Adduct of Acetylene at Sulfur in an Oxygen- and Sulfur-Bridged Open Cubane Cluster Complex of Tungsten

Formation of a single carbon−sulfur bond is described. The reaction of incomplete cubane-type sulfur and oxygen-bridged isothiocyanato tungsten cluster [W3(μ3-S)(μ-O)(μ-S)2(NCS)9]5- (7) with acetylene affords [W3(μ3-S)(μ-O)(μ-S)(μ-SCHCH2)(NCS)9]4- (8). The cluster 8 has been isolated as K0.5(Hpy)3.5[W3(μ3-S)(μ-O)(μ-S)(μ-SCHCH2)(NCS)9] (8‘), whose structure has been characterized by X-ray crystallography, electronic spectra, and 1H
and 13C NMR spectroscopy. Crystal data of 8‘:  triclinic system, space group P1̄, a = 14.465(5) Å, b = 17.353(3)
Å, c = 10.202(2) Å, α = 90.98(1)°, β = 108.59(2)°, γ = 98.13(2)°, V = 2397.6(10) Å3, Z = 2, Dc = 2.096 g
cm-3, Dm = 2.08 g cm-3, R (Rw) = 3.6 (5.5)% for 8786 reflections (I > 1.50 σ(I)). The carbon−carbon distance
is 1.27(1) Å and is almost equidistant between ethylene (1.339 Å) and acetylene (1.203 Å). The electronic spectrum
of 8‘ in 1.0 M HCl containing 1.5 M KSCN has a characteristic broad peak in the near-infrared region [λmax, nm
(ε, M-1 cm-1):  840 (650), 575 (1450)]. 1H NMR and HH correlation spectroscopy (COSY) of 8‘ in CD3CN
support the results of the X-ray structural analysis. The 1H NMR spectrum shows three signals at 2.42 (1H, dd),
4.84 (1H, d, J = 8.8 Hz), and 4.89 (1H, d, J = 16.2 Hz) ppm due to the μ-SCHCH2 moiety of 8‘. The correlation
spectrum shows spin couplings of the signal at 2.42 ppm with the signals at 4.84 and 4.89 ppm. The mechanism
of the formation of 8 is suggested to proceed through an intermediate with acetylene bridging two of the sulfur
atoms.