Generation and characterization of [(P)M-(X)-CO(TMPA)]n+ assemblies; P = porphyrinate, M = FeIII and CoIII, X = O2-, OH-, O22-, and TMPA = tris(2-pyridylmethyl)amine

Article abstract of DOI:10.1021/ic061686k

With the established chemistry of bridged [(porphyrinate)Fe ^III-X-Cu^II(ligand)]ⁿ⁺ [X = O^2- (oxo), OH^- (hydroxo), O₂^2- (peroxo)] complexes, we investigated the effect of cobalt ion substitution for copper or copper and iron. Thus, in this report, the generation and characterization of new μ-oxo, μ-hydroxo, and μ-peroxo (μ-X) assemblies of [(porphyrinate)M ^III-X-Co^II/^III(TMPA)]ⁿ⁺- assemblies is described, where M = Fe^III or Co^III and TMPA = tris(2-pyridylmethyl)amine. The μ-oxo complex [(F₈TPP)Fe ^III-O-Co^II(TMPA)]⁺ (1, F₈TPP = tetrakis(2,6-difluorphenyl)-porphyrinate) was isolated by an acid-base self-assembly reaction of a 1:1 mixture of (F₈TPP)Fe^III-OH and [Co^II(TMPA)(MeCN)]²⁺ upon addition of triethylamine. The crystal structure of 1·2C₄H₁₀O proved the presence of an unsupported Fe-O-Co moiety; ∠Fe-O-Co = 171.6° and d(Fe...Co) = 3.58 A. Complex 1 was further characterized by UV-vis (λ_max = 437 (Soret) and 557 nm), ¹H NMR [δ 40.6 (pyrrole-H), 8.8 and 8.7 (m-phenyl-H), 8.0 (p-phenyl-H), 4.4 (PY-4H), 2.6 (PY-3H), 1.0 (PY-5H), -1.1 (PY-6H), and -2.7 (TMPA-CH₂-) ppm], electrospray ionization (ESI) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric methods, Evans method NMR (μ_eff = 3.1), and superconducting quantum interference device (SQUID) susceptometry (J = -114 cm^-1, S = 1). The μ-hydroxo analogue [(F₈TPP)Fe^III-(OH)-Co^II(TMPA)] ⁺ (2) [UV-vis λ_max = 567 nm; δ 78 ppm (pyrrole-H); Evans NMR μ_eff = 3.7] was generated by addition of 1 equiv of triflic acid to 1. The protonation is completely reversible, and 1 is regenerated from 2 by addition of triethylamine. While (F₈TPP)Fe ^II/[Co^II(TMPA)(MeCN)]²⁺/O₂ chemistry does not lead to a stable μ-peroxo species, a dicobalt μ-peroxo complex [(TPP)Co^III(O₂^2-)-Co^III(TMPA)] ²⁺ (3, TPP = meso-tetraphenylporphyrinate) forms from a reaction of O₂ with a 1:1 mixture of the Co^II precursor components at -80°C [UV-vis λ_max = 435 (Soret), 548, and 583 (weak) nm; silent EPR spectrum; diamagnetic NMR spectrum]. The oxygenation/deoxygenation equilibrium is reversible; warming solutions of 3 releases ～1 equiv of O₂ and the reduced complexes are reformed.

Full text of DOI:10.1021/ic061686k

Inorg. Chem. 2007, 46, 3017−3026
+
Generation and Characterization of [(P)M
Porphyrinate, M
FeIII and CoIII, X
TMPA Tris(2-pyridylmethyl)amine
−
)
(X)
−
Co(TMPA)]n Assemblies;
-
-
2-
P
)
)
O2 , OH , O2 , and
)
|
Eduardo E. Chufa´n,† Claudio N. Verani,†,‡ Simona C. Puiu,† Eva Rentschler,§,
Ulrich Schatzschneider,§, Christopher Incarvito, Arnold L. Rheingold, and Kenneth D. Karlin*,†
|
,#
Department of Chemistry, The Johns Hopkins UniVersity, Baltimore, Maryland 21218,
Max-Planck-Institut fu¨r Strahlenchemie, D-45470 Mu¨lheim/Ruhr, Germany, and Chemistry &
Biochemistry Department, UniVersity of Delaware, Newark, Delaware 19716
Received September 6, 2006
+
-
With the established chemistry of bridged [(porphyrinate)FeIII
−X
−
CuII(ligand)]n [X
O2 (peroxo)] complexes, we investigated the effect of cobalt ion substitution for copper or copper and iron. Thus,
in this report, the generation and characterization of new -oxo, -hydroxo, and -peroxo ( -X) assemblies of
CoII III(TMPA)]n assemblies is described, where M FeIII or CoIII and TMPA
tris(2-
pyridylmethyl)amine. The tetrakis(2,6-difluorphenyl)-
-oxo complex [(F8TPP)FeIII CoII(TMPA)]+ (1, F8TPP
base self-assembly reaction of a 1:1 mixture of (F8TPP)FeIII
OH and
)
O2 (oxo), OH- (hydroxo),
2-
µ
µ
µ
µ
/
+
[(porphyrinate)MIII
−X−
)
)
µ
−O
−
)
porphyrinate) was isolated by an acid
−
−
[CoII(TMPA)(MeCN)]2 upon addition of triethylamine. The crystal structure of 1
‚
2C4H10O proved the presence of
+
an unsupported Fe
characterized by UV
8.0 (p-phenyl-H), 4.4 (PY-4H), 2.6 (PY-3H), 1.0 (PY-5H),
ionization (ESI) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric methods,
−
−
O
−
Co moiety; Fe
vis (λmax 437 (Soret) and 557 nm), H NMR [
1.1 (PY-6H), and
−
O
−
Co
)
171.6
°
and d(Fe‚‚‚Co)
)
3.58 Å. Complex 1 was further
1
)
δ
40.6 (pyrrole-H), 8.8 and 8.7 (m-phenyl-H),
−
−2.7 (TMPA CH2 ) ppm], electrospray
−
−
Evans method NMR (µeff
114 cm-1, S
1). The
ppm (pyrrole-H); Evans NMR µeff
is completely reversible, and 1 is regenerated from 2 by addition of triethylamine. While (F8TPP)FeII/[CoII(TMPA)-
(MeCN)]2+/O2 chemistry does not lead to a stable -peroxo complex [(TPP)CoIII
-peroxo species, a dicobalt
meso-tetraphenylporphyrinate) forms from a reaction of O2 with a 1:1 mixture of
the CoII precursor components at
80 C [UV vis λmax 435 (Soret), 548, and 583 (weak) nm; silent EPR
spectrum; diamagnetic NMR spectrum]. The oxygenation/deoxygenation equilibrium is reversible; warming solutions
of 3 releases 1 equiv of O2 and the reduced complexes are reformed.
)
µ
3.1), and superconducting quantum interference device (SQUID) susceptometry (J
)
78
−
)
-hydroxo analogue [(F8TPP)FeIII CoII(TMPA)]+ (2) [UV
−
(OH) vis λmax 567 nm;
−
−
)
δ
)
3.7] was generated by addition of 1 equiv of triflic acid to 1. The protonation
µ
µ
−
2-
+
(O2
)− )
CoIII(TMPA)]2 (3, TPP
−
°
−
)
∼
Introduction
basic insights into dioxygen activation by enzymes such as
cytochrome c oxidase.1,2 These complexes are formed by
reacting dissimilar copper-polypyridine and iron-porphy-
rinate building blocks; the products include [(F8TPP)FeIII-
(O22-)-CuII(TMPA)]+ and [(F8TPP)FeIII-O-CuII(TMPA)]+
(Chart 1, F8TPP ) tetrakis(2,6-difluorphenyl)porphyrinate,
and TMPA ) tris(2-pyridylmethyl)amine). The µ-peroxo
complex results from the reaction of molecular dioxygen with
the reduced components [FeII(F8TPP)] and [CuI(TMPA)-
In the past few years we have studied a series of µ-peroxo
and µ-oxo heme-copper complexes, aimed at providing
* To whom correspondence should be addressed. E-mail: karlin@
jhu.edu.
