Dicationic E4 Chains (E=P, As, Sb, Bi) Embedded in the Coordination Sphere of Transition Metals.

The oxidation chemistry of the complexes [{CpMo(CO)2 }2 (μ,η2 :η2 -E2 )] (E=P (A), As (B), Sb (C), Bi (D)) is compared. The oxidation of A-D with [Thia]+ (=[C12 H8 S2 ]+ ) results in the selective formation of the dicationic E4 complexes [{CpMo(CO)2 }4 (μ4 ,η2 :η2 :η2 :η2 -E4 )]2+ (E=P (1), As (2), Sb (3), Bi (4)), stabilized by four [CpMo(CO)2 ] fragments. The formation of the corresponding monocations [A]+ , [C]+ , and [D]+ could not be detected by cyclic voltammetry, EPR, or NMR spectroscopy. This finding suggests that dimerization is fast and that there is no dissociation in solution, which was also predicted by DFT calculations. However, EPR measurements of 2 confirmed the presence of small amounts of the radical cation [B]+ in solution. Single-crystal X-ray diffraction revealed that the products 1 and 2 feature a zigzag E4 chain in the solid state while 3 and 4 bear a central E4 cage with a distorted "butterfly-like" geometry. Additionally, 1 can be easily and reversibly converted into a symmetric and an unsymmetric form.