Metal-templated ligand architectures for trinuclear chemistry: Tricopper complexes and their O2 reactivity

Article abstract of DOI:10.1039/c2sc21758a

A trinucleating framework was assembled by templation of a heptadentate ligand around yttrium and lanthanides. The generated complexes orient three sets of two or three N-donors each for binding additional metal centers. Addition of three equivalents of c

Full text of DOI:10.1039/c2sc21758a

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Dynamic ArtVicielweALrtiinclke sOn►line
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ARTICLE TYPE
Metal-Templated Ligand Architectures for Trinuclear Chemistry:
Tricopper Complexes and Their O2 Reactivity
Davide Lionettia, Michael W. Daya and Theodor Agapie*a
A trinucleating framework was assmbled by templation of a heptadentate ligand around yttrium and lanthanides. The generated complexes
orient three sets of two or three N-donors each for binding additional metal centers. Addition of three equivalents of copper(I) leads to the
formation of tricopper(I) species. Reactions with dioxygen at low temperatures generate species whose spectroscopic features are
consistent with a µ3,µ3-dioxo-tricopper complex. Reactivity studies were performed with a variety of substrates. The dioxo-tricopper
species deprotonates weak acids, undergoes oxygen atom transfer with one equivalent of triphenylphosphine to yield triphenylphosphine
oxide, and abstracts two hydrogen atom equivalents from tetramethylpiperidine-N-hydroxide (TEMPO-H). Thiophenols reduce the
oxygenated species to a CuI3 complex and liberate two equivalents of disulfide, consistent with a four-electron four-proton process.
multidentate sites for binding of transition metals. The synthesis
of tricopper complexes and their reactivity with O2 is discussed.
Introduction
Enzyme active sites containing three metal centers perform
Results and Discussion
diverse biological functions, including electron transfer,
hydrolytic reactions, and O2 reduction.1 These enzymes display
trimetallic moieties comprising of zinc, iron, magnesium, or
copper.2 In the context of O2 reduction to water, the tricopper
active sites of laccase and ascorbate oxidase (AO) have been
studied extensively given the potential applications in fuel cell
chemistry.3 In these enzymes, a fourth copper center situated ~12
Å away provides an additional reducing equivalent.4 Synthetic
efforts have focused on modeling the tricopper site where O2
activation occurs. Mononuclear diamine complexes have been
shown to self-assemble upon reaction with O2 to form a
CuII2CuIII(µ3-O)2 species.5 Reduction of these trinuclear cores
leads to dinuclear species, however, hindering attempts for
developing catalytic versions of this reaction. An alternate
strategy has been the employment of trinucleating frameworks.6
Most systems investigated are rather flexible and do not faciliate
cooperative trinuclear reactivity. Macrocyclic ligands have been
shown to bind three CuII centers, but O2 reactivity has not been
reported with these systems.7 Beyond tricopper models, recent
ligand-design synthetic efforts have been reported on trinuclear
complexes of manganese, iron, cobalt, and zinc.8
Group 3 and lanthanide ions are known to bind heptadentate,
tripodal [O3N4]-trisphenoxide-trisimine-amine ligands in
a
fashion that positions carbon substituents ortho- to the phenoxide
oxygen about 3–4 Å apart from each other.10 This separation is in
the range observed for the copper centers in laccase and AO.
Substitution with multidentate moieties at these positions are
expected to allow for binding of three metal centers in close
proximity. Additionally, these ligating moieties were selected to
allow for orthogonal binding of different metals (e.g. first row
transition metals vs lanthanides or yttrium) at the desired sites.
