Syntheses and Photochemically Induced Rearrangements of Tetrasilyl- and Trisilylgermyl Complexes of Iron: (η5-C5R5)Fe(CO)2(SiMe 2)3EMe2Ph (R = H, Me; e = Ge, Si)

Article abstract of DOI:10.1021/om990897c

Oligosilyl and oligosilylgermyl complexes (η⁵-C₅R₅)Fe(CO)₂(SiMe ₂)₃EMe₂Ph (R = H (1), Me (2); E = Ge (a), Si (b)) have been synthesized, characterized, and photolyzed. All complexes isomerized cleanly to (η⁵-C₅R₅)Fe(CO)₂E(SiMe ₃)₂(SiMe₂Ph). Photolysis of a mixture of (η⁵-C₅Me₅)Fe(CO)₂(SiMe ₂)₃GeMe₂Ph (2a) and (η⁵-C₅H₅)Fe(CO)₂(SiMe ₂)₃SiMe₃ (1b) proved that the rearrangements occur via an intramolecular mechanism. Irradiation of 1 and 2 in the presence of HMPA resulted in the formation of (η⁵-C₅R₅)Fe(CO)(=SiMe ₂·HMPA)(SiMe₂-SiMe₂EMe₂Ph), indicating that silylene intermediates are key to the rearrangements. Attempts to use this new chemistry to perform the catalytic isomerization Me₃GeSiMe₂-SiMe₂SiMe₂H → (Me₃Si)₃GeH resulted in high yields of (Me₃Si)₃GeSiMe₂H. This product indicates the ability of (Me₃Si)₃GeH to intercept the Fe-silylene intermediates.

Full text of DOI:10.1021/om990897c

Organometallics 2000, 19, 1225-1231
1225
Syn th eses a n d P h otoch em ica lly In d u ced
Rea r r a n gem en ts of Tetr a silyl- a n d Tr isilylger m yl
Com p lexes of Ir on : (η5-C5R5)F e(CO)2(SiMe2)3EMe2P h (R )
H, Me; E ) Ge, Si)
Sneh Sharma† and Keith H. Pannell*
Department of Chemistry, The University of Texas at El Paso, El Paso, Texas 79968-0513
Received November 10, 1999
Oligosilyl and oligosilylgermyl complexes (η5-C5R5)Fe(CO)2(SiMe2)3EMe2Ph (R ) H (1),
Me (2); E ) Ge (a ), Si (b)) have been synthesized, characterized, and photolyzed. All
complexes isomerized cleanly to (η5-C5R5)Fe(CO)2E(SiMe3)2(SiMe2Ph). Photolysis of a mixture
of (η5-C5Me5)Fe(CO)2(SiMe2)3GeMe2Ph (2a ) and (η5-C5H5)Fe(CO)2(SiMe2)3SiMe3 (1b) proved
that the rearrangements occur via an intramolecular mechanism. Irradiation of 1 and 2 in
the presence of HMPA resulted in the formation of (η5-C5R5)Fe(CO)(dSiMe2‚HMPA)(SiMe2-
SiMe2EMe2Ph), indicating that silylene intermediates are key to the rearrangements.
Attempts to use this new chemistry to perform the catalytic isomerization Me3GeSiMe2-
SiMe2SiMe2H f (Me3Si)3GeH resulted in high yields of (Me3Si)3GeSiMe2H. This product
indicates the ability of (Me3Si)3GeH to intercept the Fe-silylene intermediates.
Sch em e 1
In tr od u ction
The signature chemistry of oligosilyl derivatives of the
transition metals that contain direct metal-silicon
bonds is their ability to undergo elimination reactions,
resulting in the formation of transient silylenes (Scheme
1).1-3 Such intermediates can eliminate silylenes or
undergo rearrangement reactions involving 1,3-alkyl,
-aryl, and -silyl migrations. The silylene can be trapped
intramolecularly or intermolecularly.2g,3b,e,5 The chem-
istry appears to be quite general, and related chemistry
is observed with tungsten complexes.3e Silylgermyl or
germylsilyl Fe analogues were studied in which either
the germylene or silylene intermediate was possible. Via
the characteristic 1,3-shift, it was the germylene that
formed preferentially and it was chemistry of this
intermediate that was observed (Scheme 2).4
We have shown that UV irradiation of (η5-C5H5)Fe-
(CO)2-SiMe2SiMe2SiMe2SiMe3 resulted in its high-yield
Sch em e 2
† Sneh Sharma died in El Paso, TX, May 24, 1999. She was much
loved.
(1) Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351.
(2) (a) Cervantes, J .; Hernandez, C.; Cassias, J .; Vincenti, S. P.
Organometallics 1986, 5, 1056. (b) Pannell, K. H.; Rozell, J . M.;
Hernandez, C. J . Am. Chem. Soc. 1989, 111, 4482. (c) J ones, K. L.;
Pannell, K. H. J . Am. Chem. Soc. 1993, 115, 11336. (d) Pannell, K. H.;
Wang, L.-J .; Rozell, J . M. Organometallics 1989, 8, 550. (e) Hernandez,
C.; Sharma, H. K.; Pannell, K. H. J . Organomet. Chem. 1993, 462,
259. (f) Pannell, K. H.; Brun, M.-C.; Sharma, H. K.; J ones, K.; Sharma,
S. Organometallics 1994, 13, 1075. (g) Pannell, K. H.; Sharma, H. K.;
Kapoor, R. N.; Cervantes-Lee, F. J . Am. Chem. Soc. 1997, 119, 9315.
