Reversible Bond Formation and Cleavage of the Oxo Bridge of [Ru 2 (μ‐O)(dioxolene) 2 (btpyxa)] 3+ [btpyxa = 2,7‐Di‐ tert ‐butyl‐9,9‐dimethyl‐4,5‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)xanthene] Driven by a Three‐Electron Redox Reaction

The bis(chlororuthenium) complex [Ru 2 Cl 2 (3,6‐ t Bu 2 sq) 2 (btpyxa)](PF 6 ) 2 [ 1 ](PF 6 ) 2 [3,6‐ t Bu 2 sq = 3,6‐di‐ tert ‐butyl‐1,2‐benzosemiquinone; btpyxa = 2,7‐di‐ tert ‐butyl‐9,9‐dimethyl‐4,5‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)xanthene] and the oxo‐bridged diruthenium complex [Ru 2 (μ‐O)(3,6‐ t Bu 2 sq) 2 (btpyxa)](PF 6 ) 3 [ 2 ](PF 6 ) 3 were synthesized, and the redox behavior of these complexes, which contain a non‐innocent dioxolene ligand, was investigated by electrochemical and electrospectrochemical methods. Dicationic [ 1 ] 2+ undergoes two successive metal‐centered one‐electron and a simultaneous two‐electron ligand‐based redox reaction at E 1/2 = +0.13 and +0.09 and E 1/2 = –0.75 V (vs. SCE), respectively, in CH 2 Cl 2 . The UV/Vis/NIR spectrum of tricationic [ 2 ] 3+ shows an intervalence‐transition (IT) band at 1333 nm ( ϵ = 1.52 × 10 4 M –1  cm –1 ) in a near‐IR region together with two CT bands at 766 ( ϵ = 2.21 × 10 4 M –1  cm –1 ) and 586 nm ( ϵ = 1.13 × 10 4 M –1  cm –1 ) in CH 2 Cl 2 . The mixed‐valence complex of [ 2 ] 3+ with an Ru IV –O–Ru III core is reversibly oxidized and reduced to the Ru IV –Ru IV and Ru III –Ru III oxidation states at E 1/2 = +0.63 and –0.01 V, respectively, in CH 2 Cl 2 . On the other hand, three‐electron reduction of [ 2 ](PF 6 ) 3 is accompanied by the cleavage of the Ru–O–Ru bond at E p = +0.02 V to give [{Ru(OMe)(3,5‐ t Bu 2 sq)}{Ru(OH 2 )(3,5‐ t Bu 2 sq)}(btpyxa)] + in MeOH. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)