Organic dye-based photoinitiating systems for visible-light-induced photopolymerization

Even though many organic dyes have been reported as photoinitiators/photosensitizers for free radical polymerization in the literature, the design and development of novel photoinitiating systems based on organic dyes adaptable for visible light irradiation, for example, 405 nm LED and sunlight still remains challenging. Recently, major achievements in the development of high-performance photoinitiating systems based on organic dyes as light-harvesting compounds and their uses as photoinitiators for photopolymerization under visible-light irradiation have clearly emerged, giving rise to abundant literature. In this review, an overview of the recently synthesized chromophores belonging to various families of organic dyes and used as photoinitiators of polymerization during the 2018–2021 period are presented and classified. Recent works have resulted in the development of new chromophores exhibiting remarkable visible light absorption properties and excellent photoinitiation abilities upon irradiation with LEDs and/or sunlight in free radical photopolymerization processes. These developments notably indicate that sunlight has the advantages of being a cheap, unlimited, broad emission spectrum, and energy-saving light source capable to be an efficient substitute to artificial light sources. The newly developed dye-based photoinitiating systems designed to initiate visible-light-induced photopolymerization processes are likely to expand the scope of application of photopolymerization in modern sciences and technologies.     

Transition-metal-free coupling reactions involving gem‑diborylalkanes

Due to the increasing demand for the sustainability of modern organic chemistry, the development of green and powerful methods for C-C and C-B bond formation is highly desired. Among them, the transition-metal-free coupling reactions of gem‑diborylalkanes emerge as one valuable tool for organic chemists in the last decade. The review covers selected representative examples. A comparison of these reactions with transition-metal-catalyzed reactions is provided. The recent example of α-boryl radical formation from gem‑diborylalkanes is also briefly discussed.     

Mechanistic Transformations Involving Radical and Cationic Polymerizations

Mechanistic transformation approach has been widely applied in polymer synthesis due to its unique feature combining structurally different polymers prepared by different polymerization mechanisms.Reported methods for the formation of block and graft copolymers through mechanistic transformation involve almost all polymerizations modes.However,certain polymerization processes require extensive purification processes,which can be time-consuming and problematic.Recent developments on controlled/living polymerizations involving radical and cationic mechanisms with the ability to control molecular weight and functionality led to new pathways for mechanistic transformations.In this mini-review,we systematically discussed relevant advances in the field through three main titles namely(i)from radical to cationic mechanism,(ii)from cationic to radical mechanism,and(iii)application of specific catalyst systems for both radical and cationic polymerizations.     

Ultrasound and Sonochemistry for Radical Polymerization: Sound Synthesis

The use of ultrasound as an external stimulus for promoting polymerization reactions has received increasing attention in recent years. In this Review article, the fundamental processes that can lead to either the homolytic cleavage of polymer chains, or the sonolysis of solvent (or other) small molecules, under the application of ultrasound are described. These reactions promote the production of reactive radicals, which can be utilized in chain-growth radical polymerizations under the right conditions. A full historical overview of the development of ultrasound-assisted radical polymerization is provided, with special attention given to the recently described systems that are “controlled” by methods of reversible (radical) deactivation. Perspectives are shared on what challenges still remain in polymer sonochemistry, as well as new areas that are yet to be explored.     

镍催化偶联反应机理研究进展(英文)

近期发展了很多镍催化的偶联反应作为在有机合成中高效构建C–C键的方法,同时开展了很多关于控制镍催化反应活性和选择性的机理研究.这些研究发现,镍催化反应机理往往和相应的钯催化反应机理不同,因为镍催化偶联经常包括自由基和双金属机理.本文总结了镍催化偶联反应机理的最新进展.对于这些反应机理的理解为发展具有更高效率和选择性的镍催化偶联反应提供了帮助.     

