[N,P]-pyrrole-phosphine ligand: An efficient and robust ligand for Ru-catalyzed transfer hydrogenation microwave-assisted reactions

Article abstract of DOI:10.1016/j.catcom.2018.07.009

A pyrrolyl-containing [N-P]-ligand (L1) and [Ru] were evaluated as catalytic system in transfer hydrogenation reaction of ketones. A comparison between microwave irradiation vs conventional heating conditions indicates that MW can be successfully used as energy source, improving the reaction time. The L1/Ru(II) proved to be an active, efficient and robust catalytic system. The scope of this catalytic system was evaluated using a diversity of substrates that include electron-withdrawing and electron-donor groups achieving a range of 65 to 95% conversion. Moreover, the catalytic system showed good activity even with highly sterically hindered ketones.

Full text of DOI:10.1016/j.catcom.2018.07.009

CatalysisCommunications115(2018)49–54
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
[N,P]-pyrrole-phosphine ligand: An efficient and robust ligand for Ru-
catalyzed transfer hydrogenation microwave-assisted reactions
E.P. Sánchez-Rodrígueza, A.J. Fragoso-Medinaa, E. Ramírez-Menesesb, M. Gouygouc,
M.C. Ortega-Alfarod,⁎, J.G. López-Cortésa,⁎
a
Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Coyoacán C.P. 04510, CdMx, Mexico.
Departamento de Ingeniería Química, Industrial y de Alimentos, Universidad Iberoamericana, Prolongación Paseo de la Reforma 880, Lomas de Santa Fe 01219, CdMx,
b
Mexico.
c
CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, 205, route de Narbonne, 31077 Toulouse, France.
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Coyoacán, C.P. 04510, CdMx, Mexico.
d
A R T I C L E I N F O
A B S T R A C T
Key-words:
[N,P]-ligand
Ruthenium
Transfer-hydrogenation
Microwave
A pyrrolyl-containing [N-P]-ligand (L1) and [Ru] were evaluated as catalytic system in transfer hydrogenation
reaction of ketones. A comparison between microwave irradiation vs conventional heating conditions indicates
that MW can be successfully used as energy source, improving the reaction time. The L1/Ru(II) proved to be an
active, efficient and robust catalytic system. The scope of this catalytic system was evaluated using a diversity of
substrates that include electron-withdrawing and electron-donor groups achieving a range of 65 to 95% con-
version. Moreover, the catalytic system showed good activity even with highly sterically hindered ketones.
1. Introduction
drogenation of a broad scope of ketones. [18–20]
Our group is involved in the design of a new class of [N,P]-pyrrole-
Transition-metal-catalyzed transfer hydrogenation reactions have
been considered in terms of ease, efficiency, and commercial viability,
as the most attractive procedure for reduction of unsaturated C]O and
C]N bonds. [1–6] In this process, a variety of transition metals, li-
gands, hydrogen sources, bases, reaction media, supports, and un-
saturated compounds have been used. The hydrogen donor source is
generally an alcohol such as 2-propanol, glycerol or a formate in
combination with a base as co-catalyst. [1,7] Notably, this is a valuable
alternative reduction procedure of ketones to useful secondary alcohols,
in the context of high demand of the petrochemical, pharmaceutical,
and food industries. [8–10]
Among the transition metal complexes, Ru complexes with various
combinations of ligands are by far the most widely used catalysts to
mediate this reaction. [1,11–14] Hemilabile ligands, especially mixed
[N,P]-chelate ligands [15–17], have been particularly used to assist
metals in transfer hydrogenation, where it is necessary that a ligand
fragment dissociates to allow the coordination of the organic substrate
that will undergo the transformation. For example, half-sandwich Ru-
catalysts containing [N,P]-ligands remarkably promoted transfer hy-
phosphine ligands based on pyrrole with a dimethylamino group and a
phosphine moiety as hard and soft donors, respectively. Recently, we
have demonstrated that their palladium complexes efficiently promote
Heck coupling reactions [21] and intramolecular arylations. [22] In
addition, we have successfully employed microwave irradiation to ac-
celerate these metal-catalyzed reactions(Fig. 1). [23,24]
As part of our ongoing work, we decided to explore the potential of
these [N,P]-ligands in ruthenium-catalyzed transfer hydrogenation reac-
tions using microwave irradiation as a heating source, since the reaction
rates involves polar components, it can be accelerated under these
heating conditions. Although, microwave enhanced Ru-catalyzed transfer
hydrogenation of ketones could be considered an ecofriendly approach,
only some examples have been reported using this approach. [25–28]
Herein, we report the transfer hydrogenation of various ketones catalyzed
by a [N,P]-ligand/Ru system. No inert atmosphere was necessary, neither
active catalyst previous formation. To establish the greenest and most
efficient catalytic protocol, we have also performed the reactions under
microwave conditions, and the results were compared with those ob-
tained by the conventional oil-bath heating procedure.
