Cyanosilylation of carbonyl compounds catalyzed by half-sandwich (η6-p-cymene) Ruthenium(II) complexes bearing heterocyclic hydrazone derivatives

Article abstract of DOI:10.1016/j.ica.2020.120006

A new class of half-sandwich (?⁶-p-cymene) ruthenium(II) complexes supported by heterocyclic hydrazone derivatives of general formula [Ru(?⁶-p-cymene)(Cl)(L)] where L represents N’-((1H-pyrrol-2-yl)methylene)furan-2-carbohydrazide (L

Full text of DOI:10.1016/j.ica.2020.120006

InorganicaChimicaActa514(2021)120006
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Research paper
Cyanosilylation of carbonyl compounds catalyzed by half-sandwich (η6-p-
cymene) Ruthenium(II) complexes bearing heterocyclic hydrazone
derivatives
Govindasamy Vinotha, Sekar Indiraa, Madheswaran Bharathia, Luis G. Alvesb, Ana M. Martinsc,
⁎
Kuppannan Shanmuga Bharathia,
a Department of Chemistry, School of Physical Sciences, Periyar University, Periyar Palkalai Nagar, Salem 636011, Tamil Nadu, India
b Centro de Química Estrutural, Associação do Instituto Superior Técnico para a Investigação Desenvolvimento, Av. Rovisco Pais, 1, 1049-003 Lisboa, Portugal
c Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal
A R T I C L E I N F O
A B S T R A C T
Keywords:
A new class of half-sandwich (ƞ6-p-cymene) ruthenium(II) complexes supported by heterocyclic hydrazone
derivatives of general formula [Ru(ƞ6-p-cymene)(Cl)(L)] where L represents N’-((1H-pyrrol-2-yl)methylene)
furan-2-carbohydrazide (L1), N’-((1H-pyrrol-2-yl)methylene)thiophene-2-carbohydrazide (L2) or N’-((1H-pyrrol-
2-yl)methylene)isonicotinohydrazide (L3) were synthesized. Both ligand precursors and complexes were char-
acterized by elemental and spectral analysis (IR, UV–Vis, NMR and mass spectrometry). The molecular structures
of all Ru complexes [Ru(ƞ6-p-cymene)(Cl)(L)] were determined by single-crystal X-ray diffraction as three-
legged piano-stool. The Ru(II) complexes were used as catalysts for the cyanosilylation of aldehydes (aliphatic,
aromatic, α,β-unsaturated and heterocyclic aldehydes) with trimethylsilyl cyanide (TMSCN). All reactions were
performed at room temperature and catalytic conditions as solvents, catalyst and catalyst loading were ex-
perimentally optimized. Using 0.5 mol% of Ru catalyst 3 in Et2O it was possible to prepare cyanosilylethers in
good-to-excellent isolated yields.
Pyrrole-2-carboxaldehyde hydrazone
derivatives
Ruthenium catalyst
Cyanosilylation
Cyanosilylethers
1. Introduction
using chiral organometallic and organocatalytic systems have been
described [8]. The activation of TMSCN may be promoted by a wide
Cyanosilylation of aldehydes with trimethylsilyl cyanide is the un-
ique available route to synthesize cyanohydrin derivatives through
formation of carbon-carbon bonds [1]. Chiral cyanosilyl moieties are
used as protective groups in organic synthesis [2]. They are optically
active compounds that may be converted in a wide range of multi-
functional intermediates such as α-hydroxy acids, α-amino acids, β-
amino alcohols, nitroolefins, α-hydroxy esters and α-hydroxy ketones,
and they for play a significant role in the synthesis of a large number of
pharmaceuticals, agrochemicals and insecticides [3,4]. The synthesis of
α-silyloxy nitriles involves protection of the alcohol moiety through O-
silylated cyanohydrin (OTMS) that enables further change to different
functionalities. TMSCN is commonly used as a cyanide source that is
safe and easy to handle when compared to HCN and metal cyanides as
NaCN or KCN [5].
