Sulfur donor atom effects on copper(I)/O2 chemistry with thioanisole containing tetradentate N3S ligand leading to μ-1,2-peroxo-dicopper(II) species

Article abstract of DOI:10.1021/ic101041m

To better understand the effect of thioether coordination in copper-O ₂ chemistry, the tetradentate N₃S ligand L^ASM (2-(methylthio)-N,N-bis((pyridin-2-yl)methyl)benzenamine) and related alkylether ligand L^EOE (2-ethoxy-N,N-bis((pyridin-2-yl)methyl)ethanamine) have been studied. The corresponding copper(I) complexes, [(L^ASM)Cu ^I]⁺ (1a) and [(L^EOE)Cu^I]⁺ (3a), were studied as were the related compound [(L^ESE)Cu ^I]⁺ (2a, L^ESE = (2-ethylthio-N,N-bis((pyridin- 2-yl)methyl)ethanamine). The X-ray structure of 1a and its solution conductivity reveal a monomeric molecular structure possessing thioether coordination which persists in solution. In contrast, the C-O stretching frequencies of the derivative Cu(I)-CO complexes reveal that for these complexes, the modulated ligand arms, whether arylthioether, alkylthioether, or ether, are not coordinated to the cuprous ion. Electrochemical data for 1a and 2a in CH ₃CN and N,N-dimethylformamide (DMF) show the thioanisole moiety to be a poor electron donor compared to alkylthioether (1a is ～200 mV more positive than 2a). The structures of [(L^ASM)Cu^II(CH ₃OH)]²⁺ (1c) and [(L^ESE)Cu^II(CH ₃OH)]²⁺ (2c) have also been obtained and indicate nearly identical copper coordination environments. Oxygenation of 1a at reduced temperature gives a characteristic deep blue intermediate [{(L ^ASM)Cu^II}₂(O₂^2-)] ²⁺ (1b^P) with absorption features at 442 (1,500 M ^-1 cm^-1), 530 (8,600 M^-1 cm^-1), and 605 nm (10,400 M^-1 cm^-1); these values compare well to the ligand-to-metal charge-transfer (LMCT) transitions previously reported for [{(L^ESE)Cu^II}₂(O₂ ^2-)]²⁺ (2b^P). Resonance Raman data for [{(L^ASM)Cu^II}₂(O₂ ^2-)]²⁺ (1b^P) support the formation of μ-1,2-peroxo species ν(O-O) = 828 cm^-1(Δ( ¹⁸O₂) = 48), ν_sym(Cu-O) = 547 cm ^-1 (Δ(¹⁸O₂) = 23), and ν_asym(Cu-O) = 497 cm^-1 (Δ(¹⁸O ₂) = 22) and suggest the L^ASM ligand is a poorer electron donor to copper than is L^ESE. In contrast, the oxygenation of [(L^EOE)Cu^I]⁺ (3a), possessing an ether donor as an analogue of the thioether in L^ESE, led to the formation of a bis(μ-oxo) species [{(L^EOE)Cu^III}₂(O ^2-)₂]²⁺ (3b^O; 380 nm, ε ～ 10,000 M^-1 cm^-1). This result provides further support for the sulfur influence in 1b^P and 2b^P, in particular coordination of the sulfur to the Cu. Thermal decomposition of 1b^P is accompanied by ligand sulfoxidation. The structure of [{(L^EOE) Cu^II(Cl)}₂]⁺ (3c) generated from the reductive dehalogenation of organic chlorides suggests that the ether moiety is weakly bound to the cupric ion. A detailed discussion of the spectroscopic and structural characteristics of 1b^P, 2b^P, and 3b^O is presented.

Full text of DOI:10.1021/ic101041m

Inorg. Chem. 2010, 49, 8873–8885 8873
DOI: 10.1021/ic101041m
Sulfur Donor Atom Effects on Copper(I)/O2 Chemistry with Thioanisole Containing
Tetradentate N3S Ligand Leading to μ-1,2-Peroxo-Dicopper(II) Species
Yunho Lee,† Dong-Heon Lee,‡ Ga Young Park,† Heather R. Lucas,† Amy A. Narducci Sarjeant,†
Matthew T. Kieber-Emmons,§ Michael A. Vance,§ Ashley E. Milligan,§ Edward I. Solomon,§ and
Kenneth D. Karlin*,†
†Department of Chemistry, the Johns Hopkins University, Baltimore, Maryland 21218,
‡Department of Chemistry, Chonbuk National University, Jeonju, S. Korea 561-756, and
§Department of Chemistry, Stanford University, Stanford, California 94305
Received May 24, 2010
To better understand the effect of thioether coordination in copper-O2 chemistry, the tetradentate N3S ligand
LASM (2-(methylthio)-N,N-bis((pyridin-2-yl)methyl)benzenamine) and related alkylether ligand LEOE (2-ethoxy-N,N-
bis((pyridin-2-yl)methyl)ethanamine) have been studied. The corresponding copper(I) complexes, [(LASM)CuI]þ (1a)
and [(LEOE)CuI]þ (3a), were studied as were the related compound [(LESE)CuI]þ (2a, LESE = (2-ethylthio-N,N-
bis((pyridin-2-yl)methyl)ethanamine). The X-ray structure of 1a and its solution conductivity reveal a monomeric
molecular structure possessing thioether coordination which persists in solution. In contrast, the C-O stretching
frequencies of the derivative Cu(I)-CO complexes reveal that for these complexes, the modulated ligand arms,
whether arylthioether, alkylthioether, or ether, are not coordinated to the cuprous ion. Electrochemical data for 1a and
2a in CH3CN and N,N-dimethylformamide (DMF) show the thioanisole moiety to be a poor electron donor compared to
alkylthioether (1a is ∼200 mV more positive than 2a). The structures of [(LASM)CuII(CH3OH)]2þ (1c) and
[(LESE)CuII(CH3OH)]2þ (2c) have also been obtained and indicate nearly identical copper coordination environments.
Oxygenation of 1a at reduced temperature gives a characteristic deep blue intermediate [{(LASM)CuII}2(O22-)]2þ
(1bP) with absorption features at 442 (1,500 M-1 cm-1), 530 (8,600 M-1 cm-1), and 605 nm (10,400 M-1 cm-1);
these values compare well to the ligand-to-metal charge-transfer (LMCT) transitions previously reported for [{(LESE)-
CuII}2(O22-)]2þ (2bP). Resonance Raman data for [{(LASM)CuII}2(O22-)]2þ (1bP) support the formation of μ-
1,2-peroxo species ν(O-O) = 828 cm-1(Δ(18O2) = 48), νsym(Cu-O) = 547 cm-1 (Δ(18O2) = 23), and
ν
asym(Cu-O) = 497 cm-1 (Δ(18O2) = 22) and suggest the LASM ligand is a poorer electron donor to copper than
is LESE. In contrast, the oxygenation of [(LEOE)CuI]þ (3a), possessing an ether donor as an analogue of the
thioether in LESE, led to the formation of a bis(μ-oxo) species [{(LEOE)CuIII}2(O2-)2]2þ (3bO; 380 nm, ε ∼ 10,000 M-1
cm-1). This result provides further support for the sulfur influence in 1bP and 2bP, in particular coordination of the sulfur
to the Cu. Thermal decomposition of 1bP is accompanied by ligand sulfoxidation. The structure of [{(LEOE)CuII(Cl)}2]þ (3c)
generated from the reductive dehalogenation of organic chlorides suggests that the ether moiety is weakly bound to the cupric
ion. A detailed discussion of the spectroscopic and structural characteristics of 1bP, 2bP, and 3bO is presented.
Scheme 1
Introduction
Inspired by the known copper metalloprotein activities,
copper mediated dioxygen activation studies employing a variety
of organic ligands have focused on understanding the kinetics
and thermodynamics of reactive intermediate formation and
their diverse oxidative reactivity.1-3 Previously, we have
studied an end-on μ-1,2-peroxo dicopper(II) intermediate with
the tripodal tetradentate TMPA (tris(-2-pyridylmethyl)amine)
ligand in terms of kinetics of formation, electronic structure,
and other physical-spectroscopic properties, Scheme 1.2,4,5
Detailed mechanistic studies revealed that [{(tmpa)CuII}2-
(O22-)]2þ formation occurs via a reversible reaction between
*To whom correspondence should be addressed. E-mail: karlin@jhu.edu.
(1) Hatcher, L. Q.; Karlin, K. D. J. Biol. Inorg. Chem. 2004, 9, 669–683.
(2) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. Rev. 2004, 104,
1013–1045.
(3) Lewis, E. A.; Tolman, W. B. Chem. Rev. 2004, 104, 1047–1076.
r
2010 American Chemical Society
Published on Web 09/07/2010
pubs.acs.org/IC

8874 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
a CuII-superoxo intermediate (λmax = 410 nm) with a second
cuprous monomer, the equilibrium, however, lying far to the
side of the binuclear complex.6-8 Theintensely purple[{(tmpa)-
CuII}2(O22-)]2þ species exhibits absorptions [λmax nm (ε (cm-1
M-1))] at 440 (4,000), 525 (11,500), and 590 (7,600) nm in
EtCN at -80 ꢀC, assigned as ligand-to-metal charge-transfer
(LMCT) transitions. The formulation as an end-on bound
dioxygen adduct, at the peroxide level of reduction, was con-
˚
firmed structurally (Scheme 1), with Cu Cu = 4.359 A and
3 3 3
4
˚
O-O = 1.432 A, the latter value typical for peroxides. Further
confirmation came from resonance Raman spectroscopy,
ν(O-O) = 832 (Δ(18O2) = 44) cm-1. Finally, a low energy
d-d band (1035 nm; ε, 160) was observed, that is also consistent
with the copper(II) formulation.