Computational study on the 1,2-rearrangement in beta-(nitroxy)vinyl and beta-(acetoxy)vinyl radicals

The 1,2-nitroxyl and 1,2-acetoxyl rearrangement in beta-(nitroxy)vinyl and beta-(acetoxy)vinyl radicals 13a and 13b, respectively, has been studied for the gas phase with various ab initio and density functional methods. The energetically most favorable pathway for 13a is calculated to proceed via reversible fragmentation/radical addition through transition state I-19a. In the case of 13b, rearrangement through a five-membered ring transition state III-16b and the fragmentation/radical addition pathway via transition state I-19b are competing processes. Mulliken and natural population analysis reveal a certain degree of charge separation in III-16a/b that may indicate a potential solvent effect on the rearrangement rate. A stepwise group migration through a cyclic radical intermediate V-18a/b or rearrangement through a three-membered ring transition state II-15a/b can be ruled out for both vinyl radicals. A comparison of the results of the calculations with experimental findings provides important insights into the kinetics of "self-terminating radical oxygenations". A significant method dependence on the outcome of the calculations was observed, which revealed the unsuitability of the UHF, MP2, B3LYP, and mPW1PW91 methods for computing these radical rearrangement processes. The results from BHandHLYP/cc-pVDZ calculations showed the best agreement with single-point energy calculations performed at the QCISD and CCSD(T) levels of theory.     

SULPHUR ORGANIC COMPOUNS AS PROTECTORS FOR RADIATION

Abstract

The development of the scientific principles of the protective action of various compounds and in particular sulphur organic compounds for irradiation is one of the most actual problem in the modern radiation chemistry and radiobiology. With that in view the radiolysis of the various sulphur organic compounds in stationary and pulse conditions both in pure state and in model systems has been studied and the main regularities of their radiolytic behaviour are established. The primary processes of the radiolysis of sulphurorganic compounds containing SHY -S-, NH2, COOH, C H functional groups are investipated and the radical products of the radiolysis- anion- andcation-radicals, thiyl and alkyl radicals are identified and their reactivity is studied in irradiation field.     

Role of quantum chemical calculations in molecular biophysics with a historical perspective

We discuss how the basic principles of quantum chemistry and quantum mechanics can be and have been applied to a variety of problems in molecular biophysics. First, the historical development of quantum concepts in biophysics is discussed. Next, we describe a series of interesting applications of quantum chemical methods for studying biologically active molecules, molecular structures, and some of the important processes which play a role in living organisms. We discuss the application of quantum chemistry to such processes as energy storage and transformation, and the transmission of genetic information. Quantum chemical approaches are essential to comprehend and understand the molecular nature of these processes. To conclude our work, we present a short discussion of the perspectives of quantum chemical methods in modern biophysics, the field of experimental and theoretical chiral vibrational and electronic spectroscopy.     

Growing Utilization of Radical Chemistry in the Synthesis of Pharmaceuticals

Our current unhealthy lifestyle and the exponential surge in the population getting affected by a variety of diseases have made pharmaceuticals or drugs an imperative part of life, making the development of innovative strategies for drug discovery or the introduction of refined, cost-effective and modern technologies for the synthesis of clinically used drugs, a need of the hour. Ever since their discovery, free radicals and radical cations or anions as reactive intermediates have captivated the chemists, resulting in an exceptional utilization of these moieties throughout the field of chemical synthesis, owing to their unprecedented and widespread reactivity. Sticking with the idea of not judging the book by its cover, despite the conventional thought process of radicals being unstable and difficult to control entities, scientists and academicians around the globe have done an appreciable amount of work utilizing both persistent as well as transient radicals for a variety of organic transformations, exemplifying them with the synthesis of significant biologically active pharmaceutical ingredients. This review truly accounts for the organic radical transformations including radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling with metal-complexes and radical cations coupling with nucleophiles, that offers fascinating and unconventional approaches towards the construction of intricate structural frameworks of marketed APIs with high atom- and step-economy; complementing the otherwise employed traditional methods. This tutorial review presents a comprehensive package of diverse methods utilized for radical generation, featuring their reactivity to form critical bonds in pharmaceutical total synthesis or in building key starting materials or intermediates of their synthetic journey, acknowledging their excellence, downsides and underlying mechanisms, which are otherwise poorly highlighted in the literature. Despite great achievements over the past few decades in this area, many challenges and obstacles are yet to be unraveled to shorten the distance between the academics and the industry, which are all discussed in summary and outlook.     

