Synthesis, structure, and redox properties of N-confused bis(porphyrinatonickel(II)) linked by o-xylene

Article abstract of DOI:10.1021/ic061793e

In a reaction of 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrinato nickel(II) 2 with α,α′-dibromo-o-xylene, three different complexes containing a xylene moiety were obtained in the presence of a proton scavenger. The products were characterized by mass spectrometry, UV-vis, NMR, and, in the case of the dimeric complex 3, X-ray crystallographic analysis (space group P1, a =16.455(3) A, b = 16.776(3) A, c = 18.400(4) A, α = 77.43(3)°, β = 75.31(3)°, γ = 66.20(3)°, V = 4457.1(19) A³, Z = 2). The monomeric species, diamagnetic 4 and paramagnetic 5, contain one and two bromoxylene residues, respectively, while in 3, the xylene bridge links two macrocyclic subunits, involving their internal carbons (C21) coordinated to diamagnetic nickel(II). Cyclovoltammetric measurements for o-xylene-linked bis(carbaporphyrinoid) 3 indicate cooperative effects resulting from an interaction between the subunits despite the isolation of their aromatic π-bond systems. An EPR-controlled titration of 3 with bromine allows consecutive detection of the mono- and bis-oxidized species (3Br, 3Br₂). The spectral patterns and spin-Hamiltonian parameters indicate metal-centered oxidation in 3Br (g_x = 2.358, g_y = 2.150, g_z = 2.062, A_x^Br = 15, A _y^Br = 35, A_z^Br = 129 G) and interaction of two electron spins of nickel(III) ions in 3Br₂ (g _x = 2.328, g_y = 2.195, g_z = 2.065, D = 0.0173 cm^-1, E = -0.0018 cm^-1, A_z^Br = 63 G). A product of the chemical reduction of a protonated form of the dimer was also detected by means of EPR (g₁= 2.298, g₂ = 2.218, g₃ = 2.192), although no interaction between the nickel(I) centers can be observed for the reduced species.

Full text of DOI:10.1021/ic061793e

Inorg. Chem. 2007, 46, 1617−1626
Synthesis, Structure, and Redox Properties of N-Confused
Bis(porphyrinatonickel(II)) Linked by o-Xylene
Piotr J. Chmielewski*
Department of Chemistry, UniVersity of Wroclaw, 14 F. Joliot-Curie Street,
50-383 Wroclaw, Poland
Received September 21, 2006
In a reaction of 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrinato nickel(II) 2 with
R,R′-dibromo-o-xylene, three different
complexes containing a xylene moiety were obtained in the presence of a proton scavenger. The products were
characterized by mass spectrometry, UV vis, NMR, and, in the case of the dimeric complex 3, X-ray crystallographic
analysis (space group P1, a 16.455(3) Å, b 16.776(3) Å, c 18.400(4) Å, R ) 77.43(3) â ) 75.31(3)
γ ) 66.20(3) , V 2). The monomeric species, diamagnetic 4 and paramagnetic 5, contain
4457.1(19) Å3, Z
−
h
)
)
)
°
,
°,
°
)
)
one and two bromoxylene residues, respectively, while in 3, the xylene bridge links two macrocyclic subunits,
involving their internal carbons (C21) coordinated to diamagnetic nickel(II). Cyclovoltammetric measurements for
o-xylene-linked bis(carbaporphyrinoid) 3 indicate cooperative effects resulting from an interaction between the subunits
despite the isolation of their aromatic
π-bond systems. An EPR-controlled titration of 3 with bromine allows consecutive
detection of the mono- and bis-oxidized species (3Br, 3Br2). The spectral patterns and spin-Hamiltonian parameters
indicate metal-centered oxidation in 3Br (gx
and interaction of two electron spins of nickel(III) ions in 3Br2 (gx
)
2.358, gy
)
2.150, gz
)
2.062, ABx r 35, ABz r
)
15, ABy r
)
)
)
129 G)
0.0173
)
2.328, gy 2.195, gz ) 2.065, D
)
cm-1, E ) −0.0018 cm-1, ABz r
also detected by means of EPR (g1
)
63 G). A product of the chemical reduction of a protonated form of the dimer was
2.298, g2 2.218, g3 2.192), although no interaction between the
nickel(I) centers can be observed for the reduced species.
)
)
)
Introduction
peculiar reactivity of metal complexes.25-36 The alterations
of optical, acid-base, coordination, and redox properties of
the macrocycle allow fine-tuning or profound variation of
the properties of the complex. The special character of the
confused pyrrole is reflected by its susceptibility to various
types of reaction, also in the free-base porphyrin, that lead
to the formation of many derivatives bearing substituents
Since its discovery in 1994, N-confused (inverted) por-
phyrin NCP, 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin
11-3 has continued to attract attention because of its remark-
able tendency to form a variety of rare organometallic
compounds,4-12 multimodal coordination properties,11-24 and
* E-mail: pjc@wchuwr.chem.uni.wroc.pl.
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10.1021/ic061793e CCC: $37.00
Published on Web 02/02/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 5, 2007 1617

Chmielewski
Chart 1
Scheme 1
on the external nitrogen (N2),37-40 external carbon (C3),41-43
or internal carbon (C21).44,45 A facile modification of these
properties makes 1 a potentially attractive “replacement” of
regular porphyrins in molecular46.47 and supramolecular
systems48-52 as long as the aromatic character of the
macrocycle is retained. A built-in external coordinating site
of 1 or some of its derivatives, that is, the exposed outer
nitrogen of the confused pyrrole, has been shown to be
involved in the formation of the coordinatively linked
oligomers.15,18-20,22,33,53,54 Also, a number of covalent dimers
consisting of N-confused porphyrin subunits linked either
directly43,55 or by an alkanyl bridge27,29,38 have been reported
recently.The present contribution is focused on the synthesis
(24) Toganoh, M.; Konagawa, J.; Furuta, H. Inorg. Chem. 2006, 45, 3852.
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Soc. 1996, 118, 5690.
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8917.
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L. J. Am. Chem. Soc. 2004, 126, 4420-4431.
(34) Bohle, D. S.; Chen, W.-C.; Hung, C.-H. Inorg. Chem. 2002, 41, 3334.
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M.-T. Org. Lett. 2004, 6, 1393.
and characterization of N-confused porphyrin nickel com-
plexes comprising an o-xylene fragment. One of these
complexes consists of two porphyrinoid subunits covalently
linked by such a semirigid bridge. We show here that these
subunits interact despite the lack of coupling between the
π-electron systems, which is reflected by the redox and
spectroscopic properties of the dimer.
