Aerobic oxidative coupling of 2-naphthol derivatives catalyzed by a hexanuclear bis(μ-hydroxo)copper(II) catalyst

Article abstract of DOI:10.1021/om500403k

A novel hexanuclear bis(μ-hydroxo)copper(II) complex, [L₃(Cu₂(μ-OH)₂)₃](ClO₄)₆ (1), was synthesized with dinucleating ligand N,N,N,N-tetra(pyridin-2-ylmethyl)-m-xylene diamine (L). Complex 1 is fully characterized by X-ray crystallography and magnetic susceptibility in the solid state and UV-vis and electron paramagnetic resonance spectroscopy in solution. The molecular structure of 1 possesses three dicopper cores, in which two copper centers are bridged by two hydroxide groups and separated by a distance ranging from 2.8852(15) to 2.8937(10) ?. In addition, the three dicopper cores are linked by the dinucleating ligand between each pair of adjacent dicopper cores. Importantly, aerobic oxidative coupling of 2,4-di-tert-butylphenol, 2-naphthol, and six 2-naphthol derivatives was achieved in 33-96% yield using complex 1 as a catalyst.

Full text of DOI:10.1021/om500403k

Article
pubs.acs.org/Organometallics
Aerobic Oxidative Coupling of 2‑Naphthol Derivatives Catalyzed by a
Hexanuclear Bis(μ-hydroxo)copper(II) Catalyst
Yedukondalu Meesala,† Hsyueh-Liang Wu,† Bommisetti Koteswararao,§ Ting-Shen Kuo,‡
and Way-Zen Lee*,†
†Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan, R.O.C.
‡Instrumentation Center, Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan, R.O.C.
§Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan, R.O.C.
S
* Supporting Information
ABSTRACT: A novel hexanuclear bis(μ-hydroxo)copper(II) complex,
[L3(Cu2(μ-OH)2)3](ClO4)6 (1), was synthesized with dinucleating ligand
N,N,N,N-tetra(pyridin-2-ylmethyl)-m-xylene diamine (L). Complex 1 is fully
characterized by X-ray crystallography and magnetic susceptibility in the solid
state and UV−vis and electron paramagnetic resonance spectroscopy in
solution. The molecular structure of 1 possesses three dicopper cores, in
which two copper centers are bridged by two hydroxide groups and separated
by a distance ranging from 2.8852(15) to 2.8937(10) Å. In addition, the three
dicopper cores are linked by the dinucleating ligand between each pair of
adjacent dicopper cores. Importantly, aerobic oxidative coupling of 2,4-di-tert-
butylphenol, 2-naphthol, and six 2-naphthol derivatives was achieved in 33−
96% yield using complex 1 as a catalyst.
and co-workers designed a series of copper complexes of 1,5-
diaza-cis-decalin diamines (N2s) and used them to promote the
catalysis of the oxidative couplings of 3-substituted 2-naphthols
under aerobic conditions. As the crystalline 2:1 diamine:copper
complex [(N2)Cu]Cl2 was employed in oxidative catalysis, no
biaryl product was observed. The same reaction performed by
using in situ-generated 1:1 N2:copper complex [(N2)Cu-
(OH)]3Cl3, found to be trimeric, as a catalyst (10 mol %)
produced 1,1′-bi-2-naphthols (BINOLs) in 85% yield.13
Therefore, there is still a strong demand for catalytic oxidative
coupling of 2-naphthols to BINOLs under aerobic conditions
and in the absence of additives.
Herein, we report the synthesis and detailed characterization
of a novel hexanuclear bis(μ-hydroxo)copper(II) complex,
[L3(Cu2(μ-OH)2)3](ClO4)6 (1), supported by dinucleating
ligand N,N,N,N-tetra(pyridin-2-ylmethyl)-m-xylene diamine
(L), and its catalytic ability with respect to the aerobic biaryl
coupling of substituted phenols and 2-naphthols without any
additives.
INTRODUCTION
■
The activation of O2 by copper ions is an important process in
industrial manufacture and biological systems.1 The binding of
O2 and its structure−reactivity relationships of the dinuclear
copper enzymes, such as tyrosinase, catechol oxidase, and their
model complexes, have been extensively investigated.2 It is well-
known that the reaction of copper(I) complexes with O2 gives a
stable bis(μ-hydroxo)dicopper(II) product.3 The development
of bis(μ-hydroxo)dicopper(II) complexes and their use in a
catalytic oxidation by O2 are topics of intense interest, because
O2 is abundant and an ecologically benign oxidant. On the
other hand, the oxidative coupling of phenols to dimeric
products, which has found extensive applications in chemical
synthesis, catalyzed by copper complexes is a useful procedure.4
Recently, Tolman et al. reported [Cu3O2]3+ complexes that
could react with 2,4-di-tert-butylphenol to form coupled
product 3,3′,5,5′-tetra-tert-butyl-2,2′-biphenol in high yield
(>97%).5 Also, the similar oxidation of phenols reported by
Itoh et al. using a (μ-η2:η2-peroxo)dicopper(II) or bis(μ-
oxo)dicopper(III) complex gave isolated coupling products in
∼50% yield based on the [Cu2/O2]2+ complexes.6 In addition,
other transition metal complexes, such as FeIII,7 MnIII,8 TiIV,9
RuII,10 and VIV,11 have been used as oxidants to promote the
oxidative coupling of 2-naphthols; however, these methods
suffer from difficulty in isolating the coupling product and a
waste disposal problem. Meanwhile, an aerobic oxidative
coupling of 2-naphthols catalyzed by amine-coordinated
copper(II) complexes has been shown to be very effective
and provided several promising results.12 Recently, Kozlowski
RESULTS AND DISCUSSION
■
Synthesis and X-ray Structure. Hexanuclear bis(μ-
hydroxo)copper(II) complex [L3(Cu2(μ-OH)2)3](ClO4)6 (1)
was synthesized from the reaction of Cu(ClO4)2·6H2O with
dinucleating ligand L. Ligand L, one methylene shorter than m-
14
XYLpy2 on a pyridyl N donor, was prepared by utilizing a
Received: April 16, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
literature method.15 The reaction of secondary amine bis(2-
pyridylmethyl)amine with 1,3-dibromoxylene in tetrahydrofur-
an (THF) in the presence of triethylamine afforded L in nearly
quantitative yield (Scheme 1) and in a highly pure form, which
CH3CN solution of 3. Bubbling O2 into a wet CH3CN solution
of complex 3 would afford the entitled hexanuclear bis(μ-
hydroxo)copper(II) complex 1 (Figure 1), which was
Scheme 1. Synthesis of Dinucleating Ligand L
Figure 1. Comparison of UV−vis spectra of [L3(Cu2(μ-OH)2)3]-
(ClO4)6 (1) and reactions with 3-O2 and water.
