Diamidodipyrrins: Versatile bipyrrolic ligands with multiple metal binding modes

Article abstract of DOI:10.1021/ic8011876

A straightforward, facile synthesis of diamidodipyrromethenes (diamidodipyrrins, DADP^R,R′) is presented. These tetradentate ligands readily form complexes with metal ions such as Ni²⁺ and Cu²⁺ and can adopt different binding modes with these metals. One version of the ligand (DADP^Ph,iPr) has been structurally characterized in its free base form, as a HBr salt, and as the Ni²⁺ and Cu²⁺ complexes. A symmetric NNOO donor set is found for the Cu²⁺ complex in the solid state, involving two carbonyl oxygen atoms and two dipyrrin nitrogen atoms, and this coordination mode has been confirmed in solution by electron paramagnetic resonance. An asymmetric NNNO binding mode found for the Ni²⁺ complex in the solid state persists in solution as revealed by ¹H NMR. The HBr salt form of the ligand shows an intriguing hydrogen-bonded head-to-head dimer arrangement. Experiments show that Cu²⁺, but not Ni²⁺, can mediate the rapid oxidation of the diamidodipyrromethane precursors to the diamidodipyrromethene ligands in the presence of dioxygen. The work here shows that diamidodipyrrins are a versatile new class of ligands in the area of nonporphyrinic pyrrole-based compounds that merit further investigation.

Full text of DOI:10.1021/ic8011876

Inorg. Chem. 2008, 47, 10533-10541
Diamidodipyrrins: Versatile Bipyrrolic Ligands with Multiple Metal
Binding Modes
Van S. Thoi,† Jay R. Stork,† Edwards T. Niles,‡ Ezra C. Depperman,‡ David L. Tierney,*,‡
and Seth M. Cohen*,†
Department of Chemistry and Biochemistry, UniVersity of California, San Diego, 9500 Gilman
DriVe, La Jolla, California 92093-0358, and Department of Chemistry and Chemical Biology,
UniVersity of New Mexico, Albuquerque, New Mexico 87131
Received June 27, 2008
A straightforward, facile synthesis of diamidodipyrromethenes (diamidodipyrrins, DADPR,R′) is presented. These
tetradentate ligands readily form complexes with metal ions such as Ni2+ and Cu2+ and can adopt different binding
modes with these metals. One version of the ligand (DADPPh,iPr) has been structurally characterized in its “free
base” form, as a HBr salt, and as the Ni2+ and Cu2+ complexes. A symmetric NNOO donor set is found for the
Cu2+ complex in the solid state, involving two carbonyl oxygen atoms and two dipyrrin nitrogen atoms, and this
coordination mode has been confirmed in solution by electron paramagnetic resonance. An asymmetric NNNO
1
binding mode found for the Ni2+ complex in the solid state persists in solution as revealed by H NMR. The HBr
salt form of the ligand shows an intriguing hydrogen-bonded head-to-head dimer arrangement. Experiments show
that Cu2+, but not Ni2+, can mediate the rapid oxidation of the diamidodipyrromethane precursors to the
diamidodipyrromethene ligands in the presence of dioxygen. The work here shows that diamidodipyrrins are a
versatile new class of ligands in the area of nonporphyrinic pyrrole-based compounds that merit further
investigation.
Introduction
numerous metal complexes reported.9 Dipyrrinato metal
complexes that have been described in the literature include
fluorescent complexes (with Zn2+, Ga3+, and In3+),10,11
incorporation into discrete supramolecular structures,6,12,13
and use as metalloligands for coordination polymers and
metal-organic frameworks.14-17 Perhaps the most well-
known dipyrrinato derivatives are the BODIPY dyes,18,19
Studies into the coordination chemistry of nonporphyrinic,
pyrrole-based ligands have formed an area of great interest
in coordination chemistry.1-8 Among these ligands, the
dipyrrins (dipyrromethenes) have been heavily studied, with
* Authors to whom correspondence should be addressed. Telephone:
(858) 822-5596(S.M.C.), (505) 277-2505(D.L.T.). Fax: (858) 822-5598
(S.M.C.), (505) 277-2609 (D.L.T.). E-mail: scohen@ucsd.edu (S.M.C.),
dtierney@unm.edu (D.L.T.).
(9) Wood, T. E.; Thompson, A. Chem. ReV. 2007, 107, 1831–1861.
(10) Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Yu, L.; Bocian, D. F.;
Lindsey, J. S.; Holten, D. J. Am. Chem. Soc. 2004, 126, 2664–2665.
(11) Thoi, V. S.; Stork, J. R.; Magde, D.; Cohen, S. M. Inorg. Chem. 2006,
45, 10688–10697.
†
University of California.
‡
University of New Mexico.
(1) Wampler, K. M.; Schrock, R. R. Inorg. Chem. 2007, 46, 8463–8465.
(2) Bachmann, J.; Nocera, D. G. J. Am. Chem. Soc. 2005, 127, 4730–
4743.
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Chem. 2007, 46, 5465–5467.
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Schroder, M.; Love, J. B. Angew. Chem., Int. Ed. 2007, 46, 584–586.
(6) Wood, T. E.; Dalgleish, N. D.; Power, E. D.; Thompson, A.; Chen,
X.; Okamoto, Y. J. Am. Chem. Soc. 2005, 127, 5740–5741.
(7) Sessler, J. L.; Tomat, E.; Lynch, V. M. J. Am. Chem. Soc. 2006, 128,
4184–4185.
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Soc. 1998, 120, 13537–13538.
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632.
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J. Chem. 2005, 29, 68–71.
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(16) Halper, S. R.; Do, L.; Stork, J. R.; Cohen, S. M. J. Am. Chem. Soc.
2006, 128, 15255–15268.
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15129.
10.1021/ic8011876 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 22, 2008 10533
Published on Web 10/22/2008

Thoi et al.
Chart 1. Some Dipyrrin Complexes Described in the Literature and the Diamidodipyrrin (DADPR,R′) Complexes Presented Herein (Right, in Box)
which are boron (often boron difluoride, Chart 1) adducts
that display rich optical properties including robust photo-
luminescence.
dipyrrin complexes with NNNN and NNNO donor atoms.
These new studies strongly suggested that related R-substi-
tuted dipyrrins, namely, diamidodipyrrins, should display rich
coordination chemistry. Although diiminodipyrrins, dicar-
bonyldipyrrins, and their metal complexes have been de-
scribed, the use of diamidodipyrrin ligands has not been
widely explored. The present report describes a general, high-
yielding synthesis of diamidodipyrrins, as well as their
complexes with Ni2+ and Cu2+. Diamidodipyrrins are found
to form 1:1 metal-ligand complexes with either a four- or
five-coordinate geometry. Furthermore, the diamidodipyrrin
can serve as a NNOO or NNNO donor depending on the
metal ion bound.