† The Johns Hopkins University.
‡ Present address: Department of Chemistry, Wayne State University,
Detroit, MI 48207.
§ Max-Planck-Institut.
| Present address: Institute for Inorganic Chemistry, Gutenberg Univer-
sity, D-55099 Mainz, Germany.
University of Delaware.
(1) Kim, E.; Chufa´n, E. E.; Kamaraj, K.; Karlin, K. D. Chem. ReV. 2004,
104, 1077-1133.
(2) Karlin, K. D.; Kim, E. Chem. Lett. 2004, 33, 1226-1231.
# Present address: Chemistry Department, University of California, San
Diego, La Jolla, CA 92093.
10.1021/ic061686k CCC: $37.00
Published on Web 03/20/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 8, 2007 3017

Chufa´n et al.
Chart 1
Scheme 1
(MeCN)]+ (Me ) methyl) at low temperatures, and it is
subsequently converted to a µ-oxo species upon temperature
increase.3 Independent syntheses of µ-oxo complexes could
be successfully achieved through an “acid-base” self-
assembly approach in which another building block, namely,
[(F8TPP)FeIII-OH] was treated with [CuII(TMPA)(MeCN)]2+
in the presence of base to yield [(F8TPP)FeIII-O-CuII-
(TMPA)]+.4 Analogue µ-oxo complexes having tridentate
chelates (bis-(2-pyridylethyl)-methylamine)5 or that with
dimethylamino 4-pyridyl substituents6 as the Cu(II) ligand
have similarly been synthesized and characterized. Recent
extended X-ray absorption fine structure (EXAFS) spectros-
copy and density functional theory (DFT) calculations7
indicate that [(F8TPP)FeIII-(O22-)-CuII(TMPA)]+ possesses
a µ-η2:η1-peroxo bridging geometry similar to that observed
for a X-ray structurally characterized complex studied by
Naruta and co-workers.8 [(F8TPP)FeIII-O-CuII(TMPA)]+
(Chart 1) has been thoroughly characterized (including by
X-ray diffraction) and possesses a near-linear Fe-O-Cu
moiety.9
fact, a dioxygen adduct formulated as the µ-peroxo dicobalt-
(III) species [(TPP)CoIII-(O22-)-CoIII(TMPA)]2+ (3) is also
described.
Cobalt substituted hemes, both natural and synthetic, have
been studied extensively to elucidate fundamental metal-
loporphyrin chemistry, including O2-binding.10-14 As con-
cerns analogues of heme-Cu cytochrome c oxidase models,
Collman15,16 and Boitrel17 also used Co-for-Fe and Co-for-
Cu substitutions. With a tetraphenylporphyrinate covalently
linked to a triazacyclononane or with imidazole-picket
porphyrins, Collman and co-workers synthesized binuclear
(porphyrinate)CoII/CuI compounds that react with O2 to yield
different products; a peroxo-bridged [CoIII-(O22-)-CuII]15
-
and a cobalt-superoxo [CoIII-(O2 )‚‚‚CuI]16 species were
formed, respectively. Boitrel and co-workers described a CoII/
CoII cyclam-strapped porphyrin that in the presence of excess
bulky base reacts with O2 to form a peroxo-bridged [CoIII-
(O22-)-CoIII] complex.17
In this account, we present the results obtained through
related broad approaches employing acid-base self-assembly
or metal-dioxygen reactivity strategies, but now involving
substitution of cobalt, either for the heme or for the copper
ion center. A new µ-oxo species [(F8TPP)FeIII-O-CoII-
(TMPA)](ClO4) (1) has been isolated from acid-base
synthesis and its X-ray structure, spectroscopic, and magnetic
properties are described in detail. The protonation chemistry
of this compound was also investigated, yielding the µ-hy-
droxo analogue [(F8TPP)FeIII-(OH)-CoII(TMPA)]2+ (2). In
Results and Discussion
Synthesis of 1. The acid-base synthesis used to generate
1 is described in Scheme 1. Triethylamine was added to a
1:1 mixture of (F8TPP)FeIII-OH and [CoII(TMPA)-
(MeCN)]2+ (as perchlorate salt, see Experimental Section)
to deprotonate the hydroxyl group attached to the iron center
thereby enabling adduct formation.4 This reaction was
followed by UV-vis spectroscopy. The initial and final
spectra are shown in Figure 1. Note that the initial spectrum
is dominated by the intense bands associated with (F8TPP)-
FeIII-OH. Electrospray ionization (ESI) and matrix-assisted
laser desorption ionization time-of-flight (MALDI-TOF)
(3) Ghiladi, R. A.; Hatwell, K. R.; Karlin, K. D.; Huang, H.-w.; Moe¨nne-
Loccoz, P.; Krebs, C.; Huynh, B. H.; Marzilli, L. A.; Cotter, R. J.;
Kaderli, S.; Zuberbu¨hler, A. D. J. Am. Chem. Soc. 2001, 123, 6183-
6184.
(4) Fox, S.; Nanthakumar, A.; Wikstro¨m, M.; Karlin, K. D.; Blackburn,
N. J. J. Am. Chem. Soc. 1996, 118, 24-34.
(10) Hoffman, B. M.; Petering, D. H. Proc. Natl. Acad. Sci., U.S.A. 1970,
67, 637-ff.
(5) Kopf, M.-A.; Neuhold, Y.-M.; Zuberbu¨hler, A. D.; Karlin, K. D. Inorg.
Chem. 1999, 38, 3093-3102.
(11) Doyle, M. L.; Speros, P. C.; Licata, V. J.; Gingrich, D.; Hoffman, B.
M.; Ackers, G. K. Biochemistry 1991, 30, 7263-7271.
(12) Venkatesh, B.; Manoharan, P. T.; Rifkind, J. M. Metal ion reconstituted
hybrid hemoglobins, In Progress in Inorganic Chemistry, Vol 47;
Karlin, K. D., Ed.; John Wiley & Sons Inc: New York, 1998; pp
563-684.
(6) Kim, E.; Helton, M. E.; Wasser, I. M.; Karlin, K. D.; Lu, S.; Huang,
H.-w.; Moe¨nne-Loccoz, P.; Incarvito, C. D.; Rheingold, A. L.;
Honecker, M.; Kaderli, S.; Zuberbu¨hler, A. D. Proc. Natl. Acad. Sci.
U.S.A. 2003, 100, 3623-3628.
(7) del Rio, D.; Sarangi, R.; Chufa´n, E. E.; Karlin, K. D.; Hedman, B.;
Hodgson, K. O.; Solomon, E. I. J. Am. Chem. Soc. 2005, 127, 11 969-
11 978.
(8) Chishiro, T.; Shimazaki, Y.; Tani, F.; Tachi, Y.; Naruta, Y.; Karasawa,
S.; Hayami, S.; Maeda, Y. Angew. Chem. Int. Ed. 2003, 42, 2788-
2791.
(9) Karlin, K. D.; Nanthakumar, A.; Fox, S.; Murthy, N. N.; Ravi, N.;
Huynh, B. H.; Orosz, R. D.; Day, E. P. J. Am. Chem. Soc. 1994, 116,
4753-4763.
(13) Proniewicz, L. M.; Kincaid, J. R. Coord. Chem. ReV. 1997, 161, 81-
127.
(14) Bruha, A.; Kincaid, J. R. J. Am. Chem. Soc. 1988, 110, 6006-6014.
(15) Collman, J. P.; Fu, L.; Herrmann, P. C.; Zhang, X. Science 1997, 275,
949-951.
(16) Collman, J. P.; Berg, K. E.; Sunderland, C. J.; Aukauloo, A.; Vance,
M. A.; Solomon, E. I. Inorg. Chem. 2002, 41, 6583-6596.
(17) Andrioletti, B.; Ricard, D.; Boitrel, B. New J. Chem. 1999, 23, 1143-
1150.
