铝卟啉配合物催化二氧化碳与环氧丙烷共聚反应

铝卟啉是一类土壤环境友好的金属卟啉,尽管早在1978年Inoue就已经发现它可以催化CO₂和环氧丙烷的共聚反应,但是该催化体系一直面临催化活性低、聚合物相对分子质量低等难题。 本文通过改变铝卟啉催化剂配体中苯环上取代基的种类和位置,制备出中心金属电子环境差异化的铝卟啉,并以双三苯基膦氯化铵(PPNCl)为助催化剂,探讨其对CO₂与环氧丙烷的共聚反应的催化行为。 结果表明,当铝卟啉中苯环上2,4位同时被Cl^-取代后,在90 ℃和3 MPa压力下,转化频率(TOF)达到2672 h^-1。 当利用离去能力较强的对甲苯磺酸基团(OTs^-)作为铝卟啉的轴向配体,可以合成出数均相对分子质量达1.84×10⁵的脂肪族聚碳酸酯。

Copolymerization of Carbon Dioxide and Propylene Oxide under Aluminum Porphyrin Catalyst

Aluminum porphyrin is a soil-tolerant metal porphyrin complex. Although its catalytic activity on the copolymerization of CO₂ and propylene oxide has been disclosed by Inoue in 1978, the catalytic activity is still very low, and the synthesized poly(propylene carbonate) has low relative molecular mass. It is a big challenge to make progress on the catalytic performance of aluminum porphyrin. In this work, the electronic environment of central aluminum was adjusted by delicate design of porphyrin ligand using meso-tetrasubstituted porphyrin derivatives that were employed to catalyze the copolymerization of CO₂ and propylene oxide with bis-(triphenyl phosphine) iminium chloride(PPNCl) as the co-catalyst. It was found that the electronic environment of the central aluminum ion had great effect on the catalytic performance of aluminum porphyrin catalysts, the turnover frequency(TOF) value of Cl substituted aluminum porphyrin catalyst 6a reached 2672 h^-1 at 90 ℃ and 3 MPa, while poly(propylene carbonate) with relative molecular mass of 1.84×10⁴ was afforded using catalyst 4b bearing toluene sulfonic group(OTs^-) as axial group of good leaving ability. Our work indicates that delicate designed aluminum porphyrin can become a possible candidate as high performance catalyst in the copolymerization of CO₂ and propylene oxide, under optimized copolymerization conditions.