Oxidation of phenyl propyne catalyzed by copper(II) complexes of a benzimidazolyl schiff base ligand: Effect of acid/base, oxidant, surfactant and morphology

Article abstract of DOI:10.1016/j.saa.2014.09.099

Copper(II) complexes with a new N-Substituted benzimidazolyl schiff base ligand are used as catalyst for the oxidation of 1-phenyl propyne. The oxidation is carried out under mild conditions using stoichiometric amounts of oxidant and catalytic amounts of Cu(II) complex as catalyst. Effect of acid/base, oxidant, morphology and surfactant has been studied. Two major products of phenyl propyne oxidation are the α-diketonic product and a terminal aldehyde. Diketone is the major product under acidic conditions while aldehyde formation is highest under basic conditions. The maximum conversion is found with the NO₃^- bound complex. GC-MS is used to find the percentage yields of products. SEM and PXRD of the reused complexes as catalyst suggest that morphology affects the catalytic efficiency.

Full text of DOI:10.1016/j.saa.2014.09.099

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Oxidation of phenyl propyne catalyzed by copper(II) complexes
of a benzimidazolyl schiff base ligand: Effect of acid/base,
oxidant, surfactant and morphology
⇑
Ravinder Kumar, Pavan Mathur
Department of Chemistry, University of Delhi, Delhi 110007, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Copper(II) complex of a benzimidazolyl schiff base ligand catalyze the oxidation of phenyl propyne to a
diketonic and acetylenic aldehyde product in the presence hydroperoxides.
ꢀ
A new N-Methyl benzimidazolyl
Schiff base ligand has been
synthesized & characterized
structurally.
Copper(II) complexes of this ligand
have been synthesized and
characterized spectroscopically.
The complexes are utilized
heterogeneously for the oxidation of
1-phenyl propyne.
O
ꢀ
ꢀ
ꢀ
Heterogeneous
Catalyst
[Cu(L)X]
CHO
O
SEM and PXRD are used to observe
changes in catalytic activity upon
reuse of catalyst.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 June 2014
Received in revised form 3 September 2014
Accepted 22 September 2014
Available online 30 September 2014
Copper(II) complexes with a new N-Substituted benzimidazolyl schiff base ligand are used as catalyst for
the oxidation of 1-phenyl propyne. The oxidation is carried out under mild conditions using stoichiom-
etric amounts of oxidant and catalytic amounts of Cu(II) complex as catalyst. Effect of acid/base, oxidant,
morphology and surfactant has been studied. Two major products of phenyl propyne oxidation are the a-
diketonic product and a terminal aldehyde. Diketone is the major product under acidic conditions while
aldehyde formation is highest under basic conditions. The maximum conversion is found with the NO3À
bound complex. GC–MS is used to find the percentage yields of products. SEM and PXRD of the reused
complexes as catalyst suggest that morphology affects the catalytic efficiency.
Ó 2014 Elsevier B.V. All rights reserved.
Keywords:
Benzimidazole schiff base
Copper(II)
Alkyne oxidation
Morphology
Introduction
further exploration [9–11]. In this context Scanning Electron
Microscopy (SEM) has been applied to identify microstructures
Dicarbonyl derivatives are utilized in the synthesis of organic
intermediates, especially biologically active compounds, like imi-
dazoles, quinoxalines and indolone-N-oxide. They have good anti-
tumor activity and are used as selective cyanide anion indicators or
photoinitiators [1–3]. The oxidation of alkenes and alkynes results
of functional compounds and their preferred morphology and
has been used to confirm the effect of associated anion on the
morphology [12,13] and activation/deactivation of a catalyst [14].
