Jamie Lewis - Marie Sk?odowska-Curie Fellow (October 2015 - October 2017)

Mechanically interlocked architectures (MIAs) have recently emerged as novel ligands for coordination to metal ions. Early work by Sauvage and co-workers revealed that coordination complexes of catenane ligands can have quite different properties to their non-interlocked analogues, including increased stability due to the inability of the constituent ligand components to dissociate from one another. During my Fellowship I investigated the synthesis of new rotaxane ligands and their properties, in particular for applications in water splitting. For recent review of interlocked ligands see I produced during my fellowship see: Chem. Commun. 2017, 53, 298. Chem. Soc. Rev. 2017, 46, 2577.

Results

i) Scalable methods for the synthesis of MIA ligands (Chem. Sci. 2016, 7, 3154)
Whilst a number of high-yielding methodologies have been developed for the synthesis of MIAs, these usually focus on the final mechanical bond forming step. However, the synthesis of the precursor units, such as appropriate macrocycles, can often be laborious and low yielding. To rectify this short-coming we developed a more efficient route towards these key precursors. After optimisation the reactions were found to give the desired macrocycle compounds in approximately 70% yield across a range of macrocycle structures, and allowed access to these in gram scale. We are now in talks with a company to make these molecules available to the wider community.

ii) New Methods for the Synthesis of Polynuclear MIA Ligands (J. Am. Chem. Soc. 2016, 138, 16329; Molecules 2017, 22, 89)
It was foreseeable that for our photocatalytic systems we might require two cavities formed by mechanical bonds capable of binding metal ions. Oligomeric [n]rotaxanes, where n = >2, would thus be a desirable target. We developed the first route to oligomeric rotaxanes, where the precise length and macrocycle order could be controlled exactly with precise control of the order of different macrocycles.

iii) Interlocked Porphyrin-Corrole Diads (Chem. Sci. 20178, 6679)
In collaboration with Dr Ngo from National Institute for Materials Science (Japan) I investigated the active template CuAAC synthesis of interlocked triazole functionalised porphyrinoids in excellent yield. By synthesising interlocked analogues of previously studied porphyrin–corrole conjugates, we demonstrate that this approach gives access to rotaxanes in which the detailed electronic properties of the axle component are unchanged but whose steric properties are transformed by the mechanical “picket fence” provided by the threaded rings. Our results suggest that interlocked functionalised porphyrins, readily available using the AT-CuAAC approach, are sterically hindered scaffolds for the development of new catalysts and materials.

iv) Rotaxane Ligands for Early Transition Metals and their Hydrogen Evolving Capabilities (manuscripts in preparation)
We have investigated the electrochemical and spectroscopic properties of first row transition metal complexes of tri-, tetra- and penta-dentate rotaxane ligands. Our results showed that in many instances the ligand environment and coordination behaviour of the rotaxane ligands, including their electrochemical properties, was distinct from their non-interlocked counterparts. A manuscript describing this work is currently in preparation in collaboration with Roessler at QMUL.

Conclusions

Over the course of my fellowship I have produced four research publications and two literature reviews. Three further manuscripts are in preparation. All of these articles were published in open access form and raw data made available through the UoS Repository. In addition to these 9 publications, I have presented my results at national and international meetings including the RSC Macrocyclic and Supramolecular Chemistry annual meeting, the MASC Early Career meeting, the International Symposium on Macrocyclic and Supramolecular Chemistry and the Telluride Workshop on Switches and Motors.

Overall the project has been extremely successful, . The results of this action not only bring MIA-based HECs several steps closer, they also dramatically expand the range of structures available for study in a range of applications including catalysis, sensing and materials chemistry. Furthermore, the success of the Action, as judged both by scientific results and academic publications, combined with training and mentoring from my Host, Prof Goldup, positioned me to apply for independent research positions. Ultimately, I was offered a Leverhulme Trust Early Career Fellowship and an Imperial College Junior Research Fellowship. I accepted the position at Imperial College and began my independent research career in October 2017.