Transformations Leading to the Generation of Dithiolene Ligands Initiated by Reactions of Sulfur-Rich WS(S₂)(S₂CNR₂)₂ Complexes with Dimethyl Acetylenedicarboxylate and Phenylacetylene

Purple W(S₂C₂R‘₂){SC(R‘)C(R‘)SC(NR₂)S}(S₂CNR₂) (1, donor atoms italicized) are formed in the reactions of WS(S₂)(S₂CNR₂)₂ (R = Me, Et) with dimethyl acetylenedicarboxylate (DMAC, R‘ = CO₂Me) in dichloromethane at room temperature or phenylacetylene (R‘ = Ph/H) in refluxing 1,2-dichloroethane. These complexes undergo CS−C(NR₂) bond cleavage upon photolysis to produce green thiocarboxamido species, W(S₂C₂R‘₂)₂(S₂CNR₂)(SCNR₂) (2), which in turn convert to orange, anionic, bis(dithiolene) complexes, [W(S₂C₂R‘₂)₂(S₂CNR₂)]^- (3, isolated as various tetraalkylammonium salts). The complexes have been characterized by microanalysis, IR, UV−visible, and ¹H and ¹³C NMR spectroscopy. An X-ray crystal structure of 1a·0.5H₂O (R = Me, R‘ = CO₂Me) revealed two independent, pseudo-enantiomeric, eight-coordinate complexes containing novel κ⁴-SC(R‘)C(R‘)SC(NR₂)S^- and bidentate dithiolene and dithiocarbamate ligands. Complexes 2 are fluxional at room temperature and exhibit IR and ¹³C NMR signals characteristic of thiocarboxamido (ν 1590 cm^-1, δ 226−228), dithiocarbamate (ν 1540 cm^-1, δ 190−201), and dithiolene ligands. An X-ray crystal structure of NEt₄[3a] (R = Me, R‘ = CO₂Me) revealed an S₆-donor, trigonal-prismatic anion possessing bidentate dithiocarbamate and dithiolene ligands. In the sequence of transformations, WS(S₂)(S₂CNR₂)₂→1→2→3, the construction of two dithiolene ligands from two alkyne units and three chemically distinct sulfur-donor ligands (thio, disulfido, dithiocarbamate) has been tracked for the first time.