⁎
Corresponding authors.
E-mail addresses: carmen.ortega@nucleares.unam.mx (M.C. Ortega-Alfaro), jglcvdw@unam.mx (J.G. López-Cortés).
https://doi.org/10.1016/j.catcom.2018.07.009
Received 30 May 2018; Received in revised form 7 July 2018; Accepted 9 July 2018
Availableonline11July2018
1566-7367/©2018ElsevierB.V.Allrightsreserved.

E.P. Sánchez-Rodríguez et al.
CatalysisCommunications115(2018)49–54
2. Experimental section
2.2.4. Product analysis
For all three catalytic methods, products were analyzed according to
the following procedure: After the reaction time, the reaction mixture
was evaporated under reduced pressure and analyzed by 1H NMR to
determine the conversion in reference with residual starting material.
The calculated conversion was corroborated by gas chromatography.
The catalytic reactions were done in duplicates to ensure the reprodu-
cibility of the results.
Note: The entire flasks used in each hydrogen transfer experiment
were meticulously cleaned with aqua regia to avoid the presence of
unseen ruthenium catalyst.
2.1. General considerations
All reagents and solvents were obtained from commercial suppliers
and used without further purification. Melting points were obtained on
a Melt-Temp II apparatus and are uncorrected. All compounds were
characterized by NMR spectra measured with a Bruker Avance III at
300 MHz for 1H and 75 MHz for 13C using CDCl3 as a solvent. Chemical
shifts are in ppm (δ), relative to TMS.
The calculated conversion was corroborated by gas chromatography
analyses using an Agilent 6890 system, equipped with a Cyclosilb
column (solvent: isopropanol; 30 m × 0.32 mm 0.25 μm). The GC
parameters were as follows: initial temperature, 100 °C; temperature
ramp: 5 °C/min 150 °C (0 min), 10 °C/min; final temperature, 230 °C;
final time, 23 min; injector port temperature, 240 °C; detector tem-
perature, 240 °C; injection volume,1.0 μL.
3. Results and discussion
Initially, the ligands N,N-dimethyl-1H-pyrrol-1-amine-2-diarylpho-
sphine L1 and L2 were prepared in good yields by the selective lithia-
tion of 1-(N,N-dimethylamino)pyrrole and the subsequent anion trap-
ping with chlorodiphenylphosphine (L1) or chloro-di(o-tolyl)phosphine
(L2), as we have previously reported. [21] For comparison purposes, we
have also included a [P,P]-ligand as (rac)-BINAP, usually employed in
this kind of catalytic applications.
Microwave irradiation experiments were performed using
a
Monowave 300 single-mode microwave reactor. The reaction tem-
perature is monitored by an internal fiber-optic (FO) temperature probe
(ruby thermometer) protected by a borosilicate immersion well inserted
directly into the reaction mixture. Reaction times refer to the hold time
at the desired set temperature and not to the total irradiation time.
Pressure sensing is achieved by a hydraulic sensor integrated in the
swiveling cover of the instrument. The reusable 10 mL Pyrex vial is
sealed with PEEK snap caps and standard PTFE coated silicone septa.
Reaction cooling is performed by compressed air automatically after the
heating period has elapsed.
The X-ray diffraction (XRD) patterns were recorded using a Bruker
Advanced D8-FOCUS diffractometer with Cu-kα radiation (λ = 1.54 Å)
at a scanning speed of 0.02° (2θ) min−1 in the range of 10–100°. The
morphology of selected samples was examined by scanning electron
microscopy (SEM) on a JSM-6701F JEOL microscope.
