MIXED CHLORIDE PHOSPHINE COMPLEXES OF THE DIRHENIUM CORE - 2 - NEW REACTIONS INVOLVING DIMETHYLPHENYLPHOSPHINE/

Two geometrical isomers of the composition Re2Cl5(PMe2Ph)(3), namely 1 ,2,7 and 1,3,6, have been prepared. The unusual paramagnetic 1.2,7-Re2 Cl5(PMe2Ph)(3) (1a), the first analogue of the previously reported tri methylphosphine complex 1,2,7-Re2Cl5(PMe3)(3), has been synthesized by carrying out the reaction of octachlorodirhenium anions with PMe2Ph i n benzene at room temperature. A different reaction product, 1,3,6-Re2 Cl5(PMe2Ph)(3) (1b), was obtained when [(Bu4N)-N-n](2)Re2Cl8 was react ed with PMe2Ph under the same conditions in acetonitrile. Electrochemi cal studies revealed that both la and Ib, as expected for the Re-2(5+) core, are capable of undergoing a one-electron reduction and a one-el ectron oxidation to yield the respective Re-2(4+) and Re-2(6+) dinucle ar complexes. Both processes have been accomplished chemically for the 1,2,7-isomer in the present work. One-electron reduction of la by cob altocene followed by nonredox substitution of a chloride ligand in the resulting anionic species by PMe2Ph affords triply bonded 1,2,7,8-Re2 Cl4(PMe2Ph)(4) (2), only the second example of this rare stereochemist ry with a cis-configuration of monodentate phosphines at both metal at oms in the large M2X4(PR3)4 class of compounds. One-electron oxidation of la in the presence of a chloride source, (Bu4NCl)-N-n, resulted in a quadruply bonded Re2Cl6(PMe2Ph)(2) (3), completing the full series of Re2Cl8-x(PMe2Ph)(x) (x = 2, 3, 4) compounds with Re-2(n+) (n = 6, 5 , 4) cores. The crystal structures of all complexes 1-3 have been inve stigated by X-ray diffraction. The crystallographic parameters for the se structures are as follows: 1,2,7-Re2Cl5(PMe2Ph)(3) (1a), triclinic space group P (1) over bar with a = 9.350(3) Angstrom, b = 11.102(1) A ngstrom, c = 14.558(3) Angstrom, alpha = 101.34(2)degrees beta = 92.81 (2)degrees, gamma = 90.80(2)degrees, and Z = 2; 1,3,6-Re2Cl5(PMe2Ph)(3 ) (1b), monoclinic space group P2(1)/c with a = 11.202(4) Angstrom, b = 14.357(6) Angstrom, c = 19.509(5) Angstrom, beta = 97.84(3)degrees, and Z = 4; 1,2,7,8-Re2Cl4(PMe2Ph)(4) (2), triclinic space group P (1) over bar with a = 11.847(4) Angstrom, b = 12.094(3) Angstrom, c = 13.0 56(5) Angstrom, alpha = 76.111(8)degrees beta = 88.523(9)degrees gamma = 88.95(2)degrees, and Z = 2: 1,7-Re2Cl6(PMe2Ph)(2), (3), triclinic s pace group P (1) over bar with a = 9.209(1) Angstrom, b = 11.480(2) An gstrom, c = 13.389(2) Angstrom, alpha = 81.74(2)degrees, beta = 69.89( 2)degrees, gamma = 66.35(2)degrees, and Z = 2. The Re-Re bond lengths in the Re-2(4+) (2), Re-2(5+) (1a and 1b), and Re-2(6+) (3) centered m olecules (2.260(1), 2.2313(4), 2.219(1), and 2.214(1) Angstrom) are co nsistent with bond orders of 3.0, 3.5, and 4.0, respectively.