NEW ATROPISOMERIC BIDENTATE NITROGEN-DONOR COMPOUNDS AS POTENTIAL STEREOCONTROLLERS IN MILD CO-STYRENE COPOLYMERIZATION CATALYZED BY PALLADIUM(II) SALTS

Two new atropisomeric bidentate nitrogen-donor chelating ligands, name ly )-3,3'-(1,2-dimethylethylenedioxy)-2,2'-bipyridine L(1) and )-(R)-3 ,3'-(1-methylethylenedioxy)-2,2'-bipyridine L(2), have been synthesise d and characterised. The crystal structure of L(2) confirmed its atrop isomeric nature, the dihedral angle between the planes containing the pyridine rings being 50.1(1)degrees. The interaction of the new compou nds, with palladium(II) salts led to the corresponding monochelated pa lladium complexes, [PdL(1)(O2CCF3)(2)] 1 and [PdL(2)(O2CCF3)(2)] 2, th e crystal structures of which have been determined. Both complexes cry stallised with two independent molecules in the unit cell. In the two molecules of 1 the ligand L(1) is in the same conformation while fdr 2 the two independent molecules correspond to two different atropisomer s. The co-ordination geometry around palladium is square planar in all the molecules. In the two independent molecules of 1 and 2 the dihedr al angle between the pyridine ring is considerably smaller than that o bserved in free L(2). The complexes are very active catalyst precursor s in CO-styrene copolymerisation under mild reaction conditio;ns (P-co = 1 atm, 30 degrees C). The inhibiting role of carbon monoxide is evi denced. A low asymmetric induction was observed together with short is otactic sequences in the copolymer chain.