CC Cross Research Articles

Suzuki coupling of aroyl-MIDA boronate esters – A preliminary report on scope and limitations

Recent methodological reports for synthesizing acyl-MIDA boronate esters compel an investigation of their potential use as substrates in a standard Suzuki-Miyaura cross-coupling reaction. Here we report the production of benzophenones by CC cross coupling between a benzoyl-MIDA boronate ester and a multitude of aryl bromide substrates in adequate yields following optimization under ambient conditions outside of a glove box. Under these standard conditions, none of several acyl-MIDA boronate esters (in an alkyl series) serves as a competent coupling partner. The substrate scope is also limited by the finding that the corresponding trifluoroborates of both acyl- and aroyltrifluroborates are not suitable substrates. For reasons of availability and synthetic difficulty in procuring other aroyl-MIDA boronates, this preliminary study examines the reactivity of benzoyl-MIDA boronate with several aryl bromide substrates.

Aerobic Cu and amine free Sonogashira and Stille couplings of aryl bromides/chlorides with a magnetically recoverable Fe3O4@SiO2 immobilized Pd(II)-thioether containing NHC

Two value added CC cross coupling reactions; Sonogashira and Stille couplings were achieved at milder conditions in the catalytic presence of a magnetically recoverable heterogeneous catalyst Fe3O4@SiO2@NHC^SPh-Pd(II). The catalyst was earlier reported for Suzuki-Miyaura reaction, and as an extension of its catalytic efficiency, the Stille and Sonogashira cross coupling reactions under aerobic condition has been explored in present report. The Sonogashira coupling of aryl bromides and terminal alkynes produced an excellent yield (~96% at 0.25 mol% Pd) of the desired coupling product under copper and amines free conditions. Moreover, an excellent Stille coupling of readily available and more latent aryl chlorides and trialkylstannane was obtained (yields up to 95% at 0.25 mol% Pd) in absence of toxic fluorides additives. The broad substrate scope of the catalyst for both the coupling reactions and the magnetically recoverable feature of catalyst make this reaction highly desirable for industrial applications of present heterogeneous catalysis.

Catalytic influence of light element incorporation in the lattice of palladium

The alloying of metals with foreign elements is a common approach for manipulating catalytic properties of active sites. For palladium-based catalysts, incorporation of light elements receives far less attention than Pd-metal alloys even though incorporated light element are catalytically significant. Due to their small size, light elements (H, B, C, and O) can occupy octahedral sites in Pd to form an interstitial phase, while palladium adjusts its lattice to accommodate the incorporation of larger light elements (S and P) to form distinct phases. The incorporated light element modifies the electronic structure of palladium, influencing the binding energy of substrates and reactive intermediates. Pd hydride and oxide often form in situ during hydrogenation or oxidation reactions, respectively, representing the (more, less) active phase of the catalyst. The reactive interstitial hydrogen dissolved in Pd tends to hydrogenate reactants completely and unselectively. Pd oxide can be the active phase for oxidation reactions, and the incorporated oxygen or oxygen vacancies may participate in the reaction directly. Incorporated light elements change geometric aspects of Pd ensembles, serving the role of site blocking, ensemble isolation, or serve as an additional active site, endowing Pd with bifunctional character. We review the synthetic approaches for incorporating light elements into the palladium lattice. We summarize the catalytic influence of light element incorporation into the palladium lattice with respect to electronic and geometric modification, in situ incorporated hydrogen and oxygen, and discuss the influence of light element incorporation into Pd on specific reactions (i.e., selective hydrogenation, oxidation, electrocatalysis, and CC cross coupling).

Recent advances in the construction of isoindolo[2,1-a]indol/indolin-6-ones via C[sbnd]C cross-coupling reactions

The review summaries the most recent synthetic methodologies for assembly of the 6H-isoindolo[2,1-a]indol-6-one and 10b,11-dihydro-6H-isoindolo[2,1-a]indol-6-one scaffolds, the structural motifs present in many natural and biologically interesting compounds. The literature covered in this overview dates from January 2015 to April 2020, and presented strategies are based on transition metal-catalysed CC cross coupling reactions.

Suzuki cross-coupling reaction over Pd-Schiff-base anchored mesoporous silica catalyst

A new hybrid catalyst has been prepared by tethering a palladium(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from o-vanillin and 3-[(2-aminoethylamino)propyl]trimethoxysilane (ATMS) which is chemically anchored on MCM-41 via silicon alkoxide route. The anchored Schiff-base imposed a stable planar coordination sphere on the central palladium ion. The catalyst has been characterized by elemental analysis, small angle X-ray diffraction, FT-IR, UV–vis, N2 sorption study, transmission electron microscopy (TEM) studies and scanning electron microscopy (SEM) studies. X-ray and TEM measurement showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the Suzuki CC cross coupling reaction using various phenyboronic acid in heterogeneous condition. High selectivity for the biaryl products containing both electron-donating and electron-withdrawing substituents, high turnover, mild reaction conditions and possibility of easy recycle makes the catalyst highly desirable to address the industrial needs and environmental concerns.

