Selective and stepwise bromodemethylation of the silyl ligand in iron(II) silyl complexes with boron tribromide

Article abstract of DOI:10.1021/om049762j

Treatment of Cp*(CO)₂FeSiMe₂R (Cp* = C₅Me₅, R = Me and Ph) with 1 equiv of BBr₃ at room temperature afforded Cp*(CO)₂FeSiBrMeR (R = Me and Ph) and MeBBr₂ in high yields via bromo

Full text of DOI:10.1021/om049762j

4150
Organometallics 2004, 23, 4150-4153
Selective a n d Step w ise Br om od em eth yla tion of th e Silyl
Liga n d in Ir on (II) Silyl Com p lexes w ith Bor on
Tr ibr om id e
Takahito Watanabe, Hisako Hashimoto,* and Hiromi Tobita*
Department of Chemistry, Graduate School of Science, Tohoku University,
Sendai 980-8578, J apan
Received April 2, 2004
Treatment of Cp*(CO)2FeSiMe2R (Cp* ) C5Me5, R ) Me and Ph) with 1 equiv of BBr3 at
room temperature afforded Cp*(CO)2FeSiBrMeR (R ) Me and Ph) and MeBBr2 in high yields
via bromodemethylation of the silyl ligand. Cp*(CO)2FeSiBrMeR (R ) Me and Ph) was further
converted to Cp*(CO)2FeSiBr2R (R ) Me and Ph) quantitatively on addition of another
equivalent of BBr3 and heating. Treatment of Cp*(CO)2FeSiMe2SiMe3 with 1 equiv of BBr3
at room temperature led to selective bromodemethylation at the R-silicon atom to produce
Cp*(CO)2FeSiBrMeSiMe3, which was also converted to Cp*(CO)2FeSiBr2SiMe3 on heating
with another equivalent of BBr3 at 40 °C in quantitative yield. The solid-state structure of
Cp*(CO)2FeSiBr2SiMe3 was confirmed by X-ray crystal structure determination.
In tr od u ction
complexes by using BBr3 instead of GaCl3, we unexpect-
edly found that bromodemethylation of the silyl ligand
of Cp*(CO)2FeSiMe3 occurred to produce a bromosilyl
derivative Cp*(CO)2FeSiBrMe2 via cleavage of a silicon-
carbon bond. The cleavage of a silicon-carbon bond is
an important process in synthetic chemistry, but the
cleavage of a Si-C(sp3) bond is quite rare even in
organic synthesis.6 Usually, the cleavage of a Si-C(sp2)
bond is more favorable than that of a Si-C(sp3) bond:
Trimethylsilyl-substituted arenes (ArSiMe3, Ar ) aryl)
react with BX3 to give XSiMe3 and ArBX2 via the
selective cleavage of the Si-Ar bond.7 We report here
the details of bromodemethylation of silyliron complexes
Cp*(CO)2FeSiMe2R (R ) Me, Ph, and SiMe3) with boron
tribromide. The bromination occurs regioselectively and
stepwise at the R-Si atom, and the methyl groups are
chemoselectively substituted.
Transition-metal silyl complexes have attracted great
interest because of their important roles in various
reactions of organosilicon compounds with transition-
metal complexes.1 Although there are many reports on
the synthesis, it was only recently demonstrated that
direct introduction of functional groups on the silyl
ligands is a useful method in synthesizing various
derivatives of silyl complexes.2-4 For example, Malisch
et al. reported that regioselective halogenation of R-Si-H
groups of Cp(CO)2MSiH2SiH3 (M ) Fe, Ru) proceeds on
treatment with CX4 (X ) Cl, Br) or Br2 to produce the
corresponding Cp(CO)2MSiX2SiH3 (M ) Fe, Ru) in high
yield.2c He also reported that hydroxylation of Cp-
(CO)2FeSiH2SiH3 with dimethyldioxirane occurs regio-
selectively.4d Nevertheless, only a limited number of
such examples have been reported so far.