While the study of copper(I,II) and copper(I)/O2 chemistry
with ligands possessing all nitrogen donors is of continuing
importance,9-14 a complementary interest involves studies
with thioether sulfur containing chelators for copper ions. In
part, this relates to the (stereo)specific hydroxylation reac-
tions of biological substrates which then function as neuro-
transmitters or hormones, those catalyzed by two closely
related enzymes dopamine β-monooxygenase (DβM) and
peptidylglycine R-hydroxylating monooxygenase (PHM),
Figure 1.15 Both enzymes are composed of a pair of non-
Figure 1. Enzymatic hydroxylations of substrates by DβM and PHM
(top and middle) and one proposed mechanism of PHM and DβM
(bottom). See text.
copper-oxygen species (CuII-OOH vs CuII(O2-)) have been
suggested as the initial hydrogen atom (H ) abstractor from
3
the substrate in the proposed oxidation mechanisms; however,
the nature of these species in terms of their oxidative reactiv-
ities are not well understood.15,19-22 Figure 1 illustrates the
˚
coupled copper centers separated by ∼11 A. The two sites
have distinct functions. The first (called CuH or CuA) is
responsibleforelectron transfer and the second (CuM or CuB)
for O2 activation near the substrate binding site.16-18 The
presence of mononuclear catalytic copper centers drive im-
portant questions regarding their proposedroles andreaction
mechanism and contrasts to the binuclear mechanism in
tyrosinase. PHM X-ray crystal structures reveal the catalytic
copper center possesses (His-N)2Met-S coordination. The
role of the sulfur coordination has been hypothesizedtoallow
PHM to utilize a mononuclear copper center to activate O2
and perform hydroxylation reactions. Recently, a PHM
structure has been solved with a slow substrate that shows
an end-on bound dioxygen species as the possible active
species in its substrate oxidation (Figure 1).16 Two plausible
mechanism suggested by Klinman, with a CuII-(O2-) as active
oxidant.15,19 Some of us have also suggested a CuII-(O2
)
-
oxidant, albeit with an alternative substrate rebound mecha-
nism.20-22 Two specific details arising from the postulated
mechanism are of considerable interest. First, the proposed
involvement of a high-valent “cupryl” Cu-O species (by
analogy to iron chemistry FeIV=O species) has been suggested
(Figure 1) which would be expected to be a very potent oxidant
itself and is intriguing from a coordination chemistry/bonding
perspective.23 Second, the presence of Met-S ligation in an
oxygenation site is unusual in light of sulfur itself being
susceptible to oxidation. Given the curiosity of such a donor
ligand in these active sites, determination of the role of the
Met-S and its electronic structure contributions to enzyme
reactivity is warranted.
To these ends, we and other research groups (see Results
and Discussion) have or are studying the chemistry of copper
complexes with thioether containing ligands to assess the
effect of sulfur coordination in biomimetic DβM and PHM
complexes. In fact, we were able to describe the first example
of a dioxygen adduct of copper ion employing an N3S donor
set, in ligand LESE and complex 2bP (Chart 1).24 Spectro-
scopic analysis including UV-visible, resonance Raman, and
extended X-ray absorption fine structure (EXAFS) spectro-
scopy indicated the formation of an end-on peroxo species
[{(LESE)CuII}2(O22-)]2þ(2bP) akin to that found with the
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Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8875
Chart 1
ether oxygen donor instead of sulfur has also been synthe-
sized for comparison with LESE. Peroxodicopper(II) com-
plexes are found to be generated by the reaction of O2 with 1
and 2, while a bis(μ-oxo) complex forms by oxygenation of
complex 3a with the LEOE ligand (Chart 1). To appreciate the
preferred structures of the Cu(II) ion in the coordination
spheres of the new ligands, as well as to possibly relate such
information to the coordination present in the peroxo com-
plexes (1bP)-(3bP), copper(II) complexes (1c-3c in Chart 1)
have been synthesized and characterized.
Experimental Section
General Considerations and Instrumentation. All reagents and
solvents used for this work were commercial products and are of
reagent quality unless otherwise stated. Acetonitrile (CH3CN),
dichloromethane (CH2Cl2), diethylether (Et2O), methanol (CH3-
OH), and tetrahydrofuran (THF) were purified and dried by
passing through a double alumina column solvent purification
system by Innovative Technologies, Inc. Anhydrous 2-methylte-
trahydrofuran (MeTHF; packaged under nitrogen in Sure/Seal
bottles, 99þ%) was purchased from Sigma-Aldrich, Inc. Deoxy-
genation of these solvents was achieved by bubbling Ar for 30 min
and/or carrying out three freeze/pump/thaw cycles. Air-sensitive
compounds were handled under an Ar atmosphere using standard
Schlenk techniques or within a MBraun Labmaster 130 inert-
atmosphere (N2 atmosphere;<1 ppm O2,<1 ppm H2O) glovebox.
Molecular oxygen (Airgas Inc., Radnor, PA) was dried by passing
it through a laboratory gas drying unit (W. A. Hammond Drierite
Co., Xenia, Ohio) and introduced to reaction solutions by bubbling
through an 18-gauge, 24-in.-long stainless steel syringe needle.
[CuI(MeCN)4]ClO4 and [CuI(MeCN)4]B(C6F5)4 were prepared
by literature procedures.26,27 KB(C6F5)4 or LiB(C6F5)4 were
purchased from Boulder Scientific Company. LESE and[(LESE)CuI]þ
(2a) were prepared according to literature procedures.24
Chart 2
Caution! While we have experienced no problems in working
with perchlorate compounds, they are potentially explosive, and
care must be taken not to work with large quantities.
1H NMR and 13C NMR spectra were measured on a Varian
400 MHz or Bruker 400 MHz spectrometer and chemical shifts
are reported in ppm (δ) downfield from an internal TMS
(Me4Si) reference and the residual solvent proton peak. Infrared
Spectra were recorded on a Mattson Instruments 4030 Galaxy
Series FT-IR spectrometer. Measuring the solution IR spectra
of carbonyl adducts (as a solution in THF) were recorded using
standard solution IR cells. Air sensitive cuprous THF solutions
were prepared in a glovebox (N2 filled, MBraun) and then
removed using 20 mL vials sealed with a 14/20 rubber septum.
Carbon monoxide gas (Airgas Inc., Radnor, PA) was intro-
duced to the corresponding solution via bubbling for 20-30 s
through an 18-gauge, 24-in.-long stainless steel syringe needle.
The resulting solution was transferred to a solution IR cell via a
gastight syringe under the CO atmosphere. Elemental Analyses
were performed by Desert Analytics, Tucson, AZ for air-
sensitive samples or by Quantitative Technologies Inc. (QTI),
Whitehouse, NJ for others. Mass Spectrometry was conducted
at the mass spectrometry facility either at the Johns Hopkins
University (JHU) or at The Ohio State University (OSU).
Chemical Ionization (CI) and fast atomic bombardment (FAB)
mass spectra were acquired at the JHU facility using a VG70S
double focusing magnetic sector mass spectrometer (VG Ana-
lytical, Manchester, U.K., now Micromass/Wasters) equipped
with a Xe gas FAB gun (8 kV @ 1.2 mA) and an off-axis electron
multiplier and an MSS data system (MasCom, Bremen, Germany).
TMPA ligand, with the fourth ligand alkyl thioether sulfur
also coordinated to the cupric ion.24,25 In the present report,
we describe the related ligand LASM with thioanisole group
and its CuI/O2 chemistry to compare and contrast with the
results obtained for LESE (Chart 1). LEOE (Chart 2) with an
(25) Lee, D. H.; Hatcher, L. Q.; Vance, M. A.; Sarangi, R.; Milligan,
A. E.; Narducci Sarjeant, A. A.; Incarvito, C. D.; Rheingold, A. L.;
Hodgson, K. O.; Hedman, B.; Solomon, E. I.; Karlin, K. D. Inorg. Chem.
2007, 46, 6056–6068.
(26) Liang, H.-C.; Kim, E.; Incarvito, C. D.; Rheingold, A. L.; Karlin,
K. D. Inorg, Chem. 2002, 41, 2209–2212.
(27) Liang, H.-C.; Karlin, K. D.; Dyson, R.; Kaderli, S.; Jung, B.;
€
Zuberbuhler, A. D. Inorg. Chem. 2000, 39, 5884–5894.

8876 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
The resolution of the instrument was set at 10,000 (100 ppm
peak width). Samples were mixed with m-nitrobenzyl-alcohol
matrix deposited on the target of a direct insertion probe for
introduction into the source. Nominal mass scan spectra were
acquired with a mass scan range of 10-950 amu using a magnet
scan rate of 25 s/dec For accurate mass measurements, a narrower
mass scan range was employed, with the matrix containing 10%
PEG mass calibrant. Electrospray ionization (ESI) mass spectra
(JHU facility) were acquired using a Finnigan LCQDeca ion-trap
mass spectrometer equipped with an electrospray ionization source
(Thermo Finnigan, San Jose, CA). Samples were dissolved in
CH3OH or CH3CN and introduced into the instrument at a rate
of 10 μl/min using a syringe pump via a silica capillary line. The
heated capillary temperature was 250 ꢀC and the spray voltage was
5 kV. Fast atomic bombardment (FAB) mass spectra were
acquired at the JHU facility using a VG70S double focusing
magnetic sector mass spectrometer (VG Analytical, Manchester,
U.K., now Micromass/Wasters) equipped with a Xe gas FAB gun
(7.5 kV @ 1 mA) and an off-axis electron multiplier. High
resolution ESI mass spectrometry analyses were performed at
the OSU mass-spec facility with a 3-T Finnigan FTMS-2000
Fourier Transform mass spectrometer. Samples were sprayed from
a commercial electrospray ionization source, and then focused into
the FTMS cell using a home-built set of ion optics. Electrical con-
ductivity measurements28,29 for the Cu(I) complexes [(LASM)CuI]þ
(1a) and [(LESE)CuI]þ (2a) were carried out in N,N-dimethylfor-
mamide (DMF) solvent using an Accumet AR20 pH/Conductivity
meter (Fisher Scientific) with Accumet Immersion-type four-cell
glass conductivity probe (cell constant κ = 1.0 cm-1). Air sensitive
cuprous DMF solutions (1 mM, 20 mL) were prepared in a
glovebox (N2 filled, MBraun) and then removed using 5 drum
vials sealed with a cap and electrical tape. The data were collected
from measurements with continuous strong (over the top) Ar flow.
