Synthesis, structures, and properties of strained spirocyclic [1]sila- and [1]germaferrocenophanes and tetraferrocenylsilane

Article abstract of DOI:10.1021/om971071i

The spirocyclic [1]ferrocenophanes [Fe(η-C₅H₄)₂]₂E (3, E = Si; 4, E = Ge) and Fe(η-C₅H₄)₂-Si(CH₂)₃ (5) have been prepared by the reaction of Fe(η-C₅H₄Li)₂·TMEDA (TMEDA = tetramethylethylenediamine) with SiCl₄, GeCl₄, and Cl₂Si(CH₂)₃, respectively. Single-crystal X-ray diffraction studies of 3-5 revealed that the molecules possess highly strained structures with tilt angles between the planes of the cyclopentadienyl rings of 19.4(2), 19.1(5), and 20.61(8)°, respectively. The Fe- - -Fe distances in 3 and 4 are 5.314(1) and 5.518(4) A?, and evidence for metal-metal interactions in the form of substantial redox coupling (ΔE_1/2 = 0.37 V for 3 and 0.25 V for 4) is present in the cyclic voltammograms of these species. For structural comparison, the tetraferrocenylsilane [(η-C₅H₅)Fe(η-C₅H₄)] ₄Si (6) was prepared and was characterized by single-crystal X-ray diffraction. Cyclic voltammetry of 6 showed four reversible oxidation waves with E_1/2 values of -0.03 to +0.39 V versus ferrocene; ΔE_1/2 values of 0.10-0.18 V were indicative of significant metal-metal interactions. The results of Mo?ssbauer, IR, and Raman studies of compounds 3, 4, and 6 are also discussed.

Full text of DOI:10.1021/om971071i

Organometallics 1998, 17, 1873-1883
1873
Syn th esis, Str u ctu r es, a n d P r op er ties of Str a in ed
Sp ir ocyclic [1]Sila - a n d [1]Ger m a fer r ocen op h a n es a n d
Tetr a fer r ocen ylsila n e
Mark J . MacLachlan,† Alan J . Lough,† William E. Geiger,*,‡ and Ian Manners*,†
Departments of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6,
Ontario, Canada, and University of Vermont, Burlington, Vermont 05405-0125
Received December 6, 1997
The spirocyclic [1]ferrocenophanes [Fe(η-C5H4)2]2E (3, E ) Si; 4, E ) Ge) and Fe(η-C5H4)2-
Si(CH2)3 (5) have been prepared by the reaction of Fe(η-C5H4Li)2‚TMEDA (TMEDA )
tetramethylethylenediamine) with SiCl4, GeCl4, and Cl2Si(CH2)3, respectively. Single-crystal
X-ray diffraction studies of 3-5 revealed that the molecules possess highly strained structures
with tilt angles between the planes of the cyclopentadienyl rings of 19.4(2), 19.1(5), and
20.61(8)°, respectively. The Fe- - -Fe distances in 3 and 4 are 5.314(1) and 5.518(4) Å, and
evidence for metal-metal interactions in the form of substantial redox coupling (∆E1/2
)
0.37 V for 3 and 0.25 V for 4) is present in the cyclic voltammograms of these species. For
structural comparison, the tetraferrocenylsilane [(η-C5H5)Fe(η-C5H4)]4Si (6) was prepared
and was characterized by single-crystal X-ray diffraction. Cyclic voltammetry of 6 showed
four reversible oxidation waves with E1/2 values of -0.03 to +0.39 V versus ferrocene; ∆E1/2
values of 0.10-0.18 V were indicative of significant metal-metal interactions. The results
of Mo¨ssbauer, IR, and Raman studies of compounds 3, 4, and 6 are also discussed.
In tr od u ction
The incorporation of transition metals into polymer
backbones has been shown to generate materials with
unusual physical and chemical properties.1,2 In this
regard, ferrocene represents an appealing structural
unit to include in a polymer main chain, but, until
recently, high-molecular-weight poly(metallocenes) have
been very rare.3-5 We have previously shown that
strained silicon-bridged [1]ferrocenophanes such as 1a
undergo thermal ring-opening polymerization (ROP) to
afford high-molecular-weight poly(ferrocenylsilanes) (e.g.
2a ).5 Recently, anionic and transition-metal-catalyzed
ring-opening polymerization have also been established
as facile routes to these materials.6 Ring-opened poly-
(metallocenes) are now known with a variety of bridging
elements (for example, Ge as in 2b), and studies have
shown that these materials possess intriguing physical
properties.2,7-9 As cross-linking of poly(ferrocenes) is
essential for many applications (e.g. for the formation
of redox-active gels10), we targeted a convenient method
of cross-linking materials such as 2a which would be
expected to lead to enhanced mechanical properties,
thermal stability, and ceramic yields.
We identified the spirocyclic [1]ferrocenophanes 3 and
4 as possible cross-linking agents for poly(ferrocenes)
† University of Toronto.
(6) (a) Ni, Y.; Rulkens, R.; Manners, I. J . Am. Chem. Soc. 1996, 118,
4102. (b) Ni, Y.; Rulkens, R.; Pudelski, J . K.; Manners, I. Macromol.
Rapid Commun. 1995, 16, 637. (c) Reddy, N. P.; Yamashita, H.;
Tanaka, M. J . Chem. Soc., Chem. Commun. 1995, 2263.
(7) Manners, I. Adv. Organomet. Chem. 1995, 37, 131.
(8) (a) Rulkens, R.; Resendes, R.; Verma, A.; Manners, I.; Murti,
K.; Fossum, E.; Miller, P.; Matyjaszewski, K. Macromolecules 1997,
30, 8165. (b) Liu, X.-H.; Bruce, D. W.; Manners, I. Chem. Commun.
1997, 289. (c) Pudelski, J . K.; Rulkens, R.; Foucher, D. A.; Lough, A.
J .; Macdonald, P. M.; Manners, I. Macromolecules 1995, 28, 7301. (d)
Pudelski, J . K.; Foucher, D. A.; Honeyman, C. H.; Macdonald, P. M.;
Manners, I.; Barlow, S.; O’Hare, D. Macromolecules 1996, 29, 1894.
(e) MacLachlan, M. J .; Aroca, P.; Coombs, N.; Manners, I.; Ozin, G. A.
Adv. Mater. 1998, 10, 144.
‡ University of Vermont.
(1) For recent examples of transition-metal-based polymeric materi-
als, see, for example: (a) Pittman, C. U.; Carraher, C. E.; Zeldin, M.;
Sheats, J . E.; Culbertson, B. M., Eds. Metal-Containing Polymeric
Materials; Plenum Press: New York, 1996. (b) Altman, M.; Bunz, U.
H. F. Angew. Chem., Int. Ed. Engl. 1995, 34, 569. (c) Rosenblum, M.;
Nugent, H. M.; J ang, K.-S.; Labes, M. M.; Cahalane, W.; Klemarczyk,
P.; Reiff, W. M. Macromolecules 1995, 28, 6330. (d) Chen, H.; Archer,
R. D. Macromolecules 1995, 28, 1609. (e) Stanton, C. E.; Lee, T. R.;
Grubbs, R. H.; Lewis, N. S.; Pudelski, J . K.; Callstrom, M. R.; Erickson,
M. S.; McLaughlin, M. L. Macromolecules 1995, 28, 8713. (f) Buretea,
M. A.; Tilley, T. D. Organometallics 1997, 16, 1507. (g) Southard, G.
E.; Curtis, M. D. Organometallics 1997, 16, 5618.
(2) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602.
(3) (a) Brandt, P. F.; Rauchfuss, T. B. J . Am. Chem. Soc. 1992, 114,
1926. (b) Compton, D. L.; Brandt, P. F.; Rauchfuss, T. B.; Rosenbaum,
D. F.; Zukoski, C. F. Chem. Mater. 1995, 7, 2342.
(4) Nugent, H. M.; Rosenblum, M.; Klemarczyk, P. J . Am. Chem.
Soc. 1993, 115, 3848.
(9) (a) Nguyen, M. T.; Diaz, A. F.; Dement’ev, V. V.; Pannell, K. H.
Chem. Mater. 1993, 5, 1389. (b) Tanaka, M.; Hayashi, T. Bull. Chem.
Soc. J pn. 1993, 66, 334. (c) Barlow, S.; Rohl, A. L.; Shi, S.; Freeman,
C. M.; O’Hare, D. J . Am. Chem. Soc. 1996, 118, 7578. (d) Hmyene, M.;
Yassar, A.; Escorne, M.; Percheron-Guegan, A.; Garnier, F. Adv. Mater.
1994, 6, 564.
(5) Foucher, D. A.; Tang, B.-Z.; Manners, I. J . Am. Chem. Soc. 1992,
114, 6246.
(10) Tatsuma, T.; Takada, K.; Matsui, H.; Oyama, N. Macromol-
ecules 1994, 27, 6687.
S0276-7333(97)01071-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/11/1998

1874 Organometallics, Vol. 17, No. 9, 1998
MacLachlan et al.
