Formation of 1,2,4-trisilacyclopentanes by photolysis of FpCH2SiR2SiR2SiR2CH2Fp (Fp = (η5-C5H5)Fe(CO)2)

Article abstract of DOI:10.1021/om0109657

Photolysis of FpCH₂SiMe₂SiMe₂SiMe₂CH₂Fp (1), Fp = [(η⁵-C₅H₅)Fe(CO)₂], resulted in almost quantitative formation of 1,1,2,2,4,4-hexamethyl-1,2,4-trisilacyclopentane (2) and Fp₂. Similar treatment of FpCH₂Me₂SiMeSiEtSiMe₂CH₂Fp (6) afforded 1-ethyl-1,2,2,4,4-pentamethyl-1,2,4-trisilacyclopentane (7), indicating that the central silicon of the trisilane remains associated with the silicon-silicon bond of the product. Irradiation of FpCH₂-PhMeSiSiMe₂SiMe₂CH₂Fp (11) led to the formation of the two positional isomers (ratio 4:3), 1,1,2,2,4-heptamethyl-4-phenyl-1,2,4-trisilacyclopentane (12a) and 1,1,2,4,4-heptamethyl-2-phenyl-1,2,4-trisilacyclopentane (12b), indicating that either one of the two terminal silicon atoms of the trisilane remains in the Si-Si bond of the product while the other becomes the silicon atom of the product at 4-position. A mechanism for the formation of 1,2,4-trisilacyclopentane is suggested. Irradiation of 11 also produced a small amount the rearranged product FpPhMeSiCH₂SiMe₂CH₂SiMe₂Fp (13), whereas photochemical treatment of the tetrasilane analogue, FpCH₂SiMe₂SiMe₂SiMe₂SiMe₂ CH₂Fp (15), resulted in only the high-yield rearrangement product FpMe₂SiCH₂SiMe₂SiMe₂CH₂Si Me₂Fp (17) with an absence of elimination products.

Full text of DOI:10.1021/om0109657

Organometallics 2002, 21, 503-510
503
F or m a tion of 1,2,4-Tr isila cyclop en ta n es by P h otolysis of
F p CH2SiR2SiR2SiR2CH2F p (F p ) (η5-C5H5)F e(CO)2)
Yongqiang Zhang and Keith H. Pannell*
Department of Chemistry, The University of Texas at El Paso, El Paso, Texas 79968-0513
Received November 7, 2001
Photolysis of FpCH2SiMe2SiMe2SiMe2CH2Fp (1), Fp ) [(η5-C5H5)Fe(CO)2], resulted in
almost quantitative formation of 1,1,2,2,4,4-hexamethyl-1,2,4-trisilacyclopentane (2) and Fp2.
Similar treatment of FpCH2Me2SiMeSiEtSiMe2CH2Fp (6) afforded 1-ethyl-1,2,2,4,4-pen-
tamethyl-1,2,4-trisilacyclopentane (7), indicating that the central silicon of the trisilane
remains associated with the silicon-silicon bond of the product. Irradiation of FpCH2-
PhMeSiSiMe2SiMe2CH2Fp (11) led to the formation of the two positional isomers (ratio 4:3),
1,1,2,2,4-heptamethyl-4-phenyl-1,2,4-trisilacyclopentane (12a ) and 1,1,2,4,4-heptamethyl-
2-phenyl-1,2,4-trisilacyclopentane (12b), indicating that either one of the two terminal silicon
atoms of the trisilane remains in the Si-Si bond of the product while the other becomes the
silicon atom of the product at 4-position. A mechanism for the formation of 1,2,4-
trisilacyclopentane is suggested. Irradiation of 11 also produced a small amount the
rearranged product FpPhMeSiCH2SiMe2CH2SiMe2Fp (13), whereas photochemical treatment
of the tetrasilane analogue, FpCH2SiMe2SiMe2SiMe2SiMe2CH2Fp (15), resulted in only the
high-yield rearrangement product FpMe2SiCH2SiMe2SiMe2CH2SiMe2Fp (17) with an absence
of elimination products.
Sch em e 1
In tr od u ction
The activation of the silicon-silicon bond by transi-
tion metal complexes is an important area of modern
organosilicon chemistry.1 Photolysis of oligosilyl and
oligosilylmethyl derivatives of the transition metals
results in the formation of transient silylene and silene
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Sch em e 2
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Am. Chem. Soc. 1987, 109, 5872. (b) Straus, D. A.; Zhang, C.; Quimbita,
G. E.; Grumbine, S. D. Heyn, R. H.; Tilley, T. D.; Rheingold, A. L.;
Geib, S. J . J . Am. Chem. Soc. 1990, 112, 2673. (c) Grumbine, S. D.;
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2545. (h) Grumbine, S. D.; Tilley, T. D. J . Am. Chem. Soc. 1993, 115,
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complexes via R- and â-elimination processes, respec-
tively (Schemes 1 and 2).2-4 These intermediates lead
to either silylene (or silene) eliminations or rearrange-
ments. There are now many examples of silylene and
silene transition metal complexes reported.5
By way of contrast, we recently reported that UV
irradiation of FpCH2RMeSiSiMeRCH2Fp (Fp ) (η5-
10.1021/om0109657 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/10/2002

504 Organometallics, Vol. 21, No. 3, 2002
Zhang and Pannell
under vacuum, and the residue was placed upon a 1 × 15 cm
silica gel column. Elution with hexane afforded a colorless oily
product, 2 (48 mg, 79%). Elution with a mixture of hexane and
benzene (4:1) yielded 98 mg (92%) of violet-red solid, [(η5-
C5H5)Fe(CO)2]2. Compound 2 has been previously synthesized
by cyclization of (BrMe2SiCH2)2SiMe2 in the presence of Na-K
alloy.10 1H NMR (C6D6): δ -0.25 (s, 4H, CH2), 0.13 (s, 6H,
SiMe2), 0.19 (s, 12H, Si2Me4). 13C NMR (C6D6): δ -0.97 (Si2-
Me4), 2.06 (SiMe2), 3.19 (CH2). 29Si NMR (C6D6): δ -12.86 (Si2-
C5H5)Fe(CO)2; R ) Me, Ph) resulted in the formation
of 1,3-disilacyclobutanes and Fp2, stereospecifically in
the case of R2 ) MePh (eq 1).6
Me4), 9.45 (SiMe2). MS (70 eV): m/z 202 (M+, 33), 187 (M+
-
Me, 100), 28 (Si+, 60).
