Methyl iodide oxidative addition to monocarbonylphosphine [Rh((C4H3S)COCHCOR)(CO)(PPh3)] complexes utilizing UV/vis and IR spectrophotometry and NMR spectroscopy to identify reaction intermediates: R = C6H5 or C4H3S

Article abstract of DOI:10.1016/j.ica.2007.10.052

The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH₃I to [Rh((C₄H₃S)COCHCOR)(CO)(PPh₃)], with R = C₆H₅ (Ph) or C₄H₃S, consists of three definite reaction steps and involves isomers of two distinctly different classes of a Rh^III-alkyl and two distinctly different classes of a Rh^III-acyl species according to the following reaction scheme:{A figure is presented}. The molecular formulas of all the Rh^III-alkyl and Rh^III-acyl species are [Rh((C₄H₃S)COCHCOR)(CH₃)(CO)(PPh₃)(I)] and [Rh((C₄H₃S)COCHCOR)(COCH₃)(PPh₃)(I)] respectively, but the geometry is different due to different co-ordination positions of the ligands. The equilibrium K₂ was fast enough to be maintained during the Rh^I depletion in the first reaction step and during the Rh^III-alkyl2 formation in the second reaction step. A ¹H and ³¹P NMR study of the oxidative addition of CH₃I to the different isomers of [Rh((C₄H₃S)COCHCOC₆H₅)(CO)(PPh₃)], containing an unsymmetrical β-diketonato ligand, reveals the existence of at least two structural isomers for each reaction intermediate according to the following reaction scheme:{A figure is presented}. The observed rate of formation and depletion of the two Rh^I isomers of the [Rh((C₄H₃S)COCHCO(C₆H₅))(CO)(PPh₃)] complex, as well as the different isomers of each reaction intermediate, are the same, contrary to what was previously found for the formation of the alkyl2 isomers when R = CF₃. All reaction intermediates are identified spectroscopically.

Full text of DOI:10.1016/j.ica.2007.10.052

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 2285–2295
www.elsevier.com/locate/ica
Methyl iodide oxidative addition to monocarbonylphosphine
[Rh((C4H3S)COCHCOR)(CO)(PPh3)] complexes utilizing UV/vis
and IR spectrophotometry and NMR spectroscopy to identify
reaction intermediates: R = C6H5 or C4H3S
Marrigje M. Conradie, Jeanet Conradie *
Department of Chemistry, University of the Free State, Bloemfontein, Free State 9301, South Africa
Received 4 September 2007; received in revised form 25 October 2007; accepted 26 October 2007
Available online 4 December 2007
Abstract
The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH3I to [Rh((C4H3S)COCHCOR)(CO)(PPh3)], with
R = C6H5 (Ph) or C4H3S, consists of three definite reaction steps and involves isomers of two distinctly different classes of a RhIII-alkyl
and two distinctly different classes of a RhIII–acyl species according to the following reaction scheme:
K1, k1
K2, k2
k3
k4
I +CH3 I[
Rh
RhIII-alkyl1]
[RhIII-acyl1]
[RhIII-acyl2]
[RhIII-alkyl2]
{
}
k-1
k-2
k-3
k-4
The molecular formulas of all the RhIII–alkyl and RhIII–acyl species are [Rh((C4H3S)COCHCOR)(CH3)(CO)(PPh3)(I)] and
[Rh((C4H3S)COCHCOR)(COCH3)(PPh3)(I)] respectively, but the geometry is different due to different co-ordination positions of the
ligands. The equilibrium K2 was fast enough to be maintained during the RhI depletion in the first reaction step and during the
RhIII–alkyl2 formation in the second reaction step. A 1H and 31P NMR study of the oxidative addition of CH3I to the different isomers
of [Rh((C4H3S)COCHCOC6H5)(CO)(PPh3)], containing an unsymmetrical b-diketonato ligand, reveals the existence of at least two
structural isomers for each reaction intermediate according to the following reaction scheme:
RhI-A
[RhIII-alkyl1A]
Kc2
[RhIII-acyl1A]
Kc3
[RhIII-alkyl2A]
Kc4
[RhIII-acyl2A]
Kc5
K1, k1
K2, k2
k3
k4
+ CH3I
Kc1
k-1
k-3
k-4
k-2
[RhIII-alkyl1B]
[RhIII-acyl1B]
[RhIII-alkyl2B]
[RhIII-acyl2B]
RhI-B
The observed rate of formation and depletion of the two RhI isomers of the [Rh((C4H3S)COCHCO(C6H5))(CO)(PPh3)] complex, as
well as the different isomers of each reaction intermediate, are the same, contrary to what was previously found for the formation of the
alkyl2 isomers when R = CF3. All reaction intermediates are identified spectroscopically.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: b-Diketonate; Thienyl; Rhodium; Oxidative addition; NMR; Carbonyl; Phosphine
1. Introduction
The interaction of square planar rhodium(I) complexes
*
Corresponding author. Tel.: +27 51 4012194; fax: +27 51 4446384.
with methyl iodide keeps drawing attention as a simple
E-mail address: conradj.sci@ufs.ac.za (J. Conradie).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.10.052

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M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
and convenient model of the reaction of oxidative addition,
one of the key stages of important catalytic processes such
as the methanol carbonylation to acetic acid in the presence
of [Rh(CO)2I2]ꢀ (Monsanto process) [1]. Although the first
reaction product of the carbonyl-containing square planar
[RhI(L,L0-BID)(CO)(PPh3)] complexes (L,L0-BID = mono-
anionic bidentate ligand with donor atoms L and L0,
Ph = C6H5) with methyl iodide is a RhIII–alkyl species,
mechanistic concepts suggest in many cases that the oxida-
tive addition reaction proceeds through RhIII–alkyl and
RhIII –acyl intermediates. The final or most stable reaction
products that form are octahedral or square-pyramidal
complexes of rhodium(III) with different mutual disposi-
tion of the ligands [2–11]. For instance, the final reaction
product of the oxidative addition reaction of methyl iodide
to a series square planar [RhI(L,L0-BID)(CO)(PPh3)] com-
plexes, with L and L0 = O,O [5], O,N [11] O,S [11,12] and
N,S [11,13], is a RhIII–acyl species [RhIII(L,L0-BID)-
(COCH3)(PPh3)(I)]. Oxidative addition of methyl iodide
to a series of square planar [RhI(b-diketonato)(CO)(PPh3)]
complexes yield an RhIII–alkyl species [RhIII(b-diketo-
nato)(CH3)(CO)(PPh3)(I)] as the final reaction product
[14–16]. Recently it has been shown that for the oxidative
addition of methyl iodide to [Rh(fctfa)(CO)(PPh3)] with
Hfctfa = ferrocenoyltrifluoroacetone, another reaction
step, involving the formation of a second RhIII–acyl spe-
cies, has been observed [17]. Reaction 1 summarizes the
general mechanism for the oxidative addition of methyl
iodide to square planar rhodium(I) complexes containing
a monoanionic bidentate ligand. The first alkyl species in
reaction 1 may involve an ionic intermediate [RhIII(L,L0-
BID)(CH3)(CO)(PPh3)]+(I)ꢀ [14,12,18] or a solvent path-
way [11].
