One-Pot Catalytic Approach for the Selective Aerobic Synthesis of Imines from Alcohols and Amines Using Efficient Arene Diruthenium(II) Catalysts under Mild Conditions

Article abstract of DOI:10.1002/ejoc.201701408

A green and efficient catalytic approach for the selective synthesis of imines in air at room temperature was achieved with the aid of newly synthesised diruthenium(II) complexes [(η⁶-p-cymene)₂Ru₂Cl₂(μ-L)] containing substituted 1,2-diacylhydrazine ligands. All the new complexes were fully characterised by analytical and spectroscopic techniques. The solid-state structure of a representative complex was solved by single-crystal X-ray diffraction analysis. The diruthenium(II) complexes also enable the selective aerobic oxidation of alcohols to aldehydes. The catalytic reaction operates in the presence of air as a green and cheap oxidant, and releases water as the only by-product. A plausible mechanism is proposed for the imine formation, which is believed to proceed via an aldehyde intermediate.

Full text of DOI:10.1002/ejoc.201701408

A Journal of
Accepted Article
Title: One-pot Catalytic Approach for the Selective Aerobic Synthesis
of Imines from Alcohols and Amines using Efficient Arene
Diruthenium(II) Catalysts under Mild Condition
Authors: Ramesh Rengan, Saranya Sundar, and Małecki Jan Grzegorz
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201701408
Link to VoR: http://dx.doi.org/10.1002/ejoc.201701408
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European Journal of Organic Chemistry
10.1002/ejoc.201701408
FULL PAPER
One-pot Catalytic Approach for the Selective Aerobic Synthesis
of Imines from Alcohols and Amines using Efficient Arene
Diruthenium(II) Catalysts under Mild Condition
[
a]
[a]
[b]
Sundar Saranya, Rengan Ramesh* and Jan Grzegorz Małecki
[
4]
Abstract: A green and efficient catalytic approach for the selective
presence of metal catalyst and so on.
t-Bu
synthesis of imines in open air at room temperature was achieved
HO NH
6
OH
NH
O
with the aid of newly synthesized diruthenium(II) complexes [(η -p-
O
O
OH
HN
N
N
N
O
O
2 2
cymene) Ru Cl
2
(μ-L)] comprising of substituted 1,2-diacylhydrazine
N
t-Bu
.
CH3C6H4SO3H
H
HO
O
ligands. All the new complexes have been fully characterized by
analytical and spectral techniques. The solid state structure of
representative complex was corroborated with the help of single-
crystal X-ray diffraction method. Further, diruthenium(II) complexes
enable the selective aerobic oxidation of alcohols to aldehydes. The
catalytic reaction operates in the presence of green and economic
oxidant air with the release of water as the only by-product. A
plausible mechanism is proposed for the synthesis of imines, which
is believed to proceed via an aldehyde intermediate.
NO2
Anti inflammatory agent
Antiviral agent
Antimalarial agent
O
F
OH
Cl
N
O
N
N
OH
Antimicrobial agent
Antimicrobial agent
Figure 1. Representative examples for bioactive imines
Although there are several new methodologies reported in
the recent years, acceptorless dehydrogenation of alcohols is an
efficient and atom-economical alternative, which produces
carbonyl compounds, organo-nitrogen compounds such as
imines, amines and amides. Further, the reason for this
method to be considered worthy is its synthetic applications
such as widely available cheaper and less toxic alcohols, non-
polluting by-products water or hydrogen gas and oxidant-free
synthesis.
Introduction
Azomethines/Imines are vital class of nitrogen compounds
that are considered to be one of the most versatile components
in organic synthesis, agricultural chemicals and pharmaceuticals
[
5]
[
1]
(
Figure 1). Especially, imines containing highly reactive
azomethine group are recognized as key intermediates in many
organic transformations such as asymmetric synthesis, cross-
dehydrogenative couplings, multi-component synthesis and
The catalytic direct N-alkylation of amines with alcohols by
borrowing hydrogen methodology occurs via short-lived imine
intermediates which undergo immediate hydrogenation to form
[
2]
cycloadditions. Hence, development of highly efficient and
environmentally benign methodology for the synthesis of imines
still remains a significant area of research among the synthetic
chemists.
[
5g]
the desired amines.
However, selective dehydrogenative
imine synthesis was achieved by Milstein’s ruthenium PNP-type
[
5c]
pincer complex, where the reaction stops at the imine stage.
This breakthrough synthetic methodology attracted the
Conventional synthetic routes to imines involve simple
condensation of aldehydes or ketones with amines via
azeotropic distillation or in the presence of dehydrating agent.
Several other known methodologies for imination includes
researchers towards the imine chemistry.
Several nobel
transition metal complexes of Ru, Os and Ir have been reported
for imine synthesis, which most often require high temperature,
[
3]
Schmidt reaction, Aza-Wittig reaction, Stieglitz rearrangement.
[
6]
inert atmosphere, special condition and long reaction time.
Besides, it can also be achieved by self-condensation of amines,
reaction of alkynes and amines, coupling of vinyl bromides with
amines, reaction of nitroarenes and primary alcohols in the
Besides the experimental conditions, few of them suffer from
major shortcomings in producing byproducts such as
amines/amides/esters. Though there are several pincer type Ru
and Os complexes reported for imine synthesis, non-pincer type
complexes are not much covered in the literature. Further, alkali
metal hydroxides catalysed imine synthesis has also been
[
[
a]
b]
Centre for Organometallic Chemistry
School of Chemistry
Bharathidasan University
Tiruchirappalli 620 024
[7]
reported, but the reaction proceeds only at high temperature.
Here we have focused on nobel transition metal catalysts
that operate under mild reaction condition (Scheme 1). Riisager
Tamil Nadu, India
E-mail: ramesh_bdu@yahoo.com
Homepage: http://www.bdu.ac.in/centers/comc/
Department of Crystallography
Institute of Chemistry
and co-workers employed Au/TiO
2
(0.2 mol%) heterogeneous
catalyst for the imine synthesis with dangerous pure oxygen as
[8a]
the oxidant under ambient conditions (a).
