Preparation, characterization and electrochemical and X-ray structural studies of new conjugated 1,1′-ferrocenediyl-ended [CpFe-arylhydrazone] + salts

Article abstract of DOI:10.1039/b308626g

A series of new conjugated bimetallic ferrocenyl 1,1′-bis- substituted compounds of the type (E)-[CpFe(η⁶-p-RC ₆H₄)NHN=CH(η⁵-C₅H ₄)Fe(η⁵-C₅H₄)-CH=CHC ₆H₄-p-R′]⁺PF₆^- (Cp = η⁵-C₅H₅; R, R′ = H, NO ₂, 11; Me, NO₂, 12; MeO, NO₂, 13; Cl, NO ₂, 14; Me, CN, 15; Me, Me, 16), with end-capped (E)-ethenylaryl and [CpFe(arylhydrazone)]⁺ substituents, have been prepared by the condensation reaction of 1,1′-(p-R′-arylethenyl) ferrocenecarboxaldehyde (R′ = Me, 4; NO₂, 5; CN, 6) with the organometallic hydrazine precursors [CpFe(η⁶-p-RC ₆H₄NHNH₂)]⁺PF₆ ^- (R = H, 7; Me, 8; MeO, 9; Cl, 10). In the trimetallic series, {[CpFe(η⁶-p-RC₆H₄)NHN=CH(η ⁵-C₅H₄)]₂Fe}²⁺[PF ₆^-]₂ (R = H, 17; Me, 18; MeO, 19, Cl, 20), which results from the condensation of two equivalents of the same organometallic hydrazine precursor (7-10) with 1,1′- ferrocenedicarboxaldehyde, the ferrocenediyl core symmetrically links two cationic mixed-sandwich units. These ten hydrazones (11-20) were stereoselectively obtained as their trans isomers about the N=C double bond. All the new compounds were thoroughly characterized by a combination of elemental analysis, spectroscopic techniques (¹H NMR, IR and UV-Vis) and electrochemical studies in order to prove electronic interaction between the donating and accepting units through the π-conjugated system. A representative example of each series has also been characterized by single crystal X-ray diffraction analysis. The bimetallic complex 16⁺ adopts an anti conformation with the two iron atoms on opposite faces of the dinucleating hydrazonato ligand, whereas the trinuclear complex 19²⁺ adopts a syn conformation with an Fe-Fe-Fe angle of 180°. Other salient features of these structures are the long Fe-C_ipso bond distances and the slight cyclohexadienyl character at the coordinated C₆ ring, with a folding angle of 7.4° and 7.0° for 16⁺ and 19 ²⁺, respectively.

Full text of DOI:10.1039/b308626g

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P A P E R
Preparation, characterization and electrochemical and X-ray
0
structural studies of new conjugated 1,1 -ferrocenediyl-ended
þ
[
CpFe-arylhydrazone] salts
a
a
a
a
b
Carolina Manzur,* C e´ sar Z u´ n˜ iga, Lorena Mill a´ n, Mauricio Fuentealba, Jose A. Mata,
c
a
Jean-Ren e´ Hamon* and David Carrillo*
a
Laboratorio de Qu ı´ mica Inorg a´ nica, Instituto de Qu ı´ mica, Pontificia Universidad Cat o´ lica de
Valpara ı´ so, Avenida Brasil, 2950, Valpara ı´ so, Chile. E-mail: david.carrillo@ucv.cl;
Fax: þ56 32 27 34 20; Tel: þ56 32 27 31 65
b
c
Departamento de Qu ı´ mica Inorg a´ nica y Org a´ nica, Universitat Jaume I, 12080,
Casstell o´ n, Spain
Laboratoire des Organom e´ talliques et Catalyse: Chimie et Electrochimie Mol e´ culaires CNRS
UMR 6509, Institut de Chimie de Rennes, Universit e´ de Rennes 1, Campus de Beaulieu,
3
5042, Rennes cedex, France. E-mail: jean-rene.hamon@univ-rennes1.fr;
Fax: þ33 223 23 56 37; Tel: þ33 223 23 59 58
Received (in Montpellier, France) 23rd July 2003, Accepted 23rd September 2003
First published as an Advance Article on the web 14th November 2003
0
A series of new conjugated bimetallic ferrocenyl 1,1 -bis-substituted compounds of the type
6
5
5
0
þ
ꢀ
5
(E)-[CpFe(Z -p-RC
6
H
4
)NHN=CH(Z -C
5
H
4
)Fe(Z -C
5
H
4
)–CH=CHC
6
H
4
-p-R ] PF
6
(Cp ¼ Z -C
5 5
H ; R,
0
R ¼ H, NO , 11; Me, NO , 12; MeO, NO , 13; Cl, NO , 14; Me, CN, 15; Me, Me, 16), with end-capped
2
2
2
2
þ
(
1
E)-ethenylaryl and [CpFe(arylhydrazone)] substituents, have been prepared by the condensation reaction of
0
0
0
,1 -(p-R -arylethenyl)ferrocenecarboxaldehyde (R ¼ Me, 4; NO , 5; CN, 6) with the organometallic hydrazine
þ ꢀ
6 4 2 6
2
6
precursors [CpFe(Z -p-RC
{
H
NHNH
)] PF
(R ¼ H, 7; Me, 8; MeO, 9; Cl, 10). In the trimetallic series,
2þ ꢀ
6 2
6
5
[CpFe(Z -p-RC H )NHN=CH(Z -C H )] Fe} [PF ] (R ¼ H, 17; Me, 18; MeO, 19, Cl, 20), which results
6
4
5
4
2
0
from the condensation of two equivalents of the same organometallic hydrazine precursor (7–10) with 1,1 -
ferrocenedicarboxaldehyde, the ferrocenediyl core symmetrically links two cationic mixed-sandwich units.
These ten hydrazones (11–20) were stereoselectively obtained as their trans isomers about the N=C double
bond. All the new compounds were thoroughly characterized by a combination of elemental analysis,
1
spectroscopic techniques ( H NMR, IR and UV-Vis) and electrochemical studies in order to prove electronic
interaction between the donating and accepting units through the p-conjugated system. A representative
example of each series has also been characterized by single crystal X-ray diffraction analysis. The bimetallic
þ
complex 16 adopts an anti conformation with the two iron atoms on opposite faces of the dinucleating
hydrazonato ligand, whereas the trinuclear complex 19 adopts a syn conformation with an Fe–Fe–Fe angle of
2
þ
ꢁ
1
80 . Other salient features of these structures are the long Fe–Cipso bond distances and the slight
ꢁ
ꢁ
þ
2þ
cyclohexadienyl character at the coordinated C
respectively.
6
ring, with a folding angle of 7.4 and 7.0 for 16 and 19 ,
6
þ
[
CpFe(Z -aryl)] moiety been used as an organometallic chro-
Introduction
12
mophore to achieve second-order NLO responses. In the
search for new materials with electronic communication
between terminal subunits, we have focused our interest in
the preparation of new conjugated ferrocenyl complexes with
end-capped mixed-sandwich iron(II) fragments, affording
interesting bimetallic complexes in which the organometallic
termini are connected by an asymmetric –NR–N=CR–
1
Ferrocenes play important roles in the fields of organic and
organometallic chemistry and in materials science as
components of dendrimers, polymers, molecular magnets
2
3
4
5
13
and non-linear optical (NLO) materials. Their chemistry has
been extensively explored because ferrocene-based complexes
combine chemical versatility and excellent thermal and photo-
chemical stability with exceptional electrochemical properties,
which generate considerable interest in the use of the ferro-
1
4
(R ¼ H, Me) type
I
hydrazonato
conjugated bridge.
Furthermore, non-linear optical responses can be envisaged
from electrochemical studies, electronic spectroscopy, molecu-
lar structure determinations and theoretical investigations that
suggest effective electron delocalization along the p-conjugated
5
5
cenyl moiety, [CpFe(Z -C H )] (Cp ¼ Z -C H ), as a donating
5
4
5
5
group in donor-acceptor (D-p-A) chromophores displaying
enhanced second-order NLO properties. The electron-releas-
5
,6
1
3b,d,e
ing ability of the parent ferrocenyl group is closely
similar to that of the p-methoxyphenyl group. On the other
hand, the cationic isolobal electron-acceptor counterparts of
spacer.
