Syntheses, structures, and O2-reactivities of copper(I) complexes with bis(2-pyridylmethyl)amine and bis(2-quinolylmethyl)amine tridentate ligands

Article abstract of DOI:10.1246/bcsj.79.1729

The structure and O₂-reactivity of the copper(I) complexes supported by bis[(6-phenyl-2-pyridyl)methyl]amine tridentate ligands (L5 ^R) and bis(2-quinolylmethyl)amine tridentate ligands (L6^R) have been investigated in detai

Full text of DOI:10.1246/bcsj.79.1729

Ó 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 11, 1729–1741 (2006) 1729
Syntheses, Structures, and O2-Reactivities of Copper(I)
Complexes with Bis(2-pyridylmethyl)amine and
Bis(2-quinolylmethyl)amine Tridentate Ligands
ꢀ
ꢀ
Atsushi Kunishita, Takao Osako, Yoshimitsu Tachi, Junji Teraoka, and Shinobu Itoh
Departments of Chemistry and Materials Science, Graduate School of Science,
Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585
Received May 8, 2006; E-mail: shinobu@sci.osaka-cu.ac.jp
The structure and O2-reactivity of the copper(I) complexes supported by bis[(6-phenyl-2-pyridyl)methyl]amine tri-
dentate ligands (L5R) and bis(2-quinolylmethyl)amine tridentate ligands (L6R) have been investigated in detail in order
to get insights into the steric effects of the tridentate ligands on copper(I)/O2 chemistry. In the cases of benzyl amine and
phenethyl amine derivatives [R = –CH2Ph (Bz) and –CH2CH2Ph (Phe)], the reaction between the ligands and
[CuI(CH3CN)4]þ gave the corresponding copper(I)–acetonitrile complexes having a distorted tetrahedral geometry.
On the other hand, the 2,2-diphenylethyl amine derivative L6R [R = –CH2CHPh2 (PhePh)] afforded a copper(I) com-
plex without an ancillary ligand (CH3CN) and having intramolecular d–ꢀ interaction between the copper(I) ion and the
phenyl group of the alkyl substituent PhePh. The acetonitrile complexes were then converted to the corresponding CO-
complexes by reacting with CO gas. The X-ray structures of all CO-complexes have been determined, and the complexes
have a similar distorted tetrahedral geometry. In addition, the 6-phenyl group of L5R imparts a large steric effect on the
metal-binding. The CO-complexes were converted to the copper(I) complexes without having any ancillary ligands in
order to examine their O2-reactivity. Significantly large differences in O2-reactivity were found among the copper(I)
complexes. On the basis of O2-reactivity together with the X-ray structures and the oxidation potentials of the copper(I)
complexes, the steric effects of the hetero-aromatic donor groups (6-substituted pyridine and quinoline) as well as the
alkyl substituents (R) are discussed in detail.
As a part of our continuing efforts to understand the ligand
effects on copper(I)/O2 chemistry, we have been studying the
structure and reactivity of copper(I) complexes supported by a
series of tridentate ligands L1R–L4R (Chart 1).1 Copper(I)
complexes with bis[2-(2-pyridyl)ethyl]amine tridentate ligands
L1R have been shown to afford (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II)
complexes A (Chart 2) from the reaction with O2 at a low
temperature.1–4 The side-on peroxo dicopper(II) complexes A
supported by the L1R ligands have been extensively studied
as structural and functional models of oxy-hemocyanin and
oxy-tyrosinase due to their ability to reversibly bind dioxygen
and hydroxylate aromatic compounds.5–9 Recently, we have
also demonstrated that the use of bis(2-pyridylmethyl)amine
tridentate ligand L3Phe [R = –CH2CH2Ph (Phe), Chart 1] in-
stead of L1R induces O–O bond cleavage of the peroxo com-
plex to afford a bis(ꢁ-oxo)dicopper(III) complex B under the
same reaction conditions.10 It has been reported that the elec-
tron-donor ability of pyridine of the (2-pyridylmethyl)amine
ligands, which afford a smaller 5-member chelate ring, is high-
er than that of the [2-(2-pyridyl)ethyl]amine ligands, which
comprise a larger 6-member chelate ring.11 Thus, the L3Phe
ligand with the higher electron-donor ability may enhance
O–O bond cleavage of the peroxo species and stabilize the
higher oxidation state of the metal center to give the bis(ꢁ-
oxo)dicopper(III) complex B.
R
N
R
N
R
N
N
N
N
N
N
N
6-Methyl substituent on the pyridine nucleus of L2R has been
demonstrated to cause a decrease in electron-donor ability of
the pyridine due to a steric repulsion between the substituent
and the metal ion.12 Thus, the reactivity of copper(I) com-
plex with L2Phe, [CuI(L2Phe)(MeCN)]þ (Phe = –CH2CH2Ph),
Me
Me
L1R
L2R
L3R
R
N
R
N
R
N
N
N
N
N
N
N
O
Me
Me
O
III L
LCuIII
CuII
LCuII
L
Cu
L4R
L5R
L6R
O
O
R = -CH Ph (Bz), -CH CH Ph (Phe), -CH CHPh (PhePh)
A
B
2
2
2
2
2
Chart 1.
Chart 2.
Published on the web November 9, 2006; doi:10.1246/bcsj.79.1729