Later, Qing Xus
University of Silesia
group successfully used palladium catalyst (1 mol%) for mild
one-pot synthesis of imines using air as oxidant with good yields
of the products, but the drawback is long reaction time (3 days)
40-006 Katowice, Poland
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Organic Chemistry
10.1002/ejoc.201701408
FULL PAPER
[8b]
(
b). Wang and co-workers developed Pd/DNA (Pd: 2.9 mol%)
catalyst for dehydrogenative imination in O under mild
conditions that requires nitrogen atmosphere protection (c).
In continuation of our growing interest on the
H
2
development of new catalytic systems for various coupling
[
8c]
[10]
reactions, herein we report arene dinuclear Ru(II) complex for
Kobayashi et al. obtained imines from gold/palladium alloy
nanoparticles (1.5 mol%) with molecular oxygen as an oxidant in
the direct synthesis of imines in the presence of air as greener
oxidant under mild condition. To the best of our knowledge, no
reports available for the direct synthesis of imines using arene
diruthenium(II) catalysts that operate under mild and aerobic
condition.
[
8d]
THF-TFE medium under aerobic condition (d).
One-pot
synthesis of imines was achieved using Ag(NHC) (0.1 mol %)
catalyst in dry air at room temperature (e). Though the Ag(NHC)
catalyst is efficient and versatile, it is not easily accessible from
[
8e]
the synthetic point of view.
Results and Discussion
6
Literature reports
Complexes of the type [(η -p-cymene)
2
Ru
2
Cl
2
(μ-L)] were
6
(
a) Au/TiO2, O2, KOCH3, r.t.
b) Pd(OAc)2, air, neat, r.t.
c)
synthesized from the reaction of equimolar mixture of [(η -p-
Substrates
(
Product
N
cymene)
2
Ru
2
Cl
2
(μ-Cl)
2
]
and
binucleating
ligands,
N-Benzoyl-4-
N-Benzoyl-4-
N-
(
Pd/DNA, LiOH.H2O,
R1
Benzoylbenzohydrazide
chlorobenzohydrazide
(1)
(2)
or
or
OH
0
N2 balloon, 50
C
R2
R1
(
d) PICB-Au/Pd, NaOH, O
2
methoxybenzohydrazide (3) in toluene for 2 h under reflux
condition(Scheme 2). The orange coloured complexes are air-
stable and highly soluble in polar organic solvents. All the
synthesized complexes were fully characterized with the aid of
elemental analysis, IR, UV-Vis, H and C NMR and Mass
spectral techniques. Further, the coordination of the bridging
binucleating ligand to two ruthenium metal centers is evidenced
0
balloon, 30
C
R2
NH2
(e)
Ag(NHC), BTMAH, 4 Å MS,
dry air, r.t.
This work
1
13
R2
( -p-cymene)2Ru2Cl2(-L)]
NH2

R2
[
R1
N
t-BuOK, 4 Å MS, air, r.t., 24 h
by single crystal X-ray method.
R1
-H2O
R
OH
R
O
O
H

H
N
[
( -p-cymene)2Ru2Cl2(-L)]
R1
N
Na2CO3
N
O
Cl
H2N
H
THF/H2O, 0 0
C
O
t-BuOK, 4 Å MS, air, r.t., 24 h
H2O
O
-
R= -H(1), -Cl(2), -OMe(3)
Scheme 1. Synthetic strategies of imines
The design of new bimetallic catalysts offers opportunity to
modulate the selectivity and activity of the catalytic transformations.
The enhanced activities of these catalysts could be achieved by
careful crafting of two metal active sites (Figure 2). The increased
activity and selectivity of the bimetallic systems are attributed due to
the synergic cooperation between the two metals and the bridging
ligands. Many of the dinuclear complexes were developed as
R
O
Cl
H
[(-p-cymene) Ru Cl (-Cl) ]
O
Ru
2
2
2
2
N
N
Ru
N
H
Toluene, Et3N
Reflux, 2h
N
O
O
Cl
R
[
9a-e]
selective catalysts in organic synthesis.
R= -H(4), -Cl(5), -OMe(6)
Metal pairing
tunes reaction pathway,
activity & selectivity)
Scheme 2. Synthetic route to the arene dinuclear ruthenium(II) complexes.
(
The Infrared spectra of the ligands (1
- 3) showed
−
1
characteristic peaks in the region of 3204–2998 cm , which are
[
11]
assignable to the two N–H groups. The absence of these N-H
bands in the arene dinuclear complexes confirms the
coordination of the ligands via hydrazine nitrogen in the ionized
form. These ligands also exhibited strong absorptions in the
Cl
O
Ru
Ru
N
N
O
−
1
region of 1563–1570 cm which correspond to the carbonyl
groups, whose frequencies were found to slightly decrease upon
complexation. Thus, these observations clearly indicate the
coordination of carbonyl oxygen to each ruthenium(II) ion. The
IR spectra of the complexes therefore confirm the mode of
coordination of the bridging 1,2-benzoylhydrazide ligands to
each ruthenium(II) ion via the hydrazine nitrogens and carbonyl
oxygens in the ionic and neutral form respectively.
Cl
Leaving group
R
Derivation site
sterics and electronics)
1
13
The H and C NMR spectra of complexes (4 - 6) were
recorded in CDCl and are consistent with the structure
proposed. The signals due to NHNH group were observed in the
(
Figure 2. Structure–function relationships in bimetallic system
3
1
1
region of δ 10.42 – 10.60 ppm in free uncoordinated ligands,
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European Journal of Organic Chemistry
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which disappeared upon the coordination further support that the
two ruthenium centers are spanned through the hydrazine
nitrogens in the ionized form. The unsymmetrical structural
THF and dichloromethane provided yields of 92% and 83% of
imines respectively (Table 1, entries 2 and 3). On the other
hand methanol furnished 66% of the desired imine, which was
1
arrangement of complexes 5 and 6 is well supported by the H
1
3
and C NMR spectra. The splitting pattern observed for the p-
cymene protons of complexes 5 and 6 are different from that of
complex 4. This may be attributed due to the substitution at one
of the phenyl rings of the ligands, resulting in an unsymmetrical
environment of the arene moieties attached to each Ru(II) ion.
1
3
Similarly, C NMR spectra of complexes 4-6 are consistent with
the above discussions.
