Nickel-Catalyzed Direct Alkenylation of Methyl Heteroarenes with Primary Alcohols

Article abstract of DOI:10.1021/acs.joc.9b01517

An efficient nickel-catalyzed acceptorless dehydrogenative coupling of methyl-substituted heteroarenes with primary alcohols is achieved using an in situ generated complex of inexpensive NiBr₂ and readily available 8-aminoquinoline picolinic amide ligand. The protocol is operationally simple and scalable and furnishes a series of high-value 2-alkenylheteroarenes in good yields (up to 88percent) with exclusive E-selectivity. The reaction proceeds with the release of water and molecular hydrogen, which was analyzed through gas chromatography to validate the reaction mechanism. ?

Full text of DOI:10.1021/acs.joc.9b01517

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Note
Nickel-Catalyzed Direct Alkenylation of
Methyl-Heteroarenes with Primary Alcohols
Bose Muthu Ramalingam, Isai Ramakrishna, and Mahiuddin Baidya
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01517 • Publication Date (Web): 02 Jul 2019
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Page 1 of 8
The Journal of Organic Chemistry
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Nickel-Catalyzed Direct Alkenylation of Methyl-Heteroarenes with
Primary Alcohols
5
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Bose Muthu Ramalingam, Isai Ramakrishna, and Mahiuddin Baidya*
7
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9
Department of Chemistry, Indian Institute of Technology Madras, Chennai–600 036, India.
E-mail: mbaidya@iitm.ac.in
Supporting Information
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H2
Het
Het
+
HO
Ni
N
N
H2O
ligand, base
29 examples, up to 88% yield
ABSTRACT: An efficient nickel-catalyzed acceptorless dehydrogenative coupling of methyl-substituted heteroarenes with primary
alcohols is achieved using an in situ generated complex of inexpensive NiBr2 and readily available 8-aminoquinoline picolinic amide
ligand. The protocol is operationally simple, scalable, and furnished a series of high-value 2-alkenyl heteroarenes in good yields (up to
88%) with exclusive E-selectivity. The reaction proceeds with the release of water and molecular hydrogen, which was analyzed through
gas chromatography to validate the reaction mechanism.
successfully implemented in various transfer hydrogenation
Devising catalytic protocols to forge value-added products from
feed-stock materials under environmentally benign conditions is a
continuous enterprise in contemporary organic synthesis. In this
context, the conversion of alcohols into important classes of
chemical commodities offers a useful contribution towards the
conservation of finite fossil carbon resources.1 Specifically,
catalytic dehydrogenative coupling reactions of alcohols turned
out very effective to construct various carbon-carbon and carbon-
heteroatom bonds with applications in the synthesis of pivotal
carbocycles and heterocycles.2 However, the majority of these
transformations involve precious late-transition-metal based
catalysts.2a-c Delicacy of the first-row-transition metals lies in the
fact that they are highly abundant, less toxic, and cheaper than the
late-transition-metals and thus, the utilization of first-row-
transition metal based catalysis for the advancement of similar
transformations is highly desirable.2d-e
Olefins are essential building blocks for the construction of
important molecular frameworks including natural product.3
Particularly, aryl-substituted olefins bearing N-heteroarene unit
represent various drug molecules and agrochemicals having
promising biological activities.4 They have also found
applications in the synthesis of high electron affinity polymers for
light emitting diodes (LEDs).5 Recently, as a transformative
alternative to furnish functionalized alkenes, acceptorless
dehydrogenative coupling (ADC) of alcohols with C–H acidic
compounds, where water and hydrogen are sole byproducts, has
gained significant attention.6 Following the pioneering work of
Milstein,7 there has been a rush in the scientific community and,
among the first-row transition metals, successes have primarily
been accomplished with Mn-catalysis.8 Recently, Maji group
reported Mn-NNN pincer complexes for the -olefination of
methyl substituted heteroarenes using primary alcohols (Scheme
1a, top).9At the same time, Kempe group independently utilized
isolated Mn-catalyst stabilized by PNP ligand for the olefination
of heteroarene (Scheme 1a, bottom).10 Kempe catalyst was also
successfully utilized to prepare vinyl sulfone and , unsaturated
ketones.11 While these protocols are very effective, necessity in
the use of expensive Mn(CO)5Br as the catalyst precursor and
utilization of electron-rich PNP ligand are pivotal issues.
Meanwhile, nickel catalysis has turned out very promising
alternative to noble metal catalysis for various organic
transformations and coupling processes.12 It has also been
reactions.2n,13 However, utilization of nickel catalysis in
acceptorless
dehydrogenative
olefination
processes
is
underdeveloped.14
Scheme 1. Transition-Metal-Catalyzed Olefination of Methyl-
Substituted Heteroarenes
a) Previous work: Mn-catalyzed alkenylation of methyl-substituted N-heteroarenes
Ligand
Ligand:
Me
H
N
[in situ generated
N
ref
9
complex]
N
N
Het
Catalyst:
N
Het
Mn
+
R
N
N
N
Precursor: Mn(CO)5Br
R
OH
HN
(iPr)2
N
NH
P
P(iPr)2
Mn
Isolated
H
OC
CO
ref 10
Catalyst
b) This work: Ni-catalyzed alkenylation of methyl-substituted N-heteroarenes
Ligand:
O
OH
N
H
Het
Het
+
H2
+
+
H2
O
Ni
Ar
N
N
N
N
Ar
Precursor: NiBr2
Ligand, KOtBu

inexpensive Ni-catalyst  simple ligand  exclusive E-alkene  high yield and broad scope
Herein, we report the -olefination of heteroarenes with the
extrusion of hydrogen gas through the development of a nickel-
catalyzed acceptorless dehydrogenative coupling of primary
alcohols with methyl-substituted heteroarenes (Scheme 1b).
