The persistence and continued production of commodity plastics in every sector of society has led to an accumulation of end-of-life material for which traditional disposal techniques are currently deficient in handling. A promising strategy for plastic waste mitigation is closed loop chemical recycling, in which value-added feedstock chemicals can be extracted from the waste. Organometallic catalysis can be leveraged to depolymerize these commodity plastics to platform chemicals with high atom economy, and, in some cases, high specificity to monomers. In this chapter, we review organometallic systems capable of depolymerizing the most common commodity plastics, focusing particularly on their mechanisms of action. This mechanistic overview outlines not only strategies that have proven effective for plastic depolymerization, but also gaps in knowledge that may inform on the development of next-generation methods for the catalytic chemical recycling of these polymers.
Sulfoxonium ylides play a fundamental role in a variety of chemical transformations, facilitating simplified and effective reactions, often with stereoselectivity, in the synthesis of several compounds. Many contributions have described the synthesis of various useful structures from these compounds. In this review, we will address their central importance in various metal-catalyzed reactions, highlighting both successful catalysts and their inherent limitations. Our goal is to provide an in-depth understanding of the diversity of transition metals and ligands used in current research. The main focus is on elucidating the distinctive characteristics of these ylides, especially in the functionalization of C-H bonds, whether followed by subsequent annulation or not. Additionally, we explored X-H insertion reactions, intermolecular processes, and annulations, emphasizing transformations along alternative pathways, including rearrangements and cross-coupling reactions.
Transition metal-promoted or catalyzed cyclization reactions represent one of the most powerful alternatives to design and prepare new fullerene-based materials fused to carbo- and heterocyclic rings of all sizes and incorporating all kinds of functional groups. This chapter comprehensively examines such reactions documented in the scientific literature, from the inception of fullerene chemistry, with a special focus on their mechanistic aspects. We specifically highlight reactions where fullerenes actively engage in the catalytic cycle, forming organometallic complexes with a transition metal catalyst. Furthermore, we delve into cascade reactions, wherein transition metal catalysis facilitates the formation of intermediates that subsequently react with fullerenes.
The metal-ligand cooperation (MLC) strategy, which involves synergistic reactivity between metal and ligand for bond activation and catalysis, has become a significant concept in organometallic and inorganic chemistry. This strategy has greatly advanced the use of base metals as effective homogeneous catalysts for organic synthesis and sustainable transformations. In this context, we provide an overview of recent advancements in the study of half-sandwich complexes of iron, nickel, and cobalt with MLC properties, and emphasize their structural properties and reactivity patterns, particularly with regards to bond cleavage and formation. The mechanistic aspects of catalytic processes associated with these complexes are also outlined.
Complexes with Ni(I) metal centers are of great interest to the synthetic organic community because they have been confirmed as catalytic intermediates in a wide range of chemical transformations. This review describes Ni(I) complexes that are related directly to synthetic organic catalysis. The methods to synthesize and characterize these organotransition metal complexes are described alongside mechanistic studies that implicate them in Ni-catalyzed reactions. The importance of electron paramagnetic resonance (EPR) spectroscopy in studying these species is emphasized throughout this account. This review should enable further development in the field of Ni catalysis.
This chapter compares and analyzes the chemical similarities and differences between nickel and palladium catalysts using the Mizoroki-Heck reaction (henceforth, the M-H reaction) as a case study. The focus is mainly on mechanisms and fundamental studies to better understand the problems and opportunities created when palladium is substituted with its much more abundant and affordable neighbor in the periodic table. The article begins with practical issues (availability of both metals, environmental and health hazards) and fundamental considerations (an extensive discussion of the different chemical behaviors of their compounds). This is followed by a discussion of the development of classic palladium M-H catalysts and a review of the applications of nickel catalysts. The discussion of the classic M-H reaction mechanisms is complemented with a complete survey of the literature relevant to each of the elemental steps that make up the catalytic cycle, comparing the peculiarities of Ni and Pd (precursor activation, oxidative addition, olefin migratory insertion, beta-hydrogen elimination, and base-induced reductive elimination). A general view of the complete M-H cycle is provided by discussing examples of computational modeling of the catalytic cycle. The chapter closes with an overview of the main conclusions and a brief discussion of possible developments in the near future.
