Unconjugated diimine palladium complexes as Heck coupling catalysts

Article abstract of DOI:10.1016/j.molcata.2008.01.009

Four unconjugated diimine palladium complexes have been synthesized, and spectroscopically and structurally characterized. All four palladium complexes were used as catalysts in the Heck coupling reaction between iodobenzene and methyl acrylate or butyl a

Full text of DOI:10.1016/j.molcata.2008.01.009

Available online at www.sciencedirect.com
Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
Unconjugated diimine palladium complexes as Heck coupling catalysts
Simphiwe M. Nelanaa, Jezreel Cloeteb, George C. Lisenskyc, Ebbe Nordlanderd,
Ilia A. Guzeie, Selwyn F. Mapolieb,∗, James Darkwaa,∗
a Department of Chemistry, University of Johannesburg, P.O. Box 524, Auckland Park Kingsway Campus, Auckland Park 2006, South Africa
b Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
c Department of Chemistry, Beloit College, 700 College Street, WI 53011, USA
d Inorganic Chemistry Research Group, Center for Chemistry and Chemical Engineering, Lund University, Box 124, Lund SE-221 00, Sweden
e Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA
Received 7 November 2007; accepted 4 January 2008
Available online 16 January 2008
Abstract
Four unconjugated diimine palladium complexes have been synthesized, and spectroscopically and structurally characterized. All four palladium
complexes were used as catalysts in the Heck coupling reaction between iodobenzene and methyl acrylate or butyl acrylate with very good conversion
to either methyl (2E)-3-phenylacrylate or butyl (2E)-3-phenylacrylate.
© 2008 Elsevier B.V. All rights reserved.
Keywords: Unconjugated diimine ligands; Palladium complexes; Crystal structures; Heck coupling catalysts
1. Introduction
pling catalysts/catalyst precursors, and only scarce information
is available for imine ligands in spite of the extensive use of ␣-
diimine complexes of late transition metals complexes as olefin
oligomerization and polymerization catalysts [7]. Nolan and
co-workers [8] have used the ␤-diimine ligand 1,4-diaza-1,3-
butadiene in the Suzuki coupling reaction.
Recently, Qian et al. have utilized unconjugated diimine
cobalt complexes as catalysts for ethylene oligomerization [9].
Other examples of the use of unconjugated diimines are zinc
complexes as asymmetric catalysts for enantioselective synthe-
sis of 1-phenyl-1-propanol [10] and the photoluminescence of
copper complexes [11]. Here, we report the catalytic behavior of
four unconjugated diimine palladium complexes that are capable
of catalyzing Heck coupling. To the best of our knowledge, this
is the first report on the use of unconjugated diimine complexes
in Heck coupling catalysis.
The Heck coupling reaction is one of the most important
C–C bond forming processes in organic synthesis [1]. It features
applications that range from the preparation of hydrocarbons and
industrial production of pharmaceuticals, to advanced synthesis
of natural products [2]. The most extensively used catalysts to
date are phosphine palladium complexes [3]. However, the cost
and sensitivity of phosphines to air and moisture have led to the
search for less expensive and more stable ligands as synthons
for new palladium Heck coupling catalysts. Some of these so-
called phosphine-freecatalystsarepalladiumcomplexesbearing
N-heterocyclic carbene ligands [4] or nitrogen-donor ligands
[5]. Effective phosphine-free catalysts for the Heck coupling
reaction contain either less expensive ligands or moieties that
are more stable under ambient conditions, or both. However, in
a number of cases reactions catalyzed by phosphine-free lig-
and palladium complexes require high temperatures and long
reaction times and the complexes function as precursors for
colloidal particles [6]. Complexes containing nitrogen-based
ligands remain the least explored phosphine-free Heck cou-
2. Experimental
2.1. General
All experiments were carried out under an atmosphere of
purified nitrogen using standard Schlenk techniques. All sol-
vents were purchased from Sigma–Aldrich and refluxed over
appropriate drying agents and distilled: diethyl ether was dried
∗
Corresponding authors.
E-mail address: jdarkwa@uj.ac.za (J. Darkwa).
