Synthetic, structural, electrochemical and electronic characterisation of heterobimetallic bis(acetylide) ferrocene complexes

A series of novel heterobimetallic bis(acetylide) ferrocene complexes featuring a bis[1,2-bis(diphenylphosphino)-methane]ruthenium centre and seven variously substituted aromatic acetylene ligands have been synthesised and characterised. The crystal structure of trans-[Ru(dppm)₂{C≡C(C₅H₄)Fe(C ₅H₅)}₂] shows the ruthenium centre in a distorted-octahedral environment bound to two ferrocene units in a linear fashion by 'rigid-rod'-like acetylene linkages. The conformation is stabilised by strong intramolecular CH⋯π(C≡C) interactions. Electrochemical studies showed that incorporation of donor-substituted aromatic acetylide ligands causes a cathodic shift in the Ru^II/III redox potential. Conversely, an anodic shift is observed when electron-withdrawing substituents are present in the acetylide systems. Electronic spectral measurements indicated that the systems belong to the Robin and Day 'Class II' mixed-valence species and suggest that greater electronic interaction occurs in the bis(acetylide) complexes than in the corresponding monoacetylide chloro-complex.