ONO pincer type Pd(II) complexes: Synthesis, crystal structure and catalytic activity towards C-2 arylation of quinoline scaffolds

Article abstract of DOI:10.1039/c5ra15342e

Four new palladium(II) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. These complexes showed excellent catalytic activity towards the Suzuki-Miyaura cross coupling reaction of 2-chloroquinoline derivatives with various aryl boronic acids. The main advantages over previous methodologies include low catalyst loading, less problematic reaction media (H₂O-DMF (80:20%)) and a lower reaction temperature of 60 °C for optimal performance.

Full text of DOI:10.1039/c5ra15342e

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ONO Pincer type Pd(II) complexes: Synthesis, crystal structure and catalytic
activity towards C-2 arylation of quinoline scaffolds
Vignesh Arumugama, Werner Kaminskyb and Dharmaraj Nallasamy a*
aInorganic & Nanomaterials Research Laboratory, Department of Chemistry,
Bharathiar University, Coimbatore 641 046, India.
bDepartment of Chemistry, University of Washington, Seattle, Washington 98195, USA.
Eꢀmail: dharmaraj@buc.edu.in
Fax: +91 4222422387; Tel: +91 4222428319
ABSTRACT
Four new palladium(II) complexes featuring ONO pincer type hydrazone ligands were synthesized and
characterized by spectroscopic and singleꢀcrystal XRD analysis. These complexes showed excellent
catalytic activity towards SuzukiꢀMiyaura cross coupling reaction of 2ꢀchloroquinoline derivatives with
various aryl boronic acids. The main advantages over previous methodologies include low catalyst
loading, less problematic reaction media (H2OꢀDMF (80:20%)) and a lower reaction temperature of 60
°C for optimal performance.
INTRODUCTION
Nitrogen based heterocycles are important constituents in a large number of biologically active
compounds.1 Among which quinoline scaffolds play a vital role. Several quinolines and their derivatives
are currently in use as antibacterial, antifungal, analgesics, antituberculosis, antimalarial, antiꢀ
inflammatory, anticancer, antibiotic and antiꢀHIV drugs.2 In addition, quinoline analogues are valuable
synthons for the preparation of nano and mesostructures with enhanced electronic and photonic
properties.3 Despite the numerous pharmacological activities and related synthetic methods,4 the
development of new, facile and ecoꢀfriendly synthetic approaches to 2ꢀsubstituted quinolines using mild
conditions are desirable and subject of ongoing research. 2ꢀArylated quinoline and their derivatives have
proven significant in vivo activities against Leishmaniadonovani and are in preclinical development.5
Likewise, a few other 2ꢀaryl quinolines display significant antiviral activity in HIVꢀinfected cells.6
Within the efforts to realize 2ꢀsubstituted quinolines, most established routines require elevated reaction
temperatures, prolonged reaction times, excess amounts of various reagents, including toxic compounds
and harsh reaction conditions7 which are unsuitable for sensitive substrates and thus constitute a
challenge in targeted syntheses. Palladium catalyzed SuzukiꢀMiyaura crossꢀcoupling (SMC) reactions
were tried as an alternative, but unfortunately, nitrogen containing heterocycles are problematic
substrates for SMC reactions8 because of a tendency to bind with the metal ion and thus deactivates the
catalyst.

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However, catalysts like [PdCl2(PPh3)2] and Pd(OAc)2/DtBPF (DtBPF
=
1,1′ꢀbis(ditertꢀ
butylphosphino)ferrocene) were reported to offer improved results compared to the PdꢀL catalysts with
electronꢀrich, bulky, monodentate phosphine ligands such as PtBu3 and PCy2ꢀ (biphenyl), but requiring a
high catalyst loading (5 mol %).8 (c),9
Figure1. Biologically active 2ꢀphenylquinoline derivatives
Currently, our group is actively pursuing research on the synthesis and biological applications of
hydrazone based transition metal complexes with pincer type geometry.10 More recently, we turned our
attention to evaluate hydrazone based pincer type palladium complexes as catalysts for the SMC
reaction.11 Synthesis of transition metal pincer type complexes with high stability and catalytic activity
has been a most productive area of homogeneous catalysis and coordination chemistry.12,13 The
remarkable equilibrium between stability and reactivity of the pincer complexes can be controlled by
precise ligand design and subsequent coꢀoperative construction of metal complexes.13 As a result,
research on the development of pincer ligands possessing CCC, CNC, PNP, SNS, NNN, NCN and SCS
donor atoms got much attention.14 However, studies on ONO pincer ligands and corresponding
complexes are scanty in the literature. A recent review on Ru, Ir, W, Ta, Re, Pb, Fe and Sb complexes
containing ONO pincer ligand moiety highlighted their importance as catalysts in various organic
reactions.13a, 15 In our previous study, we reported for the first time, the catalytic potential of11 ONO
pincer analogous palladium complexes for SMC of challenging aryl chlorides with various aryl boronic
acids bearing activating as well as deactivating substituents.
In this manuscript, we describe the synthesis of four new palladium(II) complexes (1 – 4) bearing ONO
pincer type ligands and their catalytic activity towards SMC reaction of 2ꢀchlroroquinoline derivatives
with substituted aryl boronic acids. To the best of our insight, this is the first study on the utility of the

