过渡金属催化的有机硼试剂对醛酮的不对称加成研究进展

手性芳基醇是一类重要的合成砌块,广泛存在于许多生物活性分子以及天然产物中,因此,高效高选择性地构建该类化合物是有机化学家们一直关注的研究热点.金属试剂对羰基化合物的不对称加成是构建手性芳基醇的一个简单高效的方法,其中,有机硼试剂由于其方便易得、稳定、低毒、官能团耐受性好等优点而被广泛用于醛、酮的不对称加成反应中.本文综述了过去二十年来过渡金属催化的有机硼试剂对醛、酮的不对称加成反应研究进展,并介绍了一些方法在生物活性手性分子合成中的应用.     

Hypothetical <Emphasis Type="Italic">Hypercloso</Emphasis> Octahedral M<Subscript>4</Subscript>N<Subscript>2</Subscript> Clusters: A New Mode of Dinitrogen Coordination?

Density functional theory (DFT) calculations carried out on a series of [M₄(CO)₁₂N₂]²⁺ and M₄(CO)₁₂N₂ (M=Fe, Ru, Os) predict that the M₄N₂ square bipyramidal (octahedral) architecture should be stable for the particular electron count of 6 skeletal electron pairs (or 60 metal valence electrons). This octahedral architecture is electron-deficient with respect to the Wade-Mingos rules and exhibits a through-cage N–N bond of order one. Thus, these hypothetical clusters present a new coordination mode of dinitrogen.     

Superatomic properties of transition-metal-doped tetrahexahedral lithium clusters: TM@Li14

ABSTRACT

The lowest energy structure of Li₁₅ cluster is a capped double centred square antiprism sharing a square face. Interestingly, when a lithium atom is substituted by a transition-metal atom TM (TM?=?Sc, Ti, V, Y, Zr, Nb, Hf, Ta and W), the lowest energy structure is found to be cage-like with a D_6d symmetry, where the outer cage is composed by fourteen lithium atoms with an endohedral transition-metal atom. The unique structures are confirmed by CALYSPO structure prediction method code and density-functional theory calculations. Superatomic properties are confirmed in all the D_6d clusters. Energy calculations predict that they are very stable, and their stability is further enhanced by the large gaps of the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO gaps). Our findings offer potential applications in building blocks for assembling materials with superatoms.     

Pd-Catalyzed Asymmetric N-Allylation of Amino Acid Esters with Exceptional Levels of Catalyst Control: Stereo-Divergent Synthesis of ProM-15 and Related Bicyclic Dipeptide Mimetics

A general and powerful method for the stereo-controlled Pd-catalyzed N-allylation of amino acid esters is reported, as a previously largely unsolved synthetic challenge. Employing a new class of tartaric acid-derived C₂-symmetric chiral diphosphane ligands the developed asymmetric amination protocol allows the conversion of various amino acid esters to the N-allylated products with highest levels of enantio- or diastereoselectivity in a fully catalyst-controlled fashion and predictable configuration. Remarkably, the in situ generated catalysts also exhibit outstanding levels of activity (ligand acceleration). The usefulness of the method was demonstrated in the stereo-divergent synthesis of a set of new conformationally defined dipeptide mimetics, which represent new modular building blocks for the development of peptide-inspired bioactive compounds.     

Acid Fluorides in Transition‐Metal Catalysis: A Good Balance between Stability and Reactivity

Several recent reports outlined the singular reactivity of acid fluorides as excellent electrophiles in transition‐metal catalysis. These species undergo oxidative addition of the metal into the C?F bond; then, retention or release of the CO moiety can occur and be controlled by tuning the catalytic system and the reaction parameters. Acid fluorides, which can be derived from carboxylic acids, show good stability and high reactivity in a wide range of possible functionalizations with nucleophiles. Their use provides an interesting alternative to that of the parent carboxylic acid derivatives (acid chlorides, esters, amides, acids, or aldehydes).     

Catalyst Control in Switching the Site Selectivity of C−H Olefinations of 1,2-Dihydroquinolines: An Approach to Positional-Selective Functionalization of Quinolines

A unique approach to achieve site-selective C−H olefinations exclusively at the C-3- or C-8-positions in the quinoline framework has been developed by catalyst control. Distal C(3)−H functionalization is achieved by using palladium catalysis, whereas proximal C(8)−H functionalization is obtained by employing ruthenium catalysis. Switching the site selectivity within a single substrate directly indicates two diverse pathways, which are operating under the palladium- and ruthenium-catalyzed reaction conditions.     

The metallic nature of two-dimensional transition-metal dichalcogenides and MXenes

Metallic two-dimensional (2D) materials such as transition-metal dichalcogenides (TMDCs) and MXenes exhibit intriguing properties, including superconductivity, magnetism and electrocatalysis. Studies on the correlation between their nanoscale structures and properties can facilitate the development of photodetectors, supercapacitors, nanocatalysts, etc., but this topic has not been reviewed systematically. Here, we provide a comprehensive overview on the key factors that dictate the structures and properties of these 2D metals. We examine their phase transitions induced by structural or electronic modifications based on microscopic imaging, spectral characterization, and electrical measurements. From the perspective of surface and interface engineering, we elucidate the influences of lattice defects, dopants, and intercalated species between adjacent layers. Moreover, heterostructures involving highly conductive 2D component(s) are discussed, which may enable the observation of fascinating phenomena and/or synergistic effects due to the interlayer interactions. Finally, we provide insights into opportunities for new applications, e.g., radio-frequency antennas and electromagnetic interference shields. Feasible routes are also proposed to overcome the current challenges.     

Site-Selective Oxidation of Monolayered Liquid-Exfoliated WS2 by Shielding the Basal Plane through Adsorption of a Facial Amphiphile

In recent years, various functionalization strategies for transition-metal dichalcogenides have been explored to tailor the properties of materials and to provide anchor points for the fabrication of hybrid structures. Herein, new insights into the role of the surfactant in functionalization reactions are described. Using the spontaneous reaction of WS₂ with chloroauric acid as a model reaction, the regioselective formation of gold nanoparticles on WS₂ is shown to be heavily dependent on the surfactant employed. A simple model is developed to explain the role of the chosen surfactant in this heterogeneous functionalization reaction. The surfactant coverage is identified as the crucial element that governs the dominant reaction pathway and therefore can severely alter the reaction outcome. This study shows the general importance of the surfactant choice and how detrimental or beneficial a certain surfactant can be to the desired functionalization.     

邻苯二硫酚桥联双核双氮过渡金属配合物N-N键活化规律的理论研究

采用密度泛函理论方法研究了具有仿生固氮结构的两类化合物[Cp*Fe(μ-η²:η²-bdt)(μ-η¹:η¹-MeN＝NMe)FeCp*]以及[Cp*Fe(μ-SEt)₂(μ-η¹:η¹-MeN＝NMe)FeCp*]的90种不同结构, 调变过渡金属中心, 研究不同自旋态下(单重态和三重态)具有side-on或end-on配位键型的双核双氮过渡金属配合物, 基于计算结果分析了BDT(邻苯二硫酚)和乙基类型配体的不同过渡金属配合物活化双氮的程度. 研究结果表明, N-N键活化程度与配合物过渡金属中心所在周期存在密切关系, 更高周期对双氮的活化程度更高, 同周期金属过渡金属配合物对N-N键的活化程度从第四副族至第八族呈现折线型下降, 同时, 过渡金属中心的外层价电子数的奇偶性对双氮的活化程度具有一定影响. 此外, side-on键型对双氮的活化程度要高于end-on键型, 具有不同基团的同种骨架配体对N-N键的活化能力没有明显区别.