Synthesis and characterization of a (μ-η2: η2-Peroxido)dicopper(II) Complex with N,N',N″-Triisopropyl- cis,cis-1,3,5-triaminocyclohexane (R3TACH, R = iPr): Selective preparation of (μ-η2:η2-peroxido)dicopper(II) and bis(μ-oxido)dicopper(III) species regulated by substituent groups

Article abstract of DOI:10.1002/ejic.201200228

The new Cu^I complex of N,N',N″-triisopropyl-cis,cis-1,3,5- triaminocyclohexane (iPr₃TACH), [Cu(iPr₃TACH)(MeCN)](X), immediately reacts with dioxygen at-80 °C to give a (μ-η²: η²-peroxido)dicopper(II) complex. This observation is significantly different from the previously reported cases of bis(μ-oxido)dicopper(III) complexes that were generated by the reaction of copper(I) complexes of other TACH ligands (Et₃TACH, iBu ₃TACH, and Bn₃TACH) with dioxygen under the same reaction conditions. Such selective preparations have been explained in terms of the structural specificity provided by the TACH ligands that surround the metal centers. The obtained (μ-η²:η²-peroxido) dicopper(II) complex exhibits ortho-hydroxylation of a phenolate to ortho-quinone with ca. 50 % yield based on the peroxido intermediate. The bis(μ-oxido)dicopper(III) complexes with other TACH derivatives are not capable of oxygenation of phenolate. The (μ-η²: η²-peroxido)dicopper core is discussed in the context of the reaction mechanism of tyrosinase.

Full text of DOI:10.1002/ejic.201200228

Job/Unit: I20228
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FULL PAPER
DOI: 10.1002/ejic.201200228
Synthesis and Characterization of a (μ-η2:η2-Peroxido)dicopper(II) Complex
with N,NЈ,NЈЈ-Triisopropyl-cis,cis-1,3,5-triaminocyclohexane (R3TACH, R =
iPr): Selective Preparation of (μ-η2:η2-Peroxido)dicopper(II) and Bis(μ-oxido)-
dicopper(III) Species Regulated by Substituent Groups
Jun Matsumoto,[a] Yuji Kajita,[a] and Hideki Masuda*[a]
Keywords: Bioinorganic chemistry / Copper / Coordination modes / Hydroxylation
The new CuI complex of N,NЈ,NЈЈ-triisopropyl-cis,cis-1,3,5-
triaminocyclohexane (iPr3TACH), [Cu(iPr3TACH)(MeCN)]-
(X), immediately reacts with dioxygen at –80 °C to give a (μ-
η2:η2-peroxido)dicopper(II) complex. This observation is sig-
nificantly different from the previously reported cases of
bis(μ-oxido)dicopper(III) complexes that were generated by
the reaction of copper(I) complexes of other TACH ligands
(Et3TACH, iBu3TACH, and Bn3TACH) with dioxygen under
the same reaction conditions. Such selective preparations
have been explained in terms of the structural specificity pro-
vided by the TACH ligands that surround the metal centers.
The obtained (μ-η2:η2-peroxido)dicopper(II) complex exhibits
ortho-hydroxylation of a phenolate to ortho-quinone with ca.
50% yield based on the peroxido intermediate. The bis(μ-
oxido)dicopper(III) complexes with other TACH derivatives
are not capable of oxygenation of phenolate. The (μ-η2:η2-
peroxido)dicopper core is discussed in the context of the re-
action mechanism of tyrosinase.
mechanisms and identifying reaction intermediates. To elu-
cidate the structure–function relationships of these en-
zymes, various bioinorganic studies have been reported.
In 1989, Kitajima et al. provided the first report of a
complex with a (μ-η2:η2-peroxido)dicopper(II) structure
[CuII2-(μ-η2:η2-peroxido)(TpiPr,iPr)2, TpiPr,iPr = hydrotris-
(3,5-diisopropylpyrazolyl)borato],[21] which was proposed
as a structural model of the oxyHc active site. The oxyHc
active site structure was confirmed by X-ray crystallography
in 1994.[22,23] Subsequently, Tolman et al. identified another
interesting bis(μ-oxido)dicopper(III) species and demon-
strated that it is reversibly converted into the (μ-η2:η2-per-
oxido)dicopper(II) species.[24–26] We also previously pre-
pared these two species using sparteine as a ligand, which
are controlled by carboxylate coordination.[27] Based on
these two intermediate species, the mechanism of tyrosinase
activity has been discussed by several groups.
Casella et al. and Itoh et al. have reported that the Ty
activity of the (μ-η2:η2-peroxido)dicopper(II) species de-
pends upon the coordination of a phenolate anion to the
metal center. However, these reports did not provide any
direct evidence.[28–34] On the other hand, Stack et al. pre-
pared a [CuII2(μ-η2:η2-peroxido)(DBED)2]2+ complex using
a bidentate DBED ligand (DBED = N,NЈ-di-tert-butyl-
ethylenediamine), and found that it is converted to a bis(μ-
Introduction
The bioinorganic chemistry of copper has inspired the
development of synthetic systems as models to help us
understand the functions of metalloproteins.[1–13] Type 3
copper centers, which are found in the active sites of copper
metalloproteins such as hemocyanin (Hc), tyrosinase (Ty),
and catechol oxidase (CaO), play an important role in bind-
ing and/or activating dioxygen at their dimetallic sites.[14–16]
These proteins contain a dinuclear copper core with six co-
ordinated histidine imidazole groups and participate in
various biologically essential functions. For example, Hc
serves as a dioxygen carrier,[17] Ty catalyzes the ortho-hy-
droxylation of phenols to ortho-quinones,[8] and CaO cata-
lyzes the oxidation of ortho-catechols to ortho-quinones.[16]
Ty not only catalyzes the ortho-hydroxylation of phenols,
but it also catalyzes reversible oxygenation reactions similar
to Hc[18] and the oxidation of phenols to catechols similar
to CaO.[19,20] In the reaction of oxytyrosinase (oxyTy) with
a phenolate substrate, the most interesting step in the
monophenolase cycle of Ty is the insertion of an oxygen
atom at the ortho position of the phenol C–OH group by
oxyTy. Model studies using low molecular weight metal
complexes can be very helpful in elucidating reaction
[a] Department of Frontier Materials, Graduate School of
Engineering, Nagoya Institute of Technology
Showa-ku, Nagoya 466-8555, Japan
oxido)dicopper(III)
species,
[CuIII2(μ-O)2(phenolate)-
(DBED)2]2+, upon axial coordination of the phenolate sub-
strate to the metal ion to give ortho-catechol and ortho-
quinone.[35,36] It was claimed that the coordination of the
phenolic oxygen atom to the metal atom promotes the for-
Fax: +81-52-735-5228
E-mail: masuda.hideki@nitech.ac.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200228.
