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