Palladium(II) complexes bearing a salicylaldiminato ligand with a hydroxyl group: Synthesis, structures, deprotonation, and catalysis

Article abstract of DOI:10.1016/j.ica.2010.12.036

Palladium complexes with a salicylaldiminato ligand bearing a hydroxyl group (1a and 1b) have been synthesized and characterized. The structures of these complexes were confirmed by X-ray crystallography. A reversible deprotonation/protonation of the hydr

Full text of DOI:10.1016/j.ica.2010.12.036

Inorganica Chimica Acta 368 (2011) 237–241
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Palladium(II) complexes bearing a salicylaldiminato ligand with a hydroxyl group:
Synthesis, structures, deprotonation, and catalysis
Yusuke Murata a,b, Hiroyuki Ohgi a, Tetsuaki Fujihara b, Jun Terao b, Yasushi Tsuji b,
⇑
a Kurashiki Research Laboratories, KURARAY CO., LTD., 2045-1 Sakazu, Kurashiki, Okayama 710-0801, Japan
b Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 August 2010
Received in revised form 8 December 2010
Accepted 15 December 2010
Available online 23 December 2010
Palladium complexes with a salicylaldiminato ligand bearing a hydroxyl group (1a and 1b) have been
synthesized and characterized. The structures of these complexes were confirmed by X-ray crystallogra-
phy. A reversible deprotonation/protonation of the hydroxyl moiety on 1b was observed, while such
behaviour was impossible with a related palladium complex (1c) bearing a methoxyl group in place of
the hydroxyl group. The deprotonation affected its catalytic behaviour: the activity for polymerization
t
of methyl acrylate catalyzed by 1b considerably decreased in the presence of 1 equiv. of BuOK.
Keywords:
Palladium
Ó 2010 Elsevier B.V. All rights reserved.
Salicylaldiminato ligand
Acid–base behaviour
Crystal structures
Polymerization
1. Introduction
2. Experimental
Much attention has been paid to transition-metal-catalyzed
polymerization catalysts bearing salicylaldiminato ligands since
both electronic and steric parameters of the ligands can be system-
atically tunable by introducing various substituents on the aro-
matic ring [1]. Among them, palladium complexes bearing the
salicylaldiminato ligands were investigated as catalysts for poly-
merization of methyl acrylate, acrylonitrile, and norbornene
[1b,2]. Meanwhile, introduction of a hydroxyl group onto the aro-
matic ring is promising because electronic nature might be regu-
lated by simple deprotonation/protonation procedures. Actually,
catalytic activity can be controlled in the presence/absence of pro-
tons on ligands [3].
We anticipated that a salicylaldimiato ligand bearing a hydroxyl
group would control the catalytic activity in the presence/absence
of the proton near a metal center. In the present study, we
designed and synthesized palladium complexes with a salicylal-
diminato ligand having a hydroxyl functionality. The structures
of these complexes were unambiguously determined by X-ray
crystallography. Deprotonation of the hydroxyl group affected
the electronic nature of the complex as well as catalytic activity
for polymerization of methyl acrylate.
2.1. General procedure
All manipulations were performed under an argon atmosphere
using standard Schlenk-type glasswares on a dual-manifold Schlenk
line. Unless otherwise noted, materials obtained from commercial
suppliers were used without further purification. THF, CH2Cl2 and
methyl acrylate were dried and purified before use by usual meth-
ods [4]. 1H, 13C{1H} and 31P{1H} NMR spectra were measured with
a JEOL ECX-400P spectrometer. The 1H NMR chemical shifts are
reported relative to tetramethylsilane (TMS, 0.00 ppm). The
13C NMR chemical shifts are reported relative to CDCl3 (77.0 ppm).