Cyclic voltammetry measurements were undertaken in CH3CN
and DMF using a BAS 100B electrochemical analyzer with a glassy
carbon working electrode and a platinum wire auxiliary electrode.
Potentials were recorded versus a Ag/AgNO3 electrode. The
voltammograms are plotted versus the [Fe(Cp)2]þ/0 potential
which was measured as an external standard.30 Scans were run at 50-
200 mV/s under an Ar atmosphere using about 0.1 M [Bu4N][PF6]
as the supporting electrolyte. X-ray Crystallography was performed
on suitable single crystals of [(LASM)CuI]þ (1a), [(LASM)CuII-
(CH3OH)]2þ (1c), and [{(LEOE)CuII(Cl)}2]2þ (3c), which were
mounted in Paratone-N oil on the end of a glass fiber and
transferred to the N2 cold stream (110 K) of an Oxford Diffraction
Xcalibur3 system equipped with Enhance optics [Mo Ka radiation
on a Bruker EMX CW-EPR spectrometer controlled with
a Bruker ER 041 XG microwave bridge operating at X-band
(∼9 GHz). The low-temperature experiments were carried out
via either a continuous-flow He(l) cryostat and ITC503 tem-
perature controller made by Oxford Instruments, Inc. or an
N2(l) finger dewar. Low Temperature UV-vis Spectra were
obtained with either a Cary 50 Bio spectrophotometer equipped
with a fiber optic coupler (Varian) and a fiber optic dip probe
(Hellma: 661.302-QX-UV-2 mm for low temperature) or a Hewlett-
Packard model 8453 diode array spectrophotometer equipped with
a custom-made quartz-windowed vacuum dewar filled with
methanol (-80 ꢀC). A low temperature unit (Neslab ULT-95 low
temperature circulator) is attached to the HP spectrophotometer
via copper tubing. The methanol temperature within the dewar was
monitored using a thermocouple probe (Omega Model 651). For
the low temperature measurements with a Cary 50 Bio spectro-
photometer, a hexane/N2(l) bath (-94 ꢀC) or a pentane/N2(l) bath
(-128 ꢀC) was used, and the steady temperature was monitored
with the type T thermocouple thermometer (Model 650, Omega
engineering, CT). Air sensitive solutions were prepared in a glove-
box (N2 filled, MBraun) and carried out in custom-made Schlenk
tubes designed for the dip probe (Chemglass: JHU-0407-271MS)
or Schlenk cuvettes. The cuvette assembly consisted of a two-
window quartz cuvette (2 mm path) connected, via a 12 cm glass
tube, to a 14/20 female ground glass joint.
Synthesis of Ligands. LASM. The compound 2-(methylthio)-
aniline (2.05 g, 14.0 mmol) and picolyl chloride hydrochloride
(7.25 g, 44.4 mmol) were dissolved in DMF (100 mL). Sodium
hydride (3.8 g, 60% dispersion in mineral oil, 95.0 mmol) was
slowly introduced with vigorous stirring in the precooled (ice
bath) solution. The reaction mixture was refluxed for 6 h under Ar.
After cooling to room temperature, ethanol (20 mL) was added
to quench the unreacted sodium hydride. The resulting solution
was filtered, and DMF was removed by rotary evaporation. The
crude yellow oil was dissolved in CH2Cl2 and washed three times
with brine. The organic layer was separated, dried over anhydrous
MgSO4, then filtered and concentrated under vacuum. The
yellow powder obtained (2.2 g, 6.9 mmol, 49.3%) was purified
by column chromatography (Silica gel, ethylacetate, Rf = 0.2).
1H NMR (CDCl3): δ 8.47 (d, J = 4 Hz, 2H), 7.65 (d, J = 7.8 Hz,
2H), 7.59 (td, J = 7.6, 1.8 Hz, 2H), 7.1 (m, 5H), 6.97 (td, J = 7.3,
1.8 Hz, 1H), 4.38 (s, 4H), 2.47 (s, 3H). 13C NMR (CDCl3): δ
158.5 (Py), 148.4 (Py), 146.3 (Py), 136.1 (Ar), 135.7 (Ar), 124.6
(Py), 124.1 (Ar), 123.5 (Ar), 122.2 (Ar), 122.0 (Py), 121.6
(Py), 59.0 (NCH2), 13.8 (CH3). FAB mass spectrum: m/z 322.2
(M þ 1)þ.
˚
(λ = 0.71073 A)] and a CCD detector. The frames were integrated
L
EOE. Bis((pyridin-2-yl)methyl)amine (PY1) (3.05 g, 15.0 mmol)
and a face indexed absorption correction, and an interframe scaling
correction was also applied with the Oxford Diffraction CrysA-
lisRED software package (CrysAlis CCD, Oxford Diffraction Ltd.,
Version 1.171.27p5 beta). The structures were solved using direct
methods and refined using the Bruker SHELXTL (v6.1) software
package. Resonance Raman spectra were obtained using a Princeton
Instruments ST-135 back-illuminated CCD detector on a Spex 1877
CP triple monochromator with 1200, 1800, and 2400 grooves/mm
holographic spectrograph gratings. Excitation was provided by a
Coherent I90C-K Krþ ion laser. The laser line, 568 nm (∼10 mW),
was chosen to coincide with the intense absorption transition of the
Cu2O2 species. The spectral resolution was <2 cm-1. Sample con-
centrations were approximately 3-4 mM with respect to Cu (1.5-
2 mM with respect to dimer). The samples were cooled to 77 K in a
quartz liquid nitrogen finger Dewar (Wilmad) and rotated by hand
to minimize sample decomposition during scan collection. Isotopic
substitution was achieved by oxygenation with 18O2. X-Band
Electron Paramagnetic Resonance (EPR) Spectra were recorded
and 2-chloroethyl ethyl ether (2.41 g, 22.2 mmol) were dissolved in
methanol (100 mL). After potassium hydroxide (1.5 g, 26.7 mmol)
was introduced, the reaction mixture was refluxed overnight under
Ar. After cooling to room temperature, the resulting solution was
filtered and solvent was removed by rotary evaporator. The crude
yellow oil was dissolved in CH2Cl2 and washed with brine three
times. The organic layer was separated, dried over anhydrous
MgSO4, filtered and concentrated under vacuum. The oil obtained
was purified by column chromatography (Silica gel, ethylacetate,
Rf = 0.3). Yield is 0.388 g (1.43 mmol, 95%). 1H NMR (CDCl3): δ
8.52 (d, J = 4 Hz, 2H), 7.64 (td, J = 7.4, 1.8 Hz, 2H), 7.57 (d, J =
7.8 Hz, 2H), 7.13 (t, J = 5.1 Hz, 2H), 3.91 (s, 4H), 3.58 (t, J = 6 Hz,
2H), 3.43 (q, J = 7 Hz, 2H), 2.83 (t, J = 6 Hz, 2H), 1.17 (t, J = 7.2
Hz, 3H). 13C NMR (CDCl3): δ 160.1 (py), 149.1 (py), 136.5 (py),
123.0 (py), 122.0 (py), 69.0 (OCH2), 66.5 (OCH2), 61.1 (NCH2),
53.9 (NCH2), 15.4 (CH3). FABmassspectrum:m/z322.2 (M þ 1)þ.
Synthesis of Cu(I) Complexes and Their Reactivity toward
O2. [(LASM)CuI]B(C6F5)4 (1a B(C6F5)4). LASM (0.26 g, 0.8 mmol)
3
and [CuI(CH3CN)4]B(C6F5)4 (0.682 g, 0.75 mmol) were dissolved
and stirred for 1 h in O2-free THF (15 mL) under Ar at room
temperature. The resulting yellow solution was filtered and trans-
ferred to a 100 mL Schlenk flask by cannula (with filter paper).
(28) Geary, W. J. Coord. Chem. Rev. 1971, 7, 81–122.
(29) Sorrell, T. N.; Borovik, A. S. J. Am. Chem. Soc. 1987, 109, 4255–
4260.
(30) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877–910.

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8877
The complex precipitated as a yellow powder upon addition of
O2-free heptane into the reaction mixture. The supernatant was
decanted, and the resulting yellow powder (0.55 g, 0.52 mmol,
70%) was washed two times with O2-free heptane and dried
under vacuum. 1H NMR (CD2Cl2): δ 8.85 (s, 2H), 7.80 (m, 4H),
∼ 7.5 (m, 6H), ∼ 4.6(s, 4H), 2.5 (s, 3H), 2.18 (s, CH3CN). Anal.
Calcd. for C43H19BCuF20N3S(1/4CH3CN): C, 48.63; H, 1.85;
N, 4.24. Found: C, 48.47; H, 1.69; N, 4.24. ESI mass spectrum:
m/z 384.35 (LCuI)þ. UV-vis (MeTHF; λmax, nm; ε, M-1 cm-1):
318;5100.
reaction flask after breaking the seal. The reaction solution was
stirred overnight, and the aliquot of reaction mixture was taken
out for the mass spectrometric analysis. ESI mass data: Calcu-
lated values for C19H19CuN3(18O)S with 92% incorporation of
18O: 400 (8.3%), 401 (1.9%), 402 (100%), 403 (22.6%), 404
(49.6%), 405 (10.8%), 406 (3.1%), 407 (0.5%). Found: 400
(4.8%), 401 (9.6%), 402 (100.0%), 403 (27.2%), 404 (49.6%),
405 (12.1%), 406 (3.5%), 407 (0.5%). After the solvent was
removed in vacuo, the residual green material was treated with
NH4OH/CH2Cl2 to demetallate the resulting product.31,32
The organic layer was separated, washed with brine (3 times),
dried over anhydrous MgSO4, then filtered and concentrated
under vacuum. Thin layer chromatography (TLC) and NMR
spectroscopy were used to confirm the purity and identity of
the sulfoxide product. Subsequent mass spectrometric ana-
lysis indicated a 92% incorporation of the labeled oxygen.
