Synthesis of New Porphyrins with Peripheral Conjugated Chelates and Their Use for the Preparation of Porphyrin Dimers Linked by Metal Ions

Article abstract of DOI:10.1021/ic035203d

This article describes the preparation of several new porphyrins bearing chelating peripheral groups fully conjugated with the macrocyclic π-system. Treatment of a 2-nitro-meso-tetraarylporphydn with phosphite gave a cyclic enamine, whose formylation gave an enaminoaldehyde. The thio analogue was obtained on treatment with Lawesson's reagent. The same reagent was also used to obtain the isomeric thioenaminoketone chelates. A enaminoketone ligand was prepared from a porphyrinic pyrrolone. All these ligands, as internal nickel complexes, could be metalated with palladium to yield porphyrinic dimers. The dimers obtained from enaminoketones and thioketones show a trans geometry, while in the enaminoaldehyde and -thioaldehyde series the cis isomer is thermodynamically favored. The bathochromic shifts of the electronic spectra of the aldehyde-derived dimers illustrate the strong electronic effect of peripheral metalation and dimerization. However, in the case of the pyrrolone-derived ligand, opposite effects were observed, due to partial reconstitution of the porphyrin chromophore on complexation. As with the dimers derived from enaminoketones, the dimers derived from the new ligands show typical splitting (up to 190 mV) of the electrochemical waves confirming large porphyrin-porphyrin interactions.

Full text of DOI:10.1021/ic035203d

Inorg. Chem. 2004, 43, 251−263
Synthesis of New Porphyrins with Peripheral Conjugated Chelates and
Their Use for the Preparation of Porphyrin Dimers Linked by Metal Ions
Se´bastien Richeter,† Christophe Jeandon,† Jean-Paul Gisselbrecht,‡ Roland Graff,§
,†
,†
Romain Ruppert,* and Henry J. Callot*
Laboratoire de Chimie des Porphyrines, UMR 7123 CNRS, Faculte´ de Chimie,
UniVersite´ Louis Pasteur, 1 rue Blaise Pascal, 67000 Strasbourg, France,
Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UMR 7512 CNRS,
UniVersite´ Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg, France, and
SerVice Commun de RMN, Faculte´ de Chimie, UniVersite´ Louis Pasteur,
1 rue Blaise Pascal, 67000 Strasbourg, France
Received October 20, 2003
This article describes the preparation of several new porphyrins bearing chelating peripheral groups fully conjugated
with the macrocyclic π-system. Treatment of a 2-nitro-meso-tetraarylporphyrin with phosphite gave a cyclic enamine,
whose formylation gave an enaminoaldehyde. The thio analogue was obtained on treatment with Lawesson’s
reagent. The same reagent was also used to obtain the isomeric thioenaminoketone chelates. A enaminoketone
ligand was prepared from a porphyrinic pyrrolone. All these ligands, as internal nickel complexes, could be metalated
with palladium to yield porphyrinic dimers. The dimers obtained from enaminoketones and thioketones show a
trans geometry, while in the enaminoaldehyde and -thioaldehyde series the cis isomer is thermodynamically favored.
The bathochromic shifts of the electronic spectra of the aldehyde-derived dimers illustrate the strong electronic
effect of peripheral metalation and dimerization. However, in the case of the pyrrolone-derived ligand, opposite
effects were observed, due to partial reconstitution of the porphyrin chromophore on complexation. As with the
dimers derived from enaminoketones, the dimers derived from the new ligands show typical splitting (up to 190
mV) of the electrochemical waves confirming large porphyrin−porphyrin interactions.
Introduction
with covalent linkages between the individual components.3-5
However, due to the sometimes very tedious syntheses,
noncovalent linkages (coordination bonds, hydrogen bonds,
etc.) have also been realized.6,7 These types of linkages made
generally use of meso-heteroaryl or aryl groups of synthetic
Porphyrins bearing external coordination sites conjugated
to the macrocycle π-system are developed in our group in
order to build oligomers. The research field of conjugated
oligomers is in constant expansion due to the promise offered
by these new molecular materials in many applications
(electronic or photonic devices). Oligomers containing
heterocycles (thiophene, pyrrole, etc.) have been widely
studied.1 More recently, porphyrin oligomers have also been
prepared to obtain materials for optical, electronic or
magnetic applications.2 These oligomers were mainly built
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1999, 1771. (b) Anderson, H. L. Chem. Commun. 1999, 2323.
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P. G.; Reid, D. C. W. Chem. ReV. 2001, 101, 2751. Selected recent
references on oligomers showing little porphyrin-porphyrin interac-
tions (for earlier references, see also articles cited in ref 9 in this
article): Yoshida, N.; Ishizuka, T.; Osuka, A.; Jeong, D. H.; Cho, H.
S.; Kim, D.; Matsuzaki, Y.; Nogami, A.; Tanaka, K. Chem.sEur. J.
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Hirakawa, K.; Wu, F. Chem. Commun. 2002, 3032. Nakano, A.;
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* Corresponding author. E-mail: callot@chimie.u-strasbg.fr (H.J.C.).
† Laboratoire de Chimie des Porphyrines, UMR 7123 CNRS, Faculte´
de Chimie, Universite´ Louis Pasteur.
‡ Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide,
UMR 7512 CNRS, Universite´ Louis Pasteur.
§ Service Commun de RMN, Faculte´ de Chimie, Universite´ Louis Pasteur.
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Chem., Int. Ed. 1998, 37, 402. (d) Martin, R. E.; Diederich, F. Angew.
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10.1021/ic035203d CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/05/2003
Inorganic Chemistry, Vol. 43, No. 1, 2004 251

Richeter et al.
porphyrins. These starting materials are easily accessible
using the highly versatile Adler or Lindsey condensations
of pyrrole and aromatic aldehydes. As a consequence, due
to the noncoplanarity of the porphyrin and the meso-aryl
groups, the interactions between individual components of
the oligomers are very weak. By using chelating coordination
sites positioned at the periphery of the porphyrin macrocycle,
one might expect that linkages through coordination bonds
to be more efficient in terms of interactions between
individual porphyrins or other related macrocycles.8
We demonstrated9 that such interactions can be observed
by using porphyrins bearing enaminoketones fully conjugated
with the aromatic ring. The synthetic route was based on
the initial preparation of a cyclic ketone 1 and the subsequent
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addition of various nitrogen nucleophiles at the â-pyrrolic
position of this conjugated system10 resulting in the formation
of the enaminoketone moiety like in 2. Metal ions coordina-
tion resulted in the formation of metalated monomers 3 and
dimers 4. Higher oligomers were later obtained from
porphyrins bearing two enaminoketone chelates.11
We aimed at increasing the number of available ligands
in order to (a) improve the stability of the metal to ligand
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Michel, S. L. J.; Hoffman, B. M.; Baum, S. M.; Barrett, A. G. M.
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252 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
Scheme 1. Possible Synthetic Routes to Enamine 5
bonds, (b) modify the geometry of the chelating group, i.e.,
to change the steric interactions between the vicinal meso
aryl group and the chelated metal + porphyrin moiety and
(c) modulate the electronic properties of the metal linked
porphyrin dimers.
In this article,12 we describe how the first requirement was
fulfilled by replacing in A oxygen by sulfur, which was
a N-containing six-membered ring fused to the meso-
tetraarylporphyrin macrocycle, we thought of reacting either
a â-nitroporphyrin with a meso-aryl group or a porphyrin
bearing a meso-o-nitroaryl group with trialkyl phosphite (see
Scheme 1). Both reactions should give the same cyclic
enamine 5. The next steps would take advantage of the
reactivity of enamines to introduce a substituent at the
pyrrolic position adjacent to the new ring. Extension of this
reaction to substrates bearing several nitro groups could in
turn give porphyrins bearing several external coordination
sites.
The route starting with a meso-o-nitroaryl substituent was
tested first. A mixture of meso-o-nitrophenylporphyrins was
easily prepared from o-nitrobenzaldehyde, 3,5-di-tert-butyl-
benzaldehyde and pyrrole under Adler’s or Lindsey’s condi-
tions.14 The products were separated by chromatography, and
the mono(o-nitrophenyl)porphyrin base was selected for the
next step and reacted with triethyl phosphite at 155 °C.
Although almost total conversion was obtained, the product
proved to be a complex mixture and this route was
abandoned in favor of that starting with â-nitroporphyrins.
The starting material, nickel 2-nitroTPP (TPP ) meso-
tetraphenylporphyrin) was prepared in high yield (90-95%)
by nitration of NiTPP (Scheme 2) or, better, of the more
soluble CuTPP, with lithium nitrate in CHCl3/Ac2O/AcOH,
followed by a demetalation-metalation sequence. These mild
and inexpensive reaction conditions were inspired by the
earliest nitration method for porphyrins15 and avoid the use
of dinitrogen tetroxide.16 When nickel 2-nitroTPP was reacted
with excess triethyl phosphite at 155 °C in 1,2-dichloroben-
zene, green enamine 5 was obtained as the major product
(75%).
expected to strengthen the metal ligand bonds, in particular
when second or third row late transition metals are con-
cerned. This substitution would also result in longer metal
porphyrin distances and thus reduce the steric interactions
caused by meso-aryl groups and this was indeed observed.
