Structural Characterization of Manganese(II) Compounds with Methylalumoxane (MAO) and AlMe₂ Units

Manganese complexes with AlMe3 have been synthesized with the aim of investigating Mn(II) active centers in catalytic ethylene polymerization. Reactions of [Mn4(μ-Cl)Cl3(μ-OCH2CH2OCH3)4(HOCH2CH2OCH3)3]2 (1) with an excess of AlMe3 at room temperature in toluene give the heterometallic cage [Mn3Al(μ3-OCH2CH2OCH3)(μ-Cl)3(μ-OCH2CH2OCH3)2(thf)2(Me)2Cl] (2; 30%). A similar reaction carried out under reflux led to the formation of the methylalumoxane species [MnAl3(μ3-O)(μ-OCH2CH2OCH3)3(Me)6] (3; 51%). X-ray diffraction studies have shown complexes 2 and 3 to contain AlMe2+ and [Al3(μ3-O)(Me)6]+ moieties capped by [Mn3(μ3-OCH2CH2OCH3)(μ-Cl)3(μ-OCH2CH2OCH3)2(thf)2Cl]- and [Mn(μ-OCH2CH2OCH3)3]- macrounits, respectively. The tendency of a manganese center to exchange aluminum methyl groups in 2 and 3 is strongly reduced by alkoxide ligands.