Structurally Characterized μ-1,2-Peroxo/Superoxo Dicopper(II) Pair

Article abstract of DOI:10.1021/jacs.1c04316

Superoxo complexes of copper are primary adducts in several O2-activating Cu-containing metalloenzymes as well as in other Cu-mediated oxidation and oxygenation reactions. Because of their intrinsically high reactivity, however, isolation of Cux(O2) species is challenging. Recent work (J. Am. Chem. Soc. 2017, 139, 9831; 2019, 141, 12682) established fundamental thermochemical data for the H atom abstraction reactivity of dicopper(II) superoxo complexes, but structural characterization of these important intermediates was so far lacking. Here we report the first crystallographic structure determination of a superoxo dicopper(II) species (3) together with the structure of its 1e- reduced peroxo congener (2; a rare cis-μ-1,2-peroxo dicopper(II) complex). Interconversion of 2 and 3 occurs at low potential (-0.58 V vs Fc/Fc+) and is reversible both chemically and electrochemically. Comparison of metric parameters (d(O-O) = 1.441(2) A for 2 vs 1.329(7) A for 3) and of spectroscopic signatures (ν(16O-16O) = 793 cm-1 for 2 vs 1073 cm-1 for 3) reflects that the redox process occurs at the bridging O2-derived unit. The CuII-O2?-CuII complex has an S = 1/2 spin ground state according to magnetic and EPR data, in agreement with density functional theory calculations. Computations further show that the potential associated with changes of the Cu-O-O-Cu dihedral angle is shallow for both 2 and 3. These findings provide a structural basis for the low reorganization energy of the kinetically facile 1e- interconversion of μ-1,2-superoxo/peroxo dicopper(II) couples, and they open the door for comprehensive studies of these key intermediates in Cux/O2 chemistry.

Full text of DOI:10.1021/jacs.1c04316

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Structurally Characterized μ‑1,2-Peroxo/Superoxo Dicopper(II) Pair
Alexander Brinkmeier, Roland A. Schulz, Moritz Buchhorn, Can-Jerome Spyra, Sebastian Dechert,
Serhiy Demeshko, Vera Krewald, and Franc Meyer*
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ABSTRACT: Superoxo complexes of copper are primary adducts
in several O2-activating Cu-containing metalloenzymes as well as in
other Cu-mediated oxidation and oxygenation reactions. Because
of their intrinsically high reactivity, however, isolation of
Cux(O2•−) species is challenging. Recent work (J. Am. Chem. Soc.
2017, 139, 9831; 2019, 141, 12682) established fundamental
thermochemical data for the H atom abstraction reactivity of
dicopper(II) superoxo complexes, but structural characterization of
these important intermediates was so far lacking. Here we report
the first crystallographic structure determination of a superoxo
dicopper(II) species (3) together with the structure of its 1e−
reduced peroxo congener (2; a rare cis-μ-1,2-peroxo dicopper(II)
complex). Interconversion of 2 and 3 occurs at low potential (−0.58 V vs Fc/Fc+) and is reversible both chemically and
electrochemically. Comparison of metric parameters (d(O−O) = 1.441(2) Å for 2 vs 1.329(7) Å for 3) and of spectroscopic
signatures (ν
̃
(16O−16O) = 793 cm−1 for 2 vs 1073 cm−1 for 3) reflects that the redox process occurs at the bridging O2-derived unit.
The CuII−O2•−−CuII complex has an S = 1/2 spin ground state according to magnetic and EPR data, in agreement with density
functional theory calculations. Computations further show that the potential associated with changes of the Cu−O−O−Cu dihedral
angle is shallow for both 2 and 3. These findings provide a structural basis for the low reorganization energy of the kinetically facile
1e− interconversion of μ-1,2-superoxo/peroxo dicopper(II) couples, and they open the door for comprehensive studies of these key
intermediates in Cux/O2 chemistry.
