Iron Aquo Complex as an Efficient and Selective Homogeneous Photocatalyst for Organic Synthetic Reactions

Abstract Owing to the inexpensiveness and non‐toxicity of iron, development of highly active and simple homogeneous iron photocatalysts is a crucially important, while challenging, for practical organic synthetic reactions. Here we report that iron(III) nitrate, which is one of the most typical iron salts and can form iron aquo complexes in aqueous and organic solutions, can be used as a highly efficient and selective homogeneous photocatalyst for fine chemical synthesis. We demonstrated the iron aquo complexes catalyzed the oxidation of cyclohexane into cyclohexanol and cyclohexanone with a turnover number (TON) of 88 and a nearly 100 % selectivity using O 2 under irradiation of solar light, whereas existing TiO 2 and α‐Fe 2 O 3 heterogeneous photocatalysts showed low TON and no activity. The iron aquo complexes impregnated within a mesoporous silica showed the improved TON of up to 100 while maintaining nearly 100 % selectivity.