3018 Inorganic Chemistry, Vol. 46, No. 8, 2007

Generation and Characterization of [(P)M-(X)-Co(TMPA)]n+
where the chelate is tethered covalently to the porphyrinate
6
periphery (i.e., in the so-called L ligand). An exceptional
case is for a complex [(5L)Fe-O-Cu]+ ( Fe-O-Cu )
141°, based on EXAFS multiple scattering analysis;18 5L is
also a heterobinucleating ligand, see ref 1), where severe 5L
binucleating ligand constraints force strong distortions. Thus,
only minor distortions from linear occur in 1.
The high-spin FeIII (vide infra) is bound to the porphyrin
macrocycle and exhibits a typical square pyramidal geometry,
being displaced by 0.56 Å above the ligand plane. The
bridging oxo atom occupies the apical position, with an
Fe-O distance of 1.75 Å being close to analogues containing
[Fe-O-Cu] and [Fe-O-Fe] cores.1,19 All Fe-N distances
are within the range of 2.10-2.12 Å, which is consistent
with a high-spin electronic configuration for a 3d5 FeIII ion.20
The cobalt center is surrounded by three methyl-pyridyl
groups attached to an amine that occupies the axial position
for the ion. The Co-NPy distances are within 2.06-2.09 Å,
whereas the apical amino-nitrogen is found at 2.18 Å, and
the Co-O distance is 1.85 Å. The Namino and the Ooxo ligands
occupy the apical positions of a trigonal bipyramid, confer-
ring a local C3V symmetry for this metal. It is evident that
the overall geometry around the cobalt ion in 1 is preserved
compared to its precursor complex [CoII(TMPA)(MeCN)]2+.21
The apical Co-N bond length is unchanged while the Co-
Npyridyl bond distances increase slightly in 1.
Figure 1. UV-vis spectra of the mixture of (F8TPP)FeIII-OH/[CoII-
(TMPA)(MeCN)]2+ (- - -) and the µ-oxo product 1 (s) upon addition of 1
equiv of Et3N in CH2Cl2 at room temperature.
As expected, the Co-Ooxo distance (1.85 Å) in 1 is shorter
than the Co-Nacetonitrile bond length in [CoII(TMPA)-
(MeCN)]2+ (2.05 Å), due to the electrostatic nature of the
interaction. This Co-Ooxo moiety is also found in other kinds
III
of oxo-bridged compounds that exhibit a square-planar Co2
-
(µ-oxo)2 core (Co-Oaverage ) 1.80 Å, varying from 1.78 to
1.83 Å).22-24 The slightly longer bond in the presently
described CoII-oxo-FeIII core of 1 can, of course, be
attributed to the presence of a lower oxidation state metal
ion (i.e., CoII and not CoIII). Interestingly, the CuII-Ooxo bond
lengths of a variety of heme-O-CuII assemblies fall in the
narrow range of 1.83-1.86 Å,1 which is the same as that of
the present cobalt case; thus, the smaller ionic radius of CuII
relative to CoII is not reflected.
NMR Spectroscopic and Magnetic Properties. 1H NMR
spectra of (F8TPP)FeIII-OH in CD2Cl2 exhibit a pyrrole
signal at 81 ppm, typical for high-spin S ) 5/2 FeIII-
porphyrinates.9 Following the reaction with [CoII(TMPA)(CH3-
CN)]2+ and formation of 1, the pyrrole resonance appears
upfield at 40.6 ppm (Figure 3). This behavior is consistent
with an assignment of 1 as an S ) 1 electronic ground state
species, which is derived from antiferromagnetic coupling
Figure 2. An ORTEP representation of the cationic portion of (1)‚ClO4‚
2C4H10O. Fe‚‚‚Co ) 3.58 Å, Co(1)-O(1) ) 1.85 Å, Co(1)-N(8) ) 2.06
Å, Co(1)-N(7) ) 2.07 Å, Co(1)-N(6) ) 2.09 Å, Co(1)-N(5) ) 2.18 Å,
Fe(1)-O(1) ) 1.75 Å, Fe(1)-N(4) ) 2.10 Å, Fe(1)-N(3) ) 2.10 Å,
Fe(1)-N(1) ) 2.11 Å, Fe(1)-N(2) ) 2.12 Å, Fe-O-Co ) 171.6°. The
crystallographic data and structural refinement parameters are reported in
Table S1 (Supporting Information).
mass spectrometry (Experimental Section) were used to
evaluate the integrity of the species both in a solution and
as a solid. In solution, a cluster of peaks at m/z ) 1176-
1179 are ascribed to the cationic species [(F8TPP)FeIII-O-
CoII(TMPA)]+, which can only be simulated by taking into
account the isotopic distribution for both cobalt and iron
centers (see Supporting Information, Figures S1 and S2).
X-ray Structure of 1. [(F8TPP)FeIII-O-CoII(TMPA)]-
ClO4‚2C4H10O was crystallized from dichloromethane/diethyl
ether at -20 °C. An Oak Ridge thermal ellipsoid plot
(ORTEP) diagram is shown in Figure 2 with key bond
distances provided; Fe‚‚‚Co ) 3.58 Å. The cation exhibits
a slightly bent [Fe-O-Co] core, with Fe-O-Co )
171.6°. For similar systems containing the [FeIII-O-CuII]
core in which the copper ion is capped by tetradentate N4-
ligands, compounds from our own research and that of Holm
and co-workers, this value is found to lie in the range 175-
178°.1 The Fe-O-Co angle in 1 most closely compares
to that found for [(6L)Fe-O-Cu]+ ( Fe-O-Cu ) 171°),
which possesses a TMPA moiety bound to copper(II) but
(18) Obias, H. V.; van Strijdonck, G. P. F.; Lee, D.-H.; Ralle, M.;
Blackburn, N. J.; Karlin, K. D. J. Am. Chem. Soc. 1998, 120, 9696-
9697.
(19) Kurtz, D. M., Jr. Chem. ReV. 1990, 90, 585-606.
(20) Scheidt, W. R.; Reed, C. A. Chem. ReV. 1981, 81, 543-555.
(21) Nanthakumar, A.; Fox, S.; Murthy, N. N.; Karlin, K. D. J. Am. Chem.
Soc. 1997, 119, 3898-3906.
(22) Dai, X. L.; Kapoor, P.; Warren, T. H. J. Am. Chem. Soc. 2004, 126,
4798-4799.
(23) Larsen, P. L.; Parolin, T. J.; Powell, D. R.; Hendrich, M. P.; Borovik,
A. S. Angew. Chem. Int. Ed. 2003, 42, 85-89.
(24) Hikichi, S.; Yoshizawa, M.; Sasakura, Y.; Akita, M.; Moro-Oka, Y.
J. Am. Chem. Soc. 1998, 120, 10 567-10 568.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3019

Chufa´n et al.
Figure 3. 1H NMR spectrum (CD2Cl2, 293 K) of 1. See text for further discussion and assignments.
of the high-spin FeIII (S ) 5/2) and high-spin CoII (S ) 3/2)
through the oxo bridging ligand. Magnetization studies
corroborate this conclusion (vide infra). The same upfield
shifting of δpyrrole (from 81 ppm) was observed for the copper
analogue [(F8TPP)FeIII-O-CuII(TMPA)]+, but the magni-
tude of the shift was much lower because of the different
electronic nature of CuII (S ) 1/2) that yields a different
ground state (S ) 2, δpyrrole ) 65 ppm). On the other hand,
the porphyrin signals due to the meso-phenyl substituents
appear at δ ) 8.8 and 8.7 ppm for the meta-positions and at
δ ) 8.0 ppm for the para-position, as is usual for metal
tetraaryl-porphyrinates.21
respectively. The room-temperature TMPA peaks at -1.1
and -2.7 ppm assigned to the 6-H and -CH2- hydrogens,
respectively, are the most affected by the lowering of the
temperature (-10.2 and -12.6 ppm at - 80 °C, respectively)
because they are the hydrogen atoms closest to the para-
magnetic CoII center. Also, they have positive extrapolated
intercepts (see Curie plot), which are consistent with the
breaking of the strong antiferromagnetic coupling as the
temperature increases and (theoretically) approaches infinity.