Syn t h esis of P h Me2SiMeSiE t SiMe2P h (3). A flask
equipped with a magnetic stirring bar and addition funnel was
charged with 10.9 g (76 mmol) of MeEtSiCl2 and 100 mL of
THF. The solution was cooled to 0 °C, and the PhMe2SiLi
solution (prepared from 27.0 g (0.16mol) of PhMe2SiCl and 4.45
g (0.64mol) of Li in 150 mL of THF) was added dropwise. Upon
complete addition the solution was allowed to warm to room
temperature and 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
138-140 °C/2 mmHg to give 16.6 g (64%) of 3 as a colorless
oil. NMR (C6D6): δ 1H, 0.13 (s, 3H, SiEtSiMeSi), 0.30, 0.31 (s,
s, 12H, Me2SiEtSiMeSiMe2), 0.69 (q, 3J ) 7.0 Hz, 2H, CH2-
CH3), 0.92 (t, 3J ) 7.5 Hz, 3H, CH2CH3), 7.16-7.20 (m, 6H,
Ph), 7.35-7.38 (m, 4H, Ph); 13C, -8.21 (SiEtSiMeSi), -2.14
(Me2SiEtSiMeSiMe2), 4.49, 10.35 (Et), 128.15, 128.84, 134.18,
140.01 (Ph); 29Si, -43.48 (SiSiSi), -19.70 (SiSiSi). MS (70
eV): m/z 342 (M+, 10), 327 (M+ - Me, 3), 207 (M+ - SiMe2Ph,
15), 179 (PhMe2SiSiMeH+, 65), 135 (PhMe2Si+, 100), 130
(MeEtSidSiMe2+, 48), 105 (MeEtSidSiMe+, 25). Anal. Calcd
for C19H30Si3: C, 66.59; H, 8.82. Found: C, 66.26; H, 9.03.
Syn th esis of ClMe2SiMeSiEtSiMe2Cl (4). To a solution
of 12.5 g (36 mmol) of 3 in 40 mL of benzene was added 0.4 g
of aluminum chloride. Dry hydrogen chloride was passed
slowly through the reaction mixture at room temperature. The
progression of the reaction was monitored by 29Si NMR
spectroscopy. The signals due to the starting material at -43.5
and -19.7 ppm disappeared after 2 h and were replaced by
the signals due to the final product 4 at -39.8 and 24.1 ppm,
indicating the completion of the reaction. At this time the
reaction was stopped, the solvent was removed under vacuum,
and 50 mL of hexane was added to the residue. The solution
was filtered to remove the catalyst, the solvent was removed
at 50 mmHg, and the residue was distilled, by using a 20 cm
Vigreux column, at 68-70 °C/1 mm Hg to give 16.6 g (64%) of
4 as a colorless oil. NMR (C6D6): δ 1H, 0.15 (s, 3H, SiEtSiMeSi),
0.42 (s, 12H, Me2SiEtSiMeSiMe2), 0.75 (q, 3J ) 7.9 Hz, 2H,
CH2CH3), 0.98 (t, 3J ) 7.8 Hz, 3H, CH2CH3); 13C, -9.56
(SiEtSiMeSi), 3.88 (Me2SiEtSiMeSiMe2), 3.27, 9.77 (Et); 29Si,
-39.83 (SiSiSi), 24.10 (SiSiSi). Anal. Calcd for C7H20Cl2Si3:
C, 32.41; H, 7.77. Found: C, 32.61; H, 7.90.
To understand more about the nature of these pho-
toreactions, we have synthesized the related trisilane
complexes FpCH2SiR2SiR2SiR2CH2Fp and the tetra-
silane complex FpCH2SiMe2SiMe2SiMe2SiMe2CH2Fp
and report the results of their photochemical irradiation.
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, BrCH2Cl, Aldrich; CF3SO3H, Lancaster; Ph2-
MeSiCl, MeEtSiCl2, Me2SiHCl, PhMe2SiCl, Gelest. Other
reagents were synthesized by literature procedures: ClCH2-
SiMe2SiMe2SiMe2CH2Cl,7 ClMe2SiSiMe2Cl,8 Ph2MeSiSiMe2H,2c
ClMe2SiSiMe2SiMe2SiMe2Cl.9 Nuclear magnetic resonance
(NMR) spectra were recorded on a Bruker ARX-300 Fourier
transform spectrometer, and infrared (IR) spectra were ob-
tained using hexane as solvent on a Perkin-Elmer 1600 series
FT-IR spectrometer. High-resolution mass spectra were ob-
tained from the Nebraska Center for Mass Spectrometry.
Elemental analyses were performed by Galbraith Laboratories.
Syn th esis of F p CH2SiMe2SiMe2SiMe2CH2F p (1). To 50
mL of a THF solution of [CpFe(CO)2]-Na+ (prepared from 2.00
g (5.60 mmol) of Fp2) was added 1.45 g (5.30 mmol) of ClCH2-
SiMe2SiMe2SiMe2CH2Cl at 0 °C. The solution was stirred at
low temperature and then allowed to warm 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 and concentrated to 5 mL and placed
upon a 2.5 × 20 cm silica gel column. Elution with hexane
developed a yellow band, which was collected and after solvent
removal afforded a yellow crystalline solid. The solid was
recrystallized from hexane to yield 1, 0.79 g (27%) as yellow
crystals. Mp: 52-4 °C. NMR (C6D6): δ 1H, 0.06 (s, 2H, CH2),
0.37 (s, 6H, SiSiMe2Si), 0.40 (s, 12H, Me2SiSiMe2SiMe2), 4.18
(s, 10H, Cp); 13C, -23.34 (FpCH2), -5.43 (SiSiMe2Si), 0.80 (Me2-
SiSiMe2SiMe2), 84.96 (Cp), 218.15 (CO); 29Si, -46.40 (SiSiSi),
-2.55 (SiSiSi). IR (νCO, cm-1): 2009(s), 1958(s). Anal. Calcd
for C22H32Fe2O4Si2: C, 47.49; H, 5.80. Found: C, 46.85; H, 5.86.
