Palladium(II) complexes bearing mixed N^N^X (X?=?O and S) tridentate ligands as pre-catalysts for the methoxycarbonylation of selected 1-alkenes

Article abstract of DOI:10.1016/j.poly.2017.09.046

The methoxycarbonylation of selected 1-alkenes catalyzed by various neutral and cationic palladium(II) complexes, containing mixed N^N^X (X = O and S) tridentate ligands 2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-6-(phenoxymethyl)pyridine (L1), 2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-(phenoxymethyl)pyridine (L2), 2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-6-(phenylthiomethyl)pyridine (L3), 2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-(phenylthiomethyl)pyridine (L4), has been investigated. Neutral complexes, [(?²-L1)Pd(CH₃)(Cl)] (1a), [(?²-L2)Pd(CH₃)(Cl)] (2a), [(?²-L3)Pd(CH₃)(Cl)] (3a), [(?²-L4)Pd(CH₃)(Cl)] (4a), and the salts, [(?³-L3)Pd(CH₃)][BAr₄^F] (3c) and [(?³-L4)Pd(CH₃)][BAr₄^F] (4c), underwent complete decomposition during the reaction to palladium black and showed no catalytic activity. However, the addition of PPh₃ to the reaction dramatically increased the catalytic activity. On the other hand, the salts, [(?²-L1)Pd(CH₃)(PPh₃)][BAr₄^F] (1b), [(?²-L2)Pd(CH₃)(PPh₃)][BAr₄^F] (2b), [(?²-L3)Pd(CH₃)(PPh₃)][BAr₄^F] (3b) and [(?²-L4)Pd(CH₃)(PPh₃)][BAr₄^F] (4b), showed good conversion of the selected olefins to branched and linear esters without PPh₃. Addition of PPh₃ to reactions with 1b-4b significantly improved catalytic activity. All decomposition of complexes led to the formation of the known palladium complexes, [Pd(PPh₃)₂(Cl)(CH₃)] and [Pd(PPh₃)₂Cl₂]. The decomposition of all palladium complexes could be followed by NMR studies and [Pd(PPh₃)₂Cl₂] could be isolated from the crude methoxycarbonylation reaction.

Full text of DOI:10.1016/j.poly.2017.09.046

Polyhedron 138 (2017) 249–257
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Palladium(II) complexes bearing mixed N^N^X (X = O and S) tridentate
ligands as pre-catalysts for the methoxycarbonylation of selected
1-alkenes
⇑
Kamlesh Kumar, James Darkwa
Department of Chemistry, University of Johannesburg, Auckland Park Kingsway Campus, Auckland Park 2006, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 July 2017
Accepted 30 September 2017
Available online 7 October 2017
The methoxycarbonylation of selected 1-alkenes catalyzed by various neutral and cationic palladium(II)
complexes, containing mixed N^N^X (X = O and S) tridentate ligands 2-[(3,5-dimethyl-1H-pyrazol-1-yl)
methyl]-6-(phenoxymethyl)pyridine
(L1),
2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-(phe-
noxymethyl)pyridine (L2), 2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-6-(phenylthiomethyl)pyridine
(
L3), 2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-(phenylthiomethyl)pyridine (L4), has been investi-
Keywords:
Methoxycarbonylation
2
2
2
gated. Neutral complexes, [(ĸ -L1)Pd(CH
3
)(Cl)] (1a), [(ĸ -L2)Pd(CH
3
)(Cl)] (2a), [(ĸ -L3)Pd(CH
3
)(Cl)] (3a),
2
3
)][BArF
3
F
[(ĸ -L4)Pd(CH
3
)(Cl)] (4a), and the salts, [(ĸ -L3)Pd(CH
3
4
] (3c) and [(ĸ -L4)Pd(CH
3
)][BAr
4
] (4c),
1
-Alkenes
underwent complete decomposition during the reaction to palladium black and showed no catalytic
activity. However, the addition of PPh
Palladium pre-catalysts
Stability
Linear and branched esters
3
to the reaction dramatically increased the catalytic activity. On
2
)][BArF
2
3 3 4
)(PPh ] (2b), [(ĸ -L3)
)][BArF
2
the other hand, the salts, [(ĸ -L1)Pd(CH
3
)(PPh
] (3b) and [(ĸ -L4)Pd(CH )(PPh
olefins to branched and linear esters without PPh
improved catalytic activity. All decomposition of complexes led to the formation of the known palladium
complexes, [Pd(PPh (Cl)(CH )] and [Pd(PPh Cl ]. The decomposition of all palladium complexes could
3
4
] (1b), [(ĸ -L2)Pd(CH
)][BArF
2
)][BAr
F
] (4b), showed good conversion of the selected
to reactions with 1b-4b significantly
Pd(CH
3
)(PPh
3
4
3
3
4
3
. Addition of PPh
3
)
3 2
3
3
)
2
2
be followed by NMR studies and [Pd(PPh
reaction.
3 2
) Cl
2
] could be isolated from the crude methoxycarbonylation
Ó 2017 Elsevier Ltd. All rights reserved.
1
. Introduction
proposed for methoxycarbonylation of olefins, however majority of
studies have suggested hydride mechanism [1,24–28].
Palladium catalyzed methoxycarbonylation of olefins is a field
The combination of hard and soft donor sites within the same
ligand system makes ligand a good candidate for catalytic reac-
tions. In general, these ligands behave as hemi-labile ligands and
such ligands are able to stabilize the catalysts, catalyst’s intermedi-
ate and also in some cases the hemi-lability enhances selectivity
towards one product [29–37]. Mainly O or S donors in combination
with P or N donors make good hemi-labile ligands for palladium(II)
complexes [38–49]. Aguirre and co-workers have reported palla-
dium complexes bearing bidentate P^N ligands to favor the forma-
tion of branched esters in the methoxycarbonylation of olefins
[50,51]. The outstanding performances of palladium(II) complexes
were ascribed to the potentially hemi-labile behavior of the P^N
ligands in the Aguirre catalysts. Recently Bredenkamp et al. also
demonstrated the importance of hemi-lability in bidentate P^O-
donor ligands towards forming branched esters in palladium(II)
catalyzed methoxycarbonylation of 1-alkenes [52].
of research that has considerable interest [1–14]. The products of
this reaction, alkyl esters, are useful reagents for the industrial pro-
duction of solvents, detergents, cosmetics and pharmaceuticals
[
15]. In general, methoxycarbonylation reaction produces a mix-
ture of two products, linear and branched esters (Scheme 1); how-
ever, it is important to produce only one regio-isomer for industrial
applications. For example, the commercial production of non-ster-
oidal anti-inflammatory drugs (naproxen, ibuprofen and ketopro-
fen) requires the branched ester of styrene-derived substrates
[
16–20]. The most effective catalysts for methoxycarbonylation
reactions are palladium(II) complexes and regio-selectivity (linear
vs branched esters) is strongly dependent on the type of catalyst
and the reaction conditions used [19,21–24]. Two different kinds
of mechanisms, namely Pd-hydride and Pd-carboalkoxy have been
There are, however, few studies reported in which tridentate
palladium(II) complexes are used as catalysts for any kind of
⇑
Corresponding author.
E-mail address: jdarkwa@uj.ac.za (J. Darkwa).
https://doi.org/10.1016/j.poly.2017.09.046
277-5387/Ó 2017 Elsevier Ltd. All rights reserved.
0

2
50
K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
O
R
Pd catalyst
R
R
OCH3
+
O
OCH3
CO, CH OH
3
1
-Alkene
Linear
Ester
Branched
Ester
Scheme 1. Palladium catalyzed methoxycarbonylation of 1-alkene.
reaction involving CO, alkenes or alkynes [29,53–57]. We recently
reported various palladium(II) complexes of mixed tridentate
N^N^X (X = O, S and Se) ligands that showed potential in catalyz-
ing CO and alkene reactions [58]. Results of our study showed
the presence of a chalcogen donor in the tridentate ligand signifi-
cantly affected the coordination chemistry and therefore the cat-
alytic activity as well.