(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) Ueno, K.; Tobita, H.; Shimoi, M.; Ogino, H. J . Am. Chem.
Soc. 1990, 112, 3415. (d) Tobita, H.; Kurita, H.; Ogino, H. Organome-
tallics 1998, 17, 2850. (e) Ueno, K.; Sakai, M.; Ogino, H. Organome-
tallics 1998, 17, 2138.
transformation to FpSi(SiMe3)3 (Fp ) (η5-C5H5)Fe(CO)2)
without any silylene elimination.2d To understand more
about the mechanistic aspects of these rearrangement
reactions, we have synthesized the tetrasilane FpSiMe2-
SiMe2SiMe2SiMe2Ph and the mixed oligosilyl-germyl
complexes FpSiMe2SiMe2SiMe2GeMe2Ph and Fp*SiMe2-
(4) (a) Pannell, K. H.; Sharma, S. Organometallics 1991, 10, 1655.
(b) Sharma, H.; Pannell, K. H. Organometallics 1994, 13, 4946. (c) Koe,
J . R.; Tobita, H.; Ogino, H. Organometallics 1992, 11, 2479.
(5) Ueno, K.; Nakano, K, Ogino, H. Chem. Lett. 1996, 459.
10.1021/om990897c CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/01/2000

1226 Organometallics, Vol. 19, No. 7, 2000
Sharma and Pannell
SiMe2SiMe2GeMe2Ph (Fp* ) (η5-Me5C5)Fe(CO)2). The
photochemistry of these complexes is reported, including
attempted crossover experiments, along with the ob-
servation of complexed silylene intermediates. Catalytic
transformations of germylsilanes were also accom-
plished.
nificant products were observed by NMR analysis of the
crude reaction products.
The formation of complexes containing an Fe-Ge
bond reinforces our earlier observations that the ger-
mylene-iron intermediates are more stable than their
silylene-iron analogues when a dynamic equilibrium
between them is possible. A further driving force for the
rearrangement is the large enthalpy gain associated
with the exchange of three Ge-C bonds for three Si-C
bonds. This is presumably greater than any potential
loss associated with the transformation of Si-Si bonds
to Si-Ge bonds and the Fe-Si to a Fe-Ge bond. Our
proposed mechanism for this rearrangement is il-
lustrated in Scheme 3.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The syntheses of
the new iron complexes were accomplished in moderate
to good yields by salt-elimination reactions (eqs 1-3).
[Fp]Na + Cl(SiMe2)4Ph f
FpSiMe2SiMe2SiMe2SiMe2Ph + NaCl (1)
P h otoch em istr y in th e P r esen ce of HMP A. Ogino
and co-workers have shown that when disilyl-Fp spe-
cies are irradiated in the presence of hexamethylphos-
phoramide (HMPA), HMPA-stabilized silylene species
are generated.5 Since the mechanisms that we have
proposed for the rearrangements of oligosilyl, and now
oligosilylgermyl, Fp complexes contain many steps,
there is always the possibility that alternative mecha-
nisms to that outlined in Scheme 3 might be important.
We have irradiated the new complexes in the presence
of HMPA to see if it might be possible to observe at least
the first step in the process depicted in Scheme 3.
Indeed, monitoring the photolysis of FpSiMe2SiMe2-
SiMe2ER3 (ER3 ) SiMe3, SiMe2Ph, GeMe2Ph) in the
presence of HMPA by NMR spectroscopy showed the
formation of silylene‚HMPA iron complexes (Figure 1,
Table 1).
[Fp]Na + Cl(SiMe2)3Cl f
FpSiMe2SiMe2SiMe2Cl + NaCl (2)
Fp(SiMe2)3Cl + [PhMe2Ge]Li f
FpSiMe2SiMe2SiMe2GeMe2Ph + LiCl (3)
The new complexes are either low-melting solids or
oils. Their spectroscopic and analytical data, recorded
in Table 1, are in accord with their proposed structures.
29Si NMR spectroscopy is particularly helpful for
characterization of the new complexes. For example, the
tetrasilyliron complex FpSiMe2SiMe2SiMe2SiMe2Ph ex-
hibits signals in the 29Si NMR spectrum at 22.9, -17.6,
-32.5, and -42.9 ppm. These can be assigned on the
basis of our previous extensive analysis of oligosilyl Fp
complexes.1 The low-field signal at 22.9 ppm is due to
the silicon atom directly attached to the iron and
exhibits an ∼40 ppm downfield shift from the perm-
ethylated tetrasilane Me3SiSiMe2SiMe2SiMe3. The sig-
nal at -17.6 ppm is assigned to the terminal -SiMe2Ph,
the signal at -42.9 is due to -SiMe2SiMe2Ph, and the
-32.5 ppm resonance is due to a silicon in the â-position.