Catalysis with Palladium Complexes Photoexcited by Visible Light

Palladium catalysis induced by visible light is an emerging field of catalysis. In contrast to classical reactions catalyzed by Pd complexes in the ground state, which mostly proceed through two‐electron redox processes, the mechanisms of these new methods based on photoexcited Pd complexes usually operate through transfer of a single electron. Such processes lead to putative hybrid Pd/radical species, which exhibit both radical and classical Pd‐type reactivity. This Minireview highlights the recent progress in this rapidly growing area.     

Metal‐Catalyzed β‐Functionalization of Michael Acceptors through Reductive Radical Addition Reactions

Transition‐metal‐catalyzed radical reactions are becoming increasingly important in modern organic chemistry. They offer fascinating and unconventional ways for connecting molecular fragments that are often complementary to traditional methods. In particular, reductive radical additions to α,β‐unsaturated compounds have recently gained substantial attention as a result of their broad applicability in organic synthesis. This Minireview critically discusses the recent landmark achievements in this field in context with earlier reports that laid the foundation for today′s developments.     

Synthesis and characterisation of BODIPY radical anions

The redox processes associated with BODIPY analogues are studied by electrochemical and spectroscopic methods revealing a characteristic profile for the persistent BODIPY radical and quenching of fluorescence upon reduction.     

Relationship between one-electron transition-metal reactivity and radical polymerization processes

Controlled radical polymerization has come along in leaps and bounds following the development of efficient transition-metal catalysts for atom-transfer radical polymerization. Another type of controlled radical polymerization process, namely organometallic radical polymerization, uses the reversible formation of metal-carbon bonds. Metals are also implicated in catalytic chain transfer, a process that involves the abstraction of hydrogen atoms. This Minireview discusses the importance of one-electron transition-metal reactivity in metal-mediated controlled radical polymerization processes.     

Electron transfer reactions relevant to atom transfer radical polymerization

The continuous development of more active and stable catalysts in atom transfer radical polymerization (ATRP) has increasingly required a thorough knowledge of concurrent electron transfer reactions that can affect catalyst performance. Special attention is provided in this short review to such processes, including disproportionation, most pronounced in Cu-mediated ATRP, the reduction of radicals to carbanions or oxidation to carbocations, and radical coordination to the metal catalyst resulting in the interplay of controlled radical polymerization mechanisms.     

High-spin radical cations of alternating poly(m-p-anilines)

Three alternating poly(m-p-anilines) have been synthesized via palladium-catalyzed amination reactions. Polymers were oxidized to radical cations by the use of chemical and electrochemical methods. The presence of radical cations was manifested by the appearance of two new bands in UV-vis spectra and a strong EPR signal. Moreover, EPR spectra at low temperatures confirmed the formation of a high-spin state. The magnetization measurements of polymers oxidized to radical cations revealed the paramagnetic-type behavior with weak antiferromagnetic interactions. Radical cations underwent the degradation processes in the presence of air, which led to the decrease of spin concentration.     

Photochemistry of 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate: an experimental and computational investigation

The aqueous photochemistry of the sodium salt of 1-(N,N-diethylamino)-diazen-1-ium-1,2-diolate (3) has been investigated by both experimental and computational methods. Photolysis results in the formation of the N-nitrosodiethylamine radical anion (5) and nitric oxide (NO) via a triplet excited state. The nitrosamine radical anion either undergoes electron transfer with NO before cage escape to form triplet NO(-) and nitrosamine (minor process) or rapidly dissociates to form an additional molecule of NO and ultimately amine (major process). The production of nitrosamine radical anion 5 upon photolysis of diazeniumdiolate 3 is confirmed by low-temperature EPR spectroscopy. The calculated energetics for the ground and excited states of the parent diazeniumdiolate ion at the CIS and B3LYP levels of theory as well as B3LYP calculations on the fragmentation processes were very effective in rationalizing the observed photodissociation processes.     

