Synthesis and characterization of new (pyrazolyl)aryl phosphinite PCN pincer palladium(II) complexes

Article abstract of DOI:10.1016/j.jorganchem.2011.04.034

Two unsymmetrical PCN pincer Pd(II) complexes 3a-3b which are based on (pyrazolyl)aryl phosphinite ligands and contain two fused six-membered palladacycles have been synthesized from 3-(3,5-dimethylpyrazol-1-ylmethyl) benzyl alcohol (2) by one-pot phosphorylation/palladation reaction via C-H bond activation of the related ligands. The pyrazole-coordinated phosphine-free Pd(II) complex (4) was also isolated in the preparation of pincer complex 3a. The new complexes were characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P {¹H} NMR (for pincer complexes) and IR spectra. And the molecular structures of 3b and 4 have been further determined by X-ray single-crystal diffraction. The pincer Pd complexes 3a and 3b exhibited rather low activity in the allylation of benzaldehyde.

Full text of DOI:10.1016/j.jorganchem.2011.04.034

Journal of Organometallic Chemistry 696 (2011) 2857e2862
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Synthesis and characterization of new (pyrazolyl)aryl phosphinite
PCN pincer palladium(II) complexes
*
*
An-Ting Hou, Yan-Jing Liu, Xin-Qi Hao, Jun-Fang Gong , Mao-Ping Song
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Zhengzhou University, Zhengzhou 450052, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two unsymmetrical PCN pincer Pd(II) complexes 3ae3b which are based on (pyrazolyl)aryl phosphinite
ligands and contain two fused six-membered palladacycles have been synthesized from 3-(3,5-dime-
thylpyrazol-1-ylmethyl)benzyl alcohol (2) by one-pot phosphorylation/palladation reaction via CeH
bond activation of the related ligands. The pyrazole-coordinated phosphine-free Pd(II) complex (4) was
also isolated in the preparation of pincer complex 3a. The new complexes were characterized by
elemental analysis, 1H NMR, 13C NMR, 31P {1H} NMR (for pincer complexes) and IR spectra. And the
molecular structures of 3b and 4 have been further determined by X-ray single-crystal diffraction. The
pincer Pd complexes 3a and 3b exhibited rather low activity in the allylation of benzaldehyde.
Ó 2011 Elsevier B.V. All rights reserved.
Received 15 March 2011
Received in revised form
26 April 2011
Accepted 28 April 2011
Keywords:
Unsymmetrical
PCN pincer palladium(II) complex
Pyrazolyl
Phosphinite
1. Introduction
unsymmetrical pincer Pd complexes do outperform the related
symmetrical ones on catalytic activity under certain circumstances.
Pincer palladium complexes with monoanionic terdentate
ligands have found wide applications in organometallic homoge-
neous catalysis [1]. For example, they have been used as efficient
catalysts for a variety of CeC bond forming reactions including
allylation of aldehydes and imines with allylic stannanes [2e8],
palladium-catalyzed cross-coupling reactions such as the Heck
reaction [9e12], SuzukieMiyaura [13e18] and Sonogashira
For example, Klein Gebbink and Szabó et al. have demonstrated
that the unsymmetrical PCS palladium pincer is the fastest catalyst
in aldol condensation reaction between benzaldehyde and methyl
isocyanoacetate among the three pincer complexes including
symmetrical SCS and PCP complexes [26]. We have also found that
in the Suzuki couplings conducted at 40e50 ꢀC, the unsymmetrical
(pyrazolyl)aryl phosphinite or (imino)aryl phosphinite PCN Pd
complexes exhibit much higher activity than the related symmet-
rical bis(phosphinite) PCP complexes [27,28]. Despite the facts,
reports on the unsymmetrical Pd complexes are relatively few
compared to the symmetrical ones and one obvious reason for this
