Kinetic-Mechanistic and Solid-State Study of the Oxidative Addition and Migratory Insertion of Iodomethane to [Rhodium(S,O-BdiPT or N,O-ox)(CO)(PR1R2R3)] Complexes

Article abstract of DOI:10.1002/ejic.201800293

Rhodium(I) carbonyl complexes containing bidentate X,O-Bid [S,O-BdiPT or N,O-ox; S,O-BdiPTH = N-benzoyl-N′,N′-(diphenyl)thiourea; N,O-oxH = 8-hydroxyquinoline] ligands of the form [Rh(X,O-Bid)(CO)(PR¹R²R³)] (R¹, R², R³ = Ph or Cy) bearing different phosphine ligands, were investigated, the structural characterization of four example complexes is described and an extensive spectroscopic kinetic-mechanistic study of the oxidative addition of iodomethane thereto is discussed. Reaction with iodomethane led to Rh^III-acyl species as secondary (final) products, whereas the primary Rh^III-alkyl complexes, although rapidly formed, were only observed as intermediates, in small quantities for S,O-BdiPT (large S–Rh–O bite angle of 90–91°) but in significant amounts for N,O-ox complexes (less steric with a smaller N–Rh–O bite angle of 79–80°). Overall, almost an order-of-magnitude difference in rate constants was observed for the S,O-BdiPT complexes, with the PPh₂Cy- and PPhCy₂-bearing complexes showing the largest variation. In both the S,O-BdiPT and N,O-ox ligand systems an associative activation is inferred from the large negative ΔS^≠ values. The relative reactivity of Rh^I-X,O-Bid complexes, where X = O, S or N, follows a surprising similar reactivity relationship when stepwise varying the PPh₃, PPh₂Cy, PPhCy₂ and PCy₃ tertiary phosphine ligands, suggesting a systematic behavior by the PR₃ ligands, independent of the X,O-Bid ligand at the Rh^I metal center.

Full text of DOI:10.1002/ejic.201800293

A Journal of
Accepted Article
Title: Kinetic-Mechanistic and Solid State Study of the Iodomethane
Oxidative Addition to and Migratory Insertion in [Rhodium(S,O-
BdiPT or N,O-ox)(CO)(PR1R2R3)] Complexes
Authors: Andreas ROODT, Stefan Warsink, Stefanus Otto, Rickert P.D.
Kotze, Inus J.M. Janse van Rensburg, Johan Andries Venter,
and Ebrahiem Botha
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201800293
Link to VoR: http://dx.doi.org/10.1002/ejic.201800293

10.1002/ejic.201800293
European Journal of Inorganic Chemistry
Kinetic-Mechanistic and Solid State Study of the Iodomethane Oxidative
Addition to and Migratory Insertion in [Rhodium(S,O-BdiPT or N,O-
ox)(CO)(PR1R2R3)] Complexes
Stefan Warsinka, P. D. Riekert Kotzea,b, J.M. (Inus) Janse van Rensburga,c, Johan A. Venter a,*, Stefanus
Ottoa,b, Ebrahiem Bothaa, Andreas Roodta,*
a Department of Chemistry, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa;
b Sasol Technology, R&D Division, 1 Klasie Havenga Street, Sasolburg 1948, South Africa.
c Current address: Wildlife Pharmaceuticals (PTY) Ltd, 38 Wilken Street, Rocky Drift, White River 1240,
South Africa.
Keywords
Rhodium. Oxidative addition. Mechanism. Kinetics. Crystal structures. Bidentate thiourea. Oxine.
Graphic Contents Illustration
Synthesis and structural characterization of [Rh(X,O-Bid)(CO)(PR1R2R3)] (X,O-BidH: N-benzoyl-
N’,N’-(diphenyl)thiourea= S,O-BdiPTH; N,O-oxH = 8-hydroxyquinoline) rhodium(I) carbonyl com-
plexes (A) bearing different PR3 ligands are described, with focus on relative reactivities of iodome-
thane oxidative addition reactions via intermediate RhIII-alkyl complexes (B) to RhIII-acyl species (C).
1
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
Abstract
Rhodium(I) carbonyl complexes containing bidentate X,O-Bid (S,O-BdiPT or N,O-ox; N-benzoyl-N’,N’-
(diphenyl)thiourea= S,O-BdiPTH; N,O-oxH = 8-hydroxyquinoline) ligands of the form [Rh(X,O-
Bid)(CO)(PR1R2R3)] (R1, R2, R3 = Ph or Cy) bearing different phosphine ligands, were investigated, the
structural characterization of four example complexes is described and an extensive spectroscopic ki-
netic-mechanistic study of the iodomethane oxidative addition thereto is discussed. Reaction with iodo-
methane led to RhIII-acyl species as secondary (final) products, whereas the primary RhIII-alkyl com-
plexes, although rapidly formed, were only observed as intermediates, in small quantities for S,O-BdiPT
(large S-Rh-O bite angle of 90-91) but in significant amounts for N,O-ox complexes (less steric with a
smaller N-Rh-O bite angle of 79-80). Overall, almost an order-of-magnitude difference in rate con-
stants was observed for the S,O-BdiPT complexes, with the PPh2Cy- and PPhCy2-bearing complexes
showing the largest variation. In both the S,O- BdiPT and N,O-ox ligand systems an associative activa-
tion is inferred from the large negative ∆S values. The relative reactivity of RhI-X,O-Bid complexes,
where X=O, S or N, follows a surprising similar reactivity relationship when stepwise varying the PPh3,
PPh2Cy, PPhCy2 and PCy3 tertiary phosphine ligands, suggesting a systematic behavior by the PR3 lig-
ands, independent of the X,O-Bid ligand at the Rh(I) metal centre.
Introduction
Oxidative addition reactions on metal complexes represent key steps in many catalytic processes, in-
cluding the carbonylation of methanol. It has been argued that it is the rate-determining step in the cata-
lytic cycles of some of these processes, and therefore any influence on this step can determine the
course of the complete catalytic cycle. Due to the vital role of this reaction, a significant amount of re-
search has thus been focused on oxidative addition reactions in order to understand its kinetic properties
and responses to external and internal influences.1
Iodomethane oxidative addition on rhodium carbonyl complexes is important in industrial production
plants utilising the Monsanto and Cativa processes2 and has been studied intensively with a variety of
mono- and bidentate ligands.3 In general, it was discovered that changing the type of ligand or altering
the stereo-electronic properties of the ligand result in significant changes in the outcome of the catalytic
process. The carbonyl ligand is essential to allow the formation of acyl adducts via migratory insertion
into the metal alkyl bonds formed during the oxidative addition of alkyl iodides. In the Monsanto
2
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
process the metal carbonyl species is [RhI(I)2(CO)2]-, which is relatively unstable. Rhodium carbonyl
species containing phosphine ligands and/or bidentate ligands are generally found to be more stable, alt-
hough some interesting recent metallophilic interactions have been described in Rh(I) dicarbonyl com-
4
plexes. Furthermore, by tuning the stereo-electronic properties of these ligands, the carbonylation pro-
cess is directed towards different outcomes. For example, other products might arise if hydrogenation
precedes the reductive elimination.
In the case where bidentate ligands containing a sulfur donor atom, in particular thioacetylacetone, were
used, the oxidative addition of iodomethane primarily led to the formation of RhIII-acyl complexes.5,6,7
As we were interested in the synthesis and isolation of RhIII-acyl complexes in our studies towards the
reductive carbonylation of methanol, we pursued the synthesis and application of [Rh(S,O-
BdiPT)(CO)(PR1R2R3)] species, because in conjunction with the fact that sulfur-containing bidentate
ligands lead to RhIII-acyl formation, little data is available on rhodium complexes bearing S,O-bidentate
ligands. 3,7
However, we further opted to introduce a smaller bite angle N,O-ox ligand 8-hydroxyquinoline (oxine)
to compare the behavior with the said S,O-BdiPT thiourea based chelates therewith and evaluate/ quan-
tify the origin of the behavior as a function of donor atom (S vs.N vs.O) since it is known that RhI-ox-
inato complexes yielded alkyl species as products. 8
We are in particular aware that much current 'mechanistic research' often involves purely the analysis of
reactants and products, while the time-resolved details are much less studied. Thus, here we emphasize
the importance of detailed structure-reactivity studies in basic catalytic processes to ensure that the com-
plete picture is considered. Moreover, we illustrate here the fact that two clear consecutive reactions as
observed, should be carefully considered taking the broader system into account, before simplified to
‘one’ reaction.
