Heterogeneously catalysed Strecker-type reactions using supported Co(ii) catalysts: Microwave vs. conventional heating

Article abstract of DOI:10.1039/c1gc15741h

A range of α-aminonitriles could be efficiently prepared from various aldehydes/ketones and primary or secondary amines using a highly active and stable Co(ii) complex supported on different mesoporous supports at both room temperature and low temperature microwave irradiation under solventless conditions. Catalysts were also highly reusable under the investigated reaction conditions and could be reused at least 10 times without loss of catalytic activity. The Royal Society of Chemistry.

Full text of DOI:10.1039/c1gc15741h

View Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Green Chemistry
Cite this: Green Chem., 2011, 13, 3282
www.rsc.org/greenchem
PAPER
Heterogeneously catalysed Strecker-type reactions using supported Co(II)
catalysts: microwave vs. conventional heating†
Fatemeh Rajabi,*a Saghar Nourian,b Sara Ghiassian,b Alina M. Balu,c Mohammad Reza Saidi,*b
Juan Carlos Serrano-Ruizc and Rafael Luquec
Received 23rd June 2011, Accepted 15th August 2011
DOI: 10.1039/c1gc15741h
A range of a-aminonitriles could be efficiently prepared from various aldehydes/ketones and
primary or secondary amines using a highly active and stable Co(II) complex supported on
different mesoporous supports at both room temperature and low temperature microwave
irradiation under solventless conditions. Catalysts were also highly reusable under the investigated
reaction conditions and could be reused at least 10 times without loss of catalytic activity.
of the range of the substrates as well as the use of more
Introduction
challenging compounds, including natural products,5 protocols
The Strecker reaction is among the most important processes
for optimisation and improvement of the reaction conditions
in organic synthesis and can grant access to a wide range of
and finally, but not least importantly, the development of
interesting compounds such as a-aminonitriles.1–3 The former
belong to a major class of naturally occurring compounds that
possess important biological activities as well as being basic
motifs for the synthesis of proteins (via hydrolysis to aminoacids
and then peptides synthesis). Traditionally, the synthesis of
a-aminonitriles is carried out by reacting acetaldehyde with
ammonia and hydrogen cyanide, and then further hydrolysis
of the formed adduct to alanine, an important aminoacid.4
As highlighted in the previous example, it is obvious that
the classical protocol of the Strecker reaction is of limited
applicability, aside from the corrosive and toxic nature of HCN,
and it is often associated with energy intensive protocols, poor
variability of substrates and the generation of a wide variety of
by-products.
Several alternatives have been developed over the past few
years in order to overcome these drawbacks, as well as de-
vising novel pathways to efficiently produce other families of
a-aminonitrile-type compounds.5–9 The majority of advances
in Strecker-type chemistry have been focused on four areas
of research: the design of novel and more efficient catalytic
systems,6,7 the applicability of the reaction in terms of extension
asymmetric Strecker syntheses.8,9
With regard to the design of novel catalytic systems, var-
ious heterogeneous systems have been reported to replace
the conventional homogeneous conditions and catalysts (e.g.
