Synthesis of arylated chalcone derivatives via palladium cross-coupling reactions

A useful protocol for arylation of the olefin double bond of chalcones to afford tri- and tetra-substituted chalcone derivatives is reported. The protocol begins with the Heck reaction between chalcones and aryl iodides providing β-arylchalcones. This reaction tolerates various functional groups on both rings, as well as deactivated aryl iodides. The products are obtained in moderate to excellent yields and the (E)-β-arylchalcones (E:Z?>?96:4) can be isolated via precipitation. Competitive Heck reactions pointed to a significant effect of ring one substituents on the reaction rate, while substituents on ring two have a much smaller effect. To access α,β-diarylchalcones, a sequential bromination-Suzuki cross coupling strategy was applied to the β-arylated compounds which afforded double arylated chalcone derivatives in 60–99% yield over two steps.     

Preparation of anionic phosphine ligands in situ for the palladium-catalyzed Buchwald/Hartwig amination reactions of aryl halides

2-Phenylindenyl phosphine ligand can be changed into anionic phosphine ligand in situ and utilized in the palladium-catalyzed Buchwald/Hartwig amination reactions in DME, providing good to excellent yields of amination products from aryl chlorides, bromides and iodides. ³¹P NMR studies show that the resonance for the anionic phosphine appeared between those of the (2-phenylindenyl)-dicyclohexyl phosphonium salt and (2-phenylindenyl)dicyclohexylphosphine. The calculated results were consistent with the experimental results.     

P,N-Type benzimidazolyl phosphine ligands for the palladium-catalyzed Suzuki coupling of potassium aryltrifluoroborates and aryl chlorides

This study describes the efficacy of P,N-type benzimidazolyl phosphine ligands, which can be easily synthesized from commercially available and inexpensive starting materials. The application of this ligand array in palladium-catalyzed Suzuki-Miyaura coupling reaction of aryl chlorides with potassium aryltrifluoroborates is described. The air stable benzimidazolyl phosphines in combination with a palladium metal precursor provides highly effective catalysts for the Suzuki-Miyaura coupling of unactivated aryl chlorides and can achieve a catalyst loading of only 0.05 mol %.     

Hydroxylated terphenylphosphine ligands for palladium-catalyzed ortho-selective cross-coupling of dibromophenols, dibromoanilines, and their congeners with Grignard reagents

p-Terphenylphosphines bearing one or two hydroxy groups were used as ligands to palladium in the cross-coupling of dibromophenols, dibromoanilines, and their congeners with Grignard reagents. High ortho-selectivity that cannot be achieved using other phosphine ligands was observed. ortho-Preference was also observed in competitive cross-coupling reactions of two substrates. A significant effect of the concentration of the Grignard reagent on the ortho-selectivity was observed, when the hydroxylated terphenylphosphines were used. Kinetic studies on this effect showed that high concentrations of the Grignard reagent retard the cross-coupling reaction only at the para-position, but not at the ortho-position.     

1,1′-Bis(oxazolinyl)ferrocene-based palladium catalysts: Synthesis, X-ray structures and applications in Suzuki and Heck coupling reactions

1,1′-Bis(oxazolinyl)ferrocene-based palladium dichloride complexes 2a and 2b were synthesized. X-ray single-crystal diffraction analyses showed that they are of the N,N′-chelating type, and that the coordination mode of 2a, which has an isopropyl group, is of the cis type, whereas that of 2b, which has a tert-butyl group, is the trans one. These two complexes were employed as catalysts for Suzuki and Heck reactions, and showed high catalytic activities in coupling reactions with various aryl halides and counterparts (phenylboronic acid or n-butyl acrylate). Particularly, the catalyst 2a afforded the coupled product of aryl bromide with phenylboronic acid at room temperature.     

l-Arginine as a base and ligand for the palladium-catalyzed C-C and C-N cross-coupling reactions in aqueous media

l-Arginine (2-amino-5-guanidinopentanoic acid) acts as a base and ligand in reaction medium, exhibits a very high activity and recyclability to palladium-catalyzed C-C and C-N cross-coupling reactions in aqueous media. The corresponding Suzuki products were obtained in good to excellent yields by using various aryl halides (I, Br, Cl). Also, the cross coupling reactions of arylboronic acids with various amines in aqueous medium proceed in good to excellent yield under same conditions. Furthermore, the catalyst could be easily separated from the reaction mixture and could be recycled several times without significant loss in its catalytic activity.     

