One-pot stepwise reductive amination reaction by N-coordinate sulfonamido-functionalized Ru(II) complexes in water

Article abstract of DOI:10.1002/aoc.4558

New complexes of formula [RuCl(p-cymene)(L)] (7–12) were prepared with [RuCl₂(p-cymene)]₂ and pre-synthesized N-arenesulfonly-o-phenylenediamines (1–6) and characterized using ¹H NMR, ¹³C NMR, Fourier transform

Full text of DOI:10.1002/aoc.4558

Received: 8 June 2018
DOI: 10.1002/aoc.4558
Revised: 18 July 2018
Accepted: 20 July 2018
F U L L P A P E R
One‐pot stepwise reductive amination reaction by
N‐coordinate sulfonamido‐functionalized Ru(II)
complexes in water
Nilgün Kayacı1 | Serkan Dayan1
Nilgün Kalaycıoğlu Özpozan1
| Namık Özdemir2
| Osman Dayan3
|
1 Department of Chemistry, Faculty of
Science, Erciyes University, 38039 Kayseri,
Turkey
2 Department of Mathematics and Science
Education, Faculty of Education,
Ondokuz Mayıs University, 55139
Samsun, Turkey
3 Department of Chemistry, Faculty of
Arts and Science, Çanakkale Onsekiz
Mart University, 17100 Çanakkale, Turkey
New complexes of formula [RuCl(p‐cymene)(L)] (7–12) were prepared with
[RuCl2(p‐cymene)]2 and pre‐synthesized N‐arenesulfonly‐o‐phenylenediamines
(1–6) and characterized using 1H NMR, 13C NMR, Fourier transform
infrared and UV–visible spectroscopic techniques, and single‐crystal X‐ray
diffraction analysis was performed for one complex (8). Complexes 7–12 were
investigated in the reduced imine synthesis reaction (in the presence of
HCOONa/HCOOH). The best turnover frequency values were found to be
100 h−1 for 1 and 99 h−1 for 6 in the transfer hydrogenative reductive amination
reaction of 4‐methoxyaniline and 3,4,5‐trimethoxybenzaldehyde. The most
important feature of this reaction is that it is an environmental friendly
procedure because of being conducted in an aqueous environment. That no
organic solvent is used allows one to say that this reaction represents green
chemistry.
Correspondence
Nilgün Kalaycıoğlu Özpozan, Department
of Chemistry, Faculty of Science, Erciyes
University, 38039 Kayseri, Turkey.
Email: nozpozan@erciyes.edu.tr
Funding information
Erciyes University (ERUBAP), Grant/
Award Number: FDK‐2015‐6143 ID: 6143;
TUBITAK (BIDEB)
KEYWORDS
catalytic, reductive amination reaction, ruthenium, sulfonamido
1 | INTRODUCTION
their complexes usually containing various metals such
as Pd, Ir, Rh and Ru are preferred. This is because the
Sulfonamides have a great position in chemical reactions
because of nitrogen and sulfur groups in their structures.
Also, the syntheses of their various compounds by
industrial catalytic reactions are of great interest in
chemistry.[1] The sulfonamides, known with anticancer,
antibacterial, antifungal, antiviral and anti‐inflammatory
properties, are versatile pharmaceutical drugs.[2–5] The
sulfonamides are utilized as drugs, which play active
roles in many chemical processes such as molecular
modelling, luminescence and analytical applications.[6–8]
They are also used in various catalytic reactions as both
homogeneous and heterogeneous catalysts because of
the functional groups in their structures. While the
sulfonamides themselves are used in catalytic reactions,
complexes exhibit greater catalytic activity by using the
catalytic effects of both ligand and metal. Ruthenium,
which has many advantages when used as a catalyst,
has wide coordination patterns (Ru–arenes, N‐coordinate
Ru, Ru–N‐heterocyclic carbenes, etc.).[9–12] Thus, it can
easily be linked to different functional groups and inspire
various economic processes.[13,14]
In transfer hydrogenation (TH) reactions, secondary
alcohols are used as a hydrogen source instead of direct
use of H2 gas and organic or inorganic bases activating
the catalysts are effective in the classic TH processes.
With the conditions for true and suitable green chemistry
provided, the desired conversions are obtained.[15–20] In
general, ruthenium complexes have been used recently
Appl Organometal Chem. 2018;e4558.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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KAYACI ET AL.
as catalysts in TH reactions and reductive amination (RA)
reactions. On the other hand, complexes bearing Cu, Au,
Ir and Pd metals are also used as catalysts in the RA reac-
tions.[21–25] The amine compounds obtained from RA
reactions are present in natural or agricultural products,
and the preference for RA has led to more economical
production methods. For this reason, the one‐pot step-
wise RA reactions are notable in the literature.
Generally, while RA reactions are carried out in two ways
as stoichiometric boron reduction and heterogeneous
hydrogenation, the use of sodium borohydride produces
much waste, further toxicity and poor selectivity are seen
as the major disadvantages of these types of reactions.
