Structural characterization of organometallic reaction intermediates and vibrational mechanics of water cages with temperature-controlled cryogenic ion spectroscopy

Yale University, New Haven CT

Investigators

Abstract

With this award, the Chemical Structure, Dynamics and Mechanisms program is supporting fundamental research of Professor Mark A. Johnson at Yale University. Johnson is developing a new type of scientific instrument that yields precise structural information on complex molecular architectures extracted from solution. Under this grant, he will expand the scope of the method to enable the capture and structural characterization of key reaction intermediates that underlie the mechanisms of small molecule (e.g., alkenes, H2O, H2) activation by contemporary homogeneous organometallic catalysts. The motivation to identify these transient species is that, at present, much of the effort in catalyst design involves extensive trial and error based on overall yield, while little is often known about exactly what aspects of the chemical transformation are being affected by the various modifications. Students and visiting faculty involved in this endeavor integrate elements of bioanalytical chemistry with atomic, molecular and optical (AMO) physics to create a new platform for chemical analysis. As such, this program directly interfaces physical chemistry students with immediate challenges addressed by synthetic colleagues, and consequently prepares a new generation of scientists with a versatile skill set, well centered in the chemical sciences. An ongoing and extensive collaboration with theoretical colleague Prof. Anne McCoy at Ohio State further broadens the impact of the work by creating an interactive venue for young theorists to sharpen their skills on emergent scientific themes. Graduate students and postdocs directly involved in the project also work in close collaborations with laboratories in Germany. This also contributes to their preparedness to perform at an increasingly competitive international level in the elite arena of basic science. Closer to home, this program integrates faculty from undergraduate institutions through summer research opportunities, and students from nearby universities without graduate programs are incorporated into ongoing work by carrying out senior research projects at Yale. Finally, this program has a longstanding tradition of opening its doors to students in the New Haven schools to illustrate how the basic science principles they are learning are in play at the foundation of the new methods under development. Cryogenic Ion Vibrational Predissociation Spectroscopy (CVIP) is a new instrumental technique which integrates mass spectrometry with high resolution infrared spectroscopy. One key feature of the approach is the implementation of cryogenic processing of the gas phase ions to effectively quench the reactive species into well-defined structures that yield sufficiently sharp features in their vibrational spectra to allow structure determination. This is carried out using vibrational predissociation spectroscopy of very weakly bound adducts attached to target ions in a custom built, radio frequency ion trap held at 5K. In addition to its application to catalysis, the proposed work also addresses key unanswered questions regarding the critical local interactions that underlie bulk behavior of pure water as well as the layer of water molecules in direct contact with charged solutes. Because the microscopic behavior of water is central to so many fields of science, this aspect of the work is ongoing, and has impacted efforts ranging from the mechanism of vision to the remediation of heavy metals in contaminated environments.