The latter resonance exhibits an ∼12 ppm downfield
shift compared to the permethylated tetrasilane. In the
related germanium complex FpSiMe2SiMe2SiMe2GeMe2-
Ph, the silicon signal due to -SiMe2GeMe2Ph is shifted
to low field, by about 9.0 ppm, to -33.6 ppm. Similar
7-9 ppm low-field shifts were observed in the silicon
NMR spectra of the iron silylgermyl complexes com-
pared to signals for their silyl analogues.4
F igu r e 1.
In the case of FpSiMe2SiMe2SiMe2SiMe3, the 29Si
NMR spectrum of the silylene complex exhibited a
doublet at 114.9 ppm due to coupling with the 31P atom
of HMPA (J ) 28 Hz) and signals at 13.6, -15.4, and
-39.0 ppm. The doublet nature and low-field shift of
the signal at 114.9 ppm compared to that of the starting
compound (22.4, -14.8, -32.9, and -43.2 ppm) clearly
indicate the formation of a silylene coordinated to an
HMPA molecule, while the other 29Si signals are com-
parable to those of FpSiMe2SiMe2SiMe3 (i.e., 19.0,
P h otoch em istr y. The oligosilyl and oligosilylgermyl
complexes are photochemically labile. The tetrasilyliron
complex FpSiMe2SiMe2SiMe2SiMe2Ph undergoes a pho-
tochemical rearrangement, without silylene elimination,
to produce FpSi(SiMe3)2(SiMe2Ph) (eq 4).
1
-14.7, and -37.9 ppm). The H NMR spectrum showed
FpSiMe2SiMe2SiMe2SiMe2Ph f
two doublets at 2.42 and 2.25 ppm for free and coordi-
nated HMPA molecules, respectively, and resonances
at 0.63 and 0.66 ppm, assigned to the methyl groups of
the HMPA-coordinated SiMe2 ligand. The signals at
0.58, 0.38, 0.42, and 0.29 are assigned to FeSiMe2,
FeSiMe2SiMe2, and SiMe3. The 13C NMR spectrum
shows that all the methyl groups attached to the R- and
â-silicon atoms are nonequivalent. These NMR data
support the formula (η5-C5H5)(CO)Fe(dSiMe2‚HMPA)-
(SiMe2SiMe2SiMe3) and are compatible with the data
reported by the Ogino group. Irradiation of FpSiMe2-
SiMe2SiMe2SiMe2Ph and FpSiMe2SiMe2SiMe2GeMe2Ph
in the presence of HMPA provided similar results, with
the formation of single products, (η5-C5H5)(CO)Fe-
FpSi(SiMe3)2(SiMe2Ph) (4)
The reaction is very clean, and no intermediates or
significant amounts of any other products were observed
in the NMR spectra of the crude product. This result is
similar to a rearrangement we have previously reported,
i.e., FpSiMe2SiMe2SiMe2SiMe3 f FpSi(SiMe3)3.2d
The photochemistry of the oligosilylgermyl iron com-
plexes is unique. The two complexes FpSiMe2SiMe2-
SiMe2GeMe2Ph and Fp*SiMe2SiMe2SiMe2GeMe2Ph each
photochemically rearranged cleanly to yield a single
product containing an Fe-Ge bond, i.e., FpGe(SiMe3)2-
(SiMe2Ph) and Fp*Ge(SiMe3)2SiMe2Ph. No other sig-

Tetrasilyl- and Trisilylgermyl Complexes of Iron
Ta ble 1. Sp ectr oscop ic a n d An a lytica l Da ta for New Com p lexesa
FpSiMe2SiMe2SiMe2SiMe2Ph
Organometallics, Vol. 19, No. 7, 2000 1227
yield, %
mp, °C
50
43
anal. found (calcd)
C, 51.4 (51.8); H, 6.77 (7.04)
29Si NMR
22.9 (FpSiMe2), -17.6(SiMe2Ph), -32.5 (SiMe2), -42.9 (SiMe2)
-4.68, -2.84, -2.44, 5.56 (SiMe2), 83.2(η5-C5H5), 128.2, 128.9, 134.3, 142.0 (Ph)