1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2008.01.009

S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
73
over sodium, dimethylformamide (DMF) over calcium hydride,
acetonitrile and dichloromethane over phosphorus pentoxide
and acetone over anhydrous calcium chloride and kept over
procedure described for 1. Yield: 0.14 g (82%). Anal Calcd. for
C29H26Cl2N2Pd: C, 60.07; H, 4.52; N, 4.83. Found: C, 59.53;
H, 4.56; N, 4.81. 1H NMR (DMSO-d6): δ 7.65 (m, 20H, C6H5),
3.88 (t, 4H, CH2), 2.51 (m, 2H, CH2).
˚
4 A molecular sieves. N,N-dimethylacetamide (DMA) was pur-
chased from Sigma–Aldrich and was used without further
purification. The ligand, L1, (N,Nꢀ-bis(diphenylmethylene)1,2-
ethanediamine) was synthesized according to the modified
method which has been published by Chowdhury et al. [11], and
[PdClMe(COD)] [12] and [PdCl2(NCMe)2] [13] were prepared
by literature procedures.
IR spectra were recorded as nujol mulls on a PerkinElmer
Paragon 1000 PC FT-IR spectrometer. NMR spectra were
recorded on a Varian Gemini 2000 instrument (1H at 200 MHz,
13C at 50 MHz). Chemical shifts are reported in ppm and refer-
enced to residual proton and carbon signals (7.25 and 77.0 ppm
for CDCl3 and 2.50 and 39.0 ppm for DMSO-d6). Elemental
analysis was performed in the Department of Chemistry at the
University of the Cape Town. Heck coupling reaction products
were analyzed on a Shimadzu GCMS-QP 2010 version 2 gas
chromatograph; fitted with a flame ionization detector (FID) and
a 30 m × 0.25 mm, 100% dimethoxypolysiloxane ZB1 column.
Products were quantified via internal standard techniques.
2.3.3. [PdClMe{(C6H5)2C N(CH2)2N C(C6H5)2}] (3)
To a mixture of [PdClMe(COD)] (0.20 g, 0.77 mmol) and L1
(0.30 g, 0.77 mmol) was added diethyl ether (20 mL). The color
changed to light yellow and a precipitate formed after stirring
at room temperature for 6 h. The product was isolated as a light
yellow solid and recrystallized from CH2Cl2/hexane at −4 ◦C.
Yield: 0.29 g (69%). Anal Calcd. for C29H27ClN2Pd·2CH2Cl2:
C, 52.04; H, 4.37; N, 3.92. Found: C, 52.82; H, 4.18; N, 3.82.
1H NMR (CDCl3): δ 8.30 (d, 2H, J = 7.40 Hz, C6H5), 7.66
(d, 2H, J = 7.20 Hz, C6H5), 7.54 (m, 16H, C6H5), 0.40 (s, 3H,
Pd–Me).
2.3.4. [PdClMe(C6H5)2C N(CH2)3N C(C6H5)2] (4)
Complex 4 was prepared from [PdClMe(COD)] (0.20 g,
0.76 mmol) and L2 (0.30 g, 0.76 mmol) as described for 3. Crys-
tals suitable for X-ray analysis were obtained after 2 days.
Yield: 0.23 g (47%). Anal Calcd. for C30H29ClN2Pd·CH2Cl2:
C, 57.78; H, 4.85; N, 4.35. Found: C, 57.83; H, 4.31; N, 4.43.
1H NMR (CDCl3): δ 8.37 (d, 2H, J = 7.00 Hz, C6H5), 7.78
(d, 2H, J = 7.20 Hz, C6H5), 7.34 (m, 16H, C6H5), 0.32 (s, 3H,
Pd–Me).
2.2. Ligand synthesis
2.2.1. (N,Nꢀ-bis(diphenylmethylene)1,3-propanediamine
(L2)
A solution of benzophenone (10.87 g, 60.00 mmol) and
freshly distilled 1,3-propanediamine (2.5 mL, 30.0 mmol) in
anhydrous methanol (50 mL) were refluxed for 10 days. Three
pieces of Drierite were added to the solution every two days.
The yellow solution was filtered and the volume of the filtrate
reduced to half its volume in vacuo. The white solid that pre-
cipitated was filtered and the crude product recrystallized from
boiling heptane to give fine white crystals. Yield: 3.10 g (26%),
m.p.: 82–85 ◦C, MS (m/z): 402 (M+, 100%). 1H NMR (CDCl3):
δ 7.32 (m, 20H, C6H5), 3.46 (t, 4H, CH2), 2.05 (quintet, 2H,
CH2).
2.4. Crystallographic experimental section
Details regarding the data collections are summarized in
Table 1 and are fully described in the Supplementary Material.
