Thiomethyl substituted dicopper complexes: Attempts to reproduce the asymmetry of the active site from type 3 copper enzymes

Article abstract of DOI:10.1002/zaac.201300059

Two new dinucleating phenol-based ligands (m-HL_SMe and p-HL _SMe) bearing pyridine-containing pendant arms with a SMe group on one pyridine (meta or para position relative to the pyridine nitrogen atom) have been synthesized. After coordination by two copper(II) ions, the corresponding μ-phenoxido, μ-hydroxido dicopper(II) complexes were isolated and characterized by UV/Vis, EPR spectroscopy, single-crystal X-ray analysis (for the complex with the SMe substituent at the meta position) and electrochemistry. The presented compounds mimic the active site of type 3 copper enzymes and in particular the distinct environments of the copper ions.Both complexes are active as catalysts for the oxidation of 3, 5-di-tert-butylcatechol to the respective quinone. The catalytic properties of the complexes depend on substrate binding, as reflected by the K_M values determined for the complexes in presence of 3, 5-dtbc and are not correlated directly with the redox properties of the dicopper center. Copyright

Full text of DOI:10.1002/zaac.201300059

ARTICLE
DOI: 10.1002/zaac.201300059
Thiomethyl Substituted Dicopper Complexes: Attempts to Reproduce the
Asymmetry of the Active Site from Type 3 Copper Enzymes
Wassim Rammal,[a,b] Katalin Selmeczi,[a,c] Christian Philouze,[a] Eric Saint-Aman,[a]
Jean-Louis Pierre,[a] and Catherine Belle*[a]
Keywords: Bioinorganic chemistry; Copper; Catechol oxidase; Tyrosinase; Structure-property relationships
Abstract. Two new dinucleating phenol-based ligands (m-HLSMe and mimic the active site of type 3 copper enzymes and in particular the
p-HLSMe) bearing pyridine-containing pendant arms with a SMe group distinct environments of the copper ions.Both complexes are active as
on one pyridine (meta or para position relative to the pyridine nitrogen
catalysts for the oxidation of 3,5-di-tert-butylcatechol to the respective
atom) have been synthesized. After coordination by two copper(II) quinone. The catalytic properties of the complexes depend on substrate
ions, the corresponding μ-phenoxido, μ-hydroxido dicopper(II) com-
binding, as reflected by the KM values determined for the complexes
plexes were isolated and characterized by UV/Vis, EPR spectroscopy,
in presence of 3,5-dtbc and are not correlated directly with the redox
single-crystal X-ray analysis (for the complex with the SMe substituent properties of the dicopper center.
at the meta position) and electrochemistry. The presented compounds
apart in a trigonal pyramidal arrangement (Figure 1A). In the
Introduction
reduced deoxy state, the copper atoms are not bridged
(CuI···CuI distance = 4.4 Å) and a water molecule is coordi-
nated to CuA. The coordination sphere of CuA is distorted tri-
gonal pyramidal, whereas the coordination sphere of CuB,
which is bonded to three histidine ligands, can be described as
square planar with a vacant coordination site.
