A highly efficient tetradentate PNNP-type Ir photocatalyst, Mes-IrPCY2, was developed for the reduction of carbon dioxide. The photocatalyst furnished formic acid (HCO 2 H) with 87% selectivity together with carbon monoxide to achieve a turnover number of 2560, which is the highest among CO 2 reduction photocatalysts without an additional photosensitizer. Mes-IrPCY2 exhibited outstanding photocatalytic CO 2 reduction activity in the presence of the sacrificial electron source 1,3-dimethyl-2phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) in CO 2 -saturated N,N-dimethylacetamide under irradiation with visible light. The quantum yield was determined to be 49% for the generation of HCO 2 H and CO. Electron paramagnetic resonance and UV−vis spectroscopy studies of Mes-IrPCY2 with a sacrificial electron donor revealed that the one-electron-reduced species is the key intermediate for the selective formation of HCO 2 H.

A series of Ir complexes has been developed as multifunctional photocatalysts for CO2 reduction to give HCO2H selectively. The catalytic activities and photophysical properties vary widely across the series, and...

We herein report that an iron (Fe) complex bearing a tetradentate PNNP ligand catalyzes photochemical carbon dioxide (CO2) reduction to produce mainly carbon monoxide (CO) together with formic acid (HCO2H) combined with a photosensitizer. The structurally bulky phosphine moieties stabilized the catalyst and improved its durability over a few days (∼72 h) to give the turnover number (TON) of 397. Operando subnanosecond laser-induced transient absorption measurements allowed us to observe the direct electron transfer from a reduced photosensitizer to the Fe catalyst.

A novel mononuclear ruthenium (Ru) complex bearing a PNNP-type tetradentate ligand is introduced here as a self-photosensitized catalyst for the reduction of carbon dioxide (CO2). When the pre-activation of the Ru complex by reaction with a base was carried out, an induction period of catalyst almost disappeared and the catalyst turnover numbers (TONs) over a reaction time of 144 h reached 307 and 489 for carbon monoxide (CO) and for formic acid (HCO2H), respectively. The complex has a long lifespan as a dual photosensitizer and reduction catalyst, due to the sterically bulky and structurally robust (PNNP)Ru framework. Isotope labeling experiments under 13CO2 atmosphere indicate that CO and HCO2H were both produced from CO2.

We describe a new type of nitrogen-centered polycyclic scaffold comprising a unique combination of 5-, 6-, and 7-membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1-naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3-fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X-ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density-functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.