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-Re₂Cl₅(PMe₂Ph)₃ (1a), the first analogue of the previously reported trimethylphosphine complex 1,2,7-Re₂Cl₅(PMe₃)₃, has been synthesized by carrying out the reaction of octachlorodirhenium anions with PMe₂Ph in benzene at room temperature. A different reaction product, 1,3,6-Re₂Cl₅(PMe₂Ph)₃ (1b), was obtained when [Buⁿ₄N]₂Re₂Cl₈ was reacted with PMe₂Ph under the same conditions in acetonitrile. Electrochemical studies revealed that both 1a and 1b, as expected for the Re₂⁵⁺ core, are capable of undergoing a one-electron reduction and a one-electron oxidation to yield the respective Re₂⁴⁺ and Re₂⁶⁺ dinuclear complexes. Both processes have been accomplished chemically for the 1,2,7-isomer in the present work. One-electron reduction of 1a by cobaltocene followed by nonredox substitution of a chloride ligand in the resulting anionic species by PMe₂Ph affords triply bonded 1,2,7,8-Re₂Cl₄(PMe₂Ph)₄ (2), only the second example of this rare stereochemistry with a cis-configuration of monodentate phosphines at both metal atoms in the large M₂X₄(PR₃)₄ class of compounds. One-electron oxidation of 1a in the presence of a chloride source, Buⁿ₄NCl, resulted in a quadruply bonded Re₂Cl₆(PMe₂Ph)₂ (3), completing the full series of Re₂Cl_8-x(PMe₂Ph)_x (x = 2, 3, 4) compounds with Re₂ⁿ⁺ (n = 6, 5, 4) cores. The crystal structures of all complexes 1-3 have been investigated by X-ray diffraction. The crystallographic parameters for these structures are as follows: 1,2,7-Re₂Cl₅(PMe₂Ph)₃ (1a), triclinic space group P1̄ with a = 9.350(3) Å, b = 11.102(1) Å, c = 14.558(3) Å, α = 101.34(2)°, β = 92.81(2)°, γ = 90.80(2)°, and Z = 2; 1,3,6-Re₂Cl₅(PMe₂Ph)₃ (1b), monoclinic space group P2₁/c with a = 11.202(4) Å, b = 14.357(6) Å, c = 19.509(5) Å, β = 97.84(3)°, and Z = 4; 1,2,7,8-Re₂Cl₄(PMe₂Ph)₄ (2), triclinic space group P1̄ with a = 11.847(4) Å, b = 12.094(3) Å, c = 13.056(5) Å, α = 76.111(8)°, β = 88.523(9)°, γ = 88.95(2)°, and Z = 2; 1,7-Re₂Cl₆(PMe₂Ph)₂, (3), triclinic space group P1̄ with a = 9.209(1) Å, b = 11.480(2) Å, c = 13.389(2) Å, α = 81.74(2)°, β = 69.89(2)°, γ = 66.35(2)°, and Z = 2. The Re-Re bond lengths in the Re₂⁴⁺ (2), Re₂⁵⁺ (1a and 1b), and Re₂⁶⁺ (3) centered molecules (2.260(1), 2.2313(4), 2.219(1), and 2.214(1) Å) are consistent with bond orders of 3.0, 3.5, and 4.0, respectively.