Synthesis, characterization, structure and catalytic activity of (NNN) tridentate azo-imine nickel(II), palladium(II) and platinum(II) complexes

Article abstract of DOI:10.1016/j.poly.2015.12.050

The newly designed tridentate ligand, 2,2′-(bisdiamino)azobenzene, H₂L, 1 derived from the oxidative coupling of o-phenylenediamine in presence of NaOH base, upon reaction with Ni(II), Pd(II) and Pt(II) separately in methanol yielded [(HL)Ni(PPh₃)]ClO₄, 2, [(HL)Pd(PPh₃)]ClO₄, 3 and [(L)Pt(PPh₃)], 4 which were characterized by spectral data and authenticated by single crystal X-ray diffraction of 1-4. The diffraction analysis revealed that the ligand binds the metals (Ni(II), Pd(II)) in monoanionic and Pt(II) in dianionic tridentate (N,N,N) fashion offering distorted square planar geometry where fourth position is occupied by one PPh₃group. One ClO₄^-ion satisfies the charge of the former aggregate [(HL)Ni(PPh₃)]⁺and [(HL)Pd(PPh₃)]⁺. Suzuki and Heck coupling reactions were carried out, in presence of air and moisture, using [(HL)Pd(PPh₃)]ClO₄, 3 as catalysts for a variety of substrates.

Full text of DOI:10.1016/j.poly.2015.12.050

Accepted Manuscript
Synthesis, characterization, structure and catalytic activity of (NNN) tridentate
azo-imine nickel(II), palladium(II) and platinum(II) complexes
Paritosh Mandal, Chia-Her Lin, Paula Brandão, Dasarath Mal, Vitor Felix, Jahar
Lal Pratihar
PII:
S0277-5387(15)00800-1
DOI:
http://dx.doi.org/10.1016/j.poly.2015.12.050
POLY 11749
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
7 September 2015
26 December 2015
Please cite this article as: P. Mandal, C-H. Lin, P. Brandão, D. Mal, V. Felix, J.L. Pratihar, Synthesis,
characterization, structure and catalytic activity of (NNN) tridentate azo-imine nickel(II), palladium(II) and
platinum(II) complexes, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.12.050
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Revised Manuscript
Ms. Ref. No.: Poly-D-15-00840
Synthesis, characterization, structure and catalytic activity of
(NNN) tridentate azo-imine nickel(II), palladium(II) and
platinum(II) complexes
Paritosh Mandal,a Chia-Her Lin,b Paula Brandão,c Dasarath Mal,c Vitor Felix,c,d and Jahar
Lal Pratihar,a*
aDepartment of Chemistry, Kandi Raj College, Murshidabad 742137, India
bDepartment of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan
cDepartamento de Química, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
dDepartamento de Química, IBIMED and CICECO, Universidade de Aveiro, 3810-193, Aveiro,
Portugal.
______________________________________________________________________________________
Abstract
The newly designed tridentate ligand, 2,2/-(bisdiamino)azobenzene, H2L,1 derived from the
oxidative coupling of o-phenylenediamine in presence of NaOH base, upon reaction with Ni(II),
Pd(II) and Pt(II) separately in methanol yielded [(HL)Ni(PPh3)]ClO4,2, [(HL)Pd(PPh3)]ClO4, 3 and
[(L)Pt(PPh3)], 4 which were characterized by spectral data and authenticated by single crystal x-
ray diffraction of 1-4. The diffraction analysis revealed that the ligand binds the metals (Ni(II),
Pd(II))in monoanionic and Pt(II) in dianionic tridentate (N,N,N) fashion offering distorted square
-
planar geometry where fourth position is occupied by one PPh3 group. One ClO4 ion satisfies the
charge of the former aggregate [(HL)Ni(PPh3)]+ and [(HL)Pd(PPh3)]+. Suzuki and Heck coupling
reactions were carried out, in presence of air and moisture, using [(HL)Pd(PPh3)]ClO4, 3as
catalysts for a variety of substrates.
_______________________________________________________________________________
Keywords: Crystal structure, Ni(II), Pd(II) and Pt(II), Suzuki and Heck Reaction
_______________________________________________________________________________
Corresponding author. Fax.: +91 3484 255230; E-mail address: jlpr@rediffmail.com (J. L.
Pratihar)
1

1. Introduction
Transition metal complexes with azo chromophore have received much attention in research
areas both fundamental and a variety of applications such as colouring agent [1-4]. The strong
electronic absorption can be changed by ring substitution which controls the chemical fine-tuning of
color [4]. Moreover the coordination chemistry incorporating ortho substituted azo benzene ligands
have versatile properties such as C-H activation [5-11], C-C activation [12-16], C-C coupling [17],
-N=N- bond cleavage [18-21], electron transfer reaction [13-16, 22-25], hydroxylation [26-29],
isomerization [30], photoisomerization [31-35], cytotoxicity toward cancer cells and application in
catalytic transformations [36-40]. Metal complexes of chelating ligands with azo-imine function
have significant properties i.e. isomerization, metal assisted transformation, catalytic and
biological activity [30,38,39, 41-44]. Among them, azo-imine complexes of (C,N,N) and (N,N,N)
donor have specific properties for example oxidative addition, structural isomerization, metal
assisted transformation and catalytic activity [30,38,39,45]. The N,N,N donors, where one “N” is
pyridyl nitrogen, between another two “N” one is azo nitrogen and other is secondary amino
nitrogen or one “N” is azo nitrogen another two “N” are secondary amino nitrogen is known [22-
25,30,38,45,46]but2,2/-(bisdiamino)azobenzene ligand where one “N” is azo nitrogen and other
two “N” are primary amino nitrogen have not been utilized to explore the chemistry of transition
metal ions.
Herein we report the reactions of tridentate 2,2/-(bisdiamino)azobenzene, H2L, 1 ligand
with Ni(ClO4)2.6H2O, Na2PdCl4 and K2PtCl4 separately to form complexes of composition
[(HL)Ni(PPh3)]ClO4, 2, [(HL)Pd(PPh3)]ClO4, 3 and [(L)Pt(PPh3)], 4 respectively where the ligand
offers (N,N,N) binding mode to the metal. The ligand and complex have been characterized by the
spectroscopic data. The x-ray structure of the ligand H2L, 1 and complexes 2-4 have
2

