Mixed halide/phosphine complexes of the dirhenium core. Part 7. Reactions of [Re₂I₈]^2- with monodentate phosphines

Reactions of the octaiododirhenate anion [Re₂I₈]^2- with monodentate phosphines (PR₃ = PMe₃ (1), PMe₂Ph (2), PEt₃ (3), and PEt₂Ph (4)) have been studied in two different solvents, ethanol and benzene, at room temperature. The reactions in ethanol resulted in two-electron reduction products having the Re⁴⁺₂ core, Re₂I⁴(PR₃)₄ (R₃ = Me₃ (1a) and Me₂Ph (2a)), for which X-ray diffraction study revealed a 1,3,6,8 isomer type. The reaction of [Re₂I₈]^2- with PMe₃ in benzene led to an intermediate edge-sharing bioctahedral dirhenium(III) complex, Re₂(μ-I)₂I₄(PMe₃)₄ (1b), with no metal-metal bond. The interaction of PEt₃ with [Re₂I₈]^2- in benzene again yielded a kinetic product with a different stoichiometry and a Re⁵⁺₂ core, [Buⁿ₄N][Re₂I₆ (PEt₃)₂] (3c). The analogous reactions of [Re₂I₈]^2- with PMe₂Ph and PEt₂Ph in benzene involved two-electron reductions and gave complex 2a and Re₂I₄(PEt₂Ph)₄ (4a), as products. Reduction of 1b with KC₈ gave 1a as the main product along with a few crystals of 1,3,6-Re₂I₅(PMe₃)₃ (1d). Mixed iodide/phosphine complexes of the dirhenium core Reⁿ⁺₂, where n = 4 (1a, 2a, 4a), 5 (1d, 3c), and 6 (1b) have for the first time been characterized by X-ray crystallography. In addition, these products have been further identified by a combination of mass spectrometry and cyclic voltammetric measurements.