Exogenous photocatalyst-free aryl radical generation from diaryliodonium salts and use in metal-catalyzed C-H arylation.

We demonstrate (1) detectable halogen bonding is not critical for enabling light-driven radical generation from diaryliodonium salts and (2) radicals generated by this route can be captured by transition-metals for C-H arylation reactions. These results are the first step toward developing new metal-catalyzed aryl radical couplings without exogenous photocatalysts.

Copper-Catalyzed Dehydrogenative Amidation of Light Alkanes.

The functionalization of C-H bonds in light alkanes, particularly to form C-N bonds, remains a challenge. We report the dehydrogenative coupling of amides with C1-C4 hydrocarbons to form N-alkyl amide products with tBuOOtBu as oxidant, and a copper complex of a phenanthroline-type ligand as catalyst. The reactions occurred in good yields in benzene or supercritical carbon dioxide as solvents.

Iridium-Catalyzed Silylation of Unactivated C-H Bonds.

The functionalization of primary C-H bonds has been a longstanding challenge in catalysis. Our group has developed a series of silylations of primary C-H bonds that occur with site selectivity and diastereoselectivity resulting from an approach to run the reactions as intramolecular processes. These reactions have become practical by using an alcohol or amine as a docking site for a hydrosilyl group, thereby leading to intramolecular silylations of C-H bonds at positions dictated by the presence common functional groups in the reactants.

Understanding the Activity and Enantioselectivity of Acetyl-Protected Aminoethyl Quinoline Ligands in Palladium-Catalyzed β-C(sp)-H Bond Arylation Reactions.

Chiral acetyl-protected aminoalkyl quinoline (APAQ) ligands were recently discovered to afford highly active and enantioselective palladium catalysts for the arylation of methylene C(sp)-H bonds, and herein, we investigate the origins of these heightened properties. Unprecedented amide-bridged APAQ-Pd dimers were predicted by density functional theory (DFT) calculations and were confirmed by single-crystal X-ray diffraction studies. Comparison of structural features between APAQ-Pd complexes and an acetyl-protected aminoethylpyridine APAPy-Pd complex strongly suggests that the high activity of the former originates from the presence of the quinoline ring, which slows the formation of the off-cycle palladium dimer.

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis.

Primary aminoboranes (RNHBR ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one-pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions.

What Are the Radical Intermediates in Oxidative N-Heterocyclic Carbene Organocatalysis?

The oxidation of the Breslow intermediate resulting from the addition of an N-heterocyclic carbene (NHC) to benzaldehyde triggers a fast deprotonation, followed by a second electron transfer, directly affording the corresponding acylium at E > -0.8 V (versus Fc/Fc). Similarly, the oxidation of the cinnamaldehyde analogue occurs at an even higher potential and is not a reversible electrochemical process.

Copper-catalyzed dehydrogenative borylation of terminal alkynes with pinacolborane.

LCuOTf complexes [L = cyclic (alkyl)(amino)carbenes (CAACs) or N-heterocyclic carbenes (NHCs)] selectively promote the dehydrogenative borylation of C(sp)-H bonds at room temperature. It is shown that σ,π-bis(copper) acetylide and copper hydride complexes are the key catalytic species.

Spectroscopic Evidence for a Monomeric Copper(I) Hydride and Crystallographic Characterization of a Monomeric Silver(I) Hydride.

(1,3-bis[2,6-bis[di(4-tert-butylphenyl)methyl]-4-methylphenyl]imidazol-2-ylidene)CuOPh [(IPr**)CuOPh] reacts with poly(methylhydrosiloxane) as the hydride donor to afford the monomeric (IPr**)CuH complex, which was spectroscopically characterized. The latter is in equilibrium in solution with [(IPr**)CuH] , the dimer being exclusively present in the solid state. These results support the hypothesis that copper hydride aggregates dissociate in solution.

Catalyst-free dehydrocoupling of amines, alcohols, and thiols with pinacol borane and 9-borabicyclononane (9-BBN).

Contrary to recent reports, the dehydrocoupling of pinacol borane and 9-borabicyclononane with a variety of amines, alcohols and thiols can be achieved under mild conditions without catalyst. This process involves the formation of Lewis acid-base adducts featuring a hydridic B-H in close proximity to an acidic Nu-H.

The Janus Face of the X Ligand in the Copper-Catalyzed Azide-Alkyne Cycloaddition.

To understand the effect of the anion (X) in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) catalytic process, the kinetic profiles of the successive steps of the catalytic cycle have been studied by performing stoichiometric reactions using copper complexes LCuX in which L is a cyclic (alkyl)(amino)carbene (CAAC) ligand and X = OTf, Cl, OAc, OPh, or OtBu. Basic ligands favor the metalation step but disfavor the formation of the catalytically active σ,π-bis(copper) acetylide, whereas non-nucleophilic ligands favor the latter but slowly promote the former. We show that acetate is a good compromise, and in addition, it is very efficient in the proto-demetalation step.