Solvent-free cyclopalladation on silica gel

Article abstract of DOI:10.1016/j.jorganchem.2009.10.040

Tertiary, secondary and primary benzylamines, as well as structurally different oxazolines readily reacted with Pd(OAc)₂ on silica gel to form cyclopalladated complexes containing a five or six-membered palladacycle with a (sp²)C-Pd or (sp³)C-Pd bond. The complexes were obtained in 45-98% yield, which is comparable with or exceeds the yields reported for preparation of the same compounds in solution. Aliphatic (sp³)C-H bond activation took place in the cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline on SiO₂ leading to the exclusive formation of the corresponding endo palladacycle, whereas two products were reported for the same reaction performed in AcOH.

Full text of DOI:10.1016/j.jorganchem.2009.10.040

Journal of Organometallic Chemistry 695 (2010) 360–364
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Solvent-free cyclopalladation on silica gel
*
Irina P. Smoliakova , Jessica L. Wood, Valeria A. Stepanova, Relindis Y. Mawo
Chemistry Department, University of North Dakota, 151 Cornell Street, Stop 9024, 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:
Received 4 August 2009
Received in revised form 24 October 2009
Accepted 26 October 2009
Available online 3 November 2009
Tertiary, secondary and primary benzylamines, as well as structurally different oxazolines readily reacted
with Pd(OAc)2 on silica gel to form cyclopalladated complexes containing a five or six-membered palla-
dacycle with a (sp2)C–Pd or (sp3)C–Pd bond. The complexes were obtained in 45–98% yield, which is
comparable with or exceeds the yields reported for preparation of the same compounds in solution. Ali-
phatic (sp3)C–H bond activation took place in the cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazo-
line on SiO2 leading to the exclusive formation of the corresponding endo palladacycle, whereas two
products were reported for the same reaction performed in AcOH.
Keywords:
Cyclopalladated complexes
Cyclopalladation
Ó 2009 Elsevier B.V. All rights reserved.
Reactions on silica gel
Solvent-free reactions
1. Introduction
an organic preligand with a Pd(II) derivative, such as Na2PdCl4 or
Pd(OAc)2, in an appropriate solvent. The goal of this study was to
Silica gel’s relatively inert composition and amphoteric nature
make it ideal for use as a solid support in solvent-free chemical
transformations [1]. There are a number of benefits to reactions
performed on silica gel, including reducing the amount of solvent
used, minimizing hazardous waste and, in many cases, simplified
procedures. In addition, reactions carried out on SiO2 often proceed
with high regio- and stereoselectivity and generally under milder
conditions than those in solution [2–6]. Although organic transfor-
mations on silica gel are well documented, there have been only
several reports regarding metalation reactions on SiO2 or Al2O3
[7–11]. Transformations of Pt(II) coordination complexes with ben-
zophenone-derived ligands to the corresponding cycloplatinated
derivatives on SiO2 at 150–200 °C were studied by the Eisenberg
and Kukushkin groups [7]. Formation of the (sp2)C–Ru and
(sp2)C–Pd bonds on SiO2 at 50 and 75 °C, respectively, was
reported by Chakravorty and co-workers [8,9]. Ortho-palladation
develop a general method for the cyclopalladation of various preli-
gands on SiO2 [12]. Effect of SiO2 on regioselectivity of cyclopalla-
dation was also tested.
2. Results and discussion
The tertiary amine N,N-dimethylbenzylamine (1a) was chosen as
a representative preligand to examine the conditions of cyclopalla-
dation on SiO2 (Scheme 1). This amine has been shown to undergo
cyclopalladation readily in solvents, particularly using Li2PdCl4 or
PdCl2 in MeOH at rt, to provide the cyclopalladated dinuclear com-
plex 2a in 96% and 68% yield, respectively [15]. In the cyclopallada-
tion of 1a on SiO2, palladium source, time, temperature and silica gel
size were varied to determine the best parameters for cyclopallada-
tion (Table 1). Two palladium salts, Pd(OAc)2 (Method A) and
Na2PdCl4 (Method B), were tested. At rt, the use of the stronger pal-
ladating agent Pd(OAc)2 afforded a higher yield of 2a compared to
that of Na2PdCl4 (entries 3 and 6); however, at 85 °C, both methods
provided comparable yields of the cyclopalladated complex (entries
1 and 4). In the case of MethodA, temperaturedid nothave an impact
on the yield of product 2a (entries 1–3, 87–92%), while in the reac-
tions with Na2PdCl4 a better yield was obtained at a higher temper-
ature (entries 4 and 6). The time reduction from 8 h to 4 h in the
reactions with Na2PdCl4 at 85 °C resulted in a decreased yield of 2a
from 84% to 70% (entries 4 and 5). Increasing the reaction time in
Method B at rt from 8 h to 49 h gave only a slight improvement in
the yield from 59% (entry 6) to 64% (entry 7).