INTRODUCTION
■
Superoxo complexes are the first intermediates formed upon
binding of O2 to redox active metal ions accompanied by 1e−
transfer. They represent key reactive species in a variety of
biological oxidases and oxygenases, in particular in iron and
copper containing metalloenzymes, and they are also
considered as crucial intermediates in important catalytic
Figure 1. Structurally characterized end-on (η1) (superoxo)copper-
processes such as water oxidation or O2 reduction.1−3 The
(II) complex A10 (left) and μ-1,2-peroxo dicopper(II) motifs (right).
study of metal-superoxo complexes has thus received much
interest, but because of their mostly high reactivity the
the first structural characterization of a cis-μ-1,2-peroxo
isolation and crystallization have remained challenging.4,5
dicopper(II) complex (CP type) that was shown to strongly
•−
Although a number of mononuclear CuII−O2 complexes
interact with Na+ ions both in solution and in solid state (B,
have meanwhile been identified and their electronic structures
Scheme 1).14 Further elaboration via elongation of the ligand
have been analyzed in great detail,6−9 crystallographic
side arms in [L2]− induced a shortening of the Cu···Cu
information is scarce. So far, only for a single example of an
distance and a Cu−O−O−Cu torsion angle close to 90° in the
end-on (η1) (superoxo)copper(II) complex could the molec-
(peroxo)dicopper(II) complex C; such near-orthogonal
ular structure be determined by X-ray diffraction (A, Figure
1).10
In Cu2/O2 chemistry, (μ-η2:η2-peroxo)dicopper(II) com-
Received: April 26, 2021
Published: June 30, 2021
plexes and their valence tautomeric bis(μ-oxo) forms as well as
dicopper(II) complexes with a trans-μ-1,2-peroxo bridge (TP;
Figure 1) have been quite well studied.8,11 Employing a
compartmental pyrazolate/tacn hybrid ligand [L1]− (tacn =
1,4,7-triazacyclononane),12,13 a few years ago we contributed
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successful isolation and crystallization of any reactive oxy-
genated intermediates formed from 1. We thus devised an
improved synthesis of complex 1 by changing the solvent from
propionitrile (EtCN) to methanol (MeOH) and precipitating
the target compound with NaBPh4, followed by recrystalliza-
tion from acetone/diethyl ether (see the Supporting
Information for synthesis and spectroscopic details). 1(BPh4)
could now be isolated as single-crystalline material and its
molecular structure was determined via X-ray diffraction
(Figure 2). The two copper ions are coordinated in strongly
Scheme 1. Dinucleating Pyrazolate/Tacn Hybrid Ligands
[L1]− and [L2]− and Their Previously Studied Dicopper(II)
Peroxo and Superoxo Complexes
C
T
arrangement in between the P and P forms was shown to
lead to ferromagnetic coupling and an unprecedented S = 1
ground state.15
In subsequent work, it was demonstrated that C can be
reversibly oxidized at low potential (−0.59 V vs Fc/Fc+),
giving the spectroscopically characterized μ-1,2-superoxo
dicopper(II) complex D (Scheme 1) whose H atom
abstraction (HAA) thermochemistry could be established.16
Using a ligand scaffold with a central phenolate bridge, Karlin
Figure 2. Molecular structures of 1 (top) and 2 (bottom) in solid
state with thermal displacement ellipsoids given at 30% probability.
−
Counterion BPh4 not shown and all hydrogen atoms omitted for
et al. studied a related CuII (O2•−) complex, which was
clarity.