FAB mass data: Calculated values for C19H19CuN3(18O)S
with 92.5% incorporation of 18O: 338 (8.1%), 339 (1.8%), 340
(100%), 341 (22.7%), 342 (6.9%), 343 (1.2%). Found: 338
(8.24%), 339 (5.29%), 340 (100%), 341 (22.3%), 342 (7.5%),
343 (1.6%).
[(LASM)CuI]ClO4 (1a ClO4). LASM (0.500 g, 1.6 mmol) and
3
[CuI(CH3CN)4]ClO4 (0.51 g, 1.6 mmol) were dissolved and
stirred for 1 h in O2-free CH3CN (15 mL) under Ar at room
temperature. The resulting yellow solution was filtered and
transferred to a 100 mL Schlenk flask by cannula (with filter
paper). The complex precipitated as a yellow powder upon
addition of O2-free diethylether and heptane into the reaction
mixture. The supernatant was decanted, and the resulting yellow
powder (0.57 g, 1.2 mmol, 75%) was washed two times with O2-
free ether/heptane and dried under vacuum. 1H NMR (DMSO-d6):
δ 8.66 (d, J = 4.4 Hz, 2H), 7.87 (td, J = 8, 1 Hz, 4H), ∼ 7.4 (m,
6H), ∼ 4.3 (s, 4H), 2.5 (s, 3H), 2.11 (s, CH3CN). Anal. Calcd. for
C19H19ClCuN3O4S(1/3CH3CN): C, 47.42; H, 4.05; N, 9.37.
Found: C, 47.11; H, 4.06; N, 9.25. ESI mass spectrum: m/z
384.14 (LCuI)þ.
[(LEOE)CuI]þ (3a). LEOE (75 mg, 0.28 mmol) and [CuI(CH3-
CN)4]B(C6F5)4 (245 mg, 0.27 mmol) were stirred for 1 h in
O2-free THF (5 mL) under Ar at room temperature (RT). The
complex was precipitated as yellowish white powder upon
addition of (oxygen free) heptane into the reaction mixture.
The supernatant was decanted. The resulting yellow powder was
washed two times with O2-free heptane and dried under vacuum.
1H NMR (CD3NO2): δ 9.08 (s, 4H), 7.97 (s, 2H), 7.56 (s, 1H),
7.37 (s, 1H), 5.42 (s, 4H), 4.56 (s, 2H), 2.85 (s, 2H), 2.29 (s, 2H),
1.28 (s, 3H). Anal. Calcd. for C40H21BCuF20N3O: C, 47.38; H,
2.09; N, 4.14. Found: C, 47.04; H, 2.46; N, 4.10. ESI mass
spectrum: m/z 334.57 (LCuI)þ. UV-vis (THF; λmax, nm; ε, M-1
cm-1): 330; 4,300.
LAS(O)M Formation. [(LASM)CuI]þ (1a) (0.13 g, 0.12 mmol)
was dissolved in O2-free THF (5 mL) under Ar in a 25 mL
Schlenk flask. While O2 gas was bubbling through the yellow
solution (∼2 min) at -77 ꢀC, it turned deep blue corresponding
to peroxo species [{(LASM)CuII}2(O22-)]2þ (1bP). This solution
was then slowly warmed and stirred overnight at room tem-
perature. The solvent was removed by rotary evaporation and
the residual green material was demetalated with NH4OH/
CH2Cl2.31,32 The organic layer was separated, washed three
times with brine, dried over anhydrous MgSO4, then filtered and
concentrated under vacuum. The resulting yellow powder was
purified by column chromatography (Al2O3, ethylacetate, Rf =
0.13) to give 15 mg (0.045 mmol, 37%) product. 1H NMR
(CDCl3) δ: 8.53 (dm, J = 4.4 Hz, 2H), 7.93 (dd, J = 7.2, 1.8 Hz,
1H), 7.60 (td, J = 7.6, 2.1 Hz, 2H), ∼ 7.3 (m, 4H), ∼ 7.2 (m, 3H),
4.39 (ABq, J = 14.5 Hz, 4H), 2.90 (s, 3H). 13C NMR (CDCl3): δ
157.1 (Py), 149.0 (Py), 147.4 (Py), 141.1 (Ar), 136.1 (Ar), 130.9
(Py), 125.3 (Ar), 124.1 (Ar), 123.1 (Ar), 122.9 (Py), 122.1 (Py), 60.0
(NCH2), 42.1 (CH3). FAB mass spectrum: m/z 338.1 (M þ 1)þ.
LAS(18O)M Formation: 18O2 Labeling Experiment. [(LASM)-
CuI]þ (1a) (0.092 g, 0.086 mmol) was dissolved in O2-free THF
(5 mL) under Ar in a 25 mL Schlenk flask connected to a three-
way valve, and a vacuum was applied and an 18O2 bulb (25 mL,
99 atom %, 1 atm from ICON, part number IO 6393) was
connected. At RT, dioxygen 18O2 was allowed to diffuse into the
ESI mass data of oxidized copper complex shows 92% 18O incorporation
(left) and FAB mass data of the oxidized ligand shows 92.5% 18O
incorporation (right). Blue bars represent calculated values and red bars
represent experimental values.
Synthesis and Characterization of Cu(II) Complexes. [(LASM)-
CuII(CH3OH)]2þ (1c). LASM (0.45 g, 1.4 mmol) and CuII(ClO4)2
3
6H2O (0.52 g, 1.4 mmol) were dissolved in CH3OH (5 mL) and
stirred for 1 h at room temperature. The resulting blue solution was
filtered and transferred to a 100 mL Schlenk flask by cannula (with
filter paper). The solution was layered with diethylether and
crystallization/precipitation slowly took place in a refrigerator.
After the supernatant was decanted, the resulting powder was
washed two times with diethylether and dried under vacuum to
give 0.79 g (1.29 mmol, 74%) product. UV-vis (CH3OH; λmax
,
nm; ε, M-1 cm-1): 256, 12,700; ∼ 400, ∼ 70; 710, 76. Anal. Calcd.
for C19H21Cl2CuN3O9S(1/2 H2O): C, 37.35; H, 3.63; N, 6.88.
Found: C, 37.41; H, 3.57; N, 6.70. EPR: X-band spectrometer
(ν = 9.186 GHz) in 2-methyltetrahydrofuran/CH3CN (1:1) at
77 K; g|| = 2.28, A|| =158 gauss; g^ = 2.06. X-ray quality blue
crystals were obtained from this synthesis.
(31) Karlin, K. D.; Nasir, M. S.; Cohen, B. I.; Cruse, R. W.; Kaderli, S.;
€
Zuberbuhler, A. D. J. Am. Chem. Soc. 1994, 116, 1324–1336.
(32) Sanyal, I.; Mahroof-Tahir, M.; Nasir, S.; Ghosh, P.; Cohen, B. I.;
Gultneh, Y.; Cruse, R.; Farooq, A.; Karlin, K. D.; Liu, S.; Zubieta, J. Inorg.
Chem. 1992, 31, 4322–4332.

8878 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
[{(LEOE)CuII(Cl)}2]2þ (3c). 3a B(C6F5)4 (40 mg, 0.039 mmol)
Scheme 2
3
was dissolved in CH2Cl2 (3 mL) and stirred for 30 min at room
temperature under Ar. The blue solid was slowly precipitated
out and supernatant was decanted by cannula (with filter paper).
The resulting powder was washed two times with CH2Cl2 and
dried under vacuum to give 38 mg (0.036 mmol, 92%) product.
UV-vis (CH3CN; λmax, nm; ε, M-1 cm-1): 679; 58. ESI mass
spectrum: m/z 369.31 (LCuI)þ. Anal. Calcd. for C41H23BCl3-
CuF20N3O: C, 43.41; H, 2.04; N, 3.70. Found: C, 43.22; H, 2.23;
N, 3.66. X-ray quality blue crystals were obtained from 3a THF/
CH2Cl2 solution layered with pentane.
Results and Discussion
donor does not seem to influence formation of mono-
nuclear Cu-O2 or dinuclear bis-μ-oxo dicopper(III) pro-
ducts; for the latter, the R-S-X donor does not bind to the
copper ion. Zhou and co-workers showed the oxygena-
tion chemistry of a imidazolyl N2S-copper(I) complex
(R = H, L = CH3CN, F, Chart 1) led to a 20% yield
of a sulfoxidation product.44 More recently, these same
researchers generated a series of ligands similar to F, but
with different R groups (including R=H) and varying
substituents on the S-atom (e.g., -tBu, -trityl); resulting
(ligand)-CuI/O2 reactivity studies led to a variety of product
types, including dialkoxo and dihydroxo bridged dicopper(II)
complexes, ligand hydroxylated species, and ligand disul-
fide products (following detritylation chemistry).45 Most
recently, we reported on the reaction depicted in G, a new
structural type, that is, a μ-η2:η2-peroxodicopper(II) com-
plex which includes a thioether ligand donor.46 In spite of
all these known chemistries, studies systematically interro-
gating the direct influence of sulfur coordination on copper-
dioxygen complex formation are rare.
Synthesis of New Ligands and Copper(I) Complexes.
Ligands LASM and LEOE and their copper complexes were
synthesized and characterized. LASM was prepared by
reaction of 2-(methylthio)aniline with picolyl chloride
and base. The ether ligand LEOE was generated from the
reaction of bis((pyridin-2-yl)methyl)amine (PY1) and
2-chloroethyl ethyl ether under basic conditions (Scheme 2).
