STRUCTURE AND BONDING IN CATIONIC CYCLOPENTADIENYLIRON COMPLEXES CONTAINING THIOETHERS, SELENOETHERS, AND TELLUROETHERS AS LIGANDS

An extended Huckel MO study based on X-ray structure determinations of [C5H5Fe(CO)2(ER2)]BF4 complexes (I: E = S, R = CH3, C6H5; E = Se, Te, R = CH3) and their chemistry confirms and rationalizes the inertness and stability of the Fe-E bond in these cations in the order E = Te >> Se > S > O on the basis of electronegativity, orbital diffuseness, and size considerations. No important pi-bonding effect is found, and a comment on the photochemical replacement of CO is made. The different lability trend for the related [C5H5Fe(CO)2(E'R3)]+ cations (II: E' = N-Bi, R = CH3) is compared and briefly discussed on the basis of extended Huckel MO calculations. The complexes [C5H5Fe(CO)2(E(CH3)2)]BF4 crystallize in the monoclinic space group P2(1)/n (E = S) or P2(1)/c (E = Se, Te) with the unit cell parameters (in the order S, Se, and Te) a = 8.133 (2), 8.256 (3), 8.393 (2) angstrom, b = 12.801 (5), 12.798 (5), 12.890 (5) angstrom, c = 13.269 (2), 13.404 (5), 13.411 (7) angstrom, beta = 106.89 (1), 109.21 (3), 109.46 (3)-degrees, and Z = 4. The complex [C5H5Fe(CO)2(S(C6H5)2)]BF4 crystallizes in the orthorhombic space group Pbca with the unit cell parameters a = 9.783 (2) angstrom, b = 19.452 (5) angstrom, c = 20.554 (6) angstrom, and Z = 8. All complexes show a three-legged piano-stool geometry around the iron center with Fe-E distances of 2.264 (2) and 2.283 (4) angstrom (E = S, R = CH3 and C6H5), 2.381 (1) angstrom (E = Se), and 2.533 (1) angstrom (E = Te).