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 TiO 4 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 TiO 4 chromophore. Photoexcitation of the Ti IV —O II → Ti III —O I ligand to metal CT in the anchored complex in the presence of CO 2 and H 2 O provided the adsorbed HCOOH and HO· (and/or SiO·) 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 2 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.