An EPR and DFT investigation of the products formed in the reaction of group 11 metal atoms with three-membered heterocyclic compounds

Abstract

Transition metals have been shown to be efficient catalysts in a variety of organic reactions. In particular, Group 11 metals have emerged as essential components in the carboxylation or metal-catalyzed ring expansion of three-membered heterocyclic compounds. Previous reports have speculated the presence of short-lived metal-substrate complexes and metallacyclic intermediates along the reaction path, yet to date there is no direct evidence for their existence. Using cryogenic matrix isolation EPR spectroscopy, we were able to characterize several highly reactive intermediates formed in the reactions of Group 11 metal atoms, Cu, Ag, and Au, with small, strained, heterocyclic compounds, namely, oxiranes, thiiranes, and aziridines. Experimental data indicates that the major products formed are mononuclear metal complexes, M-XCH2CH2 (X = O, S or NH). In addition, reaction mixtures containing Cu atoms and oxiranes or thiirane yield novel metallacycles, i.e., cupraoxetane and cuprathietane, respectively. DFT calculations were also used to support the structural assignments of the M-XCH2CH2 complexes.