1730 Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006)
Copper(I) Complexes of Tridentate Ligands
toward O2 is almost lost.13 In this case, the weaker electron-
donor ability of the 6-methylpyridine of L2Phe makes the oxi-
dation potential of copper(I) complex higher as compared to
that of the copper(I) complexes with L1R, thus stabilizing
the lower oxidation state of copper(I). On the other hand, the
introduction of methyl group at C-6 of pyridine of L3R to give
L4R (Chart 1) resulted in formation of the side-on peroxo com-
plex A rather than the bis(ꢁ-oxo) complex B in the oxygena-
tion reaction of the copper(I) complexes of L4R.14 Thus, the
introduction of 6-methyl substituent shifted the equilibrium
between A and B toward the peroxo side. In this case as well,
the 6-methyl substituent in L4R decreases the electron-donor
ability of pyridine, prohibiting the O–O bond cleavage to give
the peroxo complex A as the major product.
In this study, the structure and O2-reactivity of the copper(I)
complexes supported by bis[(6-phenyl-2-pyridyl)methyl]amine
tridentate ligands L5R and bis(2-quinolylmethyl)amine triden-
tate ligands L6R (Chart 1) have been investigated in detail to
understand further the steric effects of the tridentate ligands
on copper(I)/O2 chemistry. Although the structure and reactiv-
ity of some copper(I) complexes supported by the tetradentate
ligands with 6-phenyl-2-pyridyl and 2-quinolyl donor groups
have been reported,15–17 denticity of the supporting ligands,
i.e. tridentate vs tetradentate, has been well documented to
cause large effects on the O2-reactivity of copper(I).3,4 Thus,
this study using the tridentate ligands with the bulky donor
groups will give significantly important information about
how the ligands control the Cu(I)–O2 reactivity in the N3-tri-
dentate ligand systems.
potentials were recorded with respect to an Ag/AgNO3 (0.01 M)
reference electrode. All electrochemical measurements were car-
ried out in a glovebox filled with Ar gas at 25 ꢂC. Elemental anal-
yses were recorded with a Perkin-Elmer or a Fisons instruments
EA1108 Elemental Analyzer.
Synthesis. N,N-Bis[(6-phenyl-2-pyridyl)methyl]benzylamine
(L5Bz): To a methanol solution (40 mL) containing benzylamine
(702 mg, 6.5 mmol) and 6-phenyl-2-pyridinecarboxaldehyde (2.4 g,
13.0 mmol)22 was added acetic acid slowly to adjust the pH of the
solution to 4, and the mixture was stirred for 1 h at room temper-
ature. NaBH3CN (806 mg, 13.0 mmol) was then added slowly to
the solution, and the mixture was stirred at room temperature
for 3 days. After the reaction, the mixture was acidified to pH 1
by adding conc. HCl while cooling with an ice bath. Removal
of the solvent by evaporation gave an oily material, which was
dissolved into an NaOH aqueous solution (pH 14). The aqueous
solution was then extracted with CHCl3 (40 mL ꢃ 5), and the
combined organic layer was dried over Na2SO4. After removal
of Na2SO4 by filtration, evaporation of the solvent gave a brown
material, from which L5Bz was isolated as an oily material by
silica-gel column chromatography (eluent: hexane:AcOEt = 6:1)
in a 50% yield (1.5 g); 1H NMR (CDCl3, 400 MHz) ꢃ 3.81 (2H, s,
–CH2–), 3.96 (4H, s, –CH2–N–CH2–), 7.24 (1H, t, J ¼ 8:0 Hz),
7.30–7.51 (10H, m), 7.59 (4H, dd, J ¼ 3:6 and 7.6 Hz), 7.73
(2H, t, J ¼ 7:6 Hz), 8.00 (4H, br d, J ¼ 7:6 Hz); HRMS (FABþ)
m=z ¼ 442:2271, calcd for C31H28N3 = 442.2283.
N,N-Bis[(6-phenyl-2-pyridyl)methyl]-2-phenethylamine
(L5Phe): This compound was prepared by following the same
procedures as described for L5Bz using phenethylamine instead
of benzylamine in a 49% yield. 1H NMR (CDCl3, 400 MHz) ꢃ
2.94 (4H, s, –CH2CH2–), 4.03 (4H, s, –CH2–N–CH2–), 7.13–7.27
(5H, m), 7.36 (2H, d, J ¼ 7:6 Hz), 7.40 (2H, d, J ¼ 7:2 Hz), 7.45
(4H, t, J ¼ 7:2 Hz), 7.56 (2H, d, J ¼ 8:0 Hz), 7.65 (2H, t, J ¼ 7:8
Hz), 8.00 (4H, br d, J ¼ 8:0 Hz); HRMS (FABþ) m=z ¼ 456:2441,
calcd for C32H30N3 = 456.2440.
Experimental
General. The reagents and the solvents used in this study,
except the ligands and the copper complexes, were purchased
with the highest available purity and were further purified using
the standard methods, if necessary.18 N,N-Bis(2-pyridylmethyl)-
benzylamine (L3Bz) and N,N-bis(2-quinolylmethyl)benzylamine
(L6Bz) were prepared by the reported procedures.19,20 N,N-Bis(2-
quinolylmethyl)-2-phenethylamine (L6Phe) and N,N-bis(2-quino-
lylmethyl)-2,2-diphenylethylamine (L6PhePh) were obtained from
the previous study.21 FT-IR spectra were recorded on a Jasco
FTIR-4100, and UV–visible spectra were taken on a Jasco V-
570 or a Hewlett Packard 8453 photo diode array spectrophotom-
eter equipped with a Unisoku thermostated cell holder designed
for low-temperature measurements (USP-203). 1H NMR spectra
were recorded on a JEOL FT-NMR Lambda 300WB or a JEOL
FT-NMR GX-400 spectrometer. ESR spectra were recorded on
a JEOL JES-FE2XG spectrometer at ꢁ150 ꢂC. Mass spectra were
recorded on a JEOL JMS-700T Tandem MS-station mass spec-
trometer. ESI–MS (electrospray ionization mass spectra) mea-
surements were performed on a PE SCIEX API 150EX. Raman
scattering was excited by a He/Cd laser (Kinmon Electrics,
CDR80SG) and an Ar laser (NEC GLG3300), and the resonance
Raman light was dispersed with a JEOL 400D Raman spectrom-
eter equipped with a modified cryostat cell holder USP-203 for
the Raman measurements. Cyclic voltammetric measurements
were performed on an ALS-630A electrochemical analyzer in dea-
erated CH3CN containing 0.10 M NBu4PF6 as a supporting elec-
trolyte. The Pt working electrode (BAS) was polished with BAS
polishing alumina suspension and rinsed with acetone before
use. The counter electrode was a platinum wire. The measured
Caution: The perchlorate salts used in this study are all poten-
tially explosive and should be handled with care.
[CuI(L3Bz)(CH3CN)]PF6 (3Bz CH CN): Ligand L3Bz (144.7
Á
3
mg, 0.5 mmol) was treated with an equimolar amount of [CuI-
(CH3CN)4]PF6 (186.2 mg, 0.5 mmol) in CH3CN (2 mL) under Ar
atmosphere in a glovebox. After stirring the mixture for 5 min at
room temperature, an insoluble material was removed by filtra-
tion. Addition of ether (100 mL) to the filtrate caused a pale yel-
low powder to precipitate upon standing for several minutes.
The supernatant was then removed by decantation, and the re-
maining pale yellow solid was washed three times with ether
and dried to give complex 3Bz CH CN in a 60% yield. H NMR
1
Á
3
(CD3CN, 400 MHz) ꢃ 1.91 (3H, s, CH3CN), 3.79 (4H, s, –CH2–
N–CH2–), 3.84 (2H, s, –CH2–), 7.18–7.32 (5H, m), 7.32–7.43
(4H, m), 7.77 (2H, dt, J ¼ 1:6 and 8.0 Hz), 8.51 (2H, d, J ¼
4:8 Hz); FT-IR (KBr) 835 cmꢁ1 (PF6ꢁ); HRMS (FABþ): m=z
352.0871, calcd for C19H19CuN3 352.0875; Anal. Calcd for
[CuI(L3Bz)(CH3CN)]PF6 H2O (C21H24CuF6N4OP): C, 45.29; H,
4.34; N, 10.06%. Found: C, 45.25; H, 4.05; N, 10.10%.
[CuI(L3Bz)(CO)]PF6 (3Bz CO): (107.7 mg, 0.2 mmol) was
suspended into EtOH (5 mL) under CO atmosphere. After stirring
the mixture for 30 min at ꢁ40 ꢂC, insoluble material was removed
by filtration. Addition of ether (100 mL) to the filtrate caused a
pale white powder to precipitate upon standing for several mi-
nutes. The supernatant was then removed by decantation, and
the white solid was washed three times with ether and dried to
give complex 3Bz CO in a 73% yield. Micro crystals of 3Bz CO
ꢄ
Á
Á
Á

