Anion recognition and redox sensing by a metalloporphyrin-ferrocene- alkylammonium conjugate

Article abstract of DOI:10.1039/b411870g

The synthesis and characterization of a novel redox molecular receptor is reported. This chemosensor is structured on a ferrocene fragment whose cyclopentadienyl moieties have been connected to distinct and complementary zinc porphyrin and alkylammonium binding sites, enabling multipoint recognition and detection of anionic species. Cumulative effects of multiple anchoring points on this ammonium-ferrocene-metalloporphyrin chemosensor allowed the unprecedented ferrocene-based voltammetric sensing of halide anions.

Full text of DOI:10.1039/b411870g

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P A P E R
Anion recognition and redox sensing by a metalloporphyrin–
ferrocene–alkylammonium conjugatew
Christophe Bucher,* Charles H. Devillers, Jean-Claude Moutet,* Guy Royal and
Eric Saint-Aman
´
Laboratoire d’Electrochimie Organique et de Photochimie Redox (CNRS UMR 5630), Institut
de Chimie Moleculaire de Grenoble (CNRS FR 2607), Universite Joseph Fourier, BP 53,
´
´
´
38041 Grenoble cedex 9, France
Received (in Toulouse, France) 2nd August 2004, Accepted 10th September 2004
First published as an Advance Article on the web 17th November 2004
The synthesis and characterization of a novel redox molecular receptor is reported. This chemosensor is
structured on a ferrocene fragment whose cyclopentadienyl moieties have been connected to distinct and
complementary zinc porphyrin and alkylammonium binding sites, enabling multipoint recognition and
detection of anionic species. Cumulative effects of multiple anchoring points on this ammonium–ferrocene–
metalloporphyrin chemosensor allowed the unprecedented ferrocene-based voltammetric sensing of
halide anions.
binding sites. On one side an alkylammonium group, known to
Introduction
bring about efficient electrochemical recognition properties in
ferrocene-based receptors,4 has been introduced to promote
favourable electrostatic interactions with anionic substrates.
The opposing cyclopentadienyl ring has likewise been inti-
mately connected to the p-electronic system of a zinc porphy-
rin, whose electron-deficient orbitals allow the axial
coordination of nucleophilic species.5 Along with the effective
electrochemical sensing of oxoanions, we show that the cumu-
lative effect of multiple anchoring points allows the unprece-
dented ferrocene-based electrochemical sensing of halide
anions.
The design of molecular architectures able to electrochemically
sense anions is a particularly challenging task. The complexity
of such an undertaking unambiguously arises from the neces-
sity to combine different but interacting complexing and
signalling units in one unique molecular material.1 In practice,
a host–guest type recognition event has to be ‘‘seen’’ by an
internal redox probe through the perturbation of its electro-
chemical activity. Although most anion binding events greatly
suffer from their solvent- and pH-sensitive nature, complexa-
tion of negatively charged species in artificial receptors is
generally achieved through hydrogen bonding, electrostatic
interactions, or coordination to a metal cation.2 Most of the
redox active receptors described in the literature involve only
one of these binding modes at a time and the anion complexa-
tion in close proximity to the redox-active fragment allows
electrochemical detection of the substrate.
Results and discussion
Synthesis
ꢁ
The synthesis of the ferrocene–porphyrin receptor [1]1 ꢀ BF4
(Scheme 1) started with the mono-protection of diformyl
ferrocene 76 according to a literature procedure7 to give 6 in
70% yield. The acid-catalyzed (TFA) MacDonald-type con-
densation of the latter with pyrrole and p-tolualdehyde in
dichloromethane, followed by oxidation with chloranil, af-
forded a mixture from which 5 could be isolated with 10%
yield. 4 was obtained from 5 by removal of the cyclic dithio-
ketal using Ag1 ions and N-chlorosuccinimide (NCS) as the
oxidizing agent.7 A nitrogenous ‘‘tail’’ was then introduced
onto the ferrocene moiety by reaction of n-hexylamine in
anhydrous THF with the regenerated formyl group to produce
3 in good yield. Insertion of zinc(II) into the macrocyclic cavity
In order to improve both recognition and detection ability of
chemosensors, we turned our attention towards molecular
systems combining multiple complementary binding sites and
redox-active reporters. A multipoint molecular recognition
event could then be followed and signalled by different re-
dox-active probes distributed at strategic locations on the
receptor. The electrochemical, spectroscopic and chemical
features of ferrocene–porphyrin conjugates make them out-
standing candidates to reach such a goal.3 Besides the high
chemical stability, the well-defined redox characteristics and
chemical versatility of both ferrocene and porphyrin frag-
ments, the generation of cationic species upon electrochemical
oxidation of both redox moieties is moreover favourable to a
strengthening of the anion-receptor interactions and thus to
efficient electrochemical recognition of anionic species.
Here, we report the synthesis and characterization of a new
electrochemical chemosensor [1]1 enabling multipoint recogni-
tion and detection of anionic species (Fig. 1). This receptor is
structured on a ferrocene fragment whose cyclopentadienyl
moieties have been connected to distinct and complementary
w Electronic supplementary information (ESI) available: HMQC and
COSY of 2. See http://www.rsc.org/suppdata/nj/b4/b411870g/
Fig. 1 Cooperative interactions between an anion (Aꢁ) and the
ferrocene–ammonium–porphyrin [1]1Bꢁ (R: Tol, R1: Me, R2: Hexyl).
