Increasing the Electrophilicity at Boron via Carborane Substituents

Baylor University, Waco TX

Investigators

Abstract

With the support of the Chemical Synthesis program in the Division of Chemistry, Caleb Martin and his research team at Baylor University will study the synthesis of strong boron Lewis acids that feature non-conventional electron withdrawing substituents. Strong Lewis acids are essential to many important catalytic industrial and laboratory processes. Currently, boron compounds that contain fluorine are used in these reactions. However, there are pending Environmental Protection Agency mandates that will restrict the use of fluorine containing reagents that are set to begin 2025. Thus, replacements for the current boron-fluorine catalysts are essential. This project will develop an alternative to fluorine for boron-based catalysts for bond activation chemistry. This project also involves efforts to engage homeless high school students to stimulate their interest in science fields. Additionally, an annual advanced instrumentation workshop will host students and faculty from local small colleges. In this project, the Martin research team will synthesize boranes that feature icosahedral carborane clusters as electron withdrawing groups. A goal is to obtain boranes whose Lewis acidity is enhanced over that of their fluoroaryl counterparts. This enhancement will reflect electronic effects of the carborane substituent as well as the impact of carborane steric profiles upon the Lewis acid properties of these new boron-centered systems. The bulk and Lewis acidity of tris(ortho-carboranyl)borane will be investigated in frustrated Lewis pair chemistry. The other target, bis(1-methyl-ortho-carboranyl)borane, features a highly polar B-H bond. The reactivity of this bond as well as the stability of aryl variants will be studied. The proposed work will investigate the reactivity and properties of the newly synthesized borane Lewis super-acids. If successfully, the development of such new classes of non-fluorine-based boron-centered Lewis acids, could have a broad impact on synthetic and mechanistic chemistry, with implications for sustainable chemistry. 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.