Other relevant information obtained from the NMR data
relates to the coupled structure of FeIII-O-CoII that remains
undissociated in CH2Cl2 solution. Nonetheless, dissociation
does occur in CH3CN, as indicated by the formation of (F8-
TPP)FeIII-OH, observed with δpyrrole ) 81 ppm (not shown).
Magnetic Susceptibility. Data for polycrystalline 1 were
collected in the temperature range of 2-290 K (Figure 4)
and were aimed at the evaluation of the magnetic exchange
interaction described by the coupling constant (J) resulting
from the possibility of either or both antiferromagnetic (AF)
and ferromagnetic (F) exchange interactions, with J ) JAF
+ JF.
At 290 K, the compound exhibits ømolT ) 2.06 emu
K‚mol-1, therefore much lower than the expected value of
6.25 emu K‚mol-1 for a bimetallic system with SFe ) 5/2
and SCo ) 3/2. By decreasing the temperature to 20 K, the
values of ømolT decrease monotonically, with ømolT values
varying from 2.02 to 1.46 emu K‚mol-1. Further cooling
causes an abrupt inflection that reaches ømolT ) 0.93 emu
K‚mol-1, which is in agreement with an S ) 1 ground state.
The best fit yields J ) -114 cm-1, with gFe ) gCo ) 2.5,
and confirms the AF nature of the coupling. The elevated
values of the g-factor may reflect spin-orbit contributions
expected for a system containing d7 ions. The fact that neither
the CoII nor the FeIII ions stand in an octahedral geometry
can also contribute to elevated g-values. Complex 1 ap-
proaches an overall low-symmetry Cs, with local C3V trigonal
bipyramidal symmetry for the CoII ion and square pyramidal
C4V local FeIII geometry. The high-spin configurations for
both ions deviate considerably from the usual octahedral
[CoII(TMPA)(CH3CN)]2+ itself exhibits considerably shifted
1
but sharp (τs ≈ 10-11 s for CoII) contact-shifted H NMR
signals.21 From the present study, we discovered that there
were modest errors in the resonances that we previously21
reported for this complex, and with new, careful, and multiple
measurements, we find that TMPA hydrogen signals occurred
at 109.1 (-CH2-), 60.7 (5-H), 41.6 (3-H), and -4.6 (4-H)
ppm in dichloromethane, see the spectrum in Figure S3
(Supporting Information). For 1, all of these signals moved
as expected for a magnetically coupled system, with the
peaks occurring at 4.4 (4-H), 2.6 (3-H), 1.0 (5-H), -1.1
(6-H, shifted dramatically from >125 ppm downfield in
[CoII(TMPA)(CH3CN)]2+), and -2.7 (-CH2-) ppm. These
tentative assignments (in parentheses) are based on analogy
to the FeIII-O-CuII system21 and on the observed temper-
ature dependent behavior (see below). Thus, variable tem-
perature NMR studies were carried out for 1 (see Figure S4,
Supporting Information), and revealed that the pyrrole
downfield-shifted signal moved further downfield with the
decrease in temperature while the TMPA hydrogen upfield-
shifted signals moved further upfield. This phenomenon was
also observed for the coupled copper containing µ-oxo
compound [(F8TPP)FeIII-O-CuII(TMPA)]+, thus being con-
sistent with strong antiferromagnetic coupling.21 Plots of
chemical shift vs 1/T for the range 193-293 K (see Figure
S5, Supporting Information) show linear Curie and anti-Curie
behavior for the iron-porphyrinate and Co(TMPA) protons,
3020 Inorganic Chemistry, Vol. 46, No. 8, 2007

Generation and Characterization of [(P)M-(X)-Co(TMPA)]n+
Scheme 2
FeIII-O(H)-CuII(ligand)]n+ (ligand ) TMPA4 or bis(2-(2-
pyridyl)ethyl)amine5) complexes; the hydroxo-bridged com-
plexes formed by protonation of the µ-oxo compounds can
be reconverted to the original oxo species by means of
addition of a base such as triethylamine.4 Therefore, the
reaction of 1 with triflic acid/triethylamine was investigated
in order to assess and compare its protonation/deprotonation
profile with that of other compounds, especially [(F8TPP)-
FeIII-O-CuII(TMPA)]+.
Addition of 1 equiv of triflic acid to a dichloromethane
solution of 1 (λmax ) 557 nm) yields a new UV-vis spectrum
(λmax ) 567 nm) attributed to a µ-hydroxo species [(F8TPP)-
FeIII-(OH)-CoII(TMPA)]2+ (2), shown in Scheme 2. After
addition of 1 equiv of triethylamine, the original spectrum
of 1 is observed. This cycle of protonation/deprotonation can
be repeated three times without detecting significant decom-
position (see Supporting Information, Figure S6).
1H NMR spectroscopy was used to further investigate this
reaction and characterize the protonated product (Figure 5).
After addition of 0.45 equiv of triflic acid (HOTf) to a
dichloromethane-d2 solution of 1, a new pyrrole-associated
broad signal is observed at 78 ppm while the original signal
at 40.5 ppm (due to 1) is diminished. The reaction is almost
complete with the addition of 0.9 equiv of the acid (Figure
5). This new signal at 78 ppm relates quite well to the typical
pyrrole signal of (F8TPP)FeIII-OH normally found at 81
ppm,9 but here it is measurably shifted upfield, reflecting
the AF coupling to the cobalt center in 2.
To further provide evidence that the protonation product
is a hydroxo-bridged compound, the magnetic moment of
the starting compound and the products were determined by
the Evans NMR method (see Experimental Section). Com-
plex 1 exhibits µeff ) 3.1 that is consistent with that expected
for a S ) 1 system (vide supra). After addition of 1 equiv of
triflic acid, a value of µeff ) 3.7 is observed. This magnetic
moment is also consistent with an S ) 1 system arising from
an AF coupling between a high-spin FeIII and a high-spin
Figure 4. Magnetochemical behavior of complex 1 (ømolT vs temperature,
T). The black diamonds denote the measured magnetization and the solid
red line is the simulation of the data. The high-spin electronic configurations
for the metal ions are also shown at the top.
scheme and need to be taken into account for an evaluation
of the magnetic pathway. On the basis of orbital distribution
arguments and the X-ray structure, it is well-established that
the A1 (dz2) orbital of the iron center will be pointing out of
the macrocyclic plane. Similarly, DFT calculations for the
precursor [CoII(TMPA)(CH3CN)]+ indicate that the z-axis,
as would be expected, is clearly defined along the Namine
-
Co-Nacetonitrile in this trigonal bypyriamidal complex.25 As
such, the main superexchange pathway for the dominant AF
coupling observed for 1 is σ in nature.
In fact, the exchange coupling constant for 1 (J ) -114
cm-1) is comparable to that found for the iron analogue [(F8-
TPP)FeIII-O-FeIII(TMPA)(Cl)]+ (J ) -108 cm-1).26 Here,
a high-spin FeIII ion replaces the CoII ion in a very similar
coordination environment. However, for the previously well-
studied analogue [(F8TPP)FeIII-O-CuII(TMPA)]+, where
CuII ions replace the CoII ion, a stronger coupling is observed,
J ) -174 cm-1.9 This result may be general in that the FeIII-
O-CuII core also possesses larger |J| values, as J g |-200|
cm-1 for both [(OEP)FeIII-O-CuII(Me6tren)]+ and for [(6L)-
FeIII-O-CuII]+.1
Protonation of 1. The Brønsted basic behavior of oxo-
bridged heme-containing bimetallic complexes has been
observed for compounds with iron-copper, iron-iron, and
other [MA-O-MB] cores.1,27 Furthermore, a reversible oxo/
hydroxo equilibrium has been demonstrated for [(F8TPP)-
(25) Schatzschneider, U.; Verani, C. N.; Karlin, K. D., et al, unpublished
observations.