is their relatively complicated synthesis. Recently, we have devel-
oped a facile, direct method based on one-pot phosphorylation/
palladation reaction for the preparation of unsymmetrical PCN
couplings [14,19] as well as aearylation of ketones [20]. Palladium
pincers have also been successfully applied to the synthesis of
organometallic reagents such as allyl [2] or allenyl [21] stannanes,
where in most cases they cannot be replaced with simple Pd
sources like Pd(OAc)2, Pd(PPh3)4 and Pd2(dba)3. Among the pincer
Pd catalysts, the most common ones are symmetrical ECE type with
two identical donor groups (E ¼ PR2, OPR2, NR2, pyridine, N-con-
taining heterocycles, SR, etc.) in the side arms of the central aryl
ring and two equivalent five-membered palladacycles, particularly
those of PCP and NCN Pd pincers. The reactivities of the Pd center in
these symmetrical complexes can be easily tuned by appropriate
choice of substituents on the heteroatom donors or/and hetero-
atom donors. Nonetheless, introduction of two different donors in
the pincer ligand, which gives unsymmetrical pincer Pd complexes,
also seems to be an appealing strategy to improve the properties of
the ensuing complexes [22e25]. In fact, it has been found that some
pincer palladium complexes containing
a phosphinito group
(Scheme 1) [27e30]. By using this method, a variety of achiral and
chiral Pd pincers which comprise pyrazolyl-, amino-, imino- or
chiral imidazolinyl as a N-donor and phosphinito as a P-donor have
been conveniently synthesized in good yields (42e72%). Among
them, the (pyrazolyl)aryl phosphinite PCN compound 1 (Scheme 2)
containing fused five- and six-membered metallacycles was ob-
tained by the reaction of pyrazolyl-containing m-phenol derivative,
which was derived from m-hydroxybenzaldehyde, with diphenyl-
chlorophosphine in the presence of Et3N, followed by the addition
of PdCl2 [27]. In continuation of this investigation, herein we would
like to report the synthesis of new (pyrazolyl)aryl phosphinite PCN
* Corresponding authors. Tel.: þ86 371 67763869; fax: þ86 371 67766667.
E-mail addresses: gongjf@zzu.edu.cn (J.-F. Gong), mpsong@zzu.edu.cn (M.-P. Song).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.04.034

2858
A.-T. Hou et al. / Journal of Organometallic Chemistry 696 (2011) 2857e2862
N
H
N
R2PCl, Et3N; then PdCl2
toluene, reflux
O
Cl
Pd
N
Pd
Cl
Ph2P
N
CH3
OH
O P R
R
CH3
N
= N-donor group
1
Scheme 1. One-pot phosphorylation/palladation reaction for the synthesis of the
unsymmetrical PCN pincer palladium(II) complexes.
Scheme 2. Structure of the (pyrazolyl)aryl phosphinite PCN pincer Pd(II) complex 1
containing fused five- and six-membered palladacycles.
Pd(II) complexes 3ae3b containing two six-membered metalla-
cycles by one-pot phosphorylation/palladation reaction of
pyrazolyl-containing m-benzyl alcohol derivative 2 (Scheme 3). The
pincer Pd complexes were applied to the allylation of aldehydes.
The results are shown as below.
of complex 3b. The results indicated that phosphorylation of
hydroxymethyl with dialkylchlorophosphine was relatively diffi-
cult compared to that of phenolic-hydroxy group under similar
conditions.
All of the new Pd complexes are air- and moisture- stable both in
the solid state and in solution. They were well characterized by
elemental analysis, 1H NMR, 13C NMR, 31P {1H} NMR (for pincer
complexes) and IR spectra. The formation of the pincer complexes
2. Results and discussion
was confirmed by the single resonance at
d about 117 ppm (for
2.1. Synthesis and characterization
Ph2PO) or 160 ppm (for t-Bu2PO) in the 31P{1H} NMR spectra and
the absence of the singlet corresponding to the central aryl proton
located ortho to both eCH2OR and eCH2Pz in the 1H NMR spectra.
