1,1-Bis(1″,2″,3″,4″,5″-pentamethylferrocen- 1′-yl)ethene

Article abstract of DOI:10.1016/S0022-328X(98)00924-3

1,1-Bis(1″,2″,3″,4″,5″-pentamethylferrocen- 1′-yl)ethene (6) was synthezised as a prototype of two metallocenes that are bridged by the sp²-carbon center of a vinylidene group. Starting from 6-N,N-dimethylamino-6-methylfulvene, the iron-containing intermediates were a pentamethylferrocenyl-substituted fulvene and an ethene that was geminally disubstituted by a Cp anion and a pentamethylferrocenyl moiety. Besides other methods, the ferrocenes were characterized by NMR spectroscopy including full signal assignment. The bimetallic compound 6 showed moderate interactions between the two ferrocenes in the cyclic voltammogram (ΔE_1/2=150 mV). According to X-ray crystal structure analysis compound 6 is a twisted molecule; the vinylidene moiety and the Cps of the neighboring ferrocenes are not coplanar.

Full text of DOI:10.1016/S0022-328X(98)00924-3

Journal of Organometallic Chemistry 574 (1999) 94–98
1,1-Bis(1¦,2¦,3¦,4¦,5¦-pentamethylferrocen-1%-yl)etheneꢀ
Oliver M. Heigl, Martin A. Herker, Wolfgang Hiller, Frank H. Ko¨hler *, Andreas Schell
Anorganisch-chemisches Institut, Technische Uni6ersita¨t Mu¨nchen, D-85747 Garching, Germany
Received 23 June 1998; received in revised form 24 August 1998
Abstract
1,1-Bis(1¦,2¦,3¦,4¦,5¦-pentamethylferrocen-1%-yl)ethene (6) was synthezised as a prototype of two metallocenes that are bridged
by the sp2-carbon center of a vinylidene group. Starting from 6-N,N-dimethylamino-6-methylfulvene, the iron-containing
intermediates were a pentamethylferrocenyl-substituted fulvene and an ethene that was geminally disubstituted by a Cp anion and
a pentamethylferrocenyl moiety. Besides other methods, the ferrocenes were characterized by NMR spectroscopy including full
signal assignment. The bimetallic compound 6 showed moderate interactions between the two ferrocenes in the cyclic voltam-
mogram (DE1/2=150 mV). According to X-ray crystal structure analysis compound 6 is a twisted molecule; the vinylidene moiety
and the Cps of the neighboring ferrocenes are not coplanar. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Ferrocenes; Bimetallic compounds; Cyclic voltammetry
1. Introduction
within and the length and the rigidity of the bridge. The
shortest bridge is just one bond, and we have recently
terminated work on bimetallocenes (A) which feature
striking differences in the magnetic behavior all the way
from weakly antiferromagnetic to strongly ferromag-
netic interaction [2]. When one sp3-hybridized atom per
bridge is introduced, as for instance by using SiMe2
groups in B [3], considerable damping of the interaction
is observed. A good candidate for further testing the
tuning bandwidth of the interaction should be a one-
sp2-carbon bridge as present in vinylidene-bridged
metallocenes (C). In contrast to the intensively studied
ferrocenes separated by conjugated chains (D) [4] only
little is known about C. An isomeric iron derivative of
C was mentioned in a series of products that demon-
strated the usefulness of a new CpFe+ transfer reaction
[5a]. A ferrocene having the bridging ligand of C was
reported recently [5b], and corresponding t-butyl-sub
stituted ligands are also known [5c]. Here we report the
syntheses, the redox properties, and the structure of
vinylidene-bridged pentamethylferrocenes.
The title compound 1,1-bis(1¦,2¦,3¦,4¦,5¦-pen-
tamethylferrocen-1%-yl)ethene is a new member of the
family of bridged ferrocenes which has been the focus
of many research projects [1]. The reason for the wide-
spread interest is that, with certain bridges, the fer-
rocenes are no longer independent of each other.
Rather interactions occur that bring about new
properties.
The ultimate goal of the approach would be to
transfer some of these properties to high-nuclear com-
pounds or even polymeric materials. However, it is
advisable to perform a property tuning with di- and
trinuclear model compounds in order to reduce the
number of interfering parameters such as the bonding
ꢀ In honor of the late Professor Rokuro Okawara.
