(η6-Benzene)Ru(II) half-sandwich complexes of pyrazolated chalcogenoethers for catalytic activation of aldehydes to amides transformation

Article abstract of DOI:10.1016/j.jorganchem.2018.09.019

The reaction of [(η⁶-C₆H₆)RuCl(μ-Cl)]₂ with chalcogenoether substituted 1H-pyrazole ligands (L1-L3) in methanol have yielded three novel Ru(II) half-sandwich complexes [(η⁶-C₆H₆)RuCl(L)]PF₆ (1–3) in high yield under the ambient reaction conditions. The NMR, MS and FT-IR analytical techniques were used to identify their structures. The molecular structures of the complexes 2 and 3 were established with X-ray crystallographic analysis and revealed a pseudo-octahedral half sandwich piano-stool geometry around ruthenium in each complex. Complexes 1–3 are thermally robust and were found to be insensitive towards the air and moisture. All the complexes were found to be catalytically active and produced the excellent yields of amides (up to 95%) from corresponding aldehydes. In contrast to the previous reported catalytic systems for aldehyde to amide transformation, the present complexes 1–3 are very efficient and have several advantages in terms of low catalyst loading, reaction time, temperature and wide applicability for various substituted aldehydes. Owing to the stronger σ-donor coordination properties of selenium containing ligands, the complex 2 was found to be more efficient as compare to the sulphur and tellurium analogues.

Full text of DOI:10.1016/j.jorganchem.2018.09.019

Accepted Manuscript
6
(η -Benzene)Ru(II) half-sandwich complexes of pyrazolated chalcogenoethers for
catalytic activation of aldehydes to amides transformation
Kamal Nayan Sharma, Munsaf Ali, Avinash Kumar Srivastava, Raj Kumar Joshi
PII:
S0022-328X(18)30729-0
10.1016/j.jorganchem.2018.09.019
JOM 20576
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 22 August 2018
Revised Date: 20 September 2018
Accepted Date: 21 September 2018
6
Please cite this article as: K.N. Sharma, M. Ali, A.K. Srivastava, R.K. Joshi, (η -Benzene)Ru(II)
half-sandwich complexes of pyrazolated chalcogenoethers for catalytic activation of aldehydes to
amides transformation, Journal of Organometallic Chemistry (2018), doi: https://doi.org/10.1016/
j.jorganchem.2018.09.019.
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ACCEPTED MANUSCRIPT
(
η6-Benzene)Ru(II) half-sandwich complexes of pyrazolated chalcogenoethers
for catalytic activation of aldehydes to amides transformation
Kamal Nayan Sharma, Munsaf Ali, Avinash Kumar Srivastava and Raj Kumar Joshi*
Department of Chemistry, Malaviya National Institute of Technology Jaipur, J.L.N. Marg, Jaipur
302017, Rajasthan, India
E-mail: rkjoshi.chy@mnit.ac.in
Keywords: Thioether • selenoether • telluroether • half-sandwich complexes • aldehyde to amide
transformation
TOC Graphic

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ABSTRACT
The reactions of [(η6-C6H6)RuCl(µ-Cl)]2 with chalcogenoether substituted 1H-pyrazole ligands
(L1-L3) in methanol has endowed three novel Ru(II) half-sandwich complexes [(η6-
C6H6)RuCl(L)]PF6 (1-3) in high yield under the ambient reaction conditions. The NMR, MS and
FT-IR spectral techniques were used to acquaint with their structures. The molecular structures
of the complexes 2 and 3 was established with X-ray crystallographic analysis and revealing a
pseudo-octahedral half sandwich piano-stool geometry around ruthenium in each case.
Complexes 1-3 are thermally robust and found insensitive towards the air and moisture. All the
complexes were found catalytically active and produce the excellent conversion of aldehyde to
amide (up to 95%). In contrast to previously reported complexes, complexes 1-3 have several
advantages in term of catalyst loading, time of reaction, temperature and optimum reaction
conditions. Owing to the stronger soft donor properties of the selenium, the complex 2 was found
to be more efficient than the sulphur and tellurium analogues.

