LG

To P(III) or not to P(III). A three-component mixture containing primary phosphine, chalcogen, and an imine affords a bis-α-aminophosphine chalcogenide. Mechanistic studies show an interesting dichotomy between the relative reactivities of P(III) vs. P(V) species towards imines.

Abstract

Reactivity of primary phosphines with two stoichiometric equivalents of imine results in the formation of bis-α-aminophosphines (2 a–e), which can be subsequently oxidized in the presence of S₈ or H₂O₂ to generate air stable bis-α-aminophosphine sulfides (2 b–m(S/O)). To elucidate the mechanism of this three-component reaction, Hammett analysis, kinetic isotope effect (KIE), and trapping experiments were performed. Ultimately a P(V)–P(III) tautomerization is invoked, followed by nucleophilic attack by the P(III) species to generate the desired products.

Nature Communications, Published online: 08 July 2022; doi:10.1038/s41467-022-31634-4

A visible-light-induced nickel/photoredox-catalyzed mono-Suzuki–Miyaura cross-coupling of 1,2-bis-boronic esters has been accomplished, which is selective for the most sterically hindered boronic ester. High regioselectivities were achieved through a facile radical 1,2-boron shift process, wherein the initially generated primary β-boryl radical is rapidly converted to the thermodynamically more stable secondary radical before nickel-catalyzed cross-coupling.

Abstract

Site-selective transition-metal-catalyzed mono-deboronative cross-couplings of 1,2-bis-boronic esters are valuable methods for the synthesis of functionalized organoboron compounds. However, such cross-couplings are limited to reaction of the sterically less hindered primary boronic ester. Herein, we report a nickel/photoredox-catalyzed mono-deboronative arylation of 1,2-bis-boronic esters that is selective for coupling of the more sterically hindered secondary/tertiary position. This is achieved by taking advantage of a 1,2-boron shift of primary β-boryl radicals to the thermodynamically favored secondary/tertiary radicals, which are subsequently intercepted by the nickel catalyst to enable arylation. The mild conditions are amenable to a broad range of aryl halides to give β-aryl boronic ester products in good yields and with high regioselectivity. This method also allows stereodivergent coupling of cyclic cis-1,2-bis-boronic esters to give trans-substituted products.

Abstract

An electrochemical oxidative C−H/S−H cross-coupling reaction between acetonitrile and heteroaryl thiols has been developed. Me₄NBr is employed as a redox catalyst to oxidize both the Csp ³−H of acetonitrile and S−H of heteroaryl thiols. Heteroaryl vinyl sulfides were afforded under metal-free and oxidant-free reaction conditions in good yields and stereoselectivities with excellent functional group tolerance. The synthetic applicability of the electrochemical method was further highlighted by its easy scalability.

Recent progress on convergent paired electrolysis has been summarized in this concept article. Four strategies based upon metal catalysis, persistent radical effects, microfluidic chemistry, and alternating current electrolysis are discussed in relation to their underlying mechanisms.

Abstract

Convergent paired electrolysis combines both anodic and cathodic reactions simultaneously in an electrochemical transformation. It provides a highly energy-efficient and divergent approach to conventionally challenging and useful structures. However, the physical separation of the two half-electrode reactions makes it extremely difficult to couple the intermediates arising from the two electrodes. In this concept article, four strategies used in convergent paired electrolysis will be discussed from the perspective of the reaction mechanism: a) metal-catalyzed convergent paired electrolysis, b) convergent paired electrolysis enabled by persistent radical effects, c) microfluidic chemistry applied to convergent paired electrolysis, and d) alternating current electrolysis.

Coupled photo and thermal energies can help to improve the reaction activity of a certain reaction process. And kinetic studies are the key means (or way) to clarify light-specific contributions and even reaction mechanism in the photo-thermo catalysis, which would help to pave the way in “rational catalyst design”.

