Syntheses and molecular structures of novel Ru(II) complexes with bidentate benzimidazole based ligands and their catalytic efficiency for oxidation of benzyl alcohol

Article abstract of DOI:10.1016/j.molstruc.2016.06.017

Five bidentate ligands derived from quinoline-2-carboxylic acid, i.e. 2-(1H-benzimidazol-2-yl)quinoline (L1), 2-(1-benzyl-1H-benzimidazol-2-yl)quinoline (L2), 2-[1-(2,3,5,6-tetramethylbenzyl)-1H-benzimidazol-2-yl]quinoline (L3), 2-[1-(4-chlorobenzyl)-1H-benzimidazol-2-yl]quinoline (L4), and 2-[1-(4-methylbenzyl)-1H-benzimidazol-2-yl]quinoline (L5) were synthesized. Treatment of L1-5 with [RuCl₂(p-cymene)]₂ and KPF₆ afforded six-coordinate piano-stool Ru(II) complexes, namely, [RuCl(L1)(p-cymene)]PF₆ (C1), [RuCl(L2)(p-cymene)]PF₆ (C2), [RuCl(L3)(p-cymene)]PF₆ (C3), [RuCl(L4)(p-cymene)]PF₆ (C4), and [RuCl(L5)(p-cymene)]PF₆ (C5). Synthesized compounds were characterized with different techniques such as ¹H and ¹³C NMR, FT-IR, and UV-vis spectroscopy. The solid state structure of L1 and C3 was confirmed by single-crystal X-ray diffraction analysis. The single crystal structure of C3 verified coordination of L3 to the Ru(II) center. The Ru(II) center has a pseudo-octahedral three legged piano stool geometry. The complexes C1-5 were tested as catalysts for the catalytic oxidation of benzyl alcohol to benzaldehyde in the presence of periodic acid (H₅IO₆) (Substrate/Catalyst/Oxidant = 1/0.01/0.5). The best result was obtained with C2 (3 h→90%).

Full text of DOI:10.1016/j.molstruc.2016.06.017

Journal of Molecular Structure 1123 (2016) 35e43
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Syntheses and molecular structures of novel Ru(II) complexes with
bidentate benzimidazole based ligands and their catalytic efficiency
for oxidation of benzyl alcohol
,
*
a
b
Osman Dayan a , Melek Tercan , Namık Ozdemir
€
a Department of Chemistry, Faculty of Arts and Sciences, Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey
b Department of Secondary School Science and Mathematics Education, Faculty of Education, Ondokuz Mayıs University, 55139, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Five bidentate ligands derived from quinoline-2-carboxylic acid, i.e. 2-(1H-benzimidazol-2-yl)quinoline
(L1), 2-(1-benzyl-1H-benzimidazol-2-yl)quinoline (L2), 2-[1-(2,3,5,6-tetramethylbenzyl)-1H-benzimi-
dazol-2-yl]quinoline (L3), 2-[1-(4-chlorobenzyl)-1H-benzimidazol-2-yl]quinoline (L4), and 2-[1-(4-
methylbenzyl)-1H-benzimidazol-2-yl]quinoline (L5) were synthesized. Treatment of L1-5 with
[RuCl2(p-cymene)]2 and KPF6 afforded six-coordinate piano-stool Ru(II) complexes, namely, [RuCl(L1)(p-
cymene)]PF6 (C1), [RuCl(L2)(p-cymene)]PF6 (C2), [RuCl(L3)(p-cymene)]PF6 (C3), [RuCl(L4)(p-cymene)]
PF6 (C4), and [RuCl(L5)(p-cymene)]PF6 (C5). Synthesized compounds were characterized with different
techniques such as 1H and 13C NMR, FT-IR, and UVevis spectroscopy. The solid state structure of L1 and
C3 was confirmed by single-crystal X-ray diffraction analysis. The single crystal structure of C3 verified
coordination of L3 to the Ru(II) center. The Ru(II) center has a pseudo-octahedral three legged piano stool
geometry. The complexes C1-5 were tested as catalysts for the catalytic oxidation of benzyl alcohol to
benzaldehyde in the presence of periodic acid (H5IO6) (Substrate/Catalyst/Oxidant ¼ 1/0.01/0.5). The best
result was obtained with C2 (3 h/90%).
Received 21 December 2015
Received in revised form
2 May 2016
Accepted 4 June 2016
Available online 7 June 2016
Keywords:
Ru (II) complexes
Piano-stool complexes
Oxidation of benzyl alcohol
Bidentate chelates
2-(2-quinolinyl)-1H-benzimidazole
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
benzimidazole ligands have been reported as catalysts
[17,18,21e23]. Related transition metal complexes containing 2-(2’-
It is known that ruthenium (II) complexes are the most useful
catalysts for many reactions [1e5]. Complexes of Ru containing
acceptor nitrogen-bearing ligands, especially N-heteroaromatic
systems like pyridyl-based benzimidazolyl ligands have been
quinolyl)benzimidazoles are very rare. However, some researchers
show that their related Ni, Cu, Ir, Re, Pd, Ti, Zn and Ru complexes
have good optoelectronic and catalytic properties [24e33]. To our
best knowledge, there is only one ruthenium complex with a
similar ligand [30].
p-
widely studied. The pyridine ring as a good
stabilize the Ru(II) acceptor center and the imidazole and its de-
rivatives exhibit moderate -donor properties [6]. Thus the steric
p-acceptor tends to
Because of restricted raw material supplies, developments of
new catalysts for the selective oxidation of benzyl alcohol to
benzaldehyde are important from the environmental perspective
[34]. Traditional methods usually need stoichiometric amounts of
oxidants such as manganese and chromium oxides which are
hazardous [5]. Many materials were synthesized and tested for
oxidation of benzyl alcohol to benzaldehyde as homogeneous or
heterogeneous catalysts to date [35e39]. But, ruthenium-based
homogenous catalysts are relatively rare in this field [40]. The
oxido-ruthenium species, which are formed from ruthenium (II/III)
complexes by using various oxidants, make the oxygen-transfer
reactions possible. Many mono- and dinuclear- Ru complexes of
tpa-based ligands have attracted interest for catalytic oxidation
reactions and have shown high catalytic efficiency towards alkene
p
and electronic properties around the metal centre can be changed
with benzimidazole type ligands.
Benzimidazoles have attracted much attention due to their us-
age in many applications in coordination-, medicinal- and
supramolecular-chemistry [7e12]. Because of having high thermal
stability, good catalytic performance and superior optical proper-
ties, metal complexes with benzimidazole ligands are important
[13e20]. Recently, many efficient Ru(II) complexes of
* Corresponding author.