In present work, we report the catalytic performance of known
and new palladium(II) complexes (Scheme 2) in the methoxycar-
bonylation of 1-alkenes. This study provides insights in the under-
standing of the actual catalytic system under reaction condition
used for the reaction and also the stability of palladium pre-cata-
lysts as well as intermediates that are generated.
Fig. 1. Molecular structure of complex 2a (50% probability ellipsoids). Hydrogen
atoms have been omitted for clarity.
2
. Result and discussion
except for 4b also indicate the formation of a mixture of two pal-
ladium salts in each reaction (Figs. S2–S11). Again, we proposed
t
2.1. Synthesis and characterization of complexes
the bulky PPh
3
and Bu groups play a role in the formation of
two types of palladium salts; one where PPh
dine-N and another where CH is trans to the pyridine-N. The H
NMR peaks in compounds 3b and 4b are broad and barely visible
3
is trans to the pyri-
1
We recently reported the synthesis of the neutral palladium
complexes (1a, 3a and 4a) and the palladium salts (3c and 4c)
58]. Compound 2a has not previously been reported, and this
3
1
[
at room temperature, but fairly well-resolved at À50 °C. The
H
was synthesized from the reaction of 2-[(3,5-di-tert-butyl-1H-
NMR spectra of 3b and 4b show downfield shifts of signals for
the pyrazolyl protons compared to similar protons in the corre-
sponding neutral palladium complexes 3a and 4a. This suggested
pyrazol-1-yl)methyl]-6-(phenoxymethyl)pyridine (L2) and [Pd
1
(
COD)(Cl)(CH
3
)]. The H NMR spectrum of compound 2a (Fig. S1)
showed two sets of peaks, which is contrary to the similarly
reported neutral complex 1a. On the basis of NMR study, we pro-
posed that compound 2a is a mixture of two compounds: (a) where
Npy^Npz coordination mode of the ligands in the cations of the salts
(1b-4b), which was confirmed from the solid state structure of 4b
(Fig. 3). In the corresponding neutral complexes (3a and 4a) the
ligands show Npy^S coordination mode [58].
3
the CH is trans to the pyridine N and (b) where the Cl is trans to
the pyridine N in a 62:38 percent ratio as shown in Scheme 2.
We are able to get the single crystals for compound 2a which con-
firms that the CH is trans to the pyridine N (Fig. 1). The formation
3
Positive and negative ion mass spectrometry data were also col-
lected for palladium salts 1b-4b to establish their composition. The
positive ion mass spectra of these compounds showed the molec-
ular ion peaks of the cations along with various other peaks corre-
of a mixture of two compounds can be due to the bulkiness of the
t
+
+
Bu groups on the pyrazolyl moiety.
sponding to [MÀPd–CH
3
–PPh
3
+H] and [MÀPPh
3
]
molecular
We have also synthesized palladium salts (1b-4b) from the
fragments. All four palladium salts (1b-4b) showed a negative
reaction of the neutral palladium complexes 1a-4a with NaBArF
ion mass spectral molecular ion peak at m/z 863.0 (100%) confirm-
4
FÀ
and PPh
3
. In these palladium salts, Cl group in the corresponding
ing the presence of the counter anion, BAr
4
in the palladium salts.
neutral compound is replaced by PPh
3
and charge on the com-
Molecular structures of compounds 2a, 2b and 4b were also
determined by single crystal X-ray diffraction method as part of
the characterization of these three compounds. Single crystals
FÀ
plexes is balanced by BAr
4
counter anion (Scheme 3, Figs. 2 and
1
31
1
3). The H and P{ H} NMR spectra of all the palladium salts,
R
R
O
O
N
BAr F
N
N
N
N
4
S
Pd
N
H C Pd
N
R
R
3
Pd
Cl
Cl
N
N
H3C
Ph3P
R
R
H3C
t
t
R = CH3 (3a), Bu (4a)
R = CH3 (1a), Bu (2a)
t
R = CH3 (1b), Bu (2b)
BAr F
4
S
BAr F
N
N
4
S
N
N
Pd
H C
N
R
R
H C
Pd
R
3
N
Ph3P
3
R
t
t
R = CH3 (3c), Bu (4c)
R = CH (3b), Bu (4b)
3
Scheme 2. Palladium complexes used in the study.

K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
251
O
O
tBu
[Pd(Cl)(CH )(COD)]
N
N
3
tBu
tBu
tBu
N
Pd
N
Cl Pd
3
H C
O
N
Ether
N
N
N
N
H C
Cl
tBu
3
tBu
L2
Cl trans to pyridine N
CH3 trans to pyridine N
2a
Scheme 3. Synthesis of palladium complex 2a.
bidentate coordination mode; therefore, the four coordination sites
of the palladium centres are occupied by pyridine nitrogen (Npy),
pyrazole nitrogen (Npz), methyl and fourth coordination site is
occupied by either chloro (in 2a) or PPh (in 2b and 4b). It is clear
3
from Figs. 1–3 that the Npy and the methyl group are trans to each
other in all complexes.
The arrangement of ligands around the palladium centre in 2a is
similar to the solid structure of 1a [58]. However, the steric bulk of
the tert-butyl substituents on the pyrazolyl moiety result in the
lengthening of the Pd1–N3 (2.083(3) Å) and Pd1–C25 (2.058(4) Å)
and the shortening of the Pd1–N1 (2.189(3) Å) bond lengths in
2
a compared to 1a in which these values are 2.036(2), 2.024(2)
and 2.228(1) Å respectively [58]. The presence of tert-butyl sub-
stituents also distorts the geometry around the palladium centre
by pushing methyl group away from the ideal square planar geom-
etry. The dihedral angle between two planes (N1–N3–Pd1–Cl1 and
Cl1–C25–N3–Pd1) is 10.54° whilst similar planes in 1a has a dihe-
dral angle of 4.74°.
The palladium salts, 2b and 4b, in their solid state structures
exhibit similar arrangement of ligands around the palladium metal
centres. However, the cation and anion fragments of the salts show
severe positional disorders but were modelled satisfactory as dis-
cussed in experimental section. Both cations have comparable
bond lengths for Pd1–N1, Pd1–N3, Pd1–P1 and Pd1–C25 bonds
around palladium centre. The Pd–C bond lengths, however, are
Fig. 2. Molecular structure of complex 2b (50% probability ellipsoids). Hydrogen
FÀ
atoms and counter anion, BAr
4
have been omitted for clarity.
longer than the reported bond lengths for similar compounds,
2
e.g. [Pd(CH
3
)(PPh
3
)(ĸ -N^N)] [59–63]. The steric interaction
between the PPh
3
ligand and the PhO or PhS moiety of the
N^N^X (X = O or S) ligands in both cations is quite significant
and this manifests itself in the large P1–Pd1–N1 angle of ꢀ101°
and the angles between two planes, N1–N3–Pd1–P1 and P1–
C25–N3–Pd1, of 13.28 and 14.28° for 2b and 4b respectively. The
3
steric bulk of PPh ligand also results in the tilting of the phenoxy
and thiophenoxy groups over the pyridine ring in both compounds.
2.2. Methoxycarbonylation of 1-alkenes
Screening of all palladium complexes for methoxycarbonylation
of olefins were carried out using 1-hexene as substrate. The cat-
alytic reactions were performed at 90 °C with 5 MPa of CO pres-
sure, and a [Pd]:HCl:1-hexene ratio of 1:10:200 in methanol-
3
toluene solvent mixture and in the absence or presence of PPh .