Catechol oxidases (COs)[1] belong to the family of type 3
copper enzymes, which also includes tyrosinases (Tys).[2]
A
vast body of literature concerning plant and fungal enzymes
use the designation of polyphenol oxidases (PPOs) without
distinguishing between Ty and CO. Both catalyze the oxidation
of o-diphenols to o-quinones in the presence of dioxygen,
while tyrosinases can also convert monophenols to
o-diphenols. These enzymes are characterized by a dinuclear
copper active site in a native met CuII–CuII form that is EPR-
silent due to a strong antiferromagnetic coupling between the
bridged copper(II) ions. The crystal structure of catechol ox-
idase from sweet potatoes (Ipomoea batatas, ibCO) has been
reported in different states: the oxidized CuII–CuII met form,
the reduced deoxy CuI–CuI form, and the species with bound
phenylthiourea (ptu) inhibitor.[3] In the met state, both metal
binding sites involve three histidine ligands, and the two cupric
ions, which are likely bridged by a hydroxide ion, are 2.87 Å
Figure 1. The active site of (A) Ipomoea batatas catechol oxidase (met
form - PDB code: 1BT3)[3] and (B) Agaricus bisporus mushroom tyro-
sinase (reduced form - PDB code: 2y9w).[4]
* Dr. C. Belle
Fax: +33-476-514-836
E-Mail: catherine.belle@ujf-grenoble.fr
[a] Département de Chimie Moléculaire, Equipe CIRe
Université J. Fourier, UMR-CNRS 5250, ICMG FR-2607
BP 53, 38041, Grenoble, Cedex 09, France
An interesting feature of the dinuclear metal center is a
covalent thioether bond between a carbon atom of His109,
[b] Present adress: Laboratoire de Physio-Toxicité Environnementale, which is a ligand on CuA, and the sulfur atom of Cys92 (Fig-
EDST ER 017
ure 1A). The recent X-ray structure of reduced Vitis vinifera
PPO[5] reveals that this covalent bond puts additional structural
Université Libanaise
Faculté des Sciences, Section V
Nabatieh, Lebanon
restraints on the ligand sphere of the CuA center. A similar
type of bond was reported some time ago in the sequence ho-
mology of Neurospora crassa tyrosinase[6] and more recently
in the solved three-dimensional structure of mushroom Aga-
ricus bisporus tyrosinase (reduced form, Figure 1B).[4] The ab-
sence of such a Cys-His bridge in bacterial and human tyrosi-
[c] Present adress: Laboratoire SRSMC
Université de Lorraine
UMR-CNRS 7565
BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex, France
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201300059 or from the au-
thor.
Z. Anorg. Allg. Chem. 2013, 639, (8-9), 1477–1482
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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W. Rammal, K. Selmeczi, C. Philouze, E. Saint-Aman, J.-L. Pierre, C. Belle
ARTICLE
nase indicates that thioether modification does not play a direct
role in the functional activity of the enzymes and only imposes
structural constraints (i.e., ensuring trigonal pyramidal geome-
try) around the CuA copper center. This thioether bond may
also prevent both the displacement of the His bound to the Cys
and bidentate binding of the substrate to a single CuII ion.
This may, in turn, optimize the redox potential of the metal for
catechol substrate oxidation and allow rapid electron transfer
during redox processes. Despite clarification of the active-site
structures of different forms of CO and Ty by X-ray crystal-
lography, the role of this thioether bond at the binuclear copper
center remains unclear.[7]
Results and Discussion
Synthesis
The new unsymmetrical ligands, m-HLSMe and p-HLSMe
,
were synthesized from intermediate 1 (Scheme 1) according a
known procedure.[13] They possess a thiomethyl group in the
meta or para position, respectively with respect to the pyridine
nitrogen atom. The general synthetic pathways for m-HLSMe
and p-HLSMe are depicted in Scheme 1. Details of the synthe-
ses of the m-HLSMe and p-HLSMe ligands and secondary
amines 2 and 3 are given in the Experimental Section and Sup-
porting Information, respectively.
Well-suited biomimetic models can be used to elucidate the
likely behavior of the two copper atoms in distinct environ-
ments and the involvement of the Cys-His thioether bond in
the catalytic activity of the enzyme. A large number of dinu-
clear model complexes of CO and Ty are described in litera-
ture,[8] but few complexes that mimic the Cys-His thioether
bond have been reported.[9] The rational design of a dinucleat-
ing ligand that induces controlled synthesis of the targeted un-
symmetrical complexes is a prerequisite for such models.[10]
Dinucleating phenol-based ligands have previously been suc-
cessfully applied as structural and functional models of the CO
active site;[8a,11] the introduction of a thioether group to one
arm of this series of ligands (Scheme 1) may provide new
model complexes. Such unsymmetrical ligands have contrib-
uted heavily to improved understanding of the spectroscopic
properties and reactivity of corresponding homo- or hetero-
dinuclear complexes with respect to their symmetrical ana-
logs.[12] In this paper, we describe the synthesis and catalytic
activities of two new models with unsymmetrical dinuclear
copper chelating ligands (Scheme 1). The asymmetry arises
from the presence of a thiomethyl substituent introduced at the
para or meta position relative to the pyridine nitrogen atom on
one arm of the ligand. In this way, the SMe group can influ-
ence the electron density on the nitrogen atom coordinated to
the metal ion via the electron donating (p-SMe) or electron
withdrawing (m-SMe) effect.
