A PGSE NMR approach to the characterization of single and multi-site halogen-bonded adducts in solution

We demonstrate here that the Pulsed field Gradient Spin Echo (PGSE) NMR diffusion technique can be effectively used as a complementary tool for the characterization of mono- and multi-site intermolecular halogen bonding (XB) in solution. The main advantage of this technique is that it provides the possibility of unambiguously determining the stoichiometry of the supramolecular adduct, information that is particularly important when multi-site molecular systems are studied. As an example, PGSE NMR measurements in chloroform indicate that hexamethylenetetramine (HMTA), a potentially four-site XB acceptor, actually exploits only two sites for the interaction with the XB donor N-bromosuccinimide (NBS), leaving the other two nitrogen sites unoccupied. Charge displacement calculations suggest that this is due also to the anti-cooperativity of the XB interaction between HMTA and NBS

Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis

As known, the electron density of covalently bound halogen atoms is anisotropically distributed, making them potentially able to establish many weak interactions, acting at the same time as halogen bond donors and hydrogen bond acceptors. Indeed, there are many examples in which the halogen and hydrogen bond coexist in the same structure and, if a correct bond analysis is required, their separation is mandatory. Here, the advantages and limitations of coupling the charge displacement analysis with natural orbital for chemical valence method (NOCV-CD) to separately analyze orthogonal weak interactions are shown, for both symmetric and asymmetric adducts. The methodology gives optimal results with intermolecular adducts but, in the presence of an organometallic complex, also intramolecular interactions can be correctly analyzed. Beyond the methodological aspects, it is shown that correctly separate and quantify the interactions can give interesting chemical insights about the systems

Disclosing the multi-faceted world of weakly interacting inorganic systems by means of NMR spectroscopy

The potential of NMR spectroscopy to investigate inorganic systems assembled by, or whose reactivity is affected by, non-covalent interactions is described. Subjects that have received particular attention in recent years (halogen bonding and Frustrated Lewis Pairs) and more classical subjects that remain under-explored (self-aggregation of ion pairs in low polar solvents, behavior of MAO containing metallocenium ion pairs, and hydrogen bonding/ion pairing effects in Au(I) catalysis) are considered, using an innovative approach, always focusing on the crucial information that can be provided by NMR

Metallocene to metallocene conversion. Synthesis of an oxazoline-substituted pentamethyliridocenium cation from a ferrocenyloxazoline

Reaction of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline with [(CpIrCl2)-Ir-star](2) in benzonitrile with KPF6 and NaOH gave (eta(5)-(S)-2-(4-(1-methylethyl))oxazolinylcyclopentadienyl)(eta(5)-pentamethylcyclopentadienyl)-iridium(III) hexafluorophosphate (68%). This transformation of an iron-based into an iridium-based metallocene proceeds via the rearrangement, with loss of cyclopentadienyliron, of an intermediate cationic ferrocenyliridacycle

Back-Donation in High-Valent d0 Metal Complexes: Does It Exist? the Case of NbV

In the last years, some N-heterocyclic carbene (NHC) complexes of high-valent d0 transition-metal halides have been structurally characterized, showing a significant short distance between the carbene carbon and the cis-halide ligands (Clax). Some authors attributed this arrangement to a halide â\u86\u92 Ccarbene unusual "back-donation", whereas, according to others, the M-carbene bond is purely Ï\u83. More, in general, the ability of d0 metal centers to provide back-donation to suitable ligands is still debated, and detailed bond analyses for this class of systems are missing in the literature. In this contribution, we analyze in detail the NbV-L bond within neutral, cationic, and anionic derivatives of NbCl5, with L = NHC, CO, CNH, and CN-. In [NbVCl6-x(NHC)x]x-1 complexes, with NHC being either a model carbene (1,3-dimethylimidazol-2-ylidene, IMe) or a realistic one [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IPr], we demonstrate that the metal center is really capable of back-donation to the carbene ligand by a charge flux that involves the chloride in the trans position and, directly, the metal. In this case, a direct interaction between Clax and Ccarbene can be excluded, while if different Ï\u80-acceptor ligands, such as CO or CNH, are used (instead of NHC), the direct Clax â\u86\u92 L interligand interaction becomes predominant

Charge-displacement analysis as a tool to study chalcogen bonded adducts and predict their association constants in solution

The secondary interaction between a polarized chalcogen atom and different Lewis bases, either anionic or neutral, has been studied by charge displacement analysis. Using charge displacement analysis, the charge rearrangement in the adduct upon the formation of the interaction has been quantified and described in great detail. By comparing the theoretical results with the experimental association con- stants, two linear correlations can be found for anionic and neutral bases. Such correlations can be used to reliably predict the association constants of adducts for which experimental data are not available yet

