Ligand Coupling Reactions Research Articles

Co+(C2H2)n Complexes Studied with Selected-Ion Infrared Spectroscopy and Theory.

Co+(C2H2)n (n = 1-6) complexes produced with laser vaporization in a supersonic molecular beam are studied with infrared photodissociation spectroscopy and computational chemistry. Infrared spectra are measured in the C-H stretching region using the method of tagging with argon atoms to enhance the photodissociation yields. C-H stretch vibrations for all clusters studied are shifted to lower frequencies than those of the well-known acetylene vibrations from ligand → metal charge transfer interactions. The magnitude of the red shifts decreases in the larger clusters as the interaction is distributed over more ligands. Computational studies identify various unreacted complexes with individual acetylene ligands in cation-π bonding configurations as well as reacted isomers in which ligand coupling reactions have taken place. Infrared spectra are consistent only with unreacted structures, even though the formation of reacted structures such as the metal ion-benzene complex is highly exothermic. Large activation barriers are predicted by theory along the reaction coordinates for the n = 2 and 3 complexes, which inhibit reactions in these smaller clusters, and this situation is presumed to persist in larger clusters.

N-Heteroaromatic Fluoroalkylation through Ligand Coupling Reaction of Sulfones.

Ligand coupling on hypervalent main group elements has emerged as a pivotal methodology for the synthesis of functionalized N-heteroaromatic compounds in recent years due to the avoidance of transition metals and the mildness of the reaction conditions. In this direction, the reaction of N-heteroaryl sulfur(IV) and N-heteroaryl phosphorus(V) compounds has been well studied. However, the ligand coupling of sulfur(VI) is still underdeveloped and the reaction of alkyl N-heteroarylsulfones is still elusive, which does not match the high status of sulfones as the chemical chameleons in organic synthesis. Here we present a ligand coupling-enabled formal SO2 extrusion of fluoroalkyl 2-azaheteroarylsulfones under the promotion of Grignard reagents, which not only enriches the chemistry of sulfones, but also provides a novel and practical synthetic tool towards N-heteroaromatic fluoroalkylation.

N‐Heteroaromatic Fluoroalkylation through Ligand Coupling Reaction of Sulfones

AbstractLigand coupling on hypervalent main group elements has emerged as a pivotal methodology for the synthesis of functionalized N‐heteroaromatic compounds in recent years due to the avoidance of transition metals and the mildness of the reaction conditions. In this direction, the reaction of N‐heteroaryl sulfur(IV) and N‐heteroaryl phosphorus(V) compounds has been well studied. However, the ligand coupling of sulfur(VI) is still underdeveloped and the reaction of alkyl N‐heteroarylsulfones is still elusive, which does not match the high status of sulfones as the chemical chameleons in organic synthesis. Here we present a ligand coupling‐enabled formal SO2 extrusion of fluoroalkyl 2‐azaheteroarylsulfones under the promotion of Grignard reagents, which not only enriches the chemistry of sulfones, but also provides a novel and practical synthetic tool towards N‐heteroaromatic fluoroalkylation.

Atomic layer deposition mechanism of hafnium dioxide using hafnium precursor with amino ligands and water

As a unique nanofabrication technology, atomic layer deposition (ALD) has been widely used for the preparation of various materials in the fields of microelectronics, energy and catalysis. Hafnium dioxide (HfO2), as an excellent high-κ oxide, is widely used as a substitute gate dielectric for conventional SiO2 in field effect transistor devices. Currently, HfO2 high-κ gate dielectric in MOSFET devices was prepared via ALD technology using tetrakis(dimethylamino)hafnium(IV) (Hf(NMe2)4, TDMAHf) and water (H2O) as the precursors. In this work, the complicated surface reaction mechanism of HfO2 H2O-based ALD using Hf(NMe2)4 was investigated using density functional theory calculations. In the TDMAHf reaction, the dimethylamino group of the precursor was eliminated by ligand exchange reaction with the hydroxyl group on the surface. Subsequently, a second dimethylamino group of TDMAHf could further be eliminated by another hydroxyl group on the surface. In the H2O reaction, ligand exchange reactions and coupling reactions could both occur. By the ligand exchange reactions, water molecule could react with the dimethylamino group on the surface. Simultaneously, the hydroxyl and amino groups could also react with neighboring hydroxyl groups to eliminate dimethylamine and water molecules via the coupling reactions. All these insights into the complicated surface reaction mechanism of H2O-based ALD could promote the further development of ALD chemistry and materials.

