Palladium complexes with meso-bioxazoline ligands for alternating styrene/CO copolymerisation: Counterion effect

Abstract

Two sets of mono- and dicationic palladium complexes ( 8) and ( 10), having CF 3 SO 3 - , BF 4 - and PF 6 - as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd(( R, S)-Bn-Box)(CH 3)(NCCH 3)](X) ( 8) in solution, was investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and ( 1H, 19F)-HOESY NMR spectroscopy. A high degree of ion-pairing was found in each complex. The HOESY spectra showed that the BF 4 - and PF 6 - anions take up selective positions, on the side of the complex remote from the benzyl groups, but close to the acetonitrile ligand, while the triflate is, partially, occupying a pseudo fifth coordination position on the side of the cation remote from the two benzyl-groups. The complexes 8 and 10 were used as catalyst precursors for the copolymerisation of styrene with carbon monoxide, producing syndiotactic copolymers, with the exception of complex 10a, that led to isotactic copolymers.