beendetermined to confirm the molecular structure. The complex [(HL)Pd(PPh3)]ClO4, 3 acts as
potential catalyst towards C-C bond formation for a variety of substrate.
2. Experimental
2.1. Materials
The solvents used in the reactions were of reagent grade (E. Marck, Kolkata, India) and
were purified and dried by general procedure [47]. Orthophenylenediamine was purchased from
Loba, India. Palladium chloride, sodium hydroxide, triphenyl phosphine and sodium chloride were
purchased from E. mark, India. Sodium perchlorate, Potassium tetrachloroplatinate, Iodo benzene,
Bromo benzene, 1-Iodo-2-nitrobenzene, 1-Iodo-3-nitrobenzene, 1-Bromo-2-nitrobenzene, Phenyl
boronic acid, Nickel(II) perchlorate hexahydrate and Styrene were purchased from Aldrich.
Sodium tetrachloropalladate was prepared following reported procedure [48].
2.2. Physical measurements
Microanalysis (C, H, N) was performed using a Perkin-Elmer 2400 C, H, N, S / O series II
elemental analyzer. Infrared spectra were recorded on a Parkin-Elmer L120-00A FT-IR
spectrometer with the samples prepared as KBr pellets. Electronic spectra were recorded on a
Shimadzu UV- 1800 PC spectrophotometer. 1H NMR spectra were obtained on Brucker 400 NMR
spectrometers in CDCl3 using TMS as the internal standard.
2.3. Syntheses
2.3.1. Synthesis of ligand 1
o-Phenylenediamine (10 g) and sodium hydroxide (5.2 g) were mixed and triturated
followed by heating at 70oC with constant scratching for 2h. The dark pasty mass thus obtained
was cooled to room temperature and extracted with benzene. The benzene soluble part was
3

subjected to column chromatography on a silica gel (60-120 mesh) column. The orange band that
eluted by benzene-petroleum ether mixture (1/1; V/V) were collected and upon evaporation of
solvents, the pure H2Lwas obtained. Yield:10%. Anal. Calcd for C12H12N4: C, 67.90; H, 5.70; N,
26.40%. Found: C, 67.72; H, 5.39; N, 26.85%. UV/VIS (λmax/nm (ε/ dm2 mol-1), dichloromethane):
1
450 (11280); 315 (11035); 260(13328). IR (KBr, cm−1): 3462, 3363 ν(NH2), 1457 ν(N=N). H
NMR (400 MHz, CDCl3): 5.48 (NH2, s, 4H), 6.75-6.80 (ArH, m, 4H), 7.15-7.19 (ArH, m, 2H),
7.67 (ArH, d, 2H).
2.3.2. Synthesis of complex 2
A solution of Ni(ClO4)2.6H2O (205 mg, 0.62 mmol) in methanol (15 mL) a solution of
ligand H2L(130 mg, 0.62mmol) in methanol (10 mL) was added under stirring. The solution
immediately changed to pink-violet and the stirring was continued for 1h at room temperatureand
then added PPh3 (185 mg, 0.7 mmol). The resulting pink-violet solution was then filtered and
allowed to stand. After slow evaporation of the solvent at room temperature, dark coloured x-ray
quality crystals were obtained. Yield: 80%. Anal. Calcd. For C30H26ClN4NiO4P: C, 57.04; H, 4.15;
N, 8.87%. Found: C, 57.35; H, 4.26; N, 8.65%. UV/VIS (λmax/nm (ε/ dm2 mol-1),
dichloromethane): 580 (10530); 540 (11030); 365 (18490); 270(44900). IR (KBr, cm−1): 3480,
1
3343 ν(NH2, NH), 1346 ν(N=N), 1100 ν(Cl-O), 1434 and 697 ν(PPh3). H NMR (400 MHz,
CDCl3): 4.64 (NH2, s, 2H), 6.32 (ArH, d, 1H),6.84 (ArH, t, 1H), 7.14 (ArH, t, 1H), 7.27 (ArH, t,
1H), 7.38 (ArH, t, 1H), 7.48 (ArH, d, 1H), 7.65-7.77 (PPh3, m, 9H), 7.83 (ArH, d, 1H), 7.95-8.0
(PPh3, t, 6H), 8.32 (ArH, d, 1H).
2.3.3. Synthesis of complex 3
A solution of H2L (85 mg, 0.4 mmol) in 10 cm3 methanol was added to a solution of
Na2PdCl4 (120 mg, 0.4 mmol) in 5 cm3 methanol. The mixture was stirred for 1 h and then added
PPh3 (130 mg, 0.52mmol). The dark solid precipitate was separated by filtration and purified by
column chromatography using silica gel (60-120 mesh). The eluent was toluene-acetonitrile (95:5)
4