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titled complexes as catalysts in SMC reactions of 2ꢀchlroroquinoline derivatives with substituted aryl
boronic acids in H2OꢀDMF system to synthesis a library of 2ꢀarylquinolines.
RESULTS AND DISCUSSIONS
Direct reactions of palladium precursor [PdCl2(PPh3)2] with the pincer type ligands H3L1–H3L4 ( where,
H3L is pincer type ligand derived from the condensation of salicylaldehyde with salicylichydrazide
(H3L1) or 3ꢀhydroxynaphthoic acid hydrazide(H3L2), and 4ꢀmethoxysalicylaldehyde with
salicylichydrazide (H3L3) or 3ꢀhydroxynaphthoic acid hydrazide (H3L4)) yielded complexes 1–4 of the
type [Pd(HL)(PPh3)] as depicted in Scheme 1.
Where R = H or OCH3
Scheme 1. Synthesis of ligands and their respective Pd(II) complexes.
IR spectra of the four complexes were compared with corresponding free ligands. The absorption due to
free OH groups of the ligands observed respectively, at 3719, 3614, 3610 and 3640 cmꢀ1. A strong band
observed at 3185, 3260, 3181, and 3249 cmꢀ1 indicated the presence of a N−H functional group in the
free ligands. Intense C=O absorption bands were found at 1618, 1641, 1624, and 1623 cmꢀ1 in the
spectrum of the free ligands. All four ligands exhibited a very sharp band at 1555, 1572, 1556, and
1556 attributed to the C=N group. In the IR spectra of the complexes discussed here, nonꢀexistence of a
strong band from free OH indicated the deprotonation of phenolic oxygen and its coordination to the
palladium(II) ion. The N−H and C=O stretching vibrations were missing thus proving that the ligands
underwent enolisation followed by deprotonation prior to coordination with the palladium(II) ion.16a In
addition, a new band occurred due to the C=N−N=C group at 1494, 1472, 1488, and 1473 cmꢀ1,
respectively. The absorption related to a C−O group was identified as a new sharp band at 1255, 1299,
1222 and 1303 cmꢀ1 in for complexes 1 ꢀ 4. The IR spectral features unambiguously prove that the
pincer type ligands H3L1, H3L2, H3L3, and H3L4 were coordinated to palladium(II) ion via the
phenolate oxygen, the azomethine nitrogen and the imidolate oxygen in complexes 1−4.16b
1H NMR spectra of them were recorded in order to study the exact coordination mode of the pincer type
ligand in the palladium complexes 1−4. None displayed any signal due to a N−H proton and thus
indicated that the oxygen is coordinated to the palladium ion in the imidolate form. Sharp singlet
observed in the spectra of complexes 1–4 at 8.61, 9.15, 8.20, and 9.39 ppm, respectively were assigned
to the azomethine proton of the pincer ligand. The nonꢀinvolvement of OH groups, despite their
presence in the phenyl/naphthyl ring of the corresponding pincer type ligands in coordination with

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palladium ion is confirmed by the singlet resonances at 6.38, 5.77, 5.36, and 5.40 ppm, respectively.
However, in the spectra of complexes 3, and 4 a sharp singlet at 3.81 and 3.42 ppm, respectively
confirmed the presence of a methoxy group. Aromatic protons present in complexes 1–4 were identified
in the region of 8.34 to 6.98 ppm.17 Similarly, the 13C NMR resonance of the complexes showed
downfield signals at 159.2, 159.3, 159.2, and 157.8 ppm, respectively, owing to the imidolate carbon
(N=C–O) involved in coordination. The azomethine carbon of the complexes 1–4 gave signals at 151.5,
151.6, 151.5, and 148.5, respectively. Signals featuring in the region of 143.8–105.1 and at 55.2/51.4
ppm have been assigned to aromatic and methoxy carbons present in complexes 1–4.17
The molecular structure of complexes 1–4 were determined by singleꢀcrystal Xꢀray diffraction to
study the exact coordination mode of the pincer type ligands with palladium ion. Selected bond angles
and bond distances are gathered in Table 1 in the ESI. The ORTEP diagrams provided in Figure 2–5
shows pincer type ligands coordinated to the palladium ion via the phenolate oxygen, azomethine
nitrogen and deprotonated imidole oxygen. Complex 1 crystallized in the triclinic system, but the other
three were primitive monoclinic with space groups Pꢀ1, P21/a , P21/c and P21/c, respectively. The Pd(II)
ion adopts a distorted squareꢀplanar geometry in all four structures by accommodating the ligand as a
binegative tridentate ONO donor and the fourth site is occupied by a triphenylphosphine. The bite
angles of O(1)– Pd(1)–O(2) in 1–4 are 174.29(8), 174.30(13), 174.37(6), and 173.74(15), respectively.
Similarly, angles N(1)–Pd(1)–P(1) are 174.77(7), 173.09(9), 179.17(5), and 172.74(13). Unit cell
packing diagrams of complexes 1–4 are provided in ESI. The observed bond lengths and bite angles are
very similar to those observed in other palladium(II) complexes.18 Relevant data concerning data
collection and details of the structure refinements are summarized Table 2 in the electronic
1
13
supplementary information (ESI). Based on H, C NMR and singleꢀcrystal XRD data, the pincer type
hydrazone ligand is coordinated to the palladium ion in a tridentate fashion by replacing both chloride
ions and the triphenylphospine from the starting precursor.
Figure 2. ORTEP diagram of complex 1 with thermal ellipsoids at the 50% probability level.

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(Catalyst 1)
Figure 3. ORTEP diagram of complex 2 with thermal ellipsoids at the 50% probability level
.
(Catalyst 2)
Figure 4. ORTEP diagram of complex 3 with thermal ellipsoids at the 50% probability level.
(Catalyst 3)

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Figure 5. ORTEP diagram of complex 4 with thermal ellipsoids at the 50% probability level.
(Catalyst 4)

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Table 1. Optimization of reaction conditions
B(OH)2
Catalyst 2 (0.01 mol %)
+
N
Base (5 mmol), 4-6 h, 50-70 °C,
solvent (5 mL).
N
Cl
Entry
1
Catalyst
Base
Solvent
Yield (%)
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 2
Catalyst 1
Catalyst 2
Catalyst 3
No base
No base
KOH
H2O
No reaction
19
2
H2O / DMF
3
H2O / DMF
90
4
K2CO3
NaOH
Na2CO3
CH3COONa
Et3N
H2O / DMF
85
5
H2O / DMF
84
6
H2O / DMF
79
7
H2O / DMF
52
8
H2O / DMF
45
9
Pyridine
KOH
H2O / DMF
39
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
H2O / DCM
40
KOH
H2O / toluene
H2O / CHCl3
H2O / DMF
41
KOH
43
KOH
90
KOH
H2O / CH3CN
H2O / THF
72
KOH
61
KOH
H2O / DMSO
H2O / EtOAc
H2O / benzene
H2O / DMF (10 %)
H2O / DMF (20 %)
H2O / DMF (30 %)
H2O / DMF (40 %)
H2O / DMF (50 %)
H2O / DMF (20 %)
H2O / DMF (20 %)
H2O / DMF (20 %)
82
KOH
55
KOH
53
KOH
80
KOH
90
KOH
83
KOH
76
KOH
70
KOH
85
KOH
90
KOH
79