Eur. J. Inorg. Chem. 0000, 0–0
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J. Matsumoto, Y. Kajita, H. Masuda
FULL PAPER
mation of bis(μ-oxido)dicopper(III) species from (μ-η2:η2- using electronic absorption, electrochemical, IR, and X-ray
peroxido)dicopper(II) species, and that the active intermedi- analytical methods, and also discuss the oxidation reactivity
ate of Ty is the bis(μ-oxido)dicopper(III) species. Costas et of the (μ-η2:η2-peroxido)dicopper(II) complex with respect
al. have also shown that the bis(μ-oxido)dicopper(III) cores to phenolate.
induce ortho-hydroxylation of phenolate anions using the
dinuclear dicopper complex with a dinucleating ligand,
which has three or four coordination sites.[37] Furthermore,
it was reported that a trans-μ-η1:η1-peroxidodicopper(II)
complex with an unsymmetrical heptadentate ligand is also Results and Discussion
capable of ortho-hydroxylation of phenolate.[38,39] On the
other hand, Casella et al. demonstrated in spectroscopic
Synthesis and Characterization of Copper(I) Complexes
studies using native Ty that the active species of Ty is the
(μ-η2:η2-peroxido)dicopper(II) species and that the ortho-
The copper(I) complexes with the iPr3TACH ligand, [Cu-
(MeCN)(iPr3TACH)]X [1iPr(MeCN)·X, X = SbF6 or OTf],
were synthesized by the reactions of [Cu(MeCN)4]X (X =
SbF6 or OTf) with iPr3TACH in tetrahydrofuran (THF) un-
der anaerobic conditions. The formulations for the com-
plexes were determined by 1H NMR spectroscopy, IR spec-
troscopy, mass spectrometry, and elemental analysis.
hydroxylation of phenol proceeds through coordination of
phenol to the copper atom.[40] Tuczek and Casella et al.
described ortho-hydroxylation using a model system com-
prised of a dinuclear copper complex with α,αЈ-bis[bis{2-
(1Ј-methyl-2Ј-benzimidazolyl)ethyl}amino]-m-xylene,[30]
and recently Tuczek et al. succeeded in observing catalytic
hydroxylation of a coordinated phenolate anion using a
mononuclear copper(I) complex with a bidentate ligand
2,2-dimethyl-1-[2-(pyrid-2-yl)ethyl]iminopropane, phenol-
ate, and triethylamine.[41] The actual reaction mechanism of
Ty has not yet been confirmed.
1
iPr(MeCN)·SbF6 and 1iPr(MeCN)·OTf were recrystallized
from THF/Et2O. The coordination of MeCN to the cop-
per(I) ions in 1iPr(MeCN)·SbF6 and 1iPr(MeCN)·OTf was
confirmed by the observation of IR bands assigned to
ν(CϵN) at 2264 and 2265 cm–1, respectively, which lie in
the range of those of the previously reported copper(I)
complexes with other TACH ligands and an MeCN mole-
cule; 2280 cm–1 for Et3TACH, 2250 cm–1 for iBu3TACH,
and 2270 cm–1 for Bn3TACH. The carbonylcopper(I) com-
plexes with iPr3TACH, [Cu(CO)(iPr3TACH)]OTf [1iPr(CO)·
OTf] and [Cu(CO)(iBu3TACH)]PF6 [1iBu(CO)·PF6], were
We previously synthesized copper(I) complexes of
N,NЈ,NЈЈ-trialkyl-cis,cis-1,3,5-triaminocyclohexane deriva-
tives (R3TACH), which have ethyl (Et3TACH), isobutyl
(iBu3TACH), or benzyl groups (Bn3TACH) at the second-
ary amine nitrogen atoms, as Hc and/or Ty active center
models, and studied their reactions with dioxygen to pro-
duce the corresponding bis(μ-oxido)dicopper(III) com-
plexes. The reaction intermediates are capable of oxidizing
THF as an exogenous substrate to give 2-hydroxytetra-
hydrofuran and γ-butyrolactone, but they do not oxidize
phenol.[42,43] At this stage, we synthesized a new triamino-
cyclohexane derivative ligand, N,NЈ,NЈЈ-triisopropyl-cis,cis-
1,3,5-triaminocyclohexane (iPr3TACH), in which the α-car-
bon atom is a tertiary one. This is slightly different from
the previously designed R3TACH ligands, which have a sec-
ondary carbon atom. The R3TACH ligands may be slightly
flexible in coordinating the metal atom, whereas iPr3TACH
is expected to be less flexible and to form a tight structure
for coordinating the metal ion as shown in Figure S1. Ad-
ditionally, as speculated from the crystal structures of bis(μ-
hydroxido)dicopper(II) complexes with R3TACH (R = Et,
iBu, or Bn), the substituent groups can easily rotate around
the N–CR bond because of the intramolecular steric hin-
drance between two ligands[43] as compared with the iso-
propyl group in iPr3TACH. Interestingly, the copper(I)
complex with iPr3TACH immediately reacts with dioxygen
to form only the (μ-η2:η2-peroxido)dicopper(II) complex.
This is in contrast to the previously reported copper(I) com-
plexes with other R3TACH ligands that only form bis(μ-
oxido)dicopper(III) species. Here we have succeeded in the
prepared by treating complexes 1iPr(MeCN)·OTf and 1iBu
(MeCN)·PF6 with CO in CH2Cl2 at 0 °C. Single crystals of
iPr(CO)·OTf and 1iBu(CO)·PF6 suitable for X-ray analysis
-
1
were obtained by recrystallization from CH2Cl2/Et2O under
Ar. IR spectra for 1iPr(CO)·OTf and 1iBu(CO)·PF6 have ab-
sorption bands assignable to ν(CϵO) at 2058 and
2068 cm–1, respectively. These values are in the range of pre-
viously reported carbonylcopper(I) complexes with other
TACH derivative ligands (Bn3TACH, iBu3TACH, and
Et3TACH) and N,NЈ,NЈЈ-triisopropyl-1,4,7-triazacyclo-
nonane (iPr3TACN), and N,NЈ,NЈЈ-triisopropyl-1,5,9-tri-
azacycldodecane
(iPr3TACD);[43,44]
2055 cm–1
for
Et3TACH, 2057 cm–1 for iBu3TACH, 2076 cm–1 for
Bn3TACH, 2063 cm–1 for iPr3TACD, and 2067 cm–1 for
iPr3TACN. These results are indicative of carbonylcop-
per(I) complexes with tetrahedral geometry.
Crystal Structures of Copper(I) Complexes
The structure of 1iPr(MeCN)·SbF6 was determined by X-
selective preparation of (μ-η2:η2-peroxido)dicopper(II) and ray crystallography. The crystallographic data are listed in
bis(μ-oxido)dicopper(III) cores using copper complexes Table 8. The structure of the cationic part of 1iPr(MeCN)·
with R3TACH derivative ligands. In this paper, we describe SbF6 and selected bond lengths and angles are shown in
the preparation and characterization of these complexes Figure 1 and Table 1, respectively.