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1. Introduction
Amides are amongst the most important organic compounds which have been extensively
explored as synthetic modules in various organic transformations [1-3]. The presence of amide
functional group [4-9] as a key chemical connection in nitrogen containing biologically active
compounds [10], various commercially available pharmaceutical drugs [11-13], and polymers
[14, 15], shows the immense prevalence of amide bond formation in synthetic chemistry.
Classically, amides are synsthesized by the stoichiometric reaction of carboxyilic acids and
derivatives (halides, esters or anhydrides) with amines [16]. The spontaneous formation of amide
is not possible through unifying these two functional groups at ambient temperature, the essential
water elimination requires high temperature ≥200 °C [17]. The formation of undesired products
and low atom economy in such process curtails their employability in industrial applications.
Hence, the development of advanced atom-efficient catalytic methods for amide formation
becomes desirable in modern synthetic chemistry [18, 19]. In this context, several metal-
catalysed approaches have been developed for amide bond formation [20]. Many transition
metals including the scandium [21], nickel [22], copper [23-25], zinc [26], and palladium [27]
based catalysts have been reported for the catalytic transformations of aldehydes [24, 25, 27-30],
or oximes [22, 23, 28] into corresponding amides. Alumina supported rhodium [31, 32],
titanosilicates loaded with rhodium [33], and [Ir(Cp*)Cl2]2 [34] have been found promising
candidates for amide synthesis. However, the requirement of an inert atmosphere to handle the
air-sensitive metal catalysts and harsh reaction conditions which are typically detrimental to the
integrity of the substrates are some of the major disadvantages of these protocols. Moreover,
some functional groups do not withstand under such severe ambiance and the selectivity of the
desired product decreases. In addition, high catalyst loading and stoichiometric amount of
additional reagents, produces the significant quantity of undesired products. Crabtree and co-
workers developed a ruthenium complex of terpyridine based NNN type pincer ligand that could
efficiently catalyzed the one-pot conversion of aldehydes into amides without the use of
additives [35]. The prime goal of current work is the development of an elegant and more
efficient method for the one-pot synthesis of amide from aldehyde which can effectively reduced
the formation of hazardous wastage. Moreover, the present ruthenium based catalysts are less
expensive as compare to the reported methods in which very precious Rh/Ir/Pd metals based
catalytic systems were used. The half sandwich ruthenium(II) complex of terdentate N-

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heterocycles based organochalcogen ligands had shown promising catalytic activity in various
catalytic reactions such as asymmetric catalysis and hydration of nitrile [36, 37], transfer
hydrogenation of ketones and oxidation of alcohols [38, 39]. The potential of various metal
complexes of pyrozole containing ligands has been already proven in various earlier reports [40-
48]. The strong donor properties of chalcogen donor sites present within the organochalocogen
ligands make the resulting complexes suitable catalysts [49-56]. Apart from efficiency,
organochalcogen ligand based catalytic systems are attractive due to their insensitivity to air and
moisture, solubility in various organic solvents and stability in solution. The catalytic strength of
metal complexes of organochalcogen ligands for this particular transformation is not investigated
yet. Also, to the best in our knowledge, we are the first to report the ruthenium complex of
pyrazole based organochalcogen ligands. Therefore, moving towards the ligand chemistry and
application of N-heterocycles based chalcogenated ligands and keeping all these facts in mind,
we have synthesised three new and novel mononuclear Ru(II) complexes of pyrazole based
organochalcogen ligand and investigated them for catalytic transformation of aldehyde to amide.
The comparative study of the catalytic efficiency of these three complexes is investigated for the
one-pot synthesis of primary amides from a wide range of aryl aldehydes in the presence of
NH2OH.HCl and a base. Present catalytic system does not require any hazardous additives and
convert aldehyde into amides in good to excellent yield under the aerobic reaction conditions
without forming any by-products.
2. Results and discussion
The systematic methodology adopted for the synthesis of Ru(II) complexes (1-3) is illustrated in
Scheme 1. The previously reported methods [46, 57] were used to prepare the pyrazole based
thio/seleno/telluro-ether functionalized bidentate ligands (L1-L3). Three new half-sandwich (η6-
benzene)ruthenium(II) complexes (1-3) were synthesized by reacting [(η6-C6H6)RuCl(µ-Cl)]2
with methanolic solution of L1/L2/L3 under ambient reaction conditions. The characterization
techniques such as NMR, MS, and FT-IR were used to determine the structures of newly
synthesized complexes 1-3. The NMR and mass spectra of complexes 1-3 are provided in
Supplementary data (Figures S1-S9) which were found consistent with their molecular structures
illustrated in Scheme 1.

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Scheme 1. Synthesis of half-sandwich (η6-benzene)ruthenium(II) complexes 1-3.
Due to the inadequate solubility of 1-3 in CDCl3, their NMR spectra were recorded in CD3CN.
1
13
The signals in H and C{1H} spectra of 1-3 appeared deshielded up to 0.9 ppm and 8.6 ppm,
respectively, with relative to those of corresponding free ligands [46, 57], corraborating the
coordination of ligand with Ru(II) in a bidentate chelate mode. Moreover, in 13C{1H} NMR
spectra, signals of C9, C6 and C5 were found more deshielded relative to those of other carbon
atoms of the complex. The protons attached to these carbons also appeared somewhat more
deshielded than other protons present in the complexes. The high magnitude of shift for these
carbon atoms and proton is probably due to the fact that they are very close to donor sites (N and
1
S/Se/Te). Additionally, H and 13C{1H} NMR of each of the complexes 1-3 how a typical
resonance (most intense signal) for six protons and carbons of η6-benzene in the range of 5.59-

