A high (Z)/(E) ratio obtained during the 3-hexyne hydrogenation with a catalyst based on a Rh(I) complex anchored on a carbonaceous support

Article abstract of DOI:10.1007/s10562-011-0761-5

The (Z)/(E) ratio was analyzed for the 3-hexyne semi-hydrogenation at 275, 290 and 303 K. [RhCl(NH₂(CH₂)₁₂CH ₃)₃] pure and supported on a carbonaceous material were used as catalysts. The supported complex showed high values of conversion and selectivity, and its behaviour was much better than the Lindlar catalyst used as a reference. Graphical abstract: Conversion to (Z)-3-hexene versus 3-hexyne total conversion as a function of temperature for: (1) Lindlar catalyst, (2) homogeneous complex and (3) anchored complex on RX3.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-011-0761-5

Catal Lett (2012) 142:231–237
DOI 10.1007/s10562-011-0761-5
A High (Z)/(E) Ratio Obtained During the 3-Hexyne
Hydrogenation with a Catalyst Based on a Rh(I) Complex
Anchored on a Carbonaceous Support
Domingo A. Liprandi
Jos e´ F. Paredes
Juan M. Badano
M o´ nica E. Quiroga
•
Edgardo A. Cagnola
•
•
•
Received: 14 November 2011 / Accepted: 13 December 2011 / Published online: 23 December 2011
Ó Springer Science+Business Media, LLC 2011
Abstract The (Z)/(E) ratio was analyzed for the 3-hexyne
semi-hydrogenation at 275, 290 and 303 K. [RhCl(NH2
and petrochemical substances, examples of fine and
industrial chemicals, are closely related to selective alkyne
hydrogenation [1, 2].
(
CH ) CH ) ] pure and supported on a carbonaceous
2 12 3 3
material were used as catalysts. The supported complex
showed high values of conversion and selectivity, and its
behaviour was much better than the Lindlar catalyst used as
a reference.
Regarding non-terminal alkyne semi-hydrogenation, the
main goals are to avoid hydrogenation to single bond and
to give priority to the highest possible conversion and
selectivity to the (Z)-alkene [3–5]. The control over con-
version and selectivity of a catalytic reaction can be
exerted in different ways, e.g.: by varying (a) the active
species or (b) the support, and/or by adding (c) a promoter/
a poison/a modifier, and finally, and not less important,
modifying the reaction temperature. Examples of the factor
(b) are: mesoporous [6] and siliceous [7] materials, a
pumice [8], carbons [9], and hydrotalcite [3]. Cases of
factor (c) are the typical Lindlar catalyst (palladium het-
erogenized on calcium carbonate poisoned by lead acetate
Keywords (Z)/(E) Ratio ꢀ 3-Hexyne partial
hydrogenation ꢀ Rhodium complex ꢀ Carbonaceous support
1
Introduction
The synthesis and manufacture of food additives, flavors
and fragrances, as well as pharmaceutical, agrochemical
or lead oxide, Pd–CaCO –Pb) [10] and the presence of
3
quinoline and triphenylphosphine [11, 12]. Research on the
factors (a) and (c) include bi-elemental systems such as
Ni–B, Pd–Cu, etc. [13–19]. An example of the effect of the
reaction temperature is a paper by Choi and Yoon [20],
who found that the selectivity to (Z)-alkene increases when
the temperature decreases using a Ni catalyst.
D. A. Liprandi ꢀ E. A. Cagnola (&) ꢀ J. F. Paredes ꢀ
M. E. Quiroga
Qu ´ı mica Inorg a´ nica, Departamento de Qu ´ı mica, Facultad de
Ingenier ´ı a Qu ´ı mica (UNL), Santiago del Estero 2829, S3000AOJ
Santa Fe, Argentina
On the other hand, transition metal complexes are a
group of substances widely used as catalysts for homoge-
neous and heterogeneous hydrogenation reactions. In the
context of the previous paragraph they could be considered
as a new active species or as a metal conditioned by its
ligands, a kind of ‘‘poison’’ or a modifier for the metal
atom [21]. These catalysts have the advantages of higher
activities and selectivities for this type of reaction, even
under mild conditions of temperature and pressure [22–26].
