Correction: Acridine-based copper(I) PNP pincer complexes: catalysts for alkyne hydroboration and borylation of aryl halides.

Correction for 'Acridine-based copper(I) PNP pincer complexes: catalysts for alkyne hydroboration and borylation of aryl halides' by Angus Olding et al., Dalton Trans., 2024, 53, 4471-4478, https://doi.org/10.1039/D3DT04269C.

Photochemical Povarov-type Reactions: Electron Donor-Acceptor Photoactivation by Visible Light.

This report investigates the mechanism of photochemical Povarov-type reactions of N,N-dialkylanilines and maleimides in polar solvents (DMF or dioxane) in the presence of light. Fundamental aspects of the electron donor-acceptor (EDA) photoactivation pathway proposed to underpin this chemistry are examined through integrated experimental and computational studies. This approach provided evidence supporting the involvement of an EDA complex in facilitating this chemistry via a reaction mechanism that does not involve a triplet manifold. Most notably, our findings indicate that relying solely on UV-vis absorption spectroscopic data to either account for or predict reactivity in synthetic experiments may not always provide the complete picture. More specifically, this relates to considering UV-vis absorption spectroscopic data, calculated values for association constants (KEDA) and molar extinction coefficients (ε), with the reactivity observed in associated synthetic reactions in practice.

Acridine-based copper(I) PNP pincer complexes: catalysts for alkyne hydroboration and borylation of aryl halides.

PNP pincers represent some of the most well-studied ligand systems in coordination chemistry owing to their high thermal and chemical stability, and the predictable metal coordination geometries of associated metal complexes. Examples of first-row transition metal complexes bearing acridine-based PNP pincer ligands are extremely rare. This study reports the preparation and structural authentication of acridine-based copper(I) PNP complexes, which reveal the profound effects that the steric bulk of methylene-tethered P-substituents has on metal centre coordination number and geometry. The capacity of these systems to mediate copper-catalysed alkyne hydroboration and the borylation of aryl halides is also investigated.

Advancing Gold Redox Catalysis: Mechanistic Insights, Nucleophilicity-Guided Transmetalation, and Predictive Frameworks for the Oxidation of Aryl Gold(I) Complexes.

Gold redox catalysis, often facilitated by hypervalent iodine(III) reagents, offers unique reactivity but its progress is mainly hindered by an incomplete mechanistic understanding. In this study, we investigated the reaction between the gold(I) complexes [(aryl)Au(PR3 )] and the hypervalent iodine(III) reagent PhICl2 , both experimentally and computationally and provided an explanation for the formation of divergent products as the ligands bonded to the gold(I) center change. We tackled this essential question by uncovering an intriguing transmetalation mechanism that takes place between gold(I) and gold(III) complexes. We found that the ease of transmetalation is governed by the nucleophilicity of the gold(I) complex, [(aryl)Au(PR3 )], with greater nucleophilicity leading to a lower activation energy barrier. Remarkably, transmetalation is mainly controlled by a single orbital - the gold dx 2 -y 2 orbital. This orbital also has a profound influence on the reactivity of the oxidative addition step. In this way, the fundamental mechanistic basis of divergent outcomes in reactions of aryl gold(I) complexes with PhICl2 was established and these observations are reconciled from first principles. The theoretical model developed in this study provides a conceptual framework for anticipating the outcomes of reactions involving [(aryl)Au(PR3 )] with PhICl2 , thereby establishing a solid foundation for further advancements in this field.

Distinctive Arbutin-Containing Markers: Chemotaxonomic Significance and Insights into the Evolution of Proteaceae Phytochemistry.

Natural products isolation studies of eight endemic Tasmanian Proteaceae species - Agastachys odorata, Persoonia juniperina, Hakea megadenia, Hakea epiglottis, Orites diversifolius, Orites acicularis, Orites revolutus, and Telopea truncata - and three endemic Australian Proteaceae species Banksia serrata, Banksia praemorsa, and Banksia marginata were undertaken. Two previously unreported glycoside-derived natural products were identified, in addition to four other tremendously rare arbutin esters. The results of this study provide further evidence consistent with the proposal that these distinctive arbutin esters represent markers that can provide valuable insights into the chemical evolution of plant species within the family Proteaceae.

Furanosesquiterpenes and Related Natural Products from Myoporum Species: Isolation and Semisynthesis.

