Hexacarbonyl complexes of dirhenium(I) containing E2Ph4(E = P, As, or Sb) ligands; X-ray crystal structure of [Re2Br2(CO)6(Sb2Ph4)]

Abstract

The E₂Ph₄ complexes of rhenium(I), [Re₂X₂(CO)₆(E₂Ph₄)](X = Br, E = As or Sb; X = I, E = P, As, or Sb), have been prepared by the reactions of [Re₂Br₂(CO)₆(thf)₂](thf = tetrahydrofuran) or [Re₂I₂(CO)₈] with the appropriate E₂Ph₄. The crystal and molecular structure of one of the compounds, namely [Re₂Br₂(CO)₆(Sb₂Ph₄)], has been solved by X-ray diffraction methods. The crystals are monoclinic, space group P2₁/n, with a= 16.585(8), b= 22.036(13), c= 19.764(19)Å, β= 109.34(6)°, and Z= 8. Data collection yielded 2 197 observed reflections, R= 0.040. The molecule consists of two pseudo-octahedral rhenium(I) centres joined by bromide and Sb₂Ph₄ bridges. Average distances include Re–Br 2.663(4), Sb ⋯ Br 3.640(3), Re ⋯ Re 3.970(2), and Sb–Sb 2.826(4)Å. The rhenium–P₂Ph₄ complex undergoes nucleophilic attack by PPh₂^– to form an anionic rhenium(I) carbonyl species. The small angle of folding along the Br ⋯ Br vector produces the appearance of the number of i.r. carbonyl stretches expected for the local C_2v symmetry of the Re₂(CO)₆ core, presumably due to a better coupling of the two Re(CO)₃ moieties. Chemical evidence and mass spectral data indicate that the stability of the rhenium(I) complexes decreases with increasing atomic weight of the Group 5 donor atom.