Thus, in this report, the synthesis of selected [Rh(N,O-ox)(CO)(PR1R2R3)] and [Rh(S,O-
BdiPT)(CO)(PR1R2R3)] complexes (PR1R2R3 = PPh3, PPh2Cy, PPhCy2, and PCy3; S,O-BdiPTH= N-ben-
zoyl-N’,N’-(diphenyl)thiourea and N,O-oxH=oxine; 8-hydroxyquinoline) is described to carefully evalu-
ate the effects resulting from the introduction of the N,O-bidentate and S,O-bidentate ligand systems. In
particular, the latter (S,O-BdiPT) contains a softer donor atom combination but a larger bite angle (six
membered chelate ring) while in the former (N,O-ox) a smaller bidentate bite angle (five membered che-
late) is introduced; thus varied steric crowding at the Rh(I) centre. Additionally, the kinetic and thermo-
dynamic aspects of the oxidative addition of iodomethane are discussed in relation with the previously
3
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
reported O,O-acetylacetonato (acac) complexes.7 Four crystal structures of the starting complexes are
reported and are carefully correlated with the steric and electronic properties of the said complexes.
Results and discussion
Ligand and complex synthesis. The ligand N-benzoyl-N’,N’-(diphenyl)thiourea (S,O-BdiPT)H was syn-
thesized in two steps from benzoyl chloride (Scheme 1).9 First, the isothiocyanate was formed, followed
by addition of diphenyl amine, which gave the product 1 in an overall yield of 98%.
The 1H NMR of 1 features a signal at 11.19 ppm, which corresponds with the acidic proton on the thiou-
rea-nitrogen. In the 13C NMR, the thiourea- and amide-signals are observed at 184.5 and 167.3 ppm, re-
spectively.
Scheme 1. Synthesis of N-benzoyl-N’,N’-(diphenyl)thiourea (S,O-BdiPT)H (1).
In order to obtain complexes 2 - 5, ligand 1 was added to a DMF solution of tetracarbonyl-dichlorido-
dirhodium(I),10 after which the mononuclear dicarbonyl thioureato complex was precipitated with ice
water. This complex was only stable in the solid state for a short time and was consequently employed
in the next step without detailed characterization. The infrared doublet, characteristic of the symmetric
and asymmetric stretching bands of the reactant were clearly observed on ATR. The solid obtained was
taken up in diethyl ether, after which the tertiary phosphine ligand was added to the reaction mixture.
The desired rhodium(I)-complex precipitated from the solution, from which it was isolated by filtration
in yields of 60 - 65% over two steps (Scheme 2). Similarly, complexes 7-10 were obtained as described
above for the S,O-BdiPT complexes by reacting stoichiometric amounts of 8-hydroxyquinoline with
tetracarbonyl-dichlorido-dirhodium(I) in DMF as solvent, whereafter the title compound was obtained
by adding PPh3, PPh2Cy, PPhCy2, and PCy3 in acetone. Through slow evaporation of the solvent, crys-
tals were obtained. [Rh(N,O-ox)(CO)(PPh3)] (7) and [Rh(N,O-ox)(CO)(PCyPh2)] (8) were prepared as
11
already reported previously.
4
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European Journal of Inorganic Chemistry
Scheme 2. Synthesis of RhI-carbonyl complexes bearing (i) different monodentate tertiary phosphine and
(ii) different S,O-BdiPT [N-benzoyl-N’,N’-(diphenyl)thiourea (S,O-BdiPT)H] or N,O-ox (8-hydroxyquin-
oline; oxine) ligands.
All complexes could be well characterized by infrared and NMR, of which characteristic spectroscopic
details are presented in Table 1. The disappearance of the signal for the thiourea hydrogen atom on lig-
and 1 in the 1H NMR spectrum upon coordination is indicative of the formation of the monoanionic lig-
and.7
As shown in Table 1, all the [Rh(S,O-BdiPT)(CO)(PR1R2R3)] complexes (PR1R2R3 = PPh3, PPh2Cy,
PPhCy2, and PCy3) show characteristic signals in the 31P NMR for the phosphorus ligands between 38
and 50 ppm. Only one doublet is observed for each compound, indicating the formation of only one iso-
mer, which is expected to have the phosphine and the sulfur-donor in mutual trans-positions. Moreover,
a single carbonyl vibration was observed in the IR spectrum between 1960 and 1980 cm-1 for each, cor-
roborating the fact that only one isomer is present after the reaction. A high field shift is observed in the
31P NMR when going from complex 2 to complex 5, i.e. towards more electron donating phosphine lig-
ands. The same trend is observed in the 13C NMR signals of the thioureato-carbon atom and the car-
bonyl ligand. These observations are commensurate with the higher electron density imparted on the
rhodium by the phosphine ligand. The first-order rhodium-phosphorus coupling (JRh-P) and the CO-
stretching vibration of the carbonyl ligand decrease from 2 to 5 as expected for this ligand series. In the
carbonyl ligand, this is caused by a reduced C-O bond order, due to increased π-back bonding to accom-
modate the higher electron density on the rhodium metal centre.
5
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European Journal of Inorganic Chemistry
Similar behavior with respect to the IR and 31P NMR spectroscopic data is observed for the correspond-
ing [Rh(N,O-ox)(CO)(PR1R2R3)] complexes (7-10), see Table 1.
Table 1. Summary of spectroscopic data (solution and solid state) for 2-5, 7-10.
PR3
2a
3a
4a
5a
7b
8b
9b
10b
IR
υCO (cm-1) 1979 1972 1969
υCO (cm-1) 1963c 1966c 1961d
1963
1952c
49.9
146
1965
1959d
41.2
164
1968
1959d
52.8
163
1952
1952d
53.6
161
1946
1946d
54.8
156
31P NMR δ(ppm)
38.2
152
49.5
149
49.5
149
JRh-P/Hz
c
a CH2Cl2, unless otherwise stated; b Acetone, unless otherwise stated; Neat samples, ATR; d IR KBr
X-ray crystallography. Detailed structural information of these complexes was obtained from crystallo-
graphic analyses. Single crystals were obtained by slow evaporation of a dichloromethane/acetone solu-
tion of complexes 2, 3, 5 and 10, yielding the subsequent molecular structures (Figure 1). Despite our
best efforts, no crystals suitable for X-ray analysis could be obtained for complexes 4 and 9. Complexes
7 and 8 are referenced11 from literature for completeness. The basic crystallographic parameters and
data collection details are given in the Supplementary Information. All four complexes crystallized in
the monoclinic crystal system, with 2, 3 and 5 in space group P21/c, and 10 in C2/c. In Table 2 a com-
parison between selected bond lengths and angles of the complexes is presented.
(a)
(b)
6
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European Journal of Inorganic Chemistry
(c)
(d)
Figure 1. Displacement ellipsoid plots of (a) 2' (only 1 molecule displayed; other one very similar, (b) 3,
(c) 5; (30% probability level) and (d) 10 (50% probability level). H-atoms are omitted for the sake of
clarity and only relevant atoms are labeled.
Complex 2 crystallized with two slightly different independent molecules (relative variation in bonds
and angles indicated in Table 2) in the asymmetric unit. Both are very similar in terms of their basic
bond lengths and angles, with the main difference being the rotation of the phenyl rings, both on the
phospine and the S,O-BdiPT ligands.
All complexes show a slightly distorted square planar geometry, amongst other due to the larger than 91
° bite angle of the S,O-BdiPT ligand (S-Rh-O1). The bidentate ligand shows delocalization of electron
density, borne out by the bond lengths that lie between those of single and double bonds (for full crystal-
lographic data, see Supporting Information). To accommodate the square planar geometry, the S,O-
BdiPT ligand shows a small rotation with respect to its backbone as manifested by the torsion angle.
