Aminoferrocenes and aminocobaltocenes as redox-active chelating ligands: Syntheses, structures, and coordination chemistry

Article abstract of DOI:10.1021/om9602771

The enamine reaction can be applied to secondary amines and 3,4-diphenylcyclopentenone to produce the corresponding aminodiphenylcyclopentadienes in yields between 42 and 52%. Deprotonation of these cyclopentadienes and reaction with Fe(II) and Co(II) salts gave the respective diaminotetraphenylferrocenes and diaminotetraphenylcobaltocenes in yields of around 50%. In the amines chosen for our study the nitrogen atoms are part of a chelating ligand, which is able to form complexes with metal ions. Hence, the formation of stable complexes of Zn²⁺ and Co²⁺ salts with 1,1′-bis(di-2-picolylamino)-3,3′,4,4′-tetraphenylferrocene (12) was investigated. In the X-ray crystal structure of 12·2ZnBr₂ it is apparent that the nitrogen atoms directly bonded to the ferrocene 12 take part in the coordination of Zn²⁺. This nitrogen donor thus acts as a relay, enhancing the electronic communication between the redox-active ferrocene center and the metal ion (Zn²⁺ or Co²⁺); consequently in the cyclic voltammograms of 12 addition of metal salts leads to very large changes in the redox potential of the ferrocene unit. The relative anodic shift upon addition of Zn(CF₃SO₃)₂ is Δ(ΔE_1/2) = +330 mV (12·Zn²⁺) and Δ(ΔE_1/2) = +720 mV (12·2Zn²⁺). Upon complexation of Co²⁺ each metal ion produces a Δ(ΔE_1/2) = +380 mV; thus the redox potential of 12·2Co²⁺ is shifted by Δ(ΔE_1/2) = +760 mV relative to that of 12. This corresponds to a reduction in the stability constant for the complexation of Co²⁺ by approximately 3.4 × 10⁶ per Co²⁺. It is apparent therefore that our concept of attaching donor atoms directly to the redox-active ferrocene unit leads to very large redox-switching effects.

Full text of DOI:10.1021/om9602771

4054
Organometallics 1996, 15, 4054-4062
Am in ofer r ocen es a n d Am in ocoba ltocen es a s
Red ox-Active Ch ela tin g Liga n d s: Syn th eses, Str u ctu r es,
a n d Coor d in a tion Ch em istr y1
Herbert Plenio*,† and Dirk Burth
Institut fu¨r Anorganische und Analytische Chemie, Albertstr. 21, 79104 Freiburg, Germany
Received April 11, 1996X
The enamine reaction can be applied to secondary amines and 3,4-diphenylcyclopentenone
to produce the corresponding aminodiphenylcyclopentadienes in yields between 42 and 52%.
Deprotonation of these cyclopentadienes and reaction with Fe(II) and Co(II) salts gave the
respective diaminotetraphenylferrocenes and diaminotetraphenylcobaltocenes in yields of
around 50%. In the amines chosen for our study the nitrogen atoms are part of a chelating
ligand, which is able to form complexes with metal ions. Hence, the formation of stable
complexes of Zn2+ and Co2+ salts with 1,1′-bis(di-2-picolylamino)-3,3′,4,4′-tetraphenylferrocene
(12) was investigated. In the X-ray crystal structure of 12‚2ZnBr2 it is apparent that the
nitrogen atoms directly bonded to the ferrocene 12 take part in the coordination of Zn2+
.
This nitrogen donor thus acts as a relay, enhancing the electronic communication between
the redox-active ferrocene center and the metal ion (Zn2+ or Co2+); consequently in the cyclic
voltammograms of 12 addition of metal salts leads to very large changes in the redox potential
of the ferrocene unit. The relative anodic shift upon addition of Zn(CF3SO3)2 is ∆(∆E1/2) )
+330 mV (12‚Zn2+) and ∆(∆E1/2) ) +720 mV (12‚2Zn2+). Upon complexation of Co2+ each
metal ion produces a ∆(∆E1/2) ) +380 mV; thus the redox potential of 12‚2Co2+ is shifted by
∆(∆E1/2) ) +760 mV relative to that of 12. This corresponds to a reduction in the stability
constant for the complexation of Co2+ by approximately 3.4 × 106 per Co2+. It is apparent
therefore that our concept of attaching donor atoms directly to the redox-active ferrocene
unit leads to very large redox-switching effects.
In tr od u ction
an electronic point of view since this bridge effectively
insulates the two metal centers from each other. It is
obvious therefore that a transmission of electronic
effects via bonding electrons would be much more
efficient.5 The best way to realize this would be to
directly link at least one donor atom of a chelating
ligand to the cyclopentadienyl ring of a ferrocene. The
efficiency of such an approach has recently been dem-
onstrated by Wrighton et al. for metal carbonyl com-
plexes of 1,1′-bis(diphenylphosphino)ferrocene (dppf),
where carbonyl reactivity could be modulated reversibly
by changing the oxidation state of the appended fer-
rocene unit.6
Our target therefore was to synthesize ferrocenes in
which a nitrogen atom bonded to the cyclopentadienyl
ring is part of a chelating ligand and can thus act as a
transmitter enhancing the electronic communication
between two metal centers.
Metallocenes which have a nitrogen atom directly
bonded to the five-membered ring are not very common
since substitution reactions at the aromatic ring are not
straightforward, neither with nitrogen-based nucleo-
philes nor with electrophiles which are strong oxi-
dantsssuch as NO2+sor relatively unstable compounds
such as hydroxylamine derivatives.7,8
Numerous ferrocenes have been described in recent
years in which the metallocene is linked to a chelating
ligand. Interesting effects such as the redox-switched
bonding of metal ions within ferrocene crown ethers or
investigations into the potential use of such compounds
as amperometric sensors for metal ions or protons have
been among the highlights of this development.2,3
The performance of such molecular devices depends
on an efficient electronic communication between the
ferrocene and the metal ion coordinated within the
chelating ligand. The situation so far has not been ideal
as in most ferrocene chelate metal complexes the two
metal centers “talk” to each other mainly via Coulomb
type interactions.4 This obviously is a structural con-
sequence of the fact that in most substituted ferrocenes
the chelating ligand and the metallocene are separated
by a CH2 group.2,3 This linker may facilitate the
synthesis of these compounds, but it is less ideal from
† E-mail: plenio@ruf.uni-freiburg.de.
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) Dedicated to Prof. Dr. M. Herberhold on the occasion of his 60th
birthday.
(2) (a) vanVeggel, F. C. J . M.; Verboom, W.; Reinhoudt, D. N. Chem.
Rev. 1994, 94, 279. (b) Beer, P. D. Adv. Inorg. Chem. 1992, 39, 79. (c)
Medina, J . C.; Goodnow, T. T.; Rojas, M. T.; Atwood, J . L.; Lynn, B.
C.; Kaifer, A. E.; Gokel, G. W. J . Am. Chem. Soc. 1992, 114, 10583. (d)
Chen, Z.; Pilgrim, A. J .; Beer, P. D. J . Chem. Soc., Faraday Trans.
1995, 4331. (e) Beer, P. D.; Crane, C. G.; Danks, J . P.; Gale, P. A.;
McAleer, J . F. J . Organomet. Chem. 1995, 490, 143. (f) Plenio, H.;
Diodone, R. J . Organomet. Chem. 1995, 492, 73. (g) Plenio, H.; Burth,
D.; Gockel, P. Chem. Ber. 1993, 126, 2585.
(3) (a) Tendero, M. J . L.; Benito, A.; Martinez-Manez, R.; Soto, J .;
Paya, J .; Edwards, A. J .; Raithby, P. R. J . Chem. Soc., Dalton Trans.
1996, 343. (b) Plenio, H.; El-Desoky, H.; Heinze, J . Chem. Ber. 1993,
126, 2403.
Up to our work only very few aminocyclopentadienes9
were known.10 Probably the best synthesis originates
from work by Boche et al., who prepared several N,N-
dialkylaminocyclopentadienes in good yields from O-
tosylated N,N-dialkylhydroxylamines and C5H5-. This
(5) Schmittel, M.; Ammon, H.; Wo¨hrle, C. Chem. Ber. 1995, 128,
845.
(4) (a) Plenio, H.; Yang, J .; Diodone, R.; Heinze, J . Inorg. Chem.
1994, 33, 4098. (b) Plenio, H.; Diodone, R. Inorg. Chem. 1995, 34, 3964.
(6) Lorkovic, I. M.; Wrighton, M. S.; Davis, W. M. J . Am. Chem. Soc.
1994, 116, 6220.
S0276-7333(96)00277-4 CCC: $12.00 © 1996 American Chemical Society

Aminoferrocenes and Aminocobaltocenes
Organometallics, Vol. 15, No. 19, 1996 4055
Sch em e 1. Syn th esis of
Sch em e 2. Syn th esis of th e
3,4-Dip h en ylcyclop en t-2-en on e
Am in ocyclop en ta d ien es a n d th e 2-Am in oin d en es
approach consequently led to the synthesis of the
respective aminoferrocenes as well as other η5-bound
metal complexes in good yields.11,12 On the other hand,
however, the number of hydroxylamines is rather
limited and the handling of these compounds poses
certain risks,13 which severly limits the scope of this
reaction. Another drawback is the fact that aminocy-
clopentadienes of the type C5H5NR2 are thermally and
oxidatively rather sensitive compounds.