An example of this kind of systems is the complex
e-mail: ecagnola@fiq.unl.edu.ar
D. A. Liprandi
e-mail: dlipran@fiq.unl.edu.ar
J. F. Paredes
e-mail: jparedes@fiq.unl.edu.ar
M. E. Quiroga
e-mail: mquiroga@fiq.unl.edu.ar
J. M. Badano ꢀ M. E. Quiroga
INCAPE, Instituto de Investigaciones en Cat a´ lisis y
Petroqu ´ı mica, (FIQ-UNL, CONICET), Santiago del Estero 2654,
S3000AOJ Santa Fe, Argentina
[
PdCl (NH (CH ) CH ) ] supported on c-Al O or on a
2
2
2 12
3 2
2
3
e-mail: jbadano@fiq.unl.edu.ar
micro-porous carbon [27, 28].
123

2
32
D. A. Liprandi et al.
To our knowledge there are few publications that use
to a procedure previously described [31]. Determinations
were carried out on a Shimadzu ESCA 750 electron
spectrometer coupled to a Shimadzu ESCAPAC 760 Data
System. The superficial electronic states of rhodium,
nitrogen and chlorine were studied following the maximum
position of the Rh 3d5/2, N 1 s and Cl 2p3/2 peaks respec-
tively; the C 1s1/2 line was taken as an internal standard at
285.0 eV [32].
transition metal complexes as catalysts for the partial
hydrogenation of long chain non-terminal alkynes. Thus,
the objective of this work was to study the (Z)/(E) product
ratio for the partial hydrogenation of 3-hexyne, under dif-
ferent reaction temperatures (275, 290 and 303 K), using
[
RhCl(NH (CH ) CH ) ], pure and supported on a com-
2 2 12 3 3
mercial carbonaceous material (NORIT RX3) as catalysts.
Activity and selectivity of the Rh(I) complex catalysts were
evaluated and compared against those obtained with the
conventional Lindlar catalyst.
2.5 Catalytic Runs
To evaluate the (Z)/(E) ratio for the 3-hexyne partial
hydrogenation, a batch stainless-steel stirred tank reactor
was used. The reaction tests were performed using the
following catalysts: (1) commercial Lindlar catalyst
2
Experimental
-
3
2
.1 Synthesis of Pure [RhCl(NH (CH ) CH ) ]
2
(Aldrich cat. 20,573-7) (4.5 9 10 g), (2) [RhCl(NH2
2 12
3 3
-
CH ) CH ) ] (1.6 9 10 g), and (3) [RhCl(NH2
3
(
2 12 3 3
-
2
The [RhCl(NH (CH ) CH ) ] complex (hereafter NH
2
(CH ) CH ) ]/RX3 (7.5 9 10 g), at three temperatures:
2 12 3 3
2 12
3 3
2
3
(
(
CH ) CH = TDA) was prepared by reaction of RhCl
2
T = 275 K, T = 290 K and T = 303 K, with 150 kPa
1 2 3
12
3
Aldrich, cat. 30786-6) and TDA (Fluka, cat 91950) fol-
of hydrogen pressure. In all the cases, 100 mL of a 2%
(v/v) solution of 3-hexyne (Aldrich cat. 30,689-4) in tolu-
ene was used, with a 3-hexyne/M (M = Rh or Pd) molar
lowing a method already reported [29].
3
2
.2 Immobilization of [RhCl(NH (CH ) CH ) ]
2 12
ratio ca. 8.05 9 10 . All of the catalytic tests were carried
2
3 3
on RX3
out at a stirring velocity of 600 rpm, during 120 min. To
avoid the possible contamination of the reaction media
with metal cations, the reactor and the stirrer were
poly(tetrafluoroethylene) coated. To study the possibility of
the existence of external and internal diffusional limitations
in the catalytic tests performed, experiments at different
stirring velocities and various particle sizes were mounted
[33, 34]. On the one hand the stirring velocity was varied
from 180 to 1,400 rpm, with a constancy of activity and
selectivity above 500 rpm, ensuring that external diffu-
sional limitations were absent at the rotary speed selected.
On the other hand, the heterogenized complex catalyst was
crushed up to 1/4 of the original size of the RX3 pellets
used as support. In every case, the conversion and selec-
tivity values obtained were the same than those corre-
sponding to the non-crushed catalyst, concluding that
internal diffusional limitations were absent at the opera-
tional conditions of this work. Additionally, the catalyst
cylinders were properly treated and weighed after ending
the reaction. The difference in the mass of catalyst cylin-
ders, before and after the test reaction, was within the
experimental error of the analytical balance method,
meaning that there was no mass loss from the cylinders.
