Abstract:

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.

Key words: aluminum porphyrin, carbon dioxide, propylene oxide, poly(propylene carbonate)