2
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(μ-η2:η2-Peroxido)dicopper(II) Complex
Tolman et al. have reported on the relationship between
the structures and oxygenation reactivities of copper(I)
complexes with iPr3TACN and iPr3TACD ligands.[44] It was
concluded that the dioxygen reactivity is significantly affec-
ted by the magnitude of the deviations of the Cu ion from
the mean plane defined by the three N-donor atoms (the N3
plane) and the mean plane defined by the three iPr methine
carbon atoms [the (CH)3 plane] for the macrocyclic li-
gands.[44] Copper complexes with smaller macrocyclic li-
gands exhibit higher oxygenation reactivities relative to
those of copper complexes with larger ligands. It is unclear
if this also applies to the current complex. The deviations of
the copper(I) ions from the N3 plane and the (CH)3 plane
in the N-alkyl substituent groups for 1iPr(MeCN)·SbF6 are
1.0724(16) and 0.6860(16) Å, respectively (Table 2 and Fig-
ure 2). Interestingly, these values are significantly smaller
than those of copper(I) complexes with other TACH deriv-
ative ligands; 1.1046(6) and 0.7177(6) Å for Et3TACH,
1.1161(3) and 0.7713(3) Å for iBu3TACH, 1.1187(17) and
0.7079(17) Å for Bn3TACH. This indicates that the metal
ion of 1iPr(MeCN)·SbF6 is compressed relative to the metal
Figure 1. ORTEP view of the cationic portions of 1iPr(MeCN)·
SbF6 with the atom numbering scheme (30% probability ellip-
soids).
Table 1. Selected bond lengths [Å] and angles [°] for 1iPr(MeCN)·
SbF6.
Cu–N(1)
Cu–N(2)
Cu–N(3)
Cu–N(4)
2.114(6)
2.049(6)
2.114(6)
1.875(6)
N(1)–Cu–N(4)
N(2)–Cu–N(4)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(2)–Cu–N(3)
N(3)–Cu–N(4)
113.8(2)
135.9(2)
96.8(2)
94.9(2)
96.5(2)
110.9(2)
ion in 1Et(MeCN)·SbF6,
1 -
iBu(MeCN)·SbF6, and 1Bn
(MeCN)·SbF6. As described in the electrochemistry section
below, 1iPr(MeCN)·SbF6 has a higher redox potential than
the other copper(I) complexes with R3TACH (R = Et, iBu,
and Bn). The higher potential may be related to this struc-
tural feature.
The molecular structure of the cationic part of
1
iPr(MeCN)·SbF6 has tetrahedral geometry with three sec-
ondary amine nitrogen atoms of the iPr3TACH ligand and
an MeCN molecule coordinated to the metal ion. The
average Cu–NTACH bond, 2.092(6) Å, is slightly shorter
than those of the copper(I) complexes with other TACH
ligands reported previously; Cu–NTACH 2.108(5) Å for
Et3TACH, 2.120(2) Å for iBu3TACH, and 2.1318(6) Å for
Bn3TACH.[43] These results may suggest that the ability of
iPr3TACH to donate electrons to the metal ion is greater
than the electron-donor capability of Et3TACH, iBu3-
TACH, and Bn3TACH. However, the coordinated MeCN
molecule is affected by the supporting ligands, and the Cu–
NMeCN bond of 1iPr(MeCN)·SbF6, 1.875(6) Å, tends to be-
come shorter than those of copper(I) complexes with other
TACH ligands [Cu–NMeCN 1.881(5) Å for Et3TACH,
1.900(2) Å for iBu3TACH, and 1.880(2) Å for Bn3TACH].
In general, stronger electron donation from the supporting
ligands to the copper(I) ions makes the binding of MeCN
weaker based on consideration of Pauling’s neutralization
Figure 2. Deviation of copper ions from the N3 plane defined by
three amine nitrogen atoms (A) and the (CHx)3 plane defined by
three methylene or methine carbon atoms (B).
The carbonylcopper(I) adduct, 1iPr(CO)·OTf, was recrys-
theory.[45] The results obtained here are the opposite. Al- tallized from CH2Cl2/Et2O to produce a single crystal suit-
though we do not have specific evidence to explain this phe- able for X-ray structure analysis. For comparison, we also
nomenon, it is possible that the copper ion is repulsively synthesized 1iBu(CO)·PF6 and characterized it by X-ray
compressed by the iPr methyl groups as seen in the space- structure analysis. Crystal data and relevant experimental
filling model in Figure S1.
details are summarized in Table 8. Molecular structures and
Table 2. FTIR spectroscopic data [cm–1] and deviations of copper ions from the planes defined by three amine nitrogen atoms and three
α-carbon atoms [Å].
Complex
iPr(MeCN)·SbF6
ν(NϵC)
Cu···N3
Cu···(CH)3/Cu···(CH2)3
Ref.
1
2264
2280
2250
2270
–
1.0724(16)
1.1046(6)
1.1161(3)
1.1187(17)
1.40
0.6860(16)
0.7177(6)
0.7713(3)
0.7079(17)
0.70
this work
[43]
1Et(MeCN)·SbF6
[43]
[43]
[44]
[44]
1
1
iBu(MeCN)·SbF6
Bn(MeCN)·SbF6
[Cu(MeCN)(iPr3TACN)]BPh4
[Cu(MeCN)(iPr3TACD)]SbF6
–
1.26
–0.02
Eur. J. Inorg. Chem. 0000, 0–0
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J. Matsumoto, Y. Kajita, H. Masuda
FULL PAPER
selected bond lengths and angles for 1iPr(CO)·OTf and bon monoxide ligand. The Cu–C and CϵO bond lengths
1
iBu(CO)·PF6 are given in Figures 3 and 4, and Tables 3 of 1iPr(CO)·OTf and 1iBu(CO)·PF6 are 1.808(4)/1.103(5) and
and 4, respectively.
1.800(2)/1.110(3) Å, respectively. The Cu–C and CϵO bond
lengths of the previously reported carbonylcopper(I) com-
plex with Bn3TACH, 1Bn(CO)·SbF6, in which the crystal
contains two independent molecules in the unit cell, were
1.813(5)/1.129(7) and 1.777(6)/1.152(7) Å, respectively. The
stronger coordination of the carbonyl ligand to the metal
atom appears to have weakened the CϵO bonds. The Cu–
C and CϵO bonds of 1iPr(CO)·OTf tend to be slightly
longer and shorter, respectively, than those of the other two
complexes. These findings indicate that the electron-donat-
ing capability of iPr3TACH is slightly weaker than those
of the iBu3TACH and Bn3TACH ligands. The average Cu–
NTACH bonds of 1iPr(CO)·OTf and 1iBu(CO)·PF6, 2.088(3)
and 2.087(2) Å, respectively, are slightly longer than those
of the carbonylcopper(I) complexes with Bn3TACH
[2.058(8), 2.060(7) Å]. These tendencies do not correlate
with the results from the crystal structures of the acetoni-
trile complexes. The Cu–NTACH bonds for the carbonyl
complexes are all shorter than those of the corresponding
acetonitrile complexes; this is considered to have been
caused by a decrease in the electron density of the copper(I)
ion by backdonation to the carbonyl ligand. From these
results, the effect of the steric hindrance of the substituents
does not significantly affect these carbonylcopper(I) sys-
tems. In terms of the displacement of the metal ion from
the N3 and (CH)3 planes, the same tendency observed for
(acetonitrile)copper(I) systems was also identified in the
carbonylcopper(I) systems; however, these differences are
less than those in the (acetonitrile)copper(I) systems. The
Cu···N3 and Cu···(CH)3 distances for 1iPr(CO)·OTf are
1.0739(5)/0.6664(5) Å. These distances are shorter than
Figure 3. ORTEP view of the cationic portions of 1iPr(CO)·OTf
with the atom numbering scheme (30% probability ellipsoids).