mixed solvent. The volume of the solution was reduced to ~20 ml and added NaClO4 (75 mg, 0.6
mmol). Upon evaporation of solvent the pink solid of pure [(HL)Pd(PPh3)]ClO4 was obtained.
Yield: (60%). Anal. Calcd. For C30H26ClN4O4PPd: C, 53.04; H, 3.86; N, 8.25%. Found: C, 53.25;
H, 4.12; N, 8.15%. UV/VIS (λmax/nm (ε/ dm2 mol-1), dichloromethane): 520 (13100); 270 (17200).
1
IR (KBr, cm−1): 3401, 3336 ν(NH2, NH), 1344 ν(N=N), 1097 ν(Cl-O), 1435 and 696 ν(PPh3). H
NMR (400 MHz, CDCl3): 5.60 (NH2, s, 2H), 6.37 (ArH, d, 1H),6.71 (ArH, t, 1H), 7.13-7.18 (ArH,
m, 1H), 7.45-7.48 (NH and ArH, m, 3H), 7.52-7.57 (ArH, m, 1H), 7.52-7.69 (PPh3, m, 9H), 7.73-
7.78 (PPh3, m, 6H), 7.85 (ArH, d, 1H), 8.30 (ArH, d, 1H).
2.3.4. Synthesis of complex 4
A solution of H2L (65 mg, 0.3mmol) in 10 cm3 methanol was added to a solution of
K2PtCl4 (125 mg, 0.3mmol) in 5 cm3 methanol. The mixture was stirred for 1 h and then added
PPh3 (105 mg, 0.4 mmol). The dark solid precipitate was separated by filtration and purified by
column chromatography using silica gel (60-120 mesh). The eluent was benzene-acetonitrile
(90:10) mixed solvent. Upon evaporation of solvent the pink solid of pure [(L)Pt(PPh3)] was
obtained. Isolated yield: (50%). Anal. Calcd. For C30H25N4PPt: C, 53.97; H, 3.77; N, 8.39%.
Found: C, 53.75; H, 3.95; N, 8.48%. UV/VIS (λmax/nm (ε/ dm2 mol-1), dichloromethane): 525
(12300); 270 (19240). IR (KBr, cm−1): 3401, 3336 ν(NH2, NH), 1345 ν(N=N), 1098 ν(Cl-O), 1435
1
and 696 ν(PPh3). H NMR (400 MHz, CDCl3): 5.52 (NH2, s, 2H), 6.72 (ArH, d, 1H),6.75-6.82
(ArH, m, 2H), 6.90 (NH, s, 1H), 7.14 (ArH, t, 1H), 7.17-7.22 (ArH, m, 1H), 7.30-7.37 (ArH and
NH, m, 2H), 7.47-7.60 (PPh3, m, 9H), 7.81-7.86 (PPh3, m, 6H), 8.27 (ArH, d, 1H), 8.83 (ArH, d,
1H).
2.3.5. General procedures for the Suzuki reaction
5

To the catalyst (1.0 mol%) dissolved in 10 ml THF, aryl halide (1.0 mmol), phenyl boronic
acid (1.2 mmol), K2CO3 (2.0 mmol) were all added. The mixture was heated to reflux for 3 h.
Then, the mixture was evaporated to dryness, water was added and the product was extracted with
diethyl ether. The organic layer was washed with brine, dried over MgSO4, filtered, passed through
silica column (60-120 mesh), the complex remain trapped. Upon evaporation of the ether, solid of
pure products were obtained. The yields of the products obtained from all the reactions were
1
determined after isolation and characterized by H NMR spectra and melting points with the
literature data.
2.3.6. General procedures for the Heck reaction
Aryl halide (0.5 mmol), styrene (1.0mmol) were combined with K2CO3 (1 mmol) and
catalyst (1 mol%) in THF (10 ml) in a small round-bottom flask. The mixture was heated to reflux
for 4 h. Then, the mixture was evaporated to dryness, water was added and the product was
extracted with diethyl ether. The organic layer was washed with brine, dried over MgSO4, filtered,
passed through silica column (60-120 mesh), the complex remain trapped. After extraction of
desired compound complex was extracted using dichloromethane. Upon evaporation of the ether,
solid of pure products were obtained. The yields of the products obtained from all the reactions
were determined after isolation andidentified by 1H NMR spectroscopy and melting points with the
literature data.
2.4. Crystallography
Single crystal ofH2L, 1, [(HL)Ni(PPh3)]ClO4, 2, [(HL)Pd(PPh3)]ClO4, 3 and [(L)Pt(PPh3)],
4 were grown by diffusion of dichloromethane into petroleum ether at 298 K. Data were collected
by ω- scan technique on a Bruker Smart CCD diffractometer with monochromated Mo-Kα
radiation(λ = 0.71073 Å). Structure solution was done by direct method with SHELXS–
6

2013program [49,50]. Full matrix least square refinements on F2 were performed using SHELXL–
2013program [49,50]. All non-hydrogen atoms were refined anisotropically using reflections I >
2σ (I). The C-bound hydrogen atoms were included in calculated positions and refined as riding
atoms. The N-H hydrogens were obtained by difference electron density synthesis. Data collection
parameters and relevant crystal data are collected in Table 1.
------------------------------------------------------------------------------------------------------------
Please insert Table 1 here
------------------------------------------------------------------------------------------------------------
3. Results and discussion
3.1. Synthesis
The new ligand 2,2/-(bisdiamino)azobenzene, H2L,1 has been prepared by oxidative
coupling of o-phenylenediamine in the presence of strong base sodium hydroxide (Scheme 1). The
------------------------------------------------------------------------------------------------------------
Please insert Scheme 1 here
------------------------------------------------------------------------------------------------------------
ligand was isolated as orange solid after column chromatographic purification. The reactions of
H2L, 1 with Ni(ClO4)2.6H2O, Na2PdCl4 and K2PtCl4 separately in methanol in the presence of PPh3
afforded pink-violet [(HL)Ni(PPh3)]ClO4, 2, and pink [(HL)Pd(PPh3)]ClO4, 3 and [(L)Pt(PPh3)], 4
respectively (Scheme 1). In complexes [(HL)Ni(PPh3)]ClO4 and [(HL)Pd(PPh3)]ClO4 the ligand
binds in tridentate (N, N, N) fashion through one deprotonated imino N, azo N and amino N
whereas in the case of [(L)Pt(PPh3)] the ligand bind the metal in similar fashion through both
deprotonated imino N and azo N atom forming two fused rings- one six membered and other five
membered.
3.2. Characterization
Ligand H2L, 1 and complexes 2-4 are soluble in common organic solvents furnished orange
and pink-violet and pink colours respectively. UV-vis spectra of the ligand and complex were
7

