Trinuclear nickel and cobalt complexes containing unsymmetrical tripodal tetradentate ligands: Syntheses, structural, magnetic, and catalytic properties

Article abstract of DOI:10.1039/c6dt02701f

The coordination chemistries of the tetradentate N₂O₂-type ligands N-(2-pyridylmethyl)iminodiethanol (H₂pmide) and N-(2-pyridylmethyl)iminodiisopropanol (H₂pmidip) have been investigated with nickel(ii) and cobalt(ii/iii) ions. Three novel complexes prepared and characterized are [(Hpmide)₂Ni₃(CH₃COO)₄] (1), [(Hpmide)₂Co₃(CH₃COO)₄] (2), and [(pmidip)₂Co₃(CH₃COO)₄] (3). In 1 and 2, two terminal nickel(ii)/cobalt(ii) units are coordinated to one Hpmide^- and two CH₃CO₂^-. The terminal units are each connected to a central nickel(ii)/cobalt(ii) cation through one oxygen atom of Hpmide^- and two oxygen atoms of acetate ions, giving rise to nickel(ii) and cobalt(ii) trinuclear complexes, respectively. Trinuclear complexes 1 and 2 are isomorphous. In 3, two terminal cobalt(iii) units are coordinated to pmidip^2- and two CH₃CO₂^-. The terminal units are each linked to a central cobalt(ii) cation through two oxygen atoms of pmidip^2- and one oxygen atom of a bidentate acetate ion, resulting in a linear trinuclear mixed-valence cobalt complex. 1 shows a weak ferromagnetic interaction with the ethoxo and acetato groups between the nickel(ii) ions (g = 2.24, J = 2.35 cm^-1). However, 2 indicates a weak antiferromagnetic coupling with the ethoxo and acetato groups between the cobalt(ii) ions (g = 2.37, J = -0.5 cm^-1). Additionally, 3 behaves as a paramagnetic cobalt(ii) monomer, due to the diamagnetic cobalt(iii) ions in the terminal units (g = 2.53, =D= = 36.0 cm^-1). No catalytic activity was observed in 1. However, 2 and 3 showed significant catalytic activities toward various olefins with modest to good yields. 3 was slightly less efficient toward olefin epoxidation reaction than 2. Also 2 was used for terminal olefin oxidation reaction and was oxidised to the corresponding epoxides in moderate yields (34-75%) with conversions ranging from 47-100%. The cobalt complexes 2 and 3 promoted the O-O bond cleavage to ～75% heterolysis and ～25% homolysis.

Full text of DOI:10.1039/c6dt02701f

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Trinuclear nickel and cobalt complexes containing unsymmetrical tripodal
tetradentate ligands: syntheses, structural, magnetic, and catalytic properties
Jong Won Shin,a Ah Rim Jeong,a Sun Young Lee,b Cheal Kim,*,b Shinya Hayami,c and Kil Sik Min*,d
a Department of Chemistry, Kyungpook National University, Daegu 41566, Republic of Korea
b Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul 01811,
Republic of Korea
c Department of Chemistry, Graduate School of Science and Technology, Kumamoto University,
Kumamoto 860ꢀ8555, Japan
d Department of Chemistry Education, Kyungpook National University, Daegu 41566, Republic of
Korea
Eꢀmail: minks@knu.ac.kr (K. S. M.), chealkim@seoultech.ac.kr (C. K.)
1

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Abstract
The coordination chemistries of the tetradentate N2O2ꢀtype ligands Nꢀ(2ꢀpyridylmethyl)iminodiethanol
(H2pmide) and Nꢀ(2ꢀpyridylmethyl)iminodiisopropanol (H2pmidip) have been investigated with
nickel(II) and cobalt(II/III) ions. Three novel complexes prepared and characterized are
[(Hpmide)2Ni3(CH3COO)4] (1), [(Hpmide)2Co3(CH3COO)4] (2), and [(pmidip)2Co3(CH3COO)4] (3). In 1
−
and 2, two terminal nickel(II)/cobalt(II) units are coordinated to one Hpmide− and two CH3CO2 . The
terminal units are each connected to a central nickel(II)/cobalt(II) cation through one oxygen atom of
Hpmide− and two oxygen atoms of acetate ions, giving rise to nickel(II) and cobalt(II) trinuclear
complexes, respectively. Trinuclear complexes 1 and 2 are isomorphous. In 3, two terminal cobalt(III)
units are coordinated to pmidip2 and two CH3CO2 . The terminal units are each linked to a central
−
−
cobalt(II) cation through two oxygen atoms of pmidip2 and one oxygen atom of a bidentate acetate
−
ion, resulting to a linear trinuclear mixedꢀvalence cobalt complex. 1 shows a weak ferromagnetic
interaction through the ethoxo and acetato groups between the nickel(II) ions (g = 2.24, J = 2.35 cm–1).
However, 2 indicates a weak antiferromagnetic coupling through the ethoxo and acetato groups
between the cobalt(II) ions (g = 2.37, J = –0.5 cm–1). Additionally, 3 behaves as a paramagnetic
cobalt(II) monomer, due to the diamagnetic cobalt(III) ions in the terminal units (g = 2.53, |D| = 36.0
cm–1). No catalytic activity was observed in 1. However, 2 and 3 showed significant catalytic activities
toward various olefins with modest to good yields. 3 was slightly less efficient toward olefin
epoxidation reaction than 2. Also 2 was used for terminal olefin oxidation reaction and showed the
oxidation to the corresponding epoxides in moderate yields (34ꢀ75%) with conversions (47ꢀ100%).
The cobalt complexes 2 and 3 promoted the OꢀO bond cleavage to ~75% heterolysis and ~25%
homolysis.
2

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Introduction
Multinuclear coordination compounds incorporating polynucleating ligands have received
considerable interest, because of their interesting structures and potential applications in molecular
magnetism and catalysis.1–3 The introduction of hydroxyl group in polynucleating ligands is able to
form a variety of multinuclear and polymeric compounds, due to deprotonation of the group.4 In this
context, tetradentate tripodal ligands including hydroxyl group have been used for preparation of
various multinuclear transition metal complexes.5 The deprotonation of the hydroxylꢀbased
tetradentate ligands forms hydroxoꢀbridged multinuclear coordination compounds.
In previous studies we have reported triꢀ/tetranuclear complexes based on an N3Oꢀtype N,N–
bis(2ꢀpyridylmethyl)ꢀ2ꢀaminoethanol (bpaeOH) ligand. The complexes are a mixedꢀvalence trinuclear
cobalt
complex
[Co3(bpaeO)2(NO3)(N3)4](NO3)
and
a
tetranuclear
iron(III)
complex
[Fe4(bpaeO)2(CH3O)2(N3)8]. The former is a paramagnetic species as Co(III)ꢀCo(II)ꢀCo(III) trimer and
shows efficient catalytic activities in the olefin epoxidation and alcohol oxidation reactions, and the
latter displays interesting magnetic properties with both ferroꢀ and antiferromagnetic interactions
between the iron(III) ions.6
Furthermore, the use of N2O2ꢀtype ligand Nꢀ(2ꢀpyridylmethyl)iminodiethanol (H2pmide) induces
more diverse structures in coordination compounds, due to the deprotonation of two hydroxyl groups.
Until now, six multinuclear coordination compounds based on Nꢀ(2ꢀpyridylmethyl)iminodiethanol
(H2pmide)
have
been
reported
and
studied.