[RhI(L,L0-BID)(CO)(PPh3)] complexes containing an
unsymmetrical L,L0-BID = b-diketonato ligand. For b-
diketonato = tta, the final reaction product was two
RhIII–alkyl isomers which formed at different rates [16].
The final product for b-diketonato = fctfa, however, was
two RhIII–acyl isomers. The observed rate of formation
or depletion of all the reaction intermediates for the oxida-
tive addition of methyl iodide to [Rh(fctfa)(CO)(PPh3)],
however, was the same [17].
Utilizing a variety spectrophotometric (UV/vis and IR)
and spectroscopic (1H and 31P NMR) techniques, this
paper describes the extension of this project to include
the bidentate ligands (C4H3S)COCHCORꢀ with R =
C6H5 (Ph) or C4H3S in an attempt to further understand
the role of different bidentate ligands in the overall process
taking place during the general type of reaction [RhI(L,L0-
BID)(CO)(PPh3)] + CH3I.
Reactivity of rhodium(I) dicarbonyl complexes is
defined by the electron state of rhodium centre. The latter
depends inter alia on donor–acceptor characteristics of the
substituents R1 and R2 in the cyclic b-diketonato fragment
(R1COCHCOR2)ꢀ of [RhI(R1COCHCOR2)(CO)(PPh3)]
complexes. We were interested to establish whether a more
electron donating fragment (such as C6H5 (Ph) or C4H3S)
as part of a b-diketonato ligand in complexes of the type
[RhI((C4H3S)COCHCOR)(CO)(PPh3)] may enhance the
oxidative addition step which is the rate determining step
of the Monsanto catalytic cycle. Furthermore, this study
focuses on determining the nature of the final or most sta-
ble reaction product as well as the reaction rates of the dif-
ferent isomers of the reaction intermediates in the overall
process taking place during the reaction [RhI((C4H3S)-
COCHCOR)(CO)(PPh3)] + CH3I with R = C6H5 (Ph) or
C4H3S.
K1, k1
k2
[RhI(L,L'-BID)(CO)(PPh3)] + CH3I
alkyl1
k-1
k-2
k3
k4
ð1Þ
acyl2
acyl1
alkyl2
2. Experimental
k-3
k-4
product for cacsm,
product for acac,
tfaa, tfdma, hfaa,
sacac, tta
product for
fctfa
hacsm, macsm, macsh,
cupf, ox, anmeth, dmavk
2.1. Materials and apparatus
Solid reagents used in preparations (Merck, Aldrich
and Fluka) were used without further purification.
Liquid reactants and solvents were distilled prior to
use; water was doubly distilled. Organic solvents were
dried according to published methods [19]. Melting
points (m.p.) were determined with an Olympus BX51
system microscope assembled on top of a Linkam
THMS600 stage and connected to a Linkam TMS94
temperature programmer.
(Note, for some of the reactions in reaction 1, e.g. [Rh(sa-
cac)(CO)(PPh3)] + CH3I, the backward rate constants
k
ꢀ1 = kꢀ2 = kꢀ3 = 0. Hcacsm = methyl(2-cyclohexylamino-
1-cyclopentene-1-dithiocarboxylate), Hhacsm = methyl(2-
amino-1-cyclopentene-1-dithiocarboxylate), Hmacsm =
methyl(2-methylamino-1-cyclopentene-1-dithiocarboxylate),
Hmacsh = methyl(2-methylamino-1-cyclopentene-1-dithio-
carboxylate),
Hcupf = N-hydroxy-N-nitroso-benzenea-
mine, Hox = 8-hydroxyquinoline, Hanmeth = 4-methoxy-
N-methylbenzothiohydroxamate, Hdmavk = dimethylami-
novinylketone, Hacac = 2,4-pentanedione, Htfaa = 1,1,1-
2.2. Synthesis
trifluoro-2,4-pentanedione,
Htfdma = 1,1,1-trifluoro-5-
methyl-2,4-hexanedione, Hhfaa = 1,1,1,5,5,5-hexafluoro-
2,4-pentanedione, Htta = 2-thenoyltrifluoroacetone Hsacac
= thioacetylacetone.)
Only two of the above mentioned studies distinguish
between the reaction rates of the different isomers of
The thienyl-containing b-diketones 1,3-di(2-thenoyl)-
1,3-propanedione, Hdtm, and 1-phenyl-3-(2-thenoyl)-1,3-
propanedione, Hbth, were prepared according to published
procedures [20].

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2287
2.2.1. [Rh(b-diketonato)(CO)2] complexes 1 and 2
The general procedure was as follow: [Rh2Cl2(CO)4] was
prepared in situ by refluxing RhCl3 ꢁ 3H2O (0.1 g,
0.38 mmol) in DMF (3 ml) until the colour changed from
red to yellow (ca 30 min) [21]. The dimer-containing solu-
tion was allowed to cool on ice and an equivalent amount
of solid b-diketone (0.38 mmol) was slowly added while
stirring. After 30 min of stirring at room temperature, the
crude product [Rh(b-diketonato)(CO)2], complexes
[Rh(dtm)(CO)2] 1 and [Rh(bth)(CO)2] 2, was precipitated
with an excess of water, filtered, air dried and recrystallized
from chloroform (1) or hexane (2).
3J = 4 Hz, isomer B CH), 7.27 (1H, dd, 3J = 5 Hz,
4J = 1 Hz, isomer A CH), 7.42 (14H, m, CH), 7.47 (9H,
m, CH), 7.52 (1H, dd, 3J = 5 Hz, 4J = 1 Hz, isomer B
CH), 7.75 (12 H, m, CH), 7.76 (1H, dd, 3J = 4 Hz,
4J = 1 Hz, isomer B CH), 8.01 (2H, m, isomer A CH). Ele-
mental Anal. Calc. for RhC32PH24SO3: C, 61.7; H, 3.9.
Found: C, 61.5; H, 3.7%.