Fig. 3. Molecular structure of complex 4b (50% probability ellipsoids). Hydrogen
Products formed in the reactions were analyzed by GC and GC–
MS. In all reactions two products were formed; namely, methyl
heptanoate (A) (linear product) and methyl 2-methylhexanoate
(B) (branched product) (Scheme 4). Generally, the activity and
selectivity in methoxycarbonylation reactions are dependent on
nature of catalyst used. It is interesting to note that all the neutral
palladium complexes (1a-4a) and the palladium salts (3c and 4c)
FÀ
atoms and counter anion, BAr
4
have been omitted for clarity.
suitable for X-ray crystallographic analyses were obtained by slow
evaporation of solvents from their corresponding solutions (CH Cl
for 2a, CH Cl -pentane-hexane for 2b and CH Cl -hexane for 4b).
2
2
2
2
2
2
The details of crystal data and structure refinement parameters
can be found in Table 1. Molecular structures of 2a, 2b and 4b with
numbering schemes are shown in Figs. 1–3. Selected bond lengths
and bond angles for these compounds are given in the Table 2. The
palladium centre in all complexes displays a distorted square pla-
nar coordination geometry as indicated by angles around the pal-
ladium centre. Ligands in these complexes exhibit Npy^Npz
did not form products in the absence of PPh
without PPh , we observed the complete decomposition of the pal-
ladium complexes to palladium black. However, when reactions
were carried out in the presence of added PPh , compounds 1a-
3
. In all these reactions
3
3
4a and 3c and 4c showed good catalytic activity (Table 3) and no
formation of palladium black.

2
52
K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
Table 1
Crystal data and structure refinement parameters for complexes 2a, 2b and 4b.
2
a
2b
4b
Empirical formula
Formula weight
T (K)
C
25
H
34ClN
3
OPd
C
75
H
61BF24
N
3
OPPd
75 3
C H61BF24N PPdS
1640.50
100(2)
534.40
100(2)
1624.44
100(2)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
P1ꢀ
triclinic
P1ꢀ
triclinic
P1ꢀ
10.241(2)
11.282(3)
12.314(2)
77.297(6)
89.995(5)
70.095(5)
1300.6(5)
2
15.231(10)
15.809(10)
17.697(12)
104.166(14)
104.870(13)
109.402(13)
3621(4)
2
15.3686(10)
15.8153(10)
17.6671(11)
103.745(2)
105.717(2)
109.939(2)
3618.2(4)
2
a
(°)
b (°)
(°)
c
3
V (Å)
Z
q
l
À3
calc
(
g cm
)
1.365
0.836
1.490
0.387
1.506
0.415
À1
(mm
)
3
Crystal size/mm
Index ranges
0.269 Â 0.193 Â 0.09
À13 ꢁ h ꢁ 6
À15 ꢁ k ꢁ 14
À16 ꢁ l ꢁ 16
19753
0.553 Â 0.331 Â 0.12
À20 ꢁ h ꢁ 20
À21 ꢁ k ꢁ 21
À23 ꢁ l ꢁ 23
97459
0.651 Â 0.358 Â 0.128
À20 ꢁ h ꢁ 20
À21 ꢁ k ꢁ 21
À23 ꢁ l ꢁ 23
69350
Reflections collected
Data/restraints/parameters
6416/0/287
1.013
18068/341/1081
1.037
18088/236/1017
1.059
Goodness-of-fit on F2
Final R indexes [I ꢂ 2
r
(I)]
R
1
= 0.0482
wR = 0.1375
= 0.0625
wR = 0.1466
R
1
= 0.0402
wR = 0.0941
= 0.0495
wR = 0.1011
R
1
= 0.0524
wR = 0.1292
1
R = 0.0663
2
2
2
Final R indexes [all data]
R
1
R
1
2
2
2
wR = 0.1390
Table 2
Selected bond lengths and bond angles for complexes 2a, 2b and 4b.
O
N
BAr4F
2a
2b
4b
Ph3P Pd
N
R
PPh3
N
Bond lengths (Å)
Pd1–N1
Pd1–N3
Pd1–Cl1/P1
Pd1–C25
N1–C13
N1–C17
N2–N3
N3–C5
O
2.189(3)
2.083(3)
2.3170(10)
2.058(4)
1.351(5)
1.349(5)
1.369(4)
1.338(4)
2.177(2)
2.168(3)
2.2324(12)
2.069(3)
1.356(3)
1.350(3)
1.385(2)
1.33(3)
2.170(2)
2.174(2)
2.2288(7)
2.078(4)
1.347(4)
1.347(4)
1.375(3)
1.339(3)
N
CH
2
Cl
2
H C
3
R
Cl Pd
N
F
R
NaBAr
4
N
H C
3
O
N
R
BAr4F
t
N
R = CH (1a), Bu (2a)
H C Pd
3
R
3
N
Ph3P
R
Bond angles (°)
Cl1/P1–Pd1–C25
Cl1/P1–Pd1–N1
Cl1/P1–Pd1–N3
C25–Pd1–N1
C25–Pd1–N3
N3–Pd1–N1
t
87.95(10)
94.91(8)
178.62(9)
169.49(13)
93.36(13)
83.88(11)
83.95(9)
83.37(12)
100.83(6)
166.04(6)
174.23(15)
95.71(14)
81.17(7)
R = CH
3
(1b), Bu (2b)
101.14(6)
167.63(5)
173.82(10)
95.37(10)
81.04(7)
S
N
F
BAr4
R
N
Ph3P Pd
N
R
R
N
N
N
PPh3
H C
3
S
CH
NaBAr4F
2
Cl
2
R
After establishing the importance of PPh
3
ligand in the
Pd
Cl
methoxycarbonylation reactions with neutral palladium com-
plexes (1a-4a) and the salts (3c and 4c), we synthesized the palla-
dium salts (1b-4b) (Scheme 3). All the palladium salts (1b-4b)
were also evaluated as catalysts in methoxycarbonylation reac-
H C
3
S
BAr4F
N
t
R = CH
3
(3a), Bu (4a)
H C
Pd
N
R
3
N
tions in the absence and presence of PPh
active for the methoxycarbonylation of 1-hexene (Table 4). How-
ever, the activity was lower in the absence of PPh as there was
palladium black formation in these reactions. Reactions in which
PPh was added showed improved catalytic activity and no forma-
3
, and were found to be
Ph3P
R
t
R = CH (3b), Bu (4b)
3
3
Scheme 4. Synthesis of palladium salts 1b-4b.
3
tion of palladium black.
From Table 3 (entry 3) and Table 4 (entries 1 and 3), it is evident
that catalysts 2a, 1b and 2b showed similar activities, therefore
catalyst 2a was used for further methoxycarbonylation reactions
with other olefins substrates; namely, 1-heptene, 1-octene, 1-
decene and styrene (Fig. 4). The catalytic activity of 2a and prod-
ucts formed were significantly affected by the nature of the olefin
substrate. Increasing the chain length of the olefin from 1-hexene
showed a gradual decrease in activity, with 1-decene being the
least active; although the ratio of branched to linear products is
not affected. When the olefin substrate was changed to styrene;
the products was predominantly methyl 2-phenylpropanoate
(88%), the branched isomer.
Interestingly confirmed the formation of [Pd(PPh ) Cl ] by sin-
3 2 2
gle crystal X-ray crystallography as one of the decomposition prod-
ucts in the catalytic reactions that involved PPh3. The formation of
[Pd(PPh
the actual species that catalyzed the methoxycarbonylation when
PPh was either added or was part of the palladium complex used
3 2 2
) Cl ] in the catalytic reactions raised the question about
3

K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
253
Table 3
Methoxycarbonylation of 1-hexene with catalysts 1a-4a, 3c and 4c.
Table 5
3 2 2
Methoxycarbonylation of styrene with catalysts 2a and [Pd(PPh ) Cl ].
