Synthesis and structure of [Fe(η5-C9Me6) (η5-C5H4)SiMe2]: A mixed-ring [1]ferrocenophane

Article abstract of DOI:10.1021/om980988u

A new bridged ligand incorporating the hexamethylindenyl moiety has been synthesized and used to prepare the corresponding ansa ferrocene, [Fe(η⁵-C₉-Me₆)(η⁵-C ₅H₄)SiMe₂], 10, which is the first mixed-ring [1]ferrocenophane to be structurally characterized. Comparison of the crystal structure of 10 with those of [Fe-(η⁵-C₅H₄)₂SiMe₂], 1, and rac-[Fe(η⁵-C₉Me₆)₂SiMe ₂], 5a, shows many structural features, such as the ring tilt of 17°, to be intermediate between those of the two model compounds, while the average Si-C(ipso) bond length is much closer to that in 5a.

Full text of DOI:10.1021/om980988u

Organometallics 1999, 18, 2281-2284
2281
Syn th esis a n d Str u ctu r e of [F e(η5-C9Me6)(η5-C5H4)SiMe2]:
A Mixed -Rin g [1]F er r ocen op h a n e
J onathan Tudor, Stephen Barlow, Benjamin R. Payne, and Dermot O’Hare*
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road,
Oxford, OX1 3QR, U.K.
Paul Nguyen, Christopher E. B. Evans, and Ian Manners
Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario M5S 3H6, Canada
Received December 4, 1998
Summary: A new bridged ligand incorporating the hex-
amethylindenyl moiety has been synthesized and used
to prepare the corresponding ansa ferrocene, [Fe(η5-C9-
Me6)(η5-C5H4)SiMe2], 10, which is the first mixed-ring
[1]ferrocenophane to be structurally characterized. Com-
parison of the crystal structure of 10 with those of [Fe-
(η5-C5H4)2SiMe2], 1, and rac-[Fe(η5-C9Me6)2SiMe2], 5a ,
shows many structural features, such as the ring tilt of
17°, to be intermediate between those of the two model
compounds, while the average Si-C(ipso) bond length
is much closer to that in 5a .
In tr od u ction
One of the most interesting and useful features of [1]-
ferrocenophanes is their ability to undergo stoichiomet-
ric ring-opening reactions. These reactions have been
used to obtain high molecular weight organometallic
polymers,1-3 which have been studied for applications
ranging from electrochromic films4 to precursors for new
ceramics,5 and to derivatize surfaces6 and the walls of
mesoporous solids.7-9 As part of an effort to understand
the relationship between the electronic and structural
features of these compounds, we have reported studies
of a series of ring-methylated SiMe2-bridged [1]ferro-
cenophanes (1-4, Figure 1) using 57Fe Mo¨ssbauer, UV-
vis and UV-photoelectron spectroscopy, crystallogra-
phy, electrochemistry, and density functional theory.10,11
We have also reported the synthesis and structure of
F igu r e 1. Some SiMe2-bridged [1]ferrocenophanes.
F igu r e 2. Some parameters useful for the discussion of
the structures of [1]ferrocenophanes.
the first dibenzo[1]ferrocenophane (i.e., the first bridged
bis(indenyl)iron complex): [Fe(η5-C9Me6)2SiMe2], 5 (Fig-
ure 1).12 We found a correlation between the electro-
chemical oxidation potential, E1/2, and the crystallo-
graphically determined ring tilt, R (defined by Figure
2); both E1/2 and R decrease along the series 1, 2, 4, 5,
the decrease in R being compensated by an increase in
the structural distortion of the bridging group. This
correlation can be understood in terms of the greater
energy cost calculated to be associated with ring tilt in
more electron-rich methylated metallocenes.11 We were
interested in investigating what structural features
would be found in a compound such as 3, in which the
two coordinated rings differed markedly in their elec-
tronic properties. However, crystals of 3 suitable for a
structure determination have not been obtained. Hence,
we report here on the synthesis, structure, and polym-
erization behavior of [Fe(η5-C9Me6)(η5-C5H4)SiMe2], 10,
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58.
