Unsymmetrical chiral PCN pincer palladium(II) and nickel(II) complexes with aryl-based aminophosphine-imidazoline ligands: Synthesis via aryl C-H activation and asymmetric addition of diarylphosphines to enones

Article abstract of DOI:10.1021/om200350h

Figure Persented: Chiral 3-(2′-imidazolinyl)anilines 3a-c were easily synthesized by converting the carboxyl and nitro groups in commercially available 3-nitrobenzoic acid to chiral imidazoline and amine, respectively. The one-pot phosphorylation/metalati

Full text of DOI:10.1021/om200350h

ARTICLE
pubs.acs.org/Organometallics
Unsymmetrical Chiral PCN Pincer Palladium(II) and Nickel(II)
Complexes with Aryl-Based AminophosphineꢀImidazoline Ligands:
Synthesis via Aryl CꢀH Activation and Asymmetric Addition of
Diarylphosphines to Enones
Ming-Jun Yang, Yan-Jing Liu, 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
S Supporting Information
b
ABSTRACT:
Chiral 3-(20-imidazolinyl)anilines 3aꢀc were easily synthesized by converting the carboxyl and nitro groups in commercially
available 3-nitrobenzoic acid to chiral imidazoline and amine, respectively. The one-pot phosphorylation/metalation reaction of
3-(20-imidazolinyl)anilines 3aꢀc, where the amino group in 3aꢀc was first phosphorylated by reaction with PPh2Cl, followed by
metalation with PdCl2 or anhydrous NiCl2 in situ, afforded the three unsymmetrical chiral PCN pincer Pd(II) complexes 4aꢀc and
the Ni(II) complex 5a with aryl-based aminophosphineꢀimidazoline ligands via aryl CꢀH bond activation of the related ligands. All
of the new compounds were characterized by elemental analysis (HRMS for ligand precursors), 1H and 13C NMR, 31P{1H} NMR
(for pincer complexes), and IR spectra. The molecular structures of Pd complexes 4a,c and that of Ni complex 5a have been
determined by X-ray single-crystal diffraction. Each complex adopts a typical distorted-square-planar geometry. The potential of the
obtained chiral pincers in the asymmetric addition of diarylphosphines to β-substituted enones or trans-β-nitrostyrene was
investigated. The Pd pincer 4c, the chirality of which originated from L-phenylglycinol, was found to be an effective catalyst for the
asymmetric addition of diphenylphosphine to a series of β-aryl enones with high enantioselectivities (12 examples, 51ꢀ94% ee's). In
particular, excellent yields and enantioselectivities (>90% yields and g90% ee's) were obtained when β-aryl groups in the enones
bore an electron-withdrawing group such as p-NO2.
’ INTRODUCTION
Rh-, Pt-, and Ru-Phebox complexes have exhibited high perfor-
mance in asymmetric conjugate reductions (up to 98% ee),
reductive aldol reactions (up to 96% ee), and alkylation of
aldimines (up to 82% ee) as well as hydrogenation (up to 98%
ee) and transfer hydrogenation of ketones (up to 97% ee).4,5 The
chiral pyrroloimidazolone-based NCN pincer Pd complexes
showed high levels of enantioselectivities (up to 83% ee) in the
Michael reaction between vinyl ketones and R-cyano
carboxylates.6 In addition, the axially chiral 1,10-bi-2-naphthol-
and 1,10-biphenanthrol-based bis(phosphite) PCP pincer Pd
complexes have been found to be effective catalysts for asym-
metric allylation of aldehydes (up to 62% ee) and sulfonimines
(up to 85% ee) as well as condensation of sulfonimines and
isocyanoacetate (up to 86% ee).7 Despite considerable progress,
much less research has been done on chiral pincer metal
complexes than on achiral complexes.8 Novel asymmetric
Transition-metal pincer complexes of the ECE type,1 which
contain one carbanion from the central aryl ring as the C donor
and two identical neutral E species such as P, N, S, or Se donors in
the side arms of the central aryl ring, have been intensively
investigated and used in organic synthesis, catalysis, and other
related areas since the pioneering work of Shaw,2 van Koten, and
Noltes3 on PCP and NCN pincer complexes in the 1970s. The
existence of the MꢀC σ bond supported by two neutral E donors
in such complexes makes them exhibit generally high stabilities
toward heat, air, and moisture. More importantly, their reactiv-
ities and/or stereoselectivities can be readily tuned by an appro-
priate choice of substituents on the heteroatom donors and/or
substituents on the heteroatom donors. As a result, numerous
pincer metal-mediated organic transformations have been devel-
oped. Of particular interest are the highly selective asymmetric
versions. For example, the chiral bis(oxazolinyl)phenyl
(abbreviated as Phebox) NCN pincer metal complexes have
emerged as one versatile chiral pincer complex family and the
Received: April 26, 2011
Published: June 28, 2011
r
2011 American Chemical Society
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reactions catalyzed by the known chiral metal pincers as well as
the synthesis and/or applications of the new chiral pincers will
still be important contributions to the field of pincer chemistry.
On the other hand, introduction of two different neutral E and
E0 donors into the side arms of the central aryl ring gives
unsymmetrical ECE0 pincer metal complexes. Interest in these
species has considerably increased in the last few years due to the
unique reactivities provided by the two varied donors.9,10 Up to
now, there have been far fewer reports on unsymmetrical pincer
complexes than on symmetrical complexes; especially those on
unsymmetrical and chiral pincer metal complexes are rather
limited.11 One obvious reason for this is their relatively compli-
cated synthesis. Recently, we have developed a facile, direct
method based on a one-pot phosphorylation/metalation reac-
tion for the preparation of unsymmetrical PCN pincer palladium
and nickel complexes (Chart 1). By using this method, a variety
of achiral Pd pincers which comprise pyrazole, amine, or imine as
the N-donor and phosphinite as the P-donor have been readily
synthesized via the CꢀH activation of the related ligands in good
yields (45ꢀ72%) from inexpensive, easily available starting
materials.12 Particularly, unsymmetrical and chiral PCN Pd and
Ni pincers containing chiral imidazoline as the N-donor and
phosphinite as the P-donor could also be conveniently obtained.
It was found that the chiral Pd pincers were active catalysts for the
asymmetric SuzukiꢀMiyaura reaction of 1-iodo-2-methoxy-
naphthalene with 1-naphthaleneboronic acid. Unfortunately,
the enantioselectivity of the axially chiral biaryl product was
rather moderate (up to 32% ee).13 Considering that the chirality
in the imidazoline ring can be easily introduced and tuned by the
use of various chiral amino alcohols, and also in continuation of
our study on the unsymmetrical pincer metal complexes, herein
we wish to report in detail the preparation and characterization of
chiral PCN pincer Pd(II) and Ni(II) complexes containing chiral
imidazoline as the N-donor and aminophosphine as the P-donor.
The key step in their synthesis is the similar one-pot phos-
phorylation/metalation reaction of 3-(imidazolinyl)anilines
(Scheme 1). Investigations into the potential of the obtained
chiral pincers in the asymmetric addition of diarylphosphines to
β-substituted enones or trans-β-nitrostyrene are also presented.
’ RESULTS AND DISCUSSION
Synthesis of Chiral 3-(20-Imidazolinyl)anilines and the
Unsymmetrical PCN Pincer Pd(II) and Ni(II) Complexes.
The construction of a chiral imidazoline ring in the required
3-(20-imidazolinyl)anilines 3 started from a carboxyl group
following a procedure similar to that for chiral 1,3-bis(20-
imidazolinyl)benzene8c and chiral imidazolinyl-containing m-
phenol derivatives.13 Thus, treatment of commercially available
3-nitrobenzoic acid with thionyl chloride, followed by the reac-
tion of the crude 3-nitrobenzoyl chloride with various chiral
amino alcohols, including L-valinol, L-phenylalaninol, and L-
phenylglycinol, respectively, easily gave 3-nitrobenzamido alco-
hols 1aꢀc (Scheme 1). Then the amido alcohols were converted
to the corresponding imidazolines 2aꢀc by successive reactions
with thionyl chloride and p-toluidine as well as basic workup with
10% NaOH. Next, the nitro group in 2aꢀc was readily and
cleanly reduced to an amino group by catalytic hydrogenation in
the presence of Pd/C to afford the expected PCN pincer ligand
precursors 3aꢀc. With the ligand precursors in hand, the one-pot
phosphorylation/metalation reaction was attempted in order to
get the chiral pincer Pd(II) complexes 4 and Ni(II) complex 5a
with aryl-based aminophosphineꢀimidazoline ligands. This was
achieved by phosphorylation of the amino group in 3aꢀc with
Ph2PCl in the presence of triethylamine in refluxing toluene for
Chart 1. One-Pot Phosphorylation/Metalation Reaction for
the Synthesis of Unsymmetrical PCN Pincer Palladium(II)
and Nickel(II) Complexes Containing a Phosphinito Group
Scheme 1. Synthesis of Unsymmetrical and Chiral PCN Pincer Pd(II) and Ni(II) Complexes with Aryl-Based Aminopho-
sphineꢀImidazoline Ligands
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Table 1. Selected 1H NMR Data (δ, ppm) of 3-(20-Imidazolinyl)anilines 3aꢀc, Pd Complexes 4aꢀc, and Ni Complex 5aa
central Ar (4H or 3H)
imidazoline
NAr (4H)
compd (solvent)
Ar2
Ar4
Ar5
Ar6
NCH
NCHH
NCHH
Ar3,5
Ar2,6
3a (DMSO-d6) 6.78 (s)
4a (CDCl3)
6.44 (d)
5.99 (d)
5.92 (d)
6.40 (d)
5.87 (d)
6.91 (t)
6.67ꢀ6.61 (m, 2H)
6.59 (t)
6.56 (d) 3.91ꢀ3.87 (m) 3.96 (app t) 3.50 (dd) 6.95 (d)
6.67 (d)
4.42ꢀ4.37 (m) 4.00 (app t) 3.78 (dd) 7.21 (d)
7.14 (d)
7.13 (d)
5a (CDCl3)
6.41 (d) 4.16ꢀ4.12 (m) 4.02 (app t) 3.78 (dd) 7.20 (d)
3b (DMSO-d6) 6.73 (s)
4b (CDCl3)
6.91ꢀ6.88 (m)b 6.53 (d)b 4.40ꢀ4.36 (m) 3.95 (app t) 3.49 (dd) 6.91ꢀ6.88 (m)b 6.53 (d)b
6.65ꢀ6.59 (m, 2H)
4.70ꢀ4.65 (m) 4.02 (app t) 3.74 (dd) 7.23ꢀ7.17 (m)b 7.13 (d)
3c (CDCl3)
4c (CDCl3)
7.06ꢀ7.02 (m)b 6.68 (dd) 7.06ꢀ7.02 (m)b 6.83 (d) 5.31 (dd)
4.42 (dd)
3.88 (dd) 6.98 (d)
6.75 (d)
6.05 (d)
6.68ꢀ6.64 (m, 2H)
5.47 (dd)
4.38 (app t) 3.96 (dd) 7.36ꢀ7.26 (m)b 7.23ꢀ7.16 (m)b
a For convenience of comparison, the atom labels for compounds 3aꢀc as well as the pincer complexes 4aꢀc and 5a are the same. b Overlapped.
