An examination of the palladium/Mor-DalPhos catalyst system in the context of selective ammonia monoarylation at room temperature

P,N-Coordinating Ylide-Functionalized Phosphines (NYPhos): A Ligand Platform for the Selective Monoarylation of Small Nucleophiles

Palladium-catalyzed coupling reactions of small nucleophiles are of great interest, but challenging due to difficulties in selectivity control. Herein, we report the development of a new platform of P,N-ligands consisting of ylide-functionalized phosphines with aminophosphonium groups (NYPhos) to address this challenge. These phosphine ligands are easily accessible in a wide structural diversity with highly modular electronic and steric properties. Based on a family of 14 ligands the selective monoarylation of acetone as well as other challenging ketones and amides was accomplished with record-setting activities even for aryl chlorides at room temperature including late-stage functionalizations of drug molecules. Moreover, ammonia and other small primary amines could be coupled at mild conditions. Isolation and structure analyses of palladium complexes within the catalytic cycle confirmed that the P,N-coordination mode is necessary to achieve the observed selectivities. It also demonstrated the facile adjustability of the N-donor strength, which is beneficial for the targeted design of tailored P,N-ligands for future applications.

Metal-catalyzed reactions for the C(sp2)–N bond formation: achievements of recent years

The review deals with the main catalytic methods for the C(sp2)–N bond formation, including Buchwald–Hartwig palladium-catalyzed amination of aryl and heteroaryl halides, renaissance of the Ullmann chemistry, i.e., the application of catalysis by copper complexes to form the carbon–nitrogen bond, and Chan–Lam reactions of (hetero)arylboronic acids with amines. Also, oxidative amination with C–H activation, which has been booming during the last decade, is addressed. Particular attention is paid to achievements in the application of heterogenized catalysts.

The bibliography includes 350 references.

From Academia to the Market - Air-stable Ni(ii)/Josiphos Catalysts

The design, synthesis, commercialization and application of air-stable Ni(II)/Josiphos complexes has been realized in a collaboration between Solvias and ICBMS (University Lyon 1). The Ni-complexes are utilized as versatile precatalysts for diverse cross-coupling reactions. Apart from being active in established C-C and C-N couplings at low catalyst loadings, the novel Ni-precatalysts enabled the development of the challenging monoarylation of ammonia, ammonia surrogates and even alkylammonium chlorides with aryl carbamates. Finally, the α-arylation of acetone with aryl chlorides, carbamates and pivalates was demonstrated using the Ni(II)/Josiphos precatalysts.

Palladium-Catalyzed Cross-Couplings by C-O Bond Activation

Although palladium-catalyzed cross-coupling of aryl halides and reactive pseudohalides has revolutionized the way organic molecules are constructed today across various fields of chemistry, comparatively less progress has been made in the palladium-catalyzed cross-coupling of less reactive C-O electrophiles. This is despite the fact that the use of phenols and phenol derivatives as bench-stable cross-coupling partners has been well-recognized to bring about major advantages over aryl halides, such as (1) natural abundance of phenols, (2) avoidance of toxic halides, (3) orthogonal cross-coupling conditions, (4) prefunctionalization of phenolic substrates by electrophilic substitution or C-H functionalization, (5) ready availability of phenols from a different pool of precursors than aryl halides. In this review, we present an overview of recent advances made in the field of palladium-catalyzed cross-coupling of C-O electrophiles with a focus on (1) catalytic systems, (2) reaction type, and (3) class of C-O coupling partners. Although the field has been historically dominated by nickel catalysis, it is now evident that the use of more versatile, more functional group tolerant and highly active palladium catalysts supported by appropriately designed ancillary ligands enables the cross-coupling with improved substrate scope and generality, and likely represents a practical solution to the broadly applicable cross-coupling of various C-O bonds across diverse chemical disciplines. The review covers the period through June 2020.

How bulky ligands control the chemoselectivity of Pd-catalyzed N-arylation of ammonia

Steric bulk has been recognized as a central design principle for supporting ligands in the widely utilized Buchwald-Hartwig amination. In a recent example, it was shown that a Pd-catalyst carrying a phosphine ligand can successfully aminate aryl halides using ammonia as the nitrogen source. Interestingly, the chemoselectivity of this reaction was found to depend on the steric demand of the phosphine ligand. Whereas a sterically less demanding phosphine affords diphenylamine as the major product, it was shown that the amination reaction can be stopped after the first amination to give aniline if a sterically more encumbering phosphine ligand is used. Density functional theory calculations were carried out to examine the relationship between the steric demand of the phosphine ligand and the chemoselectivity. It was found that the key feature that leads to the chemoselectivity is the ability of the phosphine ligand to rotate the biaryl moiety of the ligand away from the Pd-center upon amine addition to release some of the steric crowding from the Pd-coordination site.