It is worth noting that, during the preparation of our manuscript,
Balaraman et al. communicated a nickel-NNN pincer complex for
the synthesis of styrenes and stilbenes from benzyl alcohols and
sulfones.15
We commenced our investigations by following the reaction of
2-methylquinoline 1a and benzyl alcohol 2a using different Ni-
catalysts in combination with diverse N-based amide ligands
(Table 1). Satisfyingly, olefination proceeded smoothly when
mixture of 1a and 2a in t-BuOH was exposed to Ni-complex
generated in situ from NiCl2 and 8-aminoquinoline picolinic
o
amide ligand L1 in the presence of t-BuOK at 140 C and the
desired product 2-styryl quinoline 3a was isolated in 70% yield
(entry 1). The reaction was also efficient with NiCl2.DME (73%)
and yield further improved to 88% when NiBr2 was employed
(entries 2-3). Notably, the alkylation product 3a’ was not detected
for these cases. Further screening of ligands revealed that the
reaction was unfruitful with ligand L2 and only 40% yield of 3a
was obtained with ligand L3 (entries 4-5). Screening of bidentate
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ligand L4–L6 gave inferior results (entries 6-8). Changing the
and 3q in 74% and 68% yields, respectively. Substitutions in the
quinoline ring were also considered; 6-chloro, 6-bromo, and 7-
chloro substituted 2-methylquinolines gave desired products 3r–t
in uniformly high yields.
Unfortunately, under the present reaction conditions, benzyl
alcohols with strongly electron withdrawing substituents (nitro,
ester), secondary alcohol, and aliphatic alcohol such as 1-octanol
did not deliver the desired alkenylation products 3u-x (Scheme 2).
Scale up was also suitable; gram scale reaction of 1a with 2a
gave the desired product 3a in 79% yield, which is comparable to
the small scale reaction (Scheme 2).
1
2
3
4
5
6
7
8
reaction solvent from t-BuOH to THF (38%), dioxane (17%), and
toluene (59%) also showed detrimental effect (entries 9-11).
Control experiments revealed that all the components, Ni-catalyst,
ligand, and base were essential for this reaction and the reaction
was ineffective in the absence of any of them (entries 12-14).
Table 1. Optimization of the Nickel-Catalyzed Olefinationa
OH
[Ni]-Cat.
ligand L1-L5
+
N
9
t-BuOK, solvent
N
N
140 °C, 48 h
3a'
Scheme 2. Olefination Scope with 2-Methylquinolines and
Primary Alcoholsa
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1a
2a
3a
(not detected)
entry
1
[Ni]-catalyst
NiCl2
ligand (L)
solvent
yield(%)b
70
NiBr2 (10 mol%)
L1 (10 mol%)
Ar
Ar
HO
L1
L1
L1
L2
L3
L4
L5
L6
L1
L1
L1
L1
-
t-BuOH
t-BuOH
t-BuOH
t-BuOH
t-BuOH
t-BuOH
t-BuOH
t-BuOH
THF
t-BuOK, t-BuOH
N
N
140 °C, 48 h
1
2
3
2
NiCl2.DME
NiBr2
NiBr2
NiBr2
NiBr2
NiBr2
NiBr2
NiBr2
NiBr2
NiBr2
-
73
with benzyl alcohol derivatives
Me
OMe
3
88
N
N
N
4
trace
40
3a, 88%
gram scale (79%)
3b, 87%
3c, 79%
5
Me
OMe
6
18
N
N
N
3d, 82%
3e, 76%
3f, 83%
Me
7
22
8c
28
N
N
N
9
38
tBu
N
3i, 84%
OMe
3g, 82%
3h, 71%
10
11
12
13
14d
dioxane
toluene
t-BuOH
t-BuOH
t-BuOH
17
59
N
N
N
<10
<10
0
F
Cl
Br
3j, 69%
3k, 76%
3l, 81%
with polycyclic aromatic alcohols
NiBr2
NiBr2
L1
N
N
N
aReaction conditions: 1a (0.5 mmol), 2a (0.25 mmol), [Ni]-cat.
(0.025 mmol, 10 mol %), ligands L1–L6 (0.025 mmol, 10 mol%),
t-BuOK (0.275 mmol, 1.1 equiv), solvent (0.5 mL), 140 °C, 48 h.
3m, 80%
3n, 82%
3o, 79%
with heterocyclic alcohols
bIsolated yield of 3a. L6 was bipyridine. In the absence of t-
c
d
BuOK.
N
N
S
S
3p, 74%
3q, 68%
Ligands:
with substituted quinoline derivatives
Br
O
O
O
O
O
Cl
N
H
N
N
N
N
H
H
H
H
N
N
N
Et2
N
Et2
N
N
N
N
N
Cl
N
N
N
L1
L2
L5
L3
L4
3s, 75%
3t, 83%
3r, 78%
unfruitful quinoline derivatives
With the optimized reaction conditions in hand, we explored the
scope of this olefination reaction and results are summarized in
Scheme 2. The high efficiency shown by the NiBr2/L1 catalyst
system in the model reaction was effectively translated to a wide
variety of substituted 2-methylquinoline derivatives 1 with
different alcohol derivatives 2 and exclusive E-selectivity was
observed in all cases. Alcohols having electron-donating
substituents such as methyl (3b,d,f), methoxy (3c,e,i), t-butyl
(3g), diphenylamino (3h) and electron-deficient halogen
substituents (3j–l) at para-, meta-, and ortho-positions of the aryl
ring delivered 2-olefinated quinolines in good yields (69-88%).
Interestingly, sterically hindered aromatic alcohols such as 1-
napthylmethanol, 9-anthracenemethanol and 1-pyrenemethanol
underwent cross-dehydrogenative coupling smoothly to afford the
alkene products 3m–o in high yields. Also, heterocyclic primary
alcohols, for examples 2-thiophenemethanol and benzothiophene-
2-methanol, furnished unsymmetrical 1,2-heteroaryl alkenes 3p
3u (R = NO2), 0%
3v (R = CO2Et), 0%
N
N
N
( )6
3w, 0%
3x, 0%
R
aReaction conditions: 1 (0.5 mmol), 2 (0.25 mmol), NiBr2 (0.025
mmol, 10 mol%), L1 (0.025 mmol, 10 mol%), t-BuOK (0.275
mmol, 1.1 equiv), t-BuOH (0.5 mL), 140 °C, 48 h. Yields of
isolated products were given.
The versatility of the protocol was further explored by studying
olefination with different heteroarenes (Scheme 3). Under the
standard reaction conditions, 2-methylpyrazine cleanly reacted
with benzyl alcohol, p-tolylmethanol, and 1-naphthalenemethanol
to produce corresponding 2-olefinated pyrazines 5a-c in high
yields. 2-Methylquinoxaline was also a good substrate for this
process, offering 5d–e in very high yields. 4-Methylquinoline and
3-methylbenzo[f]quinoline also rendered desired olefins 5f and 5g
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The Journal of Organic Chemistry
in 74% and 70% yields, respectively. Other alkyl heteroarenes
such as 2-methylbenzothiazole and 1-benzyl-2-
methylbenzimidazole were also effectively participated in this
cross-dehydrogenative olefination reaction, forging 5h and 5i,
respectively, in synthetically useful yields (Scheme 3).
