Transcyclopalladation on silica gel

Article abstract of DOI:10.1016/j.poly.2013.01.030

A possibility of transcyclopalladation on silica gel was shown using reactions of acetato- and chloro-bridged dimeric cyclopalladated complexes derived from N,N-dimethylbenzylamine with benzyl methyl sulfide, benzyl phenyl sulfide, benzyldiphenylphosphine, 8-methylquinoline and 1,3- bis(methylthiomethyl)benzene in the presence of equimolar amount of CF ₃CO₂H. The reaction provided the corresponding C,S-, C,N-, C,P- and S,C,S-palladacycles in 39-65% yield.

Full text of DOI:10.1016/j.poly.2013.01.030

Polyhedron 53 (2013) 202–207
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Polyhedron
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Transcyclopalladation on silica gel
1
⇑
Jessica R. Lamb , Valeria A. Stepanova, Irina P. Smoliakova
Department of Chemistry, 151 Cornell Street, University of North Dakota, Grand Forks, ND 58202-9024, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A possibility of transcyclopalladation on silica gel was shown using reactions of acetato- and chloro-
bridged dimeric cyclopalladated complexes derived from N,N-dimethylbenzylamine with benzyl methyl
sulfide, benzyl phenyl sulfide, benzyldiphenylphosphine, 8-methylquinoline and 1,3-bis(methylthiom-
ethyl)benzene in the presence of equimolar amount of CF3CO2H. The reaction provided the corresponding
C,S-, C,N-, C,P- and S,C,S-palladacycles in 39–65% yield.
Received 25 October 2012
Accepted 29 January 2013
Available online 5 February 2013
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Transcyclopalladation
Cyclopalladated ligand exchange
Reactions on silica gel
Cyclopalladated complexes
1. Introduction
transcyclopalladation, a preligand (A) reacts with a dimeric CPC
(B) to form a new dimeric CPC (C) and a free preligand (D,
Organic synthesis on silica gel using solvents on the purification
step only is a well-known practice [1,2]. Interest in such reactions
can be explained by a number of factors. First, use of silica gel in-
stead of potentially harmful solvents results in the reduction of
pollution. Secondly, for a number of organic transformations per-
formed on silica gel and other absorbents, product yields are
at least as high as those obtained under conventional conditions
[1–4]. In some cases, reactions on silica gel require milder condi-
tions [5]. It was also shown that the products’ regio- and stereo-
chemistry can be different from that observed for compounds
obtained using traditional solvent conditions [2].
In contrast, the preparation of organometallic derivatives on
SiO2 [6,7] or Al2O3 [8] is rather limited due to the fact that these
absorbents contain water and compounds with a carbon-metal
bond are usually moisture-sensitive. Our group’s research is fo-
cused on the synthesis of new cyclopalladated complexes (CPCs)
and their applications. One direction is the preparation of CPCs
on silica gel. Recently, we reported a general procedure for the
preparation of C,N- and C,P-palladacycles – including those con-
taining aromatic (sp2)C–Pd, benzylic (sp3)C–Pd and aliphatic
(sp3)C–Pd bonds – on silica gel [9–12]. The reported preparations
were based on direct cyclopalladation of the corresponding preli-
gands with Pd(OAc)2 or Na2PdCl4.
Scheme 1). The dimeric CPC B acts as a source of Pd(II). The reac-
tion is reversible and apparently is governed by the difference in
thermodynamic stabilities of the starting and final palladacycles
[14,15]. For the series of aryl-substituted N,N-dialkylbenzylamines,
it was shown that, in D3CO2D–CHCl3 solutions, the equilibrium
favors the CPC derived from a more electron-rich ligand, e.g. 3,4-
dimethoxy vs. 4-nitro-substituted derivative [14]. However, in
acetic acid, a strong thermodynamic preference was observed for
the palladacycles derived from electron-poor ligands [14].