2a and 2b, respectively. In addition, as silacyclobutanes
workers. However, the workup procedure was modified
to improve the product yields. Filtration through a
short column of alumina allowed any chlorinated silane/
germane species and salts to be removed. The products
isolated after the filtration were stable indefinitely in
solution. The yield of 3 was improved significantly
(70%), but the yield of 4 was still very low (<5%),
probably due to a competition between Cp-Ge bond
formation and anion-induced cleavage. Both 3 and 4
are air-stable red crystalline compounds. To allow
additional comparison, we synthesized tetraferrocenyl-
silane 6 by the reaction of FcLi with SiCl4 using a
procedure analogous to that briefly described by Rosen-
berg in a patent.17
are also known to undergo thermal and transition-
metal-catalyzed ROP, the novel spirocyclic [1]silaferro-
cenophane 5 incorporating a silacyclobutane group was
also expected to function as a cross-linking agent. It is
noteworthy that compounds such as 3-5 may also
function as volatile precursors to novel composite
materials.8e In this paper, we report full details on the
synthesis, characterization, and properties of all three
potential cross-linking agents (3-5). We also describe
the synthesis and properties of tetraferrocenylsilane 6,
which provided useful comparative spectroscopic and
structural data for 3. Details of the polymerization
behavior of 3 and 5 and the properties of the novel cross-
linked poly(ferrocene) products, which were briefly
described in a recent communication,11 will be discussed
in detail elsewhere.12
The spirocyclic species 3 and 4 were characterized by
1H, 13C, and 29Si NMR, mass spectrometry, and IR,
1
Raman, Mo¨ssbauer, and UV-vis spectroscopy. The H
NMR spectrum of 3 is interesting, as it displays a pair
of pseudo-triplets in CDCl3, as expected for an A2B2 spin
system, but only a singlet in C6D6. When a sample of 3
in CDCl3 was treated with a few drops of C6D6, the
pseudo-triplets remained, confirming, as expected, that
an unusual exchange mechanism was not reponsible for
the magnetic equivalence of the protons. Since rotation
of the Cp rings is impossible without ring-opening, there
must be a fortuitous magnetic equivalence of the Cp
protons in C6D6. This could be a consequence of
unsymmetric proton shielding from the solvent. Due
to steric crowding of the molecule, the â-protons are
more accessible to solvent and may experience enhanced
shielding from the aromatic ring of C6D6 relative to the
R-protons. Exact compensation for the greater shielding
usually observed for the Cp R-protons (closest to the Si
substituent) would therefore arise. In contrast to 3, the
1H spectrum of the germanium analogue 4 is typical of
a symmetric [1]ferrocenophane, with two pseudo-triplets
in both C6D6 and CDCl3. Compounds 3 and 4 display
13C NMR spectra consistent with the assigned struc-
tures. The 13C NMR chemical shifts for the resonances
assigned to the ipso carbon atoms for 3 and 4 were found
at 31.1 and 27.8 ppm, respectively. These resonances
show a dramatic high-field shift compared to those for
unstrained species, which is characteristic of [1]ferro-
cenophanes.14 Due to its limited solubility and the long
spin-lattice relaxation time (T1) of the Si nucleus (no
R-protons for polarization transfer), the 29Si NMR
spectrum of 3 was difficult to obtain and required a very
long pulse delay and long acquisition time. The single
resonance detected for 3 at -16.6 ppm is upfield of the
phenylated [1]silaferrocenophane Fe(η-C5H4)2SiPh2 (δ
-11.7 ppm). Interestingly, the 29Si resonance of tetra-
ferrocenylsilane 6 also lies downfield at -10.1 ppm (CD2-
Cl2). The additional shielding observed in 3 might be
attributed to a weak dative Fe- - -Si interaction and is
consistent with the single-crystal X-ray structure and
Mo¨ssbauer data (vide supra). Both 3 and 4 have UV-
vis absorptions between 480 and 490 nm typical of [1]-
ferrocenophanes. In contrast, 6 has λmax ) 452 nm,
similar to that for other unstrained ferrocene deriva-
tives.
Resu lts a n d Discu ssion
Syn th esis of th e Spir ocyclic [1]Fer r ocen oph an es
3-5 a n d Tetr a fer r ocen ylsila n e 6. In 1975, Osborne
and Whiteley reported the synthesis of 3, which was the
first characterized spirocyclic [1]ferrocenophane.13 These
researchers isolated 3 in very low yield (7%) from the
reaction of
2 equiv of dilithioferrocene‚TMEDA
(fcLi2‚TMEDA) with tetrachlorosilane, and the product
was characterized by mass spectrometry, 1H NMR, and
UV-vis spectroscopy. In 1980, the same group reported
further spectroscopic studies (Mo¨ssbauer, 13C NMR) of
the compound and a slight improvement in the yield
(17%).14 Interestingly, they attempted to determine the
X-ray crystal structure of 3 but reported that the
crystals obtained were disordered and not suitable for
X-ray diffraction studies. The synthesis of the spirocy-
clic [1]germaferrocenophane 4 was also reported by
Osborne and co-workers via an analogous route from
GeCl4.15 This species was obtained in a low, unquan-
tified yield and was characterized by mass spectrometry,
NMR, and elemental analysis. The authors indicated
that the isolation and purification of 4 were frustrated
by decomposition in solution. Both compounds, 3 and
4, have subsequently been investigated for protective
derivatization of photoelectrochemical n-doped Si sub-
strates.16
In our laboratory, 3 and 4 were synthesized using the
same route as that described by Osborne and co-
(11) MacLachlan, M. J .; Lough, A. J .; Manners, I. Macromolecules
1996, 29, 8562.
(12) MacLachlan, M. J .; Kulbaba, K.; Manners, I. Manuscript in
preparation.
(13) Osborne, A. G.; Whiteley, R. H. J . Organomet. Chem. 1975, 101,
C27.
Spirocyclic metalloarenophanes bridged by silacy-
clobutane rings (7 and 8) were first synthesized by
(14) Osborne, A. G.; Whiteley, R. H.; Meads, R. E. J . Organomet.
Chem. 1980, 193, 345.
(15) Blake, A. J .; Mayers, F. R.; Osborne, A. G.; Rosseinsky, D. R.
J . Chem. Soc., Dalton Trans. 1982, 2379.
(16) Rosseinsky, D. R.; Osborne, A. G.; Mayers, F. R. Opt. Mater.
1996, 6, 83.
(17) Rosenberg, H. U.S. Patent 3,410,883, 1968; Chem. Abstr. 1969,
13149w.

Spirocyclic Ferrocenophanes
Organometallics, Vol. 17, No. 9, 1998 1875
F igu r e 1. Molecular structure of the spirocyclic [1]-
ferrocenophane 3 (thermal ellipsoids drawn at the 50%
probability level).
Elschenbroich in 1995.18 These mononuclear species
were used as control compounds in the study of metal-
metal interactions in dinuclear compounds bridged by
disilacyclobutane moieties. Silacyclobutanes are known
to undergo thermal or transition-metal-catalyzed ROP,
and their polymerization behavior has recently been
reviewed.19 We anticipated that incorporation of a
ferrocenophane ring and a silacyclobutane ring into the
same molecule should afford a tetrafunctional monomer
suitable as a cross-linking agent for poly(ferrocenes).
The reaction of Fe(η-C5H4Li)2‚TMEDA with an excess
of Cl2Si(CH2)3 afforded red, hygroscopic, air-sensitive
1
needles of 5. Both the H and 13C NMR chemical shifts
were consistent with the assigned structure; the 13C
resonance of the ipso carbon atoms was observed at 31.9
ppm. The 29Si NMR spectrum showed one singlet, at
3.6 ppm; this is shifted upfield from the resonance at
18.3 ppm observed in dichlorosilacyclobutane and down-
field from the resonance at -4.6 ppm for 1a . The UV-
vis spectrum of 5 shows a peak at 482 nm with a weak
shoulder at shorter wavelength. In addition, the mass
spectra of 3-6 were all consistent with their structures,
giving the molecular ion as the dominant peak.
X-r a y Str u ctu r es of th e [1]Sila fer r ocen op h a n e
3 a n d th e [1]Ger m a fer r ocen op h a n e 4. As no previ-
ous crystallographic data for spirocyclic [1]ferroceno-
phanes had been reported, single-crystal X-ray diffrac-
tion studies of 3 and 4 were undertaken. Orange-red
prisms of 3 suitable for X-ray diffraction were grown at
-55 °C from a solution of the compound in CH2Cl2 and
hexanes (ca. 1:1). Red crystals of 4 were obtained by
slow evaporation from a solution of 4 in C6D6 inside a
glovebox. Figures 1 and 2 show views of the molecular
structures of 3 and 4, respectively. A summary of cell
contents and data collection parameters is included in
Table 1, and selected bond lengths and bond angles are
listed in Tables 2 and 3. A summary of important
structural features for 3 and 4 is presented in Table 4.
Both 3 and 4 crystallize in the same space group (C2/
c) and are isostructural. The Si and Ge atoms lie on
special positions (on a 2-fold axis) in the unit cell,
reflecting the C2v symmetry of the molecule. To accom-
modate the larger atomic size of Ge (covalent radius of
122 pm for Ge vs 117 pm for Si), the unit cell of 4 is ca.
2% larger (by volume) than 3. Similarly, the Fe- - -Fe
distance in 4 (5.518(4) Å) is greater than in 3 (5.314(1)
F igu r e 2. Molecular structure of the spirocyclic [1]-
ferrocenophane 4 (thermal ellipsoids drawn at the 50%
probability level).
