Application of Chiral Amine-Imine Ligands in Palladium-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 sp3 and one sp2 nitrogen atom have been applied to the CO/vinyl arene copolymerization reaction catalyzed by the corresponding monocationic palladium(II) complexes [Pd(CH3)(CH3CN)(N*-N)][PF6]. The ligand fragment containing the sp2 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 result in very low activity species. The stereochemistry of the synthesized polyketones depends on the sp2 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.

两对具备一个sp³杂化氮原子与一个sp²杂化氮原子的对映纯手性双齿氮供体配体（N*-N），被应用于由对应单阳离子型钯(II)配合物[Pd(CH₃)(CH₃CN)(N*-N)][PF₆]催化的CO/芳乙烯共聚反应中。含sp²杂化氮原子的配体片段为2-吡啶基或8-喹啉基结构单元，而配体的手性骨架则源自(S)-(+)-2,2′-(2-氮杂丙烷-1,3-二基)-1,1′-联萘或反式-2,5-二甲基吡咯烷基。带有联萘基团的配体所制备的催化剂表现出中等活性，而带有吡咯烷基片段的配体所得催化剂活性极低。所合成聚酮的立体化学取决于含sp²杂化氮原子的片段：带有2-吡啶基的配体可得到无规共聚产物，而带有喹啉基的配体则得到等规聚酮。本研究考察了作为氧化剂加入反应混合体系的醌类的性质对反应的影响。基质辅助激光解吸电离飞行时间质谱（MALDI-TOF）分析显示，生成了多条带有不同端基的聚合物链。