silica-bonded sulfonic acid, FeCl3, zirconia and acidic resins
including Nafion).10–13 Interestingly, the reaction has been mostly
reported to efficiently take place using aldehydes, while three-
component Strecker processes using ketones as substrates are
generally highly challenging and often unfeasible for less reactive
ketones.7–9,14 For instance, ketimines have rarely been employed
as substrates in Strecker-type cyanations owing to their lower
electrophilic character compared to aldimines.9 Their utilisation
in these processes therefore remains a significant challenge in
organic synthesis9 and becomes of utmost interest in asymmetric
processes.8,9
Recent research efforts from our group have been funda-
mentally devoted to the design of more efficient heterogeneous
catalytic systems for green chemical applications, focused on
highly active, stable and reusable supported nanoparticles,15 and
supported complexes on mesoporous materials.16–19 Particularly
related to Strecker-type reactions, we recently reported the
application of a simple and efficient Co(II) complex supported
on mesoporous SBA-15 in the synthesis of a range of a-
aminonitriles from ketimines and ketiminium salts.20 This cata-
lyst was also previously employed in a series of heterogeneously
catalysed processes, including aerobic oxidations,16 the chemos-
elective deprotection of acetates,17 the acetylation of alcohols18
and C–heteroatom bond-forming reactions.19 However, in all
cases, the Co(II) complex was always stabilised on SBA-15 and
no comparable examples of different supports were attempted
in order to investigate the potential effect of the support on the
activity of the supported material. Furthermore, microwaves are
aDepartment of Science, Payame Noor Univesity, P. O. Box: 19395-4697,
Tehran, Iran. E-mail: f_rajabi@pnu.ac.ir; Fax: +98 2813344081;
Tel: +98 2813336366
bDepartment of Chemistry, Sharif University of Technology, P. O. Box
11465-9516, Tehran, Iran. E-mail: saidi@sharif.edu; Fax: +98 21 6601
2983; Tel: +98 21 6600 5718
cDepartamento de Qu´ımica Orga´nica, Universidad de Cordoba, Campus
de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396,
E14014, Cordoba, Spain. E-mail: q62alsor@uco.es
† Electronic supplementary information (ESI) available: Experimental
and spectral data. See DOI: 10.1039/c1gc15741h
3282 | Green Chem., 2011, 13, 3282–3289
This journal is
The Royal Society of Chemistry 2011
©

View Online
also a highly useful tool that are increasingly being utilised in
organic chemistry to improve rates of reaction (often as well as
selectivities), decreasing at the same time times of reaction and
energy consumption.21
In this work, we aimed to expand the utilisation of our
Co(II) catalyst in Strecker-type reactions based on three different
points: the use of more challenging substrates, the comparison of
low temperature microwave irradiation and conductive heating,
and a detailed investigation on the effect of various supports
(SBA-15 as compared to hexagonal mesoporous silica, MCM-41
and a commercial porous silica) on the activity of the supported
Co(II) complex.
Preparation of HMS-cobalt(II) catalyst. Salicylaldehyde
(2 mmol, 0.244 g) was added to excess absolute MeOH, to which
aminopropyl-functionalized HMS material (2.9 g, loading of
NH2 group was 0.69 mmol g-1) was then added. The solution
became yellow due to imine formation. After 6 h, cobalt(II)
acetate, Co(OAc)2·2H2O (1 mmol, 0.248 g), was added to the
solution, and the mixture stirred for a further 24 h to allow the
new ligands to complex the cobalt; a color change from pink
to olive green was observed. The final product was washed with
MeOH and water until the washings were colorless. Further
drying of the solid product was carried out in an oven at 80 ◦C
for 8 h. The Co loading was found to be 0.32 mmol g-1, very
similar to that obtained for all the investigated materials in this
process.
Experimental
Co/silica. Salicylaldehyde
(2
mmol,
0.244
g)
Material preparations
was added to excess absolute MeOH, to which 3-
aminopropyl(trimethoxy)silane (2 mmol, 0.352 g) was
then added. The solution instantly became yellow due to
imine formation. After 3 h, cobalt(II) acetate, Co(OAc)2·2H2O
(1 mmol, 0.248 g), was added to the solution, and the mixture
stirred for a further 3 h to allow the new ligands to complex the
cobalt; a color change from pink to olive green was observed.
Co/SBA-15. Co/SBA-15 was prepared as previously
reported.22 Salicylaldehyde (2 mmol, 0.244 g) was
added to an excess of absolute MeOH, to which 3-
aminopropyl(trimethoxy)silane (2 mmol, 0.352 g) was
subsequently added. The solution instantly became yellow due
to imine formation. After 3 h, cobalt(II) acetate, Co(OAc)2·2H2O
(1 mmol, 0.248 g), was added to the solution, and the mixture
further stirred for 3 h to allow the new ligands to complex the
cobalt. A colour change from pink to olive green was observed.
