Synthesis and photochemistry of the three isomeric Si2C2 diiron complexes (see abstract)

Article abstract of DOI:10.1021/om020644a

Photolysis of FpCH₂SiMe₂SiMe₂CH₂Fp (1; Fp = (η⁵-C₅H₅)Fe(CO)₂) for 4 h resulted in the quantitative formation of 1,3-tetramethyldisilacyclobutane (9) and Fp₂. Similar irradiation of meso-FpCH₂SiMePhSiMePhCH₂Fp (2a) led to trans-1,3-dimethyl-1,3-diphenyl-1,3-disila-cyclobutane (10t), while photolysis of the racemic isomer (2b) afforded only cis-1,3-disilacyclobutane (10c) and Fp₂. Photolysis of a mixture of 1 and 2a proved that the process was intramolecular. Irradiation for 35 h of FpCH₂SiMe₂CH₂SiMe₂Fp (3), an isomer of 1, led to clean conversion to 9 and Fp₂ and irradiation of FpCH₂SiMePhCH₂SiMePhFp, a 1:1 mixture of the two diastereomers 6a and 6b, afforded a mixture of 10t and 10c (1:1). The third isomer of 1, FpSiMe₂CH₂CH₂SiMe₂Fp (7), is photochemically inert. Photolysis of the tungsten analogue of 1, WpCH₂SiMe₂SiMe₂CH₂Wp (8; Wp = (η⁵-C₅H₅)W(CO)₃), produced a complex mixture of products.

Full text of DOI:10.1021/om020644a

Organometallics 2002, 21, 5859-5867
5859
Syn th esis a n d P h otoch em istr y of th e Th r ee Isom er ic
Si2C2 Diir on Com p lexes F p CH2SiR2SiR2CH2F p ,
F p CH2SiR2CH2SiR2F p , a n d F p SiMe2CH2CH2SiMe2F p (F p
) (η5-C5H5)F e(CO)2): Ster eosp ecific F or m a tion of
1,3-Disila cyclobu ta n es
Yongqiang Zhang, Francisco Cervantes-Lee, and Keith H. Pannell*
Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968-0513
Received August 9, 2002
Photolysis of FpCH2SiMe2SiMe2CH2Fp (1; Fp ) (η5-C5H5)Fe(CO)2) for 4 h resulted in the
quantitative formation of 1,3-tetramethyldisilacyclobutane (9) and Fp2. Similar irradiation
of meso-FpCH2SiMePhSiMePhCH2Fp (2a ) led to trans-1,3-dimethyl-1,3-diphenyl-1,3-disila-
cyclobutane (10t), while photolysis of the racemic isomer (2b) afforded only cis-1,3-
disilacyclobutane (10c) and Fp2. Photolysis of a mixture of 1 and 2a proved that the process
was intramolecular. Irradiation for 35 h of FpCH2SiMe2CH2SiMe2Fp (3), an isomer of 1, led
to clean conversion to 9 and Fp2 and irradiation of FpCH2SiMePhCH2SiMePhFp, a 1:1
mixture of the two diastereomers 6a and 6b, afforded a mixture of 10t and 10c (1:1). The
third isomer of 1, FpSiMe2CH2CH2SiMe2Fp (7), is photochemically inert. Photolysis of the
tungsten analogue of 1, WpCH2SiMe2SiMe2CH2Wp (8; Wp ) (η5-C5H5)W(CO)3), produced a
complex mixture of products.
In tr od u ction
with respect to the metal center, and thus â-elimination
chemistry results in the transient formation of iron-
silene intermediates that lead to rearrangements (eq 3;
R ) H, (SiMe2)nSiMe3, GeMe3). In the specific case of R
) GeMe3 and Wp ) (η5-C5H5)W(CO)3 (eq 4) a unique
silene elimination occurs.4
The activation of the silicon-silicon bond by transi-
tion metals has implications in catalysis and materials
science.1 The family of oligosilyl Fp derivatives (Fp )
(η5-C5H5)Fe(CO)2) containing direct iron-silicon bonds
exhibit photochemically induced R-elimination reac-
tions, resulting in the formation of silyl(silylene) inter-
mediates, (η5-C5H5)Fe(CO)(SiR3)(dSiR2). These inter-
mediates lead to either silylene eliminations (eq 1) or
rearrangements (eq 2).2,3
Fp-CH2SiMe2R f Fp-SiMe2CH2R
(3)
(4)
Wp-CH2SiMe2R f Wp-R + Me2SidCH2
The silene iron intermediates in these photochemi-
cally induced â-elimination reactions have been char-
acterized only by low-temperature matrix-isolation tech-
niques;5 however, many stable transition-metal silene
complexes have been isolated and structurally charac-
terized.6
Fp-SiMe2SiMe3 f Fp-SiMe3 + [SiMe2]
(1)
Fp-SiMe2SiMe2SiMe2SiMe3 f Fp-Si(SiMe3)3 (2)
The oligosilylmethyl Fp complexes FpCH2(SiMe2)nMe
have the potentially labile silyl group in the â-position
We recently communicated that the photolysis of the
diiron complexes FpCH2SiR2SiR2CH2Fp (R2 ) Me2 (1),
MePh (2)) resulted in stereospecific formation of 1,2-
disilacyclobutanes.7 To further study the factors that
control such chemistry, we now present the synthesis
and photochemical treatment of FpSiR2CH2SiR2CH2Fp
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S.; Kapoor, R. N.; Cervantes-Lee, F.; Pannell, K. H. Polyhedron 1991,
10, 1177. (c) Pannell, K. H.; Kobayashi, T.; Kapoor, R. N. Organo-
metallics 1992, 11, 2229. (d) Sharma, S.; Pannell, K. H. Organo-
metallics 1993, 12, 3979. (e) Pannell, K. H.; Kobayashi, T.; Cervantes-
Lee, F.; Zhang, Y. Organometallics 2000, 19, 1.
(3) (a) Tobita, H.; Ueno, K.; Ogino, H. Chem. Lett. 1986, 1777. (b)
Ueno, K.; Tobita, H.; Shimoi, M.; Ogino, H. J . Am. Chem. Soc. 1988,
110, 4092. (c) Tobita, H.; Ueno, K.; Ogino, H. Chem. Lett. 1990, 1. (d)
Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H. J . Am. Chem. Soc. 1990,
112, 3415. (e) Koe, J . R.; Tibita, H.; Suzuki, T.; Ogino, H. Organo-
metallics 1992, 11, 1, 150. (f) Tobita, H.; Kurita, H.; Ogino, H.
Organometallics 1998, 17, 2844. (g) Tobita, H.; Kurita, H.; Ogino, H.
Organometallics 1998, 17, 2850. (h) Tobita, H.; Sato, T.; Okazaki, M.;
Ogino, H. J . Organomet. Chem. 2000, 611, 314.
(5) (a) Lewis, C.; Wrighton, M. S. J . Am. Chem. Soc. 1983, 105, 7768.
(b) Randolf, C. L.; Wrighton, M. S. Organometallics 1987, 6, 365.
(6) (a) Berry, D. H.; Procopio, L. J . J . Am. Chem. Soc. 1989, 111,
4099. (b) Koloshi, T. S.; Carroll, P. J .; Berry, D. H. J . Am. Chem. Soc.
1990, 112, 6405. (c) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Am.
Chem. Soc. 1990, 112, 4079. (d) Campion, B. K.; Heyn, R. H.; Tilley,
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10.1021/om020644a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/16/2002

5860 Organometallics, Vol. 21, No. 26, 2002
Zhang et al.