First,
dinuclear
complexes,
[(Hpmide)Fe(NO3)]2(NO3)2•2CH3OH, [(pmide)Fe(N3)]2, and [Cu(H2pmide)(NO3)Cu(Hpmide)](NO3)2
have been prepared and characterized.7,8 The iron(III) dinuclear complexes have monoꢀ and diꢀ
deprotonated H2pmide ligands depending on anions and show different magnetic interactions and
catalytic effects depending on the different conformations.7 In the case of the copper(II) dimer, it has
an asymmetric structure and exhibits a strong antiferromagnetic coupling.8 Second, trinuclear
complexes [{Ni(Hpmide)}2Ni(CH3CO2)2(HCO2)2] and [(pmide)2Co3(CH3CO2)2(NCS)2]—4CH3OH have
been reported. In the nickel(II) trimer, the Ni(Hpmide) units are each connected to a central nickel(II)
cation through the
ꢀ ꢀ1ꢀbridged acetate, and one ꢀ
2ꢀoxygen of Hpmide–, one 2ꢀbridged formate.9
Unfortunately, the magnetic data of the nickel(II) trimer have not been reported. The latter is
composed of two terminal subunits {Co(pmide)(NCS)(CH3CO2)}– and a central cobalt(II) cation. The
terminal units are each linked to a central cobalt(II) cation via two ꢀ ꢀ2ꢀ
2ꢀoxygen of pmide2– and one
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bridged acetate.8 This is a mixedꢀvalence Co(III)ꢀCo(II)ꢀCo(III) trimeric complex and shows a
paramagnetic property with large ZFS value. Third, octanuclear complex
[Mn8O4(Hpmide)4(EtCO2)6]•(ClO4)2 has been reported. The structure of the octamer shows four
manganese(II) and four manganese(III) ions and has three faceꢀsharing cubes with manganese
cations on alternate corners. The octamer behaves as a singleꢀmoleculeꢀmagnet and also displays a
spinꢀfrustration effect.10
In the efforts to explore the role of metal ions, anions and ligands, we have synthesized three
trinuclear coordination compounds based on H2pmide and H2pmidip ligands (H2pmide = Nꢀ(2ꢀ
pyridylmethyl)iminodiethanol, H2pmidip
= Nꢀ(2ꢀpyridylmethyl)iminodiisopropanol). That is, the
trinuclear complexes can be shown significant structures, magnetic and catalytic properties by
controlling the factors, i.e., metal ion, anion, and ligand. The H2pmidip ligand is prepared and
characterized as a new ligand to check electronic and steric effects for multinuclear coordination
compounds. Herein, we report the synthesis, crystal structure, magnetic properties, and catalytic
activity of bisꢀethoxyꢀbridged trinickel(II) complex [(Hpmide)2Ni3(CH3COO)4] (1), tricobalt(II) complex
[(Hpmide)2Co3(CH3COO)4] (2), and mixedꢀvalence cobalt trinuclear complex [(pmidip)2Co3(CH3COO)4]
(3). Interestingly, complexes 1 and 2 are shown antiferromagnetic and ferromagnetic interactions,
respectively. In contrast to 1, complexes 2 and 3 exhibited significant catalytic activities toward a
variety of olefins.
Experimental
General
All chemicals used in the synthesis were of reagent grade and used without further purification. Nꢀ(2ꢀ
Pyridylmethyl)iminodiethanol (H2pmide) was prepared according to the literature procedure.10 Olefins,
epoxides, 2ꢀcyclohexenꢀ1ꢀol, 2ꢀcyclohexenꢀ1ꢀone, benzaldehyde, acetonitrile, dichloromethane,
dodecane, MCPBA (65%) were purchased from Aldrich Chemical Co. and were used without further
purification. PPAA was synthesized on reference to the method described in the literature.11 UV/Vis
absorption spectra were recorded with a SCINCO Sꢀ2100 spectrophotometer and a Perkin Elmer
model Lambda 2S UV/Vis spectrometer. Infrared spectra were recorded with a Thermo Fisher
Scientific IR200 spectrophotometer (±1 cm−1) using KBr disk. Elemental analyses were carried out
1
using a Fisons/Carlo Erba EA1108 instrument in air. HꢀNMR spectra were measured on Bruker
4

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AVANCE digital 400 spectrometer. Xꢀray powder diffraction (XRPD) patterns were measured at room
temperature with the 120 mm detector distance in the 2θ range 5ꢀ50˚ on an ADSC Quantumꢀ210
detector using synchrotron radiation (
λ = 0.90013 Å, Si(111) double crystal monochromator) in the
beamline 2D SMC at the Pohang Accelerator Laboratory (PAL), Korea. Magnetic susceptibilities were
measured in applied field of 5000~10000 Oe between 2 and 300 K on a Quantum Design MPMS
superconducting quantum interference device (SQUID) magnetometer. Diamagnetic corrections were
made [404.1 (1), 411.1 (2), and 448.6 × 10−6 (3) emu/mol] by using Pascal’s constants. Product
analysis for olefin epoxidation and PPAA experiment was conducted by using Perkin Elmer gas
chromatograph equipped with a FID detector and a 30 m capillary column (HewlettꢀPackard, DBꢀ5 or
HPꢀFFAP).
Syntheses of compounds
Nꢀ(2ꢀPyridylmethyl)iminodiisopropanol (H2pmidip). Diisopropanolamine (6.50 g, 48.8 mmol)
was dissolved in 60 mL isopropanol followed by the addition of 2ꢀ(chloromethyl)pyridine hydrochloride
(8.0 g, 48.8 mmol) and sodium carbonate (5.13 g, 48.8 mmol), then was refluxed overnight. The
resultant solution was evaporated to dryness and 100 mL dichloromethane was added and a white
precipitate was filtered. The dichloromethane solution was washed by concentrated brine and dried by
MgSO4. After removing the organic solvent, pale red oil was obtained and used without further
1
purification. Yield: 5.93 g (54%). H NMR (400 MHz, D2O, 297 K): δ = 0.96 (dd, J = 4, 4 Hz, 6H),
2.30∼2.52 (m, 4H), 3.54∼3.83 (m, 4H), 7.24 (t, J = 4 Hz, 1H), 7.37 (d, J = 4 Hz, 1H), 7.71 (t, J = 8 Hz,
1H), 8.33 (d, J = 4 Hz, 1H).
[(Hpmide)2Ni3(CH3COO)4] (1). To a methanol solution (2 mL) of Ni(CH3COO)2•4H2O (149 mg,
0.60 mmol) was added dropwise an acetonitrile solution (4 mL) of H2pmide (79 mg, 0.40 mmol), and
the solution was stirred for 30 min at room temperature. Green crystals of 1 were obtained by
diffusion of diethyl ether into the green solution for several days, and were collected by filtration and
washed with diethyl ether and dried in air. Yield: 63 mg (39%). FTꢀIR (KBr, cm−1): 3422, 3089, 2927,
2871, 1582, 1540, 1417. Anal Calcd for C28H43N4Ni3O12.5: C, 41.43; H, 5.34; N, 6.90. Found: C, 41.47;
H, 5.40; N, 6.72.
[(Hpmide)2Co3(CH3COO)4] (2). To a methanol solution (2 mL) of Co(CH3COO)2•4H2O (150 mg,
0.60 mmol) was added dropwise an acetonitrile solution (4 mL) of H2pmide (79 mg, 0.40 mmol), and
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the color became purple, and the solution was stirred for 30 min at room temperature. Purple crystals
of 2 were obtained by diffusion of diethyl ether into the purple solution for several days, and were
collected by filtration and washed with diethyl ether and dried in air. Yield: 127 mg (79%). FTꢀIR (KBr,
cm−1): 3427, 3083, 2927, 2879, 1604, 1575, 1412, 1339, 1275, 1083, 920, 890, 772. Anal. Calcd for
C28H42Co3N4O12: C, 41.86; H, 5.27; N, 6.97. Found: C, 41.73; H, 5.39; N, 7.03.
[(pmidip)2Co3(CH3COO)4] (3). To a methanol solution (2 mL) of Co(CH3COO)2•4H2O (75 mg,
0.30 mmol) was added dropwise an acetonitrile solution (4 mL) of H2pmidip (45 mg, 0.20 mmol), and
the color became purple, and the solution was stirred for 30 min at room temperature. Dark violet
crystals of 3 were obtained by diffusion of diethyl ether into the purple solution for several days, and
were collected by filtration and washed with diethyl ether and dried in air. Yield: 42 mg (49%). FTꢀIR
(KBr, cm−1): 3410, 3044, 2966, 2857, 1591, 1570, 1414, 1376, 1313, 1140, 1065, 945, 867, 692. Anal.