recorded in dichloromethane solutions (Fig. 1). Ligand shows three absorption bands at 450 nm,
315 nm and 260 nm attributed to the intraligand π−π* and n−π* transitions [51,52].
------------------------------------------------------------------------------------------------------------
Please insert Fig. 1 here
------------------------------------------------------------------------------------------------------------
A Characteristic low energy absorption band for all the complexesin the range 520-580 nm is
assigned to the MLCT transition [51,52].
The IR spectrum of the ligand in solid KBr support νNH2 appeared as twin band in 3462 and
3363 cm-1, whereas for the complexes 2-4, the νNH2 and νNH (dissociation of the amino proton on
complexation) appeared as multiple bands in the range 3481-3332cm-1 [21,53]. The νN=N of the
ligand (1457 cm-1) shifted to lower frequency upon complexation (1344-1346), consistent with
coordination of the azo nitrogen [21,38-44]. A very strong broad band in the range 1097-1100 cm-1
and strong band near 622 cm-1 are observed in the IR spectra of the Ni(II) and Pd(II) complexes,
which could be due to the antisymmetric stretching and bending of uncoordinated perchlorate ions,
respectively [54]. Two new bands near 1435 cm-1 and 696 cm-1 assigned for the coordinated
triphenylphosphine ligand for the all complexes [55].
1
The ligand H2L, 1 and complexes 2-4 shows highly resolved H-NMR spectra in CDCl3,
which are in complete agreement with the X-ray structures of the ligand and complexes. A sharp
singlet at 5.48 ppm is assigned for an NH2 proton of the ligand which is shifted to 4.64-5.60 in the
complexes. All the aromatic protons appeared in the range of 6.75-7.75 ppm, appeared as one
doublet, and two set of multiplet which are matched well with the composition of the ligand in
solution. In all the complexes 2-4 the aromatic protons (except PPh3) appeared in the range 6.22-
8.83 ppm for different eight protons as separate doublets, triplets and multiplets. Fifteen PPh3
8

protons appeared as two set of multiplets in the range 7.47-7.60 ppm and 7.73-7.80 ppm for nine
and six protons respectively.
3.3. X-ray crystallography
The structures of 1-4 were determined by single crystal X-ray diffraction method. Thermal
ellipsoid plots of ligand 1 and complexes 2-4 are shown in Figs. 2–5 respectively. The
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Please insert Fig.2-5& Table 2-5 here
------------------------------------------------------------------------------------------------------------
crystallographic and measurement data are shown in Table 1. Selected bond lengths and bond
angles are listed in Tables 2-5.Ligand 1and complexes 2-3 are monoclinic, complex 4 is
orthorhombic and crystallize in the space group C2/c, P21/n, P21/c and P212121 with Z = 4
respectively.
The centrosymmetric structure of H2L reveals the planar geometry of the ligand. All the
non hydrogen atoms of H2L make a good plane (mean deviation 0.017 Å). The N(1)-C(1) 1.418(2)
Å and N(2)-C(2) 1.376(2) Å lengths of free ligand are closed to C-N single bond length. The N1-
N1# length (1.261(3) Å) is very similar to azo (-N=N-) length [46].
The nickel and palladium ion in each complexes are coordinated by one anionic ligand via
the N, N, N atoms, producing a six membered chelate ring with the imino N and azo N atom and a
five membered ring with amino N and azo N atoms. The fourth coordination site of both the
complexes is occupied by the P atom of the triphenylphosphine ligand and [(HL)M(PPh3)]+
(M=Ni, Pd) is satisfied by one perchlorate ion. The asymmetric unit of [(HL)Ni(PPh3)]+ contains
one methanol solvent. The tridentate monoanionic (HL)- ligand binds the metal (M=Ni and Pd) in
N,N,N fashion. The structures of 2 and 3 adopt a near square planar geometry with N(1)–Ni–N(2),
N(3)–Ni–P and N(1)–Pd1(1)–N(2), N(3)–Pd(1)–P(1) bond angles 170.72(15), 168.03(10) and
171.91(11), 174.31(7), respectively. The Ni–N(1), Ni–N(2), Ni–N(3) and Ni–P and Pd(1)–N(1),
9

Pd(1)–N(2),Pd(1)–N(3) and Pd(1)–P(1) bond lengths in 2 and 3 are 1.801(3), 1.945(3), 1.868(3),
2.2070(11) and 1.956(3), 2.057(3) and 2.007(2), 2.2952(7) Å, respectively, which are in agreement
with the reported values for such distances [7,25,28,38,40,46,51,53,56-59]. The bond lengths
within the ligand backbone (six membered rings) are suitably altered due to delocalization of the
negative charge. The C(1)-N(1) length (~1.33Å) is shorter than the C-N single bond C(7)-N(3),
(~1.42Å) in the same molecule (Ni(II) & Pd(II)) and is close to the imine distance. Due to
delocalization the effect of imine formation is reflected in the adjacent phenyl ring. The quinonoid
distortion in the phenyl ring (C1, C2, C3, C4, C5 and C6) adjacent to the chelate ring (six
membered) with four longer (~1.42 Å) and two shorter bonds (~1.35Å) is consistent with the
delocalization.
The geometry about Pt(II) is distorted square planar with N(1)–Pt(1)–N(2) and N(3)–Pt(1)–
P(1) bond angles 170.6(3) and 177.19(19)Å where dinegative L2- binds tridentate (N,N,N) fashion,
producing a six membered chelatering with the imino N and azo N atom and a five membered ring
with another imino N and azo N atoms. The fourth coordination site of the complex is occupied by
a P atom of the triphenylphosphine ligand. The Pt(1)-N(1), Pt(1)-N(2), Pt(1)-N(3) and Pt(1)-P(1)
lengths 1.983(6), 1.963(6), 2.025(5) and 2.2549(14)Å are within the normal range [56, 58-62]. The
bond lengths within the ligand backbone (six membered ring) are suitably altered due to
delocalization of the negative charge. The C(12)-N(2) length (1.327(9) Å) is shorter than the C-N
single bond C(6)-N(3), 1.431(9) Å in the same molecule and is close to the imine distance. The
quinonoid distortion similar to Ni(II) and Pd(II) in the phenyl ring (C7, C8, C9, C10, C11 and
C12) adjacent to the chelate ring (six membered) with four longer (~1.41 Å) and two shorter bonds
(~1.34 Å) is also in accordance with the delocalization and imine formation.
3.4. The Suzuki and Heck coupling reactions
10

