Synthesis and properties of structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron complexes: Modification on the bridge

Article abstract of DOI:10.1021/om8005905

A series of new structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron complex (η⁵, η⁵-C₅H₄XC₅H₄)Fe ₂(CO)₄, where X = MeSi[μ-(CH₂)₄] SiMe (3), CH₂SiMe₂ (7), and SiMe₂SiPh ₂ (10), were synthesized and their properties studied with emphasis on the thermal rearrangement that had been demonstrated to occur when X = SiMe₂SiMe₂. It was found that the presence of the cyclic structure on the Si-Si bridge for complex 3 prohibited the thermal rearrangement, but oxygen insertion into the Si-Si bond took place under thermal conditions to give the new Si-O-Si bridged complex {η⁵, η⁵-C₅H₄MeSi(μ-O)[μ-(CH ₂)₄]SiMeC₅H₄]Fe₂(CO) ₄ (4). Using CH₂SiMe₂ as the bridging group in complex 7 also resulted in failure of the rearrangement because the C-Si bond could not be activated by the iron center. Complex 10, with the unsymmetric bridging group SiMe₂SiPh₂, underwent thermal rearrangement, producing the expected product cyclic-[(Me₂Si- η⁵-C₅H₄)Fe(CO)₂(Ph ₂Si-η⁵-C₅H₄)Fe(CO)₂]- (11) with two Si-Fe bonds. When the reaction was performed in the presence of P(OPh)₃, incorporation of the phosphite ligand in the rearranged product took place, providing two regioisomers, cyclic-{(Me₂Si- η⁵-C₅H₄)Fe(CO)[P(OPh)₃](Ph ₂Si-η⁵-C₅H₄)Fe(CO)₂]- (12a) and cyclic-[(Me₂Si-η⁵-C₅H ₄)Fe(CO)₂(Ph₂Si-η⁵-C ₅H₄)Fe(CO)[P(OPh)₃]}- (12b), in a 1:1.8 ratio. The reaction of 10 with I₂ led to Fe-Fe bond cleavage, affording di-iodide (η⁵η⁵-C₅H₄Me ₂SiSiPh₂C₅H₄)[Fe(CO) ₂I]₂ (13). The molecular structures of 3, 4, 7, 10, 11, and 13 have been determined by X-ray diffraction methods.

Full text of DOI:10.1021/om8005905

Organometallics 2008, 27, 4505–4512
4505
Synthesis and Properties of Structural Variants of the Si-Si
Bridged Bis(cyclopentadienyl)tetracarbonyldiiron Complexes:
Modification on the Bridge
Huailin Sun,* Qiuhua Liu, Jianli Gu, Chengxun Zhang, Zhensheng Zhang, and
Qiuchang Wang
Department of Chemistry and the State Key Laboratory of Elemento-Organic Chemistry,
Nankai UniVersity, Tianjin 300071, People’s Republic of China
ReceiVed June 25, 2008
A series of new structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron complex
(η5,η5-C5H4XC5H4)Fe2(CO)4, where X ) MeSi[µ-(CH2)4]SiMe (3), CH2SiMe2 (7), and SiMe2SiPh2 (10),
were synthesized and their properties studied with emphasis on the thermal rearrangement that had been
demonstrated to occur when X ) SiMe2SiMe2. It was found that the presence of the cyclic structure on
the Si-Si bridge for complex 3 prohibited the thermal rearrangement, but oxygen insertion into the
Si-Si bond took place under thermal conditions to give the new Si-O-Si bridged complex {η5,η5-
C5H4MeSi(µ-O)[µ-(CH2)4]SiMeC5H4}Fe2(CO)4 (4). Using CH2SiMe2 as the bridging group in complex
7 also resulted in failure of the rearrangement because the C-Si bond could not be activated by the iron
center. Complex 10, with the unsymmetric bridging group SiMe2SiPh2, underwent thermal rearrangement,
producing the expected product cyclic-[(Me2Si-η5-C5H4)Fe(CO)2(Ph2Si-η5-C5H4)Fe(CO)2]- (11) with
two Si-Fe bonds. When the reaction was performed in the presence of P(OPh)3, incorporation of the
phosphite ligand in the rearranged product took place, providing two regioisomers, cyclic-{(Me2Si-η5-
C5H4)Fe(CO)[P(OPh)3](Ph2Si-η5-C5H4)Fe(CO)2}- (12a) and cyclic-{(Me2Si-η5-C5H4)Fe(CO)2(Ph2Si-η5-
C5H4)Fe(CO)[P(OPh)3]}- (12b), in a 1:1.8 ratio. The reaction of 10 with I2 led to Fe-Fe bond cleavage,
affording di-iodide (η5,η5-C5H4Me2SiSiPh2C5H4)[Fe(CO)2I]2 (13). The molecular structures of 3, 4, 7,
10, 11, and 13 have been determined by X-ray diffraction methods.
the reversible “twisting” reaction involving activation of the
C-H bond on the Cp ring,4,5 a series of topologically similar
skeleton rearrangements involving activation of the bridging
C-C, C-Si, and Si-Si bonds by the metal centers have been
reported (eqs 1-3).
Introduction
Ring-bridged bis-cyclopentadienyl bimetallic complexes (η5,η5-
C5H4XC5H4)M2(CO)4 (M ) Fe and Ru, X ) alkyl and silyl)
have received continuous attention during the past several
decades due to their unique structural and chemical properties.1
Interest in such complexes was initially focused on the structural
feature of the cis conformation due to the constraint of the two
cyclopentadienyl (Cp) groups by the bridging group and the
possible cooperative behaviors of the two metal centers located
in close proximity.2,3 Recently, a number of interesting new
reactions have been found to occur in such systems. Besides
* To whom correspondence should be addressed. E-mail: sunhl@
nankai.edu.cn. Tel: +86-22-2349 8132. Fax: +86-22-2349 8132.
(1) For some of the pioneering works, see:(a) Weiss, E.; Hu¨bel, W.
Chem. Ber. 1962, 95, 1186–1196. (b) King, R. B.; Bisnette, M. B. Inorg.
