Unsymmetrical chiral PCN pincer palladium(II) and nickel(II) complexes of (imidazolinyl)aryl phosphinite ligands: Synthesis via ligand C-H activation, crystal structures, and catalytic studies

Article abstract of DOI:10.1021/om100232n

Six unsymmetrical chiral PCN pincer Pd(II) complexes 3a-f based on (imidazolinyl)aryl phosphinite ligands were easily synthesized from imidazolinyl-containing m-phenol derivatives 2a-e by one-pot phosphorylation/palladation reaction via C-H bond activatio

Full text of DOI:10.1021/om100232n

Organometallics 2010, 29, 2579–2587 2579
DOI: 10.1021/om100232n
Unsymmetrical Chiral PCN Pincer Palladium(II) and Nickel(II)
Complexes of (Imidazolinyl)aryl Phosphinite Ligands: Synthesis via
Ligand C-H Activation, Crystal Structures, and Catalytic Studies
Ben-Shang Zhang, Wei Wang, Dan-Dan Shao, Xin-Qi Hao, Jun-Fang Gong,* and
Mao-Ping Song*
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Zhengzhou
University, Zhengzhou 450052, People’s Republic of China
Received March 26, 2010
Six unsymmetrical chiral PCN pincer Pd(II) complexes 3a-f based on (imidazolinyl)aryl phos-
phinite ligands were easily synthesized from imidazolinyl-containing m-phenol derivatives 2a-e by
one-pot phosphorylation/palladation reaction via C-H bond activation of the related ligands. An
unsymmetrical chiral PCN pincer Ni(II) complex, 4a, was first obtained in a similar way. The
palladium-chloride complex 3e could be readily converted to the corresponding iodide derivative 5e
by the halide exchange reaction with KI. All eight complexes were characterized by X-ray crystal
structure determination. Each complex adopts a typical distorted-square-planar geometry. The Pd
complexes were shown to be active catalysts with rather moderate enantioselectivities (up to 32% ee)
for asymmetric Suzuki-Miyaura reaction.
Introduction
pincer metal complexes. Among the chiral pincers, the sym-
metrical NCN bis(oxazolinyl)phenyl (abbreviated as Phebox)
metal complexes including Rh, Pd, Pt, Ru, and Ni have been
extensively investigated and widely used in asymmetric
catalysis.10,11 The chirality in these complexes can be easily
introduced and tuned by the use of the readily available chiral
Organometallic pincer complexes incorporating triden-
tate ligands represent an important and exciting class of
structures, particularly from the point of view of their wide
applications in catalysis.1 Research into their chemistry
has been dominated by various symmetrical and achiral
pincer complexes consisting of a monoanionic bis-ortho-
chelating YCY ligand (YCY = [C6H3(Y)2-2,6]-,Y=CH2NR2,2
CHdNR,3 CH2PR2,4 OPR2,4b,5 NHPR2,6 CH2SR,7 etc.),
while reports on the chiral8 or unsymmetrical complexes9 are
relatively few, especially those on unsymmetrical and chiral
ꢀ
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Cramer, R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300-302, 958.
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ꢀ
2000, 24, 745. (c) Morales-Morales, D.; Redon, R.; Yung, C.; Jensen, C. M.
Chem. Commun. 2000, 1619. (d) Eberhard, M. R.; Wang, Z. H.; Jensen,
C. M. Chem. Commun. 2002, 818. (e) Kimura, T.; Uozumi, Y. Organome-
tallics 2006, 25, 4883. (f) Churruca, F.; SanMartin, R.; Tellitu, I.; Domínguez,
E. Tetrahedron Lett. 2006, 47, 3233. (g) Naghipour, A.; Sabounchei, S. J.;
ꢀ
*To whom correspondence should be addressed. Tel: þ86 371
67763869. E-mail: mpsong9350@zzu.edu.cn (M.-P.S.) or gongjf@zzu.
edu.cn (J.-F.G.).
Morales-Morales, D.; Canseco-Gonzalez, D.; Jensen, C. M. Polyhedron
2007, 26, 1445, and references therein. (h) Pandarus, V.; Zargarian, D.
Organometallics 2007, 26, 4321. (i) Chakraborty, S.; Krause, J. A.; Guan,
H. Organometallics 2009, 28, 582.
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Crabtree, R. H. Coord. Chem. Rev. 2004, 248, 2239. (e) Dupont, J.; Consorti,
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2010 American Chemical Society
Published on Web 05/14/2010
pubs.acs.org/Organometallics

2580 Organometallics, Vol. 29, No. 11, 2010
Zhang et al.
amino alcohols during the ligand synthesis. We recently de-
scribed a series of chiral NCN pincer Pt and Pd pincer com-
plexes with bis(imidazolinyl)phenyl (abbreviated as Phebim)
where the chirality also originated from chiral amino
alcohols.12 It was found that metalation of the ligand’s central
C-H bond was more facile with Phebim-H versus Phebox-H.
For instance, the Pd(Phebim) complexes could be prepared by
the ligand C-H activation method, while this process did not
seem to be applicable to the Phebox-H ligands.11b,13 Addition-
ally, the yields of Pt(Phebim) complexes were obviously higher
(51-84%) than those of the related Pt(Phebox) complexes
(9-49%)13g,14 when this direct metalation methodology was
used. On the other hand, we previously developed a facile,
direct method based on one-pot phosphorylation/palladation
reaction for the preparation of unsymmetrical PCN pincer
palladium complexes containing a phosphinito group.15 These
compounds were conveniently synthesized by the reaction
of N-donor (such as pyrazolyl, amino, or imino)-containing
m-phenol derivatives with dialkylchorophosphine in the pre-
sence of triethylamine in refluxing toluene, followed by the
addition of palladium chloride (Scheme 1). This one-pot
phosphorylation/palladation strategy avoided the usually
troublesome step of isolating the air- and moisture-sensitive
phosphinite ligands and achieved the metalation of the related
ligands’ central C-H bond in the meanwhile. To our knowl-
edge, only Motoyama et al. reported chiral versions of un-
symmetrical PCN pincer palladium and platinum complexes,
Scheme 1. One-Pot Phosphorylation/Palladation Reaction
for the Synthesis of Unsymmetrical PCN Pincer Palladium
Complexes
which were based on (oxazolinyl)phenyl phosphinite ligands
and prepared via oxidative addition of an appropriate bromo-
substituted derivative (Scheme 2). Single-crystal structures
and applications of the obtained chiral complexes were not
studied.16 Considering the different reactivties of Phebox-H
and Phebim-Hligands toward metalation as mentioned above,
we were interested to see whether the unsymmetrical chiral
PCN pincer complexes with (imidazolinyl)aryl phosphinite
could also be synthesized by the one-pot phosphorylation/
metalation reaction via C-H activation of the related ligands
(Scheme 3). Herein, we report in detail the preparation and
crystal structures of a series of PCN pincer Pd(II) complexes
bearing (imidazolinyl)aryl phosphinite ligands. A chiral Ni(II)
complex with an unsymmetrical PCN ligand was first synthe-
sized in a similar way.17 Additionally, the catalytic activities of
these complexes in the asymmetric Suzuki-Miyaura coupling
reaction are presented.
Results and Discussion
(9) (a) Gandelman, M.; Shimon, L. J. W.; Milstein, D. Chem.;Eur.
J. 2003, 9, 4295. (b) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.;
Rozenberg, H.; Ben-David, Y.; Milstein, D. Chem.;Eur. J. 2004, 10, 4673.
(c) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.; Ben-
Preparation of Chiral Ligand Precursors and the Pincer
Pd(II) and Ni(II) Complexes. The required chiral imidazolinyl-
containing m-phenol derivatives 2a-e were prepared in a four-
step sequence from commercially available m-hydroxybenzoic
acid as shown in Scheme 4. Acetylation of 3-hydroxybenzoic
acid with acetic anhydride in the presence of sodium hydroxide
in water easily gave 3-acetoxybenzoic acid in a 94% yield. Then
treatment with thionyl chloride and subsequently with chiral
amino alcohols in the presence of triethylamine in THF at 0 °C
afforded the corresponding 3-acetoxybenzamido alcohols
1a-c as white solids. The obtained amido alcohol reacted with
excess thionyl chloride, followed by the addition of arylamine
to promote cyclization and deprotection of acetate during basic
workup with 10% NaOH. After purification by preparative
TLC on silica gel plates, five chiral compounds, 2a-e, were
isolated in 38-43% yields as white solids. With the expected
ligand precursors in hand, the one-pot phosphorylation/meta-
lation reaction was attempted. Thus, 2a-e were treated with
Ph2PCl or i-Pr2PCl in the presence of triethylamine as a base
in refluxing toluene for 3 h, followed by the addition of PdCl2
(or PdCl2(CH3CN)2 for 3f) and refluxing for another 12 h. We
were pleased to find that the new chiral PCN pincer palladium
complexes 3a-f were obtained in 45-52% isolated yields as
pale yellow solids after chromatography on silica gel. An
unsymmetricalchiralPCN pincerNi(II) complex,4a, could be
prepared in a similar way in 41% yield when NiCl2(THF)x
was used instead of the Pd(II) salt (Scheme 5). To our
ꢀ
David, Y.; Milstein, D. Organometallics 2005, 24, 1082. (d) Ines, B.;
SanMartin, R.; Churruca, F.; Domínguez, E.; Urtiaga, M. K.; Arriortua,
M. I. Organometallics 2008, 27, 2833. (e) Gagliardo, M.; Selander, N.;
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Herrero, M. T.; Domínguez, E. Curr. Org. Chem. 2009, 13, 878. (i) Hao,
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Nelyubina, Y. V.; Lyssenko, K. A.; Vasil'ev, A. A.; Petrovskii, P. V.; Odinets,
I. L. Organometallics 2010, 29, 2054.
(10) For a very recent review on the preparation and catalytic
reactions of NCN metal-Phebox complexes, see: Nishiyama, H.; Ito,
J.-I. Chem. Commun. 2010, 46, 203.