Preliminary experiments using the ligand L1 in the catalytic transfer
hydrogenation of acetophenone as a model substrate were conducted
using KOH as base (25 mol%), 2-propanol as solvent and hydrogen
source, L1 (1.2 mol%) and [Ru(PPh3)3Cl2] (1 mol%) under different
heating conditions (Table 1). We have compared the effect of using
conventional heating versus microwave irradiation. The percentage
conversions were determined by 1H NMR spectroscopy by comparing
the integration of the methyl signal of acetophenone (s, δ 2.59) and
methyl signal of 1-phenylethanol (d, δ 1.49) of the crude products.
These results were also confirmed by gas chromatography technique.
Under conventional oil-bath heating, the reaction was conducted at
2-propanol reflux (82 °C) for reaction time of 18 h, including 3 h of the
catalytic species formation. According with the mechanism accepted for
the transfer hydrogenation, [29] the active catalytic species
[RuH2L2PPh3] is formed in the pre-activation step, and then when the
substrate is added, the reaction starts (Table 1, entry 1). During the pre-
activation step, we observe a color change of the solution before the
addition of substrate, which could indicate the coordination of the
[N,P]-ligand. Likewise a screening by thin layer chromatography
showed the total consumption of [N,P]-ligand and the presence of PPh3
in solution. Thus, we conducted a coordination experiment using the
ligand L1 and the ruthenium precursor in anhydrous THF at room
temperature. Unfortunately, despite efforts to isolate the new ruthe-
nium complex, we could not isolate or identify this compound, ob-
taining in all cases an insoluble solid in the common solvents used for
spectroscopic characterization. For this reason, we decided to generate
this species in situ.
The pyrrole-containing [N,P]-ligands L1 and L2 were synthetized
according to the methodology previously described [21]. NMR data of
all secondary alcohols 2a-l and 4a-d agreed with the literature (See, SI).
2.2. General procedure for transfer hydrogenation
2.2.1. Procedure under traditional oil-bath heating
The catalytic species was prepared under nitrogen atmosphere by
dissolving ligand L1, [RuCl2(PPh3)3] and KOH (25 mol%) in 2-propanol
(3 mL). The system was heated at 82 °C for 3 h, observing the formation
of a deep red solution, this is the pre-activation time. Then, acet-
ophenone (1 equiv) was added. After magnetic stirring for 15 h, the
reaction mixture was cooled and filtered through a celite-alumina pad
to remove any catalyst.
The product (2a) was yielded in 97%, after chromatography pur-
ification (Table 1, entry 3). Under the same conditions, using the half of
the catalytic system load (entry 4), the calculated conversion was 88%.
When the reaction was conducted without the pre-activation step, no
conversion was obtained (entry 2), which indicates that this step is
crucial under conventional heating.
When, this reaction was assisted by microwave heating at 100 °C for
60 min, we observe that pre-activation step was not necessary, ob-
taining practically the same conversion in both cases, 91 and 90%,
respectively (Table 1, entries 6 and 7). At this temperature, the mi-
crowave reactor reaches a pressure of 5 bars. The conversion obtained
under these conditions shows that the microwave method is compar-
able to that performed under conventional reflux heating. However, the
reaction time is drastically reduced from 18 to 1 h and the pre-activa-
tion step is not required to form the catalytically active species. Like-
wise, to demonstrate the influence of the [N,P]-ligand, two control
experiments were performed (Table 1, entries 1 and 5), these reactions
afforded modest conversions.
2.2.2. Procedure under microwave heating with catalyst pre-activation
The catalytic species was prepared in a 30 mL microwave-trans-
parent process vial by dissolving ligand L1 (0.5 mol%), [RuCl2(PPh3)3]
(0.5 mol%) and KOH (5% mol) in 2-propanol (3 mL). The system was
heated at 100 °C for 5 min, observing the formation of a deep red so-
lution. Then, acetophenone (1 equiv) was added. After 60 min, the re-
action mixture was cooled and filtered through a celite-alumina pad to
remove any catalyst.
2.2.3. General procedure under microwave irradiation without catalyst pre-
activation
In a 30 mL microwave-transparent process vial were added the
corresponding ligand, [RuCl2(PPh3)3], KOH (5 mol%) and ketone in 2-
propanol (3 mL). The mixture was heated at 100 °C during the required
reaction time. Then, the reaction mixture was cooled and filtered
through a celite-alumina pad to remove any catalyst.
50

E.P. Sánchez-Rodríguez et al.
