Catalytic hydrosilylation of olefins with organolanthanides: A DFT study. Part I: Hydrosilylation of propene by SiH4

Investigation of the catalytic hydrosilylation of propene by primary silane in the presence of Cp(2)SmH has been carried out using DFT calculations. Using SiH(4) as a model, it is shown that a catalytic cycle based on the hydride complex is unlikely. The activation of silane after insertion of propene is not competitive compared to the allylic activation of propene or the silyl formation. An alternative catalytic cycle, based on a silyl complex, is proposed. This alternative pathway accounts for the experimental observation. The allylic activation of propene is shown to be one of the main routes for the catalyst deactivation.     

Dual Catalysis Sees the Light: Combining Photoredox with Organo‐, Acid,and Transition‐Metal Catalysis

The photoredox activation of organic substrates with visible light is a powerful methodology that generates reactive radical species under very mild conditions. When combined with another catalytic process in a dual catalytic system, novel, visible‐light‐promoted transformations have been realized that do not proceed using either catalyst in isolation. In this minireview, the state of the art in organic reactions mediated by dual catalytic systems merging photoredox activation with organo‐, acid or metal catalysis is discussed.     

Catalytic coupling of haloolefins with anilides

A strategy in which C-H activation reactions promoted by Pd(II) have been combined with beta-heteroatom elimination to create a catalytic cycle achieving the arylation of haloacrylates is reported. The catalytic cycle can be subdivided into four parts: (1) C-H activation; (2) the functionalization step, migratory insertion of the olefin into a metal-carbon bond; (3) beta-heteroatom elimination; and (4) exchange of metal halide (if X = halogen) for a less coordinating anion. In this catalytic cycle, the oxidation state of the metal does not change, and an oxidant is not required. The method is more functional group tolerant compared with the existing alkene-arene coupling methods based on electrophilic C-H activation.     

Rh-catalyzed decarbonylation of conjugated ynones via carbon–alkyne bond activation: reaction scope and mechanistic exploration via DFT calculations

In this full article, detailed development of a catalytic decarbonylation of conjugated monoynones to synthesize disubstituted alkynes is described. The reaction scope and limitation has been thoroughly investigated, and a broad range of functional groups including heterocycles were compatible under the catalytic conditions. Mechanistic exploration via DFT calculations has also been executed. Through the computational study, a proposed catalytic mechanism has been carefully evaluated. These efforts are expected to serve as an important exploratory study for developing catalytic alkyne-transfer reactions via carbon–alkyne bond activation.     

Kinetics and mechanism of oxidative polymerization of phenylenediamines

Kinetics of oxidative polymerization of three isomeric phenylenediamines in aqueous hydrochloric acid solutions initialed by ammonium persulfate has been studied, and kinetic parameters of non-catalytic and catalytic stages of polymerization have been determined. The observed effect of the isomeric substrates structure on the activation energy of the catalytic and non-catalytic stages has been explained.     

Review: active homogeneous reagents and catalysts in n-alkane activation

The development of selective, efficient, and direct routes for activation and functionalization of naturally abundant n-alkanes could lead to a new paradigm in materials and energy technologies. In this context, the use of homogeneous catalysts to functionalize C–H bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint. Despite the large body of work on stoichiometric C–H activation reactions produced over the last three decades, relatively few systems have been developed to allow catalytic functionalization of hydrocarbons. This review deals with homogeneous catalytic processes available in the literature for paraffin activation and functionalization. The key intermediates involved in catalytic systems are highlighted, providing important information in the design of new and efficient catalysts. Also, some of the key challenges and approaches to rational development of the next generation of organometallic catalysts will be highlighted.     

Thermal-catalytic degradation of polyethylene over silicoaluminophosphate molecular sieves—A thermogravimetric study

The present work is aimed at recycling plastic wastes economically and efficiently, for which pure high density polyethylene (HDPE) has been initially selected for the investigations. Thermogravimetric technique has been used to investigate, analyze and compare the thermal and catalytic degradation of HDPE. The catalytic degradation was investigated over the medium pore silicoaluminophosphate, SAPO-11 molecular sieve. The thermogravimetric evaluation was performed using 2–30 wt% catalyst, and the apparent activation energies for the thermal and catalytic polymer degradation were estimated using various iso-conversional methods. The apparent activation energy was found to be lower when SAPO-11 was used compared to the direct thermal degradation of HDPE. The activation energy and coke levels are comparable to the medium pore zeolite ZSM-5 and lower than the values obtained over large pore zeolites reported in literature.     

