Electron spin resonance and kinetic studies on tin centered radicals r3sn. with bulky substituents

ESR data of stannyl radicals R3Sn. with residues R of considerable bulkiness in solution are presented. With R = neophyl (PhMe2C-CH2), (g = 2.0150) an alternating linewidth effect indicating hindered rotation around the Sn-C bonds is found. The radical is non-planar by 14.0° and configurationally stable. The radicals (2, 4, 6-alkyl3Ph) Sn., alkyl = H, Me, Et, i-Pr show singlets (g = 2.0023 - 2.0078) broadened by unresolved hyperfine interactions with ring and alkyl protons, aH ≤ 0.05 mT. They are non-planar by 15.1 – 16.1°, (i-Pr3Ph)3Sn. being less pyramidal than Ph3Sn because of steric repulsions between the substituents, and are in recombination-dissociation equilibria with the corresponding distannanes. The Sn-Sn bond energies drop from 205 kj (alkyl = Me) to 36 kJ (alkyl = i-Pr). For (Et3Ph)3Sn., the activation energy of recombination is 38 kJ/mol.