Organic Tellurium-Centered Radicals Evidenced by EPR Spin Trapping and Mass Spectrometry Experiments:  Insights into the Mechanism of the Hydrotelluration Reaction

• Published in: Organometallics Vol. 25; no. 21; pp. 5059 - 5066
• Main Authors: Keppler, Artur F, Cerchiaro, Giselle, Augusto, Ohara, Miyamoto, Sayuri, Prado, Fernanda, Di Mascio, Paolo, Comasseto, João V
• Format: Journal Article
• Language: English
• Published: American Chemical Society 09.10.2006
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om060560s

The first experimental evidence for the formation of an organic tellurium-centered radical (RTe•, R = Ph or n Bu groups) during the hydrotelluration of alkenes and alkynes is provided. The radicals were detected by electronic paramagnetic ressonance (EPR), using DBNBS (3,5-dibromo-4-nitrosobenzenesulfonate) as the spin trap. The radical adducts (DBNBS/•Te n Bu and DBNBS/•TePh) presented an EPR spectrum characterized by a triplet of triplets due to one nitrogen and two equivalent hydrogen atoms (a N = 21.6 G and a H = 0.7 G) and a g value of 2.0060. The presence of tellurium radical adducts was confirmed by isotopic substitution (125Te) and by electrospray and chemical ionization mass spectrometry and MS/MS analysis. The products showed isotopic patterns expected for compounds containing Br and Te. These results provide evidence for organic tellurium-centered radical formation and suggest that the hydrotelluration reactions occur by a free radical mechanism.