Thus, it can be considered that the attrition effect is absent
or is negligible enough to play a role in determining an
additional mass transfer limitation.
Immobilization of the complex was carried out on RX3
hereafter [RhCl(NH (CH ) CH ) ]/RX3), a pelletized
(
2
2 12
3 3
Ò,
commercial carbon from NORIT
incipient wetness technique [30].
by means of the
2
RX3 presents a BET surface area of 1,411 m g , a
-1
-
total pore volume of 1.217 mL g , with a distribution of
1
pore volume and sizes as follows, micropores: 0.356 mL
-
1
-1
g
/\0.7 nm, supermicropores: 0.333 mL g /0.7–2 nm,
mesopores: 0.098 mL g /2–7.5 nm and macropores:
-1
-
1
.430 mL g /7.5–50 nm [31].
0
A solution of [RhCl(NH (CH ) CH ) ] in chloroform/
2
2 12
3 3
methanol (5/1, v/v), in a suitable concentration, was used
for impregnation to obtain a 0.3 Rh wt% catalyst. The
solvent was let evaporate in a desiccator at 298 K, until
constant mass was verified.
2
.3 Elemental Composition
After catalytic runs, [RhCl(NH (CH ) CH ) ]/RX3 was
3 3
2
2 12
analyzed by standard chemical techniques for the presence
of rhodium, chlorine and nitrogen and their weight percent
values, on a C- and H- free base [29].
2
.4 X-Ray Photoelectron Spectroscopy (XPS)
Reactants and products were analyzed by gas chroma-
tography, using a flame ionization detector and a CP WAX
52 CB capillary column. All runs were carried out in
triplicate; the relative experimental error was about 3%.
Fresh [RhCl(NH (CH ) CH ) ]/RX3 was analyzed by
3 3
2
2 12
XPS to determine the presence of rhodium, nitrogen and
chlorine, their electronic states and atomic ratios, according
1
23

A High (Z)/(E) Ratio Obtained During the 3-Hexyne Hydrogenation
233
2
.6 Possibility of Complex Leaching
3.1.2 Rhodium Local Site Symmetry, HOMO-LUMO
Electron Configuration and Complex Geometry
The possibility of complex leaching from the supported
catalyst during the hydrogenation tests was checked,
after each catalytic run, determining the presence of
rhodium in the remaining solutions by Atomic Absorption
Spectrophotometry.
Knowing that tetra-coordinated rhodium(I) complexes have
a square-planar geometry [35] and that the complex for-
mula is [RhCl(NH (CH ) CH ) ], two facts can be
2
2 12
3 3
considered:
(
I) A C2v local site symmetry for the closest rhodium
atom environment; in this site symmetry, with tride-
cylamine as an electron-donating r ligand and chlo-
ride as an electron-withdrawing r/p ligand and the
two-fold rotation axis along the z cartesian axis, the
Angular Overlap Model (AOM) [36] was used to
predict the HOMO-LUMO frontier orbitals. Applying
3
3
3
Results and Discussion
.1 Supported Complex Structure
.1.1 Rhodium Coordination Sphere and Complex
Minimum Formula
8
this model, with Rh(I) as a d central atom, we
determined the following orbital distribution in an
increasing order of energy: non-bonding (d ), anti-
xy
According to previously published results [25] of elemental
composition and XPS (Table 1) for the pure complex, it
was suggested that the rhodium coordination sphere is
formed by chloro and TDA ligands; and that the complex
empirical formula could be [RhCl(NH (CH ) CH ) ] [29].
bonding double-degenerate e* ((d , d )*), 7/4 e*
r
p
xz
yz
((d )*) and 9/4 e*r ((dx2–y2)*). Assigning the
eight electrons to this scheme, it turns out that
z2
À
Á
ꢁ
ꢁ
ðdz2Þ (z direction) is the HOMO and dx2ꢂy2 (x
and y directions) is the LUMO frontier orbitals, with a
relatively high energy due to the low oxidation
number of the rhodium atom. The former is useful
to produce the cleavage of the H–H bonding, gener-
ating hydrogen atoms and the latter is available to
receive electron density from the substrate molecule,
weakening the C–C triple bond; both of them are key
factors in the catalytic cycle leading to the hydroge-
nation of the substrate.
