Über Metallalkyl- und -arylverbindungen, 51. Mittlg.* Unsymmetrische Diorganomagnesiumverbindungen. MgRR'(L) und solvensgetrennte Ionenpaare mit R = Me, Et, R' = Cyclopentadienyl, Indenyl, Fluorenyl, Phenylethinyl, L = Tetramethylethylendiamin, Pentamethyldiethylentriamin / On Metal Alkyl and Aryl Compounds, Part 51 Unsymmetrical Diorganomagnesium Compounds. MgRR'(L) and Solvens Separated Ion Pairs with R = Me, Et, R' = Cyclopentadienyl, Indenyl, Fluorenyl, Phenylethynyl, L = Tetramethylethylenediamine, Pentamethyldiethylenetriamine

Abstract

Abstract Amine adducts of diorganomagnesium compounds MgR2(L) are soluble in hydrocarbons and therefore valuable synthons for reactions in non-polar solvents. In this way unsymmetrically substituted derivatives MgRR'(L) become available by substituting one organic group by a different carbanion via acid-base reactions, according to eq. (1): R2Mg(L) + HR' -> RR'Mg(L) + HR (1) with HR' being stronger CH-acids than HR. Using the amin adducts R2Mg(L) (R = Me, Et) with chelating amines (L = tetramethyl­ ethylenediamine, TMEDA, pentamethylethylenetriamine, PMDTA) and the strong CH-acids cyclopentadiene, indene, fluorene and alkynes the following compounds have been synthesized and their structures derived by X-ray analyses: MgMe(η3-cyclopentadienyl)(tmeda) (1), MgMe(η3-indenyl)(tmeda) (2), MgMe(η1-fluorenyl)(tmeda) (3), [Mg2Me2(pmdta)2]2+[fluorenyl]− 2 benzene (4) and [Mg2Et(phenylethynyl)3(tmeda)]2 ∙ benzene (5). It is remarkable, that cyclopentadienyl, indenyl, and fluorenyl ligands have a lower hapticity than η5 to the metal, due to steric repulsion by the other ligands. In 4 the bulky tridentate base PMDTA prevents any direct interaction between the fluorenide anion and magnesium, giving solvens separated ion pairs with the unusual and hitherto rare example of an organomagnesium cation [Mg2Me2(pmdt)2]2+. The 1:3 compound 5 has a more complicated structure, related to that of alkali metal alkynyl magnesates.