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Reactions that form C–C bonds are at the heart of many important transformations, both in industry and in academia. From the myriad of catalytic approaches to achieve such transformations, those relying on C–H functionalization are gaining increasing interest due to their inherent sustainable nature. In this short review, we showcase the most recent advances in the field of C–C bond formation via C–H functionalization, but focusing only on those methodologies relying on copper catalysts. This coinage metal has gained increased popularity in recent years, not only because it is cheaper and more abundant than precious metals, but also thanks to its rich and versatile chemistry.1 Introduction2 Cross-Dehydrogenative Coupling under Thermal Conditions2.1 C(sp3)–C(sp3) Bond Formation2.2 C(sp3)–C(sp2) Bond Formation2.3 C(sp2)–C(sp2) Bond Formation2.4 C(sp3)–C(sp) Bond Formation3 Cross-Dehydrogenative Coupling under Photochemical Conditions3.1 C(sp3)–C(sp3) Bond Formation3.2 C(sp3)–C(sp2) and C(sp3)–C(sp) Bond Formation4 Conclusion and Perspective

Furanic di-carboxylate derivatives of 5-Hydroxymethylfurfural (HMF) are nowadays important in the polymer industry as they are used as building blocks for bio-based polyesters. The high reactivity of HMF compels to avoid harsh synthetic conditions. Therefore, developing mild catalytic processes for its selective oxidation is a challenging task. Herein, we report the first oxidative esterification of HMF to dimethyl furan-2,5-dicarboxylate (FDCM) under flow conditions using oxygen as oxidant. For that purpose, a new series of nitrogen-doped carbon-supported bimetallic Co/Ru heterogeneous catalysts were prepared and characterized by XRD, XPS and N2 physisorption. These analyses revealed that the porosity of the materials and order of impregnation of the metals to the carbon supports lead to varying catalytic activities. Under optimized conditions the flow reactor showed a 15-fold increase on the production of FDCM compared to batch conditions. �� 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

A series of hybrid porous polymers (HPPs) based on polyhedral oligomeric silsesquioxane (POSS) were synthesized, characterized, and successfully used as metal-free heterogeneous photocatalysts for cross-dehydrogenative coupling reactions (CDC), for which the aza-Henry coupling of tetrahydroisoquinolines and nitroalkanes was studied as the model reaction. The reactions run smoothly at room temperature under visible (blue) light irradiation using gaseous oxygen as an oxidant under atmospheric pressure. These novel metal-free heterogeneous photocatalysts can be readily recovered and reused without a significant loss of reactivity. Mechanistic investigations revealed the intermediacy of 1O2, obtained from 3O2 sensitization (energy transfer) by the photoexcited catalyst.

Catalytic allylation reactions are important methodologies to introduce the versatile allyl functionality into molecules to produce fine chemicals and synthetic building blocks. Since the first reports by Tsuji and Trost, many improvements on allylation technologies have been reported. The introduction of photocatalytic techniques marked one of the major breakthroughs in this field, complementing the existing thermal chemo-catalyzed protocols, providing high selectivity under milder conditions. This review discloses state-of-the-art photocatalyzed allylation methodologies, their reaction mechanisms, and synthetic applications. The reactions are classified according to the employed catalysts, namely single photocatalyst and dual-catalytic approaches. Finally, each methodology is individually presented and evaluated based on the performance of the reaction.

Silicones and silicone rubbers are ubiquitous in our daily lives, being used in a broad range of applications ranging from consumer products and adhesives to medicinal and electronic devices. The chemistry and synthesis of these versatile materials have been reviewed so many times that it is difficult to have a comprehensive overview. Hence, with this tutorial review we aim to provide a concise account of the most important reactions and industrial processes to furnish silicones, focusing specially on reactive silicones, specifically in telechelic OH-terminated polysiloxanes, which represent one of the most relevant members of this important materials family.