2.3. Spectroscopy and spectrophotometry
NMR measurements at 298 K were recorded on a Bru-
ker Advance DPX 300 NMR spectrometer [1H
(300.130 MHz)] and a Bruker Advance II 600 NMR spec-
trometer [1H (600.130 MHz) and 31P (242.937 MHz)]. The
chemical shifts were reported relative to SiMe4 (0.00 ppm)
[Rh(dtm)(CO)2] 1: Yield: 0.0858 g, 57.3%. M.p. 149.2–
1
149.9 °C. IR (cmꢀ1) = 1992 and 2057. H NMR (d/ppm,
CDCl3) 6.75 (1H, s, CH), 7.13 (2H, dd, 3J = 5 Hz,
3
4
3J = 4 Hz, CH), 7.56 (2H, dd, J = 5 Hz, J = 1 Hz, CH),
1
3
4
for the H spectra, and relative to 85% H3PO4 (0 ppm) for
7.72 (2H, dd, J = 4 Hz, J = 1 Hz, CH). Elemental Anal.
Calc. for RhC13H7S2O4: C, 39.6; H, 1.8. Found: C, 39.4;
H, 1.6%.
the 31P spectra. Positive values indicate downfield shift. IR
spectra were recorded from neat samples on a Digilab FTS
2000 infrared spectrophotometer utilizing a He–Ne laser at
632.6 nm. UV/vis spectra were recorded on a Cary 50
Probe UV/vis spectrophotometer.
[Rh(bth)(CO)2] 2: Yield: 0.1187 g, 80.5%. M.p. 147.2–
1
148.8 °C. IR (cm ꢀ1) = 1996 and 2058. H NMR (d/ppm,
CDCl3) 6.85 (1H, s, CH), 7.13 (1H, dd, 3J = 5 Hz,
3J = 4 Hz, CH), 7.47 (2H, m, CH), 7.53 (1H, m, CH),
7.58 (1H, dd, 3J = 5 Hz, 4J = 1 Hz, CH), 7.75 (1H, dd,
4
3J = 4 Hz, J = 1 Hz, CH), 7.93 (2H, m, CH). Elemental
2.4. Kinetic measurements
Anal. Calc. for RhC15H9SO4: C, 46.4; H, 2.3. Found: C,
Oxidative addition reactions were monitored on the IR
(by monitoring formation and disappearance of the car-
bonyl peaks), on the UV/vis (by monitoring the change
in absorbance at the indicated wavelength) spectrophotom-
eters and on the NMR (by monitoring the change in inte-
gration units of the specified signals) spectrometer. All
kinetic measurements were monitored under pseudo-first-
order conditions with [CH3I] 10–5000 times the concentra-
tion of the [RhI(b-diketonato)(CO)(PPh3)] complex in the
specified solution. The concentration [RhI(b-diketo-
nato)(CO)(PPh3)] ffi 0.00005 mol dmꢀ3 for UV/vis mea-
surements, ffi 0.008 mol dmꢀ3 for IR measurements and ffi
0.014 mol dmꢀ3 for NMR measurements. Kinetic measure-
ments under pseudo-first-order conditions for different
concentrations of [RhI(b-diketonato)(CO)(PPh3)] at a con-
stant [CH3I], confirmed that the concentration of [RhI(b-
diketonato)(CO)(PPh3)] did not influence the value of the
observed kinetic rate constant. The observed first-order
rate constants were obtained from least-squares fits of
absorbance (IR and UV/vis) or integration units (NMR)
versus time data [22].
46.5; H, 2.1%.
2.2.2. [Rh(b-diketonato)(CO)(PPh3)] complexes 3 and 4
The general procedure was as follow: to a solution of
[Rh(b-diketonato)(CO)2] (0.2 mmol) in chloroform (for 3,
warm n-hexane for 4) (3 cm3) was added a solution of
PPh3 (0.2 mmol) in chloroform (for 3, warm n-hexane for
4) (3 cm3). The resulting reaction mixture was stirred for
ca 1 min, until no more CO gas was released, and filtered.
Pure
crystals
of
the
desired
complexes
[Rh(dtm)(CO)(PPh3)] 3 and [Rh(bth)(CO)(PPh3)] 4 were
obtained.
[Rh(dtm)(CO)(PPh3)] 3: Yield: 0.0662 g, 52.7%. M.p.
180.0–184.5 °C. IR (cmꢀ1) = 1971. 1H NMR (d/ppm,
CDCl3) 6.65 (1H, s, CH), 6.89 (1H, dd, 3J = 5 Hz,
3J = 4 Hz, ring B CH), 7.08 (1H, dd, 3J = 4 Hz, 4J =
3
3
1 Hz, ring B CH), 7.11 (1H, dd, J = 5 Hz, J = 4 Hz, ring
A CH), 7.27 (1H, dd, J = 5 Hz, J = 1 Hz, ring B CH),
3
4
3
7.41 (6H, m, CH), 7.45 (3H, m, CH), 7.52 (1H, dd, J =
5 Hz, 4J = 1 Hz, ring A CH), 7.73 (1 H, dd, 3J = 4 Hz,
4J = 1 Hz, ring A CH), 7.74 (6 H, m, CH). Elemental Anal.
Calc. for RhC30PH22S2O3: C, 57.3; H, 3.5. Found: C, 57.0;
H, 3.2%.
The [RhI(b-diketonato)(CO)(PPh3)] complexes 3 and 4
were tested for stability in chloroform by means of overlay
1
IR and UV/vis spectra for at least 24 h. A H NMR spec-
[Rh(bth)(CO)(PPh3)] 4: Yield: 0.0830 g, 66.7%. M.p.
149.1–189.5 °C. IR (cmꢀ1) = 1970. 1H NMR (d/ppm,
CDCl3) 6.74 (1H, s, isomer A CH), 6.75 (1H, s, isomer B
CH), 6.89 (1H, dd, J = 5 Hz, J = 4 Hz, isomer A CH),
7.10 (3H, m, isomer B CH), 7.10 (1H, dd, 3J = 4 Hz,
4J = 1 Hz, isomer A CH), 7.11 (1 H, dd, 3J = 5 Hz,
trum of the title compound after 48 h in solution of CDCl3
confirmed stability in solution. A linear relationship
between UV/vis absorbance (A) and concentration (c) con-
firms the validity of the Beer Lambert law (A = ecl with
l = path length = 1 cm) for 3 and 4.
