Metal-metal communication through carborane cages supporting electroactive [η5-CpFe(CO)2] substituents

Article abstract of DOI:10.1021/om030514h

A family of η⁵-CpFe(CO)₂-substituted closo-carboranes was synthesized and characterized, including cyclic voltammetry measurements. Like the previously reported bimetallic compound 1,12-[η⁵-CpFe(CO)₂]₂-1,12-C₂ B₁₀H₁₀ (8), 1,10-[η⁵-CpFe(CO)₂]₂-1,10-C₂ B₈H₈ (9) produces two dissimilar and irreversible one-electron oxidations within the same range, suggesting that it also exhibits through-cage electronic communication between iron centers. Structures determined by X-ray diffraction studies are reported for 1-[η⁵-CpFe(PPh₃)(CO)]-1,12-C₂B₁₀ H₁₁ (5), 1,12-[η⁵-CpFe(CO)₂]₂-1,12-C₂ B₁₀H₁₀ (8), and 1,10-[η⁵-CpFe(CO)₂]₂-1,10-C₂ B₈H₈ (9).

Full text of DOI:10.1021/om030514h

482
Organometallics 2004, 23, 482-489
Meta l-Meta l Com m u n ica tion th r ou gh Ca r bor a n e Ca ges
Su p p or tin g Electr oa ctive [η5-Cp F e(CO)2] Su bstitu en ts
Timothy J . Wedge, Axel Herzog, Ramon Huertas, Mark W. Lee,
Carolyn B. Knobler, and M. Frederick Hawthorne*
Department of Chemistry and Biochemistry, University of California, Los Angeles,
Los Angeles, California 90095
Received J uly 1, 2003
A family of η5-CpFe(CO)2-substituted closo-carboranes was synthesized and characterized,
including cyclic voltammetry measurements. Like the previously reported bimetallic
compound 1,12-[η5-CpFe(CO)2]2-1,12-C2B10H10 (8), 1,10-[η5-CpFe(CO)2]2-1,10-C2B8H8 (9)
produces two dissimilar and irreversible one-electron oxidations within the same range,
suggesting that it also exhibits through-cage electronic communication between iron centers.
Structures determined by X-ray diffraction studies are reported for 1-[η5-CpFe(PPh3)(CO)]-
1,12-C2B10H11 (5), 1,12-[η5-CpFe(CO)2]2-1,12-C2B10H10 (8), and 1,10-[η5-CpFe(CO)2]2-1,10-
C2B8H8 (9).
In tr od u ction
been extended to include 1,12-C2B10H12. This was ac-
complished3 through the synthesis of 1-[η5-CpFe(CO)2]-
1,12-C2B10H11 (3), 1-[η5-CpFe(CO)2-1,12-C2B10H10-12-
yl]2Hg (6), and 1,12-[η5-CpFe(CO)2]2-1,12-C2B10H10 (8).
Cyclic voltammetry measurements demonstrated single
irreversible one-electron oxidations for the monometallic
3 and 6 but two irreversible one-electron oxidations for
the bimetallic compound 8. The UV-vis absorption
spectra also provided strong evidence of electronic
communication between the iron centers through the
carborane cage. The extinction coefficient of the lowest
energy peak of 5 was exactly double that of its parent
compound 3, while the extinction coefficient of coupled
8 was 6 times that of 3.
The closo-1,10-C2B8H10 and closo-1,12-C2B10H12 p-
carboranes are highly symmetric cage cluster molecules
that are also three-dimensionally aromatic. Their chem-
istry is firmly established, including well-described
methods for achieving cage substitution at either the
carbon or boron vertices.1 The protons attached to the
carboranyl carbon atoms can be easily removed by
strong bases to provide nucleophilic carboranyl anions
having the ability to react with electrophilic reagents.
Wade et al. coupled the dianion of p-C2B10H12 to aryl
electron-donor and -acceptor moieties to study electronic
transmission through the icosahedral carborane cage.2
This was accomplished by monitoring the 13C NMR
chemical shifts and UV-vis spectra of a series of
disubstituted 1,12-C2B10H10-1,12-ylene derivatives. This
study established that the p-carborane cage has the
ability to transmit electronic information from one
carbon terminus to the other.
Expanding on Wade’s findings and the fact that the
use of similar metal-bonded carboranes for this purpose
had not been previously described, Hawthorne et al.
investigated a series of η5-CpFe(CO)2-substituted p-
carborane derivatives for evidence of electronic com-
munication through the cage.3 Although the syntheses
of η5-CpFe(CO)2-substituted icosahedral cages 1-CH3-
1,2-C2B10H10-2-yl4 and 1,7-C2B10H11-1-yl5 as well as the
smaller cage compound 1,10-[η5-CpFe(CO)2]2-1,10-C2B8H8
(9)4 were previously described, this chemistry had not
Complementary to the Hawthorne findings, Low and
co-workers found evidence for electronic communication
through a p-carborane cage.6 They investigated a 1,12-
[Co2C2(SiMe3)(CO)4(dppm)]2-1,12-C2B10H10 system formed
by the reaction of 1,12-bis((trimethylsilyl)ethynyl)-1,-
12-C2B10H10 with [Co2(CO)6(dppm)]. The resulting prod-
uct exhibited two reversible one-electron oxidations in
a cyclic voltammogram trace. The fact that the oxida-
tions were reversible demonstrated the stability of these
complexes, in contrast to those studied by Hawthorne.
This was excellent evidence for the ability of carborane
cages to transmit electronic information and for the use
of cyclic voltammetry to detect such phenomena.
Presented here is a full account of a family of η5-CpFe-
(CO)2-substituted closo-carboranes, expanding on those
previously described and including the synthesis and
cyclic voltammetry measurements of these derivatives.
Structures from X-ray diffraction studies are presented
for 1-[η5-CpFe(PPh3)(CO)]-1,12-C2B10H11 (5), 1,12-[η5-
CpFe(CO)2]2-1,12-C2B10H10 (8), and 1,10-[η5-CpFe(CO)2]2-
1,10-C2B8H8 (9). Attempts to synthesize a more robust
ferracarborane are also described.
* To whom correspondence should be addressed. Tel.: +1-310-825-
7378. Fax: +1-310-825-5490. E-mail: mfh@chem.ucla.edu.
(1) Grimes, R. N. Carboranes; Academic Press: New York, 1970; p
54.
(2) Fox, M. A.; MacBride, J . A. H.; Peace, R. J .; Wade, K. J . Chem.
Soc., Dalton Trans. 1998, 401.
(3) Bitner, T. W.; Wedge, T. J .; Hawthorne, M. F.; Zink, J . I. Inorg.
Chem. 2001, 40, 5428.
(4) Smart, J . C.; Garrett, P. M.; Hawthorne, M. F. J . Am. Chem.
Soc. 1969, 91, 1031.
(5) Zakharkin, L. I.; Orlova, L. V.; Denisovich, L. I. Zh. Obsch. Khim.
1972, 42, 2217.
(6) Fox, M. A.; Paterson, M. A. J .; Nervi, C.; Galeotti, F.; Puschmann,
H.; Howard, J . A. K.; Low, P. J . Chem. Commun. 2001, 1610.
10.1021/om030514h CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/03/2004

Metal-Metal Communication through Carborane Cages
Organometallics, Vol. 23, No. 3, 2004 483
Sch em e 1
Sch em e 2
Attempts were made to produce a more robust ferra-
carborane molecule. On the basis of similar chemistry
described for alkynyl systems,7 it was determined that
a different iron complex should be investigated, i.e., one
with bulkier ligands to protect the iron(II) center from
oxidation. Thus, monolithio-p-carborane was reacted
with η5-Cp*Fe(CO)2Cl (Fp*-Cl)9 in diethyl ether in an
attempt to synthesize the Fp* homologue of 3. Unfor-
tunately, even at elevated temperature, no reaction
occurred. This is most likely due to the fact that the
iron center with the large Cp* ligand was too sterically
encumbered to react with the bulky carborane anion.