Entry
Complex
PPh
3
Conversion (%)
b/la
Catalyst
PPh
3
Conversion (%)
b/la
1
2
3
4
5
6
7
8
9
1a
1a
2a
2a
3a
3a
4a
4a
3c
3c
4c
4c
2
0
2
0
2
0
2
0
2
0
2
0
88.3
0
94.7
0
83.3
0
65.7
0
82.6
0
67.23
0
40/60
0
36/64
0
37/63
0
38/62
0
37/63
0
37/63
0
2a
2a
[Pd(PPh
[Pd(PPh
2
0
2
0
100
0
98.4
87.7
88/12
0
84/16
88/12
3
)
)
2
Cl
Cl
2
]
]
3
2
2
Reaction conditions: catalyst, 0.02 mmol; styrene, 4 mmol; HCl (32%), 0.2 mmol;
PPh , 0.04 mmol; CO, 5 MPa; temperature, 90 °C, time, 24 h, MeOH (3 mL) + toluene
5 mL).
3
(
a
Branched/linear (b/l) ester ratio determined by GC-FID analysis.
1
1
1
0
1
2
of b/l esters are comparable to that of 2a in presence of PPh
can, therefore, conclude that complex 2a is not very stable in pres-
ence of PPh and HCl, and forms [Pd(PPh Cl ].
We further investigated the stability of complex 2a by NMR
spectroscopy after adding PPh3. After mixing 2a (2.67 mg, 0.005
3
. We
Reaction conditions: catalyst, 0.02 mmol; 1-hexene, 4 mmol; HCl (32%), 0.2 mmol;
PPh , 0.04 mmol; CO, 5 MPa; temperature, 90 °C, time, 24 h, MeOH (3 mL) + toluene
5 mL).
3
3
3
)
2
2
(
a
Branched/linear (b/l) ester ratio determined by GC-FID analysis.
mmol) and PPh
3
(2.62 mg, 0.01 mmol) in CDCl
P{ H} NMR spectra were recorded. We observed the complete
decomposition of complex 2a and formation of a mixture of [Pd
PPh (Cl)(CH )] and uncoordinated ligand (L2) (Scheme 5). The
formation of [Pd(PPh (Cl)(CH )] [64] was confirmed by a single
solvent, 1H and
3
3
1
1
Table 4
Methoxycarbonylation of 1-hexene with catalysts 1b-4b.
(
3
)
2
3
Entry
Complex
PPh
3
Conversion (%)
b/la
3
)
2
3
3
1
1
peak at 30.23 ppm in P{ H} NMR spectrum and a triplet peak
1
2
3
4
5
6
7
8
1b
1b
2b
2b
3b
3b
4b
4b
2
0
2
0
2
0
2
0
95.5
66
37/63
41/59
33/67
43/57
36/64
43/57
38/62
44/56
1
at À0.05 ppm in H NMR spectrum (Figs. S12 and S13). The other
1
94.4
50.3
84.7
38.6
66.0
28.8
peaks in the H NMR spectrum of the reaction are consistent with
the peaks of uncoordinated ligand (L2). The reaction of 2a with
PPh
which was carried out only with PPh
spectra were immediately recorded after mixing all the reagents;
a (2.67 mg), PPh (2.62 mg), 32% HCl (5 L) and CDCl in NMR
tube (Figs. S14 and S15). The NMR studies clearly showed the for-
mation of [Pd(PPh (Cl)(CH )], [Pd(PPh Cl ] and protonated
uncoordinated ligand (L2) (Scheme 6). We also observed CH peak
)] was com-
] after keeping the reaction mix-
3
in presence of HCl is somewhat different from the reaction
1
31
1
3
. The H and P{ H} NMR
2
3
l
3
Reaction conditions: catalyst, 0.02 mmol; 1-hexene, 4 mmol; HCl (32%), 0.2 mmol;
PPh , 0.04 mmol; CO, 5 MPa; temperature, 90 °C, time, 24 h, MeOH (3 mL) + toluene
5 mL).
3
(
3
)
2
3
3
)
2
2
a
Branched/linear (b/l) ester ratio determined by GC-FID analysis.
4
1
3 2 3
in the H NMR spectrum. Complex [Pd(PPh ) (Cl)(CH
pletely converted to [Pd(PPh
ture for 1 h (Scheme 7).
3 2 2
) Cl
The results from all these experiments strongly indicate that
complex 2a, and for that matter any of the palladium complexes
used as pre-catalysts for the methoxycarbonylation of olefins,
undergoes decomposition under the reaction conditions used for
methoxycarbonylation, eventually forms [Pd(PPh
the question still remained as to whether the complete catalysis
occur with [Pd(PPh Cl ] or partially with [Pd(PPh Cl ] and other
species that eventually dies. Since the formation of [Pd(PPh Cl
3 2 2
) Cl ]. However,
3
)
2
2
3
)
2
2
3
)
2
2
]
is possible only in presence of HCl, we also performed the
methoxycarbonylation of 1-hexene in presence of p-toluene
sulfonic acid as a promotor. We observed only 35% conversion of
1
-hexene to branched and linear esters in this reaction which indi-
cates a partial catalysis products were formed by [Pd(PPh (Cl)
CH )]. We, therefore, conclude that [Pd(PPh Cl ] is the main cat-
3 2
)
(
3
3
)
2
2
alyst in our methoxycarbonylation reactions; although there are
possible involvement of other active but less stable palladium spe-
cies that can be formed with all the pre-catalysts used when PPh
and HCl are added in the reactions.
3
Fig. 4. The effect of olefins on percentage conversion and regio-selectivity towards
branched product using catalyst 2a, 0.02 mmol; olefin, 4 mmol; HCl (32%) 0.2
mmol; PPh , 0.04 mmol; CO, 5 MPa; temperature, 90 °C, time, 24 h, MeOH (3 mL)
3
OCH3
and toluene (5 mL).
O
Pd catalyst
CO
A
+
1
-hexene
in the reaction. We, therefore performed the methoxycarbonyla-
CH OH
3
tion reaction of styrene with [Pd(PPh
complex was the active catalyst. The results of the reaction with
Pd(PPh Cl ] are given in Table 5. It is clear from these results
that the catalytic activity of [Pd(PPh Cl ] and regio-selectivity
3 2 2
) Cl ] to test if this palladium
O
OCH3
B
[
3
)
2
2
3
)
2
2
Scheme 5. Methoxycarbonylation products from 1-hexene.

2
54
K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
O
N
Ph3P
Cl
O
PPh
3
+
Pd
N
N
tBu
H C
PPh
3
3
Pd
N
tBu
CDCl
3
N
N
Cl
tBu
H C
3
tBu
2
a
3
Scheme 6. Products from the reaction of 2a with PPh .
O
O
PPh3
N
H
Ph3P
Cl
N
Pd
N
tBu
PPh3
H C
3
Pd
N
tBu
HCl
CDCl3
HN
tBu
+
N
Cl
H C
3
tBu
Ph3P
Cl
-CH4
2
a
Pd
Cl
PPh3
3
Scheme 7. Products from the reaction of 2a with PPh and HCl in less than 1 h.
3
. Conclusion
room temperature. The reaction mixture was heated to 90 °C and
stirred for 24 h. At the end of the reaction time, the reactor was
cooled, excess CO was vented off and reaction mixture was ana-
lyzed using GC and GC–MS to determine the percentage conversion
of the alkene to esters. GC analyses were performed on a Varian
series CP-3900 equipped with a capillary column (Wcot Fused Sil-
ica 50 m  21 mm CP SIL PONA CB DF = 0.5UM) and a flame ioniza-
tion detector (FID). GC–MS analyses were performed on a
Shimadzu GC–MS-QP2010 fitted with a quadrupole mass detector.
We have studied the methoxycarbonylation of selected linear
-alkenes using various neutral palladium(II) complexes and
1
palladium salts as pre-catalysts. These methoxycarbonylation
reactions gave linear esters as major products; whilst with styrene
as the olefin substrate there was high selectivity to the branched
ester product. Most of these methoxycarbonylation reactions
3
required addition of PPh ; otherwise we observed the formation
of palladium black with little or no catalytic activity. Studying
the palladium complexes isolated from some of the initial palla-
dium compounds used in the catalytic reactions showed that the
4
4
.3. Synthesis of ligand and palladium complexes
decomposition products, [Pd(PPh
were both active for the methoxycarbonylation reaction. However,
Pd(PPh Cl ] was found to be the main catalyst in all the
methoxycarbonylation reactions.
