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

• Published in: Angewandte Chemie International Edition Vol. 58; no. 1; pp. 297 - 301
• Main Authors: Chandrasena, Lalangi, Samedov, Kerim, McKenzie, Iain, Mozafari, Mina, West, Robert, Gates, Derek P., Percival, Paul W.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 02-01-2019
• Edition: International ed. in English
• Subjects: Free radicals; isotope effects; Magnetic properties; muon spin spectroscopy; Muonium; Muons; phosphaalkenes; Phosphorus; radicals; Spectroscopy; isotope effects; phosphaalkenes; radicals; muon spin spectroscopy
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201810967

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−C.Me2 (1 b, 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 (that is, Mu=μ++e−). To confirm the identity of the major product 1 b, its spectral features were compared to its isotopologue, MesPH‐C.(Me)CH2Mu (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 μSR and compared to DFT‐calculated values.
Phosphaalkene and muonium get radical: Muonium, an H‐atom analogue, reacts with a phosphaalkene to form two radicals, a carbon‐centered radical (major product) and a phosphinyl (minor product). Muon, proton, and 31P hyperfine coupling constants are reported for these radicals and an isotopologue generated from an alkene.