Hydrophosphorylation of Terminal Alkynes Catalyzed by Palladium

A series of new 1-aryl-, 1-heteroaryl-, and 1-alkylethenylphosphonates was prepared by hydrophosphorylation of terminal acetylenes catalyzed by palladium. A stable in air complex Pd₂(dba)₃·CHCl₃ was applied as catalyst. The reaction mechanism is discussed.     

Palladium-Catalyzed Amination and Amidation of Benzo-Fused Bromine-Containing Heterocycles

Amination and amidation of bromoindole, 6-bromo-1,2,3,4-tetrahydrocarbazol-1-one, and 8-bromo-2,4,5,6-tetrahydro-1H-pyrazino[3,2,1-jk]carbazole derivatives was effected in the presence of palladium complexes. The use of the catalytic system Pd₂dba₃⋅CHCl₃-2-[di(tert-butyl)phosphino]biphenyl in the amination and of Pd₂dba₃⋅CHCl₃-Xantphos [or 3,5-(CF₃)₂Xantphos] in the amidation ensured moderate to high yields of the corresponding products.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 881–894.Original Russian Text Copyright © 2005 by Sergeev, Artamkina, Velezheva, Fedorova, Beletskaya.     

Phospha-adamantanes as ligands for organopalladium chemistry: aminations of aryl halides

The use of Pd₂dba₃·CHCl₃ and 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phospha-adamantane has been shown to facilitate the effective amination of aryl halides with aromatic or aliphatic amines in high yields.     

Solid-phase Suzuki cross-coupling reactions using a phosphine ligand based on a phospha-adamantane framework

The use of a catalyst system based on Pd₂dba₃·CHCl₃ and 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phospha-adamantane allows for Suzuki coupling aryl halides with an array of boronic acids on a solid-phase platform. The reactions can be carried out at room temperature with low palladium loadings in high yields.     

Synthesis of 1,2-dihydroisoquinolines via palladium(0)-catalyzed addition-cyclization of chloroform to ortho-alkynylaldimines

Addition-cyclization of chloroform to ortho-alkynylaldimines proceeded in the presence of PdCl₂(PPh₃)₂/dppe or Pd₂dba₃·CHCl₃/dppe at 100 °C to afford the corresponding 1-(trichloromethyl)-1,2-dihydroisoquinolines in good to high yields.     

Palladium-Catalyzed Synthesis of Arylamines from Diphenyliodonium Tetrafluoroborate and Secondary Amine

The hetero-cross coupling reaction of diphenyliodonium tetrafluoro-borate with secondary amine in the presence of LiNTMS₂ or NaOtBu as base, Pd₂(dba)_3°CHCl₃ as catalyst, and tri-o-tolylphosphine as ligand afforded arylamines at room temperature under mild conditions.     

Bis(triphenylphosphine)palladium(II)succinimide as a precatalyst for Suzuki cross-coupling—subtle effects exerted by the succinimide ligand

A new palladium(II) precatalyst for Suzuki cross-coupling of aryl halides and organoboronic acids has been identified, namely bis(triphenylphosphine)palladium(II)succinimide [(Ph₃P)₂Pd(N-Succ)₂] 2. The precatalyst is easily prepared from palladium(0) precursors, such as (Ph₃P)₄Pd or Pd₂dba₃·CHCl₃/Ph₃P and succinimide, is air, light and moisture stable, and may be employed with a variety of substrates to give the cross-coupled products, in good yields and in reasonable time, at relatively low catalyst loadings.     

Variation of xanthene-based bidentate ligands in the palladium-catalyzed arylation of ureas

A series of xanthene-based bidentate ligands containing various substituents on diphenylphosphino groups were synthesized and tested in the palladium-catalyzed arylation reaction of urea with unactivated aryl bromides. It was found that both steric and electronic properties of the ligands have a pronounced effect on the yields and ratios of the products. Arylation of urea and phenylurea with unactivated aryl bromides in the presence of Pd₂dba₃·CHCl₃/3,5-(CF₃)₂Xantphos and Cs₂CO₃ as base in dioxane at 100°C gave the corresponding N,N′-diarylureas in 62-98% yields.     

