The isolation and characterization of the first examples of pairs of α- and β-isomers of dirhenium(II) of type Re 2X 4(LL) 2 (X = Cl or Br, LL = bidentate phosphine ligand)

Abstract

The complexes Re 2Br 4(depe) 2 and Re 2X 4(dppee) 2 (X = Cl or Br, depe = Et 2PCH 2CH 2PEt 2, dppee = cis-Ph 2PCHCHPPh 2) have been prepared in their α- (eclipsed rotational geometry, chelating phosphine ligands) and β- (staggered rotational geometry, bridging phosphine ligands) isomeric forms. The chloro complex β-Re 2Cl 4(depe) 2 has also been isolated. In the case of α- and β- Re 2Br 4(depe) 2, the preparations involve the reactions of Re 2Br 4(P- n-Pr 3) 4 with depe in toluene-ethanol. While α-Re 2X 4(dppee) 2 are prepared from the reactions of ( n-Bu 4N) 2Re 2X 8 with dppee in various solvents, the β-isomers are obtained upon reacting Re 2X 4(PR 3) 4 (R = Et or n-Pr) with dppee in benzene. These are the first examples of triply bonded dirhenium(II) complexes that have been isolated in both their α- and β-forms. β-Re 2X 4(dppee) 2 (X = Cl or Br) constitute the first examples of complexes of this structural type which contain both CC and MM units within the same fused decalin-like ring system. The isomers β-Re 2Cl 4(depe) 2 and β-Re 2X 4(dppee) 2 (X = Cl or Br) are oxidized by NOPF 6 in acetonitrile to give paramagnetic β-[Re 2Cl 4(depe) 2]PF 6 and β-[Re 2X 4(dppee) 2]PF 6. These oxidized complexes in turn react with CH 3CN in the presence of T1PF 6 to afford β-[Re 2Cl 3(depe) 2(NCMe)](PF 6) 2 and β-[Re 2X 3(dppee) 2(NCMe)](PF 6) 2, respectively. The cleavage of the ReRe bonds of α- and β-Re 2Cl 4(dppee) 2 occurs upon their reaction with CCl 4-CH 2Cl 2 to give cis-ReCl 4(dppee). The related bromo complex cis-ReBr 4(dppee) is formed when β-Re 2Br 4(dppee) 2 is reacted with CH 2Cl 2-Br 2.