Acceptorless dehydrogenation of amines and alcohols using simple ruthenium chloride

Article abstract of DOI:10.1016/j.jcat.2020.03.025

A highly efficient, economic and environmental friendly catalyst system has been developed for the dehydrogenation of alcohols and amines using simple RuCl₃·nH₂O and N-benzylhexamethylenetetramine. The in situ catalyst system efficiently oxidized the primary and secondary amines and secondary alcohols into nitrile, imine and ketone products, respectively in moderate to excellent yields. The developed catalyst system was also found to be efficient for the dehydrogenation of N-heterocyles. A detailed mechanism study revealed the first example of N-benzylhexamethylenetetramine (HMTA-Bz) being simultaneously acting as base, reducing agent and hydride source to generate the [Ru(II)(H)₂] species as the active catalyst. The mechanism studies also revealed both the alcohol and amine oxidation involves dehydrogenative pathway with the evolution of hydrogen as the only by-product. The developed catalyst system also provides possible platform for the release of hydrogen from liquid organic hydrogen carriers (LOHCs).

Full text of DOI:10.1016/j.jcat.2020.03.025

Journal of Catalysis 386 (2020) 1–11
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Acceptorless dehydrogenation of amines and alcohols using simple
ruthenium chloride
⇑
Muthukumar Kannan, Parul Barteja, Preeti Devi, Senthilkumar Muthaiah
National Institute of Technology Kurukshetra, Kurukshetra 136119, Haryana, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient, economic and environmental friendly catalyst system has been developed for the dehy-
drogenation of alcohols and amines using simple RuCl3ÁnH2O and N-benzylhexamethylenetetramine. The
in situ catalyst system efficiently oxidized the primary and secondary amines and secondary alcohols into
nitrile, imine and ketone products, respectively in moderate to excellent yields. The developed catalyst
system was also found to be efficient for the dehydrogenation of N-heterocyles. A detailed mechanism
study revealed the first example of N-benzylhexamethylenetetramine (HMTA-Bz) being simultaneously
acting as base, reducing agent and hydride source to generate the [Ru(II)(H)2] species as the active cat-
alyst. The mechanism studies also revealed both the alcohol and amine oxidation involves dehydrogena-
tive pathway with the evolution of hydrogen as the only by-product. The developed catalyst system also
provides possible platform for the release of hydrogen from liquid organic hydrogen carriers (LOHCs).
Ó 2020 Elsevier Inc. All rights reserved.
Received 28 January 2020
Revised 21 March 2020
Accepted 24 March 2020
Keywords:
Ruthenium
Catalysis
Amine
Alcohol
Oxidation
1. Introduction
and nitrogen for the synthesis of N-doped graphenes [3g].
Recently, our group explored the chemistry of HMTA as base and
The excellent catalytic activities of transition metal complexes
combined with the advent of green organometallic chemistry have
led to a great demand in the development of efficient, selective,
cost effective and environmental friendly catalyst systems for the
chemical synthesis [1]. The role of additives in transition metal cat-
alyzed organic transformations is very crucial in deciding the over-
all catalytic activity and selectivity of the catalyst. Apart from
inorganic acids, bases and metal salts [2], several nitrogen based
compounds including hexamethylenetetramine (HMTA) are also
being used as additives in the literature (Fig. 1) [2d].
HMTA (1) under various reaction conditions, was reported to
decompose to afford products such as NH3, H2, HCN, HCHO, CO,
CO2, and many others, which makes HMTA an attractive candidate
in the field of synthetic chemistry [3,4]. HMTA is a well-known
methylating agent and is used in the synthesis of several industri-
ally important products including Bakelite [3]. In a seminal report,
Afanasiev showed that coordinated HMTA can act as a reducing
agent during the synthesis of molybdenum nitride from (HMTA)2(-
NH4)4-Mo7O24 salt [3e]. Following this, Fu and co-workers reported
the use of HMTA as both ligand as well as reducing agent in copper
catalysed AGET-ATR batch emulsion polymerization [3f]. Qiang
and co-workers have utilized HMTA as a single source of carbon
hydride donor in the ruthenium catalysed oxidation of amines
[5]. Notwithstanding its potential application as a cheap and eco-
friendly additive, HMTA has rarely been used in catalysis [3,5].
To the best of our knowledge HMTA and its derivatives or any
other additives have not been used as a single source of hydride
group, base as well as reducing agent.
Oxidation of alcohol and amine compounds is one of the most
important methodologies in the field of organic synthesis [6]. The
oxidation products such as ketone, nitrile and imine are being used
as intermediates for the synthesis of several industrially important
products such as pharmaceuticals, dye, pesticide, polymer, etc [6].
As a result, a plethora of methods are available for the oxidation of
both alcohol and amine compounds [6]. The transition metal catal-
ysed oxidation reactions are considered to be superior compared to
the conventional methods which make use of stoichiometric
amounts of oxidising agents [7]. Observing the transition metal
catalysed oxidation of alcohols and amines with the evolution of
hydrogen and in the absence of any hydrogen acceptor is very chal-
lenging and considered to be a greener methodology with high
atom economy (Fig. 2). Moreover, the dehydrogenative oxidation
strategy provides a possible solution for the hydrogen storage
and transportation as both alcohols and amines are considered as
liquid organic hydrogen carriers (LOHCs) [8].
Acceptorless alcohol dehydrogenation (AAD) catalysed by tran-
sition metal complexes was first reported by Murahashi and co-
⇑
Corresponding author.
E-mail address: msenthil@nitkkr.ac.in (S. Muthaiah).
https://doi.org/10.1016/j.jcat.2020.03.025
0021-9517/Ó 2020 Elsevier Inc. All rights reserved.

2
M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
N
N
X
R
where
;
N
N
N
N
2
R = Methyl, X = I ( )
N
N
R = Benzyl, X = Br (3)
1
2 & 3
Fig. 1. Role of additives in catalysis and HMTA and its derivatives used in this study.
Fig. 2. Ruthenium catalysed dehydrogenative oxidation of amines and alcohols.
workers [9a]. Following this report several other catalyst systems
have been report for the similar transformation [9]. Some of the
notable examples of commercially available catalysts that are
employed for the acceptorless alcohol oxidation are RuCl3ÁnH2O/
phosphine/NaOH system and [RuCl2(p-Cymene)]2/diamine ligand,
both reported by Beller and co-workers, Grubb’s catalyst in pres-
ence of KOH by Williamson et. al., base free Shvo complex by Hong
et. al., and Ru-pincer complexes reported by Milstein and co-
workers (Fig. 3) [10].
Similar to acceptorless alcohol dehydrogenation, the acceptor-
less dehydrogenation of amines is also very challenging. Some of
the important examples for the ruthenium catalysed acceptorless
oxidation of secondary amines are RuH2(CO)(PPh3)3 and Shvo’s cat-
alyst systems reported by Hong and co-workers [10d] and Ru(II)-
NNC pincer complex used by Wang et.al. [10e]. Compared to the
dehydrogenation of secondary amines, double dehydrogenation
of primary amines to form nitriles are very scarce and
challenging. To the best of our knowledge, only one report is
available on the ruthenium catalysed base free, acceptorless
double dehydrogenation of primary amines to afford nitriles
using NNN-Ru(II) hydride system reported by Szymczak and co-
workers [11]. Bera and co-workers reported an efficient ruthenium
pyrazole complex that catalyses acceptorless dehydrogenation of
primary amines into nitriles in the presence of KOBut [12].