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27
Catalyst 4
KOH
H2O / DMF (20 %)
96

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Catalysis
Catalytic activity of the complexes 1–4 were investigated towards SMC reactions of 2ꢀ
chloroquinoline derivatives with different substituted aryl boronic acids. Reaction conditions were
optimized by utilizing 2ꢀchloroquinoline and phenylboronic acid as model substrates in aqueous–
organic media and the results are summarized in Table 1.
Initially, the catalytic reaction was studied with various bases such as KOH, NaOH, K2CO3,
NaHCO3, Na2CO3, CH3COONa, Et3N, and pyridine, where KOH provided a coupled product of
90% isolated yield. No reaction was observed in neat water, because of catalyst insolubility
(Table 1, entry 1). This problem was circumvented by adding organic solvents to help dissolve the
catalyst in the reaction media. A 80:20% mixture of H2OꢀDMF was found to be most effective for
the titled coupling reaction. A comparative catalytic study was carried out involving all the four
catalysts towards the chosen SMC reaction. Catalysts 2 and 4 performed better than the other two
which may be related to a napthyl unit in the coordinated pincer ligand. In particular catalyst 4
with a methoxy substituent in the salicylaldehyde part, is more effective than catalyst 2, which is
composed of nonꢀsubstituted salicylaldehyde in its molecular architecture. The role of
triphenylphosphine ligand in the catalysts 1–4 is to help in activating C–Cl bonds in quinolines.19
Figure 6. Effect of temperature on the SMC reaction
.
In addition, the effect of temperature on this coupling reaction was investigated by using 2ꢀ
chloroquinoline (3 mmol), phenylboronic acid (4 mmol), KOH (5 mmol), catalyst 4 (0.01 mol
%) in H2OꢀDMF (80:20%) and the isolated yield of coupled products were illustrated in Figure
6. A distinct optimum was reached at 60 °C.

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To further explore the scope and application of the reaction, we studied the reaction of various
aryl boronic acids with 2ꢀchloroquinoline derivatives under the optimized conditions mentioned
above. Aryl boronic acids featuring an electronꢀ donating group such as –CH3, –OCH3, t–
(CH3)3C–, –OH, and –NR2 furnished the reaction smoothly and afforded 65–92% of the coupled
products over a period of 4–6 h (Table 2 entries 1c, 1f, 1k, 2c, 2f and 2k). Interestingly, sterically
hindered aryl boronic acids afforded a 82–90% yield (Table 2 entries 1b, 1d, 1e, 1g, 1h, 1i, 2b,
2d, 2e, 2g, 2h and 2i). Similarly, boronic acids bearing moderate electron with drawing groups
such as Br and –COCH3 efficiently underwent the coupling reaction, to afford the products in
74–90% (Table 2 entries 1j, 1l, 2j and 2l). Not even a trace of neither homocoupling of aryl
boronic acids nor coupling with –OH and –Br groups of the substrates were observed (Table 2,
entry 1g, 1j, 2g, and 2j). This offers an opportunity to conduct further crossꢀcoupling reactions
by exploiting the halogenated positions available on selective boronic acids (Table 2, entry 1j
and 2j).
Catalyst loading tests of complex 4 revealed best performance for 0.01 mol%. Reducing catalyst
stacking from 0.01–0.0001 mol% under optimized conditions resulted in low yield as reported
earlier.20 On the other hand, use of 0.0001 mol% catalyst resulted in high turnover number
(Table 3).
Reusability of the selected catalyst 4, 0.01 mol% was screened and the trend of the isolated yield
is summarized in Figure 7. A 20 mL round bottom flask was charged with 2ꢀchloroquinoline (3.0
mmol) and phenylboronic acid (4 mmol), KOH (5 mmol) in H2OꢀDMF (80:20%). To this
reaction mixture was added catalyst 4 (0.01 mol%) and heated to 60 °C. After completion of the
reaction, the mixture was extracted with ethyl acetate and the organic layer was subjected to
column chromatography to separate the catalyst and product using silica gel and petroleum ether/
ethyl acetate (90/10%) as an eluent. The recovered catalyst was washed with distilled water,
dried and utilized for the next cycle under same reaction conditions. The identity of the
recovered catalyst was confirmed by Rf value (0.54) and melting point of the original catalyst
219ꢀ221 °C. The first cycle afforded 96% of the corresponding coupled product, but yield
decreased steadily in subsequent cycles (Figure 7).

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Table 2. SMC reaction of 2ꢀchloroquinolines with substituted phenylboronic acids using
complex 4 as catalysta

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a=Reaction conditions: 2ꢀchloroquinoline or 6ꢀmethylꢀ2ꢀchloroquinoline (3.0 mmol), aryl boronic acid
(4.0 mmol), 0.01 mol % of complex 4, KOH (5.0 mmol), H2O (4 mL), and DMF (1 mL) stirred for 4–6 h
at 60 °C.
b=Isolated yield after column chromatography, TON =Turnover number = ratio of moles of product
formed to moles of catalyst used, TOF = Turnover frequency = TON/h.
Table 3. Low catalyst loading on SMC reaction
Entry
Mol %
Isolated yield %
TON
1
2
3
0.01
96
92
85
9,600
0.001
0.0001
92,000
850,000
Figure 7. Reusability of catalyst 4
Very recently, P. T. Perumal et al21 reported a SnCl2.2H2O mediated synthesis of 2–substituted
quinolines in ethanol via A3ꢀ coupling followed by reductive cyclization in 89% yield.
Advantageously, we herein demonstrated that SMC of aryl boronic acids with 2ꢀchloroquinolines

