Researchers of the Zelinsky Institute investigated the nature of the bond between carboxylate radicals and metals

Metal complex catalysis is currently one of the most promising approaches to the synthesis of many organic compounds. However, the development of efficient catalytic systems is impossible without a detailed understanding of the processes occurring between the substrate, the metal center of the catalyst, and the ligand. One of the most difficult questions in metal-catalyzed oxidation processes is the nature of active intermediates. Is there a generation of free radical species? Or are these particles bound to the metal? Or maybe we are dealing with a metal center in higher oxidation states?

Scientists from the Laboratory for the Study of Homolytic Reactions of the ZIOC together with colleagues from Florida State University, answer these questions in their work on metal-catalyzed acyloxylation of C(sp3)-H bonds with cyclic diacyl peroxides. The reaction proceeds through the formation of carboxylate radicals, which are able to avoid decarboxylation while remaining reactive.

As a rule, carboxylate radicals bind to the metal as an X-ligand and lose their radical nature. Using computational and experimental methods, the authors found that there was a way to make the carboxylate a monodentate L-ligand and retain the radical character. It was shown that the carboxylate radical acted as L-ligand with some high-spin transition metal centers. Such coordination retains the O-radical character necessary for the activation of the C-H bond through the transfer of a hydrogen atom. Interception of the new C-radical by the metal and subsequent reductive elimination leads to formal acyloxylation of the C-H bond.

Source:

Leah Kuhn, Vera A. Vil’, Yana A. Barsegyan, Alexander O. Terent’ev, Igor V. Alabugin Carboxylate as a Non-innocent L-Ligand: Computational and Experimental Search for Metal-Bound Carboxylate Radicals Org. Lett., 2022, accepted manuscript. DOI: 10.1021/acs.orglett.2c01356.