Palladium catalyzed-dehalogenation of aryl chlorides and bromides using phosphite ligands

The catalytic system based on Pd-phosphite for the dehalogenation reactions of aryl chlorides and bromides is described. The Pd-phosphite catalyst effectively promoted the dehalogenation of aryl halides to give dehalogenated products in moderate to excellent yields. The aryl chlorides required strong bases such as NaO^tBu for this transformation, whereas the aryl bromides were dehalogenated in the presence of weak bases such as Cs₂CO₃. This catalytic system exhibited tolerance to functional groups such as methoxy, amine, hydroxyl, ether, amide, benzyl and ketone groups. It also demonstrated chemoselectivity in that bromochlorobenzene was converted only to chlorobenzene.     

Sonogashira reaction of aryl halides with propiolaldehyde diethyl acetal catalyzed by a tetraphosphine/palladium complex

All-cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyzes the Sonogashira reaction of propiolaldehyde diethyl acetal with a variety of aryl bromides and chlorides. A minor electronic effect of the substituents of the aryl bromide was observed. Similar reaction rates were observed in the presence of activated aryl bromides such as 4-trifluoromethylbromobenzene and deactivated aryl bromides such as bromoanisole. Turnover numbers up to 95,000 can be obtained for this reaction. Even aryl chlorides and heteroarylbromides or chlorides have been successfully alkynylated with this catalyst. Moreover, a wide variety of substituents on the aryl halide such as fluoro, trifluoromethyl, acetyl, benzoyl, formyl, nitro, dimethylamino or nitrile are tolerated.     

Sonogashira cross-coupling reactions of aryl chlorides with alkynes catalysed by a tetraphosphine-palladium catalyst

A range of aryl chlorides undergoes cross-couplings with alkynes in good yields in the presence of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as catalyst. A variety of aryl chlorides such as chloroacetophenone, chlorobenzonitrile, chloronitrobenzene, chloroanisole or chlorotoluene have been used successfully. The reaction also tolerates several alkynes such as phenylacetylene, dec-1-yne, ethynylcyclohexene or alk-1-ynols. Furthermore, this catalyst can be used at low loading with some substrates.     

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl₂(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 °C in toluene with K₂CO₃ as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h⁻¹ can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid; lower reaction rates are obtained with substrates bearing EDG substituents on the aryl group.     

Palladium-catalyzed cross-coupling of trimethoxysilylbenzene with aryl bromides and chlorides using phosphite ligands

Phosphites were employed as ligands in palladium-catalyzed Hiyama coupling reactions. The optimized reaction conditions were equimolar amounts (5 mol % each) of Pd(acac)₂ and phosphite 1 in p-xylene at 80 °C with TBAF as an additive. This catalyst system exhibited high activities in the reactions with trimethoxysilylbenzene and aryl bromides that have electron-donating or electron-withdrawing groups. In the case of aryl chlorides, substrates possessing electron-withdrawing groups gave the coupled products in high yields.     

An inexpensive cyclodiphosphazane as an efficient ligand for the palladium-catalyzed amination of aryl bromides and chlorides

An economic and novel ligand, cyclodiphosphazane [ClPN(t-Bu)]₂ (1), was introduced in the palladium-catalyzed amination of unactivated aryl halides. The catalyst allows for the amination of aryl chlorides and bromides with secondary cyclic amines and anilines in good yields.     

Suzuki Coupling of Cyclopropylboronic Acid With Aryl Halides Catalyzed by a Palladium–Tetraphosphine Complex

The tetraphosphine all‐cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) in combination with [Pd(C₃H₅)Cl]₂ affords a very efficient catalyst for the coupling of cyclopropylboronic acid with aryl bromides and aryl chlorides. Higher reactions rates were observed with aryl bromides than with aryl chlorides; however, even in the presence of 1–0.4% of catalyst, a few aryl chlorides gave the coupling products in good yields. A wide variety of substituents such as alkyl, methoxy, trifluoromethyl, acetyl, benzoyl, formyl, carboxylate, nitro, and nitrile on the aryl halides are tolerated. The coupling reaction of sterically very congested aryl bromides such as bromomesitylene or 2,4,6‐triisopropylbromobenzene also proceeds in good yields.     

