Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH3C(CH2P(X)Ph2)3] {X = O, S, Se} and their reactivity

Article abstract of DOI:10.1016/j.molcata.2009.08.007

The reaction of dimeric rhodium precursor [Rh(CO)₂Cl]₂ with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH₃C(CH₂P(X)Ph₂)₃](L), where X = O(a)

Full text of DOI:10.1016/j.molcata.2009.08.007

Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines,
[CH3C(CH2P(X)Ph2)3] {X = O, S, Se} and their reactivity
Dipak Kumar Duttaa,∗, J. Derek Woollinsd, Alexandra M.Z. Slawind, Amy L. Fullerd, Biswajit Deba,
Podma Pollov Sarmaha, Madan Gopal Pathakb, Dilip Konwarc
a Materials Science Division, North East Institute of Science and Technology (CSIR), Jorhat 785006, Assam, India
b Analytical Chemistry Division, North East Institute of Science and Technology (CSIR), Jorhat 785006, Assam, India
c Synthetic Organic Chemistry Division, North East Institute of Science and Technology (CSIR), Jorhat 785006, Assam, India
d School of Chemistry, University of St. Andrews, St. Andrews, KY16 9ST, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2009
Received in revised form 7 August 2009
Accepted 10 August 2009
Available online 18 August 2009
The reaction of dimeric rhodium precursor [Rh(CO)2Cl]2 with two molar equivalent of 1,1,1-
tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH3C(CH2P(X)Ph2)3](L), where X = O(a),
S(b) and Se(c) affords the complexes of the type [Rh(CO)2Cl(L)] (1a–1c). The complexes 1a–1c have been
characterized by elemental analyses, mass spectrometry, IR and NMR (1H, 31P and 13C) spectroscopy and
the ligands a–c are structurally determined by single crystal X-ray diffraction. 1a–1c undergo oxidative
addition (OA) reactions with different electrophiles such as CH3I, C2H5I and C6H5CH2Cl to give Rh(III)
complexes of the types [Rh(CO)(COR)ClXL] {R = –CH3 (2a–2c), –C2H5 (3a–3c); X = I and R = –CH2C6H5
(4a–4c); X = Cl}. Kinetic data for the reaction of a–c with CH3I indicate a first-order reaction. The cat-
alytic activity of 1a–1c for the carbonylation of methanol to acetic acid and its ester is evaluated and a
higher turn over number (TON = 1564–1723) is obtained compared to that of the well-known commer-
cial species [Rh(CO)2I2]− (TON = 1000) under the reaction conditions: temperature 130 2 ◦C, pressure
30 2 bar and time 1 h.
Keywords:
Rhodium
Carbonyl complexes
Chalcogen donor
Functionalized tripodal phosphine
Reactivity
Carbonylation
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
[Rh(CO)2I2]− as an efficient catalyst for carbonylation of methanol
to acetic acid, considerable efforts have been made to improve the
The chemistry of phosphines and their derivatives have aroused
much interest in the last few decades because of their reactiv-
ity, structural novelty and catalytic activity [1–5]. The tripodal
polyphosphines such as CH3C(CH2PPh2)3 (triphos), have been
employed in several metal complex systems [6–10] and there are
a number of reports of five coordinate Rh(I) and Ir(I) complexes
containing flexible ␩2–P binding mode [10–15], which exhibit
kinetic lability of MI–P bonds (M = Rh, Ir) leading to structural and
chemical variability. Metal complexes of multidentate phosphine
chalcogen donor ligands play an important role on the stability
and reactivity of the compounds. The most important feature of
these ligands is that they can stabilize the metal complexes by
chelate formation and may create vacant coordination sites at the
metal centre by the cleavage of relatively weaker metal chalco-
gen bonds, which is a prerequisite criteria for catalytic reactions.
The oxidative addition (OA) reactions of Rh(I) complexes contain-
ing labile ligands have a great impact in catalytic carbonylation
of methanol. Since the introduction of the Monsanto’s species i.e.
catalysts by incorporating different ligands into its coordination
sphere [16–21]. Though the Rh carbonyl complexes of mono- and
ditertiary phosphine chalcogenides and their catalytic carbonyla-
tion of methanol are documented in the literature [5b,22], but to our
best knowledge, there is no report of rhodium carbonyl complexes
containing tripodal phosphine chalcogenides and their utilization
as catalysts for carbonylation reaction. As a part of our continuing
research activities [5,22,23], herein we report the synthesis, reac-
tivity and catalytic carbonylation of rhodium(I) carbonyl complexes
containing 1,1,1-tris(diphenylphosphino methyl)ethane trichalco-
genide [P3X3, where X = O(a), S(b) and Se(c)] ligands. The X-ray
structural characterization of the three P3X3 ligands (a–c) and their
donor effects on the nucleophillicity of the metal centre have also
been demonstrated.
