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Nature Chemistry, Published online: 28 February 2025; doi:10.1038/s41557-025-01754-7

P→B motifs are readily and regioselectively appended to pyrene and anthracene. In contrast with the borylative fusion approach recently developed for related N→B-functionalized polycyclic aromatic hydrocarbons, such P→B functionalization does not extend the π-system. Nevertheless, it significantly impacts the electronic, photophysical, and electrochemical properties.

Abstract

The functionalization of polycyclic aromatic hydrocarbons (PAHs) with N→B Lewis pairs, so-called borylative fusion, has recently emerged as a simple and powerful means to modulate their electronic and photophysical properties thanks to the extension of the π system. Herein, we considered a new class of PAHs appended with phosphine→borane Lewis pairs and investigated pyrene as well as anthracene derivatives. In these compounds, strong P→B interactions are enforced geometrically, but the π-system is not extended. Nevertheless, such P→B functionalization was found to significantly impact the optical and electrochemical properties. The P,B-functionalized PAHs display noticeably reduced HOMO–LUMO gaps and enhanced fluorescence. Both the number and position of P→B units turned out to play a significant role.

An efficient Pt-based electrocatalyst from commercially available PtCl₂ is reported for the electrohydrogenation of olefins under unusual high current density (J _Geo up to 133 mA cm⁻²) using protons and electrons as the hydrogen source and reductant, respectively. This reaction exhibits broad functional group compatibility and substrate scope. Additionally, highly regioselective electrocatalytic hydrogenation of olefins (r.r. > 19:1) is demonstrated using PtCl₂ and 2,2′-bipyridine.

Abstract

Electrochemical synthesis offers a powerful and sustainable alternative to conventional chemical manufacturing techniques. The direct and selective electrohydrogenation of olefins has enormous potential applicability; however, this reactivity has not been sufficiently demonstrated. Herein, we show that an efficient Pt-based electrocatalyst from commercially available PtCl₂ can promote such transformations. This approach enables olefins to be electrohydrogenated (often below −3.0 V vs. Ag/AgCl) at high current density (J _Geo up to 133 mA cm⁻²) using protons and electrons as the hydrogen source. This reaction exhibits broad functional group compatibility, requires low catalyst loading, and affords a diverse series of valuable molecules (more than 60 examples) with high chemoselectivity. In addition, highly regioselective electrocatalytic hydrogenation of olefins (r.r. > 19:1) is demonstrated using PtCl₂ and 2,2′-bipyridine.

This study examines the viability of competing inner-sphere (ISET) and outer-sphere electron transfer (OSET) processes in [Cu(dap)₂]⁺-mediated atom-transfer radical additions of olefins and CF₃SO₂Cl that can deliver both R−SO₂Cl and R−Cl products. R−SO₂Cl/R−Cl product ratios are primarily governed by the relative rates of ground state direct catalyst regeneration {i.e., [Cu(dap)₂SO₂Cl]⋅⁺+R⋅} and ligand exchange {i.e., [Cu(dap)₂SO₂Cl]⋅⁺+Cl⁻ }.

Abstract

This integrated computational and experimental study comprehensively examines the viability of competing inner-sphere electron transfer (ISET) and outer-sphere electron transfer (OSET) processes in [Cu(dap)₂]⁺-mediated atom-transfer radical additions (ATRA) of olefins and CF₃SO₂Cl that can deliver both R−SO₂Cl and R−Cl products. Five sterically- and electronically-varied representative alkenes were selected from which to explore and reconcile a range of experimentally observed outcomes. Findings are consistent with photoexcited [Cu(dap)₂]⁺ initiating photoelectron transfer via ISET and the subsequent regeneration of the oxidized catalyst via ISET in the ground state to close the catalytic cycle and liberate products. R−SO₂Cl/R−Cl product ratios appear to be primarily governed by the relative rates of direct catalyst regeneration {i.e., [Cu(dap)₂SO₂Cl]⋅⁺+R⋅} and ligand exchange {i.e., [Cu(dap)₂SO₂Cl]⋅⁺+Cl⁻ }. Through this work, a more consistent and more complete conceptual framework has been developed to better understand this chemistry and how catalyst regeneration occurs. It is this important ground state process, which closes the catalytic cycle, and ultimately controls the enantioselectivity of ATRA reactions employing chiral copper photocatalysts.

