Redox‐Responsive Rhodocenium [O,O]‐, [N,O]‐, [N,N]‐, and [N,C,N]‐Metalloligands

Abstract

AbstractAs we have recently shown, the doubly substituted [1,2‐O,O]H, [1,2‐O,N]H, [1,2‐N,N]H, and [1,3‐N,N]H pentafulvenes are convenient N/O‐functionalized cyclopentadienide (Cp) precursors. Deprotonation of the pentafulvenes by potassium hydride followed by reaction with [Cp*RhCl2]2 or [Cp*IrCl2]2 gave access to the first functionalized rhodocenium and iridocenium salts that contain two acyl and/or imidoyl substituents. These air‐stable compounds represent interesting bis(acyl/imidoyl) or mixed acyl/imidoyl metalloligand systems that combine an axially shielding, electrochemically active metallocene moiety with directly attached, conjugating oxygen and/or nitrogen donor sites. The structural properties of these novel metallocene metalloligands in solution and in the solid state were studied by NMR spectroscopy (1H, 13C, 103Rh) and by single‐crystal structure analysis. The electrochemical investigations on complexes 5a, 6b, and 7a showed the effect of the appended functional groups on the potential and on the reversibility of the rhodocenium/rhodocene reduction and provided evidence for the dimerization that followed the reduction. Further redox processes that were due to the heteroatom functions included the stepwise reduction of the 1,2‐diketo entity of 5a and the oxidation of the 1,2‐diimino moiety of 7a.