of
a triarylphosphite during chromatographic purification on
aluminum oxide was reported by Tune and Werner [10]. Most
recently, the Dunina group reported preparation of a C,N-pallada-
cycle on SiO2 [11] using our general procedure reported at the
ACS conference [12].
Our group’s research has been focused on preparation and
applications of cyclopalladated complexes. These air-stable com-
pounds have been used as catalysts or precatalysts, chiral auxilia-
ries and reagents in organic synthesis [13,14]. Preparation of
cyclopalladated complexes is usually accomplished by reacting
It is known that addition of a weak base often increases the
yield of cyclopalladated complexes [16]. To check the effect of a
* Corresponding author. Tel.: +1 701 777 3942; fax: +1 701 777 2331.
E-mail address: ismoliakova@chem.und.edu (I.P. Smoliakova).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.10.040

I.P. Smoliakova et al. / Journal of Organometallic Chemistry 695 (2010) 360–364
361
ladated complex on SiO2, its conversion to the
l
-Cl analogs fol-
Method A
lowed by the treatment with PPh3 – were carried out as a one-
pot reaction sequence (Scheme 2). The cyclopalladation step was
accomplished on SiO2 using Pd(OAc)2 at 50 and 85 °C. For the
PPh3 adduct 3b obtained from the secondary amine 1b, the overall
yield of the three step sequence was 98% regardless of the reaction
temperature. It is noteworthy that the cyclopalladation of amine
1. Pd(OAc)2
SiO2
2. LiCl
Me2CO
Me
Me
N
Me
N
Pd
Cl
2a
Me
Na2PdCl4
SiO2
2
1a
1b with Pd(OAc)2 in benzene at 50 °C for 24 h afforded the
OAc dimeric complex 4b in 89% yield, conversion of 4b to the
l-
-
l
Method B
Cl analog 2b proceeded in 74% yield, and 3b was obtained from
2b in 90% yield [19]. In the reaction of the primary benzylamines
1c and 1d on SiO2 at 85 °C, the yields of the final products 3c
and 3d were 85% and 55%, respectively, while at 50 °C only 23%
of 3c was obtained and no 3d was isolated. It is noteworthy that
the cyclopalladation of amine 1c in benzene at 60 °C furnished
Scheme 1.
Table 1
Cyclopalladation of N,N-dimethylbenzylamine (1a) on silica gela.
the
l-OAc dimer 4c in 53% yield and the conversion of the latter
Entry
Methodb
NaOAc addition
Time (h)
Temp. (°C)
Yield (%)c
to 2c took place in 63% yield [19].
The lower yield of 55% for the preparation of 3d on SiO2 at 85 °C
compared to that for 3c was not surprising because addition of an
electron-withdrawing group in the para position of benzylamines
greatly reduces the ease of cyclopalladation [16]. It is noteworthy
that the 55% yield of 3d is nearly identical to the reported 54% yield
over three steps using a conventional solvent procedure [22]. The
reported cyclopalladation of 1d was carried out in acetone at reflux
for 7 h [22].
1
2
3
4
5
6
7
8
9
10
A
A
A
B
B
B
N
N
N
N
N
N
N
N
Y
8
8
8
8
4
8
49
8
8
8
85
50
21
85
85
21
21
85
85
85
87
88
92
84
70
59
64
88
86
90
B
B
Bd
Be
Y
Cyclopalladation on SiO2 was also tested for oxazolines. The
reaction of (S)-4-tert-butyl-2-phenyl-2-oxazoline (1e) with
Pd(OAc)2 on SiO2 was carried out under the conditions of Method
A at 85 °C for 8 h (Scheme 3). The final product of the two-step
reaction, the cyclopalladated complex 2e, was isolated in 72% yield.
When the reaction temperature was reduced to 50 °C, the yield
dropped to 57%. The literature yield for this complex was 71% over
two steps using cyclopalladation in acetic acid [23].
