Jiahao Liu

α-Keto-, β-acetoxy- and β-amidoalkylsilyl peroxides are prepared from various precursors and utilized for Fe-catalyzed and visible-light-promoted radical functionalization with coupling partners under mild conditions with a broad substrate scope.

The first implementation of a molybdenum complex with an easily accessible bis‐N‐heterocyclic carbene ligand to catalyze β‐alkylation of secondary alcohols via borrowing‐hydrogen (BH) strategy using alcohols as alkylating agents is reported. Remarkably high activity, excellent selectivity, and broad substrate scope compatibility with advantages of catalyst usage low to 0.5 mol%, a catalytic amount of NaOH as the base, and H₂O as the by‐product are demonstrated in this green and step‐economical protocol. Mechanistic studies indicate a plausible outer‐sphere mechanism in which the alcohol dehydrogenation is the rate‐determining step.

Metal hydride complexes are key intermediates for N-alkylation of amines with alcohols by the borrowing hydrogen/hydrogen autotransfer (BH/HA) strategy. Reactivity tuning of metal hydride complexes could adjust the dehydrogenation of alcohols and the hydrogenation of imines. Herein we report ruthenium(II) complexes with hetero-bidentate N-heterocyclic carbene (NHC)-phosphine ligands, which realize smart pathway selection in the N-alkylated reaction via reactivity tuning of [Ru–H] species by hetero-bidentate ligands. In particular, complex 6cb with a phenyl wingtip group and BArF⁻ counter anion, is shown to be one of the most efficient pre-catalysts for this transformation (temperature is as low as 70 °C, neat conditions and catalyst loading is as low as 0.25 mol%). A large variety of (hetero)aromatic amines and primary alcohols were efficiently converted into mono-N-alkylated amines in good to excellent isolated yields. Notably, aliphatic amines, challenging methanol and diamines could also be transformed into the desired products. Detailed control experiments and density functional theory (DFT) calculations provide insights to understand the mechanism and the smart pathway selection via [Ru–H] species in this process.

The electronic effect is crucial for the electrocatalytic reduction of CO₂. In contrast to the previous understanding of the monotonic influence of the electronic effect on the selectivity of CO₂ reduction, the dual roles of the electronic effect on the selectivity are revealed in the present study, i.e., (1) the electronic effect on redox originating from σ-donation and (2) the electronic effect on π-back-donation, via comprehensive DFT studies on four representative classes of pincer NHC Ni^II catalysts. On the one hand, the electron-rich C, B-coordinating (CCC and CBC) ligands guarantee that the catalysts possess the driving force to reduce CO₂ in a lower-electron reduction state (Ni^I), leading to lower free energy barriers for the formation of HCOOH, which results from the lower ligand-field deformation energies for the hydride transfer and the stronger p–σ* interactions in the metal–hydride intermediates. In contrast, the less electron-rich N-coordinating (CNC and C(B)NC) ligands require an Ni⁰ electron reduction state to reduce CO₂, preferring kinetic-controlled CO formation due to the higher free energy barriers for the generation of HCOOH. This redox effect well explains the unprecedented experimentally observed selectivity of HCOOH in the stronger electron donor CCC-Ni system, which is different from the traditional understanding of the electronic effect. On the other hand, at an identical reduction state, the electronic effect plays an important role in tuning the back-donation ability of the metal center, benefiting the π-back-donation in the metal–carbonyl intermediates, and thus favors the formation of CO. This back-donation effect is consistent with the traditional understanding of selectivity. This work provides comprehensive insights into the dual role of the electronic effect on the selectivity for CO₂ reduction, which can be instructive for the future design and development of catalysts.

The implementation of earth-abundant metals mediated chemistry is a major goal in homogeneous catalysis. Borrowing hydrogen/hydrogen autotransfer (BH/HA) reaction, as a straightforward and sustainable synthetic method, has attracted considerable attention in the development of earth-abuandant metal catalysts. Herein, we report a tungsten-catalyzed N-alkylation reaction of amines with primary alcohols via BH/HA. This phosphine-free W(phen)(CO)4 (phen=1,10-phenthroline) system was demonstrated as a practical and easily accessible in-situ catalysis for a broad range of amines and alcohols (up to 49 examples, including 16 previously undisclosed products). Notably, this tungsten system can tolerate numerous functional groups, especially the challenging substrates with sterically hindered substituents, or heteroatoms. Mechanistic insights based on experimental and computational studies are also provided.

A sustainable and green route to access diverse functionalized ketones via dehydrogenative–dehydrative cross‐coupling of primary and secondary alcohols is demonstrated. This borrowing hydrogen approach employing a pincer N‐heterocyclic carbene Mn complex displays high activity and selectivity. A variety of primary and secondary alcohols are well tolerant and result in satisfactory isolated yields. Mechanistic studies suggest that this reaction proceeds via a direct outer‐sphere mechanism and the dehydrogenation of the secondary alcohol substrates plays a vital role in the rate‐limiting step.

The first example of room temperature non-noble metal homogeneous system catalyzed selective N-alkylation of anilines with alcohols by a bis-NHC manganese complex is presented. This system was applied to a large range of alcohols and anilines, including biologically relevant motifs and challenging methanol. Experimental and computational studies suggest an outer-sphere mechanism for this NHC–Mn system.

Through the strategy of combining bifunctional 2-hydroxypyridine and a thermally stable N-heterocyclic carbene ligand, an Ir-catalyzed N-monoalkylation reaction has been developed in aqueous media under base-free conditions. This reaction proceeds smoothly with high yields of various aromatic amines and sulfonamides with a wide range of primary alcohols. Experimental and computational studies revealed a metal–ligand cooperative mechanism and its thermal stability during the bifunctional catalysis in aqueous media.