Rhodium complex encapsulated functionalized hexagonal mesoporous silica for heterogeneous hydroaminomethylation

Article abstract of DOI:10.1016/j.apcata.2012.12.021

HRh(CO)(PPh₃)₃ complex was encapsulated into the pores of amino functionalized hexagonal mesoporous silica. The catalyst was characterized by physico-chemical techniques like P-XRD, ³¹P-CPMAS NMR, FT-IR, SEM, ICP and N₂ adsorption analysis. The catalyst was active for hydroaminomethylation and a variety of alkenes and amines were used as reactants for hydroaminomethylation. The catalyst afforded to achieve 100% conversion with high (>95%) selectivity to corresponding amines. Parametric variations were performed by taking 1-hexene and morpholine as representative reactants for the study of catalyst amount, temperature, pressure and 1-hexene:morpholine ratio. Significant amounts of aldehydes and enamines were observed during the course of the reaction indicating that there could be two possible rate determining steps. The catalyst was effectively recycled up to five times without much loss in its activity and selectivity.

Full text of DOI:10.1016/j.apcata.2012.12.021

Applied Catalysis A: General 453 (2013) 159–166
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Rhodium complex encapsulated functionalized hexagonal
mesoporous silica for heterogeneous hydroaminomethylation
N. Sudheesh, Ram S. Shukla∗
Discipline of Inorganic Materials and Catalysis, Council of Scientific and Industrial Research, Central Salt and Marine Chemicals Research Institute, G.B.
Marg, Bhavnagar 364 002, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
HRh(CO)(PPh3)3 complex was encapsulated into the pores of amino functionalized hexagonal meso-
porous silica. The catalyst was characterized by physico-chemical techniques like P-XRD, 31P-CPMAS
NMR, FT-IR, SEM, ICP and N2 adsorption analysis. The catalyst was active for hydroaminomethylation
and a variety of alkenes and amines were used as reactants for hydroaminomethylation. The catalyst
afforded to achieve 100% conversion with high (>95%) selectivity to corresponding amines. Parametric
variations were performed by taking 1-hexene and morpholine as representative reactants for the study
of catalyst amount, temperature, pressure and 1-hexene:morpholine ratio. Significant amounts of alde-
hydes and enamines were observed during the course of the reaction indicating that there could be two
possible rate determining steps. The catalyst was effectively recycled up to five times without much loss
in its activity and selectivity.
Received 1 October 2012
Received in revised form
12 December 2012
Accepted 14 December 2012
Available online xxx
Keywords:
Hexagonal mesoporous silica
Rhodium complex
Hydroaminomethylation
Heterogeneous catalyst
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
atom economic, efficient process for the synthesis of amines.
Hydroaminomethylation has closer applications for the synthesis
Aliphatic amines are one of the very important classes of com-
pounds used in bulk as well as fine chemicals in the chemical
and pharmaceutical industry [1,2]. Around one million tons of
amines are produced annually for different uses. General meth-
ods for amine synthesis include hydrocyanation of olefins followed
by reduction, reductive amination of carbonyl compounds and
alkylation of organic halides with ammonia. These methods gen-
erally have drawbacks of expensive starting materials, formation
of byproducts and the need of protecting and deprotecting steps
involved during the synthesis. From both economic and envi-
ronmental points of view, developing new versatile and direct
single pot synthesis routes to amines from inexpensive and easily
available feedstock is most desirable. Hydroamination [3–5] and
hydroaminomethylation [6–10] are such processes for synthesis of
amines with very high atom efficiency. Both these reactions have
cheaper starting materials, an olefin and an amine. Hydroamination
is still a very challenging reaction due to the very low TOF [11–16].
Hydroaminomethylation is a reaction that has potential to develop
for industrialization.
of nylon, drugs and various bulk and fine chemicals.
The study of this domino reaction has undergone progress
in last decade with noteworthy contributions from the research
groups of Eilbracht et al. [20–23] and Beller and co-workers
[24,25]. The investigations in hydroaminomethylation showed
that the hydroformylation catalyst can perform equally toward
hydroaminomethylation reactions by tuning the reaction condi-
tions [17]. A variety of rhodium based catalysts have been already
found to be active for hydroaminomethylation [25–32].