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5.90 ppm and 86.2-87.3 ppm, respectively, and match with the earlier reported half-sanwich
ruthenium complex of η6-benzene [58]. In mass spectra of 1, 2 and 3, the intense peak at (m/z)
496.9025, 544.8474 and 624.8472 appeared respectively, is attributable to [M−PF6]+.
Crystal structures
The The solubility of complexes 1-3 was found to be good in acetonitrile, DMF and DMSO,
while close to negligible in dichloromethane, chloroform and methanol, and completely
insoluble in diethyl ether and n-hexane. The suitable quality single crystals of complexes 2 and 3
were grown by slow evaporation of their saturated solution in acetonitrile/methanol (1:1) and
subjected to analyse through single crystal X-ray crystallography. The thermal ellipsoid diagrams
of 2 and 3 are depicted in figures 1 and 2 with some selected bond length and bond angles, while
the details parameters are provides in Table S1 of SI. The bidentate coordination of ligand
through N of pyrazol ring and Se/Te with Ru results the formation of a six membered chelate
ring. In the cation of each complex, Ru adopt a pseudo-octahedral half-sandwich “pianostool”
geometry. The distances for Ru-Se and Ru-Te bonds in 2 and 3, was obtained at 2.511 Ǻ and
2.648 Ǻ, respectively, and fall in the range of previously reported ruthenium complexes [38, 59].
Fig. 1. Molecular structure of 2 with thermal ellipsoids set at the 30% probability level. H atoms and PF6
counter anion are omitted for clarity. Bond lengths (Å): Ru(1)–N(2) 2.105(11), Ru(1)–Se(1) 2.5106(17);
Bond angles (°): N(2)–Ru(1)–Se(1) 87.0(3), Se(1)–Ru(1)–Cl(1) 91.59(11).

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Fig. 2. Molecular structure of 3 with thermal ellipsoids set at the 30% probability level. H atoms and PF6
counter anion are omitted for clarity. Bond lengths (Å): Ru(1)–N(2) 2.105(5), Ru(1)–Te(1) 2.6486(10);
Bond angles (°): N(2)–Ru(1)–Te(1) 86.0(17), Te(1)–Ru(1)–Cl(1) 81.6(6).
Table 1 Crystal Data and Structural Refinement Parameters for 2 and 3
Compound
Complex 2
Complex 3
Empirical Formula
C17H17BrClN2RuSe. PF6
C18H19BrClN2ORuTe. PF6
Formula Wt.
689.68
768.34
Crystal Size [mm]
0.31×0.25×0.21
0.29×0.28×0.22
Crystal System
Space Group
Triclinic
P 1
Monoclinic
P 2(1)/n
Unit Cell Dimension
a = 7.583(2)Å
b = 7.862(2)Å
c = 9.861(3)Å
α = 102.363(5)°
β = 101.494(5)°
γ = 91.189(5)°
561.5(3)
a = 10.808(4)Å
b = 10.070(4)Å
c = 22.907(9)Å
α = 90.00°
β = 98.559(7)°
γ = 90.00°
2465.6(17)
4
Cell Volume [Å3]
Z
Density (Calc.) [Mg.m–3]
Absorption Coeff. [mm–1]
F(000)
1
2.040
4.344
332
2.070
3.649
1464
θ Range [°]
3.030–24.998
2.21–25.14

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Index Ranges
−8≤ h ≤ 9
−9≤ k ≤ 9
−12≤ h ≤ 12
−11≤ k ≤ 11
−27≤ l ≤ 27
19039
4064(0.1195)
0.451/0.331
4064/0/290
1.017
R1 = 0.0524,
wR2 = 0.1185
R1 = 0.0833,
wR2 = 0.1331
1.134/–1.485
−11≤ l ≤ 11
5359
3964 (0.0319)
0.405/0.247
3874/0/271
1.003
R1 = 0.0525,
wR2 = 0.1044
R1 = 0.0601,
wR2 = 0.1083
0.786/–0.621
Reflections Collected
Independent Reflections (Rint.)
Max./Min. Transmission
Data/Restraints/Parameters
Goodness-of-Fit on F2
Final R Indices
[ I >2σ(I)]
R Indices (All Data)
Largest Diff. Peak/Hole [е.Å–3]
Evaluation of catalytic potential of Ru(II) complexes (1-3) for aldehyde to amide
transformation
Previously, the half-sandwich Ru(II) complexes have been found to be promising
candidates in the catalysis of various organic transformations including conversion of aldehyde
into amides which was traditionally achieved by the reaction of carboxylic acid or its derivatives
i.e. anhydrides, esters or halides with amines at high temperature [16, 17]. In this context, metal
based homogeneous [20-25] as well as heterogeneous [31-33], catalysts have been developed.
Most of the methods suffer from several disadvantages like requirement of inert conditions, high
catalyst loading, stoichiometric amount of additional reagents and harsh reaction conditions,
those are not advisable for the substrate’s integrity. Therefore, for the employment of the
attractive soft donor properties of chalcogen donor sites of N-heterocycles based
organochalcogen ligands, insensitivity of their metal complexes to air and moisture, the catalytic
strength of present Ru(II) complexes (1-3) were explored for catalytic conversion of a series of
aryl aldehydes into corresponding amides. All three complexes were found highly efficient at 0.1
mol% of catalyst loading at 100 °C temperature in inert free conditions. Moreover, the current
reaction does not demand any hazardous additives and produced the amides in good to excellent
yield without generating any by-products. For the optimization of reaction parameters, initially,
benzaldehyde was chosen as model substrate and a series of the reactions using the ruthenium
complexes 1, 2 and 3 as catalyst was performed (Table 2).