Mesoporous SBA-15 (average pore diameter 6 nm, 3 g) was
activated by refluxing in concentrated hydrochloric acid (6 M),
washing thoroughly with de-ionized water and drying before
undergoing chemical surface modification. This activation
treatment readily hydrolysed the siloxane Si–O–Si bonds to
Si–OH species, which are key to anchoring the cobalt complex.
The complex and activated silica were then mixed and stirred
overnight. The solvent was removed using a rotary evaporator,
and the resulting olive green solid dried at 80 ◦C overnight. The
final product was washed with MeOH and water (to remove all
physisorbed metal species) until the washings were colourless.
Furth◦er drying of the solid product was carried out in an oven
at 80 C for 8 h. The catalyst had a surface area of 470 m2 g-1,
with a pore size of 3.55 nm and a 0.78 mL g-1 mesoporous pore
volume; the Co loading was found to be 0.35 mmol g-1.
˚
Mesoporous silica (average pore diameter 60 A, 3 g) was
activated by refluxing in concentrated hydrochloric acid (6 M),
then washing thoroughly with de-ionized water and drying
before undergoing chemical surface modification. Hydrated
mesporous silica was then added and the mixture stirred
overnight. The solvent was removed using a rotary evaporator
and the resulting olive green solid dried at 80 ◦C overnight.
The final product was washed with MeOH and water until the
washings were colourless. Further drying of the solid product
was carried out in an oven at 80 ◦C for 8 h. The Co loading was
found to be 0.39 mmol g-1.
Co/MCM-41.
Preparation of MCM-41 support. 6.0 g of cetyltrimethyl
ammonium bromide (CTAB) was dissolved in 48 mL distilled
water. NH4OH (25%, 24.5 mL) was added to the solution, which
was then heated to 30 ◦C. After this, 25 g of TEOS was added
to the solution. The mixture was heated at 30 ◦C for 24 h under
stirring before being heated to 100 ◦C for 48 h. The resulting
powder was filtered, washed with distilled water, dried at 60 ◦C
and then calcined at 550 ◦C for 8 h.
Similarly, Co/MCM-41, Co/HMS and Co/silica were syn-
thesized in this work. The materials were prepared as follows:
Co/HMS.
Preparation of MCM-cobalt(II) catalyst. Salicylaldehyde
(2 mmol, 0.244 g) was added to excess absolute MeOH, to
which 3-aminopropyl(trimethoxy)silane (2 mmol, 0.352 g) was
then added. The solution instantly became yellow due to
imine formation. After 3 h, cobalt(II) acetate, Co(OAc)2·2H2O
(1 mmol, 0.248 g), was added to the solution, and the mixture
stirred for a further 3 h to allow the new ligands to complex
the cobalt; a colour change from pink to olive green was
observed. MCM-41 (3.3 g) was then added and the mixture
stirred overnight. The solvent was removed using a rotary
evaporator and the resulting olive green solid dried at 80 ◦C
overnight. The final product was washed with MeOH and water
until the washings were colourless. Further drying of the solid
product was carried out in an oven at 80 ◦C for 8 h. The Co
loading was found to be 0.37 mmol g-1.
Preparation of HMS-modified support. A typical preparation
of an organomodified HMS was as follows: to a stirred solution
of n-dodecylamine (5.08 g, 27.5 mmol) in aqueous ethanol
(46 mL of absolute ethanol and 53 mL of distilled water) at
25 ◦C was added separately, but simultaneously and rapidly,
TEOS (17.36 g, 0.08 mol) and aminopropyl(trimethoxy)silane
(3.58 g, 0.02 mol). The cloudy solution was stirred for 18 h.
The solution first became milky (typically after ca. 5 min) then
thickened. After 18 h, the thick solution was filtered and the
white solid washed with ethanol. The damp solid product was
then refluxed in ten times its weight of ethanol for 3 h and filtered
again to remove the template. The solvent reflux was repeated
twice to completely remove the template from the material. The
final solid was then dried in an oven at 80 ◦C.
