STEREOCHEMICAL NONRIGIDITY OF YLHALOGENOSILYLMETHYL)-N-(1-PHENYLETHYL)ACETAMIDES IN SOLUTIONS

The structure and dynamic behavior of (O-Si)-chelate N-(dimethylhaloge nosilyl)methyl acetamides of the type MeC(O)N(CH(Ph)Me)CH2SiMe2 X, whe re X = F, Cl, Br with the OSiC3X coordination set, were studied by mul tinuclear (H-1, C-13, O-17, Si-19) and dynamic H-1 NMR spectroscopy. L igand permutation at silicon was detected. The observed influence of t he solvent, nucleofugacity of the X substituent and the external nucle ophile on the calculated values of the free energies of activation tes tify to the dissociative and/or associative mechanisms of the process, but including the stages in which the regular (pseudo-rotation or 'tu rnstile') mechanism takes place. At lower temperatures (up to -90 degr ees C) the H-1, C-13, Si-29 NMR spectra of N-(dimethylchlorosilyl)meth yl acetamide contain the signals of two species of unequal intensity. This effect was explained by an equilibrium between monomers containin g the intramolecular O --> Si bond and dimers with a hexacoordinate si licon and the bridging chlorine atoms.