A. Kunishita et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006) 1731
were obtained by liquid–liquid phase diffusion of ether into a
CH3CN solution of the complex. FT-IR (KBr) 2091 cmꢁ1 (C=O),
835 cmꢁ1 (PF6ꢁ); HRMS (FABþ): m=z 352.0878, calcd for
C19H19CuN3 352.0875; Anal. Calcd for [CuI(L3Bz)(CO)]PF6-
(C20H19CuF6N3OP): C, 45.68; H, 3.64; N, 7.99%. Found: C,
45.31; H, 3.61; N, 7.89%.
5Phe CO instead of 5Bz CO in a 96% yield. Micro crystals of
Á
Á
5Phe were obtained by vapor diffusion of ether into a CH2Cl2 solu-
tion of the complex. FT-IR (KBr) 1116 and 621 cmꢁ1 (ClO4ꢁ);
HRMS (FABþ): m=z 518.1656, calcd for C32H29CuN3 518.1658;
Anal. Calcd for [CuI(L5Phe)]ClO4 2/3H2O (C32H30:333ClCuN3-
ꢄ
O
N, 6.44%.
4:666): C, 60.95; H, 4.85; N, 6.66%. Found: C, 60.81; H, 4.88;
[CuI(L5Bz)(CH3CN)]ClO4 (5Bz CH CN): This compound
Á
3
was prepared by following the same procedures as described for
3Bz CH CN using L5Bz (132.3 mg, 0.3 mmol) and [CuI(CH3-
[CuI(L6Bz)(CH3CN)]ClO4 (6Bz CH CN): This compound
was prepared by following the same procedures as described for
Á
3
Á
3
CN)4]ClO4 instead of L3Bz and [CuI(CH3CN)4]PF6, respectively.
In this case, CH2Cl2 (4 mL) was used as the solvent instead of
CH3CN, and the solid product was obtained by adding n-hexane
3Bz CH CN using L6Bz (117.0 mg, 0.3 mmol) and [CuI(CH3-
Á
3
CN)4]ClO4 instead of L3Bz and [CuI(CH3CN)4]PF6, respectively,
in an 80% yield. 1H NMR (CD2Cl2, 400 MHz) ꢃ 2.19 (3H, s, CH3-
CN), 4.02 (2H, d, J ¼ 16:0 Hz, –NCHH–), 4.11 (2H, s, –CH2–),
4.33 (2H, d, J ¼ 16:0 Hz, –NCHH–), 7.24 (3H, d, J ¼ 6:4 Hz),
7.38 (3H, d, J ¼ 8:4 Hz), 7.45 (1H, d, J ¼ 5:6 Hz), 7.65 (2H, t,
J ¼ 8:4 Hz), 7.92 (4H, t, J ¼ 8:4 Hz), 8.29 (2H, d, J ¼ 8:4 Hz),
8.53 (2H, d, J ¼ 8:4 Hz); FT-IR (KBr) 1093 and 620 cmꢁ1
(ClO4ꢁ); HRMS (FABþ): m=z 452.1191, calcd for C27H23CuN3
1
to the filtrate. The yield was 87%. H NMR (CD2Cl2, 400 MHz)
ꢃ 1.73 (3H, br s, CH3CN), 3.96 (2H, br s, –N–CH2–), 4.06 (4H,
br s, –CH2–N–CH2–), 7.20–7.35 (11H, m), 7.44 (2H, t, J ¼ 7:4
Hz), 7.49–7.58 (6H, m), 7.85 (2H, t, J ¼ 8:0 Hz); FT-IR (KBr)
1092 and 621 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 504.1501,
calcd for C31H27CuN3 504.1501; Anal. Calcd for [CuI(L5Bz)-
(CH3CN)]ClO4 1.5H2O (C33H33ClCuN4O5:5): C, 58.93; H, 4.95;
ꢄ
452.1188; Anal. Calcd for [CuI(L6Bz)(CH3CN)]ClO4 0.5H2O
ꢄ
N, 8.33%. Found: C, 58.69; H, 4.58; N, 8.49%.
[CuI(L5Bz)(CO)]ClO4 (5Bz CO): This compound was pre-
(C29H27ClCuN4O4:5): C, 57.81; H, 4.52; N, 9.30%. Found: C,
58.07; H, 4.39; N, 9.21%.
Á
pared in a similar manner as described for the synthesis of 3Bz
[CuI(L6Bz)(CO)]ClO4 (6Bz CO): This complex was prepared
Á
Á
CO by using 5Bz CH CN (73.0 mg, 0.11 mmol) instead of 3Bz
in a similar manner as described for the synthesis of 3Bz CO by
Á
Á
Á
Á
3
CH3CN as a white powder in an 81% yield. Micro crystals of 5Bz
using 6Bz CH CN (119.0 mg, 0.2 mmol) instead of 3Bz CH CN
Á
Á
3
3
CO were obtained by diffusion of n-hexane into a CH2Cl2 solu-
tion of the complex. FT-IR (KBr) 2098 and 2088 cmꢁ1 (C=O),
1091 and 622 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 532.1442,
calcd for C32H27CuN3O 532.1450; Anal. Calcd for [CuI(L5Bz)-
(CO)]ClO4 (C32H27ClCuN3O5): C, 60.76; H, 4.30; N, 6.64%.
Found: C, 60.64; H, 4.21; N, 6.52%.
[CuI(L5Bz)]ClO4 (5Bz): This complex was prepared by re-
moving CO from 5Bz CO. Thus, a methanol solution of the
CO-complex was heated on an oil bath at 70 ꢂC for 30 min, and
then the solvent was removed under reduced pressure to give a
yellow oily material of 5Bz in a 95% yield. FT-IR (KBr) 1083
and 623 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 504.1495, calcd
for C31H27CuN3 504.1501.
as a white powder in an 89% yield. Micro crystals of 6Bz CO
Á
were obtained by diffusion of n-hexane into a CH2Cl2 solution
of the complex. FT-IR (KBr) 2088 cmꢁ1 (C=O), 1089 and 621
cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 452.1184, calcd for C27H23-
CuN3 452.1188; Anal. Calcd for [CuI(L6Bz)(CO)]ClO4 (C28H23-
ClCuN3O5): C, 57.93; H, 3.99; N, 7.24%. Found: C, 57.90; H,
3.90; N, 7.09%.
[CuI(L6Bz)]ClO4 (6Bz):
This complex was prepared in a
Á
Á
similar manner as described for the synthesis of 5Bz using 6Bz
CO instead of 5Bz CO as a yellow oily material in a 95% yield.
Á
452.1185, calcd for C27H23CuN3 452.1188.
FT-IR (KBr) 1091 and 621 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z
[CuI(L6Phe)(CH3CN)]ClO4 (6Phe CH CN): This compound
was prepared by following the same procedures as described for
3Bz CH CN using L6Phe (321.0 mg, 0.8 mmol) and [CuI(CH3-
Á
3
[CuI(L5Phe)(CH3CN)]ClO4 (5Phe CH CN): This compound
was prepared by following the same procedures as described for
3Bz CH CN using L5Phe (91.2 mg, 0.2 mmol) and [CuI(CH3-
Á
3
Á
3
CN)4]ClO4 instead of L3Bz and [CuI(CH3CN)4]PF6, respectively,
in an 86% yield. 1H NMR (CD2Cl2, 400 MHz) ꢃ 2.24 (3H, s,
CH3CN), 2.92–3.09 (2H, m, –NCH2CH2Ph), 3.20–3.38 (2H, m,
–NCH2CH2Ph), 4.16 (2H, d, J ¼ 16:0 Hz, –NCHH–), 4.42 (2H, d,
J ¼ 16:0 Hz, –NCHH–), 7.07–7.20 (2H, m), 7.20–7.34 (3H, m),
7.43–7.55 (2H, m), 7.62–7.75 (2H, m), 7.88–8.06 (4H, m), 8.34
(2H, d, J ¼ 8:3 Hz), 8.51 (2H, d, J ¼ 8:6 Hz); FT-IR (KBr) 1109,
1090, and 625 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 466.1347,
calcd for C28H25CuN3 466.1345; Anal. Calcd for [CuI(L6Phe)-
(CH3CN)]ClO4 (C30H28ClCuN4O4): C, 59.31; H, 4.65; N, 9.22%.
Found: C, 58.99; H, 4.74; N, 9.00%.
Á
3
CN)4]ClO4 instead of L3Bz and [CuI(CH3CN)4]PF6, respectively,
in a 51% yield. 1H NMR (CD2Cl2, 400 MHz) ꢃ 1.85 (3H, s, CH3-
CN), 2.90 (2H, t, J ¼ 7:4 Hz, –NCH2CH2–), 3.08 (2H, t, J ¼ 7:4
Hz, –NCH2CH2–), 4.10 (4H, br, –CH2–N–CH2–), 6.85 (1H, t, J ¼
7:0 Hz), 7.00–7.09 (3H, m), 7.28 (5H, t, J ¼ 8:0 Hz), 7.40 (2H, d,
J ¼ 8:0 Hz), 7.45–7.51 (6H, m), 7.55 (2H, d, J ¼ 7:6 Hz), 7.90
(2H, t, J ¼ 8:0 Hz); FT-IR (KBr) 1092 and 623 cmꢁ1 (ClO4ꢁ);
HRMS (FABþ): m=z 518.1643, calcd for C32H29CuN3 518.1657;
Anal. Calcd for [CuI(L5Phe)(CH3CN)]ClO4 (C34H32ClCuN4O4):
C, 61.91; H, 4.89; N, 8.49%. Found: C, 61.71; H, 4.79; N, 8.27%.
[CuI(L5Phe)(CO)]ClO4 (5Phe CO): This complex was pre-
[CuI(L6Phe)(CO)]ClO4 (6Phe CO): This complex was pre-
Á
Á
pared in a similar manner as described for the synthesis of 3Bz CO
pared in a similar manner as described for the synthesis of 3Bz CO
Á
Á
CH3CN as a white powder in an 84% yield. Micro crystals of
by using 5Phe CH CN (100.0 mg, 0.15 mmol) instead of 3Bz
by using 6Phe CH CN (285.0 mg, 0.47 mmol) instead of 3Bz
Á
Á
Á
Á
3
3
CH3CN as a white powder in a 79% yield. Micro crystals of 5Phe
Á
CO were obtained by diffusion of n-hexane into a CH2Cl2 solu-
tion of the complex. FT-IR (KBr) 2102 and 2092 cmꢁ1 (C=O),
1092 and 622 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 546.1588, calcd
for C33H29CuN3O 546.1606; Anal. Calcd for [CuI(L5phe)(CO)]-
ClO4 (C33H29ClCuN3O5): C, 61.30; H, 4.52; N, 6.50%. Found:
C, 61.10; H, 4.44; N, 6.52%.
6Phe CO were obtained by liquid–liquid phase diffusion of n-
Á
hexane into a CH2Cl2 solution of the complex. FT-IR (KBr)
2101 cmꢁ1 (C=O), 1091 and 622 cmꢁ1 (ClO4ꢁ); HRMS (FABþ):
m=z 466.1344, calcd for C28H25CuN3 466.1345; Anal. Calcd for
[CuI(L6phe)(CO)]ClO4 (C29H25ClCuN3O5): C, 58.59; H, 4.24; N,
7.07%. Found: C, 58.42; H, 4.25; N, 6.97%.
[CuI(L6Phe)]ClO4 (6Phe): This complex was prepared in a
similar manner as described for the synthesis of 5Bz using
[CuI(L5Phe)]ClO4 (5Phe): This complex was prepared in a
similar manner as described for the synthesis of 5Bz using

