Solar CO reduction using a molecular Re() catalyst grafted on SiO amide and alkyl amine linkages

Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO) 3 Cl where bpy is 2,2′-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO 2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO) 3 Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO) 3 Cl onto SiO 2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re( i ) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO 2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re( i )-OH species on SiO 2 . Furthermore, the amine group likely contributes to the stabilization of a surface Re( i )-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re( i ) catalyst containing the alkyl amine linkage. Local basicity of the amine group led to formation of a Re( i )-OH species and stabilization of a Re( i )-carboxylato species.