Porous Bimetallic Ti-MOFs for Photocatalytic Oxidation of Amines in Air.

A family of microporous titanium-containing metal-organic frameworks (denoted as MTi-CPCDC, M = Mn, Co, Ni) has been synthesized by using a bimetallic [MTi(μ-O)(COO)] cluster and a tritopic carbazole-based organic ligand HCPCDC. MTi-CPCDC are stable and display permanent porosity for N and CO uptake, ranking among the most porous titanium-based metal-organic frameworks. MTi-CPCDC crystals exhibit n-type semiconductor behavior. Further catalytic studies demonstrate that all MTi-CPCDC materials are applicable for triggering photo-oxidative reactions of amines in air. More specifically, amines with electron-donating groups afford the aldehydes as the main products, while amines bearing electron-withdrawing groups give rise to imines as the main product. Among them, MnTi-CPCDC exhibit the best photocatalytic activity, with conversion of benzylamine up to 99% and selectivity of 99%. MnTi-CPCDC could be recycled in at least three runs while retaining crystallinity and catalytic activity. The reaction mechanism indicates that photoinduced hole (h), superoxide radical anion (O), and singlet oxygen (O) are the main active species involved in the photo-oxidation process.