ACS Organic & Inorganic Au最新文献

An arylation strategy allowing the conversion of alkyl 2-((diphenoxyphosphoryl)oxy)-2-arylacetates to α,α-diaryl esters is reported. This transformation can be promoted by TfOH when the starting organic phosphates do not carry para-alkoxy groups on their aryl rings, but it does not require any additives when such groups are present. These alkyl 2-((diphenoxyphosphoryl)oxy)-2-arylacetates can be readily accessed from the insertion of diphenyl phosphate into aryldiazoacetates.

Topochemistry refers to a generic category of solid-state reactions in which precursors and products display strong filiation in their crystal structures. Various low-dimensional materials are subject to this stepwise structure transformation by accommodating guest atoms or molecules in between their 2D slabs or 1D chains loosely bound by van der Waals (vdW) interactions. Those processes are driven by redox reactions between guests and the host framework, where transition metal cations have been widely exploited as the redox center. Topochemistry coupled with this cationic redox not only enables technological applications such as Li-ion secondary batteries but also serves as a powerful tool for structural or electronic fine-tuning of layered transition metal compounds. Over recent years, we have been pursuing materials design beyond this cationic redox topochemistry that was mostly limited to 2D or 1D vdW systems. For this, we proposed new topochemical reactions of non-vdW compounds built of 2D arrays of anionic chalcogen dimers alternating with redox-inert host cationic layers. These chalcogen dimers were found to undergo redox reaction with external metal elements, triggering either (1) insertion of these metals to construct 2D metal chalcogenides or (2) deintercalation of the constituent chalcogen anions. As a whole, this topochemistry works like a “zipper”, where reductive cleavage of anionic chalcogen–chalcogen bonds opens up spaces in non-vdW materials, allowing the formation of novel layered structures. This Perspective briefly summarizes seminal examples of unique structure transformations achieved by anionic redox topochemistry as well as challenges on their syntheses and characterizations.

Since the discovery of decamethylsilicocene over three decades ago, chemists have successfully isolated a variety of divalent silicon compounds by orchestrating steric and electronic effects to their advantage. Two broad strategies of electronic stabilization appear to have been widely deployed, namely, π-conjugation as in diaminosilylenes and π-complexation as in decamethylsilicocene and silapyramidanes. Herein, we attempted to identify quantitative metrics for the electronic stabilization of silylenes. Singlet–triplet gaps and electron affinities, both physical observables, proved useful in this regard. Thus, the most stable silylenes exhibit unusually large singlet–triplet gaps and very low or negative gas-phase electron affinities. Both metrics signify low electrophilicity, i.e., a low susceptibility to nucleophilic attack. The chemical significance of the ionization potential associated with the Si-based lone pair, on the other hand, remains unclear.

Hexavalent chromium is a contaminant of concern and is found in drinking water supplies. Electrochemical methods are well-suited to accomplish the reduction of toxic Cr(VI) to Cr(III). However, high overpotentials and plating of Cr(III) products on electrodes have stymied the development of efficacious purification methods. The Cr(VI) reduction reaction necessitates the transfer of multiple protons and electrons, which is accompanied by a high kinetic barrier. Following recent advances in the electrocatalytic energy storage community, we report that the use of [Fe(CN)₆]^3– as a small molecular electrocatalyst not only diminishes the overpotential for Cr(VI) reduction on carbon electrodes by 0.575 V, but also prevents electrode fouling by mediating solution-phase homogeneous electron transfers.

Phosphinooxazoline (PHOX) ligands have been used to control the regio- and enantioselectivity in a wide variety of metal-catalyzed reactions. Despite their widespread use, PHOX ligands have never been studied in metal-aryne complexes. Herein we report the first example of a PHOX-Ni aryne complex. As demonstrated in other systems, the differentiated P versus N donors and different steric environments of the unsymmetric ligand are able to induce regiocontrol. A 81:19 mixture of o-methoxy substituted aryne complexes is observed. Single-crystal X-ray crystallographic analysis, UV/vis spectroscopy, and cyclic voltammetry are used to gain further insight into the molecular and electronic structure of these complexes. Lastly, a methylation/deuteration sequence shows retention of the PHOX ligand-induced regiocontrol in the difunctionalized products and that the regiospecificity of these difunctionalizations is due to the trans influence of the P donor.

Radical reactions have recently experienced a resurgence in organic chemistry after many decades of being considered to be too unselective to offer a viable solution for complex synthetic problems. Radical intermediates often have a number of different reaction pathways available to them that are all associated with insubstantial reaction barriers so that reaction outcomes can be controlled by proximity and dynamics. Cage effects consist of the effect of the surrounding medium, such as the solvent or the enzyme pocket, on the movement of radical intermediates and the medium’s resulting influence over reaction outcomes and selectivity. Cage effects substantially affect the outcome of all transformations in condensed phases, which feature the intermediacy of radical pairs, and a suitable choice of the cage should thus constitute a key optimization parameter for radical reactions. This Perspective provides an overview of key aspects of the cage effect that can be of importance in synthetic chemistry and highlights its role in a number of recently reported transformations that forge C–X bonds via the intermediacy of radicals.

Pyridine is a ubiquitous building block for the design of very diverse ligand platforms, many of which have become indispensable for catalytic transformations. Nevertheless, the isosteric pyrazine, pyrimidine, and triazine congeners have enjoyed thus far a less privileged role in ligand design. In this review, several applications of such fragments in the design of new catalysts are presented. In a significant number of cases described, diazine- and triazine-based ligands either outperform their pyridine congeners or offer alternative catalytic pathways which enable new reactivities. The potential opportunities unlocked by using these building blocks in ligand design are discussed, and the origin of the enhanced catalytic activity is highlighted where mechanistic studies are available.

A distinguished triplet splitting pattern for the ¹⁴N–¹H couplings in the proton signals of a series of protonated nitrogen bases─aliphatic and aromatic amines, as well as pyridines─with the weakly coordinating tetrakis(pentafluorophenyl)borate anion, [B(C₆F₅)₄]⁻, is observed for the first time in nonaqueous media at room temperature. The effects of ion pairing, solvent parameters, and correlation between the δ_H, ¹J_NH, and pK_a values are reported.

Total synthesis is a field in constant progress. Its practitioners aim to develop ideal synthetic strategies to build complex molecules. As such, they are both a driving force and a showcase of the progress of organic synthesis. In this Perspective, we discuss recent notable total syntheses. The syntheses selected herein are classified according to the key strategic considerations for each approach.