Transformations of Main-Group Organometallics Induced by Transition Metals

AbstractThe oxidative dehydrometallation of silyl or boron enolates is induced by palladium(II) catalyst to result in the versatile introduction of α,β-unsaturated carbon–carbon double bonds via palladium enolates. Selective oxidative cross- and homo-coupling reactions of silyl or boron enolates induced by vanadium(V) oxidant provide a selective synthetic method for accessing 1,4-dicarbonyl compounds in a nucleo­phile-nucleophile coupling mode. The ligand coupling reaction of main-group organometallic compounds induced by vanadium(V) oxi­dant provides a unique method for intramolecular carbon–carbon bond formation of nucleophiles. The last two reactions are a complementary strategy for the nucleophile-electrophile coupling reaction. The dehydrometallation and coupling reactions probably proceed through two- and one-electron oxidation processes, respectively.1 Introduction2 Palladium-Catalyzed Dehydrometallation3 Homo- and Cross-Coupling of Main-Group Organometallic Compounds4 Oxidative Ligand Coupling of Main-Group Organometallic Compounds5 Conclusion

Synthesis of Bis-heteroaryls Using Grignard Reagents and Pyridylsulfonium Salts.

Herein are reported ligand-coupling reactions of Grignard reagents with pyridylsulfonium salts. The method has wide functional group tolerance and enables the formation of bis-heterocycle linkages, including 2,4′-, 2,3′-, and 2,2′-bipyridines, as well as pyridines linked to pyrimidines, pyrazines, isoxazoles, and benzothiophenes. The methodology was successfully applied to the synthesis of the natural products caerulomycin A and E.

Diaryliodonium Salts: Structures and Synthesis

Due to similar reactivity in comparison with aromatic organometallic reagents, diaryliodonium salts are currently in broad usage as less toxic, highly efficient, stable and mild electrophilic reagents in organic synthesis. The hypervalent iodine center of diaryliodonium salts can lead to unique reactivity, which thus is frequently presented in metal-free arylations or metal-involved elementary reactions such as oxidative addition, reduction elimination, ligand coupling and ligand exchange reaction. As such, diaryliodonium salts have experienced explosive growth by transferring aromatics to the target molecules. In contrast to the reviews on the synthetic utility or aryl transformations by using diaryliodonium salts, this review provides a summary of their structures and the synthetic strategies towards them during recent decades.

Studies on diverse chemical species derived from chalcogen atoms ~ The Footprint of Professor Naomichi Furukawa in Heteroatom Chemistry ~

AbstractThis account summarizes representative contributions of Prof. Naomichi Furukawa to the field of heteroatom chemistry. Ligand‐coupling reactions (LCRs) and ligand‐exchange reactions (LERs) of chalcogen derivatives were developed from reactions of trivalent chalcogen species with organometallic reagents. Prof. Furukawa has also reported a large number of mono‐ and dicationic compounds generated via transannular and intermolecular interactions. Furthermore, the detection and isolation of hypercoordinated chalcogen species bearing only carbon ligands and an efficient method for the synthesis of thiophene S‐oxides and their reactivity are described.

