Catalytic activity of dicarbonylrhodium complexes of aminobenzoic acid ligands on carbonylation of alcohol

Article abstract of DOI:10.1016/S1381-1169(02)00331-X

Rhodium(I) complexes of the type, [Rh(CO)₂ClL] (1), where L = 2-aminobenzoic acid (1a), 3-aminobenzoic acid (1b), and 4-aminobenzoic acid (1c), were synthesized. Oxidative addition (OA) of 1 with electrophiles like RI (R = CH₃, C₂H₅) produced Rh(III) complexes of the type [Rh(CO)(COCH₃)IClL] and [Rh(CO)(COC₂H₅)IClL]. The OA reactions of complexes 1 with RI followed a two stage kinetics and the observed rate constants were in the order 1b > 1c > 1a irrespective of stages. The complexes 1 displayed higher catalytic activity for carbonylation of methanol and ethanol than that of [Rh(CO)₂I₂]^-.

Full text of DOI:10.1016/S1381-1169(02)00331-X

Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
Catalytic activity of dicarbonylrhodium complexes of
aminobenzoic acid ligands on carbonylation of alcohol
Manab Sharma, Nandini Kumari, Pankaj Das,
Pratap Chutia, Dipak Kumar Dutta∗
Material Science Division, Regional Research Laboratory, CSIR, Jorhat 785 006, Assam, India
Received 17 January 2002; accepted 25 May 2002
Abstract
Rhodium(I) complexes of the type, [Rh(CO)2ClL] (1), where L = 2-aminobenzoic acid (a), 3-aminobenzoic acid (b) and
4-aminobenzoic acid (c), have been synthesised. Oxidative addition (OA) of complexes 1 with electrophiles like RI (R = CH3,
C2H5) produce Rh(III) complexes of the type [Rh(CO)(COCH3)IClL] (2) and [Rh(CO)(COC2H5)IClL] (3). The OA reactions
of complexes 1 with RI follow a two stage kinetics and the observed rate constants are in the order 1b > 1c > 1a irrespective
of stages. The complexes 1 show higher catalytic activity for carbonylation of methanol and ethanol than that of the well
known species [Rh(CO)2I2]−.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Rhodium complexes; Aminobenzoic acid; Oxidative addition; Two stage kinetics; Catalyst; Carbonylation of alcohol
1. Introduction
as ligands, particularly 2-aminobenzoic acid [11,12],
have been used as efficient catalyst for the reductive
carbonylation of nitroaromatics as well as in hy-
drogenation [13,14]. This prompted us to undertake
an investigation on the catalytic activity of rhodium
complexes containing aminobenzoic acid of the type
[Rh(CO)2ClL] (1), where L = 2-aminobenzoic acid
(a), 3-aminobenzoic acid (b), 4-aminobenzoic acid (c)
towards the carbonylation of alcohols, like methanol
and ethanol. As a part of our continuing work [15–17],
i.e. effect of various ligands on rhodium catalysed
carbonylation of alcohol, we have reported in the
present communication the positional effect of sub-
stituent of the ligands a–c on oxidative reactivity of
the complexes 1 towards the electrophiles RI (where
R = CH3, C2H5), which is a key step in the metal
catalysed carbonylation reaction [18], and the cat-
alytic activity in the carbonylation of methanol and
ethanol.
Transition metal complex catalysed carbonylation
is one of the most useful methods for the direct in-
troduction of carbonyl group into alcohol molecules
to produce acid and its esters. Recently, rhodium
complexes have gained much importance as efficient
catalyst in carbonylation reactions [1–6]. One of the
most important species, [Rh(CO)2I2]−, has been still
considered as a preferred catalyst in the industrial ap-
plication of carbonylation of methanol [7]. Research
activities are continued to modify the catalyst either
by simple ligand tailoring or by changing the central
metal atom [3–6,8–10]. Literature survey reveals that
rhodium(I) complexes containing aminobenzoic acids
∗
Corresponding author. Tel.: +91-376-3370121x529;
fax: +91-376-3370011.
E-mail address: dipakkrdutta@yahoo.com (D.K. Dutta).
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00331-X