Synthesis and Characterization of the Dinuclear Copper(II)
Complexes
The synthesis of the doubly bridged dinuclear copper(II)
complex [Cu2(L)(μ-OH)](ClO4)2 from the symmetric HL li-
gand was described previously by us.[14] A similar procedure
was applied using m-HLSMe and p-HLSMe (Scheme 2). Two μ-
phenoxido, μ-hydroxido dicopper(II) complexes were prepared
via the addition of two equivalents of Cu(ClO4)2·6H2O to a
solution of m-HLSMe or p-HLSMe in acetonitrile containing
three equivalents of triethylamine. The complexes (Scheme 2)
were isolated in the solid state as green powders. Crystals of
Scheme 2. Dicopper(II) complexes included in this work.
Scheme 1. Dinucleating ligands included in this work and the synthetic strategy.
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Thiomethyl Substituted Dicopper Complexes
[Cu2(m-LSMe)(μ-OH)](ClO4)2 suitable for X-ray single-crystal TheCu1–O1–Cu2,Cu1–O2–Cu2, O1–Cu1–O2,andO1–Cu2–O2
analysis were obtained by slow diffusion of tetrahydrofuran angles are 100.99, 104.23, 77.49, and 76.99°, respectively,
into an acetonitrile solution.
leading to a Cu1···Cu2 distance of 2.9755(8) Å, which is sim-
ilar to the intermetallic distance (2.966 Å) in [Cu2(L)(μ-
OH)](ClO4)2.[14]
Crystal Structure Description
The solid-state structure of [Cu2(m-LSMe)(μ-OH)](ClO4)2
contains one associated THF solvent molecule. An ORTEP
view of dicationic complex is shown in Figure 2 for the ma-
jority form (see the Experimental Section for details on the
crystal structure parameters). Selected bond lengths and angles
are given in Table S1. The crystal structure reveals that the two
copper atoms are doubly bridged by phenoxido and hydroxido
groups. Cu1 and Cu2 are pentacoordinated by the tertiary
amine, two pyridine nitrogen atoms, and two bridging oxygen
atoms. Similar to the coordination geometry of each copper
center in [Cu2(L)(μ-OH)](ClO4)2,[14] the geometries of the
copper ions are distorted trigonal bipyramidal (with σ val-
ues[15] of 0.85 and 0.69 for Cu1 and Cu2, respectively).
Characterization in Solution
UV/Vis spectra of [Cu2(m-LSMe)(μ-OH)](ClO4)2 and
[Cu2(p-LSMe)(μ-OH)](ClO4)2 recorded in acetonitrile at 298 K
show two transitions in the regions of 440–460 and 785–820
nm (Table 1). The first transition corresponds to charge trans-
fer from the phenoxido and hydroxido bridges to the copper(II)
ions, whereas the second one is assigned to the d–d transition
of the CuII ions.[16] These transitions are slightly affected by
the position of the electron-donating SMe substituent (i.e.,
para or meta) with respect to the corresponding pyridine nitro-
gen atom.
As previously observed with [Cu2(L)(μ-OH)](ClO4)2,[14] the
two μ-phenoxido, μ-hydroxido complexes are EPR silent in
frozen solutions, which indicates a strong antiferromagnetic
coupling (S = 0) ground spin state between the two copper(II)
atoms. This observation is consistent with
a doubly
bridged structure and the short copper–copper distance evi-
[14]
denced in the solid state for [Cu2(L)(μ-OH)](ClO4)2
[Cu2(m-LSMe)(μ-OH)](ClO4)2.
