Palladium-Based Catalysts Supported by Unsymmetrical XYC–1 Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of Octinoxate Utilizing the Mizoroki–Heck Reaction

A Journal of

Accepted Article

Title: Palladium-based Catalysts Supported by Unsymmetrical XYC-1

Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of

Octinoxate Utilizing Mizoroki-Heck Reaction

Authors: Ankur Maji, Ovender Singh, Sain Singh, Aurobinda Mohanty,

Pradip K Maji, and Kaushik Ghosh

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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000211

Link to VoR: http://dx.doi.org/10.1002/ejic.202000211

10.1002/ejic.202000211

European Journal of Inorganic Chemistry

FULL PAPER

Palladium-based Catalysts Supported by Unsymmetrical XYC^-1

Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of

Octinoxate Utilizing Mizoroki-Heck Reaction

Ankur Maji_,Ovender Singh, Sain Singh, Aurobinda Mohanty, Pradip K Maji*^[b]Kaushik Ghosh*^[a]

Dedication ((optional))

Abstract: A series of new unsymmetrical (XYC^-1type) palladacycles

forming reactions are essential and frequently exploited in

(C1-C4) were designed and synthesized with simple anchoring

ligands 2-((2-(4-methoxybenzylidene)-1-

L^1-4(L¹H=

phenylhydrazinyl)methyl)pyridine, N,N-dimethyl-4-((2-

L²H=

phenyl-2-(pyridin-2-ylmethyl)hydrazono)methyl)aniline, L³H= N,N-

diethyl-4-((2-phenyl-2-(pyridin-2 ylmethyl)hydrazono)methyl)

syntheses of pharmaceuticals and organic materials on both in

laboratories as well as in industry.^[2]Several functionalized

organometallic palladium complexes have been reported for

H

various

reactions

namely

hydrogenations,^[3]

hydrophosphinations,^[4]C–H functionalization,^[5]Hiyama

reaction,^[6]Suzuki–Miyaura reactions,^[7]Sonogashira coupling

reactions^[8]Mizoroki–Heck reactions^[9]and Buchwald–Hartwig

reactions^[10]etc.

aniline and L⁴H= 4-(4-((2-phenyl-2-(pyridin-2ylmethyl)hydrazono)

methyl)phenyl)morpholine H= dissociable proton). Molecular

structure of catalysts (C1-C4) were further established by single X-

ray crystallographic studies. The catalytic performance of

palladacycles (C1-C4) was explored with the direct Csp²−H

arylation of imidazoles with aryl halides derivatives. These

pallacycles were also applied for investigating of Mizoroki-Heck

reactions with aryl halides and acrylate derivatives. During catalytic

cycle in situ generated Pd(0) nanoparticles were characterized by

XPS, SEM and TEM analysis and possible reaction pathways were

proposed. The catalyst was employed as a pre-catalyst for the

gram-scale synthesis of octinoxate which is utilized as a UV-B

sunscreen agent.

The arylation of C–H bond of heterocycles, such as imidazole

derivatives are imperative as they construct the building blocks

of various biological and pharmaceutical compounds.^[11]The

selective C-5 arylation of 1-methyl-1H-imidazole or 1,2-

dimethyl-1H-imidazole with aryl halides to obtain 5-arylated 1-

methyl-1H-imidazole or 5-arylated 1,2-dimethyl-1H-imidazole

derivatives respectively have been established by using

palladium-based catalysts.^[12]Though these metal catalysts

efficiently perform the arylation of imidazoles, very often harsh

reaction conditions, strong bases and expensive phosphine-

based ligands^[13]and NHC ligands^[14]were utilized for

satisfactory conversion. Moreover, the stability of catalyst in

the air as well as thermal stability, are significant concerns,

which enforces the usage of high catalyst loading (more than

0.5 mol%) in many reactions. Recently Liu and co-workers

reported bis(imino)acenaphthene (BIAN)-supported palladium

complexes. Further, these complexes effectively catalyzed

cross-coupling reaction of (hetero)aryl bromides with azoles at

low palladium loading of 0.5 mol%.^[12b]Similar cross-coupling

reaction was also reported by Lee and co-workers however

they have utilized palladium carbene complexes featuring

NHC/amidate/phenoxide donor atoms as catalyst (2 mol% of

catalyst loading) in their reactions. Investigation of the

literature indicated that palladium complexes derived from

pincer-type ligands might be productive and robust catalysts

for such direct cross-coupling reaction.^[15]

Introduction

Organic syntheses and chemical processing require highly

effective (high turnover number i.e. TON) transition-metal

based catalysts because it allows the use of minimum amounts

of toxic or might be precious transition metals.^[1]

Organometallic palladium complex catalyzed C-C bond-

[a]

[b]

A. Maji, O. Singh, S. Singh, A. Mohanty, Prof. K. Ghosh

Department of Chemistry, Indian Institute of Technology Roorkee

Roorkee 247667, Uttarakhand, India. E-mail: ghoshfcy@iitr.ernet.in ,

kaushik.ghosh@cy.iitr.ac.in

Homepage:https://www.iitr.ac.in/departments/CY/pages/People+Facu

lty+ghoshfcy.html

Dr. P. K. Maji

Department of Polymer and Process Engineering,Indian Institute of

Technology Roorkee Saharanpur Campus, SaharanpurUP 247001,

India, E-mail: pradip.fpt@ iitr.ac.in

Homepage:https://www.iitr.ac.in/departments/PPE/pages/People+Pra

dip_K__Maji.html

Supporting information for this article is given via a link at the end of

the document.((Please delete this text if not appropriate))

10.1002/ejic.202000211

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potential hemilability and thermal stability of the catalyst and

exhibits better catalytic activity.^[20]Unsymmetrical pincer

palladacycles are comparatively novel, however, the synthesis

of their respective ligands often possess difficulty than their

symmetrical ligands.^[9d]

Imidazole derivatives exhibit a broad spectrum of biological

and pharmacological activities.^[21]Trifenagre having 5-arylated

imidazole moiety is a potent arachidonate cyclooxygenase

(COX) inhibitor. 5-arylated imidazole derivatives is an

important scaffold present several biologically active

molecules. For example, SB203580 is a potent anti-cancer

agent. Eprosartan, which also contain 5-arylated imidazole ring

is utilised as an angiotensin II receptor antagonist.^[22]

Octinoxate (2-ethylhexyl-4-methoxycinnamate), which is an

essential organic molecule utilized for UV-B sunscreen agent

(shown in Figure 1).^[9a]

Scheme 1. Schematic representation of cross-coupling reaction.

On the other hand, palladium-catalyzed Mizoroki-Heck

reaction of aryl halides with alkenes is another pathway for C–

C

bond-forming processes in synthetic and medicinal

chemistry.^[9]Palladacycles are effectively used in the Mizoroki-

Heck reaction.^[9a,16]The performance of these metal catalysts

are useful in reaction, but sometimes punitive reaction

conditions and costly phosphine-based ligands^[17]are essential

for satisfactory conversion. Uozumi and co-workers reported

NNC-pincer based palladium complex as catalyst for Mizoroki-

Heck reaction of aryl halides (iodides, bromides, or

chlorides).^[9a]The present challenge for palladium-catalyzed

coupling reactions demands novel catalysts with high-

performance utilizing environmentally benign and sustainable

reaction conditions. These reports prompted us to study

Mizoroki-Heck reaction exploring newly synthesized

palladacycles with a catalyst loading of as low as 0.001 mol%.

In recent years organometallic palladium-based catalysts were

explored as a pre-catalyst for several C-H bonds activating

reactions.^[9a,23]In most of these cases, Pd(0) nanoparticles

were active species for such organic conversion. The

anchoring ligands to palladium play important role in the

stabilization of Pd(0) nanoparticles.^[7d,9a,24]Most of the ligands

in this regard are combination of phosphorous, sulphur and

selenium based organometallic complexes, however, NNC

based pincer-type ligands were less explored for such Pd(0)

nanoparticles based organic transformation.^[7d,24]These types

of in-situ generated Pd(0) nanoparticles familiarized a new era

of C5 arylation of imidazole derivatives.

Hence investigation of literature reports clearly expresses that

palladacycles supported by pincer-type ligand would be

interesting to explore novel reactivity studies. Herein we report

the synthesis of palladacycles (C1-C4) and their

characterization by IR, NMR, ESI-MS and single-crystal X-ray

diffraction. These complexes were utilized for C5 arylation of

imidazole derivatives as well as Mizoroki-Heck reactions with

aryl halide (bromides, or chlorides). A total of 24 and 36

substrates were tested for C5 arylation of imidazole derivatives

and Mizoroki-Heck reactions respectively. With the knowledge

and lessons gained in the present study, we tried to synthesize

octinoxate (2-ethylhexyl-4-methoxycinnamate), which is an

essential organic molecule utilized for UV-B sunscreen agent.

They are useful as homogeneous catalysts towards C5

arylation of imidazole derivatives and Mizoroki-Heck reactions.

In the present study, we have also tried to propose a possible

Figure 1. Some of biological active scaffolds.

Screening of literature, only a single report where palladium-

based catalyst efficiently catalyzed C-5 arylation of imidazole

(catalyst loading 2.5 mol%) derivatives as well as Mizoroki-

Heck (catalyst loading 0.5 mol%) reaction.^[18]However, pincer

based comparatively less explored for such C-5 arylation of

imidazole derivatives as well as Mizoroki-Heck reaction

(Scheme 1). Pincer ligands are in general symmetrical XC⁻¹X

type (X = neutral donor) however, unsymmetrical ligand frames

such as XC⁻¹Y and XYC⁻¹(X,Y= neutral donor) are also known

in the literature.^[19]Pd–C σ-bond plays a crucial role in terms of

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reaction mechanism. Generation of Pd(0) nanoparticles during

the catalytic reaction was authenticated by XPS analysis, TEM

analysis, SEM analysis, hot filtration test and Hg, PPh₃poising

test.

and 371.2356 (L⁴H-H^-)⁺ion for L⁴H respectively (shown in

supporting information Figure S24-S27).

Catalysts design

Palladacycles (C1C4) were synthesized using Na₂[PdCl₄] and

neutral ligand L¹H, L²H, L³H and L⁴H in the equimolar ratio in

dichloromethane and methanol solvent at room temperature

(Scheme 2). Coordination of ligands with the metals was

analyzed based on IR, NMR and ESI spectral studies. During

IR spectral studies coordination of the nitrogen to the metal

center resulted in a shift in the stretching frequency of ν_(–HC=N)

in the range of 1576-1588 cm^-1. (shown in supporting

information Figure S7-S10). It indicates the possible ligation to

metal centers in all the palladium complexes. The ¹H-NMR

signal of –CH₂ group for all the catalysts (C1-C4) was shifted

from 5.24 ppm to 4.81 ppm due to the metal-ligand

corporation. Also, the doublet peak of pyridine center shifted

from 8.63 ppm to 9.37 ppm.^[25c](depicted in supporting

information Figure S18-S23). ESI-MS analysis of all the

catalysts was recorded in acetonitrile shows molecular ion

peak with the loss of a chloride ion. Positive mode ESI‐MS

spectra in acetonitrile exhibited m/z peaks 422.0542 [Pd(L¹)-

Cl^-]⁺for C1, 435.0786 [Pd(L²)-Cl^-]⁺for 463.1169 C2, 463.1169

[Pd(L³)-Cl^-]⁺for C3 and 477.1173 [Pd(L⁴)-Cl^-]⁺for C4

respectively. (depicted in supporting information Figure S28-

S31).

Scheme 2. Schematic representation of synthesized palladacycles (C1-

C4)

Results and discussion

Synthesis of ligands

Ligands L¹H-L⁴H were synthesized by condensation of

corresponding benzaldehyde derivatives and 2-(1-2-((1-

phenylhydrazinyl)methyl)pyridine

in

equimolar

ratio

respectively in methanol.^[25]After 8 hours, white-colored

precipitate of ligands L¹H-L⁴H was obtained and characterized

by several spectroscopic techniques. The IR spectra of the

ligands show strong vibration observed at 1590–1596 cm⁻¹in

the ligands corresponding to ν_C=Nof Schiff bases (shown in

supporting information Figure S3-S6).^[25b]The ¹H-NMR spectra

of the ligands show the signals in the expected regions.^[25b]The

¹H-NMR signal of -CH₂- group for all the ligand (L¹H-L⁴H)

shows one singlet around 5.24 ppm (shown in supporting

information Figure S11-S17). Positive mode ESI‐MS spectra in

acetonitrile exhibited m/z peaks 318.1998 (L¹H+H⁺)⁺ion for

L¹H, 330.2189 (L²H) ⁺for L²H, 359.2348 (L³H+H⁺)⁺ion for L³H

Structural studies

Even though the analytical and spectral data gave some ideas

about the molecular formulae of the complexes, they do not

provide precise coordination. Yellow-colored crystals of

complexes C1-C4 were obtained by slow evaporation of

Figure 2. ORTEP plot (30% probability level) of (a) palladacycles C1 and (b) palladacycles C2. Hydrogen atoms are not shown for clarity.