It is known that the homogeneous catalysts have the draw-
back of catalyst separation and recycling. Hydroaminomethylation
currently performing in homogeneous condition also follows
with the same. Hence a development of heterogeneous cata-
lyst for hydroaminomethylation can contribute toward solving
the above said problem. But the developments of catalyst sys-
tem toward this route are scanty in literatures. There is
a
pressing need to develop catalyst system to carry out an eco-
nomic, atom efficient and easily separable single pot synthesis
of amines; however less attention is paid in this direction.
Here we have attempted to heterogenize the well known
HRh(CO)(PPh3)3 complex into the hexagonal mesoporous silica
for hydroaminomethylation of olefins. HRh(CO)(PPh3)3 complex
being well known for hydroformylation of olefins, its develop-
ment into a heterogeneous catalyst would be an important concern.
Investigation on various parameters like temperature, pressure,
amount of the catalyst and olefin to amine substrate ratio are also
performed.
Hydroaminomethylation (Scheme 1) is the single pot synthe-
sis of amines from an olefin, amine (alkyl amines, morpholine,
pyrollidine etc.) and syngas (H2, CO) [17–19]. It is an elegant,
∗
Corresponding author. Tel.: +91 278 2567760; fax: +91 278 2566970.
E-mail addresses: sudhinarayanan@gmail.com (N. Sudheesh),
rshukla@csmcri.org, ramshukla55@yahoo.in (R.S. Shukla).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.12.021

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N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
NR2R3
NR2R3
O
HNR2R3
R1
R1
R1
H2, Cat.
Linear
CO/H2
NR2R3
NR2R3
CHO
R1
Catalyst
HNR2R3
H2, Cat.
Branched
R1
R1
Scheme 1. Hydroaminomethylation of olefin.
2. Experimental
determination of catalyst morphology. Analysis was carried out
at an accelerating voltage of 20 kV and probe current of 102 pA.
Thermo gravimetric analysis (TGA) was carried out using Mettler
TGA/DTA 851e, in nitrogen flow rate at 50 mL/min.
2.1. Materials
Tetraethyl orthosilicate, dodecylamine, aminopropyl trimeth-
oxysilane, hydridocarbonyl tristriphenylphosphine rhodium(I)
were procured from Sigma–Aldrich, USA for the synthesis of
catalyst. The reactants alkenes and amines were procured from
Sigma–Aldrich, USA. H2 and CO were procured from Ami Traders,
Bhavnagar, Gujarat, India.
2.5. Hydroaminomethylation and product analysis
Hydroaminomethylation were carried out in a 100 mL stainless
steel autoclave reactor (Autoclave Engineers, USA). The experimen-
tal setup, safety precautions and procedures were similar to that
described elsewhere [33]. The weighed amount of reactants (alkene
and amine) and catalyst were taken in the SS-autoclave with a mix-
ture of 30 mL of toluene and 20 mL of methanol. The autoclave was
raised to desired temperature and then CO and H2 were pressurized
in the ratio required. The progress of the reaction was monitored
by observing the pressure drop. Aliquots of product mixture were
withdrawn to analyze the conversion and selectivity at regular time
intervals. The product was analyzed by GC (Schimadzu 17A, Japan)
and GC–MS (Schimadzu GCMS-QP2010, Japan). To ensure repro-
ducibility the experiments were repeated under identical reaction
conditions.
2.2. Synthesis of the support and functionalization
Hexagonal mesoporous silica (HMS) was synthesized according
to the procedure reported elsewhere [33,34]. The synthesized HMS
was calcined at 650 ◦C for 6 h to remove the organic template and
is then taken for functionalization.
The HMS has to be functionalized in order to have a good bind-
ing between the support and metal complex. In a typical synthesis
procedure, 1 g of calcined HMS was taken in 15 mL of refluxing
toluene and added 0.5 g of APTMS (aminopropyl trimethoxysilane).
The stirring was continued for 24 h and the resultant functionalized
HMS was filtered and washed with toluene and dried. The amino
functionalized HMS was denoted as HMS-F.
3. Results and discussions
3.1. Catalyst characterization
2.3. HRh(CO)(PPh3)3 encapsulated HMS (Rh-HMS-F)
Low angle powder X-ray diffraction (PXRD) of calcined HMS,
functionalized HMS and HRh(CO)(PPh3)3 encapsulated HMS were
given in Fig. 1. These materials showed an intense reflection corre-
sponding to 1 0 0 plane near 2Â values of 2–2.5◦ which corresponds
to the formation of HMS [35–38]. The intensities of the peak
HRh(CO)(PPh3)3 (92 mg) was dissolved in 15 mL of toluene
taken in a round bottom flask (RBF). This solution was placed in
an oil bath set at 110 ◦C equipped with magnetic stirrer and RBF
was connected with water condenser under nitrogen atmosphere.