The different phosphine ligands have the expected effect on bond lengths, with the more electron-donat-
ing but bulky ligands having a longer bond to rhodium (Rh-P) and conversely lengthening the bond to
the trans-ligand (Rh-S) as well. The phosphine ligands also influence the carbonyl ligands, although the
shortening of the Rh-C39 bond length and the elongation of the C39-O2 bond length with more basic
phosphines is not significant. It is noted that the carbonyl ligand shows a slight distortion from linearity
in its coordination in the solid state, although the cause for this is unclear and might be due to packing
effects.
The Rh-P bond lengths (trans to the S-atom) of the S,O-Bid ligands in this study are ca 2.27-2.30 Å and
significantly longer when compared to the Ph-P bonds (trans to O-atom) of ca. 2.23-2.24 Å, i.e., with
7
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that of the acac ligand (O,O-Bid ligand) in a previous investigation, clearly showing an increase in Rh-P
bond lengths, in agreement with the larger trans influence of the S-donor ligand. The increase in bond
lengths is also manifested in the 1J(31P-103Rh) coupling constants shown in Table 1 (around 155 Hz for
the S,O-Bid ligands, compared to ca. 170 Hz for the O,O-Bid ligands such as acac).7
Table 2. Selected bond lengths (Å) and angles (°) for complexes 2, 3, 5, 8 and 10.
[Rh(S,O-BdiPT)(CO)(PR3)]
Bond/
Angle
[Rh(N,O-ox)(CO)(PR3)]
Bond/
Angle
811
10
2
2' a
3
5
Rh-S
Rh-O1
2.304(1) 2.312(1)
2.039(2) 2.037(2)
2.291(1) 2.278(1)
1.791(3) 1.804(3)
1.154(4) 1.153(4)
2.312(1)
2.037(3)
2.287(1)
1.798(5)
1.155(5)
3.110
2.329(1)
2.057(3)
2.302(1)
1.788(5)
1.157(6)
3.153
Rh-N
2.128(2)
2.060(2)
2.091(4)
2.036(4)
Rh-O1
Rh-P
Rh-P
2.2798(8) 2.2557(15)
Rh-C39
Rh-C10
C8-O1
1.803(3)
1.328(3)
2.676(3)
79.41(9)
93.11(6)
1.1817(6)
1.321(7)
2.671(5)
80.65(16)
91.14(11)
C39-O2
S···O1 (distance)
S-Rh-O1 (bite)
O1-Rh-P
3.105
91.1(1)
87.5(7)
93.0(1)
88.9(1)
3.126
N···O
91.7(1)
89.5(1)
88.5(1)
90.1(1)
91.1(1)
89.5(1)
89.0(1)
90.1(1)
177.8(4)
91.7(1)
88.7(1)
90.2(2)
90.2(2)
178.0(5)
O1-Rh-N
P-Rh-O1
C10-Rh-P
N-Rh-C10
Rh-C10-O2
P-Rh-C39
C39-Rh-S
Rh-C39-O2
88.70(10) 90.89(18)
99.10(12) 97.3(2)
175.3(3) 177.6(3)
179.6(3)
176.5(5)
a 2' second molecule in the asymmetric unit
Complex 10 crystallized with eight molecules in the unit cell (Z=8) in the monoclinic space group C2/c.
Figure 1 shows the general numbering scheme of 10 and the most important bond distances and angles
are reported in Table 2. The fused ring system of the bidentate ligand is almost planar, with an r.m.s de-
viation between atoms C1-C9 and N of 0.0139 Å, as further emphasized by the dihedral angle between
the two aromatic rings of 1.5(3)º. The distorted square-planar metal coordination polyhedron is illus-
trated by the bite angle of 80.65(16) º and a C10-Rh-P bond angle of 90.89(18)º. The carbonyl ligand is
close to linearity with a Rh-C10-O2 angle of 176.5(5)º. A slight molecular bending is displayed by the
dihedral angle of 7.18(10)º which formed between the fused ring system plane and the metal coordina-
tion plane. The rhodium metal centre is displaced 0.170(5) Å from the fused ring system plane and
0.0118(5) Å out of the metal coordination plane. By calculating the effective cone angle (θE) 167º and
using the actual Rh-P bond distance of 2.256(2) Å, steric demand of the tricyclohexylphosphine in the
8
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solid state, could be determined.14,15 The molecular crystal packing is stabilized by a ligand π-π stack-
ing and soft contacts between the aryl substituted rings of the phosphorous ligand and the quinoline lig-
and of the next molecule.
Compound 8 crystallized in the monoclinic space group P21/n, (Z=4). Figure 1 contains the general
atom numbering used for 8. The fused ring system of the bidentate ligand is bending slightly, with a
r.m.s. deviation from planarity of 0.0214 Å and a dihedral angle of 2.0(1)º between the two aromatic
rings of the oxinate ligand, indicating a slight distortion in the ligand backbone. A further distortion is
observed between the bidentate N,O-ox backbone and the metal coordination plane, yielding a dihedral
angle of 11.3(1)º. In the five membered chelate ring, the N,O-ox ligand has a small bite angle of
79.41(9)º and a C10-Rh-P angle of 88.70(10)º, which illustrates the distorted square-planar metal coor-
dination polyhedron. The rhodium atom lies in a general position and is slightly displaced out of the co-
ordination plane by 0.062 (1) Å (r.m.s. displacement of fitted atoms = 0.098 Å). The carbonyl ligand is
mostly linear with an Rh-C10-O2 angle of 179.6(3)º. The significant steric demand of the cyclohexyldi-
phenylphosphine ligand (in the solid state) was determined to be 151º. This was done by calculating the
effective cone angle (θE) using the actual Rh-P bond distance of 2.2798(8) Å. The most important bond
distances and angles are reported in Table2.
Kinetic experiments.
[Rh(S,O-BdiPT)(CO)(PR3)] complexes. When complex 2 was reacted with iodomethane in dichloro-
methane under pseudo first-order conditions, in situ IR-spectroscopy showed [Fig. 2(a)] that the car-
bonyl signal of the reactant at 1979 cm-1 disappeared, while a signal at 1715 cm-1 appeared virtually
simultaneously. The latter signal corresponds to a rhodium(III)-acyl species, indicating that conversion
of the RhI-carbonyl complex proceeds to the insertion product. However this proceeds via a RhIII-alkyl
complex, which is only minutely observed by the signal at 2065 cm-1. This implies that the rate of con-
version to the rhodium(III)-alkyl complex would be difficult if not virtually impossible to analyze and
that the major reaction rate involved is the ‘direct’ conversion of 2 to the RhIII-acyl complex.
The iodomethane oxidative addition/ reductive elimination, and subsequent migratory carbonyl insertion
are illustrated in Scheme 3, which suggests the formation of the intermediate RhIII-alkyl species B and
the subsequent formation of the RhIII-acyl species C.
9
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European Journal of Inorganic Chemistry
Scheme 3. Oxidative addition of iodomethane followed by migratory insertion of CO [X,O-Bid= S,O-
BdiPT or N,O-ox).
The change in the IR absorbance values for the different species over the time period in which the reaction
was studied, is shown in Figure 2(a). The seemingly ‘direct’ conversion of the starting complex 2 to the
RhIII-acyl complex is evident by comparing the disappearing and formation rates of the two seperate spe-
cies. Note that the reaction was completed after less than 60 min, yielding a pseudo first-order rate for the
disappearance of the starting complex [Rh(S,O-BdiPT)(CO)(PPh3)] (1.840.01) x10-3 s-1, very similar to
the rate of formation of the acyl species [Rh(S,O-BdiPT)(COMe)(I)(PPh3)] (2.010.02) x10-3 s-1). The
difference between these two values is attributed to baseline drift during the measurement and the small
contribution from the formation of the intermediate RhIII-alkyl species.
This behavior has been reported previously by several authors, where the oxidative addition of iodome-
thane to rhodium complexes bearing a bidentate ligand incorporating a sulfur donor atom led primarily
to the formation of RhIII-acyl complexes.5,12 Furthermore, in these publications it was also shown that
only a small amount of the RhIII-alkyl species was observed. Recent work showed again that by chang-
ing the bidentate ligand from an S,O-BdiPT to an O,O-Bid type, the reaction can be influenced to ensure
slower acyl-formation compared to the oxidative addition.13 This was indeed the case for the N,O-ox lig-
ands, see discussion below.