This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 3282–3289 | 3283
©

View Online
Materials characterisation. All chemicals were obtained from
Aldrich. Nitrogen adsorption/desorption experiments were
carried out using a Coulter SA3100 surface area analyser.
Prior to analysis, samples were de-gassed at 130 ◦C for 5 h.
Surface areas were determined using the BET equation. The
metal content in the materials and filtrate after reuse were
determined using inductively coupled plasma (ICP) in a Philips
PU 70000 sequential spectrometer equipped with an Echelle
monochromator (0.0075 nm resolution). Solid samples were
digested in HNO3 and subsequently analyzed by ICP.
Scheme 1 Three-component Strecker reaction of various aldehydes,
pyrrolidine and TMSCN catalyzed by Co/SBA-15.
Interestingly, the addition of 1 mol% catalyst was found to be
sufficient to provide excellent yields of products (>90%) after
relatively short reaction times (typically between 1–5 h). Lower
catalyst loadings and reaction times (less than 1 h) turned out
to be inefficient and resulted in significantly reduced yields (75%
and below).20 The protocol was also amenable to a range of
substrates, including different amines as well as more challenging
substrates, such as ketimines and ketiminium salts (Table 1 and
Table 2), with products being obtained in excellent yields for
all the investigated substrates (88–97%), regardless of the nature
and position of the subtituents and/or the aliphatic/aromatic
nature of the amine.
Catalytic experiments.
Conventionally heated reactions. In a typical reaction run,
TMSCN (1.1 mmol) was added to a mixture of the aldehyde
(1 mmol), amine (1 mmol) and catalyst Co/SBA-15 (34 mg;
~1 mol% Co/SBA-15) in a 25 mL sealed tube, and the mixture
was stirred at 500 rpm at room temperature for the appropriate
time, as indicated in Table 1. In some cases where starting
materials were solid, a few drops of solvent (e.g. ethyl acetate)
were added to ensure that the reactants were properly mixed.
Upon reaction completion (as monitored by TLC), the
mixture was diluted with ethyl acetate and filtered to obtain the
crude product. In some cases, the crude product was purified
by column chromatography on silica gel to afford the pure a-
aminonitrile in good to excellent yield.
Heterogeneously catalysed methodologies employing ke-
timines/ketiminium salts as substrates are considered a sig-
nificant challenge, particularly for the asymmetric cyanation
of ketimines.8,9 In any case, reactions take a longer time to
reach completion for these more challenging substrates (10–
24 h) as compared to aldehydes, which provide quantitative
conversion to products in 1–5 h of reaction. Interestingly, a
series of optimisation experiments pointed to a remarkable
acceleration of reaction rates, and therefore yields, in the
cyanation of ketimines and ketimine salts at slightly increased
Reuse of the catalyst in the investigated reactions was
performed in a similar way to that described above, but
the aforementioned quantities of catalyst and reagents were
increased up to 3-times (for the first run) to ensure that enough
Co-catalyst was able to be reutilised in the reaction.
◦
reaction temperatures. Temperatures as low as 40 C provided
almost quantitative yields of products at reduced reaction times
(ranging from 3 to 12 h; Table 2, left part). Yields were slightly
reduced for substrates with larger chains, but in any case the
devised protocol was suitable for both aromatic and aliphatic
(cyclic and acylic) substituents. A further increase in temperature
(from 40 to 60 ◦C) did not have much influence on the yields of
products as compared to those at 40 ◦C (Fig. 1).
Microwave-assisted reactions. Microwave reaction experi-
ments were conducted in a CEM-DISCOVER microwave re-
actor model with PC control. Reagents were added in iden-
tical quantities to those described in the experiments under
conventional heating for comparative purposes. In a typical
reaction, TMSCN (1.1 mmol) was added to the corresponding
substrates (ketiminium salts and ketimines, 1 mmol) and catalyst
Co/SBA-15 (34 mg; ~1 mol% Co/SBA-15) in a microwave
pyrex vessel, and the mixture microwaved at 40 ◦C for 30–
45 min. Experiments were conducted on a closed vessel (pressure
controlled) under continuous stirring, and the temperature in
the reactions was measured using an IR probe. The microwave
method was generally temperature-controlled, where samples
were irradiated with different power outputs (30 W average
power of reaction runs) to achieve the desired temperature of
40 ◦C, which was subsequently maintained typically for 30–
45 min. Samples were then collected and processed in a similar
way to those under conventional heating.
