New Photosensitizers Based on Heteroleptic Cu$^{I}$ Complexes and CO$_{2}$ Photocatalytic Reduction with [Ni$^{II}$(cyclam)]Cl$_{2}$

Earth‐abundant metal complexes have been attracting increasing attention in the field of photo(redox)catalysis. In this work, the synthesis and full characterisation of four new heteroleptic Cu$^{I}$ complexes are reported, which can work as photosensitizers. The complexes bear a bulky diphosphine (DPEPhos=bis[(2‐diphenylphosphino)phenyl] ether) and a diimine chelating ligand based on 1‐benzyl‐4‐(quinol‐2′yl)‐1,2,3‐triazole. Their absorption has a relative maximum in the visible‐light region, up to 450 nm. Thus, their use in photocatalytic systems for the reduction of CO$_{2}$ with blue light in combination with the known catalyst [Ni$^{II}$(cyclam)]Cl$_{2}$ was tested. This system produced CO as the main product through visible light (λ =420 nm) with a TON up to 8 after 4 hours. This value is in line with other photocatalytic systems using the same catalyst. Nevertheless, this system is entirely noble‐metal free.