Nickel-catalyzed transfer hydrogenation of ketones using ethanol as a solvent and a hydrogen donor

Article abstract of DOI:10.1039/c6dt02725c

We report a nickel(0)-catalyzed direct transfer hydrogenation (TH) of a variety of alkyl-aryl, diaryl, and aliphatic ketones with ethanol. This protocol implies a reaction in which a primary alcohol serves as a hydrogen atom source and solvent in a one-pot reaction without any added base. The catalytic activity of the nickel complex [(dcype)Ni(COD)] (e) (dcype: 1,2-bis(dicyclohexyl-phosphine)ethane, COD: 1,5-cyclooctadiene), towards transfer hydrogenation (TH) of carbonyl compounds using ethanol as the hydrogen donor was assessed using a broad scope of ketones, giving excellent results (up to 99% yield) compared to other homogeneous phosphine-nickel catalysts. Control experiments and a mercury poisoning experiment support a homogeneous catalytic system; the yield of the secondary alcohols formed in the TH reaction was monitored by gas chromatography (GC) and NMR spectroscopy.

Full text of DOI:10.1039/c6dt02725c

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: N. Castellanos-
Blanco, A. Arevalo and J. J. Garcia, Dalton Trans., 2016, DOI: 10.1039/C6DT02725C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Page 1 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
NickelꢀCatalyzed Transfer Hydrogenation of Ketones Using
Ethanol as Solvent and Hydrogen Donor
Nahury Castellanos-Blanco, Alma Arévalo and Juventino J. García*
Facultad de Química, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad
Universitaria, Mexico City 04510, Mexico.
juvent@unam.mx
ABSTRACT
We report a nickel(0)-catalyzed direct transfer hydrogenation (TH) of a variety of alkyl-aryl,
diaryl, and aliphatic ketones with ethanol. This protocol implies a reaction in which a primary
alcohol serves as a hydrogen atom source and solvent in a one-pot reaction without any added
base. The catalytic activity of the nickel complex [(dcype)Ni(COD)] (e) (dcype: 1,2-
bis(dicyclohexyl-phosphine)ethane, COD: 1,5-cyclooctadiene), towards transfer hydrogenation
(TH) of carbonyl compounds using ethanol as the hydrogen donor was assessed using a broad
scope of ketones; giving excellent results (up to 99 % yield) compared to other homogeneous
phosphine-nickel catalysts. Control experiments and a mercury poisoning experiment support a
homogeneous catalytic system; the yield of the secondary alcohols formed in the TH reaction
was monitored by gas chromatography (GC) and NMR spectroscopy.
Keywords: Homogeneous catalysis, nickel, transfer hydrogenation, ketones, ethanol, secondary
alcohols.
1

Dalton Transactions
Page 2 of 30
View Article Online
DOI: 10.1039/C6DT02725C
1. INTRODUCTION
The catalytic transfer hydrogenation (TH) of ketones is currently recognized as one of the most
valuable synthetic methods for obtaining a number of value-added products including alcohols,
due to its operational simplicity, easy access to hydrogen sources, lower cost, and safety.1
Regularly, the catalysts used for the transfer hydrogenation of ketones are based on Ru,2 Rh,3 Ir,4
Fe,5 and Co,6 exhibiting very good activity and selectivity under low to higher temperatures
(generally 20 – 150 ºC).
Ruthenium and Rhodium compounds with N-heterocyclic carbenes (NHCs) have been widely
used as catalysts in the transfer hydrogenation process of carbonyl compounds.2b, 3d, 6d Albrecht
et al. reported the first rhodium(III) complexes bound to C4-coordinating N-heterocyclic
dicarbenes.2d The exceptionally strong donor ability of carbenes in such a C4-coordination mode
increases the catalytic activity of the rhodium center and allows the efficient TH of
benzophenone in 2 h using iPrOH/KOH and 1 mol % catalyst loading. Recently, Ding et al.
found that the phosphine bis-benzothienyl iridium(III) complex can be used in the hydrogenation
of acetophenone.3a A secondary alcohol was obtained by using 2 mol % of catalyst, tBuOK, at
110 ºC, and 2-propanol as a hydrogen source, and the product was obtained with 65 %
conversion. However, the limited availability, high cost, and toxicity of these precious metals
demand their replacement with earth-abundant, inexpensive, and nontoxic metals. For this
reason, reactions catalyzed by first-row metals such as nickel have attracted increasing
attention.1d, 8
Some complexes of nickel have also been used in the transfer hydrogenation of carbonyl
compounds although in a lesser extent;8 furthermore, several reports emerged describing the
application of supported nickel nanoparticles (NiNPs), 8c, 8d, 8f and a few homogeneous nickel-
2

Page 3 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
based catalysts have been reported for the transfer hydrogenation of ketones; for example, Sattar
et al. reported the use 10 mol % of [Ni(P(OPh)3)4] to catalyze the TH of alkyl and aryl ketones
using HCOONH4.8a This is the first example of a homogeneous Ni(0) catalyst being active in the
reduction of ketones in high yields (68 - 97 %) at 110 ºC with a reaction time of 5 to 24 h and
acetic acid as the solvent. Varghese et al. investigated the use of [NiCl2(PPh3)2] as a catalyst for
the reduction of ketones and aldehydes.8g As a result, phenylmethyl alcohol was produced in
high yield (82 %) using a load of 15 mol % of the nickel complex, NaOH, and reflux for 30 h.
This reaction did not proceed in the absence of NaOH.
The reduction of ketones furnishes secondary alcohols as the principal products;9 they are key
structural units present in various biologically and pharmaceutically active compounds.1c, 1d
Direct hydrogenation of ketones with H2 is a widely used method employed for secondary
alcohols.1e, 6a, 20. In previous work, our group reported one of the few examples using nickel in
homogeneous hydrogenation of ketones using dihydrogen to give the corresponding secondary
alcohols or alkanes successfully.20 However, the use of hazardous pressurized H2 and its limited
availability demand their replacement with other hydrogen donors. Hence, developing more
efficient and green transfer hydrogenation methodologies utilizing non-hazardous and easily
available starting materials would be most desirable for sustainable processes.10 Recently, less
toxic and more readily available molecules such as alcohols,11, 7 formic acid-triethylamine
mixture12, and HCOONa in water13 were used as the hydrogenation agents of carbonyl
compounds for synthesis of secondary alcohols as an alternative to H2.
In most of the cases, 2-propanol is the conventional hydrogen donor/solvent of choice and is also
readily available and inexpensive. Also, the presence of bases such as KOtBu or KOH are
usually necessary for most TH processes in 2-propanol,11 the presence of a strong base can
3