Results and discussion
Fig. 1 The effect of reaction temperature on the activity of Co/SBA-
15 for the cyanation of 4-methyl-N-(pentan-3-ylidene)aniline with
TMSCN. Reaction conditions: 1.1 mmol TMSCN, 1 mmol substrate,
1 mol% Co/SBA-15, 12 h reaction.
Optimisation experiments were initially performed at room tem-
perature using a range of aldehydes as substrates and Co/SBA-
15 as the heterogeneous catalyst, as previously reported20
(Scheme 1). Blank runs (in the absence of catalyst) gave no
conversion in the systems after a 24 h reaction. Similar results
(<5% conversion to products) were obtained when the support
alone was utilised in the reaction.
As compared to the fast formation of imine intermediates
in the Strecker reaction (1st step, from the reaction between
the aldehyde/ketone and the amine), the cyanation of this
3284 | Green Chem., 2011, 13, 3282–3289
This journal is
The Royal Society of Chemistry 2011
©

View Online
Table 1 Three-component Strecker reaction of aldehydes, amines and TMSCN catalyzed by Co/SBA-15 at r.t.
Entry
1
Substrate
Amine
Time/h
1
Yield (%)a
99
2
1
99
3
4
2.5
4
95
97
5
5
90
6
7
1.5
1.5
99
99
8
9
3
96
94
3.5
10
11
12
13
4
92
98
98
97
1.5
1.5
3
a Isolated yields.
This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 3282–3289 | 3285
©

View Online
Table 2 Activity comparison of conventional heating (CH) vs. microwave irradiation (MW) of Co/SBA-15 in the TMSCN cyanation of ketimines
and ketiminium ionsa
Entry
1
Substrate
Product
CH/MW time/h
3/0.5
CH yield (%)a
95
MW yield (%)a
90
2
3/0.5
95
99
3
4
5
6
3/0.5
98
98
99
92
95
92
90
96
3.5/0.5
2.5/0.5
6/0.5
7
8
10/0.6
12/0.6
87
88
80
85
9
12/0.8
90
95
10
11
12
10/0.8
12/0.8
12/0.8
95
92
90
92
86
82
a Reaction conditions (conventional heating): 1 mmol substrate, 1.1 mmol TMSCN, 1 mol% Co/SBA-15 (34 mg), 40 ◦C. Reaction conditions
(microwave irradiation): 1 mmol substrate, 1.1 mmol TMSCN, 1 mol% Co/SBA-15 (34 mg), MW, 40–45 ◦C (average temperature), 30 W (average
power).
intermediate (2nd step, nucleophilic attack of the cyanide
reagent on the imine) is believed to be the rate-determining
step of the whole process. These findings supported a cyanation
mechanism recently proposed by Zhang et al. for the phos-
phoric acid-catalysed Strecker reaction of ketones, amines and
TMSCN.7 Ketimines, obtained as intermediates in the Strecker
reaction (starting materials in this work), can be protonated
by the catalyst (in our case the Co/SBA-15 material has been
shown to have an interesting Lewis acidity) to produce a more
electrophilic and activated iminium ion, which is subsequently
attacked by the nucleophilic cyanide reagent to give the final
a-aminonitrile product.
