Thermal Stability and Absorption Spectroscopic Behavior of (μ-Peroxo)dicopper Complexes Regulated with Intramolecular Hydrogen Bonding Interactions

Article abstract of DOI:10.1002/ejic.200300178

In order to clarify the effect of hydrogen bonding on the stabilities of (μ-peroxo)dicopper complexes with a trans-μ-1,2-peroxo form, novel copper complexes with intramolecular hydrogen bonding interaction sites have been synthesized, and their spectroscopic properties and thermal stabilities studied. The selected tripodal tetradentate ligands were tris(2-pyridylmethyl)amine (TPA) derivatives bearing pivalamido and amino groups at the 6-position of the pyridine ring in TPA, {[6-(pivalamido)pyrid-2-yl]methyl}bis(pyrid-2-ylmethyl)amine (MPPA) and [(6-aminopyrid-2-yl)methyl]bis(pyrid-2-ylmethyl)amine (MAPA). The single-crystal X-ray structure of a monomeric Cu^II complex with N₃^- namely [Cu(mppa)N₃]ClO₄ (1a), revealed an interligand hydrogen bonding interaction between the substituent NH group of MPPA and the azide nitrogen atom in the axial position. The Cu ^I complexes of MPPA and MAPA were immediately oxygenated with dioxygen in acetone solution at -78 °C to give the μ-peroxo dinuclear copper(II) complexes [{Cu(mppa)}₂(O₂)]²⁺ (1b) and [{Cu(mapa)}₂(O₂)]²⁺ (2b). These complexes exhibited two kinds of characteristic absorption bands (π* _σ→d_σ, π*_v→ dσ) originating from the ligand-metal charge transfer (LMCT) of O ₂^2- to Cu. Affected by the hydrogen bonding interaction, the π*_σ→d_σ CT band shifted significantly to a higher energy region and the π*_v→ d_σ CT absorbance decreased due to stabilization of the π*_σ orbital and restriction of the Cu-O bond rotation. The thermal stabilities of the (μ-peroxo)dicopper(II) complexes were estimated from their decomposition rates which decreased in the order, 2b ≈ [{Cu(tpa)}₂(O₂)]²⁺ (3b) > 1b ? [{Cu(6-metpa)}₂(O₂)]²⁺ (4b) {6-MeTPA = [(6-methylpyrid-2-yl)methyl]bis(pyrid-2-ylmethyl)amine}. The above findings indicate that the interligand hydrogen bonding interaction, although overcome to some extent by the adverse effect of the steric bulk of the NH group, is inclined to stabilize (μ-peroxo)dicopper(II) complexes. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300178

FULL PAPER
Thermal Stability and Absorption Spectroscopic Behavior of (µ-Peroxo)dicopper
Complexes Regulated with Intramolecular Hydrogen Bonding Interactions
Syuhei Yamaguchi,[a] Akira Wada,[a] Yasuhiro Funahashi,[a] Shigenori Nagatomo,[b]
Teizo Kitagawa,[b] Koichiro Jitsukawa,*[a] and Hideki Masuda*[a]
Keywords: Copper / Peroxides / Tripodal ligands / Hydrogen bonding interactions
In order to clarify the effect of hydrogen bonding on the
stabilities of (µ-peroxo)dicopper complexes with a trans-µ-
1,2-peroxo form, novel copper complexes with intramolecu-
lar hydrogen bonding interaction sites have been synthe-
sized, and their spectroscopic properties and thermal stabilit-
complexes exhibited two kinds of characteristic absorption
bands (π*σǞdσ, π*vǞdσ) originating from the ligand−metal
charge transfer (LMCT) of O22− to Cu. Affected by the hydro-
gen bonding interaction, the π*σǞdσ CT band shifted signi-
ficantly to a higher energy region and the π*vǞdσ CT ab-
ies studied. The selected tripodal tetradentate ligands were sorbance decreased due to stabilization of the π*σ orbital and
tris(2-pyridylmethyl)amine (TPA) derivatives bearing pival-
amido and amino groups at the 6-position of the pyridine ring
restriction of the Cu−O bond rotation. The thermal stabilities
of the (µ-peroxo)dicopper(II) complexes were estimated from
in TPA, {[6-(pivalamido)pyrid-2-yl]methyl}bis(pyrid-2-ylme- their decomposition rates which decreased in the order, 2b ഠ
thyl)amine (MPPA) and [(6-aminopyrid-2-yl)methyl]bis(py-
[{Cu(tpa)}2(O2)]2+ (3b) Ͼ 1b ϾϾ [{Cu(6-metpa)}2(O2)]2+ (4b)
rid-2-ylmethyl)amine (MAPA). The single-crystal X-ray {6-MeTPA = [(6-methylpyrid-2-yl)methyl]bis(pyrid-2-ylmeth-
structure of a monomeric CuII complex with N3 namely
[Cu(mppa)N3]ClO4 (1a), revealed an interligand hydrogen
bonding interaction between the substituent NH group of
yl)amine}. The above findings indicate that the interligand
hydrogen bonding interaction, although overcome to some
extent by the adverse effect of the steric bulk of the NH
−
MPPA and the azide nitrogen atom in the axial position. The group, is inclined to stabilize (µ-peroxo)dicopper(II) com-
CuI complexes of MPPA and MAPA were immediately oxy- plexes.