Myoporum species are recognized as toxic plants. Essential oils from the leaves of these species contain furanosesquiterpenes, which comprise the active toxins. In this report, natural products isolation studies of three Myoporum species (M. insulare, M. parvifolium, and M. montanum) afforded two previously unreported furanosesquiterpenes (24 and 25) and three unprecedented γ-lactone-containing analogues (26-28), along with nine previously reported furanosesquiterpenes and five other natural products. Among the 14 furanosesquiterpenes and related compounds isolated in this study, we observed three distinct types of furanosesquiterpene structures isolated from each of these Myoporum species. Semisyntheses of four sesquiterpene natural products were completed from (-)-ngaione over two steps in each case. This included the synthesis of the lactam-containing sesquiterpene myoporumine A.

Structural authentication of intermediates of mechanistic significance in palladium- and nickel-catalysed cross-couplings: case studies.

This article examines a selection of case studies that highlight key strategies that have enabled the structural authentication of important species that shed light on fundamental on-cycle intermediates in palladium- and nickel-catalysed C-C, C-N, and C-O cross-coupling reactions. Particular emphasis is placed on studies in which the structures of rather intractable intermediates have been confirmed unambiguously by X-ray crystallography, while also contextualising the mechanistic insights that these reports have contributed.

Pretransmetalation Intermediates in Suzuki-Miyaura Cross-Couplings: Synthesis of Csp3-, Csp2- and Csp-Organopalladium(II) Boronates.

Organopalladium(II) boronates represent fundamental pretransmetalation intermediates in Suzuki-Miyaura cross-couplings. These species are typically kinetically unstable, making them particularly elusive. In this study, a range of unprecedented, kinetically stable alkyl-, alkenyl-, allenyl-, and alkynylpalladium(II) boronates were prepared from various Csp3, Csp2, and Csp electrophiles via a simple, general method. The structures of these complexes were secured by X-ray crystallography, and the chemical competence of a number of these intermediates in transmetalation was demonstrated.

Rhenium-catalysed reactions in chemical synthesis: selected case studies.

This Perspective presents and discusses a selection of examples that reinforce the enabling and distinctive reactivity provided by homogeneous rhenium catalysis in chemical synthesis. Specifically, the ability for lower oxidation state rhenium-carbonyl catalysts to engage alkyne, allene, and enol substrates in various carbon-carbon bond-forming reactions is highlighted. The inherent capacity of Lewis acidic, higher oxidation state oxorhenium catalysts to facilitate the transposition/isomerisation of allyl alcohols and attendant functionalisation via reaction cascades is also showcased. A brief overview of representative rhenium catalysts that have allowed for reductions of imines, carbonyls, and related compounds is also provided.

Photoactive Metal Carbonyl Complexes Bearing N-Heterocyclic Carbene Ligands: Synthesis, Characterization, and Viability as Photoredox Catalysts.

This report details the synthesis and characterization of a small family of previously unreported, structurally related chromium, molybdenum, tungsten, manganese, and iron complexes bearing N-heterocyclic carbene and carbonyl supporting ligands. These complexes have the general form [ML(CO)3X] or [ML(CO)3], where X = CO or Br and L = 1-phenyl-3-(2-pyridyl)imidazolin-2-ylidene. Where possible, the solid-state, spectroscopic, electrochemical, and photophysical properties of these molecules were studied using a combination of experiment and theory. Photophysical studies reveal that decarbonylation occurs when these complexes are exposed to ultraviolet light, with the CO ligand being replaced with a labile acetonitrile solvent molecule. To obtain insights into the potential utility, scope, and applications of these complexes in visible-light-mediated photoredox catalysis, their capacity to facilitate a range of photoinduced reactions via the reductive or oxidative functionalization of organic molecules was investigated. These chromium, molybdenum, and manganese catalysts efficiently facilitated atom-transfer radical addition processes. In light of their photolability, these types of catalysts may potentially allow for the development of photoinduced reactions involving less conventional inner-sphere electron-transfer pathways.

Cationic Charge-Appended Abnormal Carbenes: Synthesis and Study of Electronically Modified Abnormal N-Heterocyclic Carbenes.