P h otolysis of 1: F or m a tion of 1,1,2,2,4,4-Hexa m eth yl-
1,2,4-tr isila cyclop en ta n e (2). A 5 mm Pyrex NMR tube was
charged with 0.17 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. The progress of the reaction was
Syn th esis of ClCH2Me2SiMeSiEtSiMe2CH2Cl (5). Into
a 250 mL three-necked flask equipped with a magnetic stirring
bar, rubber septum, nitrogen inlet tube, and low-temperature
thermometer were placed 5.50 g (21.1 mmol) of 4 and BrCH2-
Cl (5.48 g, 42.2 mmol) 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, 26.4 mL (42.2 mmol)
of a 1.6 M solution of n-butyllithium in hexane. The solution
was allowed to warm to room temperature and stirred over-
night 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 108-110 °C/2 mmHg to give 5.70
g (94%) of 5. NMR (C6D6): δ 1H, 0.05 (s, 3H, SiEtSiMeSi), 0.11
(s, 12H, Me2SiEtSiMeSiMe2), 0.64 (q, 3J ) 7.9 Hz, 2H, CH2-
1
monitored by H, 13C, and 29Si NMR. The color of the solution
changed from yellow to dark red upon irradiation, and after 2
h complete disappearance of 1 and formation of 1,2,4-trisila-
cyclopentane 2 and iron dimer [(η5-C5H5)Fe(CO)2]2 were noted,
along with a trace of ferrocene. The solvent was then removed
(6) Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H. J . Am. Chem. Soc.
2000, 122, 8327.
(7) Kobayashi, T.; Pannell, K. H. Organometallics 1991, 10, 1960.
(8) Sakurai, H.; Tominaga, K.; Watanabe, T.; Kumada, M. Tetra-
hedron Lett. 1966, 5493.
3
CH3), 0.91 (t, J ) 7.6 Hz, 3H, CH2CH3), 2.70 (s, 4H, CH2Cl);
(9) Kumada, M. Ishikawa, M.; Maeda, S. J . Organomet. Chem. 1964,
2, 478.
(10) Fritz, G.; Grunert, B. Z. Anorg. Allg. Chem. 1976, 419, 249.

Formation of 1,2,4-Trisilacyclopentanes
Organometallics, Vol. 21, No. 3, 2002 505
13C, -8.51 (SiEtSiMeSi), -3.31 (Me2SiEtSiMeSiMe2), 4.20,
10.30 (Et), 31.51 (CH2Cl); 29Si, -44.09 (SiSiSi), -12.32 (SiSiSi).
MS (70 eV): m/z 237 (M+ - CH2Cl, 13), 179 (M+ - Me2SiCH2-
Cl, 10), 151 (ClCH2MeHSiSiEtH+, 100), 73 (SiMe3+, 33). Anal.
Calcd for C9H24Cl2Si3: C, 37.61; H, 8.42. Found: C, 38.01; H,
8.69.
1.89 g (270 mmol) of Li in 120 mL of THF) was added dropwise
via the addition funnel. Upon completing addition the solution
was allowed to warm to room temperature and stirred over-
night 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 at 234-
1
236 °C/2 mmHg to give 17.7 g (67%) of 8 as a colorless oil. H
Syn t h esis of F p CH 2Me2SiMeE t SiSiMe2CH 2F 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 1.38 g (4.8 mmol) of 5 at
0 °C. The solution was stirred at low temperature and then
allowed to warm to room temperature and further 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 placed upon a 2.5 × 20 cm silica
gel column. Elution with hexane developed a yellow band,
which was collected and after solvent removal afforded a yellow
oily product of 6 (1.22 g, 44%). NMR (C6D6): δ 1H, 0.10 (s, 4H,
FpCH2), 0.35 (s, 3H, SiEtSiMeSi), 0.43 (s, 12H, Me2SiEt-
SiMeSiMe2), 0.95, 1.27 (bd s, bd. s, 5H, Et), 4.21 (s, 10H, Cp);
13C, -22.67 (FpCH2), -7.70 (SiEtSiMeSi), 1.45 (Me2SiEt-
SiMeSiMe2), 5.34, 11.07 (Et), 84.98 (Cp), 218.22 (CO); 29Si,
-40.34 (SiSiSi), -2.46 (SiSiSi). IR (νCO, cm-1): 2009(s),
1957(s). HRMS (FAB): calcd for (C23H34Fe2O4Si3 + Na) m/z
NMR (C6D6): δ 0.23, 0.25 (s, s, 12H, SiMe2SiMe2Ph), 0.53 (s,
3H, SiMePh2), 7.16-7.48 (m, 15H, Ph). 13C NMR (C6D6): δ
-5.29 (PhMe2Si), -3.61 (Ph2MeSi), -2.88 (SiSiMe2Si), 128.28,
128.39, 128.94, 129.29, 134.29, 135.38, 137.84, 139.52 (Ph). 29Si
NMR (C6D6): δ -43.48 (SiSiSi), -19.64, -19.21 (SiSiSi). MS
(70 eV): m/z 390 (M+, 4), 375 (M+ - Me, 2), 255 (M+ - SiMe2-
Ph, 39), 197 (Ph2MeSi+, 100), 178 (PhMeSiSiMe2+, 42), 135
(PhMe2Si+, 91). Anal. Calcd for C23H30Si3: C, 70.70; H, 7.34.
Found: C, 70.59; H, 7.97.
Syn t h esis of ClP h MeSiSiMe2SiMe2Cl (9).
A flask
equipped with a magnetic stirring bar and addition funnel was
charged with 14.7 g (37.7 mmol) of 8 and 50 mL of toluene.
The solution was cooled to -30 °C, and 11.3 g (75.4 mmol) of
trifluoromethane sulfonic acid was added dropwise via the
addition funnel. Upon completing addition, the solution was
allowed to warm to room temperature and stirred for an
additional 2 h. 29Si NMR monitoring of the reaction mixture
indicated the disappearance of 8. The new resonance signals
appearing at -46.81, 29.31, 44.15 ppm were assigned to the
complex (CF3SO3)PhMeSiSiMe2SiMe2(CF3SO3). The reaction
mixture was added dropwise to a solution of 3.20 g (75.4 mmol)
of LiCl in 40 mL of THF at 0 °C. Upon completing addition,
the solution was permitted to warm to room temperature and
stirred for an additional 2 h. The solvents were removed under
vacuum, and 100 mL of hexane was added to precipitate the
salts. The hexane solution was filtered and the filtered
material washed with an extra 50 mL of hexane. The hexane
fractions were concentrated under reduced pressure, and the
residue was distilled, by using a 20 cm Vigreux column, at
136-140 °C/2 mmHg to give 3.7 g (32%) of 9 as a colorless oil.
