Phosphine-functionalized dendrimers for transition-metal catalysis

Dendrimers are well-defined hyperbranched macromolecules with characteristic globular structures for the larger systems, of which their use has been explored for various applications including catalysis. Dendritic catalysts potentially combine the advantages of both homogeneous and heterogeneous catalysis since the soluble dendritic catalyst can be separated from the product-stream by nano-filtration. In addition, dendritic effects on transition-metal catalysis can be expected, depending on the position of the catalytic site(s) as well as the spatial separation of the catalysts within the dendritic framework. We have prepared both core- and periphery-functionalized dendritic catalysts that are sufficiently large to enable separation by nano-filtration techniques. Here we review our findings using these promising novel transition metal-functionalized dendrimers as catalysts in several reactions. To cite this article: J.N.H. Reek, C. R. Chimie 6 (2003).     

Synthesis of Dendrimer-supported Chiral Bis(oxazoline) Ligands and Their Applications in Aldol Reaction via Aqueous Media

Chiral bis(oxazoline) ligands have been applied in many enatioselective reactions. Recently, studies of the immobilization of bis(oxazoline) on both soluble and insoluble supports have been of great interest. Among the different methods to anchor the homogeneous catalysts, a soluble, polymer-supported catalyst usually achieves higher stereoselectivity and activity because the catalysis can be separated and recycled via simple methods such as solvent precipitation. Dendrimers are highly branche…     

手性树状分子膦配体在不对称催化氢化中的应用

树状大分子作为一类组成精确的超支化结构大分子,近十多年来引起了科学家们的广泛关注.作为一类新型可溶性载体应用于均相催化剂,尤其是手性均相催化剂的负载化研究是树状大分子的重要应用领域之一.本文主要介绍了手性树状大分子膦配体,包括膦配体位于树状分子核心、末端和表面的几种类型,重点对它们与金属配合物形成的催化剂在不对称催化氢化反应中的应用研究进行总结,同时对负载催化剂的分离与回收、树状分子载体的结构和体积对催化剂性能的影响进行了讨论.     

Effect of guest molecule flexibility in access to dendritic interiors

[structure: see text] Dendrimers are attractive scaffolds for catalysis, since catalytic sites can be isolated and the catalysts are recoverable and reusable. Herein, we show that conformationally constrained molecules have better access to dendritic cores compared to the more flexible counterparts. The results reported here should have implications in utilizing dendrimers as scaffolds for artificial selectivity in catalysis.     

Supramolecular catalysts by encapsulating palladium complexes within dendrimers

Dendrimers are well-defined and highly branched macromolecules. By utilizing their capsular architectures, dendrimers encapsulating various catalytically active species can be prepared, which often bring about unique catalysis. Treatment of the alkylated PPI dendrimer with 4-diphenylphosphinobenzoic acid and [PdCl(C3H5)]2 afforded the dendrimer-encapsulated Pd complex using ionic interactions. The dendrimers encapsulating Pd complexes acted as unique supramolecular catalysts for the Heck reaction and allylic amination. The specific nanoenvironment created by the dense amino groups inside the dendrimers can provide high catalytic activity and stability for the Pd complexes. Facile recovery of the dendritic catalysts could be achieved by thermomorphic systems.     

Frustrated Lewis Pairs in Heterogeneous Catalysis: Theoretical Insights

Frustrated Lewis pair (FLP) catalysts have attracted much recent interest because of their exceptional ability to activate small molecules in homogeneous catalysis. In the past ten years, this unique catalysis concept has been extended to heterogeneous catalysis, with much success. Herein, we review the recent theoretical advances in understanding FLP-based heterogeneous catalysis in several applications, including metal oxides, functionalized surfaces, and two-dimensional materials. A better understanding of the details of the catalytic mechanism can help in the experimental design of novel heterogeneous FLP catalysts.     

Dendrimeric phosphines in asymmetric catalysis

Dendrimers are hyperbranched nanosized and precisely defined molecules, attracting increasing attention each year due to their numerous properties in catalysis, materials science, and biology. This tutorial review concerns the use of dendrimers as catalysts and focuses more precisely on their properties as enantioselective catalysts. Emphasis is put on chiral phosphine complexes constituting the core or the end groups of various types of dendrimers. The effect of the location of the catalytic entities, the effect of the size (generation) and the nature of the dendritic skeleton on the enantiomeric excesses are discussed.     