However, the development of various homogeneous cata-
lytic systems has contributed recently to the improvement
of the transfer hydrogenative RA reactions. Moreover,
such reactions have been realized in organic solvents as
well as in the aqueous environment. But the environmen-
tal point of view is towards the use of green solvents.[26–
30] There are topics in the literature that need to be inves-
tigated such as the development of an appropriate cata-
lyst and green conditions. Starting from these
considerations, we synthesized [RuCl(p‐cymene)(L)]
complexes involving various sulfonamide ligands, and
these complexes were used as catalysts in transfer
hydrogenative RA reactions of diverse aldehyde and
amine derivatives in the presence of HCOONa/HCOOH
in aqueous media. The new amine compounds were
obtained with one‐pot stepwise reactions.
2 | EXPERIMENTAL
2.1 | General Synthesis Process of N‐
Arenesulfonyl‐o‐phenylenediamines (1–6)
Pure reactants and solvents were used at all stages of
synthesis of the N‐arenesulfonyl‐o‐phenylenediamine
derivatives. Synthesis procedure of N‐arenesulfonyl‐o‐
phenylenediamines was modified from other synthesis
methods of similar materials in the literature.[9]
A
tetrahydrofuran (THF) solution (10 ml) of
benzenesulfonyl chloride (5 mmol) was prepared in a
Schlenk tube and a solution of triethylamine (5 mmol)
in THF (5 ml) slowly was added with a dropping
funnel to the solution. After 10 min, a solution of
o‐phenylenediamine in THF (5 ml) slowly was added
to the mixture and the resulting mixture was mixed
on a magnetic stirrer at ambient temperature for 12 h.
Then, the mixture was filtered and the solvent of the
remaining filtrate was removed under reduced pressure
(Figure 1).
2.2 | Data for N‐Arenesulfonyl‐o‐
phenylenediamines (1–6)
Compounds 1–5 were synthesized and their data exam-
ined in previous fieldwork by our working partners.[9]
The data for compound 6 are presented herein.
FIGURE 1 General synthesis schema of
N‐arenesulfonyl‐o‐phenylenediamines (1–
6) and [RuCl(p‐cymene)(L)] (7–12).

KAYACI ET AL.
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1595, 1505, 1340 (─SO2), 1261, 1152 (─SO2), 1077, 927,
799, 749, 581. UV–visible (λ, nm (ε, M−1 mm−1)): 396
(916); 300 (4095); 257 (9241).
2.2.1 | Data for [N‐4‐
fluorobenzenesulfonyl‐o‐
phenylenediamine] (6)
1
Colour: dark brown; yield: 82%; m.p. 112.0°C. H NMR
(CDCl3, δ, ppm): 3.97 (br., 2H, ─NH2), 6.48–6.55 (m,
2H, ─H3,1), 6.73 (d, 1H, Ј = 8 Hz, ─H4), 7.05 (t, 1H,
Ј = 8 Hz, ─H2), 7.12 (d, 2H, Ј = 8 Hz, ─Hb), 7.77 (d,
4H, Ј = 8 Hz, ─Ha). 13C NMR (CDCl3, δ, ppm): 116.2,
117.1, 120.68, 128.53, 129.0, 130.3, 134.8, 144.5, 163.9,
166.5. IR (cm−1): 3413 (─NH2), 3232 (─NH2), 3106 ‐(‐
NH), 3066, 2926, 2796, 1907, 1612, 1591, 1494, 1397,
1319 (─SO2), 1240, 1214, 1152 (─SO2), 1086, 1012, 917,
836, 761, 680, 540. UV–visible (λ, nm (ε, M−1 mm−1)):
298 (324); 241 (990); 203 (3126).
2.4.2 | For {[N,N‐benzenesulfonyl‐o‐
phenylenediamine](p‐cymene)
chlororuthenium(II)} (8)
1
Colour: dark green; yield: 79%; m.p. 105.0°C. H NMR
(DMSO‐d6, δ, ppm): 1.19 (d, 6H Ј = 8 Hz, Hm), 2.08 (s,
3H, ─Hk), 2.83 (m, 1H, ─Hl), 5.78 (d, 2H, Ј = 4 Hz,
─Hy), 5.81 (d, 2H, Ј = 4 Hz, ─Hx), 6.39 (t, 1H, Ј = 8 Hz,
─H3), 6.63 (d and d, 2H Ј = 8 Hz, ─H1, ─H4), 6.88 (t, 2H
Ј = 8 Hz, ─H2), 7.53 (t, 2H Ј = 8 Hz, ─Hb), 7.60 (t, 2H
Ј = 8 Hz, ─Hc), 7.70 (d, 2H Ј = 8 Hz, ─Ha), 9.33 (br., 2H,
─NH2). 13C NMR (DMSO‐d6, δ, ppm): 18.5 (─CH3), 22.0
(─CH(CH3)2), 30.4 (─CH (CH3)2), 31.2 (─CH), 85.9
(─Cx), 86.8 (─Cy), 100.2, 106.8, 116.3, 116.9, 127.2, 127.3,
127.8, 129.5, 133.2, 140.6. IR (cm−1): 3300 (─NH2), 3247
(─NH2), 3104, 3062, 2971, 2901, 1601, 1496, 1446, 1324
(─SO2), 1258, 1154 (─SO2), 1066, 873, 753, 687, 582, 548.
UV–visible (λ, nm (ε, M−1 mm−1)): 401 (1049); 299
(4785); 258 (9912).