3
3

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M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
O
O
2.5. Calculations
S
2
R
DMF
OC
OC
Cl
Cl
CO
CO
Pseudo-first-order rate constants, kobs, were calculated
2
RhCl3.H2O
Rh
R
Rh
Rh
by fitting [22] kinetic data to the first-order equation [23]
½AŠ ¼ ½AŠ0eðꢀkobstÞ
ð2Þ
t
R
R
O
O
O
O
O
CO
CO
CO
PPh3
PPh3
CO
Kc1
with [A]t and [A]0 the absorbance of the indicated species at
time t and at t = 0 (UV/vis or IR experiments) or integral
values for the specified peaks on NMR spectra. The exper-
imentally determined pseudo-first-order rate constants
were converted to second order rate constants, k1, by deter-
mining the slope of the linear plots of kobs against the con-
centration of the incoming CH3I ligand. Non-zero
intercepts implied that
2 PPh3
- 2 CO
2
Rh
Rh
O
S
S
S
isomer A
isomer B
(1) R = C4H3S
(2) R = C6H5 (Ph)
(3) R = C4H3S
(4) R = C6H5 (Ph)
Scheme 1. Synthetic routes for the synthesis of the [RhI(b-diketo-
nato)(CO)2] complexes and
and [RhI(b-diketonato)(CO)(PPh3)]
1
2
complexes 3 and 4 from RhCl3 ꢁ 3H2O.
kobs ¼ k1½CH3IŠ þ k
ð3Þ
ꢀ1
and that the k step in the proposed reaction mechanism
ꢀ1
exists.
The activation parameters DH# (activation enthalpy)
and DS# (activation entropy), for the oxidative addition
reactions were determined from least-squares fits [22] of
the reaction rate constants versus temperature data
according to the Eyring relationship, [24] in the linear
form
chelate ring as isomer A, while the other isomer is labelled
isomer B (Scheme 1). Focussing on the positions of the sig-
nals of the 1H NMR spectrum of the thienyl group of
[Rh(bth)(CO)(PPh3)] 4, the set of signals belonging to an
isomer in the more upfield position, due to the shielding
effect through space of the PPh3 group, is assigned to iso-
mer B. The position of the thienyl resonances of the two
k
DH# DS#
kB
h
1
isomers was confirmed by two dimensional H–1H TOC-
ln ¼ ꢀ
þ
þ ln
R
ð4Þ
T
RT
SY. The equilibrium constant, defined as Kc = [isomer B]/
[isomer A] and applicable to the equilibrium shown in
Scheme 1, may be determined by calculating the ratio of
peak integral values of non-overlapping corresponding sig-
nals of each isomer and averaging all answers giving
Kc1 = 1.0 in CDCl3 or Kc1 = 0.8 in acetone-d6 for 4. The
time required for the two isomers of 4 to reach the solution
equilibrium position, according to Scheme 1, was shorter
than the time required to dissolve the complex and to
record data for a NMR spectrum.
with k = rate constant, kB = Boltzmann’s constant,
T = temperature, h = Planck’s and R = universal gas con-
stant. The activation free energy DG# = DH# ꢀ TDS#.
All kinetic mathematical fits were done utilizing the
fitting program MINSQ [22]. The error of all the data is
presented according to crystallographic conventions. For
example kobs = 0.0236(1) sꢀ1 implies kobs = (0.0236
0.0001) sꢀ1
.
3. Results and discussion
3.2. Kinetics
3.1. Synthesis and identification of complexes
3.2.1. Infrared study
The route utilized to obtain the new dicarbonyl rho-
dium(I) complexes of general formula [Rh((C4H3S)COCH-
COR)(CO)2] is given in Scheme 1. The new brick-red
[Rh(b-diketonato)(CO)(PPh3)] complexes 3 and 4 with b-
diketonato = dtm (3) and bth (4) respectively were
obtained by reacting an equivalent amount of PPh3 with
[Rh(b-diketonato)(CO)2] in a chloroform medium (for 3,
warm n-hexane for 4). The [Rh(b-diketonato)(CO)(PPh3)]
product immediately precipitates out. The thenoyl-contain-
ing rhodium complexes 1–4 are all acid sensitive and
decompose on silicagel. NMR studies therefore had to be
performed in CDCl3 which was passed through basic alu-
mina prior use. 1H NMR spectra show that, for the
[Rh(bth)(CO)(PPh3)] 4, two isomers exist in solution.
Regarding the two possible isomers of 4, we chose to label
the isomer with CO trans to the oxygen atom nearest to the
more electron donating thienyl group of the b-diketonato
Kinetic measurements for the reaction of [Rh(dtm)-
(CO)(PPh3)] 3 or [Rh(bth)(CO)(PPh3)] 4 with methyl iodide
in CHCl3 were first carried out using IR spectroscopy by
monitoring the changes in absorbance of peaks at different
m(CO) bands. This technique is ideal to distinguish between
CO bonds in metal–CO complexes that resonate at ꢂ1980–
2000 cmꢀ1 for RhI–carbonyl complexes, at ꢂ2050–2100
cmꢀ1 for RhIII–carbonyl complexes and CO bonds in
metal–COCH3 complexes that resonates at ꢂ1700–
1750 cmꢀ1 for RhIII–acyl complexes [25]. A typical series
of the spectra of the oxidative addition reaction of CH3I
to 3 or to 4, as well as the subsequent carbonyl insertion
and deinsertion steps, are shown in Fig. 1. The first reac-
tion step for 3 indicates the disappearance of the m(CO)
band of the rhodium(I) reactant at 1987 cmꢀ1 and the
simultaneous appearance of two new m(CO) bands at
2079 cmꢀ1 and 1720 cmꢀ1 exactly at the same rate as the

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
2289
Fig. 1. Illustration of the oxidative addition reaction between CH3I and [Rh(dtm)(CO)(PPh3)] 3 (left) and [Rh(bth)(CO)(PPh3)] 4 (right) as monitored on
the IR spectrophotometer between 1650 and 2150 cmꢀ1 in chloroform at 25 °C. Both complexes follow the same reaction sequence. The first reaction is
indicated by the disappearance of RhI and the simultaneous appearance of RhIII–alkyl1 and RhIII–acyl1, all at the same rate. The second reaction is
indicated by the simultaneous disappearance of RhIII–alkyl1 and RhIII–acyl1 and the formation of a RhIII–alkyl2 species. The third reaction is indicated by
the disappearance of RhIII–alkyl2 and the formation of a RhIII–acyl2 species. The numbering of the different intermediates is as indicated in Table 1. The
y-axis represents relative absorbance.
disappearance of 3. The band at 2079 cmꢀ1 is assigned to a
RhIII–alkyl product [Rh(dtm)(CH3)(CO)(PPh3)(I)] 5 and
[CH3I] = 0.1 mol dmꢀ3
.