Chem. 1964, 3, 801–807. (c) Weaver, J.; Woodward, P. J. Chem. Soc.,
Dalton Trans. 1973, 1439–1443. (d) Tobita, H.; Habazaki, H.; Shimoi, M.;
Ogino, H. Chem. Lett. 1988, 1041–1044. (e) Cox, M. G.; Soye, P.; Manning,
A. R. J. Organomet. Chem. 1989, 369, C21–C22. (f) van den Berg, W.;
Cromsigt, J. A. M. T. C.; Bosman, W. P.; Smits, J. M. M.; de Gelder, R.;
Gal, A. W.; Heck, J. J. Organomet. Chem. 1996, 524, 281–284. (g)
Bitterwolf, T. E. J. Organomet. Chem. 1986, 312, 197–206. (h) Janda, K. D.;
McConnell, W. W.; Nelson, G. O.; Wright, M. E. J. Organomet. Chem.
1983, 259, 139–143. (i) Moran, M.; Pascual, M. C.; Cuadrado, I.; Losada,
J. Organometallics 1993, 12, 811–822.
(2) (a) Bryan, R. F.; Greene, P. T.; Newlands, M. J; Field, D. S. J. Chem.
Soc. (A) 1970, 3068–3074. (b) Cotton, F. A.; Kruczynski, L.; White, A. J.
Inorg. Chem. 1974, 13, 1402–1407. (c) Cotton, F. A.; Hunter, D. L.;
Lahuerta, P.; White, A. J. Inorg. Chem. 1976, 15, 557–564.
(3) (a) Wegner, P. A.; Uski, V. A.; Kiester, R. P.; Dabestani, S.; Day,
V. W. J. Am. Chem. Soc. 1977, 99, 4846–4848. (b) Nelson, G. O.; Wright,
M. E. J. Organomet. Chem. 1982, 239, 353–364. (c) Nelson, G. O.; Wright,
M. E Organometallics 1982, 1, 565–568. (d) Wegner, P. A.; Sterling, G. P.
J. Organomet. Chem. 1978, 162, C31–C34.
The first example is the photochemically induced rearrange-
ment of the diruthenium complex (η5,η5-C5H4-C5H4)Ru2(CO)4
with directly linked Cp rings, reported by Vollhardt and co-
(4) Bitterwolf, T. E.; Shade, J. E.; Hansen, J. A.; Rheingold, A. L. J.
Organomet. Chem. 1996, 514, 13–21.
(5) Burger, P. Angew. Chem., Int. Ed. 2001, 40, 1917–1919.
10.1021/om8005905 CCC: $40.75
2008 American Chemical Society
Publication on Web 08/15/2008

4506 Organometallics, Vol. 27, No. 17, 2008
Sun et al.
workers, which could be thermally reversed (eq 1).6 Another
example is the photochemical rearrangement of the silicon-
bridged diruthium complexes (η5,η5-C5R4SiMe2C5R4)Ru2(CO)4,
reported first by Bitterwolf and co-workers as a side process
and developed later by Burger into the clean reaction (eq 2).4,7
In 1993, we reported the synthesis of the first Si-Si bridged
diiron complex (η5,η5-C5H4Me2SiSiMe2C5H4)Fe2(CO)4, which
has resulted in the finding of the thermal rearrangement via
metathesis of the Si-Si and Fe-Fe bonds (eq 3).8,9 Since then,
considerable effort has been devoted to investigation of the scope
and mechanism of the thermal rearrangement. During this
course, many analogous complexes have been synthesized by
introducing various substituents onto the Cp rings and by using
phosphines and isocyanides to replace the CO ligand. Most of
these studies, however, have been restricted to the use of the
same Me2SiSiMe2 bridge, and little has been done for modifica-
tion of the bridge structure.
Scheme 1
Very recently, we have reported the use of the phenyl- and
n-butyl-substituted groups PhMeSiSiMePh and (n-Bu)MeSiSi-
Me(n-Bu) as the bridge for study of the stereochemistry of the
thermal rearrangement.8c Herein, we describe further modifica-
tion of the Si-Si bridge by using a series of novel bridging
groups, including MeSi[µ-(CH2)4]SiMe, with the Si-Si bond
being constrained by the cyclic structure, CH2SiMe2 with a
Si-C bond replacing the Si-Si bond, and SiMe2SiPh2 with an
unsymmetric Si-Si structure. The structural and chemical
properties of the new complexes were studied, which provided
helpful information for understanding the scope and some details
of the thermal rearrangement. It should be noted that the
syntheses of some of the complexes have been briefly mentioned
in the previous communication.10
the Fe-Fe bond (for a side view of the molecule, see Figure
S1 in the Supporting Information), which is similar to the trans
isomer of the (n-Bu)MeSiSiMe(n-Bu)-bridged complex8c and
is believed to be due to the Si-Si bond being longer than the
space between two the Cp groups on the top. The six-membered
ring on the bridge adopted a chair-like conformation. The length
of the Si-Si bond [2.306(2) Å] is shorter than that in the above
n-butyl-substituted complex [2.339(7) Å], while the Fe-Fe bond
[2.581(1) Å] is slightly longer than in the n-butyl case
[2.5518(16) Å].8c
One of the significant features of 3 was that it did not undergo
thermal rearrangement through metathesis of the Si-Si and
Fe-Fe bonds owing to the presence of the cyclic structure on
the bridge. It could be slowly transformed into a new product,
however, upon refluxing in p-xylene, as indicated by TLC
Results and Discussion
Complex with a Cyclic Structure on the Bridge. Synthesis
of the complex with a cyclic structure on the Si-Si bridge was
accomplished by using 1,2-dichloro-1,2-dimethyl-1,2-disilacy-
clohexane (1) as the starting material. Thus, the reaction of 1,
prepared by the literature procedures,11 with 2 equiv of
cyclopentadienyllithium provided the biscyclopentadienyl ligand
2; the latter reacted subsequently with pentacarbonyliron in
refluxing p-xylene, producing the desired complex 3(Scheme 1).