The relative compositions of the complexes have been
studied using HR-ESI-MS spectral technique. The positive ESI
mass spectra of the complexes
corresponding to the cationic fragments [M – Cl – HCl] at m/z (4,
39.1068), (5, 745.0551), (6, 709.0955) respectively. These
4 – 6 showed peaks
+
7
results imply that the two chloro (Cl−) groups are labile and
possibly replaced under the catalytic reaction condition.
6
Molecular structure of [(η -p-cymene)
2
Ru
2
Cl
2
(μ-L1)] (4)
has been determined by single-crystal X-ray diffraction analyses.
Figure 3. ORTEP plots of complex 4. Thermal ellipsoids are shown at the
Crystals of 4 grew from slow diffusion of dichloromethane into
pet-ether solutions and crystallized in the monoclinic with P2 /n
1
30% probability level. Selected bond lengths (Å) and angles (deg): Ru1−O1 =
2
.066 (2), Ru1−N1 = 2.087 (3), Ru1−Cl1 = 2.4121 (10), N1−N1i = 1.427 (6),
Ru1−C8 = 2.217 (4), Ru1−C9 = 2.185 (4), Ru1−C10 = 2.165 (4), Ru1− C11 =
.192 (4), Ru1−C12 = 2.142 (4), Ru1−C13 = 2.186 (4); O1−Ru1− N1= 76.40
11).
space group. The molecular structure of the complex 4 is shown
in Figure 3, which indicate the formation of the arene dinuclear
Ru(II) complexes by the coordination of the bridging ON∩NO
ligand in a monoionised bidentate manner to each ruthenium(II)
ion via the hydrazine nitrogen and carbonyl oxygen including
one chlorine atom and p-cymene ring. It adopts a piano-stool
pseudo octahedral geometry around each Ru(II) ion. In this case,
the two η6-coordinated arene seats of the piano-stool and
chlorine atoms are trans to each other. The bridging chelating
ligand binds to each Ru(II) ion via N and O atoms forming two
stable five membered chelate rings. The bite angles for O(1)-
Ru(1)-N(1), O(1)-Ru(1)-Cl(1) and N(1)-Ru(1)-Cl(1) are
2
(
accompanied by considerable amounts of side-products
1
determined by the H NMR spectral analysis of the crude (Table
1, entry 4). Hence, THF is a choice of solvent from the
optimization. The reaction which showed no reactivity in THF in
the absence of base at room temperature, proceeded smoothly
under reflux conditions with an appreciable yield of 71% of the
corresponding imine (Table 1, entries 5 and 6). The reaction did
not proceed in the absence of catalyst, both at r.t. and at 66 °C
(
Table 1, entries 7 and 8). Since we were interested in exploring
7
6.40(11)°, 85.02(9)° and 84.04(9)° respectively. The bond
the imination under mild condition, we carried out the base
optimisation at room temperature. (Table 1, entries 9 – 11). Out
of the screened bases, t-BuOK was found to be the best choice.
Further, the reaction time was extended to 48 h to enhance the
product yield, but regrettably no significant improvement was
observed (Table 1, entry 12). It is to note that no appreciable
yields have been observed when Ru(II) arene and other
conventional Ru(II) precursors were used as catalysts.
lengths for Ru(1)-N(1), Ru(1)-O(1) are 2.087(3)Å and 2.066(2)Å
respectively. Further, the Ru···Ru distance in this complex is
i
4.920(5) Å. The N1−N1 bond distance is 1.427(6) Å,
corresponding to N−N single bond. Similarly, the bond length of
C1−O1 is 1.280(4) Å, which is consistent with a C=O double
bond. Hence, the X-ray crystallographic studies authenticate the
structure proposed with the aid of other spectroscopic
techniques.
To further evaluate the catalytic efficiency of complexes 5 and 6,
the model substrates were allowed to react under optimised
With a new of class of arene dinuclear Ru(II) complexes(4
-
6) in hand, we commenced our study by investigating the
condition for 24
h at room temperature to yield N-(4-
catalytic activity towards synthesis of imines by the coupling of
alcohols and amines. In light of this, 4-methoxy benzyl alcohol
methoxybenzylidene)-4-methoxybenzenamine in 63% and 84%
respectively (Table 1, entries 13 and 14). Thus we were pleased
to find that complex 4 is relatively active among the three
complexes. Furthermore, the effect of catalyst loading was also
performed. On decreasing the catalyst loading of catalyst 4 from
(
1a) and p-anisidine (2a) were taken as benchmark substrates
complex 4 (1 mol%) as a model catalyst to optimise the reaction
condition. It is known from the literature that there is no set of
rules that a particular solvent or a base helps to achieve the
greatest efficacy. In order to classify the scope of the catalyst,
imination was optimised through the variation of solvents such
as toluene, THF, DCM MeOH in the presence of t-BuOK as
,
base at different temperature for 12 h.
To our delight, apolar solvent toluene yielded 90% of the
desired imine (Table 1, entry 1). Polar aprotic solvents such as
1
mol% to 0.25 mol%, a substantial drop in the yields of the
products were observed (Table 1, entries 15 - 17). Thus, from
the data summarised in Table 1, the finest optimum conditions
for the diruthenium(II) catalysed imination was achieved by
operating the reaction at room temperature under open air with 1
mol % of catalyst 4 in the presence of t-BuOK for 24 h.
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European Journal of Organic Chemistry
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FULL PAPER
After arriving at the optimized reaction conditions, we
wished to probe the substrate scope and consistency of this
methodology. Therefore, we experimented the imine formation
by varing the substituents on alcohols and amines in order to
examine the breadth of substrates including electron rich and
deficient groups tolerated in the reaction (Table 2). In the
dehydrogenative imination reaction, p-anisidine reacted
[a]
Table 2. Aerobic Oxidative synthesis of Imines from Alcohols and Amine
2
R
Catalyst 4, (1 mol%)
R1
H N
R2
R1
H2O
OH
2
N
3
t-BuOK(10 mol%), 4 ÅMS
THF, air, r.t., 24 h
1
2
[
b]
Entry
1
2
3
Conv.
