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The kinetics of the conversion of thiophenols into sulfenyl chlorides using N-chlorosuccinimide (NCS) in dichloromethane have been investigated by in situ 1H NMR and stopped-flow UV–vis spectroscopy. The study reveals that a slow direct chlorination of the thiophenol by NCS initiates a more rapid but indirect process involving in situ generation of a disulfide and then its cleavage by transient Cl2. The latter is released from NCS by HCl and the switch in dominant pathway results in sigmoidal kinetics for the thiophenol consumption. The overall reaction rate can be attenuated by using an alkene to scavenge the sulfenyl chloride before it reacts with the thiophenol. The presence of water in the dichloromethane induces two distinct kinetic regimes, dependent on whether the water is below or above a critical concentration. The value of this critical concentration is dependent on the amount of HCl in the system. As the exogenous water is increased to the critical concentration, there is a proportionate acceleration of the HCl-mediated release of Cl2 from the NCS. At water concentrations above this, there is a progressive reduction in the rate of Cl2 release due to {H2O + nHCl} undergoing a change in speciation or physical phase. Alcohols, e.g., i-PrOH, efficiently catalyze the conversion of thiophenols into sulfenyl chlorides, with further oxidation retarded by trace amounts of disulfide, indicative of analogous HCl-catalyzed slow-release of Cl2. High reactant concentrations can lead to sufficient exothermicity to trigger an abrupt and vigorous release of gaseous HCl. Potential methods to mitigate against developing these hazardous conditions are also discussed.

Herein, we show the detailed behavior of palladium leaching from palladium on charcoal by aqueous HCl, directly observed by X-ray absorption spectroscopy measurement employing a simplified reaction setup. While Pd0 is not affected by the addition of HCl, palladium oxide in nanoparticles readily reacts with HCl to form the ionic species [PdIICl4]2–, even though these ions mostly remain adsorbed on the surface of activated charcoal and can only be detected at a low level in the solution phase. This finding provides a new aspect for control of the leaching behavior and robust usage of palladium on charcoal in organic reactions.

The mechanism of the reactions between dppf-Ni0 complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ2-dppf)(κ1-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalysed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.

[Rh(κ2-PP-DPEphos){η2η2-H2B(NMe3)(CH2)2tBu}][BArF4] acts as an effective precatalyst for the dehydropolymerization of H3B·NMeH2 to form N-methylpolyaminoborane (H2BNMeH)n. Control of polymer molecular weight is achieved by variation of precatalyst loading (0.1-1 mol %, an inverse relationship) and use of the chain-modifying agent H2: with Mn ranging between 5 500 and 34 900 g/mol and between 1.5 and 1.8. H2 evolution studies (1,2-F2C6H4 solvent) reveal an induction period that gets longer with higher precatalyst loading and complex kinetics with a noninteger order in [Rh]TOTAL. Speciation studies at 10 mol % indicate the initial formation of the amino-borane bridged dimer, [Rh2(κ2-PP-DPEphos)2(μ-H)(μ-H2BN=HMe)][BArF4], followed by the crystallographically characterized amidodiboryl complex [Rh2(cis-κ2-PP-DPEphos)2(σ,μ-(H2B)2NHMe)][BArF4]. Adding ∼2 equiv of NMeH2 in tetrahydrofuran (THF) solution to the precatalyst removes this induction period, pseudo-first-order kinetics are observed, a half-order relationship to [Rh]TOTAL is revealed with regard to dehydrogenation, and polymer molecular weights are increased (e.g., Mn = 40 000 g/mol). Speciation studies suggest that NMeH2 acts to form the precatalysts [Rh(κ2-DPEphos)(NMeH2)2][BArF4] and [Rh(κ2-DPEphos)(H)2(NMeH2)2][BArF4], which were independently synthesized and shown to follow very similar dehydrogenation kinetics, and produce polymers of molecular weight comparable with [Rh(κ2-PP-DPEphos){ η2-H2B(NMe3)(CH2)2tBu}][BArF4], which has been doped with amine. This promoting effect of added amine in situ is shown to be general in other cationic Rh-based systems, and possible mechanistic scenarios are discussed.