Toward assembling such multinucleating ligand architecture, a
variant (2) of the [O3N4]-trisphenoxide-trisimine-amine
framework with dipicolylamine substitutents was prepared via a
condensation between tris(2-amino-ethyl)amine and three
equivalents of previously reported aldehyde 1 (Scheme 1).11
Metallation was perfomed via alkane elimination with an yttrium
trialkyl precursor. NMR spectroscopic characterization shows a
single phenoxide and pyridine environment, consistent with
yttrium binding to the [O3N4]-trisphenoxide-trisimine-amine
moiety to generate a high-symmetry species (3). Addition of three
equivalents of CuI precursor (Cu(CH3CN)4OTf) dissolved in
acetonitrile (MeCN) to a suspension of 3 in MeCN leads to the
generation of a homogeneous mixture and to a color change from
light yellow to gold. In contrast to 3, the generated species is
soluble in acetonitrile but not soluble in less polar solvents (e.g.:
THF) suggesting the formation of an ionic complex. Single
crystal X-ray diffraction studies show the formation of a
tricationic Cu3Y species, 4 (Figure 1), with the seven-coordinate
yttrium center bound to the [O3N4]-trisphenoxide-trisimine-amine
We have investigated 1,3,5-triarylbenzene frameworks,
appended with a variety of donors, capable of supporting
9
multimetallic systems.8c, The reaction of O2 with a tricopper
complex based on this framework was complicated in part
because of the presence of alcohol groups which lead to a bridged
alkoxide species upon oxidation to CuII.9b We report here a novel
strategy for the generation of trimetallic moieties based on
templating a ligand scaffold around yttrium or lanthanides to
generate
a seven-coordinate complex that displays three
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Page 2 of 7
site, the three copper centers bound to the dipycolylamine
moieties, and three outer-sphere triflate anions. Acetonitrile
molecules bind to the copper centers to complete distorted
tetrahedral coordination environments. The selectivity for yttrium
binding to the [O3N4] motif, despite the presence of nine
additional nitrogen donors is notable, and indicates that this
strategy may be more general with respect to changes in the
nature of chelating ligands and metals decorating the [YO3N4]
unit. In the solid-state, the copper centers are twisted away from
dimethylhydrazino)-dimethylhydrazone-3-penten-2-one (C)
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These complexes were all self-assembled
12
by Tolman et al.5,
from concentrated solutions of monocopper(I) precursors
supported by bidentate amines. To test the behavior of the present
architecture with other donor sets, a ligand variant with only two
nitrogen donors per copper-binding arm was synthesized for
comparison – for each arm, one pyridyl group was replaced with
phenyl. The related Cu3Y complex, 6, was prepared, and its
reaction with O2 led to a new species (7) with spectroscopic
1
each other leading to separations of ~9 Å. H NMR studies show
features similar to those of 6 (Figure 2). Spectroscopic
only one pyridine environment, despite the fact that the solid state
structure is pseudo-C3 symmetric. This indicates that in solution
the conformation of the molecule is fluxional, with the copper
centers potentially approaching closer orientations.
comparison (UV-Vis and EPR, see also SI) with A, B, and C
(Table 1) and the reaction stoichiometry support the assignment
of species 5 and 7 as displaying the CuII2CuIII(µ3-O)2 motif.13
Additionally, no evidence of the presence of H2O2 was observed
when a solution of 5 was treated with formic acid (5 equiv) and
Ti(IV)oxysulfate solution.12c, 14
OH
N
N
N
N
N
O
N
N
N
N
2
1
N
N
NH2
N
N
3
N
O
+ YR3(THF)2
R=CH2SiMe3
O
N
3 CuOTf
O
N
N
Y
N
3
HO
N
MeCN
L=MeCN
N
3
2
2
N
N
N
N
+3
+3
3
N
N
N
O
N
N
N
N
N
N
LCu
N
CuL
Cu
N
Cu
CuL
Cu
N
N
O
N
O2, -78 o
EtCN
C
O
O
O
O
O
O
Y
Y
N
N
N
N
N
N
N
N
4
5
CH
CH
N
CH
+3
+3
N
CH
LCu
O
N
N
N
N
CuL
Cu
CH
Figure 1. Solid-state structure of tricationic complex 4. Thermal ellipsoids
Cu
CuL
Cu
CH
N
N
N
shown at 50% probability. Hydrogen atoms are omitted for clarity.
N
N
O
N
The synthesis of 5 and 7 is notable given the lack of precedent
for preassembled trinuclear complexes that show similar
reactivity with O2. The generation of 5 is particularly noteworthy
given that previous studies of copper-dipicolylamine complexes
do not report trinuclear reactivity.15 This difference in behavior
indicates that the formation of the CuII2CuIII(µ3-O)2 unit in this
case may be a consequence of preassembling the three copper
centers in close proximity. To further test this hypothesis, two
related monocopper complexes were prepared, 8 and 9, both
displaying copper-dipicolylamine moieties (Scheme 2). The
amine moiety in complex 8 is substituted with a methyl-aryl ether
fragment, removing the yttrium binding site. Complex 9 is
analogous to 4 by containing the Y-[O3N4] motif, but displays a
single dipicolylamine arm resulting in a monocopper complex.