%
Yield
%
[b]
[c]
O
efficiently with
a
number of alcohols under the standard
NH2
NH2
:(3a) >99
95
86
OH
1
2
N
O
O
[
a]
O
O
Table 1. Optimization of the reaction conditions
O
91
OH
OH
:(3b)
:(3c)
N
OH
Catalyst 4 - 6
air, conditions
N
O
O
H2N
O
NH2
NH2
93
91
85
O
O
4
Å
MS
3
4
3
a
N
1
a
2
a
O
O
:(3d)
>
99
[
d]
OH
N
Entry
Complexes
Solvent
Base
T
Yield(%)
Cl
F
O
Cl
O
[
[
[
[
b]
b]
b]
b]
o
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
4 (1 mol%)
4 (1 mol%)
4 (1 mol%)
4(1 mol%`)
4 (1 mol%)
4 (1 mol%)
-
Toluene
THF
DCM
MeOH
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
t-BuOK
t-BuOK
t-BuOK
t-BuOK
-
70
C
90
92
83
66
NR
71
NR
NR
95
91
30
95
63
84
89
78
60
:(3e) 94
82
80
NH2
NH2
OH
OH
F
o
5
6
N
66 C
O
O
o
:
(3f) 96
40 C
N
o
65 C
Br
O
Br
:(3g) 90
88
76
81
r.t.
OH
NH2
N
7
8
o
-
66 C
:(3h) 89
t-BuOK
t-BuOK
t-BuOK
KOH
r.t.
NH2
N
OH
OH
o
-
66 C
:
(3i) 86
(3j) 76
NH2
4 (1 mol%)
4 (1 mol%)
4 (1 mol%)
4 (1 mol%)
5 (1 mol%)
6 (1 mol%)
4 (0.75 mol%)
4 (0.50 mol%)
4 (0.25 mol%)
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
N
9
O
0
1
2
3
4
5
6
7
O
:
71
NH2
NH2
LiOH.H2O
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
OH
OH
N
1
0
[
c]
:(3k) 82
77
78
N
11
12
O
Br
O
:
(3l) 79
NH2
NH2
N
OH
Br
Br
O
O
:(3m) 92
84
81
N
OH
1
3
4
Br
:(3n) 90
[
4
a] Conditions: 1a (1 mmol), 2a (1 mmol), catalyst (4 - 6), 10 mol % of base,
Å MS, open air and 5 mL solvent for 24 h. [b] Reaction time was 12 h [c]
NH2
N
OH
OH
1
Reaction time was 48 h. [d] Isolated yields.
:(3o) 84
80
82
N
NH2
NH2
conditions (Table 2, entries1-6). The reaction of p-anisidine with
15
O
:
(3p) 96
4-methoxybenzyl alcohol went smoothly to afford N-(4-
S
N
OH
methoxybenzylidene)-4-methoxybenzenamine (Table 2, entry 1)
as the sole product with complete conversion and excellent
isolated yield (95%). para- and meta- substituted methyl benzyl
alcohols participated well in the imine formation furnishing good
yields with excellent conversions (Table 2, entries 2 and 3).
Similarly, the straight forward imination was achieved by the
benzyl alcohol bearing electron withdrawing (4-chloro, 3-fluro, 2-
bromo) substituents in good isolated yields (Table 2, entries 4, 5
and 6). Further, we extended our investigation by varying the
substituents on amines (Table 2, entries 7 - 19). Comparative
studies on para-, meta-, and ortho- methyl aniline with various
benzyl alcohols (4-methyl, benzyl, 4-methoxy) furnished the
16
17
S
O
O
:(3q) >99
:(3r) 80
:(3s) 79
93
75
NH2
NH2
O
O
O
N
OH
O
O
O
O
N
OH
OH
18
O
O
O
O
O
70
16
NH2
N
1
9
O
N
:(3t)
30
OH
NH2
2
2
0
1
O
O
O
:(3u)
-
Trace
OH
NH2
NH2
N
O
O
O
the corresponding imines in good yields (Table 2, entries 7 - 11).
Noteworthy, ortho- substituted anilines reacted sluggishly which
may be due to the steric hindrance of the methyl group.
Coupling of 4-bromoaniline with benzyl alcohol bearing electron
donating substituents (4-methyl, 4-methoxy) gave desired imines
in moderate yields (Table 2, entries 12, 13). Aniline reacted with
:(3v)
-
-
-
2
2
OH
C5H11
C5H11
N
-
23
OH
N
C5H11 :(3w)
C5H11
NH2
O
O
[
a] Reaction conditions: 1a (1 mmol), 2a (1 mmol), catalyst 4 (1 mol %), t-
BuOK (10 mol%), 4 Å molecular seives and THF (5 mL) stirred at r.t. for 24 h
in open air.[b] Reactions monitored by GC-MS. [c] Isolated yields.
benzyl
alcohol
yielding
81%
of
N-
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European Journal of Organic Chemistry
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FULL PAPER
benzylidenebenzenamine(Table 2, entry, 14). On the other hand, afforded corresponding imines in good to moderate yields (Table
The reaction of benzyl amine and benzyl alcohol yielded the
corresponding imine in 80% (Table 2, entry, 15). It is gratifying to
note that the reaction of thiophen-2-yl-methanol proceeded well
to yield the desired imine in good yield. (Table 2, entry 16).
Further, piperonyl analogues are considered to be
pharmaceutically active. Hence, we wish to explore a range of
piperonyl based imines, whose synthesis using this methodology
is less covered in the literature. Gratifyingly, we achieved the
desired imines with reasonable conversions in good yields
3, entries 4 - 7). The formation of aldehyde clearly indicates that
imination proceeds via an initial oxidation step.
The excellent selectivity of the diruthenium arene catalyst
in the aerobic imine synthesis encouraged us to propose a
plausible mechanism. As shown in scheme 3, the imination
process is believed to be initiated by the formation of
ruthenium−alkoxide species (B) from the diruthenium arene
complex (A). Further, β-hydride abstraction by complex (B)
produces ruthenium−hydride complex (C) by releasing the
aldehyde intermediate (Table 3) which further reacts with
amines to produce imines with the elimination of water. Complex
(C) enters into the next catalytic cycle by forming (B) with the
release of water.