(26) Wasser, I. M.; Martens, C. F.; Verani, C. N.; Rentschler, E.; Huang,
H. W.; Moenne-Loccoz, P.; Zakharov, L. N.; Rheingold, A. L.; Karlin,
K. D. Inorg. Chem. 2004, 43, 651-662.
(27) Kramarz, K. W.; Norton, J. R. In Progress in Inorganic Chemistry,
Vol 42; John Wiley & Sons Inc: New York, 1994;pp 1-65.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3021

Chufa´n et al.
we can expect longer iron-hydroxo and cobalt-hydroxo
bond distances compared to an oxo analogue, and bending
of the Fe-(OH)-Co core is also likely (as one goes from
formally sp hydridized oxo to sp2 hybridized hydroxo
ligands).4,29
After addition of excess triflic acid (2.6 equiv), (F8TPP)-
FeIII-(OTf) (δpyrrole ) 53 ppm) is identified,30 further showing
that the 78 ppm resonance ascribed to 2 is correct and that
the bridge has not been broken in this product. [CoII(TMPA)-
1
(H2O)]2+ is the presumed coproduct (see Figure 5 for H
NMR spectroscopic identification) (Scheme 2), having the
same pyridyl-ligand chemical shift as that previously found
for the close acetonitrile analogue [CoII(TMPA)(CH3CN)]2+
(vide supra, Figure 3). The magnetic moment of the product
solution, µeff ) 6.7, is consistent with that of an uncoupled
mixture of an admixed-spin-state FeIII compound (S ) 5/2,3/
2) expected for (F8TPP)FeIII-(OTf)30 and a high-spin CoII
complex (theoretical µeff ) 6.81).
To further investigate the nature of this second equilibrium
where bridging ligand cleavage occurs (Scheme 2), an UV-
vis spectroscopic experiment was carried out. Following the
addition of 2 equiv of HOTf to a solution of 1 (CH2Cl2, λmax
) 558 nm), the characteristic30 spectrum of (porphyrinate)-
-
-
FeIII-(weak-anion) (e.g., weak-anion ) OTf-, ClO4 , BF4 )
complex [(F8TPP)FeIII-triflate] is formed (λmax ) 504, 572,
and 635 nm) (see Supporting Information, Figure S8).
Reversible generation of the original oxo-bridged compound
1 is observed upon addition of 2 equiv of triethylamine
(Figure S8), confirming the weak nature of the FeIII-triflate
bond, the full acid-base reversibility in the system (Scheme
2), and therefore the (kinetic or thermodynamic) stability of
the µ-oxo/hydroxo assemblies 1 and 2.
Dioxygen Chemistry of [(F8TPP)FeII]/[CoII(TMPA)-
(CH3CN)]2+. On the basis of the established O2 chemistry
of (F8TPP)FeII/[CuI(TMPA)(CH3CN)]+ 1:1 mixtures (also see
Introduction),3 it was envisioned that the substitution of CuI
by CoII could lead to the generation of a more stable peroxo
species by encompassing Fe/Co systems with a 3d6 electronic
configuration for the cobalt-ligand moiety.15-17,31-43 Upon
(29) Scott, M. J.; Zhang, H. H.; Lee, S. C.; Hedman, B.; Hodgson, K. O.;
Holm, R. H. J. Am. Chem. Soc. 1995, 117, 568-569.
(30) Boersma, a. D.; Goff, H. M. Inorg. Chem. 1982, 21, 581-586.
(31) Hu, X. L.; Castro-Rodriguez, I.; Meyer, K. J. Am. Chem. Soc. 2004,
126, 13 464-13 473.
(32) Gavrilova, A. L.; Qin, C. J.; Sommer, R. D.; Rheingold, A. L.; Bosnich,
B. J. Am. Chem. Soc. 2002, 124, 1714-1722.
Figure 5. Protonation of 1 by sequentially adding 0.45 equiv, 0.90 equiv,
and excess (2.60 equiv) triflic acid followed by 1H NMR spectroscopy (CD2-
1
(33) Bakac, A. Prog. Inorg. Chem. 1995, 43, 267-351.
(34) Busch, D. H.; Alcock, N. W. Chem. ReV. 1994, 94, 585-624.
(35) Solomon, E. I.; Tuczek, F.; Root, D. E.; Brown, C. A. Chem. ReV.
1994, 94, 827-856.
Cl2, room temperature). H NMR spectra showing the expanded -2 to 15
ppm region are provided in Supporting Information, Figure S7.
(36) Suzuki, M.; Furutachi, H.; Okawa, H. Coord. Chem. ReV. 2000, 200-
202., 105-129.
CoII; however, the coupling is less effectively propagated
when mediated by a µ-hydroxo group compared to a µ-oxo
ligand.1 This follows what was previously observed for µ-oxo
and µ-hydroxo [(heme)FeIII-O(H)-CuII(ligand)] pairs of
complexes.1,28 While we do not currently have X-ray or other
structural information pertaining to the µ-OH- complex 2,
(37) Hikichi, S.; Akita, M.; Moro-Oka, Y. Coord. Chem. ReV. 2000, 198,
61-87.
(38) Niederhoffer, E. C.; Timmons, J. H.; Martell, A. E. Chem. ReV. 1984,
84, 137.
(39) Fallab, S.; Mitchell, P. R. AdV. Inorg. Bioinorg. Mech. 1984, 3, 311-
377.
(40) Collman, J. P.; Yan, Y. L.; Eberspacher, T.; Xie, X.; Solomon, E. I.
Inorg. Chem. 2005, 44, 9628-9630.
(28) A reviewer has pointed out that the observed value of µeff ) 3.7 may
in fact be more consistent with a S ) 3/2 assignment. Additional
temperature-dependent magnetic susceptibility measurements with
greater accuracy would be required to sort this out.
(41) Spingler, B.; Scanavy-Grigorieff, M.; Werner, A.; Berke, H.; Lippard,
S. J. Inorg. Chem. 2001, 40, 1065-1066.
(42) Egan, J. W.; Haggerty, B. S.; Rheingold, A. L.; Sendlinger, S. C.;
Theopold, K. H. J. Am. Chem. Soc. 1990, 112, 2445-2446.
3022 Inorganic Chemistry, Vol. 46, No. 8, 2007

Generation and Characterization of [(P)M-(X)-Co(TMPA)]n+
Scheme 3
Figure 6. An UV-vis spectra of the mixture of [(TPP)CoII]/[CoII(TMPA)-
(MeCN)]2+ (reduced species) and of the product 3 upon reaction with O2
at -80 °C in methylene chloride.
Compelling evidence supporting this formulation and stated
stoichiometry of the reversible reaction (Scheme 3) is the
observation that we detect close to 1 equiv of O2 being
released from the -80 °C solutions 3 that have been purged
of any excess dioxygen and then warmed; see Experimental
Section. (Note: repeated attempts to obtain resonance Raman
spectroscopic confirmation of the peroxo formulation were
not successful.) Each oxygenation cycle is complete (i.e.,
full formation of the new species, λmax ) 435 nm, Figure 6)
in less than 5 min for a 3.0 × 10-5 M solution. This is very
fast by comparison to the time normally required to oxygen-
ate porphyrinate-CoII complexes in the presence of bases.44
The same reaction was followed by electron paramagnetic
resonance (EPR) spectroscopy. The spectrum (20 K, CH2-
Cl2) of the reduced [(TPP)CoII]/[CoII(TMPA)(MeCN)]2+
mixture appears as a composite of the expected spectra for
these EPR active high-spin CoII complexes.25,45,46 However,
the product of oxygenation is EPR silent, with a small
amount of paramagnetic impurity (at 3350 G) perhaps arising
from the presence of some (TPP)CoIII(O2-‚) (see Figure S9,
Supporting Information). Thus, observed UV-vis spectral
changes combined with evidence from EPR spectroscopy
support the formation and formulation of 3 as a low-spin
diamagnetic compound17,47 (also see 1H NMR characteriza-
tion, below). The presence of a number of other possible
species can be ruled out:47 the peroxo-bridged dimer
[(TPP)CoIII]2(O22-) from [(TPP)CoII]/O2 is not known. We
can rule out the formation of a superoxo species (base)(TPP)-
CoIII(O2-‚) because we generated an authentic complex, (1,5-
dicyclohexylimidazole)(TPP)CoIII(O2-‚), by mixing the com-
ponents at the same concentration (1 mM) and solvent; this
species is EPR active (see Figure S9) unlike 3. Another
possibility to consider is that only CoII(TMPA) chemistry is
involved; although [CoII(TMPA)(CH3CN)]2+ reacts with O2
addition of O2 to an acetonitrile solution containing equimolar
amounts of (F8TPP)FeII and [CoII(TMPA)(CH3CN)]2+ at -40
°C, a new spectrum (λmax ) 414 (Soret) and 558 nm), was
observed. However this product, possibly the putative [FeIII-
peroxo-CoIII] complex, proved to be very unstable and
decomposed rapidly (i.e., seconds) into (F8TPP)FeIII-OH (λ
) 408 (Soret) and 568 nm). Despite efforts made in different
solvents and lower temperatures (e.g., propionitrile, acetone,
and dichloromethane at -80 °C), a stable µ-peroxo adduct
could not be generated or characterized. We also attempted
resonance Raman spectroscopic interrogation of the low-
temperature oxygenated solutions, but no peroxo species (i.e.,
with new isotope sensitive O-O stretching vibration in the
∼800 cm-1 region) were detected.
