Reduction of [Cp∗Fe(η5-As5)] with [Cp″2Sm(thf)] (Cp″=η5-1,3-(tBu)2C5H3) under various conditions led to [(Cp″2Sm)(μ,η4:η4-As4)(Cp∗Fe)] and [(Cp″2Sm)2As7-(Cp∗Fe)]. Both compounds are the first polyarsenides of the rare-earth metals. [(Cp″2Sm)(μ,η4:η4-As4)(Cp∗Fe)] is also the first d/f-triple decker sandwich complex with a purely inorganic planar middle deck. The central As42- unit is isolobal with the 6π-aromatic cyclobutadiene dianion (CH)42-. [(Cp″2Sm)2As7(Cp∗Fe)] contains an As73- cage, which has a norbornadiene-like structure with two short As-As bonds in the scaffold. DFT calculations confirm all the structural observations. The As-As bond order inside the cyclo As4 ligand in [(Cp″2Sm)(μ,η4:η4-As4)(Cp∗Fe)] was estimated to be in between an As-As single bond and a formally aromatic As42- system.
- triple-decker sandwich complex