Thiophene based imino-pyridyl palladium(II) complexes: Synthesis, molecular structures and Heck coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2017.04.022

The new compounds (5-methyl-2-thiophene-2-pyridyl(R))imine [R = methyl (L1); R = ethyl (L2)] and (5-bromo-2-thiophene-2-pyridyl(R)imine [R = methyl (L3); R = ethyl (L4)] were successfully synthesized via Schiff base condensation reaction and obtained in g

Full text of DOI:10.1016/j.jorganchem.2017.04.022

Accepted Manuscript
Thiophene based imino-pyridyl palladium(II) complexes: Synthesis, molecular
structures and Heck coupling reactions
Fatma M. Elantabli, Mduduzi P. Radebe, William M. Motswainyana, Bernard O.
Owaga, Samir M. El-Medani, Erik Ekengard, Matti Haukka, Ebbe Nordlander, Martin
O. Onani
PII:
S0022-328X(17)30258-9
10.1016/j.jorganchem.2017.04.022
JOM 19909
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 25 January 2017
Revised Date: 10 April 2017
Accepted Date: 18 April 2017
Please cite this article as: F.M. Elantabli, M.P. Radebe, W.M. Motswainyana, B.O. Owaga, S.M.
El-Medani, E. Ekengard, M. Haukka, E. Nordlander, M.O. Onani, Thiophene based imino-pyridyl
palladium(II) complexes: Synthesis, molecular structures and Heck coupling reactions, Journal of
Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.04.022.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Eight Pd(II) complexes of the general formulae [PdCl2(L)] and [PdClMe(L)] have been
synthesized and characterized (L = the new pyridyl-imine ligands (5-methyl-2-thiophene-2-
pyridyl(R))imine and (5-bromo-2-thiophene-2-pyridyl(R)imine [R = methyl,ethyl]). The
complexes showed good activity as catalysts for standard Heck coupling reactions.

ACCEPTED MANUSCRIPT
Thiophene based imino-pyridyl palladium(II) complexes: synthesis,
molecular structures and Heck coupling reactions
Fatma M. Elantablia,d†, Mduduzi P. Radebeb†, William M. Motswainyanab, , Bernard O. Owagac, Samir
M. El-Medanid, Erik Ekengarda, Matti Haukkae, Ebbe Nordlandera*, Martin O. Onanib*
aInorganic Chemistry Research Group, Chemical Physics, Center for Chemistry and Chemical
Engineering, Lund University, SE-22100 Lund, Sweden
bDepartment of Chemistry, University of the Western Cape, Private Bag X17, Bellville,7535, South
Africa
cSchool of Chemistry and Physics, University of KwaZulu Natal, Private Bag X54001, 4000 Durban,
dDepartment of Chemistry, Faculty of Science, Fayoum University, 63514, Egypt
eDepartment of Chemistry, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
ABSTRACT
The new compounds (5-methyl-2-thiophene-2-pyridyl(R))imine [R = methyl (L1); R = ethyl
(L2)] and (5-bromo-2-thiophene-2-pyridyl(R)imine [R = methyl (L3); R = ethyl (L4)] were
successfully synthesized via Schiff base condensation reaction and obtained in good yields.
These potential ligands were reacted with [PdCl2(COD)] and [PdClMe(COD)] to give the
corresponding complexes [PdCl2(L)] (L=L1-L4; 1-4) and [PdClMe(L)] (L=L1-L4; 5-8). All
compounds were characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis and
mass spectrometry. The molecular structures of 1, 2, 6 and 8 were confirmed by X-ray
crystallography. The complexes were evaluated as catalyst precursors for standard Heck
coupling reactions and showed significant catalytic activities that could be correlated with
steric and electronic influences.
Keywords: Imino-pyridyl; Palladium; Synthesis; Molecular structures; Heck reactions
† These authors have contributed equally to this work.
1

ACCEPTED MANUSCRIPT
1. Introduction
The palladium-catalyzed olefination of aryl halides (Heck reaction) has emerged as one of the
most powerful methods for carbon-carbon bond formation in organic synthesis since its
inception in 1971 [1-3]. It features applications that range from fine chemical synthesis of
various hydrocarbons and industrial production of pharmaceuticals, to advanced syntheses of
natural products [4-7]. The wide application of the Heck reaction is encouraged by its high
tolerance to various functional groups [8] as well as an ability to proceed under mild reaction
conditions [9]. Palladium complexes containing phosphine ligands have been widely used to
catalyze Heck reactions [10-16]. These catalysts have been preferentially used because they
provide thermally robust catalysts [15,16]. In general, these catalyst precursors contain P-P
and P-N ligand moieties, and the substituents on the ligands have been successively
optimized by different researchers to increase the catalyst turnover and efficiency. However,
the ligands that are normally used to prepare such palladium catalysts are in general
expensive, toxic and also sensitive to air and moisture. They generally undergo phosphine
degradation by P-C bond cleavage [17]. In view of this, much research effort is currently
directed at the development of phosphine-free palladium catalysts. For example, many
catalytic systems consisting of nitrogen-based heterocyclic compounds [18-20] diimine [21-
26], dipyridine [27-29], bisimidazole [30,31], pyrazole [32-35] and hydrazone [36]
derivatives have been reported. These stronger donor ligands have started to receive attention
as possible replacements of phosphine-based catalysts because of the ease of synthesis and
their resistance to oxidation reactions [27]. The substituents on the ligands make their
complexes display robust properties. Their nature has been found to exert a strong influence
on catalyst activity such that electron-withdrawing substituents tend to enhance activity
while, conversely, electron-donating substitutents decrease activity. However, the
electronic/steric influence of the ligand also depends on the nature of the metal, ring
2

ACCEPTED MANUSCRIPT
substituents in ligands and their position within the ligands. When the ligands in general
possess aromatic or hetero-aromatic rings with substituents in their –ortho and –para
positions, they will afford highly active catalysts, but one drawback is that they usually
require multi-step procedures to prepare, leading to very low yields. Palladium complexes
with P-N type ligands have been reported to show pronounced catalytic activity in olefin
polymerisation, which was attributed to the discussed electronic influence [37]. Recently, we
reported new imino-pyridyl nickel(II) thiolate complexes [38a] and phenylene-bridged bis-
(imino-quinolyl) binuclear palladium(II) complexes [38b] with high activity in Heck coupling
reactions. However, they were non-substituted and there were thus no electronic effects to
consider. In the same context, we have successfully synthesized and characterized substituted
thiophene based imino-pyridyl palladium(II) complexes. The new compounds have been
investigated as Heck coupling catalysts of aryl halides with methyl acrylate. The impact of
ligand substituents on catalytic performance has also been investigated.
2.
Experimental
2.1
General
All reactions were carried out under oxygen free atmosphere using a dual vacuum/nitrogen
line and standard Schlenk techniques, unless stated otherwise. The solvents were purified by
heating under reflux and nitrogen in the presence of a suitable drying agent. The metal
precursors [PdCl2(COD)] and [PdClMe(COD)] were prepared following literature methods
[39]. The chemical reagents were of analytical grade or higher. They were purchased from
Sigma Aldrich and were used without further purification.
3

