Synthesis, structure and reactivity of novel palladiumdichloride-2,2′-bipyridine with 4,4′-bis(fluorous-ponytail)

With the readily available fluorous alkanols RfCH2OH, a series of novel fluorous-ponytailed bpy ligands, 4,4′-bis(RfCH2OCH2)-2,2′-bpy (1a–e), were prepared and treated with [PdCl2(CH3CN)2] to result in the corresponding novel Pd complexes [PdCl2(4,4′-bis(RfCH2OCH2)-2,2′-bpy)] (2a–e) where Rf = n-C3F7 (a), HCF2(CF2)3 (b), HCF2(CF2)7 (c), n-C8F17 (d), n-C10F21 (e). The new ligands and Pd complexes were spectroscopically characterized by multi-nuclei NMR (1H, 19F and 13C), FTIR and high resolution mass (FAB). The structure for the Pd complex 2b, the first with fluorinated ponytails on bpy and not on phosphine, was also established by a single crystal X-ray diffraction study. The TGA data of both ligands and Pd complexes indicated that the Pd-complexes were resistant to higher temperatures than the corresponding ligands. The Pd catalysts derived from 2a–c showed an almost quantitative conversion and could be reused for eight runs with Heck reactions, in that the products and unspent reactants were directly removed by distillation. With the highest fluorine content in the series, Pd complex 2e was successfully applied in the Heck reaction using the fluorous biphasic catalysis strategy.

Graphical abstractThe TGA curves of fluorous-ponytailed 4,4′-bis(RfCH2OCH2)-2,2′-bpy 1a–e and the corresponding Pd complexes [PdCl2(4,4′-bis(RfCH2OCH2)-2,2′-bpy)] 2a–e, where Rf = n-C3F7 (a), HCF2(CF2)3 (b), HCF2(CF2)7 (c), n-C8F17 (d), n-C10F21 (e), indicated that the Pd complexes are thermally more stable than the corresponding ligands. With the highest fluorine content in the series, Pd complex 2e was successfully applied in the Heck reaction, using the fluorous biphasic catalysis strategy.Figure optionsDownload full-size imageDownload as PowerPoint slide