8 h, followed by the addition of PdCl2 or anhydrous NiCl2 in situ
for metalation in toluene at reflux for another 12 h. Although the
yields of the obtained pincer Pd complexes (around 40%) and Ni
complex (30%) in this last step were not very high, the procedure
was easy to handle by avoiding the usually troublesome isolation
of the air- and moisture-sensitive P-containing ligands. Further-
more, it should be mentioned that these chiral pincers were
prepared via the aryl CꢀH activation of the related ligands, a
method which is more simple and convenient than the oxidative
addition and transmetalation methods.
All of the unsymmetrical chiral PCN pincer Pd and Ni
complexes are air and moisture stable both in the solid state
and in solution. They were fully characterized by elemental
1
analysis and H, 13C, and 31P{1H} NMR, DEPT, HSQC, and
1
IR spectra. In the H NMR spectra of the complexes, the
Figure 1. Molecular structure of 4a. Hydrogen atoms are omitted
disappearance of the signal corresponding to the central aryl
for clarity.
proton located ortho to both the ꢀNHR group and imidazoline
ring confirmed the occurrence of C-metalation. In comparison
with the corresponding 3-(20-imidazolinyl)anilines 3aꢀc, the
Molecular Structures of Pd and Ni Complexes. The
signals of central aryl protons for the complexes shifted upfield,
while the signals of the N-aryl protons as well as the imidazoline
ring protons shifted downfield in most cases due to NꢀM
coordination and CꢀM bond formation in the complexes
molecular structures of the pincer Pd(II) complexes 4a,c as well
as the Ni(II) complex 5a were determined by X-ray single crystal
analysis. The molecules are shown in Figures 1ꢀ3, respectively.
Selected bond lengths and angles are collected in Table 2. The
metal(II) center in each complex adopts a distorted-square-
planar configuration with the ligand coordinated to the metal
via aminophosphine P, the central aryl C, and imidazoline N in a
terdentate manner and the chloride ligand occupying the fourth
coordination site. The small values for CꢀMꢀN (79ꢀ82°) and
CꢀMꢀP angles (81ꢀ83°) in these complexes are also typical for
pincers consisting of two fused five-membered-ring metallacycles
and reflect the relative steric strain of the system.10e,j,l,12b,13,14
The metalꢀligand distances and bond angles around the Pd(II)
center in complexes 4a,c are similar, with the bond lengths of
PdꢀC being around 1.98 Å and PdꢀN around 2.10 Å, which are
comparable to those in related chiral PCN pincer Pd complexes
with aryl-based phosphiniteꢀimidazoline ligands. However, the
PdꢀP distances are slightly longer (2.22ꢀ2.24 Å vs 2.20 Å).13
1
(selected H NMR data are given in Table 1). The diagnostic
multiplets at approximately δ 7.90 and 7.40 ppm in a ratio of 4:6
for Ph2P in the 1H NMR spectra and the singlet at about δ 91
ppm (86 ppm for the Ni complex) in the 31P{1H} NMR spectra
indicated the formation of a NHPPh2 group. In the 13C NMR
spectra of 3-(20-imidazolinyl)anilines 3aꢀc, the resonances due
to the carbon atom of imidazolinyl CdN appeared around 161
ppm and those due to C-2 atom of central aryl appeared around
114 ppm. For the pincer complexes 4aꢀc and 5a, the corre-
sponding resonances obviously shifted downfield. The former
were observed around 170 ppm and the latter around 151 ppm,
again indicative of NꢀM coordination and CꢀM bond forma-
tion in the complexes. In addition, the 13C NMR spectra of the
13
complexes exhibited intense 31Pꢀ C couplings.
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ARTICLE
Pd pincer containing an aryl-based phosphiniteꢀimidazoline
ligand.13 Similar to the case for its Pd analogue 4a, the MꢀP
distance in 5a is slightly shorter than that in the symmetrical PCP
bis(aminophosphine) pincer Ni complex (2.18 Å).14 Finally, a
comparison of Ni complex 5a and Pd complex 4a reveals that the
metalꢀterdentate ligand bond lengths in the two complexes
follow the expected pattern of Ni < Pd.
Catalytic Studies. Catalytic asymmetric hydrophosphination
of the electron-deficient alkenes with secondary phosphines (1,4-
addition of R2PH to the alkenes) can provide direct, efficient
access to potentially useful chiral phosphine compounds.15
Among the few asymmetric catalysts reported, a Ni(II) complex
could catalyze hydrophosphination of methacrylonitrile (up to
94% ee),16 a Pd(II) complex catalyzed that of enones (up to 99%
ee after a recrystallization),17 and some organocatalysts showed
high levels of enantioselectivities in the hydrophosphination of
R,β-unsaturated aldehydes18 as well as nitroalkenes.19 Further-
more, the related highly enantioselective addition of R2P(O)ꢀH
to activated alkenes, including nitroalkenes,20 and R,β-unsatu-
rated ketones21 (phospha-Michael reaction) were also described.
Very recently, Duan and co-workers reported the first pincer Pd
complex catalyzed asymmetric hydrophosphination of β-substi-
tuted enones with diarylphosphines. The chiral bis(phosphine)
PCP pincer Pd complex A, bearing a benzylic C-stereogenic
center (Scheme 2), was used as the catalyst, giving chiral
phosphine derivatives with excellent enantioselectivities (13
examples, 90ꢀ99% ee's).22 These results encouraged us to
investigate the potential of the obtianed chiral pincer complexes
in this reaction. For convenience of operation in the experiments,
the phosphine adducts were oxidized to the corresponding
phosphine oxides for analysis as described in the literature.22
The addition of diphenylphosphine to chalcone was first chosen
as a model to optimize the reaction conditions (Table 3). The
reaction was performed with 1 equiv of Ph2PH and 1.5 equiv of
chalcone using 5 mol % of pincer complex as the catalyst in the
presence of KOAc as base. It can be seen from Table 3 that initial
results (entries 1ꢀ4) were far from satisfactory when the reaction
was conducted at 25 °C in CH2Cl2; the pincer Pd complex 4c
gave the best results with 81% yield and 37% ee (entry 3). For
comparison, the new chiral bis(imidazoline) NCN pincer Pd(II)
complexes 6 (Scheme 2) were prepared according to the
procedure reported by us.8c Among them, complex 6a, with
the same imidazoline ring as complex 4c, was obtained in a rather
low yield (only 8%). Thus, the potential of complex 6b, which
contains two C-stereogenic centers in one imidazoline ring, was
Figure 2. Molecular structure of 4c. Hydrogen atoms are omitted for
clarity.
Figure 3. Molecular structure of 5a. Hydrogen atoms are omitted for
clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 4a,c and 5aa
4a
4c
5a
MꢀC
1.978(4)
1.975(3)
2.083(2)
2.2188(7)
2.4006(8)
79.47(10)
80.87(8)
159.82(7)
175.18(8)
95.73(7)
103.95(3)
1.873(2)
1.9197(19)
2.1430(7)
2.2167(8)
82.51(9)
83.02(7)
165.27(6)
178.02(8)
96.09(6)
98.30(3)
MꢀN
2.104(3)
MꢀP
MꢀCl
2.2356(11)
2.4159(11)
79.06(14)
81.07(12)
159.76(10)
175.55(12)
96.49(10)
103.36(4)
first tested (the molecular structure of 6b 2CHCl3 as well as
3
CꢀMꢀN
CꢀMꢀP
NꢀMꢀP
CꢀMꢀCl
NꢀMꢀCl
PꢀMꢀCl
selected bond lengths and angles are given in the Supporting
Information). Unfortunately, complex 6b afforded a racemic
product in moderate yield under the same reaction conditions
(entry 5). The enantioselectivity was only 14% ee with the
known chiral PCN pincer Pd complex 713 containing an aryl-
based phosphiniteꢀimidazoline ligand as the catalyst, though an
excellent yield was obtained (entry 6). Gratifyingly, the enantios-
electivity significantly improved to 71% with complex 4c as the
catalyst when toluene instead of CH2Cl2 was employed as the
solvent at 25 °C (entry 7). Other solvents, including THF,
CH3CN, CH3OH, and a mixed solvent of toluene and hexane,
did not give better results (entries 8ꢀ11). Then, lowering the
reaction temperature from 25 to 0 °C in toluene led to a further
enhancement in enantioselectivity (entry 12, 82% ee). The
enantioselectivities and particularly the yields of the product
decreased with a lower catalyst loading (2 mol %) or at ꢀ20 °C
a For complexes 4a,c, M = Pd; for complex 5a, M = Ni.