2
obtained by reacting the mixed-valent CuICuII precursor with
O2 and was shown to consist of a mixture of μ-1,2 and μ-1,1
superoxo isomers in rapid equilibrium.17,18 A kinetically facile
superoxo/peroxo interconversion with low reorganization
energy (at E = −0.24 V vs Fc/Fc+) was revealed, reflecting
that the redox process occurs at the O2-derived unit.18,19 Most
recent work focused on correlations between properties of the
supporting ligands and superoxo HAA capabilities,20 in view of
the very different OO-H bond dissociation free energies
(BDFEs) of the hydroperoxo products derived from D21 and
distorted tetrahedral geometry, and the wide open cleft
between them appears predestined for accommodating O2 in
a μ-η1:η1 bridging mode. As expected, the Cu···Cu distance in
1 (4.15 Å) is significantly larger than in the related complex
[L2Cu2]+ that has longer chelate arms (3.97 Å),15 reflecting
that the metal···metal separation can be tuned by the ligand
scaffold; further crystallographic details and metric parameters
are provided in the Supporting Information. When dry O2 is
added to a colorless solution of 1(BPh4) in MeCN at −40 °C,
the solution turns deep purple immediately. After workup and
Et2O diffusion into a solution of the oxygenated complex in
acetone at −26 °C, single-crystalline material was obtained and
the structure of the μ-η1:η1 cis-peroxo complex 2(BPh4) could
be determined crystallographically (see the Supporting
Information for further details). The molecular structure of
the cation 2 shows two copper ions in a distorted trigonal
bipyramidal coordination environment (τ5(Cu1) = 0.63,
τ5(Cu2) = 0.60)23 with a Cu···Cu separation of 3.741 Å,
significantly shorter than in the precursor complex 1. The O−
O bond length in “naked” 2 (1.441(2) Å) is in the range
typical for end-on bound peroxides but clearly shorter than in
the sodium ion adduct B (1.498(7)).14 The Cu2/O2 core in 2
one of Karlin’s phenolate-based CuII (O2•−) complexes (69.4
2
kcal/mol22 vs 81.8 kcal/mol).16,20 However, crucial structural
characterization of any dicopper superoxo species is lacking so
far.
Here we report the first X-ray crystallographic structure
determination of a cis-μ-1,2-superoxo dicopper(II) complex,
based on the dinucleating ligand scaffold [L1]−. In addition, we
report the molecular structure of the parent type B peroxo
complex without associated Na+, viz with a “naked” cis-peroxo
bridge, which allows for the direct comparison of unperturbed
μ-1,2-peroxo and μ-1,2-superoxo dicopper(II) units in
identical ligand settings.
C
RESULTS AND DISCUSSION
features a P geometry with a Cu−O−O-Cu torsion angle of
■
Dicopper(I) and μ-Peroxo Dicopper(II) Complexes.
Initial experiments showed that high-purity material of the
dicopper(I) starting complex [L1Cu2]+ (1) is essential for
55.3°, which is 10.1° smaller compared to the previously
reported B (vide infra). Density functional theory calculations
find isoenergetic triplet and open-shell singlet configurations
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for 2 with geometries that match the experiment (OSS2:
d
CuCu,calc = 3.750 Å, dOO,calc = 1.391 Å; T2: dCuCu,calc = 3.784 Å,
dOO,calc = 1.382 Å; ΔE(OSS2, T2) < 1 kcal/mol, see the
Supporting Information for details).
Peroxo complex 2 in MeCN solution is thermally unstable
above −20 °C. It shows a characteristic UV−vis absorption
spectrum with two maxima at 648 nm (ε = 3900 M−1 cm−1;
TDDFT: excitation from Cu ions into the π-manifold) and 527
nm (ε = 5000 M−1 cm−1; TDDFT: excitation within the π-
manifold on the Cu−O2−Cu unit) and a shoulder at 456 nm
(ε = 2600 M−1 cm−1; TDDFT: excitation within the π-
manifold on the Cu−O2−Cu unit) (see also Figure 5 below;
for TDDFT assignments, see Table S5). Although the
T
spectrum looks similar to those of related P systems whose
electronic structures have been analyzed in detail,24 these
LMCT bands for 2 are less intense, as was previously observed
for CP species C and the Na+ adduct B.14 Raman spectroscopy
of solid 2 (λex = 633 nm; Figure 3) shows a pronounced
Figure 4. Cyclic voltammogram of a 2.8 mM solution of 2(BPh4) in
MeCN at 100 mV/s (0.1 M [nBu4N]PF6, T = 0 °C). The inset shows
the process at E° = −0.58 V vs Fc/Fc+ at different scan rates; the
anodic peak current Ip shows a linear dependence on the square root
of the scan rate (v1/2; see Figure S5).