1H and 13C NMR analysis of the product indicated that it
was a single isomer, with either the cis or the trans conformation
for the two methyl groups at the Si-Si bridge. The molecular
structure determined by the X-ray diffraction method clearly
demonstrated that the two methyl groups were in a trans
relationship (Figure 1). The Si-Si bridge stayed on the top of
the molecule but twisted away from the direction parallel to
(6) (a) Vollhardt, K. P. C.; Weidman, T. W. J. Am. Chem. Soc. 1983,
105, 1676–1677. (b) Boese, R.; Cammack, J. K.; Matzger, A. J.; Pflug, K.;
Tolman, W. B.; Vollhardt, K. P. C.; Weidman, T. W. J. Am. Chem. Soc.
1997, 119, 6757–6773.
(7) Fox, T.; Burger, P. Eur. J. Inorg. Chem. 2001, 795–803.
(8) (a) Sun, H.; Xu, S.; Zhou, X.; Wang, H.; Yao, X. J. Organomet.
Chem. 1993, 444, C41–C44. (b) Sun, H.; Zhang, Z.; Pan, Y.; Yang, J.;
Zhou, X. Inorg. Chem. 2003, 42, 4076–4081. (c) Sun, H.; Pan, Y.; Huang,
X.; Guo, Z.; Zhang, Z.; Zhang, H.; Li, J.; Wang, F. Organometallics 2006,
25, 133–139.
(9) (a) Zhou, X.; Xie, W.; Xu, S. Chin. Chem. Lett. 1996, 7, 385–386.
(b) Xie, W.; Wang, B.; Dai, X.; Xu, S.; Zhou, X. J. Chem. Soc., Dalton
Trans. 1999, 1141–1146. (c) Zhang, Y.; Xu, S.; Zhou, X. Organometallics
1997, 16, 6017–6020.
(10) Sun, H.; Gu, J.; Zhang, Z.; Lin, H.; Ding, F.; Wang, Q. Angew.
Chem., Int. Ed. 2007, 46, 7498–7500.
Figure 1. ORTEP plot of 3 (30% probability level). Selected bond
lengths (Å) and angles (deg): Fe(1)-Fe(2) 2.581 (1), Si(1)-Si(2)
2.306(2); Si(1)-Si(2)-C(16) 109.08(13), Si(2)-Si(1)-C(9)
109.18(12).
(11) Tamao, K.; Kumada, M.; Ishikawa, M. J. Organomet. Chem. 1971,
31, 17–34.

Si-Si Bridged Tetracarbonyldiiron Complexes
Organometallics, Vol. 27, No. 17, 2008 4507
Scheme 2
Thus, we synthesized the first C-Si bridged bis-cyclocpen-
tadienyl complex, which was accomplished by using bromom-
ethyldimethylchlorosilane (5) as the starting material, which
reacted with 2 equiv of cyclopentadienyl lithium, producing the
bis-cyclopentadienyl ligand 6; the latter reacted subsequently
with pentacarbonyliron under thermal conditions, providing the
desired complex 7 (Scheme 2).
The molecular structure of 7 was determined by the X-ray
diffraction method (Figure 3). In the crystalline state, the
CH2SiMe2 bridge in the complex moved to one side of the
molecule, similar to the Me2SiSiMe2-bridged case,8a but the
carbon atom of the bridge was quite close to the top, as
the result of the shortening of the C-Si bridge (1.883 Å) as
compared to the Si-Si bond (2.346 Å).8a The two Cp groups
took a partially staggered conformation (for a side view of
the molecule, see Figure S3 in the Supporting Information).
The Fe-Fe bond (2.550 Å) is slightly longer than in the
Me2SiSiMe2-bridged complex (2.526 Å).8a All other bond
lengths and angles are normal, indicating that there is not
much strain in the molecule.
Figure 2. ORTEP plot of 4 (30% probability level). Selected bond
lengths (Å) and angles (deg): Fe(1)-Fe(2) 2.5386(14), Si(1)-O(5)
1.621(3), Si(2)-O(5) 1.622(3); Si(1)-O(5)-Si(2) 145.39(18).
monitoring of the reaction process. This product after isolation
was found to be complex 4, with the Si-O-Si bridge (Scheme
1). X-ray diffraction study revealed that the two methyl groups
on the Si-O-Si bridge of this complex were in a cis
relationship, indicating that inversion of the conformation on
the bridge has occurred (Figure 2). Compared with other cis-
conformed Si-Si bridged complexes previously reported, the
Si-O-Si bridge in this complex is tilted to a greater extent
toward one side of the molecule, due probably to the lengthening
of the bridge (for a side view of the molecule, see Figure S2 in
the Supporting Information). The two Cp groups were in a nearly
eclipsed conformation. The length of the Fe-Fe bond is
2.5386(14) Å, which is shorter than that before oxygen insertion.
Clearly, insertion of oxygen into the Si-Si bond has taken
place, and the conformation of the groups at the bridge has
inversed. Although the mechanism of the process has not been
clarified yet, it is likely that the oxygen insertion might be caused
by the trace amount of molecular oxygen in the inert gas, since
similar insertion of oxygen into the Si-Si bond of the starting
cyclic compound 1 has been found to facilely occur upon
exposure to the air. In addition, the change of the conformation
of the bridge might be attributed to the high reaction temperature
that would result in formation of thermal dynamic products.
These points will be addressed elsewhere in the future.
It was found that complex 7 did not undergo thermal
rearrangement when refluxed in p-xylene. This result remained
unchanged even after substitution of a CO ligand with
P(OPh)3,10 which has been well known to be able to accelerate
Complex with the C-Si Bridge. In the past, the thermal
rearrangement of the Si-Si bridged bis(cyclopentadienyl)diiron
complexes has been found to extensively occur. However,
whether such rearrangement could take place for the C-Si bond
bridged analogous complex has never been tested. In fact, there
has never been any report of C-Si bridged bis-cyclopentadienyl
bimetallic complexes, although a large number of C-C and
Si-Si bridged systems exist in the literature. To our knowledge,
the only report of the C-Si bridged complexes was the bis-
fluorenyl zirconium and hafnium mononuclear compounds.12,13
Figure 3. ORTEP plot of 7 (30% probability level). Selected bond
lengths (Å) and angles (deg): Fe(1)-Fe(2) 2.550(2), Si(1)-C(10)
1.883(3),C(10)-C(11)1.475(8),Si(1)-C(5)1.881(7);Si(1)-C(10)-C(11)
120.8(4), C(10)-Si(1)-C(5) 107.8(3).
