Structural Influence of a Sulfonyl Group in Eight-Membered Rings of Diorganosilanes1

The new monocyclic diorganosilanes O 2 S(Me 2 C 6 H 2 O) 2 SiMe 2 ( 1 ) and O 2 S[( 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 O 2 S(Me 2 C 6 H 2 OH) 2 ( 5 ) and O 2 S[( 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 {O 2 S[( t -Bu)MeC 6 H 2 O] 2 Si(OH)} 2 O ( 4 ), prepared as a hydrolysis product, possesses a similar pentacoordinate structure at each of the silicon centers. VT 1 H 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. 13 C and 29 Si NMR data also were recorded. The 29 Si chemical shifts are indicative of the types of ligands attached to silicon.