Synthesis, Reactivity, and Kinetics of Substitution in W₃PdSe₄ Cuboidal Clusters. A Reexamination of the Kinetics of Substitution of the Related W₃S₄ Cluster with Thiocyanate

The reaction of Pd(dba)2 (dba = dibenzylideneacetone) with [W3Se4(H2O)9]4+ in 2 M HCl gives the cuboidal cluster [W3(PdCl)Se4(H2O)9]3+, which undergoes edge-to-edge condensation and crystallizes from Hpts solutions as edge-linked double-cubane cluster [{W3PdSe4(H2O)9}2](pts)8·18H2O (pts− = p-toluenesulfonate). The substitution of Cl− by different ligands, including phenylsulfinate PhSO2−, was explored. The phenylsulfinate complex was crystallized as a 2:1 adduct with cucurbit[6]uril (C36H36N24O12), [W3(Pd(PhSO2)Se4(H2O)8.58Cl0.42]2(C36H36N24O12)Cl5.16·16.83H2O, and its structure was determined by X-ray diffraction. Solution studies indicate that the Pd atom is able to stabilize the pyramidal tautomer of hypophosphorous and phosphorous acid: HP(OH)2 and P(OH)3. Kinetic studies were carried out on the reactions with H3PO2 and thiocyanate, which were found to proceed in two and three kinetically resolvable steps, respectively. The kinetic results are discussed in terms of the mechanistic proposals put forward in the literature for related complexes. To gain insight into the details of the substitution kinetics in these kinds of clusters, the reaction of the related [W3S4(H2O)9]4+ complex with NCS− has been reexamined, and the results obtained provide for the first time information about the rates of substitution of the whole set of nine-coordinated water molecules.