Nickel(II) thiosemicarbazone complex catalyzed Mizoroki–Heck reaction

Convenient synthesis of a new square planar nickel(II) naphthaldehyde thiosemicarbazone complex has been described. The composition of the complex has been established by elemental analysis, spectral methods, and single crystal X-ray crystallography. The new complex acts as an active homogeneous catalyst for the Mizoroki–Heck reaction of electron deficient (activating) and electron rich (deactivating) aryl bromides with various olefins under optimized conditions.     

Efficient Mizoroki–Heck coupling reactions using phosphine-modified Pd(II)–picolinate complex

Efficient Mizoroki–Heck couplings were obtained using a very easily synthesizable palladium(II) complex of hemilabile N–O ligand (picolinate), with high turnover frequencies up to >10,000?h^?1, in just 15?min, with high selectivity of >99% to the desired products. Wide applicability of the simple-looking palladium complex catalyst was established with differently functionalized substrates. Catalyst screening studies revealed intricate details of dependence of catalyst performance on different reaction parameters and conditions and arriving at the optimized facile methodology.     

Palladium tetrazole–supported complex as an efficient catalyst for the Heck reaction

Abstract  

A tetrazole-supported polymeric ligand has been synthesized. The palladium complex derived from the polymeric material has been evaluated as a catalyst for the Heck reaction of aryl iodides and bromides with styrene to provide the corresponding products in high yields. The reaction proceeded smoothly in the presence of 1 mol% with respect to Pd of catalyst in DMF at 125 or 140 °C within 1–3 h. Recycling studies showed that the catalyst can be readily recovered and reused for several times without significant loss of catalytic activity.     

An eco-friendly and energy-efficient protocol for the Heck reaction under solar radiation catalyzed by rice husk silica‐anchored cinchonine.Pd nanocomposite

An environmentally friendly and energy-efficient method for the carbon–carbon bond formation via cross-coupling Heck reaction using rice husk silica-anchored cinchonine.Pd nanocomposite as a heterogeneous catalyst under concentrated solar radiation is being reported. In this investigation, first, silica nanoparticles were synthesized using rice husks as available agricultural bioresources. Then, the surface of nano silica was modified by grafting (3-mercaptopropyl) trimethoxysilane, and after that, thiol-ene free radical reaction of its SH groups with alkene function of cinchonine by azobisisobutylonitrile initiator. Finally, the target nanocomposite, nano SiO₂-S-Cin.Pd, was created via loading palladium nanoparticles into the mesoporous nanocomposite by its reaction by palladium acetate, followed by ethanol reduction. The structure and morphology of the nano SiO₂-S-Cin.Pd nanocomposite was characterized using Fourier transform infrared spectra, X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The catalytic ability of this nanocomposite was investigated in the arylation of olefins in both concentrated solar radiation and conventional thermal conditions. A comparison of the conventional and CSR methods for C–C bond formation in PEG, showed that the CSR approach is a better alternative route with a high energy-saving strategy. The nanocatalyst is easily removed from the mixture and has been tested on several runs without a loss of catalytic activity. The heterogeneity of the nano SiO₂-S-Cin.Pd catalyst was confirmed by hot filtration test. This method has the advantages of simple methodology, easy work-up, high yields, short reaction times, and greener conditions. In addition to convenience, this technology improves product purity and offers economic and environmental benefits.     

Heterogeneous asymmetric Diels–Alder reactions using a copper–chiral bis(oxazoline) complex immobilized on mesoporous silica

A chiral bis(oxazoline)–copper complex was immobilized onto mesoporous silica and the resulting heterogeneous catalyst was employed in asymmetric Diels–Alder reactions. Reactions using the catalyst exhibited good enantioselectivity of 78% enantiomeric excess and endo/exo-selectivity (17:1) better than the corresponding homogeneous reaction. The catalyst could be easily recovered and reused several times without significant loss of the remarkable reactivity, diastereoselectivity and enantioselectivity.     

An asymmetric iodolactonization reaction catalyzed by a zinc bis-proline–phenol complex

The intramolecular zinc bis-proline-phenol complex 2a was found to promote enantioselective iodolactonization reactions of both electron-rich and electron-poor 5-aryl-5-hexenoic acids affording δ-iodolactones in good chemical yields with up to 82% enantiomeric excess. The reactions were found to be insensitive to air and moisture, providing an experimentally simple protocol for synthetically useful compounds.     

