The influence of an ethynyl spacer on the electronic properties in 2, 5-ferrocenyl-substituted heterocycles. (28th January 2015)

• Record Type: Journal Article
• Authors: Pfaff, Ulrike; Hildebrandt, Alexander; Korb, Marcus; Lang, Heinrich
• Is Part Of: Polyhedron. Volume 86(2015)
• Page Start: 2
• Page End: 9
• Publication Date: 2015-01-28
• Subjects: Ferrocene -- Alkyne -- Heterocycles -- (Spectro)electrochemistry -- Electron transfer; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2014.02.008
• Languages: English
• ISSNs: 0277-5387

Abstract

Abstract : Graphical abstract: A series of 2, 5-(FcCC)2 - c C4 H2 E (E = NPh, S, O) was prepared using the Sonogashira C, C cross-coupling protocol. The results of electro- and spectroelectrochemical measurements in comparison to 2, 5-Fc2 - c C4 H2 E are discussed. The occurrence of IVCT absorptions in the UV–Vis/NIR spectra shows that the 2, 5-diethynylferrocenyl heterocycles are class II systems according to Robin and Day. Abstract: A series of binuclear complexes based on five-membered heterocycles featuring alkynyl ferrocenyl groups, 2, 5-(FcCC)2 - c C4 H2 E (E = NPh, 3a ; S, 3b ; O, 3c ), has been synthesized using the Sonogashira C, C cross-coupling protocol. The molecular structures of3a and3c in the solid state are discussed. The influence of the ethynyl unit on the electronic and (spectro)electrochemical properties of these compounds is shown by cyclic voltammetry (CV), square wave voltammetry (SWV) and in situ UV–Vis–NIR and IR spectroscopy. The high Δ E p values (140–204 mV) of the single reversible redox events indicate that two individual oxidation processes take place in a close potential range. Nevertheless, the NIR measurements indicate weak and broad intervalence charge transfer (IVCT) absorptions for the mixed-valent monocationic species3a –c + . Compared to 2, 5-Fc2 - c C4 H2 E (E = NPh, S, O) the absorptions for the IVCT transitions are shifted hypsochromically, showing that the charge transfer process is promoted at higher excitation energies, due to larger metal–metal distances in3a –c . The occurrence of IVCT absorptions demonstrates that the 2, 5-diethynylferrocenyl heterocycles are class II systems according to Robin and Day.