Andreu Tortajada Navarro

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 andreu.tortajadanavarro@unifr.ch
 https://orcid.org/0000-0002-2635-8030

Research and publications

  • Publications
    24 publications
  • Research projects

    Design and Synthesis of New Biorenewable Jet Fuels Using Alkali-Metal Amides
    Status: Ongoing

    Start 01.03.2025
    End 28.02.2026
    Funding SNSF  Open project sheet
    With the growing impacts of global warming emphasizing the urgency for sustainable transportation fuel development, the focus on energy-dense renewable alternatives like biofuels and sustainable aviation fuels (SAF) becomes imperative to reduce greenhouse gas emissions and achieve carbon neutrality in the aviation industry by 2050. While current options exist, such as hydrotreatment of fatty acids and esters, biomass conversion to syngas, and alcohol-to-jet approaches, expanding the availability and diversity of efficient pathways for obtaining these fuels from sustainable sources is crucial. Most of the current industrialized routes generate synthetic paraffinic kerosenes comprising blends of acyclic lineal and branched alkanes, with limited volumetric heats of combustion due to their modest densities. In contrast, however, cycloalkanes offer improved properties, such as increased densities, high heats of combustion, and in many cases, viscosities compliant with the specifications for conventional jet fuel. Isoprene and cyclic monoterpenes are an important class of polyenes obtained from biomass, which hold potential for the creation of cutting-edge biobased jet fuels. Globally, researchers are actively exploring biosynthetic pathways for generating monoterpenes using genetically modified microorganisms, which will allow the production of high-performance alternative fuel blendstocks from biomass sources. However, for the obtention of high-performance fuels, these molecules need to be converted into their cyclic and hydrogenated analogues. Despite the recent efforts for the preparation of 4-, 5-, 6- and 8-membered ring scaffolds, the preparation of 7-membered ring cycloalkanes has not been achieved. Breaking ground in this field, this project aims to utilize earth abundant alkali metal amides, particularly widely available sodium and potassium, due to their superior reactivity, to develop a novel synthetic pathway for producing 7-membered-ring hydrocarbons without the use of precious transition metals or harsh conditions, offering a new avenue for sustainable aviation fuel production. Designed to provide proof of concept results, this SPARK project comprises two main work packages: WP1 focuses on the catalytic dimerization of isoprene, a precursor to biofuels, while WP2 will develop a unique method for the regioselective metalation of heptatrienyls and the synthesis of 7-membered rings via a cyclization reaction. Advanced analytical techniques, including single crystal X-ray diffraction and multinuclear NMR spectroscopy, will be employed to characterize reaction intermediates and products. The overarching research plan underscores the critical importance and profound impact of advancing the development of novel biofuels obtained from renewable resources. Through the strategic utilization of alkali-metal catalysis, this project will broaden the spectrum of chemical structures that can be harnessed for biofuel synthesis. By pioneering innovative approaches to biofuel production, this initiative not only addresses pressing environmental concerns but also plays a pivotal role in shaping a more sustainable future for air transportation.

    Unlocking Low-valent First-row Transition Metals for Catalytic Cycloaddition Reactions
    Status: Ongoing

    Start 01.01.2025
    End 31.12.2028
    Funding SNSF  Open project sheet
    With an ever-growing population and the increase of life standards, the need for raw materials, bulk and fine chemicals is expected to rise in the following years. To face this challenge, a move towards a circular economy and the look for new more sustainable processes are needed. If we look at the preparation of chemicals, many processes still rely on the use of precious transition metals. Trying to move away from these metals, in recent years Earth-abundant transition metals have become a viable sustainable alternative, with the advantage of having lower price, being more environmentally benign and giving access also to unique reactivity. These metals have more oxidations states available, ranging from highly oxidized to highly reduced, reaching even formal negative oxidation state. Despite these different features, the mechanistic understanding on the chemistry of Earth abundant transition metals still remains in its infancy in comparison with that of precious transition metals. This is primarily because many of their metal complexes are difficult to access and highly unstable which coupled with their diverse redox behavior, has stalled their rational development and limited their possibilities to be used as catalysts. Particularly, their use for the activation of poorly reactive substrates, such as simple alkenes or ethers, has not been widely studied, missing an opportunity to develop catalytic applications that deliver chemical complexity from simple and available substrates. Filling this important gap on the knowledge, this project will transcend the current state of the art in the field by delivering a new family of earth abundant organometallic complexes in low oxidation state. Using a rational-driven approach a new synthetic route based on M–H deprotonation will be developed, which will allow their access and modulation of their characteristics to finely tune their reactivity. By systematically assessing their constitution and reactivity, with the aid of X-ray crystallography, advanced spectroscopic techniques and DFT calculations, reactivity patterns on stoichiometric transformations will be gained and applied to catalytic regimes Our focus will be put in cycloaddition reactions, a key organic transformation where the combination of unactivated and ready available unsaturated building blocks will provide in a single step the formation of more complex and synthetically valuable organic structures, such as 4-, 6-, 7- or 8-member rings with and without heteroatoms, scaffolds that currently are difficult to access without the use of transition metal catalysis. Breaking new ground in this field, the vision behind this project is to pioneer the applications of reduced first-row transition metals in cycloaddition reactions, using a metal-focused approach to deliver new catalytic applications. This will be achieved through four interconnected work-packages (WPs). A systematic synthesis of Co(-1) complexes will deliver a pool of organometallic compounds, which will advance the understanding of their reactivity and bonding to unactivated unsaturated motifs (WP1). Their reduction via deprotonation with alkali-metal bases will allow the expansion of this synthetic route to other metals and the isolation of a range of transition metal complexes in low (or even negative) oxidation state (WP2). New knowledge obtained from these WPs will be used to study the reactivity of these complexes with other unsaturated scaffolds and accessing catalytic regimes (WP3). Finally, we will combine transition metal catalysis with photocatalysis, to open new reaction avenues, expanding the synthetic possibilities of first-row transition metals (WP4). Overall, this program will increase the repertoire of transformations catalyzed by Earth-abundant transition metals and advance the understanding on their reactivity, propelling the development of more sustainable processes for the synthesis of chemicals. By realizing these aims, I will strengthen my leadership and independence skills towards becoming a world leading researcher in the field of synthesis and catalysis.

Teaching and courses

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