Copolymerization of carbon monoxide with ethene catalyzed by bis-chelated palladium(II) complexes containing diphosphine and dinitrogen ligands

Several bis-chelated palladiumn(II) complexes, [Pd(P-P)(N-N)(x)](PF6)(2), containing binary combinations of diphosphine and dinitrogen ligands have been prepared and characterized. The diphosphine ligands comprise 1,3-bis(diphenylphasphino)propane (dppp), meso-2,4-bis(diphenylphosphino)pentane (meso-bdpp), rac-2,4-bis(diphenylphosphino)pentane (rac-bdpp) and 2,2'-bis(diphenylphosphinoethyl)pentane (Etdppp), while the dinitrogen ligands are either 2,2'-bipyridine (bipy; x = 1) or 1,8-naphthyridine (napy; x = 2). The structure of [Pd(meso-bdpp)(N,N'-bipy)](PF6)(2). CH2Cl2 has been determined by an X-ray structural analysis. All the Pd(II) complexes have been tested as catalyst precursors for the copolymerization of car;bon monoxide and ethene in methanal solution in either autoclaves or high-pressure sapphire :NMR tubes. The combination of meso-bdpp and bipy at palladium, in conjuction with both 1,4-benzoquinone and p-toluenesulfonic acid, has shown the best catalytic performance. The different catalytic activities exhibited by the stereoisomers [Pd(meso-bdpp)(N,N'-bipy)](PF6)(2) and [Pd(rac-bdpp)(N,N'-bipy)](PF6)(2) has been interpreted in terms of the different spatial distribution of the phenyl rings around the metal center determined by the conformation of the six-membered metallaring.