T h i s j o u r n a l i s & 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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Scheme 1 Reagents and conditions: (i) 70% yield, CH2Cl2, Ar,
SH(CH2)2SH, BF3 ꢀ OEt2, col. chromat. (SiO2, hexane–20% EtOAc);
(ii) 10% yield, CH2Cl2, Ar, pyrrole, p-tolualdehyde, TFA, 30 min;
chloranil, col. chromat. (SiO2, CH2Cl2–50% hexane); (iii) 70% yield,
THF–CH3CN–H2O, AgNO3, NCS, col. chromat. (SiO2, CH2Cl2–0.5%
MeOH); (iv) 80% yield, THF, mol. sieves, Ar, CH3(CH2)5NH2, 16 h;
diethyl ether–EtOH, NaBH4, 3 h, col. chromat. (SiO2, CH2Cl2–5%
MeOH); (v) 91% yield, CH2Cl2, ZnOAc2 ꢀ H2O/MeOH, 10 h, col.
chromat. (SiO2, CH2Cl2–5% MeOH); (vi) 80% yield, anhydr. THF,
MeI, anhydr. K2CO3, col. chromat. (SiO2, CH2Cl2–5% MeOH); (vii)
ion exchange col. chromat. (BF4ꢁ–IRA96, CH3CN).
1
Fig. 2 Part of the H NMR spectra of (A) 2 (CDCl3, 500 MHz) and
(B) [1]1 ꢀ BF4 (DMSO–d6, 400 MHz).
ꢁ
addition of D2O, this signal was attributed to the –NH–
proton, which logically is strongly affected by the porphyrin-
based anisotropic shielding cone. Surprisingly, even the ferro-
cene protons were seen to be significantly shifted and were
observed between 2.1 and 5 ppm. Assuming that the ring
current effect strongly depends on the distance between the
porphyrin and a given proton, the ferrocene signal observed at
2.1 ppm was attributed to the closest proton to the coordinated
amine fragment [Fig. 2(A), proton h]. On the other hand, 1D
NOE difference experiments allowed us to evidence through-
space interactions between the more deshielded b-pyrrole pro-
ton and a ferrocene hydrogen atom located on the Cp ring
was achieved in MeOH–CH2Cl2 using zinc acetate to produce
a zinc porphyrin–ferrocene intermediate 2.8 Finally, The amine
‘‘tail’’ of 2 was quaternized in anhydrous THF using an excess
of methyl iodide to afford [1]1 ꢀ Iꢁ in 80% yield. The latter was
ꢁ
then submitted toꢁion exchange using a resin in its BF4 form
to yield [1]1 ꢀ BF4
.
NMR characterization
directly linked to the porphyrin [Fig. 2(B), proton k].
1
As expected and proven by the H NMR spectrum of [1]1
ꢀ
The 1H NMR spectrum of 2 recorded in CDCl3 [Fig. 2(A)]
evidences the coordination of the amine ‘‘tail’’ on a porphyrin
metal centre, resulting in five broad, poorly resolved, signals
observed at high field between 0 and ꢁ5 ppm, reflecting the
effect of the porphyrin ring current on the coordinated amine
fragment.
BF4ꢁ, the quaternization of the hexylamine ‘‘tail’’ induced the
cleavage of the self-assembled supramolecular structure. In
both non-coordinating (CDCl3) and coordinating (DMSO-d6)
solvents no signals were observed below 0 ppm, reflecting the
suppression of the amine’s coordinating ability towards the
metalloporphyrin centre [Fig. 2(B)]. As a result, all the signals
attributed to the hexyl chain logically appeared between 0.5
and 1.5 ppm and the ferrocene signals were observed between
4.2 and 5.6 ppm.
These NMR features are a clear consequence of a self-
assembly phenomenon that has been presented in a previous
communication.8 This association process could indeed be
further characterized from vapour pressure osmometry mea-
surements performed in toluene at 60 1C in the 5–15 ꢂ 10ꢁ3 M
concentration range, which yielded an effective molecular
weight of 1957 ꢃ 30 in full accordance with a dimeric structure.
In agreement with the relative weakness of the secondary
amine nitrogen zinc bond, the use of a coordinating NMR
solvent such as deuterated DMSO induced the cleavage of this
self-assembled structure, as proven by the shift of all the
1H NMR signals above 0 ppm.
Electrochemical sensing of anions
Cyclic (CV), rotating disk electrode (RDE) and differential
pulsꢁed (DPV) voltammetry investigations carried out on [1]1
ꢀ
BF4 in CH2Cl2 containing 0.1 M TBAP revealed three one-
electron reversible oxidation processes [Fig. 3(A,B); also see
Fig. 5(C) below] at E1/2
¼
645, 940 and 1200 mV
1
Most of the H NMR signals observed on the spectrum of
{vs. [Fe(Cp*)2]0/1; Fe(Cp*)2 ¼ bis(pentamethylcyclopentadienyl)
2 recorded in non-coordinating CDCl3 were assigned using
1H–1H and 1H–13C correlation spectroscopies. Although the
broadest 1H NMR signals: e, f, g and h [Fig. 2(A)], did not
iron}.
In accordance with previous studies on ferrocene–porphyrin
derivatives,9 the first process was attributed to the ferrocene/
ferrocenium couple, followed by two consecutive oxidations of
the metalloporphyrin, known to afford successively a radical
cation and a dicationic species.10 Such a well-defined electro-
chemical signature turned out to strongly contrast with that of
the amine precursor 2. Indeed, the electrochemical features
of the latter showed up to five distinct oxidation processes
1
exhibit H–13C cross peaks in the HMQC map, their attribu-
tion could be achieved from 1H–1H correlation experiments
that in particular revealed the successive vicinal coupling
throughout the hexyl chain (see ESI). Moreover, considering
the lack of cross peaks in the 1H–1H correlation map involving
the signal observed at ca. ꢁ5 ppm and its disappearance upon
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 5 8 4 – 1 5 8 9
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Fig. 4 Evolution of (A) the ferrocene-based and (B) the porphyrin-
based DPV oxidation peak potentials for [1]1 ꢀ BF4ꢁ (5 ꢂ 10ꢁ4 M) as a
function of added molar equivalents of TBANO3 and TBAHSO4.
chemical titration, strongly suggest similar ion pairing effects
between the doubly charged ferricinium–ammonium fragment
and these anionic species. In contrasts, the stronger basicity of
ꢁ
HSO4 was clearly evidenced by the significant differences
Fig. 3 Differential pulsed (A) and cyclic (B) voltammograms of a 5 ꢂ
10ꢁ4 M CH2Cl2 (TBAP, 0.1 M) solution of [1]1, BF4ꢁ; (C) cyclic
voltammogram of a 5 ꢂ 10ꢁ4 M CH2Cl2 (TBAP, 0.1 M) solution of 2;
3 mm diameter carbon working electrode; n ¼ 100 mV sꢁ1 (CV) and
observed in the porphyrin-based electrochemical response.
