Convincing and consistent evidence for the existence of hydrogen bonding to gold has been obtained. An ammonium or pyridinium group has been shown to be an efficient hydrogen bond donor unit for gold(I) coordination centers, and the assembly leads to the structural pattern typical for standard hydrogen bonds. This constitutes the first rigorous, scrutinizing, and comprehensive study of hydrogen bonds to a metal atom, with gold being an ideal model element because of relativistic effects.

Thanks for the lift, mate! A molecular machine based on a rotaxane embedded in a lipid bilayer can carry potassium ions across the membrane by taking advantage of the stochastic shuttling motion of its macrocyclic ring.

Touched for the very first time! It is herein highlighted how acetaldehyde silyl enol ethers undergo enantioselective Mukaiyama aldol reaction with aliphatic and aromatic aldehydes. The chemistry relies on the use of the highly efficient and substrate-selective imidodiphosphorimidate catalyst, which displays some of the features of enzymatic catalysis.

e^---lucidation of structures: The microcrystal electron diffraction (MicroED) method promises to significantly accelerate the ability of synthetic chemists to gain structural information about small organic molecules and might be crucial for the acceleration of innovations across many fields.

One half of The Nobel Prize for Chemistry 2018 was awarded to Frances H. Arnold for the directed evolution of enzymes, and the other half jointly to George P. Smith and Sir Gregory P. Winter for the phage display of peptides and antibodies. This Highlight acknowledges the impact of the Nobel Laureates contributions and summarizes the history, state of the art, challenges, and applications of directed evolution and phage display.

New sides of eosin Y: Neutral eosin Y-derived photoexcited states have been found to serve as photoacids and direct hydrogen atom transfer (HAT) catalysts in the activation of glycals and C−H bonds, respectively. These studies pave the way for further use of eosin Y in photochemical synthesis.

Ready for the open waters? Recent developments have fundamentally changed our knowledge of vinyl cation reactivity. The myth that they are too reactive for a predictable reaction design has been debunked, and the applicability of their most distinguished feature, namely their carbene-like reactivity, has taken a major leap forwards. Vinyl cations have thus matured into distinct reactive intermediates with a bright future ahead.

A highly regioselective hydroalkenylation of imines or aldehydes with styrene derivatives was realized by dual catalysis with Ni(cod)₂/PCy₃ and either TsNH₂ or PhB(OH)₂. This process provides an atom-, step-, and redox-economic pathway towards synthetically useful allylic amines and alcohols, and opens up a new avenue for the design of more versatile coupling reactions.

Finally stereoselective: Enantioselective variations have been developed for many multicomponent reactions; however, it has been missing for the Ugi four-component reaction. This has now changed with the discovery of an efficient catalytic enantioselective variant for the four-component reaction of isocyanides, primary amines, aldehydes or ketones, and carboxylic acids.

Like candles on a Christmas tree describes the arrangement of the spins in the Co-Kagome nets of Sn₂Co₃S₂. Giant anomalous Hall effects are now related to its electronic finger print of a Weyl semimetal.

Ketenes in the limelight: The influential role of ketenes has never been adequately acknowledged in zeolite chemistry and catalysis; unlike other first generation highly reactive intermediates, such as carbocations, carbanions, radicals, and carbenes. In fact, the role that ketenes play during catalysis—whether beneficial or detrimental—is a contentious subject that requires further consideration.

Meisenheimer's missing! Anionic σ-complexes, best known as Meisenheimer complexes, have long been assumed to be intermediates in S_NAr reactions. New evidence now suggests that these intermediates may only be formed in select cases and that a concerted pathway is more common. These claims are supported by ¹²C/¹³C kinetic isotopes effects, determined using a new method based on ¹⁹F NMR, and DFT calculations.

Follow the yellow brick road: Functional polymers can be prepared directly at room temperature from elemental sulfur by the Willgerodt–Kindler reaction. This method opens a new synthetic door for the synthesis and application of polythioamides and polythioureas.

The first stable anionic aluminium nucleophile was isolated by Goicoechea, Aldridge and co-workers. The aluminyl compound showed very high reactivity in metathesis reactions as well as in the oxidative addition of substrates such as dihydrogen and benzene, which opens up new perspectives in main group chemistry.

The study of OCF₃-substituted molecules is somewhat hampered by a lack of diverse synthetic methods to access them. By introducing a new mild and practical reaction system for accessing the ^.OCF₃ radical, a recent study by Liu, Ngai, and co-workers has the potential to dramatically expand the scope of direct trifluoromethoxylation. The features of this ground-breaking system are discussed and placed into context with other recent advances on nucleophilic trifluoromethoxylation.

Photoswitches: Exciting recent progress realized in the field of light-controlled polymeric materials is highlighted. It is discussed how the rational choice of azobenzene molecules and their incorporation into complex materials by making use of physical interactions can lead to genuine photocontrollable polymeric systems.

Avoiding white phosphorus: Cummins and Geeson have recently described the conversion of phosphoric acid into the novel bis(trichlorosilyl)phosphide anion (see picture), which serves as a key intermediate in the synthesis of organophosphines, hexafluorophosphate, and phosphine gas in a reaction sequence that does not rely on white phosphorus.

A new concept has been introduced for the preparation of high-molecular-weight poly(aminoborane)s with diverse substituents on the nitrogen atom. Whereas previous methods were oxidative and relied largely on catalytic dehydrocoupling, the new process is based on an uncatalysed polymerisation reaction promoted by amine–aminoborane exchange, and should give access to previously inaccessible polymers.

No metal needed: Boron does the job! The activation of the inert dinitrogen molecule has fascinated chemists for ages. In a ground-breaking study Braunschweig and co-workers have now demonstrated that N₂ activation can be achieved with the aid of the p-block element boron—a reactivity previously restricted to transition metals.

Machines learn chemistry: An artificial intelligence algorithm has learned to predict the outcomes of C−N coupling reactions from a few thousand nanomole-scale experiments. This Highlight discusses this work in the context of other state-of-the-art approaches for predicting the yields of organic reactions and explains the significance of the results.