EPR evidence for α-triphenylstannylvinyl radicals in the O-directed hydrostannation of dialkylacetylenes with Ph3SnH/cat. Et3B/O2.

Here we provide definitive EPR evidence for the existence of α-triphenylstannylvinyl radicals in the low temperature O-directed free radical hydrostannation of dialkyl propargylic alcohols with Ph3SnH/cat. Et3B and O2 in PhMe. Isotropic hyperfine splitting patterns and spectral simulations confirm the assignments made. In the case of the α-triphenylstannylvinyl radical (Z)-2, an isotopic 119/117Sn hyperfine coupling constant of 9.5 mT (95 G) was measured along with a 1Hβ hyperfine coupling constant of 1.1 mT.