FORMATION AND X-RAY STRUCTURE OF THE MU-ALKYLIDENE COMPLEX FE-2(CO)(6)(MU-ETA(3), ETA(3)-C(CH=CHPH)(2)) UPON DEOXYGENATION OF FE-2(CO)(8)(MU-ETA(2),ETA(2)-C(O)(CH=CHPH)(2)) WITH METHYL LITHIUM

Di-iron nonacarbonyl reacts with dibenzylideneacetone (5) to produce, depending on the reaction conditions, either a mixture of the three complexes Fe(CO)(4)[eta(2)(CO)(CH = CHPh)(2)] (6), Fe-2(CO)(8)[eta(2), eta(2)(CO)(CH = CHPh)(2)] (7), and Fe(CO)(3)[eta(4)(CO)(CH = CHPh)(2)] (8), or solely complex 7 in which the ligand is bound in a eta(2), mu-eta(2), eta(2) or eta(4) fashion. All three complexes have been fully characterized by X-ray crystallography. Crystal data for complex 6: C21H14FeO5, monoclinic, space group P2(1)/n, a = 6.326(2) Angstrom b = 14.567(2) Angstrom, c = 20.504(2) Angstrom, beta = 96.91(2)degrees, U = 1875(4) Angstrom(3), D-c = 1.42 g cm(-3), Z = 4. For complex 7: C25H14Fe2O9 triclinic, space group ($) over bar P1, a = 9.677(5) Angstrom, b = 10.635(5) Angstrom, c = 13.471(6) Angstrom, alpha = 104.24(3)degrees, beta = 105.46(4)degrees, gamma = 104.75(4)degrees, U = 1216.7(8) Angstrom(3), D-c = 1.56 g cm(-3), Z = 2. For complex 8: C20H14FeO4, orthorhombic, space group Pbca, a = 13.397(2) Angstrom, b = 10.041(3) Angstrom, c = 26.579(2) Angstrom, U = 3575.1(8) Angstrom(3), D-c = 1.39 g cm(-3), Z = 8. Upon reaction with MeLi under an atmosphere of CO, all of the three complexes each gave a mixture of the expected eta(4)-ketene complex Fe(CO)(4)(eta(4)-PhCH = CH(C = C = O)CH = CHPh) (9) as the result of a deoxygenation-carbonylation reaction, and the new mu-alkylidene complex Fe-2(CO)(6)(mu - eta(3),eta(3)-C(CH = CHPh)(2)) (10) as the result of a deoxygenation reaction of the starting complex followed by the trapping of the intermediate alkylidene complex by Fe(CO)(3). Complex 10, C23H14Fe2O6, has been fully characterized by X-ray crystallography and shown to be orthorhombic, space group Pbcn, a = 17.155(4)Angstrom b = 7.842(2) Angstrom c = 15.857(2) Angstrom, U = 2133.2(5) Angstrom(3), D-c = 1.55 g cm(-3), Z = 4.