We are striving to extend the dimension of organometallic ligand design towards a supramolecular organometallic chemistry. Hereby, we are currently developing macrocyclic NHC ligand platforms to yield multinuclear complexes with defined cavities. These cavities are envisioned to act as selective host for guest recognition or nano-reactors for molecular catalysis.
A big motivation is to enable multi-electron redox processes to (electro-)catalytically activate small molecules, e.g. CO2. For that, we are using a family of hybrid imidazoline-ylidene/pyrazolato-based cyclophanes, which we introduced as a ligand for dinuclear saddle-sahped nickel complexes (‘crisps’) in 2015. The ligand is designed to combine the formidable properties of NHC donors and the electronic communication of pyrazolate as a bridging moiety. Catalytic studies are currently ongoing. Interestingly, slight modification of the ligand – namely expanding the cyclophane by two methylene groups – enables the formation of supramolecular complexation via encapsulation of halides. We reported the formation of these so-called ‘capsoplexes’ in the 2016 Emerging Investigators issue of Chem. Commun.. Such a capsoplex formation now is tested towards other small anionic guests.
A highly interesting further class of supramolecular host compounds are the ‘pillarplexes’, which we introduced in J. Am. Chem. Soc. very recently. These complexes with unique properties are formed, when the very same cyclophane ligand is applied to linearly coordinating metals as Ag(I) or Au(I).
First, the pillarplexes possess a pore, which is exclusively selective to incorporate linear molecules. Second, the Au-pillarplexes are photoluminescent emitters in the blue region of the visible spectrum. Third, their solubility is easily tunable by simple anion exchange – altogether properties, which render the pillarplexes as highly interesting compounds for a plethora of applications. Now, we are systematically investigating the host-guest interactions of the pillarplexes by employing different guest molecules. We are furthermore studying their electronic properties, which are potentially interesting for catalytic applications.
Another main topic of our research is the development and investigation of ligand platforms featuring carbocyclic carbene donors – more precisely cycloheptatriene-ylidene (CHT) based systems. These ligands are very interesting, since they are similar strong donors as the NHCs but show a more complex reactivity. We used this flexibility to synthesize the first NHC/CHT-hybrid ligand via an exclusive on-site synthesis at the metal as well as to rationally produce imidazolium-substituted [Pd3L2Br3]Br complexes (metal sheet sandwich complex). The chemistry and (catalytical) properties of these compound are currently investigated.
Prof. Polly Arnold (Univ. Edinburgh)
Dr. Ove Alexander Høgmoen Åstrand (Univ. Oslo)
Prof. Thorsten Bach (TUM, Munich)
Prof. Angela Casini (Univ. Cardiff)
PD Dr. Friedrich Esch (TUM, Munich)
Prof. Roland A. Fischer (TUM, Munich)
Prof. Michael J. Hannon (Univ. Birmingham)
Prof. Corinna Hess (TUM, Munich)
Prof. Lukas Hintermann (TUM, Munich)
Prof. Fritz E. Kühn (TUM, Munich)
Prof. Jason Love (Univ. Edinburgh)
Dr. Estelle Mossou (ILL, Grenoble)
Prof. Bernhard Rieger (TUM, Munich)