Nature Chemistry, Published online: 20 January 2025; doi:10.1038/s41557-024-01728-1

Nature Chemistry, Published online: 03 January 2025; doi:10.1038/s41557-024-01695-7

Nature Chemistry, Published online: 07 January 2025; doi:10.1038/s41557-024-01702-x

Hitherto elusive side-on Pd(0) arene and organic carbonyl complexes are reported, as well as the catalytic hydrodefluorination of hexafluorobenzene by cyclohexene. Detailed spectroscopic studies and quantum-chemical calculations reveal that bonding between Pd(0) and π-ligands may occur, opposed to common belief, by two different mechanisms. Hence, we present evidence for selective π-Lewis base activation of π-systems.

Abstract

We report hitherto elusive side-on η²-bonded palladium(0) carbonyl (anthraquinone, benzaldehyde) and arene (benzene, hexafluorobenzene) palladium(0) complexes and present the catalytic hydrodefluorination of hexafluorobenzene by cyclohexene. The comparison with respective cyclohexene, pyridine and tetrahydrofuran complexes reveals that the experimental ligand binding strengths follow the order THF<C₆H₆<C₆F₆<cyclohexene<pyridine<benzaldehyde<anthraquinone. To understand this surprising order, the complexes’ electronic structures were elucidated by nuclear magnetic resonance (NMR), single crystal X-Ray diffraction (sc-XRD), ultraviolet/visible (UV/Vis) electronic absorption, infrared (IR) vibrational, Pd L₃-edge X-ray absorption (XAS), and X-ray photoelectron (XP) spectroscopic techniques, complemented by Density Functional Theory (DFT) calculations including energy decomposition (EDA-NOCV) and effective oxidation state (EOS) analyses. For benzene, pyridine and cyclohexene, bonding follows the donor/acceptor picture of the Dewar–Chatt–Duncanson model. In stark contrast, hexafluorobenzene, benzaldehyde and anthraquinone bind via essentially the π-channel only and thus as π-analogues of Z-acceptor ligands. This contribution elucidates the control of functional-group selectivity in palladium(0) catalysis and delineates a novel strategy to activate electron-deficient π-systems.

Electrochemical, fully stereoselective P(V)-hydrophosphorylation of olefins and carbonyl compounds using a P(V) reagent is disclosed. By strategically selecting the anode material. Radical reactivity is accessible for alkene hydrophosphorylation, whereas a polar pathway operates for ketone hydrophosphorylation. A comprehensive investigation into the mechanistic intricacies of the chemoselectivity was conducted, providing deeper insight into the underlying reaction pathways and selectivity factors.

Abstract

Electrochemical, fully stereoselective P(V)-radical hydrophosphorylation of olefins and carbonyl compounds using a P(V) reagent is disclosed. By strategically selecting the anode material, radical reactivity is accessible for alkene hydrophosphorylation whereas a polar pathway operates for ketone hydrophosphorylation. The mechanistic intricacies of these chemoselective transformations were explored in-depth.

It has been found that oxidative species derived from H₂O exhibit a stronger competitive adsorption ability compared to alcohol substrates during photoelectrochemical (PEC) alcohol oxidation, leading to poor formation of pre-oxidized intermediates and excessive alcohol oxidation. However, after PEC polarization, the adsorption of alcohol substrates is significantly enhanced, enabling competition with oxidative species. This boosts the formation of pre-oxidized intermediates, effectively suppressing alcohol over-oxidation and enhancing the oxidation kinetics of alcohol-to-aldehyde conversion.

Abstract

Suppressing over-oxidation is a crucial challenge for various chemical intermediate synthesis in heterogeneous catalysis. The distribution of oxidative species and the substrate coverage, governed by the direction of electron transfer, are believed to influence the oxidation extent. In this study, we presented an experimental realization of surface coverage modulation on a photoelectrode using a photo-induced charge activation method. Through the surface coverage modulation, both pre-oxidized alcohol substrates and surface coverage were increased, which not only improved the reaction kinetics but also suppressed the over-oxidation of the generated aldehydes/ketones. As a demonstration, the Faradaic efficiency for the conversion of glycerol to dihydroxyacetone increased from 31.8 % to 46.8 % (with selectivity rising from 47.6 % to 71.3 %), from 73.4 % to 87.8 % for benzyl alcohol to benzyl aldehyde (selectivity increasing from 76.7 % to 92.4 %) and from 4.2 % to 53.6 % for ethylene glycol to glycolaldehyde (selectivity increasing from 6.2 % to 62.7 %). Our findings offer a promising strategy for the production of high-value carbon products in heterogeneous catalysis.