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 Mo(CO) } (μ,η -E )] (E=As, Sb; Cp =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp* Sm] and [(Cp ) 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 anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.