Palladacycles bearing tridentate CNS-type benzamidinate ligands as catalysts for cross-coupling reactions

Article abstract of DOI:10.1039/c2dt11097k

Three pendant benzamidines, [Ph-C(NC₆H₅)-{NH(E)}] [E = -(CH₂)₂SMe (1); -(CH₂)₂S ^tBu (2); -o-C₆H₄SMe (3)], are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)₂ in CH₂Cl₂ give the palladacyclic complexes, [Ph-C{-NH(η¹-C₆H₄)}{N(E)}]Pd(OAc) [E = -(CH₂)₂SMe (4); -(CH₂)₂S ^tBu (5); -o-C₆H₄SMe (6)], as mononuclear palladium complexes respectively. A minor product described as 5′, {[Ph-C{-N(C₆H₅)}{-N(CH₂)₂S ^tBu}]Pd(OAc)}₂, was isolated as benzamidinate-bridged dinuclear palladium complex upon recrystallizing from Et₂O/hexane solution. Treatment of 1, 2 or 3 with one molar equivalent of PdCl₂ in the presence of NEt₃ in CH₂Cl₂ gives the palladacyclic complexes, [Ph-C{-NH(η¹-C₆H ₄)}{N(E)}]PdCl [E = -(CH₂)₂SMe (7); -(CH ₂)₂S^tBu (8); -o-C₆H₄SMe (9)], as mononuclear palladium complexes respectively. The crystal and molecular structures are reported for compounds 5, 5′ and 6-8. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.

Full text of DOI:10.1039/c2dt11097k

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PAPER
Palladacycles bearing tridentate CNS-type benzamidinate ligands as catalysts
for cross-coupling reactions†
Wei-Chi Wang, Kuo-Fu Peng, Ming-Tsz Chen and Chi-Tien Chen*
Received 11th June 2011, Accepted 6th December 2011
DOI: 10.1039/c2dt11097k
Three pendant benzamidines, [Ph–C(vNC6H5)–{NH(E)}] [E = –(CH2)2SMe (1); –(CH2)2StBu (2);
–o-C6H4SMe (3)], are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)2 in
CH2Cl2 give the palladacyclic complexes, [Ph–C{–NH(η1-C6H4)}{vN(E)}]Pd(OAc) [E = –(CH2)2SMe
(4); –(CH2)2StBu (5); –o-C6H4SMe (6)], as mononuclear palladium complexes respectively. A minor
product described as 5′, {[Ph–C{–N(C6H5)}{–N(CH2)2StBu}]Pd(OAc)}2, was isolated as benzamidinate-
bridged dinuclear palladium complex upon recrystallizing from Et2O/hexane solution. Treatment of 1, 2
or 3 with one molar equivalent of PdCl2 in the presence of NEt3 in CH2Cl2 gives the palladacyclic
complexes, [Ph–C{–NH(η1-C6H4)}{vN(E)}]PdCl [E = –(CH2)2SMe (7); –(CH2)2StBu (8); –o-C6H4SMe
(9)], as mononuclear palladium complexes respectively. The crystal and molecular structures are reported
for compounds 5, 5′ and 6–8. The application of these palladacyclic complexes to the Suzuki and Heck
coupling reactions was examined.
Introduction
Results and discussion
Mono-anionic amidinate ligands with the general formula
[R1C(NR2)(NR3)]−1 exhibited versatile coordination properties,
and displayed their potential to act as ancillary ligands in metal
complexes.1 Over the past couple of decades, many metal–ami-
dinato compounds have been achieved and these have been
reviewed by several research groups.1,2 Due to the ease of substi-
tution on either or both N and C atoms, the steric and electronic
properties of amidinato ligands can be modified by variation of
the substituents. According to reported literatures, the existence
of pendant arm could play an important role in coordinated be-
haviour and tuned the reactivity of metal complexes in catalytic
reactions.3 Recently some palladium benzamidinato compounds
bearing pendant functionalities have been reported by us.4 We
also found these complexes prefer to proceed via orthometalla-
tion on the phenyl group rather than deprotonation of the nitro-
gen atom with pendant functionalities. In this paper, we report
the preparation and structural properties of pendant benzami-
dines with thioether functionalities and their orthometallated pal-
ladium complexes. The catalytic activities of these palladacyclic
complexes towards the Suzuki and Heck coupling reactions are
also investigated.
Preparation of ligand precursors and palladacycles
Ligand precursors were prepared following a classical route for
the synthesis of N,N′-disubstituted amidines, as shown in
Scheme 1.4,5 Compounds are characterised by NMR spec-
troscopy as well as elemental analyses. Complex and broad
signals were found in 1H NMR spectrum for compound 3, which
are always observed for compounds with tautomeric rotation.
Therefore high temperature spectroscopic data were reported
for it.
Three amidines with pendant thioether functionalities react
readily with one molar equivalent of Pd(OAc)2 in dichloro-
methane to afford complexes 4, 5 and 6, which are expected to
form a mononuclear species4,6 rather than the dimeric or oligo-
meric structures.7–10 A summary of the syntheses and proposed
structures of palladacycles is shown in Scheme 2. In each palla-
dium acetate compound, one NH singlet around δ 10–11 ppm
(10.57 ppm for 4; 10.23 ppm for 5; 11.27 ppm for 6) was found
on the 1H NMR spectrum and one more tertiary carbon appeared
in the region of the phenyl ring on the 13C{1H} NMR spectrum,
which indicates the preference of carbon metallation rather than
the NH deprotonation.4 Suitable crystals of 5 and 6 for structural
determination were obtained from a CH2Cl2/hexane solution.