Recently, our group reported an in situ catalyst system generated
from [Ru(benzene)Cl2]2 and HMTA for the efficient conversion of
both primary and secondary amines into nitriles and imines,
respectively (Fig. 4) [5].
Herein, we reported a very efficient process for the dehydro-
genation of both amines and alcohols using an in situ catalyst sys-
tem generated from the commercially available and simple
hydrated
RuCl3
and
easily
available
N-
benzylhexamethylenetetramine (3). We also gathered several
pieces of experimental evidences to strongly indicate this work
represented the first example on the usage of HMTA derivative
being simultaneously acting as base, reducing agent and hydride
Fig. 3. Ruthenium complexes used for the dehydrogenation of alcohols.

M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
3
Fig. 4. Ruthenium chloride catalysed alcohol and amine oxidation.
donor in the field of catalysis. The mechanistic studies revealed
that the dehydrogenation reactions involes ruthenium-dihydride
as active catalyst and amine dehydrogenation involves formation
of imine as intermediate (Fig. 5).
was employed (entries 3 & 4). Interestingly, in both cases the
reactions resulted in exclusive formation of nitrile product
avoiding formation of possible side products such as imine,
secondary amine and amide [13]. Most importantly, the catalyst
system showed excellent activity even in the absence of any oxi-
dizing agent or hydrogen acceptor. In order to check the role of
ruthenium chloride, a blank reaction was carried out without
ruthenium chloride and in presence of additive 3 which resulted
in no formation of product (entry 5). After identifying the suitable
catalyst/additive combination, the reaction solvent was also opti-
mized and toluene was found to be most suitable (entries 4, 6 &
7). The ratio between ruthenium chloride and compound 3 was
also optimized and found that 1:2 ratio was ideal under the given
reaction condition (entries 4 & 8). Several other conditions were
attempted with reduced catalyst/additive loadings and the catalyst
system gave the product 5a in excellent yield even while using
0.5 mol% of catalyst with a turn over number of 194 (entry 10). Fur-
ther decrease in the catalyst/3 loading resulted in decrease in the
yield of the product, however highest turnover number of 328
was obtained while using 0.25 mol% of the catalyst (entries 11–
13). Decreasing both the reaction time and temperature gave the
product in low yields (entries 14–15).
2. Results and discussion
In view of exploring the chemistry of HMTA and it’s derivatives
as additive in the field of catalysis, we have chosen the ruthenium
catalysed amine dehydrogenation reaction. In a seminal report
Hong and co-workers have shown that RuCl3 can act as a potential
catalyst for the dehydrogenation reactions during the synthesis of
amide from amine and alcohol [13b]. Inspired by Hong’s work and
Tang’s report [13a], hydrated RuCl3 catalysed conversion of
benzylamine (4a) to benzonitrile (5a) was chosen as model
reaction and several reactions were attempted to optimize the
reaction conditions (Table 1). Primarily, 5 mol% of hydrated RuCl3
was tested in the absence of any additive under open condition
to nitrogen, using toluene as the solvent at 110 °C for 24 h,
which afforded 5a in poor yield (Table 1, entry 1). When
hydrated ruthenium chloride was tested in the presence of
HMTA (1), benzonitrile (5a) was obtained as the product,
however with low yield leaving lot of unreacted starting material
(entry 2). In view of improving the product yield, we tested the
hydrated ruthenium chloride in combination with N-methyl (2)
and N-benzyl (3) derivatives of HMTA. To our delight, the yield of
the corresponding nitrile product was increased while using
compound 2 as additive and excellent yield was obtained when 3
Having optimized condition for the dehydrogenation of benzy-
lamine, we then explored the substrate scope of our catalytic sys-
tem for the acceptorless dehydrogenative oxidation of several
other primary amine compounds. Compared to the reported cata-
lyst systems all the amine compounds afforded the dehydro-
genated products either in comparable or better yields as
Fig. 5. Ruthenium catalysed dehydrogenation of amines and alcohols.

4
M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
Table 1
a
Optimization of reaction conditions for the dehydrogenation of benzylamine (4a) to benzonitrile (5a)
S.No.
Mol% of [Ru]
L (mol%)
Solvent
Temp (o C)
Time (h)
% Yield of 5a (TON)a
1.
2.
3.
4.
5.
6.
7.
8.
5
5
5
5
Nil
5
5
–
Toluene
-do-
-do-
-do-
-do-
110
-do-
-do-
-do-
-do-
64
24
17
1 (10)
2 (10)
3 (10)
3 (10)
3 (10)
3 (10)
3 (5)
3 (5)
3 (1)
3 (0.5)
3 (0.4)
3 (0.2)
3 (1)
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
12
19 (3.8)
43 (8.6)
97 (19.4)
–
8
–
THF
DCM
Toluene
-do-
-do-
-do-
-do-
-do-
-do-
-do-
40
5
110
-do-
-do-
-do-
-do-
-do-
-do-
70
15
9.
2.5
0.5
0.25
0.2
0.1
0.5
0.5
96 (38.4)
97 (1 9 4)
82 (3 2 8)
62 (3 1 0)
19 (1 9 0)
56
10.
11.
12.
13.
14.
15.
3 (1)
24
Trace
a
GC yields using dodecane as the internal standard and average of at least two runs.
depicted in Table 2. Despite comparable yields of the nitrile prod-
ucts, our system makes use of the simple and commercially avail-
able RuCl3ÁnH2O as the catalyst precursor and easily available
HMTA-Bz as the additive compared to the reported catalyst sys-
tems [5,11,12]. In the beginning, electronic effect on the yields of
nitrile products obtained from oxidation of several substituted
derivatives of benzylamine was studied. The presence of electron
donating groups such as methyl and methoxy substituents in the
p-position of benzylamine gave the corresponding nitrile products
5b and 5c in excellent yields (entries 2 & 3). On the otherhand, the
presence of electron withdrawing groups such as chlorine, fluorine
and nitro groups in the p-position, resulted in decreased yields of
the corresponding nitrile products 5d, 5e and 5f, respectively and
showed a trend in moving from chlorine to fluorine to nitro sub-
stituents (entries 4–6). However, it was observed that the halo
and nitro groups were retained in the nitrile products, which
showed the very good functional group tolerance of our catalyst
system. The dehydrogenation of 4-aminobenzylamine having both
H2N-CR2- and H2N-CH2- groups resulted in modest yield of the
nitrile product 5g, which is similar to the results obtained from
reported catalyst systems (entry 7) [5,11a]. Despite its low yield,
the formation of 5g as the only product showed the high chemos-
electivity of our catalyst system and also showed the advantage of
dehydrogenative amine oxidation over aerobic oxidation in the
presence of oxidizing agents.