The data 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 equiv-
alent measurements [14]. For both 3a and 4, the systematic
absences in the diffraction data were uniquely consistent for
the space group P21/n that yielded chemically reasonable and
computationally stable results of refinement [14]. For both com-
pounds, a successful solution by direct methods provided most
non-hydrogen atoms from the electron density map. The remain-
ing non-hydrogen atoms were located in an alternating series
of least-squares cycles and difference Fourier maps. All non-
hydrogen atoms (except C29 in the case of 3a) were refined
with anisotropic displacement coefficients. All hydrogen atoms
were included in the structure factor calculations at idealized
positions and were allowed to ride on the neighboring atoms
with relative isotropic displacement coefficients.
In the structure of complex 3a, the Pd complex resides
on a crystallographic inversion centre. There is Cl/Me com-
positional disorder about the Pd centre. The Cl/Me ratio
is 0.736(3):0.264(3); thus, three different compositions of
the complex are possible: [PdCl2(L1)2] [PdMe2(L1)2] and
[PdClMe(L1)2], and the complexes of different composition
have apparently co-crystallized. For complex 4, there is one
molecule of solvate dichloromethane per Pd complex in the lat-
2.3. Synthesis of complexes
2.3.1. [PdCl2{(C6H5)2C N(CH2)2N C(C6H5)2}] (1)
To a solution of [PdCl2(NCMe)2] (0.08 g, 0.30 mmol) in ace-
tone (5.0 mL) was added a solution of L1 (0.11g, 0.30 mmol)
in acetone (5.0 mL). The resultant orange solution changed to
yellow with immediate precipitation of a yellow solid. The mix-
ture was stirred for 15 min at room temperature, the precipitate
was then allowed to settle and the supernatant liquid decanted.
The residue was washed twice with acetone (2 × 10 mL) and the
product was dried in vacuo. Yield: 76% (0.13 g). Anal. Calcd. for
C28H24Cl2N2Pd: C, 54.44; H, 4.28; N, 4.95. Found: C, 54.84;
H, 3.70; N, 4.82. 1H NMR (DMSO-d6): δ 7.53 (m, 20H, C6H5),
4.15 (s, 4H, CH2).
2.3.2. [PdCl2{(C6H5)2C N(CH2)3N C(C6H5)2}] (2)
Complex 2 was prepared from [PdCl2(NCMe)2] (0.08 g,
0.30 mmol) and L2 (0.11 g, 0.30 mmol), following the synthetic
tice. The final difference Fourier map contained two high peaks
3
˚
(ca. 2.8 and 1.5 e/A ) in the vicinity of the solvent molecule in

74
S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
Table 1
Crystal data and structure refinement for 3a and 4
3a
4
Empirical formula
Formula weight
Temperature (K)
Wavelength
C28H24N2Cl1.472Me0.528Pd
C31H31Cl3N2Pd
644.33
943.46
105(2)
100(2)
˚
˚
0.71073 A
0.71073 A
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/n
Unit cell dimensions
˚
˚
12.5058(4) A
a
b
c
9.1303(9) A
˚
˚
˚
18.2917(17) A
14.0500(13) A
12.5694(4) A
˚
17.7373(6) A
β
103.913
93.0020(10)
3
3
˚
˚
Volume
Z
Density (calculated)
Absorption coefficient
F(0 0 0)
2277.31(16) A
2784.31(16) A
4
2
1.376 Mg/m3
0.537 mm−1
976
1.537 Mg/m3
0.978 mm−1
1312
Crystal size
␪ range for data collection
0.26 mm × 0.24 mm × 0.20 mm
0.42 mm × 0.34 mm × 0.33 mm
1.86–29.16◦
2.04–26.39◦
Index ranges
−12 ≤ h ≤ 12
25 ≤ h ≤ 24
−15 ≤ h ≤ 15
−15 ≤ k ≤ 15
−22 ≤ l ≤ 22
−19 ≤ h ≤ 19
Reflections collected
39614
22582
Independent reflections
Completeness to θ = 26.39◦
Absorption correction
Max. and min. transmission
Refinement method
6099 [R(int) = 0.0409]
99.3%
Empirical with SADABS
0.9002 and 0.8730
Full-matrix least-squares on F2
6099/0/292
5676 [R(int) = 0.0216]
99.6%
Multi-scan with SADABS
0.7384 and 0.6841
Full-matrix least-squares on F2
5676/0/335
Data/restraints/parameters
Goodness-of-fit on F2
1.022
1.022
Final R indices [I > 2sigma(I)]
R1 = 0.0295,
R1 = 0.0373,
wR2 = 0.0699
R1 = 0.0387,
wR2 = 0.1012
R1 = 0.0387,
R indices (all data)
wR2 = 0.1025
0.530 and −0.281 e A
wR2 = 0.1025
2.796 and −1.614 e A
−3
−3
˚
˚
Largest diff. peak and hole
chemically unreasonable positions; these peaks were considered
noise.