ACCEPTED MANUSCRIPT
2.2
General procedure for the synthesis of ligands L1-L4
An equimolar amount of pyridyl amine was added dropwise to a MeOH solution (15 mL) of
substituted thiophene carboxaldehyde. Anhydrous magnesium sulfate was added in excess
(ca. 1 g) to remove water formed as a byproduct in the Schiff condensation. The reaction was
allowed to proceed at room temperature for 12 h and was monitored by IR spectroscopy. At
the end of the reaction, the magnesium sulfate was filtered off and the solvent evaporated
under reduced pressure to obtain an orange oil. The oily product was washed with water (10
mL), extracted with CH2Cl2 (2 x 10 mL), and again dried over magnesium sulfate. The
solvent was evaporated to obtain the ultimate product which was a light orange oil.
2.2.1 (5-Methyl-2-thiophene-2-pyridylmethyl)imine (L1)
The ligand was prepared following the above general procedure using 5-methyl-2-
thiophenecarboxaldehyde (0.612 g, 4.85 mmol) and 2-picolylamine (0.524 g, 4.85 mmol)
1
Yield: 0.943 g, (89%) IR (nujol, cm-1); ν(C=N) 1632, ν(C=C) 1591, 1570, H NMR (500
MHz, CDCl3) δ 8.55 (d, J = 4.7 Hz, 1H), 8.44 (s, 1H, -CH=N), 7.66 (t, J = 7.6 Hz, 1H), 7.39
(d, J = 7.8 Hz, 1H), 7.16 (d, J = 6.9 Hz, 2H), 6.74 (d, J = 2.5 Hz, 1H), 4.89 (s, 2H), 2.50 (s,
13
3H). C NMR (50 MHz, CDCl3): δ 159.3 (C=N); 156.4, 149.1, 144.5, 136.6, 131.5, 125.8,
122.2, 121.9 (py and thiophen); 66.1 (CH2); 15.8 (CH3). EI-MS: m/z 217 [M]+. Anal. Calcd
for C12H12N2S: C, 66.63; H, 5.59; N, 12.95; Found: C, 66.85; H, 5.77; N, 12.84
2.2.2 (5-Methyl-2-thiophene-2-pyridylethyl)imine (L2)
The ligand was prepared according to the general procedure using 5-methyl-2-
thiophenecarboxaldehyde (0.530 g, 4.20 mmol) and 2-(2-pyridylethyl)amine (0.514 g, 4.20
1
mmol). Yield: 0.839 g (87%) IR (nujol, cm-1); ν(C=N) 1632, ν(C=C)1593, 1569; H NMR
(500 MHz, CDCl3): δ 8.53 (d, J = 4.9 Hz, 1H), 8.15 (s, 1H, -CH=N), 7.55 (dd, J= 6.6, 2.8 Hz,
4

ACCEPTED MANUSCRIPT
1H), 7.16 (d, J = 7.8 Hz, 1H), 7.09 (dd, J = 7.3, 5.0 Hz, 1H), 7.01 (d, J = 3.5 Hz, 1H), 6.69 (d,
J = 3.5 Hz, 1H), 3.93 (t, J = 7.2 Hz, 2H), 3.15 (t, J = 7.3 Hz, 2H), 2.48 (s, 3H). 13C NMR (50
MHz, CDCl3): δ 159.5 (C=N); 154.8, 149.0, 143.7, 139.8, 136.0, 130.6, 125.4, 123.6, 121.0
(py and thiophen); 60.5, 39.4 (CH2); 15.5 (CH3); EI-MS: m/z 231 [M]+. Anal. Calcd for
C13H14N2S: C, 67.79; H, 6.13; N, 12.16; Found: C, 67.99; H, 6.38; N, 12.34
2.2.3 (5-Bromo-2-thiophene-2-pyridylmethyl)imine (L3)
The ligand was prepared according to the general procedure using 5-bromo-2-
thiophenecarboxaldehyde (0.955 g, 5 mmol) and 2-picolylamine (0.541 g, 5 mmol). Yield:
1
0.940 g (68%) IR (nujol, cm-1); ν(C=N) 1630, ν(C=C) 1590, 1570, H NMR (500 MHz,
CDCl3) δ 8.54 (d, J = 4.1 Hz, 1H), 8.40 (s, 1H, -CH=N), 7.66 (dd, J = 6.6, 4.6 Hz, 1H), 7.38
(d, J = 7.8 Hz, 1H), 7.16 (dd, J = 15.6, 8.9 Hz, 1H), 7.07 (d, J = 3.9 Hz, 1H), 7.03 (d, J = 3.8
Hz, 1H), 4.87 (s, 2H). 13C NMR (50 MHz, CDCl3): δ 158.7 (C=N); 155.4, 149.2, 143.8,
136.7, 130.9, 130.3, 122.2, 122.1, 117.4 (py and thiophen); 66.05 (CH2); EI-MS: m/z 218
[M]+. Anal. Calcd for C11H9BrN2S: C, 46.99; H, 3.23; N, 9.96; Found: C, 46.84; H, 3.09; N,
10.18
2.2.4 (5-Bromo-2-thiophene-2-pyridylethyl)imine (L4)
The ligand was prepared according to the general procedure using 5-bromo-2-
thiophenecarboxaldehyde (0.955 g, 5 mmol) and 2-(2-pyridylethyl)amine (0.611 g, 5 mmol).
1
Yield: 0.985 g (79%) IR (nujol, cm-1); ν(C=N) 1632, ν(C=C) 1590, 1568, H NMR (500
MHz, CDCl3) δ 8.55 (d, J= 4.2, 1H), 8.12 (s, 1H, -CH=N), 7.57 (dd, J = 7.7, 1.8 Hz, 1H),
7.16 (d, J = 7.8 Hz, 1H), 7.13 (dd, J = 3.9, 1.9 Hz, 1H), 6.99 (d, J = 3.8 Hz, 1H), 6.95 (d, J =
3.2 Hz, 1H), 3.94 (t, J = 7.1 Hz, 2H), 3.15 (t, J = 7.2 Hz, 2H). 13C NMR (50 MHz, CDCl3): δ
159.3 (C=N); 153.8, 149.1, 143.8, 136.0, 130.1, 130.1, 123.6, 121.1, 116.6 (py and thiophen);
5

