Polypyrrole-Supported Graphite Felt for Acetylene Coupling Reaction in Solid Phase

Abstract

Substrate immobilization on graphite felt for solid-phase acetylene coupling reaction was achieved by electrochemical polymerization of the substrate precursor containing a pyrrole side chain, where the amount of substrate on the electrode surface was easily controlled by the number of repeated cyclic voltammetric scannings. Couplings between terminal acetylenes and the iodobenzene-modified graphite felt electrode or aromatic iodides and the terminal acetylene-modified graphite felt electrode in the presence of palladium catalyst proceeded smoothly in satisfactory yields.

Sonogashira reaction - solid-phase synthesis - poly­pyrrole - electrochemical polymerization - modified electrode

References

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General Procedure for Electrochemical Polymerization.
Electrochemical polymerization was performed in a one-compartment cell with graphite felt (3.0 × 1.0 × 0.5 cm) as the working electrode and a platinum wire as the counter electrode, respectively. An Ag/AgCl electrode was used as the reference electrode. All electrochemical polymerization experiments were performed in MeCN solution with 0.01 M monomer concentration and 0.1 M tetraethylammonium perchlorate as the supporting electrolyte. Repeated cyclic voltammetric scans between 0 and +1.5 V at 50 mV/s led to the formation of a conducting polymer film at the GF electrode.

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General Procedure for Sonogashira Reaction on the Iodobenzene-Modified GF Electrode.
The iodobenzene-modified GF electrode (3.0 × 1.0 × 0.5 cm) was added to the dry DMF solution (10 mL) containing Et₃N (10 mmol), terminal acetylene (5 mmol), Pd(PPh₃)₄ (0.25 mmol) and CuI (0.5 mmol). The reaction mixture was stirred for 12 h at r.t. At the end of the reaction, the GF electrode was separated, and washed three times with THF. Then, this GF electrode was added to THF (10 mL) and 28% NaOMe in MeOH (5 mL). The reaction mixture was stirred for 1 h at r.t. At the end of the reaction, this reaction mixture was added to H₂O (10 mL) and 3 N HCl (10 mL), extracted three times with EtOAc (10 mL × 3), and filtered in vacuo. This extracted solution was evaporated, and the product was identified by ¹H NMR spectroscopy.