Biocompatible starch-halloysite hybrid: An efficient support for immobilizing Pd species and developing a heterogeneous catalyst for ligand and copper free coupling reactions

Combining the exceptional features of halloysite and starch, a unique hybrid was synthesized based on conjugation of amine-functionalized starch with Cl-halloysite nanoclay followed by coordination of Pd (II) acetate. The resultant hybrid catalyst, Pd@Hal-SA, was used as a heterogeneous catalyst for promoting copper and ligand-free coupling reactions under mild reaction condition. The catalyst exhibited high catalytic activity and recyclability (up to 10 reaction runs) with slight loss of the catalytic activity that stemmed from slight Pd leaching. The comparison of the catalytic activity of Pd-Hal, Pd-SA and Pd@Hal-SA confirmed the superior performance of the latter, indicating the contribution of two components, SA and Hal to the catalysis. Moreover, the catalytic activity of Pd@Hal-SA was higher than that of Pd@Hal + SA, implying that the use of hybrid system was more efficient that use of individual components in a separated form, due to the synergism between SA and Hal.

Ternary hybrid system of halloysite nanotubes, polyacrylamides and cyclodextrin: an efficient support for immobilization of Pd nanoparticles for catalyzing coupling reaction

Abstract Taking advantage of the properties of polyacrylamide (P), the capability of cyclodextrin (CD) to form inclusion complex and outstanding features of halloysite nanoclay as catalyst support, a ternary hybrid system, Hal-P-CD, was designed and synthesized through growing polyacrylamide on the surface of functionalized halloysite nanotubes followed by introduction of β-cyclodextrin. The hybrid system was successfully used for immobilization of Pd nanoparticles and formation of a heterogeneous catalyst, Pd@Hal-P-CD. The structure of Pd@ Hal-P-CD was confirmed by using SEM/EDS, TEM, XRD, BET, ICP-AES, TGA, FTIR and elemental mapping analysis and its catalytic activity was studied for promoting ligand and copper-free Sonogashira coupling reaction in aqueous media (1:1 mixture of water and ethanol). The results established that Pd@Hal-P-CD could catalyze the coupling reaction to afford the desired products in high yields and short reaction times. Notably, the catalytic activity of Pd@Hal-P-CD was superior to those of Pd@Hal-P and Pd@Hal. The study of the reusability of the catalyst up to 7 reaction runs as well as Pd leaching confirmed the heterogeneous nature of the catalysis and the efficiency of Hal-P-CD for suppressing the Pd leaching. Additionally, this catalyst could also be successfully used for promoting Heck coupling reaction.

A new preparation strategy for surface modified PLA nanoparticles to enhance uptake by endothelial cells

Nanoparticles are promising drug delivery systems to overcome physiological barriers such as the blood-brain barrier. In this respect nanoparticle uptake into endothelial or epithelial cells is the first necessary step to overcome these obstacles. Therefore, a new strategy for the covalent attachment of drug targeting ligands on poly(lactic acid) (PLA) nanoparticles was developed and the influence of the resulting surface properties on the uptake behaviour in cerebral endothelial cells was investigated. PLA nanoparticles were modified on their surface by apolipoprotein E, penetratin, or ovalbumin using a newly developed vinyl sulfone-modified poly(vinyl alcohol)-derivative (VS-PVA) as steric stabilizer. With this approach an easy option for ligand coupling reactions to PVA-stabilized nanoparticles was achieved. All obtained formulations showed a favourable behaviour concerning cytotoxic effects on endothelial cells, not compromising their viability. Furthermore, a clear relation between cellular uptake and surface coupled functional ligand could be determined: Penetratin- and apolipoprotein E-modified nanoparticles showed a distinct higher cellular uptake than ovalbumin-modified or unmodified nanoparticles, which both can be explained by mechanistic reasons. Overall the use of the reactive VS-PVA as stabilizer for nanoparticle preparation is an universal and effective approach to couple several functional ligands to the particles’ surface for targeting applications.

ChemInform Abstract: Versatile C(sp2)—C(sp3) Ligand Couplings of Sulfoxides for the Enantioselective Synthesis of Diarylalkanes.

