Palladium Complexes Derived from Waste as Catalysts for C-H Functionalisation and C-N Bond Formation

Three-way catalysts (TWCs) are widely used in vehicles to convert the exhaust emissions from internal combustion engines into less toxic pollutants. After around 8–10 years of use, the declining catalytic activity of TWCs causes them to need replacing, leading to the generation of substantial amounts of spent TWC material containing precious metals, including palladium. It has previously been reported that [NnBu4]2[Pd2I6] is obtained in high yield and purity from model TWC material using a simple, inexpensive and mild reaction based on tetrabutylammonium iodide in the presence of iodine. In this contribution, it is shown that, through a simple ligand exchange reaction, this dimeric recovery complex can be converted into PdI2(dppf) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), which is a direct analogue of a commonly used catalyst, PdCl2(dppf). [NnBu4]2[Pd2I6] displayed high catalytic activity in the oxidative functionalisation of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of an oxidant, PhI(OAc)2. Near-quantitative conversions to the desired product were obtained using a catalyst recovered from waste under milder conditions (50 °C, 1–2 mol% Pd loading) and shorter reaction times (2 h) than those typically used in the literature. The [NnBu4]2[Pd2I6] catalyst could also be recovered and re-used multiple times after the reaction, providing additional sustainability benefits. Both [NnBu4]2[Pd2I6] and PdI2(dppf) were also found to be active in Buchwald–Hartwig amination reactions, and their performance was optimised through a Design of Experiments (DoE) study. The optimised conditions for this waste-derived palladium catalyst (1–2 mol% Pd loading, 3–6 mol% of dppf) in a bioderived solvent, cyclopentyl methyl ether (CPME), offer a more sustainable approach to C-N bond formation than comparable amination protocols

Enhanced selectivity for acidic contaminants in drinking water: From suspect screening to toxicity prediction

A novel analytical workflow for suspect screening of organic acidic contaminants in drinking water is presented, featuring selective extraction by silica-based strong anion-exchange solid-phase extraction, mixed-mode liquid chromatography-high resolution accurate mass spectrometry (LC-HRMS), peak detection, feature reduction and compound identification. The novel use of an ammonium bicarbonate-based elution solvent extended strong anion-exchange solid-phase extraction applicability to LC-HRMS of strong acids. This approach performed with consistently higher recovery and repeatability (88 ± 7 % at 500 ng L-1), improved selectivity and lower matrix interference (mean = 12 %) over a generic mixed-mode weak anion exchange SPE method. In addition, a novel filter for reducing full-scan features from fulvic and humic acids was successfully introduced, reducing workload and potential for false positives. The workflow was then applied to 10 London municipal drinking water samples, revealing the presence of 22 confirmed and 37 tentatively identified substances. Several poorly investigated and potentially harmful compounds were found which included halogenated hydroxy-cyclopentene-diones and dibromomethanesulfonic acid. Some of these compounds have been reported as mutagenic in test systems and thus their presence here requires further investigation. Overall, this approach demonstrated that employing selective extraction improved detection and helped shortlist suspects and potentially toxic chemical contaminants with higher confidence

Disclosure and rationality: Comparative risk information and decision-making about prevention

With the growing focus on prevention in medicine, studies of how to describe risk have become increasing important. Recently, some researchers have argued against giving patients "comparative risk information," such as data about whether their baseline risk of developing a particular disease is above or below average. The concern is that giving patients this information will interfere with their consideration of more relevant data, such as the specific chance of getting the disease (the "personal risk"), the risk reduction the treatment provides, and any possible side effects. I explore this view and the theories of rationality that ground it, and I argue instead that comparative risk information can play a positive role in decision-making. The criticism of disclosing this sort of information to patients, I conclude, rests on a mistakenly narrow account of the goals of prevention and the nature of rational choice in medicine

SWERN Oxidation. Transition State Theory is OK

We investigate the model originally used to compare deuterium kinetic isotope effects (KIE) computed for the intramolecular hydrogen transfer step in the mechanism of the Swern oxidation of alcohols to aldehydes with those measured. Whereas the replication of the original computed values reported in 2010 for the gas-phase proved entirely successful, several issues were discovered when a continuum solvent model was used. These included uncertainty regarding the parameters and methods used for the calculations and coordinates for the original reactant and transition states, via their provision as data in the electronic supporting information (ESI). The original conclusions, in which a numerical mis-match between the magnitude of the computed and experimentally measured KIE was attributed to significant deviations from transition state theory, are here instead rationalised as a manifestation of basis-set effects in the computation. Transition state theory appears to be operating successfully. We now recommend the use of basis sets of triple- or quadruple-ζ quality, rather than the split-valence level previously employed, that dispersion energy corrections be included and that a continuum solvent model using smoothed reaction cavities is essential for effective geometry optimisation and hence accurate normal coordinate analysis. An outlying experimental KIE obtained for chloroform as solvent is attributed to a small level of an explicit hydrogen bonded interaction with the substrate. A temperature outlier for the measured KIE at 195K is suggested for further experimental investigation, although it may also be an indication of an unusually abrupt incursion of hydrogen tunnelling, which would need non-Born-Oppenheimer methods in which nuclear quantum effects are included to be more accurately modelled. We predict KIE for new substituents, of which those for R=NMe2 are significantly larger than for R=H. This approach could be useful in designing variations of the Swern reagent that could lead to synthesis of aldehydes incorporating much higher levels of deuterium. The use of FAIR data rather than the traditional model of its inclusion in electronic supporting information (ESI) is discussed

A Unifying Stereochemical Analysis for the Formation of Halogenated C₁₅-Acetogenin Medium-Ring Ethers From <i>Laurencia</i> Species via Intramolecular Bromonium Ion Assisted Epoxide Ring-Opening and Experimental Corroboration with a Model Epoxide

A unifying stereochemical analysis for the formation of the constitutional isomeric halogenated C₁₅-acetogenin medium-ring ether natural products from <i>Laurencia</i> species is presented, where an intramolecular bromonium ion assisted epoxide ring-opening reaction of enantiomerically pure epoxides can account for ring-size, the position of the halogen substituents, and relative and absolute configurations of the known natural products. Experimentally, a model epoxide corroborates the feasibility of this process for concurrent formation of 7-, 8- and 9-ring ethers corresponding to the halogenated medium-ring ethers of known metabolites from <i>Laurencia</i> species