Search

“Welcome Rare Earthers.” In 1965, this message appeared on a Holiday Inn sign in Ames, Iowa, to greet the attendees of the 5th Rare Earth Research Conference (RERC). Rare-earth chemistry was at a fulcrum point in its history. Previously, during World War II, chemists working in Ames at Iowa State University had played a critical role in rare-earth technology. As part of the Manhattan Project in 1942, the researchers developed methods to remove traces of rare-earth metals from the uranium used to create the first nuclear chain reaction and to make the first nuclear bombs. Not much was known about the chemistry of the rare earths in the 1940s, or even by the 1960s. This group of 17 elements, which include the lanthanides—lanthanum to lutetium—along with scandium and yttrium, seemed to consist of fairly unreactive metals that all behaved similarly. Most of the research and development involving the elements was

Heat-and-serve thermal paper bypasses bisphenol A Chemists regularly come up with great products that are later discovered to have a shortcoming. With green chemistry principles as a guide, that’s an opportunity to go back to the drawing board and find a game-changing solution. Thermal paper used for printing cash register receipts, tickets, and labels is one such success story. In traditional thermal paper, a colorless dye and a chemical developer such as bisphenol A are coated on the paper. When heated, BPA interacts with and protonates the dye to alter the structure, switching its color from white to black. However, concerns over the estrogen-mimicking properties of bisphenols have led chemists to replace them where possible to reduce retail worker and consumer exposures. Dow Chemical and papermaker Koehler jointly landed the Designing Greener Chemicals Award for a technology that uses a polymer coating on paper to create fade-resistant thermal-printed images stemming

Heating a liquid until it evaporates is one of the most fundamental ways to separate chemical mixtures. Just turn on the heat and wait. On the industrial scale, the problem is not so much the wait, but the heat. The chemical industry requires a lot of it to separate chemical compounds using distillations—as much as 15% of the U.S.’s energy consumption, according to an Oak Ridge National Laboratory report. Chemical manufacturers are more cognizant than ever of the need to cut energy use and prevent pollution. It’s one part green chemistry and sustainability. But another part is keeping an eye on the company bottom line, because with commodity chemicals, price is important and saving every penny in production counts. Even so, chemical companies find that it’s tough to adopt alternatives to large-scale distillation that don’t rely on heating. That’s because distillation is a dependable, well-understood method that works, and replacing

As a teenager in the 1960s, Charles V. Johnson of Lake Geneva, Wis., was tinkering with his chemistry set when he discovered that earwax could serve as a catalyst for making pigments. Later on, as a zoology undergraduate student at the University of Wisconsin, Madison, Johnson took a daring chance in a chemistry lab: He applied earwax to a boiling chip and substituted it for a palladium catalyst in an organic synthesis experiment. It worked well to make trans-stilbene, although his professor didn’t seem impressed. “That’s the thing that has bothered me most,” Johnson told C&EN in a 2012 interview. “My instructors didn’t think there was anything to it.” After graduating, Johnson worked as a chemical technician at Sigma-Aldrich until he retired. He occasionally toyed with using earwax as a catalyst over the years to, for example, polymerize a methacrylate-based material he bummed off his dentist. Johnson often contemplated what

When you mention boron to people and ask them what it brings to mind, there’s no shortage of answers. Some will think about borax (sodium borate), which is used to make glass and the playful concoction known as slime. Others may bring up boron fiber fishing rods. From chemists, you get the nerdy responses: Suzuki-Miyaura cross-coupling reactions, a beautiful green flame test, and funky bonding. Nearly everyone has a different answer to the boron question, and that diversity speaks volumes. Boron is a quirky little element with four bonding orbitals but only three valence electrons. The odd number of electrons makes boron electron-poor yet rich with opportunities for chemical reactivity and influencing materials properties. Examples of boron’s prowess were on display last month at Boron in the Americas (BORAM), a biennial conference hosted this year by the chemistry department at Queen’s University in Kingston, Ontario. The iconic element has a