Figure 4. ORTEP view of the cation of 1iBu(CO)·PF6 with the atom
numbering scheme (30% probability ellipsoids).
Table 3. Selected bond lengths [Å] and angles [°] for 1iPr(CO)·OTf.
Cu–C(16)
Cu–N(1)
Cu–N(2)
Cu–N(3)
1.808(4)
2.092(3)
2.093(2)
2.080(3)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(2)–Cu–N(3)
C(16)–Cu–N(1)
C(16)–Cu–N(2)
C(16)–Cu–N(3)
94.40(12)
97.06(12)
96.29(10)
118.40(16)
120.03(16)
124.24(17)
those of
1 1
iBu(CO)·PF6 and Bn(CO)·SbF6, 1.0849(3)/
0.6867(3), and 1.0805(7)/0.6961(7) and 1.1209(7)/
0.7501(7) Å, respectively (Table 5). This result is also justi-
fied above.
Table 4. Selected bond lengths [Å] and angles [°] for 1iBu(CO)·PF6.
Cu–C(19)
Cu–N(1)
Cu–N(2)
Cu–N(3)
1.800(2)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(2)–Cu–N(3)
C(19)–Cu–N(1)
C(19)–Cu–N(2)
C(19)–Cu–N(3)
95.73(5)
95.51(5)
95.07(5)
114.03(9)
122.37(8)
127.12(7)
2.0967(14)
2.0631(15)
2.1025(12)
Electrochemical Properties
In order to study the reactivity of 1iPr(MeCN)·SbF6 with
dioxygen and its reversible oxygenation activity, the redox
Both 1iPr(CO)·OTf and 1iBu(CO)·PF6 have tetrahedral potential of 1iPr(MeCN)·SbF6 was measured by cyclic vol-
coordination geometry with the copper atoms bonded to tammetry in a CH2Cl2/MeCN (9:1, v/v) mixed solution
three amine nitrogen atoms of the TACH ligand and a car- (Figure S2 and Table 6).
Table 5. FTIR spectral data [cm–1] and deviations of the copper ions from the planes defined by three amine nitrogen atoms and three
α-carbon atoms [Å].
Complex
iPr(CO)·OTf
ν(CϵO)
Cu···N3
Cu···(CH)3/Cu···(CH2)3
Ref.
1
2058
2055
2057
2068
2076
1.0739(5)
–
–
1.0849(3)
1.1209(7)
1.0805(7)
–
–
0.6664(5)
–
–
0.6867(3)
0.7501(7)
0.6961(7)
–
–
this work
[43]
1Et(CO)·SbF6
[43]
1
1
1
iBu(CO)·SbF6
iBu(CO)·PF6
Bn(CO)·SbF6
this work
[43]
[43]
[44]
[44]
[Cu(MeCN)(iPr3TACN)]BPh4
[Cu(MeCN)(iPr3TACD)]SbF6
2063
2067
4
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(μ-η2:η2-Peroxido)dicopper(II) Complex
Table 6. Electrochemical properties [mV] for copper(I) complexes.
of the other complexes. This suggests that 1iPr(MeCN)·SbF6
has an efficient reversible oxygenation ability.
[b]
[b]
[b]
[b]
Complex
iPr(MeCN)·SbF6
1Et(MeCN)·SbF6
iBu(MeCN)·SbF6
Bn(MeCN)·SbF6
E1/2
ΔEp
Epa
Epc
Ref.
[a]
1
447
344
394
346
99
496
398
450
398
397 this work
289
337
293
[43]
109
113
105
510
180
Reactions of Copper(I) Complexes with O2
[43]
1
1
[43]
As expected from its electrochemical properties,
[44]
[44]
[Cu(MeCN)(iPr3TACN)]BPh4 570
[Cu(MeCN)(iPr3TACD)]SbF6 600
1
iPr(MeCN)·SbF6 reacts with O2 in THF or acetone at
–80 °C, and the solution immediately changes from color-
less to purple. The UV/Vis (Figure 5), resonance Raman,
and ESR spectral features of the purple solution suggest
the formation of 2iPr with a (μ-η2:η2-peroxido)dicopper(II)
core.[6,7,9,21] This complex is ESR-silent, indicating that
there is an antiferromagnetic interaction between the two
copper(II) ions. The complex in solution has two character-
istic absorption bands at 362 (ε = 20000) and 526 (ε = 1400)
nm, which are assigned as πσ* Ǟ dxy and πν* Ǟ dxy charge-
transfer bands originating from the peroxido oxygen atom
to the copper(II) ion for the (μ-η2:η2-peroxido)dicopper(II)
species. These absorption bands are very similar to those of
the previously reported (μ-η2:η2-peroxido)dicopper(II) spe-
cies[9] as well as those of oxyHc[46,47] and oxyTy.[8,48,49] This
feature is clearly different from those of the bis(μ-oxido)-
dicopper(III) (3R) species generated from copper(I) com-
plexes with Et3TACH, iBu3TACH, and Bn3TACH reported
previously (Table 7).
[a] Potentials were measured in a CH2Cl2/MeCN (9:1, v/v) mixed
solution with the supporting electrolyte 0.1 m nBu4NClO4 (TBAP).
The working, counter, and reference electrodes used were GC, Pt,
and Ag/Ag+(MeCN), respectively. The scan rate is 50 mV/s. [b] Re-
ported vs. SCE.
A quasireversible wave was observed with an E1/2 value
of 447 mV vs. SCE and an ΔEp value of 99 mV. The E1/2
value of 1iPr(MeCN)·SbF6 is significantly higher than those
of 1Et(MeCN)·SbF6 (344 mV), 1iBu(MeCN)·SbF6 (394 mV),
and 1Bn(MeCN)·SbF6 (346 mV) in spite of the fact that the
TACH derivatives all have a secondary amine. This is very
similar to the case of copper complexes with TACN and
TACD derivative ligands; the redox potentials of the copper
complexes with the iPr group are observed in the positive
region relative to those of their corresponding copper(I)
complexes with methyl and benzyl groups. The electrochem-
ical study indicated that the iPr3TACH stabilizes the lower
oxidation states, but the crystal structure of 1iPr(MeCN)·
SbF6 suggested that the donation ability of iPr3TACH li-
gand is stronger than the others. In order to elucidate the
contradictory findings, we carefully examined the angles
around the Cu–N bond. We found an interesting value in
the CR–N–CTACH angle. The CR–N–CTACH bond angle of
1
iPr(MeCN)·SbF6 [av. 114.0(6)°] is slightly larger than the
corresponding angles for 1Et(MeCN)·SbF6 [av. 112.6(4)°],
iBu(MeCN)·SbF6 [av. 111.9(2)°], and 1Bn(MeCN)·SbF6 [av.
1
112.2(4)°]. Although all of these angles are significantly
larger than the 109.28° angle of an idealized sp3-hybridized
orbital, the corresponding angle of 1iPr(MeCN)·SbF6 is es-
pecially large. This larger bond angle for 1iPr(MeCN)·SbF6
may be influenced by the steric repulsion between the iso-
propyl methyl groups and the TACH skeleton. This repul-
sion may have induced the depression of the metal atom by
Figure 5. Electronic absorption spectral change developed on oxy-
genating 1iPr(MeCN)·SbF6 in THF at –80 °C (0.07 mm).
