Three-metal coordination by novel bisporphyrin architectures

Article abstract of DOI:10.1021/ic101170k

The synthesis and characterization of a new type of bisporphyrin system is reported where the two macrocycles are linked in a cofacial arrangement by a substituted carbazole bridge. The three nitrogen atoms of the carbazole bridge in the compounds may complex a metal ion and thus provide a new parameter for varying the physical properties and flexibility of the dyad after formation of a three-metal system. In the present study, four bis-metalloporphyrin complexes were synthesized and examined by electrochemistry and thin-layer spectroelectrochemistry in CH₂Cl₂ and PhCN. Two of the examined compounds contain Cu(II) or Zn(II) porphyrins and a carbazole linker with a bound Cu(II) ion, giving a three metal system, while the other two examined compounds contained the same porphyrins but with a carbazole bridge which lacks the Cu(II) component. Since carbazoles and Cu(II) ions are both electroactive, redox properties of several unlinked carbazoles with and without bound Cu(II) ions were also examined as to their electrochemical behavior under the same solution conditions as the dyads to better understand the redox reactions which may occur at the carbazole group linking the two porphyrin macrocycles. Several mononuclear porphyrins with structures related to macrocycles in the dyads were also investigated.

Full text of DOI:10.1021/ic101170k

Inorg. Chem. 2010, 49, 8929–8940 8929
DOI: 10.1021/ic101170k
Three-Metal Coordination by Novel Bisporphyrin Architectures
Jean-Michel Barbe,*,† Benoit Habermeyer,† Tony Khoury,†,§ Claude P. Gros,† Philippe Richard,† Ping Chen,‡ and
Karl M. Kadish*,‡
†
ꢀ
Universite de Bourgogne, ICMUB (UMR 5260), 9, Avenue Alain Savary, BP 47870, 21078 Dijon Cedex,
France, and ‡Department of Chemistry, University of Houston, Houston, Texas 77204-5003. §Present address:
School of Chemistry, F11, The University of Sydney, NSW 2006, Australia
Received June 10, 2010
The synthesis and characterization of a new type of bisporphyrin system is reported where the two macrocycles are linked in a
cofacial arrangement by a substituted carbazole bridge. The three nitrogen atoms of the carbazole bridge in the compounds
may complex a metal ion and thus provide a new parameter for varying the physical properties and flexibility of the dyad after
formation of a three-metal system. In the present study, four bis-metalloporphyrin complexes were synthesized and examined
by electrochemistry and thin-layer spectroelectrochemistry in CH2Cl2 and PhCN. Two of the examined compounds contain
Cu(II) or Zn(II) porphyrins and a carbazole linker with a bound Cu(II) ion, giving a three metal system, while the other two
examined compounds contained the same porphyrins but with a carbazole bridge which lacks the Cu(II) component. Since
carbazoles and Cu(II) ions are both electroactive, redox properties of several unlinked carbazoles with and without bound
Cu(II) ions were also examined as to their electrochemical behavior under the same solution conditions as the dyads to better
understand the redox reactions which may occur at the carbazole group linking the two porphyrin macrocycles. Several
mononuclear porphyrins with structures related to macrocycles in the dyads were also investigated.
Introduction
π-π interaction between the two macrocycles and the overall
properties of the compound.4 Extensive studies have been
reported in literature where cofacial metalloporphyrins have
been used in the area of catalysis and energy transfer,4,5 with
the geometry of the dyad varied to optimize the desired physi-
cal requirements. Many other supramolecular assemblies
involving metalloporphyrin units where metals are inter-
acting through various types of bonding have been described
and recently collected in two reviews.6
Herein we report the synthesis and characterization of a
bisporphyrin system where the two macrocycles are linked in a
cofacial arrangement by a substituted carbazole bridge as seen
in Chart 1. The three nitrogen atoms of the bridge in com-
pounds 9 and 11 may complex a metal ion and thus provide a
One of the most important reactions on earth is photo-
synthesis. An X-ray crystal structure of the photosynthetic
purple bacteria1 led scientists to try to mimic not only the light
harvesting System One (LH1) and Two (LH2) but also the
photosynthetic reaction center (PRC). In the naturally occur-
ring special pair, porphyrinic systems are involved and metallo-
porphyrins are therefore expected to be good candidates for
artificial light harvesting systems and applications in photo-
voltaics, catalysis, and molecular electronics.2
“Pacman porphyrins” are well-known3 and consist of two
porphyrins linked in a face-to-face (cofacial) arrangement by
a “rigid” bridge. Changes in the bridge structure have been
used to control the distance between the two porphyrin
moieties in the dyad as well as the degree of opening and
closing which is directly related to changes in the extent of
(4) (a) Bolze, F.; Gros, C. P.; Drouin, M.; Espinosa, E.; Harvey, P. D.;
Guilard, R. J. Organomet. Chem. 2002, 89–97. (b) Gros, C. P.; Brisach, F.;
Meristoudi, A.; Espinosa, E.; Guilard, R.; Harvey, P. D. Inorg. Chem. 2007, 46,
125–135. (c) Harvey, P. D.; Stern, C.; Gros, C. P.; Guilard, R. Coord. Chem. Rev.
2007, 251, 410–428. (d) Harvey, P. D.; Stern, C.; Gros, C. P.; Guilard, R. J. Inorg.
Biochem. 2008, 102, 395–405. (e) Takai, A.; Gros, C. P.; Barbe, J.-M.; Guilard,
R.; Fukuzumi, S. Chem.;Eur. J. 2009, 15, 3110–3122.
(5) (a) Fukuzumi, S.; Okamoto, K.; Gros, C. P.; Guilard, R. J. Am. Chem.
Soc. 2004, 126, 10441–10449. (b) Fukuzumi, S.; Okamoto, K.; Tokuda, Y.; Gros,
C. P.; Guilard, R. J. Am. Chem. Soc. 2004, 126, 17059–17066. (c) Gros, C. P.; Aly,
S. M.; El Ojaimi, M.; Barbe, J.-M.; Brisach, F.; Abd-El-Aziz, A. S.; Harvey, P. D.
J. Porphyrins Phthalocyanines 2007, 11, 244–257. (d) Tanaka, M.; Ohkubo, K.;
Gros, C. P.; Guilard, R.; Fukuzumi, S. J. Am. Chem. Soc. 2006, 28, 14625–14633.
(6) (a) Beletskaya, I.; Tyurin, V. S.; Tsivadze, A. Y.; Guilard, R.; Stern, C.
Chem. Rev. 2009, 109, 1659–1713. (b) Drain, C. M.; Varotto, A.; Radivojevic, I.
Chem. Rev. 2009, 109, 1630–1658.
*To whom correspondence should be addressed. E-mail: jean-michel.barbe@
u-bourgogne.fr (J.-M.B.), kkadish@uh.edu (K.M.K.).
(1) (a) McDermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-
Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Nature 1995, 374,
517–521. (b) Koepke, J.; Hu, X. C.; Muenke, C.; Schulten, K.; Michel, H.
Structure 1996, 4, 581–597.
(2) In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; Academic Press: Boston, 2000; Vol. 6.
(3) (a) Chang, C. J.; Loh, Z.-H.; Deng, Y.; Nocera, D. G. Inorg. Chem.
2003, 42, 8262–8269. (b) Collman, J. P.; Hutchison, J. E.; Lopez, M. A.; Tabard,
A.; Guilard, R.; Seok, W. K.; Ibers, J. A.; L'Her, M. J. Am. Chem. Soc. 1992, 114,
9869–9877. (c) Guilard, R.; Lopez, M. A.; Tabard, A.; Richard, P.; Lecomte, C.;
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Brandes, S.; Hutchison, J. E.; Collman, J. P. J. Am. Chem. Soc. 1992, 114, 9877–
9889. (d) Rosenthal, J.; Nocera, D. G. Prog. Inorg. Chem. 2007, 55, 483–544.
r
2010 American Chemical Society
Published on Web 09/07/2010
pubs.acs.org/IC

