Synthesis of a cobalt - Phospholyl half-sandwich complex and its transformation into a phosphacobaltocene

Low-temperature reaction of [Li(PC₄H₂t-Bu ₂)·2thf] (thf = tetrahydrofuran) (7) with [Co(acac) ₂] (Hacac = acetylacetone) gives the reactive half-sandwich complex [Co(η⁵-PC₄H₂t-Bu₂)(acac)] (6). The crystal structure of 6 shows an unusual ene/2-phosphaallyl distortion, which indicates an a' symmetric SOMO of the type found in the related alicyclic complex [M(η⁵-Cp*)(acac)] (5). Reaction of 6 with the bulky lithium cyclopentadienide Li(1,3-C₅t-Bu₂H₃) (12) results in the displacement of acetylacetonate and formation of the corresponding air-sensitive purple monophosphacobaltocene [Co(η⁵- 2,5-PC₄t-Bu₂H₂)-(η⁵-1,3-C ₅t-Bu₂H₃)] (10), which shows fluxional behavior in solution.