2
2 12
3 3
Elemental composition weight % values of the sup-
ported complex after catalytic evaluations, for Rh, Cl and
N on a C- and H- free base were 57.0, 19.8 and 23.0,
respectively. According to these results, the Rh, Cl and N
molar stoichiometry can be expressed as ca. 1:1:3, in total
accordance with the corresponding values for the pure
complex [29].
Additionally, XPS results of binding energies and
atomic ratios, for the anchored and pure complex are
shown on Table 1. From this information, it can be
observed that: (a) the atomic ratios Cl/Rh and N/Rh are in
total accordance with the results obtained from elemental
composition for the pure complex; and (b) there was a
constancy of the Rh 3d5/2, N 1 s and Cl 2p3/2 XPS BE,
meaning that their electronic state remain unchanged. Item
(II) The approximate molecular size of the metal com-
plex was estimated in order to study structural
aspects related to its location on the support porosity.
We did this taking into account the square planar
geometry, typical covalent radii, a 109.5° C–C–C
angle and basic trigonometry, determining the
longest dimensions, the TDA–Rh–TDA and the
Cl–Rh–TDA lengths, as ca. 4 and 2.3 nm, respec-
tively. On the other hand, according to the distribu-
tion of pore sizes given in the ‘‘Experimental’’
section it can be concluded that the complex can be
located only in the meso and macropores (2–7.5 and
7.5–50 nm respectively), thus occupying ca 43% of
the support total pore volume available.
(
a) indicates that the supported complex may be considered
as tetra-coordinated, maintaining its chemical identity
when it is anchored, and item (b) suggests that Rh is not in
contact with the carbon surface, and in this way the het-
erogenization of the complex took place via a physico-
chemical interaction between the last part of the TDA
hydrocarbon chains and the carbon basal planes, i.e. an
anchoring showing a kind of ‘‘table’’ arrangement.
3 3
Table 1 Rh 3d5/2, N 1 s, and Cl 2p3/2 peaks binding energies (BE) and the atomic ratios N/Rh and Cl/Rh for [RhCl(TDA) ] and [RhCl(TDA) ]/
RX3
Sample
Rh 3d5/2 (eV)
N 1 s (eV)
Cl 2p3/2 (eV)
N/Rh (at./at.)
Cl/Rh (at./at.)
[
RhCl(TDA)
3
] (from Ref. [29])
]/RX3
307.1
307.1
402.1
401.9
198.1
198.0
3.00
3.00
1.01
1.02
[
RhCl(TDA)
3
123

2
34
D. A. Liprandi et al.
3
.2 Possibility of Complex Leaching
by hydrogenation of the alkyne or the alkene isomers
[
7, 37]. Last but not least, [RhCl(NH (CH ) CH ) ]/RX3
2 2 12 3 3
Results from Atomic Absorption Spectrophotometry
revealed that no rhodium was present in the remaining
solution from all the heterogeneous catalytic runs, meaning
that the complex was not leached under the reaction con-
ditions, and kept anchored on the carbonaceous support.
showed the lowest conversion values to the (E) isomer and
to the alkane.
In Fig. 2, a detail from Fig. 1, it can be observed that,
for a given catalytic system, the variation of conversion to
(Z)-3-hexene versus 3-hexyne total conversion follows an
increasing tendency as the temperature is raised. However,
it can be noted that the performance of Rh(I) complex
heterogeneous system is slightly sensitive to temperature
changes while the homogeneous system and the Lindlar
catalyst are considerably sensitive to temperature changes.
For a given temperature, the [RhCl(NH (CH ) CH ) ]/
3
.3 Catalytic Evaluation
3
.3.1 Chemical Considerations
(
Z)-3-hexene, (E)-3-hexene and n-hexane were the only
products detected by GC during the catalytic runs using the
catalytic systems: (1) commercial Lindlar catalyst (2)
2
2 12
3 3
RX3 system shows the highest conversions to (Z)-3-hexene
at the highest 3-hexyne total conversions (maximum value:
X(Z) = 95.0% at X = 99.8%), followed by [RhCl(NH
[RhCl(NH (CH ) CH ) ], and (3) [RhCl(NH (CH ) CH ) ]/
2 2 12 3 3 2 2 12 3 3
T
2
RX3. In Fig. 1 the conversions to (Z)-3-hexene and
E)-3-hexene are shown as a function of the 3-hexyne total
(CH ) CH ) ] and then by the Lindlar catalyst.