confirmed by X-ray crystallography after recrystallization from
an Et2O/CH3CN mixed solvent. In addition, a bis(μ-hydroxo)-
dicopper(II) complex, [L′2Cu2(μ-OH)2](ClO4)2 (4) [L′ =
N,N-bis(2-pyridylmethyl)benzylamine], was prepared accord-
ing to a literature method for spectroscopic and reactivity
comparison with complex 1.16
The X-ray structural analysis reveals that complex 1 possesses
three dicopper cores, in which two copper centers are bridged
by two hydroxide groups, three linkers of the dinucleating L
ligand between adjacent dicopper cores (Figure 2a), and six
perchlorate anions. Each copper ion is coordinated by one
amine N and two pyridyl N donors of L and two bridging
hydroxide groups forming a five-coordinated distorted square
pyramidal geometry (τ = 0.39).17 For the coordination of the
tridentate N3 donor of L in 1 wrapping around the copper ion,
one pyridyl Npy1 is bound axially and the amine Nam and the
other pyridyl Npy2 are bound equatorially. The hydroxide-
bridged Cu···Cu distances range from 2.8852(15) to
2.8937(10) Å, and the two bridging hydroxide O atoms are
separated by 2.51−2.52 Å. For five-membered chelate rings, the
N−Cu−N angles [Nam−Cu−Npy1, 76.6(2)−78.9(2)°; Nam−
Cu−Npy2, 82.0(2)−83.4(2)°; and Npy1−Cu−Npy2, 102.4(2)−
104.12(19)°] are typical for this type of five-membered copper
chelate.18 The coordination of L in complexes 2 and 3 is similar
to that of 1. However, each copper ion is bound to two
molecules of CH3CN instead of two bridging hydroxide groups
in 2 (Figure 2c) and one molecule of CH3CN in complex 3
(Figure 2d). The distance between two copper ions in complex
2 (9.91 Å) is larger than that in complex 3 (7.88 Å). The
hydroxide-bridged Cu···Cu distances of 1 are similar to those of
the dinuclear copper(II) complexes previously reported by
Manzur et al.,16 which have OH−, RO−, F−, or Cl− as a bridging
ligand. The selected bond lengths and angles of 1−3 are listed
was confirmed by thin layer chromatography and nuclear
magnetic resonance (NMR) spectroscopy.15 To synthesize
hexanuclear bis(μ-hydroxo)copper(II) complex 1, a dicopper-
(II) complex, [L(Cu(CH3CN)2)2](ClO4)4 (2), was prepared
first by adding L to 2 equiv of Cu(ClO4)2·6H2O in CH3CN
under a N2 atmosphere. The reaction mixture was transformed
into a blue solution. The resulting solution was stirred for 1 h
followed by removal of the solvent under vacuum. The
resulting blue residue after washing with THF was redissolved
in a small amount of CH3CN, which allowed slow diffusion of
Et2O into the CH3CN solution to yield X-ray quality crystals of
2. Addition of 2 equiv of NaOH, predissolved in a CH3CN/
H2O mixed solvent, to complex 2 afforded a pale blue solution
of 1 (Scheme 2). After isolation and recrystallization by slow
diffusion of Et2O into the CH3CN solution of 1, sky blue
crystals suitable for X-ray analysis were obtained over a week.
Alternatively, hexanuclear bis(μ-hydroxo)copper(II) complex 1
could also be prepared from a copper(I) complex,
[L(CuCH3CN)2](ClO4)2 (3). Complex 3 was synthesized by
reacting 2 equiv of [Cu(CH3CN)4](ClO4) with 1 equiv of L in
a THF/CH3CN (2:1) mixed solvent at room temperature
under a N2 atmosphere. To determine the structure of cationic
−
[L(CuCH3CN)2]2+, counterion ClO4 of 3 was changed to
−
PF6 by adding an aqueous solution (5 mL) of NH4PF6 to a
Scheme 2. Synthesis of [L3(Cu2(μ-OH)2)3](ClO4)6 (1)
B
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 2. ORTEP representations of (a) [L3(Cu2(μ-OH)2)3](ClO4)6 (1), (b) the dicopper core of 1, (c) [L(Cu(CH3CN)2)2](ClO4)4 (2), and (d)
[L(CuCH3CN)2](PF6)2 (3) showing 50% probability thermal ellipsoids. Hydrogen atoms and counteranions have been omitted for the sake of
clarity.
in Table 1, and their crystal data and structural refinement
statistics are listed in Table 2.
for 4) being greater than the values of g⊥ (2.064 for 1 and 2.061
for 4) with hyperfine coupling constants A∥ (180 G for 1 and
176 G for 4). Unlike many reported complexes possessing a
bis(μ-hydroxo)dicopper(II) core,2d,19d,20 in which a strong
antiferromagnetic coupling between two copper(II) ions would
occur and result in an EPR silent signal in the frozen solution,
the EPR spectra of 1 and 4 in frozen CH3CN are typical axial
spectra for distorted square pyramidal complexes with a
UV−Vis and Electron Paramagnetic Resonance (EPR)
Spectroscopy of 1 and 4. The UV−vis spectra of bis(μ-
hydroxo)copper(II) complexes 1 and 4 were recorded in
CH3CN and displayed an intense absorption band (257 nm, ε
= 29850 M−1 cm−1 for 1; 258 nm, ε = 9690 M−1 cm−1 for 4)
and a weak d−d transition band (634 nm, ε = 670 M−1 cm−1
for 1; 654 nm, ε = 207 M−1 cm−1 for 4) (Figure 3). EPR
spectroscopy was employed to study the electronic behavior of
complexes 1 and 4 in solution. The EPR measurements for
both copper(II) complexes 1 and 4 were performed in frozen
CH3CN at 77 K (Figure 4). The spectra revealed typical axial
spectra19 with the observed values of g∥ (2.258 for 1 and 2.223
mononuclear copper(II) center having a dx −y ground state.21
This result suggests that the exchange coupling between two
copper ions in the bis(μ-hydroxo)dicopper(II) core of 1 and 4
is a weak antiferromagnetic interaction, which was clearly
shown in the magnetic studies.
2
2
C
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
result can also be found in the insets of panels a and b of Figure
5, which illustrates clearly that μeff is affected and falls below T
< θCW for the respective complexes 1 and 4. Because the Cu−
O−Cu bond angles in the bis(μ-hydroxo)dicopper core for
complexes 1 and 4 are in the range of 96−98, weak
antiferromagnetic couplings are expected according to Good-
enough−Kanamori rules.22 The presence of weak antiferro-
magnetic coupling in complexes 1 and 4 is also evidenced by
their EPR spectra (Figure 4).