8930 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
Chart 1. Structures of Examined Bisporphyrins and Carbazole Linking Groups
new parameter for varying the physical properties and flexi-
bility of the dyad after formation of the three-metal systems in
compounds 10 and 12.
Scheme 1
The four synthesized tris-metal complexes in Chart 1 were
spectroscopically characterized and also examined by electro-
chemistry and thin-layer spectroelectrochemistry in CH2Cl2
and PhCN. Carbazoles are known to be electroactive,7 and
the three unlinked carbazoles shown in the lower part of Chart 1
were also examined as to their redox properties under the same
solution conditions to better understand reactions of the dyads.
Results and Discussion
Two different precursors are needed to obtain the desired
porphyrin dimer; the first is tert-butyl diformylcarbazole whose
synthesis was reported elsewhere;8 the second is the amino-
linker-porphyrin which is synthesized as described in Scheme 1.
Direct condensation of the two separate parts leads to forma-
tion of the desired porphyrin dimer as shown in Scheme 2.
The nitro-porphyrin 3 was prepared in about 50% yield by
reaction of the a,c-biladiene 19 and 4-nitrobenzaldehyde 2 with a
catalytic amount of para-toluene sulfonic acid (PTSA) in reflux-
ing ethanol (Scheme 1). Compound 3 was reduced using tin(II)
chloride dihydrate in a stirring solution of hydrogen chloride in
diethyl ether (1.0 M), leading to the desired aminoporphyrin 4in
2 h. A small quantity of chloroform was required to enhance the
solubility of the porphyrin. Under these conditions, the 4-amino-
porphyrin 4 was afforded in 84% yield. Metalation of 4 with
zinc(II) and copper(II) was successfully achieved to give the
metalated derivatives 5 and 6 in 85 and 93% yield, respectively.
The aminoporphyrin 4 (2 equiv) was reacted with diformyl-
carbazole 7 (1 equiv) to force condensation of the two amine
functions with the two aldehyde counterparts. After refluxing
a mixture of 4 and 7 in pyridine for 3 days, the bisporphyrin
(7) (a) Ambrose, J. F.; Carpenter, L. L.; Nelson, R. F. J. Electrochem.
Soc. 1975, 27, 876–894. (b) Ambrose, J. F.; Nelson, R. F. J. Electrochem. Soc.
1968, 115, 1159–1164.
(8) Gibson, V. C.; Spitzmesser, S. K.; White, A. J. P.; Williams, D. J.
Dalton Trans. 2003, 35, 2718–2727.
(9) Harris, D.; Johnson, A. W.; Gaete-Holmes, R. Biorg. Chem. 1980, 9,
63–70.
carbazole 8 was obtained in 85% yield (Scheme 2). The mole-
cular weight of 8 was confirmed by the high resolution mass
spectroscopy (HRMS)-electrospray ionization (ESI) spectrum,
which exhibited a pseudo-molecular ion, [MþH]þ at 1382.8099
Da (4 ppm deviation with respect to calculated mass).

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8931
Scheme 2
A comparison of the 1H NMR spectrum (in D5-py) of the
free-base monoporphyrin 4 and free-base bisporphyrin carba-
zole 8 provides evidence that no interaction occurs between the
two porphyrin macrocycles in 8 under these solution condi-
tions. Indeed, the inner NH proton resonances appear at -2.67
ppm for 4 and -2.66 ppm for 8. Any interaction which might
have occurred would have shielded this NH proton resonance
for the bisporphyrin compared to the monoporphyrin. It is
noteworthy to point out that the imine bond (-CdN-) of 8 is
strongly stabilized by the aromatic pathway of the molecule,
and this was demonstrated by the failure of the reaction when
NaBH4 hydrogenation was attempted. The monoporphyrin
carbazole aldehyde was concomitantly obtained in 7% yield.
Addition of Zn(II) to the two macrocycles of 8 was achieved
by refluxing the bisporphyrin with zinc(II) acetate dihydrate
and sodium acetate in a chloroform/methanol solution for
10 min to afford the bis-zinc(II) bisporphyrin carbazole 9 in
84% yield. In the absence of sodium acetate, the yield was dec-
reased considerably because of acid attack of the imine bond by
protons generated during the metalation process. 9 was charac-
Figure 1. Electronic absorption spectra in CH2Cl2 of copper(II) amino-
porphyrin 6 (blue), tris-copper(II) bisporphyrin carbazole 10 (red) and
unlinked carbazolide copper(II) 14 (green).
carbazole 10 in 98% yield (Scheme 2). The structure of 10
was confirmed by HRMS (ESI) and matrix-assisted laser
desorption/ionization-time of flight (MALDI-TOF) mass spec-
trometry (Supporting Information, Figure S1). The identity of
the ligand bound to the Cu(II) ion in the carbazole bridge part
of the molecule in 10 was not definitively proven but it is
reasonably speculated to be acetate since this is the only anion
employed in the reaction, and a Cu(II)OAc/Cu(I) redox pro-
cess is observed as described later in the manuscript.
The UV-visible absorption spectra of copper(II) amino-
porphyrin 6 (blue), tris-copper(II) bisporphyrin carbazole 10
(red), and unlinked carbazolide copper(II) 14 (green) com-
plexes are shown in Figure 1.
1
terized by HRMS (ESI) and H NMR (See Experimental
Section).
The UV-visible absorption data for the zinc(II) amino-
porphyrin 5 and the bis-zinc(II) bisporphyrin carbazole 9 are
given in the Experimental Section. Nearly identical spectra
are obtained for both compounds which can be explained by
the minimal interaction which occurs between the two zinc-
(II) porphyrins in the dyad. Similarly, only minor variations
in the chemical shifts are observed in the 1H NMR spectra of
5 or 9. This indicates that both porphyrin macrocycles are far
apart in the dyad, thus avoiding any detectable interaction.
Although zinc could not be inserted into the carbazole bridge,
the metalation of 8 with copper(II) acetate in the presence of
sodium acetate directly afforded the tris-copper(II) bisporphyrin
In addition to the Soret and Q bands, the spectrum of
the tris-copper(II) dimer 10 possesses a broad band at about
460 nm which is not observed in the UV-vis spectrum of the
monomer species 6. This band results from an absorption of

8932 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
Scheme 3
the copper carbazolide part of the molecule. Indeed, the
isolated carbazole complex 14 has an absorption band at 438
nm (see Figure 1, green spectrum). Finally, UV-vis data for
the neutral form seems to show that the tris-copper(II)
bisporphyrin carbazole 10 behaves in solution as two sepa-
rate porphyrin macrocycles without any interaction between
the two π-ring systems, but this is not the case upon oxidation
as described later in the manuscript. Non-interacting macro-
cycles in the neutral compound 10 are also observed in the
solid state (See Supporting Information, Figure S2).
The direct formation of the bis-copper derivative 11 from the
free-base bisporphyrin 8 using reported conditions failed since
copper was also readily inserted in the carbazole bridge thus
affording the tris-copper derivative 10. Therefore, the coupling
reaction of the copper amino porphyrin 6 with the carbazole
aldehyde 7 was carried out in pyridine for 3 days leading to the
quantitative formation of the bis-copper complex 11 (Scheme3).
One goal of the synthesis was to prepare a dimer species in-
corporating two different types of metal ions and then to inves-
tigate their electrochemical, spectroscopic, and axial ligand
binding properties.
Figure 2. ESR spectra of bis-copper 11 (top) and tris-copper dyad 10
(bottom) at 100 K in a dichloromethane/toluene mixture 1/1. (Inset:
Observed half-field transition in the tris-copper dyad 10).
Scheme 4
Copper was chosen because of its facile coordination with
the nitrogen atoms of the bridge (vide supra). The copper(II)
bis-zinc(II) bisporphyrin carbazole 12 was readily obtained by
refluxing a solution of the bis-zinc complex 9 with excess
copper(II) acetate hydrate (Scheme 4). The formation of 12
was clearly demonstrated by MALDI-TOF and HRMS (ESI),
with the appearance in the spectra of a single ionic pattern
corresponding to [M - X]þ (X being probably AcO-) (See
Experimental Section). Electron spin resonance (ESR) is a more
sensitive technique than UV-visible spectroscopy to detect any
interaction which might exist between the two linked copper
porphyrin macrocycles of 10 and 11 in solution, and these spec-
tra were therefore recorded at 100 K in a 1:1 CH2Cl2/toluene
mixture (Figure 4). The measured g tensors and coupling con-
stants for both complexes as well as those of the monometallic
copper aminoporphyrin 6 and the copper carbazole bridge
analogue 14 (see Chart 1) are given in Supporting Information,
Table S1.
The ESR spectrum of 11 looks like that of a classical
copper(II) porphyrin with g|| and g^ equal to 2.19 and 2.05
and A||Cu and A^N equal to 203 ꢀ 10-4 cm-1 and 16.5 ꢀ 10-4
cm-1, respectively. The spectrum of 10, which contains two
Cu(II) porphyrin macrocycles and a Cu(II) carbazole, exhi-
bits a less resolved signal from which only the perpendicular
g^ value of 2.06 can be undoubtedly extracted (see Figure 2
and Supporting Information, Table S1). Such a low resolution
and broadened spectrum is often indicative of spin-spin inter-
actions between two copper(II) nuclei.10 In the present case, the
contribution of the carbazolide copper part can also induce a
(10) (a) Eaton, S. S.; Eaton, G. R.; Chang, C. K. J. Am. Chem. Soc. 1985,
ꢁ
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107, 3177–3184. (b) Suspene, C.; Brandes, S.; Guilard, R. Chem.;Eur. J. 2010,
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DOI: 10.1002/chem.200903148; (c) Brandes, S.; David, G.; Suspene, C.; Corriu,
R. L. P.; Guilard, R. Chem.;Eur. J. 2007, 13, 3480–3490.

