Stereochemistry of the reaction products of the oxidative addition reaction of methyl iodide to [Rh((C4H3S)COCHCOR)(CO)(PPh3)]: A NMR and computational study. R = CF3, C6H5, C4H<

Article abstract of DOI:10.1016/j.ica.2008.04.046

A NMR study of the reaction mixture of the square planar [Rh((C₄H₃S)COCHCOR)(CO)(PPh₃)] complex and CH₃I, where R = CF₃, C₆H₅ or C₄H₃S, revealed that two ty

Full text of DOI:10.1016/j.ica.2008.04.046

Inorganica Chimica Acta 362 (2009) 519–530
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Stereochemistry of the reaction products of the oxidative addition reaction of
methyl iodide to [Rh((C4H3S)COCHCOR)(CO)(PPh3)]: A NMR and computational
study. R = CF3, C6H5, C4H3S
*
Marrigje M. Conradie, Jeanet Conradie
Department of Chemistry, University of the Free State, Nelson Mandela Drive, Bloemfontein 9301, Bloemfontein, Free State, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
A NMR study of the reaction mixture of the square planar [Rh((C4H3S)COCHCOR)(CO)(PPh3)] complex and
CH3I, where R = CF3, C6H5 or C4H3S, revealed that two types of alkyl and one (R = CF3) or two (R = C6H5 or
C4H3S) types of acyl species exist in the system. Two isomers of each species with an unsymmetrical
b-diketonato ligand were observed. 1H–1H NOESY NMR unambiguously showed that the PPh3 group is
in the apical position in the more stable RhIII-alkyl product. Theoretical computations of the equilibrium
geometry of the possible reaction products, consistent with experimental observations, revealed that the
first alkyl product results from trans addition to RhI and that the second thermodynamic alkyl product
adopts an octahedral geometry with the PPh3 group and the iodide above and below the square planar
plane. Theoretical computations also revealed that the thermodynamic acyl product adopts a square-
pyramidal geometry with the COCH3 group in the apical position.
Received 4 January 2008
Received in revised form 29 April 2008
Accepted 29 April 2008
Available online 7 May 2008
Keywords:
Rhodium
b-Diketone
Thienyl
NMR
Ó 2008 Elsevier B.V. All rights reserved.
Computational
DFT
HF
[RhI(L,L'-BID)(CO)(PPh3)] isomers +C H3I
1. Introduction
K1, k1
RhIII-alkyl1 isomers
k-1
Methanol carbonylation with the original Monsanto catalyst
has been studied in detail, not only experimentally [1–7], but also
from a theoretical point of view [6,8–11]. In contrast, the same
reaction promoted from [RhI(b-diketonato)(CO)(PPh3)] and related
complexes has been the subject of detailed experimental research
[12–19], but not from a theoretical point of view. This is despite
the potential of computational chemistry to contribute to the
understanding of the role of the steric and electronic properties
of the different ligands to determine the relative rate of the two
most important steps of the catalytic cycle i.e. the oxidative addi-
tion and the CO migratory insertion steps resulting in RhIII-alkyl
and RhIII-acyl products.
k2
k-2
RhIII-acyl1 isomers
product for cacsm,
hacsm, macsm,
ð1Þ
k-3 k3
macsh, cupf, dmavk
RhIII-alkyl2 isomers
product for acac,
tfaa, tfdma, hfaa,
tta, sacac
k4
k-4
On the basis of extensive kinetic studies of these reactions,
some mechanistic schemes have been proposed for the oxidative
addition of methyl iodide to [RhI(L,L0-BID)(CO)(PPh3)] where L,L0-
BID = monoanionic bidentate ligand with donor atoms L and L0 or
b-diketonato complexes. They can be summarized as
RhIII-acyl2 isomers
product for
fctfa, bth, dtm
The notation RhIII-alkyl1 and RhIII-acyl1 in the above equation
indicates the first formed alkylated [RhIII(L,L0-BID)(CH3)(CO)-
(PPh3)(I)] or acylated [RhIII(L,L0-BID)(COCH3)(PPh3)(I)] species.
When the last number in the notation changes to ‘‘2”, such as in
RhIII-alkyl2, it shows that after the first alkylated or acylated species
has formed, it converted to a second, different but more stable, alkyl-
ated or acylated structural isomer. (Htfaa = 1,1,1-trifluoro-2,4-pen-
* Corresponding author. Tel.: +27 51 4012194; fax: +27 51 4446384.
E-mail address: conradj.sci@ufs.ac.za (J. Conradie).
tanedione,
Htfdma = 1,1,1-trifluoro-5-methyl-2,4-hexanedione,
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.046

520
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
Hhfaa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione [12], Hacac = 2,4-
pentanedione [13], Hsacac = thioacetylacetone [14], Hcacsm =
methyl(2-cyclohexylamino-1-cyclopentene-1-dithiocarboxylate),
Hhacsm = methyl(2-amino-1-cyclopentene-1-dithiocarboxylate),
Hmacsm = methyl(2-methyl-amino-1-cyclopentene-1-dithiocar-
boxylate), Hmacsh = methyl(2-methylamino-1-cyclopentene-1-
dithiocarboxylate) [16–18], Hcupf = N-hydroxy-N-nitroso-ben-
zeneamine [27], Hdmavk = dimethylaminovinylketone [32],
Htta = 2-thenoyltrifluoroacetone [21], Hfctfa = 1-ferrocenyl-
4,4,4-trifluorobutane-1,3-dione [20], Hbth = 1-phenyl-3-(2-the-
noyl)-1,3-propanedione and Hdtm = 1,3-di(2-thenoyl)-1,3-prop-
anedione [21]).
