Supramolecular Ensemble of a TICT-AIEE Active Pyrazine Derivative and CuO NPs: A Potential Photocatalytic System for Sonogashira Couplings Harnimarta Deol, Subhamay Pramanik, Manoj Kumar, Imran A. Khan, and Vandana Bhalla* Department of Chemistry, UGC Sponsored Centre for Advanced Studies-II, Guru Nanak Dev University, Amritsar 143005, Punjab, India * S Supporting Information ABSTRACT: The donor-acceptor system 4 having pyrazine scaffold as an acceptor moiety coupled to donor amino groups through rotatable phenyl rings has been synthesized, which formed aggregates in aqueous media, exhibited copper induced restriction to intramolecular rotation, and served as a “not quenched” probe for the detection of copper(II) ions. During this process, the aggregates of derivative 4 acted as reactors and stabilizers for the generation of CuO NPs and themselves became oxidized to form polyamine derivative 6. Interestingly, the oxidized species 6 in combination with copper oxide nanoparticles served as light-harvesting antennas and exhibited excellent photocatalytic efficiency in Sonogashira coupling under mild and eco-friendly conditions (room temperature, aqueous media, aerial conditions, and visible light irradiation). KEYWORDS: pyrazine, TICT, AIEE, CuO NPs, photocatalyst, Sonogashira cross-coupling 1. INTRODUCTION Sonogashira coupling is one of the most powerful carbon- carbon bond forming reactions for the preparation of many important intermediates of various materials, drugs, and natural products. 1 Under conventional conditions, Sonogashira cou- pling is catalyzed by palladium and requires harsh reaction conditions, 2,3 which restrict the large-scale industrial applica- tions of this reaction. Over the years, enormous efforts have been made to replace the costly and toxic palladium-based catalytic system with relatively cheap and benign metal-based catalytic systems. Further, growing environmental concern has encouraged scientists to develop new synthetic approaches having minimal effects on the ecosystem. In this direction a variety of catalytic systems based on copper, 4 nickel, 5 silver, 6 and iron 7 have been developed; however, most of these systems require the assistance of additional ligands and heating at high temperature for prolonged times to furnish the desired products in good yields. Recently, CuCl has been reported as a photocatalyst to carry out palladium-free Sonogashira coupling at room temperature under blue LED irradiation. 8 The utilization of visible-light radiation 9 for carrying out coupling is an economically viable approach and is beneficial to the environment; however, in the presence of this catalytic system all reactions were carried out in organic media under an inert atmosphere and completion of these reactions required irradiation with a blue LED for a longer period (15-27 h). Thus, the development of a novel catalytic system for carrying out Sonogashira coupling under mild and environmentally friendly condition is still a challenge. Our research work involves the development of supra- molecular aggregates which serve as reactors for the preparation of different types of metal nanoparticles 10 and their utilization for carrying out various types of organic transformations such as click synthesis of triazoles, 11 Beckmann rearrangement of aldoximes/ketoximes to primary/secondary amides, 12 and Suzuki and Sonogashira couplings. 13 Recently, we developed supramolecular assemblies of aggregation-induced emission enhancement (AIEE) active hexaphenylbenzene derivatives which served as “not quenched” reactors for the preparation of α-Fe 2 O 3 nanoparticles. 10 The in situ generated α-Fe 2 O 3 NPs exhibited high catalytic efficiency in Sonogashira coupling between alkyl halides and terminal alkynes. 14 The reaction conditions required the presence of K 2 CO 3 as a base, ethylene glycol as solvent, and heating at 80 °C under inert conditions. In a continuation of this work, we were then interested in the development of a new catalytic system which could harvest the solar energy to carry out Sonogashira coupling in aqueous media under aerial conditions at room temperature. We envisioned that semiconductor nanoparticles in combination with dyestuff could serve as light-harvesting antennas for carrying out Sonogashira coupling under photocatalytic Received: February 6, 2016 Revised: April 27, 2016 Published: May 3, 2016 Research Article pubs.acs.org/acscatalysis © 2016 American Chemical Society 3771 DOI: 10.1021/acscatal.6b00393 ACS Catal. 2016, 6, 3771-3783