In My Element: Copper

The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, Pedro Pérez gives his story on copper

Ruthenium-Catalyzed Heck-Type Alkenylation of Alkyl Bromides

The complex [Cp*RuCl(PPh3)2] displays a high catalytic activity for the Heck-type alkenylation of alkyl bromides, in the first example using this metal under thermal conditions. The coupling reaction proceeds efficiently with a variety of functionalized tertiary, secondary, and primary alkyl bromides. The presence of Hünig’s base has been revealed crucial for this transformation. Preliminary mechanistic studies support the participation of alkyl radicals in the reaction.We thank MINECO for a grant (CTQ2017-82893-C2-1-R). We also thank Francisco Molina for X-ray structure determinatio

Dimensioning the term carbenoid

The current use of the term carbenoid is discussed, particularly in the context of carbene transfer reactions from diazo compounds, where intermediates of type LnM=CR1R2, or one of its resonance forms, are tagged which such name. We herein discuss this issue, on the basis of the data evidencing the metal-carbene nature of those intermediates, as well as the existence of carbenoids of type (N2)(M)C R1R2 en route to the formation to LnM=C R1R2’ from diazo reagents. We propose the exclusive use of the carbenoid term to species of type (X)(M)C R1R2 with a tetrasubstituted carbon center that upon loss of X afford an effective carbene transfer process.The authors wish to thank MINECO for financial support (CTQ2014-52769-C03-01) and Junta de Andalucia (P12-FQM-1765)

Carbene-Controlled Regioselective Functionalization of Linear Alkanes under Silver Catalysis

Control of the regioselectivity in the functionalization of C–H bonds of linear alkanes C2H2n+2 via carbene transfer from diazo compounds is restricted to the use of rhodium-based catalysts, which govern the reaction outcome employing donor–acceptor diazo reagents. At variance with that catalyst-controlled strategy, we present an alternative approach in which employing the appropriate silver complexes containing trispyrazolylborate ligands as catalysts with large differences in their steric and electronic properties, the regioselection is mainly governed by the diazo reagent, which leads to the functionalization of primary or secondary sites of linear alkanes (lacking any activating or directing groups). Donor–acceptor aryl diazoacetates exclusively provide the functionalization of the secondary sites of hexane or pentane, whereas acceptor ethyl diazoacetate leads to an unprecedented level of primary functionalization.We thank to Ministerio de Ciencia e Innovación for Grant PID2020-113797RB-C21. We also thank Junta de Andalucía (P18-1536) and Universidad de Huelva (P.O.Feder UHU- 202024). M.A. thanks Junta de Andalucia for a postdoctoral fellowship

The TpxM Core in Csp3–H Bond Functionalization Reactions: Comparing Carbene, Nitrene, and Oxo Insertion Processes (Tpx = Scorpionate Ligand; M = Cu, Ag)

A comparison between three TpxM‐catalyzed (Tpx = scorpionate ligand; M = Cu, Ag) reactions leading to the functionalization of non‐activated, alkane Csp3–H bonds by carbene, nitrene or oxo insertion is presented. Analogies and differences in these transformations are discussed, including main reactive intermediates, selectivity trends and mechanistic interpretations.Support for this work was provided by the MINECO (CTQ2017-82893-C2-1-R)

Atom Transfer Radical Reactions as a Tool for Olefin Functionalization : On the Way to Practical Applications

Transition-metal-catalyzed atom transfer radical reactions of halogenated compounds with olefins constitute a versatile tool in organic synthesis within the area of C–C bond forming transformations. The inter- or intramolecular versions, atom transfer radical addition (ATRA) or cyclization (ATRC), respectively, lead to the atom-economic, useful synthesis of compounds that can be further functionalized. This contribution summarizes the recent developments in this area in terms of catalyst design as well as the applicability of this methodology in sequential, domino, or tandem reactions.We thank the Ministerio de Ciencia e Innovacion (grants CTQ2008-00042BQU and CTQ2008-06866-CO2-02/BQU), Consolider Ingenio 2010 (CSD2006-0003), and the Junta de Andalucia (Grant P07-FQM-02794) for financial support

