Nickel 0-catalyzed cross-coupling of alkyl arenesulfonates with aryl Grignard reagents

The nickel-catalyzed cross-coupling reactions of neopentyl arenesulfonates with arylmagnesium bromides, involving nucleophilic aromatic substitution of alkyloxysulfonyl groups by aryl nucleophiles, take place in high yields. Optimal efficiencies are obtained by adding 3 + 2 equiv of the Grignard reagent to a mixture of dppfNiCl(2) and the sulfonate in refluxing THF. Neopentyl arenesulfonates are useful sources of the electrophilic aryl groups in these transition metal-catalyzed cross-coupling reactions. Aryl sulfonates are inappropriate due to their ambident reactivity under the reaction conditions. This new cross-coupling reaction can be used for the creative elimination of alkyloxysulfonyl groups from aromatic compounds and for the preparation of unsymmetric terphenyls and oligophenyls.     

NiCl(2)(dppe)-catalyzed cross-coupling of aryl mesylates, arenesulfonates, and halides with arylboronic acids

An investigation of the NiCl(2)(dppe)-, NiCl(2)(dppb)-, NiCl(2)(dppf)-, NiCl(2)(PCy(3))(2)-, and NiCl(2)(PPh(3))(2)-catalyzed cross-coupling of the previously unreported aryl mesylates, and of aryl arenesulfonates, chlorides, bromides, and iodides containing electron-withdrawing and electron-donating substituents with aryl boronic acids, in the absence of a reducing agent, is reported. NiCl(2)(dppe) was the only catalyst that exhibited high and solvent-independent activity in the two solvents investigated, toluene and dioxane. NiCl(2)(dppe) with an excess of dppe, NiCl(2)(dppe)/dppe, was reactive in the cross-coupling of electron-poor aryl mesylates, tosylates, chlorides, bromides, and iodides. This catalyst was also efficient in the cross-coupling of aryl bromides and iodides containing electron-donating substituents. Most surprisingly, the replacement of the excess dppe from NiCl(2)(dppe)/dppe with excess PPh(3) generated NiCl(2)(dppe)/PPh(3), which was found to be reactive for the cross-coupling of both electron-rich and electron-poor aryl mesylates and chlorides. Therefore, the solvent-independent reactivity of NiCl(2)(dppe) provides an inexpensive and general nickel catalyst for the cross-coupling of aryl mesylates, tosylates, chlorides, bromides, and iodides with aryl boronic acids.     

Ferrocenylmethylphosphines as ligands for room temperature Ni(0)-catalyzed Suzuki-Miyaura cross-coupling reactions of aryl arenesulfonates and aryl chlorides

Readily available ferrocenylmethylphosphine was found as an efficient ligand for room temperature Ni(0)-catalyzed Suzuki-Miyaura cross-couplings of aryl arenesulfonates. Ferrocenylmethylphosphine and its polymeric form were also found as useful ligands for Ni(0)-catalyzed Suzuki-Miyaura couplings of deactivated aryl chlorides.     

Triphenylphosphine as a ligand for room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl chlorides with arylboronic acids

Room-temperature Ni(0)-catalyzed cross-coupling reactions of deactivated aryl chlorides with arylboronic acids with inexpensive triphenylphosphine (PPh3) as a supporting ligand have been accomplished in good to excellent yields. Air-stable Ni(PPh3)2Cl2 has also been established as catalyst precursor, and highly active nickel catalysts were obtained when the reduction of Ni(PPh3)2Cl2 with n-BuLi was carried out in the presence of an aryl chloride.     

Nickel-catalyzed cross-coupling of aryl phosphates with arylboronic acids

The Suzuki-Miyaura cross-coupling of aryl phosphates using Ni(PCy(3))(2)Cl(2) as an inexpensive, bench-stable catalyst is described. Broad substrate scope and high efficiency are demonstrated by the syntheses of more than 40 biaryls and by constructing complex organic molecules. The poor reactivity of aryl phosphates relative to aryl halides is successfully employed to construct polyarenes by selective cross-coupling using Pd and Ni catalysts.     

NiCl2(dppp)]-catalyzed cross-coupling of aryl halides with dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphine

We present a general approach to C-P bond formation through the cross-coupling of aryl halides with a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane by using [NiCl(2) (dppp)] as catalyst (dppp=1,3-bis(diphenylphosphino)propane). This catalyst system displays a broad applicability that is capable of catalyzing the cross-coupling of aryl bromides, particularly a range of unreactive aryl chlorides, with various types of phosphorus substrates, such as a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane. Consequently, the synthesis of valuable phosphonates, phosphine oxides, and phosphanes can be achieved with one catalyst system. Moreover, the reaction proceeds not only at a much lower temperature (100-120?°C) relative to the classic Arbuzov reaction (ca.?160-220?°C), but also without the need of external reductants and supporting ligands. In addition, owing to the relatively mild reaction conditions, a range of labile groups, such as ether, ester, ketone, and cyano groups, are tolerated. Finally, a brief mechanistic study revealed that by using [NiCl(2) (dppp)] as a catalyst, the Ni(II) center could be readily reduced in situ to Ni(0) by the phosphorus substrates due to the influence of the dppp ligand, thereby facilitating the oxidative addition of aryl halides to a Ni(0) center. This step is the key to bringing the reaction into the catalytic cycle.     