Dalton Transactions
Page 4 of 30
View Article Online
DOI: 10.1039/C6DT02725C
adversely affect selectivity, and it cannot be used for base-sensitive ketones. Primary alcohols
(i.e., ethanol or methanol) are generally not employed as hydrogen donors because of the
unfavorable redox potential of the primary vs. secondary alcohols.11c However, in the last few
years, ethanol has been used efficiently as a reducing agent in TH with formation of
acetaldehyde or ethyl acetate4h, but its use as hydrogen source and solvent has been relatively
less explored.11
Thus, we focused our study on developing a simple catalytic system that works under relatively
mild conditions as well as challenging substrates. We have been interested in the design of
phosphine-nickel(0) complexes and their application in transfer hydrogenation of molecules such
as alkynes14, 15 and α,β-unsaturated ketones16, 17 using ammonia-borane, sodium borohydride,
water, triethylsilane, methanol, and amines as hydrogen sources.14-17 For these reactions, we
found that the best catalysts were nickel (0) complexes using chelating bisphosphines with
electron-donor ligands. Herein, we disclose the use of homogeneous nickel catalysts, in which
[(dcype)Ni(COD)] (dcype: 1,2ethylene-bis(dicyclohexylphosphine)ethane, COD: 1,5-
cyclooctadiene) was used as catalytic precursor showing high catalytic activity for easily
oxidizable alcohols and their use in TH of a variety of ketones using moderate reaction
conditions and high conversions.
2. RESULTS AND DISCUSSION
We previously reported20 the synthesis of nickel complexes [(dippe)Ni(η2-O,C-ketone)] by the
reaction of [(dippe)Ni(ꢀ-H)]2 with a variety of ketones or 1,2-diketone at room temperature.
Thus, considering the exceptional activity of bisphosphine-nickel(0) complexes in homogeneous
hydrogenation of ketones using H2, we are interested in developing active nickel catalysts for
efficient and green transfer hydrogenation of ketones using alcohols as hydrogen sources.
4

Page 5 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
We initially focussed on using primary and secondary alcohols as hydrogen donors for the
reduction of ketones. The results showed that on using 2 mol % of [Ni(COD)2] and 3 mol % of
chelating bisphosphine (dippe: 1,2-bis(di-isopropylphosphino)ethane) performed better using
alcohols as reagent and solvent, for the reduction of acetophenone (Table 1). As seen in Table 1,
the use of methanol resulted in poor conversion of the substrate 1a, and the yield of α-
methylbenzyl-alcohol is low (13 %) (entry 1). The reaction using ethanol as the hydride donor
gave the best conversion and the highest selectivity (entry 2), and the α-methylbenzyl-alcohol
(2a) was produced with a 95 % yield. Using secondary alcohols such as isopropanol and
isobutanol under the same reaction conditions, the yield of product 2a in both cases decreases,
showing that isobutanol is more reactive compared with isopropyl alcohol (53 %) (entry 4).
Furthermore, monitoring the reaction by GC-MS, the corresponding aldehydes were observed by
dehydrogenation of the used alcohols. Dehydrogenative oxidations of the primary alcohols can
proceed in the absence of a base, and generally, secondary alcohols require sub-stoichiometric
amounts of base.11c, 18 Thus, ethanol was converted to acetaldehyde and acetic acid ethyl ester
(ethyl acetate) according to GC-MS analysis (SI, Fig. S39-S40).
Therefore, we focused on performing the transfer hydrogenation under neat conditions with
ethanol and then assessed different amounts of catalyst, time, and temperature for this nickel-
catalyzed methodology (Table 2).
5

Dalton Transactions
Page 6 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Table 1. MetalꢀMediated TH Results with Acetophenone Using Alcohols as the Hydrogen
Source a
Entry
Alcohol b
Conversion (%)
2a (%)
1
13
13
Methanol
Ethanol
2
3
95
4
95
4
Isopropanol
Isobutanol
4
53
53
a 1a (1.1 mmol, 130.8 mg), Alcohol (7 mL), [Ni(COD)2] (0.022 mmol, 6 mg), (dippe) (0.033 mmol, 8.7
mg); All reactions were completed in 130 ºC and 48 h; Yields were determined by GC-MS. b The
alcohol was used as reactant and solvent.
In order to further improve the catalytic system, we investigated a variety of reaction conditions
for the reaction of acetophenone 1a and ethanol, with catalytic amounts of [Ni(COD)2] and the
ligand dippe. On decreasing the temperature to 100 ºC, the reaction gave a low yield of 2a (2 %)
Table 2, entry 1. In this case, ∼97% acetophenone remained unchanged. As mentioned
previously, a high yield of 2a was observed when the temperature was increased at 130 ºC during
48 h (entry 2). Increasing the temperature to 150 ºC both conversion and yield of 2a were
quantitative. A screening of different alkyl phosphines (dcype and dtbpe) at 130 ºC showed that
6

Page 7 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
dcype performed better, achieving a quantitative yield of 2a (entry 6). These reactions occurred
homogeneously, as confirmed by a mercury drop test (entries 4 and 7) without significant loss of
activity.
The use of aryl phosphines [dppf, dppe, P(C6H5)3] or phosphites [P(OC2H5)3] gave, in general,
low conversion of 2a (entries 9-12) with selectivity to the formation of the α-alkylation product
(3a). The catalytic α-alkylation of 1a with ethanol consists of catalytic oxidation of the primary
alcohol into the corresponding aldehyde (acetaldehyde), which undergoes aldol condensation
with the ketone substrate 1a. Subsequent dehydration and catalytic reduction of the α,β-
unsaturated enone furnishes the saturated ketone product 3a.11c Thus, the transfer hydrogenation
of 2a was favored by using σ donor ligands, and the α-alkylation of ketone was favored by using
σ donor / π acceptor ligand under the used reaction conditions.
Screening of different phosphine nickel precursors such as [(P-P)Ni(ꢀ-H)]2 using alkyl di-
phosphines (dippe, dcype, and dtbpe), gave a high yield of a. However, the TH with these
catalytic precursors requires a high reaction temperature (150 ºC) to achieve a quantitative yield
of 2a (entries 16-18). Consequently, we selected the system [Ni(COD)2] / alkyl-phosphines
(dippe or dcype) for further investigation and the study of substrate scope, since this system is
relatively inexpensive and readily commercially available. Control experiments showed no
product formation in the absence of any ligand, [Ni(COD)2] or both (entries 13-15).
7