Figure 3. Raman spectra of crystalline material of 2(BPh4) (λex = 633
nm).
feature around 793 cm−1 that is split into two bands, which is
attributed to Fermi resonance. When using 18O2 this
absorption shifts to 752 cm−1 (Δ(18O2−16O2) = −41 cm−1,
ν
(16O−16O)/ν(18O−18O) = 1.055, calculated 1.060 for an
̃ ̃
isolated harmonic O−O oscillator), and hence these bands are
assigned to the peroxide O−O stretch. DFT calculations
support this assignment with a predicted O−O stretch at 884
cm−1 for OSS2 that shifts by −48 cm−1 with 18O isotopes (see
Table S5).
μ-Superoxo Dicopper(II) Complex. Cyclic voltammetry
of peroxo complex 2 (MeCN, 0.1 M [nBu4N]PF6, T = 0 °C;
for details see Supporting Information) revealed a reversible
redox event at −0.58 V vs Fc/Fc+, followed by an irreversible
oxidation at ca. 0.7 V (Figure 4). Monitoring the first anodic
process by UV−vis spectroelectrochemistry at a controlled
potential of −0.2 V vs Fc/Fc+ shows the formation of a new
species featuring an intense absorption at 444 nm (ε = 10
mM−1 cm−1). In view of the findings for [L2]−-based
complexes C and D (440 nm, ε = 11.5 mM−1 cm−1),16 the
event at −0.58 V is assigned to oxidation of peroxo complex 2
to the new superoxo complex 3.
Figure 5. Titration of a 70 μM solution of 2 with a solution of AgSbF6
in MeCN at −40 °C in steps of 0.11 equiv. with overall 1.1 equiv.
being added, isosbestic point at 485 nm.
other reported dinuclear superoxo complexes.16,17,21 Oxidation
of 2 to 3 is also possible with various CuII salts (e.g.,
Cu(OTf)2) and is chemically reversible, as demonstrated by
the following experiment: after 3 was generated from complex
2 and Cu(OTf)2 in MeCN (giving 3 and [Cu(MeCN)4]+), a
solution of the disodium salt of bis(salicyliden)ethylendiamin,
Na2(salen), was added. As deprotonated salen is known to
stabilize its CuII complex (E°(CuI/CuII)= −1.66 V versus Fc/
Fc+ in MeCN),25 superoxide complex 3 is reduced back to
peroxo complex 2 (now as the Na+ adduct B), concomitant
with formation of the CuII-salen complex; this sequence can be
nicely monitored via the characteristic UV−vis signatures of 2,
3, and B (cf. Scheme S1 and Figure S8).
Titration of a solution of 2(BPh4) in MeCN with AgSbF6 at
−40 °C (E0(AgSbF6) = 0.04 V vs Fc/Fc+) confirmed the
formation of a 1e− oxidized product with a characteristic
absorption at λmax = 444 nm (ε = 10 mM−1 cm−1) and a weak
shoulder at ca. 570 nm (ε = 1.5 mM−1 cm−1; Figure 5). These
features are reminiscent of the electronic absorption spectra of
The superoxo species 3 is remarkably stable, with a half-life
of ca. 8 h at 20 °C in MeCN. However, extensive screening of
crystallization conditions was required to finally yield single-
crystalline material. This was obtained when using
26
[(iPr3TACN)CuII(CH3CN)2](SbF6)2 as a 1e− oxidant in
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acetone solution and diffusion of Et2O into the reaction
mixture at −36 °C within a few days. The molecular structure
of the cation of 3(BPh4)(SbF6) determined by X-ray
diffraction is shown in Figure 6. The O−O bond length in 3
Figure 7. Relative electronic energies (kcal/mol) for a relaxed surface
T
scan of the Cu−O−O−Cu dihedral angle in 2 (blue) and D3 (red);
the lines are drawn strictly as a guide to the eye. The energies of
models in which the dihedral angle is fixed to the crystal structure
value are shown as squares (peroxo, light blue; superoxo, orange).
