Spiro-λ4-sulfanes with O-ligands of different electronegativity in axial positions. A comparison of CH2O–SIV–OCO and CH2O–S+IV · · · OC bond systems

Abstract

Two novel diaryl(alkoxy)(acyloxy)spiro-λ⁴-sulfanes (3 and 5) exhibiting isomerism in relation to swapping of the five- and six-membered spiro-rings and two analogous cyclic alkoxysulfonium salts (4 and 6) with intramolecular S · · · O interaction have been prepared and their molecular structures determined by X-ray diffraction. In all cases the arrangement of the ligands about the central sulfur atom shows a slightly distorted trigonal bipyramidal (TBP) geometry. In unsymmetrical spiro-λ⁴-sulfanes the S–O(alkoxy) and the considerably polarized S–O(acyloxy) bond lengths are 1.686(2) and 2.109(2) Å for 3 and 1.683(2) and 2.047(2) Å for 5, respectively. In the analogous cyclic sulfonium salts the corresponding interatomic distances are 1.645(3) and 2.255(3) Å for 4 and 1.616(2) and 2.349(2) Å for 6, respectively. The sums of the individual S–O interatomic distances found in the investigated spiro-λ⁴-sulfanes and cyclic alkoxysulfonium salts are 3.795(2) and 3.730(2) Å for 3 and 5, whereas they are 3.900(3) and 3.965(2) Å for 4 and 6, showing a significant difference between the two intervals. The individual S–O(alkoxy), S–O(acyloxy), S · · · O(carbamoyl) and S–C_ar bond lengths, as well as the C_ar–S–C_ar bond angles are compared and discussed. The five- and six-membered spiro-rings assume a flattened envelope and a somewhat inverted half-chair conformation, respectively. The almost linear O–S–O bond system is not affected significantly by the different size of the spiro-rings except the case of sulfur–oxygen nonbonded interaction.