Synthesis and electrochemistry of niobium complexes incorporating asymmetrically substituted ansa-ligands

The following asymmetric ansa-niobocene(IV) dichloride complexes have been prepared: [Nb{Me2Si(η5-C5Me4)(η5-C5H3R)}Cl2] (R=H (1a), Me (2a), SiMe3 (3a), Pri (4a), PPh2 (5a)). The ESR spectra of 1a–5a have been recorded. Oxidation and reduction potentials have also been measured and compared with nonansa-niobocene complexes. The new niobocene complexes [Nb(η5-C5H4R)2}Cl2] (R=Pri (6a), PPh2 (7a)) have been also synthesized. In addition, reduction of 1a in the presence of ligand (RCCR) (R=Me, Ph) to give [Nb{Me2Si(η5-C5Me4)(η5-C5H4)}Cl(RCCR)] (R=Me (8a), Ph (9a)) is described.