Preparation of α,β-unsubstituted meso-arylbidipyrrins via metal-templated, oxidative coupling of dipyrrins

Article abstract of DOI:10.1039/b412620c

A three-step, one-pot procedure provides meso-aryl-α,β- unsubstituted bisdipyrrinato nickel complexes; oxidative coupling of these ligands followed by demetallation affords an unprecedented class of meso-aryl-α,β-unsubstituted bidipyrrins.

Full text of DOI:10.1039/b412620c

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L E T T E R
Preparation of a,b-unsubstituted meso-arylbidipyrrins
via metal-templated, oxidative coupling of dipyrrinsw
ꢀ
Hubert S. Gill, Isaac Finger, Ivana Bozidarevic, Florence Szydlo and Michael J. Scott*
´
Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611 USA.
E-mail: mjscott@chem.ufl.edu; Fax: +1 352 392 3255; Tel: +1 352 846 1165
Received (in Montpellier, France) 15th August 2004, Accepted 28th October 2004
First published as an Advance Article on the web 9th December 2004
A three-step, one-pot procedure provides meso-aryl-a,b-unsub-
stituted bisdipyrrinato nickel complexes; oxidative coupling of
these ligands followed by demetallation affords an unprece-
dented class of meso-aryl-a,b-unsubstituted bidipyrrins.
by Dolphin and co-workers in 1998.4 In the following years,
Broring and co-workers isolated a similar metal-free octa-
¨
alkylbidipyrrin using modified procedures,5 and they expanded
the scope of their methodology to include the preparation of
the previously unprecedented meso-arylbidipyrrins. Their ap-
proach, employing diacylbipyrroles, represents the only syn-
thetic scheme for the preparation of meso-arylbidipyrrins to
date. Unfortunately, the reaction requires harsh conditions,
involving a reflux in neat POCl3, and the methodology is not
compatible with either reactive meso-aryl groups or with the
preparation of a- or b-unsubstituted meso-arylbidipyrrins.
Oxidative biaryl coupling reactions have been employed in
the preparation of numerous classes of compounds, including
polycyclic aromatic hydrocarbons,1a fused porphyrin arrays,1b
and natural products.1c Direct carbon-carbon bond-forming
reactions are among the most challenging transformations in
synthetic chemistry, often requiring harsh reaction conditions
and unpleasant metal reagents or expensive catalysts. Further-
more, due to the lack of regiospecificity, intermolecular dehydro-
genation reactions of aromatic compounds frequently result in
polymers or complex product mixtures, unless directing or
protecting groups are utilized. Inspired by the successful
oxidative biaryl coupling methodology recently employed for
the synthesis of large, flat porphyrins,2 we were interested in
applying these concepts to a divergent area of synthetic
chemistry. In this system, a late transition metal was incorpo-
rated into the macrocycle to lower the oxidation potential of
the ligand, and the pre-organization of the carbons to be
coupled facilitated the cyclo-dehydrogenation under very mild
oxidative conditions. With these issues in mind, we examined
the reactivity of metal complexes with meso-aryl-a,b-unsubsti-
tuted bidipyrrins (Fig. 1) since coupling of two of the
a-carbons would produce a bidipyrrin, a difficult molecule to
prepare by known methodology.
For reasons enumerated by Broring, meso-arylbidipyrrins
¨
offer advantages over their meso-unsubstituted analogs.5 Aryl
moieties incorporated at the meso-positions of bidipyrrins
provide points for synthetic elaboration, allow for the fine-
tuning of steric and electronic properties. The range of aryl
substituents that may be incorporated at the bidipyrrin meso-
positions by the methodology of Broring is limited to para- and
¨
meta-substituted aryl moieties, as ortho-substituted aryl groups
hinder the acylation reaction.6 In addition, the absence of
a-alkyl substituents on bidipyrrins is a desirable feature for
many applications, including monomers for electropolymeriza-
tion, and the ability to further derivatize at these free a
positions may allow for the preparation of macrocycles.
