Sebastian Sobottka

A Divalent Pentastable Redox-Switchable Donor-Acceptor Rotaxane

Donor-acceptor materials with small HOMO-LUMO gaps are important in molecular electronics, but are often difficult to synthesise. A simple and efficient way to position tetrathiafulvalene (TTF) as the donor and naphthalene diamide (NDI) as the acceptor in close proximity to each other in a divalent crown/ammonium pseudo[2]rotaxane is presented. The divalent design provides high chelate cooperativity and much stronger binding compared with a monovalent analogue. The pseudo[2]rotaxane was then doubly interlocked by stoppering it in a catalyst-free 1,3-dipolar cycloaddition. UV/Vis and cyclic voltammetry experiments with the resulting [2]rotaxane revealed the optoelectronic properties of an intramolecular charge transfer with a small HOMO-LUMO energy gap. Redox-switching experiments showed the rotaxane to be pentastable. DFT calculations provided insights into the electronic structures of the five redox states.

Gauging Donor/Acceptor Properties and Redox Stability of Chelating Click-Derived Triazoles and Triazolylidenes: A Case Study with Rhenium(I) Complexes

Bidentate ligands containing at least one triazole or triazolylidene (mesoionic carbene, MIC) unit are extremely popular in contemporary chemistry. One reason for their popularity is the similarities as well as differences in the donor/acceptor properties that these ligands display in comparison to their pyridine or other N-heterocyclic carbene counterparts. We present here seven rhenium(I) carbonyl complexes where the bidentate ligands contain combinations of pyridine/triazole/triazolylidene. These are the first examples of rhenium(I) complexes with bidentate 1,2,3-triazol-5-ylidene-containing ligands. All complexes were structurally characterized through 1H and 13C NMR spectroscopy as well as through single-crystal X-ray diffraction. A combination of structural data, redox potentials from cyclic voltammetry, and IR data related to the CO coligands are used to gauge the donor/acceptor properties of these chelating ligands. Additionally, a combination of UV-vis-near-IR/IR/electron paramagnetic resonance spectroelectrochemistry and density functional theory calculations are used to address questions related to the electronic structures of the complexes in various redox states, their redox stability, and the understanding of chemical reactivity following electron transfer in these systems. The results show that donor/acceptor properties in these bidentate ligands are sometimes, but not always, additive with respect to the individual components. Additionally, these results point to the fact that MIC-containing ligands confer remarkable redox stability to their fac-Re(CO)3-containing metal complexes. These findings will probably be useful for fields such as homogeneous- and electro-catalysis, photochemistry, and electrochemistry, where fac-Re(CO)3 complexes of triazoles/triazolylidenes are likely to find use.

Chromium Complexes with Oxido and Corrolato Ligands: Metal-Based Redox Processes versus Ligand Non-Innocence

Metal- versus ligand-centered redox processes and the effects of substituents on the ligands on the spectroscopic properties of the metal complexes are at the heart of research on metal complexes with non-innocent ligands. This work presents three examples of chromium complexes that contain both oxido and corrolato ligands, with the substituents on the corrolato ligands being different in the three cases. Combined X-ray crystallographic, electrochemical, UV/Vis/NIR/EPR spectroelectrochemical, and EXAFS/XANES measurements, together with DFT calculations, have been used to probe the complexes in three different redox forms. This combined approach makes it possible to address questions related to chromium- versus corrolato-centered redox processes, and the accessibility (or not) of CrIV , CrV , and CrVI in these complexes, as well as their spin states. To the best of our knowledge, these are the first EXAFS/XANES investigations on Cr-corrolato complexes in different redox forms, and hence these data should set benchmarks for future investigations on such complexes by this method.