(11) Recent examples: (a) Stol, M.; Snelders, D. J. M.; Godbole,
M. D.; Havenith, R. W. A.; Haddleton, D.; Clarkson, G.; Lutz, M.;
Spek, A. L.; van Klink, G. P. M.; van Koten, G. Organometallics 2007,
26, 3985. (b) Bugarin, A.; Connell, B. T. Organometallics 2008, 27, 4357.
(c) Kimura, T.; Uozumi, Y. Organometallics 2008, 27, 5159. (d) Ito, J.-I.;
Ujiie, S.; Nishiyama, H. Chem. Commun. 2008, 1923. (e) Ito, J.-I.; Ujiie, S.;
Nishiyama, H. Organometallics 2009, 28, 630.
(12) (a) Hao, X.-Q.; Gong, J.-F.; Du, C.-X; Wu, L.-Y.; Wu, Y.-J.;
Song, M.-P. Tetrahedron Lett. 2006, 47, 5033. (b) Wu, L. -Y.; Hao, X.-Q.;
Xu, Y.-X.; Jia, M.-Q.; Wang, Y.-N.; Gong, J.-F.; Song, M.-P. Organometal-
lics 2009, 28, 3369.
(13) (a) Motoyama, Y.; Makihara, N.; Mikami, Y.; Aoki, K.;
Nishiyama, H. Chem. Lett. 1997, 951. (b) Stark, M. A.; Richards, C. J.
Tetrahedron Lett. 1997, 38, 5881. (c) Denmark, S. E.; Stavenger, R. A.;
Faucher, A.-M.; Edwards, J. P. J. Org. Chem. 1997, 62, 3375. (d) Stark,
M. A.; Jones, G.; Richards, C. J. Organometallics 2000, 19, 1282.
(e) Motoyama, Y.; Kawakami, H.; Shimozono, K.; Aoki, K.; Nishiyama,
H. Organometallics 2002, 21, 3408. (f) Takemoto, T.; Iwasa, S.; Hamada, H.;
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(17) (a) For the first examples of achiral and unsymmetrical PCN
pincer Ni(II) and Ni(III) complexes, see ref 9g. (b) We have recently
reported a P-chiral and unsymmetrical PCN pincer Ni(II) complex; see:
Niu, J.-L.; Chen, Q.-T.; Hao, X.-Q.; Zhao, Q.-X.; Gong, J.-F.; Song,
M.-P. Organometallics 2010, 29, 2148.

Article
Organometallics, Vol. 29, No. 11, 2010 2581
Scheme 2. Synthesis of Unsymmetrical Chiral PCN Pincer Pd and Pt Complexes Based on (Oxazolinyl)phenyl Phosphinite Ligands via
Oxidative Addition
Scheme 3. Synthesis of Unsymmetrical Chiral PCN Pincer
Metal Complexes with (Imidazolinyl)aryl Phosphinite by
One-Pot Phosphorylation/Metalation Reaction
accordance with pincers consisting of two five-membered-
ring metallacycles5a,e,h,9d,9g,15b,18 and reflect a relative steric
strain of the almost planar multicyclic system. The bond
lengths of Pd-C (around 1.97 A) and Pd-P (around 2.20 A)
in Pd complexes 3a-f and 5e are comparable to those in the
related achiral PCN pincer Pd complexes,9d,15b but slightly
shorter than those found in the symmetrical PCP-bis(phos-
phinite) pincer Pd complexes (1.97-2.02 and 2.26-2.29 A,
respectively).5a,b,e In comparison to the related (amino)phos-
phinite PCN pincer Ni complexes,9g complex 4a also displays
similar Ni-C (1.87 A) and Ni-P (2.12 A) bond lengths,
which are somewhat shorter than those in the symmetrical
PCP-bis(phosphinite) nickel complexes (1.88 and 2.16 A).5h,18
The Pd-N distances (around 2.10 A) in Pd complexes 3a-f
and 5e are slightly longer than NCN bis(imidazoline) pincer Pd
complex (Pd-N(1), 2.031; Pd-N(2), 2.078 A),12b but shorter
than those in the (imino)phosphinite PCN Pd complexes
(around 2.18 A).15b
Catalytic Studies. The Suzuki-Miyaura coupling reaction
of organic halides and organoboron reagents is one of the
most versatile and successful synthetic tools for the forma-
tion of carbon-carbon bonds.19,20 Some of the achiral
pincer Pd(II) complexes have been successfully applied as
catalysts for this coupling by us9i,15 and others.5b,e,7,9d,f,21 In
addition, the chiral Pd(Phebox) was found to exhibit mod-
erate stereoselectivity in the asymmetric Suzuki-Miyaura
coupling for the synthesis of axially chiral biaryl compounds
(up to 49% ee).13f Accordingly, the potential of the obtained
chiral PCN pincer complexes in the asymmetric Suzuki-
Miyaura reaction was examined. It was found that except for
Pd complex 3b, with a i-Pr2PO- group, the other Pd com-
plexes were effective catalysts in the coupling reaction of
1-iodo-2-methoxynaphthalene with 1-naphthaleneboronic
acid, of which complex 3a was the most active, giving a
92% yield of the product (Scheme 7). Unfortunately, the
enantioselectivities of the product was rather moderate (up
to 32% ee) though a variety of reaction conditions were
attempted. Additionally, the chiral Ni(II) complex 4a was
found to be inactive in this coupling under similar reaction
conditions even with a catalyst loading as high as 20 mol %.
The details of these results are summarized in the Supporting
Information.
knowledge, this is the first example of unsymmetrical chiral
PCN pincer Ni(II) complexes. The palladium-chloride com-
plex 3e was readily converted to the corresponding iodide
derivative 5e by a halogen exchange reaction with excess
amounts of KI in MeOH-CH2Cl2 in 87% isolated yield as
yellow solids (Scheme 6).
All of the chiral pincer Pd and Ni complexes are air- and
moisture-stable both in the solid state and in solution. They
were fully characterized by elemental analysis, 1H NMR, 13
C
NMR, 31P{1H} NMR, DEPT, HSQC, and IR spectra. The
formation of the pincer complexes was confirmed by the
single resonance at about 155 ppm (for Ph2PO) or 200 ppm
(for i-Pr2PO) in the 31P{1H} NMR spectra and the absence of
the singlet corresponding to the proton located ortho to both
1
OH and the imidazoline ring in the H NMR spectra. The
13C NMR spectra of the complexes exhibited intensive
31P-13C couplings.
Molecular Structures of Pd and Ni Complexes. The struc-
tures of all the complexes 3a-f, 4a, and 5e were unambigu-
ously determined by single-crystal X-ray analysis. The mole-
cules of three representative complexes, 3a H2O, 3f CH2Cl2
3
3
and 4a 0.5CH2Cl2, are illustrated in Figures 1-3, respec-
3
tively. Selected bond lengths and bond angles are listed in
Table 1. Crystal data are given in Table 2 (the molecules of
the other five complexes and the related data are given in the
Supporting Information). The structural features of the eight
metal pincer complexes are almost identical. The ligand in
each one is coordinated to the metal(II) center via imidazo-
linyl-N, phosphinite-P, and the central aryl-C in a tridentate
manner, and a tetracyclic system is thus formed by the
central aryl ring, the imidazoline ring, and the two five-
membered metallacycles. It is found that the four rings are
approximately coplanar. However, the N-aryl ring is not
coplanar with the four rings, and the dihedral angles between
the N-aryl ring and the attached imidazoline ring in com-
plexes 3a-f, 4a, and 5e are 76.0°, 71.7°, 66.6°, 69.5°, 87.5°,
85.9°, 74.0°, and 86.8°, respectively. The metal(II) center in
each Pd or Ni complex adopts a typical distorted-square-
planar configuration with bond angles of N-M-P being
around 160° and C-M-X being 176-179°, which are in
Several researchers have reported that pincer Pd com-
plexes act as precatalysts or mere reservoirs of catalytically
(19) Reviews: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(b) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58, 9633.