We also describe the synthesis of two new porphyrin series
bearing enaminocarbonyl moieties: an enaminoketoporphy-
rin B derived from an isomeric naphthoporphyrin, as well
as an enaminoaldehyde C and the corresponding enami-
nothioaldehyde which were expected to show significant
differences in steric hindrance around the chelating site. To
our surprise, these seemingly minor modifications resulted
in (a) a change in stereochemistry of the dimeric species
from trans to cis in the case of enaminoaldehydes and (b) a
hypsochromic shift of the visible absorption of metalated
monomeric and dimeric species derived from the isomeric
enaminoketone, in contrast to the effect of previously known
metalation reactions.
The proposed structure of enamine 5 was confirmed by
its NMR and crystal data (Figure 1). The N-H signal was
found as a broad singlet at 9.2 ppm and the adjacent pyrrolic
proton shifted upfield to 8.01 ppm. In addition, the four
protons of the cyclized phenyl were differentiated and the
aromatic proton close to the adjacent pyrrole ring shifted
downfield to 8.91 ppm. Cyclization led to a downfield shift
Results and Discussion
1. Synthesis of the Enaminoaldehyde Ligand. The
reaction of nitro compounds with trialkyl phosphites is a very
efficient route to nitrogen heterocycles.13 In the hope to form
(13) Cadogan, J. I. G. Q. ReV. 1968, 22, 222.
(14) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827. Littler, B. J.;
Ciringh, Y.; Lindsey, J. S. J. Org. Chem. 1999, 64, 2864. Lindsey, J.
S. In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard,
R., Eds.; Academic Press: Boston, MA, 2000; Vol. 1, p 45.
(15) Giraudeau, A.; Callot, H. J.; Jordan, J.; Ezahr, I.; Gross, M. J. Am.
Chem. Soc. 1979, 101, 3857. Johnson, A. W.; Oldfield, D. J. Chem.
Soc. 1965, 4303.
(11) (a) Richeter, S.; Jeandon, C.; Ruppert, R.; Callot, H. J. Chem. Commun.
2002, 266. (b) Richeter, S.; Jeandon, C.; Sauber, C.; Gisselbrecht, J.-
P.; Ruppert, R.; Callot, H. J. J. Porphyrins Phthalocyanines 2002, 6,
423.
(12) Selected results were presented at the 2nd International Conference
on Porphyrins and Phthalocyanines (ICPP2), Kyoto (Japan), June 30-
July 5, 2002.
(16) Catalano, M. M.; Crossley, M. J.; Harding, M. M.; King, L. G. J.
Chem. Soc. Chem. Commun. 1984, 1535.
Inorganic Chemistry, Vol. 43, No. 1, 2004 253

Richeter et al.
Scheme 2. General Synthetic Route to Enaminoporphyrins
Scheme 3. Formylation of Enamine 5, 6, and 7
Figure 1. X-ray structure of enamine 5 (top and side view: meso-phenyl
omitted for clarity).
8 showed typical NMR signals for the aldehyde group
(singlet at 9.09 ppm) and a broad N-H singlet shifted to
12.5 ppm, due to H bonding.
of the two protons of the pyrrole adjacent to the cyclized
phenyl. The nickel(II) cation was found in an almost perfect
square planar environment. The four Ni-N distances are
similar (1.902, 1.915, 1.913, and 1.93 Å), the four N-Ni-N
angles were close to 90° (89.8, 90.6, 90.2, and 89.4°) and
the deviation from the plane of each nitrogen atom is less
than 2°. The porphyrin itself is far from being planar. The
geometry of the aromatic core is best described as ruffled,
the angles C5-Ni-C15 and C10-Ni-C20 being both close
to 160°. The cyclized meso-phenyl group, the additional six-
membered ring and the adjacent pyrrole are in contrast almost
coplanar (less than 5° deviation from planarity between the
three rings).
The structure of enaminoaldehyde 8 was confirmed by an
X-ray study. The porphyrin geometry is very similar to the
one found for enamine 5. The meso-phenyl group, the
additional six-membered ring, the adjacent pyrrole, and the
aldehyde group are almost coplanar. In the case of the
aldehyde, this is probably due to the intramolecular hydrogen
bond formed between the carbonyl oxygen atom and the
enamine N-H (dCO-HN ) 2.15 Å). Conjugation of the
aldehyde group with the enamine functionality (vinylogous
of a formamide) is also reflected in the shortening of the
C-N bond and lengthening of the pyrrolic C-C bond
compared to the same bonds in the enamine. This is also
reflected in the electronic properties: whereas the addition
of a carbonyl function to a chromophore should lead to a
bathochromic shift, we observed a slight decrease of the
longest wavelength (from 630 nm for enamine 5 to 626 nm
for enaminoaldehyde 8).
At this stage, it is of importance to stress the fact that the
reactivity of nucleophilic enamine 5 opens a general route
to 1,2-substituted porphyrins which is complementary to that
starting from electrophilic 2-nitroporphyrins developed earlier
by other groups.17 (Scheme 2).
Under Vilsmeier-Haack conditions (DMF + POCl3 in
dichloromethane) the formylation of enamine 5 proceeded
smoothly at 20 °C to give enaminoaldehyde 8 in 90% yield
(Scheme 3). The reaction conditions had to be carefully
adjusted, since the conditions first used (2-8 equiv; 45 °C)
led to complex mixtures along with starting material. On
the contrary, a large excess of reagent (100 equiv; dichlo-
romethane at room temperature) and very short reaction times
yielded the enaminoaldehyde in 90% yield. Enaminoaldehyde
2. Thionation of Porphyrins Bearing Enaminoketone
and Enaminoaldehyde Groups. The reagent of choice for
the conversion of a carbonyl into a thiocarbonyl group is
Lawesson’s reagent (2,4-bis(4-methoxyphenyl)-1,3-dithia-
2,4-diphosphetane-2,4-disulfide).18 Since thioamides are
notably more stable than the corresponding thioketones, we
expected the thio analogues of enaminoketones and -alde-
hydes to be stable enough to be isolated and characterized
prior to be complexed by metal ions. This proved to be true,
(17) Crossley, M. J.; King, L. G. J. Org. Chem. 1993, 58, 4370. Crossley
M. J.; Harding, M. M.; Tansey, C. W. J. Org. Chem. 1994, 59, 4433.
For a review, see: Jaquinod, L. In The Porphyrin Handbook; Kadish,
K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: Boston, MA,
2000; Vol. 1, p 201.
(18) Lawesson, S. O.; Shabana, R.; Rasmussen, J. B. Tetrahedron 1980,
36, 3047. Pradere, J.-P.; N’Guessan, Y. T.; Quiniou, H. Tetrahedron
1975, 31, 3059. Walter, W.; Proll, T. Synthesis 1979, 12, 941. For a
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254 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
5). While nickel ketone 15 showed exceptionally high
absorbance at low energy (λ ) 720 nm, ꢀ ) 17 000), the
amination led to a large hypsochromic shift of the lowest
energy band to 678 nm (see detailed discussion of the
electronic spectra of ligands and metal complexes below).
In the case of enaminoketones 17 and 18, we were unable
to prepare the corresponding thioderivatives. Reaction of
enaminoketones 17 and 18 with Lawesson’s reagent led to
complex mixtures of products, most of them still containing
phosphorus (originating from the reagent).
4. Preparation of Acetylacetonatopalladium Derivatives
and Porphyrin Dimers. We have observed that, although
they can be characterized, dimers of porphyrin enaminoke-
tones connected with nickel ion are of moderate stability and
will decompose under attempted chromatography or in dilute
solution.9 In the case of the thio derivatives (thioenaminoke-
tones or -aldehydes), the dimers connected with first row
transition metal ions were found to be by far more stable.
However, to ensure that comparisons could be made between
pairs of stable and well characterized dimers, we chose to
restrain this study to dimers of nickel porphyrins linked by
palladium ions (Scheme 6). The nickel(II) ion in porphyrins
usually does not coordinate axial ligands and remains in a
square planar geometry as does palladium(II) with chelates
like enaminoketones.
Figure 2. X-ray structure of enaminoaldehyde 8 (top and side view: meso-
phenyl omitted for the seek of clarity).
Scheme 4. Thionation of Enaminoaldehyde 8 and Enaminoketone 2
In the already studied dimers 4 of enaminoketone 2, the
square planar complexes were found as trans isomers in all
cases.9b It is known, since the initial publications of Chatt
and Wilkins,21 that the cis-trans isomerism is governed by
different factors: electrostatic interactions, steric effects,
difference in bond energies, and solvation. Modification of
the external chelate, in a geometric or electronic way, might
therefore modify the geometry around the connecting metal
ion and as a consequence the extent of the interaction
between the two connected porphyrins. The replacement of
the oxygen atom by the softer sulfur atom in the chelate
should, for example, favor the cis isomer.22
and the treatment of enaminoketone 2 and enaminoaldehyde
8 (both as nickel complexes) with Lawesson’s reagent
(Scheme 4) under standard conditions (refluxing benzene)
gave thioenaminoketone 12 and thioenaminoaldehyde 11 in
97 and 78% yield, respectively.
The reaction of thioenaminoketone 12 with palladium(II)
bis(acetylacetonate) (Pd(acac)2) led quantitatively to a single
compound identified as the trans isomer 19 (analogue of
dimer 4) by 1H-1H COSY and ROESY NMR experiments.
The cis isomer has a plane of symmetry and the trans isomer
a center of symmetry: as a consequence NOE correlations
between protons belonging to different porphyrins can be
observed only in the case of the trans isomer. We were unable
to isolate the externally metalated porphyrin monomer.
