novel macrocyclic multinuclear ni(ii) and zn(ii) complexes
TRANSCRIPT
Novel Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
for Catalytic CO2 Conversions
September 2019
Bikash Dev Nath
(Doctor’s Course)
Graduate School of Natural Science and Technology
Okayama University, Japan
Contents
Chapter 1. General Introduction
1.1. Catalytic Conversions of CO2 into Value-Added Chemicals 2
1.2. Macrocyclic Multinuclear Metal Complex Catalysts for CO2 Fixation
3
1.3. Metal Catalysts for N-Functionalization of Amines with CO2 9
1.4. Advantages of Macrocyclic Multinuclear Metal Complexes in Catalysis
11
1.5. This Work 12
1.6. References 14
Chapter 2. Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
2.1. Abstract 19
2.2. Results and Discussion 20
2.3. Experimental Section 34
2.4. References 46
Chapter 3. Synthesis of Cyclic Carbonates from Epoxides and CO2
3.1. Abstract 49
3.2. Results and Discussion 50
3.3. Experimental Section 55
3.4. References 62
Chapter 4. N-Formylation and N-Methylation of Amines
4.1. Abstract 63
4.2. Results and Discussion 64
4.3. Experimental Section 69
4.4. References 77
List of Publication 78
Acknowledgement 79
Chapter 1: General Introduction
1
Chapter 1. General Introduction
Chapter 1: General Introduction
2
1.1. Catalytic Conversions of CO2 into Value-Added Chemicals
Numerous scientific works have been going on to utilize CO2 as a renewable raw material
for the production of value-added organic compounds, and a number of important catalytic
reactions have been reported (Scheme 1).1,2 Organocatalysts as well as mono- and multinuclear
metal complexes have shown various catalytic activities for the conversions of CO2 into value-
added chemicals.3–29
Scheme 1. Conversions of CO2 into Value-Added Chemicals
C–H bondformation
Scheme 2. Conversion of CO2 into Cyclic Carbonate and Polycarbonate
Among organocatalysts, bifunctional quaternary phosphonium salts,3 carbenes,4 chiral
macrocyclic organocatalysts,5 calix[4]pyrroles,6 hemisquaramide tweezers,7 squaramide-based
organocatalysts,8 polystyrene-supported bifunctional resorcinarenes,9 N,N′-phenylenebis(5-
tert-butylsalicylideneimine),10 pincer-type compounds possessing an N-heterocyclic carbene
and a carboxyl group,11 and charge-containing thiourea catalysts12 exhibited significant
catalytic activities for the successful conversion of CO2 and epoxides into cyclic carbonates
(Scheme 2). Several monometallic complexes were also reported,13–23 such as rare-earth metal
catalysts,13 Mg and Al complexes,14,15 metalloporphyrin catalysts,16 chiral binaphthyl-strapped
Zn(II) porphyrin catalysts,17 unsymmetrical pyridine-bridged bis-pincer-type Fe(II)
Chapter 1: General Introduction
3
complexes,18 bifunctional aluminum catalysts,19 pyridine-based o-aminophenolate zinc
complexes,20 and imidazolium-based ionic liquid-decorated zinc porphyrin catalysts.21
Monometallic complexes can also successfully catalyze the copolymerization of epoxides
and CO2.22,23 In this respect, the catalytic activities of multinuclear metal complexes are very
high, and they can provide excellent selectivity during the polymerization reaction,24-29 such as
dinickel bis(benzotriazole iminophenolate) complexes,24 heterodinuclear metal complexes,25,26
rare earth metal–zinc based heterometallic catalysts,27 bimetallic nickel complexes bearing
diamine-bis(benzotriazole phenolate) derivatives,28 and dinuclear Co(III) complexes.29
1.2. Macrocyclic Multinuclear Metal Complex Catalysts for CO2 Fixation
In recent years, several macrocyclic multinuclear metal complexes have been developed
which can successfully convert CO2 into various materials. Typical examples are given below:
Scheme 3. Cycloaddition of CO2 with Epoxides
(a) Conversion of CO2 into cyclic and polycarbonates
Kleij and co-workers reported complexes 1–3 (Scheme 3a), which catalyzed the ring-
opening reactions of epoxides with CO2.30 Complex 1 showed the best catalytic activity,
providing 100% conversion of epoxides even after 5 consecutive runs of the recycled catalyst.
The selectivity (>99%) and the yield (>92%) of the cyclic carbonate were high. The metal-
Chapter 1: General Introduction
4
bound anion (iodide) is dissociated upon heating to be a nucleophile, which increases the Lewis
acidity of the metal centers to facilitate the coordination and activation of the epoxide.
Liu and co-workers synthesized several anion-induced 3d–4f coordination clusters
Zn2Ln2L4 (Ln = Eu3+, Tb3+, Er3+, Yb3+, Nd3+) and Zn4Ln2L4 (Ln = Tb3+, Nd3+) and obtained a
maximum TON of ~9000 and TOF of ~660 h–1 (>99% selectivity) with Tb3+/Zn2+ complex 4
for the conversion of CO2 and epoxides into cyclic carbonates (Scheme 3b).31 The complex
was effective enough to catalyze the ring-opening reactions of a wide range of epoxides under
solvent-free conditions.
Jing and co-workers used chiral dinuclear Co complexes 5 and 6, in the kinetic resolution
of propylene oxide (PO) with CO2 (Scheme 3c).32 The enantioselectivity is likely to result from
the synergic effect of the chiral BINOL-frame and salen-backbone.
Scheme 4. Copolymerization of CO2 and CHO
Williams and co-workers developed several macrocyclic multimetallic complexes showing
high activity for the copolymerization of cyclohexene oxide (CHO) and CO2 (Scheme 4). They
reported highly robust catalyst 7 capable of catalyzing the copolymerization of CO2 (1 atm)
and CHO with 0.1 mol% catalyst loading at 80–100 ºC to form poly(cyclohexene carbonate)
with a TON of 430–530 and a TOF of 18–25 h–1.33 Increasing the CO2 pressure resulted in the
increase of both TON (838) and TOF (38 h–1). When catalyst loading was decreased to 0.01
mol%, TON and TOF were increased to 3350 and 140 h–1, respectively.
A mechanism was proposed on the basis of kinetic studies (Scheme 5).34 DFT calculations
suggested that the ring opening of CHO through the nucleophilic attack of the zinc–carbonate
group in the propagation cycle is the rate-determining step.35
Chapter 1: General Introduction
5
Scheme 5. Proposed Mechanism for the Copolymerization of CHO and CO2
Dinuclear Co complexes 8 and 9 showed comparable catalytic activity at 1 atm CO2
pressure.36,37 Complex 8 possessing a mixed valence Co(II)/Co(III) metal core exhibited ~20
times higher TOF than complex 7. At higher CO2 pressure (10 atm), both 8 and 9 showed much
higher catalytic activities, and complex 8 displayed an excellent TOF of 3700 h–1 at 100 ºC. A
maximum TOF of 730 h–1 was observed for Mg complex 10 with catalyst loading of 0.01 mol%
at 100 ºC at a CO2 pressure of 12 atm. Because of weaker Lewis acidity and lower
electronegativity compared to Zn, the Mg–carbonate bond might become more nucleophilic,
which could facilitate the ring opening of the epoxide. This could accelerate the
copolymerization process of complex 10.38 Fe(III) complex 12 was also capable of catalyzing
copolymerization of CHO and CO2 under mild conditions.39 Complex 12 exhibited 8 times
higher activity at 10 atm CO2 pressure than at 1 atm CO2 pressure. Williams group reported the
first heterodinuclear (Zn/Mg) macrocyclic complex 13,40 and complex 14 was the first isolated
heterometallic complex synthesized from a macrocyclic ancillary ligand.41 The mixed catalyst
system 13 was remarkably more effective than either homodinuclear Zn complex 7 or Mg
complex 10.40 The catalytic activity of complex 14 was about 5 times higher than that of a 1:1
mixture of the homodinuclear Zn and Mg complexes.41 14 was more than twice as active as 11
while a Zn analog of 11 showed no activity at all. 14 was also highly selective, providing >99%
carbonate linkages. Heterodinuclear (Ti/Zn) complexes 15 and 16 were also synthesized,42 and
about 50% conversion was obtained with 1 mol% catalyst loading for 15 and 16 after 24 h at 1
atm CO2 pressure and 80 ºC. With 0.01 mol% catalyst loading, complex 14 showed a
competitive TOF of 624 h–1 compared to other catalysts involving halide initiating
groups.39,41,43,44 The enhanced reactivity of 14 might be due to the synergistic effect between
the two different metal ions.
After performing a mechanistic study using DFT calculations for the copolymerization of
CHO or propylene oxide (PO) and CO2 with complex 7,45 Rieger and co-workers synthesized
complex 17 containing two β-diketiminato zinc units (Figure 1).46,47 Complex 17 showed a
TOF of 9130 h–1 at 100 ºC and 40 bar CO2 pressure. The catalytic activity decreased at higher
Chapter 1: General Introduction
6
temperature (120 ºC) most probably due to the decomposition of the catalyst. Several other
catalysts with modified structures were also synthesized, and their catalytic activities for the
copolymerization of CHO and CO2 were studied by online ATR-IR measurements.48
Surprisingly, in situ IR spectroscopic measurement revealed TOF values of up to 23,300 h–1
for complex 17 at 30 bar CO2 pressure and 100 ºC. Complexes 18 and 19 containing Cl and
CF3 groups were expected to have metal centers with enhanced Lewis acidity. Complex 19
exhibited exceptionally high catalytic activity for the copolymerization of CHO and CO2 with
a TOF of up to 155,000 h–1.
Figure 1. Macrocyclic Zn complexes 17–19.
Okuda, Mashima, and co-workers synthesized a family of heterometallic tetranuclear
complexes comprising the macrocyclic tris(Zn–salen) unit and one lanthanide ion, among
which CeZn3 complex 20 (Figure 2) was the most effective for the copolymerization of CHO
and CO2 with a TOF of over 370 h–1 with high carbonate linkages (>99%) even at a CO2
pressure of 0.6 MPa.49 The molecular weight of the polymer was controlled by adding
ammonium salts as chain-transfer agents. A rapid exchange of acetate anions is believed to be
a key factor in the control of telomerization.
Figure 2. Structure of LaZn3 complex 20.
Chapter 1: General Introduction
7
Ko and co-workers reported macrocyclic dinuclear Co and Ni complexes 21–22 for CO2
coupling with epoxides (Scheme 6). Without any co-catalyst, Ni complex 22 exhibited the best
catalytic activity, providing PCHC (Mn > 30,000 g mol–1, carbonate linkage > 99%) from CHO
and CO2 with a TOF of 265 h–1.50 In the presence of co-catalyst (n-Bu4NBr <1 mol%), Co
complex 21 provided cyclohexene carbonate (CHC) (>99% cis-selectivity) with a TOF of 174
h–1. Scheme 6. Formation of PCHC and CHC
(b) Reduction of CO2 to oxalate
Murray and co-workers reported macrocyclic trinuclear copper complexes Cu3(µ3-S)L (23)
and Cu3(µ3-Se)L (24) capable of selectively reducing CO2 to oxalate (95% yield, TON = 24)
(Scheme 7).51 The efficiency was much higher than that of reported copper complexes for
similar reactions.52 Anionic complex [Cu3EL]– acted as a reductant for CO2 to form C2O42–.