[
12]
(
Table 2, entries 17 - 19). To our delight, coupling of piperonyl
alcohol with 4-methoxyaniline gave N-(benzo[d][1,3]dioxol-5-
ylmethylene)-4-methoxybenzenamine in 93% isolated yield with
good conversion (Table 2, entry 17). A chiral amine such as (R)-
(
+)-α-methylbenzylamine with 4-methoxybenzyl alcohol gave
poor yield of 16% of the corresponding imine under the
optimised condition (Table 2, entry 20). We could not succeed in
obtaining the expected imines when aromatic secondary
alcohols, aliphatic alcohols, and aliphatic amine were used as
substrates (Table 2, entries 21 - 23). The isolated imine products
Cl
Ru
O
N
N
Ru
O
Cl
A)
1
13
were confirmed by H and C NMR spectral techniques and
compared with the literature.
(
KOtBu
2 R1CH2OH
2 R1CH2OK
-
2 KCl
In order to investigate the versatility of the catalyst, we
carried out the oxidation using a range of alcohols in the
absence of amines under atmospheric air. para- substituted
benzyl alcohols reacted efficiently to furnish the corresponding
aldehydes in excellent isolated yields (Table 3, entries 1 and 3).
On the other hand, meta- and ortho- substituted alcohols
- tBuOH
H
R1
H
O
O
Ru
N
2
H2O
N
Ru
O
O
H
[
a]
Table 3. Aerobic oxidation of Alcohols to Aldehydes
Catayst 4, (1 mol%)
R1
H
O
O +2 H
2
2
2
R1
(B)
R1
R1
OH
O
2
H O
R2 NH2
2
t-BuOK (10 mol%), 4 Å MS
THF, air, r.t., 24 h
1
4
R2
[
b]
R1CH2OH
2
H2O
2
2
Entry
1
1
4
Yield %
N
R1
H
O
O
OH
O
N
:(4a)
Ru
9
8
N
Ru
O
O
O
H
O
OH
O
2
3
:(4b)
:(4c)
96
O
O
(C)
OH
O
89
Cl
Cl
Scheme 3. Plausible Mechanism for Imination
OH
O
4
5
:(4d)
7
8
The life span and level of reusability of a catalytic system
[
13]
are crucial factors in homogeneous catalysis.
Although
OH
O
O
:
recovery of homogeneous catalyst from the reaction mixture has
some drawbacks, we made an effort to recover and reuse the
(4e)
7
3
O
present
catalytic
system
in
further
cycles.
N-(4-
OH
Br
6
7
O
methoxybenzylidene)-4-methoxybenzenamine obtained by the
coupling of 4-methoxy benzyl alcohol and p-anisidine was
extracted after the completion of the reaction. The catalyst was
recovered from the reaction mixture and reused for the next
cycle. Thus, we found that the catalyst remains active up to five
consecutive runs with gradual decrease in the activity from 95 to
:
(4f)
6
6
Br
OH
O
:
NH2
(4g)
7
1
NH2
a
[
4
a] Reaction conditions: 1 (1 mmol), catalyst 4 (1 mol %), t-BuOK (10 mol %),
Å molecular seives and THF (5 mL) stirred at r.t. for 24 h in open air. [b]
Isolated yields.
63%.
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European Journal of Organic Chemistry
10.1002/ejoc.201701408
FULL PAPER
1
00
1
36.48, 135.61, 134.92, 131.44, 129.76, 129.50, 128.01, 127.86, 100.22,
80
60
40
20
0
100.17, 100.09, 99.88, 83.40, 81.57, 79.96, 79.92, 79.82, 30.46, 30.41,
-1
22.58, 22.38, 22.35, 22.26, 18.80 18.75. FT-IR (cm ). 1534, 1483, 1386,
3
-1
-1
2 2
1034. UV-vis (CH Cl , λmax nm; ε dm mol cm ): 460 (630), 325 (4,300),
229 (10,700). HR-ESI-MS m/z [Found (Calcd)]: 745.0551 (745.0708)
+
+
{
[M–Cl – HCl] ≡ [ C34
Synthesis of dinuclear [(η -p-Cymene)
Solid. Yield: 89%; Found: C, 51.84; H, 5.01; N, 3.47%. Calc. for
36 2 2 2
H N O ClRu ] }
6
2 2 2
Ru Cl (μ-L3)] (6): Orange
1
2
3
4
5
-
1
1
C
35
H40Cl
2 2
N
O
3
Ru
2
: (809.75 g mol ): C, 51.91; H, 4.98; N, 3.46%. H
Catalytic runs
NMR (400 MHz, CDCl
3
): δ (ppm), 7.96 (m, 4 H, ArH), 7.45 (m, 3 H, ArH),
Conclusions
3
6
.96 (d, JH−H = 8 Hz, 2H, ArH), 5.11 (m 2H, CH p-cym), 5.00 (m 2H, CH
3
3
p-cym), 4.55 (d,
J
H−H = 5.6 Hz, 1H, CH p-cym), 4.50 (d,
J
H−H = 5.6 Hz,
In conclusion, we have synthesized and characterized a
new air stable arene diruthenium(II) complexes. Further, the
complexes were developed as catalysts for the selective aerobic
synthesis of imines from various alcohols and amines producing
water as the only byproduct. The oxidative imination preceded
efficiently using the catalyst 4 with 1 mol% catalyst loading at
room temperature under aerobic conditions. The current system
tolerates a wide range of substrates and afforded imines in good
to excellent yields. In addition, selective aerobic oxidation of
alcohols to aldehydes was also arrived in order investigate the
underlying mechanism and to test the versatility of the catalytic
system. Hence, the scientific value of this methodology is
proved by the development of non-pincer type diruthenium(II)
catalysts for the direct synthesis of imines and detailed
mechanistic studies are underway.
3
1
H, CH p-cym), 3.93(d,
J
H−H = 5.6 Hz, 1H, CH p-cym), 3.87(s, 3H, O-
3
CH ), 3.70 (d, J
3
H−H
3 2
= 5.6 Hz, 1H, CH p-cym), 2.61 (sept, 2H, CH(CH ) ),
3
2.17 (s, 3H, CH
3
), 2.12 (s, 3H, CH
3
), 1.11 (m,
JH−H = 6 Hz, 12H,
13
CH(CH
3
)
2
).