2.3 | General Synthesis Process of
[RuCl(p‐cymene)(L)] (7–12)
Solutions of 1–6 (4 mmol) containing electron‐withdraw-
ing and electron‐donating groups (─CH2CH2CH3 (7), ─H
(8), ─NO2 (9), ─OCH3 (10), ─C (CH3)3 (11) and ─F (12))
in methanol (5 ml) were prepared in Schlenk tubes
under argon atmosphere. Then, each mixture was added
to a solution of [RuCl2(p‐cymene)]2 (2 mmol) prepared
in methanol (5 ml). The clear mixture obtained was
stirred at 60°C for 12 h and, after the reaction time,
the volatiles were removed under reduced pressure.
The resulting residue was crystallized with MeOH and
a single crystal of complex 8 was obtained from this
route (Figure 1).
2.4.3 | For {[N,N‐4‐nitrobenzenesulfonyl‐
o‐phenylenediamine](p‐cymene)
chlororuthenium(II)} (9)
Colour: dark red; yield: 86%; m.p. 104.0°C. 1H NMR
(DMSO‐d6, δ, ppm): 1.18 (d, 6H Ј = 8 Hz, Hm), 2.08 (s,
3H, ─Hk), 2.82 (m, 1H, ─Hl), 5.79 (d, 2H, Ј = 4 Hz,
─Hy), 5.81 (d, 2H, Ј = 4 Hz, ─Hx), 6.42 (t, 1H,
Ј = 8 Hz, ─H3), 6.62 (d, 1H, Ј = 8 Hz, ─H4), 6.71 (d,
1H, Ј = 8 Hz, ─H1), 6.91 (t, 1H Ј = 8 Hz, ─H2), 7.91
(d, 2H Ј = 8 Hz, ─Hb), 8.36 (d, 2H Ј = 8 Hz, ─Ha),
9.95 (br., 2H, ─NH2). 13C NMR (DMSO‐d6, δ, ppm):
18.3 (─CH3), 21.9 (─CH(CH3)2), 30.4 (─CH(CH3)2),
85.9 (─Cx), 86.8 (─Cy), 116.3, 116.8, 123.8, 124.8,
127.3, 127.9, 128.3, 128.9, 144.6, 146.3, 150.1. IR
(cm−1): 3317 (─NH2), 3229 (─NH2), 2960, 2804, 2604,
2496, 2485, 2352, 1604, 1525, 1347 (─SO2), 1157
(─SO2), 1087, 1031, 1008, 854, 738, 685, 609, 550, 463.
UV–visible (λ, nm (ε, M−1 mm−1)): 493 (777); 460
(977); 259 (14341).
2.4 | Data for [RuCl(p‐cymene)(L)] (7–12)
2.4.1 | For {[N,N‐4‐n‐
propylbenzenesulfonyl‐o‐
phenylenediamine](p‐cymene)
chlororuthenium(II)} (7)
1
Colour: light brown; yield: 85%; m.p. 110°C. H NMR
(DMSO‐d6, δ, ppm): 0.86 (t, 3H, Ј = 8 Hz, ─CH2CH2CH3),
1.18 (d, 6H Ј = 8 Hz, ─Hm), 1.58 (m, 2H, ─CH2CH2CH3),
2.08 (s, 3H, ─Hk), 2.61 (t, 2H, Ј = 8 Hz, ─CH2CH2CH3),
2.83 (m, 1H, ─Hl), 5.78 (d, 2H, Ј = 4 Hz, ─Hy), 5.81 (d,
2H, Ј = 4 Hz, ─Hx), 6.37 (t, 1H, Ј = 8 Hz, ─H3), 6.62 (d
and d, 2H Ј = 8 Hz, ─H1, ─H4), 6.86 (t, 2H Ј = 8 Hz,
─H2), 7.33 (d, 2H Ј = 8 Hz, ─Hb), 7.59 (d, 2H Ј = 8 Hz,
─Ha), 9.20 (br., 2H, ─NH2). 13C NMR (DMSO‐d6, δ,
ppm): 13.9 (─CH2CH2CH3), 18.3 (─CH3), 21.9 (─CH
(CH3)2), 24.1 (─CH2CH2CH3), 30.4 (─CH (CH3)2), 37.3
(─CH2CH2CH3), 85.9 (─Cx), 86.8 (─Cy), 100.5, 106.8,
116.1, 121.4, 127.3, 127.7, 129.3, 138.0, 144.8, 147.7,
155.6. IR (cm−1): 3238 (─NH2), 3159 (─NH2), 2961,
2.4.4 | For {[N,N‐4‐
methoxybenzenesulfonyl‐o‐
phenylenediamine](p‐cymene)
chlororuthenium(II)} (10)
Colour: black; yield: 82%; m.p. 102.0°C. 1H NMR (DMSO‐
d6, δ, ppm): 1.18 (d, 6H Ј = 8 Hz, Hm), 2.08 (s, 3H, ─Hk),
2.83 (m, 1H, ─Hl), 3.80 (s, 3H, ─OCH3), 5.79 (d, 2H,

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KAYACI ET AL.
Ј = 4 Hz, ─Hy), 5.81 (d, 2H, Ј = 4 Hz, ─Hx), 6.43 (t, 1H,
Ј = 8 Hz, ─H3), 6.64–6.66 (d and d, 2H, Ј = 8 Hz, ─H1,
─H4), 6.89 (t, 1H Ј = 8 Hz, ─H2), 7.04 (d, 2H Ј = 8 Hz,
─Hb), 7.60 (d, 2H Ј = 8 Hz, ─Ha), 9.23 (br., 2H, ─NH2).