(see SI for ligand and complex syntheses) If intermolecular
copper self-assembly reactivity upon reaction with O2 was
responsible for the spectroscopic features of 5 and 7, mononuclear
CuI complexes 8 and/or 9 were expected to undergo reactivity
similar to 4 and 6 given the steric and electronic similarities.
Reaction of either complex with O2, however, leads to a species
that has spectroscopic features different from 5 and 7 (Figure S32
in the Supporting Information). Even substantial increase in
concentration (0.2-10.0 mM) does not lead to the signature of the
CuII2CuIII(µ3-O)2 core. In contrast, 5 and 7 are formed at
concentrations as low as 0.05 mM. The literature intermolecular
O2, -78 o
EtCN
C
O
O
O
O
O
O
N
N
Y
N
N
Y
N
N
N
N
6
7
CH
N
N
N
N
N
N
N
Ph
2
N
N
Scheme 1 Synthesis of ligands and tetrametallic, tricopper system com-
plexes, and reactivity with O2.
The reaction of compound 4 with O2 was monitored by UV-Vis
spectroscopy at low temperatures (Figure 2). A new species (5) is
generated within a minute at -78 ºC and within seconds at -40 ºC.
This species is stable for at least 24 hours at -78 °C; about 30%
decay is observed over the same period at -40 °C and complete
decay is observed within minutes at 25 °C. Volumetric
measurements carried out with a Toepler pump indicate that
0.97±0.01 equivalents of O2 are consumed per equivalent of 4,
supporting the formation of a complex with the stoichiometry
“Cu3O2”. This corresponds to the
previously reported with bidentate ligands: N,N,N’,N’-
tetraalkylcyclohexanediamines (A, for N,N,N’,N’-
tetramethylcyclohexanediamine) by Stack et al., N,N-dimethyl-2-
picolylethanamine (B) by Itoh el al., and more recently 4-(2,2-
CuII2CuIII(µ3-O)2 core
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Page 3 of 7
Chemical Science
examples are generated at concentrations of 10 mM (Stack, Itoh)
N
View Article Onl+in3e
N
or 1.0 mM (Tolman). These findings suggest that the reactivity of
precursors 4 and 6 is intramolecular in copper and, moreover, the
formation of the CuII2CuIII(µ3-O)2 moiety is facilitated by the
presence of the three Cu centers in close proximity on the same
ligand framework.
N
N
LCu
N
3
N
N
CuL
CuL
N
2
i) Ln(HMDS)3
N
N
HO
N
ii) Cu(CH3CN)4OTf
L=MeCN
N
N
2
O
O
O
Ln
N
N
N
N
N
+3
N
H3CCN
O
N
N
N
(OTf)
N
OMe
(OTf)
H3CCN
Cu
N
N
Cu
CuI
Cu
N
Ln = La (10), Lu (11)
N
Cu
N
O
N
N
N
N
tBu
tBu
O2, -78 o
EtCN
C
O
O
N
N
O
8
tBu
Ln
N
Ln = La, Lu
O
O
N
O
N
N
N
N
Y
N
9
N
N
Scheme 3. Preparation and O2 reactivity of Cu3Ln complexes
N
Reactions of 5 and 7 with substituted ferrocenes were
N
performed to estimate their reduction potentials, similarly to
previous reports in the literature for products of O2 activation by
copper complexes.5a, 18 In each case the 480 nm band decayed
completely over 6 h upon treatment with decamethylferrocene
(EFc*/Fc*+ = -0.05 V vs SCE)19 at -40 °C. Treatment with 1,1’-
dimethylferrocene (EFcMe2/FcMe2+ = 0.34 V vs SCE)19 over the
same time period does not lead to decay of 5 or 7 beyond
background decomposition. This indicates that the reduction
potential of both 5 and 7 is between 0.34 and -0.05 V vs SCE. In
contrast, the reduction potentials of previously reported Cu3O2
species supported by neutral ligands lie between 0.79 and 0.48 V
vs. SCE as determined by analogous reactivity with ferrocene and
acetylferrocene.5a Furthermore, several CuIII2(µ2-O)2 species were
reported to have a reduction potential near 0.5 V vs SCE.20
Hence, 5 and 7 are significantly weaker oxidants. This may be
due to the presence of electron rich phenoxide substituents on the
nitrogen donors. Indeed, the Cu3O2 motif supported by more
electron rich, anionic ligands recently reported by Tolman are
unreactive toward decamethylferrocene.12c
Scheme 2. Mononuclear CuI complexes for reactivity comparison to tri-
copper Cu3Y variants.