(prepared from 2.00 g (5.60 mmol) of [(η5-C5H5)Fe(CO)2]2) was
added 1.14 g (5.30 mmol) of ClCH2Me2SiSiMe2CH2Cl at 0 °C.
The solution was stirred at low temperature and then warmed
to room temperature and further stirred overnight. The solvent
was removed under vacuum, and the residue was extracted
with a mixture of hexane and methylene chloride (90/10). The
solution was filtered and concentrated to 5 mL and placed upon
a 2.5 × 20 cm silica gel column. Elution with the same solvent
mixture developed a yellow band that was collected and after
solvent removal afforded a yellow crystalline solid. The solid
was recrystallized from a mixture of hexane/methylene chlo-
ride to yield 1.70 g (64%) of orange-yellow crystals of 1.
Complex 2 was similarly synthesized as a mixture (meso/dl
) 5:1) of two isomers in 23% yield by treatment of [CpFe-
(CO)2]-Na+ with ClCH2MePhSiSiPhMeCH2Cl in THF. Recrys-
tallization of 2a and 2b from a mixture of CH2Cl2 and hexane
yielded cubic prisms (2a , meso) and rectangular prisms (2b,
dl) that were separated mechanically.
(R2 ) Me2 (3), MePh (6)) and FpMe2SiCH2CH2SiMe2Fp
(7) complexes, where the chains bridging the two Fe
atoms are isomeric with 1, together with a tungsten
analogue of 1, WpCH2Me2SiSiMe2CH2Wp (8).
Exp er im en ta l Section
All manipulations were carried out under an argon atmo-
sphere or under high vacuum. Tetrahydrofuran was distilled
under a nitrogen atmosphere from sodium benzophenone ketyl
prior to use. The following reagents were used as received from
the suppliers named: silica gel (grade 62, 60-200 mesh),
anhydrous HCl, Br(CH2)4Br, and BrCH2Cl, Aldrich; Ph2MeSiCl,
ClMe2SiCH2Cl, Cl2MeSiCH2Cl, PhMeHSiCl, Me3SiSiMe3, and
ClMe2SiCH2CH2SiMe2Cl, Gelest. Other reagents were synthe-
sized by literature procedures with some modifications: ClCH2-
Me2SiSiMe2CH2Cl,8 PhMeHSiCH2Cl,8 ICH2Me2SiSiMe2CH2I,9
Ph2MeSiSiMePh2,10 ClPhMeSiCH2Cl,11 and ClSiMe2CH2Si-
Me2CH2Cl.12 Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker ARX-300 Fourier transform spectrom-
eter. Infrared (IR) spectra were obtained on a Perkin-Elmer
1600 series FT-IR spectrometer using hexane as solvent.
Elemental analyses were performed by Galbraith Laboratories.
Syn t h esis of ClP h MeSiSiMeP h Cl. To a solution of
Ph2MeSiSiMePh2 (20.0 g, 50.8 mmol) in 100 mL of toluene was
added dropwise trifluoromethanesulfonic acid (15.2 g, 101.6
mmol) at -30 °C. The reaction mixture was warmed to room
temperature over 1 h and was stirred for an additional 2 h.
The reaction mixture was transferred to a dropping funnel and
was slowly added to a solution of lithium chloride (6.48 g, 159
mmol) in 70 mL of THF at 0 °C. The reaction mixture was
then stirred overnight at room temperature. The solvents were
removed under vacuum. 300 mL of hexane was added to the
residue, and this solution was then filtered to remove the
lithium salts. The solvent was removed from the filtrate by
rotary evaporation, and the residue was distilled at 128-132
°C/0.7 mmHg (lit.13 141-146 °C/2 mmHg) to afford 10.1 g (64%)
of the crystalline product ClPhMeSiSiMePhCl as a mixture
of two isomers (1:1).
This compound was also prepared by reacting Cl2Me-
SiSiMeCl2 with the Grignard reagent PhMgBr.13 1H NMR
(C6D6): δ 0.65 (s, 6H, SiMe), 0.71 (s, 6H, SiMe), 7.09-7.19 (m,
12H, Ph), 7.49-7.52 (m, 4H, Ph), 7.62-7.65 (m, 4H, Ph). 13C
NMR (C6D6): δ 0.23 (SiMe), 128.65, 128.75, 130.90, 130.97,
133.95, 134.03, 134.14, 134.19 (Ph).29Si NMR (C6D6): δ 6,60,
6.82.
Syn th esis of ClCH2P h MeSiSiMeP h CH2Cl. Into a 250
mL three-necked flask equipped with a magnetic stirring bar,
rubber septum, nitrogen inlet tube, and low-temperature
thermometer were placed 6.22 g (0.02 mol) of ClPhMeSiSi-
MePhCl and 5.18 g (0.04 mol) of BrCH2Cl in 100 mL of dry
THF. To this mixture, maintained between -78 and -70 °C,
was added on the cold wall of the flask, via syringe over 30
min, 25 mL (0.04 mol) of a 1.6 M solution of n-butyllithium in
hexane. The solution was warmed to room temperature, stirred
overnight, and then hydrolyzed and extracted with hexane.
The extract was washed with water and dried over CaCl2. The
solvent was removed, and the residue was distilled, by using
a 20-cm Vigreux column at 150-152 °C/0.7 mmHg to give 5.70
g (85%) of ClCH2MePhSiSiPhMeCH2Cl as a mixture of two
isomers (10:7).
Syn th esis of F p CH2SiMe2CH2SiMe2F p (3). To 50 mL of
a THF solution of [CpFe(CO)2]-Na+ (prepared from 2.00 g (5.6
mmol) of Fp2) was added 1.14 g (5.3 mmol) of ClCH2SiMe2-
CH2SiMe2Cl at 0 °C. The solution was warmed to room
temperature and stirred overnight. The solvent was removed
under vacuum, and the residue was extracted with hexane.
The solution was filtered and concentrated to 5 mL and then
placed upon a 2.5 × 20 cm silica gel column. Elution with
hexane developed a yellow band that was collected and after
solvent removal afforded a yellow crystalline product of 3 (0.91
g, 35%). Mp: 78-80 °C. 1H NMR (C6D6): δ 0.15 (s, 2H, FpCH2)
0.32 (s, 6H, SiMe2), 0.40 (s, 2H, SiCH2Si), 0.68 (s, 6H, FpSiMe2),
4.14 (s, 10H, Cp). 13C NMR (C6D6): δ -21.20 (FpCH2), 3.70,
8.99 (SiMe2), 15.83 (SiCH2Si), 83.98, 85.21 (Cp), 216.84, 218.42
(CO). 29Si NMR (C6D6): δ 9.66 (FpCH2SiMe2), 43.01 (FpSiMe2).
IR (νCO, cm-1): 2011 (s), 1995 (s), 1959 (s), 1941 (s). Anal. Calcd
for C20H26Fe2O4Si2: C, 48.21; H, 5.26. Found: C, 47.77; H, 5.33.