ACCEPTED MANUSCRIPT
60.4, 39.2 (CH2); EI-MS: m/z 297 [M]+. Anal. Calcd for C12H11BrN2S: C, 48.82; H, 3.76; N,
9.49; Found: C, 48.73; H, 3.88; N, 9.62
2.3 General procedure for the synthesis of imino-pyridyl complexes
A CH2Cl2 solution (10 ml) of either [PdCl2(COD)] or [PdClMe(COD)] was added dropwise
to a dichloromethane solution (10 ml) of the appropriate ligand. The reaction was allowed to
proceed with stirring at room temperature for 8 h, resulting in the formation of a light yellow
precipitate for complexes 1-4. In the case of complexes 5-8, the solution was concentrated to
almost half the original volume before excess Et2O was added to precipitate out light yellow
solid. The precipitate was filtered and the solvent evaporated under reduced pressure to
obtain the product. The solid was washed with Et2O (2 x 5 mL) and dried under reduced
pressure.
2.3.1 Dichloro-[(5-methyl-2-thiophene-2-pyridylmethyl)imine]palladium (II) (1)
The complex was prepared according to the general procedure using [PdCl2(COD)] (0.097 g,
0.34 mmol) and L1 (0.067 g, 0.34 mmol). Single crystals suitable for X-ray crystallography
were obtained when the solid was recrystallized from a solution of CH2Cl2 and hexane.
1
Yield: 0.102 g (76%), mp: 182 °C, IR (KBr, cm-1); ν(C=N) 1607, ν(C=C) 1599; H NMR
(500 MHz, DMSO-d6) δ 8.92 (d, J = 5.7 Hz, 1H), 8.84 (s, 1H, -CH=N), 8.12 (t, J = 7.7 Hz,
1H), 7.92 (d, J = 3.9 Hz, 1H), 7.75 (d, J = 8.0 Hz, 1H), 7.55 (t, J = 6.6 Hz, 1H), 7.18 (d, J =
3.7 Hz, 1H), 5.49 (s, 2H), 2.62 (s, 3H); EI-MS: m/z 400 [M]+; Anal. Calcd for
C12H12Cl2N2PdS: C, 36.62; H, 3.07; N, 7.12; Found: C, 36.70; H, 3.21; N, 7.31
6

ACCEPTED MANUSCRIPT
2.3.2 Dichloro-[(5-methyl-2-thiophene-2-pyridylethyl)imine]palladium (II) (2)
The complex preparation was carried out according to the general procedure using
[PdCl2(COD)] (0.057 g, 0.20 mmol) and L2 (0.048 g, 0.20 mmol). Single crystals suitable for
X-ray crystallography were obtained when the solid was recrystallized from a solution of
CH2Cl2 and hexane. Yield: 0.068 g (84%), mp: 179 °C, IR (KBr, cm-1); ν(C=N) 1609,
1
ν(C=C) 1597; H NMR (500 MHz, DMSO-d6): δ 8.76 (s, 1H, -CH=N), 8.70 (d, J = 5.3 Hz,
1H), 8.02 (t, J = 4.3 Hz, 1H), 7.83 (d, J = 3.8 Hz, 1H), 7.64 (d, J = 7.8 Hz, 1H), 7.46 (t, J =
3.3 Hz, 1H), 7.12 (d, J = 5.2 Hz, 1H), 3.83 (t, J = 4.3 Hz, 2H), 3.52 (t, J = 4.1 Hz, 2H), 2.56
(s, 3H); EI-MS: m/z 408 [M]+; Anal. Calcd for C13H14Cl2N2PdS: C, 38.30; H, 3.46; N, 6.87;
Found: C, 38.41; H, 3.63; N, 6.96
2.3.3
Dichloro-[(5-bromo-2-thiophene-2-pyridylmethyl)imine]palladium (II) (3)
The complex preparation was carried out according to the general procedure using
[PdCl2(COD)] (0.066 g, 0.23 mmol) and L3 (0.065 g, 0.23 mmol). Yield: 0.082 g (78%), mp:
1
179 °C, IR (KBr, cm-1); ν(C=) 1621, ν(C=C) 1596; H NMR (500 MHz, DMSO-d6): δ 8.91
(d, J = 5.7 Hz, 1H), 8.89 (s, 1H, -CH=N), 8.14 (t, J = 7.7 Hz, 1H), 7.98 (d, J = 4.0 Hz, 1H),
7.80 (d, J = 7.9 Hz, 1H), 7.62 (d, J = 4.1 Hz, 1H), 7.59 – 7.55 (m, 1H), 5.48 (s, 2H); EI-MS:
m/z 460 [M]+; Anal. Calcd for C11H9BrCl2N2PdS: C, 28.82; H, 1.98; N, 6.11; Found: C,
29.07; H, 2.18; N, 6.35
2.3.4 Dichloro-[(5-bromo-2-thiophene-2-pyridylethyl)imine]palladium (II) (4)
The complex preparation was carried out according to the general procedure using
[PdCl2(COD)] (0.118 g, 0.25 mmol) and L4 (0.069 g, 0.25 mmol). Yield: 0.061 g (85%), mp:
182 °C, IR (KBr, cm-1); ν(C=N) 1619, ν(C=C) 1598; 1H NMR (500 MHz, DMSO-d6): δ 8.61
(d, J = 5.5 Hz, 1H), 8.38 (s, 1H, -CH=N), 7.99 (t, J = 7.2 Hz, 1H), 7.63 (d, J = 8.3 Hz, 1H),
7

ACCEPTED MANUSCRIPT
7.62 (d, J = 4.4 Hz, 1H), 7.44 (d, J = 7.1 Hz, 1H), 7.42 (d, J = 3.8 Hz, 1H), 3.58 (t, J = 10.9
Hz, 2H), 3.55 (t, J =13.6 Hz, 2H); EI-MS: m/z 478 [M]+; Anal. Calcd for C12H11BrCl2N2PdS:
C, 30.50; H, 2.35; N, 5.93; Found: C, 30.73; H, 2.49; N, 6.18
2.3.5 Chloromethyl-[(5-methyl-2-thiophene-2-pyridylmethyl)imine]palladium (II) (5)
The complex preparation was carried out according to the general procedure using
[PdClMe(COD)] (0.050 g, 0.23 mmol) and L1 (0.041 g, 0.23 mmol) Yield: 0.058 g (68%),
1
mp: 138 °C, IR (nujol cm-1); ν(C=N) 1618, ν(C=C) 1599; H NMR (500 MHz, CDCl3): δ
9.03 (d, J = 5.2 Hz, 1H, py), 8.93 (s, 1H, -CH=N), 8.50 (d, J = 5.9 Hz, 1Hiso,py), 8.39 (s,
1Hiso, -CH=N), 7.89 – 7.78 (m, 3H, py), 7.54 (d, J = 3.7 Hz, 1H, thiophene), 7.47 (d, J = 8.1
Hz, 1H, thiophene), 7.37-7.33 (m, 3Hiso, py), 7.00 (d, J = 3.3 Hz, 1Hiso, thiophene), 6.94 (d, J
= 2.9 Hz, 1Hiso, thiophene), 5.28 (s, 2H, =N-CH2), 5.13 (s, 2Hiso, =N-CH2), 2.63 (s, 3H), 2.61
(s, 3Hiso), 0.89 (s, 3Htrans iso with imine nitrogen, Pd-CH3), 0.80 (s, 3Hcis iso with imine nitrogen, Pd-CH3);
EI-MS: m/z 374 [M]+; Anal. Calcd for C13H15ClN2PdS: C, 41.84; H, 4.05; N, 7.51; Found: C,
41.97; H, 4.22; N, 7.68
2.3.6 Chloromethyl-[(5-methyl-2-thiophene-2-pyridylethyl)imine]palladium (II) (6)
The preparation of this complex was carried out according to the general procedure using
[PdClMe(COD)] (0.061 g, 0.23 mmol) and L2 (0.053 g, 0.23 mmol). Single crystals suitable
for X-ray crystallography were obtained when the solid was recrystallized from a solution of
CH2Cl2 and hexane. Yield: 0.066 g (74%), mp: 138 °C, IR (nujol, cm-1); ν(C=N) 1621,
ν(C=C) 1601; 1H NMR (500 MHz, CDCl3): δ 8.80 (d, J = 4.0 Hz, 1H), 8.21 (s, 1H), 7.64 (t, J
= 6.9 Hz, 1H), 7.38 (d, J = 3.7 Hz, 1H), 7.21 (dd, J = 7.6, 2.9 Hz, 2H), 6.77 (d, J = 3.6 Hz,
1H), 4.59 – 4.54 (m, 2H), 3.66 (m, 2H), 2.59 (s, 3H), 0.74 (s, 3H, Pd-CH3); EI-MS: m/z 390
8