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catalyzed by new ONO pincer type palladium(II) complex led to similar 2ꢀarylquinolines in an
excellent yield up to 97% in H2OꢀDMF over a period of 4–6 h with low catalyst loading (0.01
mol %).
CONCLUSIONS
Herein, we portrayed the synthesis of four new palladium complexes bearing ONO pincer type
ligands along with thorough characterization using IR, 1H and 13C NMR and singleꢀcrystal XRD
techniques. These complexes showed strong performance in the Suzuki–Miyaura coupling
reaction between 2ꢀchloroquinoline scaffolds and aryl boronic acids with low catalyst loading in
H2OꢀDMF (80:20%) at moderate temperature. We feel that the present palladium catalyzed
methodology offers a simple and straight forward route to synthesize a series of biologically
important 2ꢀarylquinolines possessing both activating and deactivating groups in excellent
yields.
EXPERIMENTAL SECTION
All chemicals utilized for the synthesis of ligands and their complexes were obtained from
SigmaꢀAldrich, India. Solvents were purified and dried according to standard procedures.22
Elemental analysis (C, H and N) was performed on a Vario EL III Elemental analyzer
instrument. IR spectra (4000–400 cm−1) were recorded on a Nicolet Avatar Model FTꢀIR
spectrophotometer. Melting points were determined with a Lab India instrument.1H and 13C
NMR spectra were recorded in deuterated CHCl3 as solvent on BRUKER 400 and 100 MHZ
instruments, respectively.
Synthesis of ligands
Pincer type ligands H3L were synthesized by condensing equimolar amounts of salicylaldheyde
or 4ꢀmethoxy salicylaldheyde with salicylhydrazide (H3L1 and H3L3) or 3ꢀhydroxyꢀ2ꢀnaphthoic
acid hydrazide (H3L2 and H3L34) in ethanol according to literature method (Scheme 1).The
reaction mixture was then refluxed on a waterꢀbath for 4 h and poured into crushed ice. The
corresponding solid pincer type ligand formed was filtered, washed several times with distilled
water and recrystallized from ethanol in 80–90% yield. The purity of the ligands were checked
by various analytical techniques and is in accordance with literature reports.23
General method for the synthesis of the palladium complexes
To a warm methanolic solution (20–30 mL) of appropriate ligands (1 equiv.) were added a
chloroform solution of [PdCl2(PPh3)2] (1 equiv.) followed by two drops of triethylamine. The
reaction mixture was refluxed 6–7 h and kept at room temperature for crystallization. Needle like

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reddish brown crystals suitable for Xꢀray studies were obtained on slow evaporation over 45–60
days.
[Pd(HL1)(PPh3)] (complex 1) Yield 71%. M.p. 207–210 °C. Elemental analysis (%) calculated
for C32H25N2O3PPd; C, 61.70; H, 4.05; N, 4.50. Found (%); C, 61.68; H, 4.03; N, 4.46. UVꢀ
visible (solvent: DMSO, nm): 296, 313, 372, and 400. Selected IR bands (KBr, ν in cm−1): 3322,
1596, 1494, and 1255. 1H NMR (CDCl3, δ ppm) 8.61 (s, 1H), 8.34 (d, J = 9.2 Hz, 2H), 8.20 (d, J
= 8 Hz, 2H), 7.56 (t, J = 9.8 Hz, 2H), 7.42–7.48 (m, 9H), 7.31–7.41 (m, 4H), 7.28 (d, J = 6.8 Hz,
13
2H), 6.38 (s, 1H). C NMR (CDCl3, δ ppm) 159.2, 151.5, 143.8, 141.55, 140.3, 137.7, 135.5,
133.7, 132.3, 131.4, 129.3, 128.1, 127.2, 126.5, 126.1, 125.4, 125.1, 124.8, 113.3, 110.0.
[Pd(HL2)(PPh3)] (complex 2) Yield 69%. M.p. 215–218 °C. Elemental analysis (%) calculated
for C36H27N2O3PPd; C, 64.25; H, 4.04; N, 4.16. Found (%); C, 64.23; H, 4.02; N, 4.14. UVꢀ
visible (solvent: DMSO, nm): 298, 316, 371, and 400. Selected IR bands (KBr, ν in cm−1):
1
3322,1593, 1472 and 1299. H NMR (CDCl3, δ ppm) 9.15 (s, 1H), 8.10 (s, 3H), 7.80–7.84 (m,
13
6H),7.57 (t, J = 7.8 Hz, 5H), 7.48 (t, J = 9.6 Hz, 7H), 7.31 (t, J = 2.6 Hz, 4H), 5.77 (s, 1H). C
NMR (CDCl3, δ ppm) 159.3, 151.6, 143.2, 141.7, 137.6, 132.7, 132.6, 132.0, 130.9, 128.5,
128.0, 127.4, 126.3, 126.1, 125.8, 125.1, 124.9, 123.5, 119.8, 114.3, 110.7.
[Pd(HL3)(PPh3)] (complex 3) Yield 76%. M.p. 212–214 °C. Elemental analysis (%) calculated
for C33H27N2O4PPd; C, 60.70; H, 4.17; N, 4.29. Found (%); C, 60.68; H, 4.15; N, 4.26.UVꢀ
visible (solvent: DMSO, nm): 299, 316, 360, and 391. Selected IR bands (KBr, ν in cm−1): 3416,
1597, 1488, and 1222. 1H NMR (CDCl3, δ ppm) 8.20 (s, 1H), 7.81 (d, J = 7.6 Hz, 4H), 7.53–7.56
(m, 3H), 7.48 (t, J = 9.8 Hz, 4H), 7.28–7.39(m, 8H), 6.98 (d, J = 8.4 Hz, 3H), 5.36 (s, 1H), 3.81
(s, 3H). 13C NMR (CDCl3, δ ppm) 159.2, 151.5, 143.6, 141.7, 139.4, 137.3, 133.5, 133.1, 132.3,
131.6, 129.4, 128.9, 128.5, 126.5, 126.4, 125.6, 125.3, 124.4, 123.0, 113.6, 110.7, 51.4.
Pd(HL4)(PPh3)] (complex 4) Yield 74%. M.p. 219–221 °C. Elemental analysis (%) calculated
for C37H29N2O4PPd; C, 63.21; H, 4.16; N, 3.98. Found (%);C, 63.20; H, 4.14; N, 3.94. UVꢀ
visible (solvent: DMSO, nm): 291, 319, 372, and 401. Selected IR bands (KBr, ν in cm−1): 3416,
1
1593, 1473, and 1303. H NMR (CDCl3, δ ppm) 9.39 (s, 1H), 8.09 (s, 5H), 7.96 (t, J = 11.6 Hz,
3H), 7.65 (t, J = 8.0 Hz, 4H), 7.59 (d, J = 8.0 Hz, 5H), 7.39–750 (m, 4H), 7.37 (d, J = 8.0 Hz,
3H), 5.40 (s, 1H), 3.42 (s, 3H). 13C NMR (CDCl3, δ ppm) 157.8, 148.5, 143.1, 141.9, 141.8,
136.1, 134.8, 131.1, 129.3, 128.6, 128.1, 127.5, 126.9, 126.5, 126.4, 125.5, 124.6, 123.1, 122.7,
118.6, 105.1, 55.2.