Previously, Ueno et al. performed the reaction of a
silyliron(II) complex Cp*(CO)2FeSiMe3 (Cp* ) C5Me5)
with a Lewis acid GaCl3 that led to the cleavage of the
iron-silicon bond to produce Cp*(CO)2FeGaCl2 and
ClSiMe3 in almost quantitative yield.5 In the course of
our application of this method to the synthesis of boryl
Resu lts a n d Discu ssion
When a trimethylsilyliron(II) complex Cp*(CO)2-
FeSiMe3 (Cp* ) η5-C5Me5) (1a ) was treated with 1 equiv
of BBr3 in C6D6 at room temperature, the reaction
completed within 1 h to afford the bromodimethylsily-
liron(II) complex Cp*(CO)2FeSiMe2Br (2a ) quantita-
tively (eq 1) via bromodemethylation of the silyl group.
Complex 2a further reacted with another equivalent of
BBr3 in C6D6 on heating (40-60 °C) to lead to the
quantitative formation of dibromomethylsilyliron(II)
complex Cp*(CO)2FeSiMeBr2 (3a ). Complex 3a was also
obtained directly from the reaction of 1a with more than
2 equiv of BBr3 on heating in high yield. Analytically
pure 2a was obtained as yellow crystals by the prepara-
* To whom correspondence should be addressed. Fax: +81-
22-217-6543. E-mail: tobita@mail.tains.tohoku.ac.jp, hhashimoto@
mail.tains.tohoku.ac.jp.
(1) (a) Tilley, T. D. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24.
(b) Eisen, M. S. In The Chemistry of Organic Silicon Compounds, Vol.
2; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998; Chapter
35. (c) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175.
(2) (a) Malisch, W.; Kuhn M. Chem. Ber. 1974, 107, 2835. (b)
Malisch, W.; Ries, W. Chem. Ber. 1979, 112, 1304. (c) Malisch, W.;
J ehle, H.; Mo¨ller, S.; Thum, G.; Reising, J .; Gbureck, A.; Nagel, V.;
Fickert, C.; Kiefer, W.; Nieger, M. Eur. J . Inorg. Chem. 1999, 1597.
(3) Nikonov, G. I.; Kuzmina, L. G.; Vyboishchikov, S. F.; Lemen-
ovskii, D.; Howard, A. J . A. K. Chem. Eur. J . 1999, 5, 2947.
(4) (a) Malisch, W.; Lankat, R.; Fey, O.; Reising, J .; Schmitzer, S.
J . Chem. Soc., Chem. Commun. 1995, 1917. (b) Malisch, W.; Neumayer,
M.; Fey, O.; Adam, W.; Schuhmann, R. Chem. Ber. 1995, 128, 1257.
(c) Mo¨ller, S.; Fey, O.; Malisch, W.; Seelbach, W. J . Organomet. Chem.
1996, 506, 239. (d) Malisch, W.; J ehle, H.; Saha-Mo¨ller, C.; Adam, W.
Eur. J . Inorg. Chem. 1998, 1585. (e) Malisch, W.; Hofmann, M.; Kaupp,
G.; Ka¨b, H.; Reising, J . Eur. J . Inorg. Chem. 2002, 3235.
(5) Ueno, K.; Watanabe, T.; Ogino, H. Appl. Organomet. Chem. 2003,
17, 403.
(6) Brook, M. A. In Silicon in Organic, Organometallic, and Polymer
Chemistry; Wiley: New York, 2000; Chapter 16.
(7) (a) Haubold, W.; Herdtle, J . Gollinger, W.; Einholz, W. J .
Organomet. Chem. 1986, 315, 1. (b) Kaufmann, D. Chem. Ber. 1987,
120, 853. (c) Kaufmann, D. Chem. Ber. 1987, 120, 901. (d) Gross, U.;
Kaufmann, D. Chem. Ber. 1987, 120, 991.