7
In a continuation of these studies, we have now prepared
0
conjugated ferrocenyl 1,1 -bis-substituted compounds with
end-capped arylethenyl substituents and [CpFe(arylhydra-
6
ferrocene, the robust mixed-sandwich derivatives [CpFe(Z -
arene)] , have also been the subject of intense synthetic,
þ
8
þ
zone)] groups for the bimetallic series 11–16, whereas in the
trimetallic series 17–20, the ferrocenediyl core symmetrically
links two cationic mixed-sandwich units. The full analytical
9
electron transfer, electrochemical
10
11
and photochemical
investigations. Despite this interest, only in one case has the
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
134
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4

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1
and spectroscopic characterization (IR, UV-VIS, H NMR) of
Characterization of the new products 3 and 4 was mainly
achieved by means of IR and H NMR spectroscopies and
1
these ten new organometallic hydrazone complexes and of the
0
new 1,1 -(p-tolylethenyl)ferrocenecarboxaldehyde (4) and its
satisfactory elemental analysis (see Experimental). In the pro-
ton NMR spectra, both E isomers 3 and 4 are identified by
their AB quartet with a coupling constant of ca. 17 Hz, in
accord with the expected trans stereochemistry. Four triplets
were observed for the substituted Cp rings, while the phenyl
protons appear as two doublets. On the other hand, the car-
boxaldehyde function of compound 4 exhibited the character-
protected 1,3-dioxolane precursor 3 (see below) are reported
here. Their electronic and electrochemical properties have been
investigated and the crystal structures of a representative
example of each series, namely compounds 16 and 19, have
also been determined. Structurally related dicationic trinuclear
organoiron oligomers have recently been prepared by Abd-El-
1
5
ꢀ1
Aziz et al. in order to synthesize a new class of mixed-charge
0
istic strong n(C=O) stretching vibration at 1679 cm in the
iron-containing polymers. In addition, 1,1 - bis-ethenediyl fer-
rocene complexes with various pendant groups such as pyri-
infrared spectrum, and low field singlets at d 9.91 and d
1
13
1
192.7 in the H and C{ H} NMR spectra, respectively.
The cyclovoltammogram of complex 4 displayed the chemi-
cally reversible ferrocene/ferricinium couple with ipa/ipc ¼ 1.0
in CH Cl . The large peak-to-peak separation (196 mV) may
1
6
17
18
19
dine, p-cyano, p-bromo and p-iodophenylene have
been used by several authors to synthesize trimetallic deriva-
tives that show very interesting structural features and high
non-linear optical responses.
2
2
be due to a combination of uncompensated solution resistance
2
3
and slightly slow electron transfer kinetics. As expected as
the result of substituting an electron-withdrawing group
(
potential of the ferrocenediyl core for 4 (267 mV) is less ano-
NO , CN) for an electron-releasing one (Me), the half-wave
2
Results and discussion
dic, with respect to ferrocene, than those measured for 5
17
310 mV) and 6 (330 mV), indicating some degree of electron
Synthesis and spectroscopy of 3 and 4
(
transfer between the p-Me substituent and the iron center.
As pointed out by most authors, the E-type conformation of
the p-bridge is known to provide a good coplanarity of the
conjugated spacer and hence to increase the electronic commu-
nication between the donating and accepting ends of a dipolar
Synthesis and spectroscopy of 11–20
0
0
5
1
7–21
The
1-carboxaldehyde-1 -p-R -(E)-styrylferrocenes
0
(Z -
system.
Therefore, we first attempted to prepare the new
5
0
0
C H CHO)Fe(Z -C H –(E)–CH=CH–C H -p-R ) (R ¼ Me,
bis-substituted ferrocene compound (E)-1,1 -(p-methylstyryl)-
ferrocene carboxaldehyde (4, Scheme 1) by conventional
Wittig methods, the most appropriate strategy for short-length
chained complexes, according to the procedure described by
Peris and co-workers for the analogous derivatives 5 and 6,
bearing the p-nitro and p-cyano electron-withdrawing groups,
5
4
5
4
6
4
4
2
; NO , 5; CN, 6) are indeed of interest in the design of new
materials, since the presence of the carboxaldehyde group
can provide access to a variety of functional groups. Thus,
the new dinuclear organoiron hydrazones 11–16 (see Experi-
mental and Table 1) were successfully prepared by a condensa-
tion reaction of the ionic organometallic hydrazine precursors
1
7
respectively. The reaction afforded a poor yield of an untract-
able mixture and therefore, in order to obtain our target mole-
cule 4, we applied the multi-step procedure developped by
6
þ
ꢀ
[
CpFe(Z -p-RC H NHNH )] PF (R ¼ H, 7; Me, 8; MeO,
6
4
2
6
9; Cl, 10) with the ferrocene-based aldehyde building blocks
4–6 (Scheme 2).
On the other hand, the trimetallic hydrazones [{CpFe(Z -p-
RC H NHN=CH–Z -C H )} Fe] [PF6 ]2 (17–20; see Exp-
erimental and Table 2) were synthesized by the reaction of 2
equiv. of organoiron hydrazine precursors 7–10 with 1,1 -fer-
2
1
Manoury et al. (Scheme 1). This involves the preparation
0
6
of the monoacetal 2 from 1,1 -ferrocenedicarboxaldehyde 1,
2
5
2þ
ꢀ
2
which is readily accessible from ferrocene. The free aldehyde
function was then used to build the first substituent by reacting
6
4
5
4
2
0
2
prisingly, compound 3 was stereoselectively formed, in 59%
6 4 3
with the in situ generated (p-MeC H ) ylide. Sur-
CH=PPh
5
rocenedicarboxaldehyde (Z -C
5
H
4
CHO)
2
Fe (Scheme 3). It is
1
yield, as the E isomer as demonstrated by H NMR spectro-
interesting to note that the bis functionalized p-chloro deriva-
tive 20 represents an attractive monomeric unit for the pre-
paration of polymers containing both neutral and cationic
cyclopentadienyliron complexes in their structures, in light of
scopy (see below). The Wittig reaction generally leads to a
mixture of E and Z isomers. Hydrolytic deprotection of the
1,3-dioxolane intermediate 3 furnished the desired bis-substi-
1
5
the recently communicated synthetic methodology.
tuted ferrocene carboxaldehyde 4 in 47% yield (Scheme 1).
The new free formyl group has then been used in the building
up of the second substituent as described in the following
section.
In all cases, the reactions were carried out in refluxing etha-
nol solution containing catalytic amounts of concentrated
acetic acid. The bi- and trinuclear complexes were obtained
as spectroscopically pure air- and thermally stable, brownish
red to dark red (11–16) and orange or red-orange (17–20)
microcrystalline solids in reasonable yields ranging from 40
2 2 2
to 59%, after recrystallization from CH Cl –Et O (1:1).
The cationic compounds exhibit a good solubility in common
polar organic solvents, but are insoluble in diethyl ether,
hydrocarbons and water. The structures of these ten new
homobi- and homotrimetallic hydrazones were inferred from
1
satisfactory elemental analyses (Table 3), H NMR, IR and
UV-Vis spectroscopies (Table 4) and, additionally, in the case
of complexes 16 and 19, by X-ray diffraction analysis (vide
infra).
The most remarkable common features observed in the IR
spectra of these ten powdered compounds (11–20 in Table 4)
were: (i) the existence of a sharp intense band at ca. 1570
ꢀ
1
cm , which is due to the asymmetric stretching vibration of
the C=N imine group, (ii) the typical weak to medium N–H
stretching vibration in the region from 3316 to 3344 cm
ꢀ
1
ꢀ
1
and (iii) a very strong n(PF
and strong d(P–F) band at 557–559 cm . In addition, the
6
) band at ca. 840 cm and a sharp
ꢀ
1
Scheme 1
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4
135

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a
Table 1 Reactions of organoiron hydrazine complexes with p-substituted styrylferrocenecarboxaldehydes
0
þ
6ꢀ
0
-p-R
Compound
R, R
[CpFe(p-RC
6
H
4
NHNH
2
)] PF
(C
5
H
4
CHO)Fe(C
5
H
4
–CH=CHC
6
H
4
Yield
11
12
13
14
15
16
H, NO
Me, NO
MeO, NO
Cl, NO
2
49.8 mg, 0.138 mmol
53.6 mg, 0.138 mmol
55.8 mg, 0.138 mmol
56.5 mg, 0.138 mmol
100.0 mg, 0.258 mmol
50.0 mg, 0.129 mmol
49.8 mg, 0.138 mmol
49.8 mg, 0.138 mmol
49.8 mg, 0.138 mmol
49.8 mg, 0.138 mmol
87.0 mg, 0.255 mmol
43.0 mg, 0.130 mmol
55%, 54 mg
58%, 58 mg
55%, 57 mg
53%, 55 mg
40%, 72 mg
56%, 50 mg
2
2
2
Me, CN
Me, Me
a
The reactions listed in this table were all run under the general conditions given in the Experimental.
2
4
9.26–9.59) of the acidic benzylic N–H signal may be attribu-
infrared spectra of compounds 11–16 showed a weak band in
ꢀ
1
8a,25
the 1588–1620 cm region assigned to the n(C=C) stretching
mode of the phenylethenyl pendant group. More specifically,
the IR spectra of compounds 11–14 exhibited a strong band
ted to the electronic effect of the organometallic moiety,
and/or its participation in molecular association via intermole-
Finally, the upfield-shifted aromatic pro-
ring and the deshielded sharp
proton resonance at ca. 7.90 ppm assigned to the azomethine
1
3d
cular H-bonding.