1
2
3
4
5
6
7
8
Scheme4. Mechanistic Investigations and Plausible Reaction
Mechanism
(a) Hydrogen detection
NiBr2 (10 mol%)
L1 (10 mol%)
H2
+
+
HO
Ph
t-BuOK, t-BuOH
140 °C, 6 h
N
N
Ph
Scheme 3. Scope of -Olefination with Diverse Methyl-
Substituted N-heteroarenesa
(observed in GC)
1a
2a
3a
(b) Reaction with benzaldehyde
NiBr2 (10 mol%)
L1 (10 mol%)
X
X
Ar Het
N
NiBr2 (10 mol%)
L1 (10 mol%)
Ar Het
HO
+
Ph
t-BuOK, t-BuOH
O
N
4
9
t-BuOK, t-BuOH
N
N
Ph
140 °C, 48 h
2
5
140 °C, 6 h
1a
3a, 68%
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with various heteroarenes
N
N
N
N
N
(c) In the absence of 1a
A
Ni/L1 complex
(10 mol%)
N
5a, 81%
5b, 75%
Me
5c, 73%
5f, 74%
H2
(observed in GC)
HO
Ph
Ph
+
O
t-BuOK, t-BuOH
140 °C, 6 h
2a
N
N
N
O
(d) Reaction with isolated Ni-L1 complex
N
N
N
A
Ni-L1 complex
(10 mol%)
N
Ni
Br
N
5d, 84%b
5e, 72%b
Me
+
HO
Ph
A
t-BuOK, t-BuOH
N
N
Ph
ESI-HRMS
MH+ = 385.9439 (expected)
140 °C, 48 h
1a
2a
3a 86%
N
S
N
N
,
385.9449 (observed)
(e) Hg drop experiment
N
Ph
Ni/L1 complex A
(10 mol%)
5g, 70%
5h, 59%
5i, 62%
HO
Ph
+
t-BuOK, t-BuOH
140 °C, 48 h
Hg (50 equiv)
N
N
Ph
aReaction conditions: 4 (0.5 mmol), 2 (0.25 mmol), NiBr2 (0.025
mmol, 10 mol%), L1 (0.025 mmol, 10 mol%), t-BuOK (0.275
mmol, 1.1 equiv), t-BuOH (0.5 mL), 140 °C, 48 h. Yields of
isolated products weregiven.b4 (0.25 mmol) and 2 (0.50 mmol)
were used.
1a
2a
3a
, 79%
(f) Plausible mechanism
O
O
N
HO
t-BuOK
-KBr
N
Ni
O
Ar
N
N
N
or
N
Ni
Br
A
N
3
5
To gain mechanistic insight of this alkenylation reaction,
various experiments were carried out. Gas chromatography
analysis during the course of the reaction under optimal reaction
conditions confirmed the formation of hydrogen gas and
benzaldehyde (Scheme 4a). Under standard reaction conditions,
1a also smoothly reacted with benzaldehyde to give desired
product 3a (Scheme 4b). Further, when 2a was treated under the
reaction conditions in the absence of 1a, benzaldehyde was
formed along with the liberation of hydrogen gas (Scheme 4c).
These findings suggest that the present alkenylation reaction
proceeds via acceptorless dehydrogenative coupling pathway.
Further, Ni-L1 complex A was isolated and characterized through
1H-NMR, 13C-NMR, and HRMS spectroscopic techniques.16
When the benchmark reaction of 1a with 2a was tested using
isolated Ni-L1 complex under optimal reaction conditions, product
3a was isolated in
B
t-BuOK
H2
(NiBr2/L1 complex)
H
O
Ar
N
4
1
or
O
HO
N
N
Ni
H
N
C
In conclusion, we have identified a Ni(II) complex of readily
available 8-aminoquinoline picolinic amide ligand for
acceptorless dehydrogenative coupling (ADC) of primary
alcohols with 2-methylheteroarenes. A series of high-value -
olefinated heteroarenes were prepared in good to very high yields
with complete E-selectivity. The catalytic protocol is scalable,
uses inexpensive NiBr2 as the catalyst precursor, and is
environmentally benign as water and molecular hydrogen are sole
byproducts. Further, applications of such catalytic processes are
currently ongoing in our laboratory.
86% yield (Scheme 4d). When the olefination reaction was
performed in the presence of excess mercury (50 equiv), the
expected product was obtained in 79% yield, confirming the
homogeneity of the present catalytic system and refuting the
involvement of metal nanoparticles (Scheme 4e).
Based on these findings and previous literature reports,14a-c
a
EXPERIMENTAL SECTION
plausible reaction mechanism of Ni-NNN pincer catalyst for
alkenylation of methyl-substituted heteroarene with primary
alcohol is depicted in Scheme 4f. The active complex A thus
formed from NiBr2 and ligand L1 reacts with primary alcohol in
the presence of t-BuOK to give Ni-alkoxide species B. It then
undergoes -H elimination to give the corresponding aldehyde
and nickel-hydride species C. The liberated aldehyde condensed
with 2-alkyl heteroarene (1 or 4) to afford alkenylated product 3
or 5. Further, reaction of primary alcohol with nickel-hydride
species C generates alkoxy complex B with the liberation of
hydrogen and continues the catalytic cycle.
All non-aqueous reactions were carried out under an argon
atmosphere in flame-dried glassware and were stirred using a
magnetic stir plate. All the 2-Methylheteroarenes (1 and 4) and 4-
methyquinoline were received from Aldrich and ABC labtory
companies and used without further purification. All reactions
were carried out using anhydrous solvent unless otherwise noted.
DMSO and DMF were purchased from Acros Organic Company.
Dry toluene, xylene, tetrahydrofuran and 1,4-dioxane were
prepared by distilling over sodium ketyl. Anhydrous potassium
tert-butoxide and anhydrous tert-Butyl alcohol was purchased
from Aldrich Company.All reactions were monitored by thin layer
3
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chromatography (TLC) on WhatmanPartisil®K6F TLC plates
156.8, 148.3, 136.2, 129.9, 129.7, 129.6, 129.5, 129.2, 127.6,
127.4, 127.3, 126.1, 125.6, 120.9, 119.1, 111.1, 55.6.