Dehydrogenation of 2-methylbenzylamine (4h) afforded the
corresponding nitrile product 5h in moderate yield and replacing
methyl group with electron withdrawing chloro group (4i) resulted
in further decrease in the yield of the product 5i (entries 8 & 9).
Following this, few alkyl amines were also tested and all of
them resulted in very good yields of the nitrile products (entries
10–12). Double dehydrogenation of 2-phenylethylamine (4j)
afforded 2-phenylacetonitrile (5j) in very good yield (entry 10).
Similarly, 1-heptylnitrile (5k) and 1-octylnitrile (5l) were also pro-
duced in very good yields from double dehydrogenation of the cor-
responding amines (entries 11 & 12).
Table 2
a
Dehydrogenative oxidation of amines to nitriles
b
S.No.
1.
Substrate
Product
% Yield
91
2.
3.
4.
90
93
85
5.
6.
83
77
7.
8.
42
63
9.
58
82
In view of extending the substrate scope further, we also tested
the present catalytic system for the dehydrogenative oxidation of
secondary amines as shown in Table 3. The dehydrogenation of
secondary amines such as dibenzylamine (4m) and N-
benzylanilne (4n) resulted in the imine products 5m and 5n,
respectively in very good yields (entries 1 & 2). It has been reported
in the literature that compared to their carbon analogues, nitrogen
containing heterocyclic compounds are easier to dehydrogenate
and considered as potential hydrogen storage meterials [14]. So,
our catalyst system was also tested for the dehydrogenative oxida-
10.
11.
12.
72
79
a
Reaction conditions: Reactions were carried out with amine substrate
(0.5 mmol), RuCl3ÁnH2O (0.5 mol%) and ligand 3 (1 mol%) in toluene (0.6 ml) under
reflux for 24 h (oil bath temperature 115 °C).
b
Isolated yields and average of at least two runs.

M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
5
Table 3
Table 4
a
a
Dehydrogenative oxidation of secondary amines
Dehydrogenative oxidation of alcohols to ketones
b
S.No.
1.
Substrate
Product
% Yield
74
S.No
1.
Substrate
Product
Yielda
84%
2.
68
2.
3.
87%
85%
3.
4.
5.
6.
7.
74
77
88
91
85
4.
5.
6.
74%
73%
70%
a
Reaction conditions: Reactions were carried out with amine substrate
(0.5 mmol), RuCl3ÁnH2O (0.5 mol%) and ligand 3 (1 mol %) in toluene (0.6 ml) under
7.
8.
64%
66%
reflux (oil bath temperature 115 °C).
b
Isolated yields and average of at least two runs.
tion of nitrogen containing heterocyclic compounds. Dehydrogena-
tion of the nitrogen containing heterocyclic compounds 1,2,3,4-
tetrahydroquinoline (4o) and 1,2,3,4-tetrahydroisoquinoline (4p)
resulted in the exclusive formation of the fully dehydrogenated
products quinoline (5o) and isoquinoline (5p), respectively in very
good yields without forming any partially dehydrogenated prod-
ucts, which proves the high efficiency and selectivity of our cata-
lyst system (entries 3 & 4). Dehydrogenation of indoline and 2-
methylindoline proceeded to indole (5q) and 2-methyl-1-H-
indole (5r), respectively in excellent yields (entries 5 & 6). Dehy-
drogenation of 5-methoxyindoline also gave the corresponding
dehydrogenated product 5s in very good yield (entry 7).
Encouraged by the dehydrogenation of amine compounds, we
also examined our catalyst system for the acceptorless oxidation
of alcohol compounds. Initially, we optimized the conditions for
the conversion of 2-phenylethanol (6a) into acetophenone (7a)
using RuCl3ÁnH2O and 3 as the precatalyst and additive, respec-
tively (Table S1). Out of several attempted conditions, we observed
that the acetophenone (7a) was formed in excellent yield while
using 0.5 mol% of RuCl3ÁnH2O and 1 mol% of 3 under toluene reflux
condition for 24 hrs, which is similar to the conditions used for the
amine oxidation. Using the optimized conditions oxidation of sev-
eral alcohol substrates have been explored as depicted in Table 4.
Initially, the dehydrogenation of substituted derivatives of 1-
phenylethanol was tested. The presence of electron donating sub-
stituents such as methyl and methoxy groups in the para position
of 1-phenylethanol resulted in excellent yields of the correspond-
ing ketones 7b and 7c, respectively (entries 2 & 3). The presence
of halogen substituents in the para position resulted in decreased
yields and gave the dehydrogenated products in good yields (en-
tries 4 & 5). Similarly the presence of electron withdrawing nitro
group yielded the corresponding ketone 7f in good yield (entry
6). The presence of substituents in the ortho and meta positions
9.
58%
61%
10.
11.
12.
41%
52%
13.
79%
14.
15.
52%
54%
(continued on next page)

6
M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
after 30 min, vanished after 1 h and resulted in the appearance
Table 4 (continued)
of a new band at 362 nm. The band at 362 nm was in good agree-
ment with Ru(II) complexes reported in the literature [15,16]. Sim-
ilar reactvity and UV pattern (364 nm) was obtained when
unsubstituted HMTA (1) was used in place of HMTA-Bz (3) in com-
bination with RuCl3ÁnH2O (Fig. S36). To get further insight, we have
synthesized the RuCl3(HMTA) complex using the literature proce-
dure [17] and UV-Vis studies were performed (Scheme 2).
S.No
16.
Substrate
Product
Yielda
58%
At room temperature, the DMSO solution of the RuCl3(HMTA)
complex showed a single band at 435 nm and upon heating the
solution at 90 °C for 50 min, the band at 435 nm vanished and
resulted in a new band at 366 nm. The apperance of bands at
435 and 366 nm are in good agreement with the UV-Vis studies
carried out on the in situ reaction between RuCl3 and HMTA. These
results indicated that during the catalytic process, the HMTA ligand
coordinates to the Ru center to form RuCl3.HMTA complex, fol-
lowed by its decomposition under the given reaction condition to
generate the catalytically active Ru(II) species. The observation of
Ru(II) species in UV studies suggests that HMTA and its derivatives
can act as reducing agents, which is in good agreement with the lit-
erature reports [3e,3f].
After identifying that the catalytically active species contained
Ru (II) unit, a series of NMR studies were carried out in order to
gather further insights into the mechanism (Fig. 7). A solution of
hydrated ruthenium chloride and HMTA-Bz (3) in 1:2 ratio in
DMSO-d6 showed the peaks corresponding to 3. When the reaction
mixture was heated in the NMR tube up to 80 °C, no change in peak
positions were observed. However, when the sample was heated at
90 °C for 20 min, the 1H NMR spectrum showed a complex reaction
mixture, suggesting that the decomposition of HMTA-Bz (3) starts
at this temperature leading to the formation of the active catalyst.