(12) Schertl, P.; Alt, H. G. J. Organomet. Chem. 1997, 545-546, 553–
557.
(13) Leino, R.; Luttikhedde, H. J. G.; Lehtonen, A.; Wilen, C.-E.;
Nasman, J. H. J. Organomet. Chem. 1997, 545-546, 219–224.

4508 Organometallics, Vol. 27, No. 17, 2008
Sun et al.
Scheme 3
the thermal rearrangement.14 This means that the C-Si bond
could not be activated by the iron center, according to the
previously suggested mechanism of thermal rearrangement,8c
which is also in accordance with the notion that the C-Si bond
should be much more difficult to activate by transition metals
than Si-Si bonds.15
Figure 4. ORTEP plot of 10 (30% probability level). Selected bond
lengths (Å) and angles (deg): Fe(1)-Fe(2) 2.5593(7), Si(1)-Si(2)
2.3348(11),Si(1)-C(9)1.874(3),Si(2)-C(24)1.877(3);Si(2)-Si(1)-C(9)
108.02(9), Si(1)-Si(2)-C(24) 106.45(9).
Complex with the Unsymmetric Si-Si Bridge. Previous
works on the Si-Si bridged complexes were restricted to the
use of symmetric bridges, such as Me2SiSiMe2, (n-Bu)MeSiSi-
Me(n-Bu), and PhMeSiSiMePh. The synthesis of the first
unsymmetric Si-Si bridged complex was accomplished here
by using 1,2-dichloro-1,1-diphenyl-2,2-dimethyldisilane (8) as
the starting material, which reacted with cyclopentadienyllithium
and then with pentacarbonyliron in a similar fashion to those
described above. Complex 10 was obtained as dark red crystals.
Meanwhile, the rearranged product 11 was obtained as yellow
crystals. The rearrangement from 10 to 11 was confirmed by
heating of the former in refluxing p-xylene (Scheme 3).
Both complexes were fully characterized and their molecular
structures determined by X-ray diffraction methods. Complex
10 (Figure 4) took a conformation very similar to that of the
parent complex with the Me2SiSiMe2 bridge; that is, the Si-Si
bond stayed on the top of the molecule but twisted away from
the direction parallel to the Fe-Fe bond (for a side view of the
molecule, see Figure S4 in the Supporting Information). This
has been attributed to fact that the Si-Si bond is somewhat
longer than the space between the two Cp groups. The Si-Si
bond (2.3348 Å) is slightly shorter than that in the parent
complex (2.346 Å), while the Fe-Fe bond (2.5593 Å) is a little
longer than in the same complex (2.526 Å).8c
Figure 5. ORTEP plot of 11 (30% probability level). Selected bond
lengths (Å) and angles (deg): Si(1)-Fe(2) 2.3093(10), Si(2)-Fe(1)
2.3200(9),Si(1)-C(9)1.879(3),Si(2)-C(16)1.899(3);Fe(1)-Si(2)-C(16)
111.72(9), Fe(2)-Si(1)-C(9) 112.88(9).
Complex 11 took a chair-like conformation for the six-
membered ring of the skeleton (Figure 5). The lengths of the
two Si-Fe bonds have little difference, with one (2.3200 Å)
slightly longer than the other (2.3093 Å), due to the steric
reasons. Both bonds are much shorter than the lengths of either
Si-Si or Fe-Fe bonds, indicating the extraordinary stability
of the Si-Fe linkage, which is believed to be one of the major
driving forces for the thermal rearrangement.
Si-Si bridged complex 10 was also performed in the presence
of the phosphite ligand P(OPh)3. A pair of cis and trans isomers,
12a and 12b, were obtained through incorporation of the
phosphite into the rearranged products (Scheme 4). The ratio
of 12a and 12b was about 1:1.8; that is, the trans isomer, having
the phosphite ligand and the larger SiPh2 group at opposite sides,
was produced preferentially.
The incorporation of the phosphite ligand into the rearranged
products should be accomplished by ligand substitution prior
to the rearrangement, according to our previous knowlegde.14
Such ligand substitution would produce two regioisomers, 10′a
and 10′b (Scheme 4), in nearly equal amounts that should be
Properties of the New Me2SiSiPh2-Bridged Complex. The
thermal rearrangement of the newly obtained unsymmetric
(14) Sun, H.; Teng, X.; Huang, X.; Hu, Z.; Pan, Y. J. Organomet. Chem.
2000, 595, 268–275.
(15) Zhang, Z.; Gu, J.; Zhang, C.; Sun, H. Organometallics 2008, 27,
2149–2151.

Si-Si Bridged Tetracarbonyldiiron Complexes
Organometallics, Vol. 27, No. 17, 2008 4509
Scheme 4
techniques. THF and p-xylene were distilled from sodium/ben-
zophenone. Chloroform was dried by refluxing over P2O5 and
distilled under an inert atmosphere. Elemental analysis was
performed using an Elementary Vario EL instrument. IR spectra
were recorded with a Magna-560 FT-IR spectrometer. 1H and 13
C
NMR spectra were recorded with Varian Unity Plus-400 and Bruker
Avance 300 spectrometers. 1,2-Dichloro-1,2-diphenyl-1,2-disila-
cyclohexane (1) and ClPh2SiSiMe2Cl (8) were prepared according
to the literature procedures. BrCH2SiMe2Cl (5) was purchased from
Alderich.
Synthesis of {η5,η5-C5H4MeSi[µ-(CH2)4]SiMeC5H4}Fe2(CO)4(3).