13C NMR (DMSO‐d6, δ, ppm): 18.3 (─CH3), 21.9
(─CH(CH3)2), 30.4 (─CH(CH3)2), 56.0 (─OCH3), 79.9,
85.9 (─Cx), 86.8 (─Cy), 100.5, 106.8, 114.5, 116.7, 127.3,
127.7, 129.4, 129.8, 132.1, 162.7. IR (cm−1): 3296 (─NH2),
3240 (─NH2), 3062, 2960, 2116, 1898, 1593, 1495, 1456,
1324 (─SO2), 1302, 1256, 1149 (─SO2), 1087, 1020, 912,
802, 755, 665, 555. UV–visible (λ, nm (ε, M−1 mm−1)):
554 (2124); 496 (2061); 291 (6848); 256 (21555).
2.5 | X‐ray Analysis
2.5.1 | Crystal structure determination
Intensity data of the compound were collected with an
STOE diffractometer with an IPDS II image plate detector.
The diffraction measurements were performed at room
temperature using graphite monochromated Mo Kα radia-
tion by applying the ω‐scan method. Data collection and
cell refinement were carried out using X‐AREA while data
reduction was applied using X‐RED32 (X‐AREA Version
1.18 and X‐RED32 Version 1.04, Stoe & Cie, Darmstadt,
Germany). The structure was solved by a dual‐space algo-
rithm using SHELXT‐2014[31] and refined with full‐matrix
least‐squares calculations on F2 using SHELXL‐2016[32]
implemented in the WinGX[33] program suit. All H atoms
were positioned geometrically and treated using a riding
model, fixing the bond lengths at 0.89, 0.93, 0.98 and
0.96 Å for NH2, aromatic CH, methine CH and CH3 atoms,
respectively. The displacement parameters of the H atoms
were fixed at Uiso(H) = 1.2Ueq (1.5Ueq for methyl) of their
parent atoms. In the final difference Fourier map of the
compound, the two high residual peaks (1.26 and
1.17 e Å−3) located 1.15 and 1.14 Å from atom Ru1, respec-
tively, were essentially meaningless. Crystal data, data col-
lection and structure refinement details are summarized
in Table 1. Molecular graphics were generated using
ORTEP‐3.[33]
2.4.5 | For {[N,N‐4‐tert‐
butylbenzenesulfonyl‐o‐
phenylenediamine](p‐cymene)
chlororuthenium(II)} (11)
Colour: dark blue; yield: 76%; m.p. 122.5°C. 1H NMR
(DMSO‐d6, δ, ppm): 1.19 (d, 6H Ј = 8 Hz, Hm), 1.27 (s,
9H, ─C(CH3)3), 2.08 (s, 3H, ─Hk), 2.82 (m, 1H, ─Hl),
5.79 (d, 2H, Ј = 4 Hz, ─Hy), 5.81 (d, 2H, Ј = 4 Hz,
─Hx), 6.43 (t, 1H, Ј = 8 Hz, ─H3), 6.67 (d, 1H Ј = 8 Hz,
─H1), 6.69 (d, 1H Ј = 8 Hz, ─H4), 6.89 (t, 1H Ј = 8 Hz,
─H2), 7.55 (d, 2H Ј = 8 Hz, ─Hb), 7.64 (d, 2H Ј = 8 Hz,
─Ha), 9.32 (br., 2H, ─NH2). 13C NMR (DMSO‐d6, δ,
ppm): 18.3 (─CH3), 21.9 (─CH(CH3)2), 30.4
(─CH(CH3)2), 31.2 (─C(CH3)3), 35.3 (─C(CH3)3), 85.9
(─Cx), 86.8 (─Cy), 100.6, 106.8, 116.7, 117.3, 122.2,
126.3, 127.1, 127.6, 137.9, 140.2, 156.1. IR (cm−1): 3234
(─NH2), 3162 (─NH2), 2964, 2901, 1594, 1507, 1465,
1394, 1337 (─SO2), 1263, 1156 (─SO2), 1078, 935, 742,
619, 577, 547. UV–visible (λ, nm (ε, M−1 mm−1)): 557
(2026); 296 (5699); 259 (10452).
2.6 | Transfer Hydrogenative RA Reaction
in Water
Generally, water and preferred acidic environment to
increase the amine yield are used as solvent media in
transfer hydrogenative RA reactions.[12,15] In accordance
with this information, [RuCl(p‐cymene)(L)] (0.01 mmol)
and water (1 ml) were added to a mixture including
aniline (1.2 mmol) and benzaldehyde (1 mmol) as a
model reaction. Then, a solution of HCOONa (1 mmol)/
HCOOH in water (1 ml) as pH adjuster was added to
the mixture and stirred for 1 h at 80°C. The occurring
products in the water were extracted with dichlorometh-
ane (DCM) and filtered from short silica column with
extra DCM and the crude products analysed by GC and
NMR spectroscopy (Figure 2).
