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Published on: October 18, 2019
Coexistence of Metallocene Cations and Anions
Nico Gino Kub1, Robin Sievers1, Marc Reimann2,3
1Institut für Chemie und Biochemie - Anorganische Chemie, Freie Universität Berlin, Fabeckstr. 34-36, Berlin 14195, Germany.
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We report the synthesis and structural characterization of the rhodocene anion [Rh(C5Me5)(C5(CF3)5)]- [1]- as the [Co(C5Me5)2]+ salt, representing an unprecedented coexistence of metallocene cations and anions in different oxidation states. [Co(C5Me5)2]+ [1]- was synthesized by the reduction of the rhodocenium cation [Rh(C5Me5)(C5(CF3)5)][BF4] ([1]+[BF4]-) with two equivalents of decamethylcobaltocene [Co(C5Me5)2], since the strongly electron-withdrawing effect of the [C5(CF3)5]- ligand shifts the first and second reduction potentials of [1]+ to moderate values of -0.90 and -1.46 V vs FcH0/+. [Co(C5Me5)2]+[1]- was characterized by single-crystal X-ray diffraction (XRD), providing the first example of a structurally characterized 4d metallocene anion. Whereas the RhIII cation has two η5-bound Cp ligands, the perfluorinated Cp* ligand is only η3-bound in the RhI anion in order to obey the 18-electron rule. The reduction of the rhodocenium center is accompanied by a significant shift of the 103Rh NMR signal from -9308 ppm of [1]+ to -6895 ppm of [1]- (referenced to Rh(acetylacetonate)3).
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