Stereospecific formation of 1,3-disilacyclobutanes by photochemical treatment of bimetallic precursors FpCH2SiR2SiR2CH2Fp (Fp = (η5-C5H5)Fe(CO)2) [15]

Full text of DOI:10.1021/ja994392p

J. Am. Chem. Soc. 2000, 122, 8327-8328
8327
Stereospecific Formation of 1,3-Disilacyclobutanes by
Photochemical Treatment of Bimetallic Precursors
FpCH2SiR2SiR2CH2Fp (Fp ) (η5-C5H5)Fe(CO)2)
Yongqiang Zhang, Francisco Cervantes-Lee, and
Keith H. Pannell*
Department of Chemistry, UniVersity of Texas at El Paso
El Paso, Texas 79968-0513
ReceiVed December 16, 1999
ReVised Manuscript ReceiVed March 1, 2000
The activation of the silicon-silicon bond by transition metal
complexes is an area of chemistry that has implications in catalysis
and materials science.1 Our studies on the chemistry of oligosilyl
compounds substituted with the Fp group showed that R-elimina-
tion chemistry results in the intermediacy of iron-silylene
complexes, Fp ) (η5-C5H5)Fe(CO)2). These intermediates lead
to either silylene eliminations, eq 1, or rearrangements, eq 2; both
may be effected catalytically under appropriate conditions.2,3
Figure 1. Structure of 2a.
significant differences in chemistry that may exist due to the
capacity for metal-metal (Fe-Fe) interactions.
Fp-SiMe2SiMe3 f Fp-SiMe3 + [SiMe2]
Fp-SiMe2SiMe2SiMe2SiMe3 f FpSi(SiMe3)3
(1)
(2)
We have now synthesized the bimetallic complexes FpCH2-
MeRSiSiRMeCH2Fp, R ) Me (1) and Ph (2), and report an
unprecedented photoreaction leading to the quantitative formation
of 1,3-disilacyclobutanes. Complex 18 was prepared in 64% yield
from the reaction of ClCH2Me2SiSiMe2CH2Cl9 with [Fp]-Na+,
while similar treatment of ClCH2MePhSiSiMePhCH2Cl10 afforded
2 in 24% yield, eq 5.
When the metal substituent is attached to the oligosilyl group
via a bridging methylene group, â-elimination chemistry results
in the formation of iron-silene intermediates that lead either to
rearrangements, eq 3 (R ) H, (SiMe2)nSiMe3, GeMe3), or silene
elimination, eq 4 (R ) GeMe3, Wp ) (η5-C5H5)W(CO)3).2a,4
[Fp]-Na+ + [ClCH2SiMeR]2 f
Fp-CH2SiMe2R f Fp-SiMe2CH2R
(3)
(4)
FpCH2SiMeRSiMeRCH2Fp (5)
Wp-CH2SiMe2R f Wp-R + Me2SidCH2
1H and 13C NMR spectra of 2 indicate a mixture of two isomers,
with one isomer dominant (meso/dl ) 5:1). Recrystallization of
2 from a mixture of CH2Cl2/hexane yielded prisms and the isomers
2a (meso) and 2b (dl) could be separated mechanically.11
The single-crystal structure of 2a is illustrated in Figure 1.12
The molecule consists of two identical [(η5-C5H5)Fe(CO)2CH2-
SiMePh] moieties bonded by a Si-Si bond and has Ci symmetry.
The Fe-C(8) bond length (2.092(3) Å) is in the range of the
normal Fe-C (sp3) bond distances (2.08-2.16 Å).13 The Si-Si
The silene metal intermediates involved in eq 3 (R ) H)4a have
been characterized only by low-temperature matrix-isolation
techniques.5 However, many stable transition metal silene com-
plexes have been isolated and characterized by the research groups
of Berry and Tilley.6
Scheme 1
(6) (a) Koloshi, T. S.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 1990,
112, 6405. (b) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc.
1990, 112, 4079.
(7) (a) Pannell, K. H.; Sharma, H. K. Organometallics 1991, 10, 954. (b)
Ueno, K.; Hamashima, N.; Ogino, H. Organometallics 1991, 10, 959.
(8) Mp 104-6 °C. Anal. Calcd. for C20H26Fe2O4Si2: C, 48.21; H, 5.26.
Found: C, 47.76; H, 5.54. 1H NMR (C6D6) δ 0.16 (s, 4H, CH2), 0.47 (s,
12H, SiMe), 4.27 (s, 8H, Cp). 13C NMR (C6D6) δ -23.6 (CH2), 0.16 (SiMe),
85.0 (Cp), 218.3 (CO). 29Si NMR (C6D6) δ -6.03. IR (νCO, cm-1) 2009(s),
1958(s).
(9) Kobayashi, T.; Pannell, K. H. Organometallics 1991, 10, 1960.
(10) ClCH2MePhSiSiPhMeCH2Cl was similarly synthesized as a mixture
of two isomers (1:0.7) in 85% by a literature procedure.9 1H NMR (C6D6) δ
The related chemistry of bimetallic systems is less studied.