Because of the presence of the soft sulfur atom, which should
destabilize the remaining acac ligand as soon as the first
porphyrin is coordinated, even the use of a large excess of
Pd(acac)2 led almost quantitatively to the porphyrin dimer.
The reaction of enaminoketones 17 or 18 with excess Pd-
(acac)2 led as excepted to the metalated porphyrin monomers
20 or 21 and to palladium(II)-connected dimers 22 or 23
Both 11 and 12 are stable enough to be chromatographed
and fully characterized. Their NMR data are similar to that
of the starting materials, differing mainly for the aldehyde
signal (10.37 ppm for 11, to be compared with 9.09 ppm
for 8) and the N-H signal (15.4 ppm for 11, to be compared
with 12.5 ppm for 8). Replacement of oxygen by sulfur led
also to a significant bathochromic shift of the lowest energy
band, respectively 43 or 24 nm for the enaminothioketone
or -aldehyde vs the starting enaminoketone or -aldehyde.
3. Isomeric Enaminoketones 17 and 18. The starting
materials, nickel ketones 15 (and 16), were obtained from
the porphyrin free bases (prepared from aldehydes 13 and
14 according to the procedure described by Ishkov19) after
metalation with nickel acetylacetonate. Treatment of the
resulting nickel complexes with 4-amino-4H-1,2,4-triazole20
gave the required ligands in 61% (and 83%) yield (Scheme
(19) Ishkov, Y. V. Russ. J. Org. Chem. 2001, 37, 288.
(20) (a) Bakke, J. M.; Svensen, H.; Trevisan, R. J. Chem. Soc., Perkin
Trans. 1 2001, 376. (b) Katritzky, A. R.; Laurenzo, K. S. J. Org. Chem.
1986, 51, 5039. (c) Katritzky, A. R.; Laurenzo, K. S. J. Org. Chem.
1988, 53, 3978.
(21) Chatt, J.; Wilkins, R. G. J. Chem. Soc. 1952, 273 and 4300. Harvey,
J. N.; Heslop, K. M.; Orpen, A. G.; Pringle, P. G. Chem. Commun.
2003, 278. Anderson, K. M.; Orpen, A. G. Chem. Commun. 2001,
2682.
(22) Pearson, R. G. Inorg. Chem. 1973, 12, 712.
Inorganic Chemistry, Vol. 43, No. 1, 2004 255

Richeter et al.
Scheme 5. Preparation of Enaminoketones 17 and 18
Scheme 6. Preparation of Palladium(II)-Linked Enaminothione Dimer 19
Scheme 7. Preparation of Metalated Porphyrin Monomers 20 and 21 and Palladium-Linked Dimers 22 and 23 from Enaminoketones 17 and 18
(Scheme 7). These dimers, as for the dimer built with
enaminoketone 2, were established to be the trans isomer
by 1H-1H COSY and ROESY NMR experiments. Although
metalation of the external coordination site, to give acetyl-
acetonatopalladium derivatives or dimers, led in all previ-
ously studied compounds to a large bathochromic shift of
the UV-visible bands, the opposite was observed in this
series, and led us first to doubt the structure of the dimer.
The lowest energy absorption band found at 678 nm for
enaminoketone 18 shifted to 658 nm for metalated monomer
21 and to 662 nm for dimer 23.
monitoring of the advancement of the reaction clearly showed
their formation) (Scheme 8). Stopping the reaction before
complete conversion of the starting enaminoaldehyde, al-
lowed to separate and isolate the two dimers by careful silica
gel chromatography. Both isomeric dimers presented almost
superimposable electronic spectra, within a 3-4 nm range,
with broadening and splitting of the Soret bands and
bathochromic shifts of the lower wavelength bands. One
isomer could be obtained in only 90-95% purity (checked
by 1H NMR) in all attempts. This dimer was found unstable
and led quantitatively to the other dimer when kept in
solution for a few hours (followed by NMR, see Supporting
Information). Once again, since we were unable to grow
single crystals suitable for an X-ray structure determination,
In contrast to both enaminoketone series which only
yielded trans dimers, the reaction of enaminoaldehyde 8 with
Pd(OAc)2 led to the formation of two dimeric products (TLC
256 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
Scheme 8 Cis and Trans Isomeric Dimers Obtained from Enaminoaldehydes 8 and 9 and Cis Dimer Obtained from Enaminothioaldehyde 11
Table 1. Electronic Spectra and Selected IR Wave Numbers of
the structure of the dimers (cis or trans isomer) was
Porphyrin Monomers and Dimers
1
established by H-1H COSY and ROESY NMR experi-
ments.
wavelength
ν(CO) ν(N-H)
compound
λ > 400 nm
(cm-1
)
(cm-1
)
ref
11b
The most stable dimer showed at high field (6.69 ppm) a
1
462, 650, 686
1650
signal attributed to the cyclized phenyl (in all monomers and
dimers so far studied the corresponding signals are located
in the 9-7.5 ppm range). This strongly suggested that the
two cyclized phenyl rings were overlapping, and that, in
contrast to the other series, the cis dimer 26 was the most
2
3
4
458, 599, 649
1628 3311, 3473 10b
420, 458, 484, 640, 686
439, 470, 500, 638, 696
428, 473, 496, 654, 692
450, 524, 654, 682, 732
406, 462, 490, 657, 720
414, 450, 476, 624, 650, 678
412, 446, 466, 606, 636, 658
416, 450, 472, 486, 608, 640, 662 1568 3344
446, 560, 626
450, 478, 560, 622, 668
1611 3355
1607 3353
10b
10b
12
19
16
18
21
23
8
26
11
28
this work
1698
this work
1655 3309, 3467
1570 3366
1
stable isomer. Because of overlapping signals the H NMR
spectra of dimers 24 and 26 could not be fully assigned,
this work
this work
1
and H-1H COSY and ROESY NMR experiments that
confirmed the stereochemical assignments were run on the
meso-tolyl-substituted dimers 25 and 27 (see Supporting
Information). The geometry of the cis dimers must induce a
distortion around the palladium(II) ion, which can no longer
stay in a true square planar environment, as shown in Scheme
8. As a direct consequence, these dimers exists as two
enantiomeric chiral ∆ and Λ species. The trans isomer was
clearly the kinetic product since NMR of the reaction
medium after 24% conversion showed that the trans/cis
isomer ratio was close to four (19 and 5%). However, due
to isomerization during the course of the reaction and the
purification of the products, the cis isomer was the major
product recovered.
422, 470, 568, 598, 650
432, 506, 572, 628, 714
4)9b to a large bathochromic shift of the UV-visible bands.
The electronic spectra shown in Table 1 demonstrate that
either a bathochromic or a hypsochromic shift was observed
depending on the starting porphyrins used to build the
metalated monomers or the dimers. Using enaminothioketone
12, enaminoaldehyde 8, or enaminothioaldehyde 11 to build
dimers 19, 26, or 28, led as expected to bathochromic shifts
upon formation of the palladium(II)-linked dimers. These
effects are due to the delocalization of the electron density
in the six-membered ring formed by the chelates and the
metal(II) ions. In these cases, the metal chelation might be
seen as the addition of a new six-membered ring, almost
aromatic in character, thus leading to the observed batho-
chromic shifts. These effects (generally called “metalloaro-
maticity”) have been reviewed recently23 and first described
by M. Calvin for simple copper bis(acetylacetonate) com-
plexe.24
Reaction of enaminothioaldehyde 11 with Pd(OAc)2 led
to a single dimeric compound identified as the cis isomer
28. The overlap of the two cyclized phenyl rings was again
1
reflected in the H NMR spectrum by the presence of an
aromatic signal at 6.14 ppm. The fact that we could not
observe the presence of the trans isomer reflects the much
stronger trans effect induced by the soft sulfur atom in the
enaminothioaldehyde chelate.22
5. Spectroscopic Properties. Metalation of the external
coordination site led in the previously studied series (for
example: enaminoketone 2, metalated monomer 3, and dimer
Metalation of enaminoketone 18 to build metalated
monomer 21 or dimer 23 led to hypsochromic shifts in the
electronic spectra (see Table 1). However, the same electronic
delocalization effects might be invoked to explain these
Inorganic Chemistry, Vol. 43, No. 1, 2004 257

Richeter et al.