E-mail address: osmandayan@comu.edu.tr (O. Dayan).
http://dx.doi.org/10.1016/j.molstruc.2016.06.017
0022-2860/© 2016 Elsevier B.V. All rights reserved.

36
O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
oxygenation of unsaturated hydrocarbons [41].
-H5); 7.15e7.19 (1 H, m, -H13); 7.59e7.77 (2 H, m, -H3,6); 7.81e7.84
(1 H, m, -H14); 8.00e8.23 (2 H, m, -H9,10); 8.42 (1 H, m, -H12);
In this work, we synthesized 2-(20-quinolyl)benzimidazole type
ligands and the Ru complexes of these ligands. All of the synthe-
sized compounds were characterized by 1H and 13C NMR, IR and
UVevisible spectroscopic techniques. Then their catalytic activities
in the selective oxidation of benzyl alcohol to benzaldehyde were
investigated.
8.53e8.57 (1 H, m, -H15). 13C NMR (150.92 MHz, DMSO-d6,
d ppm):
15.98 (-CH3); 20.61(-CH3); 46.61 (-Ca); 112.22; 120.33; 122.49;
122.64; 123.87; 127.77; 128.12; 128.48; 129.62; 130.77; 131.78;
133.07; 133.78; 133.99; 136.95; 137.57; 142.82; 146.76; 150.30
(-C8); 151.27 (-C1). FTIR (
2923, 2866, 1614, 1595, 1560, 1496, 1439, 1328, 1166, 846, 739.
UVeVis (nm): 204, 244, 285, 349 ( * and n/ *).
y
/cmꢁ1): 3480, 3052, 3007, 2973, 2949,
2. Experimental
p
/p
p
Chemicals were obtained from commercial suppliers and used
as purchased. L1 [42] was synthesized using the method in the
published procedure. Information about techniques and devices
used are given in supporting information.
2.1.2.3. Data for 2-[1-(4-chlorobenzyl)-1H-benzimidazol-2-yl]quino-
line (L4). White solid, 78% yield, m.p.: 188 ꢀC. 1H NMR (600 MHz,
DMSO-d6,
d ppm): 6.40 (2 H, s, -Ha); 7.26e7.29 (2 H, m, -Hc);
7.31e7.39 (4 H, m, -H3,4,d); 7.68 (1 H, ddd, J ¼ 8.07, 6.97 and 1.10 Hz,
-H5); 7.70e7.75 (1 H, m, -H13); 7.82 (1 H, ddd, J ¼ 8.34, 6.69 and
1.47 Hz, -H14); 7.85 (1 H, dd, J ¼ 6.97 and 1.10 Hz, -H6); 8.02 (1 H, d,
J ¼ 7.70 Hz, -H9); 8.05 (1 H, dd, J ¼ 8.25 and 0.92 Hz, -H10);
8.52e8.57 (2 H, m, -H12,15). 13C NMR (150.92 MHz, DMSO-d6,
2.1. Synthesis of ligands
2.1.1. Synthesis of 2-(1H-benzimidazol-2-yl)quinoline (L1)
Quinaldic acid (10 mmol, 1.731 g) and o-phenylenediamine
(10 mmol, 1.081 g) were stirred in polyphosphoric acid (20 mL) for
4 h at 200 ꢀC under argon. At the end this time, the green-colored
molten fluid was poured into iced water. Then the solution was
neutralized with ammonium hydroxide and the obtaining solid was
filtered off. Finally, the product was recrystallized by EtOH.
Beige solid, 84% yield, m. p.: 238 ꢀC. 1H NMR (600 MHz, DMSO-
d
ppm): 47.86 (-Ca); 111.21; 119.94; 121.28; 122.85; 123.99; 127.37;
127.63; 127.97; 128.46; 128.54; 128.98; 130.34; 131.68; 136.89;
137.22; 142.15; 146.43; 148.69 (-C8); 149.76 (-C1). FTIR (
/cmꢁ1):
y
3052, 2998, 2947, 1951, 1922, 1895, 1615, 1600, 1564, 1510, 1490,
1459, 1442, 1328, 1078, 833, 738. UVeVis (nm): 206, 244, 285, 334,
349 (p/p* and n/p*).
d6,
d
ppm): 7.25 (1 H, t, J ¼ 7.52 Hz, -H4); 7.30 (1 H, t, J ¼ 7.70 Hz,
2.1.2.4. Data for 2-[1-(4-methylbenzyl)-1H-benzimidazol-2-yl]quin-
-H5); 7.63 (1 H, d, J ¼ 7.70 Hz, -H3); 7.67 (1 H, ddd, J ¼ 8.07, 6.79 and
1.28 Hz, -H13); 7.77 (1 H, d, J ¼ 8.07 Hz, -H6); 7.86 (1 H, ddd, J ¼ 8.44,
6.97 and 1.47 Hz, -H14); 8.06 (1 H, dd, J ¼ 8.07 and 1.47 Hz, -H10);
8.17 (1 H, dd, J ¼ 8.25 and 0.92 Hz, -H9); 8.49 (1 H, d, J ¼ 8.4 Hz,
-H12); 8.54 (1 H, d, J ¼ 8.4 Hz, -H15); 13.22 (1H, s, -NH). 13C NMR
oline (L5). White solid, 82% yield, m.p.: 157 ꢀC. 1H NMR (400 MHz,
CDCl3, d ppm): 2.31 (3 H, s, -CH3); 6.28e6.42 (2 H, m, -Ha); 7.12 (2 H,
d, J ¼ 6.87 Hz, -Hc); 7.23e7.40 (4 H, m, -H3,4,d); 7.74 (1 H, dd, J ¼ 9.39
and 2.52 Hz, -H6); 7.96 (1 H, t, J ¼ 7.56 Hz, -H5); 8.14e8.21 (2 H, m,
-H10,13); 8.22e8.28 (1 H, m, -H14); 8.39 (1 H, d, J ¼ 8.70 Hz, -H9);
8.83e8.88 (1 H, m, -H12); 8.93 (1 H, d, J ¼ 9.16 Hz, -H15). 13C NMR
(150.92 MHz, DMSO-d6,
d ppm): 112.27; 119.20; 119.55; 122.05;
123.58; 127.28; 128.06; 128.22; 128.73; 130.44; 135.18; 137.39;
143.92; 147.18; 148.71 (-C8); 150.70 (-C1). FTIR (
3056, 1948, 1930, 1890, 1852, 1810, 1655, 1597, 1564, 1537, 1497,
1444, 1414, 1318, 1105, 830, 741. UVeVis (nm): 242, 287, 323, 345
(100.53 MHz, CDCl3, d ppm): 20.98 (eCH3); 48.94 (eCa); 110.75;
y
/cmꢁ1): 3482,
120.24; 121.74; 122.82; 123.84; 126.81; 127.21; 127.59; 127.69;
129.18; 129.58; 129.68; 134.59; 136.53; 136.88; 137.11; 142.12;
149.61 (eC8); 150.24 (eC1). FTIR (
1599, 1563, 1509, 1497, 1459, 1445, 1329, 1076, 742, 736. UVeVis
(nm): 218, 243, 285, 334, 349 ( * and n/ *).
