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.