Synthesis, structure, and photochemistry of disilyl derivatives of the Fp (Fp = (η5-C5H5)Fe(CO)2) system: FpMeSi(CH2)4SiMeFp and FpPhMeSiSiMePhFp

Article abstract of DOI:10.1021/om030026+

The synthesis of FpMeSi(CH₂)₄SiMeFp (1a) is reported (Fp = [(η⁵-C₅H₅)Fe(CO)₂), along with small amounts of [FpMeSi(CH₂)₄SiMe]₂O (2). Photolysis of 1a with a medium-pressure Hg lamp for 8 h resulted in the formation of two different types of intermediate silylene-bridged complexes, [(η⁵-C₅H₅)Fe(CO)]₂(μCO)(μ- SiMeSi(CH₂)₄) (4) and [(η⁵-C₅H₅)Fe(CO)]₂(μ-CO)(μ -Si(CH₂)₄SiMe₂) (5), each existing as a mixture of three equilibrating geometrical isomers, respectively; 4 slowly photoisomerized to the isomers 5 prior to expulsion of the second CO group. Prolonged irradiation of 5 gave a mixture of the cis and trans isomers of the bis(silylene)-bridged complex [(η⁵-C₅H₅)Fe(CO)]₂ (μ-SiMe₂) (μ-Si(CH₂)₄) (6). Similar photolysis of FpMePhSiSiPhMeFp (3) resulted in the sequential formation of the mono(silylene)-diiron complex [(η⁵-C₅H₅)Fe(CO)]₂(μ-CO)(μ -SiMeSiMePh₂) (7) and the bis(silylene)diiron complex [(η⁵-C₅H₅)Fe(CO)]₂ (μ-SiPh₂)(μ-SiMe₂) (8). The molecular structures of 1a, 5a, and 6a have been determined by X-ray diffraction analysis.

Full text of DOI:10.1021/om030026+

Organometallics 2003, 22, 2517-2524
2517
Syn th esis, Str u ctu r e, a n d P h otoch em istr y of Disilyl
Der iva tives of th e F p (F p ) (η5-C5H5)F e(CO)2) System :
F p MeSi(CH2)4SiMeF p a n d F p P h MeSiSiMeP h F p
Yongqiang Zhang, Francisco Cervantes-Lee, and Keith H. Pannell*
Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968-0513
Received J anuary 14, 2003
The synthesis of FpMeSi(CH2)4SiMeFp (1a ) is reported (Fp ) [(η5-C5H5)Fe(CO)2), along
with small amounts of [FpMeSi(CH2)4SiMe]2O (2). Photolysis of 1a with a medium-pressure
Hg lamp for 8 h resulted in the formation of two different types of intermediate silylene-
bridged complexes, [(η5-C5H5)Fe(CO)]2(µ-CO)(µ-SiMeSi(CH2)4) (4) and [(η5-C5H5)Fe(CO)]2(µ-
CO)(µ-Si(CH2)4SiMe2) (5), each existing as a mixture of three equilibrating geometrical
isomers, respectively; 4 slowly photoisomerized to the isomers 5 prior to expulsion of the
second CO group. Prolonged irradiation of 5 gave a mixture of the cis and trans isomers of
the bis(silylene)-bridged complex [(η5-C5H5)Fe(CO)]2(µ-SiMe2)(µ-Si(CH2)4) (6). Similar pho-
tolysis of FpMePhSiSiPhMeFp (3) resulted in the sequential formation of the mono(silylene)-
diiron complex [(η5-C5H5)Fe(CO)]2(µ-CO)(µ-SiMeSiMePh2) (7) and the bis(silylene)diiron
complex [(η5-C5H5)Fe(CO)]2(µ-SiPh2)(µ-SiMe2) (8). The molecular structures of 1a , 5a , and
6a have been determined by X-ray diffraction analysis.
In tr od u ction
silylene can be trapped intramolecularly or inter-
molecularly.6h-j,7b,f,g,8
The synthesis and study of silylene- (or silene-)
transition-metal complexes is an intriguing area of
organosilicon chemistry, since numerous metal-cata-
lyzed processes proceed via their intermediacy.1-5 Pho-
tochemical treatment of oligosilyl Fp complexes, FpSiR2-
SiR3 (Fp ) (η5-C5H5)Fe(CO)2), that contain direct iron-
silicon bonds results in the formation of the silyl silylene
intermediates (η5-C5H5)Fe(CO)(SiR3)(dSiR2) via R-elim-
ination reactions.6,7 Such intermediates can eliminate
silylenes or undergo rearrangement reactions involving
1,3-alkyl, -aryl, and -silyl migrations (eqs 1 and 2). The
Fp-SiMe2SiMe3 f Fp-SiMe3 + [SiMe2]
(1)
Fp-SiMe2SiMe2SiMe2SiMe3 f Fp-Si(SiMe3)3 (2)
The related bimetallic systems exhibit significantly
different chemistry due to the capacity for metal-metal
interactions.9,10 For example, photochemical treatment
of FpSiMe2SiMe2Fp resulted in the sequential formation
of mono(silylene)- and bis(silylene)-bridged diiron com-
plexes (Scheme 1).10b,c Such reactions also proceed via
equilibrating silyl silylene intermediates. To examine
the potential of this chemistry in ring systems, we report
the synthesis, characterization, and photochemistry of
FpMeSi(CH2)4SiMeFp. We also study the related diiron
(1) Tilley, T. D. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24, p
1415.
(2) Zybill, C.; Handwerker, H.; Friedrich, H. Adv. Organomet. Chem.
1994, 36, 229.
(3) Lickiss, P. D. Chem. Soc. Rev. 1992, 271.
1,2-diphenyl-1,2-dimethyldisilyl system FpMePhSiSiPh-
MeFp.
(4) Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351.
(5) Ogino, H.; Tobita, H. Adv. Organomet. Chem. 1998, 42, 223.
(6) (a) Pannell, K. H.; Rice, J . J . Organomet. Chem. 1974, 78, C35.
