Multiconfigurational Electronic Structure of Nickel Cross-Coupling Catalysts Revealed by X‑ray Absorption Spectroscopy

• Published in: The journal of physical chemistry letters 2025-01, Vol.16 (1), p.87-94
• Main Authors: Nelson, Kacie J., Kazmierczak, Nathanael P., Cagan, David A., Follmer, Alec H., Scott, Thais R., Raj, Sumana L., Garratt, Douglas, Powers-Riggs, Natalia, Gaffney, Kelly J., Hadt, Ryan G., Cordones, Amy A.
• Format: Article
• Language: English
• Subjects: Covalent bonding; Electronic structure; Letter; Ligands; Metal to ligand charge transfer; Metals; Physical Insights into Chemistry, Catalysis, and Interfaces
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c02917

NiII 2,2′-bipyridine complexes are commonly invoked intermediates in metallaphotoredox cross-coupling reactions. Despite their ubiquity, design principles targeting improved catalytic performance remain underdetermined. A series of Ni­(Rbpy)­(R′ Ar)Cl (R = MeOOC, t-Bu, R′ = CH3, CF3) complexes were proposed to have multiconfigurational electronic structures on the basis of multiconfigurational/multireference calculations, with significant mixing of Ni → bpy metal-to-ligand charge transfer (MLCT) configurations into the ground-state wave function. Here, Ni K-edge and L2,3-edge X-ray absorption spectroscopies provide experimental support for the highly covalent and multiconfigurational electronic structures of these complexes. The pre-edge intensity in the K-edge spectrum reflects highly covalent Ni–aryl bonding. The L3-edge spectral shape is dependent on ligand functionalization, and a feature reflecting the MLCT character is assigned using prior ab initio and new semiempirical calculations. The results suggest the push/pull effects of the aryl/bpy ligands moderate the changes in electron density on Ni during the multiredox cross-coupling reaction cycle.