Platform-Supported Pairs of Lewis Acidic Metal Cations to Control and Catalyze Dinitrogen Functionalization

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

With the support of the Chemical Synthesis (SYN) Program of the Chemistry Division, Professor Polly Arnold of the University of California–Berkeley, is studying the structure, bonding, and reactivity of f-block molecules with the long-term, ambitious goal of converting atmospheric nitrogen to ammonia and amines. Nitrogen gas (N2) is the major component of the atmosphere and potentially an inexpensive, chemically benign starting material for the industrial preparation of a vast variety of important chemical products. Currently, it is the feedstock for a single commercialized reaction, the Haber-Bosch process, which converts nitrogen to ammonia. This process is used on an enormous scale and provides the major source of nitrogen fertilizer worldwide. However, it functions at high temperatures and pressures, both consuming much energy and generating roughly 1% of global annual carbon dioxide emissions. Consequently, the discovery of more efficient processes to convert nitrogen to useful projects is extremely important. This project seeks to develop rare earth compounds that will mediate the conversion of nitrogen into ammonia and related compounds at low temperatures and pressures without generating carbon dioxide. The fundamental research proposed herein is expected to make fundamental contributions to important, unanswered questions about the chemical bonding in compounds composed of some of the heaviest atoms in the periodic table. It will also train members of the future workforce in the chemistry of the technology-critical rare earth elements, and in sustainable catalysis, both of which are high priority science areas for the nation. Under this award, the Arnold team will develop bimetallic rare earth and related Lewis acidic metal complexes supported by rigid tetraphenolate ligands with important and challenging goal of arriving at entries into the first catalytic conversion of dinitrogen N2 to secondary silylamines by a non-radioactive complex. The proposed program will work with specific lanthanides and co-reductants, according to their size, redox potentials, and Lewis acidity, to define the role of d- and f-orbitals in the stabilization of reduced intermediates and to enable the synthesis of new functionalized amines. Because electrons can be stored and transported through the ligand framework, the proposed program is also designed to tease apart metal/ligand contributions and develop new, lower-energy ways to deliver the reducing equivalents to the N2. The project will train students is the handling and manipulation of sensitive rare earth compounds and in the development of these into reagents for the reduction of small molecules. 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.