* Corresponding author. Tel.:+49-89-2891-3109; fax: +49-89-
2891-3762; e-mail: f.h.koehler@lrz.tu-muenchen.de.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00924-3

O.M. Heigl et al. / Journal of Organometallic Chemistry 574 (1999) 94–98
95
2.2. Spectroscopic characterisation and cyclic
6oltammetry
Besides mass spectroscopy, which showed the ex-
pected isotopic patterns of the molecular ions of 4 and
6, NMR spectroscopy was applied to establish the
ferrocene derivatives. The 1H-NMR signals could be
assigned straightforwardly except for those of the five-
membered ring protons of 4, 5, and 6. H-2%,5% and
H-3%,4% were distinguished by recording a NOE-differ-
ence spectrum of 6. The signal at 4.11 ppm was as-
signed to H-2%,5%, because it experienced a NOE
enhancement when the signal of the neighboring
methylene protons was irradiated. The same signal
sequence of H-2%,5% and H-3%,4% was assumed for 4 and
5. The fulvene protons of 4 were assigned according to
literature precedents [10]. All five-membered ring pro-
tons appeared as pseudo triplets for which the sum
3JH,H+4JH,H [11] is given in the Section 3. Based on the
1H-NMR results the non-trivial assignments of the
13C-NMR signals were assured by H,C-HMQC and
H,C-HMBC experiments [12]. Interestingly, in 6 the
nuclei H-2%,5%, H-3%,4%, C-2%,5% and C-3%,4% are equivalent
thus implying C2 symmetry which is higher than that
found in the crystal (see below). We conclude that in
solution the two ferrocene moieties of 6 undergo a
rapid oscillation about the bonds C-1–C-6 and C-6–C-
8 with the coplanar arrangement being energetically less
favorable. Similarly, the ferrocene 4 has a dynamic
structure in solution owing to torsional flexibility about
the bond C-1–C-6. This follows from the fact that for
the nuclei in positions 2%-5% of 4 only two 1H- and
13C-NMR signals were found. Temperature-dependent
1H-NMR spectra down to 185 K did not show any
splitting or even a selective broadening of the signals of
H-2%,5% and H-3%,4%. Hence the corresponding energy
barriers must be low. The NMR data of 4 and 6 may
serve as a basis for the signal assignment of similar
2. Results and discussion
2.1. Synthesis
With a more generally applicable synthesis in view
we decided to prepare the bridging ligand first and to
subsequently attach the Cp*Fe moieties rather than
starting from a substituted ferrocene [5b]. Thus, the
fulvene-substituted Cp anion 3 was prepared as de-
picted in Scheme 1. The aminofulvene 2, which belongs
to a well known class of y-systems [6], was prepared by
analogy to the non-methylated compound [7]. Its con-
version to 3 proceeded in an equilibrium reaction which
was pushed by the addition of crown ether [8]. The
isolation of 3 was hampered by polymerization.
In a stepwise reaction (Scheme 2) the anion 3 was
first converted into the mixed-ligand ferrocene 4 by
reaction with the TMEDA adduct of Cp*FeCl [9].
Subsequent deprotonation of 4 with the lithium salt of
2,2,6,6-tetramethylpiperidide, and renewed reaction
with the iron half-sandwich afforded the desired vinyli-
dene-bridged pentamethylferrocene 6 which was ob-
tained in an analytically pure form in an overall yield of
27% starting from 2.
compounds;
examples
are
6-(pentamethylferro-
Scheme 2. Synthesis of the bridged ferrocene 6. (a)
Cp*FeCl(TMEDA); (b) lithium 2,2,6,6-tetramethylpiperidide.
Scheme 1. Synthesis of the bridging ligand 3. (a) (CH3O)2SO2, DT;
(b) NaCp; (c) 18-crown-6, NaCp; (d) –(CH3)2NH.

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O.M. Heigl et al. / Journal of Organometallic Chemistry 574 (1999) 94–98
metallocene interactions, as seen by cyclic voltammetry,
do not change very much on passing from a bridge
containing one sp3-carbon to a bridge containing one or
two sp2-carbons.
2.3. Molecular structure of 6
The vinylidene-bridged biferrocene 6 is a rather dis-
torted molecule (Fig. 2). Not only are there angles of
5.0 and 5.4° between the two Cp planes at Fe(1) and
Fe(2), respectively; but also, and more strikingly, the
bridging ligand is twisted. Relative to the plane C(1),
C(6), C(7), C(8) the twist angle of the Cp planes
C(1)–C(5) and C(8)–C(12) is 11.0 and 10.3°, respec-
tively. The molecular symmetry in the crystal is C1 as
opposed to C2 in solution (see above). In the end, the
distorsion of 6 is related to that of the thoroughly
investigated biphenyl [16], because in 6 the steric inter-
ference of H(7) and H(2)/H(12) (and H(5)/H(9) after
rotation about the bonds C(1)–C(6) and C(6)–C(8))
resembles that of the 2,2%,6,6%-protons of biphenyl.