The utilization of early-abundant metals in catalysis represents a pivotal step towards sustainable chemistry, providing cost-effective and environmentally benign alternatives to rare and precious metals. On the other hand, N-heterocyclic carbene (NHC) ligands have emerged as indispensable tools in modern organometallic chemistry, offering unparalleled control over reactivity, selectivity, and catalytic efficiency. In this chapter, we cover the recent advances in the catalytic applications of manganese, iron, and cobalt complexes featuring NHC ligands in various chemical processes. These transition metal complexes have garnered significant attention due to their versatile reactivity and catalytic prowess. The discussion encompasses a wide range of catalytic transformations facilitated by these complexes, including but not limited to, hydrogenation, alkylation, CO2 fixation, oxidation, cross-coupling reactions, additions, C-H functionalization, among others. The unique stereoelectronic properties conferred by NHC ligands play a pivotal role in modulating the reactivity and selectivity of these metal complexes, thereby enabling efficient catalysis in diverse chemical transformations. This chapter aims to provide the reader with a comprehensive overview of the utility and significance of such metals in modern synthetic chemistry.
Bimetallic reagents featuring one main-group element and a first-row transition metal centre have been the focus of extensive research due to their numerous applications. In particular, the regioselective activation of C-H bonds using bimetallic complexes has attracted significant attention because of the ubiquitous presence of these bonds in organic compounds, as well as the mild reaction conditions and good atom economy that these complexes offer. However, their reactivity is often not well understood, which has prompted density functional theory (DFT) studies to shed light into the underlying mechanisms. In this chapter, we review some of the challenges associated with the computational modelling of bimetallic C-H metallation processes (and related reactions) which may compromise the conclusions drawn from these studies. Some illustrative examples are provided to highlight, for instance, the often-neglected effects that silent donors and non-innocent solvents can have on chemical speciation and ligand scrambling with bimetallic systems, which intimately determine their chemical reactivity. In addition, we discuss the importance of choosing an appropriate theoretical model when dealing with ion-pair species and outline some computational tools to get further insights into relevant interactions influencing stability, while also examining their potential uses and misuses. Finally, we discuss an approach that combines hybrid solvation models and microkinetic modelling to correctly describe the influence of coordinating solvents on chemical reactivity.
Since its early stages, ligands incorporating P-stereogenic phosphine/aminophosphine donor groups have shown significant potential in metal-catalyzed asymmetric hydrogenation. Despite the initial promise, their synthesis presented challenges that led to a period of reduced attention from the scientific community. However, recent advancements in the development of more straightforward methodologies for introducing chirality to the phosphine moiety have given rise to new P-stereogenic phosphine/aminophosphine-containing ligands for this process. This chapter summarizes the progress made in this field from the end of 2010 to the present.
Organotechnetium chemistry is driven by the search for technetium radio-pharmaceuticals, their appearance in liquid, low-level nuclear waste and, more fundamentally, due to the manifold differences to the organometallic chemistry of the neighboring elements in the periodic table. This chapter provides a synthetically oriented overview over recent advances in organotechnetium chemistry with an emphasis on fundamental reactivity patterns. Nevertheless, also the most important aspects of well-established regimes of organotechnetium chemistry are covered. A technetium complex is the first hexakis(isocyanide) complex of any transition metal containing three different isocyanide ligands. An analog of [Tc-I(CO)(5)](-), containing technetium in a formally negative oxidation state of "-1", has been prepared. The chemistry of technetium with NHCs has been extended to chelating carbene ligands. New synthons for unsaturated technetium-based Lewis-acids have been developed that show a rich ligand exchange chemistry and prove Tc-99 NMR spectroscopy as an invaluable, in situ applicable tool for the synthetic (organo)technetium chemist. Metal ligand cooperativity has been observed for the first time at technetium. Technetium alkynido complexes were unlocked in high and low oxidation states. Functionalized arenes were introduced as ligands. The history of some challenges is outlined and compared with the related chemistry of rhenium. The plethora of new developments and future challenges in different areas of organotechnetium chemistry as compiled in this practical guide to the structural chemistry of technetium-99 may inspire and motivate future organotechnetium chemists to tackle long-standing but still open questions regarding fundamental differences between technetium and the other group 7 elements manganese and rhenium.