Using the same methodology, the negative potential shift of
the first porphyrin-based oxidation peak indeed allowed us to
differentiate both anionic species since it reaꢁched –140 and ꢁ90
10 mV sꢁ1 (DPV); E(V) vs. [Fe(Cp*)2]0/1
.
ꢁ
mV when 20 molar equivalents of HSO4 and NO3 were
added, respectively.
Interestingly, as proven by rotating disk electrode measure-
ments, the initial one-electron porphyrin-based oxidation
[Fig. 3(C)]: a reversible ferrocene-based oxidation at E1/2 ¼ 580
mV {vs. [Fe(Cp*)2]0/1}, followed by four porphyrin-based
oxidations at Epa ¼ 880 (shoulder), 960, 1240 and 1440 mV
{vs. [Fe(Cp*)2]0/1]. As already observed for polymeric struc-
tures,11 the shoulder at 880 mV on the first porphyrin oxidation
wave can been attributed to interactions between the porphyrin
rings in the supramolecular assembly. The second porphyrin-
based irreversible oxidation at 1240 mV leads then to an
electrophilic species known to irreversibly lead to isoporphyr-
ins in the presence of nucleophiles.12 The last oxidation process
at 1440 mV thus most presumably results from the oxidation of
an isoporphyrin cation wherein the nitrogenous ‘‘tail’’ has been
incorporated into the porphyrin framework.
Upon quaternization to form [1]1, the complex electroactiv-
ity of 2 thus evolved into three well-defined reversible redox
systems, accompanied by a shift towards more positive poten-
tial values of the ferrocene redox couple, directly influenced by
the electron-withdrawing character of the ammonium. On the
other hand, the overall simplification of the cyclic voltammo-
gram further shows that the complex oxidation pattern ob-
served for 2 arises from the nucleophilic characteristic of the
amine, leading to interactions between the porphyrin rings and
to isoporphyrin formation.
wave, attributed to the P/P1 redox couple, evolved into a
d
two-electron oxidation process upon adding an excess of
anionic species. A careful analysis of the electrochemical data
revealed the progressive decrease of the P1d/P21 oxidation
signal, along with the growth of a new system overlapping the
first porphyrin-based oxidation wave (Fig. 5).
It is noteworthy that a similar overlap, which resulted in
the observation of only one porphyrin-based oxidation wave in
the accessible anodic potential range, wꢁas also observed when
the electrochemical study of [1]1 ꢀ BF4 was performed in a
nucleophilic solvent like DMSO (0.1 M TBAP). Such features,
already observed for basket handle and picket fence porphyr-
When increasing amounts of selected anions were added to a
solution of [1]1 ꢀ BF4ꢁ (5 ꢂ 10ꢁ4 M in CH2Cl2 þ 0.1 M TBAP),
both ferrocene and porphyrin oxidation processes initially
observed at 645 and 938 mV, respectively, underwent signifi-
cant negative potential shifts. The advantage associated with
such a multi-redox detection is clearꢁly put forward when
considering the recognition of HSO4 and NO3ꢁ. In both
cases, the progressive ferrocene-based potential shifts, induced
upon adding tetrabutylammonium hydrogensulfate or nitrate
and measured using differential pulsed voltammetry, turned
out to be almost identical [Fig. 4(A), DE E ꢁ80 mV after
adding 20 molar equivalents of anion].
Fig. 5 (A) Cyclic voltammogram of a 5 ꢂ 10ꢁ4 M CH2Cl2 (TBAP, 0.1
M) solution of [1]1 ꢀ BF4ꢁ. (B) Cyclic voltammogram of a 5 ꢂ 10ꢁ4 M
CH2Cl2 (TBAP, 0.1 M) solution of [1]1 ꢀ BF4ꢁ þ 1 equiv. of TBANO3.
(C) Evolution of the RDE curve as a function of added TBANO3:
(curve 1) 0, (curve 2) 0.5, (curve 3) 1, (curve 4) 5 equiv. of TBANO3.
These changes in the redox potential of the ferrocene centre,
which retains quasi-reversible features throughout the electro-
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ins,13 strongly suggest the existence of an ECE-type mechanism
in which the reaction of the electrogenerated porphyrin-based
radical cation with a nucleophilic species would produce a new
species that is oxidized at the same or lower potential as the
ferrocene-appended tetraaminophenylporphyrin based chemo-
sensors reported to date.15
The cumulative effect of multiple anchoring points was
revealed by studying independently both fragments constitut-
ing [1]1 ꢀ BF4ꢁ: (i) ferrocene–ammonium and (ii) ferrocene–
porphyrin receptors, which did not show such a well-defined
‘‘two-wave’’ behaviour in the presence of chloride anions. As
an example, the ferrocene-based oxidation waves of [Fc–CH2–
initial P/P1 redox couple. CV experiments performed
d
throughout the electrochemical titration with nitrate and hy-
drogensulfate revealed that such a coalescence phenomenon
was occurring with a significant loss of reversibility in the
porphyrin-based oxidation process. A specific sensing of both
anionic substrates could nevertheless be achieved through the
significant modifications in the porphyrin-based electrochemi-
cal activity monitored using differential pulsed voltammetry
[Fig. 4(B), porphyrin-based transduction].