C.Li thanks the Prof. & Mrs Purdie Bequests Scholarship and AstraZeneca PhD Studentship. A family of six structurally related heteroleptic copper(I) complexes of the form of [Cu(N^N)(P^P)]+ bearing a 2,9-dimethyl-1,10-phenanthroline diimine (N^N) ligand and a series of electronically tunable xantphos (P^P) ligands have been synthesized and their optoelectronic properties characterized. The reactivity of these complexes in the copper-photocatalyzed Aza-Henry reaction of N-Phenyltetrahydroisoquinoline was evaluated, while the related excited state kinetics were comprehensively studied. By subtlety changing the electron-donating properties of the P^P ligands with neglegible structural differences, we could tailor the photoredox properties and relate it to their reactivity. Moreover, depending on the exited-state redox potential of the catalysts, the preferred mechanism can shift between reductive quenching, energy transfer and oxidative quenching pathways. A combined study of structural modulation of copper(I) photocatalysts, optoelectronic properties and photocatalytic reactivity resulted in a clearer understanding of both the rational design of the photocatalyst and the complexity of competing photoinduced electron and energy transfer mechanisms. Publisher PDF

An efficient, novel photocatalyzed allylic-alkynylation methodology via copper-based cross-dehydrogenative coupling (CDC) is described. Different types of 1,4-enyne compounds were synthesized in one step at room temperature using copper(I) terpyridyl complex as photocatalyst/initiator. This procedure is an improvement and to some extent complementary to previously reported thermal CDC methods. Preliminary investigations on the reaction mechanism are also presented.

Herein we re-evaluate the synthesis of Poly(e-caprolactone) (PCL) by ring-opening polymerization (ROP) using simple dialkylmagnesium compounds as catalysts. This old reaction has been never studied thoroughly before and a consensus on the intervening mechanism is lacking, being an anionic pathway proposed in the classic literature. In our hands, all tested catalysts exhibit high efficiency and complete conversion was achieved within a few hours with high yield and high number-average molecular weight (Mn) in a living fashion. Moreover, kinetic studies revealed that the ROP of e-CL has a first order dependency on monomer (e-CL) as well as catalyst concentration. Furthermore, mechanistic studies of the ROP demonstrated that the reaction follows a coordination-insertion mechanism where the alkyl group initiates the polymerization and is incorporated as one of the terminal groups in the polymer chain.

The development of strategies for the sustainable management and valorization of agricultural waste is of outmost importance. With this in mind, we report the use of rice husk (RH) as feedstock for the preparation of heterogeneous catalysts for hydrogenation reactions. The catalysts were prepared by impregnating the milled RH with a silver nitrate solution followed by carbothermal reduction. The composition and morphology of the prepared catalysts were fully assessed by IR, AAS, ICP-MS, XPS, XRD and STEM techniques. This novel bio-genic silver-based catalysts showed excellent activity and remarkable selectivity in the hydrogenation of nitro groups in both aromatic and aliphatic substrates, even in the presence of reactive functionalities like halogens, carbonyls, borate esters or nitriles. Recycling experiments showed that the catalysts can be easily recovered and reused multiple times without significant drop in performance and without requiring re-activation. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH

Herein we report the synthesis of isotactically enriched poly(cyclohexene carbonate) (PCHC) by the bulk alternating copolymerization of meso-cyclohexene oxide and carbon dioxide using dialkylmagnesium compounds as catalyst. These simple achiral catalysts showed good activity for the isoselective copolymerization, with high yield and high carbonate-linkage contents, in a controlled manner under mild conditions and atmospheric CO2 pressure. The triad sequences in the 13C NMR spectra of these polymers were assigned using Bernoullian statistical methods in order to determine the tacticity of the copolymer. Differential scanning calorimetry analysis confirmed the formation of highly isotactic polycarbonate. Furthermore, kinetic studies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry investigations allowed us to shed light on the reaction mechanism of the polymerization process.

Hypervalent iodine (III) five-membered heterocycles have found broad application as atom-transfer reagents for organic synthesis. Among them, 1-Phenyl-1,2-benziodoxol-3-(1H)-one is known as a traditional benzyne precursor, but no further synthetic applications have been reported. Herein, we report the first synthetic application of 1-phenylbenzidoxole to the synthesis of Phthalides using only CuI as catalyst. High selectivity and yield were achieved under mild reaction conditions with good functional group tolerance. During our investigations, the efficiency of different CuI and CuII catalysts under various reaction conditions were studied. The nature of the leaving group, the substituents on the substrate and temperature, play an important role on both yield and selectivity. Moreover, a plausible mechanistic pathway for this transformation was proposed based on our observations and previous literature reports.