Results and Discussion
Synthesis and Characterization. Complexes 3-5 can be
obtained by combining the NCP nickel(II) complex 2 with
1,2-bis(bromomethyl)benzene (XylBr2), depending on the
reaction conditions (Scheme 1). Several factors, such as
excess of the alkylation agent, type of proton scavenger
applied, and reaction temperature, influence the relative yield
of 2- or 21-substituted products. Similar effects have been
observed previously for mono- or dihaloalkanes.27,28 In the
case of XylBr2, however, the reaction with 2 can be
optimized either with respect to the dimer 3 or to the systems
comprising one (4) or two (5) 2-(bromomethyl)benzyl groups
(Scheme 1). Although known as being a reactive electro-
phile,38 the bromobenzyl group remains intact under the
present reaction conditions and with the applied separation
methods, except for the relatively slow formation of the
dimer 3. It makes monomeric systems 4 and 5 readily
obtainable and promising intermediates for the construction
of bigger molecular assemblies containing the N-confused
porphyrin fragment and o-xylene bridges. The mass spectra
of complexes 3, 4, and 5 (m/z ) 1556.8, 911.2, and 1174.1
amu, respectively) are in agreement with their compositions.
The optical spectra of 3 and 4 (Figure 1) are almost
identical except for the molar extinction coefficients which
are about twice as high for each of the bands in the spectrum
(36) Furuta, H.; Maeda, H.; Osuka, A. Org. Lett. 2002, 4, 181.
(37) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. J. Chem. Soc., Perkin Trans.
2 1995, 503.
(38) Chmielewski, P. J. Org. Lett. 2005, 7, 1789.
(39) Qu, W.; Ding, T.; Cetin, A.; Harvey, J. D.; Taschner, M. J.; Ziegler,
C. J. J. Org. Chem. 2006, 71, 811.
(40) Li, X.; Chmielewski, P. J.; Xiang, J.; Xu, J.; Li, Y.; Liu, H.; Zhu, D.
Org. Lett. 2006, 8, 1137.
(41) Schmidt, I.; Chmielewski, P. J. Tetrahedron Lett. 2001, 42, 1151.
(42) Schmidt, I.; Chmielewski, P. J. Tetrahedron Lett. 2001, 42, 6389.
(43) Chmielewski, P. J. Angew. Chem., Int. Ed. 2004, 43, 5655.
(44) Ishikawa, Y.; Yoshida, I.; Akaiwa, K.; Koguchi, E.; Sasaki, T.; Furuta,
H. Chem. Lett. 1997, 453.
(45) Furuta, H.; Ishizuka, T.; Osuka, A.; Ogawa, T. J. Am. Chem. Soc.
1999, 121, 2945.
(46) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L. Coord. Chem. ReV. 2000, 204,
113.
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2001, 101, 2751.
(48) Atwood, J. L.; Davies, J. E.; MacNicol, D. D.; Vogtle, F. E.
ComprehensiVe Supramolecular Chemistry; Pergamon: Oxford, U.K.,
1996.
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Commun. 2006, 1866.
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WCH: Wenheim, Germany, 1995.
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S.; Araki, Y.; Ito, O. Inorg. Chem. 2006, 45, 5057.
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5077.
1618 Inorganic Chemistry, Vol. 46, No. 5, 2007

N-Confused Bis(porphyrinatonickel(II))
Figure 1. Optical spectra (CH2Cl2) of 3 (black solid line), 4 (red dashed),
and 5 (blue dotted).
of the dimeric complex than those of the monomeric species.
That reflects the identity of chromophores in these systems
and lack of conjugation between the aromatic subunits in
the dimeric system 3, which would lead to a vibronic splitting
of the Soret-type band at 434 nm.43 On the other hand, the
spectral features observed for 5, that is, a significant decrease
of the Soret-like band and increase of the band intensities at
higher wavelengths, are related to a reduction of the aromatic
character of the system.
1H and 13C NMR spectroscopy, including homo- and
heteronuclear 2D techniques, were applied for the charac-
terization of the new compounds. The low symmetry of 1
and its derivatives makes their NMR spectra complicated
but rich in structural information, sometimes allowing
observation of a unique signal for each proton.27,29,38,53
Because of their aromatic character, the close distance
between porphyrinoid subunits as well as their arrangement
can be recognized on the basis of characteristic up- or
downfield shift of particular proton signals caused by the
macrocyclic ring current.
Figure 2. 1H NMR spectra (500 MHz, CDCl3, 298 K) of 3 (trace A) and
4 (trace B). The assignments are as follows: pyrr ) â-pyrrole, Me ) para-
methyl groups of meso-tolyl substituents, 21-CH2 ) diastereotopic meth-
ylene groups bound to the internal carbon (the a and b indices are introduced
to distinguish diastereomers), CH2Br ) one of the signals of diastereotopic
bromomethyl group (the other is obscured by Me signals), 3, 3a, and 3b )
protons on the external carbon of the confused pyrrole in 4 and in
diastereomers of 3; x-o, x-m ) phenylene ortho and meta protons of the
xylene bridge.
In the Figure 2, the effect of proximity of two aromatic
macrocyclic rings in 3 is clearly seen as a strong upfield
shift (2 ppm) of signals of the diastereotopic methylene
protons of the xylene fragment (21-CH2) with respect to that
in the monomeric complex 4. Also the signal of H3, that is,
the proton bound to the external carbon C3 of the confused
Figure 3. 1H NMR spectrum of 5 (500 MHz, 3, 298 K). The assignments
are as follows: pyrr ) â-pyrrole protons, 21-CH2 and 2-CH2 ) methylene
protons of the substituents attached to the internal carbon and external
nitrogen of the confused pyrrole, respectively, 3 ) proton on the external
nitrogen of the confused pyrrole, s ) solvent. The signal of water dissolved
in CDCl3 is marked with asterisk.
1
pyrrole, and those of the â-pyrrole protons in the H NMR
spectrum of 3 are shifted to lower frequencies relative to
those observed for 4. The synergetic effect of two ring
currents indicates an eclipsed arrangement of the porphy-
rinoid subunits. The spectrum of 3 or 3a consists of two
sets of signals of the same intensity which is accounted for
by a presence of a pair of diastereomers. It is particularly
well demonstrated by the presence of four doublets of the
diastereotopic methylene protons in the high-field region
around -3 ppm. Also, in the case of 3, eight signals of
methyl groups of the meso-tolyl substituents occur in the
region of 2.9-2.3 ppm. Although the molecule of dimer
possesses an effective twofold symmetry, each of the two
coordinated sp3 carbons of the confused pyrrole (C21)
constitutes a stereogenic center. Thus, two NMR-distinguish-
able stereoisomers can be observed: a pair of RR and SS
1
enantiomers and an achiral RS meso form. In the H-13C
HMBC experiments (3a, CDCl3, 298 K), protons H3 and
the diastereotopic methylene 21-CH2 correlate with carbon
C21 at 39.4 (diastereomer a) and 39.6 ppm (diastereomer
b), that is, in the region typical for sp3 carbons. That indicates
similarity of the coordination core structure of 3 or 3a to
other 21-alkylated nickel(II) complexes.25,27,28,29,53
The 1H NMR spectrum of 5 (Figure 3) reveals the
paramagnetic character of the 2,21-bis(bromoxylene)-
substituted system. The triplet ground state of the nickel(II)
ion is caused by changes in the coordination properties of
Inorganic Chemistry, Vol. 46, No. 5, 2007 1619

Chmielewski
1
Figure 4. Dependencies of chemical shifts (A) and of logarithms of H NMR line half-widths (B) on reciprocal temperature for pyrrole and methylene
protons of 5.
