Mechanism of the two-electron reduction of trans-oxoaquaruthenium(IV) to trans-diaquaruthenium(II)

Abstract

The kinetics and mechanism of the reduction of trans-[Ru^IVL(O)(H₂O)]²⁺ to trans-(Ru^IIIL(OH)(H₂O))²⁺(L = 6,7,8,9,10,11,17,18-octahydro-6,10-dimethyl-5H-dibenzo[e,n][1,4,8,12]dioxadiazacyclo-pentadecine) in aqueous solution by cis-[Ru^II(NH₃)₄(isn)₂]²⁺(isn = isonicotinamide) and of trans-[Ru^IIIL(OH)(H₂O)]²⁺ to trans-[Ru^IIL(H₂O)₂]²⁺ by [Ru^II(NH₃)₄(bipy)]²⁺(bipy = 2,2′-bipyridine) have been studied. The reactive intermediates are trans-[Ru^IVL(OH)(H₂O)]³⁺ and trans-[Ru^IIIL(H₂O)₂]³⁺ respectively. The rate constants k_e1 and k_e2 for the reduction of trans-[Ru^IVL(OH)(H₂O)]³⁺ and trans-[Ru^IIIL(H₂O)₂]³⁺ have been obtained and can be correlated with the Marcus cross-relation. The estimated self-exchange rate constants of the trans-[RuL(OH)(H₂O)]^3+/2+ and trans-[RuL(H₂O)₂]^3+/2+ couples are 3.1 × 10^–4 and 3.9 × 10³ dm³ mol^–1 s^–1 respectively. The complex trans-[Ru^IIIL(OH)(H₂O)][ClO₄]₂ has been characterised by X-ray crystallography: space group P, a= 11.108(2), b= 11.683(1), c= 12.349(1)Å, α= 89.38(1), β= 64.81(1), γ= 71.44(1)° and Z= 2.