Photochemical ring-contraction of a tetrasilaferracyclohexane of the (η5-C5H4)Fe(CO)2 system to trisilaferracyclopentanes

Article abstract of DOI:10.1021/om060320c

Treatment of (η⁵-C₅H₅)Fe(CO) ₂(SiMe₂)_nCl (n = 3, 4) with lithium diisopropylamide leads directly to new trisila- (1) and tetrasilaferracycles (2) [(η⁵-C₅H₄)Fe(CO)₂(SiMe ₂)_n]. The trisilaferracycle (1) exhibits a degree of ring strain as noted by ²⁹Si NMR spectroscopy and single-crystal X-ray analysis but is stable with respect to limited attempts at ring-opening polymerization and photochemical transformation. In contrast, 2, with no ring strain, readily transforms via photochemical irradiation by way of iron silyl-(silylenes) to a trimethylsilyl-substituted trisilaferracycle 4, which in turn transforms to 1 upon prolonged irradiation.

Full text of DOI:10.1021/om060320c

Organometallics 2006, 25, 3969-3973
3969
Photochemical Ring-Contraction of a Tetrasilaferracyclohexane of
the (η5-C5H4)Fe(CO)2 System to Trisilaferracyclopentanes
Hemant K. Sharma, Francisco Cervantes-Lee, and Keith H. Pannell*
Department of Chemistry, UniVersity of Texas at El Paso, El Paso, Texas 79968-0513
ReceiVed April 10, 2006
Treatment of (η5-C5H5)Fe(CO)2(SiMe2)nCl (n ) 3, 4) with lithium diisopropylamide leads directly to
new trisila- (1) and tetrasilaferracycles (2) [(η5-C5H4)Fe(CO)2(SiMe2)n]. The trisilaferracycle (1)
exhibits a degree of ring strain as noted by 29Si NMR spectroscopy and single-crystal X-ray analysis but
is stable with respect to limited attempts at ring-opening polymerization and photochemical transformation.
In contrast, 2, with no ring strain, readily transforms via photochemical irradiation by way of iron silyl-
(silylenes) to a trimethylsilyl-substituted trisilaferracycle 4, which in turn transforms to 1 upon prolonged
irradiation.
Introduction
We have demonstrated that the linear trisilyl, tetrasilyl, and
cyclic polysilyl complexes of iron undergo clean photochemical
isomerization to the branched oligosilyl iron complexes via the
intermediacy of iron silyl(silylenes),1-3 e.g., eq 1.
We now report the synthesis of the related trisila- and
tetrasilaferracycles and the results of ultraviolet irradiation of
these new complexes.
Results and Discussion
The reaction between [(η5-C5H5)Fe(CO)2]Na and the perm-
ethylated R,ω-dichlorotrisilane and -tetrasilane, Cl(SiMe2)nCl,
n ) 3, 4, in THF at low temperature produced Fp(SiMe2)nCl in
60% (n ) 3)3a,6 and 26% (n ) 4) yields, respectively, eq 4.
Recently we also reported the formation of new silaferracycles
by base-treatment of (η5-C5H5)Fe(CO)2SiR2CH2Cl, FpSiR2CH2-
Cl, that could lead to ring-opened polymers,4 e.g., eq 2.
[Fp]-Na+ + Cl(SiMe2)nCl f Fp(SiMe2)nCl + NaCl (4)
In the case of the reaction with the 1,4-dichlorooctamethyltet-
rasilane significant amounts of Fp(SiMe2)4Fp were obtained as
a yellow crystalline solid.7 However, its low solubility in hexane
permitted ready separation from Fp(SiMe2)4Cl. Treatment of
either Fp(SiMe2)nCl complex with lithium diisopropylamide,
LDA, in THF at 0 °C, resulted in formation of the corresponding
silaferracycles 1 and 2 in moderate yields, eq 5.
(2) (a) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. (b)
Tilley, T. D. In The Chemistry of Organic Silicon Compounds; Patai, S.,
Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24.
(3) (a) Tobita, H.; Kurita, H.; Ogino, H. Organometallics 1998, 17, 2844.
(b) Okazaki, M.; Tobita, H.; Ogino, H. J. Chem. Soc., Dalton Trans. 2003,
493. (c) Tobita, H.; Matsuda, A.; Hashimoto, H.; Ueno, K.; Ogino, H.
