Cymantrene Radical Cation Family: Spectral and Structural Characterization of the Half-Sandwich Analogues of Ferrocenium Ion

The anodic one-electron oxidation of three members of the half-sandwich family of piano-stool compounds MnCpγ(CO)3, where Cpγ is a generic cyclopentadienyl ligand, has been studied in a CH2Cl2/[NBu4][TFAB] electrolyte (TFAB = [B(C6F5)4]−). The long-sought 17 e− radical cation of the parent complex MnCp(CO)3 (cymantrene, 1, E1/2 = 0.92 V vs ferrocene) has been shown to be persistent in solutions that use weakly coordinating anions in place of more nucleophilic traditional electrolyte anions. Spectroscopically characterized for the first time, 1+ was shown to absorb in the visible (530 nm), near-IR (2066 nm), and IR (2118, 1934 cm−1) regions. It was ESR-active at low temperatures (g∥ = 2.213, g⊥ = 2.079, A∥ (Mn) = 79.2 G, A⊥ (Mn) = 50 G) and NMR active at room temperature (δ = 22.4 vs TMS). The radical cations of the Cp-functionalized analogues, Mn(η5-C5H4NH2)(CO)3, 2, E1/2 = 0.62 V, and MnCp*(CO)3 (Cp*= η5-C5Me5, 3), E1/2 = 0.64 V, were generated electrochemically as well by the chemical oxidant [ReCp(CO)3...