In order to couple dipyrrinato groups, two properties are
important for the metal template: a propensity towards square-
planar coordination and the formation of charge neutral
complex with both the bisdipyrrinato and bidipyrrinato li-
gands. Nickel offers several advantages over metals such as
palladium or platinum for this purpose. The stronger Lewis
acidity of Ni(II) weakens the C–H bonds of coordinated ligands
to a greater degree than Pd(II) or Pt(II), and the small ionic
radius of Ni(II) brings the a-hydrogens of bisdipyrrinato Ni(II)
complexes into close contact (2.481 and 2.532 A), as illustrated
in the solid-state structure of Ni-2b depicted in Fig. 2. Addi-
tionally, the removal of the metal template should be facile,
since Ni(II) complexes are typically easier to demetallate than
analogous chelates of Pd(II) or Pt(II).
Bidipyrrins represent the class of bile pigments with two
dipyrromethene units linked directly by a-carbons. With an eye
towards utilizing these tetrapyrroles as synthons for corrole
forming reactions, Johnson and Price first described their
preparation in 1960,3 but little work was pursued with this
ligand prior to the report of a dimeric zinc complex (M2L2)
a,b-Unsubstituted-5-aryldipyrromethanes are needed for the
synthesis presented in Fig. 3. These readily available molecules
offer several desirable attributes for precursors, including their
Fig. 1 General bidipyrrin and bisdipyrrinato compounds and their
respective numbering schemes.
w Electronic supplementary information (ESI) available: 1H NMR
spectra for all compounds and magnetic analysis of Ni-2b (wT vs. T
plot). See http://www.rsc.org/suppdata/nj/b4/b412620c/
Fig. 2 Solid-state structure of Ni-2b (40% ellipsoids). Carbon atoms
are drawn with arbitrary radii and hydrogen atoms other than those on
the a-carbons have been omitted for clarity.
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
68
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 8 – 7 1

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spectra of the phenyl and p-nitrophenyl complexes.8b The
dihedral angle between the planes containing N(1)–Ni(1)–N(4)
and N(2)–Ni(1)–N(3) indicates the degree of tetrahedral dis-
tortion for square-planar complexes, and the structural char-
acterization of the phenyl derivative revealed a dihedral angle
of 38.51, which is considerably smaller than the tetrahedral
angle of 76.31 calculated from the X-ray structure of
[bis(1,3,7,9-tetramethyldipyrrinato)]Ni(II).10c In view of the
properties of the phenyl and p-nitrophenyl congeners, Ni-2a
and Ni-2b were expected to be diamagnetic, low-spin com-
plexes and the 1H NMR spectrum of Ni-2a (see electronic
supplementary information, ESI) did indeed exhibit sharp
signals. In contrast, the resonances in the spectrum of Ni-2b
were broadened and many were shifted downfield relative to
their analogous positions in the spectrum of Ni-2a (see ESI).
The a-carbon protons experienced the most significant shift,
from a value of 9.23 ppm in Ni-2a to 15.62 ppm in Ni-2b. When
Ni(II) complexes adopt geometries in an intermediate range
between square planar and tetrahedral, they often exhibit a
temperature-dependent magnetic moment; in the structure of
Ni-2b the angle between N(1)–Ni(1)–N(4) and N(2)–Ni(1)–
N(3) planes has opened up in comparison to the phenyl
derivative to a value of 49.61.8b This 11.11 increase is appar-
ently sufficient to induce thermal population of a paramagnetic
state for the d8 Ni(II) ion and preliminary magnetic data is
consistent with this observation.11
Fig. 3 Illustration of the three-step, one-pot reaction sequence em-
ployed for the preparation of bisdipyrrinato Ni(II) complexes followed
by oxidation and demetallation to afford dibipyrrins.