1H NMR (C6D6): δ 0.22, 0.23, 0.30, 0.39 (s, s, s, s, 12H, SiMe2-
SiMe2Cl), 0.68 (s, 3H, SiMePhCl), 7.19-7.21 (m, 3H, Ph), 7.58-
7.60 (m, 2H, Ph). 13C NMR (C6D6): δ -7.13, -7.09 (SiSiMe2Si),
-1.78 (SiPhMeCl), 3.07, 3.21 (SiMe2Cl), 128.62, 130.46, 133.66,
136.26 (Ph). 29Si NMR (C6D6): δ -44.10 (SiSiSi), 14.30
(SiPhMeCl), 24.38 (SiMe2Cl).
593.0363, found m/z 593.0389. HRMS (EI): calcd for C22H31
-
Fe2O4Si3 (M - CH3) m/z 555.0226, found m/z 555.0233. LRMS
(EI): m/z 555.0 (M+ - Me, 21), 235 (FpSiMe2+, 97), 186 (Fc+,
70), 121 (CpFe+, 100), 73 (Me3Si+, 29).
P h otolysis of 6: F or m a tion of 1-Eth yl-1,2,2,4,4,-p en ta -
m eth yl-1,2,4-tr isila cyclop en ta n e (7). A 5 mm Pyrex NMR
tube was charged with 0.10 g (0.18 mmol) of 6 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. The color
of the solution changed from orange to dark red upon irradia-
tion, and after 2 h complete disappearance of 6 and formation
of 7 and iron dimer [(η5-C5H5)Fe(CO)2]2 were noted, along with
a trace of ferrocene. The solvent was removed under vacuum,
and the residue was subjected to a 1 × 10 cm silica gel column.
Elution with hexane afforded a colorless oil of 7 (25 mg, 67%)
upon removing the solvent very cautiously. Elution with a
mixture of benzene/hexane (1:3) developed a red band, which
was collected and after solvent removal afforded 46 mg (74%)
of violet crystals of iron dimer [(η5-C5H5)Fe(CO)2]2. For 7: NMR
1
(C6D6): δ H, -0.25 (m, 4H, CH2), 0.13, 0.15, 0.16, 0.20, 0.21
Syn th esis of ClCH2P h MeSiSiMe2SiMe2CH2Cl (10). Into
a 250 mL three-necked flask equipped with a magnetic stirring
bar, rubber septum, nitrogen inlet tube, and low-temperature
thermometer were placed 2.76 g (9.0 mmol) of 9 and BrCH2Cl
(2.33 g, 18.0 mmol) in 70 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, 11.3 mL (18.0 mmol)
of a 1.6 M solution of n-butyllithium in hexane. The solution
was allowed to warm to room temperature and stirred over-
night 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 at 164-
(s, s, s, s, s, 15H, SiMe), 0.65 (q, 3J ) 7.9 Hz, 2H, CH2CH3),
1.03 (t, 3J ) 7.8 Hz, 3H, CH2CH3); 13C, -3.54 (EtSiCH3), -0.73,
-0.59 (SiSiMe2), 0.78 (EtMeSiCH2SiMe2), 2.03, 2.22 (CH2-
SiMe2CH2), 3.38 (Me2SiCH2SiMe2), 7.92 (CH2CH3), 8.79
(CH2CH3); 29Si, -12.76 (SiSiMe2), -8.28 (MeEtSiSi), 9.67
(SiMe2). HRMS (EI): calcd for C9H24Si3 m/z 216.1186, found
m/z 216.1181. LRMS (EI): m/z 216.1 (M+, 40), 201.1 (M+
-
Me, 23), 187.1 (M+ - Et, 100), 173.1 (M+ - C3H7, 47). Anal.
Calcd for C9H24Si3: C, 49.92; H, 11.17. Found: C, 48.92; H,
11.40.
Syn th esis of P h 2MeSiSiMe2Cl. A flask equipped with a
magnetic stirring bar and a refluxing condenser was charged
with 20.0 g (0.078 mol) of Ph2MeSiSiMe2H and 1.0 g (4 mmol)
of benzoyl peroxide in 100 mL of CCl4. The solution was
refluxed for 10 h and was permitted to cool to room temper-
ature. The solvent was removed under vacuum, and 100 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,
by using a 20 cm Vigreux column, at 148-150 °C/2 mmHg
(lit.2c 106-108 °C/0.2 mm Hg) to give 20.2 g (89%) of Ph2-
MeSiSiMe2Cl as a colorless oil.
Syn th esis of P h 2MeSiSiMe2SiMe2P h (8). A flask equipped
with a magnetic stirring bar and addition funnel was charged
with 19.6 g (67.5 mmol) of Ph2MeSiSiMe2Cl and 70 mL of
hexane. The solution was cooled to 0 °C, and the PhMe2SiLi
solution (prepared from 11.5 g (67.5 mmol) of PhMe2SiCl and
1
170 °C/2 mmHg to give 2.38 g (79%) of 10. H NMR (C6D6): δ
0.08 (s, 6H, SiSiMe2Si), 0.20, 0.22 (s, s, 6H, SiMe2CH2Cl), 0.47
(s, 3H, SiMePhCH2Cl), 2.64 (s, 2H, SiMe2CH2Cl), 2.98 (AB, 2J
) 13.6 Hz, 2H, SiMePhCH2Cl), 7.20-7.22 (m, 3H, Ph), 7.38-
7.40 (m, 2H, Ph). 13C NMR (C6D6): δ -6.01 (SiMePhCH2Cl),
-5.76, -5.58 (SiSiMe2Si), -4.30 (SiMe2CH2Cl), 29.99, 31.30
(CH2Cl), 128.54, 129.76, 134.39, 136.01 (Ph). 29Si NMR
(C6D6): δ -48.90 (SiSiSi), -16.12 (SiPhMeCH2Cl), -12.15
(SiMe2CH2Cl). MS (70 eV): m/z 285 (M+ - CH2Cl, 6), 227 (M+
- Me2SiCH2Cl, 37), 191 (M+ - Me2SiCH2Cl-HCl, 95), 165 (M+
- MePhSiCH2Cl, 100), 135 (ClCH2MeSidSiMe+, 82), 73
(SiMe3+, 93). Anal. Calcd for C13H24Cl2Si3: C, 46.24; H, 7.21.