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Figure 3. ORTEP plot (30% probability level) of (a) palladacycles C3 and (b) palladacycles C4. Hydrogen atoms are not shown for clarity.

complexes in dichloromethane and hexane mixture (1:4) at

room temperature within a week. The solid-state structure of

complexes C1-C4 was determined by single X-ray

crystallography. The crystal data and structure refinement

parameters for complexes C1-C4 are summarized in Tables

S2-S3 and selected bond lengths and bond angles are

depicted in Tables S4-S7. The ORTEP view of complexes C1-

C4 given in Figures 2–3. The structures confirm that the

ligands L¹H- L⁴H are coordinated to the palladium center in the

targeted NNC fashion and another site co-ordinates to chloride.

A distortion from square planar geometry, probably due to the

uncommon combination of 5- and 6-membered rings in the

metal coordination sphere. Each structure consists of a

palladium center surrounded by two nitrogens donor’s atom

one carbon belonging to tridentate ligands (L¹H-L⁴H) along

with a monodentate chloride to complete a geometry best

described as distorted square planar. The bond distances

involving the donor atoms in L¹HL⁴H with the Pd(1)N3

2.007(10) (Å), 2.006(10) (Å), 2.004(4) (Å) and 1.993(6) (Å)

which is lower compared to the reported by Sun and

cowokers^[9d]but higher than Bhattacharya and co-workers.^[7c]

The bond distances Pd(1)N(1) 2.178(9) (Å) and 2.162(10) (Å),

2.165(11) (Å) and 2.180(6) (Å) respectively for complexes C1-

C4 is lower than the Dominguez and co-workers^[26]and higher

than Sun and co-workers.^[9d]The bond distances Pd(1)C(19)

are2.002(12) (Å), 2.001(11) (Å), 1.993(9) (Å), and 1.997(6) (Å)

respectively for complex C1- C4 which are higher than Solan

and co-workers^[27]and comparable with Dominguez and co-

workers^[26]This strong Pd−C bond would play a better

anchoring role to palladium. The bond lengths of Pd1–Cl1

ranged between 2.307(4) (Å) for C1, 2.334(4) (Å) for C2,

2.320(6) (Å) for C3 and 2.322(7) (Å) for C4 in following the

related CNN pincer palladacycles.^[9d,28]Complexes (C2-C4)

display unusual short-range C–H/π, and halogen

bonding interactions are observed for C2, C3 and C4

with distances of 2.713, 3.123 and 2.713 A˚ respectively,

between adjacent molecules indicative of favorable Van der

Waals interactions which give rise to

a

zigzag

arrangement one-dimensional tape in the solid-state (Shown

in supporting information Figure. S32-34).

C_sp²−H arylation of imidazoles derivatives

Initially, the reaction conditions for the arylation reaction of 4-

bromobenzaldehyde (1c) with 1-methyl-1H-imidazole (2a)

using the C2 catalyst were optimized by varying the

Scheme 3. Optimization of direct C5 arylation of 1-methyl-1H-imidazole

in the presence of palladacycles C2.

concentrations of the catalyst, base, and solvent (Scheme 3,

shown in supporting information Figure S1). When

a

dimethylacetamide (DMA) solution containing 1 mmol of 4-

bromobenzaldehyde, 1 mmol of 1-Methyl-1H-imidazole, 2

mmol of K₂CO₃, 0.03 mmol pivalic acid and 0.05 mol% of

Table 1. Optimization of reaction conditions for direct arylation reaction

Entry

Base

Solvent

% Yield

1

K₂CO₃

Toluene

40

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2

K₂CO₃

NMP

DMF

45

61

occurred in the presence of 0.05 mol% of catalysts to give

isolation of 1-methyl-5-phenyl-1H-imidazole (3aa) 81-90%

yield (Table 2). The arylation of 1-methyl-1H-imidazole with 4-

COCH₃, 4-CHO, 4-CN, 4-NO₂, 4-Cl, and 4-F bromobenzene

afforded the corresponding arylated products good to excellent

yield up to 80-96% (Table 2, 3ab-3ag). Electron-rich

bromobenzene derivatives 4-OMe, 4-Me and 3-OMe also

reacted similarly with 1-methyl-1H-imidazole to obtain the

corresponding products 3ah, 3ai and 3aj in moderate yield

73% to 86% respectively. The possibilities of expanding this

reaction for the synthesis of hetero and sterically hindered

arylation were also explored by reacting 1-methyl-1H-

imidazole with hetero and sterically hindered bromobenzene to

the formation of 3-(1-methyl-1H-imidazol-5-yl)pyridine and 1-

methyl-5-(naphthalen-1-yl)-1H-imidazole moderate yield in the

presence of catalysts (C1-C4) up to 85% yield (Table 2, 3ak

and 3al). The direct arylation substituted imidazole, 1,2-

dimethyl-1H-imidazole with aryl and heteroaryl halides having

various substituents (electron-rich, electron-deficient and

sterically hindered). The C5-monoarylated imidazole was

obtained as the predominant product (yield up to 96%) in the

process catalyzed with C1−C4. (Table 2, 4aa-4al). We also

investigated the direct arylation substituted N-methyl imidazole

and 1,2-dimethyl-1H-imidazole with aryl and heteroaryl

chlorides having various substituents (electron-rich, electron-

deficient and sterically hindered). The C5-monoarylated

imidazole was obtained as the predominant product (yield up

to 79%) in the process catalyzed with C1.

3

K₂CO₃

4

5

6

K₂CO₃

KOH

DMSO

DMA

67

92

60

7

NaOH

DMA)

67

8

9

Na₂CO₃

NaOAc

DMA

85

69

10

11

12

13

14

15

16

KOAc

K₃PO₄

NaHCO₃

K^tOBu

Et₃N

DMA

71

49

47

71

43

K₂CO₃

0^a/ 0^b

20^c

Reaction conditions: C2 (0.05 mol%), 1a (1.0 mmol), 2a (1 mmol), base

(2 mmol), Pivalic acid (0.03 mmol) solvent (2.0 mL), 130 °C, 10 h. ^aIn

absent of catalyst C2. ^bin presence of L²H. ^cIn present of Na₂PdCl₄0.05

mol%.

complex C2 was heated at 130 °C in a sealed tube to give 4-

(1-methyl-1H- imidazol-5-yl)benzaldehyde (3ac) in 92%

isolated yield after column purification (Table 1, entry 5).

A control experiment performed for this reaction in the absence

of catalyst C2 showed no formation of 4-(1-methyl-1H-

imidazol-5-yl)benzaldehyde (Table 1, entry 15). In the

presence of only ligand, no formation 3ac and only in the

presence of Na₂PdCl₄small conversion of 3ac. (Table 1, entry

15, 16). This result shows that the ligand has a crucial role in

the arylation reaction. Among the different bases, K₂CO₃and

Na₂CO₃give rise promising results up to isolated yield 92% and

85%, respectively (Table 1, entry 5, 8). Remarkably, heating of

the reaction mixture containing 0.05 mol% of catalyst C2, 1

mmol of 4-bromobenzaldehyde, 1 mmol of 1-methyl-1H-

imidazole, 2 mmol of K₂CO₃and 0.03 mmol pivalic acid at 130

°C for 10 h, provided 1a in 92% yield. We next performed

different acid additive for arylation of imidazoles reaction.^[29]

Among the different acid additives, pivalic acid found to be

more promising results up to isolated yield 92%. (shown in

supporting information Table S1) To explore the scope of the

arylation reaction, several aromatic bromobenzenes were

examined in the presence of catalysts C1-C4 (Table 2). The

reaction of simple bromobenzene and 1-methyl-1H-imidazole

A comparison of the catalytic properties of C1-C4 reported in

the recent past for direct arylation of aryl halides derivatives

were investigated. Liu and co-workers^[30]reported Pd(II)

complexes derived from bis(imino)acenaphthene-supported

N-heterocyclic carbene (loading 0.5 mol%), which less

effective compare to C1-C4. Lee and co-workers^[31]recently

reported imidazopyridine-based abnormal carbene ligands

based palladium catalyst (catalyst loading 0.5 mol%), which

has less effect. Singh and co-workers^[32]synthesized

N-Heterocyclic carbene amidates ligand-based palladium

complexes, which also less effective. Mao et al^[33]Pd/C as a

the heterogeneous catalyst for direct arylation of imidazoles

derivative catalyst loading 1 mol%. Among the reported

catalysts, the reported catalysts by us are most active,

additionally air-stable Schiff base as anchoring catalysts.

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Table 2. Direct arylation of 1-methyl-1H-imidazole/1,2-dimethyl-1H-imidazole with aryl halides in the presence of catalysts (C1-C4).

C1 87%

C3 92%

C2 91%

C4 95%

a

C1 87%

C3 91%

C2 93%

C4 96%

a

C1 92%

C3 90%

C2 89%

C1 81%

C3 90%

C2 89%

C4 93%

a

C4 86%

a

C1 76%

C1 70%

C1 72%

C1 73%

C1 76%

C3 82%

C2 78%

C1 87%

C3 90%

C2 89%

C1 89%

C3 91%

C2 91%

C1 84%

C3 86%

C2 81%

C4 80%

C4 86%

a

C4 94%

a

C4 94%

a

C1 65%

C1 77%

C1 73%

C1 79%

C3 85%

C2 81%

C4 83%

a

C1 76%

C3 80%

C2 81%

C1 76%

C3 81%

C2 79%

C1 73%

C3 80%

C2 75%

C4 83%

a

C4 85%

a

C1 65%

a

C1 71%

C1 63%

C1 67%

C1 90%

C3 94%

C2 93%

C1 83%

C3 93%

C2 91%

C1 90%

C3 91%

C2 94%

C4 96%

a

C1 88%

C3 93%

C2 91%

C4 89%

a

C4 93%

a

C4 95%

a

C1 73%

C1 79%

C1 77%

C1 88%

C3 94%

C2 91%

C4 96%

a

C1 78%

C3 82%

C2 81%

C4 84%

C1 76%

C3 80%

C2 75%

C4 83%

a

C1 73%

C1 78%

C3 82%

C2 81%

C4 84%

C1 70%

a

C1 67%

C1 80%

C3 84%

C2 83%

C4 87%

C1 76%

C3 80%

C2 75%

C4 83%

C1 78%

C3 83%

C2 81%

C4 86%

C1 80%

C3 84%

C2 83%

C4 87%

a

C1 65%

C1 63%

C1 62%

C1 75%

Reaction conditions Aryl bromide1.00 mmol, 1-methyl-1H-imidazole/ 1,2-dimethyl-1H-imidazole 1 mmol, Pallacycles C1-C4, 0.05 mol %;

PivOH, 0.3 mmol; temperature, 130 °C; reaction time, 8 h; under aerobic conditions. ^aaryl chloride derivatives, catalyst loading C1 0.1 mol%.

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Figure 4. XPS spectra of the 3d level of palladium and deconvolution peaks of the Pd species: experimental light grey), deconvoluted (red), Pd(II) (wine and

dark yellow), Pd(0) (navy, magenta), (a) precatalyst C2 (b) Precatalyst C2 after treatment with K₂CO₃, 4-bromobenzaldehyde with 1-methyl-1H-imidazole in

DMA at 140 ⁰C after 4h.

Probable mechanism

reveals the polycrystalline nature of palladium nanoparticles.

Besides, Pd nanoparticles provide excellent surface-to-volume

ratio, which significantly amplifies the proximity between

reactants and catalyst. This experiment shows that the C1-C4

is pre-catalyst of this catalytic cycle. To confirm the

observations, Hg poisoning test was conducted. Under

optimization reaction condition, in the presence of catalyst C2,

4-bromo benzaldehyde, 1-methyl-1H-imidazole, K₂CO₃and

pivalic acid in DMA solvent, we found [4-(1-methyl-1H-

imidazol-5-yl)benzaldehyde a coupled product 33% after 10 h

in the presence of 1 drop Hg. These results unambiguously

proved a generation of ligandless palladium species which

may be catalytically active species in this reaction. Assembling

of observations from XPS, TEM, Hg poisoning test and

literature, a probable mechanistic pathway can be sketched

out (shown in Scheme 4). Palladium complexes (C1-C4) were

the pre-catalysts which form the palladium(0) species or

palladium(0) clusters in the equilibrium under the reaction

conditions (A'⇄ A'').^[16a,34]Due to the in-situ formation Pd

nanoparticles during the arylation of imidazoles high surface

area of Pd(0) or Pd(0) cluster shown excellent catalytic activity.

Subsequently, oxidative addition of bromobenzene to give rise

the intermediate B. The ligand exchange happens with

potassium salts of pivalic acid provided intermediate C. The

C−H bond (C5) cleavage step 1-methyl-1H-imidazole/1,2-

dimethyl-1H-imidazole with the aid of pivalate generates

intermediate C via CMD transition state^[34,37]which undergoes

reductive elimination give rise to the arylated product and

regenerates Pd(0) intermediate (A).