Calcd for C32H50Co3N4O13: C, 43.90; H, 5.76; N, 6.40. Found: C, 43.88; H, 5.68; N, 6.47.
Catalytic olefin epoxidations by MCPBA in the presence of cobalt complexes
MCPBA (0.07 mmol) was added to a mixture of substrate (0.035 mmol) and complex (2 or 3, 1.24 x
10–3 mmol) in CH3CN/CH2Cl2 (1:1 v/v; 1 mL). The mixture was stirred for 10 min at room temperature.
The reaction was monitored by GC/mass analysis of 20 ꢁL aliquots withdrawn periodically from the
reaction mixture. Dodecane as an internal standard was used to quantify the yields of products and
conversions of substrates. All reactions were run at least three times, and the average conversions
and product yields are presented. Conversions and product yields were based on substrate.
Analysis of the O−O bond cleavage products from the oxidation reactions of substrates by
PPAA in the presence of cobalt complexes
PPAA (0.04 mmol) was added to a mixture of substrate (0–0.16 mmol) and complex (2 or 3, 1.24 x
10–3 mmol) in CH3CN/CH2Cl2 (1:1 v/v; 1 mL). The mixture was stirred for 10 min at room temperature.
The reaction was monitored by GC/mass analysis of 20 ꢁL aliquots withdrawn periodically from the
reaction mixture. Dodecane as an internal standard was used to quantify the yields of products and
conversions of substrates. All reactions were run at least three times, and the average conversions
and product yields are presented. Conversions and product yields were based on substrate or PPAA.
6

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Xꢀray crystallographic data collection and refinement
Single crystals of 1 and 3 were coated with paratoneꢀN oil and the diffraction data measured at
100(2)~102(2) K with synchrotron radiation (λ = 0.63000 Å) on an ADSC Quantumꢀ210 detector at 2D
SMC with a silicon (111) double crystal monochromator (DCM) at the Pohang Accelerator Laboratory,
Korea. The ADSC Q210 ADX program12 was used for data collection (detector distance is 63 mm,
omega scan; ∆ω = 1º, exposure time is 1 sec per frame) and HKL3000sm (Ver. 703r)13 was used for
cell refinement, reduction and absorption correction. Single crystals of 2 were mounted on a Bruker
SMART APEX CCDꢀbased diffractometer (Korea Basic Science Institute, Chonju Branch). Xꢀray data
for 2 were collected at 200(2) K and using Mo Kα radiation (λ = 0.71073 Å, graphite monochromator).
The raw data were processed to give structure factors using the Bruker SAINT program and corrected
for Lorentz and polarization effects.14 The crystal structures of 1−3 were solved by direct methods,15
and refined by fullꢀmatrix leastꢀsquares refinement using the SHELXLꢀ2013 computer program.16 The
positions of all nonꢀhydrogen atoms were refined with anisotropic displacement factors. All hydrogen
atoms were placed using a riding model, and their positions were constrained relative to their parent
atoms using the appropriate HFIX command in SHELXLꢀ2013, except the hydrogens of hydroxyl
groups in 1−2. The crystallographic data and the result of refinements are summarized in Table 1.
Chart 1
N
N
HO
HO
OH
OH
N
N
H2pmide
H2pmidip
[(Hpmide)2Ni3(CH3COO)4]
(1)
[(Hpmide)2Co3(CH3COO)4] (2)
[(pmidip)2Co3(CH3COO)4] (3)
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Results and discussion
Synthesis and characterization
The reaction of two equiv of H2pmide and three equiv of Ni(OAc)2•4H2O in methanol/acetonitrile under
an aerobic condition affords air stable [(Hpmide)2Ni3(CH3COO)4] (1) in moderate yield (39%). The
complex is a linear trinuclear compound, which is formed through ethoxo and acetate groups. IR
spectrum of 1 in KBr had peaks characteristic of coordinated Hpmide− and acetate anions. The IR
spectrum of 1 showed strong absorptions at 1582 and 1417 cm−1 that are assigned to the acetate
anions as bridging with nickel(II) ions.17 The bands of the C−H of Hpmide− ligand appeared at 3089,
2927, and 2871 cm−1 and the band of the O−H of Hpmide− ligand appeared at 3422 cm−1. The
reaction of 2 equiv of H2pmide and 3 equiv of Co(OAc)2•4H2O in mixed solvent (MeOH/MeCN) under
an aerobic condition affords air stable [(Hpmide)2Co3(CH3COO)4] (2) in good yield (79%). As expected,
the structure of 2 is the same to that of 1. IR spectrum of 2 in KBr had peaks characteristic of
coordinated Hpmide− and acetate anions. The IR spectrum of 2 showed strong absorptions at 1575
and 1412 cm−1 that are assigned to the acetate anions as bridging with cobalt(II) ions.17 The bands of
the C−H of Hpmide− ligand appeared at 3083, 2927, and 2879 cm−1 and the band of the O−H of
Hpmide− ligand appeared at 3427 cm−1. The reaction of 2 equiv of H2pmidip and 3 equiv of
Co(OAc)2•4H2O in mixed solvent (MeOH/MeCN) under an aerobic condition affords air stable
[(pmidip)2Co3(CH3COO)4] (3) in moderate yield (49%). In this case, different to 2, complex 3 is formed
as a mixedꢀvalence trimeric Co(III)−Co(II)−Co(III) species. This can be attributed to the basicity of the
H2pmidip ligand. IR spectrum of 3 in KBr had peaks characteristic of coordinated pmidip2− and acetate
anions. The IR spectrum of 3 showed strong absorptions at 1570 and 1414 cm−1 that are assigned to
the acetate anions as bridging with cobalt(II/III) ions.17 The bands of the C−H of pmidip2− ligand
appeared at 3044, 2966, and 2857 cm−1. The composition of 1−3 was also identified by elemental
analyses, infrared spectroscopy, and single crystal Xꢀray diffraction.
Description of crystal structures
Structure of 1. Compound 1 crystallizes in the monoclinic P21/n space group, and the unit cell
includes two trinuclear complexes, and the ORTEP drawing of 1 is shown in Fig. 1. The selected bond
lengths and angles are listed in Table S1. The crystal structure of 1 consists of discrete centroꢀ
symmetric trinuclear unit of formula [(Hpmide)2Ni3(CH3COO)4]. The central nickel(II) ion (Ni2) which
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lies on an inversion center is bonded to four oxygen atoms of acetate anions (av. Ni−Oacetate = 2.091(1)
Å) and to two bridged oxygen atoms of Hpmide− ligand (av. Ni−OHpmide = 2.024(1) Å). On the other
hand, the terminal nickel(II) ions (Ni1) are bonded to two nitrogen atoms of Hpmide− ligand and two
oxygen atoms from acetate anions (av. Ni−NHpmide = 2.093(1), Ni−Oacetato = 2.077(1) Å) and to one
bridged ethoxy group (Ni−Oethoxy = 2.0036(9) Å) and to one oxygen atom of hydroxyl group in Hpmide−
ligand (Ni−Ohydroxyl = 2.1524(9) Å). All nickel ions adopt distorted octahedral geometries with two
Hpmide− ligands and four acetate anions. The H2pmide ligands in 1 are monodeprotonated to give
Hpmide−. The four acetate anions bind to the three nickel(II) ions in different modes. Two of them are
ꢀ
1,3ꢀacetato ligands for Ni1 and Ni2, and the other are ꢀ1,1ꢀacetato ligands for Ni1 and Ni2. The
distorted octahedral coordination sphere of the central nickel (Ni2) involves an O6 donor set including
ꢀOalkoxo (Hpmide−), two O (
sphere of the external nickel (Ni1) shows an N2O4 donor set including one Npy (Hpmide−), Namine
(Hpmide−), one Oalkoxo (Hpmide−), Ohydroxyl (Hpmide−), one O (
two
ꢀ
ꢀ1,3ꢀacetato), and two O (ꢀ1,1ꢀacetato). The octahedral coordination
ꢀ
1,3ꢀacetato), and one O (ꢀ1,1ꢀacetato).