ꢀ
1
in the range 1333–1340 cm attributed to the p-NO substitu-
ent, whereas the C=N stretching vibration appeared at 2221
2
tons of the coordinated C
6
ꢀ1
13
cm in the IR spectrum of 15. Finally, the spectra of the
homotrimetallic compounds 17 and 20 showed two N=C,
fragment (N=CH) appeared in the expected regions.
ꢀ
PF
6
(and C–Cl for 20) stretching frequencies (see Table 4),
Crystal structures
a phenomenon that we have already encountered for homobi-
metallic ferrocenyl hydrazone complexes, which is compatible
with the presence of at least two conformers in the solid sta-
6
The molecular structures of the cationic (E)-[CpFe(Z -
p-MeC H )–NHN=CH–(Z -C H )Fe(Z -C H )–CH=CH–
5
5
6
4
5
4
5
4
1
3b
þ
þ
6
te.
Interestingly, the organoiron hydrazones 11–20 are stereose-
lectively formed as the sterically less hindered trans (about the
C H -p-Me] (16 ) and of the dicationic [{CpFe(Z -p-
6
4
5
2þ
2þ
(19 ) organome-
tallic moieties, along with the atom labelling schemes, are
MeOC H )–NHN=CH–(Z -C H )} Fe]
6
4
5
4
2
N=C double bond) isomer as indicated by the unique set of
signals in their H NMR spectra (acetone-d , 297 K, see Table
presented in Fig. 1 and Fig. 2, respectively. Key bond lengths
1
þ
2þ
6
and angles for 16 and 19 are listed in Table 5. In both
complexes, high anisotropic thermal motion and/or disorder
was observed for the carbon atoms of the Cp ligand
of the mixed-sandwich units. Such a phenomenon has fre-
quently been reported for mixed-sandwich iron(II) com-
4
and 19 (see below). For all the compounds, the two sandwich
) and definitively assigned from the structural analyses of 16
6
þ
5
moieties [CpFe(Z -p-RC
clearly identified by the characteristic sharp singlet of the Cp
6
H
4
–)]
5 4 2
and [(Z -C H ) Fe] are
1
3b, 13c, 24, 26, 27
proton resonance observed at ca. 5.0 ppm while the two mono-
substituted C rings appeared as broad singlets or unresolved
plexes.
partial rotation of the C ring about the Fe–Cp centroid axis.
The orientation is presumably due to
5
5
5
6
triplets in the 4.80–4.86 and 4.53–4.56 ppm ranges, corre-
sponding to the spectrum of an A B system. Only one pair
The metrical parameters (see Table 5) are typical of Z –Fe–Z
5 5 28–31
2
2
and Z –Fe–Z metallocene-type coordination.
The carbo-
of H
a
and H
b
resonances is observed for the trimetallic com-
cyclic rings coordinated to the same iron center are essentially
parallel with one another and the ring centroid–iron–ring cen-
troid vectors are almost collinear, both in the [Cp–Fe–arene]
pounds 17–20, consistent with a symmetrical structure with
an inversion center at the ferrocenediyl iron atom, in agree-
ment with the solid state structure of 19 (see below). The p-
substituted phenylethenyl pendant groups of the bimetallic
derivatives 11–16 exhibited the same resonance and coupling
constant patterns as those reported above for the ferrocene-
based aldehyde 4, indicating that the trans stereochemistry
about the HC=CH double bond is retained after the construc-
þ
and in the ferrocenic subunits.
Complex 16 adopts an anti conformation13b with the two
þ
iron atoms on opposite faces of the dinucleating hydrazonato
ligand (Fig. 1), whereas the trinuclear complex 19 adopts
2þ
1
3b
a syn conformation
ꢁ
with an Fe(1)–Fe(2)–Fe(1a) angle of
180 (Fig. 2). Both [CpFe(arene)] moieties occupy opposite
sites and they are related by symmetry through the inversion
þ
tion of the hydrazone framework. The low field position (d
center of the molecule. In both complexes, the p-conjugated
ꢀ
bridging ligands, [p-RC
1
6
H
4
–NHN=CH–C
6 ; MeO, 19 ), are similar and, therefore, the through-bond
H
5 4
]
(R ¼ Me,
þ 2þ
˚
Feꢂ ꢂ ꢂFe distances (9.714 and 9.633 A, respectively) are closely
related, whereas the through-space Feꢂ ꢂ ꢂFe distance is much
þ
˚
2þ
˚
longer in 16 (8.064 A) than in 19 (6.925 A). In complex
þ
1 the ferrocenylidene groups adopt an eclipsed conforma-
tion whereas the staggered one is observed for complex 19
6
2þ
(see Figs. 1 and 2). The conformation adopted by the dinuclear
þ
complex 16 allows a certain interaction between the coordi-
nated and free phenyl groups, although the dihedral angle
ꢁ
between them is 41.65 (see Fig. 1). On the other hand, the
coordinated and non-coordinated phenyl groups are not
0
coplanar with the corresponding Cp and Cp ligands of the
ꢁ
ferrocenylidene group, subtending dihedral angles of 21.31
ꢁ
and 18.96 , respectively. The phenyl group of the trimetallic
species is not coplanar with the Cp ligand, subtending a dihe-
ꢁ
dral angle of 27.70 (see Fig. 2). These significant but not large
deviations from planarity might, however, allow an efficient
p-electron delocalization or electronic interaction between
the electron-donating and electron-accepting termini through
the entire hydrazonato skeleton.
Scheme 2
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
136
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4

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0
a
Table 2 Reactions of organoiron hydrazine complexes with 1,1 -ferrocenedicarboxaldehyde
þ
6ꢀ
Compound
R
[CpFe(p-RC
6
H
4
NHNH )] PF
2
(C
5
H
4
CHO)
2
Fe
Yield
17
18
19
20
H
101.0 mg, 0.270 mmol
109.5 mg, 0.282 mmol
115.1 mg, 0.285 mmol
51.5 mg, 0.126 mmol
32.0 mg, 0.132 mmol
34.0 mg, 0.140 mmol
34.6 mg, 0.143 mmol
15.0 mg, 0.062 mmol
55%, 69 mg
51%, 70 mg
50%, 73 mg
59%, 37 mg
Me
MeO
Cl
a
The reactions listed in this table were all run under the general conditions given in the Experimental.
3
2–34
A careful examination of Table 5 reveals some interesting
structural features provoked by the strong electron-withdraw-
ing effect of CpFe on the arene ligand in both complexes.
both bands have some d-d character.
are in agreement with previously reported theoretical and
experimental data.
These assignments
5
3
þ
17,19–21,36,37
The energy and intensity of
˚
Thus, the Fe(1)–C(6) bond lengths, 2.193(5) and 2.144(4) A for
these transitions are influenced by the nature of the ancillary
ligands, giving rise to bathochromic shifts in its absorption
maximum as the result of a lowering of the energy of the p*
orbital of the ligand. The effect can be further amplified
by increasing the acceptor strength of the electron deficient
center. Examination of the UV-vis data (Table 4) for the series
þ
2þ
1
6
and 19 , respectively, are longer than the mean value of
the other Fe(1)–C(C ring) bond lengths (see Table 5). Such an
Fe–C elongation has already been reported by us for the binuc-
6
5a,37a
1
3b,13c
lear organometallic hydrazones.
This remarkable elonga-
tion is a consequence of a partial delocalization of the electron
pair located on the N(1) atom toward the mixed-sandwich
moiety and is reflected by (i) a depyramidalization of the
5
of four compounds containing the same [(Z -C
5
H
4
)Fe-
frame-
work and bearing various pendant accepting groups,
NO CN)
such as (p-CH=CH–C ) (12), (p-CH=CH–C
(15), (p-CH=CH–C
Me) (16) and [CpFe (Z -p-MeC
5
6
þ
ꢀ
(Z -C
H
5 4
)–CH=N–NH–(Z -p-MeC
6
H
4
)FeCp] PF
6
2
N(1) atom with typical bond angles of an sp -hybridized nitro-
˚
gen atom (Table 5), (ii) a C(6)–N(1) bond length of 1.359(6) A
6
H
4
2
6 4
H
þ
˚
for 16 and 1.366(4) A for 19 , values that are intermediate
2þ
þ
6
6
H
4
6 4
H -
between those of a single and a double carbon–nitrogen
bond and (iii) a slight cyclohexadienyl-like character at the
NHN=CH)] (18), indicates that the energies and the
oscillator strengths of both the low and high energy bands
are sensitive to the acceptor strength. Thus, while compound
16 exhibits lmax at 302 and 453 nm, these values progressively
shift to longer wavelengths in going to 18 (309 and 473 nm), 15
(311 and 478 nm) and finally to 12 (321 and 492 nm). Similar
3
1
ꢁ
ꢁ
coordinated phenyl ring with a folding angle of 7.4 and 7.0
about the C(7)–C(11) axis for both complexes, respectively.