Similarly powder XRD is employed as a finger print tool for
identification/confirmation of lattice structures of inorganic com-
pounds, non porous structures, unit cell changes upon reactions/
adsorptions of organic compounds, and distortion/size contraction
in materials [15]. In this paper we report the oxidation of 1-phenyl
propyne using copper(II) complexes of N-substituted benzimidaz-
olyl schiff base, in the presence of tert.butyl hydroperoxide (TBHP)
in the formation of dicarbonyls [4–6], ester [7], and a, b-acetylenic
ketones [8]. Thus oxidation of alkynes is an area which requires
⇑
Corresponding author. Tel.: +91 27667725; fax: +91 27666605.
E-mail address: pavanmat@yahoo.co.in (P. Mathur).
http://dx.doi.org/10.1016/j.saa.2014.09.099
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

R. Kumar, P. Mathur / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
819
as an alternate source of oxygen. SEM, PXRD and UV–Visible spec-
troscopy is used to monitor the above reaction.
monochromatized Cu K
and step size 0.02° at 298 K over the range of 2h = 5–35°. The
EPR measurements were made on X-band Bruker system
a1 radiation with a scan rate of 1.0 s/step
a
ESP300, equipped with a Bruker ER035 M gaussmeter and a HP
5350B microwave counter from Indian Institute of Technology,
Bombay (India) and Indian Institute of Technology, Kanpur, India.
Experimental sections
Materials and method
N-Methyl-o-phenylenediamine (Thomas Baker, Mumbai), b-
alanine (Merck), 2-hydroxy-1-naphaldehyde (Alfa-Aesar), K2CO3
(Thomas Baker), CuCl2Á5H2O (Thomas Baker), Cu(NO3)2 (Thomas
Baker), KCNS, 1-phenyl propyne (Merck) and 70% TBHP(Lancaster)
were used as obtained. N-Methyl-2-aminoethylbenzimidazole
dihydrochloride (N-Me-AB.2HCl) was prepared according to the
procedure as reported by Cescon and Day [16].
X-ray crystallography
Single crystal of schiff base ligand HL suitable for X-ray diffrac-
tion studies were grown by slow evaporation in CH3CN: MeOH
(3:2). The intensity data for HL were collected at 298(2) K on an
X’calibur CCD diffractometer with graphite monochromatized
Mo/Ka. Radiation (k = 0.71073 Å) from USIC, University of Delhi,
Instrumentations
Delhi, India. For HL, a total of 5448 reflections were measured of
which 2843 were unique and 2555 were considered observed
Elemental analysis of the ligand and their complexes were
obtained on VARIO EL III from USIC, University of Delhi, India. IR
spectra were recorded on a Perkin–Elmer FT-IR-2000 spectrometer
using KBr disks in the range of 400–4000 cmÀ1. UV–Vis spectra
were recorded in DMF with a Shimadzu UV–Vis-1601 spectrome-
ter. The morphological changes in the copper(II) complexes was
studied by scanning electron microscopy (SEM) model FEI Quanta
200F with oxford –EDS system IE 250 X Max 80 with gold coating
at SMITA research lab IIT Delhi, India. GC–MS spectra were
recorded at AIRF, JNU, New Delhi on a GCMS-QP2010 (plus) Schi-
madzu instrument. The powder X-ray diffraction patterns were
recorded using High resolution D8 Discover Bruker diffractometer,
equipped with point detector (scintillation counter), employing
(I > 2r (I)]. The data were corrected for Lorentz and polarization
effects. Multi-scan absorption correction was applied. The struc-
ture was solved by direct methods using SHELXS-97 [17] and
refined by full-matrix least-squares refinement techniques on F2,
using SHELXL-97 [17]. All calculations were done with the help
of WINGX programme [18]. For the molecular graphics, the pro-
gramme Diamond2 [19] and Mercury [20] were used. All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were fixed geometrically with Uiso values of 1.2 times the Uiso val-
ues of their respective carrier atoms. The hydrogen on lattice water
was located from difference Fourier map. The final residual index
for HL are; R 0.0356, Rw 0.0777 for the observed and R 0.0410,
Rw 0.813 for all reflections using 218 parameters and two restraint.
Table 1
The percentage conversion of the phenyl propyne to products using copper complexes of (1)–(3).
