Abstract Over the past decade, visible light activation has transformed palladium catalysis by enabling reactivity patterns that are inaccessible under purely thermal conditions. Whereas early photocatalytic strategies relied on discrete photosensitizers or dual photoredox manifolds, a distinct paradigm has emerged in which palladium itself serves as both the light‐absorbing species and the catalytic center. Photoexcitation of palladium complexes directly perturbs the conventional two‐electron organometallic pathways, diverting them into single‐electron manifolds, thus giving rise to hybrid Pd‐radical intermediates. More specifically, phosphine‐ligated Pd(0) complexes exemplify this behavior, enabling mild generation of aryl and alkyl radicals and unlocking diverse transformations, including desaturation reactions, alkyl‐Heck‐type processes, multicomponent alkene functionalizations, and asymmetric CH amination. More recent studies have further revealed excitation‐enabled modulation of PdH reactivity, establishing hydricity regimes distinct from the ground‐state behavior and allowing access to electron‐deficient alkenes and unconventional radical precursors. This chapter surveys the evolution of visible light‐induced palladium catalysis, emphasizing reaction classes and mechanistic principles that define this rapidly advancing field.
Abstract Palladium, a platinum‐group metal, has emerged as a material of growing biomedical and environmental relevance, driven by its extensive industrial use, increasing environmental dissemination and expanding application in medicine. Its biological and toxicological behavior is determined by dynamic speciation occurring in biological and environmental media. Palladium exists as ions, complexes, nanoparticles, or metallic alloys, each exhibiting distinct reactivity, bioavailability, and toxicodynamic properties. In biological systems, ligand exchange, dissolution, aggregation, protein corona formation, and redox transformations significantly influence its behavior, enabling both ion release and catalytic surface reactivity. Ionic and nanoparticulate forms show pronounced cytotoxicity, oxidative stress induction, immunomodulation, and organ toxicity, while certain organometallic complexes and nanostructures demonstrate selective anticancer and antimicrobial activity with reduced systemic toxicity. Environmental studies indicate that palladium can undergo bioaccumulation, trophic transfer, and speciation‐dependent ecological toxicity. This review critically analyzes the chemical forms, biological transformations, and mechanistic pathways underlying palladium's toxicity and therapeutic potential. It emphasizes the need for speciation‐aware assessment strategies, green synthesis, and rational ligand design to harness palladium's biomedical promise while minimizing environmental and biological risks.
Abstract As a unique type of electron‐rich alkyne, ynamides have been developed as important building blocks in organic synthesis. More importantly, the catalytic enantioselective transformation of ynamides can provide diverse valuable enantioenriched N ‐containing molecules in a step‐economic manner. Therefore, the development of an effective enantiocontrol strategy is crucial for the enantioselective reaction of ynamides. This article summarizes the recent advances in chiral copper‐catalyzed cyclization of N ‐propargyl ynamides through vinyl cation intermediates, for the efficient synthesis of valuable chiral N ‐heterocycles via remote control of enantioselectivity. The effective enantiocontrol of vinyl cations enabled a variety of enantioselective reactions, including intramolecular CH functionalization, cyclopropanation, [1,2]‐Stevens‐type rearrangement, one‐carbon ring expansion, dearomatization reaction, intermolecular annulations with styrenes and ketones, and different types of atroposelective cyclizations. This article highlights the advancements in the chiral copper‐catalyzed cyclization of N ‐propargyl ynamides since 2019, which have been developed as a general approach for the generation and enantioselective transformation of vinyl cations. These studies are expected to inspire new strategies for the asymmetric transformations of ynamides, as well as new insights into the enantioselective functionalization of vinyl cations and other related reactive intermediates.
