Rhodium(III) and ruthenium(II) complexes of redox-active, chelating N-heterocyclic carbene/thioether ligands

Half-sandwich rhodium(III) and ruthenium(II) complexes bearing a new redox-active ferrocenyl NHC-thioether ligand have been prepared. The synthesis of ferrocenyl thioether-imidazolium salts 3a and 3b was carried out via intermediate 2 using an improved procedure. Rhodium(III) complex 4 and ruthenium(II) complex 5 were obtained in good yields and were fully characterised by NMR spectroscopy, X-ray diffraction analysis and electrochemistry. Complex 4 shows a complex ABCD system by H-1 NMR, which denotes conformational rigidity due to the presence of several bulky groups. Electrochemical analysis by cyclic voltammetry reveals reversible redox behaviour about the iron centre in 4 and 5, and indicates electronic communication between iron and rhodium or ruthenium.