Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP•-CMu(Me)2 (1a, minor product) and MesPMu-C•Me2 (1b, major product), were detected by muon spin spectroscopy (µSR) when a solution of MesP=CMe2 (1: Mes = 2,4,6-trimethylphenyl) was exposed to a beam of positive muons (µ+). The µ+ serves as a source of Mu (i.e. Mu = µ+ + e–). To confirm the identity of the major product 1b, its spectral features were compared to its isotopologue, MesPH-C•(Me)CH2Mu (2a). Conveniently, 2a is the sole product of the reaction of MesPH(CMe=CH2) (2) with Mu. For all observed radicals, muon, proton and phosphorus hyperfine coupling constants were determined by µSR and compared to DFT-calculated values.