SusChEM: Applying Redox Noninnocence: Tetrazine-Assisted Reduction of N2

Indiana University, Bloomington IN

Investigators

Abstract

This project, funded by the NSF Chemical Synthesis Program, supports the research of Professor Kenneth Caulton of Indiana University to design and prepare new ligand structures that will wrap around low cost and sustainbable metal centers. The resultant complexes are used in the unusual catalytic conversion of poorly-reactive, thermodynamically-stable molecular nitrogen into value-added products. The new ligands contains imine functionalities, which makes them readily reducible so that they can temporarily store electrons to favor both the capture and reduction of nitrogen. Desirable nitrogen-containing products are formed using either organic trapping reagents or protons. The Caulton group employs low cost elements such as iron and vanadium in their catalysts making the materials more sustainable that those using precious metal catalysts. This project also systematizes and utilizes new ligand connectivities and electronic structures. Postdoctoral, graduate, and undergraduate researchers are actively involved in both the experimental and theoretical aspects of the project. The students receive excellent training in multiple characterizational techniques including electron paramagnetic resonance and x-ray photoelectron spectroscopies. Professor Caulton is active in the local chemistry community often lecturing on Nobel Prize-winning research to diverse audiences. This research project focuses on the design and experimental investigation of a new tridentate, redox-active ligand, bis(tetrazinyl) pyridine (btzp), which acts in supporting metal-centered, multi-electron reduction processes such as the reduction of molecular nitrogen using the first row transition metals iron and vanadium. The imine-rich btzp ligand serves as electron reservoir, promoting redox reactions within a very narrow potential range. The availability of a number of nitrogen sites on the pincer ligand leads to novel reactivity including proton-coupled electron transfer or hydrogen atom transfer processes. The pincer nitrogens are directed outward and have a demonstrated ability to shuttle hydrogens, which converts the bound nitrogen to ammonia and amines; these products are commercially important chemicals. The conversion of molecular nitrogen into value-added products is of particular interest as it uses environmentally-friendly and low cost metals in the active catalyst.