Viability of a trinuclear hetereoleptic Ir(III) photosensitiser for visible-light-promoted CO2 fixation to access α-amino acids: Serendipitous carbon‑carbon bond formation

Two novel Ir(III) polypyridyl photosensitizers ( Ir1 and Ir2 ) incorporating an N^N -benzimidazole ancillary ligand were successfully synthesised and thoroughly characterised. Their photophysical, photostability and electrochemical properties were investigated, revealing strong visible-light absorption suitable for excitation with commercial blue LEDs. Both complexes demonstrated remarkable stability under prolonged 405 nm irradiation, underscoring their robust structural integrity. Complexes, Ir1 and Ir2 exhibited comparable photophysical properties to related Ir(III) benzimidazole complexes. Electrochemical studies showed reversible Ir(III/IV) couples linked to metal-centred or C^N ligand-centred oxidation events, supporting their suitability for photochemical applications. The photocatalytic performance of Ir1 and Ir2 was evaluated in the photoredox-catalysed carboxylation of ketimines with CO₂. Serendipitously, reactions with these complexes produced a novel C C bond-containing by-product, for which a mechanistic pathway is proposed. • Ir(III) polypyridyl photosensitizers incorporating an N^N-benzimidazole ancillary ligand were prepared. • Show strong visible-light absorption suitable for excitation with commercial blue LEDs. • Exhibit higher quantum emission yields and shorter triplet excited-state lifetimes. • Evaluated in the photoredox-catalysed carboxylation of ketimines with CO₂. • A novel C C bond-containing byproduct was produced.