Historically, only a few examples of dipyrrin ligands with
additional ligating groups in the R position of the pyrroles
have been described. Martell et al. utilized 3,3′,4,4′-tetra-
chloro-5,5′-diethoxycarbonyldipyrromethene (Chart 1,
A),20,21 which contains both nitrogen and oxygen donors,
as ligands for Co2+, Ni2+, Cu2+, and Zn2+ ions.21 The Co2+
and Zn2+ complexes were reported to have nearly tetrahedral
coordination geometries, based on IR spectroscopy, from
which the authors concluded that an ML2 complex, with four
pyrrolic nitrogen atoms from two dipyrrin ligands, was
formed. The same study presented X-ray diffraction and
electron paramagnetic resonance (EPR) data of the Ni2+ and
Cu2+ complexes that suggested a distorted octahedral coor-
dination sphere; it was concluded that these metals were
coordinated to two ligands via two pyrrolic nitrogen atoms
and one oxygen atom from each ligand. Unfortunately, these
structural assignments were not confirmed with single-crystal
X-ray diffraction experiments.
More recently, a greater variety of R-substituted dipyr-
romethane and dipyrromethene ligands have been investi-
gated for their anion22,23 and metal-binding properties. Love
and co-workers have reported a number of interesting
systems based on R-substituted dipyrromethane ligands.5,24,25
Diamidopyridine-dipyrromethane hybrid macrocycles have
been reported to coordinate to Pd2+ through pyrrolic and
imino nitrogen atoms.26 The synthesis of diiminodipyr-
romethane and diiminodipyrromethene complexes of Ni2+,
Pd2+, and Pt2+ has also been described.3 These complexes
use a NNNN donor set, comprised of two pyrrolic and two
imino nitrogen atoms, to chelate to the metal (Chart 1, B).
Interestingly, these diiminodipyrromethane complexes react
with dioxygen and oxidize to form a variety of R-substituted
Experimental Section
General. Unless otherwise noted, starting materials were ob-
tained from commercial suppliers and used without further purifica-
tion. Mass spectrometry was performed at the University of
California, San Diego Mass Spectrometry Facility in the Department
of Chemistry and Biochemistry. A ThermoFinnigan LCQ-DECA
mass spectrometer was used for electrospray ionization (ESI) or
atmospheric pressure chemical ionization analysis, and the data were
analyzed using the Xcalibur software suite. Elemental analysis was
performed at NuMega Resonance Laboratories, San Diego, Cali-
1
fornia. H/13C NMR spectra were recorded on Varian FT-NMR
spectrometers at the Department of Chemistry and Biochemistry,
University of California, San Diego. UV-visible absorption spectra
were recorded using a Perkin-Elmer Lambda 25 spectrophotometer
with the UVWinLab 4.2.0.0230 software package. Absorbance
spectra are reported as λmax/nm (ε/M-1 cm-1).
N-Isopropyl-1H-pyrrole-2-carboxamide (1a). Trichloroacetylpyr-
role (5.0 g, 24 mmol) was added to 50 mL of isopropylamine, and
the mixture was stirred at room temperature. The originally clear
solution became light brown. After 17 h, the solvent was removed
with a rotary evaporator to yield an off-white precipitate (3.4 g, 22
1
mmol, 94%). H NMR (400 MHz, DMSO-d6): δ 11.37 (s, 1H),
7.70 (d, J ) 8.1 Hz, 1H), 6.81 (d, J ) 4.4 Hz, 1H), 6.76 (d, J )
5.9 Hz, 1H), 6.05 (s, 1H), 4.04 (m, 1H), 1.13 (d, J ) 6.6 Hz, 6H).
13C NMR (CDCl3): δ 160.8, 121.7, 109.7, 94.5, 41.6, 23.2. ESI-
MS: m/z 153.10 [M + H]+.
(20) Motekaitis, R. J.; Martell, A. E. Inorg. Chem. 1970, 9, 1832–1839.
(21) Murakami, Y.; Matsuda, Y.; Sakata, K.; Martell, A. E. Dalton Trans.
1973, 1729–1734.
(22) Vega, I. E.; Gale, P. A.; Hursthouse, M. B.; Light, M. E. Org. Biomol.
Chem. 2004, 2, 2935–2941.
[1,1′-Isopropylamide-5-phenyl-4,6-dipyrromethane] (2a). To
a solution of 1a (1.0 g, 6.5 mmol) suspended in 30 mL of toluene
was added benzaldehyde (0.33 g, 3.2 mmol) and p-toluenesulfonic
acid (p-TSA, ∼5 mg), and the resulting solution was heated to 120
°C. After 16 h, a pink precipitate was filtered and washed with 60
mL of toluene (1.0 g, 2.5 mmol, 78%). 1H NMR (400 MHz, DMSO-
d6): δ 11.25 (s, 2H), 7.63 (d, J ) 8.1 Hz, 2H), 7.28-7.11 (m, 5H),
6.65 (d, J ) 3.7 Hz, 2H), 5.74 (d, J ) 3.7 Hz, 2H), 5.48 (s, 1H),
(23) Katayev, E. A.; Boev, N. V.; Khrustalev, V. N.; Ustynyuk, Y. A.;
Tananaev, I. G.; Sessler, J. L. J. Org. Chem. 2007, 72, 2886–2896.
(24) Givaja, G.; Volpe, M.; Leeland, J. W.; Edwards, M. A.; Young, T. K.;
Darby, S. B.; Reid, S. D.; Blake, A. J.; Wilson, C.; Wolowska, J.;
McInnes, E. J. L.; Schroder, M.; Love, J. B Chem.sEur. J. 2007, 13,
3707–3723.
(25) Reid, S. D.; Blake, A. J.; Kockenberger, W.; Wilson, C.; Love, J. B.
Dalton Trans. 2003, 4387–4388.
(26) Katayev, E. A.; Ustynyuk, Y. A.; Lynch, V. M.; Sessler, J. L. Chem.
Commun. 2006, 4682–4684.
