Synthesis of a Heterobimetallic Arsenic Triple-Decker Complex and Its Fragmentation Chemistry

The synthesis of the metastable triple-decker complex [(Cp*Fe)­(Cp‴Co)­(μ,η⁵:η⁴-As₅)] (3) (Cp* = penta­methyl-cyclopentadienyl, Cp‴ = 1,2,4-tritertbutyl-cyclopentadienyl) is reported. 3 is sensitive toward thermal activation (and in solutions of acetonitrile), which converts 3 selectively into [(Cp*Fe)­(Cp‴Co)­(μ,η³:η³-As₃)] (4) and [(Cp*Fe)₂(Cp‴Co)₂ (μ₄,η⁴:η⁴:η⁴:η³-As₁₁)] (5). Harsher thermal reaction conditions lead to a further fragmentation into [Cp*Fe­(η⁵-As₅)] (1b), [(Cp‴Co)₂(μ,η²:η²-As₂)₂] (6), and [(Cp*Fe)₂(Cp‴Co)­(μ₃,η²:η²:η²-As₃)₂] (7), which can be completed by longer reaction times or higher temperatures. The fragmentation was investigated by variable-temperature and time-dependent NMR spectroscopy, and a fine-tuning of the selectivity can be achieved by applying different reaction conditions. All compounds were fully characterized, and their electronic structures were elucidated by DFT calculations.