Stereoselective single (copper) or double (platinum) boronation of alkynes catalyzed by magnesia-supported copper oxide or platinum nanoparticles

Optimization of Metal-Support Cooperation for Boosting the Performance of Supported Gold Catalysts for the Borylation of C-O and C-N Bonds

The cooperation of multiple catalytic components is a powerful tool for intermolecular bond formation, specifically, cross-coupling reactions. Supported metal catalysts have interfacial sites between metal nanoparticles and their supports where multiple catalytic elements can work in cooperation to efficiently promote intermolecular reactions. Hence, the establishment of novel guidelines for designing active interfacial sites of supported metal catalysts is indispensable for heterogeneous catalysts which enable efficient cross-coupling reactions. In this article, we performed kinetic and theoretical studies to elucidate the effect of metal-support cooperation for the borylation of C-O bonds by supported gold catalysts and revealed that the Lewis acid density of the supports determined the number of active sites at which metal nanoparticles (NPs) and Lewis acid at the surface of the supports work in cooperation. Furthermore, DFT calculations revealed that strong adsorption of diborons at the interface between Au NPs and supports and a decrease in the LUMO level of adsorbed diboron were responsible for efficient C-O bond borylation. Supported Au catalysts with the optimized metal-metal oxide cooperation sites, namely, Au/α-Fe2O3 catalyst, showed excellent activity for C-O bond borylation, and also enabled the synthesis of organoboron compounds by using continuous-flow reactions. Furthermore, Au/α-Fe2O3 showed high activity for direct C-N bond borylation without the transformation of amino groups to ammonium cations. The results described herein suggest that the optimization of metal-metal oxide cooperation is beneficial for taking full advantage of the potential performance of supported metal catalysts for intermolecular reactions.

Heterovalent Metal Pair Sites on Metal-Organic Framework Ordered Macropores for Multimolecular Co-Activation

The precise design of catalytic metal centers with multiple chemical states to facilitate sophisticated reactions involving multimolecular activation is highly desirable but challenging. Herein, we report an ordered macroporous catalyst with heterovalent metal pair (HMP) sites comprising CuII-CuI on the basis of a microporous metal-organic framework (MOF) system. This macroporous HMP catalyst with proximity heterovalent dual copper sites, whose distance is controlled to ∼2.6 Å, on macropore surface exhibits a co-activation behavior of ethanol at CuII and alkyne at CuI, and avoids microporous restriction, thereby promoting additive-free alkyne hydroboration reaction. The desired yield enhances dramatically compared with the pristine MOF and ordered macroporous MOF both with solely isovalent CuII-CuII sites. Density functional theory calculations reveal that the Cu-HMP sites can stabilize the Bpin-CuII-CuI-alkyne intermediate and facilitate C-B bond formation, resulting in a smooth alkyne hydroboration process. This work provides new perspectives to design multimolecular activation catalysts for sophisticated matter transformations.

Stabilizing Single-Atomic Pt by Forming PtFe Bonds for Efficient Diboration of Alkynes

Precisely tailoring the oxidation state of single-atomic metal in heterogeneous catalysis is an efficient way to stabilize the single-atomic site and promote their activity, but realizing this approach remains a grand challenge to date. Herein, a class of stable single-atomic catalysts with well-tuned oxidation state of Pt by forming PtFe atomic bonds is reported, which are supported by defective Fe₂ O₃  nanosheets on reduced graphene oxide (PFARFNs). These as-synthesized materials can greatly enhance the catalytic activity, stability, and selectivity for the diboration of alkynes. The PFARFNs exhibit high conversion of 99% at 100 °C with an outstanding turnover frequency (TOF) of 545 h^-1 , and a relatively high conversion of 58% at room temperature (25 °C) with a TOF of 310 h^-1 , which has been hardly achieved previously. Through both experimental and theoretical investigation, it is demonstrated that the fast electron transfer from Fe to Pt in Fe-Pt-O atomic sites in PFARFNs can not only stabilize the single-atomic Pt, but also significantly improve their catalytic activity.

