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