During the progress of direct arylation reactions, black particles

develop into the surface of the reaction vials. It might be

existing palladacycles (C1-C4) are not real catalysts. In situ

formation of palladium nanoparticles (Pd NPs) has also been

recognized in many cases during the catalytic process.^[34]Thus

reactions of 4-bromobenzaldehyde with 1-methyl-1H-

imidazole in DMA catalyzed with C2 under optimum conditions

have been examined in detail to explain the nature of black

particles produced in situ during the catalytic pathway. To

confirm the same, X-ray photoelectron spectroscopy (XPS)

study has been performed of the catalyst as well as the

reaction mixture of the direct arylation reaction. The surface

compositions of palladium species (shown in Figure 4). 3d

core-level pallidum of complex C2 fitted with two main peaks,

where the Pd 3d5/2 and 3d3/2 peak at 342.9 eV and 337.7 eV

was assignable to the Pd(II) species.^[35]To characterize the

intermediate species generated during direct arylation reaction

XPS analysis was inspected in the presence of catalyst C2.

The dominant Pd 3d5/2 peak shifted to the binding energy at

343.4 eV from 342.9 eV and 3d3/2 peak shifted at 337.9 eV

from and 337.7 eV which could be assigned to new Pd(II)

species. Two different new peaks at 342.6 eV and 337.2 eV

which consigned Pd 3d5/2 and Pd 3d3/2 of Pd(0) species. ^[35,36]

This peak confirms that both Pd(II) and Pd(0) species were

involved during the catalytic cycle. TEM analysis of the reaction

mixture after the reaction in the presence of catalyst C2.

Palladium nanoparticles were observed in the reaction mixture

(Figure 5). From the size distribution curve, the average size of

these nanoparticles was estimated to be 4-5 nm. SAED pattern

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Figure 5. (a) TEM image of NPs obtained respectively during SMC (scale bar 50 and 20 nm). (b)The particle size distribution of spherical Pd nanoparticles

obtained during C_sp2−H arylation of imidazoles. (c) SAED pattern of NPs obtained during the catalysis

Scheme 4. Probable reaction pathway of C-H activation of imidazole derivatives.

Mizoroki-Heck reactions

handling of non-phosphine cyclometalated palladium complexes

are accountable for their universality and rising importance in

catalysis.

We explored the synthesized palladacycles (C1- C2) for Mizoroki-

Heck coupling reactions (Scheme 5). For the optimization of

catalyst, C2 as a model catalyst has been chosen.

Table 3. Optimization of Mizoroki-Heck coupling reaction between

bromobenzene and methyl acrylate in the presence of palladacycles C2.

Scheme 5. Optimization of Mizoroki-Heck coupling in the presence of

palladacycles C2.

Entry

Base

K₂CO₃

NaOAc

Solvent

NMP

% Yield

21

1

2

Nitrogen-based ligands are economical and air-stable, unlike

phosphine-basedligands.^[1b]Simplesynthesis, stabilityandsmooth

NMP

37

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3

Na₂CO₃

NMP

53

92

optimization condition, it has been found that electron-deficient

arenes such as 4-COCH₃, 4-CHO, 4-NO₂, 4 –CN, 4-F, 4-Cl)

bromobenzene (Table 4, 7ac, 7ad, 7af, 7ai-7ak) effectively

converted corresponding cross-coupled product in a higher

yield as well as higher turnover number (TONs) yield up to

91%. However, when electron-rich halo arene 4-OH and 4-CH₃

(Table 4, 7ab, 7ae) introduced, the effectively converted

corresponding cross-coupled product with moderate yield

upto79%. This catalyst also effectively converted 3-NO₂and 2-

NO₂bromobenzene corresponding coupled product good to

moderate yield 70% to 85% (Table 4, 7ag, 7ah). Sterically

hindered 2-napthylbromobenzene gives rise to moderate yield

61% to 69%. Hetraoarene, like 3-bromopyridine, also afforded

good to moderate yield 75%-83% (Table 4, 7al). The coupling

reaction of other haloarenes with tert-butyl acrylate give rise to

good to excellent result (Table 4, 8aa-8ah). When styrene used

reaction with bromobenzenes proceeded smoothly to give the

corresponding stilbenes derivative in good yields. On the other

hand, bromobenzenes containing electron-rich and electron-

poor offer the corresponding stilbene derivatives in moderated

yields. (Table 4, 9aa-9al). The coupling reaction of other hetero-

haloarenes with tert-butyl acrylate give rise to good to excellent

result(Table 4, 10aa-10ac). Mizoroki-Heck reactions of arenes

with aryl chloride derivatives also effective give rise to good to

moderate yield up to yield 73% in the presence of C1. The

catalytic properties of C1-C2 with catalysts reported in the

recent past for the Mizoroki-Heck reactions with aryl halides

derivatives were investigated. Uozumi and co-workers

reported^[38]Pd(II) complexes derived from

4

Et₃N

5

NaOH

KOH

KOAc

Et₃N

NMP

49

6

NMP

43

7

NMP

33

8

DMF

77

9

Et₃N

Toluene

DMSO

NMP

71

10

11

12

Et₃N

75

Et₃N

0^a/0^b

31^c

Et₃N

NMP

Reaction conditions: 1.0 mmol aryl halides, 1.2 mmol arene, 2 mmol

Base, 0.001 mol% Pd(II) C2, 140 °C, 8 h. solvent: 2 mL, ^aIn absent of

catalyst C2. ^bin presence of L²H. ^cIn present of Na₂PdCl₄0.05 mol%.

The most appropriate reaction parameters have been found when

the coupling was performed in N-methyl-2-pyrrolidone (NMP) at

140 °C in the presence of triethylamine (Et₃N) for 8 h resulting in a

92% conversion of methyl acrylate (Table 3, entry 4). Some other

solvent like dimethylformamide (DMF), toluene and dimethyl

sulfoxide (DMSO) also examined similar conditions, but these all

proved less effective (Table 3, entry 8-10). Control experiments

revealed that the Mizoroki-Heck coupling reaction does not

proceed in the presence of only ligand (L²H) and absent of C2

(Table 4, entry 11). Commonly available palladium(II)-salt

Na₂PdCl₄were also found to be ineffective (Table 4, entries 12).

These control experiments suggest that the catalyst has an

essential role in such coupling reaction. As expected, using more

activated arenes led to higher conversions. Based on the

promising results obtained for the Mizoroki-Heck coupling of

bromobenzene with methyl acrylate, it has been decided to

explore the potential of C1 and C2 for the coupling reaction of

other haloarenes with methyl acrylate, tert-butyl acrylate and

styrene, the results are summarized in Table 4. Under the

Table 4. Mizoroki-Heck coupling of C1 and C2 with functionalized aryl halides and acrylate derivatives and styrene.

C1 88%

C2 91%

C1 72%

C2 75%

C1 76%

C2 80%

C1 88%

C2 91%

C1 68%^a

C1 70%^a

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C1 78%

C2 79%

C1 87%

C2 89%

C1 70%

C2 75%

C1 81%

C2 85%

C1 61%^a

C1 66%^a

C1 69%^a

C1 87%

C2 89%

C1 84%

C2 86%

C1 80%

C2 83%

C1 67%

C2 71%

C1 65%^a

C1 89%

C2 91%

C1 81%

C2 79%

C1 81%

C2 85%

C1 89%

C2 93%

C1 69%^a

C1 71%^a

C1 79%

C1 89%

C2 81%

C1 88%

C2 90% C1 80%

C2 85%

C1 65%

C1 91%

C2 70%

C2 95%

C1 68%^a

C2 91%

C1 70%

C2 75%

C1 82%

C2 87%

C1 69%^a

C1 73%^a

C1 72%

C2 74%

C1 82%

C2 86%

C1 71% C2 75%

C1 81%

C2 86%

C1 71%^a

C1 68%^a

C1 86%

C2 89%

C1 79%

C2 81%

C1 76%

C2 80%

C1 67%

C2 70%

C1 67% ^a

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C1 75%

C2 81%

C1 77%

C2 79%

C1 80%

C2 83%

Reaction conditions: 1.0 mmol aryl halides, 1.2 mmol arene, 2 mmol Et₃N, 0.001 mol% Pd(II) cat., 140 °C, 8 h. ^aaryl chloride derivatives.

NCN (0.0001 mol% catalyst loading) in the reaction mixture;

however, in this report, only iodoarene derivatives were utilized.

Sun and co-workers recently reported unsymmetrical CNN-

palladacycles ligands^[9d](catalyst loading 0.002 mol%) though

in this report, bromoarene and iodoarene derivatives were

exploited, less effective compare to C1-C2.

Uozumi and co-workers synthesized NNC-Pincer ligand-based

palladium^[9a]complexes (catalyst loading 10 mol ppm), which

comparatively effective than C1-C2. However, they utilized

bromoarene, iodoarene chloroarene derivatives. Xiao and co-

workers (N,C,N)^[9c]pincers having a bis(azole) ligand-based

palladium complexes (catalyst loading 0.1 mol%) for coupling

reaction utilized bromoarene, iodoarene derivatives. However,

with C1 and C2, Mizoroki-Heck reactions in good yield are

achieved with 0.001 mol% loading of catalyst at 140 ^oC in 8 h.

Additionally, chlorobenzene derivatives also effectively

coupled with different acrylate derivatives in the presence of

catalyst C2 (catalyst loading 0.001 mol%).

Probable reaction pathway

The catalytic pathway of the Mizoroki-Heck reactions. For the

establishment of the reaction cycle, we did Hg poisoning test,

under the standard reaction condition, the addition of mercury

(1 drop) to the reaction mixture, after 8 hours, when the yield

of 4aa was 15%, significantly impeded the reaction. This

reaction exposes that the ligandless monomeric palladium

species and or palladium cluster may be palladium

nanoparticles involves in the reaction mixture. Next, we

Figure 6. XPS spectra of the Pd 3d level and deconvolution peaks of the

Pd species: deconvoluted (red), Pd(II) (magenta and navy), Pd(0) (dark

yellow and wine) precatalyst C2 after treatment with Et₃N, arene and

bromobenzene in NMP at 140 ⁰C after 8h

Figure 7. (a) TEM image of NPs obtained respectively during SMC (scale bar 50). (b)The particle size distribution of spherical Pd nanoparticles obtained during )

precatalyst C2 after treatment with Et₃N, methyl acrylate and bromobenzene in NMP at 140 ⁰C after 8h.

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Scheme 6. Probable mechanism of Mizoroki-Heck reactions

Scheme 7. Gram-scale synthesis of octinoxate.

performed XPS analysis of the reaction mixture under the

standard condition in the presence of catalyst C2 (shown in

Figure 6). We found four peaks at 336.0 eV and 337.8 eV,

341.2 and 342.9 eV, which assigned of Pd(0) and Pd(II) are

present in the reaction mixture.^[36,37]Further, TEM analysis of

the reaction mixture in the presence of palladium complexes

C2 we observed palladium nanoparticle. (shown in Figure 7).

From the size distribution curve, the average size of these

nanoparticles was estimated to be 3.5 nm to 4.5 nm.^[9a]This

data indicates that the active surface area of the reaction

mixture is very high and showed excellent catalytic activity.

On the above experimental finding and literature under the

elevated temperature and basic reaction conditions,

nanoparticles Pd(0) species are finely tuned of the

reactivity/selectivity of the catalytic reaction by ligands (here

L¹H-L⁴H).^[16,40]

Therefore catalysts C1-C4 are a precursor of the actual

catalytically active species in this reaction. Based on literature

reports and experimental findings at first, the palladium(II)

precatalyst has to be reduced to palladium(0) nanoparticles or

palladium(0) cluster in the equilibrium under the reaction

conditions (I'⇄ I'') to enter the catalytic cycle. After that, the

oxidative addition of bromobenzene occurred and the

formation of intermediate II. Followed by migratory insertion

happens formed intermediate III. Then β-elimination happens

and formed the coupled products and intermediate IV. In the

presence of base regenerate the catalyst Pd(0) or palladium(0)

clusters and continue the reaction cycle. (shown in Scheme 6).

palladacycle (C2) undergoes reduction. It provides

catalytically active Pd(0) complex with the cleavage of the Pd–

bond.^[39]The catalytic efficiencies of these release

a

C

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Gram-scale synthesis of the UV-B sunscreen agent

octinoxate

well as reported literature. These palladacycles are potent

catalysts for the gram-scale synthesis of UV-B sunscreen

agent octinoxate. The successful synthesis of palladacycles

could give inspiration in the development of efficient catalysts

for direct transformation of C-H bond to C-C bond in organic

transformation. Other catalytic studies of these palladacycles

are under progress.

Importantly, the current methodology could be utilized to

directly prepare a gram-scale synthesis of the UV-B sunscreen

agent

octinoxate

(2-ethylhexyl(E)-3-(4methoxyphenyl)

acrylate) (Scheme 7). The reaction of 1-bromo-4

methoxybenzene (10 mmol) and 2-ethylhexyl acrylate (12

mmol) give rise to (2-ethylhexyl(E)-3-(4-methoxyphenyl)

acrylate) with 73% yield in the presence of catalyst C2.

