Reactions of 1,1-dichloro-, 1-chloro-1-phenyl- and 1-chloro-1-methylsilacyclopent-3-ene with Na[Cp(CO)2Fe]. X-ray diffraction study of the 1-(dicarbonylcyclopentadienyl-ferrio)-1-[4-(dicarbonylcyclopentadienylferrio) but-1-oxy]silacyclopent-3-ene resulting from insertion of an opened THF molecule into a Si-Fe bond

Article abstract of DOI:10.1016/S0022-328X(98)00578-6

The reaction of 1,1-dichlorosilacyclopent-3-ene (1), 1-chloro-1-phenylsilacyclopent-3-ene (2) and 1-chloro-1-methylsilacyclopent-3-ene (3) with Na[Cp(CO)₂Fe] in a 1/1 ratio yielded yellow crystalline powders of the Cp(CO)₂Fe(ClSiC₄H₆) (5), Cp(CO)₂Fe(PhSiC₄H₆) (6) and Cp(CO)₂Fe(MeSiC₄H₆) (7) complexes, respectively. ¹H-NMR spectra indicated that the silacyclopent-3-ene ring in all complexes is puckered in solution. When 1,1-dichlosilacyclopent-3-ene was reacted with two equivalents of Na[Cp(CO)₂Fe] in THF, a different complex 8 was produced, resulting from the insertion of an opened THF molecule into a Si-Fe bond. Its crystal structure was determined by single-crystal X-ray diffraction: triclinic, space group P1, a = 7.9334(12), b = 11.596(2), c = 12.939(3) A, α = 75.73(2), β = 75.38(2), γ = 80.05(1)°, Z = 2, R = 0.040, Rw = 0.045. Complex 8 contains two Cp(CO)₂Fe fragments, one of which is directly bonded to the Si atom of a silacyclopent-3-ene unit, whereas the other is at the carbon end of an opened THF molecule whose oxygen atom is bonded to same Si atom. Both iron(II) centres possess a pseudo-octahedral coordination created by one Cp ring, two cis CO ligands and, in one case, a Si atom and, in the other, the terminal CH₂ group of the opened THF molecule thus acting as a bridging unit between Si and a Cp(CO)₂Fe group. Under similar conditions, the above ligands failed to react with Na[Co(CO)₄], but the related Co(CO)₄(1,3-Me₂SiC₄H₅) molecule was synthesized from 1,3-dimethylsilacyclopent-3-ene via a hydrosilylation reaction.

Full text of DOI:10.1016/S0022-328X(98)00578-6

Journal of Organometallic Chemistry 563 (1998) 53–60
Reactions of 1,1-dichloro-, 1-chloro-1-phenyl- and
1-chloro-1-methylsilacyclopent-3-ene with Na[Cp(CO)2Fe]. X-ray
diffraction study of the 1-(dicarbonylcyclopentadienyl-
ferrio)-1-[4-(dicarbonylcyclopentadienylferrio)but-1-oxy]sila-
cyclopent-3-ene resulting from insertion of an opened THF molecule
into a Si–Fe bond
Pascal Dufour a, Miche`le Dartiguenave a,*, Yves Dartiguenave a, Michel Simard b,
Andre´ L. Beauchamp b
a Laboratoire de Chimie Inorganique, Uni6ersite´ P. Sabatier, 118 route de Narbonne, 31062 Toulouse, France
b De´partement de Chimie, Uni6ersite´ de Montre´al, C.P. 6128, Succ. Centre-6ille, Montre´al, Que´. H3C 3J7, Canada
Received 3 December 1997; received in revised form 17 March 1998
Abstract
The reaction of 1,1-dichlorosilacyclopent-3-ene (1), 1-chloro-1-phenylsilacyclopent-3-ene (2) and 1-chloro-1-methylsilacy-
clopent-3-ene (3) with Na[Cp(CO)2Fe] in a 1/1 ratio yielded yellow crystalline powders of the Cp(CO)2Fe(ClSiC4H6) (5),
Cp(CO)2Fe(PhSiC4H6) (6) and Cp(CO)2Fe(MeSiC4H6) (7) complexes, respectively. 1H-NMR spectra indicated that the silacy-
clopent-3-ene ring in all complexes is puckered in solution. When 1,1-dichlosilacyclopent-3-ene was reacted with two equiva-
lents of Na[Cp(CO)2Fe] in THF, a different complex 8 was produced, resulting from the insertion of an opened THF molecule
into a Si–Fe bond. Its crystal structure was determined by single-crystal X-ray diffraction: triclinic, space group P1, a=
˚
7.9334(12), b=11.596(2), c=12.939(3) A, h=75.73(2), i=75.38(2), k=80.05(1)°, Z=2, R=0.040, Rw=0.045. Complex 8
contains two Cp(CO)2Fe fragments, one of which is directly bonded to the Si atom of a silacyclopent-3-ene unit, whereas the
other is at the carbon end of an opened THF molecule whose oxygen atom is bonded to same Si atom. Both iron(II) centres
possess a pseudo-octahedral coordination created by one Cp ring, two cis CO ligands and, in one case, a Si atom and, in the
other, the terminal CH2 group of the opened THF molecule thus acting as a bridging unit between Si and a Cp(CO)2Fe
group. Under similar conditions, the above ligands failed to react with Na[Co(CO)4], but the related Co(CO)4(1,3-Me2SiC4H5)
molecule was synthesized from 1,3-dimethylsilacyclopent-3-ene via a hydrosilylation reaction. © 1998 Elsevier Science S.A. All
rights reserved.