CatalysisCommunications115(2018)49–54
O
[N,P]-ligand
[Pd]
X
O
Z
OMe
+
OMe
Base, MW
R
R
O
I
O
Our previous
work
[N,P]-ligand
[Pd]
Z
Z = O, NR1
Base, MW
R
R
[N,P]-ligand
[Ru], 2-PrOH
O
OH
Me
Ar
Me
R
P
Ar
Base, MW
N
N
This work
R
O
[N,P]-ligand
[Ru], 2-PrOH
OH
[N,P]-ligand
Base, MW
Fig. 1. Catalytic applications of [N,P] pyrrole-phosphine ligands.
Following with the screening to find the optimal conditions for as-
sisted-microwave transfer hydrogenation, we conducted several ex-
periments. First, we tested several bases (Table 2, entries 1–5). The best
result was obtained using KOH (91%) and followed very close by NaOH
(89%). We choose the former because of its easier handling and better
solubility in 2-propanol. Next, the KOH load was modified to 1, 5 and
15 mol%. With the lowest load, the conversion falls to 31% (entry 6),
and with 5 and 15%, the results were the same as 25% (entries 7, 8),
thereby 5% of KOH was used for the following experiments. Likewise,
formic acid/triethylamine was used as hydrogen source, however, the
reaction does not take place (entry 9). The reaction was conducted at
lower temperatures (60 °C and 80 °C, respectively), obtaining a low
conversion (Table 2, entries 10–11). At higher temperature (110 °C,
entry 12) the conversion was very low, 15%, probably due to possible
decomposition of catalyst. Thus, the optimal temperature was 100 °C.
We also modified the reaction time, observing that at 30 min, the re-
action reached the maximum conversion (entry 13). An increasing in
the reaction time, does not improve the conversion (entry 14).
conversion (Table 2, entry 15) and using 2 equivalents of L1 per [Ru]
precursor, the conversion notably increases (entry 16). Likewise, when
we added a relation 1:1 [Ru]/L1, the conversion remains practically the
same than using 0.5:0.5 [Ru]/L1 (Table 2, entries 7 and 17).
Using the optimized conditions, the analogous L2 (N,N-dimethyl-
1H-pyrrol-1-amine-2-di(o-tolyl)phosphine and the commercially avail-
able (rac)-BINAP, widely used in asymmetric transfer hydrogenation,
were evaluated. We observed an important difference in the catalytic
activity of these ligands, obtaining with L2 59% conversion (entry 18)
and only 44% with (rac)-BINAP (entry 19). In the last case, the excellent
binding ability of (rac)-BINAP presumably favors the formation of
[RuCl2(rac)BINAP], however this complex only catalyzes the hydro-
genation of ketones under higher pressure conditions and long reaction
times. [30] Both steric and electronic effect play an important role in
the catalytic performance of the system L/Ru. For instance, the differ-
ence between L1 and L2 activities could be explained in terms of the
ligand cone angle model [31]. Thus, we can infer that the change of
phenyl to o-tolyl groups, implies a greater steric effect causing a partial
loss of the ligand activity because of its lower binding ability to ru-
thenium core. Likewise, comparing the electronic characteristics
The catalyst load was also revised, when 0.1% mol of ruthenium
precursor and 0.2% mol of L1 was added, we only obtain 18%
Table 1
Comparison between conventional and microwave irradiation heating.a
Entry
Heating method
Pre-activation time
Reaction time
Catalyst load [Ru]/L1
Conv. (%)d
TOF
f
(h−1
)
1
2
3
4
5
6
7
Thermalb
Thermalb
Thermalb
Thermalb
MWc
0
0
3 h
3 h
0
15 h
15 h
15 h
15 h
60 min
60 min
60 min
1/0
61
0
4.7
–
1/1.2
1/1.2
0.5/0.5
0.5/0
0.5/0.5
0.5/0.5
97e
88
58
91e
90
5.4
9.8
136
182
167
MWc
0
MWc
5 min
a
All the experiments were carried out using Ru(PPh3)3Cl2 as [Ru] source, 25 mol% of KOH and 2-propanol as solvent and hydrogen source.
Reaction conducted at 82 °C.
b
c
d
e
f
Reaction conducted at 100 °C.
Calculated by 1H NMR analysis.
The calculated conversion was corroborated by gas chromatography.
TOF was calculated as [mol product/mol catalyst]/total time.
51

E.P. Sánchez-Rodríguez et al.
CatalysisCommunications115(2018)49–54
Table 2
a
Optimization conditions for acetophenone transfer hydrogenation microwave-promoted.