10534 Inorganic Chemistry, Vol. 47, No. 22, 2008

Diamidodipyrrins
4.00 (m, 2H), 1.07 (d, J ) 6.6 Hz, 12H). 13C NMR (DMSO-d6): δ
160.4, 143.2, 137.0, 128.8, 127.0, 126.6, 126.2, 110.7, 108.3, 43.4,
23.3. ESI-MS: m/z 393.08 [M + H]+, 415.17 [M + Na]+.
was removed on a rotary evaporator. The residue was taken up in
50 mL of CH2Cl2 and washed with 2 × 50 mL of 5% citric acid
and 50 mL of brine. The organic layer was dried with Na2SO4 and
filtered. The solvent was evaporated, and a light brown solid was
[1,1′-Isopropylamide-5-phenyl-4,6-dipyrrin] (HDADPPh,iPr). A
solution of 2,3-dicyano-5,6-dichloro-1,4-benzoquinone (DDQ, 0.13 g,
0.59 mmol) in 25 mL of tetrahydrofuran (THF) was added dropwise
to a solution of 2a (0.20 g, 0.51 mmol) suspended in 50 mL of
THF and 30 mL of CHCl3 over 15 min. Upon addition, the solution
became a turbid, orange mixture, and after 23 h, the solution was
dark red. The solvent was removed with a rotary evaporator, and
the residue was purified by flash chromatography on a silica gel
column (CH2Cl2). A red band was isolated and yielded a bright
1
obtained (1.5 g, 7.4 mmol, 78%). H NMR (500 MHz, CDCl3): δ
9.43 (s, 1H), 7.37-7.31 (m, 5H), 6.94 (s, 1H), 6.22 (q, J ) 5.8
Hz, 1H), 5.72 (d, J ) 6.8 Hz, 1H), 3.93 (m, 1H), 2.02-1.16 (m,
10H). 13C NMR (CDCl3): δ 161.8, 138.8, 129.0, 127.9, 127.7, 125.9,
122.4, 109.8, 109.8, 43.5. ESI-MS: m/z 193.22 [M + H]+.
[1,1′-Benzylamide-5-phenyl-4,6-dipyrromethane] (2c). To a
solution of 1c (1.5 g, 7.5 mmol) suspended in 30 mL of toluene
was added benzaldehyde (0.39 g, 3.7 mmol) and p-TSA (∼5 mg).
The mixture became pale pink upon heating to 94 °C, and a
precipitate formed after 2.5 h. The solution was filtered, and the
precipitate was washed with 50 mL of toluene (0.40 g, 0.8 mmol,
22%). 1H NMR (400 MHz, DMSO-d6): δ 11.35 (s, 2H), 8.43 (q, J
) 5.8 Hz, 2H), 7.31-7.15 (m, 15H), 6.61 (q, J ) 5.8 Hz, 2H),
5.58 (q, J ) 5.8 Hz, 2H), 5.52 (s, 1H), 4.39 (q, J ) 5.8 Hz, 4H).
13C NMR (DMSO-d6): δ 161.3, 143.2, 140.7, 137.4, 128.9, 128.8,
127.8, 127.3, 127.0, 126.2, 111.0, 108.5, 43.5, 42.8. ESI-MS: m/z
489.16 [M + H]+, 511.26 [M + Na]+, 527.15 [M + K]+.
1
orange product (0.18 g, 0.47 mmol, 93%). H NMR (400 MHz,
CDCl3): δ 7.48 (m, 5H), 6.77 (d, J ) 4.4 Hz, 2H), 6.63 (d, J ) 4.4
Hz, 2H), 6.55 (d, J ) 8.1 Hz, 2H), 4.29 (m, 2H), 1.32 (d, J ) 6.6
Hz, 12H). 13C NMR (CDCl3): δ 160.3, 149.4, 144.7, 142.0, 136.5,
131.2, 130.3, 129.9, 128.1, 117.2, 41.9, 23.0. ESI-MS: m/z 319.17
[M + H]+. λmax (15%CH3OH/CH2Cl2): 456 (15000), 334 (5600).
Anal. calcd for C23H26N4O2 ·H2O: C, 67.63; H, 6.91; N, 13.72.
Found: C, 67.55; H, 7.01; N, 13.70.
N-Cyclohexyl-1H-pyrrole-2-carboxamide (1b). Trichloro-
acetylpyrrole (3.0 g, 14 mmol) was added to 10 mL of cyclohexy-
lamine, and the mixture was stirred at room temperature. The
mixture became a turbid suspension with a white precipitate
overnight. The white precipitate was filtered and washed with 40
mL of Et2O (1.3 g, 6.8 mmol, 48%). 1H NMR (500 MHz, CDCl3):
δ 9.60 (s, 1H), 6.90 (s, 1H), 6.51 (s, 1H), 6.218 (d, J ) 5.8 Hz,
1H), 5.72 (d, J ) 6.8 Hz, 1H), 3.93 (m, 1H), 2.02-1.16 (m, 10H).
13C NMR (DMSO-d6): δ 160.3, 127.2, 121.6, 110.4, 109.0, 48.1,
33.4, 26.0, 25.7. ESI-MS: m/z 193.22 [M + H]+.
[1,1′-Benzylamide-5-phenyl-4,6-dipyrrin] [HDADPPh,Bz]. A
solution of DDQ (65 mg, 0.29 mmol) in 25 mL of THF was added
dropwise to a solution of 2c (0.10 g, 0.20 mmol) in 25 mL of THF
over 15 min. Upon addition, the solution was red and transparent.
After 2 h, the reaction was complete by TLC, and the solvent was
removed on a rotary evaporator. The residue was purified by flash
chromatography on a silica gel column (2% MeOH in CH2Cl2),
1
and a red solid was isolated (0.10 g, 0.19 mmol, 99%). H NMR
(400 MHz, CDCl3): δ 7.52-7.28 (m, 15H), 7.12 (s, 2H), 6.81 (d,
J ) 4.4 Hz, 2H), 6.64 (d, J ) 4.4 Hz, 2H), 4.68 (d, J ) 5.9 Hz,
2H). 13C NMR (CDCl3): δ 161.6, 149.0, 142.4, 138.2, 136.5, 131.2,
130.5, 130.0, 129.0, 128.1, 128.0, 127.7, 117.7, 43.8, 29.9. ESI-
MS: m/z 487.21 [M + H]+, 509.20 [M + Na]+. λmax (CH2Cl2):
458, 340 nm. Anal. calcd for C31H26N4O2 ·1.75H2O: C, 71.87; H,
5.74; N, 10.81. Found: C, 72.12; H, 6.12; N, 10.95.
[1,1′-Cyclohexylamide-5-phenyl-4,6-dipyrromethane] (2b). To
a suspension of 1b (0.80 g, 4.2 mmol) in 30 mL of toluene was
added benzaldehyde (0.22 g, 2.1 mmol) and p-TSA (∼5 mg). The
mixture became transparent pink upon heating to 120 °C. After
heating overnight, a pink precipitate formed, which was filtered
1
and washed with 70 mL of toluene (0.80 g, 1.6 mmol, 82%). H
N-Phenyl-1H-pyrrole-2-carboxamide (1d). This compound was
prepared according to a literature procedure from freshly distilled
NMR (400 MHz, DMSO-d6): δ 11.26 (s, 2H), 7.62 (s, 2H),
7.30-7.12 (m, 5H), 6.68 (q, J ) 5.8 Hz, 2H), 5.74 (q, J ) 5.8 Hz,
2H), 5.50 (s, 1H), 3.68 (m, 2H), 1.78-1.11 (m, 10H). 13C (DMSO-
d6): δ 160.3, 143.2, 137.0, 129.6, 128.8, 126.5, 110.8, 108.3, 48.1,
33.4, 26.0, 25.7. ESI-MS: m/z 473.23 [M + H]+, 495.34 [M +
Na]+.
aniline (48% yield).27 mp ) 152-154 °C (lit: 152-155 °C). H
1
NMR (300 MHz, DMSO-d6): δ 11.66 (s, 1H), 9.73 (s, 1H), 7.73
(d, J ) 7.7 Hz, 2H), 7.32 (t, J ) 7.4 Hz, 2H), 7.02-7.07 (m, 2H),
6.96 (m, sh, 1H), 6.16 (m, sh, 1H).
