Recent reports in the literature have shown that a Ru–H complex can react with O2 in cells to generate H2O2 (via insertion of O2 into the Ru–H bond), therefore the principle of microscopic reversibility dictates that H2O2 is mechanistically capable of reacting with a Ru complex to form a Ru–H species and release O2 via β-hydride elimination. Reacting in this manner, H2O2 would be functioning as a hydride donor. Although the reaction of Ru–H with O2 to give H2O2 is well-known, and a bedrock principle of mechanistic chemistry establishes the existence of the reverse reaction, to date there have been no demonstrations of H2O2 functioning as a hydride source. Herein we unambiguously demonstrate that H2O2 functions as a terminal reductant for Ru1-catalyzed reduction of radicals in aerobic, buffered aqueous solution and we provide evidence that this reactivity is derived from hydride transfer from H2O2 to Ru. Results from rate law and other mechanistic studies indicate that (i) a mononuclear Ru-containing species is the catalyst for radical reduction, (ii) H2O2 is the terminal reductant, (iii) H2O2 coordination to Ru occurs before the rate-determining step, (iv) the two H-atoms from H2O2 depart as H+ and H–, with concomitant release of O2, and (v) the transition state for the rate determining step involves ligand fragmentation and dissociation, consistent with β-hydride elimination from a hydroperoxo ligand.

Hydrogen peroxide as a hydride donor and reductant under biologically relevant conditions

2019 Spring National Meeting

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