Synthesis of a Cobalt−Phospholyl Half-Sandwich Complex and Its Transformation into a Phosphacobaltocene

Low-temperature reaction of [Li(PC4H2t-Bu2)·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-C5t-Bu2H3)] (10), which shows fluxional behavior in solution.