Homogenous and heterogeneous test

Experimental

The reported methods were used for the synthesis of 2-

picolylphenylhydrazine.^[25]All aldehydes, Aryl bromides and

chlorides, 1-methyl-1H-imidazole, 1,2-dimethyl-1H-imidazole,

methyl acrylate, tert-butyl acrylate, styrene K₂CO₃and were

purchased from Avra, Himedia, TCI Chemicals (India) Pvt. Ltd.

Solvents used for spectroscopic studies were HPLC grade and

purified by standard procedures before use. Palladium chloride

was obtained from Arora Matthey, Kolkata, India. Infrared

spectra were recorded as KBr pellets on a Nicolet NEXUS

Aligent 1100 FT–IR spectrometer, using 50 scans and are

reported in cm^–1. Transmission electron microscopy (TEM,

Tecnai G2 20SeTWIN, FEI Netherlands) was used for the

morphological characterization of catalytically active species.

¹H-NMR and ¹³C-NMR spectra were measured with a Bruker

AVANCE 500.13 MHz spectrometer and JEOL 400 MHz

spectrometer, chemical shifts were reported in δ (ppm) units

relative to tetramethylsilane (TMS) as an internal standard.

Proton coupling patterns are described as singlet (s), doublet

(d), triplet (t), quartet (q), multiplet (m), and broad (br). (ESI‐

MS) experiments were performed on a Brüker micrOTOFTM‐

Q‐II mass spectrometer.

To conclude whether the palladacycles is actually working in a

heterogeneous manner, or whether it is merely a reservoir for

more active soluble forms of Pd, various tests were performed.

A hot filtration test confirmed the leaching of palladium species

in both the catalytic reaction. In case of after 1 h, reaction was

filtered and reaction further run additional conversion (from

37% (after 1h) to 88% (10 h) in case of arylation of imidazole

and from 21% (after 1h) to 69% (8 h) in case of Mizoroki-Heck

coupling in the presence of catalyst C2) was measured in the hot

filtration test.^[41]This test suggested that the involvement of a

homogeneous pathway. In the presence of 1 drop Hg,

retardation of the catalytic process also indicated the

palladacycles are a reservoir for more active soluble forms of

Pd. PPh₃poisoning test also conducted for the catalytic

reaction gives rise to cross-coupled 31% and 41% yield of

arylation reaction and Mizoroki-Heck coupling reaction,

respectively. The results suggest that discrete Pd(0)

nanoparticles generated in-situ in the reaction mixture it

behaves like a homogenous catalysts.^[42]

Conclusion

X-ray crystallography

A new family of palladacycles (C1-C4) derive from designed

unsymmetrical XYC^-1type pincer ligands were synthesized and

characterized. These palladacycles were pre-catalysts for the

Csp²−H arylation of imidazoles with aryl halides as well as

Mizoroki-Heck reactions. The reactions offer advantages of

operational simplicity, mild conditions, good to excellent yield,

broad substrate scope low catalyst loading 0.05 mol% for arylation

of imidazoles with aryl bromides (TON up to 1.9x10³) aryl

chlorides bromides (TON up to 7.9x10²) and 0.001 mol% for

Mizoroki-Heck reactions with aryl bromides (TON up to

9.5x10⁴) and with aryl chlorides (TON up to 7.3x10⁴). We tried

to investigate the reaction pathway of the above reactions and

found out the generation of Pd(0) nanoparticles in situ.

Probable mechanisms established based on experimental as

Yellow crystals of C1-C4 were obtained by slow evaporation of

solution from the complexes in dichloromethane and methanol.

The X-ray data collection and processing for complexes were

performed on a Bruker Kappa Apex-II CCD diffractometer by

using graphite monochromated Mo-Kα radiation (λ = 0.71073

Å) at 296 K for C1, 130 K for C2, 296 K for C3 and 293 K for

C4. Crystal structures were solved by direct methods.

Structure solutions, refinement and data output were carried

out with the SHELXTL program. ^[43-45]All non-hydrogen atoms

were refined anisotropically. Hydrogen atoms were placed in

geometrically calculated positions and purified using a riding

model. ORTEP diagrams were generated with the DIAMOND

program. ^[46]

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Synthesis of L¹H

6H). ¹³C-NMR (101 MHz, CDCl₃) δ 156.73, 149.93, 147.96,

137.25, 134.19, 129.25, 127.79, 122.40, 120.88, 120.06,

114.33, 111.61, 52.12, 44.55, 12.68. ESI‐MS: 359.2348

(L³H+H⁺)⁺ion. Yield: 72% Yield: 544.9 mg, 76%.

Synthesis of L⁴H

4-anisaldehyde (0.272 g, 2.00 mmol) and 2-((1-phenyl

hydrazinyl)methyl)pyridine (0.398 g, 2.00 mmol) were

dissolved in 10 mL of methanol. The reaction mixture was

stirred at room temperature. Within 1 h, a white solid began to

separate and stirring was continued for another 3 h. The white

precipitate was filtered, washed thoroughly with methanol,

diethyl ether and then dried in vacuum and recrystallized in

dichloromethane.

L⁴H was prepared by following the procedure described above

for

L¹H,

instead

of

4-anisaldehyde

used

4-

morpholinobenzaldehyde (0.382 g, 2.00 mmol).

Selected IR data: (KBr, ν/cm^-1): 1597 (ν_C=N). Anal. calcd for

C₂₃H₂₄N₄O:C, 74.17; H, 6.49; N, 15.04 found C, 74.09; H, 6.55;

N, 14.78. ¹H NMR (400 MHz, CDCl₃) δ 8.63 (d, J = 5.6 Hz, 1H),

7.56 (t, J = 6.8 Hz, 1H), 7.51 (d, J = 8.8 Hz, 2H), 7.40 – 7.34

(m, 3H), 7.33 – 7.27 (m, 2H), 7.21 – 7.15 (m, 1H), 7.08 (d, J =

7.8 Hz, 1H), 6.92 (d, J = 7.2 Hz, 1H), 6.88 (d, J = 8.8 Hz, 2H),

5.24 (s, 2H), 3.21 – 3.15 (m, 4H), 1.68 (m, 4H). ESI‐MS:

371.2356 (L⁴H-H^-)⁺ion. Yield: 528.9 mg, 71%.

Selected IR data: (KBr, ν/cm^-1): 1590(ν_C=N) Anal. calcd for

C₂₀H₁₉N₃O:C, 75.69; H, 6.03; N, 13.24 found C, 75.57; H, 6.12;

N, 13.15. ¹H-NMR (500 MHz, CDCl₃) δ 8.63 (d, J = 4.2 Hz, 1H),

7.58 – 7.54 (m, 3H), 7.40 – 7.35 (m, 3H), 7.31 (t, J = 8.0 Hz,

2H), 7.20 – 7.16 (m, 1H), 7.08 (d, J = 7.9 Hz, 1H), 6.93 (t, J =

7.2 Hz, 1H), 6.86 (d, J = 8.8 Hz, 2H), 5.25 (s, 2H), 3.79 (s, 3H).

¹³C-NMR (101 MHz, CDCl₃) δ 159.77, 150.03, 147.74, 137.31,

132.87, 129.31, 127.64, 122.52, 120.77, 120.66, 114.62,

114.10, 55.43, 52.27. ESI‐MS: 318.1998 (L¹H+H⁺)⁺ion. Yield:

463.4, 73%.

Syntheses of Complexes C1-C4

0.10 mmol of ligands (L¹H-L⁴H) was stirred in 10 mL

dichloromethane for 15 min. Methanolic solution of Na₂[PdCl₄]

(0.029 g, 0.10 mmol) [Na₂PdCl₄was prepared in situ PdCl₂(0.1

mmol and 6 equivalent NaCl stirred for 1 h)] were added to it.

The mixture was stirred further for 6 h at room temperature.

The yellow color solid formed was collected by filtration and

air-dried overnight to obtain Catalyst C1-C4.

Synthesis of L²H

L²H was prepared by following the procedure described above

for

L¹H,

instead

of

4-anisaldehye

used

4-

(dimethylamino)benzaldehyde (0.298 g, 2.00 mmol)

Selected IR data: (KBr, ν/cm^-1): 1596 (ν_C=N) Anal. calcd for

C₂₁H₂₂N₄: C, 76.33; H, 6.71; N, 16.96 found C, 76.25; H, 6.83;

N, 16.84. ¹H-NMR (500 MHz, CDCl₃) δ 8.63 (d, J = 4.2 Hz, 1H),

7.54-7.50 (m, 3H), 7.40 – 7.36 (m, 3H), 7.30 (t, J = 8.0 Hz, 2H),

7.17 (dd, J = 6.9, 5.2 Hz, 1H), 7.08 (d, J = 7.9 Hz, 1H), 6.90 (t,

J = 7.2 Hz, 1H), 6.68 (d, J = 8.9 Hz, 2H), 5.24 (s, 2H), 2.95 (s,

6H). ¹³C-NMR (101 MHz, CDCl₃) δ 156.64, 150.59, 149.95,

147.90, 137.29, 133.97, 129.27, 127.52, 124.84, 122.44,

120.86, 120.19, 114.38, 112.35, 52.16, 40.59. ESI‐MS:

330.2189 (L²H)⁺ion. Yield: 508.9 mg, 77%.

The single crystals of each of the two complexes were obtained

from a mixture of dichloromethane: hexane (1:3)

Catalyst C1

Selected IR data: (KBr, ν/cm^-1): 1587 (ν_C=N). Anal. calcd for

C₂₀H₁₈ClN₃OPd: C, 52.42; H, 3.96; N, 9.17 found C, 52.49; H,

3.87; N, 9.25. ¹H NMR (400 MHz, CDCl₃) δ 9.36 (d, J = 5.4 Hz,

1H), 8.12 (s, 1H), 7.66 – 7.61 (m, 2H), 7.25 (s, 1H), 7.22 – 7.17

(m, 2H), 7.10 (s, 2H), 7.04 (d, J = 8.4 Hz, 2H), 6.87 (t, J = 6.8

Hz, 1H), 6.61 (d, J = 9.4 Hz, 1H), 4.81 (s, 2H), 3.89 (s, 3H). ¹³

C

NMR (101 MHz, CDCl₃) δ 173.69, 163.53, 161.37, 160.81,

152.81, 151.18, 150.86, 148.30, 133.62, 129.69, 122.50,

120.96, 117.91, 112.25, 61.52, 55.68. ESI‐MS: 422.0542

[Pd(L¹)-Cl^-]⁺ion. Yield: 30.7 mg, 67%.

Synthesis of L³H

L³H was prepared by following the procedure described above

for L¹H, instead of 4-anisaldehyde used 4-(diethylamino)

benzaldehyde (0.354 g, 2.00 mmol).

Catalyst C2

Selected IR data: (KBr, ν/cm^-1): 1595 (ν_C=N). Anal. calcd for

C₂₃H₂₆N₄: C, 77.06; H, 7.31; N, 15.63 found C, 77.15; H, 7.23;

N, 15.51. ¹H-NMR (500 MHz, CDCl₃) δ 8.63 (d, J = 4.5 Hz, 1H),

7.54 (t, J = 8.5 Hz, 1H), 7.49 (d, J = 8.8 Hz, 2H), 7.40 – 7.35

(m, 3H), 7.30 (t, J = 7.9 Hz, 2H), 7.19 – 7.15 (m, 1H), 7.08 (d,

J = 7.9 Hz, 1H), 6.90 (t, J = 7.2 Hz, 1H), 6.63 (d, J = 8.8 Hz,

2H), 5.24 (s, 2H), 3.35 (q, J = 7.1 Hz, 4H), 1.15 (t, J = 7.1 Hz,

Catalyst C2 was prepared by following the procedure

described above for catalyst C1, instead of L¹H used L²H.

Selected IR data: (KBr, ν/cm^-1): 1576 (ν_C=N). Anal. calcd for

C₂₁H₂₁ClN₄Pd: C, 53.52; H, 4.49; N, 11.89 found C, 53.41; H,

1

4.34; N, 11.76. H NMR (400 MHz, CDCl₃) δ 9.36 (d, J = 7.5

Hz, 1H), 7.95 (s, 1H), 7.60 (t, J = 7.6 Hz, 1H), 7.47 (d, J = 2.5

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1

Hz, 1H), 7.10 (t, J = 8.0, 5.2 Hz, 3H), 7.05– 7.03 (m, 2H), 6.83

(t, J = 7.1 Hz, 1H), 6.32 (d, J = 11.1 Hz, 1H), 4.81 (s, 2H), 3.10

(s, 6H) ESI‐MS: 435.0786 [Pd(L²)-Cl^-]⁺ion. Yield: 30.6 mg,

65%.

(20/1) as an eluent. H NMR and ¹³C NMR data are depicted

in supporting information Figures S42-S87.

Catalysed products

1-methyl-5-phenyl-1H-imidazole^[32](3aa) Yellow solid. Yield

128.1 mg 81% (Catalyst C1), 140.8 mg 89% (Catalyst C2)

142.4 mg 90% (Catalyst C3),136.0 mg 86% (Catalyst C4); 1H

¹H-NMR (500 MHz, CDCl₃) δ 7.50 (s, 1H), 7.42 (t, J = 7.3 Hz,

2H), 7.36 (dd, J = 13.9, 7.4 Hz, 3H), 7.08 (s, 1H), 3.65 (s, 3H).