ACCEPTED MANUSCRIPT
[M]+; Anal. Calcd for C14H17ClN2PdS: C, 43.42; H, 4.42; N, 7.23; Found: C, 43.24; H, 4.63;
N, 7.08
2.3.7 Chloromethyl-[(5-bromo-2-thiophene-2-pyridylmethyl)imine]palladium (II) (7)
The preparation of this complex was carried out according to the general procedure using
[PdClMe(COD)] (0.041 g, 0.15 mmol) and L3 (0.043 g, 0.15 mmol). Yield: 0.066 g (87%),
1
mp: 138 °C, IR (nujol, cm-1); ν(C=N) 1624, ν(C=C) 1597; H NMR (500 MHz, CDCl3): δ
9.03 (d, J = 4.4 Hz, 1H, py), 8.97 (s, 1H, -CH=N), 8.52 (d, J = 5.4 Hz, 1Hiso, py), 8.43 (s,
1Hiso, -CH=N), 7.91 (t, J = 8.3 Hz, 1H, py), 7.82 (t, J = 8.3 Hz, 1Hiso, py), 7.51 (d, J = 4.0 Hz,
1H, thiophene), 7.49 – 7.46 (m, 2H, py), 7.39 (d, J = 7.2 Hz, 2Hiso, py), 7.32 (d, J = 4.2 Hz,
1H, thiophene), 5.25 (s, 2H, =N-CH2), 5.08 (s, 2Hiso, =N-CH2), 0.92 (s, 3Htrans iso with imine
nitrogen, Pd-CH3), 0.81 (s, 3Hcis iso with imine nitrogen, Pd-CH3); EI-MS: m/z 439 [M]+; Anal. Calcd
for C12H12BrClN2PdS: C, 32.90; H, 2.76; N, 6.39; Found: C, 33.06; H, 2.87; N, 6.53
2.3.8 Chloromethyl-[(5-bromo-2-thiophene-2-pyridylethyl)imine]palladium (II) (8)
The complex preparation was carried out according to the general procedure using
[PdClMe(COD)] (0.069 g, 0.26 mmol) and L4 (0.062 g, 0.26 mmol). Single crystals suitable
for X-ray crystallography were obtained when the solid was recrystallized from a solution of
dichloromethane and hexane. Yield: 0.092 g (87%), mp: 138 °C, IR (nujol, cm-1); ν(C=N)
1
1624, ν(C=C) 1599; H NMR (500 MHz, CDCl3): δ 8.80 (d, J = 6.3 Hz, 1H), 8.23 (s, 1H, -
CH=N), 7.80 (t, J = 7.5 Hz, 1H), 7.68 – 7.65 (m, 1H), 7.28 (d, J = 3.9 Hz, 1H), 7.23 (d, J =
4.3 Hz, 1H), 7.07 (d, J = 4.0 Hz, 1H), 4.18-4.15 (m, 2H), 2.69 – 2.67 (m, 2H), 0.76 (s, 3H,
Pd-CH3); EI-MS: m/z 453 [M]+; Anal. Calcd for C13H14BrClN2PdS: C, 34.54; H, 3.12; N,
6.20; Found: C, 34.46; H, 3.30; N, 6.48
9

ACCEPTED MANUSCRIPT
2.4 X-ray structure determinations of complexes 1, 2, 6 and 8
The crystals were immersed in cryo-oil, mounted in a MiTeGen loop, and measured at a
temperature of 170(2) K (for 6, 120 K). The X-ray diffraction data was collected on a Bruker
KAPPA APEX II CCD diffractometer using Mo Kα radiation (λ = 0.71073 Å). The
Denzo/Scalepack program package [40] was used for cell refinements and data reductions.
The structure was solved by the charge flipping method using the SHELXT program. A multi-
scan absorption correction based on equivalent reflections (SADABS-2012/1 [41]) was
applied to the data. Structural refinement was carried out using SHELXL-2014 [42] with the
UCSF Chimera [43] and SHELXLE-2014 graphical user interfaces. Hydrogen atoms were
positioned geometrically and constrained to ride on their parent atoms with C-H = 0.95–0.99
Å and Uiso = 1.2-1.5 Ueq(parent atom). For complex 8, single-crystal X-ray diffraction data
were collected on a Bruker KAPPA APEX II DUO and Nonius Kappa-CCD diffractometer
using graphite-monochromated Mo-Kα radiation (χ = 0.71073 Å). Data collection was
carried out at 173(2) K. Temperature was controlled by an Oxford Cryostream cooling
system (Oxford Cryostat). Cell refinement and data reduction were performed using the
program SAINT [44]. The data were scaled and absorption correction performed using
SADABS [45]. The structures were solved by direct methods using SHELXS-97 and refined
by full-matrix least-squares methods based on F2 using SHELXL-97 [42] and using the
graphics interface program X-Seed [42]. All non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were placed in idealized positions and refined with
geometrical constraints.
2.5
General procedure for Heck reactions
A dry 100 ml capacity Schlenk tube equipped with a magnetic stirrer bar was charged with
aryl halide (10 mmol), methyl acrylate (10 mmol) and triethylamine (10 ml). The catalyst
10

ACCEPTED MANUSCRIPT
(0.1 mmol) was dissolved in DMF (10 mL) and transferred quantitatively into the reaction
vessel. The reaction was heated while stirring at 110 °C. Samples were drawn at regular
intervals and analyzed by GC. The coupling product was isolated by pouring the reaction
mixture in water (50 mL) and extracted with CH2Cl2 to give a pure product which was
confirmed by 1H NMR spectroscopy.
3.
Results and discussion
3.1
Synthesis and characterization of ligands and complexes
The thiophene-based imino-pyridyl compounds L1-L4 were prepared via Schiff base
condensation of the appropriate substituted thiophene carboxaldehyde with an appropriate
pyridyl amine in methanol. Their corresponding palladium(II) complexes 1-8 were prepared
by equimolar reactions of the potential ligands with either [PdCl2(COD)] or [PdClMe(COD)]
(Scheme 1).
<Scheme 1>
1
13
All new compounds were characterized using IR, H and C NMR spectroscopy, elemental
analysis, mass spectrometry and, for 1, 2, 6 and 8, single crystal X-ray diffraction studies.
Elemental analysis and mass spectra were consistent with the proposed formulae of the
compounds. In the IR spectra of the ligands, the imine formation was confirmed by the strong
absorption bands observed in the region 1630 – 1632 cm-1 [46-49]. The other bands observed
between 1593 cm-1 and 1568 cm-1 were attributed to the ν(C=N) and ν(C=C) pyridyl
vibrations, respectively [48]. The evidence of coordination of the ligands to the metal center
was observed by the imine absorption bands being shifted to lower frequencies (between
1624 and 1607 cm-1) compared to the corresponding free ligands [46-49]. Further evidence of
imine formation was derived from the NMR spectra of the compounds. For example, in the
11