2. Experimental
2.1. Synthesis
[Rh(tta)(CO)2] {1}, [Rh(bth)(CO)2] {2}, [Rh(dtm)(CO)2] {3},
[Rh(tta)(CO)(PPh3)] {4}, [Rh(bth)(CO)(PPh3)] {5} and [Rh(dtm)(CO)-
(PPh3)] {6} were prepared according to the literature [21,23].
2.2. Spectroscopy
NMR measurements at 298 K were recorded on a Bruker Ad-
vance II 600 NMR spectrometer [1H (600.130 MHz) and 31P
(242.937 MHz)]. The chemical shifts were reported relative to
SiMe4 (0.00 ppm) for the 1H spectra and relative to 85% H3PO4
(0 ppm) for 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.
During these reactions, various RhIII-alkyl and RhIII-acyl prod-
ucts have been observed. Characterization of the RhIII reaction
products, include
1. distinction between RhIII-alkyl and RhIII-acyl products on IR
[12–18],
2. a NMR spectral study of the products formed by the reac-
tion between [RhI(L,L0-BID)(CO)(PPh3)] and methyl iodide
[20,22,23] and
2.3. Quantum computational methods
The pure density functional theory (DFT) calculations were car-
ried out using the Amsterdam Density Functional 2006 (ADF) pro-
gram system [34] with the PW91 (Perdew-Wang, 1991) exchange
and correlation functional [35]. As a check on the performance
of the PW91 functional, the OLYP [36] (OPTX exchange func-
tional [36] combined with the Lee–Yang–Parr correlation func-
tional [37]), the BLYP (Becke’s gradient-corrected exchange
functional [38] with the Lee–Yang–Parr gradient-corrected correla-
tion functional [37]) and the OPBE [39] Generalized Gradient
Approximation (GGA) were also used for selected geometry opti-
mizations. The TZP (Triple f polarized) basis set, a fine mesh for
numerical integration (5.5 for geometry optimizations and 6.0 for
frequency calculations), a spin-unrestricted (gas phase) formalism
and full geometry optimization with tight convergence criteria as
implemented in the ADF 2006 program, were used. Calculations
in solution, as contrasted to the gas phase, were done using the
conductor-like screening model (COSMO) [40–42] of solvation as
implemented in ADF [43].
Pure DFT, pure ab initio (Hartree–Fock) and combined Hartree–
Fock/density functional theory (Hybrid DFT) calculations were car-
ried out using the Gaussian program package, version 03 [44]. The
B3LYP [45] (B3 Becke 3-parameter exchange and Lee–Yang–Parr
correlation) functional for both exchange and correlation, with
the CEP-31G [46] (Stevens/Barch/Krauss effective core potential
triple-split) basis set were used for the Hybrid DFT calculations.
Calculations at the Hartree–Fock levels of theory used the SDD
[47] (Stuttgart/Dresden effective core potential) and CEP-31G
[46] basis sets. Pure DFT calculations using the Gaussian program
package, were done using the PW91 [35] and BLYP [37,38] func-
tionals with the CEP-31G [46] basis set.
3. crystal structure determination of selected products [20,24–33].
The crystal structures of the products of the oxidative
addition of methyl iodide to [RhI(L,L0-BID)(CO)(PPh3)] can
conveniently be combined into three classes (see Fig. 1 and Supple-
mentary material Figs. S1 and S2 for a schematic presentation of
the structures):
Type 1 : RhIII-alkyl products where the methyl and the iodide are
above and below the square planar plane (L,L0-BID = ox
(Hox = 8-hydroxyquinoline) [24], (PhCOCHPPh2)ꢀ [25],
dmavk [26]).
Type 2 : RhIII-alkyl products where the PPh3 and the iodide are
above and below the square planar plane (L,L0-BID = cupf
[27], (OCO(C9H6N))ꢀ [28], neocupf [29], fctfa [20]).
Type 3 : RhIII-acyl products where the acyl moiety is in the apical
position in all the crystal structures (L,L0-BID =
(PhCOCHPPh2)ꢀ [30], mnt [31], dmavk [32], stsc [33]).
However, the specific stereochemistry of the RhIII-alkyl1, RhIII-
alkyl2, RhIII-acyl1 and RhIII-acyl2 isomers in the course of the reac-
tion, as given by Eq. (1), is unknown. In this paper we present the
results of a NMR study of the reaction mixture of [Rh((C4H3S)COCH-
COR)(CO)(PPh3)] + CH3I (R = CF3, C6H5 (Ph) or C4H3S) in the course
of these reactions. These NMR measurements allowed us to detect
the formation of the intermediates and to make some suggestions
on the stereochemistry. The NMR study is complimented by an ab
initio (Hartree–Fock), a combined Hartree–Fock/density functional
theory (Hybrid DFT) and pure DFT calculations on some of the as-
pects of the CH3I oxidative addition and the CO migratory insertion
products.
