Palladium meditated CPhenyl-H bond activation of 2-furylimines versus tert-2-furylbenzylamines

Article abstract of DOI:10.1016/j.poly.2014.03.041

The reactions of 2-furylimines 2a-f and Na₂PdCl₄ in the presence of NaOAc at 8-10°C result in nitrogen-palladium coordinated complexes 3a-f. Reduction of 2d-f with NaBH₄ followed by N-methylation leads to the corresponding tert-2-furylbenzylamines 5a-c. Treatment of 5a-c with Na₂PdCl₄ at the same reaction condition as mentioned above affords palladacycles 6a-c where the Pd atoms connect to the phenyl ring rather than the furyl ring. The fact that 5a-c are more active than 2d-f in C_Phenyl-H bond activation implies that the electron density of C10 or C8 atom in former is higher than those in latter. Compounds 3a-f, 5a-c, 6a-c were identified by elemental analysis, IR and NMR. In addition, the structures of 3b, 3f and 6c were also confirmed by their single crystal X-ray diffractions.

Full text of DOI:10.1016/j.poly.2014.03.041

Polyhedron xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Palladium meditated CPhenyl–H bond activation of 2-furylimines versus
tert-2-furylbenzylamines
a
a
a
b
a,
⇑
Zhao-Xia Hu , Nan Ma , Jin-Hua Zhang , Wen-Ping Hu , Hong-Xing Wang
a
Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
2
The reactions of 2-furylimines 2a–f and Na PdCl4 in the presence of NaOAc at 8–10 °C result in nitrogen–
Received 21 February 2014
Accepted 22 March 2014
Available online xxxx
palladium coordinated complexes 3a–f. Reduction of 2d–f with NaBH
4
followed by N-methylation leads
to the corresponding tert-2-furylbenzylamines 5a–c. Treatment of 5a–c with Na
2
PdCl at the same reac-
4
tion condition as mentioned above affords palladacycles 6a–c where the Pd atoms connect to the phenyl
ring rather than the furyl ring. The fact that 5a–c are more active than 2d–f in CPhenyl–H bond activation
implies that the electron density of C10 or C8 atom in former is higher than those in latter. Compounds
Keywords:
Palladium
Cyclometalation
C–H bond activation
Coordination
Regioselectivity
3
a–f, 5a–c, 6a–c were identified by elemental analysis, IR and NMR. In addition, the structures of 3b, 3f
and 6c were also confirmed by their single crystal X-ray diffractions.
Ó 2014 Elsevier Ltd. All rights reserved.
1
. Introduction
bulky 2-furylimines or 2-thienylimines and Na
the palladium coordinated complexes (B), the endo and exo palla-
dacycles requiring CFuryl–H and Aliphatic–H bond activations,
2 4
PdCl produced
Donating group assisted C–H bond activation, e.g. cyclopallada-
C
tion has emerged as a powerful tool in a variety of transformations
including C–C, C–X (X = F, Cl, Br, I, N, O, S) bond formations [1].
With the rapid development of drug chemical industry, chemists
are eager to obtain some pharmaceutically active compounds
which cannot be synthesized by convention methods. However,
regioselective cyclopalladation reaction provides such an opportu-
nity. Regioselective cyclopalladation has been investigated exten-
sively so far for many kinds of ligands [2] particular for
benzylideneamines [3]. For an example, Martínez and co-workers
reported that when benzylbenzylideneamines were treated with
palladium(II) acetate, the formation of five-membered endo palla-
dacycles was dominated [3b] and the major reason was attributed
to the pseudo-aromatic character of the endo palladacycles (also
called endo effect) [4]. The authors [3b] also found that the forma-
tion of five-membered exo palladacycles only took place (A) when
endo cyclometalation required the formation of a six-membered
compound via aliphatic C–H bond activation or when the steric
hindrance affected the planarity of the imines in an important
way. Chang and co-workers [5] observed that the reactions of
respectively were not isolated. Our previous studies on the cyclo-
metalations of tert-ferrocenylamines revealed that the C–H bond
activation by platinum(II) always occurred at the ferrocenyl ring
rather than phenyl ring [6]. Since a lot of cyclometalations are in
electrophilic substitution process, how the electron densities of
the aromatic or aliphatic carbons affect the regioselective C–H
bond activation will become an interesting topic. In this paper,
we will present here the comparative studies on the cyclopallada-
tion of N-(2-furylmethylene)benzylamines and tert-N-(2-furylm-
ethyl)benzylamines. In order to better elucidate the
regioselectivity, the reactions of three furylimines, N-(2-furylmeth-
ylene)anilines (R = 4-CH
3
, H, 2-Cl) and Na
2
PdCl
4
will be also added.
CH3
O
O
Pd
X
HC
Cl
N
CH3
2
N
Pd
N
H C
Cl
3
CH
X
R
R= H, CH3
X= N, S
⇑
Corresponding author. Tel./fax: +86 22 27403475.
E-mail address: hongxing_wang@tju.edu.cn (H.-X. Wang).
A
B
http://dx.doi.org/10.1016/j.poly.2014.03.041
277-5387/Ó 2014 Elsevier Ltd. All rights reserved.
0
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2
Z.-X. Hu et al. / Polyhedron xxx (2014) xxx–xxx
2
. Results and discussion
2
Cl
2
Cl
R
2.1. Synthesis of complexes 3a–f and palladacycles 6a–c
Pd
R
Pd
N
(CH
n=0, 1
endo
2 n
)
N
The reactions of furan-2-carbaldehyde 1 with anilines and ben-
zylamines resulted in aldimines 2a–f in good yields (Scheme 1).
