Phosphinite- and phosphite-based Type I palladacycles as highly active catalysts for addition reactions of arylboronic acids with aldehydes, α,β-unsaturated ketones, α-ketoesters, and aldimines

Phosphinite- and phosphite-based type I palladacycle-catalyzed additions of arylboronic acids with aldehydes, α,β-unsaturated ketones, α-ketoesters, and aldimines are described. Our study showed that readily available phosphinite- and phosphite-based type I palladacycles could possess higher catalytic activity than phosphine-based palladacycles and were highly active, practical catalysts. Our study may pave the road for development of optically active phosphinite- and phosphite-based palladacycles for asymmetric catalysis.     

Highly active oxime-derived palladacycle complexes for Suzuki-Miyaura and Ullmann-type coupling reactions

Oxime-derived chloro-bridged palladacycles 12 and 13 are efficient complexes for the Suzuki-Miyaura reactions of aryl-, allyl-, and benzyl halides with arylboronic acids. The isolated catalysts are thermally stable, not sensitive to air or moisture, and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions with aryl bromides and chlorides, displaying turnover numbers (TON) of up to 5 x 10(5) and turnover frequencies (TOF) of up to 198 000 h(-1) for aryl bromides. Aryl chlorides undergo the Suzuki reaction with arylboronic acids with TON of up to 4700 and TOF up to 4700 h(-1). Even inexpensive and readily available benzyl and allyl chlorides undergo the coupling reaction with good turnover numbers. Complexes of 12 catalyze the syntheses of symmetrical biaryls in good yields via reductive coupling of iodoarenes in the presence of Hünig's base.     

Orthoplatinated triarylphosphite as a highly efficient catalyst for addition reactions of arylboronic acids with aldehydes: low catalyst loading catalysis and a new tandem reaction sequence

Readily available, air/moisture-stable orthoplatinated triarylphosphite catalyzes the addition reactions of arylboronic acids with aldehydes with the catalyst loading as low as 0.01%. It also cataylzes a new tandem reaction of arylboronic acids with alpha,beta-unsaturated aldehydes to form 1,3-diaryl-1-propanols. Our study provides a new paradigm for the application of orthoplatinated triarylphosphites, and may pave the road to develop other Pt(II) catalysts for such addition reactions and other tandem reactions with such addition reactions as part of the reaction sequence.     

Synthesis of novel palladacycles and their application in Heck and Suzuki reactions under aerobic conditions

[reaction: see text] Design and synthesis of a novel family of furancarbothioamide-based palladacycles are reported herein. These palladacycles are thermally stable, not sensitive to air or moisture, and are applied effectively in the Heck reaction of aryl halides with terminal olefins and in the Suzuki reaction of aryl halides with arylboronic acids. These reactions were performed under aerobic conditions, leading to turnover numbers (TONs) up to 1 x 10(5).     

Palladium(II) catalyst systems for the addition of boronic acids to bicyclic alkenes: new scope and reactivity

[reaction: see text] The palladium-catalyzed ring-opening addition of arylboronic acids to heterobicyclic alkenes is reported. Excellent yields are obtained for the addition of a wide variety of arylboronic acids to aza- and oxabicyclic alkenes. This methodology is especially useful in the synthesis of 1-amino-2-aryldihydronaphthalene scaffolds, for which rhodium catalysts are currently unreactive or give complex mixtures. Asymmetric versions of these reactions are under development, and preliminary results are reported.     

Synthesis and characterizations of arsine– and stibine–ligated Schiff base palladacycles and their applications in Suzuki–Miyaura cross‐coupling reactions

A series of arsine‐ and stibine‐ligated Schiff base palladacycles were synthesized by the reaction of μ‐Cl‐bridged Schiff base palladacycles [Pd(C₆H₄CH]NC₆H₂R)(μ‐Cl)]₂ (R = 2,4,6‐trimethyl or 2,6‐diisopropyl) with AsPh₃ or SbPh_3. The new arsine‐ and stibine‐ligated palladacycles were fully characterized using ¹H NMR, ¹³C NMR and infrared spectroscopies, high‐resolution mass spectrometry, elemental analysis and single‐crystal X‐ray diffraction. Further exploration of the catalytic application of the palladacycles for Suzuki–Miyaura cross‐coupling reactions of aryl bromides with arylboronic acids was carried out. It was found that the new palladacycles are considerably active for these coupling reactions. Copyright © 2016 John Wiley & Sons, Ltd.     