Palladium(II) chalcogenolate complexes as catalysts for C[sbnd]C cross-coupling and carbonylative Suzuki coupling reactions

The catalytic activity of palladium chalcogenolate complexes, [PdCl(ECH2CH2NMe2)]3 (E=S or Se), [PdCl(ECH2CH2CH2NMe2)]2 and [PdCl(SeCH2CH2NMe2)(PPh3)] has been investigated in carbonylative Suzuki coupling reactions. The phosphine complex has also been used as a catalyst in CC cross coupling reactions involving an aryl halide and either triaryl bismuth or aryl boronic acid (Suzuki coupling). The catalytic system was also explored for other carbonylation reactions including carbonylative Sonogashira coupling and amino carbonylation reaction. The phosphine complex showed better activity in carbonylative Suzuki coupling reactions than dimeric and trimeric complexes. All the complexes showed comparable activity in Suzuki coupling reactions.

High-[formula omitted] NC and CC cross sections at HERA and proton structure

A review of the recent HERA-II measurements from the H1 and ZEUS detectors on neutral-current and charged-current deep inelastic scattering of longitudinally polarized lepton beams with a proton up to a center-of-mass energy of 318 GeV are presented. Dependence of the cross sections on the polarization of the lepton beam is shown. The lepton charge asymmetry of the neutral current cross section is used to extract the structure function x F ˜ 3 . Electroweak couplings of the u and d quarks are determined from a combined QCD and electroweak analysis of the data. Results on searches for physics beyond the Standard Model are presented. No deviations from the theory is seen, from which limits are derived on the presence of four fermion contact interactions, heavy leptoquarks and on the quark radius.

Relations Between NC and CC Neutrino Structure Functions for Nucleons and Nuclei

The relations between neutrino NC and CC structure functions and cross sections, which are driven by isospin symmetry, are discussed for nucleons and nuclei.

Theoretical Study on Structures and Stability of SiC2S Isomers

The structures, energetics, spectroscopies, and isomerization of singlet and triplet SiC2S isomeric species are explored at various levels. At the B3LYP/6-311G(d) level, a total of 29 minimum isomers and 37 interconversion transition states are located. At the higher CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest lying isomer is the linear SiCCS 11 with a resonance structure mainly between SiCCS and Si⋮C−C⋮S. In contrast to the C3S molecule that has no kinetically stable singlet species besides CCCS, SiC2S has another two kinetically very stable species, i.e., the SiCC three-membered ring with exocyclic SSi bonding 15 at 23.2 kcal/mol, and the SiCSC four-membered ring with CC cross bonding 17 at 44.3 kcal/mol. Particularly, isomer 15 possesses considerable Si⋮S and C⋮C triple bonding character and can be viewed as a charge-transfer species containing SiS+ and C2-. Isomer 17 has a very short CC crossed bond due to the existence of two sets of π-bonding orbital and the weak electron-accepting ability of silicon. The remaining singlet and all the triplet species except triplet SiCCS 31 either have much higher energy or much lower kinetic stability and have little chance of existence. The bonding nature and possible formation strategies of 11, 15, and 17 are discussed.

Global analysis of solar neutrino oscillations including SNO CC measurement

For active and sterile neutrinos, we present the globally allowed solutions for two neutrino oscillations. We include the SNO CC measurement and all other relevant solar neutrino and reactor data. Five active neutrino oscillation solutions (LMA, LOW, SMA, VAC, and Just So2) are currently allowed at 3 sigma; three sterile neutrino solutions (Just So2, SMA, and VAC) are allowed at 3 sigma. The goodness of fit is satisfactory for all eight solutions. We also investigate the robustness of the allowed solutions by carrying out global analyses with and without: 1) imposing solar model constraints on the 8B neutrino flux, 2) including the Super-Kamiokande spectral energy distribution and day-night data, 3) including a continuous mixture of active and sterile neutrinos, 4) using an enhanced CC cross section for deuterium (due to radiative corrections), and 5) a optimistic, hypothetical reduction by a factor of three of the error of the SNO CC rate. For every analysis strategy used in this paper, the most favored solutions all involve large mixing angles: LMA, LOW, or VAC. The favored solutions are robust, but the presence at 3 sigma of individual sterile solutions and the active Just So2 solution is sensitive to the analysis assumptions.

