Research Projects

Our research group has been extensively engaged in metal-catalyzed C–H functionalization of organic molecules via the deprotonation pathway for the past 15 years. Notably, 16-electron palladium complexes are capable of activating C–H bonds via an intramolecular pathway. Thus, palladium complexes can activate a wide range of C–H bonds in organic molecules, including the challenging primary C(sp³)–H bonds of aliphatic compounds. Although pioneering reports using strong bidentate directing groups face certain drawbacks, such as the strongly bound palladacycle representing thermodynamic stability and hindering subsequent functionalization steps. So, the alternative route is to directly activate the desired C(sp³)–H bonds with various monodentate or less chelating power bearing directing groups in comparison to the bidentate ones. The poor reactivity of simple Pd salts with the monodentate groups is one of the prime challenges in this field. In order to deal with the poor chelating power, an external ligand is required to accelerate the C(sp³)–H cleavage step. The selection of a proper ligand is crucial to the activation of C(sp³)–H bonds. It has been observed that a bidentate-based ligand could do the required activation effectively. One of the sites of the bidentate ligand acts as the internal base, which facilitates the C-H activation step, and the other site of the ligand coordinates strongly with the palladium center. Hence, the synergistic nature of the bidentate ligands plays a significant role in the palladium-catalyzed transformations. For the past few years, our group has been working on the development of new methodologies for the functionalization of unreactive C-H bonds via palladium-catalyzed C(sp³)-H bond activation, along with the help of external ligands. Hence, this proposal will portray an efficient route for the design of a new set of bidentate ligands that are essential for the selective activation of C(sp³)–H bonds. We will aim for the synthesis of the N-heterocyclic carbene (NHCs) complexes and rigid bifunctional N, S-directed molecules and will utilize these molecules as the novel bidentate ligands for the C(sp³)-H activation reaction. The inherent properties of NHCs, along with the protected amide/pyridone part in a single structure, could serve as a promising novel set of bidentate ligands for activating C-H bonds. The newly developed ligands would then be successfully utilized in the proximal and distal/remote C-H functionalization of aliphatic frameworks. In the next part of the proposal, we have demonstrated several C(sp³)-H bond functionalization pathways of an olefin bearing hydrocarbon skeletons. The C(sp³)-H activation of unactivated olefins could be successfully achieved with the palladium-hydride protocols and also with allylic C-H bond functionalization methods. Moreover, along with the inclusion of a new set of ligands, our proposal has also highlighted the discovery of new directing groups (monodentate/bidentate) and implementation of such directing groups in the C-H bond transformations. Further, in the later part of the proposal, a major effort has also been devoted towards the transition metal-catalyzed asymmetric transformations of C(sp3)-H bond.