The First Structurally Characterized Homoleptic Aryl-Manganese(III) Compound and the Corresponding Isoleptic and Isoelectronic Chromium(II) Derivative

The homoleptic organochromium(II) compound [Mg(THF)6][CrII(C6F5)4] (1) was obtained
as an extremely air-sensitive solid by reaction of [CrCl2(THF)] with C6F5MgBr. The arylation
of MnBr2 under similar conditions proceeded with oxidation of the metal center to give [Mg(THF)6][MnIII(C6F5)4]2 (2). The crystal structures of 1 and 2 (X-ray diffraction) contain the
anions [Cr(C6F5)4]2- and [Mn(C6F5)4]-, respectively, both with approximate square-planar
(SP-4) geometry around the metal center. In the solid state there is no sign of any covalent
interaction or ion-pairing between these anions and the virtually octahedral (OC-6) [Mg(THF)6]2+ cations. The average MnIII−C distance in 2, 2.068(4) Å, is slightly shorter than
the mean CrII−C bond length in 1, 2.158(6) Å, a fact that can be attributed mainly to the
different oxidation states of the metal centers in each case. The use of 2 as an initiator itself
and as a weakly coordinating anion in Pd-catalyzed polymerization processes of strained
olefins has also been assayed.