Two bridging Ni1−O1−Ni2 and Ni1−O6−Ni2 angles are 100.17(4) and 91.90(4)°, respectively. The
Ni1•••Ni2 and Ni1•••Ni1(−x+1, −y, −z) distances within the trimeric cation are 3.0895(6) and 6.1790(12)
Å, respectively.
Structure of 2. Compound 2 crystallizes in the monoclinic P21/n space group, and the unit cell
includes two trinuclear complexes, and the ORTEP drawing of 2 is shown in Fig. 2. The selected bond
lengths and angles are listed in Table S2. The core structure of 2 is composed of one CoIICoIICoII
trimer and four acetate anions. The central cobalt(II) ion (Co2) is bonded to four oxygen atoms of
acetate anions (av. Co–Oacetate = 2.153(2) Å) and to two bridged oxygen atoms of Hpmide– ligand (av.
Co–OHpmide = 2.016(3) Å). On the other hand, the terminal cobalt(II) ions (Co1) are bonded to two
nitrogen atoms of Hpmide– ligand and two oxygen atoms from acetate anions (av. Co–NHmide
=
2.220(3), Co–Oacetate = 2.055(3) Å) and to one bridged ethoxy group (Co–Oethoxy = 1.987(4) Å), and to
one oxygen atom of hydroxyl group in Hpmide– ligand (Co–Ohydroxyl = 2.196(4) Å).6b,18 All cobalt ions
adopt distorted octahedral geometries with two Hpmide– ligands and four acetate anions. The
H2pmide ligands in 2 are monodeprotonated to give Hpmide–. The four acetate anions bind to the
three cobalt ions in different modes. Two of them are
ꢀ1,3ꢀacetato ligands for Co1 and Co2, and the
other are 1,1ꢀacetato ligands for Co1 and Co2. The distorted octahedral coordination sphere of the
ꢀ
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central cobalt (Co2) involves an O6 donor set including two
ꢀ ꢀ1,3ꢀ
ꢀOalkoxo (Hpmide–), and two O (
acetato), and two ꢀ2ꢀO (
shows an N2O4 donor set including one Npy (Hpmide–), Namine (Hpmide–), one Oalkoxo (Hpmide–), Ohydroxyl
(Hpmide–), one O (
ꢀ1,1ꢀacetato). The octahedral coordination sphere of the external cobalt (Co1)
ꢀ
1,3ꢀacetato), and one O (ꢀ1,1ꢀacetato). Two bridging Co1−O1−Co2 and
Co1−O6−Co2 angles are 102.92(17) and 89.56(14)°, respectively. The Co1•••Co2 distance within the
trimeric cation is 3.1314(2) Å and the bond distance compares well with those previously reported for
cobalt(II) ions.19 The Co1•••Co1 (ꢀx+2, ꢀy+1, ꢀz) distance is 6.62627(4) Å and the shortest Co•••Co
distance between the trimers is 7.2362(5) Å. The bond angles relating to the external cobalt (Co1)
and internal cobalt (Co2) lie from 78.74(17) to 175.14(16)° and 80.14(15) to 180.00(16)°, respectively.
According to the bond angles, the central cobalt (Co2) is closer to octahedral geometry than the
external cobalt (Co1). The structure of 2 is isomorphous to that of 1.
Structure of 3. Compound 3 crystallizes in the monoclinic P21/c space group, and the unit cell
includes two trinuclear complexes, and the ORTEP drawing of 3 is shown in Fig. 3. The selected bond
lengths and angles are listed in Table S3. The core structure of 3 is composed of one mixedꢀvalence
CoIIICoIICoIII trimer bridged with oxygen atoms of pmidip2– and acetate ions. The central cobalt(II) ion
is bonded to two oxygen atoms of acetate anions (av. Co2–Oacetate = 2.098(2) Å) and to four oxygen
atoms of pmidip2– ligand (av. Co2–Opmidip = 2.117(1) Å). On the other hand, the terminal cobalt(III)
ions are bonded to two nitrogen atoms of pmidip2– ligand and two oxygen atoms from acetate anions
(av. Co1–Npmidip = 1.941(1), Co1–Oacetate = 1.927(1) Å) and to two bridged methyl ethoxy group (Co1–
O = 1.895(1) Å).6b,18,20 The bond distances relating to Co1 ion are in good agreement with those of
lowꢀspin cobalt(III) ions reported previously,6b while the bond lengths around Co2 ion are somewhat
longer than those of Co2 ion and indicate a highꢀspin cobalt(II) ion.21
All cobalt ions adopt distorted octahedral geometries with two pmidip2– ligands and four acetate
anions. The H2pmidip ligands in 3 are fully deprotonated to give pmidip2–. The four acetate anions are
coordinated to three cobalt ions in two different binding modes. Two of them are linked between Co1
and Co2 ions in ꢀ1,3ꢀacetato mode, the other are bonded to Co1 as monodentate ligand. The distorted
octahedral coordination sphere of the central cobalt (Co2) involves an O6 donor set including four
Oalkoxo (pmidip2ꢀ) and two O (acetato) donors. The octahedral coordination sphere of the external
cobalt (Co1) shows an N2O4 donor set including one Npy (pmidip2–), Namine (pmidip2–), two Oalkoxo
(pmidip2–), and two O (acatato) donors. Two bridging Co1−O1−Co2 and Co1−O2−Co2 angles are
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98.21(6) and 95.47(6)°, respectively. The CoII•••CoIII distance within the trimeric unit is 3.0045(6) Å,
which is shorter than that of 2 (CoII•••CoII 3.1314(2) Å).21a The CoIII•••CoIII (ꢀx, ꢀy+1, ꢀz+1) distance is
6.0090(11) Å and the shortest Co•••Co distance between the trimers is 7.6033(11) Å. The bond
angles relating to the external cobalt (Co1) and internal cobalt (Co2) lie from 85.25(8) to 177.00(7)°
and 75.02(5) to 180.00(3)°, respectively. Due to the bond angles, the central cobalt (Co2) is closer to
octahedral geometry than the external cobalt (Co1). In order to determine the oxidation states of
cobalt ions in 3 using the bond lengths of Co−N/O, we have used the bond valence sum (BVS)
method. Bond valences (s) are obtained using the equation, s = exp[(ro – r)/B], where B = 0.37 Å and
ro is used from published tables.22 The BVS for cobalt ion is then the sum of bond valences for each
bond made to the cobalt ion. The BVS calculations give the valence sums of 3.46 for Co1 and 2.12 for
Co2. The results indicate that the Co1 and Co2 ions are trivalent and divalent, respectively. That is,
this strongly demonstrates the +2 oxidation state for central cobalt ion (Co2) and the +3 oxidation
states for terminal cobalt ions (Co1), i.e., CoIII(S = 0, LS)−CoII(S = 3/2, HS)−CoIII(S = 0, LS).22
Magnetic properties. The magnetic susceptibilities,
χ(T), of 1−3 were measured between 2 to
300 K (external field 5000~10000 Oe), and plotted as
MT)1/2], is 5.53
ꢀB/Ni3, and it is nearly constant with decreasing
ꢀeff(T), Fig. 4. For 1, at 300 K, the effective
magnetic moment, ꢀeff [= (8
χ
temperature until 50 K. The value of ꢀeff at room temperature is larger than the 4.90 ꢀB expected for
independent three S = 1, Ni(II) spins, and is attributed to a high effective g value, i.e. geff = 2.24.
Below 50 K,
increase in
ꢀ
eff(T) increases abruptly to 6.74
eff(T) with decreasing temperature from 300 to 5 K is suggestive of ferromagnetic
(T) was simulated with the julX program package for exchange coupled
ꢀB, at 5 K (Fig. 4). It should be noted that the continuous
ꢀ
interaction in 1. The
χ
systems.23 The simulation is based on the spinꢀHamiltonian operator for a trinuclear system of three
highꢀspin nickel(II) ions with spin Sa = Sb = Sc = 1 (H = −2J(Sa•Sb + Sb•Sc)).24 The best fit had J (= Jab
= Jbc) = +2.35 cm−1 and g (= ga = gb = gc) = 2.24. Complex 1 has three exchange pathways, i.e., ꢀ2ꢀ
ethoxo, ꢀ2ꢀacetato, and synꢀsyn carboxylato. ꢀ2ꢀEthoxo and ꢀ2ꢀacetato bridges can transmit either
ferroꢀ or antiferromagnetic interaction depending on NiꢀO(ethoxo/acetato)ꢀNi bridging angles.