[1,1′-N-Phenylamide-5-phenyl-4,6-dipyrromethane] (2d). A
round-bottomed flask was charged with 1d (2.5 g, 13 mmol),
benzaldehyde (0.71 g, 6.7 mmol), p-TSA (∼30 mg), and 30 mL of
toluene, and the mixture was refluxed for 15 h. The hot slurry was
filtered, then washed with hot toluene and benzene to afford 2d as
an off-white powder (2.5 g, 5.5 mmol, 83%). 1H NMR (400 MHz,
DMSO-d6): δ 11.66 (s, 2H), 9.67 (s, 2H), 7.71 (d, J ) 8.1 Hz,
4H), 7.29-7.33 (m, 6H), 7.19-7.24 (m, 3H), 7.03 (t, J ) 7.3 Hz,
2H), 7.00 (t, 2H, J)2.93 Hz), 5.88 (t, J ) 2.9 Hz, 2H), 5.63 (s,
1H). 13C NMR (DMSO-d6): δ 159.1, 142.3, 139.4, 137.8, 128.6,
128.2, 128.2, 126.4, 125.5, 122.9, 119.8, 111.6, 108.2, 42.8. ESI-
MS: m/z 461.12 [M + H]+, 483.21 [M + Na]+. Anal. calcd for
C29H24N4O2: C, 75.63; H, 5.25; N, 12.17. Found: C, 75.40; H, 5.63;
N, 12.11.
[1,1′-Cyclohexylamide-5-phenyl-4,6-dipyrrin] [HDADPPh,Cy]. A so-
lution of DDQ (0.16 g, 0.70 mmol) in 30 mL of THF was added
dropwise to a solution of 2b (0.22 g, 0.47 mmol) in 50 mL of CHCl3
over 15 min. Upon addition, the solution became red and transpar-
ent. After 5 h, the reaction was complete by thin-layer chroma-
tography (TLC), and the solvent was removed on a rotary
evaporator. The residue was purified by flash chromatography on
a silica gel column (CH2Cl2), and a red band was isolated. The
product was chromatographed on a second silica gel column in
CH2Cl2 with 3% MeOH, yielding a red film (0.20 g, 0.4 mmol,
1
91%). H NMR (400 MHz, CDCl3): δ 7.52-7.46 (m, 5H), 6.79
(d, J ) 3.7 Hz, 2H), 6.65 (m, 4H), 3.98 (m, 2H), 2.06-1.25 (m,
20H). 13C NMR (CDCl3): δ 160.6, 149.5, 142.0, 136.6, 131.2, 130.4,
130.0, 128.1, 117.5, 48.7, 33.2, 31.2, 25.7, 25.1. ESI-MS: m/z
471.29 [M + H]+. λmax (CH2Cl2): 460, 350 nm. Anal. calcd for
C29H34N4O2 ·1.25H2O: C, 70.63; H, 7.46; N, 11.36. Found: C, 70.70;
H, 7.79; N, 11.03.
N-Benzyl-1H-pyrrole-2-carboxamide (1c). Trichloroacetylpyr-
role (2.0 g, 9.4 mmol) was added to a solution of 1.1 mL of
benzylamine and 20 mL of Et3N. The mixture was stirred at room
temperature overnight and became an amber solution. The solvent
[1,1′-N-Phenylamide-5-phenyl-4,6-dipyrrin] (HDADPPh,Ph). A
solution of DDQ (0.17 g, 0.74 mmol) in 5 mL of THF was added
dropwise to a solution of 2d (0.31 g, 0.67 mmol) in 25 mL of THF
over 15 min. Upon addition, the solution became dark orange. The
(27) La Regina, G.; Silvestri, R.; Artico, M.; Lavecchia, A.; Novellino,
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922–931.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10535

Thoi et al.
Figure 1. X-band EPR spectra (bold lines), and relevant simulations (thin lines), of Cu(DADPPh,iPr)Cl in frozen solution (A) and in fluid solution (B). The
gray vertical lines are included to aid in comparison of the visible features in the experimental spectra with features in the simulations; the red vertical lines
in B represent the additional features anticipated when more than two equivalent 14N atoms are coordinated, as described in the text.
reaction was continued for 3 h, and the precipitate was collected
and washed with 10 mL of THF followed by ethyl ether (2 × 10
mL) to afford the product as a red powder (0.15 g, 0.32 mmol,
47%). 1H NMR (400 MHz, CDCl3): δ 10.46 (s, 2H), 7.85 (d, J )
8.6 Hz, 4H), 7.55-7.66 (m, 5H), 7.37 (t, J ) 8.1 Hz, 4H),
7.12-7.16 (m, 4H), 6.70 (d, J ) 4.4 Hz, 2H). 13C NMR (CDCl3):
δ 159.2, 149.4, 145.3, 140.9, 138.4, 135.7, 130.6, 130.2, 129.9,
128.6, 128.0, 123.8, 119.8, 118.9. ESI-MS: m/z 459.18 [M + H]+.
[1,1′-Isopropylamide-5-phenyl-4,6-dipyrrinato]CuCl [Cu-
(DADPPh,iPr)Cl]. A solution of CuCl2 ·2H2O (14 mg, 0.08 mmol)
in 3.0 mL of CH3OH was added to a solution of DADPPh,iPr (20
mg, 0.05 mmol) in 3.0 mL of CHCl3. Upon addition, the solution
turned from red to a magenta color. Triethylamine (Et3N, 0.20 mL)