Tolman et al. previously reported that the copper com-
other isopropyl methyl groups as described above. This plex system with iPr3TACN undergoes an interconversion
small displacement makes the donating ability of the between the (μ-η2:η2-peroxido)dicopper and bis(μ-oxido)di-
amines weaker and shifts the redox potential to a positive copper species when different solvents are used. The former
region. Additionally, the smaller ΔEp value for 1iPr(MeCN)· is generated in CH2Cl2, and the latter is generated in
SbF6 (99 mV) compared to those of 1Et(MeCN)·SbF6 THF.[24,25] In our case, only the (μ-η2:η2-peroxido)dicopper
(109 mV), 1iBu(MeCN)·SbF6 (113 mV), and 1Bn(MeCN)· species is formed at –80 °C in THF, CH2Cl2, and acetone
SbF6 (105 mV) indicates that its electrochemical reversibil- and also at –120 °C in MeTHF (Figure S3), although it was
ity between the CuI and CuII states is smoother than those observed that the complex is unstable in CH2Cl2 at –80 °C.
Table 7. UV/Vis and Raman spectroscopic data for 2iPr and 3R (R = Et, iBu, and Bn).
Complex
λmax [nm] (ε [m–1 cm–1])
ν(16O–16O) [ν(18O–18O)] [cm–1]
ν(Cu–16O) [ν(Cu–18O)] [cm–1]
Ref.
2iPr
362 (20000), 526 (1400)
309 (15000), 408 (18000)
321 (16000), 412 (19000)
308 (17000), 413 820000)
757 [715]
this work
[43]
3Et
553, 581 [547]
571 [546]
585 [560]
3iBu
[42]
[43]
3Bn-d2
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J. Matsumoto, Y. Kajita, H. Masuda
FULL PAPER
Figure 6. Rotations around the N–C bond in R3TACH and iPr3TACH.
Such an interconversion was not observed for this system
in any organic solvent used here. This behavior may be a
result of the ability of the ethyl, isobutyl, and benzyl groups
of Et3TACH, iBu3TACH, and Bu3TACH, respectively, to
rotate around the N–C bond. The small –CH2– groups in
Et3TACH, iBu3TACH, and Bu3TACH would allow free ro-
tation unimpeded by intramolecular steric hindrance be-
tween two ligands in the side-on peroxido complex, al-
though it is not impossible for the isopropyl group in iPr3-
TACH to rotate around the N–C bond (Figure 6).
The isopropyl group of iPr3TACH may cause steric hin-
drance and disturb the rotation of the dimethyl groups of
the isopropyl substituent. In the iPr3TACH system, it may
be difficult to form a dinuclear complex with a short
Cu···Cu distance as is formed in the bis(μ-oxido)dicopper
core in the copper systems with Et3TACH, iBu3TACH, and
Bn3TACH.
Figure 7. Resonance Raman spectra of
1
a THF solution of
iPr(MeCN)·SbF6 treated with 16O2 (upper line) and 18O2 (bottom
line) at –80 °C (λex = 532 nm).
ever, we have been unable to obtain a single crystal suitable
for X-ray analysis. We tested 1iPr(MeCN)·SbF6 for revers-
ible oxygenation. The 1iPr species reacts with dioxygen to
generate an O2 adduct under O2 at –70 °C in acetone. This
adduct releases O2 at 0 °C with Ar bubbling. After three
cycles of O2 binding and release, the extent of decomposi-
tion of 2iPr was about 10% as judged from the absorption
intensity (Figure 8).
Evidence for the formation of the (μ-η2:η2-peroxido)di-
copper species is indicated by resonance Raman spectral
measurements of the reaction product of 2iPr with 16O2/18O2
dioxygen. A band at 757/715 cm–1 is visible, which is assign-
able to an O–O stretching vibration band of a peroxido spe-
cies, ν(16O–16O)/ν(18O–18O) (Figure 7). This stretching vi-
bration is similar to that of native oxyTy (755/714 cm–1),
although it has a slightly higher value than that of oxyHc
(741/697 cm–1). For the O–O stretching vibration bands of
(μ-η2:η2-peroxido)dicopper(II) species of the model systems
observed hitherto,[9,13,50,51] those of the (μ-η2:η2-peroxido)-
dicopper(II) species coordinated with π-system ligands
(725–765 cm–1), such as imidazole, pyridine, or pyrazole,
are observed in a comparatively higher energy region than
complexes with σ-donating ligands (713–739 cm–1), such as
secondary and tertiary amines. However, all three of the
coordinating atoms of the iPr3TACH ligand are σ-donating
amines. This may be explained as follows: the approach of
two copper ions has been restricted by the steric repulsion
between the isopropyl groups of iPr3TACH ligands when
the (μ-η2:η2-peroxido)dicopper(II) core is formed, so the
O–O bond in this system cannot be further weakened be-
cause of its steric restriction.
Figure 8. Electronic absorption spectra showing the reversible O2
binding of 1iPr·SbF6 in acetone. Spectrum 2 was obtained from the
solution of 2iPr. Spectrum 1 was obtained after Ar bubbling at 0 °C.
Spectrum 2Ј was obtained after O2 addition to the resultant solu-
tion. Spectra 1Ј, 2ЈЈ, and 1ЈЈ were observed after the second and
third cycles.
We attempted to obtain 2iPr as a solid, and, fortunately,
a purple precipitate was obtained from a THF solution at
–80 °C upon standing overnight. As the solubility of this
precipitate in THF is low, a UV/Vis spectrum of the purple
solid was measured by dissolving it in acetone. The spec-
Decomposition of the (μ-η2:η2-Peroxido)dicopper Complex
We previously reported that the bis(μ-oxido)dicopper-
trum is similar to that of the (μ-η2:η2-peroxido)dicopper (III) complex with Et3TACH converts to the bis(μ-hy-
complex 2iPr, indicating that 2iPr is isolable as a solid. How- droxido)dicopper(II) complex in a reaction with THF.[42]
6
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(μ-η2:η2-Peroxido)dicopper(II) Complex
Figure 9. Possible mechanisms of phenol hydroxylation catalyzed by Ty.
However, the (μ-carbonato)dicopper(II) species, as mea- dence of the binding of phenolate to the metal atom, al-
sured using ESI-TOF-MS, was detected as a decomposition though we also performed a stopped-flow spectroscopic
product of the (μ-η2:η2-peroxido)dicopper(II) complex with measurement.
iPr3TACH, 2iPr, and the bis(μ-hydroxido)dicopper(II) spe-
We previously reported that the bis(μ-oxido)dicop-
cies, which was detected in the decomposition products of per(III) complexes of R3TACH (R = Et, iBu, and Bn) oxid-
[Cu2(O)2(Et3TACH)2]2+ reported previously, was not ob- ize THF or have N-dealkylation of the TACH ligands. Phe-
served in this system. Additionally, the bis(μ-hydroxido)di- nolate was not oxidized. Interestingly, 2iPr cannot oxidize
copper(II) species was not generated by the reaction of THF and also has no N-dealkylation activity. We therefore
CuX2 (X = Cl, OTf) with the iPr3TACH ligand. This may conclude that 2iPr oxidizes phenolate through coordination
mean that the (μ-η2:η2-peroxido)dicopper(II) complex with of the phenolate oxygen atom to the metal center in an elec-
iPr3TACH, 2iPr, does not generate the bis(μ-oxido)dicop- trophilic reaction. In the reaction of 2iPr with phenolate, the
per(III) species in the reaction.