Table 1.1. Percentage conversion of products using complex (1)–(3) under neutral conditions with TBHP
Complex
Substrate
Products
%Conversion
Total conversion (%)
49
Cu(L)Cl (1)
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
19
17
13
Cu(L)NO3 (2)
Cu(L)NCS (3)
1-Phenyl propyne
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
23
20
17
60
33
PhACOACOACH3
PhAC„CACHO
PhACOOH
13
10
10
Table 1.2. Percentage conversion of phenyl propyne to products using complex (2) under basic conditions with TBHP
Complex
Cu(L)NO3
Substrate
Under basic conditions
%Conversion
Total conversion (%)
81
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
25
42
14
Table 1.3. Percentage conversion of products using complex (2) under acidic conditions with TBHP
Complex
Cu(L)NO3
Substrate
Under acidic conditions
%Conversion
Total conversion (%)
69
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
47
17
5
Table 1.4. Percentage conversion of products using complex (2) under basic conditions with H2O2
Complex
Cu(L)NO3
Substrate
With H2O2
%Conversion
Total conversion (%)
18
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
6
8
4
Table 1.5. Percentage conversion of products using complex (2) under basic conditions with TBHP in presence of surfactant
Complex
Cu(L)NO3
Substrate
Under basic conditions
%Conversion
Total conversion (%)
22
1-Phenyl propyne
PhACOACOACH3
PhAC„CACHO
PhACOOH
14
5
3

820
R. Kumar, P. Mathur / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
Details of the crystallographic data and structure refinement for
ligand HL are given in Table S6.1.
Synthesis of [Cu(L)NO3] (2)
Powder X-ray diffraction patterns were obtained using High
resolution D8 Discover Bruker diffractometer, equipped with point
detector (scintillation counter), employing monochromatized Cu
This complex was prepared by following a procedure as
reported for complex (1) except that copper(II) nitrate (76 mg,
0.317 mmol) was used for complexation. The light green colored
powder so obtained was filtered and air dried in vacuo over P2O5.
The compound analyzed for the composition C20H16CuN4O4. Yield:
80%; m.p.: 247 °C.
Ka1 radiation with a scan rate of 1.0 s/step and step size 0.02° at
298 K over the range of 2h = 5–40°. The Le-Bail fitting of the
observed PXRD pattern of all the complexes of this series was
obtained by using the crystal parameters of similar Schiff base cop-
per(II) complexes with CCDC No. are 932003, 932005 and 893788
respectively (unpublished work).
Anal. Found(Calc.) for C20H16N4O4Cu: C 54.5(54.6), H 3.5(3.6), N
12.5(12.7). Selected IR(KBr, cmÀ1); m(AC@NAC@CA) 1442, m(NH)(H-
bonded) 3058, m(C@N) 1622, mC@C benzene 741. UV–Vis kmax/nm (loge)
in DMF: 271(4.3), 280(4.2), 317(4.1), 391(3.9), 628(2.2).
Synthesis of schiff base ligand (HL)
Synthesis of complex [Cu(L)SCN] (3)
N-Methyl 2-aminoethyl benzimidazolyl dihydrochloride (N-
Me-GB.2HCl) was prepared by adopting a procedure reported ear-
lier [21]. This was dissolved in water and neutralized by adding
requisite amount of aqueous K2CO3. A stirred methanolic solution
of 2-hydroxy-1-naphthaldehyde was added slowly to the above
solution. After about ½ h of constant stirring a yellow solid sepa-
rated out. The solid was filtered off, washed with water, acetone
and petroleum ether, dried in vacuo over P2O5. It was finally
recrystallized from acetonitrile.