Dioxygen Chemistry of [(TPP)CoII]/[CoII(TMPA)-
(CH3CN)]2+. The remaining question about the capability
of the [CoII(TMPA)(CH3CN)]2+ precursor to form hetero-
binuclear metalloporphyrinate with non-porphyrin metal
dioxygen adducts was addressed by substituting the heme
precursor by the complex (TPP)CoII. It is known that
(porphyrinate)-CoII complexes react with O2 in the presence
of a Lewis base as porphyrinate axial ligand (e.g., pyridines
and imidazoles) yielding superoxo-CoIII complexes, [(por-
phyrinate)-CoIII(O2-‚)].40 In the absence of the added base,
the [(porphyrinate)-CoII] is inert to O2.44
Remarkably, equimolar amounts of [(TPP)CoII] and
[CoII(TMPA)(CH3CN)]2+ react with O2 in a dichloromethane
solution at -80 °C in the absence of a base. The reaction
with dioxygen is followed by noticeable changes in the UV-
vis spectral features of the original solution; the Soret band
is shifted from 413 to 435 nm, and the alpha band at 528
nm changes to 548 nm with a new weak absorption also
being observed at 583 nm (Figure 6). Also noteworthy is
the fact that by warming up the solution the original spectrum
reappears indicating that the reaction is reversible and that
the reduced temperature facilitates binding to form what we
formulate as the µ-peroxo complex 3 (see Scheme 3).
(45) Assour, J. M. J. Chem. Phys. 1965, 43, 2477-2489.
(46) Walker, F. A. J. Am. Chem. Soc. 1970, 92, 4235.
(47) A reviewer has suggested consideration of the formulation of 3 as
being a µ-(hydr)oxo-bridged dicobalt(III) complex or a bis-µ-oxo
dicobalt(IV) complex. The former can be ruled out since O2 is evolved
upon warming 3. The latter cannot be completely ruled out, but such
a species is unprecedented (however evolution of O2 from a bis-µ-
oxo-dicopper(III) complex is known, see H. Hayashi et al., J. Am.
Chem. Soc. 2000, 122, 2124-2125.).
(43) Rybak-Akimova, E. V.; Otto, W.; Deardorf, P.; Roesner, R.; Busch,
D. H. Inorg. Chem. 1997, 36, 2746-2753.
(44) Yang, J. P.; Huang, P. C. Chem. Mater. 2000, 12, 2693-2697.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3023

Chufa´n et al.
to form a µ-peroxo complex (unpublished observations), the
UV-vis changes observed here (Soret absorption shift, Vide
supra) clearly indicate the presence of a porphyrin moiety
which is involved and undergoing reaction/change.
(2) A µ-oxo complex (1) was, however, generated by
acid-base assembly and its X-ray structure determined.
Structural comparisons with analogue [FeIII-O-CuII] and
other µ-oxo metal complexes were made.
(3) The magnetic properties of µ-oxo complex 1 were
deduced and comparisons with [FeIII-O-FeIII] and [FeIII-
O-CuII] analogues were made. The latter showed to be more
strongly magnetically coupled.
(4) A µ-hydroxo complex (2) is formed by addition of 1
equiv acid to the µ-oxo complex 1. Production of 2 was also
proved to be completely reversible by addition of a base
(triethylamine).
(5) Formation of an asymmetric µ-peroxo complex (3) was
accomplished by dioxygen chemistry of [(TPP)CoII]/[CoII-
(TMPA)(MeCN)]2+ at low temperature. It was also found
that the oxygenation/deoxygenation equilibrium is reversible
and that the original reduced complexes and dioxygen can
be recovered by increasing the temperature.
1
The formation of 3 was also monitored by H NMR
spectroscopy at -80 °C in dichloromethane-d2. The spectrum
of the starting mixture [(TPP)CoII]/[CoII(TMPA)(CH3CN)]2+
shows the paramagnetically shifted signals for both com-
plexes, moved further (up or downfield) from the established
room-temperature chemical shifts48 (See Supporting Informa-
tion Figure S10). Following the addition of excess O2, the
starting material resonances disappear and new absorptions
are observed in the diamagnetic region (Figure S10) con-
sistent with the formulation of a low-spin CoIII (d6)-peroxo-
CoIII (d6) compound. A binuclear complex derived only from
the oxygenation of [CoII(TMPA)(MeCN)]2+ can be ruled out
as the main product (based on the UV-vis criterion
mentioned above) as well as from NMR spectroscopy.49
One could speculate on the possibility that a detached
(unligated) pyridyl ligand arm from [CoII(TMPA)(MeCN)]2+
acts as an axial base for stabilization of a [base-(TPP)CoIII-
(O2-‚)] species. However, both the reaction time frame
(which is very fast compared to that known for [(base)-
(porphyrinate)-CoIII-(O2-‚)] formation),44 as well as just
the fact that [CoII(TMPA)(CH3CN)]2+ is involved (i.e., the
1H NMR peaks for CoII(TMPA) disappear), rule out this
supposition.
Experimental Section
Materials and Methods. Reagents including the meso-tetra-
phenylporphyrin CoII complex were used as received from com-
mercial sources or otherwise noted. Acetone was predried and
distilled over Dreirite. Acetonitrile was predried and distilled over
fresh CaH2. Dichloromethane was purified through an alumina
column. The solvents were deoxygenated by direct argon bubbling
(30 min) or by five freeze/pump/thaw cycles. The air- and moisture-
sensitive samples were handled and stored using standard Schlenk
glassware and drybox facilities. Elemental analyses were performed
by QTI Inc. (Whitehouse, NJ). Infrared spectra were measured from
4000 to 400 cm-1 as KBr pellets on a Mattson Galaxy 4030 Fourier
transform (FT) IR spectrometer. Blank spectra were recorded to
ensure the anhydrous character of the KBr matrix. 1H NMR spectra
were carried out using a Varian unit 400 MHz FT-NMR
spectrometer. Mass spectrometry (ESI in the positive ion mode)
was measured on a Thermo-Finnigan LCQ Deca. Low- and room-
temperature UV-vis spectra in the range of 200-1200 nm were
recorded on a diode array HP-8453 UV-vis spectrophotometer
interfaced with a Neslab refrigerated circulating bath. The temper-
ature-dependent susceptibility measurements of the Co-precursors
were performed in the range of 2-295 K at 1 T on a Quantum
Design MPMS SQUID-magnetometer. The Heisenberg-Dirac-van
Vleck (HDvV) model was used to analyze the data, and the fitting
of the temperature-dependent magnetization was carried out using
a least-squares fitting computer program50 as reference with a full
matrix diagonalization approach. The software uses the spin
Hamiltonian operator Htotal ) HZ + HZFS + HHDvV, where the
exchange coupling is described by HHDvV ) -2JS1 × S2, the
Zeeman interactions are given by HZ ) µBBgiSi and the axial single-
As previously mentioned, [(TPP)CoII] is unreactive toward
O2 without a base, and there is no base present here. Thus,
chemical reasoning would suggest that 3 may form via initial
reaction of [CoII(TMPA)(CH3CN)]2+ with O2 to give a
metastable [(TMPA)CoIII(O2-‚)]2+ species that now is reac-
tive toward [(TPP)CoII], leading to 3.
