Arsenic-Rich Polyarsenides Stabilized by Cp*Fe Fragments.

The redox chemistry of [Cp*Fe(η -As )] (1, Cp*=η -C Me ) has been investigated by cyclic voltammetry, revealing a redox behavior similar to that of its lighter congener [Cp*Fe(η -P )]. However, the subsequent chemical reduction of 1 by KH led to the formation of a mixture of novel As scaffolds with n up to 18 that are stabilized only by [Cp*Fe] fragments. These include the arsenic-poor triple-decker complex [K(dme) ][{Cp*Fe(μ,η -As )} ] (2) and the arsenic-rich complexes [K(dme) ] [(Cp*Fe) (μ,η -As )] (3), [K(dme) ] [(Cp*Fe) (μ,η -As )] (4), and [K(dme) ] [(Cp*Fe) (μ ,η -As )] (5). Compound 4 and the polyarsenide complex 5 are the largest anionic As ligand complexes reported thus far. Complexes 2-5 were characterized by single-crystal X-ray diffraction, H NMR spectroscopy, EPR spectroscopy (2), and mass spectrometry. Furthermore, DFT calculations showed that the intermediate [Cp*Fe(η -As )] , which is presumably formed first, undergoes fast dimerization to the dianion [(Cp*Fe) (μ,η -As )] .