Selective substitution of an imido ligand in alkyl- and aryl-imido rhenium(VII) complexes; crystal structures of (2,6-dimethylphenyl)ammonium trichlorobis(2,6-dimethylphenyl-imido)methylrhenate(VII) and bis(2,6-dimethylphenylimido)methylbis(neopentyl)rhenium(VII)

Abstract

Reaction of ReMeO₃ and 2,6-dimethylphenyl isocyanate gives the imido complex [ReMe(NR)₃](R = 2,6-Me₂C₆H₃). Complexes of the type [ReMe(NR)₃] or [ReMe(NBu^t)₃] undergo selective substitution of only one imido ligand to form bis(imido) derivatives. Thus, [ReMe(NBu^t)₃] reacts with the weak acid catechol via protonation of one imido ligand to form a stable five-co-ordinate complex [ReMe(NBu^t)₂(O₂C₆H₄)]. In contrast, [ReMe(NR)₃] forms a complex which can only be isolated in a pure state by the addition of pyridine (py) to give the six-co-ordinate [ReMe(NR)₂(O₂C₆H₄)(py)]. The complex [ReMe(NR)₃] also reacts with thiophenol to give five-co-ordinate [ReMe(NR)₂(SPh)₂]. Reaction of [ReMe(NR)₃] with HCl gives the ionic complex [NH₃R][ReMeCl₃(NR)₂]. The crystal structure of this complex was determined by X-ray crystallography. The neutral dihalide complexes [ReMe(NR)₂X₂(py)](X = Cl or Br) are prepared from [ReMe(NR)₃] by the addition of 2 equivalents of pyridinium halide. Alkylation of the dichloro or dibromo derivative with neopentylmagnesium chloride gives the novel mixed-alkyl complex [ReMe(CH₂Bu^t)₂(NR)₂] as a mixture of two isomers, the structure of one of which was determined by X-ray crystallography.