Carbon–carbon formation at di-iron centres. Part 2. Reactivity of [Fe2(CO)6(µ-COEt){µ-C(R)C(R)H}] complexes toward MeOC(O)CCC(O)OMe (R = Ph) and CF3CCCF3(R = Ph or H); X-ray crystal structures of [Fe2(CO)5{µ-C(OEt)C[C(O)OMe]C[C(O)OMe]}{µ-C(Ph)C(Ph)H}]·H2O and [Fe2(CO)6{µ-C(CF3)C(CF3)CHCHCH(OMe)}]
Abstract
The complexes [Fe2(CO)6(µ-COEt){µ-C(R)C(R)H}](R = H or Ph), which result from the reaction of triethyloxonium tetrafluoroborate with [Fe2(CO)6(µ-CO){µ-C(R)C(R)H}]–, react at room temperature with MeOC(O)CCC(O)OMe (R = Ph) and CF3CCCF3(R = H or Ph). For R = Ph, the complexes [Fe2(CO)5{µ-C(OEt)C(R′)C(R′)}{µ-C(R)C(R)H}][R′= CF3 or C(O)OMe] have been isolated. The structure has been established by a single-crystal X-ray diffraction study of the derivative with R′= C(O)OMe. The complexes result from the loss of one molecule of carbon monoxide and from the insertion of the alkyne into the iron–carbon bond of the carbyne bridge to give a dimetalla-allyl group. When R = H, the complex formed has the formulation [Fe2(CO)6{µ-C(CF3)C(CF3)CHCHCH(OEt)}], as established by an X-ray structure determination of the methoxy derivative. This complex results from the insertion of hexafluorobut-2-yne into the iron–carbon σ bond of the vinyl group, the coupling of the vinyl end of this new fragment with the ethoxycarbyne, and the 1,2-hydrogen shift of one hydrogen to the carbyne group. In this compound, the ethoxy group is very labile and can be replaced by a methoxy group by action of methanol. This replacement is reversible. The ethoxy group can also be replaced by a diethylamino-group by the action of diethylamine, but in this case the reaction is not reversible. This lability of the alkoxy group is explained by the unsymmetrical mode of bonding to one iron of the π-bonded CHCH(OEt) end of the organic bridge, which favoured nucleophilic attacks.