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M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
2. Experimental
2.1.2. Synthesis of [Rh(CO)(COR)IClL], where R
= CH3 (2), R= C2H5 (3)
All the solvents used were distilled under N2
prior to use. Elemental analyses were done on a
Perkin-Elmer 2400 elemental analyser. FT-IR spectra
(4000–400 cm−1) were recorded using a Perkin-Elmer
2000 spectrophotometer in CHCl3 and as KBr discs.
The 1HNMR (300 MHz) spectra were recorded in
CDCl3 solution on a Bruker DPX-300 Spectrometer
and chemical shifts were reported relative to SiMe4 as
an internal reference. The carbonylation of alcohols
were carried out in a 100 cm3 teflon coated high pres-
sure reactor (HR-100 Berghof, Germany) fitted with
a pressure gauge and the reaction products were anal-
ysed by GC (Chemito 8510, FID). RhCl3·3H2O was
purchased from M/S Arrora Matthey Ltd., Kolkata,
India. All the ligands were purchased from Aldrich,
USA and used as received.
A total of 0.3017 mmol of complex 1a–c was dis-
solved in 10 cm3 acetone and to this 6 cm3 RI (R =
CH3, C2H5) was added. The reaction mixture was then
stirred at RT for about 4 and 24 h for CH3I and C2H5I,
respectively and the solvent was evaporated under vac-
uum. Yellow-reddish coloured compounds so obtained
were washed with diethyl ether and stored over silica
gel in a desiccator.
Analytical data for the complexes 2a–c and 3a–c
are as follows:
2a: Colour: reddish brown; yield: 93%; anal. calcd.
for C10H10ClINO4Rh (%): C, 25.35; H, 2.11; N, 2.96;
found: C, 25.30; H, 2.10; N, 2.92.
2b: Colour: reddish brown; yield: 94%; anal. calcd.
for C10H10ClINO4Rh (%): C, 25.35; H, 2.11; N, 2.96;
found: C, 25.32; H, 2.12; N, 2.90.
2c: Colour: reddish brown; yield: 92%; anal. calcd.
for C10H10ClINO4Rh (%): C, 25.35; H, 2.11; N, 2.96;
found: C, 25.37; H, 2.13; N, 2.96.
2.1. Starting material
All the complexes were synthesised from [Rh-
(CO)2Cl]2 which was prepared by passing CO gas
over RhCl3·3H2O at 100 ◦C [19].
3a: Colour: brown; yield: 92%; anal. calcd. for
C11H12ClINO4Rh (%): C, 27.09; H, 2.46; N, 2.87;
found: C, 27.12; H, 2.44; N, 2.92.
3b: Colour: brown; yield: 92%; anal. calcd. for
C11H12ClINO4Rh (%): C, 27.09; H, 2.46; N, 2.87;
found: C, 27.21; H, 2.50; N, 2.91.
3c: Colour: brown; yield: 92%; anal. calcd. for
C11H12ClINO4Rh (%): C, 27.09; H, 2.46; N, 2.87;
found: C, 27.19; H, 2.48; N, 2.90.
2.1.1. General procedure for the synthesis of the
complexes [Rh(CO)2ClL] (1) (L = 2-aminobenzoic
acid (a), 3-aminobenzoic acid (b) and
4-aminobenzoic acid (c))
An amount of 0.0257 mmol of [Rh(CO)2Cl]2 was
dissolved in 10 cm3 CH2Cl2 and to this 0.0514 mmol
of the respective ligands, a–c, in 10 cm3 acetone so-
lution, was added. The reaction mixture was stirred at
room temperature (RT) for about 10 min and the sol-
vent was evaporated under vacuum. The compound
so obtained was washed with diethyl ether and stored
over silica gel in a desiccator.
Analytical data for the complexes 1a–c are as fol-
lows:
1a: Colour: light yellow; yield: 95%; anal. calcd.
for C9H7ClNO4Rh (%): C, 32.59; H, 2.11; N, 4.22;
found: C, 32.42; H, 2.10; N, 4.25.
1b: Colour: reddish brown; yield: 93%; anal. calcd.
for C9H7ClNO4Rh (%): C, 32.59; H, 2.11; N, 4.22;
found: C, 32.45; H, 2.12; N, 4.20.
1c: Colour: deep violet; yield: 97%; anal. calcd. for
C9H7ClNO4Rh (%): C, 32.59; H, 2.11; N, 4.22; found:
C, 32.51; H, 2.10; N, 4.21.
2.2. Carbonylation of methanol and ethanol using
complexes 1 as the catalyst precursors
A total of 0.099 mol of ROH (R = CH3, C2H5),
0.016 mol of RI, 0.055 mol of H2O, 0.054 mmol of
complexes 1 were taken in the reactor and then pres-
surised with CO gas (20 bar at RT, 0.080 mol). The
reaction vessel was then placed into the heated jacket
of the autoclave and the reactions were carried out
at 130 5 ◦C (corresponding pressure 35 2 bar)
with variation of reaction time. The products were
collected and analysed by GC. The recycle experi-
ments were done by maintaining the same experi-
mental conditions as described above with the dark
brown solid mass as catalyst obtained by evaporat-
ing the carbonylation reaction mixture under reduced
pressure.

