QUANTUN
Quantum Mechanical Tunneling in Organic Chemistry
Project: Quantum Mechanical Tunneling in Organic Chemistry: New Reactivity Paradigms and Avenues for Molecular Design
Principal Investigator: Rui Fausto | Co-Principal Investigator: Cláudio M. Nunes
Host Institution: University of Coimbra
Consultants: Donald Truhlar, University of Minnesota (USA); Mischa Bonn, Max Planck Institute Mainz (DE); Robert McMahon, University of Wisconsin-Madison (USA)
Funding [250 k € ]: PTDC/QUI-QFI/1880/2020, funded by National Funds via the Portuguese Foundation for Science and Technology (FCT)
Summary
This project aims to develop the cutting-edge concepts of quantum mechanical tunneling (QMT) of atoms as tools applied to organic chemistry reactions, defining new paradigms in chemical reactivity, and exploring novel avenues for molecular design, such as (i) vibrational activated tunneling, (ii) conformational control of proton tunneling, (iii) tunneling through crossing potential energy surfaces, and (iv) isotope-controlled tunneling. It aims to induced QMT for the first time in synthesis strategies and reactions' planning, in order to create opportunities for discovering of new chemical transformations and bringing QMT to the organic chemistry laboratory. The project will also set the state for harvesting QMT contributions in catalytic C-H bond activation reactions and, in this way, bring new visions for catalytic reactions design aiming more efficient and selective synthetic innovative strategies.
Chronology and Milestones
11.22 Our new discovery of an unprecedented case of simultaneous tunneling control reactions, which completely breaks the reactivity predictions inferred by classical transition state theory, has just been published in J. Am. Chem. Soc. (link).
We present here a new example that highlights how quantum tunneling can have profound consequences on the chemical reaction outcome. The syn and anti conformers of a triplet 2-formylphenylnitrene, generated in a nitrogen matrix, do not interconvert by rotation around a single bond. Instead, they take much higher energy barrier pathways and rearrange independently to the corresponding 2,1-benzisoxazole and imino-ketene, respectively. These results completely break the classic transition state rules and can only be rationalized by the new reactivity paradigm of tunneling control.
Chemists typically try to control the selectivity of a reaction by tunning the energy barriers between competitive possible products. Our work shows a system where selectivity does not depend on the energy barrier at all. It showns that tunneling reactivity can be a game changer for selectivity.
7.21 Our work demonstrating how to switch ON H-tunneling upon conformational control by vibrational excitation has just been published in J. Am. Chem. Soc. (link or repository).
We have investigated the possibility to achieve conformation control of proton tunneling reactions using vibrational excitation. The realization of such goal was demonstrated with a triplet 2-hydroxyphenylnitrene generated in an N2 matrix at 10 K by UV-irradiation of an azide precursor. The anti-orientation of the nitrene’s OH moiety was converted to syn-orientation by selective vibrational excitation at the 2ν(OH) frequency, thereby moving the H atom closer to the vicinal nitrene center. This triggers the spontaneous H-tunneling to a singlet 6-imino-2,4-cyclohexadienone.
These results are a joined effort of the aCTIVE and QUANTUN projects and provide a conceptual strategy to harness the control of QMT, which is likely to inspire new advances that can extend from enzymatic catalysis to quantum switches.
3.21 Our QUANTUN project start today!