(b) Pannell, K. H.; Cervantes, J .; Hernandez, C.; Cassias, J .; Vincenti,
S. P. Organometallics 1986, 5, 1056. (c) Pannell, K. H.; Rozell, J . M.;
Hernandez, C. J . Am. Chem. Soc. 1989, 111, 4482. (d) Pannell, K. H.;
Wang, L.-J .; Rozell, J . M. Organometallics 1989, 8, 550. (e) J ones, K.;
Pannell, K. H. J . Am. Chem. Soc. 1993, 115, 11336. (f) Hernandez, C.;
Sharma, H. K.; Pannell, K. H. J . Organomet. Chem. 1993, 462, 259.
(g) Pannell, K. H.; Brun, M.-C.; Sharma, H. K.; J ones, K.; Sharma, S.
Organometallics 1994, 13, 1075. (h) Pannell, K. H.; Sharma, H. K.;
Kapoor, R. N.; Cervantes-Lee, F. J . Am. Chem. Soc. 1997, 119, 9315.
(i) Sharma, S.; Pannell, K. H. Organometallics 2000, 19, 1225. (j)
Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H. J . Organomet. Chem.
2001, 634, 102.
(7) (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.; Tobita, H.; Suzuki, T.; Ogino, H. Organome-
tallics 1992, 11, 150. (f) Tobita, H.; Kurita, H.; Ogino, H. Organome-
tallics 1998, 17, 2844. (g) Tobita, H.; Kurita, H.; Ogino, H. Organo-
metallics 1998, 17, 2850. (h) Tobita, H.; Sato, T.; Okazaki, M.; Ogino,
H. J . Organomet. Chem. 2000, 611, 314.
Exp er im en ta l Section
All manipulations were carried out under a nitrogen 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
(8) Ueno, K.; Nakano, K.; Ogino, H. Chem. Lett. 1996, 459.
(9) (a) Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H. J . Am. Chem.
Soc. 2000, 122, 8327. (b) Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H.
Organometallics 2002, 21, 5859. (c) Zhang, Y.; Pannell, K. H. Orga-
nometallics 2002, 21, 503.
(10) (a) Malish, W.; Ries, W. Angew. Chem., Int. Ed. Engl. 1978,
17, 120. (b) Pannell, K. H.; Sharma, H. Organometallics 1991, 10, 954.
(c) Ueno, K.; Hamashima, N.; Shimoi, M.; Ogino, H. Organometallics
1991, 10, 959. (d) Sharma, H.; Pannell, K. H. Organometallics 1994,
13, 4946. (e) Hashimoto, H.; Tobita, H.; Ogino, H. J . Organomet. Chem.
1995, 499, 205. (f) Malish, W.; Vo¨gler, M.; Ka¨b, H.; Wekel, H.-U.
Organometallics 2002, 21, 2830.
10.1021/om030026+ CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/24/2003

2518 Organometallics, Vol. 22, No. 12, 2003
Zhang et al.
collected and after solvent removal afforded a yellow oily
product. This oily product was dissolved in 20 mL of hexane.
The solution was cooled to -5 °C, and the orange-yellow
precipitate was collected via filtration. The solid was further
recrystallized from a hexane/methylene chloride solvent mix-
ture to yield 0.64 g (26%) of orange-yellow crystals of 3. 1H,
13C, and 29Si NMR spectra of 3 showed a mixture of two
diastereomers (3a and 3b) in the ratio of 5:1. 3a (rac) and 3b
(meso) could be separated by recrystallization from a solvent
mixture of CH2Cl2 and hexane.
Sch em e 1
1
3a : mp 158-160 °C; H NMR (C6D6) δ 1.07 (s, 6H, CH3),
4.02 (s, 10H, Cp), 7.18-7.28, 7.74-7.76 (m, 6H, 4H, Ph); 13C
NMR (C6D6) δ 4.09 (CH3), 83.7 (Cp), 128.1, 128.2, 134.9, 147.8
(Ph), 216.2, 216.5 (CO); 29Si NMR (C6D6) δ 19; IR (νCO, cm-1
)
the suppliers named: silica gel (grade 62, 60-200 mesh),
anhydrous HCl, Br(CH2)4Br, Aldrich; CF3SO3H, Lancaster;
Ph2MeSiCl, Gelest. Other reagents were synthesized by lit-
erature procedures with some modifications: Ph2MeSiSi-
MePh2,11 ClPhMeSiSiMePhCl,9b and 1,2-dichloro-1,2-dimethyl-
1,2-disilacyclohexane.12 Nuclear magnetic resonance (NMR)
spectra were recorded on a Bruker ARX-300 Fourier transform
spectrometer. Infrared (IR) spectra were obtained using hex-
ane or THF as solvent on a Perkin-Elmer 1600 series FT-IR
spectrometer. High-resolution mass spectra were obtained
from the Nebraska Center for Mass Spectrometry. Elemental
analyses were performed by Galbraith Laboratories.
2003 (s), 1994 (s), 1949 (s). Anal. Calcd for C28H26Fe2O4Si2:
C, 56.58; H, 4.41; Found: C, 56.51; H, 3.98.
1
3b: mp 258-260 °C; H NMR (C6D6) δ 1.14 (s, 6H, CH3),
3.98 (s, 10H, Cp), 7.26-7.28, 7.84-7.87 (m, 6H, 4H, Ph); 13C
NMR (C6D6) δ 5.62 (CH3), 83.5 (Cp), 128.1, 128.2, 134.9, 147.7
(Ph), 216.2, 216.7 (CO); 29Si NMR (C6D6) δ 19.9; IR (νCO, cm-1
)
2004 (s), 1995 (s), 1949 (s). Anal. Calcd for C28H26Fe2O4Si2:
C, 56.58; H, 4.41; Found: C, 56.47; H, 4.42.