range of nucleophiles, such as amines, phosphines, phosphazanes and
alkaline earth metal oxides. On the other hand, Lewis acid catalysts
have been widely investigated because they can act as electrophilic
catalyst for the activation of carbonyl compounds. Examples of this type
of cyanosilylation reactions were performed with simple metal salts as
catalysts, viz. Yb(OTf)3 [9], Yb(CN)3 [10], Cu(OTf)2 [11], ZnI2 [12],
KCN:18-crown-6 [13], LiCl and LiClO4 [14], R2SnCl2 an Sn-montmor-
illonite [15], MgBr2.Et2O [16], Zr(KPO4)2 [17], VO(OTf)2 [18], FeCl3
[19], InBr3 [20], NbF5 [21] and Fe(Cp)2PF6 [22]. Other procedures
using a hydrazone-based Cu(II) catalyst [23] a 3-aminopyrazine-2-
carboxylate based Pb(II) catalyst [24], a flexible tricarboxylate Gd(II)
coordination polymer [25] and a 3,3′,5,5′-azobenzentetracarboxylic
acid based Mg(II) catalyst [26] have also been described.
Curiously, for ruthenium, which is well-known for its unique cata-
lytic behaviour, only very few reports have come out in the literature
(Scheme 1) [27]. Ohkuma and co-workers described the synthesis of
cyanosilyls from TMSCN and carbonyl compounds (aldehydes
Many reports on CeC bond formation by cyanosilylation reactions
using both homogeneous [6] and heterogeneous catalysis are available
[7]. Chiral homogeneous systems, based on well established procedures
⁎ Corresponding author.
E-mail address: nksbharathi@periyaruniversity.ac.in (K. Shanmuga Bharathi).
https://doi.org/10.1016/j.ica.2020.120006
Received 9 July 2020; Received in revised form 3 September 2020; Accepted 4 September 2020
Availableonline09September2020
0020-1693/©2020ElsevierB.V.Allrightsreserved.

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
Scheme 1. Ruthenium(II) catalysts for the synthesis of cyanosilylethers.
[27(a,b)], keto esters [27c], α,α-dialkoxy ketones, β,β-dialkoxy ke-
tones, α-alkoxy, α-amino and alkynyl ketones [27(d,e)]) using biaryl
diphosphine Ru(II) aminoacids as catalysts (A) and, more recently,
Ghosh et al. reported a class of cationic ruthenium(II) arene complexes
displaying O-functionalized N-heterocyclic carbenes that act as cata-
lysts for cyanosilylation reactions at room temperature, under solvent-
free conditions (B) [27f].
2.2.1. Synthesis of N’-((1H-pyrrol-2-yl)methylene)furan-2-carbohydrazide
(HL1)
Yield: 76%; m.p.: 238 °C; Anal. calcd. for C10H9N3O2: C, 59.11; H,
4.46; N, 20.68. Found: C, 59.07; H, 4.44; N, 20.65. FT-IR: pyrrole –NH,
3199 cm−1; NH, 3113 cm−1; C]N, 1641 cm−1; C]O, 1563 cm−1
.
UV–Vis (DMSO, λmax [nm] (10−3 ε [M−1 cm−1]): 382 (1157), 284
(2188). 1H NMR (400 MHz, DMSO‑d6) (δ ppm): 11.56 (s, 1H, –NH),
11.33 (s, 1H, pyrrole –NH), 8.29 (s, 1H, HC = N), 7.91–6.14 (over-
lapping, 6H total, ArH). 13C NMR (100 MHz, DMSO‑d6) (δ ppm): 154.3
(C]O), 141.4 (HC = N), 147.4, 145.9, 127.5, 123.1, 114.8, 114.0,
112.5, 109.8 (HC = N, ArPyrrole and ArFurane). ESI-MS: m/z = 203.07
Taking in account that catalysts with heterocyclic moieties display,
in general, better activity than those having simple aryl groups, we
prepared complexes with two different heterocyclic fragments (C). Here
we report new half-sandwich ruthenium(II) complexes with hetero-
cyclic hydrazone ligands and its behaviour as catalyst for the cyanosi-
lylation of a wide range of carbonyl compounds, at room temperature,
with excellent yields.
[M + H]+
.