Å). The Cp rings of both 3 and 4 are eclipsed (torsion
angles of 1.1 and 0.8°, respectively) and are essentially
planar; mean deviations of 0.002 and 0.005 Å from the
plane containing C(1)-C(5) and 0.003 and 0.003 Å for
the C(6)-C(10) plane are present in 3 and 4, respec-
tively. The tilting of the planes of the cyclopentadienyl
ligands with respect to one another in 3 (R ) 19.4(2)°)
is less than in 1a (R ) 20.8(5)°),20 indicating that
introduction of a second ferrocenophane ring at silicon
slightly reduces the ring tilt observed. On the other
hand, the ring tilt of 4 (R ) 19.1(5)°) is similar to the
ring tilts of 3 and 1b (R ) 19.0(9)°),21 although the large
estimated standard deviations of the angles for 1b and
4 make meaningful comparisons difficult. The Si-Cipso
bond lengths in 3 (1.871(3) and 1.874(3) Å) are similar
to the bond lengths in 1a (1.858(9) Å) and tetraferro-
cenylsilane 6 (1.851(7)-1.870(6) Å) (see below). Like-
wise, the Ge-Cipso bond lengths in 4 (1.952(9) Å) are
only slightly shorter than the same bond lengths in 1b
(1.978(6) Å). The values of the angle â between the
planes of the Cp ligands and the Cipso-bridging atom
bonds for 3 and 1a indicate that 3 possesses a larger
distortion from planarity at the ipso carbon atom than
does 1a (â ) 39.5(1)° for 3, â ) 37.0(6)° for 1a ). For
ferrocenophane 4, the â angle is 37.5(4)°, consistent with
the value for 1b (â ) 37.0(6)°). While the C-C-C
angles in the Cp ring of ferrocene are 108°, there is a
small distortion from a perfect pentagon in the Cp rings
of 3 and 4. The Cipso-E-Cipso bond angles in 3 (98.5(1)°)
and 4 (94.7(4)°) are significantly smaller than the ideal
(18) Elschenbroich, C.; Bretschneider-Hurley, A.; Hurley, J .; Be-
hrendt, A.; Massa, W.; Wocadlo, S.; Reijerse, E. Inorg. Chem. 1995,
34, 743.
(19) Ushakov, N. V.; Finkel’shtein, E. S.; Babich, E. D. Polym. Sci.,
Ser. A 1995, 37, 320.
(20) Finckh, W.; Tang, B.-Z.; Foucher, D. A.; Zamble, D. B.; Ziem-
binski, R.; Lough, A.; Manners, I. Organometallics 1993, 12, 823.
(21) Foucher, D. A.; Edwards, M.; Burrow, R. A.; Lough, A. J .;
Manners, I. Organometallics 1994, 13, 4959.

1876 Organometallics, Vol. 17, No. 9, 1998
Ta ble 1. Su m m a r y of Cr ysta l Da ta a n d Da ta Collection P a r a m eter s for 3-6
MacLachlan et al.
3
4
5
6
empirical formula
Mr
C
20H16Fe2Si
C20H16Fe2Ge
440.62
C13H14FeSi
254.18
C40H36Fe4Si
768.18
396.12
temp (K)
wavelength (Å)
cryst syst
space group
a, Å
168(2)
168(2)
168(2)
168(2)
0.710 73
monoclinic
C2/c
20.771(2)
10.304(1)
7.424(1)
100.99(1)
1559.8(3)
4
0.710 73
monoclinic
C2/c
21.130(9)
10.293(4)
7.437(4)
100.61(1)
1589.8(13)
4
0.710 73
monoclinic
P21/n
10.603(2)
6.085(1)
17.210(2)
98.60(1)
1097.9(3)
4
0.710 73
orthorhomic
Pca21
15.326(2)
14.087(1)
14.590(2)
90
3149.9(6)
4
1.620
b, Å
c, Å
â, deg
V, Å3
Z
D
calc, g cm-3
1.687
19.31
808
1.841
36.73
880
1.538
14.42
528
µ(Mo KR), cm-1
F(000)
18.73
1576
cryst size (mm)
θ range collected, deg
total no. of rflns
no. of unique rflns
weighting scheme aa
Rint
0.3 × 0.3 × 0.1
3.41-27.00
1748
1703
0.0331
0.2 × 0.2 × 0.05
3.41-26.00
1603
1562
0.0505
<0.5 × 0.5 × 0.5
3.56-30.00
3365
3209
0.0399
0.31 × 0.15 × 0.15
2.66-27.00
3573
3573
0.0236
0.0372
0.0710
0.0236
0.0000
abs cor
semiempirical
0.0747
0.0317
semiempirical
0.1283
0.0511
semiempirical
0.0713
0.0266
semiempirical
0.0764
0.0377
wR2 (all data)
R1 (I > 2σ(I))
GOF
0.838
0.870
1.012
0.850
(∆/σ)max in last cycle
0.000
130
+0.395/-0.290
0.0020(2)
0.088
106
+0.737/-0.673
0.0000(2)
0.001
178
+0.444/-0.412
none
0.002
408
+0.313/-0.357
0.00036(6)
-0.13(6)
no. of params
residual electron density (e Å-3
extinction coeff
abs struct param
)
Weight ) 1/[σ2(Fo)2 + (aP)2], where P ) (Max(Fo2,0) + 2Fc2)/3.
a
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4
Distances
Distances
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
Fe(1)-C(10)
Si(1)-C(1)
2.6572(5)
2.017(3)
2.032(3)
2.084(3)
2.075(3)
2.027(3)
2.019(3)
2.028(3)
2.068(3)
2.077(3)
2.031(3)
1.874(3)
Si(1)-C(6)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
C(6)-C(10)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
1.871(3)
1.441(4)
1.448(4)
1.429(5)
1.423(5)
1.422(5)
1.450(4)
1.451(4)
1.421(5)
1.420(5)
1.413(5)
Fe(1)-Ge(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
Fe(1)-C(10)
Ge(1)-C(1)
2.759(2)
2.021(9)
2.021(9)
2.089(10)
2.082(10)
2.026(8)
2.041(9)
2.057(8)
2.085(8)
2.081(9)
2.030(9)
1.948(9)
Ge(1)-C(6)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
C(6)-C(10)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
1.955(9)
1.461(12)
1.422(11)
1.436(14)
1.432(14)
1.420(12)
1.472(12)
1.433(13)
1.441(13)
1.447(13)
1.391(14)
Angles
Angles
Si(1)-C(1)-C(2)
Si(1)-C(1)-C(5)
Si(1)-C(6)-C(7)
Si(1)-C(6)-C(10)
C(1)-Si(1)-C(6)
C(1)-C(2)-C(3)
C(1)-C(5)-C(4)
C(2)-C(3)-C(4)
119.7(2)
116.3(2)
118.4(2)
117.9(2)
98.48(12)
109.4(3)
109.3(3)
107.7(3)
C(2)-C(1)-C(5)
C(3)-C(4)-C(5)
C(6)-C(7)-C(8)
C(6)-C(10)-C(9)
C(7)-C(8)-C(9)
C(7)-C(6)-C(10)
C(8)-C(9)-C(10)
105.5(3)
108.1(3)
108.9(3)
109.7(3)
108.5(3)
105.1(3)
107.8(3)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(5)
Ge(1)-C(6)-C(7)
Ge(1)-C(6)-C(10)
C(1)-Ge(1)-C(6)
C(1)-C(2)-C(3)
C(1)-C(5)-C(4)
C(2)-C(3)-C(4)
118.9(7)
117.9(6)
117.5(7)
118.8(6)
94.7(4)
109.3(9)
109.6(8)
106.4(9)
C(2)-C(1)-C(5)
C(3)-C(4)-C(5)
C(6)-C(7)-C(8)
C(6)-C(10)-C(9)
C(7)-C(8)-C(9)
C(7)-C(6)-C(10)
C(8)-C(9)-C(10)
105.8(8)
108.9(9)
107.7(8)
110.9(8)
107.6(8)
105.7(8)
108.1(9)
tetrahedral value (109.5°), consistent with the analogous
angles in other [1]silaferrocenophanes and [1]germa-
ferrocenophanes. However, these angles are larger than
in 1a (95.7(4)°) and 1b (91.7(3)°), suggesting that the
Si and Ge tetrahedral environments are less distorted
in 3 and 4. It is probably the combination of near-
tetrahedral geometry at the bridging atom and the steric
hindrance imparted by four Cp rings that is responsible
for the unusual air and moisture stability in these [1]-
ferrocenophanes.
X-ray crystallography. A structural investigation of
tetraferrocenylsilane was undertaken to permit a com-
parison with the spirocyclic [1]silaferrocenophane 3.
Crystals of 6 were obtained by slow evaporation of a
solution of 6 in C6D6 under a nitrogen atmosphere.
Figure 3 gives a view of the molecular structure of 6.
The cell contents and data collection parameters are
summarized in Table 1, and selected bond lengths and
bond angles are listed in Table 5.
