SULFUR DONOR ACTION IN CYCLIC SILANES - A TETRAHEDRAL TO TRIGONAL BIPYRAMIDAL REACTION COORDINATE

Reaction of Me(2)SiCl(2) with diols in the presence of Et(3)N yielded a series of new cyclic organosilanes, S(Me(2)C(6)H(2)O)(2)SiMe(2) (1), S [(t-Bu)MeC(6)H(2)O](2)SiMe(2) (2), CH2(C6H4O)(2)SiMe(2) (4), and CH 2[(t-Bu)(2)CsH2O](2)SiMe(2) (5). X-ray diffraction studies of 1 and 2 as well as a previously synthesized cyclic silane, S [(t-Bu)(2)C6H2O]S i-2(CH2)(4) (3), yielded geometries that are displaced from a tetrahed ron toward a trigonal bipyramid. The increase in coordination was due to a silicon--sulfur interaction resulting from the presence of sulfur in an eight-membered ring in each silane. The X-ray structure of 4 wi th a methylene group in place of a ring sulfur atom was obtained for c omparison. This represents the first series of this type showing silic on-sulfur acid-base interaction. The decrease in the Si-S distance in 1-3 correlates with ring conformational changes. H-1 and Si-29 NMR dat a also are reported. A comparison of solid state and solution values o f Si-29 shifts indicates little structural change on solution. Silane 1 crystallizes in the triclinic space group P (1) over bar with a 9.20 5(3) Angstrom, b = 12.862(2) Angstrom, c 15.774(2) Angstrom, alpha 97. 87(1)degrees, beta 101.58(2)degrees, gamma = 94.08(2)degrees, and Z = 4. Silane 2 crystallizes in the monoclinic space group P2(1)/m with a = 6.278(1) Angstrom, b = 22.822(7) Angstrom, c = 8.432(1) Angstrom, be ta = 97.79(1)degrees, and Z = 2. Silane 3 crystallizes in the monoclin ic space group Cc with a 19.960(6) Angstrom, b = 17.784(7) Angstrom, c = 9.843(2) Angstrom, beta = 112.70(2)degrees, and Z = 4. Silane 4 cry stallizes in the orthorhombic space group Cmc2(1) with a 13.978(2) Ang strom, b = 12.388(2) Angstrom, c = 8.006(2) Angstrom, and Z = 4. The f inal conventional unweighted residuals are 0.036 (1), 0.047 (2), 0.063 (3), and 0.041 (4).