Synthesis, structural analysis and reactivity of alkynyl sulfide anions

Ketenyl anions are versatile, isolable reagents that facilitate the formation of ketenes, carbonyl-containing compounds, and functionalized heterocycles. In contrast, their thio analogues have only been prepared in situ and their alkali metal complexes remain elusive. Here, we report the facile synthesis and isolation of a series of thioketenyl anions through CS-for-CO exchange, using carbon disulfide or thioisocyanates as CS transfer reagents. Spectroscopic and crystallographic studies, combined with quantum chemical calculations, reveal that the electronic structure of these anions is best described by the alkynyl sulfide form with a C-C triple bond, with a minor contribution from the thioketenyl structure. This differs from previously reported related anions and can be attributed to the enhanced π-accepting properties of the carbon monosulfide ligand, which can be rationalized by the Dewar-Chatt-Duncanson model. This insight bridges the bonding in these carbanionic species with that in transition metal complexes. The unique bonding in alkynyl sulfides is reflected in their reactivity patterns, opening pathways to sulfur-heterocycles and neutral alkynyl sulfides via S-centered reactivity.