In another effort to create a stable ferracarborane, 3
was photolyzed with triphenylphosphine in benzene to
exchange the labile CO ligands with bulky triphen-
ylphosphine groups (Scheme 2). This resulted in the
formation of compound 5 as a racemic mixture of R and
S enantiomers in nearly quantitative yield as a red
crystalline solid. Again, the sterically crowded iron
center influenced product formation and allowed only
one CO to be exchanged for PPh3.
Compound 5 was slightly more stable than its parent
3, which allowed for single crystals suitable for an X-ray
diffraction study to be isolated by slow evaporation of a
mixture of benzene and heptane in the presence of air.
Although single crystals formed, a large fraction of the
sample decomposed. A similar reaction was attempted
whereby compound 8 (described below) was photolyzed
with 1,2-bis(diphenylphosphino)ethane (DIPHOS) in
benzene in an attempt to exchange both CO ligands on
the iron centers with the bridged phosphines. This also
failed to produce the desired compound, and thus
further efforts to synthesize more stable ferracarboranes
in this fashion were abandoned.
The diferracarboranyl mercury compounds 6 and 7
were synthesized by initial lithiation of their parent
compounds 3 and 4, respectively, followed by the addi-
tion of 1/2 equiv of mercury(II) dichloride in diethyl ether
(Scheme 3). The reaction mixture was subjected to an
aqueous workup procedure for product 6 but was flashed
through alumina with benzene without water extraction
for product 7. The crude products were purified by flash
chromatography through activated basic alumina (Al-
drich, Brockmann I, ∼150 mesh) with various ratios of
petroleum ether and benzene as the eluting solvents.
In both cases, unreacted ferracarborane starting mater-
ial eluted first from the column. The yellow products
were then removed from their respective columns with
benzene. The mercury-linked products were isolated as
yellow powders in low yields. The 199Hg{1H} NMR
spectra were indicative of product formation, and each
Resu lts a n d Discu ssion
Syn th esis. The monoferracarborane compounds 1-4
were prepared in an analogous manner following pre-
parative methods described for 3 (Scheme 1).3 The
desired products were independently synthesized by
reacting the monolithio derivatives of 1,2-C2B10H12, 1,7-
C2B10H12, 1,12-C2B10H12, and 1,10-C2B8H10 with η5-
CpFe(CO)2Cl (Fp-Cl) in diethyl ether at room temper-
ature. The reactions could be either subjected to an
aqueous workup procedure or simply flashed through
alumina with benzene to remove the lithium salts. The
crude products were purified by flash chromatography
through activated basic alumina (Aldrich, Brockmann
I, ∼150 mesh) with various ratios of petroleum ether
and benzene as the eluting solvents. This purification
method worked well, because the unreacted carboranes
eluted first with pure petroleum ether and unreacted
Fp-Cl adhered strongly to the stationary phase after the
products were removed. The product-containing fraction
could be easily seen on the column, since all four desired
products are yellow. In each case, after the yellow
fractions were collected and the solvent removed under
vacuum, the yellow crystalline products were pure and
required no further purification. The pure products were
easily identified by their unique 11B{1H} NMR spectra,
as well as by the use of other standard characterization
techniques.
The four monoferracarborane compounds were found
to be sensitive to light and oxygen. In solution, all
compounds decomposed in less than 1 h, but as solids,
they remained intact for longer periods of time. Even
in the solid state, surface decomposition was observed
(they became brown) if left in an oxygen-containing
atmosphere. To maintain the ferracarboranes in a pure
condition, they were stored in a glovebox under an argon
atmosphere in brown glass bottles. Under these condi-
tions the compounds were stable for extended periods
of time.
(7) Coat, F.; Lapinte, C. Organometallics 1996, 15, 477.
(8) Kaszynski, P.; Pakhornov, S.; Young, V. G. Collect. Czech. Chem.
Commun. 2002, 67, 1061.
(9) Fp*-Cl was synthesized in a manner analogous to that for Fp-
Cl.11

484 Organometallics, Vol. 23, No. 3, 2004
Wedge et al.
Ta ble 1. Cyclic Volta m m etr y Mea su r em en ts (V)
for [η5-Cp F e(CO)2]-Su bstitu ted Com p ou n d s
(Oxid a tion P oten tia ls vs Ag/AgCl Refer en ce
Electr od e)
Sch em e 3
compd
acetonitrile
methylene chloride
[η5-CpFe(CO)2]Cl
1.29
1.68
1.58
1.27
1.66
1.59
1
2
3
1.54
1.58
4
1.48
1.54
6
1.49
1.55
7
1.41
1.48
8
9
10
1.44; 1.58
1.34; 1.54
1.45
1.47; 1.65
1.38; 1.57
1.41
activated basic alumina (Aldrich, Brockmann I, ∼150
mesh) with petroleum ether/benzene (2:1) as the eluant.
Although the yellow product did not elute from the
column with this solvent mixture, it could be removed
from the column with benzene, leaving any unreacted
Fp-Cl behind. The product was isolated as yellow
crystals in 67% yield. The same method was employed
in an attempt to obtain the diferracarborane analogues
of 1 and 2, but neither reaction succeeded and only
starting material was recovered. In contrast to the above
results, compounds 9 and 10 could be synthesized
directly from their non-Fp-substituted parent com-
pounds, albeit in low yields.
Sch em e 4
Cyclic Volta m m etr y. Oxidation potentials for this
family of [η5-CpFe(CO)2]-substituted compounds were
obtained in both acetonitrile and methylene chloride
solution. These data are presented in Table 1 and
indicate no significant difference between the potentials
obtained using these two solvents. For simplicity, the
discussion is based upon the electrochemical data
obtained in acetonitrile solution.
The monosubstituted compounds 1-4 each exhibit
one irreversible single-electron oxidation potential. The
potentials for the icosahedral cage molecules decrease
as the carborane cage is varied from ortho to meta to
para. The [η5-CpFe(CO)2]-substituted 1,10-C2B8-cage
molecule 4 has a lower oxidation potential than its 1,-
12-C2B10-cage analogue 3. The bimetallic systems con-
sisting of two [η5-CpFe(CO)2]-substituted carborane
cages connected by a mercury atom, 6 and 7, each have
only one irreversible oxidation potential (1.49 and 1.41
V, respectively, in CH3CN). These values are similar to
those of their monometallic parent compounds 3 (1.54
V) and 4 (1.48 V).
There is evidence for electronic communication be-
tween the metal centers in the carborane-bridged
compounds 8 and 9. If there were no communication,
both metals would be oxidized at the same potential,
much like the mercury-linked compounds 6 and 7, but
if electronic communication exists, the second oxidation
potential would be significantly different from that of
the first oxidation. Both bimetallic species with one
bridging carborane cage, 8 and 9, show two irreversible
oxidation potentials, 1.44 and 1.58 V for 8 and 1.34 and
1.54 V for 9. These results demonstrate that the two
metal centers exhibit electronic communication across
a single carborane cage. Interestingly, compound 10,
which is also a bis-substituted system, has only one
oxidation potential (1.45 V). This is most likely due to
the poor p-orbital overlap between the ethynyl modules
and the p-orbital of the carboranyl carbons.8
contained single resonances similar to those in known
mercury(II) carboranyl compounds.10
Synthesis of a mercury-linked ferracarborane with the
m-carborane parent 2 was attempted but failed. It is
unclear whether the reaction failed because the forma-
tion of the m-ferracarborane anion did not occur or
because of the reduced nucleophilicity of this anion
toward an electrophilic center.
Direct synthesis of the diferracarborane compound 8
was attempted by room-temperature reaction of the
dilithio-1,12-C2B10H10 reagent with 2 equiv of Fp-Cl.
This produced only the monosubstituted product 3.
