Cyclosilthianes : I. Stereoisomers of phenylmethylcyclosilthianes

Abstract

trans-1,3,5-Trimethyl-1,3,5-triphenylcyclotrisilthiane (I) was prepared by treating methylphenyldichlorosilane with hydrogen sulfide in the presence of pyridine. Compound(I) exists in the boat form in the solid state. Rapidly interconverting twist boat or boat forms and possibly chair forms of (I) are believed to be present in solution on the basis of PMR data. Upon distillation at reduced pressure, (I) is converted into an equimolar mixture of cis and trans isomers of 1,3-dimethyl-1,3-diphenylcyclodisilthiane (II), and (III). One of these isomers was isolated by recrystallization from solution. The interconversion of the cis,trans-isomers (II) and (III) was found to be complete in 30 min at 179° in 1,2,4-trichlorobenzene. The interconversion of cyclosilthianes (I), (II), and (III) in solution was studied by NMR.