Ruthenium-cymene containing pyridine-derived aldiimine ligands: Synthesis, characterization and application in the transfer hydrogenation of aryl ketones and kinetics studies

Article abstract of DOI:10.1016/j.jorganchem.2019.04.022

Five electron-rich N[sbnd]N′?pyridylimine ligands, which form five-membered chelate ring when coordinate to a metal center, have been synthesized by the easily accessible condensation between 2-pyridinecarboxyaldhehyde and the corresponding substituted an

Full text of DOI:10.1016/j.jorganchem.2019.04.022

Accepted Manuscript
Ruthenium-cymene containing pyridine-derived aldiimine ligands: Synthesis,
characterization and application in the transfer hydrogenation of aryl ketones and
kinetics studies
Thiago S. Ramos, Diego M. Luz, Rebecca D. Nascimento, Andressa K. Silva, Luciano
M. Lião, Victor M. Miranda, Victor M. Deflon, Márcio P. de Araujo, Leonardo T. Ueno,
Francisco B.C. Machado, Luís R. Dinelli, André L. Bogado
PII:
S0022-328X(19)30162-7
DOI:
https://doi.org/10.1016/j.jorganchem.2019.04.022
JOM 20772
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 28 February 2019
Revised Date: 18 April 2019
Accepted Date: 23 April 2019
Please cite this article as: T.S. Ramos, D.M. Luz, R.D. Nascimento, A.K. Silva, L.M. Lião, V.M. Miranda,
V.M. Deflon, Má.P. de Araujo, L.T. Ueno, F.B.C. Machado, Luí.R. Dinelli, André.L. Bogado, Ruthenium-
cymene containing pyridine-derived aldiimine ligands: Synthesis, characterization and application in the
transfer hydrogenation of aryl ketones and kinetics studies, Journal of Organometallic Chemistry (2019),
doi: https://doi.org/10.1016/j.jorganchem.2019.04.022.
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ACCEPTED MANUSCRIPT
Ruthenium-cymene containing pyridine-derived aldiimine ligands: synthesis,
characterization and application in the transfer hydrogenation of aryl ketones
and kinetics studies
a
a
a
b
Thiago S. Ramos , Diego M. Luz , Rebecca D. Nascimento , Andressa K. Silva , Luciano M.
b
c
c
d
e
Lião , Victor M. Miranda , Victor M. Deflon , Márcio P. de Araujo , Leonardo T. Ueno ,
e
a
a,*
Francisco B.C. Machado , Luís R. Dinelli , André L. Bogado
a
Departamento de Química, Instituto de Ciências Exatas e Naturais do Pontal, Universidade
Federal de Uberlândia, Rua vinte, 1600, CEP 38304-402, Ituiutaba - MG , Brazil
b
Instituto de Química, Universidade Federal de Goiás, Avenida Esperança, s/n, Campus
Samambaia, CEP 74690-900, Goiânia – GO, Brazil
c
Instituto de Química de São Carlos, Universidade de São Paulo, CP 780, 13560-590 São Carlos
–
SP, Brazil
d
Departamento de Química, Universidade Federal do Paraná, Centro Politécnico, CP 19081,
Curitiba – PR, Brazil.
e
Departamento de Química, Instituto Tecnológico de Aeronáutica, Comando-Geral de
Tecnologia Aeroespacial, São José dos Campos, São Paulo 12228-900, Brazil
*
To whom correspondence should be addressed: bogado@ufu.br
1

ACCEPTED MANUSCRIPT
Abstract
Five electron-rich N-N′−pyridylimine ligands, which form five-membered chelate ring
when coordinate to a metal center, have been synthesized by the easily accessible condensation
between 2-pyridinecarboxyaldhehyde and the corresponding substituted aniline in diethyl ether
solution, in the presence of catalytic amount of p-toluenesulfonic acid. The reaction of N-N′–
pyridylimine ligands with [RuCl (p-cym)] (1) in the presence of excess of KPF led to the
2
2
6
formation of mononuclear adducts with general formula [RuCl(p-cym)(N-N′)]PF , where N-N′=
6
N-phenyl-1-(pyridin-2-yl)methanimine
(Amp)
(2),
N-(4-chlorophenyl)-1-(pyridin-2-
yl)methanimine (Clmp) (3), N-(4-methylphenyl)-1-(pyridin-2-yl)methanimine (Memp) (4), N-(4-
tert-butylphenyl)-1-(pyridin-2-yl)methanimine (Tbump) (5), N-(2,6-diethylphenyl)-1-(pyridin-2-
yl)methanimine (Diemp) and N-[2,6-bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine
(Diipmp) (7). Additionally, the reaction of 2-acetylbenzenolate (O-O′) with (1) produces a less
bulky neutral congener [RuCl(p-cym)(O-O′)] (8). All complexes were isolated and fully
characterized by molar conductivity, elemental analysis, cyclic voltammetry and spectroscopic
methods, including single crystal X-ray diffraction of (4), (7) and (8). The structures (2) – (7)
were also optimized with the Density Functional Theory (DFT) and theoretical absorption spectra
were obtained with TD-DFT formalism. The complexes (2) – (8) were applied as pre-catalyst in
the transfer hydrogenation of the acetophenone and 4-methylacetophenone, showing good
−1
catalytic activity, with productivity up to 90%, and TOF up to 302 h within 3h of reaction;
except for (8), which has no activity for the catalytic reduction performed in this work. A kinetic
investigation using (3) and (7) as pre-catalysts showed that the time dependence for the
production of 1-phenylethanol has a sigmoidal shape, with an induction time of 20 min. The
catalytic activity of (3) is more sensitive to the temperature variation and its rate constant (k)
2

ACCEPTED MANUSCRIPT
increases faster than for (7). An Arrhenius plot reveals a smaller activation barrier (E
a
) for the
−1
≠
rate-determining step for (7) than for (3), E = 14.75 and 49.38 kJ mol , respectively. The ∆S
a
values obtained from an Eyring plot suggest an associative mechanism in the transition state of
the catalytic reactions.
Keywords
half-sandwich complexes; organometallic ruthenium complexes; Schiff base; DFT; transfer
hydrogenation; catalysis.
3

ACCEPTED MANUSCRIPT
1
. Introduction
Ruthenium complexes containing phosphine and diphosphine ligands are in general
efficient catalysts in homogeneous hydrogenation of apolar double bonds or transfer
hydrogenation of polar double bonds[1–3]. The use of P-donor groups coordinated to the metal
center is almost mandatory in this field, owing to the structure of aromatic phosphines and
diphosphines, which may provide strong back-bonding with the metal center, stabilizing lower
oxidation states of the ruthenium center [4]. Associated to that, the most important mechanism for
H -hydrogenation of imines and ketones was proposed by Noyori [5,6] (Nobel Prize laureate in
2
2
001), using diamines as a key ligand and coined the term “metal-ligand bifunctional catalysis”
to refer to the catalytic systems utilizing the outer-sphere hydrogenation ligand-assisted
mechanism. These findings have provided a favorable perspective to explore the synthesis and
application of new mixed diamine/diphosphine [7,8] and diimine/diphosphine [8–11] containing
ruthenium complexes as alternative pre-catalysts for the reduction of aryl ketones.
Outside the “Ru(P) ” or “Ru(P-P)” core, it is possible to find the use of “Ru-arene”
2
moiety with several ancillary ligands as a new highway to reach active pre-catalysts for transfer
hydrogenation reactions of ketones. Keeping this in mind, attention should be pointed out to the
increasing use of the following ancillary ligands associated to ruthenium-arene core:
amide/diamine[12], thioamides[13], sulfonamide fragment[14], N-heterocyclic carbenes[15–18],
imidazolin-2-imine[19] and molten salts-based phosphine[20].
In this regard, the use of Schiff base obtained from the condensation between 2-
piridinecarboxyaldhehyde and the substituted anilines appears as an accessible source of N-
N′−pyridylimine ligands, which are interesting electron-rich chelating ligands to stabilize a metal
center. In this context, it is worth to mention the work described by Friedrich and co-workers, in
4

