of 4. The thermal
ellipsoids are drawn at the 40% probability level; hydrogen and methyl
carbon atoms are omitted for clarity.
n ) 6
n ) 7
n ) 8
n ) 9
Fe(2)-Fe(1)-C(n)
In(1)-Fe(1)-C(n)
In(2)-Fe(1)-C(n)
45.81(8) 114.9(1)
116.49(9) 127.23(8)
89.99(8)
86.26(8) 172.5
89.02(9) 172.53(9) 84.90(8)
83.67(9)
88.94
pm) are quite similar to the corresponding bond lengths in Fe3-
(CO)12 (268 pm16), while the bridged bond Fe(1)-Fe(2) is much
elongated from 255 pm in the pure carbonyl to 286.7 pm in 2.
We observed an even larger elongation in (CO)3Fe(µ-InR)3Fe-
(CO)3 with three bridging InR groups and an Fe-Fe distance
of 299.2(2) pm;13 similar long distances have been observed
before in several organometallic diiron complexes.17 The
difference between the starting carbonyl and 2 might strongly
depend on steric restrictions, and the much shorter Fe-C bond
lengths of carbonyl bridges (205 pm) compared to the Fe-In
bonds in the Fe-In-Fe bridges could result in a shorter Fe-
n ) 3
n ) 4
n ) 5
n ) 6
Fe(1)-Fe(2)-C(n) 127.8(1)
119.8(1)
177.7(1)
90.4(1)
112.15(9)
82.93(9)
169.08(9)
46.19(8)
90.76(8)
85.65(8)
In(1)-Fe(2)-C(n)
In(2)-Fe(2)-C(n)
87.1(1)
87.9(1)
In(1)-Fe(1)-In(2)
In(2)-Fe(1)-Fe(2)
In(1)-Fe(1)-Fe(2)
89.12(2) In(1)-Fe(2)-In(2)
58.23(1) In(1)-Fe(2)-Fe(1)
57.44(2) In(2)-Fe(2)-Fe(1)
88.79(2)
58.01(2)
57.12(1)
C(1)-In(1)-Fe(2)
C(1)-In(1)-Fe(1)
Fe(2)-In(1)-Fe(1)
144.96(7) C(2)-In(2)-Fe(1)
150.47(7) C(2)-In(2)-Fe(2)
64.55(2) Fe(1)-In(2)-Fe(2)
144.83(7)
150.07(7)
64.65(1)
Fe distance. The angles on the bridging atoms are more acute
in the In derivative (67.0° in 2 and about 77° in Fe3(CO)1216).
The equatorial FeIn2 triangle is almost equilateral with long
interatomic distances of In(1)‚‚‚In(2) 381.2 pm, Fe(3)‚‚‚In(1)
390.1 pm, and Fe(3)‚‚‚In(2) 377.5 pm, which indicate no
significant bonding interaction. The angle between the normals
of the planes (In(1)Fe(1)Fe(2)) and (In(2)Fe(1)Fe(2)) is 59.8°,
and between (In(1)Fe(1)Fe(2)) and (Fe(1)Fe(2)Fe(3)) it is
117.3°. The In-C bond lengths are slightly shortened compared
to those of 1 (219.8-225 pm) as often observed before in
reaction products of 1,5,6,18 and the indium atoms are almost
planar, coordinated by their substituents with the In atoms 5.4
and 6.3 pm above the plane (sum of the angles: In(1), 359.8°;
In(2), 359.7°).
(15) (a) Preut, H.; Haupt, H.-J. Acta Crystallogr., Sect. B 1979, 35, 2191.
(b) Atwood, J. L.; Bott, S. G.; Hitchcock, P. B.; Eaborn, C.;
Shariffudin, R. S.; Smith, J. D.; Sullivan, A. C. J. Chem. Soc., Dalton
Trans. 1987, 747. (c) Cassidy, J. M.; Whitmire, K. H. Acta Crystal-
logr., Sect. C 1990, 46, 1781. (d) Albano, V. G.; Cane, M.; Iapalucci,
M. C.; Longoni, G.; Monari, M. J. Organomet. Chem. 1991, 407, C9.
(e) Clarkson, L. M.; Norman, N. C.; Farrugia, L. J. Organometallics
1991, 10, 1286. (f) Merzweiler, K.; Rudolph, F.; Brands, L. Z.
Naturforsch., B 1992, 47, 470. (g) Fischer, R. A.; Behm, J.; Priermeier,
T.; Scherer, W. Angew. Chem., Int. Ed. Engl. 1993, 32, 746. (h) Lin,
C.-C.; Kong, G.; Cho, H.; Whittlesey, B. R. Inorg. Chem. 1993, 32,
2705. (i) Fischer, R. A.; Herdtweck, E.; Priermeier, T. Inorg. Chem.
1994, 33, 934. (j) Braunstein, P.; Knorr, M.; Strampfer, M.; DeCian,
A.; Fischer, J. J. Chem. Soc., Dalton Trans. 1994, 117. (k) Reger, D.
L.; Mason, S. S.; Rheingold, A. L.; Haggerty, B. S.; Arnold, F. P.
Organometallics 1994, 13, 5049. (l) Carmalt, C. J.; Norman, N. C.;
Pember, R. F.; Farrugia, L. J. Polyhedron 1995, 14, 417.