The decomposition of free and metal coordinated HMTA into prod-
ucts such as NH3, H2, HCN, CH4 and many others is well docu-
mented in the literature [4d,4e] In addition to the appearance of
decomposition product signals, two hydride signals were also
observed at À0.14 and À0.87 ppm. The decomposition of HMTA-
Bz (3) in the presence of RuCl3ÁnH2O in a closed NMR tube under
deaerated condition excludes the possibility of external oxygen
taking part in the reaction. These results indicated that HMTA
and its derivatives can act as the source of hydride, which is in
good agreement with our recent report [5]. It is also evident from
the literature that the hydrogen by-product which is formed from
decomposition of 3 may act as the potential source of hydride
group [19]. The observation of small amount of benzaldehyde in
1H NMR spectrum is attributed to the decomposition of HMTA-Bz
due to inadvertent presence of water. The decomposition of
17.
Nil
a
Reaction conditions: Reactions were carried out with alcohol substrate
(0.5 mmol), RuCl3ÁnH2O (0.5 mol%) and ligand 3 (1 mol %) in toluene (0.6 ml) under
reflux (oil bath temperature 115 °C). Isolated yields and average of at least two runs.
of 1-phenylethanol resulted in moderate yields of the ketone prod-
ucts, showing the present catalyst is sensitive to the steric factor
(entries 7–12). Diphenylmethanol (6m) was also oxidised to ben-
zophenone (7m) in very good yield (entry 13).
Dehydrogenative oxidation of few cyclic aliphatic alcohols were
also tested and all of them resulted in the formation of correspond-
ing ketones in moderate yields (entries 14 – 16). It was observed
that our catalyst system was ineffcient for the oxidation of primary
alcohols. Thus, no product formation was observed while using our
catalyst system for the dehydrogenation of benzylalcohol (6q),
leaving only the unreacted starting material (entry 17).
In order to ascertain the evolution of hydrogen and dehydro-
genative pathway, the oxidation of benzylamine (4a) was carried
out in the presence of cyclohexene as hydrogen acceptor as shown
in the following scheme. In a typical closed vessel reaction, a mix-
ture of benzylamine and cyclohexene in 1:10 equivalent ratio in
dry toluene in the presence of 0.5 mol% of RuCl3ÁnH2O as catalyst
and 1 mol% HMTA-Bz as additive were heated at 110 °C for 24 h
(Scheme 1). This reaction proceeded to the formation of cyclohex-
ane in 29% yield. Similarly, the oxidation of 1-phenylethanol (6a) in
the presence of cyclohexene gave the acetophenone (7a) and cyclo-
hexane in 48% and 23% yields, respectively. The formation of cyclo-
hexane from both the reactions suggested that the reactions
involved hydrogen evolution and followed the dehydrogenative
pathway. The decrease in the yields of dehydrogenated products
5a and 7a may be attributed to the availabilty of lesser head space
in the closed vessel compared to the open vessel.
To investigate the role of HMTA-Bz (3) and nature of active cat-
alyst, UV-Vis studies were carried out on a mixture of RuCl3ÁnH2O
and 3 using DMSO as solvent (Fig. 6).
The electronic sepctra of a DMSO solution of RuCl3ÁnH2O and 3
(1:2 ratio) showed a single band at 404 nm. The solution was then
heated at 90 °C, cooled before collecting the UV-Vis data. It was
observed that the intensity of the band at 404 nm was decreased
RT
0.5hr
1hr
404nm Ru(III)
362nm Ru(II)
407nm Ru(III)
300
400
500
600
Wavelength (λ/nm)
Scheme 1. Oxidation of benzylamine (4a) and 1-phenylethanol (6a) in the presence
of cyclohexene.
Fig. 6. UV-Vis studies of a solution of RuCl3ÁnH2O and HMTA-Bz in DMSO.

M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
7
Scheme 2. Synthesis of ruthenium-HMTA complex.
Scheme 3. Oxidation of benzylamine (4a) using anhydrous ruthenium chloride.
HMTA-Bz in presence of water to form benzaldehyde has been con-
firmed with the help of 1H NMR study (Figure S38). Further, to
ascertain the metal induced decomposition of HMTA-Bz, similar
1H NMR studies were performed using anhydrous RuCl3 and
HMTA-Bz in DMSO-d6, which resulted in the formation two
hydride peaks at À0.39 and À0.50 ppm (Fig. S39). The observed
hydride peaks are in good agreement with the values obtained
for the product obtained from a reaction between [Ru(benzene)
Cl2]2 and HMTA reported by our group [5]. In addition, we also car-
ried out the NMR tube reaction of a mixture of RuCl3ÁnH2O and
unsubstituted HMTA (1) in DMSO-d6, which also resulted in the
formation of of hydride peaks at À0.24 and À0.61 ppm in the 1H
NMR spectra (Fig. S40).
We also carried out the oxidation of benzylamine in the pres-
ence of anhydrous ruthenium chloride and 3, under identical reac-
tion condition as shown in Scheme 3. It was observed that the
dehydrogenated product benzonitrile was formed in 92% yield.
Similarly, the anhydrous RuCl3 catalysed 1-phenylethanol resulted
in acetophenone in 81% yield. These results suggested that water or
some other oxygen source is not necessary for the generation of
active catalyst.
investigations are underway to identify the exact structure and
mechanism for its formation. Based on the above experimental
studies and literature reports [5,11b] the following mechanism
has been proposed for the double dehydrogenation of amines
(Fig. 8).
According to the proposed mechanism, the active catalyst [Ru
(II)(H)2] (A) generated from the reaction of HMTA-Bz and RuCl3-
ÁnH2O undergoes oxidative addition with amine, followed by H2
elimination to form Ru-H intermediate B. The Ru-H intermediate
B undergoes b-hydrogen transfer to form imine coordinated inter-
mediate C. The formation of imine as intermediate during the
course of reaction was confirmed with the help of 1H NMR study
(Fig. S41) and was in agreement with the mechanism proposed
for the [Ru(benzene)Cl2]2/HMTA catalysed amine dehydrogenation
by our group [5]. Compound C with the elimination of hydrogen
forms nitrile coordinated ruthenium complex D, which further
undergoes elimination of nitrile compound to regenerate the active
catalyst A.
The mechanism of dehydrogenative alcohol oxidation has been
studied extensively in the literature. In a seminal report Bäckvall
and co-workers proposed the mechanism for the oxidation of alco-
hols using a ruthenium-dihydride active catalyst and following this
several other groups including ours reported the oxidation mecha-
nism involving ruthenium-dihydride species as the active catalyst
These observations clearly indicated that HMTA-Bz acted as
reducing agent, base and source of hydride group and generated
[Ru(II)(H)2] complex as the catalytically active species. Further
Fig. 7. Evidence for the formation of Ru-(H)2 intermediate from RuCl3ÁnH2O and HMTA-Bz.

8
M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
4. Experimental section
4.1. General information
All procedures were carried out under purified nitrogen envi-
ronment using standard Schlenk apparatus. All the apparatus were
oven dried prior to use. Airless procedure was followed for all syn-
theses irrespective of air stability of the final compounds. All the
solvents were used after drying and degassing process. Other
chemicals were purchased from commercial suppliers and used
as received without further purification. HMTA derivatives
HMTA-Me (2) and HMTA-Bz (3) were synthesized using the litera-
ture report [20].