To the best of our knowledge, all known transpalladation reac-
tions have been carried out in solvents. At least in some cases, a
newly formed CPC precipitates from a reaction mixture, so the rel-
ative solubility of two CPCs can also be considered a contributing
factor determining the equilibrium position of the ligand exchange
reaction in solution [16,17]. In the present study, we report the
preparation of CPCs using transcyclopalladation on silica gel using
solvents for purification only.
2. Results and discussion
For our study, we chose cyclopalladated acetato- and chloro-
bridged dimeric complexes 1a,b as the Pd(II) sources. These deriv-
atives of N,N-dimethylbenzylamine are common starting CPCs in
transpalladations [18,19] and, according to Ceder and co-workers
they are among the less thermodynamically stable CPCs [20].
Benzyl methyl sulfide (2) was selected as a model preligand to
determine whether transpalladation on SiO2 is plausible and, if
so, the best conditions for the transformation. Sulfide 2 is a com-
mercially available air stable compound. It readily undergoes
cyclopalladation using Pd(OAc)2 in acetic acid for 30 min at either
Another method for synthesis of CPCs is transcyclopalladation,
which is also known as cyclopalladated ligand exchange [13]. In
⇑
Corresponding author.
E-mail addresses: irina.smoliakova@und.edu, ismoliakova@chem.und.edu (I.P.
Smoliakova).
1
Undergraduate researcher.
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.030

J.R. Lamb et al. / Polyhedron 53 (2013) 202–207
203
our experiments, reactions without CF3CO2H did not provide even
traces of CPC 3.
To determine whether the size of the silica gel affects the reac-
tion, two adsorbents with larger particle sizes, 100–230 and 35–60
mesh, have been tested in addition to the 230–400 mesh (entries
8–10). Experiments with different samples of silica gel gave similar
results, although the reaction carried out on silica gel with the size
of 100–230 mesh afforded a slightly higher yield of CPC 3, 61%.
To show that transcyclopalladation on silica gel without using a
solvent is not limited to only one substrate, other preligands have
been tested as well. Benzyl phenyl sulfide (5) is a similar preligand
to sulfide 2 and was, therefore, expected to react in a comparable
manner. Akin to compound 2, only the coordination complex
Pd(HL)Cl2 was produced in solution when sulfide 5 was reacted
with Na2PdCl4 [24]. There has only been one report of the success-
ful cyclopalladation of this preligand to form CPC 6 in 50% yield, in
which the authors used Pd(OAc)2 in acetic acid at 90 °C for 1 h [25].
Scheme 1. General scheme for cyclopalladation.
90 or 118 °C followed by treatment with LiCl to afford CPC 3 in 72%
or 80% yield, respectively [17,21]. Our recent study showed that
this preligand also reacts with Pd(OAc)2 on SiO2 to give 3b in good
yields [12]. To the best of our knowledge, transcyclopalladation of
sulfide 2 has never been reported. It is noteworthy that only three
sulfur-containing compounds, (4-MeOC6H4)2C@S, (Me2N)2C@S and
1,3-(MeSCH2)2C6H4, have been successfully transcyclopalladated in
solution; the source of Pd(II) in those reactions was CPC 1b [17].
In our experiments, complex 1a (or 1b), sulfide 2, and silica gel
were thoroughly mixed. Then this dry mixture was stirred for 24–
96 h either at rt or a higher temperature. In the end of all reactions
with the acetato-bridged CPC 1a, the silica gel mixture was washed
with acetone and LiCl was added at rt to convert the acetato-bridged
No studies on transcyclopalladation of sulfide
5 have been
reported.
We found that benzyl phenyl sulfide 5 undergoes transcyclopal-
ladation on silica gel using CPC 1a at 80 °C in the presence of equi-
molar amount of CF3CO2H furnishing CPC 6 in 56% (Scheme 2 and
entry 1 in Table 2). Increasing the temperature to 100 °C resulted in
quick decomposition of the reaction mixture with appearance of Pd
black (entry 2).