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Table 2 Optimization of base, solvent and temperature for aldehyde to amide transformation.
Entry Base
Solvent
toluene
THF
Temp. (˚C) Yielda (%)
1
NaOH
100
100
95
83
45
25
nd
nd
80
40
50
10
nd
nd
17
nd
2
NaOH
NaOH
NaOH
NaOH
NaOH
3
acetonitrile 100
1,4-dioxane 100
4
5
water
DMF
100
100
100
100
100
100
100
100
80
6
7
NaHCO3 toluene
8
KOH
toluene
toluene
9
K2CO3
10
11
12
13
14
Cs2CO3 toluene
Base free
KtOBu
NaOH
NaOH
toluene
toluene
toluene
toluene
rt
Aldehyde (1.0 mmol, 0.106 g), NH2OH.HCl (1.0 mmol,
0.064 g), catalyst 2 (0.1 mol%), base (1.0 mmol.), solvent
a
(5 ml), time (12 h), nd (not detected), isolated yields after
purification.
For maximum conversion of aldehyde to amides, 0.1 mol% amount of the catalyst was found
suitable. Below 0.1 mol%, the yield of the desired product was significantly reduced, while a
continuously increasing the mol% from 0.1 to 0.5 does not bring any significant change in yield
of product. Further, during the solvent optimization, the highest yield of product was obtained in
toluene (Table 2, Entry 1), the THF, acetonitrile and 1,4-dioxane also produced the desire
product (Table 2, Entry 2-4), but yield is drastically reduced. Water and DMF were also checked
as solvent but the reaction was not initiated and failed to produce the desire products (Table 2,
Entry 4-5). The effect of various bases was also investigated and the highest yield (95%) of
benzamide was obtained with NaOH (Table 2, Entry 1). Other bases including the NaHCO3,
KOH, K2CO3 and Cs2CO3 afforded relatively lower yields 80%, 40%, 50% and 10%,
respectively (Table 2, Entries 7-10). It was also observed that reaction did not produce any

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product in the absence of base (Table 2, Entry 11), hence, careful selection of the base is a prime
requisite to initiate the present catalytic transformation. Furthermore, the highest yield of the
amide was obtained in between 95-100 ˚C temperature, while drastic changes in the yield were
observed when temperature was reduced at 80 ˚C (Yield 17%, Table 2, entry 13), and
furthermore lowering the temperature of the reaction failed to bring the desired transformations
(Table 2, entry 14)
Below, the Figure 3 shows the reaction time profile of representative reactions for the
synthesis of benzamide under optimized rection conditions. The initial formation of the desired
product was detected after 4 h in the reaction. The continuous increase in the yield was observed
with time and after 12 h the yield of reaction was found to be constant (95%).
100
80
60
40
20
0
2
4
6
8
10
12
14
Time (h)
Fig. 3. Time profile of the synthesis of benzamide using complex 2 as catalyst.
In order to check the wide scope of the reaction, various functionally different aldehydes were
used under the optimized reaction conditions and reaction was completely generalized (Table 3).
One pot methodology for the synthesis of the primary amides from various aldehydes was
developed by using the Ru(II) complexes (1-3). It seems that the substituent present on the
aromatic ring of benzaldehyde do not affect the formation of product, however, some minor
differences in the products yield were observed. The catalytic activity of 1, 2 and 3 was found in
order of 2 > 1 > 3. The variation observed in catalytic efficiency with chalcogen ligands (L1-L3)
may be arises due to the difference in the donor properties of S/Se/Te as the other donor site i.e.,
N of pyrazole moiety is common in the three complexes. It was found that the catalytic activity
of 2 is best among the three complexes. Moreover, similar trend of catalytic activity (Se > S) of

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the previously reported[40] Ru(II) complexes was found for transfer hydrogenation of ketones
and oxidation of alcohols.
Table 3 Aldehyde to amide transformations using 1, 2 and 3 as catalyst.
Yielda (%)
Entry Substrate
1
Product
1
2
3
83
95
56
2
3
4
5
6
80
86
84
80
85
89
91
94
93
90
50
47
59
58
48
7
8
9
82
82
81
88
85
94
45
42
42