P h otolysis of 1a : F or m a tion of 4 a n d 5. A 5 mm Pyrex
NMR tube was charged with 0.10 g (0.20 mmol) of 1a and 1
mL of C6D6 and sealed under vacuum. Irradiation was carried
out with a 450 W medium-pressure Hg lamp at a 10 cm
distance from the lamp. The progression of the reaction was
monitored by 1H, 13C, and 29Si NMR spectroscopy. The color
of the solution changed from yellow to violet-red upon irradia-
tion, and the 29Si NMR spectrum obtained after 2 h of
irradiation showed the formation of two different types of
silylene-bridged complexes, 4 and 5, each existing as a number
of isomers. Prolonged irradiation for 15 h resulted in the
complete disappearance of the starting material 1a and slow
conversion of complexes 4 to the more stable 5 as a mixture of
three geometrical isomers. Further irradiation for 30 h led to
an almost complete conversion of 4 to 5. At this stage the
irradiation was stopped. When the reaction mixture was stored
at -5 °C for 10 days, red-violet crystals of 5a were obtained
exclusively. The crystals were collected and washed with
hexane to give 63 mg of product (67%). We could not assign
Syn th esis of 1 a n d 2. To 50 mL of a THF solution of
[Fp]-Na+ (prepared from 2.00 g (5.60 mmol) of [(η5-C5H5)Fe-
(CO)2]2) was added 1.13 g (5.30 mmol) of 1,2-dichloro-1,2-
dimethyl-1,2-disilacyclohexane at 0 °C. The solution was
stirred at low temperature and then warmed to room temper-
ature and further stirred overnight. The solvent was removed
under vacuum, and the residue was extracted with hexane.
The solution was filtered, concentrated to 5 mL, and placed
upon a 2.5 × 20 cm silica gel column. Elution with a hexane/
benzene solvent mixture (90:10) developed a yellow band,
which was collected and after solvent removal afforded a yellow
solid product. The solid was further recrystallized from a
mixture of hexane and methylene chloride solvents to yield
1.53 g (58%) of orange-yellow crystals. H, 13C, and 29Si NMR
1
spectra of the yellow crystals indicated a mixture of two
compounds (1 and 2) in a ratio of 3:1. 1 and 2 could be
separated by recrystallization from a mixture of CH2Cl2 and
hexane.
1
the 13C and H NMR data to each isomer of 4, since there are
a total of seven different complexes coexisting in the reaction
mixture before the complete disappearance of 4.
4: 29Si NMR (C6D6) δ 8.13, 8.39, 9.41 (Si(CH3)), 228.5, 237.1,
240.3 (µ-Si).
1
1a : mp 132-134 °C; H NMR (C6D6) δ 0.69 (s, 6H, CH3),
1.15-1.20, 1.38-1.45, 1.68-1.77, 2.02-2.07 (br m, (CH2)4),
4.31 (s, 10H, Cp); 13C NMR (C6D6) δ 4.08 (CH3), 25.9, 28.5
((CH2)4), 83.4 (Cp), 216.84, 216.77, 216.52, (CO); 29Si NMR
(C6D6) δ 30.9; IR (νCO, cm-1) 1993 (s), 1944 (s), 1936 (sh, m).
Anal. Calcd for C20H24Fe2O4Si2: C, 48.40; H, 4.87; Found: C,
48.44; H, 4.96.
5: 1H NMR (C6D6) δ 0.28, 0.41 (s, s, 3H, 3H, Si(CH3)2, 5c),
0.31 (s, 6H, Si(CH3)2, 5b), 0.46 (s, 6H, Si(CH3)2, 5a ), 1.15, 1.77,
2.04 (bd m, 2H, 2H, 4H, (CH2)4, 5a ), 1.03-1.11, 1.72-1.76,
1.88-2.01 (bd m (CH2)4, 5b + 5c), 4.12 (s, 10H, Cp, 5a ), 4.22
(s, 10H, Cp, 5b), 4.30, 4.47 (s, s, 5H, 5H, Cp, 5c); 13C NMR
(C6D6) δ -0.88, 0.09 (CH3, 5c), -0.79 (CH3, 5a ), 0.24 (CH3,
5b), 21.02, 27.33, 27.91, 30.29 ((CH2)4, 5b), 19.93, 27.21, 30.62,
31.06 ((CH2)4, 5a ), 20.32, 27.26, 30.04, 30.10 ((CH2)4, 5c), 83.66
(Cp, 5b), 84.26 (Cp, 5a ), 84.39, 84.96 (Cp, 5c), 213.17 (CO, 5a ),
213.34 (CO, 5c), 213.38 (CO, 5b), 274.36 (µ-CO, 5b), 275.03
(µ-CO, 5a ), 276.74 (µ-CO, 5c); 29Si NMR (C6D6) δ -7.64 (Si-
(CH3)2, 5a ), -6.38 (Si(CH3)2, 5c), -5.14 (Si(CH3)2, 5a ), 236.02
(µ-Si, 5b), 242.52 (µ-Si, 5a ), 245.65 (µ-Si, 5c); IR (νCO, cm-1) in
THF 1992 (s), 1962 (s), 1929 (s), 1773 (s, µ-CO); HRMS (EI)
calcd for C19H2456Fe2O3Si2 m/z 467.9962, found m/z 467.9958.
LRMS (EI): 468.0 M+, 16; 412.0 [M - 2CO]+, 75; 291.0 [M -
2CO - CpFe]+, 100; 186.0 Fc+, 62; 120.9 [CpFe]+, 66. Anal.
Calcd for C19H24Fe2O3Si2: C, 48.74; H, 5.17. Found: C, 48.49;
H, 5.30.
1
2: mp 140-142 °C; H NMR (C6D6) δ 0.43, 0.61 (s, s, 6H,
6H, CH3), 0.93-1.53, 2.03 (br m, 12H, 4H, (CH2)4), 4.30 (s, 10H,
Cp); 13C NMR (C6D6) δ 0.97, 1.46 (CH3), 22.4, 22.6, 27.2, 27.7
((CH2)4), 83.4 (Cp), 215.78, 215.83 (CO); 29Si NMR (C6D6) δ 7.75
(SiOSi), 13.0 (Fp-Si); IR (νCO, cm-1) 1996 (s), 1945 (s). Anal.
Calcd for C26H38Fe2O5Si4: C, 47.70; H, 5.85; Found: C, 47.72;
H, 5.85.
Syn th esis of F p P h MeSiSiMeP h F p (3). To 50 mL of a
THF solution of [Fp]-Na+ (prepared from 2.00 g (5.60 mmol)
of [(η5-C5H5)Fe(CO)2]2) was added 1.31 g (4.20 mmol) of
ClPhMeSiSiMePhCl 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 hexane. The
solution was filtered, concentrated to 5 mL, and placed upon
a 2.5 × 20 cm silica gel column. Elution with a hexane/benzene
solvent mixture (90:10) developed a yellow band, which was
P h otolysis of 1a : F or m a tion of 6. A 5 mm Pyrex NMR
tube was charged with 0.10 g (0.20 mmol) of 1a and 1 mL of
C6D6 and sealed under vacuum. Irradiation was carried out
as above for 110 h or until NMR monitoring showed the
complete disappearance of 1a and 5 and the formation of 6,
as a mixture of two isomers, 6a (cis) and 6b (trans). At this
(11) Gilman, H.; Lichtenwalter, G. D. J . Am. Chem. Soc. 1958, 80,
608.