Dalton Transactions
Page 8 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Table 2. Optimization of Catalyst and Condition for Transfer Hydrogenation of
Acetophenone Using Ethanol a
Entry
[Ni]
Ligand
dippe
T (ºC)
100
130
150
150
130
130
130
130
130
130
t (h)
24
48
48
48
48
48
48
48
48
48
Conv. (%)
2a (%)
3a (%)
1
2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
Ni(COD)2
2
95
100
94
90
100
96
3
2
95
100
94
90
100
96
-
-
-
dippe
3
dippe
-
4b
5
dippe
-
dtbpe
-
6
dcype
-
7b
8
dcype
-
dppe
3
15
-
9
[(C6F5)2PCH2-]2
P(C6H5)3
15
0
-
10
-
8

Page 9 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
11
12
Ni(COD)2
P(OC2H5)3
130
130
130
130
130
150
48
48
48
48
48
48
13
0
-
13
-
Ni(COD)2
dppf
-
-
13c
14d
15
Ni(COD)2
-
dippe
-
0
-
-
-
0
-
-
0
-
-
[(dippe)Ni(ꢀ-H)]2
16
96
96
-
[(dcype)Ni(ꢀ-H)]2
[(dtbpe)Ni(ꢀ-H)]2
17
18
150
150
48
48
98
89
98
89
-
-
a
1a (1.1 mmol, 130.8 mg), ethanol (119.88 mmol, 7 mL), [Ni] (0.022 mmol), Ligand (0.033 mmol);
b
c
Conversion and yields were determined by GC-MS. Hg drop test (0.30 mmol). [Ni(COD)2] (0.022
mmol).d dippe (8.7 mg, 0.033 mmol).
In order to identify some of the catalytically active species in the TH of acetophenone, we
carried out the stoichiometric reaction between [Ni(COD)2] and dippe. As depicted in Scheme 1,
complexes [(dippe)Ni(COD)] (c) and [(dippe)2Ni] (d) were observed as the main products when
using 2 equivalents of [Ni(COD)2] (a) and 3 equivalents of 1,2-bis(di-isopropyl-
phosphino)ethane (dippe) (b) in THF-d8 at room temperature. The 31P{1H} spectrum of this
mixture showed a singlet at 53.92 ppm, which is characteristic of complex [(dippe)2Ni] 19, 20
(Figure 1). The 31P{1H} singlet at 70.15 ppm was assigned to the complex [(dippe)Ni(COD)]
(c). Thus, we synthetized complexes (c) and (b) independently, and their reactivity with
acetophenone was investigated in order to identify the possible active species in the TH of
ketone 1a (Figures 2ꢀ3).
9

Dalton Transactions
Page 10 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Scheme 1. Coordination of the dippe Ligand to [Ni(COD)2]
Figure 1. 31P{1H}-NMR spectrum of reaction between 2 equiv of (a) and 3 equiv of (b) at RT in
THF-d8.
10

Page 11 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
Freund et al.21 reported the use of 1 equiv of (dcype) and 1 equiv of [Ni(COD)2] in THF at room
temperature to produce [(dcype)Ni(COD)] in high yields. Thus, we followed a similar procedure
to prepare [(dippe)Ni(COD)] (c) with an isolated yield of 89 % (see the experimental section and
SI, Fig. S2-S3). Then, the reaction of (c) with acetophenone 1a in THF-d8 was monitored by
31P{1H} NMR spectroscopy (Figure 2). The mixture of acetophenone 1a and complex (c) was
gently heated, increasing the temperature from 25 to 130 ºC. The 31P{1H} NMR spectrum at
room temperature shows the signal assigned to [(dippe)Ni(COD)], at P P P P P P P P . The
spectrum at 50 ºC shows two doublets between 71 and 65 ppm with 2JP-P = 70.36 Hz,
characteristic of similar nickel(0) complexes with diphosphine ligands,19, 20 in agreement with
η2-C=O coordination of ketones proposed for complex [(dippe)Ni(η2-C,O-C8H8O)] 3. When the
temperature was increased to 130 ºC, the original small doublets increased due to the formation
of complex [(dippe)Ni(η2-C,O-C8H8O)] 3 (Figure 2).
(3)
2JP-P = 70.36 Hz
[(dippe)2Ni]
4 h, 130 ºC
(c)
8 h, 90 ºC
4 h, 70 ºC
4 h, 50 ºC
0 h, 25 ºC
Figure 2. 31P{1H} NMR spectra of reaction between complex (c) and acetophenone 1a (THF-d8,
121.32 MHz).
11

Dalton Transactions
Page 12 of 30
View Article Online
DOI: 10.1039/C6DT02725C
The complex [(dippe)2Ni] (d) was obtained in good yield (92 %) using 1 equiv of [Ni(COD)]2
and 2 equiv of (dippe) at room temperature (see the Experimental section and SI, Fig. S4-S5). As
seen in Figure 3, the reaction of complex d with acetophenone 1a does not proceed at low
temperatures, formation of 3 was detected at high temperatures (90 ºC) and longer reaction times
compared to the reaction time with the complex c, and the 31P{1H} NMR spectrum shows the
appearance of two doublets between 71 and 65 ppm with 2JP-P = 70.36 Hz assigned to complex
[(dippe)Ni(η2-C,O-C8H8O)] 3.
The coordination of other ketones such as 4-fluoroacetophenone and 2-furyl-methyl-ketone to c
was also assessed in THF-d8 at 100 ºC during 24 h, allowing the complete formation of η2-C,O
complexes with formula [(dippe)Ni(η2-C,O-ketone)] (3ꢀ5), Scheme 2.
3
2JP-P = 70.36 Hz
10 h, 130ºC
(d)
8 h, 90ºC
4 h, 70ºC
4 h, 50ºC
0 h, 25 ºC
Figure 3. 31P{1H} NMR spectra of reaction between d and 1a (THF-d8, 121.32 MHz).
12