Keywords: Iron; Cobalt; Silacyclopentene; Opened THF; X-ray diffraction
1. Introduction
precursors leading to inorganic polymers via ring open-
ing processes (ROAP) (Scheme 1) [1].
Alkyl- or aryl-substituted silacyclopent-3-enes have
attracted a great deal of attention as monomeric
Although these planar molecules present two poten-
tial metal coordination sites, namely the CꢀC bond and
the Si atom, their ability to bind metal centers and their
coordination chemistry are still poorly developed. In
contrast, metal-coordinated alkyl and aryl silanes are
* Corresponding author. Tel.: +33 5 61556118; fax: +33 5
61556118; e-mail: dartigue@iris.ups-tlse.fr
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00578-6

54
P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
numerous and compounds have been described in
which nearly all transition metals form stable |
metal–silicon bonds. They were synthesized mainly via
nucleophilic substitution of a silicon-bonded halogen
atom by a metallate anion [2], a method that can be
easily applied to silacyclopent-3-ene.
Scheme 1.
We report here the synthesis of the first compounds
containing a silacyclopentene unit | bonded to the
17-electron metallic fragment Cp(CO)2Fe, which were
isolated by reacting 1,1-dichlorosilacyclopent-3-ene (1),
1-chloro-1-phenylsilacyclopent-3-ene (2) and 1-chloro-
1-methylsilacyclopent-3-ene (3) with Na[Cp(CO)2Fe] in
1/1 and 1/2 ratios. As expected, the reactions are
highly sensitive to temperature, concentrations and the
other experimental conditions. When 1,1-dichlorosila-
cyclopent-3-ene was reacted with two equivalents of
the metal salt in THF, a different type of complex was
precipitated, which is a scarce example of insertion of
a THF molecule-after ring opening-into a Si–Fe bond.
The X-ray structure of this complex is reported. At-
temps were made to synthesize the related Co(CO)4
complexes without success. Interestingly, the only
compound of this type was obtained with 1,3-
dimethylsilacyclopent-3-ene (4) via an hydrosilylation
reaction.
tral de Microanalyses du CNRS, Lyon, and by the
Service de Microanalyses du LCC, Toulouse.
2.2. Preparati6e work
2.2.1. 1-(Dicarbonylcyclopentadienylferrio)-1-
chlorosilacyclopent-3-ene (5)
[CpFe(CO)2]2 (0.62 g, 1.75 mmol) in 40 mL of THF
was stirred for 2 h with sodium amalgam (4 mL Hg/
0.5 g Na). After filtration, the solution was cooled to
−40°C and added dropwise to a solution of 0.54 g
(3.5 mmol) of 1 in 30 mL of THF. The mixture was
stirred for 45 min, then warmed up slowly to r.t. and
stirred again for 24 h. After removal of THF in
vacuo, the solid was extracted with pentane. Cooling
the solution to −20°C gave 0.72 g of a yellow crys-
talline powder (yield: 70%). Anal: Calcd (Found) for
C11H11ClFeO2Si: C, 44.85 (44.95); H, 3.76 (3.77). IR
1
(pentane): w(CO), 2005 (vs), 1960 (vs) cm−1. H- and
2. Experimental section
13C{1H}-NMR: see Table 3.
