Silicon−Nitrogen Interaction in Cyclic Organooxysilanes. Dimer to Monomer Conversion1

New cyclic diorganodioxysilanes containing a ring nitrogen atom were prepared by the reaction of either Me 2 Si(NMe 2 ) 2 in the case of (C 10 H 6 CH 2 O) 2 NMeSiMe 2 ( 1 ) and [(Me 2 C 6 H 2 CH 2 O) 2 NMeSiMe 2 ] 2 ( 2 ) or R 2 SiCl 2 in the case of (Me 2 C 6 H 2 CH 2 O) 2 NMeSiMePh ( 4 ) and (Me 2 C 6 H 2 CH 2 O) 2 NMeSiPh 2 ( 5 ) with an applicable diol. Similarly, reaction of Me 3 SiCl with a nitrogen-containing diol gives the disilylated product (C 10 H 6 CH 2 OSiMe 3 ) 2 NMe ( 6 ) and a small amount of the monosilylated compound (C 10 H 6 CH 2 OH)(C 10 H 6 CH 2 OSiMe 3 )NMe ( 7 ). The 20-membered cyclic dimeric silane forms the 10-membered cyclic monomer (Me 2 C 6 H 2 CH 2 O) 2 NMeSiMe 2 ( 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 1 H and 29 Si 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 1 H 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.