genated with dioxygen in acetone solution at −78 °C to
give the µ-peroxo dinuclear copper(II
)
complexes
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
[{Cu(mppa)}2(O2)]2+ (1b) and [{Cu(mapa)}2(O2)]2+ (2b). These
Introduction
models.[14Ϫ35] The binding of dioxygen to dinuclear copper
complexes has been previously found to result in (trans-µ-
1,2-peroxo)dicopper(),[14Ϫ25] [µ-(η2:η2)-peroxo]dicopper-
(),[14,26Ϫ31] and [bis(µ-oxo)]dicopper() forms.[14,32Ϫ35]
These coordination modes in dicopper sites are known to
depend on the stereochemistry of the coordination environ-
ment. The geometries of dicopperϪdioxygen complexes are
likely to be regulated by the number of coordinating
ligands;[14Ϫ35] (trans-µ-1,2-peroxo)dicopper() comple-
xes[14Ϫ25] have been generally formed using tetradentate li-
gands and the structural and spectroscopic properties of
(trans-µ-1,2-peroxo)dicopper() complexes were first sys-
tematically investigated by Karlin and co-workers.[16Ϫ23]
In biological systems, O2 binding and its activation by
metalloenzymes are important processes for respiratory and
metabolic systems.[1] Detailed examinations using biomi-
metic model systems are required for understanding the
natural processes, such as dioxygen transport, oxidation,
oxygenation, and dehydrogenation.[1Ϫ3] These processes are
catalyzed by heme iron,[4,5] non-heme iron[6,7] and copper
centers[8Ϫ13] at the active sites of the metalloenzymes. In
order to clarify the catalytic reaction mechanism of the di-
copper-containing enzymes, dicopperϪdioxygen adduct
complexes have been investigated as biomimetic
In biological catalysts, environmental factors such as the
proximal effect of amino acid residues are frequently re-
quired for regulating reaction intermediates and activating
substrates. We have demonstrated that the hydrogen bond-
ing interaction can control the reactivity of metalϪdioxygen
species, and have succeeded in the preparation of the stable
monomeric (hydroperoxo)copper(II) complex [CuII(bppa)-
(OOH)]ϩ [BPPA ϭ bis{[6-(pivalamido)pyrid-2-yl]methyl}-
(pyrid-2-ylmethyl)amine].[36] The crystal structure of this
[a]
Department of Applied Chemistry, Nagoya Institute of
Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
Fax: (internat.) ϩ 81-52-7355228
E-mail: masuda@ach.nitech.ac.jp
[b]
Center of Integrative Bioscience, Okazaki National Research
Institutes,
Myodaiji, Okazaki 444-8585, Japan
4378
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200300178
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386

Thermal Stability and Absorption Spectroscopic Behavior of (µ-Peroxo)dicopper Complexes
FULL PAPER
complex revealed a hydrogen bonding interaction between
Results and Discussion
the pivalamido NH group of BPPA and the ligating hydro-
peroxo oxygen atom.[36] The remarkable stability of
[CuII(bppa)(OOH)]ϩ was acquired by the intramolecular
hydrogen bonding interaction. From this point of view, it
has been previously discussed that the interligand hydrogen
bonding interaction can stabilize (superoxo)-, (alkylper-
oxo)-, and (hydroxo)metal complexes with tripodal tetra-
dentate ligands.[37Ϫ43]
Formation of CuII؊L؊N3 Complexes (L ؍ mppa, mapa,
tpa, 6-metpa) and Their Spectroscopic Properties
[CuII(mppa)](ClO4)2
ylmethyl){[6-(pivalamido)pyrid-2-yl]methyl}amine]
synthesized by mixing equimolar amounts
(1)
[mppa
ϭ
bis(pyrid-2-
was
of
CuII(ClO4)2·6H2O and MPPA in methanol. Addition of
NaN3 to 1 in CH3CN results in a color change of the solu-
tion from blue to green, indicating formation of
[CuII(mppa)(N3)]ϩ (1a). [CuII(L)(N3)]ϩ complexes [L ϭ
mapa (2a), tpa (3a),[46] and 6-metpa (4a)] were also pre-
pared in CH3CN solution by a similar procedure and the
azide complexes all showed almost the same spectroscopic
properties corresponding to the analogous coordination
geometries. Electronic absorption and ESR spectroscopic
data for [CuII(L)(N3)]ϩ, 1a, 2a, 3a and 4a, are listed in
Tables 1 and 2, respectively. The electronic absorption spec-
trum of 1a exhibited d-d transition bands centered at
647 nm (300 Ϫ1cmϪ1) and 833 nm (220 Ϫ1cmϪ1), and an
intense absorption band at 395 nm (2700 Ϫ1cmϪ1). The
latter intense absorption band in the UV region can be as-
signed to LMCT since the other azide complexes,
[Cu(mapa)(N3)]ϩ (2a) and [Cu(tpa)(N3)]ϩ (3a), exhibited
As an expansion of our previous research, tripodal li-
gands having the hydrogen bonding feature, such as {[6-
(pivalamido)pyrid-2-yl]methy}bis(pyrid-2-ylmethyl)amine
(MPPA) and [(6-amino-2-pyridyl)methyl]bis(pyrid-2-ylme-
thyl)amine (MAPA) (Scheme 1), have been newly prepared
for complexation with copper ions. It was expected that
these tetradentate ligands would form (trans-µ-1,2-peroxo)-
dicopper() complexes that would be dominated by their
coordination numbers. In this paper, we describe details of
the following: (i) the coordination structures and hydrogen
bonding modes of copper complexes with MPPA and
MAPA and (ii) formation of the corresponding µ-peroxo
dinuclear copper complexes and their characteristic absorp-
tion spectroscopic behavior and thermal stabilities. We also
discuss the intrinsic effect of the proximal hydrogen bond-
ing interaction in µ-peroxo dinuclear copper complexes in
detail and compare these with the cases of copper complex
systems of TPA and Cu-6-MeTPA {6-MeTPA ϭ [(6-
methyl-2-pyridyl)methyl]bis(pyrid-2-ylmethyl)amine} with-
out a hydrogen bonding site (Scheme 1).[44,45]
Ϫ
intense LMCT bands between the bound N3 anion and
the copper ion in the same region [at 403 nm (2940
[46]

Ϫ1cmϪ1
(Table 1).
)
and 413 nm (2130 Ϫ1cmϪ1), respectively]
[CuII(6-metpa)(N3)]ϩ (4a) also showed the same charac-
teristic LMCT band at 414 nm (2600 Ϫ1cmϪ1), indicating
that the azide ion is bound to the CuII center. The frozen
solution ESR spectrum of the azide complex 1a at 77 K
2
gave signals typical for a CuII complex with a dz ground
state (g|| ϭ 2.03 Ͻ gЌ ϭ 2.20, |A|| | ϭ 71 G, and |AЌ| ϭ 130
G). Including other azide complexes, the ESR spectroscopic
patterns of 1a, 2a, and 3a are characteristic of a trigonal-
bipyramidal geometry (g|| Ͻ gЌ) which agrees well with
those speculated from their absorption spectroscopic fea-
tures showing lower d-d transition energies (Table 2).
Crystal Structures of [Cu(mppa)](ClO4)2 (1) and
[Cu(mppa)(N3)]ClO4 (1a)
[Cu(mppa)](ClO4)2 (1) and [Cu(mppa)(N3)]ClO4 (1a)
were obtained as blue and green crystals, respectively, which
were suitable for X-ray structural analysis. The molecular
structures of the cationic parts of 1 and 1a are shown in
Figures 1 and 2, respectively. Selected bond lengths and
angles around the copper cores are listed together in
Table 3. The CuII ion in 1 is coordinated by three pyridine
˚
nitrogen atoms of MPPA [CuϪN(2) ϭ 1.970(6) A,
˚
˚
CuϪN(3) ϭ 2.062(6) A, CuϪN(4) ϭ 2.079(6) A] in the trig-
onal plane and by one tertiary amine nitrogen and one
˚
pivalamido oxygen atom of MPPA [CuϪN(1) ϭ 2.006(7) A
II
˚
and CuϪO(1) ϭ 1.940(6) A] in the axial positions. The Cu
ion in the azide complex 1a has almost the same coordi-
nation mode as in 1 except for substitution of an azide ion
for the pivalamido oxygen atom of MPPA. The copper
Scheme 1. Tripodal pyridylamine ligands
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4379