Angew. Chem., Int. Ed. 2004, 43, 221. (d) Hashimoto, H.; Matsuda, A.;
Tobita. H. Chem. Lett. 2005, 1374.
Upon treatment with LDA the related 1-Fp-2-chlorotetrabu-
tyldisilane provided a stable disilaferracycle, which does not
lead to polymer formation; however, direct polymer formation
was obtained when the smaller methyl groups were substituted
on the silicon atoms, eq 3. We assume this polymer was formed
via an unobserved silaferracycle intermediate.5
(4) Sharma, H. K.; Cervantes-Lee, F.; Pannell, K. H. J. Am. Chem. Soc.
2004, 126, 1326.
(5) Sharma, H. K.; Pannell, K. H. Chem. Commun. 2004, 2556.
(6) Sharma, S.; Pannell, K. H. Organometallics 2000, 19, 1225.
(7) Hengge, E.; Eibl, M.; Stadelmann, B. Monatsh. Chem. 1993, 124,
523.
(1) (a) Pannell, K. H.; Wang, L.-J.; Rozell, J. M. Organometallics 1989,
8, 550. (b) Hernandez, C.; Sharma, H. K.; Pannell, K. H. J. Organomet.
Chem. 1993, 462, 259.
10.1021/om060320c CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/30/2006

3970 Organometallics, Vol. 25, No. 16, 2006
Sharma et al.
Figure 1. Structure of 1. Thermal ellipsoids are drawn at 50%
probability.
In the reaction used to obtain 1 a significant amount of an
insoluble material, possibly polymeric, was formed; however,
we have not been able to obtain any useful information via solid-
state NMR spectroscopy. The trisilaferracycle 1 was character-
ized by NMR spectroscopy and single-crystal X-ray diffraction.
The 29Si NMR spectrum of 1 exhibited three resonances at 28.4
ppm (SiR, Fe-Si), -9.06 ppm (Siâ, Fe-Si-Si), and -21.2 ppm
(Siγ, Fe-Si-Si-Si-C5H4). An important feature of these data
is the significant low-field shift (∆δ ) 27 ppm) for the â-Si
resonance relative to the â-Si resonance of the related linear
1a,2
permethyltrisilane iron complex FpSiMe2SiMe2SiMe3
pre-
sumably due to the ring strain.
Reports concerning disilametallacyclopentanes8 have appeared
in the literature, but there are only two examples of a
trisilametallacycle, a trisilairidacyclopentane,9a in which the C
atom is a methylene carbon, and a trisilazirconacyclopentane9b
in which the C atom is also part of a fused three-membered
ring, N-Zr-C. In both cases the five-membered ring adopts
an envelope conformation with dihedral angles of 124.7° and
158°, respectively. The X-ray structure of 1 (Figure 1) exhibits
average Si-Si bond lengths of 2.338 Å, typical of the Si-Si
bond lengths in Fp-oligosilyl complexes.2 The five-membered
ring composed of Fe, C, and three Si atoms is distorted, with
bond angles Fe-C1-Si3 ) 126.47(16)°, Fe-Si1-Si2 )
103.82(5)°, C1-Si3-Si2 ) 101.78(11)°, Si3-Si2-Si1 )
96.26(6)°, and C1-Fe-Si1 ) 90.70(9)°, respectively, illustrat-
ing the greater strain at the central silicon atom, as suggested
by the 29Si NMR data. The ring is close to an envelope
conformation, with C1, Fe, Si2, and Si3 not completely coplanar
but showing a dihedral angle of 175.5° between planes (C1-
Si3-Si2) and (C1-Si2-Fe) with Si1 at the tip of the envelope,
resulting in a 134.5° dihedral angle between planes (C1-Si2-
Fe) and (Si2-Fe-Si1).
Figure 2. Structure of 3. Thermal ellipsoids are drawn at 50%
probability.
of Si-Si bonds or metal-initiated rearrangement1,2 (eq 6), a
distinctive photochemistry compared to that of the related linear
Fp-oligosilanes noted in eq 1. Irradiation of 1 alone resulted in
no observable chemistry.