The accuracy of the different computational methods was eval-
uated by comparing the root-mean-square deviations (RMSD’s) be-
tween the optimized molecular structure and the crystal structure,
using the non-hydrogen atoms in the molecule (phenyl and CF3 ex-
cluded). RMSD values were calculated using the ‘‘RMS Compare
Structures” utility in CHEMCRAFT Version 1.5 [48]. No symmetry lim-
itations were imposed in the calculations. The deviation from
experiment of the metal–ligand bond lengths, d, is quantified by
calculating the standard deviation of the rhodium–ligand (Rh–L)
bond lengths by
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2
2
2
ðD
dRh—O1Þ þ ð
D
dRh—O2Þ þ ð
D
dRh—C9Þ þ ð
DdRh—P
Þ
Fig. 1. The three types of geometrical structures from crystal structure determi-
nation of isolated products of the oxidative addition of methyl iodide to [RhIII(L,L0-
BID)(CO)(PPh3)] where L,L0-BID = monoanionic bidentate ligand with donor atoms L
and L0. (See Supplementary material Figs. S1 and S2 for a schematic presentation of
the crystal structures.)
ð2Þ
3
where
D
dRh–L = dRh–L (experimental) ꢀ dRh–L (calculated) [49].

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
521
matic character. The pseudo aromatic character of the core of the
b-diketonato ligand is also clear from the crystal structure of
[Rh(tta)(CO)(PPh3)] {4}, showing a C@C bond of 1.345 Å (more dou-
ble bond character) and a C–C bond of 1.432 Å (more single bond
character) next to the methine proton (Fig. 2 left) [50]. The signals
of the methine protons of the [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2
isomers at 5.72 and 5.80 ppm (one for each isomer), however, lie
towards the aliphatic region, implying that the aromaticity of the
pseudo aromatic core of the b-diketonato ligand is destroyed while
changing from [Rh(tta)(CO)(PPh3)] {4} to [Rh(tta)(CH3)(CO)(P-
Ph3)(I)]-alkyl2. It is thus expected that the C–C bonds next to the
methine proton in [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 will be
similar in length (Fig. 2 right). A similar shift in the position of
the signals of the methine proton of the b-diketonato ligand in
[Rh(b-diketonato)(CO)(PPh3)] relative to [Rh(b-diketonato)(CH3)-
(CO)(PPh3)(I)]-alkyl2 is observed for the b-diketonato ligands
1-phenyl-3-(2-thenoyl)-1,3-propanedionato (bth) and 1,3-di(2-
thenoyl)-1,3-propanedionato (dtm) (Supplementary material Ta-
ble S1). A difference of 0.56 ppm in the position of the signals of
the methine proton of the b-diketonato ligand in [Rh(acac)-
(CO)(PPh3)] and in [Rh(acac)(CH3)(CO)(PPh3)(I)]-alkyl2 is reported
by Varshavsky et al. [22], in agreement with this study.
3. Results and discussion
3.1. Spectroscopic properties of the rhodium(III) complexes
For the [Rh((C4H3S)COCHCOR)(CO)(PPh3)] (R = CF3 or C6H5 (Ph))
complexes containing an unsymmetrical b-diketonato ligand, at
least two structural isomers for each rhodium(III) reaction inter-
mediate (according to Eq. (1)) are observed on the NMR. The two
main isomers of each intermediate will be referred to as A and B,
e.g. RhIII-alkyl1A and RhIII-alkyl1B. The choice of the labels is arbi-
trary and has no significance. For the [Rh((C4H3S)COCH-
COR)(CO)(PPh3)] (R = C4H3S) complexes containing a symmetrical
b-diketonato ligand, at least one structural isomer for each rho-
dium(III) reaction intermediate (according to Eq. (1)) is observed
on the NMR. (See Supplementary material Table S1 for the spectral
properties and equilibrium constants of the various RhIII reaction
products as determined during the course of the reaction between
[Rh((C4H3S)COCHCOR)(CO)(PPh3)] (R = C4H3S, CF3 or C6H5 (Ph))
and methyl iodide according to Eq. (1).)
In CDCl3 at 25 °C, the signals of the methine proton of the b-
diketonato ligand in the two [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2
isomers are presented as singlets at 5.72 and 5.80 ppm. The corre-
sponding signals of the [Rh(tta)(CO)(PPh3)] {4} isomers are at 6.42
and 6.43 ppm (Fig. 2) [23]. A chemical shift of 6.4 ppm lies in the
aromatic region, implying that the O–C–C–C–O backbone of the
b-diketonato ligand in [Rh(tta)(CO)(PPh3)] {4} has a pseudo aro-
1H–1H NOESYs are recorded to establish the relative disposi-
tions of the ligands in [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2. When
pulsing on the CH3 group of [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2
(Fig. 3 top left), a strong coupling with the PPh3 protons is
Fig. 2. Experimental structure of [Rh(tta)(CO)(PPh3)] {4}B (left) and the minimum energy PW91/TZP optimized geometry of [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 (right),
illustrating the shielding effect of the phenyl ring on the methine proton resulting in an upfield shift. Middle: The methine region of the 1H NMR of [RhI(tta)(CO)(PPh3)] {4}B
and [RhIII(tta)(CH3)(CO)(PPh3)(I)]-alkyl2.