Page 13 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
Complexes 3ꢀ5 typically display two doublets in the range 60-75 ppm with 2JP-P around 68-71
Hz. These doublets are characteristic of two non-equivalent phosphorus atoms coordinated to a
metal center and the magnitude of the 2JP-P characteristic of coordination to a Ni(0) center (see
the Experimental Section and SI, Fig. S6-S14).20
Scheme 2. Formation of [(dippe)Ni(η2ꢀC,Oꢀketone)] complexes 3ꢀ5
With these results, we decided to explore the possibility that the phosphine-nickel(0) derivatives
could activate ethanol and possibly generate hydride species that would be active in the base-free
transfer hydrogenation process. Additionally, to optimize the hydrogenation reaction conditions
and explore the catalytic activity of our Ni catalyst, several nickel phosphine complexes (c) – (f)
were prepared following the method of Freund et al.21 The complexes were isolated as brown or
yellow solids in good yields (79 % - 92 %) and characterized by 1H and 31P{1H} NMR
spectroscopy. The corresponding signals are consistent with experimental values reported from
the literature21 (see Supporting Information). Scheme 3 shows the complexes used in TH of
acetophenone.
13

Dalton Transactions
Page 14 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Scheme 3. Phosphine Nickel Complexes evaluated in Transfer Hydrogenation Catalysis
[(dippe)Ni(COD)]
(c)
[(dippe)2Ni]
(d)
[(dcype)Ni(COD)]
(e)
[(dcype)2Ni]
(f)
When using 2 mol % of Ni catalyst for 12 h and 130 ºC, not conversion of acetophenone was
observed in all cases (Figure 4). The complex [(dippe)Ni(COD)] (c) displayed similar activity as
complex [(dcype)Ni(COD)] (e) to yield 2a in 78 % and 95 % for 24 h, respectively, as seen in
Figure 4. On the other hand, complexes [(dippe)2Ni] (d) and [(dcype)2Ni] (f) were also tested,
but they were found to be less effective at 24 h. Only when increasing the reaction time to 36 h
were some acceptable yields observed (Figure 4). It is important to note that 99 % yield of 2a
was observed after 36 h using the pre-catalyst (e) and a lower conversion was achieved with (c)
(90 %). Due to the relatively high temperature of reaction and the induction period up until 24 h,
selected experiments were performed at 36 h using the mercury drop test to confirm the
homogeneity of the system (see SI, Table S1) and no significant differences in yields of 2a were
observed. These results suggest that nickel catalyst was performed by molecular nickel
complexes and not by nickel nanoparticles.
A decrease in catalyst load to 1 mol % resulted in a significant decrement to produce 2a in
moderate yields (52 % to 72 %) at 48 h and 130 ºC (Figure 5). A catalytic load of 1 mol %
turned out to be ineffective at 36 h; consequently, the most efficient conditions for hydrogenation
14

Page 15 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
of acetophenone are 2 % mol of [(dcype)Ni(COD)] (e), 130 ºC, and 36 h using ethanol as the
hydrogen source and solvent.
Considering these optimized conditions, we turned our attention in the TH of challenging
aliphatic, alkyl-aryl and diaryl ketones, which are difficult to reduce by other nickel catalysts8b,
8g, 8k to obtain the corresponding secondary alcohols (Table 3).
Figure 4. Activity of different nickel pre-catalysts at 130 ºC.
15

Dalton Transactions
Page 16 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Figure 5. Activity of different nickel pre-catalysts using lower catalyst load at 130 ºC.
Key results for the substrate screening are shown in Table 3. Complex (e) catalyzed
hydrogenation of acetophenone to 1-phenylethanol with 99 % conversion at 130 ºC and 36 h.
(entry 1). The yields were also high with the use of acetophenones with electron-donor and
electron-withdrawing substituents (entries 2-4). The details of percent yields, TONs and TOFs
are given in Table 3.
Likewise, good to excellent yields were achieved for the transfer hydrogenation of diaryl
ketones, (entries 6-7). In the case of heteroaromatic ketones such as 2-furyl-methyl-ketone and
di-(2-pyridyl) ketone, yields of 99 % and 95 % were obtained for the secondary alcohol products
1-(furan-2-yl) ethanol and di(pyridine-3-yl)methanol, respectively (entries 7-8).
Similarly, the use of aliphatic ketones such as 2-adamantanone and cyclohexanone gave the
corresponding secondary alcohols in excellent yields of 98 % (entries 9-10). Interestingly, under
16

Page 17 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
the same reaction conditions, benzyl shows 100 % conversion but 65 % selectivity to 1,2-
diphenylethane-1,2-diol (entry 11), 29 % of 1,2-diphenyl ethane, and 6 % of 1,2-diphenyl
ethanol (see SI, Fig. S35-S38). To the best of our knowledge, a Ni-catalyzed TH of ketones using
ethanol as the hydrogen donor and solvent has not been reported so far.8
Table 3. Scope of substrates a
Entry
Ketone (1)
Alcohol (2)
Yield (%)
TON TOF (hꢀ1)
99
50
49
48
1.5
1.4
1.3
1
98
96
2
3
99
99
50
50
1.5
1.5
4 b
5
17

Dalton Transactions
Page 18 of 30
View Article Online
DOI: 10.1039/C6DT02725C
98
99
95
98
99
49
50
48
49
50
1.4
6
7
1.5
1.3
1.4
1.5
8
9
10
65
33
1
11
a Carbonyl compound (1.1 mmol), ethanol (119.88 mmol, 7 mL), [(dcype)Ni(COD)] (0.022 mmol);
Conversion and yields were determined by GC-MS. b Reaction carried out at 150 ºC.
At the beginning of the reaction ethanol was consumed to produce acetaldehyde during the
induction period (12-24 h), then ethyl-acetate began to be produced to yield a final (1:1) ratio.
Thus, we believe the induction period is associated with the production of hydrides involved in
catalysis, and then acetaldehyde reacts with ethanol to yield ethyl-acetate with hydrogen release
(see SI, Scheme1). 4h, 3f
18