For chemists and chemical engineers, it’s not easy being green. It’s a creative challenge to choose safer reagents and solvents, design more efficient catalysts, develop cleaner chemical manufacturing processes, use biobased materials when possible, and find better ways to dispose of or recycle waste. Being green is also a challenge for educators, who are working to modernize curriculum materials for training the next generation of chemists. For a quarter-century, since the concept of green chemistry was formally introduced, the chemistry community has been chipping away at these challenges. Hundreds of scientists and engineers gathered to celebrate their progress last month in Portland, Ore., one of the world’s most environmentally conscious cities, at the annual Green Chemistry & Engineering Conference (GC&E). It was a milestone event, marking 25 years since the U.S. Environmental Protection Agency established its Green Chemistry Program and the 20th year of the conference, which is organized by

Few people could argue that using vegetable oil instead of crude oil, replacing platinum catalysts with iron, or potentially avoiding the use of billions of liters of toxic and corrosive acids in petrochemical plants isn’t a good deal. These are the benefits of some of the innovations that have been recognized with this year’s Presidential Green Chemistry Challenge Awards. The award winners were unveiled on June 13 at a ceremony held in Portland, Ore., in conjunction with the 20th annual Green Chemistry & Engineering Conference. The Green Chemistry Awards are administered by the Environmental Protection Agency and supported by the American Chemical Society and its Green Chemistry Institute, which select an independent panel to judge the nominations and determine the award winners. As its name suggests, the awards program challenges chemists, chemical engineers, and the chemical industry and academic community to do better and recognizes their successes in developing innovative

In December 2008, a dike collapsed at a waste storage pond at the Tennessee Valley Authority’s Kingston power plant in northeastern Tennessee. The incident released more than 3.8 billion L of water containing 4.1 million m3 of coal ash, which is the cremated remains of burning coal. The spill inundated several homes and contaminated the Emory River. The cleanup, which took until 2015 to complete, cost $1.1 billion. The Kingston incident points to modern society’s biggest dilemma: In pursuit of our greatest need—generating electricity—we generate an unsustainable amount of pollution. In the case of burning coal, we regularly lament the amount of carbon dioxide being pumped into the atmosphere. But we tend to forget that other substances emitted by burning coal—including sulfur, mercury, and coal ash—are piling up on the ground. Coal ash is the second-largest waste material in the U.S. behind household trash. Utility companies and the ash management

In what is being called an honest mistake, a research group has reported that the structure of the headline compound from a paper it published in 2002 is incorrect. To set the record straight, the team has retracted the paper and at the same time published a new paper reporting the actual structure. The original paper published by Chris Orvig and his group at the University of British Columbia reported the synthesis of a new tetraazamacrocycle ligand (Inorg. Chem. 2002, DOI: 10.1021/ic010716a). The researchers made the compound to see how replacing two methylene groups in a macrocyclic ring with phosphinate groups affected the stability of complexes formed with lanthanide ions. Such complexes are of interest as contrast agents for magnetic resonance imaging. Orvig says all the characterization data were consistent with the ligand having a dimeric structure. But the team had a hard time growing crystals of the ligand and

For decades, (–)-sparteine was a workhorse chemical reagent. The chiral diamine natural product extracted from the seeds of several types of plants had been widely used as a ligand in asymmetric syntheses and as a cocatalyst in ring-opening polymerization reactions. Chemists also studied (–)-sparteine’s potential as a drug. But in 2010, the compound went missing. At first, chemists had trouble buying (–)-sparteine—the supply chain that academic research labs and chemical companies relied on was drying up. Then, the compound was nowhere to be found. After a drought of several years, the reagent is now available again. However, (–)-sparteine remains sparse. And it’s much more costly than it once was. The bottom line is no one, not even chemical companies that advertise selling it, seems to have an answer as to what happened. The case of the missing (–)-sparteine might not have the same cachet as a murder in an Agatha