Fig. 3. 1H NMR spectrum (bottom) and 1H–1H NOESY spectra (middle and top) of [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 (left) and [Rh(bth)(CH3)(CO)(PPh3)(I)]-alkyl2 (right). The
top NOE spectra results from irradiation of the methyl group at ca. 2 ppm. The middle spectra give the NOE results when irradiating the methine proton at ca 6 ppm. The NOE
interactions are as indicated. CDCl3 peak is suppressed. The proposed alkyl2 structures are as indicated, I and CO may interchange.

522
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
observed, implying that the CH3 group is adjacent to the PPh3
group. When pulsing on the methine proton of the tta ligand of
[Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 (Fig. 3 middle left), a strong cou-
pling with one of the thienyl protons and a weak coupling with
some of the PPh3 protons are observed, implying that the PPh3
group is in an axial position above (or below) the square planar
plane (formed by the two oxygens of the b-diketonato ligand and
the other two groups bonded to the rhodium centre). Taking into
account the result of the previous 1H–1H NOESY, the CH3 group
must therefore be in the plane (Fig. 3 left). From the 1H–1H NOESY
spectra it is not possible to establish whether the CO group or the I
is adjacent to the PPh3 group, since these groups do not contain any
protons. An isomer with trans-situated CO and PPh3 is hardly prob-
able since vacant p* orbitals on both CO and PPh3 accept electron
density from filled metal d orbitals to form a
p bond that supple-
ments the bond arising from lone-pair donation from :CO or
r
:PPh3. These results are consistent with the proposed structure of
[Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 in Fig. 3 (left), having the PPh3
and I positioned above and below the plane with the CH3 group
in plane.
The positioning of the PPh3 group above (or below) the plane
implies that as the PPh3 group rotates, a Ph group will be coplanar
to the O–C–C–C–O backbone of the b-diketonato ligand (Fig. 2
right). The coplanar Ph group may interfere with the electron den-
sity on the O–C–C–C–O backbone, destroying the aromaticity of the
pseudo aromatic core of the b-diketonato ligand. Thus, the ali-
phatic character of the O–C–C–C–O backbone of the b-diketonato
ligand in [Rh(tta)(CH3)(CO)(PPh3)(I)]-alkyl2 may be due to the
positioning of the PPh3 group with a Ph group rotating coplanar
to the O–C–C–C–O backbone. If the PPh3 group was in the plane,
Fig. 4. The structure of [Rh(tta)(CO)(PPh3)]{4}B indicating the numbering system as
used in Table 1.
the disruption of electron density by the Ph group would not have
been possible. Thus, the observed shift of the methine proton of the
b-diketonato ligand from the aromatic region (ꢁ6.4 ppm for RhI) to
the aliphatic region (ꢁ5.7 ppm for RhIII-alkyl2) is consistent with
the PPh3 group being positioned above (or below) the plane.
Table 1
X-ray crystal data and calculated bond lengths (Å) and bond angles (°) of [Rh(tta)(CO)(PPh3)]{4}B involving a collection of methods (pure DFT, hybrid DFT and ab initio) and
functionals
Program
Method
Exp.
ADF
DFT
Gaussian
DFT
Hybrid DFT
Ab initio
Functional
Basis set
PW91
TZP
OLYP
TZP
BLYP
TZP
OPBE
TZP
PW91
CEP-31G
BLYP
CEP-31G
B3LYP
CEP-31G
HF
SDD
HF
CEP-31G
Bond lengths (Å)
C1–C2
C2–C3
C3–C4
C4–C5
C2–O1
C4–O2
O1–Rh
O2–Rh
C9–Rh
1.463
1.432
1.345
1.520
1.261
1.288
2.085
2.052
1.781
2.245
1.464
1.421
1.385
1.542
1.280
1.282
2.111
2.093
1.847
2.298
1.473
1.424
1.391
1.562
1.275
1.275
2.131
2.151
1.829
2.301
1.473
1.428
1.390
1.552
1.286
1.288
2.141
2.120
1.870
2.338
1.469
1.418
1.388
1.557
1.271
1.270
2.111
2.130
1.809
2.263
1.477
1.449
1.411
1.547
1.326
1.326
2.064
2.056
1.833
2.370
1.485
1.456
1.415
4.556
1.332
1.333
2.090
2.080
1.852
2.413
1.480
1.448
1.405
1.549
1.311
1.314
2.081
2.069
1.846
2.392
1.469
1.431
1.374
1.532
1.264
1.276
2.109
2.099
1.951
2.486
1.483
1.445
1.389
1.543
1.271
1.283
2.122
2.111
1.963
2.494
P–Rh
Bond angles (°)
C1–C2–C3
C2–C3–C4
119.2
123.6
120.1
116.1
124.7
130.3
109.7
92.0
119.1
124.6
117.8
115.5
125.4
130.5
111.7
89.8
120.1
124.4
117.8
114.6
125.3
130.2
112.0
89.0
119.0
125.1
117.6
115.7
125.2
130.5
111.8
89.6
120.1
124.2
117.7
114.4
125.5
130.1
112.1
89.0
119.6
123.3
118.6
115.9
124.5
129.2
112.2
91.0
119.6
123.5
118.4
116.1
124.3
129.3
112.3
90.7
119.4
123.0
118.2
116.4
124.2
129.4
112.3
90.0
119.4
122.7
118.1
116.5
124.0
130.0
111.9
89.2
119.2
122.6
118.0
116.7
124.1
130.1
112.0
89.2
C3–C4–C5
O1–C2–C1
O1–C2–C3
O2–C4–C3
O2–C4–C5
O1–Rh–C9
O1–Rh–O2
C9–Rh–P
87.6
87.1
88.8
88.2
86.5
87.7
88.3
89.5
87.0
86.6
89.8
90.0
89.1
90.7
88.1
91.3
84.6
95.2
84.9
95.5
O2–Rh–P
93.3
93.4
97.0
0.17
0.076
92.7
0.13
0.090
97.8
0.18
0.051
89.2
0.10
0.079
89.6
0.12
0.107
90.6
0.11
0.093
90.9
0.14
0.173
90.3
0.15
0.183
RMSDa
0.14c,d
0.057c,d
Standard deviation
Rh–L bond lengthsb
The atom numbering is as indicated in Fig. 4.