was added, and the solution became dark purple. The solution was
evaporated, and the residue was taken up in CH2Cl2. The residue
was washed with 10 mL of ddH2O, and the organic layer was dried,
giving a dark purple precipitate (32 mg, 0.07 mmol, 99%). ESI-
MS: m/z 451.22 [M]+. λmax (15% CH3OH/CH2Cl2): 546 (25000),
362 (14000). Anal. calcd for C23H25N4CuO2: C, 56.55; H, 5.16; N,
11.47. Found: C, 56.94; H, 5.20; N, 11.23.
[1,1′-Isopropylamide-5-phenyl-4,6-dipyrrinato]Ni [Ni(DAD-
PPh,iPr)]. NiCl2 (5.4 mg, 0.04 mmol) was suspended in 3.0 mL of
CH3OH and was added to a solution of DADPPh,iPr (16 mg, 0.04
mmol) in 3.0 mL of CHCl3. Upon vigorous stirring, the solution
turned from red to a magenta color. Et3N (0.20 mL) was added,
and the solution became brown. The solution was evaporated, and
the residue was taken up in CH2Cl2 and 0.20 mL of Et3N. The
solution was diffused with hexanes and then allowed to slowly
evaporate. The residue was washed with chloroform, and red-green
dichroic crystals of the CH2Cl2 solvate were collected on a glass
frit (12 mg, 0.03 mmol, 73%). 1H NMR (500 MHz, DMSO-d6): δ
10.46 (s, br, 2H), 7.60 (t, 1H, J ) 7.4 Hz), 7.54 (t, J ) 7.5 Hz,
2H), 7.46 (d, J ) 7.5 Hz, 2H), 6.72 (d, J ) 4.0 Hz, 1H), 6.64 (d,
J ) 4.6 Hz, 1H), 6.49 (d, J ) 4.0 Hz, 1H), 6.35 (d, J ) 4.6 Hz,
1H), 3.92-3.97 (m, 1H), 3.81-3.86 (m, 1H), 1.21 (d, J ) 6.3 Hz,
6H), 0.94 (d, J ) 6.9 Hz, 6H). ESI-MS: m/z 447.17 [M + H]+.
λmax (15%CH3OH /CH2Cl2): 504 (26000), 476 (15000), 362
(11000). Anal. calcd for C23H24N4NiO2 ·0.5H2O: C, 60.56; H, 5.52;
N, 12.28. Found: C, 60.23; H, 5.62; N, 11.91.
mM) solutions were prepared in HPLC-grade THF (Fisher Scien-
tific) containing 0.80% (v/v) Et3N. Both solutions were subjected
to three freeze-pump-thaw cycles under a N2 atmosphere and then
transferred to an inert atmosphere (N2) glovebox. Air-free method:
In the glovebox, a septum-capped quartz cuvette was charged with
1.5 mL of the 2a stock solution and 1.8 mL of the CuCl2 ·2H2O
stock solution to give a final concentration of 0.18 mM in each
component. UV-visible spectra were obtained at 5 min intervals
over the course of 3 h. Aerated method: This method was identical
to the airless method except that, following the initial scan, air was
bubbled through the solution with a Pasteur pipet for 2 min. The
cuvette was then resealed, and absorbance spectra were obtained
every 5 min for 3 h. For aerated reactions involving only 2a or
only CuCl2 ·2H2O, THF with 0.80% Et3N was substituted for the
volume of the omitted reagent. In an attempt to ascertain the identity
of the reaction mixture, the aerated reaction was continued for 24 h.
UV-visible spectroscopy confirmed that the spectrum after 24 h
was essentially identical to the final spectrum after 3 h. The reaction
was concentrated to about 2 mL under reduced pressure and then
analyzed by mass spectrometry. ESI-MS, mass calcd for Cu(D-
ADPPh,iPr): m/z ) 451.12 [M]+. Found: m/z ) 452.18 [M + H]+.
Single Crystal X-Ray Crystallographic Studies. Single crystals
of each compound suitable for X-ray diffraction structural deter-
mination were mounted on nylon loops with Paratone oil and were
cooled in a nitrogen stream on the diffractometer. Data were
collected on either a Bruker AXS or a Bruker P4 diffractometer,
each equipped with area detectors. Peak integrations were performed
with the Siemens SAINT software package. Absorption corrections
were applied using the program SADABS. Space group determina-
tions were performed by the program XPREP. The structures were
solved and refined with the SHELXTL software package (Sheldrick,
G. M. SHELXTL Vers. 5.1 Software Reference Manual; Bruker
AXS: Madison, WI, 1997). All structures were solved by direct
methods; all hydrogen atoms were placed at calculated positions
and treated with a riding model, and all non-hydrogen atoms were
refined anisotropically unless otherwise noted.
EPR Spectroscopy. X-band EPR spectra were recorded with a
Bruker EMX EPR spectrometer on degassed 50 µM 80/20 CH2Cl2/
toluene solutions of Cu(DADPPh,iPr)Cl. Low-temperature spectra
were obtained using an Oxford ESR900 liquid helium cryostat. To
facilitate direct comparison of the fluid and frozen solution spectra,
both sets of data were acquired with the cryostat in place, keeping
the microwave frequency nearly constant. The spectra in Figure 1
represent the average of 16 scans each. Other conditions are as
follows: (room temperature) νMW ) 9.372 GHz (20 mW), 6 G field
modulation (100 kHz), receiver gain ) 50 000, time constant/
conversion time ) 82 ms; (8 K) νMW ) 9.385 GHz (20 µW), 6 G
field modulation (100 kHz), receiver gain ) 50 000, time constant/
1,1′-Isopropylamide-5-phenyl-4,6-dipyrrinium Bromide (H2-
DADPPh,iPrBr). (H2DADPPh,iPrBr). HDADPPh,iPr (16 mg, 0.04 mmol)
was added to a solution of concentrated HBr (4.7 µL, 0.04 mmol)
in 5.0 mL of CHCl3. After 20 min, the reaction mixture was filtered
and the solvent evaporated to afford the product in quantitative
yield. X-ray-quality single crystals of H2DADPPh,iPrBr·3CHCl3 ·H2O
grew from a concentrated CHCl3 solution at -20 °C.
Copper-Mediated Oxidation of 2a. 1,1′-Isopropylamide-5-
phenyl-4,6-dipyrromethane (2a) (0.40 mM) and CuCl2 ·2H2O (0.33
10536 Inorganic Chemistry, Vol. 47, No. 22, 2008

Diamidodipyrrins
Scheme 1. Synthesis of DADPR,R′ Ligands Starting with
Trichloroacetylpyrrolea
a The yields shown are for R ) Ph and R′ ) iPr; however, it should be
noted that, although the yields of these reactions are generally high, they
may vary with different R and R′ substituents.
Figure 2. Electronic absorbance spectrum in 15% CH3OH/CH2Cl2 of
DADPPh,iPr (s), Cu[DADPPh,iPr]Cl ( · · ·), and Ni[DADPPh,iPr] (---).
without significant changes to the approach outlined in
Scheme 1 (diamidodipyrrin ligands are abbreviated as
DADPR,R′). In this initial study, ligands containing R ) Ph
and R′ ) iPr, Cy, Ph, and Bn were readily prepared. The
versatile synthesis of these ligands is one attractive feature
for their use in exploring new metal complexes.
conversion time ) 82 ms. Spectra were simulated using the program
QPOW (QPOW is available upon request from Prof. Joshua Telser,
Roosevelt University, Chicago, IL). The low-temperature spectrum
in Figure 1A was simulated by adjusting hyperfine couplings and
g values to match peak positions and then increasing the EPR line
width, ultimately to 10 (g⊥) or 15 MHz (g||), without further
adjustment of the g and A values. An isotropic coupling of 46 MHz
to two equivalent 14N’s is also included in the low-temperature
simulation, as discussed below. The average g and A values obtained
from the low-temperature simulation were then held fixed to
generate the room temperature simulations in Figure 1B. The final
simulations include weighted contributions from both 63Cu and 65Cu,
and correlated mI and frequency-dependent contributions to the
observed line width,28 totaling less than 20% of the overall EPR
line width; the same line width parameters were used for both
simulations.
