MULTIPLE BONDS BETWEEN MAIN GROUP ELEMENTS AND TRANSITION-METALS .88. SELECTIVE SUBSTITUTION OF AN IMIDO LIGAND IN ALKYL-IMIDO 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))

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))2NR)2] as a mixture of two isomers, the structure of one of which was determined by X-ray crystallography.