Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: LXII. Alkin-Komplexe der Organorheniumoxide: Redox-Chemie und Nucleophilie der Oxo-Funktion von (η 5-Pentamethylcyclopentadienyl)(η 2-diphenylethin) oxorhenium(III)

Abstract

The novel Re III oxo alkyne complexes (η 5-C 5Me 5)Re(=O)(η 2-RCCR) ( 3a–c; R = C 6H 5, CH 3, C 2H 5) are obtained almost quantitiatively by alkaline hydrolysis of the dichloro precursor compounds (η 5C 5Me 5)ReCl 2(η 2-RCCR) ( 4a-c). An X-ray diffraction study has revealed that in the phenyl derivative 3a the alkyne group is best described as a two-electron ligand. 17O NMR spectroscopy shows the remarkable electron deficiency of the terminal oxo group. This oxo function however is sufficiently nucleophilic to be converted into the hydroxo psecies [η 2-diphenylalkyne)hydroxo(η 5-pentamethylcyclopentadienyl)rhenium(III)] tetrafluoroborate ( 5a) and [(η 2-butyne(2))hydroxo(η 5-pentamethylcyclopentadienyl)rhenium(III)] tetrafluoroborate ( 5b) by O-protonation with HBF 4. One-electron oxidation of 3a leads to the dinuclear Re IV species [(μ-O)(η 5-C 5Me 5)Re(η 2-C 6H 5CCC 6H 5) 2] 2+ without loss of the alkyne ligand. The Re V systems (η 5-C 5Me 5)Re(=O) 2(η 2-RCCR) ( 2, generated oxidatively, are not stable as they decompose rapidly by eliminating the alkyne ligand.