It is notable that the Cu···Cu distance for the bis(μ-hy- oxido)dicopper species was not observed spectroscopically.
droxido)dicopper(II) complex with the TpiPr,iPr ligand is
The reactivity of Ty towards phenolic substrates in na-
2.937 Å.[52] This distance is shorter than those of the pres- ture has been previously reported and discussed, and
ent type of (μ-η2:η2-peroxido)dicopper(II) complex (3.2– various
reaction mechanisms have been pro-
conversion of (μ-η2:η2-peroxido)dicopper(II) to the bis(μ-
3.6 Å).[9] This suggests that it is difficult to form the dinu- posed.[33,35,37,40,55–58] For Ty, a number of peroxido O–O
clear copper complex if the Cu···Cu distance is short. We bond-cleavage mechanisms have been advanced. As shown
previously reported that bis(μ-oxido)dicopper(III) com- in Figure 9,[57] (a) the binding of the phenolic oxygen atom
plexes with R3TACH (R = iBu and Bn) decomposed with to the metal ion initiates cleavage followed by attack of the
accompanying N-dealkylation.[43] Tolman et al. also re- aromatic ring, (b or c) the O–O bond cleavage occurs after
ported that bis(μ-oxido)dicopper(III) complexes with iPr3- the binding of dioxygen to the aromatic ring, and (d) O–
TACN decompose with N-dealkylation.[53] However, the de- O bond cleavage occurs concertedly in a reaction with the
composition products of 2iPr, which are produced upon aromatic ring. In this study, we have succeeded in preparing
treatment with NH4OH, only include free ligand as ob- only (μ-η2:η2-peroxido)dicopper species and in conversion
served by 1H NMR spectroscopy (Figure S4). These results of phenolate to ortho-quinone in a 50% yield based on the
indicate that the (μ-η2:η2-peroxido)dicopper(II) species is peroxido intermediate. We therefore propose the following
generated by the reaction of 1iPr(MeCN)·SbF6 with di- hydroxylation mechanism for Ty activity: the cleavage of
oxygen, but the bis(μ-oxido)dicopper(III) species has not the peroxy O–O bond in Ty concertedly proceeds through
been formed.
the binding of phenolate to the copper ion.
Oxygenation Reactivity
Conclusions
The hydroxylation of phenol by the peroxido complex
We synthesized new copper(I) complexes with the iPr3-
2iPr was investigated using the sodium salt of 2,4-di-tert- TACH ligand, which has tertiary α-carbon atoms, [Cu-
butylphenol as a phenol model in CH2Cl2 at –95 °C. The (MeCN)(iPr3TACH)]X [1iPr(MeCN)·X] (X = OTf, SbF6)
solution of 2iPr immediately changed from purple to green and [Cu(CO)(iPr3TACH)]OTf [1iPr(CO)·OTf]. Exposure of
upon addition of the phenolate salt. From the reaction dioxygen to 1iPr(MeCN)·SbF6 produces the corresponding
products, the ortho-quinone was obtained in 50% yield (μ-η2:η2-peroxido)dicopper(II) species 2iPr in THF or in
based on the peroxido intermediate, but the C–C coupling acetone at –80 °C. This reactivity is quite different from the
dimer of phenol, which is occasionally obtained in such a reactivity of the previously reported CuI complexes with
reaction[54] was also produced. The oxidation reaction was other R3TACH ligands, which have secondary α-carbon
carried out under N2, so the quinone obtained in this reac- atoms (R = Et, iBu, and Bn). These other complexes form
tion may have been generated by disproportionation of bis(μ-oxido)dicopper(III) species in the reaction with di-
semiquinone[32] or oxygenation of phenolate by 2iPr. It is oxygen.[43] Resonance Raman spectra of the 2iPr species
likely that such interactions involve coordination of phenol- have O–O stretching vibrations, ν(16O–16O)/ν(18O–18O), at
ate to the metal atom. We failed to obtain any direct evi- 757/715 cm–1. This is a higher energy region than those of
Eur. J. Inorg. Chem. 0000, 0–0
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J. Matsumoto, Y. Kajita, H. Masuda
FULL PAPER
the (μ-η2:η2-peroxido)dicopper(II) species, which have σ-
donating amine ligands.[9] Species 2iPr is capable not only
of reversible binding of dioxygen but also of hydroxylation
of phenolate. This behavior is very similar to the reactivity
of Hc, which exhibits Ty activity, although it is a dioxygen
carrier protein. Complex 2iPr oxidizes phenolate to quinone,
but does not react with THF. This is in contrast to the
bis(μ-oxido)dicopper(III) complexes with R3TACH (R =
Et, iBu, and Bn), which cannot oxidize phenolate but are
techniques or in a glove box. Solvents were dried using standard
methods and were freshly distilled under Ar before use (e.g. diethyl
ether, toluene, and THF were purified by heating to reflux in the
presence of sodium/benzophenone, and dichloromethane was
heated to reflux in the presence of CaH2). Dry sodium 2,4-di-tert-
butylphenolate was prepared according to a reported procedure.[59]
Electronic absorption spectra (UV/Vis spectra) were recorded with
a JASCO V-570 spectrophotometer. IR spectra of the solid com-
pounds were measured with a JASCO FT/IR-4200 spectrophotom-
eter by the KBr disk method. Resonance Raman spectral measure-
capable of oxidizing THF or the N-dealkylation of the ments were carried out with an NKS-1000 spectrophotometer. X-
R3TACH ligand.[43] This indicates that 2iPr oxidizes phenol-
band ESR spectra were obtained with a JEOL RE-1X spectrometer
at 77 K. 1H NMR spectral measurements were performed with a
ate through coordination of the phenolate oxygen atom in
Bruker 600 MHz NMR spectrometer with CDCl3 and CD2Cl2
solutions using Me4Si as an internal standard. Elemental analyses
were performed with a Perkin–Elmer Japan 2440II CHNO/S and
the electrophilic reaction. Hydroxylation of phenolate pro-
ceeds only at the ortho position. We were unable to directly
detect binding of phenolate by stopped-flow spectroscopy.
