Dianionic and trianionic macrocycles in cobalt N-confused porphyrin complexes

Article abstract of DOI:10.1039/b404261a

We report the syntheses of cobalt N-confused porphyrins; this work completes the series of the late first-row transition metals that have been incorporated into the core of N-confused porphyrin, and in these compounds the macrocycles can act as either a -2 or -3 anion.

Full text of DOI:10.1039/b404261a

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Dianionic and trianionic macrocycles in cobalt N-confused porphyrin
complexes†
John D. Harvey and Christopher J. Ziegler*
Department of Chemistry, University of Akron, Akron, OH 44325-3601, USA. E-mail: ziegler@uakron.edu;
Fax: (330)972-7370; Tel: (330)972-2531
Received (in West Lafayette, IN, USA) 22nd March 2004, Accepted 27th May 2004
First published as an Advance Article on the web 16th June 2004
We report the syntheses of cobalt N-confused porphyrins; this
work completes the series of the late first-row transition metals
that have been incorporated into the core of N-confused
porphyrin, and in these compounds the macrocycles can act as
either a 22 or 23 anion.
solution gradually turns from brown to greenish over 30 min.
Removal of the THF and extraction with toluene followed by
filtration to remove impurities gives a quantitative yield of 1.
Species 1 has a broad absorbance near 460 nm and Q-bands ranging
from 550 to 700 nm. Crystallization by slow evaporation of toluene
results in the isolation of single crystals and the structure of 1‡
shows a disordered axially coordinating water molecule (Fig. 1(a)).
Support for an axial water vs. a hydroxide can be made by
comparing the CoIII–O bond length in a CoTPP water complex
(1.98 Å)4 as compared to a shorter bond length (1.92 Å) in a
methoxide complex.5 As in the nickel complexes, the internal CH
is broken and the carbon atom coordinates to the metal center. The
lack of an observable proton on the external nitrogen results in a
CoIII oxidation state assignment. This species decomposes in the
presence of air.
Over the last decade, the synthesis and metallation chemistries of
porphyrin analogues and isomers have exploded as fields.1 One of
these isomers, N-confused porphyrin, is a tetrapyrrolic macrocycle
with an inverted pyrrole ring.2 This results in a peripheral nitrogen
atom along with an internal carbon that can form organometallic
bonds with transition metals. To date, all of the late first-row
transition metals from manganese to zinc have been incorporated
into the core of N-confused porphyrin with the exception of cobalt.3
Herein, the syntheses of several Co N-confused porphyrins are
reported, completing the above series of N-confused porphyrin
complexes. In these compounds, the internal carbon is activated and
forms a Co–C bond, and the macrocycle can act as either a 22 or
a 23 ligand.
If the reaction to produce 1 is followed by the introduction of
triphenylphosphine in toluene, the solution changes color to red and
a new species (2) appears (Scheme 1). In 2, the Soret band blue
shifts to 428 nm and the Q bands shift to 478 and 551 nm. Crystals
of 2 were grown from toluene–heptanes, and the elucidated
structure‡ shows that the cobalt is five-coordinate with a phosphine
axial ligand (Fig. 1(b)). The porphyrin macrocycle is saddle-shaped
and the axial phosphine is at an angle of 85.6° from the plane of the
four porphyrin core atoms. With regard to the oxidation state
assignment of the metal, the environment is similar to that of the
recently reported cobalt corrole and corrolazine complexes, which
also stabilize a CoIII and exhibit complete deprotonation of the
core.6,7 Unlike compound 1, the external nitrogen in the structure is
protonated, which indicates that the macrocycle is acting as a 22
anion and is similar to the externally protonated tautomer observed
Co(NCTPP)(H2O) (1) was generated by heating a H2NCTPP
solution in THF under anaerobic conditions with an excess of
Co(NO3)2·6H2O (Scheme 1). As the reaction progresses, the
1
in the nickel adduct.2 Evidence for this is seen in the H NMR
spectrum of 2, which shows a NH resonance at 12.11 ppm. This
chemical shift is similar to the nickel complex of NCTTP with an
external NH resonance at 10.03 ppm.2 The IR spectrum shows a
broad band at 3250 cm21 indicative of a N–H stretching vibration.
Also, in contrast to 1, this species is stable in air.
Within the unit cell of 2 is a novel bimetallic dimer,
[Co2(NO3)4(m-NO3)2]22, that acts as an anion for the cobalt N-
confused porphyrin complex (Fig. 2). The dimer lies on an
inversion center in the unit cell. Each metal center exhibits an
octahedral geometry, with four terminal bidentate nitrates and two
bridging nitrates between the cobalt ions. We can assign the
Scheme 1 Syntheses of Co(NCTPP) complexes.
† Electronic supplementary information (ESI) available: Absorption spectra
for 1, 2 and 4. See http://www.rsc.org/suppdata/cc/b4/b404261a/
Fig. 1 The structures of (a) Co(NCTPP)(H2O) (1), (b) Co(NCTPP)(PPh)3 (2), (c) Co(NCTPP)(py)2 (4). Selected bond lengths (Å) for: 1: Co(1)–N(1),
1.999(8); Co(1)–O(1), 2.12(3); 2: Co(1)–N(1), 1.982(4); Co(1)–N(2), 1.972(4); Co(1)–N(3), 1.982(4); Co(1)–C(18), 1.903(5); Co(1)–P(1), 2.2249(16); 4:
Co(1)–N(1), 1.978(3); Co(1)–C(8), 1.993(3); Co(1)–N(3), 1.982(3). The thermal ellipsoids were scaled to 30% probability for 1 and 50% for 2 and 4,
respectively. Hydrogen atoms have been omitted for clarity. Due to the disorder of the nitrogen atom at the confused pyrrole ring and high symmetry of the
crystal, one of eight possible orientations is shown for 1 and 4.
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C h e m . C o m m u n . , 2 0 0 4 , 1 6 6 6 – 1 6 6 7
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 2 0 0 4