The 31P NMR chemical shifts are reported relative to 85% H3PO4
(0.00 ppm) as an external standard. Analytical size-exclusion chro-
matography (SEC) was performed using CHCl3 as the eluent at a flow
rate of 1.0 mL/min on an HPLC (Shimadzu) equipped with a LC-10AT
HPLC pump, a RID-10A RI detector through a column set consisting
of Shodex-K-601L (0.8 ꢀ 30 cm ꢀ 2). Average molecular weights
(Mn) and the polydisperse index (PDI) of poly(methyl acrylate) were
determined by using polystyrene standards. Electron spray ioniza-
tion time-of-flight mass spectrometry (ESI-TOF mass) was carried
out on a waters LCT-Premier instrument. The sprayer was held at
a potential of +2.6 kV in the positive detection mode or ꢁ2.8 kV in
the negative detection mode. The orifice potential was maintained
at 50 V in each detection modes. Elemental analysis was carried
out at Center for Organic Elemental Microanalysis, Graduate School
of Pharmaceutical Science, Kyoto University. TLC analyses were
performed on commercial glass plates bearing a 0.25-mm layer of
⇑
Corresponding author. Fax: +81 75 383 2514.
E-mail address: ytsuji@scl.kyoto-u.ac.jp (Y. Tsuji).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.12.036

238
Y. Murata et al. / Inorganica Chimica Acta 368 (2011) 237–241
Merck Silica gel 60F254. N-(2,6-Diisopropylphenyl)-3-hydroxysali-
cylaldimine (HLOH) [1a], N-(2,6-diisopropylphenyl)-3-methoxysali-
cylaldimine (HLOMe) [1a], cis- (1,5-cyclooctadiene)dichloropalla-
dium [PdCl2(cod)] [5], and cis- (1,5-cyclooctadiene)chloromethyl-
palladium [PdClMe(cod)] [6] were also prepared according to
literature procedures.
from dichloromethane/hexane afforded 1c as yellow crystals. Yield
4
0.79 g (86%). 1H NMR(CDCl3):
d 7.97 (d, JPH = 11.4 Hz, 1H,
ArN@CH), 7.7–7.6 (m, 6H, Ar(phosphine)), 7.5–7.3 (m, 9H, Ar(phos-
3
phine)), 7.2 (m, 3H, N–Ar), 6.73 (d, JHH = 7.44 Hz, 1H, Ar), 6.72 (d,
3
3JHH = 8.43 Hz, 1H, Ar), 6.36 (t, JHH = 7.93 Hz, 1H, Ar), 3.67 (s, 3H,
3
OCH3), 3.52 (sep, JHH = 6.94 Hz, 2H, CH(CH3)2), 1.29 (d,
3
3JHH = 6.94 Hz, 6H, CH(CH3)2), 1.11 (d, JHH = 6.94 Hz, 6H,
3
2.2. Synthesis of palladium complexes
CH(CH3)2), ꢁ0.45 (d, JPH = 2.53 Hz, 3H, Pd–CH3). 13C{1H} NMR
(CDCl3): d 165.6, 160.5, 152.9, 147.7, 141.1, 135.0, 134.9, 131.9,
2.2.1. Synthesis of PdCl(PPh3)(LOH) (1a)
131.2, 130.1, 130.0, 128.1, 128.0, 127.2, 126.0, 123.2, 118.7,
2
To a solution of N-(2,6-diisopropylphenyl)-3-hydroxysalicyl-
113.2, 111.7, 55.4, 27.9, 25.0, 22.5, 1.79 (d, Jcp = 11.2 Hz, Pd–
aldimine (HLOH, 0.40 g, 1.4 mmol) in THF (5.0 mL) was added a
CH3). 31P{1H} NMR (CDCl3): d 35.9. ESI-TOF mass (in the positive
mode, MeOH), m/z 716.2 ([1c+Na]+; I = 100% in the range of m/z
100–2000). Anal. Calc. for C39H42NO2PPdꢂ0.5H2O: C, 66.62; H,
6.16; N, 1.99. Found: C, 66.63; H, 6.18; N, 1.93%.