In the current chapter, we discuss the thermochemistry of compounds with CF bonds. In the name of brevity, we limit our attention to the understanding of the enthalpies of formation of aliphatic fluorocarbons and hydrofluorocarbons. Discussions of alkanes, alkenes, and alkynes alike compose our study—there is scant mention of any species with a ring, or with unpaired electrons or a charge, or the presence of any other element other than carbon, fluorine, and usually hydrogen. Results from diverse calorimetric measurements and high‐level quantum chemical calculations are inseparably intermingled. How could it be otherwise when there are no classical calorimetric measurements reported for the determination of the enthalpy of formation of methyl fluoride, plausibly, the simplest organofluorine compound, nor any such study of the likewise simple ethyl fluoride? The chapter closes with the chemistry of perfluoro‐2‐butyne and thus unavoidably discusses trimeric derivative of alkynes, substituted benzenes. A plausible sequel to the current study, a possible new chapter entitled “The energetics of organofluorine compounds: Aromatic fluorocarbons and hydrofluorocarbons,” is casually pondered upon.
Organocobalt compounds are crucial in biology as cobalamin is termed nature ' s organometallic catalyst . Non‐corrin cobalt‐containing metalloenzymes are also present in biological systems. Numerous organocobalt compounds supported by versatile ligand platforms have been synthesized over the past decades. Ligands such as cyclopentadienyl anion, N ‐heterocyclic carbenes, and pincer ligands are major contributors to this vast array of organocobalt compounds. The diverse ligand frameworks make the structures of organocobalt compounds unique, and their geometries play important roles in directing their reactivity. The structures of the organocobalt clusters and the encapsulated compounds affect their catalytic and magnetic behavior. This chapter provides a focused overview of the structural aspects of the various organocobalt compounds.
Since the first report in 2003 of a [2 + 2 + 1] cycloaddition between enynes and carbon monoxide catalyzed by a well‐defined cobalt complex containing an NHC ligand, homogeneous catalysis using cobalt complexes in combination with NHCs as ancillary ligands has witnessed an ever‐growing interest which has been translated into various significant advances, mainly during the past decade. In this chapter, the different methodologies giving rise to well‐defined Co(NHC) complexes are surveyed. The major chemical transformations using either well‐defined Co(NHC) complexes or in situ generated catalytic systems are detailed, highlighting the role of the NHC ligand. In addition to cycloadditions, this includes hydrogenation and hydroelementation of alkenes and alkynes, cross‐couplings, CH activation/functionalization reactions, and other reactions.
Carbonylative transformations for the incorporation of a “C1 unit” in an organic molecule using readily available carbon monoxide gas or other surrogates has witnessed decades of progress under transition metal catalysis. With the necessity for energy‐efficient, economic and environmentally friendly techniques, the scientific research community has been working towards achieving this goal in varied chemical transformations. First‐row transition‐metal‐catalyzed carbonylation not only does serve the purpose but also opens gateway to new reactivity due to its ability to participate in both one‐ and two‐electron transfer reactions. In this chapter, we discuss and summarize the development of cobalt‐catalyzed carbonylative transformations providing an insight into the diverse applications that has been achieved in this field so far.
In this chapter, diverse aspects of the energetics of species with cobalt–carbon bonds are presented. Bond energies, enthalpies of formation and reaction, ionization and appearance potentials, and proton and electron affinities are discussed. Classical calorimetry plays only a minor role compared to reaction calorimetry and techniques from contemporary ion energetics. While carbonyl and cyclopentadienyl derivatives dominate the text, other species such as binary cobalt carbides and their ions are also explored. Whenever possible, quantification is given.
The development of highly efficient catalysts for alkene hydrogenation has continuously received great attention, both from academia and industry. Cobalt‐based homogeneous catalysts have emerged as attractive alternatives to “traditional” precious‐metal catalysts in alkene hydrogenation, owing to the unique properties and outstanding catalytic performance in addition to the benefits of low cost and environmentally benign nature. In this chapter, the advances in cobalt‐catalyzed homogeneous alkene hydrogenation are summarized to provide a comprehensive overview of the development of cobalt catalysts, their catalytic behavior, and the reaction mechanisms.
