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+radical dot] [DDQradical dot−] and [1+radical dot] [DDQradical dot−], respectively. 57Fe Mössbauer spectroscopy reveals the presence of low-spin FeII in [1+radical dot][DDQradical dot−] while FeII is oxidized to low-spin FeIII in [2+radical dot][DDQradical dot−]. Magnetization measurements indicate that [1+radical dot][DDQradical dot−] is paramagnetic and cannot be viewed as a simple neutral charge transfer complex reminiscent of the mixed stack diamagnetic [ferrocene]0[TCNE]0.