The coupling of the a-carbons upon going from Ni-2b to
Ni-3b appears to relieve some of the steric strain in the
complex; the Ni(II) cation assumes a coordination geometry
closer to square planar (Fig. 4), with a smaller angle between
the planes containing N(1)–Ni(1)–N(2) and N(3)–Ni(1)–N(4)
for Ni-3b (11.81) in comparison to Ni-2b (38.31). As apparent
ease of preparation, numerous choices for aryl functional
groups, and the well-established coordination chemistry of
their 2H+, 2eꢀ oxidized dipyrromethene derivatives.7,8 Pre-
parations of a,b-unsubstituted-5-arylbisdipyrrinato M(II) com-
plexes have been recently described by the groups of both
Dolphin and Lindsey.8b,e For the preparations of Ni-2a and
Ni-2b, a room temperature, three-step, one-pot procedure
similar to that utilized by Lindsey and co-workers was em-
ployed (Fig. 3). Isolation of the resulting bisdipyrrinato Ni(II)
complexes is straightforward and the complexes Ni-2a and
Ni-2b are obtained in good yields as crystalline solids, despite
the multi-step nature of the synthetic methodology.
The cyclic voltammograms measured for the bisdipyrrinato
nickel complexes revealed irreversible oxidative processes at
1.10 V for Ni-2a and 1.08 V for Ni-2b (vs. Ag/AgCl). Various
reaction conditions were attempted to affect this oxidative
change chemically, but the nickel complexes proved to be
incompatible with the Lewis acids often employed for dehydro-
genation reactions. Due to this difficulty, alternative proce-
dures were pursued; treatment of Ni-2a or Ni-2b with a slight
excess of DDQ in refluxing toluene afforded the desired
bidipyrrinato nickel complexes (Fig. 3). Filtration through a
plug of silica, followed by recrystallization, provides Ni-3a and
Ni-3b as purple microcrystalline solids. Treatment of CHCl3
solutions of Ni-3a and Ni-3b with HCl results in an immediate
color change from wine-red to bright-green. Aqueous workup
causes a change in color to indigo upon deprotonation and
solvent removal provides the metal-free ligands, H2-3a and
H2-3b, in nearly quantitative yields.
1
from the sharp signals in the H NMR spectrum of Ni-3b, the
paramagnetism observed for Ni-2b is lost and the resonance for
the hydrogens on the uncoupled a-carbons experiences a
dramatic change upon conversion to Ni-3b, changing from a
broad singlet at 15.62 ppm to a doublet of doublets at 6.02 ppm
(see ESI). Although conversion to the bidipyrrin causes a slight
increase in the separation of the uncoupled a-carbons from
3.025 A to 3.093 A, their associated hydrogens are brought in
closer proximity to each other (2.284 A for Ni-3b) relative to
the a-protons in the uncoupled complex (2.507 A for Ni-2b).
As depicted in Fig. 4, the solid-state structure of Ni-3b
reveals a helical complex, consistent with the structures of
other known Ni bidipyrrins.12 Interestingly, the degree of
helicity, as described by the angle between the planes contain-
ing N(1)–Ni(1)–N(4) and N(2)–Ni(1)–N(3), is only 11.91 for
Ni-3b. This interplanar angle is slightly smaller than the 13.01
measured for the only other a-unsubstituted bidipyrrinato
Ni(II) complex reported and significantly smaller than the
19.91 measured for an a-methyl bidipyrrinato Ni(II) complex.12
Typically, tetrahedral Ni(II) complexes have an S = 1
ground state while square-planar Ni(II) complexes are diamag-
netic, and often Ni(II) complexes with an intermediate geome-
try will exhibit temperature-dependent spin equilibrium.9
Other than Ni-2a, Ni-2b, and the related phenyl and p-nitro-
phenyl-a-unsubstituted analogs described by Dolphin and
co-workers,8b all reported bisdipyrrinato nickel complexes bear
methyl or phenyl groups at their a-carbons. The steric clash
between these groups induces a severe distortion towards
tetrahedral geometry and the complexes are paramagnetic.10
Based upon these precedents and the realization that even
hydrogen atoms on the a-carbons sterically preclude a
square-planar environment, Dolphin and co-workers were
surprised to observe sharp signals in the 1H and 13C NMR
Fig. 4 Solid-state structure of Ni-3b (40% ellipsoids). Carbon atoms
are drawn with arbitrary radii; hydrogen atoms other than those on the
a-carbons have been omitted for clarity.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 8 – 7 1
69

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The average Ni–N bond length of 1.873(2) A is consistent with
other bidipyrrinato Ni(II) complexes in the literature.12 The
relatively short bond between the coupled a-carbons of
1.437(3) A is indicative of its partial double-bond character,
as can be envisioned from the resonance form placing the two
imine nitrogens in one dipyrromethene moiety.