Scheme 9
6. Electrochemical Studies. The electrochemistry of
nickel porphyrins is well documented.25 In general, the
nickelporphyrins are oxidized in two one-electron steps and
reduced in two one-electron steps (sometimes a third
oxidation or reduction step might be observed, but close to
the electrolyte oxidation or reduction). In most cases, the
initial oxidations and reductions are not localized on the
nickel(II) ion but involve the aromatic π system. We have
studied by cyclic voltammetry the electrochemical behavior
of a series of porphyrin monomers bearing an external
enaminoketone chelate and the metal ion linked dimers build
from these compounds. In the case of nickel porphyrins, we
observed the usual reversible two oxidation and reduction
steps. For the dimers, the oxidation and reduction steps were
splitted, indicating that the resultant charge was delocalized
over both porphyrin rings (one example is reported in Table
2: monomer 2 and dimer 4).9b The redox splitting of the
electrochemical oxidation or reduction steps is generally
accepted as a proof of strong interactions in the ground state
between the two porphyrins.26
For the new nickel porphyrin monomers or dimers
presented in this study, it must be taken into account that
reducible or oxidizable functions are present at the periphery
of the macrocycle, thus giving rise to irreversible processes
or additional redox steps. It is well-known that aromatic
amines or sulfur compounds are easily oxidized or that
aromatic aldehydes might be reduced in the potential range
used in our experiments.28 Isomeric enaminoketone 17 and
metalated monomer 20 gave two reversible well-defined
reduction and oxidation signals. For dimer 22, the first and
the second reduction signals involve an uptake of two
electrons for each step. The first two oxidation steps each
involve one electron, whereas the third peak involves two
overlapping one-electron steps. The value of the redox
splitting found for the first oxidations in the new dimer 22
(140 mV) is very close to the value found for dimer 4 (160
mV). The same type of chelate, even in an isomeric form,
should give the same kind of interaction. For thioenami-
noketone 12, the situation on the oxidation side is compli-
cated by a first irreversible oxidation probably localized at
the sulfur atom. Dimer 19, where the sulfur atom is protected
by the complexation with palladium(II), has a well-defined
reversible electrochemistry on the oxidation side. As ex-
pected, the first steps are one electron processes and the value
of the splitting is found equal to 190 mV. Moreover, on the
reduction side, although the interpretation was made difficult
surprising results. A clue for this unexpected behavior is
found in the IR data for the corresponding starting ketones
and enaminoketones.
If one considers the carbonyl wavenumbers of the starting
ketones, that of 16 falls in the normal range for aryl-alkyl
or diaryl ketones, and it makes sense to describe 16 as a
ketochlorin, with very little contribution from mesomeric
form of the aromatic ring current involving the â positions
of the modified pyrrole. In contrast that of ketone 1 is atypical
and suggests a strong polarization of the carbon-oxygen
bond and a significant delocalization of the π electron density
on the â,â-bond of the modified pyrrole. Amination of the
two ketones 1 and 16 gave the isomeric enaminoketones 2
and 18. The extent of the modification of the carbonyl
wavenumbers of 2 and 18 vs 1 and 16 (-22 and -43 cm-1)
reflects the different nature of the ketones. The amination
of ketone 16 leads to a large delocalization of the carbonyl
electron density in the enaminoketone group thus diminishing
the bond order of the carbonyl bond and increasing the bond
order of the â,â-pyrrolic bond (more double bond character
and thus a more porphyrin-like spectrum; see Scheme 9).
Metalation of enaminoketone 18 increases this delocalization
to a much larger extent (shift of -85 cm-1 after metalation),
bringing the carbonyl wavenumbers in the range of acetyl-
acetonate complexes (Pd(acac)2: 1568 cm-1).
Complexation of the external coordination site is not
expected to modify significantly the macrocyclic chro-
mophore of enaminoketone 2, and the bathochromic shift
of UV-visible data will reflect the extension of the conjuga-
tion to the acetylacetonatopalladium in monomer 3 and then
to the porphyrinatopalladium group in dimer 4, as earlier
presented.9b On the other hand, the same operations, when
performed with enaminoketone 18 will have a large effect
on the macrocyclic chromophore. Starting with 18, which
has still a ketochlorin character, the extension of the
delocalization on metalation will, as did the amination,
modify the chromophore which will end even more porphy-
rin-like. Expected are then porphyrin-like bands, less intense
and at shorter wavelengths. The resulting spectrum will
reflect the relative and opposite contributions from the
organic chromophore being more porphyrin-like, which
results in a hypsochromic effect, and the metalation which
determines a bathochromic effect.
(25) Kadish, K. M.; Van Caemelbecke, E.; Royal, G. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: Boston, MA, 2000; Vol. 8, p 3. Kadish, K. M.; Lin, M.; Van
Caemelbecke, E.; De Stefano, G.; Medforth, C. J.; Nurco, D. J.;
Nelson, N. Y.; Krattinger, B.; Muzzi, C. M.; Jaquinod, L.; Xu, Y.;
Shyr, D. C.; Smith, K. M.; Shelnutt, J. A. Inorg. Chem. 2002, 41,
6673.
(26) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J. Science 1994, 264,
1105.
(27) Callot, H. J. Tetrahedron 1973, 29, 899. Chen, H. L.; Ellis, P. E., Jr.;
Wijesekera, T.; Hagan, T. E.; Groh, S. E.; Lyons, J. E.; Ridge, D. P.
J. Am. Chem. Soc. 1994, 116, 1086.
(23) Masui, H. Coord. Chem. ReV. 2001, 219-221, 957, and references
therein. The “aromatic character” of the metal(acac) six-membered
rings is reflected in their reactivity and in the ring-current effects
observed in NMR spectra. The electrophilic substitution on the acac
ligand is well-known (see, for example: Reihlen, H.; Illig, R.; Wittig,
R. Ber. Dtsch. Chem. Ges. 1925, 58B, 12; Collman, J. P. Angew. Chem.
1965, 77, 154). If several acac ligands surround the metal ion, J. P.
Collman described also intramolecular-interannular electronic effects
through the metal center, illustrated by chemical reactivity and physical
properties.
(28) See, for example: Encyclopedia of Electrochemistry of the Elements.
Organic Section; Bard, A. J., Lund, H., Eds.; Marcel Dekker Inc.:
New York: 1979, Vol XII; 1980, Vol. XIV. Weinberg, N. L.;
Weinberg, H. R. Chem. ReV. 1968, 68, 449.
(24) Calvin, M.; Wilson, K. W. J. Am. Chem. Soc. 1945, 67, 2003.
258 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
Table 2. Cyclic Voltammetry Dataa
reduction E′° in V vs Fc/Fc+
oxidation E′° in V vs Fc/Fc+
(no. of electrons exchanged)
(no. of electrons exchanged)
compound
2
4
-1.63 (1)
-1.86 (1)
-1.79 (1)
-1.85 (1)
-1.82 (2)
-1.61 (1)
≈-1.85
-1.87 (1)
-2.04 (1)
-2.05b
-1.26 (1)
-1.45 (2)
-1.44 (1)
-1.48 (1)
-1.46 (2)
-1.26 (1)
-1.35 (1)
-1.53 (1)
-1.64 (1)
-1.62 (1)
-1.39 (1)e
-1.55 (1)
-1.42b
0.60 (1)
0.32 (1)
0.37 (1)
0.40 (1)
0.41 (1)
0.44b
0.30 (1)
0.67 (1)
0.32 (1)
0.32 (1)
0.25 (1)
0.35b
0.95 (1)
-1.94(1)
≈-1.95f
0.48 (1)
0.82 (2)
0.78 (1)
0.78 (1)
0.81 (2)
0.80 (1)
0.80 (2)
0.73 (1)
0.63 (1)
0.62 (1)
0.60 (2)
0.64 (1)
0.60
17
20
22
12
19
CHOc
5d
0.55 (1)
0.49 (1)
-1.45 (1)
1.20
1.18
1.25
8
26
11
28
-2.18b
-2.02
-1.83 (1)
-1.88 (1)
-1.80
-1.70 (1)
-1.58
0.36 (1)
0.41(1)
0.27(1)
a Experimental conditions: see Experimental Section. The number of exchanged electrons is indicated in parentheses following the peak potential when
it could be determined accurately and confirmed by rotating disk voltammetry (RDV) experiments. b Peak potentials. c CHO ) nickel 2-formyl-meso-
tetraphenylporphyrin.27 d For enamine 5, it was necessary to deaerate the electrolyte carefully, since the presence of traces of oxygen led to additional waves
(at -1.84 and -2.24 V) during the reduction process. This was probably due to the generation of the oxygen radical anion in situ, which may further react
with enamine 5 to generate the corresponding hydroxylamine. e Only reversible if the potential scan is reverted after this first reduction step. f Approximative
values due to the low solubility of the reduced forms of dimer 19.
chemical behavior allows to draw the same conclusions. For
dimer 26 (“enaminoaldehyde dimer”), the redox splitting on
the oxidation side was found equal to 110 mV. However,
the behavior on the reduction side was complicated by
decomplexation problems. The first step is reversible only
if the potential scan is reverted after the first reduction.
Trying to introduce four electrons by a further increase of
the cathodic potential led to decomposition of the dimer and
recovery of the starting monomer. This could be easily
monitored by spectroelectrochemistry (appearance of the
characteristic broad Soret band of the monomeric porphy-
rin: see Supporting Information). For dimer 28 (“enami-
nothioaldehyde dimer”), the redox splitting on the oxidation
side was increased to 140 mV. For all compounds derived
from enamine 5, an additional oxidation step (at ca. 1.20 V)
was found at the limit of the potential range and might be
attributed to the oxidation of the amine. On the reduction
side, four independent one electron steps were observed, but
with loss of the reversibility, even for the first reduction step,
and decomplexation.
For the cis dimers 26 and 28, built from the enaminoal-
dehyde and enaminothioaldehyde monomers, it seems that
the peculiar coordination geometry (intermediate between
square planar and tetrahedral) around the Pd(II) connecting
ion leads to much less stable dimers. The high cathodic
potential generally needed to reduce the Pd(II) square planar
complexes prevented destruction of the other dimers since
Pd(II) was not reduced within the electrochemical range
studied. In the last two examples, dimers 26 and 28, these
potentials are less cathodic, since the coordination geometry
destabilize the +2 state compared with a square planar
coordination. Thus, within the range of potentials studied,
reduction of the connecting Pd(II) can occur and decomposi-
tion of the dimeric structures leads to the porphyrin
monomers.
