Paper
Dalton Transactions
azole-based ligands, for aerobic oxidation of benzyl alcohol enced to the Fc+/Fc couple (E1/2 = 0.466 V vs. E°′ (Ag/AgCl)).
derivatives.9,10 In addition, we have recently shown that, in the Gas chromatography (GC) experiments were performed on an
presence of tris(triazolyl)methanol (Htbtm), aerobic oxidation Agilent 6890N GC-FID chromatograph equipped with an
of CuIBr produced hexanuclear copper(II) complexes bridged Agilent column HP-5 (30 m × 0.32 mm × 0.25 µm film
by Br−, [O⋯H⋯O]3−, and triazole–alkoxide tbtm− ligands.11 In thickness).
this study, we investigated the synthesis of mononuclear and
trinuclear copper(II) complexes supported by triazole–alkoxide- X-ray crystallography
based ligands, prompted by the simple synthetic protocol for
multinuclear copper–triazole species and the high catalytic
Single-crystal X-ray diffraction measurements were performed
on a Rigaku RAXIS RAPID imaging plate and a Vari-Max with
performances of copper–triazolyl catalysts for aerobic alcohol
Mo-Kα radiation (λ = 0.71075 Å) at 223 K for 1 and 153 K for 2
oxidation. Herein we report the effects of ligand frameworks
and 3. The intensity data were collected by the ω-scanning
on the formation of copper clusters, together with the mole-
technique and numerically corrected for absorption. The struc-
cular structures and electrochemical properties. The catalytic
tures of the complexes were solved by direct methods using
activities of the resulting mononuclear and trinuclear copper
SHELXS-2013/1. Structure refinement was carried out using
complexes toward aerobic oxidation of alcohols in the presence
full matrix least-squares (SHELXL-2018/3). All calculations
were performed using the WinqGX software package. Non-
hydrogen atoms were refined anisotropically except for dis-
N-methylimidazole (NMI) with the TEMPO co-catalyst are also
reported.
ordered moieties with low occupancies. Hydrogen atoms were
placed at calculated positions. Some of the btm molecules and
2−
Experimental
the CuCl3 ion in 1 were disordered in two positions, and
their occupancies were refined to 0.64/0.36 and 0.70/0.30. The
PF6 anion in 3 was also disordered in two positions, and their
occupancies were refined to 0.58/0.42. Several restraints
(DELU, SIMU, DFIX and SADI) and constraints (EADP and
AFIX 66) were applied for modeling the chemically reasonable
structures.
General information
Air-sensitive experiments were carried out under dry N2 using
standard Schlenk techniques. Trimethylsilylacetylene and
n-butyllithium (n-BuLi) were stored under N2 in a storage flask
at 5 °C. THF was dried by distillation from sodium benzophe-
none under N2 immediately prior to use. Triethylamine was
dried over 4 Å molecular sieves for 24 h and distilled under N2
before use. Dichloromethane and ethyl acetate were also dis-
tilled prior to use. Other chemicals and solvents were of
reagent grade and used as received. De-ionized (DI) water was
(1-Benzyl-1H-1,2,3-triazol-4-yl)diphenylmethanol (HPhtm)
The HPhtm ligand was prepared following the literature
method with a slight modification.14 Under a N2 atmosphere,
a 15 mL THF solution of 1,1-diphenylprop-2-yn-1-ol (0.70 g,
3.4 mmol) and benzyl azide (0.54 g, 4.0 mmol) was stirred at
room temperature until the mixture became homogeneous.
Then, the reaction flask was covered with aluminum foil after
which triethylamine (0.50 mL, 3.4 mmol) and CuI (0.64 g,
3.4 mmol) were added. After 24 h, the reaction solution was
diluted with aqueous NH4OH (30 mL) and extracted with
CH2Cl2 (3 × 30 mL). The combined organic layers were stirred
with EDTA (0.98 g, 3.4 mmol) and 10% NH4OH (30 mL) for
4 h. Then, the organic layers were dried over anhydrous
Na2SO4, filtered, and dried under vacuum to obtain a yellow
oil. Crystallization from diethyl ether at room temperature gave
a white crystalline solid in 63% yield (0.72 g, 2.1 mmol).
1H NMR (400 MHz, CDCl3): δ 7.39–7.24 (m, 15H, ArH), 7.10 (s,
1H, trzH), 5.49 (s, 2H, CH2Ph), 3.85 (s, 1H, OH). 13C{1H} NMR
(100 MHz, CDCl3): δ 154.4, 145.7, 134.6, 129.1, 128.7, 128.0,
127.9, 127.5, 127.2, 122.4 (aromatic Cs), 54.1 (CH2).
obtained from
a
Nanopure® Analytical Deionization
system with an electrical resistivity of ≥18.2 MΩ cm. Benzyl
azide12 and bis(1-benzyl-1H-1,2,3-triazole-4-yl)phenylmethanol
(Hbtm)13 were prepared following the literature methods. NMR
spectra were recorded on a Bruker Ascend 400 high-resolution
magnetic resonance spectrometer (400 MHz for 1H NMR).
Chemical shifts are in ppm (parts per million) using residual
solvent peaks as references (CDCl3: 1H δ 7.26). Fourier trans-
form infrared (FT-IR) spectra were collected on a Bruker model
Alpha spectrometer. Electrospray Ionization Mass spectra
(ESI-MS) of 1 : 1 MeOH : CH2Cl2 (infinity pure grade, Wako
Chemical) solutions of complexes 2 and 3 were obtained in
positive-ion mode on a Bruker micrOTOF II. The temperature-
dependent dc magnetic susceptibility data for 1 were recorded
with an MPMS2-XL SQUID susceptometer (Quantum Design,
Inc.) using
a
5000 Oe field between
2
and 300 K.
CH
Electrochemical measurements were made with
a
Instrument model ALS/CHI-600E voltammetric analyser using
a glassy carbon disk electrode (0.07 cm2) at room temperature
General procedure for copper(II) complexes 1 and 2
under an Ar atmosphere. An Ag/AgCl electrode (3.0 m NaCl To a 5 mL CH2Cl2 solution of Hbtm (0.36 mmol) was added
aq.) and a platinum wire were used as reference and auxiliary CuX (X = Cl, Br) (0.36 mmol) and the reaction mixture was
electrodes, respectively. The electrochemical experiment was stirred at room temperature. After 24 h, all volatiles were
conducted in CH3CN with 0.1 M Bu4NPF6 as the supporting removed in vacuo. Layering Et2O onto a CH3OH solution of the
electrolyte and a complex concentration of 1.0 mM. Ferrocene resulting complexes afforded X-ray quality crystals of the
was used as an internal standard, and all potentials were refer- products.
Dalton Trans.
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