and
The electrochemical behavior of the series of complexes was
investigated by cyclic voltammetry (CV) in acetonitrile solu-
tion, with tetra-n-butylammonium perchlorate (TBAP) as sup-
porting electrolyte (0.1 m). The potentials were referenced to a
Ag/10 mM AgNO3 + CH3CN + 0.1 m TBAP reference elec-
trode (regular ferrocene/ferrocenium redox couple = +0.089 V
under the experimental conditions). The CV curves of both
complexes are very similar and close to the one published for
the [Cu2(L)(μ-OH)](ClO4)2,[14] suggesting that the addition of
a SMe group on one pyridine of the ligand in a m- or p-posi-
tion does not affect the electrochemical behavior of the corre-
sponding di-nuclear complex. The CV curves are characterized
by three electrochemical signals (Table 1, Figure 3). In the
negative region of the potential, the first wave at –0.95V and
Figure 2. Plot of dication [Cu2(m-LSMe)(μ-OH)]2+ in its majority form
(see Exp. Sect.). Hydrogen atoms (except for the hydroxido bridge)
and ClO4– counteranions were omitted for clarity. Ellipsoids are drawn
at the 30% probability level.
In this structure, the Cu1–O1–Cu2 bond angle is 100.95°. –0.98 V for the p- and m-substituted complexes, respectively,
The Cu–O distances in the Cu2O2 unit are in the range of is reversible and corresponds to a one-electron exchange lead-
1.884–1.938 Å and are slightly more asymmetric than the ing to a mixed valence CuII–CuI species. This signal is fol-
Cu–O distances in [Cu2(L)(μ-OH)](ClO4)2 (1.928–1.961 Å). lowed by a second one which is irreversible at the time scale
The four Cu1, Cu2, O1, and O2 atoms are in the same plane. of the CV and leading to the CuI–CuI complex at Epc = –1.26 V
Table 1. UV/Vis spectroscopic data, electrochemistry, catalytic behavior of complexes [Cu2(L)(μ-OH)](ClO4)2; [Cu2(m-LSMe)(μ-OH)](ClO4)2
and [Cu2(p-LSMe)(μ-OH)](ClO4)2.
UV/Vis, λmax/nm (ε/m–1·cm–1 a)
)
Electrochemistryb) Peaks potential/V
Catalytic activity
TONd)
c)
[c]
c)
LMCT
d-d
Epc/E1/2/Epa
Vmax
10–6
1.92
1.94
1.70
KM kcat
–1·s–1 mM 10–3 s–1 (10 min)
m
[14]
[Cu2(L)(μ-OH)](ClO4)2
445(480)
785(280)
819(208)
816(260)
–1.24/–0.96/+0.82
–1.26/–0.95/+0.79
–1.29/–0.98/+0.76
2.46 7.68
2.38 7.76
4.24 6.80
2.01
2.20
1.34
[Cu2(p-LSMe)(μ-OH)](ClO4)2 454(342)
[Cu2(m-LSMe)(μ-OH)](ClO4)2 459(490)
a) Recorded at 25 °C in CH3CN; b) 1 mM, in CH3CN + 0.1 m TBAP, WE: glassy carbon (φ = 5 mm), v = 0.1 V·s–1, E vs. Ag/AgNO3; c)
Determined at 25 °C in CH3CN from Lineweaver–Burk plot, [3,5-dtbc] = 2.5–60 mM, [complex] = 0.25 mM; d) [3,5-dtbc] = 25 mM, [complex]
= 0.25 mM.
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W. Rammal, K. Selmeczi, C. Philouze, E. Saint-Aman, J.-L. Pierre, C. Belle
ARTICLE
Figure 3. Voltammetric curves of [Cu2(L)(μ-OH)](ClO4)2 (a); [Cu2(m-LSMe)(μ-OH)](ClO4)2 (b) and [Cu2(p-LSMe)(μ-OH)](ClO4)2 (c) (1 mM) in
CH3CN + TBAP 0.1 m solution recorded at a stationary vitreous carbon working electrode (Ø = 5 mm); ν = 0.1 V·s–1; E vs. Ag/Ag+ 10–2 M;
(A) scan between –0.6 V and –1.5 V; (B) scan between –0.4 V and –1.15 V; (C) scan between +0.3 V and 0.9 V.