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which described the synthesis of half-sandwich complexes of platinum metals group containing
N-N′ donor Schiff bases and the studies of such complexes in biological assays[21,22], oxidation
of olefins[23,24] and alcohols[25], and transfer hydrogenation of ketones[26–29].
In order to contribute to this discussion, in this work we present the syntheses,
characterization, electrochemistry behavior and kinetic discussions of the transfer hydrogenation
of acetophenone and 4-methylacetophenone of six half-sandwich ruthenium complexes with
general formula [RuCl(p-cym)(N-N′)]PF {where N-N′= N-phenyl-1-(pyridin-2-yl)methanimine
6
(Amp) (2), N-(4-chlorophenyl)-1-(pyridin-2-yl)methanimine (Clmp) (3), N-(4-methylphenyl)-1-
(pyridin-2-yl)methanimine (Memp) (4), N-(4-tert-butylphenyl)-1-(pyridin-2-yl)methanimine
(Tbump) (5), N-(2,6-diethylphenyl)-1-(pyridin-2-yl)methanimine (Diemp) and N-[2,6-
bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine (Diipmp) (7). Additionally, due to the lack
of activity of the complexes to reduce the 2-hydroxyacetophenone (HAP) to the corresponding
alcohol, we performed the reaction of the deprotonated form of HAP (2-acetylbenzenolate, O-O′)
with (1) and the complex [RuCl(p-cym)(O-O′)] (8) was isolated and characterized. Suitable
single-crystals of (4), (7) and (8) were grown in organic solvents and their molecular structures
were determined by X-ray diffraction. Electronic spectroscopy data and their analyses were
supported and interpreted using DFT and TD-DFT calculations.
2
2
. Experimental section
.1.Materials and methods
All reactions were carried out under argon atmosphere using standard Schlenk techniques.
Solvents were purified by standard methods[30] and all chemicals used were of reagent grade or
comparable purity, which were supplied and used as received from Sigma/Aldrich: RuCl .xH O,
3
2
2
-pyridinecarboxyaldhehyde, aniline, 4-chloroaniline, 4-methylaniline, 4-tert-buthylaniline, 2,6-
5

ACCEPTED MANUSCRIPT
diethylaniline, 2,6-diisopropylaniline, hexadecane, acetophenone, 4-methylacetophenone, 4-
aminoacetophenone, 4-nitroacetophenone and 2-hidroxyacetophenone.
2
.2.Instrumentation
Elemental analyses were performed with a Thermo Scientific CHNS-O FLASH 2000
micro analyzer, coupled with an ultra-microbalance Mettler Toledo Model XP6.
All NMR experiments were recorded on a Bruker Avance III 500 spectrometer operated at
1
1
2
1.75 Tesla; H was observed at 500.13 MHz, using a broadband observe probehead (BBO) at
ο
1
5 C, in CDCl solution. TMS was used for internal reference for H and the signals were labeled
3
as s = singlet, brs = broad singlet, brd = broad doublet, brt = broad triplet, d = doublet, dd =
double doublet, ddd = double double doublet, dsept = double septet, t = triplet, td = triple doublet,
tt = triple triplet, q = quartet, sept = septet, m = multiplet.
FTIR spectra were recorded in an ATR apparatus with diamond cell support or
conventional KBr cell of 0.2 mm length with a Jasco FTIR 4000 spectrometer in the 4000 – 400
−1
cm range.
UV/Vis were recorded on a Shimadzu spectrophotometer, model UV-1800, coupled with
a thermoelectrically temperature controlled cell TCC-100 (at 25.0 ± 0.1 °C), using a quartz cell (1
cm), between 200 and 800 nm.
Electrochemical data were obtained using a potentiostat/galvanostat µ-autolab type III.
−3
−1
−1
Solutions of the complexes (10 mol L ) were prepared in acetonitrile using 0.1 mol L
tetrabutylammonium hexafluorophosphate (TBAH) as the supporting electrolyte. Measurements
were made with a three-electrode configuration cell using a glassy carbon and platinum disc (
∅
2
−1
mm) as working electrode and auxiliary electrode, respectively. Ag/AgCl, 0.10 mol L TBAH in
6

ACCEPTED MANUSCRIPT
acetonitrile was used as pseudo – reference electrode. Under the conditions used, Epa for the one-
5
electron oxidation of [Fe(η -C H ) ], added to the test solutions as a standard, is +0.43 V.
5
5 2
−3
−1
Molar conductivity of solutions of the half-sandwich ruthenium complexes (10 mol L
in CH
2
Cl or CH CN) was measured with a Mettler Toledo conductivity meter model FE30,
2
3
using a Pt electrode from Mettler Toledo model inLab 710 (cell constant = 0.55 cm) with sensor
temperature coupled.
The catalytic experiments were analyzed by gas chromatography with a Thermo Scientific
Focus Gas Chromatograph equipped with an FID detector. An LM-120 column
(polyethyleneglycol) (25 m long, 0.25 mm i.d., 0.25 µm film thickness) was used for the
−
1
characterization of the catalytic products and N was the carrier gas (1.0 mL min ). The
2
temperature was programed to range from 170 °C (2 min) to 200 °C at a heating rate of 10 °C
−
1
min .
2
2
.3.Syntheses of N-N′−pyridylimine ligands.
.3.1. General procedure
All N-N –pyridylimine ligands were synthesized by condensation between 2-
′
pyridinecarboxyaldhehyde (10 mmol) and the corresponding substituted aniline (10 mmol) in
diethyl ether solution (30 mL), in the presence of p-toluenesulfonic acid (1 mmol)[31]. The
resulting beige solution was stirred for 12 h at 27°C and during this period a yellow suspension
was formed. The suspension was filtered off and crystalline solid were washed with cold diethyl
ether. In the case of Amp and Tbump a crude oil was obtained after solvent evaporation under
1
13
reduced pressure. The H and C NMR listing follow the numbering described in the general
structure, which is illustrated in the Scheme 1.
7

ACCEPTED MANUSCRIPT
N-phenyl-1-(pyridin-2-yl)methanimine (Amp)
Reddish oil. Yield 80 – 85% (1.72 g). Anal. calc. for C H N (%) (exp.): C 79.09 (79.10), H
1
2
10
2
1
5
1
.53 (5.61), N 15.37 (15.03). H NMR (CD Cl 500.13 MHz) ppm: 8.50 (dd, J = 4.8, 0.9 Hz, H-
2 2
); 8.45 (s, H-6); 8.04 (dd, J = 8.0, 0.9 Hz, H-4); 7.60 (ddd, J = 8.0, 7.4, 0.9 Hz, H-3); 7.24 (tt, J
7.7, 1.2 Hz, H-10); 7.15 (ddd, J = 7.4, 4.8, 0.9 Hz, H-2); 7.13 (dd, J = 7.7, 1.2 Hz, H-8/H-12);
=
1
3
7
.10 (td, J = 7.7, 1.5 Hz, H-9/H-11). C NMR (CD Cl 125.75 MHz) ppm: 161.47 (C-6); 155.25
2 2
(C-5); 151.61 (C-1); 150.20 (C-7); 137.19 (C-3); 129.82 (C-9/C-11); 127.24 (C-10); 125.78 (C-
−1
1
2); 122.00 (C-4); 121.64 (C-8/C-12). IV (KBr, cm ): 1633 (ν
imine), 1568 (νC=N pyridine).
C=N
N-(4-chlorophenyl)-1-(pyridin-2-yl)methanimine (Clmp)
Yellow powder. Yield 80 – 85% (1.85g). Anal. calc. for C H ClN (%) (exp.): C 66.52 (66.36)
1
2
9
2
1
%
, H 4.18 (3.95) %, N 12.92 (12.93) %. H NMR (CD OD, 500,13 MHZ) ppm: 8.53 (dd, J = 4.9,
3
1
.8 Hz, H-1); 8.43 (s, H-6); 7.80 (td, J = 7.7, 1.6 Hz, H-4); 7.74 (td, J = 7.7, 1.8 Hz, H-3); 7.25
1
3
(
dd, J = 4.9, 1.6 Hz, H-2); 7.00-6.96 (m, H-9/H-11); 6.71-6.67 (m, H-8/H-12). C NMR (CH OD
3
1
25.75 MHz) ppm: 160.84 (C-6); 157.75 (C-5); 149.72 (C-1); 148.90 (C-7); 138.07 (C-3); 129.61
−1
(
C-10); 129.61 (C-9/C-11); 126.24 (C-2); 122.33 (C-4); 115.55 (C-8/C-12). IV (KBr, cm ): 1626
(νC=N pyridine), 1565(νC=N imine).
N-(4-methylphenyl)-1-(pyridin-2-yl)methanimine (Memp)
12 2
Yellow crystals. Yield 80 – 85% (1.83 g). Anal. calc. for C13H N (%) (exp.): C 79.56 (79.40), H
1
6
1
.16 (6.10), N 14.27 (14.35). H NMR (CD OD 500.13 MHz) ppm: 8.46 (dd, J = 4.9, 1.6 Hz, H-
3
); 8.39 (s, H-6); 7.97 (dd, J = 7.9, 1.1 Hz, H-4); 7.71 (ddd, J = 7.9, 7.6, 1.6 Hz, H-3); 7.29 (ddd,
1
3
J = 7.6, 4.9, 1.1 Hz, H-2); 7.03 (brs, H-8/H-9/H-11/H-12); 2.16 (s, CH -10). C NMR (CD OD
3
3
1
25.75 MHz) ppm: 159.52 (C-6); 154.49 (C-5); 149.64 (C-1); 148.41 (C-7); 137.81 (C-10);
8

