Synthesis and crystal structure of heptacarbonyl-µ3-(pent-1 -en-1 -yl-3-ylidene)-(η-1,2,3-triethylcyclopentadienyl)-triangulo-tri-iron (3 Fe–Fe) : the cleavage of an acetylenic triple bond on a metal-atom cluster

Abstract

The title complex has been synthesized by treating [Fe₃(CO)₁₂] with ethylacetylene, and characterised by i.r. and mass spectra. The crystal structure has been determined by X-ray methods. Crystals are triclinic, space group P, with Z= 2 in a unit cell of dimensions a= 7.674(8), b= 10.966(9), c= 17.652(12)Å, α= 97.5(1), β= 119.9(1), and γ= 101.8(1)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by block-diagonal least squares to R 0.042 for 2 953 observed reflections. The molecule is formed by a trimetal atom cluster; oligomerization of the alkyne and cleavage of an acetylenic triple bond afford a 1,2,3-triethylcyclopentadienyl unit η-bonded to one iron atom, and an ethylallyl unit σ- and η-bonded to all the three iron atoms. Of the seven carbonyl groups co-ordinated to the metal atoms, one unsymmetrically bridges two iron atoms and another very unsymmetrically triply bridges all the metal atoms of the cluster. An analogous complex can be obtained from n-propylacetylene. Experiments on co-oligomerization between acetylene and ethyl- or n-propyl-acetylene, and between diethyl-, di-n-propyl-, and dimethyl-acetylene and the corresponding asymmetrical acetylenes, have also been made.