When it comes to electrochemistry, the first thing that pops into mind probably isn’t C–H activation or arene cross-coupling reactions. You might think of batteries and solar cells, or industrial processes such as electroplating and the electrolytic production of metals such as aluminum. Others might think of cyclic voltammetry, a technique used to study the chemical properties of compounds and reaction mechanisms. But for plain old organic chemistry, like those arene cross-couplings, electrochemistry isn’t common in research or used widely on a preparative scale. The century-old chlor-alkali electrolysis process to prepare chlorine and sodium hydroxide from sodium chloride solution is one exception. And emerging more recently have been clean energy electrocatalytic reactions such as splitting water to make hydrogen and reducing carbon dioxide to make simple hydrocarbons. Today’s chemists have been simply reluctant to adopt electrosynthesis, believing the technology is too cumbersome or expensive. Yet as ...

In the movie “Arrival,” one of the latest films to depict extraterrestrial creatures visiting Earth, a team of scientists takes along a canary in a cage when visiting an alien spaceship. The purpose of the canary is never disclosed, but one assumes it serves as a sentinel—as the bird once did in coal mines—to alert the team if environmental conditions in the spaceship turn unfavorable. Canaries are the most familiar example of a sentinel species, which are animals and plants that serve as harbingers of danger to human health and the environment. In the case of canaries, if odorless carbon monoxide were present in a high enough concentration in a coal mine, the small bird would die first and give miners time to escape. Cats, too, have been sentinels. In the 1950s, people in the town of Minamata, Japan, began to notice that local cats were acting strangely: The cats

Hypervalent iodine compounds are versatile reagents for transferring functional groups to organic molecules. For example, these compounds have become popular as electrophilic trifluoromethylating reagents. The fluorinating reagents, first reported in 2006 by Antonio Togni and his group at the Swiss Federal Institute of Technology (ETH), Zurich, take advantage of iodine(III)’s ability to maintain two lone pairs of electrons while bonding with a CF3 group and a phenyl ring and forming a stabilizing side ring through interactions with an adjacent oxygen or nitrogen phenyl substituent (one example shown). Since 2006, Togni and coworkers have made several modifications to the original compounds by way of changing the fluorinated and phenyl substituent groups. In the latest effort, Togni and Ewa Pietrasiak in his group have gone further to replace iodine itself with its periodic table neighbor tellurium (Organometallics 2017, DOI: 10.1021/acs.organomet.7b00535). Hypervalent compounds are those that contain a gr...

Chemists over the years have explored countless ways to incorporate boron, nitrogen, oxygen, phosphorus, sulfur, and other elements into carbon ring systems. Creating these so-called heterocyclic compounds is like adding new flavors to a menu for chemists to try out, for example, when making optoelectronic materials, creating new catalysts, or developing new drugs. Continuing the trend, two research groups are reporting the addition of new types of nitrogen-phosphorus heterocycles. In one example, Hansjorg Grutzmacher of ETH Zurich, Zoltan Benkő of Budapest University of Technology & Economics, and coworkers have prepared annulated 1-aza-3,4-diphospholides by adding sodium phosphaethynolate to 2-chloropyridines (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201705473). Cyano-substituted versions of the azaphospholides are deeply colored and have widely tunable optical properties, which could make them useful as ion sensors or as precursors for fabricating light-emitting diodes. In the other example, Ian M...

Polyethylene plastic shopping bags are extremely cheap and useful, but they’re also a source of widespread pollution. A team led by biologist Federica Bertocchini of Spain’s Institute of Biomedicine & Biotechnology of Cantabria has discovered a very hungry caterpillar that eats the plastic, a finding that could turn out to be a solution to this dilemma. A hobbyist beekeeper, Bertocchini noticed that waxworm caterpillars had hatched and emerged on the panels of one of her hives. The worms are the larvae of the wax moth Galleria mellonella, which is known to infest beehives. The caterpillars were feeding on beeswax—hence their name. When Bertocchini went to dispose of the waxworms in a polyethylene bag, which is chemically similar to the long alkyl chain compounds that make up beeswax, the waxworms quickly ate through the plastic and escaped. Investigating further, Bertocchini and her colleagues found that enzymes produced by the waxworm or

