Crystal and molecular structure of two isomeric iron carbonyl derivatives which contain an extensively rearranged bis(tertiary phosphine)

Article abstract of DOI:10.1021/ic50215a038

The bis(tertiary phosphines) (C₆H₁₁)₂PC=CP(C₆H₁₁) ₂(CF₂)_n [A (n = 2), B (n = 3)] and (C₆H₅)₂PC=C(CF₂) ₂C=C-P(C₆H₅)₂(CF₂) ₂ (C) react with iron carbonyls to give a number of products of known structure, namely, (L-L)Fe(CO)₃ [(L-L) = A or B], (L-L)Fe₂(CO)₆ [(L-L) = A], and (L-L)Fe₂(CO)₈ [(L-L) = C]. In addition two isomers of formula (L-L)Fe₂(CO)₆ (V and VI) can be isolated from the reactions of C, and the structures of these were determined by conventional X-ray crystallographic techniques. The cell constants for V are a = 15.348 (6) ?, b = 9.231 (5) ?, c = 26.839 (12) ?, and β = 104.90 (3)°; the space group is P2₁/c. The cell constants for VI are a = 12.45 (2) ?, b = 17.21 (5) ?, c = 18.86 (3) ?, and β = 97.67 (9)°; the space group is P2₁/c. The structures of V and VI were refined by full-matrix least-squares techniques to conventional R indices of 0.055 and 0.072, respectively. In IV the basic structure consists of two Fe(CO)₃ moieties bridged by two different phosphide groups. One of those groups is a -P?(C₆H₅)₂ unit which has been cleaved from the ligand and the other is a -P?(C₆H₅)C=C(CF₂)₂C=C(C ₆H₅)(CF₂)₂ group formed by extensive rearrangement of the remainder of the ligand. The phenyl group migrates from the phosphorus to the end of the conjugated fluorocarbon chain. In VI, again two bridged Fe(CO)₃ fragments are present. One of these is a cleaved -P?(C₆H₅)₂ group but the other is the intact remaining portion of the ligand which forms a metal-carbon σ bond to one iron atom and coordinates to the second iron with the remaining phosphorus atom. These unusual ligand fragmentation reactions are discussed in the light of related examples.