Ferrocenyl-palladium complexes in cross-coupling reactions: a comparative study

Ferrocenecarboxaldehyde hydrazones were converted into palladium complexes on treatment with sodium tetrachloropalladate. The substitution pattern of the ferrocenylhydrazones was found to have a marked influence on the mode the palladium was attached to the organic moiety. The catalytic activity of the new palladium complexes in cross-coupling reactions was examined in detail, and it was compared with conventional catalyst systems.     

Synthesis and characterizations of N,N,N′,N′-tetrakis (diphenylphosphino)ethylendiamine derivatives: Use of palladium(II) complex as pre-catalyst in Suzuki coupling and Heck reactions

Oxidation of N,N,N′,N′-tetrakis(diphenylphosphino)ethylendiamine (1) with elemental sulfur and selenium gives the corresponding sulfide and selenide, respectively, [(Ph₂P(E))₂NCH₂CH₂N(P(E)Ph₂)₂] (E: S 1a, Se 1b). Complexes of 1 [(M₂Cl₄){(Ph₂P)₂NCH₂CH₂N(PPh₂)₂}] (M: Ni(II) 1c, Pd(II) 1d, Pt(II) 1e) were prepared by the reaction of 1 with NiCl₂ or [MCl₂(COD)] (M = Pd, Pt). The new compounds were characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of Pd(II) complex 1d was tested in the Suzuki coupling reaction and Heck reaction. The palladium complex 1d catalyses the Heck reaction between styrene and aryl bromides as well as Suzuki coupling reaction between phenylboronic acid and arylbromides affording stilbenes and biphenyls in high yield, respectively.     

Novel phosphine ligands bearing 3(5)-pyrazolyl and 4-(2-amino)pyrimidinyl groups: Synthesis and coordination chemistry

Novel triphenyl phosphine ligands bearing pyrazole or 2-aminopyrimidine groups in the ortho or meta position of one or three of the phenyl rings were obtained starting from the corresponding acyl derivatives Ph₂P(o-C₆H₄-COCH₃), Ph₂P(m-C₆H₄-COCH₃), or P(m-C₆H₄-COCH₃)₃. Conversion of the acyl groups into 3-dimethylamino-2-propen-1-onyl units was achieved by reaction with HC(OMe)₂NMe₂ which underwent ring closing with hydrazine or guanidine to yield the desired heterocycles. Two palladium complexes were synthesized using the coordinatively labile precursor (PhCN)₂PdCl₂, one of them could be characterized by X-ray structure analysis.     

Pyrazole-tethered phosphine ligands for Pd(0): useful catalysts for Stille, Kumada and Hiyama cross-coupling reactions

Combination of 3,5-dimethyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, A, and 3-tert-butyl-5-methyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, B, with Pd₂(dba)₃ furnished excellent catalysts for Stille, Kumada and Hiyama cross-coupling reactions. Effects of solvents, bases and ligand/palladium ratio on efficiency of coupling reactions were studied. Molecular structures of palladium(II) complexes of A and B determined by single-crystal X-ray diffraction method revealed a close similarity of ligand arrangement around the metal centre.     

Pd-CNT-catalyzed ligandless and additive-free heterogeneous Suzuki-Miyaura cross-coupling of arylbromides

Pd-CNT efficiently catalyzed Suzuki-Miyaura coupling of arylbromides under ligandless and additive-free conditions in aqueous media. For hydrophilic substrates, the reaction could be carried out in neat water.     