ACCEPTED MANUSCRIPT
1
1
3
37.46 (C-3); 129.82 (C-9/C-11); 125.91 (C-2); 122.35 (C-4); 121.32 (C-8/C-12); 20.32 (CH -
−1
0). IV (KBr, cm ): 1627 (ν
imine), 1565 (νC=N pyridine).
C=N
N-(4-tert-butylphenyl)-1-(pyridin-2-yl)methanimine (Tbump)
Reddish oil. Yield 70 – 80% (1.44 g). Anal. calc. for C H N (%) (exp.): C 80.63 (80.15), H
1
6
18
2
1
7
1
.61 (7.62), N 11.75 (11.99). H NMR (CD Cl 500.13 MHz) ppm: 8.53 (dd, J = 4.9, 1.6 Hz, H-
2 2
); 8.49 (s, H-6); 8.07 (dd, J = 7.8, 1.1 Hz, H-4); 7.64 (ddd, J = 7.8, 7.5, 1.6 Hz, H-3); 7.32 (brd,
J = 8.5 Hz, H-8/H-12); 7.19 (ddd, J = 7.5, 4.9, 1.1 Hz, H-2); 7.13 (brd, J = 8.5 Hz, H-9/H-11);
t
13
1
1
1
.21 (s, Bu-10). C NMR (CD
2 2
Cl 125.75 MHz) ppm: 160.67 (C-6); 155.57 (C-5); 150.58 (C-1);
50.19 (C-7); 148.95 (C-10); 137.03 (C-3); 126.71 (C-9/C-11); 125.51 (C-2); 121.87 (C-4);
t
t
−1
21.38 (C-8/C-12); 35.05 ( Bu C(CH ) ); 31.79 ( Bu C(CH ) ). IV (KBr, cm ): 1627 (ν
C=N
3
3
3 3
imine), 1566 (νC=N pyridine).
N-(2,6-diethylphenyl)-1-(pyridin-2-yl)methanimine (Diemp)
Yellow powder. Yield 80 – 85% (1.89 g). Anal. calc. for C H N (%) (exp.): C 80.63 (80.42), H
1
6
18
2
1
7
1
.61 (7.62), N 11.75 (11.99). H NMR (CD
2 2
Cl 500.13 MHz) ppm: 8.58 (dd, J = 4.8, 1.6 Hz, H-
); 8.21 (s, H-6); 8.16 (dd, J = 7.9, 1.3 Hz, H-4); 7.72 (ddd, J = 7.9, 7.5, 1.6 Hz, H-3); 7.28 (ddd,
J = 7.5, 4.8, 1.3 Hz, H-2); 6.99 (d, J = 8.5 Hz, H-9 or H-11); 6.99 (d, J = 6.7 Hz, H-9 or H-11);
6
8
1
1
.92 (dd, J = 8.5, 6.7 Hz, H-10); 2.39 (q, J = 7.5 Hz, CH -8/CH -12); 1.02 (t, J = 7.5 Hz, CH -
2 2 3
1
3
/CH -12). C NMR (CD Cl 125.75 MHz) ppm: 164.04 (C-6); 155.16 (C-5); 150.44 (C-1);
3
2
2
50.22 (C-7); 137.20 (C-3); 133.45 (C-8/C-12); 126.90 (C-9/C-11); 125.91 (C-10); 124.79 (C-2);
−1
21.55 (C-4); 23.82 (Diemp CH
2
CH
3
); 15.06 (Diemp CH
2
CH
3
). IV (KBr, cm ): 1642 (νC=N
imine), 1565 (νC=N pyridine).
9

ACCEPTED MANUSCRIPT
N-[2,6-bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine (Diipmp)
Yellow crystals. Yield 90 – 95% (1.98 g). Anal. calc. for C H N (%) (exp.): C 81.77 (80.28), H
1
8
22
2
1
7
1
.62 (8.09), N 10.60 (10.88). H NMR (CDCl 500.13 MHz) ppm: 8.73 (dd, J = 4.9, 1.6 Hz, H-
3
); 8.31 (s, H-6); 8.26 (dd, J = 7.9, 1.2 Hz, H-4); 7.85 (ddd, J = 7.9, 7.6, 1.6 Hz, H-3); 7.41 (ddd,
J = 7.6, 4.9, 1.2 Hz, H-2); 7.17 (d, J = 8.7 Hz, H-9 or H-11); 7.17 (d, J = 6.6 Hz, H-9 or H-11);
7
6
.12 (dd, J = 8.7, 6.1 Hz, H-10); 2.97 (sept, J = 6.9 Hz, CH(CH ) -8/CH(CH ) -12); 1.18 (d, J =
3 2 3 2
1
3
3 2 3 2 3
.9 Hz, CH(CH ) -8/CH(CH ) -12). C NMR (CDCl 125.75 MHz) ppm: 162.97 (C-6); 154.41
(C-5); 149.70 (C-1); 148.40 (C-7); 137.26 (C-3); 136.74 (C-8/C-12); 125.29 (C-10); 124.47 (C-
2
); 123.12 (C-9/C-11); 121.33 (C-4); 27.98 (Diipmp C(CH ); 23.44 (Diipmp C(CH ). IV
3
)
2
3 2
)
−1
(
KBr, cm ): 1633 (ν
imine), 1568 (νC=N pyridine).
C=N
2
.3.2. Syntheses of half-sandwich ruthenium (II) complexes
The general synthetic route used to synthesize the half-sandwich ruthenium (II)
complexes with general formula [RuCl(p-cym)(N-N′)](PF ) is described as follows:
6
Under an inert atmosphere of argon, [RuCl(µ-Cl)(p-cym)] (0.1 g; 0.16 mmol) was
2
dissolved in methanol (20 mL) in a Schlenk tube (100 mL) and the appropriate N-N′-
6
pyridylimine ligand (0.35 mmol) and KPF (0.066g; 0.35 mmol) were added after total
dissolution of the ruthenium precursor. The resulting red-brownish solution was kept at 27 °C and
magnetically stirred for 18 h. During this period, the color changes and a yellow solution was
obtained. Then, the solvent was removed under reduced pressure and the solid residue was
2 2
dissolved in CH Cl (3.0 mL), passed through a celite pad in order to remove KCl. The filtered
was collected in a Schlenk flask (100 mL) and addition of diethyl ether (10 mL) yielded a yellow
solid. The solid was separated by filtration, washed with diethyl ether (3 x 5 mL) and dried under
reduced pressure.
10

ACCEPTED MANUSCRIPT
The synthesis and structural characterization of (3) [23] and (7) [25] were reported
previously by Friedrich and co-workers, thus, only unpublished results will be discussed here.
1
13
The H and C NMR listing follow the numbering described in the general structure,
which is illustrated in the Scheme 1.
RuCl(p-cym)(Amp)]PF (2)
[
6
6 2
Brown powder, yield 85 – 95 % (0.093 g). Anal. calc. for C22H24ClF N PRu (%) (exp.): C 44.19
1
(
44.56), H 4.05 (4.35), N 4.69 (4.48). H NMR (CD Cl 500.13 MHz) ppm: 9.24 (brd, J = 5.6 Hz,
2
2
H-1); 7.69 (dd, J = 5.6, 2.6 Hz, H-2); 8.09-8.01 (m, H-3/H-4); 8.37 (s, H-6); 7.68-7.63 (m, H-8/H-
2); 7.55-7.46 (m, H-9/H-10/H-11); 5.65 (d, J = 6.2 Hz, p-cym); 5.38 (d, J = 6.2 Hz, p-cym); 5.32
d, J = 6.2 Hz, p-cym); 5.27 (d, J = 6.2 Hz, p-cym); 2.54 (dsept, J = 6.9, 7.0 Hz, CH(CH ) -16);
1
(
3
2
13
2
.14 (s, CH -13); 1.03 (d, J = 7.0 Hz, CH(CH ) -16); 1.01 (d, J = 6.9 Hz, CH(CH ) -16). C
3
3 2
3 2
NMR (CD
2
Cl
2
125.75 MHz) ppm: 166.16 (C-6); 156.33 (C-5); 154.84 (C-1); 152.69 (C-7);
1
1
40.30 (C-3); 130.98 (C-10); 130.56 (C-2); 130.45 (C-9/C-11); 129.91 (C-4); 122.73 (C-8/C-12);
07.71, 104.70, 87.4, 86.6, 86.5 and 85.9 (C-13 to C-18 p-Cym); 32.00 (CH(CH ) -16); 22.47
3
2
−1
and 22.28 (CH(CH ) -13/16); 19.20 (p-Cym CH ). IV (KBr, cm ): 1618 (ν
imine), 1559
3
2
3
C=N
−5
−1
−1
−1
(ν
C=N pyridine). UV/Vis (CH
3
CN, 5 × 10 mol L ) λ/nm (log ε, L mol cm ): 310 (3.94); 422
−1
(
3.52). CV (CH CN / HTBA 0.1 mol L ): E = 1.18 V, E = 1.13 V, E½ = 1.15 V. Molar
3
ox
red
−3
−1
−1
2
−1
conductivity in CH
3
CN (or CH
2 2
Cl ) (1.0 × 10 mol L ) Λm (ohm cm mol ): 73.15 (11.93).
[
RuCl(p-cym)(Clmp)]PF
6
(3)
2 6 2
Yellow powder, yield 95% (0.098 g). Anal. calc. for C22H23Cl F N PRu (%) (exp.): C 41.79
1
(
42.12), H 3.67 (3.88), N4.43 (4.53). H NMR (CD Cl 500.13 MHz) ppm: 9.22 (brd, J = 5.5 Hz,
2
2
H-1); 7.69 (dd, J = 5.5, 2.6 Hz, H-2); 8.08-8.01 (m, H-3/H-4); 8.38 (s, H-6); 7.66 (d, J = 8.5 Hz,
H-8/H-12); 7.48 (d, J = 8.5 Hz, H-9/H-11); 5.63 (d, J = 6.2 Hz, p-cym); 5.39 (d, J = 6.2 Hz, p-
11