Table 1. Spectroscopic features of CuII2CuIII(µ3-O)2 complexes.
A
B
C
5
7
λmax nm,
λmax nm,
λmax nm,
λmax nm,
λmax nm,
(ε, M-1cm-1)
(ε, M-1cm-1) (ε, M-1cm-1)
(ε, M-1cm-1) (ε, M-1cm-1)
290 (12,500)
-
-
-
355 (15,000) 343 (12,000) 328 (10,700) 355 (12,400) 340 (11,500)
480 (1,400) 515 (1,000) 420 (1,500) 480 (1,910) 455 (2,160)
620 (800)
685 (800)
590 (835)
640 (800)
690 (760)
Facilitation of trinuclear cooperative reactivity by the
tetrametallic, tricopper architecture in 4 has implications to the
reaction of O2 in biological systems, in which the protein scaffold
keeps the three copper centers in close proximity. Furthermore,
laccases and AOs bind the three copper centers using a total of
eight histidines. Compound 5 displays nine N-donors for three
coppers, which represents a more accurate model of biological
systems (eight total nitrogen donors for three copper centers) than
previous model complexes that a total of six nitrogen donors for
the Cu3O2 moiety, although in the present case, coordination of all
nitrogens has not been confirmed structurally. Although studies of
multicopper proteins have not shown evidence of a CuII2CuIII(µ3-
O)2 moiety,16 investigations of this moiety in a model system is
expected to further our understanding of O2 activation at tricopper
sites.
In order to determine whether geometric changes in the ligand
architecture would induce changes in reactivity, Cu3Ln complexes
analogous to 3 (Ln=La, 10; Lu, 11) were investigated. The size of
the central Ln(III) ion affects the relative orientation of the three
phenoxide arms, with the propeller-like turn of the aromatic rings
varying from 27.3º to 47.7º vs the axial N-Ln vector.17 Complexes
10-11 were prepared by protonolysis with suitable Ln(HMDS)3
reagents (HMDS=hexamethydisilazide, Ln=La, Lu) followed by
metalation with Cu(CH3CN)4OTf. Monitoring of O2 reactivity of
these complexes via UV-Vis spectroscopy revealed reactivity
analogous to Cu3Y complexes (Figure 2, bottom inset). The
similar reactivity of complexes of lanthanides of different sizes –
from largest, La, to smallest, Lu – further highlights the ability of
the present architechture to engender cooperative reactivity
among the three Cu centers regardless of the nature of the nature
of the central, nucleating metal.
Figure 2. UV-Vis spectra of solutions of 5 (blue) and 7 (red) in 3:2 tolu-
ene/acetonitrile. Top inset: Expanded view of the 400-800 nm region.
Bottom inset: spectra of oxygenated solutions of 10 (blue) and 11 (green)
in 1:1 toluene/propionitrile at -78ºC.
Compound 5 reacts with 2,4-di-tert-butylphenol at -40 °C (UV-
Vis spectroscopy). According to GC-MS and 1H NMR
spectroscopy, the phenol starting material is quantitatively
recovered upon work-up. This behavior is in contrast to that of
other Cu3O2 moieties supported by neutral ligands which generate
5c
biphenol.5a,
It has been previously proposed that the phenol
coordinates to copper prior to dimerization.5c The higher
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Page 4 of 7
coordination number of 5 may block phenol binding to the copper
centers. However, the analogous reaction of 7 – which has one
fewer N-donor available per Cu center – with phenol also failed to
yield dimerized product. This observation suggests that steric
differences, rather than coordination number, may be the reason
for the differences in reactivity between compounds 5 and 7 and
other Cu3O2 moieties. Nonetheless, reaction with a less bulky
phenol (4-tertbutylphenol) also showed no evidence of
oxygenation or C–C coupling. Furthermore, H-atom abstraction
by the Cu3O2 moiety was ruled out upon observing that reaction
with 2,4,6-tri-tert-butylphenol does not give rise to the known
2,4,6-tri-tert-butylphenoxyl radical as observed by UV-Vis
spectroscopy. Hence the observed reaction is proposed to involve
only protonation of the Cu3O2 moiety. The reactivity of 5 with a
variety of acids was studied. Treatment of 5 at -40 °C with
triethylammonium triflate (pKa=18.5 in acetonitrile)21 causes
complete decay of the 485 and 645 nm bands over 4 hours.22
Treatment of 5 with weaker acids results in slightly slower
reactions, as monitored by UV-Vis spectroscopy: 1,8-
diazabicyclo[5.4.0]undec-7-enium triflate (pKa=24.34)21, and
pyrrole (pKa=34.6)21, react with 5 to 50-70% completion in 6
hours. Although a pKa value cannot be assigned to 5, reaction
with acids as weak as pyrrole is consistent with the interpretation
of the reaction with phenols (pKa>25)21 also being protonation
events.