C NMR (100 MHz, CDCl
3
): δ (ppm),172.73, 172.48,
1
9
3
1
3
60.44, 136.56, 129.32, 128.96, 128.27, 127.73, 113.01, 99.95, 99.86,
9.58, 83.47, 83.04, 81.73, 81.49, 79.93, 79.86, 79.82, 55.41, 45.9,
0.33, 30.31, 22.55, 22.32, 22.19, 18.71, 18.68. FT-IR (cm ). 1537,
487, 1386, 1032. UV-vis (CH
-
1
3
-1
-1
2 2
Cl , λmax nm; ε dm mol cm ): 458 (600),
29 (4,500), 228 (10,900). HR-ESI-MS m/z [Found (Calcd)]: 709.0955
+
+
39 2 3 2
(709.0941) {[M – Cl – HCl] ≡ [C35H N O Ru ] }
Typical procedure for diruthenium-catalyzed aerobic synthesis of
imines from alcohols and amines: The mixture of alcohol (1 mmol), an
amine (1 mmol), t-BuOK (10 mol%), catalyst (1 mol%), 4 Å molecular
0
sieves was stirred in the open air at room temperature (ca. 25–30 C)
and monitored by TLC/ GC-MS until completion. After completion of the
reaction, the reaction mixture was filtered and the solvent was
evaporated under reduced pressure. Then the resulting residue was
purified by silica gel column chromatography using EtOAc:hexane to
afford imine products.
Experimental Section
General method for the synthesis of the arene diruthenium(II)
6
complexes (4-6): [RuCl
2
(η -p-cymene)]
2
(1 equiv.) and N-
Typical procedure for diruthenium-catalyzed selective oxidation
alcohols to aldehydes: The mixture of alcohol (1 mmol), t-BuOK (10
mol%), catalyst (1 mol%), 4 Å molecular sieves was stirred for 24 h in
the open air at r.t. in 5 mL THF and monitored by TLC. The reaction
mixture was filtered and the solution was evaporated under reduced
pressure and then subjected to silica gel column chromatography using
EtOAc:hexane to afford aldehyde products.
Benzoylbenzohydrazide
chlorobenzohydrazide
1
(1
(1
equiv.),
equiv.),
or
or
N-Benzoyl-4-
N-Benzoyl-4-
2
methoxybenzohydrazide 3 (1 equiv.) were dissolved in 25 mL of toluene
and refluxed for 2h. The solution was concentrated to 2 mL under
reduced pressure, and addition of petroleum ether (60−80 °C) in excess
gave a clear orange solid. The product was collected by filtration, washed
with petroleum ether, and dried in vaccuo.
6
Acknowledgements
Synthesis of dinuclear [(η -p-Cymene)
2 2
Ru Cl
2
(μ-L1)] (4): Orange
Solid. Yield: 93% ; Found: C, 52.22; H, 4.89; N, 3.58%. Calc. for
-
1
1
S.S. would like to thank the Department of Science and
Technology (DST), Govt. of India for DST-INSPIRE fellowship
(IF150745). The authors thank DST-FIST for the instruments
facilities at School of Chemistry, Bharathidasan University, India.
We thank CEFIPRA, India for GC-MS facility through the
research project (Ref. No. IFC/5005-1).
34
C H38Cl
2 2 2 2
N O Ru : (779.72 g mol ): C, 52.37; H, 4.91; N, 3.59%.
H
NMR (400 MHz, CDCl
3
): δ (ppm), 7.97 (m, 4 H, ArH), 7.45 (m, 6 H, ArH),
3
3
5
.12 (d,
J
H−H = 6 Hz, 2H, CH p-cym), 5.00 (d,
J
H−H = 6 Hz, 2H, CH p-
3
3
cym), 4.52 (d, JH−H = 5.6 Hz, 2H, CH p-cym), 3.72 (d, JH−H = 5.6 Hz, 2H,
3
CH p-cym), 2.61 (sept, 2H, CH(CH3)2), 2.13 (s, 6H, CH
3
), 1.11 (t, JH−H
): δ (ppm), 172.7,
36.58, 129.80, 129.43, 127.84, 99.96, 99.87, 83.38, 81.50, 79.96, 79.91,
=
13
6
1
3 2 3
.4 Hz, 12H, CH(CH ) ). C NMR (100 MHz, CDCl
-
1
30.40, 22.43, 22.36, 18.74. FT-IR (cm ). 1540, 1485, 1393, 1036. UV-
3
-1
-1
2
vis (CH Cl
2
, λmax nm; ε dm mol cm ): 456 (670), 328 (3,700), 230
Keywords: Diruthenium • Aerobic • Imines • Aldehydes • Green
(
–
11,000). HR-ESI-MS m/z [Found (Calcd)]: 739.1068 (739.1047) {[M – Cl
synthesis
+
+
2 2 2
HCl] ≡ [ C34H38ClN O Ru ] }
6
Synthesis of dinuclear [(η -p-Cymene)
Solid. Yield: 85%; Found: C, 50.12; H, 4.63; N, 3.40%. Calc. for
C
NMR (400 MHz, CDCl
5
cym), 4.48 (d,
CH p-cym), 3.63 (d,
CH(CH3)2), 2.09 (s, 3H, CH
1
2 2 2
Ru Cl (μ-L2)] (5): Orange
[
1] a) F. A. Davis, B.-C. Chen, Chem. Soc. Rev. 1998, 27, 13. b) H. Gröger,
Chem. Rev. 2003, 103, 2795-2828. c) R. W. Layer, Chem. Rev. 1963, 63,
-
1
1
34
H37Cl
3 2
N
O
2
Ru
2
: (814.17 g mol ): C, 50.16; H, 4.58; N, 3.44%. H
489-510. d) S. F. Martin, Pure Appl. Chem. 2009, 81, 195-204. e) S.-I.
3
): δ (ppm), 7.90 (m, 4 H, ArH), 7.40 (m, 5 H, ArH),
Murahashi, Angew. Chem., Int. Ed. Engl. 1995, 34, 2443-2465. f) A.
Erkkilä, I. Majander, P. M. Pihko, Chem. Rev. 2007, 107, 5416-5470. g) J.
Adrio, J. C. Carretero, Chem. Commun. 2011, 47, 6784-6794. h) K.-i.