The molecular structures are depicted in Fig. 1 and 2. The struc-
tural analyses show both complexes as a mononuclear species,
in which the palladium metal centre is coordinated with one
thioether sulphur atom, one imine nitrogen atom, one metallated
carbon atom, and one acetate oxygen atom to form one five-
membered metallacycle and one six-membered metallacycle.
Department of Chemistry, National Chung Hsing University, Taichung
402, Taiwan, Republic of China. E-mail: ctchen@dragon.nchu.edu.tw
†Electronic supplementary information (ESI) available. CCDC reference
numbers 829869–829873. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt11097k
3022 | Dalton Trans., 2012, 41, 3022–3029
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Scheme 1 Preparation of ligand precursors
Scheme 2 Preparation of palladium complexes
The bond angles (from 86.36(6) to 92.83(6)° for 5; from 83.07
(9) to 96.20(10)° for 6) around the Pd metal centres indicate that
each complex has a slightly distorted square planar geometry.
The bond lengths of Pd–S (2.4151(7) and 2.4256(7) Å for 5;
2.4119(12) Å for 6) and Pd–Cmetallated (1.983(2) and 1.976(3) Å
for 5; 1.983(4) Å for 6) are within those (2.240(1)–2.422(1) Å
for Pd–S; 1.971(4)–2.022(4) Å for Pd–Cmetallated) found in
metallated palladacycles.11 The bond lengths of Pd–OOAc
(2.0412(17) and 2.0457(18) Å for 5; 2.054(3) Å for 6) are
among those (2.036(2)–2.085(2) Å) found in palladacycles
bearing tridentate ligands.4,6,12 The bond lengths of Pd–NCvN
(1.998(2) and 1.995(2) Å for 5; 2.013(3) Å for 6) are close to
those (1.981(3)–2.030(3) Å) found in some palladacycles.4,6,12
The difference in C–N bond lengths of the NCN moiety is
around 0.019–0.045 Å respectively, indicating the localized
nature of the imine CvN and amine C–N bonds.4 A small
amount of a pale-yellow crystalline solid was found and isolated
by layering hexane on the diethylether extract from crude
product of 5. Further characteristic data cannot be collected due
to the low yield. The molecular structure is shown in Fig. 3.
Unlike 5 produced via carbon metallation, the molecular struc-
ture of 5′ demonstrates the deprotonation reaction of NH could
happen upon preparing the metallated pallacycles, which was
observed upon preparing amidinato-bridged binuclear palladium
complexes.7–10 The molecular structure of 5′ exhibits a dinuclear
species, in which two metal centres are bridged with two benza-
midinate ligands through the NCN moiety. Each palladium metal
centre is coordinated with one thioether sulphur atom, two nitro-
gen atoms from different benzamidinate ligands and one acetate
oxygen atom to form palladium benzamidinate complexes. The
bond angles (from 84.09(8) to 97.21(8)°) around Pd metal centre
indicate each complex having a distorted square planar geometry.
The bond length of Pd(1)–Pd(2) (2.8011(4) Å) is among those
(2.576(1)–2.9435(4) Å) found in dinuclear palladium amidinate
complexes.7–10 The bond lengths of Pd–Namidinate (1.997(3)–
2.058(3) Å) are similar to those (2.01(1)–2.112(5) Å) found in
amidinato-bridged binuclear palladium complexes.7–10 The bond
lengths of Pd–OOAc (2.057(2) and 2.049(2) Å) and Pd–S
(2.3217(9) and 2.3119(9) Å) are similar to those discussed
above.
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Fig. 1 Molecular structure of one of the crystallographically indepen-
dent molecules of 5. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and bond angles (°): Pd(1)–C(9), 1.983(2);
Pd(1)–N(2), 1.998(2); Pd(1)–O(1), 2.0412(17); Pd(1)–S(1), 2.4151(7);
N(1)–C(1), 1.346(3); N(2)–C(1), 1.301(3); C(9)–Pd(1)–N(2), 90.64(9);
C(9)–Pd(1)–O(1), 90.18(9); N(2)–Pd(1)–O(1), 179.14(8); C(9)–Pd(1)–
S(1), 176.99(7); N(2)–Pd(1)–S(1), 86.36(6); O(1)–Pd(1)–S(1), 92.83(6).
Fig. 3 Molecular structure of complex 5′. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and bond angles (°):
Pd(1)–N(2), 2.011(3); Pd(1)–O(1), 2.057(2); Pd(1)–N(3), 2.057(3);
Pd(1)–S(1), 2.3217(9); Pd(1)–Pd(2), 2.8011(4); Pd(2)–N(4), 1.997(3);
Pd(2)–O(3), 2.049(2); Pd(2)–N(1), 2.058(3); Pd(2)–S(2), 2.3119(9);
N(1)–C(1), 1.339(4); N(2)–C(1), 1.323(4); N(3)–C(22), 1.334(4); N(4)–
C(22), 1.322(4); N(2)–Pd(1)–O(1), 173.71(12); N(2)–Pd(1)–N(3), 89.62
(11); O(1)–Pd(1)–N(3), 88.87(11); N(2)–Pd(1)–S(1), 84.09(8); O(1)–
Pd(1)–S(1), 97.21(8); N(3)–Pd(1)–S(1), 173.51(8); N(4)–Pd(2)–O(3),
175.13(12); N(4)–Pd(2)–N(1), 88.95(11); O(3)–Pd(2)–N(1), 89.44(10);
N(4)–Pd(2)–S(2), 85.27(9); O(3)–Pd(2)–S(2), 96.47(8); N(1)–Pd(2)–
S(2), 173.92(8).