The structure of 3 has also been confirmed by NMR spectros-
copy and by single-crystal X-ray crystallography. The 13C NMR
spectrum of 3 exhibited different chemical shifts for the Cp car-
bons and methyl carbon atoms in the molecule due to the chiral
metal center. A doublet observed in the 29Si NMR spectrum at
16.8 ppm due to coupling between 29Si and 31P nuclei is assigned
Despite this apparent strain 1 is stable in air and does not
undergo ring-opening polymerization, thermally or in the
presence of anionic or selected transition-metal catalysts.
Furthermore, photochemical treatment of a hexane solution of
1 in a quartz tube for 10 h in the presence of a 2-fold excess of
Ph3P resulted in the formation of red crystalline phosphine-
substituted trisilaferracycle 3, in 24% yield without cleavage
2
to SiR (Fe-Si) with a large coupling constant, JSi-P ) 29.5
Hz, and a doublet at -12.9 ppm with a smaller coupling constant
(3JSi-P ) 2.4 Hz) to the Siâ atom. A singlet at -21.2 ppm is
assigned to Siγ (Cp-substituted Si). Substitution of the phosphine
ligand for a carbonyl ligand shields the three silicon nuclei about
∆δ ) 11.6 for SiR, ∆δ ) 3.8 for Siâ, and ∆δ ) 0 ppm for Siγ
in comparison with the Si resonances of ferracycle 1.2,10
The crystal structure of 3 (Figure 2) exhibits a five-membered
ring in a twisted conformation with dihedral angles of 145.2°
between planes (C1-Si3-Si2) and (C1-Si2-Fe) and 149.1°
between (C1-Si2-Fe) and (Si2-Fe-Si1) rather than the
(8) (a) Crocco, G. L.; Young, C. S.; Lee, K. E.; Gladysz, J. A.
Organometallics 1988, 7, 2158. (b) Tamao, K.; Yoshida, J.; Okazaki, S.;
Kumada, M. Isr. J. Chem. 1977, 15, 265. (c) Ueno, K.; Ito, S.; Endo, K.;
Tobita, H.; Inomata, S.; Ogino, H. Organometallics 1994, 13, 3309. (d)
Tanabe, M.; Yamazawa, H.; Osakada, K. Organometallics 2001, 20, 4453.
(e) Hoffmann, D.; Reinke, H.; Krempner, C. J. Organomet. Chem. 2002,
662, 1.
(9) (a) Mitchell, G. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1995, 14, 5472. (b) Fischer, R.; Frank, D.; Gaderbauer,
W.; Kayser, C.; Mechtler, C.; Baumgartner, J.; Marschner, C. Organome-
tallics 2003, 22, 3723.
(10) Pannell, K. H.; Bassindale, A. R. J. Organomet. Chem. 1982, 229, 1.

Ring-Contraction of a Tetrasilaferracyclohexane
Organometallics, Vol. 25, No. 16, 2006 3971
Scheme 1
envelope conformation present in 1. The Fe-Si bond and Si-
Si bonds are slightly longer than in 1, the angles in the five-
membered ring are greater than the bond angles of 1, and
importantly the Si1-Si2-Si3 angle that was 96.26(6)° in 1 has
widened to 102.95(7)° in 3. The bulky Ph3P group is oriented
away from the trisilaferracyclopentane, presumably to avoid
steric interactions.
in eq 1), resulting in the formation of the ring-contracted product
4. The low initial yield of 1 in comparison with 4 indirectly
indicates the preference of intermediate B over A in the initially
kinetically driven process. However, prolonged irradiation of 4
does lead to intermediate B, which slowly bleeds to 1, which is
the final product of photochemistry. This chemistry contrasts
with that noted in eq 1, where no significant silylene elimination
has been observed upon prolonged irradiation under the same
reaction conditions.
Tetrasilaferracycle 2 exhibits the expected four 29Si reso-
nances at 19.8 ppm (SiR), -37.8 ppm (Siâ), -46.2 ppm (Siδ),
and -20.8 ppm (Siγ) in its 29Si NMR spectrum. These values
are within (5 ppm of the data for FpSiMe2SiMe2SiMe2SiMe3
and suggest, appropriately, the absence of any significant strain
within the six-membered ring. However, contrary to the
photochemistry of 1 noted above, irradiation of a C6D6 solution
of 2 in a sealed Pyrex glass NMR tube for 10 h resulted in the
transformation of 2 into two ring-contracted trisilaferracyclo-
pentanes, 1 and 4, in 25% and 75% relative reaction yields,
respectively, as determined by GC analysis and NMR spec-
troscopy, eq 7. Prolonged irradiation of the mixture resulted in
the disappearance of 4, which slowly was transformed to 1.
