Synthesis, Characterization, and Electrochemistry of Diferrocenyl β-Diketones, -Diketonates, and Pyrazoles †

The synthesis of FcC(O)CH(R)C(O)Fc (Fc = Fe(η(5)-C(5)H(4))(η(5)-C(5)H(5)); R = H, 5; (n)Bu, 7; CH(2)CH(2)(OCH(2)CH(2))(2)OMe, 9), [M(κ(2)O,O′-FcC(O)CHC(O)Fc)(n)] (M = Ti, n = 3, 10; M = Fe, n = 3, 11; M = BF(2), n = 1, 12), and 1-R′-3,5-Fc(2)-(c)C(3)HN(2) (R′ = H, 13; Me, 14; Ph, 15) is discussed. The solid-state structures of 5, 7, 9, 12, 13, 15, and 16 ([TiCl(2)(κ(2)O,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 (Ti(II)/Ti(III)) and −520 mV (Ti(III)/Ti(IV)). 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 (ν(max) = 6250 cm(−1), Δν(½) = 4725 cm(−1), ε(max) = 240 L·mol(−1)·cm(−1)), due to the rigid C(3)O(2)B cycle, enlarging the coupling strength between the Fc groups.