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

Two sets of mono- and dicationic palladium complexes (8) and (10), having CF3SO3-, BF4- and PF6- as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH3)(NCCH3)](X) (8) in solution, was investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and (H-1, F-19)-HOESY NMR spectroscopy. A high degree of ion-pairing was found in each complex. The HOESY spectra showed that the BF4- and PF6- 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. (c) 2005 Elsevier B.V. All rights reserved.