Catalytic activation through metal enolization of nucleophile precursors and synthetic applications to enantioselective Michael additions

Catalytic activation methods of nucleophile precursors recently developed in our research group were reviewed in this paper. These include (i) the catalytic double activation method of nucleophile precursors through enol formation and of electrophiles through coordination in alcohols; (ii) the double catalytic activation method by use of both catalytic amounts of chiral Lewis acid and external achiral amine; (iii) the catalytic activation method of nucleophile precursors with a chiral cationic Lewis acid in the presence of molecular sieves; and (iv) the single catalytic activation of nucleophile precursors through metal enolization in alcohol media.     

Remarkable binuclear Schiff-based complex catalyze the epoxidation of alkenes: effects of substituent group

A series of dimolybdenum metal catalysts with different ligand have been successfully synthesized and used to catalyze the epoxidation of alkenes to generate epoxides by using tert-butyl-hydroperoxide (TBHP) as oxidant. The reaction condition was optimized by the adjustment of some key parameters, such as, temperature, to target high catalytic performance. The oxidation of cyclooctene gave 95.00% conversion and almost 100.00% selectivity. Kinetic study of the oxidation of cyclooctene under different temperature was taken out, indicating the reaction have good catalytic performance. Furthermore, it is calculated from the Arrhenius equation that different functional groups affect the activation energy of the reaction. The electron donor group substituent on the liagnd increases the catalytic activity by reducing the activation energy, and vice versa. Finally, a possible catalytic mechanism has been proposed by measuring the electronic absorption spectrum of the reaction.     

Catalytic asymmetric addition of aldehydes to oxocarbenium ions: a dual catalytic system for the synthesis of chromenes

A synergistic catalytic system for the first asymmetric addition of aldehydes to in situ generated prochiral oxocarbenium ions has been developed. The dual catalytic protocol allows the simultaneous activation of both electrophile and nucleophile and provides access to a variety of valuable chiral 2H-chromenes with excellent enantioselectivities.     

Catalytic activity and complexation-iv 2,2'-Bipyridyl as activator for the catalytic ultramicro determination of silver

The activation of the catalytic persulphate oxidation of sulphanilic acid when the catalyst, silver(I), is suitably complexed, is discussed. 2,2'-Bipyridyl is proposed as activator as it accelerates the rate-determining step of the process-the oxidation of silver(I) to silver(II). The mechanism of activation is investigated and discussed in detail. On the basis of these investigations a catalytic method has been developed for the determination of silver(I), with a sensitivity of 4 x 10(-4)mug ml and +/-7.6% relative error.     

Transition metal-catalyzed carbon-carbon bond activation

This tutorial review deals with recent developments in the activation of C-C bonds in organic molecules that have been catalyzed by transition metal complexes. Many chemists have devised a variety of strategies for C-C bond activation and significant progress has been made in this field over the past few decades. However, there remain only a few examples of the catalytic activation of C-C bonds, in spite of the potential use in organic synthesis, and most of the previously published reviews have dwelt mainly on the stoichiometric reactions. Consequently, this review will focus mainly on the catalytic reaction of C-C bond cleavage by homogeneous transition metal catalysts. The contents include cleavage of C-C bonds in strained and unstrained molecules, and cleavage of multiple C-C bonds such as C[triple bond]C triple bonds in alkynes. Multiple bond metathesis and heterogeneous systems are beyond the scope of this review, though they are also fascinating areas of C-C bond activation. In this review, the strategies and tactics for C-C bond activation will be explained.     