The next preligand tested was benzyldiphenylphosphine 7. The
results of the selected experiments with this phosphine are pre-
sented in Scheme 3 and Table 3. The highest yield of CPC 8 in
our experiments was 39%, which is higher than 21% reported by
Ryabov for the same reaction performed in a mixture of CHCl3
and CH3CO2H at rt for four days [26]. For comparison, Lohner
et al. obtained the crude complex 7 in 90% yield in the transcyclo-
palladation of phosphine 7 with CPC 1b in toluene in the presence
of CF3CO2H at reflux for 2 h [27]. It is noteworthy that reactions of
phosphine 7 with 1a or 1b on SiO2 without acid or with the weaker
acetic acid provided only complex 9. Reactions at the temperatures
below 100 °C did not give CPC 8, while keeping the reaction mix-
CPC to its l-Cl-analog 3. Depending on the conditions used, three
products were isolated in different ratios: the desired CPC 3, com-
pound 4 and the coordination complex Pd(2)2Cl2 (Scheme 2 and Ta-
ble 1). The best yield of CPC 3 was 61% (Table 1, entry 8). The
structures of all complexes were confirmed by 1H and 13C{1H}
NMR data as well as by comparison of their melting points and Rf val-
ues with the reference samples obtained by known procedures.
Transcyclopalladation of sulfide 2 required high temperature,
80–100 °C. The reaction occurred slowly: the optimal time appears
to be 24 h. Along with the two reagents and SiO2, CF3CO2H was
added in some experiments. Ryabov and Yatsimirsky, who first re-
ported transcyclopalladation [13], and other researchers [22] long
believed that these reactions require the presence of a carboxylic
acid such as acetic or trifluoroacetic acid. Later, Dunina’s group
showed that transcyclopalladations may occur in aprotic solvents
without the addition of acetic or another carboxylic acid [23]. In
tures at 100 °C for more than
a
few hours resulted in
decomposition.
1. SiO2
SR
Pd
NMe2
Pd
NMe2
Pd
SR
+
+
Pd(HL)2Cl2
+
2. LiCl
Cl
2
R
Cl
S
2
X
(HL)
Bn
HL = 2 or 5
R = Me (2)
R = Ph (5)
X = OAc (1a)
X = Cl (1b)
R = Me (3)
R = Ph (6)
R = Me (4)
Scheme 2. Preparation of C,S-palladacycles using transcyclopalladation on silica gel.
Table 1
Reactions of sulfide 2 with CPCs 1a,b.
Entry
Pd(II) source
Acid
SiO2 size (mash)
Temp. (°C)
Time (H)
Yield of 3 (%)b
Yield of 4 (%)
Yield of Pd(2)2Cl2 (%)
1
2
1b
1b
1a
1a
1a
1a
1a
1a
1a
1a
1a
230–400
230–400
230–400
230–400
230–400
230–400
230–400
100–230
100–230
35–60
rt
24
96
96
24
24
48
24
24
24
24
24
99
72
79
15
49
35
24
17
24
40
26
78
70
50
80
80
100
100
80
80
80
3
4a
5
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
26
34
46
54
61
46
51
50
18
1
6
7
8
9
10
11
no SiO2
a
The amount of silica gel was doubled.
Here and later, yields of all compounds are given after chromatographic purification and, as a rule, are averages of two or more trials.
b

204
J.R. Lamb et al. / Polyhedron 53 (2013) 202–207
Table 2
Reactions of sulfide 5 with CPC 1a on silica gel
Entry
Pd(II) source
Acid
Acid (mesh)
Temp (°C)
Time (h)
Yield of 6 (%)
1
2
3
1a
1a
1a
CF3CO2H
CF3CO2H
CF3CO2H
230–400
230–400
no SiO2
80
100
80
24
<1
24
56
7
36
NMe2
PPh2
NMe2
Pd
1. SiO2
Ph2BnP
Cl
Cl
PPh2
+
+
+
Pd
Pd
Pd
2. LiCl
2
Cl
2
2
Ph
Ph
X
Cl
P
Bn
X = OAc (1a)
X = Cl (1b)
8
10
7
9
Scheme 3. Use of phosphine 7 in transcyclopalladation reactions on silica gel.
Table 3
Reactions of phosphine 7 with CPCs 1a,b.