Syn th esis of ClCH2SiP h MeCH2SiP h MeH (4). To 30 mL
of a THF solution of 7.06 g (34.4 mmol) of ClPhMeSiCH2Cl
was slowly added a Grignard reagent (prepared from 1.18 g
(48.6 mmol) of magnesium turnings and 8.0 g (44.2 mmol) of
PhMeHSiCH2Cl in 110 mL of THF) at 0 °C. The reaction
mixture was warmed to room temperature and then refluxed
for 20 h. The reaction mixture was hydrolyzed with a saturated
aqueous solution of ammonium chloride. The organic layer was
separated, and the aqueous phase was extracted with ether
(2 × 30 mL). The extracts were combined and the organic layer
was washed with water, sodium bicarbonate, and then water
and dried over calcium chloride. The solvent was removed, and
the residue was distilled using a 20 cm Vigreux column at
150-156 °C/0.7 mmHg to give 7.20 g (68%) of 4, existing as a
mixture of two diastereomers (1:1). 1H NMR (C6D6): δ 0.21,
(d, 3J ) 3.66 Hz, 3H, SiMePhH), 0.25 (d, 3J ) 3.72 Hz, 3H,
SiMePhH), 0.34 (s, 3H, SiMePhCH2Cl), 0.36 (s, 3H, SiMePh-
2
CH2Cl), 0.33-0.44 (m, 4H, SiCH2Si), 2.76 (AB, J ) 13.6 Hz,
2H, CH2Cl), 2.80 (s, 2H, CH2Cl), 4.64 (m, 2H, SiMePhH), 7.20-
7.25 (m, 12H, Ph), 7.42-7.48 (m, 8H, Ph). 13C NMR (C6D6): δ
-4.19, -3.94 (SiMePhH), -3.42, -3.40 (SiCH2Si), -2.45
(SiMePhCH2Cl), 30.87, 30.94 (CH2Cl), 128.34, 128.39, 128.41,
129.77, 129.81, 130.03, 130.06, 134.35, 134.37, 134.54, 136.42,
136.43, 137.67, 137.72 (Ph). 29Si NMR (C6D6): δ -16.57,
-16.47 (SiMePhH), -3.06, -3.04 (SiMePhCH2Cl). MS (70
eV): m/z 289 [M - Me]+, 1; 255 [M - CH2Cl]+, 88; 211 [M -
Me - C6H6]+, 22; 177 [M - CH2Cl - C6H6]+, 100; 135
[PhMeSiHCH2]+, 18; 121 [PhMeSiH]+, 20; 91 [C7H7]+, 30; 65
[C5H5]+,12. Anal. Calcd for C16H21ClSi2: C, 63.01; H, 6.94;
Found: C, 62.36; H, 6.95.
Syn th esis of F p CH2MeRSiSiRMeCH2F p (R ) Me (1),
P h (2)). To 50 mL of a THF solution of [CpFe(CO)2]-Na+
(8) Kobayashi, T.; Pannell, K. H. Organometallics 1991, 10, 1960.
(9) Kumada, M.; Ishikawa, M. J . Organomet. Chem. 1964, 1, 411.
(10) Gilman, H.; Lichtenwalter, G. D. J . Am. Chem. Soc. 1958, 80,
608.
(11) Auner, N.; Grobe, J . J . Organomet. Chem. 1980, 188, 151.
(12) Mironov, V. F.; Mikhailyants, S. A.; Gar, T. K. Zh. Obshch.
Khim. 1969, 39, 2601; Chem. Abstr. 1970, 72, 67064d.
(13) Tamao, K.; Kumada, M.; Ishikawa. M. J . Organomet. Chem.
1971, 31, 17.
Syn th esis of ClCH2SiP h MeCH2SiP h MeCl (5). A flask
equipped with a magnetic stirring bar and a reflux condenser
was charged with 6.2 g (20.8 mmol) of ClCH2SiPhMeCH2-
SiPhMeH (4) and 0.32 g (1.3 mmol) of benzoyl peroxide in 20
mL of CCl4. The solution was refluxed for 10 h and was cooled
to room temperature. The solvent was removed under vacuum,

Isomeric Si2C2 Diiron Complexes
Organometallics, Vol. 21, No. 26, 2002 5861
and 50 mL of hexane was added to precipitate the catalysts.
The hexane solution was filtered to remove the precipitate and
the hexane solution concentrated under vacuum. The residue
was distilled using a 20 cm Vigreux column at 170-174 °C/
0.7 mmHg to give 6.1 g (86%) of 5 as a mixture of two
diastereomers (1:1). Compound 5 was previously prepared by
a ring-opening reaction of 1,3-dimethyl-1,3-diphenyl-1.3-disila-
cyclobutane with Cl2.14 1H NMR (C6D6): δ 0.30, 0.41, 0.42, 0.44
slurry. To this mixture was slowly added 1.07 g (5.0 mmol) of
ClMe2SiCH2CH2SiMe2Cl via syringe at 0 °C. The solution was
stirred for 24 h. The solvent was removed under vacuum, and
the residue was extracted with a mixture of hexane and
methylene chloride (90/10). The solution was filtered, concen-
trated to 5 mL, and placed upon a 2.5 × 20 cm silica gel
column. Elution with the same solvent mixture developed a
light yellow band that was collected and after solvent removal
afforded a yellow crystalline solid. The solid was recrystallized
from a mixture of hexane and methylene chloride to yield 0.55
2
(s, s, s, s, 12H, SiMe), 0.65 (AB, J ) 14.0 Hz, 2H, SiCH2Si),
2
2
0.67 (AB, J ) 14.2 Hz, 2H, SiCH2Si), 2.75 (AB, J ) 13.8 Hz,
2H, CH2Cl), 2.80 (s, 2H, CH2Cl), 7.18-7.24 (m, 12H, Ph), 7.35-
7.39 (m, 4H, Ph), 7.46-7.49 (m, 4H, Ph). 13C NMR (C6D6): δ
-3.95, -3.89 (SiMePhCH2Cl), 2.87, 3.05 (SiCH2Si), 3.13 (SiMe-
PhCl), 30.77 (CH2Cl), 128.38, 128.48, 130.21, 130.69, 133.54,
133.56, 134.37, 135.77, 135.81, 136.91, 137.03 (Ph). 29Si NMR
(C6D6): δ -4.27, -4.17 (SiMePhCH2Cl), 19.47, 19.49 (SiMe-
PhCl).
1
g (22%) of pale yellow crystals of 7, mp 146-148 °C. H NMR
(C6D6): δ 0.56 (s, 12H, SiMe2), 1.12 (s, 4H, CH2), 4.14 (s, 10H,
Cp). 13C NMR (C6D6): δ 4.97 (SiMe2), 19.06 (CH2), 83.49 (Cp),
216.48 (CO). 29Si NMR (C6D6): δ 43.25. IR (νCO, THF, cm-1):
1988 (s), 1931 (s). Anal. Calcd for C20H26Fe2O4Si2: C, 48.21;
H, 5.26; Found: C, 48.78; H, 5.84.
