Photocatalytic CO 2 reduction to CO by Cobalt(II) Pyridinyl-1,3,5-Triazine-Diamine complexes

The development of molecular photocatalytic systems for CO 2 reduction is a continuous challenge for chemists. Herein, the photocatalytic reductions of CO 2 by [Co II( L1)( η 1 -ONO 2 ) 2 ] ( 1 ) ( L1 = 6,6'-(pyridine-2,6-diyl)bis(1,3,5-triazine-2,4-diamine)) and [Co II (L2)(H 2 O) 2 ] 2+ ( 2 ) ( L2 = 6,6'-([2,2'-bipyridine]-6,6'-diyl)bis(1,3,5-triazine-2,4-diamine)) have been investigated. With Ir(ppy) 3 as the photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1 H -benzo[ d ]imidazole as the sacrificial reductant in DMF/triethylamine solution under irradiation by white light-emitting diode (λ > 420 nm), CO was selectively produced with a turnover number (TON) of 36 and 89 for 1 and 2 , respectively. Based on the electrochemical studies, the triply reduced [Co 0 (L2•)]ˉ species from 2 is found to be responsible for the activation of CO 2 with a large rate constant of k = 506 M −1 s −1 . However, the strong CO binding constant of Co I (L2)-CO adduct ( K = 5.01 × 10 6 ) and the slow CO release from Co 0 (L2)-CO adduct limit the catalytic efficiency.