and –1.29 V for the p- and m-substituted complex, respec- copper(II) complexes were isolated and characterized by
tively. As previously described[17] OH– bridges have a poor UV/Vis and EPR spectroscopy, single-crystal X-ray analysis
ability to bind CuI atoms and tend to dissociate upon reduction, (of the complex with the SMe substituent at the meta position),
causing the irreversibility of the electrochemical system. The and electrochemistry. The presented compounds mimic the
anodic part of the CV curves (Figure 3) displays one fully active site of type 3 copper enzymes and, in particular, the
irreversible electrochemical signal at around +0.8 V, which distinct environments of the metal ions in relation with a
likely results from oxidation centered on the phenol ligand.
thiomethyl group on the pyridine arm. To date, the experimen-
tal results from models are not sufficiently clear to enable de-
finitive and general conclusions. Nevertheless, some features
can be identified: both complexes are active catalysts for the
oxidation of 3,5-di-tert-butylcatechol to the corresponding
quinone, and the catalytic properties of the complexes depend
on substrate binding, as reflected by the KM values determined
for the complexes in the presence of 3,5-dtbc. The KM values
are associated with the ability of the complex to form an ad-
duct with the substrate and do not directly correlate with the
redox properties of the dicopper center. As this type of sulfur
ligation in copper proteins is unusual, a sound understanding
via biomimetic models remains an open research area.
Catalytic Activities
The catalytic activity of [Cu2(m-LSMe)(μ-OH)](ClO4)2 and
[Cu2(p-LSMe)(μ-OH)](ClO4)2 for the oxidation of 3,5-di-tert-
butylcatechol (3,5-dtbc) was studied and compared to that of
[Cu2(L)(μ-OH)](ClO4)2. The kinetic studies were performed in
acetonitrile solution saturated with dioxygen; the initial rate
method was used and involved monitoring the development of
the UV/Vis band at 400 nm, which corresponds to the absorp-
tion of the quinone (ε = 1640 M–1· cm–1) produced over time.
Upon treating a 0.25 mM solution of the complexes with 100
equivalents of 3,5-dtbc, [Cu2(m-LSMe)(μ-OH)](ClO4)2 and
[Cu2(p-LSMe)(μ-OH)](ClO4)2 exhibited a catechol oxidase
catalytic activity in the same range as that observed with
[Cu2(L)(μ-OH)](ClO4)2 (Table 1).The initial rate of oxidation
was also measured as a function of the substrate concentration
(2.5–60 mM) and shown that the reaction follows Michaelis–
Menten behavior. Lineweaver–Burk treatment of the data gave
the Vmax, KM and kcatvalues presented in Table 1. The cate-
cholase activity of the μ-hydroxido complexes is slightly mod-
ulated by the introduction of the thiomethyl group on one pyr-
idine arm. In the para position of the pyridine coordinated to
the copper ion, the SMe group moderately increases the ac-
tivity, while substitution in the meta position decreases the ac-
tivity. These results provide evidence that the catalytic proper-
ties of the complexes depend on substrate binding, which is
reflected by the KM value of the μ-OH dicopper(II) complexes
(Table 1) in the presence of 3,5-dtbc.
Experimental Section
General: All reagents were purchased from commercial sources and
used as received. Solvents were purified by standard methods before
use.
Caution: Although no problems were encountered, suitable care and
precautions should be taken when handling the perchlorate salts.
Elemental analyses were performed by the CNRS Microanalysis Labo-
ratory of Lyon, France. ESI mass spectra were recorded with an
Esquire 300 plus Bruker Daltonics with nanospray inlet. EPR spectra
were recorded at 100 K with a Bruker ESP 300 spectrometer operating
at 9.4 GHz (X-band) in H2O/DMSO (1/1 v/v, 1 mM).
UV/Vis spectra were obtained using a Perkin–Elmer Lambda 2 spec-
trophotometer operating in the 200–1100 nm range with quartz cells.
Temperature was maintained at 298 K with a temperature control unit.
1H NMR spectra were recorded with a Bruker Advance 300 spectrom-
eter at 298 K with the deuterated solvent as lock.
