N-Heterocyclic Tetrylenes: Potential Platforms for Multidimensional Applications

Abstract

The group 14 elements, known as N-heterocyclic tetrylenes (NHTs), typically have six electrons in their valence shell. They are currently one of the most rigorously investigated groups of ancillary ligands in modern main-group chemistry, having previously only been recognized as elusive and ephemeral laboratory curiosities. While the N-heterocyclic carbene (NHC) was found in bottleable form by Arduengo in 1991, West and Denk discovered the first N-heterocyclic silylene (NHSi) in 1994. Since then, several research groups from both academia and industry have ardently examined their potential applications in catalysis, synthesis, and stoichiometric transformations, signaling the start of a burgeoning era in low-valent main-group chemistry. NHCs have shown greater potential than their heavier congeners in the aforementioned fields. The chemistry of transition-metal complexes bearing isolable NHSi ligands has recently developed appealing and new synthetic methods with a wide range of properties that have significantly influenced organic methodologies, particularly small-molecule activations and a very small number of organic transformation reactions. We have expanded our understanding of NHTs' adaptability in transition metal chemistry, catalysis, and photophysical properties by introducing the additional facets through this thesis. The first section of the thesis demonstrated how bis-silylene reacts with chalcogens to generate Si=Ch (Ch= S, Se, and Te). Due to an unfavorable overlap between the pπ(Si) and pπ(Ch) orbitals and a significant variation in electronegativity between the Si(II) and Ch atoms, higher homologs of ketones are oligomeric or polymeric. So, isolating such molecules has always been challenging for synthetic chemists. With this work, we also establish unique C-H…Ch interactions. The bis-silylene ligand backbone also helped to stabilize reactive group 13 Lewis acid cations. Thus, in this part of the thesis, we aimed to show how bis-silylenes behave in small molecule activation and stabilizing reactive species. Utilizing various NHSis, we have also isolated several coinage metal complexes, explored their unique reactivity and bonding patterns, and ultimately used them in homogeneous catalysis. These complexes could be of great interest for their photophysical properties. By finetuning the electronic and steric properties, we explored their optoelectronic properties. Recently, NHCs have been utilized as surface-capping ligands for metal/metalloid nanoparticles. The wingtip functionalized NHC offers exclusive stability to the ligand-capped nanoparticles in the solution. This prompted us to explore the strong sigma donor cyclic alkyl amino carbene (CAAC) as a capping agent onto the gold nanoparticle (AuNP) surface. The work is also expanded with NHSis. The last part of the thesis dealt with these newly synthesized carbene functionalized AuNPs, which were well characterized using several spectroscopic techniques. Further, we utilized these AuNPs as catalysts for the electrochemical reduction of carbon dioxide and formic acid oxidation. Apart from the electrocatalytic activities, we also explored its catalytic activities towards organic transformation like nitro-arene reduction. Our work aims to pledge new insight for the main group chemist about the unforeseen potentials of NHTs as a surface capping ligand. Overall, given that main group ligands are unquestionably crucial in contemporary synthetic chemistry, this thesis work attempted to highlight the unique potentials of NHTs, particularly NHSis, towards a few real-time applications. We hope, perhaps, this will accelerate the process of comprehending the fundamental main group chemistry.