˚
Likewise, the Fe(1)–C(9) bond length of 2.116(5) A in complex
2þ
19
can be also attributed to a partial delocalization of one
oxygen lone pair toward the arene ligand, provoking a folding
trends are observed for other families of ferrocenyl p-cyano-
phenylethenyl and phenylethynyl compounds, as well as
for cationic organoiron polymers containing azo-dye-function-
ꢁ
36c,38
angle around the C(8)–C(10) axis of 5.8 . Hence, the arene
ligand adopt a slightly bowed conformation, with the C(6)
and C(9) atoms being bent out of the carbocyclic diene plane.
39
alized side chains.
The two characteristic CT bands of the dinuclear hydra-
zones 11–13, 15 and 16 exhibit bathochromic shifts (Fig. 3)
Electronic spectra
on changing from CH
2
Cl
2
(e ¼ 8.90) to DMSO (e ¼ 47.6),
Electronic absorption spectra for the cationic bi- and trinuc-
lear hydrazones 11–20 were measured in CH Cl and DMSO;
indicating increased polarity in the excited state. The more
intense p-p* band is more solvatochromic (4–22 nm) than
the lower energy band. For the dinuclear hydrazone 14 and
the trinuclear compounds 17–20, the higher energy band is also
red-shifted (6–22 nm) but the lower energy band shows a nega-
tive solvatochromism (ꢀ2 to ꢀ55 nm, see Fig. 3). This results
from a better stabilization of the equilibrium ground state than
the Franck–Condon excited state, due to solvation by solvents
2
2
the values are recorded in Table 4. In each solvent the com-
plexes exhibited similar spectra, revealing their isostructural
features with two sets of absorption maxima typical of conju-
gated ferrocenyl systems. The lower energy band (400–500 nm)
is assigned to a metal-to-ligand charge-transfer transition
(
MLCT) and the higher lying absorption in the range of 300
4
0
to 360 nm as an intraligand p-p* transition (ILCT). In fact,
of increasing polarity. Such a negative solvatochromism
(
ves,
hypsochromic shift) is mainly observed for cationic derivati-
1
3b,13d,37
since in these species the ground state dipole
1
4
moments are opposite in sign to those of the neutral species,
due to the acceptor-localized positive charges, but the charge
transfer is in the same direction as in the neutral species.
It is worth noting that the lower energy maxima for the
dicationic ferrocenediyl hydrazones 17–20 are found to be
somewhat blue-shifted compared to those of the neutral
bis-substituted ferrocenediyl-ligated phenylethenyl derivatives,
5
Fe{(Z -C
5
H
4
)-(E)-CH=CHC
reported by Peris et al. Coordination of the arene rings with
6
H
4
-p-R}
2
(R ¼ NO
2
,
CN),
1
7
þ
two [CpFe ] fragments is expected to generate stronger dica-
tionic electron-accepting termini. The half-wave oxidation
potentials of trimetallic hydrazone derivatives are indeed
slightly more anodic than those of the mononuclear neutral
species. A rather similar situation has been pointed out by
3
7b
Heck and co-workers
and two factors were argued to
explain this apparent inconsistency: (i) the generation of new
orbital frontiers, with changes in character and order, upon
complexation and (ii) the molecular orbitals involved in the
oxidation step and in the photochemical excitation can be
different.
Scheme 3
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4
137

View Article Online
1
hydrazone-linker-containing complexes and are presumably
3e
Table 3 Some properties of the new bi- and trimetallic hydrazone
complexes
due to the reduction of an in situ generated neutral zwitterionic
species.
2
4,44
As expected for the symmetric homotrimetallic
a
M. p. / C Analyses
ꢁ
Compound Color
compounds 17–20, the integrated area of the reduction wave
is twice that of the oxidation one. Note that the cyclovoltam-
mogram of 20 exhibits two reduction waves at ꢀ2.30 and
11
12
13
14
15
16
17
18
19
20
Brownish red 149
Brownish red 105
Brownish red 97
Brownish red 187
Found: C, 49.88; H, 3.87; N, 5.76
Calcd.: C, 50.24; H, 3.65; N, 5.86
Found: C, 51.12; H, 4.00; N, 5.67
Calcd.: C, 50.92; H, 3.86; N, 5.75
Found: C, 50.29; H, 3.89; N, 5.94
Calcd.: C, 49.83; H, 3.78; N, 5.62
Found: C, 48.24; H, 3.56; N, 5.98
Calcd.: C, 47.94; H, 3.35; N, 5.59
Found: C, 53.79; H, 4.12; N, 6.33
Calcd.: C, 54.04; H, 3.97; N, 5.91
Found: C, 55.25; H, 4.61; N, 4.09
Calcd.: C, 54.89; H, 4.46; N, 4.00
Found: C, 43.13; H, 3.40; N, 6.06
Calcd.: C, 42.80; H, 3.38; N, 5.87
Found: C,43.78; H, 3.78; N, 5.92
Calcd.: C, 44.02; H, 3.69; N, 5.70
Found: C, 42.80; H, 3.64; N, 5.79
Calcd.: C, 42.64; H, 3.58; N, 5.52
Found: C, 40.32; H, 3.17; N, 5.39
Calcd.: C, 39.92; H, 2.96; N, 5.48
0
/þ
ꢀ
2.44 V vs. Cp Fe , the more anodic one being attributable
2
4
5,46
to a dechlorination reaction.
On the other hand, the cyclovoltammograms of the four
appended p-NO substituent derivatives 11–14 exhibit two
fully reversible reduction waves at ca. ꢀ1.32 and ꢀ1.53 V vs.
2
0
/þ
Cp
electronic reduction of the nitro group to generate the radical
2
Fe . The first wave is confidently assigned to the mono-
Dark red
Dark red
Orange
155
215
209
263
240
ꢃ
ꢀ 47,48
, whereas the assignment of the second
anion –NO
2
49
reversible wave remains much more puzzling. Nevertheless,
this indicates that the LUMO for complexes 11–14 is localized
at the nitro substituent. For compounds 15–20, however, the
LUMO is determined by the cationic mixed-sandwich, and in
all the cases, the nature of the HOMO is dominated by the
neutral donating ferrocenyl units, in accordance with theoreti-
Orange
Orange
1
3b
cal investigations.
All these electrochemical data taken
Red-orange 215
together suggest that the electron-donating and -accepting ter-
mini communicate electronically to a significant extent and
that they behave as a donor-acceptor couple.
a
All the compounds decompose when melted.
Concluding remarks
Electrochemical studies
In conclusion, we have described the easy access to two new
0
In order to get a deeper insight into the mutual donor-acceptor
electronic influence with respect to electrochemical perturba-
tions, we have undertaken the cyclic voltammetry (CV) study
of the homobi- and homotrimetallic hydrazone complexes
homogeneous series of conjugated ferrocenyl 1,1 -bis-substi-
tuted compounds with end-capped arylethenyl substituents
þ
and [CpFe(arylhydrazone)] groups for the bimetallic series
1
1–16 whereas in the trimetallic series 17–20, the ferrocenediyl
(11–16 and 17–20, respectively). All the cyclovoltammograms
core symmetrically links two cationic mixed-sandwich units,
via condensation reactions between cyclopentadienyliron-com-
plexed hydrazines and ferrocene mono- and biscarbaldehydes,
respectively. Single crystal X-ray diffraction analyses show that
were recorded in DMF using the same setup and the electro-
chemical data thus obtained are summarized in Table 6. All
the complexes display two major features: (i) an irreversible
process attributable to Fe-centered reduction at the mixed-
þ
1
0,33b
the bimetallic complex 16 adopts an anti conformation with
the two iron atoms on opposite faces of the dinucleating
hydrazonato ligand, whereas the trinuclear complex 19
sandwich fragment
and (ii) a single chemically reversible
4
2
oxidation wave corresponding to the ferrocenyl unit in the
bridging linker (Fig. 4). As for the ferrocenediyl-based alde-
2þ
adopts a syn conformation with a linear Fe–Fe–Fe arrange-
ment. The ten new organometallic hydrazones 11–20 can be
defined as type I non-rod-shaped dipolar chromophores.
hyde precursor 4, the peak-to-peak separations (DE , see
p
Table 6) are significantly greater than the ideal value of 59
mV required for a pure Nernstian process, probably due to
1
4
6
þ
2
3
The cationic mixed-sandwich [CpFe(Z -p-RC H )–] acts as
the same reasons cited above. However, this difference is
similar to that measured for ferrocene under the conditions
of the experiment (see Experimental for details).
6
4
an electron acceptor and the neutral ferrocenediyl moiety as
an electron-donating group. Their mutual electronic influence
is mediated by the hydrazone linking spacer –NH–N=CH–.
Moreover, depending on the nature of their p-substituents,
the arylethenyl pendent groups act either as electron-with-
By comparison with the previously reported monocationic
6
5
þ 13b,43
5 4
H )FeCp] ,
series, [CpFe(Z -p-RC
the bis-substituted complexes show a greater anodic shift (ca.