10.1021/om980988u CCC: $18.00 © 1999 American Chemical Society
Publication on Web 04/25/1999

2282 Organometallics, Vol. 18, No. 11, 1999
Notes
Sch em e 1a
a
Legend: (i) Me2SiCl2, petroleum ether (bp 40-60 °C); (ii) NaCp or MgCp2, THF; (iii) nBuLi, TMEDA, petroleum ether (bp
40-60 °C); (iv) FeCl2‚1.5THF or FeBr2‚2THF, THF; (v) MeOH, THF.
which combines the ligated rings from the two extreme
members of the series 1-5.
Resu lts a n d Discu ssion
The synthesis of [Fe(η5-C9Me6)(η5-C5H4)SiMe2], 10, is
outlined in Scheme 1. Reaction of lithium 1,2,4,5,6,7-
hexamethylindenide, 6,12 with dichlorodimethylsilane
gave [(C9Me6H)SiMe2Cl], 7, which can be converted to
[(C9Me6H)(C5H5)SiMe2], 8, with either sodium cyclopen-
tadienide or magnesocene. Reaction of doubly lithiated
8 (9) with either FeCl2‚1.5THF or FeBr2‚2THF in THF
gave modest yields of [Fe(η5-C9Me6)(η5-C5H4)SiMe2], 10.
1H and 13C NMR spectroscopy, mass spectrometry,
and X-ray crystallography (vide infra) all show 10 to be
a strained monomeric species (rather than a dimer or
higher oligomer). The large spread in C5H4 1H chemical
shifts is typical of ring-tilted ferrocenes. The 13C signals
corresponding to the ipso bridgehead carbons of 10 occur
at chemical shifts (δ in C6D6) of 21.0 and 33.9 ppm.
These values, although very low δ for formally sp2
carbons, are typical for the ipso carbons of strained
ferrocenophanes, reflecting the nonplanar geometry
around these atoms (which is seen in their crystal
structures); the corresponding resonances for 1, 5a , and
5b are seen at 33.5, 21.7, and 20.3 ppm, respectively.12
Single crystals of 10 were obtained by slow cooling of
a pentane solution. The crystal structure was solved and
refined in the centrosymmetric space group P1h, with one
molecule in the asymmetric unit. Figure 3 shows the
molecular structure, while Figure 2 defines the param-
eters used in the following discussion. The Fe-C bond
lengths are similar to those in other silicon-bridged
[1]ferrocenophanes;10,12-19 the longest Fe-C bonds are
those to the carbons at the indenyl ring junction, as is
found for other η5-indenyl compounds (for examples see
refs 20-2716) including 5a .12 The ring tilt (R) for 10
F igu r e 3. Molecular structure of 10 (50% thermal prob-
ability ellipsoids, H atoms excluded for clarity). Selected
bond lengths: Fe(1)-C(1) 2.010(4) Å, Fe(1)-C(2) 2.017(5)
Å, Fe(1)-C(3) 2.063(5) Å, Fe(1)-C(4) 2.069(5) Å, Fe(1)-
C(5) 2.015(5) Å, Fe(1)-C(6) 2.010(4) Å, Fe(1)-C(7) 2.032-
(4) Å, Fe(1)-C(8) 2.056(4) Å, Fe(1)-C(9) 2.094(4) Å, Fe(1)-
C(10) 2.093(4) Å.
(17.2°) is similar to the average (17.1°) of those for 1
(20.8°)14 and 5a (average 13.4° for two inequivalent
molecules),12 consistent with 10 being electronically
intermediate between 1 and 5a . The angle (â1) between
the cyclopentadienyl ring of 10 and the ipso carbon-
silicon (C1-Si) bond is 39.2°, while the corresponding
angle, â2, for the permethylindenyl side of the molecule
is 41.2°. The angles, âav, for 1 and 5a are 37.0° and 42.2°,
(18) Pudelski, J . K.; Rulkens, R.; Foucher, D. A.; Lough, A. J .;
Macdonald, P. M.; Manners, I. Macromolecules 1995, 28, 7301-7308.