As compared with the related symmetrical PCP bis-
(aminophosphine) pincer Pd complex (2.28 Å)14 and chiral
NCN bis(imidazoline) pincer Pd complex (2.03ꢀ2.08 Å),8c
complexes 4a,c have slightly shorter PdꢀP distances and longer
PdꢀN distances. On the other hand, the nickel complex 5a
shows a comparable NiꢀC distance (around 1.87 Å), a slightly
shorter NiꢀN distance (1.92 Å vs 1.95 Å), and a slightly longer
NiꢀP distance (2.14 Å vs 2.12 Å) in comparison with a PCN
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Scheme 2. Chiral Pincer Pd(II) Complexes Used in the Asymmetric Addition of Diarylphosphines to Enones
Table 3. Optimization of Reaction Conditions for the
Asymmetric Addition of Diphenylphosphine to Chalcone
Catalyzed by Pincer Complexesa
Table 4. Asymmetric Addition of Diarylphosphines to β-
Substituted Enones Catalyzed by Pincer Pd(II) Complex 4ca
entry
R1
R2
Ar
yield (%)b ee (%)c,d
entry cat.
solvent
base temp (°C) yield (%)b ee (%)c,d
1
2
3
4
5e
6
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
p-BrC6H4
Ph
Ph
88
95
98
73
68
94
49
99
99
74
81
99
35
82
86
90
73
51
92
88
94
85
92
88
90
40
1
2
3
4
5
6
7
8
9
4a CH2Cl2
4b CH2Cl2
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
25
25
25
25
25
25
25
25
25
25
25
0
47
75
81
45
66
99
93
89
94
92
59
88
75
61
27
81
11
84
48
47
16
0
p-NO2C6H4 Ph
p-MeC6H4 Ph
o-MeOC6H4 Ph
4c CH2Cl2
5a CH2Cl2
6b CH2Cl2
37
0
0
p-MeOC6H4 p-NO2C6H4 Ph
7
CH2Cl2
14
71
49
0
Me
Me
Me
Ph
Ph
4c PhMe
4c THF
p-NO2C6H4 Ph
m-NO2C6H4 Ph
4c CH3CN
10 Me
11 Me
12 i-Bu
13 Ph
p-BrC6H4
p-ClC6H4
Ph
Ph
10 4c CH3OH
6
11 4c 2/1 PhMe/hexane KOAc
23
82
78
77
31
34
13
85
30f
30
p-NO2C6H4 Ph
Ph p-MeOC6H4
12 4c PhMe
13 4ce PhMe
14 4c PhMe
15 4c PhMe
16 4c PhMe
17 4c PhMe
18 6a PhMe
19 6b PhMe
KOAc
KOAc
KOAc
K2CO3
Et3N
a Addition reactions were performed with Ph2PH (0.2 mmol) and
β-substituted enones or trans-β-nitrostyrene (0.3 mmol) in the presence
of complex 4c (5 mol %) and KOAc as base (10 mol %) in 2 mL of
toluene at 0 °C for 12 h. b Isolated yields. c Determined by chiral HPLC.
d The absolute configurations of the known products were assigned to be
S by comparison of optical rotations with those in ref 22, and the
configurations of the new products were assigned by analogy. e The
reaction time was 24 h.
0
ꢀ20
0
0
none
0
KOAc
KOAc
KOAc
0
0
20
7
PhMe
0
a Addition reactions were performed with Ph2PH (0.2 mmol) and
chalcone (0.3 mmol) in the presence of pincer complex and base (10
mol %) for 12 h (the time was not optimized). b Isolated yields.
c Determined by chiral HPLC. d The absolute configuration was assigned
with low enantioselectivities (entries 19 and 20). Interestingly,
under these conditions the major enantiomer of the product
possesses the opposite absolute configuration with complex 6b as
the catalyst.
e
to be S by comparison of optical rotation with that in ref 22. Using
On the basis of the above results, 5 mol % of complex 4c in
toluene, 0 °C, and KOAc as the base were considered as the
optimized reaction conditions. The reaction was extended to
other β-aryl-substituted enones in addition to chalcone under the
optimized conditions to evaluate the scope of the system
(Table 4). In comparison to chalcone with a β-phenyl, both
the yields and enantioselectivities improved obviously when the
β-aryl bore an electron-withdrawing group such as p-Br and
p-NO2 (entries 2 and 3 vs entry 1). In contrast, an electron-
neutral group such as p-Me and an electron-donating group such
as o-MeO on the β-aryl led to a significant decrease in both the
yields and enantioselectivities (entries 4 and 5). The effect of
the electron-withdrawing group in enhancing the yields or/and
2 mol % of catalyst. f The absolute configuration was R.
(entries 13 and 14). When the addition was carried out in toluene
at 0 °C in the presence of another base such as K2CO3 or Et3N
instead of KOAc as well as in the absence of base, the enantios-
electivities and sometimes the yields of the phosphine adduct
dropped drastically (entries 15ꢀ17). Finally, the performance of
complexes 6 and 7 was reexamined in toluene at 0 °C in the
presence of KOAc base. In comparison with 4c complex 6a
showed slightly lower yield and higher enantioselectivity (entry
18), while the results with complexes 6b and 7 were still not
satisfactory and the adduct was obtained in yields around 48%
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Scheme 3. Plausible Reaction Mechanism for the Addition of
Diarylphosphines to Enones Catalyzed by Pincer Pd(II)
Complex 4c
β-aryl enones, giving the chiral phosphine derivatives in high
yields and enantioselectivities (up to 99% yield, 94% ee).
Furthermore, structural modification of these pincer complexes
can be easily achieved by using various chiral amino alcohols and
aromatic and aliphatic amines as well as the appropriate chlor-
ophosphines, providing ample opportunities for fine-tuning the
catalytic activities and particularly stereoselectivities of the com-
plexes. Further modification of these unsymmetrical chiral pincer
metal complexes as well as their application in asymmetric
reactions are in progress.
’ EXPERIMENTAL SECTION
General Procedures. Solvents were dried by standard methods
and freshly distilled prior to use if needed. Chiral amino alcohols,23
enone substrates,24 and bis(4-methoxyphenyl)phosphine25 used in the
asymmetric catalytic reactions 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 uncor-
rected. Infrared spectra were obtained with a Bruker VECTOR 22
spectrophotometer. 1H, 13C, and 31P{1H} NMR spectra were recorded
on a Bruker DPX-400 spectrometer 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. Elemental analyses were measured on a
Thermo Flash EA 1112 elemental analyzer. Optical rotations were
recorded on a Perkin-Elmer 341 polarimeter.
enantioselectivities was also observed in the case of enone
substrates bearing a p-MeOC6H4 (entry 6), Me (entries
7ꢀ11), or i-Bu moiety (entry 12) attached to the carbonyl
group. Particularly, a p-NO2 group on the β-aryl gave excellent
yields with excellent enantioselectivities (94ꢀ99% yields, 90ꢀ
94% ee's, entries 3, 6, 8 and 12). In addition, it was found that
bis(4-methoxyphenyl)phosphine was not an effective nucleo-
phile toward chalcone under the current conditions, providing
the expected adduct in a 35% yield with 40% ee (entry 13). Also,
the reaction of dicyclohexylphosphine with chalcone gave the
corresponding product in only 10% yield with 7% ee. Finally,
trans-β-nitrostyrene was found to react smoothly with diphenyl-
phosphine to produce the expected adduct in 99% yield. How-
ever, the enantioselectivity was only 20%.
In the catalytic cycle for the pincer Pd catalyzed addition of
diarylphosphines to enones proposed by Duan and co-workers,
the reaction begins with transphosphination between the pincer
Pd(II) complex A (X = OAc, Scheme 2) and the diarylphosphine
to give the pincer Pd(II) diarylphosphido complex. Then,
addition of the diarylphosphido group at palladium to the enone
affords an oxa-π-allylpalladium intermediate. Finally, the inter-
mediate undergoes protonolysis with HOAc to form the phos-
phine adduct along with regeneration of the active pincer Pd
complex A.22 Accordingly, and also considering the key role of
the KOAc base in the reaction, a plausible reaction mechanism
with a similar catalytic cycle for the present catalytic system was
proposed (Scheme 3). First, in the presence of KOAc the
chloride in the pincer Pd(II) complex 4c was replaced by the
acetate to afford the PdꢀOAc complex 8. Similar to the case for
Duan’s pincer Pd complex A (X = OAc), complex 8 acts as the
active catalyst in the catalytic cycle and the successive transpho-
sphination, addition, and protonolysis lead to the formation of
the phosphine adduct along with regeneration of the active Pd
complex 8.
General Procedure for the Synthesis of 3-Nitrobenzamido
Alcohols 1. A solution of 3-nitrobenzoic acid (3.34 g, 20 mmol) in
SOCl2 (14 mL, 200 mmol) was stirred at reflux for 5 h. Evaporation of
excess thionyl chloride under reduced pressure gave the crude 3-nitro-
benzoyl chloride, which was dissolved in 40 mL of CH2Cl2 and added
dropwise to a stirred solution of the chiral amino alcohol (20 mmol) and
Et3N (2.9 mL, 22 mmol) in CH2Cl2 (70 mL) at 0 °C. The reaction
mixture was then warmed to room temperature. After the mxiture was
stirred at room temperature for 12 h, water (100 mL) was added. The
layers were separated, and the organic layer was dried over Na2SO4.
