Structural influence of a sulfonyl group in eight-membered rings of diorganosilanes

The new monocyclic diorganosilanes O2S(Me(2)C(6)H(2)O)(2)SiMe(2) (1) and O2S[(t-Bu)MeC(6)H(2)O](2)SiR(2), where R = Me (2) and R = Ph (3), were prepared by a condensation reaction of the appropriate diorganodichlorosilane with either one of the new diols O2S(Me(2)C(6)H(2)OH)(2) (5) and O2S[(t-Bu)MeC(6)H(2)OH](2) (6) in ether solution in the presence of Et(3)N. X-ray crystallographic studies showed that silane 1 has the eight-membered ring in an anti chairlike conformation, whereas silanes 2 and 3 have the eight-membered rings in syn boatlike conformations. Oxygen donor coordination to silicon is evident for 2 and 3 from one of the ring sulfonyl oxygen atoms in each. As a result, 1 remains tetracoordinate while 2 and 3 are pentacoordinate with trigonal-bipyramidal geometry. Likewise, the, cyclic disiloxane {O2S[(t-Bu)MeC(6)H(2)O]Si-2(OH)}O-2 (4), prepared as a hydrolysis product, possesses a similar pentacoordinate structure at each of the silicon centers. VT H-1 NMR spectra for 1 and 2 indicate the presence of fluxional molecules where ring pseudorotation takes place, similar to that for cyclohexane. Activation energies of 9.1 and 11.0 kcal/mol were obtained for 1 and 2, respectively. C-13 and Si-29 NMR data also were recorded. The Si-29 chemical shifts are indicative of the types of ligands attached to silicon.