The reaction of chiral (hetero)aryl benzyl sulfoxides with Grignard reagents affords enantiomerically pure diarylalkanes in up to 98 % yield and greater than 99.5 % enantiomeric excess. This ligand coupling reaction is tolerant to multiple substitution patterns and provides access to diverse areas of chemical space in three operationally simple steps from commercially available reagents. This strategy provides orthogonal access to electron-deficient heteroaromatic compounds, which are traditionally synthesized by transition metal catalyzed cross-couplings, and circumvents common issues associated with proto-demetalation and β-hydride elimination.

Versatile C(sp(2) )-C(sp(3) ) Ligand Couplings of Sulfoxides for the Enantioselective Synthesis of Diarylalkanes.

The reaction of chiral (hetero)aryl benzyl sulfoxides with Grignard reagents affords enantiomerically pure diarylalkanes in up to 98 % yield and greater than 99.5 % enantiomeric excess. This ligand coupling reaction is tolerant to multiple substitution patterns and provides access to diverse areas of chemical space in three operationally simple steps from commercially available reagents. This strategy provides orthogonal access to electron-deficient heteroaromatic compounds, which are traditionally synthesized by transition metal catalyzed cross-couplings, and circumvents common issues associated with proto-demetalation and β-hydride elimination.

Versatile C(sp2)−C(sp3) Ligand Couplings of Sulfoxides for the Enantioselective Synthesis of Diarylalkanes

AbstractThe reaction of chiral (hetero)aryl benzyl sulfoxides with Grignard reagents affords enantiomerically pure diarylalkanes in up to 98 % yield and greater than 99.5 % enantiomeric excess. This ligand coupling reaction is tolerant to multiple substitution patterns and provides access to diverse areas of chemical space in three operationally simple steps from commercially available reagents. This strategy provides orthogonal access to electron‐deficient heteroaromatic compounds, which are traditionally synthesized by transition metal catalyzed cross‐couplings, and circumvents common issues associated with proto‐demetalation and β‐hydride elimination.

SbおよびTe化合物のリガンド交換・リガンドカップリング反応メカニズム

SbおよびTe化合物のリガンド交換・リガンドカップリング反応メカニズム

Theoretical Study on the Mechanism of the Ligand Coupling Reaction of Hypervalent Pentacoordinate Antimony Compounds

Abstract The ligand coupling reaction (LCR) of hypervalent pentacoordinate antimony compounds (ArnTol5−nSb; Ar = p-trifluoromethylphenyl, Tol = p-methylphenyl; n = 0–5) was analyzed via the long-range-corrected density functional theory. Although previous experimental or computational investigations have suggested apical–apical or equatorial–equatorial coupling of ArnTol5−nSb compounds, the present results lead to apical–equatorial coupling. The biased experimental ratios of the coupling products, which were grounds for apical–apical coupling, can be explained by the stability of the transition-state (TS) structure for the apical–equatorial coupling, where n–π* interaction plays an important role to the stabilization. We further investigated the potential energy surface of H5Sb, for which the intrinsic reaction coordinate (IRC) from the TS structure for LCR indicates the equatorial–equatorial coupling. It is found that the valley-ridge transition occurs along the IRC near the TS structure and the transverse vibrational mode with imaginary frequency, orthogonal to the IRC, directs to the reactant structure corresponding to the apical–equatorial coupling.

Reactivity of transition-metal borylene complexes: recent advances in B-C and B-B bond formation via borylene ligand coupling.

Terminal borylene complexes of group 6-10 metals have been prepared through a number of synthetic strategies, displaying a wide structural diversity with numerous coordination modes of the borylene ligand [:BR]. Earlier, amino-substituted borylenes were found to serve as borylene ligand transfer reagents to a range of organic and organometallic substrates. In contrast, aryl- and alkyl-substituted borylenes display metathesis behavior when combined with ketones. Recent studies on these complexes revealed new reactivity patterns involving borylene-borylene and carbonyl-borylene ligand coupling. Herein a brief account on the recent progress of these borylene ligand coupling reactions made in our laboratories is provided. These reactions offer unprecedented alternative methods for electron-precise B-B and B-C bond formation.