Found: C, 45.81; H, 7.40.
Syn th esis of F p CH 2P h MeSiSiMe2SiMe2CH2F p (11). To
50 mL of a THF solution of [CpFe(CO)2]-Na+ (prepared from
1.3 g (3.64 mmol) of Fp2) was added 0.9 g (2.7 mmol) of 10 at

506 Organometallics, Vol. 21, No. 3, 2002
Zhang and Pannell
0 °C. The solution was stirred at low temperature and then
allowed to warm to room temperature and further 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 placed upon a 2.5 × 20 cm silica
gel column. Elution with hexane developed a yellow band,
which was collected and after solvent removal afforded a yellow
oily product of 11 (1.01 g, 60%). 1H NMR (C6D6): δ -0.14,
-0.03 (s, m, 4H, CH2), 0.26, 0.40 (s, s, 12H, SiMe2), 0.69 (s,
3H, SiMePhCH2Fp), 4.05, 4.13 (s, s, 10H, Cp), 7.15-7.22 (m,
3H, Ph), 7.56-7.67 (m, 2H, Ph). 13C NMR (C6D6): δ -26.26,
-23.43 (FpCH2), -5.16, -5.07 (SiSiMe2Si), -1.63 (FpCH2-
SiMePh), 0.62 (SiMe2CH2Fp), 84.64, 85.99 (Cp), 128.16, 128.51,
134.52, 142.77 (Ph), 217.93, 218.01, 218.11 (CO). 29Si NMR
(C6D6): δ -46.52 (SiSiSi), -7.20 (FpCH2PhMeSi), -3.32
(FpCH2Me2Si). IR (νCO, cm-1): 2009(s), 1958(s). HRMS
(FAB): calcd for (C27H34Fe2O4Si3 + Na) m/z 641.0361, found
m/z 641.0363.
2.23, 2.32, 27.39, 32.81, 33.74, 33.82 ppm. We could not identify
these new species at present.
Syn th esis of ClCH2Me2SiSiMe2SiMe2SiMe2CH2Cl (14).
Into a 250 mL three-necked flask equipped with a magnetic
stirring bar, rubber septum, nitrogen inlet tube, and low-
temperature thermometer were placed 6.50 g (21.5 mmol) of
ClMe2SiSiMe2SiMe2SiMe2Cl and 5.55 g (43 mmol) of BrCH2-
Cl 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, 26.8 mL (43 mmol) of a 1.6 M solution of
n-butyllithium in hexane. The solution was allowed to warm
to room temperature and stirred overnight and then hydro-
lyzed and extracted with hexane. The extract was washed with
water and dried over CaCl2. The solvent was removed, and
the residue was distilled at 100-104 °C/1 mmHg to give 6.34
1
g (89%) of 14. H NMR (C6D6): δ 0.12, 0.13 (s, s, 12H, SiMe2),
2.70 (s, 4H, CH2Cl). 13C NMR (C6D6): δ -5.34, -3.96 (SiMe2),
31.37 (CH2Cl). 29Si NMR (C6D6): δ -47.58 (SiSiSiSi), -13.59
(SiSiSiSi). MS (70 ev): m/z 281 (M+ - CH2Cl, 1), 223 (M+
-
P h otolysis of 11: F or m a tion of 1,2,4-Tr isila cyclop en -
ta n e (12a a n d 12b) a n d F p P h MeSiCH2SiMe2CH2SiMe2F p
(13). A 5 mm Pyrex NMR tube was charged with 0.15 g (0.24
mmol) of 11 and 1 mL of C6D6 and sealed under vacuum.
Irradiation was carried out with a 450 W medium-pressure
SiMe2CH2Cl, 87), 165 (SiMe2SiMe2CH2Cl+, 65), 73 (Me3Si+,
100). Anal. Calcd for C10H28Cl2Si4: C, 36.62; H, 8.51. Found:
C, 37.13; H, 8.84.
Syn th esis of F p CH2Me2SiSiMe2SiMe2SiMe2CH2F p (15).
To 60 mL of a THF solution of [CpFe(CO)2]-Na+ (prepared
from 2.00 g (5.6 mmol) of Fp2) was added 1.56 g (4.7 mmol) of
14 at 0 °C. The solution was stirred at low temperature and
then permitted to warm to room temperature and further
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 placed upon a 2.5 × 20
cm silica gel column. Elution with hexane developed a yellow
band, which was collected and after solvent removal afforded
a yellow crystalline product of 15 (1.31 g, 45%). Mp: 120-2
°C. 1H NMR (C6D6): δ 0.04 (s, 4H, CH2), 0.40, 0.42 (s, 24H,
SiMe2), 4.16 (s, 10H, Cp). 13C NMR (C6D6): δ -23.54 (FpCH2),
-4.47, 0.84 (SiMe2), 84.98 (Cp), 218.10 (CO). 29Si NMR
(C6D6): δ -43.54 (SiSiSiSi), -1.84 (SiSiSiSi). IR (νCO, cm-1):
2010(s), 1959(s). Anal. Calcd for C24H38Fe2O4Si4: C, 46.90; H,
6.23. Found: C, 47.16; H, 6.69.
P h otolysis of 15: For m ation of FpMe2SiCH2SiMe2SiMe2-
CH2SiMe2F p (17). A 5 mm Pyrex NMR tube was charged with
0.10 g (0.24 mmol) of 15 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. The color of the solution
changed from yellow to violet-red upon irradiation, and after
1 h complete disappearance of 15 and formation of 17 was
noted, along with a small amount of the intermediate product
16. We made no attempt to isolate 16 since it was a low-
concentration transient. Irradiation was continued for 2 h and
NMR monitoring showed the complete disappearance of 16.
The solvent was then removed under vacuum, and the residue
was subjected to a 1 × 10 cm silica gel column. Elution with
hexane developed a yellow band, which was collected and after
solvent removal afforded 83 mg (83%) of 17 as yellow crystals.