Abstract

Photo-thermo catalysis utilizing light has been a promising strategy to improve the conventional thermal catalytic activity and attracts great attention nowadays. However, how heat works in synergy with light radiation is still unclear. This Concept article is trying to clarify the specific contents via summarizing the kinetic studies including 1) proposing elementary steps through pressure dependence studies, 2) estimating reaction barriers through measuring the apparent activation energies and 3) assigning the kinetically relevant step(s) with kinetic isotope effects (KIE) as well as 4) exploring the relationship of the reaction rate with the light excitation wavelength and light intensity. The challenges in kinetic studies such as describing the light-induced carrier transfer process, the surface temperature under light illumination as well as reaction intermediates were discussed at the same time. Finally, an outlook about kinetic studies in clarifying the photo-thermo catalysis reaction mechanism was proposed.

This Scientific Perspective describes current challenges in determining, reporting, and comparing performance indicators in homogeneous and heterogeneous light-driven catalysis. The need for comparative data analysis in the field is highlighted, and its role in future data reporting and big-data analysis is discussed. A minimum set of experimental parameters to be reported for light-driven catalysis is proposed.

Abstract

Light-driven homogeneous and heterogeneous catalysis require a complex interplay between light absorption, charge separation, charge transfer, and catalytic turnover. Optical and irradiation parameters as well as reaction engineering aspects play major roles in controlling catalytic performance. This multitude of factors makes it difficult to objectively compare light-driven catalysts and provide an unbiased performance assessment. This Scientific Perspective highlights the importance of collecting and reporting experimental data in homogeneous and heterogeneous light-driven catalysis. A critical analysis of the benefits and limitations of the commonly used experimental indicators is provided. Data collection and reporting according to FAIR principles is discussed in the context of future automated data analysis. The authors propose a minimum dataset as a basis for unified collecting and reporting of experimental data in homogeneous and heterogeneous light-driven catalysis. The community is encouraged to support the future development of this parameter list through an open online repository.

Nature Communications, Published online: 10 June 2022; doi:10.1038/s41467-022-30985-2

The first photo-mediated process enabling the generation of halide radicals by halogen-atom transfer (XAT) is described. This novel reactivity pattern relies on the use of 1,2-dihaloethanes for the generation of unstable carbon radicals by XAT, which after β-scission, release halide radicals that have been used in selective hydrohalogenations of unsaturated hydrocarbons.

Abstract

The first photo-mediated process enabling the generation of halide radicals by Halogen-Atom Transfer (XAT) is described. Contrary to radical transformations involving XAT reactivity, which exploit stable carbon radicals, this unique approach uses 1,2-dihaloethanes for the generation of unstable carbon radicals by XAT. These transient radicals then undergo β-scission with release of ethylene and formation of more stable halide radicals which have been used in selective hydrohalogenations of a large number of unsaturated hydrocarbons, including Michael acceptors, unactivated alkenes and alkynes. This hydrohalogenation is tolerant of a broad range of functionalities and is believed to proceed through a radical-chain manifold that propagates by the use of silane derivatives.

An eco-friendly sulfide transfer protocol is explored under a reductive Pd-catalyzed, Ni-mediated condition. Both experimental and theoretical results support the sulfide transfer over the aryl transfer. Late-functionalization of drugs and semiconducting materials highlight the importance of the method.

Abstract

Aryl sulfides are in great demands in drugs and materials sciences. To avoid using nucleophilic and noxious thiols, many efforts have been focused on exploring novel sulfide resources. Herein, a reductive Pd-catalyzed, Ni-mediated method to synthesize aryl sulfides via a sulfide transfer reaction is developed. The utility and scope of this reaction is exemplified by various aryl electrophiles and aryl sulfides. Mechanistic studies reveal two competing catalytic cycles of sulfide transfer and aryl transfer in this reaction, where the former one is favored over the later one because of the large energy barrier difference during the transmetalation. Moreover, two important chemicals are late-stage functionalized by this method, exhibiting the potential applications in drugs and materials science.