¹³C-NMR (126 MHz, CDCl₃) δ 139.07, 133.46, 129.84, 129.84,

128.74, 128.45, 128.10, 127.91, 32.54.

Catalyst C3

Catalyst C3 was prepared by following the procedure

described above for catalyst C1, instead of L¹H used L³H.

Selected IR data: (KBr, ν/cm^-1): 1588 (ν_C=N). Anal. calcd for

C₂₃H₂₅ClN₄Pd: C, 55.32; H, 5.05; N, 11.22 found C, 55.21; H,

1

5.22; N, 11.12. H NMR (400 MHz, CDCl₃) δ 9.36 (d, J = 7.5

1-(4-(1-methyl-1H-imidazol-5-yl)phenyl)ethanone^[32](3ab)

Light yellow solid. Yield 174.2 mg 87% (Catalyst C1), 182.2 mg

91% (Catalyst C2) 184.2 mg 92% (Catalyst C3), 190.2 mg 95%

(Catalyst C4); ¹H-NMR (500 MHz, CDCl₃) δ 8.00 (d, J = 7.6 Hz,

2H), 7.54 (s, 1H), 7.49 (d, J = 7.6 Hz, 2H), 7.19 (s, 1H), 3.71

(s, 3H), 2.61 (s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ 197.42,

140.13, 136.09, 134.44, 129.34, 128.86, 128.01, 32.90, 26.64.

4-(1-methyl-1H-imidazol-5-yl)benzaldehyde^[32](3ac) Off-

white solid. Yield 171.3 mg 92% (Catalyst C1), 165.7 mg 89%

(Catalyst C2) 167.6 mg 90% (Catalyst C3), 173.1 mg 93%

(Catalyst C4);¹H-NMR (500 MHz, CDCl₃) δ 10.02 (s, 1H), 7.93

(d, J = 7.6 Hz, 2H), 7.56 (d, J = 7.2 Hz, 3H), 7.22 (s, 1H), 3.73

(s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ 191.54, 140.42, 135.80,

135.31, 132.28, 130.20, 129.78, 128.29, 32.98.

4-(1-methyl-1H-imidazol-5-yl)benzonitrile^[32](3ad) Off-white

solid. Yield 159.4 mg 87% (Catalyst C1), 170.4 mg 93%

(Catalyst C2) 166.7 mg 91% (Catalyst C3), 175.7 mg 96%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.70 (d, J = 8.6 Hz,

2H), 7.55 (s, 1H), 7.50 (d, J = 8.6 Hz, 2H), 7.19 (d, J = 0.6 Hz,

1H), 3.70 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 140.64, 134.51,

132.70, 131.77, 129.96, 128.41, 118.64, 111.36, 33.00.

1-methyl-5-(4-nitrophenyl)-1H-imidazole^[32](3ae) Yellow

solid. Yield 176.8 mg 87% (Catalyst C1), 180.8 mg 89%

(Catalyst C2) 182.9 mg 90% (Catalyst C3), 191 mg 94%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 8.29 (d, J = 8.8 Hz,

2H), 7.58 (s, 2H), 7.55 (s, 1H), 7.26 (s, 1H), 3.75 (s, 3H). ¹³C-

NMR (101 MHz, CDCl₃) δ 147.03, 140.94, 136.39, 131.46,

130.44, 128.36, 124.30, 33.12.

Hz, 1H), 7.95 (s, 1H), 7.60 (t, J = 7.6 Hz, 1H), 7.47 (d, J = 2.5

Hz, 1H), 7.16 (dd, J = 8.0, 5.2 Hz, 3H), 7.11 – 7.03 (m, 4H),

6.81 (t, J = 6.9 Hz, 1H), 6.32 (d, J = 11.1 Hz, 1H), 4.81 (s, 2H),

3.46 (d, J = 7.1 Hz, 4H), 1.22 (t, J = 7.1 Hz, 6H). ¹³C NMR (101

MHz, CDCl₃) δ 172.94, 160.02, 152.93, 151.15, 148.94,

148.82, 138.05, 130.51, 129.29, 126.84, 126.10, 123.89,

122.53, 119.53, 117.26, 107.25, 61.34, 44.78, 12.89. ESI‐MS

463.1169 [Pd(L³)-Cl^-]⁺ion. Yield: 34.5 mg 69%.

Catalyst C4

Catalyst C4 was prepared by following the procedure

described above for catalyst C1, instead of L¹H used L⁴H.

Selected IR data: (KBr, ν/cm^-1): 1576 (ν_C=N) %. Anal. calcd for

C₂₃H₂₃ClN₄OPd: C, 53.82; H, 4.52; N, 10.91 found C, 53.65; H,

4.71; N, 10.84. ¹H NMR (400 MHz, DMSO) δ 7.91 (dt, J = 15.5,

7.6 Hz, 1H), 7.76 – 7.54 (m, 4H), 7.52 – 7.44 (m, 2H), 7.38 (dd,

J = 15.5, 7.4 Hz, 3H), 7.32 – 7.22 (m, 1H), 7.22 – 7.09 (m, 1H),

7.06 (t, J = 7.6 Hz, 1H), 7.01 – 6.86 (m, 1H),5.42 (s, 2H) 3.46-

3.34 (m, 4H), 1.80 (s, 4H). ESI‐MS: 477.1173 [Pd(L⁴)-Cl^-]⁺

ion.Yield: 33.9 mg, 66%.

General procedure for direct arylation reaction

An oven-dried sealed tube (10 mL) was charged with 1-methyl-

1H-imidazole (1.0 mmol) or 1,2- dimethyl-1H-imidazole 1.0

mmol), aryl halide (1.0 mmol), K₂CO₃(2.0 mmol), pivalic acid

(0.30 mmol), 0.05 mol% catalyst (one of C1−C4), and 2 mL of

DMA. The flask was placed pre-heated oil bath at 130 °C under

aerobic conditions. The mixture was cooled to room

temperature and added 10 mL of water for quenched the

reaction. This mixture was extracted with dichloromethane (3

× 10 mL). The combined extract was washed with water and

dried over anhydrous Na₂SO₄. The extracted solvent was

removed under reduced pressure with a rotary evaporator to

obtain the product. The crude products were purified by column

chromatography on silica gel using dichloromethane/methanol

5-(4-chlorophenyl)-1-methyl-1H-imidazole^[32](3af) Pale

yellow solid. Yield 161.8 mg 84% (Catalyst C1), 156 mg 81%

(Catalyst C2) 165.7 mg 86% (Catalyst C3), 154.1 mg 80%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.50 (s, 1H), 7.41

– 7.37 (m, 2H), 7.33 – 7.31 (m, 1H), 7.30 – 7.28 (m, 1H), 7.08

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(s, 1H), 3.64 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 139.47,

(ddd, J = 15.0, 5.2, 1.4 Hz, 2H), 7.14 (s, 1H), 3.39 (s, 3H). ¹³C-

NMR (101 MHz, CDCl₃) δ 138.53, 133.73, 133.00, 131.25,

129.54, 129.32, 129.16, 128.49, 127.33, 126.86, 126.29,

125.60, 125.32, 32.08.

1,2-dimethyl-5-phenyl-1H-imidazole^[32](4aa) Yellow liquid.

Yield 142.9 mg 83% (Catalyst C1), 156.7 mg 91% (Catalyst

C2) 160.2 mg 85% (Catalyst C3), 153.3 mg 89% (Catalyst C4);

¹H-NMR (400 MHz, CDCl₃) δ 7.45 – 7.37 (m, 2H), 7.34 (dd, J

= 7.8, 1.8 Hz, 3H), 6.93 (s, 1H), 3.51 (s, 3H), 2.43 (s, 3H). ¹³C-

NMR (101 MHz, CDCl₃) δ 130.66, 128.77, 128.71, 127.74,

125.91, 31.43, 13.76.

1-(4-(1,2-dimethyl-1H-imidazol-5-yl)phenyl)ethanone^[32]

(4ab) Light yellow solid. Yield 192.8 mg 90% (Catalyst C1),

201.4 mg 94% (Catalyst C2) 194.9 mg 91% (Catalyst C3),

199.3 mg 93% (Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ

7.98 (d, J = 8.5 Hz, 2H), 7.43 (d, J = 8.5 Hz, 2H), 7.03 (s, 1H),

3.55 (s, 3H), 2.59 (s, 3H), 2.43 (s, 3H). ¹³C-NMR (101 MHz,

CDCl₃) δ 197.52, 147.31, 135.84, 135.25, 132.65, 128.90,

128.04, 127.36, 31.77, 26.72, 13.87.

134.07, 132.42, 129.75, 129.08, 128.36, 32.61.

5-(4-fluorophenyl)-1-methyl-1H-imidazole^[30](3ag) Off-white

solid. Yield 156.8 mg 89% (Catalyst C1), 160.3 mg 91%

(Catalyst C2) 160.3 mg 91% (Catalyst C3), 165.6 mg 94%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.49 (s, 1H), 7.35

– 7.31 (m, 2H), 7.11 (t, J = 8.7 Hz, 2H), 7.04 (s, 1H), 3.61 (s,

3H). ¹³C-NMR (101 MHz, CDCl₃) δ 163.85, 161.39, 139.13,

130.45, 128.20, 125.97, 115.99, 115.77, 32.49.

1-methyl-5-(p-tolyl)-1H-imidazole^[30](3ah) Off-white solid.

Yield 130.9 mg 76% (Catalyst C1), 134.3 mg 78% (Catalyst

C2) 141.2 mg 82% (Catalyst C3), 148.1 mg 86% (Catalyst C4);

¹H-NMR (400 MHz, CDCl₃) δ 7.49 (s, 1H), 7.26 (d, J = 8.3 Hz,

2H), 7.22 (d, J = 8.1 Hz, 2H), 7.05 (s, 1H), 3.63 (s, 3H), 2.38

(s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 138.90, 137.92, 133.54,

129.50, 128.51, 127.76, 126.92, 32.55, 21.30.

5-(4-methoxyphenyl)-1-methyl-1H-imidazole^[32](3ai) Yellow

solid. Yield. 148.7 mg 79% (Catalyst C1), 152.5 mg 81%

(Catalyst C2) 160 mg 85% (Catalyst C3), 156.2 mg 83%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.47 (s, 1H), 7.29

(d, J = 8.8 Hz, 2H), 7.01 (s, 1H), 6.95 (d, J = 8.8 Hz, 2H), 3.83

(s, 3H), 3.61 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 159.50,

138.67, 133.29, 130.02, 127.60, 122.26, 114.24, 55.43, 32.44.

5-(3-methoxyphenyl)-1-methyl-1H-imidazole^[32](3aj) Light

yellow solid. Yield 137.4 mg 73% (Catalyst C1), 141.1 mg 75%

(Catalyst C2) 150.6 mg 80% (Catalyst C3), 156.2 mg 83%

(Catalyst C4); ¹H-NMR (500 MHz, CDCl₃) δ 7.48 (s, 1H), 7.31

(t, J = 8.2 Hz, 1H), 7.06 (s, 1H), 6.93 (d, J = 7.6 Hz, 1H), 6.88

(d, J = 6.2 Hz, 2H), 3.80 (s, 3H), 3.64 (s, 3H). ¹³C-NMR (126

MHz, CDCl₃) δ 159.73, 139.08, 133.32, 131.05, 129.78, 128.04,

120.84, 115.00, 114.31, 113.22, 55.33, 32.60.

4-(1,2-dimethyl-1H-imidazol-5-yl)benzaldehyde^[32]

(4ac)

Off-white solid. Yield 176.2 mg 88% (Catalyst C1), 182.2 mg

91% (Catalyst C2) 186.2 mg 93% (Catalyst C3), 190.2 mg 95%

(Catalyst C4);¹H NMR (400 MHz, CDCl₃) δ 10.01 (s, 1H), 7.91

(d, J = 8.7 Hz, 2H), 7.51 (d, J = 8.4 Hz, 2H), 7.07 (s, 1H), 3.58

(s, 3H), 2.45 (s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 191.66,

136.60, 135.12, 130.27, 128.35, 127.81, 31.84, 13.86.

4-(1,2-dimethyl-1H-imidazol-5-yl)benzonitrile^[32](4ad) Light

yellow solid. Yield 177.5 mg 90% (Catalyst C1), 183.4 mg 93%

(Catalyst C2) 185.4 mg 94% (Catalyst C3), 189.3 mg 96%

(Catalyst C4); ¹H-NMR (500 MHz, CDCl₃) δ 7.72 (d, J = 7.4 Hz,

2H), 7.49 (d, J = 7.5 Hz, 2H), 7.08 (s, 1H), 3.59 (s, 3H), 2.48

(s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 135.11, 132.56, 128.34,

127.86, 118.63, 110.92, 31.68, 13.74.