The Suzuki cross-coupling is a widely used method for the production of biaryls, which is
important in organic synthesis and a recurring functional group in several natural products [63-68].
Subsequently, many catalytic systems have been developed for the synthesis of biaryls derivatives.
Therefore, the catalytic activity of the new palladium complex, [(HL)Pd(PPh3)]ClO4, in the Suzuki
cross-coupling reaction (Eq 1) of a variety of aryl halides with phenyl boronic acid was
investigated in refluxing THF solvent and K2CO3 as base keeping reaction time constant (3h) and
results were summarized in Table 6. All reactions were performed in presence of air and moisture.
Isolated yields of the products varied from 82% to 96% depending upon variation of aryl halide
substrate. After completion of the reaction the palladium catalyst was intact and isolated from the
reaction mixture easily by column chromatography and the catalyst [(HL)Pd(PPh3)]ClO4, was
reused for further reaction. This reusability of the catalyst was checked up to four times for a
reaction, where the other condition intact.
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Please insert Table 6 here
-----------------------------------------------------------------------------------------------------------------------
The Heck cross-coupling reaction is an important method for carbon-carbon bond
formation in synthetic organic chemistry where the palladium-catalyzed coupling of aryl halides
with olefins [63-68]. In this case we perform the reactions using styrene and four aryl halides
(bromide and iodide) in refluxing methanol (4h) and in presence of K2CO3 as base in presence of
air and moisture and results of conversions are given in Table 7. Isolated yields of the products
varied from 75% to 94% depending upon variation of aryl halide. Similarly as mentioned in
Suzuki coupling reactions, at the completion of the reaction the colour of the solution changed
from pink-violet to light pink so the catalyst was not isolated indicating the fact that the catalyst
may be a precatalyst in these reactions.
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11

Please insert Table 7 here
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4. Conclusion
In conclusion, we have reported convenient syntheses and comprehensive characterization
of nickel(II), palladium(II) and platinum(II) complexes (2–4) containing newly synthesized azo-
imine based tridentate ligand H2L and triphenylphosphine. The solid state structures of complexes
2-4 were determined by X-ray crystallography. The complexes showed the expected square planar
geometry about the metal center. The new [(HL)Pd(PPh3)]ClO4 complex has been used as catalyst
for Suzuki and Heck coupling reactions in ambient condition. The [(HL)Pd(PPh3)]ClO4 complex is
stable under the condition of Suzuki coupling, indicating the catalytic activity of the molecular
complex itself.
Acknowledgments
Special thanks to Professor Surajit Chattopadhyay, Department of Chemistry, University of
Kalyani, for his valuable suggestions throughout this work. Author acknowledged to University
Grants Commission (under Minor Research Project, Sanction No. F.PSW/066/2011-12).
Appendix A. Supplementary data
1
Figures S1–S4 shows the IR spectra and Figs. S5-S8 H NMR spectra of the ligand HL, 1 and
complexes 2-4. CCDC 1418054, 1418055, 1418056 and 1418057 contains the supplementary
crystallographic data for compounds H2L, 1, [(HL)Ni(PPh3)]ClO4, 2, [(HL)Pd(PPh3)]ClO4, 3 and
[(L)Pt(PPh3)], 4. These data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
References
12

[1]
[2]
A. Grirrane, A. Corma, H. García, Science, 322 (2008) 1661.
R. Egli, in Colour Chemistry: The Design and Synthesis of Organic Dyes and Pigments, A.
P. Peter, H. S. Freeman, Eds. (Elsevier, London, 1991), chap. VII.
K. Venkataraman, The Chemistry of Synthetic Dyes (Academic Press, London, 1970),
chap. VI.
[3]
[4]
[5]
K. Nejati, Z. Rezvani, B. Massoumi, Dyes and Pigments, 75 (2007) 653.
D. Sardar, P. Datta, R. Saha, P. Raghavaiah, C. Sinha, J. Organomet. Chem., 732 (2013)
109.
[6]
A. N. Biswas, D. N. Neogi, P. Das, A. Choudhury, P. Bandyopadhyay, J. Organomet.
Chem., 761 (2014) 147.
[7]
[8]
[9]
J. l. Pratihar, N. Maiti, P. Pattanayak, S. Chattopadhyay, Polyhedron, 24 (2005) 1953.
R. Acharyya, S.-M. Peng, G.-H. Lee, S. Bhattacharya, Inorg. Chem., 42 (2003) 7378.
P. Gupta, R. J. Butcher, S. Bhattacharya, Inorg. Chem., 42 (2003) 5405.
[10] R. Acharyya, F. Basuli, R.-Z. Wang, T. C. W. Mak, S. Bhattacharya, Inorg. Chem., 43
(2004) 704.
[11] P. Gupta, S. Dutta, F. Basuli, S.-M. Peng, G.-H. Lee, S. Bhattacharya, Inorg. Chem., 45
(2006) 460.
[12] S. Baksi, D. K. Seth, H. Tadesse, A. J. Blake, S. Bhattacharya, J. Organomet. Chem., 695
(2010) 1111.
[13] S. Baksi, R. Acharyya, S. Dutta, A. J. Blake, M. G. B. Drew, S. Bhattacharya, J.
Organomet. Chem., 692 (2007) 1025.
[14] R. Acharyya, F. Basuli, S.-M. Peng, G.-H. Lee, R.-Z. Wang, T. C. W. Mak, S.
Bhattacharya, J. Organomet. Chem., 690 (2005) 3908.
13

