Readily Accessible Bulky Iron Catalysts exhibiting Site Selectivity in the Oxidation of Steroidal Substrates.

Bulky iron complexes are described that catalyze the site-selective oxidation of alkyl C-H bonds with hydrogen peroxide under mild conditions. Steric bulk at the iron center is introduced by appending trialkylsilyl groups at the meta-position of the pyridines in tetradentate aminopyridine ligands, and this effect translates into high product yields, an enhanced preferential oxidation of secondary over tertiary C-H bonds, and the ability to perform site-selective oxidation of methylenic sites in terpenoid and steroidal substrates. Unprecedented site selective oxidation at C6 and C12 methylenic sites in steroidal substrates is shown to be governed by the chirality of the catalysts.

Recent Advances in the Selective Oxidation of Alkyl C-H Bonds Catalyzed by Iron Coordination Complexes.

Selective and stereoretentive oxidation of alkyl C-H bonds has been described over the last decade by employing biologically inspired iron coordination complexes as catalysts and hydrogen peroxide as oxidant. Examples of catalyst dependent C-H site selectivity have started to appear. The current paper describes an account of these findings.

Regioselective oxidation of nonactivated alkyl C-H groups using highly structured non-heme iron catalysts.

Selective oxidation of alkyl C-H groups constitutes one of the highest challenges in organic synthesis. In this work, we show that mononuclear iron coordination complexes Λ-[Fe(CF(3)SO(3))(2)((S,S,R)-MCPP)] (Λ-1P), Δ-[Fe(CF(3)SO(3))(2)((R,R,R)-MCPP)] (Δ-1P), Λ-[Fe(CF(3)SO(3))(2)((S,S,R)-BPBPP)] (Λ-2P), and Δ-[Fe(CF(3)SO(3))(2)((R,R,R)-BPBPP)] (Δ-2P) catalyze the fast, efficient, and selective oxidation of nonactivated alkyl C-H groups employing H(2)O(2) as terminal oxidant. These complexes are based on tetradentate N-based ligands and contain iron centers embedded in highly structured coordination sites defined by two bulky 4,5-pinenopyridine donor ligands, a chiral diamine ligand backbone, and chirality at the metal (Λ or Δ).

An iron catalyst for oxidation of alkyl C-H bonds showing enhanced selectivity for methylenic sites.

Many are called but few are chosen: A nonheme iron complex catalyzes the oxidation of alkyl C-H bonds by using H(2)O(2) as the oxidant, showing an enhanced selectivity for secondary over tertiary C-H bonds (see scheme).

Nucleophilic aryl fluorination and aryl halide exchange mediated by a Cu(I)/Cu(III) catalytic cycle.

Copper-catalyzed halide exchange reactions under very mild reaction conditions are described for the first time using a family of model aryl halide substrates. All combinations of halide exchange (I, Br, Cl, F) are observed using catalytic amounts of Cu(I). Strikingly, quantitative fluorination of aryl-X substrates is also achieved catalytically at room temperature, using common F(-) sources, via the intermediacy of aryl-Cu(III)-X species.

Observation and mechanistic study of facile C-O bond formation between a well-defined aryl-copper(III) complex and oxygen nucleophiles.

A well-defined macrocyclic aryl–Cu(III) complex (2) reacts readily with a variety of oxygen nucleophiles, including carboxylic acids, phenols and alcohols, under mild conditions to form the corresponding aryl esters, biaryl ethers and alkyl aryl ethers. The relationship between these reactions and catalytic C-O coupling methods is demonstrated by the reaction of the macrocyclic aryl–Br species with acetic acid and p-fluorophenol in the presence of 10 mol% Cu(I). An aryl-Cu(III)-Br species 2(Br) was observed as an intermediate in the catalytic reaction.