10.1021/om049762j CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/16/2004

Bromodemethylation of the Silyl Ligand
Organometallics, Vol. 23, No. 17, 2004 4151
tive scale reaction of 1a with BBr3 in hexane and
following removal of the byproduct BBr2Me under
vacuum. Complex 3a was also fully characterized by
spectroscopic techniques. In contrast, no tribromosily-
liron(II) complex Cp*(CO)2FeSiBr3 was detected even
after 3a and a large excess of BBr3 were heated in C6D6
at 50 °C for 2 days. Analogous halodemethylation of 1a
did not occur when BCl3 or AlCl3 was used instead of
BBr3. The H/X exchange reaction of hydrosilyl com-
plexes M-SiHnR3-n with CX4 (X ) Cl, Br) or Br2 has been
known as almost the only method for halogenation of
the silyl ligand in transition-metal silyl complexes.2,3 To
our knowledge, the reaction shown in eq 1 is the first
example of halodemethylation of the silyl ligand in
transition-metal silyl complexes.
F igu r e 1. Molecular structure of 3c, showing 50% thermal
ellipsoids. Hydrogen atoms were omitted for clarity. Se-
lected bond distances (Å) and angles (deg): Fe-Si(1), 2.262-
(2); Si(1)-Br(1), 2.281(2); Si-Br(2), 2.281(2); Si(1)-Si(2),
2.343(3); Fe-Si(1)-Br(1), 113.0(1); Fe-Si(1)-Br(2), 114.5-
(1); Fe-Si(1)-Si(2), 123.7(1).
To get insight into the scope and limitation of this
bromination reaction, we next investigated the reactions
of BBr3 with silyl complexes having not only methyl
group(s) but also other substituent(s) simultaneously on
a silicon atom. When Cp*(CO)2FeSiMe2Ph (1b) was
treated with 1 equiv of BBr3 in C6D6 at room temper-
ature, a methyl group on the silyl ligand was selectively
substituted to give Cp*(CO)2FeSiMeBrPh (2b) (eq 1).
The reaction of 2b with BBr3 at 60 °C further afforded
dibromophenylsilyliron(II) complex Cp*(CO)2FeSiBr2Ph
(3b) as a single product in quantitative yield. Complex
3b was also obtained directly when 1b was heated with
more than 2 equiv of BBr3. Interestingly, bromodephe-
nylation never occurred under even more severe condi-
tions. As mentioned in the Introduction, this selectivity
is opposite that observed in the reactions of organosili-
con compounds with Lewis acids BCl3 and BBr3, which
cause the cleavage of Si-C(sp2) bonds in preference to
Si-C(sp3) bonds at ambient temperature.7 The latter
type of selectivity was also observed in the bromodem-
ethylation reactions of (silylcyclopentadienyl)zirconium
complexes (PhnMe3-nSiC5H4)2ZrCl2 (n ) 1, 2) with
BBr3.8
This bromodemethylation was found to occur also
regioselectively at the R-silicon atom in the case of a
disilanyliron(II) complex. Thus, treatment of Cp*-
(CO)2FeSiMe2SiMe3 (1c) with 1 equiv of BBr3 at room
temperature produced Cp*(CO)2FeSiMeBrSiMe3 (2c)
quantitatively (eq 2). Complex 2c further reacted cleanly
with another equivalent of BBr3 to give Cp*(CO)2-
FeSiBr2SiMe3 (3c). These complexes 2c and 3c have
been isolated and fully characterized by spectroscopic
techniques (see Experimental Section). The structure
of 3c was confirmed by X-ray crystallography (vide
infra). No â-silicon-substituted complex was observed
even by addition of an excess of BBr3 to 3c and heating
the mixture. These results imply that the iron fragment
plays an important role in determining the chemo- and
regioselectivity of this bromination reaction. It is worth
noticing that the regioselectivity of this reaction coin-
cides with that of the above-mentioned halogenation of
Cp(CO)2FeSiH2SiH3 with CX4 (X ) Cl, Br) reported by
Malisch et al.2c Unlike 1a , the reaction of the Cp
analogue, CpFe(CO)2SiMe3, with BBr3 only produced a
complicated mixture containing CpFe(CO)2SiBrMe2
(∼30%) that could not be isolated.
