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Sterically Hindered Free Radicals, IX. Generation and Structure of Stannyl Radicals R3Sn* with Bulky Groups
El-Farargy, Ahmed F.,Lehnig, Manfred,Neumann, Wilhelm P.
, p. 2783 - 2794 (2007/10/02)
Methylated phenyl groups in hexaaryldistannanes cause reversible thermal dissociation R3Sn-SnR3 (1) 2 R3Sn* (2) only if at least the 2,6-positions are methylated.Further methyl groups enhance this dissociation only when neighbouring these positions and each other, thus causing a buttressing effect .So, DSn-Sn is decreased (51.5 -> 38.5 kcal/mol).ESR data and geometry of 2 are reported, as well as those of stannyl radicals 2, R = PhmMenCCH2 (m + n = 3) generated from the corresponding hydrides.The rotation around C-Sn bonds is hindered with increasing m.A preferred conformation is concluded from ESR data.Numerous compounds 1, R3SnH, and other precursors are prepared for the first time.
