2,5-Di-(tert-butyl)phospholyl sandwich complexes containing group 14 elements (Ge, Sn, Pb). Synthesis, molecular structure, and ring transfer chemistry of [M(PC4H2But2)2] (M= Sn, Pb)
Low-temperature reaction of [Li(PC(4)H(2)t-Bu-2)center dot 2thf] (thf = tetrahydrofuran) (7) with [Co(acac)21 (Hacac acetylacetone) gives the reactive half-sandwich complex [Co(eta(5)-PC(4)H(2)t-Bu-2)(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(eta(5)-Cp*)(acac)] (5). Reaction of 6 with the bulky lithium cyclopentadienide Li(1,3-C(5)t-Bu2H3) (12) results in the displacement of acetylacetonate and formation of the corresponding air-sensitive purple monophosphacobaltocene [Co(eta(5)-2,5-PC(4)t-Bu2H2)-eta(5)1,3-C(5)t-Bu2H3) (10), which shows fluxional behavior in solution.