Copper-catalysed radical reactions of alkenes, alkynes and cyclopropanes with N–F reagents

The mild generation of nitrogen-centred radicals from N–F reagents has become a convenient synthetic tool. This methodology provides access to the aminative difunctionalisation of alkenes and alkynes and the radical ring-opening of cyclopropanes, among other similar transformations. This review article aims to provide an overview of recent developments of such processes involving radical reactions and N–F reagents using copper-based catalysts.We thank Ministerio de Economía y Competitividad (MINECO) (CTQ2017-82893-C2-1-R) and Universidad de Huelva (PO FEDER 2014-2020 UHU-1254043) for grants

Finite element modeling of energy harvesters: application to vibrational devices

[ES] En este capítulo se presenta el conjunto de ecuaciones de gobierno para estudiar el comportamiento de los materiales activos, los cuales tienen una capacidad intrínseca para acoplar varias ramas de la Física y, en consecuencia, son comúnmente utilizados para la fabricación de cosechadoras. Una vez definidas las ecuaciones, se desarrolla una formulación numérica basada en el método de los elementos finitos para modelar estos materiales. En particular, en este capítulo se estudia la producción de energía a partir de las vibraciones mecánicas presentes en puentes ferroviarios de alta velocidad. Para ello, se hace un repaso de los parámetros básicos de estos puentes, sus vibraciones, frecuencias y las características dinámicas. A continuación, se simulan cosechadores en voladizo fabricados con materiales piezoeléctricos y piezomagnéticos bajo vibraciones mecánicas típicas y se destacan varias conclusiones.[EN] This chapter presents the set of governing equations to study the behavior of active materials, which have an intrinsic ability for coupling several branches of Physics and, consequently, are commonly used for manufacturing harvesters. Once the equations are defined, a numerical formulation based on the finite element method is developed in order to model these materials. In particular, this chapter studies the energy production from mechanical vibrations present in high-speed railway bridges. For this purpose, a review of the basic parameters of these bridges, their vibrations, frequencies and the dynamic characteristics are highlighted. Then, cantilever harvesters made out of piezoelectric and piezomagnetic materials are simulated under typical mechanical vibrations and several conclusions are highlighted.Palma, R.; Pérez-Aparicio, JL.; Museros Romero, P. (2018). Finite element modeling of energy harvesters: application to vibrational devices. En Energy Harvesting for Wireless Sensor Networks: Technology, Components and System Design. De Gruyter. 3-33. https://doi.org/10.1515/9783110445053-00133

Alkenylboronates : synthesis and applications

Organoboron compounds have become one of the most versatile building blocks in organic synthesis owing to their accessible and efficient conversion into many different functional groups. In particular, alkenyl boronates have received a great deal of attention as very reactive substrates in Suzuki–Miyaura cross‐coupling reactions. Accordingly, efforts towards the development of efficient methods to prepare this type of compound are ongoing. In this contribution, the progress in the search for synthetic routes for alkenyl boronates and their use in a variety of organic transformations is accounted.The authors wish to thank MINECO for financial support (CTQ2017-82893-C2-1-R and Juan de la Cierva fellow for J.C.) and Junta de Andalucía (P12-FQM-1765)

Make It Green: Copper-Catalyzed Olefin Aziridination in Water with an Iminoiodonane

The copper complex Tp(CF3)2,BrCu(NCMe) efficiently catalyses the aziridination of olefins in water using PhI=NTs as the nitrene source, with identical activity than that observed when using dichloromethane as the solvent, under the same experimental conditions. No specific modification of catalyst or substrates are required, nor the presence of additional phase transfer catalyst. Competition experiments and Hammett plots show that the behaviour of the metal centre is the same in both reaction media. This is the first example of a catalytic system employing PhI=NTs for olefin aziridination in water.We thank financial support from the Ministerio de Ciencia e Innovación (PID2020-113797RB-C21), Junta de Andalucía (P18- RT-1536) and Universidad de Huelva (P.O.Feder UHU-1260216). Funding for open access charges is given by Universidad de Huelva/CBUA