High-Q2 deep inelastic scattering at HERA

High-Q2 NC and CC cross sections as measured at HERA can give information on two distinct areas of current interest. Firstly, supposing that all the electroweak parameters are well known, these cross sections may be used to give information on parton distribution functions (PDFs) in the new kinematic regime at high x and high Q2. Secondly, supposing that PDFs are well known after evolution in Q2 from the kinematic regime where they are already measured, these cross sections may be used to give information on electroweak parameters in a process where the exchanged boson is `spacelike' rather than `timelike'. WG1 addressed itself to clarifying the limits of our present and possible future knowledge on both these points.

A simple connection between ν( [formula omitted])-nucleon scattering and [formula omitted

Using the helicity conservation rule of PQCD it is shown that at large q 2 various ratios involving differences of CC and NC differential cross sections depend on the ratio F 1 n (q 2) F 1 p (q 2) . This form factor ratio is expected to be q 2 independent in PQCD as well as from QCD sum rules. Using input from QCD sum rules possible ranges of the various cross section ratios are predicted.

Off-energy-shell effects in energy sudden factorization relations: Computational study of He+H2 rotational–vibrational scattering

We apply an approximate off-shell version of the ES scaling developed for molecule–surface scattering by Gerber, Beard, and Kouri to the He+H2 CC cross section results of Flower and Kirkpatrick. The predicted results are in much better agreement with CC values than are those obtained using earlier on-shell versions of the ES scaling.

CS( lav) and computational study of degeneracy averaged differerential cross sections and Δ m-integral cross sections: Hez.sbndCO, HDz.sbnd

CC and l-average CS calculations of degeneracy averaged differential cross sections and Δ m-integral cross sections have been performed for Hez.sbndCO at E = 60 cm −1 and E = 80 cm −1, for HDz.sbndNe at E = 254 cm −1, and for Hez.sbndH 2 at E = 1520 cm −1. The l avz.sbndCS degeneracy averaged differential cross sections are generally in good agreement with the CC cross sections. The previously observed shifts in the diffraction oscillations for odd rotationally inelastic transitions for Hez.sbndCO and HDz.sbndNe do not occur due to proper phase choice and l̄ = l av choice rather than l̄ = 1 or l′. The l avz.sbndCS approximation gives reliable results for most Δ m-integral cross sections except for those σ cs( jm, jm′) cross sections for which the CC cross sections σ( jm; jm′) and σ( jm′; jm) differ by a large amount.

A study of vibrational relaxation of H2 in He

The vibrational relaxation rate constant kl→0 (T) over T?500 K was computed for para-H2 in He from fully converged CC cross sections. While the calculated rate constant is much too large, it displays a hump around T=100 K, presenting, for the first time, a plausible elucidation of the humps in the experimental results of Audibert et al. Analyses of the present results and that of Raczkowski et al. seem to indicate that the overestimation by the present work is perhaps mainly due to the nature of the intermolecular potential and that a close-coupling scheme and an accurate potential surface should reproduce the experimental results.

Quantum mechanical close coupling approach to molecular collisions: Averaged definite parity j z approximation with Clebsch–Gordan weights

The new averaged definite parity jz(ADPjz) approximation is considered in detail from the standpoint of the exact body frame CC cross section equations. These cross section equations are decomposed into contributions from the various possible orbital angular momenta and projections of the total angular momentum J onto the scattering vector. This decomposition then permits a clearer examination of the quantities actually approximated in jz-conserving approximations. The various contributions to the exact cross sections are regrouped into components having the same form as the jzCCS and DPjz approximate equations. It is found that the labeling of jzCCS amplitude densities by an orbital angular momentum quantum number enters in a very natural way and in fact that only labeling by l̄ is permitted for consistency. Further, it is shown that only the amplitude density is approximated and this does not require the body frame T-matrix to be diagonal in jz. After the approximate amplitude density is substituted into the exact partial cross section expression, the resulting equations for the partial cross sections σJ(j0→j) lead to an average over the effective orbital angular momenta with weights wJlλ(j ‖j0) =〈l0jλ‖Jλ〉2[(2l+1)/(2J+1)]. A similar analysis of the definite parity partial cross section leads to an average over the effective orbital angular momenta of the proper parity with weights wJplλ(j ‖j0) =〈l0jλ‖Jλ〉2[(2l+1)/(2J+1)][2/(1+δλ,0)]. This enables one to include effects of the various turning points associated with values of l satisfying ‖J−j‖⩽l ⩽J+j. The present method of including parity through the values of l averaged also can correctly describe situations where the odd parity partial cross section is larger than the even parity partial cross section. The result is an approximation which describes definite parity partial cross sections, integral cross sections, and differential cross sections with very high accuracy. Finally, the ADPjz is a general method for which other averaging weights are possible. The previously obtained constant weight version is compared to the present Clebsch–Gordan weight version by applying both to He+H2 collisions. Results for definite parity partial cross sections and integral cross sections are used as the basis of the comparison.