The First Example of Polymer-Supported Palladium Catalyst for Stereo­selective S-S Bond Addition to Terminal Alkynes

Abstract

The polymer-supported recyclable palladium catalyst was prepared for stereoselective diaryl disulphides addition to ­terminal alkynes with high yields. The 96-98% product purity was achieved after filtering the polymer-supported catalyst without ­special purification procedure.

Key words

palladium complexes - polymer-supported - catalysis - vinyl sulphides

References

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The triphenylphosphine resin 100-200 mesh, 1% DVB, 1-1.5 mmol/g was used as a polymeric ligand (ACROS organics, catalog No 35833).

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Catalyst Preparation. The Ar₂S₂ (0.2 mmol), PPh₃ resin (0.069 mmol, 1.25 mmol PPh₃/g, 0.055 g), Pd₂dba₃ (3.4 × 10^-3 mmol, 3 mg), and 0.5 mL of degassed toluene were stirred at 140 °C for 30 min in a sealed tube. The mixture was cooled to the r.t., polymer-supported catalyst was filtered and washed thrice with 2 mL of degassed toluene (all manipulations were performed under argon). The formation of polymer-supported palladium catalyst is accompanied with releasing free dba ligand (confirmed by NMR). Washing with toluene removes dba from the catalyst. The presence of Ar₂S₂ on the catalyst preparation stage is important, since oxidative addition of Ar₂S₂ converts Pd(0) to Pd(II), which is more stable and easier to handle.

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General Synthetic Procedure.
The Ar₂S₂ (0.3 mmol), the alkyne (0.45 mmol) and 1 mL of degassed toluene were combined with the polymer-supported catalyst and the mixture was stirred at 140 °C for 2 h in a sealed tube. The solution was separated and the polymer-supported catalyst was washed twice with 2 mL of degassed toluene. Combined organic solution was evaporated and dried under reduced pressure. The 2A-2H products (96-98% purity) were obtained as yellow oil. Unreacted alkyne was removed with a solvent upon evaporation. Otherwise (for 2I and 2J) flash chromato-graphy was needed to separate unreacted alkynes. The products 2A-2G were identified according to the published NMR data (see ref. 3,5). The data for the 2-H, 2-I and 2-J is given below.
Z-CH(SPh)=C(SPh)-CH₂CH₂CH₂CN (2-H): yellow oil. ¹H NMR (500 MHz, CDCl₃): δ = 1.78-1.85 (m, 2 H, CH₂), 2.27 (t, 2 H, CH₂), 2.40 (t, 2 H, CH₂), 6.68 (s, 1 H, HC=), 7.20-7.38 (m, 8 H, Ph), 7.40-7.45 (m, 2 H, Ph) ppm. ¹³C{¹H} NMR (126 MHz, CDCl₃): δ = 15.9, 23.9, 35.2, 119.1 (CN), 127.1, 127.2, 129.1, 129.2, 130.0, 130.2, 130.5, 132.4 (HC=), 132.9, 135.0 ppm. MS (EI): m/e (%) = 311 (60) [M⁺]. Anal. Calcd for C₁₈H₁₇NS₂: C, 69.41; H, 5.50; N, 4.50. Found: C, 69.35; H, 5.80; N, 4.40.
Z-HC(SPh)=C(SPh)-CH₂SPh (2-I): yellow oil. ¹H NMR (500 MHz, CDCl₃): δ = 3.65 (s, 2 H, CH₂), 6.70 (s, 1 H, HC=), 7.13-7.17 (m, 2 H, Ph), 7.20-7.33 (m, 11 H, Ph), 7.35-7.39 (m, 2 H, Ph) ppm. ¹³C{¹H} NMR (126 MHz, CDCl₃): δ = 41.3 (CH₂), 126.8, 127.0, 127.1, 127.4, 128.9, 129.0, 129.1, 129.8, 130.7, 131.1, 133.1, 134.1 (HC=), 135.0, 135.1 ppm. MS (EI): m/e (%) = 366 (20) [M⁺]. Anal. Calcd for C₂₁H₁₈S₃: C, 68.81; H, 4.95; S, 26.24. Found: C, 68.90; H, 5.00; S, 26.50.
Z-HC(SPh)=C(SPh)-CH₂SePh (2-J): yellow oil. ¹H NMR (500 MHz, CDCl₃): δ = 3.68 (s, 2 H, CH₂), 6.48 (s, 1 H, HC=), 7.13-7.17 (m, 2 H, Ph), 7.20-7.35 (m, 9 H, Ph), 7.38-7.42 (m, 2 H, Ph), 7.48-7.52 (m, 2 H, Ph) ppm. ¹³C{¹H} NMR (126 MHz, CDCl₃): δ = 35.2 (CH₂), 127.0, 127.1, 127.7, 128.6, 128.9, 129.0, 129.1, 129.6, 129.9, 130.6, 133.2, 133.3, 134.6, 135.0 ppm. MS (EI): m/e (%) = 414 (70) [M⁺]. Anal. Calcd for C₂₁H₁₈S₂Se: C, 61.00; H, 4.39; S, 15.51; Se, 19.10. Found: C, 60.81; H, 4.33; S, 15.56; Se, 19.10.

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Catalyst Recycling. After washing with toluene (see general synthetic procedure [12] ) the polymer-supported catalyst can be used in further reactions without additional treatment. When recycling, all manipulations with the catalyst should be performed under argon.