Entry
Pd(II) source
Acid
SiO2 size (mesh)
Temp. (°C)
Time (h)
Yield of 8 (%)
Yield of 9 (%)
Yield of 10 (%)
1
2
3
4
1b
1a
1a
1b
CF3CO2H
CF3CO2H
CF3CO2H
–
100–230
120–400
120–400
100-230
120
120
120
120
1
1
2
1
39
15
>90
>90
26
traces
8-Methylquinoline (11) was chosen as the next substrate be-
cause of the possibility of forming a benzylic (sp3)C–Pd bond in
the product. Hartwell et al. described the direct cyclopalladation
of 11 in MeOH/H2O at rt, but no yield was reported [28]. Starting
from CPC 1b in a CH3CO2H–CHCl3 mixture at 50 °C for 24 h, Ryabov
et al. obtained CPC 12 in 64% yield [13], which was then increased
to 95% using CPC 1a (60 °C, 12 h in CH3CO2H) [29]. In our experi-
ment, 8-methylquinoline 11 reacted with complex 1a at 100 °C
for 48 h followed by treatment with LiCl at rt (Scheme 4). The
crude product was quite insoluble in common solvents, so it was
mixed with PPh3 in order to get the more soluble cyclopalladated
adduct 13. After the purification using chromatography, complex
13 was obtained in 46% yield. The melting point of the synthesized
compound 13 matched the one reported previously [30]. The 1H
and DEPT NMR spectra of the complex confirmed conversion of
the methyl group to the methylene fragment.
because this preligand provides only one CPC of the S,C,S-pincer
type (15) [17] out of the two possible (second probable CPC arises
from double palladation of the ligand resulting in the 1,2,4,5-
tetrasubstituted aromatic ring). Transcyclopalladation of disulfide
14 in CH3CO2H–C6H6 at reflux for 2.5 h was reported to give 97%
yield of CPC 15, while the direct cyclopalladation of this preligand
afforded less than 10% yield (no conditions were given) [17]. In our
experiments, compound 14 underwent transcyclopalladation on
SiO2 using CPC 1a at 80 °C to give 65% yield of the pincer complex
15 (Scheme 5). The yield of the reaction, which was repeated sev-
eral times, was very sensitive to stirring; in the majority of the
experiments, the coordination complex 16 was isolated as well.
The structure of the new compound 16 was supported by 1H and
13C{1H} NMR spectroscopy and its composition was confirmed by
elemental analysis.
To the best of our knowledge, no examples of preparation of
palladacycles with a non-benzylic (sp3)C–Pd bond using transcy-
clopalladation in solution have been reported. To test if CPCs with
a non-benzylic (sp3)C–Pd bond can be formed as a result of
We were also interested in whether preligands leading to pincer
complexes could be transcyclopalladated on silica gel. 1,3-
Bis(methylthiomethyl)benzene (14) was selected for the study
CFCO2H
(13equiv.)
PPh3
LiCl
NMe2
N
N
+
SiO
2
Pd
N
Pd
Pd
Cl
Me
11
2
AcO
2
Cl
Ph3P
1a
12
13
Scheme 4. Transcyclopalladation of 8-methylquinoline 11 on silica gel.
Me
S
Me
S
CF3CO2H
NMe2
Pd
Cl
Cl
(1 equiv.)
SiO2
+
+
Pd
Pd
Me
Me
Me
Me
SMe
MeS Pd
N
N
2
AcO
MeS
SMe
Cl
16
1a
14
15
Scheme 5. Preparation of S,C,S-pincer CPC 15 using transcyclopalladation on silica gel.

J.R. Lamb et al. / Polyhedron 53 (2013) 202–207
205
cyclopalladated ligand exchange on SiO2, 2-tert-butyl-4,4-
dimethyl-2-oxazoline (17) was reacted with CPC 1a. This oxazoline
was chosen because we recently published our data on the suc-
cessful direct metalation of this preligand with Pd(OAc)2 on silica
gel [10] and the sample of the desired CPC was available to us.