(c) Suzuki, A. J. Organomet. Chem. 2002, 653, 83. (d) Bellina, F.; Carpita,
A.; Rossi, R. Synthesis 2004, 15, 2419. (e) Molander, G. A.; Canturk, B.
Angew. Chem., Int. Ed. 2009, 48, 9240.
(20) Some recent examples of asymmetric Suzuki-Miyaura reac-
ꢀ
tions: (a) Bermejo, A.; Ros, A.; Fernandez, R.; Lassaletta, J. M.
J. Am. Chem. Soc. 2008, 130, 15798. (b) Uozumi, Y.; Matsuura, Y.;
Arakawa, T.; Yamada, Y. M. A. Angew. Chem., Int. Ed. 2009, 48, 2708.
´
(21) Churruca, F.; SanMartin, R.; Tellitu, I.; Domınguez, E. Synlett
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(18) (a) Gomez-Benıtez, V.; Baldovino-Pantaleon, O.; Herrera-A
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lvarez, C.; Toscano, R. A.; Morales-Morales, D. Tetrahedron Lett.
2006, 47, 5059. (b) Pandarus, V.; Zargarian, D. Chem. Commun. 2007, 978.
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2005, 20, 3116.

2582 Organometallics, Vol. 29, No. 11, 2010
Scheme 4. Synthesis of Chiral PCN Pincer Pd(II) Complexes of (Imidazolinyl)aryl Phosphinite Ligands
Zhang et al.
Scheme 5. Synthesis of a Chiral PCN Pincer Ni(II) Complex of
an (Imidazolinyl)aryl Phosphinite Ligand
Scheme 6. Conversion of Pd-Cl Complex 3e to Pd-I Complex
5e by Halide Exchange Reaction with KI
Figure 1. Molecular structure of 3a H2O (ellipsoids drawn at
3
the 50% probability level). Hydrogen atoms and solvent mole-
cules are omitted for clarity.
active Pd(0) species in the C-C couplings including Suzuki-
Miyaura reactions, and the reactions proceed via a Pd(0)-
Pd(II) catalytic cycle.7a,22 However, there is still evidence
that the Pd-C bond remains intact during catalysis and the
pincer Pd complexes can be recovered and reused for Suzuki
reactions, suggesting the mechanism of a Pd(II)-Pd(IV)
catalytic cycle.6b,13f This was the case in the chiral pincer
Pd(Phebox)-catalyzedasymmetric Suzuki-Miyaurareactions.13f
As for the role of the present chiral PCN pincer Pd complex 3
or 5e in the catalysis under the given reaction conditions, we
Figure 2. Molecular structure of 3f CH2Cl2 (ellipsoids drawn
at the 50% probability level). Hydrogen atoms and solvent
molecules are omitted for clarity.
3
propose the cleavage of the Pd-C bond in the complexes and
the formation of the Pd(0) species based on the following
experimental results: (a) the original Pd complexes or the
corresponding Pd-I complexes were not detected at the end
of the catalytic reaction, (b) complex 3b gave no ee and the
(22) (a) Bolliger, J. L.; Frech, C. M. Adv. Synth. Catal. 2010, 352,
ꢀ
1075. (b) Ines, B.; SanMartin, R.; Moure, M. J.; Domínguez, E. Adv. Synth.
Catal. 2009, 351, 2124. (c) Bolliger, J. L.; Blacque, O.; Frech, C. M.
Chem.;Eur. J. 2008, 14, 7969. (d) Yu, K.; Sommer, W.; Richardson,
J. M.; Weck, M.; Jones, C. W. Adv. Synth. Catal. 2005, 347, 161.
(e) Eberhard, M. R. Org. Lett. 2004, 6, 2125.

Article
Organometallics, Vol. 29, No. 11, 2010 2583
a simple assembly from commercially available m-hydroxy-
benzoic acid, chiral amino alcohols, amines, and chloropho-
sphines. A combination of these materials provides a high
diversification of the unsymmetrical chiral PCN pincer Pd
and Ni complexes. The new Pd complexes show rather
moderate stereoselectivities in the asymmetric Suzuki-
Miyaura reaction.
Experimental Section
General Procedures. Solvents were dried with standard meth-
ods and freshly distilled prior to use if needed. 1-Iodo-2-meth-
oxynaphthalene,23 1-naphthaleneboronic acid,24 chiral amino
alcohols,25 NiCl2(THF)x,26 andPdCl2(CH3CN)227 wereprepared
according tothe literaturemethods. All other chemicalswereused
as purchased. Melting points were measured on a XT4A melting
point apparatus and are uncorrected. Infrared spectra were
Figure 3. Molecular structure of 4a 0.5CH2Cl2 (ellipsoids
3
drawn at the 50% probability level). Hydrogen atoms and
solvent molecules are omitted for clarity.
˚
Table 1. Selected Bond Lengths [A] and Angles [deg] for
1
a
obtained with a Bruker VECTOR 22 spectrophotometer. H,
Complexes 3a H2O, 3f CH2Cl2, and 4a 0.5CH2Cl2
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 and 13C NMR and 85% H3PO4 as
external standard for 31P{1H} NMR. HRMS were determined on
a Waters Q-Tof Micro MS/MS System ESI spectrometer. Ele-
mental analyses were measured on a Thermo Flash EA 1112
elemental analyzer. Optical rotations were recorded on a Perkin-
Elmer 341 polarimeter.
3
3a H2O
3
3
3f CH2Cl2
4a 0.5CH2Cl2
3
3
3
M-C
1.969(6)
2.107(5)
2.3766(18)
2.2037(16)
79.1(2)
101.93(15)
98.27(7)
80.70(17)
178.53(18)
159.78(15)
1.970(5)
2.127(4)
1.869(6)
1.949(5)
2.2106(19)
2.1156(17)
82.7(2)
101.11(15)
94.92(7)
81.27(19)
176.10(19)
163.96(15)
M-N
M-Cl
M-P
2.3875(14)
2.1948(14)
79.14(18)
101.47(12)
99.41(5)
79.85(15)
176.69(15)
158.91(11)
C-M-N
N-M-Cl
Cl-M-P
P-M-C
C-M-Cl
N-M-P
General Procedure for the Synthesis of 3-Acetoxybenzamido
Alcohol 1. To a well-stirred solution of sodium hydroxide (3.0 g,
75.0 mmol) in water (40 mL) was added commercially available
3-hydroxybenzoic acid (5.0 g, 36.2 mmol). After cooling to 0 °C,
acetic anhydride (8.64 g, 84.7 mmol) was added once. The
resultant mixture was stirred at room temperature for 6 h, fil-
tered, and washed with cold water to afford 3-acetoxybenzoic
acid (6.2 g, 94% yield). The obtained 3-acetoxybenzoic acid
(6.2 g, 34.4 mmol) was then dissolved in SOCl2 (3.8 mL, 52.0 mmol)
and one drop of DMF. After it was refluxed for 5 h, the reaction
mixture was concentrated under reduced pressure to give 3-acetox-
ybenzoyl chloride as a pale yellow oil (6.68 g, 98% yield), which was
used in the next step without further purification. To a stirred
solution of amino alcohol (12.0 mmol) and Et3N (1.65 mL, 12.0
mmol) in THF (60 mL) was added dropwise a solution of
3-acetoxybenzoyl chloride (2.0 g, 10.1 mmol) in 40 mL of THF at
0 °C. After stirring at 0 °C for 12 h, the reaction mixture was filtered
and evaporated. The residue was purified by passing through a
silica gel column with acetone-dichloromethane (1:2) as eluent,
giving the corresponding amido alcohol 1.
a For complexes 3a and 3f, M = Pd; for complex 4a, M = Ni.
Scheme 7. Asymmetric Suzuki-Miyaura Reaction of 1-Iodo-2-
methoxynaphthalene with 1-Naphthaleneboronic Acid Catalyzed
by Chiral PCN Pincer Pd Complex 3a
other six Pd complexes with different chiral imidazoline
groups exhibited similar stereoselectivity (∼25% ee), and (c)
lower reaction temperature led to a significant decrease in the
catalytic activity of the Pd complex. For example, the yield of
the product was only 45% at 70 °C in comparison with 88%
yield at 80 °C (see Supporting Information). We thought that
the markedly low activity might be caused by the slower
release of the true catalytically active Pd(0) species at lower
temperature since it was known that high temperature helped
the cleavage of stable palladacycles [Pd(II)] to form Pd(0)
species. If the above assumption of the formation of Pd(0)
species was made, it was most likely that partial or complete
dissociation of the chiral imidazoline nitrogen donor from
Pd(0) occurred, which led to low and similar enantioselectiv-
ities or even loss of enantioselectivities in the asymmetric
Suzuki-Miyaura reactions.