A 3.63 g (17 mmol) amount of 1,2-dichloro-1,2-diphenyl-1,2-
disilacyclohexane (1) was added dropwise to a solution of cyclo-
pentadienyllithium prepared from 3.51 g (53 mmol) of cyclopen-
tadiene and 28 mL of n-butyllithium (1.45 M, 41 mmol) in 45 mL
of THF at -78 °C. The resulting mixture was allowed to warm to
room temperature and stirred overnight. It was then heated at reflux
for 7 h. After cooling to room temperature, it was hydrolyzed with
a saturated solution of ammonium chloride, extracted three times
with 100 mL of ether, and then dried over anhydrous magnesium
sulfate. Removing the solvent under reduced pressure afforded a
crude product of 1,2-dicyclopentadienyl-1,2-diphenyl-1,2-disilacy-
clohexane (2) as an oil, which was used directly for the next reaction
without further purification.
in fast equilibrium owing to migration of the phosphite ligand
between two iron centers.10 Their subsequent rearrangements
leading to preferential formation of the trans rearranged product
may be rationalized on the basis of our previously suggested
mechanism of the thermal rearrangement,8c by the fact that the
initial formation of the Si-Fe bond between the phosphite-
substituted iron and the silicon should be the rate-determining
step of the rearrangement process and that in this step there
should be much less steric hindrance between P(OPh)3 and
SiMe2 for the formation of the trans product than between
P(OPh)3 and SiPh2 for the formation of the cis isomer.
The reaction of 10 with molecular iodine was performed also,
which produced the di-iodide 13 through cleavage of the Fe-Fe
bond (eq 4). The molecular structure of this molecule determined
by the X-ray diffraction method showed that the Si-Si bond
(2.367 Å) is slightly longer than that before breaking of the
cyclic structure (2.335 Å) (Figure 6). This demonstrates once
again that there is no obvious molecular strain on the bridge of
the complex.8b
The oil product obtained above was added into a 250 mL flask
containing 80 mL of p-xylene and 10 g (52 mmol) of pentacarbo-
nyliron. The resulting mixture was refluxed for 11 h. After cooling
to room temperature, the solvent was removed under reduced
pressure (unreacted pentacarbonyliron should be collected in a liquid
nitrogen trap!) to give a semisolid residue. This residue was
dissolved in a minimum amount of benzene and purified through a
column (silica, petroleum ether/dichloromethane, 2:1, v/v). Col-
lection of the red band afforded 310 mg of 3 (4% total yield) as
dark red crystals, mp 252-253 °C. IR (KBr): νCO 1760 (s), 1941
1
(s), 1989 (s) cm-1. H NMR (CDCl3): δ 0.55 (s, 6H, CH3), 0.65
(m, 2H, CH2), 1.00 (m, 2H, CH2), 1.26 (m, 2H, CH2), 2.02 (m,
2H, CH2), 4.98 (s, 2H, Cp), 5.08 (s, 2H, Cp), 5.29 (s, 2H, Cp),
5.40 (s, 2H, Cp). 13C NMR (CDCl3): δ -6.51 (CH3), 17.00 (CH2),
26.03 (CH2), 84.89 (Cp), 87.71 (Cp), 87.85 (Cp), 100.30 (Cp),
101.16 (Cp), 209.48 (terminal CO), 271.40 (bridging CO). Anal.
Calcd for C20H22O4Si2Fe2: C, 48.60; H, 4.49. Found: C, 48.61; H,
4.58.
Synthesis of {η5,η5-C5H4MeSi(µ-O)[µ-(CH2)4]SiMeC5H4}Fe2-
(CO)4(4). To a 100 mL flask was added 110 mg (0.24 mmol) of 3
and 20 mL of p-xylene. The mixture was refluxed for 18 h while
stirring magnetically. After cooling to room temperature, the solvent
was removed under reduced pressure. The residue was dissolved
in a small amount of dichloromethane and separated through a
column (neutral alumina). Elution with the mixed solvent of
petroleum ether and dichloromethane (v/v ) 1:1) gave a red band,
from which 8 mg (7% yield) of 4 was obtained as dark red crystals,
mp 115-116 °C. IR (KBr): νCO 1778 (s), 1815 (w), 1946 (s), 1996
Concluding Remarks. A variety of structural variants of the
Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron com-
plexes have been synthesized and their structures and properties
studied, providing helpful information for complete understand-
ing of the scope and the details of the thermal rearrangement.
Further effort for final clarification of the reaction mechanism
should be directed toward isolation or trapping of the reactive
intermediates after activation of the Si-Si bond by the metal
center.8c Such study would be of interest because it might
provide useful knowledge for activation of other stable σ-bonds
such as C-Si and C-C in related systems.
1
(s) cm-1. H NMR (CDCl3): δ 0.39 (s, 6H, CH3), 0.80 (m, 4H,
CH2), 1.68 (m, 4H, CH2), 4.27 (s, 2H, Cp), 5.03 (s, 2H, Cp), 5.27
(s, 2H, Cp), 5.49 (s, 2H, Cp). 13C NMR (CDCl3): δ -0.50 (CH3),
18.29 (CH2), 24.61 (CH2), 89.31 (Cp), 89.77 (Cp), 92.32 (Cp), 92.76
(Cp), 96.67 (Cp), 210.12 (terminal CO), 267.94 (bridging CO),
271.23 (bridging CO). Anal. Calcd for C20H22O5Si2Fe2: C, 47.08;
H, 4.35. Found: C, 47.36; H, 4.55.
Synthesis of (η5,η5-C5H4CH2SiMe2C5H4)Fe2(CO)4(7). To a 500
mL flask containing 15.6 g (0.20 mol) of cyclopentadiene and 180
mL of THF was added 14 mL (1.77 M, 25 mmol) of a solution of
n-butyllithium in hexane at -78 °C. The mixture was stirred at
room temperature for 1 h. It was then cooled to -78 °C once again,
and 12.2 g (65 mmol) of BrCH2SiMe2Cl in 60 mL of THF was
added dropwise. The mixture was allowed to warm to room
temperature and stirred overnight. It was then refluxed for 9 h. After
Experimental Section
General Procedures. All reactions were carried out under a
nitrogen or argon atmosphere using vacuum line and Schlenk

4510 Organometallics, Vol. 27, No. 17, 2008
Sun et al.