4.2. General procedure for dehydrogenation of amine
RuCl3ÁnH2O (0.5 mol %), HMTA-Bz (1 mol %), amine (0.25 ml)
and dry toluene (1.0 ml) were placed in a Schlenk tube. The reac-
tion mixture was stirred under open condition to nitrogen and
refluxed for 24 h. After completion of the reaction all toluene were
evaporated under vacuo, the oxidized products were isolated from
crude mixture with the help of column chromatography using hex-
ane/EtOAc as eluent. The formation of products was confirmed by
comparing the 1H NMR data with literature reports.
Fig. 8. Mechanism involving double dehydrogenation of amine.
4.3. General procedure for dehydrogenation of alcohol
RuCl3ÁnH2O (0.5 mol %), HMTA-Bz (1 mol %), alcohol (0.25 ml)
and dry toluene (1.0 ml) were placed in a Schlenk tube. The reac-
tion mixture was stirred under open condition to nitrogen and
refluxed for 24 h. After completion of the reaction all toluene were
evaporated under vacuo, the oxidized products were isolated from
crude mixture with the help of column chromatography using hex-
ane/EtOAc as eluent. The formation of products was confirmed by
comparing the 1H NMR data with literature reports.
4.4. Procedure for dehydrogenation of benzylamine in the presence of
cyclohexene
In
0.0025 mmol), HMTA-Bz (0.0016 g, 0.005 mmol), amine (0.05 ml,
0.5 mmol), cyclohexene (0.4 ml, mmol) and dry toluene
a
50 ml closed vessel reactor, RuCl3ÁnH2O (0.0005 g,
Fig. 9. Mechanism involving dehydrogenation of alcohol.
5
(0.6 ml) were taken under N2 atmosphere. The resulting mixture
was heated at 110 °C for 24 h. After completion of the reaction,
the solution was cooled to room temperature, extracted with
DCM and analyzed with the help of Gas Chromatography. GC
yields: benzonitrile 52% and cyclohexane 29%.
[18]. Based on our experimental reults and literature reports we
have put forwarded the following mechanism for the oxidation
of alcohol to ketone usig our catalyst system (Fig. 9). According
to the proposed mechanism, the active catalyst Ru(II)-dihydride
species (A) coordinates with alcohol to form the complex B, which
upon elimination of hydrogen molecule and b-elimination resulted
in the formation of Ru-alkoxy species C. The intermiediate C fur-
ther undergoes b-elimination to yield the ketone product and
regenerate the active catalyst A.
4.5. Procedure for dehydrogenation of secondary alcohol in the
presence of cyclohexene
In
a
50 ml closed vessel reactor, RuCl3ÁnH2O (0.0004 g,
0.0020 mmol), HMTA-Bz (0.0013 g, 0.0041 mmol), alcohol
(0.05 ml, 0.41 mmol), cyclohexene (0.32 ml, 4.1 mmol) and dry
toluene (0.6 ml) were taken under N2 atmosphere. The resulting
mixture was heated at 110 °C for 24 h. After completion of the
reaction, the solution was cooled to room temperature, extracted
with DCM and analyzed with the help of Gas Chromatography.
GC yields: acetophenone 48% and cyclohexane 23%.
3. Conclusions
In conclusion we have reported the first example of HMTA and
it’s derivatives simultaneously acting as reducing agent, base and
source of hydride in the simple hydrated RuCl3 catalysed acceptor-
less dehydrogenation of primary and secondary amines and alco-
hols. Mechanistic studies revealed the formation a [Ru(II)(H)2]
fragment as the catalytically active species, while oxidation of both
amines and alcohols proceeded through dehydrogenative pathway
with the evolution of hydrogen gas.
4.6. Procedure for in situ 1H NMR -study to show Ru-H formation:
RuCl3ÁnH2O (0.005 g, 0.5 mol %), HMTA-Bz (0.016 g, 1 mol %)
and DMSO-d6 as solvent (0.4 ml) were taken in a NMR tube under
N2 atmosphere. The reaction mixture was heated at 90° C for

M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
9
20 min and then was cooled to room temperature before recording
the NMR data.
NMR (CDCl3, 300 MHz): d = 8.49 (s, 1H), 7.92–7.95 (m, 2H), 7.40–
7.55 (m, 8H), 4.95 (s, 2H) ppm.
N-Benzylidene aniline (5n) [21f]: Colourless liquid; yield: 68%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz):
d = 8.49 (s, 1H), 7.94 (t, J = 3 Hz, 2H), 7.51–7.52 (m, 2H), 7.49–7.50
(m, 1H), 7.40–7.45(m, 2H), 7.28–7.29 (m, 1H), 7.26–7.28 (m, 1H),
7.24 (m, 1H) ppm.
Quinoline (5o) [21h]: Colourless liquid; yield: 74%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CD3OD, 400 MHz):
d = 8.77 (bs, 1H), 8.22–8.23 (d, J = 3 Hz, 1H), 7.98–8.00 (d,
J = 6 Hz, 1H), 7.81–7.82 (d, J = 3 Hz, 1H), 7.70–7.71 (t, J = 3 Hz,
1H), 7.51–7.54 (t, J = 6 Hz, 1H), 7.40–7.43 (t, J = 3 Hz, 1H) ppm.
Isoquinoline (5p) [21h]: Yellow liquid; yield: 77%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 400 MHz):
d = 9.32 (s, 1H), 8.53 (d, J = 3 Hz, 1H), 8.09 (d, J = 3 Hz, 1H), 7.93
(d, J = 6 Hz, 1H), 7.75–7.75 (m, 2H), 7.65–7.68 (m, 1H) ppm.
Indole (5q) [21h]: White solid; yield: 88%. Eluent: hexane/ethyl
acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz): d = 8.11(s, 1H), 7.70–
7.73 (d, 1H), 7.42–7.44(d, 1H) 6.60–6.62 (m, 1H).
2-Methyl-1H-indole (5r) [21h]: Yellow solid; yield: 91%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
300 MHz): d = 7.83 (s, 1H), 7.54–7.57 (d, J = 9 Hz 1H), 7.28–7.32
(m, 1H), 7.08–7.18 (m, 2H), 6.25–6.26 (m, 1H), 2.46 (s, 3H) ppm.
5-Methoxy indole (5s) [21h]: White solid; yield: 85%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz):
d = 8.08 (s, 1H), 7.30 (d, J = 9 Hz, 1H), 7.16–7.20 (m, 2H), 6.92 (d,
J = 6 Hz 1H), 6.53 (bs, 1H), 3.90 (s, 3H) ppm.
4.7. Procedure for in situ 1H NMR -study to show formation of imine
intermediate:
In N2 atmosphere, benzylamine (0.05 ml, 0.46 mmol), RuCl3-
ÁnH2O (0.0005 g, 0.5 mol %) HMTA-Bz (0.002 g, 1 mol %) and
toluene d8 as a solvent (0.4 ml) were taken in the NMR tube. The
reaction mixture was heated at 110 °C for 10 h and then the reac-
tion mixture was cooled to room temperature before collecting the
NMR data.
4.8. Procedure for the 1H NMR decomposition study of HMTA-Bz (3):
HMTA-Bz (0.040 g, 0.12 mmol) was weighed in open air and
transferred to a NMR tube; DMSO-d6 (0.4 ml) was added and
heated at 90 °C for 20 min. The resulting mixture was cooled to
room temperature before collecting the NMR spectra.