Monomeric gold hydrides for carbon dioxide reduction: Ligand effect on the reactivity

We analyzed the ligand electronic effect in the reaction between a [LAu(I)H]0/− hydride species and CO2, leading to a coordinated formate [LAu(HCOO)]0/−. We explored 20 different ligands, such as carbenes, phosphines and others, carefully selected to cover a wide range of electron-donor and -acceptor properties. We included in the study the only ligand, an NHC-coordinated diphosphene, that, thus far, experimentally demonstrated facile and reversible reaction between the monomeric gold(I) hydride and carbon dioxide. We elucidated the previously unknown reaction mechanism, which resulted to be concerted and common to all the ligands: the gold–hydrogen bond attacks the carbon atom of CO2 with one oxygen atom coordinating to the gold center. A correlation between the ligand σ donor ability, which affects the electron density at the reactive site, and the kinetic activation barriers of the reaction has been found. This systematic study offers useful guidelines for the rational design of new ligands for this reaction, while suggesting a few promising and experimentally accessible potential candidates for the stoichiometric or catalytic CO2 activation

Probing the structural organization of a low temperature transition mixture for CO2 capture through spectroscopic and theoretical studies

We investigated a low temperature transition mixture (LTTM) suitable for carbon capture through infrared spectroscopy, differential scanning calorimetry, absorption of CO2 and computational studies. The system, made up of a homogeneous mixture of ethylene glycol, potassium hydroxide and boric acid (3:1:1), is sensitive to temperature changes that affect the viscosity of the solvent and its capacity to exchange CO2 at the interface. The relationship between the LTTM's molecular structure and its ability to capture the gas were investigated in order to optimize the properties of the absorbing material for developing viable and reusable carbon capture systems. The results suggest that a large number of free OH groups is available to ensure an effective CO2 capture through the formation of the organic carbonate, leading to an average absorption of 22 ± 1 gCOjavax.xml.bind.JAXBElement@7fcbc253/kgsolv at room temperature. Boric acid acts as a catalyst for the carbonate decomposition and ensures the release of CO2 at 60 °C. ATR-FTIR measurements proved that the solvent is mostly regenerated after desorption and can thus continue to absorb further CO2 over a large number of cycles, making the system reusable

Investigating the genetic basis of salt-tolerance in common bean: a genome-wide association study at the early vegetative stage

Salinity poses a significant challenge to global crop productivity, affecting approximately 20% of cultivated and 33% of irrigated farmland, and this issue is on the rise. Negative impact of salinity on plant development and metabolism leads to physiological and morphological alterations mainly due to high ion concentration in tissues and the reduced water and nutrients uptake. Common bean (Phaseolus vulgaris L.), a staple food crop accounting for a substantial portion of consumed grain legumes worldwide, is highly susceptible to salt stress resulting in noticeable reduction in dry matter gain in roots and shoots even at low salt concentrations. In this study we screened a common bean panel of diversity encompassing 192 homozygous genotypes for salt tolerance at seedling stage. Phenotypic data were leveraged to identify genomic regions involved in salt stress tolerance in the species through GWAS. We detected seven significant associations between shoot dry weight and SNP markers. The candidate genes, in linkage with the regions associated to salt tolerance or harbouring the detected SNP, showed strong homology with genes known to be involved in salt tolerance in Arabidopsis. Our findings provide valuable insights onto the genetic control of salt tolerance in common bean and represent a first contribution to address the challenge of salinity-induced yield losses in this species and poses the ground to eventually breed salt tolerant common bean varieties

Depolymerization of polyethylene terephthalate (PET) under mild conditions by Lewis/Brønsted acidic deep eutectic solvents

Modern society urgently needs new recycling methods to handle the impressive amount of plastic items that are annually discarded. Deep Eutectic Solvents (DESs) have shown interesting results in the depolymerization of polyethylene terephthalate (PET), but most of the procedures still need harsh conditions of temperature and pressure. In this contribution, we propose a bifunctional Lewis/Brønsted acidic DES composed of FeCl3·6H2O, cheap and scarcely toxic, in combination with a variety of acids, both mineral and organic, including some of natural origin (citric and acetic acid). We show that the LBDES formed with methanesulfonic acid and para-toluenesulfonic acid are capable of quantitatively depolymerizing PET under mild conditions, with a temperature of 100 °C and a reaction time of 1 h, affording high purity terephthalic acid in high yield. For acetic acid, a reaction time of 3 h are necessary to obtain a quantitative depolymerization. Different strategies to optimize the PET/LBDES ratio has been successfully tested, as the consecutive addition of multiple aliquots of PET or the filtration and reuse of the solvent. The best solvent has been characterized through the comparison of theoretical and experimental eutectic phase diagram, confirming its nature of DES