(12) Tamao, K.; Kumada, M.; Ishikawa. M. J . Organomet. Chem.
1971, 31, 17.

Disilyl Derivatives of the (η5-C5H5)Fe(CO)2 System
Organometallics, Vol. 22, No. 12, 2003 2519
stage the irradiation was stopped. When the reaction mixture
was stored at -5 °C for 1 week, red-violet crystals of 6a were
obtained exclusively. The crystals were collected and washed
with hexane to give 45 mg of product (51%).
in reciprocal space in the 2θ range of 15-30°. The ω-scan
technique was applied in the 2θ range (3.5° e 2θ e 45.0° (1a ),
4.12° e 2θ e 45.08° (5a ), 5.16° e 2θ e 45.10° (6a )) with
variable scan speeds. For 6a , data collection was performed
at 198 K to improve the quality of the data. A semiempirical
absorption correction was applied to the data set, giving a
minimum/maximum transmission ratio of 0.295/0.368 for 1a .
No absorption correction was applied in the cases of 5a and
6a . All structures were solved by direct methods and refined
using the PC version of the SHELEXTL PLUS crystallographic
software by Siemens. Full-matrix least-squares refinement
minimizing ∑w(Fo - Fc)2 was carried out with anisotropic
thermal parameters for non-hydrogen atoms. There is some
unresolved disorder in the Cp rings in 5a and at the C8 and
C9 atoms in 6a , respectively. The weighing scheme has the
form w-1 ) σ2(F) + gF2, and the final R factors have the forms
6: 1H NMR (C6D6) δ 1.03, 1.27 (s, s, 3H, 3H, Si(CH3)2, 6a ),
1.15 (s, 6H, Si(CH3)2, 6b), 1.36, 1.53-1.55, 1.77-1.82, 1.98-
2.00 (br m, 8H, (CH2)4, 6a ), 1.52, 1.97 (br m, 8H, (CH2)4, 6b),
3.91 (s, 10H, Cp, 6a ), 4.01 (s, 10H, Cp, 6b); 13C NMR (C6D6) δ
13.41, 15.58 (CH3, 6a ), 15.83 (CH3, 6b), 23.5, 27.1, 28.9, 29.3
((CH2)4, 6a ), 26.88, 28.86 ((CH2)4, 6b) 80.7 (Cp, 6b), 81.5 (Cp,
6a ), 213.9 (CO, 6a ), 214.9 (CO, 6b); 29Si NMR (C6D6) δ 235.9,
251.7 (6a ), 244.5, 265.0 (6b); IR (νCO, cm-1) in THF 1933 (s);
HRMS (EI) calcd for C18H2456Fe2O2Si2 m/z 440.0014, found m/z
440.0004. LRMS (EI): 444 M+, 26; 412 [M - CO]+, 100; 382
[M - 2CO - H2]+, 43; 186.0 Fc+, 35; 121 [CpFe]+, 12. Anal.
Calcd for C18H24Fe2O2Si2: C, 49.11; H, 5.49; Found: C, 49.45;
H, 5.45.
2
2
R ) ∑w|Fo - Fc|/∑Fo and Rw ) [w|Fo - Fc| /∑wFo
]
1/2. Crystal-
lographic data are summarized in Table 1.
P h otolysis of 3a : F or m a tion of 7. A 5 mm Pyrex NMR
tube was charged with 0.10 g (0.17 mmol) of 3a and 1 mL of
C6D6 and sealed under vacuum. Irradiation after 12 h indi-
cated the complete disappearance of the starting material 3
and the formation of 7, as a mixture of three main geometrical
isomers (7a :7b:7c ) 9:12:10). After the solvent was removed,
the resulting violet-red solid was washed twice with the cold
hexane and dried under vacuum to yield 7 (31 mg, 33%).
7: 1H NMR (C6D6) δ 0.77, 0.79, 0.91 (SiCH3Ph2), 1.19, 1.35,
1.57 (SiCH3SiCH3Ph2), 4.00 (Cp, 7a ), 4.19 (Cp, 7b), 4.10, 4.39
(Cp, 7c), 7.22-7.42, 7.82-7.84, 7.94-7.96 (m, Ph); 13C NMR
(C6D6) δ -0.31, 0.06, 0.94 (SiCH3Ph2), 11.56, 12.03, 13.11
(SiCH3SiMePh2), 84.23, 84.90 (Cp, cis), 84.97, 95.83 (Cp, trans),
128.49, 128.75, 129.20, 129.62, 135.75, 136.05, 139.83, 140.03
(Ph, cis), 128.45, 128.85, 129.31, 129.69, 135.26, 136.00, 138.77,
140.12 (Ph, trans), 213.47, 213.86 (CO, cis), 213.69, 213.76 (CO,
trans), 273.81, 274.89, 276.21 (µ-CO); 29Si NMR (C6D6) δ
-10.97, -9.91, -9.57 (SiCH3Ph2), 221.46, 234.11, 235.96 (µ-
Si); IR (νCO, cm-1) 1993 (s), 1976 (sh, m), 1938 (s), 1781 (s,
µ-CO); HRMS (FAB): calcd for C27H2656Fe2O3Si2 m/z 566.0119,
found m/z 566.0116.
Resu lts a n d Discu ssion
Syn th esis a n d Sp ectr oscop ic P r op er ties. The
new complexes FpMeSi(CH2)4SiMeFp (1) and FpMePh-
SiSiPhMeFp (3) were readily prepared in THF by the
salt-elimination reactions between [Fp]-Na+ and the
corresponding dichlorodisilanes in THF (eq 3). Analysis
The 29Si NMR spectrum of this photolysis mixture also
exhibited four very weak resonances at δ -10.13, -9.96, 219.5
(µ-Si), and 223.9 (µ-Si), attributed to the formation of a small
amount of 1,3-methyl migration products (µ-SiPhSiMe2Ph),
some resonances of which have been observed in 1H and 13C
NMR spectra of the photolysis mixture. However, we could not
unambiguously assign these comparatively weaker resonances
and were unable to isolate the material.
of the crude reaction products of 1 after column chro-
matography by 1H, 13C, and 29Si NMR spectroscopy
showed that only the trans isomer (1a ) was formed
along with the disiloxane complex [FpMeSi(CH2)4SiMe]2O
P h otolysis of 3a : F or m a tion of 8. In an experiment set
up the same as that above, irradiation was continued for 70 h
or until NMR monitoring showed the complete disappearance
of both 3a and 7 and the formation of 8, as a mixture of cis
(8a ) and trans (8b) isomers. The solvent was evaporated, and
the violet-red solid was washed twice with cold hexane and
dried under vacuum to yield 8 (35 mg, 38%).