SULPHUR ORGANIC COMPOUNDS AS PROTECTORS FOR RADIATION

Abstract

The development of the scientific principles of the protective action of various compounds and in particular, sulphur-organic compounds for irradiation is one of the most actual problems in the modern radiation chemistry and radiobiology. With that end in view the radiolysis of the various sulphur organic compounds in stationary and pulse conditions both in pure state and in model systems has been studied and the main regularities of their radiolytic behaviour are established. The primary processes of the radiolysis of sulphurorganic compounds containing SH, -S-, NH₂, COOH, C₆H₅ functional groups are investigated and the radical products of the radiolysis - anion - and cation - radicals, thiyl and alkyl radicals are identified and their reactivity is studied in irradiation field.     

New approaches in radical carbonylation chemistry: fluorous applications and designed tandem processes by species-hybridization with anions and transition metal species

New approaches in radical carbonylation chemistry are described. We have successfully integrated tin mediated radical carbonylation chemistry into modern fluorous applications and separation techniques. We revealed that radical carbonylation reactions can be performed using fluorous tin mediators, such as fluorous tin hydride and fluorous allyltin reagents. Fine tuning of the reaction conditions resulted in a good efficiency equivalent to conventional tin mediators. The tedious procedure of removing organotin byproducts can be circumvented through the use of fluorous/organic liquid-liquid extraction or fluorous liquid-solid phase extraction with fluorous reverse phase silica (FRPS). Also described are newly developed tandem carbonylation reactions that are based on species hybridization approaches. Using a radical/anionic hybrid system based on zinc-induced one-electron reduction, we achieved a three-component coupling reaction consisting of 4-alkenyl iodides, carbon monoxide, and electron-deficient alkenes. We observed two types of annulations processes, namely [4 + 1](radical)/[3 + 2](anionic) and [5 + 1](radical)/[3 + 2](anionic), which lead to the production of bicyclo[3.3.0]octanols and bicyclo[3.2.1]octanols, respectively. We found a radical/palladium hybrid system to be useful in the construction of new cyclic systems that incorporate two or three molecules of carbon monoxide.     

Strongly correlated mechanisms of a photoexcited radical reaction from the anti-Hermitian contracted Schrödinger equation

Photoexcited radical reactions are critical to processes in both nature and materials, and yet they can be challenging for electronic structure methods due to the presence of strong electron correlation. Reduced-density-matrix (RDM) methods, based on solving the anti-Hermitian contracted Schro?dinger equation (ACSE) for the two-electron RDM (2-RDM), are examined for studying the strongly correlated mechanisms of these reactions with application to the electrocyclic interconversion of allyl and cyclopropyl radicals. We combine recent extensions of the ACSE to excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)] and arbitrary spin states [A. E. Rothman, J. J. Foley IV, and D. A. Mazziotti, Phys. Rev. A 80, 052508 (2009)]. The ACSE predicts that the ground-state ring closure of the allyl radical has a high 52.5 kcal/mol activation energy that is consistent with experimental data, while the closure of an excited allyl radical can occur by disrotatory and conrotatory pathways whose transition states are essentially barrierless. Comparisons are made with multireference second- and third-order perturbation theories and multireference configuration interaction. While predicted energy differences do not vary greatly between methods, the ACSE appears to improve these differences when they involve a strongly and a weakly correlated radical by capturing a greater share of single-reference correlation that increases the stability of the weakly correlated radicals. For example, the ACSE predicts a -39.6 kcal/mol conversion of the excited allyl radical to the ground-state cyclopropyl radical in comparison to the -32.6 to -37.3 kcal/mol conversions predicted by multireference methods. In addition, the ACSE reduces the computational scaling with the number of strongly correlated orbitals from exponential (traditional multireference methods) to quadratic. Computed ground- and excited-state 2-RDMs are nearly N-representable.