Electrochemical investigations of Ni-3b and H2-3b were
undertaken to provide insight into the stability and electronic
properties of these chromophores. Comparable to redox pro-
cesses observed for numerous porphyrin species,13 the cyclic
voltammogram of Ni-3b exhibits two reversible oxidations at
0.80 and 1.09 V, as well as two reversible reductions at 0.89 and
1.60 V (vs. Ag/AgCl). These observations are consistent with a
Experimental
General
1H NMR spectra were recorded on a Varian Mercury spectro-
meter at 300 MHz in CDCl3 and were referenced to the solvent
residual peak. Absorption spectra were collected in CH2Cl2 on
a Varian Cary 50 spectrophotometer. Reagents and solvents
were used as received from Aldrich or Fisher Scientific. Di-
pyrromethanes 1a and 1b were prepared following modified
literature procedures.7a
Fluorescence spectroscopy
series of measurements reported by Broring and co-workers,
¨
Steady-state photoluminescence spectroscopy and quantum
yield measurements were carried out using a SPEX Fluorolog
2 instrument. The standard used for quantum yield calcula-
tions was Ru(bipy)3Cl2 (F = 0.04). Samples H2-3a and H2-3b
were dissolved in toluene and the concentration was adjusted
so that their absorbance at the excitation wavelength (453 nm)
matched that of a standard (0.2).
which also show two reversible processes in both the oxidative
and reductive directions for most compounds of this type.14 In
addition to a reversible reduction at ꢀ1.05 V, H2-3b also
undergoes an irreversible oxidation at 0.94 V versus Ag/AgCl,
indicating that alkylation of the pyrrolic carbons is not re-
quired for stability over this broad potential range.
The electronic absorption spectra of these compounds
change substantially on going from Ni-2 to Ni-3 to H2-3 in
both series as illustrated by the spectra of the mesityl series
shown in Fig. 5. Compounds Ni-2a and Ni-2b exhibit one
broad absorption maximum around 471 and 478 nm, respec-
tively, which are slightly higher in energy than transitions
reported for other bisdipyrrinato Ni(II) complexes.8c,10 The
absorption spectra become more complex after coupling: the
main absorption bands of Ni-3a and Ni-3b are bathochromi-
cally shifted in comparison to their precursors, but they also
exhibit electronic transitions at longer wavelengths (above
550 nm). Upon demetallation, an additional low-energy fea-
ture emerges in the electronic spectra of H2-3a and H2-3b. The
metal-free compounds H2-3a and H2-3b show fluorescence
emissions at 687 and 648 nm, with quantum yields of 1%
and 5%, respectively. The higher value for H2-3b is consistent
with the observation that rigid substituents such as mesityl
groups at the meso-position in bisdipyrrinato Zn(II) complexes
significantly increase the quantum yields for emission.15
In summary, the three-step, one-pot room temperature
reaction of dipyrromethanes with DDQ, Et3N and NiCl2
described herein is a practical method to obtain meso-arylbis-
dipyrrinato Ni(II) complexes on the multigram scale. While the
para-tolyl derivative, Ni-2a, showed sharp resonances in the 1H
NMR spectrum, the mesityl analog, Ni-2b, exhibited broad
signals that were shifted downfield, indicative of temperature-
dependent paramagnetism. Furthermore, the oxidative cou-
pling of two dipyrrins by employing Ni(II) as a template is a
facile procedure for the preparation of previously unreported
meso-aryl,-a,b-unsubstituted bidipyrrins and this methodology
is compatible with aryl substituents bearing methyl groups at
the ortho-positions. Demetallation using HCl results in the
metal-free bidipyrrins and these chromophores are stable over
a potential range of B2 V. Photophysical measurements of the
dipyrrins reveal fluorescence in the low-energy region of the
visible spectrum, with the mesityl derivative giving a higher
quantum yield than the para-tolyl congener.
