Transition Metal-mediated Reactions Research Articles

Recent Advancement of Transition Metal-mediated Reactions of Diazomethane and (Trimethylsilyl)diazomethane

Abstract:Diazomethane and trimethylsilyl diazomethane are common and versatile reagents in organic synthesis and they are unique as reactants in synthetic methodology. These reagents may be used in esterification, dipolar cycloaddition, epoxidation, aziridination, cyclopropanation, and carbonyl homologation. The lack of practical, scalable methods for the construction of cyclopropanes is a long-standing problem in industrial chemistry and diazomethane/ trimethylsilyl diazomethane has the potential to significantly reduce the cost of bringing new cyclopropane-bearing compounds to market. The transition metal-mediated reactions of diazomethane and trimethylsilyl diazomethane with alkenes, terminal alkynes and carbonyl compounds are being discussed in this article. The mechanism of different coupling, insertion and rearrangement reactions are also explored in this review article. The toxicity and explosive nature of diazomethane/ trimethylsilyl diazomethane are known to all, but concurrently, their efficacy and significant role as the reagents in synthetic transformation can’t be ignored. The untoward properties of diazomethane and trimethylsilyl diazomethane combined with its versatility, make the identification of safe protocols for its use. Considering the importance of these reagents, a concise review is needed. This article will highlight recent metalmediated reactions of diazomethane and trimethylsilyl diazomethane compounds that have been reported from 2000 until 2020.

Importance of thorough conformational analysis in modelling transition metal-mediated reactions: Case studies on pincer complexes containing phosphine groups

Advances in processing capabilities of computer clusters have allowed for the full modeling of organometallic complexes that previously would have been simplified to reduce computational cost. Increased feasibility of computational modeling offers new challenges, not only in terms of limitations of methods and theory, but attention should be paid to complexes that can exist in many conformations, as the appropriate choice of conformer may be easily overlooked. In this work a series of pincer complexes with isopropyl and cyclopentyl substituents have been chosen as examples to demonstrate the importance of conformational analysis. The complexes examined contain four isopropyl or cyclopentyl groups on phosphor atoms generating between 27 and 324 possible rotamers. The importance of conformational search in a mechanistic investigation is demonstrated with the CO2 insertion into a nickel hydride bond of POCOP iPr nickel hydride complex. Results show that the reaction energy profile can be both exergonic and endergonic depending on rotamer choice. Specifically, the POCOPiPr Ni-formato complex product of the CO2 insertion reaction had an energy difference between the lowest and highest energy rotamer as high as 16.8 kcal/mol. The significant energy differences between rotamers highlight the importance of thorough conformational analysis and should be taken into consideration when evaluating the energy profile of related reactions.

Transition Metal-mediated Reactions in Biological Media.

Transition-metal catalysis has changed the way in which chemical reactions can be accomplished. While most metal-catalyzed reactions have been achieved in organic solvents, recent work has demonstrated that many of these transformations can be made compatible with water. These discoveries have stimulated the search for metal catalysts that are capable of achieving designed reactions in biological settings, and eventually behave as non-natural enzymes working in native cellular environments. Although this new field of research is still taking its first steps, there is a growing number of publications in the area, and one can predict that it will steadily grow in the years to come. Here we will briefly review some of the main contributions in the area. The contents have been organized according to the type of transformation and transition metal catalysts involved in the process.