Despite the apparent symmetry of 6, it crystallizes
in the chiral, orthorhombic space group Pca21, where
the molecule possesses no symmetry elements. The
chirality of the structure was determined unambigu-
ously by X-ray diffraction, as indicated by the small
X-r a y St r u ct u r e of Tet r a fer r ocen ylsila n e 6. A
search of the Cambridge Structural Database revealed
that no other compounds containing a silicon atom
attached to four Cp ligands have been characterized by

Spirocyclic Ferrocenophanes
Organometallics, Vol. 17, No. 9, 1998 1877
Ta ble 4. Selected Str u ctu r a l Da ta for [1]F er r ocen op h a n es
1a
3
5
1b
4
Fe-E dist, Å
2.690(3)
2.41
2.6572(5)
2.41
2.7113(5)
2.41
0.222(2)
20.61(8)
37.4(1)
95.83(6)
164.4(1)
this work
2.804(2)
2.47
2.759(2)
2.47
∑(rFe + rx),a
Å
Fe displacement,b Å
ring tilt, R, deg
â,c deg
C1-E-C6, θ, deg
Cp-Fe-Cp, δ, deg
ref
0.216(1)
20.8(5)
37.0(6)
95.7(4)
164.74(8)
20
0.210(3)
19.4(2)
39.5(1)
98.5(1)
165.3(2)
this work
0.221(9)
19.0(9)
36.8(5)
91.7(3)
165.3(5)
21
0.214(9)
19.1(5)
37.5(5)
94.7(4)
165.1(4)
this work
a
b
Sum of the covalent radii of Fe and the bridging atom E. Displacement of the iron atom from the line joining the two centroids of
the cyclopentadienyl rings. c Average of the angle(s) between the planes of the cyclopentadienyl ligands and the C(Cp)-E bonds (where
E ) bridging atom).
atom22 is consistent with the 29Si NMR data, where the
29Si resonance of 3 (-16.6 ppm) is upfield from that of
6 (-10.1 ppm). However, it was predicted that the
quadrupolar splitting values for 3 and 4 might be
significantly higher than those for other [1]sila- and
[1]germaferrocenophanes, respectively, because the atom
bridging the two ferrocenophanes would be unable to
accommodate the same degree of electron density from
the two Fe centers as in other [1]ferrocenophanes. The
observation that 3 and 4 have quadrupolar splitting
values similar to those of other [1]ferrocenophanes
suggests that other factors, such as changes in bonding
in the ferrocenophane due to ring tilting and Cipso
distortion, may be required to explain the quadrupolar
splittings. As expected, the Mo¨ssbauer spectroscopic
data for 6 are very similar to those for ferrocene, where
F igu r e 3. Molecular structure of 6 (thermal ellipsoids
drawn at the 25% probability level).
the measured isomer shift value δ (relative to Fe
powder) was 0.429(5) mm s-1 and the quadrupolar
absolute structure factor. This rigid, chiral conforma-
splitting value ∆Eq was 2.262(5) mm s-1
.
tion is probably induced by the steric demands of the
ferrocenyl substituents at Si. One can view the struc-
ture as a pinwheel of three ferrocenes with the fourth
ferrocene attached above the plane. The Fe- - -Fe
separation varies from 5.27 to 6.14 Å between the
ferrocenes. Each of the Cp ligands is essentially planar,
with very slight ring tilts of 0.7(5), 1.3(5), 2.4(5), and
3.6(6)° observed for the ferrocenyl substituents. Nota-
bly, values of the angle â between the planes of the Cp
ligands and the Cipso-bridging atom bonds in 6 are
3.0(6), 4.3(6), 4.9(6), and 6.6(6)°. This small distortion
from ideal sp2 hybridization of the ipso carbon atoms is
likely also the result of steric crowding around Si.
57F e Mo1ssba u er Sp ectr a of 3, 4, a n d 6. Mo¨ssbauer
spectra of ferrocene derivatives can provide valuable
insight into the Fe environments. Studies of [1]ferro-
cenophanes have indicated a reduction in quadrupolar
splitting relative to ferrocene (2.31 mm s-1), while the
isomer shift is similar (0.43 mm s-1) (data relative to
Fe powder). Silver has attributed the quadrupolar
splitting shift to a weak iron-to-heteroatom interac-
tion.22 Osborne et al. reported the Mo¨ssbauer spectro-
scopic data for 3 at 77 K; these workers measured the
isomer shift δ of 0.51 mm s-1 and the quadrupolar
X-r a y Str u ctu r e of 5. Single crystals of 5 suitable
for X-ray diffraction were obtained by solvent evapora-
tion from the filtered reaction mixture. Figure 4 shows
the molecular structure of 5. A summary of cell
constants and data collection parameters is included in
Table 1, and important bond lengths and angles are
listed in Table 6. A summary of important structural
features is presented in Table 4.
As in 3 and 4, the two cyclopentadienyl rings of 5 are
virtually eclipsed, and each is essentially planar with
an observed mean deviation from the plane of 0.004 Å
calculated by a weighted least-squares plane through
the cyclopentadienyl ligand containing C(1)-C(5), with
the same value for the cyclopentadienyl ligand contain-
ing C(6)-C(10). The Cp rings are tilted with respect to
one another in 5 (R ) 20.61(8)°) to a similar degree as
in 1a (R ) 20.8(5)°). The Si-Cipso bond lengths in 5
(1.883(2) and 1.884(2) Å) are in accord with those in
other [1]silaferrocenophanes such as 1a . The value of
the angle â between the planes of the Cp ligands and
the Cipso-Si bond for 5 (â ) 37.4(1)°) indicates a large
distortion from the linear sp2 hybridization at the Cipso
atom. The Cipso-Si-Cipso bond angle in 5 (95.83(6)°) is
also significantly less than the tetrahedral value (109.5°)
and agrees with the value for 1a (95.7(4)°). In 1a , a
splitting value ∆Eq of 2.01 mm s-1 14
At room temper-
.
ature, we found the isomer shift value δ (relative to Fe
powder) for 3 was 0.442(5) mm s-1, while the quadru-
polar splitting value ∆Eq was 2.013(5) mm s-1. The
corresponding values for 4 were δ ) 0.454(5) mm s-1
and ∆Eq ) 2.090(5) mm s-1. This postulate for a weak
dative interaction between the Fe and the bridging
scissoring effect is observed, giving rise to a wider CMe
-
Si-CMe angle (114.8(6)°) than expected for a tetrahedral
geometry. In 5, however, the C(11)-Si-C(13) angle
(81.10(8)°) is constrained by the silacyclobutane ring.
This leaves a large part of the Si atom exposed and may
explain why 5 is very moisture sensitive. The Fe- - -Si
distance in 5 (2.7113(5) Å) is only slightly longer than
in 1a (2.690(3) Å) but is significantly longer than in 3
(22) Roberts, R. M. G.; Silver, J .; Ranson, R. J .; Morrison, I. E. G.
J . Organomet. Chem. 1981, 219, 233.

1878 Organometallics, Vol. 17, No. 9, 1998
MacLachlan et al.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6
Distances
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
Fe(1)-C(10)
Fe(2)-C(11)
Fe(2)-C(12)
Fe(2)-C(13)
Fe(2)-C(14)
Fe(2)-C(15)
Fe(2)-C(16)
Fe(2)-C(17)
Fe(2)-C(18)
Fe(2)-C(19)
Fe(2)-C(20)
Fe(3)-C(21)
Fe(3)-C(22)
Fe(3)-C(23)
Fe(3)-C(24)
Fe(3)-C(25)
Fe(3)-C(26)
Fe(3)-C(27)
Fe(3)-C(28)
Fe(3)-C(29)
Fe(3)-C(30)
Fe(4)-C(31)
Fe(4)-C(32)
Fe(4)-C(33)
Fe(4)-C(34)
Fe(4)-C(35)
Fe(4)-C(36)
Fe(4)-C(37)
Fe(4)-C(38)
Fe(4)-C(39)
Fe(4)-C(40)
Si(1)-C(1)
2.064(6)
2.047(8)
2.051(6)
2.056(7)
2.038(6)
2.058(7)
2.027(8)
2.022(9)
2.028(9)
2.044(8)
2.061(6)
2.022(7)
2.053(6)
2.061(8)
2.057(7)
2.017(7)
2.016(8)
2.041(8)
2.033(7)
2.045(7)
2.061(7)
2.041(7)
2.046(9)
2.028(8)
2.019(8)
2.047(8)
2.046(8)
2.044(7)
2.045(7)
2.051(8)
2.060(8)
2.048(7)
2.048(7)
2.024(8)
2.046(8)
2.052(8)
2.036(9)
2.057(8)
2.067(8)
2.066(8)
1.866(6)
1.870(6)
Si(1)-C(21)
Si(1)-C(31)
C(1)-C(2)
1.869(7)
1.853(7)
1.441(8)
1.424(9)
1.438(10)
1.423(9)
1.422(9)
1.415(11)
1.391(10)
1.379(14)
1.39(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
C(6)-C(10)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
C(11)-C(15)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(16)-C(17)
C(16)-C(20)
C(17)-C(18)
C(18)-C(19)
C(19)-C(20)
C(21)-C(22)
C(21)-C(25)
C(22)-C(23)
C(23)-C(24)
C(24)-C(25)
C(26)-C(27)
C(26)-C(30)
C(27)-C(28)
C(28)-C(29)
C(29)-C(30)
C(31)-C(32)
C(31)-C(35)
C(32)-C(33)
C(33)-C(34)
C(34)-C(35)
C(36)-C(37)
C(36)-C(40)
C(37)-C(38)
C(38)-C(39)
C(39)-C(40)
1.361(13)
1.398(9)
1.434(9)
1.445(10)
1.425(12)
1.403(9)
1.394(10)
1.397(10)
1.387(9)
1.406(11)
1.412(10)
1.429(8)
1.438(9)
1.414(9)
1.443(10)
1.405(9)
1.404(10)
1.388(11)
1.394(10)
1.425(11)
1.399(10)
1.451(9)
1.454(9)
1.422(10)
1.414(11)
1.432(9)
1.447(10)
1.423(10)
1.405(12)
1.400(11)
1.432(10)
F igu r e 4. Molecular structure of 5 (thermal ellipsoids
drawn at the 50% probability level).
