Synthesis and chemical oxidation of 3-ferrocenylpyrrole and ferrocenyl-substituted triazoles: Iron versus ligand based oxidation

Copper catalyzed [3+2] cycloaddition reactions between ethynylferrocene and benzylazides yields 1-benzyl-4-ferrocenyl-1,2,3-triazoles (2–5). Reaction between phenylacetylene and azidoferrocene yields 1-ferrocenyl-4-phenyl-1,2,3-triazole (6). Anodic electrochemistry of 2–6 suggests reversible oxidation at potentials more positive than ferrocene. Chemical oxidation of 2 and 3-ferrocenylpyrrole (1) with dichlorodicyanoquinone (DDQ) yields the salts [2+] [DDQ−] and [1+] [DDQ−], respectively. 57Fe Mössbauer spectroscopy reveals the presence of low-spin FeII in [1+][DDQ−] while FeII is oxidized to low-spin FeIII in [2+][DDQ−]. Magnetization measurements indicate that [1+][DDQ−] is paramagnetic and cannot be viewed as a simple neutral charge transfer complex reminiscent of the mixed stack diamagnetic [ferrocene]0[TCNE]0.

Graphical abstractChemical oxidation of 1 and 2 with DDQ yields the salts [1+][DDQ−] and [2+][DDQ−], respectively. 57Fe Mössbauer spectroscopy reveals the presence of low-spin FeII in [1+][DDQ−] while FeII is oxidized to low-spin FeIII in [2+][DDQ−].Figure optionsDownload full-size imageDownload as PowerPoint slide