next obvious step is to compare the activity of the catalyst under
microwave irradiation and conventional heating. Microwaves
have proven to be a highly useful tool to accelerate rates
of reaction, also influencing selectivities in some cases. Most
importantly, the rapid and homogeneous heating achieved under
microwave irradiation can remarkably reduce times of reaction
from several hours to minutes.21,23–25
The results for microwave irradiation compared to conven-
tional heating are depicted in Fig. 2 and Table 2. Almost quan-
titative yields of products for the more challenging substrates
could be obtained under microwave irradiation conditions
with significantly reduced reaction times (typically 30–45 min)
at comparable temperatures (40–45 ◦C) to those utilised in
conventionally heated experiments, which generally required
In view of the improved cyanation yields for ketimine and
ketiminium salts at higher temperatures (typically 40–50 ◦C), the
3286 | Green Chem., 2011, 13, 3282–3289
This journal is
The Royal Society of Chemistry 2011
©

View Online
Table 3 Physicochemical properties of the catalysts
Entry
Catalyst
S
BET/m2 g-1
Pore diameter/nm
Pore volume/cm3 g-1
1
2
3
4
Co/SBA-15
Co/MCM-41
Co/HMS
470
494
287
197
3.5
2.6
2.7
9.3
0.78
0.54
0.54
0.46
Co/silica
of the structural and chemical features of the immobilised
species, which are likely to be dependent on the particle size
and uniformity of the materials employed rather than any
mechanistic effects involved in the reaction.
The catalyst reusability was also investigated under both sets
of conditions; the reactions were carried out under similar
conditions. Co/SBA-15 showed excellent recoverability and
reusability over 10 successive runs under the same conditions
as the first run (Fig. 3). No detectable metal traces in solution
(<0.5 ppm) were determined by ICP analysis of the final
reaction mixture for this particular catalyst, confirming the
strong coordination and stability of the cobalt on the SBA-
15 support, which prevents metal leaching during/after the
reaction. With respect to the similarly prepared Co catalysts,
almost no leaching was also observed, even if in some cases traces
of Co (0.5–2 ppm) were detected, particularly for Co/silica
(Table 6).
Fig. 2 Activity comparison of conventional heating (CH; white bars,
front) and microwaves (MW; black bars, back) in the cyanation of a
range of ketimines and ketiminium ions under comparable conditions.
Reaction conditions (CH and MW): 1 mmol substrate, 1.1 mmol
TMSCN, 1 mol% Co/SBA-15 (34 mg), 40 ◦C, 0.5 h reaction time.
longer reaction times (typically 3+ h for the best performing
ketimine).
Higher reaction temperatures (>40 ◦C) could effectively
reduce the reaction time to a few minutes (5–10 min), but the
chosen temperature was selected to have strictly comparable
results under very similar conditions for both conventional
heating and microwave irradiation.
In order to further demonstrate the activity of the Co
catalyst, a variety of similar materials containing the Co complex
supported on different supports (e.g. silica, MCM-41) were
synthesized and investigated in the process.
Table 3 summarises the main textural properties of the
different synthesized catalysts compared to the Co/SBA-15
material. With relatively similar surface areas and pore volumes,
the different catalysts only exhibited remarkably different pore
diameters, depending on the nature of the support, ranging
from ca. 2.5–3.5 nm for SBA-15, MCM-41 and hexagonal
mesoporous silica (HMS) to 9.3 for a commercial porous silica.
Excellent conversions were observed for all the supported
catalysts when using aldehydes as substrates. Most importantly,
the use of the different supports as well as blank runs (in the
absence of catalyst) gave almost no conversion (<5%) in this
system.
A comparison of activity between the four investigated
catalysts is shown in Table 4 (for conventional heating) and Table
5 (for microwave irradiation). The results presented in Table 4
clearly show that although all catalysts were effective in the
Strecker reaction of ketimines and ketiminium ions, Co/SBA-
15 exhibited a slightly higher catalytic activity compared to
the other investigated catalysts. This is believed to be due to
effects associated with the strong coordination of substrates to
the cobalt center in SBA-15, and the ordered and more stable
nanostructure of SBA-15 as compared to the silica and MCM-
41 supports. These observations point to a potential influence
Fig. 3 Reuse of the Co/SBA-15 catalyst in the conventionally heated
cyanation of 4-methyl-N-(propan-2-ylidene)aniline with TMSCN. Re-
action conditions (first run): 3 mmol substrate, 3.3 mmol TMSCN,
3 mol% Co-SBA-15 (100 mg), 40 ◦C, 10 h. Reuse (each run): 1 mmol
substrate, 1.1 mmol TMSCN, 1 mol% Co/SBA-15 (34 mg), 40 ◦C, 10 h.