Starting from inexpensive, commercially available iso-
phthalaldehyde, the 3-(3,5-dimethylpyrazol-1-ylmethyl)benzalde-
hyde could be prepared after selective reduction of one aldehyde
to hydroxymethyl, bromination and nucleophilic substitution
with 3,5-dimethylpyrazole according to the published procedure
[31] (Scheme 3). Then reduction of the remaining aldehyde
group by NaBH4 easily gave the required 3-(3,5-dimethylpyrazol-
1-ylmethyl)benzyl alcohol 2. The following “one-pot phosphory-
lation/palladation reaction” was carried out in a way similar to that
of 3-(3,5-dimethylpyrazol-1-ylmethyl)phenol. Thus, 2 reacted with
diphenylchlorophosphine or di-tertbutylchlorophosphine in the
presence of triethylamine in toluene at reflux for 8 h, followed by
the addition of palladium chloride and reflux for another 18 h. The
expected new PCN pincer palladium complexes 3a and 3b with two
six-membered palladacycles were successfully obtained as white
solids after chromatography on silica gel in 25% and 46% yields,
respectively. Interestingly, the hydroxymethyl-chlorinated and
pyrazole-coordinated phosphine-free Pd(II) complex 4 was also
isolated in the preparation of pincer complex 3a, which led to the
lower yield of 3a. Prolonging the reaction time of 2 with Ph2PCl for
phosphorylation could not inhibit effectively the formation of
compound 4, although it was not observed in the synthesis
In addition, the eCH2Pz protons appeared as a singlet at d 5.13 ppm
and the eCH2OH protons appeared as a doublet at 4.60 ppm in
the PCN ligand precursor 2. While in the Pd complexes 3a and
3b, the two protons of eCH2Pz appeared in two different
positions including the doublet at
4.96e4.85 ppm (5.59 and 4.95e4.83 ppm, respectively for 3b),
and the eCH2OPR2 protons were observed as one doublet of
doublets at 5.10 ppm and one multiplet at 4.96e4.85 ppm (only
one multiplet at
4.95e4.83 ppm for 3b). The 13C NMR spectra of
d 5.49 and the multiplet at
d
d
d
d
the pincer complexes exhibited intensive 31P-13C couplings. On the
other hand, although X-ray analysis clearly indicates that the non-
cyclometallated compound 4 adopts a trans-geometry in the solid
state with the two chloride ligands being in a trans-position (vide
infra), its 1H NMR and 13C NMR spectra demonstrated more signals
than expected, suggesting the presence of isomers in solution. For
example, the 1H NMR spectrum of 4 showed two singlets at
and 5.74 ppm, respectively for eCH2Pz protons as well as two
singlets at 4.59 and 4.46 ppm, respectively for eCH2Cl protons.
The signals for the pyrazole proton were observed at 5.90 and
2.51,
d 6.16
d
d
5.94 ppm, respectively as two singlets and the four singlets at
d
1) NaBH4
2) PBr3
NaBH4
0 oC - rt
CH3
NH
3)
N
OHC
CHO
OHC
CH3
CH3
N
N
H3C
OH
N
N
H3C
H3C
2
Cl
R2PCl, Et3N; then PdCl2
toluene, reflux
CH3
N
H3C
Cl
O
N
N
N
N
Pd
Cl
CH3
N
Pd
Cl
R2P
CH3
Cl
CH3
CH3
3a R = Ph (25%)
3b R = t-Bu (46%)
4 (34%)
Scheme 3. Synthesis of the new (pyrazolyl)aryl phosphinite PCN pincer Pd(II) complexes 3a-b with two fused six-membered palladacycles.

A.-T. Hou et al. / Journal of Organometallic Chemistry 696 (2011) 2857e2862
2859
Fig. 1. Molecular structure of pincer Pd complex 3b. Hydrogen atoms are omitted for
clarity.
Fig. 3. Molecular structure of non-cyclometallated complex 4. Hydrogen atoms are
omitted for clarity.
2.11, 2.90 and 2.04 ppm, respectively were assigned to the two CH3-
groups in the pyrazole ring. A ratio of about 1.6:1 for the two
isomers could be calculated from the above corresponding signals.
The complicated NMR spectra of 4 are most likely due to the
existence of both trans- and cis- structures in solution. Another
possibility is that all species are trans- concerning the two chloride
ligands, whereas the two N-benzyl groups may be in a syn- and
anti-configuration.