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now start a full comparison of how this macrocycle stabilizes a
variety of oxidation states in transition metals. Continued work will
focus on the redox chemistry of cobalt N-confused porphyrins and
on the catalytic chemistry of this family of metallomacrocycle.
Notes and references
‡
Crystal data: for 1: data were collected at 100 K (Bruker KRYO-
FLEX) on a Bruker SMART APEX CCD-based X-ray diffractometer
system. CoC44H30N4O 1; M = 689.65, black needle 0.5 3 0.05 3 0.05 mm,
tetragonal, space group I4/m, Z = 2 in a cell of dimensions a = 13.368(4),
c = 9.647(6) Å, V = 1724.0(14) Å3, Dc = 1.329 Mg m23, m(Mo-Ka) =
0.539 mm21, F(000) = 714; final R indices on 815 independent reflections
[I > 2s(I)]: R1 = 0.0908, wR2 = 0.2302. For 2; data were collected at 100
K (Bruker KRYO-FLEX) on a Bruker SMART APEX CCD-based X-ray
diffractometer system. Co2C69H51N7O9P 2, M = 1271.00, green–black
Fig. 2 The structure of Co2(NO3)4(m-NO3)222 anion in 2 with 50% thermal
ellipsoids. Selected bond lengths (Å) for the anion in 2: Co(1)–O(1),
2.094(5); Co(1)–O(2), 2.178(5); Co(1)–O(4), 2.180(4); Co(1)–O(5),
2.043(5); Co(1)–O(7), 2.061(4); Co(1)–O(8), 2.084(4);
¯
block 0.37 3 0.15 3 0.12 mm, triclinic, space group P1, Z = 2 in a cell of
dimensions a = 14.5294(19), b = 15.1545(19), c = 15.400(2) Å, a =
70.304(2), b = 63.161(2), g = 73.503(2)°, V = 2813.3(6) Å3, Dc = 1.500
Mg m23, m(Mo-Ka) = 0.689 mm21, F(000) = 1310, final R indices on
10936 independent reflections [I > 2s(I)]: R1 = 0.0736, wR2 = 0.1883.
For 3: data were collected at 100 K (Bruker KRYO-FLEX) on a Bruker
oxidation state of the metal in this anion based on the bond
distances about the cobalt center; all of the Co–O bonds in this
dimer are longer than 2.04 Å, which is in the range for CoII–O
bonds in nitrate complexes (2.05 and 2.69 Å).8 The Co–O bond
distances in this anion are also much longer than the CoIII–O bonds
(1.97 Å) in Co(NO3)3.9 With this anion, complete deprotonation of
the core of the porphyrin, and the presence of an external nitrogen,
the Co(NCTPP)(PPh3) is cationic and the metal is in the +3
oxidation state. The 1H NMR resonances in 2 do not exhibit
paramagnetic shifts, but are broadened due to the presence of
unpaired electron density of the [Co2(NO3)4(m-NO3)2]22 dimer
anion. A second crystal form of 2 (species 3‡) can be generated by
extracting with CH2Cl2 instead of toluene and layering with
heptanes; the only difference between the two structures is the
identity of the solvent in the void space in the unit cell.
SMART APEX CCD-based X-ray diffractometer system. Co2C63H45
-
N7O9PCl2 3; M = 1348.72, black plate 1.60 3 0.47 3 0.09 mm, triclinic,
¯
space group P1, Z = 2 in a cell of dimensions a = 12.103(3), b =
16.031(4), c 16.390(4) Å, a 91.296(4), b 102.294(4), g
=
=
=
=
73.503(4)°, V = 2911.2(12) Å3, Dc = 1.539 Mg m23, m(Mo-Ka) = 0.848
mm21, F(000) = 1378, final R indices on 11319 independent reflections [I
> 2s(I)]: R1 = 0.0640, wR2 = 0.1743. For 4: data were collected at 100 K
(Bruker KRYO-FLEX) on a Bruker SMART APEX CCD-based X-ray
diffractometer system. CoC54H38N6 4; M = 908.93, red plate 0.5 3 0.3 3
¯
0.1 mm, triclinic, space group P1, Z = 2 in a cell of dimensions a =
10.664(3), b 14.584(4), c 16.371(5) Å, a 112.333(4), b
