Anchored Oxo-Bridged Bimetallic Complexes, (SiO)3-Ti-O-Fe(corrole), on Silica Mesopores as Multi-Electron-Transfer Photosystems

The anchored molecular multielectron transfer (MET) complex, (SiO)(3)-Ti-O-Fe(tpfc) (tpfc = 5,10,15-tris (pentafluorophenyl) corrole), composed of an Fe-centered corrole and a single-site TiO4 charge-transfer (CT) chromophore, has been synthesized on the pore surface of mesoporous silica. The diffuse reflectance (DR) UV-vis and Fe K-edge X-ray absorption near edge structure (XANES) measurements showed that the anchored complex has an oxo-bridged Ti-IV-O-Fe-IV bimetallic linkage between the Fe-centered corrole and the TiO4 chromophore. Photoexcitation of the Ti-IV-O-II -> Ti-III-O-I ligand to metal CT in the anchored complex in the presence Of CO2 and H2O provided the adsorbed HCOOH and HO center dot (and/or SiO center dot) as reaction products. Fe-centered corroles have a unique ability that they can accommodate multiple electrons at the single Fe center and initiate the two-electron reduction of CO,, when the Fe center is reduced from 4+ to 1+. Therefore, the formation of adsorbed HCOOH demonstrates that the stepwise reduction of the centered Fe from 4+ to 1+ is accomplished by the sequential photoinduced CT through the confined Ti-O-Fe bimetallic linkages.