Huisgen click cycloadditions from a copper(II)-tren precatalyst without external sacrificial reductant

The copper(II) complex [Cu(C18₆tren)](Br)₂, 2, is an efficient precatalyst for the Huisgen ‘click’ cycloaddtion which can be used at low loading without the requirement of an external sacrificial reductant such as sodium ascorbate. EPR studies support the in situ reduction of 2 by the alkyne to generate a reactive copper(I) catalyst.     

Insight of the Metal–Ligand Interaction in f-Element Complexes by Paramagnetic NMR Spectroscopy

The magnetic properties of Ln^III and An^III complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest Ln^III and almost all the studied An^III. Bleaney's parameters <S_z>_a and relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of <S_z>_a and . However, the values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for Ln^III. Other parameters, such as the crystal field parameter and the hyperfine constants F_i obtained from the experimental data of the [An(ethyl-dpa)₃]³⁻ complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory.     

On the behavior of spray combustion in a turbulent spatially-evolving jet investigated by direct numerical simulation

Detailed investigations of turbulent spray combustion are very challenging due to the complexity of the underlying physicochemical processes. Experimentally, laboratory-scale burners are increasingly used to investigate these processes and support model development. One ultimate objective of these studies would be to deliver suitable benchmark data. In the present paper, the focus is similar but relying exclusively on direct numerical simulations. Conditions close that found in lab-scale burners are considered in the simulations, so that direct comparisons will ultimately become possible. The current analysis concentrates on the temporal evolution of temperature and concentrations of OH, CH₂O, and CH₄. The profiles of these variables show very complex features, therefore separate zones corresponding to characteristic physicochemical regimes have been tracked in time and space. It is found that, based on the temperature profile, four different zones coexist in the domain, associated to different degrees of competition between evaporation and reaction. It is observed that high concentrations of CH₂O and CH₄ can be used to delineate between three characteristic locations: 1) the evaporation zone; 2) close to the jet tip, at high temperatures; and 3) regions where evaporated droplets are entrained by mixing. This study demonstrates that direct numerical simulation of small spray burners can be used to deliver important information and to contribute useful benchmark data.     

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio‐calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT‐calculated spectra of the eclipsed (D_5h) and staggered (D_5d) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7–300 K), and solid (7–300 K) states. In each case the D_5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution‐phase samples (ca. 6 kJ mol^?1) than for the gas‐phase species (1–3 kJ mol^?1). The generality of the approach is demonstrated with application to tricarbonyl(η⁴‐norbornadiene)iron(0), Fe(NBD)(CO)₃. The temperature‐dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)₃ is well explained by the RCM without recourse to NMR‐like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature‐dependence of their vibrational spectra.     

Cyclometalated IrIII Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores

Cyclometalated cationic Ir^III complexes with substituted 1,10‐phenanthrolines (1,10‐phen), such as [Ir(ppy)₂(5‐R‐1,10‐phen)]Y (ppy=cyclometalated 2‐phenylpyridine; R=NO₂, H, Me, NMe₂; Y^?=PF₆^?, C₁₂H₂₅SO₃^?, I^?) and [Ir(ppy)₂(4‐R,7‐R‐1,10‐phen)]Y (R=Me, Ph) are characterized by a significant second‐order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir^III, acting as a donor push system, to π* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2‐phenylpyridine by the more π delocalized 2‐phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur‐containing 4,5‐diphenyl‐2‐methyl‐thiazole (dpmf) does not significantly affect the μβ absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron‐withdrawing NO₂ group. By using a combined experimental (the EFISH technique and ¹H and ¹⁹F PGSE NMR spectroscopy) and theoretical (DFT, time‐dependent‐DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the μβ values of these cationic NLO chromophores. In CH₂Cl₂, concentration‐dependent high absolute values of μβ are obtained for [Ir(ppy)₂(5‐NO₂‐1,10‐phen)]Y if Y is a weakly interacting anion, such as PF₆^?, whereas with a counterion, such as C₁₂H₂₅SO₃^? or I^?, which form tight ion‐pairs, the absolute value of μβ is lower and quite independent of the concentration. This μβ trend is partially due to the perturbation of the counterion on the LUMO π* levels of the phenanthroline. The correlation between the μβ value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.     