2.2.2. Synthesis
of
N’-((1H-pyrrol-2-yl)methylene)thiophene-2-
carbohydrazide (HL2)
Yield: 80%; m.p.: 249 °C; Anal. calcd. for C10H9N3OS: C, 54.78; H,
4.14; N, 19.16. Found: C, 54.72; H, 4.13; N, 19.12. FT-IR: pyrrole –NH,
2. Experimental section
3248 cm−1; NH, 3187 cm−1; C]N, 1592 cm−1; C]O, 1557 cm−1
.
2.1. General considerations
UV–Vis (DMSO, λmax [nm] (10−3 ε [M−1 cm−1]): 391 (1157), 292
(2294). 1H NMR (400 MHz, DMSO‑d6) (δ ppm): 11.57 (s, 1H, –NH),
11.19 (s, 1H, pyrrole –NH), 8.15 (s, 1H, HC = N), 7.98–6.15 (over-
lapping, 6H total, ArH). 13C NMR (100 MHz, DMSO‑d6) (δ ppm): 157.8
(C]O), 141.2 (HC = N), 139.1, 131.8, 128.9, 128.5, 127.4, 123.1,
114.0, 109.8 (HC = N, ArPyrrole and ArThiophene). ESI-MS: m/z = 219.05
The elemental analyses of the compounds were accomplished using
an analytical function testing Vario EL CHN analyser. The melting
points of the compounds were valued with the guide of Boetius micro-
heating label. Bruker 783 FT-IR spectrometer was used for recording IR
spectra. The absorption spectra of the ligands and complexes were
measured on a Cary 300 Bio UV–Vis Varian spectrophotometer from the
solutions of chloroform, 10−3 M, in quartz cuvettes (1 cm optical path)
in the range of 800–200 nm. NMR spectra of the compounds were
carried out using a Bruker Advances III HD Nanobay 400 MHz and
Bruker (Avance) 300 MHz FT- NMR spectrometer at 295 K, referenced
internally to residual proton-solvent (1H) or solvent (13C) resonances,
and reported in parts per million (ppm) related to tetramethylsilane
(0 ppm). The ESI-MS spectral analysis was performed in positive mode
on a Q-TOF-Mass Spectrometer.
[M + H]+
.
2.2.3. Synthesis of N’-((1H-pyrrol-2-yl)methylene)isonicotinohydrazide
(HL3)
Yield: 87%; m.p.: 215 °C; Anal. calcd. for C11H10N4O: C, 61.67; H,
4.71; N, 26.15. Found: C, 61.64; H, 4.69; N, 26.11. FT-IR: pyrrole –NH,
3268 cm−1; NH, 3200 cm−1; C]N, 1693 cm−1; C]O, 1595 cm−1
.
UV–Vis (DMSO, λmax [nm] (10−3 ε [M−1 cm−1]): 389 (1053), 288
(2379). 1H NMR (400 MHz, DMSO‑d6) (δ ppm): 11.76 (s, 1H, –NH),
11.61 (s, 1H, pyrrole –NH), 8.77 (s, 1H, HC = N), 8.30–6.12 (over-
lapping, 7H total, ArH). 13C NMR (100 MHz, DMSO‑d6) (δ ppm): 161.5
(C]O), 141.4 (HC = N), 150.7, 142.4, 138.7, 127.2, 123.4, 122.0,
114.4, 113.4, 109.9 (HC = N, ArPyrrole and ArPyridine). ESI-MS: m/
Commercially available RuCl3·3H2O was used as supplied from SRL
Pvt. Ltd. All the solvents, reagents and the compounds pyrrole-2-car-
boxaldehyde, 2-furoic hydrazide, thiophene-2-carboxylic acid hy-
drazide and 4-pyridinecarboxylic acid hydrazide were acquired from
Merck and Aldrich. The starting material [Ru(η6-p-cymene)Cl2]2 was
prepared according to literature [28].
z = 214.09 [M + H]+
.
2.3. Syntheses of Half-Sandwich (ƞ6-p-cymene) Ruthenium(II) complexes
(1–3)
2.2. General method for the syntheses of pyrrole-2-carboxaldehyde
hydrazone derivatives
One equivalent of [Ru(η6-p-cymene)Cl2]2 was added to
a di-
The pyrrole-2-carboxaldehyde hydrazone precursors (HL1–3) were
prepared by refluxing a mixture of pyrrole-2-carboxaldehyde (1 mmol)
and 2-furoic hydrazide, thiophene-2-carboxylic acid hydrazide or 4-
pyridinecarboxylic acid hydrazide (1 mmol) in 15 mL of ethanol for 8 h.