M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
27
Table 1
IR and 1HNMR spectral data of the rhodium carbonyl complexes
Complex/free ligand
IR spectra (cm−1
)
1HNMR δ (ppm)
␯(CO)
␯(COO)asy
␯(NH2)
a
b
c
–
–
–
1670
1633
1665
1673
1672
1683
1698
1688
1687
1684
1680
1683
3494, 3379
3428
3463, 3364
3290, 3212
3216
3276, 3196
3288, 3211
3202
3256, 3165
3286, 3206
3200
7.25 (s, NH2), 6.12–6.83 (m, C6H5)
7.14 (s, NH2), 6.21–6.84 (m, C6H5)
7.26 (s, NH2), 6.02–6.44 (m, C6H5)
7.73 (s, NH2), 6.54–7.26 (m, C6H5)
7.52 (s, NH2), 6.75–7.33 (m, C6H5)
7.47 (s, NH2), 6.28–6.69 (m, C6H5)
7.81 (s, NH2), 6.45–7.12 (m, C6H5), 3.12 (s, COCH3),
7.66 (s, NH2), 6.65–7.23 (m, C6H5), 3.22 (s, COCH3)
7.58 (s, NH2) 6.37–6.81 (m, C6H5), 3.02 (s, COCH3)
7.77 (s, NH2), 6.34–7.22 (m, C6H5), 2.27 (q, CH2), 1.88 (t, CH3)
7.71 (s, NH2), 6.59–7.20 (m, C6H5), 2.47 (q, CH2), 1.68 (t, CH3)
7.69 (s, NH2), 6.20–6.77 (m, C6H5), 2.14 (q, CH2), 1.58 (t, CH3)
1a
1b
1c
2a
2b
2c
3a
3b
3c
2096, 2027
2082, 2011
2090, 2018
2077, 1718a
2076, 1714a
2077, 1719a
2084, 1723a
2077, 1715a
2078, 1717a
3255, 3162
a Acyl ␯(CO).
3. Result and discussion
order 1a > 1c > 1b which can be explained by the
electron donating capacity of the ligand. The elec-
tron donating capacity of the –NH2 group influenced
by the presence of electron withdrawing –COOH
group at different positions in the benzene ring is
well understood from Fig. 2. This is further corrobo-
rated by the calculated data (Semiemperical MNDO
approximation method [29]) of electron density on
the N-atom i.e. −0.3829, −0.4084, −0.3951 for a,
b and c ligands, respectively. High electron density
on the N-atom will in turn increase the electron den-
sity on the central metal atom which may donate
3.1. Synthesis and characterisation of complexes 1
One equivalent of the chlorobridged dimeric com-
plex [(CO)2Rh(␮-Cl)2Rh(CO)2] undergoes a bridge
splitting reaction with two equivalent of the ligands
a–c to yield complexes of type [Rh(CO)2ClL], where
L = 2-aminobenzoic acid, 3-aminobenzoic acid and
4-aminobenzoic acid. The complexes exhibit colours
ranging from light yellow to deep violet. The IR
spectra of the complexes 1a–c (Table 1) show two al-
most equal intense terminal ␯(CO) bands in the range
2010–2100 cm−1, attributable to the cis-disposition
of the carbonyl groups [20–22]. The ␯(NH2) bands
in the complexes 1 show an appreciable shift to-
wards the lower wave number compared to that of
the free ligands (Table 1) indicating coordination oc-
curs through N-donor [23–25]. Further, the positions
of ␯(COO)asy bands in the complexes 1 indicate the
COO group is not involved in coordination [26]. The
probable structure of the complexes 1 is shown in
Fig. 1. It is interesting to note that the ligands a–c
show intra/inter-molecular hydrogen bonding in the
free state [27] and the ␯(COO)asy bands occur in
the range 1630–1670 cm−1 which shifts to a slightly
higher value (Table 1) upon complexation suggest-
ing minimisation of hydrogen bonding [28]. From
Table 1, it has been observed that the positions of
the ␯(CO) bands in these complexes 1 follow the
more d -electron to the antibonding ␲∗-orbital of the
␲
CO and consequently decrease the C–O bond order
resulting in a lowering the ␯(CO) frequency [15].
The 1HNMR values of the free ligands and the com-
plexes 1a–c are shown in Table 1. The –NH2 protons
Fig. 1. Structure of complex 1a–c.