ACCEPTED MANUSCRIPT
cym); 5.35 (d, J = 6.1 Hz, p-cym); 5.27 (d, J = 6.1 Hz, p-cym); 2.54 (dsept, J = 6.9, 7.0 Hz,
CH(CH ) -16); 2.13 (s, CH -13); 1.03 (d, J = 7.0 Hz, CH(CH ) -16); 1.01 (d, J = 6.9 Hz,
3
2
3
3 2
1
3
CH(CH ) -16). C NMR (CD Cl 125.75 MHz) ppm: 166.82 (C-6); 156.25 (C-5); 154.78 (C-1);
3
2
2
2
1
1
51.07 (C-7); 140.37 (C-3); 136.79 (C-10); 130.85 (C-4); 130.60 (C-9/C-11); 130.02 (C-2);
24.30 (C-8/C-12); 107.85, 104.63, 87.37, 86.57, 86.31 and 85.69 (C-13 to C-18 p-Cym); 31.77
−1
(
CH(CH
3 2 3 2 3
) -16); 22.47 and 22.27 (CH(CH ) -13/16); 19.12 (p-Cym CH ). IV (KBr, cm ): 1617
−5
−1
−1
(
νC=N imine), 1562 (νC=N pyridine). UV/Vis (CH CN, 5 ×10 mol L ) λ/nm (log ε, L mol
3
−1
−1
cm ): 257 (4.14); 317 (4.08), 421 (3.61). CV (CH
3
CN / HTBA 0.1 mol L ): Eox = 1.20 V, Ered
=
−3
−1
−1
1
.15 V, E½ = 1.17 V. Molar conductivity in CH CN (or CH Cl ) (1.0 × 10 mol L ) Λm (ohm
3
2
2
2
−1
cm mol ): 79.53 (9.95).
[
RuCl(p-cym)(Memp)]PF (4)
6
2 6
Yellow powder, yield 85 – 90% (0.094 g). Anal. calc. for C23H26ClN F PRu (%) (exp.): C 45.12
1
(
45.40), H 4.28 (4.27), N 4.58 (4.58). H NMR (CD
2
Cl
2
500.13 MHz) ppm: 9.21 (brd, J = 5.5 Hz,
H-1); 7.67-7.60 (m, H-2); 8.04-7.97 (m, H-3/H-4); 8.32 (s, H-6); 7.28 (d, J = 7.9 Hz, H-8/H-12);
.52 (d, J = 7.9 Hz, H-9/H-11); 5.63 (d, J = 6.2 Hz, p-cym); 5.37 (d, J = 6.2 Hz, p-cym); 5.29 (d,
J = 6.1 Hz, p-cym); 5.20 (d, J = 6.1 Hz, p-cym); 2.54 (dsept, J = 6.9, 7.0 Hz, CH(CH ) -16); 2.12
7
3
2
13
(
s, CH -13); 0.99 (d, J = 7.0 Hz, CH(CH ) -16); 0.97 (d, J = 6.9 Hz, CH(CH ) -16). C NMR
3 3 2 3 2
(
CDCl 125.75 MHz) ppm: 165.31 (C-6); 156.26 (C-5); 154.90 (C-1); 150.23 (C-7); 141.72 (C-
3
1
1
2
0); 140.25 (C-3); 130.89 (C-9/C-11); 130.27 (C-2); 129.70 (C-4); 122.60 (C-8/C-12); 107.50,
04.80; 87.37, 86.57, 86.31 and 85.69 (C-13 to C-18 p-Cym); 31.69 (CH(CH -16); 22.41 and
imine), 1560 (νC=N
3 2
)
−1
2.25 (CH(CH ) -13/16); 19.12 (p-Cym CH ). IV (KBr, cm ): 1618 (ν
C=N
3
2
3
−5
−1
−1
−1
3
pyridine). UV/Vis (CH CN, 5 ×10 mol L ) λ/nm (log ε, L mol cm ): 257 (4.11); 317 (4.08),
12

ACCEPTED MANUSCRIPT
−1
4
23 (3.62). CV (CH CN / HTBA 0.1 mol L ): E = 1.17 V, E = 1.12 V, E½ = 1.14 V. Molar
3 ox red
−3
−1
−1
2
−1
conductivity in CH CN (or CH Cl ) (1.0 × 10 mol L ) Λm (ohm cm mol ): 74.58 (13.91).
3
2
2
[
RuCl(p-cym)(Tbump)]PF (5)
6
Yellow powder, yield 85% (0.090). Anal. Calc. for C H ClN F PRu (%): calc. (exp.) C 47.75
26
32
2 6
1
(
47.64), H 4.93 (4.77), N 4.28 (4.68). H NMR (CD
H-1); 7.68-7.62 (m, H-2); 8.04-7.99 (m, H-3/H-4); 8.34 (s, H-6); 7.59 (d, J = 8.1 Hz, H-8/H-12);
.51 (d, J = 8.1 Hz, H-9/H-11); 5.66 (d, J = 6.2 Hz, p-cym); 5.39 (d, J = 6.2 Hz, p-cym); 5.33 (d,
J = 6.1 Hz, p-cym); 5.23 (d, J = 6.1 Hz, p-cym); 2.54 (dsept, J = 6.9, 7.0 Hz, CH(CH ) -16); 2.14
2 2
Cl 500.13 MHz) ppm: 9.23 (brd, J = 5.5 Hz,
7
3
2
t
(
s, CH -13); 1.31 (s, Bu C(CH ) ); 1.00 (d, J = 7.0 Hz, CH(CH ) -16); 0.99 (d, J = 6.9 Hz,
3 3 3 3 2
13
CH(CH ) -16). C NMR (CDCl 125.75 MHz) ppm: 165.31 (C-6); 156.26 (C-5); 154.90 (C-1);
3
2
3
1
1
50.23 (C-7); 140.25 (C-3); 130.89 (C-9/C-11); 130.85 (C-10); 130.27 (C-2); 129.70 (C-4);
22.60 (C-8/C-12); 107.50, 104.80; 87.37, 86.57, 86.31 and 85.69 (C-13 to C-18 p-Cym); 31.69
t
(
CH(CH
3
)
2
-16); 22.44 and 22.24 (CH(CH
3
)
2
-13/16); 19.12 (p-Cym CH
3
); 31.79 ( Bu C(CH
3
)
3
);
t
−1
2
5
2.24 ( Bu C(CH ) ). IV (KBr, cm ): 1617 (ν
imine), 1562 (νC=N pyridine). UV/Vis (CH CN,
C=N 3
3
3
−
5
−1
−1
−1
×10 mol L ) λ/nm (log ε, L mol cm ): 259 (4.08); 329 (4.03), 420 (3.61). CV (CH CN /
3
−1
HTBA 0.1 mol L ): E = 1.18 V, E = 1.15 V, E½ = 1.16 V. Molar conductivity in CH CN (or
ox
red
3
−3
−1
−1
2
−1
CH
2 2
Cl ) (1.0 × 10 mol L ) Λm (ohm cm mol ): 75.29 (12.54).
[
RuCl(p-cym)(Diemp)]PF (6)
6
Orange powder, yield 90 % (0.096 g). Anal. Calc. for C H ClN F PRu (%): calc. (exp.) C 47.75
2
6
32
2 6
1
(
48.13), H 4.93 (5.01), N 4.28 (4.33). H NMR (CD
s, H-6); 8.08 (brd, J = 7.3 Hz, H-3); 8.01 (brd, J = 7.9 Hz, H-4); 7.76 (brs, H-2); 7.36 (brt, J =
.2, H-10); 7.31 (d, J = 7.2 Hz, H-9); 7.25 (brd, J = 7.2 Hz, H-11); 5.42 (brs, p-cym); 5.34 (brd, J
6.2 Hz, p-cym); 5.29 (brs, p-cym); 5.08 (brs, p-cym); 3.10-2.98 (m, CH(CH ) -12); 2.72-2.61
2 2
Cl 500.13 MHz) ppm: 9.36 (brs, H-1); 8.37
(
7
=
3
2
13