[Cu3EL]– was formed through one-electron reduction of Cu3EL by a reductant. [K(18-crown-
6)][Cu3EL] provided (CO2K)2 via C–C coupling of CO2. The rate constant for pseudo-first-
order kinetics of [K(18-crown-6)][24] with CO2 was much higher than that of [K(18-crown-
6)][23].
Scheme 7. Formation of Oxalate from CO2
Chapter 1: General Introduction
8
Pokharel and co-workers synthesized macrocyclic dinuclear Cu complexes 25–26 capable
of reducing CO2 to oxalate (Scheme 8).53 Reduction of CO2 was accompanied by the reduction
of CuII to CuI with a reductant (ascorbate) and finally, the regeneration of the starting CuII
macrocyles was done by the acidic treatment through the release of oxalic acid.
Scheme 8. Formation of Oxalate from CO2
(c) CO2 hydrogenation
Hydrogenation of CO2 to formate with complex 27 (NiGaL) was achieved with an excellent
TON of 3150 and a TOF of 9700 h–1 at ambient temperature in the presence of strong base
(Scheme 9).54 Lu and co-workers performed an intensive mechanistic study to identify the most
favorable pathway of the hydrogenation process: (i) the binding of H2 to Ni center to form
adduct (η2-H2)NiGaL (ii) the deprotonation of the adduct by the base to generate [HNiGaL]–
species, (iii) the production of formate adduct, [(η1-HCO2)NiGaL]– through hydride transfer to
CO2, and (iv) the regeneration of catalyst 27 through the release of formate (Scheme 10).55
Scheme 9. Hydrogenation of CO2
Chapter 1: General Introduction
9
Scheme 10. Catalytic Cycle for CO2 Hydrogenation
(27)NiGaL
H2
HCOO–
HCOOH
Base-H+
BaseCO2
HCOO–
(iii)
(iv)Ga
Ni
N
P
N
P
N
P
N
Ga
Ni
N
P
N
P
N
P
N
H H
Ga
Ni
N
P
N
P
N
P
N
H
Ga
Ni
N
P
N
P
N
P
N
O
HO
(i)
(ii)
[HNiGaL]–
[( 1-HCO2)NiGaL]–( 2-H2)NiGaL
1.3. Metal Catalysts for N-Functionalization of Amines with CO2
Using amines as the functionalizing reagents, the reductive functionalizations of CO2 can
produce formamide and methylamine derivatives. Several metal catalysts have been reported.56
However, no example of macrocyclic multinuclear metal complexes capable of catalyzing N-
functionalization of amines with CO2 and hydrosilane/H2 has been reported.
Milstein and co-workers reported that Co-PNP pincer complex 28 successfully converted a
wide range of amines to their corresponding formamides under CO2 and H2 pressure with a
maximum yield of 99% (Scheme 11).56j
Scheme 11. N-Formylation of Amines in the Presence of 30
Garcia and co-workers studied selective N-methylation of aliphatic amines with CO2 and
hydrosilanes using Ni-phosphine catalyst, [(dippe)Ni(μ-H)]2.56f With 4 mol% catalyst loading,
they obtained 100% conversion of benzylamine to the methylated products (Scheme 12).
Chapter 1: General Introduction
10
Scheme 12. N-Methylation Catalyzed by Ni Catalyst
Ru-catalyzed N-formylation of amines with H2 and CO2 was reported by Ding and co-
workers.56h Ruthenium-pincer-type complex 29 efficiently produced formamide product
through the N-formylation of morpholine with H2 and CO2, providing excellent TON of up to
1,940,000 (Scheme 13).
Scheme 13. Ru-catalyzed N-Formylation of Amine
Klankermayer and co-workers developed Ru-catalyzed reductive methylation of imines and
aromatic amines using CO2 and H2 (Scheme 14).56b,d With [Ru(triphos)(tmm)] complex 30,
they obtained maximum 93% and 99% yields of the methylated products using imines and
aromatic amine, respectively.
Scheme 14. Ru-catalyzed Reductive Methylation of Imines and Aromatic Amine
Chapter 1: General Introduction
11
1.4. Advantages of Macrocyclic Multinuclear Metal Complexes in Catalysis
The binding of a substrate molecule to a metal center is a crucial step in catalysis. In this
regard, catalytic activity may be improved if the structure of the complex offers a specific
coordination site to bind and activate the substrate molecule. The cooperative effect of
multinuclear metal complexes is also important for unique catalytic performance.57–58
Cooperative catalytic activity may result from two or more closely located metal ions.
Macrocyclic ligands with multiple chelating sites can be designed to systematically introduce
different metal elements for unusual reactivity and selectivity. The macrocyclic multinuclear
metal complexes can provide high catalytic efficiency because the synergetic effect of the metal
centers can be higher in macrocyclic complexes than that of acyclic ones due to the presence
of multiple metal centers in a confined macrocyclic framework.
Another significant feature of these complexes is robustness, which may come from the
sophisticated and tight assembly of metal ions and ligands with multiple coordination bonds.
Although macrocyclic metal complexes can be created by designing macrocyclic ligands, the
self-assembly of metal ions and ligands in some cases may be assisted by more complicated
metal–ligand interactions. Various combinations of metal ions and ligands sometimes give rise
to unusual robustness.
Figure 3. Different Macrocyclic Frameworks Created by Ligand and Multinuclear Metal Ions.
Chapter 1: General Introduction
12
1.5. This Work
Synthesis of metal catalysts for effective CO2 fixations is an exciting research area. However,
the development of a multitask metal catalyst for CO2 fixations is challenging. On the other
hand, due to the lack of versatile synthetic platforms, the synthesis of macrocyclic structures is
more challenging as compared with that of acyclic ones. The macrocyclization step often
requires rigorous tuning of reaction conditions and suffers from low yields. Self-assembly of
metal ions and organic ligands can construct unprecedented molecular structures with good
synthetic accessibility. The initial target of this research was to successfully synthesize several
multinuclear metal complexes and to characterize their structural features completely.
Scheme 15. Synthesis of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
The purpose of this work was to explore the catalytic efficiency of the stable complexes for
CO2 fixations. With this target, several self-assembled macrocyclic multinuclear Ni(II) and
Zn(II) complexes were synthesized and characterized completely by X-ray crystallography
along with other analytical techniques (Scheme 15). The structural features of the complexes
were elucidated both in the solid state and in solution, and the complexes behaved differently
in two different states. The catalytic activities of both Ni(II) and Zn(II) complexes were
explored, and they exhibited the rarely observed dual catalytic activities in CO2 fixations
(Scheme 16). The complexes showed high catalytic activities for distinct CO2 fixations: (a)
synthesis of cyclic carbonates from epoxides and CO2 and (b) N-formylation/N-methylation of
amines with CO2 and hydrosilane. This is the first example of multitask catalysts for the CO2
fixations.
Chapter 1: General Introduction
13
Scheme 16. (a) Synthesis of Cyclic Carbonates and (b) N-Functionalization of Amines
Chapter 1: General Introduction
14
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51. Cook, B. J.; Di Francesco, G. N.; Abboud, K. A.; Murray, L. J. J. Am. Chem. Soc. 2018,
140, 5696–5700.
Chapter 1: General Introduction
17
52. (a) Rudolph, M.; Dautz, S.; Jäger, E.-G. J. Am. Chem. Soc. 2000, 122, 10821–10830. (b)
Angamuthu, R.; Byers, P.; Lutz, M.; Spek, A. L.; Bouwman, E. Science 2010, 327, 313–
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A. M.; Gagliardi, L.; Lu, C. C. J. Am. Chem. Soc. 2017, 139, 14244–14250.
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Chapter 1: General Introduction
18
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
19
Chapter 2. Synthesis and Characterization of Macrocyclic
Multinuclear Ni(II) and Zn(II) Complexes 2.1. Abstract
Unique macrocyclic multinuclear Zn(II) and Ni(II) complexes were synthesized by the self-
assembly of binaphthyl–bipyridyl ligands (L) and metal acetate hydrates. The novel
macrocyclic complexes possess interesting structural features, and they showed different static
and dynamic structures in the solid state and in solution, which were confirmed by X-ray
analysis and COSY, NOESY, VT 1H NMR, 13C NMR, MALDI-TOF-MS, UV-Vis, and CD
spectra. DFT calculations were also carried out. X-ray analysis revealed that these complexes
consisted of an outer ring (Zn3L3 or Ni3L3) and an inner core (Zn2 or Ni). In the Zn(II) complex,
the inner Zn2 part rotated rapidly inside the outer ring in solution on an NMR time scale. On
the other hand, a unique polymorphism was observed for Ni(II) complexes.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
20
2.2. Results and Discussion
Artificial metallosupramolecular architectures have been actively investigated, and various
macrocycles,1 cages,2 and helicates3 have been synthesized from simple ligands and metal ion
sources. Large but ordered multinuclear metal complexes can be constructed by self-assembly.
Recently, several metallosupramolecules with catalytic activities have been reported.4
Scheme 1. Synthesis of Multinuclear Zn(II) and Ni(II) Complexes
Here, new macrocyclic multinuclear Zn(II) and Ni(II) complexes 2 and 3, respectively, were
prepared by self-assembly of a binaphthyl–bipyridyl ligand (H2L; (R)-1) and metal acetate
hydrates (Scheme 1). These structures were surprising because originally the formation of
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
21
simple acyclic dinuclear complexes such as M2L(OAc)2 was expected. The complexes 2 and 3
comprise an outer ring (M3L3) and an inner core (M2 or M). In other words, they are
“complex@complex” structures. This type of structure is unprecedented, although many
multinuclear metal complexes with binaphthyl-based ligands have been reported.5
(R)-1 was synthesized via the Suzuki–Miyaura reaction of 3,3'-B(pin)-substituted (R)-1,1'-
binaphthyl6 with 6-bromo-2,2'-bipyridyl. (R)-1 and each metal acetate hydrates were self-
assembled to give the Zn(II) or Ni(II) complexes in 80–82% yields (Scheme 1).
Figure 1. X-ray crystal structures of 2. Solvent molecules are omitted for clarity.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
22
Figure 2. The unit cell configuration of 2 and the hollow interior created by the structural units.
The crystal structures of the Zn(II) complex 2 was determined by X-ray analyses (Figures 1
and 2). The Zn(II) complex 2 was found to have a unique macrocyclic pentanuclear structure,
[Zn5L3(OAc)(O)]OH (2) (Figure 1). Complex 2 contained a trinuclear macrocyclic part, a
dinuclear inner part, and a hydroxide as a counter anion, which can be represented by
[Zn2(OAc)(O)]@[Zn3L3]OH. The peripheral macrocyclic part consisted of three
hexacoordinate octahedral Zn ions (Zn1–3) and three ligands (L), which were connected via two
sets of NNO coordinations of the adjacent ligands. All three Zn1–3 centers had -chirality
induced by the (R)-binaphthyl moieties.
The inner part consisted of two distorted square pyramidal pentacoordinate Zn ions (Zn4 and
Zn5) and bridging AcO– and O2–, forming a six-membered ring (Zn4–O–C–O–Zn5–O) to fill
the cavity. This inner core is similar to the active site of a peptidase7 and a phosphotriesterase.8
The Zn1–3 ions were arranged to form a nearly isosceles triangle, and the dihedral angles of the
naphthalene rings of each binaphthyl differed: 68°, 72°, and 88°, because the inner part was
horizontally long.