The solution was concentrated and the precipitate obtained was washed
with cold ethanol followed by dried in vacuum.
chloromethane solution (15 mL) containing two equivalents of the
pyrrole-2-carboxaldehyde hydrazone derivatives (HL1–3) and few drops
of triethylamine were added. The reaction mixture was stirred at room
temperature for 5 h. A gradual colour change from reddish orange to
brown was observed. The complexes were crystallized from CH2Cl2
/hexane solutions.
2

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
2.3.1. Synthesis of [Ru(η6-p-cymene)(Cl)(L1)] (1)
Kα radiation (λ = 0.71073 Å) on a Bruker AXS-KAPPA APEX II dif-
fractometer. Cell parameters were retrieved using Bruker SMART soft-
ware and refined using Bruker SAINT on all observed reflections [29].
Absorption corrections were applied using SADABS [30]. The structures
were solved by direct methods using SIR2004 [31]. Structure refine-
ment was done using SHELXL [32], included in the WINGX-Version
1.80.01 system of programs [33]. Hydrogen atoms were inserted in
calculated positions and allowed to refine in the parent atoms. Torsion
angles, mean square planes and other geometrical parameters were
calculated using SHELX [32]. Illustrations of the molecular structures
were made with ORTEP-3 for Windows [34]. Data for structures 1–3
were deposited in CCDC under the deposit numbers 1966389,
1,966,390 and 1966391, respectively, and can be obtained free of
charge from The Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/conts/retrieving.html.
Yield: 79%; m.p. : 131 °C; Anal. calcd. for C20H22N3O2ClRu: C,
50.79; H, 4.69; N, 8.89. Found: C, 50.73; H, 4.67; N, 8.85. FT-IR: NH,
3281 cm−1; C]N, 1605 cm−1; CeO, 1227 cm−1. UV–Vis (CHCl3, λmax
[nm] (10−3 ε [M−1 cm−1]): 369 (1190), 298 (6753), 252 (7845). 1H
NMR (300 MHz, CDCl3) (δ ppm): 11.02 (s, 1H, pyrrole NeH), 8.78 (s,
1H, HC = N), 7.44–6.39 (overlapping, 6H total, ArH), 5.39 (d, 1H, p-
cym ArH), 5.28 (d, 1H, p-cym ArH), 5.00 (d, 1H, p-cym ArH), 4.71 (d,
1H, p-cym ArH), 2.62 (sept, 1H, p-cym ArCH(CH3)2), 2.24 (s, 3H, p-cym
Ar(CH3)), 1.29 (d, 3H, p-cym ArCH(CH3)2), 1.18 (d, 3H, p-cym ArCH
(CH3)2). 13C NMR (75 MHz, CDCl3) (δ ppm): 154.3 (C]O), 141.4
(HC = N), 147.4, 145.9, 127.5, 123.1, 114.8, 114.0, 112.5, 109.8,
(HC = N, ArPyrrole and ArFurane), 101.01, 98.08 (p-cym CqAr), 86.27,
84.92, 82.18, 79.04 (p-cym CHAr), 22.78, 19.01 (p-cym ArCH(CH3)2
and Ar(CH3)), 8.40, 7.44 (p-cym ArCH(CH3)2). ESI-MS: m/z = 473.04
[M−Cl]+
.
