Synthesis, characterization and crystal structures of rhenium(V) complexes with diphosphines

Two cationic complexes containing a Re-v(O)(2)(+) core have been prepared by substitution on the precursor [Re(O)(2)(PPh3)(2)I]. Careful control of reaction conditions allowed the synthesis of [Re(O)(2)L-2]I (L = bis(1,2-diphenylylphosphino)ethane (dppe), bis(1,3-diphenylphosphino)propane (dppp)) compounds in high yield. Complexes were characterized by UV-Vis and IR spectrophotometry, elemental analyses, FAB, H-1, C-13{H-1} and P-31{H-1} NMR spectra and high-performance liquid chromatography. Four compounds have also been characterized by single-crystal X-ray analyses. Cations consist of a six-coordinated rhenium atom bonded to two tr ans-oxo groups. The phosphines lie on the equatorial plane, almost perpendicular to the Re-v(O)(2)(+) core. The average value for the Re-O bond is 1.77 Angstrom, similar to that in other Re(V) dioxo complexes. Diphosphine ligands form five- and six-membered rings in which lambda delta conformation is adopted. The unexpected [Re(O)(OCH,)(dppp)(CI)2] CH,OH has been additionally characterized from X-ray data. It is also an octahedral complex with a methoxy ligand trans to an oxo group. Species are very stable towards redox processes and can be protonated in acidic media (70:30 dioxane:water, v/v) to yield [Re(OH)(2)L-2](3+). The protonation constants of the diphosphine ligands are also obtained for the first time. (C) 1999 Elsevier Science S.A. All rights reserved.