Structural, spectroscopic and theoretical studies of a diruthenium(II,II) tetraformamidinate that reversibly binds dioxygen

Abstract

The reaction of Ru 2 (O 2 CMe) 4 with N, N'-bis(3,5-dimethoxyphenyl) solution shows two redox processes, assigned as successive oxidations corresponding to the Ru 2 4+/5+ and Ru 2 5+/6 redox couples. Changes in the electronic absorption spectra associated with these oxidation processes were probed using a UV/vis spectroelectrochemical study. Ru 2 (dmof) 4 reacts with dioxygen in solution to generate a purple compound that decomposes within an hour at room temperature. Bubbling N 2 gas through the purple solution regenerates Ru 2 (dmof) 4 , as evidenced by UV/vis spectrometry and cyclic voltammetry, suggesting that the dioxygen reversibly binds to the diruthenium core.

A Synthetic Oxygen Atom Transfer Photocycle from a Diruthenium Oxyanion Complex

“…13 Related Ru–Ru=O intermediates have recently been proposed to be important in sulfide oxygenation 14 and water oxidation 15 catalysis; furthermore, Ru 2 (II/II) complexes have been shown to reversibly bind O 2 . 16 Putative Ru–Ru=O species are highly reactive and have not been observed or isolated. Due to their important catalytic applications and our previous expertise in the chemistry of Ru–Ru≡N intermediates, we sought to use the photochemical methods outlined above to access Ru–Ru=O species in order to explore their fundamental reactivity.…”

“…We recently described the first examples of MMO species (in which M = Mo or W), and we found them to display unusual reactivity . Related RuRuO intermediates have recently been proposed to be important in sulfide oxygenation and water oxidation catalysis; furthermore, Ru 2 (II/II) complexes have been shown to reversibly bind O 2 . Putative RuRuO species are highly reactive and have not been observed or isolated.…”

New Oxypyridinate Paddlewheel Ligands for Alkane-Soluble, Sterically-Protected Ru2(II,III) and Ru2(II,II) Complexes

“…The proclivity of the known Ru 2 (II,II) paddlewheel complexes to bind axial ligands can be divided into three distinct categories based on their nominal electronic ground states in C 4 symmetry: 3 A, hybridized 3 A/ 3 E (Jahn−Teller distorted to 3 A″ in C s symmetry), and 1 A. 13 The 1 A complexes often eschew axial coordination but have been known to bind π-acceptor ligands.…”

“…13 The 1 A complexes often eschew axial coordination but have been known to bind π-acceptor ligands. 17,18 On the other hand, the 3 A complexes (e.g., Ru 2 (OAc) 4 , 19 Ru 2 (chp) 4 ) strongly favor axial coordination by any available σ-donor. The single experimentally observed example of a 3 A/ 3 E hybrid, displaying a bent Ru− Ru−P angle that allows mixing of the δ* and π* orbitals, was formed upon coordination of PPh 3 to Ru 2 (chp) 4 .…”

“…The single experimentally observed example of a 3 A/ 3 E hybrid, displaying a bent Ru− Ru−P angle that allows mixing of the δ* and π* orbitals, was formed upon coordination of PPh 3 to Ru 2 (chp) 4 . While a wide variety of axially-coordinated substrates could theoretically be available to the 3 A-type complexes with carboxylate or pyridinate equatorial ligands, in practice, aggregation outcompetes axial coordination of all but the strongest σ-donors. For example, Zn reduction of Ru 2 (chp) 4 Cl (1-Cl) in tetrahydrofuran (THF) predominantly yields [Ru 2 (chp) 4 ] 2 (2, Scheme 1) alongside a small amount of the solvent adduct Ru 2 (chp) 4 (THF).…”