Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmettalen. LXIV. Methyl(trioxo)rhenium: Basenaddukte und Basenreaktionen. Kristallstruktur von [Natrium(benzo-15-krone-5)]-perrhenat

In contrast to trioxo(η⁵-pentamethylcyclopentadienyl)rhenium(VII), (η⁵-C₅Me₅)-ReO₃, the organometallic oxide methyl(trioxo)rhenium(VII), CH₃ReO₃ (1), reacts with bases, e.g., sodium hydroxide and organic amines, with expansion of the coordination sphere. Possible secondary reactions are dependent on the nature of the base. Reaction of 1 with sodium hydroxide in the presence of the crown ether benzo-15-crown-5 (B15C5) gives the perrhenate of the formula [Na(B15C5)]⁺- [ReO₄]- (3) in a fast and quantitative reaction, with concomitant liberation of methane; an intermediate of formula [Na(B15C5)]⁺[Ch₃ReO₃OH]- (2) seems plausible for this reaction. 3 exhibits a helical chain structure in the crystalline state, characterized by sodium cations in a nearly planar crown ether environment and tetrahedral perrhenate anions. These subunits are joined with each other, resulting in helical perrhenate sodium chains of pentagonal bipyramidal configuration around sodium cations. The occurrence of the short-lived intermediate 2 is supported by the observed rapid oxygen exchange between 1 and ¹⁷O-labelled water. Methyl(trioxo)rhenium (1) forms adducts with base ligands, thus expanding the coordination sphere of rhenium from 4 to 5 or 6. For example, quinuclidine (1-azabicyclo[2.2.2]-octane) forms the 1 1 adduct 4a of trigonal bipyramidal structure, while 1,4-diazabicyclo[2.2.2]-octan ("dabco") preferably gives the 2 1 adduct 4b. Primary amines are also able to complex with the "metal acid", as can be seen for the aniline complex 4c. The amine coordination entails reduced reactivity of 1, so base adducts of this type are excellent starting materials for the synthesis of derivatives of the title compound 1. Upon subsequent treatment with trimethylchlorosilane/triphenylphosphane and Grignard reagents, the complex 4d (formed from 1 and 2,2′-bipyridine) yields the novel class of compounds 6 of general formula (C₁₀H₈N₂)ReR₂(CH₃O (R = alkyl). The "base-stabilized" dichloro(methyl)(oxo)-rhenium(V) is detected as an isolable reaction intermediate. A single crystal X-ray analysis of the derivative 6c (R = CH₂Si(CH₃)₃) revealed an octahedral metal environment for this type of compounds. Ammonia forms the water-soluble complex CH₃ReO₃(NH₃₂ (4e) upon reaction with 1.