Solvent-free hydroboration of alkenes and alkynes catalyzed by rhodium-ruthenium nanoparticles on carbon nanotubes

A heterogeneous catalyst consisting of bimetallic rhodium-ruthenium particles immobilized on carbon nanotubes was used in the hydroboration reaction and proved highly effective for a variety of alkenes and alkynes. The reactions were carried out with low catalytic loadings (0.04 mol%), under solvent-free conditions, and at room temperature. In addition, to demonstrate its recyclability, the catalyst was recovered by a simple centrifugation process and reused over 5 consecutive cycles without losing any activity.

A copper nitride nanocube catalyst for highly efficient hydroboration of alkynes

The hydroboration of alkynes with bis(pinacolato)diboron is a useful method for the synthesis of vinyl boronate esters, which are essential intermediates in organic syntheses. Copper catalysts have been used extensively in these reactions. However, previously reported Cu-catalyst systems inevitably require additives and elevated temperatures. Herein, we report, for the first time, a simple and efficient hydroboration of alkynes under additive-free and mild reaction conditions (i.e., at a temperature of 30 °C) using a copper nitride nanocube (Cu₃N NC) catalyst. A wide range of alkynes can be transformed into their corresponding boronate esters. Cu₃N NCs are also applicable in the hydroboration of alkynes with tetrahydroxydiboron to synthesize vinyl boronic acids. Moreover, the Cu₃N NCs were easily separated by simple filtration and could be reused several times without any loss of their original activity. Hence, these highly active and reusable Cu₃N NC catalysts offer an environmentally friendly route for the efficient production of vinyl boronates.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Ultrathin Metal-Organic Framework Nanosheets Exhibiting Exceptional Catalytic Activity

Two-dimensional (2D) metal-organic framework nanosheets (MONs) or membranes are classes of periodic, crystalline polymeric materials that may show unprecedented physicochemical properties due to their modular structures, high surface areas, and high aspect ratios. Yet preparing 2D MONs from multiple components and two different types of polymerization reaction remains challenging and less explored. Here, we report the synthesis of MOF films via interfacial polymerization, which involves three active monomers for simultaneous polycondensation and polycoordination taking place in a confined interface. The well-defined lamellar structure of the MOF films allowed feasible and scalable exfoliation to produce free-standing 2D MONs with high aspect ratio up to 2000:1 and ultrathin thickness (∼1.7 nm). The pore structure was revealed by high-resolution TEM images with near-atomic precision. The imide-linkage of MONs provided superior thermal (up to 530 °C) and good chemical stability in the pH range from 3 to 12. More importantly, the MONs exhibited exceptional catalytic activity and superior reusability for the hydroboration reactions of alkynes, in which the turnover frequency (TOF) reached 41734 h^-1, which is 2-4 orders of magnitude greater than that reported for homogeneous and heterogeneous catalysts.

Hydroboration and Diboration of Internal Alkynes under Iridium Catalysis

Here we demonstrate the feasibility and efficiency of simple iridium-based catalytic systems in the synthesis of multisubstituted alkenyl boronates from internal alkynes with high selectivities. A variety of alkynes were smoothly decorated with HBpin under a mild [Ir(cod)Cl]₂/dppm/acetone condition to afford trisubstituted alkenyl boronic esters with up to >99:1 regioselectivity. The diboration reaction could effectively occur in the presence of [Ir(cod)Cl]₂/DCM. Plausible mechanisms were provided to illustrate these two catalytic processes, in which the intrinsic functional group of the alkyne was supposed to be important in facilitating these reactions as well as the regioselectivity.

Regio- and Stereoselective Syn-Boronation of Terminal Alkynes Catalyzed by Copper Nanospheres on Graphene Nanosheets

Evenly distributed copper nanospheres on reduced graphene oxide were prepared and showed high heterogeneous catalytic activity in converting varying terminal alkynes into (E)-β-styrene boronate esters. The excellent catalytic performance was achieved through the synergistic catalysis between Cu nanospheres and rGO. This work not only is a supplement for preparing (E)-β-styrene boronate esters but also provides a way for the rational designing of high-performance graphene-based catalysts. Meanwhile, the advancement of graphene-based nanomaterials will be motivated to promote their applications in the development of green catalytic chemistry.