Furthermore, it is known that the synꢀsyn conformations of carboxylate ligands cause
antiferromagnetic interactions.25 In 1, Ni1−O6−Ni2 angle is 91.90(4)° indicating a ferromagnetic
interaction via the O6 atom whereas Ni1−O1−Ni2 angle is 100.17(4)° meaning an antiferromagnetic
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coupling through the O1 atom. Overall, complex 1 shows a weak ferromagnetic coupling (J = +2.35
cm−1). This can be expected that the pathway of Ni1−O6−Ni2 is the most favorable in the magnetic
couplings between the Ni(II) ions. Ghosh et al. have reported two nickel(II) trinuclear complexes
[Ni3(L)2(OAc)4] and [Ni3(L)2(OAc)4(H2O)2] (HL = 2ꢀ[(3ꢀmethylaminoꢀpropylimino)ꢀmethyl]ꢀphenol).26 In
the former, the Ni−O(phenoxido)ꢀNi bridging angle is 97.63(11)° and the Ni−O(acetato)ꢀNi bridging
angle is 91.87(10)°. Due to the Ni−O(acetato)ꢀNi angle which is in the range of ferromagnetic
couplings, the trinuclear complex shows a very weak ferromagnetic interaction (J = +0.11 cm−1). In the
latter, the Ni−O(phenoxido)−Ni bridging angle is 99.89(9)° and the Ni−O(acetato)−Ni bridging angle is
96.49(9)°. Both bridging angles are greater than 93.5° (magic angle).27 As result, the nickel(II) trimer
displays a weak antiferromagnetic coupling (J = −4.3 cm−1).
For 2, at 265 K, the effective magnetic moment is 7.91 ꢁB/Co3, which is larger than the value of
6.71 ꢁB/Co3 expected for independent three highꢀspin cobalt(II) ions (g = 2, S = 3/2) because of the
strong spin–orbit coupling of cobalt(II) ions. This value decreases gradually with decreasing
temperature to 6.72 ꢀB/Co3 at 2 K. The ꢁeff(T) data were fit to an analytical expression for a coupled S
= 3/2 trinuclear spin model based on the Hamiltonian H = −2J(Sa•Sb + Sb•Sc) (Sa = Sb = Sc = 3/2).23,24
The exact expression of the Hamiltonian includes various factors, i.e. spinꢀorbit couplig, axial and
rhombic distortions, and Zeeman interactions, and we simply used the above Hamiltonian for
fitting.18b,28 The best fit had Jab = Jbc = −0.5 cm−1, g = 2.37, and θ = −0.4 K. The coupling constants (Jab
and Jbc) through the bridging oxygen atoms (ethoxo and acetate anions) are expected to be very
weak antiferromagnetic. In 2, the bridging angles of Co1ꢀO6ꢀCo2 (89.56(14)°) and Co1ꢀO1ꢀCo2
(102.92(17)°) are very close to those of Ni1ꢀO6ꢀNi2 (91.90(4)°) and Ni1ꢀO1ꢀNi2 (100.17(4)°) of 1.
Interestingly, contrary to 1, the magnetic properties of 2 indicates an antiferromagnetic coupling
between the cobalt(II) ions within the trinuclear unit. This can be expected that the antiferromagnetic
2
coupling is related to the electronic configuration of cobalt(II) ion, i.e., t2g5eg . That is, the t2g orbital
occupied with 5 electrons can be contributed to the magnetic interactions. Likewise, such magnetic
interaction is observed in [Co3(ꢀꢀOOCCF3)4(ꢀꢀH2O)2(OOCCF3)2(H2O)2(C4H8O2)] (J = −0.4 cm−1).18b
Consequently, the magnetic properties of 2 indicate that the bridges of ethoxo and acetate anions are
rather poor exchange pathways within the trinuclear unit.
Complex 3 consists of two lowꢀspin CoIII as wingtip ions and one highꢀspin CoII as the central ion,
i.e., CoIII(LS, S = 0)–CoII(HS, S = 3/2)–CoIII(LS, S = 0). The wingtip cobalt(III) ions are diamagnetic (S
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= 0), whereas the central cobalt(II) ion is paramagnetic (S = 3/2). At room temperature, the effective
moment is 4.92 ꢀB, suggesting that the cobalt(II) ion is a highꢀspin state. This value is larger than the
spinꢀonly value (3.87 ꢀB) for a highꢀspin CoII, indicative of the strong spinꢀorbit coupling.29 On lowering
the temperature, ꢀeff(T) decreases gradually with decreasing temperature to 3.62 ꢀB at 2 K (Fig. 4).
The decrease of the effective magnetic moment at lowꢀtemperature (<100 K) was most likely due to
the strong spin–orbit coupling of CoII ion. Thus the spinꢀorbit coupling highly contributes to the zeroꢀ
field splitting (ZFS).
χ
(T) for 3 was simulated with the julX program package (ver. 1.4.1).23 The
simulations are based on the usual spinꢀHamilton operator for the cobalt trimer (S = 0, S = 3/2, S = 0):
2
H = g
β
S•B + D[Sz2 – S(S+1)/3 + (E/D)(Sx2 – Sy )]
(1)
where S is the total spin multiplet (3/2), g is the average electronic g value, D is the axial zeroꢀfield
splitting parameter, and E/D is the rhombicity of the zeroꢀfield splitting. The best fit from the data had
g = 2.530, |D| = 36.0 cm–1, and the spin impurity, ρ = 0.005 (TIP = 100×10–6 emu/mol).23 The zeroꢀ
field splitting parameter between the ±1/2 and ±3/2 Kramers doublets was comparable to those for
[Co(DABPH)Br(H2O)]Br (|D| = 30.0 cm–1), [Co(DABPH)(H2O)(NO3)](NO3) (|D| = 32.0 cm–1) (DABPH =
2,6ꢀdiacetylpyridinebis(benzoic acid hydrazone)],30 and [(Me3tacn)2Co2(
(Me3tacn = 1,4,7ꢀtrimethylꢀ1,4,7ꢀtriazacyclononane).31 Additionally, above 2 K, χM−1(T) can be fit to the
M = C/(T−θ) with θ = −7.04 K (C = 3.073 emu K mol−1) for 3.32 This value can
ꢀ
ꢀCl)3]BPh4 (|D| = 40.0 cm–1)
CurieꢀWeiss expression
χ
be also related to large D value and/or intermolecular interactions.
Catalytic properties
Hydrocarbon oxidation catalyzed by cobalt complexes 2 and 3. We examined the catalytic
epoxidation of cyclohexene with mꢀchloroperbenzoic acid (MCPBA) as an oxidant in the presence of
the complex 2 or 3 as catalyst in various solvent systems. We expected that 2 and 3 with triꢀnuclear
sites might show better catalytic activities than monoꢀnuclear ones previously reported, because triꢀ
nuclear systems have three times more preꢀcatalytic sites than monoꢀnuclear ones.33 In protic
solvents such as methanol and water, small amounts (less than 20%) of products were produced,
while higher yields (50ꢀ60%) of epoxides were afforded in aprotic solvents such as CH3CN and
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CH2Cl2. In particular, the best yield of epoxide was observed in a mixture of CH3CN/CH2Cl2 (1:1 v/v).
In addition, peroxides such as hydrogen peroxide and tertꢀbutyl hydroperoxide (tꢀBuOOH) were also
tested as a potent oxidant, but they did afford trace amounts of epoxide, indicating that they were
incompetent oxidants. As the optimized condition, therefore, MCPBA (0.07 mmol) was added to a
mixture of olefin (0.035 mmol) and preꢀcatalyst (2 or 3, 1.24 x 10−3 mmol) in CH3CN/CH2Cl2 (1:1 v/v; 1
mL) at room temperature.33 The epoxidation reaction was complete less than 1 min, and we
confirmed that direct substrate oxidation by MCPBA was negligible with time control experiments.
