Preparing Early Transition Metals with Metal-Ligand Multiple Bonds: Atom- and Group-Transfer, Anchors to Support Heterobimetallics, and Carbon-Hydrogen Activation

With the support of the Chemical Synthesis (SYN) program in the Division of Chemistry Professor Daniel Mindiola of the University of Pennsylvania is studying the development of well-defined complexes that can challenge current paradigms of acid-base chemistry. Specifically, this proposal seeks the deprotonation of un-activated carbon-hydrogen bonds in vast resources such as natural and shale gases. The proposal aims to convert these vast natural resources into liquid fuels or chemical reagents of greater added-value, which have far superior advantages for both transport and storage. Acids and bases are quintessential topics covered in every general or advanced chemistry courses since these are utilized in a variety of everyday applications ranging from water purification, selective precipitation and metal refinement, but extend to biological ramifications such as buffers and the importance of pH and equilibria. An extreme of an acid is a super acid, a fundamental topic in organic chemistry, which is heavily tied to mechanisms involving the rearrangement of carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds. The other extreme, a super base, is less known. The original proposal aims to address this uncharted territory by systematically tuning the super base in a well-defined metal complex by changing one atom at a time. The systems proposed here offer the opportunity to switch one atom, without perturbing the rest of the support, and thus allow them to probe its bonding and reactivity. They can tune the systems by changing the metal ion stabilizing the super base, as well as the atom directly involved in the deprotonation event. This proposal will apply the systems for the deprotonation of hydrocarbons, atom- and group-transfer reaction involving hydrocarbons, as well as use the super bases as an anchoring site for catalysts that can activate and functionalize C-H bonds. The proposal allows students to be trained in manipulating gases, liquid and solids, but also air-free techniques. Students will also be exposed and trained in many spectroscopic and analytical methods to characterize unusual compounds. The research program will integrate the Penn Summer Chemistry Research Academy to introduce high school students to research, as well as the NSF REU program. This proposal will also communicate some of their laboratory experiments to the public through the YouTube group channel “MindiScience” and through public presentations that require more involvement of the audience. This research program seeks to synthesize and isolate earth-abundant metal complexes containing titanium, niobium, and vanadium among other base metals, and that can support a one-coordinate atom (a pnictide: N3-, P3-, As3-, Sb3-, and Bi3-). This strategy will involve making a metal-ligand multiple bond (MLMB) with the metal ion. This modular approach to making these molecules can selectively tune the metal ion as well as the pnictide making the MLMB. By changing either one of these atoms this proposal can probe the superbasicity of the pnictide, the role of charge, diagonal relationships, relativistic effects, as well as the covalency (or ionic nature) in the bonding involving the metal and the pnictide. This study will explore their super basic properties and exploit deprotonation reactions of hydrocarbons as well as pnictide and group-transfer reactions. Lastly, the proposed work will use MLMB as an anchor to support and tune catalysts that can activate and functionalize C-H bonds present in hydrocarbons, specifically those that are not useful as liquid fuels. 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.