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 C2v 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.