Aminophosphine Palladium Pincer-Catalyzed Carbonylative Sonogashira and Suzuki-Miyaura Cross-Coupling with High Catalytic Turnovers

Platform for the Immobilizing of Ultrasmall Pd Clusters for Carbonylation: In Situ Self-Templating Fabrication of ZIF-8 on ZnO

Incorporating metal clusters into the confined cavities of metal-organic frameworks (MOFs) to form MOF-supported catalysts has attracted considerable research interest with regard to carbonylation reactions. Herein, a self-templating method is used to prepare the zinc oxide (ZnO)-supported core-shell catalyst ZnO@Pd/ZIF-8. This facile strategy controls the growth of metal sources on the ZIF-8 shell layer and avoids the metal diffusion or aggregation problems of the conventional synthesis method. The characteristics of the catalysts show that the palladium (Pd) clusters are highly dispersed with an average particle size of ≈1.2 nm, making them excellent candidates as a catalyst for carbonylation under mild conditions. The optimal catalyst (1.25-ZnO@Pd/ZIF-8) exhibits excellent activity in synthesizing α, β-alkynyl ketones under 1 atm of carbon monooxide (CO), and the conversion rate of 1, 3-diphenylprop-2-yn-1-one is 3.09 and 3.87 times more than those of Pd/ZIF-8 and Pd2+, respectively, for the first 2 h. Moreover, the 1.25-ZnO@Pd/ZIF-8 is recyclable, showing negligible metal leaching, and, under the conditions used in this investigation, can be reused at least five times without considerable loss in its catalytic efficiency. This protocol can also be applied with other nucleophile reagents to synthesize esters, amides, and acid products.

Triazine-wingtips accelerated NHC-Pd catalysed carbonylative Sonogashira cross-coupling reaction

The transmetalation as the rate-limiting step was effectively accelerated by newly designed N-heterocyclic carbenes with triazine wingtips (T-NHC). By using a ppm-level precatalyst T-NHC-Pd (8), the highly efficient coupling of aryl iodide, alkyne and carbon monoxide furnished a variety of ynone compounds. T-NHC-Pd (5), which deprotonated 4-methyl-phenylacetylene under mild conditions, converted into alkynyl-coordinated catalytic active species PdCl(T-NHC)(Py)(alkynyl). In the putative Pd/Pd catalytic cycle, both triazine-wingtips and NHCs are key players for establishing the carbonylative cross-couplings with high TON and TOF.

Electrochemical Palladium-Catalyzed Oxidative Sonogashira Carbonylation of Arylhydrazines and Alkynes to Ynones

Oxidative carbonylation using carbon monoxide has evolved as an attractive tool to valuable carbonyl-containing compounds, while mixing CO with a stoichiometric amount of a chemical oxidant especially oxygen is hazardous and limits its application in scale-up synthesis. By employing anodic oxidation, we developed an electrochemical palladium-catalyzed oxidative carbonylation of arylhydrazines with alkynes, which is regarded as an alternative supplement of the carbonylative Sonogashira reaction. Combining an undivided cell with constant current mode, oxygen-free conditions avoids the explosion hazard of CO. A diversity of ynones are efficiently obtained using accessible arylhydrazines and alkynes under copper-free conditions. A possible mechanism of the electrochemical Pd(0)/Pd(II) cycle is rationalized based upon cyclic voltammetry, kinetic studies, and intermediates experiments.

Microwave-assisted nucleophilic degradation of organophosphorus pesticides in propylene carbonate

Propylene carbonate is becoming a suitable green alternative to volatile organic solvents in the study of chemical reactions. In this study, an efficient method for nucleophilic degradation of five organophosphorus pesticides, fenitrothion, malathion, diazinon, parathion, and paraoxon, using propylene carbonate as a solvent is proposed. The effect of changing the nature of the nucleophile and the influence of microwave (MW) heating were investigated. A screening of temperatures (50 °C-120 °C) was performed under microwave heating. The pesticide degradation was followed by 31P NMR, and the extent of conversion (%) was calculated by the integration of phosphorus signals. Keeping in mind that recently it has been reported that some ionic liquids play a nucleophilic role, in this work we report for the first time the degradation of organophosphorus pesticides by using an amino acid-based ionic liquid such as Bmim[Ala] as a nucleophile and a bio-based solvent (propylene carbonate) as a reaction medium in combination with microwave heating.

Soft Heteroleptic N-Heterocyclic Carbene Palladium(II) Species for Efficient Catalytic Routes to Alkynones via Carbonylative Sonogashira Coupling

N,N'-Substituted di-isopropyl (NHC-1), benzyl-isopropyl (NHC-2), and adamantyl-isopropyl (NHC-3) benzimidazolium salts react with palladium(II) bromide in pyridine to afford the corresponding trans-dibromidopyridinepalladium(II) complexes Pd-C1, Pd-C2, and Pd-C3 in high yields. A distorted square planar geometry for Pd-C2 and Pd-C3 was confirmed by single-crystal X-ray diffraction. The palladium(II) complexes show a remarkably higher catalytic activity and selectivity, compared to the literature data, in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with aryl alkynes, alkyl alkynes, and dialkynes. Excellent yields with as low as 0.03 mol % loading of the catalyst were obtained. In the series of benzimidazolium (NHC) precursors, the ¹H NMR signals of the α hydrogen show a consistent probing of the N-substituent donor strength. The density functional theory (DFT) quantum mechanical descriptors of the frontier orbitals were calculated. A linear correlation of the calculated absolute softness of the complexes versus the calculated percent buried volume (%V _bur) of their corresponding ligands was obtained. The catalytic activity experimental data are consistent with the hard soft acid base (HSAB)-predicted high affinity of the softest Pd-C3 complex for soft substrates, such as aryl iodides.

Synthesis of d-glyco-alkynone derivatives via carbonylative Sonogashira reaction

A carbonylative Sonogashira coupling approach to the synthesis of glyco-alkynones is described. Eighteen examples were obtained in moderate do nearly quantitative yields under mild conditions employing Mo(CO)6 as a safe carbon monoxide source. Functionalization of the alkynyl moiety via cycloaddition with organic azides provided six examples of glyco-triazoles.

Scope and limitation of propylene carbonate as a sustainable solvent in the Suzuki–Miyaura reaction

The Suzuki–Miyaura reaction is one of the most used transformations in drug research. Thus making this reaction more sustainable is of considerable current interest. Here we show that propylene carbonate (PC) can be used as a solvent for the Suzuki–Miyaura reaction. PC is one of the greenest solvents since it is synthesized under green conditions by the use of carbon dioxide in the air. All reactions proceeded well and good or excellent yields were observed for the biaryl products. Nonetheless in the case of pyridazinones, 2-hydroxypropyl- chain containing side-products were observed. Importantly, this fact allowed the isolation of several novel compounds which were generated under prominently green conditions.

The Suzuki–Miyaura reaction was carried out in propylene carbonate yielding an interesting side-product besides the biphenyl derivative.