0.52, 0.76 (SiMe2), 4.15 (η5-C5H5), 7.26, 7.29, 7.70 (Ph)
ν(CO) 1996.6, 1945.8
13C NMR
1H NMR
IR (hexane), cm-1
FpSi(SiMe3)2(SiMe2Ph)
yield, %
80
mp, °C
45
anal. found (calcd)
C, 51.4 (51.8); H, 6.97 (7.04)
29Si NMR
-6.06 (SiMe3), 9.16 (SiMe2Ph), -82.1 (Fp-Si)
2.13 (SiMe2Ph), 4.14 (SiMe3), 83.2 (η5-C5H5), 128.5, 128 9, 134.7, 143.1 (Ph)
0.50 (SiMe3), 0.75 (SiMe2), 4.14 (η5-C5H5), 7.26, 7.28, 7.70 (Ph)
ν(CO) 1996.6, 1947.9
13C NMR
1H NMR
IR (hexane), cm-1
FpSiMe2SiMe2SiMe2Cl
50
yield, %
bp, °C
122-124/0.02 mmHg
anal. found (calcd)
29Si NMR
13C NMR
1H NMR
C, 40.7 (40.4); H, 6.22 (5.99)
27.7 (SiMe2Cl), 20.2 (FpSiMe2), -35.6 (SiMe2)
-4.75, 3.37, 4.85 (SiMe2), 83.2 (η5-C5H5), 215.6 (CO)
0.30, 0.51, 0.58 (Si-Me), 4.15 (η5-C5H5)
FpSiMe2SiMe2SiMe2GeMe2Ph
yield, %
50 (wax)
anal. found (calcd)
C, 46.6 (47.5); H, 6.75 (6.45)
29Si NMR
22.6 (Fp-Si), -32.3 (SiMe2), -33.6 (SiMe2-Ge)
-4.16 (GeMe2), -3.18, -3.00, 5.30 (SiMe2), 83.1 (η5-C5H5), 128.3, 128.5, 133.9, 142.5 (Ph),
215.8 (CO)
13C NMR
1H NMR
0.27 (GeMe2), 0.37, 0.59 (SiMe2), 4.17 (η5-C5H5), 7.19, 7.28, 7.52
ν(CO) 1997.1, 1946.1
IR (hexane), cm-1
FpGe(SiMe3)2(SiMe2Ph)
82 (wax)
yield, %
anal. found (calcd)
C, 47.3 (47.5); H, 6.63 (6.45)
0.69 (SiMe3), -4.81 (SiMe2Ph)
29Si NMR
13C NMR
2.27 (SiMe2Ph), 4.24 (SiMe3), 82.4 (η5-C5H5), 128.4, 134.3, 143.4 (Ph), 215.7 (CO)
0.44 (SiMe3), 0.69 (SiMe2), 4.10 (η5-C5H5), 7.18, 7.52, 7.64 (Ph)
ν(CO) 1991.9, 1944.4
1H NMR
IR (hexane), cm-1
Fp*SiMe2SiMe2SiMe2Cl
56 (oil)
yield, %
anal. found (calcd)
C, 46.7 (47.3); H, 7.54 (7.28)
29 Si NMR
29.17 (SiMe2Cl), 18.50 (Fp*-Si), -35.87 (SiMe2)
-4.12, 3.88, 4.26 (SiMe2), 10.1 (CH3), 95.2 (η5-Me5C5), 218.0(CO)
0.61, 0.70, 0.75 (SiMe2), 1.58 (CH3)
ν(CO) 1980.0, 1928.7
13C NMR
1H NMR
IR (hexane), cm-1
Fp*SiMe2SiMe2SiMe2GeMe2Ph
yield, %
38
mp, °C
72-73
anal. found (calcd)
29Si NMR
13C NMR
C, 51.6 (51.9); H, 7.69 (7.37)
20.6 (Fp-Si), -32.7 (SiMe2), -33.0 (SiMe2Ge)
-3.94 (GeMe2), -2.83 (SiMe2), 4.37 (Fp-Si), 94.8 (η5-C5H5), 127.8, 128.2, 133.9, 143.3 (Ph),
218.0 (CO)
0.52, 0.55, 0.70, 0.73, 1.60 (CH3), 7.27, 7.35, 7.62 (Ph)
ν(CO) 1978.8, 1927.6
1H NMR
IR (hexane), cm-1
Fp*Ge(SiMe3)2(SiMe2Ph)
yield, %
80 (wax)
anal. found (calcd)
C, 51.9 (51.9); H, 8.01 (7.37)
29Si NMR
-1.98 (SiMe3), -5.37 (SiMe2Ph)
13C NMR
4.23 (SiMe2), 5.84 (SiMe3), 10.65 (CH3), 94.87 (η5-Me5C5), 128.34, 128.51, 135.13, 143.2 (Ph),
219.83 (CO)
1H NMR
0.64 (SiMe3), 0.86 (SiMe2), 1.52 (CH3), 7.26, 7.82, 7.86 (Ph)
ν(CO) 1977.6, 1929.1
IR (hexane), cm-1
PhSiMe2SiMe2SiMe2GeMe3
yield, %
28
bp, °C
145-155/0.05 mmHg
anal. found (calcd)
29Si NMR
13C NMR
C, 51.0 (48.8); H, 8.61 (8.74)
-17.8 (Ph-Si), -35.8 (SiMe2-GeMe3), -44.0 (SiMe2)
-5.08 (SiMe2), -4.64 (SiMe2), -2.36 (SiMe2), -1.52 (GeMe3), 128.4, 128.99, 134.3,
140.3 (Ph)
1H NMR
0.052, 0.085, 0.35 (SiMe2), 0.12 (GeMe3), 7.40, 7.29, 7.28 (Ph)

1228 Organometallics, Vol. 19, No. 7, 2000
Sharma and Pannell
Ta ble 1 (Con tin u ed )
HSiMe2SiMe2SiMe2GeMe3
yield, %
44
bp, °C
120-122/0.05 mmHg
anal. found (calcd)
29Si NMR
13C NMR
1H NMR
