CAS: Photoactive Fe and Co Organometallic Compounds Supported by Tetra-imine

Purdue University, West Lafayette IN

Investigators

Abstract

With funding from the Chemical Synthesis Program in the Division of Chemistry, Professor Tong Ren and his team at Purdue University will study complexes of interesting photo-activity based on earth abundant metals. Chemists have made great strides in molecular photovoltaics using so called dye-sensitized solar cells, and in photoredox catalysis for more efficient production of medicines. Currently, both technologies rely heavily on rare precious metals such as Ru and Ir. Due to rarity and expense of these metals, the development of molecules with similar photon-capturing capability but based on earth abundant metals such as Fe and Co is highly desirable. However, most compounds based on earth abundant metals lose the captured solar energy (so called excited state) before converting it into electricity or using it to promote a reaction. Professor Ren and his team will extend the lifetimes of excited states by using a new family of macrocycles to support Fe and Co containing molecules, and hence improve the efficiency of solar energy utilization. Professor Ren and his team will work with the Purdue College of Science K-12 Outreach team, especially in introducing new teaching modules that reflect the heightened interest in sustainable chemistry. The PI and his coworkers will also play a proactive role in the Superheroes of Science, a program of Purdue College of Science K-12 Outreach, which develops a variety of science content for educators, including virtual labs for high school students. Organometallic chemistry of metal tetra-aza macrocycle complexes is a vibrant and evolving field. This project will seek to elucidate the impact of the tetraimine macrocycle TIM (2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) on the electronic structures, photophysical and photochemical properties of its 3d metal organometallic complexes. Fe(II)-TIM complexes will be synthesized and optimized as new metal-to-ligand charge transfer chromophores. The related Fe(III)-TIM alkynyl / aryl / alkyl complexes will be developed as ligand-to-metal charge transfer chromophores. As analogues of vitamin B12, Co(III) species containing Co-C(sp2) and Co-C(Sp3) bonds, such as [CoIII(TIM)RL]+ and [CoIII(TIM)(R)(R')]+, will be investigated with a focus on photo-induced Co-C cleavage reactions therein. While the primary focus of the project is the synthesis of novel Fe/Co(TIM) organometallics, the nature of excited states will be explored using both experimental (fs transient absorption and M edge XANES) and computational (CASSCF/CASPT2) approaches through collaborations with the groups of Vura-Weis at University of Illinois Urbana-Champaign and Vlaisavljevich at South Dakota (now University of Iowa), respectively. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.