Entry
Time
(min)
Temp. (°C)
Base
Base load
(mol%)
Catalyst load
Ru]/L (mol %)
Conv. (%)a
1
2
3
4
5
6
7
8
60
60
60
60
60
60
60
60
60
60
60
60
30
90
30
30
30
30
30
100
100
100
100
100
100
100
100
100
60
KOH
NaOH
i-PrONa
i-PrOLi
t-BuOK
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
25
25
25
25
25
1
5
15
5
5
5
5
5
5
5
5
5
5
5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.1/0.1
0.5/1.0
1.0/1.0
91
89
84
79
84
31
91
91
d
9
0
10
11
12
13
14
15
16
17
18
19
10
43
15
91
91
18
76
92
59
44
80
110
100
100
100
100
100
100
100
b
0.5/0.5
0.5/ 0.5
c
KOH
a
Determined by 1H NMR and corroborated by gas chromatography.
The ligand L2 was used instead L1.
(rac)-BINAP was used as ligand.
b
c
d
HCO2H was used as hydrogen source and Et3N as base.
between PPh2 and P(o-Tol)2 fragments, the former can be considered as
the best π-acceptor group, and this behavior could help to explain the
best performance of L1 in transfer hydrogenation.
The conversions with methyl aryl ketones containing electron-donor
groups such as –Me and –OMe, were 67 and 69%, respectively (entries
6–7), however, the lowest conversion was observed with p-acetylaniline
(29%, entry 9). Apparently, the substitution pattern in the series of
acetophenones containing a -OMe group as substituent does not affect
the conversion affording almost the same result (Table 3, entries 7, 10
and 11), although the transfer hydrogenation of the p-OMe acet-
ophenone proceeds more efficiently, which can be attributed to the
steric hindrance and the negative inductive effect of methoxy group on
the other positions, doing the hydrogenation process more difficult. A
similar tendency was observed with eBr group (Table 3, entries 4 and
At the end of each experiment, we have observed the formation of a
black solid in the reaction vial, this allow us to think in the plausible
formation of ruthenium nanoparticles under the transfer hydrogenation
conditions. We thus performed SEM analyses of the crude reaction with
and without acetophenone, finding the non-presence of nanoparticles.
Fig. S1(ESI) depicts selected images where it can be observed crystals
between 0.5 and 3 μm in size. These results suggest that transfer hy-
drogenation proceeds through the formation of a molecular catalytic
species and when the reaction ends the catalytic species decomposes to
RuO2.
When the samples were exposed to air, we identified the formation
of ruthenium oxide, KHCO3 and KCl after analyses by X-ray powder
diffraction. In the case of the crude reaction with acetophenone, XRD
pattern shows the most representative peaks at 28.6°, 35.0°, 40.7°,
44.7°, 58.7°, 60.5°, 66.7°, 74.5°, 84.6 and 88° corresponding to (110),
(101), (020), (210), (220), (002), (221), (202), (231) and (400) planes
of RuO2 orthorhombic structure (JCPDS No. 01–088-0323) (Fig. 2).
Additional peaks are assigned to K(HCO3) (JCPDS No. 01–070-1167)
and KCl (JCPDS No. 00–041-1476). No evidence of RuO2 from XRD
pattern (not showed) of the crude reaction without acetophenone was
observed.
With the best catalytic conditions in hand, we have evaluated the
scope of this catalytic system L1/[Ru] for the transfer hydrogenation of
different aryl methyl ketones (Table 3) and cyclic ketones (Table 4).
Comparing the different substituents included on the para- position of
the phenyl ring, we observe that the best results are obtained with
electron-withdrawing groups –CF3 and eBr (95%, Table 3, entries 3–4),
due to their ability to attract electron density that increases the elec-
trophilic character on the carbonyl carbon, favoring the reduction
process. A similar result was obtained with –NO2, although the con-
version was slightly lower, 80% (Table 3, entry 2).
Fig. 2. XRD patterns of the crude reaction with acetophenone.
52

E.P. Sánchez-Rodríguez et al.
CatalysisCommunications115(2018)49–54
Table 3
with good to excellent conversions of 73–99.9%. For instance, the re-
duction of 2-adamantanone and tropinone proceeds in excellent yields
(Table 4, entries 3–4). The presence of an amino functionality in tro-
pinone does not affect the performance of this catalytic system, thus
evidencing its potential applications in the synthesis of ketones steri-
cally hindered.