Figure 6. Molecular structure of 3 with thermal displacement
ellipsoids given at 30% probability. Only one of the two crystallo-
−
graphically independent molecules is shown. Counteranions BPh4
−
and SbF6 are omitted for clarity; for structural parameters, see the
observed for one of the crystallographically independent
molecules in solid 3(BPh4)(SbF6) (see Figure S13).
Supporting Information.
The superoxo character of 3 was confirmed by resonance
Raman spectroscopy of a solution of 3 in MeCN (λex = 457
nm, Figure 8), which shows one oxygen isotope sensitive
(1.33 Å) is significantly shorter than in 2 (1.44 Å), reflecting
that oxidation occurs at the O2-derived ligand. The availability
of structural information for both 2 and 3 now allows for
unprecedented comparison of this pair of peroxo and superoxo
complexes. Upon oxidation, the Cu−O bonds elongate from
1.8900(13)/1.8971(14) Å in 2 to 1.924(5)/1.940(5) Å in 3,
suggesting a weakening of the Cu−O interaction. Furthermore,
the Cu···Cu separation widens from 3.741 Å in 2 to 3.816 Å in
3 and the Cu−O−O−Cu dihedral angle increases (from 55.3
to 75.4°). In contrast to 2, the coordination geometries of the
two CuII ions in 3 are distinctly different, with Cu2 in nearly
square pyramidal and Cu1 in strongly distorted trigonal
bipyramidal coordination environment (τ5 = 0.08 vs 0.63).
Selected structural parameters are collected in Table 1. DFT
Table 1. Summary of Selected Structural Parameters of
Dicopper(II) Peroxo and Superoxo Complexes 2 and 3
Figure 8. Raman spectrum of a 1.4 mM solution of 3 in MeCN
recorded at 22 °C, λex = 457 nm. The inset shows the difference
spectrum.
d(O−O)
ϕ(Cu−O2−Cu)
(Å)
d(Cu−O) (Å)
(deg)
τ5(Cu)
2
3
1.441(2)
1.329(7)
1.890(2)/1.897(2)
1.924(5)/1.940(5)
55.3
75.4
0.60, 0.63
0.08, 0.63
a
feature at 1073 cm−1 (Δ(18O−16O) = −60 cm−1; ν
ν(18
̃
(16O−16O)/
a
Values taken from the crystallographically independent molecule that
̃
O−18O) = 1.059, calculated 1.060 for an isolated harmonic
shows no disorder in the O−O part (see the Supporting Information
for details).
O−O oscillator). This is significantly higher than for peroxo
complex 2 and in the typical region for a superoxide vibration,
yet the O−O bond appears to be slightly weakened compared
•−
geometry optimizations show that a doublet ground state is
preferred over a quartet state for 3; both structures are in good
agreement with experiment (D3: d(Cu···Cu)calc = 3.777 Å,
d(O−O)calc = 1.337 Å; Q3: d(Cu···Cu)calc = 3.845 Å, d(O−
O)calc = 1.334 Å; ΔE(D3, Q3) = 8.1 kcal/mol; see the
Supporting Information for details). Importantly, the potential
associated with changes of the Cu−O−O−Cu dihedral angle
appears shallow in both the μ-1,2-superoxo and μ-1,2-peroxo
complexes: constraining this parameter close to the exper-
imental value is associated with a negligible energy penalty of
less than 1 kcal/mol. This is confirmed with a relaxed surface
scan of the dihedral angle for the peroxo and superoxo
complexes, see Figure 7. A second, slightly destabilized
minimum is found for a flipped coordination of the {O2}
bridge in both systems, which is in line with the disorder
to the mononuclear end-on CuII−O2 complex A (ν
̃
= 1122
cm−1).10 DFT calculations are in good agreement with this
assignment; the O−O stretch is found at 1011 cm−1 and shifts
by ca. −60 cm−1 for the 18O isotope.
SQUID magnetometry of a frozen solution of 3 in MeCN
confirms an S = 1/2 spin ground state in accordance with the
DFT predictions (Figure S9), indicating overall antiferromag-
netic coupling between the two CuII (d9) ions and the O2
•−
bridge. The computed electronic structure of 3 is consistent
with such an electronic configuration (Mulliken spin
•−
populations with PBE0: Cu1 0.57, Cu2 0.58, μ-O2 −0.65).