The new silaferracycle 4 was characterized by NMR and mass
spectrometry. The 29Si NMR spectrum of 4 exhibits four
resonances, which can be assigned as follows: -7.9 (SiMe3),
-5.8 (Fe-Si), -11.2 (Fe-Si-Si), and -19.4 ppm (Fe-Si-
Si-Si). Due to the Fe-Si chiral center, the various diastereotopic
1
methyl groups on silicon give six signals in both the H and
13C NMR spectra. As with the other silametallacycles, the
cyclopentadienyl ring carbon atoms are inequivalent, which
results in five resonances at 84.5, 85.2, 90.5, 91.2, and 95.8
ppm, respectively.
For confirmation of the proposal in Scheme 1, we irradiated
ferracycle 2 in the presence of hexamethylphosporamide
(HMPA). Monitoring the reaction by NMR spectroscopy we
were able to observe the initially formed intermediate A as the
HMPA-stabilized (silylene) trisilaferracycle,6,11 5.
The 29Si NMR spectrum of the silylene 5 exhibited a low-
field doublet at 113.5 ppm due to the FedSi unit, coupled with
the 31P atom of HMPA (2JSi-P ) 28 Hz), and singlets at 16.1,
-12.0, and -21.9 ppm due to R, â, and γ silicons of the
trisilaferracycle, respectively. These three signals are comparable
to the silicon resonances of 1 at 28.4, -9.1, and -21.2 ppm,
respectively, with the ∆δ values representing the change of
coordination chemistry at the Fe atom. The 1H NMR spectrum
showed two doublets at 2.26 and 2.37 ppm for coordinated and
free HMPA molecules. The 13C NMR spectrum of 5 exhibited
separate resonances due to diastereotopic SiMe2 groups at
-6.47, -5.20, -2.29, -0.96, 2.98, and 6.56 and two low-field
The ring-contracted ferracyclopentanes 1 and 4 are readily
separated by silica gel column chromatography using a 90:10
hexane/methylene chloride mixture as eluent. The formation of
1 and 4 can reasonably be explained through iron silyl(silylene)
intermediates A and B, as illustrated in Scheme 1.
The silyl(silylene) iron complex A with an exocyclic silylene
ligand undergoes silylene, :SiMe2, substitution by CO to yield
the trisilaferracycle 1. However, intermediate A can also undergo
a 1,3-methyl shift to produce a dynamic equilibrium with the
endocyclic iron silyl(silylene) intermediate B. Intermediate B
does not lose its silylene, but undergoes an isomerization via a
1,2-silyl shift (of the type responsible for the isomerization noted
(11) Ueno, K.; Nakano, K.; Ogino, H. Chem. Lett. 1996, 459.

3972 Organometallics, Vol. 25, No. 16, 2006
Sharma et al.
temperature, and the THF was removed in vacuo. The residue was
extracted with 50 mL of a 1:1 mixture of hexanes/CH2Cl2 and
filtered. The orange sticky residue was dissolved in 5 mL of hexanes
and placed upon a 2.5 × 10 cm silica gel column, and the yellow
band formed was eluted with an 80:20 hexanes/CH2Cl2 mixture.
Upon evaporation of the solvent, 2 was obtained as a yellow oil
signals due to coordinated silylene at 10.9 and 13.8 ppm. The
C resonance for coordinated and free HMPA appears as doublets
at 36.4 and 36.7 ppm, respectively. These data clearly support
the formulation of 5 as a base-stabilized silylene complex.
Attempts to isolate 5 were unsuccessful due to its extreme air
and moisture sensitivity.
1
(0.14 g, 0.34 mmol, 24% yield). H NMR (C6D6): δ 0.19, 0.21,
0.29, 0.58 (s, 24H, Me), 4.22 (t, 2H, Cp), 4.47 (t, 2H, Cp). 13C
NMR (C6D6): δ -6.06, -4.77, -2.05, 3.69 (Me), 84.5, 87.1 (ipso),
92.1 (C5H4), 216.1 (CO). 29Si NMR (C6D6): δ 19.8, -20.8, -37.8,
-46.2. IR (ν CO, cm-1) (hexane): 1994, 1942. Anal. Calcd for
C15H28FeO2Si4: C, 44.10; H, 6.91. Found: C, 43.49; H, 6.70. GC/
MS: m/z 408 [M]+, 24; 380 [M - CO]+, 100; 73 [SiMe3]+, 41.