a
RMSD values, in angstroms, are root-mean-square atom positional deviations, calculated for non-hydrogen atoms (Ph and CF3 also excluded) for the best three-
dimensional superposition of calculated structures on experimental structures.
b
Calculated by Eq. (2).
c
COSMO calculations using methanol as a solvent yielded RMSD = 0.14 and standard deviation Rh–L bond lengths = 0.056.
COSMO calculations using chloroform as a solvent yielded RMSD = 0.13 and standard deviation Rh–L bond lengths = 0.056.
d

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
523
1H-1H NOESYs of [Rh(bth)(CH3)(CO)(PPh3)(I)]-alkyl2 are also con-
sistent with the proposed structure of [Rh(bth)(CH3)(CO)(P-
Ph3)(I)]-alkyl2 in Fig. 3 (right), having the PPh3 and I positioned
above and below the plane with the CH3 group in plane.
1H–1H NOESY results previously indicated that the CH3 group of
the [Rh(bth)(CH3)(CO)(PPh3)(I)]-alkyl1 isomers is above (or below)
the square planar plane (formed by the two oxygens of the b-dike-
tonato ligands and the other two groups bonded to the rhodium
Fig. 5. The PW91/TZP calculated minimum energy geometries of the square-planar rhodium(I) complexes {4} (top), {5} (middle) and {6} (bottom) before CH3I addition.
Angles (°) and bond lengths (Å) are as indicated.

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M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
centre), with the CH3 group adjacent to the PPh3 group [21]. It is
not possible to establish whether the CO group or I is trans to the
CH3 group, since these groups do not contain any protons.
Results from NMR spectroscopy on the stereo arrangement of
the RhIII-alkyl1 and RhIII-alkyl2 isomers are also consistent with
Type 1 (CH3 and I above and below the square planar plane) and
Type 2 (PPh3 and I are above and below the square planar plane)
crystal structures, respectively, as discussed Section 1.
hybrid DFT and ab initio) and functionals, are tabulated in Table
1, with the atom numbering as indicated in Fig. 4. The experimen-
tal parameters and the root-mean-square distances (RMSD) be-
tween the theoretical and the experimental structures are also
tabulated. Semi empirical methods (AM1 and PM1 as implemented
in GAUSSIAN 03, not tabulated) yielded poor results and cannot be
recommended for geometry optimizations of transition metal
coordination compounds of the kind [RhI(b-diketonato)-
(CO)(PPh3)]. The Gaussian methods with the pure classical density
functional PW91 and the hybrid functional B3LYP, both with the
CEP-31G basis set, yielded the best results with a RMSD value of
0.10 and 0.11, respectively. None of the remaining models stands
out as particular better (or worse) than any of the others. We also
attempted to account for solvation effects using conductor-like
screening model (COSMO) [40–42] calculations on [Rh(tta)-
(CO)(PPh3)] {4}B for chloroform and methanol (not tabulated in
Table 1). COSMO calculations using the PW91 functional, the TZP
basis set and methanol or chloroform as solvent, yielded geometry
parameters that are for all practical purposes the same than those
obtained by gas phase PW91/TZP calculations.
Gas phase calculations generally give longer bond lengths than
corresponding solid state crystal structure bond lengths [51]. Sim-
ilarly, but with the exception of the C2–C3 and C4–O2 bonds, all
other calculated gas phase bond lengths were generally found to
be slightly longer than the corresponding solid state bond lengths
from crystal data. In particular, large deviation from experimental
bond lengths were found for the P–Rh bond (from 0.018 Å for
OPBE/TZP up to 0.249 Å for HF/CEP-31G). The metal bond to the
CO group, C9–Rh, deviates from 0.028 Å (OLYP/TZP) up to 0.182 Å
(HF/CEP-31G) from the experimental value. All models reproduce
the difference in length between bond C2–C3 (more single bond
character) and bond C3–C4 (more double bond character) satisfac-
tory. The C2–O1 and C4–O2 bond lengths in the b-diketonato li-
gand, 2-thenoyltrifluoroacetonato (tta), are very well produced
by most models - typically with a deviation between 0.01 and
0.02 Å from the experimental values. Since comparisons of experi-
mental metal–ligand bond lengths with calculated bond lengths
below a threshold of 0.02 Å are considered as meaningless [51],
most methods thus give a good account of the experimental bond
lengths. Focussing on the standard deviation of the rhodium–li-
gand (Rh–L) bond lengths, as quantified by Eq. (2), the PW91/TZP
outperformed the other methods.
