Efficient cyanation of aryl bromides with K4[Fe(CN)6] catalyzed by a palladium-indolylphosphine complex

This study describes a general palladium-catalyzed cyanation of aryl bromides using K₄[Fe(CN)₆] as the cyanide surrogate. The reactions can be successfully conducted under mild reaction conditions (at 50 °C) in mixed solvents (water/MeCN = 1:1) without any surfactant additives, and afford the desired aryl nitriles in good-to-excellent yields. Particularly noteworthy is that this system allows the mildest reaction temperature reported so far for palladium-catalyzed cyanation of aryl bromides with K₄[Fe(CN)₆] source in general. Common functional groups, including keto, aldehyde, free amine, and heterocyclic substrates are compatible under this system. Interestingly, the phosphine ligands bearing -PCy₂ moiety, which usually show excellent activity in aryl halide couplings, are found less effective than the corresponding ligands with -PPh₂ group.     

On the catalytic duo PdCl2(PPh3)2/AuCl(PPh3) that cannot effect a Sonogashira-type reaction: a correction

In contrast to the observation made by the Laguna group, we report that the combination of PdCl₂(PPh₃)₂ and AuCl(PPh₃) makes a unique catalytic system that allows Sonogashira-type cross-coupling of both aryl and alkyl alkynes with aryl halides in excellent yields.     

Microwave-enhanced and ligand-free copper-catalyzed cyanation of aryl halides with K4[Fe(CN)6] in water

Copper-catalyzed cyanation of aryl halides was improved to be more economical and environmentally friendly by using water as the solvent and ligand-free Cu(OAc)₂·H₂O as the catalyst under microwave heating. The suggested methodology was applicable to a wide range of substrates including aryl iodides and activated aryl bromides.     

Effects of solvent and base on the palladium-catalyzed amination: PdCl2(Ph3P)2/Ph3P-catalyzed selective arylation of primary anilines with aryl bromides

A readily accessible catalytic system, PdCl₂(Ph₃P)₂/Ph₃P, was developed for the selective arylation of primary anilines with aryl bromides. The strong influence of solvents and bases on the catalytic activity was observed. In refluxing o-xylene, triphenylphosphine shows high efficiency for Pd-catalyzed intermolecular amination reactions. By changing the bases, mono- and diarylation of primary amines could be selectively achieved in high yields. Moreover, the catalytic system showed good toleration for the steric hindrance of anilines. A series of N,N,N′,N′-tetraaryl-1,1′-biphenyl-4,4′-diamines, important intermediates of OLED hole transport materials, were synthesized facilely via coupling reactions between 4,4′-diaminobiphenyls and aryl bromides.     

trans-Pd(OAc)2(Cy2NH)2 catalyzed Suzuki coupling reactions and its temperature-dependent activities toward aryl bromides

A new catalytic system based on Pd-simple amines for Suzuki coupling reactions of aryl bromides is described. A well-defined air-stable complex, trans-Pd(OAc)₂(Cy₂NH)₂ effectively promotes Suzuki couplings of aryl bromides with a range of aryl boronic acids to give diaryl products in high yields. It also exhibits temperature-dependent activity toward aryl bromides bearing different electronic substituents under reaction conditions.     

Synthesis of arylaminotetrazoles by ZnCl2/AlCl3/silica as an efficient heterogeneous catalyst

Abstract  

Arylaminotetrazoles were efficiently synthesized from secondary arylcyanamides by application of ZnCl₂/AlCl₃/silica as a reusable heterogeneous Lewis acid catalyst. 5-Arylamino-1H-tetrazoles can be obtained from arylcyanamides carrying electron-withdrawing substituents on the aryl ring, while with electron-releasing groups 1-aryl-5-amino-1H-tetrazoles will be produced. The former isomer is also produced within longer reaction times (~20 h) even with electron-releasing groups.     