the macrocycle in 5 which has character of a monoanionic
tridentate ligand with only weak side-on interaction of C21
with metal center.25 The spectrum resembles those of nickel-
(II) complexes of 2,21-dimethylated or 2-protonated-21-
alkylated derivatives of 125,28 with strong downfield shifts
of the â-pyrrole signals (25-60 ppm), upfield shift of the
signal of proton 3 (-1.7 ppm), and strong broadening of
signals of the fragment directly bonded to the internal carbon
(21-CH2). The methylene protons are diastereotopic, but the
differentiation of their chemical shift (about 5 ppm) is much
poorer than in the case of 2-protonated-21-benzylated NCP
nickel(II) chloride complex where signal separation for the
21-CH2 fragment was close to 50 ppm at 298 K.28
The chemical shift temperature dependencies for pyrrole
protons of 5 (Figure 4A) only slightly decline from the Curie
behavior with intercepts close to the chemical shifts of
diamagnetic references. On the other hand, nonzero intercepts
are observed for the isotropic shifts of the methylene
fragments directly connected with the macrocycle indicating
some contribution of the dipolar interaction resulting from
a zero-field splitting anisotropy that introduces a T-2-
dependent curvature.56 This dipolar interaction along with
possible conformational dynamics of the molecule seem to
be also responsible for a peculiar temperature dependence
of the line width ν1/2 of one of the methylene protons attached
to the nitrogen of the confused pyrrole (2-CH2). For
Figure 5. X-ray structure of 3. (top) An ORTEP representation with 30%
nonviscous solutions, the dependencies of logarithms of ν1/2
versus T-1 are expected to be linear with the same positive
slope for all protons of the given paramagnetic system.57,58,59
As shown in Figure 4B, all but one of the dependencies of
ln(ν1/2) ) f(1/T) present similar slopes despite various
positions and distances of protons with respect to the
paramagnetic center. The exceptionally strong dependence
for one proton of the diastereotopic pair could in principle
be related to a temperature dependent conformational equi-
librium involving rotation about a C-N bond. A nonlinear
temperature dependence of signal linewidths has been
observed in the case of benziporphyrin nickel(II) complexes
thermal ellipsoids and atom numbering scheme (all hydrogens and solvent
molecules are omitted). (bottom) Two projections of wire-frame representa-
tion (all meso-aryl substituents are omitted for clarity) showing arrangement
and distortions of the subunits. The structure presents one out of the three
possible stereoisomers. The diastereomers are indistinguishable because of
a C-N site disorder on the confused pyrrole.
and rationalized in terms of conformational flexibility of the
system with aryl ring weakly interacting with metal ion.60
Solid-State Characterization of 3. The X-ray structure
of 3 confirms the integrity and identity of the compound
and reveals a face-to-face orientation of the porphyrinoid
subunits in the solid state (Figure 5). To the best of our
knowledge, this is the first example of a structurally
characterized bis(porphyrin) with a covalent linker that spans
between the coordination systems of the macrocyclic sub-
units.61 In each of the macrocyclic fragments, the nickel(II)
(56) NMR of Paramagnetic Molecules. Principles and Applications; La Mar,
G. N., Horrocks, W. D., Jr., Holm, R. H., Eds; Academic Press: New
York, 1973.
(57) Satterlee, J. D.; La, Mar, G. N.; Bold, T. J. J. Am. Chem. Soc. 1977,
99, 1088.
(58) La Mar, G. N.; Sherman, E. O. J. Am. Chem. Soc. 1970, 92, 2691.
(59) Bertini, I.; Luchinat, C. Coord. Chem. ReV. 1996, 150, 1.
(60) Stepien´, M.; Latos-Graz˘yn´ski, L.; Szterenberg, L. Inorg. Chem. 2004,
43, 6654.
1620 Inorganic Chemistry, Vol. 46, No. 5, 2007

N-Confused Bis(porphyrinatonickel(II))
ion is coordinated in a square-planar fashion which is in line
with a diamagnetic character of 3. Each coordination core
consists of three pyrrolic nitrogens and one pyramidal carbon
atom. The metal-donor distances (Å) (Ni1-C21 ) 2.012-
(7), Ni1-N22 ) 1.944(7), Ni1-N23 ) 1.957(5), Ni1-N24
) 1.946(7), Ni2-C45 ) 2.018(7), Ni2-N46 ) 1.943(6),
Ni2-N47 ) 1.958(7), Ni2-N48 ) 1.955(5)) are similar to
those observed for the nickel(II) complex of 21-methylated
derivative of 1.25 Both subunits display the same saddle-
shape distortion of the macrocyclic ring with the plane of
the confused pyrrole tipped out of the mean plane of the
macrocycle. The set of donors and the metal atom are
essentially coplanar with an average displacement from the
mean plane of 0.02 Å. The subunits are nearly parallel with
an angle between the mean macrocyclic planes of 16° and
with the dihedral angle between planes defined by the
NiCNNN atom sets of only 2.6(3)°. Because of the angular
character of the o-xylene bridge, the subunits are shifted with
respect to each other, which increases the distance between
metal centers to 5.77 Å. Although a mixture of diastereomers
is observed by the solution NMR (Figure 2A), their presence
cannot be determined in the solid-state because of the
disorder of molecule. The difference in the electron density
of nitrogen and carbon is too small to allow distinction
between atoms that actually occupy sites N2, C3, N26, and
C27. This is indicative of fourfold disorder on the confused
pyrroles.
The structure of 3 is to some extent related to the cofacial
metallobisporphyrins62-64 or metallobiscorroles65-69 except
for intrinsic chirality of one of its diastereomers and rotational
freedom on the bridging xylene fragment. Such a rotation,
which seems to be facile in solution, allows changes in the
arrangement of the macrocyclic subunits with respect to each
other and with respect to the bridge.
Protonation and Redox Properties. The external nitrogen
of the confused pyrrole in 21-substituted derivatives of NCP
nickel(II) complexes is nucleophilic, and its protonation25,28,29
or coordination to a metal ion53 has been shown for a number
of monomeric systems. In the dimeric complex 3, there are
two basic sites, and the process of their protonation may
reflect interaction between the subunits.
Figure 6. 1H NMR spectra (500 MHz, CDCl3) of [3(HCl)2] at T ) 253
(A), 233 (B), and 213 K (C).
is reflected by significant changes in the 1H NMR spectrum
with a strong paramagnetic shift of pyrrole and methylene
signals similar to those observed for the monomeric sys-
tems.25,28 Because of the fast chemical exchange at room
temperature, the spectral lines are very broad, but they
sharpen at lower temperatures allowing observation of the
high-field shifted signal of 2-NH protons and two sets of
downfield shifted â-pyrrole protons (Figure 6). The number
of resonances originates from the presence of diastereomers
described above for 3 rather than from the simultaneous
presence of mono- and bisprotonated species since the
relative intensities of signals do not vary with the amount
of acid. It seems that even at low temperature the rate of
exchange between mono- and bisprotonated complexes is
too high to allow observation of separate signals for these
species. Alternatively, the simultaneous protonation of both
nitrogen sites can be taken into account, which would imply
lack of any electrostatic interaction between the subunits.