or butyl acrylate) were mixed in a two-necked round-bottomed
flask fitted with a reflux condenser. The mixture was dis-
solved in 30 mL of acetonitrile and palladium complex
(0.15 mmol) added before the mixture was heated at 80 ◦C
in an oil bath. Samples of 0.25 mL were withdrawn periodi-
cally by syringe, diluted with dichloromethane and analyzed by
GC–MS.
2.5. General procedure for Heck reactions
Iodobenzene (15 mmol), triethylamine (15 mmol) and
15 mmol of an appropriate olefinic substrate (methyl acrylate
Scheme 1. Synthetic routes to palladium complexes 1–4.

S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
75
3. Results and discussion
The palladium complexes 1–4 were prepared as depicted in
Scheme 1. Complexes 1 and 2 were formed by reacting ligands
L1 and L2 with [PdCl2(NCMe)2] in an inert atmosphere. The
products were isolated as yellow solids in moderate to good
yields. Both complexes were found to be only sparingly soluble
in CHCl3 or CH2Cl2. 1H NMR spectra of both complexes exhib-
ited characteristic peaks and peak intensities of the respective
ligands, withslightchemicalshiftsfromthoseofthefreeligands.
The NMR data thus suggested that the two complexes could
be formulated as shown in Scheme 1. The results of elemental
analyses agreed with the proposed formulae.
Complex 3 was synthesized by adding a diethyl ether solution
of L1 to a suspension of [PdClMe(COD)] in diethyl ether. Sim-
ilarly, addition of L2 to [PdClMe(COD)] yielded 4. In the case
of the synthesis of 3, the reaction took 6 h to complete while the
reaction with L2 to form 4 required only 30 min to go to com-
pletion. However, in one experiment for the synthesis of 3 where
1.3 equivalents of L1 was used instead of the usual 1 equiva-
lent, our attempts to purify the crude 3 from a CH2Cl2 solution
yielded single crystals of an entirely new material (3a). Com-
plex 3a resides on a crystallographic inversion center and only
one half of it is symmetry independent. Thus, in the asymmetric
unit (Fig. 1(a)), the Pd atom is bound to an L1 ligand while the
other site is 73.6(3)% occupied by a chloride and 26.4(3)% by
a methyl substituent due to compositional disorder. The entire
complex contains two L1 ligands and two disordered ligands in
trans positions relative to each other (Fig. 1(b)).
All expected peaks were clearly resolved in the room temper-
ature 1H NMR spectra of complexes 3 and 4, with the exception
of the protons in the propane backbone of 4 which appeared as
a broad peak at 4.20 ppm. The 13C resonances of the propane
backbone of 4 were, however, resolved in the room tempera-
ture 13C NMR spectrum where these carbons appeared at 59.4,
56.4 and 33.9 ppm. The NMR data suggested that the propane
backbone undergoes inversion at the carbons at a rate that makes
the motion of the protons on the backbone more rapid than the
NMR timescale can detect, but the motion of carbons during
1
this inversion is not as rapid. Variable temperature H NMR
spectra of 4 showed that the fluxional behavior could be frozen
out at −50 ◦C when the distinct environments of all six protons
are evident (Fig. 2); these give rise to two triplets at 4.64 and
4.58 ppm, three doublets at 4.18, 3.72 and 1.90 ppm, and a quar-
tet at 1.27 ppm. The two most upfield signals are assigned to the
protons on the central carbon atom of the propane backbone.
The two triplets belong to protons on the two carbons next to
the imine nitrogens, and the remaining two doublets are reso-
nances from the geminal protons associated with the protons
that give rise to the triplets (cf. Fig. 2). The solid-state struc-
ture of 4·CH2Cl2 (Fig. 3) did indeed confirm the presence of the
propane backbone.