Table 1. Selected Bond Lengths (angstroms) and Angles
(degrees) for Complexes 1−3
1
2
3
Cu1···Cu2
Cu3···Cu3′
Cu1−O1
Cu1−O2
Cu2−O1
Cu2−O2
Cu3−O3
Cu3−O3′
Cu1−N1
Cu1−N2
Cu1−N3
Cu1−N7
Cu1−N9
Cu2−N4
Cu2−N5
Cu2−N6
Cu2−N8
2.8937(10)
2.8852(15)
1.927(4)
1.960(4)
1.956(4)
1.902(4)
1.910(4)
1.934(5)
2.001(5)
2.052(5)
2.228(5)
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
Catalytic Activity of 1 and 4. Many model complexes for
copper enzymes, such as tyrosinase and catechol oxidase, have
shown the reactivity for coupling of phenols.23 More
interestingly, the reaction of (μ-η2:η2-peroxo)dicopper(II)
complexes with phenols afforded C−C coupling biphenols
rather than catechols, the oxygenation products.6,23,24 On the
basis of this idea, we are inspired to examine the reactivity of
bis(μ-hydroxo)copper(II) complexes 1 and 4. Initially, an
aerobic oxidative coupling of 2,4-di-tert-butylphenol was
performed as a reference to shed light on the role of the
catalytic activity of complexes 1 and 4 (Scheme 3). The
reaction proceeded smoothly and gave 3,3′,5,5′-tetra-tert-butyl-
2,2′-biphenol rather than 3,5-di-tert-butylcatechol in CH3CN at
30 °C for 48 h under 1 atm of O2 with 2 mol % loading of
catalyst in good yield (75% for 1 and 49% for 4). With this
success, aerobic oxidative couplings of 2-naphthol using
complexes 1, 2, and 4 and copper salts, such as CuSO4,
CuCl2, and Cu(ClO4)2, as catalysts under the same aerobic
condition were further studied. While all employed copper salts
and complex 2 showed very poor oxidation catalysis, only
complexes 1 and 4 exhibited good catalytic activity [84% yield
for 2 mol % 1 and 82% yield for 6 mol % 4 (Table 4, entries 7
and 10)]. The reaction also proceeded at 40 and 60 °C and was
found to produce no increase in yield. However, if DMF was
used as the reaction solvent, conversion of 2-naphthol to 1,1′-
bi-2-naphthol (BINOL) declined to a 63% yield, and an even
lower yield of 43% using MeOH as a solvent for complex 1
(Table 4, entries 8 and 9, respectively), and the yield was
reduced to 55% with DMF and 32% with MeOH in the case of
complex 4 (Table 4, entries 12 and 14, respectively).
1.978(5)
2.026(5)
1.971(5)
2.344(6)
1.975(6)
1.978(6)
2.036(5)
1.986(5)
2.002(6)
2.315(7)
−
2.048(5)
2.243(5)
2.050(6)
1.912(6)
−
−
2.249(5)
2.039(5)
1.985(5)
−
2.074(6)
2.238(5)
2.023(6)
1.876(7)
Cu2−N10
Cu3−N11
Cu3−N12
Cu3−N13
−
−
−
−
−
1.981(7)
2.056(5)
2.269(5)
83.4(2)
78.9(2)
104.12(19)
76.6(2)
82.0(2)
103.0(2)
82.1(3)
77.2(2)
102.4(2)
80.89(16)
81.61(16)
81.51(19)
96.35(17)
97.04(18)
97.30(19)
−
−
N1−Cu1−N2
N2−Cu1−N3
N1−Cu1−N3
N4−Cu2−N5
N5−Cu2−N6
N4−Cu2−N6
N11−Cu3−N12
N12−Cu3−N13
N11−Cu3−N13
O1−Cu1−O2
O1−Cu2−O2
O3−Cu3−O3′
Cu1−O1−Cu2
Cu1−O2−Cu2
Cu3−O3−Cu3′
83.29(19)
82.4(2)
165.6(2)
82.5(2)
82.77(19)
164.7(2)
−
−
−
−
−
81.20(19)
78.8(2)
118.3(2)
80.0(2)
80.4(2)
120.6(2)
−
−
−
−
−
−
−
−
−
−
−
−
−
Having obtained bis(μ-hydroxo)copper(II) complexes 1 and
4 as the catalysts for aerobic oxidative coupling of 2-naphthol in
good yields under mild conditions, we explored the coupling
reactions in mixed solvents under similar aerobic conditions
(Table 5). To our surprise, conversion of 2-naphthol to BINOL
using a CH3CN/MeOH (4:1) mixed solvent gave 26% yield,
which increased to 69−82% in various mixed solvents using 2
mol % loading of catalyst 1 (Table 5, entries 1−5). Similarly,
the yield was promoted using mixed solvents with 2 mol %
loading of catalyst 4 for the same reaction (Table 5, entries 11−
13). These results revealed that a mixed solvent, CH3CN/
CH2Cl2 (4:1), for an aerobic oxidative coupling of 2-naphthol
would increase the yield of the reaction more than a single
solvent alone. We have also performed the reaction using 1 mol
% catalyst 1 in a CH3CN/CH2Cl2 (4:1) mixed solvent, and the
yield was slightly reduced to 73% (Table 5, entry 6). As the
ratio of the mixed solvent (CH3CN/CH2Cl2) changed to 2:1,
the yield was increased to 85% (Table 5, entry 7) in the case of
catalyst 1 and increased from 74 to 81% with 2 mol % catalyst 4
(Table 5, entries 13 and 14, respectively). In light of this
observation, the reaction conditions for the formation of
BINOL were optimized by varying the CH3CN:CH2Cl2 ratio
with the usage of 1 mol % catalyst 1. The yield was increased to
88% when a 1:1 CH3CN:CH2Cl2 ratio was used. With a further
Magnetic Properties of Bis(μ-hydroxo)copper(II) Com-
plexes 1 and 4. Magnetic susceptibility χ for both bis(μ-
hydroxo)copper(II) complexes 1 and 4 has been obtained in
the solid state over the temperature range of 2−300 K. The
plots of χ versus T (left) and 1/χ versus T (right) for complexes
1 and 4 are shown in panels a and b of Figure 5, respectively.
The χ data follow Curie−Weiss behavior for both complexes.
No signature of long-range ordering (LRO) was seen down to
2 K. The experimental data were fit to Curie−Weiss law χ(T) =
χ0 + C/(T − θCW) over temperature ranges of 30−300 K for
complex 1 and 20−300 K for complex 4, where χ0 is the
temperature-independent susceptibility, the sum of diamagnetic
susceptibility (χdia) and Van-Vleck susceptibility (χvv), C is the
Curie constant, and θCW is the Curie−Weiss temperature. The
values resulting from the Curie−Weiss fit are listed in Table 3.