10
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Figure 2. Successive IR spectra for the iodomethane oxidative addition to (a) [Rh(S,O-
BdiPT)(CO)(PPh3)] (2) under pseudo first-order conditions in CH2Cl2 at 25 °C. Spectra recorded at time
intervals of 6 min., with [Rh] = 0.0105 M, [MeI] = 0.4 M, T = 25 °C, total time = 1 hr. Insert (i) illustrates
the IR absorbance change vs. time plot; pseudo first-order rate constants indicate that the disappearance
of the RhI (red) is similar to the formation of RhIII-acyl (green) with RhIII-alkyl (blue); (b) [Rh(N,O-
ox)(CO)(PPh3)] (7), which illustrates the conversion of the RhI starting complex (1965 cm-1) to the RhIII-
alkyl species (2057 cm-1). Scans were recorded at 2 min intervals, [Rh(N,O-ox)(CO)(PPh3)] = 1.1 x 10-3
M and [MeI] = 9.82 x 10-2 M. kobs(RhI )= 3.8(2) x 10-3 s-1 and kobs(RhIII) = 4.0(2) x 10-3 s-1. Insert (ii)
illustrates of the carbonyl peak change over time with the iodomethane oxidative addition to the complex
[Rh(N,O-ox)(CO)(PPh3)], in CH2Cl2 at 25ºC. Decrease in RhI(N,O-ox) (blue); formation of RhIII-alkyl
(red).
When an equilibrium is assumed for the first step in Scheme 3 (oxidative addition),14 with reductive
elimination being the reverse reaction, it follows naturally from the observed behavior that the equilib-
rium when lying to the left (small K1= k1/k-1) and the acyl-formation (k2) in combination with the rapid
pre-equilibrium of the formation of the RhIII-alkyl species essentially dictates the turnover rate as de-
fined in Eq. 1 (Scheme 3). This was the case for the S,O-BdiPT complexes.
The observed pseudo first-order formation rate constant, kobs of the RhIII-acyl species, is thus defined in
Eq. 1.14
’
kobs = K1k2[MeI]/(1 + K1[MeI]) + k-2  k2 [MeI]
(1)
11
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European Journal of Inorganic Chemistry
’
In Eq. 1, k2 = K1k2 when K1<<1, and the reverse reaction of the migratory insertion as defined by k-2 is
negligible (zero intercept in Fig. 4).
For complexes 4 and 5 similar behavior was observed, with the ‘direct’ conversion of the starting com-
plex to the RhIII-acyl complex as most striking feature. However, in the reaction of complex 3 with io-
domethane, a more significant amount (although still quite low) of the RhIII-alkyl intermediate was ob-
served (see Supporting Information). Apparently, the equilibrium of the oxidative addition/reductive
elimination does not lie as far to the left as with the other complexes. Additionally, two signals at-
tributed to RhIII-alkyl species were observed (see Supplementary Information). This indicates that two
isomers are probably formed, corresponding to potentially cis- and trans-addition of iodomethane.
Preliminary kinetics of the formation of the RhIII-alkyl intermediate was attempted by stopped-flow
measurements with UV/vis detection, but the absorbance changes were not significant enough to allow
for accurate interpretation. However, in spite of the fact that these first reactions could not be studied
with accuracy, they were clearly and distinctly different from the mixing reaction in the stopped-flow, of
which the conversions were in agreement with the amounts identified on the Infrared Spectroscopy
stack-plots (i.e., Fig. 2, as well as Supporting Information). Moreover, these reactions were a few sec-
onds and clearly much faster than the formation of the RhIII-acyl species (several minutes). They are
also more pronounced at higher [MeI] indicating they are equilibrium reactions. The conclusion is thus
that formation of the RhIII-alkyl species is fast as shown in Scheme 3, and that Eq. 1 adequately de-
scribes the kinetics.
The conversion of the RhI- to the RhIII-form could also be observed in 31P NMR for all four complexes
(see Fig. 3 and Supporting Information), and agrees very well with that observed from the IR data.
Kinetic and spectroscopic data (where applicable) obtained from Eq. 1 for the S,O-BdiPT complexes as
described above, are summarized in Table 3 together with the Bronsted pKa of the free phosphine, as
well as the enthalpies and entropies of activation (vide infra).
[Rh(N,O-ox)(CO)(PR3)] complexes. However, interestingly in the case of the N,O-ox ligand com-
plexes, a different scenario is observed from the time resolved IR spectroscopic results, see Fig. 2(b).
The significant amount of RhIII-alkyl intermediate is clear [(CO)=2057 cm-1]. This behavior is con-
firmed by the time resolved 31P NMR spectra, see Fig. 3(b). Clearly, the RhIII-alkyl intermediate species
12
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
in this case is prominently visible on the 31P spectra (as was the case on the IR data; see Fig. 3(b)), with
the formation of the RhIII-acyl species (C in Scheme 3) being formed thereafter.
In this case, the oxidative addition of iodomethane is simply described by Eq. 2, which is obtained for
the formation of B Scheme 3 from A via a simple equilibrium as shown previously.13,14 However, in this
case this equilibrium clearly lies significantly towards B.
kobs = k1[MeI] + k-1
(2)
Thus, Eq. 2 was used to obtain the rates of oxidative addition for the N,O-ox complexes and are summa-
rized in Table 3.
Figure 3. (a) Observed 31P{1H} NMR spectra of the iodomethane oxidative addition to [Rh(S,O-
BdiPT)(CO)(PPhCy2)] in CD2Cl2. Time intervals in minutes indicated on the left of spectra. [Rh] = 0.081
1
M, [MeI] = 0.4 M, T = 25 oC; total time = 8.8 hrs. 31P NMR were recorded with the default setting of H
decoupling using the WALTZ16 method, typical 128 scans, a sweep width of 400.5 ppm (48661.8 Hz),
delay time (D1) of 2 sec. and 64 K Points. (b) Observed 31P{1H} NMR spectra of the [Rh(N,O-
13
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
ox)(CO)(PPh3)] complex undergoing iodomethane oxidative addition to form alkyl intermediate(s)
[Rh(N,O-ox)(CH3)(I)(CO)(PPh3)] and migratory insertion to form a small amount of the RhIII-acyl prod-
uct, in acetone at 25ºC. a) [Rh] = 1.44 x 10-2 M. b) [Rh] = 1.34 x 10-1 M, [MeI] = 1.05 x 10-1 M. c) [Rh]
= 1.26 x 10-1 M, [MeI] = 2.04 x 10-1 M. d) [Rh] = 1.06 x 10-1 M, [MeI] = 4.24 x 10-1 M. e-f) [Rh] = 7.71
x 10-2 M, [MeI] = 7.52 x 10-1 M.
Interestingly Fig. 3(b) shows a second alkyl species (labeled Alkyl 2) to form later [only some 20% con-
version compared to Alkyl 1 (via/ concurrent with acyl species) to Alkyl 2 after >10h] in the total reac-
tion. In contrast Alkyl 1 (monitored in the kinetic study), formed completely in only some 30 min. with
only small amounts of RhIII-acyl being present, see Fig. 2(b) and in particular, Fig. 3(b), spectrum (b).
Alkyl 2 is assumed to be the trans isomer [Me vs. I coordination], since the cis isomer is formed first in
less steric demanding bidentate ligand systems.3,8 Thus, the kinetics and dynamics of Alkyl 2, which is
formed more than one order-of-magnitude slower than Alkyl 1, was considered beyond the scope of the
current study and is therefore not considered further herein.
An important observation to be made from Table 3 is that the spectral data for complexes 2 – 5 that are
used to gauge electron-density on the metal center are not all reflected in the observed reaction rates.
On the basis of the phosphine basicity, it is expected that the rates of oxidative addition would increase
when going from complex 2 to complex 5. 15 However, no such trend is observed in the reaction rates. It
appears that the steric bulk of the phosphine ligand beyond a certain point has a significant influence, as
well as its basicity. Only a net reaction is observed, which represents a compound observed rate constant
as indicated by Eq. 1. This is best illustrated when the reaction rate observed in IR is plotted with re-
spect to the iodomethane concentration, with the solid lines representing the least-squares fit of the data
(Fig. 4(a)). An eight times de-activation of specifically complex 4 compared to complex 3 was observed,
with complexes 2 and 5 being intermediate. 3,14
Surprisingly, a very similar trend was observed within the [Rh(N,O-ox)(CO)(PR1R2R3)] complexes (7-
10), although a different reaction [direct iodomethane oxidative addition; Fig. 2(b) and 3(b)] compared
to the [Rh(S,O-BdiPT)(CO)( PR1R2R3)] complexes [overall formation of RhIII-acyl species, see Fig.