Removal of the solvent in vacuo gave white solids, which was purified by
column chromatography on silica gel or recrystallization to afford the
corresponding chiral amido alcohols 1aꢀc.
(S)-N-(1-Hydroxy-3-methylbutan-2-yl)-3-nitrobenzamide (1a). Puri-
fication was carried out by column chromatography on silica gel with ethyl
20
acetate as eluent: 90% yield; white solids; mp 115ꢀ116 °C; [R]D
=
ꢀ40° (c 0.130, CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 8.58 (s, 1H, Ar
H), 8.33 (dd, J = 1.0, 7.9 Hz, 1H, Ar H), 8.15 (d, J = 7.7 Hz, 1H, Ar H),
7.63 (t, J = 8.0Hz, 1H, ArH), 6.69 (d, J =8.5 Hz, 1H, NH), 4.01ꢀ3.96(m,
1H, CHNH), 3.84 (d, J = 3.1 Hz, 2H, CH2OH), 2.70 (s, 1H, OH),
2.07ꢀ2.01 (m, 1H, CH(CH3)2), 1.04 (d, J = 7.9 Hz, 3H, CH3CHCH3),
1.02 (d, J = 7.1 Hz, 3H, CH3CHCH3). 13C NMR (100 MHz, CDCl3): δ
165.7, 148.1, 136.1, 133.3, 129.8, 126.1, 121.8, 63.2, 57.6, 29.2, 19.5, 19.2.
IR (KBr): ν 3279, 2963, 2876, 1639, 1583, 1532, 1428, 1370, 1201, 1072,
1017, 707, 752, 699 cmꢀ1. HRMS (positiveESI;m/z): [M + H]+ calcd for
C12H17N2O4 253.1188, found 253.1186.
(S)-N-(1-Hydroxy-3-phenylpropan-2-yl)-3-nitrobenzamide (1b). Re-
crystallization was carried out from CH2Cl2ꢀpetroleum ether or purifica-
20
tionbycolumnchromatography onsilica gel with ethyl acetate/petroleum
’ CONCLUSIONS
ether (3/2) as eluent: 70% yield; white solids; mp 133ꢀ134 °C; [R]D
=
ꢀ68° (c 0.132, CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 8.50 (s, 1H, Ar
H), 8.35 (dd, J = 1.0, 7.8 Hz, 1H, Ar H), 8.07 (d, J = 7.8 Hz, 1H, Ar H),
7.63 (t, J = 7.9 Hz, 1H, Ar H), 7.35 (t, J = 7.6 Hz, 2H, Ph H), 7.37ꢀ7.26
(m, 3H, Ph H), 6.55 (d, J = 7.2 Hz, 1H, NH), 4.45ꢀ4.42 (m, 1H,
CHNH), 3.84 (dd, J = 3.4, 11.0 Hz, 1H, CH2OH), 3.75 (dd, J = 4.6, 11.0
Hz, 1H, CH2OH), 3.04 (d, J = 7.2Hz, 2H, CH2Ph). 13C NMR (100 MHz,
CDCl3): δ 165.3, 148.2, 137.3, 136.0, 133.2, 129.9, 129.2, 128.8, 127.0,
In summary, three unsymmetrical chiral PCN pincer Pd(II)
complexes and one Ni(II) complex with aryl-based aminopho-
sphineꢀimidazoline ligands have been conveniently synthesized
by a one-pot phosphorylation/metalation reaction of chiral
3-(20-imidazolinyl)anilines starting from inexpensive, commer-
cially available 3-nitrobenzoic acid. The pincer Pd complexes
readily catalyze the asymmetric addition of diphenylphosphine to
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126.1, 121.8, 63.7, 53.3, 37.0. IR (KBr): ν 3375, 3089, 2918, 2870, 1558,
65.4, 58.8, 42.1, 20.8. IR (KBr): ν 3438, 2924, 1615, 1601, 1531, 1398,
1348, 1147, 1085, 814, 699 cmꢀ1. HRMS (positive ESI; m/z): [M + H]+
calcd for C23H22N3O2 372.1712, found 372.1705.
1455, 1375, 1031, 737 cmꢀ1
.
(S)-N-(2-Hydroxy-1-phenylethyl)-3-nitrobenzamide (1c). Recrystal-
lization was carried out from 95% ethanol: 73% yield; white solids; mp
167ꢀ168 °C; [R]D20 = ꢀ70° (c 0.100, CH2Cl2). 1H NMR (400 MHz,
DMSO-d6): δ 9.18 (d, J = 8.0 Hz, 1H, NH), 8.78 (s, 1H, Ar H), 8.41(dd,
J = 1.6, 8.1 Hz, 1H, Ar H), 8.35 (d, J = 8.0 Hz, 1H, Ar H), 7.80 (t, J = 8.0
Hz, 1H, Ar H), 7.41 (d, J = 7.5 Hz, 2H, Ph H), 7.34 (t, J = 7.5 Hz, 2H, Ph
H), 7.25 (t, J = 7.2 Hz, 1H, Ph H), 5.14ꢀ5.09 (m, 1H, OH), 5.05 (t, J =
5.8 Hz, 1H, CHNH), 3.78ꢀ3.74 (m, 1H, CH2OH), 3.72ꢀ3.65 (m, 1H,
CH2OH). 1H NMR (400 MHz, DMSO-d6 + D2O): δ 8.69 (d, J = 1.7
Hz, 1H, Ar H), 8.35 (dd, J = 1.6, 8.1 Hz, 1H, Ar H), 8.26 (d, J = 8.0 Hz,
1H, Ar H), 7.74 (t, J = 8.0 Hz, 1H, Ar H), 7.35 (d, J = 7.5 Hz, 2H, Ph H),
7.30 (t, J = 7.5 Hz, 2H, Ph H), 7.21 (t, J = 7.2 Hz, 1H, Ph H), 5.05 (dd, J =
5.3, 8.4 Hz, 1H, CHNH), 3.70 (dd, J = 8.4, 11.2 Hz, 1H, CH2OH), 3.63
(dd, J = 5.3, 11.2 Hz, 1H, CH2OH). 13C NMR (100 MHz, DMSO-d6): δ
164.3, 147.9, 141.1, 136.1, 134.3, 130.3, 128.4, 127.2, 126.1, 122.3, 64.6,
56.6. IR (KBr): ν 3334, 1638, 1528, 1400, 1346 cmꢀ1. HRMS (positive
ESI; m/z): [M + Na]+ calcd for: C15H14N2NaO4 309.0851, found
309.0849.
General Procedure for the Synthesis of 3-(20-Imidazoli-
nyl)anilines 3. The obtained amido alcohol (10 mmol) was reacted
with thionyl chloride (5 mL) at reflux for 5 h. Excess thionyl chloride was
evaporated. The residue was dissolved in dry CH2Cl2 (20 mL) and
added dropwise to a solution of triethylamine (4 mL, 30 mmol) and
p-toluidine (1.6 g, 15 mmol) in CH2Cl2 at 0 °C. The mixture was then
warmed to room temperature and stirred for 24 h. After that, 10% NaOH
(25 mL) solution was added and the mixture was stirred for another
2ꢀ3 h. The aqueous layer was extracted with dichloromethane, and the
organic layer was washed with brine, dried over Na2SO4, and evaporated.
The residue was purified by column chromatography on silica gel with
ethyl acetate/petroleum ether (1/4 or 1/3 for 2c) as eluent to give
3-(imidazolinyl)nitrobenzenes 2aꢀc. Next, the nitro group in 2aꢀc was
readily reduced to an amino group by catalytic hydrogenation. The
reaction was carried out with compound 2 (3.1 mmol) in MeOH
(100 mL) in the presence of 10% Pd/C (0.1 g) under 60 psi of hydrogen
pressure at room temperature. After conversion was complete
(monitored by TLC, generally 6 h), the mixture was filtered through a
pad of Celite. The resulting solution was concentrated in vacuo to afford
a light yellow oil, which was purified by column chromatography on
silica gel with ethyl acetate/Et3N (100/1) as eluent to afford the 3-(20-
imidazolinyl)anilines 3aꢀc.
(S)-2-(3-Nitrophenyl)-4-phenyl-1-(p-tolyl)-4,5-dihydro-1H-imidazole
(2c): 65% yield; oil; [R]D20 = ꢀ49° (c 0.09, CH2Cl2). 1H NMR (400
MHz, CDCl3): δ 8.51 (s, 1H, Ar H), 8.16 (d, J = 8.2 Hz, 1H, Ar H), 7.83
(d, J = 7.7 Hz, 1H, Ar H), 7.41ꢀ7.24 (m, 6H, Ph H and Ar H), 6.99
(d, J = 8.1 Hz, 2H, NAr H), 6.77 (d, J = 8.1 Hz, 2H, NAr H), 5.36 (dd,
1H, J = 9.0, 10.2 Hz, NCH), 4.45 (app t, J = 10.2 Hz, 1H, NCHH), 3.90
(app t, J = 9.0 Hz, 1H, NCHH), 2.23 (s, 3H, CH3). 13C NMR (100 MHz,
CDCl3): δ 160.9, 147.9, 143.4, 139.8, 134.8, 134.7, 132.7, 129.9, 129.2,
128.8, 127.5, 126.8, 124.7, 124.0, 123.7, 67.9, 62.4, 20.8. IR (KBr): ν
3016, 2840, 2750, 1599, 1568, 1485, 1446, 1383, 1273, 1146, 814,
698 cmꢀ1. HRMS (positive ESI; m/z): [M + H]+ calcd for C22H20N3O2
358.1556, found 358.1548.