[(LASM)CuI]þ (1a) and [(LEOE)CuI]þ (3a) were synthe-
sized by the addition of 1 equiv of the appropriate tri-
podal ligand to [CuI(CH3CN)4]Y (Y=ClO4-, B(C6-
F5)4-) in CH3CN or THF under Ar. They are both yellow,
possessing charge-transfer absorptions at 318 and 330 nm
respectively (see the Experimental Section and figures
below). 1H NMR and elemental analysis of 1a indicate that
the complex is consistently isolated with a less than a
stoichiometric amount of CH3CN. Solution conductivity
measurements in DMF solvent indicate 1:1 electrolyte
behavior for both [(LASM)CuI]þ (1a) and [(LESE)CuI]þ
(2a) (ΛM = 77 and 78 ohm-1 cm2 mole-1, respectively),
consistent with their mononuclear formulations in this
solvent.28 While 2a is a dimer in the solid state (formed by
having one pyridyl group on each copper-ligand moiety
coordinate to the other copper-ligand group),25 1a crystal-
lizes as a mononuclear species (Figure 2 and Table 1). This
observation is most likely due to the structural rigidity of the
Previously Studied Systems. Copper complexes with
thioether containing ligands have long been of interest
because of their occurrence at electron-transfer sites in
Type 1 “blue” copper proteins. There, studies focused on
determination of the effects of RSR0 coordination upon
redox and/or structural properties.33-35 Here, as back-
ground literature, we highlight investigations of copper
complexes with thioether ligands which have been direc-
ted toward chemistries of possible relevance to DβM and
PHM (see Introduction) oxidative reactivity.
Casella and co-workers36 reported that C-H bond
activation with molecular oxygen and mediated by a
dicopper complex could occur utilizing thioether contain-
ing ligands (A, Chart 1). This aromatic hydroxylation,
which is reminiscent to previously studied xylyl systems in
our lab,31,37,38 was observed as monooxygenase type
chemistry; a sulfoxide was detected as a minor fraction
of the reacted ligand (15-20%).36 Similar sulfoxidation
chemistry was carried out by Reglier and co-workers39
from the reactions of a copper(II) complex with hydrogen
•-
peroxide. However, no superoxo copper(II) (CuII-O2
)
or hydroperoxo copper(II) (CuII-OOH) intermediates
were detected. Reacting H2O2 with sulfur containing
complexes B and C (R = C6H5, or -CH3 or iso-C3H7),
resulted in the detection of sulfoxide and sulfone pro-
ducts, and hydroperoxo copper(II) (CuII-OOH) com-
plexes were generated and studied (Chart 1).40,41 Santra
and co-workers42 reported a structural model for the
oxidized CuM site of DβH and PHM; N3OS copper(II)
complex D is an example where thioether coordination
occurs in the axial position. Tolman and co-workers43
reported a CuI/O2 reactivity study using a β-diketiminate
thioether N2S-Cu(I) complex (E, Chart 1); the thioether
(33) Rorabacher, D. B. Chem. Rev. 2004, 104, 651–697.
(34) Ambundo, E. a.; Yu, Q. Y.; Ochrymowycz, L. A.; Rorabacher, D. B.
Inorg. Chem. 2003, 42, 5267–5273.
(35) Karlin, K. D.; Yandell, J. K. Inorg. Chem. 1984, 23, 1184–1188.
(36) Alzuet, G.; Casella, L.; Villa, M. L.; Carugo, O.; Gullotti, M.
J. Chem. Soc., Dalton Trans. 1997, 4789–4794.
(37) Nasir, M. S.; Cohen, B. I.; Karlin, K. D. J. Am. Chem. Soc. 1992, 114,
2482–2494.
(38) Pidcock, E.; Obias, H. V.; Zhang, C. X.; Karlin, K. D.; Solomon, E. I.
J. Am. Chem. Soc. 1998, 120, 7841–7847.
(39) Champloy, F.; Benali-Cherif, N.; Bruno, P.; Blain, I.; Pierrot, M.;
Reglier, M.; Michalowicz, A. Inorg. Chem. 1998, 37, 3910–3918.
(40) Ohta, T.; Tachiyama, T.; Yoshizawa, K.; Yamabe, T.; Uchida, T.;
Kitagawa, T. Inorg. Chem. 2000, 39, 4358–4369.
(41) Kodera, M.; Kita, T.; Miura, I.; Nakayama, N.; Kawata, T.; Kano,
K.; Hirota, S. J. Am. Chem. Soc. 2001, 123, 7715–7716.
(42) Santra, B. K.; Reddy, P. A. N.; Nethaji, M.; Chakravarty, A. R.
Inorg. Chem. 2002, 41, 1328–1332.
(43) Aboelella, N. W.; Gherman, B. F.; Hill, L. M. R.; York, J. T.; Holm,
N.; Young, V. G.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2006, 128,
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(44) Zhou, L.; Powell, D.; Nicholas, K. M. Inorg. Chem. 2006, 45, 3840–
3842.
(45) Zhou, L.; Powell, D.; Nicholas, K. M. Inorg. Chem. 2007, 46, 7789–
7799.
(46) Park, G. Y.; Lee, Y.; Lee, D.-H.; Woertink, J. S.; Sarjeant, A. A. N.;
Solomon, E. I.; Karlin, K. D. Chem. Commun. 2010, 46, 91–93.

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8879
Figure 2. Molecular structure of the isolated cation [(LASM)CuI]þ (1a-
B(C6F5)4) from X-ray crystallographic analysis. The B(C6F5)4- counter-
anion and hydrogen atoms in the ORTEP view are omitted for clarity.
Figure 3. Solution IR spectra of copper(I) carbonyl complexes
(A: [(tmpa)CuI(CO)]þ, B: 1a-CO and C: 3a-CO) in THF at room
temperature. See Table 2 for ν(C-O) values.
Table 1. Selected Bond Distances and Angles for [(LASM)CuI]þ (1a-B(C6F5)4)
bond
distance (A)
bond
angle (deg)
Table 2. Carbonyl Stretching Frequencies for Copper(I) Carbonyl Complexes in
THF
˚
Cu-X
X-Cu-X
N(3)-Cu(1)-N(1)
N(3)-Cu(1)-N(2)
N(1)-Cu(1)-N(2)
N(3)-Cu(1)-S(1)
N(1)-Cu(1)-S(1)
N(2)-Cu(1)-S(1)
128.60 (9)
83.37 (8)
83.90 (8)
120.94 (6)
108.01 (6)
87.71 (6)
compound
wavenumber (cm-1
)
Cu(1)-S(1)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-N(3)
2.26858 (8)
2.027 (2)
2.181 (2)
1.990 (2)
[(tmpa)CuI(CO)]þ
[(PY1)CuI(CO)]þ55
[(LASM)CuI(CO)]þ
[(LESE)CuI(CO)]þ25
[(LEOE)CuI(CO)]þ
2090, 2073
2091a
2090
2094a
2090
a Measured in CH3CN.
ligand in 1a which prohibits its dimerization. In contrast, the
thioether sulfur atom in 2a is flexible and coordinates to the
“other” copper ion.25 The Cu-S distance (2.26858 (8) A) in
˚
With appropriate ligands (TMPA, LASM, and LEOE
)
˚
1a is slightly longer than that for 2a (2.2023(9) A) suggesting
Cu(I)-CO species as B(C6F5)4 complex salts were ob-
tained by bubbling carbon monoxide gas into the corre-
sponding THF solution at room temperature. The two
bands observed at 2090 and 2073 cm-1 seen for [(tmpa)-
CuI(CO)]þ (Figure 3) have been previously attributed to a
dynamic equilibrium involving overall 4- or 5-coordinate
complexes, as illustrated in Scheme 3 [Note: formulations
with superscripted 4c indicate a complex with overall
tetracoordination, while a superscripted 5c indicates overall
pentacoordination].5,55,56 The lower value is ascribed
to the pentacoordinate species where ligation of all four
N-donors provides more electron density to the Cu(I) ion,
resulting in greater back-donation to the CO π* orbital
(thus weakening the CO bond and lowering ν(C-O)).
Supporting evidence comes from the observation that a
Cu(I)-CO-complex with the tridentate PY1 ligand (see
that the dimerization leading to 2a allows the sulfur atom to
bind to copper more tightly and that the thioanisole group
in 1a is a poorer donor than the alkyl thioether ligand. In
1a, the Cu(I) is pushed out of the N1N3S1 plane (away
˚
from N2) by 0.206 A. The angle between the N1N3S1 plane
and the Cu1N2S1 plane is 88.9ꢀ. The structure of 1a shows
the copper(I) ion is out from the center of ligand coordina-
tion environment forming a distorted tetrahedral geometry,
suggestive of its facile O2 reactivity, vide infra.
Copper(I) Complex Carbon Monoxide Binding. To ob-
tain insights into the solution state structures of these
copper(I) complexes, as well as to obtain information
concerning the relative amount of electron donation to
the copper(I) ion as a function of ligand set (i.e., TMPA vs
L
ASM vs LESE vs LEOE), (ligand)CuI-CO complexes were
Scheme 3) gives a ν(C-O) = 2091 cm-1 55
for L
ESE 24,25 the copper(I)-CO complex with LASM gives
.
As reported
generated and IR spectra were recorded. We have pre-
viously used CO-adducts for such purposes when study-
ing a variety of copper(I) complexes with either tridentate
or tetradentate ligands, and possessing systematically
varied pyridyl 4-substituents.7,24 In general, copper(I)-CO
complexes have been widely studied,47-53 including to
compare/contrast to copper protein carbonyl adducts.29,54
,
only one IR peak (Figure 3, A), at 2090 cm-1, the same as
that for the 4-coordinated (N3-ligated) TMPA complex
(Scheme 3). Thus, we can conclude that the thioether donor
in [(LASM)CuI(CO)]þ 4c(1a-CO) is not ligated. Similarly,
[(LEOE)CuI(CO)]þ 4c(3a-CO), does not possess a ligated ether
oxygen donor (Figure 3, C; Scheme 3).
Electrochemical Behavior of Copper(I) Complexes. The
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Gee, A. D. Chem. Commun. 2009, 3696–3698.