NMR spectrum and one more tertiary carbon appeared in the
region of the phenyl ring in the 13C{1H} NMR spectrum, which
indicates that the carbon metallation reaction could happen in the
presence of a base. Suitable crystals of 7 and 8 for structural
determination were obtained from concentrated CH2Cl2 sol-
utions. The molecular structures are depicted in Fig. 4 and 5.
Basically, compounds 7 (with substituent methyl group instead
of tert-butyl group on sulfur atom and with coordination of
chloride atom instead of acetate group to metal center for 5) and
8 (with coordination of chloride atom instead of acetate group to
metal center for 5) are similar to compound 5. The structural
analyses show each complex as a mononuclear species, in which
the palladium metal centre is coordinated with one thioether
sulphur atom, one imine nitrogen atom, one metallated carbon
atom, and one chloride atom to form one five-membered metalla-
cycle and one six-membered metallacycle. Bond lengths and
bond angles are similar to those discussed above. The bond
lengths of Pd–Cl(2.3476(7) Å for 7; 2.3224(8) and 2.3152(8) Å
for 8) are close to those (2.3006(17)∼2.328(4) Å) found in some
metallated palladacycles.4,11a,c,d,12
Fig. 2 Molecular structure of complex 6. Hydrogen atoms on the
carbon atoms have been omitted for clarity. Selected bond lengths (Å)
and bond angles (°): Pd–C(9), 1.983(4); Pd–N(2), 2.013(3); Pd–O(1),
2.054(3); Pd–S, 2.4119(12); N(1)–C(1), 1.340(5); C(1)–N(2), 1.316(5);
C(9)–Pd–N(2), 89.55(13); C(9)–Pd–O(1), 91.39(13); N(2)–Pd–O(1),
175.30(12); C(9)–Pd–S, 172.10(10); N(2)–Pd–S, 83.07(9); O(1)–Pd–S,
96.20(10).
Catalytic studies
Treatment of 1–3 with one molar equivalent of PdCl2 in the
presence of NEt3 in stirring dichloromethane at room tempera-
ture affords complexes 7–9 (Scheme 2). Complexes 7–9 were all
characterized by NMR spectroscopy and elemental analyses. In
each palladium chloride compound, one NH singlet (δ 7.16 ppm
Since several palladium complexes containing pendant thioether
functionalities can be used as catalysts for the carbon–carbon
coupling reactions,6,11f,13 the palladacyclic derivatives 4–9 were
expected to work as catalysts toward the Suzuki-type coupling
reaction. A comparison of the activity of these complexes for the
1
for 7; 7.38 ppm for 8; 9.10 ppm for 9) was found on the H
3024 | Dalton Trans., 2012, 41, 3022–3029
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phenylboronic acid catalysed by 1 mol% 4–9 in the presence of
2 equiv. K3PO4 at 50 °C (Table 1, entries 1–6). Catalyst 6 pro-
vided the best result (Table 1, entry 3). Although other bases and
solvents were tested with this catalyst 6 for the same reaction
(Table 1, entries 7–10), the combination of K3PO4/toluene
remains the best option (compare Table 1, entry 3 with entries
7–10). Higher reactivity was observed over a period of 1 h at
80 °C (Table 1, entry 11). Similar conditions were applied in cat-
alysing electronically deactivated compounds, resulting in per-
centage conversions of 90–96% within 2–2.5 h (Table 1, entries
12–14). The results exhibited better activities than those found in
our previous work for electronically deactivated aryl halides.4 In
order to examine the catalytic activity in alcoholic solvents, com-
pound 6 was tested in two alcoholic solvents and water (Table 1,
entries 15–17). Excellent conversion was observed within
15 min using methanol as solvent at 50 °C. The coupling reac-
tions were also carried out with 1 mol% 6 using electronically
activated or deactivated aryl chlorides under the optimised con-
ditions at 100 °C. As expected, the degrees of conversions
became lower with longer period of time, even though in the
presence of NBu4Br (Table 1, entries 18–21).
We also examined the catalytic activities of 4–9 in the Heck
reaction of 4-bromoacetophenone with 1.3 equiv. styrene in the
presence of 1.5 equiv. K3PO4 in DMF at 135 °C with 1 mol%
catalysts, resulting in percentage conversion levels from 70 to
77% within 0.5 h (Table 2, entries 1–6). Similar conditions were
applied to test compounds 7–9 using electronically deactivated
aryl bromide as substrate, compound 8 exhibited better catalytic
activities after 3 h (Table 2, entries 7–9). The optimised con-
ditions for the reaction were found to be K3PO4/DMF for 8 after
a screening of various bases and solvents within 2 h at 110 °C
(Table 2, entries 10–18). When the reactions were performed at
135 °C, the difference in activity is significant after 0.75 h (con-
version, 91%), indicating that the active species is available in
solution under elevated temperature (Table 2, entry 19). Similar
conditions were applied to the reactions employing the electroni-
cally deactivated aryl bromide compounds; however, the reac-
tions took up to 5 h and 6.5 h at 135 °C (Table 2, entries 20–21).
Poor conversion levels were observed after 12 h using electroni-
cally activated 4-chloroacetophenone (Table 2, entry 22). The
percentages of conversion become higher upon increasing the
loading of NBu4Br (Table 2, entries 23–24).
