Journal of the American Chemical Society最新文献

The intermolecular N-N coupling of NO in a dinitrosyl iron complex (DNIC) induced by hydrogen bond donors in the secondary coordination sphere to form N₂O is reported. A family of complexes containing pendant anilines in the secondary coordination sphere were synthesized and characterized. Reduction of the {Fe(NO)₂}⁹ complex [Fe(^PhNHPDI)(NO)₂][BPh₄] (3) to the {Fe(NO)₂}¹⁰ Fe(^PhNHPDI)(NO)₂ (4) results in intermolecular N-N coupling to form N₂O. Similar reactions of the control {Fe(NO)₂}⁹ complex [Fe(^PhNMePDI)(NO)₂][BPh₄] (7), which does not have H-bonding groups in the secondary coordination sphere, do not result in N₂O formation. The hydrogen bonding capabilities of the complexes were explored spectroscopically and computationally.

Endowing polyethylenes with photodegradability via incorporation of low densities of in-chain keto units could reduce the problematic environmental persistency of littered polymer waste. A breakthrough enabling such materials is the recent finding of nickel catalyzed nonalternating copolymerization of ethylene-carbon monoxide. We reveal irreversible catalyst deactivation pathways operative in this reaction. Reductive elimination of the common phosphinephenolate Ni(II) motif occurs with the acyl intermediates formed upon incorporation of carbon monoxide into the growing chain, as observed by low temperature NMR spectroscopy and single crystal X-ray crystallography of the isolated product. Further, we show that such decomposition pathways are generally relevant during ethylene-carbon monoxide copolymerizations under pressure reactor conditions. These findings guide the development of more stable and productive polymerization catalysts to enable the production of environmentally benign polyethylenes.

Catalytic hydrolysis is a sustainable method for the degradation of perfluorinated compounds (PFCs) but is challenged by the high reaction temperatures required to cleave strong C-F bonds. Herein, we developed an innovative C-F activation strategy by constructing synergistic Lewis and Brønsted acid pairs over atomically dispersed Zn-O-Al sites to promote C-F bond activation for decomposition of typical PFCs, CF₄. Density functional theory (DFT) calculations demonstrate tricoordinated Al (Al_III) sites and Zn-OH functional, respectively, as Lewis and Brønsted acid sites over Zn-O-Al, synergistically enhancing the adsorption and decomposition of CF₄. X-ray absorption spectroscopy (XAS), pyridine infrared spectroscopy (Py-IR), and ammonia temperature-programmed desorption (NH₃-TPD) verified the presence of both Al_III and Zn-OH on the atomically dispersed Zn-O-Al sites. CF₄-TPD and in situ infrared spectroscopy confirmed that the Zn-O-Al sites facilitate CF₄ adsorption and C-F bond activation. As a result, the Zn-O-Al sites with synergistic Lewis and Brønsted acid pairs achieved 100% CF₄ decomposition at a low temperature of 560 °C and demonstrated outstanding stability for more than 250 h.

Understanding the semiconductor-electrolyte interface in photoelectrochemical (PEC) systems is crucial for optimizing the stability and reactivity. Despite the challenges in establishing reliable surface structure models during PEC cycles, this study explores the complex surface reconstructions of BiVO₄(010) by employing a computational workflow integrated with a state-of-the-art active learning protocol for a machine-learning interatomic potential and global optimization techniques. Within this workflow, we identified 494 unique reconstructed surface structures that surpass conventional chemical intuition-driven, bulk-truncated models. After constructing the surface Pourbaix diagram under Bi- and V-rich electrolyte conditions using density functional theory and hybrid functional calculations, we proposed structural models for the experimentally observed Bi-rich BiVO₄ surfaces. By performing hybrid functional molecular dynamics simulations with the explicit treatment of water molecules on selected reconstructed BiVO₄(010) surfaces, we observed water dissociation from molecular water. Our findings demonstrate significant water dissociation on reconstructed Bi-rich surfaces, highlighting the critical role of bare and undercoordinated Bi sites (only observable in reconstructed surfaces) in driving hydration processes. Our work establishes a foundation for understanding the role of complex, reconstructed Bi surfaces in surface hydration and reactivity. Additionally, our theoretical framework for exploring surface structures and predicting reactivity in multicomponent oxides offers a precise approach to describing complex surface and interface processes in PEC systems.