3-Acetoxybenzoic acid: white solids; mp 134-135 °C; 1H
NMR (300 MHz, CDCl3) δ 8.01 (td, J = 1.2, 8.0 Hz, 1H,
Ar-H), 7.85 (t, J = 2.0 Hz, 1H, Ar-H), 7.51 (t, J = 8.0 Hz, 1H,
Ar-H), 7.37 (ddd, J = 1.2, 2.4, 8.0 Hz, 1H, Ar-H), 2.35 (s, 3H,
Ac); 13C NMR (75 MHz, CDCl3) δ 171.3, 169.2, 150.7, 130.8,
129.6, 127.6, 127.3, 123.4, 21.1.
1
3-Acetoxybenzoyl chloride: H NMR (400 MHz, CDCl3) δ
8.01-7.99 (m, 1H, Ar-H), 7.84 (t, J = 2.0 Hz, 1H, Ar-H), 7.53
(t, J = 8.0 Hz, 1H, Ar-H), 7.43 (ddd, J = 0.9, 2.3, 8.0 Hz, 1H,
Ar-H), 2.34 (s, 3H, Ac); 13C NMR (100 MHz, CDCl3) δ 168.7,
167.2, 150.6, 134.3, 129.7, 128.5, 128.4, 124.2, 20.7.
3-Acetoxy-N-((S)-1-hydroxy-3-methylbutan-2-yl)benzamide (1a):
2.28 g, 85% yield; white solids; mp 66-68 °C; [R]2D0 -33 (c 0.126,
(23) Reddy, K. S. K.; Narender, N.; Rohitha, C. N.; Kulkarni, S. J.
Synth. Commun. 2008, 38, 3894.
(24) Lim, C. W.; Tissot, O.; Mattison, A.; Hooper, M. W.; Brown,
J. M.; Cowley, A. R.; Hulmes, D. I.; Blacker, A. J. Org. Process Res. Dev.
2003, 7, 379.
(25) McKennon, M. J.; Meyers, A. I.; Drauz, K.; Schwarm, M.
J. Org. Chem. 1993, 58, 3568.
(26) Eckert, N. A.; Bones, E. M.; Lachicotte, R. J.; Holland, P. L.
Inorg. Chem. 2003, 42, 1720.
(27) Andrews, M. A.; Chang, T. C. T.; Cheng, C.W. F.; Emge, T. J.;
Conclusions
In summary, a series of unsymmetrical chiral PCN pincer
Pd(II) and Ni(II) complexes of (imidazolinyl)aryl phosphi-
nite ligands have been prepared via C-H bond activation of
the related ligands and characterized by X-ray crystal struc-
ture determination. The complexes can be easily accessed by
Kelly, K. P.; Koetzle, T. F. J. Am. Chem. Soc. 1984, 106, 5913.

2584 Organometallics, Vol. 29, No. 11, 2010
Zhang et al.
Table 2. Summary of Crystal Structure Determination for Complexes 3a H2O, 3f CH2Cl2, and 4a 0.5CH2Cl2
3
3
3f CH2Cl2
3
3a H2O
3
4a 0.5CH2Cl2
3
3
formula
Mr
C31H32ClN2O3PPd
653.44
291(2)
0.71073
monoclinic
P2(1)/n
0.20 ꢀ 0.20 ꢀ 0.18
15.395(3)
13.024(3)
15.650(3)
90
99.36(3)
90
3095.9(11)
4
1.400
C33H34Cl3N2O2PPd
734.34
293(2)
C31.5H31Cl2N2NiO2P
630.17
291(2)
0.71073
monoclinic
P2(1)/n
0.20 ꢀ 0.18 ꢀ 0.16
15.198(3)
13.158(3)
15.455(3)
90
99.24(3)
90
3050.6(10)
2
1.372
temperature [K]
wavelength [A]
cryst syst
space group
cryst size [mm]
a [A]
b [A]
c [A]
R [deg]
β [deg]
0.71073
orthorhombic
P2(1)2(1)2(1)
0.24 ꢀ 0.20 ꢀ 0.18
9.918(2)
14.418(3)
23.256(5)
90
90
90
γ [deg]
V [A3]
3325.6(12)
4
1.467
Z
Dcalcd [g cm-3
]
μ [mm-1
]
0.770
0.879
0.894
θ range [deg]
index ranges
2.33 - 25.00
0 e h e 18
-15 e k e 15
-18 e l e 18
9622
5281
full-matrix least-squares on F2
1.103
R1 = 0.0635
wR2 = 0.1526
R1 = 0.0698
wR2 = 0.1563
1332
1.66 - 27.93
-13 e h e 12
-18 e k e 18
-30 e l e 30
40 906
7947
full-matrix least-squares on F2
1.074
R1 = 0.0501
wR2 = 0.1285
R1 = 0.0544
wR2 = 0.1370
1496
1.74 -25.00
0 e h e 17
-15 e k e 15
-18 e l e18
9502
5047
full-matrix least-squares on F2
1.046
R1 = 0.0775
wR2 = 0.1818
R1 = 0.0947
wR2 = 0.1918
1308
no. of data collected
no. of unique data
refinement method
goodness-of-fit on F2
final R indices [I>2σ(I)]
R indices (all data)
F(000)
peak/hole [e A-3
]
0.992/-0.540
0.481/ -0.554
0.626/-0.401
CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.58 (d, J = 7.7 Hz, 1H,
Ar-H), 7.50 (s, 1H, Ar-H), 7.36 (t, J = 7.9 Hz, 1H, Ar-H), 7.17(dd,
J=1.0, 7.9 Hz, 1H, Ar-H), 6.75 (d, J = 8.6 Hz, 1H, NH), 3.89-
3.86 (m, 1H, CHNH), 3.71-3.69 (m, 2H, CH2OH), 3.43-3.42
(m, 1H, OH), 2.28 (s, 3H, Ac), 1.97-1.94 (m, 1H, CH(CH3)2), 0.98
(d, J = 7.6 Hz, 3H, CH3CHCH3), 0.96 (d, J = 7.3 Hz, 3H,
CH3CHCH3); 13C NMR (100 MHz, CDCl3) δ 169.5, 167.2,
150.6, 136.2, 129.5, 124.6, 124.3, 120.6, 63.0, 57.4, 29.0, 21.0, 19.5,
19.0; IR (KBr) ν 3363, 3073, 2963, 2876, 1768, 1642, 1583, 1542,
1481, 1370, 1201, 1078, 1017, 809, 752, 699 cm-1; HRMS (positive
ESI): [M þ Na]þ calcd for C14H19NNaO4 288.1212, found
288.1206.
3-Acetoxy-N-((S)-1-hydroxy-3-phenylpropan-2-yl)benzamide
(1b): 2.50 g, 79% yield; white solids; mp 97-98 °C; [R]2D0 -60
(c 0.132, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.46 (d, J =
7.8 Hz, 1H, Ar-H), 7.43 (s, 1H, Ar-H), 7.33-7.16 (m, 7H, Ar-H),
6.67 (d, J = 7.7 Hz, 1H, NH), 4.35-4.31 (m, 1H, CHNH),
3.73-3.70 (m, 1H, CH2OH), 3.64-3.60 (m, 1H, CH2OH), 3.26
(br s, 1H, OH), 2.96 (d, J = 7.2 Hz, 2H, CH2Ph), 2.29 (s, 3H,
Ac); 13C NMR (100 MHz, CDCl3) δ 169.5, 167.0, 150.7, 137.7,
135.9, 129.7, 129.3, 128.7, 126.7, 124.8, 124.3, 120.7, 63.6, 53.3,
36.9, 21.0; IR (KBr) ν 3309, 2954, 2924, 2860, 1766, 1640, 1582,
1544, 1370, 1207, 1044, 904, 871, 811, 751, 700 cm-1; HRMS
(positive ESI) [M þ Na]þ calcd for C18H19NNaO4 336.1212,
found 336.1208.