K. Jitsukawa, H. Masuda et al.
d-d bands
FULL PAPER
Table 1. UV/Vis spectroscopic data for [Cu(L)(N3)]ϩ in MeCN
Complex
LMCT (N3ϪǞCuII)
λmax/nm (ε/Ϫ1cmϪ1
)
λmax/nm (ε/Ϫ1cmϪ1
)
[Cu(mppa)(N3)]ϩ (1a)
[Cu(mapa)(N3)]ϩ (2a)
[Cu(tpa)(N3)]ϩ (3a)
395 (2700)
403 (2940)
413 (2130)[a]
414 (2600)
647 (300), 833 (220)
670 (300), 878 (250)
674 (277), 882 (275)[a]
670 (300), 845 (210)
[Cu(6-metpa)(N3)]ϩ (4a)
[a]
Ref.[46]
60, where α and β represent two basal angles (β Ն α)],[47]
the coordination structures for 1 (0.81) and 1a (0.94) are
both almost trigonal-bipyramidal as listed in Table 3. As
shown by the above spectroscopic and structural results, it
is clear that the CuII complexes with an azide group exhibit
a trigonal-bipyramidal structure both in solution and in the
solid state. In the molecular structure of 1a, a hydrogen
bond was observed between the pivalamido NH group of
MPPA and the coordinated azide ion. The distance between
Table 2. ESR spectroscopic data for [Cu(L)(N3)]ϩ in MeCN
Complex
g||
|A|||/Gauss GЌ
|AЌ|/Gauss
[Cu(mppa)(N3)]ϩ (1a)
[Cu(mapa)(N3)]ϩ (2a)
[Cu(tpa)(N3)]ϩ (3a)
2.03 71
2.00 76
2.00 82
2.20 130
2.21 100
2.19
92
[Cu(6-metpa)(N3)]ϩ (4a) Ϫ[a]
Ϫ[a]
Ϫ[a]
Ϫ[a]
[a]
Broadened signal.
˚
N(5) and N(6) [2.893(6) A] corresponds well to a hydrogen
˚
Table 3. Selected bond lengths [A] and angles [°] for [Cu(mppa)](- bonding interaction (Figure 2), which apparently contrib-
ClO4)2 (1) and [Cu(mppa)(N3)]ClO4 (1a)
utes to the fixation of the azide ion, as found in the pre-
viously reported Cu-TPPA and Cu-BPPA complexes with
the pivalamido group [TPPA: tris{[6-(pivalamido)pyrid-2-
[Cu(mppa)](ClO4)2 (1)
yl]methyl}amine;
BPPA:
bis{[6-(pivalamido)pyrid-2-
˚
Bond length [A]
yl]methyl}(pyrid-2-ylmethyl)amine].[36Ϫ41]
Cu(1)ϪO(1)
Cu(1)ϪN(1)
Cu(1)ϪN(2)
1.940(6) Cu(1)ϪN(3)
2.006(7) Cu(1)ϪN(4)
1.970(6)
2.062(6)
2.079(6)
Bond angle [°]
O(1)ϪCu(1)ϪN(1)
O(1)ϪCu(1)ϪN(2)
O(1)ϪCu(1)ϪN(3)
O(1)ϪCu(1)ϪN(4)
176.0(2)
N(1)ϪCu(1)ϪN(2)
N(1)ϪCu(1)ϪN(3)
N(1)ϪCu(1)ϪN(4)
N(2)ϪCu(1)ϪN(3) 127.3(3)
N(2)ϪCu(1)ϪN(4) 125.3(3)
N(3)ϪCu(1)ϪN(4) 104.0(2)
85.3(3)
83.8(3)
82.6(3)
90.8(2)
98.6(3)
99.8(3)
[Cu(mppa)(N3)]ClO4 (1a)
˚
Bond length [A]
Cu(1)ϪN(6)
Cu(1)ϪN(1)
Cu(1)ϪN(2)
1.936(5) Cu(1)ϪN(3)
2.010(5) Cu(1)ϪN(4)
2.180(5) N(5)···N(6)
2.050(6)
2.070(5)
2.893(6)
Bond angle [°]
N(6)ϪCu(1)ϪN(1)
N(6)ϪCu(1)ϪN(2)
N(6)ϪCu(1)ϪN(3)
N(6)ϪCu(1)ϪN(4)
175.3(2)
96.5(2)
98.0(2)
N(1)ϪCu(1)ϪN(2)
N(1)ϪCu(1)ϪN(3)
N(1)ϪCu(1)ϪN(4)
N(2)ϪCu(1)ϪN(3) 116.7(2)
N(2)ϪCu(1)ϪN(4) 116.5(2)
N(3)ϪCu(1)ϪN(4) 119.2(2)
80.0(2)
81.0(2)
81.2(2)
Figure 1. ORTEP plots of [Cu(mppa)]2ϩ (1) with the atomic labe-
ling scheme; hydrogen atoms have been omitted for clarity
103.2(2)
Electrochemical Properties
In order to understand the electrochemical properties of
the CuII complexes with tripodal tetradentate ligands, the
center is surrounded by three pyridine nitrogen atoms from cyclic voltammograms of the azide complexes were meas-
˚
˚
MPPA [CuϪN(2) ϭ 2.180(5) A, CuϪN(3) ϭ 2.050(5) A, ured in MeCN under argon relative to the SCE. The cyclic
˚
CuϪN(4) ϭ 2.070(5) A] in the trigonal plane and one ter- voltammograms of 1a, 2a, 3a, and 4a showed a reversible
tiary amine nitrogen atom [CuϪN(1) ϭ 2.010(5) A] from one-electron redox potential wave. The redox potential val-
˚
MPPA and one azide nitrogen atom [CuϪN(6) ϭ 1.936(5) ues were converted into the NHE scale by adding 244.4
A] in the axial positions. Judging from the coordination mV,[48] and the electrochemical data are listed in Table 4.
˚
geometric parameter τ around the CuII ion [τ ϭ (β Ϫ α)/ The E1/2 values of the azide complexes are significantly dif-
4380
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386

Thermal Stability and Absorption Spectroscopic Behavior of (µ-Peroxo)dicopper Complexes
FULL PAPER
at 837 cmϪ1 for the Cu-MPPA system, which shifted to 792
cmϪ1 (∆ν ϭ 45 cmϪ1) when 18O-labeled dioxygen was used
and a corresponding peak for the Cu-MAPA complex was
observed at 847 cmϪ1, which shifted to 800 cmϪ1 (∆ν ϭ 45
cmϪ1) when 18O2 was used. The frequencies and 18O-iso-
tope shifts of these bands are characteristic of (trans-µ-1,2-
peroxo)dicopper() complexes.[14Ϫ25] The ESR spectra of
these oxygenated complexes in solution were silent which
also suggests that two copper() ions are bridged by a di-
oxygen molecule and are antiferromagnetically coupled.
On the basis of these spectroscopic observations, we con-
clude that the (trans-µ-1,2-peroxo)dicopper() complexes
[{Cu(mppa)}2(O2)]2ϩ (1b) and [{Cu(mapa)}2(O2)]2ϩ (2b)
have formed in solution.