corrected using acetanilide. Electrochemical measurements were
We therefore propose that the hydroxylation mechanism of
performed in a glove box using a Bioanalytical Systems (BAS)
Ty includes cleavage of the peroxy O–O bond in Ty concert-
edly through the binding of phenolate to the copper ion. In
this study, we succeeded in the selective preparation of (μ-
ALS/CH Instruments Electrochemical Analyzer Model 600A, with
a three-electrode system consisting of a glassy carbon working elec-
trode, a Pt wire counter electrode, and an Ag/Ag+ reference elec-
η2:η2-peroxido)dicopper(II) and bis(μ-oxido)dicopper(III) trode. All measurements were carried out at room temperature with
a sweep rate of 50 mVs–1 under Ar in a degassed CH2Cl2/MeCN
species using copper(I) complexes with TACH derivative li-
gands. This success appears to be based on the specific
structural features of the isopropyl group. When the cop-
(9:1, v/v) solution, using nBu4NClO4 (TBAP) as a supporting elec-
trolyte. The electrochemical potentials were corrected by measure-
ment of the ferrocene/ferrocenium couple ([Fe(C5H5)2]/[Fe-
per(I) complex with iPr3TACH reacts with dioxygen to
(C5H5)2]+) (E1/2 = 140 mV, ΔE = 104 mV). Electrospray ionization
form
(μ-η2:η2-peroxido)dicopper(II),
the
repulsive
time-of-flight mass spectra (ESI-TOF-MS) were measured with a
Micromass LCT spectrometer. Resonance Raman spectral mea-
surements: Raman scattering was excited at 532.0 nm with an Ar
laser (Laser Quantum, Ventus 532) and detected using a CCD de-
tector (Andor, DU420-OE) attached to a single polychromator
(Ritsu Oyo Kogaku, DG-1000). The slit width was set to 200 μm.
The laser power used was 30 mW at the sample point. All measure-
ments were carried out with samples contained in a spinning cell
(3000 rpm) at room temperature. Raman shifts were calibrated with
indene, and the accuracy of the peak positions of the Raman bands
was Ϯ1 cm–1. X-ray crystallography: Single crystals of 1iPr(MeCN)·
SbF6, 1iPr(CO)·OTf, and 1iBu(CO)·PF6 suitable for X-ray diffrac-
van der Waals interaction between the opposing isopropyl
groups improves the steric contact required for formation of
the (μ-η2:η2-peroxido)dicopper(II) core. In Ty, such steric
constraint may contribute to the formation of the (μ-η2:η2-
peroxido)dicopper core.
Experimental Section
General: All reactions and manipulations of air-sensitive com-
pounds were performed under dry Ar using conventional Schlenk
Table 8. Crystallographic data and experimental details for 1iPr(MeCN)·SbF6, 1iPr(CO)·OTf, and 1iBu(CO)·PF6.
iPr(MeCN)·SbF6 iPr(CO)·OTf iBu(CO)·PF6
1
1
1
Empirical formula
Formula mass
C17H36CuF6N4Sb
595.78
C17H33CuF3N3O4S
496.07
C19H39CuF6N3OP
534.05
Crystal system
Space group
a [Å]
b [Å]
orthorhombic
Pna21 (No. 33)
18.338(14)
7.990(6)
16.072(12)
–
2355(3)
4
1.68
orthorhombic
P212121 (No. 19)
8.7036(3)
15.0294(8)
17.3872(11)
–
2274.4(2)
4
1.449
monoclinic
P21/n (No. 14)
9.384(2)
31.50(2)
9.451(4)
115.298(4)
2525(2)
4
c [Å]
β [°]
V [Å3]
Z
ρcalcd. [gcm–3]
1.405
T [K]
173
21.055
0.71070
16970
5303
8051
298
0.0580
0.1257
173
11.029
0.71070
18132
5203
12062
295
0.0590
0.1362
173
9.873
0.71070
22790
7093
17390
319
0.0561
0.1853
μ(Mo-Kα) [cm–1]
λ [Å]
No. of reflections
No. of unique reflections
No. of observed reflections [IϾ3σ(I)]
No. of parameters
R1 [IϾ3σ(I)][a]
wR2 (all parameters)[b]
GOF
0.882
1.033
0.991
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σw(Fo2)2}1/2
.
8
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(μ-η2:η2-Peroxido)dicopper(II) Complex
tion analyses were obtained from CH2Cl2/Et2O or THF/Et2O solu-
tions upon standing for a few days under Ar. Each crystal was
mounted on a glass fiber, and diffraction data were collected using
a Rigaku/MSC Mercury CCD with graphite-monochromated Mo-
Kα radiation at –100 °C. Crystal data and experimental details are
listed in Table 8. All three structures were solved using a combina-
tion of direct methods (SIR 2004 and SIR 92) and Fourier tech-
niques. All non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were refined using a riding model. A Sheldrick
weighting scheme was applied. Plots of Σw(|Fo| – |Fc|)2 vs. |Fo|, re-
flection order in data collection, sin θ/λ, and various classes of
indices showed no unusual trends. Neutral atomic scattering factors
were taken from the International Tables for X-ray Crystallogra-
phy.[60] Anomalous dispersion effects were included in Fc,[61] where
the values for ΔfЈ and ΔfЈЈ were taken from those of Creagh and
McAuley.[62] The values for the mass attenuation coefficients are
those of Creagh and Hubbell.[63] All calculations were performed
using the crystallographic software package CrystalStructure.[64,65]
CCDC-870598 [for 1iPr(MeCN)·SbF6], -870597 [for 1iPr(CO)·OTf],
and -870596 [for 1iBu(CO)·PF6] contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
SO3), 1032 (sy, SO3), 639 (C–S) cm–1. ESI-TOF-MS: m/z = 317.2
[M – OTf]+.
[Cu(CO)(iPr3TACH)]OTf [1iPr(CO)·OTf]: [Cu(MeCN)(iPr3TACH)]-
(OTf) (89.2 mg, 1.75ϫ10–4 mol) was dissolved in CH2Cl2 (3 mL),
and the solution was stirred under CO (1 atm) at 0 °C for 1 h. The
addition of Et2O (5 mL) to the colorless solution yielded a white
solid, which was subsequently recrystallized from CH2Cl2/Et2O
(66.6 mg, 76.5%). C17H34CuF3N3O4S (497.07): calcd. C 41.16, H
6.71, N 8.47; found C 41.08, H 6.78, N 8.34. FTIR (KBr): ν =
˜
3282 (N–H), 2975, 2937 (aliphatic C–H), 2068 (C=O), 1260 (as,
SO3), 1032 (sy, SO3), 638 (C–S) cm–1. ESI-TOF-MS: m/z = 346.2
[M – OTf]+.
[Cu(CO)(iBu3TACH)]PF6 [1iBu(CO)·PF6]: [Cu(CO)(iBu3TACH)]-
PF6 was synthesized according to the previously reported method
by using [Cu(MeCN)4]PF6 in place of [Cu(MeCN)4]SbF6 as a metal
source.[43] Colorless crystals were obtained.
