Diethynyldiazafluoren-9-ylidene as a π Cross-Conjugated Platform for Redox Active Transition Metal Fragments

Abstract

Synthetic routes were developed to attach three redox-active metal fragments to cross-conjugated 3-methylidenepentadiyne covalently expanded by diazafluorenylidene: The two alkyne termini of this new ligand were end-capped via a phenylene spacer with ethynyl ferrocene, and a [Ru(bpy)2]2+ fragment was coordinated in the diimine binding site. The photophysical and electrochemical properties of both the diferrocenyl-terminated ligand and its corresponding Ru-complex were investigated by UV–vis absorption spectroscopy and cyclic voltammetry. The absorption data reveal significant interactions of the metal centers with the cross-conjugated ligand system. In the electrochemical experiments the ferrocenyl and the ruthenium centers could be addressed individually as they are separated by almost 1 V. While the presence of the Ru-fragment manifests itself in the reduction potential of the diazafluorenylidene-ligand, communication between the ferrocenyl end-caps on one hand and between the ferrocenes and the Ru-fragment on the other appears to be reduced through the freely rotating phenylene spacers.