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
Distances
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
Fe(1)-C(10)
Si(1)-C(1)
Si(1)-C(6)
Si(1)-C(11)
2.7113(5)
2.0135(14)
2.026(2)
Si(1)-C(13)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
C(6)-C(10)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
C(12)-C(13)
Si(1)-C(12)
1.869(2)
1.450(2)
1.450(2)
1.424(2)
1.418(2)
1.433(2)
1.445(2)
1.449(2)
1.426(2)
1.417(2)
1.428(2)
1.556(3)
1.560(3)
2.358(2)
2.079(2)
2.0772(14)
2.0303(14)
2.0131(14)
2.027(2)
2.074(2)
2.0775(14)
2.0248(14)
1.884(2)
1.883(2)
1.870(2)
Angles
Si(1)-C(1)-C(2)
Si(1)-C(1)-C(5)
Si(1)-C(6)-C(7)
120.48(12) C(1)-C(2)-C(3)
117.54(11) C(1)-C(5)-C(4)
118.99(11) C(2)-C(3)-C(4)
109.52(14)
109.25(14)
108.18(13)
105.13(12)
107.92(14)
109.6(2)
109.43(14)
108.04(14)
105.09(13)
107.89(14)
Si(1)-C(6)-C(10) 119.06(11) C(2)-C(1)-C(5)
Si(1)-C(11)-C(12) 86.45(11) C(3)-C(4)-C(5)
Si(1)-C(13)-C(12) 86.39(11) C(6)-C(7)-C(8)
Si(1)-C(11)
C(1)-Si(1)-C(6)
95.83(6) C(6)-C(10)-C(9)
Angles
C(1)-Si(1)-C(11) 124.39(8) C(7)-C(8)-C(9)
C(1)-Si(1)-C(13) 121.11(8) C(7)-C(6)-C(10)
C(6)-Si(1)-C(11) 118.15(7) C(8)-C(9)-C(10)
C(1)-Si(1)-C(11)
C(1)-Si(1)-C(21)
C(1)-Si(1)-C(31)
C(11)-Si(1)-C(21) 109.4(3)
C(11)-Si(1)-C(31) 111.7(3)
C(21)-Si(1)-C(31) 111.9(3)
Si(1)-C(1)-C(2)
Si(1)-C(1)-C(5)
Si(1)-C(11)-C(12) 124.4(6)
Si(1)-C(11)-C(15) 129.0(5)
Si(1)-C(21)-C(22) 130.2(5)
Si(1)-C(21)-C(25) 124.6(5)
Si(1)-C(31)-C(32) 128.5(6)
Si(1)-C(31)-C(35) 125.0(5)
C(1)-C(2)-C(3)
C(1)-C(5)-C(4)
C(2)-C(1)-C(5)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(6)-C(7)-C(8)
C(6)-C(10)-C(9)
C(7)-C(6)-C(10)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
108.5(3)
109.2(3)
106.1(3)
C(12)-C(13)-C(14) 106.6(7)
C(13)-C(14)-C(15) 107.9(7)
C(16)-C(17)-C(18) 108.6(7)
C(16)-C(20)-C(19) 108.0(7)
C(17)-C(16)-C(20) 108.0(7)
C(17)-C(18)-C(19) 108.3(7)
C(18)-C(19)-C(20) 107.1(7)
C(21)-C(22)-C(23) 110.7(6)
C(21)-C(25)-C(24) 110.0(7)
C(22)-C(21)-C(25) 105.0(6)
C(22)-C(23)-C(24) 106.4(7)
C(23)-C(24)-C(25) 107.9(7)
C(26)-C(27)-C(28) 109.3(8)
C(26)-C(30)-C(29) 108.4(8)
C(27)-C(26)-C(30) 107.7(7)
C(27)-C(28)-C(29) 106.4(7)
C(28)-C(29)-C(30) 108.2(7)
C(31)-C(32)-C(33) 108.2(7)
C(31)-C(35)-C(34) 108.9(7)
C(6)-Si(1)-C(13) 118.68(8) C(11)-C(12)-C(13) 102.59(13)
C(11)-Si(1)-C(13) 81.10(8)
C-Si-C and C-C-C bond angles significantly less
than 109.5°. Interestingly, the silacyclobutane ring in
5 is puckered23 by only 20.6(2)° from planarity, signifi-
cantly less than in bis(η5-benzene)vanadium 7 (23°)18
and 4-sila-3,3-spiroheptane, (CH2)3Si(CH2)3 (30(2)° by
electron diffraction24).
Cyclic Volta m m etr y of 3-6. Cyclic voltammetry
(CV) of 5 showed a single, reversible oxidation with E1/2
) 0.11 V vs ferrocene in CH2Cl2. This is typical of
[1]silaferrocenophanes; for example, 1a exhibits a single
reversible oxidation with E1/2 ) 0.00 V with respect to
the ferrocene/ferrocenium couple.25 CV of 3 showed two
oxidations. The first, with E1/2 ) 0.14 V, corresponds
to the formation of the mixed-valent FeII/FeIII compound;
this wave was reversible at all of the scan rates studied.
Surprisingly, the second oxidation, corresponding to the
124.3(5)
129.5(5)
108.6(6)
109.8(6)
106.2(6)
107.6(6)
107.8(6)
108.9(10) C(32)-C(31)-C(35) 105.9(6)
109.2(9)
105.7(9)
107.1(10) C(36)-C(37)-C(38) 106.9(7)
109.1(10) C(36)-C(40)-C(39) 108.4(7)
C(32)-C(33)-C(34) 109.5(7)
C(33)-C(34)-C(35) 107.4(7)
C(11)-C(12)-C(13) 109.5(8)
C(11)-C(15)-C(14) 109.6(8)
C(12)-C(11)-C(15) 106.5(6)
C(37)-C(36)-C(40) 107.3(7)
C(37)-C(38)-C(39) 110.4(8)
C(38)-C(39)-C(40) 107.0(8)
(23) We define the ring pucker as the angle between the plane
defined by Si, C(11), and C(13) and the plane defined by C(11), C(12),
and C(13). Thus, it quantifies the fold in the silacyclobutane ring.
(24) Mastryukov, V. S.; Dorefeeva, O. V.; Vilkov, L. V.; Cyvin, S. J .;
Cyvin, B. N. J . Struct. Chem. (Engl. Transl.) 1975, 16, 438.
(25) Pudelski, J . K.; Foucher, D. A.; Honeyman, C. H.; Lough, A. J .;
Manners, I.; Barlow, S.; O’Hare, D. Organometallics 1995, 14, 2470.
(2.6572(5) Å). There is possibly a weak interaction
between the Fe and Si atoms in 5, just as has been
proposed for other [1]silaferrocenophanes. The carbosi-
lane ring in 5 is also clearly strained with skeletal

Spirocyclic Ferrocenophanes
Organometallics, Vol. 17, No. 9, 1998 1879
F igu r e 5. Cyclic voltammogram of 5 mM 4 in dichlo-
romethane (scan rate 1.0 V s-1). The peaks marked by
asterisks are from the internal reference, decamethylfer-
rocene.
formation of an FeIII/FeIII species, was irreversible. A
large separation between the two oxidations, ∆Eox
)
0.37 V (scan rate 0.25 V s-1), indicates a significant
Fe- - -Fe interaction between the two ferrocenophane
units.
F igu r e 6. (a) Cyclic voltammogram of 0.31 mM 6 in
benzonitrile at a Pt-disk electrode (scan rate 0.05 V s-1).
(b) Differential pulse voltammogram of 0.31 mM 6 in
benzonitrile at a Pt-disk electrode (scan rate 2 mV s-1, drop
time 1 s).
CV of 4 also showed two oxidations (Figure 5). In this
case, the first oxidation, at E1/2 ) 0.11 V, was reversible
at all scan rates. The second oxidation at E1/2 ) 0.36 V
was reversible for all scan rates faster than ca. 0.25 V
s-1. As expected, the E1/2 separation, ∆E1/2, was less
for 4 (∆E1/2 ) 0.25 V) than for 3 (∆Eox ) 0.37 V),
implying a larger Fe- - -Fe interaction for the Si bridge
compared to that for Ge. Clearly, the large ∆E1/2 values
for 3 and 4 indicate a significant Fe- - -Fe interaction
in these molecules (cf. ∆E1/2 ) 0.34 V in biferrocene26
(CH2Cl2)).
