Remote C(sp³)–H Oxygenation of Protonated Aliphatic Amines with Potassium Persulfate

This letter describes the development of a method for selective remote C­(sp³)–H oxygenation of protonated aliphatic amines using aqueous potassium persulfate. Protonation serves to deactivate the proximal C­(sp³)–H bonds of the amine substrates and also renders the amines soluble in the aqueous medium. These reactions proceed under relatively mild conditions (within 2 h at 80 °C with amine as limiting reagent) and do not require a transition metal catalyst. This method is applicable to a variety of types of C­(sp³)–H bonds, including 3°, 2°, and benzylic C–H sites in primary, secondary, and tertiary amine substrates

Catalytic Cycle for Palladium-Catalyzed Decarbonylative Trifluoromethylation using Trifluoroacetic Esters as the CF₃ Source

This paper demonstrates a catalytic cycle for Pd-catalyzed decarbonylative trifluoromethylation using trifluoroacetic esters as CF₃ sources. The proposed cycle consists of four elementary steps: (1) oxidative addition of a trifluoroacetic ester to Pd⁰, (2) CO deinsertion from the resulting trifluoroacyl Pd^II complex, (3) transmetalation of a zinc aryl to Pd^II, and (4) aryl–CF₃ bond-forming reductive elimination. The use of RuPhos as the supporting ligand enables each of these steps to proceed under mild conditions (<100 °C). These studies set the stage for the development of catalytic arene trifluoromethylation and perfluoroalkylation reactions using inexpensive trifluoroacetic acid derived CF₃ sources

Merging Visible-Light Photocatalysis and Transition-Metal Catalysis in the Copper-Catalyzed Trifluoromethylation of Boronic Acids with CF₃I

This communication describes the development of a mild method for the cross-coupling of arylboronic acids with CF₃I via the merger of photoredox and Cu catalysis. This method has been applied to the trifluoromethylation of electronically diverse aromatic and heteroaromatic substrates and tolerates many common functional groups

Mild Copper-Mediated Fluorination of Aryl Stannanes and Aryl Trifluoroborates

This communication describes a mild copper-mediated fluorination of aryl stannanes and aryl trifluoroborates with <i>N</i>-fluoro-2,4,6-trimethylpyridinium triflate. This protocol demonstrates broad substrate scope and functional group tolerance, and does not require the use of any noble metal additives. The reaction is proposed to proceed via an arylcopper­(III) fluoride intermediate

Synthesis of Fluoroalkyl Palladium and Nickel Complexes via Decarbonylation of Acylmetal Species

The synthesis and characterization of a series of fluoroalkyl palladium­(II) and nickel­(II) complexes via decarbonylation of the corresponding acylmetal species is reported. At palladium­(II), labile supporting ligands such as tri<i>-o</i>-tolylphosphine are required to achieve decarbonylation within 30 min at 85 °C. In contrast, decarbonylation at (PPh₃)₂Ni­(C­(O)­R_F)­(OCOR_F) (R_F = fluoroalkyl) complexes proceeds rapidly at or below room temperature

Platinum-Catalyzed, Terminal-Selective C(sp³)–H Oxidation of Aliphatic Amines

This Communication describes the terminal-selective, Pt-catalyzed C­(sp³)–H oxidation of aliphatic amines without the requirement for directing groups. CuCl₂ is employed as a stoichio­metric oxidant, and the reactions proceed in high yield at Pt loadings as low as 1 mol%. These transformations are conducted in the presence of sulfuric acid, which reacts with the amine substrates <i>in situ</i> to form ammonium salts. We propose that protonation of the amine serves at least three important roles: (i) it renders the substrates soluble in the aqueous reaction medium; (ii) it limits binding of the amine nitrogen to Pt or Cu; and (iii) it electronically deactivates the C–H bonds proximal to the nitrogen center. We demonstrate that this strategy is effective for the terminal-selective C­(sp³)–H oxidation of a variety of primary, secondary, and tertiary amines

Catalytic CO₂ Hydrogenation to Formate by a Ruthenium Pincer Complex

This paper reports the hydrogenation of carbon dioxide to formate catalyzed by the Ru pincer complex Ru­(PNN)­CO­(H) (PNN = 6-(di-<i>tert</i>-butylphosphinomethylene)-2-(<i>N</i>,<i>N</i>-diethylaminomethyl)-1,6-dihydropyridine). Stoichiometric studies are presented that support the feasibility of the individual steps in a proposed catalytic cycle for this transformation. The influence of base and solvent on catalyst performance is explored. Overall, under optimized conditions (using diglyme as the solvent and potassium carbonate as the base) up to 23,000 turnovers of formate and a turnover frequency of up to 2,200 h^–1 can be achieved

Mechanism of the Palladium-Catalyzed Arene C–H Acetoxylation: A Comparison of Catalysts and Ligand Effects

This article describes detailed mechanistic studies focused on elucidating the impact of pyridine ligands on the Pd-catalyzed C–H acetoxylation of benzene. Three different catalysts, Pd­(OAc)₂, Pd­(OAc)₂/pyridine (1:1), and Pd­(OAc)₂/pyridine (1:2), are compared using a combination of mechanistic tools, including rate and order studies, Hammett analysis, detailed characterization of catalyst resting states, and isotope effects. The data from these experiments implicate C–H activation as the rate-limiting step in all cases. The major difference between the three catalysts is proposed to be the resting state of Pd. Under the reaction conditions, Pd­(OAc)₂ rests as an acetate bridged dimer, while the Pd­(OAc)₂/pyridine (1:2) catalyst rests as the monomer (pyridine)₂Pd­(OAc)₂. In contrast, a variety of experiments suggest that the highly active catalyst generated from the 1:1 combination of Pd­(OAc)₂ and pyridine rests as the dimeric structure [(pyridine)­Pd­(OAc)₂]₂

Catalytic CO₂ Hydrogenation to Formate by a Ruthenium Pincer Complex

This paper reports the hydrogenation of carbon dioxide to formate catalyzed by the Ru pincer complex Ru­(PNN)­CO­(H) (PNN = 6-(di-<i>tert</i>-butylphosphinomethylene)-2-(<i>N</i>,<i>N</i>-diethylaminomethyl)-1,6-dihydropyridine). Stoichiometric studies are presented that support the feasibility of the individual steps in a proposed catalytic cycle for this transformation. The influence of base and solvent on catalyst performance is explored. Overall, under optimized conditions (using diglyme as the solvent and potassium carbonate as the base) up to 23,000 turnovers of formate and a turnover frequency of up to 2,200 h^–1 can be achieved

Asymmetric Chiral Ligand-Directed Alkene Dioxygenation

A Pd-catalyzed asymmetric alkene 1,2-dioxygenation reaction is described. The diastereoselectivity of the reaction is controlled by tethering a chiral oxime ether directing group to the alkene substrate. The best selectivities are obtained with 8-substituted menthone-derived oxime ether auxiliaries