A very important perturbation in the electrochemical fea-
tures of [1]1 was observed upon addition of dihydrogenpho-
sphate anions, which resulted in a negative shift of the Fc/Fc1
redox couple up to ꢁ240 mV in the presence of 20 molar
equivalents of H2PO4ꢁ. However, the electrochemical recogni-
tion properties of [1]1 towards this anion could not be accu-
rately assessed and compared to the other species, since these
changes in electroactivity proceeded with significant loss of
reversibility in both ferrocene- and porphyrin-based oxidation
waves. Such a behaviour, already observed in the case of simple
ferrocene–ammonium probesꢁ,4 puts forward the strong ion
pairing effect between H2PO4 and oxidized ferrocenyl recep-
tors that frequently leads to adsorption phenomena.
ꢁ
N1(CH3)2–(CH2)11–CH3] ꢀ BF4 and 5-ferrocenyl-10,15,20-tri
(p-tolyl)porphyrin underwent only limited potential shifts (0 r
–DE r 50 mV) upon addition of 1 equiv. of TBACl. Given the
small amplitude of these shifts, the well-behaved two-wave
recognition process detailed above can thus be regarded as
resulting from the cooperative effect of both binding fragments
connected to the same ferrocene redox probe.
Spectrophotometric titration performed on [1]1 ꢀ BF4 in
ꢁ
CH2Cl2 þ 0.1 M TBAP solution resulted in a bathochromic
shift, accompanied by a well-defined isosbestic point of the
Soret, a and b bands observed in the visible spectra. Analysis of
the new Soret band absorbance as a function of added chloride
[Fig. 6(B)] was consistent with the formation of a 5-coordinate
complex with an estimated stability constant Kred[11 ꢀ Clꢁ] ¼
104
M
ꢁ1, which turns out to be 40 times higher than that
obtained in the same conditions with ZnTTP used as a
reference (Keq[ZnTTPClꢁ] ¼ 2.5 ꢂ 102 Mꢁ1).16 Kred[11 ꢀ Clꢁ],
combined with the potential shift measured upon complexa-
In contrast, the quasi-reversible features of the ferrocene-
based wave in the presence of chloride anions allowed a clear
and efficient amperometric-type redox sensing.14 Using differ-
ential pulse voltammetry, the addition of increasing amounts
of tetrabutylammonium chloride to a dichloromethane solu-
tion, allowed us to determine the stability constant Kox[121
ꢀ
Clꢁ] of the complex formed between the oxidized ferrocenium
form of the receptor and the chloride anion, which is essential
to fully account for the specific electrochemical response
detailed above (see on Fig. 6 the upper scheme summarizing
redox and complexation equilibria for the [1]1 þ Clꢁ sys-
tem).17 The magnitude of Kox[121 ꢀ Clꢁ], estimated at 1.7 ꢂ 106
ꢁ
tion of [1]1 ꢀ BF4 led to the progressive decrease of the initial
ferrocene-based DPV peak at Ep ¼ 645 mV, along with the
growth at a less negative potential of a new peak (Ep ¼ 515 mV,
DE ¼ ꢁ130 mV) corresponding to the complexed receptor
[Fig. 6(A)]. The initial wave corresponding to the free ligand
completely disappeared and the new peak reached full devel-
opment after the addition of 1 molar equivalent of chloride
anions. This behaviour starkly contrasts with the potentio-
metric-type ‘‘one-wave’’ redox sensing observed with the rare
M
ꢁ1, not only explains the specific chloride sensing but also
clearly highlights the beneficial effect of oxidation processes in
anionic electrochemical recognition. The in situ generation of
cationic species strongly enhances the binding strength through
the reinforcement of electrostatic forces between the anionic
species and the oxidized receptor. The anion-sensing properties
of [1]1 proved further to be halide specific since a clear ‘‘two-
wave’’ behaviour was also observed in the presence of increas-
ing amounts of TBA1 ꢀ Brꢁ or TEA1 ꢀ Fꢁ, with new waves
growing at a less positive potential for fluoride (DE ¼ ꢁ152
mV) than for bromide (DE ¼ ꢁ112 mV), in accordance with
their relative basicity. These anion-specific potential shifts can
be directly related to the halides’ relative binding strengths
measured by spectrophotometric titration.18 In the same con-
ditions as in Fig. 6(B) (CH2Cl2, 0.1 M TBAP), the stability
constant of [11 ꢀ Brꢁ] could be estimated as Kred ¼ 2.5 ꢂ 102
M
ꢁ1, which is in full agreement with a weaker binding
of bromide than chloride for which Kred[11 ꢀ Clꢁ] reached
104 Mꢁ1
.
Conclusion
In conclusion, we have synthesized an ammonium–ferrocene–
metalloporphyrin chemosensor allowing a sensitive assessment
of the anion’s electrostatic and nucleophilic features. The well-
defined electrochemical signature associated with a strong
reinforcement of the anion binding properties upon oxidation,
which produces up to three additional positive charges delo-
calized throughout the receptor, turns out to be especially
suited to achieve efficient electrochemical sensing of anionic
species.
The direct connection between the ferrocenyl–ammonium
and the metalloporphyrin’s p-electronic network, coupled to
the cumulative effect of multiple anchoring points, allowed an
unprecedented ferrocene-based ‘‘two-wave’’-type electrochemi-
cal sensing of halide anions. Such behaviour, based on ion
pairing effects and metal–ligand binding, emphasizes the
Fig. 6 Evolution of (A) the DPV peak (scan rate 10 mV sꢁ1, same
conditions as in Fig. 3) and (B) the Soret visible absorption band (4.8 ꢂ
10ꢁ6 M, CH2Cl2, 0.1 M TBAP) of [1]1 ꢀ BF4 as a function of added
ꢁ
chloride (0 to 1 and 0 to 500 equiv. for A and B, respectively). The
equilibria involved in these evolutions are depicted to the right of the
titration curves.