Figure 6. ORTEP plot of 13 (30% probability level). Selected bond lengths (Å) and angles (deg): Si(1)-Si(2) 2.3666(16), Fe(1)-I(1)
2.5986(8), Fe(2)-I(2) 2.6091(7), Si(1)-C(9) 1.892(4), Si(2)-C(24) 1.885(4); Si(1)-Si(2)-C(24) 100.83(13), Si(2)-Si(1)-C(9) 113.89(13).
Table 1. Crystal Data and Structure Refinement for 3, 4, and 7
3
4
7
formula
fw
C20H22Fe2O4Si2
494.26
C20H22Fe2O5Si2
510.26
C17H16O4Fe2Si
424.09
temperature [K]
cryst syst
space group
a [Å]
b [Å]
c [Å]
294(2)
113(2)
monoclinic
P2(1)/n
15.109(9)
8.955(5)
16.008(9)
90
109.277(8)
90
2044(2)
4
1.658
1.566
293(2)
monoclinic
P2(1)/n
7.876(5)
25.804(8)
8.950(6)
90
108.951(13)
90
triclinic
j
P1
7.747(4)
10.621(5)
14.710(7)
85.807(6)
78.435(8)
68.61
1104.2(9)
2
1.480
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
Z
1720.3(17)
4
1.637
Fcalc [g/cm-3
]
µ [mm-1
]
1.444
1.773
cryst size [mm]
θ range [deg]
index ranges
0.24 × 0.20 × 0.12
1.41 to 25.02
-8 e h e 9
-12 e k e 11
-17 e l e 16
5539
0.24 × 0.22 × 0.20
1.61 to 27.77
-19 e h e 19
-11 e k e 11
-20e l e 20
18 399
0.32 × 0.20 × 0.18
2.53 to 26.44
-8 e h e 9
-23e k e 32
-11 e l e 10
9481
no. of reflns collected
no. of indep reflns
3861
4730
3435
no. of obsd reflns [I g 2σ(I)]
no. of params
2487
384
4015
265
1627
219
goodness of fit
1.021
1.129
0.925
R1 indices (obsd data)
wR2 indices (obsd data)
0.0404
0.0815
0.525/-0.294
0.0590
0.1088
0.454/-0.536
0.0693
0.1106
0.665/-0.661
largest diff peak/hole [e Å-3
]
cooling to room temperature, the mixture was hydrolyzed with a
saturated solution of ammonium chloride, extracted with ether,
washed with water, and dried over anhydrous magnesium sulfate.
Evaporation of the solvent under reduced pressure gave 12.8 g of
the crude product 6 as an oil, which was used directly for the next
reaction without further purification.
alumina column. Elution with petroleum ether/dichloromethane (2:
1) gave a red band, from which 0.93 g of 7 (22% yield) was
obtained as dark red crystals,16 mp 184-186 °C. IR (KBr): νCO
1
1982 (s), 1937 (s), 1810 (s), 1770 (s) cm-1. H NMR (CDCl3): δ
0.22 (s, 6H, SiMe2), 1.46 (s, 2H, CH2), 4.64 (m, 2H, C5H4), 4.86
(m, 2H, C5H4), 5.12 (m, 2H, C5H4), 5.42 (m, 2H, C5H4). 13C NMR
(CDCl3): δ -1.04 (SiMe2), 14.12 (CH2), 82.62 (C5H4), 83.66
(C5H4), 96.70 (C5H4), 88.77 (C5H4), 94.53 (C5H4), 99.46 (C5H4),
99.82 (C5H4), 102.75 (C5H4), 209.82 (terminal CO), 209.93
(terminal CO), 272.93 (bridging CO). Anal. Calcd for
C17H16O4Fe2Si: C, 48.11; H, 3.77. Found: C, 47.94; H, 3.55.
Synthesis of (η5,η5-C5H4SiMe2SiPh2C5H4)Fe2(CO)4(10). A 7.84 g
(25 mmol) amount of ClPh2SiSiMe2Cl was added dropwise to a
solution of cyclopentadienyllithium, prepared from 5.05 g (77
mmol) of cyclopentadiene and 40 mL of n-butyllithium (1.50 M,
60 mmol) in 120 mL of THF at -78 °C. The resulting mixture
was allowed to warm to room temperature and then stirred
To a 250 mL flask containing 100 mL of p-xylene were added
the oil product obtained above and 33.0 g (0.17 mol) of pentacar-
bonyliron. The mixture was refluxed for 20 h. After cooling to room
temperature, the solvent was removed under reduced pressure
(unreacted pentacarbonyliron should be collected in a liquid nitrogen
trap!) to give a solid residue, which was purified through a neutral
(16) The structure assignment of the byproduct in a previous study of
7, without support of X-ray diffraction data, appears now to be incorrect.
Therefore, its structure still remains to be determined. See: Sun, H.; Zang,
H.; Zang, Z. Chin. J. Chem. 2006, 24, 1476–1479.

