Synthesis and crystal structure of 1,1′-bis[4-(2,2′:6′,2″-terpyridin-4′-yl)phenyl]octamethylferrocene

Article abstract of DOI:10.1016/S0022-328X(01)00896-8

1,1′-Bis[4-(2,2′:6′,2″-terpyridin-4′-yl)phenyl]octamethylferrocene was prepared from iron(II) chloride and lithiated 4′-[4-(2,3,4,5-tetramethylcyclopenta-1,3-dien-1-yl)phenyl]-2,2′:6′,2″-terpyridin and was structurally characterised by X-ray diffraction,

Full text of DOI:10.1016/S0022-328X(01)00896-8

Journal of Organometallic Chemistry 637–639 (2001) 733–737
www.elsevier.com/locate/jorganchem
Note
Synthesis and crystal structure of
1,1%-bis[4-(2,2%:6%,2¦-terpyridin-4%-yl)phenyl]octamethylferrocene
Ulrich Siemeling a,*, Udo Vorfeld a, Beate Neumann b, Hans-Georg Stammler b,
Marco Fontani c, Piero Zanello c
a Department of Physics, Uni6ersity of Kassel, D-34109 Kassel, Germany
b Department of Chemistry, Uni6ersity of Bielefeld, D-33501 Bielefeld, Germany
c Department of Chemistry, Uni6ersity of Siena, I-53100 Siena, Italy
Received 15 December 2000; received in revised form 20 February 2001; accepted 21 February 2001
Abstract
1,1%-Bis[4-(2,2%:6%,2¦-terpyridin-4%-yl)phenyl]octamethylferrocene was prepared from iron(II) chloride and lithiated 4%-[4-(2,3,4,5-
tetramethylcyclopenta-1,3-dien-1-yl)phenyl]-2,2%:6%,2¦-terpyridin and was structurally characterised by X-ray diffraction, which
revealed pronounced p-stacking of the six-membered aromatic rings. Its electrochemistry was investigated by cyclic voltammetry
and controlled potential coulometry and compared with that of related compounds. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Cyclopentadienes; Iron; Oligopyridine ligands; p-Stacking; Cyclic voltammetry
excellent ligands for iron(II), ferrocenes containing such
substituents have exclusively been prepared by a less
1. Introduction
direct method, namely by functionalisation of
Donor-functionalised ferrocenes are of great current
ferrocene.
interest. They have been utilised, inter alia, as catalysts,
We have been interested in the limitations of the
sensors, thermotropic liquid crystals and non-linear
direct approach and have investigated this by utilising
optical materials [1]. A wide variety of ferrocenes con-
taining N-heterocyclic substituents such as pyridyl,
the terpyridyl-functionalised cyclopentadiene 1H as the
starting material.
bipyridyl and terpyridyl units have been reported in this
context [2]. The most straightforward way of preparing
ferrocenes starts from a cyclopentadiene, which is de-
protonated and subsequently allowed to react with
iron(II) chloride. In fact, this method has been widely
used for the preparation of a large variety of ferrocenes
containing N-, P-, O- and S-donor functionalities [3].
However, since oligodentate N-heterocyclic groups are
* Corresponding author. Present address: Metallorg Chem FB18/
In view of the extremely large complex formation
Physik, Univ. Gesamthochschule Kassel, Heinrich-Plett-Straße 40,
constant of [Fe(tpy)2]2+ (tpy=2,2%:6%,2¦-terpyridine)
this represents a rather extreme case [4].
D-34123 Kassel, Germany. Fax: +49-561-8044777.
E-mail address: siemeling@uni-kassel.de (U. Siemeling).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00896-8

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U. Siemeling et al. / Journal of Organometallic Chemistry 637–639 (2001) 733–737
2. Results and discussion
consisted of a black, paramagnetic solid. Owing to the
insolubility of the starting materials in toluene, rather
forcing reaction conditions were required (100 °C, 4
days).
The structure of (1)2Fe was determined by a single-crys-
tal X-ray diffraction study and is reminiscent of that of
1,1%-bis(2,2%:6%:2¦-terpyridyl)ferrocene, which had previ-
ously been prepared by functionalisation of ferrocene [5].