3 2 3 3 2 2
) (Cl)(CH )] and [Pd(PPh ) Cl ],
.3.1. Synthesis of 2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-
(
phenoxymethyl)pyridine (L2)
[
3
)
2
2
A mixture of 2-(chloromethyl)-6-[(3,5-di-tert-butyl-1H-pyra-
zol-1-yl)methyl]pyridine (319.8 mg, 1.0 mmol), phenol (141 mg,
.5 mmol), and K CO (415 mg, 3 mmol) in acetonitrile (20 mL)
1
2
3
4
. Experimental
was heated under reflux for 24 h. After cooling to the room tem-
perature, reaction mixture was filtered and residue was washed
with acetonitrile (2 Â 3 mL). The solvent was evaporated from
combined acetonitrile fraction under reduced pressure. The result-
ing compound was dissolved in dichloromethane (20 mL) and
washed with 2% aq. NaOH (2 Â 10 mL) followed by water to
remove excess phenol. The dichloromethane fraction was collected
4.1. Material and general methods
All manipulations were carried out under argon atmosphere
using standard Schlenk techniques. All organic solvents were dried
and purified on MBRAUN solvent drying system. The synthesis of
complexes 1a, 3a, 4a, 3c and 4c are reported from this laboratory
and dried over anhyd. MgSO
resulted in a pure white solid of L2. Yield: 346.8 mg (ꢀ92%).
NMR (400 MHz, CDCl , d ppm): 7.56 (t, 1H, J = 8.0 Hz), 7.34 (d,
4
. The removal of dichloromethane
1
13
1
31
1
1
[
58]. H, C{ H} and P{ H} NMR spectra were recorded on a Bru-
ker 400 or 500 MHz instrument and chemical shift values (d) are
reported in ppm and referenced to the residual CHCl in CDCl
H: 7.24 ppm and C{ H}: 77.00 ppm). Elemental analyses were
H
3
1H, J = 7.6 Hz), 7.27 (t, 2H, J = 8.0 Hz), 6.95 (m, 2H), 6.37 (d, 1H, J
= 8.0 Hz), 5.93 (s, 1H), 5.57 (s, 2H), 5.17 (s, 2H), 1.31 (s, 9H), 1.23
3
3
1
13
1
(
1
3
1
performed on a Thermo Scientific Flash 2000 Elemental analyzer
and HRMS spectra were recorded on a Waters Synapt G2 instru-
ment. The ESI-MS spectra (Waters API Quattro micro-spectropho-
tometer) were recorded at mass spectrometry unit, University of
Stellenbosch, South Africa.
3
(s, 9H). C{ H} NMR (100 MHz, CDCl , d ppm): 160.9, 159.0,
158.4, 156.5, 152.1, 137.6, 129.5, 121.1, 119.7, 119.4, 114.9,
100.5, 70.5, 56.3, 32.0, 31.3, 30.6, 30.3. HRMS (ESI): m/z (%)
+
378.2552 ([M+H] , 100%).
2
4
.3.2. Synthesis of ĸ -2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-
4
.2. Catalysis experiment
(phenoxymethyl)-pyridine)(methyl)palladium(II) chloride (2a)
Complex 2a was synthesized from 2-[(3,5-di-tert-butyl-1H-
pyrazol-1-yl)methyl]-6-(phenoxymethyl)pyridine (377.5 mg, 1.0
The catalytic reaction was carried out in 35 mL stainless steel
autoclave fitted with pressure gauze. A typical experiment
involved the addition of catalyst 2a (10.7 mg, 0.02 mmol), PPh
mmol) and [Pd(Cl)(CH
3
)(COD)] (265.1 mg, 1.0 mmol) following
3
the procedure reported for complex 1a. Yield: 432.8 mg (ꢀ80%).
1
(
10.5 mg, 0.04 mmol), 1-hexene (0.5 mL, 4 mmol), 32% HCl (20
3
H NMR (400 MHz, CDCl , d ppm): 7.84 (t, 1H, J = 7.6 Hz)iso, 7.72
l
L, 0.2 mmol), methanol (3 mL) and toluene (5 mL) to the reactor.
(t, 1H, J = 7.6 Hz), 7.62 (d, 1H, J = 8.0 Hz), 7.42 (d, 1H, J = 7.6 Hz)
iso, 7.32–7.22 (m, 6H), 7.05 (d, 2H, J = 8.0 Hz), 7.00–6.94 (m, 2H),
The reactor was then degassed and pressurized with CO (5 MPa) at

K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
255
6
.16 (d, 1H, J = 15.2), 5.93 (s, 1H), 5.80 (s, 1H)iso, 5.68–5.62 (m, 2H)
7.21–7.10 (m, 11H), 6.80 (d, 2H, J = 7.0 Hz)iso, 6.74 (d, 2H, J = 7.5
Hz), 6.67 (d, 1H, J = 7.5 Hz), 6.29 (d, 1H, J = 14.5 Hz)iso, 6.17 (d,
1H, J = 15.0 Hz), 5.93 (s, 1H), 5.56 (s, 1H)iso, 5.27 (d, 1H, J = 15.0
Hz)iso, 5.22 (d, 1H, J = 14.5 Hz), 4.50 (d, 1H, J = 13.5 Hz)iso, 4.00
(d, 1H, J = 14.0 Hz), 3.55 (d, 1H, J = 13.5 Hz)iso, 3.33 (d, 1H, J =
14.0 Hz), 2.34 (s, 3H)iso, 2.25 (s, 3H), 2.20 (s, 3H), 1.08 (s, 3H)iso,
0.80 (d, 3H, J = 3.0 Hz), 0.32 (d, 3H, J = 2.5 Hz)iso. 31P{ H} NMR
iso, 5.57 (d, 1H, J = 14.8 Hz), 5.45 (d, 1H, J = 15.2 Hz), 1.54 (s, 9H),
1
3
.52 (s, 9H)iso, 1.42 (s, 9H), 1.41 (s, 9H)iso, 1.00 (s, 3H), 0.76 (s,
H)iso. Elemental analysis (%) calcd. for C25 34ClN PdO: C, 56.19;
H
3
H, 6.41; N, 7.86. Found: C, 56.01; H, 6.48; N, 7.97. HRMS (ESI):
+
+
m/z 498.1763 ([MÀCl] , 10%), 378.2571 [MÀPd–CH
3
–Cl and H] ,
1
1
00%).
(
202 MHz, CDCl , d ppm): 37.77, 30.27. Elemental analysis (%)
3
2
4
.3.3. Synthesis of ĸ -2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-6-
calcd. for C69H49BF24N PPdS: C, 53.25; H, 3.17; N, 2.70. Found: C,
3
(
phenoxymethyl)pyridine)(methyl)(triphenylphosphine)palladium(II)
52.98; H, 3.10; N, 2.75. Positive ion ESI-MS: m/z (%) = 692.1466
+
+
tetrakis(3,5-trifluoromethylphenyl)borate (1b)
(5%) [M] , 430.0573 (100%) [MÀPPh
3
] . Negative ion ESI-MS: m/z
F
À
Solid NaBAr
4
(197 mg, 0.22 mmol) was added in small portions
(58
(%) 863.0604 (100%) [M] .
to the solution of complex 1a (100 mg, 0.22 mmol) and PPh
mg, 0.22 mmol) in dichloromethane (15 mL). The reaction mixture
was stirred at room temperature for 24 h under argon and then fil-
tered through syringe filter with 0.45 lm pore size. The evapora-
tion of solvent on rotary evaporator and further drying under
3
2
4
.3.6. Synthesis of ĸ -2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-
(
(
phenylthiomethyl)-pyridine)(methyl)(triphenylphosphine)palladium
II) tetrakis(3,5-trifluoromethyl-phenyl)borate (4b)
Compound 4b was synthesized from complex 4a (100 mg, 0.18
mmol), PPh
mmol) following the procedure used for the synthesis of complex
b. The titled compound was obtained as a spongy orange solid.