96.324(5), g = 91.474(5)°, V = 2334.4(12) Å3, Dc = 1.293 Mg m23
m(Mo-Ka) 946, final R indices on 9037
0.416 mm21, F(000)
independent reflections [I > 2s(I)]: R1
=
=
=
=
,
=
=
= 0.0808, wR2 = 0.2210. CCDC
234035–234038. See http://www.rsc.org/suppdata/cc/b4/b404261a/ for
crystallographic data in CIF or other electronic format.
If 1 is dissolved in pyridine, a third absorbance spectrum is
produced (species 4) that exhibits a sharp Soret at 462 and Q bands
at 555, 736 and 808 nm (Scheme 1). Crystallization of species 4
from pyridine/heptanes results in the isolation of 4,‡ a bis-pyridine
complex (Fig. 1(c)), where the metal centers lie on individual
inversion centers. As in the analogous manganese complex, the
metal center is six-coordinate with two coordinating pyridine
ligands. Unlike the Mn(NCTPP)(py)2, the axial pyridines are at an
angle of nearly 90° from the plane of the 24-atom porphine ring.10
The axially bound pyridines are similar in orientation to those in the
cobalt pentafluorophenyl corrole adduct, with a dihedral angle of
zero,6 as compared to a 90° dihedral angle found in cobalt
complexes of octaalkyl corrole and corrolazine.7 Unlike the
Co(NCTPP)(PPh3) complexes, the external nitrogen is deproto-
1 A. Jasat and D. Dolphin, Chem. Rev., 1997, 97, 2267; J. L. Sessler, A.
Gebaued and E. Vogel in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, San Diego, CA, 2000, vol.
2, p. 1; J. L. Sessler, A. Gebaued and S. T. Weghorn, in: The Porphyrin
Handbook, ed. K. M. Kadish, K. M. Smith and R. Guilard, Academic
Press, San Diego, CA, 2000, vol. 2, p. 55.
2 H. Furuta, T. Asano and T. Ogawa, J. Am. Chem. Soc., 1994, 116, 767;
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Angew. Chem., Int. Ed. Engl., 1994, 33, 779.
3 J. D. Harvey and C. J. Ziegler, Coord. Chem. Rev., 2003, 247, 1.
4 Y. Iimura, T. Sakurai and K. Yamamoto, Bull. Chem. Soc. Jpn., 1988,
61, 821.
5 C. Riche, A. Chiaroni, M. Perrée-Fauvet and A. Gaudemer, Acta
Crystallogr., Sect. B, 1978, 34, 1868.
6 A. Mahammed, I. Giladi, I. Goldberg and Z. Gross, Chem.-Eur. J., 2001,
7, 4259.
1
nated with no external NH resonance observed in the H NMR
7 R. Guilard, C. P. Gros, F. Bolze, F. Jéroˆme, Z. Ou, J. Shao, J. Fischer,
R. Weiss and K. M. Kadish, Inorg. Chem., 2001, 40, 4845; B.
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8 J. G. Bergman Jr. and F. A. Cotton, Inorg. Chem., 1966, 5, 1208.
9 J. Hilton and S. C. Wallwork, Chem. Commun., 1968, 871.
10 J. D. Harvey and C. J. Ziegler, Chem. Commun., 2003, 2890.
11 W. R. Scheidt, J. Am. Chem. Soc., 1974, 96, 84.
spectrum and no anion is present in the unit cell, therefore the
NCTPP motorcycle is acting as a 23 anion in this structure. Further
support of the CoIII oxidation state is found in the axial Co–N bond
lengths of 1.982 Å, which is similar in the length (2.060 Å) to the
cationic CoIII porphyrin piperidine complex and much shorter than
the Co–N length of 2.436 Å in the CoII porphyrin complex with
piperidine.11,12
This study completes the series of late first-row transition metals
that have been bound to the core of N-confused porphyrin. We can
12 W. R. Scheidt, J. A. Cunningham and J. L. Hoard, J. Am. Chem. Soc.,
1973, 95, 8289.
C h e m . C o m m u n . , 2 0 0 4 , 1 6 6 6 – 1 6 6 7
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