The dependence of the chemical shifts in the limited
temperature range (253-213 K) displays Curie behavior and
thus no effects are observed that could be related to an
interaction of the paramagnetic centers.
The two-stage character of the protonation of 3 can be
inferred from a spectrophotometric titration of the dimer with
trifluoroacetic acid (TFAH) where spectral changes indicate
consecutive formation of two species, which is dependent
on acid concentration (Figure 7A). Importantly, alkalization
of the solution fully reverses the spectral changes indicating
that none of them is related with an acid-induced demetal-
lation. In contrast, formation of only one protonated species
is observed upon addition of TFAH to the solution of
monomeric complex 4 up to 3-fold excess and further
changes are attributed to the demetallation (see Supporting
Information).
Acidification of 3 by addition of chloroform saturated with
gaseous hydrogen chloride leads to changes of the ground
state of the nickel(II) from singlet to triplet because of
concurrent coordination of the chloride to the metal ion. It
Oxidation of 3 with bromine was monitored by UV-vis
spectrometry. The spectrophotometric titration with Br2
indicates that the process consists of two well-separated steps
(Figure 7B) suggesting presence of two redox-active sites
of various oxidation potentials.
Cyclovoltammetric measurements were performed in
dichloromethane using [BuN4]ClO4 supporting electrolyte
and referenced against a ferrocene/ferrocenium couple as an
internal standard. The representative electrochemical experi-
ments are presented in Figure 8, and the data are collected
in Table 1.
(61) Setsune, J.; Ito, S.; Takeda, H.; Ishimaru, Y.; Kitao, T.; Sato, M.;
Ohya-Nishiguchi, H. Organometallics 1997, 16, 597.
(62) Collman, J. P.; Wagenknecht, P. S.; Hutchison, J. E. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1537.
(63) Chang, C. J.; Deng, Y.; Heyduk, A. F.; Chang, C. K.; Nocera, D. G.
Inorg. Chem. 2000, 39, 959.
(64) Deng, Y.; Chang, C. J.; Nocera, D. G. J. Am. Chem. Soc. 2000, 122,
410.
(65) Jerome, F.; Billier, B.; Barbe, J. M.; Espinosa, E.; Dahaoui, S.;
Lecomte, C.; Guilard, R. Angew. Chem., Int. Ed. Engl. 2000, 39, 4051.
(66) Guilard, R.; Gros, C. P.; Bolze, F.; Jerome, F.; Ou, Z.; Shao, J.; Fischer,
J.; Weiss, R.; Kadish, K. M. Inorg. Chem. 2001, 40, 4845.
(67) Guilard, R.; Jerome, F.; Barbe, J. M.; Gros, C. P.; Ou, Z.; Shao, J.;
Fischer, J.; Weiss, R.; Kadish, K. M. Inorg. Chem. 2001, 40, 4856.
(68) Jerome, F.; Barbe, J. M.; Gros, C. P.; Guilard, R.; Fischer, J.; Weiss,
R. New J. Chem. 2001, 93.
The cyclic voltammogram of 3 consists of two reduction
couples separated by 150 mV and two irreversible oxidation
(69) Pacholska, E.; Espinosa, E.; Guilard, R. Dalton Trans. 2004, 3181.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1621

Chmielewski
Figure 7. Selected spectra recorded upon spectrophotometric titration of 3 with TFAH (A) and with Br2 (B). Black solid line, 0 equiv; red dashed, 1.2
equiv; blue dotted, 4 equiv.
unprotonated species. It reflects a higher tendency of the
positively charged system to accept an additional electron.
On the other hand, such a strong anodic shift can be related
to the change of the reduction site from the ligand in 3 to
the metal ion in its diprotonated form [3(TFAH)2]. As it was
in the case of the unprotonated dimer, the reduction wave is
split into two reversible couples indicating stepwise addition
of electrons and, thus, interaction between the subunits also
in their protonated forms. However, the oxidation processes
in the case of [3(TFAH)2] are represented by only one broad,
unresolved, and irreversible wave appearing at the potential
close to the mean value of the two oxidation potentials
observed for 3.
The differences of the oxidation/reduction potentials of
the consecutive steps of electron removal/addition arise from
the Coulombic interaction between the redox centers, but
they can be also interpreted in terms of the relative stability
of a “mixed valence” species.70,71 In general, the processes
Figure 8. Cyclic voltammograms (CH2Cl2, 0.1 M TBAP) of 4 (A), dimeric
complex 3 (B), and its bisprotonated form [3(HTFA)2] (C).
Table 1. Anodic (Ea) and Cathodic (Ec) Peak Potentials of the Redox
Couples in Cyclovoltammograms Recorded for 3 and 4 in CH2Cl2
that occur in the system can be represented as follows
oxidation
reduction
Ox-Ox + e- a Ox-Red (E1)
complex
Ea
Ec
Ea
Ec
3
210
420
190
385
235
835
340
55
80
25
300
109
776
100
-1476
-1630
-1467
-1620
-1554
-1700
-1542
-1690
-1405
Ox-Red + e- a Red-Red (E2)
3a
4
Ox-Ox + Red-Red a 2Ox-Red (Kcom
)
where E1 and E2 are formal potentials of the consecutive
redox processes and Kcom is an equilibrium constant for a
comproportionation reaction reflecting stability of the mixed-
valence species. The difference of potentials, ∆E ) E2 -
E1, is related to Kcom by eq 1
[3(HTFA)2]
-897
-997
-962
-1063
wave potentials of which differ by more than 200 mV (Figure
8B). These features indicate a strong cathodic shift of the
second reduction and considerable anodic shift of the second
oxidation potentials because of an electrostatic interaction
between the subunits after addition/abstraction of the electron.
This observation is in agreement with the two-stage chemical
oxidation of 3 described above for the spectrophotometric
titration with bromine. For the reference monomeric complex
4, there is only one reduction and one oxidation process
observed in the respective potential ranges (Figure 8A).
Upon protonation of 3 with an excess of TFAH (Figure
8C), the HOMO-LUMO gap, represented here by the
separation of the first reduction and first oxidation potentials,
decreases by about 500 mV with respect to that of the
∆E ) 0.059 log Kcom
(1)
A value of Kcom ) 4 (equivalent with ∆E ) 35 mV) is
assumed for a purely statistic case where no interaction
between the redox centers takes place, while the lower values
indicate instability of the mixed-valence species. For Kcom
. 4 the monooxidized or monoreduced compound is
expected to be stable. Thus, the value of Kcom ) 3625
(70) Gagne, R. R.; Spiro, C. L.; Smith, T. J.; Hamann, C. A.; Thies, W.