Further evidence that there
exists a fast equilibrium between the RhIII–alkyl1 and
RhIII–acyl1 products are found from the observation
that the RhIII–alkyl1 5 at 2079 cmꢀ1 disappears at the same
rate as the RhIII–acyl1 6 at 1720 cmꢀ1. Since the second
reaction is much slower than the first reaction, it was
treated in isolation. Data from the interface at the bound-
ary between the two reactions were, however, disregarded.
This second reaction was found to be independent of
[CH3I]. The kinetic data of the second reaction are consis-
tent with:
the band at 1720 cmꢀ1 to
a
RhIII–acyl product
[Rh(dtm)(COCH3)(PPh3)(I)] 6. These first RhIII–alkyl and
RhIII–acyl products that form will be labelled RhIII–alkyl1
and RhIII–acyl1 for further indication. The RhIII–acyl1
results from the migration insertion of the methyl group
of the RhIII–alkyl1 to the carbonyl group. The exponential
decay observed for the reactant m(CO) band for 3 showed
the reaction to be first order in [rhodium(I)]. The second
order rate constants, k1, for the oxidative addition reaction
of CH3I to both 3 and 4, are given in Table 2.
2, k2
k3
The result that the RhIII–alkyl1 5 species forms at
exactly the same rate as the RhIII–acyl1 6 species, is consid-
ð6Þ
[RhIII-alkyl1]
[RhIII-acyl1]
[RhIII-alkyl2]
{
}
k-3
k-2
ered to imply that an equilibrium exists between the RhIII
–
The second reaction was followed by a very slow (t1/2 ꢃ 2
days) third reaction. This third reaction, also illustrated in
Fig. 1, includes the slow first-order disappearance of the
RhIII–alkyl2 7 (kobs = 0.0000036(3) sꢀ1) at 2056 cmꢀ1 and
the appearance, at the same rate, of a new acyl product,
alkyl1 5 and RhIII–acyl1 6 that is fast enough to be main-
tained on the timescale of [Rh(dtm)(CO)(PPh3)] 3 disap-
pearance [16]. The first reaction that can thus be
presented as follow:
RhIII–acyl2
8
at 1713 cmꢀ1 (kobs = 0.0000044(2) sꢀ1).
K1, k1
K2, k2
I + CH3I
[RhIII-alkyl1]
[RhIII-acyl1]
ð5Þ
Rh
These two rates are within experimental error identical
(average = 0.0000040 sꢀ1). Both are independent of
[CH3I]. The long half-life of the third reaction implied that
it could not be followed with great accuracy, as solvent
evaporation became difficult to control. The kinetic data
of the third reaction are consistent with:
{
}
k-1
k-2
A second much slower (t1/2 ꢃ 6 h) reaction, as observed on
the IR, is also illustrated in Fig. 1. The reaction products of
the reaction between 3 and CH3I, the RhIII–alkyl1 5 at
2079 cmꢀ1 and the RhIII–acyl1 6 at 1720 cmꢀ1 disappear
at the same rate (kobs = 0.000033(1) sꢀ1) as the formation
k4
[RhIII-acyl2]
ð7Þ
[RhIII-alkyl2]
of a second alkyl product, RhIII–alkyl2, 7 (kobs
=
k-4
0.000034(1) sꢀ1), at another m(CO) = 2056 cmꢀ1. By com-
paring the rate constants, the second reaction is 0.0026/
0.000034 ꢃ75 times slower than the first reaction for
The overall reaction sequence for this oxidative addition
reaction may therefore be represented as

2290
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
K1, k1
K2, k2
k3
k4
[RhIII-alkyl1]
[RhIII-acyl1]
[RhIII-acyl2]
RhI + CH3I
[RhIII-alkyl2]
{
}
k-3
k-4
k-1
k-2
ð8Þ
First reaction
Third reaction
Second reaction
The same reaction pattern (Eq. (8)) was observed on the IR
for the oxidative addition reaction of CH3I to
[Rh(bth)(CO)(PPh3)] 4 (Fig. 1). Though, the third reaction,
that involves the formation of a second acyl species, ob-
served for both 3 and 4, was not observed for the oxidative
addition and the following carbonyl insertion and deinser-
tion of [RhI((C4H3S)COCHCOCF3)(CO)(PPh3)] + CH3I
[16].
It was possible, due to the long half-life of the second
reaction, to isolate the [Rh(dtm)(CO)(PPh3)]–alkyl2 7 and
the [Rh(bth)(CO)(PPh3)]–alkyl2 11 from the reaction mix-
ture before the formation of the RhIII–acyl2 species. The
spectroscopic data of 7 and 11 are included in Table 1.
Complexes 7 and 11 were stable in the solid state, but in
solution and in the presence of an excess CH3I, CO inser-
tion occurred at a slow rate to form the RhIII–acyl2
product.
all three reaction steps could be identified for both reac-
tants (Fig. 2). The reaction rate constant obtained for the
first step corresponded to the rate constant for the disap-
pearance of the RhI monocarbonyl species as observed
by IR. The rate constant for the second and third steps also
corresponded to the rate constant for the second and third
reactions as observed on the IR spectrophotometer. The
second step is the formation of the RhIII–alkyl2 species
and the third step is the formation of the final reaction
product, the RhIII–acyl2 species.
In chloroform, the first, second and third reactions were
best followed at 440, 380 and 450 respectively for 3 and at
430, 380 and 395 nm respectively for 4. All three the reac-
tion steps of 3 and 4 could be followed at 450 and 395 nm
respectively, giving rate constants in agreement with those
obtained at other wavelengths (Fig. 2).
Plots of kobs for the first reaction of both 3 and 4 versus
[CH3I] are linear (Fig. 3), indicating the reaction to be first
order in CH3I and hence second order overall. Second
order rate constants, k1 in reaction 8, and activation
parameters (Eyring plots insets in Fig. 3) are listed in
Table 2.
3.2.2. UV/vis study
The reaction between CH3I and [Rh(dtm)(CO)(PPh3)] 3
and the reaction between CH3I and [Rh(bth)(CO)(PPh3)] 4
were also monitored on an UV/vis spectrophotometer and
Table 1
1H, 31P NMR and IR spectral parameters of the [RhI(b-diketonato)(CO)(PPh3)], RhIII(b-diketonato)(CH3)(CO)(PPh3)(I)] and [RhIII(b-diketo-
nato)(COCH3)(PPh3)(I)] complexes (b-diketonato = bth or dtm)
No.