After stirring a mixture of heterocycle 17, CPC 1a and CF3CO2H in
a 2:1:2 ratio on SiO2 at 80 °C for 24 h, the 1H NMR spectrum of
the reaction mixture as well as the analytical TLC plate showed
no indication of the CPC formation.
Organics, 8-methylquinoline 11 from Alfa Aesar and benzyldiphe-
nylphosphine 8 from Sigma–Aldrich; all were used without purifi-
cation. 1,3-Bis(methylthiomethyl)benzene 14 was synthesized
according to the procedure published by Fujihara et al. [31].
2-tert-4,4-Dimethyl-2-oxazoline 17 was prepared according to
the procedure published by Stepanova et al. [10]. Di(l-aceta-
to)bis-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}dipalladium(II)
1a was obtained as described earlier [32].
1H and 13C NMR spectra as well as the melting points of coordi-
nation complexes Pd(2)2Cl2 and Pd(5)2Cl2 obtained in this study
were identical to those reported previously [12,24,33]. NMR spec-
tra and the melting points of coordination complex 10 isolated in
this study were identical to those reported by others [34,35] and
us [11].
Finally, we checked whether transcyclopalladation might occur
without either a solvent or silica gel by mixing the appropriate
neat reagents. A slurry of liquid sulfide 3 and solid CPC 1a in a mo-
lar ratio of 2:1 was mixed with 2 M equiv. (10 lL) of CF3CO2H. The
resulting mixture was heated at 80 °C for 24 h. CPC 3 was still
formed in this reaction in 51% yield (Table 1, entry 11); however,
the formation of Pd black was apparent and the sticky reaction
mixture was almost impossible to stir. Interestingly, this obtained
yield is only 11% less than the best yield using silica gel. In a similar
experiment with sulfide 5, which has the melting point of 40–
45 °C, the corresponding CPC 6 was also formed, but in a lower
yield of 36% (Table 2, entry 3). Therefore, in general, transcyclopal-
ladation may occur not only without solvent but also without silica
gel, particularly when the ligand to be palladated is a liquid. How-
ever, even in these cases, the use of silica gel as a reaction medium
results in a better mixing of the reagents, less decomposition and
higher yields. It appears that mixing two solid reagents in the pres-
ence of silica gel is much more efficient than just mixing them
alone. Furthermore, one should not assume that all transcyclopal-
ladation and palladation [9–11] reactions that are possible on SiO2
will occur without silica gel. Attempts to heat a mixture of complex
1a with solid BnPh2P 7 (m.p. 77–83 °C) resulted in the formation of
a black sticky material insoluble in any common solvents. For com-
parison, we previously reported that cyclopalladation of phosphine
7 with Na2PdCl4 occurs on silica gel to give the corresponding CPC
in 56% yield, while mixing the phosphine with the palladating
agent under the same conditions without SiO2 did not result in
the formation of even traces of the desired cyclometallated com-
plex [11].
3.2. General procedure
Using a syringe (if the preligand was liquid) or a spatula (if so-
lid), the preligand, e.g., benzyl methyl sulfide
0.127 mmol), was placed in a small round-bottomed flask. Then
SiO2 (230–400 mesh, 0.0909 g; 750 mg per mmol of the preligand)
2 (0.0176 g,
and
di-(l-acetato)bis-{2-[(N,N-dimethylamino)methyl]phenyl-
C,N}dipalladium(II) 1a (0.0361 g, 0.0602 mmol) were added to
the flask and the components were vigorously mixed with a spat-
ula until the mixture attained a homogenous color. A magnetic stir
bar was added and the flask was capped with a septum and
immersed in a preheated oil bath. A syringe was then used to
add trifluoroacetic acid (10 lL, 0.14 mmol) dropwise through the
septum directly onto the reaction mixture. A CaCl2-filled syringe
was poked through the septum and the reaction mixture (which
looked like a dry uniform powder) was set to stir. In the end of
the reaction, the product was washed from SiO2 using acetone
(5 ꢀ 3 mL) into a round-bottomed flask containing LiCl (0.0103 g,
0.243 mmol). The reaction mixture was then stirred overnight at
rt. The solvent was then removed and the obtained solid residue
was purified using preparative TLC (SiO2, 10:1 benzene–acetone
or another eluent).
