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.     

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.     

Comparison of arylboron-based nucleophiles in Ni-catalyzed Suzuki-Miyaura cross-coupling with aryl mesylates and sulfamates

The efficiency of arylboron-based nucleophiles, boronic acid, potassium trifluoroborate, neopentylglycolboronate, and pinacol boronate in nickel-catalyzed Suzuki-Miyaura cross-coupling reactions with the two C-O electrophiles, mesylates, and sulfamates was compared. Arylboronic acid is the most reactive and most atom-economic of the four boron species studied. Arylpotassium trifluoroborate cross-couples efficiently only in the presence of water. In the absence of water, aryl neopentylglycolboronate is more efficient, less expensive, and more atom-economic than aryl pinacolboronate.     

Two-step, one-pot Ni-catalyzed neopentylglycolborylation and complementary Pd/Ni-catalyzed cross-coupling with aryl halides, mesylates, and tosylates

Two-step, one-pot neopentylglycolborylation of aryl iodides and bromides catalyzed by NiCl2(dppe) and NiCl2(dppp) is reported. Electron-rich and electron-deficient aryl neopentylglycolboronates were efficiently cross-coupled with aryl iodides, bromides, chlorides, mesylates, and tosylates by exploiting complementary Pd/Ni and Ni/Ni catalysis. The borylation route was further extended to a three-step, one-pot synthesis of biaryls via in situ Ni-catalyzed borylation and Pd-mediated cross-coupling.     

Ligation state of nickel during CO bond activation with monodentate phosphines

The oxidative addition of phenolic electrophiles at Ni(0) in the presence of monodentate phosphine ligands was studied with both dispersion-free and dispersion-containing DFT methods. With the popular bulky ligand PCy₃, consideration of dispersion has a striking effect on the predicted ligation state of nickel during oxidative addition of aryl sulfamates. Dispersion-containing methods such as M06L indicate a clear preference for a bis-phosphine ligated transition state (TS), while dispersion free methods like B3LYP strongly favor a mono-phosphine ligated TS. This discrepancy in predicted ligation state is also found with small phosphines (PMe₃) in combination with some aryl electrophiles (carbamates, acetates, pivalates, chlorides), but a bis-PMe₃-ligated TS is predicted regardless of dispersion for other electrophiles (sulfamates, mesylates, tosylates). DFT calculations that include dispersion also offer a possible explanation for the observed poor efficacy of P^tBu₃ as a ligand in Ni-catalyzed cross-coupling reactions.     

Rapid nickel-catalyzed Suzuki-Miyaura cross-couplings of aryl carbamates and sulfamates utilizing microwave heating

High-speed and scalable nickel-catalyzed cross-coupling of arylboronic acids with aryl carbamates and sulfamates is achieved by using sealed-vessel microwave processing.     

Diaminophosphine oxides as preligands for Ni-catalyzed Suzuki cross-coupling reactions of aryl chlorides with arylboronic acids

The first investigation of air- and moisture-stable diaminophosphine oxides as preligands in the Ni-catalyzed Suzuki cross-coupling reactions of aryl chlorides with arylboronic acids has been reported. The results show that under the optimized reaction conditions, the new catalytic system with a Ni(II) σ-aryl complex as precatalyst and a diaminophosphine oxide as preligand tolerates a variety of functional groups and is efficient for both electron-rich and electron-deficient aryl chlorides, though it shows higher efficiency for activated arylboronic acids than deactivated ones. Steric effects were observed for both aryl chlorides and arylboronic acids.     

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.     

Cross-coupling reactions of aryl pivalates with boronic acids

The first cross-coupling of acylated phenol derivatives has been achieved. In the presence of an air-stable Ni(II) complex, readily accessible aryl pivalates participate in the Suzuki-Miyaura coupling with arylboronic acids. The process is tolerant of considerable variation in each of the cross-coupling components. In addition, a one-pot acylation/cross-coupling sequence has been developed. The potential to utilize an aryl pivalate as a directing group has also been demonstrated, along with the ability to sequentially cross-couple an aryl bromide followed by an aryl pivalate, using palladium and nickel catalysis, respectively.     

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.     

Room-temperature Ni0-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids

Room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids are described. The Ni(0) catalyst, derived from Ni(COD)2 and PCy3, proved to be a general one for the Suzuki-Miyaura cross-coupling of a variety of aryl arenesulfonates. The mild reaction condition, the readily availability of the catalyst, and excellent coupling yields make aryl arenesulfonates potentially useful substrates in organic synthesis.     