4(b). The N,O-ox complexes were approximately one order-of-magnitude progressively faster than the
corresponding S,O-BdiPT complexes. This will be highlighted further later in the Discussion.
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European Journal of Inorganic Chemistry
(a)
(b)
Figure 4. Effect of phosphine ligands on the observed rate constants kobs vs. [MeI] for oxidative addition
to (a) Rhodium(I)-S,O-BdiPT complex 2 - 5, [Rh] = 0.010 M in CH2Cl2/ at 25°C; (b) rhodium(I)-N,O-ox
for the formation of [Rh(N,O-ox)(CH3)(I)(CO)(PR3)] for 7-10, in acetone at 25ºC. [Rh(N,O-
ox)(CO)(PPh3)] = 2.394 x 10-4 M, [Rh(N,O-ox)(CO)(PPh2Cy)] = 2.119 x 10-4 M, [Rh(N,O-
ox)(CO)(PPhCy2)] = 2.230 x 10-4 M, [Rh(N,O-ox)(CO)(PCy3)] = 2.276 x 10-4 M, λ= 380 nm.
Table 3. Kinetic, spectroscopic and thermodynamic data for the iodomethane oxidative addition/ migra-
tory insertion at 25 °C to 2 - 5 to [Rh(S,O-BdiPT)(CO)(PR3)] in CH2Cl2; and 7 - 10 [Rh(N,O-
ox)(CO)(PR3)] (PR3= PPh3, PPh2Cy, PPhCy2, PCy3) complexes, in acetone.
Cone
anglec
a
b
103 k'2
103k1
νCO
(cm-1) (ppm) (Hz)
δ 31P
1JRh-P
pKa d free
∆H
∆S
Complex
(M-1s-1)
(M-1s-1)
phosphine
(kJ/mol) (J/K.mol)
(°)
2
-
1979 38.0
1972 45.3
1969 49.3
1963 49.9
1965 41.2
1968 52.8
1952 53.6
1946 54.8
152
149
149
146
164
163
161
156
145
153
-
3.28
5.87
8.46
11.3
3.28
5.87
8.46
11.3
5.10.3
422
421
481
462
-1477
-1463
-1444
-1406
3
-
6.40.3
4
-
0.820.08
5
-
156
156
151
-
2.80.02
-
-
-
-
7
39 1
862
8 1
28 1
58.90.2 -74.10.06
8
-
-
-
-
-
-
9
167
10
a Calculated from Fig. 4(a) using Eq. 1; b Obtained from least-squares fitting of the data in Fig. 4(b) to
Eq. 2; c Calculated from solid state data; d Obtained from Ref. 16
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To enable the calculation of the activation parameters for the overall reaction on complexes 2 - 5, a tem-
’
perature study was performed. From the obtained values for k2 , an Eyring plot was obtained (Fig. 5),
which in turn was used to calculate the activation enthalpy and entropy (Table 3). Similar calculations
were performed for 7 (using the k1 data, see Fig. 4(b); Supporting Information) for which the values are
also reported in Table 3.
Figure 5. Eyring plot for the oxidative addition of iodomethane / methyl migration to [Rh(S,O-
BdiPT)(CO)(PR3)] (2 – 5) in CH2Cl2.
The data for the reactions suggest that overall they proceed with large negative entropies of activation,
which corresponds to the associative character of the reaction. This holds for both the formation of the
octahedral intermediate RhIII-alkyl species, and the subsequent formation of the square-pyramidal RhIII-
acyl complex. Furthermore, there is a hint that ∆S becomes less negative for complexes bearing more
basic phosphine ligands, although it has to be noted that the differences are not significant.
These results suggest that an increase in the electron-donating properties of the phosphine ligand led to
an increase in order in the transition state by forming stronger bonds between the metal centre and the
entering iodomethane, typical of oxidative addition reactions. 7 The enthalpy of activation is similar for
all four complexes, and the values are in a range often found for this reaction, and correlates also di-
rectly with the alkyl formation for the beta-diketone complexes with the corresponding four phosphine
3,14
ligands listed here, as reported previously.
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Finally, the data in Table 3 for the S,O-BdiPT and N,O-ox complexes were normalized [considering
PPh3=1, and adjusting all the other three rate constants accordingly], and plotted together with that ob-
served for the [Rh(O,O-acac)(CO)(PR3)] (PR3= PPh3, PPh2Cy, PPhCy2, PCy3) from literature,3 as illus-
trated in Fig. 6. The relative reactivity of RhI-X,O-Bid complexes, where X=O, S or N, follows a surpris-
ing similar reactivity relationship when stepwise varying the PPh3, PPh2Cy, PPhCy2 and PCy3 tertiary
phosphine ligands. Superficially, it seems as if the differences within the S,O-BdiPT series is less signif-
icant than that in the O,O-acac and the N,O-ox series. This might be linked to the fact that in the former
the rate constants used (k2’) are combined constants, for which there might be some offset in the other
steps making up the constant used. Be that as it may, the similar tendency for all three systems is clear,
and indicates the surprising net difference between PPh2Cy and PPhCy2, wherein the latter clearly has a
significant decelerating effect compared to the former.
This will be explored further in future with other model systems, which might prove valuable to exploit
the unexpected acceleration/ deceleration by the PPh2Cy and PPhCy2 ligands, respectively.
Figure 6. Normalized reaction rate constants (relative to the PPh3, =1) for X,O-Bid = oxinato (N,O-ox),
acetylacetonato (O,O-acac) and thioureato (S,O-BdiPT); PR3 where R= Ph or Cy for all complexes at 25
°C.
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Conclusions
The synthesis and characterization of [Rh(S,O-BdiPT)(CO)(PR1R2R3)] and [Rh(N,O-
ox)(CO)(PR1R2R3)] (PR1R2R3= PPh3, PPh2Cy, PPhCy2 and PCy3) complexes, including four single
crystal structure determinations (compounds 2, 3, 5 and 10) were performed, followed by a detailed
mechanistic investigation into the iodomethane oxidative addition thereto.
The oxidative addition to a range of [Rh(S,O-BdiPT)(CO)(PR1R2R3)] complexes (S,O-BdiPT = N-ben-
zoyl-N’,N’-diphenylthioureato, R = phenyl or cyclohexyl) was well-defined and led primarily to the ‘di-
rect’ formation of the RhIII-acyl species, [Rh(S,O-BdiPT)(COMe)(I)(PR1R2R3)], via the RhIII-alkyl inter-
mediate, [Rh(S,O-BdiPT)(Me)(CO)(I)(PR1R2R3)], which was only observed in small quantities. This
was manifested in a fast equilibrium for the oxidative addition/reductive elimination which lies to the
left side, coupled with a slower, rate-determining migratory insertion step. The reason for this was con-
cluded to be in the steric effect exerted by primarily the S,O-BdiPT ligand and was nicely supported by
the solid state data.
The reaction rate for the different complexes increased in the order of [Rh(S,O-BdiPT)(CO)(PPhCy2)] <
[Rh(S,O-BdiPT)(CO)(PCy3)] < [Rh(S,O-BdiPT)(CO)(PPh3)] < [Rh(S,O-BdiPT)(CO)(PPh2Cy)].
However, in the case of the [Rh(N,O-ox)(CO)(PR1R2R3)] complexes [small N,O-ox steric effect], the
formation of the RhIII-alkyl species as intermediate was well defined and significant amounts were ob-
served.
The exact same order with respect to the PR3 ligand was observed within the [Rh(N,O-
ox)(CO)(PR1R2R3)] complexes, although the second order forward rate constants for the N,O-ox com-
plexes were approximately one order-of-magnitude progressively larger than for the corresponding S,O-
BdiPT complexes. This order of reactivity was concluded to be the result of a combined effect of the ste-
ric (as primarily manifested in the X-Rh-O bite angles) and electronic properties of the ligands.