The functionalized HMS (1 g) was added to this refluxing solution
and stirred for 24 h. The pale yellow precipitate of the heteroge-
neous catalyst was filtered off and dried in vacuum desiccator. The
catalyst was denoted as Rh-HMS-F.
2.4. Characterization techniques
Powder X-ray diffraction (P-XRD) of the samples were recorded
with Phillips X’Pert MPD system equipped with XRK 900 reaction
˚
chamber, using Ni-filtered Cu K␣ radiation (ꢀ = 1.54050 A) over
a 2Â range of 1–10◦ at a step time of 0.05◦ s−1. The FT-IR spec-
tra of the samples were recorded from 400 to 4000 cm−1 with
a PerkinElmer Spectrum GX FT-IR system using KBr pellets. 31P-
CPMAS NMR was recorded in a Bruker 500 Ultrashield system.
Inductively coupled plasma optical emission spectroscopy (ICP-
OES) analysis (Optima 2000DV, PerkinElmer instruments) was used
to determine the rhodium content in the catalyst. The surface area
analysis and pore size distribution of the support and catalyst were
determined by nitrogen adsorption at 77.4 K using a Sorptome-
ter (ASAP-2010, Micromeritics). All the samples were degassed at
80 ◦C for 4 h prior to the measurements. SEM (Leo Series VP1430)
equipped with EDX facility (Oxford instruments) was used for the
Fig. 1. PXRD of catalyst.

N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
161
Fig. 4. FT-IR spectrum of Rh-HMS-F.
heterogeneous catalytic systems for hydroformylation [38]. The
31P-CPMAS NMR of HRh(CO)(PPh3)3 showed a peak at 43.40 ppm
[33]. The shift in the position of peak from 43.40 to 34.37 ppm value
may be attributed to the geometrical constraints experienced by
the complex in the pores. Also the NH2 group on the function-
alized HMS will get coordinated with the Rh metal center which
may increase the electron density around the P atom resulting in
the shift of the peak to lower ppm value [33,38].
Fig. 2. N2 adsorption isotherm.
Table 1
N2 adsorption properties of the synthesized catalyst.
Material
SBET (m2/g)
Pore volume (cm3/g)
Pore diameter (nm)
HMS
HMS-F
Rh-HMS-F
726
510
462
0.83
0.52
0.46
3.4
3.5
3.9
The FT-IR spectrum of Rh-HMS-F is shown in Fig. 4. The
FT-IR spectrum of Rh-HMS-F showed the characteristic band at
1067 cm−1 for asymmetric stretching of Si
O
Si and 799 cm−1 for
were decreased on functionalization and encapsulation process.
This observation is due to the pore filling by functionalization and
encapsulation. There had been a shift toward lower 2Â values which
is due to the expansion of pores during the encapsulation process.
The N2 sorption analysis was done to investigate the surface area
analysis of the synthesized catalysts. The sorption isotherms of the
synthesized materials are given in Fig. 2. HMS, HMS-F and Rh-HMS-
F showed typical Type-IV isotherm. The increased adsorption in the
P/P0 region 0.20–0.40 and the hysterises indicated the existence
of uniform mesopores. The lower adsorption and decrease in the
surface area and pore volume (Table 1) for the HMS-F and Rh-HMS-
F was due to the pore filling occurred during functionalization and
encapsulation process.
tetrahedral SiO4 structural units. The bands at 2937 and 1486 cm−1
are assigned to C H asymmetric stretching and NH2 scissor respec-
tively, of the functionalized APTMS present in pores. The band at
3438 cm−1 is corresponding to the surface OH groups and also to
the NH2 group present in the HMS matrix. The band at 1633 cm−1
is for the C C stretching vibrations of the phenyl ring of the PPh3
ligand. Rh-HMS-F showed distinguishable ꢁRh-CO and ꢁRh-P bands
at 1978 cm−1 and 698 cm−1 respectively which had evidenced the
encapsulation of HRh(CO)(PPh3)3 in to the pore of HMS.