Fig. 4 Molecular structure of complex 7. Hydrogen atoms on carbon
atoms have been omitted for clarity. Selected bond lengths (Å) and bond
angles (°): Pd–C(9), 1.993(3); Pd–N(2), 2.018(2); Pd–Cl, 2.3476(7);
Pd–S, 2.3974(8); N(1)–C(1), 1.349(3); N(2)–C(1), 1.297(3); C(9)–Pd–
N(2), 90.53(9); C(9)–Pd–Cl, 95.46(7); N(2)–Pd–Cl, 173.88(7); C(9)–
Pd–S, 176.01(7); N(2)–Pd–S, 85.89(7); Cl–Pd–S, 88.15(3).
In conclusion, three novel benzamidines bearing pendant
thioether functionalities have been prepared. Six novel pallada-
cycles bearing CNS-type benzamidinate ligands have been pre-
pared and have demonstrated catalytic activities for the Suzuki
and Heck coupling reactions. Under optimised conditions, com-
pound 6 exhibits catalytic efficiency in the Suzuki coupling reac-
tions whereas compound 8 exhibits better catalytic activities in
the Heck coupling reactions. A dramatic increase in activities
was observed for the Suzuki coupling reaction when using
methanol as reaction medium. Molecular structure of 5′ demon-
strated different bonding mode for benzamidinate ligands with
pendant functionalities in quite lower yield, supplying important
information that versatile bonding modes could happen upon
preparing the palladium complexes with multidentate benzamidi-
nate ligands. Preliminary studies on the modification of benzami-
dines with different substituents and their application in the
synthesis of metal complexes are currently being undertaken.
Fig. 5 Molecular structure of one of the crystallographically indepen-
dent molecules of 8. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and bond angles (°): Pd(1)–C(9), 1.993(3);
Pd(1)–N(2), 2.010(2); Pd(1)–Cl(1), 2.3224(8); Pd(1)–S(1); 2.4229(7);
N(1)–C(1), 1.335(3); N(2)–C(1), 1.304(3); C(9)–Pd(1)–N(2), 89.35(10);
C(9)–Pd(1)–Cl(1), 92.54(8); N(2)–Pd(1)–Cl(1), 176.87(6); C(9)–Pd(1)–
S(1), 172.22(8); N(2)–Pd(1)–S(1), 84.17(6); Cl(1)–Pd(1)–S(1), 94.13(3).
Suzuki-Miyaura coupling reaction is shown in Table 1. We per-
formed the coupling of 4-bromoacetophenone with 1.5 equiv.
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Table 1 Suzuki-type coupling reaction catalysed by new palladium complexesa
Entry
Catalyst
Aryl halide
Base
Solvent
[Pd] (mol%)
t (h)
Conv. (%)b
Yield (%)c
1
2
3
4
5
6
7
8
4
5
6
7
8
9
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromotoluene
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Cs2CO3
KF
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
28
65
80
75
28
44
9
—
—
75
68
—
—
—
—
—
—
93
82
85
90
90
—
—
—
—
—
8
9
50
35
99
90
91
96
97
34
Trace
12
13
Trace
18
10
11d
12d
13d
14d
15
16
17
18d
19d,e
20d
21d,e
DMF
Toluene
Toluene
Toluene
Toluene
MeOH
EtOH
1-Bromo-4-tert-butyl-benzene
4-Bromoanisole
2
2.5
0.25
0.25
0.25
12
12
24
24
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Chloroacetophenone
4-Chloroacetophenone
4-Chloroanisole
H2O
Toluene
Toluene
Toluene
Toluene
4-Chloroanisole
1
a Reaction conditions: 1 mol% [Pd], 1 mmol aryl halide, 1.5 mmol phenylboronic acid, 2.0 mmol base, 2 mL solvent, 50 °C. b Determined by H
NMR. c Isolated yield (average of two experiments). d 100 °C. e 50 mol% NBu4Br.
Table 2 Heck coupling reaction catalysed by new palladium complexesa
Entry
Catalyst
Aryl halide
Base
Solvent
[Pd] (mol%)
T (°C)
t (h)
Conv. (%)b
Yield (%)c
1
2
3
4
5
6
7
8
4
5
6
7
8
9
7
8
9
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoanisole
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Cs2CO3
KF
K3PO4
Cs2CO3
KF
K3PO4
Cs2CO3
KF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
DMA
DMA
Toluene
Toluene
Toluene
DMF
DMF
DMF
DMF
DMF
DMF
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
135
135
135
135
135
135
135
135
135
110
110
110
110
110
110
110
110
110
135
135
135
135
135
135
0.5
0.5
0.5
0.5
0.5
0.5
3
3
3
2
2
2
2
2
2
2
2
2
0.75
5
70
73
73
76
75
77
51
59
34
97
89
22
6
47
4
24
42
4
91
92
93
30
68
82
4-Bromoanisole
4-Bromoanisole
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23d
24e
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromotoluene
88
80
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
77
87
88
—
—
75
4-Bromoanisole
6.5
12
12
12
4-Chloroacetophenone
4-Chloroacetophenone
4-Chloroacetophenone
1
a Reaction conditions: 1 mol% [Pd],1 mmol aryl halide, 1.3 mmol styrene, 1.5 mmol base, 2 mL solvent. b Determined by H NMR. c Isolated yield
(average of two experiments). d Added 20 mol% NBu4Br. e Added 50 mol% NBu4Br.
