One-bond spin-spin coupling constants of X-1H proton donors in complexes with X-H-Y hydrogen bonds, for X = 13C, 15N, 17O, and 19F: predictions, comparisons, and relationships among 1J X-H, 1K X-H, and X-H distances

Ab initio calculations at the equation-of-motion coupled cluster (EOM-CCSD) level of theory have been carried out to investigate one-bond (13)C-(1)H, (15)N-(1)H, (17)O-(1)H, and (19)F-(1)H coupling constants in a systematic study of monomers and hydrogen-bonded complexes. Computed coupling constants ((1)J(X-H)) for monomers are in good agreement with available experimental data. All reduced Fermi-contact terms and reduced coupling constants ((1)K(X-H)) for monomers and complexes are positive. Plots of (1)K(X-H) versus the X-H distance for the 16 monomers and the 64 complexes in which these monomers are proton donors exhibit significant scatter. However, a linear relationship has been demonstrated for the first time between coupling constants and X-H distances for different X atoms by plotting the ratios of the coupling constants for complexes and corresponding monomers versus the ratios of distances for complexes and corresponding monomers times the square of the Pauling electronegativity. Since the ratio removes the dependence of coupling constants on the magnetogyric ratios of X, this relationship holds for both (1)K(X-H) and (1)J(X-H). The decrease in reduced coupling constants ((1)K(X-H)) as the X-H distance increases is due primarily to the increased proton-shared character of the hydrogen bond.     

Microwave-assisted decarboxylative three-component coupling of a 2-oxoacetic acid, an amine, and an alkyne

A novel and efficient microwave-assisted decarboxylative three-component coupling of a 2-oxoacetic acid, an amine, and an alkyne (OA(2)-coulpling) has been developed. This new multicomponent coupling constitutes an efficient approach for the synthesis of polysubstituted propargylamines in the presence of a catalytic amount of copper(I) catalyst.     

Selected Copper‐Based Reactions for C−N,C−O,C−S,and C−C Bond Formation

Metal‐catalyzed cross‐coupling reactions belong to the most important transformations in organic synthesis. Copper catalysis has received great attention owing to the low toxicity and low cost of copper. However, traditional Ullmann‐type couplings suffer from limited substrate scopes and harsh reaction conditions. The introduction of several bidentate ligands, such as amino acids, diamines, 1,3‐diketones, and oxalic diamides, over the past two decades has totally changed this situation as these ligands enable the copper‐catalyzed coupling of aryl halides and nucleophiles at both low reaction temperatures and catalyst loadings. The reaction scope has also been greatly expanded, rendering this copper‐based cross‐coupling attractive for both academia and industry. In this Review, we have summarized the latest progress in the development of useful reaction conditions for the coupling of (hetero)aryl halides with different nucleophiles. Additionally, recent advances in copper‐catalyzed coupling reactions with aryl boronates and the copper‐based trifluoromethylation of aromatic electrophiles will be discussed.     

Intermolecular enolate heterocoupling: scope, mechanism, and application

This full account presents the background on, discovery of, and extensive insight that has been gained into the oxidative intermolecular coupling of two different carbonyl species. Optimization of this process has culminated in reliable and scalable protocols for the union of amides, imides, ketones, and oxindoles using soluble copper(II) or iron(III) salts as oxidants. Extensive mechanistic studies point to a metal-chelated single-electron-transfer process in the case of copper(II), while iron(III)-based couplings appear to proceed through a non-templated heterodimerization. This work presents the most in-depth findings on the mechanism of oxidative enolate coupling to date. The scope of oxidative enolate heterocoupling is extensive (40 examples) and has been shown to be efficient even on a large scale (gram-scale or greater). Finally, the method has been applied to the total synthesis of the unsymmetrical lignan lactone (-)-bursehernin and a medicinally important 2,3-disubstituted succinate derivative.     

An efficient, microwave-assisted, one-pot synthesis of indoles under Sonogashira conditions

A microwave-assisted, one-pot, three-component coupling reaction for the synthesis of indoles has been developed. The reaction is carried out in two steps under standard Sonogashira coupling conditions from an N-substituted/N,N-disubstituted 2-iodoaniline and a terminal alkyne, followed by the addition of acetonitrile and an aryl iodide. A variety of polysubstituted indoles have been prepared in moderate to excellent yields using the present method.     