8: 1H NMR (C6D6) δ 1.17, 1.45 (Si(CH3)2, 8a ), 1.43 (Si(CH3)2,
8b), 4.11 (Cp, 8a ), 4.15 (Cp, 8b), 7.25-7.96 (bd. m. Ph); 13C
NMR (C6D6) δ 14.63 (CH3, 8b), 15.40, 18.76 (CH3, 8a ), 80.65,
81.54 (Cp), 127.5, 128.2, 128.3, 128.5, 128.9, 134.12, 134.4,
134.6, 149.9, 151.8, 153.5 (Ph), 215.1, 215.27 (CO); 29Si NMR
(C6D6) δ 219.5, 228.2, 234.7, 236.2;. IR (νCO, cm-1) in THF 1908
(s); HRMS (EI) calcd for C26H2656Fe2O2Si2 m/z 538.0170, found
m/z 538.0173. LRMS (EI): 538.0 M+, 28; 510.0 [M - CO]+,
100; 361.0 [CpFed(SiPhMe)2]+, 33; 296.0 [Fed(SiPhMe)2]+, 66;
186.0 Fc+, 28; 120.9 [CpFe]+, 25.
X-r a y Diffr a ction Stu d ies. Crystals (1a , 5a , and 6a )
suitable for X-ray diffraction analysis were obtained from
different solutions: CH2Cl2 and hexane (1a ) and benzene-d6
(5a and 6a ). Intensity data were collected on a Nicolet-Siemens
R3m/V four-circle diffractometer at room temperature, using
graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å).
Unit cell parameters and standard deviations were obtained
by a least-squares fit of 25 reflections randomly distributed
(2). 1a and 2 could be separated by recrystallization
from a mixture of methylene chloride and hexane. The
formation of 2 possibly resulted from the hydrolysis of
small amounts of FpMeSi(CH2)4SiMeCl during the
column chromatography. 1H, 13C, and 29Si NMR spectra
of 3 showed a mixture of the two diastereomers 3a (rac)
and 3b (meso), in the ratio of 5:1. 3a and 3b could also
be separated by recrystallization from a mixture of
hexane and CH2Cl2.
The new complexes exhibit spectroscopic data in total
accord with the proposed structures. The 29Si NMR
spectrum of 1a exhibits a signal at 30.9 ppm, which is
comparable to that of the tetramethyldisilyl analogue
FpSiMe2SiMe2Fp at 29.2 ppm. Compound 2 shows two
29Si NMR signals at 12.96 and 7.75 ppm, which are
assigned to FpSiSi and SiSiOSiSi, respectively. Similar
FpSiSi resonances are observed in the related complexes
FpSiMe2SiMe2OMe,7b FpSiMe2SiMe2Cl,10b and FpSiMe2-
SiMe2Fc.10b The infrared spectra of 1-3 exhibit either
two broad stretching frequencies at ∼1995 and 1945
cm-1 (2) or four frequencies at ∼2003, 1995, 1945, and
1937 cm-1 (1 and 3) due to the presence of isomers in

2520 Organometallics, Vol. 22, No. 12, 2003
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1a , 5a , a n d 6a
Zhang et al.
1
5a
6a
C18H24Fe2O2Si2
empirical formula
fw
C
496.3
20H24Fe2O4Si2
C
19H24Fe2O3Si2
468.26
440.25
cryst size (mm)
group syst
space group
unit cell dimens
a (Å)
0.42 × 0.60 × 0.70
monoclinic
P21/n
0.62 × 0.60 × 0.52
orthorhombic
P212121
0.42 × 0.28 × 0.28
monoclinic
P21/n
7.984(3)
13.482(4)
20.937(8)
90
97.87(3)
90
2232.4(14)
4
1.477
10.197(5)
12.773(9)
15.581(6)
90
90
90
2029.4(19)
4
1.533
15.63
296
8.735(3)
15.769(3)
13.772(3)
90
96.11(2)
90
1886.2(8)
4
1.550
b (Å)
c (Å)
R, deg
â, deg
γ, deg
V (Å3)
Z
d
calcd (g.cm-1
)
µ, cm-1
14.26
296
16.73
198
temp (K)
2θ range (deg)
index ranges
3.5-45.0
4.12-45.08
5.16-45.10
h
k
l
0-8
-10 to 10
-5 to 10
-2 to 14
-13 to 13
-1 to 18
-22 to 22
3805
2927 (Rint ) 2.77%)
semiempirical
R ) 3.08, Rw ) 4.53
1.17
-16 to 16
3825
1543 (Rint ) 6.87%)
N/A
R ) 10.59, Rw ) 27.33
1.503
-16 to 16
3827
3313 (Rint ) 8.44%)
N/A
R ) 7.15, Rw ) 19.75
0.795
no. of rflns collected
no. of indep data
abs cor
final R indices (obsd data) (%)
goodness of fit
Sch em e 2
solution. The molecular structures of 1a and 3b have
been determined by X-ray diffraction analysis.
P h otoch em istr y of 1a . A C6D6 solution of 1a in a
flame-sealed Pyrex NMR tube was irradiated using a
450 W medium-pressure Hg lamp. Periodic monitoring
1
by H, 13C, and 29Si NMR spectroscopy indicated that
after 8 h of irradiation 1a had partially transformed to
the two new silylene-bridged complexes 4 and 5, each
existing as a mixture of three geometrical isomers,
respectively (Scheme 2). Prolonged irradiation resulted
in the gradual decrease of 1a and 4 and increase of 5.
The spectra obtained after 15 h of irradiation showed
the complete disappearance of the starting material 1a .