The value of C for complex 1 is inconsistent with the value of C
1
expected for S = /2 spin (1.73 μB) systems, whereas the value
of C of complex 4 is slightly larger than 1.73 μB, suggesting the
effect of weak spin−orbit coupling in complex 4. The negative
values of θCW for complexes 1 and 4 (−10 and −1 K,
respectively) suggest that the exchange interactions between
two copper(II) ions are weak antiferromagnetic coupling. This
D
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 2. Crystal Data and Structural Refinement Statistics for 1−3
1
2
3
molecular formula
formula weight
temperature (K)
wavelength (Å)
crystal system
space group
C96H102Cl6Cu6N18O31
2597.90
C40H44Cl4Cu2N10O16
1189.73
C36H38Cu2F12N8P2
999.76
200(2)
200(2)
200(2)
0.71073
0.71073
0.71073
monoclinic
C2/c
monoclinic
P21/c
triclinic
P1
̅
a (Å)
16.5608(5)
34.7656(8)
23.6980(6)
90
9.0132(3)
31.3362(9)
18.9321(5)
90
11.2980(16)
12.948(3)
17.812(4)
106.601(14)
98.692(14)
99.664(9)
2406.4(8)
2
b (Å)
c (Å)
α (deg)
β (deg)
90.063(2)
90
96.4750(10)
90
γ (deg)
volume (Å3)
13644.0(6)
4
5313.1(3)
4
Z
density (calcd) (Mg/m3)
absorption coefficient (mm−1
F(000)
1.265
1.487
1.380
)
1.105
1.075
1.030
5312
2432
1012
crystal size (mm3)
θ range (deg)
no. of reflections collected
0.52 × 0.36 × 0.30
1.17−25.06
47823
0.52 × 0.39 × 0.22
2.26−25.00
30061
0.46 × 0.38 × 0.07
1.74−25.19
19981
no. of independent reflections
completeness to θ (%)
11739 (Rint = 0.0471)
97.1
9322 (Rint = 0.0530)
99.6
8483 (Rint = 0.0994)
98.0
absorption correction
multiscan
0.7329 and 0.5974
11739/0/668
1.073
multiscan
0.7979 and 0.6049
9322/0/587
1.037
multiscan
maximal/minimal transmission
data/restraints/parameters
0.9314 and 0.6487
8483/0/506
0.905
goodness of fit on F2
final R1 and wR2 indices [I > 2σ(I)]
R1 and wR2 indices (all data)
largest difference peak and hole (e Å−3
0.0780, 0.2351
0.1099, 0.2538
1.186 and −0.858
0.0771, 0.2078
0.1077, 0.2217
0.712 and −0.741
0.0849, 0.2050
0.1509, 0.2352
1.134 and −0.697
)
Figure 4. X-Band EPR spectra of (a) [L3(Cu2(μ-OH)2)3](ClO4)6 (1)
and (b) [L′2Cu2(μ-OH)2](ClO4)2 (4) in CH3CN.
Figure 3. UV−vis spectra of (a) [L3(Cu2(μ-OH)2)3](ClO4)6 (1) and
(b) [L′2Cu2(μ-OH)2](ClO4)2 (4) in CH3CN. The inset shows the
intensity of the d−d band.
increase in the quantity of CH2Cl2 (1:2 CH3CN:CH2Cl2 ratio),
the yield decreased to 82% and further decreased to 74% when
E
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. Synthesis of 3,3′,5,5′-Tetrabutyl-1,1′-bi-2,2′-
phenol
Table 4. Conversion of 2-Naphthol to BINOL Derivatives
Using Various CuII Compounds
a
entry
Cu complex
solvent
yield (%)
b
1
Cu(ClO4)2
CH3CN
DMF
5.4
b
2
Cu(ClO4)2
3.3
b
3
Cu(ClO4)2
MeOH
CH3CN
DMF
trace
trace
trace
c
4
2
c
5
2
c
6
2
MeOH
CH3CN
DMF
trace
d
e
7
1
1
1
4
4
4
4
4
84 (75)
c
8
63
c
9
MeOH
CH3CN
CH2Cl2
DMF
43
Figure 5. Magnetic susceptibility of (a) [L3(Cu2(μ-OH)2)3](ClO4)6
(1) and (b) [L′2Cu2(μ-OH)2](ClO4)2 (4) (left) and inverse magnetic
susceptibility (right) vs temperature in the solid state. The inset shows
the plot of μeff vs T.
f
g
h
h
10
11
12
13
14
82 (81), (73), (60)
e
71
e
55
e
(CH3)2CO
MeOH
53
e
32
a
b
Yield of the product isolated via column chromatography. Reaction
c
performed in 12 mol % 1. Reaction performed in 2 mol % 1.
a 1:4 CH3CN:CH2Cl2 ratio was used (Table 5, entries 8−10).
A similar phenomenon was observed in the case of catalyst 4
(Table 5, entries 15−17).
d
e
Reaction performed in 1 mol % 1. Reaction performed in 6 mol % 4.
f
g
Reaction performed in 4 mol % 4. Reaction performed in 2 mol % 4.
h
Reaction performed in 1 mol % 4.
Under the optimized conditions described above, oxidative
couplings of several 2-naphthol derivatives were examined.
Moderate yields were obtained in the reactions of 6-cyano- and
3-iodo-2-naphthols (Table 6, entries 3 and 6, respectively).
Much to our delight, the reaction yield was 90% with 7-
methoxy-2-naphthol was applied, 94% with 6-bromo-2-
naphthol, and 96% with 6-phenyl-2-naphthol using 1 mol %
catalyst 1 (Table 6, entries 7, 2, and 4, respectively).
EXPERIMENTAL SECTION
■
General Information. All manipulations were performed under
nitrogen using standard Schlenk and glovebox techniques. Methanol
was dried in magnesium/iodine prior to use. Acetonitrile was distilled
once from P2O5 and freshly distilled from CaH2 before being used.
Diethyl ether and THF were dried in a sodium benzophenone still
prior to being used. α,α′-Dibromo-m-xylene, dipicolyl amine, 2,4-di-
tert-butylphenol, 2-naphthol, 6-bromo-2-naphthol, 7-methoxy-2-naph-
thol, and 6-cyano-2-naphthol are commercially available and were used
as received. UV−vis spectra were recorded on an absorption
spectrophotometer. Infrared (IR) spectra were recorded using KBr
pellets or the solution cell method. NMR spectra were recorded on a
400 MHz NMR spectrometer. EPR measurements were performed at
the X-band using a spectrometer equipped with a superhigh-sensitivity
cavity. CuII complexes 1 and 4 were dissolved in CH3CN in a 2 mm
EPR tube. The sample solutions were frozen with liquid nitrogen, and
the X-band EPR spectra of 1 and 4 were recorded at 77 K with a
microwave power of 15.000 mW (frequency of 9.6608 GHz,
conversion time of ∼2.048 ms). The magnetic susceptibility data
CONCLUSIONS
■
Hexanuclear bis(μ-hydroxo)copper(II) complex 1 supported
by a dinucleating ligand, N,N,N,N-tetra(pyridin-2-ylmethyl)-m-
xylene diamine (L), has been successfully synthesized and was
spectroscopically and structurally characterized. Notably,
complex 1 can serve as a catalyst for the aerobic oxidative
coupling of 2-naphthols to form BINOLs. The reaction
proceeded smoothly via oxidative coupling rather than
oxygenation under an O2 atmosphere.
