The coordination of alkali-metal nickelates to organic π-systems: synthetic, structural and spectroscopic insights

• Published in: Dalton transactions : an international journal of inorganic chemistry 2024-05, Vol.53 (19), p.8382-839
• Main Authors: Borys, Andryj M, Vedani, Luca, Hevia, Eva
• Format: Article
• Language: English
• Subjects: Anthracene; Bonding strength; Chemical reactions; Chemistry; Coordination; Cross coupling; Crystallography; Ethers; Imines; Ketones; Ligands; Lithium; Nitriles; NMR spectroscopy; Phenanthrene; Polycyclic aromatic hydrocarbons; Reagents; Single electrons; Stoichiometry; Substrates
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d4dt00889h

Low-valent nickelates have recently been shown to be key intermediates in challenging cross-coupling reactions using aryl ethers as electrophiles. Key for the success of these transformations is the activation of the substrate through π-coordination to the nickelate intermediate, however there is still limited knowledge about the fundamental structure and coordination chemistry of these heterobimetallic complexes. Herein, we report the synthesis, structures, and spectroscopic analysis of a diverse family of alkali-metal nickelates derived from phenyl-alkali-metal reagents and Ni( ttt -CDT), where ttt -CDT = trans , trans , trans -1,5,9-cyclododecatriene. The co-complexation of PhLi with Ni( ttt -CDT) was found to yield 1 : 1, 2 : 1 or 4 : 2 lithium nickelates depending on the stoichiometry and reaction conditions employed. The high lability of the ttt -CDT ligand enables facile ligand exchange with an assorted series of organic π-acceptors, ranging from polyaromatic hydrocarbons to ketones, imines and nitriles. For anthracene and phenanthrene, a homologous series of Li, Na and K nickelates could be obtained, which lead to different structural motifs or degrees of aggregation in the solid-state spanning solvated monomers to complex polymeric arrangements. For π-extended systems such as perylene or coronene, competing single-electron-transfer to give the corresponding radical anions was observed, illustrating the highly reducing nature of the alkali-metal nickelates. X-ray crystallographic analysis and NMR spectroscopy of the phenyl-alkali-metal nickelates reveal extreme back-bonding from Ni(0) to the organic π-acceptors due to strong σ-donation from the carbanionic ligands. By assessing of the co-complexation chemistry of PhM (M = Li, Na or K) with Ni( ttt -CDT) in the presence of organic π-acceptors, new structural and spectroscopic insights into the coordination chemistry of alkali-metal nickelates have been gained.