O
O
exo
Treatment of 2a–f with Na PdCl at 8–10 °C in the presence of
2
4
NaOAc in methanol afforded the coordinated complexes 3a–f as
yellow or orange solids. But the endo palladacycles from 2a–f
and exo palladacycles from 2d–f (Chart 1) were not isolated. Later,
we realized that the reaction temperature might affect the forma-
tion of palladacycles, so we increased the reaction temperature to
Chart 1. The forms of palladacycles (left, from 2a–f. right, from 2d–f).
that H4, H5 are diastereotopic because the nitrogen atom in com-
pound 6 is a chiral centre. Additionally, the chemical shifts of N–
CH
3
in 6 move to the lower magnetic field with d ꢀ 2.90 ppm.
2
5 °C and even to 50 °C. However, the results were same as
described previously.
2
.3. Crystal structures of 3b, 3f and 6c
Frustrated by the results of 2 particular for 2d–f, we turn our
attention to the cyclopalladation of 5a–c (also Scheme 1). As illus-
trated in Scheme 1, Ligands 5a–c were prepared from 2d–f after
The structures of complexes 3b, 3f and palladacycle 6c
were confirmed further by their single crystal X-ray diffractions
Figs. 1–3). The crystallographic data and refined parameters for
b, 3f and 6c are tabulated in Table 1, and their selected bond
lengths and angles are listed in Table 2. X-ray diffraction studies
demonstrates that two molecules of 3b or 3f (Figs. 1 and 2) coordi-
nate to palladium(II) atom in a trans orientation. A similar trans
reduction with NaBH
hyde and NaBH CN. Furylamines 5a–c were allowed to react with
Na PdCl at 8–10 °C in the presence of NaOAc. After the reactions
completed (monitored by TLC), the solvent was evaporated and
the residues were dissolved in acetone followed by addition of ace-
4
followed by N-methylation with formalde-
(
3
3
2
4
3
tone solution of PPh . Removal of acetone afforded the crude prod-
3
coordination pattern between N atom and PPh (Fig. 3) is also
ucts. After purification with chromatography, yellow solids were
isolated in moderate yields and were finally characterized as palla-
dacycles 6a–c.
observed in 6c. The average N–Pd bond lengths in 3b (2.012 Å)
and 3f (2.011 Å) are slight shorter than that of palladium(II) coor-
dinated bulky furylimines (2.050 Å) [5]. However, the N–Pd bond
length in 6c (2.154 Å) is longer than those of 3b, 3f probably
because of the formation of five-membered rigid palladacycle.
The C–Pd bond length (2.013 Å) is longer than that of the reported
cyclopalladated amines (2.000 Å) [2a]. The N1–Pd–N2 bond angle
in 3b (178.59 ) is very close to the idea 180 angle. However, the
N1–Pd–N2 bond angle in 3f (173.50 ) and the N–Pd–P angle in 6c
2.2. Characterization of 3a–f, 5a–c, and 6a–c
The structures of 3a–f, 4a–c, 5a–c and 6a–c were identified by
elemental analysis, IR and NMR. In IR spectra, the C@N stretch
À1
vibration absorption of 2 appears at
absorption of 3 shifts to
m
ꢀ 1624 cm whereas the
À1
m
ꢀ1613 cm
indicating that the
1
(
173.75 ) are smaller than ideal 180 . In 6c, palladium(II) atom is
CH@NÁ Á ÁPd coordination pattern in 3 is present. The H NMR spec-
in a slight distorted square-planar environment, bonded to Cl, P,
N and CPhenyl atoms. The deviations of the atoms from the mean
plane defined by the former five atoms are Pd À0.0482, Cl
tra of 3 clearly demonstrate that both the chemical shifts of H4 in
3
a–f and H5 in 3d–f locate at the downfield, and they are
d ꢀ 8.50 ppm and d ꢀ 4.60 ppm, respectively. However, the IR
absorption of 6 does not show significant changes compared to
the IR spectra of 5 due to the characteristics of saturated nitrogen
atoms. In 5a–c, the satellites of H5 are singlet (d ꢀ 3.70 ppm). But,
they are split into a typical AB coupling system in 6a–c and shift to
downfield (d ꢀ 4.35 ppm). The H4 give out a similar splitting pattern
as H5 demonstrated. A better explanation for this phenomenon is
0
.1725, P À0.1503, N À0.1852 and CPhenyl 0.2111 Å, respectively.
2.4. Regioselective cyclopalladation
As we know, the electrophilic and nucleophilic substitutions
easily take place at the
a- and b-positions of the furyl ring,
O
O
1
anilines or benzylamines
O
R
(CH2)n
Cl Pd Cl
N
R
R
NaBH4
Na PdCl /NaOAc
2 4
H
O
o
N
EtOH-H O
8-10 C
2
3
.
.