3-Acetoxy-N-((S)-1-hydroxy-3,3-dimethylbutan-2-yl)benzamide
(1c): 2.28 g, 81% yield; white solids; mp 92-93 °C; [R]2D0 -14
(c 0.259, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.60 (d, J =
7.2 Hz, 1H, Ar-H), 7.49 (t, J = 1.9 Hz, 1H, Ar-H), 7.40 (t, J =
7.9 Hz, 1H, Ar-H), 7.22-7.19 (m, 1H, Ar-H), 6.46 (d, J = 9.2 Hz,
1H, NH), 4.04-3.99 (m, 1H, CHNH), 3.89-3.84 (m, 1H,
CH2OH), 3.68-3.62 (m, 1H, CH2OH), 2.86-2.84 (m, 1H, OH),
2.30 (s, 3H, Ac), 1.01 (s, 9H, C(CH3)3); 13C NMR (100 MHz,
CDCl3) δ 169.5, 167.6, 150.7, 136.3, 129.6, 124.8, 124.3, 120.6,
62.7, 59.8, 34.0, 27.0, 21.1; IR (KBr) ν 3383, 3073, 2963, 2901,
2876, 1768, 1643, 1584, 1540, 1479, 1369, 1201, 1126, 1049, 1019,
815, 751, 698 cm-1; HRMS (positive ESI) [M þ Na]þ calcd for
C15H21NNaO4 302.1368, found 302.1371.
General Procedure for the Synthesis of 3-(Imidazolinyl)phenol
2. The obtained amido alcohol (7.5 mmol) was reacted with
thionyl chloride (2.2 mL, 30.0 mmol) at reflux for 6 h. Excess
thionyl chloride was evaporated. The residue was dissolved in
dry diethyl ether (25 mL) and filtered to remove insoluble impu-
rities. To this solution was added dry triethylamine (3.2 mL, 22.5
mmol), followed by the corresponding amine (8.25 mmol). After
stirring for 12 h at room temperature, 10% NaOH (20 mL) was
added and stirred for another 6 h. The aqueous solution was
extracted with dichloromethane, and the organic layer was washed
with brine, dried over MgSO4, and evaporated. The residue was
purified by preparative TLC on silica gel plates to afford the
corresponding 3-(imidazolinyl)phenol 2.
3-((S)-4-Isopropyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)phenol (2a): 0.98 g, 43% yield; white solids; mp 153-
154 °C; [R]2D0 þ561 (c 0.196, CH2Cl2); 1H NMR (400 MHz,
CDCl3) δ 7.56 (s, 1H, Ar-H), 6.89 (t, J = 7.9 Hz, 1H, Ar-H),
6.79 (d, J = 8.9 Hz, 2H, NAr), 6.72 (d, J = 8.9 Hz, 2H, NAr), 6.68
(dd, J = 1.7,8.0 Hz 6.48 (d, J = 7.5 Hz, 1H, Ar-H), 4.24 (app t,
J = 10.0 Hz, 1H, NCHH), 4.17-4.11 (m, 1H, NCH), 3.74 (s, 3H,
OCH3), 3.57 (dd, J = 6.6, 9.2Hz, 1H, NCHH), 2.00-1.96 (m, 1H,
CH(CH3)2), 1.03 (d, J = 6.6 Hz, 3H, CH3CHCH3), 1.02 (d, J =
6.5 Hz, 3H, CH3CHCH3); 13C NMR (100 MHz, CDCl3) δ 163.8,
158.1, 156.4, 135.1, 130.4, 129.0, 124.7, 119.0, 118.2, 116.6, 114.0,
67.7, 56.1, 55.3, 33.0, 18.0, 17.6; IR (KBr) ν 3448, 2954, 2862, 1584,
1569, 1509, 1455, 1395, 1242, 1175, 1040, 878, 833, 797, 711,
685 cm-1; HRMS (positive ESI) [M þ H]þ calcd for C19H23N2O2
311.1760, found 311.1753.
3-((S)-4-Isopropyl-1-phenyl-4,5-dihydro-1H-imidazole-2-yl)-
phenol (2b): 0.79 g, 38% yield; white solids; mp 197-198 °C;
1
[R]2D0 þ546 (c 0.174, CH2Cl2); H NMR (400 MHz, CDCl3) δ
7.49 (s, 1H, Ar-H), 7.17 (t, J = 7.8 Hz, 2H, NPh), 7.00 (t, J =
7.1 Hz, 1H, NPh), 6.92 (t, J = 7.9 Hz, 1H, Ar-H), 6.81 (d,
J = 8.1 Hz, 2H, NPh), 6.72-6.69 (m, 1H, Ar-H), 6.54 (d, J =
7.5 Hz, 1H, Ar-H), 4.30 (app t, J = 10.1 Hz, 1H, NCHH),
4.17-4.11 (m, 1H, NCH), 3.66 (dd, J = 6.2, 9.4 Hz, 1H,
NCHH), 2.00-1.95 (m, 1H, CH(CH3)2), 1.02 (d, J = 6.8 Hz,
3H, CH3CHCH3), 1.01 (d, J = 6.8 Hz, 3H, CH3CHCH3); 13
C

Article
Organometallics, Vol. 29, No. 11, 2010 2585
NMR (100 MHz, CDCl3) δ 163.2, 158.2, 141.6, 130.4, 129.2,
128.7, 123.8, 122.4, 119.1, 118.5, 116.4, 67.5, 55.4, 33.0, 18.0,
17.6; IR (KBr) ν 3061, 2960, 2929, 2884, 2807, 1586, 1497,
1453, 1416, 1377, 1306, 1263, 1135, 967, 853, 789, 758, 697
cm-1; HRMS (positive ESI) [M þ H]þ calcd for C18H21N2O
281.1654, found 281.1652.
3.85 (s, 3H, OCH3), 3.78 (dd, J = 5.8, 10.0 Hz, 1H, NCHH),
2.85-2.80 (m, 1H, CH(CH3)2), 0.95 (d, J = 6.7 Hz, 3H, CH3-
CHCH3), 0.94 (d, J = 6.9 Hz, 3H, CH3CHCH3); 13C NMR
(100 MHz, CDCl3) δ 169.7, 162.5 (d, 2JP-C = 11.7 Hz), 159.2,
151.2, 135.7, 133.8 (d, 1JP-C = 52.1 Hz), 133.4 (d, 1JP-C = 53.3 Hz),
133.0, 131.9, 131.8 (d, 2JP-C = 15.1 Hz), 131.6 (d, 2JP-C = 17.3 Hz),
128.8 (d, 3JP-C = 11.7 Hz), 128.7 (d, 3JP-C = 11.5 Hz), 128.2, 125.5,
121.1, 115.0, 114.3 (d, 3JP-C = 16.7 Hz), 66.3, 55.6, 30.1, 18.8, 14.6;
IR (KBr) ν 3428, 3054, 2954, 2921, 2867, 1564, 1531, 1523, 1463,
3-((S)-4-Isopropyl-1-p-tolyl-4,5-dihydro-1H-imidazole-2-yl)-
phenol (2c): 0.90 g, 41% yield; white solids; mp 164-165 °C;
1
[R]2D0 þ398 (c 0.125, CH2Cl2); H NMR (400 MHz, CDCl3) δ
7.33 (s, 1H, Ar-H), 6.99 (d, J = 8.3 Hz, 2H, NAr), 6.92 (t, J =
8.0 Hz, 1H, Ar-H), 6.77 (dd, J = 2.1, 8.4 Hz, 1H, Ar-H), 6.74
(d, J = 8.3 Hz, 2H, NAr), 6.59 (d, J = 7.7 Hz, 1H, Ar-H), 4.28
(app t, J = 10.6 Hz, 1H, NCHH), 4.14-4.08 (m, 1H, NCH),
3.65 (dd, J = 6.6, 9.8 Hz, 1H, NCHH), 2.26 (s, 3H, CH3),
1.98-1.91 (m, 1H, CH(CH3)2), 0.99 (d, J=6.4 Hz, CH3CHCH3),
0.98 (d, J = 6.6 Hz, CH3CHCH3); 13C NMR (100 MHz, CDCl3)
δ163.6, 158.2, 138.3, 134.7, 129.6, 129.3, 128.9, 123.1, 119.3, 119.1,
116.6, 66.2, 55.8, 32.7, 20.9, 18.0, 17.3; IR (KBr) ν 3445, 3031,
2958, 2917, 2872, 1569, 1513,1479, 1451, 1391, 1307, 1245, 1133,
863, 817, 789, 716 cm-1; HRMS (positive ESI) [M þ H]þ calcd for
C19H23N2O 295.1810, found 295.1805.