R.; Shiemke, A. K. J. Am. Chem. Soc. 1981, 103, 4073.
(71) Gagne, R. R.; Koval, C. A.; Smith, T. J.; Cimolino, M. C. J. Am.
Chem. Soc. 1979, 101, 4571.
1622 Inorganic Chemistry, Vol. 46, No. 5, 2007

N-Confused Bis(porphyrinatonickel(II))
addition of 3 to the solution of bis-oxidized complex 3Br2
resulted in the reappearance of the spectrum diagnostic for
the mixed-valence species 3Br. This comproportionation
process, indicating relatively high stability of the mixed-
valence species, is expected on the basis of the electrochemi-
cal observations (vide supra).
The oxidation products were concurrently characterized
by ESI mass spectrometry. For the solution containing the
mono-oxidized species, the molecular ion peak of 3 (1556
amu) is accompanied by a signal at 1636 amu in agreement
with the composition of 3Br. Both these signals are still
present in a mass spectrum recorded for the solution
containing bisoxidized species, but a new peak appearing at
1718 amu indicates the formation of the complex consisting
of two bromide ligands, that is, 3Br2. Under electrospray
ionization conditions, the oxidized species undergo decom-
position since in both mass spectra the fragmentation peaks
appear at 831 and 726 amu representing the 21-xylene-
substituted and unsubstituted monomeric nickel complexes
of NCP, respectively. It suggests bond cleavage between
coordinated C21 and the benzylic carbon similar to that
observed under oxidative conditions for benzyl- or allyl-
substituted complexes.28,53
Figure 9. Selection of frozen-solution X-band EPR spectra (77 K, CH2-
Cl2) taken upon a titration of 3 with a Br2 solution: A, 0.9 equiv; B, 2
equiv; C, 4 equiv.
calculated for the oxidation of 3 suggests stability of the
monooxidated species, although it must be taken with care
since the electrochemical oxidation processes are irreversible.
For the reduction of 3, the comproportionation constant is
significantly lower (Kcom ) 362), but a mixed-valence species
generated upon reduction of [3(TFAH)2] for which Kcom
)
68 seems to be even less stable toward disproportionation.
An EPR-controlled titration of 3 with Br2 allows spectro-
scopic identification of the chemically oxidized species. At
lower bromine concentrations, an orthorhombic signal typical
of d7 nickel(III) complexes of NCP derivatives with one
apical bromide ligand dominates the frozen solution EPR
spectrum (CH2Cl2, 77 K), which is presented in the Figure
9A. The spectral parameters of 3Br (gx ) 2.358, gy ) 2.150,
An attempt can be made for bisoxidized species 3Br2 to
rationalize the value of zero-field splitting in terms of the D
parameter dependence on the distance between paramagnetic
centers. For a purely dipolar interaction, general eq 2 provides
a relationship between zero-field splitting value and the
geometry of the system of interacting centers72
D ) 3/4(gâe)2 < (r2 - 3Z2)r-5
>
(2)
gz ) 2.062, ABr ) 15, AyBr ) 35, ABz r ) 129 G) are similar to
x
those obtained for the 21-benzyl-substituted derivative of
nickel(III) NCP complex with bromide ligand.28 Such a
spectral pattern is typical for a predominantly dz2 metal-
orbital contribution to the singly occupied molecular orbital
(SOMO) and indicates metal-centered oxidation of 3. Further
addition of Br2 to the solution of 3 results in a gradual
appearance of another signal, which eventually replaces that
of one-electron oxidized species 3Br. The spectral pattern
of this new signal (Figure 9C) indicates zero-field splitting
resulting from an interaction of two electronic spins, an
orthorhombic symmetry (gx ) 2.328, gy ) 2.195, gz ) 2.065,
D ) 0.0173 cm-1, E ) -0.0018 cm-1), and a coupling with
two bromine nuclei represented by two seven-line sets (AzBr
) 63 G). The spin-Hamiltonian parameters here are those
of the best-fit computer simulated spectrum calculated for
an electronic spin S ) 1 and two equivalent nuclear spins I
) 3/2. Significantly, the value of the hyperfine tensor
principal component ABz r in the spectrum of bis-oxidized
species 3Br2 is about half of that observed for the mixed-
valence complex 3Br. Such a decrease of the hyperfine
constant is typical for the systems with zero-field splitting.72,73
No low-field “∆Ms ) 2” transition is observed for 3Br2. The
where g is a Zeeman principal value that is coaxial with the
principal value of tensor D, âe is a Bohr magneton, r is the
mean distance between the two electrons with parallel spins,
and Z is a component of the interelectron vector expressed
in the principal-axis system. The geometric factors can be
taken from the crystal structure of 3 for a rough approxima-
tion of distances and angular dependencies considering the
semirigid character of the xylene bridge. With the z axis
normal to the molecular macrocyclic planes of the subunits
in 3, the dependence takes a form of the eq 3
D ) 3/4(gâe)2 < (1 - 3cos2Θ)r-3
>
(3)
where Θ is an angle between the axis connecting two metal
centers and the principal z axis. With r ) 5.77 Å and Θ )
34°, an unrealistic low value of 0.0055 cm-1 for |D| is
obtained from eq 3. In fact, the observed value of the zero-
field splitting (0.0173 cm-1) suggests a much shorter distance
between the paramagnetic centers that can be calculated from
eq 3 as r ) 4.31 Å for Θ ) 0°. Although the rotational
freedom on the xylene bridge allows the totally eclipsed
conformation where Θ ) 0°, the closest distance between
the nickel centers can be estimated from a molecular model
as not lower than 4.92 Å. Moreover, it is rational to anticipate
an even larger distance upon coordination of bromide to each
of the metal centers. Thus, it seems that relationship 2 gives
a rather bad approximation of the zero-field splitting
(72) Weil, J. A.; Bolton; J. R.; Wertz, J. E. Electron Paramagnetic
Resonance. Elementary Theory and Practical Applications; John Wiley
& Sons: New York, 1994.
(73) Collman, J. P.; Elliott, C. M.; Halbert, T. R.; Tovrog, B. S. Proc.
Natl. Acad. Sci. U.S.A. 1977, 74, 18.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1623

Chmielewski
Scheme 2
Figure 10. Selected frozen solution EPR spectra (X-band, CH2Cl2, 77
K) taken upon titration of [3(HBr)2] (complex 3 acidified with a 4-fold
molar excess of HBr solution in acetic acid) with bromine (solution in CH2-
Cl2): A, 0.5 equiv; B, 1.4 equiv; C, 4 equiv of Br2.
siderably different from that of 3Br. The spectrum obtained
upon addition of an excess of Br2 is characterized with similar
spin-Hamiltonian parameters as in the case of 3Br2 except
for the hyperfine splitting, and thus a similar interaction of
the paramagnetic centers can be assumed in both systems.