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8933
Scheme 5. Reduction Mechanisms of Cu Carbazole 14 in CH2Cl2
generated radical cation is unstable on the cyclic voltam-
metry time scale and rapidly undergoes a chemical reaction
in solution as shown by the lack of a reversible process and
the re-reduction peak at Ep = 0.80 V on the reverse potential
sweep (Figure 3, top). This new reduction peak is assigned to
the product of a chemical reaction following electron transfer
and was not examined in further detail. However, it most
likely involves a radical coupling mechanism as earlier
described for related carbazoles.7
In contrast to the carbazole 13, the two copper containing
derivatives 14 and 15 undergo a reversible one electron
oxidation at E1/2=1.12 (14) or 1.19 V (15) and the generated
radical cations are relatively stable as seen by the cyclic
voltammograms in Figure 3. Derivatives 14 and 15 also
undergo an irreversible reduction at Ep=-1.05 V or -0.55 V
and a re-oxidation at Epa = -0.06 V in both cases. The
reductions are both assigned to the Cu(II)/Cu(I) process
of bound CuX where X=OAc- (14) or Cl- (15) and the re-
oxidation, which is not observed in the cyclic voltammogram
of unmetalated 13, is assigned to the Cu(I)/Cu(II) reaction of
the product where the electrogenerated Cu(II) on the return
sweep is assigned to a species which is either uncomplexed or
Figure 3. Cyclic voltammograms of the investigated carbazole deri-
vatives 13-15 in CH2Cl2 containing 0.1 M TBAP.
broadening of the ESR signal. Moreover, a weak half-field
signal at g = 4.23 is observed at low temperature (see Figure 2
inset). This signal is not detected in the spectrum of 11 or related
monomer copper (S=1/2) porphyrins (Supporting Informa-
tion, Table S1) and can be again explained by the presence of
the two interacting copper(II) nuclei of the porphyrin rings11 in
frozen solution (S = 1). Although intermolecular interactions
cannot be absolutely ruled out as responsible for this signal, it
˚
should be noted that the approximate value of 6.8 A calculated
for the distance between the two interacting copper atoms of 10
from the intensity of the half-field ESR signal10a,12 compares
well with the separation determined from preliminary results of
an X-ray structure of the chloro derivative of 10 (Supporting
Information, Figures S2 and S3).
-
coordinated by a ClO4 ion from the TBAP supporting
electrolyte on the electrochemical time scale.
This reduction of Cu(II) remains irreversible for both 14
and 15 when the temperature of the CH2Cl2 solution was
lowered to -70 ꢀC, indicating an extremely rapid chemical
reaction following electron transfer, and this electrochemical
EC mechanism is proposed to involve the rapid loss of OAc-
or Cl- after generation of Cu(I). The fact that the reverse
Cu(I)/Cu(II) anodic process occurs at Ep=-0.06 V for both
compounds indicates that neither Cl- nor OAc- is involved
in the re-oxidation step. However, the lack of a reduction
coupled to process at -0.06 V also suggests an electro-
chemical EC (electron transfer with following chemical
reaction) mechanism on the re-oxidation and the rapid
binding of Cl- or OAc- after generation of Cu(II) to give
the original CuIIX species at the electrode surface.
It should also be pointed out that the much more negative
Cu(II)/Cu(I) reduction potential of the acetate bound species
(14), as compared to the chloride bound derivative (15) is
consistent with a much stronger Cu(II) binding constant for
OAc- in 14 than for Cl- in 15; in fact the 500 mV difference
in peak potentials between the two processes (-1.05 vs
-0.55 V) is consistent with a difference in formation con-
stants of approximately 10 orders of magnitude (assuming a
-59 mV shift in Ep for each 10-fold increase in log K).
In summary, the irreversible reduction at -1.05 (14) or
-0.55 V (15), coupled with the irreversible re-oxidation at
-0.06 V is consistent with two separate electrochemical EC
mechanisms as shown in Scheme 5 for the case of 14 and
Carbazole Electrochemistry. Since carbazoles7 and
Cu(II) complexes13 are known to be electroactive, redox
properties of the carbazoles 13-15 in Chart 1 were examined
as to their electrochemical behavior under the same solution
conditions as the dyads 9-12 to better understand the redox
reactions which may occur at the carbazole group linking the
two porphyrin macrocycles. Several mononuclear porphy-
rins related to derivatives 9-12 were also investigated.
The electrochemical properties of the carbazoles 13-15
were examined in CH2Cl2 containing three types of support-
ing electrolytes, TBAP, TBA(OAc), and TBACl, and cyclic
voltammograms in CH2Cl2, 0.1 M TBAP are illustrated in
Figure 3. As seen in the figure, all three carbazoles undergo
a one electron oxidation as was reported in the literature
for similar compounds.7 The unmetalated carbazole 13 is
oxidized at Ep = 1.29 V for a scan rate of 0.1 V/s but the electro-
(11) (a) Blondin, G.; Frapart, Y.-M. L’Actualiteꢀ Chimique 1996, 7,
112–124. (b) Drago, R. S. Physical Methods in Chemistry; 1st ed.; W.B.
Saunders Company: Philadelphia, 1977.
(12) Eaton, S. S.; More, K. M.; Sawant, B. M.; Eaton, G. R. J. Am. Chem.
Soc. 1983, 105, 6560–6567.
(13) (a) Hartman,J. A. R.;Kammier, A. L.;Spracklin, R. J.;Pearson,W. H.;
Combariza, M. Y.; Vachet, R. W. Inorg. Chim. Acta 2004, 357, 1141–1151.
(b) Rybak-Akimova, E. V.; Nazarenko, A. Y.; Chen, L.; Krieger, P. W.; Herrera,
A. M.; Tarasov, V. V.; Robinson, P. D. Inorg. Chim. Acta 2001, 324, 1–15.

