Syntheses and structural characterizations of phenylimidorhenium(V) complexes containing bi- or tetra-dentate phosphinoamido ligands

Abstract

The substitution reaction of [Re(NPh)Cl₃(PPh₃)₂] with H₂dpa [(o-aminophenyl)diphenylphosphine] led, depending on the solvent polarity, to the formation of the diamagnetic neutral phenylimido complex [Re(NPh)Cl(Hdpa)₂] 2 and the monocationic [Re(NPh)Cl(Hdpa)(H₂dpa)][ClO₄] 4. Conversely, H₂dppd {N,N′-bis[2-(diphenylphosphino)phenyl]propane-1,3-diamine} gave only the cationic compound [Re(NPh)Cl(Hdppd)]Cl 6, where the ligand is uninegative. In alkaline alcohols, the neutral complexes [Re(NPh)(OMe)(Hdpa)₂] 1 and [Re(NPh)(OEt)(dppd)] 5 were obtained. The reaction of H₂dpa in a 1∶1 ligand to precursor ratio produced the monosubstituted complex [Re(NPh)Cl₃(H₂dpa)] 3. The compound [Re(NPh)Cl(Hdpa)₂] can also be prepared by treating for several hours in refluxing xylene the isostructural oxo complex [ReO(Cl)(Hdpa)₂] and aniline. All the complexes are stable in the solid state, however those containing the bidentate ligand show instability, in particular in chlorinated solvents. This is discussed in terms of the different π-donation abilities of the amide, alkoxide and chloride ligands. Despite a predicted number of electrons largely exceeding 18, the crystal structure determinations for 1, 2 and 5 do not show significant deviation from linearity of the Re–N–Ph moiety, but only an unusual elongation of the Re–OR (R = Me or Et) bonds in 1 and 5. The NMR and structural data are compared with those of oxo analogues previously reported.