Measurement of the 29Si central atom couplings in silicon-centred radicals with phenyl substituents

Abstract

Following γ-irradiation of the completely deuteriated silicon compounds C₆D₅SiD₃, (C₆D₅)₂SiD₂ and (C₆D₅)₃SiD at 77 K, features were detected by EPR spectroscopy from the ²⁹Si satellite transitions of the corresponding silicon-centred radicals, derived from Si–D bond cleavage. Thus the anisotropic ²⁹Si hyperfine tensors could be fully evaluated, leading to the conclusion that these are still pyramidal species, but are partially delocalised, rising to a maximum of ca. 30% spin transfer to the phenyl groups in the triphenylsilyl radical. The chloro-analogues, C₆D₅SiCl₂˙ and (C₆D₅)₂SiCl˙, were also studied, following γ-radiolysis of C₆D₅SiCl₃ and (C₆D₅)₂SiCl₂ at 77 K, the latter giving rise to both these radicals and indicating a radiolytic mechanism involving both Si–C and Si–Cl bond cleavage. In order to provide ‘base’ values for couplings in related species without phenyl substituents, the radicals MeSiCl₂˙ and HSiCl₂˙ were also studied as formed by the radiolysis of MeSiCl₃ and HSiCl₃.