Spectral Changes in the LMCT Bands of O2 Adduct
Complexes Affected by a Hydrogen Bonding Interaction
Figure 2. ORTEP plots of [Cu(mppa)(N3)]ϩ (1a) with the atomic
Bubbling dioxygen into an acetone solution containing
[Cu(L)]PF6 complexes with L ϭ MPPA or MAPA afforded
[{Cu(mppa)}2(O2)]2ϩ (1b) or [{Cu(mapa)}2(O2)]2ϩ (2b),
respectively, as described above. The intense charge-transfer
bands (LMCT) observed at 517 nm for the Cu-MPPA sys-
tem and at 503 nm for the Cu-MAPA system can be attri-
buted to the formation of a (trans-µ-peroxo)dicopper()
core in each case. The absorption spectra of four kinds of
µ-peroxide complexes namely 1b, 2b, [{Cu(tpa)}2(O2)]2ϩ
(3b),[16Ϫ23] and [{Cu(6-metpa)}2(O2)]2ϩ (4b),[44] are shown
in Figure 3 and Table 5. Interesting spectroscopic behavior
was observed as follows: the LMCT bands of the complexes
exhibited blue shifts in the order 4b Ͻ 3b Ͻ 1b Ͻ 2b. The
intensities of the shoulder peaks of the LMCT bands ob-
served in the former two complexes 1b and 2b at about
600 nm were quite weak compared with those in the latter
two complexes 3b and 4b. In the following section we dis-
cuss this by use of Solomon’s theoretical consideration.
Solomon et al. first explained the LMCT bands of cop-
labeling scheme; hydrogen atoms have been omitted for clarity
ferent from each other: those of 1a and 4a are in the range
of Ϫ40 mV whilst those of 2a and 3a are Ϫ138 and Ϫ89
mV, respectively (vs. NHE).
Table 4. Electrochemical parameters for [Cu(L)(N3)]ϩ in MeCN
(reduction and oxidation potentials are given relative to the NHE)
Complex
Epa/mV Epc/mV ∆E/mV E1/2/mV
[Cu(mppa)(N3)]ϩ (1a)
[Cu(mapa)(N3)]ϩ (2a)
[Cu(tpa)(N3)]ϩ (3a)
Ϫ4
Ϫ98
Ϫ37
Ϫ84
Ϫ178
Ϫ140
Ϫ85
80
80
103
101
Ϫ44
Ϫ138
Ϫ89
[Cu(6-metpa)(N3)]ϩ (4a) ϩ16
Ϫ34
Reaction of Copper(
I) Complexes with Dioxygen and
Characterization of the Oxygenated Complexes
The reactions of the CuI-MPPA or -MAPA complexes per() peroxide complexes using a mononuclear copper()
with dioxygen were performed in acetone and EtCN solu- model with a peroxide ion in the end-on mode (Fig-
tions, which were monitored by spectroscopic methods such ure 4).[49] The highest occupied molecular orbitals of the
as electronic absorption, resonance Raman and ESR spec- peroxide have two degenerate π* sets which split into two
troscopy. Bubbling dioxygen into the solution of each CuI energy levels upon binding to the copper() ion. One π*
complex at Ϫ78 °C resulted in an intense color change from orbital (π*σ) along the CuϪO bond has a larger overlap
light yellow to violet. The absorption spectra of these violet with the dσ orbital of the copper ion and is critically stabil-
species in acetone solution showed intense bands at 517 nm ized by this interaction. The other π* orbital (π*v) perpen-
(ε ϭ 5600 Ϫ1cmϪ1) and 503 nm (ε ϭ 7500 Ϫ1cmϪ1) for dicular to the dσ orbital undergoes a weaker d-π interac-
the Cu-MPPA and Cu-MAPA systems, respectively. These tion. On the basis of this consideration, there are two types
bands exhibited shoulder bands around 600 nm (ε ϭ 1500 of CT transitions from the peroxide to the copper() ion,

Ϫ1cmϪ1). The intense absorption bands in the visible re- that is, the band in the shorter wavelength region
gion have been tentatively assigned as resulting from charge (500Ϫ540 nm) corresponds to a π*σǞdσ transition and the
transfer (CT) transitions from the trans-µ-1,2-peroxo shoulder band at longer wavelength (ഠ 600 nm) can be as-
groups to the copper() centers.[14Ϫ25] A detailed interpret- cribed to a π*vǞdσ transition.
ation of the spectroscopic features of these CT bands for
Firstly, considering the π*σǞdσ transition wavelength re-
the Cu-MPPA and Cu-MAPA systems will be discussed in gion (500Ϫ540 nm), the LMCT band for 4b was observed
the following section together with those of the Cu-TPA at 537 nm, indicating that the energy gap between the π*σ
system.[16Ϫ23] The resonance Raman spectra of EtCN or and the dσ orbitals is relatively small in comparison with
acetone solutions containing these copperϪdioxygen ad- that of 3b at 523 nm, as shown in Table 5. This low energy
duct complexes measured at Ϫ78 °C (514 nm laser exci- shift of the π*σǞdσ transition band can be explained by a
tation) showed a strong resonance enhanced Raman peak decrease in the energy splitting of the d orbitals because the
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4381

K. Jitsukawa, H. Masuda et al.
FULL PAPER
Figure 3. Absorption spectra of [(CuL)2(O2)]2ϩ complexes in acetone at Ϫ78 °C [L ϭ MPPA (a), MAPA (b), TPA (c), 6-MeTPA(d)]
Table 5. Absorption spectroscopic data for [(CuL)2(O2)]2ϩ com-
plexes
L (Ligand)
λmax/nm (ε/Ϫ1cmϪ1
)
Ref.
MPPA (1b)
MAPA (2b)
TPA (3b)
517 (5600), 600 (1500)
503 (7500), 600 (1500)
524 (12000), 600 (8000)
537 (5500), 600 (4000)
this work
this work
[16Ϫ23]
[44]
6-MeTPA (4b)
ligation of the pyridine nitrogen atoms to the copper() ion
is weakened by the steric hindrance of the methyl group
substituents at the 6-position of the pyridine ring.[44,45] On
the other hand, the π*σǞdσ CT bands of 1b (517 nm) and
2b (503 nm) were observed in a higher energy region than
that of 3b (523 nm) in spite of the larger steric hindrance of
the 6-(pivalamido)- and 6-amino substituted derivatived. In
these cases, the pivalamido and amino groups in the 6-posi-
tions of the pyridine ring in MPPA and MAPA can be con-
sidered to form intramolecular hydrogen bonding inter-
actions with the ligating peroxide ion in the same mode as
in the previously reported monomeric (hydroperoxo)-
Figure 4. Schematic diagram of the energy levels of the molecular
orbitals participating in the copperϪperoxo bond
copper() complex [CuII(bppa)(OOH)]ϩ [BPPA ϭ bis{[6- 1a, 2a, 3a and 4a, also exhibited a similar tendency: the
(pivalamido)pyrid-2-yl]methyl}(2-pyridylmethyl)amine].[36]
LMCT energies of the azide complexes with MPPA and
The electronic absorption spectra of the azide complexes, MAPA detected at 395 and 403 nm are relatively larger than
4382
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386

Thermal Stability and Absorption Spectroscopic Behavior of (µ-Peroxo)dicopper Complexes
FULL PAPER
those of the azide complexes with TPA and 6-MeTPA ob- Table 6. The effects on the thermal stabilities of the (µ-per-
served at 413 and 414 nm. Indeed, in the crystal structures oxo)dicopper() species as a result of substitution at the
of the azide complexes with MPPA and MAPA, 1a and 2a, 6-position of pyridine ring are described in detail in the
the intramolecular hydrogen bonding interactions were following discussion.