The unit cell of 2 (Figure 2) contains 32 structural units packed by van der Waals interactions.
The unique assembly of the structural units creates a hollow-interior inside the cell walls as
observed for metal–organic frameworks (MOFs).
MALDI-TOF-MS analysis also clearly demonstrated the formation of 2 (Figure 3).
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
23
abd.
0
00.20.40.60.81.0
2165 2170 2175 2180 2185 2190
2171
.223
2
2172
.226
421
73.2
224
2174
.223
9
2175
.221
221
76.2
220
2177
.219
921
78.2
202
2179
.218
6
2180
.218
721
81.2
173
2182
.217
2
2183
.216
121
84.2
159
2185
.215
1
2186
.214
821
87.2
142
2188
.214
0
2189
.213
721
90.2
136
2191
.213
6
Experimental
TheoreticalC122H75N12O9Zn5
m/z
m/z
Figure 3. HR MALDI-TOF-(+)-MS spectra of Zn(II) complex 2.
0
Experimental
[2 – OH]+ 2180.2128
[2 – OH]+
m/z
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
24
Figure 4. 1H NMR spectra of (a) (R)-1 and (b) 2 (CDCl3, 400 MHz, 20 °C).
Next, the conformations of Zn(II) complex 2 in solution were analyzed. If the Zn(II)
complex in solution retains the crystal structure with C1-symmetry, six sets of aromatic proton
signals should appear in NMR. Actually, two sets of signals were observed in 1H NMR spectra,
suggesting an averaged C3-symmetrical structure (Figure 4). 13C NMR, COSY, and NOESY
analyses also supported the structure with C3-symmetry (Figures 5 and 6). It is considered that
the inner core rotates around the z-axis like a molecular motor (Figure 4); two sets of signals
arise from an upper segment (AcO side) and a lower segment (bridging O side). Indeed, the
signal corresponding to the methyl protons of AcO appeared at a high magnetic field (0.85
ppm) due to the ring-current effect of the surrounding aromatic rings, and NOEs between the
methyl protons and protons He, Hf, and Hg on the side of the AcO ligand were detected. The
OH– proton appeared at a much higher magnetic field (–0.38 ppm in CDCl3 and –0.47 ppm in
DMSO-d6) than that of tetraethylammonium hydroxide (Et4N+OH–; 4.43 ppm in DMSO-d6),9
suggesting that the OH– of 2 was incorporated into the inner part in equilibrium to form 2OH
with a hydrogen-bond mediated eight-membered ring in solution (Figure 4). This species 2OH
was supported by DFT calculations (Figure 7).10 VT 1H NMR revealed that complex 2
maintained C3-symmetry even at –60 °C, indicating that the inner part rotated rapidly at low
temperature (Figure 8).
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
25
ab
cd e
fg
hi
j
kla
b
cd e
fg
hi
jk
lOO
ZnO
Zn
CH3
inner Zn2 moietyZn(II) complex 2
OO
N
N
N
N
NN
Zn
O
N N
Zn
O N
N
Zn Zn
ON
N
O
N
NZn
O
N
NO
O
O
O
OH–
Figure 5. Aromatic regions of 1H-1H COSY spectrum of Zn(II) complex 2 (400 MHz, CDCl3).
cc
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
26
ab
cd e
fg
hi
j
kla
b
cd e
fg
hi
jk
lOO
ZnO
Zn
CH3
inner Zn2 moietyZn(II) complex 2
OO
N
N
N
N
NN
Zn
O
N N
Zn
O N
N
Zn Zn
ON
N
O
N
NZn
O
N
NO
O
O
O
OH–
Figure 6. Partial NOESY spectrum of Zn(II) complex 2 (600 MHz, CDCl3)
cc
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
27
Figure 7. DFT-optimized structures of Zn(II) complex 2OH at the B3LYP/6-31G(d) level for the H, C, N,
and O atoms and at the B3LYP/LanL2DZ level for the Zn atoms.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
28
Figure 8. VT 1H NMR spectra of Zn(II) complex 2 (600 MHz, CDCl3).
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
29
The crystal structures of Ni(II) complexes 3–5 were also determined by X-ray analyses
(Figure 9). The complexes exhibited polymorphism (Schemes 1 and 2), and two types of single
crystals of macrocyclic complexes were obtained (Figure 9). One of them was a cocrystal of
tetranuclear complexes Ni4L3(OH)2(H2O)2 (3) and Ni4L3(OH)2 (4), and the other was a
dinuclear complex Ni2L2 (5). Complex 3 consisted of a macrocyclic part (Ni3L3) and an inner
part (Ni(OH)2(H2O)2). The macrocyclic part was very similar to that of Zn(II) complex 2. In
contrast, the inner part of 3 consisted of a hexacoordinate octahedral Ni4 ion, two OH–, and two
H2O. The Ni1–3 ions of the macrocyclic part have -chirality again. The difference between 3
and 4 was the presence or absence of two H2O molecules coordinating the inner Ni ion.
Complex 5 has two hexacoordinate Ni ions without a cavity. The average Ni–Ni distances in
the macrocyclic parts were 7.86 Å for 3 and 6.95 Å for 4, indicating that the cavity size is
somewhat variable.
Scheme 2. Plausible Equilibrium of Ni(II) Complexes 3–5
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
30
Figure 9. X-ray crystal structures of Ni(II) complexes 3–5. Solvent molecules are omitted for clarity.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
31
The Ni(II) complexes were NMR-inactive due to paramagnetism, and hence, UV-Vis and
CD spectra were analyzed instead. The solution of the cocrystal of 3 and 4 exhibited the same
spectra as that of 5 (Figure 10), which suggests a rapid equilibrium between complexes 3–5 in
solution (Scheme 2).
Figure 10. UV-Vis and CD spectra of solutions prepared from the co-crystal of 3 and 4 (red) and the
crystal of 5 (blue) (MeOH, light path length = 1 cm, 20 °C).
MALDI-TOF-MS analysis was also carried out which further demonstrated the formation
of the complexes 3–5 and their polymorphic behavior (Figure 11).
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
32
m/z
Inte
ns. [
a.u.
]
0.2
0.4
0.6
0.8
1.0
1000 2000 3000
Experimental1303.2638
[3 – 2H2O – OH]+
[4 – OH]+
2029.3158
[5 + H]+
abd.
00.20.40.60.81.0
1295 1300 1305 1310 1315 1320
1301
.257
8
1302
.261
0
1303
.257
0
Experimental
m/z
m/z
TheoreticalC80H49N8O4Ni2
1304
.257
9
1305
.255
9
1306
.255
9
1307
.254
4
1308
.254
5
1309
.253
4
1310
.253
1
1311
.252
7
1312
.252
9
1313
.252
4
1301
.261
8
1302
.264
4
1303
.263
8
1304
.266
2
1305
.266
2
1306
.264
8
1307
.264
5
1308
.268
2
1309
.263
7
1310
.261
6
1311
.264
7
1312
.269
8
1313
.258
7
1295 1300 1305 1310 1315 1320
Inte
nse.
[a.u
.]
00.20.40.6
0.81.0
Figure 11. HR MALDI-TOF-(+)-MS spectra of Ni(II) complex 3–5.
1000 2000 3000 m/z
[5 + H]+
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
33
abd.
00.20.40.60.81.0
2020 2025 2030 2035
2025
.313
4
2026
.316
5
2027
.312
9
m/z
TheoreticalC120H73N12O7Ni4 20
28.3
137
2029
.311
4
2030
.311
2
2031
.309
5
2032
.309
0
2033
.307
7
2034
.307
1
2035
.305
4
2036
.305
4
2040
[3 – 2H2O – OH]+
[4 – OH]+
Figure 11. continued.
0 2020 2025 2030 2035 2040
Experimental
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
34
2.3. Experimental Section
Melting points were measured on a Yanaco melting point apparatus (uncorrected). Optical
rotations were measured on a Horiba SEPA-300. IR spectra were recorded on a Shimadzu
IRAffinity-1. 1H NMR, 13C NMR, 1H-1H COSY, and 1H-1H NOESY spectra were recorded on
a JEOL JNM-ECS400 or a Varian NMR system PS600. Data are reported as follows: chemical
shifts in ppm using the residual solvent peak as an internal standard, integration, multiplicity
(s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), and coupling constants (Hz).
High-resolution mass spectra were performed on an Agilent G6520+G4240 or a Bruker
Ultraflextreme. UV-Vis spectra were recorded on a Shimadzu UV-2600. CD spectra were
recorded on a JASCO J-720. TLC analyses were carried out on glass sheets coated with Merck
Silica gel 60 F254 (0.25 mm), and visualization was accomplished with UV light. Column
chromatography was performed on silica gel (Fuji Silysia BW-127 ZH, 100-270 mesh).
2.3.1. Synthesis of (R)-13
A solution of (R)-11 (2.01 g, 3.21 mmol), 6-bromo-2,2’-bipyridyl (12) (2.26 g, 9.60 mmol),
Pd(PPh3)4 (188 mg, 163 mol), and Na2CO3 (1.12 g, 10.6 mmol) in a mixed solvent of 1,4-
dioxane (75 mL) and H2O (25 mL) was stirred at 90 °C for 24 h under Ar atmosphere. After
removal of the organic solvent, CHCl3 was added. The organic layer was separated and washed
with water (two times) and brine. After dried over Na2SO4, the solvent was evaporated to give
a residue. The residue was purified by column chromatography (SiO2, CHCl3/EtOAc (2:1)) to
afford (R)-13 (2.16 g, 3.16 mmol, 98%) as a colorless powder.
mp 208–210 °C; []D20 = –31 (CHCl3, c 0.11); IR (KBr) 3051, 2993, 2945, 2883, 1641,
1560, 1492, 1427, 1352, 1317, 1292, 1200, 968, 914, 829, 779, 665 cm–1; 1H NMR (400 MHz,
CDCl3) 2.48 (s, 6H), 4.57 (ABq, = 39.5 Hz, J = 5.5 Hz, 4H), 7.32 (d, J = 3.2 Hz, 4H),
7.35 (ddd, J = 1.1, 4.8, 8.1 Hz, 2H), 7.46 (dt, J = 4.0, 8.2 Hz, 2H), 7.88 (td, J = 1.8, 7.7 Hz,
2H), 7.93 (d, J = 7.8 Hz, 2H), 8.02 (d, J = 8.2 Hz, 2H), 8.06 (dd, J = 0.9, 7.8 Hz, 2H), 8.42 (dd,
J = 0.9, 8.2 Hz, 2H), 8.50 (s, 2H), 8.66 (d, J = 7.8 Hz, 2H), 8.70–8.75 (m, 2H); 13C NMR (100
MHz, CDCl3) 56.3, 99.4, 119.6, 121.6, 123.9, 125.4, 125.5, 126.5, 126.8, 127.0, 128.7, 131.0,
131.9, 134.37, 134.42, 137.1, 137.2, 149.3, 151.4, 156.1, 156.2, 156.5; HR MS (ESI+) Calcd
for C44H34N4O4Na: 705.2472 [M + Na]+. Found: 705.2456.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
35
2.3.2. Synthesis of (R)-1
A solution of (R)-13 (575 mg, 843 μmol) in a mixed solvent of 6 M HCl aq. (7.6 mL), CHCl3
(8.0 mL), and MeOH (6.0 mL) was stirred at 65 °C for 18 h under N2 atmosphere. Then a
mixed solvent of NH3 aq. and CHCl3 was added. The organic layer was washed successively
with water (two times) and brine. After dried over Na2SO4, the solvent was evaporated to give
a residue. The residue was purified by column chromatography (SiO2, CHCl3/EtOAc (2:1)) to
afford (R)-1 (498 mg, 837 μmol, 99%) as a yellow powder.
mp 209–212 °C; []D20 = –136 (CHCl3, c 0.11); IR (KBr) 3053, 2993, 1732, 1622, 1579,
1562, 1504, 1462, 1431, 1418, 1329, 1209, 1150, 1016, 935, 827, 785, 742, 619; 1H NMR
(400 MHz, CDCl3) 7.20–7.35 (m, 8H), 7.67 (td, J = 1.8, 7.8 Hz, 2H), 7.96 (d, J = 7.8 Hz,
2H), 8.06 (t, J = 8.0 Hz, 2H), 8.13 (d, J = 8.2 Hz, 2H), 8.28 (d, J = 7.8 Hz, 2H), 8.38 (d, J = 7.3
Hz, 2H), 8.59 (s, 2H), 8.65–8.75 (m, 2H); 13C NMR (100 MHz, CDCl3) 118.5, 120.1, 121.8,
121.4, 121.8, 123.4, 124.2, 125.0, 127.6, 127.8, 127.9, 129.0, 135.5, 137.4, 139.0, 149.4, 153.8,
154.4, 154.5, 157.7; HR MS (ESI–) Calcd for C40H25N4O2: 593.1983 [M – H]–. Found:
593.1972.
