Full text of DOI:10.1016/j.molstruc.2017.09.044

Journal of Molecular Structure 1151 (2018) 277e285
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Mixed diphosphine/diamine ruthenium (II) isomers: Synthesis,
structural characterization and catalytic hydrogenation of ketones
a
b
b
c
Rebecca D. Nascimento , Andressa K. Silva , Luciano M. Li a~ o , Victor M. Deflon ,
a
a
a, *
Leonardo T. Ueno , Luis R. Dinelli , Andr eꢀ L. Bogado
Faculdade de Ci ^e ncias Integradas do Pontal, Universidade Federal de Uberl a^ ndia, Rua Vinte, 1600, CEP 38304-402, Ituiutaba, MG, Brazil
Instituto de Química, Universidade Federal de Goi aꢀ s, Avenida Esperança, s/n, Campus Samambaia, CEP 74690-900, Goi a^ nia, GO, Brazil
Instituto de Química de S a~ o Carlos, Universidade de S a~ o Paulo, CP 780, 13560-590 S a~ o Carlos, SP, Brazil
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2017
Received in revised form
The complexes trans-[RuCl (dppb)(cydn)] (1), trans-[RuCl (dppb)(opda)] (2) and cis-[RuCl (dppb)(cydn)]
2
2
2
(
3) were synthesized from [{RuCl
2
(dppb)}
2
-
m
-(dppb)] {where: dppb ¼ 1,4-bis(diphenylphosphino)
butane; cydn ¼ cis and trans (±) 1,2-diaminocyclohexane, and opda ¼ o-phenylenediamine}. The com-
14 September 2017
31
1
plexes were characterized by nuclear magnetic resonance of phosphorus ( P{ H} NMR), cyclic vol-
Accepted 15 September 2017
Available online 17 September 2017
tammetry (CV), infrared and ultraviolet/visible spectra (IR and UV/vis) as well as elemental analyses
(
CHN). The X-ray structures of (1) and (3) were determined and they are presented here. DFT calculations
and experimental data showed that the trans isomers are obtained as thermodynamic products while the
cis isomers are kinetic products. This behavior is different than described in the literature for similar
complexes, where the cis isomer is obtained from the trans isomer. Additionally, the catalytic activity of
the complexes (1), (2) and (3) was investigated, as pre-catalysts, in the reduction of the acetophenone
and 4-methylacetophenone by transfer-hydrogenation.
Keywords:
Ruthenium complexes
Diphosphine
Diamine
Geometric isomers
X-ray structure
Transfer-hydrogenation
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
dppb
¼
1,4-bis(diphenylphosphino)butane and cydn
¼
1,2-
diaminocyclohexane} was first synthesized by Barata's group [14],
The coordination chemistry of ruthenium (II) is closely related to
the use of phosphines and chelating diphosphines ligands, due to
their characteristic of coordination via the P-atom. Aromatic
phosphines and diphosphines provide strong back-donation to the
metal center, stabilizing a range of ruthenium oxidation states [1],
mainly the þII state. The coordination sphere of ruthenium (II)
diphosphine complexes is versatilely and can associate with a large
number of other ligands, such as halogens, aryl groups [2,3], vi-
nylidenes [4], carbenes [5], CO [6,7], NO [8], pyridines [7,9e11],
and
[RuCl
Warad's
(dppb)(PPh
group
)] precursor, where a dissociation of the PPh
(dppb)(opda)] (2) {where
opda ¼ o-phenylenediamine}was first synthesized by Batista's
group [16], from the mer-[RuCl (dppb)(H O)] precursor by reduc-
[15],
from
the
mononuclear
2
3
3
is
required. The complex trans-[RuCl
2
3
2
tion of Ru (III) to Ru (II) in the presence of a reductive H
atmosphere.
2
Reacting the mer-[RuCl
mixture of two different complexes with P{ H} NMR signals at
47 and 26, which were assigned as trans-[RuCl (dppb)(opda)]
and trans-[RuCl
(dppb)(bqdi)] {bqdi ¼ o-benzoquinonediimine },
respectively. There is no evidence of cis product formation in the
reaction using the mer-[RuCl (dppb)(H O)] as precursor. However,
the trans-[RuCl (dppb)(opda)] complex, in the presence of molec-
ular oxygen, causes the slow oxidation of the coordinated opda to
bqdi and, in such condition, a strong signal at 26 is observed, due
(dppb)(bqdi)], which can be
3 2
(dppb)(H O)] with opda produces a
31
1
porphyrins [12], dithiocarbamates [13], as well as H and H
among others.
2
[9],
d
d
2
2
The use of diamine ligands associated with diphosphine in
ruthenium (II) complexes can be determined by different synthetic
routes, such as phosphine exchange, reduction of the metallic
center and the choice of different starting complexes [14e17]. For
3
2
2
example, the complex trans-[RuCl
2
(dppb)(cydn)] (1) {where
d
to the formation of trans-[RuCl
2
quantitatively isolated [16].
The geometry around the metal center in the mixed biphos-
phino/diamine ruthenium complexes with general formula
*
Corresponding author. Rua Vinte, 1600, Bairro Tup ~a , CEP 38.304-402, Ituiutaba,
MG, Brazil.
E-mail address: bogado@ufu.br (A.L. Bogado).
https://doi.org/10.1016/j.molstruc.2017.09.044
0
022-2860/© 2017 Elsevier B.V. All rights reserved.

