Selective Aromatic C–H Hydroxylation Enabled by η⁶-Coordination to Iridium(III)

Abstract

We report an aromatic C–H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into a catalytic cycle for C–H functionalization.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…During the past several decades, many metals have been studied in catalytic activation and functionalization of carbon-hydrogen bonds. The reader is directed to selected recent examples with gold [123], cobalt [124][125][126] chromium [127], copper [128][129][130][131] iron [132][133][134][135], iridium [136], manganese [137][138][139], molybdenum [140], nickel [141], osmium [142][143][144][145][146][147][148], palladium [149][150][151], rhenium [152], rhodium [153,154], ruthenium [155,156], and vanadium [157,158].…”

Hexacoppergermsesquioxanes as complexes with N-ligands: Synthesis, structure and catalytic properties

“…Along with numerous examples of expansive metal-based (e.g. Au [83], Ir [84], Os [85,86], Pd Scheme 1. General scheme of synthesis of hexacoppergermsesquioxanes 1e6 containing additional N-ligands (1,10-phenanthroline or 2,2 0 -bipyridine).…”

Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides

“…With a few exceptions that generally require a large excess of aromatic compounds to drive arene‐exchange in catalysis, [11] umpolung aromatic substitutions have relied on the use of stoichiometric η 6 ‐arene complexes as substrates, which are preformed and require additional steps to liberate free arenes [9] . One obstacle to realizing catalytic reactions is that some of the conditions used for liberation of the arene from the metal center, such as oxidation, [9f] photolysis, [9p] and ligand exchange, [9j,l] are incompatible with the substitutions. Specifically, η 6 ‐phenol complexes readily undergo deprotonation under the basic conditions typically required for nucleophilic addition; the resulting η 5 ‐phenoxo isomers do not undergo arene dissociation [9j,l, 11e, 12] .…”

“…One obstacle to realizing catalytic reactions is that some of the conditions used for liberation of the arene from the metal center, such as oxidation, [9f] photolysis, [9p] and ligand exchange, [9j,l] are incompatible with the substitutions. Specifically, η 6 ‐phenol complexes readily undergo deprotonation under the basic conditions typically required for nucleophilic addition; the resulting η 5 ‐phenoxo isomers do not undergo arene dissociation [9j,l, 11e, 12] . In comparison, phenyl alkyl ethers are unable to tautomerize into phenoxo isomers, and their use would thus overcome the obstacle to realization of catalytic S N Ar reactions [13] .…”