In summary, we showed that transcyclopalladation may occur
without solvent. Silica gel can be successfully used as a ‘‘green’’
medium for this reaction. For all substrates tested, cyclopalladation
on SiO2 required the presence of a strong acid such as CF3CO2H. To
obtain good yields of the CPCs with aromatic (sp2)C–Pd or benzylic
(sp3)C–Pd by transcyclopalladation on SiO2, high temperatures
(80–100 °C), long reaction times (ca. 24 h except for phosphine 7)
and efficient stirring were necessary.
3.2.1. Di-(l-chloro)bis-[2-(methylthiomethyl)phenyl-
C,S]dipalladium(II) (3)
The general procedure was followed for this reaction, with the
following reagents and amounts: benzyl methyl sulfide
(0.0230 g, 0.166 mmol), SiO2 (100–230 mesh, 0.1247 g), di-( -ace-
tato)bis-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}dipalla-
dium(II) 1a (0.0503 g, 0.0839 mmol), trifluoroacetic acid (15
0.20 mmol), and LiCl (0.0175 g, 0.410 mmol). The oil bath was pre-
heated to 80 °C and the reaction mixture was allowed to stir for
24 h. When the acid was added, the color of the reaction mixture
immediately turned from light to darker yellow. Complex 3 was
isolated in 61% yield (0.0144 g) using preparative TLC in CH2Cl2.
Rf 0.62 (benzene–acetone 10:1); m.p. 140 °C (decomposed). NMR
data matched those reported [17] for complex 3 earlier.
2
l
l
L,
3. Experimental
3.1. General methods and materials.
Purifications by preparative thin-layer chromatography (TLC)
were carried out on 200 ꢀ 250 mm glass plates with an unfixed
layer of Natland or Merck silica gel 60 (230–400 mesh) containing
5–10% of the Aldrich-Sigma thin-layer chromatography silica gel
with fluorescent indicator. Analytical TLC was performed on What-
man silica gel 60 (F254) 250 mm pre-coated plates. Compounds
were visualized on TLC plates using UV light (254 nm) and iodine
stain. 1H (500 MHz) and 13C{1H} (126 MHz) as well as DEPT, COSY,
and HMQC spectra were recorded on a Bruker AVANCE 500 NMR
spectrometer. Chemical shifts, d, are reported in ppm with SiMe4
as an internal standard. Spin-spin coupling constants, J, are given
in Hz. Spectra were recorded in CDCl3. Acetone was distilled over
KMnO4. CH2Cl2 and CHCl3 were distilled over CaH2. Benzyl methyl
sulfide 2 and benzyl phenyl sulfide 5 were purchased from Acros
3.2.2. Chloro-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}(benzyl
methyl sulfide-S)palladium(II) (4)
This coordination complex was isolated in every transpallada-
tion reaction involving preligand 2. Complex 4 was also obtained
in quantitative yield using the following procedure described
above with the following exceptions. Benzyl methyl sulfide 2
(0.0079 g, 0.057 mmol) and SiO2 (0.0429 g) were mixed with di-
(l-chloro)bis-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}dipalla-
dium(II) (1b) (0.0157 g, 0.0284 mmol) instead of CPC 1a and no
trifluoroacetic acid was added. No oil bath was used because the
reaction mixture was stirred at room temperature for 24 h. The
crude coordination complex was
a very light yellow solid
(0.0231 g, 97.5% yield). Rf 0.40 (10:1 benzene–acetone); m.p.