We have recently demonstrated that the enamine
reaction of 2-indanone with sec-amines is very efficient
in the generation of 2-aminoindenes, which can be used
to synthesize the respective η5-bound complexes such
as cymantrenes,14 zirconocenes,15 and cobaltocenes.16
We wish to report here on a general synthesis of
aminocyclopentadienes with chelating ligands in the
side chain, on the formation of the respective amino-
ferrocenes and aminocobaltocenes, on the synthesis of
complexes of metal salts with such metallocenes, and
on the consequences of metal ion coordination on the
redox behavior.17
For the synthesis of the aminocyclopentadienes and
the 2-aminoindenes described here sec-amines were
reacted with 2-indanone and 3,4-diphenylcyclopent-2-
enone, respectively. The amines used in this study were
deliberately chosen such that they contain additional
ligating groups to later allow the formation of classical
Werner type complexes. In this way a heteroditopic
ligand is generated, which offers a π-face for the bonding
of organometallic fragments and a σ-face for the coor-
dination of metal ions.
Resu lts a n d Discu ssion
Syn th esis of th e Am in ocyclop en ta d ien es a n d
2-Am in oin d en es. To stabilize the aminocyclopenta-
dienes with respect to Diels-Alder dimerization and
toward oxidative attack, additional substituents at-
tached to the five-membered ring are required. Con-
sequently 3,4-diphenylcyclopent-2-enone was chosen as
a starting material since it is easily available in large
amounts (>100 g) in a two-step reaction (Scheme 1)
using very cheap starting materials18,19 and since the
two phenyl groups will provide sufficient steric bulk as
well as electronic stabilization in the anticipated ami-
nocyclopentadienes.
While the enamine reaction with sec-amines and
2-indanone is well established,20 up to our work only a
single example of enamine formation from a cyclopen-
tenone and an amine had been described.21 We have
thus reacted 3,4-diphenylcyclopent-2-enone with differ-
ent amines such as N-methylpiperazine, trimethyleth-
ylenediamine, N,N′-dimethylethylenediamine, and di-
picolylamine in benzene in the presence of catalytic
amounts of acid. The reaction is driven to completion
by removing the reaction water azeotropically, and the
respective aminocyclopentadienes were isolated in yields
between 42 and 52%. The enamine formation of 2-in-
danone with sec-amines is straightforward; conse-
quently the reactions of 2-indanone with dipicolyamine
and N,N′-dimethylethylenediamine yielded the respec-
tive 2-aminoindenes in very good yields (Scheme 2).
In principle all sec-amines can be used for the
synthesis of aminocyclopentadienes; however, with ster-
ically demanding amines the formation of enamines is
rather slow. Changing the solvent from the low boiling
benzene to toluene or even xylene is possible with
involatile amines and leads to a marked acceleration
in the formation of the enamine. Fortunately even long
reaction times in high boiling solvents do not lead to
significant amounts of unwanted side products as long
as the condensation is carried out under strict exclusion
of oxygen. Due to the reversibility of enamine formation
(7) (a) Knox, G. R.; Pauson, P. L.; Willison, D.; Solcaniova, E.; Toma,
S. Organometallics 1990, 9, 301. (b) Knox, G. R.; Pauson, P. L. J . Chem.
Soc. 1961, 4615. (c) Herberhold, M.; Ellinger, M.; Kremnitz, W. J .
Organomet. Chem. 1983, 241, 227. (d) Arimoto, F. S.; Haven, A. C. J .
Am. Chem. Soc. 1955, 77, 6295. (e) Nesmeyanov, A. M.; Ssansonowa,
W. A.; Drosd, V. N. Chem. Ber. 1960, 93, 2717. (f) Herberhold, M.;
Ellinger, M.; Haumeier, L. In Organometallic Syntheses; King, R. B.,
Eisch, J . J ., Eds.; Elsevier: Amsterdam, 1986; Vol. 3, p 81. (g)
Herberhold, M.; Ellinger, M.; Thewalt, U.; Stollmaier, F. Angew. Chem.
1982, 94, 70; Angew. Chem., Int. Ed. Engl. 1982, 21, 74.
(8) Herberhold, M. In Ferrocenes; Togni, A., Hayashi, T., Eds.;
VCH: Weinheim, Germany, 1995.
(9) In this paper aminocyclopentadienes as well as aminoferrocenes
and aminocobaltocenes refers to compounds that have a nitrogen atom
directly bonded to the five-membered ring.
(10) (a) Macomber, D. W.; Hart, W. P.; Rausch, M. D. Adv. Orga-
nomet. Chem. 1982, 21, 1. (b) Haltermann, R. Chem. Rev. 1992, 92,
965. (c) Okuda, J . Top. Curr. Chem. 1991, 160, 97.
(11) Bernheim, M.; Boche, G. Angew. Chem. 1980, 92,1043; Angew.
Chem., Int. Ed. Engl. 1980, 19, 1010.
(12) Stahl, K. P.; Boche, G.; Massa, W. J . Organomet. Chem. 1984,
277, 113.
(13) Blais, M. S.; Rausch, M. D. Organometallics 1994, 13, 3557.
(14) Plenio, H.; Burth, D. Z. Anorg. Allg. Chem. 1996, 622, 225.
(15) Plenio, H.; Burth, D. J . Organomet. Chem. 1996, 519, 269.
(16) Plenio, H.; Burth, D. Organometallics 1996, 15, 1151.
(17) A preliminary report of this work has been published: Plenio,
H.; Burth, D. Angew. Chem. 1995, 107, 881; Angew. Chem., Int. Ed.
Engl. 1995, 34, 800.
(20) (a) Enamines: Synthesis,Structure and Reactions, 2nd ed.; Cook,
A. G., Ed.; Marcel Dekker: NewYork, 1988. (b) Blomquist, A. T.;
Moriconi, E. J . J . Org. Chem. 1961, 26, 3761.
(18) J app, F. R.; Knox, J . J . Chem. Soc. 1905, 87, 679.
(19) Geissman, T. A.; Koelsch, C. F. J . Org. Chem. 1939, 3, 498.
(21) Thompson, H. W.; Huegi, B. S. J . Chem. Soc., Perkin. Trans 1
1976, 1603.

4056 Organometallics, Vol. 15, No. 19, 1996
Plenio and Burth
Ch a r t 1. Sch em a tic Dr a w in gs of th e
Am in ocoba ltocen es a n d Am in ofer r ocen es
F igu r e 1. Crystal structure of the ferrocenophane 14
(hydrogen atoms omitted for clarity) viewed along the axis
centroid-Fe-centroid.
Sch em e 3. Syn th esis of th e Zin c Com p lex of 12
substantially increased to a respectable 61% when Fe-
(N(i-Pr)2)2 was produced by using iron(II) acetylaceto-
nate instead of FeCl2. This much higher yield is
probably due to the good solubility of iron(II) acetylac-
etonate in THF. All aminoferrocenes and aminocobal-
tocenium salts are air-stable metallocenes with the
exception of the bis(indenylamino)ferrocene 13 which,
like bis(indenyl)ferrocene22 itself, is a very oxidation
sensitive compound that can only be handled in an inert-
gas atmosphere.
Cr ysta l Str u ctu r e of th e F er r ocen op h a n e 14. In
14 the two five-membered rings are bridged by an
ethylendiamino chain, which leads to a slight tilting of
the planes of the two cyclopentadienyl rings by 10.2°.
When the structure is viewed along the axis centroid-
Fe-centroid′ (Figure 1) it is apparent that all four
phenyl groups are arranged such thatsupon projection
into a planesthey lie in a row. We believe that this is
primarily a consequence of the relative orientation of
the two Cp rings as imposed by the ethylenediamino
bridge and not so much due to steric crowding, since,
in crystal structures of related unbridged aminofer-
rocenes, phenyl groups often tend to be coplanar.
However, relative to the five-membered ring of ferrocene
the phenyl rings are tilted (26-39° in 14). A typical
feature of all aminoferrocenes is the pronounced short-
ening of the Cp(C)-N bond [138.8(5), 140.0(3) pm]. This
shortening is found in all η5-complexes of aminocyclo-
pentadienes and is roughly correlated with the electron
deficiency of the transition metal center; hence, Cp(C)-N
bonds may be as short as 132.5(7) pm in aminozir-
conocene dichlorides.15
(only the removal of water shifts the equilibrium toward
the enamine side!) workup may be difficult if the crude
product is contaminated; thus, care has to be taken to
only use high-purity starting materials.
Syn th esis of Am in ofer r ocen es a n d Am in ocoba l-
tocen es. The syntheses of aminoferrocenes and ami-
nocobaltocenes were straightforward in most cases.
Typically the aminocyclopentadiene or 2-aminoindene
were deprotonated with n-BuLi in THF and the respec-
tive lithium salt was reacted with FeCl2 or CoBr2‚2THF
leading to the formation of the respective aminofer-
rocene or aminocobaltocene (isolated as the cobaltoce-
nium salt after oxidation with iodine) in yields of around
50% (Chart 1). This general procedure was modified
for ligands containing the dipicolyl unit such as 6, to
account for the sensitivity of this group toward basic
reagents. Whereas the reaction of Fe(N(i-Pr)2)2 [gener-
ated in situ from FeCl2 and LiN(i-Pr2)2] with 6 leads to
the desired ferrocene 12 in only 35%, the yield was
Syn th esis of Com p lexes of th e Am in ofer r ocen es
w ith Meta l Sa lts. Ferrocene 10 contains two trimeth-
ylethylenediamino groups, and the ferrocene 12, two
dipicolylamino groups; both iron complexes should thus
(22) (a) Fischer, E. O.; Seus, D. Z. Naturforsch. 1954, 9b, 386. (b)
Kelly, T. R.; Meghani, P. J . Org. Chem. 1990, 55, 3684.

