EPR spectroscopic studies of N-alkyl-N-trialkylsilylmethylaminyl radicals in solution

Abstract

Photochemically-generated trialkylsilyl radicals R₃Si˙(R = Me, Et, Prⁱ) add rapidly to N methylene-tert-butylamine (H₂CNBu^t) to give silylmethylaminyl radicals R₃SiCH₂ṄBu^t which have been studied by EPR spectroscopy. These aminyl radicals prefer conformations in which the β-C–Si bond eclipses the N-2p_π orbital, formally occupied by the unpaired electron, and lineshape effects resulting from hindered rotation about the R₃SiCH₂–N bond are evident in the EPR spectra. The aminyl radicals Me₃SiCH₂ ṄBu^t and Me₃SiCH₂ṄMe have been generated by displacement from aminophosphanes of the type (EtO)₂PN(R)CH₂SiMe₃, using photochemically-generated alkoxyl radicals. The proposal in the literature that Me₃SiCH₂ṄR (R = Me or Bu^t) rearranges to give ˙CH₂N(R)SiMe₃ has been confirmed and this process has been monitored by EPR spectroscopy. Since no free silyl radicals could be trapped by Bu^t₂CCH₂, the rearrangement probably proceeds by an intramolecular 1,2-shift of the Me₃Si group from carbon to nitrogen. The rearranged radicals ˙CH₂N(R)SiMe₃ have been generated independently by hydrogen-atom abstraction from the corresponding aminosilanes Me₃SiN(R)CH₃.