3 3
2
12
(
In Fig. 3 the selectivity to (Z)-3-hexene versus the
3-hexyne total conversion values are presented. The selec-
tivity plots show an initial plateau-shaped behaviour fol-
lowed by a marked decreasing tendency for the increasing
3-hexyne total conversion. The [RhCl(NH (CH ) CH ) ]/
conversion for the Lindlar catalyst and for Rh(I) homoge-
neous and heterogeneous complex. It can be noted the
predominant formation of the (Z)-alkene stereo-isomer, the
desired product. In this respect, it can be seen, from Fig. 1,
that all of the catalytic systems show an initial part with an
almost linear slope, which takes a value of 45° for the
2
2 12
3 3
RX3 system allows to obtain a practically constant value of
a very high selectivity (not lower than 98.5%) up to a very
high 3-hexyne total conversion (ca. 85%); after that, the
selectivity decays in a very slight way. Meanwhile, in the
case of [RhCl(NH (CH ) CH ) ] and the Lindlar catalyst,
[
RhCl(NH (CH ) CH ) ]/RX3 catalyst. After that initial
2 2 12 3 3
part, all of the systems have a similar shape with an
increasing 3-hexyne total conversion, showing a maximum
value of conversion to (Z)-3-hexene. There was also a
relatively low amount of the side products: (E)-3-hexene
formed either as initial product or via Z ? E isomeriza-
tion, and n-hexane (not plotted in Fig. 1 because of the low
values obtained and for the sake of clarity) produced either
2
2 12
3 3
high values of selectivities (ca. 89.4 and ca. 94.2 respec-
tively) were obtained for a lower 3-hexyne total conversion
(ca. 44%); then both systems show a monotonously
decreasing profile shape, which is more pronounced in the
case of the Lindlar catalyst.
Fig. 1 Conversion to (Z)-3-hexene and to (E)-3-hexene versus
3
-hexyne total conversion for: Lindlar catalyst (1), [RhCl(TDA)
2), [RhCl(TDA) ]/RX3 (3); filled square/open square 275 K, filled
3
]
Fig. 2 Conversion to (Z)-3-hexene versus 3-hexyne total conversion
for: Lindlar catalyst (1), [RhCl(TDA) ] (2), [RhCl(TDA) ]/RX3 (3) (a
3 3
(
3
triangle/open triangle 290 K, filled diamond/open diamond 303 K.
Open symbols: (E)-3-hexene, solid symbols (Z)-3-hexene
detail of Fig. 1 in the zone where the three systems present the most
remarkable differences)
1
23

A High (Z)/(E) Ratio Obtained During the 3-Hexyne Hydrogenation
235
To reinforce the conclusions given in the previous
paragraphs, some relevant values of conversion and
selectivity for different reaction conditions are summarized
in Table 2.
The different activity and selectivity behaviour between
the complex species supported and unsupported could be
explained considering a higher concentration of the sub-
strate around the supported complex catalyst than that in
the bulk solution as alkynes are adsorbed more strongly
than alkenes due to a physicochemical adsorption process.
Finally, for each system the higher the temperature the
higher the selectivity and the higher the conversion to the
(
Z) isomer, although the [RhCl(NH (CH ) CH ) ]/RX3
2 2 12 3 3
system behaves as the less sensitive catalyst to that
variable.