rings. In comparison with the related (pyrazolyl)aryl phosphinite
PCN pincer Pd complexes such as 1, which has a five-membered
P-containing palladacycle, the Pd complex 3b shows slightly
longer PdeC (2.034 vs 2.005e2.012 Å) and PdeP bond lengths
(2.2416 vs 2.1823e2.1966 Å) [27]. The bond angles around Pd(II)
center in 3b are quite different from those found in complex 1. For
example, the CePdeP (89.05ꢀ) and NePdeP (173.42ꢀ) angles in 3b
are significantly bigger than those in complex 1 (79.59 and 166.62ꢀ,
respectively). The values are also markedly bigger than those in the
PCN Pd pincers containing two five-membered-ring metallacycles
(around 80 and 160ꢀ, respectively) [28,29,32]. The biggest NePdeP
angle in complex 3b with two six-membered palladacycles among
the three types of PCN Pd pincers suggests that introduction of
larger metallacycles can effectively decrease the steric strain of the
resultant complexes. In the crystal of complex 3b, chlorine atom
forms hydrogen bond with the adjacent CH3 group of pyrazole
(Cl(1)/H(9A) 2.927 Å, Cl(1)/C(9) 3.765 Å, C(9)eH(9A)/Cl(1)
146ꢀ), which constructs the one-dimensional chain structure of 3b
(Fig. 2).
2.2. Crystal structure
The molecular structures of Pd complexes 3b and 4 were
confirmed by X-ray single-crystal analysis. The molecules are
illustrated in Figs. 1 and 3, respectively. Selected bond lengths (Å)
and angles (ꢀ) are given in Table 1.
As shown in Fig. 1, in the pincer Pd complex 3b the ligand
coordinates to the Pd(II) center via the phosphinito-P atom, the
carbon atom of central aryl ring and the pyrazolyl-N atom in a tri-
dentate manner and the metal atom adopts a slightly distorted
square-planar geometry with chloride occupying the fourth coor-
dination site. The formed two palladacycles are both six-membered
Fig. 2. 1-D chain structure of complex 3b. Non-hydrogen bonding H atoms are omitted for clarity.

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A.-T. Hou et al. / Journal of Organometallic Chemistry 696 (2011) 2857e2862
Table 1
complexes in the allylation. With a catalyst loading of 5 mol%, the
allylation of benzaldehyde with allyltributyltin was carried out in
DMF at 60 ꢀC for 16 h to produce the desired homoallylic alcohol in
68, 21 and 84% yields, respectively. In the case of the activated
4-nitrobenzaldehyde, better product yields (90, 85 and 93% yields,
respectively) were obtained. However, for the slightly less elec-
trophilic 4-methylbenzaldehyde the yield dramatically decreased
to 33% using the relatively more active PCS pincer as the catalyst.
Based on the literature results, the activity of the new obtained PCN
pincer Pd complexes 3a and 3b in the allylation of benzaldehyde,
which is a non-activated aldehyde, was evaluated (Scheme 4). The
reaction was performed in DMF at 50 ꢀC for 24 h. It was disap-
pointing to find that the new pincers 3a and 3b gave the expected
alcohol product in rather low yields with a catalyst loading of 5 mol
% (29 and 24%, respectively). In contrast, the related PCN Pd
complex 1, which has been found to be effective catalyst for Suzuki
couplings [27], could afford a 67% yield (75% at 60 ꢀC) with a cata-
lyst loading of 2.5 mol%. It was reported in the literatures that the
allylation involved the transmetalation of allylstannane with pincer
Selected bond lengths (Å) and angles (ꢀ) for Pd complexes 3b and 4
3b
4
Pd(1)eC(1)
Pd(1)eN(1)
Pd(1)eP(1)
Pd(1)eCl(1)
C(1)-Pd(1)eN(1)
C(1)-Pd(1)-P(1)
N(1)-Pd(1)-P(1)
C(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
2.034(5)
2.114(4)
Pd(1)eN(1)
Pd(1)eN(1A)
2.012(2)
2.012(2)
2.3012(7)
2.3012(7)
180.0
89.84(6)
90.16(6)
90.16(6)
89.84(6)
180.0
2.2416(15)
2.4035(14)
87.17(18)
89.05(15)
173.42(10)
166.71(14)
88.49(11)
96.36(6)
Pd(1)-Cl(2)
Pd(1)-Cl(2A)
N(1A)-Pd(1)eN(1)
N(1A)-Pd(1)-Cl(2A)
N(1)-Pd(1)-Cl(2A)
N(1A)-Pd(1)-Cl(2)
N(1)-Pd(1)-Cl(2)
Cl(2A)-Pd(1)-Cl(2)
The Pd atom in the complex 4 has a square-planar coordination
geometry, which is bonded to two chloride ligands and two pyr-
azole ligands (Fig. 3). Both the two chlorides and two pyrazole
ligands are trans- to each other, with bond angles of N(1A)-Pd(1)e
N(1) and Cl(2A)-Pd(1)-Cl(2) being 180.0ꢀ. The two N-benzyl groups
are on the either side of the Pd coordination plane showing an anti-
configuration. All of the bond distances and angles around Pd(II)
centre are very close to those observed in the related pyrazole-
coordinated bis[3-(3,5-dimethylpyrazol-1-ylmethyl)phenol]palla-
dium (II) dichloride [33] and also compare well to those of
monodentate N-coordinated palladium-benzimidazole [34,35] or
pyrazole complexes [36]. Similar to the pincer complex 3b, the
complex 4 also has a one-dimensional chain structure in the crystal
formed by intermolecular hydrogen bonds between chlorine atom
and the adjacent CH2 group of N-benzyl (Cl(2)/H(6A) 2.740 Å,
Cl(2)/C(6) 3.701 Å, C(6)eH(6A)/Cl(2) 171ꢀ) (Fig. 4).