The addition of a noncoordinating base (2,4,6-collidine) to
the solution of the fully oxidized complex resulted in the
appearance of a signal identical to that observed for 3Br2,
indicating deprotonation of the external nitrogens of the
confused pyrroles.
Figure 11. Frozen solution EPR spectrum (X-band, CH2Cl2, 77 K) of the
product of reduction of 3 with N2H6Cl2. The signal of free radical that is
concurrently formed is observed at gR ) 2.003.
The reduction of 3 under acidic conditions can be
accomplished with hydrazine dihydrochloride. The reaction
was carried out by means of N2H6Cl2 dissolved in a DMF/
H2O mixture (10:1) that was shaken with a deaerated CH2-
Cl2 solution of 3. The resulting EPR spectrum of frozen
solution (77 K) consists of a signal that is almost identical
with that obtained previously for monomeric 21-alkylated
nickel complexes of NCP reduced with the same agent.28
The spin-Hamiltonian parameters (g1 ) 2.298, g2 ) 2.218,
g3 ) 2.192) indicates some rhombic distortion, but the
spectrum does not involve any features that could be assigned
to the presence of the two interacting paramagnetic centers
(Figure 11). This result suggests either a reduction of only
one nickel(II) ion in [3(HCl)2] or lack of interaction between
the paramagnetic centers in the bisreduced species. The latter
is in agreement with relatively low value of Kcom for this
process, calculated based on the separation of reduction
potentials (vide supra) and the expected low stability of the
mixed-valence species. Nevertheless, the spectral parameters,
that is, pronounced anisotropy of the Zeeman tensor indicate
a metal-centered reduction that yields nickel(I) species as
suggested on the basis of the reduction potential values for
parameter in the case of 3Br2. The reason for the higher than
expected value of D could be the contribution of some
pseudo-dipolar interaction between the paramagnetic centers
that involves the bridging phenylene ring. The conformational
space of 3 includes an eclipsed arrangement of the subunits
with the phenylene ring lying between macrocyclic planes
in a close distance of about 2.3 Å from both metal centers.
That may facilitate communication between the subunits
influencing both redox properties and electronic interaction
in the system.
Under acidic conditions, both oxidation and reduction
products can be detected by EPR in a frozen CH2Cl2 solution.
The addition of bromine to the solution of 3 acidified with
HBr results in the appearance of a rather broad signal
centered at g ) 2.18 accompanied by weaker features at g
) 2.44 and g ) 2.37 and a sharp radical line at g ) 2.003
which is often encountered upon oxidation/reduction of
porphyrin species (Figure 10). The intensity ratio of these
signals depends on the concentration of Br2; however, unlike
in the case of 3, a unique signal diagnostic for mono-oxidized
species cannot be observed even at substoichiometric amounts
of bromine. It can reflect the small difference between first
and second oxidation potentials in [3(HX)2] and, thus, the
relative instability of the mixed-valence species. It should
also be pointed out that because of the triplet spin state of
an unoxidized part of the dimer the spectrum of the
monooxidized species under acidic conditions can be con-
the protonated complex. For the monovalent nickel of
9
2
2
electronic configuration d , the contribution of the dx -y metal
orbital to the SOMO can be predominant,74,75 which may
(74) Chmielewski, P. J.; Grzeszczuk, M.; Latos-Graz˘yn´ski, L.; Lisowski,
J. Inorg. Chem. 1989, 28, 3546.
(75) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Pacholska, E. Inorg. Chem.
1994, 33, 1992.
1624 Inorganic Chemistry, Vol. 46, No. 5, 2007

N-Confused Bis(porphyrinatonickel(II))
Table 2. Crystal Data and Structure Refinement for
3·(CH2Cl2)(n-hexane)
coordinatively linked oligomeric assemblies comprising of
3 as a “conducting” bridge.
empirical formula
fw
temp
wavelength
cryst syst
space group
unit cell dimensions
a
C112H89Cl4N8Ni2
Experimental Section
1806.13
100(2) K
1.54178 Å
triclinic
P1h
Instrumentation. Absorption spectra were recorded on a diode
array Hewlett-Packard 8453 spectrometer. Mass spectra were
recorded on an AD-604 spectrometer using the electrospray
technique. NMR spectra were recorded on a Bruker Avance 500
spectrometer. The 1D and 2D experiments (COSY, NOESY,
HMQC, and HMBC) were performed by means of standard
experimental procedures of the Bruker library. The peaks were
16.455(3) Å
16.776(3) Å
18.400(4) Å
77.43(3)˚
b
c
R
referenced to the residual CHCl3 resonances in H and 13C NMR
â
75.31(3)˚
1
γ
66.20(3)˚
(7.24 and 77.2 ppm, respectively). Cyclovoltammetric measure-
ments were performed in dichloromethane on an EA9C MTM
apparatus with a glassy carbon disk as the working electrode, Ag/
AgCl as the reference electrode (ferrocene reference potential was
530 mV), and platinum wire as the auxiliary electrode. Tetrabu-
tylammonium perchlorate (0.1 M) was used as the supporting
electrolyte. EPR spectra were obtained with a Bruker ESP 300E
spectrometer. The magnetic field was calibrated with a proton
magnetometer and EPR standards. The EPR spectra were simulated
by assuming orthorhombic symmetry by means of WINEPR
SimFonia computer program.
vol
Z
4457.1(19) Å3
2
density (calcd)
abs coeff (Cu KR)
F(000)
1.346 Mg/m3
2.064 mm-1
1882
cryst size
0.3 × 0.2 × 0.15 mm3
crystal color and habit
diffractometer
θ range
black block
Oxford Diffraction Xcalibur PX
3.5-60.0°
-18 e h e 18,
-18 e k e 18,
-13 e l e 20
24 566
index ranges
reflns collected
independent reflns (Rint
abs correction
)
12 274 (0.081)
analytical
Preparation of Precursors. 5,10,15,20-Tetrakis(p-tolyl)-2-aza-
21-carbaporphyrin (1) and its nickel(II) complex (2) were synthe-
sized according to known procedures.1,3
max and min transm
solution method
refinement method
data/restraints/params
GOF on F2
0.8560 and 0.8174
direct
Synthesis of Dimer 3. In a typical synthesis, 30 mg (0.041
mmol) of 5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrinato
nickel(II) 2 and 20 mg (0.075 mmol) of 1,2-bis(bromomethyl)-
benzene were dissolved in CH2Cl2 (30 mL). A suspension of K2-
CO3 (20 mg) in ethanol (10 mL) was added to the solution, and
the mixture was stirred for 12 h at room temperature in darkness.
