Synthesis, structures, magnetism and electrochemical properties of triruthenium–acetylide complexes

Abstract

A series of triruthenium complexes with arylacetylide axial ligands Ru₃(dpa)₄(C₂X)₂(BF₄)_y (dpa = dipyridylamido; X = Fc, y = 0 (1); X = Ph, y = 0 (2); X = PhOCH₃, y = 1 (3); X = PhC₅H₁₁, y = 1 (4); X = PhCN, y = 0 (5); X = PhNO₂, y = 0 (6)) have been synthesized. The crystal structures show that the Ru–Ru bond lengths (2.3304(9)–2.3572(5) Å) of these compounds are longer than those of Ru₃(dpa)₄Cl₂ (Ru–Ru2.2537(1) Å). This is ascribed to the formation of the stronger π-backbonding from metal to axial ligand which weakens the Ru–Ru interactions and the bond order is reduced in the triruthenium unit. Cyclic voltammetry and differential pulse voltammetry show that compound 1 exhibits electronic coupling between the two ferrocenyl units with ΔE_1/2 close to 100 mV. Compounds 2–6 display three triruthenium-based reversible one-electron redox couples, two oxidations and one reduction, and the electrode potentials shift upon varying the substituents. A linear relationship is observed when the Hammett constants are plotted against the redox potentials.