0–100 mV) of their half-wave potentials, except for 16 as
expected with its donating p-Me group and, more surprisingly,
8 (see Table 6). This suggests that the extra electron-accepting
H
6 4
)NHN=CH(Z -C
drawing (p-NO , p-CN) or -releasing (p-Me) entities. We have
2
2
shown that these respective electronic properties clearly influ-
ence the values of the redox potential in the cyclovoltammo-
grams and the energies of the charge transfer bands in the
electronic spectra. As a result, these compounds are proved
to favour electronic delocalization along the conjugated chain.
Finally, the polarized structure of this type of complexes,
which endows them with solvatochromic properties, suggests
that they are good candidates for non-linear optical studies.
Further work will now be directed toward the determination
of those properties for some selected dipolar organometallic
hydrazone complexes reported here.
1
substituent has a significant electronic effect on the ferrocenyl
bridging spacer. Also surprising is the more anodic half-wave
potential of the nitrile derivative 15 compared to that of the
corresponding nitro counterpart 12, despite the known better
electron-accepting nature of the nitro group. This was already
1
7
noted for the precursor aldehydes 5 and 6. The substitution
of the arylethenyl groups by the corresponding organometallic
hydrazone ligands, 13 vs. 19, 14 vs. 20, 16 vs. 18, results in a
shift of the oxidation wave to more anodic potential, presum-
ably due to the powerful electron-accepting nature of the catio-
nic mixed-sandwich unit.
On the reduction side, the ten compounds studied undergo
an irreversible process (Fig. 4) centered at the mixed-sandwich
moiety, corresponding to the single-electron reduction of the
Experimental
General methods and materials
6
7
d , Fe(II), 18-electron complexes to the unstable d , Fe(I), 19-
All operations were performed under inert atmosphere using
standard vacuum/nitrogen line, Schlenk or syringe techniques
with protection from light to avoid decomplexation of the
1
0,33b
electron species.
6
benzaldehyde hydrazone
The very cathodic potential values (Table
) are very similar to those reported for the monometallic
2
4
þ
and homobimetallic elongated
CpFe moiety. The solvents were dried and distilled under
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
138
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4

View Article Online
Table 4 Spectroscopic data of the new bi- and trimetallic iron hydrazone complexes
UV-vis l/nm
ꢀ1
3
ꢀ1
ꢀ1
1
a
Compound IR (KBr) n/cm
(Log e/dm mol cm
)
3 3
H NMR d (CD COCD )
1
1
1
1
1
2
3
4
3328 m (NH), 1590 m (C=C),
CH
DMSO: 332 (4.33), 488 (3.62)
2
Cl
2
: 322 (4.40), 489 (3.71)
4.55 (br s, 4H, C
4.86 (br s, 2H, C
6.10–6.21 (m, 5H, coord Ph),
5
H
4
), 4.81 (br s, 2H, C
5 4
H ),
1
570 m (C=N), 1333 s (NO
40 vs and 558 m (PF
2
),
2
),
2
),
2
),
5 4
H ), 5.03 (s, 5H, Cp),
8
6
)
6
7
7
8
.88 (d, JH-H ¼ 16.3, 1H, CH=CH),
.16 (d, JH-H ¼ 16.2, 1H, CH=CH),
.60 (d, JH-H ¼ 8.8, 2H, Ph), 7.88 (s, 1H, N=CH),
.00 (d, JH-H ¼ 8.9, 2H, Ph), 9.42 (br s, 1H, NH)
3328 m (NH), 1588 m (C=C),
CH Cl : 321 (4.36), 351sh (4.32),
492 (3.67)
DMSO: 327 (4.33), 341sh (4.32),
3 5 4
2.46 (s, 3H, CH ), 4.53 (br s, 4H, C H ), 4.80
2
2
1
570 m (C=N), 1338 s (NO
40 vs and 557 m (PF
(t, JH-H ¼ 1.7, 2H, C
5
H
4
), 4.83 (t, JH-H ¼ 1.7, 2H, C
5 4
H ),
8
6
)
4.96 (s, 5H, Cp), 6.05–6.08 (m, 4H, coord Ph), 6.87
(d, JH-H ¼ 16.2, 1H, CH=CH), 7.15
5
01 (3.62)
(
d, JH-H ¼ 16.2, 1H, CH=CH), 7.60 (d, JH-H ¼ 8.8, 2H, Ph),
7
9
.88 (s, 1H, N=CH), 7.98 (d, JH-H ¼ 8.9, 2H, Ph),
.43 (br s, 1H, NH)
3330 m (NH), 1590 m (C=C),
CH Cl : 315 (4.31), 357sh (4.25),
487 (3.64)
4.02 (s, 3H, CH O), 4.53 (br s, 4H, C
(t, JH-H ¼ 1.7, 2H, C
5 4
H ), 4.80
2
2
3
1
1
5
570 m (C=N), 1337 s (NO
256 s (C–O), 840 vs and
5
H
4
), 4.83 (t, JH-H ¼ 1.7, 2H, C
5 4
H ),
DMSO: 332 (4.35), 351 (4.32),
490 (3.69)
5.00 (s, 5H, Cp), 6.00 (d, JH-H ¼ 6.9, 2H, coord Ph),
57 m (PF
6
)
6.12 (d, JH-H ¼ 6.9, 2H, coord Ph), 6.88 (d, JH-H ¼ 16.2, 1H,
CH=CH), 7.15 (d, JH-H ¼ 16.1, 1H, CH=CH), 7.61
(
d, JH-H ¼ 8.7, 2H, Ph), 7.86 (s, 1H, N=CH), 8.01
d, JH-H ¼ 8.7, 2H, Ph), 9.36 (br s, 1H, NH)
(
3324 m (NH), 1590 m (C=C),
CH Cl : 323 (4.44), 355 (4.39),
487 (3.79)
DMSO: 331 (4.38), 462 (3.71)
4.53 (t, JH-H ¼ 1.7, 2H, C
4
H ), 4.56 (t, JH-H ¼ 1.7, 2H,
5 4
2
2
5
1
1
5
558 m (C=N), 1340 s (NO
C
5
H
4
), 4.81 (t, JH-H ¼ 1.7, 2H, C
(t, JH-H ¼ 1.7, 2H, C ), 5.12 (s, 5H, Cp),
6.18 (d, JH-H ¼ 6.8, 2H, coord Ph), 6.53
H ), 4.85
098 w (C–Cl), 836 vs and
5 4
H
6
56 s (PF )
(
d, JH-H ¼ 6.6, 2H, coord Ph), 6.87 (d, JH-H ¼ 16.2,
1
7
8
H, CH=CH), 7.14 (d, JH-H ¼ 16.3, 1H, CH=CH),
.60 (d, JH-H ¼ 8.7, 2H, Ph), 7.89 (s, 1H, N=CH),
.01 (d, JH-H ¼ 8.8, 2H, Ph), 9.59 (br s, 1H, NH)
1
5
6
3331 w (NH), 2221 m (C=N),
CH
2
Cl
2
: 250 (4.26), 286 (3.96),
2.47 (s, 3H, CH
3
), 4.49 (m, 4H, C
5
H
4
), 4.78 (m, 4H, C
5
4
H ),
1
620 w (C=C), 1572 m (C=N),
38 vs and 557 s (PF
311 (4.04), 343 (4.12), 407 (3.33),
478 (3.27)
DMSO: 316 (4.24), 353 (4.11),
4.91 (s, 5H, Cp), 6.00 (d, JH-H ¼ 5.2, 2H, coord Ph),
8
6
)
6.09 (d, JH-H ¼ 5.3, 2H, coord Ph), 6.74 (d, JH-H ¼ 16.4,
1H, CH=CH), 7.00 (d, JH-H ¼ 16.2, 1H, CH=CH),
7.46 (s, 4H, Ph), 7.80 (s, 1H, N=CH), 9.30 (br s, 1H, NH)
4
CH
28 (3.17), 479 (3.26)
Cl : 274 (4.03), 302 (3.15),
1
3331 w (NH), 1620 w (C=C),
572 m (C=N), 838 vs
and 557 s (PF
2
2
2.34 (s, 3H, CH
4.84 (br s, 4H, C
3 3 5 4
), 2.52 (s, 3H, CH ), 4.55 (br s, 4H, C H ),
1
327 (3.45), 360 (3.08), 453 (3.04)
DMSO: 261 (4.38), 308 (3.93),
5
4
H ), 4.99 (s, 5H, Cp), 6.08 (d, JH-H ¼ 6.2,
6
)
2H, coord Ph), 6.17 (d, JH-H ¼ 6.3, 2H, coord Ph), 6.60
(d, JH-H ¼ 16.0, 1H, CH=CH), 6.77 (d, JH-H ¼ 16.1, 1H,
CH=CH), 7.02 (d, JH-H ¼ 7.9, 2H, Ph), 7.23 (d, JH-H ¼ 7.8,
3
31 (4.32), 418 (3.13), 465 (3.49)
2
