ic7b01963_si_001.pdf (2.15 MB)
Photosensitization Behavior of Ir(III) Complexes in Selective Reduction of CO2 by Re(I)-Complex-Anchored TiO2 Hybrid Catalyst
Version 2 2017-09-13, 15:42
Version 1 2017-09-13, 14:12
journal contribution
posted on 2017-09-13, 15:42 authored by Ha-Yeon Cheong, So-Yoen Kim, Yang-Jin Cho, Dae Won Cho, Chul Hoon Kim, Ho-Jin Son, Chyongjin Pac, Sang Ook KangA series
of cationic Ir(III) complexes ([Ir(btp)2(bpy-X2)]+ (Ir-X+: btp =
(2-pyridyl)benzo[b]thiophen-3-yl; bpy-X2 = 4,4′-X2-2,2′-bipyridine (X = OMe, tBu, Me, H, and CN)) were applied as visible-light
photosensitizer to the CO2 reduction to CO using a hybrid
catalyst (TiO2/ReP) prepared by anchoring of Re(4,4′-Y2-bpy)(CO)3Cl (ReP; Y = CH2PO(OH)2) on TiO2 particles. Irradiation of a solution
containing Ir-X+, TiO2/ReP particles, and an electron donor (1,3-dimethyl-2-phenyl-1,3-dihydrobenzimidazole)
in N,N-dimethylformamide at greater
than 400 nm resulted in the reduction of CO2 to CO with
efficiencies in the order X = OMe > tBu
≈ Me > H; Ir-CN+ has no photosensitization
effect. A notable observation is that Ir-tBu+ and Ir-Me+ are less efficient than Ir-OMe+ at an early stage of the reaction but reveal persistent
photosensitization behavior for a much longer period of time unlike
the latter. Comparable experiments showed that (1) the Ir-X+ sensitizers are commonly superior compared
to Ru(bpy)32+, a widely used transition-metal
photosensitizer, and (2) the system comprising Ir-OMe+ and TiO2/ReP is much more efficient than
a homogeneous-solution system using Ir-OMe+ and Re(4,4′-Y′2-bpy)(CO)3Cl
(Y′ = CH2PO(OEt)2). Implications of the
present observations involving reaction mechanisms associated with
the different behavior of the photosensitizers are discussed in detail.