y
/cmꢁ1): 3053, 2963, 2925, 1612,
(p/p* and n/p*).
p/p
p
2.1.2. General procedure for the synthesis of L2-5
L1 (2.04 mmol, 0.500 g) and KOH (2.04 mmol, 0.114 g) were
stirred at 150 ꢀC in DMF for 4 h. Then, appropriate substituted-
benzyl halides (2.04 mmol) were added to the reaction mixture
and further stirred at 150 ꢀC for 24 h. Volatiles were distilled under
vacuum and the remaining solid was washed with water and
recrystallized with MeOH.
2.2. General procedure for the synthesis of [RuCl(L1-5)(pesimen)]
PF6
The appropriate ligand (L1-5) (0.320 mmol) and [RuCl2(p-
cymene)]2 (0.160 mmol, 0.100 g) were refluxed in ethanol for 8 h. At
the end of this time, the mixture was cooled at room temperature
and precipitated by addition of diethyl ether. The soluble part of this
precipitate in water was treated with saturated KPF6 solution. The
precipitate was filtered off, washed and dried.
2.1.2.1. Data for 2-(1-benzyl-1H-benzimidazol-2-yl)quinoline (L2).
Yellowish brown solid, 82% yield, m.p.: 145 ꢀC. 1H NMR (600 MHz,
DMSO-d6,
d
ppm): 6.41 (2 H, s, -Ha); 7.15 (1 H, dq, J ¼ 8.62 and
4.34 Hz, -He); 7.21e7.23 (4 H, m, -H3,4,5,6); 7.32 (2 H; dddd, J ¼ 15.96,
7.24, 7.06 and 1.28 Hz, -Hd); 7.65 (1 H, ddd, J ¼ 8.07, 6.97 and 1.10 Hz,
-H13); 7.69 (1 H, dd, J ¼ 6.79 and 1.28 Hz, -H10); 7.79 (1 H, ddd,
J ¼ 8.44, 6.97 and 1.47 Hz, -H14); 7.83 (1 H, dd, J ¼ 8.07 and 1.10 Hz,
-H9); 8.02 (2 H, dt, J ¼ 8.16 and 1.79 Hz, -Hc); 8.50e8.55 (2 H, m,
2.2.1. Data for [RuCl(L1)(p-cymene)]PF6 (C1)
Reddish brown, 95% yield, m.p.> 280 ꢀC. 1H NMR (400 MHz,
DMSO-d6,
d
ppm): 0.72 (6 H, dd, J ¼ 17.63 and 7.10 Hz, -Ho);
2.18e2.22 (1 H; m, -Hn); 2.29 (3 H, s, -Hk); 6.12 (1 H, d, J ¼ 5.95 Hz,
-Hl); 6.26 (1 H, d, J ¼ 5.95 Hz, -Hl); 6.33 (2 H, dd, J ¼ 11.91 and
6.41 Hz, -Hm); 7.61e7.70 (2 H, m, -H3,4); 7.90e7.95 (1 H, m, -H6); 7.98
(1 H, t, J ¼ 7.33 Hz, -H5); 8.17e8.21 (2 H, m, -H10, 13); 8.30 (1 H, m,
-H14); 8.53 (1 H, d, J ¼ 8.24 Hz, -H9); 8.83 (1 H, d, J ¼ 9.16 Hz, -H12);
8.99 (1 H, d, J ¼ 8.24 Hz, -H15). 13C NMR (100.53 MHz, DMSO-d6,
-H12,15). 13C NMR (150.92 MHz, DMSO-d6,
d ppm): 48.37 (-Ca);
111.32; 119.88; 121.33; 122.74; 123.87; 126.66; 127.09; 127.34;
127.57; 127.95; 128.44; 128.97; 130.29; 136.99; 137.09; 138.11;
142.17; 146.44; 148.78 (-C8); 149.91 (-C1). FTIR (
3024, 2987, 1613, 1596, 1562, 1493, 1453, 1433, 1401, 1356, 1327,
1164, 842, 717. UVeVis (nm): 218, 243, 285, 333 ( * and n/ *).
y
/cmꢁ1): 3050,
d
ppm): 18.49 (-Ck); 21.16 (-Co); 21.69 (-Co); 30.32 (-Cn); 78.73;
p
/p
p
83.70; 84.20; 85.20; 102.75; 104.71; 114.34; 118.13; 118.63; 125.42;
126.60; 128.88; 129.31; 129.37; 129.55; 133.30; 134.33; 141.53;
2.1.2.2. Data for 2-[1-(2,3,5,6-tetramethylbenzyl)-1H-benzimidazol-
141.72; 147.57; 148.58; 149.98. FTIR (
2940, 2883, 1620, 1593, 1547, 1509, 1474, 1450, 1431, 1395, 1380,
1326, 1029, 828, 748, 556, 520. UV-GB (nm): 216, 249, 305 (
and n/ *), 382 [Ru(d )/ * (MLCT)].
y
/cmꢁ1): 3186, 3081, 2973,
2-yl]quinoline (L3). White solid, 72% yield, m.p: 166 ꢀC. 1H NMR
(600 MHz, DMSO-d6,
d
ppm): 1.78e2.26 (12 H, m, -CH3); 6.49 (2 H,
p/p*
s, -Ha); 6.67e6.84 (1 H, m, -H4); 6.92 (1 H, s, -He); 6.99e7.11 (1 H, m,
p
p
p

O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
37
2.2.2. Data for [RuCl(L2)(p-cymene)]PF6 (C2)
129.69; 129.75; 129.92; 132.37; 133.25; 136.49; 137.51; 140.46;
141.11; 146.99; 148.21; 149.42. FTIR (
/cmꢁ1): 3660, 3070, 2969,
2928, 2878, 1616, 1594, 1527, 1499, 1478, 1454, 1428, 1378, 1101, 831,
761. UVeVis (nm): 213, 252, 305 and n/ *), 372
[Ru(d )/ * (MLCT)].