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Single crystal X-ray diffraction studies
Data collection: singleꢀcrystal Xꢀray diffraction data of complexes 1–4 were collected on Bruker
APEX II single crystal Xꢀray diffractometer. The data was integrated and scaled using SAINT /
SADABS from within the APEX2 software package by Bruker (Version 2.1ꢀ4). Indexing and
unit cell refinement indicated complex 1 is triclinic and all other complexes were primitive
monoclinic, with space groups P1, P21/a , P21/c and P21/c, respectively. Solution by direct
methods (SHELXS, SIR97)24 produced complete heavy atom phasing models consistent with the
proposed structures. The structures were completed by difference Fourier synthesis with
SHELXL97.25,26 Scattering factors are from Waasmair and Kirfel.27 Hydrogen atoms were placed
in geometrically idealized positions and constrained to ride on their parent atoms with C–H
distances in the range 0.95–1.00 Angstrom. Isotropic thermal parameters Ueq were fixed such
that they were 1.2Ueq of their parent atom Ueq for CH's and 1.5Ueq of their parent atom Ueq in
case of methyl groups. All nonꢀhydrogen atoms were refined anisotropically by fullꢀmatrix leastꢀ
squares.
Catalysis
General procedure for Suzuki-Miyaura C–C coupling reaction and recycling of the
catalyst-4
A 20 mL round bottom flask was charged with 2ꢀchloroquinoline (3 mmol), phenylboronic acid
(4 mmol) and KOH (5 mmol) in H2OꢀDMF (80:20%). Then, the catalyst 4 (0.01 mol %) was
added to this mixture and stirred at 60 °C. The progress of the SMC reaction was monitored by
thin layer chromatography (petroleum ether/ ethyl acetate (90ꢀ10%)) and the Rf value of the
product was measured to be 0.61. After completion of the reaction, the mixture was solvent
diluted with ethyl acetate and dried over anhydrous Na2SO4. Solvent was evaporated under
vacuo and the residue was purified by column chromatography using petroleum ether/ EtOAc as
eluent to afford 2ꢀphenylquinoline as a pale yellow solid. The product was washed with distilled
13
water to remove inorganic base. The identity of the product was confirmed by 1H and C NMR
data.
NMR spectral data of coupled products as listed in Table 3.
1H and 13C NMR spectra were recorded in deuterated CHCl3 and DMSO as solvent on BRUKER
400 and 100 MHZ instruments, respectively. The signals corresponding to various protons of the
coupled products are assigned by comparison with reported data.28
Entry 1a: 2ꢀphenylquinoline: Elemental analysis (%) calculated for C15H11N; C, 87.77; H, 5.40;
1
N, 6.82. Found (%); C, 87.72; H, 5.38; N, 6.81. H NMR δ (ppm): 7.96 (d, J = 8 Hz, 2H), 7.85–
7.91(m, 3H), 7.74 (d, J = 7.6 Hz, 1H), 7.32–7.37 (m, 1H), 7.29 (d, J = 7.6 Hz, 2H), 7.26 (d, J =

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13
9.6 Hz, 1H) 7.16–7.18 (m, 1H). C NMR: δ (ppm): 157.8, 149.1, 143.1, 140.9, 139.3, 133.7,
130.4, 129.5, 128.3, 128.1, 127.7.
Entry 1b: 2ꢀoꢀtolylquinoline: Elemental analysis (%) calculated for C16H13N; C, 87.64; H, 5.98;
1
N, 6.39. Found (%); C, 87.61; H, 5.95; N, 6.38. H NMR δ (ppm): 7.93 (d, J = 8 Hz, 1H), 7.81–
7.86(m, 1H), 7.63(d, J = 7.2 Hz, 2H), 7.34–7.37 (m, 1H), 7.29–7.33 (m, 2H), 7.19 (d, J = 8.2 Hz,
13
2H), 7.13 (d, J = 7.4 Hz, 1H), 2.38 (s, 3H). C NMR: δ (ppm): 156.7, 148.9, 143.2, 141.0,
139.5, 137.9, 130.3, 129.6, 129.0, 128.8, 128.5, 126.8, 126.6, 125.3, 125.2, 21.3.
Entry 1c: 2ꢀpꢀtolylquinoline: Elemental analysis (%) calculated for C16H13N; C, 87.64; H, 5.98;
N, 6.39. Found (%); C, 87.62; H, 5.96; N, 6.37. 1H NMR δ (ppm): 7.92 (d, J = 8.4 Hz, 2H), 7.84
(d, J = 8.2 Hz, 1H), 7.80 (d, J = 7.6 Hz, 1H), 7.69 (d, J = 8 Hz, 1H), 7.25–7.38 (m, 1H), 7.10–
13
7.23 (m, 2H), 6.91 (d, J = 7.6 Hz, 1H), 6.80 (s, 1H), 2.43 (s, 3H). C NMR: δ (ppm): 158.2,
150.8, 144.2, 140.1, 138.8, 133.3, 130.2, 129.3, 127.9, 127.7, 125.4, 125.1, 124.9, 120.7, 21.6.
Entry 1d: 2ꢀ(2,3ꢀdimethylꢀphenyl)ꢀquinoline: Elemental analysis (%) calculated for C17H15N; C,
1
87.52; H, 6.48; N, 6.00. Found (%); C, 87.50; H, 6.46; N, 5.98. H NMR δ (ppm): 8.05 (d, J =
9.2 Hz, 1H),7.91 (q, J = 8.6 Hz, 2H), 7.68 (d, J = 8 Hz, 1H), 7.40–7.48 (m, 1H), 7.35–7.39 (m,
13
1H), 7.27–7.34 (m, 1H), 7.19–7.23 (m, 2H), 2.93 (s, 3H), 2.76 (s, 3H). C NMR: δ (ppm):
156.8, 150.4, 142.0, 140.8, 139.1, 138.8, 133.7, 133.4, 130.3, 129.8, 128.9, 128.7, 128.2, 127.7,
125.5, 125.2, 24.4, 21.1.
Entry 1e: 2ꢀ(2ꢀmethoxyꢀphenyl)ꢀquinoline: Elemental analysis (%) calculated for C16H13NO; C,
1
81.68; H, 5.57; N, 5.95. Found (%); C, 81.67; H, 5.55; N, 5.93. H NMR δ (ppm): 7.97 (d, J =
8.4 Hz, 1H), 7.82–7.88 (m, 2H), 7.58 (d, J = 7.8 Hz, 2H), 7.49 (d, J = 6.2 Hz, 1H), 7.47 (d, J =
7.5 Hz, 2H), 7.30–7.38 (m, 1H), 7.10–7.19 (m, 1H), 2.90 (s, 3H). 13C NMR: δ (ppm): 158.3,
150.9, 142.2, 140.1, 139.6, 128.8, 133.5, 131.8, 130.1, 129.2, 128.9, 128.5, 127.8, 127.7, 127.3,
51.4.
Entry 1f: 2ꢀ(4ꢀtertꢀbutylꢀphenyl)ꢀquinoline: Elemental analysis (%) calculated for C19H19N; C,
1
87.31; H, 7.33; N, 5.36. Found (%); C, 87.30; H, 7.32; N, 5.34. H NMR δ (ppm): 7.91 (s, 2H),
7.81 (d, J = 9.2 Hz, 1H), 7.68 (d, J = 9.6 Hz, 1H), 7.31–7.21 (m, 2H), 7.0 (m, 1H), 1.55 (s, 9H).
13C NMR: δ (ppm): 157.0, 148.8, 143.1, 141.4, 140.3, 137.4, 135.4, 129.5, 128.7, 128.2, 127.5,
126.8, 126.3, 125.9, 125.3, 124.1, 34.6, 29.6.
Entry 1g: 3ꢀquinolinꢀ2ꢀylꢀphenol: Elemental analysis (%) calculated for C15H11NO; C, 81.43; H,
5.01; N, 6.33. Found (%); C, 81.42; H, 4.99; N, 6.29. 1H NMR δ (ppm): 7.89–7.98 (m,1H), 7.87
(s, 2H), 7.71 (d, J = 7.6 Hz, 1H), 7.49 (dd, J = 2.4, 2.4 Hz, 1H), 7.34 (t, J = 8 Hz, 3H), 7.28 (d, J
= 7.2 Hz, 1H), 7.10–7.21 (m, 1H), 7.08 (s, 1H). 13C NMR: δ (ppm): 161.6, 159.1, 148.7, 143.9,
141.3, 140.5, 138.2, 134.7, 134.1, 129.7, 129.6, 128.3, 128.2, 127.0, 126.9, 125.1, 124.5.