The cyclopalladation of 2-oxazolines without a substituent at
position 4 is more difficult than that of 1e because of the absence
of steric promotion [18,23–25]; however, metalation of 2-phenyl-
2-oxazoline (1f) with Pd(OAc)2 on SiO2 was successful. Following
Method A (85 °C, 8 h), the dimeric complex 2f was isolated in
40% yield. However, the removal of this dimer from SiO2 was diffi-
cult due to its low solubility in CH2Cl2 and other common solvents.
To form the more soluble PPh3 adduct 3f, Method C (85 °C, 8 h for
a
In all experiments, except for entries 9 and 10, the 230–400 mesh SiO2 was
used.
b
Pd(OAc)2 was used in Method A and Na2PdCl4 in Method B.
c
d
e
Yields are given for the products purified by column chromatography.
The 100–200 mesh Florisil was used in this experiment.
The 100–230 mesh SiO2 was used.
base on the reactions on SiO2, NaOAc was added to one of the reac-
tion mixtures with Na2PdCl4. The yields of the reactions with and
without the base were comparable (entries 4 and 8). There was
no significant impact on the reaction yield when the 230–400
mesh silica gel used in all experiments was replaced by the 100–
230 mesh SiO2 or Florisil (magnesium silicate, 100–200 mesh) un-
der the same reaction conditions (entries 8–10).
It has been shown that the cyclopalladation of secondary and
especially primary amines in solution is more challenging than
that of tertiary amines [16–21]. Nevertheless, the cyclopalladation
of the secondary N-methylbenzylamine (1b) and two primary
amines, benzylamine (1c) and para-nitrobenzylamine (1d), proved
possible on SiO2 as well. Because the dimeric Cl-bridged cyclopal-
ladated complexes 2b–d obtained from these amines have low sol-
ubility in common organic solvents, it was difficult to remove the
products from SiO2. Instead of isolating compounds 2b–d, they
were treated with PPh3 to furnish the corresponding mononuclear
phosphine adducts 3b–d, which are more soluble in solvents. All
O
But
N
2. LiCl
1. Pd(OAc)2
O
But
Pd
Me2CO
SiO2
85 oC, 8 h
Ph
N
2
Cl
1e
2e, 72%
three steps of Method C – formation of the
l-OAc dimeric cyclopal-
Scheme 3.
R1
R1
R1
Method C
N R2
N R2
N R2
R1
3. PPh3
CH2Cl2
2. LiCl
1. Pd(OAc)2
SiO2
N
R3
3b-d
R3
R3
R2
Pd
Cl
Pd
2
Pd
OAc Me2CO
Cl
R3
2
Ph3P
1b-d
4b-d
2b-d
3b: 98% (85 oC), 98% (50 oC)
3c: 85% (85 oC), 23% (50 oC)
3d: 55% (85 oC), 0% (50 oC)
R1 = H, R2 = Me, R3 = H (b)
R1 = H, R2 = H, R3 = H (c)
R1 = H, R2 = H, R3 = NO2 (d)
Scheme 2.

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I.P. Smoliakova et al. / Journal of Organometallic Chemistry 695 (2010) 360–364
O
N
O
O
N
1. Pd(OAc)2
2. LiCl
3. PPh3
CH2Cl2
Ph
Pd
Pd
Me2CO
SiO2
N
85 oC, 8 h
Cl
2
Ph3P
3f, 62%
Cl
2f
1f
Scheme 4.
the cyclopalladation step) was also used (Scheme 4). The yield of
complex 3f was 62%, identical to the yield reported for this com-
pound using AcOH as the solvent on the cyclopalladation step
[24]. When Method C was employed at a lower temperature
(50 °C, 8 h), the yield of 3f dropped to 16% as it was observed for
the primary amines 1c and 1d.
It is known that metalation of imines to form complexes of the
exo structure, i.e. with the C@N bond in the exo position in respect
to the palladacycle, is challenging [26–28]. To check whether exo
palladacycles could be formed in the reactions on SiO2, oxazoline
1g was used. The dimeric complex 2g with a six-membered exo
palladacycle was synthesized by Method A in 45% yield (Scheme 5).
The lower yield compared to the reported 79% in solution (for the
two-step synthesis of 2g using reflux in MeCN for 3.5 h in the
cyclopalladation step) can be partially attributed to the instability
of the exo complex 2g, which decomposes quite readily upon
standing at rt [26].
