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-(CF 3) 2C 6H 3

Abstract

New bis-chelated palladium(II) derivatives [Pd(bipy R) 2] 2+ and [Pd(bipy)(bipy R)] 2+ (bipy=2,2′-bypiridine, bipy R=6-Me, 6-Et, 6- i-Pr-2,2′-bipyridine) have been isolated as [BAr′ 4] − salts (Ar′=[3,5-(CF 3) 2C 6H 3]) 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][PF 6] 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 ( p CO=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 [BF 4] − salt, but remarkably different from that of [Pd(bipy) 2][PF 6] 2.