clearly formed between the 6-amido/amino NH hydrogen
and the axially bound azide nitrogen atoms. These findings
Table 6. Decomposition rate constants of [(CuL)2(O2)]2ϩ complexes
suggest that similar hydrogen bonds can also be formed in
L (Ligand)
λmax/nm
kobsd./minϪ1 [a]
T/K
the corresponding (peroxo)dicopper() complexes, 1b and
2b. Taking this into account, it can be understood that the
higher energy shifts of the π*σǞdσ CT bands in the (per-
oxo)dicopper() species, 1b and 2b, were caused by a stabil-
izing π*σ orbital energy level giving the larger π*σϪdσ CT
energy gap.
MPPA (1b)
6-MeTPA (4b)
MPPA (1b)
MAPA (2b)
TPA (3b)
517
537
517
503
523
0.2 ϫ 10Ϫ3
39.4 ϫ 10Ϫ3
13.3 ϫ 10Ϫ3
2.5 ϫ 10Ϫ3
2.9 ϫ 10Ϫ3
183
183
213
213
213
In the π*vǞdσ transition wavelength region (ഠ 600 nm),
the shoulder LMCT bands of 1b and 2b are broadened as
shown in Figure 4. The shoulder LMCT absorbances of 1b
[a]
The kobsd. values are estimated by following the decrease of ab-
sorption band (λmax).
and 2b at 600 and 600 nm (ε ϭ 1500 and 1500 Ϫ1cmϪ1
)
The (µ-peroxo)dicopper() complex 4b is remarkably un-
are smaller than those of 3b and 4b at 600 and 600 nm (ε ϭ stable and its decomposition rate is the fastest of all the
8000 and 4000 Ϫ1cmϪ1), respectively. The decrease in the complexes listed in Table 6 (kobsd. ϭ 39.4 ϫ 10Ϫ3 minϪ1 at
π*vǞdσ CT absorbance would also be affected by the intra- 183 K). Unlike the other systems, the decomposition of 4b
molecular hydrogen bonding interaction. In the case of 3b at 213 K was too fast to allow estimation of the rate con-
and 4b without a hydrogen bonding moiety, the π*v orbital stant. This clearly indicates that the thermal stability of the
of the peroxide can overlap well with the dσ orbital of cop- (µ-peroxo)dicopper() complex is extensively decreased by
per because of the free rotation of the CuϪO bond in these the sterically hindered 6-methyl substituent around the me-
(peroxo)dicopper() complexes. In 1b and 2b, however, such tal center.[44,45] Substitution of the 6-pivalamido group in
a rotation around the CuϪO bond is apparently inhibited place of the 6-methyl substituent dramatically improves the
by the hydrogen bond formed between the groups in the 6- thermal stability and stabilized the (µ-peroxo)dicopper()
position of the pyridine ring and the ligating peroxide ion complex, 1b (kobsd. ϭ 0.2 ϫ 10Ϫ3 minϪ1 at 183 K). Further-
with the result that overlap of the π*v and the dσ orbitals more, the analogous 6-amino-substituted (µ-peroxo)dicop-
would become small enough so as to decrease the CT tran- per() complex 2b (kobsd. ϭ 2.5 ϫ 10Ϫ3 minϪ1) is more
sition probability.
stable than 1b (kobsd. ϭ 13.3 ϫ 10Ϫ3 minϪ1 at 213 K) and
In summary, the absorption spectroscopic behavior of the its thermal stability was improved to the same extent as that
(peroxo)dicopper() complexes in question can be inter- of 3b (kobsd. ϭ 2.9 ϫ 10Ϫ3 minϪ1), although the amino
preted in terms of the contribution of the hydrogen bonding group in the 6-position of pyridine ring is as bulky as the
ability of the NH group of the pivalamido or amino groups methyl group in 4b.
introduced into pyridine 6-position of the ligands.
The order of the thermal stability of these peroxo com-
plexes can therefore be determined as follows: 2b ഠ 3b Ͼ
1b ϾϾ 4b.The (µ-peroxo)dicopper complexes are partially
stabilized by the hydrogen bonding interaction, although
Thermal Stability of the (µ-Peroxo)dicopper Complexes
with Hydrogen Bonding Interaction Sites
In our previous report, we found that the copper() com- the stability was reduced by the adverse effect of the steric
plex with pivalamido at the 6-position of pyridine ring in bulk around the metal ion.
the ligand forms the stable (hydroperoxo)copper() com-
plex, [CuII(bppa)(OOH)]ϩ [BPPA ϭ bis{[6-(pivalamido)py-
rid-2-yl]methyl}(2-pyridylmethyl)amine][36] which remains
stable in solution at room temperature for more than one
Conclusion
month. The first crystal structure of a monomeric (hydro-
In order to examine the mode of the hydrogen bonding
peroxo)copper() complex [CuII(bppa)(OOH)]ϩ revealed interaction and its effect on the (µ-peroxo)dicopper() spec-
that the pivalamido NH group of BPPA interacts with the ies, we have prepared copper complexes with the tripodal
ligated hydroperoxide oxygen atom by hydrogen bonding, tetradentate ligands MPPA and MAPA which bear a hydro-
thus promoting its thermal stability.[36] Based on this study, gen bonding site . The crystal structures of the azide com-
we expected that the hydrogen bond interaction might sta- plexes 1a and 2a revealed that pivalamido and amino NH
bilize (µ-peroxo)dicopper() species generated from the Cu- groups in 6-position of the pyridine ring can interact with
MPPA and -MAPA systems. The thermal stability of these the axially coordinated azide ion via the hydrogen bond.
peroxo species at 183 or 213 K was established by monitor- The tripodal ligands with a hydrogen bonding ability ex-
ing the decrease in their LMCT absorbances. The reduction erted significant influence on two LMCT bands of the (µ-
of the LMCT bands occurred with first-order kinetics, dem- peroxo)dicopper() species. The energy of the π*σǞdσ CT
onstrating the decomposition of the (µ-peroxo)dicopper() transition was raised and the absorbance of the π*vǞdσ
species. The decomposition rate constants are listed in CT band was decreased. Such characteristic spectroscopic
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4383

K. Jitsukawa, H. Masuda et al.
FULL PAPER
2 H), 7.15 (m, 2 H), 7.28 (d, 2 H), 7.56 (d, 2 H), 7.66 (t, 3 H), 7.95
(b, 1 H), 8.06 (b,1 H), 8.10 (d, 1 H), 8.53 (d, 2 H) ppm.
behavior was interpreted in terms of stabilization of the
π*σ orbital and restriction of rotation of the CuϪO bond
by the hydrogen bond between the NH group and the
axially coordinated peroxide groups of the copper com-
plexes. Finally, the hydrogen bonding interaction was found
to overcome the adverse effect of steric bulk and thus
stabilize the (µ-peroxo)dicopper() complexes.
