Journal of the American Chemical Society最新文献

Transition-metal-catalyzed asymmetric carbene-transfer reactions represent a powerful strategy for synthesizing chiral cyclopropanes. However, current methods predominantly rely on stabilized carbene-bearing α-π-conjugated groups, restricting access to less stabilized carbenes, such as α-silyl and α-boryl carbenes. Herein, we present an unprecedented Cr(II)-based metalloradical system for the asymmetric cyclopropanation of α,β-unsaturated amides with α-boryl and α-silyl dibromomethanes in the presence of Mn as the reducing agent. Employing a chiral chromium complex, the reaction proceeds under mild conditions, yielding cyclopropanes with three contiguous stereocenters in high diastereo- and enantioselectivities. This method features a Cr-catalyzed radical-based stepwise cyclopropanation mechanism. The broad substrate scope, encompassing various α,β-unsaturated amides, demonstrates the protocol's versatility and robustness. Mechanistic insights, supported by experimental and computational studies, suggest the formation of α-Cr(III)-alkyl radical intermediates, delineating a pathway distinct from that of classical concerted cyclopropanations. This approach provides a powerful tool for synthesizing highly functionalized cyclopropanes, offering high potential for applications in drug discovery and development.

Electrocatalytically selective chlorination of olefins in Cl^--containing solutions is a sustainable method for synthesizing chlorohydrin/vicinal dichloride; however, controlling the selectivity is challenging. Here, aqueous/dimethyl carbonate (DMC) hybrid electrolytes with different H₂O/DMC ratios are designed to modulate the ·OH formation to increase the corresponding selectivities. The combined results of in/ex situ spectroscopies and molecular dynamics simulations reveal the origin of high selectivity. TFSI^- shields the transportation of free H₂O to provide moderate ·OH formation for the synthesis of chlorohydrin. DMC reconstructs hydrogen bonds with free H₂O to minimize the interaction between them and the anode, matching the requirements of vicinal dichloride production. Thus, these hybrid electrolytes not only achieve high selectivities of 80% and 76% for chlorohydrin and vicinal dichloride, respectively, but also enable the selective chlorination of other olefins with high isolated yields of up to 74%. This work provides a facile strategy to regulate the selectivity of anodic chlorination via a rational electrolyte design.

In a comprehensive investigation of the dinuclear [Mn₂O₃]⁺ cluster, the smallest dimanganese entity with two μ-oxo bridges and a terminal oxo ligand, and a simplified structural model of the active center in the oxygen-evolving complex, we identify antiferromagnetically coupled high-spin manganese centers in very different oxidation states of +2 and +5, but rule out the presence of a manganese(IV)-oxyl species by experimental X-ray absorption and X-ray magnetic circular dichroism spectroscopy combined with multireference calculations. This first identification of a high-spin manganese(V) center in any polynuclear oxidomanganese complex underscores the need for multireference computational methods to describe high-valent oxidomanganese species.

Photoelectrocatalytic cells for seawater splitting have shown promise toward large-scale deployment; however, challenges remain in operation performances, which outline clear research needs to scale up photoelectrodes with small loss of efficiency. Here, we report an approach for scalable and robust solar H₂ evolution by enhancing photogenerated charge transport in a H₂-evolving molecular photoelectrode. The photoelectrode is based on p-type conjugated polymers that are homogeneously distributed in a polycarbazole network. With a self-assembled NiS₂ catalyst, the photoelectrode under solar irradiation (100 mW cm^-2, AM 1.5 G) is capable of evolving H₂ from seawater at an external quantum efficiency (EQE) of 34.4% under an applied bias of -0.06 V vs RHE. When scaling up from 1 cm² to 25 cm², the photoelectrode generates photocurrents stabilized at 0.4 A and maintains the high EQE at an efficiency loss of less than 1%. Investigation of the photogenerated charge-transport dynamics reveals that the kinetic basis for scaling up lies in the desirable hole diffusion length that far exceeds the spacing between adjacent conjugated-polymer chains due to interchain π-π interactions.

Efficiently constructing structurally diverse and complex organic molecules through selective catalytic functionalization is a central goal in synthetic chemistry, yet achieving precise control over multiple reactive centers in multisite substrates remains a formidable challenge. Building on foundational advances in single- and dual-selective transformations, we report a multimodal strategy for the selective carbonylation of 1,3-enynes, a versatile class of multisite substrates. Through meticulous fine-tuning of the catalytic conditions, our approach enables five distinct regio- and stereoselective carbonylative transformations, including direct functionalization (1,2- and 2,1-hydroaminocarbonylation) and tandem cyclization pathways (2,4-, 1,3-, and 2,3-carbonylation). Furthermore, mechanistic studies suggested that multidimensional precise regulation enables the seamless relay of up to three tandem reactions (hydroaminocarbonylation-hydroamination-transamination) with exceptional accuracy. This unified platform not only establishes a robust framework for tackling the enduring challenges of selectivity control in multisite substrates but also broadens the chemical space accessible through 1,3-enyne transformations, exemplifying atom- and step-economic principles and paving the way for transformative advancements in drug discovery, materials science, and beyond.