2.4.6 | For {[N,N‐4‐fluorobenzenesulfonyl‐
o‐phenylenediamine](p‐cymene)
chlororuthenium(II)} (12)
1
Colour: dark brown; yield: 73%; m.p. 191.0 C. H NMR
(DMSO‐d6, δ, ppm): 1.19 (d, 6H Ј = 8 Hz, Hm), 2.08 (s,
3H, ─Hk), 2.83 (m, 1H, ─Hl), 5.78 (d, 2H, Ј = 4 Hz,
─Hy), 5.81 (d, 2H, Ј = 4 Hz, ─Hx), 6.43 (t, 1H,
Ј = 8 Hz, ─H3), 6.65 (d and d, 2H Ј = 8 Hz, ─H1, ─H4),
6.90 (d, 1H Ј = 8 Hz, ─H2), 7.37 (t, 2H Ј = 8 Hz, ─Hb),
7.71 (d, 2H, Ј = 8 Hz, ─Ha), 9.42 (br., 2H, ─NH2). 13C
NMR (DMSO‐d6, δ, ppm): 18.3 (─CH3), 21.9
(─CH(CH3)2), 30.4 (─CH(CH3)2), 85.9 (─Cx), 86.8 (─Cy),
100.5, 106.8, 116.5, 116.7, 121.2, 127.6, 128.0, 130.3,
136.9, 163.4, 165.9. IR (cm−1): 3296 (─NH2), 3247
(─NH2), 3055, 2966, 1590, 1493, 1329 (─SO2), 1232,
1153 (─SO2), 1087, 916, 836, 757, 666, 541. UV–visible
(λ, nm (ε, M−1 mm−1)): 401 (786); 300 (3637); 258 (7592).
3 | RESULTS AND DISCUSSION
3.1 | Synthesis and Characterization of
Ru(II) catalysts
Compounds 1–5 in our previous report and compound
6 were synthesized with similar simple reactions. Then,

KAYACI ET AL.
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TABLE 1 Crystal data and structure refinement parameters for
complex 8
complexes 7–12 were obtained and characterized using
various techniques with synthesis methodology that
1–6 and [RuCl2(p‐cymene)]2 were utilized with stoi-
chiometric ratios. According to the 1H NMR spectra
of complexes 7–12, the Ha and Hb protons of the
sulfonamido ring were assigned to 7.59–8.36 ppm as a
doublet and 7.04–7.91 ppm, respectively, and the peaks
of the H1–4 protons relating to the phenylenediamine
ring were observed at around 6.37–6.91 ppm. Also,
the peaks of Hm, Hk, Hl, Hx and Hy protons relating
to the p‐cymene group were observed at around 1.18–
1.19, 2.08, 2.82–2.83, 5.81 and 5.78–5.79 ppm, respec-
tively. Likewise, the proton peaks of ─CH2CH2CH3,
─OCH3 and ─C(CH3)3 for the sulfonamido ring were
assigned to 2.61 ppm as a triplet, 1.58 ppm as a multi-
plet, 0.86 ppm as a triplet, 3.80 ppm as a singlet and
1.27 ppm as a singlet, respectively. According to the
13C NMR spectra for complexes 7–12, the peaks of
functional group in the (c) position of sulfonamido ring
belonging to the ─CH2CH2CH3, ─OCH3 and ─C(CH3)3
carbons are assigned as 37.3, 24.1, 13.9, 56, 35.3,
31.2 ppm, respectively. All the chemical shifts and inte-
grations belonging to the related peaks for NMR tech-
nique are logical as per the proposed molecular
structure. The representative 1H NMR and 13C NMR
spectra of 7 are given in the supporting information
(Figures S1 and S2).
CCDC deposition no.
1528997
Colour/shape
Brown/prism
[RuCl(C10H14)(C12H11N2O2S)]
518.02
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
296(2)
0.71073 Mo Kα
Monoclinic
P21/c (No. 14)
Unit cell parameters
a, b, c (Å)
8.3942(11), 17.5095(12),
14.3878(14)
α, β, γ (°)
Volume (Å3)
Z
90, 91.443(10), 90
2114.0(4)
4
Dcalc (g cm−3
μ (mm−1
)
1.628
)
0.988
Absorption correction
Tmin, Tmax
Integration
0.8335, 0.9697
1056
F 000
Crystal size (mm3)
0.31 × 0.04 × 0.02
Diffractometer/
STOE IPDS II/rotation
measurement method
(ω scan)
In addition, in the Fourier transform infrared
spectra, the stretching frequency peaks of the ─NH2
and ─NH groups were observed 3413–3232 and
3106 cm−1, respectively for 6. For the ruthenium(II)
complexes, the stretching frequency peaks of ─NH2 were
observed at 3238–3159 cm−1 for 7; 3300–3247 cm−1 for 8;
3317–3229 cm−1 for 9; 3296–3240 cm−1 for 10; 3234–
3162 cm−1 for 11; and 3296–3247 cm−1 for (12). The
─NH stretching frequency peaks of the sulfonamide
ligands are not available in [RuCl(p‐cymene)(L)] type
complexes.
