CO activation in the reactions of iron carbonyls and alkynes. Syntheses, crystal structures, and nuclear magnetic resonance studies on hydroxyferrole and maleoyliron derivatives

Abstract

New syntheses are described for the complexes [Fe₂(CO)₆{C₄(OH)₂RR′}](‘sawhorse’ geometry), and [Fe(CO)₄-{(CO)₂C₂RR′}]; the former are obtained in anhydrous hydrocarbon solvents, and the latter in alkaline methanolic solutions. The structures of [Fe₂(CO)₆{C₂(OH)Et}₂] and [Fe(CO)₄{(CO)₂C₂Et₂}] have been determined by X-ray diffraction methods; crystals of the binuclear derivative are monoclinic, space group P2₁/c, with Z= 4, in a unit cell of dimensions: a= 13.392(8), b= 16.242(9), c= 7.617(8)Å, β= 96.05(8)°; crystals of the mononuclear derivative are tetragonal, space group I4₁/a with Z= 16, in a unit cell of dimensions: a= 20.819(12), c= 12.950(9)Å. The structures have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.038 and 0.036 respectively. Both complexes contain a five-membered heterocyclic ring formed upon CO activation. The ¹H and ¹³C n.m.r. spectra indicate CO fluxionality in the binuclear derivative. Chemical and structural relationships between these complexes are discussed and some comments made on CO activation, in the formation of the heterocyclic rings.