Synthesis of cobalt-containing monodentate phosphine ligand and application toward Suzuki cross-coupling reactions

A bulky, dicobalt complexed, mono-dentate phosphine, [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-PhCCPCy₂) (4), was prepared from the reactions of the bis(diphenylphosphino)methylene (dppm)-bridged dicobalt complex Co₂(CO)₆(μ-Ph₂PCH₂PPh₂) (2) with PhCCPCy₂ (3). Combination of 4 and Pd(OAc)₂ (1:1) gave an active catalyst for the palladium-catalyzed Suzuki coupling of aryl bromides with phenylboronic acid; the catalytic reactions can be performed even under low catalyst loadings (0.1-0.001 mol% 4/Pd(OAc)₂). Compound 4 has been proved to be an authentic and effective mono-dentate phosphine ligand. Crucial factors such as 4/Pd(OAc)₂ ratio, base being used, solvent volume, temperature, and electronic variation of the aryl bromides in reactions were also investigated and results are reported.     

A simple route to 9-fluorenylidenes by domino Suzuki/Heck coupling reactions

A palladium catalyzed domino intermolecular Suzuki followed by intramolecular Heck coupling is described. This strategy afforded a novel and convenient synthesis of various 9-fluorenylidene derivatives in one-pot under relatively mild reaction condition.     

Efficient imidazolium salts for palladium-catalyzed Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions

The system, Pd(OAc)2/imidazolium salts (L2), was found as an efficient catalyst in the Heck coupling reaction of olefins with aryl halides and Suzuki reactions of various aryl halides with aryl boronic acids under aerobic condition. This catalytic system demonstrates great tolerance to a wide range of groups on all substrates of aryl halides, alkenes and aryl boronic acids.     

Synthesis and characterization of tris{2-(N,N-bis(diphenylphosphino) aminoethyl} amine derivatives: Application of a palladium(II) complex as a pre-catalyst in the Heck and Suzuki cross-coupling reactions

The polydendate bis(phosphino)amine, tris{2-(N,N-bis(diphenylphosphino)aminoethyl}amine 1 has been prepared in a single step from the reaction of tris(2-aminoethyl)amine with six equivalents of PPh₂Cl in the presence of NEt₃ in THF. Oxidation of 1 with aqueous H₂O₂, elemental sulfur or grey selenium gave the corresponding oxide, sulfide or selenide derivatives. [{(P(E)Ph₂)₂NCH₂CH₂}₃N] (E: 2a O, 2b S, 2c Se), respectively. Reaction of [{(PPh₂)₂NCH₂CH₂}₃N] with 3 equiv. of PdCl₂(cod) or PtCl₂(cod) gave the corresponding chelate complexes, [Pd₃Cl₆1] or [Pt₃Cl₆1]. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzed the Suzuki coupling and Heck reaction affording biphenyls and stilbenes, respectively, in high yields.     

Preparation and coordination chemistry of N-diallylaminodiphenylphosphine and N-allylaminobis(diphenyl)phosphine

N-diallylaminodiphenylphosphine and N-allylaminobis(diphenyl)phosphine have been prepared by reaction of the appropriate amine with Ph₂PCl. The coordination chemistry of these phosphines has been studied with a range of metals [Pd, Pt, Rh, Ir, Au, Ru, Mo]. Whilst the majority of the complexes are simple bidentate P,P donors, in the case of N-diallylaminodiphenylphosphinecoordination can involve the CC group or the nitrogen centre.     

Solvent effect on palladium-catalyzed cross-coupling reactions and implications on the active catalytic species

Suzuki coupling of the bifunctional substrate 1 using [Pd(2) (dba)(3) ]/PtBu(3) gives selectivity for C?Cl in nonpolar solvents but for C?OTf in polar solvents. The results of computational and experimental studies suggest that the catalytically active species in polar solvents under conditions employing coordinating additives is inconsistent with monoligated [Pd(PtBu(3) )]. Instead, the data are consistent with an anionic palladium complex as the active species.