CAS: Can the Ionic Character of 1st Row and the Covalency of 2nd and 3rd Row Transition Metals Converge?

Cornell University, Ithaca NY

Investigators

Abstract

General Public Abstract: The Chemical Synthesis Program of the Chemistry Division of the National Science Foundation supports the research of Professor Peter T. Wolczanski of Cornell University. The project seeks to train candidates in the fields of metal-centered chemistry. Most commodity (bulk) and fine (pharmacological) chemicals are synthesized utilizing catalysts. These catalysts are typically transition metal compounds that accelerate the rates of reaction. Many of these catalysts use metals that are in low abundance, toxic, and expensive. This program is studying the synthesis of cheaper catalysts, but they must be modified by organic materials -- termed ligands -- in order to provide the chemical reactivity necessary to replace the current generation of catalysts used in industry. One general solution being explored is the investigation of ligands that promise to render the cheaper metals more versatile or adaptable. Another general approach is to synthesize metal systems that will underpin truly transformative processes: the preparation of compounds that are capable of multistep chemical reactions. A specific application targets the synthesis of complexes using propellar-shaped molecules that rupture to give what are called alkylidene ligands. Synthesis of alkylidene-metal compounds would have broad implications for the advanced manufacturing within the U.S. chemical industry. The Cornell group is also supports STEM education of 5th grade and high school students. The STEM efforts include lecture materials and hands-on training modules. These activities are helping to strengthen the workforce available to support the US chemical industry. Technical Abstract: The Chemical Synthesis Program of the Chemistry Division of the National Science Foundation supports the research program of Professor Peter T. Wolczanski of Cornell University. The project seeks to train PhD candidates in the fields of inorganic and organometallic chemistry. The research identifies several reactions that are potentially transformative in regards to commodity (bulk) and fine (pharmacological) chemicals production. Typical transition metals used in catalysis are in low abundance and costly, and the work proposes to supplant these species with inexpensive 1st and 2nd row species. Various ligand platforms that display redox non-innocence, including a reversible C-C bond formation, are employed to expand the redox capacity of several first-row metals. Other 3- coordinate chelates are also involved in H-transfer chemistry to further expand the scope of reactivity. Exploration of ionic vs. covalent bonding is fundamental to the work. Transfer HX and H2 additions, akin to transfer hydrogenations, and processes like hydroformylation, are targeted with early metal systems. Specific systems show potential for tandem CH activation in conjunction with olefin metathesis, leading to a net exchange of H2 for CH2, and one tridentate ligand has the potential for an alternate polymerization mechanism to Ziegler-Natta. Unique strained reagents are employed as alkylidene generators for numerous transition metals, as replacing expensive Ru-based olefin metathesis catalysts is an important target. The production of independent, versatile PhDs capable of adapting to a challenging and fluctuating academic or industrial market is a major objective, and the further development of Charge Distribution Via Reporters (CDVR) as a pedagogical alternative to formal oxidation states will continue to be tested. The Cornell group is also preparing a general 5th grade outreach program for publication based on experience, and is developing a related outreach program for high school students. 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.