Orthopalladated and -platinated bulky triarylphosphite complexes: synthesis,reactivity and application as high-activity catalysts for Suzuki and Stille coupling reactions

Bulky triarylphosphite ligands undergo facile orthometallation reactions with palladium and platinum precursors. The crystal structure of an example of the resultant palladacycles has been determined. The reactivity of some of the metallacycles with HCl, monodentate and bidentate phosphines and sodium diethyldithiocarbamate has been investigated, and the crystal structure of a diethyldithiocarbamate adduct of a palladacycle is presented. The palladacyclic complexes prove to be extremely active catalysts for the Suzuki coupling of aryl bromides with aryl boronic acids. They can also be used as catalysts for the coupling of alkylboronic acids. Meanwhile di- and trialkyl phosphine adducts of one of the palladacycles shows very high activity in the Suzuki coupling of aryl chlorides and can also be used to good effect for the Stille coupling of these substrates. The role of the phosphite ligand in the Suzuki coupling of aryl chlorides seems to be one of increasing catalyst longevity by stabilisation of the Pd(0) resting state.     

Palladacycles in catalysis - a critical survey

The application of palladacycles as catalysts for cross-coupling and similar reactions is reviewed. In the majority of cases palladacycles are likely to serve as a source of highly active but unstable zero-valent palladium species. In this respect the palladacycles resemble the so-called phosphine-free catalysts. The advantages and limitations of palladacycle catalysts are discussed.     

Rh(I)/diene-catalyzed addition reactions of aryl/alkenylboronic acids with aldehydes

[Rh(COD)Cl]₂-catalyzed addition reactions of arylboronic acids with aldehydes, with low Rh(I) catalyst loading, are described. We also found that the reaction of arylboronic acids with α,β-unsaturated aldehydes greatly depends on the solvent and the steric hindrance of the reagents/substrates.     

Synthesis of solution-phase phosphoramidite and phosphite ligand libraries and their in situ screening in the rhodium-catalyzed asymmetric addition of arylboronic acids

Herein, we report the automated parallel synthesis of solution-phase libraries of phosphoramidite ligands for the development of enantioselective catalysts. The ligand libraries are screened in situ in the asymmetric rhodium-catalyzed addition of arylboronic acids to aldehydes and imines. It is shown that the described methodology results in the straightforward discovery of leads for highly efficient enantioselective catalysts.     

[Ir(COD)Cl]2/tris(2,4-di-t-butylphenyl)phosphite-catalyzed addition reactions of arylboronic acids with aldehydes

[Ir(COD)Cl]₂/tris(2,4-di-t-butylphenyl)phosphite-catalyzed addition reactions of arylboronic acids with aldehydes were described. The Ir(I) catalyst, generated from [Ir(COD)Cl]₂ and tris(2,4-di-t-butylphenyl)phosphite, was an efficient catalyst system for the addition reactions of a variety of arylboronic acids with aromatic and aliphatic aldehydes. The easy availability of the catalyst and good yields make these reactions potentially useful in organic synthesis.     

Sequential aldol condensation-transition metal-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step.     

Chiral Nanoparticles/Lewis Acids as Cooperative Catalysts for Asymmetric 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Amides

Cooperative catalysts consisting of chiral Rh/Ag nanoparticles and Sc(OTf)₃ have been developed that catalyze asymmetric 1,4‐addition reactions of arylboronic acids with α,β‐unsaturated amides efficiently. The reaction has been considered one of the most challenging reactions because of the low reactivity of the amide substrates. The new catalysts provide the desired products with outstanding enantioselectivities (>98 % ee) in the presence of low loadings (<0.5 mol %) of the catalyst.     