2.3.3. Synthesis of Zn(II) complex 2
A mixture of (R)-1 (600 mg, 1.01 mmol), Zn(OAc)2・2H2O (464 mg, 2.11 mmol), and K2CO3
(290 mg, 2.10 mmol) in a mixed solvent of CHCl3 (12 mL) and MeOH (12 mL) was stirred at
rt for 18 h under Ar atmosphere. After removal of the solvent, CHCl3 was added. The mixture
was filtered, and the solvent of the filtrate was evaporated to give a residue. The residue was
recrystallized from CHCl3/EtOAc (7:1) to afford 2 (672 mg, 276 mol, 82%) as a yellow crystal.
mp >300 °C; []D21 = –487 (CHCl3, c 0.11); IR (KBr) 3420, 3055, 1614, 1487, 1458, 1418,
1389, 1329, 1275, 1207, 1157, 1095, 1016, 980, 950, 824, 795, 758, 718 cm–1; 1H NMR (400
MHz, CDCl3) –0.38 (s, 1H), 0.85 (s, 3H), 5.48 (d, J = 8.2 Hz, 3H), 5.57 (d, J = 8.7 Hz, 3H),
6.31 (ddd, J = 0.9, 6.5, 8.7 Hz, 3H), 6.43 (ddd, J = 0.9, 6.8, 8.4 Hz, 3H), 6.69 (d, J = 7.4 Hz,
3H), 6.76 (ddd, J = 0.9, 6.0, 7.3 Hz, 3H), 6.80 (ddd, J = 0.9, 5.5, 7.6 Hz, 3H), 6.88 (d, J = 7.8
Hz, 3H), 7.00–7.15 (m, 9H), 7.35–7.42 (m, 9H), 7.47 (td, J = 1.5, 7.7 Hz, 3H), 7.62 (td, J = 1.7,
7.7 Hz, 3H), 7.68 (s, 3H), 7.70 (s, 3H), 7.71 (d, J = 7.8 Hz, 3H), 7.79 (d, J = 7.8 Hz, 3H), 7.83
(d, J = 7.8 Hz, 3H), 7.91 (t, J = 8.0 Hz, 3H), 8.00 (d, J = 7.8 Hz, 3H), 8.46 (t, J = 8.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) 23.6, 118.2, 118.7, 120.5, 120.6, 122.7, 122.8, 122.9, 123.5,
124.3, 124.4, 124.5, 124.8, 125.8, 126.0, 126.35, 126.41, 126.6, 126.9, 128.3, 128.4, 129.0,
129.5, 130.2, 130.4, 130.7, 135.2, 139.3, 139.4, 140.3, 141.9, 146.0, 149.36, 149.42, 150.4,
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
36
150.6, 157.6, 157.7, 161.2, 161.8, 176.1; HR MS (MALDI-TOF+, DCTB) Calcd for
C122H75N12O9Zn5: 2178.2197 [M – OH]+. Found: 2178.2121.
2.3.4. Synthesis of Ni(II) complexes 3–5
A mixture of (R)-1 (200 mg, 336 mol), Ni(OAc)2・4H2O (175 mg, 703 mol), and K2CO3
(96.8 mg, 700 mol) in a mixed solvent of CHCl3 (7.0 mL) and MeOH (6.0 mL) was stirred at
rt for 20 h under Ar atmosphere. After removal of the solvent, CHCl3 was added. The solvent
of the filtrate was evaporated to give a residue. The residue was recrystallized from
MeOH/EtOAc (5:1) to afford 3–5 (186 mg, 89.3 mol, 80% based on 3) as yellow crystals.
mp >300 °C; []D21 = –121 (CHCl3, c 0.053); IR (3 and 4, KBr); 3421, 3055, 1635, 1570, 1564,
1487, 1458, 1418, 1389, 1329, 1207, 1018, 951, 870, 822, 795, 777, 756, 718 cm–1; IR (5,
KBr) 3055, 1636, 1595, 1558, 1489, 1458, 1418, 1387, 1323, 1206, 1016, 947, 883, 822, 775,
752, 718 cm–1; HR MS (MALDI-TOF+, DCTB) Calcd for C120H73N12O7Ni4: 2025.3134 [3 –
2H2O – OH]+ and [4 – OH]+. Found: 2025.3140, Calcd for C80H49N8O4Ni2: 1301.2578 [5 +
H]+. Found: 1301.2618.
2.3.5. X-ray structures
Single crystals of 2, co-crystals of 3 and 4, and single crystals of 5 were obtained by vapor
diffusion of CHCl3/EtOAc, MeOH/EtOAc, and MeOH/EtOAc solution, respectively. Data of
2, 3, and 4 were collected by a Rigaku R-AXIS RAPID diffractometer using multi-layer mirror
monochromated Cu-Kradiation. Data of 5 were collected by a Rigaku Saturn724
diffractometer using multi-layer mirror monochromated Mo-Kradiation. CIF files CCDC
1845246 for 2, CCDC 1845248 for 3 and 4, and CCDC 1845247 for 5 can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
37
Table 1. Crystal Data and Structure Refinement for Complex 2 Empirical Formula C124H78Cl6N12O10Zn5 Formula Weight 2435.67 Temperature –173.0 °C Radiation CuK ( = 1.54187 Å) Crystal System tetragonal Space Group I422 (#97) Lattice Type I-centered Lattice Parameters a = 42.5132(18) Å
c = 58.3544(12) Å V = 105468(7) Å3 Z value 32 Dcalc 1.227 g/cm3 (CuK) 25.851 cm–1 F000 39616.00 Crystal Dimensions 0.240 × 0.150 × 0.120 mm Exposure Rate 150.0 sec./° oscillation Range (=54.0, =90.0) 80.0 – 260.0° No. of Reflections Measured Total: 607032
Unique: 47631 (Rint = 0.1213) Corrections Lorentz-polarization
Absorption (trans. factors: 0.379 – 0.733)
Refinement Full-matrix least-squares on F2 No. Observations (All reflections) 47631 Goodness of Fit Indicator 1.031 Residuals: R1 (I>2.00(I)) 0.0668 Residuals: R (All reflections) 0.0877 Residuals: wR2 (All reflections) 0.1878 Maximum peak in Final Diff. Map 0.85 e–/Å3 Minimum peak in Final Diff. Map –0.42 e–/Å3
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
38
Table 2. Crystal Data and Structure Refinement for Complex 3 and 4 Empirical Formula C240H152N24Ni8O18 Formula Weight 4129.59 Temperature –173.0 °C Radiation CuK ( = 1.54187 Å) Crystal System monoclinic Space Group I2 (#5) Lattice Type I-centered Lattice Parameters a = 28.1650(5) Å
b = 30.0240(6) Å c = 30.372(5) Å
= 92.010(9)° V = 25668(4) Å3
Z value 4 Dcalc 1.069 g/cm3 (CuK) 10.813 cm–1 F000 8512.00 Crystal Dimensions 0.250 × 0.220 × 0.160 mm Exposure Rate 40.0 sec./° oscillation Range (=54.0, =60.0) 80.0 – 260.0° No. of Reflections Measured Total: 237006
Unique: 46320 (Rint = 0.0390) Corrections Lorentz-polarization
Absorption (trans. factors: 0.557 – 0.841)
Refinement Full-matrix least-squares on F2 No. Observations (All reflections) 46320 Goodness of Fit Indicator 1.050 Residuals: R1 (I>2.00(I)) 0.0625 Residuals: R (All reflections) 0.0692 Residuals: wR2 (All reflections) 0.1866 Maximum peak in Final Diff. Map 1.69 e–/Å3 Minimum peak in Final Diff. Map –1.00 e–/Å3
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
39
Table 3. Crystal Data and Structure Refinement for Complex 5 Empirical Formula C80H48N8Ni2O4 Formula Weight 1302.71 Temperature –173.0 °C Radiation MoK ( = 0.71075 Å) Crystal System monoclinic Space Group C2 (#5) Lattice Type C-centered Lattice Parameters a = 28.163(3) Å
b = 18.1117(13) Å c = 16.8220(18) Å = 112.239(5)o
V = 7942.3(14) Å3 Z value 4 Dcalc 1.089 g/cm3 (MoK) 25.851 cm–1 F000 2688.00 Crystal Dimensions 0.160 × 0.150 × 0.080 mm Exposure Rate 2.0 sec./° oscillation Range (=45.0, =90.0) –115.0 – 65.0° No. of Reflections Measured Total: 53643
Unique: 18018 (Rint = 0.0672) Corrections Lorentz-polarization
Absorption (trans. factors: 0.772 – 0.959)
Refinement Full-matrix least-squares on F2 No. Observations (All reflections) 18018 Goodness of Fit Indicator 0.958 Residuals: R1 (I>2.00(I)) 0.0487 Residuals: R (All reflections) 0.0603 Residuals: wR2 (All reflections) 0.0941 Maximum peak in Final Diff. Map 0.60 e–/Å3 Minimum peak in Final Diff. Map –0.51 e–/Å3
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
40
2.3.6. 1H NMR and 13C NMR spectra
1H NMR spectrum of (R)-13 (400 MHz, CDCl3)
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
41
13C NMR spectrum of (R)-13 (100 MHz, CDCl3)
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
42
1H NMR spectrum of (R)-1 (400 MHz, CDCl3)
OHOH
N
N
N
N
(R)-1
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
43
13C NMR spectrum of (R)-1 (100 MHz, CDCl3)
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
44
1H NMR spectra of Zn(II) complex 2 (400 MHz, CDCl3)
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
45
13C NMR spectra of Zn(II) complex 2 (100 MHz, CDCl3)
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
46
2.4. References
1. For recent reviews, see: (a) Dong. J.; Tan, C.; Zhang, K.; Liu, Y.; Low, P. J.; Jiang, J.; Cui,
Y. J. Am. Chem. Soc. 2017, 139, 1554−1564. (b) Chen, L.-J.; Yang, H.-B. Shionoya, M.
Chem. Soc. Rev. 2017, 46, 2555−2576. (c) Roberts, D. A.; Pilgrim, B. S.; Nitschke, J. R.