Intramolecular oxidative addition of C-F and C-H bonds to [Pt(dba)2]. Crystal structure of [PtCl{Me2NCH2CH2NCH(2,4,5-C6HF3)}]

The reactions of compound [Pt(dba)₂] with ligands RCHNCH₂CH₂NMe₂ (1a-1f) in which R is a fluorinated aryl ring produced activation of C-F bonds when two fluorine atoms are present in the ortho positions of the aryl ring or activation of C-H bonds for ligands containing only one fluoro substituent in ortho. Both C-F and C-H bond activation are favoured by an increase of the degree of fluorination of the ring. Further reaction with lithium halides produced cyclometallated platinum (II) compounds [PtX(Me₂NCH₂CH₂NCHR)] (X = Br, Cl) (2) containing a terdentate [C,N,N′] ligand. The obtained compounds were fully characterized including a structure determination for [PtCl{Me₂NCH₂CH₂NCH(2,4,5-C₆HF₃)}] (2d′).     

Palladium-catalyzed cyanation of aryl halides using K4[Fe(CN)6] as cyanide source, water as solvent, and microwave heating

A methodology for the cyanation of aryl iodides and activated aryl bromides is reported using water as the solvent and K₄[Fe(CN)₆] as the cyanide source. Reactions are complete within 20 min.     

Copper-catalyzed arylation of phenylurea using KF/Al2O3

A mild and efficient method for the copper-catalyzed arylation of phenylurea is described. The coupling reaction of phenylurea with different functionalized aryl iodides in the presence of air stable CuI, N,N′-dibenzylethylenediamine as a ligand, and KF/Al₂O₃ as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.     

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.     

Nano TiO2/SO4 as a heterogeneous solid acid catalyst for the synthesis of 5-substited-1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted-1H-tetrazoles from various nitriles and sodium azide is reported using nano TiO₂/SO₄²⁻ as an effective heterogeneous catalyst. A wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in good to excellent yields.     

Efficient ligand-free copper-catalyzed C-S cross-coupling of thiols with aryl iodides using KF/Al2O3 as base

We report a mild, convenient, environmentally friendly, and ligand-free synthetic protocol for the cross-coupling reaction of aryl iodides and thiols using 10 mol % CuI with KF/Al₂O₃ as the base, in DMF at 110 °C. Using this protocol, we have shown that a variety of aryl sulfides can be synthesized in excellent yields from readily available iodides and thiols.     

Platinum-alkyl-B(C6F5)3 (or BF3) ‘in situ’ systems as tin(II) halide-free enantioselective hydroformylation catalysts

The dialkyl/diaryl-platinum complexes (Pt(CH₃)₂(bdpp); PtPh₂(bdpp) and Pt(2-Thioph)₂(bdpp), where bdpp stands for (2S,4S)-2,4-bis(diphenylphosphino)pentane) were reacted either with B(C₆F₅)₃, BPh₃ or BF₃. In the presence of PPh₃ or carbon monoxide cationic species with a general formulae [PtR(L)(bdpp)]⁺ (L = PPh₃, CO) were formed exclusively. The ability of boron additives to provide vacant coordination site at the platinum made these systems suitable as hydroformylation catalysts. Enantioselective hydroformylation of styrene was carried out in the presence of in situ catalysts formed from Pt(alkyl/aryl)₂(bdpp) and B(C₆F₅)₃ or BF₃. Moderate e.e-s depending strongly on the structure of the catalytic precursor have been obtained. DFT/PCM calculations reveal an S_N2-type reaction mechanism for the alkyl/aryl ligand abstraction with a notably lower activation barrier for BF₃.     

Co2(CO)8 as a convenient in situ CO source for the direct synthesis of benzamides from aryl halides (Br/I) via aminocarbonylation

A fast, mild, and functional group tolerant method for the direct synthesis of benzamides from aryl halides (Br, I) via aminocarbonylation, using solid Co₂(CO)₈ as a convenient CO source, has been demonstrated. The developed method is applicable to a wide variety of 1° and cyclic and acyclic 2° amines. Nitro substituted (o, m and p) aryl halides have easily been converted to the corresponding benzamides, without the reduction of the nitro group, in high yields using this in situ carbonylation methodology under microwave irradiation.     