1,2-dimethyl-5-(4-nitrophenyl)-1H-imidazole^[32](4ae) Off-

white solid. Yield 191.2 mg 88% (Catalyst C1), 197.7 mg 91%

(Catalyst C2) 204.2 mg 94% (Catalyst C3), 208.5 mg 96%

(Catalyst C4);¹H-NMR (400 MHz, CDCl₃) δ 8.26 (d, J = 8.8 Hz,

2H), 7.50 (d, J = 8.8 Hz, 2H), 7.09 (s, 1H), 3.59 (s, 3H), 2.46

(s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 148.49, 147.40, 134.21,

132.26, 131.29, 129.96, 127.50, 122.86, 122.38, 31.63, 13.84.

5-(4-chlorophenyl)-1,2-dimethyl-1H-imidazole^[32](4af) Light

yellow solid. Yield 161.2 mg 78% (Catalyst C1), 167.4 mg 81%

(Catalyst C2) 169.5 mg 82% (Catalyst C3), 173.6 mg 84%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.37 (d, J = 8.5 Hz,

3-(1-methyl-1H-imidazol-5-yl)pyridine^[30](3ak) Light yellow

liquid. Yield 120.9 mg 76% (Catalyst C1), 128.9 mg 81%

(Catalyst C2) 127.3 mg 80% (Catalyst C3), 132.1 mg 85%

1

(Catalyst C4); H-NMR (400 MHz, CDCl₃) δ 7.93 – 7.88 (m,

2H), 7.63 (d, J = 7.5 Hz, 2H), 7.54 – 7.41 (m, 4H), 7.14 (s, 1H),

3.39 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 138.54, 133.72,

132.99, 131.24, 129.31, 129.15, 128.49, 127.34, 126.86,

126.28, 125.60, 125.32, 32.08.

1-methyl-5-(naphthalen-1-yl)-1H-imidazole^[32](3al) Yellow

liquid. Yield 158.3 mg 76% (Catalyst C1), 164.5 mg 79%

(Catalyst C2) 168.7 mg 81% (Catalyst C3), 177 mg 85%

1

(Catalyst C4); H-NMR (400 MHz, CDCl₃) δ 7.92 – 7.88 (m,

2H), 7.63 (d, J = 8.5 Hz, 2H), 7.53 (d, J = 7.0 Hz, 2H), 7.46

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2H), 7.26 (d, J = 8.6 Hz, 2H), 6.92 (s, 1H), 3.48 (s, 3H), 2.42

(s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 146.42, 133.72, 132.47,

129.85, 129.08, 126.35, 31.40, 13.84.

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.88 (d, J = 7.7 Hz,

2H), 7.65 (d, J = 8.2 Hz, 1H), 7.53 – 7.36 (m, 4H), 6.99 (s, 1H),

3.23 (s, 3H), 2.48 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 145.59,

133.73, 133.00, 131.19, 129.14, 128.46, 128.08, 126.76,

126.21, 125.69, 125.34, 31.08, 13.74.

5-(4-fluorophenyl)-1,2-dimethyl-1H-imidazole^[30](4ag) Off-

white solid. Yield 144.6 mg 76% (Catalyst C1), 142.7 mg 75%

(Catalyst C2) 152.2 mg 80% (Catalyst C3), 157.9 mg 83%

(Catalyst C4); ¹H-NMR (500 MHz, CDCl₃) δ 7.88 (d, J = 7.5 Hz,

2H), 7.64 (d, J = 7.5 Hz, 2H), 7.24 (s, 1H), 3.75 (s, 3H), 2.64

(s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ148.49, 147.40, 134.21,

132.26, 131.30, 129.96, 127.50, 122.68, 122.26, 31.6, 13.84.

5-(4-methoxyphenyl)-1,2-dimethyl-1H-imidazole^[32](4ah)

Off-white solid. Yield 157.8 mg 78% (Catalyst C1), 163.8 mg

81% (Catalyst C2) 165.8 mg 82% (Catalyst C3), 169.9 mg 84%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 7.25 (d, J = 8.8 Hz,

2H), 6.94 (d, J = 8.8 Hz, 2H), 6.87 (s, 1H), 3.83 (s, 3H), 3.46

(s, 3H), 2.42 (s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ 170.68,

159.28, 133.24, 130.04, 125.13, 122.94, 114.10, 55.28, 31.07,

13.56.

Typical procedure for Mizoroki-Heck reactions

An oven-dried sealed tube (10 mL) was charged with 0.001

mol% of pallacycles(II) catalyst, 1 mmol of aryl halide, 1.2

mmol of methyl acrylate/tert-butyl acrylate /styrene, 2 mmol of

Et₃N and 2.0 mL of NMP. The reaction flask was heated at 140

^oC for 8 h in an oil bath. The reaction was tested by TLC, the

reaction mixture was cooled to ambient temperature, H₂O (5

mL) was added and the organic layer was extracted with

dichloromethane (3x10 mL). The combined organic layers

were dried with sodium sulfate and concentrated. The crude

product was purified by column chromatography (ethyl

1

acetate-hexane). H NMR and ¹³C NMR data are depicted in

supporting information Figures S88-S156.

1,2-dimethyl-5-(p-tolyl)-1H-imidazole^[30](4ai) Light yellow

solid. Yield 149 mg 80% (Catalyst C1), 154.6 mg 83% (Catalyst

C2) 156.4 mg 84% (Catalyst C3), 162 mg 87% (Catalyst C4);

¹H-NMR (400 MHz, CDCl₃) δ 7.20 (s, 4H), 6.88 (s, 1H), 3.46 (s,

3H), 2.40 (s, 3H), 2.35 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ

145.78, 137.66, 133.64, 129.58, 128.75, 127.60, 125.52, 31.34,

21.28, 13.82.

Methyl cinnamate (7aa) White solid. Yield 142.7 mg 88%

(Catalyst C1), 147.6 mg 91% (Catalyst C2); ¹H-NMR (400

MHz, CDCl₃) δ 7.69 (d, J = 16.0 Hz, 1H), 7.50 (dd, J = 6.5, 3.0

Hz, 2H), 7.38 – 7.35 (m, 3H), 6.43 (d, J = 16.1 Hz, 1H), 3.79

(s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 167.50 (s), 144.97,

134.46, 130.41, 130.19, 128.58, 117.87, 51.77.

(E)-methyl-3-(4-hydroxyphenyl)acrylate (7ab) White solid.

Yield 128.3 mg 72% (Catalyst C1), 133.6 mg 75% (Catalyst

5-(3-methoxyphenyl)-1,2-dimethyl-1H-imidazole^[30]

(4aj)

1

Off-white solid. Yield 153.7 mg 76% (Catalyst C1), 151.7 mg

75% (Catalyst C2) 161.8 mg 80% (Catalyst C3), 167.9 mg 83%

(Catalyst C4); ¹H-NMR (500 MHz, CDCl₃) δ 7.33 (t, J = 7.8 Hz,

1H), 6.96 – 6.91 (m, 2H), 6.89 (d, J = 6.2 Hz, 2H), 3.82 (s, 3H),

3.52 (s, 3H), 2.43 (s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ 159.74,

146.00, 133.41, 131.86, 129.67, 125.89, 120.95, 114.38,

113.02, 55.27, 31.33, 13.62.

3-(1,2-dimethyl-1H-imidazol-5-yl)pyridine^[30](3ak) Light

yellow liquid. Yield 135.1 mg 78% (Catalyst C1), 140.3 mg 81%

(Catalyst C2) 143.8 mg 83% (Catalyst C3), 148.9 mg 86%

(Catalyst C4); ¹H-NMR (400 MHz, CDCl₃) δ 8.60 (d, J = 3.0 Hz,

1H), 8.55 (dd, J = 4.9, 1.7 Hz, 1H), 7.66 – 7.62 (m, 1H), 7.33

(dd, J = 7.5, 5.3 Hz, 1H), 6.98 (s, 1H), 3.51 (s, 3H), 2.43 (s,

3H). ¹³C-NMR (101 MHz, CDCl₃) δ 149.25, 148.81, 147.02,

135.76, 130.14, 127.03, 126.75, 123.61, 31.46, 13.75.

C2); H-NMR (400 MHz, CDCl₃) δ 7.62 (d, J = 16.0 Hz, 1H),

7.41 (d, J = 8.5 Hz, 2H), 6.83 (d, J = 8.7 Hz, 2H), 6.28 (d, J =

15.9 Hz, 1H), 3.78 (s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ

168.29, 158.05, 144.88, 130.19, 127.26, 116.06, 115.27,

51.91.

(E)-methyl 3-(4-formylphenyl)acrylate (7ac) White solid.

Yield 144.5 mg 76% (Catalyst C1), 152.2 mg 80% (Catalyst

C2); ¹H-NMR (400 MHz, CDCl₃) δ 9.53 (s, 1H), 7.41 (d, J = 8.1

Hz, 2H), 7.23 – 7.15 (m, 3H), 6.06 (d, J = 15.9 Hz, 1H), 3.33 (s,

3H). ¹³C NMR (101 MHz, CDCl₃) δ 191.57, 166.89, 143.19,

140.10, 137.26, 130.26, 128.56, 121.08, 52.00.

(E)-methyl 3-(4-acetylphenyl)acrylate (7ad) White solid.

Yield 179.7 mg 88% (Catalyst C1), 185.8 mg 91% (Catalyst

C2); ¹H-NMR (400 MHz, CDCl₃) δ 7.94 (d, J = 8.4 Hz, 2H), 7.68

(d, J = 16.1 Hz, 1H), 7.58 (d, J = 8.3 Hz, 2H), 6.50 (d, J = 16.1

Hz, 1H), 3.80 (s, 3H), 2.59 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃)

1,2-dimethyl-5-(naphthalen-1-yl)-1H-imidazole^[32](3al) Light

yellow liquid. Yield 182.2 mg 80% (Catalyst C1), 186.7 mg 83%

(Catalyst C2) 186.7 mg 84% (Catalyst C3), 193.3mg 87%

δ

197.48,167.05, 143.40,138.77, 138.09, 128.95,128.24,

120.40,52.01, 26.79.

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(E)-methyl 3-(p-tolyl)acrylate (7ae) White solid. Yield 137.4

mg 78% (Catalyst C1), 139.2 mg 79% (Catalyst C2); ¹H-NMR

(400 MHz, CDCl₃) δ 7.65 (d, J = 16.4 Hz, 1H), 7.40 (d, J = 8.2

Hz, 2H), 7.17 (d, J = 8.0 Hz, 2H), 6.37 (d, J = 16.0 Hz, 1H),

3.77 (s, 3H), 2.35 (s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ

167.76, 144.98, 140.82, 131.7, 129.72, 128.16, 116.75, 51.75,

21.56.

16.0 Hz, 1H), 3.78 (s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ

167.17, 143.41, 136.22, 132.88, 129.19, 118.40, 51.79.

(E)-methyl 3-(naphthalen-1-yl)acrylate (7al) Light yellow oil.

Yield 142.2 mg 67 (Catalyst C1), 150.7 mg 71% (Catalyst C2);

¹H-NMR (500 MHz, CDCl₃) δ 8.57 (d, J = 15.8 Hz, 1H), 8.23

(d, J = 8.4 Hz, 1H), 7.92 (t, J = 9.0 Hz, 2H), 7.79 (d, J = 7.2 Hz,

1H), 7.60 (d, J = 8.2 Hz, 1H), 7.59 – 7.54 (m, 1H), 7.52 (t, J =

7.7 Hz, 1H), 6.56 (d, J = 15.8 Hz, 1H), 3.89 (s, 3H).

(E)-methyl 3-(4-nitrophenyl)acrylate (7af) Slightly yellow

solid. Yield 180.3 mg 87% (Catalyst C1), 184.4 mg 99%

(Catalyst C2); ¹H-NMR (400 MHz, CDCl₃) δ 8.23 (d, J = 8.8 Hz,

2H), 7.70 (d, J = 16.1 Hz, 1H), 7.65 (d, J = 8.7 Hz, 2H), 6.54

(d, J = 16.1 Hz, 1H), 3.82 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃)

δ 166.58, 142.00, 140.55, 128.74, 124.27, 122.17, 52.18.

(E)-methyl 3-(2-nitrophenyl)acrylate (7ag) Slightly yellow

solid. Yield 145 mg 70% (Catalyst C1), 155.4 mg 75% (Catalyst

tert-butyl cinnamate^9a(8aa) Colorless oil. Yield 181.8 mg

89% (Catalyst C1), 185.9 mg 91% (Catalyst C2); ¹H-NMR (400

MHz, CDCl₃) δ 7.57 (d, J = 16.0 Hz, 1H), 7.48 (dd, J = 6.6, 3.1

Hz, 2H), 7.34 (dd, J = 5.0, 1.9 Hz, 3H), 6.35 (d, J = 16.0 Hz,

1H), 1.52 (s, 9H). ¹³C-NMR (101 MHz, CDCl₃) δ 166.44,

143.64, 134.77, 130.08, 128.94, 128.07, 120.27, 80.60, 28.36.

