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.