[(6-Aminopyrid-2-yl)methyl]bis(pyrid-2-ylmethyl)amine (MAPA): To
an ethanol solution (500 mL) of MPPA (3.89 g, 10.0 mmol) was
added KOH (28.1 g, 0.50 mol). The solution was stirred at 50 °C
for 1 week. After removal of the solvent from the reaction mixture
by evaporation in vacuo, the resultant crude brownish oil was dis-
solved in dichloromethane (100 mL) which was washed with water
and dried with MgSO4. The resultant solution was concentrated in
vacuo to give the crude product as an oil. Pure MAPA was ob-
tained as colorless needle-like crystals by recrystallization from di-
Experimental Section
1
ethyl ether (2.13 g, 70.0% yield). H NMR (CDCl3): δ ϭ 3.54 (s, 2
Materials and Measurements: Reagents and solvents employed were
of the highest grade available. All solvents for spectroscopy were
further purified by distillation before use. Other chemicals were
used without further purification. Tris(pyrid-2-ylmethyl)amine
(TPA) and [(6-methylpyrid-2-yl)methyl]bis(pyrid-2-ylmethyl)amine
(6-MeTPA) were prepared using literature methods.[16,44] Electronic
absorption spectra were recorded at low temperature with a JASCO
Ubest-35 spectrophotometer equipped with an Oxford Variable
Temperature Liquid Nitrogen Cryostat Optistant. X-Band ESR
spectra of frozen solutions were recorded at 77 K by using a JEOL
RE-1X ESR spectrometer. 1H NMR spectra were measured with a
Bruker Avance-600 spectrometer with chemical shift values refer-
enced relative to TMS as an internal standard. Cyclic voltammetric
measurements were performed using a Bioanalytical Systems
(BAS) CV-1B electrochemical analyzer. A three-electrode system
was used with a 3-mm diameter glassy carbon electrode as the
working electrode, a saturated calomel electrode (SCE) as the refer-
ence electrode and a Pt-wire electrode as the counter electrode in a
glass cell having a working compartment of approximately 3 mL
in volume. All measurements were made in solution at 25 °C under
H), 3.76 (s, 4 H), 5.79 (s, 2 H), 6.30 (d, 1 H), 6.73 (d, 1 H), 7.24 (t,
2 H), 7.35 (t, 1 H), 7.62 (d, 2 H), 7.77 (t, 1 H), 8.48 (d, 2 H) ppm.
Synthesis of Cu Complexes
Preparation of [Cu(mppa)](ClO4)2: To a stirred MeOH solution (10
mL) of Cu(ClO4)2·6H2O (74.1 mg, 0.2 mmol) was added MPPA
(77.8 mg, 0.2 mmol). After the resultant mixture was allowed to
stand at room temperature for a few days, blue crystals of
[Cu(mppa)](ClO4)2, suitable for X-ray structural analysis, were ob-
tained. Yield: 109 mg (85%). C23H27Cl2CuN5O9 (651.94): calcd. C
42.37, H 4.17, N 10.73; found C 42.57, H 4.16, N 11.05.
Preparation of [Cu(mppa)(N3)]ClO4: To a stirred MeCN solution
(10 mL) of [Cu(mppa)](ClO4)2 (151.9 mg, 0.2 mmol) was added
NaN3 (13.0 mg, 0.2 mmol). A green precipitate formed immedi-
ately. After filtration, recrystallization of the precipitate from
MeCN gave plate-like green single crystals, suitable for X-ray struc-
tural analysis. Yield: 85 mg (71%). C23H27ClCuN8O5 (594.51):
calcd. C 46.46, H 4.47, N 18.84; found C 46.38, H 4.47, N 19.15.
argon with tetra(n-butyl)ammonium tetrafluoroborate (0.1 ) as a X-ray Structural Analysis of [Cu(mppa)](ClO4)2 and [Cu(mppa)(N3)-
supporting electrolyte at a scan rate of 100 mVsϪ1. The potential
of the regular ferrocene/ferrocenium (Fc/Fcϩ) redox couple in
acetonitrile was Ϫ0.33 V under our experimental conditions. In
order to discuss the electrochemical values in comparison with
other data, all the electrochemical potentials were converted into
values with the normal hydrogen electrode (NHE) as a standard by
adding 244.4 mV. Resonance Raman spectra were recorded with
a liquid-nitrogen-cooled CCD detector (Model LN/CCD-1300-PB,
]ClO4: Crystals suitable for X-ray diffraction measurements were
mounted on glass fibers. The diffraction data were collected with
a Rigaku Mercury diffractometer using graphite-monochromated
Mo-Kα radiation at Ϫ100 °C with the oscillation technique. Crystal
data and experimental details are listed in Table 7. All structures
were solved by a combination of direct methods and Fourier tech-
niques. Non-hydrogen atoms were anisotropically refined by full-
matrix least-squares calculations. Hydrogen atoms were included
Princeton Instrument) attached to a 100-cm single polychromator but not refined. Refinements were continued until all shifts were
(Model MC-100DG, Ritsu Oyo Kogaku). The excitation was pro-
vided by the 476.5-nm line of an Ar laser (Model GLG3200, NEC).
smaller than one-third of the standard deviations of the parameters
involved. Atomic scattering factors and anomalous dispersion
16O2 samples were prepared by bubbling dry dioxygen into acetone terms were taken from the International Tables for X-ray Crystal-
or EtCN solutions of the copper() complexes with tetradentate
lography.[50] All calculations were carried out with a Japan SGI
ligands at Ϫ78 °C. Isotopic substitution of the peroxo oxygen workstation computer using the teXsan crystallographic software
atoms bridged to the dicopper ions was accomplished by oxygen-
ation of the copper() complexes with 18O2. All measurements were
carried out with a spinning cell maintained at Ϫ78 °C by a stream
of liquid N2 vapor.
package.[51] CCDC-211622 and -211623 contain the crystallo-
graphic data for this paper. This data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/ or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ [Fax:
(internat.) ϩ 44-1223-336-033; E-mail: depost@ccdc.cam.ac.uk].