(47.2 mg, 0.18 mmol) and NaBArF
(160 mg, 0.18
3 4
vacuum gave a spongy light orange solid. Yield: 315 mg (ꢀ93%).
1
3
H NMR (500 MHz, CDCl , d ppm): 7.75 (t, 1H, J = 8.0 Hz)iso, 7.69
(
t, 15h, J = 2.3 Hz), 7.65 (t, 2H, J = 8.0 Hz), 7.59 (d, 1H, J = 7.5 Hz)
1
1
iso, 7.49 (s, 8H), 7.46–7.43 (m, 6H), 7.35–7.25 (m, 27H), 7.20 (d,
1
6
(
(
5
=
(
Yield: 240 mg (ꢀ81%). H NMR (500 MHz, CDCl
3
, d ppm, À50 °C):
.68 (s, 8H), 7.62 (t, 2H, J = 8.0 Hz), 7.56 (t, 1H, J = 7.0 Hz), 7.47–
.43 (m, 11H), 7.37 (d, 2H, J = 7.5 Hz), 7.32–7.26 (m, 10H), 7.01
H, J = 7.5 Hz), 7.08 (t, 1H, J = 7.5 Hz)iso, 7.03 (t, 1H, J = 7.5 Hz),
.87 (dd, 2H, J = 9.0, 1.0 Hz)iso, 6.70 (dd, 2H, J = 8.5, 1.0 Hz), 6.33
d, 1H, J = 15.5 Hz)iso, 6.25 (d, 1H, J = 15.5 Hz), 5.91 (s, 1H), 5.58
s, 1H)iso, 5.44 (d, 1H, J = 13.0 Hz)iso, 5.23 (d, 1H, J = 15.0 Hz)iso,
.20 (d, 1H, J = 15.0 Hz), 5.15 (d, 1H, J = 13.0 Hz)iso, 4.83 (d, 1H, J
13.0 Hz), 4.32 (d, 1H, J = 12.5 Hz), 2.29 (s, 3H), 2.23 (s, 3H), 2.17
7
7
(
d, 2H, J = 6.5 Hz), 6.91 (d, 1H, J = 8.0 Hz), 6.66 (d, 1H, J = 15.0
Hz), 6.00 (s, 1H), 5.71 (d, 1H, J = 15.0 Hz), 4.10 (d, 1H, J = 12.5
Hz), 3.05 (d, 1H, J = 12.5 Hz), 1.42 (s, 9 H), 1.39 (s, 9H), 0.76 (d,
3
1
1
3
H, J = 3.5 Hz). P{ H} NMR (202 MHz, CDCl
3
, d ppm): 37.62. Ele-
s, 3H)iso, 1.22 (s, 3H)iso, 0.84 (d, 3H, J = 3.5 Hz), 0.42 (d, 3H, J =
mental analysis (%) calcd. for C75 PPdS: C, 54.91; H, 3.75;
H61BF24N
3
3
1
1
3
.5 Hz)iso. P{ H} NMR (202 MHz, CDCl
3
, d ppm): 38.52, 37.37.
OPPd: C, 53.80; H,
.21; N, 2.73. Found: C, 53.55; H, 3.11; N, 2.76. Positive ion ESI-
N, 2.56. Found: C, 54.72; H, 3.83; N, 2.41. Positive ion ESI-MS: m/z
+
+
Elemental analysis (%) calcd. for C69H49BF24N
3
3
MS: m/z (%) = 676.1711 (5%) [M] . Negative ion ESI-MS: m/z (%)
8
(
%) = 776.2441 (75%) [M] , 514.1525 (40%) [MÀPPh
3
] . Negative
À
ion ESI-MS: m/z (%) 863.0596 (100%) [M] .
+
À
63.0612 (100%) [M] .
4
4
.4. Crystal structure determination
.4.1. Data collections
2
4
.3.4. Synthesis of ĸ -2-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]-6-
(
(
phenoxymethyl)-pyridine)(methyl)(triphenylphosphine)palladium
II) tetrakis(3,5-trifluoromethyl-phenyl)borate (2b)
The X-ray data collections for compounds 2a, 2b and 4b were
performed similarly. Herein, we describe the representative proce-
dure for 2a.
Compound 2b was synthesized from complex 2a (107 mg, 0.20
F
mmol), PPh
3
(52.5 mg, 0.20 mmol) and NaBAr
4
(177.2 mg, 0.20
A colorless block shaped crystal of compound 2a with approxi-
mmol) following the procedure used for the synthesis of complex
b. The titled compound was obtained as a spongy light orange
3
mate dimensions 0.269 Â 0.193 Â 0.09 mm was selected under oil
1
under ambient conditions and attached to the tip of a MiTeGen
1
solid. Yield: 280 mg (ꢀ86%). H NMR (500 MHz, CDCl
.79 (t, 1H, J = 8.0 Hz)iso, 7.71–7.68 (m, 11H), 7.66–7.63 (m, 2H)
iso, 7.53–7.52 (m, 3H)iso, 7.49 (s, 5H), 7.46–7.43 (m, 4H), 7.37 (d,
3
, d ppm):
Ó
MicroMount . The crystal was mounted in a stream of cold nitro-
7
gen at 100(2) K and centered in the X-ray beam by using a video
camera. The crystal evaluation and data collection were performed
on a Bruker APEXII CCD diffractometer with Mo Ka (k = 0.71073 Å)
1
7
1
6
5
1
H, J = 7.5 Hz), 7.34–7.25 (m, 17H), 7.06 (t, 1H, J = 7.5 Hz)iso,
.02 (t, 1H, J = 7.5 Hz), 6.92 (d, 2H, J = 8.0 Hz)iso, 6.80 (d, 1H, J =
5.0 Hz)iso, 6.75 (d, 1H, J = 15.0 Hz), 6.63 (dd, 2H, J = 8.5, 1.0 Hz),
.02 (d, 1H, J = 1.0 Hz), 5.79 (s, 1H)iso, 5.75 (d, 1H, J = 15.0 Hz),
.72 (d, 1H, J = 15 Hz)iso, 5.40–5.32 (m, 2H)iso, 4.88 (d, 1H, J =
2.5 Hz), 4.29 (d, 1H, J = 12.5 Hz), 1.43 (s, 9H), 1.40 (s, 9H), 1.38
radiation and the diffractometer to crystal distance of 4.96 cm. The
reflections were successfully indexed by an automated indexing
routine built in the APEX2 program suite. The data were collected
by using the full sphere data collection routine to survey the recip-
rocal space to the extent of a full sphere to a resolution of 0.75 Å.
The highly redundant datasets were corrected for Lorentz and
polarization effects. The absorption correction was based on fitting
a function to the empirical transmission surface as sampled by
multiple equivalent measurements [65].
(
3
s, 9H)iso, 0.93 (s, 9H)iso, 0.83 (d, 3H, J = 3.0 Hz), 0.59 (d, 3H, J =
3
1
1
.0 Hz)iso. P{ H} NMR (202 MHz, CDCl
3
, d ppm): 38.03, 35.87.
OPPd: C, 55.45; H,
.79; N, 2.59. Found: C, 55.60; H, 3.68; N, 2.67. Positive ion ESI-
Elemental analysis (%) calcd. for C75H61BF24N
3
3
MS: m/z (%) = 760.2665 (5%) [M] . Negative ion ESI-MS: m/z (%)
8
+
–
63.0641 (100%) [M] .