60% reported for the cyclopalladation of oxazoline 1h in MeCN at
76 °C for 20 h [26]. In this reaction, the formation of another com-
plex with the C@N bond in the exo position in respect to the palla-
dacycle containing the (sp3)C–Pd bond (exo-2h) was possible, but
was not observed either on SiO2 or in solution [26]. This experi-
ment demonstrated that on SiO2, as in solution, the (sp2)C–H bond
activation with the formation of a six-membered endo palladacycle
is favored over the alternative (sp3)C–H bond activation leading to
a five-membered exo palladacycle.
Regioselectivity of cyclopalladation on SiO2 was also studied
using oxazolines 1i and 1j. The preligand (S)-2,4-dibenzyl-2-oxaz-
oline 1i can react to form two different six-membered palladacy-
cles, endo-2i and exo-2i. The cyclopalladation of 1i in solution
resulted in the exclusive formation of the endo isomer (70% in
AcOH, 80 °C, 3.5 h; 49% in MeCN, 78 °C, 3 h; 39% in CH2Cl2, rt,
24 h) [26]. The complete regioselectivity was also observed in the
reaction of this preligand with Pd(OAc)2 on SiO2 (Method A,
Scheme 7). The yield of endo-2i in the reaction performed at
85 °C was 94%. When the reaction temperature was reduced to
50 °C, the yield of the product dropped to 58%. The data obtained
for this oxazoline demonstrated the preference of endo metalation
over exo in reactions carried out on SiO2.
Cyclopalladation of (S)-2-benzyl-4-tert-butyl-2-oxazoline (1h)
on SiO2 provided a six-membered complex of the endo structure
(endo-2h), i.e. with the C@N bond inside of the palladacycle
(Scheme 6). The yield of the complex was 69%, this is higher than
A remarkable result was obtained in the reaction of (S)-2-tert-
butyl-4-phenyl-2-oxazoline 1j. This ligand can undergo metalation
to form an endo palladacycle with the (sp3)C–Pd bond (endo-2j)
and an exo palladacycle with the (sp2)C–Pd bond (exo-2j). It is well
known that, in general, activation of aromatic (sp2)C–H bonds pro-
ceeds more easily than that of aliphatic (sp3)C–H bonds [29]. On
the other hand, exclusive or predominant formation of endo palla-
dacycles over exo isomers in solutions has been well documented
for imines and oxazolines [30–34]. It was found that oxazoline 1j
reacted with Pd(OAc)2 on SiO2 followed by treatment with LiCl to
O
O
Me
Cl
Me
1. Pd(OAc)2
2. LiCl
N
N
Me2CO
SiO2
70 oC, 16 h
Pd
2
1g
2g, 45%
Scheme 5.
O
O
O
Me
But
N
1. Pd(OAc)2
2. LiCl
N
But
Me
N
Ph
Pd
Me2CO
SiO2
Pd
Ph
85 oC, 8 h
2
2
Cl
Cl
1h
exo-2h (not formed)
endo-2h, 69%
Scheme 6.
O
O
Ph
Ph
O
1. Pd(OAc)2
2. LiCl
Me2CO
N
N
Cl
Cl
N
Pd
Pd
SiO2
85 oC, 8 h
Ph
Ph
2
2
1i
endo-2i, 94%
exo-2i (not formed)
Scheme 7.

I.P. Smoliakova et al. / Journal of Organometallic Chemistry 695 (2010) 360–364
363
O
O
Me
Me
But
O
Ph
N
N
1. Pd(OAc)2
2. LiCl
But
Ph
Pd
2
N
Pd
Me2CO
SiO2
50 oC, 8 h
Cl
Cl
2
1j
endo-2j, 64%
exo-2j (not formed)
Scheme 8.
form exclusively endo-2j in 64% yield with no traces of the exo iso-
mer (Scheme 8). The cyclopalladation step was carried out at 50 °C;
formation of Pd black was observed at higher temperatures. For
comparison, in the cyclopalladation of this preligand in AcOH at
60 °C for 12 h followed by ligand metathesis with LiCl, both com-
plexes endo-2j and exo-2j were isolated in a 5:1 ratio in a total
yield of 59% [29]. To the best of our knowledge, the formation of
endo-2j is the first example of (sp3)C–H bond activation on SiO2.
The experiment also showed that regioselectivity of cyclopallada-
tion in solution and on SiO2 can be different.
from pivaloyl chloride and (S)-2-phenylglycinol as described in
the literature [30].