A range of palladium complexes featuring electronically modified, imidazole-based abnormal N-heterocyclic carbene (aNHC) ligands have been prepared in the hopes of accessing a new class of cationic aNHC ligands electronically distinct from normal NHCs and aNHCs. These palladium complexes represent the first examples of transition metal-ligated aNHC complexes featuring a cationic moiety adjacent to the abnormal carbene center. It was anticipated that these design principles could facilitate electron transfer between the imidazolinylidene and the cationic heterocycle, thus reducing the electron density at the abnormal carbene center. However, this case study suggests that greater conformational restrictions that allow for heterocycle coplanarity are necessary to achieve significant electron transfer and enable access to a new class of cationic charge-appended aNHCs with unique electronic properties.

Synthesis of Arylpalladium(II) Boronates: Confirming the Structure and Chemical Competence of Pre-transmetalation Intermediates in the Suzuki-Miyaura Reaction.

Palladium(II) boronates are recognized as fundamental pre-transmetalation intermediates in Suzuki-Miyaura cross-couplings. While these typically transient species have been detected and studied spectroscopically, it is conspicuous that they have never been isolated since this important reaction was discovered over forty years ago. This study reports the synthesis of a family of unprecedented arylpalladium(II) boronates that are, by design, kinetically stable at ambient temperature, both in solution and in the solid state. These properties enabled unambiguous crystallographic confirmation of their structure for the first time and their chemical competence in a Suzuki-Miyaura reaction was demonstrated.

Photochemical Activation of a Hydroxyquinone-Derived Phenyliodonium Ylide by Visible Light: Synthetic and Mechanistic Investigations.

We have identified and extensively investigated the photochemical activation and reaction of a hydroxyquinone-derived phenyliodonium ylide in the presence of visible light using experiment and theory. These studies revealed that in its photoexcited state this iodonium is capable of facilitating a range of single-electron transfer (SET) processes, including hydrogen atom transfer (HAT), a Povarov-type reaction, and atom-transfer radical addition chemistry. Where possible, we have employed density functional theory (DFT) to develop a more complete understanding of these photoinduced synthetic transformations.

Employing Pressurized Hot Water Extraction (PHWE) to Explore Natural Products Chemistry in the Undergraduate Laboratory.

A recently developed pressurized hot water extraction (PHWE) method which utilizes an unmodified household espresso machine to facilitate natural products research has also found applications as an effective teaching tool. Specifically, this technique has been used to introduce second- and third-year undergraduates to aspects of natural products chemistry in the laboratory. In this report, two experiments are presented: the PHWE of eugenol and acetyleugenol from cloves and the PHWE of seselin and (+)-epoxysuberosin from the endemic Australian plant species Correa reflexa. By employing PHWE in these experiments, the crude clove extract, enriched in eugenol and acetyleugenol, was obtained in 4-9% w/w from cloves by second-year undergraduates and seselin and (+)-epoxysuberosin were isolated in yields of up to 1.1% w/w and 0.9% w/w from C. reflexa by third-year students. The former exercise was developed as a replacement for the traditional steam distillation experiment providing an introduction to extraction and separation techniques, while the latter activity featured guided-inquiry teaching methods in an effort to simulate natural products bioprospecting. This primarily derives from the rapid nature of this PHWE technique relative to traditional extraction methods that are often incompatible with the time constraints associated with undergraduate laboratory experiments. This rapid and practical PHWE method can be used to efficiently isolate various classes of organic molecules from a range of plant species. The complementary nature of this technique relative to more traditional methods has also been demonstrated previously.

Selective and adaptable access to N,N'-asymmetrically substituted imidazol-2-ylidene bis-NHC ligands: Pd(II) complexes featuring wide variation in N-alkyl and aryl steric bulk.

N,N'-Asymmetrically substituted, methylene-linked bis(imidazol-2-ylidene) complexes have been prepared subsequent to a selective synthesis of the bis(imidazolium) salt precursors involving the quarternisation of N-alkyl and -aryl imidazoles with N-halomethyl imidazolium salts. The adaptability of the ligand precursor synthesis is illustrated through access to the N-Me/N'-Mes and N-Mes/N'-2,6-(i-Pr)2Ph systems, leading to the Pd(II) complexes [{(MeIm)(MesIm)CH2}Pd(L)2](n+), L = Cl/I (n = 0) and NCMe (n = 2), and [{(MesIm)[2,6-(i-Pr)2PhIm]CH2}Pd(L)2], L = Cl/I. The dicationic hybrid N,N'-alkyl/aryl complex was inactive in the copolymerisation of ethylene/carbon monoxide, displaying reactivity akin to N,N'-dialkyl analogues.