The drive to understand C–H activation and the ability to selectively forge new C–C and C–X bonds has captivated synthetic inorganic and bioinorganic chemistry for decades. Synthetically, C–H breaking and C–X forming reactions have traditionally been achieved using toxic and expensive second and third row TMs such as Pd, Pt, Ir, etc, capable of undergoing multi-electron, metal-centered redox. In the past decade, however, Ni has emerged as an attractive alternative to Pd and Pt for carrying out these transformations. High valent NiIV and NiIII species bearing CF3 substituents prepared by the Sanford and Mirica have enabled trifluoromethylation reactions that are desirable from the standpoint of affording useful pharmacokinetic properties to drug varants. The incorporation of CF3 groups into ligand motifs have been shown to result in highly covalent metal-ligand bonds resulting in an inverted ligand field, where the majority of electron deficiency lies on the ligand as opposed to the metal. In collaboration with Melanie Sanford we have investigated several Ni species with formal oxidation states ranging from NiII to NiIV. Through the use of Ni L2,3-Edges, Ni K-edge XAS and RIXS in concert with time-dependent density functional theory (TDDFT) and DFT-restricted open configuration interaction with singles (DFT-ROCIS) calculations we have shown that the unoccupied molecular orbitals in NiIII and NiIV are highly covalent and possess at most ~40% Ni 3d character. While the reactivity of these species has been thoroughly investigated, the electronic structure of the active catalyst, as well as the hole character on the ligand remains a major knowledge gap in this research. A thorough understanding of the physical oxidation state of the active Ni catalysts is not only fundamentally interesting, but will provide a framework for guiding the design and function of green catalyst design using environmentally friendly late-first row transition metals, as well as offer insight into our understanding of oxidation states in transitions metals as a whole.

Bridging Ni electronic structure and reactivity: A spectroscopic and theoretical approach

255th National Meeting (2018)

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