Abstract Nitrogen enrichment has played a pivotal role in the discovery of several key bioactive compounds, targeting several disease states. Nucleosides containing NN bonds have been at the forefront of these discoveries. In this chapter, the medicinal properties of NN enriched‐nucleosides such as triazoles, pyrazole, tetrazole, pyridazine, and triazines possessing a variety of substitutions will be discussed. Additionally, the chemistry driving the discovery of these important bioactive compounds will also be addressed. It is without a doubt that NN‐enriched nucleosides are at the forefront in understanding and developing pertinent bioactive probes/compounds. This will in part allow for the development of several more innovative bioactive NN‐enriched nucleoside analogs to increase the development of more medicinally relevant compounds.
Abstract The incorporation of explosophoric functional groups containing fluorine has been found to enhance the overall energetic characteristics of heterocycles. Fluorine‐containing compounds have been extensively investigated as potential high‐energy materials. Compared to nitrogen‐rich heterocycles lacking fluorine, those containing fluorine exhibit superior properties owing to their higher density and enhanced stability. By combining heterocycles with explosophoric functional groups that contain fluorine, numerous advanced high energy density materials (HEDMs) have been synthesized. This review is an overview of recent progress in the design of fluorine‐containing energetic compounds, encompassing data on their synthesis methods, physical attributes, and detonation properties wherever possible. Owing to their synthetic potential and exceptional properties, fluorine‐containing energetic materials hold great potential for the development of highly energetic materials for both civilian and military applications.
Abstract Peptoid‐based macrocycles represent precious tools in biomimetic and supramolecular chemistry for their innate propensity to recognize biopolymers, molecules, and ion guests, and also for their impressive ability to adopt stable secondary structures and display remarkable chemical diversity. The ample variety of N ‐substituted glycine available, the subtle host/guest interplay, and the efficient head‐to‐tail macrocyclization reactions greatly expand their potentials and functional capabilities. In this chapter, we report studies correlating sequence, structures, and functions of α‐/β‐cyclic peptoids reported in the chemical literature till 2021 and describe how crucial intramolecular interactions, cationic hosts, and strategically positioned stereogenic centers forge their morphologic attributes. The advances in the field of cyclic peptoids represent the first steps for the foundations of a rational design of protein mimetics and a possible model on which to base drug design and supramolecular/biomimetic chemistry.
Abstract Undoubtedly, N–N enriched molecules have been prevalent in the exploration of DNA and RNA structure and function. This prevalence has been expedited by the continued development of Huisgen [3 + 2] cycloaddition, or “click chemistry.” Click chemistry has enabled the syntheses of several varieties of N–N enriched oligonucleotides having a myriad of functionalities from gene silencing, molecular imaging to the understanding DNA polymerase activity. In this chapter, the inclusion of N–N enriched nucleobases and their impact on several scientific fields will be discussed. Emphasis will be placed on oligonucleotides having triazole, pyrazole, pyridazine, and pyrazine nucleobase modifications.
Abstract Hydroporphyrins are the synthetic or semisynthetic analogs of photosynthetic pigments. They retained the essential photophysical properties of their natural counterparts and therefore are valuable chromophores for numerous applications. Synthetic multichromophoric arrays containing hydroporphyrins have been utilized as models to mimic and study photophysical processes in natural photosynthesis, photosensitizers for photodynamic therapy, fluorophores for sensing and imaging, as well as components for solar energy conversion. In this chapter, structure, synthesis, and properties of arrays containing at least two tetrapyrrolic subunits, among which at least one is a hydroporphyrin, are presented. Their photophysical properties and applications are also briefly discussed.
Abstract The substitution of the aromatic core of 1,8‐naphthalene imides ( NIs ) with amines and other nitrogen‐rich species significantly alters their electronic properties. The class of compounds, herein called 4‐amino‐1,8‐naphthalene imides ( ANIs ), have found numerous applications as fluorescent sensors of polarity, anions, cations, and nucleic acids. In addition, the unique photoredox properties of blue‐light absorbing ANIs create a versatile set of initiators for photopolymerization and photoinduced protein or tissue cross‐linking. This chapter reviews both the synthetic strategies and photophysical properties of ANIs in the context of the inductive and steric properties of the 4‐amino substituent that govern the production and deactivation of the intramolecular charge‐transfer ( ICT ) state. The effects of mono‐ versus di‐alkylation on the 4‐amino nitrogen on both the solvent‐dependent photophysics and redox properties are also discussed. Though there is a large body of literature on the use of ANIs as fluorescent sensors, the implications of tuning the structure and environment of ANIs for specific photochemical outcomes, including photoredox‐initiated reactions, remain largely unexplored. Future opportunities to expand the scope of ANI photochemistry beyond sensor applications are discussed in this chapter.