(E)-tert-butyl 3-(4-hydroxyphenyl)acrylate (8ab) White

solid. Yield 178.4 mg 81% (Catalyst C1), 174 mg 79% (Catalyst

1

C2); H NMR (400 MHz, CDCl₃) δ 8.10 (d, J = 15.8 Hz, 1H),

1

8.03 (d, J = 8.9 Hz, 1H), 7.65 – 7.60 (m, 2H), 7.55 – 7.51 (m,

1H), 6.35 (d, J = 15.8 Hz, 1H), 3.82 (s, 3H).¹³C-NMR (101 MHz,

CDCl₃) δ 166.32, 140.26, 133.63, 130.66, 130.40, 129.22,

125.01, 122.95, 52.12.

C2); H-NMR (400 MHz, CDCl₃) δ 7.51 (d, J = 16.1 Hz, 1H),

7.34 (d, J = 9.0 Hz, 2H), 6.85 (d, J = 8.9 Hz, 2H), 6.19 (d, J =

16.0 Hz, 1H), 1.52 (s, 9H). ¹³C-NMR (101 MHz, CDCl₃) δ

168.08, 158.57, 144.41, 130.14, 126.87, 116.94, 116.15,

81.24, 28.42.

(E)-methyl 3-(3-nitrophenyl)acrylate (7ah) Slightly yellow

solid. Yield 167.8 mg 81% (Catalyst C1), 176.1 mg 85%

(Catalyst C2); ¹H-NMR (500 MHz, CDCl₃) δ 8.36 (s, 1H), 8.22

(d, J = 8.1 Hz, 1H), 7.83 (d, J = 7.6 Hz, 1H), 7.70 (s, 1H), 7.59

(t, J = 8.0 Hz, 1H), 6.56 (d, J = 16.0 Hz, 1H), 3.83 (s, 3H). ¹³C-

NMR (126 MHz, CDCl₃) δ 166.68, 148.67, 141.94, 136.11,

133.62, 129.98, 124.53, 122.42, 121.17, 115.00, 51.99.

(E)-methyl 3-(4-cyanophenyl)acrylate (7ai) White solid.

Yield 162.9 mg 87% (Catalyst C1), 166.6 mg 89% (Catalyst

C2); ¹H-NMR (500 MHz, CDCl₃) δ 7.72 – 7.66 (m, 3H), 7.62 (d,

J = 7.8 Hz, 2H), 6.54 (d, J = 16.0 Hz, 1H), 3.84 (s, 3H). ¹³C-

NMR (126 MHz, CDCl₃) δ 166.57 (s), 142.41, 138.66, 132.66,

128.40, 121.40, 118.33, 113.44, 52.02.

(E)-tert-butyl 3-(4-formylphenyl)acrylate^[9a](8ac) Colorless

oil. Yield 188.1 mg 81% (Catalyst C1), 197.4 mg 85% (Catalyst

1

C2); H-NMR (400 MHz, CDCl₃) δ 10.01 (s, 1H), 7.87 (d, J =

8.2 Hz, 2H), 7.64 (d, J = 8.2 Hz, 2H), 7.59 (d, J = 16.0 Hz, 1H),

6.47 (d, J = 16.0 Hz, 1H), 1.53 (s, 9H). ¹³C-NMR (101 MHz,

CDCl₃) δ 191.59, 165.72, 141.89, 140.51, 137.04, 130.22,

128.46, 123.53, 81.16, 28.26.

(E)-tert-butyl 3-(4-acetylphenyl)acrylate^[9a](8ad) Colorless

oil. Yield 219.2 mg 89% (Catalyst C1), 229 mg 93% (Catalyst

C2); ¹H-NMR (500 MHz, CDCl₃) δ 7.93 (d, J = 8.3 Hz, 2H), 7.59

– 7.55 (m, 3H), 6.43 (d, J = 16.1 Hz, 1H), 2.59 (s, 3H), 1.51 (s,

9H). ¹³C NMR (101 MHz, CDCl₃) δ 197.54, 165.89, 142.06,

139.15, 137.84, 128.91, 128.10, 122.85, 81.00, 28.38.

(E)-tert-butyl 3-(p-tolyl)acrylate^[9a](8ae) Colorless oil. Yield

172.4 mg 79% (Catalyst C1), 176.8 mg 81% (Catalyst C2); ¹H-

NMR (400 MHz, CDCl₃) δ 7.54 (d, J = 16.0 Hz, 1H), 7.38 (d, J

= 8.1 Hz, 2H), 7.15 (d, J = 8.0 Hz, 2H), 6.30 (d, J = 16.0 Hz,

1H), 2.34 (s, 3H), 1.51 (s, 9H). ¹³C-NMR (101 MHz, CDCl₃) δ

166.66, 143.64, 140.40, 131.98, 129.62,128.04, 119.15, 80.46,

28.30, 21.53.

(E)-methyl 3-(4-fluorophenyl)acrylate (7aj) Yellow solid.

Yield 151.3 mg 84% (Catalyst C1), 154.9 mg 86% (Catalyst

1

C2); H-NMR (500 MHz, CDCl₃) δ 7.68 (d, J = 16.0 Hz, 1H),

7.57 – 7.52 (m, 2H), 7.10 (t, J = 8.4 Hz, 2H), 6.39 (d, J = 16.0

Hz, 1H), 3.83 (s, 3H). ¹³C-NMR (126 MHz, CDCl₃) δ 167.29,

164.92, 143.56, 129.97, 117.59, 116.07, 115.00, 51.72.

(E)-methyl 3-(4-chlorophenyl)acrylate (7ak) White solid.

Yield 157.3 mg 80% (Catalyst C1), 163.2 mg 83% (Catalyst

1

C2); H-NMR (500 MHz, CDCl₃) δ 7.61 (d, J = 16.0 Hz, 1H),

(E)-tert-butyl 3-(4-nitrophenyl)acrylate^[9a](8af) Yellow solid.

Yield 219.4 mg 88% (Catalyst C1), 224.3 mg 90% (Catalyst

C2); ¹H-NMR (400 MHz, CDCl₃) δ 8.22 (d, J = 9.1 Hz, 2H), 7.64

7.43 (d, J = 8.4 Hz, 2H), 7.33 (d, J = 8.4 Hz, 2H), 6.38 (d, J =

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(d, J = 8.8 Hz, 2H), 7.59 (d, J = 16.0 Hz, 1H), 6.48 (d, J = 16.1

Hz, 1H), 1.57 (s, 9H). ¹³C-NMR (101 MHz, CDCl₃) δ 165.38,

140.95, 140.67, 128.58, 124.63, 124.22, 81.44, 28.21.

(E)-tert-butyl 3-(2-nitrophenyl)acrylate (8ag) Yellow solid.

Yield 199.4 mg 80% (Catalyst C1), 211.8 mg 85% (Catalyst

C2); ¹H-NMR (400 MHz, CDCl₃) δ 8.01 – 7.95 (m, 2H), 7.61 (d,

J = 4.0 Hz, 2H), 7.52 – 7.47 (m, 1H), 6.27 (d, J = 15.8 Hz, 1H),

1.51 (s, 9H). ¹³C-NMR (101 MHz, CDCl₃) δ 165.15, 138.79,

133.50, 130.86, 130.12, 129.19, 125.36, 124.94, 81.28, 28.20.

(E)-tert-butyl 3-(naphthalen-1-yl)acrylate^[9a]Yellow liquid.

Yield 165.3 mg 65% (Catalyst C1), 178 mg 70% (Catalyst C2);

¹H-NMR (400 MHz, CDCl₃) δ 8.22 (d, J = 15.6 Hz, 2H), 8.18 (d,

J = 8.4 Hz, 1H), 7.86(d, J = 8.4 Hz, 2H), 7.71 (d, J = 8.2 Hz,

1H), 7.56 (m, 3H), 6.45 (d, J = 15.6 Hz, 1H), 1.57 (s, 9H). ¹³C-

NMR (101 MHz, CDCl₃) δ 166.34, 140.78, 140.56, 133,72,

132.13, 131.50, 130.27, 128.76, 126.82, 126.18, 125.54,

125.00, 12371, 122.90, 81.38, 28.43.

197.61, 142.09, 136.78, 136.02, 128.97, 126.91, 126.60,

26.69.

(E)-1-methoxy-4-styrylbenzene^[9a](9ae) White solids. Yield

151.4 mg 72% (Catalyst C1), 155.6 mg 74% (Catalyst C2); ¹H-

NMR (400 MHz, CDCl₃) δ 7.46 (dd, J = 13.3, 8.0 Hz, 4H), 7.34

(t, J = 7.6 Hz, 2H), 7.22 (t, J = 7.9 Hz, 1H), 7.06 (d, J = 16.3

Hz, 1H), 6.97 (d, J = 16.3 Hz, 1H), 6.89 (d, J = 8.8 Hz, 2H),

3.82 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ 159.37, 137.72,

130.22, 128.73, 128.28, 127.79, 127.30, 126.69, 126.33,

114.21, 55.42.

(E)-1-nitro-4-styrylbenzene^[47](9af) Off-white solids. Yield

184.7 mg 82% (Catalyst C1), 193.7 mg 86% (Catalyst C2); ¹H-

NMR (500 MHz, CDCl₃) δ 7.94 (d, J = 8.2 Hz, 1H), 7.75 (d, J =

7.9 Hz, 1H), 7.62 – 7.55 (m, 2H), 7.53 (d, J = 7.7 Hz, 2H), 7.37

(t, J = 7.4 Hz, 3H), 7.31 (t, J = 7.2 Hz, 1H), 7.07 (d, J = 16.1

Hz, 1H). ¹³C-NMR (126 MHz, CDCl₃) δ 148.03, 136.51, 133.89,

133.10, 130.04, 128.84, 128.64, 128.19, 127.98, 127.11,

124.79, 123.52.

(E)-1,2-diphenylethene^[9a](9aa) White solids. Yield 160.4 mg

89% (Catalyst C1), 164 mg 91% (Catalyst C2); ¹H-NMR (400

MHz, CDCl₃) δ 7.53 (s, 2H), 7.51 (s, 2H), 7.36 (t, J = 7.6 Hz,

4H), 7.29 – 7.24 (m, 2H), 7.12 (s, 2H). ¹³C-NMR (101 MHz,

CDCl₃) δ 137.49, 128.86, 127.8, 126.68.

(E)-1-nitro-2-styrylbenzene (9ag) Off-white solids. Yield

182.4 mg 81% (Catalyst C1), 193.7 mg 86% (Catalyst C2); ¹H-

NMR (500 MHz, CDCl₃) δ 8.17 (d, J = 8.3 Hz, 2H), 7.59 (d, J =

8.3 Hz, 2H), 7.51 (d, J = 7.8 Hz, 2H), 7.35 (t, J = 7.5 Hz, 2H),

7.29 (t, J = 7.2 Hz, 1H), 7.21 (s, 2H), 7.10 (d, J = 16.3 Hz, 1H).

¹³C-NMR (101 MHz, CDCl₃) δ 148.08, 136.57, 133.95, 133.21,

133.11, 128.92, 128.72, 128.26, 128.06, 127.19, 124.88,

123.59.

(E)-4-styrylphenol (9ab) White solids. Yield 137.4 mg 70%

(Catalyst C1), 147.2 mg 75% (Catalyst C2); ¹H-NMR (400 MHz,

CDCl₃) δ 7.47 (d, J = 9.3 Hz, 2H), 7.39 (d, J = 8.9 Hz, 2H), 7.33

(t, J = 7.9 Hz, 2H), 7.24 – 7.19 (m, 1H), 7.07 – 6.92 (m, 2H),

6.81 (d, J = 8.9 Hz, 2H). ¹³C-NMR (101 MHz, CDCl₃) δ 155.53,

137.78, 130.45, 128.88, 128.33, 128.14,127.47, 126.81,

126.47, 115.83.

(E)-4-styrylbenzaldehyde^[47](9ac) White solids. Yield 170.8

mg 82% (Catalyst C1), 181.2 mg 87% (Catalyst C2); ¹H-NMR

(500 MHz, CDCl₃) δ 10.02 (s, 1H), 7.90 (d, J = 8.0 Hz, 2H),

7.68 (d, J = 8.0 Hz, 2H), 7.58 (d, J = 7.8 Hz, 2H), 7.42 (t, J =

7.5 Hz, 2H), 7.34 (t, J = 7.1 Hz, 1H), 7.31 – 7.26 (m, 1H), 7.17

(d, J = 16.3 Hz, 1H). ¹³C-NMR (126 MHz, CDCl₃) δ 191.57,

143.42, 136.56, 135.35, 132.20, 130.23, 128.83, 128.50,

127.34, 126.91.

(E)-1-nitro-3-styrylbenzene (9ah) Off-white solids. Yield

159.9 mg 71% (Catalyst C1), 168.9 mg 75% (Catalyst C2); ¹H-

NMR (400 MHz, CDCl₃) δ 8.36 (t, J = 1.9 Hz, 1H), 8.09 (ddd, J

= 8.1, 2.2, 0.8 Hz, 1H), 7.79 (d, J = 7.8 Hz, 1H), 7.56 – 7.51

(m, 3H), 7.39 (t, J = 7.5 Hz, 2H), 7.31 (t, J = 7.3 Hz, 1H), 7.23

(d, J = 14.5 Hz, 1H), 7.12 (d, J = 16.3 Hz, 1H). ¹³C-NMR (126

MHz, CDCl₃) δ 148.57, 136.68, 133.01, 132.65, 130.85,

128.80, 128.22, 126.68, 124.92, 123.52, 115.00.

