Supra-molecular synthons based on gold…π(arene) interactions

Abstract

Colloquially described as modern day “Gold Rush”, use of gold in catalysis is a research area attracting intensive and increasing attention. This is evidenced, for example, by nearly exponential increase in publications appearing in the past decade in the field of homogeneous catalysis with gold [1]. Molecular gold or in the form of nanoparticles/thin films prove to be efficient catalysts offering benefits over other transition metals, properties that relate, in no small part, to electrophilic nature of gold which, in turn, is correlated with reduction in energy of the 6s atomic orbital, owing to relativistic effects [2]. Such is the propensity for molecular gold to associate with alkynes, in particular, the term alkynophilicity is often used to describe this property. Other advantages of gold often relate to gold not being likely to be involved in oxidative addition or reductive elimination reactions unlike square planar palladium(II), for example. Not surprisingly, there are many recent and thorough reviews of gold in the catalysis literature e.g., [3–7]. Given that gold is a carbophilic Lewis acid, the question then arises: does this property influence the type of supramolecular association formed by gold in its crystal structures? Gold holds a special fascination for crystal engineers owing to its propensity to form Au...Au or aurophilic interactions [8, 9]. Not only do Au...Au interactions lead to fascinating supra-molecular architectures, the fact that the energy of stabilisation afforded to their crystal structures can match that provided by conventional hydrogen bonding [10] led to competition studies between these synthons [11–14]. By contrast, considerably less attention has been directed to ascertaining formation of Au...π(arene) interactions [15]; analogous interactions are well established in the supramolecular chemistry of the main group elements [16–18]. Herein, an overview of Au...π(arene) interactions, formed both intraand inter-molecularly, operating in the crystal structures of molecular gold compounds is given, and their presence in macro-molecular structures is also discussed, along with future prospects for this type of interaction.