1H and 13C{1H} NMR spectra were recorded either on Varian
Mercury-400 (400 MHz) or Varian Inova-600 (600 MHz) spec-
Experimental
All manipulations were carried out under an atmosphere of dini-
trogen using standard Schlenk-line or drybox techniques. Sol-
vents were refluxed over the appropriate drying agent and
distilled prior to use. Deuterated solvents were dried over mol-
ecular sieves.
trometers in chloroform-d at ambient temperature unless stated
otherwise and referenced internally to the residual solvent peak
and reported as parts per million relative to tetramethylsilane.
Elemental analyses were performed by an Elementar Vario ELIV
instrument.
3026 | Dalton Trans., 2012, 41, 3022–3029
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Benzanilide (Lancaster), PCl5 (RDH), 2-(methylthio)aniline
(Alfa Aesar), DMA (TEDIA), Pd(OAc)2 (Acros), PdCl2 (Lan-
caster), KF (Acros), K3PO4 (Lancaster), Cs2CO3 (Aldrich),
phenyl boronic acid (Acros), 4-bromoacetophenone (Acros),
4-chloroacetophenone (Acros) and styrene (Acros) were used as
supplied. NEt3 was dried over CaH2 and distilled before use.
N-(Phenyl)benzimidoyl chloride,5 HCl·H2N(CH2)2SMe14 and
HCl˙H2N(CH2)2StBu14 were prepared by the modified literature
methods.
heated at 80 °C for 3 h. The resulting mixture was cooled down
to room temperature and the volatiles were removed under
reduced pressure. The residue was washed with 20 mL hexane
and re-dissolved with de-ionized water followed by addition of
15 mL NH4OH (25%). The resulting mixture was extracted with
a mixed solution of CH2Cl2 (20 mL) and de-ionized water
(5 mL) three times. The organic layer was separated and dried
over magnesium sulphate. The filtrate was pumped to dryness to
1
afford a white solid. Yield, 0.238 g, 75%. H NMR (600 MHz,
C6D8, 373 K): δ 2.04 (s, SCH3, 3H), 6.73 (t, J = 7.8 Hz, C6H5,
1H), 6.78 (t, J = 7.8 Hz, C6H5, 1H), 6.87 (br, 1H), 6.95 (br, 4H),
7.03 (m, 2H), 7.12 (br, 2H), 7.33 (br, 2H). Anal. Calc. for
C20H18N2S: C, 75.44; H, 5.70; N, 8.80. Found: C, 75.41; H,
5.79; N, 9.14.
Preparations
[C6H5–C{NH(CH2)2SMe}vNC6H5] (1). To a flask containing
HCl˙H2N(CH2)2SMe (0.254 g, 2.0 mmol) in 15 mL CH2Cl2,
0.84 mL NEt3 (6.0 mmol) and a solution of N-(phenyl)benzimi-
doyl chloride (0.81 g, 3.8 mmol) in 15 mL CH2Cl2 was added at
0 °C. The reaction mixture was allowed to warm to room temp-
erature and reacted overnight. After 12 h of stirring, the volatiles
were removed under reduced pressure and the residue was
extracted with a mixed solution of toluene (20 mL) and de-
ionized water (20 mL) three times. The organic layer was separ-
ated and dried over magnesium sulphate. The filtrate was
pumped to dryness. The residue was washed with 20 mL hexane
to afford a white solid. Yield, 0.17 g, 62%. 1H NMR
(600 MHz): δ 2.14 (s, SCH3, 3H), 2.85 (s, CH2–CH2, 2H), 3.72
(s, CH2–CH2, 2H), 5.00 (s, NH, 1H), 6.62 (d, J = 7.2 Hz, C6H5,
2H), 6.79 (t, J = 7.2 Hz, C6H5, 1H), 7.04 (t, J = 7.2 Hz, C6H5,
2H), 7.22–7.55 (overlap, C6H5, 5H). 13C{1H} NMR (150 MHz):
δ 14.9 (s, SCH3), 33.4 (s, CH2), 38.5 (s, CH2), 121.2, 122.9,
128.2, 128.3, 128.5, 129.1 (CH–C6H5), 135.0, 151.7, 157.1 (two
[Ph–C{–NH(η1-C6H4)}{vN(CH2)2SMe}]Pd(OAc) (4). To
a
flask containing 1 (0.14 g, 0.52 mmol) and Pd(OAc)2 (0.13 g,
0.57 mmol), 20 mL of CH2Cl2 was added at room temperature.
After 12 h of stirring, the resulting mixture was filtered and the
filtrate was pumped to dryness. The residue was washed with
10 mL acetone twice to afford a pale-yellow solid. Yield,
1
0.125 g, 56%. H NMR (600 MHz): δ 1.48 (s, O–C(vO)CH3,
3H), 2.26 (br, CH2, 2H), 2.41 (s, SCH3, 3H), 3.28 (t, J = 4.8 Hz,
CH2, 2H), 6.81 (br, Ph–CH, 2H), 7.00 (t, J = 7.2 Hz, Ph–CH,
1H), 7.13 (t, J = 7.8 Hz, Ph–CH, 1H), 7.36 (t, J = 8.4 Hz,
Ph–CH, 2H), 7.41–7.45 (overlap, Ph–CH, 3H), 10.57 (s, NH,
1H). 13C{1H} NMR (150 MHz): δ 17.5 (s, SCH3), 23.4
(s, O–C(vO)CH3), 35.0 (s, CH2), 55.5 (s, CH2), 117.1, 121.5,
124.5, 128.1, 128.9, 130.0, 134.4 (CH–Ph), 130.1, 131.6, 135.7,
153.5 (two Cipso–Ph, one metallated C–Ph, and one CNN),
178.2 (s, O–C(vO)CH3). Anal. Calc. for C18H20N2O2SPd: C,
49.72; H, 4.64; N, 6.44. Found: C, 49.69; H, 4.29; N, 6.14.