(E)-4-styrylbenzonitrile^[47](9ai) White solids. Yield 176.5 mg

86% (Catalyst C1), 182.7 mg 89% (Catalyst C2); ¹H-NMR (500

MHz, CDCl₃) δ 7.66 (d, J = 8.3 Hz, 2H), 7.61 (d, J = 8.1 Hz,

2H), 7.56 (d, J = 7.7 Hz, 2H), 7.42 (t, J = 7.5 Hz, 2H), 7.35 (t, J

= 7.3 Hz, 1H), 7.29 – 7.23 (m, 1H), 7.12 (d, J = 16.3 Hz, 1H).

¹³C-NMR (126 MHz, CDCl₃) δ 141.86, 136.31, 132.51, 128.88,

126.93, 119.03, 115.00, 110.61.

(E)-1-(4-styrylphenyl)ethanone^[9a](9ad) White solids. Yield

202.3 mg 91% (Catalyst C1), 211.2 mg 95% (Catalyst C2); ¹H-

NMR (400 MHz, CDCl₃) δ 7.94 (d, J = 8.4 Hz, 2H), 7.57 (d, J =

8.3 Hz, 2H), 7.52 (d, J = 7.2 Hz, 2H), 7.37 (t, J = 7.5 Hz, 2H),

7.29 (d, J = 7.3 Hz, 1H), 7.21 (d, J = 16.3 Hz, 1H), 7.11 (d, J =

16.3 Hz, 1H), 2.59 (s, 3H). ¹³C-NMR (101 MHz, CDCl₃) δ

(E)-1-fluoro-4-styrylbenzene (9aj) White solids. Yield

156.6mg 79% (Catalyst C1), 160.6 mg 81% (Catalyst C2); ¹H-

NMR (500 MHz, CDCl₃) δ 7.54 (d, J = 7.9 Hz, 3H), 7.47 (d, J =

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European Journal of Inorganic Chemistry

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8.3 Hz, 3H), 7.40 (t, J = 7.5 Hz, 3H), 7.36 (d, J = 8.3 Hz, 3H),

7.30 (dd, J = 13.4, 6.5 Hz, 2H), 7.10 (d, J = 4.2 Hz, 3H). ¹³C-

NMR (126 MHz, CDCl₃) δ 137.01, 135.88, 133.19, 129.35,

128.81, 127.89, 127.68, 127.39, 126.57.

In a 50 mL round-bottomed flask were placed 0.001 mol% of

C2 catalyst, 1-bromo-4-methoxybenzene (10 mmol) and 2-

ethylhexyl acrylate (12 mmol), 20 mmol of Et₃N and 20 mL of

NMP. The reaction flask was heated at 140 ^oC for 8 h in an oil

bath. The reaction was monitored by TLC, the reaction mixture

was cooled to ambient temperature, H₂O (5 mL) was added

and the organic layer was extracted with CH₂Cl₂(3x15qn mL).

The combined organic layers were dried with magnesium

sulphate and concentrated. The crude product was purified by

(E)-1-chloro-4-styrylbenzene (9ak) White solids. Yield 163.2

mg 76% (Catalyst C1), 171.8 mg 80% (Catalyst C2); ¹H-NMR

(400 MHz, CDCl₃) δ 7.50 (d, J = 7.1 Hz, 2H), 7.43 (d, J = 8.5

Hz, 2H), 7.37 (d, J = 7.2 Hz, 1H), 7.35 – 7.30 (m, 3H), 7.30 –

7.25 (m, 1H), 7.06 (d, J = 2.9 Hz, 2H). ¹³C NMR (126 MHz,

CDCl₃) δ 137.07, 135.94, 133.26, 129.41, 128.92, 128.81,

127.95, 127.74, 127.45, 126.64.

1

column chromatography (ethyl acetate-hexane). H NMR and

¹³C NMR data are depicted in supporting information Figures

(E)-1-styrylnaphthalene (9al) White solids. Yield 154.3 mg

67% (Catalyst C1), 161.2 mg 70% (Catalyst C2); ¹H-NMR (500

MHz, CDCl₃) δ 8.47 (d, J = 8.0 Hz, 1H), 8.11 (dd, J = 20.0, 11.9

Hz, 2H), 8.02 (d, J = 8.1 Hz, 1H), 7.96 (d, J = 7.1 Hz, 1H), 7.82

(d, J = 7.4 Hz, 2H), 7.72 (dt, J = 15.0, 8.5 Hz, 3H), 7.63 (t, J =

7.4 Hz, 2H), 7.54 (t, J = 7.2 Hz, 1H), 7.38 (d, J = 16.0 Hz, 1H).

¹³C NMR (126 MHz, CDCl₃) δ 137.91, 135.28, 134.04, 132.03,

131.72, 129.03, 128.92, 128.34, 128.05, 127.01, 126.38,

126.37, 126.11, 124.08, 123.94.

S157-158.

2-ethylhexyl(E)-3-(4-methoxyphenyl)acrylate

(12)^[9a]

Colorless oil. 2.11g 73% (Catalyst C2); ¹H NMR (400 MHz,

CDCl₃) δ 7.62 (d, J = 16.0 Hz, 1H), 7.46 (d, J = 8.1 Hz, 2H),

6.88 (d, J = 8.6 Hz, 2H), 6.30 (d, J = 16.0 Hz, 1H), 4.11-4.07

(dd, J = 5.9, 2.6 Hz, 2H), 3.81 (s, 3H), 1.65- 1.59 (m, 6.0 Hz,

1H), 1.43-1.29 (m, 9H), 0.94 – 0.85 (m, 7H). ¹³C NMR (101

MHz, CDCl₃) δ 167.65, 161.39, 144.24, 129.79, 127.29,

115.87, 114.32, 66.89, 55.46, 38.96, 30.56, 29.05, 23.93,

23.08, 14.20, 11.11.

(E)-methyl 3-(pyridin-3-yl)acrylate (10aa) Yellow solid. Yield

122.4 mg 75% (Catalyst C1), 132.2 mg 81% (Catalyst C2); ¹H-

NMR (500 MHz, CDCl₃) δ 8.74 (s, 1H), 8.60 (d, J = 4.6 Hz, 1H),

7.83 (d, J = 7.8 Hz, 1H), 7.68 (d, J = 16.1 Hz, 1H), 7.39 – 7.30

(m, 1H), 6.51 (d, J = 16.1 Hz, 1H), 3.82 (s, 3H). ¹³C-NMR (126

MHz, CDCl₃) δ 166.71, 150.93 (s), 149.69 (s), 141.12 (s),

134.21, 130.14, 123.73, 120.00, 115.00, 51.88.

(E)-tert-butyl 3-(pyridin-3-yl)acrylate^[9a](10ab) Colorless oil.

Yield 158 mg 77% (Catalyst C1), 162.2 mg 79% (Catalyst C2);

¹H-NMR (400 MHz, CDCl₃) δ 8.67 (s, 1H), 8.52 (d, J = 4.8 Hz,

1H), 7.76 (d, J = 9.9 Hz, 1H), 7.51 (d, J = 16.1 Hz, 1H), 7.28 –

7.23 (m, 1H), 6.39 (d, J = 16.1 Hz, 1H), 1.48 (s, 9H). ¹³C-NMR

(101 MHz, CDCl₃) δ 165.61, 150.90, 149.57, 139.77, 134.20,

130.46, 123.58, 122.49, 81.00, 28.30.

(E)-3-styrylpyridine^[9a](10ac)White solids. Yield 145 mg 80%

(Catalyst C1), 150.4 mg 83% (Catalyst C2); δ (400 MHz,

CDCl₃) 8.72 (s, 1H), 8.48 (d, J = 6.3 Hz, 1H), 7.82 (dt, J = 7.9,

1.7 Hz, 1H), 7.56 – 7.49 (m, 2H), 7.37 (t, J = 7.8 Hz, 2H), 7.32

– 7.25 (m, 2H), 7.17 – 7.01 (m, 2H). ¹³C-NMR (126 MHz,

CDCl₃) δ 139.20, 136.30, 132.24, 131.80, 129.56, 128.87,

128.54, 126.85, 126.13, 122.03, 115.00.

XPS analysis

A sample for TEM analysis was prepared as follows After

C_sp²−H arylation of imidazoles of (0.0005 mmol) C2, of 1-

methyl-1H-imidazole (1.0 mmol), 4-bromo benzaldehyde (1

mmol), K₂CO₃(2 mmol), pivalic acid (0.03 mmol) DMA (2.0

mL), 130 °C, reaction mixture was dropped onto a glass slide.

Then the sample was dried under air. The resulting sample

was then examined for XPS analysis.

For Mizoroki-Heck reactions, 0.001 mol% of pallacycles catalyst

C2, 4-bromo benzaldehyde 1 mmol of, 1.2 mmol of methyl

acrylate, 2 mmol of Et₃N and 2.0 mL of NMP stirred at 140 ^oC

for 8 h in an oil bath. After completion of the reaction, the

mixture was dropped onto a glass slide. Glass slide was dried

under air. The resulting sample was then examined for XPS

analysis.

FE-SEM and TEM analysis

A sample for TEM analysis was prepared as follows Csp2−H

arylation of 1-methyl-1H-imidazole in the presence of catalyst

C2, under standard condition, the reaction mixture was diluted

with DMA. Then one drop was dropped onto a copper grid and

dried under air. The resulting sample was then examined for

TEM analysis. A similar process was also followed for the

Gram‐scale synthesis of the UV-B sunscreen agent

octinoxate

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European Journal of Inorganic Chemistry

FULL PAPER

602–625 (c) M. Lamblin, L. Nassar-Hardy, J. C. Hierso, E. Fouquet, F. X.

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Park, K. Chung, J. W. Lee, Y. K. Chung, Organometallics 2003, 22, 4715–

4720.

sample preparation of Mizoroki-Heck reaction catalyzed by C2

for TEM analysis.

Hg poisoning test

To carry out the Hg poisoning test, catalyst C2 (0.05 mol%)

was stirred with 1 drop of Hg in an oven-dried RB. After that,

1-methyl-1H-imidazole (1.0 mmol), 4-bromobenzaldehyde (1

mmol), K₂CO₃(2 mmol), pivalic acid (0.03 mmol) DMA (2.0 mL),

130 °C were added to the flask and reaction was carried out

under optimum conditions. Reaction progress was monitored

with TLC. The same procedure was followed in case of

Mizoroki-Heck reactions, 1 drop of Hg in an oven-dried RB

followed by 0.001 mol% of palladacycles catalyst C2,

bromobenzene 1 mmol, 1.2 mmol of methyl acrylate, 2 mmol of

Et₃N and 2.0 mL of NMP stirred at 140 ^oC for 8 h in an oil bath.

Reaction progress was monitored with TLC.

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PPh₃(5 mol%) was taken in a reaction flask before the addition

of

the

reactants

(1-methyl-1H-imidazole,

4-

bromobenzaldehyde or methyl acrylate and bromobenzene).

After that, the C_sp²−H arylation of imidazoles reaction or

Mizoroki-Heck reactions was carried out under optimum

conditions. After carrying out the reaction for the optimum time,

the yield of the coupled product was 31 and 41%, respectively.

Supporting information summary

Supporting information contains the experimental section,

NMR, MS, UV-Visible spectral data. X-ray crystal structural

data deposited in the Cambridge Crystallographic Data Centre

and the deposition number for Catalyst C1 is CCDC 1963207,

C2 is CCDC 1963208, C3 is CCDC 1963209 and C4 is CCDC

1963210.

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Acknowledgements

KG is thankful to CSIR, New Delhi 01(2942)/18/EMR-II

dated 01-05-2018) for ﬁnancial assistance. AM, OS, and

AM are also grateful to MHRD for fellowship. SS is

thankful to DST/INSPIRE Fellowship/2017/IF170967 for

financial support. We thank Prof. Marilyn Olmstead for her

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Conflict of interest

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The authors declare no conflict of interest.

Keywords: Palladacycles • Direct arylation • Mizoroki-

Heck • Pd(0) Nanoparticle • Octinoxate

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10.1002/ejic.202000211

European Journal of Inorganic Chemistry

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Author(s), Corresponding Author(s)*

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Title

Text for Table of Contents

\

Palladium Catalystes C1 –C4 derived from unsymmetrical pincer-

type ligands were design and synthesized and were characterized

by different spectroscpic methods. Crystal structures of C1-C4

were established. These Catalystes (C1 –C4) were employed for

C_sp²−H arylation of imidazoles derivatives and Mizoroki-Heck

reactions. Grams scale synthesis of UV-B sunscreen agent

octinoxate.

Article Doi

Palladium-Based Catalysts Supported by Unsymmetrical XYC–1 Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of Octinoxate Utilizing the Mizoroki–Heck Reaction

DOI: 10.1002/ejic.202000211

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Full text of DOI:10.1002/ejic.202000211

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