Experimental Section
All manipulations were carried out under nitrogen using vacuum
line techniques. THF was distilled under nitrogen from benzophe-
none ketyl prior to use. Other solvents, hexanes and benzene, were
dried over sodium metal and distilled before use; HMPA was
distilled over CaO; Cl(SiMe2)3Cl,12 Cl(SiMe2)4Cl,13 and Fp(SiMe2)3-
Cl3a were synthesized by previously reported procedures. NMR
spectra were recorded on a 300 MHz Bruker spectrometer; GC/
mass spectra were recorded on a Hewlett-Packard 5890/5971
spectrometer. Elemental analyses were performed by Galbraith
Laboratories, Knoxville, TN.
Photolysis of 2 in C6D6. A solution of compound 2 (0.12 g,
0.31 mmol) in 1.0 mL of degassed C6D6 was sealed in a Pyrex
NMR tube. The NMR tube was placed at a distance of 10 cm from
a 450 W medium-pressure mercury lamp and irradiated. The
1
progress of the photoreaction was monitored by H, 13C, and 29Si
NMR spectroscopy. The starting material completely disappeared
after 10 h of irradiation with the formation of ring-contracted
ferracycles 1 and 4 in 1:3 ratio. The solution was placed on a 2.5
× 10 cm silica gel column, and first a yellow band was eluted
with hexane. Upon removal of the solvent in vacuo, 0.015 g (0.04
mmol, 13% yield) of 1 along with traces of 4 was obtained. The
second yellow band was eluted with a 90:10 hexane/CH2Cl2 mixture
that after evaporation of the solvent gave 0.028 g (0.068 mmol,
22% yield) of 4. 1H NMR (C6D6): δ 0.13, 0.17, 0.36, 0.37 (s, 12H,
SiMe2), 0.33 (s, 9H, SiMe3), 0.59 (s, 3H, SiMe), 4.20 (t, 1H, Cp),
4.34-4.47 (m, 3H, Cp). 13C NMR (C6D6): δ -3.79, -3.68, -3.46,
-2.76, 1.07 (Me), 84.5, 85.2, 90.5, 91.2, 95.8 (ipso) (C5H4), 216.0,
216.5 (CO). 29Si NMR (C6D6): δ -5.88, -7.97, -11.2, -19.4.
GC/MS: m/z 408 [M]+, 24; 380 [M - CO]+, 35; 307 [M - CO -
SiMe3]+, 19; 73 [SiMe3]+, 100. HR MS (EI): exact mass found
408.0511, calcd for C15H28O2FeSi4 408.0516.
Synthesis of Trisilaferracycle 1. A 50 mL round-bottomed
Schlenk flask was charged with 1.5 g (3.88 mmol) of FpSiMe2-
SiMe2SiMe2Cl in 15 mL of THF. To this solution at -25 °C was
added 10 mL (3.90 mmol) of freshly prepared LDA in the same
solvent via cannula. The color of the solution immediately changed
to dark reddish-brown. The solution was stirred overnight at room
temperature, and yellow insoluble material precipitated. The
supernatant liquid was withdrawn via a syringe, and the THF was
evaporated under vacuum. The residue was extracted with 50 mL
of hexanes and filtered. The orange sticky residue was dissolved
in 5 mL of hexanes and placed upon a 2.5 × 10 cm silica gel
column. The yellow band was eluted with hexanes, and upon
evaporation of the solvent, a yellow crystalline solid was obtained
in 0.2 g (0.58 mmol, 15%) yield, mp 136-142 °C. 1H NMR
(C6D6): δ 0.13, 0.29, 0.63 (s, 18H, Me), 4.22 (t, 2H, Cp), 4.43 (t,
2H, Cp). 13C NMR (C6D6): δ -4.70, -3.43, 3.36 (Me), 85.2, 90.4,
96.9 (ipso) (C5H4), 216.3 (CO). 29Si NMR (C6D6): δ 28.4, -9.06,
-21.2. IR (ν CO, cm-1) (hexane): 1992, 1940. Anal. Calcd for
C13H22FeO2Si3: C, 44.55; H, 6.33. Found: C, 44.57; H, 6.50. GC/
MS: m/z 350 [M]+, 9; 322 [M - CO]+, 24; 73 [SiMe3]+, 100.