Figure 3. Typical cyclic voltammetry of monomeric and dimeric por-
phyrins (top, monomer 8; bottom, dimer 26). Plain line: inversion of the
potential sweep after the first reduction. Bold line: inversion of the potential
sweep after the fourth reduction step.
by the rather low solubility of the reduced forms of dimer
19, it is possible to conclude that 19 is reduced in four
independent one electron steps at approximately -1.35,
-1.45, -1.85, and -1.95 V. A spectroelectrochemical study
during reductive electrolysis at a potential of -1.9 V also
confirmed that the dimeric structure is maintained after
reduction. The enaminothioketone chelate complexing the
palladium(II) connecting ion seems to be a better link in term
of extent of interaction than the enaminoketone chelate,
although the distance between the two porphyrin rings is
probably larger since Pd-S bonds are longer than Pd-O
bonds.For enaminoaldehyde 8, enaminothioaldehyde 11 and
dimers 26 and 28 build from these monomers, the electro-
The electrochemistry of all palladium(II)-linked dimers,
for all new chelates used in this study, showed that this kind
of connection induces strong interactions between the two
Inorganic Chemistry, Vol. 43, No. 1, 2004 259

Richeter et al.
porphyrin (1.5 mmol in 600 mL) were added a solution of lithium
nitrate in acetic acid (1.72 g, 25 mmol in 100 mL) and acetic
anhydride (95 mL, 1 mol). The advancement of the reaction was
carefully monitored by silica gel TLC, and after completion of the
nitration (approximatively 1.5 h), the reaction mixture was neutral-
ized with an aqueous NaHCO3 solution, washed three times with
water, and the solvent evaporated. After crystallization (dichlo-
romethane/methanol) the known copper or nickel 2-nitro-meso-
tetraarylporphyrins15,16 were obtained in 90 to 95% yields (aryl )
phenyl, p-tolyl, and 3,5-di-tert-butyl-phenyl).
individual porphyrin rings. The redox splitting values found
(110-190 mV), which reflect the extent of the interactions,
compare well with the splitting values found in covalently
linked conjugated dimers. With the notable exception of the
triply fused dimers described by Otsuka et al.,5i where the
two porphyrins are connected without any spacer, thus
presenting splitting values up to 400 mV, all other covalently
linked conjugated dimers (phenyl, acetylenic, or olefinic
links) show redox splitting values in the same range (from
0 to 260 mV). A trans-ethene or ethynyl meso-meso linkage
between two porphyrins leads to values respectively equal
to 100 and 260 mV.2b Therefore, the simple metal ion
connection between two porphyrins bearing chelating sites
leads to redox splitting values close to the best results reached
with covalently linked dimers.
Nickel Enaminoporphyrins 5, 6, and 7. A degassed solution
of nickel 2-nitro-meso-tetraarylporphyrin (0.55 mmol) in 1,2-
dichlorobenzene (3 mL) and triethyl phosphite (0.5 mL, 2.9 mmol)
was heated under argon at 155 °C during 3 h. After cooling, the
reaction mixture was poured on a silica gel column (eluent hexane/
dichloromethane). The green nickel enaminoporphyrins 5, 6, or 7
were obtained in 70-75% yield after crystallization from dichlo-
romethane/methanol.
Conclusion
1
5 (Ar ) Phenyl). H NMR: δ ) 9.45, 8.83 (2d, 1 + 1H, J )
We have been able to show that the metal ion link between
two porphyrinic chromophores bearing chelating sites at their
periphery can be generalized to other chelates and is not
restricted to the initially described enaminoketone function-
alized porphyrins.9 All porphyrin dimers prepared present
strong interactions between the individual rings in the ground
state. However, while the sentence “two rings is better than
one”, which D. Arnold3 used as title for his review on
porphyrin oligomers, is still valid, in covalently connected
oligomers as well as in multiporphyrins connected by metal
ions, one should be aware that this last approach, although
flexible and easy to carry out, brings its own specific
problems. In this article, we describe two such events: on
one hand the cis-trans isomerism is illustrated by the
sensitivity of isoelectronic chelates to steric factors, on the
other, the complexation of the chelate may have unexpected
effects on the overall electronic properties of the oligomers,
if the complexation modifies the monomeric chromophore
itself. Preparation of higher oligomers (built from porphyrins
bearing two chelating sites) with the new insights taken from
this study is in progress. The replacement of the oxygen atom
in enaminoketones for sulfur presents at least three major
advantages: a higher stability of the metal ion connection,
monomeric chromophores with a very low band gap (close
to near infrared for bis(enaminothioketones)29), and an
increase of the interactions between each porphyrin.
4.8 Hz, pyrrole), 8.64, 8.58 (2s, 2 + 2H, pyrrole), 8.01 (s, 1H,
pyrrole), 8.91 (dd, 1H, J ) 7.5 and 1 Hz, cyclized phenyl), 7.96-
8.04 (m, 6H, Hortho), 7.60-7.73 (m, 12H, 9Hmeta+para + 3H cyclized
phenyl), 9.20 (broad s, 1H, NH). UV-vis (CH2Cl2): λmax ) 426
(ꢀ ) 71 500), 554 (6100), 598 (8700), 628 (15 200). Anal. Calcd
for NiC44N5H27: C, 77.22; H, 3.98; N, 10.23. Found: C, 76.87; H,
4.19; N, 9.99.
1
7 (Ar ) 3,5-Di-tert-butyl-phenyl). H NMR: δ ) 9.35, 8.83
(2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.68, 8.65 (2d, 1 + 1H, J ) 5.1
Hz, pyrrole), 8.63, 8.59 (2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.04 (s,
1H, pyrrole), 8.83 (d, 1H, J ) 2 Hz, cyclized phenyl), 7.81 (d, 1H,
J ) 2 Hz, cyclized phenyl), 7.88, 7.86, 7.84 (3d, 3 × 2H, J ) 2
Hz, Hortho), 7.72, 7.70, 7.67 (3t, 3 × 1H, J ) 2 Hz, Hpara), 9.55
(broad s, 1H, NH), 1.89, 1.57 (2s, 2 × 9H, tert-Bu), 1.49, 1.47,
1.46 (3s, 3 × 18H, tert-Bu). UV-vis (CH2Cl2): λmax ) 424 (ꢀ )
76 300), 446 (69 500 sh), 602 (11 500 sh), 634 (18 200). Anal.
Calcd (%) for NiC76N5H91‚H2O: C, 79.29; H, 8.14; N, 6.08.
Found: C, 79.44; H, 8.41; N, 5.98.
Nickel Enaminoaldehydes 8, 9, and 10. To a solution of the
nickel enaminoporphyrin 5 (or 6 or 7) in dichloromethane (0.44
mmol in 50 mL) were added dimethylformamide (2.5 mL, 32 mmol)
and phosphorus oxychloride (2.5 mL, 27 mmol). The rapid
consumption of the starting material was followed by silica gel
TLC, and after approximatively 10-15 min, the reaction was
quenched with a saturated aqueous solution of sodium acetate. The
organic phase was then washed with water (3 × 200 mL) and dried
on sodium sulfate. After evaporation and crystallization from
chloroform/methanol, the green nickel enaminoaldehyde 8 (or 9
or 10) was obtained in 90% (or 85 or 87%) yield.
Experimental Section
1
8 (Ar ) Phenyl). H NMR: δ ) 9.35, 8.79 (2d, 1 + 1H, J )
4.8 Hz, pyrrole), 8.61, 8.59 (AB, 2H, J ) 5.1 Hz, pyrrole), 8.51,
8.53 (AB, 2H, J ) 4.8 Hz, pyrrole), 8.96 (dd, 1H, J ) 7.2 and 1.5
Hz, cyclized phenyl), 8.04 (dd, 1H, J ) 7.2 and 1.5 Hz, cyclized
phenyl), 7.92-8.01 (m, 6H, Hortho), 7.62-7.82 (m, 11H, 9Hmeta+para
+ 2H cyclized phenyl), 12.51 (broad s, 1H, NH), 9.09 (s, 1H, CHO).
UV-vis (CH2Cl2): λmax ) 446 (ꢀ ) 122 000), 560 (10 000), 626
(18 400). Anal. Calcd for NiC45N5H27O‚1/2CHCl3: C, 70.78; H,
3.59; N, 9.07. Found: C, 71.09; H, 3.68; N, 9.11.
General Procedures. UV-visible spectra: Hewlett-Packard
8453 (CH2Cl2). NMR (CDCl3 at 25 °C unless otherwise stated, δ
(ppm) vs TMS): Bruker AC 300, AM 400, and ARX 500. COSY
1H-1H NMR have been run on all compounds. Elemental analyses
were performed at the Service de Microanalyse, Universite´ Louis
Pasteur, Strasbourg, France. Chromatographic separations were
obtained using Merck 9385 silica gel or Merck 1097 alumina. All
monomeric porphyrins gave correct masses (Finnigan TSQ 700,
EI, 12 eV), and all dimers gave correct molecular mass peaks (FAB
or MALDI-TOF).