The X-ray crystal structure of 3c (Figure 1) shows
that two bromine atoms are attached to the R-silicon
atom and the SiMe3 group is located at the position
farthest away from the bulky Cp* ligand. The Fe-Si(1)
bond length (2.262(2) Å) is shorter than the Fe-Si bond
lengths of trialkylsilyliron complexes (2.33-2.46 Å).9
This tendency is often observed in halo-substituted silyl
complexes in which interaction between the low-lying
Si-X σ*-orbital and a symmetry-adapted, occupied
d-orbital of the metal causes the shortening of the M-Si
bond length.10 The Si(1)-Si(2) bond length (2.343(3) Å)
of 3c is in the normal range of the values previously
reported for disilanyliron complexes (2.33-2.39 Å).9 The
Si(1)-Br(1) and Si(1)-Br(2) bond lengths (2.281(2) and
2.281(2) Å) are at the longest extreme of the Si-Br bond
lengths ever reported for organobromosilanes (2.20-
2.28 Å).9
Finally, we investigated the effect of the substituents
of the silyl ligand and the solvent on the reaction rate
of the bromodemethylation. The results are summarized
(9) (a) Vancea, L.; Bennett, M. J .; J ones, C. E.; Smith, R. A.; Graham,
W. A. G. Inorg. Chem. 1977, 16, 897. (b) Knorr, M.; Mu¨ller, J .; Schubert,
U. Chem. Ber. 1987, 120, 879. (c) Pannell, K. H.; Lin, S.-H.; Kapoor,
R. N.; Cervantes-Lee, F.; Pinon, M.; Parkanyi, L. Organometallics 1990,
9, 2454. (d) Nakazawa, H.; Yamaguchi, Y.; Kawamura, K.; Miyoshi,
K. Organometalics 1997, 16, 4626. (e) Pannell, K. H.; Kobayashi, T.;
Cervantes-Lee, F.; Zhang, Y. Organometallcs 2000, 19, 1.
(10) Lemke, F. R.; Galat, K. J .; Youngs, W. J . Organometallics 1999,
18, 1419.
(8) (a) Deck, P. A.; Fisher, T. S.; Sloan Downey, J . Organometallics
1997, 16, 1193. (b) Deck, P. A.; Cheng, X.; Stoebenau, E. J .; Slebodnick,
C.; Billodeaux, D. R., Fronczek, F. R. Organometallics 2000, 19, 5404.

4152 Organometallics, Vol. 23, No. 17, 2004
Watanabe et al.
Ta ble 1. Effect of th e Su bstitu en ts of th e Silyl Liga n d a n d th e Solven t on th e Rea ction Ra te of th e
Br om od em eth yla tion
equiv
of
BBr3
T
(°C)
time
(h)
yield
(%)b
entry
compound
solvent
product
1
2
3
4
5
6
7
8
9
1a (R ) Me)
1b (R ) Ph)
1c (R ) SiMe3)
2a (R ) Me)
2b (R ) Ph)
2c (R ) SiMe3)
2a (R ) Me)c
2a (R ) Me)c
2a (R ) Me)c
1
1
1
1.2
1.2
1.2
2
2
2
C6D6
C6D6
C6D6
C6D6
C6D6
C6D6
hexane
toluene
CH2Cl2
20
20
20
50
50
50
20
20
20
0.5
1
2a
2b
2c
3a
3b
3c
3a
3a
3a
quant.
quant.
quant.
quant.
quant.
quant.
7d
0.2
34
96
2.5
48
48
48
47d
83d
A 0.10 M solution was used. The yield was determined by H NMR. c A 0.05 M solution was used. The value shows the conversion
a
b
1
d
(%).
in Table 1. The reaction was the fastest when the
icon atom of the silyl complexes and polar solvents
accelerate the reaction. Application of this reaction
toward other transition-metal silyl complexes is in
progress.
substituent on the R-silicon atom was a SiMe3 group
(see entries 4, 5, and 6). The reaction slowed as the
substituent was changed from Me to Ph. Substitution
of a bromine atom for a methyl group significantly
deactivated the bromodemethylation (compare entries
1-2 and 4-5). Thus, the more electron-donating the
substituents became, the faster the bromination reac-
tion proceeded. With respect to the solvent effect, when
the reaction of 2a with 2 equiv of BBr3 was carried out
in hexane, toluene, or dichloromethane in the same
concentration, the percentage of conversion from 2a to
3a after 48 h was 7%, 47%, and 83%, respectively
(entries 7-9). Apparently, the more polar the solvent
became, the faster the bromination reaction proceeded.