2
N
O
(CH2)n
1
4
N
5
10
(
CH )
2 n
O
R
8
4
2
3
n=0, R = 4-CH3(a), H(b), 2-Cl(c)
n=0, R = 4-CH3(a), H(b), 2-Cl(c)
R = 4-CH O(a), 4-CH (b), H(c)
n=1, R = 4-CH O(d), 4-CH (e), H(f)
n=1, R = 4-CH O(d), 4-CH (e), H(f)
3
3
3
3
3
3
aq. HCHO HOAc
NaBH CN CH CN
3
3
PPh3
Pd
,
Cl
R
R
6
8
7
9
CH3
10
1) Na2PdCl4/NaOAc, CH3OH, 8-10 o
(2) PPh3/CH3COCH3
C
2 3
(
2
3
1
4
N
5
1
4
N
5
O
.
.
O
CH3
6 R = CH O(a), CH (b), H(c)
5
R = CH O(a), CH (b), H(c)
3 3
3
3
Scheme 1. Synthesis of complexes 3 and palladacycles 6.
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Z.-X. Hu et al. / Polyhedron xxx (2014) xxx–xxx
3
always occur at the
a-position of the furyl ring (Chart 2). Indeed,
2 4
in the reactions of 2a–f and Na PdCl , we have not observed the
endo palladacycles (see Chart 1), demonstrating that the electro-
philic cyclopalladation at C3 (b-position) of furyl ring is disfavored.
Although there is another report on the cyclopalladation of fur-
ancarbothioamides in which the C–H bond activation occurs at
the b-position of furyl ring [9], this example is not simply classified
into the category bearing the endo effect.
Since the endo products are excluded, the formation of exo pal-
ladacycles from 2d–f (Chart 1) are anticipated. Our hypothesis are
based on the following factors, i.e. first, the electron density of C8
or C10 atom in phenyl ring is comparatively higher than that of
C3 atom in furyl ring (Scheme 1). Second, both C8 and C10 atoms
in phenyl ring are not blocked and finally, no steric hindrance
affects the planarity of the imines 2d–f. From the cyclometalation
point of view and Martínez’ conclusion, all these factors will favor
the formation of exo palladacycles. Unfortunately, we are not suc-
cessful to isolate these exo products. It is believed that complexes
3
8
d–f are so stable that they prevent the C10–H or C –H bond acti-
vation to give the exo palladacycles. The other explanation is not
also excluded, i.e. the exo palladacycles may be present in the mix-
tures, but their amounts are too small to separate. Anyway, the for-
Fig. 1. Crystal structure of 3b (H atoms are omitted for clarity).
8
mation of 3d–f demonstrates that the C10–H or C –H bonds in 2d–f
are not easily activated.
To some extent, ligands 5a–c look like 2d–f in structure, but, the
nitrogen atoms in former are in the saturated state. With the expe-
rience of regioselective cyclopalladation of tert-ferrocenylbenzyl-
amines [6], we believe that if the cyclopalladations of 5a–c take
place, the five-membered palladacycles via the CPhenyl–H bond acti-
vation will be the most reasonable products as the CFuryl–H bond
activation is excluded due to its lower electron density of furyl b-
position. As we expected, palladacycles 6a–c were successfully iso-
lated (Scheme 1). However, the palladium coordinated complexes
similar to 3 have not been observed in our experiments. All these
results are in good agreement with our earlier observation in cyclo-
palladation of tert-ferrocenylbenzylamines [6]. Although 5a–c and
2
a–f are different, their coordination mode with palladium(II)
should be same. The reason why we have not isolated the palla-
dium-coordinated complexes is that they might all be transformed
into the corresponding palladacycles with the aid of NaOAc. The
successful conversion of 5a–c into the palladacycles 6a–c may
imply that the electron density of C10 or C8 atom in 5a–c is higher
than those in 2d–f.
Fig. 2. Crystal structure of 3f (H atoms are omitted for clarity).
3
. Conclusions
In summary, the regioselectivity of cyclometallation depends
entirely on the electron density of the ortho aromatic carbons of
the ligands. Obviously, the ligands tert-N-(2-furylmethyl)benzyl-
amines are more active in the CPhenyl–H bond activation than N-
(
2-furylmethylene)benzylamines.
4
. Experimental
4.1. Materials and instruments
4 3
Furan-2-carbaldehyde, anilines, benzylamines, NaBH , NaBH
CN, NaOAc, PPh
out further purification. Na
3
were obtained commercially and were used with-
PdCl was prepared in our laboratory.
2
4
All of the solvents were purified with standard methods prior to
use. Melting points were obtained on a Yanaco micro melting point
apparatus and were uncorrected. Elemental analyses were mea-
sured on a Carlo Erba 1106 Elemental analyzer. H NMR spectra
were obtained with Bruker AV-400 spectrometer (400 MHz) using
Fig. 3. Crystal structure of 6c (H atoms are omitted for clarity).
1
respectively. This knowledge is well confirmed by the facts that
cycloplatination(II) of 3-furylimines [7] or 3-thienylimines [8]
3
CDCl as the solvent and TMS as the internal standard unless they
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4
Z.-X. Hu et al. / Polyhedron xxx (2014) xxx–xxx
Table 1
Crystallographic data and refined parameters for 3b, 3f and 6c.
Compd.
