Reactions of co-ordinated ligands. Part XIII. Ring opening of 2,3-bis-(hydroxymethyl)methylenecyclopropane with nonacarbonyldi-iron; Molecular and crystal structures of tricarbonyl-η⁴-[3-methylene-endo-4-vinyldihydrofuran-2(3H)-one]iron(0) and tetracarbonyl-η²-[3-methyl-ene-exo-4-vinyldihydrofuran-2(3H)-one]iron(0)

trans- or cis-2,3-Bis(hydroxymethyl)methylenecyclopropanes react with [Fe₂(CO)₉] to produce tricarbonyl-η ⁴-[3-methylene-endo-4-vinyldihydrofuran-2(3H)-one]iron(0) and tetracarbonyl-η ²-[3-methylene-exo-4-vinyldihydro-furan-2(3H)-one]iron(0). The structural identities of these two complexes have been established by the analysis of single-crystal X-ray data recorded on a four-circle diffractometer. The tricarbonyl complex is triclinic, space group P1, with a = 7.745(5), b = 6.787(3), c = 9.873(4) Å, α = 96.46(3), β = 86.79(4), γ = 94.05(4)°, and Z = 2. Full-matrix least-squares refinement using 1 435 independent observed reflections has converged to R = 0.029, R_w 0.031. The metal co-ordination geometry approximates to that of a square pyramid with the alkene fragments in cis-equatorial positions. Four molecules of the tetracarbonyl crystailise in the monoclinic space group P2₁/a with a = 12.419(4), b = 6.527(1), c = 15.321 (4) Å, β = 91.21 (2)°. The model has been refined to R 0.041, R_w 0.044 for 1 679 reflections. In this complex the Fe(CO)₄ moiety is attached to the opposite side of the organic fragment via the rigid alkene function, which occupies one equatorial site of a trigonal bipyramidal co-ordination geometry. Analogous reactions of trans-2,3-bis(dideuteriohydroxymethyl)methylenecyclopropane and trans-2,3-dideuterio-2,3- bis(hydroxymethyl)methylenecyclopropane with [Fe₂(CO)₉] yield analogous deuteriated iron complexes with no deutcrium scrambling. ¹H and ¹³C N.m.r. spectra are reported and a plausible mechanism is presented.