130613-73-9Relevant academic research and scientific papers
Mechanism of cis-directed four-electron oxidation by a trans-dioxo complex of ruthenium(VI)
Dovletoglou, Angelos,Meyer, Thomas J.
, p. 215 - 223 (1994)
The reductions of trans-[Ru(VI)(tpy)(O)2(H2O)]2+ or trans- [Ru(VI)(tpy)(O)2(H2O)]2+ or trans-[Ru(VI)(tpv)(O)2(CH3CN)]2+ (tpy is 2,2':6',2''-terpyridine) by PPh3,Ph2PCH2CH2PPh2 (dppe), or Ph2PCH2PPh2 (dppm) occur by successive Ru(VI) → Ru(IV) and Ru(IV) → Ru(II) oxygen atom transfer steps. The products appear to be five-coordinated diphosphine oxide complexes of Ru(II). They subsequently undergo stepwise solvolysis to give the free diphosphine dioxides and [Ru(II)(tpy)(CH3- CN)3]2+. The kinetics of the individual redox steps were studied by stopped-flow/rapid-scan spectrophotometry. For PPh3 as reductant, k(VI/IV)(20 °C, CH3CN) = (2.28 ± 0.08) x 106 M-1 s-1 (ΔH((+)) = 4.2 ± 0.8 kcal mol-1; ΔS((+)) = -19 ± 4 eu) and k(IV/II(20°, CH2CN) = 1.04 ± 0.03) x 104 M-1 s-1 (ΔH((+)) = 5.9 ± 0.5 kcal mol-1; ΔS((+)) = - 20 ± 3 eu). With dppe or dppm, Ru(VI) acts as a cis-directed four-electron oxidant. The first step, {Ru(VI) → Ru(IV)}, is first order in both oxidant and diphosphine with k(VI/IV)(20 °C, CH3CN) ~4 x 108 M-1 s-1 (dppe) to give trans-[Ru(IV)(tpy)(O)(O=P(PPh2)CH2CH2PPh2)(CH3CN)]2+. In acetonitrile with no added water, the subsequent reduction of Ru(IV) to Ru(II) follows first-order kinetics with k(IV/II)(20 °C, CH3CN) = 5 x 101 s-1 for either dppe or dppm. By inference, the rate-limiting step is intramolecular isomerization of the remaining oxo group followed by rapid O- atom transfer. In acetonitrile 1.75 M in H2O the initial Ru(IV) product is trans-[Ru(IV)(tpy)(O)(O=P(PPh2)CH2-CH2PPh2)(H2O)]2+. The subsequent Ru(IV) → Ru(II) step is considerably slower, k(IV/II)(20 °C) = (6.20 ± 0.12) x 10-2 s-1. This reaction exhibits a substantial inverse solvent isotope effect, k(H2O)/k(D2O) = 0.18 ± 0.02, which arises from the transfer of a single proton on the basis of a mole fraction study. Isomerization is also rate limiting in this case, but the rate-determining step is intramolecular proton transfer.