Table 3. Magnetic Susceptibility Data for Complexes 1 and 4
complex
T (K)
χ0 (cm3/mol of Cu)
C [cm3 K−1 (mol of Cu)−1
]
μeff (μB)
θCW (K)
1
4
30−300
20−300
−(3 0.1) × 10−4
0.40
0.54
1.78
2.08
−10 (AF)
−0.7 (AF)
−(5.5 0.1) × 10−4
F
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
SIR92 or SIR97 and refined using SHELXL-97. An empirical
absorption correction by multiple scans was applied to both structures.
All non-hydrogen atoms were refined with anisotropic displacement
factors. Hydrogen atoms were placed in ideal positions and fixed with
relative isotropic displacement parameters. Detailed crystallographic
data of all complexes are provided as a CIF file.
Table 5. Optimization of the Reaction Conditions for the
Conversion of 2-Naphthol to BINOL
Synthesis of N,N,N,N-Tetra(pyridin-2-ylmethyl)-m-xylene
Diamine L. Bis(pyridin-2-ylmethyl)amine (0.9 g, 6.0 mmol) and
triethylamine (0.83 mL, 6.0 mmol) were dissolved in 10 mL of THF in
a 50 mL round-bottom flask and stirred for 10 min. A solution of α,α′-
dibromo-m-xylene (0.8 g, 3.0 mmol) in 20 mL of THF was gradually
added to the solution described above. The resulting mixture was
refluxed at 80 °C for 72 h. The precipitate of NEt3·HBr was filtered off,
and the filtrate was rotary evaporated and pumped under vacuum to
remove traces of solvent and Et3N. The resulting solution was
extracted with CH2Cl2 and washed with a brine solution. The CH2Cl2
solution was collected and dried over MgSO4. Pure golden brown oil
catalyst loading
a
entry catalyst
(mol %)
solvent
ratio yield (%)
b
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
2
2
2
2
2
1
1
1
1
1
2
2
2
2
2
2
2
CH3CN/MeOH
CH3CN/DMF
4:1
4:1
4:1
4:1
4:1
4:1
2:1
1:1
1:2
1:4
4:1
4:1
4:1
2:1
1:1
1:2
1:4
26 (51)
69
2
3
CH3CN/H2O
70
4
CH3CN/acetone
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/DMF
79
5
82
6
73
1
of L was obtained by column chromatography: yellow oil; 88%; H
7
85
NMR (400 MHz, CDCl3, 25 °C) δ 8.49−8.47 (m, 4H), 7.71−7.67 (m,
4H), 7.58−7.52 (m, 5H), 7.25 (s, 3H), 7.22−7.18 (m, 4H), 3.76 (s,
8H), 3.66 (s, 4H); 13C NMR (100 MHz, CDCl3, 25 °C) δ 159.5,
148.6, 138.7, 136.0, 128.9, 127.9, 127.3, 122.4, 121.6, 59.7, 58.2.
Synthesis of Hexanuclear Copper(II) Complex 1, [L3Cu6(μ-
OH)6](ClO4)6. A degassed solution of polydentate ligand L, N,N,N,N-
tetra(pyridin-2-ylmethyl)-m-xylene diamine (0.115 g, 0.25 mmol), was
dissolved in 5 mL of CH3CN and then transferred to a CH3CN
solution of Cu(ClO4)2·6H2O (0.185 g, 0.5 mmol) in a round-bottom
flask under an inert atmosphere. The reaction mixture was stirred for 1
h at room temperature, and NaOH (0.02 g, 0.5 mmol) dissolved in a
CH3CN/H2O mixed solvent was added to the reaction flask. The
reaction mixture was stirred for an additional 2 h followed by removal
of the solvent under vacuum. THF was added to the reaction mixture,
resulting in a pale blue residue, which was redissolved in a small
amount of CH3CN and filtered through Celite to yield a clear pale
blue solution. The filtrate was concentrated and transferred to a vial for
crystallization by slow diffusion of diethyl ether into the concentrated
CH3CN solution of 1 at −20 °C over a week. Pale blue crystals were
formed and isolated in 56% yield: IR (neat) 3433 (br, OH), 1617,
1439, 1375, 1287, 1094 cm−1 (vs, ClO4−). Anal. Calcd for
C96H112Cu6N18O35Cl6: C, 43.15; H, 4.22; N, 9.44. Found: C, 42.81;
H, 4.33; N, 9.40.
8
88
9
82
10
11
12
13
14
15
16
17
74
60
CH3CN/acetone
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
CH3CN/CH2Cl2
71
74
81
86
83
75
a
b
Yield of the product isolated via column chromatography. Reaction
performed under reflux conditions.
Table 6. Aerobic Oxidative Coupling of Various 2-Naphthols
a
yield (%)
Synthesis of Dicopper(II) Complex 2, [L(Cu(CH3CN)2)2]-
(ClO4)4. A degassed solution of polydentate ligand L, N,N,N,N-
tetra(pyridin-2-ylmethyl)-m-xylene diamine (0.115 g, 0.25 mmol), was
dissolved in 5 mL of CH3CN and then transferred to a CH3CN
solution of Cu(ClO4)2·6H2O (0.185 g, 0.5 mmol) in a round-bottom
flask under an inert atmosphere. The reaction mixture was stirred for 2
h followed by removal of the solvent under vacuum. The resulting blue
residue after being washed with THF was redissolved in a small
amount of CH3CN and filtered through Celite to yield a clear blue
solution. The filtrate was concentrated and transferred to a vial for
crystallization by the slow diffusion of diethyl ether into the
concentrated CH3CN solution of the product at −20 °C for a week.
Blue crystals were formed and isolated in 73% yield: FAB-HRMS
found 922.9722, calcd for [C32H32Cl3Cu2N6O12]+ 922.9736; IR (neat)
b
c
entry
R1
R2
R3
1
4
1
2
3
4
5
6
7
H
H
H
H
H
H
88
94
74
96
33
79
90
87
74
62
84
8
Br
H
CN
phenyl
H
H
H
COOMe
H
I
H
H
60
73
H
H
OMe
a
b
Yield of the product isolated via column chromatography. Reaction
performed in 1 mol % complex 1. Reaction performed in 2 mol %
c
complex 4.
−
3582 (sharp), 3427, 1616, 1478, 1443, 1287, 1094 cm−1 (vs, ClO4 ).
Bulk samples, even crystals, were sent for elementary analysis several
times, but no good data were obtained. We suspect that the bound
CH3CN molecules are readily dissociated from the copper centers.