t
solution of BuOK (1.0 M in THF, 2.8 mL, 2.8 mmol) at room tem-
perature. After stirring for 30 min, all volatiles were removed in va-
cuo. The resulting solid residue was dissolved in dichloromethane
(5.0 mL) and then PdCl2(cod) (0.38 g, 1.33 mmol) and PPh3 (0.35 g,
1.3 mmol) were added to the solution. After stirring at room tem-
perature overnight, triethylammonium hydrogen chloride (0.20 g,
1.5 mmol) was added. The reaction mixture was stirred for addi-
tional 30 min and then filtered. Removal of all volatiles in vacuo
gave crude products as yellow solids. Recrystallization from dichlo-
romethane/hexane afforded 1a as yellow crystals. Yield 0.63 g
2.3. General procedure for polymerization
In a glove box under a nitrogen atmosphere, a 20 mL Schlenk
flask was charged with 1 (0.011 mmol), THF (0.30 mL) and dichlo-
t
romethane (3.6 mL). In the case of the addition of BuOK (1.0 M in
THF, 11 lL, 0.011 mmol), the base was added before charging
4
(68%). 1H NMR (CDCl3): d 7.86 (d, JPH = 13.4 Hz, 1H, ArN@CH),
dichloromethane. After methyl acrylate (1.0 mL, 12 mmol) was
introduced to the flask, the reaction mixture was stirred at the
ambient temperature for 24 h. The reaction mixture was poured
into 50 mL of methanol and precipitated polymers were collected
by filtration and dried under vacuum at 60 °C for 24 h. Average
molecular weights (Mn) and the polydisperse index (PDI) of poly(-
methyl acrylate) were determined using polystyrene standards.
7.8–7.7 (m, 6H, Ar(phosphine)), 7.6–7.5 (m, 3H, Ar(phosphine)),
7.5–7.4 (m, 6H, Ar(phosphine)), 7.2–7.1 (m, 3H, N–Ar), 6.80 (dd,
4
3
3JHH = 7.44 Hz, JHH = 1.49 Hz, 1H, Ar), 6.74 (dd, JHH = 7.93 Hz,
4JHH = 1.49 Hz, 1H, Ar), 6.50 (t, JHH = 7.93 Hz, 1H, Ar), 4.99 (s, 1H,
3
OH), 3.45 (sep, 3JHH = 6.94 Hz, 2H, CH(CH3)2), 1.40 (d,
3JHH = 6.94 Hz, 6H, CH(CH3)2), 1.15 (d, JHH = 6.94 Hz, 6H,
3
CH(CH3)2). 13C{1H} NMR (CDCl3): d 163.3, 152.5, 147.7, 146.9,
141.3, 135.0, 134.8, 131.2, 131.1, 129.0, 128.6, 128.4, 128.3,
126.7, 125.1, 122.9, 118.0, 116.0, 115.6, 28.7, 24.6, 22.9. 31P{1H}
NMR (CDCl3): d 30.5. ESI-TOF mass (in the negative mode, MeOH),
m/z 698.2 ([1aꢁH]ꢁ; I = 100% in the range of m/z 100–2000). Anal.
Calc. for C37H37ClNO2PPd: C, 63.44; H, 5.32; N, 2.00. Found: C,
63.37; H, 5.43; N, 1.91%.
2.4. X-ray crystallography
A summary of crystal structure refinements of 1a–1c was given
in Table 1. Data were collected on
diffractometer using graphite-monochromated Mo K
a
Rigaku/Saturn70 CCD
radiation
a
(k = 0.71070 Å) at 153 K, and processed using CrystalClear (Rigaku)
[7]. The structures were solved by a direct method and refined by
full-matrix least-square refinement on F2. The non-hydrogen
atoms were refined anisotropically. All hydrogen atoms were lo-
cated on the calculated positions and not refined. All calculations
were performed using the CrystalStructure software package [8].