Pd complex to generate an h
1-allyl Pd intermediate, which further
underwent an electrophilic attack from the aldehyde [2e5]. The
lower activity of the complexes 3a and 3b compared to complex 1
may be caused by both steric and electronic effects. On the one
hand, the larger metallacycles in the complexes 3 (6,6-membered
vs 5,6-membered in 1) give rise to a steric effect, which may hinder
the approach of the allylstannane and/or the aldehyde to the Pd
catalyst. On the other hand, the ArCH2OPR2 group in the complexes
3 makes them electronically different from the complex 1 with
ArOPR2 group. And the complex 1 seems to have relatively balanced
electronic properties since in the allylation the transmetalation
requires an electron-deficient Pd metal-center while the electro-
philic attack is enhanced by an electron-rich metal-center [2e5,32].
The effectiveness of the complex 1 in the allylation of other
representative aldehydes with allyltributyltin was also investigated
(Scheme 4). It was found that the complex 1 displayed comparable
or higher activity (in most cases) in the allylation of the related
aldehydes in comparison with the (amino)phosphinite and (imino)
phosphinite PCN pincer Pd complexes reported by Klein Gebbink
and van Koten [32]. Details of this catalytic study are given in the
Supporting Information.
2.3. Catalytic studies
Szabó and co-workers first reported that the symmetrical
bis(phosphine) and particularly, the bis(phosphinite) PCP pincer
Pd(II) complexes were efficient catalysts for allylation of aldehydes
and sulfonimines with allylic stannanes. And it was demonstrated
that the NCN Pd pincers with bis(amine) or bis(oxazoline) ligands
exhibited low catalytic activity in these transformations [2e5].
Subsequent to their findings, the SeCSe [6] and SCS [7] pincer Pd
complexes have also been successfully applied to the allylation of
aldehydes, which can proceed smoothly at room temperature to
60 ꢀC in the presence of only 0.005e1 mol% of the SeCSe catalyst.
Recently, Klein Gebbink and van Koten [32] have investigated the
catalytic activity of the unsymmetrical (amino)phosphinite and
(imino)phosphinite PCN as well as the (phenylthio)phosphinite PCS
In conclusion, two new unsymmetrical pincer Pd(II) complexes
with (pyrazolyl)aryl phosphinite ligands have been conveniently
synthesized starting from commercially available isophthaldehyde
with the key step being one-pot phosphorylation/palladation
reaction. These new pincers contain two fused six-membered
palladacycles and exhibit rather low activity in the allylation of
benzaldehyde.
Fig. 4. 1-D chain structure of complex 4. Non-hydrogen bonding H atoms are omitted for clarity.

A.-T. Hou et al. / Journal of Organometallic Chemistry 696 (2011) 2857e2862
2861
202e203 ꢀC. 1H NMR (400 MHz, CDCl3): The complex exists as
a mixture of isomers in CDCl3 solution with a ratio of about 1.6:1.
The major isomer: d 7.39e7.32 (m, 2H, Ar-H), 7.28e7.26 (m, 1H, Ar-
O
OH
pincer Pd cat.