Advancing homogeneous catalysis for parahydrogen-derived hyperpolarisation and its NMR applications

Parahydrogen-induced polarisation (PHIP) is a nuclear spin hyperpolarisation technique employed to enhance NMR signals for a wide range of molecules. This is achieved by exploiting the chemical reactions of parahydrogen (para-H₂), the spin-0 isomer of H₂. These reactions break the molecular symmetry of para-H₂ in a way that can produce dramatically enhanced NMR signals for reaction products, and are usually catalysed by a transition metal complex. In this review, we discuss recent advances in novel homogeneous catalysts that can produce hyperpolarised products upon reaction with para-H₂. We also discuss hyperpolarisation attained in reversible reactions (termed signal amplification by reversible exchange, SABRE) and focus on catalyst developments in recent years that have allowed hyperpolarisation of a wider range of target molecules. In particular, recent examples of novel ruthenium catalysts for trans and geminal hydrogenation, metal-free catalysts, iridium sulfoxide-containing SABRE systems, and cobalt complexes for PHIP and SABRE are reviewed. Advances in this catalysis have expanded the types of molecules amenable to hyperpolarisation using PHIP and SABRE, and their applications in NMR reaction monitoring, mechanistic elucidation, biomedical imaging, and many other areas, are increasing.

We detail recent advances in homogeneous catalysts for deriving enhanced NMR signals using parahydrogen. Growing applications of this catalysis in mechanistic elucidations, mixture analysis, and biomedical imaging are also discussed.     

Water-Soluble Ligands,Metal Complexes,and Catalysts: Synergism of Homogeneous and Heterogeneous Catalysis

Rapid developments in the field of catalysis are leading to an increased demand for tailor-made catalysts. Water-soluble complex catalysts, which are being intensively investigated at the present time, combine the advantages of homogeneous and heterogeneous catalysis: simple and complete separation of the product from the catalyst, high activity, and high selectivity. From the large number of available water-soluble ligands, the appropriate catalysts can be developed for many reactions. The industrial applications in the fields of hydrogenation and hydroformylation have already indicated the wide scope of this type of catalyst. In addition, the annual production of 300 000 tons of butyraldehyde through application of water-soluble rhodium complexes at Hoechst AG in Oberhausen, Germany, has demonstrated the industrial importance of the concept of complex-catalyzed reactions in aqueous two-phase systems. The efficient operation of catalytic processes increasingly requires the loss-free recycling of the noble metal catalyst, and this can be simply and economically realized in two-phase systems. Special applications in biochemical problems open up developments in the field of water-soluble transition metal complexes that far transcend the familiar kinds of homogeneous catalysis. In the near future, the investigation and application of metal complex catalysts that are compatible with the physiological, cheap, and environmentally friendly solvent, water, is likely to become a high priority in catalysis research.     

Catalysis inside dendrimers

Catalytic sites can be placed at the core, at interior positions or at the periphery of a dendrimer. There are many examples of the use of peripherally functionalized dendrimers in catalysis and this subject has been thoroughly reviewed in the recent literature. This review is concerned only with dendrimer based catalysis involving catalytic sites at the core of a dendrimer and within the interior voids. In covering the significant achievements in this area, we have concentrated on examples that highlight key features with respect to positive and/or negative catalytic activity.     

Nanofabrication with metal containing dendrimers

Dendrimers are versatile building blocks for "bottom-up" nanofabrication because they combine molecular structure and nanoscale dimensions. Moreover, dendrimers can be functionalized at their numerous peripheral end groups, in their core, along their branches, and in the voids of their interior. This Frontier highlights the potential of metal containing dendrimers for nanofabrication.     

Potential Utilization of Metal–Organic Frameworks in Heterogeneous Catalysis: A Case Study of Hydrogen‐Bond Donating and Single‐Site Catalysis

Crystalline solid materials are platforms for the development of effective catalysts and have shown vast benefits at the frontiers between homogeneous and heterogeneous catalysts. Typically, these crystalline solid catalysts outperformed their homogeneous analogs due to their high stability, selectivity, better catalytic activity, reusability and recyclability in catalysis applications. This point of view, comprising significant features of a new class of porous crystalline materials termed as metal‐organic frameworks (MOFs) engendered the attractive pathway to synthesize functionalized heterogeneous MOF catalysts. The present review includes the recent research progress in developing both hydrogen‐bond donating (HBD) MOF catalysts and MOF‐supported single‐site catalysts (MSSCs). The first part deals with the novel designs of urea‐, thiourea‐ and squaramide‐containing MOF catalysts and study of their crucial role in HBD catalysis. In the second part, we discuss the important classification of MSSCs with existing examples and their use in desired catalytic reactions. In addition, we describe the relative catalytic efficiency of these MSSCs with their homogeneous and similarly reported analogs. The precise knowledge of discussed heterogeneous MOF catalysts in this review may open the door for new research advances in the field of MOF catalysis.     

Recyclable Catalysts for Alkyne Functionalization

In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis.     