Reversible Intramolecular Coupling of the Terminal Borylene and a Carbonyl Ligand of [Cp(CO)2MnBtBu

Cyclic complex 2 with bridging carbonyl ligands was synthesized from a facile and reversible intermolecular carbonyl-borylene ligand coupling reaction at room temperature. Complex 2 exhibits an unprecedented coordination mode for boron-metal complexes, which is also reflected in its remarkable (11)B NMR chemical shift of -57.2 ppm. Findings from spectroscopic, X-ray, and computational studies are presented, along with a proposed mechanism.

Synthesis and Reactivity of Coordinatively Unsaturated Dinuclear Ruthenium Bridging Imido Complexes

[Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) reacted with CO, t-BuNC, Ph2S═CH2, or Me3SiC≡CH to give the dinuclear ruthenium bridging imido complexes [(Cp*Ru)2(μ-NPh)(μ-L)] (2a, L = CO; 2b, L = t-BuNC; 2c, L = CH2; 2d, L = CCHSiMe3). Protonolysis of 2d with t-BuOH produced the parent vinylidene complex [(Cp*Ru)2(μ-NPh)(μ-CCH2)] (2e). Treatment of 2e with HOTf or MeOTf afforded the cationic alkylidyne complexes [(Cp*Ru)2(μ-NPh)(μ-CR)]OTf (2f, R = Me; 2g, R = Et). Hydride abstraction from 2c with Ph3CBF4 gave the methylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h). X-ray structures of 2a−c and 2f revealed short Ru−N distances (1.876−1.894 Å) consistent with Ru−N multiple bonds, and the μ-alkylidyne 2f also featured short Ru−C bonds (1.929(7) and 1.914(7) Å). In addition to giving simple Lewis base adducts such as [(Cp*Ru)2(μ-NPh)(μ-CO)(PMe3)] and [(Cp*Ru)2(μ-NPh)(μ-CH2)(t-BuNC)2], these imido complexes provided an array of novel ligand coupling reactions. Thus, 2b underwent a tandem imido−isocyanide coupling and C−H activation reaction to give an amidinate complex. Complexes 2c and 2e mediated imido−CO−methylene and imido−CO−vinylidene coupling to give [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6) and [{Cp*Ru(CO)}2(μ-PhNCOC═CH2)] (7), respectively. Complex 2c also underwent a selective coupling reaction with 2 equiv of Me3SiC≡CH to give the μ-allenylimine complex [(Cp*Ru)2{μ-Me3SiCH═C═C(SiMe3)C(Me)═NPh}] (8). The imido methylidyne complex coupled with 2 equiv of alkynes to give [(Cp*Ru)2{μ-HC(R1CCR2)(R2CCR1)NPh}]OTf (9a−c), a product of double alkyne cycloaddition to the Ru−N and Ru−C multiple bonds and C−C coupling of the resulting ruthena- and azaruthenacyclobutene moieties.

ChemInform Abstract: Heteroaromatic Sulfoxides and Sulfones: Ligand Exchange and Coupling in Sulfuranes and Ipso-Substitutions

Publisher Summary This chapter explores the chemistry of both organic sulfur compounds and azaaromatic compounds, and discusses the chemical behaviors of organosulfur compounds of azaheteroaromatics, particularly pyridine and its related six-membered derivatives. The contents are divided into the following items: (1) a new concept of ligand-coupling reactions and ligand exchange within σ-sulfuranes formed in the reactions of the sulfoxides, bearing azaheteroaromatics, with grignard and organolithium reagents; (2) ipso substitution and desulfurization reactions of the sulfoxides and sulfones in which both the sulfinyl and the sulfonyl groups become good leaving groups; (3) thione-thiol tautomerism and its applications to the organic synthesis; and (4) miscellaneous reactions on the organosulfur compounds bearing azaheterocycles. Physicochemical behavior of these heteroaromatic systems is also compared to the corresponding aromatic systems. One remarkable feature is that the heteroaromatics bearing a sulfur atom are more reactive than the corresponding aromatic derivatives mainly because of the strong electron-releasing or withdrawing property of the heteroaromatics.