2-Aminobiphenyl Palladacycles: The “Most Powerful” Precatalysts in C–C and C–Heteroatom Cross-Couplings

Facile cyclometallation of a mesitylsilylene: synthesis and preliminary catalytic activity of iridium(iii) and iridium(v) iridasilacyclopentenes

The cyclometallation of a monosilylene has been achieved in iridium(iii) and iridium(v) complexes; the former catalyse arene deuteriations and borylations.

Csp2–Br bond activation of Br-pyridine by neophylpalladacycle: formation of binuclear seven-membered palladacycle and bipyridine species

A small library of seven-membered palladacycles and asymmetric bipyridines was prepared via C–Br activation and C–C coupling reactions.

Suzuki-Miyaura cross-coupling optimization enabled by automated feedback

An automated, droplet-flow microfluidic system explores and optimizes Pd-catalyzed Suzuki-Miyaura cross-coupling reactions. A smart optimal DoE-based algorithm is implemented to increase the turnover number and yield of the catalytic system considering both discrete variables-palladacycle and ligand-and continuous variables-temperature, time, and loading-simultaneously. The use of feedback allows for experiments to be run with catalysts and under conditions more likely to produce an optimum; consequently complex reaction optimizations are completed within 96 experiments. Response surfaces predicting reaction performance near the optima are generated and validated. From the screening results, shared attributes of successful precatalysts are identified, leading to improved understanding of the influence of ligand selection upon transmetalation and oxidative addition in the reaction mechanism. Dialkylbiarylphosphine, trialkylphosphine, and bidentate ligands are assessed.

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.

Development of a Method for the N-Arylation of Amino Acid Esters with Aryl Triflates

A general method for the N-arylation of amino acid esters with aryl triflates is described. Both α- and β-amino acid esters, including methyl, tert-butyl, and benzyl esters, are viable substrates. Reaction optimization was carried out by design of experiment (DOE) analysis using JMP software. The mild reaction conditions, which use t-BuBrettPhos Pd G3 or G4 precatalyst, result in minimal racemization of the amino acid ester. This method is the first synthetic application of the t-BuBrettPhos Pd G4 precatalyst. Mechanistic studies show that the observed erosion in enantiomeric excess is due to racemization of the amino acid ester starting material and not of the product.

Remote Electronic Effects by Ether Protecting Groups Fine-Tune Glycosyl Donor Reactivity

It was established that para-substituted benzyl ether protecting groups affect the reactivity of glycosyl donors of the thioglycoside type with the N-iodosuccinimide/triflic acid promoter system. Having electron donating p-methoxybenzyl ether (PMB) groups increased the reactivity of the donor in comparison to having electron withdrawing p-chloro (PClB) or p-cyanobenzyl ether (PCNB) protecting groups, which decreased the reactivity of the glycosyl donor relative to the parent benzyl ether (Bn) protected glycosyl donor. These findings were used to perform the first armed-disarmed coupling between two benzylated glucosyl donors by tuning their reactivity. In addition, the present work describes a highly efficient palladium catalyzed multiple cyanation and methoxylation of p-chlorobenzyl protected thioglycosides. The results of this paper regarding both the different electron withdrawing properties of various benzyl ethers and the efficient and multiple protecting group transformations are applicable in general organic chemistry and not restricted to carbohydrate chemistry.

Palladacycle-Catalyzed Carbonylative Suzuki-Miyaura Coupling with High Turnover Number and Turnover Frequency

This work reports the carbonylative Suzuki-Miyaura coupling of aryl iodides catalyzed by palladacycles. More importantly, the palladacycles have been used to generate high turnover numbers (TON's) and turnover frequencies (TOF's). A range of aryl iodides can be coupled with arylboronic acids, generating TON's in the range of 10(6) to 10(7) and TOF's in the range of 10(5) to 10(6) h(-1). Comparison of the palladacycles with a conventional palladium source shows their superiority in generating high TON's and TOF's.

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.

Mono- and binuclear palladacycles via regioselective C–H bond activation: syntheses, mechanistic insights and catalytic activity in direct arylation of azoles

Hybrid “POCN”-ligated mono- and binuclear palladacycles have been synthesized via the base-assisted regioselective C–H bond activation, and their mechanistic aspects and catalytic application for the arylation of azoles have been described.

Highly electron-poor Buchwald-type ligand: application for Pd-catalysed direct arylation of thiophene derivatives and theoretical consideration of the secondary Pd0–arene interaction

Highly electron-poor SPhos ligands stabilised the Pd complex by secondary Pd⁰–arene interaction.