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importance of conjugating complementary interactions and
reporting centres.
slowly added under vigorous stirring. The resulting solution
was stirred at room temperature for 30 min, then 2,4,6-
collidine (209 ml, 1.57 mmol) was added, followed by chloranil
(385 mg, 1.56 mmol). The mixture was stirred at room tem-
perature for 3 h and brought to dryness under reduced
pressure. One hundred millilitres of an aqueous NaOH solu-
tion (2 M) were added to the oily residue and the mixture was
stirred at room temperature for 1 h. The black precipitate was
then filtered, washed with water and dried under reduced
pressure. The mixture was then purified by chromatography
(SiO2, CH2Cl2–hexane 75 : 25) to yield 5 (74 mg, 10%) as a black-
Due to the ease of modification and versatile properties of
both ferrocene and porphyrin fragments, molecular materials
based on their intimate association hold great promise in the
field of molecular electrochemical recognition. We are cur-
rently investigating related molecular architectures that could
lead us to achieve challenging redox sensing of exogenic
substrates in aqueous media.
Experimental
1
green solid. MS (FAB): m/z 869 [M þ 1]1; NMR H (CDCl3,
500 MHz): d ꢁ2.35 (s, 2H, –NH–), 2.71 (s, 3H, –Me), 2.73 (s,
6H, –Me), 3.15–3.33 [m, 4H, –S(CH2)2S–], 4.11 (m, 2H, –Fc),
4.38 (m, 2H, –Fc), 4.90 (m, 2H, –Fc), 5.53 (s, 1H, –HCS–)2),
5.59 (m, 2H, –Fc), 7.56 (m, 6H, –Tol), 8.10 (m, 6H, –Tol), 8.83
(m, 6H, b-pyrr, –Tol), 9.95 (d, 3J ¼ 4.90 Hz, 2H, b-pyrr);
Reagents, instrumentation and procedures
Prior to use dichloromethane and THF (synthesis grade) were
distilled over calcium hydride and Na/benzophenone, respec-
tively. Tetra-n-butylammonium perchlorate (TBAP) was pur-
chased from Fluka and used as received. TBAP used for the
spectrophotometric titration was obtained from Southwestern
Analytical Chemicals and dried under vacuum at 60 1C. Tetra-
n-butylammonium chloride (499%), bromide (498%) and
phosphate monobasic (499%) were obtained from Fluka and
used as received. Tetra-n-butylammonium hydrogensulfate
(497%) and nitrate (497%) were obtained from Aldrich
and used as received. Tetraethylammonium fluoride dihydrate
(497%) was obtained from Interchim and dried under
vacuum at 40 1C before use. Pyrrole and p-tolualdehyde were
purchased from Aldrich and used as received. 1,10-Diformyl
ferrocene (7),6 1-[2-(1,3-dithiolanyl)]-10-formylferrocene (6),7
lmax(CH2Cl2)/nm: 422 (S), 510 (Q), 588 (Q), 671 (Q); anal.
calcd. for C54H44FeN4S2: C 74.64, H 5.10, N 6.45%; obs. C
74.41, H 5.18, N 6.44%.
5-[10-(Formyl)ferrocenyl]-10,15,20-tri(p-tolyl)porphyrin (4). 5
(50 mg, 5.7 ꢂ 10ꢁ5 mol) dissolved in 50 ml of THF was quickly
added to a solution of N-chlorosuccinimide (56 mg, 0.42 mmol)
and silver nitrate (54.5 mg, 0.32 mmol) in 35 ml of CH3CN–
H2O (85 : 15). After stirring at room temperature for 10 min,
1 ml of saturated aqueous Na2SO3 solution was added, fol-
lowed by successive addition of saturated Na2CO3 (1 ml) and
brine (1 ml). Fifty millilitres of dichloromethane were then
added and the resulting mixture was filtered. After washing the
solid residue with dichloromethane, the organic phases were
combined, washed with water and dried over anhydrous
Na2SO4. The black powder obtained after evaporation under
reduced pressure was purified by chromatography (SiO2,
CH2Cl2–MeOH 99 : 1) to yield 4 (32 mg, 70%) as a purple
ꢁ
1-dodecanaminium, N-(ferrocenylmethyl)-N,N-dimethyl BF4
salt19 and 5-ferrocenyl-10,15,20-tri(p-tolyl)porphyrin20 were
synthesized according to literature procedures.
Molecular sieves were activated by heating at 200 1C under
vacuum for 1 h. Electrochemical experiments were conducted
with a CHI 660B electrochemical analyzer (CH instrument) in
a conventional three-electrode cell under an argon atmosphere
at 20 1C. All potentials were referenced to the [Fe(Cp*)2]0/1
redox couple whose half-wave potential relative to an Ag/
AgNO3 reference electrode (10 mM in CH3CN containing
0.1 M TBAP) is ꢁ350 mV. Rotating disc electrode (RDE)
voltammetry was carried out at a rotation rate of 600 rpm.