1
2
3
4
5
6
7
8
(silica gel 60 Å, 0.25 mm thickness) and visualized using a UV
lamp (366 or 254 nm) or by use of one of the following
visualization reagents: PMA: 10 g phosphomolybdic acid/ 100
mL ethanol, KMnO4: 0.75 g potassium permanganate, 5 g K2CO3
(E)-2-(3-Methylstyryl)quinoline 3d20: White solid, yield: 82%
(50 mg); 1H NMR (400 MHz, CDCl3) δ 8.12 (d, J = 8.5 Hz, 1H),
8.08 (d, J = 8.5 Hz, 1H), 7.78 (dd, J = 7.9, 0.8 Hz, 1H), 7.73 –
7.64 (m, 3H), 7.51 – 7.39 (m, 4H), 7.30 (t, J = 7.6 Hz, 1H), 7.15
(d, J = 7.5 Hz, 1H), 2.40 (s, 3H). 13C{1H} NMR (100 MHz,
CDCl3) δ 156.2, 148.4, 138.5, 136.6, 136.5, 134.7, 129.9, 129.6,
129.3, 129.0, 128.8, 128.1, 127.6, 127.5, 126.3, 124.6, 119.3,
21.6.
/
100mL water. Products were isolated by column
chromatography (Merck silica gel 100-200μm). Yields refer to
chromatographically and spectroscopically homogenous materials
1
unless noted otherwise. H and13C NMR spectra were recorded
on a Bruker 400 or Bruker 500 MHz spectrometers. Chemical
shift values (δ) are reported in ppm and calibrated to the residual
9
solvent peak CDCl3 δ = 7.260 ppm for 1H, δ = 77.160 ppm for 13
C
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(E)-2-(3-Methoxystyryl)quinoline 3e9:White solid, yield: 76%
(49 mg); 1H NMR (400 MHz, CDCl3) δ 8.11– 8.07 (m, 2H), 7.76
(d, J = 8 Hz, 1H), 7.72 – 7.66 (m, 2H), 7.64 (d, J = 11.5 Hz, 1H),
7.49 (t, J = 7.4 Hz, 1H), 7.41 (d, J = 16.3 Hz, 1H), 7.31 (t, J = 7.9
Hz, 1H), 7.23 – 7.19 (m, 2H), 6.89 (dd, J = 8.1, 2.1 Hz, 1H), 3.85
(s, 3H).13C{1H} NMR (100 MHz, CDCl3) δ 160.0, 156.0, 148.3,
138.0, 136.5, 134.5, 129.9 (2C), 129.4, 129.3, 127.6, 127.5, 126.3,
120.3, 119.3, 114.9, 112.0, 55.4.
calibrated to tetramethylsilane (δ = 0.00). All NMR spectra were
recorded at ambient temperature (290 K) unless otherwise noted.
1H NMR spectra are reported as follows: chemical shift
(multiplicity, coupling constant, integration). The following
abbreviations are used to indicate multiplicities: s, singlet; d,
doublet; t, triplet; q, quartet; quint, quintet; sext, sextet; sept,
septet; m, multiplet; dd, doublet of doublet; dt, doublet of triplet;
dq, doublet of quartet; td, triplet of doublet; tt, triplet of triplet; dq,
doublet of quartet; br, broad; app, apparent. Mass spectra were
recorded by electron spray ionization (ESI) method on a Q-TOF
Micro with lock spray source. GC-TCD (Agilent-7820 A) analysis
was carried out using 5A and porapak Q column connected in
series using gas switching valve.Ligands (L1 – L5)17-18 were
prepared according to the literature procedure.
(E)-2-(4-Methylstyryl)quinoline 3f20: White solid, yield: 83%
(51 mg); 1H NMR (400 MHz, CDCl3) δ 8.09 (d, J = 8.3 Hz, 2H),
7.77 (d, J = 8.1 Hz, 1H), 7.72 – 7.64 (m, 3H), 7.54 (d, J = 8.0 Hz,
2H), 7.48 (t, J = 7.5 Hz, 1H), 7.37 (d, J = 16.3 Hz, 1H), 7.21 (d, J
= 7.9 Hz, 2H), 2.38 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ
156.3, 148.4, 138.9, 136.4, 134.6, 133.9, 129.8, 129.7, 129.3,
128.2, 127.6, 127.4, 127.3, 126.2, 119.3, 27.6.
Procedure for Nickel-catalyzed direct alkenylation of alkyl-
heteroarenes with primary alcohols:
(E)-2-(4-(Tert-butyl)styryl)quinoline 3g10: White solid, yield:
1
82% (59 mg); H NMR (400 MHz, CDCl3) δ 8.10 (dd, J = 8.1,
Methyl-heteroarene 1 (0.5 mmol), primary alcohols 2 (0.25
mmol), NiBr2 (0.025 mmol, 10 mol %), Ligand L1 (0.025 mmol,
10 mol%) and t-BuOK (0.275 mmol, 1.1 equiv) were taken in a
dried schlenk tube with a magnetic stir bar under argon. Then, dry
t-BuOH (0.5 mL) was added with a syringe. The reaction tube
was closed and the resulting mixture was placed in a preheated oil
bath at 140 ºC for 48 h. After completion, the reaction was
quenched with water (3 mL) and extracted with ethyl acetate (3 x
10 mL). The combined organic layer was dried over anhydrous
Na2SO4 and concentrated under vacuum. The resulting residue
was purified by column chromatography over silica gel (100–200
mesh) with hexane/ethyl acetate mixture (95:5 to 85:15) as eluent.
6.3 Hz, 2H), 7.78 – 7.76 (m, 1H), 7.72 – 7.69 (m, 2H), 7.66 (d, J
= 7.2 Hz, 1H), 7.59 (d, J = 8.3 Hz, 2H), 7.51 – 7.49 (m, 1H) 7.44
(d, J = 8.3 Hz, 2H), 7.40 (d, J = 16.4 Hz, 1H), 1.36 (s,
9H).13C{1H} NMR (100 MHz, CDCl3) δ 156.4, 152.1, 148.4,
136.4, 134.4, 133.8, 129.8, 129.2, 128.4, 127.6, 127.4, 127.2,
126.2, 125.9, 119.2, 31.4.