278
R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
[
RuCl
2
(PeP)(NeN)] is normally distorted octahedral, because of the
The ground-state geometries were fully optimized without any
symmetry constraints at the DFT level of theory, employing the
B3LYP hybrid functional, with Becke's three-parameter hybrid
functional [21] and correlational functional of Lee, Yang and Parr
[22]. The basis set employed to build the molecular orbitals was
LanL2DZ for ruthenium and 6-311 þ G(d,p) for the remaining
atoms. All structures possessed positive definite Hessian matrices,
indicating that they were in a genuine minimum on the potential
energy surface. All calculations were made using Gaussian 09
computational package [23].
restricted bite angles of the surrounding bidentate ligands,
providing the trans or cis isomers according to the position of the
chlorido ligands. Several works describe the isomerization process
from the trans isomer to the cis isomer, which can be labeled as
kinetic and thermodynamic products, respectively. Only for sake of
illustration,
the
trans-[RuCl
2
(dppme)(cydn)]
{where
dppme ¼ H
2
C]C(CH
2
PPh } is a kinetic product, which is readily
2 2
)
isomerizes to the cis isomer (thermodynamic product) [18]. The
trans-[RuCl
2
(dppb)(dimprp)] {where dimprp ¼ 2,2-dimethyl-1,3-
propanediamine} also isomerizes to the cis isomer within 20 h of
reaction, which indicates that cis isomer is more stable than the
trans isomer [19]. However, certain biphosphino/diamine com-
plexes containing ruthenium do not present such isomerization
The catalytic experiments were analyzed by gas chromatog-
raphy 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
mm film thickness) was used for the
process [19], such as in the trans-[RuCl
diamph ¼ 2,3-diaminonaphthalene}.
2
(dppb)(diamph)] {where
characterization of the catalytic products and N
2
was the gas carrier
ꢀ1
ꢁ
(1.0 mL min ). The temperature program ranged from 170
C
ꢁ
ꢁ
ꢀ1
Herein is described the synthesis and structural characterization
(2 min) to 200 C at a heating rate of 10 C min .
of the trans-[RuCl
cis-[RuCl (dppb)(cydn)] (3) and cis-[RuCl
purpose of understanding the isomerization process involved. The
complexes were synthesized from the [{RuCl (dppb)} -(dppb)]
complex, and the catalytic activity of (1), (2) and (3) as pre-catalysts
in the transfer-hydrogenation of acetophenone and 4-
methylacetophenone is discussed. Suitable crystals of (1) and (3).
2
(dppb)(cydn)] (1), trans-[RuCl
2
(dppb)(opda)] (2),
2
2
(dppb)(opda)] (4), for the
2
2
.2. Syntheses
2
2
-m
2
.2.1. trans-[RuCl (dppb)(cydn)] (1)
It was synthesized from 101.2 mg (62.3
mmol) of the
[{RuCl (dppb)} -(dppb)] [17] and 15.9 mg (129.2 mmol) of the cis
2
2
-m
2 2
CH Cl were obtained and the X-ray analyses are presented here.
Table 1
Crystal data and structure refinement of the trans-[RuCl
2
(dppb)(cydn)] (1) and cis-
2
. Experimental
[
RuCl (dppb)(cydn)] (3).
2
2.1. General considerations
(1)
(3). CH
2 2
Cl
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
a(Å)
C
34
H
43Cl
712.60
296(2) K
2
N
2
P
2
Ru
C
35
H
44 Cl N P Ru
4 2 2
All reactions were carried out under argon atmosphere using
797.53
296(2) K
0.71073 Å
Triclinic
P-1
standard Schlenk techniques. Solvents were purified by standard
methods [20] and all chemicals used were of reagent grade or
comparable purity. Ruthenium trichloride, tetrabutylammonium
hexafluorophosphate (TBAH), 1,4-bis(diphenylphosphino)butane
0.71073 Å
Monoclinic
P2(1)/n
(
dppb), triphenylphosphine (PPh
trans (±) 1,2-diaminocyclohexane,
3
), o-phenylenediamine, cis and
acetophenone, 4-
15.1867(6)
10.9543(4)
21.8290(10)
90
90.156(2)
90
3631.5(3)
4
9.6341(5)
13.3976(6)
16.0147(8)
68.412(2)
74.914(2)
73.098(2)
1811.55(16)
2
1.462
b(Å)
c(Å)
methylacetophenone and hexadecane (Sigma-Aldrich) were used
as received.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
a
b
g
( )
ꢁ
ꢁ
( )
Ruthenium complexes were analyzed by 31P{ H}-NMR on a
Bruker Avance III 500 spectrometer operated at 11.75 T; 3 P was
observed at 202.46 MHz. The spectrometer was equipped with a
broadband observe probehead (BBO). Samples were prepared un-
der argon atmosphere and analyzed at variable temperature with a
1
( )
ꢁ
ꢁ
1
3
V(Å )
Z
Density (calculated) (Mg/
1.320
3
m )
Absorption coefficient
0.691
1472
0.844
820
ꢀ1
CD
cal shifts are with respect 85% H
Electrochemical data were obtained using a potentiostat/gal-
vanostat -autolab type III. Solutions of the complexes
2
Cl
2
capillary and dichloromethane (CH
2
Cl
2
) as solvent. Chemi-
(mm
)
F(000)
3
PO signal, as external reference.
