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)

The propargyl alcohols RC2C(H)(OH)R' (R = H, R' = Et; R = Me, R' = Et; R = Et, R' = Me; R = Ph, R' = Pr-i) reacted with [Fe-3(CO)(12)] in hydrocarbon solvents to give, as the final products, binuclear "ferrole" derivatives [Fe-2(CO)(6)L-2] or [Fe-2(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 [Fe-3(CO)(9)-(mu-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 [Fe-5(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 Fe-3 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 to the alkyne triple bond. Possible formation mechanisms are discussed.