1437, 1295, 1250, 1226, 1109, 1019, 895, 872, 838, 796, 746, 690 cm-1
;
31P{1H} NMR (162 MHz, CDCl3) δ 155.4. Anal. Calcd for
C31H30ClN2O2PPd 0.5CH2Cl2 (677.90): C, 55.81; H, 4.61; N,
4.13. Found: C, 55.90; H, 4.51; N, 3.99.
3
2-((S)-4-Isopropyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)-6-(diisopropylphosphinoxy)phenylchloropalladium(II)
(3b): 140.4 mg, 45% yield; pale yellow solids; mp 240-241 °C;
[R]2D0 þ66 (c 0.174, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.19
(d, J = 8.4 Hz, 2H, NAr), 6.94 (d, J = 8.4 Hz, 2H, NAr), 6.72
(d, J = 7.7 Hz, 1H, Ar-H), 6.68 (t, J = 7.6 Hz, 1H, Ar-H), 6.05
(d, J = 7.3 Hz, 1H, Ar-H), 4.38-4.34 (m, 1H, NCH), 3.97 (app
t, J = 10.5 Hz, 1H, NCHH), 3.86 (s, 3H, OCH3), 3.75 (dd, J =
6.0, 9.9 Hz, 1H, NCHH), 2.82-2.74 (m, 1H, CH(CH3)2),
2.48-2.38 (m, 2H, PCH(CH3)2), 1.44 (dd, J = 1.4, 7.2 Hz,
3H, PCH(CH3)2), 1.39 (dd, J = 1.5, 7.1 Hz, 3H, PCH(CH3)2),
1.35-1.24 (m, 6H, PCH(CH3)2), 0.94 (d, J = 6.8 Hz, 3H,
CH3CHCH3), 0.91 (d, J = 7.0 Hz, 3H, CH3CHCH3); 13C
3-((S)-4-Benzyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imidazole-
2-yl)phenol (2d):1.07 g, 40% yield; white solids; mp 97-98 °C; [R]D20
þ291 (c 0.216, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ
7.37 (s, 1H, Ar-H), 7.31-7.26 (m, 4H, Ph-H), 7.22-7.18 (m, 1H,
Ph-H), 6.92 (t, J = 7.9 Hz, 1H, Ar-H), 6.75 (ddd, J = 0.7, 2.3,
8.2 Hz, 1H, Ar-H), 6.68-6.64 (m, 2H, NAr), 6.61-6.57 (m, 2H,
NAr), 6.49 (d, J = 7.6 Hz, 1H, Ar-H), 4.61-4.54 (m, 1H, NCH),
4.09 (app t, J = 10.1 Hz, 1H, NCHH), 3.71 (s, 3H, OCH3), 3.67
(dd, J = 6.5, 9.7 Hz, 1H, NCHH), 3.17 (dd, J = 4.5, 13.6 Hz, 1H,
CHHPh), 2.93 (dd, J= 8.0, 13.6 Hz, 1H, CHHPh); 13CNMR(100
MHz, CDCl3) δ 163.8, 158.1, 156.8, 137.4, 134.5, 129.7, 129.5,
129.1, 128.4, 126.5, 125.1, 119.3, 118.7, 116.6, 114.0, 62.5, 58.1
(NCH2), 55.3, 41.7 (CH2Ph); IR (KBr) ν 3403, 3056, 3023, 2928,
2840, 1570, 1511, 1451, 1399, 1289, 1246, 1178, 1036, 832, 791,
706 cm-1; HRMS (positive ESI) [M þ H]þ calcd for C23H23N2O2
359.1760, found 359.1750.
3-((S)-4-tert-Butyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)phenol (2e): 0.97 g, 40% yield; white solids; mp 164-
165 °C; [R]2D0 þ696 (c 0.81, CH2Cl2); 1H NMR (400 MHz, CDCl3)
δ 7.77 (s, 1H, Ar-H), 6.88 (t, J = 7.9 Hz, 1H, Ar-H), 6.79 (d, J =
7.9 Hz, 2H, NAr), 6.73 (d, J = 7.9 Hz, 2H, NAr), 6.65 (dd, J =
1.8, 8.1 Hz, 1H, Ar-H), 6.45 (d, J = 7.6 Hz, 1H, Ar-H), 4.31 (app
t, J = 10.5 Hz, 1H, NCHH), 4.01 (dd, J = 6.3, 11.1 Hz 1H,
NCH), 3.74 (s, 3H, OCH3), 3.61 (dd, J=6.3, 9.8 Hz, 1H, NCHH),
1.04 (s, 9H, C(CH3)3); 13C NMR (100 MHz, CDCl3) δ 164.2,
158.3, 156.4, 135.1,130.3, 128.9, 124.8, 118.9, 118.1, 116.8, 114.1,
71.5, 55.38, 55.36, 34.6, 25.6; IR (KBr) ν 3411, 3050, 2955, 2900,
2868, 2835, 1573, 1511, 1451, 1396, 1365, 1309, 1280, 1245, 1178,
1035, 1003, 862, 830, 786 cm-1; HRMS (positive ESI) [M þ H]þ
calcd for C20H25N2O2 325.1916, found 325.1920.
General Procedure for the Synthesis of PCN Pincer Chloro-
palladium Complexes 3. To a stirred solution of 2a-e (0.55
mmol) and triethylamine (93 μL, 0.66 mmol) in toluene (20 mL)
was added diphenylchlorophosphine or diisopropylphosphine
(0.66 mmol) under N2 atmosphere at rt. The resultant mixture
was refluxed for 3 h. PdCl2 (97 mg, 0.55 mmol for 3a-3e) or
PdCl2(CH3CN)2 (144 mg, 0.55 mmol for 3f) was then added,
and the reaction mixture was refluxed for another 12 h. After
cooling, filtration, and evaporation, the residue was purified by
preparative TLC on silica gel plates eluting with CH2Cl2 to
afford the corresponding PCN pincer Pd(II) complexes 3a-f.
2-((S)-4-Isopropyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)-6-(diphenylphosphinoxy)phenylchloropalladium(II) (3a):
181.7 mg, 52% yield; pale yellow solids; mp 239-240 °C; [R]D20
þ89 (c 0.174, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 8.03-8.00
(m, 4H, Ph-H), 7.50-7.45 (m, 6H, Ph-H), 7.18 (d, J = 8.8 Hz, 2H,
NAr), 6.94 (d, J = 8.8 Hz, 2H, NAr), 6.88 (d, J = 8.0 Hz, 1H, Ar-
H), 6.74(t, J=8.0Hz, 1H, Ar-H), 6.09(d, J =7.7Hz, 1H, Ar-H),
4.44-4.39 (m, 1H, NCH), 3.98 (app t, J = 10.7 Hz, 1H, NCHH),
3
NMR (100 MHz, CDCl3) δ 169.4 (d, JP-C = 2.7 Hz), 163.9
2
(d, JP-C = 7.9 Hz), 159.0, 150.2, 135.8, 133.1, 128.2, 125.0,
120.6, 114.9, 113.3 (d, 3JP-C = 15.0 Hz), 66.1 (d, 3JP-C = 2.1
Hz), 55.6 (d, 4JP-C = 3.4 Hz), 55.5, 30.0, 29.0 (d, 1JP-C = 24.6
Hz), 28.9 (d, 1JP-C = 24.4 Hz), 18.7, 17.5 (d, 2JP-C = 5.8 Hz),
17.3 (d, 2JP-C = 6.3 Hz), 17.0, 16.5, 14.6; 31P{1H} NMR (162
MHz, CDCl3) δ 202.6; IR (KBr) ν 3432, 2958, 2871, 2831, 1569,
1534, 1513, 1462, 1439, 1297, 1251, 1164, 1030, 873, 838, 788,
687 cm-1. Anal. Calcd for C25H34ClN2O2PPd (567.40): C,
52.92; H, 6.04; N, 4.94. Found: C, 53.11; H, 6.00; N, 4.79.
2-(S)-4-Isopropyl-1-phenyl-4,5-dihydro-1H-imidazole-2-yl)-6-
(diphenylphosphinoxy)phenylchloropalladium(II) (3c): 163.1 mg,
49% yield; pale yellow solids; mp 255-256 °C; [R]2D0 þ99
(c 0.164, CH2Cl2); 1H NMR (400 MHz, CDCl3) 8.06-8.01
(m, 4H, Ph-H), 7.51-7.35 (m, 9H, Ph-H), 7.25-7.24 (m, 1H,
Ph-H), 7.19-7.14 (m, 1H, Ph-H), 6.89 (d, J = 8.0 Hz, 1H,
Ar-H), 6.75 (t, J = 7.7 Hz, 1H, Ar-H), 6.17 (d, J = 7.7 Hz, 1H,
Ar-H), 4.72-4.42 (m, 1H, NCH), 4.07 (app t, J = 10.6 Hz, 1H,
NCHH), 3.84 (dd, J = 5.6, 9.9 Hz, 1H, NCHH), 2.88-2.80 (m,
1H, CH(CH3)2), 0.95 (d, J = 6.8 Hz, 3H, CH3CHCH3), 0.94 (d,
J = 7.0 Hz, 3H, CH3CHCH3); 13C NMR (100 MHz, CDCl3) δ
1
169.5, 162.6, 151.3, 140.4, 135.7, 133.7 (d, JP-C = 52.3 Hz),
1
2
133.4 (d, JP-C = 53.3 Hz),131.9,131.8 (d, JP-C =15.1 Hz),
131.6 (d, 2JP-C =14.7 Hz), 129.8, 128.9 (d, 3JP-C = 11.6 Hz),
128.8 (d, 3JP-C = 11.7 Hz), 127.8, 126.6, 125.5, 121.2, 114.4 (d,
3JP-C = 16.8 Hz), 66.4, 55.3, 30.0, 18.8, 14.6; 31P{1H} NMR
(162 MHz, CDCl3) δ 155.1; IR (KBr) ν 3449, 3050, 2955, 2917,
2869, 1565, 1532, 1498, 1434, 1298, 1225, 1107, 1023, 996, 871,
794, 749, 696 cm-1. Anal. Calcd for C30H28ClN2OPPd 0.75CH2Cl2
3
(669.10): C, 55.20; H, 4.44; N, 4.19. Found: C, 55.40; H, 4.34;
N, 4.03.