ACCEPTED MANUSCRIPT
1H NMR spectra of the ligands, the signal for the imine proton appeared as singlet peaks
between 8.12 and 8.44 ppm [50,51]. The other singlet peaks observed upfield at 4.89 and
4.87 ppm were attributed to the CH2 linker protons in L1 and L3, respectively [50]. In the 13C
NMR analysis of the ligands, the signals for the imine carbons appeared at around 159.0 ppm
[50,51].
In the 1H NMR spectra of the complexes, the signals generally shifted downfield with respect
to their position in the free ligand due to coordination of the ligand [50,51]. As the five- or
six-membered Pd-N-(C)n-N rings formed by coordination of the ligands (cf. Scheme 1) are
non-planar, the methylene protons of the ligand backbones become diastereotopic. However,
if inversion of the methylene carbons is relatively rapid on the NMR time scale, averaged
signals will be observed even though the methylene protons remain diastereotopic at all
times. This appears to be the case for the complexes in this study. In an attempt to freeze out
1
backbone inversion, variable temperature H NMR spectra of complex 2 were recorded,
o
down to a temperature of -60 C (213 K). Surprisingly, the methylene signals were still
averaged at the lowest temperature, indicating a low barrier to inversion. On the other hand,
two signals for the 6-H proton of the pyridyl moiety of ligand L2 could be detected,
indicating the formation of two configurational isomers, a phenomenon that could be
confirmed by X-ray crystallography (vide infra).
1
Furthermore, sets of signals were found in the H NMR spectra of complexes 5 and 7 that
were attributed to the presence of two isomers where the methyl ligand is coordinated to the
palladium atom in a cis and trans conformation to the imine nitrogen atom or H6 of the
1
pyridine ring. The possibility of cis-trans isomerization was confirmed by H-1H NOESY
NMR experiments. The NOESY spectrum (Figure S1, Supplementary Material) for complex
5 shows a correlation between the methyl ligand protons (Pd-Me; 0.80 ppm) with the imine
nitrogen proton (8.39 ppm). It indicates the presence of the isomer in which the methyl ligand
12

ACCEPTED MANUSCRIPT
is cis to the imine nitrogen atom and trans to H6 of the pyridine ring (Fig. 1). On the other
hand, the observed correlation between the methyl ligand protons (0.89 ppm) and the H6
proton of the pyridine ring (8.50 ppm) established the formation of the isomer in which the
methyl ligand is cis to the H6 of the pyridine ring and trans to the imine nitrogen atom.
Corresponding resonances are seen in the 1H NMR spectrum of complex 7 (cf. Section 2.3.7),
and are assigned to corresponding trans- and cis-isomers of this complex (trans/cis to the
imine functionality, Fig. 1). Integration of resonances for the cis- and trans-isomers in the 1H
NMR spectra of complexes 5 and 7 indicates a slight excess of the trans-isomers for each
complex (54% and 56%, respectively) at ambient temperature (20 oC).
However, in contrast to the above observations, corresponding sets of signals for cis-/trans-
1
isomers were not observed for the related complexes 6 and 8. Instead the H NMR spectra
indicated the exclusive formation of the isomer where the methyl substituent is cis to the
imine nitrogen. This observation may be attributed to the presence of two carbons as a linker
between the imine nitrogen atom and a pyridine ring, resulting in the formation of a 6-
membered chelate ring structure that prevents rotation of the methyl ligand around the
palladium atom because of steric hindrance exerted by the pyridyl substituent. The molecular
structures 6 and 8 were corroborated by their crystal structures (vide infra).
<Fig. 1>
3.2
Molecular structures of 1 and 2
The molecular structures of complexes 1 and 2 were confirmed by X-ray crystallography.
Crystallographic data and refinement parameters are summarized in Table 1, while selected
bond lengths and bond angles are summarized in Table 2. The molecular structures of the
complexes are shown in Figs. 2 and 3, respectively. Complex 1 crystallizes in the tetragonal
P421c space system while complex 2 has two configurational isomers, 2a and 2b, where 2a
13

ACCEPTED MANUSCRIPT
crystallizes in the
Orthorhombic P2
space system while 2b crystallizes in the monoclinic
12121
P21/n space system. The ligands form a five- and a six-membered chelating ring with the
metal in complexes 1 and 2, respectively. In all three structures, the palladium atom is four-
coordinate via two N atoms of the pyridine ring and an imine, and two chloride anions,
generating a distorted square planar coordination geometry around the metal center. The
distorted geometries are confirmed by the bond angles around the palladium metal atom,
which show significant deviations from 90° [44,45], with the bond angles N(2)–Pd(1)–N(1)
and Cl(1)–Pd(1)–Cl(2) being 79.89(14)° and 92.40(4)° in 1, 89.21(13)° and 91.33(4)° in 2a
and 84.63(7)° and 89.99(8) in 2b. The Pd(1)–C1(1) bond lengths of 2.3016(10) Å in 1 and
2.2918(10) Å in 2a are in agreement with the average Pd–Cl bond distance of 2.298(15) Å for
known palladium complexes [52,53].
The two configurational isomers 2a and 2b both contain a boat conformation of the
above-mentioned six-membered chelate ring. The complexes are chiral, and 2a crystallized in
enantiopure form, while 2b crystallized as a racemate; the enantiomers of each
configurational isomer may be distinguished by considering the relative orientation of the C6-
C7 vector to the N1-N2 vector, i.e. the enantiomers are λ and δ skew isomers. Inversion
about carbons C6, C7 and nitrogens N1, N2 will interconvert the boat conformation of one
enantiomer of 2a to the boat conformation of one enantiomer of 2b. In addition, inversion
about carbons C6 and C7 in either configurational isomer, while maintaining the orientation
around the nitrogens (or vice versa), will convert the boat conformation to the corresponding
(chiral) chair conformation. As the low temperature NMR investigation shows (vide supra),
the barriers to such inversions are relatively low. Furthermore, in the solid state, the two
isomers differ in the relative orientation of the furyl moiety; this difference is likely due to
crystal packing effects.
14

ACCEPTED MANUSCRIPT
<Figs. 2 and 3>
3.2
Molecular structures of 6 and 8
The molecular structures of complexes 6 and 8 were also confirmed by X-ray
crystallography. Crystallographic data and refinement parameters are summarized in Table 1,
while selected bond lengths and bond angles are summarized in Table 2. The molecular
structures of the complexes are shown in Figs. 4 and 5, respectively. Both molecules
crystallize in the monoclinic P21/n space system. The thiophene and pyridine ring appeared
distorted for both structures. The ligands form a six-membered chelating ring with the metal
in a boat conformation. The palladium atom in both structures is four coordinated via two N
atoms of the pyridine ring and an imine, a methyl and a chloride anion, generating a distorted
square planar coordination geometry around the metal centre. The distortion in square planar
geometry is confirmed by the bond angles of N(2)–Pd(1)–N(1) and Cl(1)–Pd(1)–C(14):
84.93(6)° and 89.66(6)° in 6 and 81.66(6)° and 91.56(6)° in 8, respectively, around the
palladium metal atom, showing significant deviations from the idealized angle of 90°
[47,48]. The Pd(1)–Cl(1) bond lengths of 2.312(5)Å in 6 and 2.3296(5)Å in 8 are in
agreement with the average Pd–Cl bond distance of 2.298(15)Å for known palladium
complexes [52,53]. The Pd(1)-C(14) and Pd(1)-C(19) bond lengths in 6 and 8, respectively,
are significantly shorter than their corresponding Pd(1)-Cl(1) bond lengths, thus reflecting the
stronger trans-influence of the pyridyl group compared to the secondary amine. Furthermore,
the Pd(1)-N(1) bond lengths in 6 and 8 are considerably longer than their corresponding
Pd(1)-N(2) bond lengths due to the stronger trans-influence of the Pd-CH3 moiety.
<Figs. 4 and 5>
<Tables 1 and 2>
15

