With this award, the Chemical Synthesis Program of the Chemistry Division is funding Professors Grotjahn and Cooksy of the Department of Chemistry and Biochemistry at San Diego State University to use biomimetic design principles in developing new organometallic catalysts. Proposed bifunctional catalysts use reactivity of both a late transition metal and a group capable of proton transfer or hydrogen bonding. Ligands containing proton-donating or hydrogen-bonding groups will be synthesized and combined with a variety of metal precursors to form metal complexes. Addition and isomerization reactions are the focus of the research, because they are atom-economical and waste-free. The collaborative team will determine properties of complexes to explain how they function as catalysts. The coordination, hydrogen-bond donating and accepting properties of both catalytically active and inactive complexes will be studied by a combination of NMR and IR spectrometry, kinetics, and X-ray crystallography. Maps of the reaction potential energy surfaces using density functional theory will model the reaction mechanisms, with particular attention paid to the role(s) of hydrogen bonding or proton transfer and the ligand dependence of the reaction kinetics.
There are potential wider implications of this work for the field of catalyst design. Successful development of the methodology would likely have an impact on synthesis in the pharmaceutical and agricultural industries, and may contribute to more efficient and hence greener processes. Other broader impacts involve training undergraduate students, graduate students and postdoctoral researchers in designing, making and testing organic compounds and catalysts. Moreover, in outreach efforts to highlight the nature and importance of catalysis, SDSU students participating in the project will travel with Cooksy to local schools, where they will introduce students to 3D visualization of molecular structure and bonding.
Catalysis enables the efficient and environmentally sound synthesis of organic compounds, both on laboratory and industrial scales. Because catalysis accounts for a third of global gross domestic product, and a majority of chemical products and chemical processes, the discovery of new or improved catalysts for organic reactions and new mechanisms has tremendous practical importance, contributing to economic development and recovery. This project uses design principles of Nature’s enzymes to accelerate organometallic catalysis and reactions by new mechanisms, in several cases by factors of more than 1,000. Specifically, the project uses catalysts that not only contain a metal ion, but also a part of the catalyst called a ligand, that is designed, then made in the lab, and combined with the metal and tested. Hundreds of such metal-ligand combinations are made and tested and the results compared, in order to test our hypotheses about what makes a superior catalyst. The ligands all are designed to bind to a metal and also move hydrogen atoms (in the form of protons), thus resembling enzymes. Key outcomes of the project are as follows: (1) The most thorough study to date of why one of our catalysts is so fast was published in 2013. The catalyst had been discovered in a previous project and published in 2004, and subsequent experiments gave a better idea of how the proton-moving part of the catalyst helped the metal do its job of adding water to a carbon-carbon triple bond (an alkyne), but more than 1000 times faster without the proton-moving part. Our 2013 study used computer calculations to predict the molecular structures of fleeting forms of the catalyst (intermediates) that we could not detect by experiment, showing us that the proton-moving portion of the catalyst helped speed the overall reaction at several points of the catalyzed reaction. Ongoing further studies will use the computer to model what happens when we change the proton-moving ligand, and guide further lab experiments. (2) A recyclable version of a catalyst that moves carbon-carbon double bonds (alkenes) was published in 2014. We made a version of an alkene "zipper" isomerization catalyst (first reported by us in 2007) on a granular solid designed not to dissolve in a reaction solution. At the end of the reaction, one can filter off the solid catalyst and recover it for additional uses, making it easier to purify the product. (3) In 2014 we published the first known catalyst for simultaneously controlling two outcomes of moving a carbon-carbon double bond in a 1-alkene, which has the carbon-carbon double bond at the end of a chain of carbon atoms (and is also known as an "alpha olefin," a common petrochemical product). The two challenging outcomes are (a) moving the double bond only once, from the 1-position to the 2-position, without going any further, and (b) producing only one shape of the 2-alkene, one where the non-hydrogen groups on the alkene are opposite each other (known as trans or E). There are a few other catalysts that can achieve the first outcome but they can not achieve the second, whereas our catalyst does both and makes up to 95% of a single alkene product, which makes it significantly more useful. Ongoing studies have shown that we can make a much faster version of the catalyst we published in 2014, and we expect to publish in 2015. Both versions are subject of a patent application. (4) We have found new ways to make, use, and study a new type of catalyst, with protic N-heterocyclic carbene (protic NHC) ligands. NHC ligands have been the subject of thousands of papers in the last 20 years because of many useful properties they impart on catalysts, but protic NHC ligands are much rarer, perhaps the subject of 50 papers so far. Our goals are to see if the protic aspect improves catalysis further.