Brown, 89% yield, m.p.> 280 ꢀC. 1H NMR (400 MHz, DMSO-d6,
y
d
ppm): 0.62 (3 H, d, J ¼ 6.87 Hz, -Ho); 0.74 (3 H, d, J ¼ 6.87 Hz, -Ho);
2.08e2.19 (1 H, m, -Hn); 2.31 (3 H, s, -Hk); 6.21e6.46 (6 H, m, -Hl,m,a);
7.12 (2 H, d, J ¼ 7.33 Hz, -Hc); 7.27e7.37 (3 H, m, -H3,4,5); 7.71e7.77
(2 H, m, -Hd); 7.96 (1 H, t, J ¼ 7.56 Hz, -He); 8.12e8.31 (4 H, m,
-H6,10,13,14); 8.39 (1 H, d, J ¼ 8.70 Hz, -H12); 8.85 (1 H, d, J ¼ 8.70 Hz,
-H9); 8.93 (1 H, d, J ¼ 9.16 Hz, -H15). 13C NMR (100.53 MHz, DMSO-
(
p/p*
p
p
p
2.3. Oxidation of benzyl alcohol
d6,
d
ppm): 18.42 (-Ck); 20.97 (-Co); 21.92 (-Co); 30.22 (-Cn); 48.31
In a typical reaction, a test tube was filled with benzyl alcohol
(1 mmol), periodic acid (0.5 mmol), C1-5 (0.01 mmol) and CH3CN
(5 ml). This tube was refluxed for the appropriate time. The re-
actions were monitored by gas chromatography.
(-Ca); 84.82; 85.00; 85.22; 85.57; 112.98; 118.84; 119.82; 125.77;
125.80; 126.22; 127.21; 128.46; 128.93; 129.18; 129.76; 129.94;
133.27; 135.42; 136.50; 140.47; 141.12; 146.98; 148.23; 149.42. FTIR
(y
/cmꢁ1): 3073, 2969, 2922, 2879, 1616, 1594, 1527, 1499, 1476,
1442, 1428, 1379, 1331, 1150, 1030, 830, 739, 696, 555. UV-GB (nm):
214, 251, 305 ( * and n/ *), 373 [Ru(d )/ * (MLCT)].
2.4. X-ray analysis
p/p
p
p
p
Intensity data of the compounds were collected on a STOE IPDS
II diffractometer at room temperature using graphite-
monochromated Mo Ka radiation by applying the u-scan method.
2.2.3. Data for [RuCl(L3)(p-cymene)]PF6 (C3)
Reddish brown, 92% yield, m.p.> 280 ꢀC. 1H NMR (600 MHz,
DMSO-d6,
ppm): 0.68 (3 H, d, J ¼ 6.97 Hz, -Ho); 0.82 (3 H, d,
d
The structures were solved by direct methods using SHELXS-2013
[43] and refined with full-matrix least-squares calculations on F2
using SHELXL-2014 [43] implemented in WinGX [44] program
suite. All carbon bound H atoms were placed geometrically and
treated using a riding model, fixing the bond lengths at 0.93, 0.98,
0.97 and 0.96 Å for aromatic CH, methine CH, CH2 and CH3 atoms,
respectively. In L1, the hydrogen atoms of NH and OH2 groups were
located on a difference Fourier map and refined isotropically sub-
ject to DFIX restraints of NeH ¼ 0.86 Å and OeH ¼ 0.82 Å. The
J ¼ 6.97 Hz, -Ho); 1.98 (6 H, s, -CH3. benzyl); 2.19 (7 H, br. s., -CH3.
benzyl and -Hn); 2.29 (3 H, s, -Hk); 5.67e6.34 (6 H, m, Hl,m,a); 6.43
(1 H, m, -H3); 6.72 (1 H, d, J ¼ 8.44 Hz, -H6); 7.10 (1 H, s, -He); 7.36
(1 H, t, J ¼ 8.07 Hz, -H14); 7.55 (1 H, t, J ¼ 7.70 Hz, -H4); 8.00 (1 H, t,
J ¼ 7.52 Hz, -H5); 8.13 (1 H; d, J ¼ 8.07 Hz, -H12); 8.20 (1 H, t,
J ¼ 7.89 Hz, -H13); 8.34 (1 H, d, J ¼ 8.07 Hz, -H9); 8.86 (1 H, d,
J ¼ 8.80 Hz, -H10); 8.98 (1 H, m, -H15). 13C NMR (150.92 MHz, DMSO-
d6, d ppm): 15.38 (eCH3. benzyl); 18.39 (-Ck); 20.09 (eCH3. benzyl);
20.87 (-Co); 22.09 (-Co); 30.32 (-Cn); 48.43 (-Ca); 84.86; 85.11;
85.48; 86.34; 113.45; 118.91; 119.19; 119.84; 121.28; 125.37; 126.32;
128.46; 128.90; 129.83; 130.30; 132.42; 133.08; 133.28; 133.80;
displacement parameters of the H atoms were fixed at
Uiso(H) ¼ 1.2Ueq (1.5Ueq for methyl and water) of their parent atoms.
The crystal of L1 was twinned and the final structure was refined as
a 2-component twin with a refined value for the minor twin frac-
tion of 0.469(4)%. The twinning matrix corresponds to (0, ꢁ1, 0; ꢁ1,
0, 0; 0, 0, ꢁ1). In C3, one of the hexafluorophosphate anions in the
asymmetric unit is disordered about an inversion center and
refined with occupancy of all atoms fixed at 0.5. The poor quality of
the crystals and the additional presence of twinning in L1 led to
relatively high R-values. In the final difference Fourier map of the
compounds, the highest residual electron density located 0.99 Å
from atom H9A in L1 and 1.15 Å from atom F8 in C3 was essentially
meaningless. Data collection: X-AREA [45], cell refinement: X-
AREA, data reduction: X-RED32 [45]. Crystal data, data collection
and structure refinement details are summarized in Table 1. PLA-
TON [46] was used for the structural analysis and presentation of
the results.
134.04; 135.48; 140,68; 147.74; 149.30; 149.59. FTIR (y
/cmꢁ1):
3079, 2963, 2939, 2882, 1619, 1594, 1572, 1529, 1509, 1474, 1430,
1414, 1380, 1062, 1029, 828, 748, 660. UVeVis (nm): 216, 245, 306,
351 (p/p* and n/p*), 382 [Ru(dp)/p* (MLCT)].