UV–visible spectra of complexes 7–12 in
dimethylsulfoxide (1 × 10−4 M) solvent within the
250–750 nm range were used to determine the structures
of the complexes. Generally, metal‐to‐ligand charge
transfer (MLCT) (Ru (dπ) → π*) transitions are observed
at around 400, 450 and 500 nm, and π → π* and n → π*
bands at around 300 and 400 nm. For 7–12, MLCT (Ru
(dπ) → π*) transition peaks have been found at
396 nm, 401 nm, 393 and 460 nm, 554 and 496 nm,
557 nm and 401 nm for 7–12, respectively. In addition,
MLCT π → π* and n → π* bands were observed at
300 and 257 nm for 7, at 299 and 258 nm for 8, at
259 nm for 9, at 291 and 256 nm for 10, at 296
and 259 nm for 11 and at 300 and 258 nm for 12.
(Figures S3–S8).
Index ranges
−9 ≤ h ≤ 8, −20 ≤ k ≤ 20,
−17 ≤ l ≤ 17
θ range for data collection (°)
1.832 ≤ θ ≤ 25.046
9863
Reflections collected
Independent/observed
reflections
3683/1208
Rint
0.2574
Refinement method
Data/restraints/parameters
Goodness‐of‐fit on F 2
Final R indices [I > 2σ(I)]
R indices (all data)
Full‐matrix least‐squares on F 2
3683/7/265
0.909
R1 = 0.1017, wR2 = 0.1817
R1 = 0.2688, wR2 = 0.2489
1.26, −0.89
Δρmax, Δρmin (e Å−3
)
FIGURE 2 Transfer hydrogenative amination reaction with
[RuCl(p‐cymene)(L)] in aqueous system.

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KAYACI ET AL.
2.146(18) to 2.24(3) Å, while the S1─O1 and S1─O2 bond
lengths of 1.412(12) and 1.441(13) Å, respectively, con-
firm the double bond character, and the sulfur atom has
3.1.1 | Structural description of complex 8
The molecular structure of complex 8 is shown in
Figure 3, while the important bond lengths and angles
are given in Table 2.
TABLE 2 Selected geometric parameters for complex 8
The complex is composed of an N‐(2‐aminophenyl)
benzenesulfonamide ligand with a Ru(II) metal centre,
one p‐cymene ligand and one Cl ligand. The chelating
ligand appeared to be deprotonated and coordinated as
a monoanionic bidentate N,N′‐ligand (amine and amide
coordination) resulting in a five‐membered metallacycle
with a bite angle of 77.8(5)°. The geometry around the
Ru(II) centre is distorted pseudo‐octahedral in which
the two N atoms and the Cl atoms form the base, while
the η6‐p‐cymene ring forms the apex of a ‘three‐legged
piano stool’ structure. The coordination geometry around
the Ru atom can be considered as a tetrahedron, taking
into account the centre of the η6‐p‐cymene aromatic ring
as the fourth ligand position. If Cg is defined as the cen-
troid of the aromatic ring, the Ru─Cg distance is
1.6927(18) Å, and the Cl1─Ru1─Cg, N1─Ru1─Cg and
N2─Ru1─Cg angles are 128.35(16)°, 133.2(5)° and
131.0(4)°, respectively. The Cl1─Ru1─N1, Cl1─Ru1─N2
and N1─Ru1─N2 angles (mean 81.73°) are smaller than
the ideal tetrahedral angle (109.47°), which is
counterbalanced by the extending of the X─Ru─Cg (X is
Cl1, N1 or N2) angles (mean 130.85°).
Bond lengths (Å)
Ru1─Cl1
2.443(7)
2.100(17)
2.155(14)
2.24(3)
Ru1─C19
S1─O1
S1─O2
S1─N1
S1─C6
2.190(17)
1.412(12)
1.441(13)
1.618(14)
1.77(2)
Ru1─N1
Ru1─N2
Ru1─C14
Ru1─C15
Ru1─C16
Ru1─C17
Ru1─C18
Bond angles (°)
2.20(2)
2.146(18)
2.23(2)
N1─C7
N2─C12
1.42(2)
1.44(2)
2.15(2)
N1─Ru1─Cl1
N2─Ru1─Cl1
N1─Ru1─N2
Cl1─Ru1─C14
86.7(5)
80.7(5)
77.8(5)
88.7(7)
N1─Ru1─C19
N2─Ru1─C14
N2─Ru1─C15
N2─Ru1─C16
N2─Ru1─C17
N2─Ru1─C18
N2─Ru1─C19
O1─S1─O2
170.3(7)
135.2(6)
167.6(6)
141.6(7)
107.8(6)
91.6(6)
Cl1─Ru1─C15 103.8(6)
Cl1─Ru1─C16 136.8(5)
Cl1─Ru1─C17 168.8(6)
Cl1─Ru1─C18 137.6(6)
Cl1─Ru1─C19 103.0(6)
N1─Ru1─C14 145.2(5)
N1─Ru1─C15 113.7(6)
103.0(7)
116.1(9)
105.9(8)
113.8(8)
104.5(7)
105.8(9)
110.2(9)
116.0(13)
The bond distances of Ru─Cl1, Ru1─N1 and Ru1─N2
are found to be 2.443(7), 2.100(17) and 2.155(14) Å,
respectively, and are comparable to those found in related
Ru(II)–arene complexes with the same coordination
sphere.[34–36] The Ru─Carene distances change from
O1─S1─N1
O2─S1─N1
O1─S1─C6
N1─Ru1─C16
93.9(7)
O2─S1─C6
N1─Ru1─C17 102.0(8)
N1─Ru1─C18 132.5(7)
N1─S1─C6
S1─N1─C7
FIGURE 3 Molecular structure of complex 8 showing the atom
numbering scheme. Intramolecular C─H···Cl interaction is
represented by the dashed line. Thermal ellipsoids are drawn at the
30% probability level and only the hydrogen atom involved in
hydrogen bonding has been included for clarity.