(E)-N,N-Diphenyl-4-(2-(quinolin-2-yl)vinyl)aniline 3h: Yellow
solid, yield: 71% (71 mg); 1H NMR (400 MHz, CDCl3) δ 8.09 (d,
J = 8.6 Hz, 1H), 8.06 (d, J = 8.5 Hz, 1H), 7.76 (d, J = 8.1 Hz, 1H),
7.70 – 7.60 (m, 3H), 7.51 – 7.45 (m, 3H), 7.31 – 7.25 (m, 5H),
7.15 – 7.13 (d, J = 7.8 Hz, 4H), 7.08 – 7.05 (m, 4H). 13C{1H}
NMR (100 MHz, CDCl3) δ 156.5, 148.5, 148.4, 147.5, 136.7,
134.2, 130.3, 129.8, 129.5, 129.2, 128.3, 127.6, 127.4, 127.1,
126.1, 125.1, 123.6, 122.9, 119.2. HRMS (TOF MS ES+)
calcd.for C29H22N2H+ [M + H+] m/z 399.1861, found 399.1870.
1
(E)-2-Styrylquinoline 3a19: White solid, yield: 88% (51 mg); H
NMR (400 MHz, CDCl3) δ 8.13 (d, J = 8.6 Hz, 1H), 8.09 (d, J =
8.5 Hz, 1H), 7.79 (d, J = 8.1 Hz, 1H), 7.73 – 7.64 (m, 5H), 7.50 (t,
J = 7.5 Hz, 1H), 7.44 – 7.39 (m, 1H), 7.41 – 7.39 (m, 2H), 7.33 (t,
J = 7.2 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 156.2,
148.4, 136.7, 136.5, 134.6, 129.9, 129.4, 129.2, 128.9, 128.8,
127.6, 127.5, 127.4, 126.3, 119.4.
(E)-2-(4-Methoxystyryl)quinoline 3i20: White solid, yield: 84%
(55 mg); 1H NMR (400 MHz, CDCl3) δ 8.12– 8.06 (m, 2H), 7.77
(d, J = 8.1 Hz, 1H), 7.72 – 7.58 (m, 5H), 7.48 (t, J = 7.5 Hz, 1H),
7.28 (d, J = 17.5 Hz, 1H), 6.94 (d, J = 8.2 Hz, 2H), 3.85 (s, 3H).
13C{1H} NMR (100 MHz, CDCl3) δ 160.3, 156.5, 148.4, 136.4,
134.3, 129.8, 129.5, 129.2, 128.8, 127.6, 127.4, 127.0, 126.1,
119.3, 114.4, 55.5.
(E)-2-(2-Methylstyryl)quinoline 3b20: Colorless oil, yield: 87%
1
(53 mg); H NMR (400 MHz, CDCl3 ) δ 8.14 – 8.09 (m, 2H),
7.95 (d, J = 16.2 Hz, 1H), 7.80 – 7.67 (m, 5H), 7.50 (t, J = 7.4 Hz,
1H), 7.33 (d, J = 16.1 Hz, 1H), 7.24 (brs, 2H), 2.53 (s, 3H).
13C{1H} NMR (100 MHz, CDCl3) δ 156.4, 148.4, 136.7, 136.5,
135.7, 132.3, 130.7, 130.3, 129.9, 129.4, 128.6, 127.6, 127.5,
126.5, 126.3, 126.0, 119.5, 20.2.
(E)-2-(4-Fluorostyryl)quinoline 3j21: White solid, yield: 69%
(43 mg); 1H NMR (400 MHz, CDCl3) δ 8.11 (d, J = 8.6 Hz, 1H),
8.08 (d, J = 8.5 Hz, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.73 – 7.69 (m,
1H), 7.66 (d, J = 9.3 Hz, 1H), 7.62 – 7.59 (m, 3H), 7.52 – 7.48
(m, 1H), 7.31 (d, J = 16.3 Hz, 1H), 7.09 (t, J = 8.6 Hz, 2H).13C
{1H} NMR (100 MHz, CDCl3) δ 163.1 (d, J = 247.4 Hz), 155.9,
148.4, 136.5, 133.3, 132.8 (d, J = 3.4 Hz), 129.9, 129.3, 129.0 (d,
J =8.1 Hz), 128.8 (d, J =2.3 Hz), 127.7, 127.5, 126.3, 119.4, 116.0
(d, , J = 21.6 Hz).
(E)-2-(2-Methoxystyryl)quinoline 3c20: Colorless oil, yield: 79%
(50 mg); 1H NMR (400 MHz, CDCl3) δ 8.10 – 8.08 (m, 2H), 8.03
(d, J = 16.6 Hz, 1H), 7.77 – 7.67 (m, 4H), 7.49 – 7.45 (m, 2H),
7.33 – 7.26 (m, 1H), 7.01 (t, J = 7.5 Hz, 1H), 6.93 (d, J = 8.2 Hz,
1H), 3.92 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 157.5,
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The Journal of Organic Chemistry
(E)-2-(4-Chlorostyryl)quinoline 3k20: White solid, yield: 76%
(50 mg); H NMR (400 MHz, CDCl3) δ 8.09 (t, J = 8.5 Hz, 2H),
ES+) calcd.for C19H13NSH+ [M + H+] m/z 288.0847, found
288.0851.
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7.77 (d, J = 8.1 Hz, 1H), 7.70 (t, J = 7.7 Hz, 1H), 7.65 – 7.60 (m,
2H), 7.54 (d, J = 8.2 Hz, 2H), 7.49 (t, J = 7.5 Hz, 1H), 7.37 – 7.33
(m, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 155.7, 148.4, 136.5,
135.2, 134.4, 133.1, 129.9, 129.6, 129.3, 129.1, 128.5, 127.6,
126.4, 121.0, 119.5.
(E)-6-Chloro-2-styrylquinoline 3r20: White solid, yield: 78% (52
1
mg); H NMR (400 MHz, CDCl3) δ 8.01 – 7.99 (m, 2H), 7.74 –
7.73 (m, 1H), 7.71 – 7.62 (m, 5H), 7.42 – 7.31 (m, 4H). 13C{1H}
NMR (100 MHz, CDCl3) δ 156.3, 146.7, 136.5, 135.5, 135.0,
131.9, 130.9, 130.7, 129.0, 128.9, 128.6, 128.0, 127.4, 126.3,
120.3.