28
M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
bands of these complexes (2 and 3) occur in the higher
range compared to free ligands and thus nullifies the
1
coordination through O-donor. The HNMR spectra
of the complexes 2a–c show a singlet in the region δ
3.00–3.25 ppm apart from other characteristics reso-
nance of ligands indicating the formation of –COCH3.
In a similar manner, the 1HNMR spectra of com-
plexes 3a–c show a triplet at around δ 1.55–1.90 ppm
and a quartet at around δ 2.14–2.50 ppm corre-
sponding to the methyl and methylene protons of
the –COOCH2CH3 group (Table 1). As most of the
five-coordinated carbonyl–Rh(III)–acyl complexes
reported are square pyramidal in nature [30,31], it
is likely that the acyl complexes 2 and 3 would also
have a similar geometry. The presence of a single
high terminal ␯(CO) value is consistent with CO
group trans to a weak trans influencing chloride [32].
On the other hand, the high trans influencing nature
of the acetyl group favours strong trans directing io-
dine in its trans position [31,33] which facilitate the
elimination of RCOI molecule from the Rh(III) acyl
complex to generate the parent Rh(I) complex, during
the course of catalytic cycle. It is obvious that the
site trans to aminobenzoic acid ligand (L) lies vacant.
Thus, the most probable structure of the acyl complex
is represented in Scheme 1.
Fig. 2. Effect of electron withdrawing –COOH group on nitrogen
atom of the aminobenzoic acid ligand.
show a downfield shift compared to that of the free lig-
ands, which is due to the partial shift of electron cloud
from N-atom to the metal centre. This interaction also
causes the phenylic protons a downfield shift.
3.2. Reactivity of the complexes 1 towards various
electrophiles
The complexes 1 undergo OA reactions with
electrophiles (RI), like CH3I and C2H5I fol-
lowed by a migratory insertion reaction to form
five-coordinated rhodium(III) acyl complexes of the
type [Rh(CO)(COR)IClL], where R = CH3 (2), C2H5
(3). The acyl species is believed to form through an
unstable six-coordinated intermediate (Scheme 1).
The IR spectra of the oxidised products (2 and 3) show
a single characteristic terminal ␯(CO) band in the
range 2070–2085 cm−1 and a broad ␯(CO) band in the
range 1714–1725 cm−1 due to the acyl carbonyl group
(Table 1). Similar to complexes 1, the ␯(COO)asy
The oxidative reactivities of the complexes 1 to-
wards electrophiles CH3I and C2H5I are different.
The reaction kinetics are monitored by following the
simultaneous decay of the lower ␯(CO) absorption
of the complexes 1 in the region 2010–2027 cm−1
and the formation of acyl ␯(CO) in the region
1710–1725 cm−1. During the course of the OA re-
actions of complexes 1 with CH3I, a series of IR
Scheme 1. OA reaction of complexes with RI.