Page 19 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
A comprehensive mechanistic proposal that illustrates the TH reaction of ketones using low-
valent nickel is included in the SI section, it considers the results obtained herein and closely
reports on similar transfer hydrogenation process 11c, 17, 18 (see SI, Scheme 1).
3. CONCLUSIONS
In summary, we report an easily accessible, inexpensive, and highly active Ni catalysts for the
homogeneous hydrogenation of C=O bonds to selectively produce alcohols. The used chelating
phosphines with electron-donor ligands allowed a fine-tuning of the catalyst’s performance. The
best catalytic precursor [(dcype)Ni(COD)] operated under relative mild conditions and addresses
a broad substrate scope, covering alkyl-, aryl-, and aryl, alkyl- ketones. The transfer
hydrogenation of C=O bonds using ethanol as the hydrogen donor and solvent proceeded with
high conversion and selectivity. Current investigations are underway on further mechanistic
details and the development of the enantio-selective version of this transfer hydrogenation.
4. EXPERIMENTAL SECTION
Unless otherwise noted, all manipulations were performed using standard Schlenk techniques in
an inert-gas/vacuum double manifold or under an argon atmosphere (Praxair 99.998) in an
MBraun UniLab glovebox (<1 ppm H2O and O2). All liquid reagents were purchased as reagent
grade and were degassed before use. All ketones and [Ni(COD)2] were purchased from Aldrich
and stored in a glovebox for their use. The nickel (I) complexes [(P-P)Ni(ꢀ-H)]2 (P-P = chelating
phosphine ligand) were prepared from a n-hexane slurry of [(P-P)NiCl2] using Super-Hydride
(LiHBEt3), according to the reported procedure.19 The solvents were dried using standard
techniques and stored in the glovebox before use. Deuterated solvents were purchased from
19

Dalton Transactions
Page 20 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Cambridge Isotope Laboratories and were stored under 4 Å molecular sieves for 24 h before use.
NMR spectra were recorded at room temperature on a 300 MHz Varian Unity spectrometer
unless otherwise noted. 1H NMR spectra (δ parts per million) are reported relative to the residual
protio-solvent. 13C{1H} spectra give the characteristic carbon signal of each solvent. 31P{1H}
NMR chemical shifts (δ parts per million) are reported relative to external 85% H3PO4. Coupling
constants (J values) are given in Hz. The following abbreviations are used for the NMR data: s =
singlet; d = doublet; t = triplet, m = multiplet and br=broad. GC-MS determinations were
performed using an Agilent Technologies G3171A equipped with a column: 5 %
1
phenylmethylsilicone, 30 m * .25 mm * .25 ꢀm. H and 13C{1H} NMR spectra of the reduction
products were obtained in CDCl3. Catalytic experiments were carried out in a 100 mL stainless
steel Parr, T315SS reactor. Elemental analyses (EAs) were also performed by USAI-UNAM
using a PerkinElmer microanalizer 2400. EA where determined at USAII-FQ-UNAM.
4.1. Preparation [(dippe)Ni(COD)] (c): A yellow solution of [Ni(COD)2] (0.109 mmol, 30 mg)
in dried THF (3 mL) was added to dippe [1,2-bis(diisopropylphosphino)ethane] (0.109 mmol, 28
mg). After the dippe was dissolved, the solution was stirred for 30 minutes at room temperature.
The solvent was evaporated and further dried for six hours under vacuum to yield a brown solid.
Yield: 37.4 mg (89 %). 1H NMR (300 MHz, THF-d8, r.t.): δ = 4.12 (s, H(b), H(b’), CH-COD),
2.11 (m, H(a), H(a’), CH2-COD), δ = 1.97 (m, H(e, e’) P-CH2), 2.01-0.5 (m, H(c, c’), H(d, d’),
iPr: CH, CH3). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.) δ = 70.18 (s).
4.2. Preparation [(dippe)2Ni] (d): Similarly to the preparation for compound c (vide supra), the
reaction between [Ni(COD)2] (0.109 mmol, 30 mg) in dried THF (3 mL) was added to the liquid
dippe: [1,2-bis(diisopropylphosphino)ethane] (0.218 mmol, 57.22 mg). After the dippe had
dissolved, the solution was stirred for 30 minutes at room temperature. The solvent was then
20

Page 21 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
evaporated and dried for six hours under vacuum to obtain a brown solid. Yield: 58.54 mg (92
%). 1H NMR (300 MHz, THF-d8, r.t.): δ = 1.97 (m, H(a, a’) P-CH2), 2.01-0.87 (m, H(b, b’),
H(c, c’), iPr: CH, CH3). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.). δ = 53.96 (s).
4.3. Preparation [(dcype)Ni(COD)] (e): The nickel (0) complex [(dcype)Ni(COD)] was
prepared following the method of Freund et al.21 Solid dcype (101 mg, 0.24 mmol) was added
in one portion to a yellow solution of [Ni(COD)2] (66 mg, 0.24 mmol) that was stirred in THF (3
mL) at room temperature. After dissolution of the dcype, the yellow reaction mixture was stored
for two days at -28 ºC. Then, the formed yellow crystals were isolated by decantation, washed
with hexanes (6 mL), and dried for six hours under vacuum. Yield: 115 mg (82 %). The resulting
solid was analyzed by NMR spectroscopy: 1H NMR (300 MHz, THF-d8, r.t.): δ = 4.3 (s, H(b),
H(b’), CH-COD), 2.53 (m, H(a), H(a’), CH2-COD), 2.01-1.83 (m, H(c, c’), H(d, d’), Cy: CH,
CH2), 1.62 (m, H(e, e’) P-CH2). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.) δ = 60.
4.4. Preparation [(dcype)2Ni] (f). Similar to the preparation of compound (d), the reaction
between [Ni(COD)2] (0.109 mmol, 30 mg) in THF (3 mL) was added to a solid dcype [1,2-
bis(dicyclohexylphosphino)ethane] (0.218 mmol, 92.18 mg). After the dcype was dissolved, the
solution was stirred for 30 minutes at room temperature. The solvent was then evaporated and
dried for six hours under vacuum to produce a brown solid. Yield: 77.88 mg (79 %). 1H NMR
(300 MHz, THF-d8, r.t.): δ = 2.41-1.05 (m, H(a, a’), H(b, b’) CH2, CH-Cy), 1.62 (m, H(c, c’) P-
CH2). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.) δ = 43.8.
4.5. Preparation [(dippe)Ni(η2ꢀC,OꢀAcetophenone)] (3): A brown solution of
[(dippe)Ni(COD)] (0.145 mmol, 62.23 mg) in THF (5 mL) was added to acetophenone (C8H8O)
(0.145 mmol, 17.40 mg). The resulting dark brown reaction mixture was heated to 100 ºC and
21