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(E)-2-(4-Bromostyryl)quinoline 3l21: White solid, yield: 81%
(63 mg); 1H NMR (400 MHz, CDCl3) δ 8.13 (d, J = 8.6 Hz, 1H),
8.08 (d, J = 8.5 Hz, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.71 (t, J = 7.7
Hz, 1H), 7.65 – 7.61 (m, 2H), 7.53 – 7.48 (m, 5H), 7.40 – 7.36
(m, 1H).13C{1H} NMR (100 MHz, CDCl3) δ 155.7, 148.4, 136.6,
135.6, 133.3, 132.1, 130.0, 129.7, 129.3, 128.8, 127.7, 127.6,
126.5, 122.7, 119.5.
(E)-6-Bromo-2-styrylquinoline 3s20: White solid, yield: 75% (58
mg); 1H NMR (400 MHz, CDCl3) δ 7.99 (d, J = 8.6 Hz, 1H), 7.94
– 7.91 (m, 2H), 7.75 (dd, J = 8.9, 2.2 Hz, 1H), 7.68 (d, J = 16.3
Hz, 1H), 7.66 – 7.62 (m, 3H), 7.42 – 7.32 (m, 4H). 13C{1H} NMR
(100 MHz, CDCl3) δ 156.4, 146.9, 136.4, 135.4, 135.1, 133.3,
131.0, 129.7, 128.9 (2C), 128.6, 128.5, 127.4.120.3, 120.0.
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(E)-2-(2-(Naphthalen-1-yl)vinyl)quinoline 3m10: White solid,
1
yield: 80% (56 mg); H NMR (400 MHz, CDCl3) δ 8.53 (d, J =
(E)-7-Chloro-2-styrylquinoline 3t21: White solid, yield: 83% (55
16.0 Hz, 1H), 8.35 (d, J = 8.3 Hz, 1H), 8.17 – 8.13 (m, 2H), 7.93
– 7.71 (m, 6H), 7.61 – 7.46 (m, 5H). 13C{1H} NMR (100 MHz,
CDCl3) δ 156.2, 148.4, 136.6, 134.2, 133.9, 131.9, 131.6, 131.5,
129.9, 129.4, 129.1, 128.8, 127.7, 127.6, 126.5, 126.4, 126.1,
125.8, 124.3, 123.9, 119.7.
1
mg); H NMR (400 MHz, CDCl3) δ 8.08-8.06 (m, 2H), 7.71 (dd,
J = 7.3, 6.3 Hz, 1H), 7.68 (d, J = 1.6 Hz, 1H), 7.65 – 7.61 (m,
3H), 7.44-7.34 (m, 5H). 13C{1H} NMR (100 MHz, CDCl3) δ
157.0, 148.8, 136.5, 136.2, 135.7, 135.3, 129.0 (2C), 128.8, 128.6,
128.3, 127.5, 127.2, 125.8, 119.8.
(E)-2-(2-(Anthracen-9-yl)vinyl)quinoline 3n: Yellow solid,
1
(E)-2-Styrylpyrazine 5a9: White solid, yield: 81% (40 mg); H
1
yield: 84% (69 mg); H NMR (400 MHz, CDCl3) δ 8.63 (d, J =
NMR (400 MHz, CDCl3) δ 8.65 (d, J = 0.6 Hz, 1H), 8.55 – 8.54
(m, 1H), 8.41 (d, J = 2.4 Hz, 1H), 7.76 (d, J = 16.1 Hz, 1H), 7.60
(d, J = 7.4 Hz, 2H), 7.40 (t, J = 7.4 Hz, 2H), 7.36 – 7.34 (m, 1H),
7.16 (d, J = 16.1 Hz, 1H).13C{1H} NMR (100 MHz, CDCl3) δ
151.4, 144.5, 143.9, 142.9, 136.2, 135.4, 129.2, 129.0, 127.5,
124.2.
16.5 Hz, 1H), 8.45 – 8.43 (m, 2H), 8.32 (dd, J = 5.7, 3.3 Hz, 1H),
8.22 (d, J = 8.4 Hz, 1H), 8.15 (d, J = 8.4 Hz, 1H), 8.05 – 8.03 (m,
2H), 7.86 – 7.84 (m, 1H), 7.81 – 7.74 (m, 3H), 7.57 – 7.55 (m,
1H), 7.51 – 7.48 (m, 3H), 7.29 (dd, J = 16.4 Hz, 1H).13C{1H}
NMR (100 MHz, CDCl3) δ 155.7, 148.5, 137.6, 136.7, 134.3,
133.6, 132.0, 131.6, 131.2, 130.0, 129.8, 129.6, 128.9, 127.7,
127.4, 127.3, 126.5, 126.1, 125.9, 125.4, 119.8. HRMS (TOF MS
ES+) calcd.for C25H17NH+ [M + H+] m/z 332.1439, found
332.1450.
(E)-2-(4-Methylstyryl)pyrazine 5b9: White solid, yield: 75% (37
mg); 1H NMR (400 MHz, CDCl3) δ 8.62 (d, J = 1.4 Hz, 1H), 8.52
– 8.51 (m, 1H), 8.38 (d, J = 2.5 Hz, 1H), 7.72 (d, J = 16.1 Hz,
1H), 7.49 (d, J = 8.1 Hz, 2H), 7.20 (d, J = 8.0 Hz, 2H), 7.10 (d, J
= 16.1 Hz, 1H), 2.37 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ
151.6, 144.4, 143.8, 142.6, 139.3, 135.2, 133.4, 129.7, 127.4,
123.1, 21.5.
(E)-2-(2-(Pyren-1-yl)vinyl)quinoline 3o: Yellow solid, yield:
79% (70 mg); 1H NMR (500 MHz, CDCl3) δ = 8.83 (d, J = 15.9
Hz, 1H), 8.61 (d, J = 9.1 Hz, 1H), 8.45 (d, J = 7.9 Hz, 1H), 8.20 –
8.16 (m, 5H), 8.10 – 8.00 (m, 4H), 7.81 (dd, J = 8.5, 5.5 Hz, 2H),
7.75 (t, J = 7.8 Hz, 1H), 7.66 (d, J = 15.9 Hz, 1H), 7.54 – 7.50 (m,
1H); 13C{1H} NMR (125 MHz, CDCl3) δ 156.2, 148.4, 136.6,
131.7, 131.6, 131.6, 131.4, 131.0, 131.0, 130.0, 129.4, 129.2,
128.1, 127.9, 127.7, 127.6 (2C), 126.4, 126.2, 125.7, 125.4, 125.4,
125.2, 125.0, 124.1, 123.1, 119.8. HRMS (TOF MS ES+)
calcd.for C27H17NH+ [M + H+] m/z 356.1439, found 356.1458.