ACCEPTED MANUSCRIPT
3.3
Heck coupling reactions
The thiophene-based imino-pyridyl palladium(II) complexes were screened as catalysts for
Heck coupling reactions of iodobenzene, 4-iodotoluene and 1-iodo-4-nitrobenzene with
methyl acrylate to obtain the C-C coupled products (Scheme 2). Complexes 1, 2, 5 and 6
have a peripheral electron-donating methyl substituent on the thiophene ring that decreases
the electrophilicity of the Pd(II) ion in the active species [54]. Conversely, the electron-
withdrawing bromine substituent on the thiophene ring in complexes 3, 4, 7 and 8 causes a
strain on the ring because it reduces the donation power of the ring and increases the
electrophilicity of the Pd(II) center [52]. The electron of the soft sulfur atom contributes to
the delocalized bonding in the ring, contributing to this effect. The catalytic activities of the
complexes were compared after identical optimization experiments were carried out. A
summary of the catalytic results is given in Table 3. For comparison, the corresponding
catalytic
activities
of
the
known
complex
chloromethyl-[(2-pyridyl-2-
thiophenemethyl)imine]palladium(II) (9) [47] were studied and are included in Table 3
(entries 8, 14 and 20); the observed catalytic activities for the reference complex were in all
cases lower than those found for the complexes in this study. In general, the complexes were
effective towards arylation of methyl acrylate, giving yields of up to 87%, with the exclusive
formation of the desired trans-methyl cinnamate as confirmed by 1H NMR spectroscopy. In
particular, complexes 4 and 8 gave quantitative yields in Heck coupling of iodobenzene
(Table 3, entries 4 and 7) and electron-deficient 1-iodo-4-nitrobenzene (Table 3, entries 17
and 19), indicating the effect of peripheral bromine on the thiophene ring. Complex 2 was the
least active in the Heck coupling of 4-iodotoluene and 1-iodo-4-nitrobenzene, giving low
yields of 64% and 70%, respectively (Table 3, entries 9 and 15), highlighting the negative
effect of the methyl substituent on the catalytic activity. A similar effect was observed in the
Heck coupling of iodobenzene by complex 1 (Table 3, entry 1); in this reaction, there was a
16

ACCEPTED MANUSCRIPT
long induction period, and less than 50% yield of product was obtained after 2h. Because of
this poor catalytic performance, further investigations of the catalytic activity of complex 1
were therefore not pursued. The alkyl linker on the ligand backbone appears to have an effect
on the catalytic activities of the complexes. In particular, the more flexible ethylene linker
substantially influenced the rate of substrate conversion compared to the methylene linker,
leading to high yields (compare, for example, Table 3, entries 3 vs 4 and entries 10 vs 11). A
mercury drop test was carried out on the complexes under the same reaction conditions to test
the homogeneity of the reactions. There was no significant difference in conversions between
experiments with or without mercury, suggesting that the Heck reactions were catalyzed by
the Pd(II) complexes rather than Pd(0) nanoparticles. Also there was no observed precipitate,
indicating homogeneity.
<Scheme 2>
4.
Summary and Conclusions
We have successfully prepared and fully characterized new thiophene-containing imino-
pyridyl palladium(II) complexes. The complexes were evaluated as catalyst precursors in
Heck coupling reactions of aryl halides with methyl acrylate and they proved to be effective
catalysts. The substituent on the thiophene ring and the alkyl linker on the ligand backbone
had pronounced effects on the catalytic activities of the complexes. The bromine- substituted
complexes yielded high activity in converting substrates to Heck products. The bromine
substituent increases the electrophilicity of the Pd ion and this may facilitate the activation of
the aryl halide that takes place (via oxidative addition) in the catalytic reaction. Furthermore,
the complexes with the longer ethylene linker in the ligand backbone were found to exhibit
higher activities than those with the shorter methylene linker. The crystal structures of the
complexes (vide supra) reveal that the pyridyl moiety of the pyridyl imine ligand is more
17

ACCEPTED MANUSCRIPT
coplanar with the square plane of the metal complex in the case of complex 1, which has a
methylene ligand backbone, than in complexes 2 and 8, which have ethylene ligand
backbones. As oxidative addition of an aryl halide to a Pd(0) intermediate in the Heck
reaction takes place, a square planar coordination geometry is enforced. On the basis of the
crystal structures, a more crowded steric environment may be expected for Pd(II) complexes
of the ligands with methylene backbones, consistent with complexes with these ligands
giving lower product yields than the analogous ligands with ethylene backbones.
Acknowledgements
The authors are grateful for the financial support from University of the Western Cape Senate
Research and National Research Foundation (Thuthuka), CSIR, and the Erasmus Mundus
EUROSA program. F.E. thanks the Culture affair and Mission sector of the Egyptian
Ministry of Higher Education for financial support.
Supplementary material
CCDC entries no. 1510203, 1510204, 971206, 1525885 and 971205 contain the
supplementary crystallographic data for compounds 1, 2a, 2b, 6 and 8, respectively. Copies
of this information may be obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk). Two-dimensional NOESY spectrum for complex 5.
18

