Copolymerization of Carbon Monoxide with Ethene Catalyzed by Bis-chelated Palladium(II) Complexes Containing Diphosphine and Dinitrogen Ligands

Several bis-chelated palladium(II) complexes, [Pd(P-P)(N-N)x](PF containing binary combinations of 6)2 , diphosphine and dinitrogen ligands have been prepared and characterized. The diphosphine ligands comprise 1,3- bis(diphenylphosphino)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)](PF has been determined by an X-ray structural analysis. All the Pd(II) 6)2 ÉCH2Cl2 complexes have been tested as catalyst precursors for the copolymerization of carbon monoxide and ethene in methanol 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 bestcatalytic performance. The di erent catalytic activities exhibited by the stereoisomers [Pd(meso-bdpp)(N,N@-bipy)]-(PF and [Pd(rac-bdpp)(N,N@-bipy)] has been interpreted in terms of the di erent spatial distribution of the 6)2 (PF6)2 phenyl rings around the metal center determined by the conformation of the six-membered metallaring.