New complexes of palladium(II) with chelating heterocyclic nitrogen ligands.: Characterization and catalytic activity in CO–styrene copolymerization. Crystal structure of [Pd(bipy)2][BAr′4]2, Ar′=[3,5-(CF3)2C6H3]

New bis-chelated palladium(II) derivatives [Pd(bipyR)2]2+ and [Pd(bipy)(bipyR)]2+ (bipy=2,2′-bypiridine, bipyR=6-Me, 6-Et, 6-i-Pr-2,2′-bipyridine) have been isolated as [BAr′4]− salts (Ar′=[3,5-(CF3)2C6H3]) and tested as catalyst precursors in the CO–styrene or 4-tert-butylstyrene (TBS) copolymerization. The comparison of their activity with that of [Pd(bipy)2][BAr′4]2 prepared for comparative purpose shows that the presence of a 6-substituent on the bipy has a negative effect. On the other hand, comparison of the activities of [Pd(bipy)2][BAr′4]2 and [Pd(bipy)2][PF6]2, reported to be one of the best catalytic precursors for this reaction, shows that the [BAr′4]− anion increases the activity under various reaction conditions. The results obtained with [Pd(bipy)2][BAr′4]2 at low pressure (pCO=10 atm) are among the best reported for this type of precatalysts. A study related to the use of 2,2,2-trifluoroethanol (TFE), as solvent, allows the optimisation of the amount of alcohol required for the copolymerization reaction. The X-ray structure of [Pd(bipy)2][BAr′4]2 shows that the conformation of the cation is similar to that observed in the corresponding [BF4]− salt, but remarkably different from that of [Pd(bipy)2][PF6]2.