Redox- and NIR-Active Iron(III) Triradicals as Catalysts for Radical Polymerization of Acrylamides and Methacrylates

Two unprecedented redox-active, low-spin Fe(III)-triradical complexes, [Fe(III)(SS-NHC═S^•-)₃]·NHC═S (1·NHC═S; E═S) and [Fe(III)(SS-NHC═Se^•-)₃] (2; E═Se) have been synthesized and structurally characterized by SCXRD. They were further characterized spectroscopically using IR, Raman, EPR, and UV-vis-NIR spectroscopy. The low-spin electronic configuration of the central Fe(III) ion (1) and the nature of the magnetic interaction between the Fe(III) center and the three unpaired electrons in 1 have been investigated by magnetic measurements. In addition, the bonding stability and electron density distribution in 1 were studied by quantum chemical calculations and correlated with experimental results. Finally, a series of well-defined functional homopolymers were synthesized via catalytic polymerization reactions using [Fe(III)(SS-NHC═S^•-)₃] (1) as a catalyst at ambient temperature. These reactions yielded poly(N, N-dimethylacrylamide) (PDMA), poly(N-isopropyl acrylamide) (PNIPAM), poly(dimethyl amino ethyl methacrylate) (PDMAEMA), and poly(benzyl methacrylate) (PBzMA) with low dispersities ranging from 1.2 to 1.22. The successful synthesis of various diblock copolymers confirmed excellent chain-end fidelity of the synthesized homopolymers. These homopolymers and diblock copolymers highlight the versatile catalytic polymerization reactions of these Fe-radical complexes. Herein, we present a report on the polymerization of various acrylamides and methacrylates using a redox-active Fe-dithiolene complex for the first time.