Scientists from the ZIOC have for the first time experimentally established the spatial structure of the oxime radical

Oxime radicals (iminoxyls) are key presumable intermediates in the oxidation of oximes, including the processes of CH-functionalization and in the synthesis of functionalized isoxazolines by oxidative cyclization of oximes. The fundamental feature distinguishing iminoxyls from other N-oxyl radicals is their belonging to the class of sigma radicals. In other words, in oxime radicals, the unpaired electron is not delocalized along the main pi-system of the molecule (as in most stabilized radicals, called pi-radicals), but is located on an orbital orthogonal to this pi-system. As a rule, oxime radicals rapidly decompose and, due to the lack of X-ray diffraction data, knowledge about their structure has been based on indirect spectral data (EPR, IR) and quantum chemical calculations.

In one of the latest works by researchers from the Laboratory for the Study of Homolytic Reactions of the Zelinsky Institute, the structure of the diacetyliminoxyl radical was established for the first time by X-ray diffraction analysis by obtaining a single crystal of its complex with copper(II) hexafluoroacetylacetonate (Cu(hfac)2). It was shown that the oxime radical coordinated with copper ions through the oxygen atoms of carbonyl groups without the direct participation of the C=N–O• fragment. The structure of the coordinated diacetyminoxyl is in good agreement with the density functional theory (DFT) prediction for free diacetyliminoxyl due to the very weak interaction of the radical molecule with copper ions. This study not only makes a fundamental contribution to the understanding of the structure and reactivity of oxime radicals, but also demonstrates for the first time the possibility of using oxime radicals in the design of molecular magnets.

Source:

Budnikov, A. S.; Krylov, I. B.; Ushakov, I. E.; Subbotina, I. R.; Monin, F. K.; Nikishin, G. I.; Efimov, N. N.; Gorbunov, D. E.; Gritsan, N. P.; Tretyakov, E. V.; Yu, B.; Terent’ev, A. O. Two Discoveries in One Crystal: σ-Type Oxime Radical as an Unforeseen Building Block in Molecular Magnetics and Its Spatial Structure // Inorg. Chem. 2023, 62, 10965–10972. DOI: 10.1021/acs.inorgchem.3c00947.