For 16: 13C NMR (C6D6): δ -23.64 (FpCH2), -5.78, 0.28, 0.75,
9.08 (SiMe2), 10.82 (SiCH2Si), 83.89, 85.00 (Cp), 216.59, 218.11
(CO). 29Si NMR (C6D6): δ -46.53 (SiCH2SiSiSiCH2), -13.85
(SiCH2SiSiSiCH2), -2.72 (SiCH2SiSiSiCH2), 44.84 (SiCH2-
SiSiSiCH2). For 17: Mp: 80-2 °C. 1H NMR (C6D6): δ 0.34 (s,
16H, CH2Me2SiSiMe2CH2) 0.63 (s, 12H, FpSiMe2), 4.11 (s, 10H,
Cp). 13C NMR (C6D6): δ -0.46, 9.09 (SiMe2), 9.76 (CH2), 83.91
(Cp), 216.61 (CO). 29Si NMR (C6D6): δ -17.35 (SiCH2SiSiCH2-
Si), 44.64 (SiCH2SiSiCH2Si). IR (νCO, cm-1): 1996(s), 1942(s).
Anal. Calcd for C24H38Fe2O4Si4: C, 46.90; H, 6.23. Found: C,
46.70; H, 6.51.
1
Hg lamp. The progress of the reaction was monitored by H,
13C, and 29Si NMR spectroscopy. The 29Si signals due to the
starting material at δ -46.52, -7.20, -3.32 ppm disappeared
after 2 h and were replaced by eight new resonance signals,
which were assigned to the complexes 12a (-12.95, 5.60 ppm),
12b (-13.68, -11.86, 9.97 ppm), and 13 (1.45, 36.84, 42.84
ppm), respectively. The solvent was removed under vacuum,
and the residue was subjected to a 1 × 10 cm silica gel column.
Elution with hexane afforded a colorless oil of 12 (44 mg, 69%)
1
upon removing the solvent very cautiously. H NMR and GC/
MS spectra of 12 indicate that the two positional isomers, 12a
and 12b, exist as a ratio of 4:3 in the mixture. Elution with a
mixture of benzene/hexane (1:10) developed a yellow band,
which was collected and after solvent removal afforded 16 mg
(16%) of 13 as a yellow oil. Further elution with a mixture of
benzene/hexane (1:3) developed a red band, which was col-
lected and after solvent removal afforded 64 mg (75%) of violet
crystals of iron dimer [(η5-C5H5)Fe(CO)2]2. For 12: 1H NMR
(C6D6): δ -0.15 (AB, 2J ) 13.97 Hz, CH2, 12b), 0.06 (AB, 2J )
13.89 Hz, CH2, 12a ), 0.07 (AB, 2J ) 14.22 Hz, CH2, 12b), 0.16,
0.19, 0.26, 0.29, 0.33, 0.45 (s, s, s, s, s, SiMe), 7.16-7.31, 7.54-
7.61 (m, m, Ph). 13C NMR (C6D6): δ -1.83 (PhMeSiSi, 12b),
-1.03, 0.96 (Me2SiSiMe2, 12a ), -0.81, -0.42 (PhMeSiSiMe2,
12b), 1.31 (Me2SiCH2SiMe2, 12b), 1.41 (PhSiMe, 12a ), 1.65
(CH2, 12a ), 2.09, 2.34 (CH2SiMe2CH2, 12b), 3.29 (Me2SiCH2-
SiMePh, 12b), 128.18, 129.22, 134.03, 141.56 (Ph, 12a ), 128.31,
128.88, 134.54, 139.95 (Ph, 12b). 29Si NMR (C6D6): δ -12.95
(Si2Me4, 12a ), 5.60 (PhSiMe, 12a ), -13.68, -11.86 (PhMe-
SiSiMe2, 12b), 9.97 (SiMe2, 12b). Anal. Calcd for C13H24Si3:
C, 59.01; H, 9.14. Found: C, 58.54; H, 9.62. For 13: 1H NMR
(C6D6): δ 0.13 (s, 3H, Me), 0.20 (s, 2H, CH2), 0.21 (s, 3H, Me),
0.33 (s, 2H, CH2), 0.61, 0.63 (s, s, 6H, FpSiMe2), 0.90 (s, 3H,
FpSiMePh), 3.94, 4.06 (s, s, 10H, Cp), 7.16-7.27 (m, 3H, Ph),
7.68-7.71 (m, 2H, Ph). 13C NMR (C6D6): δ 3.10, 3.46 (CH2-
SiMe2CH2), 6.35 (FpSiMePh), 8.76, 8.81 (FpSiMe2), 12.05
(FpSiMePhCH2), 14.87 (FpSiMe2CH2), 83.93, 84.50 (Cp), 128.09,
128.32, 133.15, 148.03 (Ph), 216.63, 217.02 (CO). 29Si NMR
(C6D6): δ 1.45 (CH2SiCH2), 36.84 (FpSiPhMe), 42.84 (FpSiMe2).
IR (νCO, cm-1): 1995(s), 1943(s). HRMS (FAB): calcd for
(C27H34Fe2O4Si3 + Na) m/z 641.0381, found m/z 641.0363.
P h otolysis of 13. A 5 mm Pyrex NMR tube was charged
with 30 mg (0.05 mmol) of 13 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 29Si NMR spectroscopy. The signals due to the
starting material at δ 1.45, 36.84, 42.84 ppm disappeared after
24 h and was replaced by several new resonance signals at δ
Resu lts a n d Discu ssion
Syn th esis a n d P h otolysis of F p CH2SiMe2SiMe2-
SiMe2CH2F p (1). Complex 1 was readily prepared by

Formation of 1,2,4-Trisilacyclopentanes
Organometallics, Vol. 21, No. 3, 2002 507
reacting ClCH2SiMe2SiMe2SiMe2CH2Cl with [Fp]-Na+
in THF (eq 2).
Sch em e 3
[Fp]-Na+ + ClCH2(SiMe2)3CH2Cl f
FpCH2(SiMe2)3CH2Fp (2)
The 29Si NMR spectrum of 1 exhibits two signals at
-2.55 and 46.4 ppm, which are assigned to the Si atoms
â and γ with respect to the Fe atom, i.e., the terminal
and central atoms of the trisilane unit, respectively.
