Synthesis of Trioxy- and Tetraoxysilatranes with All Six-Membered Rings. Structure and Dynamic NMR Behavior 1
2000; American Chemical Society; Volume: 19; Issue: 26 Linguagem: Inglês
10.1021/om0008225
ISSN1520-6041
AutoresN.V. Timosheva, A. Chandrasekaran, Roberta O. Day, Robert R. Holmes,
Tópico(s)Organometallic Complex Synthesis and Catalysis
ResumoA series of silatranes containing all six-membered rings N[CH2(Me2C6H2)O]3SiR was prepared using tris(2-hydroxy-3,5-dimethylbenzyl)amine, 7, as the encapsulating agent in the case of 2 (CH2Cl), 4A (CHCH2), 4B (CHCH2), 5 (CH2Ph), and 6 (CH2CH2(C5H4N)). Silatranes 1 (OC6H4-4-Br) and 3 (OC6H4-4-CMe3) were synthesized by transesterification of a previously known silatrane B, where R = OMe. Their structures were established by X-ray analyses and correlated with 29Si NMR data. VT 1H NMR spectra reflected fluxional behavior for all of these chiral molecules 1−6. The activation energies for enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like silatranes 1−6 increased as the Si−N distance decreased. This trend paralleled an increase in structural rigidity associated with the ring system as supported by ring torsional data supplied by the X-ray analyses. The degree of nitrogen donor interaction depends primarily on electronegativity effects induced at silicon by the exocyclic ligand. Also, the Si−N distances, which are shown to linearly reflect the degree of trigonal bipyramidal character, agreed with 29Si chemical shifts in indicating a correspondence between the solid and solution state structures.
Referência(s)