Transformations of the cyclo-P₄ ligand in [Cp'''Co(η⁴-P₄)]

The reactivity of the cyclo-P₄ ligand complex [Cp'''Co(η⁴-P₄)] (1) (Cp''' = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated. By using K[CpFe(CO)₂], a selective reduction to the dianionic complex [(Cp'''Co)₂(μ,η³:η³-P₈)]^2- (2) was achieved. The reaction of 1 with BuLi and LiCH₂SiMe₃ as carbon-based nucleophiles yielded [Cp'''Co(η³-P₄R)]^- (R = Bu (4), CH₂SiMe₃ (7)), which, depending on the reaction conditions, undergo subsequent reactions with another equivalent of 1 to form [(Cp'''Co)₂(μ,η³:η³-P₈R)]^- (R = Bu (5), CH₂SiMe₃ (8)). In the case of 4, a different pathway was observed, namely a dimerisation followed by a fragmentation into [Cp'''Co(η³-P₅ Bu₂)]^- (6) and [Cp'''Co(η³-P₃)]^- (3). With OH^- as an oxygen-based nucleophile, the synthesis of [Cp'''Co(η³-P₄(O)H)]^- (9) was achieved. All compounds were characterized by X-ray crystal structure analysis, NMR spectroscopy and mass spectrometry. Their electronic structures and reaction behavior were elucidated by DFT calculations.