M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
29
Fig. 3. Series of IR spectra (␯(CO) region) showing the OA reaction of [Rh(CO)2ClL] (L = 2-aminobenzoic acid) with CH3I at room
temperature. The arrows (↑) and (↓) indicate the decrease and increase in intensity of the terminal and acyl ␯(CO) bands, respectively
with the progress of the reaction.
spectra were recorded with different time intervals
and a typical set of spectral pattern for complex 1a
is shown in Fig. 3. It reveals that out of the two ter-
minal ␯(CO) bands, the intensity of the ␯(CO) band
occurring at 2027 cm−1 decreases while the higher
␯(CO) band at 2096 cm−1 shifts to a slightly lower
region at 2079 cm−1 with little decrease in inten-
sity. During the initial period of the OA reaction, a
number of spectra show an additional weak terminal
␯(CO) band at 2066 cm−1 which disappears within a
few minutes. It is most likely that this weak band is
due to the lower ␯(CO) absorption of the dicarbonyl
alkyl intermediate (Scheme 1, R = CH3). The other
higher ␯(CO) absorbance is probably enveloped by
the ␯(CO) band of complexes 1 at 2096 cm−1. Similar
type of observation was also reported earlier [34,35].
The rate of the OA reaction was found to be depen-
dent on both the concentration of complexes 1 and RI.
To find out the concentration dependence on reaction
rate, the OA reaction was carried out with a varying
concentration of CH3I (2.0×10−5 to 6.4×10−5 M) in
dichloromethane solution of complexes 1 (10 mg) at
35 ◦C. The kinetics measurements were made by mon-
itoring the decay of the absorbance of the ␯(CO) band
occurring at around 2027 cm−1 for the complexes 1.
It is worth to mention here that same kinetics is ob-
served if it is measured from the growth of the acyl
band at around 1716 cm−1
.
A plot is made for ln A0/At versus time, where A0
and At are the absorbance at time t = 0 and t, respec-
tively, as shown in Fig. 4. A two stage linear fit, each
of pseudo-first order, is observed for the entire course
of the OA reaction with CH3I. During the OA reac-
tion with 2.0 × 10−5 M CH3I (Fig. 4A), a slow first
stage was observed up to a period of about 160, 70 and
150 min for the complexes 1a–c, respectively indicat-
ing an induction period and thereafter the reactions
become very fast for second stage. It is obvious from
Fig. 4 that as the concentration of CH3I increases, the
time required for the completion of first and second
stage, in general, decreases. During the induction pe-
riod, the concentration of the intermediate is likely to
increase to a certain value which might be responsible
for the sharp enhancement of the rate of the second

30
M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
Fig. 4. Plot of ln A0/At against t (time) of the OA of complexes 1 with: (A) 2.0 × 10−5 M; (B) 3.6 × 10−5 M; (C) 6.4 × 10−5 M of CH3I.

M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
31
Table 2
The kobs values for the OA reactions of complexes 1 with RI
RI
[RI] (M)
kobs (s−1
)
1a
1b
1c
First stage
Second stage
First stage
Second stage
First stage
Second stage
CH3I
2.0 × 10−5
3.6 × 10−5
6.4 × 10−5
6.2 × 10−5
0.5 × 10−5
1.5 × 10−5
2.3 × 10−5
1.3 × 10−5
2.8 × 10−4
4.0 × 10−4
4.5 × 10−4
1.1 × 10−4
2.0 × 10−5
3.2 × 10−5
5.3 × 10−5
1.8 × 10−5
4.8 × 10−4
8.5 × 10−4
14.0 × 10−4
2.0 × 10−4
0.8 × 10−5
1.7 × 10−5
2.7 × 10−5
1.5 × 10−5
3.0 × 10−4
4.6 × 10−4
5.0 × 10−4
1.6 × 10−4
C2H5I
stage. The rate of formation of the acyl complex from
the intermediate may be represented by the following
rate equation:
The OA of complexes 1 with C2H5I was found
to be slower than that of CH3I. Therefore, to find
out the kobs, a typical OA reaction was carried out
with 6.2 × 10−5 M of C2H5I and 10 mg of complexes
1. Such reactions follow a two stage kinetics like
that of CH3I addition. The slow first stage continue
up to a period of about 910, 680 and 840 min and
thereafter the reactions follow the fast second stage
up to a period of about 1420, 1020 and 1240 min
for the complexes 1a–c, respectively (Fig. 5). Sim-
ilar to OA of CH3I, the C2H5I reactions also show
that the second stage is faster than that of the first
stage irrespective of complexes 1a–c (Table 2). It may
be worth to mention here that no additional weak
terminal ␯(CO) band was observed for the proposed
alkyl intermediate (Scheme 1, R = C2H5) during
the course of the reaction. In this case also, a con-
centration factor of the undetectable intermediate is
d[acyl complex]
= kobs[intermediate]
dt
where kobs is the observed first order rate constant.
From the slope of the plot of ln A0/At versus t, the
rate constants (kobs) for both the stages of the reac-
tion were calculated. The values of kobs measured in
various concentrations of CH3I are given in Table 2.
It reveals that, in general, the second stage reaction is
faster than that of the first stage and as the concentra-
tion of CH3I increases the rate of the OA reaction also
increases accordingly irrespective of reaction stages.
When kobs was plotted against the concentration of
CH3I, a good linear fit was observed revealing that the
reactions are of first order in CH3I.
Fig. 5. Plot of ln A0/At against t (time) of the OA of complexes 1 with 6.2 × 10−5 M of C2H5I.