2.2.4. Data for [RuCl(L4)(p-cymene)]PF6 (C4)
Brown, 83% yield, m.p.> 280 ꢀC. 1H NMR (600 MHz, DMSO-d6,
d
ppm): 0.63 (3 H, d, J ¼ 6.97 Hz, -Ho); 0.75 (3 H, d, J ¼ 6.97 Hz, -Ho);
2.12e2.16 (1 H, m, -Hn); 2.30 (3 H, s, -Hk); 5.99 (1 H, d, J ¼ 5.87 Hz,
-Hl); 6.26 (1 H, d, J ¼ 6.24 Hz, -Hm); 6.29 (1 H, d, J ¼ 6.24 Hz, -Hm);
6.31e6.35 (2 H, m, -Ha); 6.39 (1 H, d, J ¼ 5.87 Hz, -Hl); 7.16 (2 H, d,
J ¼ 8.80 Hz, -Hc); 7.42 (2 H, d, J ¼ 8.80 Hz, -Hd); 7.72e7.78 (2 H, m,
-H3,4); 7.97 (1 H, t, J ¼ 7.70 Hz, -H13); 8.15e8.20 (2 H, m, -H5,6);
8.23e8.28 (2 H, m, -H12,14); 8.40 (1 H, d, J ¼ 8.80 Hz, -H10); 8.87 (1 H,
d, J ¼ 8.44 Hz, -H9); 8.93 (1 H, d, J ¼ 8.80 Hz, -H15). 13C NMR
(150.92 MHz, DMSO-d6,
d
ppm): 18.88 (-Ck); 21.41(-Co); 22.44 (-Co);
3. Results and discussion
30.70 (-Cn); 48.24 (-Ca); 80.42; 85.36; 86.00; 86.87; 113.44; 119.37;
120.31; 126.76; 127.75; 128.31; 129.01; 129.61; 130.27; 130.43;
133.25; 133.78; 135.00; 136.91; 137.75; 140.98; 141.72; 147.36;
3.1. Synthesis and characterization of compounds
148.68; 149.95. FTIR (
1641, 1591, 1551, 1545, 1435, 1312, 1055, 821, 747, 692. UVeVis (nm):
253, 305 ( * and n/ *), 373 [Ru(d )/ * (MLCT)].
y
/cmꢁ1): 3076, 2954, 2917, 2891, 2842, 1659,
In this work, 2-(2-Quinolinyl)-1H-benzimidazole (L1) was syn-
thesized by the reaction of quinaldic acid and o-phenylenediamine
in polyphosphoric acid at 200 ꢀC with high yields. N-substitution
products (L2-5) of L1 were achieved in the presence of KOH with
different benzylhalides. The Ru(II) complexes of L1-5 were pre-
pared from the reaction of [Ru(p-cymene)Cl2]2, L1-5 and KPF6
(Scheme 1). All compounds (L1-5 and C1-5) were soluble in many
solvents such as EtOH, MeOH, DMF, DMSO and CH2Cl2. Synthesized
compounds were characterized by 1H and 13C NMR, FT-IR and
UVevis. All spectra of compounds are given in supporting
information. Furthermore, solid state structure of L1 and C3 was
determined by single crystal-X-ray diffraction.
p
/p
p
p
p
2.2.5. Data for [RuCl(L5)(p-cymene)]PF6 (C5)
Brown, 78% yield, m.p.> 280 ꢀC. 1H NMR (400 MHz, DMSO-d6,
ppm): 0.63 (3 H, d, J ¼ 6.87 Hz, -Ho); 0.74 (3 H, d, J ¼ 6.87 Hz,-Ho);
d
2.10e2.17 (1 H, m, -Hn); 2.22 (3 H, s, -Hk); 2.31 (3 H, s, -CH3. benzyl);
5.98 (1 H, d, J ¼ 5.95 Hz, -Hl); 6.17e6.41 (5 H, m, -Hl,m,a); 7.01 (2 H, d,
J ¼ 8.24 Hz, -Hc); 7.14 (2 H, d, J ¼ 7.79 Hz, -Hd); 7.71e7.77 (2 H, m,
-H3,4); 7.96 (1 H, t, J ¼ 7.56 Hz, -H13); 8.13e8.19 (2 H, m, -H12,14);
8.23e8.28 (2 H, m, -H5,6); 8.39 (1 H, d, J ¼ 8.70 Hz, -H10); 8.85 (1 H,
d, J ¼ 8.70 Hz, -H9); 8.93 (1 H, d, J ¼ 8.70 Hz, -H15). 13C NMR
In 1H NMR spectra of L1, aromatic protons were seen at various
peaks around 7.25e8.54 ppm. eH4 and eH5 protons on benzimi-
dazol fragment of L1 observed as triplet at 7.25 and 7.30 ppm,
respectively. The other two protons from the benzimidazole
(100.53 MHz, DMSO-d6,
d ppm): 18.42 (-Ck); 20.57 (eCH3. benzyl);
21.89 (-Co); 30.71(-Cn); 48.14 (-Ca); 80.24; 80.29; 85.35; 86.07;
112.97; 118.82; 119.87; 125.75; 126.19; 127.17; 128.46; 128.93;

38
O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
Table 1
Crystal data and structure refinement parameters for L1 and C3.