Dimensionality Expansion of a Butterfly Shaped Pd4 Framework: Constructing Edge-Sharing Pd6 Tetrahedra

The construction of well-defined transition-metal clusters has attracted substantial attention due to their unique chemical and/or physical properties. Metal clusters with 1D or 2D structures are now accessible by template-synthesis methods, in which multiple metal atoms are arranged with the aid of template molecules and their 1D or 2D structures. However, the rational synthesis of 3D clusters remains challenging, mostly due to a lack of appropriate template molecules. Herein, we report the rational synthesis of a 2D butterfly shaped Pd₄ framework ( 2 ) and 3D edge-sharing Pd₆ tetrahedra ( 5 ) by treatment of easily available organosilicon compounds with Pd(CNtBu)₂. The diphenylsilylene moiety thereby serves as the key component to generate the butterfly structure of the Pd₄ clusters in 2 . A dimensionality expansion, induced by two Cl atoms, of two butterfly shaped Pd₄ subunits supported by two diphenylsilylene moieties afforded the edge-sharing tetrahedral architecture of the Pd₆ cluster in 5 .     

Palladium catalyzed three component coupling reaction between chromones, alcohols, and allylic acetates: diversity-oriented synthesis of highly substituted chromones

This paper describes the palladium catalyzed highly efficient three component coupling (TCC) reactions between chromones, allylic acetates, and alcohols, which lead to a library of multiply substituted chromones. The activity of various palladium catalysts, such as Pd(PPh₃)₄ and Pd₂dba₃·CHCl₃ and their combination with various bisphosphine ligands, was investigated by using THF as a solvent, which revealed that Pd(PPh₃)₄ catalyst was the best one. The reaction most probably proceeds via the formation of benzopyrilium cation, generated from the reaction between chromones and allyl acetate, in the presence of palladium catalyst. The subsequent trapping of the benzopyrilium cation by alcohols would give the corresponding products in excellent yields. This alkoxy-allylation reaction was highly diastereoselective and only one diastereomer was obtained in all the cases.     

Palladium-catalyzed monoamination of dihalogenated benzenes

The palladium-catalyzed monoamination of symmetric dibromobenzenes can be performed using a catalyst based on Pd₂dba₃ and BINAP in the presence of NaO(t-Bu). The analogous transformation of non-symmetric bromoiodobenzenes is most effectively performed with Xantphos as the ligand, while reactions with BINAP were non-selective. These transformations can be scaled uneventfully to >10 g quantities. They do not require drybox or Schlenk techniques, and all reagents are weighed out in air. The resulting monobromoanilines are versatile intermediates for further synthetic transformations.     

Palladium-catalyzed Arylation of Ureas

Urea arylation with aryl halides in the presence of catalyst precursor Pd₂dba₃-CHCl₃/Xantphos and Cs₂CO₃ in dioxane at 100°C affords symmetrical N,N'-diarylureas in 64-92% yield. With the same catalytic system the reaction between N-phenylurea and aryl bromides containing electron-withdrawing substituents in the para-position provided N-aryl-N'-phenylureas in 64-91% yields.     

Regioselective synthesis of benzimidazole thiophene inhibitors of polo-like kinase 1

A regioselective synthesis of novel 1-(2-thienyl)-benzimidazole inhibitors of polo-like kinase 1 is described. Amination of substituted 2-iodo or -bromo nitrobenzenes with a 2-aminothiophene derivative catalyzed by Pd₂dba₃ and XANTPHOS in the presence of excess Cs₂CO₃ afforded good yields of the coupled products. Subsequent reduction and cyclization of these intermediates provided the desired benzimidazole compounds.     

Palladium catalyzed thiol cross-coupling of cystein derivatives with aryl and alkenyl halides

Palladium catalyzed cystein thiol cross-coupling reactions with aryl and vinyl halides have been investigated: Pd₂dba₃-CHCl₃ and dppf are the key choice in these reactions. The role of the base in these reactions was also questioned: it has been shown that base can be replaced by an HX-scavenger such as propylene oxide.     