3b
3f
6c
Empirical formula
Formula weight
Wavelength(Å)
Crystal system, space group
a (Å)
C
68
H
63Cl
6
N
6
O
8
Pd
3
C
24
H
22Cl
2
N
2
O
2
Pd
31
C H29ClNOPPd
604.37
0.71073
1624.14
0.71073
triclinic, P1ꢀ
547.74
0.71073
monoclinic, P2(1)/n
9.666(2)
10.026(2)
23.473(5)
90
92.27(3)
90
2273.1(8)
4
1.601
1.075
monoclinic, C2/c
35.871(4)
9.374(1)
16.711(2)
90
106.76(2)
90
5380.5(2)
8
9.400(2)
12.541(3)
15.095(3)
76.37(3)
84.51(3)
76.93(3)
1682.9(6)
1
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
Z
q
l
À3
calc (Mg m
)
1.603
1.090
1.492
0.873
À1
(mm
)
F(000)
817
1104
2464
h Range for data collection
Limiting indices
1.71°6 h 6 25.02°
À9 6 h 6 11,
1.74°6 h 6 27.87°
À12 6 h 6 12,
À13 6 k 6 10,
À30 6 l 6 30
16691/5417[R(int) = 0.0451]
0.9583, 0.8818
5417/0/280
0.0311, 0.0705
0.691, À0.997
2.25°6 h 6 25.02°
À42 6 h 6 42,
À11 6 k 6 8,
À19 6 l 6 19
13496/4737[R(int) = 0.0274]
0.9024, 0.8177
4737/0/326
0.0223, 0.0548
0.284, À0.288
À11 6 k 6 14,
À17 6 l 6 17
Reflections collected/unique
Maximum and minimum transmission
Data/restraints/parameters
10078/5889[R(int) = 0.0326]
0.9375, 0.8988
5889/129/463
Final R1, wR
2
[I > 2r
(I)]
0.0453, 0.1201
1.049, À0.801
À3
Largest difference peak and hole (e Å
)
Table 2
Selected bond lengths and angles for 3b, 3f and 6c.
CH(CH )C H
3
6
5
β
N
β
N
3
b
3f
6c
Pt
CH
Pt
CH3
N(CH3)2
S(CH3)2
α
α
O
S
Bond lengths (Å)
3
Pd(1)–N(2) 2.007(3)
Pd(1)–N(1) 2.016(3)
Pd(1)–Cl(2) 2.3024(1)
Pd(1)–Cl(1) 2.3202(1)
Pd(1)–N(2) 2.0042(2)
Pd(1)–N(1) 2.0179(2)
Pd(1)–Cl(2) 2.3026(7)
Pd(1)–Cl(1) 2.3076(7)
Pd(1)–C(31) 2.013(2)
Pd(1)–N(1) 2.1541(2)
Pd(1)–P(1) 2.2613(6)
Pd(1)–Cl(1) 2.4121(6)
Chart 2. Reported cycloplatinated 3-furylimines and 3-thienylimines.
aldimine 2b was obtained after the recrystallization or column
chromatography (silica gel, ethyl acetate/hexane = 1:5, v/v).
Bond angles (°)
N(2)–Pd(1)–N(1)
N(2)–Pd(1)–N(1)
173.50(7)
C(31)–Pd(1)–N(1)
81.86(8)
1
78.59(1)
N(2)–Pd(1)–Cl(2)
0.66(9)
N(1)–Pd(1)–Cl(2)
9.44(9)
N(2)–Pd(1)–Cl(1)
9.32(9)
N(1)–Pd(1)–Cl(1)
0.59(9)
Cl(2)–Pd(1)–Cl(1)
79.40(3)
C(7)–N(1)–Pd(1)
22.4(2)
C(1)–N(1)–Pd(1)
16.1(2)
C(18)–N(2)–Pd(1)
26.5(2)
C(12)–N(2)–Pd(1)
15.6(2)
N(2)–Pd(1)–Cl(2)
90.20(6)
N(1)–Pd(1)–Cl(2)
90.31(6)
N(2)–Pd(1)–Cl(1)
88.55(6)
N(1)–Pd(1)–Cl(1)
91.04(6)
Cl(2)–Pd(1)–Cl(1)
178.46(2)
C(8)–N(1)–Pd(1)
117.12(2)
C(7)–N(1)–Pd(1)
120.31(1)
C(20)–N(2)–Pd(1)
127.63(2)
C(31)–Pd(1)–P(1)
98.55(7)
N(1)–Pd(1)–P(1)
173.75(5)
C(31)–Pd(1)–Cl(1)
165.06(7)
N(1)–Pd(1)–Cl(1)
91.06(5)
4
.2.1. [
4 3 6 4 3
a-(C H O)CH@NC H CH -4 (2a)
9
A light-yellow solid. Yield: 85%. M.p. 42–43 °C (Lit. [10] m.p.
1–42 °C). IR:
600(m), 1557(m), 1504(m), 1478(m), 830(s) cm
8
4
1
m
3113(m), 3027(w), 2960(w), 2880(w), 1624(vs),
À1
.
8
9
4
4 3 6 5
.2.2. [a-(C H O)CH@NC H (2b)
P(1)–Pd(1)–Cl(1)
89.92(2)
A yellow–brown solid. Yield: 70%. M.p. 57–58 °C (Lit. [11] m.p.
1
56–57 °C). IR:
1
m
3113(m), 3055(w), 3021(w), 1625(vs), 1585(m),
1
À1
557(m), 1472(m),766(s), 695(s) cm
.
1
4
.2.3. [
a
-(C
4 3 6 4
H O)CH@NC H Cl-2 (2c)
1
A yellow solid. Yield: 81%. M.p. 66–67 °C. Anal. Calc. for C11
H
8
C(19)–N(2)–Pd(1)
112.54(1)
1
ClNO: C, 64.25; H, 3.92; N, 6.81. Found: C, 64.11; H, 3.90; N,
6
1
.79%. IR:
462(m), 750(s) cm
m
3106(w), 3062(w), 1627(vs), 1577(m), 1553(m),
À1
.
are mentioned elsewhere. IR spectra were recorded on a BIO-RAD
3
000 spectrophotometer, KBr pellet was used to get the IR spectra.