Anal. Found(Calc.) for C20H17N3O: C 76.2(76.1), H 5.5(5.3), N
13.1(13.3); Selected IR(KBr, cmÀ1): m(AC@NAC@CA) 1420, m(AHC@N)
1610, mOH 2924, mring pulsation 751. 1H NMR (400 MHz, DMSO-
d6, d ppm): 14.3(s, 1H, OH), 9.4(s, 1H, ACH@NA), 6.79–8.14(d, m,
10H, aromatic), 5.23(s,ACH2A), 3.86(s, ACH3). 13C NMR
(100 MHz) (ppm) (DMSO-d6): 176.6, 158.19, 153.03, 148.48–
To
a
methanolic solution (10 ml) of CuCl2Á2H2O (53 mg,
0.31 mmol), KCNS (31 mg, 0.31 mmol) dissolved in 5 ml methanol
was added drop wise until KCl precipitated out. The resulting
brown colored solution of Cu(SCN)2 solution was added dropwise
to the methanolic solution of ligand. During addition the product
formed immediately as a brownish green solid. The brownish
green colored powder so obtained was filtered, washed with cold
methanol and air dried in vacuo over P2O5. The compound ana-
lyzed for the composition C21H16CuN4OS. Yield: 80%; m.p.: 178 °C.
Anal. Found(Calc.) for C21H16CuN4OS: C 57.4(57.8), H 3.8(3.6), N
12.6(12.8), S 7.1(7.3). Selected IR(KBr, cmÀ1); m(AC@NAC@CA) 1451,
m(NH)(H-bonded) 3184, m(C@N) 1608, mC@C benzene 736. UV–Vis kmax
nm (log ) in DMF: 272(4.2), 281(4.2), 316(4.0), 625(2.0).
/
e
Results and discussion
106.09, 49.06, 30.65. UV–Vis kmax/nm (loge) in DMF: 422(3.9),
402(3.9), 306(4.1), 283(4.0), 271(4.2).
The crystal structure of the ligand L shows that one hydrogen is
deprotonated from hydroxyl group of naphaldehyd-2-ol and binds
to the N atom of imine group. The bond length of CAO group of the
napthyl rings is 1.269(2) suggesting that they have partial double
bond character that corresponds to the keto–enol tautomeric
between the oxygen of napthyl and nitrogen of azomethine group
(Fig. 1). The hydrogen on azomethine nitrogen is involved in intra-
molecular H-bonding with naphthalene oxygen, N3AH. . ..O1
(1.920 Å, i = Àx, +y, Àz + 1/2). Fig. S1. Bond distances and bond
angles between the atoms are shown in Tables S6.2 & S6.3
respectively.
Synthesis of complex [Cu(L)Cl] (1)
To a methanolic solution of Ligand, (100 mg, 0.317 mmol), in
10 mL methanol, was added CuCl2Á2H2O (54 mg, 0.317 mmol), pre-
dissolved in 5.0 mL methanol at room temperature. During addi-
tion the product formed immediately as a green solid. The green
colored powder so obtained was filtered, washed with cold meth-
anol and air dried in vacuo over P2O5. The compound analyzed for
the composition C20H16ClCuN3O. Yield: 84%; m.p.: 196 °C.
Anal. Found(Calc.) for C20H16N3OCuCl: C 58.0(58.1), H 3.6(3.8), N
Since suitable single crystals of copper(II) complexes with this
ligand could not be grown, therefore powder X-ray diffraction pat-
terns were obtained. The Le-Bail fitting [22] of powder X-ray dif-
fraction pattern of the [Cu(L)Cl] (Fig. S2), [Cu(L)NO3] (Fig. S3)
10.2(10.1). Selected IR(KBr, cmÀ1
)
m(AC@NAC@CA) 1419, m(NH)(H-bonded)
3125, m(C@N) 1621, mbenzene
746. UV–Vis kmax/nm (log ) in
e
strech
DMF: 271(4.3), 280(4.2), 317(4.2), 395 (3.9), 648(2.1).
Fig. 1. Ortep diagram of ligand drawn in 30% thermal probability ellipsoids with asymmetric unit.

