Synthesis, crystal structures and electrochemistry of ferrocenyl-substituted 1,3,4-oxadiazoles

Abstract

Two ferrocenyl-substituted 1,3,4-oxadiazoles, 2-ferrocenyl-1,3,4-oxadiazole (1) and 2,5-diferrocenyl-1,3,4-oxadiazole (2), have been prepared from the corresponding hydrazides, (ferrocenecarbonyl)hydrazine (3) and 1,2-bis(ferrocenecarbonyl)hydrazine (4), and characterized by conventional spectroscopic methods (IR, NMR, MS) and elemental analyses. The solid-state structures of 1, 2 and 4 have been determined by single-crystal X-ray diffraction analysis. The redox behavior of 1 and 2 was studied by electrochemical methods. Compound 1 underwent a reversible one-electron oxidation attributed to the ferrocene/ ferrocenium couple (E o ′ = +0.28 V vs ferrocene/ferrocenium). On the other hand, compound 2 showed two closely separated anodic waves corresponding to two consecutive redox changes, indicating some degree of electronic communication between the ferrocenyl moieties in positions 2 and 5 at the 1,3,4-oxadiazole ring. Substituted 1,3,4-oxadiazoles have found various applications as biologically active compounds and building blocks for materials chemistry 1 . Despite their frequent use in the latter field, there is only little known about the redox-active, ferrocenyl-modified 1,3,4-oxadiazoles. Indeed, the archetypal compounds, 2-ferrocenyl-1,3,4-oxadiazole (1) (ref. 2 ) and 2,5-diferrocenyl-1,3,4-oxadiazole (2) (ref. 3 ) have already been reported. The former compound was obtained by the conventional condensation of ferrocenecarbohydrazide, FcCONHNH 2 (3; Fc = ferrocenyl), with triethyl orthoformate, whereas the diferrocenylated compound 2 and some related compounds, including the unsymmetric derivative (Ph/Fc), were obtained by POCl 3 -mediated cyclization of the respective 1,2-diacylhydrazines,

The Intramolecular Electronic Interaction Regulated by Five-membered Heterocycle Spacer

“…However, when diferrocenyl derivatives containing aromatic rings spacers, the charge transfers are in uenced by various complex factors, including metalmetal center distance 19 , position of substituent 20 , center ring geometric properties 21 , topology 22 and aromatic properties 23,24 , which in uencing factor is the primary factor of intramolecular electron transfer is still an academic debate. In order to further explore this problem, more and more researchers are engaged in numerous heterocycle spacers' studies, especially the ve-membered aromatic heterocycle spacers 25,26 , because these spacers involves π-conjugate structure and heteroatom, which can provide changing chemical structure for studying.…”