32
M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
Table 3
Results of carbonylation of methanola in presence of complexes 1 as catalyst precursors
Catalyst
Duration (min)
Methyl acetate (%)
Acetic acid (%)
Total conversion (%)
TONb
1a
30
45
60
75
90
33.60
37.64
44.27
48.12
51.56
36.14
37.55
4.51
9.3
38.11
46.99
60.37
75.05
87.42
95.62
92.94
588
725
937
1158
1349
1475
1434
16.46
26.93
35.86
59.48
55.39
120
120c
1b
1c
30
45
60
75
90
39.49
42.29
42.59
44.23
41.35
40.17
41.06
2.22
13.58
27.14
40.28
54.56
57.83
55.25
41.71
55.87
69.73
84.51
95.91
98.00
96.31
644
862
1075
1304
1480
1512
1486
120
120c
30
45
60
75
90
33.31
37.97
42.32
49.37
48.31
40.62
51.68
4.98
9.21
38.29
47.18
60.86
75.18
87.91
96.33
97.37
590
728
939
1160
1356
1486
1510
18.54
25.81
39.60
55.71
45.69
120
120c
a Reaction conditions: catalyst:substrate = 1:1600; temperature, 130 5 ◦C; pressure, 35 2 bar.
b TON = mole of product per mole of catalyst.
c Recycled; TON obtained by using precursor [Rh(CO)2Cl]2 are 460, 572, 648, 788, 951 and 1159 with corresponding reaction time
30, 45, 60, 75, 90 and 120 min.
Table 4
Results of carbonylation of ethanola in presence of complexes 1 as catalyst precursors
Catalyst
Duration (min)
Ethylpropanoate (%)
Propanoic acid (%)
Total conversion (%)
TONb
1a
60
90
120
150
150c
33.36
41.96
45.98
60.34
57.19
3.06
4.31
16.04
27.67
26.87
36.42
46.27
62.02
88.01
84.06
562
714
957
1358
1297
1b
1c
60
90
120
150
150c
37.36
49.57
51.45
60.91
57.01
4.19
5.06
18.22
29.11
28.67
41.54
54.63
69.67
90.02
85.68
641
843
1075
1389
1322
60
90
120
150
150c
34.28
42.33
45.82
63.62
61.78
3.24
4.79
1711
25.23
23.12
37.52
47.12
62.93
88.85
84.90
579
727
971
1371
1310
a Reaction conditions: catalyst:substrate = 1:1600; temperature, 130 5 ◦C; pressure 35 2 bar.
b TON = mole of product per mole of catalyst.
c Recycled; TON obtained by using precursor [Rh(CO)2Cl]2 are 387, 564, 748 and 921 with corresponding time 60, 90, 120 and 150 min.