[15] S. Baksi, R. Acharyya, F. Basuli, S.-M. Peng, G.-H. Lee, M. Nethaji, S. Bhattacharya,
Organometallics, 26 (2007) 6596.
[16] S. Nag, P. Gupta, R. J. Butcher, S. Bhattacharya, Inorg. Chem.,43 (2004) 4814.
[17] S. Halder, R. Acharyya, S.-M. Peng, G.-H. Lee, M. G. B. Drew, S. Bhattacharya, Inorg.
Chem., 45 (2006) 9654.
[18] N. D. Paul, S. Samanta, T. K. Mondal, S. Goswami, Inorg. Chem., 50 (2011) 7886.
[19] A. K. Ghosh, P. Majumdar, L. R. Falvello, G. Mostafa, S. Goswami, Organometallics, 18
(1999) 5086.
[20] K. Majumder, S.-M. Peng, S. Bhattacharya, J. Chem. Soc., Dalton Trans., (2001) 284.
[21] J. l. Pratihar, N. Maiti, S. Chattopadhyay, Inorg. Chem, 44 (2005) 6111.
[22] I. Chatterjee, N. S. Chowdhury, P. Ghosh, S. Goswami, Inorg. Chem., 54 (2015) 5257.
[23] S. Dutta, S.-M. Peng, S. Bhattacharya, J. Chem. Soc., Dalton Trans., (2000) 4623.
[24] S. Das, P. Banerjee, S.-M. Peng, G.-H. Lee, J. Kim, S. Goswami, Inorg. Chem., 45 (2006)
562.
[25] A. Saha, P. Majumdar, S.-M. Peng, S. Goswami, Euro. J. Inorg. Chem., (2000) 2631.
[26] K. Kamaraj, D. Bandyopadhyay, Organometallics, 18 (1999) 438.
[27] C. Sinha, D. Bandyopadhyay, A. Chakravorty, Inorg. Chem., 27 (1988) 1173.
[28] P. Pattanayak, J. L. Pratihar, D. Patra, A. Burrows, M. Mohan, S. Chattopadhyay,
Euro. J. Inorg. Chem., (2007), 4263.
[29] P. Pattanayak, D. Patra, J. L. Pratihar, A. Burrows, M. F. Mahon, S. Chattopadhyay,
Inorg. Chim. Acta, 363 (2010) 2865.
[30] S. Joy, P. Pal, M. Mahato, G. B. Talapatra, S. Goswami, Dalton Trans., 39 (2010) 2775.
[31] M. Yamamura, N. Kano, T. Kawashima, J. Organomet. Chem., 692 (2007) 313.
[32] N. Kano, M. Yamamura, X. Meng, T. Yasuzuka, T. Kawashima, Dalton Trans., 41
(2012) 11491.
14

[33] N. Kano, M. Yamamura, T. Kawashima, J. Am. Chem. Soc., 126 (2004) 6250.
[34] N. Kano, F. Komatsu, M. Yamamura, T. Kawashima, J. Am. Chem. Soc., 128 (2006) 7097.
[35] M. Yamamura, N. Kano, T. Kawashima, J. Am. Chem. Soc., 127 (2005) 11954.
[36] S. Kannan, R. Ramesh, Y. Liu, J. Organomet. Chem., 692 (2007) 3380.
[37] M. Panda, S. Das, G. Mostafa, A. Castiñeiras, S. Goswami, Dalton Trans., (2005) 1249.
[38] J. L. Pratihar, P. Pattanayak, D. Patra, C.-H. Lin, S. Chattopadhyay, Polyhedron, 33 (2012)
67.
[39] J. L. Pratihar, S. Bhaduri, P. Pattanayak, D. Patra, S. Chattopadhyay, J. Organomet. Chem.,
694 (2009) 3401.
[40] P. Pattanayak, J. L. Pratihar, D. Patra, C.-H. Lin, S. Chattopadhyay, Polyhedron, 63 (2013)
133.
[41] S. K. Sarkar, M. S. Jana, T. K. Mondal, C. Sinha, J. Organomet. Chem., 716 (2012) 129.
[42] P. Dutta, D. Mallick, S. Roy, E. L. Torres, C. Sinha, Inorg. Chim.Acta, 423 (2014) 397.
[43] P. Datta, D. Mallick, T. K. Mondal, C. Sinha, Polyhedron, 71 (2014) 47.
[44] P. Pattanayak, J. L. Pratihar, D. Patra, S. Mitra, A. Bhattacharyya, H. M. Lee, S.
Chattopadhyay, Dalton Trans., (2009) 6220.
[45] N. D. Paul, T. Krämer, J. E. McGrady, S. Goswami, Chem. Commun., 46 (2010) 7124.
[46] D. Patra, P. Pattanayak, J. L. Pratihar, S. Chattopadhyay, Polyhedron, 51 (2013) 46.
[47] D. D. Perrin, W.L.F. Armarego, Purification of laboratory chemicals, 3rd edn, Pergamon,
New York, 1988.
[48] L. Malatesta, M. Angoletta, J. Chem. Soc., (1957) 1186.
[49] T. Gruene, H. W. Hahn, A. V. Luebben, F. Meilleur, G. M. Sheldrick, J. Appl. Crystallogr,
47 (2014) 462.
[50] J. Lübben, C. Volkmann, S. Grabowsky, A. Edwards, W. Morgenroth, F. P. Fabbiani, G.
M. Sheldrick, B. Dittrich, Acta Crystallogr A Found Adv. 70 (2014) 309.
15