Scheme 1 illustrates the sequential formation of silylene iron
complexes by photolysis of FpSiMe2SiMe2Fp,7 indicating the
2
0.42 (s, 6H, SiMe), 2.93 (AB, J ) 13.6 Hz, 4H, CH2), 7.11-7.34 (m, 10H,
2
Ph), 0.43 (s, 6H, SiMe), 2.92 (AB, J ) 13.5 Hz, 4H, CH2), 7.11-7.34 (m,
(1) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351.
(2) (a) Pannell, K. H.; Rice, J. J. Organomet. Chem. 1974, 78, C35. (b)
Pannell, K. H.; Cervantes, J.; Hernandez, C.; Cassias, J.; Vincenti, S. P.
Organometallics 1986, 5, 1056. (c) Pannell, K. H.; Wang, L.-J.; Rozell, J. M.
Organometallics 1989, 8, 550. (d) Jones, K.; Pannell, K. H. J. Am. Chem.
Soc. 1993, 115, 11336. (e) Pannell, K. H.; Brun, M.-C.; Sharma, H. K.; Jones,
K.; Sharma, S. Organometallics 1994, 13, 3, 1075.
(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.
(4) (a) Pannell, K. H. J. Organomet. Chem. 1970, 21, 17. (b) Sharma, S.;
Kapoor, R. N.; Cervantes-Lee, F.; Pannell, K. H. Polyhedron 1991, 10, 1177.
(c) Pannell, K. H.; Kobayashi, T.; Kapoor, R. N. Organometallics 1992, 11,
1, 2229. (d) Sharma, S.; Pannell, K. H. Organometallics 1993, 12, 2, 3979.
(5) Randolf, C. L.; Wrighton, M. S. Organometallics 1987, 6, 365.
10H, Ph). 13C NMR (C6D6) δ -6.18, -5.91 (SiMe), 29.5, 29.6 (CH2), 128.5,
129.9, 134.6, 134.7 (Ph). 29Si NMR (C6D6) δ -18.6, -18.5.
(11) For 2a: Mp 146-8 °C. Anal. Calcd for C30H30Fe2O4Si2: C, 57.89;
H, 4.86. Found: C, 58.17; H, 4.39. 1H NMR (C6D6) δ 0.02 (d, 2J ) 12.6 Hz,
2H, CH2), 0.44 (d, 2J ) 12.6 Hz, 2H, CH2), 0.66 (s, 6H, SiMe), 3.97 (s, 8H,
Cp), 7.23, 7.55 (m, m, 10H, Ph). 13C NMR (C6D6) δ -26.6 (CH2), -2.42
(SiMe), 84.6 (Cp), 128.0, 128.5, 134.7, 142.4 (Ph), 217.86, 217.93 (CO).29Si
NMR (C6D6) δ -9.00. IR (νCO, cm-1) 2011(s), 1959(s). For 2b: Mp 116-8
°C. Anal. Calcd. for C30H30Fe2O4Si2: C, 57.89; H, 4.86. Found: C, 57.10; H,
3.78. 1H NMR (C6D6) δ 0.04 (d, 2J ) 12.6 Hz, 2H, CH2), 0.43 (d, 2J ) 12.6
Hz, 2H, CH2), 0.64 (s, 6H, SiMe), 4.00 (s, 8H, Cp), 7.22, 7.57 (m, m, 10H,
Ph). 13C NMR (C6D6) δ -26.8 (CH2), -2.16 (SiMe), 84.7 (Cp), 128.0, 128.5,
134.7, 142.3 (Ph), 217.9 (CO). 29Si NMR (C6D6) δ -9.07. IR (νCO, cm-1
2009(s), 1959(s).
)
10.1021/ja994392p CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/11/2000

8328 J. Am. Chem. Soc., Vol. 122, No. 34, 2000
Communications to the Editor
bond length (2.359(1) Å) is equivalent to those in LFeSiMe2-
SiMe3 (2.361-2.364 Å)14 and shorter than that of the bimetallic
complex FpSiMe2SiMe2Fp (2.390(4) Å).15
Scheme 2
Irradiation of a C6D6 solution of 1 with a medium-pressure
Hg lamp in a sealed NMR tube resulted in the quantitative
formation of [(η5-C5H5)Fe(CO)2]2 and 1,3-tetramethyldisilacy-
clobutane 3 (eq 6).16
Photolysis of 2a (meso) for 2 h afforded only the trans-1,3-
disilacyclobutane 4t, while similar photolysis of 2b (dl) afforded
only the cis-1,3-disilacyclobutane 4c, eq 7.17 The photoreactions
are stereospecific.