We present detailed findings on the imaging, structure, and vibrational properties of novel hybrids of the red-emitting octahedral cluster-based compound Cs₂Mo₆Br₁₄ encapsulated within single-walled carbon nanotubes (SWCNTs) of varying diameter. We explore the subtle relationship between the SWCNT internal diameter and Cs₂Mo₆Br₁₄ cluster packing and find a hierarchical relationship between the nature of the cluster packing and a progressive tendency toward formation of one-dimensional (1D) structures as the SWCNT diameter narrows from 24 to 11 Å. As the internal SWCNT van der Waals radius approaches the outside diameter (OD) of the [{Mo₆^IIBr₈ⁱ}Br₆^a]^2- (more simplistically, [Mo₆^IIIBr₁₄]^2-) molecular anion species, SWCNT steric confinement causes a compositional elimination and polymerization resulting in the formation of reduced extended [Mo₂^IIIBr₆]_x nanoribbons which approximate 1D Ising model structures. Our experimental results, obtained through high-resolution transmission electron microscopy and Raman spectroscopy, are supplemented by density functional theory (DFT) calculations.

Despite a few successful examples, controlling the enantioselectivity in the asymmetric synthesis of non-C₂-symmetric biaryldiols has long been challenging. To address the issues of enantioselectivity and regioselectivity, we introduced a novel organoelectrocatalytic strategy enabling asymmetric aryl-aryl dehydrogenative cross-coupling reactions. Using this approach, valuable non-C₂-symmetric biaryldiols were obtained in up to 95% yields and 97% enantiomeric excesses (ees), and these compounds could be further applied as versatile ligands in asymmetric reactions. Detailed mechanistic studies supported a sequential diradical cross-coupling followed by a central-to-axial chirality conversion pathway.

Stereochemistry, usually associated with the three-dimensional arrangement of atoms in molecules, is crucial in processes like life functions, drug action, or molecular reactions. This three-dimensionality typically originates from sp³ hybridization in organic molecules, but it is also present in out-of-plane sp²-based molecules as a consequence of helical structures, twisting processes, and/or the presence of nonbenzenoid rings, the latter significantly influencing their global stereochemistry and leading to the emergence of new exotic properties. In this sense, on-surface synthesis methodologies provide the perfect framework for the precise synthesis and characterization of organic systems at the atomic scale, allowing for the accurate assessment of the associated stereochemical effects. In this work, we demonstrate the importance of the initial diastereomeric configuration in the surface-induced skeletal rearrangement of a substituted cyclooctatetraene (COT) moiety-a historical landmark in the understanding of aromaticity-into a cyclopenta[c,d]azulene (CPA) one in a chevron-like graphene nanoribbon (GNR). These findings are evidenced by combining bond-resolved scanning tunneling microscopy with theoretical ab initio calculations. Interestingly, the major well-defined product, a CPA chevron-like GNR, exhibits the lowest bandgap reported to date for an all-carbon chevron-like GNR, as evidenced by scanning tunneling spectroscopy measurements. This work paves the way for the rational application of stereochemistry in the on-surface synthesis of novel graphene-based nanostructures.

Radical-radical cross-coupling (RCC) offers a promising approach for carbon-carbon bond formation in organic synthesis, particularly for creating complex, three-dimensional molecules. However, achieving both cross- and enantioselectivity in RCC reactions has remained a significant challenge. Here, we report a novel metallaphotoredox platform that enables highly enantioselective decarboxylative coupling of carboxylic acid derivatives with aldehydes. Our strategy leverages independent control over radical generation and subsequent enantioselective bond formation through fine-tuning of a common photocatalyst and a simple chiral bis(oxazoline) nickel catalyst. This redox-neutral protocol requires no exogenous oxidants or reductants and demonstrates broad substrate scope and functional group compatibility in the synthesis of enantioenriched α-aryl and α-amino ketones. The α-amino ketone products can be readily transformed into valuable β-amino alcohols, streamlining access to these important motifs. Furthermore, we showcase the potential of this approach for more challenging enantioselective C(sp³)-C(sp³) alkyl-alkyl RCC reactions. This unified platform for enantioselective alkyl-acyl radical cross-coupling represents a significant advance in asymmetric catalysis and underscores the potential for metallaphotoredox catalysis to exploit new mechanisms to solve long-standing synthetic problems.