4
.2.4. [
A yellow liquid. Yield: 88%. Anal. Calc. for C13
H, 6.09; N, 6.51. Found: C, 72.32; H, 6.07; N, 6.49%. IR:
4 3 2 6 4 3
a-(C H O)CH@NCH C H OCH -4 (2d) [12]
H13NO
2
: C, 72.54;
3025(w),
4.2. Synthesis of 2a–f
m
2
8
956(m), 2881(w), 2835(w), 1623(vs), 1583(m), 1483(m),1463(m),
General method for the synthesis of 2a–f is exemplified by the
synthesis of 2b.
À1
22(s) cm
.
To a 100 mL round bottomed flask was added 25 mmol of 2-fur-
aldehyde and 25 mmol aniline in 20–40 mL dry methanol. The
mixture was stirred for complete dissolution at room temperature
and was monitored by TLC (ethyl acetate/petroleum ether). The
solid was precipitated and filtered. If no solid precipitated, the mix-
ture was evaporated in vacuo to afford the residue. The final pure
4.2.5. [
a
-(C
4
H
3
O)CH@NCH
2
C
6
H
4
CH
3
-4 (2e)
A yellow liquid. Yield: 82%. Anal. Calc. for C13
6.58; N, 7.03. Found: C, 78.32; H, 6.54; N, 7.00%. IR:
2917(m), 2863(m), 2866(w), 1624(vs), 1564(m), 1511(m),
1485(m), 1439(m), 811(s) cm
H
13NO: C, 78.36; H,
m
3030(w),
À1
.
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Z.-X. Hu et al. / Polyhedron xxx (2014) xxx–xxx
5
4
.2.6. [
An orange liquid. Yield: 80%. Anal. Calc. for C13
H, 5.99; N, 7.56. Found: C, 77.63; H, 5.97; N, 7.54%. IR:
a
-(C
4
H
3
O)CH@NCH
2
C
6
H
5
(2f) [13]
4.4. Synthesis of 4a–c
H
11NO: C, 77.81;
3030(m),
969(m), 2923(w), 2875(w), 1623(vs), 1580(s), 1484(m), 1453(m),
m
General method for the synthesis of 4a–c is exemplified by the
synthesis of 4c.
2
7
À1
47(s), 698(s) cm
.
To a 100 mL round bottom flask was added 15 mmol of 2f in
3
0–40 mL dry ethanol, stirring for complete dissolution to obtain
4
.3. Synthesis of 3a–f
a yellow solution. Then, sodium borohydride (1.961 g, 53 mmol)
was added portion wise and slowly bubbled through the reaction
mixture, with magnetic stirring. After the addition was complete
the reaction mixture was stirred at room temperature for 2–4 h.
After completion of the reaction, 20 mL of water was added slowly
under an ice bath, the reaction mixture was rapidly becoming
orange and the sodium borohydride was continued to break down
under constant stirring. The aqueous phase was extracted three
General method for the synthesis of 3a–f is exemplified by the
synthesis of 3b.
To a 50 mL round bottomed flask was added 2b (2 mmol) and
sodium acetate (1.05 mmol) in methanol (20 mL). Then, with con-
tinuous stirring,
1 mmol) was slowly added and completed within 30 min. The
reaction was carried out under constant stirring at 8–10 °C for
0 h. The mixture was filtered and then washed with methanol
and ether, respectively to afford the coordinated complex 3b.
2 4
a methanol (17.7 mL) solution of Na PdCl
(
times with CH
with water, saturated brine and dried (MgSO
rated. Column chromatography gave pure 4c.
2
Cl
2
and the combined organic phase was washed
2
4
), filtered and evapo-
4
.3.1. Pd[Cl{
A yellow solid. Yield: 67%. M.p. >250 °C. Anal. Calc. for C24
Pd: C, 52.62; H, 4.05; N, 5.11. Found: C, 52.32; H, 4.03; N,
3113(m), 3021(w), 2958(w), 2881(w), 1613(vs),
a
-(C
4
H
3
O)CH@NC
6
H
4
CH
3
-4}
2
(3a)
4.4.1. [
An orange liquid [14]. Yield: 92%. Anal. Calc. for C13
71.87; H, 6.96; N, 6.45. Found: C, 71.87; H, 6.90; N, 6.44%. IR: m
4 3 2 2 6 4 3
a-(C H O)CH NHCH C H OCH -4 (4a)
H
22
2
H15NO : C,
Cl
5
1
2
N
2
O
2
.09%. IR:
m
3334(w), 2920(m), 2836(w), 1612(m), 1513(m), 1489(w),
À1
1
À1
600(w), 1559(m), 1502(m), 831(s) cm
.
H NMR: d 8.51(s, 1H,
1464(m), 810(s) cm
4.4.2. [ -(C O)CH
.