Moreover, complexes 2 and 3 seemed to be stable enough during the catalytic reactions according to
UV/Vis spectroscopy and XRPD patterns (Figs. S1 and S2).
The epoxidation results obtained under the optimized conditions are summarized in Table 2.
With preꢀcatalyst 2, cyclic olefins such as cyclopentene, cycloheptene, and cyclooctene were oxidized
to the corresponding epoxides (60.8−79.1%; entries 1−3), with conversions in the range of 77.2 to
86.4%. In the case of cyclohexene (entry 4), it afforded the major product cyclohexene oxide (63.9%)
along with small amounts of 2ꢀcyclohexeneꢀ1ꢀol (2.8%) and 2ꢀcyclohexeneꢀ1ꢀone (2.0%). These
results suggest that the radical oxidation reactions were little involved in the epoxidation reaction.11,34
Terminal olefins such as 1ꢀhexene and 1ꢀoctene (entries 5 and 6), wellꢀknown as difficultꢀtoꢀoxidize
substrates,35 were converted to the corresponding epoxides with moderate yields (69.3% and 36.4%;
respectively). cisꢀ2ꢀHexene and cisꢀ2ꢀoctene were used to probe the epoxidation stereochemistry,
which were oxidized to cisꢀ2ꢀhexene oxide and cisꢀ2ꢀoctene oxide (28.1% and 30.2%) in addition to
transꢀ2ꢀhexene oxide and transꢀ2ꢀoctene oxide (32.9% and 30.3%; entries 7 and 9). These results
demonstrate that the stereochemical retention were low in this epoxidation reaction. transꢀ2ꢀHexene
and transꢀ2ꢀoctene were oxidized to transꢀ2ꢀhexene oxide and transꢀ2ꢀoctene oxide (66.8% and
58.5%; entries 8 and 10). Styrene was oxidized to styrene epoxide (22.9%; entry 11),
phenylacetaldehyde (58.2%) and benzaldehyde (6.5%). While cisꢀstilbene produced dominantly transꢀ
stilbene oxide (54.0%) with some benzaldehyde (20.0%) and cisꢀstilbene oxide (5.7%; entry 12),
transꢀstilbene was converted to transꢀstilbene oxide (45.3%; entry 13) and benzaldehyde (20.3%).
Preꢀcatalyst 3 was slightly less efficient toward olefin epoxidation reaction than preꢀcatalyst 2
(columns 5 vs 7 in Table 2). These results indicate that the preꢀcatalysts 2 and 3 are more selective
and efficient than those previously reported for the olefin epoxidation and hydrocarbon
hydroxylation.36 In the previous catalytic systems with diꢀ and triꢀnuclear Co complexes, tꢀBuOOH was
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often used as an oxidant. It decomposed to tꢀBuO• or tꢀBuOO• species via the homolytic OꢀO bond
cleavage or radical process, which oxidize the olefins or hydrocarbons nonꢀselectively to the products.
Terminal olefins are particularly considered as difficultꢀtoꢀoxidize olefins because of their
electronꢀdeficient nature,35 while their corresponding products 1,2ꢀepoxides are known as the
versatile starting materials for the synthesis of more complicated compounds. Since reasonable yield
of terminal epoxide from 1ꢀhexene was obtained with 2 (entry 5 in Table 2), thus, we investigated the
terminal olefin epoxidation by using 2. The results are summarized in Table 3. All of the terminal
olefins were oxidized to the corresponding epoxides in moderate yields (34.3−75.0%), with
conversions in the range of 47.4−100%, indicating that our catalytic system could be useful for the
epoxidation reaction of a variety of terminal olefins.
Product distribution of the O−O bond cleavage of PPAA with complexes 2 or 3. To gain a
clearer insight into the reactive oxidants that are involved in olefin epoxidation, we used
peroxyphenlyacetic acid (PPAA) as a mechanistic probe, because the cleavage mode could be easily
determined by quantitative analysis of the degradation products derived from PPAA.37 When the OꢀO
bond of the coordinated anion of PPAA undergoes heterolytic OꢀO bond cleavage or directly oxidizes
the substrate, phenylacetic acid (PAA) is produced. On the other hand, the homolytic cleavage of the
OꢀO bond generates an acyloxyl radical, which degrades to benzyl alcohol, benzaldehyde, and
toluene.37a,b First, a control experiment with PPAA as oxidant under the same reaction conditions as
used for MCPBAꢀepoxidation with preꢀcatalyst 2 was carried out in the absence of substrate (entry 1
in Table 4). The heterolytic cleavage product, PAA (72.4% based on PPAA), and the homolytic
cleavage products, benzaldehyde (14.8%) and benzyl alcohol (3.8%), were formed in a ratio of
79.6:20.4 (column 8). These results suggest that the CoIICoIICoIIꢀOOC(O)R species (4) formed from
the reaction of 2 and MCPBA underwent the partition of simultaneously heterolytic (79.6%) and
homolytic (20.4%) OꢀO bond cleavage to produce CoIICoIICoIV=O (5) and CoIICoIICoIV=O (6) species
(Scheme 1). Next, we varied the concentration of the substrate to examine the concentration
dependence on the ratio of the heterolysis to homolysis. If the CoIICoIICoIIꢀOOC(O)R species
contributed to the epoxidation reaction, the ratio of heterolysis to homolysis would vary according to
the concentration of substrate,38 because direct olefin epoxidation by CoIICoIICoIIꢀOOC(O)R species
generates the heterolytic cleavage product, PAA. When we changed the concentration of an easyꢀtoꢀ
oxidize substrate, cyclohexene, from 0 to 160 mM, the ratio of the heterolysis increased slightly from
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79.6 to 83.8 within possible experimental error, as shown in Table 4 (entries 1ꢀ5). These results imply
that the CoIICoIICoIIꢀOOC(O)R species are a little involved in this oxidation reaction when the
concentration of cyclohexene is very high. We changed the substrate from cyclohexene to a difficultꢀ
toꢀoxidize olefin, 1ꢀoctene, to examine the cleavage mode of PPAA on the type of substrate.38a The
partition of the heterolysis and the homolysis was nearly identical, without respective to 1ꢀoctene
concentration (entries 1ꢀ5 in Table 5), suggesting that the CoIICoIICoIIꢀOOC(O)R species would not be
involved in the epoxidation of 1ꢀoctene, even in the presence of the high concentration of it.
Analogous results were also obtained for 3 (entries 6ꢀ10 in Tables 4 and 5).
Based on the product distributions of the O−O bond cleavage of PPAA, we propose the plausible
olefin epoxidation mechanism catalyzed by the preꢀcatalyst 2 with peracids (Scheme 1). 2 reacts with
peracid to form CoIICoIICoIIꢀOOCCO)R intermediate (4), which underwent the OꢀO bond cleavage to
~75% heterolysis (pathway (a)) and ~25% homolysis (pathway (c)) to produce CoIICoIICoIV=O (5) and
CoIICoIICoIII=O (6) species, respectively. We assume that the active oxidant CoIICoIICoIV=O (5) might
be responsible for efficient olefin epoxidation and the radical types of the products stem from the
intermediate CoIICoIICoIII=O (6). Moreover, the intermediate CoIIIꢀOOC(O)R species could contribute a
little to the catalytic epoxidation in the presence of the easyꢀtoꢀoxidize olefin (pathway (b)), while it
was inactive with the difficultꢀtoꢀoxidize substrate such as 1ꢀoctene. Similar olefinꢀepoxidation
mechanism can be proposed for the preꢀcatalyst 3 (Scheme S1).
On the other hand, the difference of the catalytic activities between 2 and 3 may be explained
with the presence of the proton of the ethanol moiety in the complex 2, which might act as a general
acid catalyst for promoting the heterolytic OꢀO bond cleavage of Coꢀacylperoxide intermediate 4.