(19) Zechel, D. L.; Hultzsch, K. C.; Rulkens, R.; Balaishis, D.; Ni,
Y. Z.; Pudelski, J . K.; Lough, A. J .; Manners, I. Organometallics 1996,
15, 1972-1978.
(20) Treichel, P. M.; J ohnson, J . W.; Calabrese, J . C. J . Organomet.
Chem. 1975, 88, 215.
(21) Honan, M. B.; Atwood, J . L.; Bernal, I.; Herrmann, W. A. J .
Organomet. Chem. 1979, 179, 403-410.
(22) Bell, W. L.; Curtis, C. J .; Eigenbrot, C. W.; Pierpont, C. G.;
Robbins, J . L.; Smart, J . C. Organometallics 1987, 6, 266-273.
(23) Westcott, S. A.; Kakkar, A. K.; Stringer, G.; Taylor, N. J .;
Marder, T. B. J . Organomet. Chem. 1990, 394, 777-794.
(24) Bonifaci, C.; Ceccon, A.; Gambaro, A.; Ganis, P.; Santi, S.; Valle,
G.; Venzo, A. Organometallics 1993, 12, 4211-4214.
(25) O’Hare, D.; Murphy, V. J .; Kaltsoyannis, N. J . Chem. Soc.,
Dalton Trans. 1993, 383-392.
(26) O’Hare, D.; Murphy, V.; Diamond, G. M.; Arnold, P.; Mountford,
P. Organometallics 1994, 13, 4689-4694.
(27) Barlow, S.; Cary, D. R.; Drewitt, M. J .; O’Hare, D. J . Chem.
Soc., Dalton Trans. 1997, 3867-3878.
(13) Stoeckli-Evans, H.; Osborne, A. G.; Whiteley, R. H. Helv. Chim.
Acta 1976, 59, 2402-2406.
(14) Finckh, W.; Tang, B.-Z.; Foucher, D. A.; Zamble, D. B.; Ziem-
binski, R.; Lough, A. J .; Manners, I. Organometallics 1993, 12, 823-
829.
(15) Pannell, K. H.; Dementiev, V. V.; Li, H.; Cervantes-Lee, F.;
Nguyen, M. T.; Diaz, A. F. Organometallics 1994, 13, 3644-3650.
(16) Foucher, D. A.; Lough, A. J .; Manners, I.; Rasburn, J .; Vansco,
J . G. Acta Crystallogr. 1995, C51, 580-582.
(17) Edwards, M.; Foucher, D. A.; Lough, A. J .; Manners, I. Z
Kristallogr. 1995, 210, 865-867.

Notes
Organometallics, Vol. 18, No. 11, 1999 2283
used as an internal reference. Oxygen- or water-sensitive
materials were handled using standard Schlenk techniques
or a Vacuum Atmospheres glovebox. Where necessary, solvents
were dried by distillation under nitrogen from potassium
(THF, benzene-d6) or sodium-potassium alloy (pentane, pe-
troleum ether (bp 40-60 °C), diethyl ether). Reagents were
either synthesized according to the references given or were
purchased from Aldrich and used without further purification,
unless stated otherwise.
respectively. The Fe-Si distance of 2.668(1) Å and the
angles δ (167.5°), θ (97.4(2)°) and Me-Si-Me (106.8-
(3)°) are also intermediate between the corresponding
values for 1 and 5a . However, while the average Si-
C(ipso) bond lengths steadily increase from 1.858(9)° for
1 to 1.905(8)° for 5a as R decreases, both the Si-C(ipso)
bonds in 10 are rather long: Si-C1 (cyclopentadienyl)
and Si-C6 (permethylindenyl) distances for 10 are
1.886(5)° and 1.927(4)°, respectively.