(S)-3-(4-Isopropyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)aniline
(3a): 92% yield; oil; [R]D20 = ꢀ25° (c 0.23, CH2Cl2). 1H NMR (400
MHz, DMSO-d6): δ 6.95 (d, J = 8.0 Hz, 2H, NAr H), 6.91 (t, J = 7.6 Hz,
1H, Ar H), 6.78 (s, 1H, Ar H), 6.67 (d, J = 8.0 Hz, 2H, NAr H), 6.56 (d,
J = 7.6 Hz, 1H, Ar H), 6.44 (d, J = 6.8 Hz, 1H, Ar H), 5.15 (s, 2H, NH2),
3.96 (app t, J = 9.6 Hz, 1H, NCHH), 3.91ꢀ3.87 (m, 1H, NCH), 3.50
(dd, J = 7.6, 8.8 Hz, 1H, NCHH), 2.18 (s, 3H, CH3), 1.75ꢀ1.71 (m, 1H,
CH(CH3)2), 0.95 (d, J = 6.8 Hz, 3H, CH3CHCH3), 0.88 (d, J = 6.8 Hz,
3H, CH3CHCH3). 13C NMR (100 MHz, DMSO-d6): δ 160.9, 148.4,
141.2, 132.4, 131.5, 129.0, 128.4, 121.8, 115.8, 115.0, 113.6, 69.5, 56.2,
32.8, 20.2, 18.5, 18.0. IR (KBr): ν 3353, 3330, 3188, 2949, 2868, 1605,
1575, 1461, 1418, 1378, 310, 1134, 995, 811, 776, 697 cmꢀ1. HRMS
(positive ESI; m/z): [M + H]+ calcd for C19H24N3 294.1970, found
294.1973.
(S)-3-(4-Benzyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)aniline (3b):
90% yield; white solids; mp 97ꢀ98 °C; [R]D20 = +2° (c 0.12, CH2Cl2).
1H NMR (400 MHz, DMSO-d6): δ 7.27ꢀ7.24 (m, 4H, Bn H),
7.19ꢀ7.16 (m, 1H, Bn H), 6.91ꢀ6.88 (m, 3H, Ar H and NAr H),
6.73 (s, 1H, Ar H), 6.53 (d, J = 8.2 Hz, 3H, Ar H and NAr H), 6.40 (d, J =
7.4 Hz, 1H, Ar H), 5.15 (s, 2H, NH2), 4.40ꢀ4.36 (m, 1H, NCH), 3.95
(app t, J = 9.8 Hz, 1H, NCHH), 3.49 (dd, J = 7.5, 9.2 Hz, 1H, NCHH),
2.95 (dd, J = 5.8, 13.6 Hz, 1H, CHHPh), 2.75 (dd, J = 7.2, 13.6 Hz, 1H,
CHHPh), 2.16 (s, 3H, CH3). 13C NMR (100 MHz, DMSO-d6): δ 161.4,
148.6, 141.2, 138.7, 132.4, 131.9, 129.6, 129.2, 128.6, 128.2, 126.2, 122.2,
116.0, 115.3, 113.9, 64.9, 58.2, 42.1, 20.5. IR (KBr): ν 3349, 3331, 3185,
3025, 2920, 2710, 1603, 1571, 1514, 1464, 1418, 1381, 1312, 1243, 811,
739, 700 cmꢀ1. HRMS (positive ESI; m/z): [M + H]+ calcd for
C23H24N3 342.1970, found 342.1967.
(S)-4-Isopropyl-2-(3-nitrophenyl)-1-(p-tolyl)-4,5-dihydro-1H-imidazole
(2a): 80% yield; oil; [R]D20 = ꢀ35° (c 0.409, CH2Cl2). 1H NMR (400
MHz, CDCl3): δ 8.40 (t, J = 1.9 Hz, 1H, Ar H), 8.20ꢀ8.17 (m, 1H, Ar
H), 7.80ꢀ7.78 (m, 1H, Ar H), 7.43 (t, J = 8.0 Hz, 1H, Ar H), 6.99 (d, J =
8.3 Hz, 2H, NAr H), 6.69 (d, J = 8.3 Hz, 2H, NAr H), 4.15ꢀ4.09 (m, 2H,
NCH and NCHH), 3.68ꢀ3.61 (m, 1H, NCHH), 2.25 (s, 3H, CH3),
1.96ꢀ1.91 (m, 1H, CH(CH3)2), 1.06 (d, J = 6.8 Hz, 3H, CH3CHCH3),
0.97 (d, J = 6.8 Hz, 3H, CH3CHCH3). 13C NMR (100 MHz, CDCl3): δ
159.6, 147.6, 139.9, 134.3, 133.9, 132.9, 129.4, 128.8, 124.2, 123.6, 123.1,
70.2, 56.9, 32.9, 20.5, 18.6, 17.7. IR (KBr): ν 3086, 3029, 2950, 2870,
1571, 1531, 1484, 1417, 1272, 1200, 815, 732 cmꢀ1. HRMS (positive
ESI; m/z): [M + H]+ calcd for: C19H22N3O2 324.1712, found 324.1713.
(S)-4-Benzyl-2-(3-nitrophenyl)-1-(p-tolyl)-4,5-dihydro-1H-imidazole
(S)-3-(4-Phenyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)aniline (3c):
20
90% yield; white solids; mp 55ꢀ57 °C; [R]D = ꢀ61° (c 0.111,
CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 7.40ꢀ7.35 (m, 4H, Ph H),
7.28ꢀ7.26 (m, 1H, Ph H), 7.06ꢀ7.02 (m, 2H, Ar H), 6.98 (d, J = 8.0 Hz,
2H, NAr H), 6.83 (d, J = 7.6 Hz, 1H, Ar H), 6.75 (d, J = 8.0 Hz, 2H, NAr
H), 6.68 (dd, J = 1.9, 7.6 Hz, 1H, Ar H), 5.31 (dd, J = 8.2, 10.8 Hz, 1H,
NCH), 4.42 (dd, J = 9.6, 10.8 Hz, 1H, NCHH), 3.88 (dd, J = 8.2, 9.6 Hz,
1H, NCHH), 3.66 (br s, 2H, NH2), 2.26 (s, 3H, CH3). 13C NMR
(100 MHz, CDCl3): δ 162.8, 146.3, 144.2, 140.6, 133.1, 132.1, 129.3,
129.0, 128.6, 127.2, 126.8, 122.7, 119.3, 116.7, 115.4, 67.5, 62.0, 20.8. IR
(KBr): ν 3444, 3325, 3202, 3026, 2921, 2855, 1601, 1569, 1512, 1456,
1417, 1382, 1307, 1243, 1129, 994, 861, 817, 788, 757, 699 cmꢀ1. HRMS
(positive ESI; m/z): [M + H]+ calcd for C22H22N3 328.1814, found
328.1816.
20
(2b): 83% yield; oil; [R]D = +2.1° (c 0.780, CH2Cl2). 1H NMR
(400 MHz, CDCl3): δ 8.37 (s, 1H, Ar H), 8.19 (d, J = 8.2 Hz, 1H, Ar H),
7.76 (d, J = 7.8 Hz, 1H, Ar H), 7.44 (t, J = 8.0 Hz, 1H, Ar H), 7.31ꢀ7.22
(m, 5H, Bn H), 6.93 (d, J = 8.1 Hz, 2H, NAr H), 6.51 (d, J = 8.1 Hz, 2H,
NAr H), 4.61ꢀ4.56 (m, 1H, NCH), 4.06 (app t, J = 9.9 Hz, 1H,
NCHH), 3.69 (dd, J = 7.3, 9.5 Hz, 1H, NCHH), 3.20 (dd, J = 4.6, 13.6
Hz, 1H, CHHPh), 2.90 (dd, J = 8.1, 13.6 Hz, 1H, CHHPh), 2.24 (s, 3H,
CH3). 13C NMR (100 MHz, CDCl3): δ 160.2, 147.9, 139.7, 137.8,
134.6, 134.5, 132.8, 129.7, 129.6, 129.1, 128.4, 126.5, 124.6, 124.0, 123.5,
General Procedure for the Synthesis of PCN Pincer
Chloropalladium(II) Complexes 4 and Chloronickel(II) Com-
plex 5a. To a stirred solution of 3aꢀc (0.5 mmol) and triethylamine
(61 mg, 0.6 mmol) in toluene (20 mL) was added diphenylchloropho-
sphine (110.3 mg, 0.5 mmol) under N2 atmosphere at rt. The resultant
mixture was refluxed for 8 h. PdCl2 (89 mg, 0.5 mmol) or anhydrous
NiCl2 (for 5a, 65 mg, 0.5 mmol) was then added, and the reaction
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mixture was refluxed for another 12 h. After cooling, filtration, and
evaporation, the residue was purified by column chromatography on
silica gel with CH2Cl2 as eluent to produce the corresponding PCN
pincer complexes 4aꢀc and 5a.
1H NMR (400 MHz, CDCl3): δ 7.97ꢀ7.90 (m, 4H, PPh H), 7.48ꢀ7.26
(m, 6H, PPh H), 7.20 (d, J = 8.2 Hz, 2H, NAr), 7.13 (d, J = 8.2 Hz, 2H,
NAr), 6.59 (t, J = 7.6 Hz, 1H, Ar H), 6.41 (d, J = 7.6 Hz, 1H, Ar H), 5.92
(d, J = 7.6 Hz, 1H, Ar H), 4.54 (s, 1H, NH), 4.16ꢀ4.12 (m, 1H, NCH),
4.02 (app t, J = 10.4 Hz, 1H, NCHH), 3.78 (dd, J = 4.4, 9.8 Hz, 1H,
NCHH), 2.64ꢀ2.58 (m, 1H, CH(CH3)2), 2.39 (s, 3H, CH3), 0.95 (d,
J = 6.9 Hz, 3H, CH3CHCH3), 0.84 (d, J = 7.0 Hz, 3H, CH3CHCH3).