H, Ph), 7.86 (s, 1H, N=CH), 9.26 (br s, 1H, NH)
17
18
19
20
3316 w (NH), 1570 s and
CH
2
Cl
2
: 240(3.95), 277(3.30),
5 4 5 4
4.54 (br s, 4H, C H ), 4.85 (br s, 4H, C H ),
1
560 s (C=N), 842 vs,
31 vs and 558 m (PF
312(3.85), 351(3.45), 410(3.09),
491 (2.92)
DMSO: 319 (3.84), 356 (3.59),
5.01 (s, 10H, Cp), 6.06–6.51 (m, 10H, Ph),
8.00 (s, 2H, N=CH), 9.54 (s, 2H, NH)
8
6
)
419 (3.15), 466 (3.05)
CH Cl : 239 (4.15), 274 (3.40),
3336 m (NH), 1568 s (C=N),
44 vs, 826 vs and 558 s (PF
2.44 (s, 6H,CH
), 4.54 (br s, 4H, C
4.85 (br s, 4H, C H ), 4.94 (s, 10H,Cp),
5 4
H ),
2
2
3
8
6
)
309 (3.98), 349 (3.71), 407 (3.16),
73 (3.13)
DMSO: 272 (3.47), 315 (3.46),
5 4
4
6.10 (br s, 8H, Ph), 7.83 (s, 2H, N=CH),
9.23 (s, 2H, NH)
355 (3.34), 407 (2.62), 457 (2.76)
CH Cl : 242 (3.88), 274 (3.78),
3344 m (NH), 1570 s (C=N),
3.98 (s, 6H, CH
O), 4.53 (br s, 4H, C
5 4
H ),
2
2
3
1
5
252 s (C–O), 841 vs and
58 s (PF
313 (3.80), 354 (3.61), 404 (3.00),
470 (2.99)
DMSO: 270 (3.80), 319 (3.61),
5 4
4.83 (br s, 4H, C H ), 4.98 (s, 10H,Cp),
6
)
6.03 (d, JH-H ¼ 6.9, 4H, Ph),
6.11 (d, JH-H ¼ 7.1, 4H, Ph),
360 (3.46), 417 (3.16), 468 (3.01)
CH Cl : 240 (3.86), 290 (2.88),
7.79 (s, 2H, N=CH), 9.17 (s, 2H, NH)
3329 m (NH), 1570 s and
2
2
5 4 5 4
4.54 (br s, 4H, C H ), 4.85 (br s, 4H, C H ),
1
1
8
560 s (C=N), 1092 w and
062 w (C–Cl), 843 vs,
302 (3.59), 345 (3.56), 416 (2.91),
487 (2.89)
DMSO: 274 (3.81), 324 (3.79),
5.10 (s, 10H, Cp), 6.23 (br s, 4H, Ph),
6.53 (br s, 4H, Ph), 7.83 (s, 2H, N=CH),
9.49 (s, 2H, NH)
29 vs and 557 s (PF
6
)
3
59 (3.43), 433 (3.13)
a
Recorded at 200 MHz for 11–16 and at 400 MHz for 17–20.
nitrogen by standard methods prior to use. Microanalytical
data were obtained by the Institut de Chimie de Rennes Micro-
analysis Service on a Thermo-Finigan Flash EA 1112 CHNS
analyser. IR spectra were obtained with a Perkin Elmer Model
multinuclear Bruker DPX 200 and Avance 400 Digital NMR
Bruker spectrometers at 297 K; all chemical shifts are reported
in parts per million (ppm) relative to internal tetramethylsilane
4
(Me Si), with the residual solvent proton resonance as internal
1
600 FT-IR spectrophotometer. Electronic spectra were
recorded in CH Cl and DMSO solutions with a Spectronic
Genesys 2 spectrophotometer. All the H NMR spectra
were recorded in acetone-d , unless otherwise stated, on
standards. Coupling constants are given in Hertz (Hz).
Electrochemical measurements were performed using a
Radiometer Analytical model PGZ 100 All-in-One potentio-
stat, using a standard three-electrode setup with a vitreous
2
2
1
6
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4
139

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title compound was purified by column chromatography on
silica gel washed beforehand with hexane. First, the use of hex-
ane as eluant produced the release of an orange band that
allowed to collect unreacted ferrocene. The deep purple band
eluted afterwards with a hexane –CH
discarded, and finally elution with pure CH
2
Cl
2
(1:1) mixture was
Cl produced the
2
2
release of the desired red band, which was collected. The sol-
vent was removed under reduced pressure and the product
was dried in vacuo, yielding 3.80 g (15.7 mmol, 60%) of 1 as
a
shiny red microcrystalline powder, authentified by
comparison of its H NMR parameters with those reported
1
2
2b
in the original article.
0
(
E)-2-[1 -(4-Methylstyryl)ferrocenyl]-1,3-dioxolane (3). Potas-
Fig. 1 Molecular structure and atom numbering scheme for the
sium tert-butoxide (667 mg, 5.94 mmol) was mixed with 2.29 g
5.13 mmol) of 4-(p-methylbenzyl)triphenylphosphonium bro-
mide in 20 cm of dry toluene and refluxed for 3 h under N .
2
6
5
5
cation (E)-[CpFe(Z -p-MeC
6
H
4
)–NHN=CH–(Z -C
-p-Me] (16 ). Hydrogen atoms and counter anion
5 4 5 4
H )Fe(Z -C H )–
(
þ
þ
CH=CH–C
H
4
3
6
ꢀ
PF
6
have been omitted for clarity. Displacement ellipsoids are at
the 50% probability level.
After cooling to room temperature, a solution of 551 mg (1.93
0
mmol) of 2-(1 -formylferrocenyl)-1,3-dioxolane (2), dissolved
in 15 cm of dry toluene, was added and the solution was
3
warmed again to reflux for 3 h. After cooling back to room tem-
perature, the solution was concentrated to 5 cm and then
absorbed on a column containing silica gel and eluted with a
pentane–diethyl ether mixture (1:2 v/v) to produce the release
of an orange band, which was collected and concentrated to
dryness on a rotary evaporator. The orange microcrystalline
2 2
carbon (in DMF) or Pt (in CH Cl ) working electrode,
3
platinum wire auxiliary electrode and Ag/AgCl as the refer-
ence electrode. DMF and CH Cl solutions were 1.0 mM of
the compound under study and 0.1 M of the supporting
2
2
þ
ꢀ
0/þ
couple, located at
electrolyte n-Bu
.560 and 0.445 V under those conditions in DMF and
CH Cl , respectively, was used as an internal reference for
the potential measurements. E is defined as equal to
4
N PF
6
. The Cp
2
Fe
0
powder of 3 was collected and dried in vacuo. Yield: 422 mg
2
2
ꢁ
1
2
(
(
(
4
2
1.13 mmol, 59%). M.p. 115 C. Anal. calcd for C22
H
22FeO
2
1
%): C, 70.60; H, 5.93; found: C, 70.75; H, 5.73. H NMR
400 MHz, CD COCD ) d: 2.32 (s, 3H, CH ), 3.86–4.01 (m,
), 4.41 (t, 2H, C
, JH–H ¼ 1.8 Hz), 4.66 (t,
, JH–H ¼ 1.8 Hz), 4.67 (t, 2H, C , JH–H ¼ 1.8
(
E
pa þ Epc)/2, where Epa and Epc are the anodic and cathodic
peak potentials, respectively.
Chromatography columns (typically ca. 20 cm in length and
ca. 2 cm in diameter) were packed with silica gel (Aldrich, 60
3
3
3
H, CH
H, C
2
–CH
2
5 4
H
5
H
4
5 4
H
˚
A). Melting points were determined in evacuated capillaries
Hz), 4.79 (t, 2H, C H , J
H–H
¼ 1.8 Hz), 5.68 (s, 1H, O–CH–
5
4
O), 6.78 (d, 1H, CH=CH, JH–H ¼ 17 Hz), 6.93 (d, 1H,
CH=CH, JH–H ¼ 16 Hz), 7.16 (d, 2H, Ph, JH–H ¼ 7.3 Hz),
and were not corrected.
