A. Lei, Z. Yang et al.
4H), 1.86–1.74 (m, 2H), 3.36–3.28 (m, 2H), 3.92–3.79 (m, 2H), 7.81 (t,
J=6.9 Hz, 1H), 8.05 (d, J=7.2 Hz, 1H), 8.12 ppm (d, J=7.2 Hz, 1H);
13C NMR (300 MHz, CDCl3, 258C, TMS): d=13.96, 20.82, 32.13, 32.21,
52.51, 54.80, 124.82, 125.55, 136.96, 157.35, 157.80, 160.88, 167.74 ppm;
HRMS (MALDI/DHB): m/z calcd for C60H85N12S8Pd4 [M+H]+:
1653.0925; found: 1653.0920.
Mechanistic pathways were proposed on the basis of pre-
liminary results. Further detailed mechanistic studies are un-
derway in and will be reported in due course.
Ethyl 2-butylbenzoate (6n): Zinc chloride (6 mmol) was added to a
Schlenk tube in glove box, which was sealed with a rubber septum and
transferred out. After THF (3 mL) was injected into the tube, the reac-
tion mixture was cooled to 08C and n-butylmagnesium bromide
(6 mmol) was added dropwise. Then the mixture was stirred for 1 h at
258C, and Pd complex 3 (1.3 mg, 0.003 mmol) and ethyl 2-iodobenzoate
(828.2 mg, 3 mmol) were added. The resultant mixture was stirred for an-
other 2 h at 258C. The suspension generated was quenched with dilute
hydrochloric acid (5 mL, 2m) and extracted with ethyl acetate. The com-
bined extracts were washed with aqueous NaHCO3 solution and Na2S2O3
solution, dried over anhydrous Na2SO4, and subjected to silica-gel chro-
matography to give pure 6n was (519.8 mg, 84% yield). 1H NMR
(300 MHz, CDCl3, 258C, TMS): d=7.75 (d, J=7.8 Hz, 1H), 7.29 (t, J=
7.5 Hz, 1H), 7.15–7.10 (m, 2H), 4.26 (q, J=7.2 Hz, 2H), 2.85 (t, J=
7.5 Hz, 2H), 1.54–1.44 (m, 2H), 1.34–1.27 (m, 5H), 0.84 ppm (t, J=
7.2 Hz, 3H); 13C NMR (75.4 MHz, CDCl3, 258C, TMS): d=13.83, 14.11,
22.65, 33.88, 34.05, 60.57, 125.45, 129.78, 130.29, 130.70, 131.44, 144.25,
167.76 ppm; HRMS: m/z calcd for C13H18O2 [M]+: 206.1307; found:
206.1310.
Experimental Section
All manipulations were carried out under an inert atmosphere by using
an argon-filled glove box or standard Schlenk techniques. All glassware
was oven-dried at 1208C for more than 1 h prior to use. Dichloromethane
was dried and distilled from calcium hydride. Tetrahydrofuran was dried
and distilled from sodium/benzophenone immediately prior to use under
nitrogen atmosphere. CH3CN was distilled from P2O5 and degassed by
purging with nitrogen for more than 45 min. DMF was obtained from
commercial sources and dried with molecular sieves (4 ꢂ). 1H and
13C NMR spectra were recorded on a Varian Mercury 300 MHz NMR
spectrometer. High-resolution mass spectra (HRMS) were measured with
a Waters Micromass GCT instrument and accurate masses are reported
for the molecular ion [M+]. GC yields were recorded with a Varian GC
3900 gas chromatography instrument with an FID detector. For the
ReactACHTUNGTRENNUNGIR kinetic experiments, the reaction spectra were recorded on an
IC 10 from Mettler-Toledo AutoChem fitted with a diamond-tipped
probe. Data manipulation was carried out with the iC IR software, ver-
sion 1.05. Crystal diffraction intensity data were collected on a Bruker
CCD 4K diffractometer with graphite-monochromatized MoKa radiation
(l=0.71073 ꢂ). Lattice determination and data collection were carried
out with SMART version 5.625 software. Data reduction and absorption
corrections were performed with SAINT version 6.45 and SADABS ver-
sion 2.03. Structure solution and refinement were performed with the
SHELXTL version 6.14 software package.