Palladium-Catalyzed Cross-Coupling of Organolead Compounds with Hypervalent Iodonium Salts

The palladium-catalyzed cross-coupling of hypervalent iodonium salts with organolead triacetates was achieved with Pd₂(dba)₃·CHCl₃ (5 mol %) in the presence of NaOMe (2 equiv) in CHCl₃ at room temperature.     

Synthesis of chiral N,N′-disubstituted 1,2-benzenediamines from o-dibromobenzene

Palladium-catalyzed amination of o-dibromobenzene provided chiral N,N′-disubstituted 1,2-benzenediamines in good to excellent yields. The amination was executed stepwise and in one pot to give unsymmetrically and symmetrically substituted 1,2-benzenediamines. Incorporation of chiral primary amines was possible without racemization using catalytic Pd₂dba₃–BINAP.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

High Nuclearity Bimetallic Rhodium–Palladium Carbonyl Cluster Complexes. Synthesis and Characterization of Rh6(CO)16[Pd(PBu t 3)]3 and Rh6(CO)16[Pd(PBu t 3)]4

The reaction of Rh₄(CO)₁₂ with Pd(PBu ^t ₃)₂ yielded the high nuclearity bimetallic hexarhodium-tripalladium cluster complex Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₃, 10, in 11% yield. Compound 10 was converted to the hexarhodium-tetrapalladium cluster Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₄, 11, in 62% yield by reaction with an additional quantity of Pd(PBu ^t ₃)₂. Both compounds were characterized crystallographically. Structurally, both compounds consist of an octahedral cluster of six rhodium atoms with sixteen carbonyl ligands analogous to that of the known compound Rh₆(CO)₁₆. Compound 10 also contains three Pd(PBu ^t ₃) groups that bridge three Rh–Rh bonds along edges of the Rh₆ octahedron to give an overall D₃ symmetry to the Rh₆Pd₃ cluster. Compound 11 contains four edge bridging Pd(PBu ^t ₃) groups distributed across the Rh₆ octahedron to give an overall D_2d symmetry to the Rh₆Pd₄ cluster. Each Rh–Pd connection in both compounds contains a bridging carbonyl ligand that helps to stabilize the bond between the Pd(PBu ^t ₃) groups and the Rh atoms. Both compounds can be regarded as Pd(PBu ^t ₃) adducts of Rh₆(CO)₁₆.     

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles

Palladacycles of pyrido[1,2-a]quinoline complexes were synthesized via a one pot reaction of quinolines with XyNC (Xy = 2,6-Me ₂C₆H₃) in the presence of Pd(dba)₂ (4:1). These palladacycles were also obtained via reaction of quinolines with Pd(dba)₂ in the presence of PPh ₃ (1:2) in acetone to give the intermediate complexes of dinuclear palladaphosphaquinoline complexes. Dinuclear complexes were converted into palladacycles via reaction with XyNC in CH₂Cl₂. The crystal structure of the dinuclear palladium complex was determined by X-ray diffraction studies. Correspondence: Abdel-Sattar S. Hamad Elgazwy, Department of Chemistry, Faculty of Science, University of Ain Shams, Abbassia 11566, Cairo, Egypt.     

Statistical experimental design-driven discovery of room-temperature conditions for palladium-catalyzed cyanation of aryl bromides

A combination of Pd₂(dba)₃·CHCl₃ (0.5 mol %) and commercially available, air-stable phosphonium salt [(t-Bu)₃PH]BF₄ (1.4 mol %) in a presence of Zn powder and Zn(CN)₂ as the cyanide source comprises an extremely efficient catalyst system for the cyanation of a diverse array of aryl bromides, at room temperature. This result emerged from an experimental strategy that combines the advantages of parallel, automated experimentation with the design of experiments (DOE) for the effective definition of an optimal set of reaction conditions.