4
3
Crystal size (mm )
Theta range for data
collection
0.29 ꢂ 0.24 x 0.20
0.36 ꢂ 0.05 x 0.02
ꢁ
ꢁ
1.63 to 25.21
1.388 to 25.24
m
ꢀ
3
ꢀ1
(
0
10 mol L ) were prepared in dichloromethane (CH
2
Cl
2
) using
Index ranges
ꢀ15 ꢃ h<¼18
ꢀ11 ꢃ h<¼11
ꢀ16 ꢃ k<¼14
ꢀ19 ꢃ l<¼19
22420
ꢀ
1
ꢀ
13 ꢃ k<¼12
26 ꢃ l<¼24
.1 mol L tetrabutylammonium hexafluorophosphate (TBAH) as
ꢀ
the supporting electrolyte. Measurements were made with a three-
Reflections collected
Independent reflections
Completeness to theta
maximum (%)
Absorption correction [29] Semi-empirical from
equivalents
28970
electrode configuration cell. A platinum foil was used as the
6374 [R(int) ¼ 0.0292] 6470 [R(int) ¼ 0.0424]
ꢀ1
working and auxiliary electrodes and Ag/AgCl, 0.10 mol L TBAH in
q
25.21 , 97.4% 25.24 , 98.7%
ꢁ
q
ꢁ
0
CH
2 2
Cl as the reference electrode. Under the conditions used, E for
5
Semi-empirical from
equivalents
0.7452 and 0.6828
Full-matrix least-
squares on F2
6470/0/397
the one-electron oxidation of [Fe(
h
5 5 2
-C H ) ], added to the test so-
lutions as an internal calibrant, is þ0.43 V.
Max. and min. transmission 0.7452 and 0.6834
Refinement method
Elemental analyses were performed with a Thermo Scientific
CHNSeO FLASH 2000 micro analyzer.
Full-matrix least-
squares on F2
Data/restraints/parameters 6374/0/463
Optical spectra were recorded on a Shimadzu spectrophotom-
eter, model UV-1800, coupled with a thermoelectrically tempera-
Goodness-of-fit on F2
1.247
1.064
Final R indices [I > 2
s(I)]
R1 ¼ 0.0642
wR2 ¼ 0.1502
R1 ¼ 0.0675
wR2 ¼ 0.1516
R1 ¼ 0.0510
ꢁ
ture controlled cell TCC-100 (at 25.0 ± 0.1 C), using a quartz cell
wR2 ¼ 0.1262
R1 ¼ 0.0741
(
1 cm), between 200 and 800 nm. IR spectra were recorded in a
R indices (all data)
spectrometer FT-IR Frontier Single Range e MIR from Perkin Elmer
coupled with an attenuated total reflectance (ATR) apparatus with
wR2 ¼ 0.1409
2.799 and ꢀ0.725
Largest diff. peak and hole 0.628 and ꢀ0.737
ꢀ3
ꢀ
1
(e.Å
)
diamond cell, in the 4000e200 cm range.

R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
279
and trans (±) 1,2-diaminocyclohexane (cydn) in toluene (20 mL)
under argon atmosphere. The solution was stirred for 5 h at 30 C
d
NH2def.), 1497 and 1433 (medium,
C-N), 901, 797 and 743 (strong,
n
arom.), 1097 and 1042 (strong,
ꢁ
n
t
NH2), 696 (very strong,
n
Ru-P) 261
ꢀ
4
ꢀ1
and then the volume was reduced under vacuum to 3 mL and
diethyl ether (10 mL) was added to obtain a yellow powder. The
product was thoroughly washed with diethyl ether (3 ꢂ 5 mL). The
(medium,
l
n
Ru
e
Cl). UV/vis (see Fig. 1S) (CH
2
Cl
2
, 1.27 ꢂ 10 mol L ),
ꢀ
1
ꢀ1
/nm (ε/L mol cm ) 322 (4451), 463 (546), 537 (702), 648 (254).
42 2 2 2
yield was 96.0 mg (95%). Anal. calc. (found) for C34H N Cl P Ru: C,
2
.2.3. cis-[RuCl
2
(dppb)(cydn)] (3)
31
1
6
1.19% (60.73); H, 6.26% (6.05); N, 3.48% (3.40); P{ H}-NMR
It was synthesized from 104.9 mg (64.6
{RuCl (dppb)} -(dppb)] [17] and 16.2 mg (141.9 mol) of the cis
and trans (±) 1,2-diaminocyclohexane (cydn) in CH Cl (5 mL)
mmol) of
(
0
202.46 MHz, CH
2
Cl
2
/D
2
O):
d
45.19 (singlet, dppb), CV (TBAH,
[
2
2
-m
m
ꢀ1
ꢁ
ꢀ1
.1 mol L CH
2
Cl
2
, 25 C, scan rate ¼ 0.1 V s ): Epa ¼ 0.52 V,
ꢀ1
2
2
E
pc ¼ 0.40 V, E½ ¼ 0.46 V, jIpa/Ipcj ¼ 1.10. IR {KBr,1 cm }: 3331, 3257
and 3054 (weak, N-H), 2931 and 2855 (weak, alkyl-H), 1988, 1895,
831, 1744 (very weak, harmonic), 1562 (medium,
and 1433 (medium, arom.), 1093 and 1023 (strong,
43(strong, NH2), 695 and 512 (very strong,
Cl). UV/vis (see Fig. 1S) (CH
under argon atmosphere. The result mixture was stirred for
1
hexane (20 mL), which produced a pale yellow solid. The remained
solid was filtered off by cannula filtration and washed with hexane
n
n
ꢁ
0 min at 30 C, and after that the reaction was stopped with
1
d
NH2def.), 1482
n
nC-N), 896 and
7
t
n
Ru-P), 290 (medium,
n
(
3 ꢂ 10 mL) and dried under vacuum. The yield was 101.7 mg (97%).