The TGA data of 2 confirm this idea. The bound CH3CN molecules
start to dissociate from the copper centers at 40 °C (see Figure S1 of
the Supporting Information). Therefore, the sample for elementary
analysis lost the bound CH3CN molecules before it entered the
combustion chamber, and no good elementary analysis data for 2 were
obtained.
Synthesis of Dicopper(I) Complex 3, [L(CuCH3CN)2](ClO4)2. A
degassed solution of polydentate ligand L, N,N,N,N-tetra(pyridin-2-
ylmethyl)-m-xylene diamine (0.25 g, 0.5 mmol), was dissolved in 5 mL
of dry CH3CN and then transferred to a THF solution of
Cu(CH3CN)4(ClO4) (0.327 g, 1 mmol) in a round-bottom flask
were obtained on powder samples of 1 and 4 using SQUID-VSM in
the temperature range from 2 to 300 K, under a magnetic field (H) of
10 kOe. Electrospray ionization mass spectrometry spectra were
recorded using a LCQ Advantage spectrometer. Elemental analyses for
C, H, and N were recorded at the MST Regional Instrumental Center
at National Taiwan University.
Determination of X-ray Structure. Crystals of a suitable size for
the CCD X-ray diffractometer were selected under a microscope and
mounted on the tip of a glass fiber fashioned on a copper pin. X-ray
data for complexes 1−3 were collected on a CCD diffractometer
employing graphite-monochromated Mo Kα radiation (λ = 0.7107 Å)
at 200 K in θ−2θ scan mode. The space groups for complexes were
determined on the basis of systematic absences and intensity statistics,
and the structures of 1−3 were determined by direct methods using
G
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
under an inert atmosphere. The reaction mixture was stirred for 2 h
followed by removal of the solvent under vacuum. The resulting
yellow residue after being washed with diethyl ether was redissolved in
MeOH, and to the mixture was further added an aqueous solution (5
mL) of NH4PF6 (0.327 g, 2.01 mmol) to afford a yellow-green
powder. The resulting suspension was dissolved by addition of
CH3CN (∼3 mL) to give a yellow-green solution, to which diethyl
ether was diffused at −20 °C to give yellow-green crystals. The crystals
were collected by filtration and dried in vacuo: yield 0.513 g (97%); 1H
NMR (400 MHz, CDCl3, 25 °C) δ 8.55−8.54 (m, 4H), 7.83−7.79 (m,
4H), 7.46 (s, 1H), 7.41−7.32 (m, 10H), 7.25−7.23 (m, 1H), 3.86 (s,
4H), 3.84 (s, 8H); 13C NMR (100 MHz, CDCl3, 25 °C) δ 156.8,
149.0, 138.1, 135.5, 132.9, 130.6, 128.2, 124.1, 124.0, 60.1, 58.8. Anal.
Calcd for C36H38Cl2Cu2N8O8·2H2O: C, 45.77; H, 4.48; N, 11.86.
Found: C, 45.85; H, 3.85; N, 12.09.
General Procedure for Aerobic Oxidative Coupling of 2-
Naphthols. The typical procedure of oxidative coupling of 2-napthols
with bis(μ-hydroxo)copper(II) complex 1 or 4 is described here. To a
solution (4 mL) of 2-naphthol or its derivatives (1 mmol) was added
bis(μ-hydroxo)copper(II) complex 1 or 4 (1 mol % for 1 and 2 mol %
for 4) at room temperature. After being stirred for 48 h, the reaction
mixture was washed with water and a brine solution. The residue was
purified by column chromatography on silica gel (4:1 hexane/ethyl
acetate) to give the biaryl product. Characterizations of the C−C
coupling biaryl products are listed in the Supporting Information.
Rev. 1994, 94, 737. (e) Kitajima, N. Adv. Inorg. Chem. 1992, 39, 1.
(f) King, A. E.; Huffman, L. M.; Casitas, A.; Costas, M.; Ribas, X.;
Stahl, S. S. J. Am. Chem. Soc. 2010, 132, 12068. (g) Crawford, W. H.;
Richardson, H. W.; Wasson, J. R.; Hodgson, D. J.; Hatfield, W. E.
Inorg. Chem. 1976, 15, 2107. (h) Ruiz, E.; Alemany, P.; Alvarez, S.;
Cano, J. Inorg. Chem. 1997, 36, 3683. (i) Osako, T.; Ueno, Y.; Tachi,
Y.; Itoh, S. Inorg. Chem. 2003, 42, 8087. (j) Itoh, S.; Fukuzumi, S. Bull.
Chem. Soc. Jpn. 2002, 75, 2081. (k) Suzuki, M.; Furutachi, H.; Otawa,
H. Coord. Chem. Rev. 2000, 200−202, 105. (l) Rojas, D.; Garcia, A. M.;
Vega, A.; Moreno, Y.; Venegas-Yazigi, D.; Garland, M. T.; Manzur, J.
Inorg. Chem. 2004, 43, 6324. (m) Kaim, W.; Titze, C.; Schurr, T.;
Sieger, M.; Lawson, M.; Jordanov, J.; Rojas, D.; Garcia, A. M.; Manzur,
J. Z. Anorg. Allg. Chem. 2005, 631, 2568. (n) Schindler, S. Eur. J. Inorg.
Chem. 2000, 2311. (o) Schatz, M.; Raab, V.; Foxon, S. P.; Brehm, G.;
Schneider, S.; Reiher, M.; Holthausen, M. C.; Sundermeyer, J.;
Schindler, S. Angew. Chem. 2004, 116, 4460; Angew. Chem., Int. Ed.
2004, 43, 4360.
(4) (a) Bringmann, G.; Walter, R. Angew. Chem., Int. Ed. 1990, 29,
977. (b) Hay, A. S. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 505.
(c) Higashimura, H.; Kubota, M.; Shiga, A.; Fujisawa, K.; Moro-oka,
Y.; Uyama, H.; Kobayashi, S. Macromolecules 2000, 33, 1986.
(5) Gupta, A. K.; Tolman, W. B. Inorg. Chem. 2012, 51, 1881.
(6) (a) Osako, T.; Ohkubo, K.; Taki, M.; Tachi, Y.; Fukuzumi, S.;
Itoh, S. J. Am. Chem. Soc. 2003, 125, 11027. (b) Itoh, S.; Fukuzumi, S.
Acc. Chem. Res. 2007, 40, 592. (c) Tachi, Y.; Aita, K.; Teramae, S.;
Tani, F.; Naruta, Y.; Fukuzumi, S.; Itoh, S. Inorg. Chem. 2004, 43,
4558.
(7) Selected reports on iron-catalyzed reactions: (a) Matsumoto, K.;
Egami, H.; Oguma, T.; Katsuki, T. Chem. Commun. 2012, 48, 5823.
(b) Egami, H.; Katsuki, T. J. Am. Chem. Soc. 2009, 131, 6082.