Chem. Soc. Rev. 2018, 47, 626−644. (d) Chakraborty, S.; Newkome, G. R. Chem. Soc. Rev.
2018, 47, 3991−4016.
2. For recent examples, see: (a) Fujita, D.; Ueda, Y.; Sato, S.; Mizuno, N.; Kumasaka, T.; Fujita,
M. Nature 2016, 540, 563−566. (b) Bloch, W. M.; Abe, Y.; Holstein, J. J.; Wandtke, C. M.;
Dittrich, B.; Clever, G. H. J. Am. Chem. Soc. 2016, 138, 13750−13755. (c) Leenders, S. H.
A. M.; Becker, R.; Kumpulainen, T.; de Bruin, B.; Sawada, T.; Kato, T.; Fujita, M.; Reek, J.
N. H. Chem. Eur. J. 2016, 22, 15468−15474. (d) Musser, A. J.; Neelakanden, P. P.; Richter,
J. M.; Mori, H.; Friend, R. H.; Nitschke, J. R. J. Am. Chem. Soc. 2017, 139, 12050−12059.
(e) Peterson, D.; Lewis, J. E. M.; Crowley, J. D. J. Am. Chem. Soc. 2017, 139, 2379−2386.
(f) Li, X.-Z.; Zhau, L.-P.; Yan, L. L.; Dong, Y.-M.; Bai, Z.-L.; Sun, X.-Q.; Diwu, J.; Wang,
S.; Bünzil, J.-C.; Sun, Q.-F. Nat. Commun. 2018, 9, 547. (g) Zhang, L.; August, D. P.; Zhong,
J.; Whitehead, G. F. S.; Victoria-Yrezabal, I.; Leigh, D. A. J. Am. Chem. Soc. 2018, 140,
4982−4985. (h) Samanta, D.; Galaktionova, D.; Gemen, J.; Shimon, L. J. W.; Diskin-Posner,
Y.; Avram, L.; Král, P.; Klajn, R. Nat. Commun. 2018, 9, 641.
3. For recent examples, see: (a) Gidron, O.; Ebert, M. O.; Trapp, N.; Diederich, F. Angew.
Chem., Int. Ed. 2014, 53, 13614−13618. (b) Gidron, O.; Jirásek, M.; Trapp, N.; Ebert, M.-
O.; Zhang, X.; Diederich, F. J. Am. Chem. Soc. 2015, 137, 12502−12505. (c) Chan, M. H.-
Y.; Ng, M.; Leung, S. Y.-L.; Lam, W. H.; Yam, V. W.-W. J. Am. Chem. Soc. 2017, 139,
8639−8645. (d) Mateus, P.; Wicher, B.; Ferrand, Y.; Huc, I. Chem. Commun. 2018, 54,
5078−5081.
4. For reviews, see: (a) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond, K. N. Chem.
Rev. 2015, 115, 3012−3035. (b) Tan, C.; Chu, D.; Tang, X.; Liu, Y.; Xuan, W.; Cui, Y.
Chem. Eur. J. 2019, 25, 662−672. For recent examples, see: (c) García-Simón, C.; Gramage-
Doria, R.; Raoufmoghaddam, S.; Parella, T.; Costas, M.; Ribas, X.; Reek, J. H. N. J. Am.
Chem. Soc. 2015, 137, 2680−2687. (d) Kaphen, D. M.; Levin, M. D.; Bergman, R. G.;
Raymond, K. N.; Toste, F. D. Science 2015, 350, 1235−1238. (e) Cullen, W.; Misuraca, M.
C.; Hunter, C. A. Williams, N. H.; Ward, M. D. Nat. Chem. 2016, 8, 231−236. (f) Howlader,
P.; Das, P.; Zangrando, E.; Mukherjee, P. S. J. Am. Chem. Soc. 2016, 138, 1668−1676. (g)
Ueda, Y.; Ito, H.; Fujita, D.; Fujita, M. J. Am. Chem. Soc. 2017, 139, 6090−6093. (h) Zhao,
L.; Wang, J.; Wu, P.; He, C.; Guo, X.; Duan, C. Sci. Rep. 2017, 7, 14347. (i) Jiao, J.; Tan,
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
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C.; Li, Z.; Liu, Y.; Han, X.; Cui, Y. J. Am. Chem. Soc. 2018, 140, 2251−2259. (j) Holloway,
L. R.; Bogie, P. M.; Lyon, Y.; Ngai, C.; Miller, T. F.; Julian, R. R.; Hooley, R. J. J. Am.
Chem. Soc. 2018, 140, 8078−8081.
5. (a) Escudero-Adán, E. C.; Belmonte, M. M.; Benet-Buchholz, J.; Kleij, A. W. Org. Lett.
2010, 12, 4592−4595. (b) Endo, K.; Ogawa, M.; Shibata, T. Angew. Chem., Int. Ed. 2010,
49, 2410−2413. (c) Akine, S.; Shimada, T.; Nagumo, H.; Nabeshima, T. Dalton Trans. 2011,
40, 8507−8509. (d) Ma, L.; Jin, R.; Bian, Z.; Kang, C.; Chen, Y.; Xu, J.; Gao, L. Chem. Eur.
J. 2012, 18, 13168−13172. (e) Wu, B.; Gallucci, J. C.; Parquette, J. R.; RajanBabu, T. V.
Chem. Sci. 2014, 5, 1102−1117. (f) Deng, Y.; Karunaratne, C. V.; Csatary, E.; Tienrney, D.
L.; Wheeler, K.; Wang, H. J. Org. Chem. 2015, 80, 7984−7993. (g) Fleming, J. T.; Waddell,
P. G.; Probert, M. R.; Clegg, W.; Higham, L. J. Eur. J. Inorg. Chem. 2017, 2837−2844. (h)
Cheng, K.-Y.; Wang, S.-C.; Chen, Y.-S.; Chan, Y.-T. Inorg. Chem. 2018, 57, 3559−3567. (i)
Arai, T.; Sato, K.; Nakamura, A.; Makino, H.; Masu, H. Sci. Rep. 2018, 8, 837.
6. (a) Yu, H.-B.; Hu, Q.-S.; Pu, L. J. Am. Chem. Soc. 2000, 122, 6500−6501. (b) Ma, L.; Jin,
R.-Z.; Lü, G.-H.; Bian, Z.; Ding, M.-X.; Gao, L.-X. Synthesis 2007, 2461−2470.
7. Jozic, D.; Bourenkow, G.; Bartunik, H.; Scholze, H.; Dive, V.; Henrich, B.; Huber, R.; Bode,
W.; Maskos, K. Structure 2002, 10, 1097−1106.
8. Gotthard, G.; Hiblot, J.; Gonzalez, D.; Elias, M.; Chabriere, E. PLoS One 2013, 8, e77995.
9. Attri, P.; Venkatesu, P.; Kumar, A. J. Phys. Chem. B 2010, 114, 13415−13425.
10. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J.
R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.;
Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.;
Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini,
F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski,
V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda,
R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Throssell, K.; Montgomery, Jr., J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.
J.; Brothers, E. N.; Kudin, K. N. Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand,
J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.;
Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16, revision A.03;
Gaussian, Inc.: Wallingford CT, 2016.
Chapter 2: Synthesis and Characterization of Macrocyclic Multinuclear Ni(II) and Zn(II) Complexes
48
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
49
Chapter 3. Synthesis of Cyclic Carbonates from Epoxides and CO2
3.1. Abstract:
The catalytic activities of multinuclear Ni(II) and Zn(II) complexes were studied for the
conversion of epoxides and CO2 into cyclic carbonates in the presence or absence of a co-
catalyst. Both Ni(II) and Zn(II) complexes exhibited appreciable catalytic activity and only 0.1
mol% catalyst loading provided 97% and 70% isolated yields of the product at 120 °C for Ni(II)
and Zn(II) complexes, respectively without a co-catalyst. The catalytic activity of Ni(II)
complex was higher than that of Zn(II) complex, and it provided a modest enantioselectivity
as well.
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
50
3.2. Results and Discussion
CO2 is a promising C1-building block as an alternative to petroleum-based chemicals, and
catalysts for CO2 fixations have been developed extensively.1 For example, synthesis of cyclic
carbonates from epoxides and CO2 has been actively studied.2 Cyclic carbonates are raw
materials of polycarbonates and polyurethanes. A multitask catalyst for these CO2 fixations
have not been reported, and its development presents a significant challenge. In view of the
quite unique static and dynamic structures of the Zn(II) and Ni(II) complexes 2 and 3, it was
decided to investigate the latent catalytic activity of 2 and 3.
Table 1. Synthesis of Cyclic Carbonate 7a from Styrene Oxide (6a) and CO2a
aConditions: 6a (2.0 mmol), CO2 (1.7 MPa), cat. (amount indicated above), co-cat. (3 mol %). bTetrabutylammonium chloride (TBAC), bromide (TBAB), and iodide (TBAI). cIsolated yield.
dEquilibrium mixture of 3–5. The amounts (mol %) are based on 3. eAfter four-time recycling of the
catalyst. fAfter nine-time recycling of the catalyst.
entry cat. X (mol %)
co-cat.b temp (°C)
time (h)
yield (%)c
1 2 2 TBAC 50 12 15 2 2 2 TBAB 50 12 59 3 2 2 TBAI 50 12 73 4 3d 2 TBAC 50 12 31 5 3d 2 TBAB 50 12 68 6 3d 2 TBAI 50 12 95 7 3d 2 – 50 12 16 8 – 2 TBAI 50 12 11 9 2 0.1 – 120 24 70 10 3d 0.1 – 120 24 97 11 Zn(OAc)2·2H2O 2 – 120 24 0 12 Ni(OAc)2·4H2O 2 – 120 24 0 13e 2 2 – 120 24 99 14f 3d 1 – 120 24 97
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
51
In the context of the ongoing research for CO2 fixations,3 these metal complexes were tested
for the synthesis of cyclic carbonate 7a from CO2 and epoxide 6a (Table 1). The combinations
of 2 or 3 (2 mol %) and tetrabutylammonium halide (TBAX) were screened at 50 °C under
solvent-free conditions (entries 1–6), expecting that the metal ions and halide anions act as a
Lewis acid and a nucleophile, respectively. The simultaneous use of complex 2 or 3 and TBAI
yielded 7a in high yield (73–95%, entries 3 and 6). The reaction did not proceed significantly
in the presence of either metal complex alone or TBAI alone (entries 7 and 8). The substrate
scope of 3 and TBAI was broad; styrene oxides, glycidyl ethers, and hexene oxide 6b−i were
efficiently converted into the corresponding cyclic carbonates (Scheme 1).
Scheme 1. CO2 Fixation of Epoxides 6b–i Using Ni(II) Complex 3
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
52
Table 2. Influence of Temperature and Amount of Catalyst on Cyclic Carbonate Formation
aEquilibrium mixture of 3–5. The amounts (mol %) are based on 3.