Benzonitrile (5a) [21a]: Colourless oil; yield: 91%. Eluent: hex-
ane/ethyl acetate (4.5:0.5). 1H NMR (CDCl3, 400 MHz: d = 7.60–7.61
(m, 2H), 7.55–7.59 (m, 1H), 7.41–7.45 (m, 2H) ppm.
4-Methylbenzonitrile (5b) [21d]: Colourless oil; yield: 90%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
300 MHz): d = 7.55 (d, J = 9 Hz, 2H), 7.28 (d, J = 9 Hz, 2H), 2.44
(s, 3H) ppm.
4-Methoxybenzonitrile (5c) [21a]: Colourless oil; yield: 93%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
300 MHz): d = 7.46(d, J = 9 Hz, 2H), 6.87 (d, J = 9 Hz, 2H), 3.86 (s,
3H) ppm.
Acetophenone (7a) [22a]: Colourless oil; yield: 84%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz:
d = 7.94–7.96 (d, 2H)., 7.53–7.58 (m, 1H), 7.42–7.45(m, 2H), 2.60
(s, 3H) ppm.
4-Chlorobenzonitrile (5d) [21c]: White solid; yield: 85%.
Eluent: hexane/ethyl acetate, (4.7:0.3). 1H NMR (CDCl3,
300 MHz): d = 7.57 (d, J = 9 Hz, 2H), 7.46 (d, J = 9 Hz, 2H) ppm.
4-Fluorobenzonitrile (5e) [21b]: Colourless oil; yield: 83%.
Eluent: hexane/ethyl acetate, (4.7:0.3). 1H NMR (CDCl3,
300 MHz): d = 7.95 (d, J = 9 Hz, 2H), 7.47 (d, J = 9 Hz, 2H) ppm.
4-Nitrobenzonitrile (5f) [21c]: White solid; yield: 77%. Eluent:
hexane/ethyl acetate, (4.3:07). 1H NMR (CDCl3, 300 MHz): d = 8.09
(d, J = 9 Hz, 2H), 7.46 (d, J = 9 Hz, 2H) ppm.
4-Aminobenzonitrile (5g) [21a]: Pale yellow Solid; Yield: 44%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz):
d = 7.41 (d, J = 9 Hz, 2H), 6.64 (d, J = 9 Hz, 2H), 4.15(s, 2H) ppm.
2-Methylbenzonitrile (5h) [21d]: Colourless oil; yield: 63%.
Eluent: hexane/ethyl acetate, (4.2:0.8). 1H NMR (CDCl3,
300 MHz): d = 7.52–7.54 (d, J = 8 Hz, 1H), 7.42–7.46 (t, J = 8 Hz,
1H), 7.21–7.28 (m, 2H), 2.49 (s, 3H) ppm.
2-Chlorobenzonitrile (5i) [21e]: Colourless oil; yield: 58%.
Eluent: hexane/ethyl acetate, (4.2:0.8). 1H NMR (CDCl3,
300 MHz): d = 8.34 (t, J = 3z, 1H), 7.58–7.63 (m, 1H), 7.16–7.20
(m, 2H), ppm.
2-Phenylacetonitrile (5j) [21h]: Colourless liquid; yield: 82%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
400 MHz): d = 7.33–7.36 (m, 5H), 3.72 (s, 2H) ppm.
1-Heptanenitrile (5k) [21g]: Colourless liquid; yield: 72%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
400 MHz): d = 2.29 (t, J = 8 Hz, 2H), 1.57–1.64 (p, J = 6 Hz, 2H),
1.38–1.42 (p, J = 8 Hz, 2H), 1.24–1.29 (m, 4H), 0.85(t, J = 4 Hz,
3H) ppm.
Octanenitrile (5l) [21g]: Colourless liquid; yield: 79%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 400 MHz):
d = 2.34–2.38 (t, J = 8 Hz, 2H), 1.64–1.72 (p, J = 8 Hz, 2H), 1.38–
1.42 (p, J = 8 Hz, 2H), 1.24–1.29(t, J = 8 Hz, 6H), 0.84.0.87 (t,
J = 4 Hz, 3H) ppm.
4-Methyl acetophenone (7b) [22a]: Colourless oil; yield: 87%.
Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz:
d = 7.84–7.87 (d, 2H), 2.58 (s, 3H), 7.24–7.27 (d, 2H), 2.41 (s, 3H)
ppm.
4-Methoxy acetophenone (7c) [22a]: Pale yellow solid; yield;
85%. Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
300 MHz: d = 7.92–7.95 (m, 2H), 6.92– 6.95(m, 2H), 2.56 (s, 3H),
3.87 (s, 3H) ppm.
4-Bromo acetophenone (7d) [22a]: White solid; yield: 74%.
Eluent: hexane/ethyl acetate, (4.4:0.6). 1H NMR (CDCl3, 300 MHz:
d = 7.80–7.83 (d, 2H), 7.58–7.61 (d, 2H), 2.58 (s, 3H) ppm.
4-Chloro acetophenone (7e) [22a]: Yellow solid; yield; 73%
Eluent: hexane/ethyl acetate, (4.4:0.6). 1H NMR (CDCl3, 300 MHz:
d = 7.87–7.90 (d, 2H), 7.41–44 (d, 2H), 2.58 (s, 3H) ppm.
4-Nitro acetophenone (7f) [22a]: Yellow solid; yield: 70%.
Eluent: hexane/ethyl acetate, (4.2:0.8). 1H NMR (CDCl3, 300 MHz:
d = 8.30–8.33 (d, 2H), 8.10–8.13 (d, 2H), 2.68 (s, 3H) ppm.
2-Methyl acetophenone (7g) [22a]: Colourless oil; yield: 64%.
Eluent: hexane/ethyl acetate, (4.6:0.4). 1H NMR (CDCl3, 300 MHz:
d = 7.69–7.71 (m, 1H), 7.35–7.41 (m, 7.35–7.41 (1H), 7.24–7.26
(m, 2H), 2.58 (s, 3H), 2.53 (s, 3H) ppm.
2-Methoxy acetophenone (7h) [22a]: Yellow solid; yield: 66%.
Eluent: hexane/ethyl acetate, (4.7:0.3). 1H NMR (CDCl3, 300 MHz:
d = 7.72–7.75 (m, 1H), 7.43–7.49 (m, 1H), 6.95–6.99 (m, 2H), 3.91
(s, 3H), 2.61(s, 3H) ppm.
2-Bromo acetophenone (7i) [22a]: Yellow solid; yield: 58%.
Eluent: hexane/ethyl acetate, (4.6:0.4). 1H NMR (CDCl3, 300 MHz:
d = 7.98–8.01(m, 2H), 7.53–7.63(m, 1H), 7.48–7.50 (m, 1H), 4.47
(s, 3H) ppm.
2-Hydoxy acetophenone (7j) [22d]: Colourless oil; yield: 61%.
Eluent: hexane/ethyl acetate, (4.4:0.6). 1H NMR (CDCl3, 300 MHz:
d = 12.27 (s, 3H), 7.72–7.75 (m, 1H), 7.45–7.50 (m, 1H), 6.88–
6.99(m, 1H), 2.63(s, 3H) ppm.