Cyclic voltammetry (CV) curves were recorded at a scan rate of
0.1 V sꢁ1 and the differential pulse voltammetry (DPV) curves
were recorded at a 10 mV sꢁ1 scan rate with a pulse height of
25 mV and a step time of 0.2 s. The working electrode was a
vitreous carbon disc (3 mm in diameter) polished with 1 mm
diamond paste before each recording. ESI (positive mode)
mass spectra were recorded with a Bruker Esquire 3000 Plus
ion trap spectrometer. FAB (positive mode) mass spectra were
recorded with an AEI Kratos MS 50 spectrometer fitted with
an Ion Tech Ltd gun and using m-nitrobenzyl alcohol as
matrix. MALDI-TOF spectra were obtained with a Bruker
autoflex using ditranol as matrix (dried drop). NMR spectra
were recorded at 25 1C on Bruker AC 250, Bruker Advance
400 MHz or Varian Unity Plus 500 MHz spectrometers. 1H
chemical shifts (ppm) were referenced to residual solvent
peaks. UV-Vis spectra were recorded on a Varian Cary 100
spectrophotometer using quartz cells (l ¼ 1 cm). Elemental
analyses were performed by the Service Central d’Analyses,
CNRS, Lyon.
1
solid. MS (FAB): m/z 793 [M þ 1]1; NMR H (CDCl3, 250
MHz): d ꢁ2.36 (br s, 2H, –NH–), 2.67 (s, 3H, –Me), 2.69
(s, 6H, –Me), 4.44 (m, 2H, –Fc), 4.83 (m, 2H, –Fc), 4.92 (m, 2H,
–Fc), 5.59 (m, 2H, –Fc), 7.51–7.56 (m, 6H, –Tol), 8.03–8.08
(m, 6H, –Tol), 8.74–8.82 (m, 6H, b-pyrr), 9.81 (d, 2H, 3J ¼ 4.8
Hz, b-pyrr), 9.90 (s, 1H, –CHO); lmax(CH2Cl2)/nm: 423 (S),
528 (Q), 576 (Q), 600 (sh), 666 (Q).
5-[10-(Hexylaminomethyl)ferrocenyl]-10,15,20-tri(p-tolyl)por-
phyrin (3). 4 (150 mg, 0.19 mmol) and hexylamine (30 ml, 0.22
mmol) were added to an argon-flushed 50 ml round-bottom
flask containing 20 ml of anhydrous THF and activated
molecular sieves. The resulting mixture was stirred at room
temperature under argon for 16 h, filtered to remove the
molecular sieves, which were washed well with anhydrous
THF, and finally concentrated under reduced pressure. After
adding NaBH4 (63 mg, 1.66 mmol) dissolved in absolute
ethanol, the solution was stirred at room temperature for 3 h
and evaporated to dryness. The resulting crude solid was
dissolved in 50 ml of dichloromethane and washed with water.
The organic phase was dried over anhydrous sodium sulfate,
filtered and evaporated to afford a crude product, which was
purified by chromatography (SiO2, CH2Cl2–MeOH 99 : 1) to
yield 3 (132 mg, 80%). MS (FAB): m/z 878 [M þ 1]1; NMR 1H
(CDCl3, 250 MHz): d ꢁ2.33 (s, 2H, NH), 0.50–0.90 (m, 11H, –
hexyl), 2.08 (m, 2H, NHCH2CH2–), 2.66 (s, 3H, –Me), 2.69 (s,
6H, –Me), 3.29 (br s, 2H, –FcCH2–), 4.09 (br s, 2H, –Fc), 4.22
(br s, 2H, –Fc), 4.73 (br s, 2H, –Fc), 5.48 (br s, 2H, –Fc), 7.53–
7.56 (m, 6H, –Tol), 8.05–8.09 (m, 6H, Tol), 8.75–8.80 (m, 6H,
b-pyrr), 9.94 (d, 2H, 3J ¼ 4.8 Hz, b-pyrr); lmax(CH2Cl2)/nm (log
e): 422 (5.56) (S), 512 (4.09) (Q), 598 (3.98) (Q), 673 (3.97) (Q).
Syntheses
5-{10-[2-(1,3-Dithiolanyl)]ferrocenyl}-10,15,20-tri(p-tolyl)por-
phyrin (5). Samples of pyrrole (219 ml, 3.14 mmol), p-tolualde-
hyde (279 ml, 2.35 mmol) and 6 (250 mg, 0.78 mmol) were
dissolved in 80 ml of dry CH2Cl2 at room temperature in a 150
ml round-bottom flask fitted with a vented rubber septum and
flushed for 15 min with argon. The mixture was then protected
from light and trifluoroacetic acid (121 ml, 1.57 mmol) was
Zinc(II)
(p-tolyl)porphyrin (2). One millilitre of methanol saturated with
5-[10-(hexylaminomethyl)ferrocenyl]-10,15,20-tri
1588
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 5 8 4 – 1 5 8 9

View Article Online
zinc(II) acetate was added to 3 (50 mg, 0.56 ꢂ 10ꢁ4 mol)
dissolved in 20 ml of dichloromethane. The resulting mixture
was stirred at room temperature for 10 h. This solution was
then washed with water, dried over anhydrous sodium sulfate,
filtered and evaporated to dryness. The crude product was then
purified by chromatography (SiO2, CH2Cl2–MeOH 99 : 1) to
yield 2 (48 mg, 91%). MS (MALDI-TOF): m/z 939.2 [M]1 ; 1H
NMR (CDCl3, 500 MHz, 293 K): d ꢁ5.18 (br s, 1H), ꢁ2.54
(br s, 2H), ꢁ1.98 (br s, 2H), ꢁ1.76 (br s, 2H), ꢁ0.86 (br s, 2H),
Cocks, K. C. Gordon, G. B. O. Jameson, D. L. Officer and
Z. Zhao, Chem. Commun., 1999, 637; (g) S. W. Rhee, B. B. Park,
Y. Do and J. Kim, Polyhedron, 2000, 19, 1961; (h) S. W. Rhee, Y.
H. Na, Y. Do and J. Kim, Inorg. Chim. Acta, 2000, 309, 49; (i) S. J.
Narayanan, S. Venkatraman, S. R. Dey, B. Sridevi, V. R. G.