Ultimately, the preparation of 8 was achieved using a
preparation similar to that for 6 described above. The
precursor, 3, was lithiated with tert-butyllithium in
diethyl ether followed by the addition of 1 equiv of Fp-
Cl with heating at reflux for 20 h (Scheme 4). The
reaction does not proceed at room temperature. Unre-
acted 3 was removed by flash chromatography through
(10) For a review of carborane-mercury compounds, see: Wedge, T.
J ., Hawthorne, M. F. Coord. Chem. Rev. 2003, 240, 111.

Metal-Metal Communication through Carborane Cages
Organometallics, Vol. 23, No. 3, 2004 485
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t Deta ils for Com p ou n d s 5, 8, a n d 9
5
8
9
mol formula
C
26H31B10FeOP
C16H20B10Fe2O4
C16H18B8Fe2O4
fw
553.92
496.12
472.48
temp (K)
293(2)
298(2)
293(2)
wavelength (Å)
cryst syst
space group
0.710 73
monoclinic
P21/n
0.710 73
monoclinic
P21/n
0.710 73
monoclinic
P21/c
a (Å)
b (Å)
c (Å)
10.263(8)
18.676(15)
14.737(12)
97.471(16)
4
8.1515(19)
11.133(3)
12.275(3)
92.320(4)
13.781(2)
12.539(2)
13.112(2)
110.727(3)
â (deg)
Z
2
4
density (calcd) (Mg/m3)
1.314
0.617
1.480
1.325
1.481
1.389
abs coeff (mm-1
)
F(000)
1142
500
952
cryst size (mm3)
0.05 × 0.15 × 0.2
0.1 × 0.2 × 0.5
0.25 × 0.25 × 0.15
1.58-28.29
-18 e h e 17
-16 e k e 15
-17 e l e 12
12 213
θ range for data collecn (deg)
index ranges
1.77-28.35
2.47-28.25
-8 e h e 13
-10 e h e 10
-11 e k e 14
-12 e l e 16
6531
-22 e k e 24
-19 e l e 19
no. of rflns collected
no. of indep rflns
completeness to θ (%)
abs cor
17 140
6606 (R(int) ) 0.0972)
94.3
2523 (R(int) ) 0.0639)
91.8
4748 (R(int) ) 0.0385)
90.2
SADABS
none
SADABS
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
full-matrix least squares on F2
6606/0/363
full-matrix least squares on F2
2523/0/136
full-matrix least squares on F2
4748/0/275
0.888
0.974
0.886
R1 ) 0.0725, wR2 ) 0.1791
R1 ) 0.1947, wR2 ) 0.2293
1.052 and -0.677
R1 ) 0.0531, wR2 ) 0.1319
R1 ) 0.0764, wR2 ) 0.1435
0.565 and -0.439
R1 ) 0.0460, wR2 ) 0.0913
R1 ) 0.1048, wR2 ) 0.1067
0.404 and -0.294
largest diff peak and hole (e Å-3
)
Ta ble 3. Selected Bon d Len gth s (Å) for 1-[(η5-
Cyclop en ta d ien yl)(tr ip h en ylp h osp h in e)ca r bon yl-
ir on ]1,12-d ica r ba -closo-d od eca bor a n e (5)
Fe(1)-C(1L)
Fe(1)-C(1)
Fe(1)-C(2C)
Fe(1)-C(1C)
Fe(1)-C(3C)
Fe(1)-C(5C)
Fe(1)-C(4C)
Fe(1)-P(1)
C(1)-B(3)
1.729(8)
2.093(6)
2.089(7)
2.081(8)
2.085(8)
2.106(9)
2.158(9)
2.271(2)
1.711(10)
1.720(9)
1.739(9)
C(1)-B(6
1.745(9)
1.751(9)
1.701(12)
1.685(11)
1.692(10)
1.689(11)
1.703(11)
1.141(8)
1.832(6)
1.831(6)
1.842(6)
C(1)-B(5)
B(7)-C(12)
B(8)-C(12)
B(9)-C(12)
B(10)-C(12
B(11)-C(12)
C(1L)-O(1L)
P(1)-C(13P)
P(1)-C(7P)
P(1)-C(1P)
C(1)-B(4)
C(1)-B(2)
Fe atoms are 7.3588(15) Å apart, and the two cage C
atoms are 3.246(6) Å apart. Other selected bond dis-
tances and angles are given in Tables 5 and 6.
F igu r e 1. ORTEP diagram showing the molecular struc-
ture of 1-[(η5-cyclopentadienyl)(triphenylphosphine)carbonyl-
iron]-1,12-dicarba-closo-dodecaborane (5).
Molecu la r Str u ctu r e of 1,10-Bis[(η5-cyclop en ta -
d ien yl)d ica r bon ylir on ]-1,10-d ica r ba-closo-d eca bo-
r a n e (9). The structure of 9 was confirmed by X-ray
crystallography and is presented in Figure 3. A sum-
mary of the crystallographic data is presented in Table
2. The Fe-cage-Fe unit is linear (Fe1-C1- - -C10 )
177.93(15)°, C1- - -C10-Fe2 ) 178.23(15)°). The Cp
carbon atoms are coplanar within 0.004(3) and 0.006-
(2) Å. Fe1 is 1.725(2) Å from its Cp plane, and Fe2 is
1.723(2) Å from its Cp plane. The Fe atoms are 1.64(2)
and 1.63(2) Å from the planes through the 5 Cp H
atoms, respectively. The two Fe atoms are 7.524(1) Å
apart, and the two cage C atoms are 3.476(4) Å apart.
The closest interatomic approach between two non-
hydrogen atoms is 3.159(4) Å (O6A‚‚‚O7A). A weak
hydrogen interaction links C1L and O7A (C1L‚‚‚H1L )
0.85(4) Å, H1L‚‚‚O7A ) 2.66(4) Å, C1L‚‚‚O7A ) 3.427-
(5) Å, C1L-H1L-O7A ) 150(4)°). Other selected bond
distances and angles are given in Tables 7 and 8.
Discu ssion of Exp er im en ta l Str u ctu r es of 5, 8,
a n d 9. Comparable bond lengths for compounds 5, 8,
and 9 are presented in Table 9. The Fe-C(carboranyl)
Molecu la r Str u ctu r e of 1-[(η5-Cyclop en ta d ien yl)-
(tr ip h en ylp h osp h in e)ca r bon ylir on ]-1,12-d ica r ba -
closo-d od eca bor a n e (5). The structure of 5, confirmed
by X-ray crystallography, is presented in Figure 1. A
summary of the crystallographic data is presented in
Table 2. The Fe-cage-H unit is linear (Fe1-C1- - -C12
) 177.9(3)°), and Fe1 is 1.722(4) Å from its Cp plane.
Other selected bond distances and angles are given in
Tables 3 and 4.
Molecu la r Str u ctu r e of 1,12-Bis[(η5-cyclop en ta -
d ien yl)d ica r b on ylir on ]-1,12-d ica r b a -closo-d od e-
ca bor a n e (8). The structure of 8 was confirmed by
X-ray crystallography and is presented in Figure 2. The
molecule is centrosymmetric. A summary of the crystal-
lographic data is presented in Table 2. The Fe-cage-
Fe unit is linear (Fe1-C1- - -C12 ) 177.56(16)°). The
Cp carbon atoms are coplanar within 0.004(3) Å. Fe1 is
1.725(2) Å from its Cp plane. The Fe atom is 1.66(3) Å
from the plane through the five Cp H atoms. The two

486 Organometallics, Vol. 23, No. 3, 2004
Wedge et al.
