82950-36-5Relevant academic research and scientific papers
Steric control of the site preference in five-coordinate iron carbonyl derivatives: Molecular structures of (η2-diethyl fumarate)(triphenylphosphine)tricarbonyliron, Fe(CO)3(PPh3)(DEF), and (η2-diethyl maleate)(triphenylphosphine)tricarbonyliron, Fe(CO)3(PPh3)(DEM)
Stainer, Matthew V. R.,Takats, Josef
, p. 4044 - 4049 (2008/10/08)
The structures of Fe(CO)3(PPh3)(DEF) and Fe(CO)3(PPH3)(DEM) (Ph = C6H5, DEF = diethyl fumarate, DEM = diethyl maleate) have been determined by single-crystal X-ray diffraction techniques. The crystals of Fe(CO)3(PPh3)(DEF) are monoclinic, space group C2/c, with unit cell constants a = 17.674 (4) ??, b = 16.551 (4) ?, c = 19.491 (6) ?, β = 91.98 (2)°, and Z = 8. Fe(CO)3(PPh3)(DEM) crystallizes in triclinic space group P1 with unit cell constants a = 14.792 (21) ?, b = 10.420 (1) ?, c = 10.807 (2) ?, α = 112.41 (1)°, β = 65.89 (1)°, γ = 90.51 (1)°, and Z = 2. Full-matrix least-squares refinement of the structures with 3541 and 3119 unique reflections (Fo2 ≥ 3(σFo))2) led to final discrepancy indexes of R = 0.056, Rw = 0.073 and R = 0.053, Rw = 0.064 for Fe(CO)3(PPh3)(DEF) and Fe(CO)3(PPh3)(DEM), respectively. Both molecular structures are based on the trigonal bipyramid with the olefin bonded in an equatorial position, as is expected from electronic considerations. The PPh3 ligand occupies an axial site in the maleate complex, while in the fumarate derivative it coordinates in the electronically less favored equatorial site. The unexpected equatorial disposition of the phosphine ligand in Fe(CO)3(PPh3)(DEF) is assigned to the steric hindrance caused by the trans substituents of the DEF moiety at the axial sites of the trigonal bipyramid. The Fe-CO and Fe-C(olefin) distances appear to reflect the relative π acidity of the coordinated olefins. This is also borne out by the degree of deformation of the olefinic ligands. Noteworthy is the fact that, whereas in the DEF moiety both substituents are almost coplanar with the plane of the olefin, in the DEM ligand only one substituent is oriented in this fashion; the other is approximately perpendicular to this. The resulting asymmetric nature of this olefin is reflected in the M-C(olefin) distances; the bond to the carbon bearing the π-acceptor substituent is longer.
