A metal-free photoredox C-H alkylation of heteroaromatics from readily available carboxylic acids using an organic photocatalyst and hypervalent iodine reagents under blue LED light is reported. The developed methodology tolerates a broad range of functional groups and can be applied to the late-stage functionalization of drugs and drug-like molecules. The reaction mechanism was investigated with control experiments and photophysical experiments as well as DFT calculations.

The photocatalytic hydroboration of alkenes and alkynes is reported. The use of newly‐designed copper photocatalysts with B2Pin2 permits the formation a boryl radical, which is used for hydroboration of a large panel of alkenes and alkynes. The hydroborated products were isolated in high yields, with excellent diastereoselectivities and a high functional group tolerance under mild conditions. The hydroboration reactions were developed under continuous flow conditions to demonstrate their synthetic utility. The reaction mechanism was studied and suggested an oxidation reaction between an in situ formed borate and the Cu‐photocatalyst in its excited state for the boryl radical formation.

We report detailed mechanistic investigations of an iron‐based catalyst system, which allows the α‐C−H oxidation of a wide variety of amines. In contrast to other catalysts that effect α‐C−H oxidations of tertiary amines, the system under investigation exclusively employs peroxy esters as oxidants. More common oxidants (e. g. tBuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α‐C−H oxidation products in combination with the described catalyst system. The investigations described herein employ initial rate kinetics, kinetic profiling, DFT calculations as well as Eyring, kinetic isotope effect, Hammett, ligand coordination, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C−H abstraction at a coordinated substrate molecule. This rate‐determining step occurs either through an Fe(IV) oxo pathway or a 2‐electron pathway at an Fe(II) intermediate with bound oxidant. DFT calculations indicate that the Fe(IV) oxo mechanism will be the preferred route of these two possibilities. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO3tBu to tBuOOH. Overall, the obtained mechanistic data support a non‐classical, Fe catalyzed pathway that requires substrate binding, inducing selectivity for α‐C−H functionalization.

Visible light photoredox catalysts with strongly oxidizing excited states have been broadly applied in organic synthesis. Following photon absorption by the photocatalyst, electron transfer from an organic reagent is the most common mechanistic outcome for this class of reaction. Reduction potentials for organic reagents are therefore useful to predict reactivity, and density functional theory (DFT) proved to be useful as a predictive tool in this regard. Due to the complex mechanisms that follow electron transfer, kinetics play a crucial role in the success of photoredox reactions. We extend the predictive tools of DFT to estimate the electron-transfer rates between an excited photocatalyst and various organic substrates. To calibrate our model, 49 electron-transfer rate constants were experimentally measured in acetonitrile for the catalyst Ir[dF(CF 3 )ppy] 2 (dtbpy) + . The quenching rate constants, k q , gave a trend when compared to calculated ionization energies, which was a better predictor than standard reduction potentials in our case. The calculated k q gave an average error of 10% for log(k q ) values between 4.6 and 10.2. This simple method can rapidly predict the reactivity of reagents in silico. Notably, the calculations offered insight that we could translate into success for the C−H activation of 2,4-pentanedione as a proof of concept.

Novel gold nanoparticle@niobium oxide perovskite composites promote the photoreduction of para-substituted nitroarenes, where electron-withdrawing groups accelerate the photocatalytic reaction.