Synthesis of Ligands
Reaction of [Cu(L)]PF6 (L ؍ MPPA, MAPA, TPA, 6-MeTPA) with
Dioxygen: Sample solutions of [Cu(L)]PF6 (L ϭ MPPA, MAPA,
TPA, 6-MeTPA) were prepared by mixing [Cu(MeCN)4]PF6
{[6-(Pivalamido)-2-pyridyl]methyl}bis(pyrid-2-ylmethyl)amine
(MPPA): Reaction of the primary amine, 2-(aminomethyl)-6-(pival-
amido)pyridine,[37,38] (2.80 g, 13.5 mmol) with 2 equiv. of 2-(chloro- (0.7 mg, 2.0 mmol) and each ligand (2.1 mmol) in acetone (4 mL)
methyl)pyridine (5.25 g, 32.0 mmol) was carried out in a dioxane/
at room temperature under nitrogen. The resultant solutions con-
H2O (4:1) solution (300 mL) containing KOH (2.92 g, 52.0 mmol). taining [Cu(L)]PF6 were oxygenated by bubbling dioxygen through
The solution was stirred at 50 °C for 3 d followed by removal of them at Ϫ78 °C. The formation and decomposition of the peroxo
the solvent by evaporation in vacuo. Dissolving the resultant crude
brownish oil in diethyl ether and allowing it to stand at room tem-
intermediates were monitored by following the increase or decrease
in their characteristic ligandϪmetal change transfer (LMCT) ab-
sorption bands at λmax ϭ 517, 503, 524, and 537 nm, for
perature gave colorless needle-like crystals of MPPA (2.32 g, 45.9%
1
yield). H NMR (CDCl3): δ ϭ 1.33 (s, 9 H), 3.78 (s, 2 H), 3.89 (s, [{Cu(L)}2(O2)]2ϩ [L ϭ MPPA (1b), MAPA (2b), TPA (3b), 6-
4384
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386

Thermal Stability and Absorption Spectroscopic Behavior of (µ-Peroxo)dicopper Complexes
FULL PAPER
Table 7. Crystallographic data for [Cu(mppa)](ClO4)2 (1) and [Cu(mppa)(N3)]ClO4 (1a)
[Cu(mppa)](ClO4)2 (1)
[Cu(mppa)(N3)]ClO4 (1a)
Empirical formula
Formula mass
Crystal system
Space group
C21H26Cl2CuN5O9
743.64
C23H27ClCuN8O5
594.52
triclinic
monoclinic
P21/a (No. 14)
14.156(2)
10.032(1)
18.645(2)
90
102.262(7)
90
2587.5(6)
4
1.526
1228.00
9.98
0.71070
173
¯
P1 (No. 2)
˚
a [A]
11.721(4)
14.191(2)
9.897(1)
103.058(10)
90.34(2)
73.26(2)
1535.6200
2
1.608
752.00
14.39
0.71070
298
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
V [A ]
Z
Dcalcd. [g cmϪ3
F(000)
]
µ [cmϪ1
λ [A]
]
˚
T [K]
No. of refls. measured
4361
2616
0.081/0.111
1.02
5832
4452
0.094/0.235
1.61
No. of refls. used [I Ͼ 2σ(I0)]
[b]
R1 [a]/Rw
GOF
[a]
[b]
2
R1 ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|. Rw ϭ [Σw(|Fo| Ϫ |Fo|)2/Σw|Fo|2]1/2; w ϭ 4Fo /σ2(Fo)2.
[11]
K. D. Karlin, Z. Tyeklar, A. D. Zuberbuhler, in Bioinorganic
Chemistry (Ed.: J. Reedijk), Marcel Dekker, Inc., New York,
1993, p. 261.
E. I. Solomon, F. Tuczek, D. E. Root, C. A. Brown, Chem.
Rev. 1994, 94, 827Ϫ856.
MeTPA (4b)], respectively. The thermal stability of the peroxo spec-
ies was examined under constant temperature (183 or 213 K) by
following the absorption intensity at 5-min intervals for 12 or 24 h.
The decomposition process of the respective complex was analyzed
using first order kinetics in which ln([A]/[A0]) values were plotted
according to the time course (where [A0] and [A] are absorption
intensities of the LMCT bands observed initially and at a given
time). It was observed that decreasing of the LMCT bands exhib-
ited good first-order kinetics for each peroxo complex.
[12]
[13]
[14]
E. I. Solomon, M. D. Lowery, Science 1993, 259, 1575Ϫ1581.
A. G. Blackman, W. B. Tolman, in Structure and Bonding (Ed.:
B. Meunier), Springer Verlag, Berlin, 2000, 97, p. 179Ϫ211.
S. Schindler, Eur. J. Inorg. Chem. 2000, 2311Ϫ2326.
[15]
[16]
´
R. R. Jacobson, Z. Tyeklar, A. Farooq, K. D. Karlin, S. Liu,
J. Zubieta, J. Am. Chem. Soc. 1988, 110, 3690Ϫ3692.
M. J. Baldwin, P. K. Ross, J. E. Pate, Z. Tyeklar, K. D. Karlin,
[17]
[18]
[19]
´
E. I. Solomon, J. Am. Chem. Soc. 1991, 113, 8671Ϫ8679.
N. Wei, N. N. Murthy, Q. Chen, J. Zubieta, K. D. Karlin, Inorg.
Chem. 1994, 33, 1953Ϫ1965.
Acknowledgments
This work was supported partly by a Grant-in-Aid for Scientific
Research (No. 11228203, 12304039) from the Ministry of Edu-
cation, Science, Sports, and Culture of Japan and in part by a grant
from the NITECH 21st Century COE Program (S. Y. and H. M.)
to which our thanks are due. A. W. is grateful to the Japan Society
for the Promotion of Science for a JSPS Research Fellowship for
Young Scientists.
´
D.-H. Lee, N. Wei, N. N. Murthy, Z. Tyeklar, K. D. Karlin, S.
Kaderli, B. Jung, A. D. Zuberbühler, J. Am. Chem. Soc. 1995,
117, 12498Ϫ12513.
[20]
[21]
[22]
[23]
K. D. Karlin, D.-H. Lee, S. Kaderli, A. D. Zuberbühler, Chem.
Commun. 1997, 475Ϫ476.
K. D. Karlin, S. Kaderli, A. D. Zuberbühler, Acc. Chem. Res.
1997, 30, 139Ϫ147.
C. X. Zhang, S. Kaderli, M. Costas, E. Kim, Y.-M. Neuhold,
K. D. Karlin, Inorg. Chem. 2003, 42, 1807Ϫ1824.
M. Schatz, M. Becker, F. Thaler, F. Hampel, S. Schindler, R.
R. Jacobson, Z. Tyeklar, N. N. Murthy, P. Ghosh, Q. Chen, J.
Zubieta, K. D. Karlin, Inorg. Chem. 2001, 40, 2312Ϫ2322.
M. Becker, F. W. Heinemann, S. Schindler, Chem. Eur. J. 1999,
5, 3124Ϫ3129.
M. Weitzer, S. Schindler, G. Brehm, S. Schneider, E. Hoerm-
ann, B. Jung, S. Kaderli, A. D. Zuberbuehler, Inorg. Chem.
