1,1′-Ferrocenylene-Bridged Bis(N-Heterocyclic Olefin) Derivatives

The 1,1′-ferrocenylene (fc)-bridged bis(N-heterocyclic olefin) compounds (IMes=CH)₂fc (1, IMes=1,3-dimesitylimidazolin-2-ylidene) and (IPr=CH)₂fc (2, IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were synthesised from (ICH₂)₂fc (3) and the respective N-heterocyclic carbene IMes or IPr. Ligand substitution reactions of 1 and 2 with [BH₃(THF)] afforded the complexes [1(BH₃)₂] and [2(BH₃)₂] as mixtures of the rac- and meso-diastereomers. The new ferrocene derivatives 1–3 and the complexes meso-[1(BH₃)₂], rac-[1(BH₃)₂] and rac-[2(BH₃)₂] were structurally characterised by single-crystal X-ray diffraction. 1 and 2 represent a new class of ferrocene-based, and hence redox-active, bidentate ligands. The presence of three redox-active moieties, viz. the ferrocene unit and the two NHO units, is reflected by three consecutive oxidations according to an electrochemical investigation exemplarily performed with 2 by cyclic voltammetry.