C
ipso–C6H5 and one CNN). Anal. Calc. for C16H18N2S:
C, 71.07; H, 6.71; N, 10.36. Found: C, 70.69; H, 6.73; N, 10.16.
[Ph–C{–NH(η1-C6H4)}{vN(CH2)2StBu}]Pd(OAc) (5). To
a
[C6H5–C{NH(CH2)2StBu}vNC6H5] (2). To a flask containing
HCl˙H2N(CH2)2StBu (0.34 g, 2.0 mmol) in 15 mL CH2Cl2,
0.56 mL NEt3 (4.0 mmol) and a solution of N-(phenyl)benzimi-
doyl chloride (0.254 g, 1.0 mmol) in 15 mL CH2Cl2 was added
at 0 °C. The reaction mixture was allowed to warm to room
temperature and reacted overnight. After 12 h of stirring, the
volatiles were removed under reduced pressure and the residue
was extracted with a mixed solution of toluene (20 mL) and de-
ionized water (20 mL) three times. The organic layer was separ-
ated and dried over magnesium sulphate. The filtrate was
pumped to dryness. The residue was washed with 20 mL hexane
to afford a white solid. Yield, 0.17 g, 78%. 1H NMR
(600 MHz): δ 1.36 (s, SC(CH3)3, 9H), 2.94 (s, CH2–CH2, 2H),
3.70 (s, CH2–CH2, 2H), 5.00 (s, NH, 1H), 6.62 (d, J = 6.6 Hz,
C6H5, 2H), 6.79 (t, J = 6.6 Hz, C6H5, 1H), 7.04 (t, J = 7.2 Hz,
C6H5, 2H), 7.22–7.25 (overlap, C6H5, 5H). 13C{1H} NMR
(150 MHz): δ 28.0 (s, CH2), 31.1 (s, SC(CH3)3), 41.4 (s, CH2),
42.4 (s, SC(CH3)3), 121.2, 122.9, 128.17, 128.25, 128.5, 129.0
(CH–C6H5), 135.0, 150.8, 157.0 (two Cipso–C6H5 and one
CNN). Anal. Calc. for C19H24N2S: C, 73.03; H, 7.74; N, 8.97.
Found: C, 72.83; H, 7.80; N, 8.76.
flask containing 2 (0.312 g, 1.0 mmol) and Pd(OAc)2 (0.245 g,
1.1 mmol), 20 mL of CH2Cl2 was added at room temperature.
After 12 h of stirring, the resulting mixture was filtered and the
filtrate was pumped to dryness. A small portion of residue was
extracted with 10 mL Et2O. The extract was layered with 10 mL
hexane and stood at room temperature for couple of days to
afford brown crystals (5′). The residue after extraction was
washed with 15 mL acetone to afford a white solid. Yield,
0.20 g, 42%. 1H NMR (600 MHz, DMSO-d6): δ 1.47 (s,
SC(CH3)3, 9H), 1.84 (s, O–C(vO)CH3, 3H), 2.61 (t, J = 5.4
Hz, CH2, 2H), 3.36 (t, J = 6.0 Hz, CH2, 2H), 6.75(t, J = 7.2 Hz,
Ph–CH, 1H), 6.96 (t, J = 6.6 Hz, Ph–CH, 1H), 7.03 (d, J = 7.8
Hz, Ph–CH, 1H), 7.36 (d, J = 7.8 Hz, Ph–CH, 1H), 7.51 (m,
Ph–CH, 2H), 7.57–7.61 (overlap, Ph–CH, 3H), 10.23 (s, NH,
1H). 13C{1H} NMR (150 MHz, DMSO-d6): δ 24.8 (s,
O–C(vO)CH3), 29.5 (overlap, CH2 and SC(CH3)3), 47.4 (s, SC
(CH3)3), 56.8 (s, CH2), 115.7, 121.0, 124.5, 128.1, 129.0, 130.3,
133.9(CH–Ph), 129.2, 132.7, 134.3, 152.9 (two Cipso–Ph, one
metallated C–Ph, and one CNN), 174.2 (s, O–C(vO)CH3).
Anal. Calc. for C21H26N2O2SPd: C, 52.89; H, 5.49; N, 5.87.
Found: C, 52.83; H, 5.32; N, 5.79.
[C6H5–C{NH(o-C6H4SMe)}vNC6H5] (3). A storage tube con-
taining N-(phenyl)benzimidoyl chloride (0.254 g, 1.0 mmol), 2-
(methylthio)aniline (0.12 mL, 1.1 mmol) and 2 mL toluene was
[Ph–C{–NH(η1-C6H4)}{vN(o-C6H4SMe)}]Pd(OAc) (6). To a
flask containing 3 (0.318 g, 1.0 mmol) and Pd(OAc)2 (0.246 g,
1.1 mmol), 20 mL of CH2Cl2 was added at room temperature.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 3022–3029 | 3027

View Article Online
[Ph–C{–NH(η1-C6H4)}{vN(CH2)2StBu}]PdCl (8). To a flask
containing 2 (0.165 g, 0.52 mmol) and PdCl2 (0.103 g,
0.58 mmol), 20 mL of CH2Cl2 and 0.15 mL NEt3 (1 mmol)
were added at room temperature. After 48 h of stirring, the
resulting mixture was filtered and the filtrate was washed with
20 mL de-ionized water three times. The organic layer was sep-
arated and dried over magnesium sulphate. The filtrate was
pumped to dryness and the residue was extracted with 20 mL
After 12 h of stirring, the resulting mixture was filtered and the
filtrate was pumped to dryness. The residue was washed with
15 mL acetone to afford a yellow solid. Yield, 0.328 g, 68.5%.