N-Benzylidene-1-phenylmethanamine (5m) [21f]: Colourless
2-Bromo 4-methyl acetophenone (7 k) [22e]: Colourless oil;
liquid; yield: 74%. Eluent: hexane/ethyl acetate, (4.2:0.8). 1H
yield: 39%.Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,

10
M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
(c) S.A. Sojka, R.A. Wolfe, G.D. Guenther, Macromolecules 14 (1981) 1539–
1543;
(d) J.M. Dreyfors, S.B. Jones, Y. Sayed, Am. Ind. Hyg. Assoc. J. 50 (11) (1989)
579–585;
(e) S. Chouzier, M. Vrinat, T. Cseri, Appl. Catal., A 400 (2011) 82–90, and
references therein.
300 MHz: d = 7.90(m,1H), 7.88(m,1H) 7.28–7.31 (s, 1H), 4.43 (s,
3H), 2.43 (s,3H) ppm.
3-Methoxy acetophenone (7l) [22c]: Colourless oil; yield: 52%.
Eluent: hexane/ethyl acetate, (4.3:0.7). 1H NMR (CDCl3, 300 MHz:
d = 7.47–7.54 (m, 2H), 7.33–7.38 (m, 1H), 7.08–7.12 (m, 1H) 3.83
(s, 3H), 2.58 (s, 3H) ppm.
Benzophenone (7m) [22a]: White solid; yield: 79%. Eluent:
hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3, 300 MHz: d = 7.8
1–7.84(m, 4H), 7.58–7.63 (m, 2H), 7.47–7.52(m, 4H) ppm.
Cycloheptanone (7n) [22b]: Colourless oil; yield: 54%. Eluent:
hexane/ethyl acetate, (4.8:0.2). 1H NMR (CDCl3, 300 MHz: d = 2.4
5–2.49(m, 4H), 1.65–1.69 (m, 8H) ppm.
Cycloocatnone (7o) [22b]: Colourless oil; yield: 58%. Eluent:
hexane/ethyl acetate, (4.7:0.3). 1H NMR (CDCl3, 300 MHz: d = 2.3
7–2.41(m, 4H), 1.82–1.90 (m, 4H), 1.49–1.57(m, 4H), 1.35–1.37
(m, 2H) ppm.
[5] M. Kannan, S. Muthaiah, Organometallics 38 (19) (2019) 3560–3567.
[6] (a) J.-E. Bäckvall, In: modern oxidation methods, Wiley-VCH, Weinheim, 2004,
pp. 193–222;
(b) R.A. Sheldon, J.K. Kochi, Metal-catalyzed oxidations of organic compounds,
Academic Press, New York, 1981;
(c) P. Pollak, G. Romeder, F. Hagedorn, H.-P. Gelbke, Nitriles In Ullmann’s
encyclopedia of industrial chemistry, Wiley-VCH, Weinheim, Germany, 2012;
(d) A. Kleemann, J. Engel, B. Kutscher, D. Reichert, Pharmaceutical substance:
synthesis patents, applications, 4th ed., Georg Thieme Verlag, Stuttgart, 2001;
(e) R.C. Larock, Comprehensive organic transformations: a guide to functional
group preparations, Wiley-VCH, Weinheim, 1989, pp. 819–995;
(f) R.W. Layer, The chemistry of imines, Chem. Rev. 63 (5) (1963) 489–510;
(g) M.E. Belowich, J.F. Stoddart, Chem. Soc. Rev. 41 (2012) 2003–2024;
(h) S.F. Martin, Pure Appl. Chem. 81 (2) (2009) 195–204.
[7] (a) R. Ray, A.S. Hazari, G.K. Lahiri, D. Maiti, Chem. Asian J. 13 (2018) 2138–
2148, and references therein;
(c) P.P. Fu, R.G. Harvey, Chem. Rev. 78 (1978) 317–361;
(d) A.J. Bailey, B.R. James, Chem. Commun. 20 (1996) 2343–2344;
(e) K. Yamaguchi, N. Mizuno, Angew. Chem. Int. Ed. 42 (2003) 1480–1483.
[8] (a) R.H. Crabtree, Chem. Rev. 117 (2017) 9228–9246;
(b) E. Clot, O. Eisenstein, R.H. Crabtree, Chem. Commun. (2007) 2231–2233.
[9] (a) S. Murahashi, T. Naota, K. Ito, Y. Maeda, H. Taki, J. Org. Chem. 52 (19) (1987)
4319–4327;
3,4-dihydronaphthalen-1(2H)-one (7p) [22a]: Dark brown oil;
yield: 58%. Eluent: hexane/ethyl acetate, (4.5:0.5). 1H NMR (CDCl3,
300 MHz: d = 8.02–8.05(m, 1H), 7.44–7.47(m, 1H), 7.24–7.33(m,
2H), 2.95–2.99 (t, 1H), 2.64–2.68 (q, 1H), 2.12–2.18(t, 1H) ppm.
Declaration of Competing Interest
(b) M. Bertoli, A. Choualeb, A.J. Lough, B. Moore, D. Spasyuk, D.G. Gusev,
Organometallics 30 (2011) 3479–3482;
(c) C. Gunanathan, D. Milstein, Science 341 (2013) 1229712;
(d) T.C. Johnson, D.J. Morris, M. Wills, Chem. Soc. Rev. 39 (2010) 81–88, and
references therein;
(e) C. Vicent, D.G. Gusev, ACS Catal. 6 (2016) 3301–3309;
(f) Z. Wang, B. Pan, Q. Liu, E. Yue, G.A. Solan, Y. Ma, S. Yanping, W.-H. Sun,
Catal. Sci. Tech. 7 (8) (2017) 1654–1661.
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
[10] (a) H. Junge, M. Beller, Tetrahedron Lett. 46 (2005) 1031–1034;
(b) H. Junge, B. Loges, M. Beller, Chem. Commun. (2007) 522–524;
(c) G.R.A. Adair, J.M.J. Williams, Tetrahedron Lett. 46 (2005) 8233–8235;
(d) S. Muthaiah, S.H. Hong, Adv. Synth. Catal. 354 (2012) 3045–3053;
(e) W. Qingfu, C. Huining, Y. Zhengkun, Organometallics 37 (4) (2018) 584–
591;
Authors acknowledge the financial support from Science and
Engineering Research Board, India in the form of Start-Up Research
Grant (Young Scientists, NO. 58/FT /C5-092/2014). Authors also
acknowledge TEQIP-III for the financial assistance. In addition we
would like to dedicate this work to Prof. Shunmugasundaram
Arunachalam on the occassion of his 75th birthday.
(f) J. Zhang, M. Gandelman, L.J.W. Shiman, H. Rozenberg, D. Milstein,
Organometallics 23 (2004) 4026–4033;
(g) C. Gunanathan, D. Milstein, Chem. Rev. 114 (2014) 12024–12087, and
references therein.