core in 5 to CuI.27 A solution of 5 that was allowed to warm to
room temperature to yield the decomposition products of 5 still
View Article Online
displayed reactivity with 4-tert-butylthiophenol, but only 50% of
the expected disulfide product was obtained, and the reduced
1
tricopper species was observed (~50% yield, H NMR) but could
not be isolated cleanly.
Ph3PO (1 equiv)
+ TEMPO-H
TEMPO (2 equiv)
+ Ph3P
-40 o
C
-40 o
C
S
S
EtCN/tol
-40 o
+
5
7
tBu
SH
C
tBu
tBu
(2 equiv)
Scheme 4. Reactivity of complex 5.
The present Cu3(µ3-O)2 moiety is a weaker oxidant relative to
other dicopper and tricopper oxo species with reported reduction
potentials. This may explain its lack of oxidative C–C coupling
reactivity with alkylphenols.28 X–H bond activation by 5 was
observed only with substrates that have weak X–H bonds. Since
X–H bond activation is controlled by both the reduction potential
and basicity of the metal-oxo species,29 it is not surprising that,
despite a qualitatively basic center, reactivity with stronger X–H
bonds is not observed, in view of the more negative reduction
potential. This behavior is consistent with the function of
tricopper sites in laccases and AOs, which are oxidases and hence
do not perform C–H oxygenations. Oxygenation reactivity would
likely be detrimental to these proteins, as it would lead to the
functionalization of amino-acid side chains.
The reactions of 5 with phosphine and H-atom transfer agents
were investigated (Scheme 4). Compound 5 was found to react to
completion with triphenylphosphine (5 eq) in 3 hours to give
triphenylphosphineoxide (0.84 ± 0.10 equivalents, 31P-NMR
spectroscopy). In contrast, treatment of 7 with PPh3 yielded ca. 2
equivalents of (O)PPh3, suggesting that the lower possible
coordination number of the Cu centers in 7 facilitates transfer of
the second oxygen atom to phosphine. Decay of the spectroscopic
signature of 5 was also observed upon treatment with N-hydroxy-
Conclusions
In summary, ligand frameworks displaying a total of sixteen or
thirteen oxygen and nitrogen donors were selectively templated
by yttrium(III) and lanthanides binding to a tripodal [O3N4]-
trisphenoxide-trisimine-amine moiety. The remaining three
pycolylamine-based metal binding sites coordinate copper(I).
Reactions of these CuI3Y complexes with O2 generate
CuII2CuIII(µ3-O)2 motifs according to spectroscopic comparison to
literature compounds and the measured reaction stoichiometry.
Since two related mononuclear copperdipicolylamine complexes
do not generate CuII2CuIII(µ3-O)2 species, the preorganized
tricopper core is necessary for this reactivity with O2. Similarly to
multicopper oxidases, the close arrangement of three metal
centers leads to cooperative activation of O2. Compound 5 is less
oxidizing than previously reported CuII2CuIII(µ3-O)2 complexes
and does not perform phenol dimerization. Oxygenation of
triphenylphosphine and activation of the weak O–H bond of
TEMPOH were observed, however. Oxidation of thiol to generate
two equivalents of diaryldisulfide show the ability of 5 to reduce
to a tricopper(I) core using four electrons and four protons.