(E)-2-(2-(Naphthalen-1-yl)vinyl)pyrazine 5c: White solid, yield:
73% (42 mg); 1H NMR (400 MHz, CDCl3) δ 8.69 (s, 1H), 8.62 –
8.59 (m, 2H), 8.45 – 8.44 (m, 1H), 8.30 (d, J = 8.3 Hz, 1H), 7.90
– 7.84 (m, 3H), 7.60 – 7.50 (m, 3H), 7.22 (d, J = 15.7 Hz, 1H).
13C{1H} NMR (100 MHz, CDCl3) δ 151.5, 144.6, 144.1, 143.0,
133.9, 133.8, 132.4, 131.6, 129.5, 128.8, 126.8, 126.6, 126.2,
125.7, 124.3, 123.8. HRMS (TOF MS ES+) calcd.for C16H12N2H+
[M + H+] m/z 233.1079, found 233.1086.
(E)-2-(2-(Thiophen-2-yl)vinyl)quinoline 3p20: White solid,
1
yield: 74% (44 mg); H NMR (400 MHz, CDCl3) δ 8.10 (d, J =
8.6 Hz, 1H), 8.06 (d, J = 8.5 Hz, 1H), 7.84 (d, J = 16.0 Hz, 1H),
7.79 – 7.74 (m, 1H), 7.72 – 7.68 (m, 1H), 7.58 (d, J = 8.6 Hz,
1H), 7.51 – 7.46 (m, 1H), 7.30 – 7.29(m, 1H), 7.24 – 7.19 (m,
2H), 7.06 – 7.04 (m, 1H).13C{1H} NMR (100 MHz, CDCl3) δ
155.7, 148.4, 142.2, 136.5, 129.9, 129.2, 128.3, 128.3, 128.0,
127.6, 127.5, 127.4, 126.3, 126.2, 119.5.
(E)-2-Styrylquinoxaline 5d9: White solid, yield: 84% (49 mg);
1H NMR (400 MHz, CDCl3) δ 9.03 (s, 1H), 8.08– 8.05 (m, 2H),
7.86 (d, J = 16.3 Hz, 1H), 7.77 – 7.73 (m, 1H), 7.71 – 7.64 (m,
3H), 7.44 – 7.34 (m, 4H). 13C{1H} NMR (100 MHz, CDCl3) δ
150.7, 144.5, 142.5, 141.7, 136.5, 136.1, 130.4, 129.4 (2C), 129.3
(2C), 129.0, 127.6, 125.4. HRMS (TOF MS ES+) calcd.for
C16H12N2H+ [M + H+] m/z 233.1079, found 233.1086.
(E)-2-(2-(Benzo[b]thiophen-2-yl)vinyl)quinoline 3q: White
solid, yield: 68% (49 mg); 1H NMR (400 MHz, CDCl3) δ 8.14 (d,
J = 8.6 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 15.9 Hz,
1H), 7.82 – 7.70 (m, 4H), 7.62 (d, J = 8.6 Hz, 1H), 7.53 – 7.49
(m, 1H), 7.43 (s, 1H), 7.37 – 7.32 (m, 2H), 7.26 (d, J = 15.9 Hz,
1H).13C{1H} NMR (100 MHz, CDCl3) δ 155.3, 148.5, 142.3,
140.2, 139.7, 136.6, 130.8, 130.0, 129.4, 128.0, 127.7, 127.6,
126.5, 125.7, 125.5, 124.8, 124.0, 122.5, 119.9. HRMS (TOF MS
(E)-2-(4-Methylstyryl)quinoxaline 5e: White solid, yield: 72%
(44 mg); 1H NMR (400 MHz, CDCl3) δ 9.02 (s, 1H), 8.07 – 8.04
(m, 2H), 7.84 (d, J = 16.3 Hz, 1H), 7.76 – 7.67 (m, 2H), 7.55 (d,
J = 7.8 Hz, 2H), 7.33 (d, J = 16.3 Hz, 1H), 7.26 – 7.22 (m, 2H),
2.39 (s, 3H) ppm. 13C{1H} NMR (100 MHz, CDCl3) δ 151.0,
144.6, 142.6, 141.6, 139.6, 136.6, 133.4, 130.4, 129.8, 129.4,
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129.2, 128.5, 127.6, 124.5, 21.6 ppm. HRMS (TOF MS ES+)
calcd.for C17H14N2H+ [M + H+] m/z 247.1235, found 247.1240.
HRMS (TOF MS ES+) calcd.for C15H10BrN3NiOH+ [M + H+]
m/z 385.9439, found 385.9449(See SI page S34-S36 for spectra).
Procedure for Reaction with isolated Ni-L1 complex: In a 15
mL Schlenk tube, complex A (0.025 mmol, 10 mol%), 2-
methylquinoline 1 (0.50 mmol), benzyl alcohol 2 (0.25 mmol), t-
BuOK (0.275 mmol), and t-BuOH (0.5 mL) were added under
argon. The reaction mixture was heated for 48 h. Then, it was
cooled, quenched with water (4 mL) and extracted with ethyl
acetate (3 x 10 mL). The organic layer was dried over anhydrous
Na2SO4 and volatiles were evaporated under reduced pressure.
The residue was purified by column chromatography and the
desired product 3a was isolated in 86% yield.
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(E)-4-Styrylquinoline 5f9: White solid, yield: 74% (43 mg); H
NMR (400 MHz, CDCl3) δ 8.91 (d, J = 4.6 Hz, 1H), 8.22 (d, J =
8.5 Hz, 1H), 8.14 (d, J = 8.5 Hz, 1H), 7.82 (d, J = 16.1 Hz, 1H),
7.76 – 7.72 (m, 1H), 7.65 – 7.58 (m, 4H), 7.44 (t, J = 7.5 Hz, 2H),
7.38 – 7.33 (m, 2H). 13C{1H} NMR (100 MHz, CDCl3) δ 150.2,
148.7, 143.0, 136.6, 135.2, 130.1, 129.4, 128.9, 128.8, 127.2,
126.6, 126.4, 123.5, 122.9, 117.1.