R. Kumar, P. Mathur / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
821
and [Cu(L)NCS] (Fig. S4) suggests a Monoclinic P21/c (Higher sym-
metry), Triclinic P-1 (Lower symmetry) and Monoclinic P21/c
(Higher symmetry) lattice system respectively. The lattice con-
stants obtained after the Le-Bail fitting are shown in Table S1.
only 18%, while TBHP gives 81% conversion under similar
conditions.
Control experiments were carried out keeping similar condi-
tions of reaction as reported above:
(1) In the absence of the catalyst.
(2) Substituting the catalyst for the salt Cu(NO3)2.
Catalytic studies: effect of addition of acid/base and oxidant
Copper(II) complexes [Cu(L)Cl] (1), [Cu(L)(NO3)] (2) and
[Cu(L)NCS] (3) being insoluble in acetonitrile were used heteroge-
neously for the oxidation of 1-phenyl propyne. In a typical reaction,
catalysts (0.021 mmol), substrate (0.109 mmol) and tert-butyl
hydroperoxide (TBHP) (0.109 mmol, 70%) in ratio of [1:5:5] were
mixed in 15 mL acetonitrile and stirred at 35–40 °C for 10 h. The
progress of the reaction was monitored by TLC and formation of
DNP derivative confirms the formation of carbonyl compound.
The reaction mixture was centrifuged after a 10 h reaction to isolate
the copper(II) catalyst. The clear filtrate was subjected to GC–MS
analysis using naphthalene as an internal standard and the
products formed are given in Table 1.1. The complex [Cu(L)NO3]
(2) shows maximum percentage conversion among all the other
complexes. Thus complex (2) was used to study the effect of added
acid or base on the catalytic activity. In these cases the reaction
solution was made acidic by the addition of 0.5 ml of 0.2 M sodium
acetate + acetic acid buffer, or made basic by adding 0.6 ml of
10 mM sodium acetate to the reaction solution.
The GC–MS analysis shows a conversion of 3.6% of oxidized
product for (1), while a conversion of 14.2% is found for (2). This
compares the efficiency of the present catalyst.
SEM and PXRD measurements
The SEM micrograph shows that the mononuclear copper(II)
complexes of this series are found to possess a rod type morphol-
ogy (Fig. 2). In order to observe the impact of catalytic activity on
surface morphology, the catalysts [Cu(L)NO3] (2) and [Cu(L)NCS]
(3) were recovered after the oxidation reaction and a gold coated
samples were prepared for SEM measurement. The catalyst (2)
and (3) after participation in the oxidation of alkynes show
changes in their morphology as observed in Figs. 3B and C and
4B. Minimal morphology changes take place when the complex
[Cu(L)NO3] (2) is reacted only with oxidant in the absence of sub-
strate under similar experimental conditions. When the complex
[Cu(L)NO3] (2) is used under basic conditions, all the rods collapse
and cluster formation take place (Fig. 3C). When the complex is
used with surfactant the rods remain intact during catalysis, but
the catalytic activity is greatly diminished. In the case of
To understand the effect of oxidant, the oxidation reaction was
carried out in presence of H2O2 under basic conditions by following
the same procedure as reported above. The result shows that per-
centage conversion to oxidized products obtained by using H2O2 is
Fig. 2. Morphology of the complexes. (A): [Cu(L)Cl] (1), (B): [Cu(L)NO3] (2), (D): [Cu(L)NCS] (3).
Fig. 3. Variation in the morphology of the [Cu(L)NO3] complex during catalysis: (A) pure complex (B) after reaction with substrate under neutral conditions. (C) After reaction
with substrate under basic conditions.

822
R. Kumar, P. Mathur / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
Fig. 4. Variation in the morphology of the [Cu(L)NCS] complex during catalysis: (A) pure complex (B) after reaction with substrate under neutral conditions.
diffraction planes associated with these low angle peaks could be
involved in the promotion of catalysis [21a] The catalytic efficiency
is larger for the nitrate bound copper(II) complex as it exposes a &
c-axis for catalytic purpose while in case of thiocyanate bound
complex only the b-axis is exposed. Thus there is a role of
morphology in their catalytic activity [21a,23].
