Synthesis, Crystal Structure, EPR and DFT Studies, and Redox Properties of [2]Tetramethyldisilacobaltocenophane

The first [2]silacobaltocenophane, [(Me2Si)2(η5-C5H4)2Co] (1), was synthesized by dilithiation of 1,2-bis(cyclopentadienyl)-1,1,2,2-tetramethyldisilane with BuLi and subsequent reaction with [CoBr2(dme)]. EPR spectroscopic investigations of frozen pentane solutions of 1 at X-band showed a fully anisotropic g tensor (g1 = 1.914, g2 = 2.005, and g3 = 2.084) with hyperfine couplings on all three components (A1 = 145 MHz, A2 = 67 MHz, and A3 = 424 MHz). DFT studies using the B3LYP functional with its 20% exact exchange provide the best agreement with experiment and reproduce the g and A tensors well. Spin−orbit contributions to the isotropic coupling (APC) and to the anisotropies (Aidip,2) were found to be significant. As was shown by cyclic voltammetry in THF, 1 is quasi-reversibly oxidized to the neutral cobaltocenium cation [(Me2Si)2(η5-C5H4)2Co]+ (8) at a potential of E°1/2 = −1.27 V (vs the Fc/Fc+ couple) and quasi-reversibly reduced to the corresponding anion [(Me2Si)2(η5-C5H4)2Co]− (9) at E°1/2 = −2.40 V. The preparative oxidation of 1 with 1 equiv of ferrocenium hexafluorophosphate ([Fc][PF6]) provided the diamagnetic [PF6]− salt of the cation 8 in high yields. The molecular structures of both complexes (1 and 8) were confirmed by X-ray diffraction analysis, and a significant decrease in molecular strain was depicted. DFT findings support the experiments.