Synthesis of Well‐Defined Diphenylvinyl(cyclopropyl)phosphine‐Palladium Complexes for the Suzuki–Miyaura Reaction and Buchwald–Hartwig Amination

The well‐defined diphenylvinylphosphine‐palladium complex 1 and the diphenylcyclopropylphosphine‐palladium complex 2 were successfully synthesized. The crystal structures of these complexes were obtained by X‐ray crystallographic analysis. Both complexes were air‐ and moisture‐stable, and could be prepared on a gram scale. These palladium complexes catalyzed the Suzuki–Miyaura reaction of aryl bromides [turnover numbers (TON) up to 196,000] and aryl chlorides (TON up to 50,000). Furthermore, complex 2 catalyzed the Buchwald–Hartwig amination of aryl chlorides and aromatic/aliphatic amines with a low catalyst loading. These complexes showed different reactivities for the coupling of 2‐chloropyridine, and the origin of this difference is discussed.     

Evaluation of Aromatic Amination Catalyzed by Palladium on Carbon: A Practical Synthesis of Triarylamines

A heterogeneous palladium on carbon (Pd/C)‐catalyzed coupling between amines and aromatic halides including aromatic chlorides has been achieved using sodium tert‐butoxide (NaO‐t‐Bu) and 1,1′‐bis(diphenylphosphino)ferrocene (dppf) as a ligand in cyclopentyl methyl ether (CPME). The use of potassium tert‐butoxide (KO‐t‐Bu) in place of NaO‐t‐Bu brought about the benzyne‐mediated aromatic amination even without Pd/C and dppf, giving a mixture of regioisomers when 4‐substituted bromobenzenes were employed as the substrate. The combination of Pd/C, dppf, NaO‐t‐Bu could be utilized for the syntheses of a broad range of triarylamines by replacing CPME with mesitylene which can provide a higher reaction temperature. The Pd/C could be quantitatively recovered and reused until at least the fourth cycle without any loss in catalytic activity. The quite low leaching of palladium (<1.1%) was demonstrated by an inductively coupled plasma‐atomic emission spectrometric analysis.     

A General Approach to Substituted Benzimidazoles and Benzoxazoles via Heterogeneous Palladium‐Catalyzed Hydrogen‐Transfer with Primary Amines

The synthesis of benzimidazoles starting from o‐phenylenediamines and amines in the presence of palladium on charcoal as catalyst is reported. Under microwave dielectric heating it is possible to use a tertiary, a secondary, and even a primary amine as the substrate for a palladium‐mediated process to get 2‐substituted or 1,2‐disubstituted benzimidazoles, depending on the nature of the o‐phenylenediamine employed. Primary amines are the most suitable reagents for the atom economy of the overall process that resulted to be general as several different substituted benzimidazoles were obtained in good yield. Benzoxazoles can be also prepared starting from primary amines and o‐aminophenol. The reaction is also highly selective as no (poly)‐alkylated phenylenediamines or cross‐contaminated benzimidazoles are obtained starting from N‐monoalkylphenylenediamines. This behavior was interpreted as a scarce aptitude to dehydrogenation of the methylene bonded to the aromatic NH of N‐alkylarylamines. The experiments carried out consent to draw an almost complete picture of the reaction pathways occurring during the process. The catalyst can be recycled several times and, although far from optimal performances, catalyst TON=90 is encouraging for further large‐scale optimization protocols. In addition, the palladium on charcoal‐catalyzed microwave‐assisted reaction of o‐phenylenediamine gives de‐alkylation of tertiary amines and transformation into the secondary ones.     

Nanocrystalline Magnesium Oxide‐Stabilized Palladium(0): An Efficient and Reusable Catalyst for Selective Reduction of Nitro Compounds

An efficient, mild and selective synthesis of aromatic and aliphatic amines from the corresponding nitro compounds has been realized by using a ligand‐free heterogeneous nanocrystalline magnesium oxide‐stabilized palladium(0) catalyst, employing molecular hydrogen as the reductant. The catalyst is recovered quantitatively by simple filtration and was reused for several cycles with consistent activity.     

Aminocarbonylation of (Hetero)aryl Bromides with Ammonia and Amines using a Palladium/DalPhos Catalyst System

Variants of the DalPhos [2‐aminophenylbisadamantyl)phosphine] ligand family were examined in a palladium‐catalyzed carbonylative amination reaction using inexpensive carbon monoxide and ammonia as reagents. As a result of this survey, the Pyr‐DalPhos ligand was identified as being effective for the selective aminocarbonylation of aryl bromides with ammonia, as well as primary and secondary alkylamines. A variety of primary aromatic, heteroaromatic and N‐substituted benzamides were formed in moderate to good yields. As part of this study, a (Mor‐DalPhos)Pd‐benzoyl complex was prepared and crystallographically characterized, thereby showing the viability of the carbonyl insertion step.     