P h otolysis of 1: F or m a tion of 1,1,3,3-Tetr a m eth yl-1,3-
d isila cyclobu ta n e (9). A 5 mm Pyrex NMR tube was charged
with 0.15 g (0.3 mmol) of 1 and 1 mL of C6D6 and sealed under
vacuum. Irradiation was carried out with a 450 W medium-
pressure Hg lamp at a distance of 2-5 cm. The progression of
the reaction was monitored by 1H, 13C, and 29Si NMR spec-
troscopy. The color of the solution changed from yellow to dark
red upon irradiation, and after 4 h complete disappearance of
1 and formation of 9 and Fp2 was noted, along with traces of
ferrocene. After removal of the solvent the resulting violet-
red solid Fp2 was washed twice with cold hexane and dried
under vacuum. Yield: 95 mg (89%). 9 and the solvent C6D6
could not be separated by distillation, but a solution of 9 in
C6D6 could be obtained by distillation under vacuum. 9 was
Syn th esis of F p CH2SiP h MeCH2SiP h MeF p (6). To 50
mL of a THF solution of [CpFe(CO)2]-Na+ (prepared from 2.00
g (5.6 mmol) of Fp2) was added 1.60 g (4.7 mmol) of ClCH2-
SiPhMeCH2SiPhMeCl at 0 °C. The solution was stirred at low
temperature for 30 min and then warmed to room temperature
and stirred overnight. The solvent was removed under vacuum,
and the residue was extracted with hexane. The solution was
filtered and concentrated to 5 mL and then placed upon a 2.5
× 20 cm silica gel column. Elution with hexane developed a
yellow band that was collected and after solvent removal
afforded a yellow oily product of 6 (2.08 g, 71%) as a mixture
1
of two diastereomers (6a :6b ) 1:1). H NMR (C6D6): δ -0.08
2
2
(AB, J ) 13.6 Hz, 2H, FpCH2), 0.04 (AB, J ) 12.5 Hz, 2H,
FpCH2), 0.39, 0.51 (s, s, 6H, FpCH2SiPhMe), 0.64, 0.91 (s, s,
6H, FpSiPhMe), 1.11 (AB, 2J ) 14.1 Hz, 2H, SiCH2Si), 1.13
1
characterized by H, 13C, and 29Si NMR and GC/MS (temper-
ature 140 °C, solvent delay 2 min).18
2
(AB, J ) 14.0 Hz, 2H, SiCH2Si), 3.96, 3.97, 3.98 (s, s, s, 20H,
P h otolysis of 1 in th e P r esen ce of CH3OH (or t-Bu OH).
A 5 mm Pyrex NMR tube was charged with 0.10 g (0.2 mmol)
of 1, 76 mg (2.4 mmol) of CH3OH, and 1 mL of C6D6. The
solution was subjected to three freeze-pump-thaw cycles and
then sealed under vacuum. Irradiation was carried out as
Cp), 7.20-7.33 (m, 12H, Ph), 7.57-7.79 (m, 8H, Ph). 13C NMR
(C6D6): δ -23.19, -22.01 (FpCH2), 0.03, 0.76, (FpCH2SiPhMe),
6.07, 6.76 (FpSiPhMe), 12.06, 12.24 (SiCH2Si), 84.47, 84.83,
84.93 (Cp), 127.86, 127.96, 128.01, 128.10, 128.24, 128.59,
128.77, 133.20, 133.24, 143.96, 144.22, 148.01, 148.29 (Ph),
216.72, 216.76, 217.03, 217.06, 218.02, 218.08 (CO). 29Si NMR
(C6D6): δ 4.94, 5.13 (SiMePhCH2Fp), 36.72, 36.74 (FpSiMePh).
IR (νCO, cm-1): 2010 (s), 1994 (s), 1959 (s), 1942 (s). Anal. Calcd
for C30H30Fe2O4Si2: C, 57.89; H, 4.86. Found: C, 58.22; H, 4.99.
Syn th esis of Wp CH2Me2SiSiMe2CH2Wp (8). To a solution
of [CpW(CO)3]-Na+ (8.5 mmol) in 60 mL of THF was added
1.5 g (3.75 mmol) of ICH2Me2SiSiMe2CH2I in 10 mL of THF,
and the solution was stirred overnight. Infrared monitoring
of the reaction showed the presence of unreacted tungsten
carbonylate, and therefore, the solution was heated to reflux
for 24 h. This resulted in the completion of the reaction. The
solvent was removed, and the resulting yellowish brown liquid
residue was extracted with a mixture of hexane and methylene
chloride (90/10). The solution was filtered, concentrated to 5
mL, and placed upon a 2.5 × 20 cm silica gel column. Elution
with the same solvent mixture developed a yellow band that
was collected and after solvent removal afforded an orange
crystalline solid. The solid was recrystallized from a mixture
of hexane and methylene chloride to yield 2.04 g (67%) of
1
above. The progression of the reaction was monitored by H,
13C, and 29Si NMR spectroscopy. The color of the solution
changed from yellow to dark red upon irradiation, and after 2
h the starting material 1 completely disappeared and 9 was
formed with Fp2. Similar treatment of 0.10 g (0.2 mmol) of 1
and 150 mg (2 mmol) of t-BuOH afforded the same result as
above.
P h otolysis of 2a a n d 2b: F or m a tion of 1,3-Dim eth yl-
1,3-d ip h en yl-1,3-d isila cyclobu ta n e (10). A 5 mm Pyrex
NMR tube was charged with 0.10 g (0.16 mmol) of 2a and 1
mL of C6D6 and sealed under vacuum. The sample was
irradiated as above, and the reaction was monitored by 1H,
13C, and 29Si NMR spectroscopy. The color of the solution
changed from yellow to dark red upon irradiation, and after 2
h complete disappearance of 2a and formation of the trans
isomer 10t and Fp2 was noted, along with traces of ferrocene.
The solvent was removed under vacuum, and the residue was
extracted with hexane. The extracts were placed upon a silica
gel column. Elution with hexane afforded complex 10t. The
violet-red solid left after extraction was dried under vacuum
to afford 46 mg (82%) of Fp2. Compound 10t was characterized
1
yellow crystals of 8, mp 124-126 °C. H NMR (C6D6): δ 0.24
(s, 4H, CH2), 1.12 (s, 12H, SiMe2), 4.56 (s, 10H, Cp). 13C NMR
(C6D6): δ -38.40 (CH2), 0.98 (SiMe2), 91.62 (Cp), 218.90,
230.69 (CO). 29Si NMR (C6D6): δ -6.28. IR (νCO, cm-1): 2015
(s), 1927 (s). Anal. Calcd for C22H26O6Si2W2: C, 32.61; H, 3.23;
Found: C, 31.95; H, 3.26.
1
by H, 13C, and 29Si NMR spectroscopy and GC/MS.
Similar photolysis of 2b afforded only the cis isomer 10c
and Fp2. 10c was also characterized by 1H, 13C, and 29Si NMR
spectroscopy and GC/MS.19
Syn th esis of F p Me2SiCH2CH2SiMe2F p (7). A solution of
[CpFe(CO)2]-Na+ was prepared by reacting 2.00 g (5.60 mmol)
of [(η5-C5H5)Fe(CO)2]2 with Na-Hg amalgam in 50 mL of THF.
The solvent was removed completely under vacuum, and 70
mL of hexane was then added to the residue to produce a
(15) Kruger, C.; Barnett, B. L.; Brauer, D. The Organic Chemistry
of Iron. In Structure and Bonding in Organic Iron Compounds; Koerner
Von Gustorf, E. A., Grevels, F. W., Fischler, I., Eds.; Academic Press:
New York, 1978; Vol. 1, p 3.
(16) Pannell, K. H.; Lin, S.-H.; Kapoor, R. N.; Cervantes-Lee, F.;
Pinon, M.; Parkanyi, L. Organometallics 1990, 9, 2454.
(17) Pannell, K. H.; Cervantes, J .; Parkanyi, L.; Cervantes-Lee, F.
Organometallics 1990, 9, 859.
(14) Derine, A. M.; Griffin, P. A.; Haszeldine, R. N.; Newlands, M.
J .; Tipping, A. E. J . Chem. Soc., Dalton Trans. 1975, 1822.
(18) Kriner, W. A. J . Org. Chem. 1964, 29, 1601.

5862 Organometallics, Vol. 21, No. 26, 2002
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1, 2a , a n d 2b
Zhang et al.
