Oxazolone copper(I) complexes inspired by the methanobactin active site

Two oxazolone-derived potential ligands with enethioether substituents have been synthesized that differ by the terminal thioether moiety (S-Et in L1, S–C6H4(OMe)-2 in L2). Both L1 and L2 behave as bidentate {NS} chelate ligands to form stable complexes with copper(I) triflate that crystallize as dimeric complexes [L2Cu2(OTf)2] (4 and 5) featuring a central {Cu2S2} diamond core with distinctly different Cu–S bonds. L1 as well as 4 and 5 have been characterized by single crystal X-ray diffraction. NMR spectroscopy including 1H and 19F DOSY experiments reveals that 4 and 5 dissociate into monomeric species [LCu(OTf)] (4′ and 5′) in CDCl3 solutions. 4′ and 5′ retain the {NS} binding motif of the oxazolone-derived ligands, but are in slow equilibrium with their {OS} isomers 4″ and 5″ that result from E/Z isomerization of the exocyclic enethioether double bond.