Johannes Klein, Alexandra Stuckmann, Sebastian Sobottka, Lisa Suntrup, Margarethe van der Meer, Paul Hommes, Hans‐Ulrich Reissig, Biprajit Sarkar

The combination of 2,2':6',2″-terpyridines (tpy) and RuII is known to deliver molecular and supramolecular assemblies with remarkable properties. We present here new RuII complexes with modified tpy ligands substituted with varying numbers of dimethlyamino groups. Electrochemistry shows that the incorporation of the strongly electron-donating groups on the tpy ligands leads to a negative shift of the RuII oxidation potential by close to 1 V. The reductive electrochemical responses are strongly dependent on the nature of the working electrode, with glassy carbon and gold working electrodes showing the best results. These observations led us to develop a modified Optically Transparent Thin Layer Electrochemical (OTTLE) cell, based on a gold working electrode. The use of UV-vis-NIR spectroelectrochemical results with that OTTLE cell, together with simulations of the cyclic voltammograms, allow us to characterize four reduction steps in these complexes, the final two of which lead to bond activations at the ruthenium center. This observation is to the best of our knowledge unprecedented in coordinatively saturated complexes of type [Ru(tpy)2]2+. The various redox states of the complexes were characterized by EPR spectroelectrochemistry and through DFT calculations. The results presented here establish these substituted tpy ligands as highly attractive ligands in coordination chemistry, and display the utility of a gold-based OTTLE cell for spectroelectrochemical measurements.