3. Results and discussion
2.3.2. Synthesis of [Ru(η6-p-cymene)(Cl)(L2)] (2)
Yield: 84%; m.p.: 208 °C; Anal. calcd. for C20H22N3OSClRu: C,
49.12; H, 4.53; N, 8.59. Found: C, 49.09; H, 4.50; N, 8.53. FT-IR: NH,
3252 cm−1; C]N, 1600 cm−1; CeO, 1230 cm−1. UV–Vis (CHCl3, λmax
[nm] (10−3 ε [M−1 cm−1]): 371 (4456), 300 (3035), 262 (4070). 1H
NMR (300 MHz, CDCl3) (δ ppm): 11.58 (s, 1H, pyrrole NeH), 8.93 (s,
1H, HC = N), 7.90–6.28 (overlapping, 6H total, ArH), 5.58 (d, 1H, p-
cym ArH), 5.43 (d, 1H, p-cym ArH), 5.22 (d, 1H, p-cym ArH), 5.00 (d,
1H, p-cym ArH), 2.28 (sept, 1H, p-cym ArCH(CH3)2), 2.16 (s, 3H, p-cym
Ar(CH3)), 1.41 (d, 3H, p-cym ArCH(CH3)2), 1.22 (d, 3H, p-cym ArCH
(CH3)2). 13C NMR (75 MHz, CDCl3) (δ ppm): 168.7 (C]O), 141.8
(HC = N), 159.2, 148.9, 147.8, 145.7, 139.8, 128.5, 127.4, 121.2
(HC = N, ArPyrrole and ArThiophene), 101.2, 98.7 (p-cym CqAr), 92.5,
89.5, 85.6, 82.9 (p-cym CHAr), 22.8, 19.5 (p-cym ArCH(CH3)2 and Ar
The ligand precursors and the ruthenium complexes described are
presented in Schemes 2 and 3, respectively. Pyrrole-2-carboxaldehyde
hydrazones (HL1–3) were synthesized with excellent yields by a simple
and direct method that consists in the 1:1 reaction of aldehydes with 2-
carboxylic acid hydrazine derivatives. Treatment of [Ru(η6-p-cymene)
(Cl)2]2 with HLi (i = 1–3) in a 1:2 M ratio led to the formation of
complexes of general formula [Ru(η6-p-cymene)(Cl)(Li)] (1–3) in high
yields.
The IR spectral data of the ligand precursors show absorptions in the
regions 3268–3199 cm−1, 3200–3113 cm−1, 1693–1592 cm−1 and
1595–1557 cm−1 that are assigned to νpyrrole-NH, νhydrazide-N-H, νC=N and
νC=O, respectively. In the IR spectra of the complexes the bands due to
hydrazone νN-H and carbonyl νC=O groups are not present due to the
coordination of ruthenium in the imidolate enolate form. New bands
due to the coordination of azomethine nitrogen and imidolate oxygen
to the ruthenium come up at 1663–1605 cm−1 and 1240–1227 cm−1
respectively [35].
(CH3)), 11.1, 8.8 (p-cym ArCH(CH3)2). ESI-MS: m/z
= 489.02
[M−Cl]+
.
2.3.3. Synthesis of [Ru(η6-p-cymene)(Cl)(L3)] (3)
Pyrrole-2-carboxaldehyde hydrazone precursors (HL1–3
) display
Yield: 89%; m.p.: 178 °C; Anal. calcd. for C21H23N4OClRu: C, 52.12;
H, 4.79; N, 11.58. Found: C, 52.08; H, 4.76; N, 11.51. FT-IR: NH,
3239 cm−1; C]N, 1663 cm−1; CeO, 1240 cm−1. UV–Vis (CHCl3, λmax
[nm] (10−3 ε [M−1 cm−1]): 377 (2663), 279 (1831), 248 (1737). 1H
NMR (300 MHz, CDCl3) (δ ppm): 11.03 (s, 1H, pyrrole NeH), 8.78 (s,
1H, HC = N), 8.63–6.41 (overlapping, 7H total, ArH), 5.43 (d, 1H, p-
cym ArH), 5.31 (d, 1H, p-cym ArH), 5.04 (d, 1H, p-cym ArH), 4.70 (d,
1H, p-cym ArH), 2.60 (sept, 1H, p-cym ArCH(CH3)2), 2.24 (s, 3H, p-cym
Ar(CH3)), 1.19 (d, 3H, p-cym ArCH(CH3)2), 1.17 (d, 3H, p-cym ArCH
(CH3)2). 13C NMR (75 MHz, CDCl3) (δ ppm): 171.4 (C]O), 145.4
(HC = N), 151.9, 149.8, 139.5, 132.2, 125.8, 123.0, 122.4, 117.5,
111.3 (HC = N, ArPyrrole and ArPyridine), 102.6, 100.5 (p-cym CqAr),
92.6, 84.4, 81.7, 81.2 (p-cym CHAr), 22.2, 18.5 (p-cym ArCH(CH3)2 and
Ar(CH3)), 12.0, 8.6 (p-cym ArCH(CH3)2). ESI-MS: m/z = 484.06
absorption bands at 292–288 nm and 391–382 nm, assigned to the π-π*
and n-π* transitions. The latter transitions are particularly intense in
the spectra of the complexes at 262–248 nm and 300–279 nm.
