Arsenic‐Rich Polyarsenides Stabilized by Cp*Fe Fragments

The redox chemistry of [Cp*Fe(η 5 ‐As 5 )] ( 1 , Cp*=η 5 ‐C 5 Me 5 ) has been investigated by cyclic voltammetry, revealing a redox behavior similar to that of its lighter congener [Cp*Fe(η 5 ‐P 5 )]. However, the subsequent chemical reduction of 1 by KH led to the formation of a mixture of novel As n scaffolds with n up to 18 that are stabilized only by [Cp*Fe] fragments. These include the arsenic‐poor triple‐decker complex [K(dme) 2 ][{Cp*Fe(μ,η 2:2 ‐As 2 )} 2 ] ( 2 ) and the arsenic‐rich complexes [K(dme) 3 ] 2 [(Cp*Fe) 2 (μ,η 4:4 ‐As 10 )] ( 3 ), [K(dme) 2 ] 2 [(Cp*Fe) 2 (μ,η 2:2:2:2 ‐As 14 )] ( 4 ), and [K(dme) 3 ] 2 [(Cp*Fe) 4 (μ 4 ,η 4:3:3:2:2:1:1 ‐As 18 )] ( 5 ). Compound 4 and the polyarsenide complex 5 are the largest anionic As n ligand complexes reported thus far. Complexes 2 – 5 were characterized by single‐crystal X‐ray diffraction, 1 H NMR spectroscopy, EPR spectroscopy ( 2 ), and mass spectrometry. Furthermore, DFT calculations showed that the intermediate [Cp*Fe(η 5 ‐As 5 )] − , which is presumably formed first, undergoes fast dimerization to the dianion [(Cp*Fe) 2 (μ,η 4:4 ‐As 10 )] 2− .