Compound
31P NMR
1H NMR
IR
d31P/ppm 1J(31P–103Rh)/ d1H methine proton Methyl protons from CH3I
Kc
m
CO/cmꢀ1
Hz
b-diketonato
ligand/ppm
d1H/ 2J(1H–13C–103Rh)/ 3J(1H–13C–103Rh–31P)/
ppm
Hz
Hz
b-diketonato = dtm
3
5
6
7
8
RhI
47.61
31.22
37.16
28.93
35.5
176
126
154
117
159
6.65
6.74
6.68
6.03
a
1987
2079
1720
2056
1713
RhIII–alkyl1
RhIII–acyl1
RhIII–alkyl2
RhIII–acyl2
1.60
3.03
1.83
3.05
1.5
1.8
2.2
3.8
–
b-diketonato = bth
4A
4B
9A
9B
RhI–A
RhI–B
47.41
49.21
176
177
128
128
154
154
121
121
156
160
6.74
6.75
6.67
6.78
6.80
6.83
6.10
1.0 1983
0.4 2079
0.8 1720
1.4 2056
1709
RhIII–alkyl1A 31.03
1.59
1.60
3.02
3.09
1.85
1.85
3.00
3.04
1.7
1.7
2.2
2.2
RhIII–alkyl1B
10A RhIII–acyl1A
10B
RhIII–acyl1B
34.21
38.50
36.89
11A RhIII–alkyl2A 28.62
11B
12A RhIII–acyl2A
12B
RhIII–acyl2B
2.0
2.0
3.8
3.8
RhIII–alkyl2B
29.21
35.16
35.81
6.09
a
a
Kc = [isomer-B]/[isomer-A] at equilibrium at 25 °.
a
Not determined due to overlapping of peaks.

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
2291
Fig. 2. Absorbance vs. time data at 25 °C for the UV/vis monitored oxidative addition reaction and alkyl and acyl interconversions for the reaction
between CH3I and [Rh(dtm)(CO)(PPh3)] 3 (left) and [Rh(bth)(CO)(PPh3)] 4 (right) in chloroform at 450 and 395 nm respectively, illustrating the three
reactions observed for both complexes. The insets give enlargements of the first reaction.
Fig. 3. Temperature and CH3I concentration dependence of the oxidative addition of CH3I to [Rh(dtm)(CO)(PPh3)] 3 (left) and [Rh(bth)(CO)(PPh3)] 4
(right), as monitored on the UV/vis spectrophotometer in chloroform, for the first reaction {RhI + CH3I ꢀ [RhIII–alkyl1 ꢀ RhIII–acyl1]}. Inset: Linear
dependence between ln(k1/T) and 1/T as predicted by the Eyring equation.
Incorporation of a more electron donating fragment
(such as C6H5 or C4H3S) in the b-diketonato ligand
(C4H3S)COCHCORꢀ thus significantly enhances the rate
of the oxidative addition step (first reaction step) of the reac-
tion [RhI((C4H3S)COCHCOR)(CO)(PPh3)] + CH3I when
compared to the rate of oxidativeꢀaddition step of the corre-
sponding ðC4H3SÞCOCHCOCF3 complex containing the
electron withdrawing CF3 group in the cyclic b-diketonato
fragment: k1 (dm3 molꢀ1 sꢀ1) = 0.022(6) (R = C4H3S),
0.026(3) (R = C6H5) and 0.00171(4) (R = CF3).
to obtain additional insight into this reaction. NMR
spectroscopy is an excellent technique for the
identification of the different isomers resulting from the
oxidative addition reaction of [RhI(b-diketonato)(CO)-
(PPh3)] with methyl iodide. By carefully comparing the
positions and integrals of the different signals, the spec-
tral parameters of the different reaction products during
the oxidative addition reaction and subsequent carbonyl
insertion and deinsertion reactions, could be identified
(Table 1). The same reaction sequence, as observed on
IR and UV/vis, was observed on 1H NMR (Fig. 4)
and 31P NMR (Fig. 5). The new feature introduced by
the NMR study is the existence of more than one isomer
for each intermediate of the reaction products of the two
1
3.2.3. H and 31P NMR study
The reaction between CH3I and 3 and between CH3I
1
and 4 were also monitored by H and 31P NMR in order

2292
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
Table 2
The kinetic rate constants of the oxidative addition reaction between CH3I and [Rh(b-diketonato)(CO)(PPh3)] as obtained by various spectrophotometric
and spectroscopic methods in chloroform at 25 °C for b-diketonato = bth, dtm and tta
Method
k1/dm3 molꢀ1 sꢀ1
k
ꢀ1/sꢀ1
k3/sꢀ1
k4/sꢀ1
DH#(k1)/kJ molꢀ1
DS#(k1)/J molꢀ1 Kꢀ1
DG#(k1)/kJ molꢀ1
[Rh(dtm)(CO)(PPh3)] 3
IR
0.026(3)
0.029(1)
0.0296(2)
0.023(2)
0.0003(2)
0.0002(2)
0.000032(6)
0.0000349(5)
0.000030(2)
0.000030(5)
0.000004(1)
0.000005(1)
0.000004(1)
a
UV/vis
1H NMR
131P NMR
40(6)
ꢀ130(20)
80(3)
[Rh(bth)(CO)(PPh3)] 4
a
IR
0.022(6)
0.0265(6)
0.028(3)
0.0226(9)
0.0000(2)
0.0000(1)
0.000029(9)
0.000059(3)
0.000049(5)
0.000029(6)
UV/vis
0.000003(2)
a
16.8(8)
31.1(5)
ꢀ218(3)
ꢀ194(2)
82(2)
89(1)
11H NMRb
131P NMRb
a
[Rh(tta)(CO)(PPh3)] [16]
UV/vis 0.00171(4)
c
0.000023(6)
0.0005(1)
k1, k3 and k4 are the rate constants associated with the first, second and third stages of the reaction of CH3I to [Rh(b-diketonato)(CO)(PPh3)].
a
The disappearance of the RhIII–alkyl2 and the appearance of the RhIII–acyl2 were observed, but due to the long half-life (ꢂ2 days) of the third reaction,
the kinetics could not be followed with accuracy.
b
Two isomers observed for each product. The observed rate constants for each isomer were the same within experimental error.