Electrochemistry
Electrochemical measurements were made on an EG&G PAR
VersaStatII potentiostat with a Pt disc working electrode, a Pt
wire counter electrode, and an aqueous Ag/AgCl reference
electrode (NaCl, 3 M) fitted with a Vicor frit as a salt bridge. In
all cases dry, degassed C6H5CN was used as the solvent and
tetra-N-butylammoniumhexafluorophosphate, at a concentra-
tion of 0.100 M, was used for the supporting electrolyte.
A small portion of ferrocene (Fc) was added to the cell after
each series of measurements to confirm the potential of the
reference electrode. The E1/2 for the Fc/Fc+ couple remained
constant at 0.46(1) V versus Ag/AgCl. The analyte concentra-
tion was 2.5(2) mM and all measurements were made at room
temperature.
X-Ray crystallographyz
Unit cell dimensions were obtained and intensity data collected
on a Bruker CCD SMART diffractometer at low temperature,
with monochromatic Mo-Ka radiation (l = 0.710 73 A). The
data collections nominally covered over a hemisphere of
reciprocal space by a combination of three sets of exposures;
each set had a different f angle for the crystal and each
exposure covered 0.31 in o. The crystal-to-detector distance
was 5.0 cm. The data sets were corrected empirically for
absorption using SADABS.16 The structure was solved and
refined using the Bruker SHELXTL software package.17
Crystal data for Ni-2b. C36H34N4Ni, M = 581.38, mono-
clinic, C2/c, m ¼ 0.695 mmꢀ1, a = 30.6299(16), b = 8.0062(4),
c = 26.6950(14) A, b = 116.586(1)1, V = 5854.2(5) A3, Z = 8,
rcalcd = 1.319 g cmꢀ3, T = 193(2) K, 19861 reflections
collected, 6896 unique (Rint ¼ 0.0230), R1 = 0.0347, wR2 =
0.0867 for all 5825 data [I 4 2s(I)].
Crystal data for Ni-3b. C36H32N4Ni, M = 579.37, mono-
clinic, P21/c, m ¼ 0.694 mmꢀ1, a = 12.1071(7), b =
31.5677(17), c = 8.0986(4) A, b = 108.907(1)1, V =
2928.2(3) A3, Z = 4, rcalcd = 1.314 g cmꢀ3, T = 193(2) K,
19801 reflections collected, 6821 unique (Rint ¼ 0.0247),
R1 = 0.0392, wR2 = 0.0951 for all 5818 data [I 4 2s(I)].
z CCDC reference numbers 254228 and 254229. See http://
www.rsc.org/suppdata/nj/b4/b412620c/ for crystallographic data
in .cif or other electronic format.
Fig. 5 Electronic absorption spectra of Ni-2b, Ni-3b and H2-3b.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 8 – 7 1
70

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J = 4.3 Hz), 6.80 (d, 2H, J = 4.5 Hz), 6.61 (dd, 2H, J1 =
4.0 Hz, J2 = 1.2 Hz), 6.41 (dd, 2H, J1 = 4.0 Hz, J2 = 1.9 Hz),
2.47 (s, 6H); HRMS-EI (m/z): M+ calcd for C32H26N4,
466.2157; found 466.2160.