Anand and T. K. Chandrashekar, Synlett., 2000, 12, 1834; (j) H. J.
H. Wang, L. Jaquinod, D. J. Nurco, M. G. H. Vicente and K.
Smith, Chem. Commun., 2001, 2646; (k) V. A. Nadtochenko, D. V.
Khudyakov, E. V. Vorontsov, N. M. Loim, F. E. Gostev, D. G.
Tovbin, A. A. Titov and O. M. Sarkisov, Russ. Chem. Bull., 2002,
51, 986.
3
ꢁ0.03 (br s, 2H), 0.43 (t, J ¼ 7 Hz, 3H, –CH2CH3), 0.52 (m,
4
5
(a) O. Reynes, J.-C. Moutet, J. Pecaut, G. Royal and E. Saint-
´
2H, –CH2CH3), 2.23 (br s, 2H, –Fc), 2.72 (s, 3H, –PhCH3),
2.73 (s, 6H, –PhCH3), 3.64 (br s, 2H, –Fc), 4.24 (br s, 2H, –Fc),
5.0 (br s, 2H, –Fc), 7.53–7.60 (m, 6H), 8.07–8.15 (m, 6H), 8.87
(m, 6H), 9.82 (br s, 2H, b-pyr); 13C NMR (CDCl3, 62.5 MHz,
293 K): d 13.5, 21.5, 22.0, 23.9, 24.9, 30.2, 42.8, 42.9, 69.4, 69.5,
71.0, 78.2, 82.5, 90.7, 116.1, 120.2, 120.9, 127.1, 130.7, 131.4,
131.5, 134.3, 134.7, 136.7, 140.2, 140.4, 149,2, 149.8, 150.0,
150.2; lmax(CH2Cl2)/nm (log e): 429 (5.43), 580 (4.06), 631
(4.28); anal. calcd. for C58H53FeN5Zn: C 74.00, H 5.67,
N 7.44%; obs. C 73.15, H 5.66, N 7.30%.
Aman, New J. Chem., 2002, 26, 9; (b) O. Reynes, J.-C. Moutet,
G. Royal and E. Saint-Aman, Electrochim. Acta, 2004, 49, 3727.
(a) J. Weiss, J. Inclusion Phenom. Macrocyclic Chem., 2001, 40, 1;
(b) P. D. Beer, D. P. Cormode and J. J. Davis, Chem. Commun.,
2004, 4, 414.
G. G. A. Balavoine, G. Doisneau and T. Fillebeen-Khan, J.
Organomet. Chem., 1991, 412, 381.
B. Basu, S. K. Chattopadhyay, A. Ritzen and T. Frejd, Tetra-
hedron: Asymmetry, 1997, 8, 1841.
6
7
8
9
C. Bucher, C. H. Devillers, J.-C. Moutet, G. Royal and E. Saint-
Aman, Chem. Commun., 2003, 888.
(a) E. S. Schmidt, T. S. Calderwood and T. C. Bruice, Inorg.
Chem., 1986, 25, 3718; (b) A. K. Burrell, W. M. Campbell, D. L.
Officer, S. M. Scott, K. C. Gordon and M. R. McDonald, J.
Chem. Soc., Dalton Trans., 1999, 3349; (c) A. Arounaguiry, R. W.
Wagner, P. D. Rao, J. A. Riggs, P. Hascoat, J. R. Diers, J. Seth,
R. K. Lammi, D. F. Bocian, D. Holten and J. S. Lindsey, Chem.
Mater., 2001, 13, 1023.
Zinc(II) [5-{10-(methanaminium,N-hexyl-N,N-dimethyl)ferro-
cenyl}-10,15,20-tri(p-tolyl)porphyrin]tetrafluoroborate (1). An-
hydrous K2CO3 (12.8 mg, 7.87 ꢂ 10ꢁ5 mol) and 2 (74.1 mg,
6.44 ꢂ 10ꢁ5 mol) were placed under an argon atmosphere in a
25 ml round-bottom flask, fitted with a rubber septum. Twelve
millilitres of anhydrous THF were then added with a syringe,
followed by methyl iodide (366 ml, 5.87 mmol). The resulting
mixture was stirred at room temperature for 24 h and then
filtered. The solid was washed with THF and the solution was
concentrated under reduced pressure to give a green crude
solid, which was purified by chromatography (SiO2, CH2Cl2–
MeOH 95 : 5) to afford [1]1 ꢀ Iꢁ (69 mg, 80%). The latter was
then submitted to ion exchange chromatography using an
IRA-96 resin first conditioned with a 40% HBF4 aqueous
solution and washed well with water and acetonitrile. [1]1 ꢀ Iꢁ
was dissolved in acetonitrile and passed through the resin to
obtain quantitatively [1]1 ꢀ BF4ꢁ. MS (ESIþ): m/z 968.6 [M]1;
1H NMR [(CD3)2SO, 400 MHz, 293 K]: d 0.72 (t, 3J ¼ 7.2 Hz,
3H, –CH2CH3), 0.99 (m, 4H, –CH2–), 1.09 (m, 2H, –CH2–),
1.39 (m, 2H, –CH2–), 2.65 (s, 3H, –CH3), 2.68 (s, 6H, –CH3),
2.70 (s, 6H, –CH3), 2.90 (m, 2H, –NCH2CH2–), 4.20 (s, 2H, –
N1–CH2Fc), 4.42 (m, 2H, –Fc), 4.65 (m, 2H, –Fc), 4.96 (m, 2H,
–Fc), 5.58 (m, 2H, –Fc), 7.57–7.61 (m, 6H), 8.00–8.04 (m, 6H),
10 K. M. Kadish, E. Van Caemelbecke and G. Royal, in The
Porphyrin Handbook, eds. K. M. Kadish, K. M. Smith and
R. Guilard, Academic Press, San Diego, CA, 2000, vol. 8, ch. 55.
11 (a) K. Funatsu, T. Imamura, A. Ichimura and Y. Sasaki, Inorg.