Conclusions
We have prepared and characterized three novel trinuclear compounds using H2pmide/H2pmidip and
Ni(II)/Co(II) metal ions. 1 is a trinuclear nickel(II) complex showing ferromagnetic coupling between
nickel(II) ions within trimeric unit, whereas 2 is a trinuclear cobalt(II) complex showing weak
antiferromagnetic coupling between cobalt(II) ions within the trimer. 1 and 2 have isomorphous
structures. 3 has different bonding modes, although the trinuclear cobalt complex of 3 is bridged by
ethoxo and acetato ligands. Different to 2, 3 is a mixedꢀvalence trinuclear cobalt complex, CoIII(S =
0)–CoII(S = 3/2)–CoIII(S =0) and displays the magnetic properties (large D value) of a cobalt(II) ion in a
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highꢀspin state. Complexes 2 and 3 showed significant catalytic activities toward various olefins with
modest to good yields. Complex 3 was slightly less efficient toward olefin epoxidation reaction than
complex 2. Also complex 2 was used for terminal olefin oxidation reaction and showed the oxidation
to the corresponding epoxides in moderate yields with conversions. The cobalt preꢀcatalysts 2 and 3
promoted the OꢀO bond cleavage to ~75% heterolysis and ~25% homolysis. The intermediate Coꢀ
OOC(O)R species might contribute a little to the catalytic epoxidation in the presence of the easyꢀtoꢀ
oxidize olefin.
Acknowledgements
This research was supported by Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No.
2015R1D1A1A01059872 and 2014R1A2A1A11051794). We thank Prof. Joel S. Miller and J. E.
Sussman for obtaining the magnetic data of 2. Xꢀray crystallography at the PLSꢀII 2DꢀSMC beamline
was supported in part by MEST and POSTECH.
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Table 1 Summary of the crystallographic data for 1−3
Compound
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
1
2
3
C28H42N4Ni3O12
802.73
Monoclinic
P21/n
C28H42Co3N4O12
803.45
Monoclinic
P21/n
C32H48Co3N4O12
857.53
Monoclinic
P21/c
11.479(2)
10.789(2)
13.770(3)
90
11.6737(12)
10.8739(12)
13.8627(15)
90
7.9190(16)
23.274(5)
9.4900(19)
90
b (Å)
c (Å)
α (°)
113.00(3)
90
112.781(2)
90
94.12(3)
90
β
(°)
γ (°)
V (Å3)
1569.8(6)
2
1622.4(3)
2
1744.5(6)
2
Z
dcalc (g cm−3)
1.698
1.645
1.632
0.63000
102(2)
1.329
0.71073
200(2)
1.584
0.63000
100(2)
1.060
λ
(Å)
T (K)
ꢀ
(mm−1)
F(000)
836
830
890
Reflections collected
Independent reflections
Reflections with I>2σ(I)
Goodnessꢀofꢀfit on F2
R1a [I>2σ(I)]
22005
6179
11458
21064
5861
4020
5971
2699
4241
1.037
1.149
1.027
0.0281
0.0776
1456726
0.0534
0.1221
0.0445
0.1155
1456728
wR2b [I>2σ(I)]
CCDC no.
1456727
2 2
2 2 1/2
a R1 = Σ||Fo| − |Fc||/Σ|Fo|. b wR2 = [Σw(Fo2 − Fc ) /Σw(Fo ) ] .
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Table 2 Olefin epoxidations by MCPBA with cobalt complexes 2 and 3 in CH2Cl2/CH3CN (1:1) at
room temperature[a]
2
3
Entry Substrate
Product
Conversion Yield
Conversion Yield
[%][b]
[%][b]
[%][b]
[%][b]
±
±
1
2
3
4
cyclopentene
epoxide
76.3±0.2
49.2±5.7
80.3 0.5
68.8 0.7
±
±
cycloheptene
cyclooctene
cyclohexene
epoxide
80.9±0.8
75.2±0.7
73.7±1.0
77.9±0.6
59.2±1.5
55.2±2.6
2.1±0.1
86.4 2.5
79.1 0.9
±
±
epoxide
77.2 3.6
60.8 0.4
±
±
epoxide
70.0 0.8
63.9 4.8
±
2ꢀcyclohexeneꢀ1ꢀol
2ꢀcyclohexeneꢀ1ꢀone
epoxide
2.8 0.9
±
4.1±0.1
2.0 0.4
±
±
5
6
7
1ꢀhexene
55.1±0
29.4±1.1
33.0±0.2
29.7±3.7
36.5±4.4
54.5±4.9
27.1±0.8
32.1±0.6
50.0±0.8
37.7±1.3
6.2±0.1
75.8 8.0
69.3 0.1
±2.4
70.8
±
1ꢀoctene
epoxide
57.2±0.3
70.8±5.0
36.4 0.4
±
±
cisꢀ2ꢀhexene
cisꢀoxide
82.4 1.0
28.1 0.5
±
transꢀoxide
32.9 0.2
±
±
8
9
transꢀ2ꢀhexene transꢀoxide
72.3±7.1
79.8±0.4
89.9 3.6
66.8 1.3
±
±
cisꢀ2ꢀoctene
cisꢀoxide
82.6 0.6
30.2 0.4
±
transꢀoxide
30.3 0
±
±
10
11
transꢀ2ꢀoctene transꢀoxide
82.6±0.7
92.5±2.0
80.3 4.4
58.5 0.7
±
±
styrene
epoxide
97.5 2.5
22.9 1.4
±
benzaldehyde
6.5 1.0
±
phenylacetaldehyde
cisꢀstilbene oxide
transꢀstilbene oxide
benzaldehyde
3.5±0.1
58.2 0.2
±
±
12
13
cisꢀstilbene
88.0±0.1
96.6±0.4
7.0±0.2
84.4 1.5
5.7 0.7
±
33.5±2.8
15.4±0.6
5.7±0.4
54.0 2.3
±
20.0 0.9
2ꢀ
phenylacetophenone
94.7±
0.8
±
transꢀstilbene
transꢀstilbene oxide
47.0±5.0
16.3±0.1
5.8±0.1
45.3 0.4
±
benzaldehyde
20.3 2.9
2ꢀ
phenylacetophenone
[a] Reaction conditions: olefins (0.035 mmol), complexes (1.24 x 10ꢀ3 mmol), MCPBA (0.07 mmol), and
solvent (1 mL, CH2Cl2/CH3CN =1:1). [b] Based on substrate.
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Page 20 of 33
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DOI: 10.1039/C6DT02701F
Table 3 Terminal olefin epoxidations by MCPBA with cobalt complex 2 in CH2Cl2/CH3CN (1:1) at
room temperature[a]
Entry
Substrate
Product
Conversion (%)[b] Yield (%)[b]
1
1ꢀhexene
1,2ꢀepoxyhexane
100±0
70.1±0.5
54.5±0.3
45.6±0.3
50.6±1.9
48.9±1.2
53.1±0.5
48.5±0.4
34.3±2.6
46.1±0.6
75.0±3.2
61.2±1.9
46.2±1.0
2
1ꢀoctene
1,2ꢀepoxyoctane
98.2±0.6
52.0±1.0
98.4±0.1
95.2±0.9
96.8±0.4
97.4±0.6
95.9±1.5
96.2±0.5
95.8±1.0
91.2±1.5
47.4±0.4
3
1ꢀnonene
1,2ꢀepoxynonane
4
1ꢀdecene
1,2ꢀepoxydecane
5
1ꢀundecene
1ꢀdodecene
1ꢀtridecene
1ꢀtetradecene
1ꢀpentadecene
1ꢀhexadecene
1ꢀoctadecene
vinylcyclohexane
1,2ꢀepoxyundecane
1,2ꢀepoxydodecane
1,2ꢀepoxytridecane
1,2ꢀepoxytetradecane
1,2ꢀepoxypentadecane
1,2ꢀepoxypentadecane
1,2ꢀepoxypentadecane
2ꢀcyclohexyloxirane
6
7
8
9
10
11
12
[a] Reaction conditions: olefin (0.035 mmol), complex (1.24 x 10ꢀ3 mmol), MCPBA (0.13 mmol), and
solvent (1 mL, CH2Cl2/CH3CN =1:1). [b] Based on substrate.
