Synthesis of bis[(4,10-diaza-4,10-ditosyl-benzo-12-crown-4) 4′-yl] diaminoglyoxime and its complexes

A new macrocyclic ligand (HL) has been synthesised by reaction of 4-amino-4,10-diaza-4,10-ditosyl-benzo-l2-crown-4 with 1,2-dichloroethanedial-dioxime. Protonation constants of the ligand and overall formation constants have been calculated from potentiometric data using the program TITFIT. Both amino and hydroxyimino groups provide donor atoms together with hydroxyl ions at higher pH values. The order of formation constants of the mononuclear complexes are U(VI)O₂>Cu(II)>Ni(II)=Co(II)>Cd(II).Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August 1995.     

Reactions of diheteroaryl sulfoxides with heteroaryllithiums—ligand coupling and exchange reactions

The reactions of heteroaryl sulfoxides with heteroaryllithiums gave various biheteroaryls and diheteroaryl sulfoxides as ligand coupling and ligand exchange products through sulfurane intermediates. Especially, the reaction of di-2-furyl sulfoxide with 2-pyridyllithium proceeded first by a ligand exchange reaction to form 2-furyllithium and 2-furyl 2-pyridyl sulfoxide, which then underwent ligand coupling with 2-pyridyllithium to afford 2,2′-bipyridyl. Furthermore, it was found that the occurrence of the ligand coupling reaction depends on the stereoisomerism of the sulfurane intermediate formed. © 1996 John Wiley & Sons, Inc.     

Ion-selective electrodes – istory and conclusions

 The working mechanism of ion-selective electrodes has been investigated. The contradictions of theories deduced from so-called analogous phenomena are discussed in detail. Based on experiments made by the author’s research group the conclusion was drawn that only the surface (the active groups located there) takes part in the potential-determining reaction and the bulk resistance of the membrane plays a role only in the selection of the instrument used for potential measurement. Received: 15 May 1995/Revised: 12 August 1995/Accepted: 11 August 1995     

Ion-selective electrodes – istory and conclusions

 The working mechanism of ion-selective electrodes has been investigated. The contradictions of theories deduced from so-called analogous phenomena are discussed in detail. Based on experiments made by the author’s research group the conclusion was drawn that only the surface (the active groups located there) takes part in the potential-determining reaction and the bulk resistance of the membrane plays a role only in the selection of the instrument used for potential measurement. Received: 15 May 1995/Revised: 12 August 1995/Accepted: 11 August 1995     

Phosphine-triggered complete chemo-switch: from efficient aldehyde-alkyne-amine coupling to efficient aldehyde-alkyne coupling in water

[reaction: see text] A phosphine ligand served as a remarkable chemo-switch for the silver-catalyzed reaction of alkynes with aldehydes in the presence of amines in water. Exclusive aldehyde-alkyne-amine coupling product was observed in the absence of phosphine, whereas in the presence of a phosphine ligand, exclusive aldehyde-alkyne coupling product was obtained.     

On the mechanism of Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones: density functional theory survey

In this article, we have theoretically investigated the possible reaction mechanisms for Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones. The ωb97X-D method and C-PCM solvent model are used to describe the reaction processes. After the formation of allenylpalladium through C–O bond cleavage from propargylic carbonates, both decarboxylation and ligand exchange processes are explored. Then, depending on different conditions, we considered three possible types of reaction mechanisms, carbene insertion triggered by N₂ release, C–C coupling reactions without N₂ release, and C–C coupling reactions via the out-sphere attack of diazo compound. Our results indicate that it is favorable to undergo the carbene insertion into allenylpalladium after ligand exchange with diazo compound, which is partially agreement with the experimental suggestions. Although the decarboxylation is more difficult than ligand exchange, the reaction rate could be limited by Pd-catalyzed N₂ dissociation from diazo compound. Additionally, it should be essential to select DFT-D method to describe this reaction.     

Synthesis of new axially dissymmetric ligand with large perfluoroalkyl groups

A new axially dissymmetric ligand with large perfluoroalkyl groups, 2,2′-bis(1-hydroxy-1H-perfluorooctyl)biphenyl (1c), which could not be obtained by the coupling reaction of the aryl bromide using copper powder, was synthesized successfully by the coupling reaction using Ni(COD)₂. This ligand showed much higher asymmetric induction in the reaction of diethylzinc with benzaldehyde than the trifluoromethyl (1a) or pentafluoroethyl (1b) analogues.     

