Doubly N-Functionalized Pentafulvenes and Redox-Responsive [N,N]- and [N,C,N]-Pincer Bis(imidoyl)pentamethylruthenocene Metalloligands

Abstract

New doubly functionalized pentafulvenes are easily obtained by a regioselective one-pot reaction of sodium cyclopentadienide with imidoyl chlorides of different electrophilicity. Under thermodynamic control, benzimidoyl chlorides as electrophiles afford hydrogen-bridged 6-arylamino-2-benzimidoylfulvenes, whereas under kinetic control trifluoroacetimidoyl chlorides afford non-hydrogen-bridged 6-arylamino-3-imidoylfulvenes. Structurally, these [N,N]H fulvenes exist either as pairs of rapidly interconverting tautomers (fulvenes with intramolecular hydrogen bridges) or as regular fulvenes (fulvenes without intramolecular but with intermolecular hydrogen bridges) in solution and in the solid state, as shown by NMR studies and single-crystal X-ray diffraction. Both types of fulvenes represent interesting ambidentate [N,N]H ligands per se as well as precursors to novel doubly functionalized bis(imidoyl)metallocenes. Synthetically, after deprotonation of these acceptor-substituted [N,N]H-fulvenes, 1,2- or 1,3-bis(imidoyl)pentamethylruthenocenes are easily accessible by reaction with [CpRu(CH3CN)3]PF6 as a source of the electron-rich CpRu+-synthon. Structurally, these new [N,N]-pentamethylruthenocene metalloligands are related to diazabutadienes or bis(imino)-[N,C,N]H pincer ligand systems, respectively. Electrochemical investigations show that the bis(imidoyl)(pentamethyl)ruthenocenes are novel redox-active metalloligands and reveal the strongly electron-withdrawing effect of the appended imine moieties. All new compounds were fully characterized by spectroscopic methods and by a total of 11 single-crystal X-ray analyses.