Attempts to compare the electrochemistry of 10 to
that of 1-5 were complicated by the appearance of
additional features in the cyclic voltammogram, and of
a precipitate, after several scans. Thus, 10+ is rather
less stable than the cations of 1-5; the reasons for this
are unclear. We estimate the half-wave potential for the
10+/10 couple to be -150 mV vs ferrocenium/ferrocene.
It is surprsing that this value is much closer to that for
1 (0 mV) than for 5 (-690 mV). The value for 3 (-210
mV), by contrast, is close to the average of the values
for 1 and 4 (-390 mV).
Differential scanning calorimetric (DSC) studies of 10
showed endotherms at 50 and 160 °C, with no evidence
for any polymerization exotherm below 300 °C (the
highest temperature examined). Gel permeation chro-
matography (GPC) showed no high molecular weight
products from a bulk polymerization attempt at 260 °C
(8 h), although 1H NMR spectroscopy showed that no
10 remained, thus suggesting that the higher of the two
endotherms relates to decomposition of 10. Attempts to
thermally ring-opening polymerize 5 also result in
decomposition.28 [1]Ferrocenophanes have also been
polymerized at room temperature using late transition
metal catalysts;29,30 therefore, we attempted to polymer-
ize 10 using platinum(II) chloride in C6D6. After 5 days,
1H NMR spectroscopy showed only unchanged 10 and
GPC showed no high molecular weight products.
The reaction of 10 with methanol gave a single ring-
opened product, [Fe(η5-C9Me6H)(η5-C5H4SiMe2OMe], 11,
with no evidence for the formation of [Fe(η5-C9Me6-
SiMe2OMe)(η5-C5H5)]. The observed regiospecificity sug-
gests that this ring-opening may proceed via protonation
of the most electron-rich ipso carbon, rather than by
nucleophilic attack at silicon followed by ring opening
to give the most stable carbanion. The same regioselec-
tivity was observed when 10 was ring-opened to func-
tionalize the pores of the mesoporous silica FSM-16.9
Syn th esis. [(C9Me6H)SiMe2Cl], 7. A solution of dimeth-
yldichlorosilane (freshly distilled from magnesium turnings,
34 mL, 280 mmol) in petroleum ether (bp 40-60 °C) (500 mL)
was added dropwise to a stirred slurry of [C9Me6HLi],12 6, (53.0
g, 257 mmol) in petroleum ether (bp 40-60 °C) (100 mL) at
room temperature. After stirring the reaction mixture for a
further 18 h, the mixture was filtered through Celite, concen-
trated under reduced pressure, and cooled to -80 °C. [C9Me6-
HSiMe2Cl], 7 (14.5 g, 49 mmol, 66%), was obtained as white
1
needles. Anal. Found (calcd): C, 69.9 (69.7); H, 9.0, (8.6). H
NMR (C6D6): δ -0.09 (s, 3H), 0.20 (s, 3H), 2.06 (s, 3H), 2.12
(apparent s, 6H), 2.13 (s, 3H), 2.15 (s, 3H), 2.42 (s, 3H), 3.48
(s, 1H). 13C NMR (C6D6): δ -0.5, 3.21, 15.2, 15.3, 16.2, 16.3,
16.4, 19.2, 49.7, 126.5, 127.5, 130.4, 133.1, 134.4, 137.9, 139.7,
142.1. MS (EI): m/z 293 (M+, 71%), 258 (M+ - Cl, 96), 200
(M+ - SiMe2Cl, 50).
[(C9Me6H)(C5H 4)SiMe2], 8. Met h od A. A solution of
sodium cyclopentadienide31 (1.36 g, 15.4 mmol) in THF (50 mL)
was added dropwise to a solution of 7 (4.5 g, 15.4 mmol) in
THF (75 mL) at 0 °C. The reaction mixture was then allowed
to warm to room temperature and stirred for a further 20 h.
Excess solid ammonium chloride was then added to the
reaction mixture, the solvent was removed under reduced
pressure, and the residue was extracted with pentane. Evapo-
ration of the pentane extracts under reduced pressure afforded
a white solid (3.27 g, 9.86 mmol, 60%).