[51] P. Pattanayak, J. L. Pratihar, D. Patra, P. Brandão, D. Mal, V. Felix, Polyhedron, 59 (2013)
23.
[52] P. Pattanayak, D. Patra, C-H.Lin, J. L. Pratihar, J. Chem. Res., 1 (2012) 1.
[53] N. Maiti, S. Pal, S. Chattopadhyay, Inorg. Chem., 40 (2001) 2204.
[54] P. Stepnicka, M. Lama, I. Csarov, Polyhedron, 23 (2004) 921.
[55] M. M. Tamizh, B. F. T. Cooper, C. L. B. Macdonald, R. Karvembu, Inorg. Chim. Acta, 394
(2013) 391.
[56] V. K. Jain, L. Jain, Coord. Chem. Rev., 254 (2010) 2848.
[57] T. S. Lobana, P. Kumari, R. J. Butcher, T. Akitsu, Y. Aritake, J. Perles, F. J. Fernandez, M.
C. Vega, J. Organomet. Chem.,701 (2012) 17.
[58] V. K. Jain, L. Jain, Coord. Chem. Rev., 249 (2005) 3075.
[59] P. Pattanayak, S. P.Parua, D.Patra, J. L.Pratihar, P.Brandão,V. Felix, S.Chattopadhyay,
Polyhedron 70 (2014) 1.
[60] N. Deibel, S. Hohloch, M. G. Sommer, D. Schweinfurth, F. Ehret, P. Braunstein, B. Sarkar,
Organometallics, 32 (2013) 7366.
[61] J. L. Pratihar, B. Shee, P. Pattanayak, D. Patra, A. Bhattacharyya, V. G. Puranik, C. H.
Hung, S. Chattopadhyay, Eur. J. Inorg. Chem., (2007) 4272.
[62] E. Bosch, C. L. Barnes, Organometallics, 19 (2000) 5522.
[63] I. Bauer, H.-J. Knölker, Chem. Rev., 115 (2015) 3170.
[64] E. Negishi, A. de Meijere, Handbook of Organopalladium Chemistry for Organic
Synthesis; Wiley-Interscience: New York, 2002.
[65] J. Tsuji, Palladium Reagents and Catalysts; Wiley: UK, Chichester, 2004.
[66] R. F. Heck, Palladium Reagents in Organic Synthesis, Academic Press, London, 1985.
[67] L. Yin, J. Liebscher, Chem. Rev., 2007, 107, 133.
[68] G. Zeni, R. C. Larock, Chem. Rev., 2006, 106, 4644.
16

Synthesis of 2,2/-diaminoazobenzene
NH2
NH2
2
NaOH
NH2
N
N
NH2
K2PtCl4
MeOH
Na2PdCl4
MeOH
NaClO4
PPh3
PPh3
H2L
NH
M
NH
Pt
PPh3
PPh3
N
N
N
N
Ni(ClO4)2.4H2O
MeOH
ClO4
NH2
NH
PPh3
[(HL)M(PPh3)]ClO4
M = Pd(II), Ni(II)
[(L)PtPPh3]
Scheme 1.Synthesis of 2,2/-diaminoazobenzene and metal complexes.
Equation 1
R
R
THF
Reflux
B(OH)2
...
(1)
X +
K2CO3
X = I or Br
R = H, NO2
Equation 2
MeOH
Reflux
X
...
(2)
+
K2CO3
R
R
X = I or Br
R = H, NO2
17

Table 1
Crystallographic data for H2L, [(HL)Ni(PPh3)]ClO4, [(HL)Pd(PPh3)]ClO4 & [(L)Pt(PPh3)]
Chemical formula
C12H12N4
C30H26N4PNi,ClO4, C30H26N4PPd,
C30H25N4PPt
CH3OH
ClO4
Formula weight
Crystal system
212.26
663.72
679.37
667.60
Monoclinic
Monoclinic
Monoclinic
Orthorhombic
space group
a/Å
C2/c
P21/n
P21/c
P212121
22.285(2)
5.8593(6)
8.9005(4)
16.2489(7)
11.8856(5)
14.2644(6)
10.4172(1)
13.2278(1)
b/Å
c/Å
8.2532(7)
90
20.4720(9)
90
16.7476(6)
90
18.2993(2)
90
α/deg
β/deg
γ/deg
λ /Å
106.404(4)
90
94.926(3)
90
97.405(2)
90
90
90
0.71073
0.71073
0.71073
0.71073
V /Å3
1033.80(17)
448
2949.8(2)
1376
2815.7(2)
1376
2521.58(4)
1310
F(000)
Crystal Size [mm]
0.02x0.02x0.20 0.2x0.10x0.02
0.20x0.20x0.20
0.08x0.18x0.20
Z
4
4
4
4
T/K
120(2)
1.364
0.087
150(2)
295(2)
100(2)
D/mg/m-3
1.495
1.603
1.759
µ /mm-1
0.851
0.855
5.655
Theta Min-Max [deg] 3.606 -27.115
reflections measured 3276
reflections 1137, 0.0315
1.602, 29.253
31419
1.728, 28.328
27192
1.900, 28.295
25517
unique
(Rint)
7993, 0.0769
6986, 0.0384
6200, 0.0606
No. of reflections 826
4875
5046
5038
used [I> 2σ(I)]
R1,wR2(all data)
R1, wR2[I> 2σ(I)]
GOF
0.0691, 0.1207 0.1267, 0.1678
0.0464, 0.1097 0.0664, 0.1437
0.0653, 0.0892
0.0389, 0.0792
1.023
0.0526, 0.0536
0.0342, 0.0487
0.972
1.062
1.023
18

Table 2
Selected Bond Distances (Å) and Angles (deg) for Compound H2L.
Distances
N1-C1
N2-C2
C1-C2
C2-C3
N1-N1#
1.418(2)
1.376(2)
1.407(2)
1.400(2)
1.261(3)
C1-C6
C3-C4
C4-C5
C5-C6
1.397(2)
1.378(2)
1.395(2)
1.379(2)
Angles
N1-C1-C2
N2-C2-C1
120.44(14)
114.84(17)
114.81(14)
N1#- N1-C1
19