H4), 7.32(d, 1H, H1), 7.11–7.34(t, 4H, PhH), 6.18(bs, 1H, H3),
5
.21(m, 1H, H2), 2.45(s, 3H, Ph–CH
3
) ppm.
a
4
H
3
2 2 6 4 3
NHCH C H CH -4 (4b)
An orange liquid. Yield: 90%. Anal. Calc. for C13
H15NO: C, 77.58;
4
.3.2. Pd[Cl{
An orange solid. Yield: 72%. M.p. >162 °C (dec.). Anal. Calc. for
Pd: C, 50.84; H, 3.49; N, 5.39. Found: C, 50.55; H,
.44; N, 5.37%. IR: 3057(w), 3019(w), 1614(vs), 1581(m),
505(m), 1452(m), 767(s), 695(s)cm
a
-(C
4
H
3
O)CH@NC
6
H
5
}
2
(3b)
H, 7.51; N, 6.96. Found: C, 77.31; H, 7.45; N, 6.96%. IR: m
3410(w),
3120(m), 2919(s), 2851(w), 1618(m), 1520(m), 1461(m), 809(s)
À1
C
3
1
22
H18Cl
2
N
2
O
2
cm
.
m
À1
1
.
H NMR: d 8.52(s, 1H,
4.4.3. [
An orange liquid [15]. Yield: 89%. Anal. Calc. for C12
76.98; H, 7.00; N, 7.48. Found: C, 77.00; H, 6.93; N, 7.46%. IR:
318(w), 3079(m), 3023(w), 2959(s), 2921(m), 2859(w),
4 3 2 2 6 5
a-(C H O)CH NHCH C H (4c)
H4), 7.32(d, 1H, H1), 7.09–7.36(m, 5H, PhH), 6.21(s, 1H, H3),
5
H13NO: C,
.23(m, 1H, H2) ppm.
m
3
4
.3.3. Pd[Cl{
A yellow solid. Yield: 80%. M.p. >230 °C (dec.). Anal. Calc. for C22
Pd: C, 44.89; H, 2.74; N, 4.76. Found: C, 44.61; H, 2.73;
3106(w), 3062(w), 1613(vs), 1582(m), 1501(m),
a
-(C
4
H
3
O)CH@NC
6
H
4
Cl-2}
2
(3c)
2831(w), 1490(w), 1451(m), 1104(m), 1042(m), 762(s), 703(vs)
À1
cm
.
H
4 2 2
16Cl N O
N, 4.73%. IR:
450(m), 750(s) cm
H1), 7.31–7.62(m, 4H, PhH), 6.31(d, 1H, H3), 5.32(t, 1H, H2) ppm.
m
4.5. Synthesis of 5a–c
À1
1
1
. H NMR: d 8.56(s, 1H, H4), 7.52(d, 1H,
General method for the synthesis of 5a–c is exemplified by the
synthesis of 5c.
4
.3.4. Pd[Cl{
A yellow solid. Yield: 74%. M.p. 171–172 °C. Anal. Calc. for C26
Pd: C, 51.38; H, 4.31; N, 4.61. Found: C, 60.55; H,
3101(w), 2952(m), 2928(w), 2834(w),
a
-(C
4
H
3
O)CH@NCH
2
C
6
H
4
OCH
3
-4}
2
(3d)
To a stirred solution of 4c (8 mmol) in acetonitrile, sodium cya-
noborohydride (1.508 g, 24 mmol) in 10 mL acetonitrile was added
a solution of formaldehyde (80 mmol) in 6.7 mL water. Then,
0.80 mL of acetic acid and 16 mL of acetonitrile was added drop-
wise and completed in 30 min. The mixture was stirred for 4–5 h
at room temperature and added acetic acid until the solution
was neutral. The aqueous phase was washed with potassium
hydroxide solution and extracted with dichloromethane
H
4
1
2 2 4
26Cl N O
.87; N, 2.19%. IR:
m
À1
1
614(vs), 1602(m), 1583(m), 1512(m), 1463(m), 822(s) cm
.
H
NMR: d 8.51(s, 1H, H4), 7.30(d, 1H, H1), 6.85–7.26(q, 4H, PhH),
.20(d, 1H, H3), 5.22(t, 1H, H2), 4.60(m, 2H, H5), 3.89(s, 3H,
OCH ) ppm.
6
3
(
3 Â 50 mL). The combined organic phase was washed with satu-
4
.3.5. Pd[Cl{
A yellow solid. Yield: 78%. M.p. 153–155 °C. Anal. Calc. for C26
Pd: C, 54.23; H, 4.55; N, 4.86. Found: C, 53.94.12; H,
3030(w), 2954(m), 2923(m), 2853(w),
a
-(C
4
H
3
O)CH@NCH
2
C
6
H
4
CH
3
-4}
2
(3e)
rated brine and separated. The extracts were dried over Na SO
2
4
and removed to give crude products which were further purified
by column chromatography (ethyl acetate/petroleum ether (60–
90 °C, v/v = 1:3) to afford 5c.
H
4
1
2 2 2
26Cl N O
.53; N, 4.85%. IR:
m
À1
1
615(vs), 1564(m), 1511(m), 1464(m), 1439(m), 811(s) cm
.
H
NMR: d 8.52(s, 1H, H4), 7.29(d, 1H, H1), 6.72–7.21(q, 4H, PhH),
.21(d, 1H, H3), 5.21(t, 1H, H2), 4.61(m, 2H, H5), 2.50(s, 3H, Ph–
CH ) ppm.