Synthesis of FpSiMe2SiMe2SiMe2SiMe2Cl. To a 30 mL THF
solution of Fp-Na+ (prepared from 1.0 g, 2.82 mmol of [(η5-C5H5)-
Fe(CO)2]2) was added 1.74 g (5.61 mmol) of Cl(SiMe2)4Cl in 10
mL of THF at -25 °C. The solution was stirred at this temperature
for 1 h and then warmed to room temperature and stirred overnight.
The solvent was removed in vacuo, and the residue was extracted
with 60 mL of a 1:1 mixture of hexanes/CH2Cl2. The solution was
filtered through Celite and the filtrate concentrated to 10 mL. A
yellow solid containing 0.35 g of Fp(SiMe2)4Fp was precipitated.
The solid had poor solubility in hexanes and was readily separated
by filtration. The solvent was removed from the filtrate and
dissolved in 8 mL of cold hexanes, and traces of an insoluble yellow
residue of Fp(SiMe2)4Fp were removed by filtration. This process
was repeated and the solvent was removed under vacuum, and an
orange oily residue containing 0.64 g (26% yield) of >90% pure
FpSiMe2SiMe2SiMe2SiMe2Cl along with traces of Fp(SiMe2)4Fp
Photolysis of 2 in the Presence of HMPA. A 5 mm Pyrex NMR
tube was charged with a mixture of 0.085 g (0.19 mmol) of 2 and
0.14 g of HMPA (0.78 mmol) in 1.0 mL of degassed C6D6, and
the tube was sealed under vacuum. The sealed NMR tube was
irradiated with a 450 W medium-pressure mercury lamp, and the
1
reaction was monitored by H, 13C, and 29Si NMR spectroscopy.
After 3 h of irradiation, the starting material had disappeared and
spectral data showed the formation of the HMPA-stabilized
(silylene)trisilametallacycle, 5. All attempts to isolate the complex
led to its decomposition. 1H NMR (C6D6): δ 0.39, 0.40, 0.45, 0.48,
0.60, 0.64, 0.70 (s, SiMe2), 2.26 (d, 2JP-H ) 10.2 Hz, coordinated
HMPA), 2.37 (d, free HMPA), 4.15-4.19, 4.45-4.54, 4.66, 4.86
(complex m, Cp). 13C NMR (C6D6): δ -6.47, -5.20, -2.29,
-0.96, 2.98, 6.56 (SiMe2), 10.9 (s), 13.8 (d, dSiMe2), 36.4 (d,
2JP-C ) 5 Hz, coordinated HMPA), 36.7 (d, free HMPA), 77.0,
84.7, 85.6, 87.3, 90.8 (ipso) (C5H4), 219.7 (CO). 29Si NMR
2
(C6D6): δ 113.1 (d, JSi-P ) 28 Hz), 16.1, -12.0, -21.9.
Synthesis of Trisilametallacycle 3. To a solution of 1 (0.175
g) (0.5 mmol) in 30 mL of hexane, in a quartz tube, was added
0.30 g (1.14 mmol) of Ph3P. The solution was irradiated with a
Hanovia 450-W medium-pressure mercury lamp at a distance of 4
cm. The progress of the photochemical reaction monitored by
infrared spectroscopy indicated that after 10 h the ν(CO) bands of
the starting material 1 had been replaced by a single CO stretching
frequency at 1920 cm-1 and the solution became dark red. The
hexane solution was filtered through Celite, and the solvent was
evaporated. The red residue was placed upon a silica gel column,
and a red band was eluted with a 1:1 hexane/benzene mixture. Upon
evaporation of solvent, a red compound was obtained, which was
recrystallized from hexanes. Yield: 0.07 g (0.12 mmol, 24%); mp
1
was obtained. H NMR (C6D6): δ 0.27, 0.51, 0.86, 1.22 (s, 24H,
Me), 4.22 (s, 5H, Cp). 13C NMR (C6D6): δ -7.25, -5.52, 2.29,
3.59 (Me), 83.11 (C5H5), 215.63 (CO). 29Si NMR (C6D6): δ 22.69,
15.09, -40.69, -50.20. IR (ν CO, cm-1) (hexane): 1997, 1947.