The X-band EPR spectrum of 3 also reflects the S = 1/2 cupric
superoxide signature (Figure 9). Excellent simulations of the
EPR spectrum were obtained when hyperfine coupling to both
CuII ions was assumed, which is best reflected by the second
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Authors
Alexander Brinkmeier − Institut fu
̈
r Anorganische Chemie,
Universität Göttingen, D-37077 Göttingen, Germany
Roland A. Schulz − Institut fur Anorganische Chemie,
̈
Universität Göttingen, D-37077 Göttingen, Germany
Moritz Buchhorn − Fachbereich Chemie, Theoretische
Chemie, Technische Universität Darmstadt, D-64287
Darmstadt, Germany
Can-Jerome Spyra − Institut fu
Universität Göttingen, D-37077 Göttingen, Germany
r Anorganische Chemie,
Universität Göttingen, D-37077 Göttingen, Germany;
orcid.org/0000-0002-2864-2449
̈
r Anorganische Chemie,
Sebastian Dechert − Institut fu
̈
Figure 9. X-band EPR spectrum of a 0.01 M frozen solution of 3 in
MeCN, recorded at 161 K (left) and second derivative spectrum
(right); the red line is the simulation with parameters given in the
text.
Serhiy Demeshko − Institut fur Anorganische Chemie,
̈
Universität Göttingen, D-37077 Göttingen, Germany
Vera Krewald − Fachbereich Chemie, Theoretische Chemie,
Technische Universität Darmstadt, D-64287 Darmstadt,
Germany; orcid.org/0000-0002-4749-4357
derivative spectrum, yielding gx = 2.03, gy = 2.08, gz = 2.15
(with a1 = 5.2 G, a2 = 5.0 G, a3 = 73 G).
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c04316
SUMMARY AND CONCLUSION
■
Author Contributions
In summary, we were able to crystallographically characterize a
μ-1,2-superoxo dicopper(II) complex as well as its 1e− reduced
peroxo congener, the latter representing the first structurally
authenticated example of a “naked” cis-μ-1,2-peroxo dicopper-
(II) complex of the CP type. Comparison of metric parameters
for this unique pair of complexes, together with their
spectroscopic signatures, supports that the redox process
occurs at the O2-derived unit within the bimetallic cleft.
Experimental and computational evidence reveal an S = 1/2
spin ground state for the CuII−O2•−−CuII core and a negligible
energy penalty associated with moderate changes of the Cu−
O−O−Cu dihedral angle in both the peroxo and superoxo
species. This work provides a structural basis for the previously
observed18,19 low reorganization energy of the kinetically facile
1e− interconversion of such superoxo/peroxo dicopper(II)
couples.
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partly supported by the Deutsche Forschungs-
gemeinschaft in the framework of the IRTG 1422 Metal sites in
Biomolecules: Structures, Regulation and Mechanisms (PhD
scholarship for A.B.). We thank Dr. Eckhard Bill (MPI-CEC,
Mulheim an der Ruhr, Germany) for assistance with the
̈
simulation of the EPR spectrum. All calculations were
conducted on the Lichtenberg high-performance computer at
TU Darmstadt; the Hessian Competence Center for High
Performance Computing is gratefully acknowledged.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c04316.
■
sı
REFERENCES
■
(1) Quist, D. A.; Diaz, D. E.; Liu, J. J.; Karlin, K. D. Activation of
dioxygen by copper metalloproteins and insights from model
complexes. J. Biol. Inorg. Chem. 2017, 22, 253−288.
Experimental details and synthetic procedures, further
spectroscopic and analytical data, crystallographic
information, details of DFT calculations (PDF)
(2) Adam, S. M.; Wijeratne, G. B.; Rogler, P. J.; Diaz, D. E.; Quist,
D. A.; Liu, J. J.; Karlin, K. D. Synthetic Fe/Cu Complexes: Toward
Understanding Heme-Copper Oxidase Structure and Function. Chem.