Moreover, the spectra of the complexes also reveal low intense bands in
the range 377–369 nm that are assigned to Ru(dπ)-to-(Lπ*) (MLCT)
transitions [36].
The 1H NMR spectra of the ligands (HL1–3) show three singlets at δ
11.76–11.56 ppm, δ 11.61–11.19 ppm and δ 8.77–8.26 ppm that cor-
respond to hydrazide-NH, pyrrole-NH and imine HC = N protons re-
spectively. The aromatic protons appear at δ 8.30–6.12 ppm.
The solid‐state molecular structures of complexes 1–3 were de-
termined by single crystal X‐ray diffraction. Compounds 2 and 3 crys-
talize in the monoclinic P21/c space group while 1 crystalizes in the
triclinic P-1 space group. ORTEP depictions of the molecular structures
of 1–3 are displayed in Figs. 1–3, respectively, and relevant distances
and angles are shown in Table 2.
[M−Cl]+
.
2.4. General procedure for the synthesis of cyanosilylethers
All complexes display a typical three‐legged piano‐stool geometry
Catalyst 3 (0.5 mol%) was added to a mixture of aldehyde (1 mmol)
with TMSCN (1.5 mmol) and diethyl ether (3 mL). The reaction mixture
was stirred at room temperature for 6 h and the reaction was monitored
by TLC. After the completion of the reaction, the solvent was evapo-
rated under vacuum. The analysis of the products was performed by
proton NMR spectra and the isolated yield was calculated.
with distances between ruthenium and the ring centroids (Ru‐PhCT
)
ranging from 1.666(2) to 1.682(2) Å. The distances between the metal
centre and the chloride and the bidentate ligands are within the usual
ranges observed for this type of bonds [37]. In general, the structural
parameters obtained for 1–3 agree with those reported for other [Ru
(η6‐p‐cymene)(Cl)(L)] complexes [38]. Hydrogen bonds are established
between Cl(1) and the hydrogen atoms H(3 N) and H(4 N) of the pyr-
role rings in complexes 1–3 with distances between of 2.32(3) and
2.58(4) Å (see Table 3 for details) [39].
2.5. General procedure for X-ray crystallography
Crystallographic and experimental details of data collection and
crystal structure determinations for the compounds are available in
Table 1. Suitable crystals of compounds 1–3 were coated and selected in
Fomblin® oil. Data were collected using graphite monochromated Mo-
3.1. Catalytic studies for the synthesis of Cyanosilylether derivatives
The ruthenium complexes (1–3) were successfully used as catalysts
3

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
Table 1
Crystal data and structure refinement for compounds 1–3.