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10
11
12
89
86
84
92
94
91
41
47
35
Reaction Conditions: Aldehyde (1.0 mmol), NH2OH.HCl (1.0
mmol), catalyst (0.1 mol%), NaOH (1.0 mmol), toulene (5 ml), time
(12 h), temperature (100 ˚C), a Isolated Yield.
The plausible reaction mechanistic for present ruthenium catalyzed transformation of aldehyde
into amide, based on the previous reports on such metal catalyzed reactions [31, 60, 61], is
depicted in figure 4. Most probably, the active catalytic species (I) is generated in situ from the
catalyst in presence of NaOH. Thereafter, the aldoxime which is produced by the reaction [35] of
aldehyde and hydroxyl amine hydrochloride in the presence of base), gets coordinated to Ru(II)
catalyst through OH group (1/2/3) to form (η6-C6H6)Ru(L)(−O−N=CHR) species (II) together
with the elimination of a water molecule (step 1). In the next step, species II eliminates (η6-
C6H6)Ru(L)(OH) species (I) to give nitrile intermediate [62] which probably again binds to the
metal centre of I with the simultaneous nucleophilic attack of coordinated hydroxide on the
nitrile to form a ruthenium iminolate species (III) in the step 3 [31, 60]. Finally, in the step 4, the
hydrolysis of the ruthenium iminolate species (III) leads to regeneration of the catalyst with
concomitant formation of the final product.

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Br
Ru
N
Cl
E
N
R
-NaCl
NaOH
NH2OH.HCl
R'
N
O
R' CHO
OH
NaOH
H
Br
R'
NH2
Ru
E
- NaCl, 2H2O
N
N
HO
Step 4
Step 1
H2O
I
H2O
R
R'
Br
Br
R'
N
Ru
Ru
HO
R
N
N
N
N
N
O
E
H
E
III
II
R
Step 3
Step 2
R'
C
N
Br
Ru
E
R'
N
C
HO
N
N
I
R
Fig. 4. Plausible mechanism for aldehyde to amide transformation catalyzed with 1/2/3. PF6
Counter anion is omitted for clarity in each step.
Comparison of catalytic efficiency of present ru catalysts (1-3) with previously reported
catalytic systems for aldehyde to amide transformations
The catalytic transformation of aldehydes to amides with the present Ru(II) complexes
1/2/3 is quite efficient in terms of catalyst loading, reaction time, reaction temperature and use of
additives in comparison to reported metal based catalysts for amide synthesis [22, 34, 63, 64].
The first metal catalyzed transformation of aldoximes to amides was carried out in xylene at high
temperature (138 °C) and high catalyst loading (5.6 mol% nickel acetate), moreover, it also
associated formation of by-products [22]. The iridium catalyst [Ir(Cp*)Cl2]2 [34] has been used
for the amide synthesis but required loading is again high (2.5 mol %). Furthermore, the reaction
temperature needed was 111 °C, more than the present catalysis by 1/2/3. Williams and co-

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workers [63] have reported a Ru catalyst that efficiently catalyzed the rearrangement of
aldoximes to amides but this system also requires p-toluenesulfonic acid as additives and formed
amide with considerable amount of nitrile. Crabtree and co-workers reported ruthenium catalyst
based on NNN pincer ligand [terpyRu(PPh3)Cl2], however, it was found very effective for
aldehyde to amide conversion in good yields with using NaHCO3 as additive at 1.0 mol%
loading, but long reaction time (17 h) is again a drawback. An η6-arene-ruthenium(II) complex
[RuCl2(η6-C6Me6){P(NMe2)3}] has also been established as an effective catalyst for aldoxime to
primary amides in water at 100 °C but high catalyst loading of 5 mol% put this catalyst on
inferior side with respect to those 1/2/3 [64]. Thus, the present ruthenium half-sandwich
complexes (1-3) may be labeled as efficient catalyst for aldehyde to amide transformation as the
yields were up to 95% in 12 h under aerobic reaction conditions.
3. Conclusions
Three new Ru(II) half-sandwich complexes have been synthesized in high yield by reacting
pyrazole-based chalcogenoethers with [(η6-C6H6)RuCl(µ-Cl)]2 in methanol under ambient
1
13
reaction conditions and authenticated with H, C{1H} NMR, mass and FT-IR spectroscopic
techniques. Single crystal X-ray diffraction analysis of 2 and 3 revealed pseudo-octahedral half
sandwich piano-stool geometry at Ru metal centre in both the complexes. The complexes 1-3
have been found efficient, thermally robust and moisture/air insensitive catalysts for
transformation of aldehyde to primary amide in high yield (95%) in 12 h, with 0.1 mol% catalyst
loading and 100 °C reaction temperature. Complex 2, consisting the selenium ligand has been
found more efficient than their sulphur and tellurium analogues.
4. Experimental section
Physical measurement. The NMR spectra were recorded on a JEOL ECS-400 spectrometer
1
13
operating at 400 MHz and 101 MHz for H and C nuclei, respectively. FT-IR spectra were
recorded on a Perkin-Elmer 10.4.00 FT-IR spectrometer within the range 4000–400 cm−1 using
KBr pellets of the sample. High-Resolution Electron Impact Mass Spectra (HR-EIMS) were
obtained with Xevo G2-S Q-Tof (Waters, USA). The diffraction data on a single crystal of 2 and
3 were collected on a Bruker AXS SMART Apex CCD Diffractometer using Mo-Kα (0.71073
Å) radiation at 298(2) K. The software SADABS [65] was used for absorption correction (if