Palladium on Charcoal as a Recyclable Catalyst for C?S Cross‐Coupling of Thiols with Aryl Halides under Ligand‐Free Conditions

S‐Arylation of a wide variety of substituted aryl and aliphatic thiols with aryl halides using a catalytic amount of palladium on charcoal as a heterogeneous catalysis with potassium hydroxide as the base in dimethyl sulfoxide (DMSO) at 110 °C is accomplished in good yields. The C S bond formation reaction functions under ligand‐free conditions, and the palladium on charcoal catalyst can be is reused for five runs without any loss of activity.     

Access to 2‐Aminopyridines – Compounds of Great Biological and Chemical Significance

2‐Aminopyridines are key structural cores of bioactive natural products, medicinally important compounds, and organic materials and thus, extremely valuable synthetic targets. The few reported 6‐substituted 2‐aminopyridines and the lack of flexible, efficient and general applicable methods for their synthesis demonstrates the urgent need of new methods for their preparation. Reactions between 2,6‐dibromopyridine and primary or secondary, cyclic or acyclic, and aliphatic or aromatic amines were shown to selectively yield the respective 6‐bromopyridine‐2‐amines in very high yields which were successfully used as substrates for subsequent C C cross‐coupling reactions. The recently introduced dichloro‐bis[1‐(dicyclohexylphosphanyl)piperidine]palladium ( 1 ) was used as catalyst for the cross‐coupling of 6‐bromopyridine‐2‐amines with arylboronic acids, diaryl‐ and dialkylzinc reagents or olefins and hence, is also an excellent C C cross‐coupling catalyst for this type of substrate. Moreover, all the reaction protocols presented were in each of the catalyses uniformly applied. The scope of both the amination and the cross‐coupling reactions are well defined and allow one to simply adapt the reaction protocols directly to other amines and/or coupling partners and, thus, provide for the first time a very flexible and generally applicable reaction protocol to get access to 2‐aminopyridines.     

Copper‐Catalyzed Intermolecular Amination of Acidic Aryl C?H Bonds with Primary Aromatic Amines

A copper‐catalyzed intermolecular aerobic oxidative C H bond amination of various polyfluorobenzenes with an array of primary aromatic amines was achieved for the first time. The reactivity of the polyfluorobenzenes was observed to depend on the acidity of C H bonds. Under similar reaction conditions, the C H bond amination of azoles also occurred.     

Palladium‐ and Copper‐Catalyzed Site Selective Monoamination of Dibromobenzoic Acid

The carboxylate anion has been used as a directing group in the aromatic amination of electronically equivalent aryl bromides to afford selective ortho‐substituted derivatives (>99:1 selectivity; 60–80% yield) in the case of copper(I) catalysis. The solvent, base and equivalents of base were important factors in the success of this reaction. Complementary selectivity was achieved with palladium catalysis where the para‐substituted derivatives were produced selectively (>99% selectivity, 70–80% yield).     

氨化法合成3,5-二甲基苯胺的工艺研究

在钯碳催化剂存在下,3,5-二甲基苯酚通过部分加氢再氨化,生成3,5-二甲基苯胺。3,5-二甲基苯酚的转化率为95％,3,5-二甲基苯胺的产率为52％。     

Ligand-Exchange Chromatography of Aromatic Amines on Resin-Bound Cobalt Ion

Abstract

The use of cobalt metal for the selective separation of aromatic amines is completed with a chemically bonded diamine and glyoxime functional groups onto Lycopodium clavatum. Oximes and amines are excellent complexing agents for transition metal ions. Cobalt(II) metal ions can easily be immobilized on bis-diami-noethyl-glyoximated sporopollenin (bDAEG-sporopollenin). The ligand-exchange behavior of modified Lycopodium clavatum with respect to aromatic amines was, investigated. This will permit the evaluation of bDAEG-sporopollenin ligand exchangers for their utilization as sorbents in the recovery, pollution control, and elimination of amines from wastewater.     

A Novel (2,2‐Diarylvinyl)phosphine/Palladium Catalyst for Effective Aromatic Amination

A new series of diarylvinylphosphine ligands was designed and synthesized. A catalyst system, consisting of the ligands and palladium species, effectively catalyzed the coupling reaction of aryl bromides and chlorides with amines to afford the corresponding products in good to excellent yields. The efficiency is likely derived from an interaction between the palladium center and the cis‐aryl moiety on the diarylvinylphosphine ligand stabilizing a catalytic intermediate during the coupling reaction.     

2,6‐Diisopropoxyphenyl(dicyclohexyl)phosphine: A New Ligand for Palladium‐Catalyzed Amination Reactions of Aryl Chlorides with Potassium Hydroxide as the Base

A new, readily available monophosphine tetrafluoroborate salt [ L2 ⋅ HBF₄ ] was developed for the palladium‐catalyzed amination reaction of aryl chlorides in moderate to high yields with the cheap and easily available potassium hydroxide as the base. The reaction enjoys a wide scope, lower reaction temperatures, shorter reaction times, high yields, and low catalyst loading when compared to some of same amination reactions reported in the literature. Based on a kinetic study, ³¹P NMR measurements, and DFT calculations, a mechanism involving a 1:1 Pd/L species is proposed.     