Ta ble 4. Selected Bon d An gles (d eg) for 1-[(η5-
Cyclop en ta d ien yl)(tr ip h en ylp h osp h in e)ca r bon yl-
ir on ]-1,12-d ica r ba -closo-d od eca bor a n e (5)
Ta ble 6. Selected Bon d An gles (d eg) for 1,12-Bis-
[(η5-cyclop en ta d ien yl)d ica r bon ylir on ]-1,12-d ica r ba -
closo-d od eca bor a n e (8)
C(1L)-Fe(1)-C(1)
92.3(4)
C(1C)-Fe(1)-P(1)
C(3C)-Fe(1)-P(1) 158.6(3)
C(5C)-Fe(1)-P(1) 93.7(3)
C(4C)-Fe(1)-P(1) 121.7(4)
95.6(2)
C(7L)-Fe(1)-C(6L) 93.3(2)
C(1)-Fe(1)-C(2C) 105.76(16)
C(1L)-Fe(1)-C(2C) 81.3(4)
C(1)-Fe(1)-C(2C) 130.4(3)
C(1L)-Fe(1)-C(1C) 101.2(4)
C(1)-Fe(1)-C(1C) 158.4(3)
C(2C)-Fe(1)-C(1C) 37.9(3)
C(1L)-Fe(1)-C(3C) 96.4(5)
C(7L)-Fe(1)-C(1)
C(6L)-Fe(1)-C(1)
91.80(14) C(4C)-Fe(1)-C(2C) 63.9(2)
92.61(14) C(3C)-Fe(1)-C(2C) 37.8(2)
C(7L)-Fe(1)-C(4C) 94.1(2)
C(6L)-Fe(1)-C(4C) 112.4(3)
C(1)-Fe(1)-C(4C) 153.9(3)
C(7L)-Fe(1)-C(3C) 125.3(3)
C(6L)-Fe(1)-C(3C) 88.7(2)
C(1)-Fe(1)-C(3C) 142.7(2)
C(4C)-Fe(1)-C(3C) 37.2(3)
C(7L)-Fe(1)-C(5C) 95.8(2)
C(6L)-Fe(1)-C(5C) 152.2(3)
C(1)-Fe(1)-C(5C) 113.2(3)
C(4C)-Fe(1)-C(5C) 40.9(3)
C(3C)-Fe(1)-C(5C) 64.7(3)
C(7L)-Fe(1)-C(1C) 131.0(2)
C(6L)-Fe(1)-C(1C) 135.3(2)
C(5C)-Fe(1)-C(2C) 64.4(2)
C(1C)-Fe(1)-C(2C) 36.73(18)
C(2C)-C(1C)-Fe(1) 71.7(2)
C(5C)-C(1C)-Fe(1) 69.7(3)
C(1C)-C(2C)-Fe(1) 71.6(3)
C(3C)-C(2C)-Fe(1) 70.0(3)
C(4C)-C(3C)-Fe(1) 71.1(3)
C(2C)-C(3C)-Fe(1) 72.2(3)
C(3C)-C(4C)-Fe(1) 71.7(3)
C(5C)-C(4C)-Fe(1) 70.2(3)
C(1C)-C(5C)-Fe(1) 71.0(2)
C(4C)-C(5C)-Fe(1) 68.9(3)
O(6L)-C(6L)-Fe(1) 176.7(4)
O(7L)-C(7L)-Fe(1) 176.9(3)
122.65(19)
B(3)-C(1)-Fe(1)
B(4)-C(1)-Fe(1)
B(2)-C(1)-Fe(1)
B(6)-C(1)-Fe(1)
B(5)-C(1)-Fe(1)
118.0(4)
120.0(4)
119.3(4)
122.2(4)
122.4(4)
C(1)-Fe(1)-C(3C)
96.9(3)
C(2C)-Fe(1)-C(3C) 36.5(3)
C(1C)-Fe(1)-C(3C) 65.1(4)
C(1L)-Fe(1)-C(5C) 144.3(4)
C(1)-Fe(1)-C(5C) 119.7(3)
C(2C)-Fe(1)-C(5C) 66.1(3)
C(1C)-Fe(1)-C(5C) 43.6(4)
C(3C)-Fe(1)-C(5C) 66.2(4)
C(1L)-Fe(1)-C(4C) 140.4(5)
O(1L)-C(1L)-Fe(1) 176.9(8)
C(5C)-C(1C)-Fe(1) 69.1(4)
C(2C)-C(1C)-Fe(1) 71.4(5)
C(3C)-C(2C)-Fe(1) 71.6(5)
C(1C)-C(2C)-Fe(1) 70.7(4)
C(2C)-C(3C)-Fe(1) 71.9(5)
C(4C)-C(3C)-Fe(1) 70.4(4)
C(3C)-C(4C)-Fe(1) 65.6(5)
C(5C)-C(4C)-Fe(1) 70.2(5)
C(1C)-C(5C)-Fe(1) 67.3(5)
C(4C)-C(5C)-Fe(1) 74.6(6)
C(13P)-P(1)-Fe(1) 116.2(2)
C(7P)-P(1)-Fe(1) 121.24(19)
C(1)-Fe(1)-C(4C)
91.8(3)
C(2C)-Fe(1)-C(4C) 66.4(4)
C(1C)-Fe(1)-C(4C) 67.0(4)
C(3C)-Fe(1)-C(4C) 44.0(4)
C(5C)-Fe(1)-C(4C) 35.2(3)
C(1)-Fe(1)-C(1C)
91.66(14) B(5)-C(1)-Fe(1)
C(4C)-Fe(1)-C(1C) 65.5(2)
B(2)-C(1)-Fe(1)
118.26(18)
121.32(19)
120.80(18)
118.45(19)
C(3C)-Fe(1)-C(1C) 62.78(18) B(4)-C(1)-Fe(1)
C(5C)-Fe(1)-C(1C) 39.4(3)
B(6)-C(1)-Fe(1)
C(1L)-Fe(1)-P(1)
C(1)-Fe(1)-P(1)
C(2C)-Fe(1)-P(1) 129.8(3)
96.4(3)
C(7L)-Fe(1)-C(2C) 157.36(19) B(3)-C(1)-Fe(1)
C(6L)-Fe(1)-C(2C) 99.93(19)
99.68(16) C(1P)-P(1)-Fe(1) 113.29(18)
F igu r e 3. ORTEP diagram showing the molecular struc-
ture of 1,10-bis[(η5-cyclopentadienyl)dicarbonyliron]-1,10-
dicarba-closo-decaborane (9).
F igu r e 2. ORTEP diagram showing the molecular struc-
ture of 1,12-bis[(η5-cyclopentadienyl)dicarbonyliron]-1,12-
dicarba-closo-dodecaborane (8).