4.4.2. Structure solution and refinement
2
For all three compounds 2a, 2b and 4b, the systematic absences
4
(
(
.3.5. Synthesis of ĸ -2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-6-
ꢀ
in the diffraction data were consistent for the space groups P1 and
P1. The E-statistics strongly suggested the centrosymmetric space
phenylthiomethyl)pyridine)(methyl)(triphenylphosphine)palladium
II) tetrakis(3,5-trifluoromethylphenyl)borate (3b)
Compound 3b was synthesized from complex 3a (100 mg, 0.21
(56.2 mg, 0.21 mmol) and NaBAr
mmol) following the procedure used for the synthesis of complex
b. The titled compound was obtained as a spongy orange solid.
ꢀ
group P1 that yielded chemically reasonable and computationally
F
stable results of refinement [66–68]. The successful solutions were
obtained from SHELXT [69] structure solution program and were
mmol), PPh
3
4
(190 mg, 0.21
2
refined on F by the full-matrix least-squares technique using the
1
1
Yield: 290 mg (ꢀ89%). H NMR (500 MHz, CDCl
3
, d ppm, À50 °C):
SHELXL [70] program package. All non-hydrogen atoms were refined
with anisotropic displacement coefficients. All hydrogen atoms
7
.68–7.63 (m, 23H), 7.53–7.43 (m, 23H), 7.42–7.28 (m, 19H),

2
56
K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
were included in the structure factor calculations at idealized posi-
tions and were allowed to ride on the neighboring atoms with rel-
ative isotropic displacement coefficients.
There were partially occupied disordered solvent molecules
present in the asymmetric unit of compound 2a. A significant
amount of time was invested in identifying and refining the disor-
dered molecules. Bond length restraints were applied to model the
molecules but the resulting isotropic displacement coefficients
suggested the molecules were mobile. In addition, the refinement
was computationally unstable. Option SQUEEZE of program PLATON
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at https://doi.org/10.
1016/j.poly.2017.09.046.
References
[
1] G. Kiss, Chem. Rev. 101 (2001) 3435.
[
2] O.V. Gusev, A.M. Kalsin, P.V. Petrovskii, K.A. Lyssenko, Y.F. Oprunenko, C.
Bianchini, A. Meli, W. Oberhauser, Organometallics 22 (2003) 913.
[
71] was used to correct the diffraction data for diffuse scattering
[3] C. Bianchini, A. Meli, W. Oberhauser, M.A. Zuideveld, Z. Freixa, P.C.J. Kamer, A.L.
Spek, O.V. Gusev, A.M. Kal’sin, Organometallics 22 (2003) 2409.
effects and to identify the solvate molecules. SQUEEZE computed
the upper limit of volume that can be occupied by the solvent to
[
[
[
[
4] B. Liang, J. Liu, Y.-X. Gao, K. Wongkhan, D.-X. Shu, Y. Lan, A. Li, A.S. Batsanov, J.A.
H. Howard, T.B. Marder, J.-H. Chen, Z. Yang, Organometallics 26 (2007) 4756.
5] D.B.G. Williams, M.L. Shaw, M.J. Green, C.W. Holzapfel, Angew. Chem. Int. Ed.
47 (2008) 560.
6] T. Fanjul, G. Eastham, N. Fey, A. Hamilton, A.G. Orpen, P.G. Pringle, M. Waugh,
Organometallics 29 (2010) 2292.
3
be 127.9 Å or 9.8% of the unit cell volume. The program calculated
5
0 electrons in the unit cell for the diffuse species. This approxi-
mately corresponds to one molecule of CH Cl in the asymmetric
Cl molecule is dis-
2
2
unit (42 electrons). It is very likely that this CH
ordered over two or three positions.
2
2
7] J.T. Christl, P. Roesle, F. Stempfle, P. Wucher, I. Göttker-Schnetmann, G. Müller,
S. Mecking, Chem. Eur. J. 19 (2013) 17131.
[
[
8] G. Walther, A. Martin, A. Köckritz, J. Am. Oil Chem. Soc. 90 (2013) 141.
9] A. Pews-Davtyan, X. Fang, R. Jackstell, A. Spannenberg, W. Baumann, R. Franke,
M. Beller, Chem. Asian J. 9 (2014) 1168.
The molecules in 2b and 4b exhibited positional and rotational
disorders at various points of the molecules. In the molecule of 2b,
the CH
major component contribution of 64.6(5)%. Two phenyl rings,
C26–C31 and C38–C43 of PPh ligand were also disordered over
3
group at C25 was disordered over two positions with a
[10] C. Holzapfel, T. Bredenkamp, ChemCatChem 7 (2015) 2598.
[11] M. Amézquita-Valencia, G. Achonduh, H. Alper, J. Org. Chem. 80 (2015) 6419.
[12] P.H. Gehrtz, V. Hirschbeck, I. Fleischer, Chem. Commun. 51 (2015) 12574.
[13] P. Kalck, M. Urrutigoïty, Inorg. Chim. Acta 431 (2015) 110.
3
two positions and these were modeled with idealized constrained
geometry with a major component contribution of 62.7(10) and
[14] V. Goldbach, L. Falivene, L. Caporaso, L. Cavallo, S. Mecking, ACS Catal. 6 (2016)
8229.
[
15] S. Boyde, Green Chem. 4 (2002) 293.
5
0.5(17)% respectively. The methyl groups at C4 of tert-butyl sub-
[
16] H. Zhou, J. Cheng, S. Lu, H. Fu, H. Wang, J. Organomet. Chem. 556 (1998) 239.
stituent was affected by rotational disorder which was modeled
over two distinct positions with a major component contribution
of 59.1(13)%. CF groups at C66 and C67 showed typical rotational
3
disorder and these were modeled over two (C66) or three (C67)
positions with a major component contribution of 62.83(15) and
[17] E.J. Jang, K.H. Lee, J.S. Lee, Y.G. Kim, J. Mol. Catal. A: Chem. 138 (1999) 25.
[18] Z. He, Z. Hou, Y. Luo, Y. Dilixiati, W. Eli, Catal. Sci. Technol. 4 (2014) 1092.
[
[
[
[
19] I. del R ´ı o, N. Ruiz, C. Claver, L.A. van der Veen, P.W.N.M. van Leeuwen, J. Mol.
Catal. A: Chem. 161 (2000) 39.
20] A. Seayad, A.A. Kelkar, L. Toniolo, R.V. Chaudhari, J. Mol. Catal. A: Chem. 151
(2000) 47.
21] H. Li, K. Dong, H. Jiao, H. Neumann, R. Jackstell, M. Beller, Nat. Chem. 8 (2016)
5
0.4(2)% respectively. The phenyl ring C52-C57 together with its
two CF groups at C54 and C56 was disordered over three positions
and this was modeled with a minor component contribution of
1159.
3
22] J.D. Nobbs, C.H. Low, L.P. Stubbs, C. Wang, E. Drent, M. van Meurs,
Organometallics 36 (2017) 391.
[
[
23] T. Bredenkamp, C. Holzapfel, Catal. Commun. 96 (2017) 74.
24] P. Roesle, L. Caporaso, M. Schnitte, V. Goldbach, L. Cavallo, S. Mecking, J. Am.
Chem. Soc. 136 (2014) 16871.
2
2.30(16)%.
Similarly, molecule of compound 4b also showed positional and
rotational disorders. The CH
two positions with a major component contribution of 65.3(7)%.
Again, two phenyl rings, C38–C43 and C32–C37 of PPh ligand
3
group at C25 was disordered over
[25] R.P. Tooze, K. Whiston, A.P. Malyan, M.J. Taylor, N.W. Wilson, J. Chem. Soc.,
Dalton Trans. (2000) 3441.
[
26] G.R. Eastham, R.P. Tooze, M. Kilner, D.F. Foster, D.J. Cole-Hamilton, J. Chem.
Soc., Dalton Trans. (2002) 1613.