ACCEPTED MANUSCRIPT
3 2 3 2 3 2
(m, CH(CH ) -8); 2.61-2.54 (m, CH(CH ) -16); 2.54-2.43 (m, CH(CH ) -12); 2.33-2.21 (m,
CH(CH ) -8); 2.08 (s, CH -13); 1.06 (brs, CH(CH ) -16); 1.22 (brs, CH(CH ) -12); 0.98 (brs,
3
2
3
3 2
3 2
13
CH(CH ) -8). C NMR (CDCl 125.75 MHz) ppm: 170.81 (C-6); 156.65 (C-5); 154.32 (C-1);
3
2
3
1
50.11 (C-7); 140.49 (C-3); 138.10 (C-8); 134.77 (C-12); 130.45 (C-9); 130.22 (C-11); 130.00
(C-10); 128.29 (C-2); 127.61 (C-4); 109.40, 101.17; 88.58, 88.14, 85.96 and 85.78 (C-13 to C-18
p-Cym); 31.72 (CH(CH ) -16); 26.18 and 24.92 (Diemp CH CH ); 22.54, 22.46 and 18.82 (p-
3
2
2
3
−1
Cym CH
3
); 16.26 and 15.76 (Diemp -CH
2
CH
3
). IV (KBr, cm ): 1616 (νC=N imine), 1559 (νC=N
−5
−1
−1
−1
pyridine). UV/Vis (CH CN, 5 ×10 mol L ) λ/nm (log ε, L mol cm ): 264 (4.11); 364 (3.65),
3
−1
4
27 (3.51). CV (CH
3
CN / HTBA 0.1 mol L ): Eox = 1.21 V, Ered = 1.16 V, E½ = 1,18 V. Molar
−3
−1
−1
2
−1
conductivity in CH CN (or CH Cl ) (1.0 × 10 mol L ) Λm (ohm cm mol ): 78.92 (16.33).
3
2
2
[
RuCl(p-cym)(Diipmp)]PF (7)
6
Yellow powder, yield 95 % (0.105 g). Anal. Calc. for C H ClN F PRu (%): calc. (exp.) C 49.31
2
7
36
2 6
1
(
49.14), H 5.32 (5.38), N 4.11 (4.01). H NMR (CD Cl 500.13 MHz) ppm: 9.36 (brd, J = 5.5 Hz,
2 2
H-1); 8.28 (s, H-6); 8.11 (ddd, J = 7.9, 7.6, 1.1 Hz, H-3); 8.03 (brd, J = 7.9 Hz, H-4); 7.80 (ddd, J
7.6, 5.5, 1.6 Hz, H-2); 7.44 (brt, J = 8.0, H-10); 7.36 (d, J = 8.0 Hz, H-9); 7.35 (d, J = 8.4 Hz,
H-11); 5.62 (d, J = 6.2 Hz, p-cym); 5.47 (d, J = 6.2 Hz, p-cym); 5.33 (d, J = 6.1 Hz, p-cym); 5.05
=
(
d, J = 6.1 Hz, p-cym); 3.69 (sep, J = 6.8 Hz, CH(CH ) -12); 2.66 (sep, J = 6.7 Hz, CH(CH ) -8);
3 2 3 2
2
1
.54 (dsept, J = 6.9, 7.0 Hz, CH(CH ) -16); 2.15 (s, CH -13); 1.43 (d, J = 6.8 Hz, CH(CH ) -12);
3 2 3 3 2
.26 (d, J = 6.8 Hz, CH(CH ) -12); 1.13 (d, J = 6.7 Hz, CH(CH ) -8); 0.84 (d, J = 6.7 Hz,
3
2
3 2
13
CH(CH ) -8). C NMR (CDCl 125.75 MHz) ppm: 170.97 (C-6); 156.87 (C-5); 154.18 (C-1);
3
2
3
1
48.84 (C-7); 142.52 (C-12); 140.55 (C-8); 139.90 (C-3); 130.54 (C-10); 130.31 (C-9); 130.23
C-11); 125.63 (C-2); 125.22 (C-4); 108.46, 102.31; 88.32, 87.21, 86.36 and 85.28 (C-13 to C-18
p-Cym); 31.65 (CH(CH -16); 28.75, 28.47, 27.56 and 26.27 (Diipmp C(CH ); 24.00 (Diipmp
(
3
)
2
3 2
)
14

ACCEPTED MANUSCRIPT
−1
C(CH ) ); 22.98, 22.39 and 18.97 (p-Cym CH ). IV (KBr, cm ): 1615 (ν
imine), 1563 (νC=N
3
2
3
C=N
−5
−1
−1
−1
pyridine). UV/Vis vis (CH CN, 5 ×10 mol L ) λ/nm (log ε, L mol cm ): 266 (4.08), 368
3
−1
(
3.51), 428 (3.58). CV (CH CN / HTBA 0.1 mol L ): E = 1.20 V, E = 1.16 V, E½ = 1.18 V.
3
ox
red
−3
−1
−1
2
−1
Molar conductivity in CH
3
2 2
CN (or CH Cl ) (1.0 × 10 mol L ) Λm (ohm cm mol ): 71.72
(16.88).
[RuCl(p-cym)(O-O′)] (8)
Deprotonation of 2-hydroxyacetophenone (HAP, 40 µL; 0.33 mmol) was carried out in a
Schlenk tube (100 mL) with a solution of methanol (5 mL) containing NaOH (14.6 mg; 3.6
mmol) under Ar atmosphere. After 1h of reaction, the binuclear complex [RuCl(µ-Cl)(p-cym)]2
(0.1 g; 0.16 mmol) was added and the reaction was magnetically stirred for 24 h at 60 °C. Then,
the solvent removed under reduced pressure and the solid residue was dissolved in CH Cl (3.0
2
2
mL), passed through a celite pad in order to remove NaCl. The filtered was collected in a Schlenk
flask (100 mL) and addition of hexane (10 mL) yielded a brown solid. The solid was separated by
filtration, washed with hexane (3 x 5 mL) and dried under reduced pressure.
Brown powder, yield 95 % (124.76 mg). Anal. Calc. for C H ClO Ru (%): calc. (exp.) C 53.27
18
21
2
1
(
53.38), H 5.21 (5.29). H NMR (CDCl 500.13 MHz) ppm: 7.36 (d, J = 8.0 Hz, 1H 2-
3 HH
acetylbenzenolate); 7.17 (t, JHH = 8.0 Hz, 1H 2-acetylbenzenolate); 6.77 (d, JHH = 8.0 Hz, 1H, 2-
acetylbenzenolate); 6.36 (t, JHH = 8.0 Hz, 1H 2-acetylbenzenolate); 5.21 (dd, JHH = 5.9 Hz, 2H p-
cym.) 2.89 (sept. JHH = 6.9 Hz, p-cym.); 2.51 (s, CH
3
, 2-acetylbenzenolate); 2.22 (s, CH
3
, p-
1
3
cym.);1.32 (d, JHH = 6.9 Hz, 6H p-cym.). C NMR (CDCl 125,75 MHz) ppm: 198.53 (C-7);
3
1
70.34 (C-1); 137.14 (C-3); 133.15 (C-5); 125.08 (C-6); 120.58 (C-4); 114.72 (C-2); 100.36,
9
7.82, 83.47, 82.81, 79.73, 79.41 (p-Cym. arom.); 31.49 (p-Cym. CH(CH ) .); 27.19 (2-
3
2
−1
3 3
acetylbenzenolate CH ); 22.72, 22.62 and 18.23 (p-Cym CH ). IV (KBr, cm ): 1587 (νC=O).
15