2.1. Reactants and methods
Solvent distillation and all other manipulations were
performed in dry N2 atmosphere using standard
Schlenk techniques. Tetrahydrofuran, toluene and
ether were stirred with sodium wire and distilled over
Na/benzophenone prior to use. Pentane and hexane
Table 1
Crystal data for compound 8
Formula
C22H24Fe2O5Si
508.21
Triclinic
P1
were
distilled
from
Na
just
before
use.
Formula weight
Crystal system
Space group
Dichloromethane was dried over P2O5. All solvents
were degassed by three freeze-thaw cycles.
Unit cell dimensions
1,1-Dichlorosilacyclopent-3-ene
(1),
1-chloro-1-
˚
a (A)
7.9334(12)
11.596(2)
12.939(3)
75.73(2)
75.38(2)
80.05(1)
1108.4(4)
2
phenylsilacyclopent-3-ene (2) and 1-chloro-1-methylsi-
lacyclopent-3-ene (3) were prepared by literature
methods [3]. [CpFe(CO)2]2 and Co2(CO)8 (Strem) were
used without purification. Na[CpFe(CO)2] and Na[-
Co(CO)4] were synthesized from the corresponding
dimer by reduction with Na/Hg [4] or by reaction with
K[BH(sec-Bu)3] [5].
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
V (A )
Z
Dcalc (g cm−3
)
1.523
1.54056
11.34
˚
Radiation (u, A)
1
The H- and 13C{1H}-NMR spectra were recorded
v (mm−1
)
on Bruker WM-200 or WH-80 spectrometers using
CDCl3 or C6D6 as solvent. The chemical shifts were
referenced to the residual solvent signals: CDCl3,
l(1H)=7.27 ppm and l(13C)=77.0 ppm; C6D6,
l(1H)=7.25 ppm and l(13C)=128.0 ppm.
Temperature (K)
No. measured reflections
No. independent reflections
No. reflections with I\3|(I)
Ra
295
8274
4205
3348
0.040
0.045
Rwa
Microanalyses were performed by the Service Cen-

P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
55
Table 2
1-(Dicarbonylcyclopentadienyl-
ferrio)-1-[4-(dicarbonylcyclopentadienyl-
ferrio)but-1-oxy]silacyclopent-3-ene (8)
Atomic coordinates and equivalent isotropic temperature factors
2
˚
(A×10 ) for the non-hydrogen atoms of compound 8
Compound 1 (0.85 g, 5.51 mmol) in 15 ml THF
was added dropwise to a cold solution (−40°C) of
2.02 g (11.02 mmol) of Na[CpFe(CO)2] prepared as
above from [CpFe(CO)2]2 (2.72 g, 5.51 mmol) and
sodium amalgam (4 mL Hg/0.5 g Na). The mixture
was stirred at this temperature for 1 h, then warmed
up to r.t., and stirred again for 12 h. After removal
of the solvent in vacuo and work up of the residue
with ether, 1.8 g of a yellow crystalline powder was
obtained (yield: 65%). Recrystallization in ether/pen-
tane gave single crystals suitable for X-ray work.