Rev. 2018, 118, 10840−11022.
Accession Codes
(3) Ray, K.; Pfaff, F. F.; Wang, B.; Nam, W. Status of Reactive Non-
Heme Metal−Oxygen Intermediates in Chemical and Enzymatic
Reactions. J. Am. Chem. Soc. 2014, 136, 13942−13958.
(4) Noh, H.; Cho, J. Synthesis, characterization and reactivity of
non-heme 1st row transition metal-superoxo intermediates. Coord.
Chem. Rev. 2019, 382, 126−144.
CCDC 2079339−2079341 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(5) Fukuzumi, S.; Lee, Y.-M.; Nam, W. Structure and reactivity of
the first-row d-block metal-superoxo complexes. Dalton Trans. 2019,
48, 9469−9489.
AUTHOR INFORMATION
Corresponding Author
̈
Franc Meyer − Institut fur Anorganische Chemie, Universität
■
(6) Cramer, C. C.; Tolman, W. B. Mononuclear Cu−O2 Complexes:
Geometries, Spectroscopic Properties, Electronic Structures, and
Reactivity. Acc. Chem. Res. 2007, 40, 601−608.
(7) Itoh, S. Developing Mononuclear Copper−Active-Oxygen
Complexes Relevant to Reactive Intermediates of Biological
Oxidation Reactions. Acc. Chem. Res. 2015, 48, 2066−2074.
(8) Elwell, C. E.; Gagnon, N. L.; Neisen, B. D.; Dhar, D.; Spaeth, A.
D.; Yee, G. M.; Tolman, W. B. Copper−Oxygen Complexes
Göttingen, D-37077 Göttingen, Germany; International
Center for Advanced Studies of Energy Conversion
(ICASEC), Universität Göttingen, D-37077 Göttingen,
Germany; orcid.org/0000-0002-8613-7862;
Email: franc.meyer@chemie.uni-goettingen.de
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Journal of the American Chemical Society
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Article
Revisited: Structures, Spectroscopy, and Reactivity. Chem. Rev. 2017,
117, 2059−2107.
J. S. Copper Dioxygen (Bio)Inorganic Chemistry. Faraday Discuss.
2011, 148, 11−39.
(9) Solomon, E. I. Dioxygen Binding, Activation, and Reduction to
H2O by Cu Enzymes. Inorg. Chem. 2016, 55, 6364−6375.
(25) Hirotsu, M.; Kuwamura, N.; Kinoshita, I.; Kojima, M.;
Yoshikawa, Y.; Ueno, K. Steric, geometrical and solvent effects on
redox potentials in salen-type copper(II) complexes. Dalton Trans.
2009, 7678−7683.
(10) Wurtele, C.; Gaoutchenova, E.; Harms, K.; Holthausen, M. C.;
̈
Sundermeyer, J.; Schindler, S. Crystallographic Characterization of a
Synthetic 1:1 End-On Copper Dioxygen Adduct Complex. Angew.
Chem., Int. Ed. 2006, 45, 3867−3869.
(26) Yang, L.; Tolman, W. B. Type 1 copper site synthetic model
complexes with increased redox potentials. J. Biol. Inorg. Chem. 2012,
17, 285−291.
(11) Hamann, J. N.; Herzigkeit, B.; Jurgeleit, R.; Tuczek, F. Small-
molecule models of tyrosinase: From ligand hydroxylation to catalytic
monooxygenation of external substrates. Coord. Chem. Rev. 2017, 334,
54−66.
(12) Dalle, K. E.; Meyer, F. Modelling Binuclear Metallobiosites:
Insights from Pyrazole-Supported Biomimetic and Bioinspired
Complexes. Eur. J. Inorg. Chem. 2015, 3391−3405.
(13) Dalle, K. E.; Dechert, S.; Meyer, F. Improved Synthesis and
Detailed Characterization of a Hybrid Pyrazole-TACN Dinucleating
Ligand. Z. Anorg. Allg. Chem. 2015, 641, 2181−2189.
(14) Dalle, K. E.; Gruene, T.; Dechert, S.; Demeshko, S.; Meyer, F.
