Hemicarcerand ligands for the systematic investigation of sigma-alkane complexes

The selective functionalisation of alkanes is an area of contemporary importance - motivated by the desire to make efficient and effective use of these inexpensive and abundant hydrocarbons in organic synthesis and as feedstocks for the chemical industry. Such objectives are encumbered by the chemical inertness of alkanes, conferred upon them by the strong constituent C-C and C-H bonds. Through the action of soluble transition metal catalysts, progress has been made in overcoming these limitations although many substantial challenges remain for large-scale practical implementation. One of the key stumbling blocks has proven to be establishing the fundamental mechanistic chemistry of these processes: encumbered by their transient and extremely reactive nature, metal-based intermediates involved in alkane activation processes are exceedingly difficult to investigate using conventional approaches. Such information constitutes vital prerequisite knowledge for the rational development of useful catalytic systems.

The proposed research project involves the development of an unprecedented supramolecular approach for systematically investigating the transition metal mediated activation of alkanes, in particular elusive sigma-alkane intermediates. The approach entails the preparation and use of well-defined macromolecular cavitand ligands, which both promote and stabilise the formation of transition metal sigma-alkane complexes through encapsulation of the alkane within the interior of the macromolecule. The inclusion of the alkanes within these supramolecular systems effectively circumvents detrimental problems associated with conventional strategies and allows effective interrogation of the metal-alkane interaction. Ultimately, this approach will generate a definitive body of fundamental chemistry that will enable a step change in understanding of alkane activation methods.

The direct exploitation of alkanes as chemical feedstocks has been a long-term goal of chemical researchers. At its heart, this project addresses challenges associated with this objective: the selective transformation of these cheap and abundant hydrocarbon resources into valuable chemicals under mild conditions (using transition metal catalysts). In addition to significant academic interest, there are major UK stakeholders in the petroleum and chemical industries. The UK chemical industry, like the petroleum industry, is a significant provider of jobs and creator of wealth for the UK - with an annual turnover of £60 billion and employment of over 200,000 people [UKTI]. Whilst of a fundamental nature, the research described in this project has long-term potential for enhancing economic prosperity of these industries, through knowledge driven innovation. Moreover, the associated energy and environmental benefits (reduction in energy inputs and reduction in waste) that can be achieved through advances in catalyst technologies leads to societal impact. Ultimately, the impact of this proposed work will be imparted through the short-term delivery of significant academic contributions to the fields of organometallic chemistry and catalysis. As such, the proposed work will significantly contribute to the research excellence and scientific competiveness of the UK in the EPSRC core areas of synthetic coordination chemistry, synthetic supramolecular chemistry and the nationally important growth area of catalysis.

With sustainable energy and chemical practices increasingly coming to the forefront of public and policy-makers attention, continued engagement with scientists is paramount for progress. Hydrocarbons are important raw chemical resources and how they are utilised has major environmental and technological consequences. This project provides an opportunity to showcase innovative new research in hydrocarbon chemistry in the context of the challenging nature of this work. Alongside dissemination to the academic community, significant breakthroughs made during the project will be shared with the public through both press releases and outreach activities to showcase the work and its context.