Reinvestigation of arylmanganese chemistry – Synthesis and molecular structures of [(thf)4Mg(μ-Cl)2Mn(Br)Mes], [Mes(thf)Mn(μ-Mes)]2, and (MnPh2)∞ (Ph = C6H5; Mes = mesityl, 2,4,6-Me3C6H2)

The reaction of 2,4,6-trimethylphenylmagnesium bromide (MesMgBr) with manganese(II) chloride in an equimolar ratio yields [(thf)4Mg(μ-Cl)2Mn(Br)Mes] (1) with two bridging chloro ligands and a Mn–C bond length of 2.136(5) Ǻ. A molar ratio of 2:1 leads to a metathesis reaction and the formation of [Mes(thf)Mn(μ-Mes)]2 (2) with two bridging mesityl groups. Whereas THF-free [MnMes2]3 crystallizes as a trimer from toluene solution, the reduced bulkiness of the phenyl groups in (MnPh2)∞ (3) leads to the formation of a chain-like structure with Mn–C bond lengths of 2.245(3) Ǻ.

The synthesis of diarylmanganese proceeds from arylmagnesium bromide with manganese(II) chloride in THF via different intermediates. The first reaction step is an addition product shown in the picture (Mg blue, Mn violet, Cl green, Br blue, O red) with the aryl group already transferred to the manganese atom. Thereafter, the second Br atom can be substituted by another aryl ligand and magnesium(II) halide precipitates.Figure optionsDownload as PowerPoint slide