Synthesis of 1,3-Dimetallo-1,3-diphosphetane-2,4-diones. X-ray Structure Analysis of Cp*(CO)₂FeP[Cr(CO)₅]C(O)P[Fe(CO)₂Cp*]C(O) (Cp* = η⁵-C₅Me₅)

Reaction of the lithoxy phosphaalkyne (DME)₂LiOC⋮P (1) with 1 equiv of the complexes (η⁵-C₅R₅)(CO)₂FeBr (2); C₅R₅ = C₅Me₅ (a), 1,3-t-Bu₂C₅H₃ (b), 1,2,4-i-Pr₃C₅H₂ (c)) afforded the 1,3-diferrio-1,3-diphosphetane-2,4-diones (η⁵-C₅R₅)(CO)₂FePC(O)P[Fe(CO)₂(η⁵-C₅R₅)]C(O) (3a−c) as red amorphous solids in 32−37% yield. By treatment with ((Z)-cyclooctene)Cr(CO)₅, compound 3a was converted into the red complex Cp*(CO)₂FeP[Cr(CO)₅]C(O)P[Fe(CO)₂Cp*]C(O) (4). Constitutions and configurations of 3a−c and 4 were determined by elemental analyses and spectra (IR, ¹H, ¹³C, and ³¹P NMR, MS). The molecular structure of 4 was established by a single-crystal X-ray analysis.