DMF, 50 oC, 24 h
Sn(n-Bu)3
+
R
H
R
H), 7.02 (d, J ¼ 7.5 Hz, 1H, Ar-H), 5.94 (s, 1H, Pz-H), 5.74 (s, 2H,
R = Ph, with cat. 3a (5 mol%), 29% yield; cat. 3b (5 mol%), 24% yield;
with cat. 1 (2.5 mol%), 67% yield
CH2Pz), 4.46 (s, 2H, CH2Cl), 2.90 (s, 3H, CH3), 2.04 (s, 3H, CH3). The
Other aldehydes with cat. 1 (2.5 mol%), 15 examples, 33-97% yields
minor isomer:
2H, CH2Pz), 5.90 (s, 1H, Pz-H), 4.59 (s, 2H, CH2Cl), 2.51 (s, 3H, CH3),
2.11 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3):
150.4, 143.6, 138.2,
138.0, 135.7, 135.6, 129.2, 129.0, 128.1, 127.9, 127.5, 127.1, 127.0, 126.8,
108.1, 53.3, 52.9, 45.9, 15.2, 14.9, 11.9. IR (KBr, cmꢁ1):
3122, 3084,
d 7.48 (s, 1H, Ar-H), 7.23e7.19 (m, 3H, Ar-H), 6.16 (s,
Scheme 4. Allylation of aldehydes with allyltributyltin catalyzed by the pincer Pd
complexes 1, 3a and 3b.
d
y
3. Experimental
2963, 2921,1607,1555,1467,1420,1391,1354,1318,1267,1216,1154,
813, 791, 755, 707, 674. Anal. Calcd for C26H30Cl4N4Pd: C, 48.28; H,
4.68; N, 8.66. Found: C, 48.06; H, 4.67; N 8.46%.
3.1. General
2-(3,5-dimethylpyrazol-1-ylmethyl)-6-(diphenylphosphinoxyme-
thyl)phenylchloropalladium(II) (3a) 25% yield, white solids. m.p.
Toluene and triethylamine were distilled over sodium/benzo-
phenone and CaH2, respectively. N,N-Dimethylformamide was
dried over CaCl2 or molecular sieves and distilled under reduced
pressure. The 3-(3,5-dimethylpyrazol-1-ylmethyl)benzaldehyde
[31] and 2-(3,5-dimethylpyrazol-1-ylmethyl)-6-(diphenylphosphi-
noxy)phenylchloropalladium(II) (1) [27] were prepared according
to the literature methods. All other chemicals were used as
purchased. Melting points were measured on an XT4A melting
point apparatus and are uncorrected. IR spectra were collected on
a Bruker VECTOR22 spectrophotometer in KBr pellets. 1H, 13C and
31P{1H} NMR spectra were recorded on a Bruker DPX-400 or Bruker
DPX-300 spectrometer in CDCl3 with TMS as an internal standard
for 1H, 13C NMR and 85% H3PO4 as the external standard for 31P{1H}
NMR. Mass spectra were performed on the Agilent LC/MSD Trap
XCT instrument. Elemental analyses were measured on a Thermo
Flash EA 1112 elemental analyzer.
244e246 ꢀC. 1H NMR (400 MHz, CDCl3):
d 8.00e7.95 (m, 2H, Ph-H),
7.91e7.86 (m, 2H, Ph-H), 7.48e7.35 (m, 6H, Ph-H), 7.07e7.04 (m, 1H,
Ar-H), 7.00e6.98 (m, 2H, Ar-H), 5.83 (s,1H, Pz-H), 5.49 (d, J ¼ 14.0 Hz,
1H, CH2Pz), 5.10 (dd, J ¼ 8.0,11.6 Hz,1H, CH2OPR2), 4.96e4.85 (m, 2H,
CH2OPR2 and CH2Pz), 2.59 (s, 3H, CH3), 2.32 (s, 3H, CH3). 13C NMR
(100 MHz, CDCl3):
d
150.4 (d, J ¼ 2.8 Hz),147.0 (d, J ¼ 3.6 Hz),139.1 (d,
J ¼ 2.2 Hz), 138.5, 138.4, 134.8 (d, J ¼ 58.2 Hz), 133.2 (d, J ¼ 12.7 Hz),
132.6, 131.8 (d, J ¼ 13.4 Hz), 131.3 (d, J ¼ 2.1 Hz), 131.1 (d, J ¼ 2.4 Hz),
128.2 (d, J ¼ 11.7 Hz),128.0 (d, J ¼ 11.2 Hz),127.2,126.7,124.6,106.6 (d,
J ¼ 3.5 Hz), 76.3 (d, J ¼ 4.9 Hz), 55.2,14.7,11.2. 31P{1H} NMR (121 MHz,
CDCl3): d y 2923, 2854, 1546, 1464, 1439, 1396,
116.6. IR (KBr, cmꢁ1):
1266,1107,1029, 983, 781, 742, 696. Anal. Calcd for C25H24ClN2OPPd:
C, 55.47; H, 4.47; N, 5.18. Found: C, 55.31; H, 4.63; N 5.05%. MS (m/z,
ESIþ): 505.2 (M ꢁ Cl).