Ta ble 7. Red ox P oten tia ls of 6 fr om Cyclic
Volta m m etr y
E1/2 (V vs
E1/2 (V vs
oxidn wave
ferrocene)a
oxidn wave
ferrocene)a
6/[6]+
-0.03
+0.29
[6]+/[6]2+
[6]3+/[6]4+
+0.15
+0.39
[6]2+/[6]3+
a
In benzonitrile. See Experimental Section for details.
Cyclic voltammetry of 6 in CH2Cl2 and THF provided
poor resolution of the four oxidation waves. In benzoni-
trile, however, the four reversible oxidations were
readily resolved. Figure 6 shows the cyclic voltammo-
gram and differential pulse voltammogram of 6. The
redox potentials (versus ferrocene) for each oxidation
are listed in Table 7.
Recently, a number of papers have appeared reporting
the preparation and electrochemical characterization of
multiply ferrocenyl-substituted complexes.27 These stud-
ies are relevant in general to the question of how
biological systems deliver several electron equivalents
to redox sites.27,28 It has been demonstrated, for ex-
ample, that the four Fe centers in cytochrome c3 undergo
electron transfer at very similar potentials, the spread
of the four FeII/FeIII E1/2 values being only 0.11 V.29
In the present work on compound 6, the spread of the
four potentials is 0.42 V, implying appreciable interac-
tions between the ferrocenyl moieties as they are
successively oxidized. This fact stands in contrast to
the case for MeSi[(aryl)Cr(CO)3]3, in which the oxida-
tions of the three Cr(CO)3 groups occur at virtually the
same potential, implying electronic isolation of the redox
centers.30 The results for 6 are more in line with those
of a multiferrocenyl analogue having boron as the
bridging atom, namely fc4B, which was formulated as
the zwitterion (ferrocenium)tris(ferrocenyl)borate.31 This
complex showed four reversible one-electron oxidations
with E1/2 values (versus Ag/AgCl) of -0.18, -0.09, 0.29,
and 0.41 V. The overall spread of 0.59 V is even larger
than that measured for complex 6. It may be concluded
that single bridging atoms of group 13 or group 14 both
allow significant interactions between ferrocenyl sub-
stituents in their multiply ferrocenyl-substituted com-
plexes.
Vibr a tion a l Sp ectr oscop y. The vibrational spec-
troscopy of [1]ferrocenophanes is unexplored. A sys-
tematic vibrational analysis of [1]ferrocenophanes may
reveal trends in vibrational frequencies as a function
of ring tilt, distortion from sp2 hybridization at the Cipso
(26) Brown, G. M.; Meyer, T. J .; Cowan, D. O.; Levanda, C.;
Kaufman, F.; Roling, P. V.; Raush, M. D. Inorg. Chem. 1975, 14, 506.
(27) For leading references, see: Tendero, M. J . L.; Benito, A.; Cano,
J .; Lloris, J . M.; Martinez-Manez, R.; Soto, J .; Edwards, A. J .; Raithby,
P. R.; Rennie, M. A. J . Chem. Soc., Chem. Commun. 1995, 1643.
(28) Steiger, B.; Shi, C.; Anson, F. C. Inorg. Chem. 1993, 32, 2107.
(29) Sokol, W. F.; Evans, D. H.; Niki, K.; Yagi, T. J . Electroanal.
Chem. Interfacial Electrochem. 1980, 108, 107.
(30) Reike, R. D.; Tucker, I.; Milligan, S. N.; Wright, D. R.; Willeford,
B. R.; Radnovich, L. J .; Eyring, M. W. Organometallics 1982, 1, 938.
(31) Cowan, D. O.; Shu, P.; Hedberg, F. L.; Rossi, M.; Kistenmacher,
T. J . J . Am. Chem. Soc. 1979, 101, 1304.

1880 Organometallics, Vol. 17, No. 9, 1998
MacLachlan et al.
Ta ble 8. In fr a r ed Ba n d s of 3 a n d 4
Ta ble 9. Ra m a n Ba n d s of 3, 4, 6, a n d F er r ocen e
3
4
assignta
3
4
6
ferrocenea
assigntb
3095 w
3081 w
2851 w
3095 w
3081 w
νC-H (sym)
3099 s
3099 s
3112 s
3092 m
3100 s
3085 w
3070 w
1412 m
νC-H(sym)
νC-H
νC-H
νC-C(sym)
νC-C
νC-H
3086 m
3077 w
1400 m
1378 m
3086 m
3077 w
1401 m
1376 m
1292 m
1182 s
1154 w
1418 m
1383 w
1369 w
1357 w
1194 w
1159 m
1111 s
1178 m
δC-H
ip
1119 w
1123 m
1032 s
1019 m
1013 m
890 m
880 s, 882 s
856 w
852 m
1349 w
1180 w
1347 w
1187 w
1356 w
1175 w
νC-C
δC-H
1114 s
1021 s
sym ring breath
ip
δC-H
δC-H
oop
1119 s
1060 s
1116 s
1060 s
1105 s
1059 m
sym ring breath
ip
1006 w
888 w
876 s
852 w
848 m
832 w
815 w
803 s
1065 m
δC-H
oop
ring distortion
1046 vw 1046 vw 1040w
1023 w
1017 w
901 vw
878 m
854 vw
838 vw
817 vw
807 vw
723 vw
714 m
1021 w
1009 w
898 vw
873 m
851 vw
836 vw
816 vw
805 vw
δC-H
ring idp istortion
ip
1005 w
888 w
999 w
892 w
δC-H
δC-H
oop
827 w
815 w
805 s, 802 s
δC-H
835 w
δC-H
δC-H
oop
oop
690 w
661 m
594 w
oop
696 m
596 w
567s
δC-C
oop
536 m
513 m
510 m
531 m
689 m
593 vw
594 vw
556 w
615 w
600 w
δC-C
oop
510 s
505 m
539 w
450 vw
535 w
Cp-Fe-Cp deform
a
Legend: ν ) stretch; δ ) bend; ip ) in plane; oop ) out of
435 m
419 s
plane
422 s
403 m
390 vs
335 w
292 s
410 m
398 m
333 m
316 s
265 m
248 w
397 vs
390 s
301 s
ring tilt (sym)
atom, or other geometric properties. Furthermore, these
techniques offer the possibility of examining structural
dynamics in solution and the gas phase. To corroborate
the structures of the spirocyclic molecules 3 and 4, both
IR and Raman spectra were obtained. Table 8 lists the
IR absorption frequencies for compounds 3 and 4, along
with tentative peak assignments. Table 9 presents the
Raman peaks for compounds 3, 4, and 6 with their
tentative assignments.
Molecules of 3 and 4 both possess C2v symmetry and
are identical except for the bridging atom. As expected,
the Raman and IR spectra of both compounds are thus
very similar. Though a normal-coordinate analysis of
the vibrational modes of these compounds, as well as
in 6, is beyond the scope of this paper, many of the
vibrations can be identified by comparison with other
ferrocene derivatives in the literature.32-34
The Raman spectra of 3 and 4 are very similar
between 800 and 4000 cm-1 (Figure 7, top). By com-
parison with the assignments of Raman-active modes
of ferrocene and some ferrocene derivatives, tentative
peak assignments have been made. Surprisingly, all
of the vibrations observed in ferrocene that are at-
tributed to Cp vibrations could be readily assigned to
peaks in the Raman spectra of 3 and 4. Three peaks
near 3100 cm-1 are due to C-H stretching modes of the
Cp rings. Though there are only two C-C stretching
modes observed near 1400 cm-1 in ferrocene, we have
assigned three peaks to C-C stretching in accord with
Butler’s assignments for ferrocene derivatives.33 The
C-C stretches in 3 (1349 and 1400 cm-1) and 4 (1347
and 1401 cm-1) are observed at lower frequency than
in ferrocene (1356 and 1412 cm-1).32 Raman modes due
325 s
256 m
248 s
241 w
234 m
νFe-Cp(sym)
246 s
228 w
184 vw
142 vw
231 w
143 vw
a
b
Reference 32. Legend: ν ) stretch; δ ) bend; ip ) in plane;
oop ) out of plane
to C-H deformations (in plane and out of plane of the
Cp rings) and ring distortions are consistent with the
spectrum of ferrocene. All of the peaks between 800 and
4000 cm-1 appear to be independent of the bridging
element, indicating that they are due only to cyclopen-
tadienyl modes.
Between 100 and 800 cm-1, however, many of the
Raman frequencies of 3 and 4 are significantly different,
suggesting that these peaks are coupled to the pseudo-
tetrahedral bridging element (Figure 7, bottom). In-
deed, Si-C and Ge-C stretching modes are expected
in this spectral region. The mode near 390 cm-1 has
been assigned to the symmetric ring tilt of the Cp rings.
It is interesting that this mode is nearly unperturbed
from the same mode in ferrocene. This may reflect some
torsional freedom along the Cp-E bond.