Probably the closest relative of 6 is 1,1-di(p-tolyl)ethene
which is twisted in much the same way [17]. This
structural feature is also present in diferrocenylketones
[13,18] and some more complicated bridged ferrocenes
[19].
Fig. 1. Cyclic voltammogram of 6 in EtCN (0.86 mmol l−1) at 295 K.
Scan rate 200 mV s−1. Potential scale given relative to internal
Cp2Co/Cp2Co+
.
cenyl)fulvene and bis(pentamethylferrocenyl)ketone [13]
for which too many signals were reported and most
NMR signals were not assigned.
The cyclic voltammogram of 6 (Fig. 1) displayed two
reversible electron transfers (ETs) at 1.02 and 1.17 V
(relative to the ET of internal Cp2Co/Cp2Co+) with
DEp=55 and 60 mV, respectively (DEp=separation of
the anodic and cathodic peak potentials). It follows
that, upon increasing the potential, the expected succes-
sive formation of the mono- and dication of 6 was
observed, which in turn established the interaction be-
tween the ferrocene moieties. The ET separation of
DE1/2=150 mV is moderate; stronger interactions are
known for decamethylbiferrocene (molecule A with
M=Fe; DE1/2=375 mV in EtCN [2a] and 240 mV in
THF [14]), while they are similar in E-1,2-bis(ferro-
cenyl)ethene (molecule D with n=1; DE1/2=170 mV in
CH2Cl2 [4]), and in diferrocenylmethane (DE1/2=100
mV in EtOH [15]). Although the DE1/2 values are
modulated by solvent effects, it is evident that the
˚
It is worth noting that C(6)–C(7) (1.338(3) A) is an
isolated double bond while the bonds between C(6) and
the ferrocenyl carbons C(1) and C(8) (1.472(3) and
˚
1.480(3) A, respectively) are normal single bonds be-
tween sp2-carbons. The metal-Cp distances (1.646(4)–
˚
1.653(4) A) are in the usual range, the Fe…Fe distance
˚
is 5.602(4) A, and the other bond lengths and angles do
not deviate from what is known from the plethora of
ferrocenes.
3. Experimental section
The synthetic work and the physical measurements
were carried out under purified dinitrogen, and dry,
oxygen-free solvents were used. The mass spectra were
obtained from a Varian Mat 50 instrument and the
NMR spectra from Jeol JNM 270 and Jeol Lambda
400 spectrometers. The signal shifts (l) were measured
relative to the solvent signals of C6D6 (l (1H)=7.15, l
(13C)=128.0) and DMSO-d6 (l (1H)=2.49) and calcu-
lated relative to TMS. The digital resolution of the 1D
spectra was 0.23 Hz/data point, and for the HMQC
and HMBC spectra 1024×1024 and 2048×512 data
points, respectively, were used. Cyclic voltammetry ex-
periments were run with equipment described previ-
ously [20]. Before adding the compound the 0.1 M
solution of n-Bu4NPF6 in EtCN was dried in the cell by
passing it several times over activated Al2O3. The ele-
mental analyses were carried out by the in-house Mi-
croanalytical Laboratory.
Fig. 2. Molecular structure of 6 (ORTEP plot, displacement ellipsoids
at the 50% probability level). For clarity the H-atoms were omitted
and only the basic numbering is given.

O.M. Heigl et al. / Journal of Organometallic Chemistry 574 (1999) 94–98
97
Table 1
mixture was allowed to come to room temperature (r.t.)
overnight, THF was stripped under reduced pressure,
and the remaining solid was extracted with hexane. The
solution was cooled to −78°C, and a precipitate of
unreacted 2 was filtered off. Subsequently, the solvent
was removed in vacuo, and the oily residue was freed
from the by-products deca- and pentamethylferrocene
by sublimation (1 mbar, 100°C) leaving behind 1.31 g
of deep violet 4 which contained little impurities ac-
Crystal data and structure refinement of 6
Molecular formula
Molecular weight
Temperature (K)
Wavelength (pm)
Crystal system
Space group
a (pm)
C32H40Fe2
536.34
193(2)
71.073
Monoclinic
C2/c
2890.4(3)
830.4(1)
2209.6(2)
92.87(1)
5.296(1)
8
1.345
1.114
2272
0.55×0.26×0.20
3 to 26
05h535, 05k510,
−275l526
5274
5169 [Rint=0.0183]
4213
Empirical
1.000 and 0.595
Full-matrix least squares
on F2
b (pm)
c (pm)
1
cording to H-NMR spectroscopy.
