FIRST STRUCTURAL CHARACTERIZATION OF A 3- SILAOXETANE AND A 3-SILATHIETANE IN THE CRYSTAL AND IN SOLUTION

The 3-silaoxetane 3,3-dimethyl-2,2,4,4-tetraphenyl-1-oxa-3 silacyclobu tane (1) and the 3-silathietane 3,3-dimethyl-2,2,4,4-tetraphenyl- 1-si la-3-thiacyclobutane (2) were synthesized and studied in the solid sta te and in solution. The crystal structures of 1 and 2 were investigate d by X-ray diffraction. Furthermore, 1 and 2 were characterized by sol id-state NMR spectroscopy (C-13 and Si-29 CP/MAS). The cyclobutane rin g of 1 is planar with a C-Si-C angle of 75.07(9)degrees and a C-O-C an gle of 105.3(2)degrees. 2 crystallizes with a non-planar cyclobutane r ing with a C-Si-C angle of 89.00(11)degrees and a C-S-C angle of 93.25 (11)degrees. The Si-O distance of 241.5(3) pm for 1 and the Si-S dista nce of 263.9(3) pm for 2 are shorter than the sum of the van der Waals radii of these atoms. The results obtained by X-ray diffraction are c onsistent with those from solid state C-13-NMR spectroscopy for 1 and 2. Different Si-29-NMR spectra in solution and the solid state indicat e unusual electronic or steric effects around the silicon atom of 2 in the solid.