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

Abstract

Formation of a single carbon-sulfur bond is described. The reaction of incomplete cubane-type sulfur and oxygen-bridged isothiocyanato tungsten cluster [W3(mu3-S)(mu-O)(mu-S)2(NCS)9]5- (7) with acetylene affords [W3(mu3-S)(mu-O)(mu-S)(mu-SCH=CH2)(NCS)9]4- (8). The cluster 8 has been isolated as K0.5(Hpy)3.5[W3(mu3-S)(mu-O)(mu-S)(mu-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 P1, a = 14.465(5) A, b = 17.353(3) A, c = 10.202(2) A, alpha = 90.98(1) degrees, beta = 108.59(2) degrees, gamma = 98.13(2) degrees, V = 2397.6(10) A(3), Z = 2, D(c) = 2.096 g cm(-3), Dm = 2.08 g cm(-3), R (Rw) = 3.6 (5.5)% for 8786 reflections (I > 1.50 sigma(I)). The carbon-carbon distance is 1.27(1) A and is almost equidistant between ethylene (1.339 A) and acetylene (1.203 A). 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 [lambda(max), nm (epsilon, M(-1) cm(-1)): 840 (650), 575 (1450)]. (1)H NMR and HH correlation spectroscopy (COSY) of 8' in CD3CN support the results of the X-ray structural analysis. The (1)H 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 mu-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.

On the Critical Effect of the Metal (Mo vs. W) on the [3+2] Cycloaddition Reaction of M3S4 Clusters with Alkynes: Insights from Experiment and Theory

“…In contrast, cluster [ 1 ] + does react with all the new alkynes tested, both symmetrical (i.e., dmad) and asymmetrical (i.e., PrA, PhA, F PhA, and PhA). This is in line with previous results showing that the aqua cluster [Mo 3 S 4 (H 2 O) 9 ] 4+ reacts with acetylene leading to the corresponding type I product,5b whereas the tungsten analogue does not 5c…”

Mechanism of [3+2] Cycloaddition of Alkynes to the [Mo3S4(acac)3(py)3][PF6] Cluster

“…The spectra calculated for different species (Figure 4) indicate that the first step converts the starting compound into an intermediate with a band at λ =870 nm, which is converted into a different product in the second step; the latter process is signaled by a shift in the band to λ =855 nm. Although such a shift was not observed for the reaction of adc with [Mo 3 (μ 3 ‐S)(μ‐S) 3 (H 2 O) 9 ] 4+ ,7 it has been previously reported for related systems 6b. On the other hand, a satisfactory fit of the spectral changes recorded for the disappearance of the near‐IR band also require a model with two steps (rate constants k 3obs and k 4obs ), and the calculated spectra (see the Supporting Information) indicate the formation of an intermediate with a band located at λ ≈595 nm.…”

Cycloaddition of alkynes to diimino Mo3S4 cubane-type clusters: a combined experimental and theoretical approach

“…An interesting experimental feature of the reaction between [Mo 3 S 4 (acac) 3 (py) 3 ] + and alkynes consists in the appearance of subsequent kinetic steps for the formation of additional compounds beyond the so-called type I product formed in the initial [3+2] cycloaddition (Scheme 2). This behaviour has been observed for a number of other cuboidal clusters, 4,5,28 and Shibahara et al proposed that such species are formed via protonation of the type I product, 5 which leads to the cleavage of one of the C-S bonds with formation of the so-called type II product, which again features a MS 2 unit available for the subsequent [3+2] cycloaddition of the second alkyne molecule, finally leading to the type III product. Dithiolate protonation is therefore required in this model to provide the MoS 2 unit necessary for a second cycloaddition.…”

“…This contrasts with the reactivity reported for the water soluble clusters [W 3 (m 3 -S)(m-O)(m-S) 2 (NCS) 9 ] 5À and [Mo 3 (m 3 -S)(m-S) 3 (Hnta) 3 ] 2À (nta = 2,2 0 ,2 00 -nitrilotriacetic acid), which have been shown to form type II cycloaddition products via protonation of the corresponding type I products in the presence of acid excess. 4,28 The results herein represent, on the one hand, an optimised procedure for the synthesis of the so-called type I cycloaddition products, with potential application for catalytic purposes; and on the other hand, they also provide a new starting point for the synthesis of type II and III products.…”