Chem., 1998, 37, 1798; (b) C. Ikeda, Y. Tanaka, T. Fujihara, Y.
Ishii, T. Ushiyama, K. Yamamoto, N. Yoshioka and H. Inoue,
Inorg. Chem., 2001, 40, 3395.
12 (a) H. J. Shine, A. G. Padilla and S.-M. Wu, J. Org. Chem., 1979,
44, 4069; (b) K. M. Kadish and R. K. Rhodes, Inorg. Chem., 1981,
20, 2961; (c) A. S. Hinman, B. D. Pavelich, A. E. Kondo and
S. Pons, J. Electroanal. Chem., 1987, 234, 145; (d) L. Persaud and
C. H. Langford, Inorg. Chim. Acta, 1987, 129, 31.
13 (a) Overlapping of porphyrin-based oxidation processes have
already been described in the literature. See, for examples: L.
Geng and R. W. Murray, Inorg. Chem., 1986, 25, 3115; (b) L.
Geng, A. G. Ewing, J. C. Jernigan and R. W. Murray, Anal.
Chem., 1986, 58, 852; (c) K. M. Kadish, D. Sazou, G. B. Maiya,
B. C. Han, Y. M. Liu, A. Saoiabi, M. Ferhat and R. Guilard,
Inorg. Chem., 1989, 28, 2542; (d) A. El-Kasmi, D. Lexa,
P. Maillard, M. Momenteau and J.-M. Saveant, J. Am. Chem.
´
Soc., 1991, 113, 1586; (e) J. A. Hodge, M. G. Hill and H. B. Gray,
Inorg. Chem., 1995, 34, 809.
3
8.68–8.72 (m, 4H), 8.78 (d, J ¼ 4.8 Hz, 2H, b-pyr), 10.04 (m,
14 Well-behaved redox sensing of halides is of special interest since
they frequently undergo catalytic oxidation by ferrocene-based
receptors. See: M. Buda, A. Ion, J.-C. Moutet, E. Saint-Aman and
R. Ziessel, J. Electroanal. Chem., 1999, 469, 132 and references
therein.
15 (a) P. D. Beer, M. G. B. Drew and R. Jagessar, J. Chem. Soc.,
Dalton Trans., 1997, 881; (b) M. C. Hodgson, A. K. Burrell, P. D.
W. Boyd, P. J. Brothers and C. E. F. Rickard, J. Porphyrins
Phthalocyanines, 2002, 6, 737.
2H, b-pyr); lmax(CH2Cl2)/nm (log e): 424 (5.48) (S), 563 (4.19)
(Q), 610 (4.09) (Q); anal. calcd. for C60H58BF4FeN5Zn ꢀ H2O:
C 67.02,
N 6.52%.
H 5.62, N 6.51%; obs. C 67.04, H 5.50,
References
16 This is in full agreement with literature values obtained with
ZnTPP in similar conditions: (a) M. Nappa and J. S. Valentine,
J. Am. Chem. Soc., 1978, 100, 5075; (b) A. S. Hinman and B. D.
Pavelich, J. Electroanal. Chem., 1989, 269, 53.
1
(a) P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40,
486; (b) P. D. Beer and E. J. Hayes, Coord. Chem. Rev., 2003
240, 167.
(a) H.-J. Schneider, Angew. Chem., Int. Ed. Engl., 1991, 30, 1417;
(b) F. P. Schmidten and M. Berger, Chem. Rev., 1997, 97, 1609; (c)
M. M. Antonisse and D. N. Reinhoudt, Chem. Commun., 1998,
443.
For ferrocenyl directly linked to a porphyrin, see: (a) R. G.
Wollmann and D. N. Hendrickson, Inorg. Chem., 1977, 16,
3079; (b) N. M. Loim, N. V. Abramova and V. I. Sokolov,
Mendeleev Commun., 1996, 46; (c) N. M. Loim, N. V. Abramova,
R. Z. Khaliullin and V. I. Sokolov, Russ. Chem. Bull., 1997, 46,
1193; (d) N. M. Loim, N. V. Abramova, R. Z. Khaliullin, Y. S.
Lukashov, E. V. Vorontsov and V. I. Sokolov, Russ. Chem. Bull.,
1998, 47, 1016; (e) V. A. Nadtochenko, N. N. Denisov, V. Y. Gak,
N. V. Abramova and N. M. Loim, Russ. Chem. Bull., 1999, 48,
1900; (f) P. D. W. Boyd, A. K. Burrell, W. M. Campbell, P. A.
2
17 (a) R. Miller, D. A. Gutowski, Z. H. Chen, G. W. Gokel, L.
Echegoyen and A. E. Kaifer, Anal. Chem., 1988, 60, 2021; (b) P. D.
Beer, P. A. Gale and G. Z. Chen, J. Chem. Soc., Dalton Trans.,
1999, 1897.
3
18 Attempts to fit the experimental data obtained upon Fꢁ addition
did not lead to satisfactory results.
19 1-Dodecanaminium, N-(ferrocenylmethyl)-N,N-dimethyl Brꢁ salt
was synthesized according to T. Saji, K. Hoshino and S. Aoyagui,
J. Am. Chem. Soc., 1985, 107, 6865 and submitted to anion
exchange chromatography using an IRA-96 resin conditioned
with a 40% HBF4 aqueous solution (see synthesis of [1]1 ꢀ BF4ꢁ).
20 S. J. Narayanan, S. Venkatraman, S. R. Dey, B. Sridevi, V. R. G.
Anand and T. K. Chandrashekar, Synlett., 2000, 12, 1834.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 5 8 4 – 1 5 8 9
1589