SYNTHESIS, STRUCTURE, AND REACTIONS OF THE FIRST ROTATIONAL ISOMERS OF STABLE THIOBENZALDEHYDES, 6-TRIS[BIS(TRIMETHYLSILYL)METHYL]THIOBENZALDEHYDES

The first rotational isomers of thiobenzaldehydes, TbtCH=S (2a and 2b; Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), were synthesized and isolated as stable crystalline compounds by the desulfurization of the corresponding overcrowded cyclic polysulfides TbtCHS(n) (n = 5 or 8) with phosphine reagents. The molecular structures of 2a and 2b in the solid state, determined by X-ray crystallographic analysis, differ ed in their conformations, which were essentially identical with those in solution as revealed by H-1{H-1} nuclear Overhauser effect (NOE) e xperiments. The isomeric thiobenzaldehydes 2a and 2b wore found to und ergo thermal interconversion, A kinetic study of this process gave rea sonable kinetic and thermodynamic parameters for conformational isomer izations of this type. Interesting differences in reactivity among the two isomers 2a,b and 2,4,6-tri-tert-butylthiobenzaldehyde (1) were sh own in the reactions with hydrazine and m-chlorogeroxybenzoic acid.