In both the S,O-BdiPT and N,O-ox ligand systems an associative activation is inferred from the large
negative ∆S values. Moreover, the relative reactivity of RhI-X,O-Bid complexes, where X=O, S or N,
follows a surprising similar reactivity relationship when stepwise varying the PPh3, PPh2Cy, PPhCy2
and PCy3 tertiary phosphine ligands, suggesting a clear systematic behavior by the PR3 ligands, inde-
pendent of the X,O-Bid ligand at the Rh(I) metal centre.
Experimental section
General Procedures and Instrumentation. NMR spectroscopic data was acquired on a Bruker Advance
II 600 MHz spectrometer. 1H NMR data are listed in the order: chemical shift (δ, reported in ppm and
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
referenced to the residual solvent peak of DMSO-d6 [δ = 2.50 ppm] or CD2Cl2 [δ = 5.33 ppm]), multi-
plicity, number of protons, assignment, coupling constant (J, in Hz). Proton decoupling experiments
were used to assist in the assignment of proton signals. Proton decoupled 13C NMR data are listed in the
order: chemical shift (δ, reported in ppm and referenced to the residual solvent peak of DMSO-d6 [δ =
39.5 ppm] or CD2Cl2 [δ = 77.0 ppm]), multiplicity, number of carbons, assignment, coupling constant
(J, in Hz) where appropriate. HMQC experiments were performed to assist in the allocation of signals.
Proton and carbon decoupled 31P NMR data are listed in the order: chemical shift (δ, reported in ppm
and referenced to triphenylphosphine oxide [δ = 29.9 ppm]), multiplicity, number of phosphorus atoms,
coupling constant (J, in Hertz) where appropriate. FT-IR spectra were recorded on a Bruker Tensor 27
spectrophotometer in the range of 3000-600 cm-1 via the ATR.
Synthesis. N-benzoyl-N’,N’-(diphenyl)thiourea (S,O-BdiPT)H (1) was synthesized according to a modi-
fied literature procedure:9 ammonium thiocyanate (1.31 g, 0.017 mol) was dissolved in hot acetone (10
mL). Benzoyl chloride (2 mL, 0.017 mol) was then added drop-wise upon which the reaction mixture
changed to a milky, light yellow solution. The by-product ammonium chloride precipitated as the reac-
tion proceeded. After 20 minutes the reaction mixture was filtered, the filtrate was collected and heated.
Diphenylamine (0.017 mol) was then slowly added to the solution, after which the reaction mixture was
allowed to stir for 30 minutes. The thiourea ligand was then precipitated with distilled water, collected
by filtration and washed with a few portions of water. The product was then recrystallized from ethanol.
The product was obtained as a white solid in a yield of 98%. 1H NMR (600 MHz, DMSO-d6, 25 °C): δ
11.19 (s, 1H, CONHCS), 7.63 (d, 2H, o-benzoyl-H, JH-H = 8.4 Hz), 7.51 (t, 1H, p-benzoyl-H, JH-H = 7.3
Hz), 7.39 (t, 2H, m-benzoyl-H, JH-H = 7.8 Hz), 7.36- 7.35 (m, 4H, m-Ph-H), 7.30-7.28 (m, 4H, o-Ph-H),
7.23- 7.21 (m, 2H, p-Ph-H). 13C{1H} NMR (151 MHz, DMSO-d6, 25 °C): δ 184.5 (s, 1C, thiourea),
167.3 (s, 1C, amide), 145.6 (s, 2C, i-Ph-C), 132.7 (s, 1C, i-benzoyl-C), 132.3 (s, 1C, p-benzoyl-C),
129.1 (s, 4C, o-Ph-CH), 128.2 (s, 2C, o-benzoyl-CH), 128.1 (s, 2C, m-benzoyl-CH), 127.0 (s, 2C, p-Ph-
CH), 126.8 (s, 4C, m-Ph-CH). IR νmax ATR/cm-1: 3215-3125 (broad, N-H); 1691 (C=O); 1504-1447
(broad, phenyl rings); 1354 (aromatic amide C-N); 1255 (C=S); 1183, 1160 and 1072 (C-N). Elemental
analysis (%): Found C, 72.1; H, 5.0; N, 8.35. Calculated for C20H16N2SO: C, 72.3; H, 4.85; N, 8.4.
General synthesis of rhodium(I) S,O-BdiPT carbonyl phosphine complexes. RhCl3.xH2O (125.9 mg,
0.478 mmol) was heated in DMF (5 mL) at 180 °C to produce tetracarbonyl-dichloro-dirhodium(I).10 N-
benzoyl-N’,N’-(diphenyl)thiourea (S,O-BdiPTH) 1 eq, 0.478 mmol) was slowly added to the cooled so-
lution, which caused the colour of the solution to change from yellow to a bright orange, indicating the
19
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European Journal of Inorganic Chemistry
formation of the expected [Rh(S,O-(S,O-BdiPT)(CO)2] complex. After about 10 minutes the complex
was precipitated as a bright orange solid by the addition of ice water. After centrifugation the complex
was taken up in diethyl ether and carefully removed from the excess water. Phosphine ligand (1 eq,
0.478 mmol) was added slowly to the ether solution. After a short time the desired complex [Rh(S,O-
BdiPT)(CO)(PR1R2R3)] precipitated from solution as a yellow microcrystalline solid. The product was
filtered and washed with several portions of ether. Crystals suitable for X-ray analysis were obtained by
redissolving the complex in dichloromethane and layering the solution with hexane.
Rhodium(I) (S,O-(N-benzoyl-N’,N’-diphenylthiourea) carbonyl triphenylphosphine [Rh(S,O-
BdiPT)(CO)(PPh3)] (2). The product was obtained as a yellow microcrystalline solid in a yield of 65%.
1H{31P} NMR (600 MHz, CD2Cl2, 25 °C): δ 7.69-7.66 (m, 5H, o-benzoyl-H, p-PPh-H), 7.47-7.38 (m,
16H, m-benzoyl-H, o-NPh-H, m-NPh-H, o-PPh-H), 7.33-7.31 (m, 2H, p-NPh-H), 7.19 (tt, 1H, p-ben-
zoyl-H, 3JH-H = 7.5 Hz, 4JH-H = 1.5 Hz) 6.89-6.82 (m, 6H, m-PPh-H). 13C{1H} NMR (151 MHz, CD2Cl2,
25 °C): δ 191.1 (dd, 1C, carbonyl, 1JRh-C = 74.1 Hz, 2JC-P = 21.1 Hz), 178.9 (s, 1C, thiourea), 170.7 (s,
1C, amide), 145.8 (s, 2C, i-NPh-C), 137.5 (s, 1C, i-benzoyl-C), 134.9 (d, 6C, o-PPh-CH, 3JC-P = 12.1
Hz), 133.4 (d, 3C, i-PPh-C, JC-P = 44.7 Hz), 131.7 (s, 1C, p-benzoyl-CH), 130.9 (s, 3C, p-PPh-CH),
130.0 (s, 2C, o-benzoyl-CH), 129.8 (s, 4C, o-NPh-CH), 129.0 (s, 4C, m-NPh-CH), 129.0 (s, 6C, m-PPh-
CH), 128.0 (s, 2C, m-benzoyl-CH), 127.7 (s, 2C, p-NPh-CH). 31P{1H, 13C} NMR (121 MHz, CD2Cl2,
25 °C): δ 38.2 (d, 1JRh-P = 152.3 Hz). IR νmax CH2Cl2,/cm-1: 1979 (CO), νmax ATR/cm-1: 1963 (CO). Ele-
mental analysis (%): Found C, 64.6; H, 4.1; N, 3.95. Calculated for RhC39H30N2SO2P: C, 64.6; H, 4.2;
N, 3.9.