Fabricating polyoxometalates-stabilized single-atom site catalysts in confined space with enhanced activity for alkynes diboration

Effecting the synergistic function of single metal atom sites and their supports is of great importance to achieve high-performance catalysts. Herein, we successfully fabricate polyoxometalates (POMs)-stabilized atomically dispersed platinum sites by employing three-dimensional metal-organic frameworks (MOFs) as the finite spatial skeleton to govern the accessible quantity, spatial dispersion, and mobility of metal precursors around each POM unit. The isolated single platinum atoms (Pt₁) are steadily anchored in the square-planar sites on the surface of monodispersed Keggin-type phosphomolybdic acid (PMo) in the cavities of various MOFs, including MIL-101, HKUST-1, and ZIF-67. In contrast, either the absence of POMs or MOFs yielded only platinum nanoparticles. Pt₁-PMo@MIL-101 are seven times more active than the corresponding nanoparticles in the diboration of phenylacetylene, which can be attributed to the synergistic effect of the preconcentration of organic reaction substrates by porous MOFs skeleton and the decreased desorption energy of products on isolated Pt atom sites.

It is of great significance to exert the synergistic effect between single atom and support. Here, the authors prepare polyoxometalates-stabilized single-atom site catalysts in confined space with enhanced activity for alkynes diboration.

α,β-Enone Borylation by Bis(Pinacolato)Diboron Catalyzed by Cu3(BTC)2 Using Cesium Carbonate as a Base

Cu₃(BTC)₂ (BTC: 1,3,5-benzenetricarboxylate) as a heterogeneous catalyst in the presence of cesium carbonate as a base is reported for the borylation of α,β-conjugated enones by bis(pinacolato)diboron (B₂pin₂). According to the hot-filtration test, Cu₃(BTC)₂ is acting as a heterogeneous catalyst. Further, Cu₃(BTC)₂ exhibits a wide substrate scope and can be reused in consecutive runs, maintaining a crystal structure as evidenced by powder X-ray diffraction (XRD). A suitable mechanism is also proposed for this transformation using Cu₃(BTC)₂ as catalyst.

Atomic-dispersed platinum anchored on porous alumina sheets as an efficient catalyst for diboration of alkynes

An atomic-dispersed Pt catalyst (Pt/dp-Al₂O₃) was fabricated via a simple wet impregnation method and demonstrated to be highly active and stable for the diboration of phenylacetylene, which is due to Pt/dp-Al₂O₃ providing unique catalytic sites.

Hydroboration of internal alkynes catalyzed by FeH(CO)(NO)(PPh3)2: a case of boron-source controlled regioselectivity

The Fe–H complex FeH(CO)(NO)(Ph₃P)₂ catalyzes the stereoselective, regiodivergent hydroboration of internal alkynes using either pinacolborane (HBpin) or bis(pinacolato)diboron (B₂pin₂) as a boron source.

Catalytic Performance of Nanoporous Metal Skeleton Catalysts for Molecular Transformations

Nanoporous metal (MNPore) skeleton catalysts have attracted increasing attention in the field of green and sustainable heterogeneous catalysis owing to their unique three-dimensional nanopore structural features. In general, MNPores are fabricated through chemical or electrochemical corrosive dealloying of monolithic alloys. The dealloying process produces various MNPores with an open nanoporous network structure by formation of concave and convex hyperboloid-like ligaments. The large surface-to-volume ratio compared to bulk metals and high density of steps and kinks on ligaments of the unsupported MNPores make them promising heterogeneous catalyst candidates for highly active and selective molecular transformations. In this context, a variety of heterogeneous catalytic reactions using MNPores as nanocatalysts under gas- and liquid-phase conditions were developed over the last decade. In addition, the bulk metallic shape and mechanistic rigidity of the MNPore catalysts make the processes of catalyst recovery and reuse more facile and greener. This Minireview mainly focuses on the catalytic performance of nanoporous Au, Pd, Cu, and AuPd with respect to the achievements on catalytic applications in various molecular transformations.