2-(3,5-dimethylpyrazol-1-ylmethyl)-6-(di-tertbutylphosphinox-
ymethyl)phenylchloropalladium(II) (3b) 46% yield, white solids. m.p.
161e163 ꢀC 1H NMR (400 MHz, CDCl3):
d 6.97 (s, 3H, Ar-H), 5.79 (s,
3.2. Synthesis of 3-(3,5-dimethylpyrazol-1-ylmethyl)benzyl alcohol 2
1H, Pz-H), 5.59 (d, J ¼ 13.9 Hz, 1H, CH2Pz), 4.95e4.83 (m, 3H,
CH2OPR2 and CH2Pz), 2.49 (s, 3H, CH3), 2.31 (s, 3H, CH3), 1.69 (d,
J ¼ 14.5 Hz, 9H, t-Bu), 1.09 (d, J ¼ 14.9 Hz, 9H, t-Bu). 13C NMR
To a stirred solution of 3-(3,5-dimethylpyrazol-1-ylmethyl)
benzaldehyde (428 mg, 2 mmol) in methanol (20 mL) was added
sodium borohydride (38 mg, 1 mmol) at 0 ꢀC, followed by stirring at
room temperature for 5 h. Then the reaction was quenched with
water and the PH value of the solution was adjusted to 6-7 by
diluted HCl. The aqueous was extracted with dichloromethane and
the organic layers were dried over Na2SO4, filtered, and evaporated.
The residue was purified by preparative TLC on silica gel plates
eluting with EtOAc to afford white solids of 2. 92% yield. m.p.
(100 MHz, CDCl3):
d
149.8 (d, J ¼ 2.1 Hz), 147.9 (d, J ¼ 4.8 Hz), 138.7
(d, J ¼ 1.9 Hz), 138.4, 138.1 (d, J ¼ 10.0 Hz), 126.6, 126.3, 124.2, 106.5
(d, J ¼ 3.1 Hz), 78.5, 55.4, 41.6 (d, J ¼ 21.6 Hz), 38.2 (d, J ¼ 26.1 Hz),
29.6 (d, J ¼ 3.9 Hz), 27.9 (d, J ¼ 5.0 Hz), 14.5, 11.2. 31P{1H} NMR
(121 Hz, CDCl3):
d y 2958, 2923, 1628, 1549,
160.2. IR (KBr, cmꢁ1):
1470, 1438, 1398, 1365, 1291, 1188, 1026, 988, 808, 762, 729. Anal.
75e76 ꢀC. 1H NMR (400 MHz, CDCl3):
d 7.28e7.22 (m, 2H, Ar-H),
Table 2
7.05 (s, 1H, Ar-H), 6.91 (d, J ¼ 7.1 Hz, 1H, Ar-H), 5.84 (s, 1H, Pz-H),
5.13 (s, 2H, CH2Pz), 4.60 (d, J ¼ 3.4 Hz, 2H, CH2OH), 2.94 (br s, 1H,
CH2OH), 2.22 (s, 3H, CH3), 2.13 (s, 3H, CH3). 13C NMR (100 MHz,
Summary of crystal structure determination for Pd complexes 3b and 4
3b
4
Formula
Mr
C21H32ClN2OPPd
501.31
C26H30Cl4N4Pd
646.74
CDCl3):
d
147.6, 141.8, 139.2, 137.5, 128.8, 125.9, 125.5, 124.9, 105.5,
3250, 2916, 2850, 1548, 1487,
64.7, 52.3, 13.4, 11.1. IR (KBr, cmꢁ1):
y
crystal size (mm)
0.30 ꢂ 0.24 ꢂ 0.20
15.555(3)
8.6177(17)
17.262(4)
90
92.28(3)
90
2312.2(8)
4
0.37 ꢂ 0.21 ꢂ 0.04
7.6818(10)
8.0810(10)
12.7020(16)
83.3870(10)
80.2630(10)
67.0590(10)
714.62(16)
1
1462, 1384, 1309, 1214, 1151, 1039, 984, 888, 816, 779, 743, 695. MS
a (Å)
b (Å)
c (Å)
(m/z, ESIþ): 217.1 (M þ H), 239.1 (M þ Na), 255.0 (M þ K).