Anal. Calcd. (Found) for C22H24Fe2O5Si: C, 51.99
(52.05); H, 4.76 (4.80). IR (pentane): w(CO), 1998
Atom
x
y
z
Baiso
Fe(1)
Fe(2)
Si
O(1)
C(2)
C(3)
C(4)
C(5)
C(6)
0.21874(7)
−0.29803(8)
0.39946(12)
0.2966(3)
0.1808(5)
0.1336(5)
−0.0207(5)
−0.0594(5)
0.5901(5)
0.7328(5)
0.7075(6)
0.23017(5)
0.79069(5)
0.28594(9)
0.3643(2)
0.4715(3)
0.5262(3)
0.6257(4)
0.6834(4)
0.3654(4)
0.3105(4)
0.2150(4)
0.1633(3)
0.1546(3)
0.1854(3)
0.4768(3)
0.3779(4)
0.9080(3)
0.8610(4)
0.9505(3)
0.8864(4)
0.1554(5)
0.0671(4)
0.0835(6)
0.1853(6)
0.2322(4)
0.6943(4)
0.6302(4)
0.7002(4)
0.8102(4)
0.8077(4)
1.01816(5)
0.54762(5)
0.8502 2(8)
0.7540(2)
0.7610(3)
0.6521(3)
0.658 8(3)
0.5469(3)
0.8434(3)
0.7623(4)
0.7354(4)
0.7848(3)
1.1026(3)
1.0682(3)
1.0313(3)
1.0265(3)
0.3240(2)
0.4119(3)
0.6351(3)
0.6014(4)
0.9356(4)
1.0081(5)
1.1048(5)
1.1048(5)
0.9931(5)
0.5097(4)
0.6046(4)
0.6847(3)
0.6383(4)
0.5310(4)
2.05(2)
2.51(2)
2.03(4)
2.5(1)
2.7(2)
2.5(2)
2.9(2)
2.9(2)
3.1(2)
3.9(2)
3.7(2)
2.8(2)
4.0(2)
2.7(2)
4.2(2)
2.8(2)
4.4(2)
3.0(2)
6.3(2)
3.8(2)
4.9(3)
5.0(3)
5.7(3)
5.7(3)
5.3(3)
3.6(2)
3.2(2)
3.5(2)
4.2(2)
4.0(2)
C(7)
C(8)
C(9)
0.5385(5)
0.5339(4)
0.4087(5)
0.2080(4)
O(10)
C(10)
O(20)
C(20)
O(30)
C(30)
O(40)
C(40)
C(51)
C(52)
C(53)
C(54)
C(55)
C(61)
C(62)
C(63)
C(64)
C(65)
1
(vs), 1940 (vs) cm−1. H-NMR (d, ppm, CDCl3) (see
Table 3 for atom labelling): 1.47 (4H, m, CHAHB),
1.24, 1.74, 1.94, 3.58 (8H, m, THF CH2); 4.71 (5H, s,
Cp), 4.78 (5H, s, Cp); 5.98 (2H, s, ꢀCHC); 13C{1H}-
NMR (d, ppm, CDCl3): 24.24 (ring CH2), 63.66,
37.69, 34.38, 3.46 (THF CH2), 85.39, 83.53 (Cp),
131.31 (ꢀCH), 214.22 (CO).
0.2094(5)
−0.1643(4)
−0.2150(5)
−0.1581(6)
−0.2147(7)
0.0869(7)
0.1571(6)
0.0871(7)
−0.0305(6)
−0.0295(6)
−0.4995(6)
−0.4161(5)
−0.4664(6)
−0.5585(6)
−0.5591(5)
2.2.5. 1-(Tetracarbonylcobaltio)-1,3-
dimethylsilacyclopent-3-ene (11)
In a flask equipped with a condenser were added
1.32 g (3.9 mmol) of Co2(CO)8 dissolved in pentane
(30 mL) and 0.96 g (8.6 mmol) of 1,3-dimethylsilacy-
clopent-3-ene (4) in pentane (10 mL). This mixture
was refluxed for 24 h until complete disappearance of
Co2(CO)8. Concentration of the solution in vacuo and
work up gave 0.87 g of 11 as a dark powder (yield:
40%). Anal. Calcd. (Found) for C10H11CoO4Si: C,
42.56 (42.07); H, 3.93 (3.81). IR (pentane): w(CO),
a Biso is the mean of the principal axes of the thermal ellipsoid.
2008, 2034, 2052, 2096 cm−1 1H-NMR (l, ppm,
.
CDCl3, 80 MHz): 5.80, (m br, 1H, ꢀCH); 1.62 (m br,
4H, CH2); 1.44 (s, 3H, C–CH3); 0.73 (s, 3H, Si–
CH3).
1-(Dicarbonylcyclopentadienylferrio)-1-
phenylsilacyclopent-3-ene(6)
By using the same procedure as above, 1.10 g (3.1
mmol) of [CpFe(CO)2]2 and 1.22 g (6.2 mmol) of 2
gave 1.40 g of a yellow powder of 6 (yield: 67%).