British chemist Humphry Davy is best known for being the first person to isolate several elements, including sodium and calcium. Davy carried out his work electrolytically more than 200 years ago as an early experimenter with batteries. Less known about Davy is that during experiments on water electrolysis, in which water is split into hydrogen and oxygen, he found that ammonia formed on the cathode in his electrolysis cell. Davy had unexpectedly coupled N2 dissolved in the water from the air with the H2 being formed to make NH3 (Phil. Trans. R. Soc. Lond. 1807, DOI: 10.1098/rstl.1807.0001). Scientists and engineers have been fixated on this so-called nitrogen-fixing process ever since, primarily as a means to make NH3 to prepare fertilizer. We now know that bacteria in the soil produce nitrogenase enzymes to pull N2 from the air to make NH3. The ammonia is subsequently converted to nitrate by other bacteria

When hearing someone describe the typical preparation of organosulfur compounds, it’s clear the approach is not a very sustainable one. Mixtures of sulfur compounds naturally found in crude oil are first treated with hydrogen in a catalytic refinery process to remove the sulfur—the goal is to pull out as much sulfur as possible to create cleaner transportation fuels. The hydrogen sulfide that forms in this hydrodesulfurization step is converted to elemental sulfur. Chemists then pair this sulfur with selected reactants to reconstruct desired organosulfur compounds one product at a time. Overall, the energy-intensive, multistep process is costly and generates a significant amount of waste. A new strategy reported by Valentine P. Ananikov of the Russian Academy of Sciences’ Zelinsky Institute of Organic Chemistry and coworkers enables unprecedented direct C–H functionalization and separation of only one sulfur component at a time from mixtures of organosulfur compounds (ACS Omega 2017, DOI: 10.1021/acsomega...

A hole remained in the periodic table where element 43 should have been until 1937, when the invention of the cyclotron facilitated the discovery of technetium as the first and lightest artificially produced element. At the ACS meeting, Alfred P. Sattelberger of Argonne National Laboratory described a decade’s worth of new research on this “hot element.” Working with Kenneth R. Czerwinski, Frederic Poineau, and their students at the University of Nevada, Las Vegas, Sattelberger has produced some 40 research papers on various aspects of technetium chemistry, including one recently that discussed how technetium’s nuclear makeup causes it to be radioactive (J. Chem. Educ. 2017, DOI: 10.1021/acs.jchemed.6b00343). “There are three good reasons to study technetium,” Sattelberger said. First, researchers need to know how Tc compares with its next-door neighbors regarding its synthetic and structural chemistry. Second, the radioisotope 99mTc, with a half-life of six hours, is a workhorse in diagnostic medicine

Researchers have traditionally prepared difluoromethylated compounds by the deoxyfluorination of aldehydes using harsh electrophilic fluorinating reactions. More recently, chemists have taken a milder approach by using preformed reagents to transfer a CF2H group to a target molecule. In this case, the preformed reagent is often made from fluoroalkyl halides such as chlorodifluoromethane, ClCF2H, an inexpensive industrial chemical used for making fluorinated polymers. Xingang Zhang and coworkers at Shanghai Institute of Organic Chemistry wondered if they couldn’t simplify difluoromethylations further by using ClCF2H directly in a catalytic process. The researchers have found that they indeed can carry out palladium-catalyzed coupling reactions between ClCF2H and aryl and heteroaryl boronic acids and esters to create an array of aromatic difluoromethyl derivatives, providing new opportunities to develop bioactive compounds used as pharmaceuticals, agrochemicals (one example shown), and flavors and fragrance...

Carbon dioxide is a ubiquitous stable gaseous molecule with O=C=O bonding. Yet in one of the quirks of the periodic table, silicon dioxide—the next heaviest group 14 dioxide—is remarkably unstable as a monomeric species. There’s plenty of SiO2 around, but it forms network structures, for example in sand, held together by Si–O single bonds. Chemists have looked for the means to create molecules containing individual O=Si=O units and have come close with SiO and SiO, but until now the seemingly simple species has remained elusive. Antoine Baceiredo and Tsuyoshi Kato of the University of Toulouse and their colleagues finally solved this challenge by finding the right combination of stabilizing ligands to get the job done (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201611851). The researchers previously created several main-group complexes containing Si=O, O–Si=O, or O=Si-OH units supported by electron-donating and/or electron-accepting ligands. Ultimately they found that pairing an amine-substituted pyrid...

