Synthesis of Silatranes with All Six-Membered Rings. Influence of Steric Effect on Structure and NMR Behavior1a,b

New silatranes containing all six-membered rings, N[CH 2 (Bu t MeC 6 H 2 )O] 3 SiR, where R = CH 2 Cl ( 1 ), Cl ( 2 ), Ph ( 3 ), OH ( 4 ), Me ( 5 ), and CCl 3 ( 6 ), were synthesized starting with tris(2-hydroxy-3- tert -butyl-5-methylbenzyl)amine ( 7 ) as the encapsulating agent. The silatranes other than 4 were prepared by the reaction of the triphenol 7 with an appropriate chlorosilane, whereas 4 resulted from the hydrolysis of 2 . Their structures were established by X-ray analyses and 29 Si NMR data. VT 1 H NMR spectra revealed fluxional behavior for 3 and 4 . Activation energies for the enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like silatranes correlated with increased structural rigidity associated with the ring system. The presence of tert -butyl groups on the aryl ring system located adjacent to the axial R groups introduces a steric effect that is largely responsible in restricting the donor−acceptor interaction to a narrow range of Si−N distances. The latter range is comparable to that found in previous studies which invariably concentrated on silatranes possessing five-membered rings. The present study confirms that unencumbered silatranes with six-membered rings provide the most effective way to study the influence of substituent effects on nitrogen−silicon donor−acceptor interactions.