C-Cl Bond Activation and Orthogonal Cascade Reactions Targeting Fluorophores and Molecular Dyads with Low Content Ru-Pd Nanocluster at Zeolite-NaY: A Combined Experimental and Theoretical Study

Abstract

The synthesis of value-added biaryl products from low-cost aryl chlorides through the Suzuki-Miyaura cross-coupling (SMCC) process is highly desirable. However, the diversity in the product synthesis through the cleavage of the C-Cl bond is limited due to its high bond energy. This work addresses the restrictions associated with the substrate scope selectivity in C-Cl bond activation by boosting the activity of Pd-nanoclusters through alloying with Ru and decorating over microporous zeolite-NaY. The bimetallic Ru-Pd@zeolite metal catalyst serves as an excellent true heterogeneous catalyst, providing a large scope selectivity. By activating the C-Cl bond, a total number of 69 versatile SMCC products bearing biayls derivatives, heterocyclic building blocks, and light-emitting molecules with high product yield are synthesized. Among this large variety of substrates, 11 molecules are new molecules having pyrazole, indole, and morpholine backbone. There are 16 molecules showing the luminescence behavior (fluorophore) under UV light. This work also describes a sequential orthogonal cascade reaction, by coupling the SMCC process with a Friedel-Crafts reaction for the synthesis of covalently linked molecular dyads. The donor (triphenylamine unit) and acceptor (naphthol core) are connected through a -CH2- group having a (angle Cdonor-C(CH)2 -Cacceptor) bond angle of 115.86-115.97 degrees in four molecular dyads. They show low fluorescence intensity with an energy separation of 3.56-3.85 eV between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). Aiming for a thorough understanding, density functional theory (DFT) calculations provided strong evidence of the role of Ru in activating the C-Cl bond of chlorobenzene. Kinetics study implied that the first-order kinetics exhibits isosbestic points, providing further evidence about the progress of the reaction without any byproducts.