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needed) and SHELXTL for space group, structure determination, and refinements. All
nonhydrogen atoms were refined anisotropically. Hydrogen atoms were included in idealized
position with isotropic thermal parameters set at 1.2 times that of the carbon atom to which they
are attached. The least-square refinement cycle on F2 was performed until the model converged.
The melting point of solids were determined in an open capillary and reported as such. The
yields given are refered as isolated yields of compounds which have purity ≥95%.
Chemicals and reagents
4-Bromopyrazole, phenyl diselenide, thiophenol, sodium borohydride, ruthenium chloride,
ammonium hexafluorophosphate were procured from Sigma-Aldrich (USA), and used as
received. Bis(4-methoxyphenyl) ditelluride, L1, L2 and L3 were prepared by previously reported
methods [46, 47]. Prior to use, all the solvents were dried and distilled by standard procedures
[66]. The common chemicals and reagents which were available commercially within the country
were used as received.
Synthesis of complexes [(η6-C6H6)Ru(L1/L2/L3)Cl].PF6 (1-3)
Brick red solid [Ru(η6-C6H6)Cl2]2 (0.050 g, 0.1 mmol) was added to a solution of L1 (0.057 g,
0.2 mmol) / L2 (0.066 g, 0.2 mmol) / L3 (0.082 g, 0.2 mmol) made in 25 mL of methanol, and
the reaction mixture was stirred for 12 h at ambient temperature. The resulting reaction mixture
was filtered, and the volume of the filtrate was reduced to 5 mL at rotary evaporator. It was
mixed with solid NH4PF6 (0.032 g, 0.2 mmol) and further stirred at rt for 3h. The resulting
precipitated solid was filtered, washed with 5 mL of ice-cold methanol, and dried in vacuo.
Single crystals of complexes 2 and 3 were obtained by slow evaporation of solution made in
methanol.
1
1. Yellow solid, Yield: 0.096 g, 75%. mp: 195 °C. H NMR (400 MHz, CD3CN) δ (ppm): 8.08
(s, 1H, H9), 7.89 (s, 1H, H7), 7.63-7.46 (m, 5H, H1-3), 5.92 (s, 6H, η6-C6H6), 4.83-4.78 (m, 1H,
13
H6), 4.46-4.35 (m, 1H, H6), 3.45-3.42 (m, 1H, H5), 2.98-2.92 (m, 1H, H5). C{1H} NMR (101
MHz, CD3CN) δ (ppm): 148.5 (C9), 136.7 (C7), 130.8 (C3), 130.6 (C2), 129.7 (C1), 125.9 (C4),
93.7 (C8), 86.2 (η6-C6H6), 49.9 (C6), 34.5 (C5). HR-MS (CH3CN) [M−PF6]+ (m/z) Found:
496.9025; Calc. value for [C17H17BrClN2RuS]+: 496.9028. FT-IR (KBr, νmax/cm−1): 3093 (m,