Flash chromatography on silica gel with CH2Cl2 that was eventually
replaced with a CH2Cl2/EtOH mixture (5% of ethanol) allows the
separation of reaction product 3 from the residual starting material
2 (fastest migrating green band) and monomeric product of
alkylation 4 (second reddish band migrating with 2% EtOH). Yields
(crystallization from CH2Cl2/hexane): 3, 19 mg, (60%); 4, 10 mg,
(23%). Selected data for 3. UV-vis (CH2Cl2) λ/nm (ꢀ ×10-3): 247
sh, 290 (65), 363 (75), 434 (118), 462 sh, 612 sh, 772 sh. 1H NMR
(500 MHz, CDCl3, 298 K): δ 8.74 (s, 1H), 8.60 (s, 1H), 8.34 (d,
3J ) 4.6 Hz, 1H), 8.33 (d, 3J ) 4.2 Hz, 1H), 8.30 (d, 3J ) 4.6 Hz,
1H), 8.29 (d, 3J ) 4.3 Hz, 1H), 8.12 (d, 3J ) 4.8 Hz, 1H), 7.98 (d,
3J ) 4.6 Hz, 1H), 7.86 (b, 1H), 7.71 (b, 2H), 7.69 (d, 3J ) 4.2 Hz,
1H), 7.58 (b, 2H), 7.54 (b, 2H), 7.51 (d, 3J ) 7.6 Hz, 2H), 7.38 (d,
3J ) 8.0 Hz, 1H), 7.36 (d, 3J ) 4.2 Hz, 1H), 7.28 (d, 3J ) 4.2 Hz,
full-matrix least-squares on F2
6502/6/1111
1.012
final R indices [I > 2σ(I)]a
R1 ) 0.0903, wR2 ) 0.2308
R1 ) 0.1378, wR2 ) 0.2732
0.98 and -0.76 e‚Å-3
R indices (all data)a
largest diff peak and hole
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑[w(Fo - Fc )2/∑[w(Fo )2]]1/2
.
2
2
2
reduce the interaction between the unpaired spins in the face-
to-face-arranged dimers in contrast to the bis(nickel(III))
complexes where an “axial” dz metal orbital is involved in
the singly occupied molecular orbital in each subunit. The
change of the arrangement of the subunits with respect to
each other upon the protonation/reduction that results in an
unfolded conformation of the dimer where the subunits are
no longer cofacial can also be taken into account.
Scheme 2 summarizes redox properties observed for 3 and
its protonated form.
2
Conclusion
3
1H), 7.22 (b, 4H), 7.05 (d, J ) 7.8 Hz, 2H), 6.91 (m, 1H), 6.89
The structural, nucleophilic, and redox properties of the
21,21′-xylene-linked bis(NCP nickel(II)) complex resemble
to some extent those of the monomeric analogues,27-29
although cooperative effects caused by the dimeric character
of 3 are evident. The interaction between the subunits can
be observed despite isolation of their aromatic π-electron
systems. The diversity of the oxidation and spin states that
the system can adopt is important for potential applications
in molecular electronics. The nucleophilic sites on the
perimeter of each of the subunits allow modification of the
redox properties by protonation. Since the outer nitrogen of
the confused pyrrole has been shown to coordinate metal
ions in several systems15,16,18-20,22,24,33,54 including those of
21-alkylated nickel(II) NCP complexes,53 dimer 3 possessing
two such donors can be exploited for a preparation of
(m, 1H), 6.75 (d, 3J ) 7.1 Hz, 2H), 6.66 (d, 3J ) 4.3 Hz, 1H), 5.55
(m, 1H), 5.52 (m, 1H), 2.79 (s, 3H), 2.76 (s, 6H), 2.74 (s, 3H),
2.49 (s, 3H), 2.43 (s, 3H), 2.40 (s, 3H), 2.35 (s, 3H), -2.85 (d, 2J
) 15.1 Hz, 1H), -2.95 (d, 2J ) 14.9 Hz, 1H), -3.03(d, 2J ) 14.9
Hz, 1H), -3.26 (d, 2J ) 15.1 Hz, 1H). 13C NMR (126 MHz, CDCl3,
298 K): δ 177.1, 176.8, 155.8, 155.6, 155.3, 155.1, 152.7, 152.5,
152.3, 151.9, 149.9, 149.7, 149.0, 148.8, 147.3, 147.2, 146.7, 146.5,
138.3, 138.1, 138.0, 137.9, 137.9, 137.6, 137.5, 137., 137.4, 137.4,
136.6, 136.6, 136.3, 136.2, 135.6, 135.6, 135.5, 135.3, 135.2, 134.3,
134.3, 133.5, 133.0, 132.3, 132.3, 132.1, 131.9, 131.5, 131.4, 131.0,
130.9, 130.7, 130.0, 129.4, 128.4, 128.4, 128.2, 128.1, 127.8, 127.7,
127.2, 126.7, 125.8, 125.7, 125.1, 124.9, 123.9, 123.8, 122.4, 122.3,
40.0, 39.9, 29.3, 21.7, 21.7, 21.6, 21.4, 21.3, 21.2. MS (ESI): m/z
1556.8 (obsd), 1557.2 (calcd for C104H78N8Ni2).
The same procedure was applied for the synthesis of 3a except
that the 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrinato nickel-
Inorganic Chemistry, Vol. 46, No. 5, 2007 1625

Chmielewski
(II) was used instead of tetratolyl derivative as the starting NCP
nickel(II) complex 2. Selected data for 3a. H NMR (500 MHz,
benzene (16 mg, 0.061 mmol) in dichloromethane solution (50 mL)
containing 2 mg of dibenzo-18-crown-6 and a suspension of K2-
CO3 (10 mg) was refluxed for 2 h under a blanket of nitrogen. The
solvent was evaporated under reduced pressure. The solid was
dissolved in dichloromethane and chromatographed on a silica gel
column. The second brown-reddish band that contained 4 was eluted
with dichloromethane/ethanol (2% EtOH) and crystallized from a
CH2Cl2/hexane mixture. Yield: 21 mg (57%). Selected data for 4.