Scope of transfer hydrogenation of aryl methyl ketones, using L1 as ligand.a
4. Conclusion
Entry
Product
R
Time (min)
Conv. (%)b,c
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2 g
2 h
2i
H
30
91
80
95
95
78
67
69
29
51
77
74
94
The readily available [N,P]-ligand L1 is active, efficient and robust
as component of the catalytic system used for the transfer hydrogena-
tion mediated by Ru (II), using microwave irradiation as heating
method. This methodology allows the hydrogenation transfer of dif-
ferent ketones under air atmosphere and without the catalytic active
species preformation. Methyl-ketones with electron withdrawing
groups and cyclic ketones were efficiently hydrogenated with good to
excellent conversions. Nevertheless, methyl ketones containing electron
releasing groups afforded modest to good conversions. This behavior
can be attributed to the major electron density over the carbonyl group
provoked by the electronic rich substituents included in the substrates
1f-k. Studies performed by X-ray powder diffraction and SEM analyses
evidence that transfer hydrogenation proceeds through the formation of
a molecular catalytic species and when the reaction ends the catalytic
species decomposes to RuO2.
p-NO2
p-CF3
p-Br
180
150
90
60
180
30
p-F
p-Me
p-OMe
p-NH2
o-Me
o-OMe
m-OMe
m-Br
90
9
180
180
180
180
10
11
12
2j
2 k
2 l
a
All the experiments were carried out using Ru(PPh3)3Cl2 as Ru source, [Ru]
/ L1: 0.5 / 0.5 mol%, 5 mol% of KOH, at 100 °C.
b
Calculated by 1H NMR analysis.
The calculated conversion was corroborated by gas chromatography.
c
Acknowledgements
Table 4
The authors would like to acknowledge the technical assistance
provided by Martin Cruz Villafañe, Héctor Rios Olivares, M. Paz Orta
Perez, Lucero M. Rios Ruiz, Carmen Márquez Alonso. We thank to the
LIA Mexico-France: Laboratoire de Chimie Moléculaire avec applica-
tions dans les Matériaux et la Catalyse (LCMMC), Conacyt 285,722 and
ECOS M13P02 (Conacyt 229,470) projects.
Scope of transfer hydrogenation of cyclic ketones, using L1 as ligand.a
Appendix A. Supplementary data
Entry
1
Product
Structure
Time (min)
180
Conv. (%)b,c
99.9
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.catcom.2018.07.009.
4a
References
2
4b
120
73
[1] D. Wang, D. Astruc, Chem. Rev. 115 (2015) 6621–6686.
[2] Y.-Y. Li, S.-L. Yu, W.-Y. Shen, J.-X. Gao, Acc. Chem. Res. 48 (2015) 2587–2598.
[3] F. Foubelo, C. Nájera, M. Yús, Tetrahedron Asymmetry 26 (2015) 769–790.
[4] S.H. Lee, G.I. Nokonov, ChemCatChem 7 (2015) 107–109.
[5] P.-G. Echeverria, T. Ayad, P. Phansavath, V. Ratovelomanana-Vidal, Synthesis 48
(2016) 2523–2539.
[6] A. Matsunami, Y. Kayaki, Tetrahedron Lett. 59 (2018) 504–513.
[7] O. Prakash, H. Joshi, K.N. Sharma, P.L. Gupta, A.K. Singh, Organometallics 33
(2014) 3804–3812.
3
4
4c
4d
120
180
99.9
90
[8] M. Miyagi, J. Takehara S. Collet, K. Okano, Org. Process. Res. Dev. 4 (2000)
346–348.
[9] G.K.M. Verzijl, A.H.M. de Vries, J.G. de Vries, P. Kapitan, T. Dax, M. Helms,
Z. Nazir, W. Skranc, C. Imboden, J. Stichler, R.A. Ward, S. Abele, L. Lefort, Org.
Process. Res. Dev. 17 (2013) 1531–1539.
[10] S. Duan, B. Li, R.W. Dugger, B. Conway, R. Kumar, C. Martinez, T. Makowski,
R. Pearson, M. Olivier, R. Colon-Cruz, Org. Process. Res. Dev. 21 (2017)
1340–1348.
[11] S. Gladiali, E. Alberico, Chem. Soc. Rev. 35 (2006) 226–236.