Rhodium(I) (S,O-(N-benzoyl-N’,N’-diphenylthioureato) carbonyl cyclohexyldiphenylphosphine
[Rh(S,O-BdiPT)(CO)(PPh2Cy)] (3). The product was obtained as a yellow crystalline solid in a yield of
60%. 1H{31P} NMR (600 MHz, CD2Cl2, 25 °C): δ 7.83-7.81 (m, 4H, o-benzoyl-H, p-PPh-H), 7.45-7.44
(m, 8H, o-NPh-H, m-NPh-H), 7.43-7.38 (m, 6H, m-benzoyl-H, o-PPh-H), 7.33 (m, 2H, p-NPh-H), 7.25-
7.22 (m, 1H, p-benzoyl-H), 6.95-6.94 (m, 4H, m-PPh-H), 2.75-2.73 (m, 1H, 1-Cy-H), 2.11 and 1.80 (m,
4H, 2-Cy-H, 6-Cy-H), 1.73 and 1.19 (m, 2H, 4-Cy-H), 1.45-1.41 (m, 4H, 3-Cy-H, 5-Cy-H). 13C{1H}
NMR (151 MHz, CD2Cl2, 25 °C): δ 191.4 (dd, 1C, carbonyl, 1JRh-C = 73.8 Hz, 2JC-P = 21.3 Hz), 179.2 (s,
1C, thiourea), 170.6 (s, 1C, amide), 146.9 (s, 2C, i-NPh-C), 137.7 (s, 1C, i-benzoyl-C), 134.2 (d, 4C, o-
PPh-CH, JC-P = 10.6 Hz), 132.6 (d, 2C, i-PPh-C, JC-P = 39.9 Hz), 131.6 (s, 1C, p-benzoyl-CH), 130.5 (s,
2C, p-PPh-CH), 130.0 (s, 2C, o-benzoyl-CH), 129.7 (s, 4C, o-NPh-CH), 129.0 (s, 4C, m-NPh-CH),
128.9 (s, 4C, m-PPh-CH), 128.0 (s, 2C, m-benzoyl-CH), 127.7 (s, 2C, p-NPh-CH), 35.9 (d, 1C, 1-Cy-
CH, 3JC-P = 27.6 Hz), 29.4 (s, 2C, 3-Cy-CH2, 5-Cy-CH2), 27.5 (d, 2C, 2-Cy-CH2, 6-Cy-CH2, JC-P = 12.7
20
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Hz), 26.7 (s, 1C, 4-Cy-CH2). 31P{1H, 13C} NMR (121 MHz, CD2Cl2, 25 °C): δ 45.3 (d, 1JRh-P = 149.4
Hz). IR νmax CH2Cl2/cm-1: 1972 (CO), νmax ATR/cm-1: 1966 (CO). Elemental analysis (%): Found C,
64.1; H, 5.0; N, 4.1. Calculated for RhC39H36N2SO2P: C, 64.1; H, 5.0; N, 3.8.
Rhodium(I) (S,O-(N-benzoyl-N’,N’-diphenylthioureato) carbonyl dicyclohexylphenylphosphine
[Rh(S,O-BdiPT)(CO)(PPhCy2)] (4). The product was obtained as a yellow crystalline solid in a yield of
57%. 1H{31P} NMR (600 MHz, CD2Cl2, 25 °C): δ 7.80-7.77 (m, 3H, o-benzoyl-H, p-PPh-H), 7.50-7.47
(m, 8H, o-NPh-H, m-NPh-H), 7.40-7.36 (m, 4H, m-benzoyl-H, o-PPh-H), 7.35 (m, 2H, p-NPh-H), 7.24-
7.22 (m, 1H, p-benzoyl-H), 6.92-6.90 (m, 2H, m-PPh-H), 2.69-2.67 (m, 2H, 1-Cy-H), 2.15 and 1.84 (m,
8H, 2-Cy-H, 6-Cy-H), 1.70 and 1.21 (m, 4H, 4-Cy-H), 1.47-1.43 (m, 8H, 3-Cy-H, 5-Cy-H). 13C{1H}
NMR (151 MHz, CD2Cl2, 25 °C): δ 191.0 (dd, 1C, carbonyl, 1JRh-C = 74.2 Hz, 2JC-P = 21.4 Hz), 179.0 (s,
1C, thiourea), 169.9 (s, 1C, amide), 145.40 (s, 2C, i-NPh-C), 137.4 (s, 1C, i-benzoyl-C), 135.1 (d, 2C,
o-PPh-CH, JC-P = 7.8 Hz), 131.0 (s, 1C, p-benzoyl-CH), 130.1 (s, 1C, p-PPh-CH), 129.3 (s, 2C, o-ben-
zoyl-CH), 129.1 (s, 4C, o-NPh-CH), 128.5 (broad s, 1C, i-PPh-C), 127.8 (s, 4C, m-NPh-CH), 127.7 (s,
2C, m-PPh-CH), 127.4 (s, 2C, m-benzoyl-CH), 127.0 (s, 2C, p-NPh-CH), 32.2 (d, 2C, 1-PCy-CH, 3JC-P
= 20.5 Hz), 28.6, 27.8 (s, 4C, 3-PCy-CH2, 5-PCy-CH2), 26.9, 26.7 (s, 4C, 2-PCy-CH2, 6-PCy-CH2),
26.1 (s, 2C, 4-PCy-CH2). 31P{1H, 13C} NMR (121 MHz, CD2Cl2, 25 °C): δ 49.5 (d, 1JRh-P = 149.0 Hz).
IR νmax CH2Cl2/cm-1: 1969 (CO), νmax ATR/cm-1: 1961 (CO). Elemental analysis (%): Found C, 63.7; H,
5.8; N, 4.0. Calculated for RhC39H42N2SO2P: C, 63.6; H, 5.8; N, 3.8.
Rhodium(I) (S,O-(N-benzoyl-N’,N’-diphenylthioureato) carbonyl tricyclohexylphosphine [Rh(S,O-
BdiPT)(CO)(PCy3)] (5). The product was obtained as a yellow crystalline solid in a yield of 63%.
1H{31P} NMR (600 MHz, CD2Cl2, 25 °C): δ 7.68 (dd, 2H, o-benzoyl-H, JH-H = 8.4 Hz, JH-H = 1.5 Hz),
7.44-7.43 (m, 8H, o-Ph-H, m-Ph-H), 7.37 (tt, 1H, p-benzoyl-H, 3JH-H = 7.4 Hz, 4JH-H = 1.2 Hz), 7.33-
7.31 (m, 2H, p-Ph-H), 7.21 (t, 2H, m-benzoyl-H, 3JH-H = 7.8 Hz), 2.33-2.27 (m, 3H, 1-Cy-H), 2.05 and
1.80 (d, 12H, 2-Cy-H, 6-Cy-H, 3JH-H = 12.0 Hz), 1.65 and 1.25 (m, 18H, 3-Cy-H, 4-Cy-H, 5-Cy-H).
13C{1H} NMR (151 MHz, CD2Cl2, 25 °C): δ 191.9 (dd, 1C, carbonyl, 1JRh-C = 75.2 Hz, 2JC-P = 20.7 Hz),
179.8 (s, 1C, thiourea), 171.0 (s, 1C, amide), 146.0 (s, 2C, i-Ph-C), 138.7 (s, 1C, i-benzoyl-C), 131.7 (s,
1C, p-benzoyl-CH), 130.1 (s, 2C, o-benzoyl-CH), 129.7 (s, 4C, o-Ph-CH), 129.1 (s, 4C, m-Ph-CH),
128.2 (s, 2C, m-benzoyl-CH), 127.6 (s, 2C, p-Ph-CH), 34.2 (d, 3C, 1-Cy-CH, 2JC-P = 21.1 Hz), 30.6 (s,
6C, 3-Cy-CH2, 5-Cy-CH2), 28.3 (d, 6C, 2-Cy-CH2, 6-Cy-CH2, 3JC-P = 10.7 Hz), 27.1 (s, 3C, 4-Cy-CH2).
31P{1H, 13C} NMR (121 MHz, CD2Cl2, 25 °C): δ 49.9 (d, 1JRh-P = 145.6 Hz). IR νmax CH2Cl2/cm-1: 1963
(CO), νmax ATR/cm-1: 1952 (CO). Elemental analysis (%): Found C, 62.7; H, 6.55; N, 3.9. Calculated for
RhC39H48N2SO2P: C, 63.1; H, 6.5; N, 3.8.
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
Dicarbonyl(oxinato)rhodium(I), [Rh(N,O-ox)(CO)2], (6). The complex [Rh(N,O-ox)(CO)2] was pre-
pared as reported in literature8,11 by dissolving [Rh2CO4Cl2] (100 mg, 0.257 mmol) in DMF (10 ml) and
by the drop wise addition of 8-hydroxyquinoline (82.05 mg, 0.565 mmol) in DMF (5 ml) to the stirring
reaction mixture. The product was obtained as a brown precipitate by addition of ice water, collected by
filtration and washed with water. (Yield: 74.7 mg, 94 %). 1H NMR (300 MHz, CDCl3, 25 ºC): 8.653 (d,
1H), 8.374 (d, 1H), 7.502 (m, 2H), 7.134 (m, 2H). IR KBr: νCO = 2075 and 2005 cm-1.
