novel macrocyclic multinuclear ni(ii) and zn(ii) complexes

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



3.4. References 62

Chapter 4. N-Formylation and N-Methylation of Amines

4.1. Abstract 63



4.4. References 77

List of Publication 78

Acknowledgement 79

Chapter 1: General Introduction

1

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)


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-


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


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


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.


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


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


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).


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


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.


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.


13

Scheme 16. (a) Synthesis of Cyclic Carbonates and (b) N-Functionalization of Amines


14

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54. Cammarota, R. C.; Vollmer, M. V.; Xie, J.; Ye, J.; Linehan, J. C.; Burgess, S. A.; Appel,

A. M.; Gagliardi, L.; Lu, C. C. J. Am. Chem. Soc. 2017, 139, 14244–14250.

55. Ye, J.; Cammarota, R. C.; Xie, J.; Vollmer, M. V.; Truhlar, D. G.; Cramer, C. J.; Lu, C. C.;

Gagliardi, L. ACS Catal. 2018, 8, 4955–4968.

56. (a) Motokura, K.; Takahashi, N.; Kashiwame, D.; Yamaguchi, S.; Miyaji, A.; Baba, T.

Catal. Sci. Technol. 2013, 3, 2392–2396. (b) Beydoun, K.; vom Stein, T.; Klankermayer,

J.; Leitner, W. Angew. Chem. Int. Ed. 2013, 52, 9554–9557. (c) Frogneux, X.; Jacquet, O.;

Cantat, T. Catal. Sci. Technol. 2014, 4, 1529–1533. (d) Beydoun, K.; Ghattas, G.; Thenert,

K.; Klankermayer, J.; Leitner, W. Angew. Chem. Int. Ed. 2014, 53, 11010–11014. (e)

Santoro, O.; Lazreg, F.; Minenkov, Y.; Cavallob, L.; Cazin, C. S. J. Dalton Trans. 2015,

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Organometallics 2015, 34, 763–769. (g) Nguyen, T. V. Q.; Yoo, W.-J.; Kobayashi, S.

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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.


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


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.


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).


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


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).


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


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


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.


28

Figure 8. VT 1H NMR spectra of Zn(II) complex 2 (600 MHz, CDCl3).


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


30

Figure 9. X-ray crystal structures of Ni(II) complexes 3–5. Solvent molecules are omitted for clarity.


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).


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]+


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


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.


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,


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.


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


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





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





40

2.3.6. 1H NMR and 13C NMR spectra

1H NMR spectrum of (R)-13 (400 MHz, CDCl3)


41

13C NMR spectrum of (R)-13 (100 MHz, CDCl3)


42

1H NMR spectrum of (R)-1 (400 MHz, CDCl3)

OHOH

N

N

N

N

(R)-1


43

13C NMR spectrum of (R)-1 (100 MHz, CDCl3)


44

1H NMR spectra of Zn(II) complex 2 (400 MHz, CDCl3)


45

13C NMR spectra of Zn(II) complex 2 (100 MHz, CDCl3)


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,


47

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.


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.


50


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


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


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


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


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.


55


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).


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).


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


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


58

abun

danc

e0

1.0

2.0

3.0

4.0

5.0


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


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


59

abun

danc

e0

1.0

2.0

3.0

4.0

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 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


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


60

abun

danc

e0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0


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


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


61

abun

danc

e0

1.0

2.0

3.0

4.0


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


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.


64


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


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


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.


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.


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.


69


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


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).


71

4.3.2. 1H NMR spectra

abun

danc

e0

10.0

20.0


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


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


72

abun

danc

e0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0


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


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


73

abun

danc

e0

1.0

2.0

3.0

4.0

5.0

6.0


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


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


74

abun

danc

e0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0


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


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


75

abun

danc

e0

1.0

2.0

3.0

4.0

5.0

6.0

7.0


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

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416

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386

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306

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300

7.28

97.

285

7.26

67.

260

7.20

47.

202

7.19

67.

186

7.18

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180

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5.87

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874

5.86

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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

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14

1.05

1.00

1.00

abun

danc

e0

2.0

4.0

6.0

8.0

10.0


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


76

abun

danc

e0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0


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

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635

1.61

61.

598

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560

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926

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2.26

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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


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

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316

7.31

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301

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77.

278

7.26

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186

7.18

27.

178

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4

3.80

23.

783

3.76

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1.61

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592

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554

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517

0.91

10.

893

0.87

53.

00

2.22

2.15

2.05

1.99

1.02

1.01


77

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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

novel macrocyclic multinuclear ni(ii) and zn(ii) complexes

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