Dalton Transactions
Page 22 of 30
View Article Online
DOI: 10.1039/C6DT02725C
stirred during 1 d. The solvent was then evaporated and dried during six hours to give a brown
solid. Yield: 46.04 mg (72 %). NMR spectroscopy: 1H NMR (300 MHz, THF-d8, r.t.): δ = 7.97
(d, H(b), H(b’) CH-Ph), 7.54 (t, H(d), CH-Ph), 7.44 (t, H(c, c’), CH-Ph), 2.53 (s, H(a) CH3), 2.2-
0.5 (m, H(e, e’), H(f, f’), H(g, g’) dippe: CH, CH2, CH3). 31P{1H} NMR (121.32 MHz, THF-d8,
r.t.) δ = 70.20 (d, 2JP-P = 70.36 Hz), δ = 66.50 (d, 2JP-P = 70.36 Hz), selected IR: v (C=O) 1658.39
cm -1.
4.6. Preparation [(dippe)Ni(η2ꢀC,Oꢀ4ꢀFluoroacetophenone)] (4): Similar to the preparation of
compound (3) (vide supra), a brown solution of [(dippe)Ni(COD)] (0.108 mmol, 46.56 mg) in
THF (5 mL) was added to a liquid 4-Fluoroacetophenone (C8H7FO) (0.108 mmol, 15 mg). The
resulting dark brown reaction mixture was heated to 100 ºC and stirred for 1 d. The solvent was
then evaporated and dried for six hours under vacuum to produce a brown solid. Yield: 39.42 mg
(72 %). Anal. Calcd. for (4), C22H39NiOP2F: C, 57.5; H, 8.5; O, 3.5. Exp: C, 57.3; H, 8.6; O, 3.5.
NMR spectroscopy: 1H NMR (300 MHz, THF-d8, r.t.): δ = 7.19 (t, H(b), H(b’) CH-Ph), 6.76 (t,
H(c), H(c´) CH-Ph), 2.52 (s, H(a) CH3), 1.48-0.43 (m, H(d, d’), H(e, e’), H(f, f’) dippe: CH,
CH2, CH3). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.) δ = 70.20 (d, 2JP-P = 70.36 Hz), δ = 66.40
(d, 2JP-P = 70.36 Hz), selected IR: v (C=O) 1683.82 cm -1.
4.7. Preparation [(dippe)Ni(η2C,Oꢀ2ꢀfurylꢀMethylꢀKetone)] (5): Similar to the preparation of
compound (3) (vide supra), a brown solution of [(dippe)Ni(COD)] (0.109 mmol, 46.71 mg) in
THF (5 mL) was added to a liquid 2-furyl-Methyl-Ketone (C6H6O) (0.109 mmol, 12 mg). The
resulting dark brown reaction mixture was heated to 100 ºC and stirred for 1 d. Then, the solvent
was evaporated and dried for six hours under vacuum to produce a brown solid. Yield: 35.26 mg
(75 %). Anal. Calcd. for (5), C20H38NiO2P2: C, 55.7; H, 6.9; O, 7.4. Exp: C, 56.0; H, 6.8; O, 7.2.
22

Page 23 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
1H NMR (300 MHz, THF-d8, r.t.): δ = 7.25 (br, H(d), CH-furyl), 7.17 (d, H(b), CH-furyl), 6.56
(br, H(c) CH-furyl), 2.38 (s, H(a) CH3), 2.2-0.6 (m, H(e, e’), H(f, f’), H(g, g’) dippe: CH, CH2,
CH3). 31P{1H} NMR (121.32 MHz, THF-d8, r.t.) δ = 69.8 (d, 2JP-P = 69.15 Hz), δ = 68.9 (d, 2JP-P
= 69.15 Hz), selected IR: v (C=O) 1675.82 cm -1.
4.8. Preparation αꢀMethylbenzyl alcohol (2a): The reaction was made in a 100 mL Parr reactor
typically charged with an amount of [(dcype)Ni(COD)] (0.022 mmol, 12.94 mg), C8H8O =
Acetophenone 1a (1.1 mmol, 130.8 mg) and ethanol (119.88 mmol, 7 mL). The solution was
heated with vigorous stirring at 130 ºC for 36 h (entry 1, Table 3). After this time, the reactor
was opened in a well-vented hood prior to workup. Orange or yellow colored solutions were
formed. During the reaction monitoring, yields and conversions were determined by GC-MS
chromatography. Afterwards, the solvent was evaporated under vacuum, and the product was
characterized by 1H and 13C{1H} NMR. 1H NMR (300 MHz, CDCl3): δ = 7.32 (H(d, d’), (H(e,
e’), (H(f), CH-Phenyl), 4.85 (m, J H-H = 6 Hz, H(b), CH), 3.63 (br, H(a), OH), 1.44 (H(c), CH3).
13C{1H} NMR (75.36 MHz, THF-d8, r.t.): δ = 146.11 (s, C(c), C-Phenyl), 128.42 (s, C(f), CH-
aromatic), 127.30 (s, C(e), CH-aromatic), 125.48 (s, C(d), CH-aromatic), 70.13 (s, C(a), CH-
OH), 25.25 (s, C(b), CH3).
4.9. Catalytic Studies. All reactions were made in a 100 mL Parr reactor typically charged with
[(dcype)Ni(COD)] (0.022 mmol) and the corresponding ketone (1.1 mmol), [(dcype)Ni(COD)]
(0.022 mmol) and ethanol (119.88 mmol, 7 mL). The solution was heated with vigorous stirring at
130 ºC for the corresponding reaction time. After this, the reactor was opened in a well-vented
hood prior to workup. Orange or yellow colored solutions were formed. During the reaction
monitoring, yields and conversions were determined by GC-MS chromatography. Products and
23

Dalton Transactions
Page 24 of 30
View Article Online
DOI: 10.1039/C6DT02725C
intermediates were characterized by 1H NMR and 13C{1H} NMR after column chromatography
purification using n-hexanes/THF mixtures using a silica gel.
4.10. Mercury Drop Test. Following the procedure described in Table 2 (entry 4 and 7), these
reactions were prepared, and one drop of elemental Hg was added to the reaction mixture. At the
end of each run, the corresponding solution was filtered over celite and analyzed by CG-MS.
ASSOCIATED CONTENT
• Supporting Information available. Includes complete experimental procedures, selected
IR, NMR spectra, and GC-MS determinations of all products. This material is available
free of charge via the Internet.
AUTHOR INFORMATION
Corresponding Author
E-mail: juvent@unam.mx
ACKNOWLEDGMENTS
We thank CONACYT (0178265), PAPIIT-DGAPA-UNAM (IN-202516) and PAIP-FQ for their
financial support to this work. N.C.-B. thanks CONACYT for a graduate studies grant.
REFERENCES
1. Reviews: (a) D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621 – 6686; (b) J.-E.
Bäckvall, J. Organomet. Chem., 2002, 652, 105 – 111; (c) Y. Wei, X. Wu, C. Wang and
24

