Abstract
We report the synthesis and structural characterization of the rhodocene anion [Rh(C(5)Me(5))(C(5)(CF(3))(5))](-) [1](-) as the [Co(C(5)Me(5))(2)](+) salt, representing an unprecedented coexistence of metallocene cations and anions in different oxidation states. [Co(C(5)Me(5))(2)](+) [1](-) was synthesized by the reduction of the rhodocenium cation [Rh(C(5)Me(5))(C(5)(CF(3))(5))][BF(4)] ([1](+)[BF(4)](-)) with two equivalents of decamethylcobaltocene [Co(C(5)Me(5))(2)], since the strongly electron-withdrawing effect of the [C(5)(CF(3))(5)](-) ligand shifts the first and second reduction potentials of [1](+) to moderate values of -0.90 and -1.46 V vs FcH(0/+). [Co(C(5)Me(5))(2)](+)[1](-) was characterized by single-crystal X-ray diffraction (XRD), providing the first example of a structurally characterized 4d metallocene anion. Whereas the Rh(III) cation has two η(5)-bound Cp ligands, the perfluorinated Cp* ligand is only η(3)-bound in the Rh(I) anion in order to obey the 18-electron rule. The reduction of the rhodocenium center is accompanied by a significant shift of the (103)Rh NMR signal from -9308 ppm of [1](+) to -6895 ppm of [1](-) (referenced to Rh(acetylacetonate)(3)).