Photocatalytic CO₂ reduction to CO by Cobalt(II) Pyridinyl-1,3,5-Triazine-Diamine complexes

The development of molecular photocatalytic systems for CO2 reduction is a continuous challenge for chemists. Herein, the photocatalytic reductions of CO2 by [Co(II()L1)(eta(1)-ONO2)(2)] (1) (L1 = 6,6'-(pyridine-2,6-diyl)bis(1,3,5-triazine-2,4-diamine)) and [Co-II(L2)(H2O)(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-1H-benzo[d]imidazole as the sacrificial reductant in DMF/triethylamine solution under irradiation by white light-emitting diode (lambda > 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 center dot)] species from 2 is found to be responsible for the activation of CO2 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 x 10(6)) and the slow CO release from Co-0(L2)-CO adduct limit the catalytic efficiency.