3
were also disordered in two distinct positions were modeled with
idealized constrained geometry with a major component contribu-
tion of 63.9(4) and 50.6(15)% respectively. The CF groups at C66
3
was over three rotational positions with a major component con-
tribution of 48.1(2)%. The phenyl ring C52–C57 together with its
[27] G. Cavinato, A. Vavasori, L. Toniolo, F. Benetollo, Inorg. Chim. Acta 343 (2003)
183.
[
28] V. de la Fuente, M. Waugh, G.R. Eastham, J.A. Iggo, S. Castillón, C. Claver, Chem.
Eur. J. 16 (2010) 6919.
[
29] R.E. Rulke, V.E. Kaasjager, P. Wehman, C.J. Elsevier, P.W.N.M.v. Leeuwen, K.
Vrieze, J.F.a.K. Goubitz, A.L. Spek, Organometallics 15 (1996) 3022.
30] M. Nandi, J. Jin, T.V. RajanBabu, J. Am. Chem. Soc. 121 (1999) 9899.
31] P.J.W. Deckers, B. Hessen, J.H. Teuben, Angew. Chem. Int. Ed. 40 (2001) 2516.
32] M.H. Chisholm, J.C. Gallucci, G. Yaman, Inorg. Chem. 46 (2007) 8676.
[
[
[
two CF
and this was modeled with a minor component contribution of
3.9(2)%.
3
groups at C54 and C56 was disordered over three positions
2
[33] G.R. Fulmer, W. Kaminsky, R.A. Kemp, K.I. Goldberg, Organometallics 30 (2011)
627.
1
[
34] R. Lindner, B. van den Bosch, M. Lutz, J.N.H. Reek, J.I. van der Vlugt,
Organometallics 30 (2011) 499.
Acknowledgements
[
35] W.-C. Lee, J.M. Sears, R.A. Enow, K. Eads, D.A. Krogstad, B.J. Frost, Inorg. Chem.
5
2 (2013) 1737.
Financial support for this project from the National Research
Foundation (NRF), South Africa, the DST–NRF Centre of Excellence
in Catalysis (c⁄change), South Africa, and the University of Johan-
nesburg is gratefully acknowledged. K. K. thanks the University
of Johannesburg for a postdoctoral fellowship. The authors grate-
fully acknowledge Prof. Ilia Guzei, University of Johannesburg
[36] L. Crawford, D.J. Cole-Hamilton, M. Bühl, Organometallics 34 (2015) 438.
[37] D.G. Gusev, ACS Catal. 6 (2016) 6967.
38] A. Bader, E. Lindner, Coord. Chem. Rev. 108 (1991) 27.
39] Y. Kataoka, Y. Tsuji, O. Matsumoto, M. Ohashi, T. Yamagata, K. Tani, J. Chem.
Soc., Chem. Commun. (1995) 2099.
[
[
[40] S. Mecking, W. Keim, Organometallics 15 (1996) 2650.
[
41] M.J. Green, G.J.P. Britovsek, K.J. Cavell, F. Gerhards, B.F. Yates, K. Frankcombe, B.
W. Skelton, A.H. White, J. Chem. Soc., Dalton Trans. (1998) 1137.
42] D. Kruis, N. Ruiz, M.D. Janssen, J. Boersma, C. Claver, G. van Koten, Inorg. Chem.
Commun. 1 (1998) 295.
43] P. Braunstein, F. Naud, Angew. Chem. Int. Ed. 40 (2001) 680.
44] A. Zhang, T.V. RajanBabu, Org. Lett. 6 (2004) 1515.
45] C.S. Slone, D.A. Weinberger, C.A. Mirkin, Prog. Inorg. Chem. (2007) 233.
46] C.J. Stephenson, J.P. McInnis, C. Chen, M.P. Weberski, A. Motta, M. Delferro, T.J.
Marks, ACS Catal. 4 (2014) 999.
(
South Africa) and University of Wisconsin (USA) for his consistent
[
help and useful discussions related to X-ray crystal structures.
[
[
[
[
Appendix A. Supplementary data
CCDC 1543685–1543687 contains the supplementary crystallo-
graphic data for 2a, 2b and 4b. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
[47] C.M. McGuirk, J. Mendez-Arroyo, A.M. Lifschitz, C.A. Mirkin, J. Am. Chem. Soc.
36 (2014) 16594.
1
[
48] G.S. Nyamato, S.O. Ojwach, M.P. Akerman, Organometallics 34 (2015) 5647.
49] A.E. Díaz-Álvarez, C. Vidal, F.J. Suárez, J. Díez, V. Cadierno, P. Crochet,
Organometallics 34 (2015) 3670.
[

K. Kumar, J. Darkwa / Polyhedron 138 (2017) 249–257
257
[
[
[
[
[
[
[
[
50] P.A. Aguirre, C.A. Lagos, S.A. Moya, C. Zuniga, C. Vera-Oyarce, E. Sola, G. Peris, J.
[60] H. Liang, J. Liu, X. Li, Y. Li, Polyhedron 23 (2004) 1619.
[61] P.J. Bailey, M. Melchionna, S. Parsons, Organometallics 26 (2007) 128.
[62] M. Bortoluzzi, G. Paolucci, B. Pitteri, A. Vavasori, V. Bertolasi, Organometallics
28 (2009) 3247.
[63] S.O. Ojwach, A.O. Ogweno, M.P. Akerman, Catal. Sci. Technol. 6 (2016) 5069.
[64] P.K. Byers, A.J. Canty, H. Jin, D. Kruis, B.A. Markies, J. Boersma, G.V. Koten, G.S.
Hill, M.J. Irwin, L.M. Rendina, R.J. Puddephatt, Inorg. Synth. (2007) 162.
[65] Bruker-AXS APEX2, SADABS, and SAINT. Bruker-AXS Inc, Madison, Wisconsin,
USA (2009).
[66] Bruker-AXS APEX2, COSMO, AXScale, and SAINT. Bruker-AXS Inc, Madison,
Wisconsin, USA, (2010).
[67] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Cryst. 42 (2009) 339.
C. Bayon, Dalton Trans. (2007) 5419.
51] S. Zolezzi, S.A. Moya, G. Valdebenito, G. Abarca, J. Parada, P. Aguirre, Appl.
Organomet. Chem. 28 (2014) 364.
52] C. Arderne, l.A. Guzei, C.W. Holzapfel, T. Bredenkamp, ChemCatChem 8 (2016)
1
084.
53] R.E. Rulke, V.E. Kaasjager, D. Kliphuis, C.J. Elsevier, P.W.N.M.v. Leeuwen, K.
Vrieze, K. Goubitz, Organometallics 15 (1996) 668.
54] G.J.P. Britovsek, K.J. Cavell, M.J. Green, F. Gerhards, B.W. Skelton, A.H. White, J.
Organomet. Chem. 533 (1997) 201.
55] M. Schreuder Goedheijt, J.N.H. Reek, P.C.J. Kamer, P.W.N.M. van Leeuwen,
Chem. Commun. (1998) 2431.
56] M.J. Green, K.J. Cavell, P.G. Edwards, R.P. Tooze, B.W. Skelton, A.H. White,
Dalton Trans. (2004) 3251.
[68] I.A. GUZEI, Internal laboratory computer programs Gn. 2013.
[69] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L.D. Caro, C.
Giacovazzo, G. Polidori, D. Siliqi, R. Spagna, J. Appl. Cryst. 40 (2007) 609.
[70] G.M. Sheldrick, Acta Cryst. A 64 (2008) 112.
57] C. Obuah, M.K. Ainooson, S. Boltina, I.A. Guzei, K. Nozaki, J. Darkwa,
Organometallics 32 (2013) 980.
[
58] K. Kumar, J. Darkwa, Dalton Trans. 44 (2015) 20714.
59] A. Bayler, A.J. Canty, P.G. Edwards, B.W. Skelton, A.H. White, J. Chem. Soc.,
Dalton Trans. (2000) 3325.
[
[71] A.L. Spek, Acta Cryst. D 65 (2009) 148.