The most characteristic peak in the spectra of 3 and
4 is the symmetric ring-metal stretching mode near 300
cm-1. This frequency is strongly affected by the bridg-
ing element as the peak is observed about 30 cm-1
higher in 3 than in 4. The frequency of this mode has
a strong dependence on the substituents of the Cp rings,
as exemplified by the difference between ferrocene (306
cm-1), decamethylferrocene (169 cm-1), and 1,1′-dichlo-
roferrocene (344 cm-1).34
(32) Long, T. V., J r.; Huege, F. R. Chem. Commun. 1968, 1239.
(33) Butler, I. S.; Harvey, P. D.; Allen, G. C. J . Raman Spectrosc.
1987, 18, 1.
(34) Phillips, L.; Lacey, A. R.; Cooper, M. K. J . Chem. Soc., Dalton
Trans. 1988, 1383.
The Raman spectrum of 6 shows stretching vibrations
due to the cyclopentadienyl rings that are consistent

Spirocyclic Ferrocenophanes
Organometallics, Vol. 17, No. 9, 1998 1881
F igu r e 7. Raman spectra of (i) 3 and (ii) 4. For clarity, the spectra have been divided into two regions: 4000-800 cm-1
(top) and 800-100 cm-1 (bottom).
with those of other ferrocene derivatives. Moreover, the
positions of the ring stretching and deformation modes
are not significantly different from those observed for
3 and 4. The intense resonance at 316 cm-1 has been
tentatively assigned to the Fe-Cp symmetric stretch
after comparison with ferrocene and the spirocyclic [1]-
ferrocenophanes.
proximity, significant metal-metal interactions were
observed by cyclic voltammetry. Furthermore, Mo¨ss-
bauer studies of the spirocyclic [1]ferrocenophanes
showed smaller quadrupolar splittings than for fer-
rocene. A possible interpretation of this is the presence
of a metal-bridging atom interaction. Tetraferrocenyl-
silane 6 was prepared and structurally characterized
for comparison with 3 and 4. This compound showed
four reversible one-electron oxidations by cyclic volta-
mmetry, which were also consistent with metal-metal
interactions. The first vibrational analysis of [1]ferro-
cenophanes was reported, and many vibrations of the
ferrocenyl moiety could be assigned by analogy with the
spectra of ferrocene. Detailed studies of the controlled
Su m m a r y
The strained, spirocyclic [1]ferrocenophanes 3-5 were
synthesized and characterized by a variety of tech-
niques. Single-crystal X-ray diffraction studies revealed
the presence of highly strained, ring-tilted structures.
As the Fe centers in compounds 3 and 4 are in close

1882 Organometallics, Vol. 17, No. 9, 1998
MacLachlan et al.
used by Osborne, but with modifications to the workup which
we found to improve the yield substantially.
cross-linking of poly(ferrocenes) by spirocyclic [1]ferro-
cenophanes will be reported elsewhere.12
Tetrachlorosilane (0.65 mL, 5.7 mmol) was added slowly via
syringe to a suspension of dilithioferrocene‚TMEDA (4.47 g,
14.2 mmol) in 100 mL of hexanes cooled to -78 °C. The
solution was then warmed slowly to room temperature over a
period of 3 h, giving a deep red solution with an orange
precipitate. The reaction mixture was then heated to reflux
for 3 h. After the solution was cooled to room temperature
with a water bath, 0.5 mL of n-butanol was added to quench
the excess dilithioferrocene and the mixture was stirred for
10 min. The solution was cooled to -10 °C and filtered on a
Buchner funnel. The orange residue was dissolved in dichlo-
romethane to give a cloudy, red solution. Following filtration
through a Buchner funnel and a 10 cm column (5 cm diameter)
of alumina (BDH, Brockman, activity II; 100-200 mesh) under
air, the solution was rotary-evaporated to dryness. The solid
was redissolved in a minimum of dichloromethane and was
chromatographed on a 30 cm × 5 cm column of alumina
(hexanes), and the initial yellow band (ferrocene) was dis-
carded. Compound 3 eluted with dichloromethane and was
rotary-evaporated to dryness, affording 1.57 g (4.0 mmol, 70%)
of 3. Compound 3 is obtained as red, air-stable crystals
moderately soluble in toluene, benzene, THF, dichloromethane,
and chloroform and nearly insoluble in hexanes and DMSO.
Da ta for 3: 13C NMR (100.5 MHz, C6D6) δ 78.3 (Cp), 75.5
(Cp), 31.1 (ipso-Cp) ppm; 1H NMR (400 MHz, C6D6) δ 4.47 (s,
16H, Cp) ppm; 29Si NMR (79.5 MHz, C6D6) δ -16.6 ppm. MS
(EI, 70 eV) m/z (%) 396 (M+, 100); Mo¨ssbauer spectrum
doublet, IS ) 0.44, QS ) 2.01 mm s-1; UV-vis (CH2Cl2) λ (ꢀ)
483 (590) nm (L mol-1 cm-1); IR (Nujol mull) 1178, 1122, 1032,
Exp er im en ta l Section
Ma ter ia ls. Ferrocene, 1.6 M butyllithium in hexanes,
silicon tetrachloride (semiconductor grade; 99.999%), and
tetramethylethylenediamine (TMEDA) were purchased from
Aldrich. Germanium tetrachloride (Strem) and cyclotrimeth-
ylenedichlorosilane (Gelest) were used as received.
Dilithioferrocene‚TMEDA and tributylferrocenylstannane (Fc-
SnnBu3) were synthesized as reported previously.35-37
Equ ip m en t. All reactions and manipulations were carried
out under an atmosphere of prepurified nitrogen using either
Schlenk techniques or an inert-atmosphere glovebox (Innova-
tive Technologies), unless otherwise noted. Solvents were
dried by standard methods, distilled, and stored under nitro-
gen. The 400 MHz 1H NMR spectra and 100.5 MHz 13C NMR
spectra were recorded on a Varian Unity 400 spectrometer.
The 79.5 MHz 29Si NMR spectra were recorded on a Varian
Unity 400 spectrometer using either a normal (for 3 and 6) or
a DEPT (for 5) pulse sequence and were referenced externally
to TMS. Room-temperature 57Fe Mo¨ssbauer spectra were
obtained using a Ranger Scientific Inc. VT-1200 instrument
with a MS-1200 digital channel analyzer. The γ-ray source
was a 6 mCi 57Co sample supplied by Amersham. The data
were collected in
a
-15.8 to +15.8 mm s-1 range and
referenced to Fe powder. Data were acquired as long as was
required to obtain a suitable fit to standard independent
Lorentzian line shapes for sinusoidal baselines. Cyclic volta-
mmograms of 3-5 were obtained under N2 by analysis of ca.
5 mM dichloromethane solutions (0.1 M [Bu4N][PF6] electro-
lyte) using an EG&G Princeton Applied Research Model 273
potentiostat with a Pt working electrode, a W secondary
electrode, and a Ag-wire pseudo-reference electrode in a Luggin
capillary. Cyclic voltammetry of 6 was performed under
ambient conditions under N2 by analysis of a 0.31 mM solution
in benzonitrile using a PAR Model 173 potentiostat with a 250
µm diameter Pt disk (polished with diamond paste before use)
as the working electrode and an aqueous SCE as the reference
electrode, separated from the analyte solution by a fine frit.
Potentials in this paper are given versus the ferrocene/
ferrocenium couple. This was not used as the internal
standard, however, because its wave overlapped those of the
analytes. Rather, decamethylferrocene was employed as an
internal standard (E1/2 ) -0.07 V versus SCE in the present
experiments) and potentials were converted to the ferrocene
scale by subtraction of 0.51 V for benzonitrile and 0.55 V for
dichloromethane solutions. A PAR 174 potentiostat was
employed for differential pulse voltammetry measurements,
using a 1 s drop time and 25 mV modulation amplitude
settings. UV-vis spectra were obtained in CH2Cl2 (ca. 5 ×
10-4 M) on a Perkin-Elmer Lambda 900 UV-vis-near-IR
spectrometer using a 1 cm quartz cuvette. IR spectra were
obtained as Nujol mulls with a Nicolet Magna-IR 550 spec-
trometer. FT-Raman spectra were collected on a Bomems MB-
157 FT-spectrometer with a Spectra Physics diode pumped Nd:
YLF laser (1064 nm; 350 kHz repetition rate). The instrument
was configured in 180° backscattering mode using sealed glass
capillary tubes to hold the neat, crystalline samples. Electron
impact (EI) mass spectra were obtained with a VG 70-250S
mass spectrometer. Elemental analyses were performed by
Quantitative Technologies Inc., Whitehouse, NJ .
1019, 1013, 890, 881, 852, 803 (d), 696, 567, 536, 509 cm-1
.
Syn th esis of th e Sp ir ocyclic [1]Ger m a fer r ocen op h a n e
4. This compound was synthesized in the same manner as
was used by Osborne and co-workers, but a modified workup
procedure afforded a measurable yield. Germanium tetra-
chloride (0.75 mL, 6.6 mmol) was added dropwise via syringe
to a stirred suspension of dilithioferrocene‚TMEDA (4.92 g,
15.7 mmol) in 100 mL of hexanes at -78 °C. The solution
was warmed to room temperature over 3 h. After the reaction
mixture was refluxed for 10 min, the hot mixture was gravity-
filtered under air. The filtrate was rotary evaporated to
dryness, giving an orange-red crystalline solid. Once redis-
solved in dichloromethane, the clear, red solution of 4 was
flash-chromatographed through a 10 cm × 5 cm column of
alumina (BDH, Brockman, activity II; 100-200 mesh). The
red solution was rotary-evaporated to dryness to give red
crystals which were ca. 95% pure by NMR, with ferrocene as
the major impurity. Recrystallization from dichloromethane
afforded ca. 100-150 mg (0.23-0.34 mmol, 3-5%) of red, air-
stable crystals. Variation of reaction conditions including
longer reflux times, lower reaction temperature, different
solvents (THF, ether) and stoichiometries, and alternative
workup procedures (e.g. omission of the flash chromatography)
gave no improvement in the yield.