An efficient and simple ligand from phthalandione for palladium-catalyzed Suzuki reaction in aqueous media

An efficient and simple ligand derived from phthalandione was used for palladium catalyzed Suzuki coupling reaction in water/ethanol (V/V = 2/1) under aerobic conditions. The reaction exhibited a high catalytic efficiency even with lower Pd loading (0.002 mol %). In this work, the catalyst could be successfully used in coupling reaction between various aryl halides with phenylboronic acid in excellent yields with high turnover number (TON) (the maximal TON was up to 49,000 for the reaction of bromobenzene with phenylboronic acid). Moreover, this new ligand had been elucidated by ¹H NMR, ¹³C NMR and X-ray crystal diffraction.     

Palladium-catalyzed asymmetric coupling reactions between allylic acetates and organozinc reagents. Mechanistic implications

Asymmetric induction and deuterium distribution studies have provided information about the mechanism of the palladium-catalyzed coupling reaction between allylic acetates and phenylzinc chloride, namely the presence of a symmetric η³-allylic ligand in the intermediate, probably along with a monodentate phosphine ligand.     

Regioselective control of the nickel-mediated coupling of acetylene and carbon dioxide - A DFT study

The nickel-mediated coupling of asymmetric alkynes with carbon dioxide is known to be highly regioselective with respect to the formation of nickelacycle intermediates and α,β-unsaturated carboxylic acid products. Using density functional theory (DFT), we have investigated the effect that parameters such as acetylene-substituent, ancillary ligand and solvent have on the potential energy surface of the nickelacycle coupling reaction. 3-R-substituted nickelacycles are the thermodynamically preferred product in all cases surveyed, however, the transition structure characterised by the attack of CO₂ on the alkyne carbon distal from the R-group is generally lower in energy, making the 2-R-substituted nickelacycle the kinetically favoured product. Ligating the zerovalent nickel species with the diazabicyclo[5.4.0]undec-7-ene (DBU) ancillary ligand in preference to 2,2′-bipyridine (BIPY) leads to lower activation energies for the coupling reaction and products that are less susceptible to steric bulk in the 2-position of the nickelacycle. Solvation with dimethylformamide (DMF) has the advantage of lowering the activation barrier for the coupling reaction when compared to tetrahydrofuran (THF).     

Studies on the mechanism of allylic coupling reactions: a hammett analysis of the coupling of aryl silicate derivatives

Hammett analysis of the palladium-catalyzed allyl-aryl coupling reaction has demonstrated that the rate of the coupling reaction is enhanced by electron-withdrawing groups on the aryl siloxane. The positive slope of the Hammett plot indicated involvement of a charged transition state in which negative charge on the aryl ring is stabilized inductively. This result is consistent with either transmetalation or reductive elimination being the rate-determining step in the coupling process. Furthermore, the influence of ligand on the metal site has been assessed from competition studies as a function of ligand type, cone angle, and electronic effects. From the relative ratios of coupling products produced in the Hammett study, it is possible to gather insight into the role of the electronic as well as the steric effects of ligands on the mechanism of the coupling reaction.     

Bipyridine‐Modulated Palladium‐Catalyzed Oxidative Heck‐Type Reactions of Arylboronic Acids with Olefins

We have demonstrated that 4,4′‐dimethyl 2,2′‐bipyridine as ligand for Pd(II) catalysts was very efficient for oxidative Heck‐type coupling reaction of arylboronic acids with olefins in DMA or CH₃CN under atm air at 80 °C. The presence of chelated bipyridine ligand isindispensable to achieve high reaction yields and to suppress the formation of biphenyl as homocoupled byproduct.     

On the stereoselectivity of nitrone addition to (R)4-0-benzyl-4-lide

The title reaction was investigated for both known achiral and new chiral optically pure nitrones. In all cases, formation of only two diastereomeric cycloadducts was observed.Department of Organic Chemistry, Slovak Technical University, 812 37 Bratislava, Slovak Republic. Department of Organic Chemistry, University of Stuttgart, D-70569 Stuttgart, Germany. Published in Khimiya Geterotsiklicheskikh Soedinenii No. 10, pp. 1350–1352. October, 1995. Original article submitted August 24, 1995.     

Transition‐Metal‐Free Cross‐Coupling of Benzothiophenes and Styrenes in a Stereoselective Synthesis of Substituted (E,Z)‐1,3‐Dienes

A transition metal‐free one‐pot stereoselective approach to substituted (E,Z)‐1,3‐dienes was developed by using an interrupted Pummerer reaction/ligand‐coupling strategy. Readily available benzothiophene S‐oxides, which can be conveniently prepared by oxidation of the parent benzothiophenes, undergo Pummerer coupling with styrenes. Reaction of the resultant sulfonium salts with alkyllithium/magnesium reagents generates underexploited hypervalent sulfurane intermediates that undergo selective ligand coupling, resulting in dismantling of the benzothiophene motif and the formation of decorated (E,Z)‐1,3‐dienes.     

