Photo-induced ring-expansion reactions mediated by B₁₂-TiO ₂ hybrid catalyst

Vitamin B₁₂-TiO₂ heterogeneous hybrid catalyst (B₁₂-TiO₂) mediated ring-expansion reactions and their reaction mechanism were clarified by various spectroscopic methods. Diffuse reflectance UV/VIS (DR-UV/VIS) studies showed that B₁₂-TiO ₂ was activated to form the supernucleophilic Co(i) species of B ₁₂ by irradiation with ultraviolet light. DR-UV/VIS and electron spin resonance (ESR) studies then elucidated the formation of the photo-sensitive intermediate on heterogeneous surfaces. The photo-excited B₁₂- TiO₂ catalyzed ring-expansion reactions were efficient and eco-friendly. This catalytic efficiency was strongly dependent on the kind of solvent. The oxidation reaction of the solvent by holes at TiO₂ nanoparticle surfaces had a crucial role in the overall catalytic reaction.