13C NMR (100 MHz, CDCl3): δ 168.8 (d, JPꢀC = 1.9 Hz), 154.2 (d,
(S)-2-(4-Isopropyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)-6-((dip-
henylphosphino)amino)phenylpalladium(II) Chloride (4a): 40% yield;
yellow solids; mp >290 °C; [R]D20 = +127° (c 0.056, CH2Cl2). 1H NMR
(400 MHz, CDCl3): δ 7.92ꢀ7.87 (m, 4H, PPh H), 7.49ꢀ7.39 (m, 6H,
PPh H), 7.21 (d, J = 8.0 Hz, 2H, NAr H), 7.14 (d, J = 8.0 Hz, 2H, NAr
H), 6.67ꢀ6.61 (m, 2H, Ar H), 5.99 (d, J = 7.1 Hz, 1H, Ar H), 4.71 (s, 1H,
NH), 4.42ꢀ4.37 (m, 1H, NCH), 4.00 (app t, J = 10.4 Hz, 1H, NCHH),
3.78 (dd, J = 5.4, 9.9 Hz, 1H, NCHH), 2.83ꢀ2.79 (m, 1H, CH(CH3)2),
2.40 (s, 3H, CH3), 0.92 (d, J = 7.2 Hz, 3H, CH3CHCH3), 0.90 (d, J = 7.4
Hz, 3H, CH3CHCH3). 13C NMR (100 MHz, CDCl3): δ 169.7, 153.1
(d, JPꢀC = 24.3 Hz), 151.2, 138.0, 137.6, 135.4, 134.0 (d, JPꢀC = 54.0
Hz), 133.4 (d, JPꢀC = 54.0 Hz), 132.2 (d, JPꢀC = 13.9 Hz), 131.9
(d, JPꢀC = 13.5 Hz), 131.2 (virtual t, JPꢀC = 2.8 Hz), 130.2, 128.75
(d, JPꢀC = 11.3 Hz), 128.73 (d, JPꢀC = 11.3 Hz), 126.5, 124.7, 118.2,
112.0 (d, JPꢀC = 18.3 Hz), 66.2, 55.5, 30.0, 21.2, 18.8, 14.6. 31P{1H}
NMR (162 MHz, CDCl3): δ 90.6. IR (KBr): ν 3437, 3251, 2954, 2865,
1538, 1511, 1363, 1297, 1105, 1040, 884, 726, 694 cmꢀ1. Anal. Calcd for
C31H31ClN3PPd (618.44): C, 60.20; H, 5.05; N, 6.79. Found: C, 60.03;
H, 5.14; N, 6.74.
J
PꢀC = 26.9 Hz), 149.8 (d, JPꢀC = 32.2 Hz), 137.44, 137.40, 136.6, 133.3
(d, JPꢀC = 47.1 Hz), 132.8 (d, JPꢀC = 49.6 Hz), 132.12 (d, JPꢀC = 12.0
Hz), 132.09 (d, JPꢀC = 11.9 Hz), 130.8 (d, JPꢀC = 2.3 Hz), 130.1, 128.54
(d, JPꢀC = 10.5 Hz), 128.50 (d, JPꢀC = 10.5 Hz), 126.1, 124.6, 116.9 (d,
J
PꢀC = 1.1 Hz), 111.0 (d, JPꢀC = 14.7 Hz), 64.1 (d, JPꢀC = 1.7 Hz), 55.9
(d, JPꢀC = 2.3 Hz), 30.2, 21.2, 18.7, 14.4. 31P{1H} NMR (162 MHz,
CDCl3): δ 86.0. IR (KBr): ν 3243, 2954, 2921, 2867, 1564, 1510, 1439,
1299, 1103, 1043, 880, 690 cmꢀ1. Anal. Calcd for C31H31ClN3NiP
(570.72): C, 65.24; H, 5.47; N, 7.36. Found: C, 64.82; H, 5.62; N, 7.16.
Procedure for the Synthesis of Chiral Bis(imidazoline)
NCN Pincer Chloropalladium(II) Complexes 6a,b. Complex
6a was prepared according to the procedure reported by us.8c For the
preparation of complex 6b, a mixture of 1,3-bis((S,S)-1-cyclohexyl-4,5-
diphenyl-4,5-dihydro-1H-imidazol-2-yl)benzene (136.6 mg, 0.2 mmol)
and Pd(OAc)2 (44.9 mg, 0.2 mmol) in dry HOAc (60 mL) was refluxed
for 36 h under a nitrogen atmosphere. The solvent was removed under
reduced pressure. The residue was purified by flash silica gel column
chromatography with CH2Cl2 as eluent and further recrystallized from
CH2Cl2/n-hexane, giving the PdꢀCl compound 6b instead of the
expected PdꢀOAc complex.
(S)-2-(4-Benzyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)-6-((diphen-
ylphosphino)amino)phenylpalladium(II) Chloride (4b): 42% yield;
20
pale yellow solids; mp >290 °C; [R]D = +176° (c 0.111, CH2Cl2).
1H NMR (400 MHz, CDCl3): δ 7.97ꢀ7.89 (m, 4H, PPh H), 7.46ꢀ7.37
(m, 8H, PPh H and Bn H), 7.23ꢀ7.17 (m, 3H, Bn H and NAr H), 7.13
(d, J = 8.0 Hz, 2H, NAr H), 7.12ꢀ6.63 (br s, 2H, Bn H), 6.65ꢀ6.59 (m,
2H, Ar H), 5.87 (d, J = 7.2 Hz, 1H, Ar H), 4.87 (s, 1H, NH), 4.70ꢀ4.65
(m, 1H, NCH), 4.02 (app t, J = 10.2 Hz, 1H, NCHH), 3.74 (dd, J = 4.9,
9.9 Hz, 1H, NCHH), 3.49 (dd, J = 3.2, 13.4 Hz, 1H, CHHPh), 3.10 (dd,
J = 8.1, 13.4 Hz, 1H, CHHPh), 2.37 (s, 3H, CH3). 13C NMR (100 MHz,
CDCl3): δ 170.1 (d, JPꢀC = 2.7 Hz), 153.1 (d, JPꢀC = 24.1 Hz), 151.3,
137.7 (d, JPꢀC = 4.3 Hz), 137.4, 135.2, 133.8 (d, JPꢀC = 52.6 Hz), 133.5
(d, JPꢀC = 53.8 Hz), 132.0 (d, JPꢀC = 13.8 Hz), 131.9 (d, JPꢀC = 13.6 Hz),
2,6-Bis((S)-4-phenyl-1-p-tolyl-4,5-dihydro-1H-imidazol-2-yl)phenyl-
palladium(II) Chloride (6a): 8% yield; yellow solid; mp 184ꢀ185 °C;
[R]D20 = +57° (c 0.154, CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 7.49
(d, J = 7.6 Hz, 4H, Ph H), 7.33 (t, J = 7.6 Hz, 4H, Ph H), 7.26ꢀ7.21 (m,
6H, Ph H and NAr H), 7.16 (d, J = 8.0 Hz, 4H, NAr H), 6.59 (t, J = 7.8
Hz, 1H, Ar H), 6.42 (d, J = 7.8 Hz, 2H, Ar H), 5.39 (dd, J = 4.2, 10.8 Hz,
2H, NCH), 4.42 (app t, J = 10.4 Hz, 2H, NCHH), 4.03 (dd, J = 4.2, 9.6
Hz, 2H, NCHH), 2.40 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3): δ
174.6, 169.6, 142.6, 138.1, 137.1, 133.2, 130.4, 128.6, 127.5, 127.04,
127.02, 126.3, 121.9, 64.6, 63.5, 21.2. IR (KBr): ν 3428, 3054, 3028,
2919, 2850, 1571, 1532, 1509, 1455, 1425, 1298, 1160, 1038, 1011, 820,
758, 729, 696 cmꢀ1. HRMS (positive ESI; m/z): [M ꢀ Cl]+ calcd for
C38H33N4Pd 651.1740, found 651.1743.
131.2 (d, JPꢀC = 1.8 Hz), 130.1 (d, JPꢀC = 3.4 Hz), 128.8 (d, JPꢀC
=
11.3 Hz), 128.7 (d, JPꢀC = 11.3 Hz), 128.1, 126.5, 126.2, 124.7, 118.1,
112.2 (d, JPꢀC = 18.3 Hz), 62.4 (d, JPꢀC = 2.2 Hz), 59.3 (d, JPꢀC
=
3.2 Hz), 41.1, 21.0. 31P{1H} NMR (162 MHz, CDCl3): δ 90.9. IR
(KBr): ν 3442, 3220, 2931, 1535, 1439, 1298, 1105, 1019, 882, 745,
697 cmꢀ1. Anal. Calcd for C35H31ClN3PPd (666.49): C, 63.07; H, 4.69;
N, 6.30. Found: C, 62.57; H, 4.81; N, 6.06.
