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 W3(μ3-S)(μ-S)3 cores
with acetylene and its derivative dimethylacetylenedicarboxylate (DMAD). The reaction of the isothiocyanate tungsten
cluster [W3(μ3-S)(μ-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, [W3(μ3-S)(μ3-SCHCHS)(μ-SCHCH2)(NCS)9]4- (6), and the
presence of two kinds of intermediates [W3(μ3-S)(μ-S)(μ3-SCHCHS)(NCS)9]5- (7) and [W3(μ3-S)(μ-S)2(μ-SCHCH2)(NCS)9]4- (8) was observed. The reaction of the diethyldithiophosphate (dtp) tungsten cluster [W3(μ3-S)(μ-S)3(μ-OAc)(dtp)3(CH3CN)] (10) with DMAD in acetonitrile containing acetic acid resulted in the formation of another
complex having two DMAD molecules of different adduct formation modes, [W3(μ3-S)(μ-SC(CO2)CH(CO2CH3))(μ3-SC(CO2CH3)C(CO2CH3)S)(μ-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 μ-SCHCH2
moiety in 6 is different from that of the corresponding moiety in [W3(μ3-S)(μ-O)(μ-S)(μ-SCHCH2)(NCS)9]4- (4).
Introduction of the second acetylene molecule to the intermediate [W3(μ3-S)(μ-S)2(μ-SCHCH2)(NCS)9]4- (8) resulted
in the formation of 6. The clusters were characterized by UV−vis spectroscopy, 1H NMR spectroscopy, and X-ray
crystallography (for (Hpy)4·6·1.33py·0.5H2O and 11·CH3CN), and the formation of 6 and 11 was examined in
detail from a mechanistic point of view.