Murahashi Cross-Coupling at −78 °C: A One-Pot Procedure for Sequential C−C/C−C,C−C/C−N,and C−C/C−S Cross-Coupling of Bromo-Chloro-Arenes

The coupling of organolithium reagents, including strongly hindered examples, at cryogenic temperatures (as low as −78 °C) has been achieved with high-reactivity Pd-NHC catalysts. A temperature-dependent chemoselectivity trigger has been developed for the selective coupling of aryl bromides in the presence of chlorides. Building on this, a one-pot, sequential coupling strategy is presented for the rapid construction of advanced building blocks. Importantly, one-shot addition of alkyllithium compounds to Pd cross-coupling reactions has been achieved, eliminating the need for slow addition by syringe pump.     

Total synthesis of 3,3′,4-tri-O-methylellagic acid from gallic acid

Total synthesis of 3,3′,4-tri-O-methylellagic acid has been described from commercially available gallic acid. Construction of the crucial unsymmetric Ar-Ar bond has been carried out in various methods such as Heck coupling, Heck coupling followed by oxidation or anionic Fries rearrangement, Suzuki cross-coupling, etc., but all the attempts were unsuccessful. Then, finally it has been achieved by intramolecular Ullmann coupling reaction.     

Exploring SmBr2-, SmI2-, and YbI2-mediated reactions assisted by microwave irradiation

The use of microwave heating in lanthanide(II) halide (LnX2 = SmBr2, SmI2, and YbI2) mediated reduction and coupling reactions has been investigated for a variety of functional groups including alpha,beta-unsaturated esters, aldehydes, ketones, imines, and alkyl halides. Good to quantitative transformations were obtained within a few minutes without the addition of any co-solvents, such as hexamethyl phosphoramide (HMPA). The redox potential of YbI2 in tetrahydrofuran (THF) has been determined as -1.02+/-0.05 V (versus Ag/AgNO3) by cyclic voltammetry. A large selectivity difference in various reactions was observed depending on the redox potential of the LnX2 reagent. The more powerful reductant, SmBr2, afforded mainly pinacol-coupling products of ketones whereas the weaker reductant YbI2 afforded mainly reduction products. The results indicate that the reducing power of LnX2 has a large impact on not only the pinacol coupling/reduction product ratio of ketones but also on other substrates in which there are competing coupling and reduction reactions. The use of in situ generated LnX2 has also been explored and proven useful in many of these reactions.     

Catechol violet as new, efficient, and versatile ligand for Cu(I)-catalyzed C-S coupling reactions

Combination of CuI and Catechol violet (CuI-CV) was employed as catalyst for the first time in the C-S coupling reaction of a wide variety of aromatic halides, such as aryl iodides, bromo pyridines, activated aryl chlorides, and vinyl iodide with thiols to afford the corresponding thioethers in good to excellent yields. Broad range of functional group tolerance present in both the coupling partners has been observed in this reaction protocol.     

Highly efficient one-pot synthesis of N-sulfonylamidines by Cu-catalyzed three-component coupling of sulfonyl azide, alkyne, and amine

A highly efficient, mild, practical, and catalytic multicomponent reaction for the synthesis of N-sulfonylamidines has been developed. This reaction has an extremely wide scope with regard to all three coupling components of alkyne, sulfonyl azide, and amine. Two plausible mechanistic pathways involving ketenimine or triazole intermediate are tentatively presented for the copper-catalyzed three-component coupling reactions.     

Azulenesulfonium Salts: Accessible,Stable, and Versatile Reagents for Cross‐Coupling

Azulenesulfonium salts may be readily prepared from the corresponding azulenes by an S_EAr reaction. These azulene sulfonium salts are bench‐stable species that may be employed as pseudohalides for cross‐coupling. Specifically, their application in Suzuki–Miyaura reactions has been demonstrated with a diverse selection of coupling partners. These azulenesulfonium salts possess significant advantages in comparison with the corresponding azulenyl halides, which are known to be unstable and difficult to prepare in pure form.     