8934 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
group at one meso-position of the three (EtxMeyPhP)M deri-
vatives where xþ y= 8 and allows for the use of (OEP)M as
a comparison compound in place of (EtxMeyPhP)M when
the desired monomeric porphyrin is not available for study.
The two ring-centered oxidations of (OEP)Zn (E1/2
0.62 and 1.09 V) are separated by 370 mV in potential and
=
this compares to a 290 mV separation in E1/2 between the
two ring-centered oxidations of the bis-metal dyad 9 (E1/2 =
0.65 and 0.94 V). As seen from Figure 4, the first oxidation of
9 is harder than the first oxidation of (OEP)Zn by 30 mV
while the first reduction of 9 is easier by 80 mV than the first
reduction of (OEP)Zn. The exact potentials for each redox
processes of these compounds are given in the Table 1.
The gap between the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital
(LUMO) of (OEP)Zn is 2.27 V which compares to 2.22 V
in the case of 9. There is also a reversible third oxidation of 9
at E1/2 =1.39 V whose peak current is approximately half
that of the first two oxidations. This suggests half as many
electrons are abstracted at E1/2 = 1.39 V as compared to the
reactions at 0.65 or 0.94 V which involve the two linked macro-
cycles each undergoing a one electron transfer. The relative
peak currents are also consistent with a one-electron abstrac-
tion from the carbazole part of dyad which also occurs in the
case of the unlinked carbazoles 13-15 (Figure 3).
It is important to point out that no “splitting” of half wave
potentials is observed for the two oxidation peaks of 9 as
would be expected for electrode reactions involving two
equivalent and interacting redox centers.16 The electro-
chemical data thus clearly indicates that two non-interacting
redox centers are involved in the electron transfer processes
at 0.65 or 0.94 V. Under these conditions, each oxidation of 9
must involve an overlapping of two one-electron abstrac-
tions at the same potential, one at each Zn porphyrin unit to
give first a dyad with two linked porphyrin π cation radicals
and then, after the second oxidation, another dyad with two
linked porphyrin dications. The last electron transfer of 9 at
E1/2 = 1.39 V involves a one electron abstraction and must
occur at the carbazole bridge as described earlier in the
manuscript for unlinked carbazoles with similar structures to
those in the dyads.
Quite different electrochemical behavior is seen for the
tris-metal Zn dyad 12 which contains Cu(II) in the carbazole
bridge. Unlike the case of 9 which shows no interaction
between redox centers under the electrochemical solution
conditions, the first oxidation of 12 is split into two processes
of approximately equal height at E1/2 = 0.57 and 0.75 V,
consistent with an interaction between the two redox active
sites of the porphyrin in the tris-metal dyad. Thus, the pre-
sence of a Cu(II) ion in the carbazole bridge must contribute
to an enhanced π-π interaction between the two porphyrin
macrocycles, as is also suggested by the low temperature
ESR data described earlier in the manuscript for the same
tris-Cu dyad.
Figure 4. Cyclic voltammograms of (a) (OEP)Zn, (b) bis-metal Zn dyad
9, (c) tris-metal Zn dyad 12, and (d) diphenylcarbazole Cu(OAc) 14 in
CH2Cl2 containing 0.1 M TBAP.
described above for both 14 and 15. As will be demonstrated
later in the manuscript, the same Cu(II)/Cu(I) reactions
occur upon reduction of 10 and 12, all of which contain
Cu(II) bound to OAc- in the carbazole bridge.
Electrochemistry of Tris-Metal and Bis-Metal Dyads.
The electron transfer reactions of the investigated dyads can
occur at the conjugated π-ring system of the two porphyrin
macrocycles and at the electroactive carbazole bridge. The
exact site of electron transfer will depend upon the presence
or absence of Cu(II) in the carbazole bridge and can be
assigned, with some degree of certainty by comparing
oxidation and reduction potentials for the individual redox
active parts of the molecule when measured outside of the
dyad. An example of this is given in Figure 4, which com-
pares cyclic voltammograms of the dyads 9and 12 in CH2Cl2
with that of (OEP)Zn which is used as a monomeric por-
phyrin in place of (Et2Me6PhP)Zn and the unlinked Cu car-
bazole 14 under the same solution conditions. The measured
E1/2 values for the first oxidation and first reduction of OEP
and the Et4Me4PhP, Et2Me6PhP, or Et6Me2PhP derivatives
with a given central metal ion (Zn,4e Co,14 or Cu15) are
almost identical within experimental error in CH2Cl2. This
suggests a negligible substituent effect of the single phenyl
Additional oxidations beyond the initial split peaks
of 12 are ill-defined and located at Ep=1.14 and 1.36 V as
(16) (a) Guilard, R.; Barbe, J.-M.; Stern, C.; Kadish, K. M. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: San Diego, 2003; Vol. 18, pp 303-349; (b) Le Mest, Y.; L' Her, M.;
Saillard, J.-Y. Inorg. Chim. Acta 1996, 248, 181–191. (c) Le Mest, Y.; L'Her, M.;
Courtot-Coupez, J.; Collman, J. P.; Evitt, E. R.; Bencosme, C. S. J. Electroanal.
Chem. 1985, 184, 331–346. (d) Le Mest, Y.; L'Her, M.; Hendricks, N. H.; Kim,
K.; Collman, J. P. Inorg. Chem. 1992, 31, 835–847.
ꢀ
(14) (a) Kadish, K. M.; Fremond, L.; Shen, J.; Chen, P.; Ohkubo, K.;
Fukuzumi, S.; El Ojaimi, M.; Gros, C. P.; Barbe, J. M.; Guilard, R. Inorg.
Chem. 2009, 48, 2571–2582. (b) Zhu, W. H.; Zhao, X. F.; Ou, Z. P.; Zhou, F.; Wang,
X. H.; Kadish, K. M. J. Porphyrins Phthalocyanines 2009, 13, 1233–1242.
(15) Guilard, R.; Gros, C. P.; Barbe, J.-M.; Espinosa, E.; Jerome, F.;
Tabard, A.; Latour, J.-M.; Shao, J.; Ou, Z.; Kadish, K. M. Inorg. Chem.
2004, 43, 7441–7455.
ꢀ ^

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8935
Table 1. Half-Wave and Peak Potentials (V versus SCE) for Reduction of Zn Dyads and Related Carbazoles in CH2Cl2 Containing 0.1 M TBAX Where X = ClO4-, Cl-, or OAc-
bridge
porphyrin
2nd
anion of supporting electrolyte
compound
bis-metal Zn 9
tris-metal Cu-Zn 12
carbazole Cu 14 (OAc-)
carbazole Cu 15 (Cl-)
bis-metal Zn 9
tris-metal Cu-Zn 12
carbazole Cu 14 (OAc-)
bis-metal Zn 9
Cu (II)/Cu(I)
1st
4b (V)
-
ClO4
none
-1.57
-1.53
-1.00a
-1.05a
-0.55a
none
-1.67a
0.14
Cl-
-1.55a
-1.41
-1.70a
-1.60a
0.15
0.19
-0.60a
-0.68a
none
-0.90a
OAc-
-1.68a
-1.45
-1.75a
-1.72a
0.07
0.27
tris-metal Cu-Zn 12
-0.90a
-0.93a
carbazole Cu 15 (Cl-)
a Peak potential at a scan rate of 0.1 V/s. b 4 = potential difference between two reductions.
seen in Figure 4. These processes involve overlapping
macrocycle and bridge-centered oxidations.
Two other features should be pointed out as significant in
the cyclic voltammogram of 12. The first is the presence of a
broad reduction peak at Ep ≈ -1.00 V and the second a
“new” peak at Ep = -1.67 V, neither of which is observed in
cyclic voltammograms of (OEP)Zn or the bis-metal Zn dyad
9. Both of these “new” redox processes in 12 are associated
with the Cu(II)/Cu(I) reaction of the bridge, the first directly
and the second indirectly as described below.
The most obvious evidence for assigning the broad
redox process at Ep ≈ -1.00 V to a Cu(II) reduction in
the tris-metal Zn dyad 12 comes from comparison with
the unlinked copper carbazole 14 which is irreversibly
reduced at Ep = -1.05 V under the same experimental
conditions in CH2Cl2 (see Figure 3). Additional evidence
for the Cu(II)/Cu(I) reduction of 12 comes from spectro-
electrochemical data of the type shown in Figure 5 which
presents UV-vis spectra of the Cu carbazole 14 and the
tris-metal Zn dyad 12 as the reductions are carried out
under a controlled applied potential in PhCN.
As the first reduction of the carbazole 14 proceeds at an
applied potential of -1.20 V in PhCN, the band at 444 nm
decreases in intensity and shifts to 450 nm as two absorptions
grow up at 329 and 487 nm (Figure 5a). These changes are
associated with the conversion of Cu(II) to Cu(I), the only
reduction which occurs in compound 14 up to the negative
potential limit of the solvent. Similar spectral changes are
observed for reduction of the tris-metal Zn 12 (Figure 5b),
and this suggests the same copper-centered electrode reac-
tion in both compounds. Finally, when the controlled poten-
tial for reduction of 12 is switched from -1.20 to -1.70 V
(Figure 5c), the Soret band at 409 nm decreases substantially
in intensity while a broad and weak visible band appears
at 754 nm, indicating formation of a porphyrin π-anion
radical.17
Of some significance when comparing the cyclic voltammo-
grams of 9 and 14 in Figure 4 is the fact that the porphyrin
ring-centered reduction, which appears as a single process
Figure 5. UV-vis spectral changes for (a) diphenylcarbazole Cu 14
during controlled potential reduction at -1.20 V (see CV in inset), (b) tris-
metal Zn dyad 12 during reduction at the same potential (see CV on the
top of spectral changes) and (c) 12 during further reduction at -1.70 V in
PhCN containing 0.2 M TBAP.
at E1/2 = -1.57 V in 9, is split into two processes in 12, one
of which is located at E1/2 = -1.53 V and the other at Ep=
-1.67 V in CH2Cl2 containing 0.1 M TBAP. Because only
one porphyrin-centered reduction is observed for 9 under the
same solution conditions, the “extra” process of 12 could be
rationalized as resulting from two possibilities. The first one
is the interaction between two macrocycles and the second is
two different forms of the Zn(II) porphyrin in the tris-metal
dyad. The latter is proposed where one of two porphyrins in
(17) (a) Fuhrhop, J. H. Struct. Bonding (Berlin) 1974, 18, 1–67.
(b) Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138–163. (c) Perrin, M. H.;
Gouterman, M.; Perrin, C. L. J. Chem. Phys. 1969, 50, 4137–4151.

