CAREER: CAS: Rational Development of Titanium Photocatalysis for the Generation, Utilization, and Control of Heteroatom-Centered Radicals

This project is developing catalysts based on earth-abundant titanium to promote value-adding chemical transformations of organic molecules driven by light. Photoactive metal catalysts are commonly used for organic synthesis. A key step in these reactions is the movement of electrons between the catalyst and the substrate. An alternative approach relying on catalyst-substrate interactions to turn on photoactivity will allow for new types of reactions and selectivities to be realized. Furthermore, while the former type of photocatalyst typically relies on rare precious metals, titanium is one of the most abundant metals in the earth's crust. Through rational design of the ligand environment on titanium, these catalysts can be fine-tuned to enable a multitude of valuable reactions. In addition, the project will support the expansion of an annual regional symposium focused on photochemistry to bring together researchers and students from various types of institutions to share science and provides opportunities to seed collaborations and facilitate the development of a near-peer mentoring network among students at local primarily undergraduate institutions and major research universities. Finally, the project will also support the development of a graduate-level course on photochemistry which crosses disciplinary silos to engender deeper understanding of this essential topic in modern chemical research. This project will rationally develop titanium-based catalysts capable of ligand-to-metal charge-transfer (LMCT) excitation to drive the generation and control of high-energy heteroatom centered-radicals. Through rational design of the ligand set on Ti, photophysical, photochemical, and redox properties can be fine-tuned to enable reactions transiting through oxidizing chlorine and alkoxyl radicals for carbon–hydrogen and carbon–carbon/carbon-oxygen bond functionalizations, respectively. This project will establish Ti-LMCT as a versatile platform for photocatalysis operating with a tunably wide redox window, with particular reaction pathways selected through catalytic control. Platforms will be developed for: (1) C–H bond functionalization through hydrogen atom-transfer (HAT) using novel, bench-stable bipyridinyl titanium chloride complexes; (2) alcohol C–C bond functionalization for enabling molecular derivatizations through catalyst-controlled, non-intrinsic selectivity paradigms; and (3) cascade activation by photochemically-driven Ti radical redox to functionalize C–O and C–C bonds in sequence for nominally inert bond activation. The proposed work will not only lead to the development of empowering chemical transformations driven by catalysts based on earth-abundant titanium, but will also lead to deeper understanding of strategies to leverage early transition metal photochemistry for catalysis and exert control over highly reactive radical species. 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. NSF Award ID: 2541378 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Jeffrey Lipshultz | Institution: SUNY at Stony Brook, STONY BROOK, NY | Award Amount: $800,566 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2541378 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2541378.html