4.5.1. [
A yellow oil. Yield: 78%. Anal. Calc. for C14
7.41; N, 6.06. Found: C, 72.72; H, 7.33; N, 6.05%. IR:
4 3 2 3 2 6 4 3
a-(C H O)CH N(CH )CH C H OCH -4 (5a)
6
H
17NO
2
: C, 72.70; H,
3051(w),
947(w), 2903(w), 2830(m), 1602(w), 1513(m), 1447(m),
3
m
2
À1
1
4
.3.6. Pd[Cl{
A yellow solid. Yield: 76%. M.p. 148–152 °C. Anal. Calc. for C24
Pd: C, 52.62; H, 4.05; N, 5.11. Found: C, 52.35; H,
3035(m), 3023(m), 2905(w), 2848(w),
a
-(C
4
H
3
O)CH@NCH
2
C
6
H
5
}
2
(3f)
1071(m), 763(s), 704(vs) cm
.
H NMR: d 7.39(bs, 1H, H1),
6.85–7.26(t, 4H, PhH), 6.33(m, 1H, H2), 6.20(d, 1H, H3), 3.80(s,
3H, OCH ), 3.56(s, 2H, H4), 3.48(s, 2H, H5), 2.22(s, 3H, N–CH ) ppm.
H
22Cl
2
N
2
O
2
3
3
4
1
8
1
.02; N, 5.08%. IR:
m
À1
1
614(vs), 1498(m), 1468(m), 739(s), 696(s) cm
.
H NMR: d
4.5.2. [
A yellow oil. Yield: 77%. Anal. Calc. for C14
7.96; N, 6.51. Found: C, 78.12; H, 7.89; N, 6.48%. IR:
4 3 2 3 2 6 4 3
a-(C H O)CH N(CH )CH C H CH -4 (5b)
.55(s, 1H, H4), 7.31(d, 1H, H1), 7.18–7.52(m, 5H, PhH), 6.23(d,
H, H3), 5.22(t, 1H, H2), 4.60(m, 2H, H5) ppm.
H17NO: C, 78.10; H,
m
3045(w),
Please cite this article in press as: Z.-X. Hu et al., Polyhedron (2014), http://dx.doi.org/10.1016/j.poly.2014.03.041

6
Z.-X. Hu et al. / Polyhedron xxx (2014) xxx–xxx
2
8
922(m), 2842(m), 2784(m), 1599(m), 1514(s), 1453(s), 1363(s),
for data collection. Semi-empirical absorption corrections were
À1
1
01(s), 731(s) cm
.
H NMR: d 7.37(bs, 1H, H1), 7.13–7.26(t, 4H,
applied using the SABABS program [15]. The structure was solved
by direct methods and refined by the full-matrix least-squares pro-
PhH), 6.32(m, 1H, H2), 6.18(d, 1H, H3), 3.78 (s, 2H, H4), 3.75(s,
2
2
H, H5), 2.34(s, 3H, Ph–CH
3 3
), 2.21(s, 3H, N–CH ) ppm.
cedure on F using the SHELX suite of programs [16]. Crystallo-
graphic data and refined parameters for 3b, 3f and 6c are
summarized in Table 1. Their selected bond lengths and bond
angles are tabulated in Table 2.
4
.5.3. [
4 3 2 3 2 6 5
a-(C H O)CH N(CH )CH C H (5c)
A yellow oil. Yield: 75%. Anal. Calc. for C13
H15NO: C, 77.58; H,
7
2
1
6
2
.51; N, 6.96. Found: C, 77.58; H, 7.45; N, 6.96%. IR:
m 3058(w),
927(w), 2841 (s), 2786(m), 1600(m), 1496(m), 1453(m),
Acknowledgements
À1
1
075(m), 999(m), 748(s), 695(s) cm . H NMR: d 7.35(s, 1H, H1),
.53–7.23 (m, 5H, PhH), 6.29 (s, 1H, H2), 6.12(bs, 1H, H3), 3.81(s,
H, H4), 3.77(s, 2H, H5), 2.23(s, 3H, N–CH ) ppm.
3
We are grateful to Li-Ke Chemical Corporation limited (China)
for the financial support for this project.
4.6. Synthesis of 6a–c
Appendix A. Supplementary data
General procedure: To a stirred methanol solution (15 mL) of
a–c (1 mmol) and NaOAc (1.05 mmol) were added dropwise a
CCDC 979319, 979320 and 979318 contain the supplementary
crystallographic data for complexes 3b, 3f and 6c, respectively.
These data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
5
solution of Na
was stirred for 20 h at 8–10 °C and then evaporated. The residue
was dissolved in acetone and a solution of acetone (PPh , 0.78 g,
mmol) was added. The mixture was stirred for another 1 h. The
2 4
PdCl (1 mmol) in 30 mL methanol. The mixture
3
3
solvent was removed in vacuo, and the residue was purified by col-
umn chromatography (silica gel, ethyl acetate/hexane = 1:3, v/v) to
give 6.
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(
4
4
.6.1.
A yellow solid. Yield: 54%. M.p. 171–172 °C. Anal. Calc. for C32
31ClNO PPd: C, 60.58; H, 4.92; N, 2.21. Found: C, 60.55; H, 4.87;
3050(w), 1588(m), 1565(m), 1465(m), 1436(m),
3 4 3 2 3 2 6 3 3
a-[PdCl(PPh ){a-(C H O)CH N(CH )CH C H OCH -4 (6a)
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(
(
(
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N, 2.19%. IR:
m
À1
1
1
1
6
094(m), 808(m)cm
5H, PPh ), 6.95(d, 1H, H8), 6.88(s, 1H, H6), 6.81(d, 1H, H9),
.50(m, 1H, H2), 6.39(d, 1H, H3), 4.52(d, 2H, H4), 4.35(m, 2H,
), 2.97(s, 3H, N–CH ) ppm.