It is reported that “unstable” silenes carrying small alkyl
substituents readily dimerize in a head-to-tail fashion to yield 1,3-
disilacyclobutanes,18 while stable silenes, e.g. (Me3Si)2SidC-
(OSiMe3)R, preferentially yield the head-to-head dimers, 1,2-
disilacyclobutanes.19 Since the photoreactions involving free silene
yield a mixture of the cis and trans isomers of 1,3-disilacyclobu-
tanes, it is unlikely that free silene was produced by photolysis
of 1 and 2.20 Furthermore, the chemistry noted in eq 4 in which
silene is liberated never produced silacyclobutanes.4b To further
prove this point we have photolyzed a mixture of 1 and 2a and
observed no cross-over products; the photoreactions proceed via
an intramolecular pathway.
The stereospecific formation of 4 suggests a special interaction
of the complexed silenes upon adjacent metal centers prior to
elimination of the product. The mechanism presented in Scheme
2 is our current suggestion. Each step must be stereospecific and
the transient formation of iron centers which themselves are
potentially enantiomeric may play an important role in the
stereochemical outcome of the coupling reaction. It is possible
that a direct 1,4-elimination reaction and transient 1,2-disilacy-
clobutanes are involved, but presently we have no evidence for
these species. Finally, as is often the case in the area of
organosilicon chemistry, early studies by the Kumada group are
relevant. In 1977 they reported that the reaction of XCH2SiMe2-
SiMe2CH2X (X ) Br, I) with Mg resulted in the formation of 3.
Furthermore, 1-metallo-3,4-disilacyclopentanes of Pt and Ni also
led to formation of 3 under certain conditions. Bis-silene metal
intermediates were suggested.21
(12) Data collected using a Siemens R3m/V diffractometer and Mo KR
radiation. 2a: triclinic; space group P1h; a ) 8.607(2) Å, b ) 9.509(2) Å, c
) 9.819(2) Å, R ) 86.84(2)°, â ) 64.95(1)°, γ ) 86.58(2)°; Z ) 1; R )
4.13; GOF ) 1.03. Selected bond distances (Å) and angles (deg): Fe-C(8)
2.092(3), Si-SiA 2.359(1), Fe-C(8)-Si 120.5(1).
(13) Kruger, C.; Barnett, B. L.; Brauer, D. Structure and Bonding in
Organic Iron Compounds; The Organic Chemistry of Iron; Koerner Von
Gustorf, E. A., Grevels, F. W., Fischler, I., Eds.; Academic Press: New York,
1978; Vol. 1, p 3.
(14) Pannell, K. H.; Lin, S.-H.; Kapoor, R. N.; Cervantes-Lee, F.; Pinon,
M.; Parkanyi, L. Organometallics 1990, 9, 2454.
(15) Pannell, K. H.; Cervantes, J.; Parkanyi, L.; Cervantes-Lee, F. Orga-
nometallics 1990, 9, 859.
(16) Complex 3 has been characterized by 1H, 13C, and 29Si NMR and GC/
Overall the new chemistry presents a very unusual and
potentially general route to coupling of reagents bonded to
adjacent metals and we are continuing our study to flush out the
details and generality of the process.
1
MS. H NMR (C6D6) δ 0.12 (s, 4H, CH2), 0.24 (s, 12H, SiMe2). 13C NMR
(C6D6) δ 2.56 (SiMe2), 3.99 (CH2).29Si NMR (C6D6) δ -2.54. Mass: m/e
144 (M, 20%), 129 (M - Me, 100%). Kriner, W. A. J. Org. Chem. 1964, 29,
1601.
1
(17) Compounds 4t and 4c have been characterized by H, 13C, and 29Si
NMR and GC/MS and are in accord with the literature where 4t and 4c were
separated by preparative GLC and the single-crystal structure of 4t was also
reported. Hayakawa, K.; Tachikawa, M.; Suzuki, T.; Choi, N.; Murakami,
M. Tetrahedron Lett. 1995, 36, 3181l.
(18) For reviews see: (a) Gusel’nikov, L. E.; Nametkin, N. S. Chem. ReV.
1979, 79, 529. (b) Baines, K. M.; Brook, A. G. AdV. Organomet. Chem. 1986,
25, 1.
(19) (a) Brook, A. G.; Harris, J. W.; Lennon, J.; El Sheikh, M. J. Am.
Chem. Soc. 1979, 101, 83. (b) Baines, K. M.; Brook, A. G.; Ford, R. R.;
Lickiss, P. D.; Saxena, A. K.; Chatterton, W. J.; Sawyer, J. F.; Behnam, B.
A. Organometallics 1989, 8, 693.
(20) (a) Braddock-Wilking, J.; Chiang, M. Y.; Gaspar, P. P. Organome-
tallics 1993, 12, 197. (b) Volkova, V. V.; Gusel’nikov, L. E.; Volvina, E. A.;
Buravtseva, E. N. Organometallics 1994, 13, 4661.
Acknowledgment. This research was supported by the Robert A.
Welch Foundation, Houston, TX (grant no. AH-546).
Supporting Information Available: Listings of crystal data, date
collection, solution and refinement, complete atomic coordinates, bond
distances and angles, and anisotropic thermal parameters for 2a and
synthetic details (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA994392P
(21) Tamao, K.; Yoshida, J.; Okazaki, S.; Kumada, M. Isr. J. Chem. 1977,
15, 265.