University of Oulu

J. Am. Chem. Soc. 2023, 145, 26, 14484–14497,

Rational design of persistent phosphorus-centered singlet tetraradicals and their use in small-molecule activation

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Author: Zander, Edgar1; Bresien, Jonas1; Zhivonitko, Vladimir V.2;
Organizations: 1Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
2NMR Research Unit, University of Oulu, P.O. Box 3000, 90014, Oulu, Finland
3Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 6.1 MB)
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Language: English
Published: American Chemical Society, 2023
Publish Date: 2023-08-08


Biradicals are important intermediates in the process of bond formation and breaking. While main-group-element-centered biradicals have been thoroughly studied, much less is known about tetraradicals, as their very low stability has hampered their isolation and use in small-molecule activation. Herein, we describe the search for persistent phosphorus-centered tetraradicals. Starting from an s-hydrindacenyl skeleton, we investigated the introduction of four phosphorus-based radical sites linked by an N–R unit and bridged by a benzene moiety. By varying the size of the substituent R, we finally succeeded in isolating a persistent P-centered singlet tetraradical, 2,6-diaza-1,3,5,7-tetraphospha-s-hydrindacene-1,3,5,7-tetrayl (1), in good yields. Furthermore, it was demonstrated that tetraradical 1 can be utilized for the activation of small molecules such as molecular hydrogen or alkynes. In addition to the synthesis of P-centered tetraradicals, the comparison with other known tetraradicals as well as biradicals is described on the basis of quantum mechanical calculations with respect to its multireference character, coupling of radical electrons, and aromaticity. The strong coupling of radical electrons enables selective discrimination between the first and the second activations of small molecules, which is shown by the example of H₂ addition. The mechanism of hydrogen addition is investigated with parahydrogen-induced hyperpolarization NMR studies and DFT calculations.

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Series: Journal of the American Chemical Society
ISSN: 0002-7863
ISSN-E: 1520-5126
ISSN-L: 0002-7863
Volume: 26
Issue: 145
Pages: 14484 - 14497
DOI: 10.1021/jacs.3c03928
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
116 Chemical sciences
Funding: We thank the University of Rostock for access to the cluster computer and especially Malte Willert for his assistance with the queueing system and software installations. We would like to thank Dr. Kathrin Junge and Prof. Matthias Beller for giving us access to the high-pressure equipment and Florian Taube for the measurement of EPR spectra. E.Z. wishes to thank the Fonds der Chemischen Industrie for financial support (Kekulé fellowship) and Prof. Dr. Frank Breher as well as Dr. Alexander Hinz for many helpful discussions. V.V.Z. acknowledges the financial support from the Academy of Finland (grant 323480) and the University of Oulu (Kvantum Institute). This research was supported by the Deutsche Forschungsgemeinschaft (DFG, SCHU 1170/12-2).
Academy of Finland Grant Number: 323480
Detailed Information: 323480 (Academy of Finland Funding decision)
Copyright information: © 2023 American Chemical Society.