Phenolate-bonded bis(μ-oxido)-bis-copper(iii) intermediates: hydroxylation and dehalogenation reactivities. (14th February 2022)

• Record Type: Journal Article
• Authors: Kang, Peng; Lin, Bo-Lin; Large, Tao A. G.; Ainsworth, Jasper; Wasinger, Erik C.; Stack, T. Daniel P.
• Is Part Of: Faraday discussions. Volume 234(2022)
• Page Start: 86
• Page End: 108
• Publication Date: 2022-02-14
• Subjects: Chemistry -- Periodicals; Metallurgy -- Periodicals; Electrochemistry -- Periodicals; 540
• DOI: 10.1039/d1fd00071c
• Languages: English
• ISSNs: 1359-6640

Abstract

Abstract : A Cu(iii ) intermediate, A DBPD, effects novel dehalogenation–hydroxylations of exogenous phenolates; it is best formulated as containing 2 phenolates/Cu2 O2 core. Abstract : Exogenous phenolate ortho -hydroxylation by copper oxidants formed from dioxygen is generally thought to occur through one of two limiting mechanisms defined by the structure of the active oxidant: an electrophilic μ-η 2 :η 2 -peroxo-bis-copper(ii ) species as found in the oxygenated form of the binuclear copper enzyme tyrosinase (oxyTyr), or an isomeric bis(μ-oxido)-bis-copper(iii ) species (O ) with ligated phenolate(s) as evidenced by most synthetic systems. The characterization of the latter is limited due to their limited thermal stability. This study expands the scope of an O species with ligated phenolate(s) using N, N ′-di- tert -butyl-1, 3-propanediamine (DBPD ), a flexible secondary diamine ligand. Oxygenation of the [(DBPD )Cu(i )] 1+ complex at low temperatures ( e.g., 153 K) forms a spectroscopically and structurally faithful model to oxyTyr, a side-on peroxide intermediate, which reacts with added phenolates to form a bis(μ-oxido)-bis-copper(iii ) species with ligated phenolates, designated as an A species. The proposed stoichiometry of A is best understood as possessing 2 rather than 1 bonded phenolate. Thermal decomposition of A results in regiospecific phenolate ortho -hydroxylation with the ortho -substituent as either a C–H or C–X (Cl, Br) group, though the halogen displacement is significantly slower. DFT and experimental studies support an electrophilic attack of an oxide ligand into the π-system of a ligated phenolate. This study supports a hydroxylation mechanism in which O–O bond cleavage of the initially formed peroxide by phenolate ligation, which precedes phenolate aromatic hydroxylation.