A view of the molecule is shown in Fig. 1.
Deprotonation of a colourless solution of 1H in
THF–hexane with LDA at −95 °C afforded a dark
green solution. Upon warming of the solution to room
temperature, 1Li precipitated as a brownish black solid,
which was collected by filtration, washed with toluene and
dried in vacuo. Reaction of the solid with D2O gave 1D
in quantitative yield. 1Li is essentially insoluble in all
common organic solvents, except DMSO, where it gives
a dark blue solution. The intensely dark colour of 1Li
is indicative of an extended chromophore such as that
present in the quinoid resonance structure B, which
appears to be more important than the cyclopentadienide
structure A.
Series of reactions of 1Li with iron(II) chloride in THF,
diethyl ether and THF–hexane were performed at tem-
peratures between −80 and 25 °C, but failed to yield
even trace amounts of the ferrocene (1)2Fe. In each case
a black, insoluble solid was obtained, which proved to
be paramagnetic. However, when the reaction was per-
formed in toluene in the absence of polar solvents, the
desired ferrocene was indeed formed, albeit in very low
yield (2–3%). The main part of the product again
Fig. 1. Molecular structure of (1)2Fe in the crystal. Selected bond lengths (pm): N(1)ꢀC(18) 134.3(4), N(1)ꢀC(19) 134.8(4), N(2)ꢀC(21) 134.1(4),
N(2)ꢀC(23) 134.0(4), N(3)ꢀC(26) 135.2(4), N(3)ꢀC(28) 133.6(4), N(4)ꢀC(48) 134.0(4), N(4)ꢀC(49) 135.0(4), N(5)ꢀC(51) 133.6(4), N(5)ꢀC(53)
133.9(4), N(6)ꢀC(56) 134.6(4), N(6)ꢀC(58) 133.8(4), C(5)ꢀC(10) 147.7(4), C(10)ꢀC(11) 139.4(4), C(10)ꢀC(15) 140.0(4), C(11)ꢀC(12) 138.3(4),
C(12)ꢀC(13) 139.1(4), C(13)ꢀC(14) 139.4(4), C(13)ꢀC(16) 148.6(4), C(14)ꢀC(15) 138.6(4), C(16)ꢀC(17) 138.9(4), C(16)ꢀC(20) 139.0(4), C(17)ꢀC(18)
139.3(4), C(18)ꢀC(21) 149.3(4), C(19)ꢀC(26) 149.0(4), C(21)ꢀC(22) 138.5(4), C(22)ꢀC(25) 138.0(5), C(23)ꢀC(24) 137.6(5), C(24)ꢀC(25) 137.2(5),
C(26)ꢀC(27) 138.7(5), C(27)ꢀC(30) 137.3(5), C(28)ꢀC(29) 137.2(5), C(29)ꢀC(30) 138.6(5), C(35)ꢀC(40) 147.9(4), C(40)ꢀC(41) 139.3(4), C(40)ꢀC(45)
140.6(4), C(41)ꢀC(42) 138.0(4), C(42)ꢀC(43) 139.9(4), C(43)ꢀC(44) 139.4(4), C(43)ꢀC(46) 148.9(4), C(44)ꢀC(45) 138.8(4), C(46)ꢀC(47) 139.7(4),
C(46)ꢀC(50) 139.3(4), C(47)ꢀC(48) 139.3(4), C(48)ꢀC(51) 149.9(4), C(49)ꢀC(50) 138.3(4), C(49)ꢀC(56) 149.0(4), C(51)ꢀC(52) 138.7(4), C(52)ꢀC(55)
138.7(5), C(53)ꢀC(54) 138.6(5), C(54)ꢀC(55) 137.0(5), C(56)ꢀC(57) 139.0(4), C(57)ꢀC(60) 137.6(4), C(58)ꢀC(59) 137.8(5), C(59)ꢀC(60) 138.6(5).

