RUI: Mechanisms of C-F and S-F Bond Activation and Cross-coupling with Bidentate N-heterocyclic Carbene Nickel Catalysts

In this RUI project, with support from the Chemical Structure, Dynamics & Mechanisms-B Program of the Chemistry Division, S. Chantal E. Stieber of the Department of Chemistry at California State Polytechnic University, Pomona is studying earth-abundant nickel catalysts for installing fluorine onto molecules with potential for future use in imaging and pharmaceuticals. The goal of this work is to determine how the structure of the nickel catalyst affects the reactivity with carbon-fluorine and sulfur-fluorine bonds, and the resulting catalytic performance. This work involves advanced organometallic, organic, and inorganic research training for students at a primarily undergraduate institution. This grant will additionally support paid summer research training positions, development of new research tutorial videos, and hosting diverse seminar speakers. Combined, these efforts will broaden participation in science and provide workforce training at an under-resourced Hispanic-serving institution. Nickel systems for carbon-fluorine and sulfur-fluorine activation are not widely explored, but have the potential to provide new routes for installing fluorine on molecules for 19F labeling, silylation, and borylation. This work will probe the fundamental reactivity of nickel toward carbon-fluorine and sulfur-fluorine bonds in aryl fluorides and sulfonyl fluorides as a function of the ligand environment and resulting effects on cross-coupling reactions. A series of bidentate N-heterocyclic carbene (NHC) nickel complexes will be synthesized to answer the following questions: (i) How do the ligand and the substrate affect cis- versus trans-oxidative addition of carbon-fluorine or sulfur-fluorine bonds at nickel? (ii) Does cis- versus trans-oxidative addition of carbon-fluorine and sulfur-fluorine bonds at nickel affect cross-coupling reactivity for silylation and borylation catalysis? and (iii) How does nickel react with sulfonyl fluorides as compared to aryl fluorides? These studies are expected to provide fundamental information on the structural features that confer maximal reactivity on Ni-NHC complexes for C-F and S-F bond activation. 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.