New bis(fluoro-ponytailed) bipyridine ligands for Pd-catalyzed Heck reactions under fluorous biphasic catalysis condition

Abstract

Three highly fluorinated bipyridine derivatives (4,4′-bis(R fCH 2OCH 2)-2,2′-bpy) {R f=HCF 2(CF 2) 7 ( 1a), n-C 8F 17 ( 1b), n-C 10F 21 ( 1c)} have been synthesized using 4,4′-bis(BrCH 2)-2,2′-bpy and the corresponding fluorinated alkoxides. The fluorine contents of ligands 1a– c are 58.3, 59.8, and 62.3%, respectively. Despite its high fluorine content, the ligand 1a with a –CF 2H polar terminal group is more soluble in organic solvents. The ligand 1b is a white solid and is still moderately soluble in CH 2Cl 2. The ligand 1c has a high fluorophilicity, the partition ratio being 42:1 for the n-C 8F 18/CH 2Cl 2 system. The reaction of ligands 1a– c with [PdCl 2(CH 3CN) 2] results in the novel Pd complexes [PdCl 2(4,4′-bis-(R fCH 2OCH 2)-2,2′-bpy)] where R f=HCF 2(CF 2) 7 ( 2a), n-C 8F 17 ( 2b), n-C 10F 21 ( 2c), respectively. The Pd complex 2b is a pale yellow solid, and has been tested unsatisfactorily for FBC. Insoluble in organic solvents, the Pd complex 2c dissolves only in fluorinated solvents, for instance FC77, which is mainly n-C 8F 18. The novel Pd complex 2c has been tested as a catalyst in Heck reactions under a fluorous biphasic catalysis condition. It was found that the Pd complex 2c, after an easy separation, keeps its catalytic activity (>90% yield), even after seven runs. The TGA studies indicate that the Pd complexes 2a– c are stable up to 330 °C.