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 (H2CNBut) to give silylmethylaminyl radicals R3SiCH2ṄBut which have been studied by EPR spectroscopy. These aminyl radicals prefer conformations in which the β-C–Si bond eclipses the N-2pπ 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 ṄBut 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 But) 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 But2CCH2, 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.