Copper-catalyzed arene amination in pure aqueous ammonia

A simple protocol for copper-catalyzed arene amination using aqueous ammonia without any additional ligands and organic coordinating solvents has been developed. The reaction pathway via a Cu(i)/Cu(iii) mechanism is proposed based on the results of control experiments as well as DFT calculations.

Developing backbone-modified Mor-DalPhos ligand variants for use in palladium-catalyzed C–N and C–C cross-coupling

The present contribution describes the systematic structural diversification of the κ2-P,N DalPhos ligand family in an effort to improve catalytic efficiency in the monoarylation of ammonia and acetone. The study is focused primarily on modifying the backbone phenylene linker, while retaining the same bite angle and steric bulk as the Mor-DalPhos ligand through the use of P(1-Ad)2 and morpholine donors. Eight new variants of Mor-DalPhos were prepared; two of these feature a pyridine linker (L1, L2), and five others feature either electron-donating (L3, L4) or electron-withdrawing (L5–L7) substituents on the phenylene linker. Additionally, thiomorpholino substitution (L8) was performed to investigate the effects of a possible tridentate coordination mode. Precatalyst complexes of the general formula LPd(cinnamyl)Cl were prepared and characterized in both solution and solid state. Solution studies demonstrated a significant degree of lability in the Pd–N bond, whereby dynamic behavior is seen to be dependent on the nature of the ligand backbone. The utility of these new ligands in the palladium-catalyzed monoarylation of ammonia or acetone was then surveyed. Notably, pyridine-derived ligand variants (L1, L2) were observed to out-perform parent Mor-DalPhos in the latter transformations.

Probing the effect of donor-fragment substitution in Mor-DalPhos on palladium-catalyzed C–N and C–C cross-coupling reactivity

The competitive catalytic screening of 18 known and newly prepared Mor-DalPhos ligand variants in the palladium-catalyzed cross-coupling of chlorobenzene with aniline, octylamine, morpholine, indole, ammonia, or acetone is presented, including ligands derived from the new secondary phosphine HP(Me2Ad)2 (Me2Ad = 3,5-dimethyladamantyl). Although triarylphosphine ancillary ligand variants performed poorly in these test reactions, ligands featuring either PAd2 or P(Me2Ad)2 donors (Ad = 1-adamantyl) gave rise to superior catalytic performance. Multiple Mor-DalPhos variants proved effective in cross-couplings involving aniline, octylamine, or morpholine; conversely, only a smaller subset of ligands proved useful in related cross-couplings of indole, ammonia, or acetone. In the case of the N-arylation of indole, a Mor-DalPhos ligand variant featuring ortho-disposed PAd2 and dimethylmorpholino donor fragments (L13) proved superior to all other ligands surveyed, including the parent ligand Mor-DalPhos (L5). Conversely, L5 was found to be superior to all other ligands in the palladium-catalyzed monoarylation of ammonia. Ligand L6 (i.e., the P(Me2Ad)2 variant of L5) proved superior to all other ligands in the monoarylation of acetone and, with the exception of indole N-arylation, was the most broadly useful of the Mor-DalPhos ligands surveyed herein.

Tailoring the structure, pH sensitivity and catalytic performance in Suzuki–Miyaura cross-couplings of Ln/Pd MOFs based on the 1,1′-di(p-carboxybenzyl)-2,2′-diimidazole linker

Four Pd/Ln MOFs have been synthesized and tested as catalysts in Suzuki–Miyaura reactions in neat water, neat ethanol as well as water–ethanol mixtures.

Synthesis of 2-Alkenyl-Tethered Anilines

Three general routes for the synthesis of (E)-2-alkenyl-tethered anilines have been developed. The first route involves a 3-aza-Cope rearrangement of N-allylic anilines in the presence of a Lewis acid. The requisite N-allylic anilines were prepared by the addition of vinyl-magnesium reagents to the corresponding aldimines. The second route details a direct cross-metathesis of 2-allylic or 2-homoallylic anilines with styrenes. The third route involves a palladium-catalyzed C-N cross-coupling of aryl halides. Taken together, these three strategies allowed access to the requisite aniline substrates with pendant alkenes at the 2-position with excellent trans selectivities.