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8880 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
Scheme 3
X-ray quality crystals could be obtained for [(LASM)CuII-
(CH3OH)]2þ (1c), Figure 5.
Figure 5 depicts the solid-state structure of [(LASM)CuII-
(CH3OH)]2þ (1c), revealing that thioether sulfur-CuII coor-
˚
dination does in fact occur, Cu-S = 2.5276 (6) A. This
suggests that an interaction with this S-donor ligand may also
occur in the peroxo complex which forms from the 1a/O2
reaction, see below. The other three nitrogen atoms in LASM
and one solvent derived methanol O-ligand are bound in
˚
equatorial positions; the copper(II) atom sits 0.1033(9) A out
of the best plane formed by N1, N2, N3 and O1 (rms devia-
˚
tion =0.0998 A) (Figure 5). Hexacoordination is completed
by weak ligation from an oxygen atom of a perchlorate anion,
˚
Cu-O = 2.6160 (17) A (Figure 5). This structure is very
reminiscent of the closely related and previously reported25
thioether LESE-copper(II) structure, [(LESE)CuII(CH3OH)]2þ
(2c), Figure 6. A comparison of bond distances and angles for
1c versus 2c shows most to be nearly identical (Table 4);
there is a noticeable elongation of the CuII-Sthioerether
bond distance (by 0.13 A) in the LASM complex 1c.59,60
˚
Solution Behavior of [(LASM)CuII(CH3OH)]2þ (1c); EPR
Spectroscopy. A frozen solution EPR spectrum of [(LASM)-
CuII(CH3OH)]2þ (1c) indicates a typical axial signature
(Figure 7) suggesting 1c is either 6-coordinate like in the
X-ray structure (vide supra) or possibly five-coordinate but
with SP or distorted SP coordination geometry. The EPR
spectrum and derived spectral parameters are very similar to
those observed for [(LESE)CuII(CH3OH)]2þ (2c).25 It is not in
a trigonal bipyramidal (TBP) environment, the geometry
most often found for five-coordinate complexes with TMPA,
[(tmpa)CuII-X]2þ/þ (X = H2O, CH3CN, Cl-).61-63 The
optical spectrum for 1c (Experimental Section) does not
exhibit a distinctive charge-transfer band which might sug-
gest Sthioether coordination.41,42,59,64-72 However, an axial
measured by cyclic voltammetry in DMF and CH3CN
solvents under Ar, and compared (side-by-side, under the
same conditions, Figure 4) with the behavior of [(LESE)-
CuI]þ (2a) and [(tmpa)CuI(CH3CN)]þ to assess any differ-
ences in tetradentate ligand donor ability. As discussed
above, CO-binding experiments did not provide such infor-
mation because the thioether ligand arm did not coordinate.
E1/2 values (vs [Fe(Cp)2]þ/0) for the compounds are listed in
Table 3. All exhibit quasi-reversible one-electron redox pro-
cesses. There is a marked difference in E1/2 values for the three
compounds with the TMPA-complex being most negative
(favoring Cu(II) relative to Cu(I)), while the LASM complex
has the most positive redox potential. Thus, the two thioether
containing ligands raise the complex E1/2 values relative to the
pyridyl donor in TMPA, presumably because of the well-
established and favorable “soft-soft” cuprous ion/thioether
interactions.33,57 Comparing the redox couples of LASM and
(59) Gilbert, J. G.; Addison, A. W.; Nazarenko, A. Y.; Butcher, R. J.
Inorg. Chim. Acta 2001, 324, 123–130.
(60) Description of the coordination geometry around Cu(II) in each
complex, 1c and 2c, as if they were pentacoordinate and without the axially
weakly bound perchlorate O-donor, indicates that both are distorted from
square-based pyramidal, τ = 0.24 and 0.25, respectively; τ = 0.0 for a perfect
square pyramid (SP); τ = 1 for a perfect trigonal bipyramidal (TBP) geometry;
see: Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
L
ESE, the former is a poorer donor to the copper in [(LASM)-
CuI]þ (1a) versus [(LESE)CuI]þ (2a), Table 3, and this finding
is consistent to the differences observed crystallographically,
in which the Cu-S distance in 1a is slightly longer than that
of 2a (vide supra). Thus, the ethylthioether group in LESE is
more electron-donating compared to the thioanisole moiety
in LASM. It is noteworthy that another important factor
for E1/2 variations among copper complexes is chelate ring
size. In the present case, this factor is not at work given the
design of the ligands in which all chelate ring sizes are five-
membered. Small differences might be expected because of
changes in hybridization as in the thioanisole versus
ethylthioether moieties in 1a and 2a; however, the structural
data shows those angles to be the same.
(61) Karlin, K. D.; Hayes, J. C.; Shi, J.; Hutchinson, J. P.; Zubieta, J.
Inorg. Chem. 1982, 21, 4106–4108.
(62) Zubieta, J.; Karlin, K. D.; Hayes, J. C. Structural Systematics of
Cu(I) and Cu(II) Derivatives of Tripodal Ligands. In Copper Coordination
Chemistry: Biochemical and Inorganic Perspectives; Karlin, K. D., Zubieta, J.,
Eds.; Adenine Press: Albany, NY, 1983; pp 97-108.
€
(63) Fox, S.; Nanthakumar, A.; Wikstrom, M.; Karlin, K. D.; Blackburn,
N. J. J. Am. Chem. Soc. 1996, 118, 24–34.
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Rheingold, A. L.; Karlin, K. D. Inorg. Chem. 2006, 45, 10098–10107.
(65) Aronne, L.; Dunn, B. C.; Vyvyan, J. R.; Souvignier, C. W.; Mayer,
M. J.; Howard, T. A.; Salhi, C. A.; Goldie, S. N.; Ochrymowycz, L. A.;
Rorabacher, D. B. Inorg. Chem. 1995, 34, 357–369.
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104, 143–172.
X-ray Structure of a Cu(II) Complex with the N3S
Thioether Ligand LASM. To better understand the nature
of copper(II) ion binding with the tripodal ligands being
studied here, a copper(II) complex with LASM was synthesized.
(68) Solomon, E. I.; Penfield, K. W.; Wilcox, D. E. Struct. Bonding
(Berlin) 1983, 53, 1–57.
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Chem. Soc. 1976, 98, 8344–8350.
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D. B. Inorg. Chem. 1999, 38, 4233–4242.
(58) Fry, H. C. Ph.D. Dissertation, Johns Hopkins University, Baltimore,
MD, 2004.

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8881
Figure 4. Cyclic voltammograms of [(LASM)CuI]þ (1a, red) and [(LESE)CuI]þ (2a, blue) measured in CH3CN (left) and DMF (right) under Ar. E1/2 values
reported (Table 3) are versus [Fe(Cp)2]þ/0 (black) measured as an external standard under the same conditions.
Table 3. Cyclic Voltammetry Data for Cuprous Complexes in CH3CN and
Reductive Dechlorination Reaction of [(LEOE)CuI]þ
(3a). Dissolving [(LEOE)CuI]þ 3a in dichloromethane
solvent instantly gives a blue solution at room tempera-
ture under a nitrogen atmosphere. During a 30 min
reaction time, a blue precipitate formed, and the resulting
product was isolated in good yield (>90%). ESI mass
spectrometry and elemental analysis reveal the product
identity as the LCuII-Cl complex shown in the diagram
below. The product is derived from a dehalogenation
reaction well-known for copper chemistry with TMPA5,73
and its analogues.74-78
DMFa
in CH3CN
in DMF
compounds
Epc
Epa
E1/2
Epc
Epa
E1/2
[(tmpa)CuI(CH3CN)]þ
[(LESE)CuI]þ (2a)
[(LASM)CuI]þ (1a)
b
b
-40025,58 -640 -580 -610
-350 -210 -280
-110 þ10 -50
b ΔEp ∼ 100 mV.58
-410 -545 -480
-230 -365 -300
a mV vs [Fe(Cp)2]þ/0
.
A suitable single crystal was obtained for [{(LEOE)CuII-
(Cl)}2]2þ (3c). The geometry of the cupric ion is distorted
octahedral with three nitrogen donors and one chloride
anion in equatorial positions (Figure 8). The ether oxygen
donor is weakly axially coordinated to the copper ion,
Figure 5. Molecular structure of a cationic portion {[(LASM)CuII(CH3-
OH)](ClO4)}þ {(1c)ClO4} from X-ray crystallographic analysis. A non-
coordinated perchlorate counteranion and hydrogen atoms (except that
for the coordinated MeOH group) have been omitted for clarity.
˚
Cu O = 2.4765 A), while the other chloride ligand
from the partner complex is weakly occupied in the other
3 3 3
˚
axial position with much longer distance (2.9536 A).
Pentacoordination in mononuclear complexes is more
typical for such tripodal tetradentate ligands with all N
donors, for example, (ligand)CuII-Cl,5,74-78 It seems
that with the weak Oether donor, the cupric ion is able to
also interact with a sixth ligand, here the chloride from the
other ligand-copper(II) moiety, to form the observed dimer.
ꢀ
(73) Jacobson, R. R.; Tyeklar, Z.; Karlin, K. D. Inorg. Chim. Acta 1991,
181, 111–118.
(74) Lucchese, B.; Humphreys, K. J.; Lee, D.-H.; Incarvito, C. D.;
Sommer, R. D.; Rheingold, A. L.; Karlin, K. D. Inorg. Chem. 2004, 43,
5987–5998.
ꢀ
(75) Lee, D.-H.; Wei, N.; Murthy, N. N.; Tyeklar, Z.; Karlin, K. D.;
Figure 6. Molecular structure comparison between isolated cations of
{[(LASM)CuII(CH3OH)](ClO4)}þ ([1c]ClO4) and {[(LESE)CuII(CH3OH)]-
(ClO4)}þ ([2c]ClO4) derived fromX-ray crystallographic analysis. Hydro-
gen atoms are omitted for clarity.
