Pnictogenium Ions as a Powerful Tool for the Synthesis of Three‐ and Five‐Membered Interpnictogen Chains

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The synthesis and characterization of novel three‐ and five‐membered interpnictogen chain compounds are presented. In a systematic study, the heterodipnictogen complexes [{CpMo(CO)2}2(μ,η2:2‐EE′)] (Mo2PAs: E = P, E′ = As; Mo2PSb: E = P, E′ = Sb; Mo2AsSb: E = As, E′ = Sb) are reacted with in situ generated pnictogenium ions of a third pnictogen. Phosphenium ions insert into the AsSb bond of Mo2AsSb to give [{CpMo(CO)2}2(μ,η1:1:1:1‐AsPPh2Sb)][TEF] (1) ([TEF]− = [Al{OC(CF3)3}4]−). In contrast, arsenium, stibenium, and bismuthenium ions, respectively, coordinate to the phosphorus atom of Mo2PAs and Mo2PSb. The obtained complexes [{CpMo(CO)2}2(μ,η2:2‐SbPAsCy2)][BArF24] (2), [{CpMo(CO)2}2(μ,η2:2‐AsPSbPh2)][BArF24] (3), and [{CpMo(CO)2}2(μ,η2:2‐EPBiPh2)][BArF24] (E = As (5), E = Sb (6)) all contain three different pnictogen atoms in a chain. To even elongate these chains, the stibenium substituted tetrahedranes 3 and [{CpMo(CO)2}2(μ,η2:2‐SbPSbPh2)][BArF24] (4) are reacted with an additional equivalent of Mo2PAs or Mo2PSb yielding novel five‐membered chains of the type E‐P‐SbPh2‐P‐E′ (E = E′ = As (7); E = E′ = Sb (8); E = As, E = Sb (9)), with alternating pnictogen sequences. 7–9 are found to be only stable in the solid state whereas a rapid equilibration with their respective starting materials 3 or 4 and Mo2PAs or Mo2PSb is observed in solution.