1
2a
2b
C30H30Fe2O4Si2
empirical formula
fw
C
498.3
20H26Fe2O4Si2
C
30H30Fe2O4Si2
622.4
622.4
cryst size (mm)
group syst
cryst space
unit cell dimens
a (Å)
0.32 × 0.50 × 0.60
monoclinic
P21/c
0.16 × 0.22 × 0.36
0.28 × 0.08 × 0.36
monoclinic
P21/c
triclinic
P1h
8.867(2)
6.873(2)
19.038(4)
90
98.15(2)
90
1148.5(5)
2
1.441
13.86
3.5-45.0
ω
8.607(2)
9.509(2)
9.819(2)
86.84(2)
64.95(1)
86.58(2)
726.3(3)
1
12.490(6)
18.956(8)
13.856(8)
90
112.11(4)
90
3039(3)
4
1.360
10.62
3.5-45.0
ω
b (Å)
c (Å)
R, deg
â, deg
γ, deg
V (Å3)
Z
d
calcd (g cm-3
)
1.423
11.11
µ, cm-1
2θ range (deg)
3.5-50.0
scan type
2θ-θ
scan speed (deg/min)
scan range (ω) (deg)
std rflns
4-20
1.20
3-15
4-20
1.20
1.20
3 measd every 197 rflns
index ranges
h
k
l
0-9
0-10
-13 to 13
-20 to 20
-14 to 14
8578
0-7
-11 to 11
-10 to 11
2771
-20 to 20
1624
no. of rflns collected
no. of indep rflns
1510
2581
3989
no. of obsd data
abs cor
1382 (F > 4.0σ(F))
n/a
2181 (F > 3.0σ(F))
semiempirical
3270 (F > 3.0σ(F))
semiempirical
final R indices (obsd data) (%)
R
Rw
4.17
6.35
1.69
3.33
4.34
1.03
6.46
7.48
1.59
goodness of fit
P h otolysis of 1 a n d 2a . A 5 mm Pyrex NMR tube was
charged with 30 mg (0.05 mmol) of 2a , 24 mg (0.05 mmol) of
1, and 1 mL of C6D6 and sealed under vacuum. Irradiation
was monitored by 1H, 13C, and 29Si NMR spectroscopy. The
color of the solution changed from yellow to dark red upon
irradiation, and after 2 h the starting materials 2a and 1
completely disappeared and the trans isomer 10t and 9 were
formed along with Fp2. No crossover product was detected.
P h otolysis of 3: F or m a tion of 1,1,3,3-Tetr a m eth yl-1,3-
d isila cyclobu ta n e (9). A 5 mm Pyrex NMR tube was charged
with 0.10 g (0.2 mmol) of 3 and 1 mL of C6D6 and sealed under
P h ot olysis of 6: F or m a t ion of 1,3-Dim et h yl-1,3-d i-
p h en yl-1,3-d isila cyclobu ta n e (10). A 5 mm Pyrex NMR
tube was charged with 0.18 g (0.29 mmol) of 6 (6a :6b ) 1:1)
and 1 mL of C6D6 and sealed under vacuum. Irradiation was
carried out with a 450 W medium-pressure Hg lamp. The
progress of the reaction was monitored by 1H, 13C, and 29Si
NMR spectroscopy. After 11 h 29Si NMR spectroscopy indicated
the complete disappearance of the starting material 6 and the
formation of 10 as a mixture of the cis and trans isomers (10t:
10c ) 1:1). The solvent was removed under vacuum, and the
residue was placed onto a 1 × 10 cm silica gel column. Elution
with hexane afforded a colorless oil of 10 (69 mg, 89%) upon
removing the solvent. Elution with a mixture of benzene and
hexane (1:3) developed a red band, which was collected and
after solvent removal afforded 78 mg (76%) of violet crystals
of Fp2.
1
vacuum. Irradiation was monitored by H, 13C, and 29Si NMR
spectroscopy. The color of the solution changed from yellow to
dark red upon irradiation, and after 35 h complete disappear-
ance of 3 and formation of 9 and Fp2 was noted. After removal
of the solvent, the resulting violet-red solid Fp2 was washed
twice with cold hexane and dried under vacuum (65 mg, 92%).
9 and the solvent C6D6 could not be separated by distillation,
but a solution of 9 in C6D6 could be obtained by distillation
P h otolysis of 3 a n d 6. A 5 mm Pyrex NMR tube was
charged with 30 mg (0.05 mmol) of 6, 24 mg (0.05 mmol) of 3,
and 1 mL of C6D6 and sealed under vacuum. Irradiation was
1
under vacuum. 9 was characterized by H, 13C, and 29Si NMR
1
monitored by H, 13C, and 29Si NMR spectroscopy. After 12 h
spectroscopy and GC/MS.
the starting materials 6 and 3 had completely disappeared and
9 and 10 were formed along with Fp2. No crossover product
was detected.
P h otolysis of 3 in th e P r esen ce of CH3OD (or P P h 3).
A 5 mm Pyrex NMR tube was charged with 0.10 g (0.2 mmol)
of 3, 24 mg (0.73 mmol) of CH3OD, and 1 mL of C6D6 and
sealed under vacuum. Irradiation was monitored by 1H, 13C,
and 29Si NMR spectroscopy. The color of the solution changed
from yellow to dark red upon irradiation, and after 45 h the
complete disappearance of 3 and only the formation of 9 and
Fp2 was noted.
Similar photolysis of 3 in the presence of PPh3 for 3 h
resulted in the disappearance of the starting material and the
formation of several new unidentified products (29Si NMR,
43.09, 43.03, 10.20, 10.16, 6.67, 0.29, -23.66, -23.70 ppm).
Only trace amounts of 9 and Fp2 were observed.
X-r a y Diffr a ction Stu d ies. Crystals (1, 2a , and 2b)
suitable for X-ray diffraction analysis were obtained from
hexane solution. Intensity data were collected on a Nicolet-
Siemens R3m/V four-circle diffractometer at room tempera-
ture, using graphite-monochromated Mo KR radiation (λ )
0.710 73 Å). The ω-scan technique was applied in the 2θ range
3.5° e 2θ e 45.0° with variable scan speeds except for complex
2a (3.5° e 2θ e 50.0°). The structures were refined by
anisotropic, full-matrix least squares. Hydrogen atomic posi-
tions were generated from the assumed geometry. Crystal-
lographic data are summarized in Table 1, and selected bond
lengths and angles are presented in Tables 2 (1), 3 (2a ), and
4 (2b).
(19) Hayakawa, K.; Tachikawa, M.; Suzuki, T.; Choi, N.; Murakami,
M. Tetrahedron Lett. 1995, 36, 3181l.

Isomeric Si2C2 Diiron Complexes
Resu lts a n d Discu ssion
Organometallics, Vol. 21, No. 26, 2002 5863
Syn th esis a n d Sp ectr oscop ic P r op er ties of th e
F p Der iva t ives. The compounds FpCH2MeRSiSi-
RMeCH2Fp (R ) Me (1), Ph (2)) and FpCH2SiMe2CH2-
SiMe2Fp (3) were readily prepared in THF by the salt-
elimination reactions outlined in eq 5.
2[Fp]-Na+ + [ClCH2SiMeR]2 f
FpCH2MeRSiSiRMeCH2Fp (5a)
2[Fp]-Na+ + ClCH2SiMe2CH2SiMe2Cl f
FpCH2SiMe2CH2SiMe2Fp (5b)
F igu r e 1. Molecular structure of 1.
