Silicon-nitrogen interaction in cyclic organooxysilanes. Dimer to monomer conversion

New cyclic diorganodioxysilanes containing a ring nitrogen atom were prepared by the reaction of either Me2Si(NMe2)(2) in the case of (C10H6CH2O)(2)NMeSiMe2 (1) and [(Me2C6H2-CH2O)(2)NMeSiMe2](2) (2) or R2SiCl2 in the case of (Me2C6H2CH2O)(2)NMeSiMePh (4) and (Me2C6H2CH2O)(2)NMeSiPh2 (5) with an applicable diol. Similarly, reaction of Me3SiCl with a nitrogen-containing diol gives the disilylated product (C10H6CH2OSiMe3)(2)NMe (6)and a small amount of the monosilylated compound (C10H6CH2OH)(C10H6CH2OSiMe3)NMe (7). The 20-membered cyclic dimeric silane forms the 10-membered cyclic monomer (Me2C6H2CH2O)(2)-NMeSiMe2 (3) quantitatively on heating or with a hydroxyl-containing catalyst at room temperature in a 50% yield. A dimer-monomer mechanism is advanced via an intermediate resembling the X-ray structure of 7. The X-ray structures of 1-4 also are reported, as well as H-1 and Si-29 NMR characterization of 1-7. Weak nitrogen to silicon atom coordination is present; in 1, 3, and 4, giving flexible 10-membered rings in a geometry displaced toward trigonal bipyramidal. Interesting fluxional behavior is studied by variable-temperature H-1 NMR. Activation energies of 9-10 kcal/mol are obtained for proposed intramolecular exchange between isomers of identical energy. Proton shielding for the organosilanes suggests retention of the solid-state structures in solution and indicates that the structure for 5 is similar to those of 1, 3, and 4 resulting from the X-ray studies.