Strukturen von polaren Magnesiumorganylen: Synthese und Struktur von Basen‐Addukten des Bis(cyclopentadienyl)magnesiums

Structures of Polar Magnesium Organyls: Synthesis and Structure of Base Adducts of Bis(cyclopentadienyl)magnesium Eight donor‐acceptor complexes of bis(cyclopentadienyl)magnesium ( 1 ) with N ‐ and O ‐donor Lewis bases have been synthesized and characterized by X‐ray structure analysis. With acetonitrile, dimethoxyethane, diethyleneglycoldimethylether, dioxane, and tetramethylethylenediamine simple 1:1 adducts are formed ( 2 – 6 ). In some cases a change of the hapticity of one cyclopentadienylring from η 5 to η 2 or η 1 is observed ( 4 – 6 ). In the adduct with pentamethyldiethylenetriamine ( 7 ) one C 5 H 5 ‐ring is removed from the magnesium atom forming the cation [Mg(C 5 H 5 )(PMDTA)] + and an uncoordinated five‐ring anion. With the crown ether 15‐crown‐5 the two ionic Mg compounds 8 and 9 are formed which have a [Mg(15‐crown‐5)L 2 ] 2+ ‐cation [L = pyridine, THF] and two uncoordinated cyclopentadienyl anions. Cyclopentadienyl‐methyl‐magnesium reacts with 15‐crown‐5 to the salt [Mg(CH 3 )(15‐crown‐5)] + C 5 H 5 − ( 10 ) which has also a free cyclopentadienyl anion.