An Insight into Solventless Reaction Techniques of Monovalent Coinage Metal Complexes

Abstract

The use of solventless synthetic methods is becoming important in green chemistry, as they allow the production of synthetic organic molecules in a way that is less environmentally harmful and requires less waste, energy, and impact than traditional solvent-mediated methods. In this review, the recent advances in the use of solventless synthetic routes to prepare monovalent complexes of coinage metals will be discussed. Moreover, the mechanistic information and structure-property relationships derived from solventless reactions compared to those conducted in solution will be highlighted. In addition to a comparison of the reaction pathways, product selectivity and the physical and chemical properties of coinage metal complexes prepared under solventless conditions, a discussion is provided of some of the different approaches that have been employed in the activation of coinage metals under solventless conditions. The various methods employed for solventless activation include microwave activation, photo-activation, thermal activation, activation using solid-gas, co-sublimation, and mechano-chemical grinding. Literature examples of the use of each of these methods will be presented, and a comparative evaluation of these methodologies is also provided. Solventless activation of low-valent coinage metals can be accomplished by the use of properly designed ligands, including phosphines, N-heterocyclic carbenes, and cyclopentadiene-type ligands. This article addresses the impact of the use of these solventless activation methods on the efficiencies, yields, structural diversities, and functional properties of coinage metals, particularly in terms of their use as catalysts and material by-products. Current challenges associated with overall understanding of solventless studies are also discussed, alongside the potential of solventless methodologies in coordination chemistry and the future opportunities for sustainable synthesis of coinage metal complexes.