Aminoferrocenes and Aminocobaltocenes
Organometallics, Vol. 15, No. 19, 1996 4057
Ta ble 1. Cr ysta l Da ta a n d P a r a m eter of Str u ctu r e Refin em en t Su m m a r y
compd
14
12‚2ZnBr2‚3CH3CN
empirical formula
C38H34FeN2
574.52
C62H57Br4FeN9OZn2
1416.33
fw (g mol-1
temp (K)
)
293(2)
293(2) K
cryst system
space group
orthorhombic
Pbca
monoclinic
P21/c
unit cell dimens (pm, deg)
a
16.934(3)
14.352(3)
23.793(5)
12.316(2)
13.033(3)
38.752(8)
91.06(3)
b
c
â
V (Å)
5783(2)
6219(2)
Z
8
4
D (g cm-3
)
1.320
1.513
abs (mm-1
F(000)
)
0.552
3.610
2416
2824
cryst size (mm)
0.6 × 0.6 × 0.5
2.41-25.98
-20/0, -17/0, -29/0
5667/5667
4792/373
1.059
0.8 × 0.6 × 0.6
3.06- 26.00
-15/4, -16/0, -47/47
12 778/12 179
9289/731
1.062
θ range (deg)
index range (hkl)
reflcns collcd/indepdt
data/params
GooF
final R indices [I > 2σ(I)]: R1, wR2
0.0354, 0.0942
0.0719, 0.299
+0.343, -0.277
0.0552, 0.141
0.151, 0.202
+0.579, -0.692
final R indices (all data): R1, wR2
largest peak and hole (eÅ-3
)
Ta ble 2. Selected Bon d Len gth s (p m ) a n d An gles
(d eg) in 12‚2Zn Br 2 (Esd ’s in P a r en th eses)
Zn(1)-N(1)
Zn(1)-N(2)
Zn(1)-N(3)
Zn(1)-Br(1)
Zn(1)-Br(2)
C(1)-N(1)
249.3(5)
207.6(6)
208.2(6)
238.51(12)
245.05(13)
141.7(8)
Zn(2)-N(4)
Zn(2)-N(5)
Zn(2)-N(6)
Zn(2)-Br(3)
Zn(2)-Br(4)
C(6)-N(4)
267.7 (7)
210.5(6)
206.1(6)
236.28(14)
244.43(13)
140.1(8)
N(1)-Zn(1)-N(2)
N(1)-Zn(1)-N(3)
73.5(2)
73.5(2)
N(4)-Zn(2)-N(5)
N(4)-Zn(2)-N(6)
70.8(2)
71.1(2)
89.2(2)
N(1)-Zn(1)-Br(1) 114.35(12) N(4)-Zn(2)-Br(3)
N(1)-Zn(1)-Br(2) 131.07(12) N(4)-Zn(2)-Br(4) 168.7(2)
N(2)-Zn(1)-N(3)
N(2)-Zn(1)-Br(1)
N(2)-Zn(1)-Br(2)
N(3)-Zn(1)-Br(2)
N(3)-Zn(1)-Br(1)
145.4(2)
99.1(2)
97.5(2)
96.5(2)
73.5(2)
N(5)-Zn(2)-N(6)
101.3(2)
N(5)-Zn(2)-Br(3) 125.1(2)
N(5)-Zn(2)-Br(4) 101.8(2)
N(6)-Zn(2)-Br(3) 120.1(2)
N(6)-Zn(2)-Br(4) 102.8(2)
Br(3)-Zn(2)-Br(4) 102.16(5)
Br(1)-Zn(1)-Br(2) 114.56(5)
postions, whereas Br(1), Br(2), N(1), and Zn(1) are
situated in the equatorial plane, in which also lie the
two coplanar pyridine rings. However, the angle N(1)-
Zn(1)-N(2) does not amount to the ideal 180° but is only
145° since N(2) and N(3) are drawn toward N(1).
Whereas the N(2) and N(3) distances to Zn(1) are
normal [207.6(6), 208.2(6) pm], the equatorial N(1) is
located at a much longer distance of 249.3(5) pm.
Additional bond lengths and angles are listed in Table
2.
The coordination sphere around Zn(1) is comparable
to that of L1ZnBr2 (L1 ) bis(2-benzimidazol-2-ylmethyl)-
methylamine) described by Vahrenkamp et al.23 and
L2Zn(SCN)2 (L2 ) (bis(2-benzimidazolylmethyl)amino)-
ethanol) by Takahashi et al.24
The coordination sphere of Zn(2) is quite different to
that of Zn(1) and may be described as a distorted
tetrahedron consisting of Br(3), Br(4), N(5), and N(6).
The aliphatic N(4) attempts to push in between N(5)
and N(6) but cannot get closer than 267.7(7) pm to Zn(2),
which is almost 20 pm longer than the related Zn(1)-
N(1) distance. The coordination geometry around Zn2+
may be compared to L3ZnBr2 [L3 ) bis(benzimidazol-2-
ylmethyl) sulfide]25 in which the bridgehead sulfur at
best weakly participates in the bonding of the metal ion.
F igu r e 2. Crystal structure of 12‚2ZnBr2 (hydrogen atoms
omitted for clarity).
be able to form strong complexes with metal salts. To
investigate the influence of the ferrocene unit onto the
coordination behavior we have reacted 10 and 12 with
different zinc salts. After the addition of 2 equiv of
ZnCl2 to a solution of 10 dissolved in ethanol, ether was
slowly allowed to diffuse into the reaction mixture,
which led to the precipitation of a red complex, with the
stoichiometry of 10‚2ZnCl2‚4H2O.
Addition of ZnBr2 to a solution of 12 in 2-propanol
held under reflux led to the precipitation of an orange-
colored precipitate, which was redissolved with small
amounts of acetonitrile. Slowly cooling this solution led
to the formation of X-ray-quality single crystals of the
composition 12‚2ZnBr2.
Cr ysta l Str u ctu r e of 12‚2Zn Br 2. In Figure 2 it can
be seen that the two ZnBr2 units are easily accom-
modated by 12, since the two metal ions and the
dipicolylamino unit are located above and below the
ferrocene unit (Table 1). To our surprise the two Zn2+
ions in this complex display rather different coordina-
tion geometries and will thus be discussed separately.
The environment of Zn(1) can be described as roughly
trigonal bipyramidal with N(2) and N(3) occupying axial
(23) Wirbser, J .; Vahrenkamp, H. Z. Naturforsch. 1992, 47b, 962.
(24) Takahashi, K.; Nishida, J .; Kida, S. Bull. Chem. Soc. J pn. 1984,
57, 2628.

4058 Organometallics, Vol. 15, No. 19, 1996
Plenio and Burth
Ta ble 4. Red ox P oten tia ls (V vs Ag/AgCl) of th e
Am in ofer r ocen es (CH3CN, Sca n 100 m V/s)
E1/2(0/+I)
E1/2(+I/+II)
E1/2(+II/+III)
(C5H5)2Fe
+0.40
-0.23
-0.05
-0.20
+0.07
-0.10
-0.22
-0.01
(C5H4N(CH3)2)2Fe
+0.53
+1.23
+1.32
9
10
11
12
13
14
+0.91
+0.17
+0.98
+1.08
Ta ble 5. Red ox P oten tia ls (V vs Ag/AgCl) of th e
Am in ocoba ltocen es (T ) -40 °C, Sca n 50 m V/s)
E1/2(-I,0)
-1.82a
E1/2(0/+I)
(C5H5)2Co
(C5H4NMe2)2Co11
(C5H4NH2)2Co38
(C9H7)2Co39
15+Br-
-0.94b
-1.35b
-1.34a
-0.53b
-1.15
-1.08
-1.27
-0.89
-0.81
-
F igu r e 3. UV spectra of (C9H7)2Co+ClO4 (- - -) and (2-
-2.21a
-1.68b
-1.80
d
-1.88
-1.92
d
(Me2NC2H4N(Me))C9H6)2Co+I- (s).
16+I-
Ta ble 3. UV Absor p tion s of Am in ocoba ltocen es in
Eth a n ol betw een 250 a n d 800 n m
17+I-
19+I-
λ (nm)
20+I-
cobaltocene
solvent dmf. b solvent CH3CN. c solvent SO2. not determined.
a
d
(C5H5)2Co+PF6
16+I-
263
249
247
323
302
279
299
275
291
405
347
377
-
443
470
460
460
463
545
17+I-
Cyclic Volta m m etr y of Am in ofer r ocen es a n d
Am in ocoba ltocen e. All aminoferrocenes and ami-
nocobaltocenes described here can be oxidized reversibly
to the monocation; the respective redox potentials are
listed in Tables 4 and 5. For the aminoferrocenes the
0/+I redox potentials range from +0.07 to -0.21 V,
which is more negative than ferrocene itself but not as
negative as 1,1′-bis(dimethylamino)ferrocene, which can
be attributed to the +M-effect of nitrogen on the one
side and the electron-withdrawing effect of the phenyl
groups on the other.29 In the case of the aminofer-
rocenes 9, 10, and 12 a second irreversible oxidation was
observed between +0.98 and +1.08 V, which is much
more positive than the (irreversible) oxidation of (C5H4-
NMe2)2Fe (+0.53 V). Another irreversible oxidation
process was seen in the CV of 10 at +1.32 V [cor-
respondingly in Fe(C5H4N(CH3)2)2 at +1.23 V].11
The indenylcobaltocenes 18-20 are oxidized to the
monocation between -0.81 and -0.92 V, and the cyclo-
pentadienylcobaltocenes 15-17 between -1.08 and
-1.27 V. If the CV experiment is carried out at low
temperatures (-40 °C), a reversible reduction to the
monoanion is also possible at very negative potentials
of between -1.80 and -1.92 V.