1732 Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006)
Copper(I) Complexes of Tridentate Ligands
6Phe CO instead of 5Bz CO as yellow powder in a 96% yield.
ddd, J ¼ 1:2, 6.8, and 8.8 Hz), 7.77 (2H, d, J ¼ 8:4 Hz), 8.03
(2H, d, J ¼ 8:4), 8.15 (2H, d, J ¼ 8:4 Hz); ESI-MS (pos.) m=z ¼
420:0 (M þ 1).
Á
Á
Micro crystals of 6Phe were obtained by diffusion of n-hexane into
a CH2Cl2 solution of the complex. FT-IR (KBr) 1083, and 620
cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 466.1326, calcd for C28H25-
CuN3 466.1344; Anal. Calcd for [CuI(L5phe)]ClO4 (C28H25Cl-
CuN3O4): C, 59.36; H, 4.45; N, 7.42%. Found: C, 59.39; H, 4.36;
N, 7.20%.
X-ray Structure Determination. A single crystal was mount-
ed on a CryoLoop (Hamptom Research Co.) or a glass-fiber. The
X-ray crystallographic analyses of 5Bz CO were performed on a
Rigaku Mercury CCD area detector with graphite monochromated
Á
[CuI(L6PhePh)]ClO4 (6PhePh): Ligand L6PhePh (71.4 mg, 0.15
mmol) was treated with [CuI(CH3CN)4]ClO4 (47.7 mg, 0.15
mmol) in CH2Cl2 (5 mL) under Ar atmosphere in a glovebox. Af-
ter stirring for 5 min at room temperature, insoluble material was
removed by filtration. Addition of ether (100 mL) to the filtrate
cause a pale yellow powder to precipitate upon standing for sev-
eral minutes. The supernatant was then removed by decantation,
and the remaining pale yellow solid was washed three times with
ether and dried to give complex 6PhePh in a 93% yield. FT-IR
(KBr) 1108, 1090, and 625 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z
542.1650, calcd for C34H29CuN3 542.1658; Anal. Calcd for [CuI-
(L6PhePh)]ClO4 (C34H29ClCuN3O4): C, 63.55; H, 4.55; N, 6.54%.
Found: C, 63.25; H, 4.52; N, 6.43%.
Mo Kꢄ radiation (ꢅ ¼ 0:71070 A) controlled by a Windows NT
˚
running the CrystalClear software package (Rigaku Corp., 1999).
The crystal to detector distance was 34.80 mm. The data were
collected at a temperature of ꢁ120 ꢂC to 2ꢆmax of 55ꢂ. X-ray dif-
fraction data for 6Phe CH CN, 3Bz CO, 5Phe CO, 6Bz CH CN,
Á
Á
Á
Á
3
3
6Bz CO, 6Phe CO, 6Phe, 6PhePh, 7, and 8 were collected by using
Á
Á
a Rigaku RAXIS-RAPID imaging plate area detector with graph-
˚
ite monochromated Mo Kꢄ radiation (ꢅ ¼ 0:71070 A) to 2ꢆmax of
55.0ꢂ. All data were corrected for Lorentz and polarization effects.
All crystallographic calculations were performed by using Crystal
Structure software package of the Molecular Structure Corpora-
tion [Crystal Structure: Crystal Structure Analysis Package ver-
sion 3.5.1, Rigaku and Rigaku/MSC (2000–2003)]. The structures
were solved by direct methods and refined by the full-matrix least
squares using SIR-9223 or SHELXS97.24 The non-hydrogen atoms
were refined anisotropically and hydrogen atoms were refined us-
ing the riding model. Crystallographic data have been deposited
with Cambridge Crystallographic Data Centre: Deposition num-
Product Analysis of the Oxygenation Reactions of 6Bz and
6Phe
.
Complex 6Bz (60.0 mg, 0.11 mmol) was dissolved in deaer-
ated acetone (20 mL) under anaerobic conditions, and the solution
was exposed to O2 gas at ꢁ80 ꢂC and stirred for 2 h at the same
temperature. Addition of ether (100 mL) to the solution cause a
green powder to precipitate upon standing for several minutes.
The supernatant was then removed by decantation, and the re-
maining green solid was washed with ether three times and dried
to give bis(ꢁ-hydroxo)dicopper(II) complex 7 in a 68% yield. Mi-
cro crystals of 7 were obtained by vapor diffusion of ether into an
acetone solution of the complex. FT-IR (KBr) 3538 cmꢁ1 (OH),
1093 and 621 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z 452.1176,
calcd for C27H23CuN3 452.1188; Anal. Calcd for [(CuIIL6Bz)2-
(ꢁ-OH)2](ClO4)2(CH3OCH3)2(H2O) (C60H62Cl2Cu2N6O13): C,
56.60; H, 4.91; N, 6.60%. Found: C, 56.58; H, 4.59; N, 6.64%.
The reaction of 6Phe was carried out similarly, and the single
crystals of product 8, (ꢁ-hydroxo)(ꢁ-alkoxo)dicopper(II) com-
plex, were obtained in the similar manner. FT-IR (KBr) 3519
cmꢁ1 (OH), 1095 and 622 cmꢁ1 (ClO4ꢁ); HRMS (FABþ): m=z
482.1288, calcd for C28H25CuN3O 482.1294; Anal. Calcd for
[CuII2(L6phe)(L6phe-O)(ꢁ-OH)](ClO4)2(CH3OH)(CH3CH2OCH2-
CH3) (C61H64Cl2Cu2N6O12): C, 57.64; H, 5.07; N, 6.61%. Found:
C, 57.70; H, 4.85; N, 6.23%.
bers CCDC-610488 for compound 3Bz CO, CCDC-610489 for
Á
compound 5Bz CO, CCDC-610490 for compound 5Phe CO,
Á
Á
CCDC-610491 for compound 6Bz CO, CCDC-610492 for com-
Á
pound 6Phe, CCDC-610493 for compound 6Phe CH CN, CCDC-
Á
3
610494 for compound 6Phe CO, CCDC-610495 for compound
Á
6PhePh, CCDC-610496 for compound 7, and CCDC-610497 for
compound 8. Copies of the data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge, CB2 1EZ, UK; Fax: +44 1223 336033; e-mail: deposit@
ccdc.cam.ac.uk).
Kinetic Measurements. Kinetic measurements for the oxy-
genation reactions of copper(I) complexes 6Bz and 6Phe and the
decomposition process of the peroxo intermediate derived from
6Phe were performed using a Hewlett Packard 8453 photo diode
array spectrophotometer with a Unisoku thermostated cell holder
designed for low-temperature measurements (USP-203, a desired
temperature can be fixed within ꢅ0:5 ꢂC) in acetone at ꢁ94 ꢂC.
The second-order rate constants for the formation of Cu2O2
intermediates were determined from the slopes of the plots of
ðA0 ꢁ AÞ=f½Cu-complexꢆ ðA ꢁ A Þg vs time based on the time
Isolation of the Modified Ligand in the Reaction of 6Phe with
O2. Complex 6Phe (52.0 mg, 0.092 mmol) was dissolved in dea-
erated acetone (15 mL) under anaerobic conditions, and the solu-
tion was exposed to O2 gas at ꢁ80 ꢂC and stirred for 2 h at the
same temperature. A mixture of organic materials was obtained
after an ordinary work-up treatment of the reaction mixture with
an NH3 aq and following extraction by CH2Cl2. Yield of the hy-
droxylation product was determined to be 73% based on the cop-
1
0
courses of the absorption change at ꢅmax due to the intermediates.
Pseudo-first-order rate constants for the decomposition processes
of the peroxo intermediate of L6Phe were determined from the
slopes of the plots of lnðA ꢁ A Þ vs time based on the time cours-
1
es of the absorption change at ꢅmax due to the intermediate.
1
per(I) starting material by using an integral ratio in the H NMR
spectrum between the methine proton (–CHOH–) at ꢃ 4.97 of
the hydroxylation product. The hydroxylated ligand L6phe-OH
was isolated by a silica gel column chromatographic treatment
on the mixture of organic material (eluent: AcOEt–MeOH);
1H NMR (400 Hz, CDCl3) ꢃ 2.95 (1H, dd, J ¼ 10:0 and 13.0 Hz,
–N–CH–CHOH–), 3.11 (1H, dd, J ¼ 2:6 and 13.5 Hz, –N–CH–
CHOH–), 4.18 (2H, d, J ¼ 15:6 Hz, –N–CH2–), 4.31 (2H, d, J ¼
15:6 Hz, –CH2–N–), 4.97 (1H, dd, J ¼ 2:6 and 10.0 Hz, –N–CH–
CHOH), 7.07 (1H, br s), 7.20 (1H, t, J ¼ 7:2 Hz), 7.28 (1H, t, J ¼
6:8 Hz), 7.37 (2H, d, J ¼ 8:0 Hz), 7.47–7.54 (4H, m), 7.72 (2H,
Results and Discussion
Syntheses and Structural Characterizations of Copper(I)
Complexes. In this study, the structure and reactivity of the
copper(I) complexes of L3Bz, L4Bz, L5Bz, and L6Bz with a ben-
zyl substituent (R = –CH2Ph, Chart 1) have been compared in
detail in order to give further insights into the steric effects of
the metal-binding site of the tridentate ligands. The structure
and reactivity of the copper(I) complexes of L5Phe, L6Phe
and L6PhePh (Phe = –CH2CH2Ph; PhePh = –CH2CHPh2)
,