Page 25 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
J. Xiao, Catal. Today., 2015, 247, 104 – 116; (d) Y.-Y. Li, S.-L. Yu, W.-Y. Shen and J.-
X. Gao, Acc. Chem. Res., 2015, 48, 2587 – 2598; (e) S. E. Clapham, A. Hadzovic and R.
H. Morris, Coord. Chem. Rev., 2004, 248, 2201 – 2237.
2. Ru catalysts: (a) F. E. Fernández, M. C. Puerta and P. Valerga, Organometallics., 2011,
30, 5793 – 5802; (b) S. Burling, M. K. Whittlesey and J. M. J. Williams, Adv. Synth.
Catal., 2005, 347, 591 – 594; (c) Y. Xu, T. Cheng, J. Long, K. Liu, Q. Quian, F. Gao, G.
Liu and H. Li, Adv. Synth. Catal., 2012, 354, 3250 – 3258; (d) O. Prakash, P. Singh, G.
Mukherjee and A. K. Singh, Organometallics., 2012, 31, 3379 – 3388; (e) N. A. Cortez,
G. Aguirre, M. Parra-Hake, R. Somanathan, A. J. Arita, A. L. Cooksy, C. Anaya and G.
Huelgas, Synth. Commun., 2011, 41, 73 – 84; (f) G. Kang, S. Lin, A. Shiwakoti and B.
Ni, Catal. Commun., 2014, 57, 111 – 114; (g) A. M. Kalsin, T. A. Peganova, V. V.
Novikov, A. I. Zhamoytina, L. Gonsalvi and M. Peruzzini, Chem. Eur. J., 2014, 20, 846 –
854; (h) L. Xu, Z. H. Huang, C. A. Sandoval, L. Q. Gu and Z. S. Huang, Org. Process.
Res. Dev., 2014, 18, 1137 – 1141; (i) P. Braunstein, F. Naud and S. T. Rettig, New. J.
Chem., 2001, 25, 32 – 39; (j) L. T. Ghoochany, C. Kerner, S. Farsadpour, F. Menges, Y.
Sun, G. Niedner-Schatterburg and W. R. Thiel, Eur. J. Inorg. Chem., 2013, 24, 4305 –
4317; (k) S. Dayan, N. O. Kalaycioglu, J.-C. Daran, A. Labande and R. Poli, Eur. J.
Inorg. Chem., 2013, 18, 3224 – 3232; (l) O. R. Allen, L. D. Fiel, A. M. Magill, K. Q.
Vuong and M. M. Bhadbhade, Organometallics., 2011, 30, 6433 – 6440; (m) X. Guo, Y.
Tang, X. Zhang and M. Lei, J. Phys. Chem. A., 2011, 115, 12321 – 12330; (n) A. Del
Zotto, C. Greco, W. Baratta, K. Siega and P. Rigo, Eur. J. Inorg. Chem., 2007, 18, 2909 –
2916; (o) J. M. Joerger, J. M. Paris and M. Vaultier, Arkivoc., 2006, 4, 152 – 160; (p) G.
A. Carriedo, P. Crochet, F. J. García Alonso, J. Gimeno and A. Presa-Soto, Eur. J. Inorg.
25

Dalton Transactions
Page 26 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Chem., 2004, 18, 3668 – 3674; (q) L. Wang, H. Ma, L. Song, L. Li, Y. Wang and H.
Wang, RSC Adv., 2014, 4, 1567 – 1569; (r) M. Aydemir, A. Baysal, S. Özkar and L. T.
Yildirim, Inorg. Chim. Acta., 2011, 367, 166 – 172; (s) S. Dayan, F. Arslan, N. Kayaci
and N. O. Kayaycioglu, Spectrochim. Acta. Part A., 2014, 120, 167 – 175.
3. Rh catalysts: (a) D. Wang, K. Zhao, S. Yang and Y. Ding, Z. Anorg. Allg. Chem., 2015,
641, 400 – 404; (b) S. Ruiz-Botella and E. Peris, Chem. Eur. J., 2015, 21, 15263 – 15271;
(c) K. Rafikova, N. Kystaubayeva, M. Aydemir, C. Kayan, Y. S. Ocak, H. Temel, A.
Zazybin, N. Gürbüz and I. Özdemir, J. Organomet. Chem., 2014, 758, 1 – 8; (d) L. Yang,
A. Krüger, A. Neels and M. Albrecht, Organometallics., 2008, 27, 3161 – 3171; (e) K.
Farrell, H. Müller-Bunz and M. Albrecht, Organometallics., 2015, 34, 5723 – 5733; (f) C.
Tejel, M. A. Ciriano and V. Pasarelli, Chem. Eur. J., 2011, 17, 91 – 95.
4. Ir catalysts: (a) A. Ruff, C. Kirby, B. C. Chan and A. R. O’ Connor, Organometallics.,
2016, 35, 327 – 335; (b) X. Wu, X.; X. Li, A. Zanotti-Gerosa, A. Pettman, J. Liu, A. J.
Mills and J. Xiao, Chem. Eur. J., 2008, 14, 2209 – 2222; (c) K. Rafikova, N.
Kystaubayeva, M. Aydemir, C. Kayan, Y. S. Ocak, H. Temel, A. Zazybin, N. Gürbüz and
I. Özdemir, J. Organomet. Chem., 2014, 758, 1 – 8; (d) M. Albrecht, J. R.
Miecznikowski, A. Samuel, J. W. Faller and R. H. Crabtree, Organometallics., 2002, 21,
3596 – 3604; (e) N. García, E. A. Jaseer, J. Munarriz, P. J. San Miguel, V. Polo, M.
Iglesias and L. A. Oro, Eur. J. Inorg. Chem., 2015, 26, 4388 – 4395; (f) A. Choualeb, A.
L. Lough, D. G. Gusev, Organometallics., 2007, 26, 5224 – 5229; (g) Z. E. Clarke, P. T.
Maragh, T. P. Dasgupta, D. G. Gusev, A. J. Lough, K. Abdur-Rashid, Organometallics.,
2006, 25, 4113 – 4117; (h) W. P. Liu, M. L. Yuan, X. H. Yang, K. Li, J. H. Xie, Q. Zhou,
Chem. Commun., 2015, 51, 6123 – 6125.
26