The 4-(p-R-benzyl)triphenylphosphonium bromides (R ¼
ꢀ
1
7
3
1
.39 (d, 2H, Ph, JH–H ¼ 7.7 Hz). IR (KBr pellets) nmax/cm
:
NO , CN, Me) were prepared by a procedure similar to that
2
0
087w, 3014vw (CH), 2957w, 2917vw, 2841w, 2753vw (CH),
664m (C=C), 1091s, 1029s (C–O).
described in ref. 50. 2-(1 -Formylferrocenyl)-1,3-dioxolane
2
1
0
17
(
2), 1-formyl-1 -(E)-(p-nitrostyryl)ferrocene (5) and the
hydrazine complexes [CpFe(Z -p-RC
(R ¼ H, 7; Me, 8 and MeO, 9;
pared according to published procedures. 1-Formyl-1 -(E)-(p-
6
þ
ꢀ
6
H
6 4
NHNH
2
)] PF
2
6a
13b
0
R ¼ Cl, 10 ) were pre-
(E)-1 -(4-Methylstyryl)ferrocenecarboxaldehyde (4). To a
3
0
solution of 505 mg (1.35 mmol) of 3 in 15 cm of dichloro-
methane was added 50 mg (0.263 mmol) of p-toluenesulfonic
1
7
cyanostyryl)ferrocene (6) was directly obtained as the desired
pure E isomer using the protected/deprotected 1,3-dioxolane
route described in ref. 21. Other chemicals were purchased
from commercial sources and used as received.
3
acid monohydrate in 5 cm of deoxygenated water, then the
mixture was refluxed for 3 h under N . After cooling to room
2
temperature, the organic phase was separated, dried over
MgSO4 and concentrated to 3 cm , absorbed on a column
3
containing silica gel and eluted with a pentane–diethyl ether
mixture (1:2 v/v) to produce the release of a red-orange band,
which was collected and concentrated to dryness on a rotary
evaporator. The red-orange microcrystalline powder of 4 was
Syntheses
1
,1 -Ferrocenedicarboxaldehyde (1)22b. Compound 1 was
0
prepared according to literature procedure, using the same
quantities of reagents, with the following modifications to the
work-up. After the organic phase was dried over MgSO , the
collected and dried in vacuo. Yield: 208 mg (0.63 mmol,
ꢁ
47%). M.p. 96 C. Anal. calcd for C H FeO (%): C, 72.75;
20 18
4
6
5
2þ
2þ
Fig. 2 Molecular structure and atom numbering scheme for the dication [{CpFe(Z -p-MeOC
6
H
4
)–NHN=CH–(Z -C
have been omitted for clarity. Displacement ellipsoids are at the 50% probability level.
5
H
4
)}
2
Fe] (19 ). Hydro-
ꢀ
gen atoms and counter anion PF
6
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
140
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4

View Article Online
˚
Table 5 Selected bond lengths (A) and bond angles (deg.) for cations 16 and 19 . Standard deviations are given in parentheses
þ
þ a
þ
þ
1
6
19
16
19
b
b
C–C(1–5)
1.308
1.346
C–C(6–11)
C(6)–N(1)
1.406
1.392
1.366(4)
1.275(4)
1.411
C(9)–O(1)
N(1)–N(2)
C(13)–C(14)
–
1.360(5)
1.382(4)
1.421(5)
1.359(6)
1.278(6)
1.415
1.383(5)
1.448(7)
1.412
N(2)–C(13)
C–C(14–18)
b
b
C–C(19–23)
C(24)–C(25)
Fe(1)–C(1–5)
Fe(1)–C(7)
Fe(1)–C(9)
Fe(1)–C(11)
–
–
C(19)–C(24)
C(25)–C(26)
Fe(1)–C(6)
1.455(8)
1.501(8)
2.193(5)
2.064(5)
2.056(5)
2.050
–
1.296(7)
2.011
–
b
2.045
2.144(4)
2.048(4)
2.077(4)
2.039
2.087(5)
2.084(5)
2.098(5)
2.048
2.073(4)
2.116(5)
2.064(4)
Fe(1)–C(8)
Fe(1)–C(10)
Fe(2)–C(14–18)
b
b
c
Fe(2)–C(19–23)
d
–
–
Fe(1)ꢂ ꢂ ꢂFe(2)
9.714
1.675
1.658
9.633
1.658
1.649
Fe(1)ꢂ ꢂ ꢂFe(2)
8.064
1.565
1.659
6.925
1.556
Fe(1)–CpCNT
Fe(2)–CpCNT
Fe(1)–PhCNT
0
Fe(2)–Cp CNT
C(6)–N(1)–N(2)
120.7(4)
121.2(5)
126.5(6)
178.9
120.5(4)
123.2(5)
N(1)–N(2)–C(13)
C(19)–C(24)–C(25)
CpCNT–Fe(1)–PhCNT
114.9(4)
127.5(6)
179.0
117.2(4)
–
179.2
N(2)–C(13)–C(14)
C(24)–C(25)–C(26)
–
–
0
Cp CNT–Fe(2)–CpCNT
a
5
0
5
6
b
c
Abbreviations: Cp ¼ Z -C
5
H
5
, Cp ¼ Z -C
5
H
4
, Ph ¼ Z -C
6
H
4
, CNT ¼ centroid.
Average distance.
Sum of the bond distances.
d
Measured through-space distance.
1
H, 5.49; found: C, 72.97; H, 5.56. H NMR (400 MHz,
CH=CH, JH–H ¼ 17 Hz), 7.17 (d, 2H, Ph, JH–H ¼ 8.1 Hz),
7.40 (d, 2H, Ph, J
¼ 8.1 Hz), 9.91 (s, 1H, CHO).
CD COCD ) d: 2.32 (s, 3H, CH ), 4.41 (t, 2H, C H ,
3
3
3
5
4
H–H
1
C{ H} NMR (100 MHz, CDCl
1
3
J
2
H–H ¼ 1.8 Hz), 4.62 (t, 2H, C
5
H
4
, JH–H ¼ 1.8 Hz), 4.67 (t,
¼ 1.8
3
3
) d: 20.3 (CH ), 67.9
H, C H , J
4
¼ 1.8 Hz), 4.78 (t, 2H, C H , J
(C H ), 70.2 (C H ), 70.3 (C H ), 73.9 (C H ), 80.5 (q-
5
5
H–H
5
4
H–H
5
4
4
5
4
5
4
Hz), 6.82 (d, 1H, CH=CH, JH–H ¼ 17 Hz), 6.87 (d, 1H,
C
5
4
H ), 85.7 (q-C
H
5 4
), 124.2 (CH=CH), 126.0 (Ph), 127.7
(
(
CH=CH), 129.2 (Ph), 135.0 (q-Ph), 136.8 (q-Ph), 192.7
CHO). IR (KBr pellets) nmax/cm : 3090w, 3078w, 3045vw,
ꢀ
1
3
1
022vw (CH), 2924vw, 2889w, 2856vw (CH), 1679s (HC=O),
3
ꢀ1
663m (C=C). UV-vis (CH
Cl ) lmax/nm (Log e/dm mol
2 2
ꢀ
1
cm ): 263 (4.25), 318 (4.33), 366 (3.38), 464 (3.13); (DMSO):
2
64 (4.28), 320 (4.41), 374 (3.19), 474 (3.08). CV E1/2/V vs. Ag/
ꢀ
1
AgCl (DE
eous carbon) 0.813 (119); CH
p
/mV), v ¼ 0.1 V s : DMF (working electrode: vitr-
2
Cl (working electrode: Pt) 0.737
2
(
196).
Bimetallic hydrazones complexes 11–16. General procedure.
A mixture of the indicated quantities (see Table 1 for reagents,
6
stoichiometries and yields) of the solid [CpFe(Z -p-
þ
6ꢀ
RC
6
4
H NHNH
2
)] PF (R ¼ H, 7; Me, 8; MeO, 9; Cl, 10)
0
0
0
and 1-formyl-1 -(E)-(p-R -styryl)ferrocene (R ¼ Me, 4,
3
2
NO , 5; CN, 6) was dissolved in 5 cm ethanol containing 5
drops of concentrated acetic acid. The solution was refluxed
for 5 h, allowed to stand at room temperature and then at
ꢁ
ꢀ
30 C overnight (12 h). The precipitate was filtered off,
3
washed first with cold EtOH and then with 5 cm of diethyl
ether, then dried under vacuum. Crystallization from saturated
dichloromethane solutions by slow diffusion of diethyl ether at
room temperature provided the products as crystalline solids.
Color, melting point and elemental analyses of the new hydra-
zone compounds 11–16 so prepared are given in Table 3. IR,
1
UV-vis and H NMR data are gathered in Table 4.
Trimetallic hydrazone complexes 17–20. General procedure.
To a suspension of the indicated quantities (see Table 2 for
reagents, stoichiometries and yields) of solid hydrazine precur-
3
0
sors 7–10 in 5 cm of EtOH was added 0.5 equiv. of 1,1 -ferro-
cenedicarboxaldehyde (1); the reaction mixture was refluxed
for 3–5 h. After cooling to room temperature, 1 cm of diethyl
3
ether was added to the orange solution, which was then stored
ꢁ
at ꢀ30 C overnight (12 h). The precipitate was filtered off and
3
dissolved in 2 cm of dichloromethane. The solution was fil-
tered through Celite and the filtrate was concentrated to half
of its volume, then layered with an equivalent amount of
diethyl ether to yield the products as crystalline solids. Color,
Fig. 3 Electronic spectra of 12 (left) and 20 (right), recorded in
CH Cl (full line) and in DMSO (dashed line).
