SUMMARY: A new class of highly effective homogeneous palladium bis(methoxycarbonyl) complexes Pd(L1L)(COOMe) 2 , where (L1L) are substituted phenanthroline ligands, has been developed for the production of syndiotactic alternating styrene-carbon monoxide copolymers. The essential feature of this novel catalytic system is that it is formed by palladium complex, Pd(L1L)(COOMe) 2 , an acid cocatalyst, (L1L)HPF 6 , bearing a weakly coordinating counter anion, and an oxidant, such as 1,4-naphthoquinone (1,4-NQ). The palladium/acid cocatalyst molar ratio has been explored. A maximum of copolymerization activity was obtained at 1/1 molar ratio. For a series of palladium catalysts, Pd(phen)(COOMe) 2 appeared to be the most active one. The effect of substituents at the ligand in Pd(L1L)(COOMe) 2 on the copolymerization activity was studied. The tacticity of alternating copolymers obtained with different Pd(L1L)(COOMe) 2 catalysts was determined by NMR spectroscopy. The copolymers were thermally characterised by TGA and DSC.

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Reaction of [Pd(phen)(CO2CH3)2] (1) with phenanthrolinium hexafluorophosphate (2) gives in high yield the unprecedented pentacoordinate palladium complex [Pd(phen)2(COOMe)](PF6) (3) in which Pd displays a strongly distorted square pyramidal coordination. The reactivity of 3 toward bases was explored too.