The compound FpCH2MePhSiCH2SiMePhFp (6) was
also synthesized in an overall 33% yield via the multi-
step process outlined in Scheme 1.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
Fe-C(6)
Fe-C(8)
Si-C(8)
1.755(4)
2.098(4)
1.873(4)
1.147(5)
Fe-C(7)
Si-SiA
Si-C(9)
O(2)-C(7)
1.747(4)
2.354(2)
1.874(5)
1.151(5)
Sch em e 1
ClCH2SiMeCl2 PhMgBr8 ClCH2SiPhMeCl
O(1)-C(6)
ether
C(1)-Fe-C(2)
C(6)-Fe-C(7)
C(7)-Fe-C(8)
C(8)-Si-SiA
38.8(1)
93.9(2)
91.1(2)
107.8(1)
C(1)-Fe-C(3)
C(6)-Fe-C(8)
Fe-C(8)-Si
65.4(2)
85.9(2)
121.5(2)
107.5(2)
ClMgCH2SiPhMeH
ClCH SiPhMeCH SiPhMeH
8
2
2
THF
4
C(9)-Si-C(10)
benzoyl peroxide
CCl4 reflux
ClCH SiPhMeCH SiPhMeCl
8
2
2
-26.8 ppm (2); -21.20 ppm (3); -23.19, -22.01 ppm
(6); -38.4 ppm (8)), in accord with monoiron analogues.4b,c
In all cases the carbonyl groups exhibit distinctive
resonances and it is possible to distinguish the Fp-alkyl
and Fp-silyl portions of the new complexes.
5
-
+
Fp Na
FpCH SiPhMeCH SiPhMeFp
8
2
2
THF
6
The tungsten analogue of 1, WpCH2Me2SiSiMe2-
CH2Wp (8), was readily synthesized in good yield (67%)
by reacting ICH2Me2SiSiMe2CH2I with Wp-Na+ in
THF. Similar treatment of ClMe2SiCH2CH2SiMe2Cl
with [Fp]-Na+ in THF failed to yield the expected
product FpMe2SiCH2CH2SiMe2Fp (7); however, it was
obtained in 22% yield from the same reagents when
hexane was used as the solvent.
The infrared spectra of 3 and 6 also clearly indicated
the two distinct Fp groups existing in the molecules.
The stretching frequencies for the Fp-SiMe2 group and
the Fp-CH2 group are typical of Fp-silyl and Fp-alkyl
complexes and the Fp-alkyl groups exhibit higher
stretching frequencies than the Fp-silyl groups.
1H, 13C, and 29Si NMR spectra of 2 indicate a mixture
of two diastereomers, with one diastereomer dominant
(meso/dl ) 5:1). Recrystallization of 2 from a mixture
of CH2Cl2 and hexane yields prisms, and the isomers
2a (meso) and 2b (dl) could be separated mechanically.
In the 1H NMR spectra of 2a and 2b, the two chemically
inequivalent hydrogen atoms of the CH2 moiety at-
tached to the chiral silicon atom exhibited an AB system
with a large coupling constant (2J ) 12.6 Hz (2a and
2b)). 1H, 13C, and 29Si NMR spectra of 4-6 showed that
each was a mixture of two diastereomers in a ratio of
29Si NMR spectroscopy is useful for structural analy-
sis of metal-substituted oligosilanes. In general, silicon
atoms directly attached to the metal atom are signifi-
cantly shifted downfield compared to those of their
permethylated analogues; this shift is reduced as the
two atoms become separated, and the effect is also
additive when the two ends of the silicon atom are
attached by the metal-containing substituents. The 29Si
NMR spectrum of 1 exhibits one resonance signal at
-6.03 ppm, which is shifted downfield over 13 ppm
compared to the resonance at -19.5 ppm for the
permethylated disilane Me3SiSiMe3. The downfield shift
was also observed in the 29Si NMR spectra of 2 (-9.00,
-9.07 ppm) and 8 (-6.28 ppm). The 29Si NMR spectrum
of 3 exhibited two distinct resonances, which were
assigned to Fp-Si (43.0 ppm) and FpCH2-Si (9.66
ppm), respectively. Compound 6 is a mixture of two
diastereomers, and the 29Si signals at 36.72 and 36.74
ppm are assigned to Fp-Si, and the signals at 4.94 and
5.13 ppm are due to FpCH2-Si. These downfield shifts
are in the range of the normal shifts (∆δ ) 35-45 ppm)
for the R-Si atoms and (∆δ ) 5-13 ppm) for the â-Si
atoms with respect to the Fe atoms.1
1
1:1. The H NMR spectrum of 6 revealed an AB system
for all CH2 moieties in the two diastereomers.
Overall the accumulated spectral data are in total
accord with the proposed structures of the new materi-
als; however, we have confirmed several of the new
complexes via single-crystal X-ray diffraction.
Cr ysta l Str u ctu r es of 1, 2a , a n d 2b. The single-
crystal structure of 1 is illustrated in Figure 1. Selected
bond distances and angles are summarized in Table 2.
The molecule consists of two identical [(η5-C5H5)Fe(CO)2-
CH2SiMe2] moieties bonded by a Si-Si bond and has
Ci symmetry. The Fe-C(8) bond distance (2.098(4) Å)
is in the range of normal Fe-C(sp3) bond distances
(2.08-2.16 Å).15 The Si-Si bond length (2.354(2) Å) is
slightly shorter than those in LFeSiMe2SiMe3 (2.361-
2.364 Å)16 and much shorter than that of the bimetallic
complex FpSiMe2SiMe2Fp (2.390(4) Å).17
The 13C NMR spectra for these complexes were useful
for characterization of the CH2 moiety directly bonded
to the transition-metal atom. This carbon atom is
significantly shifted upfield (-23.6 ppm (1); -26.6,

5864 Organometallics, Vol. 21, No. 26, 2002
Zhang et al.
F igu r e 2. Molecular structure of 2b.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2a
Fe-C(6)
Fe-C(8)
Si-C(8)
1.743(3)
2.092(3)
1.865(3)
1.888(2)
1.143(5)
Fe-C(7)
Si-SiA
1.749(4)
2.359(1)
1.875(4)
1.149(4)
F igu r e 3. Projections of 2a (A) and 2b (B) about the Si-
Si-C(9)
O(1)-C(6)
Si bond. The Fp groups are omitted for clarity.
Si-C(10)
O(2)-C(7)
a trans conformation, possibly reducing the repulsion
between each other.
C(1)-Fe-C(2)
C(6)-Fe-C(7)
C(7)-Fe-C(8)
C(8)-Si-SiA
C(8)-Si-C(9)
38.3(1)
93.6(1)
90.7(1)
107.7(1)
113.7(1)
C(1)-Fe-C(3)
C(6)-Fe-C(8)
Fe-C(8)-Si
C(8)-Si-C(10)
C(9)-Si-C(10)
64.9(1)
86.4(1)
120.5(1)
112.3(1)
107.4(1)
P h otolysis of 1, 2, a n d 8. A C6D6 solution of 1 in a
sealed Pyrex NMR tube was irradiated using a 450 W
medium-pressure Hg lamp and led to the quantitative
formation of 1,3-tetramethyldisilacyclobutane (9) 18 and
Fp2 (eq 6).