Conclusions
Two new phenol-based ligands, m-HLSMe and p-HLSMe
,
bearing pyridine-containing pendant arms with one SMe group
The syntheses of the secondary amines 2 and 3 are described in the
were synthesized. The corresponding doubly bridged dinuclear Supporting Information.
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Z. Anorg. Allg. Chem. 2013, 1477–1482

Thiomethyl Substituted Dicopper Complexes
and dropwise addition to a large amount of ethyl ether, the green pre-
cipitate [Cu2(p-LSMe)(μ-OH)](ClO4)2 was obtained (yield = 48%). For
analytic purposes the crude product was purified on a Sephadex
Synthesis
m-HLSMe: To a solution of 1 (0.35 g, 1 mmol) in dry dichloromethane
(10 mL) at 0 °C SOCl2 (221 μL, 3 mmol) in dry dichloromethane
(2 mL) was added dropwise under nitrogen. The resulting suspension
was stirred for 3 h at 0 °C and the solvents evaporated to dryness under
reduced pressure. The resulting residue was washed with dry pentane
leading to a solid residue. At 0 °C under nitrogen, NaH (0.1 g,
2.5 mmol, 60% dispersion in mineral oil) washed with dry pentane
and amine 2 (0.247 g, 1.0 mmol) dissolved in dry CH2Cl2 (5 mL) were
slowly mixed and the solution was stirred for 2 h at 0 °C. The mixture
was then added dropwise to a solution of the former residue 2-(N,N-
bis(2-methylpyridyl)aminomethyl)-6-(chloromethyl)-4-methylphenol
in dry dichloromethane (8 mL) and triethylamine (0.43 mL, 3.0 mmol).
The resulting solution was stirred at room temperature for 2 days and
afterwards cooled in 0 °C and methanol (25 mL) was added. The solu-
tion was evaporated to dryness under reduced pressure, and the residue
was redissolved in dichloromethane. The pH of the solution was ad-
justed to about 8–9 by addition of NaHCO3. The slightly basic solution
was extracted four times with dichloromethane. The extracts were
combined, washed with brine and dried with anhydrous Na2SO4. The
solvent was removed in vacuo. The residue was purified by column
chromatography on silica gel (acetone) to give the ligand m-HLSMe
LH-20 column in dichloromethane. ESI-MS: m/z:
z
=
1,
819 = [M – ClO4 ]; z = 2, 360 = [M – 2ClO4 ]. UV/Vis
(CH3CN): 454(342) and 819(208) nm.
(ε, m–1·cm–1)
–
–
λ
=
C34H36N6O10SCu2Cl2·5H2O; C 40.11 (calcd. 40.48); H 3.56 (4.60); N
8.25 (8.33)%.
Structure Determination and Refinement: A single crystal of the
complex [Cu2(m-LSMe)(μ-OH)](ClO4)2·THF was mounted on a Kappa
CCD Nonius diffractometer equipped with graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å) at 200 K.
C34H36N6O10SCu2Cl2·C4H8O: M = 990.83 g·mol–1, emerald green nee-
dle (0.36ϫ 0.16ϫ 0.12 mm), orthorhombic, space group Pna21, a =
19.098(4) Å, b = 17.566(4) Å, c = 12.358(3) Å, α = β = γ = 90.00°, V
= 4145.7(14) Å3, Dc = 1.587 g·cm–3, Z = 4, μ(Mo-Kα) = 1.272 mm–1,
40615 reflections measured [Rint = 0.0363], 10105 unique (Friedel’s
included), 6648 with F Ͼ 2σ and final R values R1 = 0.0711
[F Ͼ 2σ]; wR2 = 0.1636 (all data).The goodness of fit on F2 was
1.071.
1
The structure was solved by direct methods implemented by SIR-
92.[18] Refinement was performed using SHELXL[19] run under
OLEX2.[20] C, N, O, S, Cl, and Cu atoms were refined anisotropically
by the full-matrix least-squares method. Hydrogen atoms were geomet-
rically placed and constrained to ride on their bearing atoms.