Further irradiation for 15 h led to the almost complete
disappearance of 4 and formation of 5 along with trace
amounts of the cis and trans isomers of 6. These results
are analogous to those obtained in the photochemistry
of FpSiMe2SiMe2Fp, but the reaction is much slower (30
h vs 2 h), and the results are more complex. Continuous
irradiation for 110 h resulted in the complete disap-
pearance of 5 and formation of 6.
The 29Si NMR signals at 8.13, 8.39, and 9.41 ppm are
assigned to the silacyclopentyl groups in three geo-
metrical isomers of 4 in which the silacyclopentyl group
is linked to the bridging silicon atom. These resonances
are about 14-16 ppm more downfield than those of the
related complexes 5 (-7.64, -6.38, and -5.14 ppm) and
[(η5-C5H5)Fe(CO)]2(µ-CO)(µ-SiMeSiMe3) (-6.72, -5.56,
and -4.70 ppm) formed in the photolysis of FpSiMe2-
SiMe2Fp. These downfield shifts are expected for the
related silacyclopentane derivatives (∆δ ) 16.77 ppm
for silacyclopentane and ∆δ ) 16.5 ppm for silacyclo-
pentene).13,14 A series of significantly downfield reso-
nances are assigned to the bridging silylenes of 4 (228.5,
237.1, and 240.3 ppm) and 5 (236.0 (5b), 242.5 (5a ), and
245.7 ppm (5c)). We could not unambiguously assign
the 29Si NMR data to each isomer of 4, and prolonged
irradiation of 4 led to its complete conversion to 5. For
complex 6, four 29Si resonances observed at 235.9 (6a ),
(13) Williams, E. A. The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, U.K., 1989; pp 511-
555.
(14) (a) Scholl, R. G.; Maciel, G. E.; Musker, W. K. J . Am. Chem.
Soc. 1972, 94, 6376. (b) Filleux-Blanchard, M.-L.; An, N. D.; Manuel,
G. Org. Magn. Reson. 1978, 11, 150.

Disilyl Derivatives of the (η5-C5H5)Fe(CO)2 System
Organometallics, Vol. 22, No. 12, 2003 2521
244.5 (6b), 251.7 (6a ), and 265.0 ppm (6b) are assigned
to the distinct bridging silylene units in the cis and trans
isomers. These resonances are comparable to those
observed in [(η5-C5H5)Fe(CO)]2(µ-SiMe2)2, (229.5 and
243.8 ppm) and [(η5-C5H5)Fe(CO)]2(µ-SiMe2)(µ-GeMe2)
(230.8 and 244.7 ppm). In the 13C NMR spectrum of 6,
the bridging dimethylsilylene unit (µ-SiMe2) exhibits
three resonances. Two SiMe resonances of equal inten-
sity observed at 13.4 and 15.6 ppm are assigned to the
cis isomer with an approximate mirror about the center
of the Fe-Fe bond, and the remaining resonance at 15.8
ppm is assigned to the trans isomer with a C2 axis about
the center of the Fe-Fe bond.
The formation of 4 and 5 is related to the observation
by Malisch et al. for the compounds [(η5-C5H5)Fe(CO)]2-
(µ-CO)(µ-SiMeX) (X ) H, Cl)10a and the chemistry noted
in Scheme 1 by ourselves and the Ogino group.10b,c,15
On the basis of the Ogino analysis of these latter
systems,15 we have briefly studied the related isomer-
F igu r e 1. Molecular structure of 1a .
1
ization of 5 by observing the H NMR spectral change
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1a
of a C6D6 solution of 5a with time. When 5a was
dissolved in C6D6 in a sealed NMR tube and the 1H
NMR spectrum recorded within 20 min, a mixture of
5a and trace amounts of 5b and 5c was observed. The
isomers equilibrate over a 5 day time period at room
Fe(1)-Si(1)
Si(1)-Si(2)
Fe(1)-C(7)
Fe(2)-C(15)
O(2)-C(7)
2.342(1)
2.362(1)
1.736(3)
1.733(4)
1.141(4)
1.148(5)
Fe(2)-Si(2)
Fe(1)-C(6)
Fe(2)-C(14)
O(1)-C(6)
2.351(1)
1.731(4)
1.736(3)
1.156(5)
1.152(4)
1
temperature, and the H NMR spectrum recorded after
O(3)-C(14)
O(4)-C(15)
5 days showed that the molar ratio of three geometrical
isomers is 5a :5b:5c ) 27:54:19. The isomer distribution
indicates that 5b (cis-SiMe2) is thermodynamically the
most stable. This result indicates that there is a steric
interaction between the bulky SiMe2CH2 group and the
Cp rings in 5b smaller than that between the less bulky
CH2 group and the Cp rings in 5a . The anomaly can be
understood if we compare the Si-Si and Si-C bond
lengths (2.342 Å vs 1.858 Å) placing the “bulky” group
further from the Cp rings and reducing the steric
interaction. The isomerization of 5a is much slower than
that of its analogues [(η5-C5H5)Fe(CO)]2(µ-CO)(µ-EMe-
SiMe3) (E ) Si, Ge).10c,d,15 For the final bis(silylene)
photoproducts, pure 6a was found to equilibrate to a
molar ratio of 6a :6b ) 23:77 over a 5 day time period
at room temperature, indicating that, as anticipated, the
trans isomer 6b is the more stable isomer.
Sin gle-Cr ysta l X-r a y Diffr a ction Stu d ies. The
molecular structure of 1a is illustrated in Figure 1, and
selected bond distances and angles are provided in Table
2. The molecule can be regarded as the replacement of
the two methyl groups of tetramethyl-1,2-disilacyclo-
hexane by two Fp units. The Fp moieties are mutually
trans to each other, and the disilacyclohexane ring
adopts a twist-chair conformation. Both the Si-Si
(2.362(1) Å) and Fe-Si bond lengths (2.342(1) and 2.351-
(1) Å) are in the normal range noted for related
complexes containing the Fe-Si-Si fragment.16 How-
ever, it is interesting that the Fe-Si bond lengths are
much shorter than that (2.390 Å) in the parent analogue
[(η5-C5H5)Fe(CO)2]2Si2Me4,16a the longest bond of this
type reported to date, possibly attributed to the ring
effect. The dihedral angle between the two Cp rings is
Fe(1)-Si(1)-Si(2)
Si(2)-Si(1)-C(8)
117.8(1) Fe(2)-Si(2)-Si(1)
112.2(1) Si(2)-Si(1)-C(9)
122.0(1)
100.0(1)
105.7(1)
105.5(2)
94.3(2)
Si(1)-Si(2)-C(12) 102.4(1) Si(1)-Si(2)-C(13)
C(8)-Si(1)-C(9)
C(6)-Fe(1)-C(7)
105.1(2) C(2)-Si(1)-C(13)
93.7(2) C(14)-Fe(2)-C(15)
104.5°. The silicon substituents take an almost stag-
gered conformation about the silicon-silicon bond with
torsion angles in the range of 34.1-45.0°.