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Entry 1h: 2ꢀnaphthalenꢀ2ꢀylꢀquinoline: Elemental analysis (%) calculated for C19H13N; C, 89.38;
1
H, 5.13; N, 5.49. Found (%); C, 89.35; H, 5.11; N, 5.45. H NMR δ (ppm): 7.83–7.90 (m, 3H),
7.65 (d, J = 11.2 Hz, 1H), 7.50 (d, J = 2 Hz, 1H), 7.34 (dd, J = 1.6, 8 Hz, 1H), 7.25–7.30 (m,
1H), 7.24 (d, J = 1.6 Hz, 2H), 7.20 (t, J = 1.4 Hz, 3H), 7.10–7.19 (m, 1H). 13C NMR: δ (ppm):
155.0, 148.8, 141.1, 140.4, 140.2, 139.5, 136.3, 133.8, 130.3, 129.9, 128.8, 128.6, 128.5, 127.7,
126.5, 125.4, 124.5, 124.0, 119.8, 118.9.
Entry 1i: 2ꢀbiphenylꢀ4ꢀylꢀquinoline: Elemental analysis (%) calculated for C21H15N; C, 89.65; H,
5.37; N, 4.98. Found (%); C, 89.62; H, 5.34; N, 4.95. 1H NMR δ (ppm): 7.91–7.94 (m, 2H), 7.88
(d, J = 8.4 Hz, 2H), 7.69 (d, J = 12 Hz, 1H), 7.31–7.37 (m, 3H) 7.28 (d, J = 2.8 Hz, 2H), 7.23 (d,
13
J = 7.2 Hz, 3H), 6.99 (d, J = 8 Hz, 2H). C NMR: δ (ppm): 155.0, 147.9, 143.0, 142.7, 139.6,
137.1, 137.0, 129.3, 129.0, 127.9, 126.8, 125.8, 125.1, 119.5, 116.7.
Entry 1j: 2ꢀ(4ꢀbromoꢀphenyl)ꢀquinoline: Elemental analysis (%) calculated for C15H10BrN; C,
1
63.40; H, 3.55; N, 4.93. Found (%); C, 63.38; H, 3.54; N, 4.91. H NMR δ (ppm): 7.48 (d, J =
7.6 Hz, 1H), 7.42 (d, J = 10.4 Hz, 1H), 7.32 (d, J = 6.8 Hz, 2H), 7.20–7.23 (m, 2H) 7.07–7.19
13
(m, 2H), 6.94 (s, 2H). C NMR: δ (ppm): 157.0, 147.6, 142.6, 140.2, 139.2, 137.4, 135.9,
130.3, 128.5, 127.5, 126.1, 125.6, 124.3, 119.4, 116.5, 89.1.
Entry 1k: dimethylꢀ(4ꢀquinolinꢀ2ꢀylꢀphenyl)ꢀamine: Elemental analysis (%) calculated for
1
C17H16N2; C, 82.22; H, 6.49; N, 11.28. Found (%); C, 82.20; H, 6.47; N, 11.25. H NMR δ
(ppm): 7.96 (d, J = 8 Hz, 1H), 7.83–7.87 (m, 2H), 7.73 (d, J = 7.6 Hz, 1H), 7.32–7.38 (m, 3H),
7.20–7.27 (m, 1H) 7.14 (d, J = 8.8 Hz, 2H), 2.83 (s, 6H). 13C NMR: δ (ppm): 156.5, 149.1,
143.4, 141.5, 141.3, 138.2, 133.5, 131.0, 130.2, 128.4, 128.1, 127.5, 127.1, 126.6, 125.5, 125.3,
124.3, 122.6, 37.8.
Entry 1l: 1ꢀ(4ꢀquinolinꢀ2ꢀylꢀphenyl)ꢀethanone: Elemental analysis (%) calculated for C17H13NO;
C, 82.57; H, 5.30; N, 5.66. Found (%); C, 82.56; H, 5.27; N, 5.65. 1H NMR δ (ppm): 7.91 (d, J =
8.4 Hz, 2H), 7.85 (d, J = 7.6 Hz, 2H), 7.63 (d, J = 8 Hz, 1H), 7.30–7.37 (m, 1H), 7.25 (d, J = 5.6
13
Hz, 1H), 7.14–7.20 (m, 1H), 6.95 (d, J = 12.4 Hz, 2H), 2.92 (s, 3H). C NMR: δ (ppm): 169.6,
159.3, 143.9, 143.5, 141.7, 141.1, 138.0, 134.1, 134.0, 132.8, 130.3, 128.5, 128.3, 127.7, 127.5,
126.1, 29.0.
Entry 2a: 6ꢀmethylꢀ2ꢀphenylꢀquinoline: Elemental analysis (%) calculated for C16H13N; C,
1
87.64; H, 5.98; N, 6.39. Found (%); C, 87.61; H, 5.95; N, 6.37. H NMR δ (ppm): 7.82 (s, 1H),
7.80 (d, J = 7.4 Hz, 2H), 7.59 (d, J = 2 Hz, 2H), 7.57 (t, J = 2 Hz, 1H), 7.49–7.55 (m, 3H), 7.37–
13
7.48 (m, 1H), 2.49 (s, 3H). C NMR: δ (ppm): 161.2, 148.1, 147.2, 135.7, 135.3, 129.4, 128.3,
128.1, 127.1, 126.4, 123.1, 122.0, 29.0.

