Synthesis, characterization, and electrochemistry of diferrocenyl β-diketones, -diketonates, and pyrazoles

Abstract

The synthesis of FcC(O)CH(R)C(O)Fc (Fc = Fe(η5-C5H4)(η5-C5H5); R = H, 5; nBu, 7; CH2CH2(OCH2CH2)2OMe, 9), [M(κ2O,O'-FcC(O)CHC(O)Fc)n] (M = Ti, n = 3, 10; M = Fe, n = 3, 11; M = BF2, n = 1, 12), and 1-R'-3,5-Fc2-cC3HN2 (R' = H, 13; Me, 14; Ph, 15) is discussed. The solid-state structures of 5, 7, 9, 12, 13, 15, and 16 ([TiCl2(κ2O,O'-PhC(O)CHC(O)Ph)2]) show that 7 and 9 exist in their β-diketo form. Compound 13 crystallizes as a tetramer based on a hydrogen bond pattern, including one central water molecule. The electrochemical behavior of 5-7 and 9-16 was studied by cyclic and square-wave voltammetry, showing that the ferrocenyls can separately be oxidized reversibly between -50 and 750 mV (5-7, 9, 12-15: Two Fc-related events; 10, 11: Six events, being partially superimposed). For complex 10, Ti-centered reversible redox processes appear at -985 (TiII/TiIII) and -520 mV (TiIII/TiIV). Spectro-electrochemical UV-Vis/NIR measurements were carried out on 5, 6, and 12, whereby only 12 showed an IVCT (intervalence charge-transfer) band of considerable strength (vmax = 6250 cm-1, Δv = 4725 cm-1, ∈max = 240 L mol-1 cm-1), due to the rigid C3O2B cycle, enlarging the coupling strength between the Fc groups.