1
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit Cell Dimensions:
a (Å)
C
20H22ClN3O2Ru
C20H22ClN3ORuS
488.99
C21H23ClN4ORu
483.95
472.93
298(2)
0.71073
Triclinic
P-1
150(2)
150(2)
0.71073
0.71073
Monoclinic
P21/c
Monoclinic
P21/c
7.798(3)
10.8300(4)
10.9087(3)
b (Å)
10.710(4)
12.5858(5)
7.6484(2)
c (Å)
12.566(5)
15.0455(5)
23.3743(7)
α (°)
111.31(1)
90
90
β (°)
100.47(2)
99.294(2)
93.380(1)
γ (°)
92.45(2)
90
90
Volume (Å3)
Z
954.6(6)
2023.8(1)
1946.82(9)
2
4
4
Calculated density (g m−3
)
1.645
1.605
1.651
Absorption coefficient (mm−1
F (000)
)
0.982
1.025
0.963
480
992
984
Crystal size (mm)
0.30 × 0.30 × 0.10
2.056 – 26.450
−9 ≤ h ≤ 9, −13 ≤ k ≤ 13,
−15 ≤ l ≤ 15
26647/3897 [0.0605]
99.4 (θ = 25.242)
Full-matrix least squares on F2
3897/0/251
0.26 × 0.28 × 0.30
3.186 – 25.675
−13 ≤ h ≤ 13, −15 ≤ k ≤ 14,
−18 ≤ l ≤ 18
30996/3838 [0.0584]
99.8 (θ = 25.242)
Full-matrix least squares on F2
3838/12/270
0.26 × 0.28 × 0.30
3.255 – 31.611
−16 ≤ h ≤ 16, −11 ≤ k ≤ 9,
−28 ≤ l ≤ 34
22779/6518[0.0509]
99.8 (θ = 25.242)
Full-matrix least squares on F2
6518/0/260
Theta range for data collection (°)
Limiting indices
Reflections collected/unique [Rint
Completeness to θ (%)
Refinement method
]
Data/restraints/parameters
Goodness-of-fit on F2
1.211
1.042
1.071
Final R indices [I > 2σ(I)]1
R1 = 0.0309, wR2 = 0.0665
R1 = 0.0368, wR2 = 0.0685
Multi-scan
R1 = 0.0256, wR2 = 0.0631
R1 = 0.0293, wR2 = 0.0650
Multi-scan
R1 = 0.0308, wR2 = 0.0736
R1 = 0.0381, wR2 = 0.0764
Multi-scan
R indices (all data)1
Absorption correction
Largest diff. peak/hole (e Å−3
)
0.570 and −0.525
0.675 and −0.567
0.652 and −0.488
1R1 = Σ ||F0| -|Fc|| / Σ |F0| ; wR2 = {Σ[w(F20 – Fc2)2]/ Σ[w(F02)2]}1/2
Scheme 2. Pyrrole-2-carboxaldehyde hydrazone derivatives (HL1–3).
Scheme 3. Synthesis of ruthenium(II) (p-cymene) complexes (1–3).
4

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
Table 2
Hydrogen bond distances (Å) and angles (°) in compounds 1, 2 and 3.
D-H…A
d(D-H)
d(H…A)
d(D…A)
(DĤA)
1
2
3
N(3)-H(3 N)…Cl(1)
N(3)-H(3 N)…Cl(1)
N(4)-H(4 N)…Cl(1)
0.86(4)
0.94(3)
0.83(2)
2.58(4)
2.32(3)
2.47(2)
3.382(3)
3.207(2)
3.244(2)
156(3)
157(3)
155(2)
Table 3
Selected distances (Å) and angles (°) of compounds 1–3.
Ru-N
Ru-Cl
Ru-O
Ru-[C6Plane]
1
2
3
2.089(2)
2.095(2)
2.084(1)
Cl-Ru-N
85.27(7)
86.27(6)
86.05(4)
2.421(1)
2.4078(6)
2.4107(5)
N-Ru-O
2.069(2)
2.066(2)
2.069(1)
O-Ru-Cl
87.67(6)
88.50(5)
87.42(4)
1.682(2)
1.666(1)
1.6717(7)
1
2
3
76.22(9)
76.07(7)
76.14(5)
Fig. 1. ORTEP diagram of 1 with thermal ellipsoids at 30% probability level.
Hydrogen atoms are omitted for clarity.
Table 4
Screening of different solvents for the synthesis of Cyanosilylether.a
Entry
Solvent
Yieldb (%)
1
Benzene
73
58
93
69
90
97
34
86
72
48
63
2
Chloroform
Dichloromethane
Toluene
3
4
5
THF
6
Diethyl ether
DMSO
7
8
Acetone
9
Acetonitrile
DMF
10
11
Methanol
[a] Conditions: Benzaldehyde (1 mmol), TMSCN (1.5 mmol), catalyst 3 (1 mol
%) in the presence of solvent (3 mL), room temperature for 6 h. [b] Isolated
yield.
Fig. 2. ORTEP diagram of 2 with thermal ellipsoids at 40% probability level.
Selected hydrogen atoms are omitted for clarity.