2. Experimental
2.1. General definition
All solvents were distilled under N2 prior to use. RhCl3·xH2O
was purchased from M/S Arrora Matthey Ltd., Kolkota, India.
[CH3C(CH2PPh2)3], elemental sulfur and selenium powder were
∗
Corresponding author. Tel.: +91 376 2370081; fax: +91 376 2370011.
E-mail address: dipakkrdutta@yahoo.com (D.K. Dutta).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.08.007

D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
101
a: Yield: 90%; IR (KBr, cm−1): 1175 [ꢀ(P O)]. 1H NMR (CDCl3,
ppm): ı 0.85 (s, 3H, CH3), ı 3.19 (d, 6H, CH2), ı 7.27–7.50,
7.65–7.85 (m, 30H, Ph). 13C NMR (CDCl3, ppm): ı 29.1 (q, CH3), ı
•
purchased from M/S Aldrich, USA and used without further purifi-
cation. H2O2 was obtained from Ranbaxy, New Delhi, India and
estimated before use.
1
41.1 (dt, CH2P S), ı 39.7 (q, C), ı 128.8–134.5 (m, Ph). 31P { H}
Elemental analyses were performed on a Perkin-Elmer 2400 ele-
mental analyzer. IR spectra (4000–400 cm−1) were recorded in KBr
discs and CHCl3 on a Perkin–Elmer system 2000 FTIR spectropho-
tometer. The 1H, 13C and 31P NMR spectra were recorded at room
temperature in CDCl3 solution on a Bruker DPX-300 Spectrometer
and chemical shifts were reported relative to SiMe4 and 85% H3PO3
as internal and external standards respectively. Mass spectra of the
complexes were recorded on ESQUIRE 3000 Mass Spectrometer.
The carbonylation reactions of methanol were carried out in a high
pressure reactor (Parr-4592, USA) fitted with a pressure gauge and
the reaction products were analyzed by GC (Chemito 8510, FID).
NMR (CDCl3, ppm): ı 31.3 [s, P(V)]. Elemental analyses; Found
(Calcd for C41H39O3P3): C, 72.91 (73.13), H, 5.38 (5.80). Mass:
672.9 (m/z+).
b: Yield: 95%; IR (KBr, cm−1): 625, 611 [ꢀ(P S)]. 1H NMR (CDCl3,
ppm): ı 0.64 (s, 3H, CH3), ı 3.8 (d, 6H, CH2), ı 6.98–7.40, 7.95–8.02
(m, 30H, Ph). 13C NMR (CDCl3, ppm): ı 26.4 (q, CH3), ı 41.8 (dt,
•
•
1
CH2P S), ı 42.3 (q, C), ı 128.3–134.2 (m, Ph). 31P { H} NMR
(CDCl3, ppm): ı 35.5 [s, P(V)]. Elemental analyses; Found (Calcd
for C41H39S3P3): C, 67.79 (68.26), H, 5.21 (5.41). Mass: 719.8
(m/z+).
c: Yield: 92%; IR (KBr, cm−1): 548 [ꢀ(P Se)]. 1H NMR (CDCl3,
ppm): ı 0.59 (s, 3H, CH3), ı 4.02 (d, 6H, CH2), ı 7.15–7.41,
7.98–8.06 (m, 30H, Ph). 13C NMR (CDCl3, ppm): ı 26.1 (q, CH3), ı
2.2. Synthesis of the ligands, [CH3C(CH2P(X)Ph2)3], where (X = O,
S, Se)
1
40.9 (dt, CH2P S), ı 42.9 (q, C), ı 128.3–132.8 (m, Ph). 31P { H}
NMR (CDCl3, ppm): ı 23.1 [s, P(V)]. Elemental analyses; Found
(Calcd for C41H39Se3P3): C, 56.93 (57.10), H, 4.35 (4.52). Mass:
861.5 (m/z+).
