Importance of steric bulkiness of iridium photocatalysts with PNNP tetradentate ligands for CO reduction.

A series of Ir complexes has been developed as multifunctional photocatalysts for CO reduction to give HCOH selectively. The catalytic activities and photophysical properties vary widely across the series, and the bulky group insertion resulted in the formation of HCOH and CO with the catalyst turnover number of >10 400.