Synthesis and molecular structure of bis(µ4-but-1-yne)-undecacarbonyl-quadro-tetrairon (4 Fe–Fe)

Abstract

The title complex has been obtained by treating [Fe₃(CO)₁₂] with but-1-yne in hydrocarbon solvents, and is 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= 8.700(7), b= 9.125(9), c= 17.541 (15)Å, α= 112.8(1), β= 104.5(1), and γ= 106.0(1). The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R 0.043 for 2 204 observed reflections. The molecule is a cluster in which the four metal atoms are in a tetrahedrally distorted square arrangement. Of the 11 carbonyl groups co-ordinated to the metal atoms, eight are terminal, one is symmetrically bridging two iron atoms, and two are very asymmetrically bridging. Each of the two alkyne ligands is σ-bonded to two iron atoms on the opposite vertices of the cluster and π-bonded to the other two. The substituted cluster has an Fe₄C₄ core in which the metal and carbon atoms occupy the vertices of a triangulated dodecahedron. Propyne, but-2-yne, and pent-1-yne complexes of similar stoicheiometry have also been obtained.