Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides VI. Further studies on isomers of the edge-sharing bioctahedral species [Re2C13(μ-dppm)2(CO)(CNxyl)2

Abstract

Abstract The different types of structural isomerism that exist for those dirhenium(II) halide complexes which contain bidentate phosphines of the type R 2 P(CH 2 )PR 2 ( n = 1 or 2) are examined. A particular focus of this report are those complexes which are formed from the reactions of Re 2 X 4 (μ-dppm) 2 (X = Cl or Br; dppm = Ph 2 PCH 2 PPh 2 ) with CO, RNC or RCN ligands; up to three of these ligands can be coordinated either alone or in combination with one another. The earlier literature is reviewed and new examples of edge-sharing bioctahedral complexes which exist in different isomeric forms are reported. Yellow and green isomers of the salts [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNxyl) 2 ]Y (Y = Cl, ReO 4 , S0 3 CF 3 or PF 6 ) have been isolated by the reactions of Re 2 C1 4 (μ-dppm) 2 (CO) and Re 2 C1 4 (μ-dppm) 2 (CO)(CNxyl) with xylNC in the presence of Tl + . Both forms contain bridging carbonyl ligands; the yellow form undergoes thermal isomerization to the symmetrical all- cis green isomer when its solutions in 1,2-dichloroethane are refluxed. The structure of the green isomer of composition [Re 2 C1 3 (u-dppm) 2 (CO)(CNxyl) 2 ](ReO 4 ) 0.82 Cl 0.18 ( IIb ) has been determined by single crystal X-ray crystallography. Crystal data for IIb at 293 K: orthorhombic space group Pnma (No. 62), a = 29.872(7)A, b = 21.948(3)A, c = 10.944(1)A, V = 7175(3)A 3 , Z = 4. The structure was refined in full-matrix least squares to R = 0.056 (R w = 0.072) for 2894 data with I > 3 σ ( I ). The Re-Re bond length of 2.576(1) A is characteristic of edge-sharing bioctahedral species that are derived from the non-redox reactions of Re 2 X 4 (μ-dppm) 2 with neutral donors.