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2b
Fe(1)-C(6)
Fe(1)-C(8)
Si(1)-C(8)
Fe(2)-C(24)
Fe(2)-C(23)
Si(2)-C(16)
O(1)-C(6)
1.745(8)
2.095(6)
1.853(6)
1.745(6)
2.106(6)
1.899(6)
1.156(9)
1.150(7)
Fe(1)-C(7)
Si(1)-Si(2)
Si(1)-C(10)
Fe(2)-C(25)
Si(2)-C(23)
Si(2)-C(22)
O(2)-C(7)
1.735(6)
2.373(3)
1.900(6)
1.756(8)
1.861(6)
1.871(6)
1.156(7)
1.146(10)
O(3)-C(24)
O(4)-C(25)
C(1)-Fe(1)-C(2)
C(6)-Fe(1)-C(7)
C(7)-Fe(1)-C(8)
C(8)-Si(1)-Si(2)
C(8)-Si(1)-C(9)
38.2(3)
94.0(3)
85.1(3)
C(1)-Fe(1)-C(3)
C(6)-Fe(1)-C(8)
Fe(1)-C(8)-Si(1)
64.5(3)
92.2(3)
122.2(2)
108.2(3)
112.0(2) C(9)-Si(1)-C(10)
111.6(3) C(24)-Fe(2)-C(25) 93.1(3)
Similarly, irradiation of 2a (meso) resulted in the
quantitative formation of trans-1,3-diphenyl-1,3-disila-
cyclobutane (10t) and Fp2, while similar photolysis of
2b (dl) afforded cis-1,3-diphenyl-1,3-disilacyclobutane
(10c),19 along with Fp2 (eqs 7a and 7b). The photo-
reactions are therefore stereospecific.
We have photolyzed a mixture of 1 and 2a and
observed no crossover products; the photoreactions
proceed via an intramolecular pathway.
C(23)-Fe(2)-C(24) 89.4(2)
Fe(2)-C(23)-Si(2)
C(23)-Fe(2)-C(25) 85.7(3)
118.8(3) C(23)-Si(2)-Si(1)
112.8(2)
The single-crystal structure of 2a has been presented
in a preliminary communication.7 Selected bond dis-
tances and angles are summarized in Table 3. The
molecular structure of 2b is shown in Figure 2. Selected
bond distances and angles are summarized in Table 4.
The molecule consists of two identical [(η5-C5H5)Fe(CO)2-
CH2SiMePh] moieties bonded by a Si-Si bond and is
asymmetric. This is also reflected in the dihedral angle
(8.5°) between the two Cp ring planes. The Si-Si bond
length (2.373(3) Å) is longer than those in LFeSiMe2-
SiMe316 but still shorter than the upper limit of the Si-
Si bond in the bimetallic complex FpSiMe2SiMe2Fp.17
The projections of 2a (meso) and 2b (rac) about the Si-
Si bond are presented in Figure 3. The silicon substit-
uents in 2a are absolutely staggered and trans relative
to one another. However, the silicon substituents in 2b
are not completely staggered relative to one another (the
larger C-Si-Si-C torsion angles fall in the range of
167.8(3)-175.0(3)°). The two phenyl substituents adopt
This is an unprecedented photoreaction leading to
the quantitative formation of 1,3-disilacyclobutanes. In
an initial attempt to extend this chemistry to other
transition metals, we synthesized and irradiated the
analogous tungsten system. We have reported that
photolysis of oligosilylmethyl-tungsten complexes LM-
CH2(SiMe2)nMe led to a facile rearrangement to LM-
SiMe2CH2(SiMe2)n-1Me complexes, a behavior that
parallels Fp chemistry.4b The ditungsten analogue
WpCH2Me2SiSiMe2CH2Wp (8) was readily prepared by
the appropriate salt-elimination reaction; however, pho-
tolysis of 8 failed to result in the formation of 1,3-
1
disilacyclobutanes and H, 13C, and 29Si NMR monitor-
ing of the photolysis indicated the formation of many
products that could not be identified.

Isomeric Si2C2 Diiron Complexes
Organometallics, Vol. 21, No. 26, 2002 5865
F igu r e 4. 13C NMR spectral changes in the cyclopenta-
dienyl region during photolysis of 3: (a) prior to photolysis;
(b) after 2 h; (c) after 6 h; (d) after 11 h; (e) after 24 h; (f)
after 35 h.
P h otolysis of 3, 6, a n d 7. To further explore the
nature and scope of the above photoreactions, the two
possible positional isomers of 1, FpCH2SiMe2CH2-
SiMe2Fp (3) and FpSiMe2CH2CH2SiMe2Fp (7), and the
positional isomer of 2, FpCH2SiPhMeCH2SiPhMeFp (6),
were synthesized and evaluated.
Photochemical irradiation of 3 resulted in the quan-
titative formation of disilacyclobutane (9) and Fp2 (eq
8). Even though this reaction took much longer than
that the introduction of the phenyl groups into the
system accelerates the photoreaction process (11 h/35
h).
As noted above, the photolysis of 1 proceeds via an
intramolecular pathway. In a separate experiment we
irradiated a mixture of 3 and 6 and examined the
photoproducts by NMR spectroscopy. Such irradiation
resulted in the formation of only 9, 10c, and 10t. Since
no crossover products were observed, we can conclude
that, as with 1 and 2, the photochemical transforma-
tions of their positional isomers proceed via intra-
molecular processes.
Complex 7 was determined to be photochemically
inert, since irradiation of a C6D6 solution of 7 in a sealed
Pyrex NMR tube for 5 days did not result in any change
except for a slight decomposition to Fp2 with no other
observable products.
Mech a n ism of 1,3-Disila cyclobu ta n e F or m a tion .
It has been reported that “unstable” silenes carrying
small alkyl substituents readily dimerize in a head-to-
tail fashion to form 1,3-disilacyclobutanes,20 while “stable”
silenes, e.g. (Me3Si)2SidC(OSiMe3)R, preferentially pro-
duce the head-to-head dimers, 1,2-disilacyclobutanes.21
Since the photoreactions involving free silenes yield a
mixture of the cis and trans isomers of 1,3-disila-
cyclobutanes, it is unlikely that free silene was produced
by photolysis of 1 and 2.22 Photolysis of 1 in the presence
of t-BuOH and MeOH led only to the formation of 1,3-
the corresponding photolysis of 1, the transformation
was very clean, and we did not observe the formation
of trace amount of any side products even after pho-
tolysis for 35 h (Figure 4). Under similar photochemical
conditions, but with much less irradiation time, pho-
tolysis of 1 usually gave trace amounts of ferrocene.
Complex 6 was prepared as a mixture of two dia-
stereomers (6a and 6b). Despite many attempts, we
have been unable to separate them; therefore, photolysis
was performed on a mixture of the two. Photochemical
irradiation of 6a and 6b (1:1) for 11 h led to a smooth
reaction with production of Fp2 and the two isomeric
1,3-disilacyclobutanes (10t and 10c) in a ratio of 1:1,
equivalent to the ratio of the two starting isomers (eq
9). In comparison with the photolysis of 3, it is evident
(20) For reviews see: (a) Gusel’nikov, L. E.; Nametkin, N. S. Chem.
Rev. 1979, 79, 529. (b) Baines, K. M.; Brook, A. G. Adv. Organomet.
Chem. 1986, 25, 1. (c) Raabe, G.; Michl, J . In The Chemistry of Organic
Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York,
1989; pp 1015-1142.
(21) (a) Brook, A. G.; Harris, J . W.; Lennon, J .; El Sheikh, M. J .
Am. Chem. Soc. 1979, 101, 83. (b) Brook, A. G.; Nyburg, S. C.;
Abdesaken, F.; Gutekunst, B.; Gutekunst, G.; Krishna, R.; Kallury,
M. R.; Poon, Y. C.; Chang, Y.-M.; Wong-Ng, W. J . Am. Chem. Soc. 1982,
104, 5667. (c) Baines, K. M.; Brook, A. G. Organometallics 1987, 6,
692. (d) Baines, K. M.; Brook, A. G.; Ford, R. R.; Lickiss, P. D.; Saxena,
A. K.; Chatterton, W. J .; Sawyer, J . F.; Behnam, B. A. Organometallics
1989, 8, 693.

