Highly Active Mechanochemically Generated Main Group and Lanthanide Complexes

Vanderbilt University, Nashville TN

Investigators

Abstract

This project is funded by the Chemical Synthesis Program of the Chemistry Division. Professor Timothy Hanusa of the Department of Chemistry at Vanderbilt University explores the extent to which common metals can replace rare-earth metals in various applications. The rare earths have hundreds of uses in medicine, electronics, and chemistry. However, they are expensive and at present there is no active source of these elements in the United States. This has resulted in uncertainties over the future supply and availability of the rare earths. As a consequence efforts to develop replacements for the rare earths is a strategic priority. This project targets the development of compounds that contain aluminum, calcium, or strontium (common inexpensive metals) and whose behavior resembles that of the rare earths. This is done using a unique technique called mechanochemistry to prepare normally inaccessible compounds of the three metals. In mechanochemistry reagents are ground or ball milled together without solvent. Because these compounds lack solvent, rare earth like behavior can be induced in them. These are then developed as replacements for rare earths in a various applications. An additional advantage of mechanochemistry is that no solvent must be disposed of and, consequently, there is less chance for pollution. The project also provides research opportunities for a variety of students including women, underrepresented minorities, and both middle and high school students. Such training and development of students is critically important for preparing the next generation of domestic science and technology personnel capable of competing in the global marketplace. This project emphasizes the use of sterically bulky allyl ligands that are compatible with a wide range of metals and possess high conformational flexibility. In conjunction with the solventless synthesis, these ligands stabilize complexes with low coordination numbers and corresponding high reactivity. The new compounds are studied with NMR spectroscopy, X-ray crystallography, and density functional theory calculations. The most promising are tested for their catalytic polymerization activity. The broader impact of the research includes the training of undergraduate and graduate students, and participation in various educational and outreach programs involving Vanderbilt during the academic year and summer. These activities encourage the students to participate in multiple areas of modern science.