2,6-Bis((S,S)-1-cyclohexyl-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-
yl)phenylpalladium(II) Chloride (6b): 31% yield; pale yellow solids; mp
20
>290 °C; [R]D = +7° (c 0.060, CH2Cl2). 1H NMR (400 MHz,
(S)-2-(4-Phenyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)-6-((diphen-
ylphosphino)amino)phenylpalladium(II) Chloride (4c): 43% yield;
CDCl3): δ 7.61 (d, J = 8.0 Hz, 2H, Ar H), 7.35ꢀ7.20 (m, 21H, Ar H and
Ph H), 4.90 (d, J = 4.4 Hz, 2H, NCH), 4.75 (d, J = 4.4 Hz, 2H, NCH),
4.34ꢀ4.29 (m, 2H, NCy H), 1.92ꢀ1.74 (m, 6H, Cy H), 1.69ꢀ1.59 (m,
4H, Cy H), 1.53ꢀ1.47 (m, 2H, Cy H), 1.42ꢀ1.25 (m, 4H, Cy H),
1.01ꢀ0.94 (m, 4H, Cy H). 13C NMR (100 MHz, CDCl3): δ 175.7,
170.5, 143.2, 143.0, 134.6, 129.0, 128.5, 128.0, 127.4, 126.4, 126.1, 125.7,
123.0, 74.1, 71.0, 56.2, 33.6, 31.9, 25.7, 25.6, 25.0. IR (KBr): ν 3434,
2929, 2854, 1637, 1568, 1521, 1496, 1433, 1384, 1350, 1267, 1168, 1050,
20
1
yellow solids; mp >290 °C; [R]D = +234° (c 0.041, CH2Cl2). H
NMR (400 MHz, CDCl3): δ 7.91ꢀ7.78 (m, 4H, PPh H), 7.49 (d, J =
7.6 Hz, 2H, Ph H), 7.36ꢀ7.26 (m, 8H, PPh H and NAr H), 7.23ꢀ7.16
(m, 5H, Ph H and NAr H), 6.68ꢀ6.64 (m, 2H, Ar H), 6.05 (d, J = 7.0 Hz,
1H, Ar H), 5.47 (dd, J = 4.2, 10.8 Hz, 1H, NCH), 5.15 (s, 1H, NH), 4.38
(app t, J = 10.4 Hz, 1H, NCHH), 3.96 (dd, J = 4.2, 9.8 Hz, 1H, NCHH),
2.40 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3): δ 170.7 (d, JPꢀC
=
759, 727, 699 cmꢀ1. Anal. Calcd for C48H49ClN4Pd 0.5CH2Cl2
2.7 Hz), 153.2 (d, JPꢀC = 24.2 Hz), 151.5, 142.9, 137.7, 137.5, 134.7, 134.1
(d, JPꢀC = 51.8 Hz), 133.2 (d, JPꢀC = 54.7 Hz), 131.8 (d, JPꢀC = 10.9 Hz),
131.7 (d, JPꢀC = 10.4 Hz), 130.8 (virtual t, JPꢀC = 2.7 Hz), 130.1, 128.44
(d, JPꢀC = 11.1 Hz), 128.42 (d, JPꢀC = 11.3 Hz), 127.2, 126.6, 124.5, 118.0,
112.4 (d, JPꢀC = 18.4 Hz), 64.1 (d, JPꢀC = 3.2 Hz), 63.7 (d, JPꢀC = 2.4 Hz),
21.0. 31P{1H} NMR (162 MHz, CDCl3): δ 91.0. IR (KBr): ν 3427, 3217,
3050, 2922, 1628,1578, 1530, 1437, 1296, 1161, 1104, 1021, 883, 791, 748,
3
(864.27): C, 67.24; H, 5.82; N, 6.47. Found: C, 66.94; H, 5.93; N, 6.22.
General Procedure for the Asymmetric Addition of Di-
phenylphosphine to Enones. Under an N2 atmosphere, a Schlenk
tube equipped with a magnetic stirring bar was charged with the pincer
Pd catalyst 4c (6.5 mg, 5 mol %), KOAc (2.0 mg, 10 mol %), and dry
toluene (2 mL). The reaction mixture was stirred for 30 min at 0 °C.
Then diphenylphosphine (37.2 mg, 0.2 mmol) was added, and stirring
was continued for 30 min. After addition of an electron-deficient
acceptor (1.5 equiv), the resulting mixture was stirred for an additional
12 h at 0 °C and then directly oxidized with H2O2 aqueous solution
(30%, 60 μL). After additional stirring at room temperature for 2 h,
695 cmꢀ1. Anal. Calcd for C34H29ClN3PPd 0.5H2O (661.47): C, 61.74;
3
H, 4.57; N, 6.35. Found: C, 61.79; H, 4.62; N, 6.24.
(S)-2-(4-Isopropyl-1-(p-tolyl)-4,5-dihydro-1H-imidazol-2-yl)-6-(-
(diphenylphosphino)amino)phenylnickel(II) Chloride (5a): 30% yield;
20
dark yellow solids; mp >290 °C; [R]D = +202° (c 0.041, CH2Cl2).
3800
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Organometallics
ARTICLE
saturated Na2S2O3 aqueous solution was added. The organic layer was
separated and the aqueous phase extracted with CH2Cl2. The combined
organic phases were dried (MgSO4), and the volatiles were removed
under reduced pressure. Purification by column chromatography on
silica gel (CH2Cl2/acetone 10/1) provided the phosphine oxides. The
analytical data of the new products are given here, and those of the
known products are shown in the Supporting Information.
Yield: 99%. White solid. Mp: 253ꢀ254 °C. The ee was determined on
a Daicel Chiralpak AD-H column with hexane/2-propanol (70/30) and
flow 1.0 mL/min and detected at a UV wavelength of 228 nm. Retention
times: 17.2 min (major), 56.1 min, 90% ee. [R]D20 = ꢀ165° (c 0.127,
CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 8.02 (d, JHꢀH = 8.6 Hz, 2H),
7.96ꢀ7.92 (m, 2H), 7.60ꢀ7.54 (m, 3H), 7.52ꢀ7.46 (m, 4H),
7.39ꢀ7.36 (m, 1H), 7.30ꢀ7.26 (m, 2H), 4.36 (ddd, JHꢀH = 9.8 and
2.6 Hz, JPꢀH = 6.8 Hz, 1H, PCHCH2), 3.31 (ddd, JHꢀH = 18.4 and 10.2
Hz, JPꢀH = 4.8 Hz, 1H, PCHCHH), 2.92 (ddd, JHꢀH = 18.4 and 2.6 Hz,
JPꢀH = 11.0 Hz, 1H, PCHCHH), 2.09 (d, JHꢀH = 6.9 Hz, 2H, CH2), 1.90
(heptet, JHꢀH = 6.8 Hz, 1H, CH(CH3)2), 0.70 (d, JHꢀH = 6.8 Hz, 3H,
CH3CHCH3), 0.66 (d, JHꢀH = 6.8 Hz, 3H, CH3CHCH3). 13C NMR
(100 MHz, CDCl3): δ 206.8 (d, JPꢀC = 12.0 Hz), 146.8 (d, JPꢀC = 2.6
Hz), 144.1 (d, JPꢀC = 5.3 Hz), 132.14 (d, JPꢀC = 47.9 Hz), 132.06 (d,
JPꢀC = 47.9 Hz), 131.09 (d, JPꢀC = 28.5 Hz), 131.08 (d, JPꢀC = 8.6 Hz),
130.57 (d, JPꢀC = 15.5 Hz), 130.55, 130.1 (d, JPꢀC = 24.7 Hz), 129.1 (d,
JPꢀC = 11.4 Hz), 128.4 (d, JPꢀC = 11.8 Hz), 123.3 (d, JPꢀC = 1.7 Hz),
52.0, 43.2, 40.9 (d, JPꢀC = 66.3 Hz), 24.6, 22.3, 22.1. 31P{1H} NMR
(162 MHz, CDCl3): δ 33.3. IR (KBr): ν 1705 (CdO) cmꢀ1. HRMS
(positive ESI; m/z): [M + Na]+ calcd for C25H26NNaO4P 458.1497,
found 458.1494; [2M + Na]+ calcd for C50H52N2NaO8P2 893.3097,
found 893.3204.
Yield: 94%. White solid. Mp: 256ꢀ257 °C. The ee was determined on
a Daicel Chiralcel OD-H column with hexane/2-propanol (70/30) and
flow 0.6 mL/min and detected at a UV wavelength of 228 nm. Retention
times: 16.4 min (major), 24.1 min, 92% ee. [R]D20 = ꢀ254° (c 0.055,
CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 8.02ꢀ7.97 (m, 4H), 7.82 (d,
JHꢀH = 8.8 Hz, 2H), 7.58ꢀ7.47 (m, 7H), 7.40ꢀ7.36 (m, 1H),
7.31ꢀ7.27 (m, 2H), 6.86 (d, JHꢀH = 8.8 Hz, 2H), 4.57 (ddd, JHꢀH
=
10.6 and 2.0 Hz, JPꢀH = 6.4 Hz, 1H, PCHCH2), 3.99 (ddd, JHꢀH = 18.1
and 10.6 Hz, JPꢀH = 4.1 Hz, 1H, PCHCHH), 3.83 (s, 3H, OCH3), 3.35
(ddd, JHꢀH = 18.1 and 2.0 Hz, JPꢀH = 10.4 Hz, 1H, PCHCHH). 13
C
NMR (100 MHz, CDCl3): δ 194.4 (d, JPꢀC = 13.0 Hz), 163.9, 146.8 (d,
JPꢀC = 2.6 Hz), 144.2 (d, JPꢀC = 5.4 Hz), 132.14 (d, JPꢀC = 49.5 Hz),
132.12 (d, JPꢀC = 49.5 Hz), 131.4, 131.1 (d, JPꢀC = 8.6 Hz), 130.7 (d,
JPꢀC = 5.9 Hz), 130.6 (d, JPꢀC = 2.2 Hz), 130.4 (d, JPꢀC = 13.0 Hz),
130.3 (d, JPꢀC = 34.9 Hz), 129.1 (d, JPꢀC = 11.4 Hz), 129.0, 128.4 (d,
JPꢀC = 11.8 Hz), 123.3 (d, JPꢀC = 1.7 Hz), 113.8, 55.5, 41.4 (d, JPꢀC
=
Yield: 99%. White solid. Mp: 208ꢀ209 °C. The ee was determined on
a Daicel Chiralpak AD-H column with hexane/2-propanol (70/30) and
flow 0.5 mL/min and detected at a UV wavelength of 228 nm. Retention
times: 23.6 min (major), 44.9 min, 85% ee. [R]D20 = ꢀ153° (c 0.111,
CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 8.06 (d, JHꢀH = 2.3 Hz, 1H),
7.99ꢀ7.96 (m, 3H), 7.71 (d, JHꢀH = 7.0 Hz, 1H), 7.62ꢀ7.55 (m, 3H),
7.49ꢀ7.44 (m, 2H), 7.36 (app t, JHꢀH = 8.0 Hz, 2H), 7.29ꢀ7.24 (m,
2H), 4.33 (ddd, JHꢀH = 10.2 and 2.8 Hz, JPꢀH = 7.2 Hz, 1H, PCHCH2),
3.35 (ddd, JHꢀH = 18.6 and 10.2 Hz, JPꢀH = 5.0 Hz, 1H, PCHCHH),
2.99 (ddd, JHꢀH = 18.6 and 2.8 Hz, JPꢀH = 10.7 Hz, 1H, PCHCHH),
2.00 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3): δ 204.6, 147.8, 138.2
(d, JPꢀC = 5.5 Hz), 135.4 (d, JPꢀC = 4.9 Hz), 132.11 (d, JCP = 48.1 Hz),
132.09 (d, JPꢀC = 48.1 Hz), 131.07 (d, JPꢀC = 8.6 Hz), 130.9, 130.6 (d,
JPꢀC = 8.9 Hz), 130.0 (d, JPꢀC = 16.4 Hz), 129.1 (d, JPꢀC = 1.8 Hz),
66.6 Hz), 38.4. 31P{1H} NMR (162 MHz, CDCl3): δ 33.3. IR (KBr): ν
1660 (CdO) cmꢀ1. HRMS (positive ESI; m/z): [M + H]+ calcd for
C28H25NO5P 486.1470, found 486.1531; [M + Na]+ calcd for
C28H24NNaO5P 508.1290, found 508.1294; [M + K]+ calcd for
C28H24KNO5P 524.1029, found 524.1132.
