Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen. LXXX. Zur Kenntnis der "Metallsäure" Methyltrioxorhenium(VII): Addition anionischer und neutraler Basen. Kristallstruktur eines 2,2′-Bipyridinium-perrhenats

Methyltrioxorhenium(VII) (1) reacts cleanly as a typical 14e metallo-acid with nucleophilic anions X^-, e.g. chloride and bromide, to yield hexa- or pentacoordinated anions formulated as [CH₃ReO₃X₂]^2- and [CH₃ReO₃X]^-, that can be isolated as tetraalkylammonium (2a,b) and bis(triphenylphosphane)immonium salts (3). It seems obvious that the size of the cationic counterion has some influence on the coordination number of the metal in the adduct thus formed. A 1/1-addition product, 4, is formed from the reaction of the "metallo-acid" 1 with 4,4′-di(t-butyl)-2,2′-bipyridine. 4 is very soluble in common organic solvents and undergoes hydrolytic decomposition to [4,4′-di(t-butyl)-2,2′-bipyridinium]perrhenate (5) with concomitant elimination of methane. This ionic compound has a crystal structure consisting of discrete ions, with the perrhenate embedded in layers formed by bipyridinium cations (single crystal X-ray diffraction).