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Hydroxylation of Aromatics by H 2 O 2 Catalyzed by Mononuclear Non‐heme Iron Complexes: Role of Triazole Hemilability in Substrate‐Induced Bifurcation of the H 2 O 2 Activation Mechanism
Author(s) -
Rebilly JeanNoël,
Zhang Wenli,
Herrero Christian,
Dridi Hachem,
SénéchalDavid Katell,
Guillot Régis,
Banse Frédéric
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201903239
Subject(s) - chemistry , homolysis , reactivity (psychology) , hydroxylation , ligand (biochemistry) , regioselectivity , heterolysis , stereochemistry , substrate (aquarium) , moiety , medicinal chemistry , catalysis , triazole , heme , enzyme , radical , organic chemistry , medicine , biochemistry , oceanography , alternative medicine , receptor , pathology , geology
Rieske dioxygenases are metalloenzymes capable of achieving cis ‐dihydroxylation of aromatics under mild conditions using O 2 and a source of electrons. The intermediate responsible for this reactivity is proposed to be a cis ‐Fe V (O)(OH) moiety. Molecular models allow the generation of a Fe III (OOH) species with H 2 O 2 , to yield a Fe V (O)(OH) species with tetradentate ligands, or {Fe IV (O); OH . } pairs with pentadentate ones. We have designed a new pentadentate ligand, mtL 4 2 , bearing a labile triazole, to generate an “in‐between” situation. Two iron complexes, [(mtL 4 2 )FeCl](PF 6 ) and [(mtL 4 2 )Fe(OTf) 2 ]), were obtained and their reactivity towards aromatic substrates was studied in the presence of H 2 O 2 . Spectroscopic and kinetic studies reflect that triazole is bound at the Fe II state, but decoordinates in the Fe III (OOH). The resulting [(mtL 4 2 )Fe III (OOH)(MeCN)] 2+ then lies on a bifurcated decay pathway ( end‐on homolytic vs. side‐on heterolytic) depending on the addition of aromatic substrate: in the absence of substrate, it is proposed to follow a side‐on pathway leading to a putative ( N 4 )Fe V (O)(OH), while in the presence of aromatics it switches to an end‐on homolytic pathway yielding a {( N 5 )Fe IV (O); OH . } reactive species, through recoordination of triazole. This switch significantly impacts the reaction regioselectivity.