2
2
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4
141

View Article Online
Table 7 Crystal data and structure refinement for complexes 16
and 19
a
Table 6 Cyclic voltammetry data
1
2
1
þ
c
2
E (p-C
E [(C
5
H
4
)
/mV)
2
Fe]/V
E
pc[CpFe
6
H
4
NO
2
) /
b
(aryl)] /V
Compound
(DE
p
V (DE
p
/mV)
16
19
1
1
1
1
1
2
3
4
0.176 (98)
0.161 (92)
0.167 (90)
0.197 (109)
ꢀ2.25
ꢀ1.36 (131)
1.53 (70)
ꢀ1.32 (72)
1.53 (70)
ꢀ1.30 (100)
1.53 (60)
ꢀ1.31 (72)
1.51 (70)
Empirical formula
FW/g mol
T/K
C
32
H
31
F
Fe
6 2
N
2
P
18 18 6 2
C H F Fe1.5N OP
ꢀ1
ꢀ
700.26
293(2)
Triclinic
507.09
293(2)
ꢀ2.31
ꢀ
Crystal system
Space group
Orthorhombic
Pbca
ꢀ2.30
P-1
˚
ꢀ
a/A
10.612(3)
11.147(3)
13.521(4)
85.155(7)
74.476(7)
77.999(7)
1506.8(8)
2
12.5730(11)
16.5448(14)
19.0521(16)
90
˚
ꢀ2.31
b/A
˚
ꢀ
c/A
a/
ꢁ
1
1
1
1
1
2
5
6
7
8
9
0
0.221 (93)
0.045 (102)
0.093 (71)
0.077 (84)
0.190 (83)
0.225 (90)
ꢀ2.27
ꢀ2.53
ꢀ2.59
ꢀ2.52
ꢀ2.48
ꢀ2.30
–
ꢁ
–
–
–
–
–
b/
90
90
ꢁ
g/
U/A
˚
3
3963.2(6)
8
1.260
Z
ꢀ1
m/mm
1.079
˚
ꢀ2.44
l(Mo Ka)/A
No. total reflect.
No. unique reflect.
0.71073
8369
5129
0.71073
27 421
4559
a
Recorded in DMF at 298 K with a vitreous carbon working elec-
þ
ꢀ
trode, 0.1 M n-Bu
4
PF
6
as supporting electrolyte, scan rate 100
R
R
int
0.0332
0.0651
0.1192
0.0949
0.1271
0.0944
0.0442
0.0951
0.1291
0.0991
ꢀ1
0/þ
couple used
as internal reference. Irreversible wave corresponding to the Fe(II)/
mV s . All potentials are quoted in V vs. the Cp
2
Fe
1
[I > 2s(I)]
[I > 2s(I)]
(all data)
2
(all data)
b
wR
2
c
Fe(I) couple. Reversible waves corresponding to the reduction of
the nitrophenyl pendant group.
R
wR
1
melting point and elemental analyses of the new hydrazone
compounds 17–20 so prepared are given in Table 3. IR, UV-
5
frames were integrated using the SAINT package and
2
5
3
1
vis and H NMR data are gathered in Table 4.
corrected for absorption with SADABS.
In the case of complex 19, the data collection was made on a
ꢁ
Bruker SMART APEX diffractometer, using 0.3 of separa-
tion between frames and 10 s per frame. The structure was
5
solved and refined using SHELXS97 and SHELXL97,
4
54
X-Ray Crystallography
5
5
respectively, both included in the WinGX software package.
The final R indices as well as further details concerning the
resolution and refinement of the crystal structures of 16 and 19
are presented in Table 7.y
6
5
Single crystals of (E)-[CpFe(Z -p-MeC H )–NHN=CH–(Z -
6
4
þ
5
ꢀ
C
[
5
H
4
)Fe(Z -C
5
H
4
)–CH=CH–C
6
H
4
-p-Me] PF (16) and of
6
6
5
2þ
ꢀ
{CpFe(Z -p-MeOC H )–NHN=CH–(Z -C H )} Fe] (PF6 )2
(19) were obtained by slow diffusion of diethyl ether into the
corresponding concentrated CH Cl solutions of complexes
6
4
5
4
2
2
2
1
6 and 19 at room temperature.
A single crystal of complex 16 was mounted on a glass fiber
Acknowledgements
in a random orientation. Data collection was performed at
room temperature on a Siemens Smart CCD diffractometer
using graphite-monochromated Mo-Ka radiation (l ¼
We thank Dr. Andr e´ s Vega (Santiago de Chile) for helpful
assistance in the structure determination of 19. We greatly
appreciate financial support for this work from the Fondo
Nacional de Desarrollo Cient ´ı fico y Tecnol o´ gico, FONDE-
˚
ꢁ
.71073 A), using 0.3 of separation between frames and 30 s
0
per frame. Space group assignments are based on systematic
absences, E statistics and successful refinement of the struc-
ture. The structure was solved by direct methods with the
aid of successful difference Fourier maps and was refined using
ꢁ
CYT (Chile), Grant N 1010318 (D. C., C. M.), to the Pro-
ꢁ
gramme International de Coop e´ ration Scientifique N 922
CNRS (France)–CONICYT (Chile and the CNRS-CONICYT
ꢁ
5
1
Project N 14531) (C. M., D. C., J.-R. H.), and to the Vicer-
rector ´ı a de Investigaci o´ n y Estudios Avanzados, Pontificia
Universidad Cat o´ lica de Valpara ´ı so, Valpara ´ı so, Chile.
the SHELXTL 5.1 software package. All non-hydrogen were
refined anisotropically. Hydrogen atoms were assigned to ideal
positions and refined using a riding model. The diffraction
References
1
Ferrocenes: Homogenous Catalysis, Organic Synthesis, Materials
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995.
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(a) D. Astruc, Pure Appl. Chem., 2003, 75, 461; (b) D. Astruc,
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y CCDC reference numbers 188753 for 16 and 209331 for 19. See
http://www.rsc.org/suppdata/nj/b3/b308626g/ for crystallographic
data in .cif or other electronic format.
þ
ꢀ
M n-Bu N PF
4
6
at T ¼ 293 K and with a voltage sweep rate v ¼ 0.1
ꢀ1
0/þ
V s , reference electrode Ag/AgCl, internal reference Cp
2
Fe
.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
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J. S. Miller and A. J. Epstein, in Research Frontiers in Magneto-
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L. A. Oro, J. Ruiz and D. Astruc, Organometallics, 2002, 21,
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5
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6
þ
28 For exemples of X-ray crystal structures of [CpFe(Z -arene)]
complexes, see: (a) J.-R. Hamon, J.-Y. Saillard, A. Le Beuze,
M. J. McGlinchey and D. Astruc, J. Am. Chem. Soc., 1982,
104, 7549; (b) See also refs 11, 13b–d, 24, 26, 27 and 29.
29 P. J. Dyson, M. C. Grossel, N. Shrinivasan, T. Vine, T. Welton,
D. J. Williams, A. J. P. White and T. Zigras, J. Chem. Soc., Dalton
Trans., 1997, 3465.
30 For structurally characterized bis-substituted ferrocene-based
p-bridged systems, see, for example, refs 16–21.
31 For a reference gathering a large number of interatomic and
metal-ligand distances obtained from the Cambridge Crystallo-
graphic Data Base Centre, see: A. G. Orpen, L. Brammer,
F. H. Allen, D. Kennard, D. G. Watson and R. Taylor, J. Chem.
Soc., Dalton Trans., 1989, S1.
32 The deconvolution of the lower energy absorption band gave rise
to a splitting into two independent bands whose lmax are observed
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N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4
143

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49 For detailed mechanistic investigations on the reduction of
44
The benzylic N–H group is indeed strongly activated by both
the electron-withdrawing organometallic moiety CpFe and the
þ
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imine functionality. Therefore, the thermally stable zwitterion
0
þ ꢀ
[
CpFe (p-RC H H )Fe(C H R )] can be easily
)N –N=CH(C
6 4 5 4 5 4
formed by deprotonation in the electrochemical medium. No
attempts were made to characterize their corresponding
non-deprotonated precursors 11–20 by CV.
50 R. Ketcham, D. Jambotkar and L. Martinelli, J. Org. Chem.,
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4
5
6
This fully irreversible wave could indeed be attributed to the 2-
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51 G. M. Sheldrick, SHELXTL, version 5.1, Bruker AXS, Inc.,
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52 SAINT, version 5.0, Bruker Analytical X-Ray Systems, Madison,
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53 G. M. Sheldrick, SADABS Empirical Absorption Program,
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54 G. M. Sheldrick, SHELXS-97, Program for solution of crystal
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ꢃ
ꢀ
mechanism for the reduction of Ar–X into Ar and X (ref. 46).
Its integrated area is twice that of the wave at ꢀ2.44 V.
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4
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55 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
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144
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 1 3 4 – 1 4 4