L. Wang et al. / Journal of Molecular Catalysis A: Chemical 196 (2003) 171–178
173
2.2. Spectroscopic measurements
oil prior to transfer to a cold nitrogen gas stream
on a Bruker CCD area-detector diffractomer system
equipped with Mo K␣ radiation (λ = 0.71073 Å).
Data were collected with narrow (Rint = 0.0534)
frame exposures. Intensities were corrected empiri-
cally for absorption, based on SADABS (Sheldrick,
1996) program, Tmin = 0.8982, Tmax = 0.9174, and
18,879 measured reflections. The structure were re-
fined on F2 values for all unique data. All H atoms
were obtained by geometrical analysis with 1740
Friedel pairs, and Flack parameter = 0.01 (10). Pro-
grams used were SHELXS97 (Sheldrick, 1997) and
SHELXTL-NT for structure solution, refinement, and
molecular graphics.
Other spectral data for [{(R)-1}Pd(H2O)2](OTf)2
(7): MS (5.68 × 104 eV) m/e (int (%)): 785 (12); 787
(10) [M−(2xOTf)]+; 861 (29); 862 (68); 863 (100);
865 (65); 867 (33); 868 (13). 1H NMR (CDCl3,
500 MHz): δ 3.57 (s, 6H, OCH3), 3.73 (d, 6H, OCH3),
6.19 (d, 2H, PyH), 7.41–7.92 (m, 20H, PhH). 31P
NMR (CDCl3, 202 MHz): δ 30.62.
31P and 1H NMR spectra were recorded on a Varian
AS500 spectrometer. Low-resolution mass spectrom-
etry was performed using a Finnigan MAT 95S model
spectrometer. GC analyses were performed on an HP
5890 apparatus equipped with FID.
2.3. Synthesis of P-Phos palladium complexes
The catalyst precursors [{(R)-1}Pd(H2O)2](OTf)2
(7), [{(R)-2}Pd(H2O)2](OTf)2 (8) and [{(R)-3}Pd-
(H2O)2](OTf)2 (9) were prepared by adopting a lit-
erature procedure [18,19]. The preparation of 7 is
described in detail as follows.
2.3.1. Synthesis of [{(R)-1}Pd(H2O)2](OTf)2
A solution of PdCl2(NCPh)2 (0.49 g, 1.29 mmol)
in toluene (50 ml) was heated to 70 ◦C. To this
reddish-brown solution was added (R)-2,2ꢀ,6,6ꢀ-tetra-
methoxy-4,4ꢀ-bis(diphenylphosphine)-3,3ꢀ-bipyridine
(P-Phos) (0.85 g, 1.32 mmol) in toluene (25 ml) drop-
wise. The solution became brighter, and a red pre-
cipitate was formed. The suspension was held for
another 2.5 h at this temperature followed by cooling
to room temperature. Addition of pentane (50 ml) in-
duced more precipitation. The complex was filtered,
washed with diethyl ether and dried under reduced
pressure. Another crop of crystals was obtained from
the mother solution by cooling at 4 ◦C overnight.
Without further purification, the combined crystals
(0.50 g, 0.62 mmol) were dissolved in tetrahydrofuran
(THF) (60 ml) and were treated with a solution of
silver trifluoromethane sulfonate (0.32 g, 1.23 mmol)
in THF (20 ml) in the exclusion of light. The reaction
mixture was stirred for 2 h at room temperature. The
precipitated AgCl was filtered off and was washed
twice with THF (5 ml). The filtrate was concentrated
to a total volume of 10 ml under reduced pressure.
Pentane was added to initiate crystallization which
was completed after 24 h at 4 ◦C. The red precipitate
was filtered and dried under reduced pressure. The
crude product was recrystallized from CH2Cl2/hexane
to give 7 in 80% yield (0.54 g, 0.50 mmol).
2.3.2. [{(R)-2}Pd(H2O)2](OTf)2 (8)
Complex 8 was prepared using a procedure similar
to 2.3.1: MS (4.95 × 104 eV) m/e (int (%)): 841 (15);
826 (40); 825 (77); 824 (100) [M−(2xOTf)-H2O]+;
807 (43); 806 (37); 205 (81); 203 (67). 1H NMR
(CDCl3, 500 MHz): δ 2.40 (d, 12H, JH,P = 15 Hz,
PhCH3), 3.57 (s, 6H, OCH3), 3.71 (s, 6H, OCH3), 6.15
(d, 2H, PyH), 7.25–7.64 (m, 12H, PhH). 31P NMR
(CDCl3, 202 MHz): δ 30.57.
2.3.3. [{(R)-3}Pd(H2O)2](OTf)2 (9)
Complex 9 was prepared using a procedure similar
to 2.3.1: MS (2.52 × 104 eV) m/e (int (%)): 899 (23)
[M−(2xOTf)]+; 897 (26); 896 (16); 205 (57); 203
(62); 183 (99); 181 (100); 137 (51) 1H NMR (CDCl3,
500 MHz): δ 2.34 (d, 12H, JH,P = 10 Hz, PhCH3),
3.61 (s, 6H, OCH3), 3.76 (s, 6H, OCH3), 6.23 (d, 2H,
PyH), 7.18–7.25 (m, 12H, PhH). 31P NMR (CDCl3,
202 MHz): δ 32.22.
2.4. General procedures for the asymmetric
bis-alkoxycarbonylation of styrene
Suitable single crystals for X-ray diffraction study
were obtained by vapor diffusion of n-hexane into
a THF solution of [{(R)-1}Pd(H2O)2](OTf)2 (7) at
room temperature. Crystals were coated in an inert
A 50 ml stainless steel autoclave was charged with
benzoquinone, the catalyst precursor, styrene, and
methanol under an atmosphere of N2. The autoclave