Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt–Oxygen Bonds

Abstract

A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine] from ring‐opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co−O bond, allowing for in situ transformation of the ROCOP active species (Salen)CoIII‐OR into the OMRP photoinitiator (Salen)CoIII‐CO2R. The proposed mechanism, which involves CO coordination to (Salen)CoIII‐OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on‐demand sequence control can be achieved for the one‐pot synthesis of polyester‐b‐polyacrylate diblock copolymers (Đ<1.15).

Cobalt‐Mediated Switchable Catalysis for the One‐Pot Synthesis of Cyclic Polymers

“…[5b, 13] Recently, our group reported the fast and quantitative transformation of Co À O bonds into Co À C bonds via migratory insertion of carbon monoxide (CO), whereby the catalytic activity of (salen)Co III Cl could be switched from ROCOP to organometallicmediated radical polymerization (OMRP). [14] Herein, we successfully tackle the challenge of synthesizing cyclic polymers directly from monomer mixtures via CO triggered switch from ROCOP of epoxides/anhydrides/CO 2 to photoinduced intramolecular radical cyclization reaction (Scheme 1). Central to this protocol is the rational design and judicious choice of a cobalt salen pentenoate complex [(salen)Co III -OPe, compound 1] as the ROCOP catalyst, where CO triggers the transformation of ROCOP active species a-alkene-w-O-Co III (salen) into a-alkene-w-O 2 C-Co III -(salen) linear precursors that are capable of undergoing photo-induced radical cyclization reaction with excellent regioselectivity.…”

Switchable Polymerization: A Practicable Strategy to Produce Biodegradable Block Copolymers with Diverse Properties

“…[80] Notably, cyclic poly(propylene carbonate) (PPC) were also successfully synthesized via the switchable catalysis, except that the ROCOP of PO and CO 2 was conducted in autoclave an airtight transparent window. [81]…”

Advances, Challenges, and Opportunities of Poly(γ-butyrolactone)-Based Recyclable Polymers

“…It might be a good choice for synthesis of PGBL-based polymers. Switchable catalysis in the absence/presence of external stimuli has been widely investigated to prepare well-defined block and multiblock copolymers. − It has promising potential to combine ROP with other controlled polymerization methods to build precise structures by using switchable catalysis. − …”