Interestingly, 2 and 3 with only 0.1 mol % loading worked well without a co-catalyst at 120
°C to produce 7a in high yields (Table 1 (entries 9 and 10) and Table 2 (entries 5 and 11)). By
contrast, Zn(OAc)2 and Ni(OAc)2 hydrates showed no catalytic activity (Table 1, entries 11
and 12). These results suggest a catalytic mechanism specific to 2 and 3. The counter anion or
ligand such as OH– and AcO–, or HCO3– generated by the reaction of OH– with CO2,4 might
act as a nucleophile, and the inner metal ion in 2 and 3 might act as a Lewis acid; the inner Zn
ions of 2 are likely to provide a vacant site by the partial dissociation of the AcO bridge, while
the inner Ni ion of 3 seems to act as a Lewis acid after loss of a H2O molecule. In addition, the
catalysts were recyclable without lowering catalytic activity at least over five cycles (Table 1,
entries 13 and 14 and Figure 1).
entry cat. X (mol %)
temp (°C)
1H NMR conversion (%)
isolated yield (%)
1 2 2 80 62 60 2 2 2 100 99 98 3 2 2 120 99 97 4 2 0.2 120 92 90 5 2 0.1 120 73 70 6 3a 1.3 80 23 22 7 3a 1.3 100 69 65 8 3a 1.3 120 100 96 9 3a 1 120 100 98
10 3a 0.5 120 100 97 11 3a 0.1 120 100 97 12 3a 0.05 120 99 96 13 3a 0.02 120 69 68 14 3a 0.01 120 72 69
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
53
Figure 1. Recycle performance of Ni(II) complex 3.
Epoxide 6a was kinetically resolved in the presence of 3 and TBAI (Table 3, entry 1). The
reaction proceeded to give (S)-7a with 21% ee and (R)-6a with 16% ee at a 44% conversion
(kS/kR = s value = 1.8). This result suggests that the macrocyclic structure was retained to some
degree during the reactions.
Table 3. Kinetic Resolution of 6a with Ni(II) Complex 3
aConversion calculated from c = ee(7)/(ee(6) + ee(7)). bIsolated yield. cCalculated from s = ln[1 − c(1
+ ee(7))]/ln[1 − c(1 – ee(7))].
0
20
40
60
80
100
1 2 3 4 5 6 7 8 9 10
isol
ated
yie
ld (%
)
number of cycles
entry co-cat. (mol %) conv.a (%)
% yieldb (% ee) sc
7a 6a
1 TBAI 44 39 (21) 34 (16) 1.8
2 TBAB 25 21 (20) 49 (7) 1.6
3 TBAC 8 6.5 (20) 67 (2) 1.5
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
54
The reaction pathway for the synthesis of cyclic carbonate 7a from epoxide 6a and CO2
catalyzed by 3 is tentatively proposed in Scheme 2.
Scheme 2. Plausible Catalytic Cycle for the Synthesis of Cyclic Carbonate 7a from Epoxide 6a and
CO2 Catalyzed by 3
At first, the apical H2O of the inner Ni is replaced with an epoxide molecule. The activated
epoxide is ring-opened through the nucleophilic attack of X– anion. Then, CO2 insertion
generates a carbonate anion. Finally, the intramolecular SN2 reaction produces the cyclic
carbonate.
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
55
3.3. Experimental Section
3.3.1. General procedure for the synthesis of cyclic carbonates 7
A mixture of epoxide 6 (2.0 mmol), catalyst (0.1–2 mol%), and TBAX (0–3 mol%) was
stirred at reaction temperature under CO2 (1.7 MPa) for reaction time. To the reaction mixture
was added CHCl3, and the mixture was washed with H2O, dried over Na2SO4, and concentrated
to give a residue. The residue was purified by silica gel column chromatography to afford cyclic
carbonate 7. Cyclic carbonates 7a5, 7b6, 7c7, 7d8, 7e9, 7f5, 7g6, 7h6, and 7i10 were characterized
according to the literature.
7a: 1H NMR (400 MHz, CDCl3) δ 4.35 (t, J = 8.2 Hz, 1H), 4.80 (t, J = 8.6 Hz, 1H), 5.67 (t,
J = 8.0 Hz, 1H), 7.36–7.38 (m, 2H), 7.42–7.47 (m, 3H).
7b: 1H NMR (400 MHz, CDCl3) δ 4.30 (t, J = 8.2 Hz, 1H), 4.80 (t, J = 8.4 Hz, 1H), 5.65 (t,
J = 7.8 Hz, 1H), 7.31 (d, J = 8.0 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H).
7c: 1H NMR (400 MHz, CDCl3) δ 4.32 (t, J = 8.2 Hz, 1H), 4.90 (t, J = 8.4 Hz, 1H), 5.80 (t,
J = 8.0 Hz, 1H), 7.57 (d, J = 8.8 Hz, 2H), 8.32 (d, J = 8.8 Hz, 2H).
7d: 1H NMR (400 MHz, CDCl3) δ 1.21 (t, J = 7.2 Hz, 3H), 3.58 (q, J = 6.5 Hz, 2H), 3.63
(d, J = 3.6 Hz, 1H), 3.67 (dd, J = 4.2, 11.0 Hz, 1H), 4.39 (dd, J = 6.2, 8.6 Hz, 1H), 4.49 (t, J =
8.2 Hz, 1H), 4.77–4.81 (m, 1H).
7e: 1H NMR (400 MHz, CDCl3) δ 0.93 (t, J = 6.8 Hz, 3H), 1.31–1.54 (m, 4H), 1.64–1.73
(m, 1H), 1.77–1.84 (m, 1H), 4.07 (t, J = 7.8 Hz, 1H), 4.52 (t, J = 8.0 Hz, 1H), 4.66–4.73 (m,
1H).
7f: 1H NMR (400 MHz, CDCl3) δ 4.15 (dd, J = 4.0, 10.4 Hz, 1H), 4.25 (dd, J = 4.2, 10.4
Hz, 1H), 4.54 (dd, J = 6.0, 8.0 Hz, 1H), 4.62 (t, J = 8.6 Hz, 1H), 5.00–5.06 (m, 1H), 6.91 (d, J
= 8.4 Hz, 2H), 7.02 (t, J = 7.2 Hz, 1H), 7.31 (t, J = 7.8 Hz, 2H).
7g: 1H NMR (400 MHz, CDCl3) δ 4.10 (dd, J = 3.6, 10.4 Hz, 1H), 4.21 (dd, J = 3.8, 10.6
Hz, 1H), 4.51 (dd, J = 5.8, 8.6 Hz, 1H), 4.61 (t, J = 8.8 Hz, 1H), 4.99–5.04 (m, 1H), 6.83 (d, J
= 8.4 Hz, 2H), 7.25 (d, J = 9.2 Hz, 2H).
7h: 1H NMR (400 MHz, CDCl3) δ 3.77 (s, 3H), 4.10 (dd, J = 1.6, 10.4 Hz, 1H), 4.18 (dd, J
= 4.2, 10.6 Hz, 1H), 4.53 (dd, J = 6.0, 8.0 Hz, 1H), 4.60 (t, J = 8.4 Hz, 1H), 4.97–5.02 (m, 1H),
6.84 (s, 4H).
7i: 1H NMR (400 MHz, CDCl3) δ 4.24 (dd, J = 3.6, 10.8 Hz, 1H), 4.37 (dd, J = 3.8, 10.6
Hz, 1H), 4.56 (dd, J = 6.0, 8.8 Hz, 1H), 4.67 (t, J = 8.4 Hz, 1H), 5.06–5.11 (m, 1H), 6.98–7.03
(m, 2H), 8.21–8.25 (m, 2H).
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
56
3.3.2. Kinetic resolution of styrene oxide (6a)
A mixture of epoxide 6a (2.0 mmol), Ni(II) complex 3 (0.6 mol%), and TBAI (1 mol%) was
stirred at 30 °C under CO2 (1.7 MPa) for 18 h. To the reaction mixture was added CHCl3, and
the mixture was washed with H2O, dried over Na2SO4, and concentrated to give a residue. The
residue was purified by silica gel column chromatography to afford cyclic carbonate 7a and
unreacted 6a. The enantiomeric purity of 6a was determined by GC with chiral column (Varian,
CP-cyclodextrin--2,3,6-M-19 column, 0.25 mm 25 m, Inj. 250 °C, Col. 75 °C, Det. 220
°C, (R) 38.2 min, (S) 40.5 min), and that of 7a was determined by HPLC with chiral column
(Daicel, Chiralcel OD-H, hexane/i-PrOH = 4:1, 0.5 mL/min, 220 nm, (R) 27.1 min, (S) 33.7
min).
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
57
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
X : parts per Million : Proton
7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6
7.47
87.
473
7.46
87.
464
7.45
67.
451
7.44
67.
438
7.43
47.
431
7.42
67.
423
7.38
87.
378
7.37
27.
367
7.26
0
5.70
05.
679
5.66
0
4.82
64.
804
4.78
3
4.37
24.
350
4.33
1
2.94
1.94
1.00
1.02
1.02
abun
danc
e0
1.0
2.0
X : parts per Million : Proton
8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0
7.43
97.
418
7.31
67.
296
7.26
0
5.67
35.
654
5.63
4
4.82
14.
801
4.77
9
4.32
34.
302
4.28
2
2.36
2.20
1.06
1.00 1.04
3.3.3. 1H NMR spectra
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
58
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
X : parts per Million : Proton
8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3
8.33
58.
313
7.57
67.
554
7.26
0
5.82
65.
806
5.78
6
4.92
34.
901
4.88
1
4.33
74.
317
4.29
6
2.00
1.98
1.01 1.05
1.02
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
X : parts per Million : Proton
5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1
4.81
94.
813
4.80
94.
804
4.79
84.
793
4.78
84.
782
4.77
3
4.51
44.
494
4.47
34.
409
4.39
34.
387
4.37
2
3.68
83.
678
3.66
13.
650
3.63
23.
623
3.59
53.
582
3.56
23.
546
1.22
31.
205
1.18
73.
16
2.21
1.05
1.05
1.04
1.01
1.00
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
59
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
X : parts per Million : Proton
4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8
4.73
64.
723
4.71
74.
703
4.69
94.
685
4.68
04.
666
4.54
44.
523
4.50
4
4.08
94.
071
4.05
0
1.84
51.
840
1.82
11.
808
1.78
71.
773
1.73
01.
717
1.70
41.
679
1.66
91.
657
1.64
31.
545
1.46
81.
435
1.42
51.
409
1.39
01.
374
1.35
01.
336
1.31
8
0.94
70.
930
0.91
3
4.28
3.00
1.01
1.00
1.00
0.95
0.94
abun
danc
e0
1.0
2.0
3.0
4.0
X : parts per Million : Proton
7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1
7.33
27.
314
7.29
37.
260
7.03
87.
019
7.00
26.
924
6.90
3
5.06
15.
051
5.04
75.
041
5.03
75.
031
5.02
65.
022
5.01
65.
007
4.64
44.
623
4.60
14.
562
4.54
74.
542
4.52
7
4.26
24.
252
4.23
64.
225
4.17
24.
162
4.14
64.
136
2.03
2.00
1.07
1.06
1.01 1.05
1.01
0.99
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
60
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
X : parts per Million : Proton
7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0
7.26
07.
237
6.84
56.
824
5.04
65.
037
5.03
15.
026
5.02
25.
015
5.01
15.
006
5.00
14.
992
4.63
14.
609
4.58
74.