Conclusions and Summary
With our ongoing studies and previous characterization
of a series of [(porphyrinate)FeIII-X-CuII(ligand)]n+ [X )
O
2- (oxo), (OH)- (hydroxo), O22- (peroxo)] complexes, our
goal here was to investigate the effect of cobalt ion
substitution for copper or copper and iron. As studied
especially by Collman and Boitrel,15-17 interesting variations
might be expected, in particular, with respect to the potential
stabilization of superoxo and/or peroxo intermediates by
virtue of the possible generation of CoIII species with
resulting 3d6 electronic configuration. Because our program
has enjoyed particular success in the derivation of these
bridged complexes via dioxygen reactivity with reduced FeII
or CuI components, we wished to explore such chemistry
when CoII was involved. Our efforts were partially successful,
and the investigations have given rise to new µ-oxo,
µ-hydroxo, and µ-peroxo complex chemistry. The main
findings of the present report are as follows:
2
ion zero-field interaction is described by HZFS ) DSZ . The ligand
TMPA and the synthons (F8TPP)FeII‚H2O and (F8TPP)FeIIIOH were
synthesized following minor modifications of previously published
procedures.5,9,51
(49) Unpublished observations show that [CoII(TMPA)(MeCN)]2+ reacts
with O2 to give a diamagnetic binuclear peroxo complex with a
distinctive broad 1H-NMR resonance in the 3-4 ppm region (Figure
S11, Supporting Information). This is observed to form in about a
15-20% yield under the reaction conditions described for the
formation of 3.
(1) Our previous kind of FeII/CuI/O2 chemistry was carried
out but now with a cobalt analogue; however, [(F8TPP)FeIII-
peroxo-CoIII(TMPA)]2+ either does not form or is very
unstable.
(50) Krebs, C. Thesis, Ruhr-Universita¨t, Bochum, Germany, 1997.
(51) Tyekla´r, Z.; Jacobson, R. R.; Wei, N.; Murthy, N. N.; Zubieta, J.;
Karlin, K. D. J. Am. Chem. Soc. 1993, 115, 2677-2689.
(48) La Mar, G. N.; Walker, F. A. J. Am. Chem. Soc. 1973, 95, 1790-
1796.
3024 Inorganic Chemistry, Vol. 46, No. 8, 2007

Generation and Characterization of [(P)M-(X)-Co(TMPA)]n+
[CoII(TMPA)(CH3CN)](ClO4)2. TMPA (0.58 g: 2.00 mmol)
was added to a dry Schlenk flask containing deaerated acetonitrile
(40 mL). After the contents of the flask were homogenized, [CoII-
(H2O)6](ClO4)2 (0.73 g: 2.00 mmol) was introduced and a purple
solution was generated. Air-free diethyl ether (100 mL) was slowly
added after 2 h to help precipitation. The microcrystalline product
was filtered and then dried for 48 h. Yield was 0.92 g (80%). IR
(KBr, cm-1); 3066 (C-H stretch), 2344-2371 (w, CtN stretch),
1611 (s, CdCPy stretch), 1439 (CH2Py scissor vib), 1091 (s, br
ClO4-), 781-767 (C-HPy out-of-plane), and 624 (CdCPy rock).
ESIpos: [M - MeCN - ClO4]+ m/z ) 448; [M - MeCN -
2ClO4]+ m/z ) 175. Elemental analysis (C20H21N5O8Cl2Co1, 589.25
g/mol) calc/found C: 40.77/40.8; H: 3.59/3.6; N: 11.89/11.7. UV-
vis (MeCN) 472 nm (ꢀ ) 82 M-1‚cm-1), 552 nm (ꢀ ) 52
1 with known concentration (4.6 mM) was prepared and placed in
a NMR tube. A H NMR spectrum was first recorded and then a
1
coaxial reference capillary filled with pure dichloromethane-d2 was
1
inserted inside the sample tube. A second H NMR spectrum was
thus obtained (now with a capillary containing pure solvent) and
in this manner was assigned unequivocally the solvent peak
corresponding to the pure deuterated solvent. Both solvent peaks
were assigned, one corresponding to the paramagnetically shifted
deuterated solvent and the second corresponding to the pure solvent
from the reference capillary. The magnetic moment was calculated
from the equation µB ) 2.84 ø T/n, where T is the temperature
x
M
(297 K) of the measurement, n is the nuclearity of the complex (n
sol
) 1 for 1), and øM ) -3/4π(∆ν/ν)1000/c + øM - øD (where
øM is the solvent susceptibility, øD is the total diamagnetic
sol
1
M-1‚cm-1), and 945 nm (ꢀ e 5 M-1‚cm-1). H NMR [400 MHz,
correction calculated from Pascal’s constants,54,55 ∆ν is the
paramagnetic shift of the solvent in Hz, ν is the frequency of the
NMR instrument in Hz, and c is the concentration of the metal
complex). In the same way the magnetic moment of 2 (prepared
by addition of 1 equiv triflic acid to a solution of 1) and the mixture
of (F8TPP)FeIII-(OTf) and [CoII(TMPA)(H2O)]2+ (prepared by
addition of 2.6 equiv triflic acid to a solution of 1) were determined.
UV-vis Absorption Spectroscopy. Dioxygen Chemistry of
CoII(TPP)/[CoII(TMPA)-(CH3CN)]2+. In a typical experiment,
equimolar amounts of CoII(TPP) and [CoII(TMPA)(CH3CN)](ClO4)2
were dissolved in CH2Cl2 (3 × 10-5 M) in an inert atmosphere
glovebox. The solution was placed in a special UV-vis cuvette,56
sealed, brought out of the glovebox, and cooled to -80 °C. The
solution was oxygenated via bubbling with excess dry O2. The UV-
vis spectra before and after oxygenation were recorded.
CD2Cl2, 300 K] δ(ppm) ) 109.1 [-CH2-], 60.7 [5-H], 41.6 [3-H],
and -4.6 [4-H] (Note these are new, corrected values, see above
text).
Preparation of 1. In an argon atmosphere the synthons (F8TPP)-
FeIIIOH (0.166 g : 0.20 mmol) and [CoII(TMPA)(CH3CN)](ClO4)2
(0.120 g: 0.20 mmol) were combined in a 50 mL flame-dried
Schlenk flask and stirred for 1 h to foster intimate contact.
Previously deaerated dichloromethane (30 mL) was added, and the
solution was stirred for 1 h. When Et3N (35 µL: 0.25 mmol) was
added, the original brownish solution immediately became reddish.
After 15 min the volume was reduced to one third and anhydrous,
air-free toluene (∼20 mL) was added. The microcrystalline product
was filtered and then vacuum-dried for 48 h. Yield was 0.25 g
(∼80%). IR (KBr, cm-1); 1622-1608 (s, CdCpyridine stretch), 1463
(pyrrole ring stretch), 1092 (br ClO4-), 999 (C-Hpyridine out-of-
plane), and 624 (CdCpyridine rock). ESIpos: [M - ClO4]+ multiplet
m/z ) 1176.1 (13% relative abundance), 1177.1 (100%), 1178.1
(73%), and 1179.1 (22%); [M - (CoIITMPA) - ClO4 + CH3CN]+
m/z ) 852.5; [M - (CoIITMPA) - ClO4]+ m/z ) 812.5. MALDI-
TOF; [M - ClO4]+ m/z ) 1178. Elemental analysis for (1)‚2CH2-
Cl2‚C7H8 (C71H50N8Cl5F8O5Fe1Co1, 1539.19 g/mol) calc/found: C
) 58.08/58.18; H ) 3.43/3.66; N ) 7.63/7.48. 1H NMR [400 MHz,
CD2Cl2, 300 K] δ(ppm) ) 40.6 [pyrrole], 8.8 [m-phenyl], 8.7
[m-phenyl], 8.0 [p-phenyl], 4.4 [4-Hpy], 2.6 [3-Hpy], 1.0 [5-Hpy],
-1.1 [6-Hpy], and -2.7 [TMPA-CH2-].