. H NMR d 7.67(bs, 1H, H1), 7.31–7.51(m,
3
Organometallics 26 (2007) 1801;
(
(
(
(
d) L. Grande, E. Serrano, L. Cuesta, E.P. Urriolabeitia, Organometallics 31
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H5), 3.86(s, 3H, OCH
3
3
[
3] (a) J. Granell, M. Martínez, Dalton Trans. 41 (2012) 11243;
4
3 4 3 2 3 2 6 3 3
.6.2. a-[PdCl(PPh ){a-(C H O)CH N(CH )CH C H CH -4 (6b)
A yellow solid. Yield: 58%. M.p. 153–155 °C. Anal. Calc. for C32
31ClNOPPd: C, 62.15; H, 5.05; N, 2.26. Found: C, 61.91; H, 5.01;
(
(
b) M. Gomez, J. Granell, M. Martinez, Organometallics 16 (1997) 2539;
c) J. Albert, L. D’Andrea, J. Granell, R. Tavera, M. Font-Bardia, X. Solans, J.
H
Organomet. Chem. 692 (2007) 3070;
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e) J. Albert, R. Bosque, M. Crespo, J. Granell, J. Rodriguez, J. Zafrilla,
(
N, 2.21%. IR:
459(m), 1435(m), 1095(m), 811(s) cm
H1), 7.34–7.59(m, 15H, PPh ), 6.95(d, 1H, H8), 6.87(s, 1H, H6),
.80 (d, 1H, H9), 6.51(d, 1H, H2), 6.30(d, 1H, H3), 4.44(d, 2H, H5),
.31(q, 2H, H4), 2.93(s, 3H, N–CH ), 2.84(s, 3H, Ph–CH ) ppm.
m 3068(w), 2926(m), 2856(m), 1589(w), 1565(w),
À1
1
1
. H NMR: d 7.72(s, 1H,
(
3
Organometallics 29 (2010) 4619;
6
4
(f) M. Benito, C. Lopez, X. Morvan, Polyhedron 18 (1999) 2583.
4] C.N. Ranninger, I.L. Solera, A.A. Valder, J.H. Rodriguez-Ramos, J.R. Masaguer, J.L.
Garcia-Ruano, X. Solans, Organometallics 12 (1993) 4104.
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Chang, Inorg. Chim. Acta 376 (2011) 144.
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Zhang, R. Jin, Inorg. Chim. Acta 359 (2006) 4114;
(
[
[
[
3
3
4
3 4 3 2 3 2 6 4
.6.3. a-[PdCl(PPh ){a-(C H O)CH N(CH )CH C H } (6c)
A yellow solid. Yield: 55%. M.p. 148–152 °C. Anal. Calc. for C31
29ClNOPPd: C, 61.60; H, 4.84; N, 2.32. Found: C, 61.57; H, 4.82;
H
b) H.X. Wang, H.F. Wu, H.C. Zhou, R. Jin, R.Q. Gao, F.Y. Geng, J. Xu, Y.J. Li, W.Q.
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8] C. Anderson, M. Crespo, M. Font-Bardıa, X. Solans, J. Organomet. Chem. 604
2000) 178.
N, 2.31%. IR:
1
7
m 3067, 2922(m), 2853(m), 1641(w), 1578(w),
434(w), 738(m), 691(s)cm–1
1
. H NMR: d 7.70(s, 1H, H1), 7.35–
[
3
.60(m, 15H, PPh ), 6.96(t, 1H, H7), 6.91(d, 1H, H8), 6.86(d, 1H,
(
H6), 6.79(t, 1H, H9), 6.57(m, 1H, H2), 6.41(t, 1H, H3), 4.51(d, 2H,
H4), 4.34(d, 2H, H5), 2.86(s, 3H, N–CH ) ppm.
[9] Z.C. Xiong, J.H. Chen, A. Li, J.H. Chen, Z. Yang, Org. Lett. 19 (2004) 3337.
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[
3
(
(
2013) 852;
b) P. Nongkunsarn, C.A. Ramsden, Tetrahedron 53 (1997) 3805.
4.7. X-ray crystallographic study of 3b, 3f and 6c
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(
[
Crystals of 3b, 3f and 6c were grown at room temperature by
(
slow evaporation of a mixture of hexane and ethyl acetate over a
period of one week. A single crystal of these complexes was
mounted on a Bruker SMART CCD diffractometer equipped with
[13] M.R. Linder, W.U. Frey, J. Podlech, J. Chem. Soc., Perkin Trans. (2001) 2566.
[14] R. Murali, H.S. Prakash Rao, H.W. Scheeren, Tetrahedron 57 (2001) 3165.
[
[
15] G.M. Sheldrick, SADABS, University of Göttingen, 1996.
16] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Programs for Crystal Structure Solution
and Refinement, University of Göttingen, 1997.
monochromated graphite Mo K
a
(k = 0.71073 Å) radiation at ambi-
–2h multi-scans technique
ent temperature (T = 293 K) using the
x
Please cite this article in press as: Z.-X. Hu et al., Polyhedron (2014), http://dx.doi.org/10.1016/j.poly.2014.03.041