Meth od B. A solution of 7 (45.0 g, 154 mmol) in THF (600
mL) was added dropwise to a solution of magnesocene32 (13.0
g, 84 mmol) in THF (200 mL) at 0 °C. The reaction mixture
was then allowed to warm to room temperature and stirred
for a further 16 h. The reaction was worked up in a fashion
analogous to method A (45.3 g, 140 mmol, 91%). In each case
8 was converted to 9 without further characterization owing
to its poor thermo- and photostability.
[(C9Me6Li)(C5H3Li)SiMe2], 9. A hexane solution of n-
butyllithium (112 mL of a 2.74 M solution, 307 mmol) was
added dropwise to a solution of 8 (45.3 g, 140 mmol) and
N,N,N′,N′-tetramethylethylenediamine (TMEDA, distilled from
calcium hydride, 46 mL, 310 mmol) in petroleum ether (bp
40-60 °C) (800 mL) at 0 °C. The reaction mixture was then
allowed to warm to room temperature and stirred for a further
12 h, after which time the precipitate was collected on a frit,
washed with diethyl ether (100 mL) and petroleum ether (bp
40-60 °C) (100 mL), and dried in vacuo to give 9 as a white
air-sensitive powder (46.4 g, 139 mmol, 99% assuming no
TMEDA incorporation).
Exp er im en ta l Deta ils
Gen er a l P r oced u r es. Elemental analyses were performed
by the analytical department of the Inorganic Chemistry
Laboratory. NMR spectra were recorded using a Bruker AM
300 or a Varian Unity Plus 500. Spectra were referenced
relative to tetramethylsilane using the residual protio-solvent
signal. Electron impact mass spectra were recorded using a
VG 70-250-S instrument. Cyclic voltammograms were recorded
using a platinum working and auxiliary and silver wire
pseudo-reference electrode. Measurements were made under
nitrogen on deoxygenated dry dichloromethane solutions ca.
10-2 M in sample and 0.1 M in [Bu4N]+[PF6]-. Ferrocene was
[F e(η5-C9Me6)(η5-C5H4)SiMe2], 10. A solution of 9 (1.19 g,
3.46 mmol) in THF (50 mL) was added dropwise over 1.5 h to
a slurry of FeCl2‚1.5THF33 (0.85 g, 4.26 mmol) in THF (50 mL)
at 0 °C. The reaction mixture was then allowed to warm to
room temperature and stirred for a further 3 h; the solvent
was then removed under reduced pressure, and the residue
was extracted with pentane. The pentane extracts were filtered
through Celite, concentrated under reduced pressure, and
cooled to -30 °C to give air-sensitive dark red crystals of 10
(0.365 g, 28%). In another reaction, FeBr2‚2THF33 was used
in place of FeCl2‚1.5THF, and the reaction mixture was only
(28) Nelson, J . M.; Nguyen, P.; Barlow, S.; Al´ıas, F. M.; O’Hare, D.;
Manners, I. Unpublished results.
(29) Reddy, N. P.; Yamashita, H.; Tanaka, M. J . Chem. Soc., Chem.
Commun. 1995, 2263-2264.
(30) Ni, Y.; Rulkens, R.; Pudelski, J . K.; Manners, I. Makromol.
Chem., Rapid Commun. 1995, 14, 637-641.
(31) Wilkinson, G. Org. Synth. 1956, 36, 31-32.
(32) Duff, A. W.; Hitchcock, P. B.; Lappert, M. F.; Taylor, R. G.;
Segal, J . A. J . Organomet. Chem. 1985, 293, 271-283.
(33) Ittel, S. D.; English, A. D.; Tolman, C. A.; J esson, J . P. Inorg.
Chim. Acta 1979, 33, 101-106.

2284 Organometallics, Vol. 18, No. 11, 1999
Notes
stirred for 0.5 h at 0 °C before solvent removal (yield, 35%).