When the reaction solution containing 5 was stored
in a sealed NMR tube at -5 °C, violet-red crystals of
5a were exclusively obtained. Similar treatment of 6
yielded violet-red crystals of 6a . The single-crystal
structures of both 5a and 6a have been determined by
X-ray diffraction analysis. The quality of the single-
crystal structure of 5a is poor, due to some unresolved
disorder in the Cp rings, but it serves to confirm the
geometrical configuration, and this is illustrated in
Figure 2, with selected bond distances and angles listed
in Table 3. The two Cp rings are mutually cis, and the
Cp ring and the µ-SiCH2 unit are also cis to each other
with respect to the four-membered ring defined by Fe1,
Si1, Fe2, and C11 atoms. This structure is one (cis-CH2)
of the two cis isomers, and the single-crystal structure
of the other cis isomer (cis-SiMe3) in the analogue [(η5-
C5H5)Fe(CO)]2(µ-CO)(µ-SiMeSiMe3)] was previously re-
ported by Ogino and co-workers.10c The Fe-Fe (2.622(3)
Å) and the Fe-Si bond lengths (2.291(4) and 2.290(4)
Å) are completely in line with those (2.622(1) Å for the
Fe-Fe bond, 2.294(1) and 2.301(1) Å for the Fe-Si
bonds) in [(η5-C5H5)Fe(CO)]2(µ-CO)(µ-SiMeSiMe3)].
The crystal structure of the bis(silylene)-bridged bis-
(cyclopentadienyl)diiron complex 6a appears to be the
first example of a bis(silylene)diiron compound, al-
though the crystal structures of several mono(silylene)-
bridged analogues are known.10c,17 To get good-quality
structural data, collection was performed at -75 °C. The
molecular structure is illustrated in Figure 3, and
(15) Ueno, K.; Hamashima, N.; Ogino, H. Organometallics 1992, 11,
1435.
(16) (a) Pannell, K. H.; Cervantes, J .; Parkanyi, L.; Cervantes-Lee,
F. Organometallics 1990, 9, 859. (b) Pannell, K. H.; Lin, H.-S.; Kapoor,
R. N.; Cervantes-Lee, F.; Pinon, M.; Parkanyi, L. Organometallics 1990,
9, 2454.

2522 Organometallics, Vol. 22, No. 12, 2003
Zhang et al.
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6a
Fe(1)-Si(1)
Fe(2)-Si(1)
Fe(1)-Fe(2)
Fe(2)-C(11)
O(1)-C(6)
Si(1)-C(7)
Si(2)-C(17)
C(7)-C(8)
2.272(4)
2.261(4)
2.7423(14)
1.723(7)
1.167(10)
1.905(8)
Fe(1)-Si(2)
Fe(2)-Si(2)
Fe(1)-C(6)
C(9)-C(10)
O(2)-C(11)
Si(1)-C(10)
Si(2)-C(18)
C(8)-C(9)
2.268(2)
2.274(2)
1.721(8)
1.531(18)
1.159(9)
1.884(8)
1.893(10)
1.39(2)a
1.867(11)
1.403(16)a
Fe(2)-Si(1)-Fe(1)
Si(1)-Fe(2)-Fe(1)
Si(2)-Fe(1)-Fe(2)
74.46(6) Fe(1)-Si(2)-Fe(2)
52.95(6) Si(2)-Fe(2)-Fe(1)
52.95(6) Si(1)-Fe(1)-Fe(2)
74.28(7)
52.77(6)
52.59(5)
101.94(8)
99.2(6)
Si(2)-Fe(1)-Si(1) 101.77(8) Si(1)-Fe(2)-Si(2)
C(7)-Si(1)-C(10)
92.1(5)
C(17)-Si(2)-C(18)
a
The disorder at the C8 and C9 atoms results in shorter C-C
single-bond distances.
F igu r e 2. Molecular structure of 5a .
F igu r e 4. Butterfly structure of the bis(silylene)iron
fragment of 6a .
Sch em e 3
F igu r e 3. Molecular structure of 6a .
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5a
Fe(1)-Si(1)
Si(1)-Si(2)
Fe(1)-C(12)
Fe(2)-C(13)
O(2)-C(12)
Si(2)-C(17)
2.291(4)
2.342(5)
1.761(13)
1.715(13)
1.097(16)
1.858(15)
Fe(2)-Si(1)
Fe(1)-C(11)
Fe(2)-C(11)
O(1)-C(11)
O(3)-C(13)
Si(2)-C(9)
2.290(4)
1.925(13)
1.887(13)
1.206(15)
1.173(17)
1.845(14)
Fe(1)-Si(1)-Fe(2)
69.83(11) Fe(2)-C(11)-Fe(1) 86.9(6)
Fe(1)-Si(1)-Si(2) 127.28(16) Fe(2)-Si(1)-Si(2) 126.24 (17)
C(11)-Fe(1)-Fe(2) 45.9(4)
Si(1)-Fe(2)-Fe(1)
C(11)-Fe(1)-Si(1)
C(11)-Fe(2)-Fe(1) 47.1(4)
55.10(9) Si(1)-Fe(1)-Fe(2) 55.07(9)
98.8(4)
C(11)-Fe(2)-Si(1) 100.0(4)
selected bond distances and angles are listed in Table
4. The molecule of 6a consists of two [(η5-C5H5)Fe(CO)]
moieties linked to each other by one Fe-Fe bond and
two bridged silylene ligands. The two Cp rings are
mutually cis to each other. The Fe-Fe bond length
(2.7423(14) Å) is longer than those found in related
mono(silylene)-bridged analogues reported to date,
2.614-2.633 Å.17 The Fe-Si bond lengths (mean 2.269
Å) are longer than those of the cis-SiMe3 isomer of
[CpFe(CO)]2(µ-CO)(µ-SiMeSiMe3)]10c but close to those
(17) (a) Kawano, Y.; Tobita, H.; Ogino, H. Angew. Chem., Int. Ed.