纳米金催化剂上CO低（常）温氧化的研究

金历来被认为是催化惰性的,但近年来有关金催化剂的研究与开发引起人们的兴趣与关注。负载纳米金催化剂显示了良好的催化性能,尤其对一氧化碳氧化反应,能够在低（常）温下将CO氧化为CO₂。和其他CO氧化催化剂相比,金催化剂具有高的催化活性、稳定性和抗潮湿的性能,预示着更加广泛的应用前景。本文从制备方法、载体的性质、微粒粒径的大小、预处理、活性机理和催化反应机理等方面进行综合与评述。     

Pentamethylcyclopentadienyl-ruthenium catalysts for regio- and enantioselective allylation of nucleophiles

Ruthenium(II) complexes containing the pentamethylcyclopentadienyl ligand efficiently perform the activation of allylic carbonates and halides to generate cationic and dicationic ruthenium(IV) complexes. This activation has been transferred as a key step to the catalytic allylation of nucleophiles. The structural and electronic properties of the allylic moieties lead to the regioselective formation of chiral products resulting from nucleophilic addition to their most substituted terminus. The catalytic activity of various Ru(Cp*) precatalysts in several allylic substitutions by C and O nucleophiles will be presented. The enantioselective version that has been demonstrated by using optically pure bisoxazoline ligands will also be discussed.     

Catalytic phosphorus(V)-mediated nucleophilic substitution reactions: development of a catalytic Appel reaction

Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates.     

Multiple active motifs grafted on cyclotriphosphazene core: a novel catalyst for the chemical activation of carbon dioxide

A novel catalyst having multiple triphenylphosphonium chloride motifs on a single cyclotriphosphazene molecule has been developed for the chemical activation of carbon dioxide for the production of propylene carbonate from carbon dioxide and propylene oxide. The unique structure and multiple catalytic sites on a single framework are the prime factors, resulted in the enhanced catalytic activity and afforded high product yield.     

Iron‐catalyzed C−H Activation

Transition‐metal‐catalyzed C–H activation and C–C formation have been receiving considerable attention because of their high atom economy and synthesis efficiency. Iron is widely used in catalytic reactions because it has the advantages of abundance, low cost, accessibility, and environmental friendliness. In recent years, research on the Fe‐catalyzed C–H activation of C–C formation has made considerable progress. This paper summarizes latest studies on iron‐catalyzed C–H activation, classifies the catalysts according to the different valence states of iron, and expounds the catalytic mechanism.     

催化反应中休眠期与诱导期之区别

许多化学反应中都存在一个被定义为"诱导期"的起始反应速率较低的阶段，例如一些自由基反应、放热反应和催化反应。与之相比，在极少数的催化反应中研究者观察到一个反应速率始终为零的特殊阶段，在这个阶段之后反应自发开始。这两种阶段形成的原因与反应的机理尤其是催化剂的活化和失活有关。然而，这两个具有明显不同特征的阶段往往被混淆。本文通过所选取的一些代表性的催化反应分别介绍了"诱导期"和"休眠期"的动力学特征，讨论了两者之间的区别。期待这些隐藏在稳态催化循环之前的阶段能够得到更多的关注，这将有利于研究人员深度理解有机化学反应中的前催化循环和详细的反应机理。     

Towards perfect catalytic asymmetric synthesis: dual activation of the electrophile and the nucleophile

The design and development of new high-performance catalysts for applications in asymmetric catalytic reactions is of ongoing interest in organic chemistry. The combination of a Lewis acid and a Lewis base working in concert is now considered state of the art in stereoselective syntheses. The synergistic activation by two or more reactive centers allows high reaction rates and excellent transfer of stereochemical information. Despite the self-quenching reaction between Lewis acids and Lewis bases that might lead to an inactive catalyst, considerable effort has been directed towards the development of the dual-activation concept. The ultimate goal is to mimic nature by the discovery of catalytic systems analogous to enzymatic processes that involve metal-ion cocatalysts. With this aim, the dual activation concept greatly broadens the range of artificial catalysts. The most efficient catalytic systems are reviewed, and the mechanisms of action are discussed.     

Surface electron properties and catalytic activity of Sr doped lanthana

The electron donating properties, surface acidity/basicity and catalytic activity of lanthana for various dopant concentrations of strontium are reported at two activation temperatures. The catalytic activity has been correlated with electron donating properties and surface acidity/basicity of the oxide.