2.2.2. Synthesis of PdMe(PPh3)(LOH) (1b)
The complex was synthesized with PdClMe(cod) (0.35 g,
1.3 mmol) instead of PdCl2(cod) by the method similar to that used
for 1a. Yield 0.82 g (91%). 1H NMR (CDCl3): d 7.99 (d, 4JPH = 11.4 Hz,
1H, ArN@CH), 7.7–7.5 (m, 6H, Ar(phosphine)), 7.5–7.3 (m, 9H,
3
Ar(phosphine)), 7.2 (m, 3H, N–Ar), 6.78 (dd, JHH = 7.44 Hz,
3
4
4JHH = 1.49 Hz, 1H, Ar), 6.64 (dd, JHH = 8.43 Hz, JHH = 1.49 Hz, 1H,
3. Results and discussion
3
3
Ar), 6.34 (dd, JHH = 7.44 Hz, JHH = 8.43 Hz, 1H, Ar), 5.76 (s, 1H,
OH), 3.46 (sep, 3JHH = 6.94 Hz, 2H, CH(CH3)2), 1.34 (d,
3.1. Synthesis and structure of palladium complexes
3JHH = 6.94 Hz, 6H, CH(CH3)2), 1.13 (d, JHH = 6.94 Hz, 6H,
3
CH(CH3)2), ꢁ0.35 (d, JPH = 2.98 Hz, 3H, Pd–CH3). 13C{1H} NMR
A ligand precursor (HLOH) was readily prepared by the reaction
of 2,3-dihydroxybenzaldehyde with 2,6-diisopropylaniline in
methanol [1a]. Palladium complexes with a salicylaldiminato li-
gand bearing a hydroxyl group (LOH) were synthesized as shown
in Scheme 1. First, the reaction of the ligand precursor with 2
equiv. of tBuOK afforded a dianionic intermediate in situ. Then,
addition of PdCl(X)(cod) (X = Cl or = Me) and PPh3 in CH2Cl2 fol-
3
(CDCl3): d 165.8, 156.9, 149.1, 147.3, 140.9, 134.7, 134.5, 131.0,
130.6, 130.9, 130.3, 128.4, 128.3, 126.2, 125.2, 123.3, 117.0,
2
113.8, 113.1, 28.0, 25.1, 22.5, 0.19 (d, Jcp = 11.2 Hz, Pd–CH3).
31P{1H} NMR (CDCl3): d 43.32. ESI-TOF mass (in the negative mode,
MeOH), m/z 678.2 ([1bꢁH]ꢁ; I = 100% in the range of m/z 100–
2000). Anal. Calc. for C38H40NO2PPd: C, 67.11; H, 5.93; N, 2.06.
Found: C, 67.05; H, 5.97; N, 2.09%.
lowed by the treatment of Et3NꢂHCl afforded PdX(PPh3)(LOH
)
(X = Cl (1a) or = Me (1b)) in good yields. For comparison, a related
palladium complex with a salicylaldiminato ligand bearing a meth-
oxyl group (LOMe), PdMe(PPh3)(LOMe) (1c), in place of the hydroxyl
group was also synthesized by the reaction of the corresponding
2.2.3. Synthesis of PdMe(PPh3)(LOMe) (1c)
To a solution of N-(2,6-diisopropylphenyl)-3-methoxysalicyl-
aldimine (HLOMe, 0.42 g, 1.4 mmol) in THF (5.0 mL) was added a
t
t
solution of BuOK (1.0 M in THF, 1.4 mL, 1.4 mmol) at room tem-
salicylaldimine with BuOK followed by adding PdClMe(cod) and
perature. After stirring for 30 min, all volatiles were removed in va-
cuo. The resulting solid residue was dissolved in dichloromethane
(5.0 mL), and then PdClMe(cod) (0.35 g, 1.3 mmol) and PPh3
(0.35 g, 1.3 mmol) were added to the solution. After stirring at
room temperature overnight, all volatiles were removed in vacuo.