(16) (a) Braga, D.; Farrugia, L.; Grepioni, F.; Johnson, B. F. G. J.
Organomet. Chem. 1994, 464, C39. (b) Braga, D.; Grepioni, F.;
Farrugia, L. J.; Johnson, B. F. G. J. Chem. Soc., Dalton Trans. 1994,
2911.
Figures 2 and 3 show the molecular structures of the diiron
compounds 3 and 4, in which one or two InR ligands occupy a
bridging position between both Fe atoms. While compound 4
is isostructural with Fe2(CO)9 with three bridging groups (one
CO and two InR) and a distorted octahedral environment of
the Fe atoms, compound 3 exhibits only one bridging InR group
besides eight exclusively terminal CO ligands. These ligands
occupy almost eclipsed positions with torsion angles between
corresponding CO groups of 9.4° (C(2)Fe(1)Fe(2)C(8)), -2.9°
(17) (a) Seyferth, D.; Anderson, L. L.; Davis, W. B.; Cowie, M. Organo-
metallics 1992, 11, 3736. (b) Schulz, H.; Pritzkow, H.; Siebert, W.
Chem. Ber. 1992, 125, 987. (c) Hogarth, G.; Kayser, F.; Knox, S. A.
R.; Morton, D. A. V.; Orpen, A. G.; Turner, M. L. J. Chem. Soc.,
Chem. Commun. 1988, 358. (d) Jinshun, H.; Manfang, W.; Jinling,
H.; Jiaxi, L. Jiegou Huaxue 1983, 2, 157 (cited from the Cambridge
Crystallographic Data Base). (e) Johnson, B. F. G.; Kaner, D. A.;
Lewis, J.; Rosales, M. J. J. Organomet. Chem. 1982, 238, C73. (f)
Girard, L.; Decken, A.; Blecking, A.; McGlinchey, M. J. J. Am. Chem.
Soc. 1994, 116, 6427. (g) Knox, S. A. R.; Morton, D. A. V.; Orpen,
A. G.; Turner, M. L. Inorg. Chim. Acta 1994, 220, 201.
(18) Uhl, W.; Graupner, R.; Pohlmann, M.; Pohl, S.; Saak, W. Chem. Ber.
1996, 129, 143.

5482 Inorganic Chemistry, Vol. 36, No. 24, 1997
Uhl et al.
(C(3) Fe(1)Fe(2)C(9)) and -11.6° (C(5)Fe(1)Fe(2)C(6)). The
Fe-Fe distance of 3 (289.3 pm, Table 3) is longer than that in
the triply bridged derivative 4 (275.9 pm, Table 4); three
bridging InR groups between two Fe(CO)3 fragments as in
(CO)3Fe(µ-InR)3Fe(CO)3 give the longest distance of 299.2
pm.13 The shorter bond in 4 might be caused by the bridging
with the small CO group; the Fe-C bond lengths to the bridging
CO ligand are similar to that observed in Fe2(CO)9 (198.6 pm
compared to 201.6 pm19), but the Fe-C-Fe angle is enlarged
to 88.0° compared to 77.6° in the carbonyl complex. The Fe-
In-Fe angles amount to 64.6° on average in 4 and 68.6° in 3.
The Fe-In bond lengths (256.7 pm (3) and 258.1 (4)) are similar
to that in compound 2 and lie in the range normally observed.
The In atoms in both compounds 3 and 4 are almost ideally
planar coordinated by the R-carbon atom of the C(SiMe3)3
group and two iron atoms, and deviate from the planes through
these three atoms by only 2.9 pm in 3 (sum of the angles 359.9°)
and 1.7 (In(1), sum of the angles 360.0°) and 7.6 pm (In(2),
sum of the angles 359.6°) in 4. The normals of the triangular
planes around the Fe-Fe axis Fe(1)Fe(2)In(1), Fe(1)Fe(2)In-
(2), and Fe(1)Fe(2)C(6) include angles of 65.6, 52.1, and 117.7°,
so that a slightly distorted trigonal bipyramidal arrangement of
the atoms Fe2In2C results. As in compound 2, the equatorial
interatomic distances are, however, very long (In(1)‚‚‚In(2)
361.7 pm, In(1)‚‚‚C(6) 326.8 pm, In(2)‚‚‚C(6) 314.2 pm); they
are slightly shorter than the sum of the van der Waals radii
(InIn 380 pm, InC 360 pm20) and indicate no significant bonding
interaction. A shorter In-In distance of 336 pm has been
observed in the derivative (CO)3Co(µ-InR)2Co(CO)3 with a
distorted tetrahedral Co2In2 molecular center,5 which is only
36 pm longer than in the In4 starting compound 1.
Acknowledgment. We are grateful to the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Industrie
for generous financial support.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for Fe3(CO)10[µ-InC(SiMe3)3]2 (2), Fe2(CO)8[µ-InC-
(SiMe3)3] (3), and Fe2(CO)6(µ-CO)[µ-InC(SiMe3)3]2 (4) are available
on the Internet only. Access information is given on any current
masthead page.
IC9704804
(20) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry, 4th
(19) Cotton, F. A.; Troup, J. M. J. Chem. Soc., Dalton Trans. 1974, 800.
ed.; HarperCollins College Publishers: New York, 1993.