Metal fragment condensation and carbon–carbon bond cleavage in reactions of [Fe3(CO)12] with internal propargyl alcohols. Structures of the “bow tie” acetylide complexes [Fe5(CO)14(C2R)2] (R =Me or Et)

Abstract

The propargyl alcohols RC₂C(H)(OH)R′ (R = H, R′ = Et; R = Me, R′ = Et; R = Et, R′ = Me; R = Ph, R′ = Prⁱ) reacted with [Fe₃(CO)₁₂] in hydrocarbon solvents to give, as the final products, binuclear “ferrole” derivatives [Fe₂(CO)₆L₂] or [Fe₂(CO)₆(L)(L − H₂O)] [L = propargyl alcohol] in several isomers. Small amounts of tri- and penta-nuclear complexes were also obtained. In particular, when R = H or Ph trinuclear complexes [Fe₃(CO)₉(μ-CO)L] 1 with a “parallel” alkyne ligand could be isolated and characterized by IR and NMR spectroscopies and mass spectrometry. When R = Me or Et the “bow tie” acetylide complexes [Fe₅(CO)₁₄(C₂R)₂] (R = Me 2a or Et 2b) were isolated; their structures were determined by X-ray diffraction. The complexes 2a and 2b are formed by two Fe₃ triangles sharing a common vertex: each triangle is co-ordinated in a perpendicular fashion by an acetylide fragment and the carbon of one of the acetylide ligands is bound to four iron atoms. Complexes 2 are new examples of an uncommon type of cluster framework; they are presumably formed upon condensation of metal fragments generated by triiron dodecacarbonyl and upon cleavage of a carbon–carbon bond α to the alkyne triple bond. Possible formation mechanisms are discussed.