A Persistent Boron Tetraradical with Tetraphenylethene-Linked Boraphenanthrene-Type Units
We report the first paramagnetic boron tetraradical, comprising four boraphenanthrene-type units with boryl radical centers bridged by a central tetraphenylethene (TPE) linker. With strongly π-accepting and sterically demanding cyclic(alkyl)(amino) carbene ligands (<b>3</b>), spin densities localize on the boron-carbene fragments (92%), consistent with a true boron-centered tetraradical. Magnetic measurements of <b>3</b> reveal minimal spin-spin coupling, consistent with four noninteracting <i>S</i> = 1/2 centers. In contrast, weaker π-accepting diamino N-heterocyclic carbene ligands delocalize spin density over the TPE core (88%), yielding a boron-containing hydrocarbon biradical (<b>4</b>). Compound <b>4</b> exhibits antiferromagnetic interactions (2<i>J</i> = -118 J·mol<sup>-1</sup>), supporting an open-shell singlet ground state with a thermally accessible triplet excited state.
Authors
- Andrew Molino (ORCID: https://orcid.org/0000-0002-0954-9054)
- Noah D. McMillion (ORCID: https://orcid.org/0000-0002-6221-9935)
- Heechan Kim (ORCID: https://orcid.org/0000-0001-6227-5745)
- Robert J. Gilliard (ORCID: https://orcid.org/0000-0002-8830-1064)
- Péter Müller (ORCID: https://orcid.org/0000-0001-6530-3852)
- David J. D. Wilson (ORCID: https://orcid.org/0000-0002-0007-4486)
- John F. Berry (ORCID: https://orcid.org/0000-0002-6805-0640)
- D.R. Ullery
- Rebecca K. Walde (ORCID: https://orcid.org/0000-0002-3320-2085)
Institutions
- University of Wisconsin–Madison (US)
- La Trobe University (AU)
- Massachusetts Institute of Technology (US)
Publication Details
- Journal
- Journal of the American Chemical Society
- Published
- 2025-09-05
- DOI
- https://doi.org/10.1021/jacs.5c11428
- Primary Topic
- Synthesis and Properties of Aromatic Compounds
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Science Foundation
- Arnold and Mabel Beckman Foundation
- Massachusetts Institute of Technology
- La Trobe University
- National Research Foundation of Korea
- Australian Research Council