Reactivity of Pd3(dppm)3(CO)n+ and Pd3(dppm)3(CO)(RCCR)n+ (n?=?0, +1, +2) Towards F?. Evidence of Reactive Intermediates and X-Ray Structure of [Pd3(dppm)3(MeO2CC≡CCO2Me)(F)]PF6

Abstract  

The reactivity of the trinuclear palladium cluster [Pd₃(dppm)₃(CO)] ⁿ⁺ (dppm = bis(diphenylphosphinomethane); n = 2, 1) towards F⁻ was investigated by electrochemical and spectroscopic methods. The reaction depends on the charge of the cluster. The chemical reduction of the cluster dication is observed in the presence of F⁻ generating the paramagnetic monocationic cluster. Spin-trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) provided evidence for the radical F^• as an intermediate. In a similar manner to the dication, the monocationic cluster [Pd₃(dppm)₃(CO)]⁺ is also reduced, but in a slower process, by the F⁻ ion to produce [Pd₃(dppm)₃(CO)]⁰. Additionally, the alkyne cluster adducts [Pd₃(dppm)₃(CO)(RCCR)] ⁿ⁺ (n = 2, 1; R = CO₂Me) are also reactive towards F⁻. Particularly, the dication adduct leads to a metastable fluoride adduct [Pd₃(dppm)₃(CO)(RCCR)(F)]⁺. The electroreductive behavior of this adduct involves electron-transfer steps and F⁻ exchange equilibriums, for which digital simulation enables the extraction of the thermodynamic parameters (standard potentials and equilibrium constants). Concurrently, the monocation adduct [Pd₃(dppm)₃(CO)(RCCR)]⁺ with F⁻, leads to a disproponation generating 0.5 equiv. of [Pd₃(dppm)₃(CO)(RCCR)(F)]⁺ and 0.5 equiv. of [Pd₃(dppm)₃(CO)(RCCR)]⁰. The former slowly evolves to [Pd₃(dppm)₃(RCCR)(F)]⁺, which was described by X-ray diffraction method.     

Novel ruthenium(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene linked to a fullerene as highly active second order NLO chromophores

Various Ru(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene are characterized by a good to very large second order NLO response, as determined by EFISH. Among these complexes, [Ru(9-fulleriden-4,5-diazafluorene)(PPh(3))(2)Cl(2)] is particularly appealing due to its huge second-order NLO response and its transparency to the second harmonic generation. The structure of cis-Cl,trans-PPh(3)-[Ru(5-NO(2)-1,10-phen)(PPh(3))(2)Cl(2))] was determined by single-crystal X-ray diffraction.     

The role of glycosides in the light-stabilization of 3-hydroxyflavone (flavonol) dyes as revealed by HPLC

Before the advent of synthetic dyes, textiles were colored primarily with extracts of plants, many of which, in the case of yellow colors, were flavonoids. One important Asian yellow dye source was buds from the pagoda tree (Sophora japonica). Using reversed phase HPLC to separate the flavonoid components of plants and of dyed textiles, and UV/Visible and mass spectrometry to detect and identify them, we have shown that the buds of pagoda trees (Sophora japonica) contain an enzyme that converts light-stable rutin, the 3-O-rutinoside of quercetin, to light-unstable quercetin. This work provides an explanation for why 3-O-substituted, rather than unsubstituted, 3-hydroxyflavones, are generally, in our experience, found in extracts of historical textiles; it also shows how, i.e., by heat inactivation of glycosidases, 3-O-substituted hydroxyflavones could have been selected for. Some other dye-producing plants, e.g., Reseda luteola and Flaveria haumanii, also appear to contain glycosidases. The need for proper processing of dyestuffs, e.g., by heat treatment, was probably recognized by dyers in ancient times, even if the processes were not understood.     

Structural characterisation of aluminium layered double hydroxides by Al solid-state NMR

²⁷Al solid-state NMR has been applied to study the local structure of pristine and chemically modified aluminium layered double hydroxides (LDH). The pristine LDH only shows six-fold coordinated, octahedral, aluminium, while the calcined and subsequently surfactant treated LDH sample shows a significant fraction of four-fold coordinated tetrahedral aluminium. The co-existence of two types of octahedral sites with different quadrupolar parameters is clearly observed in both samples. Quadrupolar coupling constants and isotropic chemical shifts have been measured from the ²⁷Al triple-quantum MAS NMR allowing to fit the ²⁷Al MAS spectra and quantify the different species in the samples. The quantitative analysis reveals that 30% of the aluminium is in four-fold coordination in the surfactant-modified LDH. We show that this chemical modification retains the two types of AlO₆ sites with a decreased intensity of the site showing the lowest quadrupolar coupling constant.     

A Re(CO)5 fragment bonded to a polyhedral oligomeric hydroxysilsesquioxane as a model which gives further evidence to the existence of an unexpected Re(CO)5 surface species

Reaction of Re(CO)5O3SCF3 with (c-C6H11)7Si8O12O-Li+ at 273 K under a CO atmosphere affords the [Re(CO)5OR] (R = (c-C6H11)7Si8O12) derivative (1). 1 is the first example of a rhenium pentacarbonyl bearing an OR ligand (R = alkyl, aryl, or silyl) stable enough to be characterized, and it represents also the first molecular model of the surface [Re(CO)5OSi] species formed by reductive carbonylation of silica-supported [Re(CO)3OH]4. At room temperature, 1 loses one carbonyl ligand and dimerizes to afford {Re(CO)4[(mu-O)O12Si8(c-C6H11)7]}2 (2), which has been characterized by X-ray diffraction and is the first reported example of a rhenium tetracarbonyl mu-oxo-bridged dimer of the type [Re(CO)4(mu-OR)]2.