Investigation of redox switchable titanium and zirconium catalysts for the ring opening polymerization of cyclic esters and epoxides

The synthesis and characterization of (thiolfan*)Zr(O'tBu)(2) (thiolfan* = 1,1'-di(2,4-di-tert-butyl-6-thiophenoxide) ferrocene) is reported, as well as its activity toward the ring-opening polymerizations of L-lactide and epsilon-caprolactone. With the titanium analogue, (thiolfan*)Ti((OPr)-Pr-i)(2), diblock copolymers (AB and BA) and a triblock copolymer (ABA) were synthesized in a one-pot, redox-controlled process. Changing the metal center from titanium to zirconium has a profound influence on the reactivity profile of the corresponding reduced and oxidized catalysts in the switchable ring opening polymerization of cyclic esters and ethers.