EPR Spectroscopy. Equimolar amounts of CoII(TPP) and
[CoII(TMPA)(CH3CN)](ClO4)2 were dissolved in CH2Cl2 (1 mM)
in a glovebox, and the solution was transferred to an EPR tube
that was capped with a rubber septum. The EPR tube was immersed
in a -80 °C bath (acetone/dry ice) when dry O2 was added via
syringe to generate 3. The solution was frozen in liquid N2, and
the X-band EPR spectrum of 3 was recorded on a Bruker EMX
spectrometer, with temperature maintained at 20 K using an Oxford
Instruments EPR 900 cryostat.
Magnetic Susceptibility Measurements. Temperature-depend-
ent magnetic susceptibility measurements were performed on a
Quantum Design SQUID-magnetometer MPMS in the temperature
range of 2-298 K in applied magnetic fields of 1 T. The response
function was measured four times for each given temperature. The
experimental data were corrected for the diamagnetic contribution
using Pascal’s constants.
1H NMR Titration. Protonation of 1. In the glovebox, a CD2-
Cl2 solution of 1 (12 mg, 0.0078 mmol, in 0.7 mL solvent) was
1
prepared and transferred to a screw-cap NMR tube, and the H
NMR spectrum was recorded. Previously distilled triflic acid (HSO3-
CF3) was used to prepare a stock solution (21 mg in 2 mL of CD2-
Cl2). Then, a 50 µL aliquot of acid (0.45 equiv) was introduced to
the solution of 1 (using a 250 µL Hamilton syringe), the tube was
Dioxygen Evolution upon Warming a Solution of 3. An
alkaline pyrogallol solution was used to detect dioxygen evolution
upon warming a solution of 3, following a previously published
protocol.57,58 In the glovebox, 32.3 mg of [CoII(TPP)] and 28.4 mg
1
shaken and the H NMR spectrum was recorded. This process of
adding aliquots of acid and recording spectra was performed twice
more (for 0.9 and 2.6 equiv acid).
(53) Ghiladi, R. A.; Kretzer, R. M.; Guzei, I.; Rheingold, A. L.; Neuhold,
Y.-M.; Hatwell, K. R.; Zuberbu¨hler, A. D.; Karlin, K. D. Inorg. Chem.
2001, 40, 5754-5767.
NMR Spectroscopy. Room temperature and variable-tempera-
ture 1H NMR spectra were recorded on a Varian Unity 400 NMR
instrument. All spectra were recorded in 5 mm o.d. NMR tubes.
The chemical shifts were reported as δ (ppm) values calibrated to
natural abundance proton solvent peak. Typically, (i) 12 mg of 1
or (ii) 8 mg of CoII(TPP)/6 mg of [CoII(TMPA)(CH3CN)](ClO4)2
(equimolar amounts) in ∼ 0.7 mL of CD2Cl2 were used for each
experiment.
(54) O’Connor, C. J. In Progress in Inorganic Chemistry, Vol 29; John
Wiley & Sons Inc: New York, 1982, pp 203.
(55) CRC Handbook of Chemistry and Physics, 80th ed.; CRC Press:
London, 1999.
(56) Karlin, K. D.; Haka, M. S.; Cruse, R. W.; Meyer, G. J.; Farooq, A.;
Gultneh, Y.; Hayes, J. C.; Zubieta, J. J. Am. Chem. Soc. 1988, 110,
1196-1207.
(57) Kim, E.; Helton, M. E.; Lu, S.; Moe¨nne-Loccoz, P.; Incarvito, C. D.;
Rheingold, A. L.; Kaderli, S.; Zuberbu¨hler, A. D.; Karlin, K. D. Inorg.
Chem. 2005, 44, 7014-7029.
(58) Ghiladi, R. A.; Huang, H. W.; Moe¨nne-Loccoz, P.; Stasser, J.;
Blackburn, N. J.; Woods, A. S.; Cotter, R. J.; Incarvito, C. D.;
Rheingold, A. L.; Karlin, K. D. J. Biol. Inorg. Chem. 2005, 10, 63-
77.
The ambient temperature solution magnetic moment of 1 was
measured by the Evans method52,53 on a Varian NMR instrument
at 400 MHz. Inside a glovebox, a dichloromethane-d2 solution of
(52) Evans, D. F. J. Chem. Soc. 1959, 2003.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3025

Chufa´n et al.
of [CoII(TMPA)(CH3CN)](ClO4)2 were dissolved in 20 mL of
deoxygenated CH2Cl2 and transferred to a 50 mL Schlenk flask
equipped with a stir-bar and capped with a rubber septum. Outside
the glovebox, the solution was cooled to -78 °C in a dry ice/acetone
cold bath, and then the peroxo complex 3 was generated by direct
bubbling of dry O2 through the solution via syringe. The solution
was allowed to stand in the cold bath for several minutes to ensure
complete formation of 3, and after that the solution was degassed
via three freeze-pump-thaw cycles to remove any free O2. In the
meantime, an alkaline pyrogallol solution [4.0 g of pyrogallol (1,2,3-
trihydroxybenzene) in 25 mL of deoxygenated 50% KOH(aq)
solution] was freshly prepared in a modified 100 mL Schlenk flask
possessing a 2 mm path length cuvette. The alkaline pyrogallol
solution started out with a faint beige color, and its UV-visible
spectrum was recorded. The solution of 3 was then allowed to warm
to room temperature. Next, using a syringe needle, argon was slowly
passing through the headspace of the Schlenk flask containing the
solution of 3 (now decomposed), thus moving the liberated O2
through a cannula to the other Schlenk flask containing the alkaline
pyrogallol solution. The liberated O2 was bubbled directly into the
pyrogallol solution whose color began to darken after 2-3 min.
After 20-30 min of purging the flask with argon, the pyrogallol
ceased becoming darker, and its UV-vis spectrum was re-recorded.
The published calibration curve,58 absorbance (400 nm) ) (0.0716
× mL O2) + 0.025, was used to determine the amount of dioxygen
evolved upon thermal decomposition of 3. Two reaction runs
produced 75 and 82% yields of O2 based on the stated stoichiom-
etry, Scheme 3.
Acknowledgment. This work was supported by grant
from National Institutes of Health (GM 34909, (to K.D.K.)
and by a grant from the Deutsche Forschungsgemeinschaft,
DFG (to E.R. and U.S.)
Supporting Information Available: Crystal data for 1 (Table
S1); ESI mass spectrum and calculated spectrum of 1 (Figures S1
1
and S2); H NMR spectrum of [CoII(TMPA)(MeCN)]2+ (Figure
1
S3); variable temperature H NMR spectra and Curie plot of 1
(Figures S4 and S5); protonation/deprotonation cycles of 1 followed
by UV-vis spectroscopy (Figure S6); protonation of 1 followed
by 1H NMR spectroscopy (Figure S7); reversible acid-base
conversion of 1 by adding 2 equiv of HOTf and 2 equiv of Et3N
and monitored by UV-vis spectroscopy (Figure S8); EPR spectra
-‚
of 3 and an authentic [(1,5-dicyclohexylimidazole)(TPP)CoIII-O2
] (Figure S9); reactions [CoII(TPP)]/[CoII(TMPA)(MeCN)]2+/O2 and
[CoII(TMPA)(MeCN)]2+/O2 followed by 1H NMR at -80 °C
(Figures S10 and S11, respectively). This material is available free
of charge via the Internet at http://pubs.acs.org.
IC061686K
3026 Inorganic Chemistry, Vol. 46, No. 8, 2007