C, 37.3 (36.9); H, 9.58 (9.62)
-36.3 (SiMe2-GeMe3), -36.8 (SiMe2H), -44.0 (SiMe2)
-5.73 (SiMe2), -5.27 (SiMe2), -1.96 (GeMe3)
0.19 (SiMe2H, d),0.20, 0.23 (SiMe2, s), 0.30(GeMe3), 4.05 (SiMe2H, m)
(Me3Si)3GeSiMe2H
mp, °C
132-134
found (calcd) HRMS, m/z
C
11H31Si474Ge 352.0946 (352.0949)
29Si NMR
-4.61 (Me3Si), -29.5 (SiMe2H)
-1.24 (SiMe2), 3.28 (SiMe3)
13C NMR
1H NMR
4.44 (sept. J ) 28 Hz, SiH), 0.358 (d, J ) 28 Hz, SiMe2), 0.304 (SiMe3)
IR (hexane), cm-1
2090.9
Cp(CO)Fe(dSiMe2‚HMPA)(SiMe2SiMe2SiMe3)
29Si NMR
1H NMR
114.9 (d, J SiP ) 28.3 Hz, SiMe2‚HMPA), 13.6 (Fe-SiMe2), -15.4 (SiMe3), -39.0 (SiMe2)
0.29 (SiMe3), 0.38, 0.42 (Fe-SiMe2), 0.58 (2 SiMe2), 0.63, 0.66 (FedSiMe2), 2.25 (d, HMPA‚SiMe2),
2.42 (d, HMPA), 4.35 (η5-C5H5)
13C NMR
-3.20, -3.16 (SiMe2), -0.68 (SiMe3), 6.02, 6.54 (Fe-SiMe2), 11.1, 13.2 (FedSiMe2),
36.6 (d, HMPA‚SiMe2) 37.0 (d, HMPA) 79.1 (η5-C5H5), 219.1 (CO)
Cp(CO)Fe(dSiMe2‚HMPA)(SiMe2SiMe2SiMe2Ph)
29Si NMR
13C NMR
115.3 (d, J SiP ) 28.4 Hz, SiMe2‚HMPA), 14.7 (Fe-SiMe2), -17.6 (SiMe2Ph), -39.1 (SiMe2)
-2.35, 2.29 (SiMe2), -1.74, -1.69 (SiMe2), 7.13, 6.71 (Fe-SiMe2), 13.8, 11.7 (FedSiMe2),
37.0 (d, HMPA), 36.7 (HMPA‚SiMe2), 79.6 (η5-C5H5), 219.7 (CO)
1H NMR
0.35, 0.41, 0.53, 0.55, 0.57, 0.60, 0.63 (SiMe), 2.21 (d, HMPA‚SiMe2), 2.42 (d, HMPA),
4.32 (η5-C5H5), 7.40 (d, J ) 3 Hz), 7.19 (d, J ) 3 Hz) (Ph)
Cp(CO)Fe(dSiMe2‚HMPA)(SiMe2SiMe2GeMe2Ph)
29Si NMR
13C NMR
115.6 (d, J SiP ) 28.4 Hz, SiMe2‚HMPA), 14.9 (Fe-SiMe2), -28.9 (SiMe2-Ge)
-2.23 (GeMe2Ph), -1.88, 1.67 (SiMe2), 6.42, 6.78 (Fe-SiMe2), 11.6, 13.6 (FedSiMe2),
36.4 (d, HMPA‚SiMe2) 36.8 (d, HMPA) 79.7 (η5-C5H5), 145.7, 134.3, 132.9, 127.6 (Ph), 219.5 (CO)
0.59, 0.60, 0.65, 0.66, 0.69, 0.70, 0.71, 0.72 (SiMe/GeMe), 2.17 (HMPA‚SiMe2, 4.38 (η5-C5H5),
7.20 (d, J ) 3 Hz), 7.62 (d, J ) 3 Hz) (Ph)
1H NMR
a
NMR spectra in C6D6, in units of ppm; IR spectra recorded in hexane.
(dSiMe2‚HMPA)(SiMe2SiMe2SiMe2Ph) and (η5-C5H5)-
(CO)Fe(dSiMe2‚HMPA)(SiMe2SiMe2GeMe2Ph), respec-
tively.
are indeed intramolecular in nature, as our mecha-
nism demands. Irradiation of a mixture of Fp*SiMe2-
SiMe2SiMe2GeMe2Ph and FpSiMe2SiMe2SiMe2SiMe3
was followed by NMR spectroscopy. Only the two
expected products were observed: there was no evidence
for any crossover products, i.e., Fp*Si(SiMe3)3 or FpGe-
(SiMe3)2(SiMe2Ph).
Ca ta lytic Tr a n sfor m a tion s. We have reported that
rearrangements of the type illustrated above can be
achieved catalytically, resulting in the isomerization of
linear oligosilanes, R3Si(R2Si)nH (Scheme 4).2f
Irradiation of M3GeMe2SiMe2SiMe2SiH was carried
out in the presence of a catalytic amount of FpSiMe3,
in the hope of obtaining high yields of (M3Si)3GeH.
When following such a reaction by 29Si NMR spectros-
copy, we did indeed observe the formation of (Me3Si)3-
GeH, but only as a low-concentration transient. The
major product obtained in the reaction was (Me3Si)3-
GeSiMe2H. The same compound was obtained in 70%
yield by an independent preparative route (irradiation
of FpSiMe2SiMe3 in the presence of (M3Si)3GeH).
