A diruthenium complex of a "nindigo" ligand

Abstract

The compound {(μ-Nindigo)[Ru(acac)2]2} = 1, H 2(Nindigo) = indigo-N,N′-diphenylimine and acac- = 2,4-pentanedionate, has been structurally characterized in the rac form, which exhibits two edge-sharing six-membered chelate rings involving ruthenium, and the former β-diketiminato functions with a twist angle of 33.9 around the central C-C bond. The metric parameters suggest a neutral π acceptor bridge containing coupled s-trans configurated α-diimines, which are coordinated by two ruthenium(II) centers. DFT calculations confirm the experimental structure and oxidation state assignment of the rac form; both diastereoisomers are present in solution according to 1H NMR spectroscopy. A very intense long-wavelength MLCT absorption at 630 nm (ε = 66 800 M -1 cm-1) and a weaker near-IR band at 1120 nm (ε = 3000 M-1 cm-1) are observed for the CH3CN solution. Reversible one-electron reduction and oxidation steps were studied by cyclic voltammetry, differential pulse voltammetry, EPR, and UV-vis-NIR spectroelectrochemistry to exhibit metal-centered oxidation and mixed metal/ligand-centered reduction. These results are supported by TD-DFT calculations of the species rac- or meso-1n, n = 3+, 2+, +, 0, -, 2-. © 2013 American Chemical Society.