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Entry 2b: 6ꢀmethylꢀ2ꢀoꢀtolylꢀquinoline: Elemental analysis (%) calculated for C17H15N; C,
1
87.52; H, 6.48; N, 6.00. Found (%); C, 87.50; H, 6.45; N, 5.98. H NMR δ (ppm): 8.50 (s, 1H),
13
7.93–8.10 (m, 5H), 7.66 (d, J = 2 Hz, 2H), 7.50–7.57 (m, 1H), 3.35 (s, 3H) 2.51 (s, 3H). C
NMR: δ (ppm): 160.3, 147.7, 147.4, 135.5, 134.9, 131.9, 128.3, 127.9, 126.9, 122.7, 121.9,
120.9, 120.1, 26.9, 19.8.
Entry 2c: 6ꢀmethylꢀ2ꢀpꢀtolylꢀquinoline: Elemental analysis (%) calculated for C17H15N; C, 87.52;
H, 6.48; N, 6.00. Found (%); C, 87.50; H, 6.45; N, 5.97. 1H NMR δ (ppm): 8.17 (s, 1H), 7.85 (d,
J = 7.6 Hz, 2H), 7.79 (d, J = 7.6 Hz, 2H), 7.54 (t, J = 7.6 Hz, 1H), 7.44 (t, J = 7.2 Hz, 1H), 7.00
(d, J = 2.4 Hz, 2H), 3.66 (s, 3H), 2.56 (s, 3H). 13C NMR: δ (ppm): 160.2, 147.9, 147.7, 136.0,
135.2, 133.1, 129.2, 128.6, 128.1, 127.0, 124.2, 121.8, 121.2, 121.1, 112.8, 21.9, 19.4.
Entry 2d: 2ꢀ(2,3ꢀdimethylꢀphenyl)ꢀ6ꢀmethylꢀquinoline: Elemental analysis (%) calculated for
1
C18H17N; C, 87.41; H, 6.93; N, 5.66. Found (%); C, 87.39; H, 6.91; N, 5.62. H NMR δ (ppm):
8.20 (s, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.84 (d, J = 7.6 Hz, 2H), 7.74 (d, J = 2.4 Hz, 1H), 7.55 (t,
J = 7.8 Hz, 2H), 7.43–7.46 (m, 2H), 3.96 (s, 3H), 3.91 (s, 3H), 2.50 (s, 3H). 13C NMR: δ (ppm):
160.4, 147.9, 135.6, 134.2, 128.3, 128.0, 127.4, 127.0, 122.9, 122.0, 119.5, 119.4, 111.8, 106.3,
26.8, 19.5, 16.2.
Entry 2e: 2ꢀ(2ꢀmethoxyꢀphenyl)ꢀ6ꢀmethylꢀquinoline: Elemental analysis (%) calculated for
1
C17H15NO; C, 81.90; H, 6.06; N, 5.62. Found (%); C, 81.88; H, 6.04; N, 5.59. H NMR δ (ppm):
8.71 (s, 1H), 8.19 (d, J = 7.6 Hz, 2H), 7.81 (d, J = 7.6 Hz, 2H), 7.68 (d, J = 8 Hz, 1H), 7.53 (t, J
13
= 7.8 Hz, 1H), 7.74–7.46 (m, 1H), 7.20–7.26 (m, 1H) 2.71 (s, 3H), 1.83 (s, 3H). C NMR: δ
(ppm): 160.4, 149.5, 146.4, 135.8, 134.4, 131.1, 129.4, 129.1, 128.8, 128.4, 128.2, 127.9, 127.4,
125.8, 12.9, 120.8, 119.5, 119.4, 111.1, 53.5, 25.1
Entry 2f: 2ꢀ(4ꢀtertꢀbutylꢀphenyl)ꢀ6ꢀmethylꢀquinoline: Elemental analysis (%) calculated for
1
C20H21N; C, 87.23; H, 7.69; N, 5.09. Found (%); C, 87.21; H, 7.66; N, 5.07. H NMR δ (ppm):
8.24 (s, 1H), 7.88 (d, J = 7.6 Hz, 1H), 7.75 (d, J = 6.8 Hz, 1H), 7.39 (d, J = 3.6 Hz, 2H), 7.61 (t,
13
J = 6.4 Hz, 1H), 7.40–7.49 (m, 2H), 7.26–7.38 (m, 1H), 2.35 (s, 3H), 1.49 (s, 9H). C NMR: δ
(ppm):161.4, 147.4, 143.9, 139.7, 137.7, 136.5, 131.6, 130.8, 129.3, 129.1, 128.6, 128.3, 127.9,
127.7, 127.5, 126.8, 126.7, 125.3, 123.1, 120.8, 120.4, 119.1, 110.7, 106.5, 31.6, 32.4, 23.4.
Entry 2g: 3ꢀ(6ꢀmethylꢀquinolinꢀ2ꢀyl)ꢀphenol: Elemental analysis (%) calculated for C16H13NO;
C, 81.68; H, 5.57; N, 5.95. Found (%); C, 81.65; H, 5.54 N, 5.92. 1H NMR δ (ppm): 8.26 (s, 1H),
8.06 (d, J = 8 Hz, 1H), 7.88 (d, J = 7.2 Hz, 1H), 7.68 (t, J = 12.4 Hz, 1H), 7.58–7.62 (m, 1H),
7.50–7.56 (m, 1H), 7.45 (t, J = 7.6 Hz, 1H), 7.42 (d, J = 11.6 Hz, 1H), 7.37 (s, 1H), 5.31 (s, 1H),
13
2.50 (s, 3H). C NMR: δ (ppm): 158.9, 149.5, 147.1, 138.1, 135.3, 130.1, 129.6, 126.6, 126.3,
123.6, 123.1, 120.7, 119.4, 118.5, 112.8, 25.8.

