Redox Switchable Copolymerization of Cyclic Esters and Epoxides by a Zirconium Complex

Abstract

ABSTRACT:A zirconium precatalyst, (salfan)Zr(O t Bu)2 (salfan = 1,1'-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene), shows activity for the redox controlled block copolymerization of L-lactide and cyclohexene oxide. The role of the oxidant is examined and several diblock (AB, BA) and triblock copolymers (ABA and BAB) were synthesized and characterized.

Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

“…The combination of the three conditions produced PCHO in 30 minutes with the lowest dispersity at 1.26 (Figure S39). We also tried using Ac FcTFSI as an alternative oxidant since Ac FcBAr F can polymerize CHO . In control experiments using Ac FcTFSI, only 4 % CHO polymerization was observed after 1 hour, which allows a wide time frame for 1 to be oxidized, and, after 24 hours, only 29 % of CHO was polymerized (Figure S22).…”

“…The aluminum analogue, (thiolfan*)Al(O t Bu), was not very selective between the two oxidation states, but could be used to synthesize various AB type diblocks with and without employing redox switching. Related supported ligands could also be used with zirconium as redox switchable catalysts: (salfan)Zr(O t Bu) 2 (salfan=1,1′‐di(2‐ tert ‐butyl‐6‐ N ‐methylmethylenephenoxy)ferrocene, Figure b) had the capability to synthesize an ABC type triblock of PBL‐PCHO‐PLA‐O t Bu, while (salfen)Zr(O i Pr) 2 (salfen=1,1′‐di(2,4‐bis‐ tert ‐butyl‐salicylimino)ferrocene, Figure c) could synthesize an ABA type PLA‐PCHO‐PLA triblock via two redox switches. When the indium analogue, (salfen)In(O t Bu) (Figure d), was examined, a high ring‐opening polymerization activity toward several lactones was observed with the reduced compound, but the catalyst was not redox switchable.…”

Controlling the Ring‐Opening Polymerization Process Using External Stimuli

“…The orthogonal discrimination between the ROP of LA and epoxide enabled the one‐pot synthesis of a poly(LA‐b‐Epoxide) diblock copolymer (Figure b). Furthermore, more complicated redox control of copolymerization reactions was achieved for the synthesis of triblock coploymers …”

Redox Control in Olefin Polymerization Catalysis by Phosphine–Sulfonate Palladium and Nickel Complexes

“…Long et al demonstrated that the reduction of an α‐diimine Ni II complex could modulate the branching density of the resulting polyethylene by up to 30 % (Scheme , III ) . It should be noted that this redox‐control strategy has been extensively studied in ring‐opening polymerization of cyclic esters, but has only been recently extended to other types of polymerization reactions …”

“…[18] It should be noted that this redoxcontrol strategy has been extensively studied in ring-opening polymerization of cyclic esters, but has only been recently extended to other types of polymerization reactions. [19][20][21][22][23][24][25][26][27] Two strategies are employed to achieve in situ redox control: (1) the oxidation or reduction of a preinstalled ferrocene unit; and (2) the oxidation or reduction of the redox-active metal center.…”