We have screened the reaction by using various solvents. The polar
solvents such as DMSO, DMF, methanol, acetonitrile and acetone (en-
tries 7, 10, 11, 9 & 8 respectively) led to moderate to high conversions
in the range 34–86%. The non-polar solvents benzene and toluene
(entries 1 & 4) led to moderate conversions of 73 & 69%. But, the
borderline polar solvents with low boiling point such as THF, DCM and
diethylether (entries 5, 3 & 6 respectively) led to excellent conversions
in the range 90–97%. Hence, the best solvent to perform the cyanosi-
lylation reaction is diethylether. Further, the results are summarized in
Table 4.
The most effective catalyst was determined (See Table 5) in diethyl
ether using the experimental conditions that were used for the choice of
the solvent. The performance of the catalysts (1, 2 and 3) are in the
following order 1 < 2 < 3, (ie., 88, 93 & 97% respectively). It is clear
Table 5
Screening of catalyst on Cyanosilylation reaction.a
Entry
Catalyst
Yieldb (%)
Fig. 3. ORTEP diagram of 3 with thermal ellipsoids at 40% probability level.
Selected hydrogen atoms are omitted for clarity.
1
2
3
[Ru(p-cymene)(Cl)(L1)] (1)
[Ru(p-cymene)(Cl)(L2)] (2)
[Ru(p-cymene)(Cl)(L3)] (3)
88
93
97
for the cyanosilylation of aryl, heteroaryl and aliphatic aldehydes with
trimethylsilyl cyanide (TMSCN) at room temperature. The catalytic
reactions were optimized using benzaldehyde and TMSCN as substrates
varying the solvents with 1 mol% of Ru-catalyst 3.
[a] Conditions: Benzaldehyde (1 mmol), TMSCN (1.5 mmol), catalyst 1–3
(1 mol%) in the presence of Et2O (3 mL), room temperature for 6 h. [b]
Isolated yield.
5

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
Table 6
that the variation in the reactivity of the catalysts (1, 2 & 3) is due to the
change in their ligand moiety (furan, thiophene & pyridine respec-
tively). However, the difference in their performance is only marginal.
It reveals the week influence of the substituents on their performance.
Hence, it is hard to specify the reason for the slightly better perfor-
mance of the catalyst 3 over other two catalysts.
Effect of catalyst loading.a
Entry
Mol % of catalyst
Yieldb (%)
1[c]
2
–
–
2.5
2.0
1.5
1.0
0.5
0.3
0.1
79
88
90
94
99
73
65
3
The effect of catalyst loading was performed by varying the con-
centration of catalyst 3 from 2.5 to 0.1 mol%. For this optimization
reaction, we have followed the same reaction conditions and substrates
in diethyl ether. The results are given in the Table 6. It reveals 0.5 mol%
of the catalyst is best suited for this cyanosilylation reaction.
4
5
6
7
8
Using the optimal reaction conditions, Et2O and 0.5 mol% of cata-
lyst 3, we have carried out the synthesis of several cyanosilylethers in
good to excellent yields using a wide variety of aldehydes viz., aryl,
fused ring aryl, aryl with extended conjugated double bond, hetero-
cyclic and aliphatic aldehydes. The results are shown in Table 7 and
[a] Conditions: Benzaldehyde (1 mmol), TMSCN (1.5 mmol), catalyst
3
(2.5–0.1 mol%) in the presence of Et2O (3 mL), room temperature for 6 h. [b]
Isolated yield. [c] Absence of catalyst.
Table 7
Ruthenium catalysed Cyanosilylether synthesis: Scope of aldehyde substratesa.
[a] Conditions: Aldehydes (1 mmol), TMSCN (1.5 mmol), catalyst 3 (0.5 mol%) in the presence of Et2O (3 mL), room temperature for 6 h. [b] Isolated yield.
6

G. Vinoth, et al.
InorganicaChimicaActa514(2021)120006
editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
The authors are grateful for the financial support from the
University Grants Commission, (UGC-BSR, NO: F. 30-319/2016)
Government of India, New Delhi, India. The first author acknowledges
Periyar University, Salem, Tamil Nadu for providing University
Research Fellowship (URF). A. M. Martins and L. G. Alves thank
Fundação para a Ciência e a Tecnologia for funding (UID/QUI/00100/
2019).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2020.120006.
Scheme 4. Plausible mechanism for silylcyanation of aldehydes.
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