206
J.R. Lamb et al. / Polyhedron 53 (2013) 202–207
146 °C (decomp.). 1H NMR data (CDCl3, d): 2.48 (s, 3H, SCH3), 2.88
(s, 6H, NCH3), 3.96 (s, 2H, SCH2), 4.32 (s, 2H, NCH2), 6.94 (t, 1H, H(5)
of C6H4Pd), 7.00 (t, 2H, H(3,4) of C6H4Pd), 7.15 (d, 1H, J = 5, H(6) of
C6H4Pd), 7.30 (d, 1H, J = 5, p-H of C6H5), 7.33 (t, 2H, m-H of C6H5),
7.47 (d, 2H, J = 5, o-H of C6H5); 13C{1H} NMR data (CDCl3, d): 29.7
(SCH3), 44.0 (SCH2), 52.5 (NCH3), 74.0 (NCH2), 122.7 (C(4) of
C6H4Pd), 125.3 (C(3) of C6H4Pd), 126.0 (C(5) of C6H4Pd), 128.5
(p-C of C6H5), 129.1 (m-C of C6H5), 130.3 (o-C of C6H5), 133.0
(C(6) of C6H4Pd), 135.0 (C(1) of C6H5), 147.5 (C(2) of C6H4Pd),
148.5 (C(1) of C6H4Pd).
crude product was 0.0119 g. The compound was then reacted with
triphenylphosphine (0.0129 g, 0.0492 mmol) to obtain complex 13
in 46% yield (0.0186 g). Rf 0.69 (ethyl acetate–hexane 2:1); m.p.
148–153 °C (decomp.; lit data [30] 148 °C).
3.2.7. Chloro-{2,6-bis(methylthiomethyl)phenyl-S,C,S0}palladium(II)
(15)
The general procedure was performed with the following com-
pounds and amounts: di-(l-acetato)bis-{2-[(N,N-dimethylamino)
methyl]phenyl-C,N}dipalladium(II) 1a (0.0197 g, 0.0329 mmol),
SiO2 (0.0505 g), 1,3-bis(methylthiomethyl)benzene 14 (0.0129 g,
0.0650 mmol), trifluoroacetic acid (5 lL, 0.07 mmol), and LiCl
3.2.3. Di-(l-chloro)bis-{2-[(phenylthio)methyl]phenyl-
C,S}dipalladium(II) (6)
The following reagents and their amounts were used for this
reaction: benzyl phenyl sulfide 5 (0.0215 g, 0.107 mmol), SiO2
(0.0059 g, 0.14 mmol). The oil bath was preheated to 80 °C. Pre-
parative TLC (25:1 CH2Cl2–acetone) yielded three fractions.
The second fraction was the desired CPC 6, which was isolated in
an average of 65% yield as a yellow oil. Rf 0.55 (20:1 CH2Cl2–ace-
tone). NMR data matched those reported [17] for complex 15
earlier.
(0.0767 g),
l-OAc-CPC 1a (0.0307 g, 0.0512 mmol), trifluoroacetic
acid (7 L, 0.1 mmol), and LiCl (0.0087 g, 0.20 mmol). The oil bath
l
was preheated to 80 °C and the reaction was set to stir for 24 h.
Preparative TLC was done in CH2Cl2–acetone, 50:1. The yield of 6
was 0.0196 g (56%). Rf 0.80 (50:1 benzene–acetone 50:1); m.p.
125–127 °C (decomp.). Spectroscopic data for this complex
matched those reported previously [25].