Anal. calc. (found) for C34 Cl Ru: C, 61.19% (60.94); H, 6.26%
6.05); N, 3.48% (3.03); P{ H}-NMR (202.46 MHz, CH Cl /D O):
Cl
ꢀ
4
ꢀ1
Ru
e
2
Cl
2
, 1.27 ꢂ 10 mol L ),
l
/nm (ε/L
H
42
N
2
2 2
P
ꢀ1
ꢀ1
mol cm ) 322 (4728), 456 (407).
31
1
(
d
2
2
2
ꢀ
1
44.85 (two broad signals, dppb). CV (TBAH, 0.1 mol L CH
2
2
,
ꢁ
ꢀ1
2
.2.2. trans-[RuCl
It was synthesized from [{RuCl
described for (1), which was used 100 mg (61.6
precursor and 15.9 mg (147 mol) of o-phenylenediamine. The
yield of pale yellow solid was 96 mg (95%). Anal. calc. (found) for
Cl Ru: C, 57.79% (57.29); H, 5.13% (4.99); N, 3.96% (3.76).
P{ H}-NMR (202.46 MHz, CH
2
(dppb)(opda)] (2)
25 C, scan rate ¼ 0.1 V s ): Epa ¼ 0.49 V, Epc ¼ 0.39 V, E½ ¼ 0.44 V,
ꢀ1
2
(dppb)}
2
-
m
m
-(dppb)] [17] as
mol) of binuclear
jIpa/Ipcj ¼ 1.10. IR {KBr, 1 cm }: 3331, 3305 and 3239 (weak,
3055, 2924 and 2853 (weak, alkyl-H), 1978, 1905, 1826, 1726 (very
weak, harmonic), 1548 (medium, NH2def.), 1497 and 1434 (medium,
arom.), 1095 and 1095 (strong, C-N), 897 (w), 796 and 743 (strong,
NH2) 696 (very strong, Ru-P), 301 and 255 (medium, Ru-Cl). UV/vis
nN-H),
n
m
d
n
t
n
C
34
H
36
N
2
2
P
2
n
n
3
1
1
ꢀ4
ꢀ1
ꢀ1
ꢀ1
2
Cl
2
/D
2
O):
d
46.36 (singlet, dppb). CV
(see Fig. 1S) (CH
322 (2824), 462 (313).
Suitable crystals of (1) and (3) grew up by slow evaporation of a
dichloromethane-diethyl ether solutions and the structures were
determinate by X-ray analysis.
2
Cl
2
, 1.27 ꢂ 10 mol L ),
l
/nm (ε/L mol cm
)
ꢀ
1
ꢁ
ꢀ1
(
TBAH, 0.1 mol L CH
2
Cl
2
, 25 C, scan rate ¼ 0.1 V s ): Epa ¼ 0.61 V,
ꢀ
1
E
3
pc ¼ 0.49 V, E½ ¼ 0.55 V, jIpa/Ipcj ¼ 1.15. IR {KBr, 1 cm }: 3305,
241 and 3057 (weak, nN-H), 2920 and 2853 (weak,nalkyl-H), 1981,
1906, 1914 and 1714 (very weak, harmonic), 1548 (medium,
Scheme 1. General structure and numeric labels of the compounds studied here [30].

280
R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
2.3. Catalytic experiments
crystal data of (1) shows pseudo orthorhombic symmetry but the
data refinement in this system, space group Pnnm, did not lead to
better results. The disordered solvate molecules as well as the
disorder found for two phenyl rings, also for the cydn ligand, give
support to the monoclinic symmetry. The ORTEP views were pre-
pared with PLATON for Windows [28]. Table 1 summarizes the data
A standard procedure is describing as follow: in a Schlenk tube,
the acetophenone or 4-methylacetophenone (10 mmol) were dis-
ꢁ
solved in 2-propanol (2 mL) and refluxed at 82 C within 5 min
under inert atmosphere of Ar. Afterward, the ruthenium complexes
(
10
m
mol) were dissolved in degassed 2-propanol (3 mL) in the
2 2
collection and experimental details for (1) and (3). CH Cl .
ꢀ
1
presence of 1 mL of KOH (0.2 mol L in 2-propanol). The mixture
was added inside the Schlenk tube with substrate. The reaction was
warmed until 82 C, and the mixture were vigorously stirred for 1 h.
3. Results and discussion
ꢁ
After that, an aliquot (1.0 mL) was withdrawn and diluted to 10 mL
3
.1. Synthesis and characterization of ruthenium complexes
ꢀ
1
with an acid solution of 2-propanol (10
Conversions were determined by gas chromatography using hex-
mL HCl; 11.0 mmol L ).