530
4.51
54.
508
4.49
4
4.22
94.
220
4.20
34.
193
4.12
04.
111
4.09
44.
085
2.04
2.01
1.06
1.02
1.00 1.01
1.02
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
X : parts per Million : Proton
7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6
7.26
0
6.84
4
5.02
65.
016
5.01
15.
006
5.00
14.
995
4.99
14.
985
4.98
04.
970
4.62
34.
601
4.58
14.
546
4.53
14.
526
4.51
1
4.20
14.
190
4.17
44.
164
4.11
14.
107
4.08
54.
081
3.77
1
4.00
3.01
1.01 1.04
1.01
1.001.
09
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
61
abun
danc
e0
1.0
2.0
3.0
4.0
X : parts per Million : Proton
8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1
8.25
88.
250
8.24
58.
233
8.22
78.
219
7.26
0
7.03
17.
027
7.01
97.
014
7.00
87.
001
6.99
56.
987
5.11
95.
110
5.10
45.
096
5.08
85.
079
5.07
45.
065
4.68
94.
669
4.64
74.
566
4.55
14.
544
4.52
94.
392
4.38
24.
365
4.35
64.
260
4.25
14.
233
4.22
4
2.032.07
1.08
1.05 1.05
1.02
1.02
Chapter 3: Synthesis of Cyclic Carbonates from Epoxides and CO2
62
3.4. References
1. For recent reviews, see: (a) Maeda, C.; Miyazaki, Y.; Ema, T. Catal. Sci. Technol. 2014, 4,
1482–1497. (b) Song, Q.-W.; Zhou, Z.-H.; He, L.-N. Green Chem. 2017, 19, 3707–3728. (c)
Gui, Y.-Y.; Zhou, W.-J.; Ye, J.-H.; Yu, D.-G. ChemSusChem 2017, 10, 1337–1340. (d) Janes,
T.; Yang, Y.; Song, D. Chem. Commun. 2017, 53, 11390–11398.
2. For recent reviews, see: (a) Martín, C.; Fiorani, G.; Kleij, A. W. ACS Catal. 2015, 5,
1353−1370. (b) Lang, X.-D.; He, L.-N. Chem. Rec. 2016, 16, 1337−1352. (c) Alves, M.;
Grignard, B.; Mereau, R.; Jerome, C.; Tassaing, T.; Detrembler, C. Catal. Sci. Technol.
2017, 7, 2651−2684. (d) Shaikh, R. R.; Pornpraprom, S.; D’Elia, V. ACS Catal. 2018, 8,
419−450.
3. For selected papers, see: (a) Ema, T.; Miyazaki, Y.; Shimonishi, J.; Maeda, C.; Hasegawa, J.
J. Am. Chem. Soc. 2014, 136, 15270−15279. (b) Maeda, C.; Taniguchi, T.; Ogawa, K.; Ema,
T. Angew. Chem., Int. Ed. 2015, 54, 134−138. (c) Maeda, C.; Shimonishi, J.; Miyazaki, R.;
Hasegawa, J.; Ema, T. Chem. Eur. J. 2016, 22, 6556−6563. (d) Takaishi, K.; Okuyama, T.;
Kadosaki, S.; Uchiyama, M.; Ema, T. Org. Lett. 2019, 21, 1397−1401.
4. (a) Ema, T.; Fukuhara, K.; Sakai, T.; Ohbo, M.; Bai, F.-Q.; Hasegawa, J. Catal. Sci. Technol.
2015, 5, 2314−2321. (b) Roshan, K. R.; Palissery, R. A.; Kathalikkattil, A. C.; Babu, R.;
Mathai, G.; Lee, H.-S.; Park, D.-E. Catal. Sci. Technol. 2016, 6, 3997−4004. (c) Rocha, C.
C.; Onfroy, T.; Pilmé, J.; Nowicki, A. D.; Roucoux, A.; Launay, F. J. Catal. 2016, 333,
29−39.
5. Ema, T.; Miyazaki, S.; Koyama, Y.; Yano, Y.; Sakai, T. Chem. Commun. 2012, 48, 4489–
4491.
6. Ema, T.; Yokoyama, M.; Watanabe, S.; Sasaki, S.; Ota, H.; Takaishi, K. Org. Lett. 2017, 19,
4070–4073.
7. Iwasaki, T.; Kihara, N.; Endo, T. Bull. Chem. Soc. Jpn. 2000, 73, 713–719.
8. Maeda, C.; Sasaki, S.; Ema, T. ChemCatChem 2017, 9, 946–949.
9. Huang, J.-H.; Shi, M. J. Org. Chem. 2003, 68, 6705–6709.
10. Wu, S.; Zhang, Y.; Wang, B.; Elageed, E. H. M.; Ji, L.; Wu, H. Gao, G. Eur. J. Org. Chem.
2017, 753–759.
Chapter 4: N-Formylation and N-Methylation of Amines
63
Chapter 4. N-Formylation and N-Methylation of Amines 4.1. Abstract
Temperature-switched N-formylation/N-methylation of amines with CO2 and hydrosilane
was studied. Zn(II) complex showed excellent catalytic activity and selectivity for N-
formylation and N-methylation of amines with CO2 in the presence of PhSiH3 under solvent-
free conditions. The reaction of N-methylaniline with CO2 and PhSiH3 in the presence of only
0.5 mol % catalyst at 30 oC provided N-formylated product in 99% yield, while the reaction at
100 oC gave N-methylated product predominantly.
Chapter 4: N-Formylation and N-Methylation of Amines
64
4.2. Results and Discussion
Because N-functionalized amines are intermediates of various chemicals such as drugs, N-
functionalization of amines with CO2 and hydrosilane have been actively studied.1,2 It was
expected that 2 and 3 might show catalytic activities for other CO2 fixations as well. First,
Zn(II) complex 2 was used as a catalyst for the N-functionalization of N-methylaniline (8a) in
the presence of CO2 (1 atm, balloon). Initial experiments were performed to find out the
suitable reaction conditions (Table 1). 0.5 mol% Zn(II) complex 2 was found to be enough to
obtain the successful conversion of 8a into 9a under solvent-free conditions. Among the silanes
examined, phenylsilane showed the best performance. Next, N-formylation and N-methylation
of amines with CO2 and phenylsilane1,2 (Table 2) were investigated.
Table 1. Screening of Experimental Conditions for N-Functionalization of N-Methylaniline (8a)
aDetermined by 1H NMR using mesitylene as an internal standard.
entry cat. (Y mol%) silane (X equiv) temp (°C)
time (h) yield (%)a 9a 10a
1 2 (1.0) Ph2SiH2 (1.5) 30 20 11 3 2 2 (1.0) Ph3SiH (1.5) 30 20 0 0 3 2 (1.0) Ph2MeSiH (1.5) 30 20 0 0 4 2 (1.0) PhSiH3 (1.5) 30 20 76 4 5 2 (0.5) PhSiH3 (1.5) 30 20 80 2 6 2 (0.1) PhSiH3 (1.5) 30 20 59 trace 7 2 (0.5) PhSiH3 (2.0) 30 24 99 0
Chapter 4: N-Formylation and N-Methylation of Amines
65
Delightfully, N-methylformanilide (9a) was obtained with complete selectivity at 30 °C
(99%, Table 1 (entry 7) and Table 2 (entry 1)). In contrast, N,N-dimethylaniline (10a) was
obtained preferentially at 100 °C (60%, Table 2, entry 3). The selectivity for 9a or 10a was
independent of the amount of phenylsilane (Table 2, entry 2) and controlled by temperature.
Ni(II) complex 3 showed much lower catalytic activity than 2 (Table 2, entries 4 and 5),
probably because the Ni(II) ions were reduced to Ni(0) during the reaction. Zn(OAc)2·2H2O
was a poor catalyst (Table 2, entries 6 and 7). When 9a was used as a substrate at 100 °C, 10a
was not obtained, but 9a was recovered (Table 2, entry 8). This result indicates that 9a is not
an intermediate leading to 10a.
Table 2. N-Formylation and N-Methylation of N-Methylaniline (8a)a
aConditions: 8a (0.25 mmol), CO2 (1 atm, balloon), cat. (0.5 mol % of 8a), PhSiH3 (amount indicated
above), 24 h. bDetermined by 1H NMR using mesitylene as an internal standard. cEquilibrium mixture
of 3–5. The amounts (mol %) are based on 3. dZn(OAc)2·2H2O (2.5 mol %). e9a was used as a substrate.
entry cat. temp (°C)
X (equiv) yield (%)b 9a 10a
1 2 30 2 99 0 2 2 30 6 97 0 3 2 100 6 9 60 4 3c 30 2 15 0 5 3c 100 6 0 21 6 Zn(OAc)2·2H2Od 30 2 0 0 7 Zn(OAc)2·2H2Od 100 6 0 10 8e 2 100 6 – 0
Chapter 4: N-Formylation and N-Methylation of Amines
66
Catalyst 2 was applicable to other aromatic amines 8b–f (Scheme 1). Although several
examples of chemoselective N-formylation/N-methylation were reported,2 the method using 2
has the following advantages: (1) catalyst loading is low (0.5 mol %), (2) the reaction proceeds
in no solvent under the CO2 pressure of 1 atm, and (3) chemoselectivity is controlled by only
temperature.
Scheme 1. N-Functionalization of Amines 8b–f with Zn(II) Complex 2a
aIsolated yield. bPhSiH3 (6 equiv) was used. cDetermined by 1H NMR using mesitylene as an
internal standard.
Chapter 4: N-Formylation and N-Methylation of Amines
67
The reaction pathway for the 2-catalyzed N-functionalization is tentatively proposed in
Figure 1. Initially, the inner Zn2 moiety of 2 is reduced to hydride complex 2H.3 Insertion of a
CO2 molecule gives formate 2OCHO. Subsequent reaction with phenylsilane gives silylformate
at 30 °C, and further successive reactions with phenylsilane take place at 100 °C to give
methoxysilane species. Silylformate and methoxysilane react with 8a to afford 9a and 10a,
respectively. DFT calculations support 2H and 2OCHO as plausible intermediates (Figure 2).
Figure 1. Proposed pathway for N-functionalization of 8a. Ecalcd values are relative energies
based on 2OH + CO2 + PhSiH3.
Chapter 4: N-Formylation and N-Methylation of Amines
68
Figure 2. DFT-optimized structures of Zn(II) complexes 2H and 2OCHO at the B3LYP/6-31G(d) level for the H, C, N, and O atoms and at the B3LYP/LanL2DZ level for the Zn atoms.
Chapter 4: N-Formylation and N-Methylation of Amines
69
4.3. Experimental Section
4.3.1. General procedure for N-formylation/N-methylation of amines 8
Catalyst (0.5 mol % of 8) was put in a dry two-necked flask (10 mL), and then amine 8 (0.25
mmol) was added. A CO2 balloon (1 atm) was attached to the flask, and the flask was quickly
evacuated and filled with CO2. The reaction mixture under CO2 (1 atm) was stirred at reaction
temperature for 10 min to make a clear solution, and PhSiH3 (62 L, 0.5 mmol, 2 equiv) or
(185 L, 1.50 mmol, 6 equiv) was added dropwise. The reaction mixture was stirred for 24 h
or 48 h. The yield was determined by using mesitylene as an internal standard, or the product
was purified by silica gel column chromatography (hexane/EtOAc (3:1)).