The measured Co content in all catalysts was, however, very
close to the initially measured value of the catalyst before the
reaction, which is indicative of the stability of the material under
the investigated reaction conditions (a long reaction time of
10 h was selected for leaching experiments). Interestingly, no
detectable Co was found for any of the synthesized catalysts for
reactions run under microwave irradiation. This is believed to
be due to the short times of reaction under these conditions
(typically 0.5 h) with respect to the longer times of reactions
required for the more challenging substrates (10+ h), which were
especially chosen to prove the stability and recyclability of the
materials.
This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 3282–3289 | 3287
©

View Online
Table 4 Comparison of activities of the different investigated Co catalysts in the conventionally heated TMSCN cyanation of selected ketimines
and ketiminium ions
Entry
1
Substrate
Product
Reaction time/h
3
Co/SBA-15
95
Co/MCM-41
92
Co/HMS
86
Co/silica
79
2
3
95
85
82
75
3
4
3
98
95
85
88
84
78
82
70
10
5
6
7
10
12
10
92
90
90
86
84
85
75
75
75
70
67
72
8
12
12
10
87
85
92
75
78
85
70
75
78
66
70
70
9
10
Table 5 Comparison of activities of the different investigated Co catalysts in the microwave-assisted TMSCN cyanation of selected ketimines and
ketiminium ions
Reaction time/h
0.5
Substrate
Product
Co/SBA-15
90
Co/MCM-41
80
Co/HMS
72
Co/silica
65
0.5
99
89
89
70
0.5
0.8
95
92
85
90
85
90
78
68
0.8
0.8
86
82
90
85
90
85
65
<60
3288 | Green Chem., 2011, 13, 3282–3289
This journal is
The Royal Society of Chemistry 2011
©

View Online
Table 6 Leaching experiments of the different Co catalysts in the conventionally heated cyanation of 4-methyl-N-(propan-2-yliene)aniline with
TMSCN
Entry
Catalyst
Co loading before reaction
Co loading after reaction (3 uses)
Co measured in the filtrate by ICP/ppm
1
2
3
4
Co/SBA-15
Co/MCM-41
Co/HMS
0.35
0.37
0.32
0.39
0.34
0.37
0.30
0.33
<0.5
1.1
1.2
Co/silica
2.1
6 (a) F. Cruz-Acosta, A. Santos-Expo´sito, P. De Armas and F. Garc-
Tellado, Chem. Commun., 2009, 6839–6841; (b) G. K. S. Prakash,
T. E. Thomas, I. Bychinskaya, A. G. Prakash, C. Panja, H. Vaghoo
and G. A. Olah, Green Chem., 2008, 10, 1105–1110; (c) B. Karimi
and D. Zareyee, J. Mater. Chem., 2009, 19, 8665–8670; (d) M. M.
Mojtahedi, M. Saeed Abae and T. Alishiri, Tetrahedron Lett., 2009,
50, 2322–2325.
Conclusions
A Co(II) complex supported on mesoporous silica materials was
demonstrated in general to be an efficient and versatile catalyst
for the three-component Strecker reaction. A range of aldehydes
and amines could be efficiently reacted with TMSCN to give the
corresponding aminonitrile products. Furthermore, the catalyst
was also proved to be very active in the cyanation of ketimines
and ketimine salts with TMSCN. For the different investigated
support materials, Co/SBA-15 exhibited the optimum stability
and activity in the investigated reactions as compared to other
Co catalysts using related mesoporous silica materials (e.g. HMS
and MCM-41). The protocol could also be extended to the use of
microwave irradiation, which was found to be more efficient with
respect to conventionally heated reactions under comparable
reaction conditions.
7 G. W. Zhang, D. H. Zheng, J. Nie, T. Wang and J. A. Ma, Org. Biomol.
Chem., 2010, 8, 1399–1405.