ACCEPTED MANUSCRIPT
2
.4. Catalytic Experiments
A standard procedure for reduction of aryl ketones is described as follow: In a Schlenk
flask, the ketone (acetophenone or 4-methylacetophenone) (10 mmol) was dissolved in 2-
propanol (2 mL) and refluxed at 82 °C within 5 min under inert Ar atmosphere. In a separate
flask, the ruthenium complex (10 µmol) was dissolved in degassed 2-propanol (3 mL) in the
−
1
presence of 1 mL of KOH (0.2 mol L in 2-propanol), and then, the resulting suspension was
transferred via cannula to the reaction flask and refluxed for 1h at 82 °C. After that, an aliquot
(1.0 mL) was withdrawn and diluted to 10 mL with an acid solution of 2-propanol (10 µL HCl;
−
1
1
1.0 mmol L ). Conversions were determined by gas chromatography using hexadecane as an
−
1
internal standard (1.46 µL; 0.1 mmol L ). [Ru]/substrate/KOH = 1/1000/20.
2
.5. Kinetic experiments
The kinetic studies of the transfer-hydrogenation of acetophenone were carried out in a
3
stainless-steel autoclave Parr – Model 4842 with a volume capacity of 100 cm equipped with an
overhead magnetic stirrer, a digital pressure indicator and a thermocouple to record temperature.
The autoclave was equipped with an electrical heating/cooling system to control the temperature
inside the vessel. In a typical reaction, the catalyst precursor (ruthenium complexes (3) and (7),
(10 µmol) was dissolved in 2-propanol (58 mL) inside the autoclave in the presence 1 mL of
−
1
KOH (0.2 mol L in 2-propanol) and acetophenone (10 mmol) under Ar atmosphere (
Ru]/substrate/KOH = 1/1000/20). After that, the autoclave was repeatedly flushed with H (3
times), and then the autoclave was pressurized with H (10 bar). The autoclave was heated to the
[
2
2
desired temperature (60 – 80°C), and stirring at 450 rpm, for 120 min. The time-dependent
analysis of the catalyzed reduction of acetophenone to 1-phenylethanol was performed after
withdrawing aliquots (1.0 mL) every 5 min, for 20 min, and then every 10 min until the final time
16

ACCEPTED MANUSCRIPT
(120 min). Each aliquot was diluted to 10 mL with an acid solution of 2-propanol (10 µL HCl;
−
1
−1
1
1.0 mmol L ) in the presence of hexadecane (1.46 µL; 0.1 mmol L ) and analyzed by gas
chromatography (GC – FID).
2
.6. X-ray diffraction data
The single-crystals were mounted on a goniometer in a Bruker KAPPA APEX II DUO
diffractometer using graphite-monochromated MoKα (λ = 0.71073 Å) radiation. The final unit
cell parameters were based on all reflections. Data were collected with the BRUKER APEX2
software package, with integration and scaling of the reflections performed using the BRUKER
SAINT program [32],[33]. Absorption correction was carried out by the multiscan method [33].
The structures were solved by direct methods with SHELXS-97 and models were refined by full-
2
matrix least-squares on F with SHELXL-2016 [34]. All hydrogen atoms were stereochemically
positioned and refined applying the riding model [34]. The MERCURY views were prepared
with Mercury 3.10.3 [35]. Table 1 summarizes the data collection and experimental details for
[
RuCl(p-cym)(Memp)PF (4), [RuCl(p-cym)(Diipmp)]PF (7) and [RuCl(p-cym)(O-O′)] (8).
6
6
2
.7. Theoretical calculations
All structures were optimized with the Density Functional Theory (DFT) method based on
the M06 functional [36]. The basis set employed was the Los Alamos effective core potential and
double-zeta valence basis set (LanL2DZ) [37] for ruthenium and 6-31G(d) [38] for the remaining
atoms. The solvation with acetonitrile was simulated with the use of the integral equation
formalism variant of Polarizable Continuum Model (IEF-PCM). The absorption spectra were
obtained with TD-DFT formalism and the above mentioned functional and basis set. All
calculations were carried out using the software Gaussian 09 [39].
17

ACCEPTED MANUSCRIPT
Table 1. Crystal data and structure refinement of the [RuCl(p-cym)(Memp)PF
6
(4), [RuCl(p-
cym)(Diipmp)PF (7) and [RuCl(p-cym)(O-O′)] (8).
6
[
RuCl(p-cym)(Memp)PF
PRu
611.95
296(2)
0.71073
6
[RuCl(p-cym)(Diipmp)PF
6
[RuCl(p-cym)(O-O′)]
Ru
405.87
296(2)
0.71073
Triclinic
P-1
Empirical formula
Formula weight
Temperature (K)
Wavelength Å
Crystal system
Space group
Unit cell dimensions
a(Å)
C
23
H26ClF
6
N
2
C
28
H
36ClF
6
N
2
PRu
18 2
C H21ClO
682.08
296(2)
0.71073
Monoclinic
P2 /n
Monoclinic
P2 /c
1
1
9.0203(11)
26.272(3)
11.2706(14)
90
17.5444(8)
10.2274(5)
17.7350(8)
90
7.6484(2)
9.4401(3)
12.7883(4)
72.8300(10)
80.4030(10)
80.1890(10)
862.61(4)
b(Å)
c(Å)
α(°)
β(°)
γ(°)
V(Å )
109.913(4)
90
2511.2(5)
108.997(2)
90
3008.9(2)
3
Z
4
4
2
Density (calculated) 1.619
1.506
1.563
3
(
Mg/m )
Absorption
coefficient (mm )
F(000)
Crystal size (mm )
Theta range for data 2.072 to 26.538
collection (°)
0.853
1232
0.721
1.067
-
1
1392
412
3
0.380 x 0.280 x 0.270
0.250 x 0.100 x 0.040
1.988 to 26.412
0.250 x 0.160 x 0.070
1.680 to 26.448
Index ranges
-11 ≤ h ≤ 11
-21 ≤ h ≤ 21
-12 ≤ k ≤ 12
-22 ≤ l ≤ 22
46914
6168 [R(int) = 0.0453]
-9 ≤ h ≤ 9
-
-
32 ≤ k ≤ 32
14 ≤ l ≤ 14
-11 ≤ k ≤ 11
-15 ≤ l ≤ 15
11623
Reflections collected
Independent
35254
5189[R(int) = 0.0431]
3542 [R(int) = 0.0208]
reflections
Completeness to theta 25.242°, 99.9 %
maximum (%)
25.242°, 100.0 %
25.24°, 100 %
Absorption
correction[40]
Refinement method
Semi-empirical
equivalents
from Semi-empirical
equivalents
from Semi-empirical
equivalents
from
Full-matrix least-squares
Full-matrix least-squares Full-matrix least-squares
on F2
2
2
on F
on F
Data
/
restraints
/
5189 / 0 / 311
6168 / 54 / 390
3542 / 0 / 203
parameters
18

ACCEPTED MANUSCRIPT
2
Goodness-of-fit on F
Final indices R = 0.0597
I>2
R indices (all data)
1.212
1
1.042
1.058
R
R = 0.0504,
R = 0.0233
1
1
[
σ
(I)]
wR
2
= 0.1382
wR
2
= 0.1287
wR
2
= 0.0580
R = 0.0653
1
R = 0.0670,
1
R = 0.0267
1
wR
2
= 0.1417
wR
2
= 0.1429
2
wR = 0.0604
Largest diff. peak and 1.037 and -1.038
hole (e. Å )
1.804 and -3.397
0.441 and -0.257
-3
3
. Results and Discussion
.1. Syntheses and structural characterization
The half-sandwich ruthenium (II) complexes with N-N′–pyridylimine ligands were
obtained from the well-known binuclear complexes described by Bennett and Smith [41],
3
[
RuCl(µ-Cl)(p-cym)] . The two chlorido bridges between the metal centers in (1) were broken in
2
−
the presence of these chelating ligands, in methanol solution containing PF salt, producing two
6
equivalents of an orange – yellow mononuclear complexes with general formula [RuCl(p-
6
cym)(N-N′)](PF ). The elemental analyses (%C, %H, %N) agree with the proposed formulation
for the complexes (2) to (7) and the molar conductivities were measured in CH Cl or CH CN
2
2
3
solutions, and are in the accepted range for 1:1 electrolytes. Scheme 1 contains the general
structure and numbering of the half-sandwich ruthenium complexes reported here. All complexes
are air stable and soluble in polar solvents such as dichloromethane, acetone or acetonitrile, and
insoluble in apolar solvents, such as hexane or diethyl ether.
19