The TGA analysis of the HMS-F and Rh-HMS-F is given in Fig. 5.
Both of the materials showed a weight loss of ∼2–4% correspond-
ing to the adsorbed water molecules in the region of 50–120 ◦C.
Then for HMS-F there was a weight loss of ∼12% from 220 to
600 ◦C corresponding to the decomposition of the functionalized
APTMS group. The similar kind of weight loss was observable for
The 31P-CPMAS NMR of the Rh-HMS-F was recorded and given in
Fig. 3. It gave a sharp peak at 34.37 ppm corresponding to the com-
plex inside the pores. Similar peak were observed in other reported
Fig. 3. 31P-CPMAS NMR of the catalyst.
Fig. 5. TGA of HMS-F and Rh-HMS-F.

162
N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
3.2.1. Effect of catalyst amount on hydroaminomethylation
The effect of catalyst amount on hydroaminomethylation was
done by varying the catalyst amount from 25 to 100 mg and the
results are tabulated in Table 3. The reaction was analyzed at two
different times of 4 and 12 h to get the exact propagation of the
reaction. The conversion was increased on increasing the catalyst
amount from 25 to 100 mg. A conversion of 22% was obtained at 4 h
for 25 mg of the catalyst (Entry 1, Table 3) which increased to 75%
for 100 mg of the catalyst (Entry 4, Table 3). Conversions of 100%
were obtained at 12 h for catalyst amounts of 50 mg and above. The
formation of amines was low at lower catalyst amounts. Significant
amounts of aldehydes were observed at both 4 and 12 h of time.
Two competitive rate determining steps, formation of enamine and
hydrogenation of enamine determines the rate and mechanism of
hydroaminomethylation. Here the formation of enamine from alde-
hydes and morpholine was the crucial step which proceeded very
slowly.
Fig. 6. SEM image of Rh-HMS-F.
3.2.2. Effect of temperature on hydroaminomethylation
The effect of temperature on hydroaminomethylation of 1-
hexene with morpholine was studied from 80 to 140 ◦C and
the results are given in Table 4. The conversion was increased
on increasing the reaction temperature from 25% (80 ◦C) to 84%
(140 ◦C) at 4 h of reaction time. Higher selectivity was observed
toward the isomerized products of 1-hexene at 4 h on increasing
the temperature. The selectivity to amine gave decreasing trend at
lower time on increasing the temperature which showed a reverse
order on increasing the reaction time. This may be because of the
increasing trend in isomerization which increases the formation
of iso-aldehydes. These iso-aldehydes react slowly to form corre-
sponding enamines and subsequently amines. The decrease in n/iso
ratio also follows the same trend of decreasing on increasing the
temperature. At 80 ◦C the reaction was very slow and the formation
of amine was only 12% at 12 h of reaction time.
The reactivity of amine (morpholine) with the linear aldehyde
(n-heptanal) was an easy and faster step compared to that of
branched aldehyde (iso-heptanal). This facile reactivity of the n-
heptanal with morpholine to linear amine was higher than that of
iso-heptanal which can be observed from the higher n/iso ratio at
lower time. This formation of enamine is believable to be the clas-
sical organic reaction occurring in the liquid phase and the catalyst
metal center does not have significant role over this particular step
[12].
Rh-HMS-F also which is ∼16% corresponding to the functionalized
APTMS along with the RhCl(TPPTS)3 encapsulated in the HMS.
The SEM image showed the spherical nature of the catalyst
which is agglomerated for the bulk (Fig. 6). Each of the spherical
particles had an approximate size of 1.5–1.7 ␮m. The ICP analysis
showed that the catalyst has 0.89 wt% of rhodium present.
3.2. Hydroaminomethylation
Hydroaminomethylation of different alkenes with different
amines were carried out using the Rh-HMS-F catalyst and the
results are shown in Table 2. The catalyst was active for the
hydroaminomethylation of alkenes and gave 100% conversion for
all the studied alkenes and amines. Amines like morpholine, pyrro-
lidine and piperidine were highly active by giving selectivity of
>95% with small formation of enamine and N-formylated prod-
uct. Reactivity of diethylamine was low toward the hydrogenation
of enamine and gave 19% of enamine for 1-hexene-diethylamine
hydroaminomethylation. The n/iso ratio of the products was near
1.0–1.2 in all the cases except for cyclopentene where there is
no possibility of iso-product. The lower n/iso ratio depends on
the regioselectivity during hydroformylation step which gener-
ally gives low value in heterogeneous conditions. A representative
alkene, 1-hexene, and an amine, morpholine, were subjected for
investigating the parametric effects in detail.
