New Redox-Active Iron(II) Acetylide Complex Bearing a (2-Pyridyl)aldimine Site. Synthesis and Complexation to Copper(I)

We report in this contribution the isolation and characterization of a new redox-active “(η²-dppe)(η⁵-C₅Me₅)FeC⋮C-4-(C₆H₄)−” complex bearing a (2-pyridyl)aldimine site on the aryl ring. This new metallo ligand, which was isolated by an unusual synthetic route from the known amino precursor complex, was structurally characterized. In accord with its “metallo ligand” denomination, we show here that it readily reacts with several Cu(I) precursors to form selectively, in good yields, complexes similar to those obtained with the corresponding organic N-aryl-(2-pyridyl)aldimines. By this method, a new dinuclear Fe(II)/Cu(I) complex and a new trinuclear Fe(II)/Cu(I)/Fe(II) complex were obtained in a straightforward way and characterized. The solid-state structure of the latter complex was also determined. Subsequently, the redox congeners of these closed-shell compounds were generated in situ by oxidation and the electronic structures of the open-shell parents were briefly investigated by infrared, ESR, and UV/vis spectroelectrochemistry. For instance, we conclusively show here that the mixed-valent (MV) state of the trinuclear complex belongs to class I in the classification of Robin and Day.