The complexes (1), (2) and (3) were prepared from the well-
known binuclear ruthenium complex described by Bressan and
Rigo [17] [{RuCl (dppb)} -(dppb)]. In the presence of diamine
ꢀ
1
adecane as an internal standard (1.46
mL; 0.1 mmol L ).
2
2
-m
2
.4. X-ray diffraction data
ligands (cydn and opda), in toluene solution, the dppb bridge be-
tween the metal centers is broken, producing two equivalents of a
mononuclear mixed diphosphine/diamine complex containing
ruthenium (Scheme 1). The chemical formulas of the complexes
(1)e(3) were matched by elemental analysis (C, H, N), which agree
The crystals were mounted on a goniometer in an BRUKER
KAPPA APEX II DUO diffractometer using the graphite-
monochromated MoK
¼ 0.71073 Å) radiation. The final unit
a (l
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 pro-
gram [24,25]. Absorption correction was carried out by the multi-
scan method [25]. The structures were solved by direct methods
with SHELXS-97 and models were refined by full-matrix least-
squares on F2 with SHELXL-2016 [26]. All hydrogen atoms were
stereochemically positioned and refined applying the riding model
with the expectation. The complex (1) and (2) with a C
present only one active Ru-Cl stretching vibration in the infrared
region, at 290 and 261 cm , respectively. Complex (3), with a C
symmetry, exhibit two active Ru-Cl stretching vibrations at 301 and
255 cm , due to the symmetrical and asymmetrical stretching of
2
v symmetry
n
ꢀ
1
1
n
ꢀ1
the cis RueCl bonds, including their optical isomers (
D or L) (see
Scheme 1).
After 5 h of reaction, the trans isomers (1) and (2) are the major
products in both syntheses. After a long period of reaction, 5 days,
there is no evidence of another isomer and only the trans isomers
(1) and (2) were observed. These results suggest that the cis isomers
(3) and (4) are the kinetic products, while the trans isomers (1) and
[26]. Residual electron density, localized in voids, was treated
3
applying the SQUEEZE routine of PLATON [27] for (1) (512 Å total
potential solvent accessible volume, summing to 127 e , consistent
with three disordered ethyl ether molecules per unit cell). The
ꢀ
Fig. 1. The time and temperature dependence on the 31P{ H}NMR data of the reaction between the [{RuCl
1
2
(dppb)}
2 2 2 2 2
-m-(dppb)] in presence of cydn (2.3 eq) in CH Cl /CD Cl solution
(
spectra from 1 to 6). Isolated cis-[RuCl
2
(dppb)(cydn)] (spectrum 7). Isolated trans-[RuCl
2
(dppb)(cydn)] (spectrum 8).

R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
281
(
2) are the thermodynamic products. This behavior is different than
two coalescent doublets, related to the cis isomer (3), since the 31P
1
that observed for related complexes described in previous works
{ H} NMR data of the isolated complex, within 10 min of reaction at
ꢁ
[18,19], where the cis isomer is obtained from the trans isomer.
30 C, show the same spectra (see spectrum 8 inside Fig. 1).
The complex (3) was obtained at the begin of the reaction be-
Finally, the yellow powder isolated after 5 h of reaction show
tween the [{RuCl
powder, within 5e10 min of reaction. The complex cis-
RuCl (dppb)(opda)] (4) was not isolated as a pure compound, but
it was observed in a monitored reaction by P{ H} NMR between
{RuCl (dppb)} -(dppb)] and opda.
The P{ H} NMR spectra of (1) and (2) agree with that described
previously in the literature [14e16], which showed only a singlet
signal at 45.19 and 46.36 respectively, due to the magnetic
2
(dppb)}
2
-
m
-(dppb)] and cydn, as a pale-yellow
only a singlet at
d
45.19, related to the trans-[RuCl
2
(dppb)(cydn)]
complex. The signal of free dppb is observed at
not showed in the Fig. 1, for clarify.
d
ꢀ17.0 ppm and is
[
2
3
1
1
31
1
The same P{ H} NMR experiment was carried out also be-
ꢁ
[
2
2
-
m
tween [{RuCl
CH Cl /CD Cl
experiment reveals two broad signals at
10 min of reaction, evidencing the formation of the cis-
[RuCl (dppb)(opda)] (4) and a reactional intermediate, respectively.
Afterward, the signal at 44.85 disappeared, and only a single
signal at 46.65 keeps constant and increases its intensity, with the
formation of the trans-[RuCl (dppb)(opda)] (2). Unfortunately, the
2
(dppb)}
2
-m-(dppb)] and opda (2.3 eq), at 1 C in
31
1
2
2
2
2
solution, with an acquisition per minute (Fig. 2). This
46.55 and 44.85, within
d
d
equivalence of P atoms of the dppb ligand.
2
The Fig. 1 shows the time and temperature dependence of the
d
reaction between [{RuCl
by P{ H} NMR. After 1 min of reaction at 1 C it is possible to see
2
(dppb)}
2
-
m
-(dppb)] and cydn monitored
d
31
1
ꢁ
2
two signals, assigned as two doublets at a first glance at
2.86. However, the coupling constant and intensity are different,
indicating no correlation between the two signals. The values of
integrals of these signals reveal that the signal at 44.85 corre-
sponds to two phosphorous, while the signal at 42.86 ppm is
consistent to one phosphor. After five more minutes a broad signal
is observed at 42.92, with no evidence of change in the signal at
44.85. After 30 min of reaction, with increasing of temperature
d
44.85 and
2
efforts to obtain the pure cis-[RuCl (dppb)(opda)] (4) failed using
the present synthetic route.