Engl. 1991, 30, 843. (b) Tobita, H.; Kawano, Y.; Shimoi, M.; Ogino, H.
Chem. Lett. 1987, 2247. (c) Kawano, Y.; Tobita, H.; Shimoi, M.; Ogino,
H. J . Organomet. Chem. 1992, 428, 125. (d) Kawano, Y.; Tobita, H.;
Shimoi, M.; Ogino, H. J . Am. Chem. Soc. 1994, 116, 8575.

Disilyl Derivatives of the (η5-C5H5)Fe(CO)2 System
Organometallics, Vol. 22, No. 12, 2003 2523
Sch em e 4
(2.270(1) and 2.272(1) Å) of the cis-H isomer of [(η5-
C5H5)Fe(CO)]2(µ-CO)(µ-SiHBut)].17a The Fe-Si-Fe angle
(mean 74.37°) is the largest of this type (68.15-71.05°)
reported to date.10c,17 The two silylene ligands are
arranged in a butterfly configuration with respect to the
Fe-Fe bond (Figure 4), with a dihedral angle of 160°.
to those obtained in the photolysis of FpSiMe2SiMe2-
Fp, but the phenyl replacement of methyl groups greatly
slows down the photoreaction (12 h vs 2 h).
1
Both 7 and 8 were characterized by H, 13C, and 29Si
NMR and high-resolution mass spectroscopy (HRMS).
The 29Si NMR resonances at -11.0, -9.91, -9.57, 221.5,
234.1, and 236.0 ppm are assigned to the three main
geometrical isomers of 7, in which the SiMePh2 unit is
P h otoch em istr y of F p MeP h SiSiP h MeF p (3a a n d
3b). Separate irradiation of the two isomers 3a and 3b
in sealed NMR tubes gave the same results, indicating
that the photoreaction is not stereospecific. Irradiation
of 3a for 12 h led to the complete disappearance of 3a
and formation of 7 along with trace amounts of the cis
and trans isomers of 8 (Scheme 3). The 29Si NMR
spectrum of the reaction mixture showed that 7 exists
as a mixture of the three main isomers 7a -7c formed
via 1,3-phenyl migration and two minor isomers formed
via 1,3-methyl migration. We could not unambiguously
1
attached to the bridging silicon atom. In the H and 13C
NMR spectra of 7, two completely different types of
methyl resonances were observed, strongly suggesting
that the three main isomers result from 1,3-phenyl
migration (µ-SiMeSiMePh2) rather than 1,3-methyl
migration (µ-SiPhSiMe2Ph). For complex 8, four 29Si
resonances observed at 219.5, 228.2, 234.7, and 236.2
ppm are assigned to the different bridging silylene units
in the cis and trans isomers. In the 13C NMR spectrum
of 8, the bridging dimethylsilylene unit (µ-SiMe2) ex-
hibits three resonances. Two SiMe resonances of equal
intensity observed at 15.4 and 18.8 ppm are assigned
to the cis isomer (8a ) with an approximate mirror about
the center of the Fe-Fe bond, while the remaining
1
assign the 13C and H NMR data to the minor isomers.
Prolonged irradiation resulted in the gradual decrease
of 7 and increase of 8. The spectra obtained after 70 h
of irradiation showed the complete disappearance of 7
and the formation of 8. These results are also analogous

2524 Organometallics, Vol. 22, No. 12, 2003
Zhang et al.
resonance at 14.6 ppm is assigned to the trans isomer
(8b) with a C2 axis about the center of the Fe-Fe bond.
A similar phenomenon was also observed in the 1H
NMR spectrum of 8.
species. Since 6* is a very strained molecule, only the
isomer 6 was formed via both 1,3-CH2 and 1,3-CH3
migration (intermediate D).
In the photolysis of 3, the predominant formation of
the (µ-SiMeSiMePh2) isomers strongly suggests that the
aryl migration is much more favorable than the alkyl
migration. Since the intermediate (η5-C5H5)Fe(CO)(d
SiPh2)SiMe2Fp (the equivalent of intermediate D in
Scheme 4) where the SiPh2 group replaces the (sila-
cyclopentyl group) is more dominant than (η5-C5H5)Fe-
(CO)(dSiPhMe)SiPhMeFp (equivalent of intermediate
A), the isomer 8 was predominantly formed rather than
8*, the equivalent of 6*, where the phenyl groups
replaces the CH2 moiety in (CH2)4.19
Mech a n ism . The results of the photochemistry of 1a
and 3 agree with the general mechanism we and the
Ogino group have proposed with respect to the disilyl-
diiron system, FpSiMe2SiMe2Fp, and is illustrated in
Scheme 4. However, since there are different silicon
substituent groups in 1a and 3, different 1,3-migration
products were observed. During the initial stage of
photolysis of 1a photoproducts 4 and 5 were formed
simultaneously; i.e., no significant preference for 1,3-
CH2 or 1,3-CH3 migration to form the intermediates C
and B was noted. However, 4 did eventually photo-
isomerize to 5 prior to expulsion of the second CO group.
We have not examined the relative amounts of 4 and 5
in the absence of irradiation and, since it has been noted
that thermal equilibria and photostationary states of
metal silylenes can be quite distinctive,18 cannot deter-
mine the relative thermodynamic stabilities of these
Ack n ow led gm en t. This research was supported by
the Robert A. Welch Foundation, Houston, TX.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal
data and data collection, solution, and refinement details,
complete atomic coordinates, bond distances and angles, and
anisotropic thermal parameters for 1a , 5a , and 6a . This
material is available free of charge via the Internet at
http://pubs.acs.org.
(18) Kawano, Y.; Tobita, H.; Ogino, H. Organometallics 1992, 11,
499.
(19) For a more detailed discussion concerning the importance of
the relative stabilities of the silylene intermediates, compared to their
rate of trapping to form final products, see: Zhang, Y.; Pannell, K. H.
Organometallics 2003, 22, 1766.
OM030026+