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
3.3. Synthesis of palladium(II) complexes 3e4
V (Å3)
To a stirred solution of benzyl alcohol 2 (108 mg, 0.5 mmol) and
Z
triethylamine (84
mL, 0.6 mmol) in toluene (20 mL) was added
space group
Monoclinic, P2(1)/n
1.440
1.000
1.73e24.99
16488
4055
Triclinic, P-1
1.503
1.045
2.74e25.50
5506
2645
Dcalcd (g cmꢁ3
)
diphenylchlorophosphine or di-tertbutylchlorophosphine (0.6 mmol)
under N2 atmosphere at r.t. The resultant mixture was refluxed for 8 h.
Then PdCl2 (90 mg, 0.5 mmol) was added and the reaction mixture
was refluxed for another 18 h. After cooling, filtration and evaporation,
the residue was purified by preparative TLC on silica gel plates eluting
with EtOAc/petroleum ether to afford the corresponding Pd
complexes. In the case of diphenylchlorophosphine, the first band
gave the Pd complex 4 and the second band was pincer complex 3a.
Bis[1-chloromethyl-3-(3,5-dimethylpyrazol-1-ylmethyl)benzene]
palladium (II) dichloride (4) 34% yield, yellow solids. m.p.
m
q
(mmꢁ1
)
range (ꢀ)
Number of data collected
Number of unique data
R (all data)
0.0667
0.0325
Rw (all data)
0.1401
0.0755
R (I > 2
s(I))
0.0536
0.0294
Rw (I > 2
s
(I))
0.1312
0.0737
F(000)
1032
0.387/ꢁ0.504
328
0.769/ꢁ0.575
peak/hole (e$Åꢁ3
)

2862
A.-T. Hou et al. / Journal of Organometallic Chemistry 696 (2011) 2857e2862
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Calcd for C21H32ClN2OPPd: C, 50.31; H, 6.43; N, 5.59. Found:
C, 50.37; H, 6.70; N 5.51%. MS (m/z, ESIþ): 465.4 (M ꢁ Cl).
3.4. X-ray diffraction studies
Crystals of 3b were obtained by recrystallization from EtOAc and
those of 4 were from CH2Cl2eCH3OH at ambient temperature. The
data for 3b were collected on a Rigaku Saturn 724 CCD diffrac-
tometer and those for 4 on a Bruker SMART APEX-II CCD diffrac-
tometer with graphite-monochromated Mo
Ka
radiation
(l
¼ 0.71073 Å). The diffraction data were corrected for Lorentz and
polarization factors. The structures were solved by direct methods
and expanded using Fourier techniques and refined by full-matrix
least-squares methods. The non-hydrogen atoms were refined
anisotropically, and the hydrogen atoms were included but not
refined. Their raw data were corrected and the structures were
solved using the SHELXS-97 program. Details of crystal structure
determination for complexes 3b and 4 are listed in Table 2.
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Acknowledgements
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R. SanMartin, B. Inés, M.T. Herrero, E. Domínguez Curr. Org. Chem. 13 (2009)
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Organometallics 27 (2008) 2833e2839.
We are grateful to the National Natural Science Foundation of
China (No. 20872133) and Key Technologies R & D Program of
Henan Province (102101210200) for financial support of this work.
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Appendix A. Supplementary material
CCDC 805500 and 804891 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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metallics 29 (2010) 2148e2156.
Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.04.034.
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References
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