U. Siemeling et al. / Journal of Organometallic Chemistry 637–639 (2001) 733–737
735
Table 1
As expected, cyclic voltammetry on the orange
dichloromethane solution of (1)2Fe (umax=480 nm)
shows an oxidation process displaying features of
chemical (ipc/ipa constantly equal to 1 with scan rate)
and electrochemical (peak-to-peak separation close to
60 mV) reversibility. Controlled potential coulometry
(Ew= +0.2 V) consumes one electron/molecule. The
resulting yellow–green solution shows a broad and very
flattened band centred at about 840 nm with the con-
comitant disappearance of the original absorption
band. In addition, it exhibits a cyclic voltammetric
profile quite complementary to the original one, thus
confirming the complete stability of the monocation
[(1)2Fe]+. Table 1 compiles the relevant formal elec-
trode potential also in comparison with those of the
closely related ferrocenyl derivatives 2, [12] 3 [2d] and 4,
[12] which bear a single terpyridyl substituent, as well
as with decamethylferrocene [6].
Not surprisingly, all three terpyridyl-functionalised
ferrocenes are much more difficult to oxidise than
decamethylferrocene. It is the nature of the spacer unit
between the ferrocene nucleus and the terpyridyl unit,
which governs the redox potential. An acetylene unit is
very effective for p-delocalisation (cf. 2), whereas a
phenylene ring is not, if it is prevented from forming
small angles with neighbouring p-systems (cf. (1)2Fe
and 3 [2d]). The redox potential of (1)2Fe, which con-
tains two terpyridyl units, is almost identical to that of
3, which contains only one terpyridyl group. However,
3 contains a spacer unit consisting of rather electroneg-
ative sp-hybridised C atoms ( 2.99) [13] instead of the
less electronegative sp2-hybridised C atoms ( 2.66) [13]
present in (1)2Fe. In 2 and also in 4 p-delocalisation
and spacer electronegativity go hand in hand, leading
to remarkably large E0% values of +0.18 and +0.14 V,
respectively.
Formal electrode potentials (V, vs. SCE) and peak-to-peak separation
(mV) for the one-electron oxidation of the ferrocene derivatives under
study (dichloromethane solution, n-Bu4NPF6 (0.2 M) supporting
electrolyte)
a
Compound
E°%
DEp
(1)2Fe
2
3
4
+0.03
+0.18
+0.06
+0.14
−0.10
63
170
62
73
70
Cp2*Fe
a Measured at 0.1 V s−1
.
Despite the presence of two large substituents, the
ferrocene nucleus is almost undistorted. The cyclopen-
tadienyl ring tilt angle is only 2.3°. The ironꢀcarbon
bond lengths range from 206.0(3) to 208.0(3) pm, the
iron–ring centroid distances being 167 pm, which is
essentially identical to the values observed for ferrocene
and decamethylferrocene [6]. The cyclopentadienyl ring
Cꢀmethyl C distances are indistiguishable within exper-
imental error (average value 150.3 pm). In contrast to
decamethylferrocene [7], the cyclopentadienyl rings of
(1)2Fe are arranged in an eclipsed conformation, which
is most likely due to the extensive p-stacking observed
for the six-membered rings in this compound. It is well
documented that such intramolecular stacking in fer-
rocenes may be pronounced in case of electron-poor
aryl substituents [8]. The nature of p–p interactions in
metal complexes with aromatic nitrogen-containing lig-
ands was recently reviewed [9]. Bond lengths and angles
are unexceptional for the six-membered rings (CꢀC
distances range from 137.0(5) to 140.6(4) pm and CꢀN
distances from 133.6(4) to 135.2(4) pm). The closest
approach between the two aromatic decks occurs be-
tween C(15) and C(41), whose distance is only 314.5(4)
pm. This is considerably shorter than the van der Waals
distance between the two p-systems (335 pm for
graphite) [10]. Each six-membered ring of one ter-
pyridylphenyl substituent is approximately parallel to
its counterpart of the other terpyridylphenyl sub-
stituent. The three C5N rings of each terpyridyl unit are
arranged in the trans–trans conformation expected for
2,2%:6%,2¦-terpyridines [11]. The values of the angle be-
tween each central C5N ring and the best plane of the
cyclopentadienyl ring connected to it by a phenylene
ring are 9.0 and 9.2°, respectively. For steric reasons,
each phenylene ring is tilted considerably out of the
planes of the two rings attached to it (angles to C5 rings
are 33.7 and 40.1° respectively; angles to C5N rings are
26.6 and 30.9°, respectively), indicating that in agree-
ment with electrochemical results (vide infra) p-delocal-
isation is attenuated by the C6 rings.
