New approach to the chemistry of technetium(V) and rhenium(V) phenylimido complexes: Novel [M(NPh)PNP](3+) metal fragments (M = Tc, Re; PNP = aminodiphosphine) suitable for the synthesis of stable mixed-ligand compounds

Ligand-exchange reactions of the aminodiphosphine ligand bis[(2-diphenylphosphino)ethyl]amine hydrochloride ((PNHPHCl)-H-.) with labile M(NPh)Cl-3(PPh3)(2) precursors (M = Re, Tc) in the presence of triethylamine yield monocationic phenylimido mer,cis-[M(NPh)Cl-2(PNHP)]Cl (M = Re, 1; Tc, 2) intermediate complexes. X-ray analyses show that. in both compounds the aminodiphosphine acts as a tridentate ligand dictating a mer,cis arrangement. Two chloride ligands, respectively in an equatorial and in the axial position trans to the linear M-NPh moiety, fill the remaining positions in a distorted-octahedral geometry, The chloride trans to the, metal-imido core is labile, and is replaced by an alcoholate group, without affecting the original geometry, as established in mer,cis-[Re(NPh)(OEt)Cl(PNHP)]Cl 4. Otherwise, ligand-exchange reactions involving the aminodiphosphine bis[(2-diphenylphosphino)ethyl]methylamine (PNMeP), in which the central secondary amine has been replaced by a tertiary amine function, or its hydrochloride salt ((PNMePHCl)-H-.) give rise to three different species, depending on the experimental conditions: fac,cis-[Re(NPh)Cl-2(PNMeP)]Cl 3a, cis,fac-Re(NPh)Cl-3(PNMeP)(HCl)-H-. 3b, and mer,trans-[Re(NPh)Cl-2(PNMeP)]Cl 3c, which are characterized in solution by multinuclear NMR studies. The monodentate groups incorporated in these intermediate compounds, either halides and/or ethoxide, undergo substitution reactions with bidentate donor ligands such as catechol, ethylene glycol, and 1,2-aminophenol to afford stable mixed ligand complexes of the type [M(NPh)(O,O-cat)(PNP)]Cl [PNP = PNHP M = Re 5, Tc 6; PNP = PNMeP M = Re 7], [Re(NPh)(O,O-gly)(PNP)]Cl [PNP = PNHP 8, PNMeP 9] and [Re(NPh)(O,N-ap)(PNMeP)]Cl 10. X-ray diffraction analyses of the representative compounds 5 and 8 reveal that the aminodiphosphine switches from the meridional to the facial coordination mode placing the heteroatom of the diphosphine trans to the phenylimido unit and the bidentate ligand in the equatorial plane. Solution-state NMR studies suggest an analogous geometry for 6, 7, 9, and 10. Comparison with similar mixed ligand complexes including the terminal nitrido group is discussed.