The diamidodipyrrin ligands are found to readily form
metal complexes under mild conditions. An appropriate metal
salt in CH3OH is added to the ligand dissolved in CHCl3 at
room temperature. The reaction can be visually monitored
by its intense color changes. For example, when adding either
CuCl2 · 2H2O or NiCl2 to a solution of DADPPh,iPr, an
immediate color change from red to magenta is observed.
The addition of a base causes the solution to become dark
purple and red-brown for the Cu2+ and Ni2+ complexes,
respectively. The addition of a base is necessary as the
reaction in the absence of a base results in the isolation of
the ligand as a hydrogen-bonded, protonated dimer (vide
infra). Electrospray ionization mass spectrometry (ESI-MS)
analysis reveal an [M]+ (m/z 451.22) and [M + H]+ (m/z
447.21) peak for Cu(DADPPh,iPr)Cl and Ni(DADPPh,iPr),
respectively.
The absorbance spectra of both complexes and DADPPh,iPr
are shown in Figure 2. Cu(DADPPh,iPr)Cl has a maximum
absorbance at 546 nm (ε ) 25 000 M-1 cm-1), while
Ni(DADPPh,iPr) has a maximum absorbance at 506 nm (ε )
26 000 M-1 cm-1). The complexes are significantly red-
shifted relative to the DADPPh,iPr ligand, which has a
maximum absorbance at 458 nm (ε ) 15 000 M-1 cm-1).
Due to the extended conjugation of the dipyrrin unit with
the carbonyl groups in the DADPPh,iPr ligand, the spectra of
the complexes reported here are also red-shifted relative to
the R-unsubstituted dipyrrinato complexes,14,29,30 which
typically display a maximum absorbance at e 500 nm.
Results and Discussion
The synthesis of diamidodipyrrins is quite facile, high-
yielding, and versatile; indeed, in our hands, the synthetic
chemistry is more straightforward than that of the parent
R-unsubstituted dipyrrins. Adapted from existing reports of
diamidodipyrromethanes,22,23 the synthesis of diamidodipyr-
rins (Scheme 1) begins with the amination of trichloro-
acetylpyrrole to yield a pyrrolamide (1). The acid-catalyzed
(p-TSA), heat-driven condensation of benzaldehyde with the
pyrrolamide in toluene generates the dipyrromethane (2) as
an insoluble precipitate. The dipyrromethane is then oxidized
with DDQ to give the expected dipyrrin product as a bright
orange solid. Unlike many previously reported R-unsubsti-
tuted dipyrrins,9,11 diamidodipyrrin ligands can be chro-
matographed on silica and isolated in high yields after
oxidation from the corresponding diamidodipyrromethane
(typically >90% for the oxidation step) with relative ease.
The synthesis described is relatively general, and the R and
R′ substituents of the diamidodipyrrins can be modified
(29) Bru¨ckner, C.; Karunaratne, V.; Rettig, S. J.; Dolphin, D. Can. J. Chem.
1996, 74, 2182–2193.
(30) Halper, S. R.; Cohen, S. M. Chem.sEur. J. 2003, 9, 4661–4669.
(28) Froncisz, W.; Hyde, J. S. J. Chem. Phys. 1980, 73, 3123–3131.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10537

Thoi et al.
disordered isopropyl group. All hydrogen atoms were located
in a difference map. The positions of the N-amide and
pyrrolic hydrogen atoms were allowed to refine freely. One
of the two molecules is displayed in Figure 4. The most
striking feature of the structure is that the deprotonated
pyrrolic nitrogen atoms (N3) accept intramolecular hydrogen
bonds from both the protonated pyrrolic hydrogen atom and
from the proximal N-amide hydrogen atom (the hydrogen
atoms bonded to N2 and N4 in the figure). The resulting
geometric arrangement, if it persists in solution, may
predispose the ligand toward a NNNO coordination mode
(vide infra). The carbonyl oxygen atom directed toward the
core of the molecule does not appear to be involved in
intramolecular hydrogen bonding. The molecules form a
hydrogen-bonded chain through intermolecular interactions
of the outwardly directed C-O and N-H groups, as shown
in Figure 4.
Structure of H2DADPPh,iPrBr. Crystals of H2DADPPh,iPr
-
Figure 3. Time-elapsed visible absorption spectroscopy of the reaction of
0.18 mM 2a and 0.18 mM CuCl2 ·2H2O in THF (0.8% by vol Et3N) in the
presence of O2. The spectrum was monitored at 5 min intervals for 3 h
(spectra shown are in 10 min intervals).
Br·3CHCl3 ·H2O grew upon cooling a concentrated solution
of H2DADPPh,iPrBr in chloroform to -20 °C (Table 1). The
red needles crystallized in the monoclinic space group P21/
n. The asymmetric unit included two independent
[H2DADPPh,iPr]+ cations and two Br- anions, as well as six
CHCl3 and two H2O solvent molecules. The cations are
arranged in a hydrogen-bonded dimer through cooperative
hydrogen bonding of the pyrrole hydrogen atoms of each
monomer with the carbonyl oxygen atoms of the other
monomer as shown in Figure 5. We have observed similar
cooperative hydrogen bonding in other [H2DADPPh,iPr]+ salts
(data not shown), which suggests the persistence of this
motif. This pattern of cooperative hydrogen bonding has also
been observed for a related dipyrromethane compound, 5,5′-
diformyl-2,2′-diphenyldipyrromethane.31
Copper-Mediated Oxidation of 2a. While preparing
solutions for electronic spectroscopic studies, we noticed that
the reaction of 1,1′-isopropylamide-5-phenyl-4,6-dipyr-
romethane (2a) and CuCl2 in the presence of air and a base
(Et3N) produced a red solution. A similar color change did
not occur when NiCl2 was used as a metal ion source. We
interpreted this color change as an indication of the copper-
mediated oxidation of the dipyrromethane to the dipyrrin,
presumably followed by the formation of a complex with
Cu2+. It has been noted in the literature that solutions of
dipyrromethanes oxidize over time to form dipyrrins; this
has also been noted for diamidodipyrromethanes as well.22
The oxidation of diiminodipyrromethene complexes of group
10 metals has also been reported.3 In an attempt to ascertain
the dependence of this reaction on the various reagents, we
monitoredthereactionbyUV-visibleabsorbancespectroscopy.
As shown in Figure 3, a broad visible band centered at
530 nm increased in intensity over time when the reaction
was exposed to the air. This band, which was responsible
for the red color, was not present when air was excluded
from the reaction. Also, there was no color change indicative
of oxidation when the experiment was performed with the
omission of either 2a or CuCl2 in aerated solutions containing
Et3N (data not shown). These results show that both CuCl2
and oxygen were required for the rapid oxidation of 2a. The
formation of the resulting Cu[DADPPh,iPr]Cl complex was
confirmed by ESI-MS on an aliquot of the reaction mixture,
as well as the growth and X-ray structure determination of
single crystals of Cu[DADPPh,iPr]Cl produced directly from
the solution.