Ligand Recovery: 1iPr(MeCN)·SbF6 (60.0 mg, 1.01ϫ10–5 mol) was
dissolved in acetone (4 mL) under argon. Oxygen was bubbled
through the solution at –70 °C, and the solution changed from col-
orless to purple. The mixture was stirred at –80 °C for 3 h and
warmed to room temperature. After the addition of CH2Cl2
(15 mL), the mixture was washed with 5% NH4OH (2ϫ5 mL) and
water (2ϫ10 mL). The organic layer was dried with MgSO4 and
filtered, and volatile materials were removed in vacuo to leave a
iPr3TACH: TACH·3HCl (2.02 g, 8.47ϫ10–3 mol) and NaOH
(1.02 g, 2.55ϫ10–2 mol) were dissolved in water (10 mL) to give a
clear solution. This was added to a solution of NaOAc (1.63 g) in
acetic acid (9 mL), acetone (10 mL), and water (10 mL), which was
cooled in an ice bath. Over 2 h, NaBH4 (4.00 g, 1.06ϫ10–1 mol)
was added in small portions. After the addition was complete, the
solution was warmed to room temperature and stirred for an ad-
ditional 2 h. Sodium hydroxide [7% (w)] was added until a pH of
12 was reached, and then the aqueous phase was extracted with
diethyl ether (40 mLϫ4). The diethyl ether fractions were com-
bined, washed once with a saturated salt solution (50 mL), and
dried with MgSO4. The solvent was evaporated to obtain a white
solid (67.5%). C15H30N3·2H2O (219.47): calcd. C 61.81, H 12.79,
1
pale-yellow solid (20.5 mg). H NMR (600 MHz, CDCl3): 0.76 (q,
3 H, CHax), 1.04 [d, 18 H, CH(CH3)2], 2.16 (d, 3 H, CHeq), 2.62
(tt, 3 H, CH), 3.00 [m, 3 H, CH(CH3)2] ppm.
Oxidation Reaction of Phenolate: A solution of 1iPr(MeCN)·SbF6
(11.8 mg, 2.0ϫ10–5 mol) in CH2Cl2 (2 mL) was stirred under oxy-
gen at –95 °C for 3 min. The solution changed from colorless to
purple. After vacuum/pumping with N2 gas several times, a solu-
tion of sodium 2,4-di-tert-butylphenolate (4.6 mg, 2.0ϫ10–5 mol)
in CH2Cl2 was added to the mixture, and the color immediately
changed to green. The solution was stirred for 3 h and was then
warmed to room temperature. The addition of n-hexane (10 mL)
to the solution resulted in the precipitation of the Cu complexes.
After filtration and addition of 1-chloronaphthalene as an internal
standard, the reaction products were monitored by GC. For 18O
tracing experiments, the reactions were carried out using 18O2, and
incorporation of 18O into quinone products was confirmed by EI-
MS (Figure S5).
N14.42; found C 61.61, H 12.82, N 14.25. FTIR (KBr): ν = 3268
˜
(N–H), 2965, 2928 (aliphatic C–H), 1652 (N–H) cm–1. 1H NMR
(600 MHz, CDCl3): δ = 0.76 (q, 3 H, CHax), 1.04 [d, 18 H,
CH(CH3)2], 1.28 (br., 3 H, NH), 2.16 (d, 3 H, CHeq), 2.62 (tt, 3 H,
CH), 3.00 [m, 3 H, CH(CH3)2] ppm. ESI-TOF-MS: m/z = 256.3
[M + H]+.
GC Conditions: Column DB-5 ms; column length 30.0 m; column
temperature 100 °C (heating to 200 °C at a rate of 10 °Cmin–1 with
an interval of 10 min); injection temperature 200 °C; 62.7 kPa. 1-
Chlorobenzene was used as an internal standard. The retention
time of 3,5-Di-tert-butylbenzoquinone is 19.8 min.[66]
Synthesis of Copper(I) Complexes: The preparations of copper(I)
complexes were carried out under Ar in a glove box.
[Cu(MeCN)(iPr3TACH)]SbF6
[1iPr(MeCN)·SbF6]:
iPr3TACH
(0.752 g, 2.94ϫ10–3 mol) and [Cu(MeCN)4](SbF6) (1.382 g,
2.98ϫ10–3 mol) were dissolved in THF (3 mL). The solution was
stirred for 10 min. After adding Et2O (5 mL), the solution was left
standing for 10 h to obtain colorless crystals (1.48 g, 84.6%).
C17H33CuF6N4Sb (592.76): calcd. C 34.27, H 6.09, N 9.40; found
Supporting Information (see footnote on the first page of this arti-
cle): Filling models (views from the upper site) of cationic parts of
1
1
iPr(MeCN)·SbF6, 1Et(MeCN)·SbF6,
1
iBu(MeCN)·SbF6, and
Bn(MeCN)·SbF6; cyclic voltammogram of 1iPr(MeCN)·SbF6; elec-
tronic absorption spectrum in MeTHF at –120 °C (0.1 mm); 1H
NMR spectrum in CDCl3 of the extracted products after the reac-
tion of 1iPr(MeCN)·SbF6 with dioxygen; GC and EI-MS data for
products obtained from the reaction of 2iPr with sodium 2,4-di-tert-
butylphenolate.
C 33.78, H 6.24, N 9.22. FTIR (KBr): ν = 3288 (N–H), 2977,
˜
2942 (aliphatic C–H), 2264 (CϵN), 658 (SbF6) cm–1. 1H NMR
(600 MHz, CDCl3): δ = 0.77 (br., 3 H), 1.06 (s, 9 H), 1.21 (s, 9 H),
1.69 (br., 3 H), 2.04 (s, 3 H), 2.65 (br., 3 H), 2.98 (d, 3 H), 3.27 (s,
3 H) ppm. ESI-TOF-MS: m/z = 317.2 [M – SbF6]+.
[Cu(MeCN)(iPr3TACH)]OTf [1iPr(MeCN)·OTf]: This complex
(yield 79.2%) was prepared according to the same method as
[Cu(MeCN)(iPr3TACH)]SbF6 using [Cu(MeCN)4](OTf) in place of
Acknowledgments
[Cu(MeCN)4](SbF6). C18H36CuF3N4O3S (509.11): calcd. C 42.46, We gratefully acknowledge the support of this work by a Grant-in-
H 7.13, N 11.00; found C 42.40, H 7.20, N 10.85. FTIR (KBr): ν
= 3257 (N–H), 2967, 2924 (aliphatic C–H), 2265 (CϵN), 1253 (as,
Aid for Scientific Research from the Ministry of Education, Cul-
ture, Sports, Science, and the Knowledge Cluster Project.
˜
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J. Matsumoto, Y. Kajita, H. Masuda
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Job/Unit: I20228
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Date: 06-08-12 11:52:01
Pages: 12
(μ-η2:η2-Peroxido)dicopper(II) Complex
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Received: March 12, 2012
Published Online: ᭿
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Job/Unit: I20228
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Date: 06-08-12 11:52:01
Pages: 12
J. Matsumoto, Y. Kajita, H. Masuda
FULL PAPER
Dicopper Complexes
J. Matsumoto, Y. Kajita,
H. Masuda* .................................... 1–12
Synthesis and Characterization of a (μ-
η2:η2-Peroxido)dicopper(II) Complex with
N,NЈ,NЈЈ-Triisopropyl-cis,cis-1,3,5-triamino-
cyclohexane (R3TACH, R = iPr): Selective
Preparation of (μ-η2:η2-Peroxido)dicop-
per(II) and Bis(μ-oxido)dicopper(III) Spec-
ies Regulated by Substituent Groups
The selective preparation of (μ-η2:η2-per-
oxido)dicopper(II) and bis(μ-oxido)dicop-
per(III) species is regulated by the substitu-
ent groups of triaminocyclohexane deriva-
tive ligands. Their structural and spectro-
scopic features and reactivity are discussed.
Keywords: Bioinorganic chemistry / Cop-
per / Coordination modes / Hydroxylation
12
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