As denizens of DNA, Chad A. Mirkin and his group at Northwestern University have used the biopolymer in combination with metal nanoparticles to assemble hundreds of differently shaped micrometer-scale colloidal crystals. Even so, they have just come up with one that hasn’t been seen before: a colloidal clathrate. The trick in making the clathrates, which are known for their cavities that can house molecules for storing, delivering, and sensing applications, was tuning the nanoparticle shape and the length and sequence of the DNA connectors. The engineering was guided by simulations carried out by Sharon C. Glotzer and her team at the University of Michigan (Science 2017, DOI: 10.1126/science.aal3919). The researchers prepared anisotropic, triangular bipyramidal gold nanoparticles that align into tetramers. Attaching a DNA monolayer to the gold leads to assembly of nanoparticle clusters that form the colloidal crystals with patterns that, rather than become densely packed, leave polygon-shaped holes. The

University of Michigan chemists have developed a Lewis acid-base pair strategy to prepare and stabilize a versatile new reagent capable of adding trifluoromethyl groups to molecules. The method promises to expand on current synthetic strategies for making fluorinated pharmaceuticals and agrochemicals while lowering costs and reducing chemical waste. Jacob B. Geri and Nathaniel K. Szymczak conducted a computational study and developed an acid-base affinity scale to help identify hexamethylborazine as the optimal Lewis acid—an electron-pair acceptor—to go with trifluoromethyl anion as the Lewis base—an electron-pair donor. They carried out the study with the aim of deriving CF3– from fluoroform (CHF3), an industrial waste product and potent greenhouse gas, while also allowing for simple CF3– transfer from the acid-base pair to a range of inorganic and organic electrophilic reagents (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b05408). Chemists have previously developed acid-base trifluoromethylating reagents...

A Columbia University research team has prepared a magnesium catalyst that can efficiently convert carbon dioxide to precursors for commodity chemicals such as formaldehyde. Carbon dioxide is usually thought of as an essential molecule for photosynthesis and as a greenhouse gas that helps control Earth’s climate. But because CO2 is abundant and cheap, it also offers much potential as a renewable carbon source for synthesizing chemicals and fuels. The catch is that the gas is not very reactive until it overreacts, so chemists need to come up with catalysts that selectively functionalize CO2 to produce targeted products. One approach is hydrosilylation, but control of the product distribution by high-priced precious-metal catalysts at the hot temperatures they require is challenging and may result in complete reduction of CO2 to methane. The new catalysts prepared by Columbia’s Michael Rauch and Gerard Parkin instead use less costly zinc or magnesium and work selectively

When it comes to electrochemistry, the first things that pop into mind might be batteries and solar cells, or industrial processes like electroplating. Organic synthesis is not usually part of the ...

Reversible, two-electron redox processes in which a substrate is added and subsequently eliminated from a transition metal are a defining feature of most catalytic cycles. This behavior is typicall...

With the aid of a powerful calcium reagent, researchers have achieved a bit of molecular trickery to do what many synthetic organic chemists thought wasn’t possible: They have carried out the first nucleophilic alkylation of benzene (Science 2017, DOI: 10.1126/science.aao5923). Friedel-Crafts alkylation is a classic example of electrophilic aromatic substitution. A Lewis acid such as AlCl3 binds the halogen of an alkyl halide, creating a positive charge on the alkyl group. This electron-poor species—an electrophile—is attracted to an electron-rich substrate—a nucleophile—such as benzene’s aromatic ring. The alkyl group then displaces a benzene hydrogen, producing an alkylbenzene. An electron-rich nucleophilic species would normally be repelled by benzene, unless an electron-withdrawing group already on the ring activates it toward nucleophilic attack. Nevertheless, a team led by Michael S. Hill of the University of Bath and Laurent Maron of the University of Toulouse found a way to allow nucleophiles to r...