3. Experimental
3.1. General considerations
All manipulations were performed in an inert atmo-
sphere (purified argon or dinitrogen) by using standard
Schlenk and cannula techniques or a conventional
glovebox. Solvents and reagents were appropriately
dried and purified by using standard procedures. NMR
spectra were recorded at 300 K with a Bruker DRX 500
1
spectrometer operating at 500.13 MHz for H-NMR;
1
TMS was used as external reference for H- and 13C-
NMR, and 1.0 M LiCl in D2O was used for 7Li.
Materials and apparatus used for the electrochemical
investigations have been described elsewhere [14]. Ele-
mental analyses were performed by the Microanalytical
Laboratory of the Universita¨t Bielefeld.

736
U. Siemeling et al. / Journal of Organometallic Chemistry 637–639 (2001) 733–737
3.2. Synthesis of 1Li
(5 ml). Insoluble material was removed by filtration
and washed with toluene (3×1 ml). The combined
toluene solutions were reduced to dryness in vacuo,
affording a light yellow solid. Yield: 99 mg (quantita-
tive). 1H-NMR (CDCl3): l=0.98 (s, 3H, Me), 1.87
(s, 3H, Me), 1.94 (s, 3H, Me), 2.08 (s, 3H, Me), 7.32
(m, 2H, terpyridyl 5,5¦-H), 7.36 (‘d’, 2H, apparent
J=8.2 Hz, C6H4), 7.85 (m, 2H, terpyridyl 4,4¦-H),
7.90 (‘d’, 2H, apparent J=8.2 Hz, C6H4), 8.66 (d,
2H, J=7.8 Hz, terpyridyl 3,3¦-H), 8.71 (d, 2H, J=
4.5 Hz, terpyridyl 6,6¦-H), 8.76 (s, 2H, terpyridyl
3%,5%-H). EIMS; m/z (%): 430 (100) [M+], 415 (33)
[M+−Me]. Anal. Found: C, 83.59; H, 6.31; N, 9.58.
Calc. for C30H26DN3 (430.57): C, 83.69; H+D, 6.55;
N, 9.76%.
A solution of 1H [15] (710 mg, 1.65 mmol) in a
mixture of THF (20 ml) and n-hexane (10 ml) was
cooled to −95 °C. A solution of LDA (115 mg, 1.80
mol) in THF (10 ml) was added dropwise with stir-
ring. The dark-green reaction mixture was allowed to
warm to room temperature (r.t.) overnight. Volatile
components were removed in vacuo. The remaining
solid was stirred with toluene (50 ml), filtered off,
washed with toluene (3×2 ml) and finally dried in
vacuo. Yield: 500 mg (70%). 1H-NMR (DMSO-d6):
l=1.90 (s, 6H, Me), 2.12 (s, 6H, Me), 7.13 (d, 2H,
apparent J=8.4 Hz, C6H4), 7.48 (m, 2H, terpyridyl
5,5¦-H), 7.59 (d, 2H, apparent J=8.5 Hz, C6H4), 8.00
(m, 2H, terpyridyl 4,4¦-H), 8.63 (d, 2H, J=8.0 Hz,
terpyridyl 3,3¦-H), 8.65 (s, 2H, terpyridyl 3%,5%-H),
8.75 (d, 2H, J=4.4 Hz, terpyridyl 6,6¦-H). 13C{1H}-
NMR (DMSO-d6): l=12.1, 14.4, 108.7, 112.5, 115.4,
115.6, 120.7, 122.8, 124.1, 125.1, 126.0, 137.2, 145.7,
149.2, 149.7, 155.1. 7Li-NMR (DMSO-d6): l=
−1.14.