€
Kaderli, S.; Jung, B.; Zuberbuhler, A. D. J. Am. Chem. Soc. 1995, 117,
12498–12513.
(76) Wei, N.; Murthy, N. N.; Chen, Q.; Zubieta, J.; Karlin, K. D. Inorg.
Chem. 1994, 33, 1953–1965.
(77) Wei, N.; Murthy, N. N.; Karlin, K. D. Inorg. Chem. 1994, 33, 6093–
6100.
thioether charge-transfer would not be expected to have
much intensity.
ꢀ
(78) Wei, N.; Murthy, N. N.; Tyeklar, Z.; Karlin, K. D. Inorg. Chem.
1994, 33, 1177–1183.

8882 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
Table 4. Selected Bond Distances and Angles of [(LASM)CuII(CH3OH)]2þ (1c) and [(LESE)CuII(CH3OH)]2þ (2c)25
[(LASM)CuII(CH3OH)]2þ (1c)
[(LESE)CuII(CH3OH)]2þ (2c)25
˚
bond distance (A)
˚
bond distance (A)
Cu-X
Cu-X
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-N(3)
Cu(1)-S(1)
Cu(1)-O(1)
Cu(1)-O(6)a
1.9746 (17)
2.0573 (16)
1.9712 (17)
2.5276 (6)
2.0029 (14)
2.6160 (17)
Cu(1)-N(2)
Cu(1)-N(1)
Cu(1)-N(3)
Cu(1)-S(1)
Cu(1)-O(1)
Cu(1)-O(8)a
1.981 (2)
2.0302 (19)
1.983 (2)
2.6551 (7)
2.0009 (17)
2.57 (1)
[(LASM)CuII(CH3OH)]2þ (1c)
[(LESE)CuII(CH3OH)]2þ (2c)25
X-Cu-X
bond angle (deg)
X-Cu-X
bond angle (deg)
N(1)-Cu(1)-N(3)
N(1)-Cu(1)-N(2)
N(2)-Cu(1)-N(3)
N(1)-Cu(1)-O(1)
N(2)-Cu(1)-O(1)
N(3)-Cu(1)-O(1)
N(1)-Cu(1)-S(1)
N(2)-Cu(1)-S(1)
N(3)-Cu(1)-S(1)
O(1)-Cu(1)-S(1)
163.36 (7)
84.28 (7)
84.07 (7)
97.79 (6)
177.89 (6)
93.82 (7)
91.80 (5)
87.79 (5)
99.57 (5)
92.57 (5)
N(2)-Cu(1)-N(3)
N(1)-Cu(1)-N(2)
N(3)-Cu(1)-N(1)
N(1)-Cu(1)-O(1)
N(2)-Cu(1)-O(1)
N(3)-Cu(1)-O(1)
N(1)-Cu(1)-S(1)
N(2)-Cu(1)-S(1)
N(3)-Cu(1)-S(1)
O(1)-Cu(1)-S(1)
164.01 (8)
84.41 (8)
82.20 (8)
178.94 (8)
96.36 (8)
96.93 (8)
87.61 (6)
90.00 (6)
98.11 (6)
93.13 (6)
a One perchlorate anion coordinates very weakly to Cu(1).
Figure 7. EPR spectra of [(LASM)CuII(CH3OH)]2þ (1c) taken with an
X-band spectrometer (ν = 9.186 GHz) in 2-methyltetrahydrofuran
(MeTHF)/CH3CN (1:1) at 77 K. g|| = 2.28, A|| = 158 gauss; g^ = 2.06.
Figure 8. X-ray structure of a cationic portion [{(LEOE)CuII(Cl)}2]2þ
(3c). The B(C6F5)4- counteranion and hydrogen atoms are omitted from
the ORTEP view for clarity.
Selected bond distances and angles for 3c are listed in
Table 5.
Table 5. Selected Bond Distances and Angles of [{(LEOE)CuII(Cl)}2]2þ (3c)
Dioxygen Reactivity of [(LASM)CuI]þ (1a B(C6F5)4);
3
End-on Peroxo-Dicopper(II) Formation. Dioxygen reacts
reversibly with 2 equiv of [(LASM)CuI]þ (1a) in 2-methyl-
tetrahydrofuran (MeTHF) at -125 ꢀC, forming the low-
temperature stable deep blue species [{(LASM)CuII}2-
(O22-)]2þ (1bP). This exhibits UV-visible absorptions
at 442 (1,500 M-1 cm-1), 530 (8,600 M-1 cm-1), and
605 nm (10,400 M-1 cm-1) (Table6), (spectrumB, Figure9).
The prominent LMCT transitions occur in the region
(500 to 650 nm), an energy region typical for end-on
peroxo species;2 however, the ∼600 nm absorption region
is relatively more intense. This appears to be a conse-
quence of the thioether ligation; we observed this same
absorption pattern with a peroxo species derived from the
analogue thioether ligand chelate LESE (Chart 2).24,25
There, analysis of the spectroscopic data (including reso-
nance Raman spectroscopy) showed that the strong
low-energy UV-vis feature in [{(LESE)CuII}2(O22-)]2þ
(2bP) was not from a Cu-S charge transfer band, but
rather the result of a geometric change around the cupric
center of the peroxo complex. The coordination geometry is
bond
distance (A)
bond
angle (deg)
˚
Cu-X
X-Cu-X
N(1)-Cu(1)-N(3)
N(1)-Cu(1)-N(2)
N(2)-Cu(1)-N(3)
N(1)-Cu(1)-Cl(1)
N(3)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(1)
N(1)-Cu(1)-O(1)
N(3)-Cu(1)-O(1)
N(2)-Cu(1)-O(1)
Cl(1)-Cu(1)-O(1)
165.40 (8)
82.13 (8)
83.62 (8)
96.33 (6)
97.77 (6)
177.25 (5)
97.15 (7)
83.23 (7)
79.10 (6)
103.38 (4)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-N(3)
Cu(1)-O(1)
Cu(1)-Cl(1)
Cu(1)-Cl(1A)
Cu(1)-Cu(1A)
1.979 (2)
2.0418 (19)
1.9854 (19)
2.4765 (16)
2.2305 (6)
2.9536 (6)
3.6254 (5)
distorted toward square-based pyramidal (SP) compared
to the TBP geometry (with axial peroxo O-ligand) known
for [{(tmpa)CuII}2(O22-)]2þ (Scheme 1). EXAFS data
clearly revealed that the thioether sulfur atom of LESE
coordinates to copper in [{(LESE)CuII}2(O22-)]2þ, with a
24
˚
Cu-Svectorof2.4 A. We do not have corresponding data
for [{(LASM)CuII}2(O22-)]2þ (1bP); however, given the close
similarity of LASM and LESE N3Sthioether ligands (Chart 1),

Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8883
Table 6. UV-vis and Resonance Raman Spectroscopic Data for Tripodal Ligand Copper-Dioxygen Adducts
complex
LMCT; λmax nm (ε M-1 cm-1
)
solvent temp
ν(O-O); Δ(18Ο2); cm-1
832; -44
ν
sym(Cu-O); Δ(18O2) cm-1
561; -26 a
[{(tmpa)CuII}2(O22-)]2þ79
[{(tmpa)CuII}2(O22-)]2þ80
435 (1,700) 524 (11,300) 615 (5,800) EtCN -80 ꢀC
430 (2,100) 520 (12,000) 590 (8,000) MeTHF -128 ꢀC
[{(LESE)CuII}2(O22-)]2þ (2bP)24 445 (2,600) 530 (9,200) 605 (11,800) MeTHF -128 ꢀC
817; -46
828; -48
545; -26 b
547; -23
[{(LASM)CuII}2(O22-)]2þ (1bP) 442 (1,500) 530 (8,600) 605 (10,400) MeTHF -128 ꢀC
a The values were obtained with [{(tmpa)CuII}2(O22-)]2þ as a powder; in propionitrile solution at 190 K, the 832 and 561 cm-1 peaks shift to 826 and
554 cm-1, respectively. b Resonance Raman measurements were carried out in CH2Cl2 as solvent.
Figure 9. Low-temperature UV-vis spectra: A (green): 1a with absorp-
tion at 318 nm, ε 5,100 M-1 cm-1. B (blue): 1bP with absorption at 445
(ε 1,500 M-1 cm-1), 530 (ε 8,600 M-1 cm-1), and 605 nm (ε 10,400 M-1
cm-1) in MeTHF at -125 ꢀC. A, B, and C (multiple spectra in a different
colors): five cycles by vacuum/purging of 1bP and O2 bubbling of 1a. D
(red): At -100 ꢀC, warmed from -125 ꢀC, the absorption intensity due to
3bP is reduced. E (orange): At -94 ꢀC, warmed from -125 ꢀC, the
absorption intensity due to 3bP is further reduced. See text.
Figure 10. Resonance Raman spectra of [{(LASM)CuII}2(O22-)]2þ (1bP)
in THF at 77 K (blue spectrum denotes 16O2, red spectrum denotes 18O2.
λ
ex = 568 nm. ν(O-O) = 828 cm-1(Δ(18O2) = 48), νsym(Cu-O) = 547
cm-1 (Δ(18O2) = 23) and νasym(Cu-O) = 497 cm-1 (Δ(18O2) = 22).
summarizes resonance Raman spectroscopic data for 1bP,
the closely related 2bP, and the TMPA complex with all
nitrogen donor ligands, [{(tmpa)CuII}2(O22-)]2þ. Both the
ν(O-O) and ν(Cu-O) stretching vibrations occur at lower
energy than is found in [{(tmpa)CuII}2(O22-)]2þ, (832 and
561 cm-1, respectively). As reported [{(LESE)CuII}2-
(O22-)]2þ (2bP) similarly shows weakening of the O-O
along with the very closely matching UV-visible absorp-
tion envelope (and see further discussion and Figure below),
we conclude that 1bP possesses the same structure as 2bP and
includes thioether S-ligation.