(c) Egami, H.; Matsumoto, K.; Oguma, T.; Kunisu, T.; Katsuki, T. J.
Am. Chem. Soc. 2010, 132, 13633. (d) Kunisu, T.; Oguma, T.; Katsuki,
T. J. Am. Chem. Soc. 2011, 133, 12937. (e) Pummerer, R.; Prell, E.;
Rieche, A. Ber. 1926, 59, 2159. (f) Toda, F.; Tanaka, K.; Iwata, S. J.
Org. Chem. 1989, 54, 3007. (g) Feringa, B.; Wynberg, H. J. Org. Chem.
1981, 46, 2547. (h) Deussen, H.-J.; Fredericksen, P.; Bjornholm, T.;
Bechgaard, K. Org. Prep. Proced. Int. 1996, 28, 484. (i) Tong-Shuang,
L.; Hui-Yun, D.; Bao-Zhi, L.; Brij, B. T.; Sheng-Hui, L. J. Chem. Soc.,
Perkin Trans. 1 1999, 291. (j) Armengol, E.; Corma, A.; Garcia, H.;
Primo, J. Eur. J. Org. Chem. 1999, 1915. (k) Bhor, M. D.; Nandurkar,
N. S.; Bhanushali, M. J.; Bhanage, B. M. Catal. Lett. 2006, 112, 45.
ASSOCIATED CONTENT
* Supporting Information
Additional data and spectra and a CIF file. This material is
■
S
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: wzlee@ntnu.edu.tw. Fax: (+886) 2-29324249. Tele-
phone: (+886) 2-77346133.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Ministry of Science
and Technology of Taiwan (102-2113-M-003-007-MY3 to W.-
Z.L.) and National Taiwan Normal University (101T3030B3 to
W.-Z.L.).
(l) Wang, K.; Lu, M.; Zhu, A. Y. X.; Wang, Q. J. Org. Chem. 2009, 74,
̈
935.
(8) (a) Yamamoto, K.; Fukushima, H.; Okarnoto, Y.; Hatada, K.;
Nakazaki, M. J. Chem. Soc., Chem. Commun. 1984, 1111. (b) Dewar, M.
J. S.; Nakaya, T. J. Am. Chem. Soc. 1968, 90, 7134.
(9) Doussot, J.; Guy, A.; Ferroud, C. Tetrahedron Lett. 2000, 41,
2545.
(10) (a) Irie, R.; Masutani, K.; Katsuki, T. Synlett 2000, 1433.
(b) Matsushita, M.; Kamata, K.; Yamaguchi, K.; Mizuno, N. J. Am.
Chem. Soc. 2005, 127, 6632. (c) Hamada, T.; Ishida, H.; Usui, S.;
Watanabe, Y.; Tsumura, K.; Ohkubo, K. J. Chem. Soc., Chem. Commun.
1993, 909.
REFERENCES
■
(1) Selected reviews: (a) Barton, D. H. R.; Martell, A. E.; Sawyer, D.
T. The Activation of Dioxygen and Homogeneous Catalytic Oxidation;
Plenum Press: New York, 1993; Vol. 497. (b) Sheldon, R. A.; Kochi, J.
K. Metal Catalyzed Oxidations of Organic Compounds; Academic Press:
́
New York, 1981; p 350. (c) Karlin, K. D., Tyeklar, Z., Eds. Bioinorganic
Chemistry of Copper; Chapman & Hall: New York, 1993. (d) Solomon,
E. I.; Sundaram, U. M.; Machonkin, T. E. Chem. Rev. 1996, 96, 2563.
(e) Blackman, A. G.; Tolman, W. B. Struct. Bonding (Berlin, Ger.) 2000,
97, 179.
(11) Selected reports on vanadium-catalyzed reactions: (a) Chu, C.-
Y.; Hwang, D.-R.; Wang, S.-K.; Uang, B.-J. Chem. Commun. 2001, 980.
(b) Barhate, N. B.; Chen, C.-T. Org. Lett. 2002, 4, 2529. (c) Tada, M.;
Taniike, T.; Kantam, L. M.; Iwasawa, Y. Chem. Commun. 2004, 2542.
(d) Guo, Q.-X.; Wu, Z.-J.; Luo, Z.-B.; Liu, Q.-Z.; Ye, J.-L.; Luo, S.-W.;
Cun, L.-F.; Gong, L.-Z. J. Am. Chem. Soc. 2007, 129, 13927.
(e) Takizawa, S.; Katayama, T.; Somei, H.; Asano, Y.; Yoshida, T.;
Kameyama, C.; Rajesh, D.; Onitsuka, K.; Suzuki, T.; Mikami, M.;
Yamataka, H.; Jayaprakash, D.; Sasai, H. Tetrahedron 2008, 64, 3361.
(2) (a) Itoh, S. In Comprehensive Coordination Chemistry II; Que, L.,
Jr., Tolman, W. B., Eds.; Elsevier: Amsterdam, 2004; Vol. 8, p 369.
(b) Halcrow, M. A.; Knowles, P. F.; Phillips, S. E. V. In Handbook on
Metalloproteins; Bertini, I., Sigel, A., Sigel, H., Eds.; Marcel Dekker Inc.:
New York, 2001; p 709. (c) Karlin, K. D.; Hayes, C. J.; Gultneh, Y.;
Gruse, R. W.; Mckown, J. W.; Hutchinson, J. P.; Zubieta, J. J. Am.
Chem. Soc. 1984, 106, 2121. (d) Kitajima, N.; Fujisawa, K.; Fujimoto,
C.; Moro-oka, Y.; Hashimoto, S.; Kitagawa, T.; Toriumi, K.; Tatsumi,
K.; Nakamura, A. J. Am. Chem. Soc. 1992, 114, 1277.
(3) (a) Wang, Y. D.; DuBois, J. L.; Hedman, B.; Hodgson, K. O.;
Stack, T. D. P. Science 1998, 279, 537. (b) Gamez, P.; Aubel, P. G.;
Driessen, W. L.; Reedijk, J. Chem. Soc. Rev. 2001, 30, 376. (c) Klinman,
J. P. Chem. Rev. 1996, 96, 2541. (d) Kitajima, N.; Moro-oka, Y. Chem.
̌
̌ ́ ́ ̌ ̌
́
(12) (a) Smrcina, M.; Polakova, J.; Vyskocil, S.; Kocovsky, P. J. Org.
Chem. 1993, 58, 4534. (b) Nakajima, M.; Miyoshi, I.; Kanayama, K.;
Hashimoto, S.; Noji, M.; Koga, K. J. Org. Chem. 1999, 64, 2264.
(c) Temma, T.; Hatano, B.; Habaue, S. Tetrahedron 2006, 62, 8559.
(d) Gu, C.; Xiong, K.; Shentu, B.; Zhang, W.; Weng, Z. Macromolecules
2010, 43, 1695. (e) Noji, M.; Nakajima, M.; Koga, K. Tetrahedron Lett.