Cyclic Volta m m etr y of th e Com p lexes of Am i-
n ofer r ocen es a n d Am in ocoba ltocen es w ith Meta l
Sa lts. In order to find out whether the nitrogen atoms
directly bonded to the cyclopentadienyl ring are able to
act as an electronic mediator between the metallocene
unit and metal ions coordinated within the chelating
ligand, we have determined the redox potentials of the
metal complexes of the aminoferrocenes and aminoco-
baltocenes 10, 12, 17+CF3SO3-, and 20+CF3SO3-. In
order to limit electron transfer processes to the metal-
locenes we have chosen to investigate complexes with
Zn(CF3SO3)2 and Co(CF3SO3)2 since both metal ions (as
well as the anion) are redox-inactive in the potential
region investigated.
(C9H7)2Co+ClO4
18+I-
-
382
385
608
636
19+I-
When the somewhat irregular coordination spheres
of Zn(1) and Zn(2) are described, it should be remem-
bered that Zn2+ is always highly flexible and that the
arrangement of the ligating atoms is mainly dominated
by the geometrical requirements of the ligand and a
maximization of interatom distances around the metal
ion (points-on-a-sphere approach26).27
The Zn(1) and the Zn(2) fragments in 12‚2ZnBr2 have
almost the same Zn-N(py) and Zn-Br distances; how-
ever, the decisive difference lies in the variable partici-
pation of the aliphatic nitrogens N(1) and N(4). The
very different roles played by N(1) and N(4) are not
reflected in significant differences in the Cp(C)-N bond
lengths [141.7(8), 140.1(8) pm] or angles, which are
around 114° and thus midway between tetrahedral and
trigonal planar. In the solid-state structure of 12
itself,17 however, angles around nitrogen are closer to
trigonal planar (average 118.1°). Other than that
bonding parameters within the ferrocene 12 do not
change significantly upon complexation of the two
ZnBr2. A comparision of the Zn(1) and Zn(2) coordina-
tion spheres is therefore well suited to demonstrate that
the energy price paid for a transition from a trigonal
bipyramidal to a distorted, tetrahedral coordination is
small.
UV Sp ectr a . The yellow (C5H5)2Co+ and the yellow-
orange (C9H7)2Co+ are very different in color from their
nitrogen-substituted relatives, which are dark-red to
violet (15-17) or dark green in the case of the (ami-
noindenyl)cobaltocenes. As can be seen upon comparing
the UV spectra of (C9H7)2Co+ and 17 (Figure 3), the
absorption structure of the aminocobaltocenes reveals
much more detail.28 Dominating in all UV spectra is the
strong CT band between 247 and 302 nm; other absorp-
tions are observed between 347 and 385, 443 and 470,
and 608 and 636 nm (Table 3).
The redox potentials of the metallocenes 10 and 17
which each have two trimethylethylenediamino ligands
(28) (a) Sohn, Y. S.; Hendrickson, D. N.; Gray, H. B. J . Am. Chem.
Soc. 1971, 93, 3603. (b) Westcott, S. A.; Kakhar, A. K.; Stringer, G.;
Taylor, N. J .; Marder, T. B. J . Organomet. Chem. 1990, 394, 777.
(29) Britton, W. E.; Kashyap, R.; El-Hashash, M.; El-Kady, M.;
Herberhold. M. Organometallics 1986, 5, 1029.
(25) Gregorzik, R.; Vahrenkamp, H. Chem. Ber. 1994, 127, 1857.
(26) Hay, B. P. Coord. Chem. Rev. 1993, 126, 177.
(27) Melnik, M.; Gyroyova, K.; Skorsepa, J .; Holloway, C. E. J .
Coord. Chem. 1995, 35, 179.

Aminoferrocenes and Aminocobaltocenes
Organometallics, Vol. 15, No. 19, 1996 4059
result insofar as the redox potential of 12‚2Zn2+ is
shifted by ∆(∆E1/2) ) +720 mV with respect to 12, which
is by far the largest metal-induced shift ever obtained!
Complexation of two Co(II) ions by 12 leads to even
larger shifts ∆(∆E1/2) ) +760 mV, whereas the ∆(∆E1/2
)
values observed for the cobaltocenes are slightly smaller.
One should attempt to understand what is happening
to Zn2+ or Co2+ after oxidation of the metallocene. The
two-wave situation shows that both metal ions remain
bound to the metallocene ligand. This may appear
surprising when one calculates the reduction in the
stability constants upon oxidation using the data from
the CV experiments. It is a fairly good approximation
to correlate ∆(∆E1/2) with the differences in the stability
constants of the complexes of the redox-active ligands
with metal ions in the different oxidation states.32 For
∆(∆E1/2) ) +380 mV for the Co(II) complex results a
3.4 × 106 fold decrease in the stability constant of 12+‚
F igu r e 4. Cyclic voltammogram of 12 in the presence of
0.5 Zn(CF3SO3)2.
Ta ble 6. Red ox P oten tia ls (V vs Ag/AgCl) of th e
Am in ofer r ocen es (10, 12), th e Am in ocoba ltocen es
(17, 20), a n d Th eir Com p lexes w ith Zn (CF 3SO3)2 or
Co(CF 3SO3)2
Co2+ with respect to 12‚Co2+ 33
which is an enormous
,
value when compared to typical ferrocene derivatives
with a CH2 group.
∆E1/2 (V)
(no metal salt)
∆E1/2 (V) +
metal salt
∆(∆E1/2)
(mV)
It can also be seen in Figure 4 that the electrochemi-
cal behavior is not fully reversible for the Zn(II) and
Co(II) complexes of 12, which brings us closer to
10 + Zn2+
17 + Zn2+
12 + 1 Zn2+
12 + 2 Zn2+
12 + 1 Co2+
12 + 2 CO2+
20 + Zn2+
20 + Co2+
-0.20
-1.27
-0.10
-0.01
-1.09
+0.23
+0.62
+0.28
+0.66
-0.20
-0.17
+190
+180
+330
+720
+380
+760
+610
+640
understand the fate of the metal ions (Zn2+ or Co2+
after oxidation of the metallocene unit.
)
-0.10
Prior to oxidation the nitrogen bonded to the cyclo-
pentadienyl ring takes part in the bonding of the metal
ion, as can be seen in the crystal structure of 12‚2ZnBr2.
After oxidation of the metallocene any donor ability of
this nitrogen is lost, as is also evident from protonation
experiments with aminocobalticinium salts and ami-
nocymantrenes.14 Furthermore the metal ion (Zn2+ or
Co2+) will feel a small repulsive electrostatic force from
the metallocene. These two factors will lead to the
metal ions being pushed toward the periphery of the
aminometallocene, where they still can be bonded to the
pyridine rings, whose donor ability will not be affected
by the oxidation. By moving away from the nitrogen
atom, the metal ions are undergoing a reorganization
of their coordination sphere, since one nitrogen donor
has been lost. This vacant site is probably substituted
by solvent molecules or the supporting electrolyte anion
(PF6-), which may explain the lack of full reversibility
in the CV’s of the metal complexes of 12.
-0.81
-0.81
were determined with and without added zinc salt. In
both cases the redox potentials were shifted toward
positive potential (Table 6). However, the anodic shifts
[∆(∆E1/2(10)) ) + 190 mV, ∆(∆E1/2(17)) ) + 180 mV]
observed are significantly smaller than expected. This
becomes more apparent upon comparison of the ∆(∆E1/2
)
values with those obtained by Beer et al. for two
ferrocene-substituted azamacrocycle, in which metal-
locene and chelating ligand are separated by a CH2
group.30 In these complexes ∆(∆E1/2) ) +85 and +135
mV were observed upon formation of Zn(II) complexes.
The +180 and +190 mV observed by us are even less
impressive when considering that 10 as well as 17
coordinate two Zn(II) ions simultaneously. Considering
these results, two conclusions are possible: either our
concept of nitrogen acting as an electronic mediator is
wrong or Zn2+ is preferably coordinated by the terminal
nitrogen atom and the interaction between the metal-
locene and Zn2+ is mainly of an electrostatic nature. The
latter explanation appears more likely since the ob-
served shortening of the Cp(C)-N bond is indicative of
a relatively weak donor ability of this nitrogen atom,
resulting in a low stability of the Zn(II) complexes of
10 and 17.