3.4. Synthesis of (1)2Fe
Toluene (100 ml) was added to FeCl2 (356 mg, 2.81
mmol) and 1Li (2.45 g, 5.63 mol) and the mixture
stirred at 100 °C for 4 days. The dark solid was
removed by filtration. The volume of the filtrate was
reduced to ca. 20 ml. The crude product was precipi-
tated by slow addition of Et2O (20 ml) and isolated
by filtration. It was dissolved in CH2Cl2 (10 ml). Slow
addition of Et2O (10 ml) at 0 °C afforded pure
(1)2Fe as an orange, microcrystalline solid. Yield: 60
mg (2.3 %). 1H-NMR (CDCl3): l=1.75 (s, 12H,
Me), 1.88 (s, 12H, Me), 7.19 (m, 4H, terpyridyl 5,5¦-
H), 7.30 (‘d’, 4H, apparent J=7.9 Hz, C6H4), 7.67
(‘d’, 4H, apparent J=8.0 Hz, C6H4), 7.75 (m, 4H,
terpyridyl 4,4¦-H), 8.46 (d, 4H, J=7.9 Hz, terpyridyl
3,3¦-H), 8.54 (d, J=4.0 Hz, terpyridyl 6,6¦-H), 8.60
(s, 4H, terpyridyl 3%,5%-H). 13C{1H}-NMR (CDCl3):
l=9.8, 10.9, 78.6, 80.8, 85.3, 118.3, 121.1, 123.4,
126.1, 131.1, 135.0, 136.6, 138.0, 147.7, 148.9, 155.5,
156.2. MS (LSIMS, NBA matrix); m/z (%): 913 (5)
[(M+H)+]. Anal. Found: C, 78.50; H, 5.81; N, 9.22.
Calc. for C60H52FeN6 (912.96): C, 78.94; H, 5.74; N,
9.21%.
3.3. Synthesis of 1D
D2O (2.00 g, 100 mmol) was added to a stirred
suspension of 1Li (100 mg, 0.23 mmol) in THF (10
ml). After 1 h volatile components were removed in
vacuo. The remaining solid was stirred with toluene
Table 2
Crystal data and structure refinement parameters for (1)2Fe
Empirical formula
Formula weight
Crystal system
C62H54Cl6FeN6
1151.66
Monoclinic
P2(1)/n
Space group
Unit cell dimensions
,
a (A)
14.2649(7)
14.2793(7)
27.3792(13)
102.749(1)
5439.5(5)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
3.5. Crystal structure determination
zcalc (g cm−3
)
1.406
Absorption coefficient (v,
mm−1
F(000)
0.619
An orange single crystal of (1)2Fe·2CHCl3 (dimen-
sions 0.3×0.1×0.1 mm3), which was obtained by
slow evaporation of a chloroform solution, was used
for data collection at 183 K on a Siemens SMART
CCD area detector diffractometer with graphite-
)
2384
Index ranges
−185h518, −185k518,
−335l535
3.0–27.1
q range for data collection (°)
Reflections collected
Independent reflections
Data/restraints/parameters
Final R indices [I\2|(I)]
Goodness-of-fit on F2
51 009
,
monochromated Mo–Ka radiation (u=0.71073 A).
11 811 [Rint=0.0767]
11811/0/684
The structure was solved by direct methods. Pro-
grams used were Siemens SHELXTL PLUS [16] and
SHELXL 97 [17]. Full-matrix least-squares refinement
on F2 was carried out anisotropically for the non-hy-
drogen atoms. Hydrogen atoms were included at cal-
R1=0.0587, a wR2=0.1272 b
1.063
Largest difference peak and hole 0.638 and −0.552
−3
,
(e A
)
a R1=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
culated positions using
crystallographic data are given in Table 2.
a riding model. Further
b wR2={ꢀ[w(Fo2−Fc2)2]/ꢀ[w(F2o)2]}0.5
.

U. Siemeling et al. / Journal of Organometallic Chemistry 637–639 (2001) 733–737
737
(f) M.E. Padilla-Tosta, R. Mart´ınez-Ma´n˜ez, J. Soto, J.M. Lloris,
Tetrahedron 54 (1998) 12039;
4. Supplementary material
(g) C.M. Liu, J.J. Zhai, Y.X. Ma, Y.M. Liang, Synth. Commun.