This tendency suggests that the transition state or
intermediate of this reaction is substantially more
polarized than the starting complex 1a . A possible
intermediate is a cationic silylene complex [Cp*-
(CO)2FedSiR2]+[BMeBr3]- produced by the abstraction
of a methyl anion from 1a with the Lewis acid BBr3.
The silylene ligand in the cationic part may be stabilized
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
using either standard Schlenk tube techniques under nitrogen
or argon atmosphere or vacuum line techniques, or in a drybox
under nitrogen atmosphere. Hexane, toluene, and THF were
dried over sodium benzophenone ketyl and freshly distilled
under a nitrogen atmosphere. K[Cp*Fe(CO)2],11 Cp*Fe(CO)2-
SiMe3 (1a ),12 and Cp*Fe(CO)2SiMe2SiMe3 (1c) (Cp* ) C5Me5)13
were prepared by the literature procedures. NMR spectra were
recorded on a Bruker ARX-300 Fourier transform spectrometer
at room temperature. IR spectra were obtained on a HORIBA
FT-730 spectrometer at room temperature. Mass spectra were
recorded on a J EOL HX-110 spectrometer at the Instrumental
Analysis Center for Chemistry, Tohoku University. Elemental
analyses were performed at the Instrumental Analysis Center
for Chemistry, Tohoku University.
Syn th esis of Cp *F e(CO)2SiMe2P h (1b). A THF (15 mL)
solution of K[Cp*Fe(CO)2] (1.0 g, 3.5 mmol) was added to
ClSiMe2Ph (0.70 mL, 4.2 mmol) in THF (10 mL) at -46 °C
with vigorous stirring. The reaction mixture was warmed to
room temperature and stirred overnight. After removal of
volatiles under reduced pressure, hexane (50 mL) was added
to the residue and insoluble material was filtered off. The
filtrate was concentrated to ca. 2 mL and cooled to -30 °C for
1 day to give orange crystals. Yield: 0.82 g (2.1 mmol, 60%).
1H NMR (300 MHz, C6D6): δ 0.78 (s, 6H, SiMe), 1.34 (s, 15H,
C5Me5), 7.20 (m, 1H, Ph), 7.27 (m, 2H, Ph), 7.78 (m, 2H, Ph).
13C NMR (75.5 MHz, C6D6): δ 5.5 (SiMe), 9.4 (C5Me5), 94.8
(C5Me5), 127.6, 134.2, 146.3 (Ph), 218.3 (CO). 13C NMR (75.5
MHz, CDCl3): δ 5.0 (SiMe), 9.7 (C5Me5), 94.8 (C5Me5), 127.1,
127.5, 133.8, 146.0 (Ph), 217.8 (CO). 29Si NMR (59.6 MHz,
C6D6): δ 20.6. IR (KBr): νCO 1905, 1963 cm-1. MS (EI, 70 eV):
m/z 382 (M+, 17), 354 (M+ - CO, 16), 326 (M+ - 2CO, 98),
311 (M+ - 2CO - Me, 32), 135 ([SiMe2Ph]+, 100). Anal. Calcd
for C20H26FeO2Si; C, 62.83; H, 6.85. Found: C, 62.74; H, 6.83.
Rea ction of 1a w ith 1 Equ iv of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr Me2 (2a ). BBr3 (70 µL, 0.74 mmol) was
added dropwise to a hexane (10 mL) solution of Cp*Fe-
(CO)2SiMe3 (200 mg, 0.624 mmol) at room temperature. The
-
by coordination of either BMeBr3 or solvent. Many
base-stabilized and also base-free cationic silylene com-
plexes have been isolated and well-characterized.1 It is
well known that the silylene ligand in cationic silylene
complexes is extremely electrophilic. This would be the
driving force for the final step, i.e., bromide transfer
-
from BMeBr3 to the silylene silicon.