Academic researchers often develop organic synthesis methods that offer efficient new routes to industrially important chemicals. But many of these methods are considered untouchable in an industry setting because they involve hazardous reagents that can’t be safely handled on a larger scale or because they are cost-prohibitive to implement. Sometimes, though, a success story does come along. An industry-academic collaboration led by Hao Xu of Georgia State University and Marino Nebuloni of Italian specialty chemical company Redox Laboratory has developed a gram-scale procedure for directly adding azides to olefins to make vicinal primary diamines (Org. Process Res. Dev. 2017, DOI: 10.1021/acs.oprd.7b00312). Xu’s group first reported the mild-mannered method in late 2015, converting unfunctionalized linear and cyclic olefins to diamines at room temperature using trimethylsilyl azide, a benziodoxole oxidizing reagent, and an iron catalyst with a tridentate ligand (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/a...

Once upon a time, carrying out a deoxyfluorination reaction to replace an alcohol group with fluorine required using brutish reagents such as sulfur tetrafluoride gas or the sulfur fluoride-based l...

In the ongoing quest for developing milder, safer, and more versatile fluorinating reagents, chemists at Massachusetts Institute of Technology have developed the first general strategy for using sulfur hexafluoride in organic synthesis (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201608792). Sulfur hexafluoride, SF6, is a colorless, odorless, inert gas that is widely used as an insulator in electrical equipment such as high-voltage circuit breakers and as a tracer gas to check ventilation systems. But because SF6 has the highest known global warming potential for any compound, these applications are being phased out. The cheap gas could still be used to an advantage in large-scale syntheses in which SF6 is destroyed. MIT’s T. Andrew McTeague and Timothy F. Jamison may have found one option. The team created a process in which an iridium photocatalyst transfers an electron to SF6 to create a reactive radical species. The radical subsequently disintegrates, providing a source

Manus Biosynthesis has announced the development of an engineered bacterium and scalable fermentation process to make commercial quantities of the sought-after zero-calorie natural sweetener rebaudioside M for the first time. Known as Reb M, the molecule is one of a set of steviol glycosides produced by the stevia plant that are popular as noncaloric sweeteners to replace sugar and high-fructose corn syrup in soft drinks and foods. Most commercial stevia products are based on stevioside and rebaudioside A, which are the most abundant steviol glycosides. However, similar to some artificial sweeteners, these compounds have subtle unfavorable bitter and metallic off-tastes that become more pronounced at higher concentrations. Among the steviol glycosides, Reb M has been flagged as having the best overall taste profile and favorable properties for beverage and food processing, according to Manus Biosynthesis founder and chief executive Ajikumar Parayil. Yet its low levels in the stevia plant

Whole grains in bread and other foods can add a healthy dose of vitamins, minerals, protein, and fiber to our diets. But scientists such as Inge S. Fomsgaard of Aarhus University are looking further at how some lesser-known bioactive grain compounds called benzoxazinoids, or BXs for short, can improve health through their immune-boosting properties. Scientists have known for a few decades that BXs help protect young cereal grain plants such as rye, wheat, and corn against weeds, insects, and diseases. But it wasn’t until 2009 that Fomsgaard’s group discovered that mature grains also contain BXs. Fomsgaard and her colleagues subsequently found that BXs survive food processing and that the composition and concentration of the compounds are enhanced via enzymatic processes during malting or baking. Using mass-spectrometry-based metabolomics methods in rats, pigs, and people, the researchers have shown that BXs are taken up, distributed, and metabolized by mammals and that a

In the course of developing new semiconducting materials, a research team including Ram Seshadri and Fred Wudl of the University of California, Santa Barbara, has solved a historical puzzle regarding the structure of the starch-iodine complex (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201601585). Iodine dissolved in potassium iodide solution has long been used as a test for the presence of starch. The helical iodide chain that forms wraps around starch molecules (amylose) to create a complex that produces a deep purple color. Although scientists have speculated that polymeric iodide chains are involved, the exact structure has remained elusive. Chemists have reported other organic polyiodide complexes, but when characterized they have been found to have chain lengths shorter than 10 iodide units and contain molecular iodine (I2) within the chain. The perylene-iodine complex, for example, made up of stacks of the planar polycyclic aromatic hydrocarbon perylene interspersed with iodide strands, was

