Efficient Rare-Earth-Based Coordination Polymers as Green Photocatalysts for the Synthesis of Imines at Room Temperature

Five new rare-earth coordination polymers (CPs) were designed in order to offer a remarkable platform that contains light-harvesting antennas and catalytic active centers to achieve solar-energy conversion as green alternatives in the synthesis of imines. These five new spirobifluorene-containing Ln-CPs, named [Er3(Hsfdc)3(sfdc)3(H2O)]·xH2O (RPF-30-Er), [Ln­(Hsfdc)­(sfdc)­(EtOH)]·S (RPF-31-Ln, where Ln = La, Nd, and Sm and S = H2O or EtOH), and [Ho­(Hsfdc)­(sfdc)­(H2O)] (RPF-32-Ho) (RPF = rare-earth polymeric framework and H2sfdc = 9,9′-spirobi­[9H-fluorene]-2,2′-dicarboxylic acid), have been solvothermally synthesized, and their structural features can be described as follows: (i) RPF-30-Er shows a 3D framework in which the inorganic trimers (secondary building units) are cross-linked by Hsfdc– and sfdc2– linkers displaying a pcu topology. (ii) The isostructural RPF-31-Ln series of materials, together with RPF-32-Ho, exhibit a 1D network of chains growing along the a axis with a ribbon-of-rings topology type. The photocatalytic activity of the RPF-n materials was tested in the oxidative coupling of amines using molecular oxygen and air as oxidizing agents under warm light. Among the materials investigated, RPF-31-Nd was chosen to further investigate the approach in the selectivity of different amine derivates.