Although it marks a cornerstone of pnictogenium ion [R2Pn]+ reactivity, the insertion of arsenium ions [R2As]+ into non-polar bonds remains highly challenging. Herein, a synthetic approach is developed, which circumvents the limitations of insertion reactivity of [R2As]+ (e.g., formal redox state of +V at As) via alleviation of ring strain in the substrate. Thus, unlocking arsenium ion bond insertion delivers the ring-expanded complexes [{LnM}(η3-Pn3AsCy2][TEF] ({LnM} = Cp‴Ni, Pn = P (1); {LnM} = {CpMo(CO)2}, Pn = P (2), As (5); Cp‴ = 1,2,4-tBu3C5H2, [TEF]− = [Al{OC(CF3)3}4]−). Computational analysis of the reaction mechanism and quantum crystallographic investigation of 1 highlight the release of ring strain as the crucial driving force for this reactivity. This rational is corroborated by the isolation of the arsenium ion coordinated [{CpMo(CO)2}2(μ,η2:2-P2AsCy2)][TEF] (3) as well as the phosphenium ion inserted [{CpMo(CO)2}(η3-As3PPh2)][TEF] (4).