Fundamental electron-transfer and proton-coupled electron-transfer properties of Ru(iv)-oxo complexes

Isolation and characterisation of Ru^IV(O) complexes were accomplished to investigate their fundamental electron transfer (ET) and proton-coupled ET (PCET) properties. Reorganisation energies (λ) in electron transfer (ET) and proton-coupled ET (PCET) from electron donors to the isolated Ru^IV(O) complexes have been determined for the first time to be in the range of 1.70-1.88 eV (ET) and 1.20-1.26 eV (PCET). It was suggested that the reduction of the λ values of PCET in comparison with those of ET should be due to the smaller structural change in PCET than that in ET on the basis of DFT calculations on 1 and 1e^--reduced 1 in the absence and presence of TFA, respectively. In addition, the smaller λ values for the Ru^IV(O) complexes than those reported for Fe^IV(O) and Mn^IV(O) complexes should be due to the lack of participation of d_σ orbitals in the ET and PCET reactions. This is the first example to evaluate fundamental ET and PCET properties of Ru^IV(O) complexes leading to further understanding of their reactivity in oxidation reactions.