Ta ble 7. Selected Bon d Len gth s (Å) for 1,10-Bis-
[(η5-cyclop en ta d ien yl)d ica r bon ylir on ]-1,10-d ica r ba -
closo-d eca bor a n e (9)
Ta ble 5. Selected Bon d Len gth s (Å) for 1,12-Bis-
[(η5-cyclop en ta d ien yl)d ica r bon ylir on ]-1,12-d ica r ba -
closo-d od eca bor a n e (8)
Fe(1)-C(7A)
Fe(1)-C(6A)
Fe(1)-C(1)
1.752(4)
1.763(4)
2.021(3)
2.089(4)
2.093(4)
2.094(4)
2.094(4)
2.098(4)
1.752(4)
1.759(4)
2.030(3)
2.083(4)
2.089(4)
2.102(4)
Fe(2)-C(3D)
Fe(2)-C(5D)
C(6A)-O(6A)
C(7A)-O(7A)
C(6D)-O(6D)
C(7D)-O(7D)
C(1)-B(4)
2.104(4)
2.110(4)
1.137(4)
1.141(4)
1.143(4)
1.139(4)
1.604(5)
1.606(5)
1.611(5)
1.618(5)
1.599(5)
1.612(5)
1.611(5)
1.601(5)
Fe(1)-C(7L)
Fe(1)-C(6L)
Fe(1)-C(1)
Fe(1)-C(4C)
Fe(1)-C(3C)
Fe(1)-C(5C)
Fe(1)-C(1C)
Fe(1)-C(2C)
1.765(4)
1.770(4)
2.057(3)
2.063(4)
2.070(5)
2.080(5)
2.097(4)
2.098(4)
C(6L)-O(6L)
C(7L)-O(7L)
C(1)-B(5)
C(1)-B(2)
C(1)-B(4)
C(1)-B(6)
C(1)-B(3)
1.132(5)
1.132(4)
1.723(5)
1.724(4)
1.727(4)
1.728(5)
1.730(4)
Fe(1)-C(4L)
Fe(1)-C(1L)
Fe(1)-C(3L)
Fe(1)-C(2L)
Fe(1)-C(5L
Fe(2)-C(6D)
Fe(2)-C(7D)
Fe(2)-C(10)
Fe(2)-C(2D)
Fe(2)-C(1D
Fe(2)-C(4D)
C(1)-B(5)
C(1)-B(2)
C(1)-B(3)
B(6)-C(10
B(7)-C(10)
B(8)-C(10)
B(9)-C(10)
distance is considerably longer (2.093(6) Å) for the
monosubstituted 5 compared to that of the disubstituted
compounds 8 (2.057(3) Å) and 9 (2.021(3) and 2.030(3)
Å). Although both Fe-C(carboranyl) distances in 8 are
required to be crystallographically equivalent, two dif-
ferent lengths are found in 9. Compound 9 also exhibits
the shortest Fe-C(carboranyl) distances in the series.
This may be attributed to the greater s character
associated with the cage carbon exo-bonding orbital of
the 1,10-C2B8H8 module present in 9.8
Å for 5 with a range from 1.711(10) to 1.751(9) Å.
Compound 8 has an average length of 1.726(4) Å and a
range of 1.723(5) to 1.730(4) Å for the same types of
bonds. Moreover, a comparison of the carboranyl C-B5
distances associated with both ends of the 5 molecule
demonstrates the dramatic effect of carboranyl carbon
substitution. The average carboranyl C-B5 distance
within the portion of the molecule σ-bonded to iron is
1.733(2) Å, as mentioned previously, while the average
carboranyl C-B5 distance for the portion of the molecule
σ-bonded to hydrogen is 1.694(8) Å.
The effect of the iron center on cage bonds can be seen
when examining the carboranyl{Fe}C-B5 distances in
compounds 5 and 8. These species can be directly
compared, since they both contain icosahedral p-carbo-
rane cages. The average length of these bonds is 1.733(2)

Metal-Metal Communication through Carborane Cages
Organometallics, Vol. 23, No. 3, 2004 487
Ta ble 8. Selected Bon d An gles (d eg) for 1,10-Bis-
[(η5-cyclop en ta d ien yl)d ica r bon yl-ir on ]-1,10-d ica r ba -
closo-d eca bor a n e (9)
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were carried out
under an argon atmosphere using standard Schlenk tech-
niques. Argon gas was dried by passage through a column of
reduced chromium oxide on silica. Diethyl ether was dried over
sodium benzophenone ketyl and freshly distilled prior to use.
All carboranes were obtained from Katchem Ltd. and used as
purchased. The η5-CpFe(CO)2Cl precursor was synthesized by
modification of literature methods.11 1,12-Bis(ethynyl)-1,12-
dicarba-closo-dodecaborane was prepared as described by
literature methods.12 All other chemicals were used as pur-
chased from various sources. Infrared spectra were obtained
using a Nicolet Nexus 470 FTIR. All NMR spectra were
recorded at room temperature using a Bruker ARX500 spec-
trometer. The EI and CI mass spectra were obtained on a VG
Autospec spectrometer. Cyclic voltammetry measurements
were recorded using a Princeton Applied Research Potentiostat
Model 263A with “PowerCV” software. Redox potentials were
measured in CH3CN and CH2Cl2 solutions containing 100 mM
(Bu4N)+(PF6)- as the electrolyte vs an Ag/AgCl reference
electrode.
Syn th esis of 1-[(η5-Cyclop en ta d ien yl)d ica r bon ylir on ]-
1,2-d ica r ba -closo-d od eca bor a n e (1). To a solution of 1,2-
dicarba-closo-dodecaborane (1.00 g, 6.93 mmol) in Et2O (30 mL)
was added nBuLi (1.6 M in hexanes, 4.33 mL, 6.93 mmol)
dropwise at -78 °C. After it was warmed to ambient temper-
ature and stirred for 3 h, the solution was cooled again to -78
°C and (η5-cyclopentadienyl)iron dicarbonyl chloride (1.47 g,
6.93 mmol) was added at once. The solution was warmed to
ambient temperature and stirred for 15 h. Solvent was
removed in vacuo, and the reddish brown residue was redis-
solved in benzene, the solution was extracted with H2O (2 ×
30 mL), and the organic phase was flashed through activated
basic alumina (Aldrich, Brockmann I, ∼150 mesh) with
petroleum ether/benzene (1:1) as the eluant. The yellow first
fraction was collected, and the solvent was removed, leaving
the crystalline product 1 (1.53 g, 69%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 3.67 (5H, s, Cp), 3.50-1.60 (10H, m, br, BH),
2.02 (1H, s, br, CH). 13C NMR (125.8 MHz, C6D6): δ (ppm)
213.32, 86.79, 68.03, 61.25. 11B{1H} NMR (160.5 MHz, C6D6,
BF3‚Et2O external): δ (ppm) -0.39 (1B), -2.33 (1B), -6.70
(4B), -9.96 (2B), -13.64 (2B). FTIR (KBr; cm-1): 3070, 2963,
2928, 2859, 2603, 2032, 1980. HRMS (EI; m/z): calcd for
C9H16B10FeO2, 322.1449; found, 322.1433 (M+, monoisotopic
mass).