[Rh(k2–PP–DPEphos){h2-H2B(NMe3)(CH2)2tBu}][BArF4] acts as an effective precatalyst for the dehydropolymerization of H3B·NMeH2 to form N-methylpolyaminoborane (H2BNMeH)n. Control of polymer molecular weight is achieved by variation of catalyst loading (an inverse relationship) and use of the chain termination/transfer agent H2: with Mn ranging between 5,500 to 34,900 g/mol and Đ between 1.5-1.8. H2 evolution studies (1,2-F2C6H4 solvent) reveal an induction period that gets longer with higher catalyst loading, and complex kinetics with a non– integer order in [catalyst]. Speciation studies indicate the initial formation of the amino–borane bridged dimer, [Rh2(k2–PP–DPEphos)2(µ–H)(µ–H2BNHMe)][BArF4], followed by the crystallographically characterized amidodiboryl [Rh2(cis–k2–PP–DPEphos)2(µ-H)(s,µ (H2B)2NHMe)][BArF4]. Adding ~2 equivs NMeH2 in THF solution to the precatalyst removes this induction period, pseudo first order kinetics are observed, and a half order relationship to catalyst is revealed, with regard to dehydrogenation and polymer molecular weights are increased (e.g. Mn = 40,000 g/mol). Speciation studies suggest NMeH2 acts to form the active precatalysts [Rh(DPEphos)(NMeH2)2][BArF4] and [Rh(DPEphos)(H)2(NMeH2)2][BArF4], which were independently synthesized and shown to follow very similar dehydrogenation kinetics and produce polymer of molecular weight comparable with the amine–doped systems. This promoting effect of added amine in situ is shown to be general in other cationic Rh-based systems, and possible mechanistic scenarios are discussed.

The intramolecular gold–catalyzed arylation of arenes by aryltrimethylsilanes has been investigated from both a mechanistic and preparative aspect. The reaction generates five to nine membered rings, and of the 44 examples studied, ten include a heteroatom (N, O). The tethering of the arene to the arylsilane not only provides a tool to probe the impact of the conforma-tional flexibility of Ar–Au–Ar intermediates, via systematic modulation of the length of aryl-aryl linkage, but also the ability to arylate neutral and electron-poor arenes - substrates that do not react at all in the intermolecular process. Rendering the arylation intramolecular also results in phenomenologically simpler reaction kinetics, and overall these features have facili-tated a detailed study of linear free energy relationships, kinetic isotope effects, and the first quantitative experimental data on the effects of aryl electron-demand and conformational freedom on the rate of reductive elimination from diaryl gold(III) species. The turnover-limiting step for the formation of a series of fluorene derivatives is sensitive to the electronics of the arene and changes from reductive elimination to π-complexation for arenes bearing strongly electron-withdrawing substitu-ents (σ >0.43). Reductive elimination is accelerated by electron-donating substituents (□ = -2.0) on one or both rings, with the individual σ-values being additive in nature. Longer and more flexible tethers between the two aryl rings results in faster reductive elimination from Ar-Au(X)-Ar, and to the π-complexation of the arene by Ar-AuX2 becoming the turnover-limiting step.

Background Animals use environmental information to make developmental decisions to maximise their fitness. The nematode Caenorhabditis elegans measures its environment to decide between arresting development as dauer larvae or continuing to grow and reproduce. Worms are thought to use ascarosides as signals of population density and this signalling is thought to be a species-wide honest signal. We compared recently wild C. elegans lines’ dauer larva arrest when presented with the same ascaroside signals and in different food environments. Results We find that the hitherto canonical dauer larva response does not hold among these lines. Ascaroside molecules can, depending on the food environment, both promote and repress dauer larva formation. Further, these recently wild C. elegans lines also produce ascaroside mixtures that induce a wide diversity of dauer larva formation responses. We further find that the lines differ in the quantity and ratios of ascaroside molecules that they release. Some of the dauer larva formation responses are consistent with dishonest signalling. Conclusions Together, the results suggest that the idea that dauer larva formation is an honestly-signalled C. elegans-wide effect does not hold. Rather, the results suggest that ascaroside-based signalling is a public broadcast information system, but where the correct interpretation of that information depends on the worms’ context, and is a system open to dishonest signalling.