Abstract Experimental heats of formation and NN bond dissociation enthalpies of nitramines and nitrosamines, in both condensed and gaseous phases, are compiled and analyzed for structural trends. These are bolstered by thermochemistry from high‐level computational methods.
Abstract This chapter provides an overview of the computed results of selected polynitrogen compounds. Compounds2 that will be discussed include organic azides, triazoles, triazines, diazonium ions, azo compounds, zinc–azide complexes, and porphyrins. Various theoretical studies involving these compounds focused on reactions such as cycloaddition reactions, rearrangements, structural analysis, and spectroscopic properties.
Abstract This chapter describes the analytical chemistry of nitrogen‐rich species, primarily azides, triazenes, hydroxytriazenes, 1,2,3‐triazoles, 1,2,4‐triazoles, tetrazoles, and formazans. Since there is a large variety of these species which have diverse chemical manifestations, our discussion is limited to elements (and species) from hydrogen to phosphorus leaving other elements (and species) for further discussion.
Abstract Bioimaging is an essential tool for investigating biological processes and detecting disease biomarkers improving both diagnosis and therapy monitoring. 19 F‐Magnetic resonance imaging ( 19 F‐MRI) has recently emerged as a powerful imaging technique with high translational potential to clinic enabling direct in vivo quantification without use of ionizing radiations. In fact, the lack of organic fluorine in living systems allows unambiguous quantitative detection of exogenous fluorinated probes as colored “hot spots” on the anatomical images obtained by conventional 1 H‐MRI protocols. If anatomical resolution is a strength, low sensitivity is a drawback of 19 F‐MRI, which requires the use of highly fluorinated contrast agents (CAs). Fluorinated CAs are twofold biorthogonal due to their innate chemical and biological inertness, linked to strong CF bonds, and to the total absence of endogenous organic fluorine. In this chapter, the main classes of 19 F‐MRI CAs, which are highly fluorinated molecules formulated with biocompatible emulsifiers, partially fluorinated amphiphilic polymers, and fluorinated inorganic nanoparticles, will be described highlighting how their chemical design is critical to achieve an effective 19 F‐MRI response. Moreover, for each class of compounds representative examples of the most important biomedical applications will be illustrated addressing the main challenges for their translation to clinic and possible future perspectives in different still unexplored fields.
Abstract This chapter presents the landmark contributions and the main advances made in the last 20 years for the synthesis of aryl and heteroaryl fluorides. The installation of a single fluorine atom into a (hetero)aromatic scaffold can be achieved via two approaches, either the fluorination of a pre‐functionalized substrate or direct C(sp 2 )H fluorination, a classification adopted in this chapter. The first section presents at first the traditional fluorination routes from diazonium salts (Balz–Schiemann reaction), triazenes (Wallach reaction), and electron‐poor arenes (via nucleophilic aromatic substitution). This is followed by fluorination reactions from suitable pre‐functionalized precursors (halides, triflates, iodonium salts, stannanes, silanes, boronic acid, organo‐magnesium, and ‐lithium derivatives), deoxyfluorinating methodologies (from phenols), and contemporary transition metal catalysis protocols. Recent advances in decarboxylative fluorination of benzoic acids via photoredox catalysis and the fluorination of aryl thianthrenium salts are also discussed. The second section presents the most recent advances in C(sp 2 )H fluorinations using either electrophilic fluorine (F + ) sources or nucleophilic fluoride (F − ) in the presence of an oxidant.
