Structural, spectroscopic and theoretical studies of a diruthenium(II, II) tetraformamidinate that reversibly binds dioxygen. (8th January 2016)

• Record Type: Journal Article
• Authors: Ring, Sam; Meijer, Anthony J.H.M.; Patmore, Nathan J.
• Is Part Of: Polyhedron. Volume 103 Part A(2016)
• Page Start: 87
• Page End: 93
• Publication Date: 2016-01-08
• Subjects: Diruthenium -- Spectroelectrochemistry -- Electronic structure -- Metal–metal bonds -- Dioxygen; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2015.09.051
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: The diruthenium(II, II) tetraformamidinate Ru2 (dmof)4 (Hdmof = N, N ′-bis(3, 5-dimethoxyphenyl)formamidine) displays a relatively long Ru–Ru bond length (2.4999(8) Å), consistent with a σ 2 π 4 δ 2 π ∗4 electronic configuration. Spectroelectrochemistry was used to monitor spectral changes that occur upon oxidation. The compound reversibly binds dioxygen, as evidenced by UV–Vis spectroscopy and cyclic voltammetry. Abstract: The reaction of Ru2 (O2 CMe)4 with N, N ′-bis(3, 5-dimethoxyphenyl)formamidine (Hdmof) in refluxing toluene solutions yields Ru2 (dmof)4 as a diamagnetic red solid that is extremely air-sensitive. The crystal structure reveals the expected paddlewheel arrangement of ligands around the Ru2 4+ core, with a relatively long Ru–Ru bond (2.4999(8) Å) that is consistent with a σ 2 π 4 δ 2 π ∗4 electronic configuration. This is supported DFT calculations that show this electronic structure results from destabilization of the δ ∗ orbital due to antibonding interactions with the formamidinate ligands. The cyclic voltammogram of Ru2 (dmof)4 in a 0.1 M n Bu4 NPF6 /CH2 Cl2 solution shows two redox processes, assigned as successive oxidations corresponding to the Ru2 4+/5+ and Ru2 5+/6 redox couples. Changes in the electronic absorption spectra associated with these oxidation processes were probed using a UV–Vis spectroelectrochemical study. Ru2 (dmof)4 reacts with dioxygen in solution to generate a purple compound that decomposes within an hour at room temperature. Bubbling N2 gas through the purple solution regenerates Ru2 (dmof)4, as evidenced by UV–Vis spectrometry and cyclic voltammetry, suggesting that the dioxygen reversibly binds to the diruthenium core.