Microwave promoted Suzuki reactions between aroyl chlorides and boronic acids catalyzed by heterogeneous and homogeneous phosphine-free palladium catalysts

Suzuki cross-coupling reactions between arylboronic acids and aroyl chlorides with phosphine-free palladium catalysis under microwave irradiation were performed to obtainment of aromatic ketones in good yields within short times. Heterogeneous and homogeneous catalysts were studied as well as their influence in the reaction selectivity relative to homocoupling of the boronic acids.     

Rhodium-catalyzed addition of arylboron compounds to nitriles, ketones, and imines

The rhodium-catalyzed addition reactions of sodium tetraphenylborate and arylboronic acids to nitriles, ketones, and imines were examined. The reaction of nitriles could be carried out efficiently in the presence of a catalyst system of [RhCl(cod)]₂-dppp and H₂O to give the corresponding monoarylated products selectively. Although unactivated ketones and imines are known to be poor electrophiles for rhodium-catalyzed arylation, the phenylation of them with use of sodium tetraphenylborate proceeded smoothly in the presence of [RhCl(cod)]₂ and Rh(acac)(cod) as catalysts, respectively. The addition of NH₄Cl was found to be crucial to effectively conduct the reaction of ketones and imines.     

Chiral Palladacycle Catalysts Generated on a Single‐Handed Helical Polymer Skeleton for Asymmetric Arylative Ring Opening of 1,4‐Epoxy‐1,4‐dihydronaphthalene

Post‐polymerization C? H activation of poly(quinoxaline‐2,3‐diyl)‐based helically chiral phosphine ligands (PQXphos) with palladium(II) acetate afforded chiral phosphapalladacycles quantitatively. In situ generated palladacycles exhibited enantioselectivities up to 94 % ee in the palladium‐catalyzed asymmetric ring‐opening arylation of 1,4‐epoxy‐1,4‐dihydronaphthalenes with arylboronic acids.     

Rhodium-catalyzed addition of arylboronic acids to alkynyl aza-heteroaromatic compounds in water

Alkynyl heteroaromatic compounds reacted with arylboronic acids to give addition products in the presence of a rhodium catalyst. The best results were obtained when a novel pyridine-substituted water-soluble phosphine ligand was used. The reactions proceed to give trisubstituted alkenes from various arylboronic acids and alkynyl heteroaromatic compounds with high regioselectivity. Only alkynes with a nitrogen atom in proximity to the triple bond were converted to the corresponding alkenes, as expected for a chelation-controlled addition.     

Highly efficient and reusable supported pd catalysts for Suzuki-Miyaura reactions of aryl chlorides

Syntheses of air- and moisture-stable heterogeneous (tert-butylarylphosphino)polystyrene-supported Pd catalysts and their use for versatile Suzuki-Miyaura reactions of aryl chlorides and arylboronic acids under non-anhydrous conditions are reported. The catalysts are easily recovered by filtration. They can be used many times (more than seven) without showing any loss of activity, and the amount of Pd leached is extremely low (<0.1%).     

Selective palladium-catalyzed C-F activation/carbon-carbon bond formation of polyfluoroaryl oxazolines

A selective palladium-catalyzed Suzuki-Miyaura coupling reaction of polyfluorophenyl oxazolines through ortho C-F activation is described. It was found that reactions with DPPF as the ligand occurred much faster than those with other ligands. A variety of arylboronic acids including challenging functionalized arylboronic acids such as enolizable ketones, aldehyde, cyano, ester, and trifluoromethyl groups were tolerated with the reaction conditions.     

Oxime palladacycles revisited: stone-stable complexes nonetheless very active catalysts

Our review critically presents the main achievements, advantages, and limitations of oxime palladacycles as high-turnover catalysts for Heck, as well as homo- and cross-coupling reactions such as Suzuki-Miyaura, Stille, Ullmann-type, Cassar-Heck-Sonogashira, sila-Sonogashira, Glaser-type, Hiyama, and alkoxycarbonylation reactions. New developments in this area are reviewed from a mechanistic and synthetic point of view. The role of oxime palladacycles as a source of highly active zero-valent palladium species is also discussed.