M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
33
likely to be responsible for such two stage kinetic
behaviour.
studied and the results are shown in Tables 3 and 4,
respectively. It has been observed from Table 3, that
as the reaction time increases from 30 to 120 min
for the complex 1a, the total conversion percentage
increases from 38.11 to 95.62% with corresponding
increase in turn over number (TON) from 588 to
1475. Like 1a, the complexes 1b and 1c also show a
similar increasing trend in TON with the increase in
reaction time and maximum TON of 1512 (1b) and
1486 (1c) with corresponding conversion of 98.00
and 96.33% have been obtained at 120 min of reaction
time. It is interesting to note that with the progress of
reaction time, the selectivity of the catalyst changes,
i.e. initially the major product was methyl acetate but
near the end of the reaction acetic acid was the major
yield (Fig. 6). It has been observed (Fig. 6) that for
It appears from Table 2 that the rate of OA reac-
tions of the complexes 1 follow the order 1b > 1c >
1a irrespective of the electrophiles. As the OA reac-
tion is believed to occur via nucleophilic attack by
the Rh-centre at the carbon atom of RI [36,37], the
observed trend is obvious from the electron donating
capacity of the ligands a–c (vide supra).
3.3. Carbonylation of methanol and ethanol in the
presence of complexes 1 as the catalyst precursors
The carbonylation of methanol and ethanol to
ethanoic and propanoic acid and their esters in pres-
ence of complexes 1 as catalyst precursors were
Fig. 6. Distribution of products ratio of acetic acid and methyl acetate against reaction time of carbonylation of methanol.

34
M. Sharma et al. / Journal of Molecular Catalysis A: Chemical 188 (2002) 25–35
the complexes 1a and 1c, a 50:50 (wt.%) product ratio
of acetic acid and its esters can be obtained at around
100 min of reaction time, while in case of complex
1b, the said ratio can be obtained at relatively lower
time, i.e. around 80 min.
Department of Science and Technology (DST), New
Delhi and Oil Industry Development Board (OIDB),
Ministry of Petroleum & Natural Gas, New Delhi, are
acknowledged for their partial financial grant. One
of the authors (PD) thanks CSIR, New Delhi, for the
award of Senior Research Fellowship (SRF). The au-
thors are thankful to Mr. P.P. Khound, JTA and Mr.
O.P. Sahu, TO, for recording the IR spectra.
Similar to carbonylation of methanol, the carbony-
lation of ethanol also shows an increase in TON with
increase in the reaction time (Table 4). At 150 min,
maximum TON of 1358, 1389 and 1371 with corre-
sponding conversion 88.01, 90.02 and 88.85% have
been obtained for the complexes 1a–c, respectively.
It may be mentioned here that throughout the reac-
tion (Table 4) the major product obtained was ethyl-
propanoate. The efficacy of the complexes 1 towards
the carbonylation of ethanol is found to be lower
than that of methanol. In both the carbonylation re-
actions, for a particular reaction time and condition,
the complexes 1 show higher TON over the well
known catalyst precursor [Rh(CO)2I2]− generated
in situ from [Rh(CO)2Cl]2 [38]. The efficacy of the
complexes 1 towards the carbonylation of alcohols is
different (Tables 3 and 4) and is found to follow an
order 1b > 1c > 1a. It is well known that in catalytic
carbonylation of alcohol, the OA of the complexes
1 with alkyl halide is the rate determining step [39],
therefore, higher the rate of OA reaction higher is the
catalytic activity. Thus, the said difference in reac-
tivity is due to the observed difference in rate of OA
reaction of the complexes 1 with RI (Table 2). Af-
ter completion of carbonylation reaction of methanol
(120 min run) and ethanol (150 min run) the catalytic
solution have been evaporated to dryness to get a
solid mass which show a multiple ␯(CO) bands that
matched well with the spectra of a mixture of parent
rhodium(I) carbonyl complexes and rhodium(III) acyl
complexes. On recycling the solid mass as catalysts
for the second time, nearly the same amount of con-
version have been found (Tables 3 and 4) indicating
longer durability as well as stability of the catalysts.
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The authors are grateful to the Director, Regional
Research Laboratory, Jorhat, India, for his kind per-
mission to publish the work. The authors thank Dr.
P.C. Borthakur, Head Material Science Division,
RRL, Jorhat, for his encouragement and support. The

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