Synthesis of Unprecedented 4d/4f‐Polypnictogens

A series of 4d/4f‐polyarsenides, ‐polyarsines and ‐polystibines was obtained by reduction of the Mo‐pnictide precursor complexes [{Cp${}^t$Mo(CO)${}_2$}${}_2$(μ,η${}^{2:2}$‐E${}_2$)] (E=As, Sb; Cp${}^t$=tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*${}_2$Sm] and [(Cp${}^{Me4nPr}$)${}_2$Sm]. For the reductive conversion of the Mo‐stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo‐arsenide a tetraarsacyclobutadiene and a second species with a side‐on coordinated As${}_2$${}^{2-}$ anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.