Browsing by Subject "Photocatalysis"

Now showing 1 - 11 of 11
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    A photochemical dehydrogenative strategy for aniline synthesis
    (Nature Research, 2020-08-06) Dighe, Shashikant; Juliá Hernández, Fabio; Luridiana, Alberto; Douglas, James J.; Leonori, Daniele; Química Inorgánica
    Chemical reactions that reliably join two molecular fragments together (cross-couplings) are essential to the discovery and manufacture of pharmaceuticals and agrochemicals1,2. The introduction of amines onto functionalized aromatics at specific and pre-determined positions (ortho versus meta versus para) is currently achievable only in transition-metal-catalysed processes and requires halogen- or boron-containing substrates3,4,5,6. The introduction of these groups around the aromatic unit is dictated by the intrinsic reactivity profile of the method (electrophilic halogenation or C–H borylation) so selective targeting of all positions is often not possible. Here we report a non-canonical cross-coupling approach for the construction of anilines, exploiting saturated cyclohexanones as aryl electrophile surrogates. Condensation between amines and carbonyls, a process that frequently occurs in nature and is often used by (bio-)organic chemists7, enables a predetermined and site-selective carbon–nitrogen (C–N) bond formation, while a photoredox- and cobalt-based catalytic system progressively desaturates the cyclohexene ring en route to the aniline. Given that functionalized cyclohexanones are readily accessible with complete regiocontrol using the well established carbonyl reactivity, this approach bypasses some of the frequent selectivity issues of aromatic chemistry. We demonstrate the utility of this C–N coupling protocol by preparing commercial medicines and by the late-stage amination–aromatization of natural products, steroids and terpene feedstocks.
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    Catalysis in the excited state: bringing innate transition metal photochemistry into play
    (American Chemical Society, 0005-03-05) Juliá Hernández, Fabio; Química Inorgánica; Facultad de Química
    Transition metal catalysis is an indispensable tool for organic synthesis that has been harnessed, modulated and perfected for many decades by careful selection of metal centers and ligands, giving rise to synthetic methods with unparalleled efficiency and chemoselectivity. Recent developments have demonstrated how light irradiation can also be recruited as a powerful tool to dramatically alter the outcome of catalytic reactions, providing access to innovative pathways with remarkable synthetic potential. In this context, the adoption of photochemical conditions as a mainstream strategy to drive organic reactions has unveiled exciting opportunities to exploit the rich excited-state framework of transition metals for catalytic applications. This Perspective examines the advances on the application of transition metal complexes as standalone photocatalysts, exploiting the innate reactivity of their excited states beyond the common use as photoredox catalysts. An account of relevant examples is dissected to provide a discussion on the electronic reorganization, the orbitals involved and the associated reactivity of different types of excited states. This analysis aims to provide practitioners with fundamental principles and guiding strategies to understand, design and apply light-activation strategies to homogeneous transition metal catalysis for organic synthesis.
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    Direct decarboxylation of trifluoroacetates enabled by iron photocatalysis
    (Wiley, Gesellschaft Deutscher Chemiker, ) Fernández-García, Sara; Chantzakou, Veronika Olga; Juliá Hernández, Francisco; Química Inorgánica
    Trifluoroacetates are the most abundant and accessible sources of trifluoromethyl groups, which are key components in pharmaceuticals and agrochemicals. The generation of trifluoromethyl reactive radicals from trifluoroacetates requires their decarboxylation, which is hampered by their high oxidation potential. This constitutes a major challenge for redox-based methods, because of the need to pair the redox potentials with trifluoroacetate. Here we report a strategy based on iron photocatalysis to promote the direct photodecarboxyla tion of trifluoroacetates that displays reactivity features that escape from redox limitations. Our synthetic design has enabled the use of trifluoroacetates for the trifluoromethylation of more easily oxidizable organic substrates, offering new opportunities for late-stage derivatization campaigns using chemical feedstocks, Earth-abundant catalysts, and visible-light.