Although this mechanism could rationalize the selec-
tive R-bromination of the disilanyl ligand, the preference
of a methyl group to a phenyl group in bromination
cannot be easily explained by this mechanism. Further
investigations on the mechanism of this reaction are
under way.
In summary, we found that the reaction of Cp*-
(CO)2FeSiMe2R (R ) Me, Ph, or SiMe3) with BBr3
causes selective and stepwise bromodemethylation of
the silyl ligand to produce the corresponding bromosilyl
complexes Cp*(CO)2FeSiBrMeR and Cp*(CO)2FeSiBr2R.
When R ) SiMe3, the bromodemethylation occurs
selectively at the R-silicon atom. These bromination
reactions proceed almost quantitatively under mild
conditions. Electron-donating substituents on the R-sil-
(11) Catheline, D.; Astruc, D. Organometallics 1984, 3, 1094.
(12) Randolph, C. L.; Wrighton, M. S.Organometallics 1987, 6, 365.
(13) Ueno, K.; Nakano, K.; Ogino, H. Chem. Lett. 1996, 459.

Bromodemethylation of the Silyl Ligand
Organometallics, Vol. 23, No. 17, 2004 4153
mixture was stirred vigorously for 1 h. After removal of
volatiles, hexane (10 mL) was added to the residue and
insoluble material was filtered off. The solvent was removed
from the filtrate under reduced pressure to give yellow crystals
excess of BBr3. BBr3 (360 µL, 3.72 mmol), 1c (470 mg, 1.24
mmol), and hexane (20 mL) were used, and the mixture was
stirred on heating at 40 °C for 6 h. Yield: 595 mg (1.17 mmol,
1
94%). H NMR (300 MHz, C6D6): δ 0.51 (s, 9H, â-SiMe), 1.47
1
of 2a . Yield: 239 mg (0.620 mmol, 99%). H NMR (300 MHz,
(s, 15H, C5Me5). 13C NMR (75.5 MHz, C6D6): δ -1.3 (â-SiMe),
9.1 (C5Me5), 97.5 (C5Me5), 214.6 (CO). 29Si NMR (59.6 MHz,
C6D6): δ -19.7 (â-Si), 84.0 (R-Si). IR (KBr): νCO 1945, 1994
cm-1. Anal. Calcd for C15H24Br2FeO2Si2: C, 35.45; H, 4.76.
Found: C, 35.82; H, 4.82.
C6D6): δ 1.07 (s, 6H, SiMe), 1.46 (s, 15H, C5Me5). 13C NMR
(75.5 MHz, C6D6): δ 9.4 (C5Me5), 12.5 (SiMe), 96.1 (C5Me5),
216.0 (CO). 29Si NMR (59.6 MHz, C6D6): δ 71.8. IR (KBr): νCO
1934, 1981 cm-1. MS (EI, 70 eV): m/z 384 (M+, 6), 356 (M+
-
CO, 31), 328 (M+ - 2CO, 32), 190 ([Fe(CO)4SiMe2]+, 100). Anal.
Calcd for C14H21BrFeO2Si: C, 43.66; H, 5.50. Found: C, 43.60;
H, 5.51.
Rea ction of 2a w ith BBr 3. BBr3 (6 µL, 0.06 mmol) was
added to a C6D6 (0.50 mL) solution of 2a (20 mg, 0.052 mmol)
in a Pyrex NMR tube at room temperature. The NMR tube
was then degassed and sealed. The solution was heated at 50
°C. The reaction was monitored by 1H NMR spectroscopy. After
34 h, 2a was converted to give 3a in quantitative yield.
Rea ction of 2b w ith BBr 3. In a procedure similar to the
reaction of 2a with BBr3, a C6D6 (0.50 mL) solution containing
2b (23 mg, 0.052 mmol) and BBr3 (6 µL, 0.06 mmol) was heated
at 50 °C for 96 h to give 3b in quantitative yield.