FIGURE 4 Part of the crystal structure of complex 8 showing the
intermolecular interactions. For the sake of clarity, only hydrogen
atoms involved in hydrogen bonding have been included.

KAYACI ET AL.
7 of 10
a distorted tetrahedral configuration which is evident
from the angles ranging from 104.5(7)° to 116.1(9)°.
The packing diagram of the complex is shown in
Figure 4, while the geometric parameters belonging to
the hydrogen‐bonding interactions are given in Table 3.
In the molecular structure of the complex, an intramolec-
ular C─H···Cl interaction leads to the formation of a six‐
membered ring with graph‐set descriptor S(7)[37]
(Figure 3). In the crystal structure, atom C5 at (x, y, z) acts
as a hydrogen‐bond donor to O2 atom at (−x + 1, −y + 1,
−z + 2), so generating by inversion a centrosymmetric
TABLE 3 Hydrogen bonding geometry for complex 8
dimer, centred at (1/2, 1/2, 1) and characterized by a
[37]
R22ð10Þ
motif. Furthermore, there is an N─H···O
D—H···A
D—H (Å) H···A (Å) D···A (Å) D—H···A (°)
interaction linking the dimers, in which atom N2 at
(x, y, z) acts as a hydrogen‐bond donor to O1 atom at
(x, −y + 1/2, z − 1/2).
C1─H1···Cl1 0.93
N2─H2B···O1i 0.89
C5─H5···O2ii 0.93
2.76
2.27
2.51
3.65(2)
3.147(18) 168
3.38(3) 154
162
i
ii
Symmetry codes: x, −y + 1/2, z − 1/2; − x + 1, −y + 1, −z + 2.
3.2 | Transfer Hydrogenative RA
Reactions
Transfer hydrogenative amination reactions are made pos-
sible in aqueous acidic conditions, and were done with
various aldehyde or ketone derivatives and amine deriva-
tives at 80°C for all the catalysts (7–12). HCOONa and
HCOOH were used to adjust the acid value of the reaction
medium. When the model reaction conditions were exam-
ined, the pH values of reaction medium were observed as
pH = 4.8 likewise in other aqueous RA reaction studies.[29]
FIGURE 5 Possible mechanism of aqueous RA reaction.
TABLE 4 Catalytic activity for transfer hydrogenative amination reaction in water catalysed by Ru(II) complexes for 4‐methoxyaniline
(substrate‐to‐catalyst molar ratio, S/C = 100/1)
Entry
Catalyst
Substrate (aldehyde)
Main product
Conversion (%)
1
2
3
4
5
6
7
8
9
10
11
12
100
68
77
60
64
99
7
8
9
10
11
12
7
8
9
10
11
12
68
62
58
64
58
70
13
14
15
16
17
18
7
8
9
10
11
12
61
60
74
58
71
73
19
20
21
22
23
24
7
8
9
10
11
12
76
77
87
76
86
85
Reaction conditions: amine (1.2 mmol), benzaldehyde (1 mmol), [RuCl(p‐cymene)(L)] (0.01 mmol), HCOONa (1 mmol), HCOOH (1 mmol), water (2 ml), 80°C,
for 1 h. S/C: 100/1.

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KAYACI ET AL.
We thought that the pH scanning tests will be compatible
due to the high conversion values observed at the same
pH. Similarly, the pH value of the reaction medium greatly
influences both the catalytic activity and the selectivity in
transfer hydrogenative RA reactions in water.[29] The
amine, which is the desired product, is obtained at a spec-
ified pH value while the alcohol forms as a by‐product of
the synthesis mechanism[26] (Figure 5).
found as the best catalyst in the reaction of 4‐bromoaniline
with 3,4,5‐trimethoxybenzaldehyde (85%) and 4‐
methylbenzaldehyde (77%). Also, complexes 7 and 11 were
the best catalysts in the reaction of 4‐bromoaniline with 4‐
methoxybenzaldehyde (80%) and 4‐chlorobenzaldehyde
(80%), respectively (Table 5). Lastly, catalyst 7 was deter-
mined as the best catalyst in the reaction of aniline with
4‐methylbenzaldehyde (53%) and 4‐methoxybenzaldehyde
(94%), and complexes 8 and 9 were determined as the
best catalysts in the reaction of aniline with 3,4,5‐
trimethoxybenzaldehyde (68%) and 4‐chlorobenzaldehyde
(90%), respectively (Table 6). When the conversion of these
reactions was examined, the best conversion was found as
100% with catalyst 7 in the reaction of 4‐methoxyaniline
with 3,4,5‐trimethoxybenzaldehyde in the presence of
HCOONa/HCOOH at 80°C for 1 h in water.