The ligands, [CH3C(CH2P(O)Ph2)3](a), [CH3C(CH2P(S)Ph2)3](b)
and [CH3C(CH2P(Se)-Ph2)3](c) were synthesized as reported in our
earlier paper [24].
2.3. Starting material
2.5. Synthesis of [Rh(CO)(COR)ClXL] (R = CH3, X = I (2); R = C2H5,
X = I (3); R = C6H5CH2, X = Cl (4)
[Rh(CO)2Cl]2 was prepared by passing CO gas over RhCl3·3H2O
at 100 ◦C in the presence of moisture [25].
[Rh(CO)2ClL] (50 mg) was dissolved in dichloromethane (5 cm3)
and each of RX (3 cm3) (RX = CH3I, C2H5I, C6H5CH2Cl) was added
to it. The reaction mixture was then stirred at r.t. for about 4, 6
and 8 h for CH3I, C2H5I and C6H5CH2Cl respectively. The colour of
the solution changed from yellowish red to dark reddish brown
and the solvent was evaporated under vacuum. The compounds so
obtained were washed with diethyl ether and stored over silica gel
in a desiccator.
2.4. Synthesis of the complexes [Rh(CO)2ClL] (1),
L = [CH3C(CH2P(O)Ph2)3](a), [CH3C(CH2P(S)Ph2)3](b),
[CH3C(CH2P(Se)Ph2)3](c)
[Rh(CO)2Cl]2 (100 mg) was dissolved in dichloromethane
(10 cm3) and to this solution, a stoichiometric quantity (Rh:L = 1:1)
of the respective ligands were added. The reaction mixture was
stirred at room temperature (r.t.) for about 30 min and the solvent
was evaporated under vacuum. The yellowish red coloured com-
pounds so obtained were washed with diethyl ether and stored
over silica gel in a desiccator.
Analytical data for the complexes 2a–2c, 3a–3c and 4a–4c are
as follows:
2a: Yield: 81%; IR (CHCl3, cm−1): 2065 [ꢀ(CO)], 1745 [ꢀ(CO)acyl],
1H NMR (CDCl3, ppm): ı 0.85 (s, 3H, CH3), ı 3.22–3.35 (6H, CH2),
•
•
•
•
•
•
Analytical data for the complexes 1a–1c and their free ligands
a–c are as follows:
ı 7.14–8.06 (m, 30H, Ph), ı 2.16 (s, 3H, CH3)MeI.
13C NMR (CDCl3,
ppm): ı 122.2–135.1 (m, Ph), ı 184.4 (s, CO), ı 207.1 (s, CO)acyl
.
1
31P { H} NMR (CDCl3, ppm): ı 33.2 [broad, P(V)].
1a: Yield: 85%; IR (KBr, cm−1): 2075, 2069, 2010, 1996 [ꢀ(CO)],
1168, 1165, 1174 [ꢀ(P O)]. 1H NMR (CD3OD, ppm): ı 0.91 (s, 3H,
CH3), ı 3.20–3.29 (6H, CH2), ı 7.09–7.58, 7.75–8.06 (m, 30H, Ph).
13C NMR (CD3OD, ppm): ı 27.5 (q, CH3), ı 40.9 (dt, CH2P O), ı
2b: Yield: 85%; IR (CHCl3, cm−1): 2068 [ꢀ(CO)], 1729 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.71 (s, 3H, CH3), ı 3.78–3.92 (6H, CH2),
•
•
•
ı 7.08–8.03 (m, 30H, Ph), ı 2.29 (s, 3H, CH3)MeI.
13C NMR (CDCl3,
ppm): ı 124.2–134.1 (m, Ph), ı 185.1 (s, CO), ı 206.6 (s, CO)acyl
.
38.1 (q, C), ı 127.2–135.1 (m, Ph), ı 183.7 (s, CO). 31P { H} NMR
1
1
31P { H} NMR (CDCl3, ppm): ı 36.8 [broad, P(V)].
2c: Yield: 84%; IR (CHCl3, cm−1): 2072 [ꢀ(CO)], 1737 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.68 (s, 3H, CH3), ı 3.98–4.25 (d, 6H,
(CD3OD, ppm): ı 32.5 [broad, P(V)]. Elemental analyses; Found
(Calcd for C43H39ClO5P3Rh): C, 58.97 (59.50), H, 4.25 (4.49). Mass:
866.9 (m/z+).
