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) (1 a, minor product) and MesPMu-(CMe2)-Me-. (1 b, major product), were detected by muon spin spectroscopy (mu SR) when a solution of MesP=CMe2 (1: Mes=2,4,6-trimethylphenyl) was exposed to a beam of positive muons (mu(+)). The mu(+) serves as a source of Mu (that is, Mu=mu(+)+e(-)). To confirm the identity of the major product 1 b, its spectral features were compared to its isotopologue, MesPH-C-.(Me)CH(2)Mu (2 a). Conveniently, 2 a 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 mu SR and compared to DFT-calculated values.