4.3. Synthesis of Cl-bridged dimeric cyclopalladated complexes using
Pd(OAc)2 on SiO2 (Method A)
4.3.1. General procedure
Pd(OAc)2 (72.5 mg, 0.323 mmol), preligand (0.325 mmol), SiO2
(0.121 g; 3:8 ratio of the 230–400 mesh SiO2 in g per preligand
in mmol) and 1 mL of CH2Cl2 were mixed together in a vial. The
slurry was stirred for 1 min, and then the solvent was completely
removed under reduced pressure at rt. The vial was fitted with a
rubber septum cap and a 1 mL syringe packed with CaCl2. The reac-
tion vial was placed on a hot oil bath to stir for 8 h at 85 °C unless
3. Conclusions
Solvent-free cyclopalladation of tertiary, secondary and primary
benzylamines, as well as several 2,4-disubstituted 2-oxazolines
with Pd(OAc)2 readily occurs on SiO2. The study showed that not
only aromatic (sp2)C–H but also aliphatic (sp3)C–H bond activation
can take place on SiO2. The developed general methods for cyclo-
palladation on SiO2 are complimentary to conventional procedures
in solution and can be used for isolating cyclopalladated complexes
either in a dimeric or a mononuclear form. It was also demon-
strated that reactions on SiO2 could be used to vary regioselectivity
of metalation.
otherwise noted. The crude l-OAc dimer was washed from SiO2 by
adding CH2Cl2 followed by filtration. CH2Cl2 was then removed un-
der reduced pressure, after which a saturated solution of LiCl in
acetone (11 mg/mL) (3.0 mL, 0.78 mmol) was added to the dark
brown residue. After stirring the reaction mixture for 15 min, the
solvent was removed. The crude product was dissolved in CH2Cl2
and the solution was filtered through Celite to remove excess LiCl.
The crude product was isolated as a yellow solid after solvent re-
moval. Recrystallization or column chromatography was required
in most cases.
4. Experimental
The following compounds were obtained using Method A:
di-
ladium(II) (2a, yield 88%, mp 185–187 °C (dec.), lit. data: mp
l
-chlorobis-{2-[(N,N-dimethylamino)methyl]phenyl-C1,N}dipal-
4.1. General
1H and 13C NMR spectra (500 and 125 MHz, respectively) were
recorded in CDCl3 using TMS as the internal standard. Measure-
ments were taken on an AVANCE 500 Bruker NMR spectrometer.
Analytical TLC was performed using Merck precoated 0.2 mm
plates of silica gel 60 F254. Melting points were measured using
a Mel-Temp apparatus. The 230–400 and 100–230 mesh SiO2
was purchased from Natland International Corporation unless
otherwise specified. Florisil, 100–200 mesh, benzylamines,
Pd(OAc)2 and 2-phenyl-2-oxazoline were purchased from Sigma–
Aldrich Co. Prior to use, Pd(OAc)2 was dissolved in hot benzene, fil-
tered, then the solvent was removed under reduced pressure. Ben-
zylamines were distilled over KOH. HPLC-grade acetone was used
as purchased. CH2Cl2 and other solvents were distilled over CaH2
prior to use.
185–188 and 183–185 °C (dec.) [15]), (S,S)-di-l-chlorobis-
[2-(4-tert-butyl-2-oxazolin-2-yl)phenyl-C1,N]dipalladium(II) (2e,
yield 72%, mp 212–213 °C, lit. data: mp 212–212.5 °C [23]), (S,S)-
di-l
-chlorobis-{2-[(2-methyl-2-oxazolin-4-yl)methyl]phenyl-C1,N}-
dipalladium(II) (2g, the cyclopalladation step: 70 °C, 16 h; yield
45%, mp 198–200 °C (dec.), lit. data: mp 198–220 °C (dec.) [26]),
(S,S)-di-
l-chlorobis-{2-[(4-tert-butyl-2-oxazolin-4-yl)methyl]-
phenyl-C1,N}dipalladium(II) (endo-2h, yield 69%, mp 143–145 °C
(dec.), lit. data: mp 143 °C (dec.) [26]), (S,S)-di-l-chlorobis-
{2-[(4-benzyl-2-oxazolin-2-yl)methyl]phenyl-C1,N}dipalladium(II)
(endo-2i, yield 94%, mp 135–136 °C (dec.), lit. data: mp 134–137 °C
[26]), (S,S)-di-l-chlorobis-[2-methyl-2-(4-phenyl-2-oxazolin-2-
yl)propyl-C1,N]dipalladium(II) (endo-2j, the cyclopalladation step:
50 °C, 8 h; yield 64%, mp 179–180 °C (dec.), lit. data: mp 180 °C
(dec.) [30]). The 1H NMR data obtained for complexes 2a, 2e, 2g,
endo-2h, endo-2i and endo-2j were identical to those reported
for these compounds [15,23,26,30].
