A radical-bridged bis(ferrocenylcopper(I)) complex: Structural identity, multifrequency EPR, and spectroelectrochemistry

The paramagnetic blue complex {(μ-adcO^tBu)[Cu(dppf)]₂}(PF₆) contains two heterodinuclear 1,1′-bis(diphenylphosphinoferrocene)copper(I) moieties, bridged by the radical anion of di-tert-butylazodicarboxylic ester (adcO^tBu). The assignment of oxidation states is supported by crystal structure determination and by variable frequency EPR spectroscopy which provides hyperfine (9.5 GHz) and g anisotropy information (285 GHz). Cyclic voltammetry and UV/Vis/NIR spectroelectrochemistry indicate reversible one-electron oxidation of the adcO^tBu⁻ bridge prior to the quasi-reversible two-electron oxidation of the well separated (12.55 Å) ferrocene termini. One-electron reduction to the adcO^tBu²⁻ bridged system occurs with concomitant loss of the long-wavelength metal-to-ligand charge transfer absorption.