8936 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
Scheme 6. Reductions of Tris-Metal Zn Dyad 12 in CH2Cl2 Containing 0.1M TBAP
the dyad contains an uncoordinated Zn(II) center while the
second one contains Zn(II) with the axially coordinated
OAc- anion that is liberated from Cu(II) after electroreduc-
tion at the bridge part of the molecule. To clarify this point,
compounds 9 and 12 as well as (OEP)Zn were selected for
examining their anion binding properties with both OAc-
and Cl- added in the form of TBAX where X is the anion.
A summary of reduction potentials for the linked porphy-
rins 9, 12 with the unlinked bridges 14 and 15 in CH2Cl2
containing 0.1 M of different supporting electrolytes is given
in Table 1, and examples of the cyclic voltammograms under
these conditions are shown in Supporting Information,
Figures S4 and S5 for 9 and 12. As seen in Table 1, the poten-
tial difference between the two split reduction processes of 12
to give the porphyrin π anion radical range from 0.14 V in
CH2Cl2 containing 0.1 M TBA(ClO4) to 0.27 V in the same
solvent containing 0.1 M TBA(OAc) as supporting elec-
trolyte. Split reduction processes are also observed for 9 in
CH2Cl2 containing 0.1 M TBACl and TBA(OAc), and this
suggests two different axially coordinated forms of the linked
Figure 6. Cyclic voltammograms of (a) (Me2Et6PhP)Cu, (b) bis-metal
Cu dyad 11, and (c) tris-metal Cu dyad 10 in CH2Cl2 containing 0.1 M
TBAP. Data on the (Me2Et6PhP)Cu are taken form ref 15.
Zn porphyrin macrocycles, each of which has a different
reduction potential.
The proposed mechanism for reduction of the tris-metal
Zn dyad 12 in CH2Cl2 containing 0.1 M TBAP is shown in
Scheme 6, where the first reduction at -1.00 V (Figure 4c)
involves the Cu(II)/Cu(I) reaction of the carbazole bridge.
This scheme is similar to the one shown in Scheme 5 for the
unlinked carbazole but in the case of the porphyrin, the
OAc- ion which dissociates from CuII(OAc)- can then axi-
ally bind to one of the two Zn porphyrin centers, thus leading
to a negative shift in the measured E1/2 value for formation of
the porphyrin π anion radical.
A splitting of the redox process for the π-anion radical
formation of compound 12 is due to the binding of OAc-
by only one of the two metalloporphyrin centers and is
specific to the ZnII complexes since acetate does not
strongly bind to the CuII.
It is interesting to point out that while no interaction is
observed for the neutral singly oxidized or doubly oxidized
bis-Zn porphyrin dyad 9 (Figure 5b), this is not the case
for the bis-Cu porphyrin dyad 11 with the same macro-
cycle where both oxidations are split into two well-defined
processes, the first at E1/2=0.72 and 0.89 V and the second
at 1.15 and 1.26 V as seen in Figure 6b. This behavior is
quite different than that of (Me2Et6PhP)Cu which shows
well-defined one electron oxidation at 0.77 and 1.16 V
(Figure 6a).
The reason for the difference in electrochemical behavior
between the structurally related Zn dyad 9 and Cu dyad 11 is
unknown, but it should also be pointed out that the tris-metal
Cu dyad 10 also shows an interaction upon oxidation, and
this can only occur if a large structure rearrangement occurs
after the abstraction of one electron (see X-ray view of neutral
molecule of 10 in Supporting Information, Figure S2). Little
to no separation is seen for the second oxidation, which
occurs at E1/2 =1.18 V (Figure 6c) and maybe overlapped
with an oxidation of the carbazole bridge.
Effect of the Third Coordinated Metal on Ligand Bind-
ing Properties of Zn Dyads. The axial ligand binding
properties of monomeric Zn porphyrins have been well
studied in non-aqueous media.18 Only a five-coordinate
(18) (a) Kadish, K. M.; Van Caemelbecke, E.; Royal, G. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San
Diego, 2000; Vol. 8, pp 1-260; (b) Kadish, K. M.; Rhodes, R. K. Inorg. Chem.
1981, 20, 2961–2966. (c) Tabata, M.; Nishimoto, J. In The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000;
Vol. 9, pp 222-413.

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8937
Figure 8. UV-vis spectra of tris-metal Zn dyad 12 (∼10-6 M) in CH2Cl2
solutions containing 0.1 M TBAX where X = ClO4-, Cl-, or OAc-.
Figure 7. UV-vis spectral change of (a) 8.40ꢀ10-6 M bis-metal Zn
dyad 9 with 0-300 equiv of TBA(OAc) in CH2Cl2. (inset shows the Hill
plot) and (b) 7.60 ꢀ 10-6 M tris-metal Zn dyad 12 with 0-9000 equiv of
TBA(OAc) in CH2Cl2 (inset shows the Hill plot).
The spectral changes upon addition of OAc- to a CH2Cl2
solution of 12 (see Figure 7b) shows that the Soret band at
402 nm loses intensity but does not disappear as a second
Soret band at 418 nm at the end of the reaction. Both the 402
and 418 nm bands have approximately half the intensity of
the initial Soret band at 402 nm which might suggest that one
Zn porphyrin is not axially ligated. Similar spectral changes
were obtained in the reactions of 12 with Cl-, and the spectra
obtained as a function of increasing ligand concentration are
given in Supporting Information, Figure S7.
The unligated species also seems to be present in CH2Cl2
solution containing high concentrations of the ligand, thus
suggesting that one of the Zn centers remains four-coordi-
nate. As shown in Figure 8, a certain amount of the unbound
12 (402-403 nm) and bound (417-421 nm) are simulta-
neously present in CH2Cl2 with 0.1 M added Cl- or OAc-,
but no such spectral behavior is seen for 9 or (OEP)Zn under
the same solution conditions (see Supporting Informa-
tion, Figures S8 and S9). Moreover, the porphyrin-centered
reduction of 12 occurs via two separate processes in
CH2Cl2 containing Cl- or OAc- (see Supporting Informa-
tion, Figures S4 and S5) also suggesting a different degree of
axial ligand binding to each macrocycle under the electro-
chemical conditions.
The Hill plot in Figure 7b gives a slope of 1.0 with an
intercept of 3.0, implying the binding of an OAc- axial
ligand to one of two zinc centers of 12 with log K = 3.0.
The proposed mechanism for binding of Cl- or OAc- to
the Zn dyads 9 and 12 is presented in Scheme 7.
Table 2 summarizes binding constants of the bis-metal
and tris-metal Zn dyads with axial ligands. As compared
to the bis-metal dyad, the binding constants are obviously
smaller in the case of the tris-metal dyad. As mentioned
earlier, the presence of a third metal ion in the carbazole
complex is formed, and the same is expected for the dyads
where each ZnII center can bind at most one axial ligand.
In the present study, binding constants of Cl- and OAc-
with the Zn dyads 9 and 12 were measured in CH2Cl2, and
the progress of the reaction was followed by UV-visible
spectroscopy. An example of the spectral changes for 9 and
12 with successive additions of TBA(OAc) to the CH2Cl2
solution is shown in Figure 7. As seen in this figure, succes-
sive additions of OAc- to a CH2Cl2 solution of 9 leads to red
shift of the Soret band from 406 to 416 nm. There are also
multiple well-defined isosbestic points in the spectra. The
Soret bands at 406 and 416 nm correspond to the unligated
and ligated species, respectively. The changes in absorbance
at 416 nm were analyzed as a function of added OAc- con-
centration, and a diagnostic plot of log((Ai - A0)/(Af - Ai))
versus log[OAc-] gave a slope of 1.0 with a zero intercept of
4.0, indicating that one OAc- molecule is bound to each zinc
center of the dyad with a formation constant of 104.
As mentioned earlier in the manuscript, an interaction
between two redox centers of the macrocycle 9 is negligible
upon reduction and the two porphyrin units are reduced
independent of each other, like a monomer with double the
concentration. This being the use, one would expect each
zinc center to bind one OAc- with log K = 4.0.
In contrast to above, the binding of OAc- to 12, however,
is quite different than in the case of 9 or (OEP)Zn (see
Supporting Information, Figure S6). For this dyad, the
UV-visible spectrum in CH2Cl2 solution with excess acetate
exhibits bands at both 402 and 418 nm, suggesting that
OAc- is bound to only one of the two Zn centers of the dyad.