Weakly Coupled Biologically Relevant CuII (μ-η1:η1-O2) cis-Peroxo
2
Adduct that Binds Side-On to Additional Metal Ions. J. Am. Chem.
Soc. 2014, 136, 7428−7434.
(15) Kindermann, N.; Bill, E.; Dechert, S.; Demeshko, S.; Reijerse,
E.; Meyer, F. A Ferromagnetically Coupled (S = 1) Peroxodicopper-
(II) Complex. Angew. Chem., Int. Ed. 2015, 54, 1738−1743.
(16) Kindermann, N.; Gunes, C.-J.; Dechert, S.; Meyer, F. Hydrogen
̈
Atom Abstraction Thermodynamics of a μ-1,2-Superoxo Dicopper-
(II) Complex. J. Am. Chem. Soc. 2017, 139, 9831−9834.
(17) Mahroof-Tahir, M.; Karlin, K. D. A Dinuclear Mixed-Valence
Cu(I)/Cu(II) Complex and Its Reversible Reaction with Dioxygen:
Generation of a Superoxodicopper(II) Species. J. Am. Chem. Soc.
1992, 114, 7599−7601.
(18) Cao, R.; Saracini, C.; Ginsbach, J. W.; Kieber-Emmons, M. T.;
Siegler, M. A.; Solomon, E. I.; Fukuzumi, S.; Karlin, K. D. Peroxo and
Superoxo Moieties Bound to Copper Ion: Electron-Transfer
Equilibrium with a Small Reorganization Energy. J. Am. Chem. Soc.
2016, 138, 7055−7066.
(19) López, I.; Cao, R.; Quist, D. A.; Karlin, K. D.; Le Poul, N.
Direct Determination of Electron-Transfer Properties of Dicopper-
Bound Reduced Dioxygen Species by a Cryo-Spectroelectrochemical
Approach. Chem. - Eur. J. 2017, 23, 18314−18319.
(20) Quist, D. A.; Ehudin, M. A.; Schaefer, A. W.; Schneider, W. L.;
Solomon, E. I.; Karlin, K. D. Ligand Identity-Induced Generation of
Enhanced Oxidative Hydrogen Atom Transfer Reactivity for a
CuII (O2•−) Complex Driven by Formation of a CuII (−OOH)
2
2
Compound with a Strong O−H Bond. J. Am. Chem. Soc. 2019, 141,
12682−12696.
(21) Kindermann, N.; Dechert, S.; Demeshko, S.; Meyer, F. Proton-
Induced, Reversible Interconversion of a μ-1,2-Peroxo and a μ-1,1-
Hydroperoxo Dicopper(II) Complex. J. Am. Chem. Soc. 2015, 137,
8002−8005.
(22) For the BDFE(OO-H) of the hydroperoxo complex derived
from D, a value of 71.7 kcal/mol was published in ref 16. This has to
be revised in view the of the recently corrected value of CG,MeCN
=
52.6 kcal mol−1 used in the potential/pKa analysis for BDFE
determination (CG is equivalent to the H+/H• standard reduction
potential in the given solvent). Wise, C. F.; Agarwal, R. G.; Mayer, J.
M. Determining Proton-Coupled Standard Potentials and X−H Bond
Dissociation Free Energies in Nonaqueous Solvents Using Open-
Circuit Potential Measurements. J. Am. Chem. Soc. 2020, 142, 10681−
10691.
(23) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor,
G. C. Synthesis, structure, and spectroscopic properties of copper(II)
compounds containing nitrogen-sulfur donor ligands: the crystal and
molecular structure of aqua[1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-
dithiaheptane]copper(II) perchlorate. J. Chem. Soc., Dalton Trans.
1984, 7, 1349−1356.
(24) Solomon, E. I.; Ginsbach, J. W.; Heppner, D. E.; Kieber-
Emmons, M. T.; Kjaergaard, C. H.; Smeets, P. J.; Tian, L.; Woertink,
10366
https://doi.org/10.1021/jacs.1c04316
J. Am. Chem. Soc. 2021, 143, 10361−10366