[12] I. Carpenter, S.C. Eckelmann, M.T. Kuntz, J.A. Fuentes, M.B. France, M.L. Clarke,
Dalton Trans. 41 (2012) 10136–10140.
[13] A.O. Ogweno, S.O. Ojwach, M.P. Akerman, Dalton Trans. 43 (2014) 1228–1237.
[14] X. Dou, T. Hayashi, Adv. Synth. Catal. 358 (2016) 1054–1058.
[15] A.S. Sinopalnikova, T.A. Peganova, N.V. Belkova, E. Deydier, J.-C. Daran,
E.S. Shubina, A.M. Kalsin, R. Poli, Eur. J. Inorg. Chem. (2018), https://doi.org/10.
1002/ejic.201701344.
a
All the experiments were carried out using Ru(PPh3)3Cl2 as Ru source, [Ru]
/ L1: 0.5 / 0.5 mol%, 5 mol% of KOH, at 100 °C.
b
Calculated by 1H NMR analysis.
The calculated conversion was corroborated by gas chromatography.
c
12). In counterpart, when the substituent on the aromatic ring has a
positive inductive effect, like methyl, the reaction proceeds more easily
with the para-substituted substrate in comparison with the ortho- sub-
stituted (Table 3, entries 7 and 10).
Likewise, the catalytic activity of the L1 was also evaluated using
cyclic ketones 3a-d (Table 4), showing that bulkiness ketones usually
difficult to reduce under transfer hydrogenation protocols, react easily
[16] G. Helmchen, A. Pfaltz, Acc. Chem. Res. 33 (2000) 336–345.
[17] M.P. Carrol, P.J. Guiry, Chem. Soc. Rev. 43 (2014) 819–839.
[18] B.V. Rokade, P.J. Guiry, ACS Catal. 8 (2018) 624–643.
[19] C. Thoumazet, M. Melaimi, L. Ricard, F. Mathey, P. Le Floch, Organometallics 22
(2003) 1580–1581.
[20] R.J. Lundgren, M.A. Rankin, R. McDonald, G. Schatte, M.A. Stradiotto, Angew.
Chem. Int. Ed. 46 (2007) 4732–4735.
[21] J.V. Suárez-Meneses, E. Bonilla-Reyes, E.A. Blé-González, M.C. Ortega-Alfaro,
R.A. Toscano, A. Cordero-Vargas, J.G. López-Cortés, Tetrahedron 70 (2014)
53

E.P. Sánchez-Rodríguez et al.
CatalysisCommunications115(2018)49–54
1422–1430.
[25] S. Lutsenko, C. Moberg, Tetrahedron Asymmetry 21 (2001) 2529–2532.
[22] J.V. Suarez-Meneses, A. Oukhrib, M. Gouygou, M. Urrutigoïty, J.-C. Daran,
A. Cordero-Vargas, M.C. Ortega-Alfaro, J.G. López-Cortés, Dalton Trans. (23)
(2016) 9621–9630.
[23] J.A. Balam-Villarreal, C.I. Sandoval-Chávez, F. Ortega-Jiménez, R.A. Toscano,
M.P. Carreón-Castro, J.G. López-Cortés, M.C. Ortega-Alfaro, J. Organomet. Chem.
818 (2016) 7–14.
[26] K. Leijondahl, A.-B.L. Fransson, J.-E. Bäckvall, J. Org. Chem. 71 (2006) 8622–8625.
[27] M.B. Díaz-Valenzuela, S.D. Phillips, M.B. France, M.E. Gunn, M.L. Clarke, Chem.
Eur. J. 15 (2009) 1227–1232.
[28] T. Marimuthu, H.B. Friedrich, ChemCatChem 4 (2012) 2090–2095.
[29] G. Zassinovich, G. Mestroni, S. Gladiali, Chem. Rev. 92 (1992) 1051–1069.
[30] R. Noyori, T. Ohkuma, M. Kitamura, H. Takaya, N. Sayo, H. Kumobayashi,
S. Akutagawa, J. Am. Chem. Soc. 109 (1987) 5856–5858.
[24] R. Corona-Sánchez, R.A. Toscano, M.C. Ortega-Alfaro, C. Sandoval-Chávez,
J.G. López-Cortés, Dalton Trans. 42 (2013) 11992–12004.
[31] C. Tolman, Chem. Rev. 77 (1977) 313–348.
54