A. Kunishita et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006) 1733
[CuI(CH3CN)4]+
[CuI(LnR)(CH3CN)]+
LnR
(n = 3, 5, 6; R = Bz, Phe)
nR•CH3CN
n = 3, R = Bz
n = 5, R = Bz or Phe
n = 6, R = Bz or Phe
CO
CH3CN
[CuI(LnR)(CO)]+
CO
∆
[CuI(LnR)]+
(n = 5, 6; R = Bz, Phe)
nR•CO
nR
n = 3, R = Bz
n = 5, R = Bz or Phe
n = 6, R = Bz or Phe
n = 5, R = Bz or Phe
n = 6, R = Bz, Phe, or PhePh
∆
(n = 3; R = Bz)
CO
disproportionation
Scheme 1.
have also been examined in order to evaluate the steric effects
of the ligand sidearm (R). The synthetic routes of the new
copper(I) complexes are summarized in Scheme 1. The syn-
theses and structures of the copper(I) complexes with L4R
have already been reported.14
and quinoline). The average bond lengths Cu–NPy(Qu) between
copper(I) ion and the nitrogen atoms of hetero-aromatic donors
Bz
Bz
˚
of the complexes are 2.046 A (3 CO), 2.053 A (4 CO),
˚
Á
Á
Bz
Bz
˚
˚
2.109 A (5 CO), and 2.041 A (6 CO). Apparently, Cu–
Á
Á
indicating that the 6-phenyl substituent on the pyridine donor
NPy bonds in 5Bz CO are relatively longer than those of others,
Á
group imparts a relatively large steric hindrance for the metal
Treatment of the ligands with an equimolar amount of
[CuI(CH3CN)4]X (X = ClO4 or PF6) under anaerobic condi-
tions (Ar) gave the corresponding copper(I) complexes with
binding. Namely, the Cu–NPy bonds in 5Bz CO are elongated
due to the steric repulsion between the 6-phenyl group and the
Á
metal ion. In this respect, the steric effect of the 6-methyl sub-
acetonitrile as a co-ligand, nR CH CN (n ¼ 3{6, R ¼ Bz or
Á
3
Phe)25 except for ligand L6PhePh which gave the copper(I) com-
plex 6PhePh without having any ancillary ligands (see
stituent in 4Bz CO is not so significant: only a 0.007 A elonga-
˚
Á
Scheme 1). Existence of the CH3CN molecule in nR CH CN
has been confirmed by H NMR and elemental analysis (see,
Experimental Section). The crystal structure of 6Phe CH CN,
which has a significantly distorted tetrahedral geometry at the
metal center is shown in Fig. S1, and the crystallographic data
and the selected bond lengths and angles are presented in
Tables S1 and S2, respectively. A similar structure was also
tion of Cu–NPy compared to 3Bz CO. It should be noted that
Á
Á
Á
3
1
the bond lengths of Cu–NQu in 6Bz CO are nearly the same
Á
as those of 3Bz CO, suggesting that the steric effect of the qui-
Á
3
noline donor group is the same as that of pyridine in the cop-
per(I) oxidation state. It should be also mentioned that the Cu–
CO lengths seem to correlate to the Cu–NPy(Qu) lengths. Name-
ly, the longer the Cu–NPy(Qu), the longer the Cu–CO (Table 2).
found for 4Bz CH CN.14
The CO ligand can be easily removed from nR CO by heat-
Á
Á
3
The acetonitrile complexes nR CH CN were then convert-
ing them in methanol. Thus, 5R CO and 6R CO (R ¼ Bz and
Á
Á
Á
3
ed to the corresponding CO-complexes nR CO by treating
Phe) were converted to the corresponding copper(I) complexes
without an ancillary ligand, 5R and 6R, as in the case of the
conversion of 4R CO to 4R.14 In the case of 3Bz CO (R =
Á
them with CO gas at low temperature.25 The crystal structures
of 3Bz CO, 5Bz CO, and 6Bz CO are shown in Fig. 1. The
Á
Á
Á
Á
Á
crystallographic data are listed in Table 1, and the selected
bond lengths and angles are summarized in Table 2, in which
–CH2Ph), however, removal of the CO ligand caused a rapid
disproportionation to give a mixture of a copper(II) complex
and copper metal.10 Thus, the copper(I) complex of L3Bz with-
out any external co-ligand could not be isolated.26 It is interest-
ing to note that 6PhePh with the large ligand sidearm PhePh
(R = –CH2CH(Ph)2) was directly obtained from the reaction
between ligand L6PhePh and [CuI(CH3CN)4]ClO4 without for-
mation of the corresponding acetonitrile complex as men-
tioned above. The large substituent PhePh may prohibit the
coordination of CH3CN.
those of 4Bz CO are also included.14 The crystal structures of
Á
5Phe CO and 6Phe CO are also presented in Fig. S2, and the
Á
Á
crystallographic data and the selected bond lengths and angles
are summarized in Tables S3 and S4, respectively. Although
all the CO-complexes exhibit a similar structure with signifi-
cantly distorted tetrahedral geometry with N3C donor set, com-
parison of the bond lengths of Cu–NPy(Qu) and Cu–CO among
nBz CO (R ¼ Bz) provide some important insights into the
Á
steric effects of the hetero-aromatic donor groups (pyridine
The crystal structures of 6Phe and 6PhePh are shown in Fig. 2.

1734 Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006)
Copper(I) Complexes of Tridentate Ligands
3Bz•CO
6Phe
5Bz•CO
6PhePh
Fig. 2. ORTEP drawings of 6Phe and 6PhePh showing 50%
probability thermal ellipsoids. The counter anions and
the hydrogen atoms are omitted for clarity.
0.29
2.0 µA
6Bz•CO
Fig. 1. ORTEP drawings of 3Bz CO, 5Bz CO, and 6Bz CO
Á
Á
Á
showing 50% probability thermal ellipsoids. The counter
anions and the hydrogen atoms are omitted for clarity.
The crystallographic data and the selected bond lengths and
angles are listed in Tables 1 and 2, respectively. As in the case
0.19
of 3Phe
,
4Phe
,
and 4PhePh
,
both 6Phe and 6PhePh have a
10,26
14
14
–0.1
0
0.1 0.2 0.3 0.4 0.5 0.6
significantly distorted trigonal pyramidal geometry involving
two nitrogen atoms N(1) and N(2) of the quinoline donor
groups and one of the phenyl carbons [C(28) in 6Phe and
C(24) in 6PhePh] in the basal plane and the tertiary amine nitro-
gen atom N(3) as the axial ligand. Thus, these complexes also
exhibit an interesting d–ꢀ interaction with an ꢇC-binding
mode between the copper(I) ion and the ortho-carbon atom
of the aromatic ring of the ligand sidearm. Although crystal
structure of 5Phe has not been determined, the complex may al-
so have a similar structure with the ꢇC-type d–ꢀ interaction.
Oxidation Potential of Copper(I) Complexes. The oxida-
tion potential of the complex is an important indicator of the
electron-donor ability of the ligands. Figure 3 shows the cyclic
E
1/2 / V (vs. Ag / 0.1 M AgNO3)
Fig. 3. Cyclic voltammogram of 5Bz CH CN (2:0 ꢃ 10ꢁ3
Á
3
M) in CH3CN containing 0.1 M TBAPF6; working elec-
trode Pt, counter electrode Pt, reference electrode Ag/
0.01 M AgNO3, scan rate 50 mV sꢁ1
.
couple was observed, from which the oxidation potentials
(E1=2) of the copper(I) complexes were determined as the
mid-pint of the oxidation and reduction peak potentials as
summarized in Table 3.
As can be seen in Table 3, the E1=2 values of 4Bz CH CN,
Á
3
6Bz CH CN, and 6Phe CH CN are nearly the same (ꢇ0:15 V
Á
Á
CH3CN is higher. This could be attributed to the steric effect of
3
3
voltammogram of 5Bz CH CN measured in CH CN as a typi-
vs Ag/0.01 M AgNO3), whereas the oxidation potential of 5Bz
Á
Á
3
3
cal example. The cyclic voltammograms for the other com-
plexes were measured under the same experimental conditions.
In all cases, a reversible or a quasi-reversible CuI/CuII redox
6-phenyl group of 5Bz CH CN. Namely, the phenyl group at
C-6 on the pyridine ring of L5Bz may induce a larger steric
Á
3