2-((S)-4-Isopropyl-1-p-tolyl-4,5-dihydro-1H-imidazole-2-yl)-
6-(diphenylphosphinoxy)phenylchloropalladium(II) (3d): 170.3
mg, 50% yield; pale yellow solids; mp 275-276 °C; [R]2D0 þ110
1
(c 0.166, CH2Cl2); H NMR (400 MHz, CDCl3) δ 8.05-8.00
(m, 4H, Ph-H), 7.51-7.43 (m, 6H, Ph-H), 7.22 (d, J = 8.1 Hz,
2H, NAr), 7.13 (d, J = 8.1 Hz, 2H, NAr), 6.88 (d, J = 8.0 Hz,
1H, Ar-H), 6.74 (dt, J = 0.9, 7.8 Hz, 1H, Ar-H), 6.16 (d, J =
7.7 Hz, 1H, Ar-H), 4.45-4.40 (m, 1H, NCH), 4.02 (app t, J =
10.6 Hz, 1H, NCHH), 3.79 (dd, J = 5.7, 10.0 Hz, 1H, NCHH),
2.85-2.80 (m, 1H, CH(CH3)2), 2.41 (s, 3H, CH3), 0.94 (d, J =
6.8 Hz, 3H, CH3CHCH3), 0.93 (d, J = 7.1 Hz, 3H, CH3CH-
CH3); 13C NMR (100 MHz, CDCl3) δ 169.6, 162.5 (d, 2JP-C
11.5 Hz), 151.2, 137.9, 137.7, 135.7, 133.8 (d, 1JP-C = 52.1 Hz),
=

2586 Organometallics, Vol. 29, No. 11, 2010
Zhang et al.
133.4 (d, 1JP-C = 53.4 Hz), 131.9, 131.8 (d, 2JP-C = 14.7 Hz),
131.6 (d, 2JP-C = 14.7 Hz), 130.4, 128.8 (d, 3JP-C = 11.6 Hz),
OCH3), 3.81 (dd, J = 4.6, 10.0 Hz, 1H, NCHH), 2.66-2.62
(m, 1H, CH(CH3)2), 0.98 (d, J = 6.8 Hz, 3H, CH3CHCH3),
0.89 (d, J = 7.0 Hz, 3H, CH3CHCH3); 13C NMR (100 MHz,
3
128.7 (d, JP-C = 11.6 Hz), 126.5, 125.5, 121.2, 114.3 (d,
3JP-C = 16.9 Hz), 66.4, 55.4, 30.1, 21.2, 18.8, 14.6; 31P{1H}
NMR (121 MHz, CDCl3) δ 154.6; IR (KBr) ν 3448, 3044, 2952,
2917, 2864, 1565, 1533, 1437, 1232, 1106, 1038, 1019, 874, 792,
CDCl3) δ 168.8, 163.8 (d, JP-C = 15.3 Hz), 159.1, 149.4 (d,
2
1
2JP-C = 35.8 Hz), 137.1, 132.8 (d, JP-C = 46.5 Hz), 132.5
(d, 1JP-C = 47.8 Hz), 132.4, 131.8 (d, 2JP-C = 12.8 Hz), 131.7
(d, 2JP-C = 12.8 Hz), 131.5 (virtual t, 4JP-C =3.1 Hz), 128.7 (d,
3JP-C =10.9 Hz), 128.6 (d, 3JP-C = 10.8Hz), 127.9, 125.7, 119.8,
114.8, 113.3 (d, 3JP-C =13.5Hz), 64.3, 56.1, 55.6, 30.4, 18.7, 14.5;
31P{1H} NMR (121 MHz, CDCl3) δ 149.0; IR (KBr) ν 3444,
3054, 2955, 2925, 2867, 1567, 1537, 1511, 1438, 1291, 1250, 1107,
1026, 870, 838, 793, 747, 696 cm-1. Anal. Calcd for C31H30ClNi-
697 cm-1. Anal. Calcd for C31H30ClN2OPPd 0.25CH2Cl2
3
(640.66): C, 58.59; H, 4.80; N, 4.37. Found: C, 58.48; H,
4.79; N, 4.32.
2-((S)-4-Benzyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)-6-(diphenylphosphinoxy)phenylchloropalladium(II) (3e):
176.6 mg, 47% yield; pale yellow solids; mp 226-227 °C; [R]D20
þ161 (c 0.102, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ
8.10-8.02 (m, 4H, Ph-H), 7.52-7.49 (m, 6H, Ph-H), 7.40 (d,
J = 6.6 Hz, 2H, Ph-H), 7.26-7.17 (m, 4H, Ph and NAr),
6.90-6.84 (m, 3H, Ar and NAr), 6.72 (t, J = 79 Hz, 2H, Ph and
Ar-H), 5.97 (d, J = 7.7 Hz, 1H, Ar-H), 4.74-4.69 (m, 1H, NCH),
4.03 (app t, J = 10.3 Hz, 1H, NCHH), 3.82 (s, 3H, OCH3), 3.75
(dd, J = 5.1, 10.0 Hz, 1H, NCHH), 3.46 (dd, J = 3.4, 13.5 Hz,
1H, CHHPh), 3.18 (dd, J = 7.6, 13.5 Hz, 1H, CHHPh); 13C
N2O2P 0.5CH2Cl2 (630.17): C, 60.04; H, 4.96; N, 4.45. Found: C,
3
60.72; H, 5.05; N, 4.40.
Procedure for the Synthesis of PCN Pincer Iodopalladium
Complex 5e. To a stirred solution of methanol (20 mL) and
dichloromethane (30 mL) were added 3e (158.4 mg, 0.24 mmol)
and potassium iodide (800 mg, 4.8 mmol) under air at room
temperature. After it was stirred for 24 h at that temperature, the
reaction mixture was filtered through a pad of Celite, and then
the filtrate was concentrated under reduced pressure. Purifica-
tion by silica gel chromatography (dichloromethane) gave yellow
solids of 5e in 87% yield (156.5 mg).
3
NMR (100 MHz, CDCl3) δ 170.1 (d, JP-C = 3.0 Hz), 162.4
=
(d, 2JP-C = 11.3 Hz), 159.1, 151.3, 137.5, 135.6, 133.6 (d, 1JP-C
52.3 Hz), 133.4 (d, JP-C = 53.1 Hz), 132.3, 131.9 (virtual t,
1
4JP-C = 2.5 Hz), 131.7 (d, 2JP-C = 14.8 Hz), 131.6 (d, 2JP-C
=
=
=
2-((S)-4-Benzyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imidazole-
2-yl)-6-(diphenylphosphinoxy)phenyliodopalladium(II) (5e): mp
226-227 °C; [R]2D0 þ114 (c 0.214, CH2Cl2); 1H NMR (400 MHz,
CDCl3) δ 8.12-8.00 (m, 4H, Ph-H), 7.52-7.46 (m, 6H, Ph-H),
7.42 (d, J = 7.0 Hz, 2H, Ph-H), 7.25-7.20 (m, 4H, Ph and NAr),
6.94 (d, J =8.0Hz, 1H, Ar-H), 6.86 (d, J= 8.0 Hz, 2H, NAr), 6.75
(t, J = 7.8 Hz, 2H, Ph and Ar-H), 5.98 (d, J = 7.6 Hz, 1H, Ar-H),
4.74-4.69 (m, 1H, NCH), 3.97 (app t, J = 10.2 Hz, 1H, NCHH),
3.82 (s, 3H, OCH3), 3.82-3.79 (m, 1H, NCHH), 3.49 (dd, J = 2.5,
13.3 Hz, 1H, CHHPh), 3.09 (dd, J = 8.2, 13.3 Hz, 1H, CHHPh);
13C NMR (100 MHz, CDCl3) δ 171.2, 161.8 (d, 2JP-C = 12.2 Hz),
14.7 Hz), 130.1, 128.9 (d, 3JP-C = 11.7 Hz), 128.7 (d, 3JP-C
3
11.7 Hz), 128.2, 126.3, 125.6, 121.0, 114.8, 114.4 (d, JP-C
16.8 Hz), 62.3 (d, 3JP-C = 2.5 Hz), 59.3 (d, 4JP-C = 3.5 Hz), 55.5,
41.0; 31P{1H} NMR (121 MHz, CDCl3) δ 154.8; IR (KBr) ν 3448,
3054, 2931, 1567, 1534, 1509, 1439, 1336, 1292, 1248, 1181, 1106,
1028, 871, 791, 747, 697 cm-1. Anal. Calcd for C35H30ClN2-
O2PPd 0.25CH2Cl2 (704.70): C, 60.08; H, 4.36; N, 3.98. Found:
3
C, 59.88; H, 4.34; N, 3.88.