2003, 42, 1800Ϫ1806.
[1]
Handbook on Metalloproteins (Eds.: I. Bertini, A. Sigel, H. Si-
gel), Marcel Dekker, Inc., New York, 2001.
[2]
J. P. Klinman, Chem. Rev. 1996, 96, 2541Ϫ2561.
[3]
Mechanistic Bioinoganic Chemistry (Eds.: H. H. Thorp, V. L.
[24]
[25]
Pecoraro), American Chemical Society, Washington, D.C.,
1995.
[4]
M. Momenteau, C. A. Reed, Chem. Rev. 1994, 94, 659Ϫ698.
[5]
J. H. Dawson, Science 1988, 240, 433Ϫ439.
[6]
A. L. Feig, S. J. Lippard, Chem. Rev. 1994, 94, 759Ϫ805.
L. Que, Jr., in Bioinorganic Catalysis (Ed.: J. Reedijk), Marcel
[26]
[7]
S. Mahaptra, S. Kaderli, A. Llobet, Y.-M. Neuhold, T. Palan-
´
che, J. A. Halfen, V. G. Young, Jr., T. A. Kaden, L. Que, Jr.,
Dekker, Inc., New York, 1999, p. 269.
S. Fox, K. D. Karlin, in Active Oxygen in Biochemistry (Eds.: J.
[8]
A. D. Zuberbühler, W. B. Tolman, Inorg. Chem. 1997, 36,
6343Ϫ6356.
S. Valentine, C. S. Foote, A. Greenberg, J. F. Liebman), Blackie
Academic & Professional, Chapman & Hall, Glasgow, 1995,
p. 188.
N. Kitajima, Y. Moro-oka, Chem. Rev. 1994, 94, 737Ϫ757.
Bioinorganic Chemistry of Copper (Eds.: K. D. Karlin, Z. Tyek-
[27]
[28]
P. L. Holland, K. R. Rodgers, W. B. Tolman, Angew. Chem.
Int. Ed. 1999, 38, 1139Ϫ1142.
H. V. Obias, Y. Lin, N. N. Murthy, E. Pidcock, E. I. Solomon,
M. Ralle, N. J. Blackburn, Y.-M. Neuhold, A. D. Zuberbühler,
K. D. Karlin, J. Am. Chem. Soc. 1998, 120, 12960Ϫ12961.
[9]
[10]
lar), Chapman & Hall, New York, 1993.
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4385

K. Jitsukawa, H. Masuda et al.
FULL PAPER
[29]
[40]
[41]
[42]
[43]
J. A. Halfen, S. Mahapatra, E. C. Wilkinson, S. Kaderli, V. G.
M. Harata, K. Jitsukawa, H. Masuda, H. Einaga, Bull. Chem.
Soc. Jpn. 1998, 71, 1031Ϫ1038.
M. Harata, K. Jitsukawa, H. Masuda, H. Einaga, Chem. Lett.
1996, 813Ϫ814.
L. M. Berreau, S. Mahapatra, J. A. Halfen, V. G. Young, Jr.,
W. B. Tolman, Inorg. Chem. 1996, 135, 6339Ϫ6342.
C. E. MacBeth, A. P. Golombek, V. G. Young, Jr., C. Yang,
K. Kuczera, M. P. Hendrich, A. S. Borovik, Science 2000,
289, 938Ϫ941.
K. Uozumi, Y. Hayashi, M. Suzuki, A. Uehara, Chem. Lett.
1993, 963Ϫ966.
H. Nagao, N. Komeda, M. Mukaida, M. Suzuki, K. Tanaka,
Inorg. Chem. 1996, 35, 6809Ϫ6815.
D. -H. Lee, N. N. Murthy, K. D. Karlin, Inorg. Chem. 1997,
36, 5785Ϫ5792.
A. W. Addison, T. N. Rao, J. Reedijk, J. Rijn, G. C. Verschoor,
J. Chem. Soc., Dalton Trans. 1984, 1349Ϫ1356.
J. O’M. Bockris, A. K. N. Reddy, Modern Electrochemistry, Ple-
num Press, New York, 1970.
J. E. Pate, R. W. Cruse, K. D. Karlin, E. I. Solomon, J. Am.
Chem. Soc. 1987, 109, 2624Ϫ2630.
Young, Jr., L. Que, Jr., A. D. Zuberbühler, W. B. Tolman, Sci-
ence 1996, 217, 1397Ϫ1400.
S. Mahapatra, J. A. Halfen, E. C. Wilkinson, G. Pan, X. Wang,
[30]
V. G. Young, Jr., C. J. Cramer, L. Que, Jr., W. B. Tolman, J.
Am. Chem. Soc. 1996, 118, 11555Ϫ11574.
P. L. Holland, W. B. Tolman, Coord. Chem. Rev. 1999, 190,
855Ϫ869.
[31]
[32]
P. L. Holland, C. J. Cramer, E. C. Wilkinson, S. Mahapatra,
[44]
[45]
[46]
[47]
[48]
[49]
[50]
K. R. Rodgers, S. Itoh, M. Taki, S. Fukuzumi, L. Que, Jr., W.
B. Tolman, J. Am. Chem. Soc. 2000, 122, 792Ϫ802.
S. Itoh, M. Taki, H. Nakao, P. L. Holland, W. B. Tolman, L.
[33]
Que, Jr., S. Fukuzumi, Angew. Chem. Int. Ed. 2000, 39,
398Ϫ400.
[34]
S. Itoh, H. Nakao, L. M. Berreau, T. Kondo, M. Komatsu, S.
Fukuzumi, J. Am. Chem. Soc. 1998, 120, 2890Ϫ2899.
V. Mahadevan, Z. Hou, A. P. Cole, D. E. Root, T. K. Lal, E.
[35]
I. Solomon, T. D. P. Stack, J. Am. Chem. Soc. 1997, 119,
11996Ϫ11997.
[36]
A. Wada, M. Harata, K. Hasegawa, K. Jitsukawa, H. Masuda,
M. Mukai, T. Kitagawa, H. Einaga, Angew. Chem. Int. Ed.
1998, 37, 798Ϫ799.
M. Harata, K. Jitsukawa, H. Masuda, H. Einaga, J. Am.
International Tables for X-ray Crystallography (Eds.: J. A. Ibers,
W. C. Hamilton), Kynoch Press, Birmingham, U. K., 1974,
vol. IV.
[37]
[51]
Chem. Soc. 1994, 116, 10817Ϫ10818.
M. Harata, K. Jitsukawa, H. Masuda, H. Einaga, Chem. Lett.
Texsan, Crystal Structure Analysis Package, Molecular Struc-
ture Corporation (1985), 1992.
[38]
1995, 61Ϫ62.
Received April 1, 2003
[39]
M. Harata, K. Jitsukawa, H. Masuda, H. Einaga, Bull. Chem.
Early View Article
Soc. Jpn. 1998, 71, 637Ϫ645.
Published Online October 22, 2003
4386
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4378Ϫ4386