Fenton-like Chemistry by a Copper(I) Complex and H2O2 Relevant to Enzyme Peroxygenase C-H Hydroxylation

Abstract

Lytic polysaccharide monooxygenases have received significant attention as catalytic convertors of biomass to biofuel. Recent studies suggest that its peroxygenase activity (i.e., using H₂O₂ as an oxidant) is more important than its monooxygenase functionality. Here, we describe new insights into peroxygenase activity, with a copper(I) complex reacting with H₂O₂ leading to site-specific ligand-substrate C-H hydroxylation. [Cu^I(TMG₃tren)]⁺ (1) (TMG₃tren = 1,1,1-Tris{2-[N²-(1,1,3,3-tetramethylguanidino)]ethyl}amine) and a dry source of hydrogen peroxide, (o-Tol₃P═O·H₂O₂)₂ react in the stoichiometry, [Cu^I(TMG₃tren)]⁺ + H₂O₂ → [Cu^I(TMG₃tren-OH)]⁺ + H₂O, wherein a ligand N-methyl group undergoes hydroxylation giving TMG₃tren-OH. Furthermore, Fenton-type chemistry (Cu^I + H₂O₂ → Cu^II-OH + ·OH) is displayed, in which (i) a Cu(II)-OH complex could be detected during the reaction and it could be separately isolated and characterized crystallographically and (ii) hydroxyl radical (·OH) scavengers either quenched the ligand hydroxylation reaction and/or (iii) captured the ·OH produced.