3d-4f Decanuclear Coordination Cage Platform with Synergistic Catalytic Activity and Confined Selectivity for Bis(indolyl)methane Synthesis.

This work reports on the structural and synergistic catalytic performance of a 3d-4f decanuclear coordination cage based on a nonsymmetric acylhydrazone ligand (H5L), namely, {[Zn4Dy6(H2L)4(HL)2(NO3)3(CH3OH)15]·2ClO4·NO3·xCH3OH·yC2H5OH·zH2O} (Zn4Dy6 cage). X-ray crystallographic characterization confirmed the presence of open structural windows and confined internal cavities within the decanuclear Zn4Dy6 cage, which are derived from the topological construction of the ligand wall. The heterogeneous catalytic activity and size selectivity of the Zn4Dy6 cage for the Friedel-Crafts alkylation of aldehydes and substituted indoles were studied in detail. The study of the substrate scope revealed that the Zn4Dy6 cage exhibits excellent catalytic activity, except when reacting with indole derivatives bearing electron-withdrawing groups (-NO2, -CN) or large molecular size aldehydes in this catalytic system. As far as we are aware, this is the first coordination complex to be employed for the synergistic catalytic synthesis of bis(indolyl)methanes using fatty aldehydes as the substrate. Furthermore, we proposed a rational cooperative catalytic reaction mechanism using the 3d-4f Zn4Dy6 cage as the catalyst.