Synthesis and crystal structure of [C6H5Hg(H2NSiMe3)][H2N{B(C6F5)3}2], a phenyl-mercury(II) cation stabilised by a non-coordinating counter-anion

The new heteroleptic mercury(II) complex PhHgN(SiMe₃)₂(1) reacts with the strong Brønsted acid [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] with cleavage of a N-Si bond to give [C₆H₅Hg(H₂NSiMe₃)][H₂N{B(C₆F₅)₃}₂] (2), a phenyl-mercury(II) cation stabilised by a primary amine and a non-coordinating counter-anion. Attempts to generate donor-free aryl mercury cations were not successful. The crystal structure of 2 · CH₂Cl₂ shows short π-bonding interactions between the metal and the phenyl ring of a neighbouring cation; the geometry about the mercury(II) atom is nearly linear. The X-ray structures of the new salts [H₂N(SiMe₃)₂ · H₃NSiMe₃][B(C₆F₅)₄]₂ and [Et₃O][H₂N{B(C₆F₅)₃}₂] · CH₂Cl₂ are also presented.     

Synthesis and structural investigation of the compounds containing HF2 anions: Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6)

Three new compounds Ca(HF₂)₂, Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF₅. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF₂)₂ was prepared by simply dissolving CaF₂ in a neutral aHF. It represents the second known compound with homoleptic HF environment of the central atom besides Ba(H₃F₄)₂. The compounds Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) represent two additional examples of the formation of a polymeric zigzag ladder or ribbon composed of metal cation and fluoride anion (MF⁺)_n besides PbF(AsF₆), the first isolated compound with such zigzag ladder. The obtained new compounds were characterized by X-ray single crystal diffraction method and partly by Raman spectroscopy. Ba₄F₄(HF₂)(PF₆)₃ crystallizes in a triclinic space group P1¯ with a=4.5870(2) Å, b=8.8327(3) Å, c=11.2489(3) Å, α=67.758(9)°, β=84.722(12), γ=78.283(12)°, V=413.00(3) Å³ at 200 K, Z=1 and R=0.0588. Pb₂F₂(HF₂)(PF₆) at 200 K: space group P1¯, a=4.5722(19) Å, b=4.763(2) Å, c=8.818(4) Å, α=86.967(10)°, β=76.774(10)°, γ=83.230(12)°, V=185.55(14) ų, Z=1 and R=0.0937. Pb₂F₂(HF₂)(PF₆) at 293 K: space group P1¯, a=4.586(2) Å, b=4.781(3) Å, c=8.831(5) Å, α=87.106(13)°, β=76.830(13)°, γ=83.531(11)°, V=187.27(18) Å³, Z=1 and R=0.072. Ca(HF₂)₂ crystallizes in an orthorhombic Fddd space group with a=5.5709(6) Å, b=10.1111(9) Å, c=10.5945(10) Å, V=596.77(10) Å³ at 200 K, Z=8 and R=0.028.     

[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.     

Br?nsted-acidic ionic liquid [HO3S(CH2)4MIM][HSO4] as efficient and reusable catalyst for one-pot synthesis of β-acetamido ketones

Abstract  

Efficient and convenient synthesis of β-acetamido ketones has been achieved by one-pot reaction of acetophenone, aryl aldehydes, acetyl chloride, and acetonitrile in the presence of 3-methyl-1-(4-sulfonylbutyl)imidazolium hydrogensulfate [HO₃S(CH₂)₄MIM][HSO₄], a Br?nsted-acidic ionic liquid, as a green and reusable catalyst in solvent-free media at room temperature. The catalyst could be recycled and reused without noticeable decrease in catalytic activity.     

[RuCl3(H2O)n]-catalyzed direct arylations

Catalytic amounts of economically attractive [RuCl₃(H₂O)_n] allow for direct arylations via C-H bond functionalization with aryl bromides under phosphine ligand-free reaction conditions. Thereby, a variety of functionalized (hetero)aryl bromides, bearing either electron-withdrawing or electron-releasing substituents, can be employed for direct arylations of pyridine, oxazoline, pyrazole, or ketimine derivatives as pronucleophiles.     

Copper-free PdCl2/PPh3-catalyzed Sonogashira coupling reaction of aryl bromides with terminal alkynes in water

A simple, copper-free and efficient catalytic system for the Sonogashira coupling reaction of aryl bromides with terminal alkynes in pure water has been developed. The use of PdCl₂/PPh₃ in the presence of pyrrolidine allows the coupling reaction to proceed at 120 °C in moderate to excellent yields.