Syn th esis of 1-[(η5-Cyclop en ta d ien yl)d ica r bon ylir on ]-
1,7-d ica r ba -closo-d od eca bor a n e (2). To a solution of 1,7-
dicarba-closo-dodecaborane (1.00 g, 6.93 mmol) in Et2O (30 mL)
was added nBuLi (1.6 M in hexanes, 4.33 mL, 6.93 mmol)
dropwise at -78 °C. After it was warmed to ambient temper-
ature and stirred for 3 h, the solution was cooled again to -78
°C and (η5-cyclopentadienyl)iron dicarbonyl chloride (1.47 g,
6.93 mmol) was added at once. The solution was warmed to
ambient temperature and stirred for 15 h. Solvent was
removed in vacuo, and the reddish brown residue was redis-
solved in benzene, the solution was extracted with H2O (2 ×
30 mL), and the organic phase was flashed through activated
basic alumina (Aldrich, Brockmann I, ∼150 mesh) with
petroleum ether/benzene (1:1) as the eluant. The yellow first
fraction was collected, and the solvent was removed, leaving
the crystalline product 2 (0.77 g, 35%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 3.80 (5H, s, Cp), 3.30-1.80 (10H, m, br, BH),
2.38 (1H, s, br, CH). 13C NMR (125.8 MHz, C6D6; δ (ppm)):
C(7A)-Fe(1)-C(6A) 91.94(17) C(6A)-Fe(1)-C(5L) 94.01(18)
C(7A)-Fe(1)-C(1)
C(6A)-Fe(1)-C(1)
90.54(15) C(1)-Fe(1)-C(5L) 152.14(17)
91.80(15) C(4L)-Fe(1)-C(5L) 38.34(16)
C(7A)-Fe(1)-C(4L) 91.82(17) C(1L)-Fe(1)-C(5L) 39.20(18)
C(6A)-Fe(1)-C(4L) 125.96(18) C(3L)-Fe(1)-C(5L) 65.34(19)
C(1)-Fe(1)-C(4L) 142.03(17) C(2L)-Fe(1)-C(5L) 65.3(2)
C(7A)-Fe(1)-C(1L) 155.08(19) O(6A)-C(6A)-Fe(1) 176.9(3)
C(6A)-Fe(1)-C(1L) 94.75(19) O(7A)-C(7A)-Fe(1) 178.0(3)
C(1)-Fe(1)-C(1L) 113.2(2)
C(2L)-C(1L)-Fe(1) 70.6(3)
C(4L)-Fe(1)-C(1L) 64.95(18) C(5L)-C(1L)-Fe(1) 70.6(3)
C(7A)-Fe(1)-C(3L) 102.47(18) C(1L)-C(2L)-Fe(1) 70.5(3)
C(6A)-Fe(1)-C(3L) 158.48(18) C(3L)-C(2L)-Fe(1) 70.4(2)
C(1)-Fe(1)-C(3L) 103.81(16) C(4L)-C(3L)-Fe(1) 70.3(2)
C(4L)-Fe(1)-C(3L) 38.94(16) C(2L)-C(3L)-Fe(1) 70.4(2)
C(1L)-Fe(1)-C(3L) 65.66(18) C(5L)-C(4L)-Fe(1) 71.2(2)
C(7A)-Fe(1)-C(2L) 140.0(2)
C(6A)-Fe(1)-C(2L) 128.1(2)
C(3L)-C(4L)-Fe(1) 70.7(2)
C(4L)-C(5L)-Fe(1) 70.4(2)
C(1)-Fe(1)-C(2L)
89.88(16) C(1L)-C(5L)-Fe(1) 70.2(3)
C(4L)-Fe(1)-C(2L) 64.95(18) B(4)-C(1)-Fe(1)
C(1L)-Fe(1)-C(2L) 38.96(19) B(5)-C(1)-Fe(1)
C(3L)-Fe(1)-C(2L) 39.17(18) B(2)-C(1)-Fe(1)
C(7A)-Fe(1)-C(5L) 116.42(19) B(3)-C(1)-Fe(1)
127.4(2)
125.7(2)
128.3(2)
129.7(2)
Ta ble 9. Com p a r a tive Bon d Len gth s (Å) for
Com p ou n d s 5, 8, a n d 9
5
8
9
Fe-C(carboranyl)
Fe-C(CO)
Fe-Cp(plane)
C-B5(carboranyl)
({Fe-}-C-B5(av))
C-O
2.093(6) 2.057(3)
1.729(8) 1.765(4)-1.770(4) 1.752(4)-1.763(4)
1.722(4) 1.725(2)
1.733(2) 1.726(4)
2.021(3), 2.030(3)
1.725(2), 1.723(2)
1.609(8)
1.141(8) 1.132(4), 1.132(5) 1.137(4), 1.141(4)
1.139(4), 1.143(4)
C-B5(carboranyl)
({H-}-C-B5(av))
1.694(0) N/A
N/A
The C-O distances in compounds 5, 8, and 9 are very
similar (∼1.137 Å). Interestingly, the Fe-C(CO) bond
lengths of the symmetric compounds, 8 and 9, are much
longer (∼0.03 Å) than that of 5. This observation may
be explained by the fact that the more tightly bound
CO in 5 is a result of competition with a weaker PPh3
ligand for π-back-bonding electrons from iron. Species
8 and 9 each contain iron centers equipped with two
strongly back-bonding and mutually competitive CO
ligands. Thus, 8 and 9 would be expected to have weaker
individual Fe-C(CO) bonds.
Con clu sion s
A series of η5-CpFe(CO)2-substituted closo-carboranes
has been synthesized. These compounds are yellow
crystalline solids, except for 1-[CpFe(PPh3)(CO)]-1,12-
C2B10H11 (5), which is red. Cyclic voltammetry measure-
ments with all of these η5-CpFe(CO)2-substituted car-
boranes reveal that 1,12-[η5-CpFe(CO)2]2-1,12-C2B10H10
(8) and 1,10-[η5-CpFe(CO)2]2-1,10-C2B8H8 (9) each show
two similar, but distinctly different, irreversible one-
electron oxidations, which suggests that they exhibit
through-cage electronic communication. Molecular struc-
tures derived from X-ray diffraction studies are provided
for 1-[η5-CpFe(PPh3)(CO)]-1,12-C2B10H11 (5), 1,12-[η5-
CpFe(CO)2]2-1,12-C2B10H10 (8), and 1,10-[η5-CpFe(CO)2]2-
1,10-C2B8H8 (9). The Fe-C(carboranyl) bond distance
observed in each of these species may be rationalized
in terms of cage carbon hybridization effects, among
others.
(11) J ohnson, E. C.; Meyer, T. J .; Winterton, N. Inorg. Chem. 1971,
10, 1673. The preparation was modified to optimize the yield by
deoxygenating all solvents prior to use and reducing the drying time
over MgSO4 from overnight to 1 h. This increased the product yield to
85%.
(12) Batsanov, A. S.; Fox, M. A.; Howard, J . A. K.; MacBride, H.;
Wade, K. J . Organomet. Chem. 2000, 610, 20.

488 Organometallics, Vol. 23, No. 3, 2004
Wedge et al.
214.18, 86.65, 63.98, 60.10. 11B{1H} NMR (160.5 MHz, C6D6,
BF3‚Et2O external; δ (ppm)): -1.18 (2B), -7.87 (4B), -11.83
(2B), -13.03 (2B). FTIR (KBr; cm-1): 3070, 2957, 2923, 2854,
2583, 2025, 1971; HRMS (EI; m/z): calcd for C9H16B10FeO2,
322.1449; found, 322.1438 (M+, monoisotopic mass).
-12.58 (5B). FTIR (CCl4 solution; cm-1): 3073, 3058, 2928,
2858, 2596, 2036, 1990, 1946. LRMS (EI; m/z): calcd for
C
26H31B10FeOP 554.2 (M+), C25H31B10FeP 526.4 (M+ - CO);
found, 526.2 (M+ - CO).
Syn th esis of Bis(12-[(η5-cyclop en ta d ien yl)d ica r bon yl-
ir on ]-1,12-d ica r ba -closo-d od eca bor a n -1-yl)m er cu r y (6).
To a solution of 3 (1.06 g, 3.30 mmol) in Et2O (40 mL) was
Syn th esis of 1-[(η5-Cyclop en ta d ien yl)d ica r bon ylir on ]-
1,12-d ica r ba -closo-d od eca bor a n e (3). To a solution of 1,-
12-dicarba-closo-dodecaborane (1.00 g, 6.93 mmol) in Et2O (30
t
added BuLi (1.2 M in pentane, 2.75 mL, 3.30 mmol) dropwise
n
mL) was added BuLi (1.6 M in hexanes, 4.33 mL, 6.93 mmol)
at -78 °C. After allowing toit was warmed to ambient
temperature and stirred for 5 h, the solution was cooled again
to -78 °C and mercury(II) chloride (0.450 g, 1.65 mmol) was
added at once. The solution was then heated at reflux for 24
h. After the solution was cooled to ambient temperature, the
solvent was removed in vacuo and the greenish yellow residue
was redissolved in benzene, the solution was extracted with
H2O (2 × 30 mL), and the organic phase was flashed through
activated basic alumina (Aldrich, Brockmann I, ∼150 mesh)
with petroleum ether/benzene (2:1) as the eluant. The yellow
first fraction was the unreacted starting material 3. The
remaining yellow fraction was flashed out of the column with
benzene and collected, and the solvent was removed, leaving
the powdery product 6 (0.67 g, 48%). 1H NMR (500 MHz, C6D6;
δ (ppm)): 3.71 (10H, s, Cp), 3.30-1.70 (20H, m, br, BH). 13C
NMR (125.8 MHz, C6D6; δ (ppm)): 214.33, 86.58, 62.11, 61.31.