After applying a vacuum and purging with Ar at -125 ꢀC
in MeTHF led to the removal of O2 from [{(LASM)CuII}2-
(O22-)]2þ (1bP), and yellow solutions of 1a (spectrum A,
Figure 9) can be regenerated. A second low-temperature
oxygenation allowed full reformation of 1bP, which indi-
cates that little or no irreversible decomposition occurs at
reduced temperatures (below -80 ꢀC). In fact, five oxyge-
nation-deoxygenation cycles could be carried out, with
the final spectrum (C, Figure 9) being essentially identical
to the first. We find that the peroxo 1bP and cuprous
complex (1a) equilibrium is sensitive to the solution tem-
perature. An increase of ∼30 degrees in temperature re-
sulted in a ∼ 40% decrease in absorption of 1bP, spectrum E
(Figure 9) measured at -94 ꢀC. We note that the oxygena-
tion and UV-vis behavior of 1a and 2a are the same as that
observed for warmer solutions (∼-90 ꢀC) in THF and
CH2Cl2 solvents.
and Cu-O bonds compared to [{(tmpa)CuII}2(O22-)]2þ 24,25
.
As already explained in detail for the case of 2bP, these
changes occur from a combination of factors; the thioether
ligand acts as a good (electronic) donor, and geometric
distortions from TBP occur, probably because of the ligand
structure changes put in place by LESE and LASM compared to
TMPA. As discussed above from cuprous structures for 1a
and 2a and their electrochemistry, the thioanisole moiety
seems to behave as a poorer donor ligand than the alkyl
thioether. It is interesting that both the ν(O-O) and the
ν(Cu-O) for 1bP are higher than that for 2bP which is
consistent with the structural and electrochemistry results
for their cuprous complexes, that is, that the thioanisole
S-atom in LASM is a poorer donor that is the alkyl-thioether
S-donor in LESE
.
Dioxygen Complex Reactivity with [(LEOE)CuI]þ (3a).
To further provide (indirect) chemical evidence that
sulfur coordination is also involved in peroxo complexes
[{(LASM)CuII}2(O22-)]2þ (1bP) and [{(LESE)CuII}2(O22-)]2þ
(2bP), we examined the copper(I)/O2 reactivity with the ether
analogue, LEOE (Chart 1). Oxygenation of [(LEOE)CuI]þ (3a)
leads to formation of a new species with prominent optical
absorption at 380 nm (ε ∼ 10,000 M-1 cm-1, b in Figure 11).
On the basis of established UV-vis criteria,2 a bis(μ-oxo)
complex [{(LEOE)CuIII}2(O2-)2]2þ (3bO) formed, and not an
end-on peroxo species. Copper(I) complexes with tridentate
Resonance Raman Spectroscopic Characterization of
[{(LASM)CuII}2(O22-)]2þ (1bP). Resonance Raman spectra
also support the formation and formulation of the
peroxo-dicopper(II) species [{(LASM)CuII}2(O22-)]2þ (1bP)
(Figure 10). Isotope dependent features were observed both
at 828 cm-1 (Δ(18O2) = 48) and 547 cm-1 (Δ(18O2) = 23).
On the basis of their energies and reduced mass considera-
tions following 18O2 isotope substitution, the features are
assigned as the ν(O-O) and ν(Cu-O) modes, respectively.
These occur in the range of those previously found for a
trans-μ-1,2-peroxodicopper(II) complex.2,24,25,79 Table 6

8884 Inorganic Chemistry, Vol. 49, No. 19, 2010
Lee et al.
Figure 12. Low-temperature UV-vis spectra: A (black), [{(tmpa)-
CuII}2(O22-)]2þ; B (blue), [{(LESE)CuII}2(O22-)]2þ (2bP); and C (red),
[{(LASM)CuII}2(O22-)]2þ (1bP).
type reaction and stoichiometry.64 An 18O2 labeling ex-
periment revealed dioxygen as the source of the sulfoxide
oxygen atom. Thus, ESI and FAB mass spectrometry
obtained on both the (LAS(O)M)-copper(II) complex in the
reaction product mixture, as well as with the isolated
sulfoxide organic (following demetallation), indicate
that the oxygen atom is transferred to LASM from labeled
18O2 in 1bP with >90% incorporation (See Experimental
Section). It is interesting to note that Kodera and
coworkers41 did not observe any thioether oxidation
when generating a copper(II)-OOH species using a ligand
with an -SPh moiety.
Figure 11. Low-temperature UV-vis spectra of A: [(LEOE)CuI]þ (3a)
absorption at 329 nm, 5,000 M-1 cm-1, B: [{(LEOE)CuIII}2(O2-)2]2þ
(3bO) absorption 380 nm (10,000 M-1 cm-1) in THF at -94 ꢀC.
Scheme 4
Comparisons of [{(LASM)CuII}2(O22-)]2þ (1bP) versus
[{(LESE)CuII}2(O22-)]2þ (2bP). As stated, the electronic
absorption spectra of both [{(LASM)CuII}2(O22-)]2þ (1bP)
and [{(LESE)CuII}2(O22-)]2þ (2bP) show an inversion in
intensity of the two dominant LMCT bands (∼ 500 and
∼600 nm) compared with those observed in [{(tmpa)-
CuII}2(O22-)]2þ, Figure 12.24,25 For 2bP, it was previously
determined to reflect the presence of the Sthioether donor
and a peroxide ligand π*σ /π*ν inversion, likely a result of
a copper(II) geometry distorted toward SP.24,25 As 2bP
possesses an extremely similar LMCT pattern (and of
course the LASM and LESE ligands are similar), the same
analysis would apply to 1bP. As described, structural
comparisonsof[(LASM)CuII(CH3OH)]2þ (1c) with [(LESE)-
CuII(CH3OH)]2þ (2c) reveal these to have very similar
cupric ion coordination geometries. All of this indirectly
supports the similarity observed in the optical spectra of the
peroxodicopper(II) complexes derived from these ligands.
The electrochemical and structural data accompanied with
the resonance Raman analysis suggests that the thioanisole
group in 1bP has a poorer electron donating ability com-
pared with the thioether moiety.
ligands like the PY1 moiety in LEOE give bis(μ-oxo) dicopper-
(III) complexes;47,81,82 the fact that this does not occur with
LASM and LESE, supports the idea that the sulfur atom is
coordinated in 1bP and 2bP.
Sulfoxidation of LASM in 1bP. A green solution was
obtained following warming solutions of [{(LASM)CuII}2-
(O22-)]2þ (1bP) to RT. After a demetallation procedure,
the decomposition product was isolated and identified as
the sulfoxide derivative of LASM, obtained in moderate
yield (∼ 37%), Scheme 4 (see Experimental Section). The
same behavior was also observed for 2bP, and the corre-
sponding sulfoxide product of LESE was obtained in 44%
yield.25 This kind of behavior suggests a monooxygenase
Summary and Conclusions
To provide further insights into the nature of sulfur
ligation to copper ion and the resulting oxidative chemistry,
we have here described the copper-O2 chemistry with thioa-
nisole containing N3S ligand LASM, the close analogue of
previously reported alkyl thioether ligand LESE 24,25
The
.
thioanisole moiety in [(LASM)CuI]þ (1a) is a poorer donor
compared to [(LESE)CuI]þ (2a), based on comparative electro-
chemistry studies, and the observation of a relatively longer
Cu-S bond distance in crystal structures of 1a versus 2a.
Both thioether containing complexes exhibit significant
differences in the optical transitions and resonance Raman
ꢀ
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Article
Inorganic Chemistry, Vol. 49, No. 19, 2010 8885
characteristics of their cupric-peroxo binuclear complexes
(i.e., their dioxygen adducts) in comparison to the properties
observed for the all nitrogen parent compound [{(tmpa)-
CuII}2(O22-)]2þ. The variations are ascribed to the thioether
ligationpresentin[{(LASM)CuII}2(O22-)]2þ (1bP) and[{(LESE)-
CuII}2(O22-)]2þ (2bP) which leads to copper(II) ion local
geometric distortions away from TBP toward SP. Support for
this postulate includes structural characteristics (SP geometries)
observed in X-ray structures of the mononuclear copper(II)
analogues, [(LASM)CuII(CH3OH)(ClO4)]þ (1c) and [(LESE)-
CuII(CH3OH)(ClO4)]þ (2c). The poorer thioether ligand do-
nating ability in LASM compared to LESE is also manifested in
observed resonance Raman spectroscopic variation in 1bP
versus 2bP; as seen before, stronger ancillary ligand donation
reduces the donor interaction of the peroxide with the Cu
orbital that leads to lowering of ν(O-O) and ν(Cu-O);83 thus
both the O-O and Cu-O bonds are weakened relative to
The correlation of variations (i.e., denticity, donor atom
type, chelate ring size) in the nature of coordinating ligands
with copper-dioxygen adduct structure and spectroscopy
continues to be an area of active inquiry. To this end, we
plan to design and investigate new systems, for example, to
explore thioether coordination effects on CuI/O2 chemistry
with only two nitrogen donors per copper ion present. Given
the observed weakening of O-O an Cu-O bonds in these
thioether containing peroxo-dicopper(II) complexes, here
and in our other studies,24,25,45 comparative substrate oxida-
tive reactivity studies are also warranted.
Acknowledgment. K.D.K., E.I.S., and M.K.E. are grate-
ful to the NIH for support (GM 28962, DK 031450, GM
085914 (postdoctoral fellowship) respectively). D.H.L. is
grateful to Chonbuk National University for support.
[{(tmpa)CuII}2(O22-)]2þ
.
Supporting Information Available: Crystallographic informa-
tion files (CIF) for [(LASM)CuI]þ (1a), [(LASM)CuII(CH3OH)]2þ
(1c), and [{(LEOE)CuII(Cl)}2]2þ (3c). This material is available
free of charge via the Internet at http://pubs.acs.org.
(83) Henson, M. J.; Vance, M. A.; Zhang, C. X.; Liang, H.-C.; Karlin,
K. D.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 5186–5192.