Muon Spin Rotation/Resonance (μSR) for Studying Radical Reactivity of Unsaturated Organophosphorus Compounds

The positive muon (mu(+)) can be regarded as a light isotope of proton and has been an important tool to study radical reactions of organic compounds. Recently, muons have been applied to produce short-lived paramagnetic species from the heavier unsaturated organic molecules including the p-block elements. This article overviews recent muon spin rotation/resonance (mu SR) studies on the phosphorus analogs of alkenes, anthracenes, and cyclobutane-1,3-diyls together with the fundamentals of mu SR. The acyclic phosphaalkene of P=C and phosphasilenes of P=Si can accept muonium (Mu=[mu(+)e(-)]) at the heavier double bonds, and the corresponding radicals have been characterized. The phosphorus atom in 9-phosphaanthracene, whose P=C double bond is stabilized by the peri-substituted CF3 groups, predominantly captures muonium to provide the corresponding paramagnetic fused heterocyclic system. The peri-trifluoromethyl groups are functional to promote the unprecedented light isotope effect of muon providing the planar three-cyclic molecular structure to consume the increased zero-point energy. The formally open-shell singlet 1,3-diphosphacyclobutane-2,4-diyl unit can accept muonium at the (ylidic) phosphorus or the skeletal radicalic carbon, and the corresponding paramagnetic phosphorus heterocycles can be characterized by mu SR. The findings on these muoniation processes to the unsaturated phosphorus-containing compounds will contribute not only to development of novel paramagnetic functional species but also to progress on muon science.

Automated summary

This article provides an overview of recent muon spin rotation/resonance (mu SR) studies on phosphorus analogs of alkenes, anthracenes, and cyclobutane-1,3-diyls. It reveals the application of muons in producing short-lived paramagnetic species from unsaturated organic molecules containing phosphorus elements, contributing to the development of novel functional species and progress in muon science.