Asymmetric domino Michael–Henry reaction of 1,2-diones with nitroolefins catalyzed by a chiral bisoxazolidine–Ni(acac)2 complex

The asymmetric domino Michael–Henry reaction of 1,2-cyclohexadione with nitroolefins catalyzed by chiral ligand bisoxazolidine 1 and Ni(acac)₂ has been developed. This process provided highly functionalized chiral bicycle[3,2,1] octane derivatives with the generation of four new stereogenic centers in high yields (76–99%), and with excellent enantioselectivities (up to 99%) and good diastereoselectivities (up to 9:1) under mild reaction conditions. The procedure presented is simple and makes this method suitable for practical use.     

Mizoroki–Heck cross-coupling reactions using palladium immobilized on DABCO-functionalized silica

Transition Metal Chemistry - A heterogeneous palladium catalyst supported on silica modified by DABCO has been prepared by post-synthetic modification of silica gel. This heterogeneous catalytic...     

The effect of framework functionality on the catalytic activation of supported Pd nanoparticles in the Mizoroki–Heck coupling reaction

Palladium nanoparticles (Pd-NPs) were supported on functional and nonfunctional Co-coordination polymers (Pd/CoBDCNH₂ and Pd/CoBDC). Advanced analytical techniques revealed that Pd-NPs are supported on the external surface of the polymer framework and the functionalized framework possesses effective influence to prevent Pd-NP aggregation. Supported Pd-NPs were effectively applied as heterogeneous recyclable catalysts in the Mizoroki–Heck C–C cross coupling reactions of iodobenzene and either aromatic or aliphatic terminal alkenes. Catalytic results exhibited that highly dispersed Pd-NPs with low loading (1%) on the functional polymer (Pd/CoBDCNH₂) are more effective than aggregated Pd-NPs with high loading (9%) on the nonfunctional polymer (Pd/CoBDC). Both catalysts can simultaneously provide high activity and selectivity to E-coupled products, high efficiency in low amounts, easy separation of heterogeneous catalyst and appropriate performance in the recycling reaction without addition of a reducing agent.     

Palladiumimmobilized on chitosan nanofibers cross-linked by glutaraldehyde as an efficient catalyst for the Mizoroki–Heck reaction

Nonwoven chitosan (CS) nanofiber mats were successfully prepared by the electrospinning of the mixture of CS and poly(ethylene oxide) (PEO) in acetic acid aqueous solution. The CS/PEO fiber mats were treated with glutaraldehyde aqueous solution to stabilize fibers in solution. The concentration of glutaraldehyde is important for incorporating swelling properties in the cross-linked CS/PEO fiber mats. The cross-linked CS/PEO fibers (CCS/PEO fibers) were then used as supports for palladium catalysts in the Mizoroki–Heck reaction. The results of the study demonstrated that the catalytic activities of Pd catalyst supported on CCS/PEO fiber (Pd-CCS/PEO fiber) were highly dependent on the concentration of glutaraldehyde in the cross-linking process. Density functional theory (DFT) calculations indicated that the Schiff bond formed between CS and glutaraldehyde could reduce the energy needed to form a chelate complex between the CCS/PEO fibers and palladium active species. This in turn could decrease the activation energy of the Mizoroki–Heck reactions which occur in the presence of the Pd-CCS/PEO fiber catalysts. The optimized Pd-CCS/PEO fiber catalyst was very efficient and stable in the Mizoroki–Heck reaction of aromatic iodides with olefins.     

Palladium–N-heterocyclic carbene complexes for the Mizoroki–Heck reaction: An appraisal

This article presents a review of the most significant developments with N-heterocyclic carbene (NHC)–palladium catalytic systems used for the Heck reaction. For more than the past two decades, a large number of new NHC–Pd complexes have been synthesized and characterized. These studies focused on NHCs as a phosphine analogue, but the current review highlights the differences with particular ligands so as to attain a suitable balance between the electronic and bulky environments around the metal. NHCs have gained wide recognition as these ligands act as excellent σ-donors that form stable metal–NHCs with strong metal–carbon bonds. For this reason, metal–NHCs are commonly used as they are highly reactive and can selectively serve as catalysts for various chemical transformations. The objective of our article is to highlight significant recent progress in NHC–Pd(II) complexes and provide an overview of their extensive interaction in the Mizoroki–Heck reaction.     

First example of a silica gel-supported optically active Mn(III)–salen complex as a heterogeneous asymmetric catalyst in the epoxidation of olefins

An optically active Mn(III)–salen complex was supported on silica gel materials: the insoluble systems obtained were employed as catalysts in the asymmetric epoxidation of some aromatic olefins. Enantiomeric excess values up to 58% were obtained.     

