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Two pairs of enantiomerically pure chiral bidentate nitrogen-donor ligands (N*-N) featuring one sp(3) and one sp(2) nitrogen atom have been applied to the CO/vinyl arene copolymerization reaction catalyzed by the corresponding monocationic palladium(11) complexes [Pd(CH3)(CH3CN)-(N*-N)][PF6]. The ligand frame containing the sp(2) nitrogen atom is a 2-pyridinyl or an 8-quinolinyl building block, while the chiral framework of the ligand derives from (S)-(+)-2.2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene or from trans-2.5-dimethylpyrrolidinyl. Ligands with the binaphthyl moiety generate catalysts showing a moderate activity, while ligands having the pyrrolidinyl fragment results in very low activity species. The stereochemistry of the synthesized polyketones depends of the sp(2) nitrogen-containing fragment: ligands with the 2-pyridinyl group lead to atactic copolymers, whereas those with the quinolinyl moiety give an isotactic polyketone. The effect of the nature of the quinone, added to the reaction mixture as oxidant, has been investigated MALDI-TOF analysis reveals the formation of several polymeric chains, differing in the presence of various end-groups.

The CO/styrene copolymerization reaction promoted by [Pd(N−N)2][PF6]2 (N−N = 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen)) complexes was investigated in detail. The stability of the catalytic system is mainly influenced by the nature of the reaction medium. By virtue of the high stability of the active species in 2,2,2-trifluoroethanol compared to methanol, no addition of 1,4-benzoquinone is required for the reaction. The analysis of the parameters that affect the stability of the catalyst when no oxidant is added revealed that (i) phen is a better ligand than bipy and the catalyst generated by the complex [Pd(phen)2][PF6]2 is active at least up to 48 h of reaction, yielding a productivity as high as 5.4 kg CP/g Pd; (ii) the stability is enhanced by addition of a mixture of the N−N ligand and the corresponding monoprotonated salt [(N−N)H][PF6]; (iii) a relatively high carbon monoxide pressure is required to protect the catalyst toward its decomposition. A correlation between these parameters and the ...