Structure of M(DADPPh,iPr) Complexes. Single crystals
of Cu(DADPPh,iPr)Cl and Ni(DADPPh,iPr) were obtained, and
their structures were determined by X-ray diffraction (Figure
6, Table 1). Red plates of Cu(DADPPh,iPr)Cl crystallized in
the orthorhombic space group P212121 with two independent
complexes in the asymmetric unit and two CH3OH and one
H2O solvent molecule. The copper center has a square-
pyramidal coordination geometry bound to a single DAD-
PPh,iPr ligand via two pyrrolic nitrogen atoms and two amide
oxygen atoms, forming a NNOO donor set. This coordination
mode is very reminiscent of the dialkyltin complexes formed
with saturated 1,9-diacyldipyrromethanes reported by Lind-
sey and co-workers.32 The apical position in Cu(DADP-
Ph,iPr)Cl is occupied by the chloride ligand. The Cu-N
distances are 1.911(3) and 1.917(3) Å and the Cu-O
distances are 2.031(2) and 2.116(3) Å. Cu2+ complexes of
R-unsubstituted dipyrrins have average Cu-N bond distances
of 1.953(17) Å, while Cu2+-Oamide distances average 2.06(17)
Å.33 Intermolecular hydrogen bonding is observed between
Structure of HDADPPh,iPr. A weakly diffracting, orange
plate of the free-base HDADPPh,iPr crystallized from a
chloroform solution by vapor diffusion with pentane (Table
1). The crystal formed in the monoclinic, P21/c, space group.
The asymmetric unit of the solvent-free crystal included two
dipyrrin molecules. Each independent molecule included a
(31) Love, J. B.; Blake, A. J.; Wilson, C.; Reid, S. D.; Novak, A.;
Hitchcock, P. B. Chem. Commun. 2003, 1682–1683.
(32) Tamaru, S.; Yu, L. H.; Youngblood, W. J.; Muthukumaran, K.;
Taniguchi, M.; Lindsey, J. S. J. Org. Chem. 2004, 69, 765–777.
(33) Allen, F. H. Acta Crystallogr. 2002, B58, 380–388.
10538 Inorganic Chemistry, Vol. 47, No. 22, 2008

Diamidodipyrrins
Table 1. Crystal Data and Data Collection Parameters for HDADPPh,iPr, H2DADPPh,iPrBr, Cu(DADPPh,iPr)Cl, and Ni(DADPPh,iPr
)
HDADPPh,iPr
H2DADPPh,iPrBr
Cu(DADPPh,iPr)Cl
Ni(DADPPh,iPr
)
empirical formula
cryst syst
space group
C23H26N4O2
monoclinic
P21/c
C23H27N4O2Br·3CHCl3 ·H2O
monoclinic
P21/n
C24H30CuN4O2.5Cl
orthorhombic
P212121
C24H26N4NiO2Cl2
monoclinic
P21/n
unit cell dimensions
a ) 15.7923(19) Å
b ) 13.3540(17) Å
c ) 21.442(3) Å
R ) 90°
a ) 13.987(3) Å
b ) 20.692(5) Å
c ) 25.444(6) Å
R ) 90°
a ) 11.850(4) Å
b ) 16.419(5) Å
c ) 25.676(8) Å
R ) 90°
a ) 8.5116(6) Å
b ) 15.8157(11) Å
c ) 17.9622(12) Å
R ) 90°
ꢀ ) 106.781(2)°
γ ) 90°
ꢀ ) 94.605(5)°
γ ) 90°
ꢀ ) 90°
ꢀ ) 90.2120(10)°
γ ) 90°
γ ) 90°
volume, Z
crystal size
temp (K)
4329.4(9) Å3, 8
0.34 × 0.25 × 0.07 Å3
100(2)
7340(3) Å3, 8
0.41 × 0.22 × 0.19 Å3
100(2)
4996(3) Å3, 8
0.15 × 0.12 × 0.08 Å3
208(2)
2418.0(3) Å3, 4
0.29 × 0.26 × 0.11 Å3
100(2)
reflns collected
independent reflns
data/restraints/params
goodness of fit on F2
final R indices I > 2σ(I)
39697
7917 [R(int) ) 0.1413]
7917/3/583
93094
19863
9634 [R(int) ) 0.0476]
9634/3/621
12149
4719 [R(int) ) 0.0380]
4719/0/309
14795 [R(int) ) 0.0545]
14795/6/805
1.018
R1 ) 0.0406
wR2 ) 0.0898
R1 ) 0.0594
wR2 ) 0.0987
1.020
1.024
1.059
R1 ) 0.0942
wR2 ) 0.1386
R1 ) 0.1806
wR2 ) 0.1660
R1 ) 0.0445
wR2 ) 0.0985
R1 ) 0.0605
wR2 ) 0.1078
R1 ) 0.0425
wR2 ) 0.0863
R1 ) 0.0691
wR2 ) 0.0955
R indices (all data)
a
2
2
4
R1 ) ∑|Fo| - |Fc|/∑|Fo|. R2 ) {∑[w(Fo - Fc )2]/∑[wFo ]}.1/2
Figure 4. A drawing of one of the two independent molecules in the crystal structure of HDADPPh,iPr (left). Atoms are shown with 50% thermal contours.
The second molecule has a similar geometry. For clarity, only one position of the disordered isopropyl group is shown. A view showing the connectivity
of a hydrogen-bonded chain in HDAPRPh,iPr is also given (right). For clarity, only ipso-isopropyl carbon atoms are shown, and hydrogen atoms are omitted.
(Figure 6, Table 1). Interestingly, Ni(DADPPh,iPr) shows a
NNNO coordination set with a square-planar coordination
geometry. The Ni-N bond lengths in Ni(DADPPh,iPr) are all
shorter than those found in Cu(DADPPh,iPr)Cl, as expected.
The Ni-Npyrrole bond lengths are 1.808(2) and 1.824(2) Å,
while the Ni-Namide and Ni-O lengths are 1.908(2) and
1.9132(18) Å, respectively. These distances may be com-
pared with the average bond lengths of 1.91(4) Å
(Ni-Npyrrole), 1.91(9) Å (Ni-Namide), and 2.05(11) Å
(Ni-Oamide). The sum of the angles about the nickel atom is
360°, with Npyrrole-Ni-Npyrrole
,
Npyrrole-Ni-Namide,
Npyrrole-Ni-O, and Namide-Ni-O angles of 88.54(10)°,
84.31(10)°, 83.92(9)°, and 103.22(9)°.33 Intermolecular
hydrogen bonding is observed between the N-H amide
group and the amide oxygen of an adjacent molecule. A
similar complex, generated via oxygen activation of a Ni2+
diiminodipyrrinato complex to obtain a Ni2+ iminocarboxy-
latodipyrrinato complex, has also been described.3 That
Figure 5. A drawing with partial naming scheme of the hydrogen-bonded
dimer in H2DADPPh,iPrBr·3CHCl3 ·H2O. Atoms are drawn with 50% thermal
contours. For clarity, only pyrrolic and amide hydrogen atoms and ipso-
carbon atoms of the isopropyl groups are shown.
the N-H amide groups and chloride ligands of an adjacent
complex.
