The selective activation of alkanes under mild conditions by well-defined molecular complexes of the transition elements is a frontier challenge, with the potential to revolutionise the way in which we exploit these vast and low-cost chemical feedstocks. The fundamental organometallic chemistry of these processes is, however, poorly understood and a much greater understanding is required before their full potential in chemical synthesis can be realised. In particular, the characterisation and reaction chemistry of sigma–alkane complexes, metal-alkane adducts formed through coordination of an intact C–H bond to the metal centre, have proven to be exceedingly difficult to investigate using conventional experimental approaches as a consequence the weakly interacting nature of alkanes and their otherwise transient presence in reactions between alkanes and highly reactive metal-based compounds.
To address this knowledge gap and inspired from supramolecular chemistry, the objective of ENTANGLED-TM-ALKANE was to develop and study of systems containing alkane substrates held in close proximity to reactive metal centres through mechanical entanglement within supporting tridentate macrocyclic ‘pincer’ ligands. These Interlocked macrocyclic Pincer–Alkane Systems (IPAS) are highly challenging synthetic targets and their realisation within the timescale of the project ultimately proved to be overly ambitious, with the exception of two pybox-based systems that are less amenable to formation of the intermolecular M∙∙∙H-C bonding interactions of interest. Nevertheless, whilst the destination may not have been reached the journey was filled with adventure and resulted in the discovery of some interesting and impactful science, which we hope will simulate further research at the interface between organometallic and supramolecular chemistry (see below).
