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 ][Cr II (C 6 F 5 ) 4 ] ( 1 ) was obtained as an extremely air-sensitive solid by reaction of [CrCl 2 (THF)] with C 6 F 5 MgBr. The arylation of MnBr 2 under similar conditions proceeded with oxidation of the metal center to give [Mg(THF) 6 ][Mn III (C 6 F 5 ) 4 ] 2 ( 2 ). The crystal structures of 1 and 2 (X-ray diffraction) contain the anions [Cr(C 6 F 5 ) 4 ] 2 - and [Mn(C 6 F 5 ) 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 Mn III −C distance in 2, 2.068(4) Å, is slightly shorter than the mean Cr II −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.