(0.355 g, 61%) as a yellow oil. H NMR (300 MHz, CDCl3, Me4Si):
δ = 10.80 (s, 1 H, OH), 8.68 (s, J = 1.9 Hz, 1 H, Py(SMe)-oH), 8.60
(d, J = 4.2 Hz, 3 H, Py-oH), 7.55 (d, J = 8.2 Hz 1 H, Py(SMe)-mH),
7.51 (td, J = 7.5 Hz, J = 7.4 Hz, 3 H, Py-mH), 7.36–7.48 (m, 4 H,
Py(SMe)-pH and Py-pH), 7.11 (t, J = 6.2 Hz, 3 H, Py-mH), 6.98 (2, 2
H, Ph-H), 3.87(s, 6 H, N-CH2-Py), 3.82 (s, 2 H, N-CH2-Py(SMe), 3.78
(s, 4 H, Ph-CH2-N), 2.44 (s, 3 H, S-CH3) and 2.23 (s, 3 H, CH3). 13C
NMR (75.5 MHz, CDCl3, Me4Si): δ = 159.5, 156.5, 153.8, 149.1,
147.4, 136.7, 135.5, 133.4, 130.0, 127.5, 124.0, 123.9, 123.1, 122.1,
60.0, 59.5, 55.1, 55.0, 20.8 and 16.3. MS (DCI): m/z (%) = 577(100%)
The space group determination led to the non centrosymmetric Pna21
group. The obtained model displays one formula unit within the asym-
metric cell. The structure refinement was not satisfying due to a race-
mic twinning with two domains in a 1:1 ratio. The model was then
refined according the twin law but despite a strong improvement, the
result was still not sufficient. Three different kinds of disorder had to
be treated to reach the final model. The first was for the two different
positions for the thiomethyl group, which were observed on the sides
of either Cu1 or Cu2 with an approximate 3:1 ratio, respectively. The
second disorder was trickier, it could be best described as follows: half
of the ligand surrounding Cu2 could be positioned on two different
positions affected from a rotation of 60° around the Cu2–N2 axis.
These two positions were roughly in a 2:1 ratio. The third disorder
came from the THF solvent molecule which appeared in two different
positions in a 1:1 ratio. Crystallographic data (excluding structure fac-
tors) for the structure reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publi-
cation no. CCDC-906835. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK [Fax: + 44 1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
+
(M ).
p-HLSme: This ligand was prepared following a similar procedure as
described for p-HLSme; however, the amine 3 was used instead of
amine 2. Yield (50%) 1H NMR (300 MHz, CDCl3, Me4Si): δ = 10.80
(s, 1 H, OH), 8.64 (d, J = 4.2 Hz, 3 H, Py-oH), 8.54 (d, J = 1.9 Hz, 1
H, Py(SMe)-oH), 7.82 (td, J = 7.5 Hz, J = 7.3 Hz, 3 H, Py-pH), 7.58
(d, J = 5.2 Hz, 3 H, Py-mH), 7.50 (d, J = 8.2 Hz, 1 H, Py(SMe)-mH),
7.29 (td, 3 H, J = 6.2 Hz, J = 7.5 Hz, Py-mH), 6.50 (s, 2 H, Ph-H),
3.95 (s, 6 H, N-CH2-Py), 3.91 (s, 2 H, N-CH2-Py(SMe), 3.88 (s, 4 H,
Ph-CH2-N), 2.47 (s, 3 H, S-CH3) and 2.35 (s, 3 H, CH3). MS (DCI):
m/z (%) = 577(100%) (M+).
[Cu2(m-LSMe)(μ-OH)](ClO4)2: To m-HLSMe, (288 mg, 0.5 mmol) dis-
solved in CH3CN (15 mL), a solution of Cu(ClO4)2·6H2O (378 mg,
1 mmol) in CH3CN (5 mL) and Et3N (210 μL, 1.12 mmol) were added
dropwise. The solution turned green and was stirred for 1 h at room
temperature. The solvent was partially removed under reduced pres-
sure and the resulting solution (3 mL) after addition of THF was al-
lowed to stand at –20 °C for four days. A green powder (321 mg) was
collected by filtration (70%). Crystals of X-ray quality were obtained
by vapor diffusion of THF in a CH3CN solution. ESI-MS: m/z:
z = 1, 819 = [M – ClO4 ]; z = 2, 360 = [M – 2ClO4 ]. UV/Vis
(CH3CN): 459(490) and 816(260) nm.