5866 Organometallics, Vol. 21, No. 26, 2002
Zhang et al.
Sch em e 2
Sch em e 3
250-380 °C.23 We have not observed any evidence for
the 1,2-isomer. More significantly, Seyferth et al. re-
ported that octamethyl-1,2-disilacyclobutane, synthe-
sized by dimethylsilylene insertion into the silacyclo-
propane ring,24 did not rearrange to the 1,3-isomer upon
pyrolysis or photolysis.25 Thus, at present we rule out
the possibility that a direct 1,4-elimination reaction and
transient 1,2-disilacyclobutanes are involved in the
stereospecific photoreaction. As early as 1977, a relevant
study was reported by the Kumada group in which
1-metallo-3,4-disilacyclopentanes of Pt and Ni also
resulted in the formation of 9 under certain conditions
and bis(silene) metal intermediates were suggested.26
FpMe2SiCH2CH2SiMe2Fp (7) is photochemically inert.
This may be attributed to the absence of â-silyl (or â-HSi)
elimination, since the energy barrier for the cleavage
of the C-C and C-H bonds is usually much higher.
However, its positional isomer FpMe2SiCH2Me2Si-
CH2Fp (3) is photolabile, and photolysis of 3 resulted
in the quantitative formation of disilacyclobutane.
Although the reaction outcome is the same as that of
photolysis of 1, the reaction rate is much slower (35 h
for 3 vs 4 h for 1). This result rules out the possibility
that 3 is an intermediate during photolysis of 1. How-
ever, it seems that 3 can also form the bis(silene-iron)
species. Although Si-C bonds are stronger than Si-Si
bonds, it is possible that â-alkyl elimination involving
the cleavage of Si-C bonds activated by transition-
metal complexes is occurring (eq 10).
disilacyclobutane; i.e., there was no change in the
chemical outcome of the reaction and we did not observe
the formation of the trapped products Me3SiOCMe3 and
Me3SiOMe. This new result is consistent with our
previously reported photolysis of FpCH2SiMe2SiMe3 in
the presence of t-BuOH that resulted only in rearrange-
ment (FpSiMe2CH2SiMe3): i.e., no trapping.4d Coupled
with the lack of crossover products formed when a
mixture of 1 and 2a is irradiated, it is now clear that in
this chemistry no free silenes are involved.
Therefore, our originally postulated mechanism in-
volving the stepwise formation of a bis(silene-iron)
intermediate by sequential (or simultaneous) â-elimina-
tion reactions seems secure (Scheme 2). Each step must
be stereospecific, and the transient formation of iron
centers which themselves are potentially enantiomeric
may play an important role in the stereochemical
outcome of the final coupling reaction. Although we have
not observed Fe-silene transients in this chemistry, the
observation of such species in matrix isolation studies
lends significant credence to their intermediacy. We are
presently pursuing the possibility of such studies using
1 as a starting material.
During sequential or simultaneous â-eliminations, or
even a direct 1,4-elimination, the formation of 1,2-
disilacyclobutanes that rearrange to the 1,3-isomer
under the reaction conditions is a possibility. Recently,
1,2-tetramethyldisilacyclobutane was prepared by cy-
clizing ClMe2SiCH2CH2SiMe2Cl with Na and/or K at
Thompson and Young have observed the cleavage of
Si-C bonds in the thermal rearrangement of [bis-
(23) Gusel’nikov, L. E.; Polyakov, Y. P.; Volnina, E. A.; Nametkin,
N. S. J . Organomet. Chem. 1985, 292, 189.
(24) Seyferth, D.; Vick, S. C. J . Organomet. Chem. 1977, 125, C11.
(25) Davidson, I. M. T.; Ostah, N.; Seyferth, D.; Duncan, D. P. J .
Organomet. Chem. 1980, 187, 297.
(26) Tamao, K.; Yoshida, J .; Okazaki, S.; Kumada, M. Isr. J . Chem.
1977, 15, 265.
(22) (a) Braddock-Wilking, J .; Chiang, M. Y.; Gaspar, P. P. Organo-
metallics 1993, 12, 197. (b) Volkova, V. V.; Gusel’nikov, L. E.; Volvina,
E. A.; Buravtseva, E. N. Organometallics 1994, 13, 4661.

Isomeric Si2C2 Diiron Complexes
Organometallics, Vol. 21, No. 26, 2002 5867
Sch em e 4
(trimethylsilyl)methyl]platinum via the intermediacy of
η2-silene complexes formed by a â-CH3 elimination
process.27 Another apparent â-CH3 migration involving
the cleavage of Si-C bonds was also observed in the
reaction of Ru(η5-C5H5)(η3-C3H5)(CH2SiMe3)Br with AgF
to yield Ru(η5-C5H5)(η3-C3H5)(CH2SiMe2F)Me.28 Both
these precedents seem to justify our suggestion, as
outlined in eq 10, that photolysis of 3 may proceed via
a bis(silene-iron) intermediate analogous to that in the
photolysis of 1 (Scheme 3).29
However, an alternative suggestion is outlined in
Scheme 4. In this case, after loss of CO from the Fe-C
end of the FeCSiCSiFe chain an intramolecular oxida-
tive addition of the Fe-Si bond can be envisaged,
followed by elimination of the disilacyclobutane. To back
up this possible mechanism, we can report that related
intermolecular chemistry has been observed in our
laboratory. Thus, photochemistry of a mixture of FpCH3
and FpSiMe3 leads to the significant formation of only
Fp2 and SiMe4 within 3 h under the identical experi-
mental conditions reported here. Since photochemistry
of the two complexes alone does not yield either ethane
or Me6Si2 in any reasonable time period (days), there is
indeed a new type of chemistry operating consistent
with oxidative addition of Fp-SiMe3 to (η5-C5H5)Fe-
(CO)CH3 formed upon photochemical elimination of CO
from Fp-CH3 and subsequent elimination of SiMe4
upon recoordination of CO.30
Notwithstanding all the above chemistry, it is also
arguable that the formation of disilacyclobutanes is
related to a free radical pathway. This pathway may
involve (i) irradiation of 3 leading to the initial homoly-
sis of the Fe-CH2 bond to form iron radicals and
silylmethyl radicals, (ii) the silylmethyl radical intra-
molecularly attacking at the other silicon atom to
produce disilacyclobutanes and the other iron radicals,
and (iii) the coupling of the two iron radicals to afford
Fp2.
Ack n ow led gm en t. This research was supported by
the Robert A. Welch Foundation, Houston, TX. K.H.P.
thanks Dr. H. Tobita for helpful comments regarding
the oxidative addition mechanism outlined in Scheme
4.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal
data and data collection and solution and refinement details,
complete atomic coordinates, bond distances and angles, and
anisotropic thermal parameters for 1, 2a , and 2b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(27) Thompson, S. K.; Young, G. B. Organometallics 1989, 8, 2068.
(28) Itoh, K.; Fukahori, T. J . Organomet. Chem. 1988, 349, 227.
(29) This scheme only illustrates that initial CO expulsion to form
a 16e intermediate occurs at the CH2-Fe end of the Fp group, since
the Fe-Ccarbonyl bond at this end is weaker.
OM020644A
(30) The generality, and full implications, of this new chemistry is
the subject of a forthcoming publication.