Parameter
L1
C3
CCDC depository
Color/shape
1036751
Colorless/prism
1036752
Orange/prism
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C16H11N3$H2O
[RuCl(C10H14)(C27H25N3)]þ$PF6ꢁ
263.29
296
0.71073 Mo K
Triclinic
Pꢁ1 (No. 2)
807.20
296
0.71073 Mo K
Triclinic
Pꢁ1 (No. 2)
a
a
Unit cell parameters
a, b, c (Å)
7.5935(5), 7.6012(5), 25.1873(17)
88.643(5), 88.691(5), 63.247(5)
1297.70(16)
4
1.348
9.6358(4), 9.8169(4), 20.2513(8)
75.804(3), 81.358(3), 83.621(3)
1830.54(13)
2
1.464
a
,
b
,
g
(ꢀ)
Volume (Å3)
Z
Dcalc (g/cm3)
m
(mmꢁ1
)
0.087
0.606
Absorption correction
Tmin, Tmax
F000
Integration
0.9788, 0.9952
552
Integration
0.8041, 0.9611
824
Crystal size (mm3)
Diffractometer/measurement method
Index ranges
0.54 ꢂ 0.48 ꢂ 0.15
0.45 ꢂ 0.22 ꢂ 0.07
STOE IPDS II/
u
scan
STOE IPDS II/u scan
ꢁ9 ꢃ h ꢃ 9, ꢁ9 ꢃ k ꢃ 9, ꢁ32 ꢃ l ꢃ 32
ꢁ12 ꢃ h ꢃ 12, ꢁ12 ꢃ k ꢃ 12, ꢁ26 ꢃ l ꢃ 26
q
range for data collection (ꢀ)
1.618 ꢃ
q
ꢃ 27.166
2.092 ꢃ
q
ꢃ 27.566
Reflections collected
Independent/observed reflections
Rint
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
17073
26026
5731/2785
0.086
8420/5195
0.1022
Full-matrix least-squares on F2
5731/8/380
Full-matrix least-squares on F2
8420/52/481
1.063
1.017
Final R indices [I > 2
s
(I)]
R1 ¼ 0.1291, wR2 ¼ 0.2797
R1 ¼ 0.1775, wR2 ¼ 0.3063
1.195, ꢁ0.295
R1 ¼ 0.0822, wR2 ¼ 0.2173
R1 ¼ 0.1236, wR2 ¼ 0.2438
1.680, ꢁ0.801
R indices (all data)
Drmax,
Drmin (e/Å3)
d
c
O
e
N
R
1. KOH
2. Benzylhalides
b
10
12
15
OH
11
a
13
14
9
8
PPA
H
N
+
N
3
2
16
1
N
NH2
NH2
N
4
N
N
7
5
6
L1
L2-5
+
R
1. [Ru(p-cymene)Cl2]2
L2
-H
2. KPF6
2,3,5,6-(Me)4
4-Cl
4-Me
L3
L4
L5
l
m
k
o
n
-
Ru+ Cl
PF6
N
L1-5
N
C1-5
Scheme 1. Synthesis of compounds and numbering scheme for the NMR.
fragment of L1 (eH3 and eH6) appeared as doublets at 7.63 and
7.77 ppm, respectively. The protons belonging quinoline moiety of
L1 appeared as doublet of doublet of doublets at 7.67 ppm for eH13
and at 7.86 ppm for eH14, as doublet of doublets at 8.06 ppm for
eH10 and at 8.17 ppm for eH9; as doublet at 8.49 ppm for eH12 and
at 8.54 ppm for eH15. eNH proton of L1 was observed at 13.22 ppm
as a broad singlet. The main difference in 1H NMR spectra of L2-5
from L1 are loss of peak for eNH proton and occurrence of new
peaks belonging benzylic protons. eHa protons were monitored as
singlet at 6.41 ppm for L2, at 6.49 ppm for L3, at 6.40 ppm for L4

O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
39
and as multiplet between 6.28 and 6.42 ppm for L5. Other aromatic
protons belonging benzylic group appeared around 6.28e8.88 ppm
in L2-5.
The main difference in 1H NMR spectra of C1 compared to L1 is
the formation of new peaks belonging p-cymene groups. The pro-
tons belonging to p-cymene groups of C1 appeared as doublet of
doublets at 0.72 ppm for eHo, as multiplet between 2.18 and
2.22 ppm for eHn, as singlet at 2.29 ppm for eHk, as doublet at
6.12 ppm for eHl, as doublet at 6.26 ppm for eHl’ and as doublet of
doublets at 6.33 ppm for eHm. Unusual peaks of eHo,l,m may be
related with the symmetry of complexes. This phenomenon was
supported by the 13C NMR spectra of C1. There are six-singlet
belonging to eCo,l,m in 13C NMR spectra of C1. After the complex-
ation, the protons belonging to quinoline and benzimidazol frag-
ments of L1 were generally shifted downfield. Surprisingly, there is
no observed NeH proton in 1H NMR spectra of C1. On the other
hand, the measurement of ionic conductivity of C1 shows that this
compound has ionic nature. Due to the excess of the aromatic
protons, the 1H NMR spectra of C2-5 were quite complicated.
However, similar trends appeared in 1H and 13C NMR spectra of C2-
5. The detailed assignment is given in the experimental section for
all compounds.
In the FT-IR spectra of L1, NeH and eC]Ne stretching vibra-
tions were observed at 3482 and 1619 cmꢁ1, respectively. The basic
difference of L2-5 from L1 is loss of NeH stretch band and occur-
rence of aliphatic CeH stretching peaks belonging to benzylic
group between 2973 and 2883 cmꢁ1. C]Ne stretching vibrations
of L2-5 were observed at 1613, 1614, 1615, and 1612 cmꢁ1, respec-
tively. After complexation, new vibrations belonging to cymene
group were observed and eC]N- stretching vibrations slightly
shifted (1620 cmꢁ1 for C1, 1616 cmꢁ1 for C2, 1619 cmꢁ1 for C3,
1641 cmꢁ1 for C4, 1616 cmꢁ1 for C5.). Additionally, there is a broad
band in the region between 3300 and 3100 cmꢁ1 belonging to
hydrated molecules on the FT-IR spectra of C1-5. Synthesized
complexes have partially hygroscopic nature in solid-state.
In UV-VIS spectra of the ligands (L1-5), the peaks belonging to
p/p* and n/p* transitions were appeared around 204e349 nm.
A new charge transfer band occurred around 372e383 nm after
complexation.
Fig. 1. (a) A view of L1 showing the atom-numbering scheme. Displacement ellipsoids
are drawn at the 30% probability level and H atoms are shown as small spheres of
arbitrary radii. (b) Part of the crystal structure of L1, showing a molecular chain along
[100]. For the sake of clarity, H atoms not involved in H-bonds have been omitted.
3.2. Description of the crystal structures
The solid-state structures of L1 and C3 have been clearly
confirmed by single crystal X-ray analysis, even if their geometric
parameters were not very accurate due to the high R-values. The
perspective ORTEP-3 [44] views of L1 and C3 with the atomic
numbering scheme are shown in Figs. 1(a) and 2(a), respectively,
while selected bond lengths and angles are given in Table 2. Both
compounds crystallize in the triclinic space group P1 and there are
two molecules in the asymmetric unit of L1, labeled as A and B. For
the sake of clarity, only one (molecule A) of the two molecules is
shown in Fig. 1(a). In the following discussion, parameters for
molecule B are given in square brackets.