Conclusion
All the three complexes show efficient catalysis for the oxida-
tion of 1-phenyl propyne. In case of 1-phenyl propyne three
diverse products are formed the diketone, aldehyde and acid.
Formation of diketone suggests complete oxidation of the triple
bond, while formation of benzoic acid suggests the cleavage of
the alkynes. The overall conversion (60%) to the three products is
highest in case of nitrate bound complex (2) in this series.
When the oxidation reaction of 1-phenyl propyne is carried out
Fig. 5. PXRD pattern of complex (2) (A) unused complex (B) after 1st use (C) after
under basic conditions by using the catalyst (2), the yield of the
aldehyde is found to be much higher than the diketone and the
total yield is enhanced to 81%, while the same reaction carried
out under acidic conditions results in higher yields for the diketone
and the overall yields is only 69%. A disadvantage under acidic con-
ditions is that the about 40% of the complex is found to dissolve
during catalysis. Thus the reaction is not completely heteroge-
neous. The data reveals that the catalyst [Cu(L)NO3] is relatively
more selective for oxidizing 1-phenyl propyne to aldehyde (42%)
in basic media (Table 1.2), while it has greater selectivity to gener-
ate the diketone (47%) in acidic media (Table 1.3).
The fact that under basic conditions, obtained by the addition of
sodium acetate causes a major increase in the% of phenyl acety-
lenic aldehyde suggests that the substrate forms a tert-butyl per-
oxy ether intermediate. It is well established that presence of a
base activates the decomposition of tert-butyl peroxy ether inter-
mediate [24]. A similar intermediate is probable, with the peroxyl
2nd use.
[Cu(L)NCS] (3) the larger rods break into smaller rods and some
cluster formation takes place after using the catalyst in the oxida-
tion reaction as shown in Fig. 4B.
The copper(II) nitrate bound complex (2) shows sharp peaks at
2h 11.1, 12.2, 16.6, 18.3, 22.4, 26.1, 27.1, 29.6 and 33.5. While the
copper(II) thiocyanate bound complex (3) shows sharp peaks at
2h 7.9, 10.1, 16.4, 19.8, 25.0, 26.7 and 38.6. After reuse of the cat-
alyst there is significant loss in intensity at the low angle peak at
11.1(1, 0, 1) for complex (2) (Fig. 5A–C). While there is significant
loss in intensity of the low angle peak at 7.9(0, 2, 0) for complex
(3) (Fig. 6A and B).This suggests that the surface carrying the
radical attacking the triple bond, rather than the
a-methylene
resulting into the diketonic product. Thus forming the two major
products during the alkyne oxidation.
Utilization of another oxidant like H2O2 under basic conditions
results in poorer yields (18%) (Table 1.4). Thus the oxidizing reac-
tion is catalyzed to a greater extent by the copper(II) complex in
the presence of TBHP rather than H2O2.
Addition of a surfactant CTAB (cetyl trimethyl ammonium bro-
mide) causes inactivation of the catalyst even in the presence of
tert-butyl hydroperoxide and only 22% conversion occurs
(Table 1.5).Thus the surfactant protects the surface, effectively
blocking the catalysis sites, yet some residual activity still remains.
This observation taken together with the blank experiment
wherein the copper nitrate salt shows a 14% activity under homog-
enous conditions suggests that some leaching of the complex may
Fig. 6. PXRD pattern of complex (3) (A) unused complex (B) after 1st use.

R. Kumar, P. Mathur / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 818–823
823
occur during the catalytic cycle. To confirm these following exper-
iments were carried out:
crystallographic data for ligand. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.saa.2014.09.099.
(a) A reaction was set up as described in the experimental pro-
cedure and after completion of reaction and centrifugation,
the sample was examined by low temperature EPR, a single
line spectrum with width ꢁ200 gauss and g–2.06, was
observed. No four line hyperfine is found as seen for the
unused complex (Supporting Information Figs. S11b and
S12).