CH2), ı 7.12–8.17 (m, 30H, Ph), ı 2.57 (s, 3H, CH3)MeI.
13C NMR
1b: Yield: 88%; IR (KBr, cm−1): 2074, 2067, 2004, 1991 [ꢀ(CO)],
622, 609, 606 [ꢀ(P S)]. 1H NMR (CDCl3, ppm): ı 0.69 (s, 3H, CH3),
ı 3.72–3.90 (6H, CH2), ı 7.03–7.48, 7.78–8.11 (m, 30H, Ph). 13C
NMR (CDCl3, ppm): ı 26.3 (q, CH3), ı 41.8 (dt, CH2P S), ı 40.2 (q,
(CDCl3, ppm): ı 126.2–137.1 (m, Ph), ı 185.9 (s, CO), ı 204.8 (s,
1
CO)acyl
.
31P { H} NMR (CDCl3, ppm): ı 24.6 [broad, P(V)].
3a: Yield: 85%; IR (CHCl3, cm−1): 2066 [ꢀ(CO)], 1728 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.89 (s, 3H, CH3), ı 3.55–3.38 (6H, CH2), ı
C), ı 127.9–132.2 (m, Ph), ı 184.2 (s, CO). 31P { H} NMR (CDCl3,
1
7.04–8.09 (m, 30H, Ph), ı 2.35 (q, 2H, CH2)EtI, ı 1.61 (t, 3H, CH3)EtI
.
13C NMR (CDCl3, ppm): ı 122.2–135.1 (m, Ph), ı 186.4 (s, CO), ı
ppm): ı 36.2 [broad, P(V)]. Elemental analyses; Found (Calcd for
1
204.1 (s, CO)acyl
.
31P { H} NMR (CDCl3, ppm): ı 33.4 [broad, P(V)].
C
43H39ClO2S3P3Rh): C, 55.85 (56.36), H, 4.05 (4.26). Mass: 915.8
(m/z+).
3b: Yield: 91%; IR (CHCl3, cm−1): 2071 [ꢀ(CO)], 1720 [ꢀ(CO)acyl].
1c: Yield: 91%; IR (KBr, cm−1): 2072, 2066, 2001, 1989 [ꢀ(CO)],
546, 543, 539 [␯(P Se)]. 1H NMR (CDCl3, ppm): ı 0.62 (s, 3H,
CH3), ı 4.04–4.38 (d, 6H, CH2), ı 7.08–7.39, 7.91–8.14 (m, 30H,
Ph). 13C NMR (CDCl3, ppm): ı 26.8 (q, CH3), ı 41.5 (dt, CH2P S),
1H NMR (CDCl3, ppm): ı 0.78 (s, 3H, CH3), ı 3.84–3.91 (6H, CH2), ı
6.98–8.05 (m, 30H, Ph), ı 2.51 (q, 2H, CH2)EtI, ı 1.53 (t, 3H, CH3)EtI
.
13C NMR (CDCl3, ppm): ı 123.9–137.1 (m, Ph), ı 184.1 (s, CO), ı
203.6 (s, CO)acyl
.
31P { H} NMR (CDCl3, ppm): ı 36.7 [broad, P(V)].
1
ı 42.5 (q, C), ı 128.7–133.5 (m, Ph), ı 185.3 (s, CO). 31P { H} NMR
1
3c: Yield: 87%; IR (CHCl3, cm−1): 2060 [ꢀ(CO)], 1735 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.72 (s, 3H, CH3), ı 3.89–4.22 (6H, CH2), ı
(CDCl3, ppm): ı 23.9 [broad, P(V)]. Elemental analyses; Found
(Calcd for C43H39ClO2Se3P3Rh): C, 48.11 (48.84), H, 3.26 (3.69).
Mass: 1056.5 (m/z+).
7.01–8.17 (m, 30H, Ph), ı 2.71 (q, 2H, CH2)EtI, ı 1.68 (t, 3H, CH3)EtI
.
13C NMR (CDCl3, ppm): ı 123.2–137.1 (m, Ph), ı 184.9 (s, CO), ı

102
D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
1
205.2 (s, CO)acyl
.
31P { H} NMR (CDCl3, ppm): ı 24.8 [broad, P(V)].