Co-Catalyzed Metal-Ligand Cooperative Approach for N-alkylation of Amines and Synthesis of Quinolines via Dehydrogenative Alcohol Functionalization

Herein we report a cobalt-catalyzed sustainable approach for C−N cross-coupling reaction between amines and alcohols. Using a well-defined Co-catalyst 1 a bearing 2-(phenyldiazenyl)-1,10-phenanthroline ligand, various N-alkylated amines were synthesized in good yields. 1 a efficiently alkylates diamines producing N, N′-dialkylated amines in good yields and showed excellent chemoselectivity when oleyl alcohol and β-citronellol, containing internal carbon-carbon double bond were used as alkylating agents. 1 a is equally compatible with synthesizing N-heterocycles via dehydrogenative coupling of amines and alcohols. 1H-Indole was synthesized via an intramolecular dehydrogenative N-alkylation reaction, and various substituted quinolines were synthesized by coupling of 2-aminobenzyl alcohol and secondary alcohols. A few control reactions and spectroscopic experiments were conducted to illuminate the plausible reaction mechanism, indicating that the 1 a -catalyzed N-alkylation proceeds through the borrowing hydrogen pathway. The coordinated arylazo ligand participates actively throughout the reaction; the hydrogen eliminated during dehydrogenation of alcohols was set aside in the ligand backbone and subsequently gets transferred in the reductive amination step to imine intermediates yielding N-alkylated amines. On the other hand, 1 a -catalyzed quinoline synthesis proceeds through dehydrogenation followed by successive C−C and C−N coupling steps forming H₂O₂ as a by-product under air.     

Novel isoxazoline ligand with ferrocene backbone: preparation and application in Heck reaction with water as solvent

Two novel isoxazoline N,N‐bidentate ligands with ferrocene backbone have been synthesized and employed for the palladium‐catalyzed Heck coupling reaction. Among them, 1,3‐bis‐(5‐ferrocenylisoxazoline‐3‐yl)benzene was found to be thermally stable and a highly effective ligand for Heck coupling reaction in neat water without N₂ protection, affording the desired coupling products in good to excellent yield with high diastereoselectivity. The developed catalytic system was also well workable for 1,2‐disubstituted alkenes, which were less involved in the Heck reaction for its larger steric hindrance. Copyright © 2014 John Wiley & Sons, Ltd.     

N‐methyliminodiacetic acid as a simple and highly efficient ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling of aryl chlorides

A simple, air‐stable, inexpensive and easily prepared molecule, N‐methyliminodiacetic acid (MIDA), is reported as a ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of phenylboronic acid with aryl chlorides. The yield of the corresponding Suzuki coupling reaction is up to around 90% at both high temperature of 80°C and room temperature under ambient atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.     

Cobalt‐Catalyzed Intermolecular C(sp2)O Cross‐Coupling

Cobalt(II)‐catalyzed C(sp²)?O cross‐coupling between aryl/heteroaryl alcohols and vinyl/aryl halides in the presence of Cu^I has been achieved under ligand‐free conditions. In this reaction, copper plays a significant role in transmetalation rather than being directly involved in the C?O coupling. This unique Co/Cu‐dual catalyst system provides an easy access to a library of aryl–vinyl, heteroaryl–styryl, aryl–aryl, and heteroaryl–heteroaryl ethers in the absence of any ligand or additive.     

L-proline promoted Ullmann-type reaction of vinyl bromides with imidazoles in ionic liquids

The Ullmann-type coupling reaction of vinyl bromides and imidazoles in ILs at 90-110 degrees C gave the corresponding N-vinylimidazoles in good to excellent yields by using L-proline as the ligand; the double bond geometry of the vinyl bromides was retained under the reaction conditions.     

Addressing Challenges in Palladium‐Catalyzed Cross‐Coupling Reactions Through Ligand Design

The development of palladium‐catalyzed cross‐coupling reactions has revolutionized the synthesis of organic molecules on both bench‐top and industrial scales. While significant research effort has been directed toward evaluating how modifying various reaction parameters can influence the outcome of a given cross‐coupling reaction, the design and implementation of novel ancillary ligand frameworks has played a particularly important role in advancing the state‐of‐the‐art. This Review seeks to highlight notable examples from the recent chemical literature, in which newly developed ancillary ligands have enabled more challenging substrate transformations to be addressed with greater selectivity and/or under increasingly mild conditions. Throughout, the importance and subtlety of ligand effects in palladium‐catalyzed cross‐coupling reactions are described, in an effort to inspire further development and understanding within the field of ancillary ligand design.