8938 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
Scheme 7. Binding Reaction of Zn Dyads with Ligands
Table 2. Binding Constants (log K) of Zn Dyads in CH2Cl2
PAR Model 173 potentiostat. Time-resolved UV-visible spectra
were recorded with a Hewlett-Packard Model 8453 diode array
spectrophotometer.
ligand
bis-metal dyad 9
tris-metal dyad 12
Cl-
2.2
4.0
1.6
3.0
Synthesis of 13,17-Diethyl-2,3,7,8,12,18-hexamethyl-5-p-
nitrophenylporphyrin 3. A solution of 1,19-dideoxy-8,12-di-
ethyl-2,3,7,13,17,18-hexamethylbiladien-a,c dibromide 1 (398 mg,
0.66 mmol) and 4-nitrobenzaldehyde 2(996 mg, 6.59 mmol) in 5 mL
of absolute ethanol was refluxed under nitrogen in a two-neck
round-bottom flask equipped with a condenser, a magnetic stirrer,
and shielded from light. To this mixture was added dropwise (1 h) a
solution of recrystallized p-toluenesulfonic acid (PTSA) (802 mg,
4.66 mmol) in 2 mL of absolute ethanol. After 3 days of reflux, the
reaction mixture was cooled to room temperature and extracted
with 100 mL of chloroform. The organic layer was then washed three
times with water, dried over magnesium sulfate and evaporated. The
solid residue was then chromatographed over silica gel and eluted
with chloroform. The first brown band was collected affording the
pure porphyrin 3 (173 mg, 46%). An analytically pure sample was
obtained by recrystallization from a chloroform/methanol solution.
UV-vis (CH2Cl2) 398 (log ε, 4.95), 501 (3.89), 533 (3.68), 569
(3.54), 622 (3.32) nm.1H NMR (300 MHz, CDCl3) δ (ppm): -3.31
(s, 1 H, inner NH); -3.22 (s, 1 H, inner NH); 1.88 (t, J=7.3 Hz, 6 H,
CH2CH3); 2.38 (s, 6 H, CH3); 3.52 (s, 6 H, CH3); 3.64 (s, 6 H, CH3);
4.03-4.11 (q, J=7.3 Hz, 4 H, CH2CH3); 8.20 (d, J=8.6 Hz, 2 H,
aryl-H); 8.57 (d, J=8.6 Hz, 2 H, aryl-H); 9.98 (s, 1 H, meso-15 H);
10.17 (s, 2 H, meso-10, meso-20 H). MS (MALDI-TOF): m/z=
572.07 [MþH]þ; 572.30 calcd for C36H38N5O2. HRMS (ESI) m/z=
572.3069 [MþH]þ; 572.3020 calcd for C36H38N5O2; m/z =
1143.6011 [2MþH]þ. 1143.5967 calcd for C72H75N10O4.
OAc-
bridge decreases the distance between the two macro-
cycles and enhances their interaction. As a result, the
binding ability of the Zn porphyrin with axial ligands is
weakened while the number of axial ligands is reduced.
Experimental Section
Materials. 1,19-Dideoxy-8,12-diethyl-2,3,7,13,17,18-hexa-
methylbiladien-a,c dibromide 1, 1,8-diformyl-3,6-di-tert-butyl-carba-
zole and 1,8-diphenylimino-3,6-di-tert-butylcarbazole were synthe-
sized according to previously reported procedures.8,9 Absolute
dichloromethane (CH2Cl2, Fluka Chemical Co.), pyridine (py,
99.8%, Aldrich Co), and 4,40-dipyridyl (dipy, 98%, Aldrich Co)
were used as received. Benzonitrile (PhCN) was purchased from
Aldrich Chemical Co. and distilled over P2O5 under vacuum prior
to use. Tetra-n-butylammonium perchlorate (TBAP), tetra-n-
butylammonium chloride (TBACl, 97%), and tetra-n-butylammo-
nium acetate ((TBA)OAc, 99%) were obtained from Fluka Chemical
Co. and dried under vacuum at 30 ꢀC for at least 1 week prior to use.
Instrumentation. 1H NMR spectra for synthesized com-
pounds were recorded on a Bruker DRX-300 AVANCE spectro-
ꢁ
meter at the “Plateforme d’Analyse Chimique et de Synthese
ꢀ
ꢀ
Moleculaire de l’Universite de Bourgogne (PACSMUB)”. Chemi-
cal shifts are expressed in parts per million (ppm) relative to
chloroform (7.26 ppm) or D5-pyridine (7.22, 7.58, and 8.74 ppm).
The mass spectra were obtained on a Bruker Daltonics Ultraflex II
spectrometer at the PACSMUB in the MALDI/TOF reflectron
mode using dithranol as a matrix. High resolution mass measure-
ments (HR-MS) were carried out in the same conditions as
previously (Bruker Daltonics Ultraflex II) using PEG ion series
as internal calibrant or on a Bruker Micro-ToF Q instrument in
ESI mode. The UV-visible spectra were recorded on a Varian
Cary 1 spectrophotometer. Cyclic voltammetry was carried out
with an EG&G Princeton Applied Research (PAR) 173 potentiostat/
galvanostat. A homemade three-electrode cell was used for cyclic
voltammetric measurements and consisted of a glassy carbon
working electrode, a platinum counter electrode, and a homemade
saturated calomel reference electrode (SCE). UV-visible spectro-
electrochemical experiments were performed with a home-built
thin-layer cell that had a light transparent platinum net working
electrode.19 Potentials were applied and monitored with an EG&G
Synthesis of 13,17-Diethyl-2,3,7,8,12,18-hexamethyl-5-p-amino-
phenylporphyrin 4. Nitrophenylporphyrin 3 (0.52 g, 0.90 mmol)
was dissolved in chloroform (15 mL), and a hydrochloric acid/
ether mixture (1 M, 35 mL) of tin(II) chloride dihydrate (3.22 g,
14.27 mmol) was added. The solution was stirred in the dark for 4 h.
The reaction mixture was poured onto ice (50 g) and when the ice
melted, chloroform (40 mL) was added. The organic layer was
washed with water (300 mL), sodium carbonate solution (10%,
200 mL), water (200 mL), and dried over magnesium sulfate. The
solvent was then removed, and the crude product was purified by
column chromatography over silica (dichloromethane/methanol;
100:5). The first red band was collected leading to aminophenyl-
porphyrin 4 (0.41 g, 84%) as a red microcrystalline solid. UV-vis
(CH2Cl2) 371sh (log ε, 4.89), 404 (5.35), 503 (4.26), 535 (3.80), 571
(3.80), 624 (3.32) nm. 1H NMR (300 MHz, CDCl3) δ (ppm): -3.26
(s, 2 H, inner NH); 1.88 (t, J = 7.5 Hz, 6 H, CH2CH3); 2.58 (s, 6 H,
CH3); 3.53 (s, 6 H, CH3); 3.64 (s, 6 H, CH3); 4.03-4.11 (q, J=7.5
Hz, 4 H, CH2CH3 overlapped with br s, 2 H, NH2); 7.05 (d, J=
8.3 Hz, 2 H, aryl H); 7.77 (d, J = 8.3 Hz, 2 H, aryl-H); 9.94 (s, 1 H,
1
(19) Lin, X. Q.; Kadish, K. M. Anal. Chem. 1985, 57, 1498–1501.
meso-15 H); 10.15 (s, 2 H, meso-10 and meso-20 H). H NMR