́ ́
1999, 35, 7983. (f) Hovorka, M.; Gunterova, J.; Zavada, J. Tetrahedron
̈
H
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Lett. 1990, 31, 413. (g) Habaue, S.; Seko, T.; Okamoto, Y.
Macromolecules 2002, 35, 2437. (h) Sakamoto, T.; Yonehara, H.;
Pac, Ch. J. Org. Chem. 1997, 62, 3194. (i) Holtz-Mulholland, M.; de
Leseleuc, M.; Collins, S. K. Chem. Commun. 2013, 49, 1835.
́ ́
(j) Koscova, S.; Roithova, J.; Hodacova, J. J. Phys. Org. Chem. 2013,
26, 715. (k) Roithova, J.; Milko, P. J. Am. Chem. Soc. 2010, 132, 281.
(l) Roithova, J.; Schroder, D. Chem.Eur. J. 2008, 14, 2180.
̈
(m) Kumar, A. S.; Poonguzhali, E.; Ganapathy, D.; Sekar, G. Adv.
Synth. Catal. 2013, 355, 2803.
(13) (a) Li, X.; Yang, J.; Kozlowski, M. C. Org. Lett. 2001, 3, 1137.
(b) Kozlowski, M. C.; Li, X.; Carroll, P. J.; Xu, Z. Organometallics
2002, 21, 4513. (c) Hewgley, J. B.; Stahl, S. S.; Kozlowski, M. C. J. Am.
Chem. Soc. 2008, 130, 12232. (d) Li, X.; Hewgley, J. B.; Mulrooney, C.
A.; Yang, J.; Kozlowski, M. C. J. Org. Chem. 2003, 68, 5500. (e) Allen,
S. C.; Walvoord, R. R.; Padilla-Salinas, R.; Kozlowski, M. C. Chem. Rev.
2013, 113, 6234.
(14) (a) Karlin, K. D.; Gultneh, Y.; Hutchinson, J. P.; Zubieta, J. J.
Am. Chem. Soc. 1982, 104, 5240. (b) Karlin, K. D.; Hayes, J. C.;
Gultneh, Y.; Cruse, W.; Mckown, J. W.; Hutchinson, J. P.; Zubieta, J. J.
Am. Chem. Soc. 1984, 106, 2121.
(15) Gultneh, Y.; Ahvazi, B.; Khan, A. R.; Butcher, R. J.; Tuchagues, J.
P. Inorg. Chem. 1995, 34, 3633.
(16) Manzur, J.; Vega, A.; García, A. M.; Acuna, C.; Sieger, M.;
̃
Sarkar, B.; Niemeyer, M.; Lissner, F.; Schleid, T.; Kaim, W. Eur. J.
Inorg. Chem. 2007, 5500.
(17) Addison, A. W.; Rao, T. N.; Reedijk, J.; Rijn, J.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349.
(18) (a) Drew, M. G. B.; Nelson, J.; Esho, F.; McKee, V.; Nelson, S.
M. J. Chem. Soc., Dalton Trans. 1982, 1837. (b) Karlin, K. D.; Gultneh,
Y.; Hayes, J. C.; Zubieta, J. Inorg. Chem. 1984, 23, 519. (c) Kitajima,
N.; Koda, T.; Hashimoto, S.; Kitagawa, T.; Moro-oka, Y. J. Am. Chem.
Soc. 1991, 113, 5664.
(19) (a) Sanyal, I.; Mahroof-Tahir, M.; Nasir, M. S.; Ghosh, P.;
Cohen, B. I.; Gultneh, Y.; Cruse, R. W.; Farooq, A.; Karlin, K. D.; Liu,
S.; Zubieta, J. Inorg. Chem. 1992, 31, 4322. (b) Calderazzo, F.;
Marchetti, F.; Dell’Amico, G.; Pelizzi, G.; Colligiani, A. J. Chem. Soc.,
Dalton Trans. 1980, 1419. (c) Shearer, J.; Zhang, C. X.; Zakharov, L.
M.; Rheingold, A. L.; Karlin, K. D. J. Am. Chem. Soc. 2005, 127, 5469.
(d) Karlin, K. D.; Gan, Q.-F.; Farooq, A.; Liu, S.; Zubieta, J. Inorg.
Chem. 1990, 29, 2549. (e) Karlin, K. D.; Kaderli, S.; Zuberbuhler, A. D.
̈
Acc. Chem. Res. 1997, 30, 139. (f) Quant Hatcher, L.; Karlin, K. D.
JBIC, J. Biol. Inorg. Chem. 2004, 9, 669. (g) Tabuchi, K.; Sugimoto, H.;
Kunishita, A.; Fujieda, N.; Itoh, S. Inorg. Chem. 2010, 49, 6820.
(h) Das, D.; Lee, Y. M.; Ohkubo, K.; Nam, W.; Karlin, K. D.;
Fukuzumi, S. J. Am. Chem. Soc. 2013, 135, 4018.
(20) (a) Monzani, E.; Battaini, G.; Perotti, A.; Casella, L.; Gullotti,
M.; Santagostini, L.; Nardin, G.; Randaccio, L.; Geremia, S.; Zanello,
P.; Opromolla, G. Inorg. Chem. 1999, 38, 5359. (b) Mahapatra, S.;
Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.; Young, V. G., Jr.;
Cramer, C. J.; Que, L., Jr.; Tolman, W. B. J. Am. Chem. Soc. 1996, 118,
11555.
(21) (a) Lee, H. W.; Sengottuvelan, N.; Seo, H.-J.; Choi, J. S.; Kang,
S. K.; Kim, Y.-I. Bull. Korean Chem. Soc. 2008, 29, 1711. (b) Aggarwal,
R. C.; Singh, N. K.; Singh, R. P. Inorg. Chem. 1981, 20, 2794.
(c) Goodman, B. A.; Rayner, B. Adv. Inorg. Chem. Radiochem. 1970, 13,
135.
(22) (a) Goodenough, J. B. Magnetism and the Chemical Bond,
Interscience Monographs on Chemistry; Inorganic Chemistry Section;
Cotton, F. A., Ed.; Interscience-Wiley: New York, 1963; Vol. I.
(b) Kanamori, J. J. Phys. Chem. Solids 1959, 10, 87.
(23) Lewis, E. A.; Tolman, W. B. Chem. Rev. 2004, 104, 1047.
(24) Obias, H. V.; Lin, Y.; Murthy, N. N.; Pidcock, E.; Solomon, E. I.;
Ralle, M.; Blackburn, N. J.; Neuhold, Y.-M.; Zuberbuhler, A. D.; Karlin,
̈
K. D. J. Am. Chem. Soc. 1998, 120, 12960.
I
dx.doi.org/10.1021/om500403k | Organometallics XXXX, XXX, XXX−XXX