No abstract

No abstract

No abstract

Two mononuclear Cu II complexes with tetrapeptides incorporating a L-2,3-diaminopropionic acid (dap) branching unit are reported to undergo PCET and catalyse water oxidation. C-terminal His extension of dap (L = 2GH) instead of Gly (L = 3G) lowers the pK a for Cu III H À2 L (9.36 vs. 9.98) and improves the TOF at pH 11 (53 vs. 24 s À1 ).Reactions requiring the synchronous transfer of multiple protons and electrons become energetically viable under mild conditions through the catalytic promotion of proton-coupled electron transfer (PCET) mechanisms that help circumventing high-energy intermediates. 1 Splitting water into its elements, which attracts growing attention as a prospective renewable tool to generate H 2 as an energy carrier, 2-4 ranks among reactions where PCET is of critical importance. Water oxidation catalysts (WOCs) can improve the efficiency of the oxidative half-reaction: 2H 2 O -O 2 + 4H + + 4e À , which has long been considered the bottleneck of the water splitting process. Bioinspired, homogeneous WOCs (Fe, 5 Co, 6 Ru, 7 or Ir 8 ), although inherently less robust than heterogeneous catalysts, 9 represent a meaningful source of mechanistic insight into the multiple proton and electron-transfer events associated with O 2 formation. A growing number of studies conclude that PCET helps in stabilising high-valent MQO or M-O intermediates by preventing charge accumulation upon oxidation and, as a consequence these intermediates can complete the O-O bond formation step. 10 Cu has rich oxygen chemistry, 11 yet, homogeneous WOCs involving this metal appeared only recently, when surprisingly robust Cu II complexes with 2,2 0 -bipyridine (bpy, TOF B 100 s À1 at pH 13) 12 and subsequently, with triglycylglycine (GGGG, or H-Gly-Gly-Gly-Gly-OH, TOF = 33 s À1