New complexes of palladium(II) with chelating heterocyclic nitrogen ligands. Characterization and catalytic activity in CO-styrene copolimerization. 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.