Year: 2016
Type: article
Abstract: Ion-pair interactions between a cationic ruthenium complex, [Ru(dtb) 2 (dea)][PF 6 ] 2, C1 2+ where dea is 4,4′-diethanolamide-2,2′-bipyridine and dtb is 4,4′-di- tert -butyl-2,2′-bipyridine, and chloride, bromide, and iodide are reported. A remarkable result is that a 1:1 iodide:excited-state ion-pair, [ C1 2+, I – ] +*, underwent diffusional electron-transfer oxidation of iodide that did not occur when ion-pairing was absent. The ion-pair equilibrium constants ranged 10 4 –10 6 M –1 in CH 3 CN and decreased in the order Cl – > Br – > I – . The ion-pairs had longer-lived excited states, were brighter emitters, and stored more free energy than did the non-ion-paired states. The 1 H NMR spectra revealed that the halides formed tight ion-pairs with the amide and alcohol groups of the dea ligand. Electron-transfer reactivity of the ion-paired excited state was not simply due to it being a stronger photooxidant than the non-ion-paired excited state. Instead, work term, Δ G w was the predominant contributor to the driving force for the reaction. Natural bond order calculations provided natural atomic charges that enabled quantification of Δ G w for all the atoms in C1 2+ and [ C1 2+, I – ] +* presented herein as contour diagrams that show the most favorable electrostatic positions for halide interactions. The results were most consistent with a model wherein the non-ion-paired C1 2+* excited state traps the halide and prevents its oxidation, but allows for dynamic oxidation of a second iodide ion.
DOI: 10.1021/jacs.6b11337
Institution: University of North Carolina at Chapel Hill
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2557319389