ACCEPTED MANUSCRIPT
νC–H aromatic), 2926 (m, νC–H aliphatic), 1579 (m, νC=N aromatic), 1440 (s, νC=C aromatic), 1303 (m, νC‒N
aliphatic), 823 (s, νC–H aromatic, bending).
1
2. Yellow solid, Yield: 0.099 g, 72%. mp: 190 °C. H NMR (400 MHz, CD3CN) δ (ppm): 8.08
(s, 1H, H9), 7.90 (s, 1H, H7), 7.79-7.76 (m, 2H, H3), 7.62-7.60 (m, 3H, H1 and H2), 5.59 (s, 6H,
η6-C6H6), 5.11-5.05 (m, 1H, H6), 4.57-4.51 (m, 1H, H6), 3.34-3.29 (m, 1H, H5), 3.02-2.95 (m,
13
1H, H5). C{1H} NMR (101 MHz, CD3CN) δ (ppm): 148.3 (C9), 136.8 (C7), 132.2 (C3), 130.8
(C2), 129.1 (C1), 124.8 (C4), 93.8 (C8), 87.3 (η6-C6H6), 52.0 (C6), 29.0 (C5). HR-MS (CH3CN)
[M−PF6]+ (m/z) Found: 544.8474; Calc. value for [C17H17BrClN2RuSe]+: 544.8472. FT-IR
(KBr, νmax/cm−1): 3098 (m, νC–H aromatic), 2958 (m, νC–H aliphatic), 1574 (m, νC=N aromatic), 1437 (s,
νC=C aromatic), 1299 (m, νC‒N aliphatic), 834 (s, νC–H aromatic, bending).
1
3. Yellow solid, Yield: 0.114 g, 74%. mp: 193 °C. H NMR (400 MHz, CD3CN) δ (ppm): 8.10
3J
3
(s, 1H, H9), 7.89 (s, 1H, H7), 7.72 (d,
= 6.6 Hz, 2H, H3), 7.12 (d, JH−H = 6.7 Hz, 2H, H2),
H−H
5.60 (s, 6H, η6-C6H6), 5.33-5.29 (m, 1H, H6), 4.53-4.46 (m, 1H, H6), 3.85 (s, 3H, OCH3), 3.03-
13
2.99 (m, 1H, H5), 2.92-2.85 (m, 1H, H5). C{1H} NMR (101 MHz, CD3CN) δ (ppm): 161.9
(C4), 148.2 (C9), 136.0 (C3), 128.4 (C7), 116.5 (C2), 103.1 (C1), 93.5 (C8), 87.3 (η6-C6H6), 55.4
(OCH3), 53.2 (C6), 13.0 (C5). HR-MS (CH3CN) [M−PF6]+ (m/z) Found: 624.8472; Calc. value
for [C18H19BrClN2ORuTe]+: 624.8475. FT-IR (KBr, νmax/cm−1): 3087 (m, νC–H aromatic), 2958 (m,
νC–H aliphatic), 1580 (m, νC=N aromatic), 1491 (s, νC=C aromatic), 1297 (m, νC‒N aliphatic), 822 (s, νC–H aromatic
(bending)).
General procedure for the catalytic reaction
In an oven-dried 100 mL two-neck round bottom flask, a mixture of aryl-aldehyde (1.0 mmol),
NH2OH.HCl (1.0 mmol), NaOH (1.0 mmol), catalyst (0.5 mol%) and solvent (5 ml) were heated
at 100 °C with continuous stirring for 12 h in air. The progress of the reaction was continuously
monitored by TLC until the maximum conversion of an aldehyde to the desired product
observed. After completion, the reaction mixture was cooled to room temperature and extracted
in ethyl acetate (2 × 25 mL). This extract was further washed with water and dried over
anhydrous Na2SO4. The product was purified by column chromatography after removing the
solvent on a rotary evaporator under reduced pressure. All the desired product obtained as white
solid was authenticated by HR-MS, 1H, and 13C{1H} NMR spectroscopy.

ACCEPTED MANUSCRIPT
1H and 13C NMR of Aldehyde to Amides Conversion Products (Table 3, Entries 1-12)
1. Benzamide[67]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 7.84 –
7.81 (m, 2H), 7.55 – 7.51 (m, 1H), 7.46 – 7.43 (m, 2H), 6.31
(br s, 2H). 13C{1H} NMR (101 MHz, CDCl3) δ (ppm):
169.68, 133.32, 131.95, 128.58, 127.29.
2. 4-Fluorobenzamide[67]
White Solid, 1H NMR (400 MHz, CDCl3) δ 7.78 – 7.72 (m,
2H), 6.95 – 6.88 (m, 2H), 6.39 (br s, 1H), 4.11 (br s, 1H).
13C NMR (101 MHz, CDCl3+DMSO-d6) δ 168.39, 165.82,
163.31, 129.95 (d, J = 8.9 Hz), 129.59, 115.18, 114.97.
3. 4-Chlorobenzamide[67]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 8.32 (d,
3JH–H = 8.6 Hz, 2H), 7.99 (d, 8.6 Hz, 2H), 6.13 (br s, 1H),
5.83 (br s, 1H). C{1H} NMR (101 MHz, CDCl3+DMSO-
13
d6) δ (ppm): 167.01, 149.30, 139.22, 128.68, 123.22.
4. 4-Bromobenzamide[67]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 7.69 (d,
2H, 3JH–H = 8.5 Hz), 7.60 (d, 2H, 3JH–H = 8.5 Hz), 6.02 (br s,
1H), 5.81 (br s, 1H). 13C{1H} NMR (101 MHz,
CDCl3+DMSO-d6) δ (ppm) 166.94, 133.40, 131.26, 129.62,
125.04.
5. 2-Chlorobenzamide[67]
White solid, 1H NMR (400 MHz, CDCl3) δ (ppm): 7.77 (dd,
1H, 3JH–H = 7.5 Hz, 1.6 Hz), 7.46 – 7.32 (m, 3H), 6.41 (br s,
2H). 13C{1H} NMR (101 MHz, CDCl3) δ (ppm): 168.24,
133.76, 131.78, 130.77, 130.59, 130.36, 127.12.
6. 4-Nitrobenzamide[68]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 7.84 –
7.75 (m, 2H), 7.53 – 7.43 (m, 2H), 6.03 (br s, 2H). 13C{1H}
NMR (101 MHz, CDCl3+DMSO-d6) δ (ppm): 168.12,
137.42, 131.87, 128.84, 128.24.