2-((S)-4-tert-Butyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)-6-(diphenylphosphinoxy)phenylchloropalladium(II) (3f):
178.6 mg, 50% yield; pale yellow solids; mp 138-140 °C; [R]D20
þ92 (c 0.242, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 8.07-8.00
(m, 4H, Ph-H), 7.51-7.44 (m, 6H, Ph-H), 7.16 (d, J = 7.1 Hz, 2H,
NAr), 6.93 (d, J = 8.9 Hz, 2H, NAr), 6.87 (d, J = 8.0 Hz, 1H,
Ar-H), 6.74 (dt, J = 0.9, 7.9 Hz, 1H, Ar-H), 6.11 (d, J = 7.7 Hz,
1H, Ar-H), 4.13 (dd, J = 3.3, 9.4 Hz, 1H, NCH), 4.00-3.93 (m,
2H, NCH2), 3.84 (s, 3H, OCH3), 1.11 (s, 9H, C(CH3)3); 13C NMR
1
159.2, 154.8, 137.5, 135.6, 133.5 (d, JP-C = 54.0 Hz), 133.2 (d,
1JP-C = 54.7 Hz), 132.6 (virtual t, 2JP-C=14.2 Hz), 132.2, 132.0
4
(d, 4JP-C = 2.3 Hz), 131.9 (d, JP-C=2.3 Hz), 130.0, 128.8 (d,
3JP-C = 11.6 Hz), 128.7 (d, 3JP-C = 11.5 Hz), 128.3, 126.4, 125.7,
120.9, 114.8, 114.6 (d, 3JP-C = 17.2 Hz), 63.4, 59.2 (d, 4JP-C
=
3.5 Hz), 55.5, 41.4; 31P{1H} NMR (121 MHz, CDCl3) δ 154.8; IR
(KBr) ν 3444, 3055, 2927, 2851, 1567, 1532, 1511, 1439, 1288, 1247,
1179, 1108, 1031, 867, 788, 747, 706 cm-1. Anal. Calcd for C35H30-
(100 MHz, CDCl3) δ170.1 (d, 3JP-C = 3.2 Hz), 162.4 (d, 2JP-C
=
11.3 Hz), 159.2, 150.7, 135.5, 133.8 (d, 1JP-C = 51.7 Hz), 133.2 (d,
IN2O2PPd C4H10O (849.04): C, 55.17; H, 4.75; N, 3.30. Found: C,
3
4
1JP-C = 54.6 Hz), 132.8, 131.9 (d, JP-C = 2.6 Hz), 131.8
(d, JP-C=14.6 Hz),131.7 (d, JP-C = 14.5 Hz), 128.8 (virtual
55.45; H, 4.26; N, 3.32.
2
2
General Procedure for Suzuki-Miyaura Coupling Reaction. A
10 mL Schlenk flask was charged with 1-iodo-2-methoxy-
naphthalene (0.2 mmol), 1-naphthaleneboronic acid (0.3 mmol),
pincer complex (5 mol %), CsF (0.93 mmol), and toluene (4 mL).
The mixture was stirred at 80 °C for 15 h under N2. After the
mixture was cooled, solvent was removed on a rotary evaporator,
and the product was isolated by thin-layer chromatography. The
purified product was identified by 1H and 13C NMR spectra and
melting point comparison with the literature data. The ee value of
the product was determined by HPLC on a chiral stationary
phase [Daicel Chiralpak AD-H column, n-hexane-i-PrOH, 98:2,
0.25 mL/min, 254 nm; tR = 20.46 min (minor) and 23.93 min
(major)].
X-ray Diffraction Studies. Crystals of 3a, 3b, 3c, 3d, and 4a
wereobtainedbyrecrystallization from CH2Cl2-petroleum ether
at ambient temperature, those of 3f from CH2Cl2-n-hexane, and
those of 3e and 5e from CH2Cl2-ethyl acetate at ambient
temperature. The data of 3a, 3c, 3d, 3e, and 4a were collected
with a Rigaku-IV imaging plate area detector, and those of 3f, 3b,
and 5e were collected on a Rigaku Saturn 724 CCD diffract-
ometer with graphite-monochromated Mo KR radiation (λ =
0.71073 A) at ambient temperature. The diffraction data were
corrected for Lorentz and polarization factors. The structures
were solved by direct methods, expanded using Fourier techni-
ques, and refined by full-matrix least-squares methods. The non-
hydrogen atoms were refined anisotropically, and the hydrogen
t, 3JP-C = 11.1 Hz), 128.3, 125.5, 121.0, 114.9, 114.2 (d, 3JP-C
=
17.0 Hz), 69.0 (d, 3JP-C = 2.8 Hz), 58.3 (d, 4JP-C = 2.9 Hz), 55.6,
36.0, 26.4; 31P{1H} NMR (121 MHz, CDCl3) δ 155.1; IR (KBr) ν
3052, 2956, 2924, 2851, 1565, 1528, 1507, 1465,1438, 1367, 1328,
1287, 1249, 1181, 1108, 1034, 1010, 979, 873, 836, 790, 745,
694 cm-1. Anal. Calcd for C32H32ClN2O2PPd CH2Cl2(734.34):
3
C, 53.97; H, 4.67; N, 3.81. Found: C, 53.77; H, 4.83; N, 3.68.
Procedure for the Synthesis of PCN Pincer Chloronickel
Complex 4a. To a stirred solution of 2a (143 mg, 0.46 mmol)
and triethylamine (77 μL, 0.55 mmol) in toluene (20 mL) was
added diphenylchlorophosphine (0.55 mmol) under N2 atmo-
sphere at rt. The resultant mixture was refluxed for 3 h. NiCl2-
(THF)0.28 (114 mg, 0.76 mmol) was then added, and the reaction
mixture was refluxed for another 12 h. After cooling, filtration,
and evaporation, the residue was purified by preparative TLC
on silica gel plates eluting with ethyl acetate and petroleum ether
(1:1) to afford the corresponding PCN pincer Ni(II) complex 4a.
2-((S)-4-iIsopropyl-1-(4-methoxyphenyl)-4,5-dihydro-1H-imida-
zole-2-yl)-6-(diphenylphosphinoxy)phenylchloronickel(II) (4a):
111.8 mg, brown solids; 41% yield; mp 147-148 °C; [R]D20
þ162 (c 0.112, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ
8.08-8.02 (m, 4H, Ph-H), 7.54-7.42 (m, 6H, Ph-H), 7.18 (d,
J = 8.8 Hz, 2H, NAr), 6.94 (d, J=8.8 Hz, 2H, NAr), 6.73-6.67
(m, 2H, Ar-H), 6.02 (d, J = 7.2 Hz, 1H, Ar-H), 4.20-4.16 (m,
1H, NCH), 4.02 (app t, J = 10.5 Hz, 1H, NCHH), 3.85 (s, 3H,

Article
Organometallics, Vol. 29, No. 11, 2010 2587
atoms were included but not refined. Their raw data were
corrected, and the structures were solved using the SHELXL-97
program.28 CCDCs 762184, 762185, 762186, 762187, 762188,
769635, 764938, and 764939 contain the crystallographic data
for complexes 3a-f, 4a, and 5e, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
Scholar of Henan Province (No. 074200510005) for fi-
nancial support of this work.
Supporting Information Available: Tables and figures giving
crystallographic data of complexes 3b-e and 5e, investigations
on the catalytic reaction, figures giving 1H NMR and 13C NMR
spectra of all the new compounds, and CIF files giving crystal-
lographic data for all the pincer complexes. This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the National
Natural Science Foundation of China (Nos. 20872133
and 20972141) and the Innovation Fund for Outstanding
(28) Sheldrick, G. M. SHELXL-97, Program for Refinement of Crystal
€
Structure; University of Gottingen: Germany, 1997.