N-formylated products 9a,4 9b,5 9c,5 9d,6 and 9e7 and N-methylated products 10a,4 10b,4
10c,4 10d,8 10e,9 and 10f10 were characterized according to the literature.
9a: 1H NMR (400 MHz, CDCl3) δ 3.32 (s, 3H), 7.16–7.18 (m, 2H), 7.26–7.29 (m, 1H),
7.39–7.43 (m, 2H), 8.48(s, 1H).
9b: 1H NMR (400 MHz, CDCl3) δ 3.27 (s, 3H), 3.82 (s, 3H), 6.94 (d, J = 16.0 Hz, 2H), 7.11
(d, J = 12.8 Hz, 2H), 8.34 (s, 1H).
9c: 1H NMR (400 MHz, CDCl3) δ 3.19 (s, 3H), 7.09–7.14 (m, 2H), 7.33–7.41 (m, 2H), 8.45
(s, 1H).
9d: 1H NMR (400 MHz, CDCl3) δ 3.30 (s, 3H), 7.04–7.06 (m, 2H), 7.50–7.54 (m, 2H), 8.46
(s, 1H).
9e: 1H NMR (400 MHz, CDCl3) δ 4.42 (dt, J = 1.4, 5.6 Hz, 2H), 5.16–5.23 (m, 2H), 5.80–
5.90 (m, 1H), 7.18–7.20 (m, 2H), 7.26–7.30 (m, 1H), 7.38–7.42 (m, 2H), 8.01 (s, 1H).
9f: 1H NMR (400 MHz, CDCl3) δ 0.89 (t, J = 7.2 Hz, 3H), 1.51–1.61 (m, 2H), 3.78 (t, J =
7.4 Hz, 2H), 7.16–7.18 (m, 2H), 7.27–7.31 (m, 1H), 7.39–7.43 (m, 2H), 8.38 (s, 1H).
10a: 1H NMR (400 MHz, CDCl3) δ 2.95 (s, 6H), 6.72–6.77 (m, 3H), 7.26 (t, J = 9.2 Hz,
2H).
10b: 1H NMR (400 MHz, CDCl3) δ 2.87 (s, 6H), 3.76 (s, 3H), 6.76–6.78 (m, 2H), 6.83–
6.86 (m, 2H).
10c: 1H NMR (400 MHz, CDCl3) δ 2.92 (s, 6H), 6.65 (d, J = 8.8 Hz, 2H), 7.18 (d, J = 8.0
Hz, 2H).
10d: 1H NMR (400 MHz, CDCl3) δ 2.92 (s, 6H), 6.60 (d, J = 8.8 Hz, 2H), 7.31 (d, J = 8.8
Hz, 2H).
10e: 1H NMR (400 MHz, CDCl3) δ 2.94 (s, 3H), 3.93 (dt, J = 1.6, 5.2 Hz, 2H), 5.13–5.19
Chapter 4: N-Formylation and N-Methylation of Amines
70
(m, 2H), 5.80–5.89 (m, 1H), 6.69–6.74 (m, 3H), 7.21–7.26 (m, 2H).
10f: 1H NMR (400 MHz, CDCl3) δ 0.92 (t, J = 7.6 Hz, 3H), 1.56–1.65 (m, 2H), 2.93 (s, 3H),
3.25–3.33 (m, 2H), 6.65–6.71 (m, 3H), 7.20–7.26 (m, 2H).
Chapter 4: N-Formylation and N-Methylation of Amines
71
4.3.2. 1H NMR spectra
abun
danc
e0
10.0
20.0
X : parts per Million : Proton
7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8
7.28
27.
260
7.23
6
6.77
76.
759
6.75
66.
748
6.74
36.
741
6.72
3
2.95
76.
00
2.91
2.09
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
X : parts per Million : Proton
8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2
8.48
0
7.43
67.
417
7.39
67.
299
7.27
97.
260
7.18
77.
183
7.16
5
3.32
43.
00
2.14
2.03
1.28
1.01
Chapter 4: N-Formylation and N-Methylation of Amines
72
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
X : parts per Million : Proton
7.0 6.0 5.0 4.0 3.0
7.26
06.
864
6.85
86.
846
6.84
16.
833
6.78
96.
766
3.76
8
2.87
46.
00
3.01
2.03
1.89
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
X : parts per Million : Proton
8.8 8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9
8.34
4
7.26
0
7.11
17.
079
6.94
66.
906
3.82
2
3.27
4
3.10
2.05
1.90
0.97
2.99
Chapter 4: N-Formylation and N-Methylation of Amines
73
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
X : parts per Million : Proton
8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2
8.45
5
7.41
97.
401
7.39
57.
384
7.37
97.
371
7.36
77.
350
7.34
57.
332
7.26
07.
142
7.13
57.
127
7.12
17.
111
7.10
57.
097
3.30
63.
11
2.18
2.00
1.09
abun
danc
e0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
X : parts per Million : Proton
7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8
7.26
07.
183
7.16
3
6.65
36.
631
2.92
86.
07
2.17
1.91
Chapter 4: N-Formylation and N-Methylation of Amines
74
abun
danc
e0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
X : parts per Million : Proton
7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8
7.31
37.
291
7.26
0
6.60
66.
584
2.92
46.
00
2.06
1.94
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
X : parts per Million : Proton
8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0
8.45
3
7.54
37.
540
7.53
67.
521
7.51
97.
514
7.50
37.
260
7.06
57.
062
7.04
3
3.29
63.
00
2.27
2.13
1.04
Chapter 4: N-Formylation and N-Methylation of Amines
75
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
X : parts per Million : Proton
8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3
8.49
1
7.42
07.
416
7.40
27.
386
7.38
17.
306
7.30
47.
300
7.28
97.
285
7.26
67.
260
7.20
47.
202
7.19
67.
186
7.18
37.
180
5.90
15.
888
5.87
65.
874
5.86
25.
859
5.84
85.
845
5.83
35.
830
5.81
95.
805
5.23
05.
221
5.21
75.
214
5.20
95.
196
5.19
25.
189
5.18
55.
179
5.17
45.
171
5.16
75.
164
4.43
24.
428
4.42
54.
418
4.41
44.
410
2.18
2.14
2.062.
14
1.05
1.00
1.00
abun
danc
e0
2.0
4.0
6.0
8.0
10.0
X : parts per Million : Proton
7.3 7.2 7.1 7.0 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8
7.26
07.
251
7.24
67.
233
7.22
97.
211
6.74
66.
725
6.70
86.
690
5.89
95.
886
5.87
45.
861
5.85
75.
849
5.84
45.
832
5.81
85.
805
5.19
65.
191
5.18
75.
169
5.16
65.
161
5.15
75.
152
5.14
95.
144
5.14
05.
136
3.93
43.
930
3.92
63.
922
3.91
73.
914
2.94
1
3.003.04
2.23
2.04
2.01
0.98
Chapter 4: N-Formylation and N-Methylation of Amines
76
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
X : parts per Million : Proton
7.0 6.0 5.0 4.0 3.0 2.0 1.0
7.26
07.
245
7.22
47.
206
6.71
16.
691
6.67
16.
654
3.33
03.
292
3.27
43.
254
2.93
3
1.65
41.
635
1.61
61.
598
1.57
91.
560
0.94
60.
926
0.90
8
3.00
3.003.04
2.29
2.26
2.02
abun
danc
e0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
X : parts per Million : Proton
8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0
8.38
1
7.43
37.
428
7.41
57.
399
7.39
47.
316
7.31
37.
301
7.29
77.
278
7.26
07.
186
7.18
27.
178
7.16
4
3.80
23.
783
3.76
5
1.61
01.
592
1.57
41.
554
1.53
61.
517
0.91
10.
893
0.87
53.
00
2.22
2.15
2.05
1.99
1.02
1.01
Chapter 4: N-Formylation and N-Methylation of Amines
77
4.4. References
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Chapter 4: N-Formylation and N-Methylation of Amines
78
List of Publication
79
List of Publication
1. Unexpected Macrocyclic Multinuclear Zinc and Nickel Complexes that Function as
Multitasking Catalysts for CO2 Fixations.
*Takaishi, K.; Nath, B. D.; Yamada, Y.; Kosugi, H.; *Ema, T. Angew. Chem. Int. Ed. 2019,
58, 9984−9988.
List of Oral/Poster Presentations
1. Synthesis and Characterization of Chiral Multinuclear Nickel and Zinc Complexes Involving
Binaphthyl-bipyridyl Moiety.
Kazuto Takaishi, Bikash Dev Nath, Yuya Yamada, Chihiro Maeda, Tadashi Ema
Conference: Chemical Society of Japan (CSJ, Annual Meeting), Tokyo (March, 2018).
Type of Presentation: Oral
2. Self-assembled Multinuclear Ni or Zn Complexes: Structural Model for Some Enzymes. Kazuto Takaishi, Bikash Dev Nath, Yuya Yamada, Chihiro Maeda, Tadashi Ema
Conference: The 12th Bio-related Chemistry Symposium, Osaka (September, 2018).
Type of Presentation: Poster
3. Macrocyclic Multinuclear Ni and Zn Complexes as Effective Catalysts for CO2 Fixation.
Bikash Dev Nath, Yuya Yamada, Hiroyasu Kosugi, Chihiro Maeda, Kazuto Takaishi, Tadashi Ema
Conference: 15th International Symposium on Applied Bioinorganic Chemistry (ISABC15),
Nara (June, 2019).
Type of Presentation: Poster
List of Publication
80
Acknowledgement
81
Acknowledgement
The studies presented in this thesis entitled “Novel Macrocyclic Multinuclear Ni(II) and
Zn(II) Complexes for Catalytic CO2 Conversions” have been carried out under the supervision
of Professor Dr. Tadashi Ema at the Division of Applied Chemistry, Graduate School of
Natural Science and Technology, Okayama University during 2016–2019.
I would like to express my sincerest gratitude to Professor Dr. Tadashi Ema for his overall
guidance and valuable discussions throughout this work. I owe a very important debt to my co-
supervisor, Dr. Kazuto Takaishi for his constant suggestion and overall support during the
course of this work. Special thanks to Dr. Shigeki Mori (Ehime University) and Dr. Hiromi
Ota (Okayama University) for X-ray analysis.
I am thankful to Dr. Chihiro Maeda and all the lab members for their continuous support. I
express my special gratitude to Mr. Yuya Yamada and Mr. Hiroyasu Kosugi for their active
assistance. I would like to offer my special thanks to all other Professors, Associate Professors
and Assistant Professors of the Division of Applied Chemistry, Graduate School of Natural
Science and Technology, Okayama University.
I acknowledge the financial support from JSPS KAKENHI Grant No. JP16H01030 for
Precisely Designed Catalysts with Customized Scaffolding and a Grant for Promotion of
Sciene and Technology in Okayama Prefecture by MEXT. I also acknowledge the financial
support from Japanese Government (Monbukagakusho: MEXT) Scholarship Program (Oct,
2016 ~ Sep, 2019).
Finally, I would like to express my heartiest gratitude to my mother Mrs. Rani Dev Nath,
my brothers Mr. Biplob Kumer Debnath and Mr. Bipul Chandra Debnath, and my wife Mrs.
Mitali Debnath for their constant assistance and encouragement.
September, 2019 Bikash Dev Nath
Division of Applied Chemistry
Graduate School of Natural Science and Technology