Transition Metal-Catalyzed Reactions of 3-Aza-2-oxabicyclo[2.2.1]hept-5-enes

Background: Transition metal catalysts are becoming increasingly more important in organic synthesis and are being used to catalyze novel reactions that allow for more efficient synthesis of many pharmaceuticals. Transition metal-catalyzed reactions of 3-aza-2-oxabicyco[2.2.1]hept-5-enes provide efficient synthetic pathways to generate a diverse range of biologically and synthetically useful products. 3-Aza-2- oxabicyclic alkenes undergo three main types of reactions: reductive N-O bond cleavage, C-O bond cleavage, and modification of the alkene component. Objective: The purpose of this review is to summarize and discuss the transition metal-mediated reactions of 3- aza-2-oxabicyclo[2.2.1]hept-5-enes, including the mechanisms of reactions based on the transition metal used, the different stereo- and regiochemical outcomes of reactions with this asymmetrical substrate, and the biological importance of exploring these reactions. Conclusion: It is clear from the review of the topic that a vast amount of work has been done in this area, and transition metals have been used to control the regio- and stereoselective reactions of 3-aza-2-oxabicyclic alkenes to create biologically active and synthetically useful products. The transition metal-catalyzed reactions of 3-aza-2-oxabicyclic alkenes proceed through three general reactions: through cleavage of the N-O bond, cleavage of the C-O bond, and modification of the alkene component. Without the use of transition metals, the substrate would not be activated and these reactions would not be possible. The use of transition metals opens up an array of new reactions that have the ability to create different functional groups with different regio- and stereoselectivities based on the metal and conditions used. The products made through these transition metalcatalyzed reactions can be useful as antibiotics, siderophores, and carbocyclic nucleosides such as noraristeromycin and carbocyclic polyoxin C.

ChemInform Abstract: Synthesis and Catalytic Applications of C3‐Symmetric Tris(triazolyl)methanol Ligands and Derivatives

AbstractReview: [83 refs.

Synthesis and catalytic applications of C3-symmetric tris(triazolyl)methanol ligands and derivatives.

Recently introduced tris(1,2,3-triazol-4-yl)methanols and derivatives (TTM ligands) have become a valuable subclass of C3-symmetric tripodal ligands for transition metal-mediated reactions. TTM-based ligand architectures are modularly constructed through regioselective, one-pot triple [3+2] cycloaddition of azides and alkynes. Applications of homogeneous systems of this type and of heterogenised (polystyrene- and magnetic nanoparticle-supported) TTM ligands in synthesis and catalysis are compiled in this Feature Article.

2‐Bromo‐6‐[18F]fluoropyridine: two‐step fluorine‐18 radiolabelling via transition metal‐mediated chemistry

Novel radiolabelling methods are important for the development of new tracers for positron emission tomography. Direct nucleophilic fluorination of aromatic rings with [(18) F]fluoride is limited to activated substrates, restricting the application of this approach. Inspired by transition metal-mediated transformations, a fluorine-18 synthon was prepared to supplement the radiolabelling methods available for molecules unsuitable for direct labelling. 2-Bromo-6-[(18) F]fluoropyridine (denoted [(18) F]1) was prepared in high yield, and palladium-mediated cross-coupling reactions were exemplified. High incorporation of fluoride and efficient cross-coupling reactions demonstrate that compound [(18) F]1 holds promise as a new synthon for construction of fluorine-18-labelled molecules via transition metal-mediated reactions.

Recent advances in transition metal-catalyzed Csp(2)-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation.

In the last few years, transition metal-mediated reactions have joined the toolbox of chemists working in the field of fluorination for Life-Science oriented research. The successful execution of transition metal-catalyzed carbon–fluorine bond formation has become a landmark achievement in fluorine chemistry. This rapidly growing research field has been the subject of some excellent reviews. Our approach focuses exclusively on transition metal-catalyzed reactions that allow the introduction of –CFH2, –CF2H, –CnF2n+1 and –SCF3 groups onto sp² carbon atoms. Transformations are discussed according to the reaction-type and the metal employed. The review will not extend to conventional non-transition metal methods to these fluorinated groups.

ChemInform Abstract: Theoretical Studies of Some Transition Metal Mediated Reactions of Industrial and Synthetic Importance

ChemInform Abstract: Theoretical Studies of Some Transition Metal Mediated Reactions of Industrial and Synthetic Importance

遷移金属錯体を用いたポルフィリンの機能化と多量化―巨大機能性分子系の構築と課題

Functionalization and multiplication of porphyrins by transition metal-mediated reactions (Sonogashira coupling, Negishi coupling, Stille coupling, Mizoroki-Heck alkenylation, Buchwald-Hartwig reaction, Suzuki-Miyaura coupling, cobalt-mediated [2+2+2] cyclization, Grubbs' metathesis reaction, etc.) are reviewed. When the above reactions are applied to porphyrins, diluted conditions (typically 110 mM) are used due to low solubility. As the dilution, relatively large amounts of metal species are used due to decreasing of turn over numbers of the catalysts. Copper reagent is excluded when free base porphyrins are treated without protection. In multiplication of porphyrins by simultaneous multiple metal-mediated couplings, each yield and existence of side-products greatly affect isolation of the target material. In this review, modified conditions and side-reactions are presented to let know the problems to chemists who synthesizes functional porphyrins and develops metal-mediated reactions.