4.2. Synthesis of preligands
(S)-tert-Butyl-2-phenyl-2-oxazoline (1e) was synthesized from
benzonitrile and (S)-leucinol using a published procedure for other
oxazolines [35]. (S)-4-Benzyl-2-methyl-2-oxazoline (1f) was
4.4. Synthesis of Cl-bridged cyclopalladated complexes using Na2PdCl4
on SiO2 (Method B)
prepared from
according to
L
-alaninol and ethylacetimidate hydrochloride
published method [26]. (S)-2-Benzyl-4-tert-
a
butyl-2-oxazoline (1h) was obtained from phenylacetonitrile and
(S)-tert-leucinol as described in the literature [27]. (S)-2,4-Diben-
zyl-2-oxazoline (1i) was synthesized from phenylacetonitrile and
4.4.1. General procedure
Na2PdCl4 (93.0 mg, 0.316 mmol), preligand (0.316 mmol), SiO2
(0.118 g; 3:8 ratio of the 230–400 mesh SiO2 in g per preligand
in mmol) and 1 mL of CH2Cl2 were mixed together in a vial. The
slurry was stirred for 1 min, and then the solvent was completely
L-phenylalaninol according to a reported procedure [28]. (S)-2-
tert-Butyl-4-phenyl-2-oxazoline (1j) was obtained in two steps

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I.P. Smoliakova et al. / Journal of Organometallic Chemistry 695 (2010) 360–364
removed under reduced pressure. The vial was fitted with a rubber
septum cap and a 1 mL syringe packed with CaCl2. The reaction vial
was placed on a hot oil bath to stir for 8 h at 85 °C unless otherwise
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4.5.1. General procedure
Pd(OAc)2 (94.4 mg, 0.420 mmol), preligand (0.422 mmol), SiO2
(0.158 g; 0.375 g of SiO2 per 1.00 mmol of preligand) and 1 mL of
CH2Cl2 were mixed together in a vial. The slurry was stirred for
1 min, and then the solvent was completely removed under re-
duced pressure. The vial was fitted with a rubber septum cap
and a 1 mL syringe packed with CaCl2. The reaction vial was placed
on a hot oil bath to stir for 8 h at 85 °C unless otherwise noted. A
saturated solution of LiCl in acetone (11 mg/mL) (1.8 mL,
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30 min, after which the solvent was removed. CH2Cl2 was added,
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0.420 mmol). The reaction mixture was stirred at rt for 24 h and
then CH2Cl2 was removed. The dry residue was washed with
hexane to remove excess PPh3 and then dissolved in CH2Cl2. The
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solution was passed through
a
frit packed with Celite
(1.5 cm  2.5 cm). After solvent removal, the crude product was
recrystallized from CH2Cl2/hexane.
The following complexes were synthesized using Method C:
chloro-{2-[(N-methylamino)methyl]phenyl-C1,N}(triphenylphos-
phine-P)palladium(II) (3b, yield 98%, mp 124–125 °C (dec.), lit.
data: mp 124 °C (dec.) [19]), chloro-[2-(aminomethyl)phenyl-C1,
N](triphenylphosphine-P)palladium(II) (3c, yield 85%, mp 176–
180 °C (dec.), lit. data: mp 183 °C (dec.) [19]), chloro-[1-(amino-
methyl)-4-nitrophenyl-C2,N](triphenylphosphine-P)palladium(II)
(3d, yield 55%, mp 205–206 °C (dec.), lit. data: mp 210 °C (dec.)
[22]), chloro-[2-(2-oxazolin-2-yl)phenyl-C1,N](triphenylphosphine-
P)palladium(II) (3f, yield 62%, mp 150–152 °C (dec.), lit. data: mp
150–152 °C (dec.) [24]). The 1H NMR data obtained for complexes
3b–d and 3f were identical to those reported for these compounds
[19,22,24].
Acknowledgements
The authors greatly appreciate financial support from ND
EPSCoR through NSF Grant No. EPS-0447679.