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(S 2C2R‘2){SC(R‘)C(R‘)SC(NR2)S}(S 2CNR2) (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(S 2C2R‘2)2(S 2CNR2)(SCNR2) (2), which in turn convert to orange, anionic, bis(dithiolene) complexes, [W(S 2C2R‘2)2(S 2CNR2)]- (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.