This result is very intriguing. On the basis of Scheme
4, the catalytic process involves a series of oxidative
addition/reductive elimination steps to form (η5-C5H5)-
Fe(CO)SiMe2SiMe2SiMe2GeMe3. This species will rear-
range to (η5-C5H5)Fe(CO)Ge(SiMe3)3 prior to a second
oxidative addition/reductive elimination process to yield
the rearranged product (M3Si)3GeH. It is apparent that
this product undergoes a further reaction via the
insertion of the elements of SiMe2 into the Ge-H
bond. The problem with this explanation is that
These results confirm that after CO loss these rear-
rangements involve an R-elimination. Although trace
1
signals due to other species can be observed in the H
NMR, the 29Si NMR spectra are very clean, as noted in
Figure 2. Thus, under our reaction conditions, upon
coordination of the silylene by HMPA, the complexes
exhibit no significant further chemistry. This result
contrasts with that reported by the Ogino group for the
irradiation of FpSiMe2SiMe2SiMe2SiMe2OMe. Several
intramolecularly base-stabilized complexes were ob-
tained involving scrambling of the tetrasilyl chain.3e To
date, the only stabilized silylene-Fe complex that
exhibits further chemistry involving silylene elimination
is the (arene)Cr(CO)3 complex we recently reported, (η5-
C5H5)Fe(CO)(dSiMe2)SiMe2C6H5Cr(CO)2.2g
In tr a m olecu la r vs In ter m olecu la r Rea r r a n ge-
m en t. Although the 1,3-migrations described in Scheme
1 have been shown to involve intramolecular mecha-
nisms, the possibility for an intermolecular process
cannot be totally ignored. For example, Liu and co-
workers have shown that fluoro-substituted iron-si-
lylene complexes dimerize in the absence of a coordi-
nating ligand that can stabilize the species.6 Further-
more, the Tilley group demonstrated intramolecular
thiotolyl group transfer from silyl-ruthenium com-
plexes to related silylene-ruthenium complexes.7 There-
fore, we performed a photochemical experiment to
confirm that the rearrangements reported in this study
(6) Horng, K. M.; Wang, S. L.; Liu, C. S. Organometallics 1991, 10,
631.
(7) Grumbine, S. K.; Tilley, T. D. J . Am. Chem. Soc. 1994, 116, 6951.

Tetrasilyl- and Trisilylgermyl Complexes of Iron
Organometallics, Vol. 19, No. 7, 2000 1229
Sch em e 3
SiMe2 elimination has not been observed in the photo-
chemical treatment of either FpSiMe2SiMe2SiMe2SiMe3
or FpSiMe2SiMe2SiMe2GeMe3 and their related ana-
logues containing at least four metalloid atoms in the
chain bound to iron. In all cases only rearrangement
reactions occurred. The result clearly implies that
although no free silylene is liberated from the iron
center during the isomerization reactions, in the pres-
ence of (M3Si)3GeH (or (M3Si)3SiH)2d the elements of this
species are transferred to the germane (silane). This
strongly suggests that the SiMe2 is transferred via the
addition of the germane (silane) to the iron silylene
functionality prior to a reductive elimination process to
yield the observed product (Scheme 5, path B).
either pick up CO to form FpSiMe2SiMe2SiMe3 or
continue the silylene elimination chemistry to form
FpSiMe2SiMe3 and FpSiMe3. Close monitoring of the
catalytic reaction did reveal the presence of each of these
Fp complexes, i.e., Fp(SiMe2)nMe (n ) 1-3), illustrating
the internal consistency of the proposed chemistry.
Since photochemical treatment of both FpSiMe2SiMe3
and FpSiMe2SiMe2SiMe3 results in the elimination of
SiMe2, which can be trapped by (Me3Si)3GeH, the very
high yield of (Me3Si)3GeSiMe2H in the present study
probably results from both processes, i.e., addition to
the metal silylene intermediate and direct silylene
insertion.
It is also possible that a reverse addition could involve
the transient formation of (η5-C5H5)Fe(CO)SiMe2H(Si-
(SiMe3)3)(SiMe2SiMe2SiMe3) followed by reductive elimi-
nation of the product (path A). Whatever the precise
mechanism, which is presently under investigation, this
suggestion demands that we also form the transient
species (η5-C5H5)Fe(CO)SiMe2SiMe2SiMe3, which would
Exp er im en ta l Section
All reactions were carried out under a nitrogen atmosphere
using oxygen-free, dry solvents. Organosilicon compounds,
PhSiMe2SiMe2SiMe2Cl,2e PhSiMe2SiMe2SiMe2SiMe2Cl,2e Cl-

1230 Organometallics, Vol. 19, No. 7, 2000
Sharma and Pannell
Sch em e 5
°C. The solution was stirred at this temperature for 1 h and
then warmed to room temperature and stirred overnight. The
solvent was removed in vacuo and the residue extracted with
60 mL of hexane. This solution was filtered and the filtrate
concentrated to 5.0 mL and placed upon a 2.5 × 20 cm silica
gel column. The yellow band developed with hexane was
collected and after removal of the solvent yielded 1.38 g of
FpSiMe2SiMe2SiMe2SiMe2Ph (51%) as a yellow solid (mp
43 °C).
F igu r e 2. 29Si NMR spectra of FpSiMe2SiMe2SiMe2SiMe3
(a) prior to photochemistry and (b) after 4 h irradiation.
