Mechanochemical techniques for the activation and use of zero-valent metals in synthesis

Activating raw, zero-valent metals is an essential capability for chemical processes, which include synthesis and catalysis. In recent years there has been the discovery and growing intensity in the use of mechanical action, through the utility of ball mills, to facilitate the activation of zero-valent metals. The complexity of the synthetic reaction systems in which these processing techniques can be used has now reached a tipping-point, with, among others, cross-electrophile coupling, radical reactions and new modes of zero-valent reactivity demonstrated. In addition, the technique of ball milling is synonymous with solvent minimization for the reaction component of a synthetic process. In this review, we demonstrate that, together, these developments paint an intriguing picture in which the combination of the technique of ball milling and chemical synthesis mediated by zero-valent metals could deliver a sustainable platform for chemical synthesis, catalysis and new reaction discovery for the future. Metals in their zero-valent form offer a great deal of potential for chemical synthesis. The reliable and straightforward activation of these raw materials has perhaps inhibited the full realization of this promise. This review examines the emergence of the technique of ball milling as a reactor technology to enable mechanical activation of zero-valent metals.