The molecule of L1 consists of a benzimidazole ring with a
quinoline ring in the 2-position of the benzimidazole and a water
solvent molecule. The benzimidazole and quinoline rings of the
molecule almost share a common plane with a dihedral angle of
3.4(2)ꢀ [3.7(3)ꢀ]. In the benzimidazole ring, the N]C imine bond
length of 1.288(8) Å [1.265(8) Å] is shorter than the amine NeC
bond length of 1.349(8) Å [1.393(7) Å], as expected. The bond
lengths and angles of L1 exhibit no unusual features.
geometry with the h6 p-bound arene ring forming the seat, and the
two nitrogen atoms of the benzimidazole and quinoline rings of the
L3 and one terminal chloride ligand as the legs of the piano-stool.
The Ru(II) ion shows a pseudo-octahedral coordination geom-
etry with the p-cymene formally occupying three facial coordina-
tion sites. However, the coordination geometry around the
ruthenium can be regarded as a tetrahedron with considerable
trigonal distortion, taking into account the center of the
h
6-p-
cymene aromatic ring as the fourth ligand position. If X is defined as
the centroid of the aromatic ring, the RueX distance is found to be
1.7021(5) Å, and the Cl1eRu1eX, N2eRu1eX and N3eRu1eX an-
gles are 129.78(7), 128.69(16) and 133.52(13)ꢀ, respectively. The
Cl1eRu1eN2, Cl1eRu1eN3 and N2eRu1eN3 angles [mean 81.91ꢀ]
are smaller than the ideal tetrahedral angle (109.47ꢀ), which is
counterbalanced by the extending of the XeRueL (L is Cl1, N2 or
N3) angles [mean 130.66ꢀ]. Similar to related Ru(II)earene com-
plexes [22e30], there are substantial differences in the CeC
[1.368(11)-1.483(17) Å] and RueC [2.164(8)-2.233(9) Å] distances
for the arene ring. In the complex, the arene ring is planar with an
r.m.s deviation from the plane of 0.0183 Å. The two N-donor atoms
The cationic complex of C3 is composed of a L3 ligand with an
Ru(II) metal center, one p-cymene ligand and one Cl ligand. The
charge is neutralized by a hexafluorophosphate anion. The complex
has the familiar half-sandwich “three-legged piano-stool”
of the bidentate ligand form
a five-membered metallocycle

40
O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
Fig. 2. (a) A view of C3 showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. The hexafluorophosphate anions and hydrogen atoms
have been omitted for the sake of clarity. (b) Part of the crystal structure of C3, showing a molecular chain along [010]. For the sake of clarity, H atoms not involved in H-bonds have
been omitted.
(containing atoms Ru1/N2/C1/C8/N3) with an r.m.s deviation from
the plane being 0.0569 Å. The bond distances of RueCl1, Ru1eN2
and Ru1eN3 are 2.380(2), 2.057(5) and 2.171(5) Å, respectively.
In the literature, many Ru(II)-arene complexes with the same
coordination environment have been reported [16,47e54]. It is
observed in these examples that the RueX, RueC, RueCl and RueN
bond lengths change from 1.674 to 1.704 Å, from 2.141 to 2.273 Å,
from 2.385 to 2.432 Å and from 2.077 to 2.130 Å, respectively. As a
result, the coordination bond distances are comparable with the
literature values.
Cg1$$$Cg3 ¼ 3.816(4) Å [3.814(4) Å], Cg1$$$Cg4 ¼ 3.777(4) Å
[3.731(5) Å], Cg2$$$Cg3 3.804(4) [3.844(5) Å] and
¼
Å
Cg2$$$Cg4 ¼ 3.901(4) Å [3.794(5) Å] (Cg1 ¼ N1/N2/C1/C2/C7,
Cg2 ¼ C2eC7, Cg3 ¼ N3/C8eC11/C16 and Cg4 ¼ C11eC16). Together,
these interactions form a molecular chain running parallel to [100]
direction for molecule A, and a molecular chain running parallel to
[010] direction for molecule B. In the crystal structure of C3, the
molecules are linked to each other by means of two CeH/F in-
teractions, generating a molecular chain along the b axis.
Partial packing diagrams of the compounds are shown in
Figs. 1(b) and 2(b), while the geometric parameters belonging to
the H-bonding interactions are given in Table 3. In the molecular
structures of both compounds, no intramolecular interactions are
observed. There are no intermolecular interactions between
molecule A and molecule B in the crystal structure of L1, and both
molecules have exactly the same pattern of H-bonding. In this
pattern, the benzimidazole-quinoline molecule is connected to the
water molecule by NeH/Cl interaction, while the water molecule
acts as a hydrogen-bond donor to N2 and N3 atoms of the
3.3. Catalytic studies
Synthesized Ru(II) complexes (C1-5) were tested as catalysts in
selective oxidation of benzyl alcohol to benzaldehyde. Preliminary
catalytic reactions were performed with C1. First, the ratios of
substrat/catalyst/oxidant (S/C/O) as 1/0.01/0.5 were chosen. Then,
different solvents were tested to determine the optimum reaction
conditions (Fig. 3). Maximum activity was observed in acetonitrile
as solvent. No oxidation reaction occurred in the absence of catalyst
with H5IO6 as oxidant. The catalytic reaction becomes notably
slower at room temperature (after 1 h/8%). According to pre-
liminary results, C1-5 (0.01 mmol), periodic acid (0.5 mmol) and
benzyl alcohol (1 mmol) were refluxed at 82 ꢀC in CH3CN (5 mL)
inversion-related molecules. There are also
p$$$p stacking in-
teractions between the benzimidazole and quinolone rings of these
inversion-related molecules, centroid-centroid separations being

O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
41
Table 2
Table 3
Selected geometric parameters for L1 and C3.
Hydrogen bonding geometry for L1 and C3.