Comparison of the 29Si NMR chemical shifts of 1 with
the permethylated analogue Me8Si3 shows that the Siâ
and Siγ atoms are characteristically shifted downfield
13.6 and 2.2 ppm, respectively,1 and the 13C NMR
spectrum exhibits a diagnostic signal for the CH2 moiety
at -23.4 ppm.4c
Syn th esis a n d P h otolysis of F p CH2SiMe2MeSiEt-
SiMe2CH2F p (6). To examine the fate of Siγ (the
initially central atom of the trisilane chain), we have
synthesized complex 6, where this atom contains both
a methyl and an ethyl substituent, Scheme 3. The 29Si
NMR spectrum of 6 shows the expected two chemical
shifts at -2.55 and -46.4 ppm, and the 13C NMR
spectrum has the CH2 group resonance at -23.4 ppm.
A C6D6 solution of 1 in a flame-sealed Pyrex NMR
tube was irradiated using a 450 W medium-pressure
Hg lamp. The progress of the reaction was periodically
1
monitored by H, 13C, and 29Si NMR spectroscopy. The
spectra obtained after 2 h showed the complete disap-
pearance of 1 and the almost quantitative formation of
1,1,2,2,4,4-hexamethyl-1,2,4-trisilacyclopentane (2)10 and
Fp2 (eq 3).
1
Photochemical irradiation of 6 was monitored by H,
13C, and 29Si NMR spectroscopy, and after 2 h 6 had
completely disappeared with an almost quantitative
formation of 1-ethyl-1,2,2,4,4-heptamethyl-1,2,4-tri-
silacyclopentane (7) and Fp2, eq 4.
We did not observe the formation of the positional
isomer of 7, 4-ethyl-1,1,2,2,4-heptamethyl-1,2,4-trisila-
cylcopetane, thereby indicating that the central SiMeEt
group is exclusively incorporated as one of the Si atoms
in the Si-Si bond of the product.
This reaction is an unprecedented photochemical
formation of 1,2,4-trisilacyclopentane from the linear
trisilane. In comparison with the linear trisilane 1, a
new structural arrangement occurs in the product 2
with one silicon-silicon bond and one 4-positional
silicon atom in the molecule. Since all the silicon atoms
have the same substituents, it is not possible to know
if there is any specificity to the Si positional transfor-
mation.
It is well known that a significant deshielding effect
on 29Si chemical shifts occurs with the ring strain in
cyclic systems.11 The 29Si NMR spectrum of 2 exhibits
two resonance signals at -12.9 and 9.45 ppm represent-
ing downfield shifts of 6.84 and 9.45 ppm compared to
the acyclic permethylated analogues (Me6Si2 and Me4-
Si, respectively). These shifts are much smaller than
that observed in related cyclic silanes (∆δ ) 16.77 ppm
for silacyclopentane12 and ∆δ ) 16.5 ppm for silacyclo-
pentene13), indicating that incorporation of several
silicon atoms in a ring decreases the effect of the ring
strain substantially.
Syn th esis an d P h otolysis of FpCH2P h MeSiSiMe2-
SiMe2CH2F p (11). The above result suggests that at
least one of the terminal Si atoms of the trisilane must
transform to the 4-position of the 1,2,4-trisilacyclopen-
tane. However, it is not clear if only one, or both, of these
terminal atoms can be transformed. To resolve this
ambiguity, we have synthesized and irradiated complex
11, with only one of the two terminal silicon atoms
distinguished with different substituents. A successful
synthesis is illustrated in Scheme 4. The 29Si and 13C
NMR data for 11 are in accord with the structural
assignment exhibiting the expected three resonances
(-46.5, -7.20, -3.32 ppm) and two Fe-CH2 resonances
at -26.26 and -23.43 ppm, respectively.
Photochemical irradiation of 11 led to a smooth
reaction with production of two isomeric 1,2,4-trisila-
cyclopentanes (12a and 12b), Fp2, and a new product,
FpPhMeSiCH2SiMe2CH2SiMe2Fp (13), eq 5. The latter
complex, formed in low yield (16%), results from two
â-elimination rearrangement reactions of the type pre-
viously noted for disilylmethyl- and trisilylmethyl-Fp
complexes and indicates that the presence of the phenyl
group can play a very subtle role in determining the
outcome of these photochemical reactions. The forma-
tion of the two isomers 1,1,2,2,4-heptamethyl-4-phenyl-
(11) Williams, E. A. The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; J ohn Wiley & Sons Ltd: New York, 1989;
pp 511-555.
(12) Scholl, R. G.; Maciel, G. E.; Musker, W. K. J . Am. Chem. Soc.
1972, 94, 6376.
(13) Filleux-Blanchard, M.-L.; An, N. D.; Manuel, G. Org. Magn.
Reson. 1978, 11, 150.

508 Organometallics, Vol. 21, No. 3, 2002
Zhang and Pannell
Sch em e 4
substituted oligosilanes can be readily distinguished
based upon the length of the oligosilane chain. Thus,
whereas for disilanes and trisilanes the overall chem-
istry involves silylene elimination and ultimate forma-
tion of Fp-monosilanes, the linear tetrasilanes undergo
a molecular rearrangement to form FpSi(Si)3 com-
plexes.1 Given the variety of chemistry observed for the
various 1,3-bis-Fpmethyltrisilanes, including the rear-
rangement to 13, it was natural to extend the silicon
chain to four atoms.
Therefore we have synthesized complex 15 via the
reaction between ClCH2SiMe2SiMe2SiMe2SiMe2CH2Cl
and [Fp]-Na+ in THF. All spectral and analytical data
are in accord with the proposed structure. Photochemi-
cal irradiation of 15 resulted in a straightforward high-
yield transformation, but unlike the disilyl and trisilyl
analogues we observed no elimination chemistry. Only
the rearrangement chemistry typical of the di- and
trisilylmethylFp complexes occurred to yield 17, eq 6.
1,2,4-trisilacyclopentane (12a) and 1,1,2,4,4-heptamethyl-
2-phenyl-1,2,4-trisilacyclopentane (12b) indicates that
either one of the two terminal silicon atoms of the initial
trisilane can be incorporated into the silicon-silicon
bond and/or 4-position of the product. It could be argued
that the introduction of the phenyl group changes the
mechanism for the formation of the 1,2,4-trisilacyclo-
pentanes; that is, the phenyl group is not an innocent
substituent. While the formation of 13 certainly indi-
cates that other reaction pathways are possible with this
substituent, Occam’s Razor leads us to doubt that a
totally new mechanistic route is offered for the forma-
tion of the cyclopentanes.