1H NMR (600 MHz, DMSO-d6): δ 1.87 (s, O–C(vO)CH3, 3H),
2.85 (s, SCH3, 3H), 6.34 (d, J = 8.4 Hz, Ph–CH, 1H), 6.80 (t,
J = 7.2 Hz, Ph–CH, 1H), 6.92 (t, J = 7.2 Hz, Ph–CH, 1H), 6.97
(t, J = 7.2 Hz, Ph–CH, 1H), 7.08 (t, J = 7.8 Hz, Ph–CH, 1H),
7.17 (d, J = 7.8 Hz, Ph–CH, 1H), 7.43–7.52 (overlap, Ph–CH,
6H), 7.64 (d, J = 7.2 Hz, Ph–CH, 1H), 11.27(s, NH, 1H).13C
{1H} NMR (150 MHz, DMSO-d6): δ 23.9 (overlap, SCH3
and O–C(vO)CH3), 115.9, 124.0, 124.6, 124.8, 125.8, 128.5,
128.7, 130.2, 131.0, 132.6, 133.6 (Ph–CH), 128.0, 130.6, 132.1,
134.0, 153.1, 155.7 (four Cipso–Ph, one metallated C–Ph
and one CNN), 175.0 (s, O–C(vO)CH3). Anal. Calc. for
C22H20N2O2SPd: C, 54.72; H, 4.17; N, 5.80. Found: C, 54.20;
H, 4.27; N, 5.55.
1
toluene to afford a pale-yellow solid. Yield, 0.146 g, 62%. H
NMR (600 MHz): δ 1.62 (s, SC(CH3)3, 9H), 2.49 (br, CH2, 2H),
3.52 (br, CH2, 2H), 6.79 (d, J = 6.6 Hz, Ph–CH, 1H), 6.92 (t,
J = 6.0 Hz, Ph–CH, 1H), 7.02 (t, J = 6.6 Hz, Ph–CH, 1H), 7.34
(d, J = 6.6 Hz, Ph–CH, 2H), 7.38 (s, NH, 1H), 7.55–7.58
(overlap, Ph-CH, 3H), 8.19 (d, J = 6.6 Hz, Ph–CH, 1H). 13C
{1H} NMR (150 MHz): δ 30.56 (s, SC(CH3)3), 30.61 (s, CH2),
49.0 (s, SC(CH3)3), 57.1 (s, CH2), 115.8, 123.0, 125.1, 127.6,
129.5, 131.1, 138.8 (CH–Ph), 129.1, 132.3, 133.6, 153.3 (two
C
ipso–Ph, one metallated C–Ph, and one CNN). Anal. Calc. for
[Ph–C{–NH(η1-C6H4)}{N(CH2)2SMe}]PdCl (7). To a flask
containing 1 (0.13 g, 0.48 mmol) and PdCl2 (0.087 g,
0.53 mmol), 20 mL of CH2Cl2 and 0.3 mL NEt3 (2 mmol) were
added at room temperature. After 12 h of stirring, the resulting
mixture was washed with 20 mL de-ionized water three times.
The organic layer was separated and dried over magnesium sul-
phate. The filtrate was pumped to dryness and the residue was
extracted with 20 mL toluene to afford yellow-brown solid.
C19H23ClN2SPd: C, 50.34; H, 5.11; N, 6.18. Found: C, 49.90;
H, 5.42; N, 6.00.
[Ph–C{–NH(η1-C6H4)}{vN(o-C6H4SMe)}]PdCl (9). To
a
flask containing 3 (0.318 g, 1.0 mmol) and PdCl2 (0.177 g,
1.0 mmol), 20 mL of CH2Cl2 and 0.30 mL NEt3 (2 mmol) were
added at room temperature. After 36 h of stirring, the resulting
mixture was filtered and the filtrate was washed with 20 mL de-
ionized water three times. The organic layer was separated and
dried over magnesium sulphate. The filtrate was pumped to
dryness and the residue was extracted with 20 mL toluene to
afford a yellow solid. Yield, 0.170 g, 37.2%. 1H NMR
(600 MHz): δ 2.88 (s, SCH3, 3H), 6.15 (d, J = 8.4 Hz, Ph–CH,
1H), 6.69 (m, Ph–CH, 1H), 6.80 (m, Ph–CH, 1H), 6.88 (m, Ph–
CH, 1H), 7.12 (m, Ph–CH, 1H), 7.23 (br, Ph–CH, 1H),
7.32–7.37 (overlap, Ph–CH, 3H), 7.42 (m, Ph–CH, 3H), 7.46 (t,
J = 7.8 Hz, Ph–CH, 1H), 9.10 (s, NH, 1H).13C{1H} NMR
(150 MHz): δ 23.0 (s, SCH3), 117.1, 124.6, 124.8, 126.0, 126.2,
1
Yield, 0.16 g, 81%. H NMR (600 MHz): δ 2.51 (br, CH2, 2H),
2.55 (s, SCH3, 3H), 3.65 (br, CH2, 2H), 6.72 (dd, J = 7.8, 1.8
Hz, Ph–CH, 1H), 6.94 (m, Ph–CH, 1H), 7.05 (m, Ph–CH, 1H),
7.16 (s, NH, 1H), 7.38–7.40 (m, Ph–CH, 2H), 7.54–7.61
(overlap, Ph–CH, 3H), 8.30 (dd, J = 7.8, 1.2 Hz, Ph–CH, 1H).