9
(E)-3-Styrylbenzo[f]quinoline 5g: White solid, yield: 70% (49
mg); 1H NMR (400 MHz, CDCl3) δ 8.92 (d, J = 8.6 Hz, 1H), 8.61
(d, J = 8.2 Hz, 1H), 8.00 (brs, 2H), 7.94 (d, J = 7.8 Hz, 1H), 7.80
– 7.62 (m, 6H), 7.46 – 7.40 (m, 3H), 7.35 – 7.32 (m, 1H). 13C{1H}
NMR (100 MHz, CDCl3) δ 155.7, 148.4, 136.8, 134.2, 131.7,
131.3 (2C), 129.8, 128.9 (2C), 128.7 (2C), 128.3, 127.4, 127.3,
127.2, 124.4, 122.7, 119.8. HRMS (TOF MS ES+) calcd.for
C21H15NH+ [M + H+] m/z 282.1283, found 282.1287.
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e) Mercury drop experiment: In a 15 mL Schlenk tube, complex
A (10 mol%), 2-methylquinoline 1a (0.50 mmol), benzyl alcohol
2a (0.25 mmol), t-BuOK (0.275 mmol), Hg (50 equiv with
respect to complex A), and t-BuOH were added under argon. The
reaction mixture was kept for heating for 48 h. Then, the reaction
mixture was filtered through celite. The filtrate was worked up
with water and ethyl acetate (3 x 10 mL). The resultant organic
layer was dried over anhydrous Na2SO4 and the solvent was
evaporated under reduced pressure. The residue was purified by
column chromatography and the desired product 3a was isolated
in 79% yield.
(E)-2-Styrylbenzo[d]thiazole 5h: White solid, yield: 59% (35
mg); 1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 8.2 Hz, 1H), 7.86
(d, J = 8.0 Hz, 1H), 7.59 – 7.58 (m, 2H), 7.55 – 7.47 (m, 2H),
7.45 – 7.36 (m, 5H). 13C{1H} NMR (100 MHz, CDCl3) δ 167.1,
154.0, 137.8, 135.5, 134.5, 129.6, 129.1, 127.5, 126.5, 125.5,
123.1, 122.3, 121.6. HRMS (TOF MS ES+) calcd for
C15H11NSH+ [M + H+] m/z 238.0690, found 238.0690.
Typical experimental procedure for nickel-catalyzed
directalkenylation of 2-methylquinoline with benzyl alcohol in
gram scale: In a 100 mL Schlenk flask, 2-Methylquinoline 1a
(2.86g, 20 mmol), benzyl alcohol 2a (1.08g, 10 mmol), NiBr2
(0.22g, 1 mmol ), Ligand L1 (0.25g, 1 mmol) t-BuOK (1.23g, 11
mmol), and t-BuOH (20 mL) were taken under argon. The
reaction tube was closed and the resulting mixture was heated at
140 ºC. The progress of the reaction was monitored by TLC.
Upon completion, the reaction was quenched with water (30 mL)
and the organic layer was extracted with ethyl acetate (3 x 40
mL). Evaporation of the combined organic layers followed by
column chromatography over silica gel (mesh 100–200 mesh)
with hexane/ethyl acetate mixture as eluent afforded (E)-2-styryl
quinoline3a in 79% (1.82 g) isolated yield.
(E)-1-Benzyl-2-styryl-1H-benzo[d]imidazole 5i9: White solid,
1
yield: 62% (48 mg); H NMR (400 MHz, CDCl3) δ 7.98 (d, J =
15.8 Hz, 1H), 7.81 (d, J = 7.9 Hz, 1H), 7.52 (d, J = 7.4 Hz, 2H),
7.38 – 7.19 (m, 9H), 7.12 (d, J = 7.2 Hz, 2H), 7.04 (d, J = 15.8
Hz, 1H), 5.45 (s, 2H).13C{1H} NMR (100 MHz, CDCl3) δ 151.2,
143.4, 137.8, 136.2, 136.0 135.8, 129.2 (2C), 128.9, 128.1, 127.4
(2C), 126.3, 123.0, 119.6, 113.1, 109.7, 47.0.
Mechanistic Investigations:
a) Qualitative analysis of hydrogen gas liberation by GC-TCD
detector: In a 15 mL Schlenk tube, 2-methylquinoline 1a (0.50
mmol), benzyl alcohol 2a (0.25 mmol), t-BuOK (0.275 mmol,
1.1 equiv), NiBr2 (0.025 mmol, 10 mol %), Ligand L1 (0.025
mmol, 10 mol%) and t-BuOH (0.5 mL) were added under argon.
The reaction mixture was kept for heating for 6 h. Then, the
gaseous mixture was analysed on GC (TCD detector) which
showed the formation of hydrogen gas (See SI page S32-S33 for
Chromatogram).
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website. Copies of 1H and 13C NMR spectra for
all compounds (PDF).
d) Reaction with isolated Ni-L1 complex:
AUTHOR INFORMATION
Procedure for Synthesis of Ni-L1 complex: To a solution of L1
(50 mg, 0.2 mmol, 1 equiv) in t-BuOH (2 mL), NiBr2 (43.8 mg, 1
equiv) and t-BuOK (22.5 mg, 1 equiv) were added and the
mixture was heated at 80 °C for 1 h. A yellow color precipitate
was formed. The precipitate was filtered off and washed with
hexane (2 x 4 mL). The yellow solid was dissolved in DCM (5
mL) and filtered through syringe filter. The filtrate was
concentrated and dried under vacuum to afford Ni-L1 complex as
a yellow solid in 82% yield.
Corresponding Author
mbaidya@iitm.ac.in
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We gratefully acknowledge DST-SERB India for financial
Characterization of Ni-L1 complex : 1H NMR (500 MHz,
CDCl3) δ 8.99 (dd, J = 17.2, 5.4 Hz, 2H), 8.69 (d, J = 7.7 Hz, 1H),
8.24 – 8.21 (m, 1H), 7.95 – 7.92 (m, 1H), 7.80 (d, J = 7.7 Hz,
1H), 7.51 (t, J = 7.9 Hz, 1H), 7.36 – 7.29 (m, 3H). 13C{1H} NMR
(125 MHz, CDCl3) δ 166.7, 156.3, 154.5, 153.8, 146.8, 143.8,
140.3, 139.1, 129.6, 129.2, 127.1, 123.8, 121.9, 120.2, 120.0.
support.
BMR
thanks
IIT
Madras
for
Institute
PostdoctorialFellowship. We also thank the Department of
Chemistry, IIT-Madras for instrumental facilities.
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