4a: Yield: 78%; IR (CHCl3, cm−1): 2071 [ꢀ(CO)], 1734 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.91 (s, 3H, CH3), ı 3.42–3.61 (6H, CH2),
ı 6.94–8.16 (m, 35H, Ph), ı 4.26 (s, 2H, CH2)Bz (Bz stands for
•
C6H5CH2Cl). 13C NMR (CDCl3, ppm): ı 124.8–133.3 (m, Ph), ı
1
185.3 (s, CO), ı 206.2 (s, CO)acyl
ı 33.2[broad, P(V)].
.
31P { H} NMR (CDCl3, ppm):
4b: Yield: 75%; IR (CHCl3, cm−1): 2066 [ꢀ(CO)], 1736 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.78 (s, 3H, CH3), ı 3.72–3.97 (6H, CH2),
•
•
ı 7.91–8.13 (m, 35H, Ph), ı 4.31 (s, 2H, CH2)Bz.
13C NMR (CDCl3,
ppm): ı 122.8–136.2 (m, Ph), ı 184.2 (s, CO), ı 205.6 (s, CO)acyl
.
1
31P { H} NMR (CDCl3, ppm): ı 36.5 [broad, P(V)].
4c: Yield: 79%; IR (CHCl3, cm−1): 2068 [ꢀ(CO)], 1742 [ꢀ(CO)acyl].
1H NMR (CDCl3, ppm): ı 0.65 (s, 3H, CH3), ı 3.94–4.15 (6H, CH2),
ı 7.01–8.17 (m, 35H, Ph), ı 4.58 (s, 2H, CH2)Bz.
13C NMR (CDCl3,
ppm): ı 122.6–138.3 (m, Ph), ı 186.5 (s, CO), ı 206.4 (s, CO)acyl
.
1
31P { H} NMR (CDCl3, ppm): ı 24.6 [broad, P(V)].
2.6. X-ray structural analysis
Single crystals of a–c were grown by layering a CH2Cl2 solution
of a–c with n-pentane. Several different crystals of each sample
were examined since the crystals were difficult to grow and of low
quality. The intensity data of the compounds were collected on a
Rigaku Saturn CCD with Mo K␣ radiation (ꢁ = 0.71073 Å) at 125 K.
The structures were solved with SHELXS-97 and refined by full-
matrix least squares on F2 using SHELXL-97 computer program
[26]. Hydrogen atoms were idealized by using the riding mod-
els.
2.7. Kinetic experiment
The kinetic experiments of OA reaction of complexes 1a–1c
with CH3I were monitored using FTIR spectroscopy in a solu-
tion cell (CaF2 windows, 1.0 mm path length). In order to obtain
pseudo-first-order condition, excess of CH3I relative to metal com-
plex was used. FTIR spectra (4.0 cm−1 resolution) were scanned
in the ꢀ(CO) region (2200–1600 cm−1) and saved at regular time
interval using spectrum software. After completion of experiment,
absorbance versus time data for the appropriate ꢀ(CO) frequencies
were extracted by subtracting the solvent spectrum and analyzed
off line using OriginPro 7.5 software. Kinetic measurements were
made by following the decay of lower frequency ꢀ(CO) band of
the complexes in the region 1996–1989 cm−1. The pseudo-first-
order rate constants were found from the gradient of the plot of
ln(A0/At) versus time, where A0 is the initial absorbance and At is
the absorbance at time t.
2.8. Carbonylation of methanol using complexes 1a–1c as
catalyst precursors
Fig. 1. X-ray crystal structures of a–c. Hydrogen atoms are omitted for clarity.
CH3OH (0.099 mol, 4 cm3), CH3I (0.016 mol, 1 cm3), H2O
(0.055 mol, 1 cm3) and catalyst (0.0514 mmol) were taken into the
reactor. The reactor was then purged with CO for about 5 min and
then pressurized with CO gas (20 1 bar) at 25 ◦C. The carbony-
lation reactions were carried out at 130 2 ◦C for 1 h under CO
pressure (30 2 bar). The products were collected and analyzed by
GC.
determined. The crystal information of a–c is summarized in
Table 1. The compound a crystallizes in a triclinic system with space
¯
group P1, while b and c crystallize in a monoclinic system with
space group P21/c. Though both the asymmetric units in b and c
contain two molecules, the X-ray crystallographic data show that
these molecules are essentially identical in both molecular dimen-
sions and conformations. The selected bond lengths of a–c are
presented in Table 2. The P–O bond lengths (1.488(2)–1.490(3) Å)
in a is similar to the P O bond length in xantphos dioxide reported
by Deb and Dutta [27] Similarly, the P–S (1.954(2)–1.971(2) Å) and
P–Se (2.106(3)–2.124(3) Å) bond lengths are also in the expected
ranges [28].