References
[1] (a) D. Tejedor, F.G. Tellado, Chem. Soc. Rev. 36 (2007) 484–491;
(b) C.D. Nicola, Y.Y. Karabach, A.M. Kirillov, M. Monari, L. Pandolfo, C. Pettinari,
A.J.L. Pombeiro, Inorg. Chem. 46 (2007) 221;
(b) As the paramagnetic species observed under EPR appeared
to be different from the starting material, another attempt
was made and a reaction was set up using twice the amount
of catalyst while keeping the other conditions same. After
completion of the reaction and centrifugation, the clear reac-
tion solution did give a slightly blue shifted d–d band at
ꢁ617 nm (Supporting Information, Fig. S13); using the
extinction coefficient of the parent complex, it was esti-
mated that the following % dissolution was occurring during
the course of reaction. [Cu(L)Cl] = 3%, [Cu(L)NO3] = 7%,
[Cu(L)NCS] = 8% in acetonitrile media.
(c) R. Gopal, A.J. Gordon, Tetrahedron Lett. 31 (1971) 2941;
(d) B. Chabaud, K.B. Sharpless, J. Org. Chem. I 44 (23) (1979).
[2] (a) G.B. Shulpin, G.S. Mishra, L.S. Shulpina, T.V. Strelkova, A.J.L. Pombeiro,
Catal. Commun. 8 (2007) 1516;
(b) A.V. Kelin, V. Gevorgyan, J. Org. Chem. 67 (2002) 95;
(c) R.M. Adlington, J.E. Baldwin, G.J. Pritchard, K.C. Spencer, Tetrahedron Lett.
41 (2000) 575;
(d) C.F. Thompson, T.F. Jamison, E.N. Jacobsen, J. Am. Chem. Soc. 123 (2001)
9974.
[3] (a) M.M. Ali, M.M.F. Ismail, M.S.A. El-Gaby, M.A. Zahran, Y.A. Ammar,
Molecules 5 (2000) 864;
(b) N.J. Lee, E.A. Theodorakis, Macromol. Res. 11 (1) (2003) 47–52.
[4] W. Ren, Y. Xia, S.J. Ji, Y. Zhang, X. Wan, J. Zhao, Org. Lett. 11 (2009) 8.
[5] (a) C.N. Cornell, M.S. Sigman, Inorg. Chem. 46 (2007) 1903;
(b) V. Kotov, C.C. Scarborough, S.S. Stahl, Inorg. Chem. 46 (2007) 1910.
[6] A. Gao, F. Yang, J. Li, Y. Wu, Tetrahedron 68 (2012) 4950.
[7] L.X. Alvarez, M.L. Christ, A.B. Sorokin, Appl. Catal. A: Gen. 325 (2007) 303.
[8] C. Perollier, A.B. Sorokin, Chem. Commun. 1548 (2002) 1549.
[9] (a) F. Babudri, V. Fiandanese, G. Marchese, A. Punzi, Tetrahedron Lett. 36
(1995) 7305;
(c) As the amount of complex leached is quite small it may lead
to a minor homogeneous catalytic activity, in contrast to this
the major portion of heterogenous catalyst shows changes in
morphology up to 76% (the average length of rods in case of
the [Cu(L)NO3] changes from 14.0 lm to 3.4 lm, Fig. S14).
Thus the major catalytic pathway is via heterogenous
(b) S.K. Singh, V. Saibaba, V. Ravikumar, S.V. Rudrawar, P. Daga, C.S. Rao, V.
Akhila, P. Hegde, Y.K. Rao, Bioorg. Med. Chem. 12 (2004) 1881.
[10] J.F. Callahan, J.L. Burgess, J.A. Fornwald, L.M. Gaster, J.D. Harling, F.
P
catalysis.
Harrington, J. Heer, C. Kwon, R. Lehr, A. Mathur, B.A. Olson, J. Weinstock, N.J.
Laping, J. Med. Chem. 45 (2002) 999.