3.2.8. Dichlorobis-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}[1,3-
bis(methylthiomethyl)benzene-S,S]dipalladium(II) (16)
The highest yield of complex 16 was obtained under the follow-
ing amounts and conditions: 1,3-Bis(methylthiomethyl)benzene
3.2.4. Di-(l-chloro)bis-{2-[(diphenylphosphino)methyl]phenyl-
C,P}dipalladium(II) (8)
14 (0.0138 g, 0.0696 mmol), SiO2 (0.0518 g),
l
-OAc-CPC 1a
(0.0205 g, 0.0342 mmol), trifluoroacetic acid (5
lL, 0.07 mmol),
The following procedure was used in place of the general
and LiCl (0.0063 g, 0.15 mmol). The oil bath was preheated to
80 °C and the reaction was set to stir for 60 h. Preparative TLC
was done in 6:1 benzene–acetone. Two compounds were isolated:
16 as a yellow oil (0.0163 g, 65%) and CPC 15 (0.0081 g, 35%). Rf
0.41 (20:1 CH2Cl2–acetone); m.p. 79–81 °C (decomp.). 1H NMR
data (CDCl3, d): 2.44 (s, 6H, SCH3), 2.88 (s, 12H, NCH3), 3.96 (s,
4H, NCH2), 4.30 (s, 4H, SCH2), 6.92 (m, 2H, CHarom of C6H4CH2-
NMe2), 6.99 (m, 4H, 2 CHarom of C6H4CH2NMe2) 7.09 (d, J = 7.9,
2H, CHarom of C6H4CH2NMe2), 7.32 (t, J = 7.9, 1H, 5-H of C6H4(CH2-
SCH3)2), 7.46 (d, J = 7.9, 2H, 4-H and 6-H of C6H4(CH2SCH3)2), 7.58
(s, 1H, 2-H of C6H4(CH2SCH3)2); 13C NMR data (CDCl3, d): 20.5
(SCH3), 43.3 (SCH2), 52.2 (NCH3), 73.7 (NCH2), 122.3 (HCarom of C6-
H4CH2NMe2), 124.9 (HCarom of C6H4CH2NMe2), 125.6 (HCarom of C6-
H4CH2NMe2), 129.1 (HCarom of C6H4(CH2SCH3)2), 129.8 (HCarom of
C6H4(CH2SCH3)2), 131.0 (HCarom of C6H4(CH2SCH3)2), 132.6 (HCarom
of C6H4CH2NMe2), 135.2 (quat. Carom), 147.0 (quat. Carom), 148.1
(quat. Carom). Anal. Calc. for C28H38Cl2N2Pd2S2: C, 44.81; H, 5.10;
N, 3.73%. Found: C, 44.53; H, 4.97; N, 3.67%.
procedure for this reaction: SiO2 (0.0561 g) and di-(l-acetato)
bis-{2-[(N,N-dimethylamino)methyl]phenyl-C,N}dipalladium(II) 1a
(0.0222 g, 0.0370 mmol) were mixed first in a small round-
bottomed flask. A stir bar was inserted and the flask, septum,
and stirring spatula were all transferred to a glove box with an
atmosphere of N2. Benzyldiphenylphosphine 7 (0.020 g, 0.072 mmol)
was then added to the flask and thoroughly mixed with the spat-
ula. The reaction was allowed to stir at room temperature in the
glove box. The flask was capped with the septum before being re-
moved from the glove box and put in a preheated oil bath (100 °C)
for 2 h. No CaCl2-filled syringe was used in this reaction. The reac-
tion mixture was filtered into a flask with LiCl as described in the
general procedure and purified using preparative TLC in CH2Cl2.
The first fraction consisted of the desired CPC 8 (39% yield). Rf
0.69 (CH2Cl2); m.p. 197–201 °C (decomposed). NMR data matched
those reported [11] for complex 8 earlier.
3.2.5. Chloro-{2-[(N,N-dimethylamino)methyl]phenyl-
C,N}(benzyldiphenylphosphine-P)palladium(II) (9)
Acknowledgement
This coordination complex was isolated as an orange solid in
some reactions involving BnPh2P. M.p. 181–183 °C. 1H NMR data
(CDCl3, d): 2.88 (s, 6H, NCH3), 3.95 (s, 2H, NCH2), 4.02 (d, 2JP,H = 12 -
The authors acknowledge financial support from ND EPSCoR
through NSF Grant No. EPS-0-0184442.
4
Hz, 2H, PCH2), 6.35 (t, JP,H = 3JH,H = 7 Hz, 1H, H(5) of C6H4Pd), 6.40
(t, 3JH,H = 7 Hz, 1H, H(4) of C6H4Pd), 6.77 (t, 3JH,H = 7 Hz, 1H, H(4) of
References
3
C6H4Pd), 6.92 (d, JH,H = 7 Hz, 1H, H(3) of C6H4Pd), 7.08 and 7.14
(two m, 5H, C6H5 of Bn), 7.31, 7.42 and 7.58 (three m, 10H, two
Ph groups of BnPh2P). Anal. Calc. for C28H29ClNPPd: C, 60.88; H,
5.29%. Found: C, 60.74; H, 5.20%.
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