ACCEPTED MANUSCRIPT
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
T. Mizoroki, K. Mori, A. Ozaki, Bull. Chem. Soc. Jpn. 44 (1971) 581.
R.F. Heck, J. Am. Chem. Soc. 93 (1971) 6896.
R.F. Heck, J.P. Nolley, J. Org. Chem. 37 (1972) 2320.
J.-P. Corbet, G. Mignani, Chem. Rev. 106 (2006) 2651.
I.P. Beletskaya, A.V. Cheprakov, Chem. Rev. 100 (2000) 3009.
M. Shibasaki, E.M. Vogl, T. Ohshima, Adv. Synth. Catal. 346 (2004) 1533.
A.B. Dounay, L.E. Overman, Chem. Rev. 103 (2003) 2945.
H. Li, Y-J. Wu, C. Xu, R.Q. Tian, Polyhedron 26 (2007) 4389.
L.F. Tietze, G. Kettschau, U. Heuschert, G. Nordmann, Chem. Eur. J. 7 (2001) 368.
[10] L.R. Moore, K.H. Shaughnessy, Org. Lett. 6 (2004) 225.
[11] C.M. So, C.P. Lau, A.S.C. Chan, F.Y. Kwong, J. Org. Chem. 73 (2008) 7731.
[12] M. Feuerstein, H. Doucet, M. Santelli, J. Org. Chem. 66 (2001) 5923.
[13] J. Dupont, M. Pfeffer, J. Spencer, Eur. J. Inorg. Chem. (2001) 1917.
[14] R.B. Benford, Chem. Commun. (2003) 1787.
[15] R. Imbos, A.F. Minnard, B.L. Feringa, J. Am. Chem. Soc. 124 (2002) 184.
[16] A. Scrivanti, M. Bertoldini, U. Matteoli, V. Beghetto, S. Antonaroli, A. Marini, B.
Crociani, J. Mol. Catal. A: Chem. 235 (2005) 12.
[17] M.L. Kantam, M. Annapurna, P.R. Likhar, P. Srinivas, N. Mirzadeh, S.K. Bhargava,
J. Organomet. Chem. 723 (2013) 129.
[18] S. Iyer, G.M. Kulkarni, C. Ramesh, Tetrahedron 60 (2004) 2163.
[19] B. Milani, A. Marson, A. Scarel, G. Mestroni, J.M. Ernsting, C.J. Elsevier,
Organometallics 23 (2004) 1974.
[20] W. Zhang, Y. Wang, J. Yu, C. Redshaw, X. Hao, W-H. Sun, Dalton Transactions 40
(2011) 12856.
19

ACCEPTED MANUSCRIPT
[21] G.A. Grasa, R. Singh, E.D. Stevens, S.P. Nolan, J. Organomet. Chem. 687 (2003) 269.
[22] K.C. Gupta, A.K. Sutat, Coord. Chem. Rev. 253 (2007) 1420.
[23] X. Guo, J. Zhou, X. Li, H. Sun, J. Organomet. Chem. 693 (2008) 3692.
[24] B. Ye, L. Wang, X. Hu, C. Redshaw, W.-H. Sun, Inorg. Chim. Acta 407 (2013) 281.
[25] Q. Ban, J. Zhang, T. Liang, C. Redshaw, W-H. Sun, J. Organomet. Chem. 713 (2012)
151.
[26] K. Song, S. Kong, Q. Liu, W-H. Sun, C. Redshaw, J. Organomet. Chem. 751 (2014)
453.
[27] M.R. Buchmeiser, T. Schareina, R. Kempe, K. Wurst, J. Organomet. Chem. 634 (2001)
39.
[28] J. Silberg, T. Schareina, R. Kempe, K. Wurst, M.R. Buchmeiser, J. Organomet.
Chem. 622 (2001) 6.
[29] C. Najera, J. Gil-Molto, S. Karlström, L.R. Falvello, Org. Lett. 5 (2003) 1451.
[30] J.C. Xiao, B. Twamley, J.M. Shreeve, Org. Lett. 6 (2004) 3845.
[31] S.B. Park, H. Alper, Org. Lett. 5 (2003) 3209.
[32] V. Montoya, J. Pons, V. Branchadell, J. Garcia-Antón, X. Solans, M. Font-Bardia, J.
Ros, Organometallics 27 (2008) 1084.
[33] F. Li, T.S. Hor, Adv. Synth. Catal. 350 (2008) 2391.
[34] M. Guerrero, J. Pons, J. Ross, J. Organomet. Chem. 695 (2010) 1957.
[35] L.L. de Olivera, R.R. Campedelli, M.C.A. Kuhn, J.-F. Carpentier, O.L. Casagrande
Jr., J. Mol. Catal. A: Chem. 288 (2008) 58.
[36] T. Mino, Y. Shirae, Y. Sasai, M. Sakamoto, T. Fujita, J. Org. Chem. 71 (2006) 6834
[37] M.A. Zuideveld, P.Wehrmann, C. Rohr, S. Mecking, Angew. Chem. 116 (2004) 887
[38] (a) W.M. Motswainyana, M.O. Onani, S.O. Ojwach, B. Omondi, Inorg. Chim. Acta
391(2012) 93.
20

ACCEPTED MANUSCRIPT
(b) W.M. Motswainyana, M.O. Onani, Inorg. Chem. Commun. 24 (2012) 221.
[39] (a) J. Wiedermann, K. Mereiter, K. Kirchner, J. Mol. Catal. A: Chem. 257 (2006) 67.
(b) E.V. Salo, Z. Guan, Organometallics 22 (2003) 5033.
[40] D. Gewirth, An Oscillation Data Processing Suite for Macromol. Cryst., 6th ed., 2003.
[41] G. M. Sheldrick, SADABS – Bruker AXS scaling and absorption correction, Bruker
AXS, Inc., Madison, Wisconsin, USA, 2012.
[42] G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
[43] E. F. Pettersen, T. D. Goddard, C. C. Huang, G. S. Couch, D. M. Greenblatt, E. C.
Meng, J. Comput. Chem., 25 (2004) 1605.
[44] L.J. Barbour, J. Supramol. Chem. 1 (2001) 189.
[45] Z. Otwinowski, W. Minor, Macromol. Cryst. Part A, C. W. Carter Jr & R. M. Sweet,
Eds., Academic Press (New York) 276 (1997) 307.
[46] W.M. Motswainyana, M.O. Onani, A.M. Madiehe, Polyhedron. 41 (2012) 44.
[47] W.M. Motswainyana, S.O. Ojwach, M.O. Onani, E.I. Iwuoha, J. Darkwa, Polyhedron.
30 (2011) 2574.
[48] W.M. Motswainyana, M.O. Onani, A.M. Madiehe, M. Saibu, J. Jacobs, L. van
Meervelt, Inorg. Chim. Acta 400 (2013) 197.
[49] J.D.A. Pelletier, J. Fawcett, K. Singh, G.A. Solan, J. Organomet. Chem. 693 (2008)
2723.
[50] D. Pou, A.E. Platero-Plats, S. Perez, C. Lopez, X. Solans, M. Font-Bardia, P.W.N.M.
van Leeuwen, G.P.F. Strijdonck, Z. Freixa, J. Organomet. Chem. 692 (2007) 5017.
[51] Y. Song, Z. Xu, Q. Sun, B. Su, Q. Gao, H. Liu, J. Zhao, J. Coord. Chem. (2007) 2351.
[52] F.H. Allen, Acta Cryst. B58 (2002) 380.
[53] W. Chen, C. Xi, Y. Wu, J. Organomet. Chem. 692 (2007) 4381.
[54] J. Wu, D. Liu, L. Wu, X. Zhang, L. Zhu, D. Fan, X. Lu, Q. Shi, J. Organomet. Chem.
749 (2014) 302
21