In summary, we have developed acid/base dependent heteroge-
neous oxidation protocol for the synthesis of 1,2-diketone and
aldehyde through alkyne oxidation, catalyzed by our copper com-
plexes. The mild and neutral conditions utilized and relatively safe
oxidant employed may be useful in organic transformations.
[11] (a) A. Corma, H. Garcıa, F.X. Llabres Xamena, Chem. Rev. 110 (2010) 4606–
4655;
(b) B.M. Weckhuysen, D.E. Kelle, Catal. Today 78 (2003) 25–46;
(c) K. Mori, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 126
(2004) 10657–10666.
[12] F. Liu, J. Wu, K. Chen, D. Xue, Microscopy: Science, Technology, Applications
and Education, A. Mendez-Vilas and J. Diaz (Eds.), Formatex Research Center
(2010) 1781–1792.
[13] T. Maiyalagan, K.R. Chemelewski, A. Manthiram, ACS Catal. 4 (2014) 421–425.
[14] G.A. Lomic, E.E. Kis, G.C. Boskovic, R.P. Marinkovic-Neducin, APTEFF, 35, 1-280
(2004) BIBLID: Rev. 1450-7188, 35 (2004) 67-77.
[15] J.S.J. Hargreaves, Crystallogr. Rev. 11 (1) (2005) 21–34.
[16] L.A. Cescon, A.R. Day, J. Org. Chem. 27 (1962) 581.
[17] G.M. Sheldrick, SHELXS97 and SHELXL97; Program for Crystal Structure
Solution and Refinement, University of Gottingen, Germany, 1997.
[18] (a) A.L. Spek, J. Appl. Crstallogr. 36 (2003) 7;
Acknowledgment
The authors are grateful to University of Delhi, Delhi for a spe-
cial grant. We are thankful to USIC-CIF, University of Delhi, Delhi,
India for NMR and Single Crystal X-ray data and AIRF JNU, New
Delhi, India for GC–MS. The author (RK) is thankful to UGC for pro-
viding senior research fellowship (SRF) One of the Author, P.
mathur, gratefully acknowledges sabbatical leave from university
of Delhi, Delhi, India.
(b) G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112;
(c) L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[19] G. Bergerhoff, M. Berndt, K. Brandenburg, J. Res. Natl. Inst. Stand. Technol. 101
(1996) 221.
[20] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M.
Towler, J.V. De Streek, J. Appl. Crystallogr. 39 (2006) 453.
[21] (a) R. Kumar, K. Mahiya, P. Mathur, Dalton Trans. 42 (2013) 8553–8557;
(b) M.R. Maurya, A. Kumar, M. Ebel, D. Rehder, Inorg. Chem. 45 (2006) 5924;
(c) R. Kumar, K. Mahiya, P. Mathur, Ind. J. Chem. 50A (2011) 775.
[22] (a) A.L. Bail, H. Duroy, J.L. Fourquet, Mater. Res. Bull. 23 (1988) 447;
(b) J. Carvajal, R., Full Prof Suite Program (version 1.00), (2007), Laboratoire
Leon, Brillouin (CEA/CNRS): CEA-Saclay, 91191, Gifsur-Yvette, Cedex, France.
[23] K. Mahiya, P. Mathur, Inorg. Chim. Acta 399 (2013) 36–44.
[24] Y. Li, T.B. Lee, T. Wang, A.V. Gamble, A.E.V. Gorden, J. Org, Chem. 77 (2012)
4628–4633.
Appendix A. Supplementary material
Contains unit cell packing of ligand (Fig. S1), Le-bail fitting pat-
tern and its parameter for complex (Figs. S2–S4, Table S1), 1H and
13C NMR (Figs. S6 and S7) UV–Visible spectra of ligand and its com-
plex (Figs. S5, S8, S9, S13), Cyclic Voltammetry (Fig. S10(a–c)) EPR
spectra of complexes 1-3 (Fig. S11(a-c) and S12) and SEM
Variation (Fig. S14). CCDC 932006 contains the supplementary