Page 27 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
5. Fe catalysts: (a) S. Enthaler, G. Erre, M. K. Tse, K. Junge and M. Beller, Tetrahedron
Lett., 2006, 47, 8095 – 8099; (b) D. E. Prokopchuk, J. F. Sonnenberg, N. Meyer, Z. M.
De Iuliis, A. L. Lough and R. H. Morris, Organometallics., 2012, 31, 3056 – 3064; (c) A.
Buchard, H. Heuclin, A. Auffrant, X. F. L. Goff and P. L. Floch, Dalton Trans., 2009, 9,
1659 – 1667; (d) V. K. M. Kandepi, J. M. S. Cardoso, E. Peris and B. Royo,
Organometallics., 2010, 29, 2777 – 2782.
6. Co catalysts: (a) S. Rösler, J. Obenauf and R. Kempe, J. Am. Chem. Soc., 2015, 137, 7998
– 8001; (b) G. Zhang and S. K. Hanson, Chem. Commun., 2013, 49, 10151 – 10153; (c)
R. Bigler and A. Mezzetti, Org. Lett., 2014, 16, 6460 – 6463; (d) N. Ding and T. S. Hor,
Dalton Trans., 2010, 39, 10179 – 10185; (e) J. M. Gichumbi, H. B. Friedrich and B.
Omondi, J. Mol. Catal. A: Chem., 2016, 416, 29 – 38.
7. Pd catalysts: (a) Sun, Y.; Guo, Y.; Lu, Q.; Meng, X.; Xiaohua, W.; Guo, Y.; Wang, Y.;
Liu, X.; Zhang, Z. Catal. Lett. 2005, 100, 3 – 4. (b) Muzart, J. Eur. J. Org. Chem. 2015,
5693 – 5707. (c) Braunstein, P.; Naud, F.; Rettig, S. J. New J. Chem. 2001, 25, 32 – 39.
8. Nickel catalysts: (a) S. Iyer and A. Sattar, Synth. Commun., 1998, 28, 1721 – 1725; (b) G.
P. Boldrini, D. Savoia, E. Tagliavini, C. Trombini and A. Umani-Ronchi, J. Org. Chem.
1985, 50, 3082 – 3086; (c) F. Alonso, P. Riente, J. A. Sirvent and M. Yus, Appl. Catal.,
A., 2010, 378, 42 – 51; (d) V. Polshettiwar, B. Baruwati and R. S. Varma, Green. Chem.,
2009, 11, 127 – 131; (e) M. D. Le Page and B. R. James, Chem. Commun., 2000, 1647 –
1648; (f) F. Alonso, P. Riente, M. Yus, Tetrahedron., 2008, 64, 1867 – 1852; (g) S. Iyer
and J. P. Varghese, J. Chem. Soc., Chem. Commun., 1995, 4, 465 – 466; (h) W. N. O.
Wylei, A. J. Lough and R. H. Morris, Organometallics., 2009, 28, 6755 – 6761; (i) B.
Saes, D. G. A. Verhoeven, M. Lutz, R. J. M. Gebbink and M.-E. Moret,
27

Dalton Transactions
Page 28 of 30
View Article Online
DOI: 10.1039/C6DT02725C
Organometallics., 2015, 34, 2710 – 2713; (j) K. Shimura, and K. I. Shimizu, Green
Chem., 2012, 14, 2983 – 2985; (k) P. Phukan and A. Sudalai, Synth. Commun., 2015, 30,
2401 – 2405.
9. C.-H. Cheng, J. Karthikeyan and P.-C. Huang, in Method for synthesis of secondary
alcohols, U.S. Patent 8,410,320 B2, Apr. 2, 2013.
10. R. A. Sheldon, I. Arends and U. Hanefeld, in Green Chemistry and Catalysis, ed. Wiley-
VCH: Weinheim, Germany, 2007, pp. 27, 335 – 339.
11. Alcohols as hydrogen donors: (a) A. Azua, J. A. Mata and E. Peris, Organometallics.,
2011, 30, 5532 – 5536; (b) O. Prakash, H. Joshi, K. Nayan, P. L. Gupta and A. K. Singh,
Organometallics., 2014, 33, 3804 – 3812; (c) H. Lundberg and H. Adolfsson, Synthesis.,
2016, 48, 644 – 652; (d) R. M. Adkins, R. M. Elofson, A. G. Rossow and C. C.
Robinson, J. Am. Chem. Soc., 1949, 71, 3622. (e) D. Wang, C. Deraedt, J. Ruiz and D.
Astruc, J. Mol. Cat. A: Chem., 2015, 400, 14 – 21.
12. A. Fujii, S. Hashiguchi, N. Uematsu, T. Ikarita and R. Noyori, J. Am. Chem. Soc., 1996,
118, 2521 – 2522.
13. S. Ogo, T. Abura, Y. Watanabe, Organometallics., 2002, 21, 2964 – 2969.
14. R. Barrios-Francisco and J. J. García, Inorg. Chem., 2009, 48, 386 – 393.
15. A. Reyes-Sánchez, F. Cañavera-Buelvas, R. Barrios-Francisco, O. L. Cifuentes-Vaca, M.
Flores-Alamo and J. J. García, Organometallics., 2011, 30, 3340 – 3345.
16. N. Castellanos-Blanco, M. Flores-Alamo and J. J. García, Organometallics., 2012, 31,
680 – 686.
17. N. Castellanos-Blanco, M. Flores-Alamo and J. J. García, Dalton Trans., 2015, 44, 15653
– 15663.
28

Page 29 of 30
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02725C
18. H. Lundberg and H. Adolfsson, Tetrahedron Lett., 2011, 52, 2754 – 2758.
19. B. L. Edelbach, R. J. Lachicotte and W. D. Jones, Organometallics., 1999, 18, 4040.
20. A. Flores-Gaspar, P. Pinedo, M. Crestani, M. Muñoz, D. Morales, B. Warsop, W. D.
Jones and J. J. García, J. Mol. Catal. A: Chem., 2009, 309, 1.
21. R. R. A. Freund, H. Görls and J. Langer, Dalton Trans., 2014, 43, 13988 – 14000.
29