CI–MS: m/z 347 ([MH]+, 100%), 210 ([MH-Cp*]+,
3%); isotope pattern of [MH]+: m/z (% exptl./calc.) 349
(5.1/3.5), 348 (23.6/27.4), 347 (100.0/100.0), 346 (4.6/
1.6), 345 (8.9/6.3). 1H-NMR (400.05 MHz, 295 K,
C6D6, numbering see Scheme 2): l 6.90 (1H, m, H-2),
6.75 (1H, m, H-5), 6.70 (1H, m, H-3), 6.66 (1H, m,
H-4), 4.12 (2H, „t, 3JH,H+4JH,H=3.4 Hz, H-2%,5%),
i (°)
V (nm3)
Z
Dcalc. (mg m−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
q range of measurement (°)
Index ranges
3
3.80 (2H, „t, JH,H+4JH,H=3.8 Hz, H-3%,4%), 2.22 (2H,
s, H-7), 1.59 (15H, s, C5(CH3)5). 13C{1H}-NMR (100.50
Reflections collected
Independent reflections
Reflections observed
Absorption correction
Max. and min. transmission
Refinement
Table 2
Atomic coordinates (×104) and isotopic displacement parameters
(pm2 10−1] of 6a
Atom
x/a
y/b
z/c
Ueq
Data, parameters
5169, 317
Goodness-of-fit
Final R values [Fo\4|(Fo)]
R values (all data)
1.097
Fe(1)
Fe(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
1502(1)
870(1)
3164(1)
3525(1)
5854(1)
4410(1)
4048(1)
3565(1)
3609(1)
4126(1)
4955(1)
5193(1)
5246(1)
5026(1)
5452(1)
5940(1)
5815(1)
3524(1)
3217(1)
2725(1)
2727(1)
3222(1)
4046(1)
3383(1)
2282(1)
2286(1)
3360(1)
5957(1)
5824(1)
6282(1)
6700(1)
6495(1)
5611(1)
5316(1)
6340(1)
7263(1)
6814(1)
24(1)
21(1)
30(1)
38(1)
43(1)
41(1)
35(1)
30(1)
47(1)
27(1)
29(1)
33(1)
34(1)
31(1)
25(1)
27(1)
30(1)
29(1)
26(1)
38(1)
44(1)
47(1)
50(1)
41(1)
26(1)
26(1)
26(1)
24(1)
25(1)
41(1)
37(1)
40(1)
36(1)
40(1)
R1=0.0287, wR2=0.0678
R1=0.0464, wR2=0.0736
−253 and 311
2212(1)
2497(3)
2473(3)
1379(3)
707(3)
1664(1)
2063(1)
1988(1)
1540(1)
1343(1)
1625(1)
1999(1)
1178(1)
719(1)
Residual electron density zmin, zmax
(e nm−3
)
1385(3)
3497(3)
4259(4)
3708(3)
3274(3)
3778(3)
4527(3)
4488(3)
5478(2)
5398(3)
4287(3)
3678(3)
4418(2)
6547(3)
6348(3)
3844(3)
2510(3)
4233(3)
103(2)
The X-ray data were obtained from an automated
four-circle diffractometer CAD4 (NONIUS) working
with Mo–Kh (u=0.71073 A) radiation. Experimental
details and the atomic positional parameters are given
in Tables 1 and 2, respectively. The structure was
solved and refined by using the program package
SHELXTL, version 5.03 (Brucker-AXS). Further data
may be obtained on request from the Director, Cam-
bridge Crystallographic Data Centre, Lensfield Road,
Cambridge CB2 lEW, UK.
