The reaction of [{η5-Cp′′′Co}2{μ,η4:4-toluene}] with yellow arsenic yields the arsenic-rich Asn ligand complexes [{Cp′′′Co(μ,η2:2-As2)}2] (1), [(Cp′′′Co)4(μ4,η4:4:2:2:1:1-As10)] (2) and [(Cp′′′Co)3(μ3,η4:4:2:1-As12)] (3), which were comprehensively characterized. The molecular structure of 1 show a triple-decker complex with two As2 units forming the middle-deck; compound 2 contains an all-arsenic As10 analogue of dihydrofulvalene in the molecular structure. The As12 ligand in 3 represents the largest Asn ligand complex reported so far.