Arsenic-Rich Polyarsenides Stabilized by Cp*Fe Fragments.

The redox chemistry of [Cp*Fe(η5 -As5 )] (1, Cp*=η5 -C5 Me5 ) has been investigated by cyclic voltammetry, revealing a redox behavior similar to that of its lighter congener [Cp*Fe(η5 -P5 )]. However, the subsequent chemical reduction of 1 by KH led to the formation of a mixture of novel Asn 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,η2:2 -As2 )}2 ] (2) and the arsenic-rich complexes [K(dme)3 ]2 [(Cp*Fe)2 (μ,η4:4 -As10 )] (3), [K(dme)2 ]2 [(Cp*Fe)2 (μ,η2:2:2:2 -As14 )] (4), and [K(dme)3 ]2 [(Cp*Fe)4 (μ4 ,η4:3:3:2:2:1:1 -As18 )] (5). Compound 4 and the polyarsenide complex 5 are the largest anionic Asn 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(η5 -As5 )]- , which is presumably formed first, undergoes fast dimerization to the dianion [(Cp*Fe)2 (μ,η4:4 -As10 )]2- .