Single-atom catalysis for organic reactions

Metal-based catalysis, including homogeneous and heterogeneous catalysis, plays a significant role in the modern chemical industry. Heterogeneous catalysis is widely used due to the high efficiency, easy catalyst separation and recycling. However, the metal-utilization efficiency for conventional heterogeneous catalysts needs further improvement compared to homogeneous catalyst. To tackle this, the pursing of heterogenizing homogeneous catalysts has always been attractive but challenging. As a recently emerging class of catalytic material, single-atom catalysts (SACs) are expected to bridge homogeneous and heterogeneous catalytic process in organic reactions and have arguably become the most active new frontier in catalysis field. In this review, a brief introduction and development history of single-atom catalysis and SACs involved organic reactions are documented. In addition, recent advances in SACs and their practical applications in organic reactions such as oxidation, reduction, addition, coupling reaction, and other organic reactions are thoroughly reviewed. To understand structure-property relationships of single-atom catalysis in organic reactions, active sites or coordination structure, metal atom-utilization efficiency (e.g., turnover frequency, TOF calculated based on active metal) and catalytic performance (e.g., conversion and selectivity) of SACs are comprehensively summarized. Furthermore, the application limitations, development trends, future challenges and perspective of SAC for organic reaction are discussed.     

树枝状大分子催化剂的研究进展

回顾了功能树枝状大分子在催化作用领域的研究成就，重点就活性中心在核附 近的树枝状大分子和表面含催化官能团的树枝状大分子的结构与催化作用进行了讨 论，并对其应用前景进行了展望。     

A Review of Surface Functionalized Amine Terminated Dendrimers for Application in Biological and Molecular Sensing

Dendrimers are three dimensional nanosized synthetic molecules that have internal cavities and numerous surface groups. In recent times they have received increased attention in sensing applications. For dendrimers to be used as sensors, they most commonly require functionalization at their surface. This is because the surface is generally the first point of contact between the dendrimer and the outside world, hence surface functionalization serves to selectively home in on the target analyte. Further, sensor signals may be transmitted through surface functionalities e.g. fluorochromic molecules. It is therefore important to document surface functionalization approaches. Dendrimers with amine surface groups have the advantage of being able to be conjugated to other molecules via an amide linkage, which is one of the most fundamental and widespread chemical bonds in nature. In this paper we demonstrate the properties of dendrimers that make them so applicable to sensing. We review several methods for functionalizing dendrimers via an amide linkage, as well as present a review of surface functionalized polyamidoamine, polyamine, and polypeptide dendrimers that have been employed for biological, chemical and molecular sensing.     

分子筛膜包覆型催化剂的制备和应用

均匀、连续、致密分子筛膜的合成和应用受到广泛关注。利用分子筛膜具有的筛分和催化作用,在传统颗粒催化剂或载体表面包覆分子筛膜形成复合型催化剂,可以实现膜基分离和催化过程的耦合,增加反应物选择性,提高目标产物收率。本文综述了近年来在不同类型颗粒催化剂或载体表面合成分子筛膜的制备方法,描述了分子筛膜包覆型复合催化剂用于不同催化反应体系的研究结果。同时,在归纳和总结已有研究成果基础上展望了分子筛膜包覆型催化剂的研究发展趋势。     

光捕获树枝形聚合物体系能量传递和电子转移研究进展

树枝形聚合物是一类围绕着中心核,外围链段和官能团呈指数增长的支化高分子.合成方法的发展使发色团可被精确地置于树枝形聚合物的核心、外围甚至支化节点处.树枝形聚合物的特殊结构使其作为模拟光捕获体系被广泛研究.光诱导电子转移和能量传递是光合作用中的重要过程,研究树枝形聚合物体系中的电子转移和能量传递对未来树枝形聚合物在光电器件中的应用有着重要意义.本文综述了近年来光捕获树枝形聚合物体系的研究进展,并重点介绍光捕获树枝形聚合物体系中的能量传递和电子转移过程研究.     

液晶性树状高分子

对树状高分子进行功能化,使之成为具有特定性能的新型材料是目前很热门的课题,树状液晶就是其中之一.树状高分子长径比很小,似乎难以形成液晶态,但人们已发现多种树状液晶分子,几乎囊括了所有在其他高分子中出现过的液晶相.本文按液晶相分类,介绍树状液晶高分子的研究进展.     

多氮螯合配位后过渡金属络合物烯烃聚合催化剂

A2二亚胺镍、钯络合物和吡啶二亚胺铁、钴络合物是近几年来发现的新一代烯烃均相聚合后过渡金属催化剂。这类催化剂具有活性高、选择性易调变、聚合物性质可控制的特点, 尤其是对官能团中的杂原子的稳定性方面优于前过渡金属催化剂。本文将近年来的有关报道归纳为4 个方面进行评述: 络合物的合成和结构; 配体结构因素对络合物催化性能的影响; 催化烯烃高聚、齐聚和共聚以及催化反应机理。