Bis(ferrocenylethynyl)-Substituted Digold-Tetrarhenium Cluster: Unusual Structure and Electronic Communication between Ferrocenyl Groups

Abstract

The digold-tetrarhenium cluster Re4(AuPPh3)2(CO)12(μ3-C≡CFc)2 (1) was obtained by the thermolysis of known complex Re2(AuPPh3)(CO)8(μ-C≡CFc) (2) and fully characterized by a single crystal X-ray diffraction study. Cluster 1 has a butterfly Re4 geometry, and both Re3 wings are capped with AuPPh3 groups. Two ferrocenylethynyl ligands symmetrically coordinated within cavity of the wings. The dihedral angle between the Re3 wings is rather narrow, 73.2°, whereas the 64e butterfly clusters usually have a more flattened structure. An examination of the carbonyl region of the 13C NMR of 1 and 2 revealed that 1 is stereochemically rigid while 2 is fluxional with respect to a σ-π interconversion of the ferrocenyl ethynyl group across the Re−Re edge of the Re2Au triangle. Complex 1 revealed a very rare electronic communication between the ferrocene units across the cluster core. According to the cyclic voltammetric (CV) data, cluster 1 undergoes two reversible redox process with ferrocene oxidations separated by 109 mV. Electronic communication between two ferrocene units of 1 is discussed on the basis of CV and NIR data.