Parameter
L1
C3
DeH/A
DeH (Å)
H/A (Å)
D/A (Å)
DeH/A (ꢀ)
Molecule A
Molecule B
L1
N1BeH1B/O1B
O1BeH1B1/N2Ba
N1AeH1A/O1A
O1AeH2A1/N3Ab
O1AeH1A1/N2Ac
O1BeH2B1/N3Bd
C3
0.86(1)
0.82(1)
0.86(1)
0.82(1)
0.82(1)
0.82(1)
1.93(2)
2.00(3)
1.96(2)
2.31(3)
2.12(5)
2.35(4)
2.760(7)
2.793(7)
2.780(7)
3.069(8)
2.828(7)
3.056(7)
163(6)
162(8)
160(6)
153(6)
145(8)
145(6)
Bond lengths (Å)
Ru1eCl1
Ru1eN2
Ru1eN3
Ru1eC29
Ru1eC30
Ru1eC31
Ru1eC32
Ru1eC33
Ru1eC34
N1eC1
N1eC2
N1eC17
N2eC1
N2eC7
N3eC8
N3eC16
e
e
2.380(2)
2.057(5)
2.171(5)
2.231(8)
2.221(8)
2.164(8)
2.233(9)
2.180(8)
2.176(7)
1.368(8)
1.409(7)
1.468(8)
1.322(8)
1.378(8)
1.315(8)
1.381(8)
1.456(8)
1.523(8)
e
e
e
e
e
e
e
e
e
e
C34eH34/F8e
C30eH30/F6f
0.93
0.93
2.49
2.45
3.409(14)
3.045(12)
169
122
e
e
e
e
e
e
Symmetry codes.
a
1.349(8)
1.427(9)
e
1.393(7)
1.408(9)
e
x, yþ1, z.
b
ꢁxþ2, ꢁyþ2, ꢁzþ1.
c
xþ1, y, z.
d
1.288(8)
1.368(7)
1.320(9)
1.425(9)
1.467(9)
e
1.265(8)
1.367(8)
1.275(8)
1.454(9)
1.520(9)
e
ꢁxþ2, ꢁyþ1, ꢁz.
e
ꢁxþ1, ꢁyþ1, ꢁzþ1.
f
ꢁxþ1, ꢁy, ꢁzþ1.
C1eC8
C17eC18
Bond angles (ꢀ)
Cl1eRu1eN2
Cl1eRu1eN3
Cl1eRu1eC29
Cl1eRu1eC30
Cl1eRu1eC31
Cl1eRu1eC32
Cl1eRu1eC33
Cl1eRu1eC34
N2eRu1eN3
N2eRu1eC29
N2eRu1eC30
N2eRu1eC31
N2eRu1eC32
N2eRu1eC33
N2eRu1eC34
N3eRu1eC29
N3eRu1eC30
N3eRu1eC31
N3eRu1eC32
N3eRu1eC33
N3eRu1eC34
N1eC1eN2
C1eN1eC2
C1eN2eC7
C1eN1eC17
C2eN1eC17
C8eN3eC16
N1eC1eC8
N2eC1eC8
N1eC17eC18
N3eC8eC1
N1eC2eC7
N2eC7eC2
e
e
85.47(16)
85.26(15)
90.1(3)
110.3(4)
147.8(4)
166.0(2)
130.0(2)
99.6(2)
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
75.0(2)
e
e
146.5(4)
164.2(4)
125.4(4)
96.3(3)
e
e
e
e
e
e
e
e
91.8(3)
e
e
112.0(3)
137.7(3)
107.0(3)
93.9(3)
e
e
Fig. 3. The oxidation of benzyl alcohol to benzaldehyde using different solvents in the
presence of C1 as catalyst and H5IO6 as oxidant at 82 ꢀC in CH3CN (the ratio of S/C/
H5IO6 is 1/0.01/0.5).
e
e
e
e
e
e
108.6(3)
141.9(3)
171.6(3)
112.0(5)
105.5(5)
107.5(5)
128.7(5)
124.8(5)
119.0(5)
131.2(5)
116.9(5)
113.9(5)
113.0(5)
106.8(5)
108.2(5)
e
e
e
e
113.1(6)
107.2(5)
104.9(6)
e
117.4(6)
104.9(5)
101.2(5)
e
e
e
118.1(6)
121.8(6)
125.0(6)
e
122.1(5)
116.8(5)
125.8(5)
e
115.8(6)
101.7(6)
112.8(7)
117.5(5)
100.7(6)
115.3(6)
(Fig. 4). Under these conditions, we show that benzaldehyde occurs
as a single product.
Fig. 4. The oxidation of benzyl alcohol to benzaldehyde using C1-5 at 82 ꢀC in
In conclusion, the results show that C2 is a more active catalyst
than the others. After 1 h, C1 has lower catalytic activity than C2-5.
These results have shown that the efficiency of the catalyst seems
to depend not only on the quinolinyl-benzimidazole fragment of
the ligands but also on the benzyl fragment of the ligands. Inter-
estingly, catalytic activity decreases when methyl or chlorine
groups are introduced to the benzyl fragment. These results show
that easily synthesized these complexes are moderately active
catalysts in the oxidation of benzyl alcohol to benzaldehyde in the
presence of periodic acid. A plausible mechanism may be proposed
for this reaction (Fig. 5). Some studies suggest that an initial
carbonyl-bound Ru(IV) species is generated upon reaction with
acetonitrile (the ratio of S/C/H5IO6 is 1/0.01/0.5).
periodic acid and concomitant loss of water molecules. The loaded
catalysts then regenerate and initiate a second catalytic cycle
[40,55].
4. Conclusion
In this work, five bidentate quinolinyl-benzimidazole ligands
(L1-5) and their heteroleptic Ru(II) complexes (C1-5) were syn-
thesized and characterized with IR, UVevis and NMR techniques.

42
O. Dayan et al. / Journal of Molecular Structure 1123 (2016) 35e43
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Ln= Other ligands
OH
HIO3 + 2H2O
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Fig. 5. Proposed mechanism for oxidation of benzyl alcohol to benzaldehyde-catalyzed
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Single-crystal X-ray diffraction studies show that solid state
structures of L1 and C3 completely agree with proposed structures.
In C3, there is a distorted octahedral environment around the
central metal ions. Ruthenium atom is coordinated by bidentate L3,
h6
p-bound p-cymene ring and one terminal chloride ligand.
Cationic complex ions are neutralized with PFꢁ6 anion. Synthesized
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order of catalytic efficiency is C2>C4>C3>C5>C1. The higher cata-
lytic efficiency of C2 compared to the others may be related with
steric parameters. Additionally, benzylic protons may play an
important role in the catalytic cycle.
Acknowledgements
We acknowledge Çanakkale Onsekiz Mart University Scientific
Research Projects Commission (Project No: FBA-2014-179) for
support and the Faculty of Arts and Sciences, Ondokuz Mayıs Uni-
versity, Turkey, for the use of the STOE IPDS II diffractometer
(purchased under grant No. Fe279 of the University Research
Fund).
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Appendix A. Supplementary data
CCDC 1036751 and 1036752 contain the supplementary crys-
tallographic data for the compounds reported in this article. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
related to this article can be found at http://dx.doi.org/10.1016/j.
molstruc.2016.06.017.
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