Palladium(ii) in liquid ammonia: an investigation of structural and dynamical properties by applying quantum mechanical charge field molecular dynamics (QMCF-MD)

The structural and dynamical properties of Pd²⁺ in liquid ammonia have been investigated via quantum mechanical charge field molecular dynamics.

The synthesis of planar chiral pseudo-gem aminophosphine pre-ligands based on [2.2]paracyclophane

We have synthesized three pseudo-gem [2.2]paracyclophane-derived P,N-ligands and report preliminary activity studies for the amination of aryl bromides and chlorides.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Assembly of Primary (Hetero)Arylamines via CuI/Oxalic Diamide-Catalyzed Coupling of Aryl Chlorides and Ammonia

A general and practical catalytic system for aryl amination of aryl chlorides with aqueous or gaseous ammonia has been developed, with CuI as the catalyst and bisaryl oxalic diamides as the ligands. The reaction proceeds at 105-120 °C to provide a diverse set of primary (hetero)aryl amines in high yields with various functional groups.

Generating Active "L-Pd(0)" via Neutral or Cationic π-Allylpalladium Complexes Featuring Biaryl/Bipyrazolylphosphines: Synthetic, Mechanistic, and Structure-Activity Studies in Challenging Cross-Coupling Reactions

Two new classes of highly active yet air- and moisture-stable π-R-allylpalladium complexes containing bulky biaryl- and bipyrazolylphosphines with extremely broad ligand scope have been developed. Neutral π-allylpalladium complexes incorporated a range of biaryl/bipyrazolylphosphine ligands, while extremely bulky ligands were accommodated by a cationic scaffold. These complexes are easily activated under mild conditions and are efficient for a wide array of challenging C-C and C-X (X = heteroatom) cross-coupling reactions. Their high activity is correlated to their facile activation to a 12-electron-based "L-Pd(0)" catalyst under commonly employed conditions for cross-coupling reactions, noninhibitory byproduct release upon activation, and suppression of the off-cycle pathway to form dinuclear (μ-allyl)(μ-Cl)Pd2(L)2 species, supported by structural (single crystal X-ray) and kinetic studies. A broad scope of C-C and C-X coupling reactions with low catalyst loadings and short reaction times highlight the versatility and practicality of these catalysts in organic synthesis.

Nickel-catalyzed amination of aryl chlorides with ammonia or ammonium salts

The nickel-catalyzed amination of aryl chlorides to form primary arylamines occurs with ammonia or ammonium sulfate and a well-defined single-component nickel(0) precatalyst containing a Josiphos ligand and an η(2)-bound benzonitrile ligand. This system also catalyzes the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts.

Sulfur-containing DalPhos ligand variants: synthesis and application in Buchwald−Hartwig amination

We report herein on our synthetic, structural, and catalytic investigations of new P,S-DalPhos ligands featuring pairings of phosphorus and sulfur donor groups as well as new sulfur-containing analogues of the previously reported P,N-ligands Me-DalPhos and Mor-DalPhos, featuring a 2,3-disubstituted thiophenyl backbone. In examining the catalytic performance of these new sulfur-containing ligands in the Buchwald–Hartwig amination of octylamine, aniline, or ammonia with 4-chlorotoluene, noteworthy differences in reactivity behavior relative to Me-DalPhos and Mor-DalPhos were observed.

Selective amination of aryl chlorides catalysed by Ni(PMe3)4

C,N-coupling reactions of aryl chlorides and aryl amines catalyzed by a nickel catalyst are reported.

Exploring the Catalytic Reactivity of Nickel Phosphine–Phosphite Complexes

In this study, we present an investigation into various nickel phosphite and phosphite–phosphine complexes for use in the Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions and the ammonia arylation reaction. In these coupling reactions, it was discovered that the Ni[P(OEt)3]4, (dppf)Ni[P(OPh)3]2, and (binap)Ni[P(OPh)3]2 catalysts were the most effective. In addition, an optimisation process for these catalytic systems as well as functional group compatibility are discussed.

Palladium-catalyzed amination of aryl chlorides and bromides with ammonium salts

We report the palladium-catalyzed coupling of aryl halides with ammonia and gaseous amines as their ammonium salts. The coupling of aryl chlorides and ortho-substituted aryl bromides with ammonium sulfate forms anilines with higher selectivity for the primary arylamine over the diarylamine than couplings with ammonia in dioxane. The resting state for the reactions of aryl chlorides is different from the resting state for the reactions of aryl bromides, and this change in resting states is proposed to account for a difference in selectivities for reactions of the two haloarenes.