Ni(COD)2/PCy3 catalyzed cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature

Reaction conditions for the Ni(COD)(2)/PCy(3) catalyzed cross-coupling of aryl neopentylglycolboronates with aryl mesylates were developed. By using optimized reaction conditions, Ni(COD)(2)/PCy(3) was shown to be a versatile catalyst for the cross-coupling of a diversity of aryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates containing both electron-donating and electron-withdrawing substituents in their para, ortho, and meta positions in THF at room temperature. This Ni-catalyzed cross-coupling of aryl neopentylglycolboronates is also effective for the synthesis of heterobiaryls and biaryls containing electrophilic functionalities sensitive to organolithium and organomagnesium derivatives. In combination with the recently developed Ni-catalyzed neopentylglycolborylation, all Ni-catalyzed routes to functional biaryls and heterobiaryls are now easily accessible.     

trans-Chloro(1-naphthyl)bis(triphenylphosphine)nickel(II)/PCy3 catalyzed cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates at room temperature

trans-Chloro(1-naphthyl)bis(triphenylphosphine)nickel(II) complex/PCy(3) system has been successfully applied as catalyst for the Suzuki-Miyaura cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature. This cross-coupling reaction tolerates various functional groups, including keto, imino, ester, ether, and cyano. Together with the nickel-catalyzed, one-pot, two-step neopentylglycolborylation, this bench stable and inexpensive Ni(II)-based catalyst can be utilized as an alternative to Ni(COD)(2)/PCy(3) to provide an inexpensive, robust, and convenient synthesis of biaryl and heterobiaryl compounds.     

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.     

The first general palladium catalyst for the Suzuki-Miyaura and carbonyl enolate coupling of aryl arenesulfonates

The first general method for the palladium-catalyzed Suzuki-Miyaura and carbonyl enolate coupling of unactivated aryl arenesulfonates was developed utilizing XPhos, 1, and Pd(OAc)2. This is of significant interest because aryl tosylates and aryl benzenesulfonates are more easily handled and considerably less expensive than aryl triflates. This catalyst system effects the coupling of a variety of aryl, heteroaryl, and extremely hindered arylboronic acids with different aryl tosylates, under mild conditions. The same catalyst was employed in the first carbonyl enolate coupling of aryl arensulfonates.     

Nickel-catalyzed amination of aryl tosylates

The cross-coupling of aryl tosylates with amines and anilines was accomplished by using a Ni-based catalyst system from the combination of Ni(II)-(sigma-aryl) complexes/N-heterocyclic carbenes (NHCs). The feature, scope, and limitation of this reaction are disclosed.     

Well-Defined Ni(0) and Ni(II) Complexes of Bicyclic (Alkyl)(Amino)Carbene (MeBICAAC): Catalytic Activity and Mechanistic Insights in Negishi Cross-Coupling Reaction

Negishi cross-coupling reaction of organozinc compounds as nucleophiles with aryl halides has drawn immense focus for C−C bond formation reactions. In comparison to the well-established library of Pd complexes, the C−C cross-coupling of this particular approach is largely primitive with nickel-complexes. Herein, we describe the syntheses of Ni(II) complexes, [(^MeBICAAC)₂NiX₂] (X=Cl ( 1 ), Br ( 2 ), and I ( 3 )) by employing the bicyclic (alkyl)(amino)carbene (^MeBICAAC) ligand. The reduction of complexes 1 – 3 using KC₈ afforded the two coordinate low valent, Ni(0) complex, [(^MeBICAAC)₂Ni(0)] ( 4 ). Complexes 1 – 4 have been characterized by spectroscopic techniques and their solid-state structures were also confirmed by X-ray crystallography. Furthermore, complexes 1 – 4 have been applied in a direct and convenient method to catalyze the Negishi cross-coupling reaction of various aryl halides with 2,6-difluorophenylzinc bromide or phenylzinc bromide as the coupling partner in the presence of 3 mol % catalyst. Comparatively, among all-pristine complexes, 1 exhibit high catalytic potential to afford value-added C−C coupled products without the use of any additive. The UV-vis studies and HRMS measurements of controlled stochiometric reactions vindicate the involvement of Ni(I)−NI(III) cycle featured with a penta-coordinated Ni(III)-aryl species as the key intermediate for 1 whereas Ni(0)/Ni(II) species are potentially involved in the catalytic cycle of 4 .     