An efficient and green synthetic method for the preparation of N,N-disubstituted tetramethylpyrazinium radical cations was developed, which does not require any solvent or strong alkylating agents. The investigation by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy proved the stability of the prepared radical cation. Moreover, it was shown for the first time that the prepared N,N-disubstituted tetramethylpyrazine can act as a powerful metal-free catalyst for the selective oxidative homocoupling of amines to the corresponding imines under solvent-free conditions. Furthermore, oxygen or even air can be employed as an efficient oxidative reagent.

This Focus Review describes state-of-the-art methods for the preparation of antimicrobial silicones. Given the diversity of antimicrobial activity and their mechanisms, the performance of these materials is highly dependent on the characteristics of the polymeric matrix. Therefore, different synthetic routes have been developed, such as 1) physical treatments, 2) chemical transformations, and 3) copolymerization. This classification is not exclusive, so some products belong to more than one class. Herein, we attempt to present a handy overview of the development of antimicrobial silicones, their most important application fields, the most relevant antimicrobial assays, and, as the title suggests, an overview of the most relevant preparation methods.

5-Hydroxymethylfurfural (HMF) has become a benchmark chemical as it can be obtained by the processing of renewable biomass, making its downstream modification an important topic both in industry an...

Due to the richness of the field of cross-dehydrogenative coupling reactions and the plethora of applications toward the synthesis and derivatization of heterocyclic molecules, there is an increasing amount of synthetic methodologies which spread across different catalytic fields and hence, yield to a huge variety of operating mechanisms. Although all the pathways follow the same underlying principles, they can be easily differentiated according to the type of activation (thermal of photocatalyzed) and the type of catalyst (metallic or metal-free). In this account, we have summarized the most recent and relevant examples under the aforementioned categories, focusing especially on those presenting the most compelling and better understood mechanisms.

Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.

C-H bond functionalization is a well-developed concept that has been thoroughly studied and gives entry to rather complex molecules without the need for previous derivatization of the substrates. The use of copper complexes in allylic C-H bond functionalization under oxidative conditions as an alternative to the well-established palladium-based methodologies remains largely underdeveloped. Here, we show for the first time a selective cross-dehydrogenative coupling reaction between underivatized allylic substrates and terminal alkynes to produce 1,4-enynes in high yields in a single step, using an in situ synthesized copper catalyst and an oxidant.

Silicones and silicone rubbers are omnipresent in household and industrial products such as lubricants, coatings, sealants, insulators, medical devices, etc. This plethora of applications arises from their unparalleled properties including hydrophobicity, low surface energy, chemical inertness, extreme temperature stability, elasticity, and biocompatibility. Even though silicones have been known for more than five decades, their chemistry is still far from fully understood. Industrially, the vast majority of processes for their synthesis, transformation, and use are based on rather well established, alas outdated technologies, which are frequently empirical and poorly investigated. This review attempts to summarize the different approaches for the synthesis of silicone rubbers by vulcanization or curing of silicone polymers, the catalysts used, and the corresponding reaction mechanisms. Apart from the well-known methods (radical, hydrosilylation, and metal-based condensation), novel approaches such as organo- and bio-catalysis are also addressed.

Investigations on synthesis of cyanopropyl-functionalized poly(dimethyl-co-methylhydro)siloxane were done to determine the correlation between conversion of SiH groups and further parameters such as nature of reactants, catalyst, stoichiometry and reaction temperature. A study on the kinetics of hydrosilylation with various siloxane starting materials and allyl cyanide were carried out between 60 and 80 °C showing that the overall reaction with polymeric siloxanes was of the second-order. Converselly, small cyclosiloxanes show first reaction order dependence. Furthermore, a two-phase kinetic behavior on the hydrosilylation reaction was observed, most likely due to catalysts deactivation.

A series of heteroleptic copper(I) complexes with bidentate PP and NN chelate ligands was prepared and successfully applied as photosensitizers in the light-driven production of hydrogen, by using [Fe3(CO)12] as a water-reduction catalyst (WRC). These systems efficiently reduces protons from water/THF/triethylamine mixtures, in which the amine serves as a sacrificial electron donor (SR). Turnover numbers (for H) up to 1330 were obtained with these fully noble-metal-free systems. The new complexes were electrochemically and photophysically characterized. They exhibited a correlation between the lifetimes of the MLCT excited state and their efficiency as photosensitizers in proton-reduction systems. Within these experiments, considerably long excited-state lifetimes of up to 54 μs were observed. Quenching studies with the SR, in the presence and absence of the WRC, showed that intramolecular deactivation was more efficient in the former case, thus suggesting the predominance of an oxidative quenching pathway.