4
The cyclic voltammetry of the complexes (1) and (2) showed
III
II
d
only one reversible process, corresponding to the Ru /Ru couple
in the range of 0.0 to þ1.0 V, with E values between 0.46 and
0.55 V (see Fig. 3 and Table 2). These values are close to the E
normally observed in the dichloride ruthenium complexes with
general formula trans or cis-[RuCl (PeP)(NeN)] {where:
PeP ¼ biphosphine and NeN ¼ diimines), which exhibit E values
around 0.60 V [31]. The shift to more cathodic region in the cyclic
voltammogram of (1) caused by the presence of stronger a -donor
group that enriches the electronic density in the metal center,
d
½
½
d
d
2
ꢁ
until 20 C, a large single signal can be observed at
evidencing a reaction intermediate, since the signal is not present
in the spectrum of the pure cis-[RuCl (dppb)(cydn)].
The two signals observed at 44.85 are tentatively assigned to
d
42.92 ppm,
½
2
s
d
Fig. 2. The time dependence on the 31P{ H}NMR data of the reaction between [{RuCl
1
(dppb)} -m-(dppb)] in presence of opda (2.3 eq) in CH Cl /CD Cl solution at 1 C.
ꢁ
2
2
2
2
2
2

282
R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
Fig. 4. ORTEP view [32] and atomic numbering of (1) showing the atom labelling and
5
2
0% probability ellipsoids. Bond Lengths (Å): P(1)-Ru(1) 2.2751(17); P(2)-Ru(1)
.2826(17); Cl(1)-Ru(1) 2.4256(17); ꢁCl(2)-Ru(1) 2.4269(19); N(1)-Ru(1) 2.176(5);
N(2)-Ru(1) 2.171(5). Bond Angles ( ): N(2)-Ru(1)-N(1) 77.7(2); N(2)-Ru(1)-P(1)
1
69.31(15); N(1)-Ru(1)-P(1) 92.81(15); N(2)-Ru(1)-P(2) 92.96(15); N(1)-Ru(1)-P(2)
2 2
Fig. 3. Cyclic voltammograms of trans-[RuCl (dppb)(cydn)] (1), trans-[RuCl (dpp-
ꢀ
3
ꢀ1
169.49(15); P(1)-Ru(1)-P(2) 95.98(6); N(2)-Ru(1)-Cl(1) 84.74(17); N(1)-Ru(1)-Cl(1)
84.72(16); P(1)-Ru(1)-Cl(1) 89.47(6); P(2)-Ru(1)-Cl(1) 89.59(6); N(2)-Ru(1)-Cl(2)
b)(opda)] (2) and cis-[RuCl
2
(dppb)(cydn)] (3) (1.0 ꢂ 10 mol L ), recorded vs Ag/AgCl
ꢀ
1
ꢀ1
in CH
2
Cl
2
, in 0.1 mol L of TBAH; sweep rate 100 mV s
.
8
9
4.37(17); N(1)-Ru(1)-Cl(2) 85.46(17); P(1)-Ru(1)-Cl(2) 100.02(7); P(2)-Ru(1)-Cl(2)
8.63(7); Cl(1)-Ru(1)-Cl(2) 166.66(7).
providing lower E
½
values. Complex (2) exhibits higher oxidation
potential than (1), due to the presence of a less
(
(
s
-donor group
opda), when it is compared with a non-aromatic diamine group
cydn). It is interesting to note that complex (3) has electrochemical
parameters slight lower than complex (1), evidencing a higher
thermodynamic stability for (1). Table 2 summarizes the electro-
chemical potential values and the chemical shift (d) of the com-
plexes (1) ꢀ (4).
2 2
The X-ray structures of (1) and (3). CH Cl are shown in the
Figs. 4 and 5, respectively. Selected bond, distances and angles are
also listed in the caption of Figs. 4 and 5.
The structures of complexes (1) and (3) are distorted octahedral,
with restricted bite angles of the surrounding bidentate ligands, as
ꢁ
ꢁ
shown by NeRueN angles < 90 , and the PeRueP angle > 90 in
the molecular structure of the complexes (Figs. 4 and 5). The RueP
distances trans to amine group in (1) Ru(1)- P(1) 2.2751(17); Ru(1)-
Table 2
31
1
P{ H}NMR data and electrochemical potentials for the ruthenium complexes.
3
1
1
a
CVb
½
pa, Epc, E (V)
Complex
P{ H} NMR
d
in ppm
E
(
(
(
(
1)
2)
3)
4)
45.19
46.65
44.85
46.55
0.52, 0.40, 0.46
0.61, 0.49, 0.55
0.49, 0.39, 0.44
e
Complexes: trans-[RuCl
RuCl (dppb)(cydn)] (3).
2
(dppb)(cydn)] (1), trans-[RuCl
2
(dppb)(opda)] (2) and cis-
[
2
31
a
1
P{ H} NMR were carried out using CH
inserted in the NMR tube).
¼ Chemical shifts which were determined with respect
to the phosphorus signal of phosphoric acid 85% (H PO ).
