Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 6. Rare or Unprecedented Isomers of [Re2Cl6(PR3)2] Stoichiometry

Several new paramagnetic dirhenium(II,III) anions of the formula [Re2Cl6P2]- (P2 = (PPrn3)2 (1), (PEt2Ph)2 (2), dppp (3)) have been isolated in the form of their tetrabutylammonium salts as the kinetic products in reactions of [Re2Cl8]2- with an appropriate phosphine ligand. All three complexes have been characterized in solution by cyclic voltammetry, ESR, and mass spectroscopy. Three different isomeric forms of the [Re2Cl6P2] core have been recognized in the solid state by X-ray crystallography. The known 1,7-isomer (C2h) with a centrosymmetric disposition of phosphine groups was found for PPrn3 (1a) and PEt2Ph (2) ligands. The compound [Bun4N][Re2Cl6(PPrn3)2] was also crystallized in the unprecedented form of a 1,6-isomer (C2) (1b) which can be derived from 1a by a 90° rotation of the ligands around the metal−metal bond. For the diphosphine, a Cs isomer of [Re2Cl6(dppp)]- (3) was discovered having the dppp ligand chelating on one rhenium atom. Crystallographic data are as follows: for 1a, monoclinic s...