Syntheses
Ni-2a. A solution of 1a (7.08 g, 30.0 mmol) in THF (240 ml)
was treated with DDQ (6.80 g, 30.0 mmol) at room tempera-
ture. After 50 min, 10 ml of Et3N were added. A methanolic
solution containing NiCl2 ꢁ 6H2O (12 g in 30 ml) was then
added to the reaction mixture. The reaction proceeded for an
additional 45 min, after which the TLC indicated no uncoor-
dinated dipyrromethene. The reaction mixture was reduced to
150 ml and was diluted with 150 ml of hexanes. This solution
was filtered through a short plug of silica, with Et2O–hexanes
(1 : 1) as the eluent. The rapidly moving deep red-orange
fraction was collected. Crystallization from an acetone–hex-
anes mixture afforded the title compound as lustrous, metallic-
green crystals. Yield: 4.60 g (59%); UV-vis [CH2Cl2, lmax/nm
H2-3b. A portion of Ni-3b (71 mg, 0.12 mmol) was treated as
described above for the preparation of H2-3a. Yield: 63 mg
(99%); UV-vis [CH2Cl2, lmax/nm (log e)]: 710 (3.75), 578
(4.22), 411 (4.16); 1H NMR (300 MHz, CDCl3): d = 7.59
(s, 2H), 6.95 (s, 4H), 6.91 (d, 2H, J = 4.2 Hz), 6.53 (d, 2H, J =
4.2 Hz), 6.35 (s, 4H), 2.37 (s, 6H), 2.13 (s, 12H); HRMS-EI
(m/z): M+ calcd for C36H34N4, 522.2783; found 522.2780.
1
(log e)]: 471 (4.73); H NMR (300 MHz, CDCl3): d = 9.23 (s,
Acknowledgements
4H), 7.39 (d, 4H, J = 3.8 Hz), 7.33 (d, 4H, J = 8.1 Hz), 7.22
(d, 4H, J = 7.8 Hz), 6.77 (d, 4H, J = 4.1 Hz), 2.44 (s, 6H);
anal. calcd for C32H26N4Ni: C, 73.17; H, 4.99; N, 10.67; found
C, 73.05; H, 4.84; N, 10.47; HRMS-EI (m/z): [M + H]+ calcd
for C32H27N4Ni, 525.1589; found 525.1602.
We thank the Ministere de l’Education Nationale et de la
Recherche (support for F. Szydlo), the Research Corporation
(Research Innovation Award), and the Alfred P. Sloan Foun-
dation for providing financial support for this work. Support
from the National Science Foundation is also gratefully
acknowledged. We thank Prof. K. Schanze for assistance
with photophysical measurements and Prof. M. Meisel and
Mr. J.-H. Park for magnetic measurements.
Ni-2b. A portion of 1b (1.000 g , 1.723 mmol) was treated as
described above for the preparation of Ni-2a. Yield: 0.620 g
(56%); UV-vis [CH2Cl2, lmax/nm (log e)]: 478 (4.64); 1H NMR
(300 MHz, CDCl3): d = 15.62 (br s, 4H), 10.86 (br s, 4H), 6.78
(s, 4H), 6.61 (s, 4H), 2.29 (s, 6H), 1.82 (s, 12H). HRMS-EI
(m/z): M+ calcd for (C36H34N4Ni), 580.2137; found, 580.2135;
anal. calcd for C36H34N4Ni: C, 74.37; H, 5.89; N, 9.64; found
C, 74.11; H, 6.02; N, 9.58.
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1
(4.64), 361 (4.47); H NMR (300 MHz, CDCl3): d = 7.46 (d,
4H, J = 8.1 Hz), 7.28 (d, 4H, J = 7.7 Hz), 6.80 (dd, 2H, J1 =
5.4 Hz, J2 = 1.3 Hz), 6.76 (d, 2H, J = 4.3 Hz), 6.61 (d, 2H,
J = 4.3 Hz), 6.42 (dd, 2H, J1 = 4.3 Hz, J2 = 1.7 Hz), 5.99
(dd, 2H, J1 = J2 = 1.5 Hz), 2.46 (s, 6H); HRMS-EI (m/z):
M+ calcd for C32H24N4Ni, 522.1354; found 522.1365.