CV ¼ cyclic voltammetry, carried out at room temperature in CH
2 2 2 2
Cl as solvent (a CD Cl capillary was
2 2
Fig. 5. ORTEP view [32] and atomic numbering of (3). CH Cl showing the atom
labelling and 50% probability ellipsoids. Bond Lengths (Å): Rue N(1) 2.117(4); RueN(2)
d
3
4
b
2.167(4); RueCl(1) 2.4857(13); RueCl(2) 2.4398(13); RueP(1) 2.2693(13); RueP(2)
2
Cl
(TBAH). The working and auxiliary electrodes consisted of
stationary Pt foil; the reference electrode was Ag/AgCl in a Luggin capillary. E
values were calculated from (Epa pc)/2. anodic peak potential;
pc ¼ cathodic peak potential and E ¼ half wave potential.
2
containing
ꢁ
ꢀ þ ꢀ
1
2.2706(13). Bond Angles ( ): N(1)-RueN(2) 78.31(15); N(1)-RueP(1) 101.42(11); N(2)-
0
.1 mol L Bu N PF
4 6
RueP(1) 93.53(11); N(1)-RueP(2) 95.23(11); N(2)-RueP(2) 171.85(11); P(1)-RueP(2)
½
92.62(5); N(1)-RueCl(2) 162.34(11); N(2)-RueCl(2) 86.48(11); P(1)-RueCl(2) 88.30(5);
þ
E
E
pa
¼
P(2)-RueCl(2) 99.04(5); N(1)-RueCl(1) 80.63(11); N(2)-RueCl(1) 83.90(11); P(1)-
RueCl(1) 176.35(5); P(2)-RueCl(1) 90.19(4); Cl(2)-RueCl(1) 88.95(5).
E
½

R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
283
Fig. 6. Energy of the optimized structures of (1)e(4) by DFT calculations [21e23].
Table 3
inverted structures for the molecules.
Hydrogenation of acetophenone by complexes (1), (2) and (3).
It is well-known that diphosphine/diimine complexes contain-
ing ruthenium have also an isomerization process from trans to cis
Pre-catalyst
Substratea
%Productb ± RSD(%)c
TOFd (h ) ± RSD(%)
ꢀ1
(
(
(
(
(
1)
1)
2)
2)
3)
1
2
1
2
1
98 ± 1
64 ± 7
4 ± 2
0
985 ± 1
636 ± 7
40 ± 2
0
[
31]. But the success of isomerization on biphosphine/diimine
environment is attributed to the rigid structure of diimines, when it
is compared with more flexible diamine ligands.
To better understand the isomerization process of the com-
plexes described in the present work, the energy of the optimized
structures of trans-[RuCl
b)(opda)] (2), cis-[RuCl (dppb)(cydn)] (3) and cis-[RuCl
b)(opda)] (4) were calculated by DFT methods. Fig. 6 presents the
relative energies differences between the cis and trans isomers. The
value 0.0 kJ mol was arbitrary attributed to the energies of the
optimized structure of the trans isomers.
87 ± 11
870 ± 11
Reactions were carried out in threefold analysis in isopropanol (10 mL), in the
presence of KOH (1.0 mL, 0.2 mol L in isopropanol), acetophenone (10 mmol), and
ꢀ1
(dppb)(cydn)] (1), trans-[RuCl
(dpp-
(dpp-
2
2
pre-catalyst (10
000/20.
m
mol) at 82 ꢁC within 1 h. Catalyst/substrate/KOH molar ratio ¼ 1/
2
2
1
a
Substrate: 1 (acetophenone) and 2 (4-methylacetophenone).
Hydrogenated products were determinate by gas chromatography using n-
b
ꢀ1
hexadecane as internal standard.
c
RSD ¼ relative standard deviation.
d
TOF ¼ turnover frequency ¼ mol of product/mol of pre-catalyst/time.
Based on the DFT results, the energy of the optimized structure
ꢀ1
(
4) is only 12.42 kJ mol higher than that of (2), while the energy of
ꢀ
1
the optimized structure (3) is 14.04 kJ mol higher than that of (1).
These results revealed that the cis isomers (3) and (4) are slight less
stable related to the their trans isomers (1) and (2), which are in
agreement with the experimental results, mainly those observed
P(2) 2.2826(17) and (3) RueP(2) 2.2706(13) are practically the
same, but slightly longer than the RueP trans to Cl in (3) RueP(1)
.2693(13), while the Ru(1)-P(2) trans to NH group in (3) is in the
same distance order than the RueP in (1). The bond distances and
angles listed in the caption of Figs. 4 and 5 are in the range expected
for ruthenium biphosphine complexes [31,33], as well as for
diamine complexes containing ruthenium [15,18,34,35].
2
31
1
by P{ H} NMR and cyclic voltammetry.
3
.2. Catalytic experiment
2 2
A monoclinic crystal structure of (3). CH Cl , was previously
The hydrogenation reactions of the acetophenone and 4-
reported by Warad [36], without further characterization and with
good agreement with the triclinic modification presented here
regarding the complex geometry, bond lengths and angles, but
showing a disordered solvate molecule. In both structure modifi-
cations, hydrogen bonds connect the complexes in pairs with
methylacetophenone catalyzed by complexes (1), (2) and (3)
were studied in triplicate and the results are shown in the Table 3.
