Application of Chiral Amine-Imine Ligands in Pd-Catalyzed Polyketone Synthesis: Effect of Ligand Backbone on the Polymer Stereochemistry

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(CH(3))(CH(3)CN)-(N*-N)][PF(6)]. 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.