Synthesis of Tetrasilaferracycle 2. A 50 mL round-bottomed
Schlenk flask was charged with 0.64 g (1.44 mmol) of FpSiMe2-
SiMe2SiMe2SiMe2Cl in 10 mL of THF. To this solution at 0 °C
was added 6 mL (1.45 mmol) of freshly prepared LDA in the same
solvent via cannula. The color of the solution immediately changed
to dark reddish-brown. The solution was stirred overnight at room
1
148-150 °C. H NMR (C6D6): δ -0.09, 0.33, 0.42, 0.43, 0.49,
0.74, (s, 18H, Me); 3.43 (m, 1H, J ) 1.5 Hz, Cp), 4.33 (m, 1H, J
) 1.2 Hz, Cp), 4.43 (m, 1H, Cp), 5.15 (m, 1H, J ) 1.2 Hz, Cp),
6.95-7.04, 7.59-7.66 (m, 15H, Ph). 13C NMR (C6D6): δ -4.65,
-4.36, -2.94, -1.31, 1.05, 6.11 (Me), 83.2, 88.1 (ipso), 89.3, 92.9,
(12) Oakley, R. T.; Stanislawski, D. A.; West, R. J. Organomet. Chem.
1978, 157, 389.
(13) Kumada, M.; Ishikawa, M.; Maeda, S. J. Organomet. Chem. 1964,
2, 478.

Ring-Contraction of a Tetrasilaferracyclohexane
Organometallics, Vol. 25, No. 16, 2006 3973
Table 1. Crystallographic and Refinement Data for 1 and 3
1
3
empirical formula
source
C13H22FeO2Si3
synthesis
red
C30H37FeOPSi3
synthesis
orange
cryst color
cryst habit
irregular fragment
prism
cryst size/mm3
a/Å
0.56 × 0.50 × 0.16
0.20 × 0.20 × 0.12
13.183(5)
13.363(2)
b/Å
c/Å
10.707(5)
14.929(3)
13.350(5)
31.447(5)
R/deg
90
90
â/deg
106.33(3)
98.188(3)
γ/deg
90
90
volume/Å3
1808.3(13)
6209.3(18)
cryst syst
monoclinic
monoclinic
space group
Z
P2(1)/n
C2/c
8
1.251
0.674
4
Dc/g cm-3
1.287
µ/mm-1
1.028
abs corr
semiempirical
Bruker SADABS program
23(2)
0.71073 Å
graphite
Bruker SMART with Apex CCD
25325
2.23-22.48 (99.6% completeness)
4464 [R(int) ) 0.0465]
direct methods
temp/°C
23(2)
wavelength
0.71073 Å
monochromator
diffractometer
no. of reflns collected
θ range/deg
no. of ind reflns
structure solution technique
structure solution program
refinement technique
refinement program
function minimized
goodness-of-fit on F2
R1,a wR2b [I>2σ(I)]
R1, wR2 (all data)
graphite
Siemens R3m/V
3480
1.92-25.05 (100% completeness)
3202 [R(int) ) 0.0495]
direct methods
SHELXS-97 (Sheldrick, 1990)
full-matrix least-squares on F2
SHELXS-97 (Sheldrick, 1997)
SHELXS-97 (Sheldrick, 1990)
full-matrix least-squares on F2
SHELXS-97 (Sheldrick, 1997)
2
2
∑w(Fo2 - Fc )2
∑w(Fo2 - Fc )2
1.014
1.252
0.0426, 0.0989
0.0633, 0.1103
0.0708, 0.01572
0.0827, 0.1639
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. bwR2 ) {∑[w(Fo -Fc )2]/∑[w(Fo )2]}1/2
.