ACCEPTED MANUSCRIPT
Scheme 1: Synthetic route, general structure and numbering of the half-sandwich ruthenium (II)
complexes [42].
The infrared spectra of the complexes (2) – (7) confirmed the coordination of the ligands
to the ruthenium center (
−1
Table 2). The νC=Nimine stretching frequencies are shifted from the range 1642 – 1626 cm
−1
for the free ligands to 1618 – 1615 cm after coordination. These shifts are due to the electron
withdrawing nature of the ligands, which allows the M→L back-bonding interaction causing the
weakening of the C=N bond and the νC=Nimine is shifted to lower wavenumbers. The νC=Npyridine is
−1
−1
also shifted to lower wavenumbers, from the range 1568 – 1562 cm to 1559 – 1563 cm . The
intensity of the bands for the metal complexes is also lower than for the free ligands, which
indicates the loss of degrees of freedom upon coordination of the N-N’ pyridylimine ligands to
the ruthenium center. This behavior may also be attributed to the change of symmetry between
20

ACCEPTED MANUSCRIPT
the species. In addition, the presence of νPF6− counter-ion was confirmed by the occurrence of an
−1
intense band around 841 – 835 cm .
1
13
The coordination of the N- N′–pyridylimine ligands was also confirmed by H and C
1
NMR spectra, by comparing the spectra of the free ligands and the complexes (2) – (7). The H
NMR spectra show a doublet signal for the pyridine hydrogen in the range 9.21 – 9.36 ppm (See
1
13
the H and C NMR spectra in the supplementary material), which is shifted when compared to
the same hydrogen signal in the free ligand. These signals are shifted to higher frequencies, due
to the deshielding of the α-hydrogen of pyridine (H-1) owing to the coordination to the metal
center (
1
Table 2). Additionally, is also observed in the H NMR spectra, a singlet signal in the
range 8.28 – 8.38 ppm corresponding to the hydrogen nucleus attributed to the azomethine group
(HC=N; H-6). In general, they were shielded when compared to the hydrogen of the azomethine
group in the free ligands (8.21 – 8.49 ppm). The coordination of imine nitrogen weakens the C=N
1
bond, thereby shielding the hydrogen of the azomethine group (see H-6 in the H NMR spectra in
the supplementary material). These results confirm the coordination of the N-N’–pyridylimine
ligands to the ruthenium center, which agree with the infrared data.
1
It is known that the aromatic H nuclei signals for the coordinated arene are found in the
range 4 – 6 ppm [43]. However, the coordination of the N-N′–pyridylimine ligand to the
ruthenium center provides a loss of the two-fold symmetry of the p-cymene arene. As a
consequence, it is observed an arrangement of four doublets in the region 5.30 – 6.00 ppm for the
aromatic hydrogen nuclei of the p-cymene. Additionally, the lower symmetry of the complexes is
1
confirmed by the H NMR spectrum of (7) (Fig. S.11), in which three septet signals attributed to
the isopropyl hydrogen (H-8, H-12 and H-16) of the p-cymene and N-N′–pyridylimine ligands
21

ACCEPTED MANUSCRIPT
are observed. This behavior has also been observed for similar ruthenium (II) complexes
previously reported [25].
1
3
The C NMR spectra of complexes (2) – (7) showed that coordination also affects the
chemical shift of methine group of imine ligands observed in the range 159.52 – 164.04 ppm, for
the free ligand, while for the complexes the range is shifted to 165.31 – 170.97 ppm (
Table 2).
1
13
Table 2: Selected IR stretching frequencies, and H and C NMR chemical shifts of the
pyridylimine ligands and complexes (2) – (7).
-
1
1
13
Free
Complex
IR stretching (cm )
H NMR (ppm)
C NMR (ppm)
ligand
HC=Nimine
HC=Npyridine
HC=Nimine
ν
C= N imine
1633
1618
1626
1617
1627
1618
1627
1617
1642
1616
1633
1615
ν
C= N pyridine
1568
1559
1565
1562
1565
1560
1566
1562
1565
1559
1568
1563
Amp
8.45
8.37
8.43
8.38
8.39
8.32
8.49
8.34
8.21
8.37
8.31
8.28
8.50
9.24
8.53
9.22
8.46
9.21
8.53
9.23
8.58
9.36
8.73
9.36
161.47
166.16
160.84
166.82
159.52
165.31
160.67
165.31
164.04
170.81
162.97
170.97
(
(
(
(
(
(
2)
3)
4)
5)
6)
7)
Clmp
Memp
Tbump
Diemp
Diipmp
The X-ray structure of (4) has a ruthenium center coordinated to the N-(4-methylphenyl)-
-(pyridin-2-yl)methanimine (Memp), to a Cl atom and to the p-cymene aromatic ring, resulting
1
in a piano-stool geometry (Figure 1). The restricted bite angle of the Memp, N(1)-Ru-N(2) angle
76.40° (17) supported the distorted structure and the torsion angle C6-N2-C7-C12 (125.8° (6))
=
supported the two planes described by the pyridine and the substituted phenyl ring. As a result,
the substituted phenyl ring is almost coplanar to the p-cymene ring, while the pyridine ring is
inclined relative to the position of the phenyl ring.
22

ACCEPTED MANUSCRIPT
The chloride atom is on the same side of the methyl group of the p-cymene ligand. This
behavior is also observed in related complexes previously described in the literature[25].
Complex (7) has crystallized in the monoclinic crystal system and P21/c space group,
which contains the N-[2,6-bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine (Diipmp), was
previously reported by Friedrich et al.[25] Here, the structure was found to belong to the P21/n
space group, with a lower value of β angle. In both structures, the classical piano-stool geometry
is also observed, with the chlorido ligand oriented to the same side of the methyl group of the p-
cymene ligand. The pyridyl ring of the Diipmp has an inclined angle much more apparent with
respect to the imine ring than the Memp coordinated to the ruthenium center (See Figure 2).
Herein, the X-ray structure of (7) has a torsion angle C6-N2-C7-C12 of the 82.5° (5), while in the
structure previously described by Friedrich et al. [25] the torsion angle is slightly larger (94.30°).
Figure 1: MERCURY view and atomic labelling of [RuCl(p-cym)(Memp)]PF (4). The
6
hydrogens were omitted for clarify. Bond Lengths (Å): C(15)-Ru 2.242(6); C(16)-Ru 2.199(5);
23

ACCEPTED MANUSCRIPT
C(17)-Ru 2.166(5); C(18)-Ru 2.219(5); C(19)-Ru 2.168(5); C(20)-Ru 2.201(5), N(1)-Ru
2
.088(4); N(2)-Ru 2.104(4); Cl(1)-Ru 2.3848(14). Bond Angles (°):Cl(1)-Ru-N(1) 83.60(12);
Cl(1)-Ru-N(2) 85.40(12); Cl(1)-Ru-C(15) 87.79(16); Cl(1)-Ru-C(16) 98.44(17); Cl(1)-Ru-C(17)
30.79(17); Cl(1)-Ru-C(18) 167.04(17); Cl(1)-Ru-C(19) 141.35(16); Cl(1)-Ru-C(20) 105.79(16);
N(1)-Ru-N(2) 76.40(17); N(1)-Ru-C(15) 135.3(2); N(2)-Ru-C(20) 168.81(19); N(1)-Ru-C(16)
71.8(2); N(1)-Ru-C(17) 143.8(2); N(1)-Ru-C(18) 108.9(2); N(1)-Ru-C(19) 93.50(19); N(1)-Ru-
1
1
C(20) 104.6(2); N(2)-Ru-C(15) 146.5(2); N(2)-Ru-C(16) 111.6(2); N(2)-Ru-C(17) 93.37(19);
N(2)-Ru-C(18) 100.60(19); N(2)-Ru-C(19) 131.47(19).
Figure 2: MERCURY view and atomic labeling of [RuCl(p-cym)(Diipmp)]PF (7). The
6
hydrogens were omitted for clarify. Bond Lengths (Å): C(19)-Ru 2.234(5); C(20)-Ru 2.196(5);
C(21)-Ru 2.195(4); C(22)-Ru 2.239(4); C(23)-Ru 2.180(4); C(24)-Ru 2.201(5); N(1)-Ru
2
.088(4); N(2)-Ru 2.115(3); Cl(1)-Ru 2.3852(11). Bond Angles (°):Cl(1)-Ru-N(1) 80.43(11);
Cl(1)-Ru-N(2) 89.67(9); Cl(1)-Ru-C(23) 149.78(15); Cl(1)-Ru-C(21) 119.89(15); Cl(1)-Ru-
C(20) 91.37(14); Cl(1)-Ru-C(24) 112.18(15); Cl(1)-Ru-C(19) 87.96(14); Cl(1)-Ru-C(22)
1
57.12(13); N(1)-Ru-N(2) 76.68(13); N(1)-Ru-C(23) 129.61(18); N(1)-Ru-N(2) 76.68(13).
24