3. Results and discussion
3.1. Single crystal X-ray structural determination of a–c
The single crystal X-ray structures (Fig. 1) of the reported
[24] trichalcogen functionalized phosphine ligands a–c have been

D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
103
Table 1
The IR spectra of 1a–1c exhibit multiple ꢀ(CO) bands in the
range 1989–2075 cm−1 indicating the formation of a mixture of
rhodium(I) carbonyl complexes of tripodal phosphine chalcogen
donor ligands. The ꢀ(P–X) bands of the complexes at around 1165,
1168 (1a), 606, 609 (1b) and 539, 543 (1c) cm−1 respectively are
lower than that of the corresponding free ligands [ꢀ(P–X) = 1175
(a); 625, 611 (b) and 548 (c) cm−1] confirming the formation of
Rh–X bonds. In addition, the occurrence of IR bands at around
1174, 622 and 546 cm−1 in the respective complexes 1a–1c due
to uncoordinated donors together with the observed peak inten-
sity suggest the presence of dangling P–X bonds in the complexes
indicating coordination to the metal centre either monodentate
and/or bidentate coordination mode to generate a mixture of iso-
mers. The presence of the mixture of isomers is also substantiated
Crystallographic data and structure refinement details for a–c.
a
b
c
Empirical formula
Formula weight
Cryst. syst.
Space group
C41H39O3P3
672.68
Triclinic
P1
2
11.2418 (15)
13.061 (2)
13.9967 (15)
109.550 (13)
113.430 (13)
92.985 (18)
0.210
C41H39S3P3
720.86
Monoclinic
P21/c
C41H39Se3P3
861.56
Monoclinic
P21/c
¯
Z
8
8
a (Å)
b (Å)
9.8624 (8)
27.549 (2)
27.387 (2)
9.9505 (8)
27.819 (2)
27.556 (2)
c (Å)
˛ (◦)
ˇ (◦)
92.957 (2)
92.851 (2)
ꢂ (◦)
ꢃ (Mo K␣) (mm−1
)
0.357
3.052
Reflections collected
R (obs. data)
wR2 (all data)
6025
0.0786
0.1996
13,025
0.1124
0.1758
13,324
0.1240
0.2037
1
by the 31P{ H} NMR spectroscopy which shows broad singlets for
the complexes 1a–1c centred at ı = 32.5, 36.2 and 23.9 ppm respec-
tively for three pentavalant P-atoms. The 1H NMR spectra of 1a–1c
show characteristic resonances for methyl, methylene and phenylic
protons. In the 13C NMR spectra of 1a–1c, only one weak signal for
the two carbonyl carbons is appeared as broad singlet in the range
183.7–185.3 ppm. The phenyl and other carbon atoms are found in
their respective ranges.
Table 2
Selected bond distances (Å) and angles (◦) for compounds a–c.
a
P(1)–O(1)
1.488(2)
P(2)–O(2)
1.488(3)
P(3)–O(3)
1.490(3)
b
c
P(1)–S(1)
P(4)–S(4)
1.954(2)
1.964(2)
P(2)–S(2)
P(5)–S(5)
1.958(2)
1.962(2)
P(3)–S(3)
P(6)–S(6)
1.970(2)
1.962(2)
3.3. Reactivity of 1a–1c towards various electrophiles
One of the most important industrial processes utilizing homo-
geneous transition-metal catalysis is the rhodium and iodide
promoted carbonylation of methanol to acetic acid. In this respect,
OA reaction of alkyl halides with metal complexes is a very impor-
tant reaction as it is the key step in the carbonylation catalysis [29].
Therefore, oxidative reactivities of 1a–1c towards various elec-
trophiles were evaluated.