UV-vis (CH2Cl2) λ/nm (ꢀ ×10-3): 242 sh, 291 (32), 364 (40),
437 (62), 464 sh, 611 sh, 779 sh.1H NMR (500 MHz, CDCl3, 298
1
CDCl3, 298 K): δ 8.79 (s, 1H), 8.65 (s, 1H), 8.34 (d, 3J ) 4.9 Hz,
1H), 8.33 (d, 3J ) 4.9 Hz, 1H), 8.30 (d, 3J ) 4.9 Hz, 2H), 8.10 (d,
3J ) 4.9 Hz, 1H), 7.96 (d, 3J ) 4.2 Hz, 1H), 7.93 (b, 1H), 7.85 (d,
3J ) 7.9 Hz, 1H), 7.81 (d, 3J ) 6.1 Hz, 1H), 7.80 (d, 3J ) 8.5 Hz,
1H), 7.78 (d, 3J ) 7.3 Hz, 1H), 7.76 (b, 3H), 7.72 (d, 3J ) 7.3 Hz,
2H), 7.70 (d, 3J ) 7.3 Hz, 2H), 7.68 (d, 3J ) 4.9 Hz, 2H), 7.66 (d,
3J ) 6.1 Hz, 1H), 7.59 (d, 3J ) 7.3 Hz, 2H), 7.57 (d, 3J ) 7.3 Hz,
2H), 7.53 (d, 3J ) 7.3 Hz, 1H), 7.48 (d, 3J ) 7.3 Hz, 1H), 7.44 (d,
3J ) 7.3 Hz, 2H), 7.42 (b, 3H), 7.39 (d, 3J ) 7.3 Hz, 1H), 7.34 (b,
2H), 7.32 (d, 3J ) 7.9 Hz, 2H), 7.27 (t, 3J ) 7.3 Hz, 2H), 7.23 (d,
3
3
K): δ 9.46 (s, 1H), 8.66 (d, J ) 4.6 Hz, 1H), 8.63 (d, J ) 4.6
3
3
Hz, 1H), 8.53 (d, J ) 4.6 Hz, 1H), 8.51 (d, J ) 4.6 Hz, 1H),
3
3J ) 4.9 Hz, 1H), 6.95 (m, 1H), 6.93 (m, 1H), 6.88 (d, J ) 6.7
8.47 (d, 3J ) 4.3 Hz, 1H), 8.43 (d, 3J ) 4.3 Hz, 1H), 8.04 (b, 1H),
7.95 (b, 3H), 7.84 (b, 1H), 7.74 (d, J ) 7.8 Hz, 2H), 7.54 (d, J
3
3
3
Hz, 2H), 6.76 (d, J ) 4.9 Hz, 1H), 5.56 (m, 1H), 5.54 (m, 1H),
-2.87 (d, 2J ) 15.2 Hz, 1H), -2.99 (d, 2J ) 15.2 Hz, 1H), -3.06
3
3
) 7.6 Hz, 2H), 7.50 (d, J ) 7.4 Hz, 4H), 7.00 (t, J ) 7.4 Hz,
1H), 6.92 (t, 3J ) 7.2 Hz, 1H), 6.78 (d, 3J ) 7.6 Hz, 1H), 5.81 (d,
3J ) 7.6 Hz, 1H), 2.90 (d, 2J ) 10.3 Hz, 1H), 2.64 (s, 6H), 2.60 (s,
3H), 2.59 (d, 2J ) 10.3 Hz, 1H), 2.58 (s, 3H), -0.72 (d, 2J ) 15.1
Hz, 1H), -1.3 (d, 2J ) 15.1 Hz, 1H). MS (ESI): m/z 911.2 (obsd),
911.2 (calcd for C56H43N4Ni + H+).
2
2
(d, J ) 15.2 Hz, 1H), -3.31 (d, J ) 15.2 Hz, 1H). 13C NMR
(126 MHz, CDCl3, 298 K): δ 176.9, 176.7, 155.9, 155.8, 155.5,
155.3, 155.3, 152.8, 152.8, 152.6, 152.4, 149.8, 149.7, 149.6, 148.9,
148.7, 147.3, 147.1, 147.0, 146.6, 146.4, 141.7, 141.1, 140.8, 140.7,
140.6, 140.6, 140.4, 140.3, 139.9, 139.6, 139.3, 138.9, 138.8, 138.7,
138.5, 136.7, 136.3, 135.5, 135.4, 135.1, 134.3, 134.1, 133.7, 133.1,
132.4, 132.3, 132.3, 132.1, 132.0, 131.6, 131.5, 131.1, 130.8, 130.1,
129.7, 129.5, 129.2, 129.1, 128.3, 128.2, 127.8, 127.7, 127.6, 127.5,
127.4, 127.3, 127.2, 127.0, 125.4, 125.2, 125.1, 123.9, 123.9, 122.6,
122.5, 39.6, 39.4, 31.5. MS (ESI): m/z 1444.3 (obsd), 1444.9 (calcd
for C96H62N8Ni2).
Synthesis of (5,10,15,20-Tetrakis(p-tolyl)-2,21-bis(2′-bromom-
ethylphenylmethylene)-2-aza-21-carbaporphyrinato)nickel(II)
Bromide (5). A mixture of 2 (30 mg, 0.041 mmol) and 1,2-bis-
(bromomethyl)benzene (40 mg, 0.15 mmol) in dichloromethane
solution (50 mL) containing 2 mg of 18-crown-6 and a suspension
of K2CO3 (10 mg) was refluxed for 8 h under a blanket of nitrogen.
The solvent was evaporated under reduced pressure. The solid was
dissolved in dichloromethane and chromatographed on a silica gel
column. The third brown-reddish band that contained 5 was eluted
with dichloromethane/ethanol (5% EtOH) and crystallized from a
CH2Cl2/hexane mixture. Yield: 27 mg (57%). Selected data for 5.
UV-vis (CH2Cl2) λ/nm (ꢀ ×10-3): 314 (26), 370 (28), 430 sh,
469 (41), 590 (8), 644 (9), 741 (11), 852 sh. 1H NMR (500 MHz,
CDCl3, 298 K): δ 67.5, 65.1, 59.6, 55.5, 50.3, 49.0, 35.2, 32.2,
26.8, 25.2, 10.8, 10.5, 9.8, 9.3, 8.6, 8.0, 7.8, 7.6, 7.5, 6.8, 6.6, 6.0,
5.8, 4.9, 4.7, 4.5, 4.3, 4.0, 3.5, 2.5, 2.4, 2.2, 1.9, -1.6. MS (ESI):
m/z ) 1174.5 (obsd), 1174.5 (calcd for C64H51N4NiBr3).
X-ray Data Collection and Refinement of 3. Crystals of 3·
(CH2Cl2)2(n-hexane) were prepared by diffusion of n-hexane into
the dichloromethane solution in a thin tube. Data were collected at
100 K using an Oxford Cryosystem device on an Oxford Diffraction
Xcalibur PX diffractometer with KM4CCD Sapphire detector. Data
collection, integration and scaling of the reflections, and analytical
absorption correction were performed by means of the CrysAlis
suite of programs (Oxford Diffraction, Poland). Crystal data are
compiled in Table 2. The structure was solved by direct methods
with SHELXS9776 and refined by the full-matrix least-squares
method on all F2 data using SHELXL9777 programs. All non-H
atoms were refined with anisotropic displacement parameters;
hydrogen atoms were included from the geometry of molecule. The
asymmetric unit contains 3, two disordered molecules of dichlo-
romethane, and one molecule of hexane disordered onto two sites.
Synthesis of (5,10,15,20-Tetrakis(p-tolyl)-21-(2′-bromometh-
ylphenylmethylene)-2-aza-21-carbaporphyrinato)nickel(II) (4).
A mixture of 2 (30 mg, 0.041 mmol) and 1,2-bis(bromomethyl)-
Acknowledgment. This work was supported by the
Ministry of Scientific Research and Information Technology
of Poland under Grant 3 T09A 162 28.
Supporting Information Available: Crystallographic data of
3 in CIF format, 2D NMR spectra for 3, 3a, and 4, and
spectrophotometric titration of 3 and 4 with TFAH. This material
is available free of charge via the Internet at http://pubs.acs.org.
(76) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany,1997.
(77) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
IC061793E
1626 Inorganic Chemistry, Vol. 46, No. 5, 2007