ChemInform Abstract: Transition Metal Mediated Reactions in Combinatorial Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Transition metal-mediated reactions using [11C]cyanide in synthesis of11C-labelled aromatic compounds

Aromatic and heteroaromatic nitriles, labelled with carbon-11 in the cyano group, have been synthesized by rapid palladium- and chromium-mediated reactions using hydrogen [11C]cyanide. The 11C-cyanation on aryl iodides, bromides, and triflate, or on heteroaromatic bromides, in the presence of tetrakis(triphenylphosphine)palladium, afforded 54–99% radiochemical yield in 5 min. The Pd0-promoted 11C-cyanation was performed with varying concentrations of substrate, down to the submicro molar scale ( > 0.1 µmol). The decay-corrected radiochemical yields of [cyano-11C]benzonitriles after purification by semi-preparative HPLC were 50–90%, based on hydrogen [11C]cyanide, with a total synthesis time of 20–25 min and a radiochemical purity >98%. Nucleophilic aromatic substitution with 11C-cyanide on tricarbonylchromium complexes of some fluoroarenes resulted in radiochemical yields of 46–74%. In a combined synthetic sequence, Pd0-assisted 11C-cyanation on chloroarene(tricarbonyl)chromium complexes, the radiochemical yields were 95%. By mono-11C-cyanation on 1,4-dibromobenzene, the difunctional precursor 4-bromo[cyano-11C]benzonitrile was obtained. Subsequent cross-coupling with phenyl(trimethyl)tin in the presence of tetrakis(triphenylphosphine)palladium afforded 4-[cyano-11C] biphenylcarbonitrile in 60% radiochemical yield. The synthesis time before purification was 15 min counted from end of bombardment.

ChemInform Abstract: Metallacarboxylic Acids. Synthesis, Structure, Reactivity and Thermal Decomposition

Abstract Metallacarboxylic acids (metal hydroxycarbonyls) are important intermediates in various transition metal-mediated reactions of CO and water, including the oxidation of CO by metal ions in aqueous solution, the homogeneously catalysed water-gas shift reaction and the formation of metal hydrides. The chemistry of the limited number of isolated metalla-carboxylic acids is surveyed and the first structural determination on such a compound, trans -Pt(CO 2 H)(C 6 H 5 )(PEt 3 ) 2 , is mentioned. Metallacarboxylic acids are amphoteric, but this behaviour is strongly dependent on the central metal atom and on the nature of the other ligands present. Although β-elimination to give a metal hydride and CO 2 is the usual mode of decomposition, this behaviour too is strongly metal- and ligand-dependent, and in the case of trans -Pt(CO 2 H)(C 6 H 5 )(PEt 3 ) 2 an alternative route has been identified, in which CO and H 2 O are lost and a dinuclear complex containing bridging CO 2 is formed.

Metallacarboxylic acids: synthesis, structure, reactivity and thermal decomposition

Metallacarboxylic acids (metal hydroxycarbonyls) are important intermediates in various transition metal-mediated reactions of CO and water, including the oxidation of CO by metal ions in aqueous solution, the homogeneously catalysed water-gas shift reaction and the formation of metal hydrides. The chemistry of the limited number of isolated metalla-carboxylic acids is surveyed and the first structural determination on such a compound, trans-Pt(CO 2H)(C 6H 5)(PEt 3) 2, is mentioned. Metallacarboxylic acids are amphoteric, but this behaviour is strongly dependent on the central metal atom and on the nature of the other ligands present. Although β-elimination to give a metal hydride and CO 2 is the usual mode of decomposition, this behaviour too is strongly metal- and ligand-dependent, and in the case of trans-Pt(CO 2H)(C 6H 5)(PEt 3) 2 an alternative route has been identified, in which CO and H 2O are lost and a dinuclear complex containing bridging CO 2 is formed.