Observation of a Metastable P‐Heterocyclic Radical by Muonium Addition to a 1,3‐Diphosphacyclobutane‐2,4‐diyl

Abstract

A 1,3-diphosphacyclobutane-2,4-diyl contains a unique unsaturated cyclic unit, and the presence of radical-type centers have been expected as a source of functionality. This study demonstrates that the P-heterocyclic singlet biradical captures muonium (Mu=[μ e ]), the light isotope of a hydrogen radical, to generate an observable P-heterocyclic paramagnetic species. Investigation of a powder sample of 2,4-bis(2,4,6-tri-t-butylphenyl)-1-t-butyl-3-benzyl-1,3-diphosphacyclobutane-2,4-diyl using muon (avoided) level-crossing resonance (μLCR) spectroscopy revealed that muonium adds to the cyclic P C unit. The muon hyperfine coupling constant (A ) indicated that the phosphorus atom bearing the t-butyl group trapped muonium to provide a metastable P-heterocyclic radical involving the ylidic MuP(<)=C moiety. The observed regioselective muonium addition correlates the canonical formula of 1,3-diphosphacyclobutane-2,4-diyl.

Muonium Addition to a peri‐Trifluoromethylated 9‐Phosphaanthracene Producing a High‐Energy Paramagnetic π‐Conjugated Fused Heterocycle

“…In the muoniation to cyclic molecules, the isotope effect could be normally characterized by elongation of the X‐Mu bond, where X is C atom or other main group elements, due to higher zero‐point vibration promoting increase of the average bond distance [14b, 17, 27–29] . However, elongation of the P‐Mu(H) bond according to our previous works [17] could not simulate the experimental muon hfc.…”

“…In the muoniation to cyclic molecules, the isotope effect could be normally characterized by elongation of the X‐Mu bond, where X is C atom or other main group elements, due to higher zero‐point vibration promoting increase of the average bond distance [14b, 17, 27–29] . However, elongation of the P‐Mu(H) bond according to our previous works [17] could not simulate the experimental muon hfc. Meanwhile, scanning the angles around the phosphorus based on the rocking and wagging motions in 1Mu was attempted, but simulating the experimental TF‐μSR and μLCR results was also unsuccessful.…”

“…Chemie Zuschriften 24238 www.angewandte.de bond according to our previous works [17] could not simulate the experimental muon hfc. Meanwhile, scanning the angles around the phosphorus based on the rocking and wagging motions in 1Mu was attempted, but simulating the experimental TF-mSR and mLCR results was also unsuccessful.…”

“…[15,16] Our previous mSR study on the 1,3-diphosphacyclobutane-2,4-diyl of open-shell singlet phosphorus heterocycle successfully characterized muonium addition to the 4-membered phosphorus heterocycle affording a metastable Pheterocyclic radical, suggesting usefulness of mSR for chemistry of transient radical species generated from phosphorus heterocycles. [17] As for the low-coordination structures involving phosphorus, muonium adducts of a phosphaalkene bearing P = C double bond were successfully characterized. [18] These findings encouraged us to attempt mSR studies on the peri-trifluoromethylated 9-phosphaanthracene.…”

Muonium Addition to a peri‐Trifluoromethylated 9‐Phosphaanthracene Producing a High‐Energy Paramagnetic π‐Conjugated Fused Heterocycle

“…Chemie bond according to our previous works [17] could not simulate the experimental muon hfc. Meanwhile, scanning the angles around the phosphorus based on the rocking and wagging motions in 1Mu was attempted, but simulating the experimental TF-mSR and mLCR results was also unsuccessful.…”