MIXED CARBOXYLATE BIS(DIMETHYLPHOSPHINO)METHANE COMPLEXES OF DIRHENIUM(II,II) AND DIRHENIUM(III,II)

The reactions between Re2(O2CR)4X2 (X = Cl, Br; R = CH3, C2H5) and the bridging phosphine ligand Me2PCH2PMe2 (dmpm) in ethanol/toluene afford the dirhenium (II) complexes [Re2(O2CR)X2(dmpm)3]X, which undergo anion exchange with n-Bu4NPF6 to give [Re2(O2CR)X2(dmpm)3]PF6. The complex [Re2(O2CCH3)Cl2(dmpm)3]Cl has also been prepared by the reaction of Re2Cl4(dmpm)3 with LiO2CCH3 in methanol. The formation of these complexes from Re2(O2CR)4X2 proceeds through the intermediacy of the paramagnetic species trans-[Re2(O2CR)2X2(dmpm)2]+, as shown by the isolation of this cation (as its PF6- salt) in the case of X = Cl and R = CH3. The structural identity of these complexes has been established by a single-crystal X-ray analysis of a crystal of composition [Re2(O2CCH3)Cl2(dmpm)3]Cl.2H2O.CH2Cl2. Crystal data (at 20-degrees-C) are as follows: tetragonal space group P4BAR2(1)c, a = 26.941 (1) angstrom, c = 9.931 (1) angstrom, V = 7208 (2) angstrom-3, and Z = 8. The structure was refined to R = 0.033 (R(w) = 0.041) for 2084 data with I > 3.0-sigma(I). The Re-Re bond distance is 2.304 (1) angstrom, and the structure contains four bridging ligands (one acetate and three dmpm ligands) and two axially bound chlorides. The acetate complexes [Re2(O2CCH3)X2(dmpm)3]PF6 (X = Cl, Br) have been oxidized by NOPF6 to the paramagnetic 1:2 salts [Re2(O2CCH3)X2(dmpm)3](PF6)2.