In complexes of 12 and 20 with Zn2+ or Co2+ the
situation should be different since the two pyridine units
will considerably increase the stability of the metal
complexes.31 In the CV experiment after addition of 0.5
molar equiv of Zn(II) to a solution of 12 a two-wave
situation is observed, which is indicative of the two
species 13 [∆E1/2 ) -0.10 V] and 12‚Zn2+ [∆E1/2 ) +0.23
V] (Figure 4). After addition of 2 equiv of Zn(CF3SO3)2
only one redox wave corresponding to 12‚2Zn2+ is
present [∆E1/2 ) +0.62 V]. This is a very remarkable
Con clu sion s
We have shown that the enamine route provides an
easy access to numerous aminocyclopentadienes, which
can be converted in good yields into the corresponding
aminoferrocenes and aminocobaltocenes. The X-ray
crystal structure of the ZnBr2 complex of 1,1′-bis(di-2-
picolylamino)-3,3′,4,4′-tetraphenylferrocene (12) shows
that the nitrogen atom linked to the cyclopentadienyl
ring participates in the bonding of metal ions. The
investigation into the redox behavior of the aminofer-
rocenes and aminocobaltocenes described here proves
the succesful realization of our concept in which nitro-
gen atoms directly bonded to the cyclopentadienyl ring
of ferrocene act as highly efficient mediators of electronic
(31) The stability constants for dipicolylamine complexes with Zn2+
(log K ) 7.57) and Co2+ (log K ) 7.74) were determined in water but
should be several orders of magnitude higher in anhydrous CH3CN:
Romari, J . K.; Barger, J . D. Inorg. Chem. 1968, 7, 1142.
(32) Miller, S. R.; Gustowski, D. A.; Chen, Z.; Gokel, G. W.;
Echegoyen, L.; Kaifer, A. E. Anal. Chem. 1988, 60, 2021.
(30) (a) Beer, P. D.; Chen, Z.; Drew, M. G. B.; Kingdom, J .; Odgen,
M.; Spencer, P. J . Chem. Soc., Chem. Comm. 1993, 1046.
(33) The decrease in the stability constant was calculated using the
following equations: ∆G ) RT ln(K) and ∆G ) -zF∆E.

4060 Organometallics, Vol. 15, No. 19, 1996
Plenio and Burth
recrystallized from toluene three times, and dried under
vacuum. Yield: 103.2 g (82%), yellow powder, mp 147 °C.
1H NMR (CDCl3): δ 2.77-3.05 (m, 2H, CH2), 3.38 (br, 1H,
OH), 6.62-6.66 (m, 1H, CH), 7.23-7.51 (m, 10H, ArH).
3,4-Dip h en ylcyclop en t-2-en on e (2). A mixture of 3,4-
diphenyl-3-hydroxycyclopent-4-enone (84.1 g, 0.34 mol), HI
(14.5 g, 0.05 mol, 45% in H2O), red phosphorus (18.8 g, 0.58
mol), and glacial acid (330 mL) was heated under reflux for 1
h and then filtered into a cold, vigorously stirred aqueous
solution of Na2S2O3. A yellow solid consisting of 3,4-diphe-
nylcyclopent-2-enone precipitated, was filtered off, and then
redissolved in diethyl ether. This solution was washed with
aqueous Na2CO3, the etheral layer was separated and dried
over MgSO4, and the volatiles were evaporated. The crude
product was recrystallized twice from petroleum ether/toluene
(2/1). Yield: 47 g (60%), pale-yellow powder, mp108-110 °C.
1H NMR (CDCl3): δ 2.46 (dd, J ) 2.0, 18.8 Hz, 1H,
cis-PhCHCH2), 3.12 (dd, J ) 7.4, 18.8 Hz, 1H, trans-Ph-
CHCH2), 4.62 (d, J ) 7.3 Hz, 1H, PhCHCH2), 6.76 (d, J ) 1.4
Hz, 1H, COCH), 7.14-7.33 (m, 8H, ArH), 7.50-7.55 (m, 2H,
ArH). 13C NMR (CDCl3): δ 46.71, 46.81, 126.96, 127.08,
127.89, 128.71, 129.06, 129.14, 130.77, 133.26, 142.45, 175.09,
208.01.
communication. This was shown experimentally since
the anodic shifts in the redox potentials of the metal
complexes of 12 [∆(∆E1/2) ) +720 mV (+2Zn2+) and
∆(∆E1/2) ) +760 mV (+2Co2+)] are by far the largest
ever observed in redox-responsive systems. Two factors
have been identified to be decisive for such large
effects: (1) the nitrogen atom directly bonded to the
ferrocene, which acts as a relay for the electronic
communication between the redox-active unit and the
metal ion; (2) strong additional ligating groups to
stabilize the metal ion in the vicinity of the ferrocene
bound nitrogen, since this nitrogen atom is not a very
good donor.
The oxidation of 1,1′-bis(di-2-picolylamino)-3,3′,4,4′-
tetraphenylferrocene effectively switches two donor
atoms of the ferrocene, whereas the pyridine units are
only marginally influenced. Metal ions which can form
stable complexes with the pyridine ligands will remain
bonded to 12, but their coordination number will
change, depending on the oxidation state of the fer-
rocene unit.
1-(N-Met h ylp ip er a zin yl)-3,4-d ip h en ylcyclop en t a -1,3-
d ien e (3). 3,4-Diphenylcyclopent-2-enone (10.0 g, 42.7 mmol),
N-methylpiperazine (4.56 g, 45.6 mmol), and p-toluenesulfonic
acid (0.05 g) in benzene (100 mL) were heated under reflux
with a water aspirator for 72 h. After removal of the solvent
in vacuum the residue was recrystallized from petroleum ether
(100 mL) three times. Yield: 7.0 g (52%), pale-yellow powder,
mp 88 °C.
We believe that the facile access to aminoferrocenes
and aminocyclopentadienes with chelating ligands,
electronically coupled to the metallocene, will open the
door for a substantial improvement of amperometric
sensory devices as well as for the realization of abiotic
enzyme models based on molecular switching devices.34
Anal. Calcd for C22H24N2 (316.45): C, 83.50; H, 7.64; N,
8.85. Found: C, 83.75; H, 7.84; N, 9.12. IR (KBr): ν 1593 s
(CpN), 1548 s (CpN). 1H NMR (CDCl3): δ 2.39 (s, 3H, NCH3),
2.55 (t, J ) 5.2 Hz, 4H, NCH2), 3.20 (t, J ) 5.2 Hz, 4H, NCH2),
3.58 (s, 2H, CpH2), 5.43 (s, 1H, CpH), 7.10-7.40 (m, 10H, ArH).
13C NMR (CDCl3): δ 42.45, 46.24, 47.86, 54.47, 105.48, 124.86,
125.42, 126.82, 126.97, 127.99, 128.26, 128.29, 137.44, 138.17,
142.61, 156.73.
1-(N,N′,N′-Tr im eth yleth ylen ed ia m in o)-3,4-d ip h en ylcy-
clop en ta -1,3-d ien e (4). A solution of 3,4-diphenylcyclopent-
2-enone (10.00 g, 42.6 mmol), trimethylethylenediamine (6.0
mL, 46.9 mmol), and p-toluenesulfonic acid (0.05 g) in benzene
(150 mL) was heated under reflux for 48 h with a water
aspirator. After removal of the solvent in vacuum the residue
was recrystallized from petroleum ether three times and the
product dried in vacuum. Yield: 6.1 g (45%), yellow powder,
mp 77 °C.
Anal. Calcd for C22H26N2 (318.46): C, 82.97; H, 8.23; N,
8.80. Found: C, 83.32; H, 8.50; N, 8.80. IR (KBr): ν 1593 s
(CpN), 1570 s (CpN), 1548 s (CpN). 1H NMR (CDCl3): δ 2.29
(s, 6H, N(CH3)2), 2.51 (t, J ) 7.3 Hz, 2H, NCH2), 2.89 (s, 6H,
NCH3), 3.31 (t, J ) 7.3 Hz, 2H, NCH2), 3.55 (s, 2H, CpH2),
5.15 (s, 1H, CpH), 7.11-7.37 (m, 10H, ArH). 13C NMR
(CDCl3): δ 38.20, 42.52, 45.81, 51.34, 56.37, 101.94, 122.97,
124.34, 126.67, 127.92, 128.20, 128.31, 137.69, 138.52, 143.68,
156.52.
N,N′-Dim eth yl-N,N′-bis(3,4-d ip h en ylcyclop en ta -1,3-d i-
en yl)eth ylen ed ia m in e (5). A solution of 3,4-diphenylcyclo-
pent-2-enone (22.00 g, 94.1 mmol), N,N′-dimethylethylenedi-
amine (5.00 mL, 47.0 mmol) and p-toluenesulfonic acid (0.05
g) in benzene (250 mL) was heated under reflux for 48 h with
a water aspirator. After removal of the solvent in vacuum the
residue was recrystallized from toluene three times and the
product dried in vacuum. Yield: 9.3 g (42%), yellow powder,
mp 145 °C (dec).
Exp er im en ta l Section
Commercially available solvents and reagents were purified
according to literature procedures. All reactions were carried
out in dry solvents under a nitrogen atmosphere. Chroma-
tography: alumina N and silica. NMR spectra were recorded
at 300 K with a Bruker AC200 F (1H NMR 200 MHz, 13C NMR
50.3 MHz). 1H NMR were referenced to residual 1H-impurities
in the solvent, and 13C NMR, to the solvent signals: CDCl3
(7.26 ppm, 77.0 ppm), C6D6 (7.16, 128.0 ppm), CD3CN (1.93
ppm, 1.30 ppm). Mass spectra: Finnigan MAT 3800. IR
spectra: Bruker IFS-25; solid materials as KBr tablets.
Elemental analyses: Mikroanalytisches Laboratorium der
Chemischen Laboratorien, Universita¨t Freiburg. Cyclic vol-
tammetry: the standard electrochemical instrumentation
consisted of an Amel System 5000 potentiostat/galvanostat.