According to the balances caused by the differences in
the pH value in the aqueous medium, the hydride of the
complex (catalyst) can be formed from the decarboxyl-
ation of the format from the solution. But under very
low acid conditions, the formation of imine will decrease
and the reduction will be slow; furthermore reduction
under basic conditions will also be limited. The occur-
rence imine reduction is provided by proton transfer from
In this paper, the synthesized reduced amine
compounds were produced from aldehydes (such as
3,4,5‐trimethoxybenzaldehyde,
4‐methylbenzaldehyde,
4‐methoxybenzaldehyde and 4‐chlorobenzaldehyde) and
amines (such as 4‐methoxyaniline, 4‐bromoaniline and
aniline). The molar ratio of the substrate – according to
aldehyde – to the catalyst in these tests is S/C = 100/1 at
80°C for 1 h. The conversions exhibit time dependence
(Tables 4–6). From the results of transfer hydrogenative
RA reactions in water, some catalysts have higher activity,
while others have lower activity. Complexes 7, 12 and
9 were determined as the best catalysts in the reaction
of 4‐methoxyaniline with 3,4,5‐trimethoxybenzaldehyde
(100%) for 7, 4‐methylbenzaldehyde (70%) for 12 and 4‐
methoxybenzaldehyde (74%) and 4‐chlorobenzaldehyde
(87%) for 9 (Table 4). Moreover, catalyst 8 has been
TABLE 5 Catalytic activity for transfer hydrogenative amination reaction in water catalysed by Ru(II) complexes for 4‐bromoaniline
(substrate‐to‐catalyst molar ratio, S/C = 100/1)
Entry
Catalyst
Substrate (aldehyde)
Main product
Conversion (%)
1
2
3
4
5
6
7
8
9
10
11
12
63
85
74
56
66
67
7
8
9
10
11
12
7
8
9
10
11
12
55
77
32
24
38
40
13
14
15
16
17
18
7
8
9
10
11
12
80
61
62
53
65
66
19
20
21
22
23
24
7
8
9
10
11
12
76
75
72
78
80
74
Reaction conditions: amine (1.2 mmol), benzaldehyde (1 mmol), [RuCl(p‐cymene)(L)] (0.01 mmol), HCOONa (1 mmol), HCOOH (1 mmol), water (2 ml), 80°C,
for 1 h. S/C: 100/1.

KAYACI ET AL.
9 of 10
TABLE 6 Catalytic activity for transfer hydrogenative amination reaction in water catalysed by Ru(II) complexes for aniline (substrate‐to‐
catalyst molar ratio, S/C = 100/1)
Entry
Catalyst
Substrate (aldehyde)
Main product
Conversion (%)
1
2
3
4
5
6
7
8
9
10
11
12
60
68
50
63
53
56
7
8
9
10
11
12
7
8
9
10
11
12
53
24
26
30
28
23
13
14
15
16
17
18
7
8
9
10
11
12
94
83
43
40
70
69
19
20
21
22
23
24
7
8
9
10
11
12
85
89
90
87
89
77
Reaction conditions: amine (1.2 mmol), benzaldehyde (1 mmol), [RuCl(p‐cymene)(L)] (0.01 mmol), HCOONa (1 mmol), HCOOH (1 mmol), water (2 ml), 80°C,
for 1 h. S/C: 100/1.
the hydride state of the complex directly to the ─C═N─
bond. At the critical value of the specified pH = 4.8, the
ketone is free and can easily provide protonation of
imine. Thus, the reduction reaction of imine is deter-
mined as the main reaction in aqueous media.[27]
various spectroscopic techniques. Complexes 7–12
were used as catalysts in one‐pot stepwise aqueous
transfer hydrogenative RA reaction system in the
presence of HCOONa/HCOOH. Thus, we are able to
examine the effects of the Ru(II) complexes in aqueous
amination reactions. The transfer hydrogenative RA
reaction was done with all the complexes and new
amine compounds were obtained in various yields. Also,
the best yield of 100% was obtained with catalyst 7 in
the catalytic reaction of 3,4,5‐trimethoxybenzaldehyde
and 4‐methoxyaniline. When these results are taken
into consideration, although the effects of ligand
variations on the catalytic performance are clearly
shown, the presence of some substrates containing
methoxy, chloro and bromo groups in the RA reaction
have a beneficial contribution in terms of the catalytic
conversions.
It was observed that the best conversion values were
achieved in the reaction between 4‐methoxyaniline and
3,4,5‐trimethoxybenzaldehyde substrates when the
conversion values of all the reactions were examined.
Moreover, the conversion values obtained in the
reaction with 4‐chlorobenzaldehyde were close to each
other and were above the mean value (65.3%).
Conversely, the conversion at the end of all reactions
with 4‐methylbenzaldehyde was found to be the lowest.
To sum up, different conversions were achieved for
aqueous reactions according to the functional groups of
both the substrates and the catalysts (7–12). Catalysts 7
and 8 are generally more active, and the catalytic conver-
sions are above the average value.
ACKNOWLEDGEMENTS
We acknowledge the support by TUBITAK (BIDEB)
(2211/C PhD Scholarship Program for Priority Areas)
and the financial support of Erciyes University
(ERUBAP) (FDK‐2015‐6143 ID: 6143).
4 | CONCLUSIONS
We reported the fabrication of six new N‐coordinate
Ru(II)–arene complexes and their characterizations with

10 of 10
KAYACI ET AL.
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Osman Dayan http://orcid.org/0000-0002-0764-1965
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One‐pot stepwise reductive amination reaction by
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