28 (1998) 2731;
Crystallographic data for the structural analysis (ex-
cluding structure factors) have been deposited with the
Cambridge Crystallographic Data Centre, CCDC no.
153715 for compound (1)2Fe. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk.
For earlier work see: (h) B. Neumann, U. Siemeling, H.-G.
Stammler, U. Vorfeld, J.G.P. Delis, P.W.N.M. van Leeuwen, K.
Vrieze, J. Fraanje, K. Goubitz, F. Fabrizi de Biani, P. Zanello,
J. Chem. Soc. Dalton Trans. (1997) 4705, and references cited
therein.
[3] (a) H. Butenscho¨n, Chem. Rev. 100 (2000) 1527 (and references
cited therein);
(b) U. Siemeling, Chem. Rev. 100 (2000) 1495 (and references
cited therein).
[4] J.I. Bullock, P.W.G. Simpson, J. Chem. Soc. Faraday Trans. 1
77 (1981) 1991.
[5] E.C. Constable, A.J. Edwards, M.D. Marcos, P.R. Raithby, R.
Mart´ınez-Ma´n˜ez, M.J.L. Tendero, Inorg. Chim. Acta 224 (1994)
11.
Acknowledgements
[6] P. Zanello, in: A. Togni, T. Hayashi (Eds.), Ferrocenes, VCH,
Weinheim, 1995 (chap. 7).
[7] D.P. Freyberg, J.L. Robbins, K.N. Raymond, J.C. Smart, J.
Am. Chem. Soc. 101 (1979) 892.
[8] For recent examples see: (a) M.P. Thornberry, C. Slebodnick,
P.A. Deck, F.R: Fronczek, Organometallics 19 (2000) 5352;
(b) M.D. Blanchard, R.P. Hughes, T.E. Concolino, A.L. Rhein-
gold, Chem. Mater. 12 (2000) 1604.
This work was generously supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemis-
chen Industrie. P.Z. gratefully acknowledges the finan-
cial support of the University of Siena (PAR 1998).
[9] C. Janiak, J. Chem. Soc. Dalton Trans. (2000) 3885.
[10] U. Mu¨ller, Anorganische Strukturchemie, 3rd ed., Teubner,
Stuttgart, 1996, p. 132.
[11] See, for example: E.C. Constable, A.M.W. Cargill Thompson,
D.A. Tocher, M.A.M. Daniels, New J. Chem. 16 (1992) 885 (and
references cited therein).
[12] U. Siemeling, J. Vor der Bru¨ggen, in preparation.
[13] J. Huheey, E. Keiter, R. Keiter, Anorganische Chemie, 2nd ed.,
de Gruyter, Berlin, 1995, p. 214.
[14] A. Togni, M. Hobi, G. Rihs, G. Rist, A. Albinati, P. Zanello, D.
Zech, H. Keller, Organometallics 13 (1994) 1224.
[15] U. Vorfeld, U. Siemeling, in preparation.
[16] G.M. Sheldrick, SHELXTL PLUS, Siemens Analytical Instruments,
Madison, WI, USA, 1990.
References
[1] (a) A. Togni, T. Hayashi (Eds.), Ferrocenes, VCH, Weinheim,
1995;
(b) N.J. Long, in: Metallocenes, Blackwell, Oxford, UK, 1998.
[2] For recent examples see: (a) J.A. Mata, S. Uriel, R. Llusar, E.
Peris, Organometallics 19 (2000) 3797;
(b) R. Pastene, H. Le Bozec, S.A. Moya, Inorg. Chem. Com-
mun. 3 (2000) 376;
(c) C.M. Liu, B.H. Chen, W.Y. Liu, X.L. Wu, Y.X. Ma, J.
Organomet. Chem. 598 (2000) 348;
(d) U. Siemeling, U. Vorfeld, B. Neumann, H.-G. Stammler, P.
Zanello, F. Fabrizi de Biani, Eur. J. Inorg. Chem. (1999) 1;
(e) M. Buda, J.-C. Moutet, E. Saint-Aman, A. De Cian, J.
Fischer, R. Ziessel, Inorg. Chem. 37 (1998) 4146;
[17] G.M. Sheldrick, SHELXL 97, University of Go¨ttingen, Germany,
1997.