Tetraphosphine/palladium catalysed Suzuki cross-coupling reactions of aryl halides with alkylboronic acids

Through the use of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides and chlorides undergoes Suzuki cross-coupling with alkylboronic acids in good yields. Several alkyl substituents such as ethyl, n-butyl, n-octyl, isobutyl or 2,2-dimethylpropyl on the alkylboronic acids have been successfully used. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

Stoichiometric and catalytic C-Cl activation of Aryl Chlorides using an NHC-stabilized nickel(0) complex

[Ni₂(ⁱPr₂Im)₄(COD)] 1 catalyzes the Suzuki-Miyaura-type cross coupling reaction of chlorobenzene and phenylboronic acid efficiently. Compound 1 compares well with other nickel catalyst reported so far with the advantage that no further excess of ligand such as PPh₃ has to be added. Oxidative addition of different aryl chlorides to complex 1 is highly selective for a broad range of substrates, ranging from activated to deactivated aryl chlorides. The stoichiometric reaction of 1 with aryl chlorides (ArCl) afforded complexes of the type trans-[Ni(ⁱPr₂Im)₂(Cl)(Ar)] (for Ar = Ph 2, 4-Me(O)CC₆H₄3, 4-H(O)CC₆H₄4, 4-MeOC₆H₄5, 4-H₂NC₆H₄6, 4-F₃CC₆H₄7, 4-ClC₆H₄8, 3-ClC₆H₄9, 2-ClC₅NH₃10 4-FC₆H₄11). All resulting nickel(II) complexes have been fully characterized, in most cases including X-ray diffraction. In contrast to the work described by Matsubara and coworkers just recently on the sterically slightly more demanding [Ni(Dip₂Im)₂] system, we have found for the [Ni(ⁱPr₂Im)₂] complexes no indication for the formation of three coordinated nickel(I) complexes.     

Ni-catalyzed cross-coupling reaction of aryl chlorides with arylboronic acids in IPA without using a reducing reagent

The coupling reaction of aryl chlorides with arylboronic acids was successfully performed in isopropanol (IPA) by using [NiCl(Ph₂PCH₂CH₂OH)₂(H₂O)]Cl (5), a cationic Ni(II)-complex, as a precatalyst in the absence of a reducing agent. The coupling reaction proceeded smoothly under mild conditions to provide biaryls in satisfactory to excellent yields, and formation of the undesired dechlorination products of aryl chlorides was completely prevented.     

Pd/Cu bimetallic co-catalyzed direct 2-arylation of benzoxazole with aryl chloride

An efficient Palladium/Copper bimetallic co-catalyzed direct 2-arylation of benzoxazoles with aryl chlorides is presented. The Pd(OAc)₂/CuI/NiXantphos-based catalyst enables the installation of various aryl and heteroaryl groups in good to excellent yields (75–99%). Preliminary mechanism investigation indicates that Pd/Nixantphos complex activates C-Cl bond of aryl chlorides via oxidative addition, and Cu/Nixantphos complex chelates with nitrogen atom to lower the pK_a of the 2-H in benzoxazoles.     

Efficient nickel/N-heterocyclic carbene catalyzed C-S cross-coupling

The cross-coupling reaction of aryl halides with aliphatic and aromatic thiols catalyzed by readily available Ni(OAc)₂ with N-heterocyclic carbene (NHC) is reported. Ni(OAc)₂/NHC catalyst showed good activities toward various aryl halides in C-S coupling reaction, even with aryl chlorides. Reactions occurred in excellent yields, broad scope, and high tolerance of functional groups.     

An efficient palladium-catalyzed Heck coupling of aryl chlorides with alkenes

Catalyst system PdCl₂(PCy₃)₂/Cs₂CO₃ in dioxane was found to be the efficient catalyst system for Heck cross-coupling reactions of deactivated, neutral, and activated aryl chlorides with a variety of alkenes under mild conditions to afford selectively E-arylated alkenes in good to excellent yields.     