Red blocks of Ni(DADPPh,iPr) were crystallized in the
monoclinic space group P21/n with one complex in the
asymmetric unit and one disordered CH2Cl2 solvent molecule
complex had an identical NNNO donor set to Ni(DADPPh,iPr
)
and quite similar metrics, with Ni-Npyrrole bond lengths of
1.829 Å and 1.845 Å, and Ni-Nimine and Ni-Ocarboxylate bond
Inorganic Chemistry, Vol. 47, No. 22, 2008 10539

Thoi et al.
Figure 6. Structures of Cu(DADPPh,iPr)Cl (left) and Ni(DADPPh,iPr) (right). The structures are drawn with 50% thermal contours.
of the four 63,65Cu hyperfine lines visibly resolved at g| )
2.194 (A||(63Cu) ) 555 MHz) and the fourth overlapping the
rich hyperfine structure at g⊥ ) 2.052 (A||(63Cu) ) 52 MHz).
The values of g| and A||(63Cu) indicate that the Cu(II) ion
remains five-coordinate in solution.38,39 In order to ad-
equately simulate the low-temperature spectrum, it was
necessary to include at least two equivalent 14N’s in order
to match the experimental line shape. The Cu-N hyperfine
coupling was assumed to be isotropic, consistent with
previous studies of Cu(II) porphyrins,34-37 and set to the
highest-field splitting observed in the room-temperature
spectrum (47 MHz, Figure 1B). The similarity of A⊥(63,65Cu)
and A⊥(14N), together with a lack of resolution at the high-
field edge of the spectrum, makes it impossible to define
the number of N donors from the low-temperature spectrum.
However, the low-temperature spectrum provides a frame-
work for analysis of the isotropic spectrum, by fixing the
values of gavg and Aavg(63Cu) at 2.100 and 220 MHz,
respectively. The room-temperature, fluid solution spectrum
(Figure 1B) shows a series of progressively sharper features
whose positions are well predicted using these values. On
the assumption that an equatorial Cu-Npyrrole hyperfine
coupling will be approximately the same as an equatorial
Cu-Namide coupling in this complex,36 the only resolvable
difference that is predicted, on going from two to three to
four equivalent N donors, is the number of lines that will be
observed at the high-field edge of the spectrum (red vertical
lines in Figure 1B). The experimental spectrum gives no
evidence of additional lines beyond those predicted in the
2N simulation, suggesting that the symmetric 2N2O coor-
dination mode, observed in the solid state, is also the
preferred geometry for this Cu2+ complex in fluid solution.
Figure 7. 1H NMR spectrum of Ni(DADPPh,iPr)·CH2Cl2 in a DMSO-d6
solution clearly showing that the asymmetric NNNO mode of binding
persists in solution. Ligand resonances are labeled according to the inset
chemical diagram, and solvent peaks are labeled with asterisks.
lengths of 1.970 Å and 1.988 Å, as well as similar bond
angles about the Ni2+.
The asymmetric NNNO binding mode of Ni(DADPPh,iPr
)
was confirmed by the 1H NMR spectrum of dissolved crystals
of Ni(DADPPh,iPr)·CH2Cl2. As shown in Figure 7, the ligand
resonances are split into two sets of peaks of equal intensity,
indicative of the asymmetric binding mode of the chelator.
For example, the resonances associated with the isopropyl
substituents show as two doublets at 0.94 and 1.21 ppm for
the methyl groups, and the ipso protons show up as two
separate multiplets at 3.84 and 3.95 ppm. The 1H NMR data
unambiguously show that the Ni2+ coordination environment
observed in the solid state is preserved in solution.
Conclusion
The facile, high-yielding syntheses of DADPR,R′ make
these ligands superb candidates for exploring the coordination
chemistry of a new class of nonporphyrinic pyrrole-derived
EPR studies of Cu(DADPPh,iPr)Cl also suggest that the
coordination mode observed in the solid state is maintained
in fluid solution. The axial spectrum observed in frozen
solution (bold line in Figure 1A) is similar in appearance to
that of axially coordinated Cu(II) porphyrins,34-37 with three
(37) Iwaizumi, M.; Ohba, Y.; Iida, H.; Hirayama, M. Inorg. Chim. Acta
1984, 82, 47–52.
(38) Bubacco, L.; van Gastel, M.; Groenen, E. J. J.; Vijgenboom, E.;
Canters, G. W. J. Biol. Chem. 2003, 278, 7381–7389.
(39) Peisach, J.; Blumberg, W. E. Arch. Biochem. Biophys. 1974, 165, 691–
708.
(34) Alston, K.; Storm, C. B. Biochemistry 1979, 18, 4292–4300.
(35) Brown, T. G.; Hoffman, B. M. Mol. Phys. 1980, 39, 1073–1109.
(36) Iwaizumi, M.; Kudo, T.; Kita, S. Inorg. Chem. 1986, 25, 1546–1550.
10540 Inorganic Chemistry, Vol. 47, No. 22, 2008

Diamidodipyrrins
ligands. Acid salts of these ligands show a strong propensity
to form hydrogen-bonded dimers in the solid state. The
ligands are readily derivatized with a variety of substitutents,
both at the amide groups and at the meso position of the
dipyrrin, and show the ability to employ different donor
atoms with different metal ions. We have also found that
Cu2+ and O2 can oxidize diamidodipyrromethanes in situ to
form the corresponding DADPR,R′ complexes.3 These new
dipyrrinato complexes may have potential in a variety of
applications, and ongoing studies to investigate their metal
complexes with transition and group 13 ions are underway.
Y. Su for performing the mass spectrometry experiments.
This work was supported by U.C.S.D., the donors of the
ACS-PRF, and the NSF (CHE-0546531). The EPR spec-
trometer was purchased with funds provided by the NSF
(CHE-0216277).
Supporting Information Available: Complete crystallographic
details (CIF file). This material is available free of charge via the
Internet at http://pubs.acs.org. X-ray crystallographic files in CIF
format are also available free of charge via the Internet at http://
www.ccdc.cam.ac.uk. Refer to CCDC reference numbers 673246,
673247, 692209, and 692210.
Acknowledgment. We thank Dr. A. G. DiPasquale and
Prof. A. L. Rheingold for help with X-ray analyses and Dr.
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Inorganic Chemistry, Vol. 47, No. 22, 2008 10541