Palladium-catalyzed Mizoroki–Heck type reaction with aryl trialkoxysilanes using hydrazone ligands

Palladium-catalyzed Mizoroki–Heck type reaction of olefines with aryl trialkoxysilanes gave the arylation products using a catalytic amount of hydrazone–Pd(OAc)₂ system with AgF at 60 °C in good yields.     

A novel hydrophobic fluorous ionic liquid for ligand-free Mizoroki–Heck reaction

Mizoroki–Heck reaction is carried out in a novel hydrophobic fluorous ionic liquid which was catalyzed by Pd-nanoparticles formed in situ from Pd(OAc)₂ used in the reaction. This reaction is operable under mild, aerobic, and ligand-free conditions in excellent yields. Aryl iodides, bromides as well as chlorides can be used showing its versatility. The key feature of the system is that catalyst along with ionic liquid can be reused at least five times with superior activity.     

Pd nanoparticles supported on reduced graphene oxide as an effective and reusable heterogeneous catalyst for the Mizoroki–Heck coupling reaction

A general method for the synthesis of palladium nanoparticles loaded on reduced graphene oxide functionalized with diethylenetriamine (PdNPs/rGO-NH₂) using a sonochemical procedure is described. The heterogeneous nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, thermogravimetric analysis, high-angle annular dark field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, UV–visible absorption, and inductively coupled plasma optical emission spectrometry. The PdNPs/rGO-NH₂ was very effective for the Mizoroki–Heck coupling reaction of several aryl iodide compounds with different alkenes in the presence of triethylamine. The reaction provides the coupling products in good to excellent yields (59–100%). Additionally, the PdNPs/rGO-NH₂ catalyst can be reutilized for six successive runs without any apparent diminution of its catalytic reactivity.     

Nanosized Pd assembled on superparamagnetic core–shell microspheres:Synthesis,characterization and recyclable catalytic properties for the Heck reaction

A series of magnetically recyclable Pd/Fe3O4@g-Al2O3 catalysts were synthesized using the superparamagnetic Fe3O4@g-Al2O3core–shell microspheres as the supporter and nano-Pd particles assembled on g-Al2O3 shell as the active catalytic component.The structure of the catalysts was characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),N2adsorption–desorption and vibrating sample magnetometer(VSM).The catalytic activity and the recyclability properties of the catalysts for the Heck coupling reaction with aryl bromides and the olefins were investigated.The results show that the microspheres of the magnetic Pd/Fe3O4@g-Al2O3 catalysts were about 400 nm and the nano-Pd particles assembled on g-Al2O3 shell were about 3–4 nm in size.The saturation magnetization(MS) of the magnetic catalysts was sufficiently high to allow magnetic separations.In the Heck coupling reactions,the magnetic Pd/Fe3O4@g-Al2O3 catalysts exhibited good catalytic activity and recyclability.With Pd/Fe3O4@g-Al2O3(0.021 mol%) catalyst,the bromobenzene conversion and product yield reached about 96.8% and 91.2%,respectively,at 120 8C and in 14 h.After being recycled for six times,the conversion of bromobenzene and the recovery of the catalyst were about80% and 90%,respectively.The nano-Pd particles were kept well dispersed in the used Pd/Fe3O4@g-Al2O3 catalysts.     

Diastereoselective synthesis of tetrahydroquinolines via a palladium-catalyzed Heck–Suzuki cascade reaction

A method for the diastereoselective synthesis of tetrahydroquinolines via a palladium-catalyzed Suzuki terminated Heck reaction is described. The reaction provides access to tetrahydroquinolines containing both quaternary and tertiary stereocenters. Ligand effects, a rationale for the high level of diastereoselectivity, and a mechanistic hypothesis are discussed.     

Efficient synthesis of 3-arylbutadiene sulfones using the Heck–Matsuda reaction

An efficient and practical method for a scalable synthesis of 3-arylbutadiene sulfones deals with the ligand-free Heck–Matsuda reaction of sulfolene with aryldiazonium tetrafluoroborates followed by triethylamine-promoted double bond shift.     

A novel N–O ligand for palladium-catalyzed Mizoroki–Heck reaction in neat water

1-(Morpholin-1-yl-pyridin-2-yl-methyl)-2-naphthol as a novel efficient N–O ligand has been developed for palladium-catalyzed Mizoroki–Heck reaction in neat water without the protection of an inert atmosphere. The reactions proceed smoothly and give the desired products in moderate to excellent yields. The catalyst system is reusable.