Specific explanation for this reactivity difference of n- and
iso-aldehydes for enamine formation is still a concern of well
understanding. But the main reason ascribed for this difference is
the steric hindrance around the carbonyl carbon of the aldehyde
Table 2
Hydroaminomethylation of alkenes with amines.
Alkene
Amine
% Conv.
% Selectivity
A
By-product
B
C
D
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexenea
1-Hexene
Cyclopentene
Cyclopentene
1-Pentene
1-Pentene
Morpholine
Hexylamine
Cyclohexyl amine
Pyrrolidine
Diethylamine
Piperidine
Pyrrolidine
Morpholine
Morpholine
Pyrrolidine
100
100
100
100
100
100
100
100
100
100
51
42
47
48
42
49
99
96
53
52
0
4
0
1
10
1
0
3
0
0
45
46
46
47
39
47
–
–
44
47
3
7
7
2
9
2
–
–
1
0
1
0
0
2
0
1
1
1
2
1
Reaction conditions: alkene = 11.9 mmol, amine = 11.9 mmol, catalyst = 50 mg, pCO = 13.5 bar, pH2 = 54 bar, temp. = 120 ◦C, toluene/methanol = 30/20 mL and time = 18 h.
By-product: N-formylated products of amine substrate.
A = n-amine, B = n-enamine/imine, C = iso-amine, D = iso-enamine/imine.
a
24 h.

N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
163
Table 3
Effect of catalyst amount on hydroaminomethylation of 1-hexene with morpholine.
Entry
Catalyst amount (mg)
Time (h)
% Conv.
% Selectivity
2/3-hexene
Aldehyde
Amine
Enamine
n/iso
1
2
3
4
25
4
12
4
12
4
12
4
12
22
65
40
100
59
100
75
43
21
27
13
23
3
39
35
32
16
32
21
28
18
16
36
38
65
42
71
48
79
2
8
3
6
3
5
3
1
6.7
4.8
4.6
2.5
4.4
2.6
4.5
2.4
50
75
100
21
2
100
Reaction conditions: 1-hexene = 11.9 mmol, morpholine = 11.9 mmol, pCO = 13.5 bar, pH2 = 54 bar, temp. = 100 ◦C and toluene/methanol = 30/20 mL.
[39]. Steric hindrance on the iso-aldehyde can result in low rate
of formation of enamine or imine and its further hydrogenation.
Therefore application of severe reaction conditions or an extended
reaction time is needed to achieve higher conversions of iso-
aldehyde. This is the reason for obtaining higher conversion of
n-aldehyde to yield n-amine at lower reaction time. Increasing the
catalyst amount also leads to the higher conversion of iso-aldehyde
by increasing the hydrogenation rate of iso-enamine. Apart from
steric effects, electronic effects also play a role in determining the
predominant reactivity of n-aldehyde over iso-aldehyde to yield
enamine or imine. Electron-donating groups (–I effect) in the car-
bonyl compound can decrease the rate of addition of amine with
carbonyl group [39]. Branched aldehyde has higher–I effect than
that of n-aldehyde leading to lower reactivity.
isomerized 1-hexene which in turn gives iso-aldehydes and results
in higher amount of iso-enamine and iso-amine.
3.2.5. Plausible reaction steps and mechanism of
hydroaminomethylation
The plausible reaction steps of hydroaminomethylation of 1-
hexene with morpholine are given in Scheme 2. Firstly, 1-hexene
undergoes hydroformylation to form n- heptanal (P2) and iso-
heptanal (P3, 2-methyl hexanal). Here the mechanism follows
the general hydroformylation mechanism. The side reaction, i.e.,
isomerization of 1-hexene to 2- and 3-hexene (P1) was also
occurred. This formed 2- and 3-hexene can again get hydroformy-
lated to aldehyde (n- and iso-heptanal). The conversion of 2- and
3-hexene to aldehyde increases the iso-heptanal which in turn
decreases the n/iso ratio at higher reaction time. The formed alde-
hyde undergoes simple condensation with morpholine to form the
enamine. The n-enamine formed from n-heptanal and morpho-
line is 4-(hept-1-en-1-yl) morpholine, P4. The iso-enamine formed
from iso-heptanal and morpholine is 4- (2-methyl hex-1-en-1-yl)
morpholine, P5. These n- and iso-enamines get catalytically hydro-
genated over Rh active center to 4-heptylmorpholine (P6, n-amine)
and 4-(2-methylhexyl) morpholine (P7, iso-amine) respectively.