Anal. Calcd. (Found) for C17H16FeO2Si: C, 60.73
(60.07); H, 4.80 (4.83). IR (pentane): w(CO), 1995
2.3. Crystallographic work on 8
Yellow crystals of 8 were grown from pentane at
−20°C. The dimensions (mm) of the specimen used
were 0.40 {001}×0.45 {010}×0.48 {100}. The X-ray
work was carried out with an Enraf-Nonius CAD-4
diffractometer using graphite-monochromatized Cu–
Kh radiation. The reduced cell was deduced from 25
reflections detected on an oscillation photograph. The
Niggli parameters ruled out any symmetry higher
than triclinic, leaving P1 and P1 as possible space
groups. The structure solved and refined normally in
the centric P1 space group. Crystal data and other
relevant crystallographic information are summarized
in Table 1.
.
(vs), 1940 (vs) cm−1 1H- and 13C{1H}-NMR: see
Table 3.
2.2.3. 1-(Dicarbonylcyclopentadieny-
lferrio)-1-methylsilacyclopent-3 -ene (4)
As above, 1.00 g (2.83 mmol) of [CpFe(CO)2]2 and
0.75 g (5.66 mmol) of 3 gave 0.93 g of 7 as a yellow
powder (yield: 60%). Anal. Calcd. (Found) for
C12H14FeO2Si: C, 52.57 (52.18); H, 5.15 (5.21). IR
(pentane): w(CO), 2000 (vs), 1950 (vs) cm−1. H- and
1
13C{1H}-NMR: see Table 3.

56
P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
Scheme 2.
The intensity data were collected by the ꢀ/2q scan
integration, transmission range: 0.02–0.17). Equivalent
reflections were averaged and corrected for the Lorentz
and polarization effects. The final data set consisted of
4205 independent reflections, of which 3348 with I\3.0
|(I), were retained for structure determination.
The structure was solved by direct methods using
SHELXS-86 [6] and difference Fourier syntheses using
NCRVAX [7]. Least-squares refinement was based on
F. All non-hydrogen atoms were refined anisotropically.
Hydrogens were initially introduced at idealized posi-
tions and refined isotropically in the last cycles. Conver-
gence was reached for R and Rw values of 0.040 and
0.045, respectively. The scattering curves were taken
from standard sources [8]. The anomalous dispersion
contributions df% and df%% for Fe and Si were from
Cromer and Liberman [9]. The final atomic positional
parameters for the non-hydrogen atoms are listed in
Table 2.
technique, with a scan range Dꢀ of (0.80+0.14 tanq)°
and a constant scan rate of 16.5° min−1. Orientation
was monitored every 400 measurements, whereas inten-
sity was checked every hour with five standard reflec-
tions. Intensity fluctuation remained within 93.4%.
The whole sphere of data (8274 reflections) was col-
lected. An absorption correction was applied (Gaussian
Table 3
1H- and 13C{1H}-NMR data for the Cp(CO)2Fe(RSiC4H6) com-
poundsa
Compound R=Cl (5)
R=Ph (6)
R=Me (7)
1H
In CDCl3
In CDCl3
In CDCl3
HA, HB
1.86, dd, 4H
1.47, dd, 4H
0.89, dd, 4H
J
AB=17.2 Hz
J
AB=17.8 Hz
JAB=15.3 Hz
HC
R
6.06, s, 2H
5.98, s, 2H
7.59; 7.31, m,
5H (Ph)
5.92, s, 2H
0.3, s, 3H (Me)
Cp
4.06, s, 5H
In C6D6
29.14
4.63, s, 5H
In CDCl3
23.34
4.72, s, 5H
In C6D6
25.50
129.75
4.60 (Me)
13C
C1, C4
C2, C3
R
3. Results and discussion
130.98
128.06
127.71, 131.49,
132.97 (Ph)
83.97
In THF at low temperature, metathesis reactions
between the different silacyclopent-3-enes and the iron
metallate anion [CpFe(CO)2]− in a 1/1 ratio were ob-
served to give good yields of the monosubstituted com-
plexes 1-(dicarbonylcyclopentadienylferrio)-1-chlorosil-
acyclopent-3-ene) (5), 1-(dicarbonylcyclopentadienylfer-
rio)-1-phenylsilacyclopent-3-ene (6) and 1-(dicarbonyl-
cyclopentadienylferrio)-1-methylsilacyclopent-3-ene (7)
(Scheme 2).
Cp
84.41
84.65
CO
213.22
213.60
213.20
a Room temperature, 80 MHz for 1H, 50.32 MHz for 13C.
The three compounds gave satisfactory spectroscopic
and elemental analysis data. The carbonyl stretches in
the IR spectra were consistent with identical local sym-
1
metry around iron in all cases. In the H-NMR spectra

P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
57
Fig. 1. ORTEP drawing of molecule 8. Ellipsoids are drawn at 40% probability level. Hydrogens are shown as small spheres of arbitrary size.
spectrum of the latter compound in solution showed
only one singlet for these methylene protons, a result
that was tentatively explained by fast exchange between
the endo and exo isomeric forms. In contrast, our
spectra indicate the presence of only one isomer in
which the metal fragment is likely located at the exo
position, as observed in complex 8 (vide infra).
(Table 3), the complexes exhibited a non-first order
doublet of doublets at 0.9–1.9 ppm for the methylene
protons HA/HB of the silacyclopent-3-ene ring, indicat-
ing the loss of ring planarity [10] upon metal coordina-
tion. Thus, the metal-bonded molecules adopt a
puckered conformation, as observed for a related com-
plex with a germacyclopentene derivative in the solid
state [11]. However, it should be noted that the NMR
Reacting 1 with two equivalents of Na[CpFe(CO)2]
under the same experimental conditions gave com-
pound 8 as an orange powder in 65% yield. Only two
w(CO) stretches appeared as strong and broad bands at
1998 and 1940 cm−1, respectively, indicating that the
two CpFe(CO)2 fragments possess similar local envi-
Table 4
˚
Selected interatomic distances (A) and bond angles (°) for 8
Fe(1)ꢁSi
2.2914(13) Fe(2)ꢁC(5)
2.077(4)
1.755(4)
1.738(5)
2.115(4)
2.113(4)
2.098(4)
2.108(4)
2.107(4)
1.532(5)
1.521(5)
1.506(7)
1.300(7)
1.491(6)
1.136(5)
1.148(6)
88.9(2)
Fe(1)ꢁC(10)
Fe(1)ꢁC(20)
Fe(1)ꢁC(51)
Fe(1)ꢁC(52)
Fe(1)ꢁC(53)
Fe(1)ꢁC(54)
Fe(1)ꢁC(55)
SiꢁO(1)
SiꢁC(6)
SiꢁC(9)
O(1)ꢁC(2)
C(2)ꢁC(3)
1.737(4)
1.731(4)
2.079(4)
2.075(4)
2.096(4)
2.095(4)
2.070(4)
1.655(3)
1.876(4)
1.880(4)
1.420(4)
1.508(5)
1.155(5)
1.162(5)
86.4(1)
Fe(2)ꢁC(30)
Fe(2)ꢁC(40)
Fe(2)ꢁC(61)
Fe(2)ꢁC(62)
Fe(2)ꢁC(63)
Fe(2)ꢁC(64)
Fe(2)ꢁC(65)
C(3)ꢁC(4)
C(4)ꢁC(5)
C(6)ꢁC(7)
C(7)ꢁC(8)
C(8)ꢁC(9)
1
ronments. The H-NMR spectra were consistent with
the presence of a silacyclopentene ring and two non-
equivalent Cp ligands in the compound. Although the
existence of a THF unit was suggested from the micro-
analysis and the NMR signals for methylene groups at
1.24, 1.74, 1.94 and 3.58 ppm, an X-ray diffraction
study was needed to definitively established the struc-
ture of this complex.
Single crystals suitable for X-ray work were obtained
by slow crystallization from pentane. The structure of 8
is illustrated in Fig. 1. Selected interatomic distances
and bond angles are listed in Table 4. The unit cell
consists of discrete molecules containing two
CpFe(CO)2 fragments: one is bonded directly to the Si
O(10)ꢁC(10)
O(20)ꢁC(20)
SiꢁFe(1)ꢁC(10)
SiꢁFe(1)ꢁC(20)
SiꢁFe(1)ꢁC(50*)a
C(10)ꢁFe(1)ꢁC(20)
O(30)ꢁC(30)
O(40)ꢁC(40)
C(5)ꢁFe(2)ꢁC(30)
C(5)ꢁFe(2)ꢁC(40)
84.7(1)
119.1(2)
93.6(2)
86.8(2)
C(5)ꢁFe(2)ꢁC(60*)a 120.9(2)
C(30)ꢁFe(2)ꢁC(40)
93.4(2)
C(10)ꢁFe(1)ꢁC(50*)a 127.5(2)
C(30)ꢁFe(2)ꢁC(60*)a 124.9(2)
C(20)ꢁFe(1)ꢁC(50*)a 130.9(2)
C(40)ꢁFe(2)ꢁC(60*)a 129.8(2)
Fe(1)ꢁSiꢁO(1)
Fe(1)ꢁSiꢁC(6)
Fe(1)ꢁSiꢁC(9)
SiꢁO(1)ꢁC(2)
O(1)ꢁC(2)ꢁC(3)
C(2)ꢁC(3)ꢁC(4)
C(3)ꢁC(4)ꢁC(5)
Fe(2)ꢁC(5)ꢁC(4)
Fe(1)ꢁC(10)ꢁO(10)
Fe(1)ꢁC(20)ꢁO(20)
114.4(1)
117.5(1)
117.6(1)
125.2(2)
109.8(3)
112.9(3)
111.7(3)
115.6(3)
179.1(3)
178.2(4)
O(1)ꢁSiꢁC(6)
O(1)ꢁSiꢁC(9)
C(6)ꢁSiꢁC(9)
SiꢁC(6)ꢁC(7)
C(6)ꢁC(7)ꢁC(8)
C(7)ꢁC(8)ꢁC(9)
SiꢁC(9)ꢁC(8)
107.6(2)
102.8(2)
94.4(1)
101.9(3)
118.8(4)
119.4(4)
102.1(3)
Fe(2)ꢁC(30)ꢁO(30)
Fe(2)ꢁC(40)ꢁO(40)
178.6(4)
178.7(5)
a
C(50*) and C(60*) are the centres of the Cp rings.
Scheme 3.

58
P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
Scheme 4.
The geometry of the silacyclopentene ring is very
similar to that of the dimethylated five-membred ring in
a disiladispirooctadecatetraene system [18]. The Si–C
atom of the silacyclopent-3-ene ring, whereas the other
is at the carbon end of an opened THF molecule
connected to the same Si atom by the oxygen end. Both
metal centers are coordinatively saturated 18-electron
systems. Their geometry is best described in terms of a
distorted octahedral environment, in which five apices
are occupied by the Cp ring (three sites) and two cis CO
ligands. In the case of Fe(1), the sixth position is filled
by a Si atom, whereas for Fe(2), it is occupied by a
methylene group of the opened THF molecule acting as
a bridging unit between Si and Fe(2).
˚
bond lengths (mean 1.878 A) correspond to the value
expected on the basis of covalent radii. The CꢀC (1.300
˚
˚
A) and C–C distances (mean 1.498 A) are also normal.
The angles in the ring carbon atoms are remarkably
close to those for sp3 and sp2 hybridizations. Therefore,
the carbon part of the ring is not greatly affected by the
presence of the long Si–C bonds, which simply reduce
the C–Si–C angle to 94.4(2)°. This very small angle is
not induced by the presence of the bulky FeCp(CO)2
group, since it is not very different (95.2(1)°) in the
dispiro compound. In fact, the five-membred ring ge-
ometry seems to be relatively insensitive to steric effects
at the Si atom. X-ray results are available for a mono-
spiro compound in which the other ring is a sustituted
silabutylene [19]. Scheme 3 compares the angles in the
five-membred rings in our complex 8 and in this spiro
compounds. It is noteworthy that the Si atom can
accommodate a very large angular variation from 78.3
to 114.4°, while producing only small changes in the
ring from 94.4(2) to 92.9(3)°. Similar differences are
found on the angles at the adjacent carbons, but the
environment of the CꢀC bond is unaffected.
Both Fe centres possess the environment typical of
CpFe(CO)2L systems. The distances from Fe(1) to the
˚
Cp carbons (mean 2.084 A) and CO ligands (mean
˚
1.734 A) are close to those found for complexes with
other Si-donor groups [12–16]. The Fe–Si distance,
however, is more sensitive the substituents: our distance
˚
of 2.291(1) A is shorter than for various compounds
˚
with non-cyclic SiMe2R groups (2.328–2.350 A), but
greater than those observed when electron withdrawing
˚
groups are present (–SiCl3, 2.216(1) A; –SiFPh2
˚
˚
2.278(1) A; SiMeF(OR), 2.267 A). In the other
CpFe(CO)2 unit, the Fe(2)–CO and Fe–C(Cp) dis-
˚
tances (mean values of 1.746 and 2.108 A, respectively)
seem to be slightly greater, whereas the CO–Fe–CO
and Cp–Fe–CO angles are a few degrees smaller than
those around Fe(1). This is consistent with the local
steric requirement of the coordinated methylene group
being greater than for the more distant Si-donor group.