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8939
(300 MHz, D5-py) δ (ppm): -2.67 (s, 2 H, inner NH); 1.88 (t, 6 H,
J=7.5 Hz, CH2CH3); 2.66 (s, 6 H, CH3); 3.42 (s, 6 H, CH3); 3.48 (s,
6 H, CH3); 3.95 (q, 4 H, J=7.5 Hz, CH2CH3); 5.33 (s, 2 H, NH2);
7.24 (d, 2 H, J=7.7 Hz, aryl-H); 7.76 (d, 2 H, J = 7.7 Hz, aryl-H);
10.17 (s, 1 H, meso-15 H); 10.33 (s, 2 H, meso-10 and meso-20 H).
MS (MALDI-TOF) m/z = 542.04 [MþH]þ; 542.33 calcd for
C36H40N5. HRMS (ESI) m/z = 542.3269 [MþH]þ; 542.3278 calcd
for C36H40N5; m/z = 1083.6399 [2MþH]þ; 1083.6484 calcd for
C72H79N10.
(200 mg, 2.44 mmol) were dissolved in chloroform (50 mL) and
methanol (25 mL) and refluxed for 10 min. The solvent was re-
moved, and the crude product was purified by chromatography
over silica (dichloromethane/heptane, 70/30). The front running red
band was collected, and the solvent was removed to give bis-zinc(II)
bisporphyrin carbazole 9 (55 mg, 84%) as a red microcrystalline
solid. UV-vis (CH2Cl2): 333 (log ε, 4.89), 405 (5.87), 469sh (3.80),
535 (4.63), 571 (4.56), 740 (2.75) nm. 1H NMR (300 MHz, CDCl3)
δ (ppm): 1.65 (s, 18 H, t-butyl H); 1.83 (t, J = 7.8 Hz, 12 H,
CH2CH3); 2.59 (s, 12 H, CH3 (β3 and 7)); 2.87 (s, 12 H, CH3 (β12
and 18)); 3.38 (s, 12 H, CH3 (β2 and 8)); 3.93-4.01 (q, J=7.8 Hz,
8 H, CH2CH3); 7.96 (d, J = 8.0 Hz, 4 H, aryl-H); 8.18 (d, J = 8.0
Hz, 4 H, aryl-H); 8.02 (d, J= 1.4 Hz, 2 H, linker H); 8.47 (d, J=1.4
Hz, 2 H, linker H); 9.33 (s, 2 H, meso-15 H); 9.70 (s, 4 H, meso-10
and meso-20 H); 9.87 (2 H, s, -CHN-); 13.19 (1 H, s, linker NH).
MS (MALDI-TOF) m/z = 1505.7 [M]þ•, 1505.6 calcd for
C94H95N11Zn2. HRMS (ESI) m/z = 1506.6347 [MþH]þ,
1506.6428 calcd for C94H96N11Zn2; 1528.6261 [MþNa]þ,
1528.6247 calcd for C94H95N11NaZn2.
Synthesis of [1,8-Bis[130,170-diethyl-20,30,70,80,120,180-hexa-
methyl-50-p-iminophenyl porphyrinato)-copper(II)]-3,6-di-tert-
butyl-9H-carbazolide]-CuOAc 10. Bisporphyrin carbazole 8 (27
mg, 0.02 mmol), copper(II) acetate monohydrate (140 mg, 0.61
mmol) and sodium acetate (84 mg, 1.02 mmol) were dissolved in
chloroform (20 mL) and methanol (10 mL) and heated at reflux for
10 min. The reaction mixture was then diluted with dichloro-
methane (40 mL), washed with water (3 ꢀ 100 mL) and the solvent
was removed. Recrystallization of the obtained product from
dichloromethane/methanol solution affords the tris-copper(II) bis-
porphyrin carbazole 10 (30 mg, 98%) as a red microcrystalline
solid. UV-vis (CH2Cl2) 330 (log ε 4.59), 401 (5.64), 454sh (4.37),
528 (4.36), 564 (4.44) nm. MS (MALDI-TOF) m/z = 1565.4
[M-X]þ 1565.6 calcd for C94H94Cu3N11. HRMS (ESI) m/z =
1565.5568 [M-X]þ, 1565.5576 calcd for C94H94Cu3N11.
Synthesis of (13,17-Diethyl-2,3,7,8,12,18-hexamethyl-5-p-amino-
phenyl)-porphyrinato Zinc(II) 5. Aminophenylporphyrin 4 (19 mg,
0.035 mmol), zinc(II) acetate dihydrate (120 mg, 0.55 mmol), and
sodium acetate (90 mg, 1.10 mmol) were dissolved in chloroform
(20 mL) and methanol (10 mL) and refluxed for 1 h. The solvent
was removed, and the crude product was purified by chromato-
graphy over silica (dichloromethane). The front running red band
was collected and led to zinc(II) aminophenylporphyrin 5 (18 mg,
85%) as a red microcrystalline solid. UV-vis (CH2Cl2) 333 (log ε,
4.33), 385sh (4.70), 406 (5.50), 500sh (3.47), 535 (4.20), 571 (4.13)
nm. 1H NMR (300 MHz, CDCl3) δ(ppm):1.84 (t, J = 7.3 Hz, 6 H,
CH2CH3); 2.49 (s, 6 H, CH3); 3.50 (s, 6 H, CH3); 3.57 (s, 6 H, CH3);
3.97-4.05 (q, J = 7.3 Hz, 4 H, CH2CH3 overlapped with br s,
2 H, NH2); 6.81 (d, J=8.2 Hz, 2 H, aryl-H); 7.67 (d, J=8.2 Hz,
2 H, aryl-H); 9.86 (s, 1 H, meso-15 H); 10.02 (s, 2 H, meso-10,
meso-20 H). MS (MALDI-TOF) m/z = 603.1 [M]þ• 603.2
calcd for C36H37N5Zn. HRMS (ESI) m/z = 603.2326 [M]þ•
,
603.2335 calcd for C36H37N5Zn; 626.2221 [MþNa]þ, 626.2233
calcd for C36H37N5NaZn; 1206.4604 [2M]þ, 1206.4675 calcd for
C72H74N10Zn2.
Synthesis of (13,17-Diethyl-2,3,7,8,12,18-hexamethyl-5-p-amino-
phenyl)-porphyrinato Copper(II) 6. Aminophenylporphyrin 4
(24 mg, 0.04 mmol), copper(II) acetate monohydrate (124 mg,
0.62 mmol), and sodium acetate (130 mg, 1.58 mmol) were dis-
solved in chloroform (20 mL) and methanol (10 mL) and refluxed
for 1 h. The solvent was removed, and the crude product was
purified by chromatography over silica (dichloromethane). The
front running red band was collected containing the copper(II)
aminophenylporphyrin 6 (25 mg, 93%) as a red microcrystalline
solid. UV-vis (CH2Cl2) 329 (log ε, 4.15), 382sh (4.60), 402 (5.44),
487sh (3.36), 528 (4.08), 564 (4.18) nm. MS (MALDI-TOF) m/z =
602.0 [M]þ•, 602.2 calcd for C36H37CuN5. HRMS (ESI) m/z =
602.2334 [M]þ•, 602.2340 calcd for C36H37CuN5; 1204.4628 [2M]þ,
1204.4685 calcd for C72H74Cu2N10.
Synthesis of 1,8-Bis(130,170-diethyl-20,30,70,80,120,180-hexam-
ethyl-50-p-iminophenyl porphyrinyl)-3,6-di-tert-butyl-9H-carba-
zole 8. Aminophenylporphyrin 4 (0.43 g, 0.79 mmol) and 1,8-
diformyl-3,6-di-tert-butyl-9H-carbazole 7 (0.13 g, 0.39 mmol) were
dissolved in degassed pyridine (125 mL), and the mixture was
refluxed for 3 days. Then the solvent was removed, and the mixture
was purified by column chromatography over silica gel (dichloro-
methane/methanol, 100/5). The main collected fraction afforded
the bisporphyrin carbazole 8 (230.0 mg, 85%) as a brown micro-
crystalline solid. 1H NMR (300 MHz, D5-py) δ (ppm): -2.66 (br s,
4 H, inner NH); 1.35 (s, 18 H, t-butyl H); 1.74 (t, J = 7.0 Hz, 12 H,
CH2CH3); 2.67 (s, 12 H, CH3); 3.42 (s, 12 H, CH3); 3.48 (s, 12 H,
CH3); 3.95 (q, J = 7.0 Hz, 8 H, CH2CH3); 7.24 (d, J = 7.8 Hz, 4 H,
aryl-H); 7.77 (d, J = 7.8 Hz, 4 H, aryl-H); 8.01 (d, J = 1.4 Hz, 2 H,
linker H); 8.75 (d, J=1.9 Hz, 2 H, linker H); 10.17 (s, 2 H, CH=N);
10.28 (s, 2 H, meso-15 H) ; 10.33 (s, 4 H, meso-10 and meso-20 H);
11.91 (br s, 1 H, linker NH). UV-vis (CH2Cl2) 332sh (log ε, 4.61),
404 (5.43), 502 (4.35), 537 (4.00), 571 (3.99), 625 (3.52) nm. MS
(MALDI-TOF) m/z = 1382.78 [MþH]þ, 1382.82 calcd for
C94H100N11. HRMS (ESI) m/z = 1382.8099 [MþH]þ, 1382.8158
calcd for C94H100N11; 1404.7929 [MþNa]þ, 1404.7977 calcd for
C94H99N11Na.
Synthesis of 1,8-Bis[130,170-diethyl-20,30,70,80,120,180-hexa-
methyl-50-p-iminophenyl porphyrinato)-copper(II)]-3,6-di-tert-
butyl-9H-carbazole 11. A mixture of copper(II) aminophenyl-
porphyrin 6 (50 mg, 0.08 mmol) and carbazole 7 (14 mg, 0.04
mmol) were refluxed in 20 mL for 3 days and then evaporated
under vacuum. The residue was then chromatographed over
silica gel and eluted with dichloromethane. The first eluting
band afforded the bis-copper bisporphyrin carbazole 11 (60 mg,
97%) as a pure solid. UV-vis (CH2Cl2) 401 (log ε 5.12), 537
(3.81), 563 (4.01) nm. HRMS (MALDI/TOF) m/z = 1503.6324
[M-X]þ, 1503.6358 calcd for C94H95Cu2N11.
Synthesis of 1,8-Bis[130,170-diethyl-20,30,70,80,120,180-hexa-
methyl-50-p-imino-phenylporphyrinato)-zinc(II)]-3,6-di-tert-butyl-
9H-carbazolide-CuOAc 12. To a solution of bis-zinc(II) bispor-
phyrin carbazole 9 (137 mg, 0.09 mmol) in 1,2-dichloroethane (50
mL) were added copper(II) acetate hydrate (365 mg, 1.83 mmol)
and sodium acetate (303 mg, 3.69 mmol) in methanol (25 mL).
After 2 h refluxing, the reaction mixture was extracted with 50 mL
of dichloromethane. The organic layer was then washed with water
(3 ꢀ 100 mL), dried over MgSO4 and evaporated. The solid residue
was then taken with dichloromethane and precipitated with
heptane giving copper(II) bis-zinc(II) bisporphyrin carbazole 12
(91 mg, 64%). UV-vis (CH2Cl2) 402 (log ε, 5.58), 532 (4.25), 567
(4.25) nm. MS (MALDI-TOF) m/z = 1567.36 [M-X]þ, 1567.56
calcd for C94H94CuN11Zn2. HRMS (ESI) m/z = 1567.5503
[M-X]þ, 1567.5567 calcd for C94H94CuN11Zn2.
Synthesis of (1,8-Diphenylimino-3,6-di-tert-butylcarbazolide)-
copper(II) Acetate 14. An analytical sample of 14 was synthe-
sized from 1 equiv of 1,8-diphenylimino-3,6-di-tert-butylcarba-
zole dissolved in chloroform, by addition of a methanol solution
of 10 equiv of copper(II) acetate hydrate and 20 equiv of anhy-
drous sodium acetate. The mixture was refluxed for 45 min,
extracted with dichloromethane, washed with water, dried
over MgSO4. After evaporation the resulting solid was crystal-
lized from a dichloromethane/pentane mixture leading almost
Synthesis of 1,8-Bis[130,170-diethyl-20,30,70,80,120,180-hexam-
ethyl-50-p-imino-phenylporphyrinato)-zinc(II)]-3,6-di-tert-butyl-
9H-carbazole 9. Bisporphyrin carbazole 8 (60 mg, 0.01 mmol),
zinc(II) acetate dihydrate (300 mg, 1.37 mmol) and sodium acetate