Nickel catalyzed cross-coupling of aryl C-O based electrophiles with aryl neopentylglycolboronates

The efficiency of mesylates, sulfamates, esters, carbonates, carbamates, and methyl ethers as C-O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their para-position. These experiments were performed in the presence of four different Ni(II)- and Ni(0)-based catalysts. Ni(II)-based catalysts mediate the cross-coupling of most 2-naphthyl C-O electrophiles with both arylboronic acids and with neopentylglycolboronates when K(3)PO(4) is used as base. The same catalysts are not efficient when CsF is used as base. However, Ni(0)-based catalysts exhibit selective efficiency, and when reactive, their efficiency is higher than that of Ni(II)-based catalysts in the presence of both K(3)PO(4) and CsF. These results provide both reaction conditions for the cross-coupling, and for the elaboration of orthogonal cross-coupling methodologies of various C-O based electrophiles with aryl neopentylglycolboronates. With the exception of mesylates and sulfamates the efficiency of all other 2-naphthyl C-O electrophiles was lower in cross-coupling with aryl neopentylglycolboronates than with arylboronic acids.     

Nickel(0)-catalyzed Heck cross-coupling via activation of aryl C-OPiv bonds

Using a Ni(dppf) catalyst generated in situ, Heck cross-coupling of aryl pivalates with a variety of olefin partners has been accomplished. This method represents one of the first examples of a C-C cross-coupling via activation of a strong C-O bond with a nonorganometallic coupling partner. It enables the transformation of phenol-based substrates into styrenyl products without generation of a halogenated byproduct or the use of expensive triflate groups.     

An efficient Negishi cross-coupling reaction catalyzed by nickel(II) and diethyl phosphite

A combination of diethyl phosphite-DMAP and Ni(II) salts forms a very effective catalytic system for the cross-coupling reactions of arylzinc halides with aryl, heteroaryl, and alkenyl bromides, chlorides, triflates, and nonaflates. The choice of solvent is quite important and the mixture of THF-N-ethylpyrrolidinone (NEP) (8:1) was found to be optimal. The reaction usually requires only 0.05 mol % of NiCl₂ or Ni(acac)₂ as catalyst and proceeds at room temperature within 1-48 h.     

Nickel(II)-aryl complexes as catalysts for the Suzuki cross-coupling reaction of chloroarenes and arylboronic acids

A series of air- and moisture-stable Ni(II)-(σ-aryl) complexes, Ni(PPh₃)₂(aryl)X (X = Cl, Br), were employed as catalyst precursors in the Ni-catalyzed Suzuki cross-coupling reaction. These pre-catalysts easily form the catalytically active Ni(0) species in situ without the need of additional reducing agents. A general catalytic system involving Ni(PPh₃)₂(1-naph)Cl and PPh₃ proved to be highly effective for the Suzuki reaction of aryl chlorides under mild conditions (at 60 °C in THF in the presence of K₂CO₃ as the base).     

An efficient catalyst for Pd-catalyzed carbonylation of aryl arenesulfonates

Aryl carboxylic esters were synthesized by Pd-catalyzed carbonylation of aryl p-fluorobenzenesulfonates or -tosylates. A unique Josiphos ligand was discovered through high-throughput catalyst screening, which was the key for the successful carbonylation of various substrates. This catalyst is effective and works well for both electron-rich and electron-poor aryl arenesulfonates. Isolated yields of up to 90% were obtained for aryl p-fluorobenzenesulfonates and -tosylates. [reaction: see text]     

Nickel(II) complexes of bidentate N-heterocyclic carbene/phosphine ligands: efficient catalysts for Suzuki coupling of aryl chlorides

Nickel(II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl(2)(L)], the stable nickel product isolated is the ionic [Ni(L)(2)]Cl(2). These Ni(II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh(3), and this suggests that the PPh(2) functionality of hybrid NHC ligand L can partially take on the role of free PPh(3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh(3) accelerates the reaction.     

Chitosan-supported palladium(0) catalyst for microwave-prompted Suzuki cross-coupling reaction in water

A chitosan-supported palladium (Pd) (0) catalyst was prepared by simple adsorption of palladium(II) ion onto chitosan beads and a subsequent reduction process. To maintain mechanical stability, the chitosan-supported palladium(0) catalyst was cross-linked with either glutaraldehyde or diglycidyl ether polyethylene glycol. The catalysts were utilized for the Suzuki cross-coupling reaction in water. The catalyst, in the presence of a tetrabutylammonium bromide (TBAB) additive, showed excellent catalytic activity in microwave-prompted Suzuki cross-coupling reactions using various aryl halides and boronic acids. In addition, the catalyst was successfully reused up to five times without significant loss of catalytic activity.     

A nickel precatalyst for efficient cross-coupling reactions of aryl tosylates with arylboronic acids: vital role of dppf

An air-stable and easy-to-handle nickel precatalyst, (9-phenanthrenyl)Ni(II)(PPh₃)₂Cl, was examined for the cross-coupling reactions of aryl tosylates with arylboronic acids. Under the optimized reaction conditions, the catalytic system tolerates a wide range of activated, neutral and deactivated substrates. The selectivity of this cross-coupling reaction towards aryl tosylates and arylboronic acids has been investigated. It is proposed that ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) plays a key role in the coupling by enforcing a cis geometry in key intermediates and the active Ni(0) species.