Yamada, K. Tomioka, Chem. Rev. 2008, 108, 2874-2886. i) P. de Armas,
D. Tejedor, F. García-Tellado, Angewandte Angew. Chem., Int. Ed. 2010,
3
3
.05 (d, 2H, JH−H = 6.4 Hz, CH p-cym), 4.96 (d, JH−H = 6.4 Hz, 2H, CH p-
3
3
J
H−H = 6 Hz, 2H, CH p-cym), 3.80 (d,
J
H−H = 5.6 Hz, 1H,
3
JH−H = 6 Hz, 1H, CH p-cym), 2.52 (sept, 2H,
3
3
), 2.05 (s, 3H, CH
3
), 1.05 (m, JH−H = 7.6 Hz,
13
2H, CH(CH
3
)
2
).
C NMR (100 MHz, CDCl ): δ (ppm),172.96, 171.77,
3
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European Journal of Organic Chemistry
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4
9, 1013-1016. j) C. S. Marques, A. J. Burke, ChemCatChem 2011, 3,
[7]
[8]
a) J. Xu, R. Zhuang, L. Bao, G. Tang, Y. Zhao, Green Chem.2012, 14,
2384-2387. b) R. R. Donthiri, R. D. Patil, S. Adimurthy, Eur. J. Org.
Chem. 2012, 2012, 4457-4460. c) B. Chen, L. Wang, S. Gao, ACS
Catal. 2015, 5, 5851-5876.
635-645. k) P. Merino, E. Marqués-López, R. P. Herrera, Adv. Synth.
Catal. 2008, 350, 1195-1208. l) A. Matusiak, J. Lewkowski, P. Rychter, R.
Biczak, J. Agric. Food Chem. 2013, 61, 7673-7678. m) M. A. Castro, J. M.
Miguel del Corral, M. Gordaliza, P. A. García, M. A. Gómez-Zurita, M. D.
García-Grávalos, J. de la Iglesia-Vicente, C. Gajate, F. An, F. Mollinedo,
A. San Feliciano, J. Med. Chem. 2004, 47, 1214-1222. n) P.
Panneerselvam, R. R. Nair, G. Vijayalakshmi, E. H. Subramanian, S. K.
Sridhar, Eur. J. Med. Chem. 2005, 40, 225-229. o) E. M. Hodnett, P. D.
Mooney, J. Med. Chem. 1970, 13, 786-786. p) E. M. Hodnett, W. J. Dunn,
J. Med. Chem. 1970, 13, 768-770. q) P. H. Wang, J. G. Keck, E. J. Lien,
M. M. C. Lai, J. Med. Chem. 1990, 33, 608-614.
a) S. Kegnaes, J. Mielby, U. V. Mentzel, C. H. Christensen, A. Riisager,
Green Chem. 2010, 12, 1437-1441. b) L. Jiang, L. Jin, H. Tian, X. Yuan,
X. Yu, Q. Xu, Chem. Commun. 2011, 47, 10833-10835. c) L. Tang, H.
Sun, Y. Li, Z. Zha, Z. Wang, Green Chemistry 2012, 14, 3423-3428. d)
J.-F. Soule, H. Miyamura, S. Kobayashi, Chem. Commun.2013, 49,
355-357. e) L. Han, P. Xing, B. Jiang, Org. Lett. 2014, 16, 3428-3431.
a) N. P. Mankad, Chem. Eur. J. 2016, 22, 5822-5829. b) K.-C. Cheung,
W.-L. Wong, M.-H. So, Z.-Y. Zhou, S.-C. Yan, K.-Y. Wong, Chem.
Commun. 2013, 49, 710-712. c) J. van Buijtenen, J. Meuldijk, J. A. J.
M. Vekemans, L. A. Hulshof, H. Kooijman, A. L. Spek, Organometallics
2006, 25, 873-881. d) T. Ohta, Y. Tonomura, K. Nozaki, H. Takaya, K.
Mashima, Organometallics 1996, 15, 1521-1523. e) J. Aguiló, L.
Francàs, R. Bofill, M. Gil-Sepulcre, J. García-Antón, A. Poater, A.
Llobet, L. Escriche, F. Meyer, X. Sala, Inorg. Chem. 2015, 54, 6782-
6791. f) C. Di Giovanni, L. Vaquer, X. Sala, J. Benet-Buchholz, A.
Llobet, Inorg. Chem. 2013, 52, 4335-4345.
[9]
[
2]
a) J. A. Ellman, T. D. Owens, T. P. Tang, Acc. Chem. Res. 2002, 35,
984-995. b) L. Hu, Y. Wu, Z. Li, L. Deng, J. Am. Chem. Soc. 2016, 138,
15817-15820. c) T. Ai, G. Li, Bioorg. Med. Chem. Lett. 2009, 19, 3967-
3969. d) T. Akiyama, H. Morita, J. Itoh, K. Fuchibe, Org. Lett. 2005, 7,
2583-2585. e) A. E. Taggi, A. M. Hafez, H. Wack, B. Young, D. Ferraris,
T. Lectka, J. Am. Chem. Soc. 2002, 124, 6626-6635. f) R. P. Wurz, G.
C. Fu, J. Am. Chem. Soc. 2005, 127, 12234-12235. g) G.-Q. Lin, M.-H.
Xu, Y.-W. Zhong, X.-W. Sun, Acc. Chem. Res. 2008, 41, 831-840.G h)
Z. Shi, F. Glorius, Angew. Chem., Int. Ed. 2012, 51, 9220-9222. i) R.
Dhawan, R. D. Dghaym, D. J. St. Cyr, B. A. Arndtsen, Org. Lett. 2006,
[10] a) E. Sindhuja, R. Ramesh, Y. Liu, Dalton Trans. 2012, 41, 5351-5361.
b) E. Sindhuja, R. Ramesh, S. Balaji, Y. Liu, Organometallics 2014, 33,
4269-4278. c) E. Sindhuja, R. Ramesh, Tetrahedron Lett. 2014, 55,
5504. d) S. Muthumari, R. Ramesh, RSC Adv. 2016, 6, 52101-52112.
[11] G. Hua, Y. Li, A. L. Fuller, A. M. Z. Slawin, J. D. Woollins, Eur. J. Org.