Table 1. Summary of the X-ray Crystallographic Data of 3Bz CO, 5Bz CO, 6Bz CO, 6Phe, 6PhePh, and 8
Á
Á
Á
3Bz CO
5Bz CO
6Bz CO
6Phe
6PhePh
8
Á
525.90
Á
Á
Formula
C20H19N3CuOPF6
C32H27N3CuClO5
632.58
C28H23N3CuClO5
580.51
C28H25N3CuClO4
566.52
C34H29N3CuClO4
642.62
C56H50N6Cu2Cl2O10
1165.04
monoclinic
P21=c (#14)
14.039(6)
29.254(10)
15.386(7)
90
101.617(20)
90
6189.7(41)
4
Formula weight
Crystal system
Space group
orthorhombic
Pna21 (#33)
9.778(13)
13.900(13)
16.111(15)
90
90
90
2189.7(40)
4
1064.00
1.595
153
orthorhombic
Pna21 (#33)
23.389(2)
11.1658(10)
22.239(2)
90
monoclinic
P21=n (#14)
12.5204(10)
11.7910(10)
17.7172(16)
90
105.410(5)
90
2521.5(4)
4
monoclinic
P21=c (#14)
11.971(10)
16.634(13)
12.628(8)
90
98.79(3)
90
2485.0(32)
4
monoclinic
P21=c (#14)
11.8255(7)
20.2106(13)
12.9974(8)
90
112.649(3)
90
2866.8(3)
4
˚
a/A
˚
b/A
˚
c/A
ꢄ/deg
ꢈ/deg
90
90
ꢉ/deg
3
˚
V/A
5808.0(10)
8
2608.00
1.447
153
Z
F(000)
Dcalcd/g cmꢁ3
T/K
1192.00
1.529
153
1168.00
1.514
153
1328.00
1.489
153
2400.00
1.250
153
Crystal size/mm3
ꢁ (Mo Kꢄ)/cmꢁ1
2ꢆmax/deg
0:20 ꢃ 0:20 ꢃ 0:10
0:20 ꢃ 0:20 ꢃ 0:10
0:20 ꢃ 0:20 ꢃ 0:20
10.176
55.0
0:40 ꢃ 0:40 ꢃ 0:40
10.275
54.9
0:40 ꢃ 0:30 ꢃ 0:20
9.006
54.9
0:40 ꢃ 0:20 ꢃ 0:20
8.292
55.0
11.384
54.9
8.902
55.0
No. of reflns measd
No. of reflns obsd
No. of variables
Ra)
19861
12203 ([I > 2:00ꢊðIÞ])
55829
40872 ([I > 3:00ꢊðIÞ])
24394
23177
27027
57661
11485 ([I > 3:00ꢊðIÞ])
367
0.0420
0.0700
1.079
4446 ([I > 2:00ꢊðIÞ])
362
0.0335
0.0408
1.004
5488 ([I > 2:00ꢊðIÞ])
415
0.0428
0.0664
0.979
7045 ([I > 1:00ꢊðIÞ])
747
0.0864
0.1050
1.008
309
812
0.0565
0.0758
1.007
0.0590
0.0640
1.034
b)
Rw
GOF
2
1=2
a) R ¼ ꢀjjFoj ꢁ jFcjj=ꢀjFoj. b) Rw ¼ ½ꢀwðjFoj ꢁ jFcjÞ =ꢀwFo2ꢆ
.

ꢂ
Bz
Table 2. Selected Bond Lengths (A) and Angles ( ) of 3 CO, 4Bz CO, 5Bz CO, 6Bz CO, 6Phe, 6PhePh, and 8
˚
Á
Á
Á
Á
3Bz CO
5Bz CO
6PhePh
Á
Á
Cu(1)–N(1)
Cu(1)–N(3)
2.059(3)
2.184(3)
Cu(1)–N(2)
Cu(1)–C(20)
2.033(2)
1.799(4)
Cu(1)–N(1)
Cu(1)–N(3)
2.067(2)
2.131(2)
Cu(1)–N(2)
Cu(1)–C(32)
2.150(2)
1.816(3)
Cu(1)–N(1)
Cu(1)–N(3)
1.9953(17) Cu(1)–N(2)
2.2144(18) Cu(1)–C(24)
2.0317(17)
2.175(2)
N(1)–Cu(1)–N(2) 111.28(13) N(1)–Cu(1)–N(3) 81.90(12) N(1)–Cu(1)–N(2) 115.26(10) N(1)–Cu(1)–N(3) 81.06(9)
N(1)–Cu(1)–C(20) 115.73(16) N(2)–Cu(1)–N(3) 81.39(12) N(1)–Cu(1)–C(32) 126.55(12) N(2)–Cu(1)–N(3) 78.12(9)
N(1)–Cu(1)–N(2) 124.87(7) N(1)–Cu(1)–N(3) 83.58(6)
N(1)–Cu(1)–C(24) 131.75(7) N(2)–Cu(1)–N(3) 81.46(7)
N(2)–Cu(1)–C(32) 106.46(14) N(3)–Cu(1)–C(32) 141.26(13) N(2)–Cu(1)–C(24) 102.06(7) N(3)–Cu(1)–C(24) 93.90(7)
N(2)–Cu(1)–C(20) 123.99(17) N(3)–Cu(1)–C(20) 132.9(2)
4Bz COa)
Molecule 1
6Bz CO
8
Á
Á
Cu(1)–N(1)
Cu(1)–N(3)
2.050(2)
2.108(2)
Cu(1)–N(2)
Cu(1)–C(28)
2.032(2)
1.797(3)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–O(6)
Cu(2)–O(6)
Cu(2)–N(5)
Cu(1)–Cu(2)
2.006(8)
2.263(7)
1.941(6)
1.931(6)
2.015(7)
Cu(1)–N(2)
Cu(1)–O(5)
Cu(2)–O(5)
Cu(2)–N(4)
Cu(2)–N(6)
2.047(8)
1.930(6)
1.901(6)
2.190(9)
2.003(8)
2.449(9)
Cu(1)–N(1)
Cu(1)–N(3)
2.063(3)
2.131(3)
Cu(1)–N(2)
Cu(1)–C(22)
2.042(2)
1.806(3)
N(1)–Cu(1)–N(2) 104.18(10) N(1)–Cu(1)–N(3) 82.03(11)
N(1)–Cu(1)–C(28) 125.63(14) N(2)–Cu(1)–N(3) 84.38(11)
N(2)–Cu(1)–C(28) 123.98(12) N(3)–Cu(1)–C(28) 122.84(14)
N(1)–Cu(1)–N(2) 105.22(9) N(1)–Cu(1)–N(3) 80.51(10)
N(2)–Cu(1)–N(3) 83.73(9)
N(3)–Cu(1)–C(33) 127.7(1)
N(1)–Cu(1)–C(22) 117.6(1)
N(2)–Cu(1)–C(22) 129.0(1)
2.937(16) O(5)–O(6)
6Phe
O(5)–Cu(1)–O(6) 78.5(2)
O(5)–Cu(1)–N(2) 174.2(3)
O(6)–Cu(1)–N(1) 166.8(3)
O(6)–Cu(1)–N(3) 109.7(2)
N(1)–Cu(1)–N(3) 80.5(3)
O(5)–Cu(2)–O(6) 79.4(2)
O(5)–Cu(2)–N(5) 106.4(3)
O(6)–Cu(2)–N(4) 106.3(3)
O(6)–Cu(2)–N(6) 85.7(2)
N(4)–Cu(2)–N(6) 80.9(3)
O(5)–Cu(1)–N(1) 90.9(3)
O(5)–Cu(1)–N(3) 105.2(2)
O(6)–Cu(1)–N(2) 98.3(3)
N(1)–Cu(1)–N(2) 91.6(3)
N(2)–Cu(1)–N(3) 80.4(2)
O(5)–Cu(2)–N(4) 112.1(3)
O(5)–Cu(2)–N(6) 162.4(3)
N(4)–Cu(2)–N(5) 102.1(3)
N(5)–Cu(2)–N(6) 81.1(3)
O(6)–Cu(2)–N(5) 146.2(3)
Molecule 2
Cu(1)–N(1)
Cu(1)–N(3)
1.982(15) Cu(1)–N(2)
2.212(15) Cu(1)–C(28)
1.989(18)
2.217(2)
Cu(2)–N(4)
Cu(2)–N(6)
2.051(3)
2.124(3)
Cu(2)–N(5)
Cu(2)–C(44)
2.054(3)
1.800(3)
N(1)–Cu(1)–N(2) 127.57(6) N(1)–Cu(1)–N(3) 83.90(6)
N(1)–Cu(1)–C(28) 125.42(8) N(2)–Cu(1)–N(3) 82.79(6)
N(2)–Cu(1)–C(28) 106.77(7) N(3)–Cu(1)–C(28) 99.65(6)
N(4)–Cu(2)–N(5) 108.0(1)
N(4)–Cu(2)–C(44) 122.2(1)
N(5)–Cu(2)–C(44) 121.8(1)
N(4)–Cu(2)–N(6) 80.6(1)
N(5)–Cu(2)–N(6) 83.68(10)
N(6)–Cu(2)–C(44) 129.0(1)
a) Data are taken from Ref. 14.