8 C. Spino, Angew. Chem., Int. Ed., 2004, 43, 1764–1766.
9 S. J. Connon, Angew. Chem., Int. Ed., 2008, 47, 1176–1178.
10 (a) G. K. S. Prakash, T. Matthew, C. Panja, S. Alconcel, H. Vaghoo,
C. Do and G. A. Olah, Proc. Natl. Acad. Sci. U. S. A., 2007, 104,
3703–3706; (b) N. H. Khan, S. Agrawal, R. I. Kureshy, S. H. R.
Abdi, S. Singh, E. Suresh and R. V. Jasra, Tetrahedron Lett., 2008,
49, 640–644.
11 K. Niknam, D. Saberi and M. N. Sefat, Tetrahedron Lett., 2010, 51,
2959–2962.
12 M. M. Heravi, M. Ebrahimzadeh, H. A. Oskooie and B. Baghernejad,
Chin. J. Chem., 2010, 28, 480–482.
13 B. M. Reddy, B. Thirupathi and M. K. Patil, J. Mol. Catal. A: Chem.,
2009, 307, 154–159.
Acknowledgements
14 A. Baeza, C. Na´jera and J. M. Sansano, Synthesis, 2007, 1230–1234.
15 (a) N. Linares, M. Rico, E. Serrano, A. M. Balu, E. Losada, R.
Luque and J. Garcia-Martinez, Chem. Commun., 2011, 47, 9024–
9035; (b) C. Gonzalez-Arellano, A. M. Balu, R. Luque and D. J.
Macquarrie, Green Chem., 2010, 12, 1995–2002; (c) R. Luque, V.
Budarin, J. H. Clark and D. J. Macquarrie, Appl. Catal., B, 2008, 82,
157–162.
16 F. Rajabi and B. Karimi, J. Mol. Catal. A: Chem., 2005, 232, 95–99.
17 F. Rajabi, Tetrahedron Lett., 2009, 50, 7256–7258.
18 F. Rajabi, Tetrahedron Lett., 2009, 50, 395–397.
19 F. Rajabi, S. Razavi and R. Luque, Green Chem., 2010, 12, 786–
789.
F. R. is grateful to Payame Noor University for partial support.
M. R. S. gratefully acknowledges Sharif University of Tech-
nology for funding and support. R. L. gratefully acknowledges
Ministerio de Ciencia e Innovacion, Gobierno de Espan˜a for
the provision of a Ramon y Cajal contract (RYC-2009-04199).
Funding from projects P10-FQM-6711 and P09-FQM-4781
(Consejeria de Ciencia e Innovacion, Junta de Andalucia) and
CTQ2008-01330 (MICINN) are also gratefully acknowledged.
20 F. Rajabi, S. Ghiassian and M. R. Saidi, Green Chem., 2010, 12,
1349–1352.
References
21 J. Moseley and C. O. Kappe, Green Chem., 2011, 13, 794–806.
22 F. Rajabi, R. Luque, J. H. Clark, B. Karimi and D. J. Macquarrie,
Catal. Commun., 2011, 12, 510–513.
1 A. Perdih and M. S. Dolenc, Curr. Org. Chem., 2007, 11, 801–832.
2 C. Najera and J. M. Sansano, Chem. Rev., 2007, 107, 4584–4671.
3 J. A. Ma, Angew. Chem., Int. Ed., 2003, 42, 4290–4299.
4 A. Strecker, Justus Liebigs Ann. Chem., 1850, 75, 27–45.
5 N. Fukuda, K. Sasaki, T. V. R. S. Sastry, M. Kanai and M. Shibasaki,
J. Org. Chem., 2006, 71, 1220–1225.
23 C. O. Kappe, Angew. Chem., Int. Ed., 2004, 43, 6250–6284.
24 V. Polshettiwar, N. M. Nagagouda and R. S. Varma, Aust. J. Chem.,
2009, 62, 16–26.
25 D. Dallinger and C. O. Kappe, Chem. Rev., 2007, 107, 2563–2591.
This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 3282–3289 | 3289
©