Copper-Catalyzed Trifunctionalization of Alkynes: Rapid Formation of Oxindoles Bearing Geminal Diboronates

A copper-catalyzed trifunctionalization of alkynes that provides rapid access to oxindoles bearing a geminal diboronate side chain, highlighted by the simultaneous formation of one C-C bond and two C-B bonds, is reported. This new reaction features simple reaction conditions (ligand-free catalysis), a general substrate scope, and excellent chemoselectivity. Mechanistic study revealed a reaction sequence constituted by, in the order, borylation, intramolecular cross-coupling, hydroboration, which has been rarely documented.

Copper-boryl mediated organic synthesis

Organoboron compounds are valuable synthetic intermediates that find application in a diverse variety of processes including both C-X and C-C bond-forming transformations. This has been achieved by using a variety of boron derivatives. Of these, boronate esters are probably the most versatile and, reflecting this, methods for the generation of boronate esters are of considerable current interest. Given the mild reaction conditions, good functional group tolerance, and low cost of the metal catalyst, the use of copper-boryl reagents is particularly attractive. In this review, methodologies in copper-boryl chemistry are discussed and the many different transformations possible are surveyed.

Cation vacancy stabilization of single-atomic-site Pt1/Ni(OH)x catalyst for diboration of alkynes and alkenes

Development of single-atomic-site catalysts with high metal loading is highly desirable but proved to be very challenging. Although utilizing defects on supports to stabilize independent metal atoms has become a powerful method to fabricate single-atomic-site catalysts, little attention has been devoted to cation vacancy defects. Here we report a nickel hydroxide nanoboard with abundant Ni²⁺ vacancy defects serving as the practical support to achieve a single-atomic-site Pt catalyst (Pt₁/Ni(OH)_x) containing Pt up to 2.3 wt% just by a simple wet impregnation method. The Ni²⁺ vacancies are found to have strong stabilizing effect of single-atomic Pt species, which is determined by X-ray absorption spectrometry analyses and density functional theory calculations. This Pt₁/Ni(OH)_x catalyst shows a high catalytic efficiency in diboration of a variety of alkynes and alkenes, yielding an overall turnover frequency value upon reaction completion for phenylacetylene of ~3000 h^-1, which is much higher than other reported heterogeneous catalysts.

Efficient heterogeneous hydroboration of alkynes: enhancing the catalytic activity by Cu(0) incorporated CuFe2O4 nanoparticles

Nano-copper ferrite supported Cu catalysts are active for hydroboration of alkynes to vinylboronates.

A nano-catalytic approach for C–B bond formation reactions

Nanoparticle-catalysed borylation is one of the most convenient methods for the synthesis of organoboranes to overcome the confines of homogeneous catalysis such as recyclability and heavy metal contamination.

Substrate-Assisted, Transition-Metal-Free Diboration of Alkynamides with Mixed Diboron: Regio- and Stereoselective Access to trans-1,2-Vinyldiboronates

A substrate-assisted diboration of alkynamides using the unsymmetrical pinacolato-1,8-diaminonaphthalenato diboron (pinBBdan) is described. The transition-metal-free reaction proceeds in a regio- and stereoselective fashion to exclusively afford trans-vinyldiboronates in good to excellent yields. Notably, Bdan and Bpin are installed on the α- and β-carbon atoms, respectively.

Transition-metal-free PhI(OAc)2-promoted highly selective hydroboration of terminal alkynes under air

A new transition-metal-free PhI(OAc)₂-promoted highly selective hydroboration of terminal alkynes with bis(pinacolato)diboron has been developed at room temperature under air.

Catalytic and catalyst-free diboration of alkynes

The present review provides a comprehensive summary of the catalytic and catalyst-free diboration of alkynes.