Efficient palladium catalysts for the amination of aryl chlorides: a comparative study on the use of phosphium salts as precursors to bulky, electron-rich phosphines

Alkyl-di-(1-adamantyl)phosphonium salts are practical ligand precursors for the palladium-catalyzed amination of aryl chlorides. In the presence of typically 0.5 mol% Pd(OAc)₂ and 1 mol% of ligand precursor a variety of activated and deactivated aryl chlorides can be aminated in good to excellent yield (73-99%). Applying optimized conditions catalyst turnover numbers up to 10,000 have been achieved.     

Highly Active Heterogeneous PdCl2/MOF Catalyst for Suzuki–Miyaura Cross-Coupling Reactions of Aryl Chloride

The exploration of highly efficient Pd/MOF heterogeneous catalyst system for the Suzuki–Miyaura cross-coupling (SMC) reactions of aryl chlorides is still challenging. Herein, a PdCl₂/UiO-67-bpydc was successfully synthesized by immobilizing a low amount of PdCl₂ onto the zirconium-based MOF (UiO-67-bpydc). PdCl₂/UiO-67-bpydc showed excellent catalytic performance and good recycle ability for the SMC reaction of aryl chlorides under an ambient condition. Furthermore, PdCl₂/UiO-67-bpydc retains the high catalytic activity even after five cycles, and exhibited excellent substrate size selectivity.     

Solvent-free palladium-catalyzed CO cross-coupling of (hetero)aryl halides with primary alcohols

A new efficient solvent-free procedure for the CO cross-coupling between (hetero)aryl halides with phenols, primary alkanols, or (hetero)arylmethanols using Pd₂(dba)₃/Bu^tBrettPhos catalytic system is proposed using 23 examples.     

PhPOCl2 as a potent catalyst for chlorination reaction of phenols with PCl5

Phenols are easily converted to the corresponding aryl chlorides by using phosphorus pentachloride (PCl₅) and a catalytic amount of phenylphosphonic dichloride (PhPOCl₂), which is a new efficient method for synthesis of aryl chloride in good yields.     

Efficient Suzuki coupling of aryl chlorides catalyzed by tricyclohexylphosphine adducts of cyclopalladated ferrocenylimines

The air and moisture stable tricyclohexylphosphine (PCy₃) adducts of dimeric cyclopalladated ferrocenylimines 5 and 6 have been easily synthesized and successfully used in palladium-catalyzed Suzuki cross-coupling of aryl chlorides. Using 0.1 mol% of 6 in the presence of 2 equivalent of Cs₂CO₃ as base in dioxane at 100 °C provided coupled products in excellent yields in the reaction of non-activated and deactivated aryl chlorides with phenylboronic acid. For activated chlorides such as 4-chloronitrobenzene and 4-chloroacetophenone, the catalyst loadings could be lowered to 0.01 mol% without loss of activity.     

Suzuki-Miyaura cross-coupling reaction of aryl chlorides with aryl boronic acids catalyzed by a palladium dichloride adduct of N-diphenylphosphanyl-2-aminopyridine

One palladium dichloride adduct of a phosphine-pyridine ligand N-diphenylphosphanyl-2-aminopyridine (L₁) [(L₁)PdCl₂] (1) has been prepared and structurally characterized. Compound 1 can be used as an effective catalyst for the Suzuki-Miyaura cross-coupling reactions of unreactive aryl chlorides with aryl boronic acids, and worked much better than its mono- or bidentate phosphine ligands. The reactions with a wide scope of substrates proceeded to give desired products in good to excellent yields.     

Palladium-catalyzed deacetonative coupling of aryl propargylic alcohols with aryl chlorides in water

A highly efficient and green process for palladium-catalyzed deacetonative coupling of aryl propargylic alcohols with aryl chlorides has been developed. The reaction occurs smoothly in neat water with 2?mol% PdCl₂ as catalyst, and various synthetically useful functional groups, including ether, aldehyde, ketone, and heterocyclics, are well tolerated. Moreover, the reaction could proceed through a consecutive Sonogashira/deacetonative process using 2-methyl-3-butyn-2-ol and aryl chlorides as coupling partners, affording the symmetric alkynes in good yields.