11B{1H} NMR (160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)):
-6.25 (10B), -9.55 (10B). 199Hg{1H} NMR (89.6 MHz, C6H6,
1.0 M PhHgCl in [D6]DMSO external; δ (ppm)): -1163. FTIR
(CCl4 solution; cm-1): 2958, 2928, 2856, 2588, 2036, 1990.
HRMS (CI; m/z): calcd for C18H30B20Fe2HgO4, 839.2545; found,
839.2600 (M+).
dropwise at -78 °C. After it was warmed to ambient temper-
ature and stirred for 3 h, the solution was cooled again to -78
°C and (η5-cyclopentadienyl)iron dicarbonyl chloride (1.47 g,
6.93 mmol) was added at once. The solution was warmed to
ambient temperature and stirred for 15 h. Solvent was
removed in vacuo, and the reddish brown residue was redis-
solved in benzene, the solution was extracted with H2O (2 ×
30 mL), and the organic phase was flashed through activated
basic alumina (Aldrich, Brockmann I, ∼150 mesh) with
petroleum ether/benzene (2:1) as the eluant. The yellow first
fraction was collected, and the solvent was removed, leaving
the crystalline product 3 (1.53 g, 69%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 3.75 (5H, s, Cp), 3.20-1.80 (10H, m, br, BH),
2.17 (1H, s, br, CH). 13C NMR (125.8 MHz, C6D6; δ (ppm)):
214.29, 86.58, 64.67, 63.76. 11B{1H} NMR (160.5 MHz, C6D6,
BF3‚Et2O external; δ (ppm)): -8.53 (5B), -12.36 (5B). FTIR
(CCl4 solution; cm-1): 3065, 2961, 2926, 2855, 2607, 2036,
1990. HRMS (EI; m/z): calcd for C9H16B10FeO2, 322.1449;
found, 322.1460 (M+, monoisotopic mass).
Syn th esis of 1-[(η5-Cyclop en ta d ien yl)d ica r bon ylir on ]-
1,10-d ica r ba -closo-d eca bor a n e (4). To a solution of 1,10-
dicarba-closo-decaborane (1.00 g, 8.29 mmol) in Et2O (60 mL)
was added nBuLi (2.0 M in hexanes, 4.36 mL, 8.71 mmol)
dropwise at -78 °C. After it was warmed to ambient temper-
ature and stirred for 8 h, the solution was cooled again to -78
°C and (η5-cyclopentadienyl)iron dicarbonyl chloride (1.85 g,
8.71 mmol) was added at once. The solution was warmed to
ambient temperature and stirred for 26 h. The reaction
mixture was flashed through activated basic alumina (Aldrich,
Brockmann I, ∼150 mesh) with benzene as the eluant as a
workup procedure. The yellow first fraction was collected, and
the solvent was removed, leaving the crude product. Another
flash column was run through basic alumina as before, but
with petroleum ether as the eluting solvent. The yellow first
fraction was collected and the solvent was removed, leaving
the crystalline product 4 (1.52 g, 62%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 6.33 (1H, s, br, CH), 4.10 (5H, s, Cp), 2.90-
1.60 (8H, m, br, BH). 13C NMR (125.8 MHz, C6D6; δ (ppm)):
215.56, 96.22 (cage CH, only one observed), 86.73. 11B{1H}
NMR (160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)): -8.98
(4B), -11.10 (4B). FTIR (KBr; cm-1): 3100, 2957, 2924, 2854,
2590, 2031, 1975. HRMS (EI; m/z): calcd for C9H14B8FeO,2
297.1131; found, 297.1125 (M+).
Syn th esis of Bis(10,10′-[(η5-cyclopen tadien yl)dicar bon -
ylir on ]-1,10-d ica r ba-closo-d eca bor a n -1,1′-yl) m er cu r y (7).
To a solution of 4 (0.600 g, 2.02 mmol) in Et2O (40 mL) was
n
added BuLi (2.5 M in hexanes, 0.90 mL, 2.22 mmol) dropwise
at -78 °C. After it was warmed to ambient temperature and
stirred for 3 h, the solution was cooled again to -78 °C and
mercury(II) chloride (0.274 g, 1.01 mmol) was added at once.
The solution was warmed slowly to ambient temperature and
then was heated at reflux for 19 h. After the solution was
cooled to ambient temperature, the reaction mixture was
flashed through activated basic alumina (Aldrich, Brockmann
I, ∼150 mesh) with benzene as the eluant as a workup
procedure. Solvent was removed in vacuo, and another flash
column was run through basic alumina as before, but with
petroleum ether as the eluting solvent. An early yellow fraction
was collected and confirmed to be the unreacted starting
material 4. The remaining yellow fraction was flashed out of
the column with benzene and collected, and the solvent was
removed, leaving the powdery product 7 (0.120 g, 15%). 1H
NMR (500 MHz, C6D6; δ (ppm)): 4.18 (10H, s, Cp), 3.00-1.70
(16H, m, br, BH). 13C NMR (125.8 MHz, C6D6; δ (ppm)):
215.77, 86.80, (cage CH carbons not observed). 11B{1H} NMR
(160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)): -7.36 (8B),
-9.70 (8B). 199Hg{1H} NMR (89.6 MHz, C6H6, 1.0 M Ph2Hg in
CH2Cl2 external; δ (ppm)): -1028. FTIR (KBr; cm-1): 3118,
2956, 2925, 2854, 2572, 2029, 1974. HRMS: not determined.
Syn th esis of 1,12-Bis[(η5-cyclop en ta d ien yl)d ica r bon -
ylir on ]-1,12-d ica r ba -closo-d od eca bor a n e (8). To a solution
Syn th esis of 1-[(η5-Cyclop en ta d ien yl)(tr ip h en ylp h os-
ph in e)car bon ylir on ]-1,12-dicar ba-closo-dodecabor an e (5).
To a deoxygenated solution of 3 (0.500 g, 1.56 mmol) in dry
benzene (15 mL) in a quartz reaction vessel was added
triphenylphosphine (0.614 g, 2.34 mmol). This was photolyzed
with a mercury source UV lamp (Hanovia, 450 W, 250 nm)
for 3 h under an argon atmosphere. The reaction mixture was
flashed through activated basic alumina (Aldrich, Brockmann
I, ∼150 mesh) with benzene as the eluant as a workup
procedure. A red fraction was collected, and the solvent was
removed in vacuo, leaving the crude product, which was
recrystallized from benzene/heptane to give the red crystalline
t
of 3 (0.38 g, 1.19 mmol) in Et2O (50 mL) was added BuLi (1.7
M in pentane, 0.700 mL, 1.19 mmol) dropwise at -78 °C. After
it was warmed to ambient temperature and stirred for 3 h,
the solution was cooled again to 0 °C and (η5-cyclopentadienyl)-
iron dicarbonyl chloride (0.280 g, 1.32 mmol) was added at
once. The solution was heated at reflux for 20 h. The reaction
mixture was cooled to ambient temperature, and solvent was
removed in vacuo. The reddish brown residue was redissolved
in benzene, the solution was extracted with H2O (2 × 30 mL),
and the organic phase was flashed through activated basic
alumina (Aldrich, Brockmann I, ∼150 mesh) with petroleum
ether/benzene (2:1) as the eluant. The yellow first fraction was
confirmed to be the monosubstituted starting material 3. The
1
product 5 (0.839 g, 97%). H NMR (500 MHz, C6D6; δ (ppm)):
7.74 (3H, s, br), 7.38 (6H, s, br), 7.03 (6H, s, br), 3.93 (5H, s,
Cp), 3.10-1.80 (10H, m, br, BH), 2.21 (1H, s, br, CH). 13C-
{31P} NMR (125.8 MHz, C6D6; δ (ppm)): 214.67, 134.15 (d, J
) 19.5 Hz), 132.39 (d, J ) 9.7 Hz), 131.52 (d, J ) 2.5 Hz),
128.51 (d, J ) 11.8 Hz), 86.30, 65.13, 64.28. 11B{1H} NMR
(160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)): -8.48 (5B),

Metal-Metal Communication through Carborane Cages
Organometallics, Vol. 23, No. 3, 2004 489
remaining yellow fraction was flashed out of the column with
benzene. The solvent was removed, leaving the crystalline
product 8 (0.400 g, 67%). H NMR (500 MHz, C6D6; δ (ppm)):
Collection a n d Red u ction of X-r a y Da ta . All X-ray data
were collected using a Bruker SMART ccd diffractometer. Data
were corrected for Lorentz and polarization effects and for
absorption (5 and 9), but not for extinction. Intensities did not
decay during the course of the experiment. Programs used in
this work are those supplied with the Bruker SMART ccd
diffractometer. The isotropic displacement parameters for
hydrogen atoms were based on the values for the attached
atoms. Scattering factors for H were obtained from Stewart
et al.,13 and those for other atoms were taken from ref 14.