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    Effects of ultraviolet photoactivation on osseointegration of commercial pure titanium dental implant after 8 weeks in a rabbit model
    (American Academy of Implant Dentistry, 2020-06-01) Sánchez Pérez, Arturo Joaquín; Cachazo-Jiménez, Carlos; Sánchez-Matás, Carmen; Martín-de-llano, José Javier; Davis, Scott; Carda-Batalla, Carmen; Dermatología, Estomatología, Radiología y Medicina Física; Facultad de Medicina
    This study investigated whether a 6-Watt ultraviolet C-lamp was capable of producing photofunctionalization on commercial implants during a medium observation term of 8 weeks. A total of 20 implants were inserted in 5 New Zealand rabbits, with each animal receiving 2 implants per tibia (one photofunctionalized and one untreated), according to a previously established randomization sequence. All implants were inserted by a single surgeon following the manufacturer's instructions. Histological analysis was performed by an evaluator who was blinded to the treatment condition. After 8 weeks of healing, the 2 groups showed no statistically significant differences in terms of bone-to-implant contact. Compared to control implants, the photofunctionalized implants showed improved wettability and more homogenous results. Within the limits of the present study, the use of this 6-W ultraviolet C-lamp, for an irradiation time of 15 minutes at a distance of 15 cm, did not improve the percentages of bone-to-implant contact in rabbits at an osseointegration time of 8 weeks.
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    Ferrioxalate Photocatalysis: A Multitasking Platform for Reductive Iron Catalysis
    (AAAS, 0001-01-01) Carlos Bernabeu; Sergio Adalid; Sara Colombo; Nojus Cironis; Partha Pratim Sen; Ken Okuno; Fabio Juliá; Juliá Hernández, Fabio; Fabio Juliá; Química Inorgánica; Fabio Juliá; Facultades de la UMU::Facultad de Química
    Iron’s abundance motivates its use in sustainable catalyst systems that also offer complementary reactivity manifolds compared to precious metals. However, the challenging reduction of benchmark iron salts to active species hinders their application in reductive transformations. Here we report a photochemical strategy that exploits the innate reactivity of ligand-to-metal charge-transfer (LMCT) excited states of iron oxalate complexes to harness oxalate salts as latent terminal 2-electron reductants in iron catalysis. The investigation of this activation mode has led to the development of a versatile catalytic platform enabling transformations hitherto inaccessible to previous iron catalyst systems. The synthetic value of this tactic is demonstrated on diverse reductive transformations using readily available building blocks with high chemoselectivity, opening new synthetic opportunities.
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    Ligand-to-metal Charge transfer (LMCT) photochemistry at 3d-metal complexes: an emerging tool for sustainable organic synthesis
    (Wiley, 2022-10) Juliá Hernández, Fabio; Química Inorgánica
    Despite the rich photochemistry of 3d-metal complexes, the utilization of excited-state reactivity of these compounds in organic synthesis has been historically overlooked. The advent of photoredox catalysis has changed the perception of synthetic chemists towards photochemistry, and nowadays the potential of photoinduced, outer-sphere single-electron transfer events is widely recognized. More recently, an emerging new mode of photoactivation has taken the spotlight, based on an inner-sphere mode of reactivity triggered by population of ligand-to-metal charge-transfer (LMCT) excited states. Contrarily to photoredox, LMCT-activation does not rely on matching redox potentials, offers unique reactivity profiles and is particularly well suited on Earth-abundant metal complexes. Those appealing features are propelling the development of methods using this blueprint to generate highly reactive open-shell species under mild conditions. The aim of this contribution is to provide a didactical tool for the comprehension of this emerging concept and facilitate the development of new synthetic methodologies to achieve sustainable chemical transformations.
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    Photocatalytic degradation of four insecticides and their main generated transformation products in soil and pepper crop irrigated with reclaimed agro-wastewater under natural sunlight.