Table 2. Bond Lengths and Angles for
(C5H4)Fe(CO)2(SiMe2)3, 1
Table 3. Bond Lengths and Angles for
(C5H4)Fe(PPh3)(CO)(SiMe2)3, 3
Bond Lengths (Å)
Bond Lengths (Å)
Fe-C7
Fe-C1
Si2-Si3
Si3-C1
O2-C7
1.737(4)
2.159(3)
2.3367(15)
1.878(4)
1.152(5)
Fe-C6
Fe-Si1
Si2-Si1
O1-C6
C1-C5
1.740(4)
Fe-C12
Fe-P
P-C19
Si2-Si3
O-C12
1.702(5)
2.1935(12)
1.845(5)
2.350(2)
1.171(5)
Fe-C1
Fe-Si1
Si1-Si2
Si3-C1
2.118(4)
2.3491(16)
2.371(2)
1.875(5)
2.3437(12)
2.3389(15)
1.155(4)
1.421(5)
Bond Angles (deg)
Bond Angles (deg)
C7-Fe-C1
C7-Fe-Si1
C1-Fe-Si1
C9-Si1-Fe
C1-Si3-Si2
Si3-C1-Fe
O2-C7-Fe
144.52(15)
82.08(13)
90.70(9)
111.36(14)
101.78(11)
126.47(16)
179.5(4)
C6-Fe-C1
C6-Fe-Si1
Si3-Si2-Si1
Si2-Si1-Fe
C5-C1-Si3
O1-C6-Fe
118.84(15)
86.61(13)
96.26(6)
103.82(5)
129.7(3)
177.5(4)
C12-Fe-P
P-Fe-Si1
Si3-Si2-Si1
93.58(15)
99.91(5)
102.95(7)
C1-Fe-Si1
Fe-Si1-Si2
O-C12-Fe
95.71(15)
103.24(7)
177.0(4)
A red prism of C30H37FeOPSi3 (3) of approximately 0.12 mm
× 0.20 mm × 0.20 mm was used for the X-ray crystallographic
analysis. The X-ray intensity data were measured at 296(2) K on
a Bruker SMART APEX diffractometer with a Bruker APEX CCD
area detector system equipped with a graphite monochromator and
a Mo KR fine-focus sealed tube. The detector was placed at a
distance of 5.953 cm from the crystal. A total of 2400 frames were
collected with a scan width of 0.3° in ω and an exposure time of
10 s/frame. The frames were integrated with the Bruker SAINT
software package14b using a narrow-frame integration algorithm.
The structures were solved and refined using the Bruker SHELXTL
(Version 6.10)14c software package.
94.1 (C5H4), 128.7 (d, JP-C ) 6.8 Hz), 129.4 (d) 133.8 (d, JP-C
)
9.8 Hz), 139.1 (d, JP-C ) 40.2 Hz), 220.2 (d, JP-C ) 29.4 Hz,
2
CO). 29Si NMR (C6D6): δ 16.8 (d, JSi-P ) 29.5 Hz), -12.9 (d,
3JSi-P ) 2.4 Hz), -20.9 (s). 31P NMR (C6D6): δ 81.9. IR (ν CO,
cm-1) (hexane): 1905. Anal. Calcd for C30H37FeOPSi3: C, 61.63;
H, 6.38. Found: C, 61.74; H, 6.57.
Structure Determinations. A red fragment of C13H22FeO2Si3
(1) of approximate dimensions 0.56 × 0.50 × 0.16 mm was
mounted in a random orientation at the tip of a glass fiber for X-ray
examination and data collection. All data were collected at 296(2)
K using the Siemens/Nicolet P3/V software14a on a Siemens R3m/V
single-crystal diffractometer with graphite-monochromated Mo KR
radiation, λ(Mo KR) ) 0.71073, and a point detector. The collection
was conducted over slightly more than one quadrant of reciprocal
space, in the range -2 e h e 15, 0 e k e 12, -15 e l e 15. The
data were corrected for Lorentz and polarization effects, and a
semiempirical absorption correction was also applied.
Pertinent crystallographic data are given in Table 1, the structures
and numbering scheme are shown in Figures 1 and 2, and selected
bond lengths and angles are presented in Tables 2 and 3.
Acknowledgment. This research has been supported by the
NIH-MARC program. We thank Nebraska Center for Mass
Spectrometry, Lincoln, NE, for recording the high-resolution
mass spectrum of 4.
(14) (a) Siemens P3/V data collection program Version 4.11; Siemens
Analytical X-ray instruments Inc.: Madison, WI, 1990. (b) SAINTPLUS
data reduction program Version 5.622; Bruker-AXS: Madison WI, 2001.
(c) SHELXTL software package Version 6.10; Bruker-AXS: Madison, WI,
2000.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM060320C