The n/iso ratio obtained at the initial hydroformylation stage deter-
mines the final n/iso ratio of product amines.
3.2.3. Effect of pressure on hydroaminomethylation
The effect of variation of total pressure on hydroaminomethy-
lation is given in Table 5. The total pressure was varied from 27.5
to 83 bars by keeping the CO:H2 ratio of 1:3. Both the conversion
and selectivity to amine got increased on increasing the total pres-
sure. The selectivity was higher toward the isomerized 1-hexene at
lower pressures with only 34% selectivity to amines at 12 h (Entry
1, Table 5). But the lower selectivity to amines always gave higher
n/iso ratio which may be due to the higher rate of enamine for-
mation for n-aldehydes than that of iso-aldehydes in the studied
conditions.
3.2.6. Comparison with other hydroaminomethylation systems
It is of interest to have an insight in to the performance
of this catalyst system in comparison of some reported cat-
alyzed hydroaminomethylation reactions associated with closely
related reaction parameters. The most of the comparison was with
homogenous systems, as to the best of our knowledge no report on
heterogeneous hydroaminomethylation was found in close relation
with the present investigation. It can be seen from the comparative
Table 7 that the catalyst under homogenous conditions had higher
reactivity in terms of lower reaction time, and regioselectivity.
The biphasic hydroaminomethyaltions with water soluble ligands
had lower reactivity and regioselectivity. Percentage conversions,
selectivity to amine and reaction temperature associated with
3.2.4. Effect of 1-hexene:morpholine ratio on
hydroaminomethylation
The effect of 1-hexene:morpholine ratio was studied and results
are given in Table 6. The conversion got decreased on increasing the
ratio of morpholine. The higher concentration of morpholine may
result in formation of inactive Rh-morpholine complexes which
decreases the catalytic activity. The selectivity to amine also fol-
lows the same trend. Higher amount of isomerized 1-hexene were
formed with increase in the morpholine ratio because of the higher
isomerization rates in presence of the base, morpholine. The n/iso
ratio was also decreased because of the same reason of formation of
Table 4
Effect of temperature on hydroaminomethylation of 1-hexene with morpholine.
Entry
Temp. (◦C)
Time (h)
% Conv.
% Selectivity
2/3-hexene
Aldehyde
Amine
Enamine
n/iso
1
2
3
4
80
4
12
4
12
4
10
4
8
25
68
40
100
68
100
84
24
32
27
13
38
6
58
37
32
16
28
17
26
13
4
12
38
65
29
73
22
76
14
19
3
6
5
4
4
4
9.6
5.2
4.6
2.5
4.9
1.8
3.2
1.5
100
120
140
48
7
100
Reaction conditions: 1-hexene = 11.9 mmol, morpholine = 11.9 mmol, catalyst = 50 mg, pCO = 13.5 bar, pH2 = 54 bar and toluene/methanol = 30/20 mL.

164
N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
Table 5
Effect of pressure variation on hydroaminomethylation of 1-hexene with morpholine.
Entry
Pressure (bar)
Time (h)
% Conv.
% Selectivity
2/3-hexene
Aldehyde
Amine
Enamine
n/iso
1
2
3
27.5
55
4
12
4
12
4
28
85
40
100
73
100
60
45
27
13
26
11
29
16
32
16
25
10
10
34
38
65
45
75
1
5
3
6
4
4
11.5
9.3
4.6
3.5
4.3
3.3
83
12
Reaction conditions: 1-hexene = 11.9 mmol, morpholine = 11.9 mmol, catalyst = 50 mg, pH2:pCO = 4:1, temp. = 100 ◦C and toluene/methanol = 30/20 mL.
Table 6
Effect of ratio of 1-hexene: morpholine on hydroaminomethylation.
Entry
1-Hexene: morpholine
Time (h)
% Conv.