ACCEPTED MANUSCRIPT
Table 1. Selected crystallographic data for complexes 1, 2, 6 and 8.
Complex
Empirical
formula
1
2a
2b
6
8
C13H14Cl2N2PdS
C13H14Cl2N2PdS
C14H17ClN2PdS
C13H14BrClN2PdS
C12H12Cl2N2PdS
407.62
407.62
387.20
452.08
Formula
weight
393.628
170(2) K
0.71073 Å
P212121
173(2)K
0.71073 Å
P21/n
120(2)K
0.71073 Å
P21/n
173(2)K
0.71073 Å
P21/n
Temperature
170(2) K
0.71073 Å
P 421c
Wavelength
Space group
Unit
cell
a = 18.3709(2) Å
b = 18.3709(2) Å
c = 9.39910(10) Å
β= 90°
a = 8.1828(2) Å
b=12.1786(3) Å
a = 9.4717(3) Å
b=11.8248(4) Å
c=13.7434(5) Å
β= 95.242(2)°
a = 9.4017(9) Å
b=11.7870(12) Å
c=13.6953(14)Å
β= 95.516(9)°
a = 10.2162 (13) Å
b=13.0265(16) Å
c=12.8089(16) Å
β= 112.256(4)°
dimensions
c=14.6943(4) Å
β= 90°
3
1532.84(9) Å3
4
1510.66(3) Å3
4
1577.6(3) Å3
4
Volume
Z
3172.10(8) Å
1464.36(6) Å3
4
4
3
1.678 Mg/m3
1.702 Mg/m3
1.903 Mg/m3
Density
1.826 Mg/m
1.849 Mg/m3
(calculated)
-1
-1
-1
-1
-1
Absorption
coefficient
1.795 mm
1.761 mm
1.51 mm
1.531 mm
4.00 mm
776
776
880
F(000)
1720
808
3
0.19 x 0.09 x
0.104 x 0.094 x
0.22x 0.18 x 0.12
Crystal size
0.310 x 0.204 x
0.256 x 0.102 x 0.062 mm
3
3
3
3
0.05 mm
0.063 mm
mm
0.198 mm
3.0 to 26.4°.
2.989 to 34.337°.
2.2 to 25.0°.
Theta range for
data collection
2.217 to 29.136°.
2.172 to 29.175°.
3117
174
6231
174
2723
173
Data collected
4185
179
3944
174
Number of
parameter s
refined
1.07
1.046
1.09
Goodness-of-
1.092
1.059
2
fit on F
R1 = 0.022,
wR2 = 0.049
R1 = 0.0294, wR2 =
0.0579
R1 = 0.016, wR2 =
0.040
Final R indices
[I>2sigma(I)]
R1 = 0.0281, wR2
= 0.0527
R1 = 0.0251, wR2 =
0.0509
-3
0.59 and -0.46
0.901 and -0.775 e.
-3
0.35 and -0.34 e. .Å
Largest diff.
0.413 and -0.591
0.481 and -0.652 e. .Å
-3
-3
-3
e. .Å
.Å
peak and hole
e.Å
22

ACCEPTED MANUSCRIPT
Table 2. Selected bond lengths [Å] and angles [°] for complexes 1, 2, 6 and 8.
Compound
1
Bond length (Å)
Bond angle (◦)
Pd(1)-N(2)
2.004(3)
N(1)-Pd(1)-N(2)
79.89(14)
93.36(10)
94.46(11)
92.40(4)
89.21(13)
89.75(9)
89.73(9)
91.33(4)
84.63(7)
89.99(8)
92.04(9)
93.42(5)
84.93(6)
89.66(6)
92.41(7)
93.07(4)
81.66(6)
91.56(6)
92.85(8)
94.00(5)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
Pd(1)-N(2)
2.024(3)
N(1)-Pd(1)-Cl(2)
N(2)-Pd(1)-Cl(1)
Cl(2)-Pd(1)-Cl(1)
N(1)-Pd(1)-N(2)
N(1)-Pd(1)-Cl(2)
N(2)-Pd(1)-Cl(1)
Cl(2)-Pd(1)-Cl(1)
N(2)-Pd(1)-N(1)
Cl(1)-Pd(1)-Cl(2)
N(2)-Pd(1)-Cl(2)
N(1)-Pd(1)-Cl(1)
N(2)-Pd(1)-N(1)
Cl(1)-Pd(1)-C(14)
N(2)-Pd(1)-C(14)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-N(2)
Cl(1)-Pd(1)-C(19)
N(2)-Pd(1)-C(19)
N(1)-Pd(1)-Cl(1)
2.3016(10)
2.2857(10)
2.040(3)
2a
2b
6
Pd(1)-N(1)
Pd(1)-Cl(1)
2.024(3)
2.2918(10)
Pd(1)-Cl(2)
Pd(1)-N(2)
2.2946(10)
2.027(19)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
Pd(1)-N(2)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(1)-C(14)
Pd(1)-N(2)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(1)-C(19)
2.034(3)
2.318(6)
2.020(2)
2.017(15)
2.144(15)
2.312(5)
2.054(18)
2.0256(16)
2.1667(17)
2.3296(5)
2.038(2)
8
23

ACCEPTED MANUSCRIPT
Table 3. Heck coupling reactions of aryl halides with methyl acrylate
Entry Catalyst
Aryl halide
Yieldb TONb TOFb
(%)
1
2
3
4
5
6
1
2
3
4
5
6
PhI
69
73
75
80
72
78
85
62
64
68
74
71
75
50
70
73
83
78
87
55
820
840
860
910
830
890
950
720
750
790
860
820
850
605
800
840
930
880
980
680
103
105
108
114
104
111
119
90
PhI
PhI
PhI
PhI
PhI
7
8
PhI
8
9
PhI
9
2
4-CH3-C6H4I
4-CH3-C6H4I
4-CH3-C6H4I
4-CH3-C6H4I
4-CH3-C6H4I
4-CH3-C6H4I
4-NO2-C6H4I
4-NO2-C6H4I
4-NO2-C6H4I
4-NO2-C6H4I
4-NO2-C6H4I
4-NO2-C6H4I
94
10
11
12
13
14
15
16
17
18
19
20
3
4
6
8
99
108
103
106
76
9
2
3
4
6
8
100
105
116
110
123
85
9
a
Reaction conditions: Aryl halide (10 mmol); Methyl acrylate (11 mmol); Et3N (10 mmol); Catalyst (0.1 mmol); Temp: 110 oC; Time: 8 h;
Solvent: DMF (10 ml); bDetermined by GC; Internal standard: mesitylene; TON: mol of substrate converted/mol of catalyst; TOF: TON/h
24

ACCEPTED MANUSCRIPT
Captions to Figures and Schemes
Figure 1. Possible configurational isomers of [(L)PdClMe] complexes (L = thiophene based
imino pyridyl ligand).
Figure 2. Mercury plot of the molecular structure of compound 1, showing the atom
numbering scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
plotted at the 30% probability level.
Figure 3. Mercury plot of the molecular structures of compound 2a (δ isomer, see text; top)
and 2b (λ isomer, see text; bottom), showing the atom numbering schemes. Hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are plotted at the 30% probability level.
Figure 4. Mercury plot of the molecular structure of compound 6, showing the atom
numbering scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
plotted at the 30% probability level.
Figure 5. Mercury plot of the molecular structure of compound 8, showing the atom
numbering scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
plotted at the 30% probability level.
25

ACCEPTED MANUSCRIPT
Scheme 1. Schematic depiction of the syntheses of imino-pyridyl ligands L1-L4 and their
palladium(II) complexes 1-8.
Scheme 2. Schematic depiction of Heck coupling of aryl halides with methyl acrylate.
26

ACCEPTED MANUSCRIPT
Figure 1
27

ACCEPTED MANUSCRIPT
Figure 2
28