Synthesis of silatranes with all six-member rings. Influence of steric effect on structure and NMR behaviour

New silatranes containing all six-membered rings, N[CH2((BuMeC6H2)-Me-t)O]( 3)SiR, where R = CH2Cl (1), Cl (2), Ph (3), OH (4), Me (5), and CCl3 (6), w ere synthesized starting with tris(2-hydroxy-3 -tert-butyl-5-methylbenzyl)a mine (7) as the encapsulating: agent. The silatranes other than 4 were prep ared:by the reaction of the triphenol 7 with an appropriate chlorosilane, w hereas 4 resulted from the hydrolysis of 2. Their structures were establish ed by X-ray analyses and Si-29 NMR data. VT H-1 NMR spectra revealed fluxio nal behavior for 3 and 4. Activation energies for the enantiomeric conversi on of the;clockwise and anticlockwise orientations of the propeller-like si latranes correlated with increased structural rigidity associated with the ring system. The presence of tert-butyl groups on the aryl ring system loca ted adjacent to the axial R groups introduces a steric effect that is large ly responsible in restricting the donor-acceptor interaction to a narrow ra nge of Si-N distances. The latter range is comparable to: that found in-pre vious studies which invariably concentrated on silatranes possessing five-m embered rings. The present study confirms that unencumbered silatranes with six-membered rings provide the most effective way to study the influence o f substituent effects on nitrogen-silicon donor-acceptor interactions.