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Entry 2h: 6ꢀmethylꢀ2ꢀnaphthalenꢀ2ꢀylꢀquinoline: Elemental analysis (%) calculated for C20H15N;
1
C, 89.19; H, 5.61; N, 5.20. Found (%); C, 89.17; H, 5.59; N, 5.18. H NMR δ (ppm): 8.20 (s,
1H), 7.95 (d, J = 6.4 Hz, 4H), 7.59 (d, J = 6 Hz, 1H), 7.50 (d, J = 2 Hz, 1H), 7.46 (t, J = 6 Hz,
2H), 7.42–7.46 (m, 1H), 7.30ꢀ7.40 (m, 1H ), 2.64 (s, 3H). 13C NMR: δ (ppm): 160.4, 147.8,
147.6, 136.3, 135.9, 133.6, 129.3, 127.9, 127.7, 127.0, 125.7, 121.6, 121.3, 121.0,111.9, 23.1.
Entry 2i: 2ꢀbiphenylꢀ4ꢀylꢀ6ꢀmethylꢀquinoline: Elemental analysis (%) calculated for C22H17N; C,
1
89.46; H, 5.80; N, 4.74. Found (%); C, 89.45; H, 5.78; N, 4.71. H NMR δ (ppm): 8.07 (s, 2H),
8.05 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 7.76 (t, J = 9 Hz, 1H), 7.68 (d, J = 6.4 Hz,
3H), 7.64 (d, J = 5.6 Hz, 1H), 7.43 (t, J = 9 Hz, 2H), 7.21–7.37 (m, 1H), 2.50 (s, 3H). 13C NMR:
δ (ppm): 160.9, 147.9, 146.8, 135.2, 133.9, 128.6, 127.8, 127.3, 126.4, 123.2, 122.0, 120.2,
119.4, 117.4, 109.9, 108.3, 31.1.
Entry 2j: 2ꢀ(4ꢀbromoꢀphenyl)ꢀ6ꢀmethylꢀquinoline: Elemental analysis (%) calculated for
C16H12BrN; C, 64.45; H, 4.06; N, 4.70. Found (%); C, 64.41; H, 4.03; N, 4.68. 1H NMR δ (ppm):
7.71 (d, J = 7.6 Hz, 2H), 7.60 (s, 1H), 7.41–7.52 (m, 2H), 7.38 (t, J = 3 Hz, 1H), 7.31 (s, 2H),
13
7.21–7.28 (m, 1H), 2.35 (s, 3H). C NMR: δ (ppm): 152.7, 141.1, 136.8, 130.9, 128.5, 124.8,
124.1, 123.2, 122.4, 119.1, 117.0, 116.4, 26.4.
Entry 2k: dimethylꢀ[4ꢀ(6ꢀmethylꢀquinolinꢀ2ꢀyl)ꢀphenyl]ꢀamine: Elemental analysis (%)
1
calculated for C18H18N2; C, 82.41; H, 6.92; N, 10.68. Found (%); C, 82.39; H, 6.89; N, 10.66. H
NMR δ (ppm): 7.79 (d, J = 12.8 Hz, 2H), 7.51 (t, J = 12.2 Hz, 2H), 7.44 (t, J = 7.2 Hz, 1H), 7.36
(t, J = 6.8 Hz, 1H), 7.29–7.34 (m, 2H), 6.92–7.15 (m, 1H), 2.96m (s, 6H), 2.34 (s, 3H). 13C
NMR: δ (ppm): 158.3, 141.9, 137.0, 133.5, 130.8, 128.2, 123.2, 122.4, 120.8, 119.8, 118.7,
115.4, 36.7, 29.4.
Entry 2l: 1ꢀ[4ꢀ(6ꢀmethylꢀquinolinꢀ2ꢀyl)ꢀphenyl]ꢀethanone: Elemental analysis (%) calculated for
C18H15NO; C, 82.73; H, 5.79; N, 5.36. Found (%); C, 82.71; H, 5.76; N, 5.32. 1H NMR δ (ppm):
8.01 (d, J = 11.2 Hz, 2H), 7.96 (d, J = 12.2 Hz, 2H), 7.74 (d, J = 14.4 Hz, 2H), 7.52 (t, J = 10.4
Hz, 2H), 7.30–7.43 (m, 1H), 3.31 (s, 3H), 2.84 (s, 3H). 13C NMR: δ (ppm): 170.9, 158.3, 140.5,
136.7, 135.4, 133.1, 129.0, 128.8, 125.6, 124.6, 124.1, 123.7, 121.0, 114.8, 29.3, 24.2.
ACKNOWLEDGMENT
Mr. Vignesh Arumugam thanks the University Grants Commission (UGC), New Delhi, India, for
the award of Junior Research Fellowship (JRF) under UGCꢀBSR RFSMS.

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DOI: 10.1039/C5RA15342E
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