Table 3
Selected Bond Distances (Å) and Angles (deg) for Compound [(HL)Ni(PPh3)]ClO4.
Distances
Ni-P
2.2070(11)
1.801(3)
1.868(3)
C2-C3
C3-C4
C4-C5
1.346(7)
1.411(7)
1.368(7)
Ni-N1
Ni-N3
Ni-N2
N1-C1
N2-C12
N3-N4
N3-C7
N4-C6
C1-C2
1.945(3)
1.346(5)
1.463(5)
1.287(4)
1.433(5)
1.355(5)
1.426(6)
C5-C6
C1-C6
P-C19
1.433(6)
1.418(6)
1.813(4)
1.372(4)
1.370(4)
1.383(5)
1.447(6)
Cl1-O1
Cl1-O2
Cl1-O3
Cl1-O4
Angles
N2-Ni-P
N3-Ni-P
91.64(10)
N1-Ni-N3
91.47(15)
114.1(3)
168.03(10)
C12-C7-N3
N3-Ni-N2
C12-N2-Ni
N4-N3-Ni
N4-N3-C7
C7-N3-Ni
N3-N4-C6
N1-C1-C6
85.78(14)
109.1(2)
132.4(3)
113.6(3)
113.9(3)
120.0(3)
121.8(4)
C7-C12-N2
O2-Cl1-O1
O2-Cl1-O3
O1-Cl1-O3
O2-Cl1-O4
O1-Cl1-O4
O3-Cl1-O4
115.3(3)
113.9(3)
110.1(3)
114.3(3)
110.9(5)
109.1(4)
97.3(5)
20

Table 4
Selected Bond Distances (Å) and Angles (deg) for Compound [(HL)Pd(PPh3)]ClO4.
Distances
Pd1-P1
Pd1-N1
Pd1-N2
Pd1-N3
N3-N4
C1-C6
C1-C2
C2-C3
N3-C7
N4-C6
C3-C4
2.2952(7)
1.956(3)
2.057(3)
2.007(2)
1.274(3)
1.435(4)
1.424(4)
1.352(4)
1.421(4)
1.351(4)
1.402(5)
C4-C5
C5-C6
C7-C8
C7-C12
P1-C13
N1-C1
N2-C12
Cl1-O1
Cl1-O3
Cl1-O2
Cl1-O4
1.349(5)
1.427(4)
1.395(4)
1.376(4)
1.817(3)
1.329(4)
1.458(4)
1.408(3)
1.375(3)
1.392(3)
1.402(4)
Angles
N1-Pd1-P1
94.51(8)
N1-C1-C6
123.4(3)
N2-Pd1-P1
N3-Pd1-P1
N1-Pd1-N2
N4-N3-C7
93.54(8)
N1-Pd1-N3
N3-Pd1-N2
O3-Cl1-O2
O3-Cl1-O4
89.86(10)
82.15(10)
113.5(2)
108.5(3)
174.31(7)
171.91(11)
115.3(2)
N4-C6-C1
128.1(3)
116.2(2)
130.69(19)
126.6(2)
110.4(2)
117.2(3)
O2-Cl1-O4
O3-Cl1-O1
O2-Cl1-O1
O4-Cl1-O1
C7-N3-Pd1
N3-N4-C6
106.6(2)
107.7(2)
112.7(2)
107.7(3)
113.93(18)
121.3(2)
C12-C7-N3
N4-N3-Pd1
C1-N1-Pd1
C12-N2-Pd1
C7-C12-N2
21

Table 5
Selected Bond Distances (Å) and Angles (deg) for Compound [(L)Pt(PPh3)].
Distances
Pt1-P1
2.2549(14)
C7-C8
1.432(10)
Pt1-N2
Pt1-N1
1.963(6)
1.983(6)
C8-C9
1.346(11)
1.395(12)
C9-C10
Pt1-N3
N1-C1
2.025(5)
1.375(9)
C10-C11
C11-C12
1.345(11)
1.419(10)
N2-C12
N3-N4
1.327(9)
1.273(7)
C7-C12
C1-C6
1.432(10)
1.385(10)
N3-C6
N4-C7
1.431(9)
1.363(9)
P1-C13
1.819(7)
Angles
N2-Pt1-P1
N4-N3-Pt1
N1-Pt1-P1
N3-Pt1-P1
N2-Pt1-N1
N2-Pt1-N3
N1-Pt1-N3
C6-N3-Pt1
N1-C1-C6
93.1(2)
N3-N4-C7
C13-P1-Pt1
N2-C12-C7
N4-C7-C12
C12-N2-Pt1
C1-N1-Pt1
N4-N3-C6
C1-C6-N3
120.1(6)
111.7(2)
122.9(7)
129.3(7)
126.6(6)
115.0(5)
116.8(6)
114.7(6)
130.8(5)
96.3(2)
177.19(19)
170.6(3)
89.6(3)
81.1(3)
112.3(5)
116.7(7)
22

Table 6
Suzuki cross coupling reaction with the catalyst [(HL)Pd(PPh3)]ClO4.
Entry
Product
Isolated yield
96
I
85
94
Br
I
NO2
NO2
82
Br
NO2
NO2
23

Table 7
Heck reaction with the catalyst [(HL)Pd(PPh3)]ClO4.
Entry
Isolated yield
94
Product
I
Br
78
88
75
I
NO2
NO2
Br
NO2
NO2
24

Fig. 1 UV-Vis spectra of H2L (—), [(HL)Ni(PPh3)]ClO4 (—), [(HL)Pd(PPh3)]ClO4 (—) &
[(L)Pt(PPh3)] (—) in dichloromethane
25

Fig. 2 Molecular structure of H2L (40% probability ellipsoids) with atom numbering scheme
26

Fig. 3 Molecular structure of [(HL)Ni(PPh3)]ClO4 (40% probability ellipsoids) with atom
numbering scheme. The hydrogen atoms, except those of the amino groups, have been omitted for
clarity.
27

Fig. 4 Molecular structure of [(HL)Pd(PPh3)]ClO4 (40% probability ellipsoids) with atom
numbering scheme. The hydrogen atoms, except those of the amino groups, have been omitted for
clarity.
28

Fig. 5 Molecular structure of [(L)Pt(PPh3)] (40% probability ellipsoids) with atom numbering
scheme. The hydrogen atoms, except those of the amino groups, have been omitted for clarity.
29