    (Elsevier, 2021-07-15) Aliste, Marina; Garrido, Isabel; Flores, Pilar; Hellín, Pilar; Pérez-Lucas, Gabriel; Navarro, Simón; Fenoll, José; Química Agrícola, Geología y Edafología
    This work is the first-ever study of the concurrence of four insecticides (chlorantraniliprole, imidacloprid, pirimicarb and thiamethoxam) and their main transformation products (TPs) in soil and pepper crop irrigated with reclaimed and non-reclaimed water under agricultural field conditions. Field experiments were conducted using different irrigation supplies: control water (CW), wastewater polluted with phytosanitary commercial products containing the studied insecticides (WW) and reclaimed wastewater after a photocatalytic processing with TiO2/ Na2S2O8 at pilot plant under sunlight (RWW). Photocatalytic treatments removed most of the insecticides and their TPs generated during the photoperiod. Neither target insecticides nor their TPs were detected in pepper samples when CW and RWW were used as irrigation source, whereas the four insecticides and two TPs were detected when WW was used. In the experiment carried out with WW, all insecticides and eight TPs were detected in soil samples. The impact of using reclaimed water on the quality of pepper crop was also assessed, showing barely any significant difference.
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    Photocatalytic pathways for hydrochlorination
    (Nature Research, 2025-01-02) Juliá Hernández, Francisco; Química Inorgánica; Facultades de la UMU::Facultad de Química
    Iron photocatalysis, in conjunction with a cooperative radical mechanism, enables the anti-Markovnikov hydrochlorination of unsaturated feedstocks, using light as an energy source.
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    Practical and regioselective amination of arenes using alkyl amines
    (Nature Research, 2019-05) Ruffoni, Alessandro; Juliá Hernández, Fabio; Svejstrup, Thomas D.; McMillan, Alistair J.; Douglas, James J.; Leonori, Daniele; Química Inorgánica
    The formation of carbon–nitrogen bonds for the preparation of aromatic amines is among the top five reactions carried out globally for the production of high-value materials, ranging from from bulk chemicals to pharmaceuticals and polymers. As a result of this ubiquity and diversity, methods for their preparation impact the full spectrum of chemical syntheses in academia and industry. In general, these molecules are assembled through the stepwise introduction of a reactivity handle in place of an aromatic C–H bond (that is, a nitro group, halogen or boronic acid) and a subsequent functionalization or cross-coupling. Here we show that aromatic amines can be constructed by direct reaction of arenes and alkyl amines using photocatalysis, without the need for pre-functionalization. The process enables the easy preparation of advanced building blocks, tolerates a broad range of functionalities, and multigram scale can be achieved via a batch-to-flow protocol. The merit of this strategy as a late-stage functionalization platform has been demonstrated by the modification of several drugs, agrochemicals, peptides, chiral catalysts, polymers and organometallic complexes.
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    Site-selective, remote sp3 C−H carboxylation enabled by the merger of photoredox and nickel catalysis
    (Wiley, 2019-06-06) Sahoo, Basudev; Bellotti, Peter; Juliá Hernández, Francisco; Meng, Qing-Yuan; Crespi, Stefano; König, Burkhard; Martin, Ruben; Química Inorgánica
    A photoinduced carboxylation of alkyl halides with CO2 at remote sp3 C@H sites enabled by the merger of photoredox and Ni catalysis is described. This protocol features a predictable reactivity and site selectivity that can be modulated by the ligand backbone. Preliminary studies reinforce a rationale based on a dynamic displacement of the catalyst throughout the alkyl side chain.
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    Visible-light-promoted atom transfer radical cyclization of unactivated alkyl Iodides
    (2016-12-06) Shen, Yangyang; Cornella, Josep; Juliá Hernández, Francisco; Martin, Ruben; Química Inorgánica
    A visible-light-mediated atom transfer radical cyclization of unactivated alkyl iodides is described. This protocol operates under mild conditions and exhibits high chemoselectivity profile while avoiding parasitic hydrogen atom transfer pathways. Preliminary mechanistic studies challenge the perception that a canonical photoredox catalytic cycle is being operative.