1
10 (Ar ) 3,5-Di-tert-butylphenyl). H NMR: δ ) 9.27, 8.80
(2d, 1 + 1H, J ) 5.0 Hz, pyrrole), 8.72, 8.65 (2d, 1 + 1H, J ) 5.1
Hz, pyrrole), 8.57, 8.53 (2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.87 (d,
1H, J ) 1.8 Hz, cyclized phenyl), 8.04 (d, 1H, J ) 1.8 Hz, cyclized
phenyl), 7.83, 7.81, 7.80 (3d, 6H, Hortho), 7.73, 7.69, 7.66 (3t, 3H,
Hpara), 13.36 (broad s, 1H, NH), 8.91 (s, 1H, CHO), 1.97, 1.58 (2s,
Preparation of 2-Nitro-meso-tetraarylporphyrins. To a warm
chloroform solution (40-45 °C) of the copper or nickel tetraaryl
(29) Richeter, S.; Jeandon, C.; Ruppert, R.; Callot, H. J. Unpublished results.
260 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
9+9H, tert-Bu), 1.47, 1.44, 1.43 (3s, 3 × 18H, tert-Bu). UV-vis
(CH2Cl2): λmax ) 454 (ꢀ ) 114 000), 564 (10 000), 608 (12 600),
634 (21 000). Anal. Calcd for NiC77N5H91O: C, 79.64; H, 7.90;
N, 6.03. Found: C, 79.61; H, 8.05; N, 5.92.
Nickel Enaminothioaldehyde 11. A degassed benzene (50 mL)
solution of nickel enaminoaldehyde 8 (150 mg, 0.21 mmol) and
Lawesson’s reagent (100 mg, 0.25 mmol) was heated under argon
at 75 °C for 10 min. After cooling, the solution was poured on a
short silica gel column and eluted with dichloromethane/hexane
1/1. Crystallization from dichloromethane/methanol afforded nickel
enaminothioaldehyde 11 in 78% yield.
11 (Ar ) phenyl). 1H NMR: δ ) 9.31, 8.77 (2d, 1 + 1H, J )
4.8 Hz, pyrrole), 8.55, 8.48 (2d, 2H, J ) 5.1 Hz, pyrrole), 8.47,
8.49 (AB, 2H, J ) 5.1 Hz, pyrrole), 8.94 (dd, 1H, J ) 7.2 and 1.5
Hz, cyclized phenyl), 8.11 (dd, 1H, J ) 7.2 and 1.5 Hz, cyclized
phenyl), 7.84 (m, 2H, cyclized phenyl), 7.89-7.98 (m, 6H, Hortho),
7.61-7.74 (m, 9H, Hmeta+para), 15.41 (broad s, 1H, NH), 10.37 (s,
1H, CHS). UV-vis (CH2Cl2): λmax ) 422 (ꢀ ) 61 000), 470
(118 000), 568 (9300), 598 (9700), 650 (22 300). Anal. Calcd for
NiC45N5H27S‚1/2H2O: C, 73.29; H, 3.83; N, 9.50; S, 4.35. Found:
C, 73.41; H, 3.72; N, 9.48; S, 4.41.
phenyl), 7.74 (d, 2H, J ) 7.7 Hz, tolyl), 7.69 (d, 2H, J ) 7.7 Hz,
tolyl), 7.50 (d, 2H, J ) 7.7 Hz, tolyl), 7.35-7.47 (3d, 3 × 2H,
tolyl), 2.60 (2s, 3+3H, Me), 2.58 (s, 3H, Me), 2.57 (s, 3H, Me).
UV-vis (CH2Cl2): λmax ) 410 (ꢀ ) 70 300), 464 (32 200), 494
(33100), 666 (12500 sh), 716 (18700). Anal. Calcd for NiC49N4H34O‚
H2O: C, 76.26; H, 4.70; N, 7.26. Found: C, 76.25; H, 4.33; N,
7.19.
Nickel Enaminoketoporphyrins 17 and 18. A solution of nickel
ketoporphyrin 15 (or 16) (0.057 mmol), sodium hydroxide (0.2 g,
5 mmol) and 4-amino-4H-1,2,4-triazole (160 mg, 1.9 mmol) in a
mixture of toluene and ethanol (50 and 5 mL) was heated under
reflux for 5 h. After cooling, trifluoroacetic acid (1 mL, 13 mmol)
was added and the solution refluxed for an additional hour. The
reaction medium was concentrated on a rotary evaporator and
dichloromethane (150 mL) added. The organic phase was then
washed three times with water and dried with sodium sulfate.
Chromatography on silica gel (eluent: dichloromethane/ethyl acetate
from 0 to 10%) and crystallization from dichloromethane/methanol
afforded green nickel enaminoketone 17 (or 18) in 61% (or 83%)
yield.
1
17 (Ar ) Phenyl). H NMR (300 MHz, CDCl3, 45 °C): δ )
Nickel Enaminothiocetone 12. A solution of nickel enamino-
cetone 2 (273 mg, 0.26 mmol) and Lawesson’s reagent (152 mg,
2.66 mmol) in benzene (150 mL) was heated under reflux until
consumption of all starting material (approximatively 2 h). After
evaporation of the solvent, the residue was chromatographed on a
silica gel column (eluent: dichloromethane/hexane 1/1). After
crystallization from dichloromethane/methanol, the green nickel
enaminothioketone 12 was isolated in 97% yield (270 mg, 254
mmol).
12. 1H NMR: δ ) 9.14, 8.70 (2d, 1 + 1H, J ) 5.0 Hz, pyrrole),
8.45, 8.30 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole), 8.42, 8.32 (2d, 1 +
1H, J ) 4.9 Hz, pyrrole), 9.12 (dd, 1H, J ) 8.1 and ∼1 Hz, cyclized
phenyl), 8.14 (dd, 1H, J ) 8.1 and ∼1 Hz, cyclized phenyl), 7.74
(ddd, 1H, J ) 8.1, 8.1 and ∼1 Hz, cyclized phenyl). 7.53 (ddd,
1H, J ) 8.1, 8.1 and ∼1 Hz, cyclized phenyl), 7.80, 7.69, 7.67 (3t,
3 × 1H, J ) 1.8 Hz, Hpara), 7.60-7.80 (broad, 6H, Hortho), 12.18,
6.21 (broad. 1 + 1H, N-H), 1.46, 1.44, 1.43 (3s, 3 × 18H, tert-
Bu). UV-vis (CH2Cl2): λmax ) 390 (ꢀ ) 51 000), 428 (59 000),
473 (46 000 sh), 496 (81 000), 654 (14 500 sh), 692 (22 000). Anal.
Calcd for NiC69N5H75S: C, 77.81; H, 7.10; N, 6.57. Found: C,
77.91; H, 7.11; N, 6.25.
8.89, 8.51 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole), 8.28, 8.22, 8.16,
8.10 (4d, 4 × 1H, J ) 4.8 Hz, pyrrole), 8.36 (dd, 1H, J ) 8.0 and
∼1 Hz, cyclized phenyl), 7.95 (dd, 1H, J ) 7.7 and ∼1 Hz, cyclized
phenyl), 7.72 (ddd, 1H, J ) 7.8, 7.8 and ∼1 Hz, cyclized phenyl).
7.45 (ddd, 1H, J ) 7.8, 7.8 and ∼1 Hz, cyclized phenyl), 7.80-
7.93 and 7.54-7.78 (m, 15H, meso phenyl). UV-vis (CH2Cl2):
λmax ) 414 (ꢀ ) 51 000), 450 (52 000), 476 (64 000), 624 (12 000
sh), 650 (15 000 sh), 678 (23 000). Anal. Calcd for NiC45N5H27O‚
H2O: C, 73.99; H, 4.00; N, 9.59. Found: C, 74.23; H, 3.76; N,
9.61.
18 (Ar ) p-Tolyl). 1H NMR: δ ) 8.90, 8.57 (2d, 1 + 1H, J )
5.1 Hz, pyrrole), 8.29, 8.21 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole),
8.25, 8.11 (2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.27 (d, 1H, cyclized
phenyl), ∼7.76 (d, 1H, cyclized phenyl), 7.60 (dd, 1H, cyclized
phenyl), 7.70-7.82 (m, 4H, tolyl), 7.54-7.65 (m, 2H, tolyl), 7.37-
7.50 (m, 6H, tolyl), 2.60 (2s, 3 + 3H, Me), 2.58 (s, 3H, Me), 2.52
(s, 3H, Me). UV-vis (CH2Cl2): λmax ) 416 (ꢀ ) 54 800), 452
(54 000), 480 (69 600), 622 (12 600 sh), 654 (18 900 sh), 678
(26 400). Anal Calcd for NiC49N5H35O‚H2O: C, 74.82; H, 4.74;
N, 8.90. Found: C, 75.02; H, 4.50; N, 8.84.
Palladium Dimer 26. To a solution of nickel enaminoaldehyde
8 (40 mg, 0.056 mmol) in 1,2-dichloroethane (30 mL) was added
dropwise (1.5 h of addition) at 60 °C under argon a solution of
palladium(II) acetate (8 mg, 0.035 mmol) in 1,2-dichloroethane (15
mL). The advancement of the reaction was followed by silica gel
TLC (eluent: hexane/dichloromethane 1/1). After 18 h, the solvent
was evaporated and the residue chromatographed on a silica gel
column (eluent: tetrachloromethane/dichloromethane from 4/1 to
1/1). After crystallization from dichloromethane/methanol, dimer
26 was obtained in 75% yield. Alternatively, when the reaction
was stopped after 30-40% conversion, rapid evaporation of the
solvent followed by rapid chromatography on a silica gel column
(same conditions as before) and evaporation of the elution solvents
afforded a solid containing 90-95% of the trans isomer 24 (or 25
in the case of the p-tolyl derivative). See Supporting Information
for the NMR characterization of this unstable isomer.