The complex (1) showed the best catalytic activity within 1 h of
reaction under the applied conditions, which produces a quanti-
ꢀ1
tatively amount of the phenylethanol with rates of 985 h ± 1%. In

284
R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
2
Scheme 2. Suggestion for the inactivation of the trans-[RuCl (dppb)(opda)] in the transfer-hydrogenation of aryl-ketones [30].
the presence of the 4-methylacetophenone, the complex (1) pro-
duced 64% ± 7% of the hydrogenated product and turnover fre-
4. Conclusion
ꢀ
1
quency (TOF) ¼ 636 h ± 7%.
The
complexes
trans-[RuCl
(dppb)(cydn)] (3) were synthe-
-(dppb)] complex. The time and
(dppb)}
-(dppb)] and cydn or opda monitored by P{ H} NMR showed
2
(dppb)(cydn)]
(1),
trans-
The structure of the active ruthenium hydride catalysts in the
diamine systems is proposed by Morris as a dihydride amine and
hydride amido-amine complexes with general formula
[RuCl
2
(dppb)(opda)] (2) cis-[RuCl
2
2 2
sized from [{RuCl (dppb)} -m
temperature dependence of the reaction between [{RuCl
2
2
-
31
1
[
Ru(H)
2
(P)
2
(diamine)] {P ¼ mono phosphine}, where the hydride
m
ligand should be trans to each other, by contrast with the more
stable cis-dihydride complex [37] (see Scheme 2). The mono-
that the isomers trans were determined as thermodynamic prod-
ucts, while the isomers cis were observed as kinetic products. DFT
calculations of the complexes (1)e(4) also revealed that the energy
of the optimized structures of the isomers cis are slight higher than
the trans-isomers. The structures of (1) and (3) were determined by
X-ray diffraction of single crystal, which provide a distorted octa-
hedral geometry for both structures. The complexes (1), (2) and (3)
were applied as catalytic precursors in the transfer-hydrogenation
of aryl-ketones in mild conditions: catalyst/substrate/KOH molar
3 2
hydride complexes [RuHCl(PPh ) (diamine)] and [RuHCl(biphos-
phino)(diamine)] are attributed as inactive catalytic species in the
hydrogenation of ketones or imines, but could be converted into
active dihydride catalysts with strong bases and a source of
hydrogen [37,38].
The catalytic activity of the complex (3), with 87% ± 11% of the
phenylethanol, suggests that the complex (3) can isomerize from
cis to trans to promote the catalytic active specie in situ. As pro-
posed by Morris [37], the cis isomer is an inactive specie in this kind
of mechanism and this fact agrees with the experimental and
theoretical observation that (1) is a thermodynamic product, while
the cis-isomer (3) is kinetic. Additionally, the pre-catalyst (3)
showed a catalytic activity slight lower than (1), suggesting a longer
induction time to obtain the active catalytic specie, which could be
associated to the isomerization process from cis-(3) to trans-(1).
The low catalytic activity of the pre-catalyst (2) can be ratio-
nalized due to the presence of an aromatic ring in the amine group,
that compose the opda ligand. The reduction process of aryl ke-
tones can promote the oxidation of the coordinated opda to o-
benzoquinone diimine (bqdi), in a side reaction between the aryl-
ketone with opda (see Scheme 2). An oxidation process of the co-
ordinated opda was described by Batista [16] and Warren [39] in
the syntheses of the complexes based on o-benzoquinone diimine
with cobalt, iron and ruthenium. The bqdi complex containing
ruthenium is apparently more stable than the amido complex
formed in the catalytic cycle, preventing the regeneration of the
NeH group, and the successive transfer of the proton from nitrogen
and hydride from ruthenium to the ketone carbonyl in the outer
coordination sphere. Warad and co-workers [18] describe similar
ꢁ
ratio ¼ 1/1000/20, in 2-propanol as hydrogen source, at 82 C,
within 1 h of reaction. Quantitative amount of the phenylethanol
was obtained when the complex (1) was applied as catalytic pre-
cursor, and it provides 64% ± 7% of the 4-methylphenylethanol,
ꢀ
1
ꢀ1
with TOF values ¼ 985 h ± 1% and 636 h ± 7% respectively. The
complex (3) showed a catalytic activity slight lower than (1), sug-
gesting an isomerization process from cis to trans geometry to
provide an active catalytic specie in situ, which agree with the
experimental and theoretical investigation of the related com-
plexes. The complex (2) showed very poor catalytic activity, which
is attributed to the oxidation of opda ligand to produce an inactive
pre-catalyst with o-benzoquinone diimine complex containing
ruthenium.
Acknowledgements
We thank FAPEMIG, CNPq, CAPES, FAPESP, FINEP and RQ-MG for
financial support. The authors are thankful to the Grupo de Mate-
riais Inorg ^a nicos do Tri ^a ngulo (GMIT) research group supported by
FAPEMIG.
2
behavior with the complex trans-[RuCl (dppb)(NeN)] {where
NeN ¼ aromatic diamine ¼ 2,3-diaminophathalene}, which has no
Appendix A. Supplementary data
catalytic activity in the hydrogenation of cinnamic aldehyde in 2-
ꢁ
propanol at 40 C under 3 bar of H
2
within 10 h of reaction (sub-
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.molstruc.2017.09.044.
strate/pre-catalyst molar ratio ¼ 1000/1).

R.D. Nascimento et al. / Journal of Molecular Structure 1151 (2018) 277e285
285
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