Starting from 4, the overall process corresponds to the reduction
of O2 to H2O. The structural features that lead to these differences
compared to previous systems are not clear at this time and
further studies will explore the reactivity of this family of
CuII2CuIII(µ3-O)2 complexes. Future studies will focus in
developing catalytic O2 reduction systems and mechanistic studies
of O2 activation at tri- and tetranuclear cores based on the present
type of complexes. The molecular architectures reported here are
expected to be generally applicable to the assembly of
2,2,6,6-tetramethylpiperidine
(TEMPO–H,
pKa>41
in
acetonitrile,23 reaction complete in 4 hours). Integration of the
electron paramagnetic resonance signal of the TEMPO–H
reaction solution and comparison to a standard solution of
TEMPO radical49 indicates that two equivalents of TEMPO
radical are generated per Cu3O2 moiety. Hence, compound 5
formally performs H-atom abstraction, rather than just
deprotonation in this reaction. No reaction was observed with
9,10-dihydroanthracene or toluene. The observed trend in
reactivity reflects the trend in X–H bond dissociation energies for
these substrates (70 kcal/mol for TEMPO–H,24 74 kcal/mol for
dihydroanthracene,25 and 88 kcal/mol for toluene).26
The reactivity of complex 5 with thiol reducing agents was
investigated. Upon treatment with 4-tert-butylthiophenol (Scheme
4) disappearance of the UV-Vis bands characteristic of 5 was
observed within 1 min at -40 ºC. After anaerobic workup at room
temperature, the reaction mixture contained two equivalents of the
diaryldisulfide product (1H NMR), corresponding to an overall
transfer of four protons and four reducing equivalents by complex
5. A reduced (diamagnetic) tricopper species was recovered in
near-quantitative yield and was found to display thiophenol
ligands (1H NMR). Although structural characterization has
eluded to date, the identity of the recovered tricopper complex
(4•3ArSH) as a tricopper(I) adduct was supported by independent
synthesis via addition of thiophenol to 4. Therefore, unlike
TEMPO-H, thiophenol is capable of delivering the four electrons
and four protons necessary for full reduction of the CuII2CuIIIO2
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Chemical Science
Inoue, C. Ikeda, Y. Kawata, S. Venkatraman, K. Furukawa and A.
View Article Online
multimetallic complexes for
including multielectron redox processes and acid-base chemistry.
a variety of transformations
Osuka, Angew. Chem. Int. Ed., 2007, 46, 2306-2309.
8. (a) Q. L. Zhao and T. A. Betley, Angew. Chem. Int. Ed., 2011, 50,
709-712; (b) S. Friedle and S. J. Lippard, Eur. J. Inorg. Chem., 2009,
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Chemical Communications, 2011, 47, 4189-4191; (d) J. A. Hatnean,
R. Raturi, J. Lefebvre, D. B. Leznoff, G. Lawes and S. A. Johnson, J.
Am. Chem. Soc., 2006, 128, 14992-14999; (e) G. L. Guillet, F. T.
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Acknowledgments
We thank Lawrence M. Henling for crystallographic assistance.
We are grateful to Caltech and the ACS Petroleum Research Fund
for funding. The Bruker KAPPA APEXII X-ray diffractometer
was purchased via an NSF CRIF:MU award to Caltech, CHE-
0639094. The 400 MHz NMR spectrometer was purchased via an
NIH award, RR027690.
9. (a) J. S. Kanady, E. Y. Tsui, M. W. Day and T. Agapie, Science,
2011, 333, 733-736; (b) E. Y. Tsui, M. W. Day and T. Agapie,
Angew. Chem. Int. Ed., 2011, 50, 1668-1672.
Notes and References
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aDepartment of Chemistry and Chemical Engineering, California Institute
of Technology, 1200 E. California Blvd. MC 127-72, Pasadena, CA
91125, USA. E-mail: agapie@caltech.edu
† Electronic Supplementary Information (ESI) available: experimental
procedures, characterization data, and crystallographic details for 4 (CIF).
See DOI: 10.1039/b000000x/
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Chemical Science
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Rev., 2011, 40, 1870-1874; (d) J. J. Warren, T. A. Tronic and J. M.
Mayer, Chem. Rev., 2010, 110, 6961-7001.
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Chemical Science
Table of Contents Graphic:
View Article Online
+3
N
N
N
+3
N
O
N
Cu
Cu
N
Cu
Cu
Cu
Cu
N
N
O2, -78 o
EtCN
C
N
O
4 ArSH
S
S
[YCuI3
+
]
2
Ar
Ar
O
O
O
Y
N
N
N
N
Three copper centres assembled in close proximity via ligand preorganization by yttrium or lanthanides
perform intramolecular trimetallic dioxygen activation chemistry.
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 7