Nickel Ketoporphyrins 15 and 16. The ketoporphyrin free bases
were prepared according to the procedure described by Ishkov19
and were metalated overnight in refluxing toluene in the presence
of nickel(II) acetylacetonate. The raw material was purified by
chromatography (short silica gel column, eluent dichloromethane)
and crystallized from dichloromethane/methanol. Nickel ketopor-
phyrins 15 and 16 were isolated in 90% and 85% yield.
1
15 (Ar ) Phenyl). H NMR (300 MHz, CDCl3, 45 °C): δ )
8.89, 8.48 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole), 8.17, 8.07, 8.01,
7.98 (4d, 4 × 1H, J ) 4.8 Hz, pyrrole), 8.50 (s, 1H, additional
ring), 8.46 (dd, 1H, J ) 7.5 and ∼1 Hz, cyclized phenyl), 8.15
(dd, 1H, J ) 7.5 and ∼1 Hz, cyclized phenyl), 7.50-7.93 (m, 17H,
6Hortho + 9Hmeta+para + 2H cyclized phenyl). UV-vis (CH2Cl2):
λmax ) 406 (ꢀ ) 66 000), 462 (32600), 490 (34300), 657 (12000
sh), 720 (17000). Anal. Calcd for NiC45N4H26O‚1/2H2O: C, 76.51;
H, 3.85; N, 7.93. Found: C, 76.78; H, 3.77; N, 8.02.
16 (Ar ) p-tolyl): 1H NMR: δ ) 8.83, 8.47 (2d, 1 + 1H, J )
5.1 Hz, pyrrole), 8.17, 8.04 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole),
8.08, 7.97 (2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.40 (s, 1H, additional
ring), 8.34 (d, 1H, J ) 8.4 Hz, cyclized phenyl), 7.91 (d, 1H, J )
1.1 Hz, cyclized phenyl), 7.62 (dd, 1H, J ) 8.4 and 1.1 Hz, cyclized
1
24 (Trans, Ar ) Phenyl). H NMR (300 MHz, C2D2Cl4, 45
°C): δ ) 9.30, 8.75 (2d, 2 + 2H, J ) 4.8 Hz, pyrrole), 8.61, 8.49
(2d, 2 + 2H, J ) 5.1 Hz, pyrrole), 8.42, 8.37 (2d, 2 + 2H, J ) 4.8
Hz, pyrrole), 8.85 (dd, 2H, J ) 7.8 and 1.2 Hz, cyclized phenyl),
8.72 (dd, 2H, J ) 7.8 and 1.2 Hz, cyclized phenyl), 8.04 (m, 8H,
Hortho), 7.93 (m, 4H, Hortho), 7.82 (m, 8H, cyclized phenyl +
Inorganic Chemistry, Vol. 43, No. 1, 2004 261

Richeter et al.
H
meta+para), 7.73 (m, 8H, cyclized phenyl + Hmeta+para), 7.67 (m,
) 1 Hz, cyclized phenyl), 7.55 (dd, 1H, J ) 8.0 and 1.0 Hz, cyclized
phenyl), 7.78 (2d, 2 + 2H, J ) 7.7 Hz, meso-aryl), 7.69 (d, 2H, J
) 7.7 Hz, meso-aryl), 7.43 (2d, 2 + 2H, J ) 7.7 Hz, meso-aryl),
7.42 (d, 2H, J ) 7.7 Hz, meso-aryl), 7.39 (s, 1H, NH), 5.45 (s, 1H,
acac), 2.55, 2.58, 2.59, and 2.61 (4s, 4 × 3H, Me tolyl), 2.11, 2.09
(2s, 3 + 3H, Me acac). UV-vis (CH2Cl2): λmax ) 414 (ꢀ )
39 600), 470 (93 300), 606 (11 400), 658 (21 800). Anal. Calcd
for PdNiC54N5H41O3‚1/2H2O: C, 66.04; H, 4.31; N, 7.13. Found:
C, 66.00; H, 4.17; N, 7.04.
Palladium Dimer 19. To a degassed solution of nickel enami-
nothioketone 12 (30 mg, 0.028 mmol) in chloroform (15 mL) was
added dropwise at 50 °C a solution of palladium(II) acetate (4 mg,
0.018 mmol) in chloroform (10 mL). After consumption of all
starting material, the solvent was evaporated and dimer 19 isolated
by crystallization from dichloromethane/methanol in 89% yield (28
mg, 0.0125 mmol).
19: 1H NMR (300 MHz, CDCl3, 40 °C): δ ) 9.03, 8.61 (2d, 2
+ 2H, J ) 5.0 Hz, pyrrole), 8.35, 8.04 (2d, 2 + 2H, J ) 5.1 Hz,
pyrrole), 8.26, 8.16 (2d, 2 + 2H, J ) 4.8 Hz, pyrrole), 9.32 (dd,
2H, J ) 7.8 and ∼1 Hz, cyclized phenyl), 8.38 (dd, 2H, J ) 7.8
and ∼1 Hz, cyclized phenyl), 7.89 (ddd, 2H, J ) 7.8, 7.8 and ∼1
Hz, cyclized phenyl). 7.80 (ddd, 2H, J ) 7.8, 7.8 and ∼1 Hz,
cyclized phenyl), 8.27, 7.69, 7.65 (3t, 3 × 2H, J ) 1.8 Hz, Hpara),
7.60-7.90 (broad m, 12H, Hortho), 8.49 (broad s, 2H, N-H), 1.57,
1.48, 1.43 (3s, 3 × 36H, tert-Bu). UV-vis (CH2Cl2): λmax ) 396
(ꢀ ) 71 000), 450 (94 000), 524 (124 000), 654 (30 000), 682
(29 400), 732 (30 000). Anal. Calcd for PdNi2C138N10H148S2‚
3H2O: C, 72.42; H, 6.78; N, 6.12. Found: C, 72.44; H, 6.68; N,
5.81.
6H, Hmeta+para), 7.35 (s, 2H, CHO).
1
26 (Cis, Ar ) Phenyl). H NMR (500 MHz, C2D2Cl4, 65 °C):
δ ) 9.20, 8.85 (2d, 2 + 2H, J ) 4.8 Hz, pyrrole), 8.59, 8.53 (2d,
2 + 2H, J ) 5.1 Hz, pyrrole), 8.47, 8.40 (2d, 2 + 2H, J ) 4.8 Hz,
pyrrole), 8.44 (dd, 2H, J ) 7.8 and 1.2 Hz, cyclized phenyl), 7.71
(dd, 2H, J ) 7.8 and 1.2 Hz, cyclized phenyl), 7.42 (ddd, 2H, J )
7.8, 7.6, and 1.2 Hz, cyclized phenyl), 6.69 (ddd, 2H, J ) 7.8, 7.6,
and 1.2 Hz, cyclized phenyl), 8.09 (broad m, 8H, Hortho), 7.96 (broad
m, 4H, Hortho), 7.84, 7.76, 7.67 (3m, 3 × 6H, Hmeta+para), 7.78 (s,
2H, CHO). UV-vis (CH2Cl2): λmax ) 415 (ꢀ ) 84 000 sh), 450
(139 000 sh), 478 (196 000), 560 (25 400), 622 (21 000), 668
(38 300). Anal. Calcd for PdNi2C90N10H52O2‚H2O: C, 69.86; H,
3.52; N, 9.05. Found: C, 70.01; H, 3.53; N, 8.82.
Palladium(II) Dimers 22 (or 23) and Palladium(II) Metalated
20 (or 21). To a solution of palladium(II)acetylacetonate (150 mg,
0.492 mmol) in chloroform (25 mL) heated at 60 °C was added
dropwise (addition over 8 h) a solution of nickel porphyrin 17 (or
18) (40 mg, 0.056 mmol) in chloroform (15 mL). The solvent was
evaporated, and the solid residue was taken up in a mixture of
dichloromethane/hexane 1/1. The less soluble dimer 22 (or 23) was
isolated by filtration in 77% (or 75%) yield. The filtrate was
concentrated and chromatographed on silica gel (eluent: dichlo-
romethane/hexane 1/1 to dichloromethane). The metalated monomer
20 (or 21) was obtained, after crystallization from dichloromethane/
methanol, in 16% (or 15%) yield.
22 (Ar ) Phenyl). 1H NMR (300 MHz, C2D2Cl4, 75 °C): δ )
9.19, 8.72 (2d, 2 + 2H, J ) 5.1 Hz, pyrrole), 8.49, 8.38 (2d, 2 +
2H, J ) 5.0 Hz, pyrrole), 8.47, 8.30 (2d, 2 + 2H, J ) 4.8 Hz,
pyrrole), 8.37 (broad dd, 2H, cyclized phenyl), 8.26 (broad dd, 2H,
cyclized phenyl), 7.86 (broad ddd, 2H, cyclized phenyl). 7.71 (broad
ddd, 2H, cyclized phenyl), 7.95-8.10, 7.80-7.92 and 7.62-7.78
(m, 30H, meso phenyl), 7.35 (broad s, 2H, NH). UV-vis (CH2-
Cl2): λmax ) 416 (ꢀ ) 60 000), 450 (93 000 sh), 472 (127 000 sh),
486 (136 000), 608 (25 000), 640 (27 000), 662 (31 000). Anal.