Synthesis of pincer ligand 1: A mixture of N2,N6-dibutylpyridine-2,6-di-
carboxamide[65] (15.27 g, 55 mmol) and Lawessonꢃs reagent (22.25 g,
55 mmol) was heated at 1008C in toluene for 4 h. The insoluble product
was filtered while hot. The solution was evaporated to dryness and puri-
fied by column chromatography (neutral alumina, 20% ethyl acetate in
petroleum ether). The product 1 was isolated as a yellow microcrystalline
solid (yield: 14.73 g; 87%). 1H NMR (300 MHz, 258C, [D6]DMSO): d=
0.91 (t, J=7.2 Hz, 6H), 1.43–1.31 (m, 4H), 1.75–1.65 (m, 4H), 3.88–3.81
(m, 4H), 8.09 (t, J=7.8 Hz, 1H), 8.66 (d, J=7.8 Hz, 2H), 11.05 ppm (br,
2H); 13C NMR (75.4 MHz, 258C, [D6]DMSO): d=13.87, 19.98, 29.47,
45.24, 127.00, 138.54, 149.73, 189.51 ppm; HRMS: m/z calcd for
C15H23N3S2 [M]+: 309.1333; found: 309.1343.
Acknowledgements
This work was support by National Natural Science Foundation of China
(20772093, 2050202003), the Excellent Youth Foundation of Hubei Scien-
tific Committee, Specialized Research Fund for the Doctoral Program of
Higher Education (20060486005), and
AHCTUNGTRENNGUUN niversity.
a startup fund from Wuhan
[1] Handb. Organopalladium Chem. for Org. Synth. (Ed.: E.-i. Negishi),
Wiley, New York, 2002, Chapter 1, pp. 229.
[4] T. Hayashi, M. Konishi, Y. Kobori, M. Kumada, T. Higuchi, K. Hir-
[6] D. J. Cꢄrdenas, Angew. Chem. 2003, 115, 398–401; Angew. Chem.
Int. Ed. 2003, 42, 384–387.
[7] G. Altenhoff, R. Goddard, C. W. Lehmann, F. Glorius, Angew.
[15] N. Hadei, E. A. B. Kantchev, C. J. OꢃBrien, M. G. Organ, Org. Lett.
Synthesis of Pd complex 2: A solution of ligand 1 (3.09 g, 10 mmol) in
CH3CN (30 mL) was added to a refluxing solution of [PdCl2ACHTNURGTNEUNG(MeCN)2]
(2.59 g, 10 mmol) in CH3CN (100 mL) under N2. An orange solid precipi-
tated immediately. The reaction mixture was stirred for 3 h under reflux.
Then mixture was cooled to room temperature, filtered, and the residue
washed with diethyl ether and dried for 2 h under vacuum to afford Pd
complex 2 (yield: 4.67 g, 93%). 1H NMR (300 MHz, 258C, [D6]DMSO):
d=0.95 (t, J=7.2 Hz, 6H), 1.50–1.37 (m, 4H), 1.83–1.73 (m, 4H), 3.78 (t,
J=6.9 Hz, 4H), 8.56 (t, J=7.8 Hz, 1H), 8.80–8.78 ppm (m, 2H);
13C NMR (75.4 MHz, 258C, [D6]DMSO): d=13.78, 20.03, 29.03, 48.23,
127.45, 140.36, 156.01, 187.81 ppm; HRMS: m/z calcd for C15H22N3S2ClPd
[MÀCl]+: 450.0057; found: 450.0064.
Synthesis of Pd complex 3: Dry THF (12 mL) and cyclohexyl zinc chlo-
ride (0.9m in THF, 1.1 mL) were added to Pd complex 2 (225.2 mg,
0.46 mmol) under N2 (50 mL), and the resulting red suspension was
stirred at room temperature overnight, till the reaction mixture became a
clear solution. Then 10 mL of water was added, and volatile substances
were removed on a rotary evaporator. The remaining mixture was ex-
tracted with CH2Cl2 (3ꢁ15 mL), and the organic phases were combined
and dried over Na2SO4. After filtration, the filtrate was concentrated till
solid appeared. On addition of hexane (20 mL), a reddish orange solid
precipitated, which was collected by filtration, washed with hexane, and
dried under vacuum for 2 h to afford 3 as a reddish orange solid (yield:
180 mg, 94%). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=0.87 (t, J=
7.4 Hz, 3H), 0.98 (t, J=7.4 Hz, 3H), 1.37–1.25 (m, 2H), 1.63–1.47 (m.
[16] N. Hadei, E. A. B. Kantchev, C. J. OꢃBrien, M. G. Organ, J. Org.
1506
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 1499 – 1507