Generation of Organozinc Reagents by Nickel Diazadiene Complex Catalyzed Zinc Insertion into Aryl Sulfonates

The generation of arylzinc reagents (ArZnX) by direct insertion of zinc into the C−X bond of ArX electrophiles has typically been restricted to iodides and bromides. The insertions of zinc dust into the C−O bonds of various aryl sulfonates (tosylates, mesylates, triflates, sulfamates), or into the C−X bonds of other moderate electrophiles (X=Cl, SMe) are catalyzed by a simple NiCl₂–1,4-diazadiene catalyst system, in which 1,4-diazadiene (DAD) stands for diacetyl diimines, phenanthroline, bipyridine and related ligands. Catalytic zincation in DMF or NMP solution at room temperature now provides arylzinc sulfonates, which undergo typical catalytic cross-coupling or electrophilic substitution reactions.     

Cobalt co-catalysis for cross-electrophile coupling: diarylmethanes from benzyl mesylates and aryl halides

The nickel-catalyzed cross-coupling of aryl halides with alkyl radicals derived from alkyl halides has recently been extended to couplings with carbon radicals generated by a co-catalyst. In this study, a new co-catalyst, cobalt phthalocyanine (Co(Pc)), is introduced and demonstrated to be effective for coupling substrates not prone to homolysis. This is because Co(Pc) reacts with electrophiles by an S_N2 mechanism instead of by the electron-transfer or halogen abstraction mechanisms previously explored. Studies demonstrating the orthogonal reactivity of (bpy)Ni and Co(Pc), applying this selectivity to the coupling of benzyl mesylates with aryl halides, and the adaptation of these conditions to the less reactive benzyl phosphate ester and an enantioconvergent reaction are presented.     

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.     

Cross-coupling of mesylated phenol derivatives with potassium cyclopropyltrifluoroborate

C-O activation of mesylates by a palladium catalyst and subsequent cross-coupling with potassium cyclopropyltrifluoroborate have been achieved with high yield. Both electron-enriched and electron-deficient aryl mesylates are suitable electrophilic partners for the Suzuki-Miyaura reaction. The scope was successfully extended to heteroaryl mesylates with yields up to 94%.     

Palladium-catalyzed Hiyama cross-coupling reactions of aryl mesylates

The combination of palladium acetate with XPhos shows high efficiency in the Hiyama cross-coupling reactions of aryl mesylates with arylsilanes. The reactions proceed smoothly to generate the corresponding biaryl compounds in good yields.     

Cross-coupling of mesylated phenol derivatives with potassium ammonio- and amidomethyltrifluoroborates

A large array of aryl and heteroaryl mesylates have been successfully employed as electrophiles in a Csp(2)-Csp(3) Suzuki-Miyaura cross-coupling with potassium ammonio- and amidomethyltrifluoroborates to afford the corresponding products in high yields.     

Nickel-catalyzed formation of cyclopentenone derivatives via the unique cycloaddition of α,β-unsaturated phenyl esters with alkynes

Oxygen-containing organic compounds, such as ethers, carboxylates, and carbamates, have recently received increasing attention because of their newly discovered applications as electrophiles in cross-coupling reactions via transition metal-catalyzed C-O bond activation. However, no cycloaddition reaction involving their C-O bond activation has been demonstrated thus far. The present study developed a Ni(0)-catalyzed unique [3+2] cycloaddition reaction of α,β-unsaturated phenyl esters with alkynes in (i)PrOH to yield cyclopentenone derivatives.     

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.     

Suzuki-Miyaura cross-coupling of aryl carbamates and sulfamates: experimental and computational studies

The first Suzuki-Miyaura cross-coupling reactions of the synthetically versatile aryl O-carbamate and O-sulfamate groups are described. The transformations utilize the inexpensive, bench-stable catalyst NiCl(2)(PCy(3))(2) to furnish biaryls in good to excellent yields. A broad scope for this methodology has been demonstrated. Substrates with electron-donating and electron-withdrawing groups are tolerated, in addition to those that possess ortho substituents. Furthermore, heteroaryl substrates may be employed as coupling partners. A computational study providing the full catalytic cycles for these cross-coupling reactions is described. The oxidative addition with carbamates or sulfamates occurs via a five-centered transition state, resulting in the exclusive cleavage of the aryl C-O bond. Water is found to stabilize the Ni-carbamate catalyst resting state, which thus provides rationalization of the relative decreased rate of coupling of carbamates. Several synthetic applications are presented to showcase the utility of the methodology in the synthesis of polysubstituted aromatic compounds of natural product and bioactive molecule interest.