Calcd for PdNi2C90N10H52O2‚CH3OH: C, 70.01; H, 3.62; N, 8.97.
Found: C, 70.02; H, 3.52; N, 8.65.
23 (Ar ) p-Tolyl). 1H NMR (500 MHz, C2D2Cl4, 80 °C): δ )
9.23, 8.78 (2d, 2 + 2H, J ) 5.2 Hz, pyrrole), 8.51, 8.40 (2d, 2 +
2H, J ) 4.8 Hz, pyrrole), 8.50, 8.40 (2d, 2 + 2H, J ) 4.5 Hz,
pyrrole), 8.16 (d, 2H, J ) 7.6 Hz, cyclized phenyl), 7.99 (d, 2H, J
∼ 1 Hz, cyclized phenyl), 7.66 (dd, 2H, J ) 7.6 and 1 Hz, cyclized
phenyl), 7.86, 7.91, and 7.92 (3d, 3 × 4H, J ) 7.7 Hz, tolyl), 7.49,
7.52, and 7.69 (3d, 3 × 4H, J ) 7.7 Hz, tolyl), 2.64, 2.65, 2.67,
and 2.84 (4s, 4 × 6H, Me). UV-vis (CH2Cl2): λmax ) 418 (ꢀ )
56 000), 486 (129 000), 610 (28 400), 664 (35 300). Anal. Calcd
for PdNi2C98N10H68O2‚2H2O: C, 70.17; H, 4.33; N, 8.35. Found:
C, 70.27; H, 4.06; N, 8.28.
Palladium Dimer 28. To a solution of nickel enaminothioalde-
hyde 11 (72 mg, 0.1 mmol) in dichloromethane (30 mL) was added
dropwise (1.5 h of addition) at 60 °C under argon a solution of
palladium(II) acetate (12 mg, 0.053 mmol) in dichloromethane (15
mL). The advancement of the reaction was followed by silica gel
TLC (eluent: hexane/dichloromethane 1/1). The solvent was
evaporated and the residue chromatographed on a silica gel column
(eluent: hexane/dichloromethane from 3/1 to 1/1). After crystal-
lization from chloroform/methanol, dimer 28 was obtained in 77%
yield.
1
28. H NMR (400 MHz, C2D2Cl4, 85 °C): δ ) 9.07, 8.80 (2d,
2 + 2H, J ) 4.8 Hz, pyrrole), 8.52, 8.48 (2d, 2 + 2H, J ) 5.1 Hz,
pyrrole), 8.40, 8.37 (2d, 2 + 2H, J ) 4.8 Hz, pyrrole), 8.38 (dd,
2H, J ) 7.8 and 1.2 Hz, cyclized phenyl), 7.95 (dd, 2H, J ) 7.8
and 1.2 Hz, cyclized phenyl), 7.29 (ddd, 2H, J ) 7.8, 7.6, and 1.2
Hz, cyclized phenyl), 6.14 (ddd, 1H, J ) 7.8, 7.6, and 1.2 Hz,
cyclized phenyl), 7.94-8.08 (m, 12H, Hortho), 7.67, 7.76, 7.85 (3m,
3 × 6H, Hmeta+para), 8.18 (s, 2H, CHS). UV-vis (CH2Cl2): λmax
)
432 (ꢀ ) 120 000), 506 (146 000), 572 (24 000), 628 (17 800), 714
(27 600). Anal. Calcd for PdNi2C90N10H52S2‚1/2CHCl3: C, 67.05;
H, 3.26; N, 8.64. Found: C, 67.20; H, 3.25 N, 8.63.
1
20 (Ar ) Phenyl). H NMR (300 MHz, CDCl3, 45 °C): δ )
9.09, 8.65 (2d, 1 + 1H, J ) 4.8 Hz, pyrrole), 8.41, 8.29 (2d, 1 +
1H, J ) 4.8 Hz, pyrrole), 8.37, 8.35 (2d, 1 + 1H, J ) 4.8 Hz,
pyrrole), ∼8.20 (broad dd, 1H, cyclized phenyl), ∼8.10 (broad dd,
1H, cyclized phenyl), ∼7.69 (broad ddd, 1H, cyclized phenyl).
∼7.40 (broad ddd, 1H, cyclized phenyl), 7.58-7.96 (m, 15H, meso
phenyl), ∼7.40 (broad s, 1H, NH), 5.43 (s, 1H, acac), 2.10, 2.09
(2s, 3 + 3H, Me acac). UV-vis (CH2Cl2): λmax ) 412 (ꢀ )
38 400), 446 (62 000 sh), 466 (85 000 sh), 606 (11 000), 636
(14 000), 658 (19 200). Anal. Calcd for PdNiC50N5H33O3‚H2O: C,
64.23; H, 3.77; N, 7.49. Found: C, 64.10; H, 3.48; N, 7.43.
Electrochemical Studies. Dichloromethane was purchased
spectroscopic grade from Merck, dried over molecular sieves (4
Å), and stored under argon prior to use. NBu4PF6 was purchased
electrochemical grade from Fluka and used as received. The
electrochemical experiments were carried out at room temperature
in dichloromethane containing 0.1 M NBu4PF6 in a classical three-
electrode cell. The working electrode was either a glassy carbon
disk electrode (3 mm diameter) or a platinum disk electrode (2
mm diameter) used either in motionless mode for cyclic voltam-
metry (CV: 10 mV‚s-1 to 10 V‚s-1) or as rotating disk electrode
for rotating disk voltammetry (RDV). The electrochemical cell was
connected to a computerized multipurpose electrochemical device,
AUTOLAB (Eco Chemie BV-Utrecht, The Netherlands), driven
1
21 (Ar ) p-Tolyl). H NMR (300 MHz, CDCl3, 45 °C): δ )
9.08, 8.66 (2d, 1 + 1H, J ) 5.1 Hz, pyrrole), 8.43, 8.29 (2d, 1 +
1H, J ) 4.8 Hz, pyrrole), 8.39, 8.34 (2d, 1 + 1H, J ) 5.1 Hz,
pyrrole), 8.11 (d, 1H, J ) 8.0 Hz, cyclized phenyl), 7.93 (d, 1H, J
262 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis of New Porphyrins
by GPES software running on a personal computer. All potentials
are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used
as an internal standard. The auxiliary electrode was a Pt wire, and
a Pt wire was also used as a pseudo-reference electrode. The
accessible potentials ranged from +1.2 to -2.4 V vs Fc/Fc+ in
dichloromethane.
diffractometer, graphite-monochromated Mo KR, 2.5 < θ < 29.13°,
and temperature 173 K. A total of 5232 unique reflections having
I > 3σ(I) were used to determine and refine the structure. Final
results: R ) 0.052, Rw ) 0.070, GOF ) 1.039, and largest peak
in final difference ) 1.183 e Å-3
.
Acknowledgment. We thank A. Decian and N. Kyrit-
sakas (Service Commun de Rayons X, Universite´ Louis
Pasteur) for solving the structures, E. Mastio, P. Wehrung,
R. Huber, and C. Dietrich for the mass spectra, and A.
Maniette for help.
Crystal Data for Nickel Enaminoporphyrin 5. C44H27N5Ni‚
CH2Cl2, M ) 769.38, triclinic, space group P1h, a ) 10.2958(2) Å,
b ) 10.5646(3) Å, c ) 16.7828(5) Å, R ) 102.178(5)°, â ) 92.441-
(5)°, γ ) 97.380(5)°, V ) 1765.04(8) Å3, Z ) 2, and Dc ) 1.45 g
cm-3. A total of 13 037 (h ( k + l reflections were collected on
a green crystal of dimensions 0.10 × 0.08 × 0.08 mm3, using a
KappaCCD diffractometer, graphite-monochromated Mo KR, 2.5
< θ < 29.10°, and temperature 173 K. A total of 6790 unique
reflections having I > 3σ(I) were used to determine and refine the
structure. Final results: R ) 0.068, Rw ) 0.086, GOF ) 1.248,
Supporting Information Available: X-ray data for compounds
5 and 8 (CIF file), text giving the NMR data for the tolyl derivatives
6, 9, and 25 (relevant NOE correlations from the ROESY spectrum
of 25, demonstrating that 25 is the trans isomer), and figures giving
the electronic spectra of monomer 8 and dimer 26, electronic spectra
of dimer 26 before and during electrolysis, MALDI-TOF spectra
of dimers 23 and 28, and X-ray structures of enamine 5 and
enaminoaldehyde 8. This material is available free of charge via
the Internet at http://pubs.acs.org.
and largest peak in final difference ) 0.907 e Å-3
.
Crystal Data for Nickel Enaminoaldehyde 8. 2(C45H27N5NiO)‚
CH2Cl2‚H2O, M ) 1527.87, monoclinic, space group P121/c1, a
) 22.5313(3) Å, b ) 9.6798(2) Å, c ) 17.6195(6) Å, â ) 107.796-
(5)°, V ) 3658.9(2) Å3, Z ) 2, and Dc ) 1.39 g cm-3. A total of
16 565 (h (k + l reflections was collected on a crystal of
dimensions 0.25 × 0.04 × 0.02 mm3, using a KappaCCD
IC035203D
Inorganic Chemistry, Vol. 43, No. 1, 2004 263