Fig. 3 Selectivity to (Z)-3-hexene versus 3-hexyne total conversion
for: Lindlar catalyst (1), [RhCl(TDA) ] (2), [RhCl(TDA) ]/RX3 (3);
filled square 275 K, filled triangle 290 K, filled diamond 303 K
From now on, the attention will be focused on the best
complex system at the optimum temperature (303 K) and
3
3
Table 2 3-hexyne total conversion (X
S(E) and S , respectively) for the following catalysts: Lindlar, [RhCl(TDA)
T
), conversions to (Z)-3-hexene (X(Z)) and selectivities to (Z)-3-hexene, (E)-3-hexene and n-hexane (S(Z)
] complex unsupported and anchored on RX3
,
n
3
Reaction time (min)
Catalyst
Lindlar
T (K)
X
T
(%)
X
(Z) (%)
S
(Z) (%)
S
(E) (%)
S
n
(%)
5
7
1
0
275
48
53
57
76
81
82
87
89
92
55
60
66
88
92
93
98
99
44
49
53
61
64
69
85
87
90
48
50
52
64
68
72
92
93
95
46
45
44
55
58
62
82
81
82
92
93
93
79
80
84
98.6
98.6
98.6
87
82
79
72
73
78
94
94
95
77
68
61
58
59
64
82
81
82
3
3
5
4
3
8
7
3
2
3
90
03
4
[
RhCl(TDA)
RhCl(TDA)
3
]
275
13
13
13
2
2
3
90
03
[
3
]/RX3
275
0.3
0.3
0.5
9
2
3
90
03
2
1.5
5
Lindlar
275
4
6
2
3
90
03
12
7
14
11
11
6
[
[
RhCl(TDA)
RhCl(TDA)
3
]
275
16
16
16
3
2
3
90
03
3
]/RX3
275
3
2
3
90
03
3
3
99.8
60
2
3
20
Lindlar
275
6
17
23
28
21
21
16
9
2
3
90
03
66
9
73
11
21
20
20
9
[
[
RhCl(TDA)
RhCl(TDA)
3
]
275
94
2
3
90
03
98
98
3
]/RX3
275
99.9
99.9
99.9
2
3
90
03
8
11
10
8
Reaction conditions: hydrogen pressure 150 kPa, and different reaction temperatures (275, 290 and 303 K) at 50, 75 or 120 min of reaction
123

2
36
D. A. Liprandi et al.
its performance will be compared with that of the Lindlar
catalyst, which is typically considered as a reference sys-
tem, at the same temperature.
In Fig. 4 the differences between the desired and side
products ((E)-3-hexene plus n-hexane) versus 3-hexyne
total conversion, for the Lindlar catalyst and for
[
RhCl(TDA) ]/RX3, are plotted. It can be seen that the
3
highest difference between the conversion to the desired
product and to the side products ((E)-3-hexene ? hexane),
for the [RhCl(NH (CH ) CH ) ]/RX3 system was
2
2 12
3 3
obtained for a 3-hexyne total conversion equal to 96.4% (at
0 min). Meanwhile, the corresponding value for the
6
Lindlar catalyst was achieved for a 3-hexyne total con-
version of 57.5% (at 50 min). For these optimum 3-hexyne
total conversions, the conversion to (Z)-3-hexene with
Fig. 5 Relative difference in selectivity to the Z species (DS)
versus 3-hexyne total conversion (X ), at 303 K. Note: DS (%) =
T
[
RhCl(NH (CH ) CH ) ]/RX3 was 94%, 1.76 times
2 2 12 3 3
higher than that corresponding to the Lindlar catalyst
53.5%). On the other hand, the selectivities to (Z)-3-hex-
ene are 97 and 93, respectively.
[
(SZComplex-SZLindlar)/SZ Lindlar] 9 100
(
The relative differences to the (Z)-3-hexene product
obtained with [RhCl(NH (CH ) CH ) ]/RX3 (SZcomplex)
used in the hydrogenation reaction, remaining adsorbed as
a whole on the support surface and (b) it is the catalytically
active species.
2
2 12
3 3
and with the Lindlar catalyst (SZLindlar) were calculated as
follows: DS(%) = [(SZcomplex-SZlLindlar)/SZLindlar] 9 100.
This DS is plotted in Fig. 5 as a function of 3-hexyne total
conversion. For a 3-hexyne total conversion of 57.5%,
although it is not the optimum for [RhCl(NH (CH )
At this point, gathering information from some of the
previous paragraphs, the best catalytic behaviour shown by
[RhCl(TDA) ]/RX3 for the 3-hexyne partial hydrogenation
3
2
2 12
can be explained by:
CH ) ]/RX3 but the best value for the Lindlar catalyst, the
3
3
(
a) A [RhCl(TDA) ] ‘‘table’’ type anchoring on RX3
3
relative difference in selectivity (DS) for the Z species favors
the former in 7.23%.
without loosing its coordination sphere structure
associated to a C2v local site-symmetry, what in turns
means to have available, on the one hand, a high
electron density (the HOMO frontier orbital) along
the z axis ready to overlap with the hydrogen r
antibonding orbital, thus favouring H–H bond break-
ing; and on the other hand, an empty orbital extended
on the xy plane (the LUMO frontier orbital) available
to interact with the electron density from the 3-hexyne
triple bond, thus weakening one of its p bonds.