A. Kunishita et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006) 1737
repulsion between the substituent and the metal ion, thus weak-
ening the coordinative interaction. This will decrease the elec-
tron-donation from the pyridine nitrogen, causing the increase
of the oxidation potential of copper(I). In fact, Cu–NPy bonds
showed virtually no reactivity toward O2. This could be attrib-
uted in part to their higher redox potential, stabilizing the cop-
per(I) oxidation sate (see Table 3). The large 6-phenyl groups
of L5R may also prevent the approach of O2 to the copper(I)
center, prohibiting the oxygenation reaction.
On the other hand, copper(I) complexes 6Bz and 6aPhe ex-
hibited relatively high reactivity toward O2 at low temperature
(ꢁ94 ꢂC). Figure 4 shows the spectral change upon introduc-
tion of O2 gas into an acetone solution of 6Bz. The absorption
bands at 362, 394, ꢇ460 (shoulder), and 535 nm gradually in-
creased as the reaction proceeded. The absorption bands at 362
and 535 nm were attributed to a (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II)
complex A, and the band at 394 nm was due to the formation
of the bis(ꢁ-oxo)dicopper(III) species B.3,4,27 This was con-
firmed by resonance Raman spectroscopy, Fig. 5. When the
reaction solution of 6Bz with 16O2 was excited with 406.7 nm
in 5Bz CO (av. 2.109 A) are longer than those of the others
˚
Á
as discussed above. On the other hand, the very negative E1=2
value of 3Bz CH CN (ꢁ0:14 V) can be attributed to the strong-
Á
3
er electron-donor ability of L3R ligand as previously reported.10
Reaction of Copper(I) Complexes and O2. As mentioned
in the Introduction, the copper(I) complex supported by ligand
L3Phe (3Phe, R = –CH2CH2Ph) has been shown to react read-
ily with O2 at low temperature (ꢁ94 ꢂC) to give the bis(ꢁ-
oxo)dicopper(III) complex B.10 It has also been shown that
introduction of a methyl group at C-6 of the pyridine nucleus
of the bis(2-pyridylmethyl)amine tridentate L3R-type ligands
to give L4R resulted in a decrease of the electron-donor ability
of pyridine nitrogen to afford the side-on peroxodicopper(II)
complex A.14 In this case, the O–O bond of peroxo complex
1.5
2.0
A supported by L4R was found to be weaker (ꢋO{O 720
ꢈ
¼
cmꢁ1) than that of the peroxo complex involving L1R
∞
394
362
(ꢋO{O 745 cmꢁ1).14
ꢈ
¼
1.0
0
In order to give further insights into the steric effects of the
C-6 substituents of pyridine on copper(I)/O2-reactivity, the
oxygenation reactions of 5Bz and 5Phe, which have the larger
6-phenyl group on the pyridine moiety, were examined under
the same experimental conditions. However, these compounds
1.0
0.5
0
0
100
Time / s
200
Table 3. Oxidation Potentials of the Copper(I) Complexes
in CH3CNa)
535
Complex
3Bz CH CN
E1=2/V vs Ag/0.01 M AgNO3
ꢁ0:14
0.15
0.24
0.16
0.15
Á
3
4Bz CH CN
Á
3
500
600
800
400
700
5Bz CH CN
Á
3
6Bz CH CN
Wavelength / nm
Á
3
6Phe CH CN
Á
3
Fig. 4. Spectral change observed upon introduction of O2
gas into an acetone solution of 6Bz (2:0 ꢃ 10ꢁ3 M) at
ꢁ94 ꢂC in a 1 mm path length UV cell. Inset: second-order
plot based on the absorption change at 400 nm.
a) In CH3CN containing 0.1 M TBAPF6; working electrode Pt,
counter electrode Pt, and reference electrode Ag/0.01 M
AgNO3.
(A)
(B)
s
s
core vibration
594
core vibration
588
O−O vibration
713
631
16O2
16O2
558
558
602
18O2
750
673
18O2
500
550
600
650
750
700
500
550
600
650
700
Raman Shift / cm-1
Raman Shift / cm-1
Fig. 5. Resonance Raman spectra of the reaction solution of 6Bz with 16O2 (solid line) and with 18O2 (dashed line) obtained with an
excitation wavelength of (A) 406.7 nm and (B) 514.5 nm in acetone at ꢁ90 ꢂC.