Rea ction of 1a w ith a n Excess of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr 2Me (3a ). BBr3 (200 µL, 2.12 mmol) was
added dropwise to a toluene (10 mL) solution of 1a (200 mg,
0.624 mmol) at room temperature. The mixture was stirred
for 36 h at 40 °C. After removal of volatiles under reduced
pressure, hexane (10 mL) was added to the residue and
insoluble material was filtered. The solvent was removed from
the filtrate to give yellow crystals of 3a . Yield: 267 mg (0.593
mmol, 95%). 1H NMR (300 MHz, C6D6): δ 1.42 (s, 15H, C5-
Me5), 1.62 (s, 3H, SiMe). 13C NMR (75.5 MHz, C6D6): δ 9.1
(C5Me5), 19.9 (SiMe), 97.2 (C5Me5), 214.3 (CO). 29Si NMR (59.6
MHz, C6D6): δ 68.9. IR (KBr): νCO 1950, 1998 cm-1. Anal.
Calcd for C13H18Br2FeO2Si: C, 34.70; H, 4.03. Found: C, 34.73;
H, 3.91.
Rea ction of 1b w ith 1 Equ iv of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr MeP h (2b). 2b was obtained as orange
crystals by a procedure similar to the reaction of 1a with 1
equiv of BBr3. BBr3 (60 µL, 0.63 mmol), 1b (200 mg, 0.523
mmol), and toluene (10 mL) were used, and the mixture was
stirred at room temperature for 6 h. Yield: 234 mg (0.523
mmol, 100%). 1H NMR (300 MHz, C6D6): δ 1.31 (s, 3H, SiMe),
1.33 (s, 15H, C5Me5), 7.15 (m, 1H, Ph), 7.24 (m, 2H, Ph), 7.98
(m, 2H, Ph). 13C NMR (75.5 MHz, C6D6): δ 9.5 (C5Me5), 12.9
(SiMe), 96.3 (C5Me5), 127.9, 129.0, 134.0, 143.6 (Ph), 216.3,
216.9 (CO). 29Si NMR (59.6 MHz, C6D6): δ 63.7. IR (KBr): νCO
1930, 1982 cm-1. MS (EI, 70 eV): m/z 446 (M+, 14), 418 (M+
- CO, 72), 390 (M+ - 2CO, 100), 375 (M+ - 2CO - Me, 59),
298 (M+ - 2CO - Me - Ph, 10). Anal. Calcd for C19H23BrFeO2-
Si: C, 51.03; H, 5.18. Found: C, 51.05; H, 5.13.
Rea ction of 1b w ith a n Excess of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr 2P h (3b). 3b was obtained as orange crystals
by a procedure similar to the reaction of 1a with an excess of
BBr3. BBr3 (130 µL, 1.38 mmol), 1b (175 mg, 0.458 mmol), and
toluene (10 mL) were used, and the mixture was stirred on
heating at 80 °C for 24 h. The workup was performed using
toluene. Yield: 234 mg (0.457 mmol, 100%). 1H NMR (300
MHz, C6D6): δ 1.32 (s, 15H, C5Me5), 7.07 (m, 1H, Ph), 7.19
(m, 2H, Ph), 8.15 (m, 2H, Ph). 13C NMR (75.5 MHz, C6D6): δ
9.0 (C5Me5), 96.8 (C5Me5), 127.8, 129.8, 133.5, 142.9 (Ph), 214.9
(CO). 29Si NMR (59.6 MHz, C6D6): δ 74.9. IR (KBr): νCO 1952,
2000 cm-1. Anal. Calcd for C18H20Br2FeO2Si: C, 42.22; H, 3.94.
Found: C, 42.05; H, 3.94.
Rea ction of 2c w ith BBr 3. In a procedure similar to the
reaction of 2a with BBr3, a C6D6 (0.50 mL) solution containing
2c (23 mg, 0.051 mmol) and BBr3 (6 µL, 0.06 mmol) was heated
at 50 °C for 2.5 h to give 3c in quantitative yield.