3.2. Computational results
3.2.1. Geometrical study of the square planar thienyl containing
rhodium(I) complexes
Since quantum computational methods are for the first time ap-
plied to [RhI(b-diketonato)(CO)(PPh3)] complexes and reported
here, some measure of the reliability of the approach had to be ob-
tained. This was addressed by comparing the known single crystal
X-ray diffraction structure of [Rh(tta)(CO)(PPh3)] {4}B [50] with
the theoretically calculated structures of the same complex ob-
tained by using a collection of methods and functionals. The RhI
isomer of {4} with the CO ligand trans to the oxygen nearest to
the electron attraction group CF3 will be referred to as B and the
other isomer as A.
Geometrical results for the ground state geometry of [Rh(tta)
(CO)(PPh3)] {4}B involving a collection of methods (pure DFT,
Table 2
Calculated and experimental carbonyl stretching frequencies (
containing rhodium(I) complexes
m
CO in cmꢀ1) of thienyl
Experimentald
Program
ADF
Gaussian
Gaussian
Method
Functional
Basis set
DFT
Hybrid DFT
B3LYP
Ab initio
HF
PW91
TZPa
CEP-31Gb
SSDc
[RhI(b-diketonato)(CO) ]
2
tta {1}
2007
2066
1996
2056
1998
2057
1880
1937
1866
1924
1868
1926
2035
2069
2019
2057
2021
2058
2008, 2026, 2033,
2078, 2098
1996
2058
1992
bth {2}
dtm {3}
2057
[RhI(b-diketonato)(CO)(PPh )]e
3
tta {4}
bth {5}
dtm {6}
1981, 1986
1974, 1977
1977
1849, 1854
1839, 1837
1834
2009, 2015
1993, 1949
2001
1981 (1991)
1970, 1980 (1983)
1971 (1987)
Bond angles within the 2-thenoyltrifluoroacetonato (tta) ligand
are generally well reproduced (within 1° from the experimental
value) for all models. The angle C3–C4–C5 is between 2° and 2.5°
too small for all models. The angle O2–C4–C5 is overestimated
by 2 (PW91/TZP) up to 2.6° (B3LYP/CEP-31G) from the experimen-
tal value. The bond angles involving the metal centre, a key indica-
tor of the structure in organometallic compounds, deviate between
a
Unscaled.
b
c
Computed values scaled by factor 0.9684 according to Ref. [58].
Computed values scaled by factor 0.9004 according to Ref. [58].
In solid state, chloroform solution mCO in brackets.
d
e
Two isomers each, except for complex {6} which is symmetrical.
Fig. 6. Experimental (left) and PW91/TZP calculated (middle and right for the two isomers) IR spectrums of [Rh(tta)(CO)(PPh3)]{4}. The crystal structure of{4}B corresponds
to the geometry of the calculated isomer in the middle.

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
525
Table 3
Relative energies (kcal/mol) of the possible alkyl and acyl reaction products of the oxidative addition reaction of [RhI(b-diketonato)(CO)(PPh3)] and CH3I
b-Diketonato
Geometry
tta
bth
dtm
16.9
Alkyl I
19.1
17.8
(19.3) [19.6] {19.3}
(18.0) [18.2] {15.7}
Alkyl II
16.8
17.0
(16.4) [16.3] {16.2}
(17.1) [17.1] {16.3}
(16.5) [16.4] {17.7}
Alkyl III
Alkyl IV
Alkyl V
16.4
16.4
(15.7) [15.1] {11.3}
(15.9) [15.5] {11.3}
15.2
14.9
13.4
(14.7) [14.3] {10.3}
(14.5) [14.1] {9.1}
(12.6) [12.3] {10.0}
12.4
12.7
(12.4) [12.6] {10.2}
(12.8) [13.7] {12.8}
Alkyl VI
Alkyl VII
Alkyl VIII
Alkyl IXa
11.7
11.2
12.3
(11.9) [12.3] {11.8}
(11.6) [12.3] {10.8}
(12.5) [13.0] {14.2}
12.3
11.8
(11.6) [11.1] {6.7}
(11.5) [10.9] {5.4}
11.7
10.1
(9.6) [9.1] {3.5}
9.1
(11.1) [10.7] {6.4}
(8.3) [7.9] {4.9}
9.1
7.4
(10.0) [11.0] {8.8}
(8.5) [9.7] {6.0}
Alkyl Xa
Alkyl XIb
Alkyl XIIb
Acyl I
7.9
7.6
6.6
(8.7) [9.5] {6.8}
(8.7) [9.9] {6.1}
(7.3) [9.8] {7.3}
6.5
6.3
(7.1) [7.7] {3.2}
(7.4) [8.0] {3.4}
5.6
6.1
4.7
(6.3) [7.0] {3.3}
(7.1) [7.3] {3.3}
(5.0) [9.3] {3.9}
10.3
9.6
(10.6) [11.0] {7.9}
(9.7) [10.3] {7.5}
Acyl II
8.6
9.7
8.6
(8.3) [9.0] {6.8}
(10.3) [11.0] {9.3}
(8.4) [8.5] {7.8}
Acyl III
7.5
7.3
(8.2) [9.0] {13.0}
(7.9) [8.7] {12.1}
Acyl IV
Acyl Vc
Acyl VIc
7.4
6.9
6.0
(8.1) [9.0] {12.6}
(7.7) [8.9] {12.2}
(6.4) [7.3] {13.1}
2.2
1.0
(2.4) [2.6] {1.8}
(1.2) [1.5] {ꢀ1.5}
0.0
0.0
0.0
(0.0) [0.0] {0.0}
(0.0) [0.0] {0.0}
(0.0) [0.0] {0.0}
The unbracketed values refer to the solution DFT values (PW91/TZP in MeOH). The round-, square- and curved-bracket values refer to the CHCl3-solution PW91/TZP, the gas
phase PW91/TZP and gas phase B3LYP/CEP-31G optimized geometries, respectively.
