Rosenboom, Jan, Florian Taube, Leon Teichmeier, Alexander Villinger, Maik Reinhard, Serhiy Demeshko, Marina Bennati, Jonas Bresien, Björn Corzilius, and Axel Schulz. “Rational Design of a Phosphorus‐Centered Disbiradical.” Angewandte Chemie International Edition, December 20, 2023, e202318210.
https://doi.org/10.1002/anie.202318210.
Phosphorus-centered disbiradicals, in which the radical sites exist as individual spin doublets with weak spin-spin interaction have not been known so far. Starting from monoradicals of the type [•P(μ-NTer)2P–R], we have now succeeded in linking two such monoradical phosphorus centers by appropriate choice of a linker. To this end, biradical [•P(μ-NTer)2P•] (1) was treated with 1,6-dibromohexane, affording the brominated species {Br[P(μ-NTer)]2}2C6H12 (3). Subsequent reduction with KC8 led to the formation of the disbiradical {•[P(μ-NTer)]2}2C6H12 (4) featuring a large distance between the radical phosphorus sites in the solid state and formally the highest biradical character observed in a P-centered biradical so far, approaching 100%. EPR spectroscopy revealed a three-line signal in solution with a considerably larger exchange interaction than would be expected from the molecular structure of the single crystal. Quantum chemical calculations revealed a highly dynamic conformational space; thus, the two radical sites can approach each other with a much smaller distance in solution. Further reduction of 4 resulted in the formation of a potassium salt featuring the first structurally characterized Pcentered distonic radical anion (5–). Moreover, 4 could be used in small molecule activation.