Fig. 1. (a) A molecular drawing of the asymmetric unit of 3a. All H atoms except
those on C29 are omitted. Atom C29 was refined isotropically. (b) A molecular
drawing of one of the three possible Pd complexes (3a, see text) present in the
lattice, drawn with 50% probability ellipsoids. The hydrogen atoms are omitted
for clarity.
solutions of each complex in dichloromethane. The molecular
structures are depicted in Figs. 1 and 3, crystallographic data are
listed in Table 1 and selected bond lengths and bond angles are
listed in Table 2. Complex 3a crystallized without solvent, while
4 crystallized with one mole of dichloromethane in the unit cell.
The structure of complex 3a has two L1 ligands instead of
one, and a Cl and a compositional disorder of Cl and Me in the
3.1. Molecular structures of 3a and 4
Crystals of 3a and 4·CH2Cl2, suitable for X-ray structure
determination, were obtained by slow diffusion of hexane into

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S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
Fig. 2. Variable temperature 1H NMR spectra of complex 4.
remaining position of a square planar arrangement, in which the
imine ligands are trans to each other. Unexpectedly L1 in 3a is
coordinated to Pd not as a bidentate ligand but in a monodentate
fashion via only one imine nitrogen, while the other imine group
in the ligand remains uncoordinated. The geometry around the
Pd is a distorted square planar. The Pd–Cl and Pd–C bonds in
acrylate (Scheme 2). Reactions were carried out under nitrogen
at 80 ◦C in CH3CN (15 mL) and triethylamine as a base; using
equivalent molar ratios of iodobenzene, methyl acrylate and tri-
ethylamine. The catalyst precursors were added at a Pd:substrate
molar ratio of 1:100. After addition of the catalyst precursor,
samples were drawn at periodic intervals and the consumption
of iodobenzene monitored by GC over 8 h. The results of these
experiments are summarized in Table 3.
For each catalyst precursor evaluated, the major prod-
uct formed by the Heck coupling reaction was the trans
stereoisomer, methyl (2E)-3-phenylacrylate or butyl
(2E)-3-phenylacrylate. The cis stereoisomer, alkyl (2Z)-
3-phenylacrylate, comprised less than 1% of the isomeric
products formed. Table 3 shows all four complexes have
similar trends of activity in the arylation reaction of methyl
˚
3a are 2.3595(12) and 2.005(12) A respectively, and are within
the expected range for each of these bond types [15,16].
The structure of complex 4 shows a bidentate co-ordination
of L2 to Pd to give a distorted square planar geometry around the
palladium with◦the chelating angle C(1)–Pd–N(1) being close to
◦
˚
90 (89.36(11) ). The Pd(1)–N(2) bond distance of 2.209(2) A
is significantly longer than the Pd(1)–N(1) bond distance of
˚
2.045(2) A due to the difference in the ligand trans influence.
3.2. Catalytic Heck reaction
The catalytic activity of complexes 1–4 were tested towards
the Heck coupling of iodobenzene with methyl acrylate or butyl
Table 2
◦
˚
Bond distances [A] and angles [ ] for complexes 3a and 4
3a
˚
Bond lengths (A)
Pd(1)–C(29)
Pd(1)–N(1)
Pd(1)–Cl(1)
2.005(12)
2.0189(13)
2.3595(12)
N(1)–C(1)
N(1)–C(14)
N(2)–C(16)
1.283(2)
1.472(2)
1.278(4)
Bond angles [◦]
C(29)–Pd(1)–N(1)
C(29)A–Pd(1)–N(1)
92.0(4)
88.0(4)
N(1)–Pd(1)–Cl(1)
C(29)–Pd(1)–N(1)A
94.40(4)
88.0(4)
4
˚
Bond lengths (A)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–Cl(1)
Cl(2)–C(31)
2.027(3)
2.045(2)
2.209(2)
2.3286(7)
1.765(4)
Cl(3)–C(31)
N(1)–C(8)
N(1)–C(15)
N(2)–C(17)
N(2)–C(24)
1.775(4)
1.291(4)
1.485(4)
1.475(4)
1.288(4)
Bond angles [◦]
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
C(8)–N(1)–C(15)
89.36(11)
173.74(11)
85.13(9)
168.79(7)
97.20(6)
120.7(2)
C(8)–N(1)–Pd(1)
C(15)–N(1)–Pd(1)
C(24)–N(2)–C(17)
C(24)–N(2)–Pd(1)
C(17)–N(2)–Pd(1)
C(3)–C(2)–C(7)
130.8(2)
108.28(17)
119.3(2)
136.2(2)
104.00(17)
119.9(3)
Fig. 3. Molecular drawing of 4 with 50% probability ellipsoids. The hydrogen
atoms are omitted for clarity.