On the other hand, considering that after catalytic
evaluation the elemental composition of the run supported
complex is equal to that of the pure complex, and that there
is no leaching at all, it can be suggested that: (a) the
coordination compound maintains its identity after being
1
00
90
80
70
60
50
40
30
20
10
0
(
b) A [RhCl(TDA) ] major distribution into the RX3 meso
3
and macropores, sites where the 3-hexyne can be easily
adsorbed, augmenting its concentration around the
complex, via a physicochemical interaction.
(3)
3
.3.2 Practical considerations
(1)
As the best catalyst system was [RhCl(NH (CH ) CH ) ]/
2
2 12
3 3
RX3, that presents high conversion and selectivity values
with a low sensitivity to the variation of temperature, some
practical-economical benefits could be mentioned: (a) the
easy and cheap way in which the catalyst is removed from
the remaining solution after ending the hydrogenation
reaction; (b) the main product does not need further puri-
fication due to a possible contamination with a heavy metal
0
10
20
30
40
50
60
70
80
90
100
3
-hexyne total conversion %
Fig. 4 Difference in conversion, versus 3-hexyne total conversion at
03 K, for: Lindlar catalyst (1), [RhCl(TDA) ],/RX3 (3). Note: DX
3
3
(
%) = [X(Z)-(X(E) ? Xhexane)]
1
23

A High (Z)/(E) Ratio Obtained During the 3-Hexyne Hydrogenation
237
compound because no complex leaching was detected; and
lastly, (c) there is no need for a costly temperature control
system.
10. Lindlar H, Dubuis R, Jones FN, McKusick FC (1973) Org Synth
Coll 5:880
1
1
1. Yu J, Spencer JB (1998) Chem Comm 1103
2. Nijhuis TA, van Koten G, Kapteijn F, Moulijn JA (2003) Catal
Today 79–80:315
1
1
3. Huang W, Li A, Lobo RF, Chen JG (2009) Catal Lett 130:380
4. Badano JM, Quiroga M, Betti C, Vera C, Canavese S, Coloma-
Pascual F (2010) Catal Lett 137:35
4
Conclusions
1
5. Nijhuis TA, van Koten G, Moulijn JA (2003) App Catal A Gen
238:259
It is possible to hydrogenate 3-hexyne to obtain (Z)-3-hex-
ene, under mild conditions using [RhCl(TDA) ] as catalyst
16. Chen JG, Qi S-T, Humbert MP, Menning CA, Zhu Y-X (2010)
Acta Phys Chim Sin 26(4):869
3
in homogeneous/heterogeneous systems with a very good
general performance, and better than that of the Lindlar
1
1
7. Shiju RN, Guliants VV (2009) Appl Catal A Gen 356:1
8. Volpe MA, Rodr ´ı guez P, Gigola CE (1999) Catal Lett 61:27
catalyst. [RhCl(TDA) ]/RX3 shows the highest 3-hexyne
3
19. Zhang W, Li L, Du Y, Wang X, Yang P (2009) Catal Lett
127(3–4):429
total conversion and selectivity to (Z) 3-hexene, the desired
product. This behaviour may be understood by considering
electronic and structural effects, which can be explained by
concepts of complex dimensions, local site symmetry,
frontier orbitals and physicochemical interactions.
2
2
0. Choi J, Yoon NM (1996) Tetrahedron Lett 37(7):1057
1. Crespo-Quesada M, Dykeman RR, Laurenczy G, Dyson PJ,
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2011.01.003
22. Giannandrea R, Mastrorilli P, Zaccaria G, Nobile CF (1996) J
Molec Catal A Chem 109:113
Additionally, the performance of [RhCl(TDA) ]/RX3 as
3
2
3. Kameda N, Yoneda T (1999) J Chem Soc Jpn Chem Indus Chem
:33
a catalyst exhibits a low sensitivity to the variation of
temperature, a factor that is useful for technological
applications, when: (a) deciding investment on temperature
control system, (b) removing the catalyst from the reactor
and (c) purifying the desired product.
1
24. Lough AJ, Morris RH, Ricciuto L, Schleis T (1998) Inorg Chim
Acta 270:238
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5. Quiroga M, Liprandi D, L’Argenti e` re P, Cagnola E (2005) J
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6. de Wolf E, Spek AL, Kuipers BWM, Philipse AP, Meeldijk JD,
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acknowledged.
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