Cyclic voltammograms were recorded in dry CH3CN under an
argon atmosphere ambient temperature (unless otherwise
noted) using Amel software on
a PC. A three-electrode
configuration was employed. The working electrode was a Pt
disk (diameter 1 mm) sealed in soft glass, and the counter
electrode, a Pt disk (area 3 cm2). The pseudoreference
electrode was an Ag wire. Potentials were calibrated inter-
nally against the formal potential of cobaltocenium perchlorate
(-0.94 V vs Ag/AgCl) or octamethylferrocene (-0.025 V vs Ag/
AgCl). Solution were ca. 2 × 10-4 mol dm-3 in compound.
NBu4PF6 (0.1 M) was used as a supporting electrolyte. The
petroleum ether used was the 60-70 °C cut. The procedures
given for 3,4-diphenyl-3-hydroxycyclopent-4-enone and 3,4-
diphenylcyclopent-2-enone are modified from the publications
by J app/Knox18 and Geissman/Koelsch.19 Starting materials
were available commercially or prepared according to litera-
ture procedures: dipicolylamine;31 iron(II) acetylacetonate.35
3,4-Dip h en yl-3-h yd r oxycyclop en t-4-en on e (1). To a
stirred suspension of benzil (105.0 g, 0.500 mol) and KOH (0.6
g) in acetone (83 mL, 1.1 mol) and ethanol (0.75 mL) was added
a solution of KOH (13.8 g, 0.25 mol) in water (45 mL),
whereupon all solid material dissolved with a change of color
to brown. The reaction mixture was stirred for 1 h at 60 °C
and then poured into hot water, whereupon a brown solid
precipitated. This crude product was filtered off, dried,
Anal. Calcd for C38H36N2 (520.72): C, 87.65; H, 6.97; N,
5.38. Found: C, 87.35; H, 7.00; N, 5.26. IR (KBr): ν 1593 s
(CpN), 1571 s (CpN), 1543 s (CpN). 1H NMR (CDCl3): δ 2.93
(s, 6H, NCH3), 3.43 (s, 4H, CH2), 3.55 (s, 4H, CH2), 5.19 (s,
2H, CpH), 7.09-7.41 (m, 20H, ArH). 13C NMR (CDCl3): δ
(35) (a) Fitch, J . W.; Lagowski, J . J . Inorg. Chem. 1965, 4, 910. (b)
Buckingham, D. A.; Gerries, A. G.; Henry, J . T. Aust. J . Chem. 1967,
20, 281.
(34) Pregel, M. J .; Dunn, E. J .; Nagelkerke, R.; Thatcher, G. R. J .;
Buncel, E. Chem. Soc. Rev. 1995, 24, 449.

Aminoferrocenes and Aminocobaltocenes
Organometallics, Vol. 15, No. 19, 1996 4061
38.70, 42.66, 50.34, 102.20, 123.30, 124.52, 126.78, 126.84,
128.02, 128.31, 128.37, 137.64, 138.51, 143.58, 155.93.
N,N′-Dim eth yl-N,N′-d iin d en -2-yleth ylen ed ia m in e (7).
Dimethylethylenediamine (0.67 g, 7.6 mmol) was added to a
stirred solution of 2-indanone (2.00 g, 15.2 mmol) in methanol
(14 mL). The white solid which formed during the next 2 h
was filtered off, washed with methanol, dried in vacuo, and
recrystallized from toluene. Yield: 1.96 g (82%) white powder,
mp 157 °C (dec).
N,N′-bis(3,4-diphenylcyclopenta-1,3-dienyl)ethylenediamine (1.30
g, 2.5 mmol) in THF (50 mL) was treated with n-BuLi (2.0
mL, 5.0 mmol, 2.5 M in hexane). After addition of [CpFe(p-
-
Xylol)]+PF6 (1.14 g, 5 mmol), the solution was irradiated for
7 h with a halogen lamp (300 W). Afterward the volatiles were
removed in vacuum and the residue purified by chromatog-
raphy (cyclohexane/HNEt2 ) 10/1). Yield: 170 mg (8%),
orange-red powder.
Anal. Calcd for C48H44N2Fe2 (760.59): C, 75.80; H, 5.83; N,
3.68. Found: C, 75.90; H, 5.58; N, 3.53. MS, m/ z (%): 760
(80) [M+]. IR (KBr): ν 1523 s, 1496 s. 1H NMR (C6D6): δ 2.46
(s, 6H, NCH3), 3.01 (s, 4H, NCH2), 4.10 (s, 5H, CpH), 4.26 (s,
4H, CpH), 7.05-7.10 (m, 12H, ArH), 7.50-7.55 (m, 8H, ArH).
13C NMR (C6D6): δ 39.78, 52.98, 57.42, 70.90, 81.85, 114.56,
126.27, 128.27, 130.14, 139.48.
1,1′-Bis(d i-2-p icolyla m in o)-3,3′,4,4′-t et r a p h en ylfer r o-
cen e (12). To a mixture of iron(II) acetylacetonate (50 mg,
0.5 mmol) and Li(N(C3H7)2) (107 mg, 1 mmol) in THF (15 mL)
held at -78 °C was added 1-(di-(2-picolylamino)-3,4-diphenyl-
cyclopenta-1,3-diene (414 mg, 1 mmol). The reaction mixture
was slowly warmed to room temperature. After 2 h the
volatiles were removed in vacuum and the residue was purified
by chromatography (cyclohexane/ethyl acetate/HNEt2 ) 10/1/
1) and by recrystallization from petroleum ether/toluene.
Yield: 270 mg (61%), orange-red powder.
Anal. Calcd for C58H48N6Fe (884.9): C, 78.25; H, 5.50; N,
9.78. Found: C, 78.72; H, 5.47; N, 9.50. IR (KBr): ν 698 s,
760 vs, 1436 s, 1501 vs, 1523 vs, 1593 s. 1H NMR (C6D6): δ
4.19 (s, 4H, CpH), 4.23 (s, 8H, NCH2py), 6.25 (ddd, J ) 1.3,
4.8, 7.4 Hz, 4H, pyH), 6.60-6.80 (m, 20H, pyH, ArH), 7.17-
7.23 (m, 8H, pyH, ArH), 8.10 (ddd, J ) 0.9, 1.8, 4.8 Hz, 4H,
pyH). 13C NMR (C6D6): δ 59.06, 60.81, 82.03, 116.61, 121.73,
122.40, 125.88, 127.90, 130.20, 135.92, 139.17, 149.51, 159.95.
1,1′-B i s (d i -2-p i c o ly la m i n o )-3,3′,4,4′-t e t r a p h e n y l-
fer r ocen e‚2Zn Br 2 (12‚2Zn Br 2). To a solution of the fer-
rocene (28.2 mg, 0.032 mol) in 2-propanol (5 mL) held at reflux
was added a solution of ZnBr2 (14.4 mg, 0.064 mmol) in the
same solvent. An orange-red solid immediately precipitated,
which was redissolved by careful addition of CH3CN. Upon
slowly cooling this solution to room temperature, X-ray-quality
crystals were grown.
Anal. Calcd for C22H24N2 (316.4): C, 83.50; H, 7.64; N, 8.85.
Found: C, 82.65; H, 7.53; N, 8.39. IR (KBr): ν 1571.5 s (IndN).
1H NMR (CDCl3): δ 2.93 (s, 6H, NCH3), 3.38 (s, 4H, NCH2),
3.43 (s, 4H, IndH2), 5.35 (s, 2H, IndH), 6.86 (dt, J ) 1.2, 7.4
Hz, 2H, IndH), 7.02 (d, J ) 7.0 Hz, 2H, IndH), 7.11-7.26 (m,
4H, IndH). 13C NMR (CDCl3): δ 37.41, 38.71, 50.52, 96.60,
116.74, 119.84, 122.69, 126.76, 136.46, 147.81, 156.35.
2-(Di-(2-p icolyla m in o)in d en e (8). 2-Indanone (132 mg,
1.0 mmol) was added to a solution of dipicolylamine (199 mg,
1.0 mmol) and p-toluenesulfonic acid (3 mg) in refluxing
methanol (10 mL). After the mixture was heated for another
2 h, the volatiles were removed in vacuum. The remaining
oil solidified after several hours and was recrystallized from
toluene/petroleum ether. Yield: 257 mg (82%), gray powder.
Anal. Calcd for C21H19N3 (313.4): C, 80.48; H, 6.11; N,
13.41. Found: C, 80.12; H, 6.54; N, 12.91. IR (KBr): ν 1587
s, 1572 s (CpN). 1H NMR (CDCl3): δ 3.53 (s, 2H, IndH2), 4.68
(s, 4H, NCH2py), 5.41 (s, 1H, IndH), 6.84 (t, J ) 7.2 Hz, 1H),
6.96 (d, J ) 7.2 Hz, 1H), 7.06-7.29 (m, 6H, pyH, IndH), 7.61
(dt, J ) 7.6, 1.6 Hz, 2H, pyH), 8.57 (d, J ) 4.2 Hz, 2H, pyH).