Chem. 2009, 2009, 1612-1618.
8, 3927-3930. j) A. R. Siamaki, D. A. Black, B. A. Arndtsen, J. Org.
Chem. 2008, 73, 1135-1138. k) D. A. Black, B. A. Arndtsen, J. Org.
Chem. 2005, 70, 5133-5138. l) M. Nyerges, D. Bendell, A. Arany, D. E.
Hibbs, S. J. Coles, M. B. Hursthouse, P. W. Groundwater, O. Meth-
Cohn, Tetrahedron 2005, 61, 3745-3753. m) I. Nakamura, T. Nemoto,
Y. Yamamoto, A. de Meijere, Angew. Chem., Int. Ed. 2006, 45, 5176-
[12] a) F. Beckford, D. Dourth, M. Shaloski Jr, J. Didion, J. Thessing, J.
Woods, V. Crowell, N. Gerasimchuk, A. Gonzalez-Sarrías, N. P.
Seeram, J. Inorg. Biochem. 2011, 105, 1019-1029. b) W. H. Burton, W.
L. Budde, C.-C. Cheng, J. Med. Chem.1970, 13, 1009-1012. (c) M.
Arshad, A. R. Bhat, S. Pokharel, J.-E. Kim, E. J. Lee, F. Athar, I. Choi,
Eur. J. Med. Chem. 2014, 71, 229-236. d) R. Kholiya, S. I. Khan, A.
Bahuguna, M. Tripathi, D. S. Rawat, Eur. J. Med. Chem. 2017, 131,
126-140.
5179. n) N. Fu, T. T. Tidwell, Tetrahedron 2008, 64, 10465-10496.
[
[
3]
4]
a) Z. Wang, in Comprehensive Organic Name Reactions and Reagents,
John Wiley & Sons, Inc., 2010. b) P. T. Lansbury, J. G. Colson, J. Am.
Chem. Soc. 1962, 84, 4167-4169 c) J. Stieglitz, P. N. Leech, J. Am.
Chem. Soc. 1914, 36, 272-301. d) K. C. Gulati, S. R. Seth, K.
Venkataraman, in Organic Syntheses, John Wiley & Sons, Inc., 2003.
a) S.-I. Murahashi, Y. Okano, H. Sato, T. Nakae, N. Komiya, Synlett
[13] M. Benaglia, in Recoverable and Recyclable Catalysts, John Wiley &
Sons, Ltd, 2009, pp. 301-340.
2007, 2007, 1675-1678. b) M. Largeron, A. Chiaroni, M.-B. Fleury,
Chem. Eur. J. 2008, 14, 996-1003. c) G. Jiang, J. Chen, J.-S. Huang,
C.-M. Che, Org. Lett. 2009, 11, 4568-4571. d) S. Biswas, B. Dutta, K.
Mullick, C.-H. Kuo, A. S. Poyraz, S. L. Suib, ACS Catal. 2015, 5, 4394-
4
403. (e) L. Liu, Z. Wang, X. Fu, C.-H. Yan, Org. Lett. 2012, 14, 5692-
695. f) R. Mir, T. Dudding, J. Org. Chem. 2016, 81, 2675-2679. g) A.
5
Tillack, I. Garcia Castro, C. G. Hartung, M. Beller, Angew. Chem., Int.
Ed. 2002, 41, 2541-2543. h) S. Kramer, K. Dooleweerdt, A. T.
Lindhardt, M. Rottländer, T. Skrydstrup, Org. Lett. 2009, 11, 4208-4211.
i) L. Liu, S. Zhang, X. Fu, C.-H. Yan, Chem. Commun.2011, 47, 10148-
10150. j) C. V. Reddy, J. V. Kingston, J. G. Verkade, J. Org. Chem.
2008, 73, 3047-3062. k) A. Zanardi, J. A. Mata, E. Peris, Chem. Eur. J.
2010, 16, 10502-10506.
[
5]
a) C. Gunanathan, Y. Ben-David, D. Milstein, Science 2007, 317, 790.
b) C. Gunanathan, D. Milstein, Angew. Chem. 2008, 120, 8789-8792. c)
B. Gnanaprakasam, J. Zhang, D. Milstein, Angew. Chem. 2010, 122,
1510-1513. d) K.-i. Fujita, T. Fujii, R. Yamaguchi, Org. Lett. 2004, 6,
3525-3528. e) M. H. S. A. Hamid, C. L. Allen, G. W. Lamb, A. C.
Maxwell, H. C. Maytum, A. J. A. Watson, J. M. J. Williams, J. Am.
Chem. Soc. 2009, 131, 1766-1774. f) K. O. Marichev, J. M. Takacs,
ACS Catal. 2016, 6, 2205-2210. g) X. Xie, H. V. Huynh, ACS Catal.
2015, 5, 4143-4151.
[
6]
a) C. Xu, L. Y. Goh, S. A. Pullarkat, Organometallics 2011, 30, 6499-
6
502. b) M. A. Esteruelas, N. Honczek, M. Oliván, E. Oñate, M.
Valencia, Organometallics 2011, 30, 2468-2471. c) J. W. Rigoli, S. A.
Moyer, S. D. Pearce, J. M. Schomaker, Org. Biomol. Chem. 2012, 10,
1746-1749. d) A. Maggi, R. Madsen, Organometallics 2012, 31, 451-
455. e) B. Saha, S. M. Wahidur Rahaman, P. Daw, G. Sengupta, J. K.
Bera, Chem. Eur. J. 2014, 20, 6542-6551.
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European Journal of Organic Chemistry
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FULL PAPER
Entry for the Table of Contents
Organoruthenium mediated synthesis
FULL PAPER
Newly
synthesized
arene
Sundar Saranya, Rengan Ramesh*
diruthenium(II) complexes were used
as efficient catalysts for the selective
synthesis of imines under mild
conditions. The reaction operates in
the presence of green and economic
air as oxidant with the release of water
as the only by-product.
and Jan Grzegorz Małecki
Page No. – Page No.
One-pot Catalytic Approach for the
Selective Aerobic Synthesis of Imines
from Alcohols and Amines using
Efficient
Arene
Diruthenium(II)
Catalysts under Mild Condition
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