ACCEPTED MANUSCRIPT
7. 4-Methylbenzamide[67]
8. 2-Ethylbenzamide[69]
White solid, 1H NMR (400 MHz, CDCl3) δ 7.65 (d, J = 8.1
Hz, 2H), 7.11 (d, J = 8.0 Hz, 2H), 6.42 (br s, 1H), 4.19 (br s,
1H), 2.27 (s, 3H). C NMR (101 MHz, CDCl3+DMSO-d6)
δ 169.60, 142.25, 129.92, 128.88, 127.40, 21.22.
13
1H NMR (400 MHz, CDCl3) δ 8.16 (dd, J = 7.8, 1.9 Hz,
1H), 7.88 (br s, 1H), 7.40 (ddd, J = 8.4, 7.4, 1.9 Hz, 1H),
7.05 – 6.977 (m, 2H), 6.90 (d, J = 8.2 Hz, 1H), 4.12 (q, J =
13
7.0 Hz, 2H), 1.44 (t, J = 7.0 Hz, 3H). C NMR (101 MHz,
CDCl3) δ 167.83, 157.47, 133.43, 132.39, 121.05, 120.77,
112.39, 64.76, 14.87.
9. 2-Methylbenzamide[70]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 7.45 (d,
3
1H JH–H = 7.6 Hz), 7.35 – 7.32 (m, 1H), 7.25 – 7.19 (m,
2H), 6.20 (br s, 1H), 5.85 (br s, 1H). C{1H} NMR (101
13
MHz, CDCl3) δ (ppm): 172.19, 136.28, 135.15, 131.17,
130.24, 126.91, 125.70, 19.95.
10. 2,4-Dimethylbenzamide[71]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 7.37 (d,
3
3
1H, JH–H = 7.7 Hz), 7.05 (s, 1H), 7.02 (d, 1H, JH–H = 7.8
Hz), 5.95 (br s, 1H), 5.79 (br s, 1H), 2.47 (s, 3H), 2.34 (s,
3H). 13C{1H NMR (101 MHz, CDCl3) δ (ppm): 172.02,
140.51, 136.55, 132.05, 127.14, 126.33, 125.71, 21.23,
20.06.
11. 2,4-Dimethoxybenzamide[72]
1
White solid, H NMR (400 MHz, CDCl3) δ (ppm): 8.09 (d,
3
3
1H, JH–H = 8.8 Hz), 7.55 (br s, 1H), 6.51 (dd, 1H, JH–H
=
8.8 Hz, 2.3 Hz), 6.41 (d, 1H, 3JH–H = 2.2 Hz 6.25 (br s, 1H),
3.85 (s, 3H), 3.77 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3) δ (ppm): 167.03, 163.72, 159.12, 134.03, 113.70,
105.14, 98.41, 55.78, 55.43.
1H NMR (400 MHz, CDCl3+DMSO-d6) δ 9.02 (s, 1H), 8.64
– 8.63 (m, 1H), 8.13 (dt, J = 7.9, 1.8 Hz, 1H), 7.37 (br s,
12. Nicotinamide[68]
13
1H), 7.32 – 7.28 (m, 1H), 6.36 (br s, 1H). C NMR (101
MHz, CDCl3+ DMSO-d6) δ 167.69, 152.24, 148.86, 135.57,
129.46, 123.34.

ACCEPTED MANUSCRIPT
5. Appendix A. Supplementary data
NMR spectra, mass spectra, crystal and refinement data, bond lengths and angles, copy of 1H and
13C NMR of all catalytic conversion products and CIFs of 2 (CCDC No. 1829142) and 3 (CCDC
No. 1829143) are available.
6. Acknowledgements
K.N.S. thanks Science and Engineering Research Board, New Delhi for start-up research grant
(YSS/2015/000698). M.A. and A.K.S. thank MANF-UGC, New Delhi and MNIT Jaipur,
respectively for providing fellowships. R.K.J. thanks the DST New Delhi, for providing financial
assistance under the INT/RUS/RFBR/P0222 scheme. Authors acknowledge MRC, MNIT Jaipur
for providing characterization facilities. IIT Delhi is also acknowledged for single crystal X-ray
analysis. .

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Highlights
•
Synthesis and characterization of three novel Ru(II) half-sandwich complexes of
pyrazolated chalcogenoether ligands.
•
•
Catalytic potential of the complexes for one-pot conversion of aldehyde to amide.
Due to the stronger σ-donor properties of selenium, the Ru complex of Se ligand was
found to be more efficient as compare to the sulphur and tellurium analogues.