Da ta for 4: 13C NMR (100.5 MHz, C6D6) δ 77.7 (Cp), 76.0
1
(Cp), 27.8 (ipso-Cp) ppm; H NMR (400 MHz, C6D6) δ 4.46 (t,
8H, Cp), 4.40 (t, 8H, Cp) ppm; MS (EI, 70 eV) m/z (%) 442
(M+, 100), 368 (M+ - Ge, 92); Mo¨ssbauer spectrum doublet,
IS ) 0.45, QS ) 2.09 mm s-1; UV-vis (CH2Cl2) λ (ꢀ) 489 (560)
nm (L mol-1 cm-1); IR (Nujol mull) 1294, 1183, 1117, 1024,
876, 848, 804, 662, 532, 514 cm-1
.
Syn th esis of Sp ir ocyclic [1]Sila fer r ocen op h a n e 5. Cy-
clotrimethylenedichlorosilane (3.0 mL, 26 mmol) was added
dropwise to a stirred suspension of 5.31 g (16.9 mmol) of
dilithioferrocene‚TMEDA in 100 mL of diethyl ether cooled to
-78 °C. The solution was warmed slowly to 0 °C over a period
of 2 h. At -60 °C the solution started to turn red and was
deep red at -40 °C. The reaction mixture was filtered through
a frit at 0 °C to give a deep red, clear solution. The ether was
removed under vacuum to leave dark red crystals. After
Syn th esis of th e Sp ir ocyclic [1]Sila fer r ocen op h a n e 3.
This compound was synthesized in the same manner as was
(35) Rausch, M. D.; Ciappenelli, D. J . J . Organomet. Chem. 1967,
10, 5025.
(36) Guillaneux, D.; Kagan, H. B. J . Org. Chem. 1995, 60, 2502.
(37) Bishop, J . J .; Davison, A.; Katcher, M. L.; Lichtenberg, R. E.;
Merrill, J . C.; Smart, J . Organomet. Chem. 1971, 27, 241.

Spirocyclic Ferrocenophanes
Organometallics, Vol. 17, No. 9, 1998 1883
drying under dynamic vacuum at room temperature for 24 h,
the product was dissolved in a minimum volume of hexanes
and filtered again. Recrystallization at low temperature gave
large red needles. Subsequent sublimation at 40 °C afforded
3.39 g (13.3 mmol, 79%) of pure 5. These deep red crystals
possess a pungent odor and are very air- and moisture-
sensitive. Compound 5 is very soluble in toluene, hexanes,
THF, benzene, and dichloromethane.
of approximately 0.3 × 0.3 × 0.1 mm and 0.2 × 0.2 × 0.05
mm, respectively. Due to surface decomposition (hydrolysis),
the dimensions of the crystal of 5 could not be measured (all
were less than 0.5 mm). The crystal of 6 was an orange needle
with approximate dimensions of 0.31 × 0.15 × 0.15 mm.
Intensity data for the compounds 3-6 were collected at 168(2)
K on a Siemens P4 diffractometer using graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). The ω-scan tech-
nique was applied with variable scan speeds. Intensities of 3
standard reflections were measured every 100 reflections; all
four crystals showed negligible decay (<1%) during the data
collection. A semiempirical absorption correction was applied
using the SHELXA-90 routine in SHELXL.38
The positions of all atoms for 3, 5, and 6 were determined
by direct methods using Siemens SHELXTL PC.39 For each
structure, all non-hydrogen atoms were refined anisotropically
by full-matrix least squares to minimize Σw(Fo2 - Fc2)2, where
w ) 1/[σ2(Fo)2 + (aP)2], P ) (Max(Fo2,0) + 2Fc2)/3, and a is the
weighting factor listed in Table 1. The structure of 4 was
solved using the solution of 3 and refined in a similar manner.
For compounds 3-6 the hydrogen atoms were refined isotro-
pically. Crystal data, details of data collection, and least-
squares parameters are listed in Table 1. Selected bond
lengths and bond angles are provided in Tables 2, 3, 5, and 6.
All calculations were performed and all diagrams (Figures
1-4) were created using SHELXTL-PC and SHELXL-93 on a
486 personal computer.
Da ta for 5: 13C NMR (100.5 MHz, C6D6) δ 78.0 (Cp), 74.7
(Cp), 31.9 (ipso-Cp), 18.3 (CH2CH2CH2), 16.0 (SiCH2) ppm; 1H
NMR (400 MHz, C6D6) δ 4.39 (s, 4H, Cp), 4.04 (s, 4H, Cp),
3
3
2.38 (qt, J HH ) 8.2 Hz, 2H, CH2CH2CH2), 1.44 (t, J HH ) 8.2
Hz, 4H, SiCH2) ppm; 29Si NMR (79.5 MHz, C6D6) δ 3.6 ppm;
MS (EI, 70 eV) m/z (%) 254 (M+, 100), 226 (M+-C2H4, 62), 213
(M+ - C3H5, 20), 148 ((C5H4)FeSi+, 38); UV-vis (CH2Cl2) λ (ꢀ)
482 (420) nm (L mol-1 cm-1); mp 92 °C. Anal. Calcd for
C
13H14FeSi: C, 61.43; H, 5.55. Found: C, 61.29; H, 5.40.
Syn th esis of Tetr a fer r ocen ylsila n e 6. This compound
was prepared by the patented procedure of Rosenberg.
A
solution of 20.25 g of FcSnnBu3 (42.6 mmol) dissolved in 125
mL of THF was cooled to -78 °C in a dry ice/acetone bath.
With stirring, 26 mL of 1.56 M nBuLi (in pentanes; 40.6 mmol)
was added via syringe to give an orange-red solution. After 2
h of stirring at -78 °C, 1.0 mL of SiCl4 (1.5 g, 8.7 mmol) was
added and the solution was slowly warmed to room temper-
ature. The reaction mixture was then refluxed for 16 h at 70
°C. The solvent was reduced to ca. 40 mL under vacuum,
giving an orange precipitate and a red liquid. Ethanol (95%,
125 mL) was added to the flask, and the solution was warmed
to 50 °C with constant stirring. After it was cooled to -55 °C
in a freezer, the crude product was isolated on a Buchner
funnel and washed with 3 × 20 mL of cold ethanol; the filtered
solution was discarded. The solid was dissolved in a minimum
of CH2Cl2 and filtered twice through a short (ca. 15 cm) column
of alumina. Rotary evaporation afforded 4.15 g of an orange-
yellow solid. Recrystallization from CH2Cl2/hexanes (ca. 2:1)
afforded 2.34 g (3.05 mmol, 35%) of orange-red needles.
Da ta for 6: 13C NMR (100.5 MHz, C6D6) δ 74.3 (Cp), 71.5
(ipso-Cp), 70.7 (Cp), 69.2 (Cp) ppm; 1H NMR (400 MHz, C6D6)
δ 4.46 (t, 3J HH ) 1.76 Hz, 8H, Cp), 4.30 (t, 3J HH ) 1.71 Hz, 8H,
Cp), 4.02 (s, 20H, Cp) ppm; 29Si NMR (79.5 MHz, CD2Cl2) δ
Ack n ow led gm en t. M.J .M. thanks the Natural Sci-
ences and Engineering Research Council of Canada
(NSERC) for a Postgraduate Scholarship (1995-1999).
I.M. thanks the Alfred P. Sloan Foundation for a
Research Fellowship (1994-1998), the NSERC for an
E.W.R. Steacie Fellowship (1997-1999), and the Uni-
versity of Toronto for a McLean Fellowship (1997-
2003).
Su p p or tin g In for m a tion Ava ila ble: Tables of all bond
lengths and angles, anisotropic thermal parameters, and
atomic coordinates (37 pages). Ordering information is given
on any current masthead page.
-10.1 ppm; MS (EI, 70 eV) m/z (%) 768 (M+, 100), 517 (M+
-
Fc - C5H5, 49); Mo¨ssbauer spectrum doublet, IS 0.43, QS )
2.26 mm s-1; UV-vis (CH2Cl2) λ (ꢀ) 452 (490) nm (L mol-1
cm-1).
X-r a y Str u ctu r e Deter m in a tion Tech n iqu e. Crystals
of 3-6 were each mounted on a glass fiber and coated with
epoxy glue. The orange-red prisms of 3 and 4 had dimensions
OM971071I
(38) Sheldrick, G. M. SHELXA 90: Program for absorption correc-
tion; University of Go¨ttingen, Go¨ttingen, Germany, 1990.
(39) Sheldrick, G. M. SHELXTL-PC; Siemens Analytical X-ray
Instruments Inc., Madison, WI, 1994.