Adducts of Acetylene and Dimethylacetylenedicarboxylate at Sulfurs in Sulfur-Bridged Incomplete Cubane-Type Tungsten Clusters

Reactions are reported of sulfur-bridged incomplete cubane-type tungsten clusters having W(3)(micro(3)-S)(micro-S)(3) cores with acetylene and its derivative dimethylacetylenedicarboxylate (DMAD). The reaction of the isothiocyanate tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(NCS)(9)](5)(-) (5) with acetylene in 0.1 M HCl afforded a novel complex having two acetylene molecules in different adduct formation modes, [W(3)(micro(3)-S)(micro(3)-SCH=CHS)(micro-SCH=CH(2))(NCS)(9)](4)(-) (6), and the presence of two kinds of intermediates [W(3)(micro(3)-S)(micro-S)(micro(3)-SCH=CHS)(NCS)(9)](5)(-) (7) and [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) was observed. The reaction of the diethyldithiophosphate (dtp) tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(micro-OAc)(dtp)(3)(CH(3)CN)] (10) with DMAD in acetonitrile containing acetic acid resulted in the formation of another complex having two DMAD molecules of different adduct formation modes, [W(3)(micro(3)-S)(micro-SC(CO(2))=CH(CO(2)CH(3)))(micro(3)-SC(CO(2)CH(3))=C(CO(2)CH(3))S)(micro-OAc)(dtp)(3)] (11), where hydrolysis of one of the four ester groups of the two DMAD groups occurred and the resultant carboxylic group coordinated to tungsten. The conformation of the micro-SCH=CH(2) moiety in 6 is different from that of the corresponding moiety in [W(3)(micro(3)-S)(micro-O)(micro-S)(micro-SCH=CH(2))(NCS)(9)](4)(-) (4). Introduction of the second acetylene molecule to the intermediate [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) resulted in the formation of 6. The clusters were characterized by UV-vis spectroscopy, (1)H NMR spectroscopy, and X-ray crystallography (for (Hpy)(4).6.1.33py.0.5H(2)O and 11.CH(3)CN), and the formation of 6 and 11 was examined in detail from a mechanistic point of view.