The resulting crude products were purified by recrystallization
PPh3 (Scheme 2). All complexes were fully characterized by ele-
mental analysis and NMR measurements.
The molecular structures of 1a–1c have been successfully deter-
mined by X-ray crystallography. Suitable single crystals of 1a–1c
were obtained by crystallization from hot heptane solution. For
1a, there are two independent molecules in a unit cell (see Table

Y. Murata et al. / Inorganica Chimica Acta 368 (2011) 237–241
239
Table 1
Crystallographic data of 1a–1c.
1a
1b
1c
Empirical formula
C37H36NO2ClPdP
C38H39NO2PdP C39H42NO2PdP
Formula weight
T (K)
699.52
153
679.11
153
682.05
153
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c (#14)
20.286(5)
11.491(2)
29.737(7)
107.427(3)
6613(3)
monoclinic
P21/c (#14)
14.422(3)
11.035(2)
21.495(5)
105.888(3)
3290(1)
4
monoclinic
P21/n (#14)
11.423(4)
24.228(7)
12.344(4)
100.144(5)
3363(1)
4
b (°)
V (Å3)
Z
8
qcacd (g cmꢁ3
)
1.405
1.371
1.371
Unique reflections
14825
7224
7444
(Rint = 0.092)
14825 (all data)
(Rint= 0.064)
7224 (all data) 7444 (all data)
(Rint = 0.085)
Observed
reflections
Goodness-of-fit
(GOF)
1.025
1.010
1.047
R1 (I > 2
r
(I))a
0.055, 0.141b
0.047, 0.095c
0.059, 0.131d
wR2 (all data)a
2
2
1=2
ðwðF2o ꢁ F2c Þ Þ=
R
wðF2o Þ ꢃ
.
a
b
c
R1
=
R
[|Fo| ꢁ |Fc|]/
R
|Fo|, wR2 ¼ ½
R
w ¼ 1=½0:7
w ¼ 1=½0:9
w ¼ 1=½0:7
r
r
r
ðF2o Þꢃ=ð4F2o Þ.
ðF2o Þꢃ=ð4F2o Þ.
ðF2o Þꢃ=ð4F2o Þ.
d
2 eq. tBuOK
THF
O
H
O
K
OH N
HLOH
OK N
O
K
PPh3
PdCl(X)(cod)
O
Et3NHCl
O
N
X
H
O
N
CH2Cl2
RT
Pd
Ph3P
Pd
Ph3P
X
1a
: X = Cl
1b: X = Me
Scheme 1. Synthesis of palladium complexes 1a and 1b.
1 eq. tBuOK
THF
PPh3
MeO
PdClMe(cod)
MeO
O
N
Fig. 1. ORTEP drawings of (a) 1a, (b) 1b and (c) 1c with thermal ellipsoids at 30%
probability levels.
OH N
HLOMe
CH2Cl2
RT
Pd
Ph3P
1c
Me
Scheme 2. Synthesis of a palladium complex 1c.
Table 2
Selected bond lengths (Å) and angles (°) for 1a.
