Executive Summary : | In the quest for mimicking the pigments of life, aromatic tetrapyrroles have fascinated the researchers and they have been explored quite extensively for various practical applications in biological, chemical and physical fields. On the contrary, although several antiaromatic porphyrinoids have been synthesized and some have potential to be used as components in fabrication of single-molecule electronics, yet they lack proper utilization. The interest on antiaromatic tetrapyrroles have gained impetus in the recent years after the discovery of a facile synthetic strategy for the isolation of the smallest known antiaromatic porphyrinoid, norcorrole (NCs) as a Ni complex. Being antiaromatic with a contracted core, planarity of the macrocycle poses challenges on attempts to metalate NC by relatively larger metal-ions. Only a few metal ions, including Ni, Fe (lack structural information due to stability issues), Cu, Pd and Pt could be inserted within the norcorrole cavity. Due to the paratropicity within the NC ring, metal complexes of NCs possess unique redox characteristics and chemical reactivity. The nascency of the coordination chemistry of norcorroles, has hindered their utilization on the basis of their redox capabilities for energy relevant purposes. Aim 1: In this proposal, attempts will be made to explore the fundamental coordination chemistry of this intriguing class of antiaromatic porphyrinoids by proper design, synthesis, characterization and thorough understanding of how the choice of metal ions and proper substitution at the periphery of NCs could possibly stabilize novel metalated NCs. Aim 2: We would like to explore their electrochemical properties to correlate the influence of various types of modifications on NC frameworks with the redox potentials of the metalated NCs. Such redox investigations would not only improve understanding but also scope of utilization of antiaromatic contracted porphyrinoids in developing various single-molecule electronics, etc. Aim 3: Based on the redox-non innocence of metalated NCs, efforts will be also laid towards utilizing them as electrocatalysts for activation of small molecules (by reduction of protons and dioxygen), relevant for alternative energy purposes. Particular efforts will be given towards understanding the mechanism of activation of such small molecules by antiaromatic complexes of NCs with proper probing of the reactive intermediates involved by in situ spectroscopic and electrochemical techniques. In the due course, analysis and quantification of the catalytic products will help ascertain the efficacies of the generated catalysts based on antiaromatic NCs. Such unprecedented utilization of norcorroles for energy relevant catalysis will open a whole new avenue of possibilities for the application of contracted antiaromatic porphyrinoids. |