NanoPhotoCatalysis: A New Dimension in Synthetic Chemistry

Abstract

Photocatalysis has emerged as a powerful tool in recent years to drive chemical transformations via electron/energy transfer, allowing access to several unstable or high energy intermediates. Thus, the design and development of new photocatalytic platforms has been of significant interest. In this regard, nanomaterials have emerged as sustainable and dynamic alternatives, offering a higher surface to volume ratio in the lower dimensions. These materials can be tailored for the desired applications via heterostructure/composite formation, doping, surface chemistry alteration etc. Most importantly, their heterogeneous nature allows for easy retrieval and reuse subsequently. However, the potential of such nanomaterials has not been harnessed much for catalysis. In this thesis, we delve into the rational fabrication of various nanomaterials and their application for a plethora of organic transformations. We begin with the synthesis of polymorphic Transition Metal Dichalcogenides (TMDs) and correlate their structure/property with their activity in oxidative coupling, followed by application in multicomponent reaction. Devising inspiration from the Hydrogen Evolution Reaction (HER), we have proposed two independent strategies for the cross-coupling of the sacrificial amine donors with relevant nucleophiles in the same pot. While the former strategy uses the nanosheets of MoS2 in synergy with Eosin Y, the latter relies on the use of MoS2 quantum dots (QDs) as a dual catalytic platform (without any external photosensitizer). Next, we explore the effect of transition metal doping of MoS2 for the synthesis of Bisindolylmethanes (BIMs) and highlight the effect of the light in escalating the Lewis acidity of the nanomaterial via access to otherwise unstable intermediate catalytic species. Additionally, the diverse toolbox of BIMs displayed excellent biological profile as antibacterial agents against methicillin resistant Staphylococcus aureus (MRSA), with a rational structure-activity relationship (SAR) and biocompatibility towards mammalian cell lines. Following this, we have demonstrated the enhanced efficacy of surface-functionalized TMDs as a bifunctional catalyst for the synthesis of benzimidazoles via induction of heterojunctions and distortions in the crystal lattice. Finally, we study the Newman Kwart rearrangement using carbon QDs to expand the regime of accessible chemical space for this transformation via a radical cation-based mechanism, which is in sharp contrast to the thermal mechanism. In each of the cases, the material was found to be recyclable in four to ten runs with no appreciable loss of activity, highlighting the advantage of using heterogeneous catalysts. Thus, this thesis collectively highlights the advantages and scope of integrating nanomaterials as photocatalysts in organic transformations.