Carbonyl(triphenylphosphine)(oxinato)rhodium(I), [Rh(N,O-ox)(CO)(PPh3)], (7). The complex
[Rh(N,O-ox)(CO)(PPh3)] was prepared as reported in literature8,11 by drop-wise addition of PPh3 (30
mg, 0.114 mmol) in acetone (10ml) to a stirring solution of [Rh(N,O-ox)(CO)2] (31 mg, 0.103 mmol) in
acetone (40 ml). Solvent evaporation to dryness yielded the product as yellow crystals. (Yield: 51 mg,
93 %). 1H NMR (300 MHz, CDCl3, 25 ºC): 8.771 (d, 1H), 8.248 (d, 1H), 7.806 – 7.646 (m, 8H), 7.482 –
7.373 (m, 9H), 6.963 (d, 1H), 6.88 (d, 1H). 1J(Rh-P) = 164 Hz. IR KBr: νCO = 1965 cm-1. λmax(acetone)
= 420 nm (ε = 3351).
Carbonyl(cyclohexyldiphenylphosphine)(oxinato)rhodium(I), [Rh(N,O-ox)(CO)(PPh2Cy)], (8). The
complex [Rh(N,O-ox)(CO)(PPh2Cy)] was prepared according to the procedure described for synthesis of
[Rh(N,O-ox)(CO)(PPh3)]. By addition of PPh2Cy (17.6 mg, 0.064 mmol) to [Rh(N,O-ox)(CO)2] (18 mg,
0.059 mmol), the product was obtained as a yellow crystalline solid. (Yield: 25 mg, 77 %). 1H NMR (300
MHz, CDCl3, 25 ºC): 8.717 (s, 1H), 8.225 (d, 1H), 7.866 – 7.417 (m, 12H), 6.918 (dd, 2H), 1.810 – 1.273
(m, 11H). 1J(Rh-P) = 163 Hz. IR KBr: νCO = 1959 cm-1. λmax(acetone) = 420 nm (ε = 4512).
Carbonyl(dicyclohexylphenylphosphine)(oxinato)rhodium(I), [Rh(N,O-ox)(CO)(PPhCy2)], (9). The
complex [Rh(N,O-ox)(CO)(PPhCy2)] (9) was synthesised according to the procedure described for syn-
thesis of [Rh(N,O-ox)(CO)(PPh3)]. By addition of PPhCy2 (18 mg, 0.069 mmol) to [Rh(N,O-ox)(CO)2]
(19 mg, 0.062 mmol), the product was obtained as a yellow solid. (Yield: 28 mg, 82 %). 1H NMR (300
MHz, CDCl3, 25 ºC): 8.819 (s, 1H), 8.612 (d, 1H), 7.924 – 7.868 (m, 2H), 7.501 – 7.459 (m, 5H), 6.784
1
(d, 1H), 1.827 – 1.728 (M.14H), 1.469 – 1.334 (m, 8H). J(Rh-P) = 161 Hz. IR KBr: νCO = 1952 cm-1.
λmax(acetone) = 420 nm (ε = 5430).
Carbonyl(tricyclohexylphosphine)(oxinato)rhodium(I), [Rh(N,O-ox)(CO)(PCy3)], (10). The complex
[Rh(N,O-ox)(CO)(PCy3)] (10) was prepared according to the procedure described for synthesis of
[Rh(N,O-ox)(CO)(PPh3)]. By addition of PCy3 (20 mg, 0.072 mmol) to [Rh(N,O-ox)(CO)2] (19 mg, 0.059
mmol), the product was obtained as a yellow crystalline solid. (Yield: 20 mg, 62 %). 1H NMR (300 MHz,
CDCl3, 25 ºC): 8.716 (s, 1H), 8.187 (d, 1H), 7.396 – 7.290 (m, 2H), 6.855 (dd, 2H), 2.163 – 1.311 (m,
33H). 1J(Rh-P) = 156 Hz. IR KBr: νCO = 1946 cm-1. λmax(acetone) = 420 nm (ε = 4224).
22
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
X-ray Data Collection, Reduction, and Refinement. Initial unit cell and data collections were per-
formed on a Bruker X8 Apex II 4K Kappa CCD diffractometer using graphite monochromated Mo Kα
radiation (λ = 0.70926 Å) with ω- and φ-scans at 100(2) K as well as the Apex2 software package.17 The
optimum measurement method to collect more than a hemisphere of reciprocal space was predicted by
COSMO.18 Frame integration and data reductions were performed using the SAINT-Plus and XPREP
software packages,1619 and a multi-scan absorption correction was performed on the data using
SADABS. The structures were solved by the direct methods package SIR97,20 and refinement using the
WinGX software package21 incorporating SHELXL.22 All non-hydrogen atoms were refined anisotropi-
cally. All H-atoms were positioned geometrically and refined using a riding model with fixed C-H dis-
tances of 0.95 Å (CH) [Uiso(H) = 1.2Ueq] for aromatic H-atoms and 0.98 Å (CH) [Uiso(H) = 1.2Ueq] for
methyl H-atoms as well as fixed N-H distances of 0.88 Å (NH) [Uiso(H) = 1.2Ueq]. Molecular diagrams
were drawn using the Mercury package23 with a 30% thermal envelope probability for non-hydrogen
atoms.
Kinetic Experiments. All kinetic experiments were carried out in air and all solvents were pre-dried
over aluminium oxide and distilled. 1H, 13C and 31P NMR spectra were recorded on either 300 MHz and
600 MHz Bruker spectrometers. The 13C, 31P and 1H FT-NMR spectra were recorded at 150.96, 243.0
and 600.28 MHz respectively on a Bruker AXS 600 MHz at 25°C chemical shifts are reported in ppm.
13C NMR spectra were calibrated relative to the 13C resonances for CD2Cl2 and to tetramethylsilane
(TMS) and 80% H3PO4 for 1H and 31P respectively. Alternatively, the 1H (300MHz) and 31P (121.495
MHz) NMR spectra were also recorded on a BRUKER advance DPX 300 spectrometer at 25 ˚C in
CD2Cl2 solution. Chemical shifts were referenced with respect to tetramethylsilane (TMS) and 80%
H3PO4 for 1H and 31P respectively. 31P NMR were recorded with the default setting of 1-H decoupling
using the WALTZ16 method, typical 64 or 128 scans, a sweep width of 400.5 ppm (48661.8 Hz) a delay
time (D1) of 2 sec. and 64 K Points.
FT-IR spectra were recorded as liquid samples in dry organic solvents (toluene or dichloromethane) in a
NaCl cell on a Bruker Tensor 27 spectrometer in the range of 2350-1600 cm-1, equipped with a tempera-
ture cell regulator accurate within 0.3 °C. UV/Vis absorbance spectra were collected on a Varian Cary
50 Conc spectrophotometer in a 1.000 ± 0.001 cm quartz cuvette, which was equipped with a
23
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
temperature cell regulator accurate within 0.1 °C. Kinetic data was analyzed with the Scientist software
package.24
Associated content
Supporting Information
X-ray crystallographic data in CIF format and has been deposited at the Cambridge Crystallographic Data
Centre for 2, 3, 5 and 10, as CCDC 1827388-1827391. This information is available free of charge via
the Internet at the Cambridge Crystallographic Data Centre; http://www.ccdc.cam.ac.uk/. Additional fig-
ures and kinetic are included in the Supplementary Information deposited at the Journal’s editorial office.
Author information
Corresponding Author
roodta@ufs.ac.za
Notes
The authors declare no competing financial interest.
Acknowledgment
The authors thank SASOL, the South African NRF and THRIP, the Swiss National Science Foundation,
and the University of the Free State Research Fund and the Materials and Nanosciences Research Cluster
for financial support. The views expressed do not necessarily represent that of the NRF.
24
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10.1002/ejic.201800293
European Journal of Inorganic Chemistry
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