13C{1H} NMR (150 MHz): δ 18.3(s, SCH3), 35.6 (s, CH2), 57.1
(s, CH2), 115.7, 123.0, 125.4, 127.5, 129.6, 131.1, 138.8
(CH–Ph), 129.3, 132.5, 133.5, 153.0 (two Cipso–Ph, one metal-
lated C–Ph, and one CNN). Anal. Calc. for C16H17ClN2SPd:
C, 46.73; H, 4.17; N, 6.81. Found: C, 45.92; H, 4.46; N, 6.49.
Table 3 Summary of crystal data for compounds 5, 5′, 6, 7, and 8
5
5′
6
7
8
Formula
Fw
T/K
Crystal system
C21H26N2O2PdS
476.90
297(2)
C42H52N4O4Pd2S2
953.80
297(2)
Monoclinic
P21/c
C22H20N2O2PdS
482.86
298(2)
Monoclinic
C2/c
C16H17ClN2PdS
411.23
297(2)
Monoclinic
P21/n
C77H94Cl6N8Pd4S4
1898.18
293(2)
Triclinic
Triclinic
ˉ
ˉ
Space group
P1
P1
a/Å
b/Å
c/Å
α/°
12.4397(11)
13.6472(12)
14.2697(12)
83.055(2)
66.2150(10)
75.150(2)
2142.3(3)
4
1.479
0.981
12004
487
12.7571(10)
16.4673(13)
25.1706(19)
90
98.628(2)
90
5227.9(7)
4
1.212
0.804
10255
493
0.0398
21.165(5)
20.675(4)
11.302(2)
90
117.472(4)
90
4388.0(16)
8
1.462
0.959
12136
253
0.0422
0.1326
1.004
7.6575(6)
13.7665(12)
15.5516(13)
90
103.395(2)
90
1594.8(2)
4
1.713
1.456
8708
190
0.0296
0.0799
1.098
9.7871(7)
11.3669(8)
19.8986(14)
102.632(10)
96.538(10)
106.833(10)
2030.0(2)
1
1.553
1.219
11427
466
β/°
γ/°
V/Å3
Z
ρc/Mg m−3
μ(Mo-Kα)/mm−1
Reflections collected
No. of parameters
a
R1
0.0287
0.0810
1.016
0.0281
0.0855
1.085
a
wR2
0.1015
1.038
GoFb
2 2
2 2
a R1 = [Σ (|F0| − |Fc|]/Σ |F0|]; wR2 = [Σ w(F02 − Fc ) /Σ w(F02)2]1/2, w = 0.10. b GoF = [Σ w(F02 − Fc ) /(Nrflns − Nparams)]1/2
.
3028 | Dalton Trans., 2012, 41, 3022–3029
This journal is © The Royal Society of Chemistry 2012

View Article Online
2 (a) G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int.
Ed., 1999, 38, 428; (b) V. C. Gibson and S. K. Spitzmesser, Chem. Rev.,
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128.0, 128.7, 130.3, 131.3, 131.5, 137.5 (Ph–CH), 128.7, 131.1,
131.2, 132.8, 153.1, 155.5 (four Cipso–Ph, one metallated C–Ph
and one CNN). Anal. Calc. for C20H17ClN2SPd: C, 52.30; H,
3.73; N, 6.10. Found: C, 53.02; H, 4.42; N, 6.29.
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General procedure for the Suzuki-type coupling reaction.
Appropriate amounts of catalyst, aryl halide (1.0 equiv.), phenyl-
boronic acid (1.5 equiv.), base (2.0 equiv.), and a magnetic stir
bar were placed in a Schlenk tube under nitrogen. Solvent
(2 mL) was added by syringe, and the reaction mixture was
heated in an oil bath to the appropriate temperature for the appro-
priate time.
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General procedure for the Heck coupling reaction. Appropri-
ate amounts of catalyst, base (2 equiv.) and aryl halide (1 equiv.)
were placed in a Schlenk tube under nitrogen. Solvent (2 mL)
and styrene (1.5 equiv.) were added by syringe, and the reaction
mixture was heated in an oil bath to the appropriate temperature
for the appropriate time.
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Crystal structure data
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Crystals were grown from CH2Cl2/hexane solution (5 and 6),
ether/hexane solution (5′), or concentrated dichloromethane sol-
ution (7 and 8), and isolated by filtration. Suitable crystals of 5,
5′, 6, 7 or 8 were sealed in thin-walled glass capillaries under a
nitrogen atmosphere and mounted on a Bruker AXS SMART
1000 diffractometer. The absorption correction was based on the
symmetry equivalent reflections using the SADABS program.
The space group determination was based on a check of the
Laue symmetry and systematic absences and was confirmed
using the structure solution. The structure was solved by direct
methods using a SHELXTL package. All non-H atoms were
located from successive Fourier maps, and hydrogen atoms were
refined using a riding model. Anisotropic thermal parameters
were used for all non-H atoms, and fixed isotropic parameters
were used for H atoms. Some details of the data collection and
refinement are given in Table 3.
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Acknowledgements
We would like to thank the National Science Council of the
Republic of China for financial support (grant number NSC 98-
2113-M-005-002-MY3).
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