Sch em e 4
Syn th esis of F p *SiMe2SiMe2SiMe2Cl. Using the same
procedure as above with a 60 mL THF solution of [(η5-C5Me5)-
Fe(CO)2]Na (prepared from 1.44 g (2.90 mmol) of [(η5-C5Me5)-
Fe(CO)2]2) and 1.43 g (5.8 mmol) of ClSiMe2SiMe2SiMe2Cl,
Fp*SiMe2SiMe2SiMe2Cl (1.5 g, 3.28 mmol, 56%) was obtained
as an orange-red waxy solid.
Syn th esis of F p *SiMe2SiMe2SiMe2GeMe2P h . A 30 mL
solution of [PhMe2Ge]Li in THF (prepared from 0.570 g, 2.6
mmol, of PhGeMe2Cl) was added dropwise to 30 mL of a stirred
THF solution of 1.20 g (2.60 mmol) of Fp*SiMe2SiMe2SiMe2-
Cl at -25 °C. The reaction mixture was stirred at low
temperature for 1 h, and then the temperature was allowed
to rise to room temperature. The reaction mixture was stirred
at room temperature for 16 h. Subsequently the solvent was
removed in vacuo and the residue was extracted with 60 mL
of hexane, filtered, and concentrated to 5.0 mL prior to
placement on a 2.5 × 20 cm silica gel column, which was
developed with hexane. The orange band was collected and
after normal workup gave 0.60 g of Fp*SiMe2SiMe2SiMe2-
GeMe2Ph (0.10 mmol, 38% yield) as a waxy orange solid.
Syn th esis of P h SiMe2SiMe2SiMe2GeMe3. [Me3Ge]Li, ob-
tained from 3.5 g (22.8 mmol) of Me3GeCl in 20 mL of dry
ether, was added dropwise to 6.62 g (22.8 mmol) of PhSiMe2-
SiMe2SiMe2Cl in 20 mL of ether at -78 °C. The solution was
warmed to room temperature slowly and stirred overnight and
then filtered to remove lithium chloride. After acidic workup
(NH4Cl) the organic layer was dried over magnesium sulfate.
The solvent was removed, and the colorless liquid residue was
distilled under vacuum. The fraction distilling at 145-150 °C/
0.05 mmHg was collected to yield 2.4 g (6.50 mmol, 28%) of
PhSiMe2SiMe2SiMe2GeMe3 as a colorless liquid.
SiMe2SiMe2SiMe2Cl,8a [Me3Ge]Li,8b and FpSiMe2SiMe2SiMe2-
Cl,3d were synthesized by known methods. (Me3Si)3GeH was
purchased from Gelest Inc.; [(η5-C5H5)Fe(CO)2]2 was purchased
from Strem Chemicals, and reagent grade silica gel (60-200
mesh) was purchased from EM Science. NMR spectra were
recorded on a Bruker 300 MHz spectrometer and IR spectra
on
a Perkin-Elmer 1600 FT IR spectrophotometer. Ele-
mental analyses were performed by Galbraith Laboratories,
Knoxville, TN.
Typical experimental procedures are outlined below.
Syn th esis of F p SiMe2SiMe2SiMe2SiMe2P h . To a 50 mL
THF solution of [(η5-C5H5)Fe(CO)2]Na (prepared from 1.0 g
(2.82 mmol) of [(η5-C5H5)Fe(CO)2]2) was added 1.93 g (5.6
mmol) of PhSiMe2SiMe2SiMe2SiMe2Cl in 10 mL of THF at 0
Syn th esis of HSiMe2SiMe2SiMe2GeMe3. Triflic acid (0.82
g, 5.4 mmol) was added dropwise through a dropping funnel
to 2.0 g (5.4 mmol) of neat PhSiMe2SiMe2SiMe2GeMe3 in a 100
mL three-necked flask at 0 °C. The reaction mixture was
brought to room temperature slowly and stirred for 2 h. The
(8) (a) Oakley, R. T.; Stanislawski, D. A.; West, R. J . Organomet.
Chem. 1978, 157, 389. (b) Wickham, G.; Young, D.; Kitching, W. F. J .
Org. Chem. 1982, 47, 4884.

Tetrasilyl- and Trisilylgermyl Complexes of Iron
Organometallics, Vol. 19, No. 7, 2000 1231
volatiles were removed in vacuo, and a colorless liquid residue
was obtained. The latter was dissolved in 10 mL of dry ether
and this solution then added slowly to 0.20 g of LiAlH4 in 20
mL of dry ether at 0 °C contained in a 100 mL three-necked
flask. The solution was brought to room temperature slowly
and stirred overnight. The reaction mixture was immersed in
an ice bath, and 20 mL of 10% aqueous ammonium chloride
solution was added dropwise. The solution was filtered to
remove the salts, and the filtrate was extracted with three
portions of 10% ammonium chloride. The organic layer was
separated and dried over magnesium sulfate. Filtration and
removal of the solvent in vacuo followed by further distillation
(120-122 °C/20 mm of Hg) yielded HSiMe2SiMe2SiMe2GeMe3
as a colorless liquid (0.70 g, 2.38 mmol).