S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
77
Scheme 2. The Heck coupling reactions studied in this investigation.
acrylate. All four catalysts achieved about 70% conversion of
iodobenzene after 1 h and 90% conversion after 8 h (Table 3,
entry 1–8). However, the activity trend of these catalysts in
the arylation reaction of butyl acrylate was slightly lower. In
these reactions about 55% conversion was achieved after 1 h;
increasing up to 75–80% conversion after 8 h (Table 3, entries
9–16). This observation highlights that the initial rates are faster
with methyl acrylate compared to butyl acrylate.
The similarity in catalytic activities of our catalysts for a
particular alkene is not surprising, since the structures of these
catalyst precursors are similar. It is also well established that in
using preformed palladium complexes as Heck coupling cata-
lysts the palladium complex is first reduced from Pd(II) to Pd(0);
thereafter the ligand in the complex plays the role of stabilizing
the Pd(0) species, which then acts as the active catalyst in the
reaction [17]. Even in so-called ligand-free catalysts described
by de Vries [6], the initial palladium colloids formed are stabi-
lized by acetate ions before the aryl halide used in the coupling
reaction oxidatively adds to the colloids.
It is noteworthy that the activity of our catalyst precur-
sors are slightly higher compared to the ␣-diimine palladium
complexes utilized in the Heck coupling reaction of 1-bromo-4-
methylbenzene with methyl acrylate by Grasa et al. [8b] using
a 1,4-dicyclohexyl-diazabutadiene (DAB-Cy) catalyst precur-
sor at a higher temperature of 100 ◦C. The 58% conversion
achieved after 6 h with the DAB-Cy catalyst precursor is lower
compared to the 80% conversion achieved with our diimine lig-
and complexes at 80 ◦C. As shown graphically in Figs. 4 and 5,
the catalysts are active for approximately 1 h, after which they
lose much of their activity. However, very little palladium black
Fig. 4. Conversion as a function of time for the arylation of methyl acrylate with
iodobenzene at 80 ◦C.
formation – a process usually associated with catalyst deactiva-
tion in Heck catalysis, was observed to accompany the loss of
activity.
To investigate the effect of temperature and solvent on the
catalytic activities of all four catalysts precursors, the Heck
reactions were performed at 120 ◦C (Table 4). As expected, the
higher reaction temperature led to an increase in conversion rate
after 1 h of reaction time (Table 4, entries 1–16). Heck cou-
pling reactions are generally performed between 120–140 ◦C,
precisely due to the improvement in the initiation rates and
Table 3
Heck coupling data using complexes 1–4 and reaction times of 1 and 8 ha
Catalyst
Alkene
Conversion (%)b 1 h
Conversion (%)b 8 h
1
2
3
4
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
74
71
69
72
88
87
88
86
Average
Methyl acrylate
71
87
1
2
3
4
Butyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
71
55
57
53
81
79
82
76
Average
Butyl acrylate
59
80
a
Amounts: PhI, 15 mmol; methyl acrylate or butyl acrylate, 15 mmol; Et3N,
15 mmol; catalyst, 0.15 mmol; solvent = CH3CN, 30 mL; temperature, 80 ◦C.
Fig. 5. Conversion as a function of time for the arylation of butyl acrylate with
iodobenzene at 80 ◦C.
b
Determined by GC.

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S.M. Nelana et al. / Journal of Molecular Catalysis A: Chemical 285 (2008) 72–78
Table 4
and the Swedish International Development Agency (SIDA),
under the NRF-SIDA collaborative programme. We also thank
Mr. Martin Jarenmark for recording the low temperature NMR
spectra.
Heck coupling data using complexes 1–4 at 120 ◦C for 1 ha
Catalyst
Alkene
Conversion (%)b
DMA
Conversion (%)b
DMF
1
2
3
4
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
93
89
94
91
91
93
92
88
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Supplementary material
CCDC 666494 and 666495 contains the supplementary crys-
tallographic data for 3a and 4. 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, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or
e-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgement
We gratefully acknowledge the financial support for this work
from the National Research Foundation (NRF) South Africa