a Alkyl1A and alkyl1B.
b Alkyl2A and alkyl2B.
c Acyl2A and acyl2B.

526
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
0° and 5° from experimental values, depending on the computa-
tional method used. The DFT method with the TZP basis set repro-
duces the angles involving the rhodium centre exceptionally well.
Focussing on the overall performance of the different methods,
the PW91/TZP model provides a solid account for calculating
[Rh(tta)(CO)(PPh3)] {4}B, as reflected by the RMSD and the stan-
dard deviation of the Rh–L bond lengths. In agreement with X-
ray data, the Rh–L experimental bond lengths are reproduced with-
in an accuracy of 0.04 Å for Rh–O, 0.07 Å for Rh–C and 0.05 Å for
Rh–P. Calculated bond lengths between atoms inside the ligands
fit the measured values generally within the range of 0.02 Å. The
angles involving Rh deviate 0.1–2.2° from the experimental value.
Structural data computed with this model for related compounds
may therefore be presented with an extrapolative equally high de-
gree of accuracy.
The different rhodium(I) complexes [Rh(tta)(CO)(PPh3)] {4},
[Rh(bth)(CO)(PPh3)] {5} and [Rh(dtm)(CO)(PPh3)] {6} (Fig. 5) were
calculated using the PW91/TZP model. The larger trans influence of
the PPh3 group, relative to the CO group, is well reproduced by the
elongated Rh–O bond trans to the PPh3 group. The calculated Rh–P
Fig. 7. The PW91/TZP calculated minimum energy geometries of the octahedral [RhIII(b-diketonato)(CH3)(CO)(PPh3)(I)]-alkyl complexes with the PPh3 group and I above and
below the plane, b-diketonato = tta (top), bth (middle) and dtm (bottom). Angles (°) and bond lengths (Å) are as indicated.

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
527
bond lengths of 2.295–2.299 Å of {4}, {5} and {6} are 2–3% longer
than the typical range of Rh–P distances of 2.232–2.252 Å for re-
lated [RhI(b-diketonato)(CO)(PPh3)] complexes (see Table S2 in
Supplementary material) [50,52–57]. The calculated Rh–C bond
lengths (1.848 Å average) are also slightly longer (2–6%) than of
Rh–C bond lengths in related experimental structures.
ing. Replacement of one of these CO groups with a PPh3 group re-
sults in a monocarbonyl phosphine [RhI(b-diketonato)(CO)(PPh3)]
complex. Subsequently only one mCO peak for each isomer of
[RhI(b-diketonato)(CO)(PPh3)] is observed, represented by the
one CO group. Frequency calculations were preformed on the opti-
mized structures to obtain the carbonyl stretching frequencies
(mCO). The calculated and experimental carbonyl stretching fre-
3.2.2. IR carbonyl stretching frequency (
containing rhodium(I) complexes
m
CO) study of thienyl
quency data of [RhI(b-diketonato)(CO)2] {1}–{3} and [RhI(b-diketo-
nato)(CO)(PPh3)] {4}–{6} (b-diketonato = tta, bth or dtm) are
tabulated in Table 2 for a DFT (PW91), a Hybrid DFT (B3LYP) and
an ab initio (HF) method. The DFT method with the pure classical
PW91 functional, illustrated graphically for [Rh(tta)(CO)(PPh3)]{4}
The dicarbonyl rhodium(I) complexes [RhI(b-diketonato)(CO)2]
give an IR spectrum with two distinctive singlet mCO peaks – one
for the symmetrical and one for the asymmetrical carbonyl stretch-
Fig. 8. The PW91/TZP calculated minimum energy geometries of the octahedral alkyl [RhIII(b-diketonato)(CH3)(CO)(PPh3)(I)]-alkyl complexes after trans CH3I addition,
b-diketonato = tta (top), bth (middle) and dtm (bottom). Angles (°) and bond lengths (Å) are as indicated.