Azulenesulfonium Salts: Accessible,Stable, and Versatile Reagents for Cross‐Coupling

Azulenesulfonium salts may be readily prepared from the corresponding azulenes by an S_EAr reaction. These azulene sulfonium salts are bench‐stable species that may be employed as pseudohalides for cross‐coupling. Specifically, their application in Suzuki–Miyaura reactions has been demonstrated with a diverse selection of coupling partners. These azulenesulfonium salts possess significant advantages in comparison with the corresponding azulenyl halides, which are known to be unstable and difficult to prepare in pure form.     

Regioselective Acceptorless Dehydrogenative Coupling of N‐Heterocycles toward Functionalized Quinolines,Phenanthrolines, and Indoles

A new strategy has been developed for the oxidant‐ and base‐free dehydrogenative coupling of N‐heterocycles at mild conditions. Under the action of an iridium catalyst, N‐heterocycles undergo multiple sp³ C? H activation steps, generating a nucleophilic enamine that reacts in situ with various electrophiles to give highly functionalized products. The dehydrogenative coupling can be cascaded with Friedel–Crafts addition, resulting in a double functionalization of the N‐heterocycles.     

Regioselective Acceptorless Dehydrogenative Coupling of N‐Heterocycles toward Functionalized Quinolines,Phenanthrolines, and Indoles

A new strategy has been developed for the oxidant‐ and base‐free dehydrogenative coupling of N‐heterocycles at mild conditions. Under the action of an iridium catalyst, N‐heterocycles undergo multiple sp³ C H activation steps, generating a nucleophilic enamine that reacts in situ with various electrophiles to give highly functionalized products. The dehydrogenative coupling can be cascaded with Friedel–Crafts addition, resulting in a double functionalization of the N‐heterocycles.     

Gmelin handbook of inorganic chemistry, 8th edit., S — Sulfur-Nitrogen Compounds,Part 2: Compounds with Sulfur of Oxidation Number IV: Springer-Verlag,Berlin, Heidelberg,New York,Tokyo, 1985, xiv + 333 pages,DM 1144, ISBN 3-540-93512-6

A close examination of the ESR spectrum of a paramagnetic complex formed from bis(ethoxythiocarbonyl)sulfide and dimanganese decacarbonyl has revealed, for the first in this type of radical adduct, ₁₃C hyperfine coupling in natural abundance from the carbonyl ligands.     

Straightforward access to 2-iminoisoindolines via three-component coupling of arynes, isocyanides and imines

A three-component coupling reaction of arynes, isocyanides and N-tosylaldimines has been developed to offer modest to high yields of diverse 2-iminoisoindolines in one step. Intermediacy of arynes in the coupling has been verified by the reaction of unsymmetrical arynes.     

Calculation of the vibronic structure of the X2Pi photoelectron spectra of XCN, X=F, Cl, and Br

The vibronic structure of the photoelectron spectra of the X (2)Pi state of XCN(+) (X=F, Cl, and Br) has been calculated, assuming that the X (2)Pi state can be considered as an isolated electronic state. The Renner-Teller coupling of the two components of the (2)Pi state via the degenerate bending mode as well as spin-orbit coupling effects are taken into account. The two stretching modes are treated within the so-called linear vibronic-coupling model. The vibronic and spin-orbit parameters have been determined by accurate ab initio electronic-structure calculations. While spin-orbit effects are small in FCN(+), the large spin-orbit splitting of the X (2)Pi state of the BrCN(+) leads to a complete quenching of the Renner-Teller effect. The X (2)Pi state of the ClCN(+) is shown to be of particular interest: here the resonance condition for linear-relativistic Renner-Teller coupling is approximately fulfilled. This coupling mechanism leads to a significant intensity transfer to vibronic levels with odd quanta of the bending mode. The calculated spectrum indicates that this novel relativistic vibronic-coupling effect should be observable in high-resolution (electron energy resolution of the order of a few meV) photoelectron spectra of ClCN.     

Orthopalladated and -platinated bulky triarylphosphite complexes: synthesis,reactivity and application as high-activity catalysts for Suzuki and Stille coupling reactions

Bulky triarylphosphite ligands undergo facile orthometallation reactions with palladium and platinum precursors. The crystal structure of an example of the resultant palladacycles has been determined. The reactivity of some of the metallacycles with HCl, monodentate and bidentate phosphines and sodium diethyldithiocarbamate has been investigated, and the crystal structure of a diethyldithiocarbamate adduct of a palladacycle is presented. The palladacyclic complexes prove to be extremely active catalysts for the Suzuki coupling of aryl bromides with aryl boronic acids. They can also be used as catalysts for the coupling of alkylboronic acids. Meanwhile di- and trialkyl phosphine adducts of one of the palladacycles shows very high activity in the Suzuki coupling of aryl chlorides and can also be used to good effect for the Stille coupling of these substrates. The role of the phosphite ligand in the Suzuki coupling of aryl chlorides seems to be one of increasing catalyst longevity by stabilisation of the Pd(0) resting state.     