1,1′-Bis(N-m eth ylp ip er a zin yl)-3,3′,4,4′-tetr a p h en ylfer -
r ocen e (9). A solution of 1-(N-methylpiperazinyl)-3,4-diphe-
nylcyclopenta-1,3-diene (1.00 g, 3.16 mmol) in THF (30 mL)
was cooled to -78 °C, and n-BuLi (1.36 mL, 3.4 mmol) added,
followed after 15 min by FeCl2 (0.20 g, 1.6 mmol). The reaction
mixture was then slowly warmed to room temperature and 2
h later the solvent removed in vacuum. The brown residue
was washed with acetonitrile (10 mL), and the solid material
was filtered off, dried in vacuum, and recrystallized from
petroleum ether. Yield: 0.46 g (46%), orange-red powder.
Anal. Calcd for C44H46N4Fe (686.7): C, 76.96; H, 6.75, N,
8.16. Found: C, 76.46, H, 6.79, N, 7.61. IR (KBr): ν 1639 s,
1487 s, 1451 s. 1H NMR (C6D6): δ 2.10 (s, 6H, NCH3), 2.23 (t,
J ) 5.1 Hz, 8H, NCH2), 2.71 (t, J ) 5.1 Hz, 8H, NCH2), 4.18
(s, 4H, CpH), 7.00-7.05 (m, 12H, ArH), 7.49-7.54 (m, 8H,
ArH). 13C NMR (C6D6): δ 46.34, 49.81, 55.20, 60.32, 82.52,
114.99, 125.91, 127.88, 130.25, 138.66.
1,1′-Bis(N,N′,N′-t r im et h ylet h ylen ed ia m in o)-3,3′,4,4′-
t et r a p h en ylfer r ocen e (10). A solution of 1-(N,N′,N′-tri-
methylethylenediamino)-3,4-diphenylcyclopenta-1,3-diene (1.16
g, 3.63 mmol) in THF (50 mL) was cooled to -50 °C and n-BuLi
(1.6 mL, 4.0 mmol) added, followed after 10 min by FeCl2 (0.23
g, 1.8 mmol), whereupon the color changed to red-brown. The
reaction mixture was slowly warmed to room temperature, and
after 2 h the volatiles were removed in vacuum. The product
was purified by chromatography (cyclohexane/ethyl acetate/
HNEt2 ) 5/5/1). Yield: 0.75 g (60%), red solid, mp 46 °C.
Anal. Calcd for C44H50N4Fe (690.76): C, 76.51; H, 7.30; N,
8.11. Found: C, 76.81; H, 7.40; N, 8.21. IR (KBr): ν 1598 s.
1H NMR (C6D6): δ 2.06 (s, 12H, N(CH3)2), 2.24 (t, J ) 7.0 Hz,
4H, NCH2), 2.42 (s, 6H, NCH3), 2.90 (t, J ) 7.0 Hz, 4H, NCH2),
4.17 (s, 4H, FcH), 7.07-7.10 (m, 12H, ArH), 7.54-7.57 (m, 8H,
ArH). 13C NMR (C6D6): δ 30.06, 38.57, 45.84, 52.30, 57.27,
59.60, 81.71, 125.70, 127.83, 130.15, 139.32.
Anal. Calcd for C58H48N6FeZn2Br4 (1335.2): C, 51.78; H,
3.30; N, 6.13. Found: C, 52.17; H, 3.62; N, 6.29. IR (KBr): ν
699 s, 765 ss, 1442 s, 1488 ss, 1572 s.
Bis[2-(m eth ylp ip er a zin yl)in d en yl]ir on (II) (13). 2-(N′-
methylpiperazinyl)indene (944 mg, 4.41 mmol) was dissolved
in THF (50 mL), cooled to -60 °C, and treated with n-BuLi
(2.9 mL, 4.4 mmol, 2.5 M in hexane), whereupon the color
changed from yellow to orange-red. After 15 min FeCl2 (280
mg, 2.21 mmol) was added, the reaction mixture was slowly
warmed to room temperature and stirred for 2 h, and then
the volatiles were removed in vacuum. The residue was
recrystallized from toluene/petroleum ether. Yield: 490 mg
(46%), gray-green powder.
Anal. Calcd for C28H34N4Fe (482.39): C, 69.72; H, 7.10; N,
11.61. Found: C, 69.36; H, 6.94; N, 11.35. MS, m/ z (%): 482
(95) [M+ ]. 1H NMR (C6D6): δ 2.19 (s, 6H, NCH3), 2.35 (t, J )
5.1 Hz, 8H, NCH2), 3.07 (t, J ) 5.1 Hz, 8H, NCH2), 4.01 (s,
4H, CpH), 6.97-7.02 (m, 4H, ArH), 7.31-7.36 (m, 4H, ArH).
13C NMR (C6D6): δ 30.16, 46.41, 46.91, 49.84, 55.22, 84.18,
116.13, 122.93, 130.79.
{2,5-D i a z a h e x a n e -2,5-d i y lb i s [3,4-d i p h e n y lc y c lo -
p en ta d ien yl]}ir on (II) (14). A solution of N,N′-dimethyl-
N,N′-bis(3,4-diphenylcyclopenta-1,3-dienyl)ethylenediamine in
THF (50 mL) was cooled to -78 °C and n-BuLi (2.9 mL, 7.37
mmol) added, followed after 10 min by FeCl2 (0.42 g, 3.4 mmol),
whereupon the color changed to brown-red. The reaction
mixture was slowly warmed to room temperature, and after 2
h the volatiles were removed in vacuum. The product was
purified by chromatography (cyclohexane/ethyl acetate ) 10/
1, N2 atmosphere!) and then recrystallized from petroleum
ether. Yield: 0.84 g (44%), orange-red powder, mp 218 °C.
Anal. Calcd for C38H34N2Fe (574.55): C, 79.44; H, 5.97; N,
4.88. Found: C, 79.22; H, 6.11; N, 4.62. MS, m/ z (%): 574
(95) [M+]. IR (KBr): ν 1598 m, 1525 s, 1502 s. 1H NMR
1,1′-Bis(N,N′,N′-t r im et h ylet h ylen ed ia m in o)-3,3′,4,4′-
tetr a p h en ylfer r ocen e‚2Zn Cl2 (10‚2Zn Cl2). The respective
solutions of the ferrocene 10 (14.6 mg, 0.021 mmol) and ZnCl2
(5.8 mg, 0.042 mmol) in ethanol (1 mL each) were mixed. The
reaction mixture was filtered and Et2O allowed to slowly
diffuse into the solution. Within several days very small red
needles formed.
Anal. Calcd for C44H50N4FeZn2Cl2‚4H2O (1035.4): C, 51.01;
H, 4.80; N, 5.41. Found: C, 51.57; H, 4.88; N, 5.49. IR
(KBr): ν 697 m, 766 m, 1457 m, 1560 ss (CpN), 3443 br (H2O).
2,5-Dia za h exa n e-2,5-d iylbis[(3,4-d ip h en ylcyclop en ta -
1,3-d ien yl)cyclop en ta d ien ylir on (II)] (11). N,N′-Dimethyl-

4062 Organometallics, Vol. 15, No. 19, 1996
Plenio and Burth
(C6D6): δ 2.60 (s, 6H, NCH3), 2.95 (s, 4H, NCH2), 4.60 (s, 4H,
FcH), 6.92-7.02 (m, 12H, ArH), 7.34-7.39 (m, 8H, ArH). 13C
NMR (C6D6): δ 38.49, 48.86, 57.68, 82.99, 111.42, 125.96,
127.78, 129.71, 138.78.
1,1′-Bis(N-m eth ylp ip er a zin yl)-3,3′,4,4′-tetr a p h en ylco-
ba ltocen iu m (III) Br om id e (15+Br -). A solution of 2-(N-
methylpiperazinyl)indene (1.50 g, 4.74 mmol) in THF (30 mL)
was cooled to -78°C and treated with n-BuLi (2.03 mL, 5.1
mmol, 2.5 M in hexane). After addition of CoBr2 ‚3THF (0.99
g, 2.3 mmol) the reaction mixture was slowly warmed to room
temperature and stirred for 2 h, and I2 (0.30 g, 1.2 mmol) was
added. The volatiles were removed in vacuum and the residue
was purified by chromatography (MeOH/HNEt2 ) 10/1).
Yield: 0.80 g (21%), dark-red powder.
Anal. Calcd for C44H46BrCoN4 (769.7): C, 68.66; H, 6.02;
N, 7.28. Found: C, 68.95; H, 6.35; N, 7.41. IR (KBr): ν 1558
s. 1H NMR (CD3OD): δ 2.20 (s, 6H, NCH3), 2.32 (br., 8H,
NCH2), 2.78 (br, 8H, NCH2), 5.38 (s, 4H, CpH), 7.18-7.35 (m,
20H, ArH). 13C NMR (CD3OD): δ 6.00, 48.26, 54.82, 65.82,
96.75, 129.14, 129.83, 130.21, 131.19, 132.54.
1,1′-Bis(N-m eth ylp ip er a zin yl)-3,3′,4,4′-tetr a p h en ylco-
ba ltocen iu m (III) Tr ifla te (15+CF 3SO3-). 15+Br- (327 mg,
0.42 mmol) was dissolved in acetonitrile (50 mL) and treated
with AgCF3SO3 (103 mg, 0.41 mmol). Precipitated AgBr was
filtered off, the filtrate evaporated in vacuum, and the residue
recrystallized from toluene. Yield: 220 mg (65%), dark red
powder. An analogous procedure was chosen to synthesize all
other cobaltocenium triflates.
NMR (CD3CN): δ 45.95, 48.47, 54.08, 54.43, 91.70, 123.44,
128.51, 130.61.
