Designing Ionic Ir(III) Cyclometalated Complexes as Photocatalysts for Light Assisted ATRP of MMA. A Combined Experimental and Mechanistic Study

A new family of ionic Ir(III)-complexes was designed, prepared and assessed for the visible light assisted ATRP of methyl methacrylate (MMA). A complete experimental and mechanistic study is performed to shed light on the key factors for the proper control of the polymerization process.

Abstract

A new family of ionic Ir(III) cyclometalated complexes with general formula [Ir(CN)₂(NN)][Br], was designed and prepared to be assessed as photocalysts for the visible light assisted ATRP polymerization of MMA. To this purpose, our design strategy involved both: i) the decoration of the cyclometalating (CN) and the ancillary (NN) ligands with various electron withdrawing and/or electron donor substituents and, ii) the use of Br⁻ as the counter anion for these cationic Ir(III) species. After an extensive screening in which the [Ir(CN)₂(NN)][Br]-type compounds were compared to the model neutral complex fac-[Ir(ppy)₃], the “fully” amino-substituted ion pairs abbreviated as [10][Br] and [11][Br], exhibited the best photocatalytic performances under irradiation with CFL lamps. It is worth noting that the outcomes of transient absorption spectroscopy (TAS) experiments combined with theoretical DFT calculations, enlightened the role played by the Ir(III) complexes in the mechanism of the photoATRP process, and suggested the rationalization of the different performances that were highlighted by our Ir(III) catalyst in the visible light assisted photopolymerization of MMA.

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