Immobilization of palladium in mesoporous silica matrix: preparation, characterization, and its catalytic efficacy in carbon-carbon coupling reactions

Palladium(0) has been immobilized into the silica-based mesoporous material to develop catalyst Pd(0)-MCM-41, which is found to be highly active in carbon-carbon coupling reactions. [Pd(NH3)4]2+ ions have been incorporated into the mesoporous material during synthesis of MCM-41 and subsequently upon treatments with hydrazine hydrate Pd2+ ions present in mesoporous silica matrix were reduced to Pd(0) almost instantaneously. The catalyst has been characterized by small-angle X-ray diffraction, N2 sorption, and transmission electron microscopy (TEM). TEM and surface area measurements clearly demonstrate that the immobilization of Pd(0) into the mesoporous silica has a significant effect on pore structure of the catalyst. Nevertheless, after immobilization of palladium the meso-porosity of the material is retained, as evidenced in the nitrogen sorption measurement. The TEM micrograph shows that both MCM-41 and Pd(0)-MCM-41 have similar types of external surface morphology; however, Pd(0)-MCM-41 was less ordered. Pd(0)-MCM-41 showed high catalytic activity toward carbon-carbon bond formation reactions like Heck and Sonogashira coupling, as evidenced in high turn-over numbers. In contrast to many other Pd-based catalysts reported so far, Pd(0)-MCM-41 acts as a truly heterogeneous catalyst in C-C coupling reactions. Notably, the new heterogeneous catalyst is found to be efficient in the activation of arylchloride to give impressive conversion in cross coupling (15-45% for Heck and 30% for Sonogashira) reactions under mild conditions.     

Plasmon coupling in nanorod assemblies: optical absorption, discrete dipole approximation simulation, and exciton-coupling model

The shape anisotropy of nanorods gives rise to two distinct orientational modes by which nanorods can be assembled, i.e., end-to-end and side-by-side, analogous to the well-known H and J aggregation in organic chromophores. Optical absorption spectra of gold nanorods have earlier been observed to show a red-shift of the longitudinal plasmon band for the end-to-end linkage of nanorods, resulting from the plasmon coupling between neighboring nanoparticles, similar to the assembly of gold nanospheres. We observe, however, that side-by-side linkage of nanorods in solution shows a blue-shift of the longitudinal plasmon band and a red-shift of the transverse plasmon band. Optical spectra calculated using the discrete dipole approximation method were used to simulate plasmon coupling in assembled nanorod dimers. The longitudinal plasmon band is found to shift to lower energies for end-to-end assembly, but a shift to higher energies is found for the side-by-side orientation, in agreement with the optical absorption experiments. The strength of plasmon coupling was seen to increase with decreasing internanorod distance and an increase in the number of interacting nanorods. For both side-by-side and end-to-end assemblies, the strength of the longitudinal plasmon coupling increases with increasing nanorod aspect ratio as a result of the increasing dipole moment of the longitudinal plasmon. For both the side-by-side and end-to-end orientation, the simulation of a dimer of nanorods having dissimilar aspect ratios showed a longitudinal plasmon resonance with both a blue-shifted and a red-shifted component, as a result of symmetry breaking. A similar result is observed for a pair of similar aspect ratio nanorods assembled in a nonparallel orientation. The internanorod plasmon coupling scheme concluded from the experimental results and simulations is found to be qualitatively consistent with the molecular exciton coupling theory, which has been used to describe the optical spectra of H and J aggregates of organic molecules. The coupled nanorod plasmons are also suggested to be electromagnetic analogues of molecular orbitals. Investigation of the plasmon coupling in assembled nanorods is important for the characterization of optical excitations and plasmon propagation in these nanostructures. The surface plasmon resonance shift resulting from nanorod assembly also offers a promising alternative for analyte-sensing assays.