8
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Ni-3b. A portion of Ni-2b (1.50 g, 2.58 mmol) was treated as
described above for the preparation of Ni-3a. Yield: 1.01 g
9
1
(68%); H NMR (300 MHz, CDCl3): d = 6.93 (s, 4H), 6.62
(dd, 2H, J1 = 4.8 Hz, J2 = 1.5 Hz), 6.50 (d, 2H, J = 4.5 Hz),
6.42 (d, 2H, J = 4.2 Hz), 6.34 (dd, 2H, J1 = 4.5 Hz, J2 =
4.8 Hz), 6.02 (dd, J1 = J2 = 1.2 Hz), 2.36 (s, 6H), 2.13 (s,
12H); UV-vis [CH2Cl2, l/nm (log e)]: 555 (4.13), 409 (4.62);
HRMS-EI (m/z): M+ calcd for C36H32N4Ni, 578.1980; found,
578.1964; anal. calcd for C36H32N4Ni: C, 74.63; H, 5.57; N,
9.67; found C, 74.81; H, 5.69; N, 9.62.
10 (a) J. E. Fergusson and C. A. Ramsey, J. Chem. Soc., A, 1965,
5222; (b) Y. Murakami and K. Sakata, Inorg. Chem. Acta, 1968, 2,
273; (c) F. A. Cotton, B. G. DeBoer and J. R. Pipal, Inorg. Chem.,
1970, 9, 783; (d) Y. Murakami, Y. Matsuda and K. Sakata, Inorg.
Chem., 1971, 10, 1728.
11 A preliminary plot of the magnetic data is included in the
supplementary material. Complete magnetic data will be presented
in a future publication.
H2-3a. A solution of Ni-3a (0.50 g, 0.96 mmol) in CHCl3
(100 ml) was treated with HCl (4 ml, 12 M) at room tempera-
ture for 10 min. The reaction mixture was washed sequentially
with 200 ml portions of 0.2 M HCl, H2O, NaHCO3, and then
H2O. The green solution turned deep violet as the pH was
increased through the second and third washings. The organic
fraction was dried on Na2SO4 and the solvent was removed.
Yield: 0.44 g (99%); Uv-vis [CH2Cl2, l/nm (log e) nm]: 710
(3.65), 588 (4.56), 558 (sh), 411 (4.40), 342 (4.27). 1H NMR
(300 MHz, CDCl3): d = 7.60 (dd, 2H, J1 = J2 = 1.5 Hz), 7.44
(d, 4H, J = 8.1 Hz), 7.28 (d, 4H, J = 7.8 Hz), 6.99 (d, 2H,
¨
12 M. Broring and C. D. Brandt, Monatsh. Chem., 2002, 133, 623.
13 K. M. Kadish, G. Royal, E. V. Caemelbecke and L. Gueletti, in
The Porphyrin Handbook, eds. K. M. Kadish, K. M. Smith and
R. Guilard, Academic Press, Burlington, MA, 2000, vol. 9, p. 1.
14 M. Broring, C. D. Brandt, J. Lex, H.-U. Humpf, J. Bley-Escrich
¨
and J.-P. Gisselbrecht, Eur. J. Inorg. Chem., 2001, 2549.
15 I. V. Sazanovich, C. Kirmaier, E. Hindin, L. Yu, D. F. Bocian,
J. S. Lindsey and D. Holten, J. Am. Chem. Soc., 2004, 126, 2664.
16 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
17 G. M. Sheldrick, SHELXTL-6.12, Program for structure solution,
refinement and presentation, BRUKER AXS Inc., Madison, WI,
2000.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 8 – 7 1
71