1a (complex A)
1a (complex B)
1). Fig. 1a shows the ORTEP drawing for 1a. The palladium atom
has a square-planar coordination geometry. The chlorine atom at-
tached to the Pd atom lies trans to the oxygen atom. Triphenyl-
phosphine ligand occupies the position trans to the nitrogen due
to a steric hindrance between PPh3 ligand and the 2,6-diisopropyl-
phenyl group. Selected bond lengths and bond angles were sum-
marized in Table 2. These bond lengths and bond angles around
the palladium atom were comparable to those of analogous palla-
dium complexes [1b,2b–d]. In the structures of 1b and 1c shown in
Fig. 1b and c, each palladium atom has also a square-planar coor-
dination geometry. The CH3 group coordinating to the Pd atom lies
trans to the oxygen atom. PPh3 ligand occupies the position trans to
the nitrogen bearing the bulky 2,6-diisopropyl group. Selected
bond lengths and bond angles were summarized in Table 3. The
Pd–Cl
Pd–N
Pd–P
Pd–O
2.2671(11)
2.074(4)
2.2513(14)
2.005(3)
2.2817(14)
2.2454(14)
2.073(4)
2.001(3)
Cl–Pd–N
Cl–Pd–O
Cl–Pd–P
N–Pd–O
N–Pd–P
O–Pd–P
91.53(11)
175.01(10)
85.87(4)
91.64(14)
174.03(12)
91.33(10)
93.49(12)
175.33(10)
84.32(4)
91.01(15)
177.80(12)
91.18(10)
Pd–C bond length of 1b (2.064(4) Å) was similar to that of 1c
(2.059(5) Å) and other Pd–C(CH3) bond lengths of the complexes

240
Y. Murata et al. / Inorganica Chimica Acta 368 (2011) 237–241
Table 3
Selected bond lengths (Å) and angles (°) for 1b and 1c.
1b
1c
Pd–C(1)
Pd–N(1)
Pd–P(1)
Pd–O(1)
2.064(4)
2.095(2)
2.2265(8)
2.099(2)
2.059(5)
2.096(4)
2.2620(16)
2.100(3)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–O(1)
C(1)–Pd(1)–P(1)
N(1)–Pd(1)–O(1)
N(1)–Pd(1)–P(1)
O(1)–Pd(1)–P(1)
92.03(13)
173.72(11)
84.08(10)
89.27(11)
175.48(9)
94.84(7)
90.99(19)
176.50(19)
83.58(16)
88.45(16)
174.18(12)
97.09(11)
bearing salicylaldiminato ligands are in the range between 2.001
and 2.046 Å [1b,2a–c].
The 1H NMR spectra of 1a–1c in CDCl3 displayed characteristic
resonances. Signals corresponding to the methyl protons of the iso-
propyl moieties on the salicylaldiminato ligand were split into two
doublets indicating rotations between the nitrogen and the ipso
carbon of 1a–1c were restricted. The ketimine (HC@N) proton res-
onances of 1a–1c were displayed as doublets near 8.0 ppm with a
phosphorus coupling (4JPH = ca. 12 Hz). These chemical shifts and
coupling constants were similar to those observed for analogous
complexes [1b,2b]. As for 1a and 1b, proton resonances of the hy-
droxyl moiety were observed at 4.99 ppm (1a) and 5.76 ppm (1b),
suggesting an existence of intramolecular hydrogen bond with the
oxygen atom coordinating to the palladium [9]. Resonances of the
Fig. 2. 1H NMR spectra of (a) 1b in THF-d8, (b) after the addition of 1 equiv. tBuOK in
THF, and (c) after further addition of 1 equiv. HCl in Et2O. ⁄Indicates TMS.
Table 4
Palladium-catalyzed polymerization of methyl acrylate.a.
b
Entry
Catalyst
Additive
Yield (%)
Mn(ꢀ10ꢁ3
)
PDIb
1
2
3
4
1b
1c
1b
1c
none
79
70
19
70
116
114
129
135
2.30
2.13
1.84
1.94
none
tBuOKc
tBuOKc
methyl group on the palladium appeared as
a doublet at
ꢁ0.36 ppm (3JPH = 2.98 Hz) for 1b and ꢁ0.45 ppm (3JPH = 2.53 Hz)
for 1c, respectively. In 13C NMR, a resonance of the methyl group
was observed as a doublet at 0.19 ppm (2JPC = 11.2 Hz) for 1b and
1.79 ppm (2JPC = 11.2 Hz) for 1c. These resonances are similar to
other methylpalladium complexes bearing salicylaldiminato li-
gands [1b]. 31P resonances of 1a–1c in CDCl3 appeared at
30.54 ppm, 43.51 ppm and 35.92 ppm, respectively.
