Operando Infrared Spectroscopy Study of Iron-Catalyzed Hydromagnesiation of Styrene: Explanation of Nonlinear Catalyst and Inhibitory Substrate Dependencies

Theoretical Study on the Mechanism of the Electrocatalytic CO2 Reduction to Formate by an Iron Schiff Base Complex

The iron(III) chloride compound 6,6'-di(3,5-ditert-butyl-2-hydroxybenzene)-2,2'-bipyridine (Fe(tbudhbpy)Cl) can effectively catalyze the electrochemical CO2 reduction in N,N-dimethylformamide. Density functional calculations were conducted to investigate the mechanism and unravel the governing factors of product selectivity. The results suggest that the initial catalyst, Fe(tbudhbpy)Cl (formally FeIII-Cl), undergoes two reduction steps, accompanied by the dissociation of Cl-, leading to the formation of the active ferrous radical intermediate 2 (formally FeI). Without phenol, 2 attacks CO2 to generate the FeIII-carboxylate intermediate FeIII-CO2, followed by a one-electron reduction to generate FeII-CO2, which reacts with another CO2 to produce CO. This aligns with the experimental result that CO is the main product when the phenol is absent. In contrast, when phenol is presented, the triple reduced species 3 is protonated at its ligand N site to yield 3pt(N) (formally Fe0-NH), which subsequently performs a nucleophilic attack on CO2 to afford formate. This process occurs via an orthogonal electron/proton transfer mechanism, where two electrons and one proton are transferred from the ligand to the CO2 moiety. The redox noninnocent nature of the ligand is thus crucial for formate formation, as it facilitates electron and proton shuttling, enabling 3pt(N) to attack CO2 through this unusual mechanism effectively.

Mechanism and selectivity of photocatalyzed CO2 reduction by a function-integrated Ru catalyst

The phosphine-substituted Ru(II) polypyridyl complex, [Ru^II-(tpy)(pqn)(MeCN)]²⁺ (RuP), was disclosed to be an efficient photocatalyst for the reduction of CO₂ to CO with excellent selectivity. In this work, density functional calculations were performed to elucidate the reaction mechanism and understand the origin of selectivity. The calculations showed that RuP was first excited to the singlet excited state, followed by intersystem crossing to produce a triplet species (3RuIII(L˙-)-S), which was then reduced by the sacrificial electron donor BIH to generate a Ru^II(L˙^-) intermediate. The ligand of Ru^II(L˙^-) was further reduced to produce a Ru^II(L^2-) intermediate. The redox non-innocent nature of the tpy and pqn ligands endows the Ru center with an oxidation state of +2 after two one-electron reductions. Ru^II(L^2-) nucleophilically attacks CO₂, in which two electrons are delivered from the ligands to CO₂, affording a Ru^II-COOH species after protonation. This is followed by the protonation of the hydroxyl moiety of Ru^II-COOH, coupled with the C-O bond cleavage, resulting in the formation of Ru^II-CO. Ultimately, CO is dissociated after two one-electron reductions. Protonation of Ru^II(L^2-) to generate a Ru^II-hydride, a critical intermediate for the production of formate and H₂, turns out to be kinetically less favorable, even though it is thermodynamically more favorable. This fact is due to the presence of a Ru²⁺ ion in the reduced catalyst, which disfavors its protonation.

Benzannulation and Hydrocarboxylation Methods for the Synthesis of a Neopentylene-Fused Analogue of Ibuprofen

Neopentylene ring fusions (ring-fused 4,4-dimethylcyclopentane polycycles) are found in many natural products, but they are largely absent from synthetic compound libraries and focused medicinal chemistry research. Here is reported a synthetic approach to one of the few non-natural product-based target compounds from medicinal chemistry that includes a neopentylene ring fusion: an analogue of ibuprofen referred to herein as "neoprofen". The approach features ring-opening fragmentation reactions of dimedone derivatives coupled with transition metal-catalyzed benzannulation and hydrocarboxylation methods.

Iron-Catalyzed Reductive Cyclization by Hydromagnesiation: A Modular Strategy Towards N-Heterocycles

A reductive cyclization to prepare a variety of N-heterocycles, through the use of ortho-vinylanilides, is reported. The reaction is catalyzed by an inexpensive and bench-stable iron complex and generally occurs at ambient temperature. The transformation likely proceeds through hydromagnesiation of the vinyl group, and trapping of the in situ generated benzylic anion by an intramolecular electrophile to form the heterocycle. This iron-catalyzed strategy was shown to be broadly applicable and was utilized in the synthesis of substituted indoles, oxindoles and tetrahydrobenzoazepinoindolone derivatives. Mechanistic studies indicated that the reversibility of the hydride transfer step depends on the reactivity of the tethered electrophile. The synthetic utility of our approach was further demonstrated by the formal synthesis of a reported bioactive compound and a family of natural products.