The complexes 1a–1c undergo OA reactions with CH3I, C2H5I
and C6H5CH2Cl followed by migratory insertion reaction to gen-
erate Rh(III) complexes of the type [Rh(CO)Cl(COR)XL] {where
R = –CH3 (2a–2c), –C2H5 (3a–3c); X = I and R = –CH2C6H5 (4a–4c),
P(1)–Se(1)
P(4)–Se(4)
2.106(3)
2.124(3)
P(2)–Se(2)
P(5)–Se(5)
2.135(3)
2.118(3)
P(3)–Se(3)
P(6)–Se(6)
2.108(3)
2.115(3)
3.2. Synthesis and characterization of 1a–1c
The reaction of the chloro-bridged dimer [Rh(CO)2Cl]2 in CH2Cl2
with two molar equivalents of the ligands, a–c affords the com-
plexes of the type [Rh(CO)2ClL] (1a–1c) [where L = a–c] (Scheme 1).
Elemental analyses and mass spectrometric results of the com-
plexes support the observed molecular composition of 1a–1c.
Scheme 1. Syntheses of Rh(I) and Rh(III) complexes containing P3X3 ligands.

104
D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
X = Cl} (Scheme 1). The IR spectra of the oxidized products
show two broad ꢀ(CO) bands in the range 2060–2072 cm−1 and
1720–1745 cm−1 characteristic of terminal and acyl carbonyl
1
groups respectively. 31P{ H} NMR spectra of each of the oxidized
products exhibit a broad singlet indicating the presence of a mix-
ture of Rh(III) species formed after oxidative addition. The 1H NMR
spectra of the complexes 2a–2c display singlet resonances in the
range ı 2.16–2.57 ppm suggesting the formation of –COCH3 group
including other characteristic bands of the ligands. Similarly, the
complexes 3a–3c show the bands for methylene and methyl pro-
tons of –COCH2CH3 group as quartet and triplet in addition to
characteristic bands for the ligands. The singlet resonances cor-
responding to methylene protons of –COCH2C6H5 group in the
complexes 4a–4c appears in the range ı 4.26–4.58 ppm. The pres-
ence of electron withdrawing phenyl group deshields the –COCH2–
proton resonances and the peaks are obtained at downfield [30].
The 13C NMR spectra of 2a–2c, 3a–3c and 4a–4c exhibit bands in
the range 203–208 ppm characteristic to the acyl carbonyl group.
Thus, it appears that the Rh(I) complexes 1a–1c undergo oxidative
addition with various alkyl halides to generate a mixture of iso-
mers of Rh(III) species 2a–2c, 3a–3c and 4a–4c, which could not be
isolated.
Attempts to substantiate the structures of different rhodium(I)
and rhodium(III) carbonyl complexes by X-ray crystal structure
determination was not possible because no suitable crystals could
be obtained in spite of numerous attempts.
Kinetic measurements for the OA reaction of the complexes
1a–1c with methyl iodide were carried out using IR spectroscopy
by monitoring the changes in the ꢀ(CO). Fig. 2 shows a typical series
of spectra of 1c when reacts with MeI at 25 ◦C, in which the bands
at around 1989 and 2066 cm−1 decay and new bands grow in the
region 2070–2075 and 1720–1745 cm−1. Finally, the two terminal
ꢀ(CO) bands at around 2066 and 1989 cm−1 are replaced by the ter-
minal ꢀ(CO) band at 2072 cm−1 and acyl ꢀ(CO) band at 1737 cm−1
.
Absorbance versus time plots for the decay of lower intensity
ꢀ(CO) bands at 1996, 1991 and 1989 cm−1 of 1a–1c respectively
are shown in Fig. 3. A linear fit of pseudo-first-order was observed
for the entire course of the reaction of CH3I with the complexes
1a–1c as is evidenced from the plot of ln(A0/At) versus time, where
A0 and At are the absorbance at time t = 0 and t respectively (Fig. 4).
From the slopes of the plots, the rate constants were calculated and
found as 7.19 × 10−5, 1.95 × 10−4 and 2.68 × 10−3 s−1 for the com-
plexes 1a, 1b and 1c respectively. The observed values of the rate
constants indicate that the rate of OA increases about tenfold on
Fig. 3. Kinetic plot showing the decay of ꢀ(CO) bands of 1a–1c during the reaction
with neat MeI at room temperature (∼25 ◦C).
introducing the ‘soft’ donor ligand which is due to the higher nucle-
ophilicity of the metal centre caused by higher electron donating
capacity of the ligands. The softness of three chalcogens varies as
O < S < Se and therefore, S and Se in complexes 1b and 1c respec-
tively interact strongly with ‘soft’ rhodium(I) in contrast to ‘hard’
oxygen (O) donors in complex 1a, which may be explained in terms
of ‘soft–hard’ and ‘soft–soft’ interactions.