A series of heteroleptic copper photosensitizers [(P _ P)Cu(N _ N(SO3Na)2)] + containing sulfonate anchor groups is described. In the presence of titanium dioxide they form composites, which are active photosensitizers in the light driven reduction of protons. Further stabilization of these systems is achieved by encapsulation within a plasma-polymerized allylamine (PPAAm) layer. The resulting PPAAm-CuPS-TiO2-composites exhibit a strong absorption in the visible region of the light. Photocatalytic hydrogen production is performed by using only nonnoble metals. In the presence of an iron reduction catalyst a maximum turnover number of 2452 is obtained.

Methyltrioxorhenium acts as a catalyst (5 10 Mol ) for the direct electrophilic trifluoromethylation of various aromatic and heteroaromatic compounds using the hypervalent iodine reagent 1 (trifluoromethyl) 12 benziodoxol 3(1H) one (1). The products are formed in up to 77 yield. Mixtures of regioisomers are obtained in the case of substituted and heteroaromatic substrates. The reaction typically carried out in chloroform solvent at 70 degrees C shows a significant induction period. Monitoring by EPR shows the involvement of radical species. A small kinetic deuterium isotope effect of 1.3 is observed for benzene.

We have prepared a series of new rhenium complexes containing chiral ferrocenyldiphosphane ligands of the Josiphos family, starting from commercially available rhenium sources. These new ReV oxido and nitrido complexes, several of which have been characterized by X-ray crystallography, are air- and moisture-stable and are active catalysts in the asymmetric transfer hydrogenation of ketones using 2-propanol as the hydrogen source in the presence of substoichiometric amounts of triethylamine (TEA). The reaction proceeds cleanly with good to excellent yields (50–99 %) but with moderate enantioselectivity (up to 58 % ee). A mechanism not involving hydridic species is proposed.

The paramagnetic Re(III) complex [ReCl3(Pigiphos)] (1) ((R)-(S)-Pigiphos = bis{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine) is accessible from [ReCl3(NCMe)(PPh3)2] and the ligand Pigiphos. 1 reacts with an excess of NaBH4, affording the polyhydride complex [ReH5(Pigiphos)] (2), which was shown to be a classic polyhydride (NMR T1(min) = 158 ms). This complex reacts readily with both Bronsted acids and hydride scavengers to give the corresponding cationic tetrahydride species, which was shown to be active in the catalytic hydrogenation of dimethyl itaconate.

New polynuclear zinc complexes containing tridentate Schiff base ligands were successfully synthesized and fully characterized. The solid-state structure of the complexes was determined using single crystal X-ray diffraction. The complexes display a tetranuclear cubane-like core structure [Zn4O4] and sowed good catalytic activity towards the ring-opening polymerization (ROP) of rac-lactide (rac-LA) and ɛ-caprolactone (ɛ-CL) under solvent-free conditions. The polylactic acid (PLA) obtained from rac-LA showed isotactic enrichment, as proved by homonuclear decoupled 1H NMR analysis. These complexes also showed good activity and superior control towards the ROP of rac-LA and ɛ-CL in the presence of benzyl alcohol as a co-initiator. Furthermore, Kinetic studies demonstrated that the ROP of rac-LA and ɛ-CL has a first order dependence on both monomer (rac-LA and ɛ-CL) and catalyst concentration. This article is protected by copyright. All rights reserved.

The provision of energy has been listed in the “Top Ten of global concerns” as the single most important issue to be faced to improve quality of life and ultimately to stop, or at least to mitigate, the environmental impact of human activities on the planet. [1] One way in which chemistry can be used to provide more sustainable and benign energy technologies is through the development of artificial photosynthesis systems, which allow for the conversion of the energy of sunlight into useful chemical energy by water splitting. [2] The resulting molecular hydrogen constitutes in principle a clean, renewable, and carbon-free energy source. [3]

In this chapter, two industrial processes of gas-phase, hydrocarbon catalytic oxidation are examined: (a) the oxychlorination of ethylene to 1,2-dichloroethane; and (b) the oxidation of n-butane to maleic anhydride. In the former case, the use of ethane as an alternative reactant has been studied, still without success, whereas in the latter case the alkane has replaced the corresponding C4 alkenes because of the better selectivity achieved. Recent developments are discussed for the two reactions, especially in terms of catalysts’ chemical-–physical and reactivity properties.