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Klaas van Leest receives Dick Stufkens Prize 2021

The Dick Stufkens Prize 2021 for the best PhD thesis of the Holland Research School of Molecular Chemistry (HRSMC) has been awarded to Klaas van Leest for his thesis 'Open- Shell Cobalt Complexes with Redox-Active Ligands; Electronic Structure and Nitrene Transfer Reactivity'. Van Leest, who is now a postdoctoral fellow at the University of Hong Kong, obtained his doctorate with the qualification 'cum laude' from the University of Amsterdam at the end of 2020.

Dr Klaas van Leest obtained his doctorate on 3 december 2020 with the distinction 'cum laude' for his thesis 'Open-Shell Cobalt Complexes with Redox-Active Ligands; Electronic Structure and Nitrene Transfer Reactivity'. His supervisor was Prof. Bas de Bruin (University of Amsterdam) and his co-supervisor Prof. Jarl Ivar van der Vlugt (University of Oldenburg). Van Leest currently works as a postdoctoral researcher at the group of Prof. Chi-Ming Che at the University of Hong Kong in the field of photoredox catalysis, for which he was awarded a Rubicon grant by the Dutch Research Council NWO. Photo: HIMS

In his thesis, Van Leest describes his studies on cobalt catalysts to achieve selective C‒N and S‒N bond formation via radical- type nitrene transfer. He provides a profound understanding of the underlying mechanisms of these catalysed conversions that are of relevance to the synthesis of medicines and other bio- active molecules.
Selecting the winner from a selection of excellent candidates, the jury for the Dick Stufkens prize 2021 unanimously decided for Klaas van Leest. They were impressed by the quality of his research and applaud his enormous productivity. Not only has Van Leest advanced the catalysis type that was the main subject of his study, he also contributed to studies on a variety of metal catalysts for a range of catalytic processes. While he reported on his PhD research in 9 papers, a further number of 22 other high-quality papers hold his name, and his publications have already been cited over 500 times. According to the jury, Van Leest thus displays an unusual combination of very high productivity with very high-quality, interesting catalysis research, achieved by fostering numerous collaborations within the HRSMC and outside the Netherlands.

Novel approach to improve atom efficiencies

The formation of carbon-nitrogen and heteroatom-nitrogen bonds often is a key step in the synthesis of medicines and other bioactive molecules. The general strategy for these conversions involves functional groups exchange, preorganisation and/or deprotecting steps, all resulting in a reduction of the atom efficiency. Employing catalytic conversions to form C‒N and S‒N bonds could substantially improve this. However, such an approach poses major challenges, especially for chemists searching to employ abundant first-row transition metal ions instead of precious second- or third-row metals. The latter often operate via two-electrons reactions, whilst the first-row metal complexes often exhibit one-electron (radical) reactivity. The particularly challenging tasks for chemists are to control the often nonselective radical processes in the desired transformation; to employ nontrivial spectroscopic tools to study the catalysts and reaction mechanisms; and to perform proper calculations on the intricate open-shell electronic structures.

Highly efficient nitrene radical transfer reactions under mild conditions

Klaas van Leest has managed to overcome all these challenges in a beautiful manner. He employed a redox-active ligand bound to cobalt that can act as an electron reservoir allowing radical nitrene transfer reactions to occur. To succeed in this novel approach, he developed an understanding of the role of the redox-active ligand on the spin-state of the cobalt complex. He also had to develop new reactions for N-group transfer to sp3 hybridized C‒H bonds, and for the selective formation of reactive nitrene radicals on cobalt by using a redox-active ligand. His efforts resulted in highly efficient nitrene radical reactions using such a cobalt complex, performed under mild conditions, in air, in the presence of moisture.

The jury was particularly impressed by Van Leest's investigations on cobalt complexes containing the macrocyclic TAML ligand, where he used a variety of techniques to elucidate the nature of the radical nitrene reactions. Noteworthy further is that the theoretical calculations were not only based on standard DFT calculations but also highly advanced multireference NEVPT2-CASSCF calculations were used. The Co-TAML catalyst is extremely fast and shows a high turnover number. Since the TAML ligand has already been upscaled for catalytic oxidation reactions (as an iron complex), there might be a potential to apply the Co-TAML complex for nitrene conversions on an industrial scale.

About the Dick Stufkens Prize

The Dick Stufkens Prize is awarded annually to the best thesis defended in the period July 1 to July 1 of the next year by a PhD student belonging to the Holland Research School of Molecular Chemistry (HRSMC). The prize – first awarded in 2008 - consists of a certificate and an amount of 2000 euro. The prize will be virtually handed over to Klaas van Leest during the HRSMC Annual Symposium to be held 18-19 November 2021 at De Duif in Amsterdam. Van Leest will present an online lecture on his award-winning research, streamed live from the University of Hong Kong where he is currently an NWO Rubicon funded postdoc.

About the HRMSC

The Holland Research School of Molecular Chemistry was founded in 1994 and has been re-accredited three times by the Royal Netherlands Academy of Arts and Sciences (KNAW). The Research School combines research groups working on synthesis, spectroscopic characterization and theoretical and computational description of molecular systems from the University of Amsterdam, VU Amsterdam, Leiden University and Radboud University Nijmegen. Apart from creating the appropriate conditions for further collaboration between the participating groups, the school also provides an internationally highly acclaimed teaching program for talented PhD and MSc students in molecular chemistry and physics. The late Prof. Dick Stufkens, scientific director during the period 1997-2001, was one of the driving forces behind the HRSMC. Among other things, his efforts have contributed greatly to the international reputation of the HRSMC.

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