1738 Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006)
Copper(I) Complexes of Tridentate Ligands
laser light, an intense Raman band was observed at 588 cmꢁ1
that shifted to 558 cmꢁ1 upon 18O2 substitution (Fig. 5A). The
peak position at 588 cmꢁ1 and its isotope shift of 30 cmꢁ1 are
within the range of those of the reported bis(ꢁ-oxo)dicop-
per(III) complexes (Cu2O2 core breathing vibration involving
Cu–O stretching).27,28 On the other hand, the Raman spectrum
obtained by excitation with 514.5 nm laser light gave a new
band at 713 cmꢁ1 that shifted to 673 cmꢁ1 with 18O2 (Fig. 5B).
The peak at 713 cmꢁ1 and its isotope shift of 40 cmꢁ1 are con-
sistent with the formation of (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II)
complex (O–O stretching vibration).29 It should be noted here
that there is an additional isotope sensitive Raman band at
631 cmꢁ1 that shifted to 602 cmꢁ1 (Fig. 5B). Judging from
the peak position and its isotope shift (29 cmꢁ1), these bands
could also be assigned to an isomeric form of the bis(ꢁ-oxo)-
dicopper(III) species; however, definitive assignment of these
bands requires further experiments. It should be also men-
tioned that the O–O bond stretching vibration of the (ꢁ-ꢂ2:ꢂ2-
peroxo)dicopper(II) complex with L6Bz (713 cmꢁ1) is nearly
identical to that of the peroxo complex with L4Bz (714
cmꢁ1), but significantly lower than that of the L1Bz-peroxo
complex (745 cmꢁ1), demonstrating that the O–O bond of A
in the L6Bz-system is also weaker than that in the L1Bz-system.
In the case of 6Phe, the reaction was much simpler as shown
in Fig. 6. In this case, the major product was the (ꢁ-ꢂ2:ꢂ2-per-
oxo)dicopper(II) complex A which has an intense absorption
band at 360 nm together with a small band at 515 nm, which
are the characteristic LMCT bands of the side-on peroxodicop-
per(II) complex.29 In this case, the resonance Raman spectra
showed two distinct bands at 737 and 724 cmꢁ1 that shifted
to one band at 692 cmꢁ1 upon 18O2-substituion (Fig. S4).
The Raman bands at 737 and 724 cmꢁ1 could be assigned to
a Fermi doublet of the O–O bond stretching vibration, since
the isotope shift of 39 cmꢁ1 obtained by subtracting the fre-
quency (692 cmꢁ1) of the 18O-derivative from the average fre-
quency (731 cmꢁ1) of the 16O-derivaitve agrees with the iso-
tope shift reported for the side-on peroxodicopper(II) com-
plexes A (38–43 cmꢁ1).3 The larger alkyl substituent (R =
Phe = –CH2CH2Ph) in the L6Phe-complex may prevent the
complex vs ꢋO{O ¼ 713 cmꢁ1 of the L6Bz complex).
For both 6Bz and 6Phe, the formation of Cu2/O2 intermedi-
ates obeyed second-order kinetics as shown in the insets of
Figs. 4 and 6, and the second-order rate constants were 7.7
and 44.7 Mꢁ1 sꢁ1, respectively. This suggests that the initial
formation of a 1:1 adduct between the copper(I) complex
and O2 is in a fast equilibrium, and the subsequent reaction
of the mononuclear copper–dioxygen adduct, which is prob-
ably a side-on superoxocopper(II) complex C30 and another
molecule of the copper(I) complex to form the (ꢁ-ꢂ2:ꢂ2-
peroxo)dicopper(II) complex A is the rate-determining step
(Scheme 2). It has been reported that the energy levels of
the (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II) complex A and the bis(ꢁ-
oxo)dicopper(III) complex B are very close, and the equilibri-
um position between A and B is easily altered by the solvent,
the counter anion, and the steric and/or electronic effects of
the supporting ligands.27 Thus, for the present system with
L6R, the equilibrium position between A and B was affected
by the steric bulkiness of the ligand sidearm R (Bz vs Phe)
as demonstrated in Figs. 4 and 6. Overall, the reactivity of
6Phe toward O2 is close to that of 4R.
It should be noted that 6PhePh having the largest alkyl sub-
stituent (–CH2CHPh2) had virtually no reactivity toward O2
2.0
10
360
∞
5
1.0
0
0
10
Time / s
20
515
500
Wavelength / nm
0
400
600
700
800
˚
two copper ions from approaching closer (ꢇ2:8 A), which is
required for the formation of the bis(ꢁ-oxo)dicopper(III) com-
plex B, thus providing the peroxo complex A (typical Cu–Cu
Fig. 6. Spectral change observed upon introduction of O2
gas into an acetone solution of 6Phe (2:0 ꢃ 10ꢁ3 M) at
ꢁ94 ꢂC in a 1 mm path length UV cell. Inset: second-order
plot based on the absorption change at 360 nm.
˚
distance ꢇ3:6 A) as the major product. This, on the other hand,
would make the O–O bond stronger in the L6Phe complex as
compared to the L6Bz complex (ꢋO{O ¼ 731 cmꢁ1 of the L6Phe
O
O
6R
CuIIL6R
L6RCuII
L6RCuII
6R
+
O2
rate-limiting
O
O
A
C
fast equilibrium
O
L6RCuIII
CuIIIL6R
O
B
Scheme 2.

A. Kunishita et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006) 1739
OH
N
N
N
L6Phe-OH
Chart 3.
Fig. 7. ORTEP drawing of [(L6Phe-O)(L6Phe)CuII2(ꢁ-OH)]-
(ClO4)2 (8) showing 30% probability thermal ellipsoids.
The counter anions and the hydrogen atoms are omitted
for clarity.
2.0
1.0
0
0
360
∞
at low temperature. This is due to the strong d–ꢀ interaction
between the copper(I) ion and the phenyl group of –CH2-
–2
31
CHPh2 (see, Fig. 2) as in the case of 1PhePh
.
The Cu2/O2 complexes (A and B) supported by L6R (R ¼
Bz and Phe) gradually decomposed even at low temperature
to give different dicopper(II) products. In the case of L6Bz, a
bis(ꢁ-hydroxo)dicopper(II) complex, [L6Bz2CuII2(ꢁ-OH)2]-
–4
0
500
1000
Time / s
(ClO4)2 (CH3)2CO (7), was isolated as the decomposition
ꢄ
product in a 68% yield as shown in Fig. S3.32 Although mech-
anistic details for the formation of bis(ꢁ-hydroxo)dicopper(II)
complex have yet to be determined fully, this is a common
product of the decomposition reaction of Cu2/O2 species.4
The complex has a center of symmetry at the center of the
Cu2O2 core, and the copper(II) center has a distorted square
pyramidal structure (ꢌ ¼ 0:156)33 consisting of quinoline ni-
trogen N(2), tertiary amine nitrogen N(3), two oxygen atoms
400
500
600
700
800
Wavelength / nm
Fig. 8. Spectral change for the aliphatic ligand hydroxyla-
tion reaction in the L6Phe system in acetone at ꢁ94 ꢂC.
Inset: first-order plot based on the absorption change at
360 nm.
ꢀ
of the hydroxo bridges O(6) and O (6) at the equatorial posi-
tions and another quinoline nitrogen N(1) as the axial ligand.
The axial ligands coordinate to the copper ions in an anti-con-
formation. The X-ray crystallographic data and selected bond
lengths and angles are listed in Tables S5 and S6, respectively.
In the case of L6Phe, on the other hand, ligand hydroxylation
occurred at one of the benzylic positions of the phenethyl
group (Phe) to give a (ꢁ-alkoxo)(ꢁ-hydroxo)dicopper(II)
complex, [(L6Phe-O)(L6Phe)CuII2(ꢁ-OH)](ClO4)2 (8), in a 73%
yield. The crystal structure of the dicopper(II) product is
shown in Fig. 7, and the X-ray crystallographic data and the
selected bond lengths and angles are summarized in Tables 1
and 2, respectively. The Cu(1) center has a distorted square
pyramidal structure (ꢌ ¼ 0:123) consisting of two quinoline
nitrogen atoms N(1) and N(2), oxygen atom of the bridging
OH group O(5), and alkoxy oxygen O(6) of the modified li-
gand sidearm L6Phe-OH (Chart 3) in the equatorial plane and
tertiary amine nitrogen atom N(3) at the axial position. The
Cu(2) center also has a distorted square pyramidal geometry
(ꢌ ¼ 0:27) involving quinoline nitrogen atom N(5), tertiary
amine nitrogen atom N(6), oxygen atom of the bridging OH
group O(5), and alkoxy oxygen O(6) in the equatorial plane
and quinoline nitrogen N(4) occupying the axial position.
Benzylic hydroxylation was unambiguously confirmed by the
X-ray structure of 8. Aliphatic ligands have been shown to
undergo hydroxylation in Cu2/O2 systems.34–36
hydroxylation reaction. As shown in the inset of Fig. 8, the re-
action obeys first-order kinetics, suggesting that the ligand hy-
droxylation is a unimolecular (intramolecular) process at the
Cu2O2 core. From the slope of the first-order plot, the first-or-
der rate constant k was obtained. The temperature-dependence
of the first-order rate constant k (Eyring Plot) was also exam-
ined as shown in Fig. 9, from which the activation parameters
of the reaction were obtained as ꢁHz ¼ 20:3 ꢅ 0:6 kJ molꢁ1
and ꢁSz ¼ ꢁ175 ꢅ 3:0 J Kꢁ1 molꢁ1. The activation parame-
ters ꢁHz and ꢁSz of the present reaction are fairly close to
those of the reported for the aliphatic ligand hydroxylation
reaction of 1Phe by O2 (ꢁHz ¼ 28:1 ꢅ 1:0 kJ molꢁ1, ꢁSz ¼
ꢁ155 ꢅ 5 J Kꢁ1 molꢁ1),34 suggesting a similar reaction mecha-
nism. Namely, the active oxygen species in this reaction may
also be a bis(ꢁ-oxo)dicopper(III) B generated by the O–O bond
homolysis of (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II) A as in the case of
the 1Phe system,34 and aliphatic C–H bond hydroxylation may
involve hydrogen-atom abstraction followed by an oxygen
rebound mechanism or its concerted variant as previously
reported.35,36
Summary
We have been investigating the ligand effects on the struc-
ture and O2-reactivity of the copper(I) complexes using a
Figure 8 shows the spectral change for the aliphatic ligand

1740 Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006)
Copper(I) Complexes of Tridentate Ligands
the (ꢁ-ꢂ2:ꢂ2-peroxo)dicopper(II) complex of L6Phe (Fig. S4).
These materials are available free of charge on the Web at:
http://www.csj.jp/journals/bcsj/.
–9.5
–10.0
–10.5
–11
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This work was financially supported in part by Grants-in-
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Supporting Information
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Á
Á
Á
3
3
5Phe CO, 5Phe CO, and 7 and the resonance Raman spectra of
have already been reported elsewhere.14
Á
Á

A. Kunishita et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 11 (2006) 1741
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