Synthesis, crystal structure, and stereochemical non-rigidity of octacarbonyl-µ3-(1,3,6-trimethylhexa-1,3,5-triene-1,5-diyl)-triangulo-tri-iron

Abstract

Crystals of the title compound, obtained by reaction of [Fe₃(CO)₁₂] with methylacetylene, are monoclinic, space group P2₁/c, with Z= 4, in a unit cell of dimensions a= 8.971(6), b= 9.881(6), c= 21.570(9)Å, β= 93.8(1)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by block-diagonal least squares to R 0.038for 2 590 observed reflections. The molecule consists of an unsymmetrical cluster of three iron atoms co-ordinated by eight carbonyls and a σ- and π-bonded organic ligand derived from three methylacetylene molecules. The organic moiety chelates to an iron atom via two σ bonds so a nearly planar six-atom heterocycle is formed. One of the carbonyl groups very unsymmetrically bridges two iron atoms. Hydrogen-1 and ¹³C n.m.r. spectra show that the solid-state structure is maintained in solution, and that the complex is stereochemically non-rigid.