Collection a n d Solu tion of X-r a y Da ta for 1-[(η5-
Cyclop en t a d ien yl)(t r ip h en ylp h osp h in e)ca r b on ylir on ]-
1,12-d ica r ba -closo-d od eca bor a n e (5). A red crystalline
plate obtained from a heptane solution was mounted on a thin
glass fiber. Unit cell parameters were determined from a least-
squares fit of 905 reflections (5.17 < 2θ < 56.16°). These
dimensions and other parameters, including conditions of data
collection, are summarized in Table 2. Atoms were located by
use of heavy-atom methods. All non-hydrogen atoms were
included with anisotropic displacement parameters. All hy-
drogen atoms were kept in calculated positions.
Collection a n d Solu tion of X-r a y Da ta for 1,12-Bis[(η5-
cyclop en t a d ien yl)d ica r b on ylir on ]-1,12-d ica r b a -closo-
d od eca bor a n e (8). A yellow crystalline needle obtained from
a benzene/heptane solution was cut and mounted on a thin
glass fiber. Unit cell parameters were determined from a least-
squares fit of 894 reflections (4.94 < 2θ < 52.61°). Atoms were
located by use of statistical methods. With the exception of
the C2B10 moiety, all non-hydrogen atoms were included with
anisotropic displacement parameters. Position parameters
were refined for all cyclopentadienyl hydrogen atoms. Carbo-
ranyl hydrogen atoms were kept in calculated positions.
Collection a n d Solu tion of X-r a y Da ta for 1,10-Bis[(η5-
cyclop en ta d ien yl)d ica r bon ylir on ]-1,10-d ica r ba -closo-d e-
ca b or a n e (9). A yellow crystalline parallelepiped obtained
from a benzene/heptane solution was cut and mounted on a
thin glass fiber. Unit cell parameters were determined from a
least-squares fit of 905 reflections (6.32 < 2θ < 55.40°). Atoms
were located by use of statistical methods. With the exception
of the C2B8 moiety, all non-hydrogen atoms were included with
anisotropic displacement parameters. Positional parameters
were refined for all hydrogen atoms.
1
3.83 (10H, s, Cp), 3.30-2.15 (10H, m, br, BH). 13C NMR (125.8
MHz, C6D6; δ (ppm)): 214.74, 86.61, 61.11. 11B{1H} NMR
(160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)): -7.03 (10B).
FTIR (CCl4 solution; cm-1): 2956, 2928, 2856, 2581, 2033,
1987. HRMS (CI; m/z): calcd for C16H20B10Fe2O4, 496.1073;
found, 496.1080 (M+).
Syn th esis of 1,10-Bis[(η5-cyclop en ta d ien yl)d ica r bon yl-
ir on ]-1,10-d ica r ba -closo-d eca bor a n e (9). To a solution of
1,10-dicarba-closo-decaborane (0.500 g, 4.15 mmol) in Et2O (25
n
mL) was added BuLi (2.5 M in hexanes, 3.65 mL, 9.13 mmol)
dropwise at -78 °C. After it was warmed to ambient temper-
ature and stirred for 3 h, the solution was cooled again to -78
°C and (η5-cyclopentadienyl)iron dicarbonyl chloride (1.94 g,
9.13 mmol) was added at once. The solution was warmed again
to ambient temperature and stirred for 20 h. The reaction
mixture was flashed through activated basic alumina (Aldrich,
Brockmann I, ∼150 mesh) with benzene as the eluant as a
workup procedure. Solvent was removed in vacuo, and another
flash column was run through basic alumina as before, but
with petroleum ether/benzene (5:1) as the eluting solvent. An
early yellow fraction was collected and confirmed as the
monosubstituted compound 4. The remaining yellow fraction
was flashed out of the column with benzene. The solvent was
removed, leaving crude product 9, which was recrystallized
from benzene/heptane (0.730 g, 37%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 4.20 (10H, s, Cp), 2.90-1.80 (8H, m, br, BH).
13C NMR (125.8 MHz, C6D6; δ (ppm)): 216.03, 92.53, 86.71.
11B{1H} NMR (160.5 MHz, C6D6, BF3‚Et2O external; δ (ppm)):
-7.45 (8B). FTIR (KBr; cm-1): 3116, 2956, 2926, 2855, 2566,
2017, 1969. HRMS (EI; m/z): calcd for C16H18B8Fe2O4, 473.0697;
found, 473.0695 (M+).
Syn th esis of 1,12-Bis(2-[(η5-cyclopen tadien yl)dicar bon -
ylir on ]eth yn -1-yl)-1,12-d ica r ba-closo-d od eca bor a n e (10).
To a solution of 1,12-bis(ethynyl)-1,12-dicarba-closo-dodecabo-
rane (0.200 g, 1.04 mmol) in Et2O (15 mL) was added nBuLi
(2.5 M in hexanes, 0.920 mL, 2.29 mmol) dropwise at -78 °C.
After it was warmed to ambient temperature and stirred for
3 h, the solution was cooled again to -78 °C and (η5-
cyclopentadienyl)iron dicarbonyl chloride (1.94 g, 9.13 mmol)
was added at once. The solution was warmed again to ambient
temperature and was stirred for 20 h. As a workup procedure,
the reaction mixture was flashed through activated basic
alumina (Aldrich, Brockmann I, ∼150 mesh) with benzene as
the eluant. Solvent was removed in vacuo, and another flash
column was run through basic alumina as before, but with
petroleum ether/benzene (3:2) as the eluting solvent. An early
orange fraction eluted and was confirmed to be a mixture of
the monosubstituted compound and unreacted (η5-cyclopen-
tadienyl)iron dicarbonyl chloride. The remaining yellow frac-
tion was flashed out of the column with benzene. The solvent
was removed, leaving crude product 10, which was recrystal-
lized from benzene/heptane (0.200 g, 35%). 1H NMR (500 MHz,
C6D6; δ (ppm)): 3.80 (10H, s, Cp), 3.70-2.50 (10H, m, br, BH).
13C NMR (125.8 MHz, C6D6; δ (ppm)): 212.54, 84.77, (alkynyl
and carboranyl carbons not observed). 11B{1H} NMR (160.5
MHz, C6D6, BF3‚Et2O external; δ (ppm)): -11.45 (10B). FTIR
(KBr; cm-1): 3101, 2958, 2925, 2854, 2611, 2122, 2040, 1984.
HRMS (EI; m/z): calcd for C20H20B10Fe2O4, 544.1075; found,
544.1084 (M+).
Ack n ow led gm en t. We thank the National Science
Foundation (Grant Nos. CHE-9730006 and CHE-
9871332) for their support of the research described
herein.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances and angles, anisotropic thermal parameters, hydro-
gen coordinates and thermal parameters, torsion angles, and
hydrogen bonds; these data are also available in electronic
form as CIF files. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM030514H
(13) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J . Chem. Phys.
1965, 42, 3175.
(14) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV.