Synthesis, structure and thermal rearrangement of tetramethyldisilane-bridged bis(cyclopentadienyl) diiron complexes with a phosphite or phosphine ligand substitution

Article abstract of DOI:10.1016/S0277-5387(99)00180-1

Photolysis of tetramethyldisilane-bridged bis(cyclopentadienyl) tetracarbonyl di-iron in the presence of phosphite or phosphine ligand afforded the corresponding Fe-Fe bond complexes with one carbonyl replaced by a phosphite or phosphine ligand: [(Me₂SiSiMe₂)Cp₂Fe₂(CO)(PR ₃)(μ-CO)₂] (R=OPh, 1; OEt, 2; Ph, 3). When these complexes were heated in refluxing xylene, they become rearranged to the corresponding products [(Me₂SiCpFe)₂(CO)₃(PR₃)] (R=OPh, 4; OEt, 5; Ph, 6). It was found that, after phosphite or phosphine ligand substitution, the rearrangement became facile. The molecular structures of 1-6 were characterized by IR, ¹H NMR spectra and elemental analyses. The crystal structures of 1 and 4 were determined by X-ray diffraction analysis. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00180-1

Polyhedron 18 (1999) 2645–2650
Synthesis, structure and thermal rearrangement of tetramethyldisilane-
bridged bis(cyclopentadienyl) diiron complexes with a phosphite or
phosphine ligand substitution
Wen-Hua Xiea, Bai-Quan Wanga, Shan-Sheng Xua, Xiu-Zhong Zhoua , , Kung-Kai Cheung
b
*
aDepartment of Chemistry, Nankai University, Tianjin 300071, PR China
bDepartment of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
Received 23 February 1999; accepted 9 June 1999
Abstract
Photolysis of tetramethyldisilane-bridged bis(cyclopentadienyl) tetracarbonyl di-iron in the presence of phosphite or phosphine ligand
afforded the corresponding Fe–Fe bond complexes with one carbonyl replaced by phosphite or phosphine ligand:
a
[(Me2SiSiMe2)Cp2Fe2(CO)(PR3)(m-CO)2] (R5OPh, 1; OEt, 2; Ph, 3). When these complexes were heated in refluxing xylene, they
become rearranged to the corresponding products [(Me2SiCpFe)2(CO)3(PR3)] (R5OPh, 4; OEt, 5; Ph, 6). It was found that, after
phosphite or phosphine ligand substitution, the rearrangement became facile. The molecular structures of 1–6 were characterized by IR,
1H NMR spectra and elemental analyses. The crystal structures of 1 and 4 were determined by X-ray diffraction analysis.
1999
Elsevier Science Ltd. All rights reserved.
Keywords: Rearrangement; Sila-bridged; Fe–Fe bond
1. Introduction
atoms of the cyclopentadienyl rings were substituted, or
the cyclopentadienyl replaced by indenyl, or the silyl
bridge replaced by germyl bridge, or using ruthenium
instead of iron, the thermal rearrangement reaction could
still occur [7–13] (Scheme 1).
In order to examine the effect of replacement of the
carbonyl ligand on the rearrangement reaction, we report
here the synthesis of tetramethyldisilane-bridged
bis(cyclopentadienyl) Fe–Fe bond complexes with a phos-
phite or phosphine ligand substitution and the effect on
their thermal rearrangement reaction.
The chemistry of transition metal–silicon complexes has
become a significant facet of the general chemistry of
silicon [1]. Another important and in many ways a more
fundamental feature of silicon chemistry that has attracted
researchers is the nature of the Si–Si bond. Since transition
metal complexes either activating or containing a Si–Si
bond were reported in 1965 and 1969 [2,3], a significant
amount of work followed these seminal studies in the
literature [4]. We have recently reported a novel thermal
rearrangement reaction involving Si–Si and Fe–Fe bonds
in the tetramethyldisilane-bridged diiron complex
(Me2SiSiMe2)[(h5-C5H4)Fe(CO)2]2(m-CO)2 [5]. A de-
tailed investigation of the reaction mechanism indicated
that it is a stereospecific intramolecular reaction via the
iron radical intermediate [6]. Later, we further studied the
scope of the reaction and found that when the hydrogen
2. Experimental
Solvents were distilled from appropriate drying agents
under argon before use. All manipulations were under
argon using standard Schlenk and vacuum-line techniques.
1H NMR spectra were obtained on a BRUKER AC-P200
or JEOL FX-90Q spectrometer, while IR spectra were
obtained on a Nicolet 5DX FT-IR spectrometer. Elemental
analyses were performed with a CHN CORDER MF-3
analyzer.
*Corresponding author. Tel.: 186-22-2350-4781; fax: 186-22-2350-
2458.
E-mail address: zhouxz@public1.tpt.tj.cn (X.-Z. Zhou)
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00180-1
1999 Elsevier Science Ltd. All rights reserved.

2646
W.-H. Xie et al. / Polyhedron 18 (1999) 2645–2650
Scheme 1.
2.1. Preparation of complex 1
0.21 g (60%) of 4 as light yellow solid, m.p.146–1478C.
Anal. Found: C, 55.77; H, 4.61. C35H35Fe2O6PSi2 Calcd.:
C, 56.01; H, 4.70%. IR (KBr): [nco /cm21] 1983.2 vs.,
1917.6 vs. 1H NMR (90 MHz, CDCl3): dH 7.38–7.15 (m,
15H), 5.30 (d, 2H), 5.06(d, 2H), 4.78(s, 2H), 4.38(m, 2H),
0.62 (s, 3H), 0.58 (s, 3H), 0.49 (s, 3H), 0.34(s, 3H) ppm.
The rearrangement reactions of 2 and 3 were carried out
under similar conditions. The reactions were completed
after about 30 min and the corresponding rearrangement
products 5 and 6 were obtained in 68% and 48% yield,
respectively.
A
solution
of
1.1
g
(2.3
mmol)
of
(Me2SiSiMe2)[CpFe(CO)]2(m-CO)2 [5] and 1.21 g (3.8
mmol) of P(OPh)3 in 50 ml of benzene was irradiated with
a 300 W high-pressure mercury lamp until disappearance
of the substrate (ca. 15 h). Then the solvent was removed
under vacuum and the residue was extracted with CH2Cl2.
The extraction was concentrated and recrystallized from
benzene/pentane to give 1.05 g (60%) of 1 as dark red
crystals, m.p. 2428C (dec.). Anal. Found: C, 55.82; H,
4.49. C35H35Fe2O6PSi2 Calcd.: C, 56.01; H, 4.70%. IR
Complex 5, m.p. 122–38C. Anal. Found: C, 45.50; H,
5.59. C23H35Fe2O6PSi2 Calcd.: C, 45.56; H, 5.82%. IR
(KBr): [nco /cm21] 1958.6 vs., 1737.1 vs. H NMR (200
MHz, CDCl3): dH 7.33(m, 15H), 5.39(s, 2H), 4.68(s, 2H),
1
1
(KBr): [nco /cm21] 1981.2 vs., 1912.5 vs. H NMR (200
4.43(s, 2H), 3.50(s, 2H), 0.15(s, 6H) ppm.
MHz, CDCl3): dH 5.08(s, 2H), 4.98(s, 2H), 4.66(t, 2H),
4.30(s, 2H), 3.96(q, 6H), 1.30(t, 9H), 0.56 (s, 3H), 0.49(s,
3H), 0.42(s, 3H), 0.26(s, 3H) ppm.
2.2. Preparation of 2 and 3
Complex 6, m.p. 1978C (dec.). Anal. Found: C, 59.60;
H, 4.89. C35H35Fe2O3PSi2 Calcd.: C, 59.84; H, 5.02%. IR
Complexes 2 and 3 were prepared by the reaction of
(Me2SiSiMe2)[CpFe(CO)]2(m-CO)2 and P(OEt)3 or PPh3
in 63% or 32% yield respectively using the similar method
described for 1.
1
(KBr): [nco /cm21] 1983.9 vs., 1916.3 vs., 1891.5 vs. H
NMR (200 MHz, CDCl3): dH 7.52–7.37(m, 15H), 5.33(s,
1H), 5.07(t, 3H), 4.83(s, 1H), 4.70(s, 1H), 4.39(s, 1H),
2.82(s, 1H), 0.70(s, 3H), 0.54(s, 3H), 0.40(s, 3H), 20.66(s,
3H) ppm.
Complex 2, m.p. 2038C (dec.). Anal. Found: C, 45.50;
H, 5.59. C23H35Fe2O6PSi2 Calcd.: C, 45.56; H, 5.82%. IR
(KBr): [nco /cm21] 1956.3 vs., 1741.2 vs. H NMR (90
1
MHz, CDCl3): dH 5.12(s, 2H), 4.80(s, 2H), 4.64(s, 2H),
4.42(s, 2H), 3.94(q, 6H), 1.32(t, 9H), 0.31(s, 6H), 0.19(s,
6H) ppm.
2.4. Crystallographic studies
Crystals of 1 suitable for X-ray diffraction were ob-
tained from benzene/pentane solution. All data were
collected on an Enraf-Nonius CAD4 diffractometer with
Complex 3, m.p. 2078C (dec.). Anal. Found: C, 60.07;
H, 5.22. C35H35Fe2O3PSi2 Calcd.: C, 59.84; H, 5.02%. IR
1
(KBr): [nco /cm21] 1960.5 vs., 1735.1 vs. H NMR (200
˚
graphite monochromated MoKa (l50.71073 A) radiation.
MHz, CDCl3): dH 5.20(s, 2H), 5.08(s, 2H), 4.78(s, 2H4),
4.56 (s, 2H), 0.41(s, 6H), 0.23(s, 6H) ppm.
Corrections for empirical absorption were applied to the
intensity data. The structure was solved by direct methods
and expanded using Fourier techniques. The non-hydrogen
atoms were refined anisotropically. Hydrogen atoms at
calculated positions with thermal parameters equal to 1.3
times that of the attached carbon atoms were not refined.
All calculations were performed using the teXsan Crystal-
lographic Software Package [15] on a Silicon Graphics
Indy computer.
2.3. Rearrangement reaction
0.35 g of 1 was heated in refluxing xylene (30 ml). The
color changed to light rapidly and became orange yellow
after about 30 min. After removal of solvent, the residue
was resolved in CH2Cl2, filtered through a Al2O3 column
(3315 cm) and eluted with CH2Cl2. The yellow solid
obtained was recrystallized from CH2Cl2 /pentane to give
Crystals of 4 suitable for X-ray diffraction were ob-
tained from CH2Cl2 /pentane solution. All data were

W.-H. Xie et al. / Polyhedron 18 (1999) 2645–2650
2647
collected on the Rigaku AFC7R diffractometer and the
structure was determined as described for 1.
tadienyl protons in 1HNMR spectra of a phosphite or
phosphine ligand substituted complex became more clear.
1
Another aspect of the HNMR spectra worth noting is the
shielding effect by aromatic ring current of a phosphite or
phosphine ligand. For example, the two protons of
cyclopentadienyl group in complex 1 appeared at a much
higher field (d 3.50) than other cyclopentadienyl protons.
It is evident that the two protons were shielded by an
aromatic ring current of P(OPh)3. It has also been sub-
stantiated by X-ray analysis. A more evident example is
that one proton of cyclopentadienyl group appeared at d
2.82 and protons of a silicon methyl group appeared at d
20.66 in complex 6. Such an upfield shift is evidently due
to the shielding effect of a nearby aromatic ring current.
3. Results and discussion
3.1. Synthesis of 1–3 and their thermal rearrangement
reaction
Photolysis of tetramethyldisilane-bridged bis(cyclopen-
tadienyl) tetracarbonyl di-iron in the presence of phosphite
or phosphine ligand afforded the corresponding Fe–Fe
bond complexes with one carbonyl replaced by a phosphite
or
phosphine
ligand:
[(Me2SiSiMe2)Cp2Fe2(CO)
(PR3)(m-CO)2] (R5OPh, 1; OEt, 2; Ph, 3) (Scheme 2).
Similar to the case of other bridged analogs,
3.3. Crystallography
E[CpFe(CO)]2(m-CO)2
[E5CH(NMe2)CH(NMe2),
CMe2CMe2], only one carbonyl was replaced even when
the irradiation time was extended [14], indicating that the
rearrangement reaction between Si–Si and Fe–Fe bonds
could not take place under irradiation.
The crystal structures of 1 and 4 were determined by
X-ray diffraction analysis. The molecular structures of 1
and 4 are presented in Figs. 1 and 2, respectively. A
summary of the crystallographic results is presented in
Table 1. Tables 2 and 3 provide selected bond distances
and angles of 1 and 4, respectively. In 1, the dihedral angle
between two cyclopentadienyl ring planes is 88.228. Si(1)
and Si(2) deviate from the linked cyclopentadienyl plane
When these complexes were heated in refluxing xylene,
they were converted to the corresponding rearrangement
products, [(Me2SiCpFe)2(CO)3(PR3)] (R5OPh, 4; OEt, 5;
Ph, 6). It was found that the rearrangement that required
more than 10 h could be accomplished in only 30 min after
phosphite or phosphine substitution. This may be rational-
ized by the fact that the Fe–Fe bond becomes weaker after
phosphite or phosphine ligand substitution. On the other
hand, phosphite or phosphine ligand substitution could
make the iron-centered radical more stable. The fact that
the rearrangement reaction rate increases significantly after
phosphite or phosphine ligand substitution also indicates
that the cleavage of Fe–Fe bond is a key step for the
rearrangement reaction and it supports the mechanism
suggested by the present authors [6].
˚
˚
by 0.152 A and 0.205 A, respectively. Si(1), Si(2), Fe(1)
and Fe(2) are co-planar on the whole. C(8) and C(17) lie
on the same side of the plane and the distances to the plane
˚
˚
are 0.413 A and 0.450 A, respectively. It indicates that the
six-membered ring formed from the above atoms takes a
boat conformation. The fragment Fe(1)–C(1)–O(1) is no
longer linear (172.68) due to the steric effect of P(OPh)3.
From Fig. 1 it can be seen that C(14) and C(15) are in the
fielding area of aromatic ring C(30)–C(35) which accounts
1
for the high field shifts in its H NMR spectrum.
Unlike many rearrangement products, 4 no longer has Ci
symmetry owing to the bulky P(OPh)3 substitution.The
dihedral angle between two cyclopentadienyl ring planes is
11.128. Like many analogues, the six-member ring Fe(1)–
Fe(2)–Si(1)–Si(2)–C(2)–C(11) still takes a chair con-
formation but with somewhat twisted (Fe(1), Fe(2), C(2)
3.2. Spectroscopy
1
Complexes 1–6 were characterized by IR, H NMR
spectra and elemental analysis. Compared to the parent
complexes, the splitting of silicon methyl and cyclopen-
Scheme 2.

2648
W.-H. Xie et al. / Polyhedron 18 (1999) 2645–2650
Fig. 1. The molecular structure of 1.
and C(11) are planar, Si(1) and Si(2) deviate from the
CB2 1EZ, UK on request, quoting the deposition numbers
CCDC 114602 and CCDC 114603.
˚
˚
plane by 0.569 A and 0.722 A). Si(1) and Si(2) deviate
˚
from the linked cyclopentadienyl plane by 0.401 A and
˚
0.202 A, respectively.
Acknowledgements
We greatly appreciate financial support from the Nation-
al Natural Science Foundation of China, the Doctoral
Foundation of State Education Department of China and
State Key Laboratory of Elemento-Organic Chemistry of
Nankai University.
4. Supplementary data
Supplementary data are available from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
Fig. 2. The molecular structure of 4.

W.-H. Xie et al. / Polyhedron 18 (1999) 2645–2650
2649
Table 1
Summary of crystal data and data collection and refinement for 1 and 4
1
4
Formula
C35H35Fe2O6PSi2?1/2C6H6
C35H35Fe2O6PSi2
750.50
M (g mol21
)
789.55
Monoclinic
C2/c(No.15)
25.880(4)
9.431(1)
31.499(7)
107.08(2)
7349(2)
8
Crystal system
Space group
Monoclinic
P21 /n(No.14)
15.504(3)
11.029(2)
21.183(2)
103.935(9)
3515.5(9)
4
˚
a (A)
˚
b (A)
˚
c (A)
b (8)
V (A )
3
˚
Z
Dc (g/cm3)
F(000)
1.427
3272
1.418
1552
Temperature (K)
m (MoKa) (cm21
2umax (8)
298(61)
9.42
45
301(61)
9.81
48
)
Reflections collected
Independent reflections
Observed reflections [I.3s(I)]
Number of refined parameters
Goodness of fit
5276
5185
3130
427
6093
5856
3616
415
2.06
2.91
Rint
0.028
0.025
Final R and Rw
Maximum D/s
Max. residual peak (e A )
0.037 and 0.040
0.01
0.59
0.061 and 0.064
0.01
1.07
3
˚
Table 2
a
˚
Selected bond distances (A) and bond angles (8) of 1
Fe(1)–Fe(2)
Fe(1)–C(8)
Fe(2)–P(1)
P(1)–O(6)
O(6)–C(30)
Si(1)–PL(1)
Fe(2)–Fe(1)–C(8)
Fe(1)–C(8)–Si(1)
Si(1)–Si(2)–C(17)
Fe(1)–Fe(2)–P(1)
Fe(2)–P(1)–O(4)
Fe(2)–P(1)–O(6)
O(4)–P(1)–O(6)
P(1)–O(4)–C(18)
P(1)–O(6)–C(30)
2.540(1)
2.179(6)
2.120(2)
1.625(3)
1.399(6)
0.152
Si(1)–Si(2)
Si(2)–C(17)
P(1)–O(4)
O(4)–C(18)
Fe(1)–PL(1)
Si(2)–PL(2)
108.6(1)
130.7(3)
113.8(2)
104.45(5)
116.2(1)
119.7(1)
2.351(2)
1.857(5)
1.602(4)
1.405(6)
1.754
0.205
Fe(1)–Fe(2)–C(17)
Fe(2)–C(17)–Si(2)
Si(2)–Si(1)–C(8)
Fe(1)–C(1)–O(1)
Fe(2)–P(1)–O(5)
O(4)–P(1)–O(5)
O(5)–P(1)–O(6)
P(1)–O(5)–C(24)
PL(1)–PL(2)
Si(1)–C(8)
Fe(2)–C(17)
P(1)–O(5)
O(5)–C(24)
Fe(2)–PL(2)
1.863(6)
2.167(5)
1.607(4)
1.396(6)
1.752
106.2(1)
132.2(3)
113.3(2)
172.6(5)
119.5(1)
97.8(2)
96.4(2)
127.3(3)
88.14
103.3(2)
124.1(3)
125.3(3)
a PL5The plane of five-membered ring.
Table 3
Selected bond distances (A) and bond angels (8) of 4
a
˚
Fe(1)–Si(1)
Si(1)–C(11)
Fe(1)–P(1)
P(1)–O(3)
O(3)–C(30)
Si(2)–PL(1)
Si(1)–Fe(1)–C(2)
P(1)–Fe(1)–Si(1)
Fe(1)–Si(1)–C(11)
Fe(2)–Si(2)–C(2)
Fe(1)–P(1)–O(1)
Fe(1)–P(1)–O(3)
O(1)–P(1)–O(3)
P(1)–O(1)–C(18)
P(1)–O(3)–C(30)
2.326(2)
1.900(7)
2.095(2)
1.640(4)
1.388(9)
0.202
Fe(2)–Si(2)
Si(2)–C(2)
P(1)–O(1)
O(1)–C(18)
Fe(1)–PL(1)
Si(1)–PL(2)
100.6(2)
93.74(8)
111.1(2)
110.6(2)
121.2(2)
2.316(2)
1.877(7)
1.599(5)
1.408(9)
1.717
0.401
Si(2)–Fe(2)–C(11)
P(1)–Fe(1)–C(2)
Fe(1)–C(2)–Si(2)
Fe(2)–C(11)–Si(1)
Fe(1)–P(1)–O(2)
O(1)–P(1)–O(2)
O(2)–P(1)–O(3)
P(1)–O(2)–C(24)
PL(1)–PL(2)
Fe(1)–C(2)
Fe(2)–C(11)
P(1)–O(2)
O(2)–C(24)
Fe(2)–PL(2)
2.112 (7)
2.136(7)
1.592(6)
1.424(9)
1.727
98.4(2)
160.1(2)
132.3(4)
138.5(4)
112.3(2)
103.2(3)
102.2(3)
125.6(5)
11.12
119.0(2)
96.1(2)
130.4(4)
122.9(4)
a PL5The plane of five-membered ring.

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W.-H. Xie et al. / Polyhedron 18 (1999) 2645–2650
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