No third reaction step observed.
c
Fig. 4. Fragments of the methyl region of the 1H NMR spectra in CDCl3 illustrating the reaction sequence during the oxidative addition and the following
carbonyl insertion and deinsertion reactions of 0.0268 mol dmꢀ3 [Rh(dtm)(CO)(PPh3)] 3 reacting with 0.150 mol dmꢀ3 CH3I (left) and 0.0262 mol dmꢀ3
[Rh(bth)(CO)(PPh3)] 4 reacting with 0.159 mol dmꢀ3 CH3I (right) in CDCl3 (T = 25 °C) at the indicated time intervals. Note that two isomers for each
species can be observed for 4 which contain an unsymmetrical b-diketonato ligand, while only one isomer for each reaction intermediate can be observed
for 3 which contain a symmetrical b-diketonato ligand. The first reaction is illustrated by the growing signals of the CH3-group of indicated RhIII–acyl1
isomers at ca. 3 ppm and of RhIII–alkyl1 isomers at ca. 1.5 ppm. The second reaction is illustrated by the decrease of the various signals representing RhIII
–
alkyl1 and RhIII–acyl1 species with the simultaneous increase in the signals of the CH3-group of the RhIII–alkyl2 spesies at ca. 1.9 ppm. The third reaction
is illustrated by the change in signal intensity of the CH3-group of the RhIII–alkyl2 isomers at ca. 1.9 ppm and the appearance of a new RhIII–acyl2 species
at ca. 3.0 ppm. The multiplet of the CH3 group of the RhIII–alkyl1 and RhIII–alkyl2 isomers is due to coupling with Rh (spin 1/2) and P (spin 1/2). The
numbering of the different isomers is as indicated in Table 1.
isomers of [Rh((C4H3S)COCHCO(C6H5))(CO)(PPh3)] 4
with methyl iodide. Only one isomer of each intermediate
[Rh((C4H3S)COCHCO(C4H3S))(CO)(PPh3)] 3, since this
complex contains a symmetrical b-diketonato ligand
(C4H3S)COCHCO(C4H3S)ꢀ.
was
observed
for
the
reaction
products
of

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
2293
Fig. 5. Selected 31P NMR spectra illustrating doublet 31P peaks of the indicated reactants and products during the three reactions for the oxidative
addition of CH3I to [Rh(dtm)(CO)(PPh3)] 3 (left) and [Rh(bth)(CO)(PPh3)] 4 (right) in CDCl3 (T = 25 °C) at the indicated time intervals. Note that two
isomers for each species can be observed for 4 (which contain an unsymmetrical b-diketonato ligand), while only one isomer for each reaction intermediate
can be observed for 3 (which contain a symmetrical b-diketonato ligand). The doublet of each signal is due to coupling with Rh (spin 1/2). The numbering
of the different isomers is as indicated in Table 1.
K1, k1
K2, k2
The two observed isomers of each intermediate in the
reaction of 4 will be referred to as A and B, see Table 1.
The choice of the labels is arbitrary and has no significance.
NMR kinetic results indicate that the A and B isomer of
each species exists in a fast equilibrium with each other,
since the observed rate constant for the depletion or forma-
tion of an A and a B isomer of the same species was found to
be, within experimental error, the same. Furthermore, the
ratio RhI–B/RhI-A = 1.0 (obtained by integral evaluation)
is not the same as the ratio RhIII–alkyl1B/RhIII–alkyl1A =
0.40 or the ratio RhIII–acyl1B/RhIII–acyl1A = 0.8, etc.
(Table 1). If the reaction was
[RhIII-alkyl1B]
[RhIII-acyl1B]
I
Rh -B
+ CH I
}
{
3
k-1
k-2
ð10Þ
k3
k4
[RhIII-acyl2B]
[RhIII-alkyl2B]
k-3
k-4
for the B isomers, and if no equilibrium between isomers
A and B existed, the ratio B:A of these isomers would
have been the same throughout the entire reaction se-
quence involving three different steps.
Taking into account that two main isomers exist of each
reactant and reaction product of 4, the complete reaction
sequence for the oxidative addition of CH3I to 4 containing
an unsymmetrical b-diketonato ligand, is therefore as given
in reaction (11)
RhI-A
[RhIII-alkyl1A]
Kc2
[RhIII-acyl1A]
Kc3
[RhIII-alkyl2A]
[RhIII-acyl2A]
Kc5
K1, k1
K2, k2
k3
k4
+ CH3I
Kc1
Kc4
k-1
k-3
k-4
k-2
[RhIII-alkyl1B]
[RhIII-acyl1B]
[RhIII-alkyl2B]
[RhIII-acyl2B]
RhI-B
ð11Þ
First reaction
Third reaction
Second reaction
1, k1
2, k2
and for the symmetrical b-diketonato ligand 3 as given in
reaction 8.
The above reaction sequence where the observed rate of
formation of the two [Rh((C4H3S)COCHCOR)(CH3)-
(CO)(PPh3)(I)]–alkyl2 isomers, R = C6H5, is the same due
to the fast equilibrium Kc4, is contrary to what was found
[RhIII-alkyl1A]
[RhIII-acyl1A]
I
Rh -A
+ CH I
{
}
3
k-1
k-2
ð9Þ
k3
k4
[RhIII-acyl2A]
[RhIII-alkyl2A]
k-3
k-4
for the A isomers and separately

2294
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
Fig. 6. 1H NMR spectrum (bottom) of a reaction mixture containing the [Rh(bth)(CH3)(CO)(PPh3)(I)]–alkyl1 isomers and the [Rh(bth)(COCH3)(P-
1
Ph3)(I)]–acyl1 isomers in a fast equilibrium with each other. At the top is the H–1H NOESY observed when irradiating on the methyl group of the two
[Rh(bth)(CH3)(CO)(PPh3)(I)]–alkyl1 isomers at 1.6 ppm. The peaks observed at 3 ppm are a result of the fast equilibrium [Rh(bth)(CH3)(CO)(PPh3)(I)]–
alkyl1 ꢀ [Rh(bth)(COCH3)(PPh3)(I)]–acyl1. CH3I peak is suppressed for clarity.
for the oxidative addition of CH3I to [Rh((C4H3S)COCH-
COR)(CO)(PPh3)], with R = CF3, where the [Rh((C4H3S)-
COCHCOCF3)(CH3)(CO)(PPh3)(I)]–alkyl2A isomer formed
at a different rate than the [Rh((C4H3S)COCHCOCF3)-
(CH3)(CO)(PPh3)(I)]–alkyl2B isomer (no [Rh((C4H3S)-
COCHCOCF3)(COCH3)(PPh3)(I)]–acyl2 isomers were
observed for the latter reaction) [16]:
the methyl signals of RhIII–acyl1 10A and 10B isomers
(1H–1H NOESY in Fig. 6). This result is only possible if
the CH3 group of the RhIII–alkyl1 isomers is below (or
above) the square planar plane (formed by the two oxygens
of the b-diketonato ligands and the other two groups), with
the CH3 group adjacent to the PPh3 group. The NOE cou-
pling to the methine proton rules out the possibility of the
CH3 group being in a position in the square planar plane.