20

Page 21 of 33
Dalton Transactions
Table 4 Yield of products derived from PPAA mediated by the cobalt complexes 2 and 3 in the absence and the presence of cyclohexene in a mixture of
CH3CN/CH2Cl2 (1:1) at room temperature[a]
Heterolysis[b]
Homolysis[b]
Oxidation products
Cyclohexene
[mM]
Hetero (5)/
Homo (6+7+8)
Entry Complex
Benzaldehyde Benzyl alcohol Toluene
PAA (5)
oxide[c]
ꢀ
ꢀol[c]
ꢀone[c]
(6)
14.8±0
(7)
3.8±0.4
(8)
72.4±0.3
75.9±0.3
78.7±0.6
72.4±5.2
78.1±4.3
59.5±2.5
59.7±5.0
65.9±0.9
68.2±2.3
71.8±1.6
3.89 (79.6/20.4)
3.55 (78.0/22.0)
3.95 (79.8/20.2)
4.36 (81.3/18.7)
5.17 (83.8/16.2)
3.16 (76.0/24.0)
2.82 (73.8/26.2)
3.23 (76.4/23.6)
3.43 (77.4/22.6)
3.92 (79.7/20.3)
1
2
3
4
5
6
7
8
9
10
2
2
2
2
2
3
3
3
3
3
0
ꢀ
ꢀ
ꢀ
16.6±0.9
15.7±0.2
12.6±0.9
11.4±0.2
14.3±0
4.8±0.1
4.2±0.1
4.0±0.2
3.7±0.1
4.5±0.1
4.5±0
34.5±0.2[d] 0[d]
22.6±0.6[d] 0[d]
24.8±2.4[e] 0[e]
26.4±0.5[e] 0.9±0.1[e]
3.8±0.1[d]
20
40
80
160
0
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3.2±0.2[d]
3.8±1.0[e]
3.7±0.1[e]
ꢀ
ꢀ
ꢀ
16.7±0.1
16.0±0.2
15.6±0.1
14.1±0.1
24.8±0.1[d] 5.8±0.2[d]
16.7±1.0[d] 4.1±0.3[d]
21.7±1.2[e] 6.8±0[e]
3.4±0.1[d]
20
40
80
160
4.4±0.1
4.3±0.3
4.2±0
2.5±0.2[d]
4.2±0[e]
30.5±2.4[e] 12.2±0.3[e] 8.5±0.1[e]
[a] Reaction conditions: substrate (0ꢀ0.16 mmol), complex (1.24 x 10ꢀ3 mmol), PPAA (0.04 mmol), and solvent (1 mL, CH3CN/CH2Cl2=1:1). [b] Based on
PPAA; 5ꢀ8 indicate phenylacetic acid, benzaldehyde, benzyl alcohol, and toluene, respectively. [c] ꢀol, ꢀone, and oxide indicate 2ꢀcyclohexenꢀ1ꢀol, 2ꢀ
cyclohexenꢀ1ꢀone, and cyclohexene oxide, respectively. [d] Based on substrate, cyclohexene. [e] Based on oxidant, PPAA.
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Page 22 of 33
Table 5 Yield of products derived from PPAA mediated by the cobalt complexes 2 and 3 in the absence and the presence of 1ꢀoctene in a mixture of
CH3CN/CH2Cl2 (1:1) at room temperature[a]
Oxidation
products
Heterolysis[b]
PAA (5)
Homolysis[b]
Cyclohexene
[mM]
Hetero (5)/
Homo (6+7+8)
Entry
Complex
Benzaldehyde Benzyl alcohol Toluene
1ꢀoctene oxide
(6)
(7)
(8)
72.4±0.3
70.1±2.8
68.9±0.7
67.6±5.6
68.2±3.9
59.5±2.5
61.9±6.1
62.7±1.4
67.9±1.1
63.8±1.0
14.8±0
3.8±0.4
3.89 (79.6/20.4)
3.34 (77.0/33.0)
3.01 (75.1/24.9)
2.86 (74.1/25.9)
3.04 (75.2/24.8)
3.16 (76.0/24.0)
3.00 (75.0/25.0)
2.96 (74.7/25.3)
3.09 (75.6/24.4)
2.97 (74.8/25.2)
1
2
3
4
5
6
7
8
9
10
2
2
2
2
2
3
3
3
3
3
0
ꢀ
ꢀ
16.7±0.2
18.2±0.4
19.0±1.4
18.4±0.2
14.3±0
4.3±0.1
4.7±0.1
4.6±0.1
4.4±0
18.0±0.6[c]
20
40
80
160
0
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
10.7±1.2[c]
15.0±0.6[d]
16.2±1.2[d]
4.5±0.1
4.5±0.2
4.4±0.1
4.5±0.1
4.4±0.1
ꢀ
20
40
80
160
15.0±1.0[c]
9.6±0.2[c]
11.2±0.1[d]
12.9±0.3[d]
16.1±0.2
16.8±0.1
17.5±0.1
17.1±0
[a] Reaction conditions: substrate (0ꢀ0.16 mmol), complex (1.24 x 10ꢀ3 mmol), PPAA (0.04 mmol), and solvent (1 mL, CH3CN/CH2Cl2=1:1). [b] Based on
PPAA; 5ꢀ8 indicate phenylacetic acid, benzaldehyde, benzyl alcohol, and toluene, respectively. [c] Based on substrate, 1ꢀoctene. [d] Based on oxidant,
PPAA.
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Page 23 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02701F
Figure captions
Fig. 1 Structure of [(Hpmide)2Ni3(CH3COO)4] (1). The atoms are represented by 50% probable thermal
ellipsoids. The hydrogen atom on the hydroxyl group is shown as small open circle; all other Hꢀ
atoms are omitted for clarity.
Fig. 2 Structure of [(Hpmide)2Co3(CH3COO)4] (2). The atoms are represented by 20% probable thermal
ellipsoids. The hydrogen atom on the hydroxyl group is shown as small open circle; all other Hꢀ
atoms are omitted for clarity.
Fig. 3 Structure of [(pmidip)2Co3(CH3COO)4] (3). The atoms are represented by 40% probable thermal
ellipsoids. The hydrogen atoms are omitted for clarity.
Fig. 4 Temperature dependence of ꢀeff(T) for 1 (○), 2 (×), and 3 (□). Solid lines represent best fits by
using parameters given in the text.
Scheme 1 Plausible olefin epoxidation mechanism catalyzed by 2 with peracids.
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Dalton Transactions
Page 24 of 33
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DOI: 10.1039/C6DT02701F
Fig. 1 Structure of [(Hpmide)2Ni3(CH3COO)4] (1). The atoms are represented by 50% probable thermal
ellipsoids. The hydrogen atom on the hydroxyl group is shown as small open circle; all other Hꢀatoms are
omitted for clarity.
24

Page 25 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02701F
Fig. 2 Structure of [(Hpmide)2Co3(CH3COO)4] (2). The atoms are represented by 20% probable thermal
ellipsoids. The hydrogen atom on the hydroxyl group is shown as small open circle; all other Hꢀatoms are
omitted for clarity.
25

Dalton Transactions
Page 26 of 33
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DOI: 10.1039/C6DT02701F
Fig. 3 Structure of [(pmidip)2Co3(CH3COO)4] (3). The atoms are represented by 40% probable thermal
ellipsoids. The hydrogen atoms are omitted for clarity.
26

Page 27 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02701F
9
8
7
6
5
4
3
2
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
3
0
50
100
150
200
250
300
Temperature, T, K
Fig. 4 Temperature dependence of
ꢀeff for 1 (○), 2 (×), and 3 (□). The solids lines are the bestꢀfit curves.
27

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Page 28 of 33
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DOI: 10.1039/C6DT02701F
Scheme 1 Plausible olefin epoxidation mechanism catalyzed by 2 with peracids.
28

Page 29 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02701F
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