[2,5-Dia za h exa n -2,5-d iylbis(2-in d en yl)]coba lt(III) Io-
d id e (19+I-). Synthesis is as described for 15: N,N′-dimethyl-
N,N′-di-inden-2-ylethylenediamine (0.40 g, 2.5 mmol), n-BuLi
(0.24 mL, 5.6 mmol, 2.5 M in hexane), CoBr2‚3THF (1.10 g,
2.5 mmol), I2 (0.32 g, 1.3 mmol), chromatography (Alu-N, 50/1
CHCl3/MeOH). Yield: 600 mg (35%), dark green powder.
Anal. Calcd for C22H22N2CoI (500.26): C, 52.82; H, 4.43;
N, 5.60. Found: C, 52.91; H, 4.56; N, 5.60. MS, m/ z (%): 373
(95) [M+]. IR (KBr): ν 1542 s. 1H NMR (CD3CN, 335 K): δ
3.34 (s, 6H, NCH3), 3.82 (s, 4H, NCH2), 6.14 (s, 4H, IndH),
6.90-6.95 (AA′, 4H, IndH), 7.17-7.22 (BB′, 4H, IndH). 13C
NMR (CD3CN, 330 K): δ 40.73, 48.12, 57.94, 123.53, 129.22.
Bis(2-(d i-2-p icolyla m in o)in d en yl)cob a lt (III) Iod id e
(20+I-). To 2-(di-2-picolylamino)indene (0.840 g, 2.7 mmol)
in THF (25 mL) at -60 °C was added a solution of Li(N(C3H7)2)
(0.28 mg, 2.7 mmol) in THF (5 mL), followed immediately by
CoBr2‚3THF (1.08 g, 2.5 mmol). The solution slowly allowed
to room temperature and treated with I2 (0.17 g, 0.7 mmol)
after 1 h, whereupon the color changed from red to green. The
volatiles were removed in vacuum and residue purified by
chromatography (Alu-N; 50/1 CHCl3/MeOH). Yield: 300 mg
(30%), green solid.
Anal. Calcd for C42H36N6CoI (810.6): C, 62.23; H, 4.44; N,
10.27. Found: C, 61.40; H, 4.52; N, 10.29. IR (KBr): ν 1532
s. 1H NMR (CDCl3): δ 4.73 (s, 8H, CH2py), 5.59 (s, 4H, IndH),
6.93 (AA′, 4H, IndH), 7.11 (ddd, J ) 1.0, 4.9, 7.4 Hz, 4H, pyH),
7.21 (BB′, 4H, IndH), 7.36 (d, J ) 8 Hz, 4H, pyH), 7.55 (dt, J
) 1.8, 7.7 Hz, 4H, pyH), 8.46 (d, J ) 7.2 Hz, 4H, pyH). 13C
NMR (CDCl3): δ 38.70, 42.66, 50.34, 102.20, 123.30, 124.52,
126.78, 126.84, 128.021, 128.31, 128.37, 137.64, 138.51, 143.58,
155.93.
Anal. Calcd for C45H46CoF3N4SO3‚2CH3OH (870.9): C,
62.52; H, 6.03; N, 6.20. Found: C, 62.67; H, 5.76; N, 5.99. IR
(KBr): ν 1555 s, 1260 s (CF3SO3), 1030 s (CF3SO3). 1H NMR
(CD3CN): δ 2.21 (s, 6H, NCH3), 2.30 (br, 8H, NCH2), 2.87 (br,
8H, NCH2), 5.21 (s, 4H, CpH), 7.21-7.43 (m, 20H, ArH). 13C
NMR (CD3CN): δ 46.05, 48.31, 54.49, 65.39, 96.02, 129.20,
129.58, 129.96, 130.97, 132.28.
Cr ysta l Str u ctu r e Deter m in a tion s. Single crystals were
mounted on top of a glass fiber. X-ray data were collected on
an Enraf-Nonius CAD4 diffractometer using Mo KR radiation
(71.069 pm) and a graphite monochromator. The structure
was solved using SHELXS-8636 and refined with SHELXL-
9337 against F2. All non-hydrogen atoms were refined using
anisotropic temperature coefficients and the hydrogen atoms
refined with fixed isotropic temperature coefficients (riding
model). An empirical absorption correction (ψ-scans) was
applied. Complex 12‚2ZnBr2 crystallizes with three solvent
molecules (CH3CN) of which two are badly disordered. The
solvent molecules do not interact with the ferrocene-zinc
complex. Further details of the crystal structure investigations
are available on request from the Fachinformationszentrum
Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany, on
quoting the depository numbers CSD-405162 and CSD-405163,
the names of the authors, and the journal citation.
2,5-Dia za h exa n -2,5-d iylbis[3,4-d ip h en ylcyclop en ta d i-
en yl]coba lt(III) Iod id e (16+I-). Synthesis is as described
for 15: N,N′-dimethyl-N,N′-bis(3,4-diphenylcyclopenta-1,3-
dienyl)ethylenediamine (474 mg, 0.91 mmol), n-BuLi (0.8 mL,
2.0 mmol, 2.5 M in hexane), CoBr2‚3THF (396 mg, 0.91 mmol),
I2 (115 mg, 0.46 mmol), chromatography (Alu-N, CHCl3),
recrystallization from ethanol. Yield: 0.262 g (41%), dark
purple crystals, mp 120 °C (dec).
Anal. Calcd for C38H34CoIN2‚1.5C2H5OH (773.6): C, 63.65;
H, 5.60; N, 3.62. Found: C, 63.71; H, 5.44; N, 3.69. MS, m/ z
(%): 577 (95) [M+]. IR (KBr): ν 1549 s. 1H NMR (CD3CN,
330 K): δ 3.35 (s, 10H, NCH3, NCH2), 6.06 (s, 4H, 4 CpH),
7.10-7.13 (m, 16H, ArH), 7.29-7.32 (m, 4H, ArH). 13C NMR
(CD3CN): δ 40.45, 48.62, 126.58, 129.43, 130.13, 130.36.
1,1′-Bis(N,N′,N′-t r im et h ylet h ylen ed ia m in o)-3,3′,4,4′-
tetr a p h en ylcoba ltocen iu m (III) Iod id e (17+I-). Synthesis
is as described for 15: 1-(N,N′,N′-trimethylethylenediamino)-
3,4-diphenylcyclopenta-1,3-diene (577 mg, 1.81 mmol), n-BuLi
(0.8 mL, 2.0 mmol, 2.5 M in hexane), CoBr2‚3THF (396 mg,
0.91 mmol), I2 (115 mg, 0.46 mmol), chromatography (Alu-N,
MeOH), recrystallization from methanol. Yield: 410 mg (55%),
red solid, mp 307 °C.
Anal. Calcd for C44H50CoIN4‚CH3OH (852.8): C, 61.97; H,
5.87; N, 6.57. Found: C, 62.23, H, 6.05; N, 6.83. IR (KBr): ν
1560 s. 1H NMR (CD3CN): δ 2.15 (s, 12H, N(CH3)2), 2.31 (m,
8H, NCH2), 2.62 (s, 6H, NCH3), 5.13 (br, 4H, CpH), 7.18-7.40
(m, 20H, ArH). 13C NMR (CD3CN): δ 30.06, 38.55, 45.84,
52.28, 57.29, 59.58, 81.73, 125.69, 127.82, 130.14, 139.31.
Ack n ow led gm en t. We thank the Graduiertenkolleg
“Ungepaarte Elektronen in Chemie und Biologie”, the
Landesschwerpunkt “Molekulare Elektrochemie”, the
Fonds der Chemischen Industrie, and Prof. Dr. Vahr-
enkamp for their support and A. Warnecke for experi-
mental assistance.
Su p p or tin g In for m a tion Ava ila ble: Tables giving the
structure determination summary and complete bond lengths,
bond angles, and positional and thermal parameters (10
pages). Ordering information is given on any current mast-
head page.
Bis[2-(N-m eth ylp ip er a zin yl)in d en yl]coba lt(III) Iod id e
(18+I-). Synthesis is as described for 15: 2-(N-methylpiper-
azinyl)indene (273 mg, 1.3 mmol), n-BuLi (0.52 mL, 1.3 mmol,
2.5 M in hexane), CoBr2‚3THF (280 mg, 0.64 mmol), I2 (100
mg, 0.39 mmol), chromatography (10/1 MeOH/Et2NH).
Yield: 179 mg (49%), dark green solid.
OM9602771
(36) Sheldrick, G. M. SHELXS-86, A Program for the Solution of
X-Ray Crystal Structures, Universita¨t Go¨ttingen, 1986.
(37) Sheldrick, G. M. SHELXL-93, A Program for the Refinement
of X-Ray Crystal Structures, Universita¨t Go¨ttingen, 1993.
(38) El Murr, N.; Laviron, E. Can. J . Chem. 1976, 54, 3350.
(39) Pauson, P. L.; Wilkinson, G. J . Am. Chem. Soc. 1954, 76, 2024.
Anal. Calcd for C28H34N4CoIN4 (612.44): C, 54.91; H, 5.56;
N, 9.15. Found: C, 54.48; H, 5.52; N, 9.19. MS, m/ z (%): 485
(2) [M+]. IR (KBr): ν 1532 s. 1H NMR (CD3CN, 320 K): δ
2.54 (br, 16H, NCH2), 3.16 (br., 6H, NCH3), 5.54 (s, 4H, IndH),
6.65-6.70 (AA′, 4H, IndH), 7.24-7.29 (BB′, 4H, IndH). 13C