Syntheses, characterization and electrochemical and spectroscopic properties of ruthenium–iron complexes of 2,3,5,6-tetrakis(2-pyridyl)pyrazine and ferrocene-acetylide ligands

Abstract

Heterodimetallic Ru–Fe complexes [(tppz)(PPh₃)₂RuL](ClO₄) (L = CCFc, [1](ClO₄); CC–C₆H₄–CCFc), [2](ClO₄); CC–C₆H₄–C₆H₄–CCFc, [3](ClO₄)) were synthesized by the reactions of [(tppz)(PPh₃)₂RuCl](ClO₄) (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) with ferrocence-acetylide ligands and characterized by ESI-MS, and ¹H and ³¹P NMR spectroscopies. The structure of [1](PF₆) was determined by X-ray crystallography. The electrochemical studies show that compounds [1](ClO₄)–[3](ClO₄) possess two widely separated anodic peaks, ascribable to one-electron oxidation of Fc and Ru^II, respectively. This assignment is further corroborated by the results of UV-vis-NIR, XPS, and theoretical calculation studies. Compound [1](ClO₄) exhibits significant Ru⋯Fe metal–metal interactions across the Ru–CC–Fc backbone. As revealed by electrochemical, spectroscopic and theoretical computational studies, one-electron oxidized species [1a](ClO₄)₂ is between the electronically delocalized and valence-trapped state and shows a typical Robin–Day class II mixed-valence behavior.