Abstract Alkynes are fundamental functional groups in organic chemistry, and the connection of multiple alkyne units through carbon–carbon single bonds gives rise to polyynes. After briefly describing the historical development of polyynes, this chapter focuses on the major synthetic strategies employed for the construction of homologous series of polyynes that offer the longest reported derivatives. Classical synthetic methods include oxidative homo‐ and heterocoupling reactions, which are most commonly catalyzed by copper and/or palladium complexes. Beyond conventional coupling approaches, the use of masked alkyne equivalents is a useful strategy to circumvent the instability of terminal polyynes and facilitate the synthesis of extended carbon chains. More recently, alkyne metathesis has been developed as an alternative method for the construction of polyyne architectures. Beyond synthesis, this chapter provides an overview of the key properties of polyynes. Beginning with fundamental structural features, it then summarizes recent progress in spectroscopic studies of homologous polyyne series as a function of molecular length, highlighting the gradual convergence of their properties toward the infinite chain limit of carbyne. Finally, the molecular conductance of polyynes is discussed in the context of archetypal molecular wires, together with recent studies on polyyne aggregation behavior.
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.
