Synthesis and characterization of rhenium(iii) complexes with (Ph₂PCH₂CH₂)₂NR diphosphinoamine ligands

The synthesis and characterization of a new series of neutral, six-coordinated compounds [Re^IIIX₃(PNPR)], where X is Cl or Br and PNPR is a diphosphinoamine having the general formula (Ph₂PCH₂CH₂)₂NR (R = H, CH₃, CH₂CH₃, CH₂CH₂CH₃, CH₂CH₂CH₂CH₃ and CH₂CH₂OCH₃) are reported. Stable [Re^IIIX₃(PNPR)] complexes were synthesized, in variable yields, starting from precursors where the metal was in different oxidation states (iii and v), by ligand-exchange and/or redox-substitution reactions. The compounds were characterized by elemental analysis, proton NMR spectroscopy, cyclic voltammetry, UV/vis spectroscopy, positive-ion electrospray ionization mass spectrometry (ESI(+)-MS) and X-ray diffraction analysis. Although the formulation of the complexes allows either meridional or facial isomers, the latter arrangement was prevalent both in the solid and solution states. Only [ReCl₃(PNPH)] showed a meridional configuration both in solution and in the crystalline state. [ReBr₃(PNPme)] prefers the meridional configuration in the crystalline state and the facial one in solution. While ESI(+)-MS and voltammetric data seem to indicate some dependency from the nature of the alkyl substituent at the nitrogen, the available structural data of the complexes show only slight differences both for angles and bond lengths upon change of the alkyl chain tethered to the nitrogen.