Small iron-carbonyl clusters bearing imidazolium-2-trithioperoxycarboxylate ligands

The reaction of [Fe₂(CO)₉] with two representative imidazolium-2-dithiocarboxylate zwitterions derived from common N-heterocyclic carbenes (NHCs) bearing mesityl (IMes) or 2,6-diisopropylphenyl substituents on their nitrogen atoms (IDip) unexpectedly afforded two small bimetallic iron-carbonyl clusters with the generic formula [Fe₂(CO)₆(μ-κ²-S,S'-κ²-S,S'-S₃C·NHC)]. After a brief optimization of the reaction conditions, these two "sulfur-enriched" products were isolated in low yields. They were fully characterized by IR, NMR, UV/Visible, and ESI-MS techniques, and their molecular structures were determined by single crystal X-ray diffraction analysis. The two compounds adopted a butterfly-type disposition in the solid state, with an [Fe₂(CO)₆] core bridged by the trithioperoxycarboxylate moiety of the in situ generated NHC·CS₃ ligands. Bond lengths recorded for the CS₃^- unit revealed that its negative charge was mostly located on the remote sulfur atom.