Abstract
Titanium dioxide (TiO2) is a promising heterogeneous photocatalyst for decomposition of harmful organic compounds due to its high oxidation activity. Application of TiO2 photocatalysis to selective organic transformations has also been studied. These are, however, unsuccessful because photocatalytic reactions usually lack sufficient selectivity and promote side reactions or subsequent decomposition of formed products. In this review article, we highlighted our recent progress in the development of TiO2 or Ti oxide photocatalysts for selective organic transformations. Our strategies are classified into three categories. The first is the use of micro- or mesoporous TiO2 materials. These pores facilitate the uptake/exclusion of substrates and products and promote selective reaction of substrates while suppressing the reaction of products. The second is the use of monomeric Ti oxide species supported on silica as the photocatalytic active site. They exhibit photocatalytic activity different from bulk oxide materials and promote several reactions selectively. The third is the loading of metal nanoparticles onto the TiO2 surface, which act as a trapping site for conduction band electrons photoformed on TiO2 and as a catalytic active site. These catalysts therefore promote photocatalytic and catalytic reactions simultaneously and facilitate several reactions in one-pot. Heterogeneous photocatalysis that can be operated at mild reaction conditions without the use of harmful chemicals has significant advantages for organic transformations in an economically- and environmentally-friendly way. This review article shows that Ti oxide-based photocatalysts have a potential as a versatile tool in green organic synthesis.