1
Following the photochemical reaction by H, 13C, and
29Si NMR spectroscopy we observed the transient
formation of FpMe2SiCH2SiMe2SiMe2SiMe2CH2Fp (16),
indicating the overall tranformation 15 f 17 was
stepwise. We made no attempt to isolate 16 since it
existed only as a low-concentration transient.
The 29Si NMR spectrum of 16 exhibits four different
signals at -46.5, -13.9, -2.72, and 44.8 ppm. The low-
field signal at 44.8 ppm is due to the silicon atom
directly attached to the iron, Fp-Si; -46.5 ppm is the
central Si atom of the trisilyl group, FpCH2SiSiSi; -2.72
is FpCH2Si; and 13.9 is FpSiCSi. All these assignments
are in total accord with previous studies on the chemical
shifts of oligosilyl Fp complexes. The 13C NMR spectrum
of 16 exhibits the high-field signal at -23.6 ppm
associated with the Fp-CH2 unit. The final product 17
exhibits two signals in the 29Si NMR spectrum at -17.4,
44.6 ppm, and the former resonance exhibits a small
downfield shift (2.4 ppm) from the permethylated disi-
lane. Unlike the trisilyl rearranged product 13, 17 is
photochemically stable, which given the presence of a
Si-Si bond is somewhat surprising; however, irradia-
tion of 17 for 2 days did not lead to any change except
for a little decomposition to Fp2.
The 29Si NMR spectrum of 12 exhibits five signals at
-13.7, -12.9, -11.9, 5.60, and 9.97 ppm. The two
signals at -12.9 and 9.97 ppm are assigned to 12a , and
the other three to 12b. Comparison of the 29Si NMR
chemical shifts to its acyclic permethylated analogues
indicates that the deshielding effect due to the ring
strain still exists.
The 29Si NMR spectrum of 13 exhibits three signals
at 1.45, 36.8, and 42.8 ppm. The two downfield signals
at 42.8 (FpSiMe2) and 36.8 ppm (FpSiMePh) are close
to those of FpSiMe3 and FpSiMe2Ph, respectively.
Surprisingly, complex 13 is photochemically labile, and
irradiation for 24 h resulted in the formation of new
species which, to date, we have been unable to identify.
However, we did not observe the formation of 12,
indicating that the formation of 13 is not reversible and
is not involved in the initial formation of 12. We
continue to investigate this aspect of the present work.
Syn th esis a n d P h otolysis of F p CH2SiMe2SiMe2-
SiMe2SiMe2CH2F p (15). The chemistry of the Fp-
Mech a n ism . We have shown that photolysis of
FpCH2MePhSiSiMePhCH2Fp resulted in the stereospe-
cific formation of 1,3-disilacyclobutane and suggested
a mechanism involving bis(silene-iron) intermediates.6
In the present examination of the chemistry of 1, 6, and

Formation of 1,2,4-Trisilacyclopentanes
Organometallics, Vol. 21, No. 3, 2002 509
Sch em e 5
11 the formation of 1,2,4-trisilacyclopentanes suggests
a related mechanism. Furthermore, since we have
demonstrated that there is some specificity to the
product formation, the γ-positional silicon atom of 6 does
not transform to the 4-position of the product, the
mechanism must take this into account. Our present
suggestion is presented in Scheme 5.14
It is clear that the formation of C1 from B is more
favorable presumably since the phenyl group in the C1
molecule is more distant from the metal center (12a :
12b ) 4:3).
Although photolysis of the tetrasilane complex 15
resulted in the stepwise formation of the rearranged
product 17 via the transient product 16, we cannot rule
The formation of 12 is involved in three possible
intermediates, A, B, and C. B can be considered as bis-
(silene-iron) intermediates with a bridging silylene unit,
structurally similar to known µ-silylene (µ-germylene
or µ-stannylene) bimetallic complexes [(η5-C5H5)Fe(CO)2]2-
ER2 (E ) Si, Ge, Sn), however also containing silene
ligands.15 Such complexes photochemically rearrange to
µ-carbonyl µ-silylene bridged diiron complexes [(η5-
C5H5)Fe(CO)]2{(µ-SiR2)(µ-CO)2},16 indicating that the
transformation from B to C is possible. The assumed
intermediates C are structurally analogous to the
known bimetallic bis(µ-silylene) complex [(η5-C5H5)Fe-
(CO)]2(µ-SiMe2)2.17,18 The distinction is that one of the
bis(µ-silylene) bridges is replaced by the µ-SiR2CH2SiR2-
CH2 bridge. The relative ratio of 12a and 12b is closely
related to the stability of the intermediates C1 and C2.
(14) The Scheme 5 illustrates a possible pathway where the initial
CO loss occurs at the terminal silicon atom with a phenyl substituent.
However, this does not rule out the possibility that the initial CO loss
occurs at the other terminal silicon atom with two methyl groups.
(15) (a) Malisch, W.; Ries, W. Chem. Ber. 1979, 112, 1304. (b) Aylett,
B. J .; Colquhoun, H. M. J . Chem. Res., Synop. 1977, 148. (c) Nesm-
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510 Organometallics, Vol. 21, No. 3, 2002
Zhang and Pannell
out the possibility of the concerted formation of 13 from
B since we did not observe the formation of the transient
product 13a by closely following the photolysis via 29Si
NMR spectroscopy. Photolysis of 1 and 6 did not result
in the formation of the rearranged products, while
similar irradiation of 11 afforded a significant amount
of the rearranged product, indicating that the phenyl
group possibly stabilizes the silene intermediates via
the electronic delocalization.
Overall, we can now understand that in the general
system FpCH2(SiR2)nCH2Fp the elimination chemistry
is essentially restricted to the shorter chain lengths
containing five or less atoms. The ability of the two
terminal iron systems to be in close proximity is
undoubtedly a key factor in this restriction. We are
continuing our studies on such systems containing other
transition metals and/or other group 14 elements, i.e.,
Ge and Sn.
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: 29Si, 13C, and 1H
NMR spectroscopic data for complexes 6, 9, 11, 12a /b, and 13.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0109657