3.4. Carbonylation of methanol to acetic acid and methyl acetate
using the complexes 1a–1c as the catalyst precursors
The results of carbonylation of methanol to acetic acid and
methyl acetate in the presence of 1a–1c as catalyst precursors are
shown in Table 3. The precursor complexes 1a–1c show a total
Fig. 2. Series of IR spectra {ꢀ(CO) region} illustrating the reaction of 1c with MeI at
25 ◦C. The arrows indicate the behavior of each band as the reaction progresses.

D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
105
Table 3
Results of carbonylation reaction of methanol.
Catalyst precursor
Time (h)
Total conv. (%)
Acetic acida (%)
Methyl acetatea
TONb
[Rh(CO)2I2]−c
1a
1b
1c
1
1
1
1
52.1
81.3
87.4
89.6
10.3
42.2
45.6
53.2
41.8
39.1
41.8
36.4
1000
1564
1683
1723
a
Yield of methyl acetate and acetic acid were obtained from GC analyses.
TON = [amount of product (mol)]/[amount of catalyst (Rh mol)].
Formed from added [Rh(CO)2Cl]2 under catalytic condition.
b
c
conversion of 81.3, 87.4 and 89.6% of CH3OH at 130 2 ◦C and
30 2 bar CO pressure with corresponding TON of 1564, 1683 and
1723. Under the same experimental conditions, the well-known
precursor [Rh(CO)2I2]− generated in situ from [Rh(CO)2Cl]2 [31]
shows only 52.1% total conversion with a TON of 1000. Thus, the
efficacy of the complexes depends on the nature of the ligands and
follows the order 1c > 1b > 1a > [Rh(CO)2Cl]2. The observed trend
is also well supported by their kinetic experiments. On examin-
ing the catalytic reaction mixture by IR spectroscopy at different
time intervals and at the end of the catalytic reaction, multiple
ꢀ(CO) bands are obtained that matched well with the ꢀ(CO) values
of solution containing a mixture of the parent rhodium(I) car-
bonyl complexes 1a–1c and rhodium(III) acyl complexes 2a–2c.
Thus, it may be inferred that the ligands remained bound to
the metal centre throughout the entire course of the catalytic
reactions.
4. Conclusions
The new complexes of the type [Rh(CO)2Cl(L)](1a–1c) where
L = 1,1,1-tris(diphenylphosphinomethyl)ethane
trichalcogenide
ligands, [CH3C(CH2P(X)Ph2)3] [X = O(a), S(b) and Se(c)] have been
synthesized and characterized and the structures of the ligands
were determined by single crystal X-ray diffraction. The complexes
1a–1c undergo oxidative addition (OA) reactions with different
electrophiles like CH3I, C2H5I and C6H5CH2Cl to afford Rh(III)
complexes of the type [Rh(CO)(COR)XL] {R = –CH3 (2a–2c), –C2H5
(3a–3c); X = I and R = –CH2C6H5 (4a–4c); X = Cl} and the kinetic
data for the OA reactions with CH3I indicate a first-order reaction.
The catalytic activities of 1a–1c for the carbonylation of methanol
to acetic acid and its ester exhibit a higher turn over number
(TON = 1564–1723) than that of the well-known commercial
species [Rh(CO)2I2]− (TON = 1000).
Supplementary data
CCDC-711100(a), 711101(b) and 711102(c) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033
e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
The authors are grateful to Dr. P.G. Rao, Director, North East Insti-
tute of Science and Technology (CSIR), Jorhat 785006, Assam, India
for his kind permission to publish the work. The Department of Sci-
ence and Technology (DST), New Delhi (Grant: SR/S1/IC-05/2006)
and Royal Society (UK) International Joint Project 2007/R2-CSIR
(India) joint research scheme are acknowledged for the partial
financial grant. The authors B. Deb and P.P. Sarmah thank to CSIR,
New Delhi for providing the Junior Research Fellowships.
Fig. 4. Plot of ln(A0/At) versus time for the OA reaction of the complexes 1a–1c with
neat MeI at ∼25 ◦C. Rate constants: 1a: 7.19 × 10−5 s−1; 1b: 1.95 × 10−4 s−1 and 1c:
2.68 × 10−3 s−1
.

106
D.K. Dutta et al. / Journal of Molecular Catalysis A: Chemical 313 (2009) 100–106
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