Computational Insights Into the Reactivity at the Sulfur Atoms of M3S4 (M = Mo, W) Clusters: The Mechanism of [3 + 2] Cycloaddition With Alkynes

Abstract Whereas the mechanistic aspects of the reactions at the metal sites of M 3 S 4 (M = Mo, W) clusters are relatively well understood, much less is known about those occurring at the sulfur atoms. In this chapter, we describe our recent results on the mechanism of the [3 + 2] cycloaddition reaction between these clusters and alkynes. In all cases, the process involves the concerted formation of two C–S bonds in a single kinetic step, as a result of the interaction between an M(μ-S) 2 moiety of the cluster and the sp C atoms of the alkyne. The effects associated with the nature of the alkyne, the metal centers, the ligands bound to them, and the solvent have been analyzed by using a methodology consisting of two main steps: (a) the study of the kinetics of the reactions by using global analysis of the UV–Vis spectral changes, and the characterization of the resulting products by means of X-ray, ESI-MS, UV–Vis, or NMR spectroscopy; (b) the computational analysis of the processes by using density functional theory methods, in some cases complemented with the use of the activation strain model and energy decomposition analysis approaches.