Rea ction s of 2a w ith BBr 3 in Va r iou s Solven ts. A
typical procedure is as follows: BBr3 (25 µL, 0.26 mmol) was
added to a hexane (2.5 mL) solution of 2a (50 mg, 0.13 mmol)
at 20 °C. A small portion (50 µL) of the reaction mixture was
collected periodically (every ca. 24 h for a week), and volatiles
were removed in vacuo. The resulting residue was dissolved
1
in C6D6, and the H NMR spectrum was measured. Similarly,
the reaction of 2a with BBr3 was performed in toluene and in
1
CH2Cl2 at 20 °C and monitored by H NMR spectroscopy.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 3c. A single-
crystal suitable for X-ray crystal structure determination was
mounted on a glass fiber. The intensity data were collected
on a Rigaku RAXIS-RAPID imaging plate diffractometer with
graphite-monochromated Mo KR radiation to a maximum 2θ
value of 55.0 at 150 K. A total of 44 images, corresponding to
220.0° oscillation angles, were collected with two different
goniometer settings. Exposure time was 1.30 min per degree.
Readout was performed in the 0.100 mm pixel mode. Numer-
ical absorption collections were applied on the crystal shape.
The structure was solved by Patterson and Fourier transform
methods. All non-hydrogen atoms were refined by full-matrix
least-squares techniques with anisotropic displacement pa-
rameters based on F2 with all reflections. All hydrogen atoms
were placed at their geometrically calculated positions and
refined riding on the corresponding carbon atoms with isotro-
pic thermal parameters. The final residue R1 and the weighted
Rw were R1 ) 0.052 and Rw ) 0.136 for 2297 reflections with
I > 2σ(I). All calculations were performed using the teXsan
crystal structure analysis package.14
Crystallographic Information has been deposited with the
Cambridge Crystallographic Data Centre (CCDC No. 229770).
Rea ction of 1c w ith 1 Equ iv of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr MeSiMe3 (2c). 2c was obtained as orange
crystals by a procedure similar to the reaction of 1a with 1
equiv of BBr3. BBr3 (60 µL, 0.63 mmol) and 1c (200 mg, 0.528
mmol) were used. Yield: 230 mg (0.519 mmol, 98%). 1H NMR
(300 MHz, C6D6): δ 0.44 (s, 9H, â-SiMe), 1.15 (s, 3H, R-SiMe),
Ack n ow led gm en t. This work was supported by the
Ministry of Education, Culture, Sports, Science and
Technology of J apan (Grants-in-Aid for Scientific Re-
search Nos. 14204065, 14078202, and 14044010).
1.48 (s, 15H, C5Me5). 13C NMR (75.5 MHz, C6D6): δ -0.6 (â-
29
SiMe), 8.1 (R-SiMe), 9.5 (C5Me5), 96.2 (C5Me5), 216.2 (CO).
-
Su p p or tin g In for m a tion Ava ila ble: Crystal structure
data for 3c, including tables of atomic coordinates, anisotropic
thermal parameters, and bond distances and angles. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Si NMR (59.6 MHz, C6D6): δ -25.6 (â-Si), 64.1 (R-Si). IR
(KBr): νCO 1934, 1982 cm-1. MS (EI, 70 eV): m/z 444 (M+,
28), 414 (M+ - CO, 86), 386 (M+ - 2CO, 100), 369 (M+
-
SiMe3, 32), 313 (M+ - 2CO - SiMe3, 36), 290 (M+ - Br -
SiMe3, 87). Anal. Calcd for C16H27BrFeO2Si2: C, 43.35; H, 6.14.
Found: C, 43.05; H, 6.08.
OM049762J
Rea ction of 1c w ith a n Excess of BBr 3: F or m a tion of
Cp *F e(CO)2SiBr 2SiMe3 (3c). 3c was obtained as orange
crystals by a procedure similar to the reaction of 1a with an
(14) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corporation, 1985 & 1999.