Yield: 81%. White solid. Mp: 225ꢀ226 °C. The ee was determined on
a Daicel Chiralpak AD-H column with hexane/2-propanol (70/30) and
flow 1.0 mL/min and detected at a UV wavelength of 228 nm. Retention
times: 10.7 min (major), 29.6 min, 88% ee. [R]D20 = ꢀ138° (c 0.140,
CH2Cl2). 1H NMR (400 MHz, CDCl3): δ 7.94ꢀ7.89 (m, 2H),
7.59ꢀ7.51 (m, 3H), 7.49ꢀ7.44 (m, 2H), 7.39ꢀ7.35 (m, 1H),
129.0 (d, JPꢀC = 14.4 Hz), 128.3 (d, JPꢀC = 11.8 Hz), 124.7 (d, JPꢀC
=
5.8 Hz), 122.1 (d, JPꢀC = 2.2 Hz), 43.2, 40.1 (d, JPꢀC = 66.8 Hz), 30.3.
31P{1H} NMR (162 MHz, CDCl3): δ 33.5. IR (KBr): ν 1706
(CdO) cmꢀ1. HRMS (positive ESI; m/z): [M + Na]+ calcd for:
C22H20NNaO4P 416.1028, found 416.1024; [M + K]+ calcd for
C22H20KNO4P 432.0767, found 432.0874.
7.30ꢀ7.24 (m, 4H), 7.14 (d, JHꢀH = 8.4 Hz, 2H), 4.19 (ddd, JHꢀH
=
10.0 and 2.8 Hz, JPꢀH = 7.0 Hz, 1H, PCHCH2), 3.28 (ddd, JHꢀH = 18.1
and 10.3 Hz, JPꢀH = 5.0 Hz, 1H, PCHCHH), 2.91 (ddd, JHꢀH = 18.1 and
2.8 Hz, JPꢀH = 10.9 Hz, 1H, PCHCHH), 1.97 (s, 3H, CH3). 13C NMR
(100 MHz, CDCl3): δ 204.9 (d, JPꢀC = 12.7 Hz), 134.0 (d, JPꢀC = 5.8
X-ray Diffraction Studies. Crystals of 4a,c and 5a were obtained
by recrystallization from CH2Cl2/n-hexane and those of 6b 2CHCl3
3
from CHCl3/n-hexane at ambient temperature. The data of 4a,c and
Hz), 133.1 (d, JPꢀC = 2.9 Hz), 132.6 (d, JPꢀC = 2.9 Hz), 132.11 (d, JCP
=
6b 2CHCl3 as well as those of 5a were collected on a Rigaku-IV imaging
3
61.9 Hz), 132.09 (d, JPꢀC = 61.9 Hz), 131.2 (d, JPꢀC = 8.7 Hz), 131.0 (d,
JPꢀC = 5.6 Hz), 130.8 (d, JPꢀC = 9.2 Hz), 129.1(d, JPꢀC = 10.4 Hz),
plate area detector, an Oxford Diffraction Gemini E diffractometer
(for 4c and 6b 2CHCl3) and Bruker SMART APEX-II CCD diffract-
3
128.9 (d, JPꢀC = 12.8 Hz), 128.5 (d, JPꢀC = 1.8 Hz), 128.3 (d, JPꢀC
=
ometer, respectively, with graphite-monochromated Mo KR radiation
11.9 Hz), 43.4, 40.2 (d, JPꢀC = 67.8 Hz), 30.5. 31P{1H} NMR (162
MHz, CDCl3): δ 33.8. IR (KBr): ν 1714 (CdO) cmꢀ1. HRMS
(positive ESI; m/z): [M + Na]+ calcd for C22H20ClNaO2P 405.0787,
found 405.0786.
(λ = 0.710 73 Å). For 6b 2CHCl3, Cu KR radiation (λ = 1.541 84 Å)
3
was used. The structures were solved by direct methods using the
SHELXS-97 program, and all non-hydrogen atoms were refined aniso-
tropically on F2 by the full-matrix least-squares technique, which used
the SHELXL-97 crystallographic software package.26 The hydrogen
atoms were included but not refined. Details of the crystal struc-
ture determination of palladium complexes 4a,c and nickel complex
5a are summarized in Table 5 (those of 6b 2CHCl3 are shown in the
3
Supporting Information).
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Organometallics
ARTICLE
Table 5. Summary of Crystal Structure Determination for Complexes 4a,c and 5a
4a
4c
5a
formula
Mr
C
31H31ClN3PPd
C34H29ClN3PPd
652.42
C31H31ClN3NiP
570.72
618.41
temp (K)
wavelength (Å)
cryst syst
space group
cryst size (mm)
a (Å)
291(2)
293(2)
296(2)
0.710 73
orthorhombic
P212121
0.20 ꢁ 0.17 ꢁ 0.17
11.909(2)
12.573(3)
18.660(4)
90
0.710 73
0.710 73
orthorhombic
P212121
orthorhombic
P212121
0.35 ꢁ 0.20 ꢁ 0.20
11.8793(2)
12.50471(19)
20.1538(4)
90
0.41 ꢁ 0.27 ꢁ 0.23
10.3071(15)
13.747(2)
20.087(3)
90
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
90
90
90
90
90
90
2794.1(10)
4
2993.78(9)
4
2846.3(7)
4
Z
Dcalcd (g cmꢀ3
μ (mmꢀ1
)
1.470
1.447
1.332
)
0.842
0.790
0.856
θ range (deg)
1.95ꢀ25.00
ꢀ13 e h e 13
0 e k e 14
ꢀ22 e l e 22
8899
3.11ꢀ26.37
ꢀ14 e h e 14
ꢀ15 e k e 15
ꢀ25 e l e 25
20205
2.47ꢀ27.50
ꢀ13 e h e 13
ꢀ17 e k e 17
ꢀ26 e l e 25
25364
index range
no. of data collected
no. of unique data
4652
6113
6499
final R indices (I > 2σ(I))
R1
0.0315
0.0786
0.0269
0.0625
0.0345
0.0738
wR2
R indices (all data)
R1
wR2
0.0339
0.0336
0.0547
0.0798
0.0660
0.0826
F(000)
1264
1328
1192
peak/hole (e Åꢀ3
)
0.309/ꢀ0.558
0.374/ꢀ0.243
0.268/ꢀ0.221
’ ASSOCIATED CONTENT
’ REFERENCES
(1) For selected reviews on pincer complexes, see: (a) Albrecht, M.;
van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. (b) Singleton, J. T.
Tetrahedron 2003, 59, 1837. (c) van der Boom, M. E.; Milstein, D. Chem.
Rev. 2003, 103, 1759. (d) Dupont, J.; Consorti, C. S.; Spencer, J. Chem.
Rev. 2005, 105, 2527. (e) Szabꢀo, K. J. Synlett 2006, 6, 811. (f) The
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S
Supporting Information. Figures, text, and tables giving
b
the molecular structure and crystallographic data for the chiral
bis(imidazoline) NCN pincer Pd complex 6b 2CHCl3, 1H
3
NMR and 13C NMR spectra of all the new compounds 1ꢀ6,
characterization data of the known asymmetric phosphine addi-
tion products, and H or/and 13C NMR spectra of all the
1
asymmetric phosphine addition products as well as their chiral
HPLC spectra and CIF files for the four pincer complexes
including 4a,c, 5a, and 6b 2CHCl3. This material is available
free of charge via the Internet at http://pubs.acs.org.
3
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’ AUTHOR INFORMATION
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Corresponding Author
*Tel.: +86 371 67763869. E-mail: mpsong@zzu.edu.cn (M.-P.S.);
gongjf@zzu.edu.cn (J.-F.G.).
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’ ACKNOWLEDGMENT
We are grateful to the National Natural Science Foundation of
China (Nos. 20872133 and 20972141) for financial support of
this work.
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