C(8)
C(9)
˚
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
400(1)
650(1)
1125(1)
1246(1)
1670(1)
1607(1)
1144(1)
923(1)
1151(1)
2099(1)
1961(1)
921(1)
424(1)
1243(1)
764(1)
505(1)
822(1)
3.1. 6-Methyl-6-(1¦,2¦,3¦,4¦,5¦-pentamethyl-
ferrocen-1%-yl)ful6ene (4)
−242(2)
481(2)
A solution of the sodium salt of 6-cyclopentadienyl-
6-methylfulvene (2) was prepared from 1.45 g (10
mmol) 6-dimethylamino-6-methylfulvene in 60 ml of
THF, 290 mg (1 mmol) of 18-crown-6 and 6.0 ml of a
1.71 M solution of NaCp (10 mmol) in THF as de-
scribed for the non-methylated analogue [8]. The result-
ing reaction mixture was cooled to −78°C, and 2.06 g
(60 mmol) of Cp*FeCl(TMEDA) [9] was added with
stirring. The reaction was accompanied by a color
change from brown–red to dark violet. The reaction
1287(2)
1049(2)
−500(3)
−1286(3)
394(3)
1278(1)
1642(1)
576(1)
−12(1)
701(1)
2161(3)
1622(3)
1716(1)
a Ueq is calculated as one third of the trace of the orthogonal Uij
tensor.

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O.M. Heigl et al. / Journal of Organometallic Chemistry 574 (1999) 94–98
MHz, 299 K, C6D6): l 149.1 (C-6), 141.7 (C-1), 131.0
(C-3), 128.8 (C-4), 122.2 (C-2), 122.0 (C-5), 85.0 (C-1%),
81.2 (C5(CH3)5), 76.4 (C-3%,4%), 73.0 (C-2%,5%), 21.3 (C-7),
10.7 (C5(CH3)5).
Acknowledgements
We thank J. Riede for collecting the X-ray data and
the Fonds der Chemischen Industrie for financial
support.
3.2. Deprotonation of 4
A total of 3.66 g (10 mmol) of compound 4 was
dissolved in diethyl ether and cooled to −78°C. When
2.21 g (15 mmol) of lithium 2,2,6,6-tetramethylpiperi-
dide was added to the stirred solution, and when the
mixture was warmed to r.t. within 2 h, the color
changed from deep violet to light orange. The excess
piperidide was filtered off, and the solvent was removed
in vacuo. After the remaining solid was washed with
hexane and dried 2.5 g (7.3 mmol, 73%) of orange
spectroscopically pure (1H-NMR) 5 was obtained.
1H-NMR (270.17 MHz, 298 K, DMSO-d6, number-
ing see Scheme 2): l 5.49 (2H, m, H-2,5), 5.27 (2H, m,
H-3,4), 4.69 (2H, s, H-7), 4.16 (2H, m, H-2%,5%), 4.02
(2H, m, H-3%,4%), 1.76 (15H, s, C5(CH3)5).
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Organometallics 14 (1995) 5566. (c) B. Bildstein, P. Denifl, K.
Wurst, et al., Organometallics 14 (1995) 4334. (d) D. Schu¨tte, T.
Oeser, H. Irngartinger, W. Wiessler, Tetrahedron Lett. 36 (1995)
5163.
2
Further cooling of the remaining solution to −78°C
gave a crystalline product from which residual Cp2*Fe
was removed by sublimation (1 mbar, 100°C) leaving
behind 37 mg (0.07 mmol, 58%) of red crystals of 6.
One of these crystals was used for X-ray crystal
analysis.
Mp: 177–178°C (slow decomposition above 150°C).
Found: C, 71.52; H, 7.59%, C32H40Fe2 requires: C,
71.62; H, 7.52; Fe 20.84%. CI–MS: m/z 536.5 ([MH]+,
100%), 346.5 ([MH–Cp*Fe]+, 27%), 256.3 ([MH–
Cp*FeC7H6]+, 72%); isotope pattern of [MH]+: m/z
(% exptl./calc.) 539 (8.6/9.7), 538 (39.5/37.3), 537
1
(100.0/100.0), 536 (5.4/4.9), 535 (12.7/14.5). H-NMR
(400.05 MHz, 295 K, C6D6, numbering see Scheme 2):
3
l 5.49 (2H, s, H-2), 4.11 (4H, „t, JH,H+4JH,H=3.6
3
Hz, H-2%,5%), 3.71 (4H, „t, JH,H+4JH,H=3.8 Hz, H-
3%,4%), 1.74 (15H, s, C5(CH3)5). 13C{1H}-NMR (100.5
MHz, 297 K, C6D6): l 141.1 (C-1), 107.9 (C-2), 86.4
(C-1), 80.0 (C5(CH3)5), 72.8 (C-3%,4%), 71.0 (C-2%,5%), 10.9
[20] H. Atzkern, J. Hiermeier, F.H. Ko¨hler, A. Steck, J. Organomet.
Chem. 408 (1991) 281.
(C5(CH3)5).
.