The planarity of the silacyclopent-3-ene ring is lost
on coordination, which confirms the NMR data. The
ring adopts an envelope conformation with a dihedral
angle of 12° between the C–CꢀC–C and C–Si–C
planes. This value is much lower than in the germacy-
clopent-3-ene analogue (30°), but the mono- and
˚
The Fe–CH2 distance (2.077(4) A) is similar to those of
other CpFe(CO)2(alkyl) systems [17].

P. Dufour et al. / Journal of Organometallic Chemistry 563 (1998) 53–60
59
Scheme 5.
2008, 2034, 2052 and 2096 cm−1, respectively, in agree-
ment with the IR data reported in the literature for
R3SiCo(CO)4 complexes (2). Since this compound
shows only one H-NMR signal for the Si–CH3 group,
a single isomer is likely formed, as noticed above for
the Fe systems.
dispiro compounds are much closer to planarity, with
dihedral angles of 13.6 and 5.3°, respectively. As ob-
served in solution, only one isomer is present in the
solid state, the one with the Si-bonded CpFe(CO)2
group occupying the least sterically hindered exo site,
the all-trans conformation of the O(CH2)4FeCp(CO)2
unit reducing the overall steric requirement of this
group.
1
4. Conclusion
Insertion of a THF molecule into the Si–Fe(2) bond
results from ring opening of the cyclic ether, a reaction
for which there is few precedents in the literature
[20,21]. A tentative mechanism can be proposed [22].
The first step corresponds to the | coordination of the
[CpFe(CO)2]− anion to the Si atom via a SN2 process
giving 5 [23]. Presence of a second [CpFe(CO)2]− anion
generates the ion-pair intermediate 9 characterized by a
strong silicon–oxygen bond [20,21,24]. Formation of 8
results then from the THF ring opening assisted by the
nucleophilic attack of the [CpFe(CO)2]‘ anion (Scheme
4). In agreement with this hypothesis is the fact that no
THF insertion was observed when two reactants were
in the 1/1 ratio, no matter the experimental conditions
applied. No other iron species were present in the
solution. Moreover, the reaction carried out with excess
[CpFe(CO)2]− in diethyl ether stopped at the monosub-
stitution stage, giving only complex 5 and in pentane,
the mixture was heterogeneous and no reaction
occurred.
Suitable experimental conditions of solvent, tempera-
ture and concentration allowed us to synthesize com-
pounds containing silacyclopent-3-ene |-bonded to
iron complexes via the Si atom without opening of the
silacyclopentene ring. These complexes are all stable.
They are characterized by the presence of a puckered
silacyclopentene ring and they illustrate the ability of
the Si atom to undergo distortions far from the tetrahe-
dral arrangement in order to accommodate substitu-
tents with a broad range of sizes.
5. Supplementary material available
Packing pattern, lists of temperature factors, hydro-
gen coordinates, bond lengths and angles, least-squares
planes, torsion angles and structure factor amplitudes
(35 pages) are available upon request from ALB.
3.1. Compounds with a | silicon-cobalt bond
Acknowledgements
No reaction took place when 1, 2 and 3 were reacted
with [Co(CO)4]− synthesized in-situ by reduction of the
dimer using Na/Hg [4] or K[BH(sec-Bu)3] [5] in THF.
In this case, the solvent favored charge delocalization
from the oxygen atom, giving polymers through Si–O–
Si bond formation [21,25,26] and dimers of the metal-
late anions [26]. No better results were obtained by
using pentane as solvent. However, the cobalt deriva-
tive 11 was successfuly prepared by hydrosilylation [2]
(Scheme 5).
We acknowledge financial support from the French
Ministe`re de l’Enseignement Supe´rieur, de la Recherche
et de la Technologie, and the Natural Sciences and
Engineering Research Council of Canada.
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