a
Conditions: methyl acylate (1.0 mL, 12 mmol), 1 (0.011 mmol, S/C = 1000), THF/
CH2Cl2 = 0.3 mL/3.6 mL, RT, 24 h.
b
Determined by analytical SEC using polystyrenes as a standard.
c
tBuOK (1.0 M solution in THF, 0.011 mmol) was used.
a catalyst, poly(methyl acrylate) was obtained in 79% yield with a
moderate polydispancy (entry 1).1 According to 1H and 13C NMR
spectra, the polymer thus obtained had atactic microstructures
[11]. As a catalyst, 1c showed the comparable result (entry 2). How-
3.2. Deprotonation of 1b
t
ever, effect of the addition of BuOK was quite different between 1b
and 1c. The catalytic activity of 1b in the presence of 1 equiv. tBuOK
drastically decreased, giving the corresponding polymer in 19% yield
(entry 3). On the other hand, in the case of 1c as the catalyst, the
reaction was not suppressed by the added tBuOK (entry 4). These re-
sults clearly indicate that the presence of potassium cation close
proximity to the palladium center affects the catalytic activity
considerably.
The complex 1b has the hydroxyl moiety in the close proximity
of the palladium center and the hydroxyl functionality can be
deprotonated by the addition of a base. In 1H NMR spectrum of
1b in THF-d8, a signal at 5.76 ppm attributed to the hydroxyl pro-
ton (signal b in Fig. 2a) disappeared on adding 1 equiv. of tBuOK in
THF (Fig. 2b). In addition, the signal a assigned to the imino proton
4
(8.08 ppm, JPH = 10.7 Hz) showed down-field shift to 8.64 ppm.
The methyl proton resonance of 1b observed as a doublet peak at
ꢁ0.36 ppm (signals
c in Fig. 2a) was shifted to 0.12 ppm
(2JPH = 3.17 Hz) on the deprotonation (Fig. 2b). Other resonances
of the salicylaldiminato ligand also moved as shown in Fig. 2b. In
addition, a 31P resonance of 1b at 43.51 ppm was shifted to
4. Conclusion
New palladium complexes with salicylaldiminato ligands
(1a–1c) were synthesized and their structures were confirmed by
X-ray crystallography. A reversible deprotonated/protonation of
the hydroxyl group of 1b was observed. Notably, the introduction
of potassium cation in close proximity to the palladium affected
the catalytic activity considerably in the polymerization of methyl
acrylate.
t
36.38 ppm after the addition of BuOK. Here, no free PPh3 reso-
nance (ꢁ4.54 ppm in THF-d8) [10] was observed. These clear spec-
t
tral changes caused with adding BuOK was not observed with 1c
bearing the methoxyl moiety in place of the hydroxyl group. Nota-
bly, 1b was restored by adding 1 equiv. HCl in Et2O to the deproto-
nated 1b (from Fig. 2b to c), indicating the reversible change
observed with 1b (Fig. 2a and b) must be due to the deprotona-
tion/protonation of the hydroxyl group on the salicylaldiminato
ligand.
Appendix A. Supplementary material
CCDC 786886, 786887, and 786888; contain the supplementary
crystallographic data for complexes 1a–c. These data can be
3.3. Polymerization of methyl acrylate
The polymerization of methyl acrylate was carried out in a mix-
ture of THF and CH2Cl2 in the presence of a catalytic amount of 1b
or 1c (S/C = 1000) at room temperature (Table 4). Employing 1b as
1
The polymerization reaction of entry 1 in Table 4 was completely halted upon the
addition of galvinoxyl, suggesting the reaction would proceed via some radical
pathway [2a].

Y. Murata et al. / Inorganica Chimica Acta 368 (2011) 237–241
241
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