8940 Inorganic Chemistry, Vol. 49, No. 19, 2010
Barbe et al.
quantitatively to 14. UV-vis (CH2Cl2) 438 (log ε, 4.54) nm.
MS (MALDI-TOF) m/z = 546.946 [M-OAc]þ, 547.204 calcd
for C34H34CuN3.
In most, but not all cases, the tris-metal dyads show a splitting
of the first oxidation and first reduction. The binding constants
of the Zn compounds with OAc- and Cl- ligands are
evaluated. In addition, it is seen that the carbazole bridge Cu
ion of the tris-metal dyads enhances the π-π (ring-ring)
interaction between the two porphyrin units as compared to
the case of the bis-metal dyads.
Synthesis of (1,8-Diphenylimino-3,6-di-tert-butylcarbazolide)-
copper(II) Chloride 15. An analytical sample of 15 was obtained
by dissolving 11 mg (17 μmol) in 5 mL of CH2Cl2. To this
solution were added 10 mL of a saturated solution of NaCl
in water. The resulting mixture was stirred for 3 h. The
organic layer was then isolated and evaporated to afford 15
(10 mg, 99%). UV-vis (CH2Cl2) 445 (log ε, 4.15) nm. MS
(MALDI-TOF) m/z = 546.897 [M-Cl]þ, 547.204 calcd for
C34H34CuN3.
Acknowledgment. The Burgundy Council is acknow-
ledged for postdoctoral fellowship to T. Khoury, the Centre
National de Recherche Scientifique (CNRS; UMR 5260),
and the Robert A. Welch Foundation (K.M.K., Grant
E-680) for research funding. The Centre National de Re-
cherche Scientifique (CNRS) is also acknowledged for
Ph.D. support grant for B.H. The authors thank Dr. S.
Conclusion
In conclusion, the straightforward, scalable (in grams)
synthesis of a new dimer porphyrin 8 is described, which is
used to prepare in high yield new bis- and tris-metalated
dimers that represent good candidates for catalysis, energy
transfer, electrochemistry, and other physical studies. It is
also possible to incorporate other metals into both the
porphyrin core and the bridge. Moreover, the same synthetic
route can be used with other amino porphyrins or amino
corroles as well as other bridges such as 1,8-diformyl-dibenzo-
furan, for example. Dimeric species can also be obtained
under these conditions.
The synthesized bis-metal and tris-metal dyads were electro-
chemically and spectroscopically characterized in several non-
aqueous solvents, and their redox behavior is compared to that
of the unlinked carbazoles and unlinked porphyrins, after
which mechanisms and electron transfer sites are proposed.
ꢁ
Brandes for recording ESR spectra.
Supporting Information Available: One figure (Figure S1) and
one Table (Table S1) of HRMS-ESI mass spectral data and ESR
parameters of Cu compounds respectively, table of half-wave
and peak potentials in PhCN and pyridine (Table S2), two
figures showing views of X-ray structure for the chloro deriva-
tive of 10 (Figures S2 and S3), two figures showing cyclic
voltammograms of 9 and 12 in CH2Cl2 containing 0.1 M TBACl
or TBA(OAc) (Figures S4 and S5) and four figures showing
UV-visible spectra of the Zn compounds under different solu-
1
tion conditions (Figures S6 to S9). Figure S10 presents the H
NMR spectra of the free-base and zinc porphyrin derivatives
and Figure S11 gives cyclic voltammograms of the copper dyads
in pyridine. This material is available free of charge via the
Internet at http://pubs.acs.org.