528
M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
in Fig. 6, yielded unscaled calculated mCO values for {1}–{6} in
excellent agreement with the experimentally obtained values, out-
performing the B3LYP and the HF calculations. The unscaled mCO
values calculated by the B3LYP functional were 63–88 cmꢀ1 too
low. Scaling of these mCO values with a factor of 0.9684 [58] re-
sulted in even worst values. The HF functional performed better
with deviations of 1–88 cmꢀ1 (after scaling of the calculated values
by 0.9004[58]) from experimental values.
was also inspected, but resulted in such high calculated relative
molecular energies, that they were discarded from this study.
The calculated relative molecular energies of all the RhIII-alkyl
and -acyl reaction products of [Rh(tta)(CO)(PPh3)] {4}, [Rh(bth)
(CO)(PPh3)] {5} and [Rh(dtm)(CO)(PPh3)] {6} with CH3I for PW91
and B3LYP gas phase calculations, as well as in solution of chloro-
form and methanol (PW91), are tabulated in Table 3.
3.2.3.1. Octahedral rhodium(III)-alkyl products. When comparing the
relative energies of the different RhIII-alkyl complexes in Table 3,
the lowest energy alkyl isomers are alkyl XI and alkyl XII. The
geometry of the alkyl XI and alkyl XII isomers (Fig. 7) is consistent
with the NMR results of the alkyl2 isomers of this study, namely
that the PPh3 group is in the apical position and the CH3 group in
the square planar plane. The acidity of the Ph-substituted phos-
phorous reduces the electron density at the rhodium atom and
3.2.3. Rhodium(III) oxidative addition products
Mathematically calculated, the different arrangements of the
groups bonded to the rhodium(III) centre after oxidative addition
of CH3I give rise to a theoretical possibility of 24 different octahe-
dral RhIII-alkyl isomers and 12 different square-pyramidal RhIII-
acyl isomers. Since the enantiomers (12 RhIII-alkyl and 6 RhIII-acyl
mirror images) display the same computational and chemical
properties, they can be excluded from this discussion. This leaves
one with 12 different RhIII-alkyl isomers and six different RhIII-acyl
isomers. The possibility of trigonal bipyramidal RhIII-acyl isomers
hence stabilizes the trans
in calculated Rh–I bond lengths trans to PPh3 (Fig. 7) ca. 0.01 Å
shorter than Rh–I bond lengths trans to CH3 (Fig. 8).
p
-electron donating ligand Iꢀ, resulting
Fig. 9. The PW91/TZP calculated minimum energy geometries of the square-pyramidal [RhIII(L,L0-BID)(COCH3)(PPh3)(I)]-acyl products after CO insertion, b-diketonato = tta
(top), bth (middle) and dtm (bottom). Angles (°) and bond lengths (Å) are as indicated.

M.M. Conradie, J. Conradie / Inorganica Chimica Acta 362 (2009) 519–530
529
In determining the geometry of the alkyl1 isomers in Eq. 1, one
Acknowledgements
can discard the upper six RhIII-alkyl isomers (three for Rh-dtm prod-
ucts) in Table 3, since they are energetically not favoured. CH3I will
either be added cis or trans to the square planar RhI complex. The
lowest energy cis addition products are alkyl VII and alkyl VIII while
the trans addition products are alkyl IX and alkyl X. Gas phase calcu-
lations did not favour the trans addition products by a clear margin
of energy. In order to fulfil in experimental conditions, calculations
taking solvent effects into account, were also performed. We were
pleased to find that in methanol or chloroform the trans addition
products, alkyl IX and alkyl X, are favoured by ca. 4 kcal/mol over
the cis addition products alkyl VII and alkyl VIII, in agreement with
NMR results. The small difference in energy between the different
alkyl and acyl isomers, makes the equilibrium between the rho-
dium(III) reaction products as given in Eq. (1), possible.
Financial assistance by the South African National Research
Foundation, under Grant No. 2067416, and the Central Research
Fund of the University of the Free State is gratefully acknowledged.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2008.04.046.
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clearly the acyl V and acyl VI isomers, with the COCH3 moiety in
the apical position. The square-pyramidal geometry with the
COCH3 group in the apical position (Fig. 9) is favoured by all com-
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Hybrid DFT (B3LYP/CEP-31G) and HF (HF/SDD and HF/CEP-31G –
not tabulated in Table 3). This geometry correlates with the
geometry of the Type 3 experimental crystal structures of the
[RhIII(L,L0-BID)(COCH3)(PPh3)(I)] class of compounds as described
in Section 1. Thus, both computational calculations and crystallog-
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Pure DFT, hybrid DFT and ab initio methods, in agreement with
crystal data, gave a solid account for the geometry of [Rh(tta)-
(CO)(PPh3)] {4}. NMR, crystal structure and computational chemis-
try results on the stereochemistry of the RhIII-alkyl1, RhIII-alkyl2
and RhIII-acyl2 reaction products, as given by Eq. (1), are mutually
consistent with the conclusion that the alkyl1 product results from
trans addition to RhI, that the thermodynamic alkyl2 product adopt
an octahedral geometry with the PPh3 group and the iodide above
and below the square planar plane (formed by the two oxygens of
the b-diketonato ligands and the other two groups bonded to the
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