N-Heterocyclic carbenes (NHCs) have attracted growing interest not only as successful ancillary ligands in a wide variety of transition-metal-catalyzed reactions but have also shown to offer photophysical and electrochemical properties. The metalation/transmetalation strategy using [Zr(NMe2)4] as initial metalating reagent offers an efficient approach to the preparation of CCC-NHC pincer complexes of the late transition metals such as Rh and Ir. In the process of investigating an intermediate and the mechanism of the metalation/transmetalation to Rh sequence, a mixed valent bimetallic CCC-NHC pincer Rh complex with two chloro ligands bridged between a [(CCC-NHC)Rh(III)] and a [Rh(I)(COD)] fragment was isolated and fully characterized for the first time. The investigation of the Rh(III)/Rh(I) bimetallic intermediate in the CCC-NHC pincer metalation/transmetalation methodology led to an improved stoichiometric synthesis of series of CCC-NHC pincer Rh complexes. The CCC-NHC pincer Rh complexes were characterized with 1H and 13C NMR spectroscopy, ESI-TOF MS and single crystal X-ray diffraction. The catalytic activity of the series of CCC-NHC pincer Rh complexes were evaluated. All the CCC-NHC pincer Rh precatalysts were found to promote the dehydrogenative silylation of vinylarenes with Et3SiH to form the corresponding (E)-vinylsilanes as the major silylation product under solvent-free conditions. The catalytic system displays wide substrate scope. Electron rich and electron deficient vinylarenes were well tolerated affording the corresponding vinyl silanes in good yields (65-86%). Mechanistic investigations indicated that Rh(III) center was responsible for the catalytic performance. The CCC-NHC pincer ligand architecture plays a role in achieving good regio- and stereoselectivities. Also, the complexes were evaluated as precatalysts towards hydrosilylation of aryl- and alkyl alkenes. The precatalysts, [(BuCiCiCBu)RhCl(µ-Cl)2Rh(COD)] and [(BuCiCiCBu)RhCl(µ-Cl)]2, were found to promote highly regioselective anti-Markovnikov hydrosilylation of aryl- and alkyl alkenes with excellent selectivity (>99%) using Et3SiH or PhMe2SiH as silane source and acetonitrile as solvent. Straight chain alkyl alkenes were tolerated without undergoing isomerization as it is the case with most known hydrosilylation catalyst systems. We extended the improved stoichiometric metalation/transmetalation methodology towards the synthesis of 1,3-di(1H-1,2,4-triazol-1-yl)benzene-based pincer Rh complexes. A series of 1,1'-(1,3-phenylene)bis(4-hexyl-1H-1,2,4-triazol-4-ium) salts were synthesized. Metalation/transmetalation of 1,1'-(1,3-phenylene)bis(4-hexyl-1H-1,2,4-triazol-4-ium) diiodide salt was successfully demonstrated to synthesize novel triazole-based CCC-NHC pincer Rh complexes.

The industrial revolution came with its downside of emission of greenhouse gases into the atmosphere. The NOAA reported in 2019 that, of the greenhouse gases emitted into the atmosphere, CO2 contributed to about 80% of the increased greenhouse gases hence the need for CO2 Sequestering and Storage (CSS) and ultimately leading to Carbon Capture and Recycling (CCR) as a viable option to convert CO2 into useful forms. The race to find the best catalyst for CCR has led to the synthesis of many organometallic compounds. Pincer complexes catalyzed CO2 reduction has gained notoriety recently because of the tunability and robustness without causing any alteration in their overall coordination geometry. Different metals and pincer motifs have been reported for the electrocatalytic and photochemical reduction of CO2. Chapter I introduces the broader project impact, N-heterocyclic carbene concepts, pincer chemistry, iron pincer chemistry, and N-heterocyclic pincer complexes of Fe for a comprehensive perspective. Chapter II addresses the scarcity of iron based NHC pincer complexes due to deprotonation challenges and octahedral coordination preferences. Bulky substituents like mesityl, adamantly, or DIPP enable mono-ligated pincer complexes by hindering ligand encapsulation, leaving no open coordination site. In-situ metalation / transmetalation, and isolated CCC-NHC Zr complexes are presented along with a method to convert between mono-ligated and bis-ligated complexes. Chapter III explores L-type ligands' reactivity to prevent ligand reorganization around the Fe center from Chapter I. Chapter IV covers CCC-NHC Fe pincer complexes' synthesis, characterization, and transient absorption studies of bis-ligated complexes. Characterization of the CCC-NHC pincer Fe complexes in Chapter I-IV were carried out using 1H and 13C NMR spectroscopy, ESI-TOF MS, EA (Elemental Analysis), cyclic voltammetry, and X-ray diffraction. Chapter V discusses catalytic experiments and data consistent with preliminary CO2 reduction with mono-ligated CCC-NHC pincer complexes.