P h otolysis of F p SiMe2SiMe2SiMe2SiMe2P h . A solution
of the title compound (0.15 g, 0.31 mmol) in 1.0 mL of degassed
C6D6 was sealed in a Pyrex NMR tube. The NMR tube was
placed 10 cm from a 450 W medium-pressure mercury lamp
and irradiated. The progress of the photochemical reaction was
monitored by 29Si NMR spectroscopy. The starting material
disappeared completely after 1.5 h of irradiation. The solution
was placed on a 2.5 × 10 cm silica gel column, and a yellow
band was eluted with hexane. Upon removal of solvent in
vacuo FpSi(SiMe3)2SiMe2Ph (0.13 g, 87%) was obtained as a
yellow crystalline solid.
P h otolysis of F p *SiMe2SiMe2SiMe2GeMe2P h . The title
compound (0.10 g) in 1.0 mL of degassed C6D6 was placed in
a Pyrex NMR tube. The sealed NMR tube was placed 8 cm
from the 450 W medium-pressure mercury lamp and irradi-
ated. The reaction was followed by 29Si NMR spectroscopy.
After 3.5 h the starting material had been consumed; i.e., the
resonances at 20.6, -32.7, and -33.0 ppm had disappeared
and new signals at -2.0 and -5.4 ppm had appeared. The
solution was placed on a 2.5 × 10 cm silica gel column, and a
yellow band was eluted with hexane. Upon removal of solvent
in vacuo Fp*Ge(SiMe3)2SiMe2Ph (0.08 g, 80%) was obtained
as an orange oil, which became solid when placed in the
freezer.
P h otolysis of HSiMe2SiMe2SiMe2GeMe3 in th e P r es-
en ce of a Ca ta lytic Am ou n t of F p SiMe3. A mixture of
HSiMe2SiMe2SiMe2GeMe3 (0.120 g, 0.41 mmol) and a 10%
equivalent of FpSiMe3 in 1 mL of C6D6 was irradiated in a
sealed Pyrex NMR tube. The progress of the reaction was
monitored by 29Si NMR spectroscopy. After 53 h 29Si NMR
analysis showed the presence of signals at -4.61 and -29.5
ppm due to the formation of (Me3Si)3GeSiMe2H and a signal
at -16.1 ppm due to Me3SiH. Some starting material was also
present.
P h otolysis of (Me3Si)3GeH + HSiMe2SiMe3 in th e P r es-
en ce of a Ca ta lytic Am ou n t of F p SiMe3. A 5 mm Pyrex
NMR tube was charged with 0.3 g (2.24 mmol) of HSiMe2-
SiMe3, 0.3 g (1.02 mmol) of (Me3Si)3GeH, and 10 mol % of
FpSiMe3 in 1 mL of C6D6 and sealed under vacuum. Photolysis,
using a Hanovia 450 W lamp at a distance of 6 cm, was
monitored by 29Si NMR spectroscopy. After 62 h the HSiMe2-
SiMe3 had been consumed and resonances associated with the
insertion product (Me3Si)3GeSiMe2H were observed (-4.6 and
-29.5 ppm) together with that due to Me3SiH (-16.3 ppm).
The contents of the tube were passed through a silica gel
column (1 × 2 cm) using hexane as eluant, and the resulting
solution was evaporated to dryness. The resulting white solid
was recrystallized from dry ethanol to yield 0.25 g of pure
(Me3Si)3GeSiMe2H (0.71 mmol, 70% yield).
P h otolysis of Fp SiMe2SiMe2SiMe2SiMe2P h in th e P r es-
en ce of HMP A. A 5 mm NMR tube was charged with 0.08 g
(0.164 mmol) of FpSiMe2SiMe2SiMe2SiMe2Ph and 0.10 g (0.56
mmol) of HMPA in 1.0 mL of degassed C6D6 and sealed under
vacuum. The sealed NMR tube was irradiated with a 450 W
medium-pressure mercury lamp, and the reaction was moni-
tored by 29Si and 1H NMR spectroscopy. After 3.0 h the starting
material had disappeared, and the 29Si NMR spectrum showed
a doublet at 115.3 ppm and singlets at 14.7, -17.6, and -39.1
ppm due to the formation of (η5-C5H5)(CO)Fe(dSiMe2‚HMPA)-
SiMe2SiMe2SiMe2Ph. Continued irradiation had no effect upon
the spectra obtained.
P h otolysis of FpSiMe2SiMe2SiMe2GeMe2P h in th e P r es-
en ce of HMP A. A mixture of 0.10 g (0.19 mmol) of FpSiMe2-
SiMe2SiMe2GeMe2Ph and 0.13 g (0.66 mmol) of HMPA in 1.0
mL of C6D6 in a 5 mm sealed Pyrex NMR tube was irradiated
for 2.0 h, and the reaction was monitored by 29Si NMR
spectroscopy. During this time the starting compound disap-
peared. The 29Si NMR spectrum at this time showed a doublet
at 115.6 ppm due to the silylene ligand coordinated by a HMPA
molecule and singlets at 14.9 and -32.6 ppm. Trace amounts
of FpSiMe2Ph (36.0 ppm) were also observed.
Ack n ow led gm en t. This research was supported by
the NIH-MARC program and the R. A. Welch Founda-
tion, Houston, TX. HRMS measurements were obtained
from the Nebraska Center for Mass Spectrometry.
OM990897C