Copper‐in‐Charcoal‐Catalyzed,Tandem One‐Pot Diazo Transfer‐Click Reactions

Copper‐in‐charcoal (Cu/C) is an effective heterogeneous catalyst for tandem diazo transfer/click reactions. In the presence of Cu/C, various azides can be generated in situ from the corresponding amines, and subsequently undergo [3+2] cycloaddition with terminal alkynes to afford triazoles in good yields. The catalyst is also easily recycled.     

离子液体中芳香醛选择性还原胺化反应研究

以离子液体为反应介质,对一系列还原胺化反应进行了研究.结果表明,经过缩合、还原两步连续反应,芳香醛与胺的产品收率在70%～98%,还原剂硼氢化钠在BMImBF4离子液体中对还原胺化反应表现出很好的还原能力和选择性,该合成反应条件温和,离子液体可稳定重复使用12次以上.     

Palladium‐Catalyzed Decarboxylative Coupling of α‐ Oxocarboxylic Acids with C(sp2)?H of 2‐Aryloxypyridines

An efficient palladium‐catalyzed decarboxylative ortho‐acylation of 2‐aryloxypyridines with α‐oxocarboxylic acids is described. In this new transformation, the aromatic C(sp²) H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding 2‐hydroxy aromatic ketones.     

Carbenes Made Easy: Formation of Unsymmetrically Substituted N‐Heterocyclic Carbene Complexes of Palladium(II), Platinum(II) and Gold(I) from Coordinated Isonitriles and their Catalytic Activity

From palladium(II) or platinum(II) bis(isonitrile) complexes and from gold(I) isonitrile complexes, both easily available from simple precursors, the corresponding mono‐N‐heterocyclic carbene (NHC) complexes could be obtained selectively in good yields under very mild conditions. The reagents are simple β‐chloroammonium salts in the presence of a weak base. Unsymmetric NHC complexes are accessible. Thus over only two steps from simple metal precursors a broad variety of NHC complexes is available, the method is ideal to quickly assemble catalyst libraries. The palladium complexes are active pre‐catalysts in Suzuki cross‐coupling even with the additional isonitrile ligand on palladium.     

An Efficient Method for the Selective Iridium‐Catalyzed Monoalkylation of (Hetero)aromatic Amines with Primary Alcohols

An efficient multi‐gram scale synthesis protocol of a variety of P,N ligands is described. The synthesis is achieved in a two‐step reaction. First, the amine is deprotonated and subsequently the chlorophosphine is added to yield the corresponding P,N ligand. Deprotonation of the amine is normally achieved with n‐BuLi at low temperature, but for the preparation of ligands with a 2,2′‐dipyridylamino backbone and phosphines with a high steric demand KH has to be employed in combination with reaction temperatures of 110 °C for the salt metathesis step. The reaction of two equivalents of a selected P,N ligand with one equivalent of the iridium complex [IrCl(cod)]₂ (cod=1,5‐cyclooctadiene) affords P,N ligand‐coordinated iridium complexes in quantitative yield. X‐Ray single crystal structure analysis of one of these complexes reveals a monomeric five‐coordinated structure in the solid state. The iridium complexes were used to form catalysts for the N‐alkylation of aromatic amines with alcohols. The catalyst system was optimized by studying 8 different P,N ligands, 9 different solvents and 14 different bases. Systematic variation of the substrate to base and the amine to alcohol ratios as well as the catalyst loading led to optimized catalytic reaction conditions. The substrate scope of the developed catalytic protocol was shown by synthesizing 20 different amines of which 12 could be obtained in isolated yields higher than 90%. A new efficient catalyst system for the selective monoalkylation of primary aromatic and heteroaromatic amines with primary aromatic, heteroaromatic as well as aliphatic alcohols has been established. The reaction proceeds with rather moderate catalyst loadings.     

An Efficient Palladium‐NHC (NHC=N‐Heterocyclic Carbene) and Aryl Amination Pre‐Catalyst: [Pd(IPr*)(cinnamyl)Cl]

The well‐defined [Pd(IPr*)(cinnamyl)Cl] complex is reported as one of the best N‐heterocyclic carbene (NHC)‐based pre‐catalysts for the Buchwald–Hartwig amination reaction. This catalytic system displays high efficiency for the coupling of numerous (hetero)aryl chlorides, with a wide range of amines, at room temperature or at extremely low catalyst loading (as low as 0.025 mol%).     

Ligand‐Free Buchwald–Hartwig Aromatic Aminations of Aryl Halides Catalyzed by Low‐Leaching and Highly Recyclable Sulfur‐Modified Gold‐Supported Palladium Material

A stable heterogeneous catalyst precursor, sulfur‐modified gold‐supported palladium material (SAPd), has proved to be an excellent source of leached, ligand‐free, Pd for the amination of aryl bromides and chlorides. The reaction‐enabling catalyst is provided in situ as leached Pd in low catalyst loading (0.21±0.02 mol%). This allows the precatalyst (SAPd) to be filtered off and used for a minimum of ten reaction cycles without loss of catalytic activity. SAPd released only trace amounts, less than 0.6 ppm, of highly active Pd during the reaction without any aggregation.