Anal. Found (calcd): C, 69.9 (70.2); H, 7.7 (7.5); Fe, 14.8 (14.5).
1H NMR (C6D6): δ 0.75 (s, 3H), 0.90 (s, 3H), 1.83 (s, 3H), 1.99
(s, 3H), 2.06 (s, 3H), 2.35 (s, 3H), 2.41 (s, 3H), 2.57 (s, 3H),
3.12 (m, 1H), 3.30 (m, 1H), 3.74 (m, 1H), 4.39 (m, 1H). 13C NMR
(C6D6): δ 2.2, 4.8, 15.2, 15.4, 16.5, 16.9, 17.5, 21.0, 22.2, 33.9,
76.4, 78.3, 79.1, 79.2, 84.5, 92.8, 93.7, 100.6, 129.4, 130.8, 132.6,
133.4. MS (EI): m/z 376 (M+, 100), 361 (M+ - Me, 55).
Rea ction of 10 w ith Meth a n ol. Methanol (1 mL) was
added to a solution of 10 (100 mg) in THF (30 mL) at -78 °C.
The reaction mixture was then allowed to warm to room
temperature and stirred for a further 12 h; the solvent was
then removed under reduced pressure, and the residue was
extracted into benzene-d6. 1H NMR (C6D6): δ 0.30 (s, 3H), 0.36
(s, 3H), 1.85 (s, 3H), 2.07 (s, 3H), 2.09 (s, 3H), 2.33 (s, 3H),
2.41 (s, 3H), 2.58 (s, 3H), 3.28 (s, 3H), 3.50 (m, 1H), 3.52 (m,
1H), 3.61 (m, 1H), 4.03 (m, 1H), 4.63 (s, 1H). 13C NMR (C6D6):
δ -1.7, -1.6, 13.9, 14.9, 16.4, 16.6, 16.8, 16.9, 50.0, 61.6, 70.2,
72.6, 73.8, 73.9, 74.0, 75.8, 85.0, 86.5, 87.6, 129.1, 129.9, 130.0,
131.3.
Cr ysta l Str u ctu r e of 10. Single crystals of C22H28FeSi, fw
) 376.40, were grown by slow cooling of a pentane solution. A
dark red plate (0.09 × 0.54 × 0.62 mm3) was mounted on an
Enraf Nonius CAD-4 diffractometer, using Mo KR radiation
and found to be triclinic with a ) 8.753(4) Å, b ) 9.251(2) Å,
c ) 12.052(3) Å, R ) 92.05(2)°, â ) 105.17(2)°, γ ) 109.21(2)°,
V ) 963(1) Å3, Z ) 2, and µ ) 0.880 mm-1; 2985 (2570
independent, 1954 with I > 2σ(I)) reflections were measured
over the range 0-23.0° at 298 K using ω-2θ scans. The
structure was solved in the space group P1h using SIR92;34 all
non-hydrogen atoms were revealed by the direct methods
solution, while hydrogen atoms were placed in geometrically
idealized positions and given isotropic thermal parameters. An
absorption correction was applied using DIFABS.35 A Cheby-
shev weighting scheme was applied in the refinement.36
Corrections for anomalous dispersion and isotropic extinction
were made via an overall extinction parameter.37 Full refine-
ment (positional and anisotropic displacement parameters of
non-hydrogen atoms, positional and isotropic displacement
parameters of hydrogen atoms) on F converged with R )
0.0480, Rw ) 0.0567, S ) 1.090, ∆Fmax ) 0.47 e Å-3, and ∆Fmin
) -0.50 e Å-3. All crystallographic calculations were per-
formed using CRYSTALS38 running on a Silicon Graphics
Indigo R3000.
Ackn owledgm en t. We thank the EPSRC and NATO
for support; J .T. thanks Shell plc for a CASE student-
ship.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
structure solution and refinement details, atomic coordinates
and equivalent isotropic displacement parameters, bond lengths
and angles, anisotropic displacement parameters, hydrogen
coordinates, and isotropic displacement parameters for 10.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM980988U
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