% Selectivity
2/3-hexene
Aldehyde
Amine
Enamine
n/iso
1
2
3
1:1
1:2
1:3
4
12
4
12
4
40
100
34
96
29
27
13
43
21
56
32
32
16
23
22
18
24
38
65
32
52
24
36
3
6
2
5
2
8
4.6
2.5
1.5
0.9
1.4
0.85
12
82
Reaction conditions: 1-hexene = 11.9 mmol, catalyst = 50 mg, temp. = 100 ◦C, pCO = 13.5 bar, pH2 = 54 bar and toluene/methanol = 30/20 mL.
Scheme 2. Plausible reactions steps for hydroaminomethylation of 1-hexene with morpholine.

N. Sudheesh, R.S. Shukla / Applied Catalysis A: General 453 (2013) 159–166
165
Table 7
Comparison of the performance of Rh-HMS-F with some closely reported systems.
Alkene
Amine
Catalyst
Temp. (◦C)
Time (h)
% Conv.
% Amine
n/iso
Ref.
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Pentene
1-Pentene
1-Pentene
Morpholine
Morpholine
Morpholine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Morpholine
Morpholine
Morpholine
Rh-HMS-F
120
130
125
120
125
125
125
125
120
125
95
10
5
6
18
17
5
4
4
18
5
12
100
97
99
100
94.1
100
99
99
100
95
73
86.7
99
96
93.4
99
92.2
92.4
97
99
34
1.8
11.9
167
1.0
38.3
49.0
198.0
126
1.2
Present study
[6]
[40]
Present study
[41]
[17]
[40]
[40]
Present Study
[17]
Rh/BISBIS–Ionic liquid
[Rh(acac)(CO)2], Tetrabi
Rh-HMS-F
[Rh(cod)2]BF4, Ionic liquid
[Rh(cod)2]BF4, Xantphos
[Rh(acac)(CO)2], Tetrabi
[Rh(cod)2]BF4, Tetrabi
Rh-HMS-F
[Rh(cod)2]BF4, Xantphos
Rh(Imes)(cod)Cl
32.3
4.5
95
[42]
Table 8
Catalyst recycling.
Entry
Recycle
Time (h)
% Conv.
% Selectivity
2/3-hexene
Aldehyde
Amine
Enamine
n/iso
1
2
3
4
5
4
12
4
12
4
12
4
12
4
40
100
39
100
39
100
37
100
35
27
13
30
15
28
14
31
17
34
21
32
16
29
14
33
16
31
12
29
15
38
65
36
64
34
64
31
63
32
60
3
6
5
7
5
6
7
8
5
4
4.6
2.5
4.7
2.4
4.6
2.4
4.8
2.5
4.5
2.3
Fresh catalyst
First recycle
Second recycle
Third recycle
Fourth recycle
12
100
Reaction conditions: 1-hexene = 11.9 mmol, morpholine = 11.9 mmol, catalyst = 50 mg, temp. = 100 ◦C, pCO = 13.5 bar, pH2 = 54 bar and toluene/methanol = 30/20 mL.
Rh-HMS-F catalyst system are almost comparable with reported
homogenous systems. However the reaction time was higher and
the n/iso ratio was lower than those of homogenous systems. The
promising advantage of the present catalyst is the heterogeneous
nature of the reaction and the use of common Rh–PPh3 complex.
amine. The catalyst was recycled effectively up to five times with-
out much loss in its activity and selectivity.
Acknowledgments
Authors thank Council of Scientific and Industrial Research
(CSIR), New Delhi, India for the financial support through Network
Project on the Development of Specialty Inorganic Materials for
Diverse Applications (NWP-0010). The authors also acknowledge
Analytical Discipline and Centralized Instrument Facility, CSMCRI
for providing instrumental analysis. NS acknowledge CSIR, New
Delhi for the award of Senior Research Fellowship.
3.2.7. Catalyst recycling
Catalyst was recycled under similar conditions by taking the cat-
alyst from the previous cycle, which was washed with toluene and
used to conduct experiments. The results of catalyst recycle are
given in Table 8. The catalyst was recycled up to five cycles without
much loss in its activity and selectivity. A selectivity of 65% was
obtained for amine in 12 h for fresh catalyst which was dropped
only to 60% in fourth cycle. The n/iso ratio was also remained almost
same from 2.5 for fresh catalyst to 2.3 for fourth cycle. The reaction
mixture after the reaction was analyzed by ICP for rhodium and
found to be less than the detectable limit.
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