Si-Si Bridged Tetracarbonyldiiron Complexes
Organometallics, Vol. 27, No. 17, 2008 4511
Table 2. Crystal Data and Structure Refinement for 10, 11, and 13
10
11
13
formula
fw
C28H24Fe2O4Si2
592.35
C28H24Fe2O4Si2
592.35
C28H24Fe2I2O4Si2
846.15
temperature [K]
cryst syst
space group
a [Å]
b [Å]
c [Å]
294(2)
294(2)
monoclinic
P2(1)/n
10.4845(18)
11.743(2)
21.997(4)
90
93.391(3)
90
294(2)
triclinic
triclinic
j
j
P1
P1
10.1855(17)
11.2228(19)
12.895(2)
77.310(3)
69.295(3)
78.967(3)
1334.6(4)
2
10.1097(17)
11.2601(18)
14.787(2)
82.990(2)
81.164(3)
69.457(2)
1553.3(4)
2
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
Z
2703.5(8)
4
1.455
Fcalc [g/cm-3
]
1.474
1.209
1.809
3.029
µ [mm-1
]
1.194
cryst size [mm]
θ range [deg]
index ranges
0.26 × 0.16 × 0.14
1.71 to 25.01
-6 e h e 12
-13 e k e 13
-15 e l e 15
6811
0.24 × 0.18 × 0.12
1.85 to 26.37
-13 e h e 8
-13 e k e 14
-25 e l e 27
14 844
0.24 × 0.20 × 0.12
1.40 to 25.01
-12 e h e 9
-12 e k e 13
-17 e l e 16
7941
no. of reflns collected
no. of indep reflns
4680
5486
5435
no. of obsd reflns [I g 2σ(I)]
no. of params
3613
327
3859
327
4004
345
goodness of fit
1.041
1.016
1.001
R1 indices (obsd data)
wR2 indices (obsd data)
0.0324
0.0784
0.303/-0.268
0.0361
0.0797
0.579/-0.441
0.0310
0.0643
0.425/-0.589
largest diff peak/hole [e Å-3
]
overnight. After refluxing for 2 h, it was cooled to room temperature
again. It was then hydrolyzed with 150 mL of a saturated solution
of ammonium chloride, extracted three times with 100 mL of ether,
and dried with anhydrous magnesium sulfate. Removing the solvent
under reduced pressure afforded the crude product of 9 as an oil,
which was used directly in the next reaction without further
purification.
The oil product obtained above was added into a 250 mL flask
containing 100 mL of p-xylene and 10 g (52 mmol) of pentacar-
bonyliron. The resulting mixture was refluxed for 8 h. After cooling
to room temperature, the solvent was removed under reduced
pressure (unreacted pentacarbonyliron should be collected in a liquid
nitrogen trap!) to give a semisolid residue, which was dissolved in
a small amount of benzene and purified through a silica column.
Elution with petroleum ether/dichloromethane (4:1, v/v) afforded
a yellow band, from which 0.35 g of compound 11 (2.3% total
yield) was obtained as yellow crystals (for the data of the complex,
see below).
5.02 (m, 2H, C5H4), 5.08 (m, 2H, C5H4), 5.24 (m, 2H, C5H4), 5.24
(m, 2H, C5H4), 7.28 (m, 6H, Ph), 7.40 (m, 4H, Ph). 13C NMR
(CDCl3): δ 6.96 (SiMe2), 84.00 (C5H4), 84.48 (C5H4), 93.46 (C5H4),
93.64 (C5H4), 94.95 (C5H4), 97.67 (C5H4), 127.53 (Ph), 128.48 (Ph),
135.33 (Ph), 142.44 (Ph), 215.22 (CO), 215.38 (CO). Anal. Calcd
for C28H24Si2Fe2O4: C, 56.77; H, 4.08. Found: C, 56.85; H, 4.00.
Synthesis of cyclo-{(Me2Si-η5-C5H4)Fe(CO)[P(OPh)3](Ph2Si-η5-
C5H4)Fe(CO)2}- (12a) and cyclo-{(Me2Si-η5-C5H4)Fe(CO)2(Ph2Si-
η5-C5H4)Fe(CO)[P(OPh)3]}- (12b). To a 50 mL flask were added
125 mg (0.21 mmol) of 10, 335 mg (1.1 mmol) of P(OPh)3, and
20 mL of p-xylene. The mixture was refluxed for 3 h, while stirring
magnetically. After removal of the solvent under reduced pressure,
the residue was dissolved in a small amount of dichloromethane
and separated through a column (neutral alumina). Elution with
petroleum ether/ dichloromethane (v/v ) 1:1) gave a light yellow
band, from which 145 mg (78% yield) of a mixture of 12a and
12b was obtained as a yellow crystalline solid. The ratio of the
two isomers was determined by 1H NMR spectroscopy to be 1:1.8.
Fractional crystallization of the mixture at -20 °C gave pure
crystals of 12a first and then 12b. 12a: mp 198-201 °C. IR (KBr):
Further elution with petroleum ether/dichloromethane (1:1, v/v)
gave a red band, from which 3.5 g of compound 10 (24% total
yield) was obtained as dark red crystals, mp 189-190 °C. IR (KBr):
ν
CO 1932 (vs), 1946 (s), 1991 (s) cm-1. 1H NMR (CDCl3): δ 0.59
ν
CO 1987 (s), 1942 (m), 1766 (s) cm-1. 1H NMR (CDCl3): δ 0.36
(s, 3H, SiMe2), 0.60 (s, 3H, SiMe2), 4.28 (m, 1H, Cp), 4.38 (m,
1H, Cp), 4.79 (m, 1H, Cp), 4.91 (m, 1H, Cp), 4.96 (m, 1H, Cp),
5.16 (m, 1H, Cp), 5.30 (m, 2H, Cp), 7.00 (d, J ) 7.8 Hz, 6H, Ph),
7.08-7.29 (m, 17H, Ph), 7.45 (m, 2H, Ph). 13C NMR (CDCl3): δ
6.81 (Me), 8.87 (Me), 80.70 (C5H4), 83.53 (C5H4), 83.88 (C5H4),
84.46 (C5H4), 90.56 (C5H4), 92.13 (C5H4), 93.81 (C5H4), 95.03
(C5H4), 96.13 (C5H4), 101.24 (C5H4), 121.08 (Ph), 124.35 (Ph),
126.99 (Ph), 127.23 (Ph), 127.74 (Ph), 128.11 (Ph), 129.48 (Ph),
135.12 (Ph), 135.43 (Ph), 142.55 (Ph), 143.93 (Ph), 152.01 (J )
11.6 Hz, Ph), 215.42 (CO), 216.08 (CO). Anal. Calcd for
C45H39Si2Fe2O6P: C, 61.80; H, 4.49; Found: C, 61.95; H, 4.47. 12b:
(s, 6H, SiMe2), 4.92 (m, 2H, C5H4), 4.95 (m, 2H, C5H4), 5.41 (m,
2H, C5H4), 5.45 (m, 2H, C5H4), 7.38 (m, 6H, Ph), 7.44 (m, 4H,
Ph). 13C NMR (CDCl3): δ -1.378 (SiMe2), 87.21 (C5H4), 87.44
(C5H4), 87.68 (C5H4), 90.14 (C5H4), 98.29 (C5H4), 99.34 (C5H4),
128.36 (Ph), 129.76 (Ph), 134.10 (Ph), 135.84 (Ph), 209.60 (terminal
CO), 209.65 (terminal CO), 271.19 (bridging CO). Anal. Calcd for
C28H24Si2Fe2O4: C, 56.77; H, 4.08. Found: C, 56.77; H, 3.87.