[11] (a) K.-N.T. Tseng, A.M. Rizzi, N.K. Szymczak, J. Am. Chem. Soc. 135 (2013)
16352–16355;
Appendix A. Supplementary material
(b) L.V.A. Hale, T. Malakar, K.-N.T. Tseng, P.M. Zimmerman, A. Paul, N.K.
Szymczak, ACS Catal. 6 (2016) 4799–4813.
[12] I. Dutta, S. Yadav, A. Sarbajna, S. De, M. Hölscher, W. Leitner, J.K. Bera, J. Am.
Chem. Soc. 140 (2018) 8662–8666.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2020.03.025.
[13] (a) R. Tang, S.E. Diamond, N. Neary, F. Mares, J. Chem. Soc. Chem. Commun. 13
(1978) 562;
(b) S.C. Ghosh, S.H. Hong, Eur. J. Org. Chem. (2010) 4266–4270.
[14] (a) R.H. Crabtree, Energy Environ. Sci. 1 (2008) 134;
(b) A. Moores, M. Poyatos, Y. Luo, R.H. Crabtree, New J. Chem. 30 (2006) 1675–
1678;
References
[1] (a) R.H. Crabtree, The organometallic chemistry of the transition metals, 4th
ed., John Wiley and Sons, Hoboken, 2005;
(b) D. Astruc, Organometallic chemistry and catalysis, Springer, Heidelberg,
Berlin, 2007;
(c) B. Cornils, W.A. Herrmann, Aqueous-phase organometallic catalysis-
concepts and applications, VCH, Weinheim, 1998;
(d) X. Wu, J. Xiao, Handbook of green chemistry, Wiley-VCH, Weinheim,
Germany, 2010, p. 105.
(c) D.E. Schwarz, T.M. Cameron, P.J. Hay, B.L. Scott, W. Tumas, D.L. Thorn,
Chem. Commun. (2005) 5919–5921;
(d) Y. Cui, S. Kwok, A. Bucholtz, B. Davis, R.A. Whitney, P.G. Jessop, New J.
Chem. 32 (2008) 1027–1037;
(e) E. Clot, O. Eisenstein, R.H. Crabtree, Chem. Commun. (2007) 2231–2233.
[15] J. Zhiqin, D.S. Huang, A.R. Guadalupe, Inorganica Chim. Acta. 305 (2000) 127–
134.
[16] S. Sathiyaraj, C. Jayabalakrishnan, J. Chil. Chem. Soc. 58 (2013) 1637.
[17] N. Katsaros, Transition Met. Chem. 8 (1983) 345–348.
[18] (a) A. Aranyos, G. Csjernyik, K.J. Szabó, J.-E. Bäckvall, Chem. Commun. (1999)
351–352;
(b) A. Bhatia, S. Muthaiah, ChemistrySelect 3 (2018) 3737–3741.
[19] (a) N. Ahmad, S.D. Robinson, M.F. Uttley, J. Chem. Soc. Dalton Trans. (1972)
843–847;
[2] (a) V.P. Ananikov, Understanding organometallic reaction mechanisms and
catalysis: computational and experimental tools, Wiley-VCH Verlag GmbH &
Co. KGaA, 2015;
(b) L. Hong, W. Sun, D. Yang, G. Li, R. Wang, Chem. Rev. 116 (2016) 4006–
4123;
(c) B. Grzybowska-Swierkosz, Top. Catal. 21 (2002) 35–46;
´
(d) Y. Kwak, K. Matyjaszewski, Polym. Int 58 (2009) 242–247.
[3] (a) J. Kaihua, B. Shuhong, Johnson Matthey Technol. Rev. 62 (1) (2018) 89–106,
and references therein;
(b) M.H.G. Prechtl, Y. Ben-David, D. Giunta, S. Busch, Y. Taniguchi, W.
Wisniewski, H. Görls, R.J. Mynott, N. Theyssen, D. Milstein, W. Leitner, Chem.
Eur. J. 13 (2007) 1539–1546.
(b) S.-L. Zheng, M.-L. Tong, X.-M. Chen, Coord. Chem. Rev. 246 (2003) 185;
(c) P.T. Ndifon, M.O. Agwara, A.G. Paboudam, D.M. Yufanyi, J. Ngoune, A.
Galindo, E. Álvarez, A. Mohamadou, Trans. Met. Chem. 34 (7) (2009) 745;
(d) X. Caillault, Y. Pouillaoua, J. Barrault, J. Mol. Catal. A Chem. 103 (1995) 117–
123;
(e) P. Afanasiev, Inorg. Chem. 41 (2002) 5317–5319;
(f) C. Cheng, S. Gong, Q. Fu, L. Shen, Z. Liu, Y. Qiao, C. Fu, Polym. Bull. 66 (2011)
735–746;
[20] V. Selvaraj, V. Rajendran, Ultrason. Sonochem. 20 (2013) 1236–1244.
[21] (a) B.V. Rokade, S.K. Malekar, K.R. Prabhu, Chem. Commun. 48 (2012) 5506–
5508;
(b) Q. Feng, Q. Song, Adv. Synth. Catal. 356 (2014) 1697–1702;
(c) Y.-J. Zhuang, J. Liu, Y.-B. Kang, Tetrahedron Lett. 57 (2016) 5700–5702;
(d) C. Tao, B. Wang, L. Sun, Z. Liu, Y. Zhai, X. Zhang, J. Wang, Org. Biomol. Chem.
15 (2017) 328–332;
(e) O. Grossman, D. Gelmam, Org. Lett. 8 (6) (2006) 1189–1191;
(f) D. Damodara, R. Arundhathi, P.R. Likhar, Adv. Synth. Catal. 356 (2014) 189–
198;
(g) Z. Xing, Z. Ju, Y. Zhao, Y. Zhu, Y. Qiang, Y. Qian, Sci. Rep. 6 (2016) 26146.
[4] (a) W. Chen, M. Hu, H. Wang, X. Wu, X. Gong, X. Yan, D. Zhen, G. He, J. Mater.
Chem. A. 5 (2017) 15038–15047;
(b) W.E. Silva, S. Alves Jr, R.F. De Farias, J. Coord. Chem. 57 (11) (2004) 967–
971;

M. Kannan et al. / Journal of Catalysis 386 (2020) 1–11
11
(g) J. Kim, S.S. Stahl, ACS Catal. 3 (2013) 1652–1656;
(h) S. Furukawa, Y. Ohno, T. Shishido, K. Teramura, T. Tanaka, ACS Catal. 1
(2011) 1150–1153.
(c) X. Du, Y. Luan, F. Yang, D. Ramella, X. Shu, New J. Chem. 41 (2017) 4400–
4405;
(d) S.B. Anand, V.J. Radha, S. Rakesh, K.T. Avesh, Catal. Commun. 40 (2013) 27–
[22] (a) Z. Yuecheng, L. Liu, C. Xiaohui, Z. Jiquan, Polyhedron. 105 (2016) 170–177;
(b) Z. Jian-Ji, P.T. Wai, L. Yungen, L. Wei, M.C. Chi, Chem. Sci. 10 (2019) 4883–
4889;
31;
(e) R.J. Faggyas, E.D.D. Calder, C. Wilson, A. Sutherland, J. Org. Chem. 82 (2017)
11585–11593.