C34H36N6O10SCu2Cl2·C4H8O; C 45.55 (calc 46.06); H 4.48 (4.47); N
8.48 (8.51)%.
Electrochemistry: Electrochemical experiments were carried out
using a PAR model 273 potentiostat equipped with a Kipp-Zonen x-y
recorder. All experiments were run at room temperature under argon. A
standard three-electrode cell was used. 0.1 m tetra-n-butylammonium
perchlorate (TBAP) in CH3CN was used as supporting electrolyte. All
potentials are referred to an Ag/10 mM AgNO3 + CH3CN + 0.1 m
TBAP reference electrode. The redox potential of the regular ferro-
cene/ferrocenium redox couple used as an internal reference was
+0.089 V under experimental conditions. The working electrode was
a vitreous carbon disc electrode (5 mm diameter) polished with 1 μm
diamond paste prior to each record.
–
–
λ
(ε, m–1·cm–1)
=
[Cu2(p-LSMe)(μ-OH)](ClO4)2: This complex was prepared by a sim-
ilar procedure as described for [Cu2(m-LSMe)(μ-OH)](ClO4)2; how-
ever, the ligand p-HLSme was used instead of m-HLSMe. An oily com-
Catecholase Activity: The catecholase activity of complexes was
pound was obtained. After dissolution in a small amount of CH3CN evaluated by reaction with 3,5-di-tert-butylcatechol (3,5dtbc) at 25 °C.
Z. Anorg. Allg. Chem. 2013, 1477–1482
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de 1481

W. Rammal, K. Selmeczi, C. Philouze, E. Saint-Aman, J.-L. Pierre, C. Belle
ARTICLE
Lutz, A. L. Spek, J. Reedijk, Eur. J. Inorg. Chem. 2004, 4036; b)
M. Merkel, N. Möller, M. Piacenza, S. Grimme, A. Rompel, B.
Krebs, Chem. Eur. J. 2005, 11, 1201.
The absorption at 400 nm, characteristic of the formed quinone (3,5-
di-tert-butyl-o-benzoquinone) was measured as a function of time. The
experiments were run in acetonitrile saturated with dioxygen. The ki-
netic parameters were determined for 2.5ϫ10–4 m solutions of com-
plexes and 2.5 mM–60 mM solutions of the substrate.
[10] a) D. E. Fenton, Chem. Soc. Rev. 1999, 28, 159; b) C. Belle, J. L.
Pierre, Eur. J. Inorg. Chem. 2003, 4137.
[11] C. Belle, K. Selmeczi, S. Torelli, J. L. Pierre, C. R. Chim. 2007,
10, 271.
Supporting Information (see footnote on the first page of this article):
Description of the syntheses of amines 2 and 3, bond lengths and
angles for [Cu2(m-LSMe)(μ-OH)](ClO4)2·THF.
[12] Recent representative examples: a) C. Bochot, E. Favre, C. Du-
bois, B. Baptiste, L. Bubacco, P.-A. Carrupt, G. Gellon, R.
Hardré, D. Luneau, Y. Moreau, A. Nurisso, M. Réglier, G. Serra-
trice, C. Belle, H. Jamet, Chem. Eur. J. 2013, 19, 3655; b) S. J.
Smith, R. A. Peralta, R. Jovito, A. Horn, A. J. Bortoluzzi, C. J.
Noble, G. R. Hanson, R. Stranger, V. Jayaratne, G. Cavigliasso,
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Acknowledgments
The authors thank the French Agence Nationale pour la Recherche
for financial support (ANR-09-BLAN-0028–01). This work has been
carried out in the framework of Labex ARCANE.
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Received: January 31, 2013
Published Online: April 9, 2013
[9] a) I. A. Koval, M. Huisman, A. F. Stassen, P. Gamez, O. Roubeau,
C. Belle, J. L. Pierre, E. Saint Aman, M. Lüken, B. Krebs, M.
1482
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1477–1482