By fusing ferrocene molecules together, a research team has prepared new iron-based macrocycles that resemble a Ferris wheel. Ferrocene linear chains and macrocycles have been made before, but they contained spacer groups separating the metallocene units, which don’t allow much interaction between the iron atoms. Michael S. Inkpen, Nicholas J. Long, and Tim Albrecht of Imperial College London and their colleagues have now made examples in which five to nine ferrocene units are fused by direct cyclopentadienyl C–C linkages. These redox-active ferrous/ferric nanorings have substantial charge delocalization and are more stable than previous ferrocene-based macromolecules, with the six-membered version representing an organometallic analog of benzene (Nat. Chem. 2016, DOI: 10.1038/nchem.2553). The researchers made the ferrocene rings via copper-mediated Ullmann coupling reactions of dilute solutions of iodinated ferrocene or linear ferrocene oligomers. The internal cavity of the molecules provides opportuniti...

The oxidation state of an atom in a molecule is an important means of electron bookkeeping and determining structure and bonding, so the question of just how high oxidation states can go is a curio...

Phosphine ligands have played a supporting role in the success of many a transition-metal catalyst, helping to tune their activity, selectivity, and stability. Among the examples, tri(tert-butyl)phosphine has long been characterized as the most electron-releasing alkylphosphine ligand for metals. Liye Chen, Peng Ren, and Brad P. Carrow of Princeton University have succeeded in raising the bar with tri(1-adamantyl)phosphine, PAd3, a ligand that now provides a bridge between trialkylphosphines and the stronger electron-releasing N-heterocyclic carbene ligands (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b03215). Adamantane is an unusual rigid C10 tricyclic alkane. Researchers have made phosphine ligands containing two adamantyl groups before, and adamantane is occasionally used as a bulky substituent for N-heterocyclic carbenes. But installing a third bulky adamantyl group on phosphorus has been a challenge, one that researchers took on with complex approaches. Carrow’s group pulled it off with a simple subs...

Palladium is the king of transition-metal catalysts. It earned the title, along with a Nobel Prize, because of its versatility in catalyzing C–H bond activation and cross-coupling reactions of many different types of organic molecules to make pharmaceuticals, agrochemicals, and electronic materials. But no king is infallible. Commercially available palladium acetate, the most popular precursor for preparing active palladium catalysts, often contains several structurally similar impurities. The presence of these impurities is no secret. But the popular belief has been that they don’t significantly impact reaction outcomes. Yet, some researchers have expressed frustration at encountering problems from time to time with the reproducibility, activity, and selectivity of palladium acetate and other palladium catalyst precursors. These problems arise when chemists move from batch to batch of material or when they switch from one supplier to another—situations that could change the amounts of the impurities. Che...

Among synthetic methods available to chemists, cyclotrimerization reactions are an efficient approach to assembling complex cyclic molecules in a single step from three simple building blocks. One ...

In an advance that simplifies gold redox catalysis, a research team led by A. Stephen K. Hashmi of Heidelberg University, in Germany, has discovered a means for carrying out visible-light-mediated reactions without the need for an auxiliary oxidant or a ruthenium or iridium photosensitizer. The additional reagents are typically needed to promote oxidation of gold(I) to gold(III) as part of the catalytic cycle. The Hashmi group determined that a phosphine gold(I) chloride catalyst can function as its own photosensitizer when irradiated with visible light. When paired with an aryldiazonium salt, the gold(I) species is oxidized to a gold(III) species that can complete the difunctionalization of alkynes to make α-aryl ketones (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201511487). What’s more, by using a P,N-bidentate ligand, the researchers were able to isolate and obtain the X-ray crystal structure of the gold(III) species (shown above). Chemists have debated whether gold(III) intermediates are involved