Synthesis of cyclo-[(Me2Si-η5-C5H4)Fe(CO)2(Ph2Si-η5-C5H4)-
Fe(CO)2]- (11). To a 50 mL flask was added 88 mg (0.15 mmol)
of 10 and 20 mL of p-xylene. The mixture was refluxed for 8 h
while stirring magnetically. After cooling to room temperature, the
solvent was removed under reduced pressure. The residue was
dissolved in a small amount of dichloromethane and separated
through a column (neutral alumina). Elution with petroleum ether
gave a light yellow band, from which 33 mg (38% yield) of 11
was obtained as yellow crystals, mp 194-195 °C. IR (KBr): νCO
1990 (s), 1929 (m) cm-1. 1H NMR (CDCl3): δ 0.50 (s, 6H, SiMe2),
mp 205-207 °C. IR (KBr): νCO 1928 (vs), 1985 (s), 1990 (s) cm-1
.
1H NMR (CDCl3): δ 0.44 (s, 3H, SiMe2), 0.49 (s, 3H, SiMe2),
4.30 (m, 1H, Cp), 4.72 (m, 1H, Cp), 4.88 (m, 1H, Cp), 4.91 (m,
1H, Cp), 4.94 (m, 1H, Cp), 5.16 (m, 1H, Cp), 5.29 (m, 1H, Cp),
5.35 (m, 1H, Cp), 6.65 (d, J ) 7.2 Hz, 6H, Ph), 7.00 (m, 4H, Ph),
7.08-7.13 (m, 11H, Ph), 7.45 (m, 2H, Ph), 7.59 (m, 2H, Ph). 13C
NMR (CDCl3): δ 6.58 (Me), 7.31 (Me), 81.88 (C5H4), 84.48 (C5H4),

4512 Organometallics, Vol. 27, No. 17, 2008
Sun et al.
83.22 (C5H4), 83.37 (C5H4), 83.55 (C5H4), 89.72 (C5H4), 93.11
(C5H4), 94.01 (C5H4), 94.74 (C5H4), 95.10 (C5H4), 96.93 (C5H4),
120.95 (Ph), 124.16 (Ph), 126.71 (Ph), 126.81 (Ph), 127.25 (Ph),
127.63 (Ph), 129.19 (Ph), 136.44 (Ph), 136.78 (Ph), 144.36 (Ph),
144.96 (Ph), 152.97 (J ) 13.0 Hz, Ph), 215.51 (CO), 215.63 (CO),
218.19 (J ) 41 Hz, CO). Anal. Calcd for C45H39Si2Fe2O6P: C,
61.80; H, 4.49. Found: 61.80; 4.34.
(Ph), 212.67 (CO), 213.16 (CO). Anal. Calcd for C28H24Si2Fe2O4I2:
C, 39.75; H, 2.84. Found: C, 39.28; H, 3.15.
X-ray Crystallography. Single crystals of 3, 4, 7, 10, 11, and
13 suitable for X-ray diffraction analyses were obtained from
hexane/CH2Cl2 solvents. Data collections were performed on a
Bruker SMART 1000 diffractometer, using the 2θ/ω scan technique
with Mo KR (λ ) 0.71073 Å) radiation. All structures were solved
by direct methods and refined using standard least-squares and
Fourier techniques. Non-hydrogen atoms are refined with aniso-
tropic thermal parameters. Hydrogen atoms were added theoretically
and refined with isotropic thermal parameters. Crystal and structure
refinement data are shown in Tables 1 and 2.
Synthesis of (η5,η5-C5H4Me2SiSiPh2C5H4)[Fe(CO)2I]2(13). To a
50 mL flask were added 107 mg (0.18 mmol) of 10 and a solution
of I2 in CHCl3 (27 mg/mL, 1.7 mL, 0.18 mmol). The mixture was
magnetically stirred for 1 h and washed three times with a saturated
solution of sodium sulfite and then another three times with water.
The resulting solution was dried over sodium sulfate. After removal
of the solvent, the residue was dissolved in a small amount of
dichloromethane and separated through a column (neutral alumina).
Elution with petroleum ether/chloroform (v/v; 1:1) gave a brown
band, from which 91 mg (60% yield) of 13 was obtained as dark
brown crystals, mp 126-127 °C. IR (KBr): 2040 (s), 2029(s) 2001
(s), 1978 (s) cm-1.1H NMR (CDCl3): δ 0.70 (s, 6H, SiMe2), 4.71
(m, 2H, Cp), 4.88 (m, 2H, Cp), 5.05 (m, 2H, Cp), 5.28 (m, 2H,
Cp), 7.46 (m, 10H, Ph). 13C NMR (CDCl3): δ -2.01, -1.95
(SiMe2), 83.50 (Cp), 84.56 (Cp), 85.67 (Cp), (Cp), 87.46 (Cp), 92.73
(Cp), 93.58 (Cp), 128.64 (Ph), 130.56 (Ph), 132.16 (Ph), 136.03
Acknowledgment. We thank the National Natural Science
Foundation of China (Nos. 20372036 and 20421202), the
Natural Science Foundation of Tianjin (no. 08JCZD-
JC21600), and the Ministry of Education of China (no.
03406) for financial support.
Supporting Information Available: The side views of the
molecular structures of 3, 4, 7, and 10, and CIF files giving X-ray
structural data for complexes 3, 4, 7, 10, 11, and 13. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM8005905