An exceptional result is that as the CH3 resonances of
RhIII–alkyl1 9A and 9B isomers are irradiated, it converts
into the RhIII–acyl1 10A and 10B isomers on the time scale
of the NMR, showing an increased intensity for the signal
of the methyl group on the RhIII–acyl1 isomers at 3.02 and
3.10 ppm. This result is indicative of the fast equilibrium
[RhIII–alkyl1 ꢀ RhIII–acyl1].
RhI-A
K1, k1
Kc1
+ CH3I
k-1
RhI-B
ð12Þ
[RhIII-alkyl1A]
[RhIII-acyl1A]
[RhIII-alkyl2A]
k3A
K2, k2
k-3A
k3B
Kc4
slow
[RhIII-alkyl2B]
Kc2
Kc3
k-2
[RhIII-alkyl1B]
[RhIII-acyl1B]
k-3B
Another result indicative of the fast equilibrium [RhIII–al-
kyl1 ꢀ RhIII–acyl1] results from 1H–1H NOESY
4. Conclusions
a
By introducing a thienyl fragment as part of a b-diketo-
nato ligand in the [Rh((C4H3S)COCHCOR)(CO)(PPh3)]
complexes with R = C6H5 or C4H3S, it was possible to pro-
vide a general reaction sequence for the oxidative addition
of iodomethane to any [RhI(L,L0-BID)(CO)(PPh3)] com-
plex with L,L0-BID = monoanionic bidentate ligand with
(Fig. 6), recorded in situ during the oxidative addition reac-
tion of 4 to establish the relative dispositions of the CH3 li-
gand in the [Rh(bth)(CH3)(CO)(PPh3)(I)]–alkyl1 isomers.
Irradiation of the CH3 resonance on the RhIII–alkyl1 iso-
mers (1.6 ppm), resulted in an NOE coupling with the
methine, phenyl, PPh3 and thienyl protons as well as with

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 361 (2008) 2285–2295
2295
donor atoms L and L0. All previously proposed reaction
mechanisms for the oxidative addition reaction of CH3I
to a variety of square planar [RhI(L,L0-BID)(CO)(PPh3)]
complexes are just special cases of the general mechanism:
[3] P. Braunstein, Y. Chauvin, J. Fischer, H. Olivier, C. Strohmann, D.V.
Toronto, New J. Chem. (Nouv. J. Chim.) 24 (2000) 437.
[4] L.J. Damoense, W. Purcell, A. Roodt, J.G. Leipoldt, Rhodium Exp. 5
(1994) 10.
[5] S.S. Basson, J.G. Leipoldt, A. Roodt, J.A. Venter, Inorg. Chim. Acta
128 (1987) 31.
K1, k1
[RhI(L,L'-BID)(CO)(PPh3)] isomers + CH3I
alkyl1 isomer
[6] M. Cano, J.V. Heras, M.A. Lobo, E. Pinilla, M.A. Monge,
Polyhedron 11 (1992) 2679.
k-1
[7] S.S. Basson, J.A. Venter, A. Roodt, in preparation.
[8] J.A. Cabeza, V. Riera, M.A. Villa-Garcia, L. Ouahab, S. Triki, J.
Organomet. Chem. 441 (1992) 323.
[9] C.H. Cheng, B.D. Spivack, R. Eisenberg, J. Am. Chem. Soc. 99
(1977) 3003.
[10] L.J. Damoense, W. Purcell, A. Roodt, Rhodium Exp. 14 (1995) 4.
[11] A. Roodt, G.J.J. Steyn, Recent Res. Dev. Inorg. Chem. 2 (2000) 1.
[12] J.G. Leipoldt, S.S. Basson, L.J. Botha, Inorg. Chim. Acta 168 (1990)
215.
[13] G.J.J. Steyn, A. Roodt, J.G. Leipoldt, Rhodium Exp. 1 (1993) 25.
[14] S.S. Basson, J.G. Leipoldt, J.T. Nel, Inorg. Chim. Acta 84 (1984) 167.
[15] S.S. Basson, J.G. Leipoldt, A. Roodt, J.A. Venter, T.J. van der Walt,
Inorg. Chim. Acta 119 (1986) 35.
k2
k3
k4
s
acyl1 isomers
alkyl2 isomers
acyl2 isomers
k-2
k-3
k-4
product for cacsm, product for acac,
hacsm, macsm, macsh, tfaa, tfdma, hfaa,
product for
fctfa, bth, dtm
tta, sacac
cupf, ox, anmeth, dmavk
The above general mechanism does not distinguish between
different rates of isomers. The observed rate of depletion
of the two RhI isomers of the [Rh((C4H3S)COCHCO-
(C6H5))(CO)(PPh3)] complex containing an unsymmetrical
b-diketonato ligand, as well as the observed rate of forma-
tion and depletion of the different isomers of each reaction
intermediate, are the same, contrary to what was found for
the rate of formation of the two [Rh((C4H3S)COCH-
COCF3)(CH3)(CO)(PPh3)(I)]–alkyl2 isomers that formed
at different rates [16].
[16] M.M. Conradie, J. Conradie, Inorg. Chim. Acta 361 (2008) 208.
[17] J. Conradie, G.J. Lamprecht, A. Roodt, J.C. Swarts, Polyhedron 23
(2007) 5057.
[18] J.A. Venter, J.G. Leipoldt, R. van Eldik, Inorg. Chem. 30 (1991)
1207.
[19] B.S. Furniss, A.J. Hannaford, P.W.G. Smith, A.R. Tatchell, Vogel’s
Textbook of Practical Organic Chemistry, 5th ed., John Wiley &
Sons, New York, 1994, p. 409.
Acknowledgements
[20] M.M. Conradie, A.J. Muller, J. Conradie, SA J. Chem. (2008), in
press.
[21] (a) Y.S. Varshavskii, T.G. Cherkasova, Russ. J. Inorg. Chem. 12
(1967) 899;
(b) A. Rusina, A.A. Vlcek, Nature (London) 206 (1965) 295.
[22] MINSQ, Least squares parameter Estimation, Version 3.12, Micro-
Math, 1990.
[23] J.H. Espenson, Chemical Kinetics and Reaction Mechanisms, second
ed., McGraw-Hill, New York, 1995, p. 15, 49, 70–75.
[24] J.H. Espenson, Chemical Kinetics and Reaction Mechanisms, second
ed., McGraw-Hill, New York, 1995, p. 156.
Financial assistance by the South African National Re-
search Foundation under Grant No. 2067416 and the Cen-
tral Research Fund of the University of the Free State are
gratefully acknowledged.
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