ACCEPTED MANUSCRIPT
3
.2. Electronic Spectroscopy
The UV/Vis spectrum of the [RuCl(µ-Cl)(p-cym)] presents two bands at λ = 421 and 327
2
−5
−1
−1
−1
nm, in acetonitrile solution (5.0 × 10 mol L ), with
ε = 1174 and 1819 cm L mol . After
coordination of the N-N′–pyridylimine ligands to the ruthenium center three bands region are
observed in the spectra (Figure 3A).
The region 1 with λ value around 260 nm has a hyperchromic effect in the presence of the
N-N`–pyridylimine ligands, mainly with the N-(2,6-diethylphenyl)-1-(pyridin-2-yl)methanimine
(Diemp) and N-[2,6-bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine (Diipmp).
The complexes (2), (3), (4) and (5), in which the p-substituents of the phenyl are –H, –
CH
912 and 10471 cm L mol ), which were designed as region 2. However, the complexes (6)
and (7) (Diethyl or diisopropyl ortho-substitutes) do not have this band resolved. Indeed, this
3
, –t-But and –Cl show an increasing of the absorbance band around 310 – 330 nm (ε between
−1
−1
8
−1
−1
band has low intensity,
respectively, and a bathochromic shift compared to the other complexes.
The region 3 around λ = 420 nm (with in the range 3235 and 4073 cm L mol )
λ values at 364 and 368 nm, with ε = 4365 and 3801 cm L mol ,
−1
−1
ε
remains virtually the same for all complexes, as observed for the precursor [RuCl(µ-Cl)(p-
cym)]2.
In order to better understand the transition involved in the regions 1, 2 and 3 a M06/TD-
DFT calculation was carried out to generate a theoretical electronic spectrum of the regions for
each complex. The calculated and experimental spectra have good correlation, as can be observed
in the Figure 3A and B.
25

ACCEPTED MANUSCRIPT
Complexes (2) and (7) were selected to illustrate the results in the TD-DFT calculation.
The composition of the orbitals involved in the transition in the region 2 for (2) and regions 1, 2
and 3 for (7) in the UV/Vis spectrum are depicted in Table 3. The molecular orbitals in the region
2
for both complexes are displayed in Figure 4. The results in all regions for the complexes (2) –
(7) are available in the supplementary material (Figures S.15 - S.20 and Schemes S.1 – S.16).
A
B
1
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
6
0000
0000
0
0
0
0
0
0
0
0
0
5
Region 1
Region 2
Region 3
(
2)
(2)
(
(
(
(
(
3)
4)
5)
6)
7)
40000
(3)
(
(
4)
5)
30000
20000
10000
0
(6)
(
7)
200
250
300
350
400
450
500
550
200
250
300
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
−5
Figure 3: A) UV/Vis spectra of the complexes from (2) to (7) in acetonitrile solution (5.0 × 10
mol L . B) Theoretical electronic spectra for the related complexes.
−1
26

ACCEPTED MANUSCRIPT
Table 3: Composition of some selected molecular orbitals of (2) and (7)
Complex
λ
Calc.
λ
Exp.
Main
Transitions
MOs
% of contributions
(
nm) (nm)
1
1′
2
Ru Cl
R
R
R
G
1
G
2
LUMO
5
23
46 13
52 11
8
59 22
8
1
35
43 10
2
8
0
0
0
0
0
0
0
5
1
1
0
0
0
0
0
1
1
1
0
0
0
0
0
0
0
6
1
2
0
0
0
0
0
1
2
4
0
0
0
3
8
7
90
61
34
HOMO-3→LUMO
HOMO-2→LUMO
(
2)
3
41 318
HOMO-3
HOMO-2
LUMO+1
LUMO
HOMO-1
LUMO
HOMO-2
HOMO-3
HOMO-4
LUMO+5
LUMO+4
LUMO+3
LUMO
HOMO-1
HOMO-3
HOMO-4
Region 2
0 22 15
HOMO-1→LUMO
(7)
411 428
4
0
0
0
0
0
4
9
4
0
5
84
10
84
87
53
HOMO-1→LUMO+1
Region 3
4
0
5
HOMO-2→LUMO
HOMO-3→LUMO
HOMO-4→LUMO
(7)
367 368
Region 2
0 10 34
0 78
0 82
0
0
0
0
14
14
4
0
2
0
4
8
2
93
84
10
53
HOMO-7→LUMO
HOMO-4→LUMO+4
HOMO-3→LUMO+4
HOMO-1→LUMO+3
HOMO-1→LUMO+4
HOMO-1→LUMO+5
3
4
9
5
(7)
8
268 267
Region 1
59 22
35
43 10
5
0 10 34
84
4
2
0
6
1
1
HOMO-72
R and R ` = ortho – substitution in the imino ring; R = para – substitution in the imino ring; G
1
=
2
p-cymene ligand and G = N-N` pyridyl – imine ligands.
27

ACCEPTED MANUSCRIPT
Complex (2)
λ
calc = 341 nm
Complex (7)
λcalc = 367 nm
LUMO
LUMO
LUMO
HOMO−4
Ru
→ G2
Ru
→ G2
HOMO−3
LUMO
HOMO−3
Ru
→ G2
Small
variation
Ru
→ G2
HOMO−2
HOMO−2
LUMO
Figure 4: Contour plots of some selected MOs of (2) and (7) in region 2 in the UV/Vis spectra
In the region 3 of the UV/Vis spectra, the complexes (2) – (7) present a mixed
contribution of both Ru and Cl to G and G , explaining the slightly variation of the absorbance
1
2
bands in this region. These bands were attributed to metal to ligand charge transfer (MLCT),
HOMO-1→LUMO and HOMO-1→LUMO+1, as can be seen in the Table 3 for the complex (7).
In the region 2 of the TD-DFT calculated spectrum (Figure 3B), the complex (2) presents
a band at 341 nm. The excited state related to this transition presents two dominant electronic
configurations, related to HOMO-3 → LUMO and HOMO-2 → LUMO transitions, which are
basically MLCT Ru → G , as can be seen in Figure 4. The complexes (3), (4) and (5) (Figure 3,
2
Schemes S.4 – S.6 and Figures S16 – S18) have the same behavior as observed for (2) in the
region 2 of the UV/Vis spectra. These facts lead to the conclusion that the p-substituent groups of
the imino ring (–H, –CH , –t-But and –Cl) do not have a significantly interference in the
3
transitions in the region 2.
28

ACCEPTED MANUSCRIPT
The complex (7) in the TD-DFT calculated spectrum presents a transition at 367 nm,
matching well with the experimental data observed at 368 nm. This excited state presents a multi-
configurational character, involving transitions from HOMO-4, HOMO-3 and HOMO-2
transitions to LUMO, (Figure 4). The HOMO-4 and HOMO-3 to LUMO relates to MLCT,
specifically from Ru to N-N`–pyridylimine ligand (G ). The HOMO-2 to LUMO relates to an
2
internal transition located at G . This transition has a small oscillator strength (f = 0.0049) and
2
this weak transition is also observed for complex (6), in agreement with the experimental spectra
(figures S.19 – S.20 and Schemes S.7 – S.8).
Additionally, in the region 1, complex (6) presents one intense transition at 267 nm and
complex (7) presents two transitions at 268 and 270 nm. The excited states related to these
transitions present high multi-configurational character, being in general dominated by Ru → G1
2
and Ru → G .
3
.3. Electrochemical Characterization
The electrochemical behavior of (2) − (7) was investigated by cyclic voltammetry,
−1
recorded at glassy carbon as working electrode in TBAH (0.10 mol L ) acetonitrile solutions. All
complexes present one irreversible anodic process (Epa) at 1.8 V, and a reversible redox process
with half-wave potential (E½) in the region 1.14 − 1.18 V, which are dependent of the E at 1.8
pa
V. A representative voltammogram for the complexes is depicted in the Figure 5A for (7).
II
III
The Epa at 1.8 V is attributed to Ru → Ru process with simultaneous displacement of
3
+
the p-cymene ring. As a result a solvento complex with general formula [Ru Cl(N-
2
+
N)(CH CN) ] is formed in the presence of acetonitrile as solvent, which is reduced to
3
3
2
+
+
[
Ru Cl(N-N)(CH CN) ] at around 1.09 V. The electrochemical behavior is depicted in the
3 3
Scheme 2 showing the species observed in the cyclic voltammograms for the complexes (2) – (7).
29